United States
                 Environmental Protection
                 Agencv
                 Offif e of Solid Waste and
                 Emerqency Response
                 Office of Emergency and
                 Remedial Response
                 Washington DC 20460
Office of Research and
Development
                 Superfund
                                 EPA/540/2-85/004 Nov 1985
£EPA
Leachate  Plume
Management

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                                          EPA/540/2-85/004
           LEACHATE PLUME MANAGEMENT
                      by
         Edward Repa and Charles Kufs
                ORB Associates
              8400 Uestpark Drive
            McLean, Virginia  22102
              EPA Project Officer
                 Naomi Barkley
 OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE
   OFFICE OF EMERGENCY AND REMEDIAL RESPONSE
     U.S. ENVIRONMENTAL PROTECTION AGENCY
             WASHINGTON, DC  20460
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
      OFFICE OF RESEARCH AND DEVELOPMENT
     U.S. ENVIRONMENTAL PROTECTION AGENCY
            CINCINNATI, OHIO  45268
                                    •   rental Protection Agenc*
                             jS. Environmental nut
                                                             ,«aS
                             Chicago, Illinois

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                               NOTICE
The information in this document has been funded, wholly or  in part,  by
the United States Environmental Protection Agency under Contract No.
68-03-3113 to Science Applications International Corporation/JRB
Associates (hereafter SAIC/JRB).  This document has been subject to the
Agency's peer arid administrative review and has been approved for
publication as an EPA document.

This handbook is intended to present information on the application of
technologies for the control of specific problems caused by  uncontrolled
waste sites.  The handbook  is not intended to address every  conceivable
waste site problem or all possible applications of these technologies.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.

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                                   FOREWORD
     This is one of a series of reports being published to  implement  CERCLA,
otherwise known as Superfund legislation.  These are documents explaining  the
hazardous response program and, in particular, the technical requirements  for
compliance with the National Contingency Plan (NCR), the  analytical and
engineering methods and procedures to be used for compliance, and the
background and documenting data related to these methods  and procedures.   The
series may include feasiblity studies, research reports, manuals, handbooks,
and other reference documents pertinent to Superfund.

     This handbook provides an overview of the fundamental  concepts,
procedures,  and technologies used in leachate plume management.  Plume
generation dynamics and delineation are discussed.  Plume control technologies
are evaluated and selection criteria for site applications  are defined.
Groundwater pumping, subsurface drains, low permeability barriers, and
innovative technologies are the aquifer restoration technologies addressed  in
this handbook.

     The handbook provides governmental and industrial technical personnel
with the means to successfully control leachate plumes from uncontrolled
hazardous waste sites.  In conjunction with other publications in this series,
this handbook will assist in meeting the national goal of a cleaner,  safer
environment.

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                                   ABSTRACT
     The problem of leachate plume management has been aggravated to some
extent by a lack of understanding of plume dynamics and the various remedial
options available.   This handbook summarizes information in the areas of
leachate plume dynamics and plume management alternatives.   The handbook
describes factors that affect leachate plume movement, key considerations in
delineating the current and future extent of the leachate plume, technologies
for controlling the migration of plumes, and criteria for evaluating and
selecting plume management alternatives.  The handbook consists of eight
chapters:

     0  Chapter 1 -- Introduction includes an overview disc'ussion of leachate
        plume generation and a summary of the handbook's contents.

     0  Chapter 2 --Plume Dynamics includes discussions on the effects of
        groundwater flow patterns, leachate characteristics, and plume and
        geologic media interactions.

     •  Chapter 3 -- Plume Delineation includes discussion on data sources and
        procedures  for estimating plume boundaries, characterizing plume
        chemistry,  and extrapolating future plume movement.

     •  Chapter 4 -- Plume Control Technologies includes an overview
        discussion  of plume control technologies and how they can be evaluated
        and selected for site applications.

     •  Chapter 5 -- Groundwater Pumping includes discussions on well
        hydraulics  and well design, installation, operation, and maintenance.

     •  Chapter 6 — Subsurface Drains includes discussions on drain
        hydraulics  and drain design, installation, and maintenance.

     •  Chapter 7 --Low Permeability Barriers includes discussions on barrier
        materials,  placement, design,  installation, and maintenance.

     •  Chapter 8 -- Innovative Technologies includes discussions on
        bioreclamation, in situ chemical treatment, and emerging technologies.


     This report was submitted in fulfillment of Contract No. 68-03-3113,
Task No. 38-1 by SAIC/JRB under the sponsorship of the U.S. Environmental
Protection Agency.
                                      IV

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                                   CONTENTS


                                                                       Page

1.0  INTRODUCTION	     1-1


2.0  PLUME DYNAMICS	     2-1

     2.1  Groundwater Flow Patterns	     2-2

          2.1.1  Basic Hydrogeologic Concepts	     2-2
          2.1.2  Effects of Subsurface Conditions	     2-15
          2.1.3  Effects of Human Activities 	     2-28

     2.2  Effects of Leachate Characteristics	     2-39

          2.2.1  Effects of Physical  Characteristics 	     2-40
          2.2.2  Effects of Geochemical  Interactions 	     2-50


3.0  PLUME DELINEATION 	     3-1

     3.1  Plume Delineation Procedures	     3-2

          3.1.1  Calculate Possible Plume Boundaries	     3-2
          3.1.2  Modify and Verify Calculated Boundaries	     3-8
          3.1.3  Extrapolate Future Plume Movement 	     3-11

     3.2  Indirect  Data	     3-16

          3.2.1  Previously Collected Data	     3-22
          3.2.2  Aerial Imagery	     3-28
          3.2.3  Geophysical  Methods 	     3-35

     3.3  Direct  Data	     3-47

          3.3.1  Hydrologic Testing	     3-49
          3.3.2  Sampling	     3-62

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                             CONTENTS (Continued)


                                                                       Page

4.0  PLUME CONTROL TECHNOLOGIES	     4-1

     4.1  Control  Techniques 	     4-2

          4.1.1  Groundwater Pumping 	     4-2
          4.1.2  Subsurface Drains 	     4-5
          4.1.3  Low Permeability Barriers	     4-9
          4.1.4  Innovative Technologies 	     4-14

     4.2  Technology Evaluation and Selection	     4-17

          4.2.1  Development of Alternatives 	     4-17
          4.2.2  Screening of Alternatives 	     4-20
          4.2.3  Detailed Analysis of Alternatives 	     4-30

     4.3  Design and Implementation of Alternatives	     4-43


5.0  GROUNDWATER PUMPING 	     5-1

     5.1  Introduction	     5-1

     5.2  Well Theory	     5-2

          5.2.1  Darcy's Law	     5-2
          5.2.2  Equilibrium Well Formula	     5-7
          5.2.3  Non-Equilibrium Well Formula	     5-11
          5.2.4  Semiconfined Aquifers  	     5-15
          5.2.5  Partially  Penetrating Wells 	     5-21
          5.2.6  Cumulative Drawdown  	     5-24
          5.2.7  Hydrogeologic Boundary Effects	     5-28
          5.2.8  Flow Between Discharge and  Recharge Wells  ....     5-31
          5.2.9  Radius of  Influence	     5-31

     5.3  Applications	     5-38

          5.3.1  Groundwater Level Adjustment	     5-38
          5.3.2  Plume Containment  	     5-39
          5.3.3  Plume Removal	     5-42

     5.4  Design and Construction	     5-44

          5.4.1  Well Design	     5-44
          5.4.2  System Design	     5-80
          5.4.3   Installation  and  Maintenance of  Wells  	     5-95

     5.5  Costs of  Well Systems	     5-109

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                             CONTENTS (Continued)


                                                                       Page

6.0  SUBSURFACE DRAINS 	      6-1

     6.1  Introduction	      6-1

     6.2  Theory	      6-8

          6.2.1  Drainage System Terminology 	      6-12
          6.2.2  Depth and Spacing	      6-17

     6.3  Design	      6-38

          6.3.1  Flow Capacity	      6-39
          6.3.2  Filters and Envelopes	      6-46
          6.3.3  Design and Selection of Pipes	      6-53
          6.3.4  Drainage Sump and Pumping Plant	      6-57

     6.4  Installation and Maintenance 	      6-60

          6.4.1  Trench Excavation 	      6-60
          6.4.2  Drain Installation	      6-81
          6.4.3  Inspection and Maintenance	      6-93


7.0  LOW PERMEABILITY BARRIERS	      7-1

     7.1  Slurry Walls	      7-2

          7.1.1  Applications and Limitations	      7-2
          7.1.2  Theory	      7-8
          7.1.3  Design and Construction	      7-37
          7.1.4  Completed Wall Costs	      7-61

     7.2  Grouting	      7-63

          7.2.1  Theory	      7-65
          7.2.2  Design and Construction	      7-81
          7.2.3  Grouting Costs	      7-104


8.0  INNOVATIVE TECHNOLOGIES 	      8-1

     8.1  Introduction	      8-1


     8.2  Bioreclamation	      8-9

          8.2.1  Applications and Limitations	      8-11
                                      vn

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                             CONTENTS  (Continued)
     8.2.2  Theory
     8.2.3  Design and Operation
8.3  Chemical  Treatment
     8.3.1  Soil  Flushing/Solution Mining
     8.3.2  Oxidation/Reduction
     8.3.3  Precipitation/Polymerization
     8.3.4  Neutralization/Hydrolysis
     8.3.5  Permeable Treatment Beds
8.4  Block Displacement
                                                                       8-15
                                                                       8-23

                                                                       8-49

                                                                       8-49
                                                                       8-53
                                                                       8-68
                                                                       8-70
                                                                       8-80

                                                                       8-92
Bibliography
COPYRIGHT NOTICE

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                                    FIGURES
Number                                                                 Page

2-1   Example Calculation of Horizontal  Hydraulic
        Gradient	     2-8

2-2   Potentiometric Surfaces in Confined and
        Unconfined Aquifers 	     2-10

2-3   Example Calculation of Vertical  Gradient	     2-12

2-4   Example of How Groundwater Velocity Can Vary with
        Differing Hydrogeologic Conditions and with
        Differing Scales of Observation  for Key Parameters	     2-13

2-5   Characteristic Plume of Miscible Contaminants in
        a Homogeneous Aquifer 	  ....     2-16

2-6   Effects of Variable Hydraulic Conductivity on
        Leachate Plume Movement in Unconsolidated Material	     2-18

2-7   Effects of Secondary Porosity on Leachate
        Plume Movement	     2-19

2-8   Effects of Groundwater Flow Direction and Geologic
        Heterogeneities on Leachate Plume Movement	     2-22

2-9   Effect of a High-Head, Semi-Confined Unit on
        Leachate Plume Movement 	     2-24

2-10  Example of the Effects of Site Geology on
        Leachate Plume Movement (Cross-Sectional View)	     2-25

2-11  Example of the Effects of Site Geology on
        Leachate Plume Movement (Map View)	  .     2-26

2-12  The Effect of Waste Site Location  Relative to
        Location of Recharge and Discharge Areas on
        Plume Migration	     2-29

2-13  Effects of Human Activities on Leachate Plume
        Movement (Map View)	     2-36
                                      IX

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                              FIGURES (Continued)


Number                                                                 Page

2-14  Effects of Human Activities on Leachate Plume
        Movement (Cross-Sectional View) 	    2-37

2-15  Effects of a Heterogeneity on the Flow of a
        High Density Plume	2-44

2-16  Effect of Density on Leachate Plume Movement	    2-46

2-17  Configurations Based on Solubility and Density	    2-47

2-18-  Types of Breakthrough Curves Generated by the
        Soil Column Technique 	    2-60

3-1   Generalized Approach to Delineating Leachate Plumes 	    3-3

3-2   Well  Configurations Used for Groundwater Monitoring 	    3-67

3-3   Well  Design for Preventing Interaquifer Contamination ....    3-74

5-1   Development of Flow Distribution about a Discharging
        Well in a Free Aquifer - A Fully Penetrating and
        33-Percent Open Hole	    5-4

5-2   Formation of Cone of Depression Around a Pumping Well ....    5-5

5-3   Effect of Storage and Transmissivity on the Shape
        of the Cone of Depression	    5-6

5-4   Unconfined Aquifer Flow . „	    5-8

5-5   Confined Aquifer Flow	    5-9

5-6   Plots of H-h Versus r for Unconfined and
        Confined Aquifers 	    5-10

5-7   Semi confined Aquifer	    5-19

5-8   Flow to Partially Penetrating Wells	    5-23

5-9   Flow in Confined Aquifer with Partially
        Penetrating Well	    5-25

5-10  Composite Drawdown in a Confined Aquifer	    5-26

5-11  Composite Drawdown in an Unconfined Aquifer 	    5-27

5-12  Effect of Recharge and Barrier Boundaries
        on Drawdown	    5-29

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                              FIGURES (Continued)


Number                                                                 Page

5-13  Method of Images for Determining Resultant
        Cone of Depression	    5-30

5-14  Recharge and Discharge Wells in a Confined Aquifer	    5-32

5-15  Distance Drawdown Diagrams for A) Varying Pumping
        Rating and B) Varying Pumping Times 	    5-35

5-16  Plume Diversion Using Injection Wells 	    5-40

5-17  Containment Using Extraction Wells	    5-41

5-18  Extraction and Injection Wells Patterns for
        Plume Removal	    5-43

5-19  Components of Typical Deep Well	    5-48

5-20  Performance Curves	    5-56

5-21  Range of Filter Selections	    5-66

5-22  Grain-Size Analysis Curve	    5-69

5-23  Componennts of One-Pipe and Two-Pipe Ejector Wells	    5-72

5-24  Driven Uellpoint (a), Jetted Wellpoint (b), and
        Drilled Wellpoint (c) 	    5-77

5-25  Basic Injection Well	    5-79

5-26  Potentiometn'c Surface Map and Geologic Cross-Section
        of Gasoline Pollution Site	    5-81

5-27  Drawdown Versus Yield and Specific Capacity for
        a Water Table Aquifer 	    5-91

5-28  Well Placement and Drawdown Superimposed onto
        Groundwater Maps	    5-93

5-29  Typical Well System Components	    5-111

6-1   The Use of Subsurface Drainage to Contain a
        Leachate Plume.	    6-4

6-2   The Use of Subsurface Drainage to Lower Groundwater
        Levels	    6-5
                             i

6-3   The Use of a One Sided Subsurface Drain for Reducing
        Flow from Uncontaminated Sources	    6-6

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                              FIGURES (Continued)


Number                                                                 Page

6-4   The Use of Subsurface Drainage in a Completely
        Encapsulated Site	     6-7

6-5   The Use of Subsurface Drainage to Prevent
        Overflow and Ponding	     6-7

6-6   Differences Between Groundwater Flow Toward
        Drains Versus Wells 	     6-9

6-7   Relationship Between Drawdown (H-h) in a Drain
        and a Well	     6-11

6-8   The Affect of Relief and Intercepter Drains  in
        Altering the Configuration of the Water Table 	     6-13

6-9   The Use of Interceptor Drains to Collect Flow
        Induced by Groundwater Mounding 	     6-14

6-10  Components of a Drainage System	     6-15

6-11  The Relationship of Drain Depth and Spacing  to
        Water Table Drawdown	     6-18

6-12  The Effect of Depth to a Low Permeability
        Barrier on Drain Spacing	     6-20

6-13  The Effect of Hydraulic Conductivity Drain Spacing	     6-21

6-14  Flow to a Drain Resting on a Low Permeability
        Barrier	     6-23

6-15  Flow to Drain Not Resting on a Low Permeability
        Barrier	     6-24

6-16  Symbols for the Ernst Equation for Flow in a Two-Layered
        Soil with (A) the Drain in the Lower Layer
        and  (B) the Drain in the Upper Layer	     6-27

6-17  Nomograph for Determining the Geometry Factor,
        in the Ernst Equation	     6-30

6-18  Site Conditions Requiring Interceptor Drains for
        Plume Management	     6-33

6-19  Location of a Subsurface Drain with Respect to
        Topography and the Direction of Groundwater Flow	     6-34
                                      xn

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                              FIGURES (Continued)


Number                                                                 Page

6-20  Symbols for the Glover and Donnan Equation for
        Calculating the Downgradient Influence of an
        Interceptor Drain 	    6-37

6-21  Capacity Chart for  N = 0.013	    6-44

6-22  Capacity Chart for N = 0.015	    6-45

6-23  Mechanical  Analysis of a Gravel Filter Material 	    6-51

6-24  Joint Design for Rigid Drain Tiles	    6-54

6-25  Typical Design of an Automatic Drainage
        Pumping Plant	    6-58

6-26  Correlation of Required Excavation Methods with
        Seismic Testing Data	    6-62

6-27  Costs of Shoring for Deep Trenches	    6-72

6-28  Pipe Drain  with Filter Fabric	    6-88

6-29  Typical Manhole Design for a Closed Drain 	    6-91

6-30  Typical Design of Sediment Trap and Wetwell	    6-93

7-1   Hanging Slurry Wall	    7-5

7-2   Hanging Slurry Wall	    7-6

7-3   Plan of Circumferential  Wall Placement	    7-7

7-4   Cut-Away Cross-Section of Circumferential
        Wall Placement	    7-7

7-5   Plan of Upgradient Placement with Drain	    7-9

7-6   Cut-Away Cross-Section of Upgradient Placement
        with Drain	    7-9

7-7   Plan of Downgradient Placement	    7-10

7-8   Cut-Away Cross-Section of Downgradient Placement	    7-10

7-9   Fluid Loss  During Filter Cake Formation 	    7-18
                                     XII 1

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                              FIGURES (Continued)


Number                                                                 Page

7-10  Relationship Between Permeability and Quantity
        of Bentonite Added to SB Backfill	    7-23

7-11  Effect of Plastic and Non-Plastic Fines Content
        on Soil-Bentonite Backfill  Permeability  	 .....    7-24

7-12  Typical Slurry Wall Construction Site	    7-44

7-13  Cross-Section of Slurry Trench, Showing
        Excavation and Backfilling Operations 	    7-53

7-14  Grouting Pipe Layout for Constructing a
        Barrier Uall	    7-98

7-15  Stage-up Grout-Port Injection Process 	    7-100

7-16  Diagram of a Double Packer Used in
        Grout Port Injection	    7-101

7-17  Vibrating Beam Grout Placement Process	    7-102

8-1   Simplified View of Groundwater BiorecTarnation 	    8-10

8-2   Typical Groundwater Temperatures (°F) at 100 Foot
        Depth in the Conterminous United States	    8-14

8-3   Simplified Selective Adaption/Mutation Process	    8-19

8-4   Configuration of Reinjection  Trenches 	    8-29

8-5   Configuration of Static Mixer 	    8-31

8-6   Possible Configuration of In  Situ Aeration
        Well  Bank	    8-34

8-7   Configuration of In Situ Oxygenation Well  System
        and Dissolved Oxygen Concentrations as a
        Function of Distance from Well	    8-36

8-8   Installation of a Permeable Treatment Bed	    8-81

8-9   Schematic Diagram of Block Displacement 	    8-94

8-10  Schematic Cross-Section of Block Displacement
        Showing Separating to Induce Displacement 	    8-97

8-11  Slurry Jet in Air Notching Operation	    8-99
                                      xiv

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                                    TABLES


Number                                                                 Page

2-1   Range of Porosity Values for Various Geologic Materials. . .     2-4

2-2   Range of Hydraulic Conductivity Values for
        Various Geologic Media	    2-6

2-3   Effects of Several Remedial  Action Measures on
        Leachate Plume Migration	    2-31

2-4   Distribution of Contaminant  Types for Superfund
        Sites	    2-40

2-5   Factors Affecting Leachate Volume Generation	    2-42

2-6   Examples of Plume Constituents Based on
        Solubility and Density	    2-48

2-7   Probable Effect of Various Processes on the
        Mobility of Constituents in Subsurface
        Waters Contaminated by Waste Disposal 	    2-55

2-8   Processes Which May Control  Amounts of Certain
        Constituents in Subsurface Waters Contaminated
        by Waste Disposal	    2-58

2-9   Behavior of Specific Chemical Wastes at Landfills 	    2-59

2-10  Pesticide Mobility Based on  Distribution
        Coefficients	    2-62

3-1   Information Sources for Calculating Velocity
        Using Darcy's Law (V = Kl/n)	    3-6

3-2   Example Calculations of Maximum Plume Limits (D ) 	    3-9

3-3   Release Rate Models	•	    3-13

3-4   Analytical Solute Transport  Models	    3-17

3-5   Numerical  Transport Models	    3-19

3-6   Type of Information Generally Available in
        U.S.  EPA Site Investigation Reports	    3-23
                                      xv

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                              TABLES (Continued)


Number                                                                 Page

3-7   Types and Sources of Maps, Reports, and
        Related Information 	    3-24

3-8   Examples of Additional  Sources of Information
        for Remedial  Investigations 	    3-29

3-9   Summary of Borehole Log Applications	    3-48

3-10  Significance of Selected On-Site Observations
        to Plume Delineation	    3-50

3-11  Laboratory Methods for  Determining Hydraulic
        Conductivities	    3-57

3-12  Effects of Various Types of Errors on Laboratory
        Measured Values of Hydraulic Conductivity 	    3-58

3-13  Single Well Tests	    3-60

3-14  Multiple-Well Pump Tests	    3-61

3-15  Advantages and  Disadvantages of Various Types
        of Monitoring Well Configurations 	    3-68

3-16  Design Specifications for Monitoring Wells	    3-70

3-17  Selected Groundwater Sample Withdrawal Methods	    3-78

3-18  Containers, Preservation, and Holding Times 	    3-79

3-19  Potential Sources of Factors Affecting
        Groundwater Sampling Validity 	    3-85

4-1   Criteria for Well Selection	    4-4

4-2   The Influence of Site Geology on the Selection and
        Performance of Leachate Migration Control Technologies. .  .    4-21

4-3   The Influence of Site Hydrology on the Selection
        and Performance of Leachate Migration
        Control Technologies	    4-22

4-4   The Influence of Plume Characteristics on the
        Selection and Performance of Leachate Migration
        Control Technologies	    4-24

4-5   The Influence of Surface Conditions on the
        Selection and Performance of Leachate Migration
        Control Technologies	    4-26
                                      xvn

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                              TABLES (Continued)


Number                                                                 Page

4-6   Factors Affecting the Relative Reliability of
        Leachate Migration Control  Technologies 	    4-32

4-7   Factors Affecting the Implementability of
        Leachate Migration Control  Technologies 	    4-34
4-8   Selected Regulatory Requirements for Aquifer
        Restoration Activities	    4-38

4-9   Relative Costs and Key Cost Hens of
        Leachate Migration Control  Technologies 	    4-42

4-10  Summary of the Four Basic Leachate Migration
        Control  Technologies	    4-44

5-1   Simplifying Assumptions for Steady State Equations.  .....    5-12

5-2   Values of W (M) for Various Values of M	    5-14

5-3   Values of the Function W (MA«T) f°r Water-Table
        Aquifers	    5-16

5-4   Values of the Function W (Mn,r ) for Water-Table
        Aquifers	    5-17

5-5   Values of Functions W (M, r/B) and W (//., r/B) for
        Various Values of M or//.	    5-20

5-6   Values of the Function H (M,0)	    5-22

5-7   Radius of Influence for Various Unconsolidated
        Materials	    5-33

5-8   Methods for Calculating the Radius of Influence (R )	    5-37

5-9   Data Requirements for Well  System Design	    5-46

5-10  Criteria for Well Selection	    5-47

5-11  Deep Well Components and Selection Criteria	    5-49

5-12  Loss of Head Due to Friction  in Smooth Pipe	    5-54

5-13  Approximate Head Loss Equivalents for Pipe Fittings  	    5-55

5-14  Recommended Well Casing Diameters 	    5-57

5-15  Well Screen Types	    5-59
                                     xvn

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                              TABLES (Continued)


Number                                                                 Page

5-16  Well  Screen Materials and Applications	     5-60

5-17  Criteria for Well  Screen Length Selection 	     5-62

5-18  Recommended Entrance Velocities for Various Filters 	     5-63

5-19  Open  Areas of Commercially Available Wellscreens	     5-64

5-20  Filter Selection Criteria 	     5-68

5-21  Well  Screen Selection for Stratified Soils	     5-70

5-22  Recommended Casing and Riser Sizes for
        Ejector Systems 	     5-73

5-23  Ejector System Performance Specifications 	     5-75

5-24  Advantages and Disadvantages of Pumping Methods 	     5-83

5-25  Radius of Influence Equations 	     5-85

5-26  Methods of Well  Installation	     5-97

5-27  Range of Costs for Selected Pumps and Accessories  	     5-113

5-28  Typical Range of Costs for Well Screens and
        Wellpoints	     5-114

5-29  Average Drilling Costs (1981) for Unconsolidated
        Materials	     5-115

6-1   Values for Equivalent Depth d(m) for r, = 4 inches
        Calculated for Different Values of Drain  Spacing (L)
        and Saturated Thickness Below Drains (D)	     6-26


6-2   Minimum Grades for Various Pipe Sizes	     6-41

6-3   Critical Velocity of Various Soil Types  	     6-41

6-4   Drain Grades for Selected Critical Velocities 	     6-42

6-5   A Classification to Determine the Need for
        Drain Filters or Envelopes	     6-50

6-6   Approximate Hourly Production in Cubic Yards
        for Ladder and Wheel Trenchers Operating  at
        100 Percent Efficiency	     6-67
                                     xv m

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                              TABLES (Continued)
Number                                                                 Page

6-7   Theoretical Hourly Production of a Hydraulic
        Backhoe	    6-69

6-8   Production Costs for Trenching Using Backhoes 	    6-69

6-9   Theoretical Hourly Production Rate of a
        Dragline Excavator	    6-70

6-10  Typical Characteristics of Self-Priming Centrifugal
        Pumps	    6-76

6-11  Representative Specifications and Performances
        of Centrifugal Submersible Pumps	    6-77

6-12  Representative Specifications and Performances
        of Diaphragm Pumps	    6-78

6-13  Cost for Open Pumping	    6-79

6-14  Specifications for Stabilizing Gravel 	 . 	    6-82

6-15  Installation Costs for Drainage Pipe	    6-85

6-16  Estimated Costs and Outputs for Backfilling
        by Dozer	    6-90

6-17  Installed Costs for Manholes	    6-92

7-1   Summary of Slurry Wall Configurations .	    7-11

7-2   Specified Properties of Bentonite and Cement
        Bentonite Slurries	    7-13

7-3   Comparison of Selected Properties of Clays	    7-15

7-4   Typical Compositions of Cement-Bentonite Slurries 	    7-20

7-5   Types of Physical Constraints and Their Effects
        on Slurry Wall Construction	    7-46

7-6   Excavation Equipment Used for Slurry Trench
        Construction	    7-49

7-7   Materials Quality Control Program for Soil-
        Bentonite Walls 	    7-54

7-8   Materials Quality Control Program for Cement-
        Bentonite Walls	    7-62
                                      xix

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                              TABLES (Continued)


Number                                                                 Page

7-9   Relation of Slurry Cut-Off Wall Costs per Square
        Foot as a Function of Medium and Depth	    7-64

7-10  Approximate Costs of Grouts	    7-105

8-1   Hazardous Soil Contaminants at Superfund Sites	    8-5

8-2   Potential Useful  Soil In Situ Treatment Processes 	    8-7

8-3   BOD5/COD Ratios for Various Organic Compounds 	    8-12

8-4   Refractory Indices for Various Organic Compounds	    8-13

8-5   Problem Concentrations of Selected Chemicals	    8-24

8-6   Solubilities of Oxygen in Water at Selected
        Temperatures	    8-31

8-7   Oxygen Solubility in Water in Equilibrium with
        Oxygen Gas at One Atmosphere	    8-35

8-8   Capital Costs for Ozone Treatment 	    8-41

8-9   Power Costs for Ozone Generator System	    8-42

8-10  Composition of Basal Salts Medium 	    8-45

8-11  Basal Salt Medium Used by GDS  Inc	    8-45

8-12  Surfactant Characteristics	    8-54

8-13  Environmental Chemical Properties of Selected
        Commercial Surfactants	    8-56

8-14  Waste Chemical Classes Ability to React with
        Hydrogen Peroxide  	 ....    8-59

8-15  Waste Chemical Classes Ability to React with Ozone	    8-62

8-16  Waste Chemical Classes Ability to React with
        Hypochlorites  	    8-64

8-17  Costs for  In Situ Detoxification of Cyanide	    8-67

8-18  Hydrolysis of  Alkyl  Hal ides	    8-72

8-19  Hydrolysis of  Epoxides	    8-73
                                       xx

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                              TABLES (Continued)


Number                                                                 Page

8-20  Hydrolysis of Esters	    8-74

8-21  Hydrolysis of Amides	    8-76

8-22  Hydrolysis of Carbamates	    8-77

8-23  Hydrolysis of Phosphoric and Phosphonic Acid Esters 	    8-78

8-24  Hydrolysis of Miscellaneous Compounds Including
        Pesticides	    8-79

8-25  Results of Chemical Analyses of Greensand
        Filtration of Pigeon Point Landfill Leachate	    8-87

8-26  Chemical Composition of Glauconites from the
        Delaware Coastal Plain	    8-88

8-27  Estimated Costs for Installation of a Permeable
        Treatment Bed	    8-93
                                      xxi

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                                    SYMBOLS


                                               2
A          Area or cross-sectional area (length )

                                         2
     Ad    Area affected by drain (length )

                                                2
     A     Area normal to flow direction (length )

                                           2
     AQ    Open area of well screen (length )


     A     Cross-sectional area of pipe

                                                 2
     A     Cross-sectional area of sample (length )
      o
                                                 2
     A     Cross-sectional area of a well  (length )
      w

a          Geometric factor for radial flow (dimensionless) or volume fraction
           (dimension less)


B          Width of area drained by a drainage pipe (length)


b          Width of trench (length)


C          Concentration of a substrate (wt/vol)


     Cf    Final concentration of substrate (wt/vol)


     C.j    Initial  concentration (wt/vol)


     C.     Concentration of oxygen in a liquid (wt/vol)


     C     Microbe concentration (wt/vol)


     C     Concentration of oxygen in a liquid (wt/vol)


           Concentration of substrate supporting half of the maximum growth
           rate (wt/vol)


     C     Uniformity coefficient (dimensionless)


c          Constant


D          Height of the drain above an impervious layer (length)


     D,     Thickness of water bearing zone below drain (length)
                                     xxii

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      Dd    Distance downgradient from the drain where the water table is
            lowered to a desired depth (length)

      De    Difference in water elevation in a pumped sump (length)

      D     Distance from the water level in a drain to the next soil  layer
            (length)

      D     Distance a leachate plume migrates from source (length)

      Dr    Aquifer thickness where radial  flow occurs (length)

      DU    Effective distance of drawdown  upgradient (length)

      DV    Aquifer thickness where vertical  flow occurs (length)

      D     Diameter (length)
       A

      D,     Distance from the ground surface to water table at  the  drain
            (length)

      D?    Distance from the ground surface to water table at  distance D,  from
            the  drain  (length)                                            °

d           Equivalent depth  of  aquifer  below drain  (length)

      dg     Effective drain depth  (length)

E           Elevation  (length)

      Ej     Groundwater  elevation  at  start of aerated  flow  (length)

      E£     Groundwater  elevation  at  end  of  aerated  flow (length)

      E      Activation energy

e           Base of  natural logarithms

G           Geometric factor  for radial flow
                                               o
g           Acceleration of gravity  (length/time  )

H           Total hydraulic head (length) or
            Maximum height of water table above the drain midway between drains
            (length)

     H^     Henry's law constant for oxygen

     H-h    Drawdown (length)

h           Height of water table after drawdown (length) or depth to bottom
            separation
                                     xxm

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     h.    Desired depth of water table after draining (length)



     h     Final head (length)



     tv    Total frictional losses in well system expressed as head (length)



     h.    Initial head (length)



     h.    Total vertical lift in a well (length)



     h     Head difference across sample (length)



     h.    Total dynamic head in a well (length)



     h     Velocity head required to produce flow in a well (length)



     h     Height of water in the well (length)



     h     Optimum drawdown (length)



  h,-h?    Difference in water table levels at two points on a line parallel

           to flow direction (length)



I          Hydraulic gradient



i          Inflow rate (vol/time)



K          Hydraulic conductivity (length/time)



     K.     Horizontal  hydraulic conductivity (length/time)



     K.     Hydraulic conductivity of lower aquifer (length/time)



     K     Hydraulic conductivity of aquifer with radial  flow (length/time)



     K     Hydraulic conductivity of aquifer with vertical flow (length/time)



     K     Weighted average hydraulic conductivity (length/time)



     K     Vertical hydraulic conductivity (length/time)



     K,    Hydraulic conductivity of aquifer above drain  (length/time)



     Kp    Hydraulic conductivity of aquifer below drain  (length/time)



     K1    Hydraulic conductivity of leaky confining layer (length/time)

                                         p

k          Intrinsic permeability (length )



     k     Acid catalyzed hydrolysis constant
      a


     k     Apparent constant
                                     xxiv

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     k.     Base catalyzed hydrolysis constant

     k.    Distribution coefficient

     k     Roughness factor

     k..    Neutral hydrolysis constant

     k     Partition coefficient of substance

L          Influence of relief drain or drain spacing (length)

     L     Length of aerated zone (length)
      a

     L     Downslope influence of drains (length)

     Lf    Length of groundwater flow path between h, and h^ (length)

     LS    Length of sample (length)

1          Length of well screen as a fraction of aquifer thickness
           (dimensionless)

m          Aquifer thickness (length)

     m     Saturated thickness at aquifer (length)

     m1     Thickness of leaky confining layer (length)

N          Roughness coefficient

n          Effective porosity (percent)

P          Air pressure (wt/vol)

     P     Average earth mass density

     AP    Pressure in excess of the overburden

p          Density (wt/vol)

Q          Discharge (vol/time)

     Q     Gravity discharge capacity (vol/time)

     Qj     Recharge rate of  injection well  (vol/time)

     Qm    Pumping discharge rate (vol/time)

     Q     Pumped  discharge  capacity (vol/time)

     O     Discharge rate of pumping well  (vol/time)
                                      xxv

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     Q     Specific capacity of fully penetrating well (vol/time)

     Q     Specific capacity of partially penetrating well (vol/time)

     Q     Expected or desired yield of well (vol/time)

     Q,     Discharge of high pressure supply water (vol/time)

     Q?     Discharge of groundwater to supply line (vol/time)

q          Rate of water flow, specific discharge, or drainage coefficient
           (length/time)

R          Hydraulic radius (length)

     R     Radius of influence of well (length)

     R     Gas content (vol)

     R.     Initial reaction rate

     R     Shear rate

     Rt     Temperature correct reaction rate

r          Distance from well  to measured drawdown (length)

     r.     Drain radius (length)

     r     Equivalent well radius (length)

     r     Well radius (length)

S          Coefficient of storage

     S     Sump storage volume (vol)

     S     Specific yield (percent)
      J
s          Slope of the angle between the water table and horizontal plane
                                 2
T          Transmissivity (length /time)

     T     Absolute temperature (degrees)
      a
     T     Initial gel strength

     TQ     Yield stress

     T     Shear stress

t          Time (time)
                                     xxvi

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     t     Cycle time of pump (time)
      L*


     t     Pumping time (time)



     t     Residence time (time)



           Half life (time)



U          Uniformity coefficient



     U     Maximum growth rate of microbes



u          Wetted perimeter and drain (length) or specific weight of fluid



V          Velocity or average linear velocity (length/time)



     V,     Water velocity in permeable treatment bed (length/time)



     V     Groundwater velocity (length/time)



     V     Entrance velocity (length/time)



v          Viscosity



     v     Apparent viscosity
      a


     v     Plastic viscosity



W(u)       Well function (dimensionless)



W,         Thickness of permeable treatment bed



x          Length of drain pipe (length)



Yd         Yield coefficient



           Volume fraction



/LU, fj.fr, T   Well functions
                                     xxvi i

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                              CONVERSION FACTORS





Length-



     1 inch (in)  = 25.4 millimeters (mm).



     1 foot (ft)  = 0.3048 meters (m).



     1 yard (yd)  = 0.9144 meters (m).



     1 mile (mi)  = 1.6093 kilometers  (km)





Area-


                      2                                2
     1 square inch (in )  = 645.2 square  millimeters  (mm )


                      2                           9
     1 square foot (ft )  = 0.0929 square meters  (m).


                      9                           2
     1 square yard (yd")  = 0.8361 square meters  (m ).


                      2                             2
     1 square mile (mi )  = 2.59  square  kilometers  (km  ).



     1 acre (ac)  = 0.4047 hectares (ha).





Volume-


                     3                              3
     1 cubic inch (in ) = 16.39  cubic  centimeters  (cm  )



     1 cubic foot (ft3) = 0.02832 cubic  meters  (m3)
                        = 28.32  liters  (1)



                        = 0.7646  cubic  meti

                        = 764.6  liters  (1)



                        ubic  meti

              = 3.785  liters  (1)



                      =  1,233.5  (

                      =  1,233,000 liters  (1)



                             =  2,451.3  cubic

                             =  2,450,000  liters  (1).
1 cubic yard (yd3)  = 0.7646  cubic  meters  (m3)
1 gallon = 0.0038 cubic  meters  (m3)
1 acre-foot (af)  = 1,233.5  cubic  meters  (m  )
                                                 2
I second foot day (sfd)  =  2,451.3  cubic  meters  (m )
                                    xxvi11

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Mass-

     1 ounce (oz.) = 28.35 grams (g).

     1 pound (Ib.) = 0.4536 kilograms (kg).

     1 ton = 907.2 kilograms (kg)
           = 0.907 tonne (t)


Velocity, linear-

     1 foot per second (ft/sec)  =  30.48 centimeters per second (cm/s)

     1 mile per hour (mph) = 1.609 kilometers per hour (km/hr) =
       4.47  x 10"  meters per second (m/s).


Flow Rate (volumetric)-

     1 gallon per minute (gprn) = Q.0631 liters per second (1/s)  = 6.309 x 10
       cubic meters per second (m  /s) = 5.451 cubic meters
       per day (m /d)

     1 cubic foot per  second (ft3/s)  = 0.02832 cubic meters per second (nr/s)
       = 28.32 liters  per second (1/s).


Transmissivity-

                              7                                        2
     1 square foot per day (ft /day)  = 0.09289 square meters per day (m /d).

     1 gallon per day  per foot (gpd/ft) = 0.01242 square meters per day
       (mVd).


Viscosity-
                      _c                                                   y
     poise = 1.45 x 10~  pounds (weight)  seconds per square inch (Ib.sec/in  )


Density-

     1 pound per cubic foot (pcf)  = 16.02 kg/m


Pressure-
                                                                            2
     1 pound per square inch (psi) =  70.31 grams per square centimeter (g/cm )
       = 68948 dynes per?square centimeters  (dynes/cm ) = 6894.8 newtons per
       square meter (N/m ).
                                     xxix

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Force-
     1 pound (Ib, weight)  = 4.448 meters = 4.448 x 10  dynes
       = 33.36 poundals.
Temperature-
     Degrees Celsius (°C) = 5/9 (°F-32)
     Degrees Kelvin (°K)  = degrees °C +  273.16

Work, Energy, Power, Quantity of Heat-
     1 kilowatt-hour = 3.6 x 106 joules  = 3,409.52 British Thermal  Units
(Btu).
     1 horsepower = 0.746 kilowatt (kW).
                                      xxx

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                               ACKNOWLEDGEMENTS

     This document was prepared by SAIC/JRB for EPA's Office of  Research  and
Development  in partial fulfillment of Contract No. 68-03-3113, Task  38.   Ms.
Naomi Barkley, of the Hazardous Waste Engineering Research Laboratory,  Land
Pollution Control Division, served as the EPA Project Officer.   Dr.  Edward
Repa and Mr. Charles Kufs were Task Managers and principal authors for
SAIC/JRB.  Other major contributors from SAIC/JRB included Mr. Paul
Rogoshewski, Ms. Kathleen Wagner, Mr. Edward Tokarski, Ms. Marjorie  Kaplan,
Mr. Philip Spooner, and Ms. Constance Spooner.

     Preparation of this handbook was aided greatly by the constructive
contributions of the following reviewers:

     Mr. Donald Sanning               U.S. EPA HWERL
     Mr. Richard Stanford             U.S. EPA OERR
     Mr. Joseph Keely                 U.S. EPA Robert S. Kerr Environmental
                                      Research Laboratory
     Dr. David D'Appolonia            ECI
     Dr. Wayne Pettyjohn              Oklahoma State University
     Dr. Rip Rice                     Rip Rice, Inc.
     Mr. William Walker               Walker Wells, Inc.

Appreciation is also extended to other numerous individuals from SAIC/JRB and
Federal, state, and industrial organizations who contributed or were contacted
on matters related to development of this handbook.
                                     xxxi

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                                   CHAPTER 1
                                 INTRODUCTION
     Cleaning up the thousands of hazardous waste sites identified across the
United States is a serious environmental challenge.  Of particular importance
is protecting and cleaning up contaminated groundwaters that now serve or
could serve as drinking water supplies.  The magnitude of this problem is
illustrated by the fact that nearly 70 percent of sites surveyed in 1983 and
now undergoing corrective action have contaminated groundwaters (JRB
Associates and Environmental Law Institute, 1983).

     Contaminants can enter the groundwater system through a variety of
mechanisms.  Some disposal sites contain fine solids or sludges that can be
transported via infiltrating solutions.  The amount of solids transported
depends on the size of the particles, the size and interconnectedness of void
spaces, the speed of percolating solutions, and the surface area of waste in
contact with the solutions.  The maximum size of a particle transported is a
function of pore space diameter and percolation rate.  As the rate of solution
movement increases, the solution's capacity to carry solids in suspension
increases.  When large areas of fine particle wastes are in contact with per-
colating solutions, a greater opportunity for transport of solids  exists.

     In areas where the geologic material  between the waste site and the
groundwater table is permeable, movement of liquid waste to the groundwater
regime is possible.   The amount of direct  liquid  waste  seepage is  highest
when:

     •  Highly permeable material  exist within the waste site and  between the
        site  and  the groundwater table
                                     1-1

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     t  The distance separating wastes  and groundwater is  minimal,  or  the
        wastes are in direct contact with the groundwater
     •  The wastes consist of uncontainerized liquids  that have  a higher
        density and lower viscosity than water.
     Waste organic and inorganic  solutions  can  dissolve  other  waste  constit-
uents, thereby greatly increasing the  mobility  of  some contaminants.
Solvents, soaps, and emulsifying  agents  can  also dissolve  or suspend waste
constituents in infiltrating solutions.   Therefore,  water  insoluble  wastes
should not necessarily be considered  immobile.

     By far the most predominant  means of contaminant movement to  the  ground-
water system is via dissolution  by infiltrating precipitation.  Wastes  dis-
solved into infiltrating solutions are carried  through the waste site  and
underlying soil, along solution  channels or  seepage  paths, and to  the
groundwater table.

     Solutions resulting from the dissolution of waste constituents  into
percolating water are called leachate.  Leachate concentration depends  in part
on waste constituent solubility,  volume  of  precipitation,  and  length of time
the infiltrating solution is in  direct contact  with  waste. Certain
constituents are more soluble in  rainwater  than distilled  water because
rainwater is chemically different from distilled, water.  For example,  the pH
of distilled water is 7.0, while  rainwater  in nonurban,  nonindustrialized
areas commonly has a pH between  5 and  6  (Freeze and  Cherry, 1979).   Part of
this acidity is caused by the presence of dissolved  C(L  which  produces  up to
one percent carbonic acid (Gilluly, et al.,  1975).   The  pH of  acid rain can be
as low as 3 to 4 because of high  sulfur  oxides  or  nitrogen oxides  in air which
dissolve to produce sulfuric and  nitric  acids in the rainwater (Freeze  and
Cherry, 1979).  In addition to low pH, rainfall also contains  dissolved solids
and can entrain microbes and other matter as it percolates through soils or
wastes.  Thus, wastes that do not have a high solubility in distilled  water
under laboratory conditions may  become mobile in rainwater.
                                     1-2

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     The final means by which contaminants can be leached from a waste dispos-
al site is dissolution by groundwater.  While this route is important only
when wastes are in direct contact with groundwater, this route can be signifi-
cant because of the large volumes of water that can become contaminated.

     Once in groundwater, contaminants are not diluted and flushed from the
system to the extent they would be in surface water because flow rates-are
slower and flow paths more tortuous.  As a result, contaminants tend not to
disperse but form slugs or plumes.  Contaminant concentrations throughout a
leachate plume can vary considerably but are generally highest in the center
of the plume and closest to the contaminant source area.  The boundaries of a
leachate plume are usually indistinct, which makes vertical  and horizontal
plume delineation and control a very complicated. process.

     Leachate plume management has been complicated to some extent by a lack
of understanding of plume dynamics and the various site remediation options
available.  Generally, methods for controlling the migration of a leachate
plume can be placed into one of four categories--groundwater pumping,
subsurface drains, low permeability barriers, and innovative technologies.
Under the Comprehensive Environmental  Response, Compensation, and Liability
Act of 1980 (CERCLA), also known as "Superfund," the Environmental  Protection
Agency is implementing a program to assess and disseminate information on
these technologies and procedures related to plume management.

     The purpose of this handbook is to serve as a summary reference on
factors that affect leachate plume movement and considerations necessary to
develop effective plume management plans.  The handbook consists of eight
chapters as follows:

     •  Chapter 1  -- Introduction.
     •  Chapter 2  — Plume Dynamics.   Includes discussions  of the factors that
        affect  a  plume's  movement  and  shape in an  aquifer.
     •  Chapter 3  -- Plume Delineation.   Includes  discussions  of plume
        delineation  techniques  such  as  the use of  models,  and  indirect and
        direct  methods.
                                     1-3

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     t  Chapter 4 -- Plume Control  Technologies.  Includes brief discussions
        about various plume control  technologies including groundwater
        pumping, drains, barriers,  and innovative technologies,  and on the
        selection of a plume control  technology to best meet site conditions.

     •  Chapter 5 -- Groundwater Pumping.   Includes discussions  of well
        hydraulics; well construction and  installation; and system design,
        operation, and maintenance.

     •  Chapter 6 -- Subsurface Drains.   Includes discussions of drain hydrau-
        lics; drain components and materials;  and system design, installation,
        and maintenance.

     t  Chapter 7 -- Low Permeability Barriers.   Includes discussions  of
        barrier placement; types of  barrier material;  and barrier design and
        installation.

     •  Chapter 8 -- Innovative Technologies.   Includes discussions of
        bioreclamation, in-situ chemical  treatments,  and emerging
        technologies.


     Many topics related to controlling  the migration  of leachate plumes are

not covered in this handbook.   Treatment of leachate  is discussed by EPA

(1980), De Renzo (1978), Hammer (1975),  and Liptak (1975).   Complementary

remedial  action technologies are summarized by EPA (1982a).   Procedures  for

safeguarding worker health and safety are  addressed by Heiss (1980), Lippitt,
et al. (1982), Allcott, et al. (1981), Turpin  (1981),  Weitzman and Cohen
(1981), and NEIC (1980).  The  role of community  relations during site
remediation is discussed by Cohen, et al .  (1981), Neuman and Drake (1982), and

ICF (1982).  Finally, case studies of leachate plume  control  have been
described by SCS (1980), JRB and ELI  (1983),  and Nielson (1982).
                                     1-4

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                                   CHAPTER 2
                                 PLUME DYNAMICS


     Leachate plumes are subject to various processes which alter their size
and shape, and their direction and flow rate.   These processes are related to
the nature of the contaminants; the groundwater flow patterns existing in the
area of concern; and the interactions between the contaminants, groundwater,
and the geologic media through which the plume moves.  While all the effects
of these processes are not known precisely and are still being researched,
general relationships have been observed or can be approximated.  The purpose
of this section is to discuss, in general terms, the processes affecting plume
movement.

     When  leachate seeps into groundwater, the leachate tends not to disperse
evenly.  Instead, variations occur in contaminant concentration depending on
position within the groundwater system.  The highest concentrations of
contaminants are generally found close to the source and near the center of
the plume  where dilution is minimal.  As plume size and degree of dilution
increase,  the relative contaminant concentration decreases.  However, the
volume of  groundwater affected increases, and thus the cost for treating
affected water also increases.

     Among other factors, plume size is determined by hydrologic factors, age
of the contaminant source, and rate of contaminant release.  The width and
depth of a plume are directly influenced by the width and thickness of the
aquifer, the aquifer's flow characteristics, and the properties of the con-
taminants.  In most instances, plumes move in the direction of groundwater
flow and are elongated in that direction.  Some hydrogeologic conditions,
however, cause anomalous plume migration patterns to develop.  Plume shape is
                                     2-1

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a reflection of the flow patterns within the aquifer and the chemical  charac-
teristics of the leachate.   In general, groundwater flow patterns tend to
exert the greatest influence on plume shape and path.

     Factors affecting plume migration can be grouped into three broad areas:

     •  Groundwater flow patterns--factors that alter groundwater flow
        patterns
     •  Leachate characteristics—the properties of the hazardous materials
     •  PI time and geologic  media interactions—the reactions between waste and
        contaminant constituents and the geologic materials.

These topics are discussed  in greater detail in the following sections.

2.1  Groundwater Flow Patterns

     Groundwater flow patterns probably exert the greatest influence on
leachate migration of all the factors affecting plume movement.  This factor
is probably the best understood of all the factors.  Nevertheless, the site-
specific influence of groundwater flow on plume movement at individual hazard-
ous waste disposal sites is often difficult to assess because of variations in
site conditions.  Variations can be a result of:

     t  Subsurface hydrogeologic conditions
     •  Surface hydrologic  conditions
     •  Human activities.

     In order to understand the effects of these conditions, certain hydro-
geologic concepts must be understood.  These concepts are outlined in the
following section.

     2.1.1  Basic Hydrogeologic Concepts

     Precipitation falling  on land can run off into surface water bodies,
directly evaporate, be taken up and used by vegetation  (transpiration), or
                                     2-2

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 infiltrate  into the  subsurface.  Once  in the subsurface, water may be forced
 back to the surface  and evaporated through capillary action, may be taken up
 by deeper root systems and transpired, or may be transported downward under
 the influence of gravity.  Water in the unsaturated material will move
 downward until it reaches the saturated zone where all available pore space
 (i.e., openings between particles making up unconsolidated materials, or
 cracks, fissures, openings in consolidated rock) are filled with water;  These
 processes and their  interactions are termed the hydrologic cycle.

     Aquifers are subsurface water bearing zones capable of supplying water in
 usable quantities (Gary, et al., 1974).  Both unconsolidated and consolidated
 (i.e., rock) materials can function as aquifers.  Groundwater flows through
 voids within the aquifer, and the ratio (usually expressed as a percentage) of
 the volume of voids  in a material to the total  volume of material is termed
 porosity (Gary, et al., 1974).  Table  2-1 lists some typical ranges of values
 for porosity for different geologic materials.   Porosity and rate of flow are
 not necessarily proportional; a sample with a high porosity may not allow the
 passage of water unless pore spaces are interconnected.  An example of this is
 cork, which has a high porosity yet is relatively impermeable.  In addition,
 some highly porous, well  interconnected samples (e.g., clays) still  do not
 allow for the passage of water for other reasons.  The effective porosity (n)
 refers to the ratio of the volume of interconnected pore spaces to total
 volume, and is equal  to the ratio of the volume of liquid that a sample will
yield under specific conditions after it is saturated (Freeze and Cherry,
 1979).  Groundwater flows through the interconnected pores, fractures, joints
 or openings that provide a flowpath.

     A measure of the rate of groundwater flow  is the hydraulic conductivity
 (K).  Hydraulic conductivity is the volume  of water that  will  move per unit
time under  a unit  hydraulic gradient through  a  unit area  measured  at  right
                                     2-3

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                                                                  TABLE 2-1.



                                           RANGE  OF  POROSITY  VALUES FOR VARIOUS GEOLOGIC MATERIALS
ro
Geolog ic
Material
Gravel , mixed
Gravel , well sorted
Gravel and sand, mixed
Sand, mixed
Coarse sand
Mediun sand
Fine sand
Silt
Clay
Glacial till
Carbonate Rocks
(e.g., limestone)
Sandstones
Shales
Crystal 1 ine Rocks
(i .e., igneous
and met amor phic
rocks)
highly fractured
relatively unfractured
Freeze and
Cherry (1979)
25-40%


25-50%



35-50%
40-70%

0-50%

5-30%
0-10%




5-50%
0-10%
Fetter (1980) Pettyjohn (1975) Linsely,
et al. (1975)
25%
25-50%
20-35% 20%
35-40% 35%
39-41%
41-48%
44-49%
35-50%
33-60% 50% 50%
10-20%
1-30% 5%

3-30% 15-20% 15%
0-10% 5%





1%
Davis and
De Wiest (1966)
25-38%



33%
36-42%
45-52%
49-51%
48-67%

2-16%

12-29%





36-40%
14%

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angles to the direction of flow (Freeze and Cherry, 1979).  K has the
dimensions of length divided by time (commonly expressed in feet/day or
centimeters/second).  A related term is intrinsic permeability (k).   Intrinsic
permeability is a property of the media through which groundwater flows, has
the dimensions of length squared, and is a measure of the resistance to fluid
flow through the media.  Of the two, K is more useful for studying plume
dynamics and delineation.  Table 2-2 lists ranges of values for K for various
geologic materials.

     While intrinsic permeability (k) is a property of the media only,
hydraulic conductivity (K) depends on both the media and the fluid.   For
example, a material with a hydraulic conductivity for pure water of 10 ft/day,
will have a lower hydraulic conductivity for a more viscous fluid.  This is
one reason leachate and waste contaminants may move slower than groundwater.
For most groundwater situations the influence of changes in liquid properties
is usually slight, and can be ignored (Freeze and Cherry, 1979).  However,
this may not be the case in highly concentrated or multiphase plumes.

     When the density of fluid varies significantly from that of pure water,
hydraulic conductivities can be calculated to account for these density
changes.  Hydraulic conductivity (K) can be redefined as follows (Jorgensen,
et al., 1982):
                               K = kpg/v = ku/v
where:
     k = intrinsic permeability
     p = density of fluid
     g = acceleration of gravity
     u = specific weight of fluid
     v = viscosity of fluid

     The new K value then can be used in subsequent calculations,
                                     2-5

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                                   TABLE  2-2

                   RANGE OF HYDRAULIC CONDUCTIVITY  VALUES
          FOR  VARIOUS  GEOLOGIC MEDIA  (After Freeze and  Cherry,  1979)
Geologic
Material
Gravel
Sand, well sorted
Silty sand
Silt
Clay, unweathered
Glacial till
Carbonate rocks
Sandstones
Shales
Crystalline rocks
Highly fractured
Relative unfractured

cm/sec
lo-1 -
io-4 -
io-5 -
io-7 -
io-10 -
io-10 -
io-7 -
10"8 -
io-11 -

io-6 -
in-12 -
Hydraulic

IO2
1
io-1
io-3
io-7
io-4
1
io-4
io-7

1
io-8
Conductivity
gal /day/
IO4
10
1
10-2
io-5
c
10 D
io-3
io-3
10'6

10"1
io-7

sq.ft.
-IO7
-IO5
- IO4
-IO2
-io-2
- 10
- IO5
- 10
-io-2

- IO5
-io-3
1 gal/day/sq.ft.  = 1.74 x 10"6  ft/day


1 gal/day/sq.ft.  = 4.72 x 10"5  cm/sec
                                     2-6

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     The average linear velocity (V )  with which groundwater flows in a. system
is related to aquifer properties through a set of empirical relationships
named after their discoverer, Henri Darcy.  Darcy's law, in its most useful
form, states:

          Vg = KIA/n.

where:  V  = average linear velocity of groundwater
        K  = hydraulic conductivity
        I  = hydraul ic -gradient
        A  = cross sectional area (usually 1)
        n  = effective porosity.

     The velocity calculated using Darcy's law is not a measure of the
velocity of a water molecule as it moves within the void spaces of an aquifer;
rather, it is the average rate of movement between two distant points along
the same groundwater flowline in an aquifer.  Darcy's law  is important in
delineating plumes because  if V  and the time (t) from which contaminants
entered groundwater are known, then the distance that groundwater, and theo-
retically contaminants, will have moved over that time period (i.e., assuming
non-degradation of contaminants) can be estimated.

     In order to use Darcy's law in a specific situation,  the hydraulic gradi-
ent (I) must be known.  Hydraulic gradient is the change in head per unit
distance in the direction of maximum rate of decrease in head (Gary, et al.,
1974).  Hydraulic head (H)  is the height above a datum (usually sea level)  to
which a column of water can be supported by the pressure at that point.  The
head represents the energy  level of the water at that point.  The hydraulic
gradient (I) is the difference in elevation of water levels in any two wells,
A and B, (assuming A and B  lie along the path of maximum rate of change in
head), divided by the distance between A and B.  The concept of head and
hydraulic gradient are illustrated in Figure 2-1.

          Hydraulic gradient can also be expanded to account for the effects
of pressure on groundwater  flow (Jorgensen, et a!., 1982).  The relationship
                                     2-7

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                                             FIGURE 2-1.
             EXAMPLE CALCULATION OF HORIZONTAL  HYDRAULIC  GRADIENT
Total
Head
           Pressure
             Head
                         Well A

                           U—
1000 Ft
 Well B

—M
        Elevation Head
                                                                                         = 80Ft
                                                               Sea Level                  ^
Horizontal Gradient =  (Elevation of the water table in Well A minus the elevation of the water table in Well B), divided by- rhp
                   horizontal distance between  the two wells
[  = 10 Ft./1000 Ft.

I  = 0 01 %
                                                 2-8

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 P = pgH can be used to convert from head change equations to pressure change
 equations when significant density variations are present.  This relationship
 points out that one may have zero head gradient but a definite pressure
 gradient because of density differences (e.g., Hj = H2, but P^ i- P? because
 P! * P2).

     Groundwater flows from higher energy levels to lower energy levels in  the
 direction of decreasing head.  In unconfined aquifers (aquifers that do not
 have a bed or layer of significantly lower K overlying the aquifer  and  causing
 the water in the aquifer to exist under pressure),  the top of the saturated
 zone represents the energy level  of the water in the aquifer and is called  the
 water table.  The water table often tends to follow land surface topography,
 such that the direction of flow is from areas of higher land elevation  to
 areas of lower elevation.  This is not the case in  all situations.   For
 example, in areas of flat terrain, the water table  may follow steep bedrock
 slopes.

     In situations where aquifers are saturated and separated from  the  land
 surface by zones of lower K, the  energy level  and direction of flow are more
 complicated to determine.   The low K zones,  known as aquitards, increase the
 hydrostatic pressure of groundwater in aquifers beneath them by limiting the
 ability of this groundwater to move upward.   In these confined aquifers, the
 energy level  of the groundwater will  be greater than the saturated  thickness
 of the aquifer.  Water levels in  wells penetrating  a confined aquifer will
 rise above the level of the aquifer/aquitard interface.

     An imaginary surface representing the energy level  of the groundwater  is
 known as the potentiometric surface.   The potentiometric surface in an
 unconfined aquifer is simply the  water table.   Groundwater always flows from
 higher to lower potentiometric elevations and may be totally independent of
 surface topography.  This  concept is  illustrated in Figure 2-2.  Note that
water levels  in wells screened in the unconfined aquifer stand at different
 elevations than the water  levels  in the artesian wells.
                                     2-9

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                                                                FIGURE 22.
                                  POTENTIOMETRIC SURFACES IN CONFINED AND UNCONFINED AQUIFERS
ro
t—•
o
                                                                                                     Potentiometnc
                                                                                                     Surface of
                                                                                                     Confined
                                                                                                     Aquifer

-------
     Groundwater can flow not only horizontally but also vertically.  For
example, two wells located close together but screened  at different depths may
indicate that there is a vertical hydraulic gradient, and thus a component of
groundwater flow in the vertical direction, by the fact that the elevation of
the potentiometric surface is different  for each.  This situation  is  illus-
trated in Figure 2-3.  A vertical gradient may also exist between  two wells
screened at the same depth and  having equal potentiometric  surface elevations
if there are sufficient differences  in the fluid density in the two wells.

     The fundamental problem with delineating and predicting the migration
pattern of contaminated groundwater  plumes is that the  subsurface  environment
is rarely homogeneous.  Zones of lower permeability and lower hydraulic con-
ductivity can exist within aquifers, and the shape and  configuration  of
aquifers may be highly variable.  Groundwater and plume flow rates and
directions will vary depending  upon  the  characteristics of  the aquifer through
which they are passing.  Figure 2-4  illustrates how groundwater velocity can
vary with changing hydrogeologic parameters.  Transmissivity (T) in Figure 2-4
is defined as the hydraulic conductivity (K) of the aquifer multiplied by the
saturated thickness of the aquifer (m).  Transmissivity is  a measure  of the
quantity of groundwater flowing through  an aquifer.

     Variations in aquifer characteristics, primarily with  regard  to  K, are
discussed in terms of homogeneity and isotropy.  If K is independent  of posi-
tion within an aquifer, the aquifer  is homogeneous.  If K is independent of
the direction of measurement at a point  in an aquifer (i.e., K in  the vertical
and horizontal  directions are equal), the aquifer is isotropic.  Most aquifers
are heterogeneous and anisotropic, (i.e., K varies depending upon  the point of
measurement and the direction of measurement).

     If an anisotropic aquifer  has a greater vertical  K than horizontal K, and
all other properties (i.e., hydraulic gradient and porosity) are equal in both
directions, then groundwater would flow  faster vertically than horizontally.
A plume in this case would tend to migrate preferentially in the vertical
direction and be limited in horizontal  extent.  If the  aquifer were also
                                     2-11

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                                                    FIGURE 2-3.
                          EXAMPLE  CALCULATION OF VERTICAL  GRADIENT
          Aquifer Discharge Region
                                                 Aquifer Recharge Region
          Well
            A
Well
 B
560 Ft
500 ft
450 Ft
Well
 C
Well
 D
                                           550 Ft
                                           500 Ft
                                           450 Ft
Vertical Recharge
Gradient
Elevation of water table in
Well A minus the elevation of
the water table in Well B,
divided by the vertical distance
between the midpoints of the
screens in the two wells.
                                Aquifer Discharge Region

                                  I = (HA-HBI/ (& -/B)

                                  I = (540-5501/1515-445)

                                  I = -10/70

                                  I = 0.14 (upward flow)

                                Aquifer Recharge Region

                                  ' = '£-J&
                                  I = (540-5301/I515-445)

                                  I = 10/70

                                  I = -0.14 (downward flow)
                                                          2-12

-------
                                                    FIGURE 24.
                     EXAMPLE OF HOW GROUNDWATER VELOCITY CAN VARY WITH DIFFERING HYDROGEOLOGIC
                       CONDITIONS AND WITH DIFFERING SCALES OF OBSERVATION FOR KEY PARAMETERS
PO
i
(jO

                                                                             S^^SSWsSS


-------
heterogeneous, then depending upon where the plume is located, the preferen-
tial flow paths would change.  For example, the vertical K may become less
than the horizontal K or the magnitude of difference between vertical K and
horizontal K may change.  The result of heterogeneity and anisotropy is that
groundwater flow paths vary within aquifers and are not perpendicular to water
level contours, thus affecting plume dynamics.   For a detailed discussion of
the effect of anisotropy on flow lines in aquifers the reader should refer to
Fetter (1981).

     In summary, groundwater flows in aquifers  from higher energy levels to
lower energy levels along paths of least resistance.   Energy levels are
represented by water levels in wells.  For unconfined aquifers, groundwater
flow direction in many cases mimics surface topography while direct measure-
ments are required for confined systems.  The rate of groundwater flow can be
calculated using Darcy's law, if hydraulic conductivity (a measure of
rate of flow in an aquifer, and indirectly a measure of resistance to flow),
hydraulic gradient (a measure of the energy level  driving the system), and
porosity are known.  Groundwater flow is complicated by the heterogeneous and
anisotropic nature of the subsurface environment.   This causes changes in
preferential flowpath directions, and in rates  of flow, depending upon
position in the aquifer and direction of movement.  This is a partial cause
for the uneven distribution of contaminants in  groundwater.

     General groundwater flow theory is more complicated than explained here.
For example, as described previously, hydraulic conductivity (K) and pressure
(P) within the aquifer can be affected by fluid density and viscosity.  These
factors can impact groundwater flow directions  and cause plumes to move in
seemingly random directions at variable rates.   However, this simplified
discussion should prove adequate to understand  the following sections
discussing plume dynamics.  Numerous introductory hydrogeology texts and
research papers are available if more information on groundwater flow is
desired.
                                     2-14

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     2.1.2  Effects of Subsurface Conditions

     The size, shape, and flow direction of a leachate plume are strongly
affected by the geometry and uniformity of the aquifer through which it flows.
The presence of geologic discontinuities and hydrologic barriers modify a
plume's shape and flow direction.  These factors are discussed below.

          2.1.2.1  Aquifer Geometry

     In large, homogeneous porous strata, the shapes of water soluble leachate
plumes are relatively easy to predict.  Figure 2-5  illustrates the "character-
istic" shape of a water soluble contaminant migrating through a homogeneous
aquifer in the direction of regional groundwater flow.  In large aquifers, a
low density (i.e., density less than water) contaminant can form a thin film
over the upper surface of the aquifer unless the spread of the low density
contaminant over the surface is inhibited for some  reason.  In this case, the
contaminants have been observed to form a mounded layer extending above the
water table (Yaniga, 1982).  This situation is most likely to occur in
relatively thin, unconfined aquifers.

     Many highly productive aquifers do not have the classical sheet or
tabular shape commonly associated with sedimentary  deposits.  One of the more
common of these aquifer shapes is the elongate or "shoestring" aquifer, which
typically consists of stream deposits.  These aquifers can appear as isolated
pods or lenses; as long, sinuous, and sometimes braided ribbons; as complex
dendroids; or as highly variable belts (Pettyjohn,  1975).   This type of
deposit is generally very difficult to trace in the subsurface and can exert a
major impact on plume migration.

     Even more complex than shoestring deposits are aquifers having major
fracture sets or solution cavities.   In these aquifers, groundwater flowpaths
are usually impossible to identify completely and are generally neither con-
tinuous nor uni-directional.   Thus,  leachate movement patterns can be highly
variable and often unpredictable.
                                     2-15

-------
                                  FIGURE 2-5.
"CHARACTERISTIC" PLUME OF MISCIBLE CONTAMINANTS IN A HOMOGENEOUS AQUIFER

-------
     Aquifer geometry, particularly aquifer thickness, also affects plume
migration rates.  In general, as groundwater velocity increases, plume
migration rates also increase.  Thinner aquifers having the same hydraulic
gradient and discharge rate as thicker aquifers have faster flow rates because
the same volume of water is forced to move through a smaller volume of
aquifer.  Because of this, aquifer size is not a reliable measure of plume
migration rates.  In situations where an aquifer decreases in thickness or
"pinches out" in the direction of flow, flow rates can be expected to
increase, increasing the migration rate of plumes.  The opposite effect can
occur in an aquifer which increases in thickness downflow.

          2.1.2.2  Aquifer Hydraulic Conductivity

     Most aquifers do not exhibit constant hydraulic conductivities throughout
their depth, width, and length.  In fact, hydraulic conductivities can vary by
orders of magnitude from area to area and commonly diminish with depth into
the aquifer.  Changes in hydraulic conductivity may be gradual,  or abrupt as
in the case of multilayered aquifers.  One example of the effect of nonuniform
hydraulic conductivity on plume movement patterns is shown in Figure 2-6.  In
this example, contaminants have moved farthest from the source area in a
deeper, gravel layer having a larger hydraulic conductivity than in the
overlying strata.  This is not an uncommon occurrence, and highlights the
importance of understanding site geology prior to designing and  implementing
plume sampling programs.

     Geologic strata which have been uplifted and tilted can alter or reverse
the direction of plume movement by channelling fluid flow along  zones of
secondary porosity (i.e., bedding planes, fractures, faults, or  solution
cavities).   Possible effects of various types of hydraluic conductivities
caused by secondary porosity are illustrated in Figure 2-7.

     Faults are discontinuities in geologic materials that exhibit vertical  or
lateral displacement or both of one side of the break with respect to the
other.  Faults can be highly permeable or nearly impervious.   If the  fault  has
                                     2-17

-------
                                                          FIGURE 26.
                                  EFFECTS OF VARIABLE HYDRAULIC CONDUCTIVITY ON LEACHATE
                                        PLUME MOVEMENT IN UNCONSOLIDATED MATERIAL
(\3

I—•
00

-------
                                                           FIGURE 2 7.

                                 EFFECTS OF SECONDARY POROSITY ON LEACHATE PLUME MOVEMENT
ro
i
<£>
                                                                                                   •v-\

-------
a low hydraulic conductivity, the fault can be a subsurface barrier  to ground-
water flow and deflect or redirect the regional  flow pattern.   If the  fault
has a higher hydraulic conductivity than surrounding strata, the  fault can
channel  groundwater either upward or laterally at  a  higher  rate than regional
flow.  Highly permeable faults can permit very rapid groundwater  flow  which
promotes extensive plume migration or expansion  within  the  groundwater system.

     Some geologic units have been subjected to various types of  stresses that
cause fracturing of the rock.  Other units, particular  carbonates, can contain
large, interconnected solution cavities.  If a sufficient number  of fractures
are present, even relatively non-porous rocks can  function  as aquifers.   Frac-
tures and solution cavities can have pronounced  effects on  leachate  plume flow
patterns and rates, as illustrated in Figure 2-7.   When these  features are
present within an aquifer, solution movement is  controlled  by the width,
length, frequency, interconnectedness, angle, and  surface area of the  frac-
tures or cavities.  If the fractured rock dips at  an angle  opposite  to the
direction of groundwater flow in  the uppermost aquifer, the direction  of  plume
flow can be altered in the lower  units.  Fractures or solution cavities can
also channel contaminants from an upper aquifer  to a lower  one.

     Fractures, faults and bedding planes may also act  as barriers to  flow.
For example, in channels that are "sealed" because of secondary deposition  of
clays and silicates, groundwater  flow rates can  be minimal.  These zones  can
impede the spread of contaminants significantly.

     Flow rates in open fractures or solution cavities  can  be many times
higher than flow rates in non-fractured media.  In unfractured water table
aquifers, flow rates generally range between 3 and 330  feet/year.  In
unfractured confined aquifers, groundwater generally flows  much more  slowly,
between 0.03 and 33 feet/year (Jackson, 1980).  Measured rates of plume
migration in unfractured deposits can range from less than  6 feet/year to more
than 4410 feet/year in a very permeable sand and gravel aquifer  (Apgar and
Langmuir, 1977; Walker, 1973).  In contrast, groundwater tracing  studies
conducted in solution cavities through a limestone formation in Jamaica found
groundwater movement through large cavities to be  occurring at rates ranging
                                     2-20

-------
 from 18,350 to 1,468,000 feet/year (Wedderburn,  1977).   From this  data,  plume
 migration rates can be highly variable  and  certain  hydrogeologic conditions  at
 the site can permit extremely rapid  flow rates.

      The migration of contaminants in fractured  rock  can  be  modified  by
 adsorption of contaminants  onto  materials lining fracture surfaces  and by
 diffusion into the rock  matrix.   These  processes are  most influential when
 flow velocities are relatively slow  and  the surface area  in  contact with the
 contaminants is large.   Other factors affecting  attenuation  include the amount
 of dispersed clay  (for metals) and the  amount  of organic  carbon (for  organic
 chemicals).   Matrix diffusion exerts a  greater influence  within porous rocks
 than relatively non-porous  rocks.  Aquifers having a  high concentration of
 adsorptive substances  coating the  fracture  faces  are  more likely to modify the
 characteristics of solutions  flowing through the fractures than are aquifers
 composed  primarily of  relatively non-reactive  substances.  Types of minerals
 that can  function  as adsorptive  substances  include various oxides, chlorite,
 illite,  other clay minerals,  and chalk,  as  well  as carbonates (Jackson, 1980).

      The  preceeding discussion focuses on faults  and  fractures as conduits for
 leachate  flow to lower permeable units.   Leakage to lower aquifers is not
 always so  rapid  or dramatic.  Some units classified as aquitards actually
 contain hairline fractures, or relatively permeable areas which can allow
 contaminants  to migrate  into  lower water bearing zones.   Although flow rates
 may  be extremely slow, a substantial  amount  of groundwater and leachate may
 migrate between aquifers when large areas of an aquitard  leak.

     Figure 2-8 illustrates one example  of how contaminants can  penetrate a
 leaky aquitard.  In  this example, contamination in the lower aquifer would
 probably not be expected because  of the  presence of the clay zone.   However,  a
 locally high  proportion of sand or hairline  fractures  in the clay  could  permit
downward leakage.  Once within the lower aquifer  system, contaminants  could
 flow in entirely different patterns than expected within the upper  aquifer.
This figure also illustrates the  differences that can  exist between  ground-
water flow patterns within separate aquifer  systems  at a given locality.
                                     2-21

-------
                                                        FIGURE 28.
                          EFFECTS OF GROUIMDWATER FLOW DIRECTION AND GEOLOGIC HETEROGENEITIES
                                              ON LEACHATE PLUME MOVEMENT
ro
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-------
     Leakage through an aquiclude does not necessarily have to be downward.
If the hydraulic pressure (i.e., head) in a serniconfined aquifer were higher
than the head in an overlying unconfined aquifer, groundwater would flow
upward as shown in Figure 2-9.  This groundwater influx could cause greater
lateral spreading of the plume, faster groundwater and plume flow, and
accelerated plume dispersion  and dilution.

     In practice, the presence of leaky aquitards tends to complicate dramat-
ically the prediction of leachate plume migration rates, extent, directions
and flow patterns.

          2.1.2.3  Site Geology

     Site geology can often have a significant effect on plume migration.  At
some sites the pattern of plume migration in the overburden (i.e., unconsoli-
dated materials overlying bedrock) may differ from the pattern in the rock
under the site.   An example of this phenomena is shown in Figure 2-10.  In
this example, water in the overburden aquifer flows through the wastes forming
leachate which is discharged  at a spring or seepage area.  The leachate then
flows over land and contaminates a nearby lake.  Some of the contaminants in
the lake then enter the permeable sandstone unit underlying the lake, thus
further spreading the zone of pollution.  In addition to the leachate that
seeps out of the hillside, a  larger volume of leachate migrates downward and
spreads through the permeable sandstone unit beneath the waste site.   Thus,
because of the geology at this site, three contaminated aquifers exist—the
overburden, and two separate  sandstone units.  Figure 2-11 is a map view of
this same example.   Situations such as this would be difficult to interpret
correctly unless the effects of site geology on plume migration patterns were
taken into account.

     This discussion of the general  effects of subsurface geology and
hydrology illustrate some of the types of plume migration patterns that can
occur.  These factors and their effects highlight the need for site-specific
                                     2-23

-------
                                                        FIGURE 29.

                          EFFECT OF A HIGH HEAD, SEMI CONFINED UNIT ON LEACHATE PLUME MOVEMENT
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-------

-------
                                                                  FIGURE 2-11.

                                EXAMPLE OF THE EFFECTS OF SITE GEOLOGY ON LEACHATE PLUME MOVEMENT

                                                                  (MAP VIEW)
                     Sand

                     stone
rsi
i
ro

                                                            Sandstone
                                                                                                                 Sandstone
                                            111
                                              m
';. Waste $&//•/;
; Disposal :;.:i •:;•;••/'.•':.
.;....site..$%y%i

-------
hydrogeo"logic  information when  attempting to predict  plume movement.   In  addi-
tion to subsurface conditions,  recharge, discharge, and other surface  con-
ditions can have a great influence on plume movement.  These effects are
described in the following section.

          2.1.2.4  Site Hydrology

     The hydrology of  unconfined aquifers is in many  cases controlled  by
surface topography.  As was described in the section  on basic hydrologic
concepts, the  water table can be a subdued expression of land surface
elevations, or topography (assuming the conditions previously noted in Section
2.1.1).  This  generalization is true where the primary form of aquifer
recharge (i.e., the addition of water to an aquifer)  is by precipitation
infiltration.  The water table  will, however, deviate from topographic
patterns at hydrologic boundaries represented by discharge or recharge areas.

     The location of a waste site relative to the recharge area of the nearest
aquifer can affect leachate flow.  Some waste sites are highly permeable  and
allow a considerable amount of  recharge (e.g., infiltration of precipitation)
to occur.  This recharge can increase the volume of leachate produced, causing
groundwater mounding under the  waste site (Freeze and Cherry, 1979).   Leachate
entering groundwater in these areas tends to flow radially outward before
gradually conforming to regional groundwater flow (Figure 2-8).   In areas
where the aquifer's vertical gradient is upward (i.e., discharge  zones),
opposing the downward migration of percolating leachate, mounding will  occur
more rapidly.   In recharge zones the natural vertical  gradient of the  aquifer
is downward, causing extensive  travel of contaminants into the aquifer, but
minimal mounding.

     Floodwaters can also recharge groundwater.  The rise in water tables as a
result of flooding can cause groundwater to contact waste not normally
saturated, increasing the rate of leachate generation.  Also, rivers at flood
stage can cause redirection of groundwater contaminant plumes because of the
temporary creation of hydraulic divides by riverbank storage effects.
                                     2-27

-------
     A third effect of recharge area location on leachate plume migration
patterns is illustrated in Figure 2-12.  Sites near recharge areas are likely
to produce plumes that flow for long distances before reaching a natural
discharge point.  Conversely, plumes from sites located near discharge areas
pollute a smaller volume of the aquifer before contaminants are dispersed into
surface waters (Fenn, et al., 1980; Lindorff and Cartwright, 1977).  At some
sites, only a portion of the leachate plume enters the surface water at
discharge areas, as was illustrated in Figures 2-10 and 2-11.

     Recharge and discharge do not typically occur at constant rates over
time.  As a result, the potentiometric surfaces of aquifers can and do change,
sometimes significantly.  This is especially true of unconfined surface
aquifers which are subject to seasonal changes in precipitation, stream flow,
evaporation and transpiration, snow melt, and other conditions.  These changes
can occasionally be of such a magnitude that water table gradients (and hence,
groundwater and pollutant flow directions)  are reversed.  Thus, these cyclic
hydrologic changes are an important consideration in an aquifer system when
assessing leachate migration patterns (refer to Pettyjohn, 1982, for more
details).

     The migration of leachate plumes is controlled by a multitude of
naturally occurring situations and processes.  The location of recharge and
discharge areas, for example, can have a large impact on plume dynamics.
Plume migration can also be either slowed or promoted by various human
activities.  These human activities are discussed in the next section.

     2.1.3  Effects of Human Activities

     A number of human activities can modify the flow patterns of both
groundwater and leachate plumes.  The types of effects that human activities
can cause include:

     •  Increasing or lowering the water table
     •  Modifying water table gradients
     •  Creating or obliterating recharge and discharge areas
                                     2-28

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                                                               FIGURE 2-12.

                      THE EFFECT OF WASTE SITE LOCATION RELATIVE TO LOCATION OF RECHARGE AND DISCHARGE

                                                      AREAS ON PLUME MIGRATION
ro
i
INJ
Water Table Mound Beneath Waste Sites
                             Permeable

                             Alluvium
                              	7*^


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     •  Diverting groundwater or plume flow
     •  Reducing or increasing leachate production

     •  Containing or removing the plume from the aquifer.


     The ways in which human activities accomplish these  effects  include:


     •  The use of extraction wells  which can cause localized  lowering  of  the
        water table, creating cones  of depression surrounding  the  wells.

     •  The use of injection wells which can  cause groundwater mounding,
        increased water table elevations, and radial  flow away from  the wells.

     •  The use of construction dewatering techniques which  can redirect
        groundwater movement near the  construction site by the installation  of
        subsurface low permeability  barriers, the construction of  drainage
        ditches, or the use of extensive pumping  from extraction wells
        surrounding the site.

     •  The presence of surface impoundments, such as lakes  and lagoons, which
        can cause groundwater recharge.

     t  The presence of irrigation or  drainage ditches which can  cause  either
        groundwater recharge or discharge.

     •  The presence of numerous other subsurface man-made  features  including
        mines, tunnels, foundations, and sewer lines.

     •  The use of various remedial  action measures to contain or  control
        leachate plumes.


     Planned human interventions in  the groundwater regime  of  a waste disposal
site (i.e., remedial actions) can cause a significant reduction of hazards to
public health and the environment.  The effects of several  types  of  remedial
actions for leachate plume control are summarized in  Table  2-3.


     Groundwater flow patterns and leachate plume migration  rates  can also be
inadvertently altered by human activity.  Figures 2-13 and  2-14 illustrate a
hypothetical example of several  types  of human activities and  their  unexpected
effects on plume migration.
                                     2-30

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                                                                   TABLE  2-3

                      EFFECTS OF SEVERAL REMEDIAL  ACTION MEASURES ON  LEACHATE  PLUME MIGRATION  (After EPA,  1982a)
                 Remedial Action Measure
          General  Effects
                                               Effects on
                                             Leachate Plume
                 Sealing of site surfaces,
                 grading, revegetating and
                 diverting surface water
                 from site
ro
                 Installing subsurface low
                 permeability barriers
                 upgradient from site
                                                     2.
1.
                                                     2.
    Reduces the amount  of  water
    (from rain, snow or surface
    run-on) that infiltrates  into
    the site and flows  through
    the wastes.

    Reduces groundwater recharge
    and mounding beneath the  site.
Initially diverts uncontaminated
groundwater away from the site
and the plume.

Initially reduces the water table
evaluation on the down-gradient
(waste site) side.
                                       1.
                                                                                               4.
1.
                                                                                               2.
Minimizes the volume of
leachate generated.

May result in a short-term
increase in the concentra-
tion of contaminants in the
plume because less dilution
will occur.

Concentrations of water
soluble constituents from
above the water table
should be reduced in the
leachate because solub111-
zation is less likely.

Radial spread of the plume
beneath the landfill will
be reduced.

Initially reduces the like-
hood of horizontal ground-
water flow through the
waste site bottom.
                                               Initially reduces  the
                                               volume  of groundwater
                                           exposed  to  the leachate.

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                                                            TABLE 2-3  (continued)
                 Remedial  Action Measure
          General  Effects
        Effects on
      Leachate Plume
                 Installing of subsurface  low
                 permeability barriers
                 upgradient from site (cont'd)
3.   Initially reduces the flow rate
    on the downgradient side
    because the hydraulic gradient
    is reduced.
CO
I
OJ
3.  Temporarily lessens the
    potential  for leachate
    dilution
                                           4.  May temporarily reduce the
                                               severity of conditions
                                               within the lower parts of
                                               the waste site.

                                           5.  Should temporarily reduce
                                               amount of dissolution
                                               occurring (if waste was
                                               previously in contact with
                                               groundwater).

                                           6.  Reduces the flow rate of
                                               the plume.

                                           7.  Slightly reduces the degree
                                               of plume extent.

                                           8.  May result in a short-term
                                               increase in the concentra-
                                               tion of contaminants in the
                                               plume because less dilution
                                               will occur.

                                           9.  Slower flow rates can allow
                                               additional attention and
                                               degradation to occur.

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                                                         TABLE 2-3  (continued)
              Remedial Action Measure
          General  Effects
        Effects on
      Leachate Plume
              Installing subsurface,
              low permeability barriers
              downgradient from the site
ro
i
OJ
CA>
              Installing subsurface, low
              permeability barriers completely
              surrounding the site
1.  Minimizes groundwater movement
    downgradient from barrier.

2.  Causes rise in water table
    elevation upgradient from wall
    unless groundwater pumping  or
    subsurface drains are used.
1.  Isolates groundwater in the
    site area from regional ground-
    water.

2.  Reduces groundwater velocity.
1.  Prevents longitudinal
    migration of plume.

2.  Causes lateral  migration of
    the plume along the sub-
    surface barrier unless
    groundwater pumping sub-
    surface drains  are used.

1.  Prevents longitudinal
    migration of plume.

2.  Minimizes dilution of
    leachate and leachate
    volume.

3.  Reduces cost of treating
    contaminated groundwater
    by minimizing the amount
    of groundwater  affected.

4.  Allows dewatering of the
    site via groundwater
    pumping or subsurface
    drains.

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                                                             TABLE  2-3 (continued)
                   Remedial  Action Measure
                                             General Effects
                                                   Effects  on
                                                 Leachate Plume
                   Permeable  Subsurface Treatment
                   Beds
ro
oo
Groundwater Pumping
                   Installing  Subsurface
                   Drainage  System
1.  Modify groundwater chemistry
    by introducing sorptive or
    chemically active substances
    such as activated carbon or
    crushed limestone.

2.  May cause local  increases in
    flow velocity through the beds.

1.  Upgradient pumping wells reduce
    the amount of groundwater flowing
    through the site and lower the
    water table elevations locally

2.  Downgradient pumping wells
    reduce the amount of groundwater
    flowing off the  site and lower
    the water table  in localized
    areas downgradient of the site.
                                   1.  Same as for groundwater pumping.
                                                                                  May reduce concentration of
                                                                                  certain contaminants via
                                                                                  sorption, precipitation
                                                                                  or neutralization.
2.  May change pH and solids
    content of leachate.

1.  Upgradient wells can  help
    stabilize the plume if
    operated carefully

2.  Downgradient wells can be
    used to extract the plume
    if pumped or divert the
    plume if used for injection

3.  Wells may not affect  all of
    plume if not properly
    sited.

1.  Same as for groundwater
    pumping but with less of a
    change of allowing enhance-
    ments to escape from  the
    system if properly
    designed.

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                                                           TABLE 2-3 (continued)
              Remedial Action Measure
     General Effects
        Effects on
      Leachate Plume
ro
to
en
              Bioreclamation
1.   Allows microbial degradation
    within contaminated aquifers.
1.   Promotes microbial degrada-
    tion of plume constituents

2.   Can alter physical and
    chemical properties of the
    leachate.

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                                                                FIGURE 2-13.
                                      EFFECTS OF HUMAN ACTIVITIES ON LEACHATE PLUME MOVEMENT
                                                                (MAP VIEW)
ro
i
oo
                               O - Urn ontamin.ited Private Wells

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                                                          FIGURE 2 14.
                                  EFFECTS OF HUMAN ACTIVITIES ON LEACHATE PLUME MOVEMENT
                                                    (CROSS SECTIONAL VIEW)
00
--J

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     The waste disposal site shown in map view in Figure 2-13 is apparently
releasing a leachate plume which has contaminated downgradient private wells
in a somewhat anomalous pattern.  A nearby lake is inexplicably free of
contaminants as are wells adjacent to the lake and between the lake and the
site.  A river system downgradient of the lake is slightly contaminated.  Some
wells between the lake and the river are contaminated and some are not.  Wells
across the river from the disposal site are uncontaminated with one exception,
a high-production industrial well.  The geology of the area is fairly uniform
and does not appear to be the cause of the contamination pattern.

     This pattern of surface and groundwater contamination might be confusing
unless changes in site hydrology from human activities are understood.  To
assist in understanding this situation, Figure 2-14 illustrates the site in
cross section.  In this figure, the lake is recharging groundwater and causing
the plume to deflect downward as it flows beneath the lake.  This causes
shallow wells nearest the lake to remain unaffected by the site and wells
extending to greater depths within the aquifer to be contaminated.  Contam-
inated groundwater flowing  under the lake discharges into the river without
affecting most of the wells located on the opposite bank.  Because a  large
volume of water is extracted from the deep industrial well a steep gradient
toward this well  is formed.  This causes groundwater flow toward the  well  and
pulls the leachate plume beneath the river.  Private wells nearby are not
contaminated because smaller volumes of water  are withdrawn from these  wells.

      In  addition  to the effects of human activities  illustrated  in the  hypo-
thetical example  given above, many other activities can  channel plumes  in
seemingly anomalous patterns.   These  include constructing high  permeability
zones,  such  as tile drainage  systems on  low-lying farmland, domestic  septic
tank  drainfield lines, and  underground mine workings;  and low  permeability
areas,  such  as foundations, retaining  walls, tunnels,  and areas where
compacted fill materials  have been  placed.  The  effects  of these features  must
be  kept  in mind when  attempting to  delineate the  areal  extent,  and  estimate
flow rates,  of  leachate  plumes.
                                      2-38

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2.2  Effects of Leachate Characteristics

     The types and concentrations of contaminants strongly influence the
physical and chemical properties of leachate.  In turn, the flow patterns and
chemical interactions of leachate are determined to a great extent by the
distinctive set of chemical and physical properties of the constituents.
Properties that influence  leachate migration patterns are described below.
These properties affect the types of interactions that can occur between
leachate, aquifer, and groundwater constituent.  Knowledge of these inter-
actions assists in understanding the data obtained from site investigations
and from studies of leachate behavior within aquifers.

     The characteristics of a plume emanating from a waste site are strongly
affected by the wastes present in the site.  However, the waste and the
leachate it produces are rarely similar in their chemical and physical
properties because of variable contaminant release rates and the effects of
dilution.  Furthermore, the extent of mixing of different types and quantities
of wastes in a disposal site will also  influence leachate characteristics.
For this reason, generalizations about  the types and concentrations of
specific contaminants found in leachates are difficult.  Nevertheless,
leachates from waste organic chemicals  probably pose the greatest environ-
mental concern.  The approximate percentages of general contaminant types
found at Superfund sites (Table 2-4) indicate that over three-quarters of the
waste constituents in these sites are organics or organics mixed with metals.
The remainder consist of metals and radioactive materials.  A survey of
leachate from solid waste  disposal facilities, on the other hand, would result
in much different findings.  Thus, great variability in plume dynamics can be
expected within any class  of leachate-producing facility because of varying
physical and chemical characteristics of the leachates produced.
                                     2-39

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                                   TABLE 2-4
             DISTRIBUTION OF CONTAMINANT TYPES FOR SUPERFUND SITES
                             (Based on EPA, 1982b)
Primary Type                      	Percentage of Sites*	
of Contaminant
at Site                           358 of 418 sites         86 of 114 sites
                                     on expanded              on initial
                                  priority listing         priority listing
Organics
Solvents, oils, fuels
PCBs
Pesticides
Organics and Metals, mixed
Metals, acids and bases,
and radioactives
54%
(42%)
(7%)
(5%)
26%
20%

44%
(32%)
(6%)
(6%)
36%
20%

*Percentages are based on varying levels of data completeness

2.2.1  Effects of Physical Characteristics

     The physical characteristics of leachate that can affect plume migration
include:

     o  Volume
     o  Viscosity
     o  Density
     o  Solubility
     o  Degree of dispersion
     o  Temperature.

These factors, which have varying degrees of  influence on migration patterns
and rates,  are described below.  Other factors which can affect plume
migration,  but not discussed herein, include  chemical stability, reactivity,
and fluid phases present in the  leachate.
                                      2-40

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          2.2.1.1  Leachate Volume

     The amount of leachate produced at a site affects both the volume  and
flow rate of the plume.  Larger volumes of leachate can produce larger  or more
concentrated plumes or both.

     The factors that affect the amount of leachate produced  include:

     •  Duration, frequency, type, and amount of precipitation
     •  Mean annual temperature, temperature fluctuation, and degree of
        insolation
     •  Surface characteristics of the site including the steepness of  the
        slopes, type and permeability of the cover material used, presence  and
        types of vegetation present, length of the slopes, and other features
        which impact percolation rates
     •  Site subsurface characteristics including the presence of water within
        the wastes, volume of flow through the wastes, and rate of flow
        through the waste site.

Table 2-5 indicates the effects of each of these parameters on leachate pro-
duction.

     For some sites, estimations of leachate volume have been made using a
water balance approach, whereby the interactive effects of climatic conditions
such as precipitation, temperature, insolation, and evapotranspiration  are
calculated to produce an estimate of the yearly volume of water available for
infiltration.  From this value, the amount of runoff is subtracted and  the
remaining water is assumed to seep through the waste site to generate
leachate.  One of the disadvantages of the water balance method is the
assumption that the waste site is not in direct contact with groundwater.
Thus, the method is not directly applicable to sites where waste material has
been disposed of below the level of the seasonal  high water table.  Additional
information on using the water balance approach to predict leachate generation
is provided in Fenn, et al. (1975) and Perrier and Gibson (1980).
                                    2-41

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                                   TABLE 2-5

             FACTORS AFFECTING  LEACHATE VOLUME GENERATION
        Factor
                    Effect
Precipitation

  Amount Per Year


  Highest 24-hour  Rainfall
Mean Annual  Temperature
Degree of Insolation
Surface Slope
Cover Permeability
o  Greater the amount of precioation,  the
   greater-volume of leachate generated.

o  No real effect, but the greater the number
   of short duration, high volume rainstorms,
   the less likely that precipitation  will
   infiltrate to waste, and the more likely
   that most will run off as surface flow.

o  Higher the mean annual temperature, the
   greater the amount of precipitation that
   will evaporate and not infiltrate into
   waste, reducing the volume of leachate
   generation.

o  Increasing insolation will increase
   evaporation, reducing the quantity of
   leachate produced.

o  Increasing slope at a disposal site will
   promote surface runoff, reducing the volume
   of precipitation infiltrating into the
   waste and thus reduce the volume of
   leachate generated.

o  Low permeability cover materials promote
   runoff, reducing infiltration and the
   volume of leachate generated.
Vegetation
Subsurface Characteristics

  Water Content of Waste
  Volume of Water Flow          o
  Through Wastes

  Rate of Flow Through Wastes   o
   Heavy vegetative cover of grasses will
   increase transpiration.  Heavy vegetative
   cover of grasses can also impede runoff
   thus increasing infiltration.

   Heavy vegetative cover of trees, bushes and
   shrubs may increase infiltration by opening
   up channels of flow into waste because of
   deep root penetration.
   An increased water content within waste
   will decrease time till leachate generation
   begins.

   Increased water flow through waste will
   increase the volume of leachate generated.

   Increased flow rates through waste will
   decrease time till start of leachate
   generation, but may decrease the
   concentration of contaminates present.
                                       2-42

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           2*.2.1.2   Leachate Viscosity

      The  resistance of a leachate to internal  flow caused by external forces
 is  termed  its  viscosity.   Solutions with a higher viscosity tend to flow more
 slowly than  less viscous ones,  thus, they would be expected to disperse less,
 and  to migrate  more slowly, than  solutions of  lower viscosity.  In addition,
 leachates  exhibiting a viscosity  substantially higher than groundwater should
 decrease  the hydraulic conductivity of the system.  Contrary to expectations
 based  on  hydraulic  conductivity equations alone,  field experience has indi-
 cated  that the  viscos-ity of a  leachate has a minor effect on hydraulic
 conductivity (Jackson, 1980).

           2.2.1.3   Leachate Density

      If the density of a plume  is significantly greater or lower than that of
 groundwater, plume  migration patterns  can be altered  dramatically.   Low
 density wastes  tend to float at the top of an  aquifer and spread out to form a
 lens of contaminants that may be  several  feet  thick.   In Mechanicsburg,
 Pennsylvania, for example,  a gasoline  spill  resulted  in formation of a
 four-foot thick gasoline  layer  above the  water column.   A fuel  oil  spill  in
 Southeastern Pennsylvania produced  a contaminant  lens that was five feet  in
 thickness (Lindorff and  Cartwright,  1977).   Low density plumes also tend  to
 remain more concentrated  than other  leachates  that disperse more readily  in
 the groundwater.

     High density plumes  can form dense  or concentrated layers near the base
 of aquifers.  For example,  chloride  contaminants  from oil  field  brines  entered
 an aquifer in New Mexico  and sank to the  bottom of the  aquifer because  they
 were more dense than  the  native groundwater  (Lindorff and Cartwright,  1977).
 If dense wastes contain  substances  that  degrade or dissolve minerals,  they
 could  eventually produce  a  breach in an  aquitard  separating an  upper  aquifer
 from an underlying  one.   In some  instances,  dense  plume constituents  can
migrate downward against the direction of  regional  groundwater flow.  An
 example of this situation is shown  in  Figure 2-15.  In  this figure,  the upper
 clay layer splits the  plume into  two sections  as  it flows.   A  small  portion  of
                                    2-43

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                         FIGURE 2-15.
EFFECTS OF A PERCHED ZONE ON THE FLOW OF A HIGH DENSITY PLUME
                  ^__—	_^  	~y



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the dense plume sinks to the base of the  lower clay  layer  and moves  against
the direction of groundwater flow.

     Density is also  important because of the effects density differences, and
subsequent pressure differences, can have on plume migration.   Flow  equations
should be formulated  in terms of pressure when variable  density conditions
(e.g., oilfield-related brine plumes) are apparent.

     Some leachates contain both low and  high density constituents.   This can
lead to the formation of a two-plume system with widely  differing chemical and
physical characteristics, as illustrated  in Figure 2-16.   Leachates  from dis-
posal facilities accepting many waste types will commonly  contain constituents
with various densities.  In these instances, the leachate  constituents  will
tend to seek levels of equivalent density, and thus  become spread throughout
the water column with light components at the top, and heavy components  lower
in the water column.

          2.2.1.4  Leachate Solubility in Groundwater

     The ability of leachate constituents to dissolve in groundwater  has dis-
tinctive effects on plume migration patterns.  Water soluble (miscible)
leachates tend to form larger, more dispersed plumes, whereas water  insoluble
(immiscible) materials tend to create small and highly concentrated  plumes.
In addition, less water soluble constituents tend to migrate more slowly than
more soluble ones (Wilson, et al., 1980).

     Solubility characteristics interact with leachate densities to  produce
modifications in the  classical plume migration profile.  Examples of  plume
migration patterns for various density and solubility combinations are  shown
in Figure 2-17.  Typical waste constituents exhibiting the solubility and
density combinations  that are shown in Figure 2-17 are listed in Table 2-6.
The characteristics of leachates containing any of these constituents will
                                    2-45

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                                                         FIGURE 2-16.

                                       EFFECT OF DENSITY ON LEACHATE PLUME MOVEMENT
ro
i
cn

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                                                                       FIGURE 2-17.
                                              CONFIGURATIONS BASED ON SOLUBILITY AND DENSITY
ro
 i
-p.
                            Low Density Plumes
                                                             Moderate Density
                                                                 Plumes
High Density
  Plumes
Water
Soluble
Plumes
         Water
        Insoluble
         Plumes

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                                                     TABLE 2-6

                           EXAMPLES OF PLUME CONSTITUENTS BASED ON SOLUBILITY  ANN  DENSITY
Constituents
Low Density
Constituents
              Moderate Density
                Constituents
                                 High  Density
                                 Constituents
Water
Sol uble
Acetone
Acrylonitrile
Ammonia
Benzene
              Acetic Acid
              Anil ine
              Most metal sal ts
              Phenol
                                 Chi oroform
                                 Halogenated  ethanes
                                 Halogenated  phenols
                                 Nitrobenzene
Water
Insoluble
Cyclohexane
Ethylbenzene
Gasoline and some
Toluene
Vinyl  chloride
Xyl ene
oil s
T-butyl  acetate
Butyl  cellosolve
Hexanol  ester-alcohol
Carbon tetrachl oride
Chiorobenzene
PCBs
Most pesticides
Most polyhal ogenated benzenes
  and phenols
Most polycyclic aromatic
  hydrocarbons

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depend on constituent concentrations and may be substantially different  than
anticipated from the properties of the pure chemicals.

     Although a leachate may be immiscible  in groundwater,  it could  form an
emulsion if emulsifiers are present.  In these situations,  the  leachate  would
most likely behave as a moderate density solution.

          2.2.1.5  Degree of Dispersion

     Contaminant transport can occur via three processes  in groundwater;
advection, diffusion and dispersion.  Contaminant transport through  the  motion
of groundwater flow is known as advection.  Solutes carried by  advection only
move at a rate equal to the average linear velocity of groundwater (Freeze and
Cherry, 1979).  However, mechanical mixing and molecular  diffusion can cause
contaminants to spread out from the path they would follow  under advection
only.  Diffusion is the process whereby constituents move under the  influence
of their kinetic activity in the direction of their concentration gradient.
Diffusion is a factor in contaminant transport at very low  velocities, and is
generally ignored during initial studies of contaminant transport.

     Dispersion caused entirely by fluid motion is known  as mechanical
dispersion, and is best understood in microscopic terms.  Freeze and Cherry
(1979) list three mechanisms involved in dispersion:

     •  Variations in molecular velocities caused by drag executed on fluids
        in close contact with particle surfaces
     •  Variations in pore size which affect groundwater velocities  in
        different pore channels
     •  Variations in possible flow channels caused by branching and inter-
        fingering.

Dispersion causes contaminants to "spread out" while moving by  advection.  The
amount of plume dispersion that occurs is greatest in granular or fractured
aquifers where turbulent flow predominates (Pettyjohn, et al., 1982).  In
                                    2-49

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general, dispersion does not reduce the concentration of hazardous plume con-
taminants to acceptable levels.  The processes of dilution and dispersion  are
too slow and ineffective to be relied upon for renovation of contaminated
groundwater (Lindorff and Cartwright, 1977).

          2.2.1.6  Leachate Temperature

     A final physical characteristic that influences plume migration patterns
is temperature.  High temperatures can be generated during aerobic degradation
of organic materials, or during exothermic chemical reactions that occur with-
in the waste site.  High temperature leachates are less dense than the same
leachate at a lower temperature, thus they tend to rise within the aquifer.
They also react more rapidly with aquifer and groundwater constituents than do
cooler leachates..  For example, hot (175°F) wastes from a furfural plant in
South Florida were injected into a slightly-saline, confined carbonate
aquifer.  The wastes collected near the top of the aquifer, where they rapidly
dissolved portions of the upper aquitard (McKenzie, 1976).

     Although a knowledge of the physical characteristics of contaminant
plumes in aquifers can assist  in predicting overall migration patterns, data
on a plume's chemical characteristics are also necessary to understand the
overall effects of the plume on an aquifer and on groundwater, and its
subsequent migration.

     2.2.2  Effects of Geochemical Interactions

     Data on the types, concentrations, and interactions of chemical con-
stituents within a leachate are of extreme importance in evaluating the degree
of hazard from the leachate and its effects on the aquifer and the ground-
water.  Information on possible leachate hazards is summarized by Mackison, et
al. (1978) and Sax (1980).  Leachates having a low concentration of hazardous
constituents generally have a  less pronounced impact on aquifer geochemistry
                                    2-50

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than  highly  concentrated  plumes.   The  concentration  of the plume is influenced
by  a  number  of  factors,  including:

      •   Volume  and  rate  of  infiltrate  percolating  through the waste site
      •   Solubility  and density  of  plume  constituents
      •   Length  of contact time  between  infiltrate  and  wastes
      •   Initial moisture  content of  wastes
      t   Age  of  the  waste  site
      •   Anthropogenic factors and  human  influence
      •   Rate of groundwater  flow receiving  percolating leachate.

      As  groundwater  passes through an  aquifer,  numerous  chemical  reactions
occur.   Although groundwater and aquifer  interactions  are complex,  the
reactions that  occur as  a result of  leachate  flow  through an  aquifer  can be
many  times more intricate.   Rather than  attempt to enumerate  the vast number
of  reactions possible, brief descriptions of  the major processes  that affect
migration are given.

      A number of processes interact  to control  the mobility of  various  wastes,
so  that  not  all of the waste placed  in a site can  leach  to groundwater.   Some
wastes can be precipitated,  biochemically degraded,  or temporarily  sorbed.
The net  result  of these processes  is to retard  the movement of  some constit-
uents through the aquifer.   This effect  is  termed  attenuation.   Important
factors  in contaminant attenuation include:

      •   Form and concentration  of each contaminant
     •   Physical and chemical properties of the  leachate  mixture
     •   Physical and chemical properties of groundwater
     •   Surface area and porosity of geologic materials
     •   Groundwater  and leachate flow rates
     •   Types and orders of  geologic materials  encountered.

     Not all  contaminants are attenuated to the same extent under a given set
of conditions.   While contaminant attenuation is a highly complex and site-
specific process,  certain generalizations can be made, as  described below.
                                     2-51

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           2.2.2.1  Attenuation  of  Inorganic  Constituents

     Many  factors  interact  to detain  various components of  leachates as plumes
migrate through  aquifers.   For  cationic  (positively  charged  ions)  metals such
as  lead, cadmium,  zinc, copper, mercury  and  chromium III, most  of  the
attenuating effects are caused  by  sorption and  precipitation.  In general,  the
amount of  cationic metal  attenuation  increases  as  the  pH, cation exchange
capacity,  free lime content, free  iron oxide content,  and surface  area  of  the
aquifer's  particles, increases.  An increase in the  ionic strength of the
leachate decreases the amount of cationic sorption that can  occur  (Fuller,
1982).

     The amount  of cation exchange that  takes place  within  an aquifer is also
affected by other reactions including the weathering of clay minerals,
decomposition of aquifer  constituents, and occurrence  of redox  (reduction-
oxidation) reactions.  Some cations such as  copper and zinc  can become  tightly
sorbed, and then undergo  secondary reactions that  render them unexchangable.
The types  of cations in the leachate  and in  the original aquifer constituents
also affect the  amount of cation exchanges that occur.  In most aquifer
                                                                      2+     2+
materials, the relative degree  of affinity for  specific cations is Ca   >  Mg
> K  = NH.  > Na .  Other metallic cations are  held  less strongly  than  the
above mentioned  common cations  (Kurtz and Melsted, 1973).

     For anionic (negatively charged) metals, such as  chromium VI,  arsenic,
and selenium, sorption increases as pH decreases.  The ionic strength of the
leachate does not seem to influence the  degree  of  anionic metal sorption
(Griffin and Shimp, 1978).

     Of the anions commonly found in  leachates, phosphate is the least  mobile.
Nitrate and chloride have approximately  the  same high mobility and  are  used  as
indicators of plume migration because very little  attenuation of these
leachate constituents occurs in most  aquifers (Lindorff and  Cartwright,  1977;
Kurtz and Melsted, 1973;  Roberts, et  al., 1980).
                                   2-52

-------
     In addition to the effects of  ionic  strength  and  pH  on  the  attenuation  of
metals, the presence of certain organic constituents can  substantially
increase metal mobility.   Under some  conditions, hydrolyzable  metals  such  as
lead can become chelated by certain organic  constituents  even  when  the lead  is
originally undissolved.  When chelated, the  metal  can  remain  in  solution but
still be unavailable for sorption or  precipitation.  For  this  reason,  chelated
metals can be highly mobile (Griffin  and  Shimp, 1978).  Chelated metals may
also be readily removed from solution  if  the chelating  agent  is  itself an
organic chemical (e.g., humic and fulvic  acids).

     Many non-ionic contaminants also  exhibit considerable sorption.   Sorption
and attenuation can also occur because of van der  Waals attractions,  weak
hydrogen bonding, covalent bonding, polar attraction,  and other processes.

     Plume migration rates can also affect attenuation.   Laboratory tests  of
leachate attenuation in soil columns  indicated that, in addition to the soil
and leachate factors mentioned above,  the amount of metal attenuation
decreased as flow rate increased (Alessi, et al.,  1980).  Aquifer physical
properties such as the presence of  low permeability layers and the  degree  of
compaction were also found to influence metal migration rates, probably as a
result of the higher surface areas  and lower flow  rates associated  with such
conditions.

          2.2.2.2  Attenuation of Organic Constituents

     When organic constituents enter groundwater,  one of  four  processes can
occur.   The constituent can be (Roberts, et  al., 1980):

     •   Rapidly and completely degraded or precipitated
     •  Completely unaffected by groundwater conditions
     •   Partially sorbed or precipitated with slowly decreasing amounts of
        sorption occurring
     •   Slowly degraded, with gradually increasing amounts of  degradation to  a
        final  steady level.
                                    2-53

-------
     Attenuation of organic chemicals in the subsurface is an extremely

complex problem in plume dynamics, and the subject of considerable ongoing

research.  Nevertheless, several generalizations can be made concerning the

overall behavior of organic constituents within aquifers.  These generaliza-
tions are as follows (Wilson, et al., 1980; Roberts, et al., 1980; Lindorff

and Cartwright, 1977).


     •  Volatilization of low molecular weight organics is inhibited by
        aquifer particles, both by the distance volatile organic compounds
        must travel before they reach a free water surface, and as a result of
        the slow turnover of soil  pore air in the unsaturated zone.

     •  Some organic constituents  can be tightly sorbed onto aquifer particles

     t  Organics tend to be attenuated less than inorganics

     t  Most of the attenuation mechanisms are biochemical, rather than
        geochemical in nature

     •  The degradation of simpler, less toxic constituents is more pronounced
        than that of complex toxic substances

     •  Degradation is primarily anaerobic within aquifers, although some
        aerobic degradation has been  found to occur

     •  The establishment of microbial degradation may occur after a phase
        during which the microbes  become acclimated to the new organic
        substrate

     •  The presence of one organic constituent can influence the sorption and
        attenuation of another

     •  Degradation of organic leachate constituents can make tracing sources
        of leachates more difficult

     •  Low solubility or hydrophobic constituents tend to move more slowly
        than high solubility or hydrophilic substances

     •  Some sorption of dissolved organics onto organic constituents within
        the aquifer may occur.


     The result of geochemical processes and attenuation  is to reduce the rate

of migration of certain constituents, remove the constituents from ground-
water, or increase the mobility of certain constituents under certain

conditions.  A summary of these processes is presented in Table 2-7.  The
                                   2-54

-------
                                   TABLE ?-7

                 PROBABLE EFFECT OF VARIOUS PROCESSES ON THE
                MOBILITY OF CONSTITUENTS IN SUBSURFACE WATERS
                        CONTAMINATED BY WASTE DISPOSAL
                                (Jackson, 1980)
Physical  Processes

     Dispersion - Causes dilution of wastes and smearing of the plume front.
          The dispersive capacity of a porous or fractured medium is directly
          dependent on the groundwater velocity and the heterogeneity of the
          aquifer materials, and is inversely proportional to the porosity.

     Filtration - Favors reduction in amounts of substances associated with
          colloidal or larger-sized particles (e.g., sediments and microbes).
          Most effective in clay-rich materials, least effective in gravels or
          fractured or cavernous rock.

     Gas movement - Requires unsaturated conditions and high porosity if not
          dissolved in groundwater.  Where gas movement can occur, favors
          aerobic breakdown of organic substances and increased rates of
          decomposition.  Constituents mobile under oxidized conditions (e.g.,
          chromium) will then predominate.  Restriction of gas movement by
          impermeable, unsaturated materials or by saturated materials can
          produce an anaerobic state and reduced rates of organic decay.  This
          will mobilize substances soluble under anaerobic conditions (e.g.,
          iron, manganese)

Geochemical  Processes

     Complexation and ionic strength - Complexes and ion pairs most often form
          by combination of ions including one or more multivalent ions and
          increase in amount with increased amounts of ions involved.  Ionic
          strength is a measure of the total  ionic species dissolved in
          groundwater.  Both ionic strength and complexation increase the
          total  amounts of species in solution that would otherwise be limited
          by processes such as oxidation,  precipitation, or sorption.

     Acid-base reactions - Most constituents increase in solubility and thus
          in mobility with decreasing pH.   In organic rich waters, the lower
          pH's (4 to 6) are associated with high values of carbonic acid and
          often also of organic acids.  These will  be most abundant in
          moisture saturated soils and rock.
                                    2-55

-------
                             TABLE 2-7 (continued)
     Oxidation-reduction - Many elements can exist in more than one oxidation
          state.  Contaminants will  often be oxidized or only partially
          reduced in unsaturated soils and groundwater recharge areas, but
          will become reduced under  saturated conditions when excess organic
          matter is present.  Mobility depends on the element and pH involved:
           chromium is most mobile under oxidizing conditions, whereas iron
          and manganese are most mobile under those reduced conditions in
          which dissolved oxygen and hydrogen sulfide are absent.

     Precipitation-dissolution - The abundance of anions such as carbonate,
          phosphate, silicate, hydroxide, or sulfide may lead to precipi-
          tation, especially of multivalent cations as insoluble compounds.
          Dilution or a change in oxygen content, where precipitation has
          resulted from oxidation or reduction, may return such constituents
          to solution.

     Sorption-desorption - Ion exchange can withhold, usually temporarily,
          cations and to a lesser extent anions, on the surfaces of clays or
          other colloidal-sized materials.  Amounts of sorbed metal cations
          will increase with increasing pH.  Molecular species may be weakly
          retained on colloidal size materials by physical sorption.  The much
          stronger binding forces caused by chemical  action result in the
          formation of surface compounds involving metal  ions and mineral
          grains.  Sorbed species may return to solution when more dilute
          solutions come in contact  with the colloidal  material, depending on
          the nature of the sorption bond and sorption of organic chemicals by
          chemical  interactions such as bonding and polar attraction.

Biochemical  Processes

     Decay and respiration - Microorganisms can break down insoluble fats,
          carbohydrates, and proteins, and in so doing release their
          constituents as solutes or particulates to subsurface waters.

     Cell  synthesis - N, C, K, and P, and some minor elements are required for
          growth or organisms, and can thus be retarded in their movement away
          from a waste disposal  site because they are temporarily incorporated
          within microbial  cells.
                                    2-56

-------
types of processes that influence specific  aquifer constituents  are  listed  in
Table 2-8 and descriptions of the overall effects of  the  various  processes  on
the mobility of leachate components are given  in Table 2-9.  The  reactions
governing geochemical processes and attenuation are so complex  and dependent
upon site specific conditions, that pollutant  attenuation  is often ignored  in
evaluating leachate plume movement.

          2.2.2.3  Estimating Leachate, Groundwater,  and  Aquifer  Interactions

     Several approaches have been used to estimate the effects of attenuation
and other processes that occur within aquifers on the migration  rates  of
inorganic and organic leachate constituents.   Three of these approaches are
described-briefly below.

     The amount of a constituent that is detained by  earth materials has  been
estimated using laboratory studies of leachate migration  through  soils or
aquifer materials under aquifer like conditions.  One method used to measure
the attenuative properties of various earth material  involves saturating  the
pores of the sample with a pollutant laden  solution.  Additional  amounts  of
the solution are allowed to flow through the sample,  under anaerobic
conditions, displacing the original pore volume of solution.  This continues
until the concentration of pollutant entering  the sample  (C ) is  equal to the
concentration of pollutant in the solution  flowing out of  the sample (C).   The
point at which C/C  equals one is termed the breakthrough  point  (Fuller,
1982).  When a contaminant concentration reaches the  breakthrough point,  the
aquifer's ability to sorb that particular contaminant is  exhausted (Roberts,
et al., 1980).

     A curve of C/C  concentrations plotted for various numbers of pore volume
displacements indicates the relative amount of pollutant that will be
attenuated by the soil at any particular point in the test (Fuller, 1982).
Typical breakthrough curves are shown in Figure 2-18.  Curve A in Figure  2-18
indicates little attenuation in occurring,  while Curve E  indicates that all of
the pollutant entering the soil is being attenuated.
                                    2-57

-------
                                                            TABLE 2-8


                                 PROCESSES  WHICH  MAY CONTROL AMOUNTS OF  CERTAIN CONSTITUENTS  IN
                                       SUBSURFACE WATERS CONTAMINATED BY WASTE  DISPOSAL*
                                            (After Jackson, 1980; Fenn, et  al.,  1977)
ro
en
00
Constituent
Physical
Dis-
persion
Organic Solutes
Microorganisms
Heavy Metal Anions
(Cr, V, Se, B, As)
Heavy Metal Cations
(Pb, Cu, Ni,
Zn, Cd, Hg)
N03
so/
po43'
Na+, K+
NH4*
?+ ?+
Ca' , Mg^
Fe , Mn
X
X
X
X
X
X
X
X
X
X
X
Filtra- Complex-
tion ation
X
X
X
X

(X)
X

X
(X)
X
Geochemical
Ionic Acid- Oxid.- Precip-
Strength Base Red. Solution
(X) X X (X)
X
(X) X X
(X) X X
X
(X) (X) X
XX X
(X)
(X) X X
X (X)
X XXX
Biochemical
Adsorp.- Decay, Cell
Desorp. Respir- Synthesis
ation
(X) X X
X X
X
X
X X
(X) (X)
XXX
X
XXX
X
X
                "(BRACKETS DENOTE MINOR CONTROLS)

-------
                                   TABLE 2-9

               BEHAVIOR OF SPECIFIC CHEMICAL WASTES AT LANDFILLS
                                (Jackson, 1980)
Chemical Waste
                   Behavior
Halogenated Organic
Compounds
Phenols
PCBs
Mineral Oils
Organic Solvents
Acids
Cyanide (CN)
Heavy metals
(e.g., Cr, Zn, Hg, Pb, Cd)
Evaporation  (because of volatility) and sorption
onto other solid wastes present may reduce the
release of halo-solvents to groundwater.

Phenols are  relatively soluble in groundwater,
undergo biodegradation slowly, and are reversibly
sorbed.

Readily soluble in hydrocarbons, but not in
water.  Biodegradation inhibited by anaerobic
conditions.  Readily sorbed.  PCBs are relatively
inert within landfills and are not leached by
water in high concentrations.

Sorption of  oils onto solid fill material is an
important attenuation process.  Floats on
groundwater  because of low density relative to
groundwater.

Some sorption on landfill materials and some
biodegradation in sands and gravels have been
observed.

Leaches sorbed contaminants and dissolves
precipitates, thereby causing deterioration of
groundwater  quality.  Inhibits microbiological
activity.  Releases harmful gases.

Most CN either volatilizes as HCN, or
precipitates as cyanoferrate II compounds.
                             +2
+2
Cd+2)
Heavy-metal cations (e.g., Pb"", Hg
controlled primarily by their insolubility as
metal sulfides, carbonates, hydroxides or
phosphates, and secondarily by sorption.  Anionic
forms (e.g., Cr90 ~ ) very mobile.
                                     2-59

-------
                                                         FIGURE 2-18.

                          TYPES OF BREAKTHROUGH CURVES GENERATED BY THE SOIL COLUMN TECHNIQUE

                                                        (FULLER, 1982)
ro
i
CD
O
                     C/Co
                                                                Time

-------
      Curve  types  vary depending  on  soil  texture,  pollutant type,  and other
 factors.   In  general, clays  attenuate  pollutants  much more effectively than
 sands,  and  inorganic  cations are attenuated more  effectively than are
 inorganic  anions  (Fuller,  1982).  However,  while  dispersed clay particles in
 the  aquifer matrix  will  very effectively undergo  ion exchange with some
 contaminants,  relatively impermeable  clay liners  and beds do not  readily
 transmit flow  and therefore  provide very little  attenuation.  Care should be
 taken when  attempting to relate  breakthrough curve test data to actual
 situations, as  test conditions rarely mimic site-specific situations.   For
 example, reports  of clay liner failure  have shown that volatile solvents and
 fuels will  strip  the  waters  of hydration from  clay and cause dessication
 cracks  through  which  seepage occurs.

     Another method used to  estimate the rates of pollutant  migration  involves
 a more mathematical approach.  For some  specific  chemicals,  data  have  been
 assembled that  can be  used to estimate  the  migration  distances  under a
 specific set of conditions.   One method  used to express  the  relative degree  of
 a chemical's mobility is to  use  a value  termed the  distribution coefficient
 (kd).  As kd increases,  the  mobility of  a substance  decreases.  Values  of  k,
 for  several pesticides are listed in Table  2-10.   Values  of  k.  can  be  used in
                                                              d
 conjunction with mathematical models to  estimate  the  size  and shape  of
 leachate plumes after  a  given period of  time.

     Many highly  complex computer models have been  developed  to numerically
 simulate pollutant migration  patterns.   These models  can  be  used  to  assist in
 a more comprehensive  interpretation of the  information on  the site.  These
modeling programs, however,  typically require a considerable  amount  of
 hydrogeologic data obtained  over a long  time period.
                                    2-61

-------
                                   TABLE 2-10
             PESTICIDE MOBILITY BASED ON DISTRIBUTION COEFFICIENTS
                             (After Jackson, 1980)
Relative Mobil ity
Highly Mobile
Somewhat Mobile
Relatively Immobile
No Significant
Leaching
Pesticides k . Val
Name
Picloram
2,4-D
Atrazine
Diuron
Ethirimol
Lindane
Parathion
DDT
Paraquat
Use Range
Herbicide 0-10
Herbicide
Herbicide
Herbicide 10-100
Fungicide
Insecticide
Insecticide 100-1,000
Insecticide +1,000
Herbicide
ues
Loam Soil -3%
organic matter
0-3
1
3
10
15
50
200
1,000
10,000+
     When models have been used to predict plume behavior under field
conditions, data from field studies have sometimes been found to contradict
computer predictions (Perlmutter and Lieber, 1970; Roberts, et al., 1979).
For this reason, many researchers recommend extreme caution when interpreting
the data from mathematical modeling studies (Cole, 1982; Fenn, et  al., 1980;
Roberts, et al., 1979).  Despite the disadvantages of various computer models,
numerical simulation can be a useful tool to assist in organizing  and
evaluating the complex geochemical, physical, and biochemical interactions
that take place within aquifers.  Models useful for plume delineation are
discussed further in Section 3.1.
                                    2-62

-------
                                   CHAPTER 3
                               PLUME DELINEATION
     Controlling the migration of a leachate plume requires a thorough under-
standing of the distribution of contaminants in the subsurface.  Because
contaminant movement is usually dominated by lateral  groundwater movement, the
direction and rate of groundwater flow must be known in order to approximate
plume boundaries.  Initial estimates of plume boundaries are made assuming
that subsurface materials are homogeneous, isotropic, and non-reactive (i.e.,
degradation and attenuation of plume constituents does not occur), and that
contaminant movement is controlled only by groundwater flow.  Initial
estimates of plume location can then be improved by making use of known con-
taminant characteristics to estimate how the plume will react in groundwater
(e.g., denser contaminants will tend to sink in the water column) and by
determining preferential flowpaths using a knowledge of subsurface geologic
conditions (e.g., faults and fractures in consolidated rock or sand and gravel
lenses in lower hydraulic conductivity clay matrices).

     In general, the more data that are available on a site, the greater the
probability that an approximation of plume boundaries will approach actual
conditions.  At a minimum, information on groundwater flow direction and rate,
contaminant characteristics and release rates, and subsurface geologic
profiles are required.  Because groundwater plumes cannot be readily observed
(unlike an oil  spill  on surface water), monitoring wells that provide direct
groundwater quality data will always be required in plume delineation studies.
However, because monitoring wells are fairly expensive to install and monitor,
well data can be optimized by the careful application of less resource inten-
sive data collection  techniques that do not provide direct groundwater quality
data.  The purpose of this chapter is to provide generalized procedures for
delineating leachate  plumes using direct and indirect methods.
                                     3-1

-------
3.1  Plume Delineation Procedures

     A generalized approach to identifying the boundaries of a contaminant
plume is illustrated in Figure 3-1.  This approach involves a number of
activities which can be summarized in three major steps:
     0  Calculate possible plume boundaries based on site hydrogeology and
        contaminant release information
     t  Modify calculated boundaries qualitatively based on site and contam-
        inant characteristics, and verify these boundaries, calculations and
        modifications using groundwater sampling data and supporting
        information
     •  Extrapolate future plume movements using the verified groundwater flow
        data and computer models, if needed.
     The objective of this approach is not only to delineate current and
future plume positions but also to ensure that information required for
implementing plume control measures will  be available.  These steps are
described in further detail below.

     3.1.1  Calculate Possible Plume Boundaries

     The first step in calculating possible plume boundaries is to identify
the direction(s) of plume movement and what aquifer, aquifers, or portions of
aquifers may be contaminated.  Because information on groundwater contamina-
tion will usually be limited at this point in the process, hydrogeologic data
on the site (e.g., groundwater levels) are generally used to identify water
bearing  zones that may lie in the path of a migrating plume.  This evaluation
should consider both horizontal and vertical  plume movement as discussed in
Chapter 2.0.  If enough data are available, a potentiometric surface map of
the potentially affected aquifers should be constructed.
                                     3-2

-------
                                  FIGURE 3-1.
GENERALIZED  APPROACH TO  DELINEATING  LEACHATE PLUMES
              Determine Flow Direction and Gradient
                               JL
                  Determine Aquifer Properties
              Determine Leachate Generation  History
                 Calculate Possible Plume Limits
               Modify Calculated Limits Qualitatively
             Verify Plume Limits with Supporting  Data
      Does
    Estimation
     Appear
     Reliable?
Reassess Values Used
in Flow Calculations and
Recalculate Plume Limits
  Develop and Implement Groundwater Sampling Program   I

                                          'No
          Yes
                                                              Reassess Values  Used
                                                              in Flow Calculations and
                                                              Recalculate Plume Limits
        Delineate Current Plume Position and Extrapolate Future Plume Movement
                                     3-3

-------
     In evaluating hydraulic head data, the following points are important to
remember:

     •  Any well  pair used to calculate a hydraulic gradient should be located
        along the same flowpath.   Wells used to establish horizontal  gradients
        should be screened in the same stratigraphic horizon; wells used to
        establish vertical gradients  should be in  close proximity to  each
        other.
     •  Water levels should be measured from an accurately surveyed,  fixed
        reference point (e.g., top of  well  casing).  Calculated  water level
        elevations and potentiometric  surface contours should not exceed the
        precision of the original  survey and the water level measuring device.
        Calculated gradients should not exceed the precision of  the elevation
        and distance-between-wells measurements.
     •  Water level  data should be collected from  all wells in a monitoring
        system at the same time to minimize temporal variations  (e.g.,
        seasonal  water level fluctuations).  Temporal variations should be
        assessed  by measuring system head levels over the course of several
        cycles.

     In the absence of reliable hydrogeologic information on the site, the
usual  assumptions are that (1) horizontal flow predominates over vertical
flow, (2)  contamination is restricted  to unconfined aquifers, and (3) contami-
nation levels will be highest in  the uppermost unconfined aquifer.  Subsequent
field investigation activities are then planned to ascertain the validity of
these assumptions.  Excellent discussions of methods for determining  the
direction  of groundwater flow are given in Fetter  (1981); Pinder, et  al.,
(1981); and Abriola and Pinder (1982).

     The second step in calculating possible plume boundaries is to estimate
the rate of groundwater and contaminant movement using Darcy's Law (refer to
Section 2.1.1).  Data required by this equation can be obtained  using a
variety of methods.

     Initial calculations typically result in ballpark estimates based on
indirect data.  Indirect data includes generalized data not based on actual
site conditions and data functionally related to the data required by Darcy's
Law.  Published reports, aerial imagery, and geophysical surveys are examples
                                     3-4

-------
 of  indirect  data  sources  which  are  described  in  more  detail  in  Section  3.2.
 More  precise calculations typically require  using  di rect  data on  site condi-
 tions.   Direct  data  for a site  is developed  using  hydrologic and  groundwater
 sampling methods  described  in Section  3.3.   Table  3-1 summarizes  the
 availability and  reliability of  several  information  sources  for Darcy's  Law
 calculations.

      Darcy's Law  is  an attractive means  for  calculating groundwater flow
 because  it is theoretically simple,  not  based on many limiting  assumptions,
 applicable to most hyd-rologic systems, and uses  parameters that can be
 estimated readily.   One major problem, however,  is that Darcy's Law loses
 validity  under  conditions of very low and very high hydraulic gradients and
 hydraulic conductivities.  The  reason for this is  that Darcy's  Law is designed
 to  predict fluid  movement through saturated media  under conditions of laminar
 flow.  Under these conditions, flow  paths are assumed  to  be layered and mini-
 mal intermolecular mixing is expected to occur.  As flow  rates  and hydraulic
 gradients increase,  however, mixing  becomes more predominant and flow less
 laminar.  When  velocity increases sufficiently turbulent  flow begins.  Under
 these conditions, flow pathways  are  nonlinear and  a great deal   of mixing may
 occur.   In most aquifers  flow rates  are  normally low  enough to  allow for
 accurate determinations of velocity  (Davis and DeWiest, 1966).   Under certain
 conditions,  however, turbulent flow  in aquifers can occur.  Conditions causing
 turbulent flow  include aquifers with extremely porous areas such as along
 fracture zones, fissures, and large  openings in subsurface units (Freeze and
 Cherry,  1979).

     Calculations of contaminant movement using Darcy's Law assumes water
 soluble, conservative contaminants in non-dispersive and unattenuative porous
media (Popkin, 1983).  Fried (1975)  and Freeze and  Cherry (1979) present
analytical methods for addressing dispersion  and  attenuation.  In  many cases,
data necessary to use the  dispersion and  attenuation equations  will not  be
available.

     The final  step in calculating possible  plume boundaries  is  to determine
the history  of a site's leachate generation.   Based on the amount  of  time (t)
                                     3-5

-------
                                                                          TABLE 3-1
                                                      INFORMATION SOURCES FOR CALCULATING  VELOCITY
                                                               USING DARCY'S LAW  (V = Kl/n)
                  Parameter
                                           Source
                  Hydraul ic
                  Conductivity
                     (K)
On site aquifer
testing results
                                      Laboratory  testing
                                      results
CO
I
01
                                      Site related  reports
                                      Regional  reports
                   Hydraulic
                   Gradient
                     (I)
                                      General  guidelines
On site surveys  of
water levels in  wells
                                  Availability
                                       Data  Reliability
Not generally available
unless previous site work
has been undertaken

Not generally available
unless previous site work
has been undertaken
Commonly available from
a variety of sources such as
feasibility studies for
water supply or construction
projects at neighboring
sites

Readily available in a
variety of forms from such
sources as the USGS, state
geological surveys, and
universities

Readily available
(see Table 2-2)

Not generally available
unless previous site work
has been undertaken
Excellent if planned  and
implemented properly
                                                                  Generally good, but are less
                                                                  reliable for unconsolidated tests
                                                                  of compressible material  such
                                                                  as clay.  False low values are a
                                                                  common problem.  Sample represen-
                                                                  tativeness is also a concern (see
                                                                  Section 3.3.1)

                                                                  Generally good depending
                                                                  on proximity of study area and
                                                                  variability of hydrogeology
                                                                  Moderate to low unless site
                                                                  data was used as part of the
                                                                  regional database
                                                                                                        Generally low
Excellent if seasonal  and
other temporal variations are
taken into account.  Generally
good otherwise if the guidelines
given in Section 3.1.1 are
followed.

-------
                                                                TABLE 3-1  (continued}
                Parameter
                Hydraulic
                Gradient
                  (I)
                (continued)
GO
i
                Porosity
                  (n)
                                         Source
Regional  and  site-
related  reports
                                    Estimation from site
                                    topography
Laboratory testing
results
                                    General  guidelines
                                  Availability
                                       Data Reliability
Commonly available from
the USGS, state geological
surveys, universities,
and other geotechnical or
engineering sources

Topographic maps are
readily available from
the USGS.  Larger
scale topographic maps
may also be available
from local government
agencies.

Not generally available
unless previous site
work has been undertaken
                                Readily  available
                                (see  Table  2-1)
Generally moderate to low
because of the highly site
specific nature of hydraulic
gradients
                                                                  Generally low
Generally moderate to good
but can be highly variable
because of problems
associated with sample
extraction and representa-
tiveness

Generally low

-------
that contaminants have been within the saturated zone and the estimated
velocity of groundwater and contaminants (V ) from Darcy's Law, the maximum
distance (D )  a plume could migrate from a source area is given by:

                                   °P - V

However, determining the timing of contaminant releases from a site is
commonly the most difficult and least reliable step in calculating possible
plume boundaries.  This is especially true of abandoned sites which lack
adequate operation records.

     The approach generally taken to estimate release time, t, is to assume
that leachate generation is simultaneous with the initiation of site
activities and then try to pinpoint the initiation of site activities.  This
approach is usually valid because the time between waste disposal and leachate
generation is typically small  relative to the age of the site.  Unfortunately,
determining when hazardous waste related site activities were initiated is not
always possible. Some possible sources of this type of information in the
absence of owner or operator records include historical aerial photographs,
county tax records, chamber of commerce records, and waste generator and
transporter records.

     Table 3-2 provides an example to illustrate how possible plume limits can
be calculated.  Other methods for calculating plume limits are described by
Pettyjohn, et al. (1982).

     3.1.2  Modify and Verify Calculated Boundaries

     Once the initial calculations of possible plume limits are completed,
they should be drawn  on map view and on several cross  sections of  the  site.
The calculated  boundaries  should then be assessed and modified as  needed based
on  the factors  affecting  plume movement as described in  Chapter 2.  The
purpose of this  step  is to help ensure  that optimal use  will  be made of each
                                      3-8

-------
                                  TABLE  3-2
            EXAMPLE  CALCULATIONS OF MAXIMUM PLUME  LIMITS  (D  )
CALCULATION
                                           METHOD
  INITIAL     Given that 0  = t(KI/n)  where:

              t = 19 years based on county records showing  purchase data  by
                  disposal facility operator  and  assumption  that  onsite
                  disposal and leachate generated began  immediately

              K = 10 ft/day based on regional  geologic reports  that the  site
                  is underlain by a thick deposit of silty  sand (see  Table
                  2-2)

              I = 0.01 based on an estimate using site topography and surface
                  water elevations

              n = 35% based on published guidelines for  silty sand.

              Maximum plume limits (assuming  zero attenuation)  can be
                  estimated
              by:

              D  =  (19 years) (365 days/year)  (10 feet/day)  (0.01)/(0.35)

              D  =  2,000  feet.


  REVISED     Given that  D  = t ((T/m) I/n) where:

               (Note:  K = T/m)

              t = 17.5 years based on more detailed site operation information
                  provided by former employees and a preliminary water balance
                  calculation for leachate generation

              T = 900 gpd/foot based on a pumping test

              m = 65 feet based on borings indicating a clay layer 90 feet
                  deep and an average depth to water of  25  feet.

               I = 0.008 predominantly in the  horizontal  direction based on
                  water levels taken on site

              n = 40% based  on borings that indicate a lower proportion of
                   sand than  previously thought and published guidelines

              Maximum plume  limits (assuming  zero attenuation)  can be
                  estimated
              by:

              D  =  (17.5 years) (365 days/year)  ((900 gpd/ft/7.48g/ft3)/65
               p    feet)  (0.008)7(0.40)

              D  =  236.4  ft
                                    3-9

-------
well and other sampling points in the site monitoring program.  The key
factors to consider in evaluating a calculated plume boundary are:

     •  Groundwater flow patterns (Section 2.1)
     •  Leachate or contaminant characteristics (Section 2.2.1)
     •  Plume and geologic media interactions (Section 2.2.2).

Of the three, groundwater flow patterns will  generally he the most important
and least difficult factor to evaluate in assessing the calculated plume
limits.  Should certain values used in the initial  flow calculation appear to
be inappropriate based on this step, the values should be modified and the
maximum plume limits recalculated.

     There are a variety of non-sampling methods for checking the validity of
groundwater and plume movement calculations including preliminary site inspec-
tions, aerial imagery, and geophysical surveys.  The types of information that
can be obtained by these and other means are outlined later in this chapter.
However, to describe succinctly how this information should be used on a site
specific basis to adjust initial  estimates is very  difficult.  Therefore,
personnel  well qualified to assess waste site hydrogeology should be involved
in delineating the location of a site's plume.

     Based on the final estimates of the plume's anticipated boundaries, a
groundwater monitoring program is developed and implemented.  Plume
delineation by groundwater sampling is discussed in Section 3.3.2.  If
utilized properly, groundwater monitoring results will  establish plume
boundaries with the accuracy needed to develop remedial  action plans.  In
addition,  the groundwater monitoring data should be used to reassess the
values used in the flow calculations to ensure their accuracy.  This is
particularly important if long term predictions of  plume movement are to be
developed.
                                     3-10

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      3.1.3  Extrapolate Future Plume Movement

      Most plume management strategies seek to contain, extract, or treat the
 plume so that  it does not pose a threat to the environment.   Some strategies,
 however, seek  to control  the plume's movement so that  it will  not affect
 sensitive receptors.   Examples of this latter strategy include diverting the
 plume away from drinking  water wells, counterpumping to prevent the plume from
 advancing in an unwanted  direction,  and not  taking  action  because an  immediate
 environmental  threat  is not  evident.   In  cases where plume movement is  being
 controlled,  or  the  "no  action  alternative"  is an  issue,  extrapolation of
 future  plume movement trends is  imperative.   Predicting  plume  movement  can  be
 accomplished manually using  calculations  such as  those described  in Section
 3.1.1  or through the  use  of  computer  models.

      There  are  many commonly accepted  models  that can  be used  in  forecasting
 leachate plume  movements  and the  effects  of  plume management plans.  These
 models  can  be divided  into two major  groups — release rate  models  and solute
 transport models.  Typically,  estimates of  leachate  quantity and  quality
 released  from a site  are  obtained  from a  release  rate  model or  through  a
 groundwater  sampling  program,  and  are  used  as input  to a solute transport
 model.   The theory behind  some of  the  models  is  fairly complex  and  can  be
 found  in  sources  such as  Bachmat,  et  al.  (1980), Mercer  and Faust  (1981),
 Anderson  (1979), Weston (1978), and Repa, et  al.  (1982).

     The  first  and probably  the most crucial  step in waste site modeling  is to
 obtain  accurate estimates of the quantity and  quality  of leachate that  has
 been  released into the subsurface  environment.  Only after adequate determina-
 tion of  leachate release can a solute  transport model  be used.  Most release
 rate models are based on dividing  the  problem  of prediction into three
 separate  components--leachate generation rates, constituent concentrations,
 and leachate release  rates from the site.  Combining the three separate
 components allows for prediction of the quantity and quality of leachate that
 can be expected to be released from the site.  Because of the unknowns
 included in estimating values for these components,  data are generally
obtained through a groundwater monitoring program and  input directly into a
                                     3-11

-------
solute transport model.  Table 3-3 summarizes six computer models that can be
used for predicting leachate release rates.

     Solute transport models utilize a set of equations, based on explicit
assumptions, to describe the physical  processes affecting pollutant transport
from a site.  These models can be divided into two types—deterministic and
stochastic.  Deterministic models attempt to define the shape and concentra-
tion of leachate plunes using the physical processes (e.g., groundwater flow)
involved, while stochastic models attempt to define causes and effects using
probabalistic methods.

     Deterministic mathematical  models can be further divided into analytical
and numerical models.  Analytical models  simplify mathematical equations,
allowing solutions to be obtained by analytical methods (i.e., functions of
real variables).  Numerical  models, on the other hand, approximate equations
numerically and result in a  matrix equation that is usually solved by computer
analysis.  Both types of deterministic models address a wide range of physical
and chemical characteristics but the analytical models usually simplify the
characteristics by assuming  steady-state  conditions.  The physical  and
chemical  characteristics considered by these models include:

     •  Boundary Conditions  -- hydraulic  head distribution, recharge and
        discharge points, and locations and types of boundaries
     •  Material Constants -- hydraulic conductivity, porosity,
        transmissivity, extent of hydrogeologic units
     •  Attenuation Mechanisms -- sorption-desorption, ion exchange,
        complexing, nuclear  decay, ion filtration, gas generation,
        precipitation-dissolution, biodegradation, chemical degradation
     •  Hydrodynamic Pi spersion  -- diffusion and dispersion (transverse and
        longitudinal)
     •  Waste Constituent Concentration -- initial and background
        concentrations, boundary conditions.

     Both mathematical model types incorporate two sets of equations to define
transport—a groundwater flow equation (generally consisting of a water
                                     3-12

-------
                                                                                           TABLE  3-3
                                                                                   RELEASE  RATE  MODELS
Model Reference Calculation Method
Drainmod/ Skaggs (1982) t Water bal ance method
Drainfil) • Drain equations
Advantages
• Calculates head levels
within site
• Predicts quantity of
drainage to leachate
collection system
« Predicts quantity of
leachate moving through
underlying clay
Disadvantages
• Data intensive
* Roes not consider process
within cell that affects
leachate quantity or
qual ity
• Untested model
OJ
 I
OJ
                         HELP/
                         HSSWDS
                         LSIPE
                         PCLTF
                         LTTM
                         Rel ease
                         Kate
                         Computation
Perrier and
Gibson (1980)
                                         Moore (1980)
                                         USEPA (1982c)
                                         Pope-Reid Associates
                                         (1982)
SCS Engineers
(1982)
                                                                   •  Water balance method
                          •  Linearized  equation with
                             simpl ified  boundary
                             conditions
                          • Analytical  equation  series
                                                                   •  Water balance method
•  Analytical  equations
                                        •  Minimal  data requirements
                                        *  Estimated horizontal  and
                                           vertical  drainage  through
                                           a maximun of 8 layers
                                        •  Estimates impingement rates
                                           on collection system

                                        •  Evaluates numerous linear
                                           design types
                                        •  Allows for nonlinear  equation
                                           with complex boundaries
                                        •  Predicts release  rates
•  Addresses all  three
   components necessary  to
   predict release  rate
   and quality
•  Assesses  7 generic sites

•  Calculates leachate volume,
   leachate  head, containment
   time,  seepage  rates,  travel
   times
•  Easy to use

•  Series of simple calculations
t  Predicts  volume  of leachate
   generated over time
                                      t  Not field tested
                                      •  Roes not evaluate leachate
                                         quality
•  Rata intensive
•  Assumes landfill  or surface
   impoundment are designed
   properly
t  Estimates through single
   cell only
•  Does not predict leachate
   qual ity

•  Data intensive
•  Untested model
                                                                                                        •  Does not address leachate
                                                                                                           quality
                                                                                                        •  Untested model
*  Equations may be over
   simpl ified
•  Roes not predict concen-
   tration of ronstltuents
•  Untes.ted model

-------
balance equation coupled with Darcy's Law) and a mass balance equation (which
describes the concentrations of a chemical species in a flow pattern).  These
equations are coupled to provide predictions of solute transport in the
groundwater system with chemical reactions considered.  For analytical models,
these equations are simplified to explicit expressions.  For either type of
model, a sensitivity analysis of model  results can be performed by varying the
input characteristics singularly or in  combination.

     One type of sensitivity analysis that can be performed involves changing
a single parameter (within known values of occurrence) to demonstrate the
effects that variations in individual parameters have on model output.  This
analysis helps identify those parameters that have the greatest influence on
model results.  A second type of sensitivity analysis involves a series of
trial runs using an array of input parameters which vary in accordance with
the expected errors associated with each parameter (i.e., Monte Carlo
simulation techniques).  This method provides a general assessment of the
overall model sensitivity and intrinsic precision by providing a range of
variations of the model outputs as a function of the error bars associated
with the input parameters (e.g., mean values, maximum values, minimum values).

     Analytical models provide estimates of waste constituent concentrations
and distributions using simplified, explicit expressions generated from
partial differential  equations.  The mathematical expressions are usually
simplified by assuming steady state conditions relative to fluid velocity,
dispersion dynamics, and other physical parameters.  For example, groundwater
flow equations can be simplified if the aquifer is assumed to have infinite
extent.  Governing equations characterize both groundwater flow and mass
transport, and may also address dilution, dispersion, and attenuation.  These
models can simulate plume migration from the source to a utilized groundwater
system allowing for attenuation and dispersion.  The method provides a quick
and inexpensive solution with minimal amounts of data as long as the
simplifying assumptions do not render results invalid.

     Numerical models characterize groundwater contamination processes without
the simplification of complex physical  and chemical characteristics required
                                     3-14

-------
by analytical models.  Numerical models reduce the partial differential
equations to a set of algebraic equations that define hydraulic head at
specific points (i.e., grid points).  These equations are solved through
linear algebra using matrix techniques.

     The numerical methods most commonly used to simulate groundwater
transport problems can be divided into four groups:  finite difference (FD);
finite element (FE); method of characteristics (MOC); and discrete parcel
random-wal k (OPRW).  In each method, the governing equations (e.g.,
groundwater flow equations) are solved by subdividing the entire problem
domain into a grid system of polygons.  Each polygon block has assigned
hydrogeologic properties (e.g., transmissivity) associated with it that define
the aquifer at that point.  Accompanying each block is a node point that
represents a position in the aquifer with an equation having unknown values
(e.g., head).  For the finite difference method, the derivatives of the
partial differential equations are approximated by linear interpolation (i.e.,
the differential approach).  In the finite element method, the partial
differential equations are transformed to integral form (functionals) and
minimized to solve the dependent variables.  The algebraic equations for each
node point, derived by the FD or FE methods, are then combined to form a
matrix equation which is solved numerically.  The FE method is better suited
for solving complex two- and three-dimensional boundary conditions than the FD
method.  When using FD or FE methods for solving contaminant transport
problems, results are subject to numerical  dispersion or numerical oscilla-
tion.  Numerical dispersion causes answers to be obscured because of
accumulated round-off error at alternating time steps.  Numerical oscillation
causes answers to overshoot and undershoot the actual solution at alternating
time steps.  Numerical oscillation is generally associated with FE methods,
while numerical dispersion is generally associated with FD methods.

     The method of characteristics and discrete parcel random-walk models were
developed to minimize the numerical  difficulties associated with the FE and FD
methods.  Both the method of characteristics (MOC) and discrete parcel random
walk method (DPRW) analyze temporal  changes in concentrations by tracking a
set of reference points that flow with the groundwater past a fixed grid
                                     3-15

-------
point.  In the MOC method, points are placed in each finite difference block
and allowed to move in proportion to the groundwater velocity at the point and
the time increment.  Concentrations are recalculated using summed particle
concentrations at the new locations.  The DPRU varies from the MOC method
because, instead of solving the transport equation, a random process defines
dispersion.  Reference points move as a function of groundwater flow,
consistent with a probability function related to groundwater velocity and
dispersion (longitudinal  and transverse).  The methods provide comparable
results but the MOC method is time consuming, expensive, and requires
considerable computer storage.

     Tables 3-4 and 3-5 list some of the available models that can be used to
predict the movement of contaminants in groundwater.  As with the release rate
models listed in Table 3-3, each model contains elements that would make it
more applicable to certain site and waste characteristics.  Only eight
analytical and nine numerical models are presented in these tables.  Many more
models exist that can be used for the prediction of chemical migration such as
Weston (1978) and Thomas, et al. (1982).

3.2  Indirect Data

     Indirect data includes generalized data not based on actual site
conditions and data only functionally related to the information required.
Field investigations involving monitoring well installation, aquifer testing,
groundwater sampling and analyses, and associated activities, are typically
the most critical and costly elements of groundwater quality assessment
projects (Popkin, 1983).  The purpose of indirect data, therefore, is to
optimize the usefulness of monitoring wells by identifying the most effective
locations based on anticipated plume limits.  This can help minimize costs as
fewer wells may be necessary.  In certain instances, risks to personnel
installing monitoring wells at hazardous waste sites can also be reduced
(i.e., in the case where wells must be located in close proximity to buried
waste).
                                     3-16

-------
                                                       TABLE 3-4
                                ANALYTICAL SOLUTE TRANSPORT MODELS (Repa, et al., 1982)
Model
Reference
Dimensions
 Madeled
Advantages
Disadvantages
SESOIL     Bonazountas  and
           Wagner (1981)
PESTAN     En field,  et  al.
           (1982)
PLUME      Wagner (1981)
                                  •   Ease of use
                                  •   Long term'fate  simulations
                                  •   Includes numerous degradation
                                      processes
                                  •   Models organics and
                                      inorganics
                                     Predicts pollutant
                                     velocity, length of pollu-
                                     tant  slug, and concentra-
                                     tions
                                     Screening model-rapid
                                     evaluations
                                     Inexpensive to run
                                     Field verified:  DDT and
                                     aldicarb predictions
                                     Two dimensional plume
                                     traces  in groundwater
                                     Incorporates degradation
                                     and sorption terms
                                     Can be  coupled with PESTAN
                                     Field verified:  chromiun
                                                   •   Unsaturated  zone  only
                                                   •   Not  field  or analytically  verified
                                                   •   May  be  overly simplistic
                                                   •   Models  only  organic  species
                                                   •   Unsaturated  zone  only
                                                   •   May  be  overly  simplistic
                                                  •   May  be  overly  simplistic

-------
                                                               TABLE 3-4 (continued)
              Model      Reference
                    Dimensions
                     Model ed
        Advantages
     Di sadvantages
              LPMP
Kent (1982)
oo
 i
co
              AT123D     Yeh (1981)
                     1-2-3
              PATHS
Nel son and
Schur (1980)
•  Predicts migration and
   mixing of contaminants in
   groundwater zone
•  Incorporates degradation
   terms, and dispersion and
   diffusion
•  Ease of use
•  Field verified:  chromiun

•  Predicts migration of
   contaminant in saturated
   and unsaturated zone
•  Incorporates wide range
   of transport mechanisms
•  Example problems provided
•  Numerous source release,
   aquifer and waste options

•  Predicts plume movements
   in saturated zone
•  Inexpensive, first cut
   evaluations
•  Can be run with data
   generally available for
   site
•  Analytically verified
•  May be overly simplistic
•  Not field or analytically
   verified
•  Not field veri fied
•  Degradation and dispersion
   options not included
•  May be overly simplistic

-------
                                                                      TABLE 3-5
                                                  NUMERICAL TRANSPORT MODELS  (Repa, et al., 1982)
               Model
Reference
Dimensions
 Modeled
                                       Advantages
   Di sadvantages
               MMT/VTT
Battelle (1982)
  1-2
               CFEST/
               UNSAT1D
Battelle (1982)
  2-3
GO
I
               Pollutant
               Movement
               Simulator
               FEMWASTE
Khaleel  and
Reddell  (1977)
                    2-3
Yen and Ward
(1981)
                                 o   Predicts  contaminant trans-
                                     port  using discrete parcel
                                     random-walk method
                                 o   Incorporated degradation terms
                                 o   Provides  graphic displays
                                 o   Field  verified:  tritium

                                 o   Predicts  contaminant trans-
                                     port  using finite element
                                     techniques
                                 o   Models complex flow systems
                                 o   Analytically verified
                   Predicts contaminant trans-
                   port using finite difference
                   techniques
                   Incorporates convection  and
                   dispersion equations using MOC
                   Field tested:   NaCl

                   Predicts contaminant trans-
                   port using finite element
                   methods
                   Incorporates convective
                   dispersion, sorption,  and
                   degradation equations
                   Field verified
Requires intensive data to run
model accurately*
Costly to run*
Degradation and sorption term
presently being incorporated
In the process of field
verification:  arsenic and
pharmaceutical chemicals
Model documentation in
preparation

Attenuation processes not
considered
In the process of being
verified for mine wastes
               *These  two disadvantages  apply to all numerical models

-------
                                                                TABLE 3-5 (continued)
              Model
Reference
Dimensions
 Modeled
      Advantages
Disadvantages
              Random
              Walk
GO
I
              Solute
              Transport,
              Dispersion
              Model
              SWIFP
Prickett, et al.
(1981)
  1-2
Konikow and
Bredehoeft (1974)
INTERA
o  Predicts contaminant trans-
   port using random walk
   methods
o  Incorporated dispersion and
   attenuation equations
o  Field verified:  fertilizers
o  Accounts for varying dis-
   charge and recharge rates

o  Predicts contaminant trans-
   port using method of
   characteristics
o  Allows for varying rechar-
   ges and discharges, and
   aquifer properties
o  Field verified:  radioactives

o  Predicts contaminant trans-
   port using finite difference
   method
o  Allows for dispersion and
   attenuation effects
o  Field verified:  sea-water,
   geothermal , rad ioacti ves ,
   and coal tar
                                                      Does  not  incorporate
                                                      attenuation  of chemical  species

-------
                                                                TABLE 3-5 (continued]
              Model
Reference
Dimensions
 Modeled
   Advantages
   Di sadvantages
00
i
ro
              LOMAM
Sykes , et al,
(1982)
 1-2-3
Predicts contaminant trans-
port using finite element
techniques
Incorporates attenuation
and dispersion equations
Field verified:  Cl, K,
radioactives, and aldicarb
Model specific to sanitary
landfills
Currently under review

-------
     This section discusses several  methods of obtaining indirect  data  useful
in estimating the limits of groundwater contamination.   They are:

     •  Previously collected data
     o  Aerial imagery
     o  Geophysical  (surface and subsurface) surveys.

     Indirect data will  not be useful  for all  sites  and each method has
theoretical  and practical  limitations  which affect the  data  obtained.   The
potential benefits to be gained from indirect  data collection efforts
(primarily geophysical  surveys) must be weighed against their cost.

     3.2.1  Previously Collected Data

     Some data will  always be available concerning sites at  which  CERCLA funds
are being used because these sites must be rated using  the Uncontrolled
Hazardous Waste Site Ranking System (40 CFR 300 Appendix A), which requires
specific data on hydrogeologic conditions, waste types, and site conditions.
The type of information  necessary to rank a site and therefore generally
available in EPA files is shown as Table 3-6.   While the EPA and state
hazardous waste management agency files and inspection  reports may provide
much of the data required to plan a remedial investigation,  some data  items
may not always be available.  In these cases,  supplemental information  can
often be obtained from published maps  and reports,  computer data banks, and
other sources.

     Published maps and  reports on various topics are  available from a  number
of sources besides EPA and state environmental agencies.  Table 3-7 lists
several sources in the Federal government.  Many of  the information items
listed in Table 3-7 are also available from sister agencies at the state and
local levels of government.  Of these  sources, probably the most useful are
the U.S. Geological Survey (USGS) and the state geological surveys.  Both the
USGS and state surveys can provide information on studies currently being
conducted in a certain geographic area and typically have on-staff experts  in
                                     3-22

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                             TABLE  3-6
          TYPE  OF INFORMATION GENERALLY AVAILABLE  IN
                 USEPA  SITE INVESTIGATION  REPORTS
WASTE DATA

     -  Type of compounds
     -  Physical  state (solubility,  viscosity,  specific  gravity)
     -  Amount
     -  Hazard assessments (toxicity,  biodegradability,  persistence,
        ignitable,  etc.)

POPULATION AREA

     -  Population  within 1,  2,  3,  or  4  mile  radii  of  site
     -  Population  served by drinking  water within  3 miles  of  site
     -  Population  served by surface water within 3 miles of site

HYDROLOGIC DATA

     -  Depth to  groundwater
     -  Depth to  aquifer
     -  Direction of groundwater flow
        Hydraulic conductivity of aquifers
     -  Net precipitation and 1  year,  24-hour rainfall
     -  Groundwater use
     -  Distance  to nearest drinking water well
     -  Groundwater sampling  results
     -  Surface water sampling results

GEOLOGIC DATA

     -  Type of overburden and bedrock
     -  Area topography
     -  Location  of sensitive environments
        Soil sampling results

SITE HISTORY

     -  Type and  extent of disposal  operations
     -  Original  and subsequent  owners
     -  Observed  contamination or release  incidents
        Regulatory  responses
                              3-23

-------
                                   TABLE 3-7
          TYPES AND SOURCES OF MAPS,  REPORTS,  AND RELATED INFORMATION
                      (ADAPTED FROM CLARK,  ET AL., 1981)
              Topic                                   Source*


              Climate                                 NCC, NOAA, NOS, NWS
              Clinometric (Slope)                      GS, SCS
              Coal  Investigations                      GS
              Earthquake Hazards                      GS
              Floodplains                             CE, FIA, GS, NOS, SCS
              Geodetic Control                         CE, GS, NOS
              Geologic                                GS
              Geophysical                             GS, NOAA
              Groundwater                             GS
              Land  Cover                              PS, SCS
              Land  Use                                GS, SCS
              Mineral Investigations                  GS
              Mines                                   BOM
              Navigable Waterways                      CE, GS, TVA
              River Basin/Watershed Surveys           GS, SCS, TVA
              River Surveys                           BR, TVA
              Soils                                   SCS
              Topography                              GS
              Water Resources                         GS
              Wildlife and Scenic  Rivers              BLM, FS, PS


*Many of these types of maps and reports are also available from State and
local government agencies and universities:

     BLM:  U.S. Bureau of Land Management
           Office of Public Affairs
           Washington, DC  20240

     BOM:  U.S. Bureau of Mines
           2401 E Street, NW
           Washington, DC

      BR:  U.S. Bureau of Reclamation
           P.O. Box 25007
           Denver,  CO  80225

      CE:  U.S. Army Engineer District
           Corps of Engineers, Chicago
           219 South Dearborn St.
           Chicago, IL  60604

                                                                     (continued)
                                     3-24

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                        TABLE  3-7  (continued)
 CE:  U.S. Army Engineer District
      Corps of Engineers, Nashville
      Post Office Box 1070
      Nashville, TN  37202

      U.S. Army Engineer District
      Corps of Engineers, Omaha
      6014 U.S. Post Office and Courthouse Bldg.
      Omaha, NE  68102

      U.S. Army.Engineer District
      Corps of Engineers, Vicksburg
      Post Office Box 60
      Vicksburg, MS  39180

FIA:  U.S. Federal  Insurance Administration
      Engineering Division
      451 7th Street, SW
      Washington, DC  20514

 FS:  U.S. Forest Service
      Information Office, Rm. 3238
      Post Office Box 2417
      Washington, DC  20013

 GS:  Eastern National  Cartographic Information Center
      U.S. Geological Survey
      Reston, VA  22092

      Mid-Continent  National  Cartographic Information Center
      U.S. Geological Survey
      1400 Independence Road
      Roll a,  MO  65401

      Rocky Mountain  National  Cartographic Information Center
      U.S. Geological Survey
      Federal  Center, Building  25
      Denver,  CO  80225

      Western  National  Cartographic Information Center
      U.S.  Geological Survey
      345 Middlefield Road
      Menlo Park, CA   94025
                                                               (continued)
                               3-25

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                         TABLE 3-7 (continued)
 NCC:   U.S. National  Climatic Center
       Federal  Building
       Asheville, NC  28801

NOAA:   U.S. National  Oceanographic and Atmospheric Administration
       Office of Public Affairs
       14th Street, NW
       Washington, DC

 NOS:   U.S. National  Ocean Survey
       Distribution Division (C-44)
       6501 Lafayette Avenue
       Riverdale, MD  20840

 NWS:   U.S. National  Weather Service
       Gramax Building
       8060 13th Street
       Silver Spring, MD  20910

  PS:   U.S. National  Park Service
       Office of Public Inquiries, Room 1013
       Washington, DC  20240

 SCS:   U.S. Soil Conservation Service
       Information Division
       Post Office Box 2890
       Washington, DC  20013

 TVA:   Tennessee Valley Authority
       Mapping Services Branch
       111 Haney Building
       Chattanooga, TN  37401
                                 3-26

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local geology.  State surveys will  probably provide more detailed  hydro-
geologic information about a specific locality than would the  USGS but
coverage is typically more limited.  Data which geologic surveys are  able to
provide include regional and local  subsurface profiles,  aquifer
characteristics, and potentiometric surface maps.

     The USGS also coordinates NAWHEX—the National  Water Data Exchange-
consisting of over 400 organizations concerned with water and water programs,
which have agreed to share their water data for maximum  use.  While the type
and quality of information varies between organizations,  the service  can
locate local  sources of water data  including well  locations, geologic
profiles, potentiometric surfaces,  water quality data, and aquifer
characteristics.

     NAWDEX services are readily available.  Requests  may be made  at  one of 60
NAWDEX offices or the USGS National Headquarters (703/860-6031) by phone,
letter, or personal  visit.  The request  is reviewed by NAWDEX  for  clarity and
completeness  and then is processed.  NAWDEX either provides the requested data
from its files or the inquiry is referred directly to organizations that hold
specific data.  NAWDEX does charge  a fee for the service  (USGS, 1980).

     While the primary function of  NAWDEX is  not to  provide data storage and
retrieval  services,  NAWDEX does have direct access to several large data banks
including:

     •  WATSTORE --  The USGS maintains a water  data  storage and retrieval
        system for geologic, hydrologic,  and chemical data  on surface water
        and groundwater in the U.S.  Data is  available from approximately
        16,000 stream gaging stations, 1,000 lakes and reservoirs, 5,200
        surface water quality stations,  30,000  water level observation
        stations and 12,500 groundwater  quality wells.  A  groundwater site
        inventory file contains information  for  nearly 700,000 wells
        (Kilpatrick, 1981).
     •  STORET --  EPA maintains a storage and  retrieval system which contains
        over  40 million  individual  observations  of water  quality parameters
        for both surface and groundwater.   Information is collected from
        several  Federal  organizations  as  well  as more than 40 state
        organizations.
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     Despite the large number of data sources, WATSTORE, STORET, and the other
data banks available through NAWDEX will  probably not contain information from
sources close enough to a particular site to be of great value.  The infor-
mation they contain may provide useful  regional geohydrologic data and the
service should be considered as an inexpensive source of background hydro-
geologic data.

     In addition to the sources described above, there are also a variety of
other sources of information that can be used in the plume delineation
process.  For example, well  drillers familiar with local conditions can
provide a wealth of information on subsurface conditions and aquifer
characteristics.  Local geotechnical contractors and testing laboratories can
be a valuable source of data on porosity, hydraulic conductivity, and other
subsurface characteristics. Geologists on the staff of local colleges and
universities should also be familiar with regional geology and hydrology.
Examples of other potential information sources are listed in Table 3-8.

     A major type of previously collected data other than maps,  reports,
computer data banks, and local contacts is aerial imagery.  Aerial  imagery is
the subject of the next section.

     3.2.2  Aerial Imagery

     Aerial imagery refers to  pictorial representations produced  by electro-
magnetic  radiation that is emitted  or  reflected from the  earth and  recorded by
aircraft-mounted sensors.  The simplest, most  common form of imagery  is  the
photograph, which uses only the visible part of the electromagnetic spectrum.
Oblique  photos  are taken at angles  to  the earth's surface and  thus  distort the
scale  of  the  picture  (i.e., objects  in the foreground are larger  and  objects
in  the  background are  smaller  than  they should be).   Perpendicular, or
stereophotos, which are taken  from  directly  above the site so  that  there is
minimal  distortion, can  be  used  in  pairs to  show  the  topography  of  the  site in
three  dimensi ons.
                                      3-28

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                                   TABLE  3-8
                 EXAMPLES OF ADDITIONAL SOURCES OF  INFORMATION
                           FOR  REMEDIAL INVESTIGATIONS
          Source
           Information
State and Local Government Agencies

     Health
     Planning and Zoning

     Tax Assessor

     Engineer


     Fi re Department


     Law Enforcement


     Water and Sewer




Utility Companies

     Gas, Electric,  Water, and
     Petroleum or Natural  Gas
     Pipelines
Reports of  unusual  health problems
related to  the site, drinking water
analyses, locations of contaminated
wells

Land use

Plat maps and land ownership

Foundation  and inspection reports,
survey benchmark locations

History of  fires or explosions at a
facility

Complaints  and violations of local
ordinances during site operation

Geotechnical studies related to water
supply or construction, locations of
buried mains and lines, data related to
quality of influent to treatment plant
Location of buried lines
                                    3-29

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                             TABLE 3-8 (Continued)
          Source
          Information
Contractors

     Building
     Soil  exploration and
     foundation

     Water supply and wel 1
     dril 1 ers
Trade Associations

     National  Water Well  Association
     500 W. Wilson Bridge Rd.
     Worthington, OH  43085
     Chamber of Commerce
Universities

     Geology Engineering,  Biology,
     and Agronomy Departments,  and
     Medical Schools
Local soils, geology, and shallow water
1evels

Local soils, geology, hydrogeology,
water levels, regulations, and
equipment availability
Local hydrogeology, aquifer properties,
water quality, and locations of
existing wells
Local well drillers and related
contractors, well design and
construction information, and water
supply and aquifer restoration
i nformation

Information on local  industries
including waste generators,
transporters, and disposers
Various types of information
on local  conditions
                                     3-30

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      The second  type of aerial  imagery uses  wavelengths  of  light  outside  the
 visible spectrum.   The most  common  and useful  type for detecting  the  effects
 of leachate is  the infrared  image.   Infrared imagery  indicates  areas  that  are
 hotter or cooler than the general  surroundings.   This  is useful  as  areas  of
 dead  vegetation  having different  radiant  heating  (albedo) characteristics  than
 vegetated areas  (JRB, 1980).

      Indicators  of leachate  can be  both spatial and spectral.   Spatial
 indicators  refer to  physical  changes  to systems caused by leachate.   These
 include gaps  in  vegetation or  snow  cover,  and  areas of wetness  indicating  an
 outbreak  of groundwater  or a  leachate  seep.  Spectral indicators  refer to
 color  changes in either  water  or in vegetation, and may  make use  of wave-
 lengths  other than  in  the visible range.   If historical  aerial  imagery is
 available,  comparisons  between new  and old imagery can indicate changes in  an
 area that may be caused  by leachate movement.  The gradual development of a
 barren  area in a forest  for unknown reasons  may indicate the presence of
 hazardous wastes.   In  general, spatial indicators are more useful and
 consistent  than  spectral  indicators (Sangrey and  Philipson, 1979).

     Gaps can occur  in snow or vegetative cover because of leachate wetness,
 toxicity  or heat.  Gaps  caused by heat would appear in close proximity to
 landfills because  heat dissipates quickly with distance and would tend to
 radiate from the landfill.  Gaps caused by excessive wetness or toxic
 substances can occur  at  greater distances  and may radiate from a site or may
 occur as  isolated patches.  Vegetative gaps can be detected  in photographs or
 near-infrared images.  Gaps can also be distinguished  in  thermal infrared and
microwave images because emissions from vegetation and base  soil are
different.  Active microwave  sensing by radar should detect  most vegetative
 soil gaps not obscured from direct view.   Gaps in  snow are easily detected in
photographs, or  near-infrared, thermal infrared,  and microwave images.  The
problem with using gaps as indicators  of  leachate  is that gaps are not limited
to leachate-affected sites.   Also,  gaps are not guaranteed to  occur  at the
limits  of plume  extent (Sangrey and  Philipson,  1979).
                                     3-31

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     Damp and saturated zones or seeps at waste sites can be distinguished
quite easily by remote sensing.  The spectral characteristics of seeps are
sufficiently distinct so that they are observable over the entire electro-
magnetic spectrum.  Increased soil moisture decreases soil reflectance in the
visible and near-infrared wavelengths, allowing for detection of near-surface
water.  During dry periods, these damp areas can be detected because of
anomalous spectral returns caused by moisture stressed vegetation.  The
spectral anomaly most often used as a leachate indicator is vegetative stress.
Vegetative stress can be noted by the use of color infrared scanners (Aronoff
and Ross, 1982).  The variations caused by vegetative stress can be a result
of death or defoliation from toxic effects,  reduction in foliages, or
temperature changes.  However, increased nutrient and moisture levels caused
by leachate have been known to enhance vegetative growth.  Spectral variations
caused by leachate seeps, oils, or other fluid coatings on water can be
detected in ultraviolet, thermal, or microwave images.

     Aerial images may indicate where contamination occurs, but will not
identify the boundary of the contaminated zone because gaps, wetness, and
stressed vegetation are not limited to occurring only at the edges of a plume.
However, these contaminated zones serve as additional data points that are
useful in site investigations. For example,  if calculations of flow rate
indicate that the maximum extent of contamination should be X yards from  a
landfill, yet stressed vegetation is readily apparent at X + 300 yards,
several explanations are possible.  First, the input data to Darcy's Law  may
be incorrect:  hydraulic conductivity may be greater than calculated, the time
from the start of contamination may be longer than estimated, the gradient may
be steeper, or porosity lower.  Second, a preferential migration pathway  which
allows contamination to move much faster than through the majority of the
geologic system may have been  overlooked.  Third, the constituents of the
plume may  be more mobile than  originally estimated (i.e., dispersion in this
system  has a large effect on migration rates).  Fourth, there may  be multiple
sources of contamination.  Finally, the  stress may not be caused by the
leachate.
                                      3-32

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     Geohydrologic conditions can also be determined or verified using aerial

imagery.  Aerial image interpretation can be used to:


     •  Identify rock and soil types, geomorphological features, the nature of
        sediments, joint and fault patterns, and outcrop areas

     9  Approximate stream flow, evapotranspiration, infiltration, and runoff
        values

     e  Map topography; streams, seeps, and other surface waters; and
        vegetation not readily apparent from ground level.


     One final use of aerial imagery is in the analysis of historial images to

analyze disposal site operations.  Historical data can set the time of the
start of disposal operations for the calculation of migration rates.  The
lateral extent and timing of disposal operations can also be estimated using
historic air photos (Erb, et al., 1981).  Finally, changes in surface
topography over time can be determined.  This last item was of value during
the investigation at Love Canal, where historical aerial  photos were used to

map old swales and drainage areas since filled and thought to act as areas of
preferential migration routes (Kufs, et al., 1981).


     EPA has three offices that can provide information on all aspects of
aerial  photography and photo interpretation:


     •  Environmental  Monitoring Systems Laboratory (EMSL)
        P.O. Box 15027
        Las Vegas, Nevada  89114

     •  Environmental  Photographic Interpretation Center (EPIC)
        P.O. Box 1587
        Vint Hill Farm Station
        Uarrenton, Virginia  22186

     9  National Enforcement Investigation Center (NEIC)
        Building 53, Box 25227
        Denver, Colorado 80225
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     Aerial  imagery is available from a  number of sources besides  EPA.
Government agencies that also perform aerial  surveys include:

     •  Agricultural  Stabilization and Conservation Service
     •  U.S.  Geological  Survey (USGS)
     •  U.S.  Forest Service
     o  National  Air  and Space Administration  (NASA)
     •  National  Oceanic and Atmospheric Administration  (NOAA)
     e  National  Archives and Record  Service
     0  National  Weather Service
     t  Soil  Conservation Service (SCS)
     •  Commodity Stabilization Service
     •  U.S.  Air  Force (USAF)
     •  Corps of  Engineers
     t  Bureau of Reclamation
     •  U.S.  Coast and Geodetic Survey
     •  Tennessee Valley Authority (TVA)

     Government sources of aerial imagery and  related data are  listed by state
by the USGS (1976).  In general, the  majority  of non-military  aerial
photography acquired  by Federal agencies can  be obtained from:

     •  National  Archives and Records Service
        Cartographic  Branch
        8 Pennsylvania Avenue, N.W.
        Washington, D.C.  20408
        (for  photographs taken prior  to 1942)
     o  EROS  Data Center
        U.S.  Geological Survey
        Sioux Falls,  South Dakota  57198
     •  Agricultural  Stabilization and Conservation Service
        U.S.  Department of Agriculture
        205 Parley's  Way
        Salt  Lake City, Utah  84109
                                     3-34

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     o  Soil Conservation Service
        U.S. Department of Agriculture
        Cartographic Section
        6505 Delcrest Road
        Hyattsville, Maryland  20782


     Private sources of aerial imagery can be obtained from the American

Society of Photogrammetry, 105 North Virginia Avenue, Falls Church, Virginia,

22046.


     3.2.3  Geophysical  Methods


     Over the last 10 years, geophysical  equipment, survey techniques, and

data processing have been refined to the  point where geophysical  methods can

provide valuable data during hazardous waste site characterizations (Evans, et

al., 1982).  Geophysical  methods can be divided into two groups:


     •  Surface Surveys  -- where instruments used in collecting data are
        located on the land surface
                      i
     o  Borehole Methods -- which require direct access to the subsurface
        through boreholes or wells.


Surface surveys provide data that indirectly determine the subsurface geology.

Data may be obtained concerning (Fetter,  1980; Glaccum, et al., 1982; Sendlien

and  Yazicigil, 1981 and  1982):


     o  Thickness of unconsolidated strata

     e  Depth to water table

     •  Fault location and joint patterns

     9  Location of solution channels

     •  Location, thickness, and extent of subsurface bodies  such as clay or
        gravel  deposits

     e  Presence, distribution, and location of buried wastes

     «  Presence and extent of certain types of contaminants  and  leachate
        plumes.
                                     3-35

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Borehole methods provide data on (Fetter, 1980):

     •  Areas of high porosity and hydraulic conductivity
     o  Water flow rate and direction
     •  Subsurface stratigraphy
     0  Lithology of subsurface units
     •  Chemical and physical characteristics of water.

     Surface geophysical methods appear to have more application to hazardous
waste site investigations than borehole methods.  Proponents of surface
geophysical methods (e.g., Sendlein and Yazicigil, 1981; Pease and James,
1981; Evans, et al., 1982; Glaccum, et al., 1982) correctly point out that
monitoring wells may poorly define contaminant plumes for a variety of
reasons.  The attractiveness of surface geophysical  surveys is that they are
able to provide a theoretically continuous profile of the subsurface and,
therefore, are much better suited to detecting preferential migration routes.
Several  surface geophysical methods measure changes  in the physical parameters
of water that may be caused by the presence of leachate or contamination, and
thus serve to outline the possible boundaries of a plume.  Surface geophysical
methods, when used in conjunction with conventional  drilling programs, can
have application to many waste site investigations (Evans, et al., 1982).

     Two things should be mentioned at this point.  First, surface geophysical
methods are not a panacea.  They are sources of valuable information but they
do not have application in all situations and are not always the most
effective method of obtaining information (USGS, 1977).  Second, geophysical
methods do not provide direct data on groundwater contamination.  Those
methods that outline possible plume boundaries measure changes in physical
parameters (e.g., specific conductivity) that may be caused by the presence of
contaminants in groundwater, but they do not provide indications of contami-
nant type and concentration  (e.g., toluene at X ppb).  Thus, groundwater
samples from monitoring wells will always be necessary to provide direct data
on contaminant type and concentration.
                                     3-36

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      The  surface  geophysical  methods  rnost  applicable  to  plume  delineation
 include:

      •  Ground  penetrating  radar
      e  Electromagnetic  conductivity
      «  Galvanic  electrical  resistivity
      •  Sei smic methods.

 The theory,  application, data use,  and limitations of  each of  these methods  is
 discussed  below.   Borehole  geophysical logging methods are also  summarized.
 As with all  investigation techniques, a  careful definition of  the problem and
 identification  of  the types of  information  required should be  made prior to
 selecting  any particular geophysical  method or suite of  methods.

           3.2.3.1  Ground Penetrating Radar (GRP)

      GPR  systems  generate electromagnetic  radiation that reflect from various
 objects because of changes  in the object's ability to  conduct  the electro-
 magnetic  wave.  The  reflections are recorded and interpreted to  provide a
 continuous subsurface profile, much like a geologic cross-section, along a
 traverse  path.  GPR systems  can  be used to  locate buried  drums, detect inter-
 faces between different geologic strata, and identify plumes of  high chemical
 concentration (Pease and James, 1981).  The depth of penetration and resolu-
 tion  are affected by site conditions, thus the applicability of  GPR must be
 decided on a site specific  basis.

      GPR systems consist of four elements:

     o  Electromagnetic radiation source
     •  Transmitting antenna
     •  Receiving antenna
     o  Data processing and display equipment.

     GPR power units and pulse transmitters feed  the pulse to the transmitter
antenna, which radiates the pulse into the subsurface.  Reflected signals are
                                     3-37

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 received, usually by the same antenna, and fed into a  receiver electronically
 isolated from the transmitter.  The reflection is amplified and processed to
 produce a waveform similar to the original but with a  longer time base.  This
 new signal can be processed further and displayed.  The most common type of
 display system uses a graphic recorder.  Most GPR systems mount all the
 necessary equipment, except for the antenna, within the survey vehicle
 (Horton, et al., 1981; Benson and Glaccum, 1979).  Antennas may be externally
 mounted on the same vehicle or on an independent frame capable of being towed.

     Prior to running a GPR survey across a site, several preliminary steps
 are usually completed.  Stakes are driven into the ground to outline the
 survey grid and the traverse path is cleared of brush, tree limbs, tall
 grasses and weeds, and any other obstacles that may hinder the smooth passage
 of the survey vehicle.  Several  preliminary scans are made to calibrate the
 system with the specific electromagnetic conditions at the site. In addition,
 the velocity of the signal  in the medium must be calculated, along with the
dielectric constant of the soil.  Once these values are calculated, the pulse
 repetition frequency is set, along with frequency and energy output.
Different settings may be used and several surveys run to obtain maximum
 resolution and depth of penetration.

     Surveys are performed by slowly moving the antenna over the ground
surface.   The survey vehicle is  moved across the grid at a set speed (usually
around 5  mph).  Precise speed must be maintained such that the area! location
of targets can be positioned within a few feet.  For more detailed studies,
discrete  readings can be taken at selected points along a traverse (Benson and
Glaccum,  1979).  After the survey is run, the data is usually taken from the
recorder  for further processing.  A graphic display can be generated on-site,
and examined in the field to provide a general  indication of the subsurface
conditions (i.e., the general locations of drums) and the effectiveness of the
 survey.  Fence diagrams can be developed from the subsurface profiles.

     Usually GPR cannot be used  to map anomalous groundwater conditions that
may be indicative of contamination.  However, GPR can be used very effec-
tively, in certain conditions, to outline the water table and indicate the
                                     3-38

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direction of groundwater flow.  GPR can  be used to outline the boundaries of
disposal sites, which is important in selecting monitoring well locations.
GPR can also map the presence of many soil features including cementation,
clay lenses, organic layers, sediment layering, water infiltration zones,
depth to bedrock, top of bedrock topography, and fractures and cavities in
bedrock.

     Because most GPR systems are vehicle mounted, they are limited to sites
that allow access to and over the area of concern.  Sites with swamp-like
conditions would probably not be good candidates for GPR surveys because of
access problems and because of the presence of silt, clays, and high water
content reducing the depth of penetration.  Likewise, sites with large
boulders, pits, or high topographic relief would not allow the required access
across the site.  The type of geologic material present at a site and the
presence of water can dramatically influence the effectiveness of GPR.  Depths
up to 30 feet are commonly attained using GPR and in certain cases up to
60 feet penetration has been reported (Evans, et al., 1982).  However, high
clay concentrations rapidly attenuate radar waves reducing penetration to less
than 3 feet (Benson and Glaccum, 1979).  Lower transmission frequencies can
yield greater penetration, but resolution is sacrificed (Lord, et al., 1980).
The use of GPR in areas with high proportions of silt and clay size particles
should be questioned.

          3.2.3.2  Electromagnetic Methods (EM)

     EM methods are available which measure the electrical  conductivity of
subsurface materials.  The conductivity (reciprocal  of resistivity) of a
substance is a measure  of  the ease with which a current passes through it.
Conductivity methods have  been used to (McNeill, 1980):

     •  Determine rock  lithology and  bedrock  depth
     •  Locate and  map  aggregate and  clay deposits
     c  Map  groundwater extent  and salinity
     •  Detect pollutant plumes
     •  Locate geothermal  areas.
                                     3-39

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     The theory behind using EM fields to induce currents in conductive media
is well established.  A magnetic current is created by passing an alternating
current through a wire loop.  When the wire loop is in close proximity to
conductors (i.e., earth materials), a current is induced in the conductor.
The strength of the current flowing through the conductor is dependent upon
its conductivity.  Since any current generates a magnetic field, the induced
current produces a secondary magnetic field with the same frequency as the
primary field, but of reduced intensity.  The secondary field induces a
current in another wire loop, the receiver.  By measuring the reduction in
voltage between the primary and secondary fields, the conductivity
(resistivity) of the material can be determined.

     The ability of soils and rocks to conduct electrical currents depends
primarily on the amount, salinity, and distribution of water (USGS, 1977).
Saturated soil and rock can be considered insulator particles immersed in a
conductive fluid.  The total resistivity of the system depends on the
conductive fluid and the impedence placed on current flow by the insulators
(McNeil 1, 1980).  Minerals in sand and silt fractions of soils are generally
excellent insulators.  Dry clay is also an excellent insulator, but moisture
allows certain ions adhering to the surface of clay particles to transmit
electrical current decreasing the resistivity.  The effect of organic matter
on resistivity has not yet been determined.  Gases dissolved in water tend to
inhibit electrical conductance and thus increase resistivity.  Water is by far
the most important influence on conductivity (McNeill, 1980).

     There are two types of EM survey techniques:

     •  Profiling -- where lateral changes in conductivity along a set depth
        from the surface are measured
     •  Sounding -- where vertical changes in conductivity are measured.

     In profiling, depth of exploration is set by separating the primary
(generator) and secondary (receiver) coils.  A traverse is surveyed and
conductivity at the set depth of exploration can be recorded continuously or
can be measured at discrete points.  Contours of equal conductivity are
                                     3-40

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plotted.  The  location and shape of subsurface  features with anomalous
conductivity values can be described, but only  at the depth of exploration.
Since profile  surveys can be run almost as  fast as a survey team can walk,
data from several surveys along the same traverse but with varying depths of
exploration can be evaluated to provide a three dimensional profile of
conductivity anomalies.

     In sounding surveys, vertical changes  in conductivity are measured by
adjusting electrode spacing and measuring changes in vertical conductivity
with depth.  Using available EM equipment for sounding is inconvenient because
most EM setups have set electrode spacings.  Sounding surveys are generally
performed using galvanic electrical resistivity equipment.

     In order  to map contaminant plumes, a  contrast in conductivity must exist
between the contaminant plume and local  geohydrologic background values.
Leachates with high total  dissolved solids  usually have high conductivity, but
an uncontaminated saturated clay lens may exhibit the same response.  In
mapping depth  to water table and groundwater flow direction, the great change
in conductivity between saturated and unsaturated materials is usually
sufficient to  allow the water table to be mapped.

     Limitations of EM conductivity include (Pease and James, 1981):

     •  Ability to detect non-conductive pollutants is limited
     •  Ability to detect plumes is limited if there is not a sharp contrast
        between plume and  natural groundwater
     e  Lateral variations in stratigraphy  complicate interpretation
     •  Buried conductive  objects may result in anomalous readings.

     Horizontal profiling  surveys using EM  conductivity and performed under
suitable conditions can rapidly trace the outlines of contaminant plumes up to
200 feet deep.  Vertical  sounding can be performed using EM conductivity,  but
is usually performed  using Galvanic electrical  resistivity.
                                     3-41

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          3.2.3.3  Galvanic Electrical  Resistivity

     Galvanic electrical  resistivity methods are among the most widely used
methods in groundwater studies (Yazicigil  and Sendlein, 1982; Fetter, 1980).
Resistivity surveys involve applying a direct electrical current into the
subsurface and measuring voltage passing between electrodes.  In applying the
current, four electrodes are used—two to  generate the current (a positive and
negative electrode) and two potential  electrodes to measure the resultant
current flow through the earth materials.   By knowing the current flowing
through the ground and the voltage between electrodes, the apparent
resistivity of earth materials between  the electrodes can be calculated
(difference between current applied and current measured).  The same
properties affecting conductivity also affect resistivity surveys and they may
be used in the same manner to detect contaminant plumes and provide data on
subsurface geology.

     There are three electrode arrays  commonly used in direct electrical
resistivity surveys (Fetter, 1980; Lord, et al., 1981; Raghunath, 1982):

     •  Wenner Array -- where the positive and negative electrodes and the
        potential electrodes are spaced evenly apart
     •  Schlumberger Array -- where the potential measuring electrodes are
        spaced close together and the  current electrodes are spaced far apart
     •  Dipole-dipole Array -- where the potential and current electrode pairs
        are spaced a mutual distance (x) apart and the pairs are an integral
        multiple of x from each other.   This array is usually limited to very
        deep surveys.

     Both sounding and profiling can be performed using electrical resistivity
equipment.  In sounding, the spacing between the potential and current
electrodes is increased.  This causes  the  current to move deeper into the
subsurface and the apparent resistivity measured incorporates the resistivity
of the deeper material.  Either the Wenner or Schlumberger Array may be used;
but the Schlumberger Array is usually  much more convenient because the two
inner electrodes are spread only occasionally (Fetter, 1980).  Sounding begins
with electrodes positioned close to each other.  After a reading is made, the
                                     3-42

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electrodes are positioned farther apart and new readings made.  A plot of
calculated apparent resistivities taken at different electrode spacings, but
centered on a single location, is termed a sounding curve.  This curve
reflects the changes in electrical characteristics with depth.  The curve is
generally interpreted as a series of horizontal subsurface layers each with a
specific resistivity (Urish, 1983).

     In horizontal profiling, electrode spacing remains constant, but the
electrodes themselves are moved in a grid pattern over the land surface.  The
Wenner Array is used most often in horizontal  profiling.  If subsurface
conditions are uniform, apparent resistivity should not change across the
study area.  Any changes can be interpreted as being caused by subsurface
heterogeneity (e.g., clay lenses in sands) or  by contaminated groundwater.   In
setting up the grid pattern, the spacing between stations can conveniently  be
equal to,  or an integral multiple of, the spacing between electrodes.  This
facilitates movement of the array.  A decision must be made as to the effort
involved in increasing  the number of stations  and the risk of bypassing
contaminant plumes if stations are farther apart.

     Direct electrical  resistivity methods, while  not as mobile as  EM methods,
allow any  depth (up to  limits of the equipment) to be explored.  However,
there are  limits  to use including (Pease and James, 1981; Urish,  1983):

     •   Ability to detect non-conductive pollutantsis limited
     t   Ability to detect plumes  is limited if sharp resistivity  contrasts  do
        not exist
     •   Lateral  variations in stratigraphy complicate interpretation
     •   Equipment range (dependent upon  electrode  spacing,  power  output and
        subsurface resistivity)  is site  specific
     t   Rocks,  trees, buildings,  and  other  obstacles  may restrict grid
        patterns
     •   Electrical  interferences,  power  lines  and  buried cables,  in general,
        must  be  kept  at  least one  electrode spacing from the  grid.
                                     3-43

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     Nevertheless, direct electrical  resistivity profiling is a relatively
fast and inexpensive method of collecting subsurface data and may be used to
outline plume boundaries prior to monitoring well  installation.  The advantage
of direct electrical resistivity over EM methods is in the ability to more
precisely set exploration depth.

          3.2.3.4  Seismic Refraction Surveys

     In a seismic refraction survey,  shock waves generated by small  explosive
charges or by heavy blows on a metal  plate travel  downward through the earth
and are refracted back to the surface from the interfaces between different
layers.  The refracted waves are picked up at various points on the ground
surface by geophones and recorded.  By knowing the arrival times of different
waves at set distances from the energy source, the velocity of propagation of
the waves through each rock layer can be calculated.  Particular rocks under
specific conditions have characteristic velocities, thus subsurface profiles
can be developed.  Depths to several  hundred feet can be probed using seismic
refraction techniques (Ragnuhath, 1982).

     The most common use of seismic methods is in mapping bedrock surface.
Buried valley aquifers, for instance, have been mapped in this way.   Water
table depth can usually be determined using seismic methods, but only if the
water table lies in unconsolidated deposits.  Furthermore, thin layers of
saturated sediments lying above bedrock may not be detected nor will layers
underlying a higher velocity layer.  In certain cases, lateral lithologic
changes in aquifers can be mapped.  However, large amounts of seismic data and
correlation with borehole data is usually required.  Vertical strati graphic
profiles are more easily developed than horizontal profiles using seismic
methods.

     While seismic refraction cannot delineate plume boundaries, determining
the depth to groundwater (in alluvium) and fault locations are two major uses
in groundwater studies.  The great depth of penetration of this method makes
seismic refraction useful in areas where other geophysical methods are not
applicable.
                                     3-44

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           3.2.3.5  Geophysical  Well  Logging

      Geophysical  well  logs are  an important tool  in defining the subsurface
 environment, and  often provide  the only practical  measurement of undisturbed
 subsurface sediments.   Geophysical logs are useful  in determining (USGS,
 1977):

      0   Lithology
      •   Geometry
      •   Resistivity
      •   Bulk density
      •   Porosity
      •   Hydraulic conductivity
      0   Moisture  content
      o   Specific  yield  of  water-bearing rocks
      o   Chemical  and physical characteristics of water.

      Borehole  logging  complements  drillers  and geologists  logs,  and soil and
 rock  samples.  Cased wells  can  often be  logged through the casing.  Borehole
 logs  correlated with surface geophysical methods usually increase the value  of
 data  obtained  from  both sources  (USGS,  1977).  There  are many logging methods
 in use today,  several of which  are described below.   Geophysical logs are
 usually  run  as pen  and  ink  strip charts.  In general, borehole systems consist
 of a  probe which  is lowered into the borehole on a cable containing powerlines
 to the probe,  transmitter cables to the  recorder, and a support cable.  The
 probe contains the  required electronics, energy or nuclear sources, and
detectors.  Types of borehole logs are summarized below.

     Caliper Logs -- Caliper logs measure the diameter of uncased boreholes in
bedrock  units.  In plume delineation studies, they can be used to indicate
solution  cavities, bedding planes, faults and joints, and other preferential
routes of water movement.

     Temperature Logs  -- A temperature  log  is a  continuous  vertical  record  of
fluid temperature in the borehole.  Temperature  logs are usually the first  log
                                     3-45

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run on a borehole to minimize mixing effects.  The assumption implicit in
temperature logging is that fluid is in equilibrium with the geologic
materials.  Temperature logs are useful in locating points of groundwater
entrance or loss from the borehole.  Temperature logs are also important in
correcting resistivity and spontaneous potential logs in deeper wells (USGS,
1977).

     Single-Point Resistance -- Single-point  resistance is one of several
methods for measuring electrical resistance.   A single electrode is lowered
into the borehole on an insulated cable while the second electrode remains on
the surface.   As the electrode is lowered into the borehole, the resistance of
the material  from land surface is measured (Fetter, 1980).  The single-point
resistance method has a very limited depth of investigation and does not
measure the resistance of specific formations.

     Resistivity --  Resistivity can be measured by spaced electrodes of
various configurations.  The short-normal configuration measures resistivity
of the zone closest to the borehole.  The long-normal method measures
resistivity farther from the borehole.  Lateral configurations can be spaced
to measure set distances from the borehole.  However, the wider the spacing
the less likely that thin beds of different material  may be found.  Resis-
tivity is an important indication of stratigraphy, lithology and water
quality.

     Spontaneous Potential -- Spontaneous potential (SP) logs measure the
natural electric potential that develops from contact between the formation
and borehole fluids.  SP logs are used chiefly for correlating geologic units,
determining bed thickness, calculating formation water quality, and separating
porous and non-porous rocks such as shale-sandstone and shale-carbonate
sequences (USGS, 1977).  SP logs consist of a surface electrode and a borehole
electrode connected to a voltmeter to measure potential.

     Nuclear Logging — Nuclear logging can be done in cased or uncased holes.
Measurements can be made of either natural radiation  or of the ability of
subsurface materials to attenuate induced radiation.   Natural-gamma logs are
                                     3-46

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 records of natural gamma radiation emitted by all rocks.  They are used
 primarily to identify lithology and correlate stratigraphy, especially in
 detrital sediments.  Neutron logging utilizes a probe with a radioactive
 source of neutrons and a detector.  Neutron logs respond to water.  Below the
 water table they measure porosity, while above they measure moisture content.
 Gamma radiation logs measure the absorption or scattering of cobalt 60.
 Absorption is proportional to bulk density of earth materials and is an
 indirect reading of porosity.

     Table 3-9 summarizes the applications of various borehole logging
 techniques.

 3.3  Direct Data

     Direct data includes any information which can be applied directly and
 precisely to delineating a leachate plume.  Direct data can be qualitative
 (e.g., observing a leachate seep is direct qualitative evidence of groundwater
 contamination at a point) or quantitative (e.g., chemical  analysis results).
 The three primary means of collecting direct data include:

     t  On-site and near-site inspections
     •  Hydrologic testing
     e  Sampling.

 These activities should be undertaken at all  sites prior to beginning aquifer
 restoration design and implementation activities.

     On-site inspections serve three purposes.   First, the  accuracy  of  the
 background data collected prior to the  site visit must be  verified.   Second,
observations that only a trained investigator can make at  a site  must be
 compiled.   Third, a decision must  be made on  what follow-up work  should be
 performed  at the site and how and  when  this work should be  accomplished.
                                     3-47

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                                   TABLE 3-9
         SUMMARY OF BOREHOLE  LOG APPLICATIONS (KEYS  AND  MacCARY,  1971)
Information Required
Applicable Logging Techniques
Lithologic and stratigraphic correla-
  tion of aquifers and associated
  rocks

Total  porosity and bulk density
Effective porosity and true resistivity
Clay and shale content

Secondary porosity--fractures,
  solution openings
Electric, sonic, or caliper logs
  made in open holes.  Nuclear logs
  made in open or cased holes.

Calibrated sonic logs in open holes;
  calibrated neutron or gamma-gamma
  logs in open or cased holes.

Calibrated long-normal  resistivity
  logs.

Gamma logs and resistivity log.

Caliper, sonic, or borehole
  television logs.
Specific yield of unconfined aquifers     Calibrated neutron  logs.
Location of water levels and saturated
  zones
Moisture content

InfiItration
Dispersion, dilution, and movement
  of waste
Source and movement of water in
  a well
Chemical and physical characteristics
  of water including salinity,
  temperature, density, and viscosity
Electric, temperature or fluid con-
  ductivity in open hole or inside
  casing.  Neutron or gamma-gamma
  logs in open hole or outside
  casing.

Calibrated neutron logs.

Time-interval nuetron logs under
  special circumstances or
  radioactive tracers.

Fluid conductivity and temperature
  logs and gamma logs for some
  radioactive wastes.

Injectivity profile.  Flowmeter or
  tracer logging during pumping or
  injection.  Temperature logs.

Calibrated fluid conductivity and
  temperature in the well.  Neutron
  chloride logging outside casing.
  Multielectrode resistivity.
                                     3-48

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                             TABLE  3-9  (continued)
 Information Required                      Applicable Logging Techniques
Construction of existing wells;           Gamma-gamma, caliper, collar,
  diameter and position of                  perforation locator, and borehole
  casing, perforations, and screens         television.

Guide to screen setting                   All  logs providing data on the
                                            lithology, water-bearing
                                            characteristics, and correlation
                                            and thickness of aquifers.

Cementing                                 Caliper, temperature, or gamma-gamma.
                                            Acoustic for cement bond.

Casing corrosion                          Under some conditions caliper or
                                            collar locator.

Casing leaks or plugged screen            Tracer and flowmeter.
Table 3-10 highlights the usefulness of selected site inspection observations

to plume delineation.  General site inspection procedures have been described

in several  sources including Sisk (1981), JRB (1980) and numerous shorter

references which will not be detailed here.  The following two sections

describe the roles of hydrologic testing and sampling in plume delineation.


     3.3.1  Hydrologic Testing


     Improving the precision of plume boundary calculations  generally  requires
hydrologic tests of aquifer properties.  However, use of aquifer testing

results is  secondary to designing plume migration control  measures  such as

pumping systems.  The most important aquifer properties  to determine for  plume

control  technology design are:


     o  Hydraulic conductivity (K)  -- a coefficient  of proportionality  that
        describes the rate at  which  water,  of a  prevailing density  and
        viscosity, can move through  a porous medium
                                     3-49

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                                                                       TABLE 3-10
                                       SIGNIFICANCE  OF SELECTED ON-SITE  OBSERVATIONS TO  PLUME  DELINEATION
                Site  Feature
          Observation
Significance to Plume Delineation
                Facility
                 Information
OJ

o
                Evidence of
                 Contamination
                Groundwater Flow
Locations  of  waste transfer, treatment,
storage,  or disposal activities

Facility  design, construction, and
operation

Locations  of  water supply or monitoring
wel 1 s

Settling  cracks  in foundations or
basement  seepage
                                        Waste types, volumes, forms, and modes
                                        of disposal
Spills

Dead, sparse, or  stunted vegetation, and
barren  areas

Discolored, disturbed, or odorous soil
Leachate  seep

Springs
Possible sources of contamination
                                                                                         Indicative  of  facility's ability to
                                                                                         control  releases

                                                                                         Possible future sampling points
Possible high water table;  possible
preferential  routes of leachate
migration (backfill for foundations)

Indicative of the possibility,
mobility, size, and hazardousness  of
the leachate  plume

Possible source of contamination

Possible effects of near-surface
contaminated  groundwater

Possible source or result of
contaminant  release

Presence of contaminated qroundwater

Intersection  of water  table with  la:id
surface; flow rate related  to water
table gradient and hydraulic conductivity
                                                                                                                     (Continued)

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                                                                    TABLE  3-10  (Continued)
             Site Feature
          Observation
Significance to Plume Delineation
             Groundwater Flow
             (continued)
oo
I
CJ1
             Surface Water
              Flow
Depth to water  in  wells
                                      Land surface topography
                                      Variations in stream discharge through
                                      site
                                      Locations, discharges, and schedules
                                      of  pumping wells
Surface water  elevations
                                      Locations
                                      Chemical quality and evidence of
                                      contamination

                                      Drainage patterns
Elevation and gradients of the water
table

Possible directions of flow in
unconfined aquifer

Possible indication of whether streams
recharge groundwater (termed losing or
influent streams) or whether ground-
water recharges streams (termed
gaining or effluent steams)

Possible effects of groundwater with-
drawal on plume movement; possible
future sampling points

Can indicate directions of ground-
water and plume flow

Possible locations of seeps; possible
sampling points; relation of site to
discharge and recharge areas in
drainage basin

Possible indication of subsurface
leachate discharge

Possibly indicative of bedrock structure
and controls on groundwater and contaminant
flow  (Howard, 1967)

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                                                                     TABLE  3-10   (Continued)
             Site Feature
          Observation
Significance to Plume Delineation
             Surface Water
              Flow
             (continued)

             Geomorphology
OJ
i
en
ro
             Vegetation
Drainage density
Slopes
                                      Sinkholes/karst topography
                                      Floodplains, meander scars, and
                                      other  stream features
                                      Dunes


                                      Wetlands


                                      Tidal  flats



                                      Glacial deposits
Type of plants (e.g.,  phreatophytes
such as willow, ash, and cottonwood)
Possibly indicative of infiltration
capacity of soil  and leachate generation
potential

Possibly indicative of infiltration capacity
and leachate generation potential; possibly
indicative of recharge and discharge areas

Usually indicative of solution channel
control of groundwater and contaminant flow

Possibly indicative of buried stream
channels and other preferential  routes
of leachate migration

Indicative of unconsolidated sand deposits
of high permeability

Near-surface water table; many seeps
1ikely

Near-surface water table; possible
changes in groundwater flow directions
because of the influences of tides

Possibly indicative of highly
stratified materials of varying permeability;
clay deposits may be fractured

Possibly indicative of general
availability of water, depth to water,
moisture retention, and other hydrologic
properties

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                                                             TABLE 3-10 (continued)
            Site  Feature
          Observation
Significance to Plume Delineation
            Vegetation
            (continued)
            Surface material
OJ
i
en
CO
Distribution  of  plant  types
                                    Stressed, dead,  or absent  vegetation
Texture (grain  size mix),  sorting,
angularity,  organic content  and  other
properties
                                    Munsell  color
                                    Soil structure
                                    Classification and distribution
                                    Bedrock outcrops (i.e.,  attitude  of
                                    bedding, joints, faults  and  other
                                    discontinuities; rock  types)
Possibly indicative of soil  or bedrock
types and structures, and site
hydrogeology

Possibly indicative of near-surface
contamination

Indicative of the hydraulic  conductivity and
porosity of the material , and
possibly the rate of groundwater
and leachate movement

Possibly indicative of moisture
conditions and leachate generation
potential

Indicative of infiltration capacity
and leachate generation potential

Possibly indicative of bedrock
conditions and groundwater movement routes

Possibly indicative of rates of ground-
water and contaminant movement

-------
     •  Transmissivity (T) -- the rate at  which water is  transmitted  through a
        unit saturated thickness (m)  of an aquifer or confining bed  under a
        unit hydraulic gradient
     «  Storativity (S) -- the volume of water an  aquifer releases from or
        takes into  storage per unit surface area of the aquifer per  unit
        change in head.

Storativity must be determined in the field.   Hydraulic conductivity  can
either be determined in the laboratory or  be  derived in the  field.   Estimates
of T can be made in the field or using the relationship:

                                    T = Km
where m is the saturated thickness of the aquifer.   The following  sections
describe some of the different types of aquifer tests  for  determining K,  T,
and S.

          3.3.1.1  Laboratory Tests

     Many methods are available to determine hydraulic conductivity  in the
laboratory.  In all  cases a sample of the earth material must  be  collected  in
the field and returned to the laboratory for testing.   The typical method for
collecting samples of unconsolidated material  is with  a tube sampler (e.g.,
Shelby tubes, split  spoons) and for collecting rock samples is  core  drilling.
Numerous references  are available from the American Society for Testing and
Materials which describe the techniques and tools available for obtaining
samples so that disturbance to the sample is minimized. Samples  collected  in
this manner are commonly labeled "undisturbed samples."  In reality,
"undisturbed samples" is a misnomer because certain sample properties (e.g.,
porosity, sorting) will change to some extent, regardless  of the  care taken  in
sample extraction.  Furthermore, gross aquifer characteristics  (e.g.,
fractures, bedding planes, cavities) are seldom represented intact  and in the
proper proportion to the rest of the sample.  As a  result, laboratory and
field studies of the same geologic unit can, under  certain conditions, produce
significantly different estimates for aquifer properties.
                                     3-54

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     Two basic methods are available for determining hydraulic conductivities
in the laboratory—the constant head method and the falling head method.  For
the constant head method, inflow fluid level is maintained at a constant head
and outflow rate is measured as a function of time.  Hydraulic conductivity is
then calculated using:

                                 K = QLs/hsAs

where:

     K  = hydraulic conductivity (ft/day)
     Q  = outflow rate (ft3/day)
     L  = length of sample (ft)
     h  = fluid head difference across sample (ft)
                                            2
     A  = cross-sectional area of sample (ft )

     For the falling head method, the head of the inflowing fluid is allowed
to decrease over time, while the fluid head at the outflow is held constant.
Assuming a large standpipe, hydraulic conductivity for this method can be
calculated using:

                         K = (2.3ApLs/Ast) log (h./he)

where:

     K  = hydraulic conductivity (ft/day)
                                               o
     A  = cross-sectional area of standpipe (ft )
     L  = length of sample (ft)
                                            2
     A  = cross-sectional area of sample (ft )
     t  = time for head level  decline (day)
     h. = initial head level  (ft)
     hg = final head level (ft)

     Several  other methods are available for determining hydraulic conduc-
tivities but  all  are generally based in part on these two simple methods.
                                     3-55

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Table 3-11 summarizes the more common methods utilized to obtain hydraulic
conductivities and their applications.  In practice, the test performed on a
sample sent to a laboratory will probably be dependent upon the instrumen-
tation available, not on the applicability of the test to the soil type.
Roberts and Nichols (1981) provide additional information on methods for
determining hydraulic conductivity.

     Uhen a laboratory hydraulic conductivity test is performed, there are
numerous potential sources for error in the estimates.  Table 3-12 lists some
of these potential sources and the effect they have on the calculated
hydraulic conductivity.  If a laboratory measured hydraulic conductivity does
not appear to be consistent with field observations, a second test should be
performed keeping in mind the areas where potential error sources can be
introduced.  Laboratory measurements of hydraulic conductivity can be many
orders of magnitude lower than field tests of a sample for a variety of
reasons.  However, most comparisons are within an order of magnitude (Olson
and Daniel , 1979).

          3.3.1.2  Field Tests

     The determination of hydraulic conductivity by a well  test is highly
dependent on the design, construction, and development of the well to be
tested.  Tests performed on improperly constructed wells will  reflect
conditions  caused by well construction rather than those of the earth
material.  In some cases, the well  to be tested will  already be in place.   For
these instances, a well  log and  as-built drawing should be obtained for the
well  so that elements  that may affect the test can be identified.   Newly
drilled wells should be designed, installed,  and developed properly to ensure
accurate test results  (refer to  Chapter 5).

     Methods available for determining an aquifer's properties based on an
in-situ field test can be divided into single well tests and multiple well
tests (i.e., a test well with observation wells).  All of these tests either
require the removal of water from the well or the injection of water into the
well.
                                     3-56

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                                                            TABLE 3-11
                                    LABORATORY METHODS FOR DETERMINING HYDRAULIC CONDUCTIVITIES
oo

CJ1
Method
Constant head
Falling head
Modified constant
head
Triaxial cell

Pressure-chamber

•
•
•
•
•
•
•
•

•
•
Application Mathematics
Best for samples with high conductivities (i.e., K = QL /h A
coarse grained) s s
Can be used with fine grained samples but test
times may be prohibitively long
Any soil type K = (2.3 A L /A t) log (h^h )
Best suited to materials having a low permeability p
Any soil type K = QL /h A
Best suited for fine-grained soils
Any soil type K = QL /h A
Especially suited for fine-grained, compacted cohesive
soils in which full fluid saturation is difficult to
achieve
Any soil type K = (2.3 A L/At) log (h./h )
Remolded samples p s s i e

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                                  TABLE 3-12
               EFFECTS OF VARIOUS TYPES OF ERRORS ON LABORATORY
            MEASURED VALUES OF HYDRAULIC CONDUCTIVITY (EPA, 1982d)
       Source of Error                                 Measured K


Voids formed in sample preparation                        High

Smear zone formed during trimming                         Low

Use of distilled water as a permeant                      Low

Air in sample                                             Low

Growth of microorganisms                                  Low

Use of excessive hydraulic gradient                    Low or High

Use of temperatures other than the                       Varies
test temperature

Ignoring volume change caused by stress                   High
change (confining pressure not used)

Performing laboratory rather than                      Usually low
in situ tests

Impedance caused by the test                              Low
apparatus, including the resistance
of the screen or porous stone used
to support the sample


     Single well tests can be utilized to measure hydraulic conductivities
when only one well  is present at a site or when other wells are located too
far away to make them usable for observation purposes.  Most of these methods,
termed slug tests, require the instantaneous removal or addition of water to
the well.  These instantaneous changes in head levels can be caused by pumping

or bailing water out of the well; by adding water into the casing very
rapidly; or by lowering a plug with known water displacement volume into the
well, waiting for the water level to stabilize, and then removing the plug
quickly.  In all slug test methods, the recovery of head level to original

levels is measured over time.  A single well pump test, on the other hand,
                                     3-58

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does not require the instantaneous change in head within the well which
permits a slower extraction of water.  Pumping, drawdown, and recovery rates
must be measured during the pump test.

     Table 3-13 presents some of the commonly accepted single well tests for
determining hydraulic conductivity.  This table also presents the appli-
cability of the test to various aquifer conditions (i.e., confined vs.
unconfined aquifers, expected hydraulic conductivity) and possible sources of
error when the test is performed.  Detailed descriptions of the methods used
in performing the tests or calculating the results are available in the
references cited.

     Multiple well  tests require either the constant withdrawal or injection
of water into a test well  and the measurement of head level changes in nearby
observation wells.   Multiple well tests measure aquifer properties over a
larger test section than either laboratory tests or single well tests, and are
considered to be far more accurate in characterizing aquifer properties.
These tests can also be used to determine the presence of hydraulic barriers
and boundaries with the proper placement of observation wells.

     Performing these tests can be expensive because special well drilling may
have to be performed (i.e., test well with observation wells), and data
acquisition and interpretation is more intensive.  Furthermore, large volumes
of contaminated groundwater may be pumped during the test requiring appropri-
ate procedures for  treatment and disposal.  However, the data generated from
such tests can save time and money because of the better understanding one can
gain of possible plume paths.  This understanding can maximize resource use in
terms of proper planning of monitoring and remedial actions.

     Table 3-14 summarizes applicability, procedures, and calculation method
for major classes of multiple well  tests.  The Jacob method is generally much
easier to use and obtain results from than the Theis method but requires
meeting certain additional  test conditions.   USGS (1977) provides a listing of
test methods  that have been developed for specific site conditions and subject
emphases, and can be used  as a reference guide to aid in selecting an appro-
                                     3-59

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                                                                       TABLE  3-13
                                                                  SINGLE  WELL  TESTS
Test Method
                                 Applicability
                                                                     Procedure
                                                                                               Calculation
                                                                                                                                     Error Sources
Conventional Slug
Test:  Confined
Aquifer (Lohman, 1972)
Pressurized Slug Test
(Bredehoeft and
Papadopulos, 1980)
Conventional Slug
Test:  Unconfined
Aquifer (Bower and
Rice, 1976)
Piezometer Test
(Hvorslev, 1951)
Pumping Test
•  Moderately permeable formations
•  Confined aquifers
*  Entire aquifer open to well
•  Aquifer uniform in all directions
t  Low to extremely low hydraulic
   conductivities (silts, clays,
   shales)
•  Confined aquifers
•  Moderately permeable formations
•  Unconfined aquifers
•  Fully or partially penetrating
   well
t  Measured value principally  in
   horizontal direction
•  Any formation
•  Unconfined aquifers
•  Fully or partially penetrating
   wells
•  Any formation
•  Confined and unconfined  aquifers
•  Slug removal  of
   water
•  Measure recovery
   rate to 85% initial
   head
   Sudden pressuriza-
   tion of packed-
   off area within
   well with water
   Pressure decay
   rate monitored
   Sudden change in
   head level  by
   removal  of
   submersed weight
   Measurement of
   water level
   recovery rates

   Sudden change in
   head levels caused
   by removal  or
   injection of water
   Measurement of
   recovery rate
   over time

   Removal  of  water
   over time by
   pumping
   Measurement of
   drawdown, pumping,
   and recovery
   rates
•  Plot of h/h  vs t on
   semi log papeV
t  Superimpose on type
   curve
t  Calculation of trans-
   missivity and storativity
•  Plot of pressure decay
   vs time
•  Superimpose plots on type
   curve
•  Calculation of transmissivity
i  Analytical equation based on
   measured parameters
•  Calculation of hydraulic
   conductivity and effective
   radius of well
•  Plot of head level change
   vs time
•  Analytical equation based on
   collected data
•  Calculation of hydraulic
   conductivity
*  Semi log plot of draw-
   down vs time
•  Analytical equation based
   on data collected
•  Calculations of transmissivity
   and storage
•  Entire thickness of
   aquifer not open to
   well
•  Flow to well not radial
t  Measurement errors in
   recovery rates and times
•  Improper type curve
   matching

•  Hydraulic properties
   throughout aquifer
   are same as packed-
   off section
I  Measurement errors in
   recovery rates and
   times

•  Measurement errors in
   recovery rates and
   times
•  Significant flow of
   water from above the
   test zone
•  Measurement errors
   recovery rates and
   times
   Measurement errors
   in drawdown rates,
   recovery rates, and
   times
   Recovery storage not
   equal to discharge
   storage

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                                                                                  TABLE  3-14
                                                                        MULTIPLE-WELL PUMP  TESTS
                 Test Method
                                                 Applicability
                                              Procedure
                                                                                          Calculation Method
                 Theis Method
                 (Theis, 1935)
oo
 i
                 Jacob Method
                 (Jacob, 1950)
Any formation  type;  although  low
hydraulic conductivity  formations are
difficult to pump  at constant rates
Confined and unconfined aquifers
Hell  fully penetrates aquifer
Requires the use of  one or more
observation wells

Any formation  (same  as  Theis)
Confined and unconfined aquifer
Fully penetrating  well
Requires the use of  one or more
observation wells
•  Pump well  at constant
   rate
•  Measure drawdown verses
   time in observation wells
•  Measure discharge rate
•  Pump well  at constant rate
•  Measure drawdown versus
   time in observation wells
   or recovery rates
   versus time in observa-
   tion wells
•  Measure discharge rate
•  Log-log plot of drawdown versus
   distance to observation  well
   divided by time
•  Match plot with type curve
   Semi log plots of:
   -  Drawdown versus time
   -  Drawdown versus observation well
      distances from  test wells
   -  Recovery versus time
   Calculate transmissivity and
   storatlvity with appropriate
   equations

-------
priate test when site conditions are  known.   Other discussions  of  the  design
and interpretation of multiple well  pump tests  are provided in  Powers  (1981),
Lohman (1972), and Stallman (1971).

     3.3.2  Sampling

     Direct sampling of groundwater  (and possibly other media)  will  always  be
required during studies concerning delineation  and management of leachate
plumes.  Sampling provides data on constituent  type and concentration  in
groundwater.  Also, sampling is required to  verify or identify  inaccurate
calculations or assumptions made concerning  plume extent,  to identify
unexpected problems or factors affecting plume  dynamics,  and to develop and
monitor remedial actions.  Procedures  involved  in completing a  sampling
program include:
     •  Planning -- Identification  of data needs  and  development  of proper
        system design and necessary activities  to collect  the  required data
     •  Implementation -- Completion  of activities  necessary to collect the
        required data, including well  installation  and development, purging,
        sample collection and handling, and laboratory analysis
     •  Data Evaluation -- Reduction  of raw data  to assess its reliability and
        integration into the overall  program to satisfy sampling program
        objectives.  Typically,  this  may include  the  calculation  of concen-
        tration gradients and the development of  isoconcentration  maps.

     The following sections discuss each phase  involved in a sampling program,
along with factors affecting sample validity.  Procedures  related  to ground-
water monitoring are discussed where  appropriate.  Publications providing more
details concerning sampling programs  include Sisk (1981),  Scalf,  et al.
(1981), USGS (1977), and EPA (1982c).
                                     3-62

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          3.3.2.1  Sampling Program Plan

     A sampling program plan should include descriptions of:

     0  Objectives -- describing the questions to be answered by the sampling
        program and the data needed to address the questions
     o  Program Design -- including sample analysis parameters, frequency,
        QA/QC, and integration of data with other media sampling programs
     •  System Design -- detailing sample site locations, numbers, depths, and
        well configuration
     o  Component Design -- describing well construction materials, screen
        type and setting, and security measures
     •  Implementation Procedures -- specifying well installation and
        development procedures and other field activities relating to sample
        collection and analysis activities
     •  Data Evaluation Procedures -- including how data will be integrated
        with other data to attain sample program objectives.

     Clearly defined program objectives should be developed prior to other
planning activities.  Identification of program objectives is important so
that the reason for monitoring is clearly understood.  The program can be
planned to meet objectives with a minimum amount of time and resources, when
all activities are focused.  Monitoring program objectives should reflect site
conditions and available data, and should be modified as needed as new data is
compiled.   If objectives are modified during a study, the monitoring program
should be reevaluated to keep activities focused on meeting the new
objectives.  A monitoring program designed to meet one set of objectives may
be totally inadequate to accomplish subsequent revisions.

     All  data necessary to attain objectives should be identified once the
objectives are clearly defined.   For example, if sampling objectives include
determination of the extent of contamination plus migration potential, then
data needs would include constituent types and concentrations over time, as
well as vertical  and horizontal  groundwater gradients,  vertical  and horizontal
                                     3-63

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concentration gradients,  and aquifer characteristics.   Data  needs  should be
evaluated as to completeness and used to develop a  data acquisition  strategy.

     The acquisition strategy includes general  procedures or components  that
must be accomplished to collect the necessary data.  For example if  surface
water and groundwater relationships appear to be important,  a sampling program
addressing only groundwater is  inadequate.  The applicability of the data
acquisition strategy to the situation can be addressed by listing  data
resulting from each step  or component of the system and comparing  this to  the
required data list developed previously.  The acquisition strategy,  in
addition to data requirements and program objectives,  will set  standards for
program, system, and component  (well) design.

     Program design refers to how the monitoring system will be implemented to
meet the stated objectives.  Items to be specified  include:

     •  Media to be sampled (e.g., groundwater, surface water)
     •  Sample types and  frequency (e.g., groundwater  grab samples at three
        month intervals)
     •  Parameters to be  measured (e.g., priority pollutants)
     •  Integration with  other media sampling programs
     o  Activities scheduled (e.g., well installation, development,  purging,
        sample collection and handling, laboratory  analyses, and data
        evaluation)
     t  QA/QC plans to ensure sample representativeness and  validity.

     One of the more critical elements of program design is  Quality Assurance/
Quality Control (QA/QC).   QA/QC procedures are essential to  produce data that
meet user requirements in terms of completeness, accuracy, representativeness,
and comparability.  QA/QC enters into each study phase and specific procedures
should be specified in the program plan.  For example, QA/QC plans for ground-
                                     3-64

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water sampling and analysis would incorporate the use of prepared samples such

as:


     e  Field Blanks -- All procedures normally followed during sampling are
        performed but deionized or distilled water is added to the sample
        bottles instead of groundwater or surface water.  This procedure
        checks for contamination resulting from sampling apparatus that come
        into contact with the sample.

     •  Spiked Samples — Known amounts  of a particular constituent  are added
        to blank samples to determine  the accuracy of laboratory procedures.
        Spiked samples can be prepared in the field or at  the laboratory.

     •  QA Samples — Duplicate or triplicate samples (taking samples  from the
        same source and placing portions into two or more  containers)  are
        collected using normal  sampling  procedures.  Samples  are identified
        independently and sent  to the  same or different laboratories to check
        for procedure precision.

     t  Trip Blanks -- Blank or spiked samples are prepared in the laboratory
        and sealed.  These accompany the sample containers from the  labora-
        tory, through field sampling and back to the laboratory.   These
        provide a check for interferences and contamination from external
        sources not related to  sampling.


     These QA/QC checks provide indications of sample method  accuracy  and

precision, as well as possible  cross-contamination resulting  from sample

collection, handling, or analysis.


     QA/QC plans should be a part of any sampling program  plan.   Several  items

of concern for groundwater sampling program components include:
     •  Sampling Program Design -- Does  the  design  result  in  all  necessary
        data?  Are schedules planned to  take advantage  of  common  activities?

     t  Well  Installation  -- Will  the installation  procedures  avoid  cross
        contamination between aquifers in  multiaquifer  systems and  between
        wells?

     •  Sample Collection  -- Will  the planned procedure  prevent cross
        contamination between samples and  from sampling  equipment?   Are  there
        adequate procedures  for purging  and  handling  purge  water, calibrating
        field measurement  equipment, and decontaminating equipment?
                                     3-65

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     o  Sample Handling -- Will  there be proper procedures for  cleaning and
        preparing bottles, and for sample preservation  and shipment?
     •  Analysis -- Is there a complete and adequate laboratory QA/QC  plan?

All these factors should be considered when developing  or  evaluating  a QA/QC
plan.
     System design refers to the relationships  between  the  individual
components of the program.  For example,  in  groundwater monitoring  studies
system design would specify:

     •  Number of wells
     •  Well  locations
     •  Screen settings (depth)
     •  Well  configurations.

     Well  configuration refers  to the  relation  of  a  well  to adjacent wells  and
to individual aquifers.  Figure 3-2  illustrates five types  of well
configurations that have been used for groundwater monitoring.  Table  3-15
lists some of the advantages and disadvantages  of  each  configuration.

     Component design refers to the  proposed construction of individual  wells
in the monitoring systems.  Typical  well  design specifications  are  listed  in
Table 3-16.  Although monitoring well  design differs significantly  from  the
design of  wells for plume extraction,  the procedures used for well  installa-
tion and development are similar. These  procedures  are described in Chapter
5.

     After the program and individual  components are designed,  three
activities can be developed to  carry out  the program.  These implementation
procedures should be detailed and in a "cookbook"  fashion such  that sample
                                     3-66

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                                                                                    FIGURE 32.
                                                     WELL CONFIGURATIONS USED FOR GROUNDWATER MONITORING
                                                                            (AFTER MASLANSKY, 1982)
                                      Single
                                      Zone
                                      Wei!
  Fully
Screened
  Well
 Multiple
Sampling
  Point
  Well
00
I
en
  Single
 Borehole
Well Nest
 Multiple
 Borehole
Well Nest

-------
                                                                           TABLE 3-15
                                     ADVANTAGES AND  DISADVANTAGES OF VARIOUS TYPES  OF MONITORING WELL  CONFIGURATIONS
                     Well Configuration
             Advantages
          Disadvantages
                     Single Zone
                     Well
                     Fully Screened
                     Well
CTl
oo
                     Multiple
                     Sampl ing Point
                     Well
•  Relatively  simple  to  install
•  Can be installed  by a variety  of methods
•  Can provide discrete  samples from  a  precise
   interval  thus  aiding  data  interpretation
•  Easy to prevent  interaquifer contamination
   if designed and  installed  properly
•  Relatively  simple  to  install
•  Can be installed  by  a variety  of methods
•  Can provide composite samples  of large
   intervals thus  reducing  the  number  of samples
•  Produces  relatively  higher yields and thus
   are more  amenable  to  pump testing
   Can provide  information  on  the  vertical
   distribution of contaminants  and  hydraulic
   gradients
   Installation is rapid  and  simple,  although
   construction takes  longer  then  for wells
   with a single screen
   Can be used  to obtain  composite
   samples
   Fewer wells  are needed in  a monitoring  system
   thus reducing costs
Vertical  distribution of contaminants
or hydraulic gradients cannot be
determined
Many wells are needed to delineate
plume increasing costs and
the time required to install  and
sample the system

Highly contaminated waters may be
diluted by less contaminated  waters
during sampling biasing results
Vertical  distributions of contaminants
and hydaulic gradients cannot be
determined
Vertical  migration of contaminants may
occur over screened interval
spreading contaminants to clean zones
Impossible to prevent interaquifer mixing
if screened over more than one aquifer

Preventing interaquifer contamination
is difficult if not impossible
Sampling  is complicated, time
consuming, and requires specialized
equipment
Cost per well is fairly high

-------
                                                                    TABLE  3-15 (continued)
                     Well  Configuration
          Advantages
             Disadvantages
                     Single-
                     Borehole
                     Well  Nest
CTl
                     Multiple-
                     Borehole
                     Well  Nest
Provides information  on  the vertical
distribution of contaminants and hydraulic
gradients
Preventing interaquifer  contamination  is
generally not difficult
Sampling is not difficult but may require
specialized equipment depending on well
diameters
Provides information on  the vertical
distribution of contaminants and hydraulic
gradients
Installation simple by a variety of methods
Preventing aquifer cross contamination  is
not difficult
Sampling is simple and usually does not
require specialized equipment
0  Number of suitable installation
   methods is restricted
•  Improper construction can reduce
   effectiveness and cause vertical
   movement of contaminants
t  Installation is fairly time consuming
   but not difficult
•  Cost per nest is fairly high
   although cost per well is low

•  Installation is fairly time consuming
   but not difficult
•  Cost per nest is very high

-------
                                                                        TABLE 3-16
                                                       DESIGN SPECIFICATIONS FOR MONITORING WELLS
                               Design  Item
                                Example Specification
                                                      Significance
i
-~j
o
Borehole diameter


Borehole depth


Well  diameter


Casing length


Screen length


Screen setting

Screen openings



Casing type


Screen type


Sump


Joints
6-inch outside diameter


25 feet below land surface (BLS)


4-inch


25 feet


10-foot (two 5-foot sections,  threaded)


25 to 20 feet BLS

10 slot/inch; micromesh



PVC or high carbon steel
                                                  PVC  or  stainless steel  (match with
                                                  casing  type)

                                                  2-foot
                                                  Threaded  couplings, welded or glued
                                                  (depending on casing type)
Must be large enough to accommodate well
and sufficiently thick sand pack

Must accommodate well and sump (if
specified)

Based on required yields and sampling
equipment to be used

Equal to the total borehole depth plus
stickup minus the screen length

Based on required yields and aquifer to
be sampled

Based on aquifer to be sampled

Based on aquifer particle sizes,
gradations of sand pack designs, and
aquifer to be sampled

Based on type of contamination expected
and costs

Based on type of contamination expected
and costs

Used as a collection basin for fine
particles passing through screen

Based on materials and installation
procedures to be used
                                                                                                                           (Continued)

-------
                                                                  TABLE 3-16  (continued)
                       Design Item
       Example Specification
          Significance
OJ

—i
                    Sand pack depth
                    Sand pack type
                    Bentonite setting
                    and thickness

                    Bentonite type
                    Grout thickness

                    Grout type


                    Well  finish


                    Protective casing


                    Security


                    Identification
At least 3 feet over top of screen
Silica sand; Q-rok fl
3 feet over sand pack
Sodium bentonite pellets
5-foot minimum

Portland cement and bentonite mix at
a ratio of 20:1

3-foot stickup
12-inch oversize casing
sunk 3 feet BLS

Locking cap and traffic guards
Numbering system with color coding
Must allow for settlement and an adequate
thickness for the seal

Based on particle sizes and gradations of
aquifer to be sampled

Used to separate sand pack from grout
Less likely to mix with sand pack than
fluid grouts

Based on total well depth

Based on groundwater quantity and quality
Based on traffic loads and needs for easy
location

Used to protect well head from most types
of damage

Used to protect well from accidental
damage or intentional tampering

Used to identify specific well locations
especially in well nests

-------
team members can use the plan to complete their activities.   The sampling plan
should also include a data evaluation section specifying:


     «  Data resulting from program activities

     •  Evaluation procedures (including references) for reducing the raw data
        into a usable form

     0  Integration of the usable data to achieve the specified objectives.


          3.3.2.2  Sample Program Implementation


     Implementation of groundwater sampling programs generally involves  four

major elements—well  installation and development, sample collection and

direct measurement, sample handling, and sample analysis. Well  installation

typically consists of the following steps:


     •  Opening a borehole to the desired depth

     •  Installing a well constructed in accordance with the component design

     •  Filling the annulus ( i.e., the space between the well  and  the
        borehole wall) with a sand pack

     •  Sealing the sand pack from surface  water infiltration  by installing  a
        bentonite seal

     •  Grouting the well in place

     •  Installing security measures to prevent tampering.


Drilling procedures and well finishing are  discussed in Chapter 5.


     One very important concern in drilling at hazardous waste sites is  to
prevent contaminant migration into an uncontaminated aquifer or zone within  an

aquifer.  This is especially important in areas consisting of  multiaquifer

systems.  A drilling program to install wells into an aquifer  separated  from

contaminated groundwater must incorporate methods to seal off  the contaminated
                                     3-72

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 zone from the uncontaminated  zones.   One  method  for  accomplishing this
 objective consists  of:

      •  Boring through  the  contaminated aquifer  and  into,  but  not through, the
         separating  less permeable  layer
      0  Installing  an outer casing to seal  off the contaminated aquifer
      0  Drilling  through  the  casing  plug  and  separating  layer  into the lower
         aquifer
      •  Installing  the  monitoring  well as described  previously.

 A  double  based  well  installed using  this  procedure is illustrated in Figure
 3-3.   The use  of  the outer  casing  and  seal  prevents  contaminants from
 migrating between aquifers.  Drilling  equipment  should be throughly
 decontaminated  before drilling into  the lower uncontaminated zone.

     Wells  should be designed and  constructed to avoid possible interference
 with sample analysis.   In general, well materials made of steel are more
 durable,  subject to  less chemical  degradation than plastics (e.g.,  PVC),  and
 cost more.  If  PVC or other plastic  material is to be used, couplings should
 be threaded and sealed with Teflon tape and not glued.  PVC glues contain
 organic solvents and other  constituents which could affect sample results.
 There  is  some concern at present as  to the effect of PVC well  material  on
 groundwater samples in areas of high concentrations of organic contaminants.
 Studies are currently underway to determine the leaching of contaminants  from
 PVC in these situations.  If metals  are of concern, high carbon steel  or
 stainless steel wells may adversely  affect sampling results for chromium,
 nickel , iron, and zinc.

     Screens should be installed  that are  compatible  with the  chemical
 contaminants anticipated and the  aquifer  grain size distribution.   If
 information is not available concerning aquifer grain size,  10 slot screens
 (i.e., screens having slot widths of  0.01  inch) and appropriate sand-pack
materials can  usually be used  with  good results  (Sisk,  1981).
                                     3-73

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                            FIGURE 3-3.
WELL DESIGN FOR PREVENTING INTERAQUIFER CONTAMINATION
                      (WICKLIIME, et al., 1983)

Land
iirfare

10"



	
	









W
-


P




\\
\S.
\\

-Jx

mmmm










p




\^
I
\\
IOv
Sf
bi
8" Ste

4" Steel
Casinq

Cement a
C

f. 	
. 	 .
	
	 	
                                                      Grout
                                                 Bentonite Seal
                                                    Grade
                                                 Well Gravel
       6" or 8"
       Borehole
                                                 4" x 10' Stainless
                                                 Screen, 10 Slot

                                                4" x 2' Plugged
                                                    Sump
                               3-74

-------
     Sample collection includes the following activities:

     0  Purging -- which involves removing a predetermined volume  of  water
        from a well prior to sampling to ensure that "stagnant"  water is
        removed
     •  Field Measurements -- which involves obtaining values  for  certain
        physical parameters at the sample site using direct reading equipment
     •  Sample Withdrawal -- which involves methods to remove  a  specific
        volume of water from a well and introducing this water into specified
        sample containers.

     Groundwater sampling should only be performed after wells have been
purged and the groundwater system has returned to equilibrium.  The amount  of
water to be purged is typically specified in terms of multiples  of the casing
volume (i.e., the volume of standing water in a well).  The number of casing
volumes to purge is a topic of discussion.  EPA recommends three to five
casing volumes, while the U.S. Army (USATHAMA) recommends  five casing volumes
(where "casing" includes the sand pack).  The merits of purging  between 10  and
20 casing volumes, and in some cases, up to 100 casing volumes have also been
presented (Schmidt, 1982).  The USGS recommends pumping until  certain water
quality parameters (e.g., pH, temperature and specific conductance) stabilize.
However, the focus of most USGS studies is basin wide as opposed to site
specific.  Pumping large quantities (i.e., more than 10 to 20  casing  volumes)
of contaminated groundwater can distort plume boundaries and movement
patterns, dilute the actual sample with groundwater from some  distance away
from the well, and cause significant purge water disposal  problems.   Reports
have noted that organic chemical concentrations changed continuously  over
several hours of pumping despite stabilization of the USGS indicator  param-
eters within only a few minutes of pumping (Keely and Wolf, 1983). Therefore,
unless there is a specific reason for pumping large volumes of water  (e.g.,
time series sampling; Keely, 1982) this practice should be avoided.   The EPA
recommendation of three to five casing volumes is probably acceptable for most
situations.

     There is a special case where purging less than three casing  volumes is
considered adequate.  Low-yield monitoring wells, usually  of shallow  depths,
                                     3-75

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can be pumped dry with the proper equipment.  In cases where recovery is
adequate, the well is usually pumped three times,  allowing partial  recovery
between pumping.  Where recharge is slow, the well  is emptied twice.

     The selection of equipment for purging depends  on the well  to  be sampled.
Limitations include well  diameter (e.g.,  a 4-inch  submersible pump  will  not
fit into a 3-inch well),  depth (e.g.,  centrifugal  pumps cannot  be used if  the
water table is more than  25 feet deep),  and the volume of  water to  be purged
(e.g., a 1 gpm pump is not appropriate if 200 gallons must be purged).

     Equipment decontamination is an important step  in preventing cross
contamination (i.e., transfer of contaminants from one well  to  another)  and as
a health and safety consideration.  Pump  decontamination is usually easier to
accomplish as components  are pulled from a well.   Distilled water  (or other
approved water) and nonresidue detergent  should be used for decontamination.

     Direct measurements  provide additional data points for subsequent
evaluation.  They can also indicate if there are changes in water type
sampled. These measurements are taken  both before  and after well purging,  and
before and after sampling.  Usually, a volume of water is  emptied into a
Nalgene (or other suitable material) bucket for measurement,  although flow-
through systems have recently been developed.  Precise values,  both before and
after sampling, usually indicate that  external  influences  have  not  affected
the sample.  Direct measurements are obtainable in the field  for a  variety of
parameters; however, the  four most often  measured  are:

     •  Specific Conductance -- a measure of the water's ability to carry  ar
        electrical current under specific conditions.  Ionized  salts  are
        measured, giving  an indication of the concentration of  dissolved
        solids in the sample and an indication  if  a  different source  of  water
        is being sampled.
     •  Temperature -- important in groundwater sampling because temperature
        may indicate that different water sources  are being sampled.   Digital
        electric probes or two calibrated thermometers can be used  to collect
        data.
     •  pH -- a measure of the effective  hydrogen-ion concentration which  can
        indicate the solution of certain  metals and  the presence of
                                     3-76

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         contaminants  or  other water  sources.   pH  can  be measured using pH
         paper  but  more precisely with  a  calibrated pH meter.

      •   Uater  Level Measurements --  used in subsequent analyses to derive the
         direction  of  groundwater flow  and calculate groundwater gradients.
         Water  level measurements are typically obtained using either a tape
         measure  with  some  water level  marking device  (i.e. wetted tape
         method), or an electrical probe  where an  electrical circuit is
         completed  by  contact with the  water and is registered on a meter.
         There  are  a variety of marking methods which can be used with tape
         measures including marking the tape with  chalk or a water soluble
         marker and noting  the depth  at which the  mark is washed off by water
         in the well.  By holding the tape at a reference point on the well
         (i.e., marked point on the well  casing that has been surveyed), the
         depth  to water is  easily determined.  Because of the possibility that
         samples may be affected by the tape marking, the electrical  probe
         method is  generally recommended. Water level measurements have limited
         usefulness unless  there is a surveyed reference point from which to
         measure.  Water levels should  be taken a  minimum of two times or until
         close  agreement with measurements is obtained.


      There are a variety of sample withdrawal methods currently available.
Some  of  these  methods are  listed in Table 3-17 along with their advantages and
disadvantages.   In most instances, using a Teflon bailer is preferable because
of ease  of use and decontamination, thus minimizing the potential  for cross
contamination.
     Sample preservation, packaging and storage is a very important step in
maintaining sample validity.  Preservatives serve to maintain the physical,

chemical, and biological or bacteriological integrity of samples  from
collection to analysis.  Preservative methods usually include pH  adjustment,
chemical addition, and refrigeration.  Table 3-18 lists recommendations for
sampling containers, preservatives, and holding times.


     In monitoring wells, siltation may cause minute quantities of  suspended
solids to be collected in samples.  Introduction of suspended solids  into
containers with acid preservatives may cause the dissolution  of metal  ions
from the solids because of the pH change.   This would increase the  concentra-
tion of dissolved metals and would indicate that groundwater  contains  higher

than actual  concentrations.   Therefore, EPA recommends filtration of  samples
for dissolved  solids.   Filtration in the field  is  performed using a vacuum
                                     3-77

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                                                                     TABLE 3-17
                                                  SELECTED  GROUNDWATER SAMPLE WITHDRAWAL METHODS
                      Method
         Advantages
            Disadvantages
GO
I
CO
                 Bailers (all  types)
                 Suction Lift  Pumps
                 Submersible Pumps
                 Gas  Lift
                 Positive  Displacement
                   Pumps
   Quick and easy to use
   Minimizes cross contamination
   Useful In almost all  situations
   Inexpensive

   Easy to use
   Fairly rapid to use
•  May be used at  any  depth
•  Fairly rapid to use
t  May be used at  any  depth
•  Can sample  from various  depths
•  May become time consuming for very deep wells
•  Sample exposed to air during withdrawal
•  Maximizes potential outgassing of samples
•  Can only be used to depths of 30 feet
•  Check valve must be used to prevent cross
   contamination
   Outside power source required
   Maximizes potential outgassing
   Difficult to prevent cross contamination
   May not work in cold weather or silted wells
   Limited to wells 2-inches in diameter or over

   Outside source of compressed gas required
   Complex equipment required
   Difficult to prevent cross contamination
   Maximizes potential outgassing of samples

   Difficult to prevent cross contamination
   Outside air or gas source required

-------
                         TABLE 3-18
CONTAINERS, PRESERVATION, AND HOLDING TIMES (U.S.  ARMY, 1982)
Measurement
Acidity
Alkalinity
Ammonia

Biochemical oxygen demand
Biochemical oxygen demand,
carbonaceous
Bromide
Chemical oxygen demand

Chloride
Chlorine, total residual
Color
Cyanide, total and
amenable to chlorination

Dissolved oxygen
Probe
Winkler
Fl uoride
Hardness
Hydrogen ion (pH)
Kjeldahl and organic
nitrogen
Metal sd
Chromium VI
Mercury

Metals except above
Container3
P
P
P

P
P

P
P

P
P
P
P



G bottle & top
G bottle & top
P
P
P
P


P
P

P
Preservative
Cool to 4°C
Cool to 4°C
Cool to 4°C
H2S04 to pH<2
Cool to 4°C
Cool to 4°C

None required
Cool to 4°C
H2S04 to pH<2
None required
Determine on site
Cool to 4°C
Cool to 4°C
NaOH to pH>12,f
0.008% Na2S203

Determine on site
Fix on site
None required
HN03 to pH<2
Determine on site
Cool to 4°C,
H2S04 to pH<2

Cool to 4°C
HNO., to pH<2,
0.05% K?Cr?07
HN00 to pH<2
o
Maximum
Holding Time0
14 days
14 days
28 days

48 hours
48 hours

28 days
28 days

28 days
2 hours
48 hours
14 days



1 hour
8 hours
28 days
6 months
2 hours
28 days


48 hours
28 days

6 months
                                                          (continued)
                              3-79

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                             TABLE  3-18 (continued)
Measurement
Nitrate
Nitrate and nitrite
Nitrite
Oil and grease
Container3
P
P
P
G
Preservative
Cool to 4°C
Cool to 4°C,
H-SO. to pH<2
COorto 4°C
Cool to 4°C,
Maximum
Holding Time
48 hours
28 days
48 hours
28 days
Organic carbon
Organic Compounds          G,  teflon
Extractables (including     lined cap
  phthalates, nitrosamines,
  organochlorine pesti-
  cides, PCBs, nitroaro-
  matics, isophorone,
  polynuclear aromatic
  hydrocarbons, haloethers,
  chlorinated hydrocarbons
  and TCDD)
Extractables (phenols)
Purgeables (halocar-
  bons, aromatics,
  acrolein, and
  acrylonitrile)

Orthophosphate

Pesticides
Phenols

Phosphorous, elemental
Phosphorous, total
                           G,  teflon
                            lined cap
                           G,  teflon
                           lined septum
                           G, teflon
                           lined cap
                                 G
                                P,G
H?SO. to pH<2
COorto 4°C,
H2S04 to pH<2

Cool  to 4°C

0.008% Na0S00-
                                                                    28 days
                                                                     7 days
                                                            r(until  extraction)
                                                                    30 days
                                                             (after  extraction)
Cool  to 4°C            7 days
              f(until  extraction)
0.008% Na?S?03        30 days
               (after extraction)
Cool  to 4°C,  f       14 days
0.008% Na0S000
Filter on site,       48 hours
Cool to 4°C
Cool to 4°C            7 days
              f(until extraction)
0.008% Na?S?0-        30 days
               (after extraction)
Cool to 4°C,          28 days
H?SO. to pH<2
Cool to 4°C           48 hours
Cool to 4°C,          28 hours
H9SO, to pH<2
                                                                    (continued)
                                     3-80

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                            TABLE 3-18 (continued)
Measurement
Container0
Preservative
   Maximum
Holding Time
Residue, total
Residue, filterable
Residue, nonfilterable
Residue, settleable
Residue, volatile
Silica
Specific conductance
Sulfate
Sulfide

Sulfite
Surfactants
Temperature
Turbidity
a - Polyethylene (P) or
b - Sample preservation
P
P
P
P
P
P
P
P
P

P
P
P
P
Glass (G).
should be perfc
Cool to 4°C
Cool to 4°C
Cool to 4°C
Cool to 4°C
Cool to 4°C
Cool to 4°C
Cool to 4°C
Cool to 4°C
Cool to 4°C,
Zinc Acetate
Cool to 4°C
Cool to 4°C
Determine on site
Cool to 4°C

)rmed immediately upon samp
14 days
14 days
7 days
7 days
7 days
28 days
28 days
28 days
28 days

48 hours
48 hours
Immediately
48 hours

le collection.
    For composite samples each aliquot should be preserved at the time of
    collection.  When use of an automatic sampler makes preservation of each
    aliquot impossible, samples may be preserved by maintaining at 4°C until
    compositing and sample splitting is completed.
c - Samples should be analyzed as soon as possible after collection.  The times
    listed are the maximum times that samples may be held.  Samples may be held
    for longer periods only if the laboratory has data on file to show that the
    specific types of samples under study are stable for the longer time.  Some
    samples may not be stable for the maximum time period given in the table.  A
    laboratory is obligated to hold the sample for a shorter time if knowledge
    exists to show this is necessary to maintain sample integrity.
d - Samples should be filtered immediately on site before adding preservative for
    dissolved metals.
e - Guidance applies to samples to be analyzed by GC, LC, or GC/MS for specific
    organic compounds.
f - This should only be used in the presence of residual  chlorine.

(Compounds not found on table should be preserved at 4°C; storage:  1 week).
                                     3-81

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pump, appropriate glassware, and filter paper.   Approved EPA filtration
holders and media are described by EPA (1982c).

     Confusion has arisen over filtered versus  unfiltered samples because os
the increased use of "Priority Pollutant  Scans"  in  hazardous waste investiga-
tions.  The confusion is a result of several  items,  the first being that the
priority pollutant values for metals specifies  total  metals  and  EPA procedures
do not call for field filtration.  Priority pollutant scans  therefore do not
require filtration which may result in elevated  metal concentrations  being
detected for groundwater.  To avoid this, filtration  can be  conducted for one
set of samples for dissolved metals analysis, while  another  unfiltered sample
is collected for total  metals.  Thus,  values  for total,  dissolved,  and
suspended metals are obtained.

     Organic chemical concentrations may  be affected  by filtering.   Phthalates
or other binders may be washed out of  filters,  thus  indicating the false
presence of these compounds in groundwater.  Nonfiltering may allow sorption
of organics to suspended particles and sediments.  One compromise is  to  decant
the clearest portion of a sample while discarding the cloudy portion  of  the
sample containing the highest concentration of  sediments and suspended solids.

     All samples must be shipped according to DOT standards.   Groundwater
samples are usually not considered hazardous  materials and may be shipped
counter to counter via  priority air freight to  the  identified laboratory.
Chain of custody (COC)  procedures should  be followed  during  transportation.
The purpose of chain of custody procedures is to document the identity of the
sample and sample handling from the point of collection until laboratory
analysis is complete and laboratory QA/QC procedures  confirm accuracy.
Documentation supports  this by providing  a written  record of procedures
followed and data collected during sampling.

     Sample analyses should follow approved EPA  procedures wherever possible.
EPA has recently published the second  edition of "Test Methods for Evaluation
of Solid Waste" (EPA, 1982c) which contains procedures that  may  be used  to
determine chemical composition of wastes  or the  presence of  hazardous wastes
                                     3-82

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in other matrices.  However, many of these methods have not yet been fully
tested.

     QA/QC procedures followed in the laboratory should be in accordance with
those outlined in EPA (1979), EPA (1980), and EPA (1982c).  Laboratories
participating in EPA's performance evaluation and quality assurance  review
program should have these procedures in place.

     Appropriate QA/QC data must accompany sample results so that  sample
validity can be determined.  The following QA/QC checks are typically provided
by laboratories:

     •  Surrogate Recovery Data -- Surrogates are chemical compounds similar
        in chemistry to the compound under analyses that are added to samples
        to monitor method efficiency.  Surrogate recovery results  outside of
        established limits may indicate poor quality data but may  also reflect
        interferences with similar chemical compounds (Gurka, et  al., 1982).
     •  Duplicate Analyses Results -- Duplicates are reanalyses of individual
        samples.  Close agreement between sample and duplicate results is a
        good indication of method precision.
     o  Field and Trip Blanks, and QA and Spiked Samples Results  --  These
        samples have been discussed previously.

     Laboratory QA/QC performance should be evaluated prior to laboratory
selection and before any samples are taken.  Performance evaluation  can be
performed by sending split samples to several laboratories for comparison.

          3.3.2.3  Evaluation

     The first step in the evaluation process is to assess the validity of the
data.  Because leachate constituent concentrations are typically  in  the parts
per million (ppm) or part per billion (ppb) range, even a seemingly  innocuous
event can have a major impact on the resulting data.  Table 3-19  summarizes
some of the factors that can affect the validity of groundwater samples.   This
assessment helps to place the results and subsequent evaluations  and
conclusions in the proper context.
                                     3-83

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     Sample results are typically reported as concentrations of specific
chemicals in mg/1 (ppm) or ug/1  (ppb).   These data can he used to plot  isocon-
centration maps and cross sections in which areas having equal concentration
of selected contaminants are connected  by contour lines.   These maps  and cross
sections are drawn in much the same manner as potentiometric surface  maps and
cross sections, but use concentration results instead of water levels.   The
problem inherent in interpreting these  isoconcentration figures is that a
three dimensional phenomenon (i.e., a leachate plume) is  being presented in
two dimensions.  Furthermore:

     0  The data typically represents only one point  in time and may  become
        obsolete quickly depending on the rate of plume movement
     •  Samples taken from wells designated as points on  a map or cross
        section may actually represent  large three dimensional surfaces within
        the aquifer
     0  Analytical results must  be extrapolated between wells  to produce
        contours
     •  There is a certain degree of natural  and analytical  variability that
        cannot be expressed easily in a figure.

These concerns should be kept in mind when interpreting sampling results.

     Initial calculations of concentration gradients  generally assume conser-
vative and nonreactive leachate  constitutents, and use linear  interpolation.
For example, if sampling results indicate that well  M-l contains 500  ppb of
some constituent and well M-2 contains  100 ppb and these wells are screened in
the same aquifer 200 feet apart  along the same groundwater flowpath,  then the
linear concentration gradient can be calculated by:

                   (500 ppb - 100 ppb)/200 feet = 2  ppb/foot
This gradient can then be used to estimate the location  of  the  plume  boundary.
In the example described above, the boundary would be 50 feet  beyond  well  M-2
along the same groundwater flowpath.
                                     3-84

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                                  TABLE 3-19
              POTENTIAL SOURCES OF FACTORS AFFECTING GROUNDWATER
             SAMPLE VALIDITY (After Fetter, 1983;  and Nacht, 1983)
   Source or Activity
Drilling Equipment
  Techniques
and
Uell  Construction
  and Materials
Sampling Equipment
 and Techniques
                             Effect
t  Equipment can be a source of organic solvents,
   diesel  fuel  and gasoline, oils  and greases,
   and cross contaminants from other drill  sites

•  Drilling fluids can add contaminants or  affect
   certain physical parameters (e.g., COD,  BOD,
   pH)

•  PVC casing and elements used to join PVC
   casing can leach organic chemicals and may
   sorb certain heavy metal compounds
                             •  Stainless steel  or high
                                release metals to water
                                organic compounds
                                     carbon  steel  may
                                     and  sorb  certain
          •  Bentonite used in  drilling fluids  or  in
             annulus seals  may  sorb heavy  metals  and
             organics

          •  Inadequate purging can introduce  stagnant
             water into sample  reducing concentrations  of
             volatile organics

          •  Excessive purging  can  dilute  contaminants
             below detectable limits by mixing  major
             concentrations with large  amounts  of
             uncontaminated formation water

          •  Pumps can sorb metals, organics,  or  induce
             outgassing of  volatile organics through
             turbulence

          •  Gas lift methods can induce outgassing and
             oxidation

          •  Field filtering of samples may add dissolved
             solids if dissolution  of organic  solvents
             occurs or cause oxidation  and  outgassing if
             contact with air is allowed

          •  Improper cleaning  may  introduce contaminants
             from one well  to another
                                                                   (continued)
                                     3-85

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                            TABLE 3-19 (continued)
Source or Activity
                      Effect
Sampling Equipment
 and Techniques (cont.)
Sample Preservation
  and Analysis
•  Excess turbulence caused while placing the
   sample in containers can result in outgassing
   and oxidation

•  Samples that are not preserved properly
   or that are held too long prior to analysis
   can undergo a variety of chemical  changes

•  Bottles cleaned with organic solvents (e.g.,
   methylene chloride) can introduce  a variety of
   contaminants into the sample depending on the
   purity (i.e., grade) of the solvent and the
   degree to which the solvent was volatilized
   from the bottle prior to sealing

•  Certain organic compounds (phthalates,
   methylene chloride, trichlorof luoromethane )
   are common contaminants in  laboratories and
   may affect sample results
     Both concentration and hydraulic gradients are not  always linear,  but
frequently exhibit logarithmic changes.   Rather than  calculate logarithmic
gradients (such as radioactive decay rates),  gradients  are generally  easier to
approximately locate if isoconcentration  contours  or  plume boundaries  are
plotted by using log paper as a reference in  the same manner that  a  ruler  is
used in linear interpolation.


     Nonlinear concentration  gradients  can  also be a  result  of pulsed  releases
of contaminants.  In general, differences of  a few 10's  of parts per  billion
are most often meaningless.  Orders  of  magnitude changes  in  concentration are
usually more reliable as plume indicators,  but may not  be suitable to  easy
interpretation in complex hydrogeologic  situations.
                                     3-86

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     Plume migration rates are calculated simply by dividing the maximum

distance the plume has moved from the source by the time since leachate

generation began.  This calculation assumes that the duration of leachate

generation is known (Section 3.1.1), the boundaries of the plume have been

correctly delineated, and the rates of leachate generation and movement are

constant over time.


     Another use of sample results involves comparing this direct data on

plume boundaries and migration rates to hydrologic calculations made with

previously collected data.  If results differ widely, some input to the

calculations must be wrong or some natural  factor is affecting plume movement.

If sample results indicate the plume has migrated farther than had been

calculated initially, then one or more of the following is true:


     •  There are preferential routes of migration that are not accounted for
        in the calculations

     •  The transmissi vity (or hydraulic conductivity), hydraulic gradient,
        porosity, or time from the beginning of leachate generation has been
        underestimated

     t  The average saturated thickness of  the aquifer has been over
        estimated.


If sampling results indicate the  plume has  not migrated as far as had been

calculated initially, then one or more of the following is true:


     •  Pollutant attenuation is  significant and the assumption cannot be made
        that leachate constituents are conservative and nonreactive

     o  Natural  or artificial factors have  at some time or times reversed or
        changed  flow directions  or patterns

     •  Leachate generation  volumes and rates have been over estimated,  or
        leachate generation  has  not been constant over time

     •  Unidentified natural  barriers to contaminant migration  are  present

     •  Plume migration patterns  are more complex than previously supposed
        because  of either subsurface hydrogeologic conditions  or the physical
        and chemical  properties  of the leachate
                                     3-87

-------
     •  The transmissivity, hydraulic gradient,  porosity,  or time  from the
        beginning of leachate generation  has  been  over estimated
     •  The average saturated thickness  has  been under estimated.
All calculations should be checked to try  to  identify  the  source  of  the
discrepancy so that modifications can be made to  the  hydrogeology  data  base
prior to planning plume control  measures.   If the sampling information
verifies the initial  calculations,  then  aquifer  restoration planning can
begin.
                                     3-88

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                                   CHAPTER  4
                          PLUME CONTROL TECHNOLOGIES
     Methods for controlling the migration of  a  leachate  plume can be  placed
into one of four categories -- groundwater pumping,  subsurface drains,  low
permeability barriers, and  innovative technologies.

     Groundwater pumping technologies involve  the extraction or  injection of
groundwater, through wells, to alter the direction of  leachate plume movement.
In pumping a groundwater extraction well, a cone of  depression is created
which causes groundwater to flow toward the well.  A cone of impression or
mound is created around a groundwater injection well which causes groundwater
to flow away from the well.  Groundwater injection and  extraction wells can be
used separately, or in combination, to change  the flow  of groundwater  in order
to contain or remove a leachate plume.

     Subsurface drains are continuous, permeable barriers designed to  inter-
cept groundwater flow.  As such, they can be used much  like pumping systems.
Groundwater collected in subsurface drains flows to  a  sump where collected
water can be pumped to a treatment system.

     Subsurface barriers consist of a vertical wall  of  low permeability
material constructed underground for the purpose of  redirecting groundwater
flow.   Impermeable barriers can be used to contain contaminant plumes
associated with waste sites by completely surrounding a waste site or plume,
or they can be used to lower a groundwater table to  prevent contact with
wastes.

     In  addition to these more established techniques,  innovative technologies
are being developed to control  leachate plume movements.  These include
                                     4-1

-------
in situ biological treatment (i.e., bioreclamation),  in situ chemical treat-
ment, permeable treatment beds, block displacement, and others.   In  situ
treatment techniques have already been used on a limited basis for aquifer
restoration.

     The purpose of this chapter is to present an overview of available
techniques for controlling the migration of leachate  plumes and to present
methods for evaluating and selecting a technique.  These techniques  are
described in more detail  in the following chapters.

4.1  Control Techniques

     4.1.1  Groundwater Pumping

     Well systems can be designed to perform several  functions with  or without
the assistance of other technologies (e.g., barrier walls).  The main applica-
tions in plume management are groundwater level adjustment, plume containment,
and pi ume removal.

     Well systems to adjust groundwater levels can be designed using extrac-
tion wells to lower water levels or using injection wells to create  ground-
water mounds.  By adjusting groundwater levels, plume migration can  be stopped
at the source or the speed and direction of the plume can be altered.  In
either case, contaminated water is not extracted from the groundwater system
as is the case with containment and removal techniques.

     Well systems used to contain a plume may incorporate extraction wells or
extraction and injection  wells in combination.   Containment differs  from
removal  in that the source of contamination generally is not stopped, so that
contamination is an ongoing process.  Because containment requires removing
contaminated groundwater, a treatment or disposal method must be developed to
handle the system discharge.

     Plume removal implies a complete purging of the groundwater system of
contaminants.  Removal  techniques are suitable  when contaminant sources have
                                     4-2

-------
been  stopped  (e.g., by waste  removal  or  site  capping)  or  contained  (e.g.,  by
barrier walls)  and  aquifer  restoration  is  desired.   Extraction  or  extraction
and  injection well  systems  can  be  used  in  plume  removal.   Numerous  arrays  and
patterns  are  available for  injection  and extraction  wells depending  on  site-
specific  suitability.  Extraction  and  injection  techniques can  also  be  used
with  flushing compounds  to  accelerate  contaminant removal.  As  with
containment strategies,  treatment  of  pumped water is  necessary.

      Previous utilization of  pumping  technologies to  manage plumes  has  shown
that  these methods  are most effective  at sites where  underlying  aquifers have
high  hydraulic  conductivities (e.g.,  coarse grained  sands)  and  where the
contaminants move readily with  groundwater (e.g., benzene).   Pumping methods
have  also be  utilized with  some effectiveness  at sites  where pollutant  move-
ment  is occurring along  fractured  or  jointed  bedrock.   However,  the  fracture
patterns must be traced  in  detail  to  ensure proper well placement.

      The  shape  and  size  of  a  well's cone of depression  is dependent  upon the
pumping rate  and cycle,  slope of the  original  water  table, location  of
hydraulic barriers, aquifer characteristics,  and location of recharge zones.
Two  aquifer characteristics important  in determining  the  cone's  configuration
are  the coefficients of  transmissivity  (T) and storage  (S).   Both of these
parameters are  inversely related to drawdown  and the  deepening  of the cone.
The  extent of the cone under  equilibrium pumping conditions  is  termed the
radius of influence.  The radius of influence  can be  used in determining well
spacing, pumping rates,  pumping cycles,  and screen lengths  when  flow rate  is
low.  However,  when moderate  flow  rates  exist  at a site,  distortion  occurs in
the  flow  lines  such that a  plume may  pass  between two  adjacent  wells even
though their cones  of depression overlap.  For these  cases velocity  plots  must
be developed to properly design  a  well  system.

      Selecting  and  designing  an  appropriate well system requires that adequate
information be  available on the  site's hydrogeologic  conditions  and  the
plume's characteristics.  Four  basic  types of  wells  are used in  plume
management:  well  points, suction  wells, ejector wells, and  deep wells.  Using
the  site data,  selection of an  appropriate well type  can  be  made.
Table 4-1 lists selection criteria for these well types.
                                     4-3

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                              TABLE 4-1.   CRITERIA FOR WELL SELECTION
                                            (Powers, 1981)
Parameters                     Well points          Suction  Wells       Ejector Wells       Deep Wells


Hydrology

•  Low hydraulic conductivity     Good                 Poor               Good            Fair to Poor
   (e.g., silty or
    clayey sands)

•  High hydraulic conductivity    Good                 Good               Poor                 Good
   (e.g., clean sands
    and gravel)

•  Heterogeneous materials        Good                 Poor               Good            Fair to Poor
   (e.g., stratified soils)

•  Proximate recharge             Good                 Poor           Good to Fair             Poor

•  Remote recharge                Good                 Good               Good                 Good

Depth of well                  Shallow  < 20 ft    Shallow  < 20 ft    Deep > 20 ft        Deep > 20 ft

Normal spacing                    5-10  ft              20-40 ft           10-20 ft           > 50 ft

Normal range of                0.1-25.0 gpm         50-400 gpm       0.1-40.0 gpm        25-3000 gpm
 capacity (per unit)

Efficiency                        Good                 Good                Poor                Fair

-------
      The installation  of wells  varies  with  geologic  materials,  well  type,  and
 diameter,  but  most  procedures  include  opening  the  borehole,  installing  casing,
 completing the well, and developing  the  well.   The first  of  these  steps
 consists of dislodging  and  removing  the  earth  materials  located  in the  path of
 the well.   Screens  and  casings  may be  installed  simultaneously with  the
 opening  of the hole or  after the  hole  has been  completed.  The sequence of
 events depends upon the technique used to open  the hole and  the  geolog-ic
 characteristics  in  the  immediate  vicinity of the hole.   Installation of
 screens,  filters, pumps,  and grout completes well  construction.  Well develop-
 ment  is  the last step and consists of  removing material that has built up on
 the well  screen  and walls of the  borehole during the previous steps.  Removal
 of  these  particles  maximizes well yield  and prevents pump damage.

      4.1.2  Subsurface  Drains

      Subsurface  drains  include  any type  of buried  conduit used to collect
 liquid discharges (e.g., contaminated groundwater) by gravity flow.  The major
 components  of  a  subsurface drainage  system include:  drain pipes, envelope or
 filter, backfill, manholes or wetwells,  and pumping stations.  Subsurface
 drains function  similarly to an infinite line of extraction wells.   That is,
 they create  a  continuous zone of depression which  runs the length of the
 drainage trench.

     Although  subsurface drains perform many of the same functions  as pumping
 systems,  drains may be more cost effective in certain circumstances.   For
 example,  they may be particularly well  suited to sites with relatively  low
 hydraulic conductivities where the cost of pumping may be prohibitively  high
 because of the need to locate wells  very close together.   However,  there are a
 number of limitations  to the use of  subsurface drains as  a remedial  technique.
 They are not well suited to areas of  high hydraulic conductivity and  high  flow
 rate.  Also, contamination at great depth may cause construction  costs to  be
 prohibitive, particularly if a substantial  amount of  hard rock  must  be
excavated.  Subsurface  drains are also  not  suitable when  the  plume  is viscous
or reactive because  this type of leachate may clog  the  drain  system.
                                     4-5

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     Functionally, there are two basic types of drains--relief drains and
interceptor drains. Relief drains are installed in areas where the hydraulic
gradient is relatively flat.  They are generally used to lower the water table
beneath a site or to prevent contamination from reaching a deeper, underlying
aquifer.  Relief drains are installed in parallel  on either side of the site
such that their areas of influence overlap and contaminated groundwater does
not flow between the drain lines (i.e., same principle of flow apply to drains
as for wells).  They can also be installed completely around the perimeter of
the site.  Interceptor drains, on the other hand,  are used to collect ground-
water from an upgradient source in order to prevent leachate from reaching
wells or surface water located hydraulically downgradient from the site.  They
are installed perpendicular to groundwater flow.  A single interceptor located
at the toe of the landfill, or two or more parallel interceptors may be
needed depending upon the circumstances.

     Drainage system are classified by function (i.e., as either relief or
interceptor drains), by the type of drain pipe, and by their configuration.
Perforated pipe, available in chemically resistant concrete, vitrified clay,
and various plastics, is the most widely used drain pipe material for remedial
action work, particularly if the drains are to be placed deep in the sub-
stratum.  Other types of drainage conduits include jointed clay  and concrete
tiles, and flexible corrugated plastic pipe.  The configuration  of the drain-
age system depends on the site configuration and size, and the groundwater
flow rate.  The system may be singular, consisting only of lateral pipes
discharging to a collection sump, or composite where laterals discharge to
larger collector pipes which may in turn discharge into a main before reaching
a collection sump.

     In a subsurface drainage system containing parallel relief  drains, depth
and spacing are interdependent design variables.   In theory, the deeper the
drains are the greater the spacing that can be used to obtain the same zone of
depression.  This relationship between depth and spacing is critical to the
design of effective parallel drainage systems.  In designing a system for
hazardous waste sites, the distance between drains located on either side of
the site must be determined so that their drawdowns intersect and thereby
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capture the entire plume.  This spacing, as with wells, will be dependent on
flow rates.  The higher the flow rates the closer the drains will have to be
placed (holding other factors constant).  Velocity plots for determining
capture zones are probably the best method available to adequately calculate
the spacing on drains.  Also, drain depth and spacing may need to be
manipulated in order to capture the entire plume.  However, in designing
parallel  drains for hazardous waste sites, a minimum spacing is often  imposed
by the boundaries of the waste since excavation through the waste material can
be extremely hazardous.  A maximum depth may be imposed by the prohibitive
cost of trench excavation.

     The shape of the drawdown curve upgradient of the site is independent of
hydraulic conductivity but is a function of head or hydraulic gradient.  The
upgradient  influence or drawdown extends for a distance which is  inversely
proportional to the water table gradient.  The distance to which  the water
table  is lowered downgradient of the interceptor drain is directly propor-
tional to the depth of the drain.  Theoretically, a true interceptor drain
lowers the  water table downgradient to  a depth equal to the depth of the
drain.  The distance downgradient to which the drain is effective in lowering
the water table  is infinite provided there is not recharge.  This however  is
never  the case since  infiltration from  precipitation recharges the ground-
water.  The quantity of flow  is also proportional to the depth of the  drain.
If an  interceptor drain is placed at the midpoint between the water table  and
an impervious layer,  a little less than 50 percent of the flow will be   inter-
cepted.  The upgradient and downgradient  influence of an interceptor can be
determined  theoretically or in the field.

      In addition to designing the subsurface drainage system for  appropriate
depth  and  spacing, the hydraulic design must also be developed.   The drain's
pipe  size  and gradient must be adequate to cause the water to flow after  it
enters the  pipe.  The gradient of the drain pipes should be great enough to
result in a flow velocity that prevents siltation, yet will not cause  turbu-
lence.  The Soil Conservation Service (1973) has published data on minimum
recommended grades for various pipe diameters and maximum velocities
recommended for various soil  types.  The diameter of the drain for a given
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capacity is dependent on flow, hydraulic gradient and the roughness
coefficient, which in turn is a function of the hydraulic resistance of the
drain material.  The formula for hydraulic design is based on the Manning
formula for rough pipes.  SCS (1973) and Cavelaars (1974) have developed
monographs for estimating pipe diameter based on the Manning formula when
hydraulic gradient, flow rate, and drainage area are known.  Roughness
coefficients have been published for all drain types.

     The other criterion for successful hydraulic design  is to ensure that the
pipe will accept the drainage water when it arrives at the drainline. To meet
this criterion, the relationship between the hydraulic conductivity of the
gravel envelope or filter material, the perforations in the drain pipe, and
the hydraulic conductivity of the base  soil material must be evaluated.  The
primary function of a filter is to prevent soil particles from entering  and
clogging the drain.  The function of an envelope is to improve water flow  into
the drains by providing a material that is more permeable than the surrounding
soil.  Although filters and envelopes  have distinctly different functions,
requirements of both a filter and an envelope can be met.  SCS (1973) has
developed distinct design criteria for  gravel filters and envelopes, whereas
the Bureau of Reclamation (1978) has developed one set of standards for a
well graded envelope which meets the requirements of both a filter and  an
envelope.  For tile drains, the criteria are based on a comparison of the
grain  sizes of the envelope and base soil material.  Where perforated pipe
drains are being  used, the minimum size of the envelope material  is based  on
the size of the perforations.   Geotextile fabrics offer  an alternative  to  the
more conventional  sand and gravel filters provided the fabrics are compatible
with the waste components in the  leachate so that the drains do not clog.
Design of the drainage sump and pumping plant  are also considered  part  of  the
total  hydraulic design.

      Construction  and  installation of  subsurface drains  can be divided  into
two major phases—trench excavation  and drain  installation.  Trench  excavation
is often the most  complex and costly aspect  of construction  and  installation.
The ease or difficulty of excavation can have  a dramatic  effect on the  cost  of
the total  installation.   Difficult excavation  may result  in exclusion of
subsurface drainage  as  a viable technique  because of  prohibitive  costs.   Once
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trench excavation is completed the components of the subsurface drain can be
installed.  This process consists of  installing drain  pipe bedding, drainage
pipe, a gravel or soil envelope, filter fabric, backfill, and  auxiliary
components including manholes and pumping  stations.

     4.1.3  Low Permeability Barriers

     Low permeability barriers can be used to divert groundwater flow away
from a waste disposal site or to contain contaminated  groundwater leaking from
a waste site.  There-are three major  types of low permeability barriers that
are applicable to leachate plume management—slurry walls, diaphragm walls,
and grout curtains.

     A slurry wall is formed by excavating a trench using a bentonite and
water slurry to support the sides.  The trench is backfilled with materials
having lower permeability than the surrounding soils.  The slurry backfill
trench or slurry wall reduces or redirects the flow of groundwater.

     A diaphragm wall is designed for structural  strength and  integrity in
addition to low permeability.  Diaphragm walls can be made of cast in place
concrete or precast panels with cast  in place joints.

     A grout curtain is formed by pressure injecting one of a variety of
special  grouts to seal and strengthen a rock or soil body.  Once in place,
these grouts set or gel  in the rock or soil voids.  This greatly reduces the
permeability of and imparts increased mechanical  strength to the grouted mass,
and results in a grout wall or curtain.  Because a grout curtain can be three
times as costly as a slurry wall, grout curtains are rarely used when ground-
water has to be controlled in soil or loose overburden.  Grout is used
primarily to seal  voids in porous or fractured rock when other methods of
controlling groundwater are impractical.

     Barrier walls are classified by the materials of which they are composed
and the  position in which they are placed  with respect to the pollution
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source.  There are three major types of barrier walls categorized according  to
material used to backfill the trench:

     t  Soil-bentonite
     •  Cement-bentonite
     t  Diaphragms.

     Soil-bentonite walls are composed of soil materials (often the  trench
spoils) mixed with small amounts of bentonite slurry from the trench.   Cement-
bentonite walls are composed of a slurry of portland cement and bentonite.
Diaphragm walls are composed of precast or cast in place reinforced  concrete
panels (diaphragms) installed by excavating a short, slurry supported  trench
section, using a clamshell bucket or other suitable piece of equipment.   Upon
completion of excavation, the trench section  is filled with a precast,  rein-
forced concrete panel  or tremied concrete around a reinforcement cage.
Alternate or primary panels are installed first, followed by the secondary
panels.  Joints between  panels are formed using stop end tubes that  are
concreted after adjacent panels are completed.  Another method involves  using
a cement-bentonite slurry as the exavation fluid which forms the joint  between
panels when set.

     In general, soil-bentonite walls can be  expected to have the lowest
permeability, the widest range of waste compatibilities, and the lowest  cost.
They also offer the least structural strength (highest elasticity),  usually
require the largest work area, and are restricted to a relatively flat
topography unless the site can be terraced.

     Cement-bentonite walls can be installed  at sites where there is
insufficient work area  to mix and place soil-bentonite backfill.  By allowing
wall sections to harden  and then continuing the wall at a higher or  lower
elevation, they can be  installed in  a more extreme topography.  Although
cement-bentonite walls  are stronger than soil-bentonite walls, they  are at
least  an order of magnitude more permeable, resistant to fewer chemicals, and
more costly.
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     Diaphragm walls are the strongest of the three types,  and are the most
costly.  Provided the joints between panels are installed correctly,  diaphragm
walls have approximately the same permeability as cement-bentonite walls  and
because of a similarity of materials, about the same chemical  compatibilities.
Diaphragm walls are most typically used in situations requiring structural
strength and relatively low permeability.

     Configuration refers to the vertical and horizontal  positioning  of a
barrier wall with respect to the location of the pollution  source and ground-
water flow.  There are two types of configuration—vertical  and horizontal.
The wall configuration, combined with any other remedial  measures (e.g.,
pumping, capping), determine barrier wall effectiveness in  controlling
leachate plume migration.

     Vertical configuration refers to the depth of the wall  with respect  to
both geologic formations and the water table.  Based on vertical  positioning,
walls are either keyed into a low permeability formation  below the aquifer  or
placed to intercept only the upper portion of the aquifer.   The latter type,
known as a hanging barrier wall, can be used to control contaminants  such as
petroleum products which do not mix with the groundwater  but float on top of
it.  In these situations, the barrier need only extend to a  depth in  the  water
table sufficient to intercept the contaminants.  Keyed barrier walls  are
excavated through the water table to a confining layer to contain contaminants
that mix with or sink to the bottom of the aquifer.  The  connection between
the wall and the confining layer is very important to the overall
effectiveness of the barrier.

     Horizontal  configuration refers to the positioning of the barrier
relative to the location of the pollution to be controlled and the direction
of groundwater flow (i.e., the gradient).  Based on horizontal  configuration,
barrier walls may completely surround the pollution source or  be  placed
upgradient or downgradient from it.

     Circumferential  placement refers to placing a barrier wall  completely
around the site.   Although this requires a greater wall length and higher cost
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than either upgradient or downgradient placement alone, some advantages are
offered.  A circumferential barrier wall, when used with a surface infil-
tration barrier such as a cap, can greatly reduce the amount of leachate a
site will release to the environment.  If a leachate pumping or drainage
system is used, as often is the case, a waste site can be virtually dewatered.
In addition to vastly reducing the amount of leachate to be treated,
dewatering can help increase the longevity of the wall.

     Upgradient wall placement refers to the positioning of a wall on the
groundwater source side of a waste site.   This type of placement theoretically
can be used where there is a relatively steep gradient across the site in
order to divert uncontaminated groundwater around the wastes.  In such cases,
clean groundwater is prevented from becoming contaminated thereby reducing
leachate treatment requirements.

     Placement of a barrier wall on the side opposite the groundwater source
is referred to as downgradient placement.  This placement configuration does
nothing to limit the amount of leachate being generated and so is practical
only in situations where there is a limited amount of groundwater or contami-
nant flow, such as near drainage divides.  This type of barrier theoretically
can contain leachate so the leachate can be recovered for treatment.  Although
this wall configuration may be keyed into a confining layer for miscible or
sinking contaminants, most often the wall is hanging to contain and recover
floating contaminants.

     Grout curtains are the most practical and efficient method for sealing
fissures, solution channels, and other voids in rock.  There are four basic
techniques for installing a grout curtain.  These are:

     •  Stage-up method
     •  Stage-down method
     0  Grout-port method
     •  Vibrating beam method.

     The first three methods are injection methods in which the grout is
injected from either the bottom of a borehole to the top (stage-up), or the
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top of a borehole to the bottom (stage-down), or through a  slotted  injection
pipe that has been sealed  into the borehole with a brittle  portland cement  and
clay mortar jacket (grout-port).  The grout port method utilizes rubber
sleeves which cover the outside of each slit (or port) permitting grout to
flow only out of the pipe.  The vibrating beam method  is not a true injection
technique, rather, the method is a way of placing the  grout  in which  an I-beam
is vibrated into the soil  to the desired depth and then raised at a controlled
rate.  As the beam is raised, grout is pumped through  a set of nozzles mounted
on the base of the beam, thus filling the newly formed cavity.   When  the
cavity is completely fil led, the beam is moved in the  direction  of the wall,
leaving a suitable overlap to ensure continuity.  The  process is continued
until a wall of the desired length is constructed (Harr, et al., unpublished).

     Grouting materials fall into three basic groups—cement, bituminous, and
chemical.  Some specific grout mixtures include portland cement, sand and
cement, clay and cement, clay and bentonite, bituminous emulsions, sodium
silicate, and acrylamide.  The applicability of each material is based on the
size of the openings in the soil or rock formation and the  anticipated area of
grout penetration.  The major grouts in use are cement and  clay  which make  up
approximately 95 percent of all  grouts used.

     Cement grouts utilize materials that set, harden, and  do not disintegrate
in water.  Because of their large particle size, cement grouts are more
suitable for rock than for soil  applications.  Materials may be  added to
cement grouts to improve their applicability.  Sand may be  added to portland
cement to create a grout suitable for coarse materials, while bentonite may be
added to improve the penetration of cement in alluvial  soils.

     Clays have been used  widely as grouts either alone or  in formulations.
In general, coarse sands and gravels are initially grouted  using clay or clay
and cement because they are inexpensive.  Bentonite is an excellent clay
grouting material  because of its swelling and gel  formation properties.

     As with slurry walls, placing a grout curtain upgradient from a waste
site can redirect  flow so that groundwater does not contact the wastes that
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are creating the leachate plume.  However, placement of a grout curtain
downgradient from a hazardous waste site may not be successful because of
grout and leachate interactions.  For example, in many instances grout setting
time is difficult to control, increasing the difficulty of emplacing  a curtain
of reliable integrity.  Additional problems can occur in attempting to grout  a
horizontal curtain or layer beneath a waste site.  Injection holes must be
drilled either directionally from the site perimeter or directly through the
wastes.  The first case may not always be feasible and may be quite costly,
and the second might be quite hazardous to construction crews.

     4.1.4  Innovative Technologies

     Groundwater pumping, subsurface drains, and low permeability barriers are
well  established technologies that were originally developed for nonhazardous
applications and have been adapted for use in controlling leachate plume
migration.  A variety of other techniques for plume management are under
development, many of which were designed specifically for application at
hazardous waste release sites.  Two technologies in particular, bioreclamation
and in situ chemical treatment, appear especially promising and have  been
demonstrated on a limited basis for site cleanup.  These two techniques are
described briefly below; other innovative technologies are described  in
Chapter 8.

          4.1.4.1  Bioreclamation

     Bioreclamation is an in situ groundwater treatment technique based on the
concept of utilizing microorganisms, combined with aeration and the addition
of nutrients, to accelerate the biodegradation rate of groundwater
contaminants.

     Many species of bacteria, actinomycetes, and fungi have been found to
degrade hydrocarbons associated with petroleum.  Bacteria are the prime
microorganisms  involved with biodegradation of organics in groundwater.
Naturally occurring species of the genera Pseudomonas, Arthrobacter,  Nocardia,
Achromobacterium, and Flavobacterium have been found to attack petroleum
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hydrocarbons and other organic chemicals (Raymond, et al., 1976).  These
bacteria can be stimulated by adding nutrients and oxygen to develop a
population that is adapted to readily degrade organic chemicals present in
groundwater.

     An alternative to developing adapted populations from naturally occurring
bacteria is to inoculate the subsurface with microorganisms developed in the
laboratory to degrade specific organic chemicals or chemical groups.  The
particular advantages of this alternative are that overall biodegradation
rates of specific organics may be increased and the time required for
adaptation of a naturally occurring population is eliminated.  In this method,
the parent microorganisms are collected from a naturally occurring source
containing the specific chemical groupings, such as oil  refinery treatment
plant sludge for phenol and cyanide treatment.  Mutant strains are developed
from irradiation and these mutant bacteria are cultured  in large amounts and
packaged for use.  The mutant bacteria can be cultured in even larger amounts
in holding ponds at the site and introduced into the subsurface by spray
irrigation, surface flooding, or subsurface injection.

     Cell  nutrients required for proper cell growth and  respiration include
nitrogen,  phosphorus, and trace elements (e.g., potassium, sulfur, sodium,
calcium, magnesium, iron, copper).   Groundwater usually only contains
sufficient amounts of nitrogen and  phosphorous for degradation of 10 to
20 milligrams per liter (mg/1) of organic material.  More nutrients must be
added for biodegradation of higher  contaminant levels.  Oxygen is also
required for the aerobic decomposition of organics by bacteria.  Roughly 3 or
4 mg/1 of oxygen are required for every mg/1 of organic  constituent degraded.
A constant supply of dissolved oxygen must be supplied to the contaminated
groundwater in order to maintain biological activity.  Subsurface aeration has
been the method most commonly used  during previous bioreclamation projects of
groundwaters contaminated with gasoline.  However, since this method can only
provide a maximum of about 10 mg/1  of dissolve oxygen, biodegradation of high
levels of organics in the subsurface can be limited.  Alternative oxygenation
techniques include the use of pure  oxygen systems, ozone, and low concentra-
tions of hydrogen peroxide.
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     The selection of bioreclamation as a plume management technique depends
on the biodegradability of the components in the contaminant plume.  Bio-
degradabilities of various organic substances can be estimated using the ratio
of Biochemical Oxygen Demand (BOD) to Chemical Oxygen Demand (COD).  Compounds
with a BOD/COD ratio of less than 0.01 are considered relatively undegradable,
compounds with a ratio of 0.01 to 0.1 are considered moderately degradable,
and componds with a ratio of 0.1 or greater are considered degradable (Lyman,
et al., 1974).

     Implementation of the bioreclamation process involves the placement of
extraction  wells to control  migration of the contaminant plume by pumping.
Groundwater pumped to the surface is mixed with nutrients and reinjected
upgradient  of the extraction wells.   Specialized bacteria may also be added
along with  the nutrients.  The groundwater may be oxygenated with air, oxygen,
or hydrogen peroxide.  The bioreclamation technique has been used successfully
in a number of cases to treat contaminated groundwater plumes from underground
gasoline and hydrocarbon leaks.

          4.1.4.2  In Situ Chemical  Treatment

     In situ chemical treatment techniques involve the injection of a chemical
into a leachate plume to neutralize, detoxify, precipitate, or otherwise
affect the  contaminant materials.  These techniques are highly dependent on
the contaminant and have in  the past been used only for spills of specific
chemicals.   Dilute solutions of acids or bases, such as nitric acid or sodium
hydroxide,  could theoretically be used to neutralize acidic or basic ground-
water contaminants.  A system of extraction and injection wells could be used
to disperse the neutralizing agent,  and contain and cycle groundwater until
the appropriate pH was attained.  Similarly, chemical agents could be used in
this manner to detoxify plume contaminants.  For instance, sodium hypo-
chlorite, has been used to oxidize cyanide contaminated groundwaters.  Other
oxidizing chemicals such as hydrogen peroxide or ozone may find potential
application in this type of remedial approach.  Solutions of sodium sulfide
have also been proposed to precipitate toxic metals from groundwater, thereby
resulting in their immobilization.  Recently, an underground spill of acrylate
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monomer was treated by the  injection of  a catalyst  which  caused  the  plume of
acrylate monomer to polymerize  and  solidify  (Williams,  1982).

4.2  Technology Evaluation  and  Selection

     Identifying the most appropriate technique  for managing  a leachate  plume
can be an extremely complex process.  The selection process  involves  the
acquisition, evaluation, and  application of  data that vary  in reliability,
applicability and depth of  detail.  Although data development is relatively
straightforward, the .evaluation  and use  of this  data can  be  difficult because
of the many interrelated elements  involved.  Furthermore, developing  and
evaluating site remediation plans  requires exercising a great deal of
technical judgement.

     Under the Comprehensive  Environmental Response, Compensation, and
Liability Act of 1980 (CERCLA or Superfund), EPA developed  the National
Contingency Plan (NCP) for  evaluating site remediation  alternatives  and  their
costs.   The NCP (47 FR 31180, July  16, 1982) specifies  a  three step  procedure
for selecting long term site remediation alternative consisting  of:

     •  Develop alternatives for resolving site problems
     •  Screen the alternatives based on site and waste characteristics
     •  Conduct a detailed  analysis of the alternatives based on expected
        implementation and  performance problems.

EPA,  et al ., (1983)  provides general guidance for using this procedure to
evaluate and select site remediation alternatives.  This chapter describes how
the procedure can be applied to selecting leachate plume management alterna-
tives.   Other sources of information on procedures for  selecting among
remedial  action  alternatives include EPA (1982a) and RADIAN (1983).

     4.2.1   Development of Alternatives

     The first step in developing a plume management plan involves identifying
and prioritizing  the problems at a site,  setting response objectives, and
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developing remedial action alternatives.  These alternatives may consist of
variations of the same basic technology (e.g., keyed, circumferential,
cement-bentonite walls; hanging, upgradient, soil-bentonite walls) or combina-
tions of different technologies (e.g., a low permeability barrier combined
with a groundwater pumping system).

     Typically, hazardous waste release sites pose many types of environmental
threats which must be prioritized and translated into a series of corrective
actions.  For example, a site may pose fire and air contamination hazards from
ignitable and volatile wastes present at the surface in addition to ground-
water contamination.  The first action at such a site might be to mitigate the
most immediate hazard by removing surface waste to safeguard the local
populace.  Once the threats of fire and noxious emissions are alleviated, a
thorough investigation can be implemented to plan long term corrective meas-
ures for groundwater contamination.   If the investigation were to identify
drinking water contamination, providing alternative supplies to local resi-
dents would take priority over implementation of plume management plans.  The
need for identifying, prioritizing, and addressing site hazards often con-
tinues throughout the response process as new data is developed and evaluated.

     Based on the assessment of a site's problems and the priorities  set for
mitigating these problems, specific response goals can be established.
Response objectives can be stated in  specific terms, like "Reduce the concen-
tration of substance X in the groundwater at point Y to less than 3 times
background levels within one year."   The objectives can also be presented in  a
more general manner, such as by stating the degree of plume control that
should be achieved.  Establishing the goals of a remediation effort prior to
the technology screening and detailed analysis steps is extremely important to
focus control efforts on the most critical  problems of the site.

     Response objectives can be used  in a number of ways.  First, they can be
used to schedule plume migration control efforts in order of priority.  One
example of such a ranking could be  (1) Protect nearby municipal wells,
(2) Reduce or eliminate plume movement, and (3) Remove the plume.  Second,
response objectives can be used during design preparation and review  to
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compare the projected efficiency of a remedial action alternative to the
actual efficiency required to control the plume.  For example, if the response
objective was to collect 90 percent of a plume and a groundwater pumping
system was projected to collect only 75 percent of the plume, then that
alternative would be considered to be 83 percent effective.  Third, response
objectives can be used to set the standards by which the efficiencies of the
various technologies are judged after implementation.  If, for example, a
pumping system were designed to collect at least 60 percent of a plume but
only collected 40 percent of the plume during operation, the pumping system
would be considered to be 66 percent effective.  In developing response
objectives for evaluating site remediation alternatives, a number of criteria
should be addressed including:

     •  Priorities -- Do the response objectives focus on the most critical
        problems at the site?
     •  Scope -- Do the response objectives address all site problems?
     •  Effectiveness -- To what extent can a given response objective be
        fulfilled?  To what extent can all response objectives be fulfilled?
     •  Feasibility -- How difficult will fulfilling a given response
        objective be?  How difficult will fulfilling all response objectives
        be?
     •  Timing -- How long before beneficial changes are apparent and how  long
        will the changes 1 ast?
     •  Requirements -- What resources will be needed to fulfill a given set
        of response objectives?
     •  Benefits -- If fulfilled, will the response objectives produce
        environmental changes that are significantly preferable to not taking
        action?

     Developing plume management alternatives based on the established
response objectives requires exercising a considerable amount of technical
judgement.  While there are basically four plume management technologies
available (i.e., well systems, subsurface drainage systems, low permeability
barriers, and in situ treatment techniques), variations and combinations of
these technologies can lead to a large number of possible plume management
alternatives to be considered.
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     To further complicate matters, many plume management technologies cannot
be used by themselves to effectively control  the contamination caused by
leachate plume migration.  One example of this situation is the use of extrac-
tion wells to remove contaminated water from an aquifer.  Once contaminated
water has been removed, the extracted water must be stored in a secure area
and treated to reduce contaminant concentrations to acceptable levels.
Residues from the treatment process must also be disposed of properly and the
treated water must be either released to surface waters, placed in seepage
basins to recharge the aquifer, or reinjected into the aquifer.  Thus, the use
of extraction well systems also requires the  use of contaminated water
storage, treatment, and disposal  facilities.

     Once the technologies and their required auxiliary measures have been
identified and developed into a site restoration alternative, a preliminary
evaluation of each alternative can be initiated.  This screening step involves
assessing the suitability of each alternative relative to specific site
conditions.

     4.2.2  Screening of Alternatives

     Screening involves making a  preliminary  comparison of the plume manage-
ment alternatives to identify those alternatives that  are precluded by site
and waste conditions, thereby, reducing the number of  alternatives for
detailed analysis to a manageable few.  There are three fundamental  criteria
to consider in screening remedial  action alternatives--technical  feasibility,
environmental and public health impacts, and  costs.

     Technical feasibility screening consists of a review of all  pertinent
site and waste characteristics to identify any conditions that would preclude
or otherwise effect the use of a  certain alternative.   Tables 4-2 through 4-5
highlight the effects that selected site and  waste characteristics can have on
the applicability and performance of the four basic plume management tech-
nologies.  Additional information on technology applications is detailed in
Chapters 5 through 8.  In conducting a technical  feasibility screening of
alternatives, a great deal of technical  judgement is required to extrapolate
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                                                     TABLE 4-2
                              THE  INFLUENCE  OF SITE  GEOLOGY ON  THE SELECTION AND
                            PERFORMANCE OF LEACHATE  MIGRATION CONTROL TECHNOLOGIES
Geologic
Characteristic
                                                   Leachate Migration Control Technologies
Groundwater  Pumping     Subsurface  Drains
                        Low Permeability Barriers    In Situ  Treatment
Soil or overburden
thickness or depth
to bedrock
Little or no effect
Ease of excavation    Little  or no effect
Soil texture and
1ithology
Stratigraphy,
horizonation,
structure
Mineralogy;
geochemistry;
soil chemistry
Will  affect  the
design of well
screens and  gravel
packs

Will  affect  well
design but not
necessarily
performance
No effect as long as
groundwater chemistry
is favorable (i.e.,
well materials will
not be corroded or
encrusted)
Drains are generally
restricted to appli-
cations in unconsoli-
dated materials less
than 100 feet deep
Difficult excavation
may preclude the use
of drains

Will affect the design
of the envelope and
filter
Will affect drain
design but not neces-
sarily performance
No effect as long as
groundwater chemistry
is favorable (i.e.,
drains are not
clogged by mineral
deposits)
Slurry walls are generally
restricted to applications
in unconsolidated materials
less than 100 feet deep;
grouts can be used at any
depth if injected

Difficult excavation may
preclude the use of barrier
walls

May be a factor in slurry
loss during installation
No effect as long as key-in
is effective and excavation
is easy
No effect as long as
groundwater chemistry is
favorable (i.e., wall
materials are not
degraded)
Little or no effect
depending on the
delivery system
Little or no effect
depending on the
delivery system

Will affect the design
of the delivery system
No effect as long as
delivery system func-
tions and biochemical
conditions are
favorable

Can have a major
affect on treatment
reaction rates and
extents

-------
                                                      TABLE  4-3
                              THE INFLUENCE OF  SITE HYDROLOGY ON  THE SELECTION AND
                             PERFORMANCE  OF LEACHATE MIGRATION CONTROL TECHNOLOGIES
Hydro-logic
Characteristic
                                                    Leachate Migration Control Technologies
Groundwater  Pumping    Subsurface Drains
                        Low Permeability Barriers    In Situ Treatment
Ji

ro
Aquifer type
Aquifer depth and
thickness
Aquifer extent
and configuration
Aquifer homogeneity
and isotropy
Aquifer properties
(e.g., transmis-
sivlty, hydraulic
conductivity,
porosity)
Can be used  in both
confined and uncon-
fined aquifers

Little or no adverse
effect
May affect  design
but generally will
not influence selec-
tion or performance

May affect  perfor-
mance 1f system  is
not designed
appropriately

Will affect design
but generally not
performance, although
well systems may not
be the most efficient
alternative for  low
transm1ss1v1ty
aquifers
Generally restricted
to unconflned aquifers
Drain depth is
generally limited
to less than 100 feet

May affect design but
generally will  not
influence selection
or performance

May affect performance
if system is not
designed appropriately
Generally restricted
to aquifers having
a low to moderate
transm1ss1v1ty
Generally restricted to
unconfined aquifers
Wall depth is generally
limited to less than
100 feet

Little or no effect
Little or no effect
Excess slurry loss may
occur in highly permeable
aquifers; grouting 1s
generally not effective
in low transmissivity
aquifers
Depends on the treat-
ment technology and
delivery system used

Depends on the
delivery system used
Aquifer configuration
may affect the design
of the delivery system
May effect performance
of delivery systems
May affect the selec-
tion of a delivery
system
                                                                                                             (continued)

-------
                                                TABLE 4-3  (continued)
Hydrologic
Characteristic
                                                    Leachate Migration Control  Technologies
Groundwater Pumping    Subsurface Drains
                                                                     Low Permeability Barriers    In Situ Treatment
Hydraulic gradient
J=»


OJ
Will affect design
but not selection
or performance
Hydraulic barriers    Will affect design
(i.e., recharge and   and performance if
discharge boundaries) barriers are not
                      Identified adequately
Aquiclude effective-
ness and adjacent
aquifers
Groundwater
chemistry
May affect perfor-
mance if system is
not designed
appropriately

Can be a factor in
corrosion and
encrustation of well
screens and pumps
Will affect the
selection of inter-
cepter drains (high
gradients) versus
relief drains (low
gradients)

Will affect design
and performance if
barriers are not
identified adequately

May affect performance
if system Is not
designed appropriately
Can be a factor in
envelope and drain
clogging
                                                                                       Generally no effect
                                                                                       although very high
                                                                                       hydraulic gradients across
                                                                                       a barrier may induce
                                                                                       failure
                                               Little or no effect
                                               especially if site is
                                               capped effectively
                                                                                       Keyed systems wi11  be
                                                                                       ineffective if aquiclude
                                                                                       leaks
                                                                                       Can be a factor in wall
                                                                                       degradation
May affect delivery
system
                                                                                                                    Will affect design and
                                                                                                                    performance of the
                                                                                                                    delivery system
May affect design and
performance of the
delivery system
Can affect the rate
and extent of some
treatment systems as
well as the delivery
system

-------
                                                                      TABLE 4-4
                                        THE  INFLUENCE  OF PLUME  CHARACTERISTICS ON THE  SELECTION AND
                                          PERFORMANCE  OF LEACHATE MIGRATION  CONTROL  TECHNOLOGIES
                     Plume
                 Characteristic
                                                                    Leachate  Migration Control Technologies
Groundwater  Pumping    Subsurface Drains
                        Low  Permeability Barriers     In Situ Treatment
                 Flow direction
                 Flow rate
 i
ro
                 Volume and extent
                 Contaminant types
                 Concentrations
                 Density
Little or  no  effect
because the system
will  readjust flow
directions

Important  in  system
design and operation
but generally does
not affect selection
or performance

Little or  no  effect
Can affect the
selection of  system
materials and
components; some
contaminants  can
clog systems

Little or no  effect
if the system is
designed and
operated properly

Will influence  the
placement of  screens
in individual wells
Little or no effect
because the system
will readjust flow
directions

High flow rates
generally preclude
the use of subsurface
drains
Generally not
practical for very
large plumes

Can affect the
selection of system
materials and
components; some
contaminants can
clog systems

High concentrations
of some contaminants
will clog drainage
systems

Can reduce system
effectiveness if
drain is not situated
properly within the
aquifer
Very important for placing
noncircumferential walls
especially if flow direc-
tions change seasonally

Can be very important
for noncircumferential
walls especially down-
gradient walls
Generally not practical
for isolating very
large plumes

Can affect wall
placement and performance
if contaminants  degrade
wall materials
High concentrations
of some contaminants
can degrade wall
materials

Very important for
hanging walls
                                                                                                                 Little or no effect
Can be very important
depending on the
treatment system used
Generally not
practical for very
large plumes

Generally the primary
consideration in
selecting a treatment
system
High contaminant con-
centrations cannot be
treated effectively by
some treatment systems

May be a factor in
the design of the
delivery system
                                                                                                                            (continued)

-------
                                                                  TABLE 4-4 (continued)
                      Plume
                  Characteristic
                                                                     Leachate Migration Control Technologies
Groundwater Pumping     Subsurface Drains
                        Low Permeability Barriers     In  Situ Treatment
                  Viscosity
                  Solubility  in
                  groundwater
ro
en
                  Reactiyeness,
                  explosiveness,
                  corrosiveness,
                  volatility
                  Toxicity
Highly viscous lea-
chate may clog
screens, pipes,
and pumps thus
reducing well
efficiency

Pumping systems can
be designed for both
soluble and insoluble
contaminants
Care must be taken
during installation
and the operation
of pumps and treat-
ment systems; some
contaminants may
degrade well
materials
Little or no effect
except for treatment
system
Highly viscous lea-
chate may clog
envelope materials
resulting in drain
failure
Drainage systems can
be designed for both
soluble and insoluble
contaminants, although
drains tend to function
more effectively when
contaminants are
soluble in groundwater

Care must be taken
during installation
and the operation
of pumps and treat-
ment systems; some
contaminants may
degrade drain
materials
Little or no effect
except for treatment
system
Little or no effect
Little or no effect
Care must be taken
during Installation;
some contaminants
may degrade wall
materials
Little or no effect
Effect depends on the
delivery system used
Effect depends on
treatment technology
used
Care must be taken in
implementing in situ
treatment activities.
The ability of con-
taminants to enter
into chemical and
biochemical reactions,
however, is a require-
ment of in situ
treatment technologies.

Effect depends on the
treatment technique
used.  Some highly
toxic contaminants can
not be bioreclaimed.

-------
                                                     TABLE 4-5
                           THE INFLUENCE  OF SURFACE CONDITIONS ON  THE SELECTION AND
                            PERFORMANCE OF LEACHATE MIGRATION CONTROL TECHNOLOGIES
Surface
Condition
                                                   Leachate Migration Control Technologies
Groundwater Pumping    Subsurface Drains
                        Low Permeability Barriers    In Situ Treatment
Climate
Topography,
slopes
Vegetation
Existing well
pumpage
Locations of
facilities
(e.g., buildings,
pipelines,
utilities,  roads)
Generally no  effect
Generally no effect
Generally no effect
except to restrict
access or require
clearing

May reduce system
effectiveness if
not accounted for
in design

Generally little
or no effect
Excess precipitation
may cause a reduction
in system effective-
ness

Installation may be
difficult or
impossible in
rough terrain

Generally no effect
except to restrict
access or require
clearing

May reduce system
effectiveness if
not accounted for
in design

May require extra
care in installation
and special design
considerations
Freeze-thaw cycles and
drought may cause wall
failure
Installation may be
difficult or
impossible in
rough terrain

Generally no effect
except to restrict
access or require
clearing

Generally no effect
May require extra
care In installation,
special procedures
to prevent slurry loss,
and special design
considerations
Some treatment
reactions are
inhibited at low
temperature

Generally no effect
depending on the
delivery system
Generally no effect
except to restrict
access or require
clearing

May effect delivery
system performance
Little or no effect
except as it
influences the
delivery system
                                                                                                            (continued)

-------
                                                                    TABLE  4-5 (continued)
i
ro
Surface
Condition
Receptors
Leachate Migration Control Technologies
Groundwater Pumping
Site security
required
Subsurface Drains
Site security
usually required
Low Permeability Barriers
Site security
usually advisable
even if site is
capped
In Situ Treatment
Site security
required
                    Potential for
                    future land
                    usefulness
Good if waste
source and  plume
are removed
Good if waste
source and plume
are removed
Not advisable
Good if waste source
is removed and
treatment process
was effective

-------
general guidelines on technology applications (such as those listed in Tables
4-2 through 4-5) to site specific plume management alternatives.  Furthermore,
certain site and waste conditions may not preclude a given alternative when
considered singly but would if considered together.  Therefore, reconsidering
some decisions made during the screening process may be necessary in subse-
quent detailed analyses.

     Screening alternatives for environmental and public health impacts
involves two major issues.  First, the anticipated effectiveness of the
alternative in reducing risks related to the site must be determined.  This
evaluation generally uses both the response objectives described previously
and the no action alternative as points of reference for the effectiveness of
the alternatives.  Second, all potential  effects of implementing the
alternative which are adverse to the environment or the public health must be
                                 •
identified.  For example, excavation of a low permeability barrier or subsur-
face drain may create dust or waste volatilization problems.  The results of
this screening step is a summary of the benefits of implementing a given
remedial action alternative.

     Cost screening is based on a review of projected capital and operation
and maintenance (O&M) costs.  Capital costs of a remedial  action alternative
can include (EPA, et al., 1983):

     •  Construction costs -- includes equipment, labor (including fringe
        benefits and workman's compensation), and materials required to
        install a remedial action.
     t  Equipment costs -- includes remedial action and service equipment.
     •  Land and site development costs -- includes land related expenses
        associated with purchase of land and development of existing property.
     •  Buildings and service costs -- includes process and nonprocess
        buildings and utility hook-ups.
     t  Relocation expenses -- includes costs for temporary or permanent
        accommodations for affected residents.
     •  Engineering expenses -- includes administration, design, construction
        supervision, drafting, and testing of remedial action alternatives.
                                     4-28

-------
     •  Legal fees, license and permit costs -- includes administrative and
        technical costs necessary to obtain licenses and permits for facility
        installation and operation.

     •  Start up and shake down costs -- includes costs incurred during
        remedial action start up.

     t  Contingency allowances -- Contingency allowances should correspond to
        the reliability of estimated costs and experience with the remedial
        action technology.


O&M costs can include (EPA, et al., 1983):


     •  Operating labor costs -- includes all wages, salaries, training,
        overhead, and fringe benefits associated with the labor needed for
        post construction operations.

     •  Maintenance materials and labor costs -- includes the cost for labor,
        parts, and other materials required to perform routine maintenance of
        facilities and equipment for the remedial  alternative.

     •  Auxiliary materials and energy -- includes such items as chemicals and
        electricity needed for treatment plant operations, water and sewer
        service, and fuel  costs.

     •  Purchased services -- includes such items as sampling costs,
        laboratory fees and professional  services  for which the need can be
        predicted.

     •  Disposal costs --  includes transportation  and disposal of any waste
        materials, such as treatment plant residues generated during remedial
        operations.

     •  Administrative costs -- includes all  costs associated with administra-
        tion of remedialaction operation and maintenance not included under
        other categories such as labor overhead.

     •  Insurance, taxes,  and licensing costs -- includes such items as
        liability and  sudden and accidental  insurance,  real  estate taxes on
        purchased land  or  right-of-way licensing fees for certain  technol-
        ogies, and permit  renewal  and reporting  costs.

     •  Maintenance  reserve and contingency funds  -- represents annual
        payments into  escrow funds to cover anticipated replacement or
        rebuilding of  equipment and any large unanticipated O&M costs,
        respectively.

     t  Other costs  --  includes all  other items  which do not fit into any of
        the above categories.
                                     4-29

-------
These costs should be updated to current values using standard costs  indices.
If the alternatives have significantly different time periods for  implementa-
tion, the costs should be adjusted by conducting a present worth analysis
(EPA, et al., 1983).

     The cost screening evaluation involves comparing the costs of competing
remedial  action alternatives to establish the relative costs of alternatives
producing similar environmental, public health, and public welfare benefits.
Competing alternatives should be eliminated if they are deemed expensive
(i.e., an order of magnitude or more) and offer similar or lesser  environ-
mental and public health benefits.  Alternatives that are more expensive but
offer greater benefits should not be eliminated.

     Alternatives that have passed this final stage of preliminary screening
will undergo a more detailed evaluation using the parameters outlined  in
Section 4.2.3.

     4.2.3  Detailed Analysis of Alternatives

     The detailed analysis of the remaining alternatives is similar to  screen-
ing  in the criteria assessed but is different in that technical judgement
plays a less significant role.  Instead, additional data are collected  bearing
on the technical feasibility, environmental and public health impacts,  and
costs of each alternative.  These data are analyzed and used as a  basis for
eliminating inappropriate alternatives and selecting the best site remediation
alternative.

     Assessing an alternative's technical feasibility involves examining  its
anticipated reliability and implementability.  The reliability of  a remedial
action alternative depends on the alternative's:

     •  Performance history -- The degree of success experienced with  the same
        or a similar remedial action alternative under similar site or  waste
        conditions or both (CERCLA funds can be used only if the technologies
        included in an alternative have been demonstrated effective for waste
        site restoration).
                                     4-30

-------
     •  Effectiveness -- The extent to which the alternative is expected to
        meet or exceed each response objective.

     •  Durability -- The projected period of effectiveness and the amount of
        maintenance required.

     •  Flexibility -- The ability of the alternative to be adapted to changes
        in  site and waste conditions without causing environmental  damage.

     •  Sensitivity -- The ability of the alternative to accommodate transient
        upset conditions without a major reduction in effectiveness.

     •  Reliance on companion measures -- The extent to which the primary
        plume control technology depends on associated remedial measures to
        achieve its maximum effectiveness.


 able 4-6 summarizes the general reliability of  the four basic leachate migra-

 ion control technologies.


     The implementability of a remedial action alternative depends on the

following alternatives:


     •  Ease of installation -- The difficulty anticipated in  installing  and
        making an alternative operational because of site conditions (e.g.,
        topography, geology, hydrology, soils, climate).

     •  Ease of construction -- The difficulties anticipated because of the
        alternative's special technical requirements (e.g., access, avail-
        ability of equipment and materials, special technical skills required,
        QA)

     •  Time to implementation -- The anticipated time necessary to collected
        additional data required, design the system, install the system, make
        the system operational, and note an improvement in environmental
        conditions.

     t  Ease of operation -- The difficulty anticipated in operating the
        system over  its design life to fulfill the response objectives and in
        monitoring the system's performance.

     •  Ease of repair -- The difficulty anticipated in repairing, replacing,
        or rehabilitating key components of the  system.

     •  Safety requirements -- The equipment and procedures needed to protect
        the health and safety of site workers and local inhabitants.


Table 4-7 summarizes the general implementabil ity of the four basic leachate

migration control technologies.
                                     4-31

-------
                                                                    TABLE  4-6
                       FACTORS AFFECTING THE RELATIVE  RELIABILITY OF LEACHATE  MIGRATION CONTROL  TECHNOLOGIES
               Reliability
               Criterion
                                                                  Leachate Migration Control  Technologies
Groundwater Pumping     Subsurface Drains
                        Low Permeability Barriers    In Situ  Treatment
               Performance
               history
i
00
ro
               Effectiveness
               Durability
Used successfully  at
many hazardous
waste sites and  for
related dewatering
applications
Generally very
effective if
designed, operated,
and maintained
properly.  Poor
operation and
maintenance are
the chief reasons
for poor
effectiveness.

Generally very
durable and easy
to maintain. Wells
can generally last
the ful1 period of
operation of the
system although pumps
require periodic
replacement.
Used successfully at
many sites but not
as commonly as well
systems; also used
frequently for
related dewatering
applications
Can be very effective
and more efficient
than pumping systems
if designed and
maintained properly.
Drain clogging and
pipe failure are the
chief reasons for
poor effectiveness.
Not as durable as
pumping systems
because drain
envelopes tend to
clog.  Maintenance
is not as simple as
for well systems.
Used successfully at
selected hazardous
waste sites; use of
slurry trenching
techniques is
increasing; grouting
applications are
relatively minor
Very effective if
installed properly
although some leakage
will generally occur
Durability will  be highly
variable depending on the
hydrologic and chemical
stresses on the wall.
Maintenance is generally
minimal.
Certain treatment
systems have been
demonstrated at
hazardous waste sites
including biorecla-
mation, flushing, and
polymerization; used
primarily for single-
chemical spills

Variable effectiveness
depending on site and
leachate characteris-
tics and the treatment
technology used
Not applicable if the
leachate source is
removed
                                                                                                                           (continued)

-------
                                                                TABLE 4-6 (continued)
                Reliability
                Criterion
                                                                    Leachate  Migration  Control  Technologies
                                      Groundwater Pumping     Subsurface  Drains
                                               Low Permeability Barriers    In Situ Treatment
                Flexibility
                Sensitivity
CO
CO
Very flexible.
System can be
adapted to changes
simply by adding
wells, revising
pumping rates and
schedules, or
changing treatment
operations.

Generally can
accommodate minor
upset conditions
such as high water
levels resulting
from heavy precip-
itation.  Pump
failure can render
portions of the
system ineffective,
however.
Not very flexible
because drain
influence cannot be
control led without
changing system design
Generally can
accommodate upset
conditions except
for major system
failure (e.g.,
clogged drainage
main)
Not flexible once
installed, although
this is typically
not restrictive
Generally can
accommodate upset
conditions except
for major wal1
failures
Somewhat flexible
depending on the
delivery system and
treatment technology
used, although this
is typically not
restrictive
Variable depending
on the type of upset
condition and the
delivery system and
treatment technology
used
                Reliance  on
                companion
                measures
Generally requires
leachate storage
and treatment
facilities; may
require source
removal or isolation
Generally requires
leachate storage
and treatment
facilities; may
require source
removal or isolation
Generally requires site
capping for circumferential
walls, and wells or drains
for downgradient and
floating walls; may
require source or leachate
removal or treatment
Requires a delivery and
recovery system such
as wells or drains;
generally requires
source removal and
treatment or disposal

-------
                                                                     TABLE  4-7
                    FACTORS AFFECTING THE RELATIVE  IMPLEMENTABILITY OF  LEACHATE  MIGRATION  CONTROL TECHNOLOGIES
                Implementabillty
                  Criterion
                                                                  Leachate Migration Control  Technologies
Groundwater Pumping    Subsurface Drains
                        Low Permeability  Barriers     In  Situ Treatment
                Ease of
                instal lation
-Pi
i
OJ
                Ease of
                construction
                Time  to
                implementation
Generally very  easy
to install  but  can
be somewhat diffi-
cult to fine tune
operations
Most systems  can
be constructed by
qualified local
drillers and  pump
installers
Fairly rapid to
install and affect
changes in plume
migration patterns
Can be very difficult
to install  if hard
rock excavation and
shoring and dewater-
ing is needed, if the
design drain depth is
large, and if the
topography is very
uneven; these
problems are not
insurmountable

Some systems may
require the use of
specialized equip-
ment and materials;
QA is an important
consideration; local
contractors may not
be qualified

Moderately time
consuming to install
but will affect
changes in plume
migration patterns
fairly rapidly
Can be difficult or
impossible to instal1
in areas of extreme
topography or climate
Some systems may require
the use of specialized
equipment and materials;
QA is an important
consideration; local
contractors may not be
qualified
Moderately time consuming
to install and may not
affect any improvement
in site conditions for
some time depending on
system placement
Variable depending
on the delivery
system and treatment
technology used.
Climate, hydrology,
and soil geochemistry
are the most signif-
icant factors.
May require special-
ized equipment and
materials.  Most
in situ treatment
is undertaken by
specialty firms
Highly variable
depending on site
size and treatment
effectiveness
                                                                                                                           (continued)

-------
                                                             TABLE 4-7 (continued)
                Implementability
                   Criterion
                                                                   Leachate Migration Control Technologies
Groundwater Pumping     Subsurface Drains
                        Low Permeability Barriers    In Situ Treatment
                Ease  of
                operation
 i
GO
CJ1
                Ease  of
                repair
                Safety
                requirements
Can be fairly complex
to fine tune system
and operate at
maximum efficiency;
treatment may also
be fairly complex

Generally, fairly
easy to rehabilitate
or replace wells,
pumps, and surface
piping; treatment
system repair may
be more complex
Generally the least
stringent of the
technologies because
subsurface distur-
bances are minimal;
can be significant
if explosive wastes
are present or if
wells must be
installed through
waste piles
Fairly simple since
groundwater collec-
tion is a function
of gravity flow;
treatment may be
fairly complex

Pipe and envelope
clogging requires
excavation and
reinstallation;
pump and treatment
system repair are
the same as for
well systems

More stringent than
well systems because
of the greater extent
of subsurface
excavation and the
potential for waste
volatilization and
dust generation;
trench cave-in is a
primary safety concern
Implementation limited
to monitoring and
operating associated
remedial action
technologies
Slurry trench sections
that have failed generally
cannot be repaired but
instead are replaced with
new wall sections; grout
failure usually cannot
be repaired effectively
Slurry trench requirements
are similar to those for
drains; grouting require-
ments are similar to those
for wells
Can be very complex
because of the
variables involved
in system operation
Generally, fairly easy
to rehabilitate or
replace system
components
Variable, but can be
as stringent or more
stringent than for
drains depending on
the delivery system
and the treatment
agents used

-------
     Conducting a detailed environmental analysis of each alternative involves
predicting all  changes (both adverse and beneficial) from existing conditions.
This applies to both sensitive biotic environments (e.g., endangered and pro-
tected species, wildlife habitats and breeding grounds, vulnerable ecosystems)
and human resource use patterns (e.g., recreational areas, fishing and hunting
grounds,  historic sites, traffic patterns, water supplies).  These changes can
be evaluated by comparing them to the response objectives, the no action
alternative, or published environmental  criteria such as those given in:

     •  "Quality Criteria for Water" (Federal Register November 28, 1980) --
        Criteria documents are available for each of 64 toxic pollutants.
     •  "Quality Criteria for Water" (Red Book, July 1976) -- Contains some
        additional  criteria not preempted by above (e.g., temperature,
        aesthetics, dissolved oxygen).
     •  Safe Drinking Water Act (40 C.F.R. 141) -- Maximum levels set for six
        contaminants.  Suggested No Adverse Response Levels (SNARLS) are given
        for others.
     •  Pesticide Residue Amendment to the Food, Drug and Cosmetic Act (40
        C.F.R.  180) -- Safe levels of 301 pesticides in soil  based on crop
        tolerance levels.

     The degree of actual or potential harm caused by the plume must also be
addressed.  Contamination of some aquifers, notably saline ones, may be con-
sidered a relatively low priority problem, whereas the presence of a hazardous
waste plume in  an aquifer that is the sole drinking water source for numerous
people is a high priority issue.

     Anticipating and preventing adverse impacts from site remediation
activities is a key step in the detailed environmental assessment.  Areas that
are disturbed during excavation of subsurface drainage trenches, construction
access roads, sumps, slurry walls, recharge basins, slurry mixing areas, and
leachate storage facilities are extremely susceptible to erosion unless
erosion prevention measures are used.  The soil carried off of the site as a
result of erosion becomes deposited in surface water bodies and can clog water
ways, interfere with wildlife, and contribute to flooding downstream.  If the
eroded sediments contain chemical contaminants, the degradation of water
                                     4-36

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quality  is considerably more  serious.   The  quality of  the  air  surrounding  the
site can also become degraded  when disturbance  of  the  waste  site  results  in
fires or explosions, volatilization  of  waste  constituents, or  production  of
toxic gases, mists, or dusts.

     When technologies that remove the  plume  from  the  aquifer  are used, the
extracted plume must be treated  to reduce  its contaminant  concentrations  to
acceptable levels.  In some cases, the  treated  water will  still contain
higher than background levels  of contaminants.   If this  water  is  discharged  to
surface waters, the treated water may result  in  a  reduction  in  surface water
quality.  Furthermore, removal of uncontaminated groundwater upgradient of the
site without recharging this  water downgradient  of the  site  can lower the
water table downgradient  and  result  in  modifications in  both groundwater  and
surface water flow and use, and  vegetation  patterns.   These  conditions would
be most pronounced if the extracted  groundwater  was diverted to a different
watershed. Hydrophillic (water loving)  plants in areas  that  formerly had  a
high water table may become replaced by less water  tolerant  species.  This
could then cause a modification  in wildlife populations  or distribution in the
affected areas.

     Also important in the detailed  environmental  assessment is an  evaluation
of the hazards that will  be posed until  a site  restoration alternative can be
implemented and the risks and  hazards associated with  the  failure of an
alternative to fulfill the response  objectives.  In addition to the technical
feasibility and environmental  impact aspects of  each alternative,  institu-
tional  and health and safety requirements should be evaluated.

     Local, state and federal  laws require provisions  for  regulating certain
activities.   Because of these  laws,  special permits, bonds or licenses may be
required to conduct certain activities  at some  sites.   For example, removal of
groundwater from some aquifers,  particularly in  arid and semiarid  areas, may
be prohibited without special  permission, and transfer of water from one
watershed to another is illegal  in some  areas.   Table 4-8 highlights regula-
tions that may be applicable to  site remediation activities.  Other important
institutional  issues to be addressed include community relations  and the need
                                     4-37

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                                   TABLE 4-8
                     SELECTED REGULATORY REQUIREMENTS FOR
                        AQUIFER RESTORATION ACTIVITIES
        Source of Requirement
     Requirement or Prohibition
                        FEDERAL PERMITS AND REGULATIONS
Resource Conservation and Recovery Act
Federal Water Pollution Control Act
(also called the Clean Water Act)
Safe Drinking Water Act
Wild and Scenic Rivers Act
Endangered Species Act
Fish and Wildlife Coordination Act
Coastal Zone Management Act
RCRA permit or interim status
authorization may be needed if
hazardous wastes are treated,
stored, or disposed

RCRA manifest needed if wastes are
to be transported from the site

National  pollutant discharge
elimination system (NPDES) permit
needed if wastewater is to be
discharged into navigable waters

Dredge or fill permit needed if
these materials are to be
discharged into navigable waters

Underground injection control
permit may be needed if treated
groundwater is reinjected into the
subsurface

Sole source aquifer permit may be
required  if reinjection involves a
sole source aquifer

Prohibits any action that will
adversely affect the wild, scenic,
or recreation status of a river on
the National   Inventory

Prohibits jeopardizing any endan-
gered or threatened species or its
habitat

Prohibits modifying a body of
water without state approval if it
will affect wildlife resources

Prohibits actions inconsistent
with Federally approved state
coastal zone management programs
                       (continued)
                                     4-38

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                             TABLE 4-8 (continued)
        Source of Requirement
     Requirement or  Prohibition
Archaeological and Historic
Preservation Act
Atomic Energy Act; Low Level
Radioactive Waste Policy Act
Flood Disaster Protection Act;
National Flood Insurance Act;
Executive Order 11988
National Environmental Protection Act
Executive Order 11990
Prohibits actions resulting  in the
loss or destruction of significant
scientific, historical, or archae-
ological data

Prohibits the transport and
disposal of radioactive wastes
in certain areas under certain
conditions

Requires Federal agencies to
evaluate potential effects of
actions planned for floodplains

Requires flood  insurances in some
cases

May require the preparation of
environmental impact statements
and environmental assessments

Requires that activities in
wetlands include all practical
means of minimizing harm to the
environment
                    STATE AND LOCAL PERMITS AND REGULATIONS
Federal delegation of authority or
state and local requirements analogous
to Federal requirements
Requires permits, rulings, or
approvals for the treatment,
storage, transport, and disposal
of hazardous wastes; for the devel-
opment, operation, and closure of
waste management facilities; for
wastewater discharges to surface
waters (NPDES); for activities
likely to result in hazardous air
emissions; for activities involving
underground injection; for dredge
or fill, wetlands, and sensitive
resources; and for activities that
may require state or local  funding
or support
                        (continued)
                                      4-39

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                               TABLE 4-8  (continued)
            Source of Requirement
     Requirement or Prohibition
    Zoning  regulations,  building codes
    (fire,  water, electrical, sewer),
    water use regulations
    Public  safety regulations
Requires permits or the  preparation
of approved plans for  construction
or demolition activities, erosion
and dust control, right-of-way,
easements, well  installation, and
water  use and discharge

Generally requires advanced plan-
ning and coordination  with local
police, fire departments,
hospitals, and rescue  squads
to coordinate  activities  with site owners and governmental  agencies (e.g.,

EPA, USGS, COE,  and  state environmental agencies).


     Safeguarding  the  health and safety of both  the  personnel installing the

plume management technologies and the people living  near the site is a primary

factor in evaluating alternatives.  In addition  to the safety hazards asso-

ciated with  any major  construction activity, construction at hazardous waste

sites involves other hazards, including potential fires and explosions, and

possible release of  chemicals from buried drums  or storage  tanks.  Personnel

working at hazardous waste sites and local residents can also be exposed to

numerous health  hazards.   These hazards can reach the worker through direct

dermal exposure, inhalation of toxic constituents, or indirect ingestion of

dusts from the site.  Direct dermal exposure can be  prevented by requiring

workers to wear  personal  protective gear when working in hot zones at the

site.  This  gear can also assist in preventing  inhalation of toxic

constituents,  if respirators or self contained  breathing apparatus (SCBA) are

used..  Indirect  ingestion of toxins can be prevented by using strict site

security to  prevent  public access, by prohibiting eating, drinking or smoking

in hazardous areas of  the site, and by requiring the workers to wash prior to

eating or smoking.
                                     4-40

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     Indirect ingestion can be a particular problem at sites where contami-
nated dusts are present.  If dusts are inhaled, the majority will be captured
in the upper respiratory tract so very little will  reach the lungs.   However,
the dust that enters the upper respiratory tract will  accumulate there until
the individual  coughs to dislodge it.  Most individuals  will  then swallow, and
the contaminated dust will  enter the digestive tract.   Site workers can be
protected from this hazard by using SCBA or respirators  with properly selected
filters.  Local inhabitants can be protected by controlling dust generation
and if necessary, by evacuation.

     In evaluating the health and safety aspects of a site restoration alter-
native, precautions for safeguarding site workers and  the public can increase
dramatically the time and resources required to implement the alternative.
Therefore, assessing both alternatives that minimize health and safety risks
and those that attempt to control risks is important.

     The cost assessment portion of the detailed analysis of alternatives is
intended to provide measures of both the total  costs and cost effectiveness
over time associated with each alternative under consideration.  The most
reliable method for comparing the costs of proposed options is to prepare
preliminary designs for each of the alternatives that  are being considered for
a site.  These designs can then be used to compile site specific cost
estimates.  These cost estimates generally have an accuracy of +50 to -30 per-
cent (EPA, et al., 1983).  Key cost items and the relative costs of the four
basic leachate migration control technologies are summarized in Table 4-9.

     The procedure recommended for conducting a cost assessment of remedial
action alternatives consists of four steps (EPA, et al., 1983):

     •  Estimate costs -- Determine capital and annual operating costs for
        remedial  alternatives.
     •  Standardize costs -- Calculate stream of payments and present worth
        for each remedial action alternative using estimated costs.
     •  Assess cost sensitivity -- Evaluate risks and  uncertainties in cost
        estimates.
                                     4-41

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                                                                         TABLE 4-9
                                   RELATIVE COSTS  AND KEY COST ITEMS  OF LEACHATE MIGRATION CONTROL TECHNOLOGIES
                      Cost
                    Criterion
                                                                        Leachate Migration  Control  Technologies
Groundwater Pumping     Subsurface  Drains
                        Low Permeability Barriers    In S1tu Treatment
I
-p.
                    CAPITAL COSTS

                      Relative cost
                      Key items
                    O&M COSTS

                      Relative cost




                      Key  items
Generally low
although groundwater
treatment, storage,
and disposal  can
have a major  Impact

t  Well Installation
   and materials

•  Pumps

•  Surface piping

•  Effluent storage
   and treatment
   facilities
High to very high
depending on treat-
ment requirements
Fairly high depending
on site size, depth
and ease of excava-
tion, and system
design

•  Drain excavation
   and Installation

•  Drain materials

•  Pumps and piping

•  Effluent storage
   and treatment
   facilities
High to very high
depending on treat-
ment requirements
t  Effluent treatment   •  Effluent  treatment

•  Pump operation
                                          •  System maintenance

                                          •  Monitoring
                                                                 •   System maintenance
                                                                    and  operations
Moderate to high depending
on site size, depth and
ease of excavation, and
system design
•  Wall excavation and
   Installation

•  Wall materials
Fairly low depending
on associated
technologies used
                        •  Monitoring

                        •  System maintenance
Highly variable
depending on site
size, treatment method
used, and associated
technologies required

•  Treatment agents

•  Delivery systems

•  Associated
   technologies
                          Monitoring
Highly variable
depending on associ-
ated technologies
used

•  Monitoring

•  System maintenance

•  System operation

-------
     •  Assess cost effectiveness — Judge the importance of the poential
        benefits for each alternative relative to its prospected costs.


Detailed descriptions of this procedure and a matrix based methodology for

assessing remedial action cost effectiveness are given  in Radian (1983)  and

EPA, et al., (1983).  Based on the cost effectiveness analysis, the best site

remediation alternative should be selected and developed in detail.  Table

4-10 presents a general summary of the advantages and limitations of the four

basic leachate migration control technologies.


     4.3  Design and Implementation of Alternatives


     Once the best (or best few) remedial action alternative(s) has been

selected, a conceptual design should be prepared.  The  conceptual design

should include:


     •  Engineering drawings showing present topography and proposed
        topographic changes; site boundaries and property lines; locations of
        buildings, waterways, and utility lines, and other surface features;
        locations of sewer lines, pipelines, and other  subsurface features;
        and locations of remediation systems (such as wells) to be installed

     •  Estimated dimensions of subsurface drains or barriers, number of wells
        or other specific size related data

     •  Lists of required auxiliary measures

     •  Estimations of equipment and materials needs

     •  Estimated implementation periods and milestones

     •  Other factors such as requirements for worker safety and public
        protection, waste removal, transport and disposal (if necessary) and
        potential for adverse environmental impacts

     •  Budget cost estimates.


During preparation of these designs, additional factors or considerations may

be identified.   These should also be incorporated into the conceptual  design

document.
                                    4-43

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                                                    TABLE  4-10
                      SUMMARY OF THE  FOUR BASIC  LEACHATE  MIGRATION CONTROL  TECHNOLOGIES
Criteria
Groundwater Pumping     Subsurface  Drains
                        Low Permeability Barriers    In Situ Treatment
Performance
history
Effectiveness


Durability



Flexibility

Sensitivity

Reliance on
companions
measures
Applied successfully
at both hazardous and
nonhazardous  sites;
poor system operation
1s the chief  cause
of performance
problems
Generally good


Excellent with
occasional  main-
tenance

Very good

Good

Usually requires
leachate treatment
Applied successfully
at both hazardous and
nonhazardous sites;
system clogging is the
chief cause of per-
formance problems
Generally good


Dependent on leachate
and groundwater
chemistry

Very good

Good

Usually requires
leachate treatment
Applied successfully
at both hazardous and
nonhazardous sites;
wall degradation
caused by chemical and
hydrologlc conditions
Is the chief cause of
performance problems
Generally good
Dependent on leachate and
groundwater chemistry
Limited

Very good

Usually requires site
capping
Limited number of
applications at
hazardous sites and
no applications at
nonhazardous sites;
effectiveness of the
delivery system is
the chief cause of
performance problems

Variable depending on
site conditions

Not applicable
Usually very limited

Limited

Usually requires
source removal

           (continued)

-------
                                                                TABLE 4-10 (continued)
                 Criteria
                      Groundwater  Pumping    Subsurface  Drains
                                               Low Permeability  Barriers     In Situ Treatment
i
-P»
tn
                  Ease  of
                  installation
                 Ease  of
                 construction
Time to
implementation
                 Ease  of  operation

                 Ease  of  repair

                 Safety requirements
Very good




Very good




Relatively short




Fairly complex

Fairly simple

Minimal relative to
other technologies
                                             Variable  depending on
                                             shoring,  dewatering,
                                             and excavation
                                             requirements

                                             Good;  some  special-
                                             ized equipment may
                                             be required
Moderate to short




Relatively simple

Fairly complex

Very stringent
because of the need
to control dust,
leachate, and ground-
water during
construction
                        Variable depending on
                        topography  and formation
                        permeability
                        Generally good; some
                        specialized equipment may
                        be required
Moderate to short




Very simple

Fairly complex

Fairly stringent because
of the need to control
dust and leachate during
construction
                             Variable depending on
                             treatment scheme and
                             the delivery system
Requires contractor
with specialized
experience, equipment,
and materials

Fairly long to system
operation but short to
completion of
treatment

Complex

Complex to simple

Very stringent
depending on the
treatment scheme and
the delivery system


           (continued)

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                                               TABLE  4-10 (continued)
Criteria
Groundwater  Pumping     Subsurface  Drains
                        Low Permeability Barriers    In Situ Treatment
Capital costs
O&M costs
General comments
Relatively low;  high
If on site treatment
is needed
Relatively high;
very high 1f on site
treatment 1s needed
Relatively high
Relatively high;  very
high if leachate
treatment Is  needed

t  Can be designed
   for nearly any
   hydrogeologic  con-
   dition and leachate
   type, although
   pumping systems
   tend to be less
   efficient  in low
   transmlsslvity
   aquifers and with
   viscous leachates
Relatively low to
very high if leachate
treatment Is needed

t  Especially useful    i
   in low transmls-
   slvlty aquifers and
   for collecting
   groundwater mounds
   beneath sites

   Use may be restricted
   by high flow rates,
   difficult excavation,
   and leachates that
   can clog drain
   components
Relatively low
   Slurry trenches can be
   used in both high and
   low transmissivity
   aquifers although slurry
   loss can be a problem in
   some cases; grouts can
   generally only be used
   in high permeability
   formations
Variable depending on
the treatment scheme
and the delivery
system

High to low depending
on system selected
   Treatment system
   selection and
   implementation is
   greatly influenced
   by groundwater and
   leachate chemistry.
   The success of the
   system will depend
   largely on these
   factors:  the
   effectiveness of
   the delivery
   systems, and the
   ability of the
   operator to adjust
   to changes in site
   conditions.
                                                                                                             (continued)

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                                                                TABLE 4-10 (continued)
                 Criteria
Groundwater Pumping    Subsurface Drains
                        Low Permeability Barriers    In Situ Treatment
                 General  comments
                 (continued)
i
-fi
—i
•  Pumping systems
   can be Installed
   rapidly and
   inexpensively by
   qualified local
   well  drillers,
   pump  installers,
   and general
   contractors

•  System design can
   be modified easily
   to accommodate
   changes in site
   conditions

•  Pumping systems
   are relatively
   simple to repair
   but difficult
   and expensive to
   operate, especially
   if on site leachate
   treatment is needed
•  Operation is
   generally simpler
   than for pumping
   systems, although
   maintenance and
   repair is more
   difficult

•  OSM costs can be
   very high if
   on site leachate
   treatment is needed
•  Circumferential walls,
   the most commonly used
   type of barrier; require
   site capping and effec-
   tive aquiclude key-in
   to be successful

•  The most significant
   limitation of barriers
   1s the ability of wall
   materials to withstand
   chemical attack by
   reactive leachates

•  Operation and main-
   tenance Is generally
   simple and relatively
   Inexpensive
•  Implementation
   generally requires
   using specialty
   firms as opposed to
   local contractors

•  No long term site
   presence required
   if leachate source
   is removed and
   treatment is
   effective

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     Engineering specifications generally provided  in the design  of  a
remediation alternative include detailed descriptions of material  requirements
and local availability, work practices, and product performance.   Other  items
described in these specifications include quality control and  quality
assurance procedures and equipment requirements.  Schedules  should also  be
provided which allow for segmenting the operations  so that convenient
stopping-points are identified in advance.  If the operation is set  up in this
manner, the difficulties associated with work stoppages, because  of  supply
shortages, strikes, funding problems or adverse weather conditions can be
minimized.  Phasing plans that allow maximum coordination between  contractors
working at the site also can reduce costs and speed construction.

     Once an acceptable leachate migration control plan is developed, site
remediation efforts can begin.   Details related to designing and  implementing
plume management systems are described in Chapters 5 through 8.
                                   4-48

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                                    CHAPTER  5
                               GROUNDWATER PUMPING

 5.1   Introduction

      This  section  describes  the theory,  applications, design considerations
 and  costs  associated with  groundwater pumping methods to contain and remove
 plumes  originating from  hazardous waste  disposal facilities.  Plume con-
 tainment is  defined here as  arresting the further spread of groundwater
 contamination  by altering  hydraulic  gradients.  Containment methods do not
 necessitate  stopping contamination  at the source.   Plume removal is defined as
 removing the contaminants  from the  groundwater system so that the aquifer is
 purged  of  harmful  constituents.  Both approaches emphasize the active
 diversion  and  removal of groundwater rather than the passive approach of
 installing hydraulic barriers.

      An associated  problem arises from utilizing groundwater pumping methods
 (or  subsurface drains) to control  plumes, that is, the treatment or disposal
 of the  removed contaminated groundwater.  Numerous treatment processes  (e.g.,
 carbon absorption)   are available to remove contaminants from the water.
 However, these techniques are beyond the scope of this document and will  not
 be discussed.  Injection of treated water back into the groundwater system
 will  however be discussed as it relates to altering groundwater gradients.

      Previous utilization of pumping technologies to manage plumes  has  shown
 that  these methods  are most effective at sites where underlying aquifers  have
 high  intergranular  hydraulic conductivities  (e.g.,  coarse grained sands)  and
with  contaminants that  move readily with the groundwater flow  (e.g.,  benzene).
 Pumping methods have also been utilized with some effectiveness at  sites  where
pollutant movement  is  occurring along fractured  or  jointed  bedrock.   However,
the fracture patterns  must  be traced in detail  to ensure proper well
piacement.
                                     5-1

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5.2  Well Theory

     The economic and effective withdrawal  of contaminated water from a
groundwater system is highly dependent on the proper design and construction
of a well.  In order to make proper design  decisions,  an  understanding of  the
principles of well hydraulics is needed.   Applications and extensions of these
theories permit solutions of problems  related to  flow  towards  wells  under  a
variety of situations.  This section provides some  of  the basic well  hydraulic
equations describing the relationships among  the  various  hydraulic character-
istics of aquifers and the response of aquifer systems to pumping wells.

     5.2.1  Darcy's Law

     Darcy's Law describes flow through a porous  medium and thus provides  the
foundation for all groundwater flow theory.   Common forms of Darcy's  law are:

                  Q = KIA = VAn
     where:
                  V = Kl/n
                  I = (hrh2)/L
     and the variables are defined  as:
                  Q = flow (ft3/day)
                  K = hydraulic conductivity  of the porous medium (ft/day)
                  I = hydraulic gradient  (dimensionless)
                                                       o
                  A = area normal to flow direction (ft )
                  V = velocity of groundwater flow  (ft/day)
                  n = effective porosity  (dimensionless)
                  h,-h? = water levels at two points along the  same
                          groundwater  flow  path (ft)
                  L = length of the flow  path between  h,  and h« (ft)

Darcy's Law is only valid when conditions of  laminar flow exist.
                                     5-2

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     Based on Darcy's Law, the hydraulic gradient varies directly with flow
velocity and indirectly with area.  This relationship can be used to explain
the formation of a cone of depression around a pumping well  (Figure 5-1).
When a well is pumped, the water level  in the vicinity of the well  is lowered
and the greatest depth of lowering occurs at the well.  Depth of lowering  or
drawdown is less at greater distances from the well  and at some point in the
aquifer lowering is nonexistent.  Because the water level is lowest at the
well, water moves from the aquifer into the well to replace  the withdrawn
water.  Gravity and water pressure (head) drive the water towards the well in
the direction of decreasing head.  As the flow converges towards the well
under an increased hydraulic gradient,  the velocity increases according to
Darcy's Law.  This process results in the typical  cone of depression
associated with pumped wells (Figure 5-2).

     The shape and size of the cone is  dependent upon the pumping rate,
pumping period (i.e., cycles), slope of the original  water table, hydraulic
barriers, aquifer characteristics, and  recharge zones.  Two  aquifer character-
istics that are important in determining the cone's  configuration are of
transmissivity (T) and coefficients of  storage (S).   Transmissivity indicates
the amount of water that can move through an aquifer. The coefficient of
storage indicates the amount of water which can be removed by pumping.
Transmissivity (T) is related to the hydraulic conductivity  (K)  of  an aquifer
by:

                  T = Km

where m is the saturated thickness of the aquifer.  The effects  of  trans-
missivity and storage on the shape of the cone of  depression is  illustrated in
Figure 5-3.  This illustration shows that drawdown is inversely  related to the
coefficients of storage and transmissivity.

     Values of transmissivity and storage are generally determined  for  an
aquifer by drilling  wells and conducting  pumping tests.   Once  these  values
                                     5-3

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                        FIGURE 5-1.
  DEVELOPMENT OF FLOW DISTRIBUTION ABOUT A
DISCHARGING WELL IN A FREE AQUIFER -  A FULLY
     PENETRATING AND 33-PERCENT OPEN  HOLE
           (BUREAU OF RECLAMATION, 1977)
Static  water  table
5-1a.  Initial stage in pumping a free aquifer Most water follows a path
      with a high vertical component from the water table to the
      screen
5-1b.  Intermediate stage in pumping a free aquifer Radial
      component of flow becomes more pronounced but contribution
      from drawdown cone in immediate vicinity of well is still
      important
                              Drawdown    _ •*• '
                               cone
 5-1c.   Approximate steady state stage in pumping a free aquifer.
       Profile of cone of depression is established Nearly all water
       originating near outer edge of  area of influence and stable
       primarily radial flow pattern established.
                       . — ~+ — Flow Lines

                       	 Equipotential Lines
                            5-4

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            FIGURE 5-2.
FORMATION OF CONE OF DEPRESSION
        FOR A PUMPED WELL
                           Cone of Depression
                 5-5

-------
                            FIGURE 5-3.
   EFFECT OF STORAGE AND TRANSMISSIVITY ON THE SHAPE
OF THE CONE OF DEPRESSION (BUREAU OF RECLAMATION, 1977)
         S, = 50S2
         All Other Factors Constant
         Static Water Level
   I 40'
   •
     60
     80
                                \ »
          1200     800
                          400

                                         400
 8QO     1200
                        Radial Distance from Well Feet

       Figure 5-3a.   Influence of storativity on drawdown in a well.
       T, = 3T2
       All Other Factors Constant

 Static Piezometric Surface
Not Coincident, but Too
Close to Be Separated at
Scale of Drawing
                             VY
                                <
                                \
       Figure 5-3b.   Influence of transmissivity on drawdown in a well.
                                 5-6

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have been obtained, predictions can be made which are critical  in designing
and constructing effective pumping systems for plume management.  Some of the
predictions which can be made are (Johnson Division, UOP  Inc.,  1975):

     •  Specific capacity of wells with differing diameters
     •  Drawdown of an aquifer at varying distances from  the well
     •  Drawdowns with varying pumping rates and times.

In plume management the radius of influence (i.e., the extent of the cone of
depression) and the resulting change to the groundwater velocity will be the
most important unknowns.  By controlling the radius of influence, the flow of
contaminants in the groundwater system can be controlled.

     5.2.2  Equilibrium Well Formula

     C. Theim and P. Forchheimer independently derived equations for
equilibrium (steady state) radial flow to wells under confined  and unconfined
aquifer conditions.  Both equations assume recharge at the edge of the cone so
that the cones dimensions remain constant as long as pumping rates remain
constant.

     The basic formula for an unconfined aquifer (Figure 5-4) is:

                H2-h^ = (QArK) In (RO/PW)
     where:
                H = saturated thickness of the aquifer (ft)
                hw = height of water in the well (ft)
                Q = pumping rate (ft /day)
                K = hydraulic conductivity (ft/day)
                RQ = radius of influence of the cone of depression (ft)
                r  = radius of the well (ft).
                                     5-7

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                                 FIGURE 5-4.
                         UNCONFINED AQUIFER FLOW
                          (DAVIS AND DeWIEST, 1966)
                                         Q = Constant
                                = (Q/nK) In (R0/rJ
The height (h) of the water table at  any distance r  from  the  well  where r is
greater than 1.5H, can be estimated by:


                h = (H2-(Q/77K)ln  (R0/rw))0'5


For solutions to h where r  is  less than 1.5H,  the empirical  relationships
developed by Boreli can be  applied.   Drawdown  (H-h)  close to  a water table
well can be estimated for ratios  of r/H between  0.3  and 1.5  by (Powers, 1981)
                H-h = Q(0.13  In  (RQ/r))(ln  10(RQ/H))/TrKH
                                      5-8

-------
and for ratios  less  than 0.3 by:
                 H-h  =  Q(0.13 ln(RQ/r) -0.0123  ln(RQ/10r) )(ln (10R0/H))/7rKH

     Equations  for drawndown resulting from  a  well  pumping in a confined
aquifer are  simpler  than those for an unconfined  aquifer.  Drawdown  (H-h)  at
any distance r  from  the well in a confined  aquifer  (Figure 5-5) is given  by:
                 H-h  = (Q/277T)ln (RQ/rw)
Plots of H-h versus  r' on semilogarithmic  paper  can be developed for  both  the
unconfined  and  confined conditions, so  that  predictions of R  and the  wetted
screen length can  be made.   Figure 5-6  shows  two  such plots.
                                 FIGURE 5-5.
                          CONFINED AQUIFER FLOW
                          (DAVIS AND DeWIEST, 1966)
                                       Q = Constant
                                                            Depression
                                                             Cone
             Confined .
              Aquifer
                      Bedrock
                             H-h =
                                      In
                                      5-9

-------
                               FIGURE 5-6.
               PLOTS OF H-h VERSUS r FOR UNCONFINED
               AND CONFINED AQUIFERS (POWERS. 1981)
        1000
                                   rift)
                                               = 1.5H
     Figure 5-6a. Equilibrium plot for a water table aquifer.  Q - 500 gpm.
     R0  = 1000 ft. K = 300 gpd/ft.2 H = 100 ft. rw =  0.5 ft.
_ 1-°
§2.0
 I 3,
a: 4,
I5
  6'
  8
  9.
  10
0
0
,0
0
.0
,0
0
.0
 1.0
                    10
100
1000
10,000
       Figure 5-6b. Equilibrium plot for a confined aquifer. Q  = 500 gpm.
       K =  300 gpd/ft.2  m = 100 ft. RQ = 2000 ft. rw = 0.5 ft.
                                 5-10

-------
     The equilibrium equations presented here are based on the simplifying
assumptions presented in Table 5-1.  Utilization of these equations  appears to
be severely limited by the simplifying assumptions, but in practice, the
assumptions customarily do not limit the equation's use.

     5.2.3  Non-Equil ibrium Well Formula

     Non-equilibrium well formulas take into account the effects of  varying
rates of pumping on well yield.  Using these equations, drawdown at  a
specified distance from a well can be predicted for any time after pumping has
started assuming the coefficients of storage and transmissivity for  a confined
aquifer and specific yield for an unconfined aquifer are known.  These values
are usually determined by pumping tests.

The Theis Equation describes non-equilibrium flow in confined aquifers.
This formula is:

                H-h = (Q/47rT)W(M)
     where  is given as:
                M= r2S/4Tt
     and:
                H-h = drawdown (ft)
                                    o
                Q  = pumping rate (ft /day)
                                                     P
                T  = coefficient of transmissivity (ft /day)
                     = well function of n (dimensionless)
                r = distance from well center to point where drawdown is
                measured (ft)
                S = coefficient of storage (dimensionless)
                t = time elapsed since pumping started (day).
                                     5-11

-------
        TABLE 5-1.  SIMPLIFYING ASSUMPTIONS FOR STEADY STATE EQUATIONS
                     (Johnson Division, UOP Inc., 1975)
Simplifying Assumption
            Practice
The water-bearing materials are
of uniform hyraulic conductivity
within the radius of influence
of the well.
The aquifer is not stratified.
For a water-table aquifer, the
saturated thickness is constant
before pumping starts; for an
artesian aquifer, the aquifer
thickness is constant.
The pumping well is 100 per cent
efficient.
Neither the water table nor
piezometric surface has any
slope; both are horizontal
surfaces.
Uniform hydraulic conductivity is seldom
found in a real aquifer, but the average
hydraulic conductivity as determined from
aquifer pumping tests has proved to be
reliable for predicting well performance.

For artesian wells where most of the
aquifer thickness is penetrated and
screened, the assumption of no stratifi-
cation is not an important limitation.  For
water-table aquifers, where drawdown reduces
the saturated thickness considerably, the
situation can be handled when the stratifi-
cation is known and taken into account  in
applying the formula.

The assumption of constant thickness is not
a serious limitation because variations in
aquifer thickness within the cone of depres-
sion in most real situations is relatively
small.  Where changes in thickness are
important, they can be taken into account.

The assumption that the well is 100 per cent
efficient can cause the calculated well
yield to be seriously in error where the
real well may be inefficient as the result
of  improper design or construction.

The assumption that the water table or  the
piezometric surface is horizontal before
pumping is never fulfilled.  The slope  or
hydraulic gradient, however, is usually very
flat and the effect on calculations of  well
yield is negligible in most cases.  The
slope of the water table or the piezometric
surface does cause distortion of the cone of
depression, making it more elliptical than
circular.

                              (Continued)
                                     5-12

-------
                            TABLE  5-1.   (Continued;
Simplifying Assumption
                                Practice
Laminar flow exists throughout
the aquifer and within the
radius of influence of the well
The pumping well penetrates to
the bottom of the aquifer.

The cone of depression has
reached equilibrium so that
both drawdown and the radius of
influence of the well do not
change with continued time of
pumping at a given rate.
                   Flow  at  all places  in  the  aquifer  is
                   considered  to  be  laminar.   Some  invest-
                   igators  have theorized  that  turbulent  flow
                   near  a well could result  in  relatively high
                   head  losses.   Actual  laboratory  and field
                   tests, however, shows  that  some  departure
                   from  laminar flow near  a well  causes
                   additional  head loss  of only minor
                   proportions.

                   Other equations given  later  describe
                   partially penetrating  wells.

                   Other equations given  later  describe
                    non-steady state pumping.
     For a calculated value of ^, a value of W(^) can be obtained from Table

5-2.  As 1/jU becomes large, the  value of W(M) becomes asymptotic and  nearly

constant.  Simplifying assumptions for the Theis formula are essentially the

same as for equilibrium formula  except the dimensions of the cone of

depression need not have reached equilibrium.


     A well pumping an unconfined aquifer under non-equilibrium conditions
does not follow the Theis equation because water flowing to the well  is
derived from storage release and specific yield.  A solution developed by

Numen for determining drawdown in unconfined aquifers that takes into account
the dual release mechanism is:
H-h = (Q/477T)W(MA,MB,r)

   ,T)  are defined as:

   = r S/4Tt  (for early drawdown)
     where W(M.,Mg,r) are defined as:
                                     5-13

-------
                 TABLE  5-2.   VALUES OF W(M) FOR VARIOUS VALUES OF M  (Ferris et  al.  as  cited by Lohman, 1972)

-------
                     9
                  = r S//4Tt (for later drawdown
               r = r2Kz/H2Kh
     and the variables not previously defined are:
               S  = specific yield
               K,  - horizontal hydraulic conductivity
               K  = vertical hydraulic conductivity.
     Once M« or Mg and  have been calculated, the function W(MA» T ) or
can be derived from Tables 5-3 and 5-4.   Type M/\ values are used for early
drawdown times when waters are derived from storage and type MD values are
used for later drawdown when gravity drainage (specific yield) is predominant
Simplifying assumptions for the formulas are similar to those for the Theis
equations.

     5.2.4  Semiconfined Aquifers

     Generally confined aquifers are not truly confined.  They receive
vertical recharge through the semipervious layers above or below  (when the
hydraulic gradient is favorable).  Two types of semipervious layers exist;
leaky confining layers without storage and leaky confining layers with
storage.  Figure 5-7 depicts a semiconfined aquifer.

     The Hantush-Jacob formula can be applied to leaky confining  layers
without storage.  The basic equation is given by:

                 H-h = (2.3Q/477T)W(/i,r/B)
     where:
                  M= r2S/4Tt

                 r/B = r(Tm'/K')°-5
     and the new variables are defined as:
                 m1 = thickness of the leaky confining layer
                 K' = hydraulic conductivity of the leaky confining layer.
                                     5-15

-------
en
                       TABLE 5-3.  VALUES  OF THE FUNCTION W(//A,T)  FOR  WATER-TABLE  AQUIFERS  (Fetter, 1980)








                        r= 0.001     r= 0.01      r= 0.06     r= 0.2        r= 0.6      r =1.0       r=2.0        T=4.0       T=6.0
4.0 x IO"1
8.0 x 10"1
1.4 x 10°
2.4 x 10°
4.0 x 10°
8.0 x 10°
1.4 x IO1
2.4 x IO1
4.0 x IO1
8.0 x IO1
i)
1.4 x 10^
y
2.4 x 10^
4.0 x 102
8.0 x IO2
1.4 x IO3
2.4 x IO3
4.0 x IO3
8.0 x IO3
1.4 x IO4
2.48
1.45
3.58
6.62
1.02
1.57
2.05
2.52
2.97
3.56

4.01

4.42
4.77
5.16
5.40
5.54
5.59
5.62
5.62
x
x
X
X
X
X
X
X
X
X

X

X
X
X
X
X
X
X
X
lO"2
io-1
io-1
ID'1
10°
10°
10°
10°
10°
10°
n
10°
n
10°
10°
10°
10°
10°
10°
10°
10°
2.
1.
3.
6.
9.
1.
1.
2.
2.
3.

3.

3.
3.
3.
3.



3.
41
40
45
33
63
46
88
27
61
00

23

37
43
45
46



46
x
x
X
X
X
X
X
X
X
X

X

X
X
X
X



X
io-2
io-1
io-1
io-1
io-1
10°
10°
10°
10°
10°
A
10°
A
10°
10°
10°
10°



10°
2.
1.
3.
5.
8.
1.
1.
1.
1.
1.

1.

1.






1.
30 x
31 x
18 x
70 x
49 x
23 x
51 x
73 x
85 x
92 x

93 x

94 x






94 x
io-2
io-1
io-1
io-1
ID'1
10°
10°
10°
10°
10°
A
10°
A
10°






10°
2.14 x 10"2 1.88x 10"2 1.70 x 10"2 1.38 x 10"2 9.33 x 10"3 6.39 x 10"3
1.19 x 10"1 9.88 x 10"2 8.49 x 10"2 6.03 x 10'2 3.17 x 10"2 1.74 x 10"2
2.79 x 10"1 2.17 x 10"1 1.75 x 10"1 1.07 x 10'1 4.45 x 10"2 2.10 x 10"2
4.83 x 10"1 3.43 x 10"1 2.56 x 10"1 1.33 x 10"1 4.76 x 10"2 2.14 x 10"2
6.88 x 10"1 4.38 x 10"1 3.00 x 10"1 1.40 x 10"1 4.78 x 10"2 2.15 x 10"2
9.18 x 10"1 4.97 x 10'1 3.17 x 10"1 1.41 x 10"1
1.03 x 10° 5.07 x 10"1
1.07 x 10°
1.08 x 10°











1.08 x 10° 5.07 x 10"1 3.17 x 10'1 1.41 x 10"1 4.78 x 10"2 2.15 x 10'2

-------
                            TABLE 5-4.  VALUES OF THE FUNCTION  W(Mg,r)  FOR WATER-TABLE AQUIFERS
01
I
I/UB T» o.ooi
4.0 x
8.0 x
1.4 x
2.4 x
4.0 x
8.0 x
1.4 x
2.4 x
4.0 x
8.0 x
1.4 x
2.4 x
4.0 x
8.0 x
1.4 x
2.4 x
4.0 x
8.0 x
1.4 x
2.4 x
4.0 x
8.0 x
1.4 x
10"4 5.62 x 10°
10-"
.3
ID'3
io-3
io-3
io-2
io-2
io-2
io-2
io-1
io-1
io-1
10"1 5.62 x 10°
10° 5.63 x 10°
10° 5.63 x 10°
10° 5.63 x 10°
10° 5.64 x 10°
IO1 5.65 x 10°
IO1 5.67 x 10°
IO1 5.70 x 10°
IO1 5.76 x 10°
IO2 5.85 x 10°
T' 0.001 T« 0.
3.46 x 10° 1.94 x









1.94 x
1.95 X
1.96 x
3.46 x 10° 1.98 x
3.47 x 10° 2.01 x
3.49 x 10° 2.06 x
3.51 x 10° 2.13 x
3.56 x 10° 2.31 x
3.63 x 10° 2.55 x
3.74 x 10° 2.86 x
3.90 x 10° 3.24 x
4.22 x 10° 3.85 x
4.58 x 10° 4.38 x
.06
10°









10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
T=0,
1.09 x








1.09 x
1.10 x
1.11 x
1.13 x
1.18 x
1.24 x
1.35 x
1.50 x
1.85 x
2.23 x
2.68 x
3.15 x
3.82 x
4.37 x
,2
10°








10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
10°
r= 0.6
5.08 x



5.08 x
5.09 x
5.10 x
5.12 x
5.16 x
5.24 x
5.37 x
5.57 x
5.89 x
6.67 x
7.80 x
9.54 x
1.20 x
1.68 x
2.15 x
2.65 x
3.14 x
3.82 x
4.37 x
io-1



io-1
ID"1
io-1
io-1
io-1
io-1
io-1
ID'1
ID'1
io-1
io-1
io-1
10°
10°
10°
10°
10°
10°
10°
T= 1.0
3.18 x 10'1



3.18 x 10"1
3.19 x 10"1
3.21 x 10'1
3.23 x 10"1
3.27 x 10"1
3.37 x 10"1
3.50 x 10"1
3.74 x 10"1
4.12 x 10"1
5.06 x 10'1
6.42 x 10"1
8.50 x 10'1
1.13 x 10°
1.65 x 10°
2.14 x 10°
2.65 x 10°
3.14 x 10°
3.82 x 10°
4.37 x 10°
T= 2.0
1.42 x 10'1



1.42 x 10"1
1.43 x 10"1
1.45 x 10"1
1.47 x 10"1
1.52 x 10'1
1.62 x 10"1
1.78 x 10'1
2.05 x 10"1
2.48 x 10"1
3.57 x 10"1
5.17 x 10"1
7.63 x 10"1
1.08 x 10°
1.63 x 10°
2.14 x 10°
2.64 x 10°
3.14 x 10°
3.82 x 10°
4.37 x 10°
T= 4.0
4.79 x 10"2
4.80 x 10-2
4.81 x 10'2
4.84 x 10'2
4.78 x 10"2
4.96 x 10"2
5.09 x 10"2
5.32 x 10"2
5.68 x 10"2
6.61 x 10~2
8.06 x 10'2
1.06 x 10"1
1.49 x 10'1
2.66 x 10"1
4.45 x 10"1
7.18 x 10'1
1.06 x 10°
1.63 x 10°
2.14 x 10°
2.64 x 10°
3.14 x 10°
3.82 x 10°
4.37 x 10°
T = 6.0
2.15 x 10'2
2.16 x 10'2
2.17 x 10'2
2.19 x 10'2
2.21 x 10'2
2.28 x 10'2
2.39 x 10"2
2.57 x 10"2
2.86 x 10'2
3.62 x 10"2
4.86 x 10"2
7.14 x 10"2
1.13 x 10'1
2.31 x 10"1
4.19 x 10'1
7.03 x 10"1
1.05 x 10°
1.63 x 10°
2.14 x 10°
2.64 x 10°
3.14 x 10°
3.82 x 10°
4.37 x 10°
                                                                                                        (Continued)

-------
                                                TABLE  5-4.   (Continued)
1/fig T= 0.001
2.4 x 102
4.0 x 102
8.0 x 102
en 1.4 x 103
oo 2.4 x 103
4.0 x 103
8.0 x 103
1.4 x 104
2.4 x 104
4.0 x 104
5.99
6.16
6.47
6.67
7.21
7.72
8.41
8.97
9.51
1.94
x
x
x
x
X
X
X
X
X
X
10°
10°
10°
10°
10°
10°
10°
10°
10°
101
T =
5.00
5.46
6.11
6.67
7.21
7.72
8.41
8.97
9.51
1.94
0.001
x 10°
x 10°
xlO°
x 10°
x 10°
x!0°
x!0°
x 10°
x 10°
x 101
r=
4.91
5.42
6.11
6.67
7.21
7.72
8.41
8.97
9.51
1.94
0.06
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 101
T =
4.91
5.42
6.11
6.67
7.21
7.72
8.41
8.97
9.51
1.94
=0.
x
x
X
X
X
X
X
X
X
X
.2
10°
10°
10°
10°
10°
10°
10°
10°
10°
101
T -
4.91
5.42
6.11
6.67
7.21
7.72
8.41
8.97
9.51
1.94
= 0.6
x 10°
x 10°
x 10°
x 10°
x 10°
xlO°
x 10°
x 10°
x 10°
x 101
r= 1.0
4.91
5.42
6.11
6.67
7.21
7.72
8.41
8.97
9.51
1.94
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 101
T =
4.91
5.42
6.11
6.67
7.21
7.72
8.41
8.97
9.51
1.94
= 2.0
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 10°
x 101
T = 4.0
4.91 x
5.42 x
6.11 x
6.67 x
7.21 x
7.72 x
8.41 x
8.97 x
9.51 x
1.94 x
10°
10°
10°
10°
10°
10°
10°
10°
10°
101
T =
4.91
5.42
6.11
6.67
7.21
7.72
8.41
8.97
9.51
1.94
= 6.0
x 10°
x 10°
x 10°
x 10°
x 10°
xlO°
xlO°
x 10°
x 10°
x 101
SOURCE:  Adapted from  S. P. Neuman, Water Resources Research, 11(1975):329-42 as cited by Fetter, 1980.

-------
                                      FIGURE 5-7.
                               SEMICONFINED AQUIFER
                              (DAVIS AND DeWIEST, 1966}
                                            Ground Surface
                                                                            t .  . ....    ,.
                                                                             Initial Watertable
      V
        *

Sealed Well
                                    Ponded Water
                       . h = Piezometnc Head in Main Aquifer
 X\X\X\N
                                                                       Semiconfining
                                                                         Stratum
    Well
   Screen
•/.vV-AylvftvtMain Aquifer F

                                                           Bedrock
                                 Leaky Confining Bed Without Storage

                                    H-h = (2.3Q/4*77 Wfa,r/B)

                                 Leaky Confining Bed with Storage

                                     H-h =(Q/4nT) Hlp.B)
  Values  of W(M,r/B) for  calculated values  of Mand  r/B  are  given  in Table  5-5.
  Underlying assumptions  for these equations are  similar  to the Theis formula
  with the addition of  (Fetter,  1980):


       •   confining bed  leakage  is vertical  and proportional  to drawdown
       •   hydraulic head  in the  leaking  layer is  constant
       •   storage  in the  confining bed  is negligible
                                           5-19

-------
                        TABLE  5-5.   VALUES  OF  FUNCTIONS W(M,r/B)  AND W(MA,  r/B)  FOR  VARIOUS VALUES  OF^ORM
CJl
 I
ro
o
U or u .
0.000001
0.000006
0.00001
0.00005
0.0001
0. 0005
0.001
0.005
0.01
0.05
0.1
0.5
1.0
5.0

0.01
9.4425
9.4413
9.4176
8.8827
8.3983
6.9750
6. 3069
4.7212
4.0356
2.4675
1.8227
0.5598
0.2194
0.0011

0.015
B.6319
"
8.6313
8.4533
8.1414
6.9152
6.3765
4.7152
4.0326
2.4670
1.8225
0.5597
0.2194
0.0011

0.03
7.2471
"
"
7.2450
7.2122
6.6219
6.1202
4.6829
4.0167
2.4642
1.8213
0. 5596
0.2193
0.0011

0.05
6.2285
•
"
"
6.2282
6.0821
5.7965
4.6084
3.9795
2.4576
1.8184
0. 5594
0.2193
0.0011

0.075
5.4228
•
"
•
11
5.4062
5.3078
4.4713
3.9091
2.4448
1.8128
0. 5588
0.2191
0.0011

0.10
4.8541
"
"
"
"
4.8530
4.8292
4.2960
3.8150
2.4271
1.8050
0.5581
0.2190
0.0011

0.15
4.0601
"
"
"
"
"
4.0595
3.8821
3.5725
2.3776
1.7829
0.5561
0.2186
0.0011

0.2
3.5054
"
"
"
11
"

3.4567
3.2875
2.3110
1.7527
O.S532
0.2179
0.0011

0.3
2.7449
"
"
"
"
"

2. 7428
2.7104
1.9283
1.6704
0.5453
0.2161
0.0011
r/B
0.4 0.5
2.2291 1.8488
" "
" "
«
"
"

2.2290
2.2253 1.8486
1.7075 1.4927
1.5644 1.4422
0.5344 0.5206
0.2135 0.2103
0.0011 0,0011

0.6
1.5550
"
"
"
"
"

"
"
1.2995
1.3115
0.5044
0.2065
0.0011

0.7
1.3210
"
"
"
"
"
"
"
"
1.2995
1.1791
0.4860
0. 2020
0.0011

0.8
1.1307
"
"

"
"
"
"
"
1.1210
1.0505
0.4658
0.1970
0.0011

0.9
0.9735
"
"
"
"
"
"
"
"
0.9700
0.9297
0.4440
0.1914
0.0011

1.8 1.5 2.0 2.5
0.8420 0.4276 0.2278 0.1247
" " " "
" " " "
" " " "
" " " "
" "
" " "
" " "
"
0.8409
0.8190 0.4271
0.4210 0.3007 0.1944 0.1174
0.1855 0.1509 0.1139 0.0803
0.0011 0.0010 0.0010 0.0009
             SOURCE-  After M.  S. Hantush, "Analysis of Data from Pumping Tests in Leaky Aquifers," Transactions, American Geophysical Union, 37 (1956): 702-14 as cited by Fetter, 1980.

-------
     •  t >(30r2 S/T)(l-(10rw/m)2)
     •  r/B<0.1.
         W

     If significant storage occurs  in the confining  layer,  then  flow  is
derived from storage in the layer during  initial time  periods.   As  pumping
continues drawdown will occur  in the unpumped  aquifer.   If  the confining  layer
has finite storage, drawdown does not occur  in the unpumped  layer,  and -time
intervals are short (S'm'/lOK1), then the drawndown  equation  for leaky
aquifers with storage becomes:

                H-h = (Q/47rT)H(M,P)
     where:
                M= r2S/4Tt

                 P= (r/4B)(S'/S)0'5

                B = (Tm'/K1)0'5

Values at H(^,p) can be obtained from Table  5-6 after  /LI and [3 are calculated.

     5.2.5  Partially Penetrating Wells

     The equations presented previously assume that  the  well  penetrates the
entire thickness of the aquifer.  In many cases, wells do not penetrate the
total thickness such that true radial flow to the well does not  exist.
Figure 5-8 shows two examples of flow to partially penetrating wells  in
confined aquifers.  These figures show that  water moving from the lower part
of an aquifer must move along curved lines to reach  the  well.  The  result is
increased flow path lengths and increased head loss  at the  well.  Therefore,
for a given yield drawdown will be greater in a partially penetrating well
than in a fully penetrating well in the same aquifer.

     Formulas for partial penetration are difficult  to solve  under  simple
conditions (i.e., homogeneous isotropic aquifers) and  extremely  difficult to
solve for complex conditions (i.e., stratified aquifers).  Kozeny developed an
                                     5-21

-------
                                                              TABLE  5-6.   VALUES OF  THE  FUNCTION
ro
ro

0.000001
0.000005
0.00001
0.00005
0.0001
0.0005
0.001
0.005
0.01
0.05
0.1
0.5
1.0
5.0

0.001
11.9842
10.8958
10.3739
9.0422
8.4258
6.9273
6.2624
4.6951
4.0163
2.4590
1.8172
0.5584
0.2189
0.00115

0.005
10.5908
9.7174
9.3203
8.3171
7.8386
6.6024
6.0193
4.5786
3.9334
2.4243
1.7949
0.5530
0.2169
0.00114

0.01
9.9259
9.0866
8.7142
7.8031
7.3803
6.2934
5.7727
4.4474
3.8374
2.3826
1.7677
0.5463
0.2144
0.00112

0.05 -
8.3395
7.5284
7.1771
6.3523
5.9906
5.1223
4.7290
3.7415
3.2752
2.1007
1.5768
0.4969
0.1961
0.00104

0.10
7.6497
6.8427
6.4944
5.6821
5.3297
4.4996
4.1337
3. 2483
2.8443
1.8401
1.3893
0.4436
0.1758
0.00093
P
0.20
6.9590
6.1548
5.8085
5.0045
4.6581
3.8527
3.5045
2.6891
2.3325
1.4872
1.1207
0.3591
0.1427
0.00076

0.50
6.0463
5.2459
4.9024
4.1090
3.7700
2.9933
2.6650
1.9250
1.6193
0.9540
0.6947
0.2083
0.0812
0.00042

1.0
5.3575
4.5617
4.2212
3.4394
3.1082
2.3601
2.0506
1.3767
1.1122
0.5812
0.3970
0.1006
0.0365
0.00017

2.0
4.6721
3.8836
3.5481
2.7848
2.4658
1.7604
1.4776
0.8915
0.6775
0.2923
0.1789
0.0325
0.00993
0.00003

5.0
3.7756
3.0055
2.6822
1.9622
1.6704
1.0564
0.8271
0.4001
0.2670
0.0755
0.0359
0.00288
0.00055


10.0
3.1110
2.3661
2.0590
1.3943
1.1359
0.6252
0.4513
0.1677
0.0955
0.0160
0.00552
0.00015
0.00002


20.0
2.4671
1.7633
1.4816
0.8994
0.6878
0.3089
0.1976
0.0493
0.0221
0.00164
0.00034



                    SOURCE:   Condensed from M.  S.  Hanfush, "Modification of  the Theory of Leaky  Aquifers,:  Journal of Geophysical  Research, 65 (1960):   3713-25 as
                             cited  by Fetter, 1980.

-------
                            FIGURE 5-8.
           FLOW TO PARTIALLY PENETRATING WELLS
               (BUREAU OF RECLAMATION, 1977)
             Figure 5-8a. Just Penetrating Top of Aquifer

 Static Piezometric Surface
  /  //////////////  /  77   7  7  7 7  777  7
            Lower Confining Bed
                       — — — - Flow Lines
                       	Equipotential Lines
               Figure 5-8b. Penetrating 50% of Aquifer

Static Piezometric Surface
       Lower Confining Bed
                       — — • — Flow Lines
                           — Equipotential Lines
                                5-23

-------
equation for partially penetrating wells in confined aquifers that are nearly
homogeneous.  His equation can be written as (Johnson Division, UOP  Inc.,
1975):
(Q/sn)/(Q/s)  =
    p
                                       w
                                        /2ml)°-5cos(7rl/2)
     where:
                Q/sn = specific capacity of a partially penetrating well
                   P   (ft/day)
                Q/s = specific capacity of a fully penetrating well (ft/day)
                r  = well radius (ft)
                m = aquifer thickness (ft)
                1 = well screen length as a fraction of aquifer thickness
                    (dimensionless)
Kozney's formula is valid when the aquifer thickness is large, the percent
penetration is small, and the well radius is small.

     A major problem associated with the use of partially penetrating wells
for the containment of plumes is that if the well does not fully penetrate the
aquifer and pumping is not sufficient, contaminants can flow under the well
(Figure 5-9).  Partially penetrating wells may be most useful  in collecting
floating contaminants.

     5.2.6  Cumulative Drawdown

     The formulas presented thus far have been for single wells pumping  an
aquifer.  When more than one well is pumping the same aquifer, their cones of
depression will possibly intersect.  For containing and removing plumes  from
an aquifer, this principle is important because it allows for  the determ-
ination of well spacing intervals, pumping rates, and pumping  times.
Theoretically, if the cones of depression (radii of influence) intersect each
other, flow will not occur between the wells and any contaminants in the
groundwater system will be extracted.  This theory is probably valid for
                                    5-24

-------
                             FIGURE 5-9.
              FLOW IN CONFINED AQUIFER WITH PARTIALLY
                         PENETRATING WELL
       Piezometric
        Surface
    V/////////////////////////////////I
V///////////////////7
aquifers with low natural  flow velocities, however, for aquifers  with  high
natural  flow velocities  overlapping cones may not be sufficient to  capture the
plume (Keely and  Tsang,  1983).

     For confined aquifers with several wells tapping the same system, the
composite pumping cone can be calculated by summing the individual  drawdowns
caused by each well  (Figure 5-10).  This can be accomplished  by graphical
superposition (i.e.,  adding the drawdown curves,  H-h, for each well) or by
                                   5-25

-------
                                    FIGURE 5-10.
                   COMPOSITE DRAWDOWN IN A CONFINED AQUIFER
                   (FREEZE AND CHERRY, 1979 AS CITED BY EPA, 1982a)
                   -- Drad*kj«Yn due to Qj  - - - Drawdown due to Q,
                                                    Total Drawdown
calculation.  For a  system  of  n  wells  pumping at any rate, the drawdown  at  a
radius r from each well  is  given  for equilbrium conditions by:
               H-h =  (
     and for non-equilibrium  conditions  by:
               H-h =  (
     where:
                  =  2
                    rS/4Tt.
for i = 1,2,...n
Linear superposition  is only valid  for  confined  aquifers because the value of
transmissivity does not change with  drawdown.

     For unconfined aquifers, linear superposition of individual well
drawdowns results  in  predicted composite  drawdowns that are less than they
will actually be because a decrease  in  saturated thickness reduces the
transmissivity.  Composite drawdowns for  unconfined aquifers under equilibrium
conditions can be  calculated from;

               H2-h2 = (Q1ln(Ro/r1)/7rK)+(Q2ln(Ro/r2)/7rK)....(Qn1n(Ro/rn)/^K)

Alternatively, composite drawdowns  can  be derived by graphical  superposition
                      2  2
using the calculated  H-h  for each  well  (Figure 5-11).  In this case the
 2  2
H -h  are added and the drawdowns are found  by taking square roots.
                                   5-26

-------
 I
INS
                                                                        FIGURE 5-11.
                                                COMPOSITE DRAWDOWN IN  AN UNCONFINED AQUIFER
                                                                (DAVIS AND  DeWlEST, 1966)
                                Figure 5-11a.  Plane View
                                                   "W   K   I Composite drawdown
                                                                                                        Figure 5-11 b. Cross-sectional View
                                                                                                                   Initial WaterTable = Ground Surface
                                                                                        0
                                                                                          0  50 100   200    300   400   500

                                                                                                                    x in ft
1000

-------
     Determining well  interference or  intersecting cones of depression  is  a
necessary exercise  in  designing well-field  layouts for  plume management.   For
aquifers that have  high flow velocities, a  velocity plot may also  need  to  be
developed to determine well field layout.   Based on these  analyses  the
following parameters can be determined:

     •  Well spacing to contain contaminants
     •  Length of pipe needed to carry discharge from the  well to  the
        treatment plant
     •  Well pump characteristics (e.g., type, horsepower)
     •  Time interval  for pumping, if not equilibrium pumping.

     5.2.7  Hydrogeologic Boundary Effects

     Typically, wells  are not located in aquifers that  have infinite area!
extent and therefore drawdown cones extend  until they intercept a recharge
boundary or a barrier  boundary.  Recharge boundaries (e.g., streams) are areas
where aquifers are replenished with water and barrier boundaries (e.g.,
impermeable zones) are where aquifers terminate.  The effect of the boundary
conditions on drawdowns is shown in Figure  5-12.  Total drawdown and the rate
of drawdown are less than theoretical predictions when  recharge boundaries  are
present and greater when barrier boundaries are present.

     Calculating the effect of barriers on  wells is usually performed using
the method of images.  Where recharge boundaries are present, rechargee image
wells are constructed and when barrier boundaries are present discharge image
wells are utilized.  Figure 5-13 shows an example for each type of boundary.
In both cases,  image wells are drawn about  the axis where the boundary occurs.
For recharging images, cones of depression  are added to obtain the resultant
cone and for discharging images, cones of depression are subtracted.
                                      5-28

-------
                     FIGURE 5-12.
  EFFECT OF RECHARGE AND BARRIER BOUNDARIES
            ON DRAWDOWN (FETTER, 1980)
s
Q
             10
                     102
103
              \
              \
104
105
             10       102       103       104

                 Time Since Pumping Began
                 10b
                        5-29

-------
                                                                      FIGURE 5 13. METHOD  OF  IMAGES FOR DETERMINING
                                                                                 RESULTANT CONE OF DEPRESSION
                                                                          (FERRIS et al., 1962,  AS CITED BY LOHMAN, 1972)
                                       Discharging Well
                     Nonpumpmg Water Level

                         Pumping Water Level
                            Figure 5-13a. Hydraulic Barrier

                                Q

                             /L.
                                                                      .•X'-V'V  Impermeable or  „-;•',»•
                                                                      jf.^.fVc/ Confining Mateial ,\*,'\
                                           •'•••I'v'v Aquifer •';••'.'•;•

                                                                           Average or Effective Position
                                                                               of Line of Zero Flow
GO
O
                                                                REAL SYSTEM
                                                                                                                       Figure 5-13b. Recharge Barrier
                                                                                                      Discharging Well
                               Perennial
                                Stream
                                                                                                                                                       Land Surface
                                                                                                                     ' Nonpumpmg
                                                                                                                      Water Level     M
                                                                                                                                       -_rir:r^ Confining Material nr"-r^r-I:
                                                                                                                                 REAL SYSTEM
                  Drawdown Component
                      of Image Well
                 Discharging
                  Real Well
                                                                        Drawdown Component
                                                                             of Real Well
                                                                                        Discharging
                                                                                        Image Well
                             Nonpumpmg
                              Watei Level
Confining Material fI-£;-£-£;-^-£>i:-£I-£I-£l- I-E>EHI-EHHH>£I- I^^^-EI^-£I-£}£H>EHHH}T_-£H--u-^
                               «	a	••	a	p-|
                        NOTE Aquifer thickness M should be very large
                        compared to resultant drawdown near real well

                       HYDRAULIC COUNTERPART OF REAL SYSTEM
         Zero Drawdown
           Boundary     \

        Buildup Component
          of Image Well
Discharging
 Real Well
              ,, Recharging
 (Cone of   f/ lmaae We"
Impression)  I'lx
     V--TK,
           H      *-^
           ii         --~._
Nonpumpmg [ j Water Level
                                                                                                                                        Drawdown Component
                                                                                                                                        -""of Real Well
                                                                                                                                                   I  r
                                                                                                                                                   .1  t
                                                   T
                                                    M
                                                                                                                                                   lif           :
                                                                                                                                         (Cone of Depression)

                                                                                                                    NOTE: Aquifer thickness M should be very large
                                                                                                                    compared to resultant drawdown near real well

                                                                                                                   HYDRAULIC COUNTERPART OF REAL SYSTEM

-------
     5.2.8  Flow Between Discharge and Recharge Wells

     Injection well theory is identical to the discharge well theory
previously described except that cones of depression and drawdowns are
inverted to above the water table or piezometric surface and become cones of
impression and additional head.  The use of recharge (injection) wells in
combination with discharging wells allows contaminants to be flushed more
rapidly or diverted (i.e., against the normal flow path) to recovery wells.
Injection wells can also be utilized to create hydraulic barriers to stop the
migration of contaminants, or to change the hydraulic head so that contam-
inants can be diverted or made to flow against the original  flow path.

     An example of an extraction and recharge well  operating in the same
confined aquifer is given in Figure 5-14.  In the example, the recharge and
discharge wells are pumping at the same rate (QR = QT).  To estimate the shape
of the piezometric surface formed by pumping these wells, the cone of
depression and the cone of impression are plotted and then the two are added.
Because the aquifer is confined, the cones can be added directly (refer to the
section on cumulative drawdown).  This technique cannot be applied directly to
unconfined aquifers because the saturated thickness changes resulting in
                                       2  2
transmissivity changes.  Plotting the H -h  for each well and then super-
imposing them will result in correct answers for unconfined aquifers.

     5.2.9  Radius of Influence

     Determining the radius of influence for a well  in a given aquifer is
critical in remedial  action design because it can be used for determining well
spacing, pumping rates, pumping cycles, and screen lengths.   *\s can be seen
from the equations presented previously, the radius of influence of a well
increases as pumping continues until equilibrium conditions are reached (i.e.,
when aquifer recharge equals the pumping rate or the discharge rate).
Recharge can occur through one or more of the following situations (Johnson
Division, UOP Inc., 1975):

     •  Storage release from the aquifer
                                     5-31

-------
                      FIGURE 5-14.
RECHARGE AND DISCHARGE  WELLS  IN  A  CONFINED
                        AQUIFER
              (DAVIS AND DeWIEST, 1966)
                 a.
     T
    h = H
s „-•
M/iW/////s/ss/sssss/s/s/js,s.
•:>:/' «;$.£:•.
y
ia.\..'^ '.>'•'••.: ••%:.•'
-V :•.•:•••.••:••;••• .::'». ^.:

N ! -i
N_K_I_
•;';.".*.'.•.. '•'• '*"_"!•'•*'•''..'.'.* ;
IsSL
h


IW
;v. ... m-,:\
irf
             Figure 5-14a. Cross-sectional View
                                                     Eauipotential
                                                        Line
                                                     Streamline
                 Figure 5-14b. Plane View
                        5-32

-------
     •  Surface water entering the aquifer
     •  Recharge from ugradient flow and from precipitation within the radius
        of influence
     0  Leakage through overlying or underlying aquifers.

Once equilibrium conditions have been reached, the shape of the cone does not
change with increased pumping time (as long as the other factors remain
constant).  The time required to reach equilibrium conditions after pumping is
started can be very short, e.g., within 2 hours, or may take as long as years.
Typically, the radius Of influence for a confined aquifer is larger than that
for an unconfined aquifer and increases as hydraulic conductivity increases.

     Estimates of the radius of influence can be made by using several tech-
niques.  Generalized values for the radius of influence for various porous
media under unconfined conditions are given in Table 5-7.  These values are
estimates and should be treated as such.
     TABLE 5-7.  RADIUS OF INFLUENCE FOR VARIOUS UNCONSOLIDATED MATERIALS
            (i.e., BASED ON TYPICAL HYDRAULIC CONDUCTIVITY RANGES)
Porous Medium                           Radius of Influence (R )
                                                  (ft)        °
Coarse Gravel                                    5,000
Fine Gravel                                   1,300-1,650
Coarse Sand                                     650-1,300
Medium Sand                                     300-650
Fine Sand                                       150-300
Very Fine Sand                                   50-150
Silty Fine Sand                                    <50
                                     5-33

-------
     Rough approximations of R  without recharge  can  be made  by  adapting  the
Jacob formul a to:

                                  0.5
                 RQ = rs + (Tt/SC)

     where :

                 r  = well radius or equivalent radius
                 T = coefficient of transmi ssivity
                 t = time
                 S = coefficient of storage
                 C = constant (based on the  units used).

The above equation is valid only for confined aquifers and the value obtained
should be adjusted downward on the basis of possible  recharge.  Using the
above relationship for unconfined aquifers provides reasonable results as long
as the drawdown (H-h ) is not a large percentage  of the saturated thickness
(H).

     Si chart and Kyrieleis (1930) developed an empirical relationship for
calculating the radius of influence  (RQ) as a function of drawdown (H-hw) and
hydraulic conductivity (K):

                 R  = 3  (H-h  )(0.47K)°-5
                  o      x   w'v      '
                                     f\
where H-h  is  in feet, K  is in gpd/ft  and RQ is in feet.  Theoretically, the
radius of influence does  not  depend  on drawdown, but  rather, depends on the
pumping  rate   which does  not  appear  in this formula.

     For  exact solutions, distance-drawdown diagrams  can be constructed using
the equations  given  previously.   Distance-drawdown diagrams are  plotted on
semil ogarithmic paper with the distance being plotted  on the  logarithmic
scale. Two such diagrams  are  shown  in  Figure 5-15.  The  radius of influence
can  be obtained from  the  intercept  of  the plots  with  the distance axis at  zero
drawdown.  For cases  where  pumping  rates  are variable  but all other  parameters
                                      5-34

-------
                                  FIGURE 5-15.
DISTANCE DRAWDOWN DIAGRAMS FOR A) VARYING PUMPING RATING
AND B) VARYING PUMPING TIMES (JOHNSON DIVISION,  UOP INC., 1975)
      o
     12
     16
     20
     24
          AS = 5.3 ft
                                                                 T = 300 mm.
                                                         Drawdown =  18.8 ft.
                                                   Q = 400 gpm
              2    3
 10      20   30    50    100    200  300   500

 Distance from Pumped Well, in Feet

Figure 5-15a.  Pumping Rates
 c   12
 I
 Q   16
    20
    24
                   Drawdown in Observation
                   Well "A" after 300 min.
                            Drawdown in Observatoin
                            Well "A" after 1000 min.
                                            Curves Constructed for Q = 200 gpm
             2    3
                              10      20   30    50    100    200  300   500
                              Distance from Pumped Well, in Feet
                             Figure 5-15b.  Pumping Times
                                      5-35

-------
pumping times are varied, however, the radius of influence is changed such
that as pumping time increases, the radius of influence increases.  This
relationship holds true until equilibrium is reached after which the radius of
influence does not increase with continued pumping.

     Two useful relationships for understanding the effects of drawdown on the
pumping volume and the radius of influence are:

                 Q/H-h = 2 7rT/ln(R0/r) = Constant  (for confined aquifers)

     and
                    o  p
                 Q/H-h  = 7rK/ln(R /r) = Constant  (for unconfined  aquifers)

Thus, the radius of influence will not change with the pumping rate under
equilibrium conditions.  The factor that affects the radius of influence
greatest under non-equilibrium conditions is the pumping time.
     Table 5-8 summarizes the equations that can be used to determine  the
    js of influence, R .   An example R  calculation for
being pumped at steady state conditions is given below.
radius of influence, R .   An example RQ calculation for an unconfined aquifer
     An unconfined aquifer is pumped at a rate of 500 gpm  and the  system  has
                                                                        2
reached equilibrium.  The aquifer's hydraulic conductivity is 300  gpd/ft  ,
drawdown in the well is 35 feet and the saturated thickness  is  100 feet.  The
radius of the pumping well is 0.5 feet.  The radius of  influence of the well
is calculated by:

                 In RQ =  (K(H2-hw2)/458Q)  + lnrw
                       =  (300(1002-652) / 458 (500))   + In0.5
                       =  6.872
                    RQ=  e6.872

                       =  965 feet.
                                    5-36

-------
       TABLE 5-8.  METHODS FOR CALCULATING THE RADIUS  OF  INFLUENCE  (R )
     Pumping           Water Table Aquifer            Confined  Aquifer
     Condition            (Unconfined)
Equilibri um

   - Exact    lnRQ =(K(H2 -hw2)/(458Q))  + lnrw   1 nRQ   =(T(H-hw)/229Q))+  Inr

Non-equil ibri um
   - Exact               Drawdown  vs.  log distance  plots  or  Theis  Method

Approximate                R  = r  +(Tt/4790S)

                           RQ  = 3(H-hw)(0.47K)0'5
     RQ =  Radius of influence (ft)
                                        o
     K  =  Hydraulic conductivity (gpd/ft  )
     H  =  Total  head (ft)
     h  =  Head  in well  (f)
      w                  '
     Q  =  Pumping rate  (gpm)
     r  =  Well  radius (ft)
      w
     T  =  Transmissivity  (gpd/ft)
     t  =  Time  (min)
     S  =  Storage coefficient (dimensionl ess)
                                    5-37

-------
     5.3  Applications

     This section briefly describes the applications of well  systems  for  plume
management.  The general types of wells that can be used  are  wellpoints,
suction wells, ejector wells, and deep wells, which can fully penetrate or
partially penetrate the aquifer.  Well placement and use  (i.e., extraction  or
injection) is highly variable and depends on the hydrogeologic characteristics
of the site and the plume's characteristics.  Well systems can be designed  to
perform almost any function from plume containment to plume removal with  or
without the assistance of other technologies (e.g., slurry walls).  The
applications for which well systems are typically designed are:

     •  Groundwater level adjustments
     •  Containment of plumes to prevent their migration
     t  Removal of plumes from the groundwater system.

     5.3.1  Groundwater Level Adjustment

     Well systems for adjusting groundwater levels can be designed using
extraction wells to lower water levels or using injection wells to create
groundwater mounds (i.e., barriers).  By adjusting groundwater levels, plume
development can be stopped at the source (e.g., lower water table under a
site) or the speed and direction of the plume can be altered.  In either  case,
contaminated water is not extracted from the groundwater  system as in the case
with containment and removal techniques described in following sections.
Groundwater level adjustments are not usually practical,  however, because of
problems associated with operation and design so as not to allow contaminants
to escape or be misdirected.  Also, contaminated water may inadvertently  be
extracted if care is not taken during adjustments.

     Plume development can be controlled at sites where the water table
intercepts disposed wastes by lowering the water table with extraction wells.
In order for the pumping technique to be effective, infiltration into the
waste pile must be eliminated and liquid wastes must be completely removed.
If these conditions are not met, the potential exists for development of  a
                                    5-38

-------
contamination plume.  The major drawback to  using well  systems  for  lowering
water tables is the continued costs  associated  with  the maintenance  of  the
system after site closure.

     Groundwater barriers can be created using  injection  wells  to change  both
the direction of the plume and the speed of  plume migration.  Figure 5-16
shows an example of plume diversion  using  a  line of  injection wells  to  protect
domestic water sources.  By creating an area with a  higher  hydraulic head, the
plume can be forced to change direction.   This  technique  may be  desirable when
short term diversions are needed or when the plume will have sufficient time
to naturally degrade so that containment and removal  is not required.

     5.3.2  Plume Containment

     Well systems can be used to contain a plume's migration (i.e.,  prevent
further migration and contamination) using extraction wells or  extraction and
injection wells in combination.  Containment differs  from removal in that the
source of contamination is not stopped and groundwater  contamination is an
ongoing process.  Because containment requires  removing contaminated ground-
water, a treatment or disposal method must also be developed.

     Figure 5-17 depicts  the use of a line  of  extraction wells  to contain a
plume and protect a domestic water supply.   The distance  between wells  is
determined such that the plume is captured,  i.e., their radii of influence
overlapped for low natural flow velocities or velocity plots developed  for
high natural flow velocity, thus preventing  contaminated  groundwater from
flowing between adjacent wells.  Wells do not necessarily have  to be drilled
in front of the plume's leading edge but can be drilled behind  it as long as
the edge is contained within the stagnation  zone developed by the pumping
well.

     Extraction and injection well systems can  also  be designed to contain a
plume.  In this type of system, injection wells are  used to direct contam-
inants to extraction wells.  Injection well  water can be derived from treated
extraction well water thus allowing for a convenient disposal method.  This
                                    5-39

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                 FIGURE 5-16.
PLUME DIVERSION USING INJECTION WELLS
                              Future Plume
                               Movement
                                                     "\
                                                      ;
Injection Wells
                          Domestic Wells
                       5-40

-------
	Impermeable Bedrock	
                K via  Cross
        Figure 5-1/»• ^
                            ..sectional View
                            Extract.cn Wells


                            w,th Radius of

                              influences
                    Figure
                           5_V7b.
                                 5-41

-------
type of system may be most advantageous  in situations where complete
dewatering of a local groundwater system  is not desired.

     Well systems can also be used in conjunction with other plume management
technologies.  The use of wells with barrier walls, for  instance,  is
potentially the most useful technology combination.  However, the  barrier  wall
used would have to be designed to be compatible with the waste  so  that  wall
degradation would not occur.

     5.3.3  Plume Removal

     Plume removal implies a complete purging of the groundwater system to
remove contaminants.  Plume removal  techniques are utilized after  contaminant
sources have been fixed, encapsulated, or removed, and aquifer  restoration  is
desired.  Plumes of this type may originate from spills, pipeline  breaks
(e.g., gas line), or other accidental discharges.  Extraction,  and extraction
and injection well systems can be used in plume removal.  As with  containment,
plume removal typically requires treatment of the extracted groundwater before
disposal.

     Plume removal through the use of extraction wells is most  appropriate
where:

     •  Hydraulic gradients are steep (i.e., >0.2 ft/ft)
     t  Contaminants are flowing with velocities equal  to or greater than the
        groundwater
     •  Removal  times can be long (i.e.,  quick removal  is not necessary).

     As with containment, wells are  placed downgradient of the  plume near the
plume's leading  edge with their radii of influence or capture zones over-
lapping so as not to allow contaminant escape.

     Extraction  and injection well systems may be designed to remove contam-
inants from the  groundwater as shown in Figure 5-18.   The major difference
                                    5-42

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                             FIGURE 5-18.
           EXTRACTION AND INJECTION WELLS PATTERNS
                        FOR PLUME  REMOVAL
                                                         Extraction Well

                                                         Injection Well

                                                         Plume Boundary

                                                         Radius of Influence
                                GW Flow
a.
b.
                                 GW Flow
                                   5-43

-------
between the two removal plans  is  the  placement  of  wells  in  relationship to
each other.   In Figure 5-18a,  extraction wells  surround  the injection  wells in
a staggered array.   In Figure  5-18b,  extraction wells  alternate  with  injection
wells in straight  lines.  Both methods  are  effective  in  plume  removal  and the
choice of pattern  would depend on the size  of the  plume  to  be  removed  and
required number of wells.  However, dead spots  (i.e.,  areas where  water
movement is very slow or nonexistent) can occur when  these  configurations are
used.  The size of a dead spot is directly  related to  the amount of overlap
between adjacent radii of influence (i.e.,  the  greater the  overlaps the
smaller the dead spots).  The  system's  efficiency  should be monitored  in  these
dead spots.  Another problem with extraction and injection  systems is
operational problems associated with  injection  wells.  These wells can  suffer
from many operation problems including  air  locks,  and  frequent maintenance  and
well rehabilitation.

     Extraction and injection  systems are most  appropriate  where:

     •  Hydraulic gradients are low (i.e.,  <0.2 ft/ft)
     •  Contaminants are flowing at velocities  less than that of the
        groundwater
     •  Required removal time  is short.

A special  case where these techniques are especially applicable  is with
contaminants that move slowly or cling  to geologic materials.  Extraction  and
injection  well systems can also be designed to  allow for flushing  (e.g.,  using
surfactants) and recovering contaminants that could not be  recovered using
normal pumping methods.

5.4  Design and Construction

     5.4.1   Well Design

     Designing the most appropriate type of well and well system requires
having adequate information on the site's hydrogeology and  the plume's
                                     5-44

-------
characteristics.  The types of data that are typically required  are  presented
in Table 5-9.  As with any design program, the more  accurate the  data  the more
likely the system designed will perform its  intended function.

     There are four basic well types that can be  used  in  plume management;
wellpoints, suction wells, ejector wells, and deep wells.   Using  the site
data, selection of an appropriate well type  can be made.   Table  5-10 lists  the
conditions under which these well types would be most  applicable  to  a
particular site.

     Wellpoint systems are the most versatile method,  being effective  in
almost any hydraulic situation.  They are best suited  for  shallow aquifers
where extraction is not needed below more than 15 to 20 feet.  Beyond  this
depth suction lifting, the standard pumping  technique  for  wellpoints,  is
ineffective.  Suction wells operate in a similar  fashion  and are  also  depth
limited.  The only advantage of suction wells over wellpoints is  that  they
have higher capacities.  For extraction depths greater than 20 feet, deep
wells and ejector wells are typically utilized.   Deep well  systems are  better
suited to homogeneous aquifers with high hydraulic conductivities and  where
large volumes of water may be pumped.  Ejector wells perform better  than deep
wells in heterogeneous aquifers with low hydraulic conductivities.   A  problem
with ejector systems is that they are inefficient and  are  sensitive  to
constituents in the groundwater which may cause chemical  precipitates  and well
clogging (Powers, 1981).

     The following section gives descriptions of  the basic  components  of wells
and the design factors in developing a system.  Wellpoints  and suction  wells
have been combined because of the similarities between the  two.

          5.4.1.1  Deep Wells

     The typical components of a deep well are a  screen,  casing,  filter pack
and seal, and turbine pump.  Motors for pumps can be submersible  and attached
to the pump, or at ground level driving the  pump  with  a shaft.  Components of
a typical deep well are shown in Figure 5-19 and described  in Table  5-11.  Not
                                     5-45

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             TABLE 5-9.  DATA REQUIREMENTS FOR WELL SYSTEM DESIGN
Geology (consolidated and unconsolidated materials)
     •  Structure
     •  Stratigraphy
     •  Lithology
Aquifer
     9  Types (i.e., confined, unconfined, perched)
     •  Thicknesses, depths, and formational  designations
     •  Boundaries
     •  Hydraulic conductivities, storativities, transmissivities
     0  Discharge and recharge zones
     t  Groundwater and surface water relationships
     •  Locations of existing wells
     0  Pump test data (e.g., drawdowns, pumping rates, times)
Plume
     •  Areal extent and depth
     t  Types of contaminants
     •  Location in aquifer
                                    5-46

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                          TABLE  5-10.  CRITERIA FOR  WELL SELECTION (Powers, 1981)
Parameters
Hydrology
• Low hydr

aulic conductivities
Wellpoints
Good
Suction Wells
Poor
Ejector Wei Is
Good
Deep
Fair
Wells
to Poor
     (e.g., silty or clayey sands)
  •  High hydraulic conductivities
     (e.g., clean sands and gravel)
  •  Heterogeneous materials
     (e.g., stratified soils)
  •  Proximate recharge
  •  Remote recharge
Depth of Well
Normal  Spacing
Normal  Range of Capacity
  (per unit)
Efficiency
Good
Good
Good
Poor
Poor
Good
Good
Fair to Poor
Good              Poor              Good to Fair      Poor
Good              Good              Good              Good
Shallow <20 ft    Shallow <20 ft    Deep >20 ft       Deep >20 ft
5 - 10 ft         20 - 40 ft        10 - 20 ft        >50 ft
0.1 - 25 gpm      50 -400 gpm       0.1 -40 gpm       25 - 3000 gpm
Good
Good
Poor
Fair

-------
             FIGURE 5-19.
COMPONENTS OF TYPICAL DEEP WELL
            (POWERS,  1981)
                       fl   A    Q
                                           i Valve
                                          T
                                          Height x
                                          i
                                             Depth z
                                    Detail of Air Line for
                                    Measuring Operating
                                    Level
                 5-48

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              TABLE 5-11.  DEEP WELL COMPONENTS  AND SELECTION CRITERIA (Powers, 1981)
Item Description
(See Figure 3-22)
                                 Selection Criteria
A   Throttle Valve



B   Check Valve


C   Turbine Pump

D   Electric Motor


E   Control Panel

F   Air Line


G   Filter Piezometer


H   Pressure Gauge

I   Seal

J   Gravel Pipe

K   Well  Screen
L   Fi Her Material
M   Casing
Prevents damage caused by pumping surges when the pump is operating at less then
the design capacity (typically after initial  drawdown), also ensures maintenance
of a constant discharge

Prevents backflow (recharge) from occurring if the pump fails in systems where a
number of wells are connected to a common manifold

Sized to suit aquifer conditions, may need to be corrosion resistant

Sized to operate within its service range under any pump load that may be
encountered

May need to be in a tamper proof enclosure

Used to measure the operating level of the well ; monitors performance of the pump
and the well

Used to measure screen loss during development  and fractional increases caused by
encrustation

Used to monitor pump wear

Prevents surface inflow of water  into well, typically cement grout or bentonite

Used to introduce new gravel  in sealed wells during subsequent  redevelopment


Size in accordance to needs,  may  need to be corrosion  resistant

-------
en
o
                                                           TABLE  5-11.  (Continued)
                   Item Description                                           Selection  Criteria

                   (See Figure 3-22)
N
0
P
Discharge Column
Meter Device
Manifold
Sized for maximum discharge with acceptable fraction; may need to
resistant, must also carry weight and hydraulic thrust of motor
Used for monitoring well discharge
Used to collect water pumped from wells and carry pumped water to
be corrosion
treatment

-------
all components listed will be utilized or  are  necessary  for  individual  wells,
but incorporation should be based  upon such  factors  as the  life  expectancy of
the well, the well's design, the treatment facilities  available,  and  the
corrosiveness of the contaminated  groundwater.

               5.4.1.1.1  Pumps

     Two types of pumps are commonly utilized  in  deep  well  applications,  the
turbine submersible pump and the vertical  line  shaft pump.   Turbine submers-
ible pumps were originally designed for water  supplies but  have  been  used
extensively in construction for dewatering.  Submersible pumps have the
advantage of being relatively slender for  their capacity allowing their use  in
small  diameter wells.  Commercially available  pumps  can  be  obtained with
capacities greater than 100 gallons per minute  and with motors of several
hundred horsepower.

     Vertical lineshaft pumps are  similar  to submersible pumps except that the
motor is located on the surface rather than  being attached  directly to  the
pump.   This type of pump is used for extracting high volumes of  groundwater
and is available in sizes ranging  from a few horsepower to  over  a thousand
horsepower.  The cost of a lineshaft pump  is typically greater than for a
submersible pump of similar horsepower sizes.

     Pump impellers and diffusers  (components  that drive water)  are available
in a variety of materials (e.g., plastic, cast  iron, bronze) and can be made
of special metals for wastes containing corrosive chemicals.  Abrasive  matter
such as sand can cause premature wearing of these parts and  lose of well
efficiency.  To avoid this, wells  should be developed  (i.e., pumped free of
fines as discussed in a later section) and cleaned to remove particles  after
drilling.  Also, the pump should be placed above  the bottom  of the well (i.e.,
>2 ft) to minimize pump plugging caused by fines.
                                     5-51

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     Numerous problems can arise when using deep well pumps for plume
management.  These include the following:

     •  Corrosion of pump parts by contaminated waters
     •  Electrical malfunction (submersible pumps)
     •  Lightning damage
     •  Excessive part wear (e.g., impeller wear caused by  intake  of fines)

These problems should be factored into the design specification to minimize
operational problems.

     Before selecting a pump for installation, accurate information on  the
required capacity of the well and the total head is necessary.  Required
capacity can be determined from the equations presented previously for  the
radius of  influence (R ) and drawdown (H-h).  Factors such  as pumping
cycles, peak loads, dynamic head, and future needs should also be  considered
in design  capacity.  Total dynamic head  (h.) can be calculated using the
formula:
             ht = he + hf + hv
     where:
             h  = total vertical lift, from the pumping  level  in  the  well  to
              e   the water discharge point (ft)
             h,: = total frictional losses expressed  as head  (ft)
             h  = velocity head required to produce  the  desired flow  (ft).
     Total vertical lift (h  )  is the sum of the vertical distance  from  the
pumping level in the well to the outlet and the hydrostatic  pressure  head  at
the discharge outlet.  Velocity head (h )  is determined  using  the  formula,
           9                           •
h  = 0.155V  .  Usually h  is very small and only taken into  account at
installations where:
     t  Very high discharges  are expected  at  very  low  lift  and  discharge head
     •  Velocity of flow  is very high.
                                     5-52

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Frictional  losses  in  pipes  and  fittings  are  calculated  using tabulated values.
Tables  5-12  and  5-13  give values  for  smooth  pipe and  fittings.

     Once the  total dynamic  head  is obtained  and the  capacity is  determined,  a
pump and motor can  be  chosen using performance  curves.   These curves typically
plot capacity  versus  total  head and percent  efficiency  of  the system.   An
example of  performance curves for 325  gallon  per minute pumps is  given in
Figure  5-20.   The most efficient operating range for  these pumps  is  between
250 gallons  per  minute and  380  gallons per minute.   If, for example, the total
calculated  head  is  200 feet  and the desired  capacity  is 300 gallons  per
minute, a 25 horsepower, 5  stage pump  would  be  selected for use  (i.e., a pump
that exceeds the expected use).

     Another criteria  in selecting a  pump that  should be considered  is the
type of drawdown anticipated and the  pumping  cycle.   If the pump  is  to be
utilized under varying head  pressures  and cyclic pumping conditions, a steep
head pump should be chosen  (i.e., steep  drawdowns).   If the pump  will  be used
for steady  pumping, resulting in a flat  drawdown,  a flat head pump  should be
chosen.  Proper  selection of either a  flat or steep head pump will  reduce O&M
cost and improve system efficiency.

               5.4.1.1.2  Well Casing  and Depth

     Casing  size (diameter)  is chosen  to satisfy two  requirements.   The casing
must be large enough to (Johnson Division, UOP  Inc.,  1975):

     •  Accommodate the pump with enough clearance for  effective  operation
     t  Ensure proper  hydraulic efficiency of the well  at  the  intake section.

The controlling  factor  is usually the  size of the pump  selected for  the
desired capacity and head.    A good rule of thumb  is that the  casing  size
should be two standard pipe  sizes larger than the nominal  diameter of  the pump
or pump bowl, and not  less than one size larger.  Recommended well casing
diameters are given in Table 5-14.  For example,  a 300  gallon per minute  pump
                                     5-53

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I
cn
                                TABLE 5-12.  LOSS OF HEAD DUE TO  FRICTION  IN  SMOOTH PIPE*
                                  (approximate head loss in ft. per  1,000  ft.  of  pipe)
                                            (Johnson Division,  UOP  Inc,  1975)
Flow
Rate
in gpm
10
15
20
25
30
40
50
60
75
100
125
150
175
200
250
300
350
400
500
600
750
1,000
1,500
2,000

1-1/4 1-1/2 2
20 9 2
44 20 6
79 35 10
123 55 16
178 79 22
142 40
222 64
90
140
258














Nominal
2-1/2


4
6
9
16
25
37
57
102
159
228












Pipe Size, in
3


1
2
3
5
8
11
18
30
46
68
90
122










4






2
3
4
8
12
17
23
30
47
70
93
123
191





inches
5








1
2
3
5
7
9
14
20
27
35
54
78
122




6











2
2
3
5
8
11
14
21
31
48
86
194


8 10













1

2

3
5 2
7
11 3
19 6
43 15
76 22

12





















2
5
10
          *For Rough  Pipe,  add  50%

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                                        TABLE 5-13.   APPROXIMATE  HEAD LOSS EQUIVALENTS FOR PIPE  FITTINGS

                                      (Johnson Division,  UOP Inc,  1975)   (expressed  in fit of  straight pipe)
en
i
en
en
Type of F itt ing
90° elbow
45° elbow
90° elbow ( long radius)
Tees
Reducer (1 step) large end
Gate valve (open)
Gate valve (1/2 open)
Globe valve (open)
Angle valve (open)
Swing check
Nominal Pipe Size, in
1.25
3.5
1.5
2.5
See
2
1
20
35
18
9
1.5
4.
2
3
note
2.
1
25
45
24
11
2
5 5.5
2.5
4
below
5 3
1.5
35
55
30
13
2.5
6.5
3
4.5

3.5
1.5
42
67
35
16
3
8
4
5

4
2
50
80
40
20
3.5
9.5
4.5
6

5
2
58
100
50
23
4
11
5
7

6
2.5
65
115
55
25
inches
5
14
6
9

8
3
80
140
70
32
6
16
8
11

10
4
100
160
80
45
8
21
10
14

12
5
130
215
110
52
10
26
13
17

15
6
170
285
140
65
12
32
15
20

18
7
200
340
175
80
                 Tees vary  with the direction of flow through them.   For straight-through  flow,  the head loss is about  equal  to that of a long

                 radius  90°  elbow; when flow is through the branch,  the head loss is approximately 3 times as great.

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                         FIGURE 5-20.
                   PERFORMANCE CURVES
                   (FLINT Er WALLING INC.)
                                 Most Efficient
                                Operating Range
   700
   600
   500
   400
tt>

I  300
   200
    100
             80

             70

             60

             50
                                                              .2
                 100       200       300
                         Gallons per Minute
400
          500
                             5-56

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                TABLE 5-14.  RECOMMENDED WELL  CASING  DIAMETERS
                             (JOHNSON DIVISION, UOP INC.,  1975)
Well Yield
(gpm)
<100
75-175
150-400
350-650
600-900
850-1,300
1200-1,800
1600-3,000
Nominal Size
of Pump Bowl
(in)
4
5
6
8
10
12
14
16
Optimum Size
of Well Casing
(in)
6 ID
8 ID
10 ID
12 ID
14 OD
16 OD
20 OD
24 OD
Minimum Size
of Well Casing
(in)
5 ID
6 ID
8 ID
10 ID
12 ID
14 OD
16 OD
20 OD
     ID = inside diameter
     OD = outside diameter
with a 6 inch diameter, an optimum casing size would be 10 inches  (inside
diameter).

     Well depth is usually determined from the geologic data (e.g., aquifer
thickness) available for the site and the plume's characteristics.  In most
cases wells will be completed to the bottom of the aquifer.  This  is typically
the case for plumes that contain contaminants that are miscible with ground-
water or are denser than groundwater or both.  The exception to full
penetration of the aquifer would be where contaminants are less dense than
groundwater such that they float at the top of the aquifer.  In this case
partially penetrating wells may be desirable.
                                    5-57

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               5.4.1.1.3  Well Screens

     The purpose of a well screen  is to  (Department  of  the  Interior,  1977):

     •  Stabilize the sides of the hole
     t  Keep soil particles out of the well
     •  Facilitate flow into and within  the well.

Screens can range from blank pipe that is perforated  inplace  to  manufactured,
continuous-slot well screens with accurately sized openings.   The  types  of
screens commercially available and commonly used for  dewatering  are  listed and
described in Table 5-15.  Most are made  in lengths ranging  from  5  to  20  feet
so that any length of screen can be created by joining  individual  sections.
The options in selecting well screens are the type,  length, diameter,  and
opening size.  The following sections provide information for making  these
choices.

     The type of well screen selected is generally based on the  availability
of screens having the proper diameter and opening size  that are  made  of  a
suitable material.  The selection of screen diameter  and opening size  is
controlled by several factors, which are discussed later.   Material  selection
is governed by the corrosive and incrusting properties  of the groundwater  and
contaminant plume, and the strength requirements imposed by column  load  and
collapse pressure.  Corrosion of the screen causes enlargement of  openings,
which could permit excessive sand entrance and premature pump wear.   If
corrosion is severe, collapse could occur.  Incrusting  is caused by mineral
deposits on the screen surface which tend to plug the openings of  the  screen
and formation.  Removal by acids is often used to remedy incrustation
problems.  Bacteria growth can also cause well incrustation in the  same  manner
as mineral deposits.  Removal of deposits is typically  done using  strong
chlorine solutions.  These problems necessitate the  use of  screens  (and
casing) made of corrosion resistant materials.  Table 5-16  lists some  common
materials and their applications.
                                     5-58

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                                      TABLE  5-15.   WELL SCREEN  TYPES  (After Powers,  1981)
Type
Diameters
(in)
Openings
(in)
Advantages
Disadvantages
              Slotted
in
i
              Continuous  Slot
              Louvered


              Mire  Mesh
4 - 12
4-36
6 - 48


4 - 24
0.010 - 0.100
0.003 - 0.250
(vertical  rods
not accounted
for in area
calculation)
0.032 - 0.250
>0.020
•  Reasonable cost
•  Easy installation

t  Resistant to corrosion
•  Screen has high open
   area

•  Precise slot dimensions

•  More effective develop-
   ment
   Can be reused
   Reasonable cost
   Reusable
   Effective in gravel
   Effective in jetted
   wells
   Effective in fine soils
                                                                       Precise slot dimensions
•  Type I PVC is brittle
•  PVC susceptible to
   degradation by chlor-
   inated hydrocarbons

•  Can have loading
   probelms with thinner
   walled pipe
•  Slots can become partly
   clogged by sand

t  Generally minimal
   opening area available

•  Must be welded to casing
                                                                                                •   Corrosion  problem  can
                                                                                                   occur depending  upon
                                                                                                   material used
•  Susceptible to corrosion
•  Limited open area

•  Not suitable for drilled
   wells
•  Limited open area
   because of holes behind
   screen

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                     TABLE 5-16.  WELL SCREEN MATERIALS AND APPLICATIONS (Johnson Division,  UOP Inc., 1975)
01
o
Material
Monel
Stainless Steel
Everdur
Silicon Red
Brass
Armco Iron
Steel
Nominal Composition
70% Nickel
30% Copper
74% Steel
18% Chromium
8% Nickel
96% Copper
3% Silicon
1% Manganese
82% Copper
16% Zinc
1% Silicon
99.84% Pure Iron
(double galvanized)
99.35/99.72 Iron
Cost
Factor
1.5
1.0
1.0
0.9
0.6
0.5
Suggested Applications
Waters with high sodium chloride and dissolved oxygen
levels such as sea water
Waters containing hydrogen sulfide, dissolved oxygen,
carbon dioxide, or iron bacteria; excellent strength
Waters having a high total hardness, high sodium
chloride content where dissolved oxygen is absent, or a
high iron content; extremely resistant to acid treatment
Same as Everdur but nor quite as good nor as strong;
used in relatively inactive waters
Not corrosion resistant; used in neutral water
Not corrosion resistant; used for temporary wells
          PVC
0.09/0.15 Carbon
0.20/0.50 Manganese
(double galvanized)

Polyvinylchloride
0.25       Highly corrosion resistant;  Type  I  PVC  is  brittle  and
           will  crack when strained;  not  useful  with  chlorinated
           organics and some organic  solvents

-------
     The well  screen choice is also determined partly on strength require-
ments.  Two loads are imposed on the screen which must be considered in screen
selection; column load and collapse pressure (Johnson Division, UOP Inc., 1975)
Column load results from the screen supporting the weight of the casing.
These forces can be considerable in deep wells.  Collapse pressure results
from earth pressure and caving materials squeezing the screen.  Resistance
to these loads is directly proportional  to the modules of elasticity of the
screen material.  For example, the strength of a stainless steel screen is
twice that of a copper alloy screen of the same size (steel  modules =  30
million psi , copper alloy modul es = 15 mill ion psi).  Screens shoul d be chosen
to have:

     t  Strength to resist load and collapse
     •  Maximum open area consistent with the strength requirements.

     The optimum length of a screen is based on the type and thickness of the
aquifer, the available drawdown, and the stratification of the aquifer.  Table
5-17 gives  some general rules that should be applied when determining screen
length.  The criteria given in Table 5-17 is for contaminants that completely
mix  in the aquifer or are denser than water.  For contaminants that are less
dense than water (i.e., floating contaminants), screen length and placement
should be determined on the basis of plume boundaries and the desired
drawdown.

     The opening size of the well screen requires that the entrance velocity
of the groundwater be less than a critical value.  Some references suggest
using a critical value equal to or less than 0.1 feet per minute (Johnson
Division, UOP  Inc., 1975), while others suggest choosing the critical value of
entrance velocity based on the hydraulic conductivity of the filter material
in contact with the screen (Powers, 1981).  Table 5-18 gives recommended
                                     5-61

-------
            TABLE 5-17.  CRITERIA FOR WELL  SCREEN  LENGTH  SELECTION
                         (After Johnson  Division,  UOP  Inc.,  1975)
Aquifer
Type
Homogeneity
            Criteria
Water Table
(unconfined)
Homogeneous
                     Heterogeneous
Artesian
(confined)
Homogeneous
                     Heterogeneous
•  Screen bottom one third of  aquifer

•  Drawdown should not exceed  the top
   of the screen or a point slightly
   above

•  Screen the most permeable
   sections, especially  in lower part
   of the aquifer

•  Screen sections that  contain
   contaminants regardless of
   permeability

•  Drawdown should not exceed  the top
   of the screen

•  70% to 80% of the aquifer's total
   thickness
   <25 ft - 70%
   25-50 ft - 75%
   >50 ft - 80%

•  Maximum allowable drawdown  should
   be the top of the aquifer

t  Screen as in a homogeneous  aquifer
   to extract contaminants

•  Drawdown should not be lower than
   the top of the screen
                                   5-62

-------
       TABLE 5-18.   RECOMMENDED ENTRANCE  VELOCITIES  FOR  VARIOUS  FILTERS
                                   (Powers,  1981)
              Hydraulic                    Entrance  Velocity
              Conductivity                     (ft/mi n)
>6,000
6,000
5,000
4,000
3,000
2,500
2,000
1,500
1,000
500
<500
12
11
10
9
8
7
6
5
4
3
2
entrance velocities for various filters.   Regardless  of the method  chosen  to
obtain critical  entrance velocities, the  open area  can  be calculated  from:
                = 19.2 Q/Vs
where:
             A  = open area of well  screen (in/ft)
             Q = expected or desired yield of  well  per  unit  length  of  screen
         (g/min-ft)
             Vs = entrance velocity (ft/min)

Once the open area has been determined, the only parameter needed to  correctly
select a well screen is the slot size.   Typical  open areas of some  commer-
cially available screens are given  in Table 5-19.
                                     5-63

-------
         TABLE 5-19.  OPEN AREAS OF COMMERCIALLY AVAILABLE WELLSCREENS
                                    (Powers, 1981)
Nominal
Diameter
(in.)
4




6




8




12




18




24




Slot
Size
(in.)
0.015
0.030
0.060
0.090
0.120
0.015
0.030
0.060
0.090
0.120
0.015
0.030
0.060
0.090
0.120
0.015
0.030
0.060
0.090
0.120
0.015
0.030
0.060
0.090
0.120
0.015
0.030
0.060
0.090
0.120

Continuous
Wire
27.6
46.6
71.2
86.4
96.7
41.2
60.0
84.8
106.9
123.2
39.3
69.3
113.0
142.6
164.3
59.2
81.5
117.4
155.9
186.5
53.5
99.2
169.6
228.1
271.3
83.2
117.5
172.3
235.1
289.4
Approximate
Double
Louvre

5.9
—
—
—
_ «
6.9
13.9
20.7
28.7
. _
9.1
18.6
27.6
38.3
_ _
13.7
27.8
41.3
57.4
_ _.
19.8
40.2
59.7
82.9
— _
25.9
52.6
78.1
108.4
Open Area
Slotted
PVC
8.9
14.4
27.1
43.4
57.6
10.1
20.2
40.3
60.5
80.6
13.0
25.9
51.8
77.8
103.7
20.2
40.3
80.5
121.0
161.3
28.8
57.6
115.9
172.8
217.5
_ w
__
__
__
— -
(in2/ft)*
Wire
Mesh
76.3
__
__
__
--
112.4
__
__
__
--
146.3
__
—
__
--
216.3
—
—
__
—
305.4
—
__
__
--
407.2
__
__
__
--
*0pen area may be less than manufacturer's specifications because of design;
 refer to Table 5-14.
                                     5-64

-------
     Determining the required slot size for the screen depends on the well
development method to be used and the filter pack.  A mechanical  analysis
(i.e., sieve analysis) must be performed on a sample representing the water-
bearing formation to select the proper slot size.  This approach differs from
that used for monitoring wells, i.e., the use of a 10-slot screen (Sisk,
1981), because wells used  in  remedial actions are typically pumped exten-
sively. Extensive pumping  with improper screens and development can result  in
low yields, premature pump wear, and possible well failure.

     Most wells used for remedial actions will probably be drilled, which
normally requires the area around the well  screen to be filled with a filter
or gravel.  This filter performs several  important functions  (Powers, 1981):

     •  Fills the annular  space  preventing  the uncontrolled collapse of the
        formation against  the screen
     t  Retains a sufficient  percentage of  fines  thus  preventing them from
        being pumped continuously
     •  Passes  some  amount of fines  and mud cake  that  have built-up on the
        sides of the hole
     •  Transmits water  freely from  the aquifer  to  the  screen during pumping.

      Procedures for  selecting filters  and  screens have  been developed by
numerous groups, however,  a method developed  by  Powers  (1981) is described
below.  The  first step  in  the procedures  is to obtain a sample at the aquifer
and  conduct  a mechanical  analysis of it.   Results of  the  analysis are plotted
as  shown  in  Figure  5-21a.  A  filter  range  is  thus established such that:

      •  The  filter  is of uniform material,  preferably  with a  uniformity
        coefficient (C  ) of  C <3.0
      •  The  filter  C is not  greater than  the  aquifer  C  unless  it is a  graded
        filter       u                                   u
      •  The  filter  D™  is  four  to eight  times greater  than the aquifer D™.
                                      5-65

-------
            FIGURE 5-21. RANGE OF FILTER SELECTIONS
                              (POWERS, 1981)
        3" 2"
                                Sieve Numbers

              V 3/4" 1/2"   1/4" 4   6  10   16 20  30 40  50 60  100 140 200 270
                 I   I	II    II	ill;   I  I   i I   I   I   I
                                                         Mechanical Analysis
                                                         of Soil
                                                         C. - 4.5
                           |9  7  |    3   |       |9  7  |     3
                          10     5.0      2.0    1.0    0.5    0.25
                                  Grain Size  (mm)
                              250 160 100 80 60  40 30 20    To  Slotted Screen
                                         11    1

1
4
Gravel
1 1 1 1 1 I 1
' 3" 1" 3" 1" 1" 1" Louvred Screen
16 8 32 16 32 64 Si|,

Coarse Sand
Medium
Sand
Fine Sand
and
Clay
      Figure 5-21 a.
                                 MA Classification
                                  Sieve Numbers

         1/4" 4    6   10    16 20  30 40  606080100140200270
t
^
100

 90

 80

 70

 60

 50

 40

 30

 20

 10
K


•1 	 '










' —


9 7
0 i

\\
V1
\


x
\ i
1



v\ ^\
(&C

N\V
\\\
Filter
Specrfi


\vi
cation ^A ,'
\]
\
3 1
> 2 1



i
\
s
9 7
\




V

-. Baa
Lu

V
V




\l
0
ft

c Filter Curve
- 2.5 DM -
! !
1
5 X 0.4 * 2.0
i
i

. — Mechanical Analysis
1 of Sou '
OBO - 0.4 c - 6 ;
\
\



!


3 | |9 7 3
5 0.25 .1 .05 .0
         0.025 in. 0.63mm           H
                                   ,  Medium ,
            Gravel       Coarte Sand    Sand  I  Fme Sand
                                                           Silt and Clay
       Figure 6-21 b.
                                      Classification
                                   5-66

-------
     The range of suitable filters is then plotted as shown  in  Figure 5-21a.
A rather broad range of filters is established  for a  soil  D5Q and  selection of
the proper filter within this range is based on the gradation of the  soil  and
the desired yield of the well.   Table 5-20 gives criteria  for determining
filter requirements more precisely.

     Once the range of acceptable filters has been narrowed  to  fit the
specific application, the results of the mechanical  analysis is replotted  as
shown in Figure 5-21b.  Typically, a set of limits within  which the filter
material must fall is furnished to a supplier.   The mechanical  analysis of the
supplied filter material is then plotted.  Well screen slot  size is finally
selected to pass about 10 percent at the fine limit and 0  percent of  the
coarse limit  (Figure 5-21b).  While this procedure appears to  be fairly
simple, a significant amount of judgement is required in applying it  to
specific site conditions.

     For naturally developed wells (i.e., wells without a  gravel pack), well
screen opening size is selected from a mechanical  analysis of  the water-
bearing  formation  (Figure 5-22).  The correct slot opening  size is chosen so
that the screen will retain from 40 percent to 50 percent  of the particles
(Johnson Division, UOP  Inc., 1975).  The 40 percent size is chosen for wells
in  non-corrosive  water and where sample  analysis  is considered   reliable.  The
50  percent  size  is chosen  for  wells  in corrosive  waters (i.e.,   to allow for
some enlarging of screen openings)  and where sample analysis reliability is in
doubt.   For the  grain  size analysis  shown  in Figure 5-22, the  screen  opening
selected would be between  0.040  inch  and 0.050  inch  (50 percent and  40  percent
retention,  respectively).

      Where  stratified  soils  are  encountered, the  screen slot opening  is chosen
according  to  the  gradation of  materials  of  the different  strata.   Table 5-21
gives  some  criteria  for  selecting  and  placing  screens  in  stratified  soils.
The examples  given  in  the  table  are  generalizations and should  be viewed as
such.   For  example,  cutting  off  silty  zones  with  blank casing  may be
preferable.   The  use of  variable  or  graded  filters may also be  necessary to
achieve good  results.   However,  a  rule  of thumb used by drillers  is  to  allow
                                      5-67

-------
          TABLE 5-20.   FILTER SELECTION CRITERIA (AFTER POWERS,  1981)
Characteristic
                    Criteria
Gradation of Soil
For uniform soil s (C  < 3):   the D™ of the fil ter
                    u —           b(J
should be in the  low range,  about 4 to 5 times the D
of the soil.
                                                                            50
                        For graded soils (4 < C   <  6):   the  Dco of the  filter
                                            —  U  —           bl)
                        can be 5 to 6 times the Dr_ of  the  soil .
                                                 bi)
                        For very well  graded soils (C  >_7)  where it may be
                        desirable to develop some  fines from the  soil :   the
                        D&0 of the filter can be as great as 8 times the D
                        of the soil.
                                                  50
Yield of Well
For low well yields per linear foot of screen in
relation to hydraulic conductivity:  the multiples of
the Drg of the filter can be increased by a factor of
1 or perhaps 2 because pore velocities are low enough
to preclude the movement of fines.

For high well  yields per linear foot of screen in
relation to hydraulic conductivity:  the multiplier of
the D   filter should not be increased.
     bL)
                                     5-68

-------
en
 i
CTl
IO
                                                      Cumulative Percent Retained



                                                                &      S
o
x o
(O >
IP
o —
^ m £)
£>S
                                                                                                                       z c

-------
            TABLE 5-21.   WELL SCREEN SELECTION FOR STRATIFIED SOILS
                       (Johnson Division,  UOP Inc, 1975)
Development
  Type
     Strati fication
         Scheme
        Criteri a
Filter Pack
Coarse material  over fine
                   Fine material  over coarse
Natural ly
Coarse material  over fine
                   Fine material  over coarse
Filter and screen  selected
  should be suitable for the
  finer materi al

Filter and screen  selected
  should be suitable for the
  coarse material  because the
  coarse material  will
  probably draw the fine
  material

Screen should be  selected
  according to each soil
  materi al

Screen should be  selected
  according to each soil
  material; screen in the
  fine material should extend
  at least 2 feet  into the
  coarse material  and the
  slot si ze in the coarse
  material should not be
  twice that of the screen in
  the fine material
the finer material to dictate screen size over the various strata because

mixing packs in the field is difficult and graded packs can differentiate in
pi ace.


          5.4.1.2  Ejector Wells


     Ejector wells or systems have certain advantages over wellpoints and deep

wells because they are not typically depth limited as wellpoints are and they

are less expensive than deep wells when close spacing is required.  The

biggest drawback to the use of ejector wells is that they are very inefficient

(typically less than 15 percent efficiency).  Ejector wells can be used
                                     5-70

-------
independently of each other or arranged so that they utilize a common pumping

system.


     The typical components of a two-pipe and a single-pipe ejector well

system are illustrated in Figure 5-23.   The lift principle for the two-pipe
model is (Powers, 1981):


     •  High pressure supply water (Q ) moves down the supply pipe through
        ports in the ejector body to the tapered nozzle where the pressure
        head is converted to water velocity

     •  Supply water exits the nozzle at less than atmospheric pressure
        creating a vacuum in the suction chamber

     •  Groundwater (Q?) is drawn into  the chamber through the foot valve
        because of the pressure differential

     •  Supply water and groundwater (Q  + Q?) are mixed in the suction
        chamber

     •  The mixed water enters the venturi where the velocity decreases
        because of divergence resulting in increased pressure

     •  The increase  in pressure develops sufficient head to return the
        combined flow to the surface.
     The lift  principle for the  single-pipe model, illustrated in Figure 5-23,
i s  (Powers, 1981):


     •  Supply water  under pressure (Q  ) flows downward between the well
        casing and the inner ejector return pipe

     •  The nozzle, suction chamber, and venturi perform as described for the
        two-pipe system

     •  A packer assembly separates the  supply water  from the groundwater so
        that different pressures are developed

     •  Foot valves located below the  packer are used  as in the two-pipe
        ejector system.


     Casing and screens used by  ejector  systems are the same as those utilized

by  deep wells  or wellpoints.  Design recommendations  for casing and riser
 sizes are given in Table 5-22.   Single-pipe ejector wells are most commonly
 used because they require less piping  and yields are  greater for smaller
diameter casings.


                                     5-71

-------
                             FIGURE 5-23.
 COMPONENTS OF ONE-PIPE AND TWO-PIPE EJECTOR WELLS
                           (POWERS, 1981)
              Overflow
                                                                  Strainer
Return Header
  Well Seal
   2 in.  (50-mm)
   Riser—	
                                  -X
                                 Supply Header
     Packer
                                           2 in. (50-mm)
                                           Return Line
                     1% in. (32-mm) Riser
                     with Turned Couplings
  tl
                    •2-in (50-mm|
                     wcllpomt
                                                Screen.
                                                               ,Well Casing
                                                                and Screen
                                                               • 1 % in.
                                                                137mm)
                                                                Supply Line
                                                                (Q
            • Ejector
             Body
            • Foot
             Valve
         Typical Single-Pipe
         Ejector Installed
         in a 2-m. (50-mm)
         Wellpoint
Typical Two-Pipe
Ejector Installed in
a 6-in. (150-mm)
Well
                                 5-72

-------
                     TABLE  5-22.   RECOMMENDED CASING AND  RISER  SIZES  FOR  EJECTOR  SYSTEMS (Powers,  1981)*
en

GO
Groundwater
Flow (Q )
(gpmr
12
20
40
70
Single Pipe
Well Casing
(in)
2.0
2.5
4.0
5.0
Ejector
Return Pipe
(in)
1.25
1.50
2.00
2.50

Well Casing
(in)
4
5
5
6
Two Pipe Ejector
Supply Pipe
(in)
1.00
1.25
1.50
2.00

Return Pipe
(in)
1.25
1.50
2.00
2.50
            *Recommended pipe sizes  are  for  a  setting  of  40 feet  with  a  supply pressure of 120 psi;  deeper
             settings or lower pressures require  larger pipe sizes.

-------
     Ejector  pumps consist  of  a water  tank  and  a  pump  with  the  required valves
and piping.   Each well can  have its own  pump  or one  pump  can  be  used  by a
number of wells.  Water from the  storage tank is  pumped  under pressure  through
a header pipe that supplies the ejector  wells.  Return flow,  a mixture  of
supply water  and groundwater,  recharges  the tank  through  the  header  system.
Excess water  in the tank  is discharged to a treatment  system.

     Selecting the proper ejector pump and  educers (i.e., nozzle and  venturi)
can be made using manufacturer's data or  through  calculations.   An example of
manufacturer's data is given in Table 5-23.   The  procedures for  calculating
the size of an ejector are to  calculate  head  ratios, estimate the capacity
ratios, and calculate the diameters of the nozzle and the venturi.  The
procedure is fairly complex and is described  in detail by Powers (1981).

     Materials for risers, swings, headers, tanks, screens, and  pumps should
be selected to minimize corrosion and encrustation.  Selection criteria are
the same as for deep well systems, however, ejectors must also be protected to
maintain well performance.  Ejectors used in  corrosive environments can be
made of plastic to eliminate the problem.  Of greater importance is the
ejectors'  sensitivity to clogging especially  if clogging results  from
encrustation,caused by the pressure reduction.  Reduction in  pressures  at the
throat of the venturi  can cause accelerated rates of chemical precipitation.
A continuous water supply to eliminate recirculation and filters may be
necessary to prevent encrustation and clogging.  A water analysis prior to
designing the system is advisable to test for problems that may  limit ejector
well use.

          5.4.1.3  Wellpoints

     Well point systems consist of a group of  closely spaced wells connected to
a header pipe and pumped by a  suction pump.    Wellpoints are best  suited  for
groundwater extraction in stratified soils where total lift or drawdown  will
not exceed approximately 22 feet.   The advantages to using wellpoints are that
the system design is flexible  and the wellpoints are relatively  inexpensive
even when  closely spaced.
                                     5-74

-------
TABLE 5-23.   EJECTOR SYSTEM PERFORMANCE SPECIFICATIONS (Burks HNAZ Series Pumps)
One-Pipe Educer
Pump Well
Dia.
HNAZ Series
5 HNAZ . 2"
1/2 Up
7 HNAZ 2"
3/4 Up
10 HNAZ 2"
1 np

Educer Pressure
No. Switch
Setting

22183 20-40
22184
22185 30-50
22171
22185 30-50
22186
22176
Control
Valve
Setting

38
35
32
35
35
42
50
Capacity in Gallons Per Hour
At Vertical Depth To Pumping Level

30'
675
515
840
495
965
550


40'
660
480
800
480
920
520


50' 60'
545 425
450 400
680 560
465 450
790 660
505 485
350 350

70'
330
350
425
420
530
450
330

80'
190
290
310
390
400
410
320

90'

250

330
285
360
295

100'

200

270
140
320
260

110' 120' 130' 140' 150' 160'

150

210 150

285 155
230 200 175 150 125 100
Max. Shutoff
Pressure At
Deepest Set'g

55
62
55
62
55
66
72

Two-Pipe Educer
Pump Min.
Well
Dia.
5 HNAZ 4"
1/2 hp
7 HNAZ 4"
3/4 hp
10 HNAZ 4"
1 hp

Educer Pressure
No. Switch
Setting
22199 20-40
22200
22196 30-50
22197
22201 30-50
22194
22202
Control
Valve
Setting
32
32
28
30
33
38
38
Capacity in
Gallons Per Hour
At Vertical Depth To Pumping

30'
585
405
860

990
575
385

40'
570
400
850

970
570
380

50' 60'
475 380
395 390
730 610
480 480
820 665
565 555
375 370

70'
305
365
505
455
525
525
365

80'
225
320
385
395
375
465
360

90'

275

330

405
355

100'

230

270

335
345
Level

110' 120' 130' 140' 150' 160'

190 150

220 180 140

275 210 155
315 260 210 175 140 105
Max. Shutoff
Pressure At
Deepest Set'g
58
61
58
63
53
59
62

-------
     A suction (vacuum) pump is typically used in wellpoint systems to lift
water.  Suction pumps accomplish lift by developing a negative pressure head
at the pump intake rather than by applying force to the water source as in
ejector pump systems.  Four factors limit the maximum lift attainable by
suction:  atmospheric pressure, vapor pressure, head losses caused by
friction, and the required inlet head of the pump.  Because of these factors,
the maximum lift theoretically attainable is about 25 feet.  In practice,
however, lifts between 15 and 22 feet are more common when centrifugal pumps
are used.

     Two types of suction pumps are commonly used, the oil sealed  and the
water sealed vacuum pump.  Pumps are usually rated by the volume of air
handled at various vacuums under standard conditions of temperature and
pressure.  Oil sealed pumps are capable of producing vacuums of 30 to
100 cubic feet per minute at 25 inches of mercury; water sealed pumps produce
vacuums of 50 to 500 cubic feet per minute at 25 inches of mercury.

     Wellpoints are specially made well-screens that are typically 1.5 to
3.5 inches in diameter and are capable of yields up to 35 gallons per minute.
Large wellpoints are available, up to 8 inches in diameter, which have
capacities greater than 35 gallons per minute.  These large wells are
generally called suction wells rather than wellpoints.  Wellpoints can be
installed using a variety of methods including jetting and driving.
Figure 5-24 shows the basic types of wellpoints.  Wellpoint screens can be
made of heavy wire mesh, continuous wire, slotted plastic, or perforated
plates.  The materials selected should minimize the potential for corrosion
and encrustation.  The guidelines for wellpoint materials are the same as for
deep wells.

     The depth at which wellpoints are set is dependent upon the hydrogeology
of the site.  Drawdown is limited to approximately 22 feet below land surface,
but the wellpoint can be set  at almost any depth depending on the  situation.
Where contaminants float at the top of the aquifer, wellpoints can be set  at
shallow depths.  Where contaminants sink  or mix with the groundwater, the
wellpoints can be set deeper.  The only criterion for wellpoint depth is to
                                     5-76

-------
                                                                      FIGURE 5-24.
                                                   DRIVEN WELLPOINT (a), JETTED WELLPOINT (b),
                                                             AND DRILLED WELLPOINT (c)
                                            (JOHNSON DIVISION, UOP INC., 1975 a & b;  POWERS,  1981c)
en
i
                     Well Casing
                                                                                    (from pump)
                   Figure 5-24a. Weilpoint Driven
                                                                              Well Casing
                                                                             Ring Seal of
                                                                             Semi-rigid Plastic
                                                                             Temporary
                                                                             Wash Pipe
                                                                         X—  Well Screen
                                                                           -- Coupling on Wash Pipe  -V
                                                                             Rests in Conical Seal

                                                                           -~ Combination Back-pressure
                                                                             Valve in Open Position
                                                                                                    ,--,;.'-. ;Varved
                                                                                                    .v. "-;.'•  siit
                                                            •
-------
 avoid  dewatering  below the screen.   If this occurs,  air enters the system and
 reduces  the vacuum and therefore the drawdown.   During normal operation of the
 system,  dewatering below the  top of a well screen can sometimes occur.  The
 problem  can be  minimized in  the  field by adjusting the values that control
 individual  wells.

     Because well points  are  typically installed  in oversized boreholes, filter
 sands  are  placed  around  the wellpoint to fill the annular space.   Besides
 filling  the annular  space, the sands perform other functions, including
 (Powers, 1981):

     •   Increasing the effective diameter of the wellpoint
     •   Decreasing the entrance  velocities  of water
     0   Preventing clogging of the  screen with fines
     •   Providing  vertical drainage  from overlying layers.

 Commercially available wellpoints are typically  designed  with openings
 suitable for  use with  washed  concrete sand  filters.   This type of  filter
 performs well when the soil penetrated  is finer  than the  concrete  sand.  If
 soils are very  fine  and  have  little  cohesion, however,  they may migrate
 towards  the  wellpoint  when concrete  sand filters are used.   In this  instance,
mortar sand  filters may  improve  well  yields  and  prevent clogging.  For some
 applications, selecting  the filter material  and  the  screen  opening specific-
 ally for each wellpoint's  application may be necessary  as described  in the
deep well section.

          5.4.1.4  Recharge Wells

     Recharge wells are  sometimes used  in plume  management  to  create  ground-
water mounds or to act as depositors  for  treated water.   The  design of a
recharge well is similar to an extraction well (Figure 5-25)  with a few
variations.  Pumps, casing, filter packs, and screens should  be designed  in a
                                    5-78

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                         FIGURE 5-25.
          BASIC INJECTION WELL (POWERS, 1981)
Air Vent-
              Meter
Control
Valve
               Recharge     l	
               Header
           Sand
          Aquifer
             - Air Vent
              Filter Replacement
             -Tube
                                         Casing
                                        . Concrete or
                                         Grout Seal
                                        • Downspout
                                        . Filter Pack
                                       - Wellscreen
                           5-79

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similar manner as outlined in the previous sections.  The  additional  features
that are normally needed are (Powers, 1981):

     •  A downspout to prevent air entrapment from cascading water when  the
        well is operated at a low level
     t  An air vent to release trapped air at start-ups
     t  A concrete or grout seal to prevent water from flowing  along  the
        casing to the surface when the well is pressurized.

Development and periodic redevelopment of an injection well  is  necessary to
maintain efficiencies because they do not continue to develop themselves  with
use as extraction wells do.

     5.4.2  System Design

     System design includes a determination of the number  of wells needed, the
patterns and spacing of the wells, the design of the individual wells, the
pumping cycles and rates needed, and the method of handling discharges.   The
following sections provide some general guidelines for well system design.

          5.4.2.1  Preliminary Requirements

     Prior to designing the well system, a complete hydrogeologic under-
standing of the site must be established.  A potentiometric surface map  (i.e.,
a map depicting contours of equal head) and a geologic cross-section  of  the
site should be developed.  Development of these two tools  is very important to
well system design.  Figure 5-26  gives an example of these for a gasoline
pipeline leak.  Other parameters that are required for system design  are  the
coefficients of transmissivity (T) and storage (S) and the discharge  (Q)  and
drawdowns (H-h ) from the pump tests.  Once data on these  parameters  are
              W
established, the design process can proceed.
                                     5-80

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                  FIGURE 5-26.
POTENTIOMETRIC SURFACE MAP AND GEOLOGIC
 CROSS-SECTION OF GASOLINE POLLUTION SITE
         (WILLIAMS AND WILDER, 1971)
                Strong Taste
                and Odor Area
 Figure 5-26a. Plane View
           -Brown Clayey Silt
             Grey Organic Clay
 Figure 5-26b. Cross-sectional View
                      5-81

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          5.4.2.2  Equilibrium vs. Non-Equilibrium Pumping

     A choice has to be made whether equilibrium or non-equilibrium  pumping  is
to be utilized at the site because this affects the extent of the radii of
influence.  As pumping time decreases the radii of influence also decrease
(refer to Figure 5-15) and this will result in a larger number of wells needed
for a given area.  Using the example given in Figure 5-15, increasing the
pumping time from 300 minutes to 1,000 minutes causes the radius of  influence
to increase from 350 feet to 650 feet.

     Equilibrium pumping will probably be utilized in most plume management
sytems, but non-equilibrium pumping does have advantages in some cases.  Table
5-24 lists the advantages and disadvantages of both approaches.  Typically,
cyclic pumping systems cost more because of the need for a larger number of
wells with greater capacities and the greater operation and maintenance
requirements.

          5.4.2.3  Well Spacing

     Determination of the proper spacing of wells to completely capture a
groundwater plume is probably the most important item in system design.  Field
practitioners have long had a standing "rule of thumb" for estimating well
spacing; adjacent cones of depression should overlap (i.e., radius of
influence should overlap).  This method is valid for aquifers that have low
natural flow velocities but will not be valid for aquifers with large natural
flow velocities.  For these latter cases (and probably all cases) velocity
distribution plots should be developed to determine well spacing and ensure
capture of the plume (Keely and Tsang, 1983).  Both of these methods are
discussed in the following sections.

               5.4.2.3.1  Radius of Influence

     The most accurate method for estimating the radius of influence is by
pumping test analysis.  Pumping tests can identify recharge boundaries,
barrier boundaries, and slow-storage release conditions.  The pumping test
                                    5-82

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         TABLE 5-24.  ADVANTAGES AND DISADVANTAGES OF PUMPING METHODS
Method
       Advantage
       Disadvantage
Equilibrium
Non-equilibrium
• Greater well spacing is
  feasible, thus reducing
  the number of wells

• Constant discharges to
  treatment

• Reduced pumping rates may
  be possible

• Better suited to
  aquifers with high
  hydraulic conductivities

• Operation and maintenance
  cost may be lower because
  cycling is hard on system
  components

• Easier to design  and operate
  effectively

• Better suited to  aquifers
  with low hydraulic
  conductivities

• May be more applicable to
  floating and sinking plumes

• May be more suitable for
  sites that have groundwater
  barriers and scant recharge
t May require long pumping
  times before cones
  intersect, which may be
  a problem with fast
  moving contaminants

• Not as workable in
  aquifers with low
  hydraulic conductivities

t May not work well where
  the flow of contaminants
  is low, where the plume
  floats, or sinks, or
  where recharge is scant
• Closer spacing of wells
  is required resulting  in
  a greater number of
  well s

• Design is fairly
  complicated

• May have higher
  operation and
  maintenance costs
  because of cycling

• Greater capacity pumps
  are usually required
                                    5-83

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should be performed until  equil ibriun  conditions  are  reached.   Typical  test
durations for a confined aquifer are  about  24  hours,  while for  an  unconfined
aquifer they may be several  days.   Once  equilibrium  conditions  have  been
reached, the radius of influence for  equilibrium  or  non-equilibrium  conditions
can be estimated using the methods  described  previously  and  the equations  in
Table 5-25.

     When pumping test data are lacking  or  incomplete,  rough estimates  of  the
radius of influence can be obtained from the  values  of  transmissivity or
hydraulic conductivity, pumping times, and  coefficient  of storage  and the
equations presented in Table 5-25.   Coefficients  of  storage  values typically
range from 0.01 to 0.35 for water-table aquifers  and  from 0.00001 to 0.001
for confined aquifers.  Typical  values are  0.2 for water-table  aquifers and
0.001 for confined aquifers.

     When using equilibrium formulas,  the radius  of  influence appears as a
logarithmic function so that percision in estimating  is  not  necessary.
However, values of RQ measured in the  field can vary from 100 to  100,000 feet
and greater orders of magnitudes are  possible.  Therefore, gross  errors in
actual R  values are possible.

     When estimates are made without  pumping  data, the  values obtained  are
rough approximations that do not take recharge into  account.  These  estimates
should be adjusted on the basis of judgments  made on the locations  of possible
recharge and discharge barriers.  Adjusting values of R  downward  is advisable
in most cases because the greater overlap of the  cones  of depression will
result in a lower probability of containment  escape  between  wells.   The
tradeoff, however, is a greater number of wells and  higher costs.

     A comparison of the results obtained for R  when pumping test  data are
used and when estimates are made is given below.   A well is an unconfined
aquifer pumped  under equil ibriun conditions provided the following
information:
     •   Q  =  500 gpd
     •   K  =  500 gpd/ft2
                                     5-84

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                  TABLE 5-25.   RADIUS OF INFLUENCE EQUATIONS
Pumping                 Unconfined Aquifer         Confined Aquifer
Method
Equilibria      1 nRQ =  (K(H2-hw2)/458Q) + lnrw   1 nRQ = (T(H-hw)/229Q) + 1
Non-equil ibriun          distance - drawdown plots or Theis Method
Estimates                    Rn = r  + (Tt/4790S)°'5*
                              (j    w
                                     f ••'
                             Ro = 3(H-hw)(0.47K)°-5

R  = radius of influence (ft)
                                   2
K  = hydraulic conductivity  (gpd/ft )
H  = total  head (ft)
h  = head in wel 1 (ft)
Q  = pumping rate (gpd)
r  = well radius (effective  radius) (ft)
 W
T  = transmissivity (gpd/ft)
t  = time (min)
S  = storage coefficient
*For  unconfined  aquifers H-h cannot be a large percentate of H
                                     5-85

-------
     •  r = 0.5 ft
         w

     e  H = 100 ft


     •  h  = 80 ft.
         w



Using the exact equation for R  given in  Table 5-25:




     lnRQ = [K(H2-hw2)/458Q] + lnrw



          = [500(1002-802)/458(500)]  + In0.5


       R  = 1296 ft.
        o



Using the first estimation equation for R  given in  Table 5-25:




     R0 = rw + (Tt/4790S)0'5


          t = 7 day  or 10080 min (assumed)


          C  = 0.2 (assumed)



        = 0.5 + [50000(10080)74790(0.2)]°'5


     R  = 725 ft.
      o


 Using the second  estimation equation for R  given in  Table 5-25:




          R  = 3(H-hw)(0.47K)°'5



             = 3(100-80)(0.47(500))°'5


          R  = 920 ft.
           0



This comparison illustrates the importance of exercising  good  judgment in

selecting well spacing.




               5.4.2.3.2  Velocity Plots




     Well spacing  for complete plume removal can more  accurately be determined


by developing velocity plots for the  pumping well (Keely  and Tsang, 1983).
                                     5-86

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Velocity of flow through an aquifer can  be expressed  as (i.e.,  from  Darcy's
Law:  Section 5.2.1):

          V = Q/An = Kl/n

     where:

          V = pore velocity (ft/day)
          Q = flow rate  (gpd)
                                               2
          A = area normal  to flow direction (ft )
          n = effective porosity (dimensionless)
                                            2
          K = hydraulic conductivity (gpd/ft )
          I = hydraulic gradient (dimensionless)
     Using Darcy's Law for calculating pore velocity, two important deri-
vations can be made:  water velocity toward a pumping well and natural fl
velocity  in the  aquifer.  Velocity toward  a well can be  represented by:
ow
           V     .    = Q/An  = Q/2vrrhn
           pumping

     where the  new  terms are:

           r  =  distance  from well  center  to  point where drawdown is measured
               (ft)
           h  =  drawdown  (ft)

 This expression is  typically  used for  pumping  wells  because Q is  usually  known
 for  the  well  and  A  can  be  easily  estimated.  The area, A,  in the  above
 equation represents the area  of the  curved  face of an  imaginery cylinder
 (refer  to Figure  5-2)  for  some  distance  away from the  well.  This area can be
 calculated by A = 2 TT rh and  substituted  into the original  Darcy equation.
                                      5-87

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     For calculating natural flow velocities the following equation  is
typically used:

          Natural = KI/n

This equation  is chosen because, for the aquifer under  investigation, the
average hydraulic conductivity (K) and hydraulic gradient (I) are usually
known or can be estimated with a relative degree of accuracy.

     Utilizing these two equations the downgradient stagnation point, i.e.,
the distance downgradient the pull of waters back toward the well by pumping
is exactly countered by the natural flow velocity of water away from the well
(Keely and Tsang, 1983), can be calculated by setting the expression for
Vpumping equal to the value of VnaturaV  This equa1ity is represented by
(Keely and Tsang, 1983):

          V        = V
           pumping    natural

          Q/2?r rhn = V  .    ,
                      natural

and then  solving for r to provide the stagnation point:

          r =  (Q/27Thn) V  .    ,
                      '  natural

where h is represented by saturated thickness of the aquifer.  This
relationship shows that the stagnation point is directly related to  the
pumping rate of the well (i.e., the higher the pumping rate the further
downgradient the stagnation point) and inversely related to the natural flow
velocity (i.e., the greater the natural flow velocity the closer the
stagnation point is to the well).

     The maximum distance to either side of the well perpendicular to
groundwater flow, and therefore the well spacing, that contaminants  are not
drawn completely into the well has been defined by Todd (1980) as  * times the
downgradient stagnation point ( Trr).   Hence, any contaminants that lie outside
                                     5-88

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the  TT r distance will not be captured by  the  well.   These  boundaries, -nr
downgradient and it r perpendicular to flow, define  the  areal  limits  of  a
pumping well's capture zone.  Keely  and Tsang  (1983)  have  noted  that  for  only
the  extremely rare case of  zero natural flow  are  the areal  boundaries of  the
capture zone identical to the calculated  cone  of  depression.   This means  that
even though the cones of depression  of two pumping  wells  intersect they may
not  be completely capturing the plume unless  their  capture  zones  intersect.
The  ramifications of the this finding on  well  spacing for  plume  removal is
paramount.

     The use of the preceding equation can be  used  to calculate  the  capture
zone of a pumping well and well spacing ( irr)  using  a simple  hand-held
calculation.  However, numerous computer  models are  available that can  perform
these calculations and provide velocity plots.  Two  such models  are  the radial
flow time series model and the RESSQ model.   Readers are referred to  Keely  and
Tsang (1983) for a detailed explanation of these  models.

     An example of the use of the equality equation  is  provided  below.  Assume
that the following data are available for the  aquifer under investigation:

          Q = 100,000 ft3/day
          K = 600 ft/day
          h = 100 ft
          I = 0.0015 (15 ft/10,0000 ft)
          n = 0.30

Using these data in the equality equation for  the downgradient stagnation
point provides the following:

          r = (Q/27Thn)  Vnatupal  = Q/27T hn(KI/n)
            = (100,000/2 7T  (100)(0.30))[(600)(0.0015)/0.30)]
            = (100,000/27T  (100)(0.30))(2.6)
            = 204 ft
                                    5-89

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The well  spacing  can therefore  be  calculated  (as  previously defined)  by ?r r =
604 ft.   This means that  a  line  of extraction  wells  placed  perpendicular to
groundwater flow  would  have  to  be  spaced  at distances  of  1208  ft  (i.e.,  2 ?rr)
to capture the  plume.

          5.4.2.4 Pumping Rates

     Pumping rates and  drawdowns are related by:

           2  2
     •  Q/H -h  = constant for  unconfined  aquifers
     •  Q/H-h = constant  for confined aquifers.

This means that increasing the pumping rates will not  affect the  radius  of
influence, but will affect the time of pumping (refer  to  Figure 5-15).
However,  in reality, this may or may not  be true  for a field situation.

     For  unconfined aquifers, the  optimum  operating characteristics have been
shown to  occur at about 67 percent  of the maximum drawdown.   This can  be
demonstrated mathematically from plots of  specific yield  versus maximum
drawdown, and specific  capacity versus maximum drawdown (Figure 5-27).   When
the product of yield and  capacity  is a maximum, optimal operating conditions
are obtained.  Drawdowns  greater than 70  percent  of the  maximum  are
uneconomical. This means  that for  an unconfined aquifer with a saturated
thickness of 100 feet,  the drawdown should be  approximately 67 feet for
optimum operating conditions to be obtained.   Drawdowns less than 67  percent
of the maximum may be desirable in cases when  steady state, long  term pumping
is anticipated because the cones of depression will  be the  same.

     For confined aquifers, the drawdown  is directly proportional to  the
discharge as long as the drawdown does not exceed the  top of the  aquifer.
Therefore, optimum operating conditions vary.   Because pumping rates  are
directly related to drawdowns and will  not affect the  cone  of depression,
pumping rates can be obtained to suit the  situation.   In  situations where the
contaminate plume floats, drawdowns and pumping rates  will  probably be small.
Large drawdowns and high pumping rates are desirable where  contaminants  are
                                    5-90

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                                   FIGURE 5-27.
                 DRAWDOWN VERSUS YIELD AND SPECIFIC CAPACITY
                           FOR A WATER TABLE AQUIFER
                        (JOHNSON DIVISION, UOP INC., 1975)
                                                             100

                                                             90

                                                             80
                                                            70
        >-
        'o
        (D
        a
        (U
        O
        o
     60  'o
                                                            50 |

                                                            40 J
                                                               "o
                                                            30 -
                                                               a>
                                                               S
                                                            20 i£
                                                            10
                         10  20  30  40   50   60   70   80
                               Percent of Maximum Drawdown
90  100
dispersed throughout  the  aquifer,  where quick removal is desired  and  natural
groundwater flow  rates  are  large.   Close spacing of wells with  large  drawdowns
and high pumping  rates  can  very quickly dewater an aquifer.

          5.4.2.5  System Integration

     Once the well  spacing, pumping rate, and drawdown have been  determined,
the system can be designed  as  a unit.   At this point, a decision must be made
on the pattern and  type  (i.e.,  injection or extraction) of wells  to be
installed.  Numerous  patterns  of extraction wells or injection wells or both
are available.  The choice  is  typically based on whether the design is for
containment or removal, the time available for recovery, and the  amount of
dewatering that is  allowable.   Straight line extraction or injection patterns
would probably be used  in containment,  while the more complex patterns of
extraction and injection  wells  would  be used for removal.  Patterns that
combine extraction  and  injection wells  allow for more rapid contaminant
removal without greatly affecting  groundwater levels.  These patterns are also
advantageous because  the  treated water  extracted can be reinjected.
                                    5-91

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     After a well pattern is chosen, the number of wells needed to control the
plume must be determined.  This is based on the estimated well spacing and the
drawdown required.  In spacing wells for plume control, it is necessary to
have the well's capture zones intersect each other so that contaminants will
not flow between wells and escape.  Where low natural flow velocities exist,
cone overlap may be small; where large natural flow velocities exist, cone
overlap should be greater to ensure capturing the plume.

     The number of wells needed can be determined by plotting the chosen map
pattern of wells with their required spacing on the potentiometric surface map
of the site.  After this is done, the drawdowns within the radii of influence
should be plotted and cumulative drawdowns determined.  This will result in a
new potentiometric surface map of the site that can be used to identify dead-
spots or where contaminants can escape.  Monitoring the system's effectiveness
in contaminant removal should also be performed utilizing wells. The location
of these wells can be determined from the revised potentiometric surface map
by identifying deadspots or areas where cones of depression overlap.  An
example of a system design for an ideal, low natural flow velocity, water-
table aquifer (i.e., homogeneous, anisotropic, unlimited extent) is given
below and shown in Figure 5-28.

     A contaminant plume originating from a landfill has been discovered and
delineated as shown in Figure 5-28.  Removal of the existing plume and
containment of any new contaminants is desired.  A pumping test conducted at
the site determined the hydrogeologic parameters to be:

     t  K = 25 gpd/ft2
     •  Q = 100 gpm
     t  H = 100 ft
     •  hw = 46 ft
     •  rw = 0.5 ft.
                                     5-92

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	Impermeable Bedrock
           Figure

-------
Continuous pumping  is to  be  used  at  the  site  because  the  source  of contam-
inants cannot be eliminated  effectively.   Based  on  this,  the  radius of
influence for a pumping well  is determined  by:
                 where x =  [K(H2-h 2)/458(Q)]  +  Inr
                                  w                w
                         =  [25(1002-462)/458(100)] +  lnO.5
                         =  4.996

        = 150 feet (approximately).

Because pumping is to be continuous, the optimum operating  conditions  for  the
well should be approximately 67 percent of the total drawdown.  Using  this
drawdown (H-h^), pump rating (Q ) and screen length can  be estimated  by:

             (H-hwm)  = °'67(H)
                     = 0.67(100)
                     = 67 feet
                h    - 33 feet
                 win         999    9
                     = (100/(1002-462)(1002-332)
                     = 113 gpm

Using the calculated information, a single 6-inch well with a radius of
influence (R )  equal to 150 feet would provide plume removal and containment
at the site (Figure 5-28).  Optimum  pumping conditions can be achieved with  a
continuously operated pump rated for approximated 113 gallons per minute.  The
length of screen installed should be less than 33 feet because drawdown will
be approximately 67 feet.   The material used for the well would be determined
by the type of contaminants present.
                                    5-94

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     5.4.3  Installation  and Maintenance of Wells

     Well  installation typically  consists  of  four  steps:

     •  Opening the borehole
     t  Installing the casing  and  screen (if  used)
     •  Completing the well
     •  Developing the well.

The first of these steps  consists  of opening  a  borehole for  the  well  by  dis-
lodging and removing earth materials.   Variations  in  the method  used  for
dislodging and removing the earth  materials are the main differences  in  well
construction techniques.  Screens  and  casings may  be  installed simultaneously
with the opening of the borehole  or after  the borehole has been  completed.
The sequence of events depends on  the  technique used  to open  the hole and  the
geologic characteristics  of the materials  in  the immediate vicinity of the
hole.  Installation of screens, filters, pumps,  and grout completes the
construction of the well.  Well development is  the last step  and consists  of
dislodging and removing fines that have built up on the well  screen,  the
filter, and walls of the  aquifer  during the previous  steps.   Removal  of  these
particles maximizes well  yield and prevents damage to the pump.

     Well maintenance generally is performed  periodically after  installation
of the well to maintain yields.   Maintenance  programs consist of recording
performance, evaluating the need  for maintenance,  and treating the well  to
improve yields.  The three basic  causes of reduced yield that require well
maintenance are pump failure, corrosion, and  incrustation.

          5.4.3.1  Opening Boreholes and Installing Casing

     There are numerous methods for opening holes  and installing  casing  which
can be classified according to the well depth:

     •  Shallow wells (<50 feet)--dug, bored, driven, and jetted  wells
                                    5-95

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     t  Deep wells (>50 feet)--drilled (e.g., hollow-core, hydraulic-rotary,
        air-rotary), cable tooled, and jetted wells.

The method chosen depends on the geologic characteristics of the soil  and
rock, the well diameter, and the hydrologic characteristics of the aquifer.
Uells can also be classified by the type of geologic materials they penetrate
(i.e., consolidated and unconsolidated).  Regardless of the method chosen for
well installation, exploration techniques should be employed prior to  and
during the opening of the borehole.  While installation is occurring,
continuous testing to monitor changes in the soil and water being removed
should be performed so that installation techniques can be modified as
necessary.  The various means of opening a borehole and installing casing and
screen are described in Table 5-26.

               5.4.3.1.1  Hand Methods

     Shallow wells up to six inches in diameter can be pushed into soft  soils
by hand methods.  Depths of these wells is generally limited to between  20  and
30 feet, but 90 foot wells have been installed in this manner.  Wells
installed by hand methods are usually wellpoints attached to a riser pipe.
The maximum depth to groundwater in these wells is generally less than 20 feet
because suction pumps are utilized.  Manual methods for opening a hole are
typically driving and augering.  The use of augers is limited because  they  are
ineffective in water saturated sands and coarse silts.  A combination  of the
two methods is often used successfully to reach greater depths.  Deeper  and
larger diameter wells can be installed if heavier driving block assemblies  are
utilized.  These blocks can weigh 75 pounds or more and can be operated  by  a
block and tackle or with a drill rig.

               5.4.3.1.2  Boring

     Wells can either be bored with large diameter auger buckets or with
continuous flight, spiral augers.  Rotary bucket augers are capable of opening
holes up to 48 inches in diameter and 90 feet deep in very soft soils.
Diameters are typically limited to about 24 inches in most materials.
                                    5-96

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TABLE 5-26.  METHODS OF WELL-INSTALLATION
Method
Basic
Hand

Boring

Jetting




Variations
Augers
Driving Points
Rotary Auger
Bucket
Spiral Auger
Self jetting
Well point/Riser
Unit
Separate Tem-
porary Jett-
ing Pipe
Separate Per-
manent
Jetting Pipe
Applications
Geologic Material Max. Well Max. Well
Dia. (in) Depth (ft)
Soft, without excess 6 20
sand and water, no
boulders
Soft soil free of 3 30
boulders
Soft soils without 48 90
excess boulders
Soft soils without 6 90
excess sand and
water, no boulders
Soft soils free 8 50
of boulders
Soft soils free 8 50
of boulders
Soft soils free 8 100
of boulders
Soft soils free 8 100
of boulders
Casing/Screen
Treatment
Driven after
opened
Driven as
hole proceeds
Driven after
hole opened
Driven after
hole opened
Drives as hole
opened
Driven as hole
opened
Placed after
hole opened
Driven as hole
opened
Comments

Wider and deeper holes
can be machine driven
Typically limited to
24-in diameter wells
or less
Can not be used below
water table, must be
used in combination
with other techniques
Jetted wells require
less development
Method uses large
quantities of water


                                                            (Continued)

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                                                  TABLE  5-26.   (Continued)
en
i
00
Method
Basic
Jetting
(cont.)
Rotary
Drilling



Cable Tool


Variations
Rotary Hole-
puncher
Conventional
Hydraulic
Reverse
Hydraulic
Air Rotary
Ai r Rotary with
Pneumatic
Hammer
Conventional
California
Stove Pipe
Appl ications
Geologic Material Max. Well Max. Well
Dia. (in) Depth (ft)
Soft soil, sandstone, 24 200
schist
Any type
Any type, boulders 60
may be a problem
Any type 12
Any type 8
Any type
Any type
Casing/Screen
Treatment
Driven as
hole opened
Placed after
hole opened
Placed after
hole opened
Placed after
hole opened
Placed after
hole opened
Driven during
or after hole
opened
Pushed with
jacks as hole
opened
Comments

Typically used for
wells, quickest
drilling method
Requires large
quantities
of water
Very fast method

Typically used for
wells, provide abi
to closely monitor
log well


deep



deep
lity
and
Quicker and less
expensive than con-
ventional cable tool

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However, this type of  auger  can  be  used  in  soils  with  minor caving problems if
the boreholes are filled  with  light  drilling  mud.   The mud not only prevents
caving but helps keep  porous materials  in  the bucket.   The use of drilling
muds  is not recommended for  use  in  contaminant monitoring wells because of
possible analytical  water quality testing  interferences.

      Spiral screw augers  are typically  limited to  diameters between 4 and
6  inches and depths  less  than  90 feet.   They  can  be ineffective when used
below the water table  or  in  sandy soils  because the screw will not lift the
soil.  Spiral augers are  used  most  commonly in conjunction with other methods.

      Tools used for  rotary bucket augers  include  the bucket,  drilling pipe or
rod,  a kelley bar, mechanical  pull  downs,  and boulder  handling equipment.   The
cylindrical bucket has cutting blades on the  bottom and is attached to the
kelly bar by rods.   Drill  rods supply the  length  necessary to reach into deep
holes and can be eliminated  in shallow holes.   The  kelly  bar  transfers the
circular motion from the  rotary  table and the downward force  of the mechanical
pull-downs to the rods and the bucket.   Any large  boulders in the path of the
borehole must be removed  using orange peel  buckets,  stone tongs,  or ram horn
tools.

     Spiral augers are less complicated  and easier  to  use than bucket augers.
The bucket, rods, and kelly bar  are  replaced  by a  screw auger which does the
cutting.  Cuttings are pushed  to the surface  by spiral  action.   Spiral  augers
are attached directly to  the rotary  table through  the  drill rods.

     Casing installation  for augered wells  can  normally be done after the  hole
has been opened to its entire depth.  One exception  is  when bucket  augers  and
drilling mud are used in  sandy soils.  In this  case, casing should  be driven
closely behind the progress of the bucket.  For applications  where  the
borehole is not in danger of caving, the casing can  be  installed  after  the
hole is completed.   Casing is normally installed by  pushing it  with a drive
block similar to the ones used for driving  wells.   The  top of the  casing  is
protected  with a drive head and the bottom with a drive shoe.
                                    5-99

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               5.4.3.1.3  Jetting


     Jetting involves opening the borehole using the force of a water jet.

Water jets typically have flow rates of 100 to 250 gallons per minute and

develop pressures of 50 to 300 pounds per square inch.  The force of the water

jet not only opens the hole but also conveys the waste materials back to the
surface.  Jetted wells can range in diameter from a few inches to about

24 inches and can reach a depth of up to 200 feet.  Jetting can be done in
geological materials as hard as sandstone and schist, but most often is used

in soil (unconsolidated) materials.  Since the equipment required for jetting

is fairly sophisticated and equipment set-up times are long, jetting is most

commonly used for installing many closely spaced wells (e.g., wellpoint
systems).


     There are six basic jetting methods.  Four of the jetting methods are

used for installing small diameter, shallow wells such as wellpoints.  These
four methods are:
     t  Self jetting, permanent drop tube—The entire wellpoint is jetted down
        and remains in place.  The permanant drop tube eliminates the need for
        temporary jetting pipes.  Riser tubes are used to extend the length of
        the well as jetting proceeds and to act as casings.

     •  Self jetting, separate drop tube—Same as the self jetting, permanant
        drop tube method except that the drop tube is removed after jetting is
        completed.

     •  Separate temporary jetting pipe—A capped pipe with cutting teeth at
        the bottom is jetted down by water forced through openings in the cap.
        If soil becomes difficult to remove, the pipe is rotated back and
        forth to aid the jetting process.  Once the well is pushed to the
        final depth, the wellpoint and riser are placed in the jetting pipe
        and the jetting pipe is removed.

     •  Separate permanent jetting pipes—Similar to the separate temporary
        method except that the wellpoint with screen is packed into the
        jetting pipe, the pipe is lifted to expose the screen, and the jetting
        pipe then becomes the riser casing.


     Deeper wells can be installed using two jetting methods; jet-percussion
and rotary holepunchers.  In the jet-percussion method, a chisel bit is used
                                     5-100

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that has jetting nozzles attached.  The nozzles direct  water  onto  the  bit  for
cleaning and at the bottom of the hole to  loosen material.  The  chisel  bit is
lifted and dropped with a block  and tackle  or motorized assembly.   The
combined action of the bit and the water jet open  the wellhole.   Drilling
water is circulated in a closed  loop to minimize water  consumption.  Once  the
water emerges from the bit,  it rises along  the outside  of  the drilling  pipe
carrying cuttings with it.   Cuttings are settled out  in a  pit and  the  water is
recycled.  Casing is driven  as the hole progresses, and well  screens are
installed through the casing.  The rotary  holepuncher method  is  similar to the
jet-percussion method .except that the bit  is rotated  by rotary drilling
methods instead of being lifted  and dropped.  Rotary  drilling methods  are
described in the next section.

               5.4.3.1.4  Rotary Drilling

     There are two basic components of rotary drilling--the drill  bit  and
stem, and the drilling fluid.  The rotary  action of the drill  bit  and  stem
being forced down by mechanical  or gravitational means  opens  the borehole.  A
continuous flow of drilling  fluid prevents  the hole from collapsing  and
removes the cuttings.  Casings and screens  are typically installed after  the
borehole has been completed.  Conventional  rotary  drilling  and its variations
can be used to install wells of  any diameter and depth  in  any geologic
material.  While this is one of  the fastest drilling methods,  equipment set-up
time and labor costs can prohibit its use  for shallow wells.

     In conventional hydraulic rotary drilling, the flow of the  drilling  fluid
is similar to that for jet-percussion where fluid  flows down  the drilling  rod,
out the drill bit, and up the sides of the  hole.   Besides  removing cuttings
and keeping the hole from collapsing, the  drilling fluid:

     •  Prevents the bit from sticking when operations  are  interrupted
     •  Seals the well hole  to prevent fluid loss
     •  Cools and cleans the drill bit
     •  Lubricates bits, pumps,  and pipes.
                                    5-101

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The properties of the drilling fluid that  can  be  controlled  to  ensure
satisfactory  performance  are  density,  viscosity,  sand  content,  gel  strength,
and filtration properties.  The disadvantages  of  using  a  drilling  fluid  is
greater drill rig decontamination time and  well development  expense.

     Reverse  circulation, rotary drilling  is a variation  of  the  conventional
method that is appropriate for soft soils  where water  tables  are greater  than
10 feet below the surface.  Reverse rotary  is  the  least expensive method  for
wells ranging from 18 to 60 inches in  diameter.   The drilling fluid  is more of
a water than  a mud in this method and  fluid losses can  be  as  great  as 500
gallons per minute.  Because  of this,  an ample water supply must be  available
and a settling pit of three times the  final borehole volume  should  be
designed.  The major difficulties with  the method  are  high fluid loss and
caving when drilling in loose, permeable soils.

     Another  variation of conventional  rotary  methods  is  the  air rotary
method.  The  drilling fluid in this case is high  pressure  air rather than a
water-based fluid.  Air rotary methods  are good for consolidated rock drilling
and will  allow faster penetrations and  longer  bit  life  as  long as water
infiltration  into the hole is small.    Typical  hole diameters  are 12  inches or
less but  larger bits are available.   This method  is frequently used  in
combination with conventional hydraulic rotary methods  to complete  a single
hole.

     A variation of the air rotary method  is air  rotary with  pneumatic
hammers.   This method may be the quickest when drilling through very hard
geologic  formations.  Well diameters  with this method are typically 8 inches
or less.   The pneumatic hammer requires air pressures greater than 300 pounds
per square inch when drilling larger  holes.  Both  air rotary methods have the
advantage of being able to observe water inflows  into the well as drilling
progresses.
                                     5-102

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               5.4.3.1.5  Cable-Tool

     The cable-tool method  (also known  as the  "percussion,"  "solid-tool,"
"standard," and "churn" method) opens a hole by  lifting  and  dropping  a  heavy
string of tools which loosen and crush  the geologic material.  The  resulting
particles or cuttings are mixed with water from  the well or  water pumped  into
the well and the resulting  slurry is removed with a bailer.  When drilling  in
soft soils, the casing closely follows  the bit to prevent caving.   In hard
rock formations the casing  can be installed after the hole has been completed.
The cable tool drilling method is typically used for deep well installation,
is relatively slow (5 to 10 ft/day  in solid rock, 50 to  100  ft/day  in soft
soil), and is high in labor costs.  Conventional cable-tool  methods and a
single variation are discussed below.

     Conventional cable-tool equipment  consists  of a bit, a  stem for  length
and weight, jars to loosen  stuck stem and bits,  and a rope socket which
connects the entire string  to the drill cable.   The up and down motion  of the
tools results from the motorized lever  called the walking beam or the spudder
(i.e., winch).  The bailer  is on a  separate cable called the sandline.  The
bailer is comprised of a pipe with  a check valve that opens  as the  pipe enters
the hole and closes as it is lifted, thereby removing cuttings.

     One variation on the standard method is the California  Stovepipe.  The
major differences are:

     •  A mud scow acts as  both bit and bailer
     •  A thin pipe within  a pipe ("stovepipe")  is used  as a casing as  opposed
        to standard line pipe
     •  The casing is pushed with jacks rather than hammered with tools.

A unique feature of the casing is that  it is too weak to pull back out  of the
hole to expose the well screen.  Therefore, perforations are blasted  into the
bottom of the casing to allow water flow and act as a screen.
                                    5-103

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           5.4.3.2  Well  Completion

     Once  the borehole  has  been  opened  installing  a screen,  filter pack, and
grout  is necessary to complete the well  prior  to well  development.  The order
that these  installations  occur is dependent  on whether the borehole is over-
sized  and  requires a filter pack or  not.   The  majority of  the  wells that are
drilled for contaminant  removal  will  require filter packs.

               5.4.3.2.1  Filter Pack Wells

     The method typically utilized for completing  a well with  an  artificial
filter is the double-casing method.   In  this method, a string  of  outside
casing, corresponding to the size of  the outside diameter  of the  filter pack
(i.e., the borehole), is  installed as the  hole  is  drilled  or after it  is
completely opened.  A second string of casing  containing the well  screen is
then centered within the outer casing.   The selected filter material  is then
placed between the inner and outer casings.  After  placement of a few  feet of
filter material, the outer casing is  pulled back an  equal  amount  and the
procedures is repeated until the filter  material is  brought to the desired
level above the screen.

     The outer casing may be removed  completely or  left in place  above the
level of the screen.   In either case, the  top  of the annular space above the
filter is sealed with grout (e.g., cement, clay).   If  the  outer casing is to
be permanent, the inner casing above  the screen may be removed as  long as the
two overlap a few feet.  The top of the  inner  casing should be sealed  using  a
lead slip packer.  The annular space  left  between the  outer casing and the
aquifer should also be sealed with grout.  Pumps are then  installed into the
inner casing and the well is developed.

     Jetted wellpoints are completed  in  a  similar manner as a  drilled  well.
In this case, filter sands are packed around the wellpoint and grout  is
installed from the top of the filter  to the surface.   The  grout prevents
surface water infiltration into the well and minimizes the chances of  air
entering the wellpoint.
                                    5-104

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               5.4.3.2.2  Naturally Developed Wells


     The method used for completing a naturally developed  well  is  the  opposite

of the method for filter pack wells.  Grouting and sealing,  if  necessary,

occur first followed by installation of the well  screen.   The two  basic

approaches to grouting are:


     •  Slurry placement method  in which grout is pumped or  gravity  fed  into
        the annular space

     0  Casing method in which well casing is used to keep the  borehole  open
        while installing grout.


Regardless of the method used, the grout must always be placed  from  the  bottom

of the well up.  If a temporary outside casing has been installed  during

drilling, the casing must be removed while the grout is still fluid.   This

allows for a good seal between the borehole walls and the grout.   Once the

grout has set, the plug can be drilled out and the well screen  installed.


     Numerous methods are available for installing well screens depending on

the type of well screen used, the drilling equipment, the geologic material,

and the presence of grout.  The types of well screen installation methods are:


     •  Pull back method—Casing is sunk to the full depth of the  borehole,
        the well screen is lowered inside the casing and the casing  is pulled
        back to expose the screen.  The casing can not be grouted.

     •  Setting in open hole—The casing is grouted in place, a hole is
        drilled through the grout to below the level of the  casing and the
        well screen is installed inside the casing in the drilled  hole.

     t  Bail-down procedure—The well screen is fitted with  a bail down  shoe
        attached to a bailing pipe, the assembly  is sunk into the  formation
        below the well casing by operating the bailer and drilling tools
        through the screen, the screen moves into the hole formed  by dis-
        placing the soil, and a packer at the top of the screen is expanded
        after the pipe is removed.  This method is good only in soft,  sandy
        soils.

     •  Wash-down method—The well screen is installed using the same method
        as for jetting techniques and a packer is used to seal  the screen and
        the casing.
                                   5-105

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 Once  the  well  screen  is  installed  the pump can be placed within the casing.
 Well  development  can  then  take  place to ensure adequate yield.

           5.4.3.3   Well  Development

      Well  development  is the  process where fine soil  materials are removed
 from  in and  around  the screen allowing  water  to flow  freely.   This process is
 accomplished by surging  water or  air through  the well screen  and into or out
 of  the surrounding  material.  The  well  development process:

      •  Removes materials  that  have  built-up  in the openings  of the screen
        during the  well  drilling  and installation processes
      t  Removes fines from  the  sides of the borehole  that resulted from the
        drilling procedure, e.g.,  drilling mud
      •  Increases the hydraulic conductivity  of adjacent geologic  materials
        and  the filter pack by  removing fine  materials
      •  Stabilizes  the fine materials that remain in  the vicinity  of the well
        and  retards their movement into the well.

 The benefits of well development are increased yields,  reduced pumping  of
 fines which  can damage pumps, and  decreased corrosion and encrustation.   The
 results of the development  process is a layer of coarse particles  adjacent to
 the screen.  The percentage of finer particles  increases with  distance  away
 from  the well.  Well development is  necessary in  any  well  because  clogging can
 occur regardless of the  drilling method  used  or  the formation  being
 penetrated.

      Wells can be developed by natural  groundwater  flow or by  artificial
means.  Prior to developing a well,  the  well  should be  bailed  to remove  sand
 that  has accumulated during construction.   Bailing  also ensures  that water
will  flow into the well.   Development procedures  can  last  from about two  hours
to two days depending on well depth  and  formation  properties.

      Natural development of wells  is accomplished by  alternately pumping  and
 allowing the well  to recover.  This method  does  not cause much of  a  surging
                                    5-106

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action and is relatively ineffective in alleviating particle bridging  and  in

removing fines.  There are seven additional methods that can be used in well
development.   They are:


     t  Overpumping—This method develops the aquifers by pumping at high
        rates and assumes that the system will be stable at normal pumping
        rates.  When the pumps are stopped, backwash helps overcome bridging.
        While this method is the simplest and quickest, it is also the least
        effective.

     •  Rawhiding--This method involves pumping intermittently to lift water
        out of the well and then adding water back into the well causing a
        surging action.  Rawhiding is limited to wells without check valves
        that  prevent backwashing. The method is not normally recommended as a
        primary development method but is used commonly as a finishing method.

     •  Recirculation—In this method, water is pumped from a high point in
        the well and discharged at a low point in the well screen.  This
        results in a mild turbulence at the screen which frees fines.  It  is
        not generally used as a sole well development method.

     •  Surge blocking—In this method, a surge block or surge plunger is
        pushed in and pulled out of the well in a plunger-like fashion.  The
        plunger can be solid or valved.  Valved plungers allow action on the
        downstroke and strong action on the upstroke, but care must be taken
        on the upstroke because screens can be collapsed.   This method is the
        most  common and highly effective method of development.

     •  Hydraulic jetting—In hydraulic jetting,  a device with two or more
        nozzles is pushed to the well screen and water is jetted through the
        screen openings.   The water reverses direction returning through the
        screen and carries fines into the well  for removal.   Pumping the well
        while jetting helps flow reversal  and fine removal,  and provides water
        for jetting.

     •  Compressed air surging—This method is  a combination  of air jetting
        and pumping with  water.   Air is gently pumped into the well  and water
        is pumped out of  the well  to start the  circulation.   The airline is
        then  closed off and  pushed  down into the  screen area  while air
        pressures build to  100  to 150 pounds per  square inch.   An  air blast is
        then  released surging through the  system.   This cycle  is repeated
        several  times.

     •  Sonic development—In this  method,  high frequency sound  waves are  sent
        through  the well  screen  and the surrounding  formation  where  they
        vibrate  and loosen  particles.  Because  the waves  effectively penetrate
        beyond the well,  this method  is very attractive for filter packed
        wells.
                                  5-107

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     The methods previously discussed can be aided with the use of dispersing
agents and acids.  Dispersing agents (such as polyphosphates) act as
deflocculants and disperse clay.  Mild acids can be used to dissolve  limestone
and open crevices.  In rock formations, blasting has been used to enhance  well
yields.  However, blasting is not a recommended procedure for most hazardous
waste release sites.

          5.4.3.4  Well Maintenance

     Pumps, casing, and screens must be maintained to ensure a constant
reliable flow of water from the well.  Proper well maintenance is especially
important in plume management because the loss of a well could result  in
contaminant escape.  The causes of well yield loss and failure are:

     •  Encrustation—The build-up of scale or other chemical or biological
        material
     t  Corrosion—A breakdown of well hardware by turbulent flow, chemical
        reactions, galvanic reactions, or fatigue stress
     t  Pump failure—Typically caused by sand intrusion, wear, or mechanical
        or electrical  failure.

     Prior to beginning any well maintenance, a preliminary evaluation must be
conducted to identify whether or not the problem can be corrected.
Operational records will determine the normal operating conditions of  the  well
and aid in evaluating the problem.  Removing the pumps and checking the casing
and screens may be necessary.  This can also be accomplished by downhole video
equipment.

     General maintenance procedures that can be used for encrustation,
corrosion, and related pump problems include:

     •  Chemical treatment of casing and screens
     0  Redevelopment of the well
     •  Chemical treatment of pumps, and mechanical and electrical
        maintenance.
                                    5-108

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Chemical treatments are designed to dissolve encrustation and corrosion that
has formed or have been deposited on the well components.  Three classes of
chemicals are generally used; acids, biocides, and phosphates.  Acids  are  used
to dissolve inorganic substances that have formed, such  as calcium, magnesium,
and iron.  Biocides are used to remove organic materials that may have devel-
oped such as iron bacteria.  The effectiveness of both of these treatments is
directly related to retention times on the affected components.  Additives are
available to aid in the treatment including:

     •  Inhibitors—Allow for the selective removal of some substances
     •  Chelates--Keep metals in solution to prevent redeposition
     •  Wetting agents—Reduce surface tension allowing chemicals to penetrate
        smaller openings.

Phosphates or surfactants act as dispersing agents which help break-up clays,
colloids, and some metals.  The effectiveness of surfactants depends only on
initial contact; prolonged contact does not increase their effectiveness.
whenever surfactants are used (especially phosphates), chlorine should be used
to prevent bacteria and algae growths.

     The best and most common application method used in chemical treatment is
the double surge block.   This method allows the application of concentrated
chemicals directly to the required areas.  If chemicals are necessary to clean
the surrounding aquifer they can be injected through the screen using
compressed air or surge blocking techniques.

     Mechanical redevelopment of the well can also be used to increase yields
and remove encrustation.  Redevelopment should always follow chemical
treatments.   The seven development methods described previously can be used.

5.5  Costs of Well  Systems

     Costs of well  systems for plume management can vary greatly from site to
site.   Some  of the  factors that detemine these costs are the geology, the
                                    5-109

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characteristics of the contaminant and naturally occurring groundwater, the

extent of contamination, the periods and durations of pumping, local wage

rates, the availability of supplies and equipment, and the electrical power

required.  Costs associated with a well system can be grouped into the

following categories (Powers, 1981):


     •  Mobilization costs

     •  Installation and removal costs
     •  Operation and maintenance costs.


     Mobilization costs include all costs incurred in obtaining equipment and

having it available at the site.  Some of the items included in mobilization

costs are (Powers, 1981):


     •  Well  components—including well screens, casing, well pumps, motors,
        controls, discharge columns, well heads, fittings, collector pipes,
        and power lines (Figure 5-29)

     •  Installation equipment—including drilling rigs, jetting equipment,
        and well development equipment

     •  Pumping equipment—including pumps, contacts, hoses, and cables

     •  Standby equipment—including generators, switches, pipes, and cables

     •  Equipment rental and repair

     •  Delivery and handling charges  for equipment

     •  Utility installation

     •  Enclosures for storing equipment

     t  Engineering and geotechnical services—including the design of the
        system, submittal  preparation,  field testing, and on-site supervision
        during installation

     •  Waste, water, and  soil treatment—including transport, treatment, and
        disposal

     t  Decontamination of drill rigs  and tools

     •  Health and safety precautions.
                                     5-110

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                                   FIGURE 5-29.
                       TYPICAL WELL SYSTEM COMPONENTS
                                  (POWERS, 1981)
                                    Discharge Line
                    Discharge Collector
                      Standby
                      Generator
           High Line
                Transformer
                     Switchgear
                                                  Discharge
                                                  Collector
Discharge
 Column '
                                                               Wellhead and
                                                                 Fittings
                                                        Pump-
                       Deep Well (typical)

                                                                  Casing
                                                                  Screen
      Installation and removal  costs include the  costs for crews  and  equipment
necessary to install the well  system at the site.   These costs should  also
include  allowances for  set-up,  clean-up, weather,  and other miscellaneous
delays that  typically occur.   Removal  costs will probably be incurred  at  all
sites at  some point when pumping  is no longer required.   Removal costs  can be
off-set  somewhat by salvage  costs  of the removed equipment.  However,  decon-
tamination of the equipment  may be more costly than salvage value.

     Operation and maintenance  costs are typically high  for pumping  systems.
In some  cases, these costs can  be  greater than the initial installation and
mobilization costs.   The following items should  be considered in preparing
cost estimates (Powers, 1981):

     t  Operating labor—continuous or intermittent manning of equipment
                                    5-111

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     •  Maintenance labor--includes servicing for pumps, well cleaning, and
        maintaining engines and electric equipment
     •  Supervision
     •  Energy—includes fuel and electricity
     •  Maintenance materials--includes materials for surface components and
        for well rehabilitation
     t  Repair and overhaul of equipment.

     The above list of cost items is not all inclusive; some sites will
require additional items.  If long term operations are expected, operation and
maintenance, and removal costs should include escalating factors.  Tables 5-27
through 5-29 give some typical costs that may be incurred for the items
mentioned above.  However, because the costs of many of these items will vary
with site location, specific  estimates from local contractors and suppliers
should be obtained.
                                     5-112

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        TABLE 5-27.   RANGE OF COSTS FOR SELECTED PUMPS AND ACCESSORIES
                     (l/ STA-RITE INDUSTRIES,  INC.)
Pump/Accessory
Description
Cost Range (1981 $)
Jet Pump '
  - shallow well

  - deep well

  - jets and valves

  - seals
  - foot valves
  - air volume controls
Submersible Pumps
  - 4 in. pump

  - control boxes
  - magnetic starters
  - check valves
  - well seals
Vacuum Pumps
 - diesel motors

 - electric motor
pumping depths  25 ft
horsepowers 1/3 to 1-1/2 HP
capacities 60 to 27000 gph
pumping to depths  320 ft
horsepowers 1/3 to 2 HP
capacities 60 to 1000 gph
single pipe jets
double pipe jets
single or double pipe
pumping depths  900 ft
horsepowers 1/3 to 3 HP
capacities 50 to 2000 gph
800 - 7000 gpm (48,000 —
  420,000 gph)
800 - 7000 gpm (48,000 —
  420,000 gph)
$220 to $430

$220 to $570

$40 to $80
$30 to $50
$15 to $25
$10 to $40
$10.00

$350 to $1400

$60 to $120
$160 to $250
$14 to $330
$15 to $100

$13,000 to $40,000

$9,000 to $31,000
                                     5-113

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      TABLE 5-28.   TYPICAL RANGE OF COSTS FOR WELLSCREENS AND WELLPOINTS
                   (Johnson Division,  UOP Inc., and Gator Plastics Inc.)
Type
Description
Costs (1981 $)
Drive Well points
Well screens
Jetting Screens
  (fittings)

Bail down Shoe
  (fittings)
stainless steel
1-1/4 to 2-in ID

low carbon steel
1-1/4 to 2-in ID

PVC plastic
1-1/4 to 2-in ID

stainless steel
1-1/4 to 36-in ID

low carbon steel
1-1/4 to 36-in ID

PVC plastic
1-1/4 to 12-in ID

cast i ron or mild steel
2 to 12-in ID

mild steel
4 to 12-in ID
$28.00 to $40.00/ft
                                                          $15.00 to $35.00/ft
                                                          $5.00 to $6.00/ft
$28.00 to $610.00
                                                          $15.00 to $170.00/ft
                                                          $10.00 to $60.00/ft
$30.00 to $270.00
$180.00 to $800.00
                                     5-114

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    TABLE 5-29.   AVERAGE DRILLING COSTS (1981) FOR UNCONSOLIDATED MATERIALS
                    (Stang Drilling and Exploration)
Drilling Technique
Drilling Costs '  Average Production  Drilling Cost
   ($/hr)           Rates (ft/hr)       ($/ft)
Conventional Hydraulic
Rotary
Reverse Hydraulic
Rotary
Air Rot ray '
Air with Pneumatic
Hammer
Auger
Bucket Auger
Cable-Tool
Hole Punchec,
(jetting)*7
Self jetting2/
$100/hr
$220/hr
$175/hr
$180/hr
$90/hr
$100 to $140/hr
$60-$70/hr


40 ft/hr
40 ft/hr
50-60 ft/hr
40-50 ft/hr
20-40 ft/hr
50 ft/hr
4 ft/hr


$2.50/ft
$5.50/ft
$3.50 -
$4.50 -
$4.50 -
$2.00 -
$15.00 -
$35/ft
$18/ft


$3.00/ft
$3.60/ft
$2.50/ft
$2.80/ft
$17.50/ft


 'consolidated material
2 /
  includes rental of all necessary equipment; e.g., wellpoints, pumps and

  headers

 'drilling costs approximately equal mobilization costs
                                     5-115

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                                   CHAPTER 6
                               SUBSURFACE DRAINS
6.1  Introduction

     Subsurface drains include any type of buried conduit used to collect
liquid discharges (e.g.,  contaminated groundwater) by gravity flow.  The key
components of a typical subsurface drainage system are:

     t  Drain pipe or gravel bed—for conveying flow to a storage tank or wet
        well
     •  Envelope—for conveying flow from the aquifer to the drain pipe or bed
     •  Filter—for preventing fine particles from clogging the system
     i  Backfill—to bring the drain to grade and prevent ponding
     •  Manholes or wet wells—to collect flow and pump the discharge to a
        treatment plant.

     The theory of groundwater flow and the effects of various aquifer proper-
ties on flow are similar  for drains and wells.  Well theory is discussed in
Chapter 5.  Specific differences and similarities between flow toward drains
and wells are described in Section 6.2.

     Section 6.3 discusses site specific variables which determine the
applicability and performance of subsurface drains.  Soil properties, leachate
characteristics, size and flow rate of the plume, aquifer properties, and site
geology are considered relative to the design and performance of subsurface
drains.  The design considerations discussed  in this section include drain
depth and spacing, hydraulic design of pipes  (pipe diameter and gradient, and
flow velocity), and envelope and filter materials.  This section also includes
                                     6-1

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a discussion of design criteria for a sump  and pumping  station  for  collection
and transfer of leachate to a treatment system.

     Equipment, methods, and unit costs for the construction,  installation
and maintenance of subsurface drainage systems are described  in  Section  6.4.
Construction and  installation can be divided  into two major  activities:
(1) excavation of the trench to the required  depth and  gradient,  and
(2) installation  of drain materials.  The discussion of trench  excavation  in
this section includes methods and equipment for trench  excavation,  wall
stabilization, dewatering, and grade control.  Drain installation  includes
materials and procedures for installing bedding, drain  pipes, envelopes, and
filter material.  This subsection also includes procedures for  backfilling  the
trench.  Unit costs are provided throughout this section for  equipment,
methods, and procedures.  The section also  provides guidance  on  the selection
of equipment and methods based on depth requirements, subsurface geology,  and
soils.

     Section 6.4.3 addresses procedures and methods for maintenance and
inspection of subsurface drains.  This section includes a discussion of
problems which might arise during construction and operation  of  the system.
Inspection, preventative maintenance, and corrective action procedures to
ensure against system failure are also discussed.  Potential  problems which
can impact the performance of drains include  clogging of envelopes  and filters
by siltation; chemical build-up or incompatibility; clogging  as  a result of
sediment build-up in manholes; root clogging  of tile drains;  and development
of sinkholes.

     Subsurface drainage can be used to control leachate plume migration for a
wide range of site conditions.  They essentially function like  an infinite
line of extraction wells.  That is, they create a continuous  zone of
depression in which groundwater within this zone of influence flows toward  the
drain.  Accordingly, subsurface drains can  perform many of the  same functions
as pumping technologies.  The decision to use one or the other  should be based
upon a cost-effective analysis.  However, drains may be more  cost-effective
than pumping at sites with substrata of low or variable hydraulic conductivity
                                     6-2

-------
and where pumping systems cannot provide a continuous hydrologic barrier.
They are limited to relatively shallow applications.

     Subsurface drains can be used to contain or remove a leachate plume or to
lower the groundwater table near a disposal site in order to prevent contact
of water with waste materials.  Containing or removing a plume located
hydraulically downgradient of a site typically requires less extensive
drainage than lowering the groundwater table.  However, containment or removal
generally requires deeper drains than systems used to lower the groundwater
table in order to ensure that the entire plume is intercepted.  This can be
seen by comparing Figures 6-1 and 6-2.

     Subsurface drains can be applied with liners or other barrier materials
to restrict inflow to one side of the drain.   A typical  situation where this
technique would be particularly applicable is when a surface water body
located near a subsurface drain was contributing a substantial flow of clean
water into the drainage system.  The use of conventional subsurface drainage
would result in large flow capacity requirements for the drain and high costs
for treating the additional  water.  One sided drainage could be used primarily
to collect the contaminated  portion of groundwater and cutoff recharge flow
from the surface water body.  The use of one  sided subsurface drainage
requires that the system be  keyed into a low  permeability formation so that
groundwater does not travel  under the barrier material (Figure 6-3).  One
sided subsurface drainage may be applicable to many other conditions where the
main objective is to restrict the flow of clean water, and thus, minimize
water treatment requirements.

     Subsurface drains are also used in conjunction with groundwater cutoff
barriers to prevent the buildup of groundwater upgradient of the barrier.  In
this application, they are not the main control  technique, but rather, serve
an ancillary function.  When used with barriers, subsurface drains may be
designed to handle the reduced flow conditions of a totally encapsulated site
(Figure 6-4) or to limit the up-gradient head increase preventing overflow and
minimizing differential  hydraulic pressures on the barrier (Figure 6-5).
                                     6-3

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                                  FIGURE 6-1.
THE USE OF SUBSURFACE DRAINAGE TO CONTAIN A LEACHATE PLUME
                                       Waste Disposal
                                           Site
                           • Groundwater Flow
                                Direction
                                                 •'Contaminated
                                                 ' Groundwater
                                                     Plume
                                                                         , Subsurface Drainage
                                                                        -ST'
        Collected groundwater
       . is pumped to treatment
r**~\/  system
                                                                                  Cross Section
                                           Waste Disposal
                                               Site
                               Contaminated
                                Groundwater
                                   Plume
V
V
* 	 ~^>-
/ ^j
J
•^
V
*
<»
>>
>
M
, Original Water
x^^- .3

                                        6-4

-------
                                    FIGURE 6-2.
THE USE OF SUBSURFACE DRAINAGE TO LOWER GROUNDWATER LEVELS
                                                                                Map View


                                                                  -Waste Disposal Site


                                                                  • Subsurface Drain
                                                                    Collected Groundwater
                                                                    Pumped to Receiving
                                                                          Stream
                                                                                Cross Section


                                                                    Waste Disposal Site


                                                                    Subsurface
                                                                      Dram
                                                                            Original Water Table
                                    Lowered Groundwater Table
                                       Under Disposal Site
                                    6-5

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 \
wD

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                                 FIGURE 6-4.
THE USE OF SUBSURFACE DRAINAGE IN A COMPLETELY ENCAPSULATED SITE
              Backfill
                                           Clay Cap
                                                                     Barrier Wall
                                                                 Subsurface Dram
                                 FIGURE 6-5.
             THE USE OF SUBSURFACE DRAINAGE TO PREVENT
                         OVERFLOW AND PONDING
                                                            Groundwater would
                                                            overflow or seep to
                                                            surface without the
                                                            use of subsurface drainage
                                 6-7

-------
     There are a number of limitations to the use of subsurface drains  as  a
remedial technique.  For example, an aquifer with a high hydraulic
conductivity and high flow rate may preclude the use of a subsurface  drain
because of the requirement for a large system capacity.  However, use of a
barrier containment system together with subsurface drains, to reduce flow,
may be effective under conditions of high flow.  Also, contamination  at great
depths may cause construction costs to be prohibitive, particularly if  a
substantial amount of hard rock would have to be excavated to install the
drain.

     Other limitations to the use of drains may include the presence  of
viscous or reactive chemicals in the contaminant plume which could clog the
drain.  Also, high concentrations of iron and manganese in the plume  or in the
groundwater could cause the eventual clogging of the drain system because of
the buildup of insoluble compounds.  Drains are fairly difficult and  costly to
rehabilitate.

6.2  Theory

     The principle of flow toward a subsurface drainage trench or pipe  is
similar to that discussed in Chapter 5 for flow toward a well.  However,
instead of the cone of depression which is observed around a pumping  well, a
water table trough develops which runs the length of the drainage trench.
This difference is illustrated in Figure 6-6.

     The similarities and differences in flow between a well and a drain can
be better appreciated from the theoretical expressions for flow.  Flow  in  an
unconfined aquifer, for example, can be most simply described by the  following
formulas:

     (1) Flow toward a drain (two sided flow)--
          Q = xK (H2-hd2)/L
     (2) Flow toward a well--
          Q =TT K(H2-hw2)/(ln RQ/rw)
                                     6-8

-------
                                 FIGURE 6-6.
DIFFERENCES BETWEEN GROUNDWATER FLOW TOWARD DRAINS VERSUS WELLS
     Flow



f















rrm







"TTTT







nrrrr







rrrn







t '. '. *. '
i















j






Tnr.
i






TTTT








(






rTTTT







TTTTT







TTTT







TTTT







TTTT




.
~~^-jL
~~f\\/'
nn
yJJ
h-\^/^
t—^\
X
                           Flow to a Perforated Drain Pipe
                            Flow to a Slotted Well Screen
                                    6-9

-------
where:
          Q  = discharge rate  (ft /sec)
          K  = hydraulic conductivity  (ft/sec)
          H  = total head  at aquifer prior  to  pumping  (ft)
          hj = desired drawdown  (ft)
          h  = height of water  in well  after pumping  (ft)
          R  = radius of influence  at  well  (ft)
          rw = radius at well,  including gravel pack  (ft)
          L  = influence of drain (ft)
          x  = unit length of pipe  (ft)

                                                       2   2
Figure 6-7 illustrates how h. in the equation Q = xK(H -h, )/L  and  h   in  the
                   •o   o    Q                            Q          W
equation  Q = TT K(H -HW )/(ln RO/TW) are similar and  how in both cases  H-h , or
H-h  is equal to the drawdown.

     Whereas flow from a given point to a well is inversely proportional  to
the radius of influence divided by well radius (R./r  ), flow to a drain is
                                                 o  w
inversely proportional to the influence of  the drain  (L) only.  That is,  the
diameter of the drain does not significantly affect flow as does the radius of
the well.  This is because the diameter of  the drain  is only a matter of
inches whereas the length of the flowlines  are many feet.  Therefore total
frictional resistance to groundwater flow through the entire system caused by
the pipe is usually ignored.

     Flow to drains in a confined aquifer is also similar to flow to wells,
and can be described by the following  formulas:

     (1)  Flow toward a drain--
          Q = 2Km (H-hd)/L
     (2)  Flow toward a well —
          Q = 27rKm(H-hw)/(ln RQ/rw)

where m is the thickness of the confined aquifer.   Figure 6-7 illustrates the
similarities between flow to drains and wells under confined and unconfined
conditions.
                                    6-10

-------
                                          FIGURE 6-7.
            RELATIONSHIP BETWEEN DRAWDOWN (H-h)  IN A DRAIN AND A WELL
                                    (AFTER POWERS,  1981)
                       Drains
                                                                  Wells
  Confined
Unconfined
                \VOsV\\\V\\
                  Confined Flow from a
                    Line Source to a
                    Drainage Trench
T
hd
                                  -H
                   Water Table Flow
                   from a Line Source
                  to a Drainage Trench
                                     H
                                          -T
                                                  Radial Flow,
                                                Confined Aquifer
                                                  Radial Flow,
                                               Water Table Aquifer
                                     6-11

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     6.2.1  Drainage System Terminology

     Functionally, there are two types of subsurface drains which  can  be  used
for collecting leachate--interceptor drains and relief drains.   Interceptor
drains are installed perpendicular to groundwater flow and are  used  to collect
groundwater from an up-gradient source.  Interceptor drains can  be used to
prevent contaminated leachate or groundwater from reaching wells or  surface
waters hydraulically downgradient from the site.  Relief drains  are  installed
in areas where the water table is relatively flat.  Relief drains  can  be  used
to lower the water table beneath a waste site and are usually installed around
the perimeter of the site or parallel on either side of the site such  that
their areas of influence overlap.  Figure 6-8 illustrates the function of
relief drains and interceptor drains in altering the configuration of  the
groundwater table.  Interceptor drains can also be used where infiltration
from a landfill or a surface impoundment results in a groundwater  mound which
induces lateral flow at the edges of the mound.   Figure 6-9 illustrates this
situation.  In general, interceptor drains are more widely used  than relief
drains.

     The major difference in the way these two types of drains  function is
that the drawdown created by interceptor drains is proportional to the
hydraulic gradient, whereas the drawdown created by relief drains  is a
function of the hydraulic conductivity and depth to the impermeable  barrier
below the drain.   Hydraulic gradient is the key consideration in choosing
which type of drain system to install.   Relief drains are used  if  the
hydraulic gradient is slight (about three percent or less), whereas  inter-
ceptor drains are used if the gradient is steep.  The rationale for  the way
these drains function is discussed in Section 6.2.2.

     The components of a relief or interceptor drainage system  are classified
by their size and function as laterals, collectors, or mains.   Laterals are
the smallest diameter component of drainage systems and collect groundwater
directly.  Collectors are larger than laterals and receive water from  one or
more lateral drains.  Mains are the largest of the three components  and
                                    6-12

-------
            X?
         r»-
        *A
        '*
     «sr 
-------
                                       FIGURE 6-9.
              THE USE OF INTERCEPTOR DRAINS TO COLLECT FLOW INDUCED BY
                                GROUNDWATER MOUNDING
                         Local
                       Groundwater
                         Flow
                                                  Impoundment
              Location for Drains
receive water from one or more  collector  drains.   These components are
illustrated  in Figure 6-10.

     Subsurface drains can  be designed  to use either pipe or a gravel layer to
transmit flow.  Drains that  use  clay  or cement tiles or plastic pipes are
called tile  or pipe drains.  Drains that  use  a high permeable bed only are
called french or gravel drains.   Pipe drains  are  somewhat more difficult and
expensive to install than french  drains but  are less susceptible to clogging
in most instances.  While both  pipe and french drains have been used for waste
site remediation, pipe drains are much  more  common.

     In summary, drainage systems are classified  by function (i.e., as relief
or interceptor systems), by  their components  (i.e.,  as  pipe or gravel drainage
systems),  and by their configuration  (i.e.,  as a  single component or singular
system, or a multi-component or composite systems).   In a singular system,
each lateral  drains into its own  sump or  collection  tank.   In a composite
                                     6-14

-------

-------
 system,  each  lateral drains  into  a  collector,  which may  in  turn  drain  into
 either  a main or  a  collection tank.   Selection of  a singular  or  a composite
 system  design depends  upon the  size of the  leachate plume,  the hydraulic
 conductivity  of the  subsurface  strata, the  hydraulic  gradient, and other
 factors.

     When  a drainage system  is  being  designed,  the following  four elements
must be  determined:

     •   Drain depth  (i.e., depth  of water table  lowering)
     0   Parallel  drain spacing
     •   Drain pipe diameter  and gradient
     t   Envelope  and filler materials and design.

Drainage system design generally  requires using  a combination of  theoretical
design considerations, field test results,  and practical experience.

     Theoretical  equations not  involving the use of computer  programs  or
electric analogues are based on various idealized conditions.  For  example,
some equations are based on the assumption  of  steady  state  conditions  (i.e.,
where the hydraulic head does not vary with time).  Others  assume  unsteady
state conditions  (i.e., a fluctuating water table).   Steady state  conditions
require that recharge rates equal the drain discharge rates so that the water
table remains relatively constant.  Non-steady state  conditions take into
account some fluctuation of the water table with time under the influence  of
non-steady recharge.  Since solutions to drainage problems  using  the steady
state assumption  are simpler to derive, most systems  are designed  based on
these conditions.   Steady state assumptions are generally valid when
considering average discharges over extended periods  of time.  However, in
areas subject to  periodic, high-intensity rainfalls followed by long dry
periods, the use of steady state equations  can result in over design (i.e.,
larger diameter pipes or narrower drain spacing than  is actually  necessary).
Another idealized  condition often assumed in drainage formulas is that the
earth materials are homogeneous and isotropic.  Such  conditions rarely exist,
but the use of average hydraulic conductivities generally results  in
                                    6-16

-------
reasonable estimates for drain design.  Experience has  shown  however  that  the
efficiency of subsurface drains  is generally  less than  predicted  by the
theoretical equations.  As a result, systems  are often  overdesigned on purpose
by placing drains closer together and by  using  larger drain pipe  than
estimated from the equations.

     6.2.2  Depth and Spacing

     This section discusses both theoretical  approaches  and field methods  for
determining the depth and spacing of relief and  interceptor drains.   In many
instances where interceptor drains are  used,  a  single drain is  adequate and
spacing is not a consideration.

          6.2.2.1  Relief Drains

     When two parallel drain lines are  installed, each  one exerts an  influence
(L) on the water table (see Figure 6-7).   If  the drains  are designed  properly
such that their influences intersect each  other, the drawdown each exerts  is
additive, resulting in an increased total  drawdown of the water table.  This
effect is greatest midway between the two  drains.  For  a site where the drain
will not rest on an impervious clay layer, the  zone of  influence  and  the depth
are interdependent design variables, which depend upon  hydraulic  conductivity,
depth to an impervious layer, and the discharge rate.   If the drains  could be
placed deeper, the effective drawdown would increase, assuming  homogeneous
earth materials, or the drains could be placed  further  apart  while maintaining
a constant effective drawdown.   If the drains can not be placed deeper, for
example because of shallow bedrock, the effective drawdown could  be increased
by spacing the drains closer together.  The relationship between  depth and
spacing is critical to the design of effective  parallel drainage  systems.

     In designing a subsurface drain system for a hazardous waste site, it
must be determined whether two parallel lateral drains on either  side of the
site will be able to effectively lower the groundwater  beneath  a  site.  The
importance of this is illustrated in Figures  6-lla through 6-llc.  If the
drains were designed with the depth and spacing shown in Figure 6-lla, the
                                     6-17

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                                 FIGURE 6-11.
THE RELATIONSHIP OF DRAIN DEPTH AND SPACING TO WATER TABLE DRAWDOWN
                                                                   Original
                                                                   Water
                                                                   Table
                                                         New Water
                                                           Table
                                                                   (b)
                                                                  (c)
                                  6-18

-------
zone of influence of the drains would not be adequate to dewater the waste
pile.  By placing the drains closer together as  illustrated  in  Figure 6-llb,
their combined drawdown would be below the  level of the waste pile  so that  it
would effectively dewater the pile.  However,  a  minimum spacing  is  often
imposed by the boundaries of the waste because excavation through the waste
material can be extremely hazardous.

     If a drainage system has been designed so that the drains  are  as closely
spaced as possible and the plume is not totally  intercepted, there  are two
possible alternatives to improve the design.   First, the drains may be placed
deeper (Figure 6-llc), provided the depth to bedrock and hydraulic
conductivity of soil layers is adequate.  Alternatively, the system can be
redesigned as a composite drainage system.  The  choice between  these two
alternatives depends on the depth to an impermeable barrier, the boundaries of
the plume and waste site, and the cost.

     As mentioned previously, drain spacing is also influenced  by the
hydraulic conductivity of the earth material in  which it is  installed and the
depth to the impervious barrier.  In theory, the deeper the  impervious barrier
below the drain the greater the thickness of the water transmitting layer,  and
consequently, the wider the drain spacing can  be to achieve the  same drawdown.
This phenomenon can be explained by the fact that there is radial flow (i.e.,
flow from all sides) to the drain from underlying soils, and the extent of
this flow is dependent upon the distance beneath the drain to the impervious
layer.  The effect of the depth to the impermeable barrier on drain spacing is
illustrated in Figure 6-12.  Determining this depth as part of  field testing
is essential.

     The effect of hydraulic conductivity on drain spacing and  the  importance
of placing drains in a permeable layer can be  appreciated by the example shown
in Figure 6-13.  If drains are laid in the layer of lower hydraulic conduc-
tivity (K^ = 1.64 feet/day) a drain spacing of only 591 feet could  be used.
If, on the other hand, the drains are placed in  the uppermost part  of a sandy
aquifer having a hydraulic conductivity of 32.8 feet/day, the drains may be
                                    6-19

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                                    FIGURE 6-12.
THE EFFECT OF DEPTH TO A LOW PERMEABILITY BARRIER ON DRAIN SPACING
                        (DE RIDDER AND VAN AART, 1974)
                    . L - 164 0 ft .
             Low Permeability -
             |V.V."-'.'..'.V.1
             [.'••y>:V:::.::| K = 1 64 ft /day
                                                  -L = 311 7 ft
                                                        203ft
                                      Low Permeability ~
                                                            -H
              Low Permeabilitv i-~
                                    6-20

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                                  FIGURE 6-13.
             THE EFFECT OF HYDRAULIC CONDUCTIVITY DRAIN SPACING
                         (DE RIDDER AND VAN AART. 1974)


                    " Low Permeability '
spaced 2034 feet apart  (DeRidder  and  Van  Aart,  1974).   This example illus-
trates the importance of  investigating  both  the layer  at and below the
envisioned drain depth.

     Drain spacing can  be determined  based either  on  field test data using
experimental plots or on  theoretical  design  formulas.   Numerous equations and
models have been developed for  determining drain spacing for various idealized
conditions.  Drain spacing equations  for  relief drains generally relate the
following factors:

     •  Precipitation and other sources of recharge
     •  Evaporation
     t  Hydraulic conductivity
     •  Depth to the impermeable  barrier
     t  Cross-sectional area of the drain
     •  Water level in  the drain.
                                    6-21

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      In  areas with  a  large natural flow velocity,  spacing  the  drains  so  that
their zones of  influence just overlap may  not  be  sufficient.   High  flow
velocity  is not accounted for by these equations  and  it may  be  necessary to
place the drains closer together than predicted by theoretical  equations to
intercept the entire  plume.

               6.2.2.1.1  Flow to Drains Reaching  an  "Impermeable"  Barrier

     Drains are often used where the depth to  a low permeability  barrier is
relatively shallow  and -the drains can be laid  just  above the barrier.  In
developing and using  drain spacing formulas for this  case, an  underlying soil
layer is considered to be "impermeable" if the hydraulic conductivity  is less
than one tenth that of the above soil layer (Wesseling, 1973).

     An equation for  flow to parallel ditches  resting on an  impermeable
barrier was developed by Donnan (1946) and described  by Wesseling (1973).   The
flow conditions illustrated in Figure 6-14 can be  described by  the  equation:

             q = (8KDH + 4KH2)/L2
where:       q = drain discharge rate per unit surface area (ft/sec)
             K = hydraulic conductivity (ft/sec)
             H = height of the water table above the  water level  in the  drain
                 midway between two drains (ft)
             D = distance between the water level   in  the drain  and  the
                 "impermeable" layer (ft)
             L = drain spacing (ft).
When D is very small compared to H,  as it is in the case of pipe drains
resting on an impermeable barrier,  the formula can be simplifed to:

             q = 4KH2/L2

               6.2.2.1.2  Flow to Drains Not Reaching an Impermeable Barrier

     In many instances,  relief drains will  not be   installed at the  top of the
impermeable barrier.  This may be because the plume can be completely
intercepted by shallow drains or because of the high cost of installing  drains
to the full  depth.
                                    6-22

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                                                           FIGURE 6-14.

                                    FLOW TO A DRAIN RESTING ON A LOW PERMEABILITY BARRIER

ro
oo
                                                                T


-------
     The Herman (1946) equation described in the previous section does  not
adequately describe the flow to a drain which does not  reach an  impermeable
barrier.  If the drain does not reach an impermeable barrier (Figure  6-15),
the flowlines will not be parallel and horizontal (as shown in Figure 6-14),
but will converge towards the drain (i.e., radial flow).  This convergence
causes a more than proportional head loss in the groundwater system which must
be accounted for in the drain spacing formula.  Hooghoudt (1940), as  described
by Wesseling (1973), developed a modified drain spacing formula  for a two
layered soil given by:

               q = (8K2dH + 4K1H2)/L2

     where:     K, ;K? = hydraulic conductivity above  (K,) and below  (K?)  the
                       drain (ft/day)
               d     = equivalent depth of the aquifer  below the drain  (ft).
                                  FIGURE 6-15.
           FLOW TO DRAIN NOT RESTING ON A LOW PERMEABILITY BARRIER
                            (VAN SCHILFGAARD. 1974)
                                              Water Table
                K,      D    I
                                                 ~*1   Low Permeability
                                                         Layer
     In the Hooghoudt  (1940)  equation  both  drain  spacing,  L,  and  equivalent
depth, d, are unknowns.  The  value of  d  is  typically  calculated from a
specified value for L, so that the Hooghoudt  (1940) equation  cannot be solved
                                      6-24

-------
explicitly in terms of L.   The use of this equation  as a  drain  spacing  formula
involves either a trial  and error procedure of  selecting  d  and  L until  both
sides of the equation are  equal  or the use of nomographs  which  have been
developed specifically for equivalent depth and drain  spacing.   Table 6-1
gives values of the equivalent depth (d) as a function of drain spacing (L)
and saturated thickness below the drains (D).  This  table shows values  of  d
for a drain pipe with a radius (r,) of four inches.   Similar tables have  been
prepared for other values  of rd (Wesseling, 1973).   For saturated thicknesses
(D) greater than 32.8 feet, the equivalent depth can be calculated from drain
spacing using the following equation (Repa et al.,  1983):

               d = 0.057 (L) + 0.845

This equation was developed by linear regression from  the values given  in
Table 6-1.

               6.2.2.1.3  Flow to Drains in a Two-layered Soil

     Although Hooghoudt1s  equation is widely used  to approximate drain
spacing, it is only accurate in two-layered soils  when the level of the drain
corresponds with the interface between the two soil  layers.  Ernst (1962), as
described by Wesseling (1973), developed an equation which offers a con-
siderable improvement over the Hooghoudt equation  for  two layered soils
insofar as the interface between the two soil layers can  be above or below the
drains.  This formula is especially useful when the  upper layer has a consid-
erably lower hydraulic conductivity than the lower layer.  The  flow to  drains
as described by Ernst is illustrated in Figure 6-16  and written as follows:

             H = (qD /K )  + (qL2/82(K.m.)) + (qL/7rK) In («D/u)
                    V  V              11            r        r
     where:
          H       = total  hydraulic head or water table height  above drain
                    level  midway between drains (ft)
          q       = drain  discharge rate per unit  surface area  (ft/day)
          L       = drain  spacing (ft)
          K       = hydraulic conductivity of the  layer with radial flow
            r        (ft/day)
                                     6-25

-------
                                                         TABLE 6-1
                                    VALUES FOR EQUIVALENT DEPTH d(m) FOR r, = 4  inches
                                   CALCULATED FOR DIFFERENT VALUES OF DRAIN SPACING  (L)
                                         AND SATURATED THICKNESS BELOW DRAINS
                                                     (Wesseling, 1973)
(D)
I
ro
L(m) 5 7.5
0(m)
0.5 0.47 0.48
0.75 0.60 0.65
1.00 0.67 0.75
1.25 0.70 0.82
1.50 0.88
1.75 0.91
2.00
2.25
2.50
2.75
3.00
3.25
3.50
3.75
4.00
4.50
5.00
5.50
6.00
7.00
8.00
9.00
10.00
0.71 0.93
10

0.49
0.69
0.80
0.89
0.97
1.02
1.08
1.13















1.14
15

0.49
0.71
0.86
1.00
1.11
1.20
1.28
1.34
1.38
1.42
1.45
1.48
1.50
1.52









1.53
20

0.49
0.73
0.89
1.05
1.19
1.30
1.41
1.50
1.57
1.63
1.67
1.71
1.75
1.78
1.81
1.85
1.88






1.89
25

0.50
0.74
0.91
1.09
1.25
1.39
1.5
1.69
1.69
1.76
1.83
1.88
1.93
1.97
2.02
2.08
2.15
2.20





2.24
30

0.50
0.75
0.93
1.12
1.28
1.45
1.57
1.69
1.79
1.88
1.97
2.04
2.11
2.17
2.22
2.31
2.38
2.43
2.48
2.54
2.57


2.58
35


0.75
0.94
1.13
1.31
1.49
1.62
1.76
1.87
1.98
2.08
2.16
2.24
2.31
2.37
2.50
2.58
2/65
2.70
2.81
2.85
2.89

2.91
40


0.75
0.96
1.14
1.34
1.52
1.66
1.81
1.94
2.05
2.16
2.26
2.35
2.44
2.51
2.63
2.75
2.84
2.92
3.03
3.13
3.18
3.23
3.24
45


0.76
0.96
1.14
1.35
1.55
1.70
1.84
1.99
2.12
2.23
2.35
2.45
2.54
2.62
2.76
2.89
3.00
3.09
3.24
3.35
3.43
3.48
3.56
50


0.76
0.96
1.15
1.36
1.57
1.72
1.86
2.02
2.18
2.29
2.42
2.54
2.64
2.71
2.87
3.02
3.15
3.26
3.43
3.56
3.66
3.74
3.88
L(m)

D(m)
0.5
1
2
3
4
5
6
7
8
9
10
12.5
15
17.5
20
25
30
35
40
45
50
60

50


0.50
0.96
1.72
2.29
2.71
3.02
3.23
3.43
3.56
3.66
3.74











3.88
75



0.97
1.80
2.49
3.04
3.49
3.85
4.14
4.38
4.57
4.74
5.02
5.20
5.30








5.38
80



0.97
1.82
2.52
3.08
3.55
3.93
4.23
4.49
4.70
4.89
5.20
5.40
5.53
5.62
5.74






5.76
85



0.97
1.82
2.54
3.12
3.61
4.00
4.33
4.61
4.82
5.04
5.38
5.60
5.76
5.87
5.96






6.00
90



0.98
1.83
2.56
3.16
3.67
4.08
4.42
4.72
4.95
5.18
5.56
5.80
5.99
6.12
6.20






6.26
ino



0.98
1.85
2.60
3.24
3.78
4.23
4.62
4.95
5.23
5.47
5.92
6.25
6.44
6.60
6.79






6.82
150



0.99
1.00
2.72
3.46
4.12
4.70
5.22
5.68
6.09
6.45
7.20
7.77
8.20
8.54
8.99
9.27
9.44




9.55
200



0.99
1.92
2.70
3.58
4.31
4.97
5.57
6.13
6.63
7.09
8.06
8.84
9.47
9.97
10.7
11.3
11.6
11.8
12.0
12.1

12.2
250



0.99
1.94
2.83
3.66
4.43
5.15
5.81
6.41
7.00
7.53
8.68
9.64
10.4
11.1
l?.l
12.9
11.4
13.8
13.8
14.3
14.6
14.7

-------
                             FIGURE 6-16.
SYMBOLS FOR THE ERNST EQUATION FOR FLOW IN A TWO-LAYERED SOIL WITH
(A) THE DRAIN IN THE LOWER LAYER AND IB) THE DRAIN IN THE UPPER LAYER

                                                            -K,
                                                            -K,
       ///A\\V//A\\ W/A\W//AUVv/\X\V//A\\\////\\VV///\\\\///
                              T
                             6-27

-------
          K       = hydraulic conductivity of the layer with vertical flow
                    (ft/day)
          D       = thickness of the layer over which vertical flow  is
           v

          D       = thickness of the layer in which radial flow occurs or
                    thickness below the drain level of the layer in which the
considered (ft)
thickness of th<
thickness below
drain is located (ft)
         2(K.m.)  = Transmissivity of the soil layers through which horizontal
                    flow is considered (ft /day)
          u       = wet perimeter of the drain (ft)
          a       = geometry factor for radial flow which depends upon flow
                    conditions (dimensionless).

Values of u,Z(K.m.), and a require further discussion.  For pipe drains in an
area of high hydraulic conductivity, u is determined from:


     u = (b + 2)(2rd)

     where the new terms are:

     b  = width of the trench (ft)
     r. = radius of the drain (ft)


If envelope material is used, it is advisable to  replace 2r . by the height of

the envelope.  2(K-m.) is equal  to the transmissivity of the entire aquifer

for a two-layered soil or l(K.m-) = K-, m, + K? m-.  Values for the geometry
factor, o, vary depending upon the relative hydraulic conductivity of the two

soil layers and whether the drains are installed  in the upper or lower layers.
The value,«, for various conditions is discussed further below.


     The Ernst equation can be used to determine  drains spacing in homogeneous

or two-layered soils.  However,  under some conditions, drain spacing estimates
using the Ernst equation will not necessarily be  any more valid then those

obtained using Hooghoudt's formula.  These situations include:


     t  Where all soil layers are homogeneous.

     •  Where drains are installed in the upper layer of a two-layer aquifer
        such that 0.1 K, is greater than K~.  In  this case the lower layer is
        considered to be an impervious barrier and the soil is considered
        homogeneous.
                                    6-28

-------
     •  Where the depth from the drain bottom to the impermeable barrier  is
        larger or suspected to be larger than 0.25L.  When this occurs, the
        hydraulic conductivity and thickness of the second layer does not have
        an effect on flow and the two layers may be considered homogeneous.


The Hooghoudt equation should be used under these circumstances to simplify

the calculations.
     Conditions where the Ernst equation is most useful  include:


     t  Where the drains are to be situated in the lower layer of a two-
        layer soil and K, < K2 (the vertical resistance  in the second  layer
        can be neglected against that in the first), so  that  (1) The geometry
        factor, a, can be neglected, (2) l(K,m,) is approximately equal to
        K2m?, (3) K  = K? and  K  = K, (K  = hydraulic conductivity of radial
        flow and K  = hydraulic conductivity of vertical flow),  (4) Dy = 2m1
        (average thickness below the water table of layer with permeability
        K-, ) and (5) D  = D  .  In this case, the formula can  be  expressed as
        f 6l lows:     r    °
        H - (q2m./K-) + (qL/8K2m2) + (qL/7rK2)  In (DQ/u)

        where D  is the distance from the water level in the drain to the next
        soil layer below having different hydraulic properties.

        Where the drain is entirely in the upper layer of a two-layer soil and
        K? >20 K,, such that «= 4, K  and K  = K,, and D  = H.   In this case,
        tne formula becomes:
             H = (qH/TrK^ + (qL/8 2(1^.))+  (qL/ir 1^) In  (4DQ/u)

     o  Where the drain is entirely in the upper layer of a two-layer soil and
        0.1 K, < K2 < 20 K,.  In this case,  the geometry  factor, a , has to be
        determined from the nomograph in Figure 6-17 and  introduced into the
        Ernst equation (Wesseling, 1973).


6.2.2.1.4  Drain Spacing Estimates Based on  Field Experiments


     Experimental or trial drains can be used to determine or verify drain

spacing calculations.  They are also used at times to determine drain spacing

where theoretical estimates are difficult to obtain because of variable soil

conditions.  For example, in areas where soils are heterogeneous,  reliable

data on hydraulic conductivity may be difficult to obtain from conventional

sampling methods.  In such cases, determination or verification of these
                                         6-29

-------
                                  FIGURE 6-17.
             NOMOGRAPH FOR DETERMINING THE GEOMETRY FACTOR a,
                     IN THE ERNST EQUATION (WESSELING, 1973)
                                                                 30  40 50
factors may be more economical or efficient using experimental drain fields.

A necessary prerequisite to using experimental drain fields is that a site can
be located which has similar hydrologic, pedologic, geologic, and topographic

conditions to the waste site.


     The dimensions of the test site are governed by:


     •  The drain spacing to be tested--Spacings which are narrower and wider
        than those calculated  or estimated should be included and the inter-
        vals should be chosen  in distinct steps.  Thus,  if the spacing is
        estimated by calculations to be 164 feet, spacings of 82 feet and 328
        feet should be included as well.

     •  A length to width ratio of at least 5  and preferably 7 to 10--Thus,
        when the test spacing  is 164 feet, the test length should be at least
        820 feet.  If the plots are too wide in relationship to the length,
        then boundary effects  (i.e.,  inflow from an undrained part of the
        area)  may be significant.
                                    6-30

-------
     The depth to which  experimental  drains  are  installed  can  be  approximated
from theoretical estimates  and  information on  the  depth  of the plume  and  depth
to permeable and impermeable  layers.

     Water observation wells  should  be  installed  at  various points  in the
experimental field to aid  in  the  evaluation  as follows  (Dieleman, 1974):

     •  Midway between drains to  measure  the hydraulic  head or the  water  table
        height above the drain
     •  Near one or more of the drains  in each field  plot  to measure  the  shape
        of the water table.   Shape should be measured at varying  points (e.g.,
        10, 20, and 50 feet from  the  drain)
     •  At the upper and lower ends of  some plots  to  observe boundary effects
     •  On top of drain tubes to  determine drain function.

     The adequacy of the drain spacing  can be determined from  the measured
hydraulic head and shape of the water table.  These  data are also used to
determine hydraulic conductivity  using  the Hooghoudt  or  other  appropriate
equation.  In using the Hooghoudt equation:

             q = (8K2dH + 4K1H2)/L2

the discharge rate per unit area drained (q=Q/A),  is measured  directly in the
field using a discharge recorder  attached to the drain outlet.

          6.2.2.2  Interceptor Drains

     Interceptor drains are designed to cut off the flow of  groundwater
originating from an up-gradient source  and are generally more  applicable  to
plume management than relief drains.
                                    6-31

-------
     There are basically two major applications for interceptor drains  in
plume management.  In the first situation (Figure 6-18a), the natural gradient
of the water table causes significant contaminant movement away from the
site.  Here, interceptor drains could be installed downgradient of the
contaminant source to cut off the contaminants flow to streams or wells.

     In the second situation (Figure 6-18b), contaminants flow outward  in
several directions from a site because of a groundwater mound which has built
up beneath the site.   This situation would require installation of parallel
interceptor drains located on either side of the site or a drainage system
which completely encircles the site.

               6.2.2.2.1  Interceptor Drains to Cut Off Natural Groundwater
                          Flow (Figure 6-18a)

     The design of interceptor drains is more often based on practical
experience than on theoretical design.  Preliminary field investigations are
undertaken to determine the direction of flow, the hydraulic gradient,  the
hydraulic conductivity, location of subsurface strata, and the boundaries of
the plume.  These data are typically obtained through an on site boring
program.  With the results of the field survey and a knowledge of how inter-
ceptors capture flow, the depth and position of the drains are estimated.
After the line is staked on the site, additional borings should be taken along
and across the staked line, and the alignment shifted, if needed, to obtain
proper interception.

     Interceptor drains are generally installed perpendicular to groundwater
flow and parallel to  the contours of the land.  Figure 6-19 illustrates the
positions of an interceptor drain relative to groundwater flow and topography.

     If soil borings  indicate that stratified soils having greatly different
hydraulic conductivities exist, the drain should be installed with a sand and
gravel envelope resting on the layer of lower hydraulic conductivity, if
possible.  If the trench line is cut through an impervious stratum, there is
danger that a significant percentage of the water moving laterally will bridge
                                    6-32

-------
                                   FIGURE 6-18.
SITE CONDITIONS REQUIRING INTERCEPTOR  DRAINS FOR PLUME MANAGEMENT
                                            Waste Disposal
                                                Site
                                                                      Private
                                                                       Well
                                                     Waste Disposal
                                                         Site
                                 Contaminated Groundwater
                                       6-33

-------
                                    FIGURE 6-19.
        LOCATION OF A SUBSURFACE DRAIN WITH RESPECT TO TOPOGRAPHY AND
                       THE DIRECTION OF GROUNDWATER FLOW
       Groundwater
          Flow   730
                                                            Land
                                                           Surface
                                                          Elevations
                  720
Interceptor
  Drain
over the drain and continue downgradient.   This  is  especially important where
a permeable layer sandwiched between two relatively impermeable layers
outcrops along the side of the  slope such  that  surface  seepage is a problem.
When this situation occurs, the flow can be  intercepted  by a drain located
just upgradient of the seep.


     For the purpose of installing  an  interceptor drain,  a layer can be
considered "impermeable"  if its hydraulic  conductivity  is  less than one tenth
that of an adjacent, more permeable layer.


     In order to decide where to position  a  drain (or drains)  to intercept the
entire leachate plume, the relationship between  depth and  flow,  and the up-
gradient and down-gradient influence of the  interceptor  drain  must be known.
                                     6-34

-------
If other boundary conditions are fixed, the shape of the drawdown curve up-
gradient of the site is independent of hydraulic conductivity, but is a
function of head.  The upgradient influence on drawdown extends for a distance
which is greater the more gradual the water table gradient.   In general, the
upgradient influence is small compared to the downgradient influence.

     The depth to which the water table is lowered downgradient of the
interceptor is proportional to the depth of the drain.  Theoretically, a true
interceptor drain lowers the water table downgradient to a depth equal to the
depth of the drain.  The distance downgradient to which it is effective in
lowering the water table is infinite provided recharge is not occurring.  This
however is never the case since  infiltration from precipitation always
recharges the groundwater.

     If a leachate plume extends from the water table to the  depth of the
impermeable layer, and an interceptor drain is placed at the midpoint between
the water table and the impervious layer, a little less than  50 percent of the
flow will be intercepted.  If the drain is placed at the top  of the imperme-
able layer nearly all of the flow will be intercepted (Van Schilfgaarde, 1974;
SCS, 1973).

     In summary, the major considerations in the design of an interceptor
drain are:
     •  To place the drains deep enough to intercept the entire plume,
        preferably to the top of an impermeable barrier
     •  To ensure that the upgradient influence of the drain is adequate to
        intercept the plume
     •  To ensure that the downgradient influence is adequate to intercept the
        plume, if necessary.  In many cases it will be adequate to cut off the
        upgradient source of the plume and allow any contaminated water
        already downgradient to continue on its course.  This will depend upon
        the size of the plume and the use of the groundwater downgradient.
                                     6-35

-------
     Interceptor drains must be properly designed  so  that  their  upgradient and
downgradient influences completely capture  and remove  the  contaminant  plume.
If after  installation, a drain  is not operating  properly,  effective plume
management can still be achieved by:

     •  Installing a cut-off wall downgradient of  the  drain  to  limit plume
        migration
     •  Installing a second drain up- or downgradient  of the first  to  cause
        further reductions in head levels
     •  Installing a second drain above or  below the  first to intercept
        leachate which bypasses the original drain.

     The  upgradient and downgradient  influence of  an  interceptor  drain can be
determined theoretically or in the field.   Evaluating  the  upgradient and
downgradient influence in the field requires that  the  first  interceptor  drain
be installed at a position and depth determined  from  soil  borings  and  ground-
water monitoring.  A period of time should  be allowed  for  the system to  come
to equilibrium before piezometers are monitored  to determine the  drawdown at
various points upgradient and downgradient  of the  interceptor.

     The  theoretical determination of the upgradient  influence of  an inter-
ceptor drain involves the use of an equation developed by  Glover  and Donnan
(1959), as described by Van Hoorn and Vandermolen  (1974):
                              i
               Du =  1.33 msl "
     where:    D  =  Effective distance of  drawdown upgradient (ft)
               ms  = Saturated thickness of the  water  bearing  strata not
                     affected by drainage (ft)
               I   = hydraulic gradient (dimensionless).

     The  theoretical determination of the downgradient influence  can be
obtained  from the following equation (Figure 6-20):
               Dd = (Kl/q) (de - hd - D2)
                                   6-36

-------
                                  FIGURE 6-20.
     SYMBOLS FOR THE GLOVER AND DONNAN EQUATION FOR CALCULATING THE
              DOWNGRADIENT INFLUENCE OF AN INTERCEPTOR DRAIN
                                       Original Water Table
                                                       Water Table
                                                      After Drainage
     where:    K  = hydraulic conductivity  (ft/day)
               I  = hydraulic gradient  (dimensionless)
               q  = drainage coefficient  (ft/day)
               d  = depth of drain  (ft)
               h. = desired depth of drawdown  (ft)
               Dp = distance from ground  surface to  water  table  prior  to
                    drainage at  the distance D, downgradient  from  the
                    drain (ft)
               D, = downgradient influence  (ft).
In the equation given above, D, and Dp are interdependent variables.   In
obtaining the solution to the equation, estimating the value of D?  is

necessary and then trial computations are made.  If the actual value of Dp  at
distance D. is appreciably different, a second calculation  is necessary.

Where I is uniform throughout the area, Dp can be considered equal  to  D,
(i.e., the distance from the ground surface to the water table measured at  the

drain).  If a second interceptor is needed to lower the water table to the
desired depth, it would be located D. feet downgradient from the first.
                                     6-37

-------
               6.2.2.2.2  Interceptor Drains for Controlling a Groundwater
                          Hound (Figure 6-18b)

     The design of subsurface drains for managing a plume generated from a
 site containing a groundwater mound depends on the direction(s) of flow from
 the site, the direction(s) of natural groundwater flow, the hydraulic
 gradient(s) and the depth to a low permeability barrier.  For this situation,
 drains can be placed completely encircling the mound, or in parallel  on either
 side of a mound.

     If the drains are installed so that they rest on top of a low permeabil-
 ity barrier and the water table is drawn down to the level  of the drain
 piping, drain spacing is not important because any part of  the plume  that lies
 outside the influence of the drains will nevertheless be contained beneath the
 site boundaries.  If the site overlies fractured bedrock or if the cost of
 construction precludes installation of the drains to the top of the low
 permeability layer, then spacing becomes an important design criteria.  This
 is because the drawdowns of the drains may not intersect, and leachate could
 flow beneath the drains or through fractured bedrock.  If the hydraulic
 gradient is not too steep, the drain  spacing formulas presented for relief
drains can be used to approximate  spacing.   These formulas  (Hooghoudt and
 Ernst equations)  can  provide a reasonable approximation of  spacing where the
 hydraulic gradient is less than three percent.  Gradient becomes  a much more
 important factor in determining flow  and drain spacing  when gradients are
greater than three percent.   Under these circumstances, the formulas  for
determining the upgradient and downgradient influence of the interceptor
drains provide a more accurate approach for drain spacing.   Computer  models
 are generally required  for these situations to ensure proper design.

6.3  Design

     In designing  a closed pipe drain,  the  pipe is  assumed  to be  able to
accept the drainage water when it  arrives at the drain!ine  and  that the pipe
will  carry away the water without  a build up of pressure.   To meet the first
criterion, the relationship  between the  hydraulic conductivity  of  the gravel
                                     6-38

-------
 envelope, the  perforations  in  the  drain  pipe,  and  the  base material  must  be

 assessed  as  described  in  the following  subsection  on filters  and  envelopes.
 To meet the  the  second  criterion,  the pipe  size  and drain  slope must be

 adequate  to  carry  away  the  water  after  it enters the pipe.


     6.3.1   Flow Capacity


          6.3.1.1  Total  Drainage  Discharge


     In order  to estimate drain diameters (i.e., the hydraulic design) and

 volume of storage  required  by  the  sump,  the total  discharge (Q) from the

 laterals, collectors, and mains must be  determined.  Estimates of  total
 discharge can  be obtained using the water balance  method.  This method

 provides  an  estimate of the amount of percolation  that will recharge the  water

 table between  the  lines of  the drain.  Once the percolation rate has been

 calculated,  discharge can be obtained by multiplying the rate times  the
                     •3                             p
 drainage  area:   Q  (ft /day) =  q (ft/day) x area (ft ).  Where water  balance

 data are  not available, the discharge from parallel relief drains  can be
 approximated from  the following formulas (Bureau of Reclamation, 1978):


               Q   = 27rKHdx/L  (for drains above a barrier)

                       2
               Q   = 4KH x/L (for drains  on a barrier)
                                                      o
     where:     Q   = total discharge from two sides (ft /day)
               H   = maximum height of the water table above the drain, midway
                    between the drains (ft)
               K   = weighted average hydraulic conductivity (ft/day)
               d   = equivalent depth (ft)
               L   = drain spacing (ft)
               x  = length of pipe (ft).

Guidance for calculating H, d,  and L is given in section 6.2.2.1.


     The rate of flow (Q) from an interceptor drain can be estimated
quantitatively using  the equation:


               Q = KIA
                                     6-39

-------
     where:
               Q = unit flow (ft3/second)
               K = hydraulic conductivity (ft/second)
               I = slope (dimensionless)             ?
               A = area through which flow occurs (ft ).

The cross sectional area intercepted by an interceptor drain  is equal to the
effective depth of the drain (i.e., the vertical distance from the bottom of
the drain to the water table) times the length of the drain:
               Q = KI dex
     where:
               d  = average effective depth of the drain (ft)
               x = length of the drain (ft).
     The use of the above equation should be reserved for situations  in which
the hydraulic conductivity, soil profile, and cross sectional area are uniform
and accurately known.  In some  instances constructing a pilot drainage system
may be more desirable to more accurately determine discharge and drain size
(SCS, 1973).

          6.3.1.2  Gradient and Velocity

     The proper installation and function of pipe drains requires rigid
control of grade and alignment  in order to prevent siltation.  The minimum
grades for a closed pipe drain where siltation is not likely to be a  hazard
are given in Table 6-2.  Steeper grades are generally more desirable.  With
steeper grades, the control required during construction is less exacting and
there is also less chance of the drains clogging.  The selected grade should
be great enough to result in a  flow velocity that prevents siltation  yet will
not cause turbulence.  Where the velocity is less than 1.4 feet/second and
siltation is a hazard, preventative measures including filters and silt traps
should be considered.  The velocity (i.e., critical velocity) at which
turbulence results varies with  soil type.  Critical velocities of various soil
types are shown in Table 6-3.   Table 6-4 gives the grades for various drain
sizes which result in the critical velocity discussed above. (SCS, 1973;
Bureau of Reclamation, 1978).
                                      6-40

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                     TABLE 6-2


 MINIMUM GRADES FOR VARIOUS  PIPE  SIZES  (SCS,  1973)
     Pipe diameter (in)    Grade  (%)
           4                 0.10
           5                 0.07
           6                 0.05
                     TABLE 6-3

CRITICAL VELOCITY OF VARIOUS SOIL TYPES  (SCS, 1973)




      Soil Types             Velocity (ft/sec)
Sand and Sandy Loam                3.5
Silt and Silt Loam                 5.0
Silty Clay Loam                    6.0
Clay and Clay Loam                 7.0
Course Sand and Gravel             9.0
                       6-41

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                                   TABLE 6-4

                 DRAIN GRADES FOR SELECTED CRITICAL VELOCITIES
Drain Size
Inches 1.4
VELOCITY (ft/sec)
3.5 5.0 6.0 7.0

9.0
                           Grade—feet per 100 feet

                        For drains with "N" =
           Clay Tile,  Concrete Tile,  and Concrete  Pipe (with  good  alignment)
     4
     5
    10
    12
.28
.21
.17
.11
.08
.07
1.8
1.3
  0
1.
0.
0.
0.4
3.6
2.7
2.1
1.4
1.1
0.8
5.1
3.9
3.1
2.1
1.5
1.2
7.0
5.3
4.1
2.8
2.1
1.6
11.5
 8.7
 6.9
 4.6
 3.5
 2.7
                          For drains  with  "N"  =  0.013
       Clay Tile, Concrete Tile,  and  Concrete  Pipe  (with  fair  alignment)
     4
     5
     6
     8
    10
    12
.41
.31
.24
.17
.12
.09
2.5
1.9
1.5
1.0
 .6
          5.2
          3.9
          3.1
          2.1
          1.6
          1.2
           7.5
           5.6
           4.4
           3.0
           2.2
           1.8
           10.2
            7.7
            6.0
            4.1
            3.0
            2.4
          16
          12.
          10.0
           6.8
           5.0
           3.9
                          For  drains  with  "N"  =  0.015

                            Corrugated  Plastic Pipe
4
5
6
8
10
12
.53
.40
.32
.21
.16
.13
3.3
2.5
2.0
1.3
1.0
.8
6.8
5.1
4.0
2.7
2.0
1.6
9.8
7.3
5.8
3.9
2.9
2.3
13.3
9.9
7.9
5.3
4.0
3.1
21.9
16.6
13.2
8.8
6.6
5.1
(a)--"N"  is  the roughness  coefficient.
                                     6-42

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          6.3.1.3   Drain  Diameter

     The size of the  drain  for  a given  capacity is  dependent  on  the flow,
hydraulic gradient, and the roughness coefficient,  N,  which  is a function  of
the hydraulic resistance  of the drain material.   The  formula  for hydraulic
design  is based on  the Manning  formula  for  pipes, which  is written  as  follows:

               Q -  AV - kmAR0-67 I  °'5
     in which: Q  =   discharge  (ft  /sec)
               R  =   hydraulic  radius (feet)  equal  to  the wetted
                      cross-sectional area,  A  ,  divided by the wetted
                      perimeter,
                      (1/4 the diameter  for  full  flowing  pipes)
               I  =   hydraulic  gradient
               k  =   roughness  factor (1/N)
               V  =   velocity,., (ft/sec)
               A  =   area (fr).
To apply the Manning  formula  in the  hydraulic design  of  drain pipes,  use  is
made of the equation:

               Q =  AV = qAd

in which q is the specific  discharge of the drain (feet/sec)  and A, is  the
                              2
area affected by the  drain  (ft  ).

     Using the calculated discharge  and knowing  the gradient of  the drain  line
and the roughness coefficient, the pipe size can  be determined from nomographs
based on the Manning  Formula.  Figures 6-21 and  6-22 are nomographs for
estimating drain size for values of N = 0.013 and N =  0.015 respectively.

     These nomographs provide a means of selecting  proper drain  size at the
starting point in the drainage system.   However,  in drainage systems with  long
laterals or mains,  common practice is to change  to  a larger pipe  size after
some distance to allow for  the increased quantity of water to be  carried.  The
following example illustrates a method for determining at what distance a
change to the next  larger pipe diameter should be made.
                                    6-43

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                                       FIGURE 6-21.
                           CAPACITY CHART FOR  N = 0.013
                             Drain Capacity Chart-N =0.013
                                -	-   r-r-1	1—
                                Drain Diameter
                                 (Flowing Full)
                                   N = 0.013
                                                       velocity
                                                          I   III

                                    o      o     o   oooooo

                              Hydraulic  Gradient (Feet per Foot)
Source: SCS, 1973

Note: The shaded area indicates where the velocity of ftow is less than 1.4 feet per second
     to indicate where drain filters may be required.
                                          6-44

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                                         FIGURE 6-22.

                              CAPACITY CHART FOR N =  0.015
                                Drain Capacity Chart-N=0.015
                                                                                  30
                                Drain Diameter

                                 (Flowing Full)*;

                                   N = 0.015 :H:
          o  o o  o o
                                                         O  o O O O
                             Hydraulic Gradient (Feet per Foot)
                                                                                         -o

                                                                                         o
                                                                                         o
                                                                                         
-------
     Assume that the  length of  a drain  is  6000  feet  and  that  the  total
discharge  at  a constant grade of 0.2 percent  is 2.40 feet  /second.   The
increase in flow or accretion would be  given  by:

           2.40 (ft3/sec)/6000 (ft) = 0.0004  (ft2/sec)
     Assuming that a 6  inch drain pipe  is  used  at  the  upper  end  of  the system,
one can determine to what  length down drain  the 6  inch  pipe  would be  adequate
by referring to Figure  6-22 (N=0.015).  From Figure  6-22,  a  6  inch  diameter
pipe on a grade of 0.2Q percent has a maximum capacity  of  0.22 ft /sec.
Letting X equal the distance downdrain  that  the 6  inch  pipe  would be  adequate,
then:

          X = 0.22 (ft3/sec)/0.0004 (ft2/sec) - 550  ft
     The 6 inch drain is therefore adequate  for 550  feet of  line.   At  this
point, the switch to an 8  inch pipe is  made.  These  computations should  be
continued progressively for the total 6000 feet of drain pipe.   If  laterals
enter the drain, the estimated yield of these should be added  at the  proper
section (SCS, 1973).

     6.3.2  Filters and Envelopes

     Performance of a drainage system is based on  the assumption that  the
drainage system will accept drainage water when it arrives at the drain!ine.
Filters and envelopes are  used to ensure that this requirement is met.

          6.3.2.1  Function of Filters  and Envelopes

     The primary function  of a filter is to prevent  soil particles  from
entering and clogging the  drain.  The function of  an envelope  is to improve
water flow into the drains by providing a material that is more permeable than
the surrounding soil.  Envelopes may also be used to provide suitable  bedding
for a drain and to stabilize the soil  material on which the  drain is being
placed.
                                     6-46

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     The filter's function and the envelope's function  are  somewhat  contradic-
tory.  Whereas filtering  is best accomplished by fine materials, coarse
materials are more appropriate for envelopes.

     As water approaches  a subsurface drain, the flow velocity  increases  as  a
result of convergence towards the perforations or joints  in the pipe.  This
increase in velocity is accompanied by an  increase  in hydraulic gradient.  As
a result, the potential for soil particles to move  towards  the  drain  is
increased.  By using a highly permeable material such as  gravel around the
pipe, the number of pore  connections at the boundary between the soil  and the
envelope will increase, thereby decreasing the flow velocity (Wesseling,
1973).

     A filter should prevent the entry of  soil particles, which could  result
in sedimentation and clogging of the drains, blocking of  perforation or tile
joints, or blocking of the envelope.  The  filter materials  should not, how-
ever, be so fine that they prevent all soil particles from passing through.
If silts and clays are not permitted to pass through, they may  clog  the
envelope resulting in increased entrance resistance, which can cause the water
level to rise above the drain (Wesseling,  1973).

     Although filters and envelopes have distinctly different functions, well
graded sands and gravels  can be used to meet the requirements of both  a filter
and an envelope.  Depending on the design manual that is  consulted, there may
or may not be a distinction made between envelopes  and  filters.

          6.3.2.2  Types of Filters and Envelopes

     Well graded sands and gravels can function both as an envelope and a
filter.  The specifications for granular filters, however, are more rigid than
those for envelopes.   Usually filter materials must be  screened and graded to
develop the desired gradation curves.  Envelope materials, on the other hand,
may have a wide range of  allowable sizes and gradings (SCS, 1973).
                                    6-47

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     A variety of soil stabilizers have been developed as a substitute for
sand and gravel envelopes.  They are added to local soils in low concentra-
tions to make stable aggregates which function as envelopes when backfilled
around the trench.  Artificial aggregates have been produced using Portland
cement, asphalt emulsions, and various polymer solutions and emulsions
(Wesseling, 1973).  With the exception of portland cement aggregates, which
have been used successfully at some sites, soil stabilizers are generally not
an economical substitute for sand and gravel.  Also in many instances, these
aggregates can react unfavorably with some components of the leachate thus
altering the hydraulic conductivity of the envelope materials and increasing
the hydraulic resistance.

     Synthetic materials are used mainly for filtration.  The most widely used
materials for synthetic filters are nylon, polypropylene, polyvinyl chloride,
polyethylene, and polyester fibers.  The most common manufacturing processes
for synthetic filters include weaving, which produces a window screen type of
material and bonding in which the density and open spaces are controlled by
fiber diameter and the number of fiber layers.  Spun bonded filters have a
large number of openings with a range of opening sizes throughout, whereas
woven filters have openings of a fixed size.  Spun bonded fabrics are most
widely used in drainage systems and are recommended for gravel and sand soils
but not for silts and clays.

          6.3.2.3  Design

               6.3.2.3.1  Sand and Gravel Filters and Envelopes

     Detailed design procedures are available for both gravel and sand
envelopes.  SCS (1973) has distinct design criteria for filters and envelopes,
whereas the Bureau of Reclamation (1978) has developed one set of standards
for a well graded envelope which meets the requirements of both a filter and
an envelope.  The separate SCS (1973) design criteria will be considered below
for the following reasons:

     •   Site specific conditions may warrant the use of only a filter or an
         envelope, but not both
                                      6-48

-------
     •   Where both a filter and an envelope are needed, the SCS design
         criteria for a filter can generally be used
     •   Use of fabric filters may be desirable with a gravel envelope.

To provide general guidelines for the use of gravel filters, SCS has divided
soils into three groups depending on their need for a filter (Table 6-5).
Soils with a high percentage of fines (the first grouping  in Table 5-5) always
require a filter.  The second group may or may not need a  filter and the last
group seldom needs a filter.

     The general procedure for designing a gravel filter is to:  (1) make a
mechanical analysis of both the soil and the proposed envelope material; (2)
compare the two particle distribution curves; and (3) decide by some set of
criteria whether the envelope is satisfactory.  The Corps  of Engineers and the
Soil Conservation Service have adopted similar criteria which set size limits
for a filter material based on the size of the base material.  These limits
are as follows:

     DKn filter/Debase = 12 to 58%
      oU         bU

     D15 filter/D15 base = 12 to 40%

Multiplying the 50 percent grain size (D5Q) of the base material by 12 and 58
percent gives the limits the 50 percent grain size of the  filter should fall
within.  Multiplying the 15 percent grain size (D15) of the base material by
12 and 40 percent gives the limits the 15 percent grain size of the filter
should fall within.  Figure 6-23 shows the upper and lower limit curves of
drain envelope suitability for a specific soil.  In this example, only filter
"No. 3" falls within the 15 percent and 50 percent limits.  When filter and
base materials are more or less uniformly graded, a generally safe filter
stability ratio  is given by:

               D1C filter/DQC filter <5
                 ID         ob
                                      6-49

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                                    TABLE 6-5
                     A CLASSIFICATION TO DETERMINE THE NEED
                   FOR DRAIN FILTERS OR ENVELOPES (SCS, 1973)
 Unified Soil
Classification
Soil  Description
    Filter
Recommendation
                                                                Envelope
                                                             Recommendation
SP (fine)

SM (fine)

ML



MH
(diatomaceous
fine)
Poorly graded sands,
gravelly sands.
Silty sands, poorly graded
sand-silt mixture.
Inorganic silts and very
fine sands, rock flour, Filter
silty. or clayey fine sands needed
with slight plasticity.
Inorganic silts, micaceous
sandy or silty soils, elastic
silts.


Not needed where
a sand and gravel
filter is used but
may be needed
with flexible
drain tubing and
other type
filters.

   GP


   SC


   GM


SM (coarse)



   GC


   CL



SP,GP (coarse)



   SW

   CH
   OL

   OH

   Pt
                Poorly graded gravels,
                  gravel-sand mixtures,
                  little or no fines.
                Clayey sands, poorly
                  graded sand-clay mix-
                  tures.
                Silty gravels, poorly
                  graded gravel-sand-
                  silt mixtures.
                Silty sands, poorly
                  graded sand-silt
                  mixtures.
                Clayey gravels, poorly
                  graded gravel-sand-clay
                  mixtures.
                Inorganic clays of low to
                  medium plasticity, gravelly
                  clays, sandy clays, silty
                  clays, lean clays.
                Same as SP & GP above.
                Well graded gravels, gravel -
                  sand mixtures, little or no
                  fines.
                Well graded sands, gravelly
                  sands, little or no fines.
                Inorganic, fat clays.
                Organic silts and organic
                  silt-clays of low plasticity.
                Organic clays of medium to
                  high plasticity.
                Peat.
                        Subject to
                        local  on-site
                        determination.
                Not needed where
                a sand and gravel
                filter is used but
                may be needed with
                flexible drain
                tubing and other
                type filters.
                             None
                Optional.
                May be needed
                with flexible
                drain tubing.
                                     6-50

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                                 FIGURE 6-23.
            MECHANICAL ANALYSIS OF A GRAVEL FILTER MATERIAL
                                  (SCS, 1973)
State
Property
                           Area
                                                     District
          John Jones
Location   T/3&. /?./#£..  SI** S
-------
For perforated pipe drains, the requirement for the minimum size of the
envelope material is affected by the size of the perforations.  SCS recommends
that the 85 percent grain size (Dgc) of the envelope material should not be
smaller than half the diameter of the perforations, and not more than 10
percent of the filter material should pass the No. 60 sieve.  SCS (1973) also
recommends a minimum filter thickness of three inches or more.

               6.3.2.3.2  Sand and Gravel Envelopes

     Envelopes are generally recommended in order to provide a permeable path
for water to move into the pipe openings.  They are also recommended to
improve the stability of certain soils during pipe installation and to provide
stability and support for corrugated flexible pipe.  The design approach
recommended by SCS (1973) is to first determine whether the drainage requires
a filter and then to determine the need for an envelope.  This is because a
well graded filter can generally also serve the function of an envelope.

     The first requirement of sand and gravel envelopes is that the envelope
have a hydraulic conductivity higher than that of the base material.  SCS
(1973) generally recommends that all of the envelope material should pass the
1.5-inch sieve, 90 percent should pass the 0.75-inch sieve, and not more than
10 percent should  pass the No. 60 sieve (0.01-inch).  This minimum limitation
is the same for filter materials, however, the gradation of the envelope is
not important since it is not designed to act as a filter.

     The optimum thickness of envelope materials has been a subject of con-
siderable debate.  Theoretically, by increasing the diameter of the pipe, the
inflow is increased.  If the permeable envelope is considered to be an
extension of the pipe, then the larger the envelope's thickness the greater
the inflow.  There are, however, practical limitations to increasing envelope
thickness.  The perimeter of the envelope through which flow occurs increases
as the first power of the diameter of the envelope, while the amount of
envelope material required increases as the square of the diameter.  Doubling
the diameter of the envelope (and consequently decreasing the inflow velocity
                                    6-52

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at the soil- envelope interface by half) would require four times the volume
of envelope material.

     Recommendations for drain envelope thickness have been made by various
agencies.  The Bureau of Reclamation recommends a minimum thickness of four
inches around the pipe, while SCS (1973) recommends a three-inch minimum
thickness.

               6.3.2.3.2  Synthetic Filters

     For synthetic materials the suitability of a filter can be determined
from the ratio of the particle size distribution to the pore size of the
fabric.  The accepted design criterion for geotextile filters is (Dupont,
1981):

               PQC (85% pore size of the filter fabric)      <^  j
               TJor (85% grain size of the subgrade material) ^
               nr P  -^ n
               or P85 ^ U85

     6.3.3  Design and Selection of Pipes

     Materials commonly used for subsurface drains include ceramic and
concrete tile and plastic pipe.  Clay and concrete tiles may be perforated, or
they may have openings or joints between the segments through which water may
enter.  Jointed concrete tiles may be manufactured with plain, tongue-and-
groove, or bell-and-spigot ends as shown in Figure 6-24.  Tongue-and-groove
and bell-and-spigot joints interlock, making them easier to place and hold
alignment.  Perforated pipe is easier to install than jointed pipe and is more
widely used for subsurface drainage at waste disposal sites.  Plastic pipe is
available as perforated and flexible corrugated pipe.  Subsurface drains may
be installed at considerable depth and the ability of the pipe to carry the
load of the backfill will be an important consideration in some cases.  The
American Society for Testing and Materials (ASTM) standards lists allowable
crushing strengths of rigid pipe drains.  These standards are listed below
under the discussion of specific pipe types.  For corrugated plastic tubing,
                                    6-53

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                 FIGURE 6-24.
  JOINT DESIGN FOR RIGID DRAIN TILES
     (BUREAU OF RECLAMATION, 1978)
       Tongue and Groove Type for Concrete Pipe
      Bell and Spigot Type for Clay or Concrete Pipe
Use 4 Wedges and Lugs for Concrete Pipe (Clay Pipe Shown)
        Plain End Type for Clay or Concrete Pipe
                6-54

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the strength depends upon  the  bedding material.   All  plastic  drains  should  be
installed  in at  least  a four-inch  gravel  envelope.   Flexible  pipe  deflects
when  loaded, which results  in  a transfer  of  the  load  to  the bedding  material.
Safe  loads  are those that  will cause 10 percent  or  less  deflection.   Equations
for determining  deflection  are presented  in  the  Bureau of  Reclamation's
Drainage Manual  (1978).

          6.3.3.1  Clay Pipes

      There  are basically two types of clay drains manufactured for subsurface
drainage—clay drain tile,  which is no longer widely  used, and perforated,
vitrified clay pipe.   Standard specifications can be  found in ASTM C4 and C700
(ASTM, Part 16,  1982), respectively.  Clay drain tile is considerably less
expensive than vitrified clay pipe, but vitrified clay is  stronger,  more
durable, and more chemically resistant than  clay tile.   Vitrified clay piping
tested over a six month exposure period was  found to  be  resistant to acids,
bases, chlorinated and aromatic solvents, chromic acid,  copper sulfate, and
numerous other chemicals.   However, vitrified clay  piping  was found  not to  be
resistant to hydrofluoric acid (Logan Clay,  1983).  Vitrified clay pipe is
available in standard  strength and extra  strength,  ranging in diameter from 3
to 42 inches.  Standards require that perforations  be 0.25 inch in diameter.

          6.3.3.2  Concrete Pipes

     Unreinforced concrete  drain pipes suitable for drainage of industrial
wastes must comply with ASTM C14,  C412, or C444 (ASTM, Part 16, 1982).
Standard C412 covers drain  tile and C14 and  C444 deal with perforated concrete
pipe.   Where concrete pipe  will be exposed to a pH of less than six  or to
sulfate concentrations in excess of 400 parts per million or both, acid and
sulfate resistant cement should be used since regular types of cement are
subject to disintegration by these materials.  Perforated asbestos cement pipe
(C-508-81)  is also resistant to acids and may be used for drainage.
                                     6-55

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          6.3.3.3  Plastic Pipes

     The most commonly used materials  in the manufacture of plastic  pipes  are
polyvinyl chloride (PVC) and high density polyethylene (HOPE). At  an equiva-
lent weight and size, PVC pipes have a somewhat higher resistance  to outside
pressure than HOPE pipes.  PVC is generally recommended for large  pipes  in
excess of six inches because of its greater strength.  However, HOPE is  less
impact resistant especially under low temperatures (Cavelaars, 1974).  PVC and
HOPE have good resistance to dilute acids and bases.  PVC is not recommended
for chlorinated and aromatic solvents.

     Plastic pipes come in smooth and corrugated varieties and there are
advantages and disadvantages to each.  Corrugated wall plastic tubes are
stronger, lighter weight, less expensive, and easier to handle because of
their flexibility than are smooth-walled plastic pipes.  Smooth pipes, on the
other hand, have a considerably lower hydraulic resistance than do corrugated
pipes. The outside diameter of smooth pipes can be about 25 percent less than
that of corrugated pipes (Cavelaars, 1974).

     Flexible corrugated tubes have gained considerable popularity in agri-
cultural drainage in recent years.  A flexible drain tube gains part of  its
vertical soil load carrying capacity by lateral support from the soil at the
sides of the conduit.  Thus, the stiffness of the conduit wall as well as the
rigidity of the soil  surrounding the tube are both structural  parameters (Van
Schilfgaarde, 1974).   This implies that the stability of the surrounding soil
is an important factor in the performance of flexible corrugated tubing.  For
conventional ceramic or concrete tile, conduit wall rigidly is the principal
parameter.

          6.3.3.4  Manholes

     Manholes are located in pipe drains to serve as junction  boxes, silt and
sand traps, observation wells, discharge measurement points,  access sites to
the drain for maintenance, and for the easy location of drains.  There are not
                                     6-56

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set criteria  for  spacing manholes.   In  general,  they should  be  used  at  junc-
tion points on a  drain  and  at major  grade  changes.   Sometimes  a manhole is  not
required  at a junction  and  a  simple  "Y"  or "T"  section  may be  adequate.

     6.3.4  Drainage  Sump and Pumping Plant

     The main steps  in  the  design of a  drainage  sump and  pumping plant  (Figure
6-25) are to  (Bureau  of Reclamation, 1978):

     •  Determine the maximum inflow to  the  sump
     •  Determine the amount of storage  required
     •  Calculate the pumping rate
     •  Determine the start, stop, and discharge  levels
     t  Determine the type  and size  of the storage tank
     •  Select the pump and the motor.

The maximum inflow to the sump is determined from the drainage  coefficient  and
the area served by a drain or drains discharging to  the sump.   As a precau-
tion, a 20 percent allowance should  be made for flow that may occur in  excess
of the design rate.  Therefore:

         QP - l'2 qg
                                           o
where:    Q  = pumped discharge capacity  (ft /day)
         Qq = gravity discharge capacity (ft /day)

     The amount of storage required depends on the inflow and the cycling
operation of  the pump.  The pump and motor are most  efficient when run
continuously,  although an 8 to 12 minute cycle is almost as efficient.
Assuming a 12 minute cycle,  for  example, during maximum inflow  there will
be 5 cycles per hour, or 5 starts per hour, with equal on and off times of
6 minutes each.   During low flow periods,  the off time will be  much longer
than the running time.  For a motor to have equal on and off times, the
storage capacity must be equal to the amount of water that would run into the
                                     6-57

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                                     FIGURE 6-25.
            TYPICAL DESIGN OF AN AUTOMATIC DRAINAGE PUMPING PLANT
                           (BUREAU OF RECLAMATION, 1978)
                                  Shelter
                                                Door

                                                Stop Collar

                                                Start Collar
                                                Float Switch
                                                 Ground Surface, El. 1306.0 -
              Pump Supports—

               Start Level
              Pipe Collector
                  El. 1296.0 -

              Stop Level
       Collector
Plug

Round Sump
Stilling Chamber
                  Concrete Base-
sump  in  one-half  the cycling  time (t  ),  or 6 minutes for  the example  used
above.   Therefore:
           Sv =  *c  Qp
                                                       Q
where:     S  is  the volume  of storage  required  (ft ).
The pumping rate,  Q  (ft /min), can then be determined using  the following
expression:
where:     t  is the  running  time of the  pump for maximum inflow (min)
                                        6-58

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 In  order to  estimate  the  size  of  the  storage  sump  required,  the  inflow and the
 minimum and  maximum water  levels  in the  sump  must  be  estimated.   In  general,
 the maximum  water  level for  starting  the pump should  be  at  the top of the pipe
 drain discharging  into  the sump.   Maximum water  level  should never exceed
 one-half of  the  pipe  diameter  over the top of the  drain.  The mimimum
 elevation  should be from  2 to  4 feet  above the base of the  sump.   The
 difference in  elevation between the water level  in the sump  and  the  discharge
 elevation  is called the pump lift (Figure 6-25).

     The volume  required  for storage  plus the requirement for a minimum water
 level above  the  bottom  of  the  sump determines the  size of the sump.   The
 distance between the  pump  cut-off and cut-on  elevation (D )  should be small to
 keep the depth of  the sump reasonable.   Assuming a D   of 2 feet  and  an inflow
                        3
 volume (S  )  of 150 feet ,  the  required diameter  (D )  for a vertical
         V                                         /\
 cylindrical  sump can  be estimated as  follows:

           Dx = (Sv/0.7854De)0'5
           DY = (150 ft3/(0.7854(2))°'5
           A
          Dx = 10 ft

     The next step in the  design  is to determine pump  type,  number,  and  size.
The type and size of  the pump  and motor  can be selected from  reliable  pump  and
motor manufacturers.  Suitable pumps must  be  able  to handle  relatively large
flows and substantial  amounts of  sediment.  The performance of the pump  varies
with head  (static lift plus  frictional losses  in the pump),  speed, discharge,
and horsepower.  Axial flow, mixed flow,  or radial  flow centrifugal  pumps  are
generally recommended.

     The size and number of  pumps are determined from  the system's required
capacity.   If the discharge  volume is large, having two pumps may be advan-
tageous to provide more efficient pumping  over a wider range  of pumping  rates.
Also, if a breakdown of one  pump occurs the system operation  will not  be
upset.   In a plant with two  pumps, one pump operation  is generally recommended
to have about half the capacity of the other.   When the pumps are not  of equal
                                     6-59

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capacity, storage should be allowed for the capacity of the largest pump
(Bureau of Reclamation, 1978; SCS, 1973).

6.4  Installation and Maintenance

     The following section describes the equipment and procedures used  in the
construction and maintenance of subsurface drain systems.  A large portion of
this section is devoted to trench excavation methods and equipment because
this portion of the drain installation process is often the most complex and
costly.  Included are sections on excavation equipment, wall stabilization,
dewatering, and grade control.  Drain installation is the next major section,
which includes the material and procedures most commonly used for placing
bedding, drain pipe, the gravel envelope, geotextile filter fabric, and
backfil1 material.

     6.4.1  Trench Excavation

     Trench excavation is the most significant step in the construction of a
subsurface drain.  The ease or difficulty of excavation can have a dramatic
effect on the cost of the total installation.  A difficult trench excavation
could even result in the exclusion of subsurface drainage as a viable
technique because of prohibitive costs.

     A number of different work elements may be involved in excavating  a
trench for a subsurface drain.  Preliminary exploration may be carried  out by
direct excavation, drilling, or seismic testing.  The presence of rock may
require that the rock be mechanically ripped, blasted, or otherwise frag-
mented.  Actual excavation of earth or rock may be carried out by a variety of
excavation equipment, the optimum being determined by the depth, width, and
length of the trench and the material being removed.  Also, a number of
alternatives are available to prevent wall failure.  These alternatives are
related to the size of the trench and the stability of the surrounding  soil.
Provisions for dewatering and proper grading are also important aspects of
trench excavation.
                                      6-60

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          6.4.1.1  Subsurface Exploration

     The selection of an excavation technique  is  intimately related to the
characteristics of the unconsolidated material or rock being removed.  Some
form of subsurface exploration should be conducted to define the various earth
layers so that proper excavation techniques can be selected, accurate cost
estimates can be developed, and proper planning can occur.

     Generally, three methods exist for subsurface exploration—direct
excavation, drilling, and seismic testing.  Direct excavation is carried out
with a backhoe or ripper.  Drilling will most  probably be occurring at a
hazardous waste site for the purposes of determining the  local geology and the
extent of groundwater and soil contamination.  For subsurface exploration
purposes, only drilling techniques in which a  drilling log can be prepared are
appropriate.  Techniques for drilling are discussed in Chapter 5.

     Seismic techniques have been used for about  75 years as a standard method
for oil exploration and for construction planning.  Seismic testing is based
on measuring the velocity of a shock wave through earth formations at various
depths.  The shock wave velocity varies considerably with respect to the
condition of the earth materials through which the wave passes.  In seismic
testing, the shock wave can be generated by a  sledge hammer and striking disk
(for limited explorations) or by blasting for  larger explorations.  The sledge
hammer-disk method can be used for distances up to 300 feet and at working
depths of about 100 feet.  Blasting, although  the preferred techniques for
large scale seismic studies, should only be used with extreme caution near
hazardous waste sites, if at all.  The shock wave generated from either
technique is measured by a sensing device called a geophone, which is located
a designated distance from the generation point.  The time interval between
shock wave generation and measurement and the distance between the two points
determines velocity.

     Seismic profiles are used in the construction industry to classify the
type of excavation required at various depths.  Generally, excavation can be
classified into three categories:  common (non-ripping), mechanical ripping,
                                      6-61

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and  blasting.  Ripping  is  further divided  into soft, medium,  hard, and
extremely hard ripping,  which helps to describe the types  of  equipment
required, production rates,  and unit costs.   General guidelines for classify-
ing  the  type of excavation and specifying  the equipment required with respect
to seismic velocities have been developed  over the years by many correlative
studies.   The guidelines  are summarized  in  Figure 6-26.


     As  shown in Figure  6-26, if seismic velocities are over  7,000 feet per
second,  rock can not be mechanically ripped  and must be fragmented in another
manner.   Blasting and other  techniques greatly increase the cost of trench
excavation.  Thus, the distance to the "drill  and shoot" or blasting zone and
the  amount of rock requiring blasting are major considerations  with respect to
the  feasibility of installing a subsurface  drain.
                                      FIGURE 6-26.
      CORRELATION OF REQUIRED EXCAVATION METHODS WITH SEISMIC TESTING DATA
                              (DERIVED FROM CHURCH, 1961)
    7000-
    6000 —
 -  5000 —
 .e  4000-
 8
    3000
 to
    2000 —
    1000
             For Heavy-Weight
              Tractor-Rippers
               300-525 HP
            100,000-160,000 Ibs.
                                     For Medium-Weight
                                      Tractor Rippers
                                       200-300 HP
                                     60,000-90,000 Ibs.
               No
             Ripping
 Soft
Ripping
Medium
Ripping
 Hard
Ripping
 Ex. Hard
 Ripping
or Blasting
                                                                             Blasting
                                       6-62

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     The operations of mechanical ripping  and  blasting  are  obviously  quite
different, and excavation by either means  mandates  a  different  set  of
considerations.  The equipment, methodology, and  limitations  with respect to
each of the techniques is briefly discussed  in  later  sections.

          6.4.1.2  Rock Fragmentation

               6.4.1.2.1  Ripping

     Mechanical ripping can now fragment rock  of  considerable consolidation
where previously only blasting was feasible.   The ripper  is basically composed
of a shank with a replaceable alloy steel  tip  attached  to a tool bar.   The
tool bar can be raised, lowered, or inclined by a series of arms and  hydraulic
cylinders known as the power assembly.  The ripper  is attached  to and  pulled
by a tractor, which usually doubles as a push  dozer.  Rock ripping  usually
takes place by lowering and angling the tip  into  the  rock while the tractor
moves slowly along at a range of 0.75 to 1.50 miles per hour.   Ripping  occurs
in igneous and metamorphic rocks by a crushing and  breaking action  and  in
sedimentary rocks by splitting and cleaving.

     Rippers for trench excavation are composed of  a  single shank and  tip
assembly, while rippers for other types of applications may have two  or three
assembles mounted on the tool bar.

     The maximum vertical reach of the largest trench ripper  available  is a
little over six feet (Alban Tractor Co., 1982).   Therefore, the use of  ripping
is limited to a trench depth of six feet.  However, if  the ripper can  enter
the trench to rip the lower lifts, a greater depth  can  be reached.  At  some
trench depths, ripping may become relatively uneconomical to  continue  to use
because the trench width needed for clearance  increases the volume of material
                                     6-63

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to be excavated.  Analysis of alternate construction techniques  as  a  function
of depth  is essential to minimize project costs.

               6.4.1.2.2  Impact Methods

     Impact methods can be used on a smaller scale  in trench work to  break
rock.  The hourly outputs of impact methods are only about one percent of the
output of a ripper.  However, they may be preferred in some cases even though
they are a more expensive option.  Three types of equipment are  available for
impact or percussive rock fragmentation—the hand-held jackhammer,  the backhoe
mounted Hobgoblin, and the Darda rock and concrete  splitter.

     The hand held jackhammer is a small percussion drill operating on about
90 pounds per square inch of air pressure and imparting about 2,000 blows per
minute (Church, 1981).  A jack hammer's use is limited to a depth of  16
inches.  The average output of a jackhammer in limestone is about six cubic
yards per hour (Richardson, 1980).  The Hobgoblin is a pneumatically  driven
impact tool  that is mounted on a backhoe arm and acts similar to a jackhammer.
A Hobgoblin also has a relatively low production rate (i.e., six cubic yards
per hour).  The Darda rock and concrete splitter uses water as the percussive
force in splitting rock.  The splitter exhibits deeper penetration  and higher
output than the jackhammer or Hobgoblin, however, the addition of water could
exacerbate pollution from a disposal  site.  The Darda splitter has  a
penetration depth of 26 inches and an average production rate of 13 cubic
yards per hour (Richardson, 1980).

               6.4.1.2.3  Blasting

     Blasting is not recommended for rock excavation purposes around  hazardous
waste sites for a number of reasons.   Blasting, even if well controlled, could
result in unwanted fracturing below the subsurface drain such that a  bypass
for the contaminant plume is created.  Ground vibration from blasting may also
cause unwanted fracturing of impermeable layers such as a previously  installed
clay cap.  The compression wave set off by blasting could cause secondary
detonation in a hazardous waste site that contains explosive materials.
                                     6-64

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Blasting also requires extensive safety provisions, causes general citizen
concern (because of noise and flyrock and air pollution) and may cause damage
or failure of trench side slopes and shoring.

     Blasting to excavate rock for a trench would be conducted using the
blasthole technique.  In this technique, holes are drilled in rock in a
specified arrangement and explosives are loaded  into the holes.  The
percussive force of the detonation fractures the rock between the holes.
Controlled blasting is a technique to reduce unwanted fracturing of nearby
rock.  This method  involves drilling a line or lines of open holes that are
not loaded with explosives between the blastholes so to create a plane of
weakness for rock fragmentation.  This action helps to contain fracturing.
However, even controlled blasting does not completely eliminate unwanted
fracturing.  Blasting ranges from $38 to $44 per cubic yard of trench
(Godfrey, 1981).

               6.4.1.2.4  Non-explosive Demolition

     Non-explosive demolition is a viable alternative to blasting as a means
of fragmenting rock.  In non-explosive demolition, holes are drilled into the
rock in a preselected pattern.  The dry demolition agent is mixed with the
appropriate amount of water and is poured into the holes.  As the material
dries it expands and exerts an expansive stress on the rock of more than 3,000
metric tons per square meter (A.M. Harris and Sons, Inc., 1982).  The rock
then fractures because of stress induced by the material's expansion and the
pattern of the drill holes.  The fracture mechanism is composed of three
phases—crack initiation, crack propagation, and the increase of crack width.
The direction of cracking can be planned by appropriately arranging the hole
spacing, depth, and inclination.  Maximum hole depth is approximately 33 feet.

     Non-explosive demolition is a process free from flyrock, noise, ground
vibration, gas, dust, and the other environmental and safety problems associ-
ated with blasting.  However, the method is expensive compared to other
fragmentation methods because of the amount and cost of the materials needed.
Costs range from $300 to $470 per cubic yard of fragmented material.  The time
                                     6-65

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 needed  for  crack  initiation  and  propagation  also  limits  the alternative's
 feasibility.

          6.4.1.3   Excavation  Equipment

      The  following  sections  describe  equipment  that  can  be  used  to remove
 earth or  fragmented  rock  for the  purposes  of  excavating  a trench.   Equipment
 includes  trenches,  backhoes, clamshells, cranes,  and  bulldozers.   In  each of
 the following  sections, the  specific  applications, limitations,  and production
 costs are discussed.

               6.4.1.3.1  Trenchers

     Trenchers or ditchers are designed to provide continuous  excavation  in
 soil  and  well  fragmented  or  weathered rock.   They consist of a series  of
 buckets mounted on  a wheel (bucket-wheel type)  or a  chain sprocket and ladder
 (bucket-ladder type).   In continuous  trenching, the  wheel or ladder is lowered
 as the revolving buckets  excavate the trench  to the  appropriate  depth.  The
 trench assembly may be mounted on wheels or on  semi-crawler or full-crawler
 frames.  The trencher moves forward simultaneously as the trench  is excavated
 resulting in a trench of  neat lines and grades.  The bucket wheel  types are
 generally used to dig shallow trenches for agricultural  drainage.   The maximum
 depth for a large wheel trencher  is about 8.5 feet (Church, 1981).  Bucket-
 ladder type trenchers can excavate trenches up to 27 feet deep and  about  6
 feet wide, although 4 feet is the maximum economical  width  (Church, 1981).

     Generally, continuous trenching  in suitable materials  is  much  faster than
 trenching via backhoe.   Hourly production rates for wheel and  ladder trenchers
 operating at 100 percent efficiency in various materials is given  in Table
 6-6.   Actual efficiencies for the entire spectrum of job conditions may range
from 20 to 90 percent (Church,  1981).   Trenchers are much more efficient  in
rural  settings where fewer obstructions are present.
                                     6-66

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                                   TABLE 6-6

          APPROXIMATE HOURLY PRODUCTION IN CUBIC YARDS FOR LADDER AND
      WHEEL TRENCHERS OPERATING AT 100 PERCENT EFFICIENCY (CHURCH, 1981)
Rock-earth formation

Alluvium, sand-gravels, lightly cemented
Weathered rock-earth:
Maximum weathering
Minimum weathering
Engine
50
210
180
120
60
horsepower
100
420
360
240
120
of
150
630
540
360
180
trencher
200
840
720
480
240
     Trenchers can be equipped with back-end modifications to provide shoring,
install a geotextile envelope, lay either tile or flexible piping, blind the
piping, and backfill with gravel or with excavated soil.  Thus, they can be
designed to perform practically all drain installation functions.  Costs for
trenching will vary according to the specific site conditions.  Costs for
deep-trenching using a ladder trencher at 31 percent efficiency (urban
setting) were estimated at $1.25 per cubic yard in 1978, including the cost of
the trencher, operation and maintenance costs, and manpower (Church, 1981).

               6.4.1.3.2  Backhoes

     The backhoe is an inverted shovel operated mechanically, hydraulically,
or by cable and used for trenching and other subsurface work.  A backhoe is
used at job sites where the excavator must be kept at ground  level and where
subsurface structures are numerous.  Backhoes can excavate earth and
fragmented rock up to one-half the bucket diameter.  Large modified backhoes
can have a digging depth range of over 70 feet; however, their large size may
exclude their use in urban areas.
                                     6-67

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     Production rates  for  various  sizes  of  backhoe  dipper  buckets  are given in
Table 6-7.  These rates  are based  on  100 percent working efficiency.   Actual
working efficiencies range from 33 to 83 percent depending  on  the  particular
site conditions (Church, 1981).

     Unit costs for excavating trenches  at  various  depths  using  various  sizes
of backhoes are given  in Table 6-8.

               6.4.1.3.3   Clamshells  and Draglines

Clamshells and draglines are crane mounted  buckets  which are sometimes used in
trench excavation operations.  Clamshells are used  when the trench depth  is
below the limit of other equipment (about 70 feet)  or when access  is  a problem
that prevents the use of other equipment.   The use  of clamshells is limited to
loose rock or earth materials.  Production  rates for clamshells  are low
compared to other methods.  Typical production rates are from  20 to 35 cubic
yards per hour.  Costs for clamshell excavation have been estimated to be
$2.93 to $4.34 per cubic yard.  If excavation is taking place  along sheeting
or a cofferdam, costs could rise to above $14 per cubic yard excavated.

     Draglines are sometimes used  to remove loose rock and earth in trench-
work.  The dragline bucket is cast outward  by the crane and pulled back  as  it
scrapes the rock or earth  into the bucket.  Draglines are generally used  when
a large reach is required  for loading or casting.   Hourly production  rates  at
100 percent efficiency are on the  same order as a backhoe, as  shown in Table
6-9.  Costs for excavating by dragline for 0.75 and 1.5 cubic  yard buckets
have been estimated to be  $2.47 and $2.76 per cubic yard respectively
(Godfrey, 1981).

          6.4.1.4  Wall Stabilization Methods

     Deep trenching requires that some form of wall  stabilization technique be
used to prevent cave-in during installation of drain pipe.  The most  common
technique used to reinforce trench openings is to use shoring, which  is a
network of wood or steel braces or both.  Freezing the ground making  up the
                                     6-68

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                            TABLE 6-7




THEORETICAL HOURLY PRODUCTION OF A HYDRAULIC BACKHOE (EPA,  1982)
Soil
Moist
Material
1
loam, 85
Bucket
1.5 2
125 175
Size (cubic yards)
2.5 3 3.5
220 275 330

4
380
sandy clay
Sand
and gravel 80
Common earth 70
Clay,








hard dense 65

PRODUCTION COSTS FOR
Trench Depth
(feet)
8
10
12
14
16
18
20
120 160
105 150
100 130
TABLE 6-8
TRENCHING USING
205 260 310
190 240 280
170 210 252

BACKHOES (GODFREY, 1982)
365
330
300


Hoe Bucket Size $/cu.yd.
(cubic yards)
0.5
0.75
1
1.25
2
2.5
3.5
2.92
2.34
1.95
1.88
1.57
1.53
1.27







                              6-69

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                                     TABLE 6-9
                         THEORETICAL HOURLY PRODUCTION RATE
                        OF A DRAGLINE EXCAVATOR (EPA,  1976)
Type of soil
Bucket size (cubic yards)

Moist loam,
sandy clay
Sand and gravel
Common earth
Clay, hard
dense
1
130
(6.6.)
130
(6.6)
110
(8.0)
90
(9.3)
1.5
180
(7.4)
175
(7.4)
160
(9.0)
130
(10.7)
2
220
(8.0)
210
(8.0)
190
(9.9)
160
(11.8)
2.5
250
(8.5)
245
(8.5)
220
(10.5)
190
(12.3)
3
290
(9.0)
280
(9.0)
250
(11.0)
225
(12.8)
3.5
325
(9.5)
315
(9.5)
280
(11.5)
250
(13.3)
4
385
(10.0)
375
(10.0)
375
(10.0)
280
(12.0)
Note:  Numbers in parentheses represent  the  maximum  digging  depth.

trench wall  is another common technique  usually applied  to  larger  underground
construction jobs.  In many cases the trench is cut  with walls  sloped  to the
angle of soil  stability.

               6.4.1.4.1   Shoring

     Shoring involves supporting the trench  walls  with wood  or  steel
structures.   A number of  different types of  shoring  exist.   Many construction
firms use slip shields, which are also known as sliding  caissons.   Slipshields
are constructed on-site by welding I-beams  between two parallel  pieces of
sheet steel.

     The slipshield is constructed for a specific  trench width.  When  a
section of trench is excavated, the slipshield is  lowered into  the  trench
using a crane.  Pipe installation then begins.  After piping is  installed and
                                     6-70

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the trench  is  filled with  gravel,  the  slipshield  is  eased out of the trench
with the crane and moved to  the  next excavated  section.   Use of the slipshield
is limited  to  the load  capacity  of the  crane.

     Adjustable  aluminum bracing  can also  be  used  for  trench wall  stabiliza-
tion.  Bracing is available  for  trenches up to  3 feet  wide at depths from 5 to
10 feet and spaced on 4 foot centers.   Costs  for rented  aluminum bracing has
been estimated to be $1.95 to $2.75 per linear  foot  of trench (Richardson,
1980).  Aluminum bracing is  much  more  economical than  using  wooden braces,
which for the  same type excavation would cost about  $2.50 to $3.25 per  linear
foot of trench.

     For deeper trenching, other  methods of shoring  are  available.  Steel
sheet piling can be driven and braced to support the trench  walls.   Also,
steel H piles  can be driven  with  horizontal wooden beams  inserted  between
them.

     Solid  wooden shoring  is  also  used  for deeper  trenches.   Wooden shoring
consists of vertical wooden  planks  supported by cross  pieces  called wales,
which are braced across the  trench  opening.  Costs for the above methods are
summarized  in  Figure 6-27.

               6.4.1.4.2   Ground  Freezing

     Ground freezing is a method of wall stabilization and groundwater  cutoff
using the technique of  refrigeration.    The method has been practiced for a
number of years by some specialty  firms, but has not been  applied  widely to
earth or rock excavation (Church,  1981).  Groundwater freezing  involves
installing a series of  vertical refrigeration pipes  into  the  ground  next to
the area of trenching.   Heat energy is  removed from  the soil  via recirculating
brine in the refrigeration pipes until   the ground freezes.  Granular soils
achieve excellent strength only a few degrees below  the freezing point.  Clay
soils may require substantially lower temperatures (down  to -20°F)  to attain
the required strength.   Although very expensive, ground freezing can also
serve as a groundwater  cut-off wall.  The combination of  both these functions
                                     6-71

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                                    FIGURE 6-27.
                       COSTS OF SHORING FOR DEEP TRENCHES
                                   (GODFREY, 1961)
 01
 I
 «j
 W
 II
26
24

22
20
18

16
14
12
10
8

6
4

2
Soldier Beams and Lagging
                                            Sheet Piling and Braces

                                    Solid Wooden Shoring
                  10
                    15
                                   20
                                     25
                                Trench Depth (ft.)
  30
                                                             35
                                                                     40
                                                                              45
may make  it  a  suitable  technique for trenchwork depths  of 25 feet and greater
(Freezwall,  Inc.,  1980).

                6.4.1.4.3   Open Cuts

     In shallow trenches,  trenches may possibly be dug  with sloped walls so
that a stable  angle  is  attained and shoring is not required.   This is called
an open cut.   The  application is of course limited to shallow trenches in most
areas, since the width  of  the trench at the surface  will  usually be limited by
other construction.   Railroad and highway design  standards specify a 1.5
(horizontal) to 1  (vertical)  slope for most conditions  and a 2 to 1 slope for
very soft soils.   Open  cuts require that more earth  is  excavated, so costs for
                                    6-72

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excavation and backfilling will be higher than for a vertical wall trench.
However, there may be an overall savings because of the  lack of  shoring, which
is generally a more expensive endeavor.

          6.4.1.5  Dewatering

     Construction of a subsurface drain to  intercept or  divert groundwater
requires excavation to a depth below that of the water table.  Maintaining
proper grade, placement, and alignment of drainage pipe  are operations  in
subsurface drain installation which are best carried out  in a "dry" environ-
ment.  Three basic options are available for dewatering  the subsurface:

     •  Open pumping
     •  Predrainage using well points or well systems
     •  Groundwater cutoff.

These techniques may be used separately or  in combination to accomplish
dewatering.  Open pumping and predrainage require the pumping of water  from
the trench excavation.  In the case of installing a subsurface drain down-
gradient of a leachate plume, there is a strong likelihood that  these
dewatering operations will be handling contaminated groundwater.  Treatment of
contaminated groundwater is required for those dewatering technologies
requiring pumping.  This may include pumping or trucking  to an existing
wastewater treatment plant, using on-site treatment equipment, reinjecting the
contaminated groundwater into the waste site, or installing and  operating the
permanent on-site treatment plant which will treat the total flow when  the
drainage system is operational.  Selection  of the proper  treatment scheme
depends on many factors, including the size of the excavation, the volume of
contaminated pumpage, the duration of excavation, the concentrations and kinds
of contaminants, and the costs for the various alternatives.
                                     6-73

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               6.4.1.5.1  Open Pumping

     Open pumping is the direct removal of water that has seeped  into  the
excavation.  This method is the least expensive of the dewatering  technolo-
gies.  Open pumping requires the construction of a sump hole  or pit  at the
lowest point of the excavation, so that water can flow towards and collect  in
the pit.  A sump pump, which may be one of several types, pumps the
accumulated water from the sump out of the excavation.

     Open pumping is applicable to shallow trench excavations with stable
soils of low hydraulic conductivity where groundwater seepage into the
excavation is minimal (Powers, 1981).  There is a possibility of  side  wall
slumping in open dewatering, therefore, the method is most applicable  in
excavations near open, undeveloped areas.  Open dewatering is used frequently
with groundwater cutoff techniques.  Open dewatering should not be used  in
areas where soils are unstable, such as uniform granular soils without plastic
fines or soft granular silts and clays because of the danger of slope
instability.  The flow of water in an excavation can also cause erosion, which
may limit the use of open dewatering.  Conditions of high flow caused  by
materials with moderate to high hydraulic conductivities or a large  head also
limit the use of open dewatering as a viable method (Powers, 1981).

     As mentioned above, there are two basic components in an open pumping
system—the sump hole and the pump.  The sump consists of a pit dug  several
feet below subgrade that is large enough to provide ample settling time to
remove sediments.  A submersible pump or inlet line from a surface pump is
placed in the pit about a foot above the pit bottom.  The pit is  surrounded  by
a large diameter corrugated steel pipe which has been perforated.  The sump
area around the corrugated steel piping is packed with gravel or  crushed rock
to provide protection against erosion and to trap sediments that  can damage
the pump.  Cleaning and maintenance of sumps is an ongoing chore  during
excavation.  In large trench excavations, there may be multiple sumps, each
handling a portion of the total flow.
                                     6-74

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     Three  types  of  pumps  are  available  for  removing  water from a sump:   cen-
trifugal suction, centrifugal  submersible,  and  diaphragm  pumps.   Centrifugal
suction pumps  are used most  commonly for removing  large volumes of water, such
as during springtime, after  flooding,  and  after shutdown  operations.   Specifi-
cations for various  sizes  of centrifugal  suction pumps  are given in Table
6-10.

     Centrifugal  submersible pumps  operate  underwater and are  used commonly in
sump holes.  Specifications  for  various  size submersible  pumps are shown  in
Table 6-11.  Diaphragm pumps have the  ability to handle many materials ranging
from clean water to  water  containing muds,  sands,  small  rocks,  and miscellane-
ous trash.  They  are used  commonly  in  the most  difficult  dewatering operations
because of their  ability to  handle  a wide range of materials.   Specifications
for diaphragm  pumps  are given  in Table 6-12.  Costs for sump pit construction
and pumping are given in Table 6-13.

               6.4.1.5.2   Predrainage  Using  Well  Points or Wells

     Well  points and deep  wells can be used  to  lower  the  water  table  near a
trench excavation.   Well points are one  of the  most widely used  and most
versatile dewatering technologies.  The  use  of  well points and  deep wells and
associated costs are discussed in Chapter 5.

               6.4.1.5.3   Groundwater Cutoff

     Groundwater cut-off barriers are used to reduce  groundwater  flow into  an
excavation.   Open pumping  is generally used  in  conjunction with  cutoff
barriers to handle the low rate of seepage through the barrier.   Cutoff
barriers may consist of steel sheet piling, concrete, or  a bentonite  slurry.
Frequently these techniques  are used as  leachate control  technologies  in
themselves as discussed in Chapter 7.  Ground freezing  is  also considered a
groundwater cutoff technique, and although expensive, may be a viable
technique  considering it serves the dual  purpose of shoring  and  acting as a
groundwater cutoff.
                                     6-75

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                               TABLE  6-10

      TYPICAL CHARACTERISTICS  OF  SELF-PRIMING CENTRIFUGAL PUMPS
              (DELIVERY  IN  GALLONS  PER MINUTE ACCORDING
                     TO  TOTAL  HEAD;  CHURCH,  1981)
Total Head Height of Pump
Including Friction Above water


15 ft
20 ft
25 ft
30 ft
40 ft
50 ft
55 ft

25 ft
30 ft
40 ft
50 ft
60 ft
70 ft

30 ft
40 ft
50 ft
60 ft
70 ft

30 ft
40 ft
50 ft
60 ft
70 ft
80 ft
10 ft
Model 4-M, 1 1/2 in
67
66
65
63
54
37
25
Model 10M, 2 in
166
164
157
145
122
85
Model 15-M, 3 in
250
230
200
160
110
Model 20-M, 3 in
333
310
275
220
160
90
20 ft

47
47
44
34
25


115
1 1 1
107
97
75

170
165
155
138
100


235
230
220
195
155
90
Model 30-M, 4 in light
30 ft
40 ft
50 ft
60 ft
70 ft
80 ft
90 ft
100 ft
NOTE: Shaft or
culated by the
hp = gal/rain x
500
495
475
450
415
355
250
100
brake horsepower must
equation:
8.34 x head
350
345
340
325
300
270
215
100
be taken
Total Head Height of Pump
Including Friction Above Water


25 ft
30 ft
40 ft
50 ft
60 ft
70 ft
80 ft
90 ft
100 ft
110 ft

25 ft
30 ft
40 ft
50 ft
60 ft
70 ft
80 ft
90 ft
100 ft

25 ft
30 ft
40 ft
50 ft
60 ft
70 ft
80 ft
90 ft
100 ft
110 ft
10ft
Model 40-M, 4 in heavy
665
660
645
620
585
535
465
375
250
65
Model 90-M, 6 in
1500
1480
1430
1350
1225
1050
800
450
100
Model 125-M, 8 in
2100
2060
1960
1800
1650
1460
1250
1020
800
570
from manufacturer" s performance curves
20 ft

475
465
455
435
410
365
300
195
50

1050
1020
970
900
775
600
265
100

1570
1560
1520
1450
1360
1250
1110
940
710
500
or cal-
efficiency x 33,000
                                   6-76

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                                   TABLE 6-11

               REPRESENTATIVE SPECIFICATIONS AND PERFORMANCES OF
                     CENTRIFUGAL SUBMERSIBLE PUMPS (CHURCH,  1981)
Specification
Nominal  Discharge Diameter (inches)
Pump:
  Discharge, diameter, in             2            4          68
  Impeller, diameter, in             11           23          8        28
  Speed, r/min                     3450         1750       1750      1750
Motor, electric, AC, 60 cycle:
  Horsepower                          2           25         60        95
  Speed, r/min                     3450         1750       1750      1750
  Phase                         Single         Three      Three     Three
  Voltage                       115-230      230-460    230-460   230-460
Complete machine:
  Cable length, ft                   50           50         50        50
  Strainer:      ?
    Open area, in                    38           48         48        48
    Openings size, in               1/4          3/8          1         1
Dimensions, in:
  Height                             23           46         57        57
  Diameter                           16           32         39        39
  Weight, approximate, Ib            50          150        450       800
Performance in gal/min
 for total head of:
   20 ft                            130          930       2160      2800
   40 ft                            100          870       1950      2720
   60 ft                             70          780       1720      2570
   80 ft                            ...          680       1480      2370
  100 ft                            ...          550       1100      2120
  120 ft                            ...          360        400      1800
                                     6-77

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                                   TABLE 6-12

                 REPRESENTATIVE SPECIFICATIONS AND PERFORMANCES
                       OF DIAPHRAGM PUMPS (CHURCH, 1981)
Specification
Nominal  Discharge Diameter (inches)
Pump, single-acting:
Strokes per minute
Length of stroke, in
Usable diameter of diaphragm, in
Displacement, in
Prime mover:
Diesel or gasoline engine, hp
Electric motor, as 60-cycle:
Horsepower
Speed, r/min
Phase and voltage
Complete machine:
Weight, wheels-tires-mount, Ib
Diesel engine
Gasoline engine
Performances, gal/min versus total head:
5-ft suction head with discharge
head of:
5 ft
15 ft
25 ft
15-ft suction head with discharge head
5 ft
15 ft
25 ft
25-ft suction head with discharge head
5 ft
15 ft
25 ft

60
2 1/2
7
71

3

1/2
1750
115-230

230
150
150



26
22
18
of:
21
19
17
of:
18
16
15

60
2 13/16
11 1/2
221

6

1 1/2
1750
115-230

350
200
200



78
66
64

68
64
60

56
60
56

52
3 3/4
12 3/4
381

10

3
1750
115-230

500
400
350



125
113
104

97
74
70

82
66
52
                                     6-78

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                                   TABLE 6-13

                     COST FOR OPEN PUMPING (GODFREY, 1981)
             Item
Unit Cost
Sump hole construction,
includes excavation, and gravel

Corrugated pipe collar (installed)
             12" pipe
             15"
             18"
             24"

Pumping 8 hr., attended 2 hrs. per day,
including 20 feet of suction, hose, and
100 feet discharge hose (rental)
             2" diaphragm
             4" diaphragm

Pumping 8 hr., attended 8 hrs. per day (rental)
             2" diaphragm
             4" diaphragm
             3" centrifugal
             6" centrifugal

Automatic Submersible sump pumps (centrifugal)
             Bronze
             TTT74~"inch, 26 GPM at 8 foot head
             1-1/4 inch, 45 GPM at 8 foot head
             1-1/4 inch, 63 GPM at 8 foot head
             1-1/4 inch, 87 GPM at 8 foot head

             Cast Iron
             1-1/4 inch, 26 GPM at 8 foot head
             1-1/4 inch, 45 GPM at 8 foot head
             1-1/4 inch, 63 GPM at 8 foot head
$0.80/cu ft
$18/ft
$22/ft
$25/ft
$35/ft
$77/day
$85/day
$310/day
$340/day
$315/day
$380/day
$180/ea
$190/ea
$280/ea
$375/ea
$115/ea
$250/ea
$280/ea
Cast iron diaphragm pumps (starter & level control included)
             2" discharge
             10 GPM at 20 foot head
             60 GPM at 20 foot head
             120 GPM at 20 foot head
             160 GPM at 20 foot head
             3" discharge
             220 GPM at 20 foot head
$370/ea
$460/ea'
$850/ea
$1450/ea

$1950/ea
                                    6-79

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          6.4.1.6  Grade  Control

     Proper grade  in a  subsurface drain  ensures  against  ponding  of  water  and
provides for a non-silting velocity  in the drainage  pipe.   Specifications for
grading were discussed  previously.   The  control  of grade during  trench
excavation is important so that the  grade of the  as-built drainage  system is
as close as possible to the design grade.  Poor  grade  control  can result  in
siltation or the need for extensive  backfilling  and  leveling,  which  drives  up
costs.

     There are two categories of grade control that  are  presently used  with
mechanical trench excavators—visual and automatic laser control.   The  visual
method is known as target grade control.  In target  control, grade  stakes (of
equal length)  are driven to the design subgrade  along  every 100  feet of the
trench line.  A line drawn through the tops of the grade stakes  would be
parallel  to the design grade of the trench.   Targets are driven  next to the
grade stakes and are adjusted to a fixed distance above  the elevation of  the
grade stakes.   The selection of this distance depends  on the depth of the
trench and the line of sight between the machine operator and  a  reference
sighting  rod on the machine.  When the trenching machine is cutting on  grade,
the targets will  align with the reference sighting rod.

     Accuracies of plus or minus 0.1 foot are easily obtainable  with the
target method.   If the depth of the trenches is also checked with respect to
the design grade at each target point, the target grade control method  can
attain an accuracy of within plus or minus 0.02 foot of the design grade
(Taylor and Willardson, 1971).

     Target grade control  enables the early detection  of errors  in setting
grade stakes or targets because any misalignment will  be apparent.  Changes  in
grading can be  accomplished quickly by resetting targets.  Target grade
control  always  proceeds trench excavation and even with modifications,  does
not hinder the  progress of conventional  trench excavation machines.
                                    6-80

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     Target grading has a few disadvantages.  The precision and accuracy of
grade control depends on the machine operators skills and alertness in
checking grades constantly to ensure proper control.  Fog and other visual
obstructions may require that targets be placed closer together.  Large
numbers of targets are difficult to handle and they will tend to have very
limited lifespans because of breakage and accidental burial.

     An alternative to the target control system is the use of  automatic grade
control with laser beams.  Many conventional trenchers (including some back-
hoes) are equipped with this control system. The basic system consists of a
portable, tripod-mounted, low-power laser beam projector and a machine-mounted
electronic tracker-receiver (Van Schilfgaarde, 1974).  The laser beam
projector emits a beam set to an elevation or grading datum, or both.  The
receiver-tracker adjusts the trenching unit hydraulically to automatically
control depth and trench grade.  A number of commercial systems are available,
some eliminating the need to ever reset the laser projector, thus enabling
change of grade at any point along the trench excavation.

     Costs for automatic grade control vary widely.  A laser beam sending unit
with tripod mounting costs approximately $8,500 (Lazer Plane Corp., 1982).  A
machine-mounted receiver for a backhoe, which simply indicates  depth, is
estimated to cost approximately $3,500 (Lazer Plane Corp., 1982).  The most
sophisticated receiver-tracker for a continuous trencher, enabling grade
change at any point during excavation, without resetting the sender would cost
from $7,500 to $11,500 (Lazer Plane Corp., 1982).

     6.4.2  Drain Installation

     Once trench excavation is completed, the components of the subsurface
drain can be installed.  The process consists of the installation of drain
pipe bedding, the drainage pipe or bed, the gravel or soil envelope, the
filter fabric, the backfill, and any auxiliary components.  Modified contin-
uous trenching machines exist which accomplish all excavation and drain
installation operations simultaneously.  However, simultaneous  excavation/
installation machinery is limited to small diameter drains in which the pipe
                                     6-81

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can be inserted into an automatic pipe feeder  and can  be  carried  along  on
rolls or wagons.  Larger diameter pipe drains  require  separate  operations.
Installation of the various components of a subsurface drain  are  discussed
below.

          6.4.2.1  Drain Pipe Bedding

     The bedding for a subsurface drain depends somewhat  on the type  of
drainage pipe to be installed and the expected loading on the pipe from the
backfill.  The simplest bedding material used  is gravel or crushed rock.
Laying a gravel bed simply consists of bringing the trench to design  grade by
excavation and backfilling and then spreading  an even  layer of  gravel over the
trench floor.  The pipe is set by placing additional gravel around the  pipe.
In the case of partial dewatering of an unstable trench floor,  the trench is
often over excavated and backfilled with a larger sized stabilizing gravel, as
specified in Table 6-14.  This enables proper  drainage to the sump without
soil loss and instability.  The bedding material can then be  laid on  top of
the stabilized floor.
                                  TABLE 6-14
                     SPECIFICATIONS FOR STABILIZING GRAVEL



          Gradation of stabilizing material               Percent
          Retained on 5-inch screen                        0
          Retained on 4-inch screen                        0 to 20
          Retained on 3-inch screen                        0 to 30
          Retained on 2-inch screen                       20 to 50
          Retained on 3/4-inch screen                     20 to 50
          Passing No. 4 sieve                             Less than 8
                                    6-82

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     Gravel beddings  are  used with  larger  diameter  drainage  pipes  of  perfo-
rated concrete, vitrified  clay,  and  rigid  plastic construction.   For  alignment
purposes, trench floors are often cut  in a semicircle  so  that  the  gravel  fill
forms a cradle for the pipe.  Costs  for gravel  are  approximately $8.60  to
$10.10 per cubic yard (Godfrey,  1981).

     In tile drainage systems where  proper alignment  is crucial,  the  trench
floor is brought up to grade with soil compacted to  its original  density.  A
small V-notch is then excavated  along  the  trench bottom to serve  as an  align-
ment guide for laying the  tile.  Soil must be removed  around bell-and-spigot
joints for proper alignment.  Bedding  for  corrugated flexible  pipe consists  of
digging a semi-circular groove instead of  a V-notch to prevent pipe collapse
during backfilling.  A groove may not  be required if backfilling  is very  well
controlled, such as on continuous excavation and installation machines. As
mentioned earlier, bedding may be part of  a continuous excavate,  install  drain
and backfill procedure or  it may be  conducted separately  from  the  other
operations.

      When unstable soils  are encountered  (oftentimes  because  of  dewatering
problems), timber cradles may be used  to ensure proper grade and  alignment.
Timber cradles consist of  wooden supports  on which the pipe  is laid.  These
cradles are supported by piles or long stakes driven into a  solid  base.   This
is an expensive operation  since each pile  or stake must be checked to be  sure
it is aligned, driven into a solid base, and cutoff at the proper  grade.
Timber cradles are used mostly for concrete and clay pipe.   Concrete pipe
cradles are also used for these purposes.

          6.4.2.2  Installation of Drain Pipe

     Installation procedures for drain pipe vary widely according  to the  type,
diameter, and length of pipe being used.   Pipe  installation  is usually
initiated at the lowest trench elevation and proceeds upgrade.  Flexible
plastic pipe can be installed from rolls mounted on a trenching machine and
continuously fed into the trench as the excavation proceeds.   Flexible pipe
                                     6-83

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can also be fed by hand from rolls mounted on wagons.   Lengths of  pipe  can  be
joined at the surface between rolls.

     The installation of flexible plastic pipe has some inherent disadvan-
tages.  Stretching the pipe will cause a loss of structural strength  and
possible collapse.  Stretching should be guarded against, especially  in
periods of hot weather.  Some drain contractors use sun  shields over  their
pipe rolls in hot weather work.  Brittleness and difficulty in unbending  are
problems that are encountered in cold weather.  Also, flexible plastic  pipe
tends to float and partial dewatering may present problems.

     The installation of rigid pipe can not be done automatically.  Laying
tile pipe can be a semi-automatic operation in which a  worker feeds tile  into
a tile chute which properly aligns, spaces, and holds each tile until the
backfill is added.  Where bell-and-spigot type joints are used, the bell  end
should always be installed upgrade.  When tiling manually, care must  be taken
to ensure proper spacing between tiles.  A tile should  always be held by  hand
or other means until  the next tile is ready to be placed.  Cracked or broken
tile should be discarded (Van Schifgaarde, 1974).  If a  tile is warped, the
tightest fit should be made on the top.  Tile should be  cut to maintain even
spacing when working  around curves.

     Long lengths of  rigid pipe are either hand carried  or lowered by crane
into the trench for installation depending on their size.  Perforated pipes of
PVC, polyethlene, concrete, bituminous fiber, and vitrified clay commonly come
in long lengths.

     When extending drainage systems under roadways, structures, root zones,
or areas not requiring drainage, unperforated pipe (or  in the case of tile,
cemented joints) should be specified.

     Installed costs  for various types and sizes of pipe, excluding excavation
and backfilling, are  given in Table 6-15.
                                     6-84

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                                  TABLE 6-15

                     INSTALLATION COSTS FOR DRAINAGE PIPE
                                (GODFREY, 1981)
                    Item
$ Per Linear Foot
Asbestos Cement, class 4000 underdrain, perforated
                4" diameter
                6" diameter

                8" diameter
               10" diameter

               12" diameter
               Unperforated, 4" diameter

Bituminous fiber, perforated underdrain
                3" diameter
                4" diameter
                5" diameter
                6" diameter

Corrugated steel or aluminum perforated, asphalt coated
                6" diameter, 18 ga.

                8" diameter, 16 ga.
               10" diameter, 16 ga.

               12" diameter, 16 ga.
               18" diameter, 16 ga.

Plain steel or aluminum, corrugated
                6" diameter, 18 ga.

                8" diameter, 16 ga.
               10" diameter, 16 ga.

               12" diameter, 16 ga.
               18" diameter, 16 ga.
        3.30
        4.33

        6.40
        7.25

        9.60
        2.57
        2.10
        2.32
        3.37
        3.94
        4.16

        5.45
        6.90

        8.60
       12.15
        3.78

        5.10
        6.50

        8.15
       11.35
Porous wall






concrete underdrain, std. strength
4" diameter
6" diameter
8" diameter
12" diameter
15" diameter
18" diameter

3.17
3.35
4.80
7.70
9.15
12.30
                                                                   (Continued)
                                     6-85

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                            TABLE 6-15  (continued)
                    Item                                  $ Per Linear Foot
Porous wall concrete underdrain, std. strength (continued)
               Extra strength
                6" diameter                                       3.57
                8" diameter                                       4.96

               10" diameter                                       7.90
               12" diameter                                       9.10

               15" diameter                                      10.35
               18" diameter                                      14.00

Vitrified clay, perforated, 2' lengths (C-211)
                4" diameter                                       3.09
                6" diameter                                       4.45
                8" diameter                                       7.10
               12" diameter                                      10.10

Vitrified clay sewer pipe, premium joint (C-200)
                4' and 5' lengths, 4" diameter                    4.10
                4' and 5' lengths, 6" diameter                    5.60
                8" diameter                                       7.20
               10" diameter                                       9.45

               12" diameter                                      12.25
               15" diameter                                      19.75

               18" diameter                                      26
               24" diameter                                      55

               30" diameter                                      73
               36" diameter                                     110

               3'  lengths, add 30% to above
               2'  lengths, add 60% to above

PVC, perforated underdrain                                            ,  ,
               3"                                                 $0.64}aj
               4"                                                 $0.82
               6"                                                 $1.85

Flexible  PVC,  perforated, 4"                                      $0.29
                                                                      (b)
;?
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          6.4.2.3  Gravel or Soil Envelopes

     Gravel envelopes are installed around the pipe drain to increase flow
into the drain and reduce the buildup of sediments in the drain line.  Gravel
envelopes may be placed by hand, backhoe, or by a hopper cart or truck.   In
continuous trencher-drain installation machines, gravel filling may be ongoing
along with other operations.

      When placing the gravel envelope, the gravel must be  in complete contact
with the pipe.  Specifications for gravel envelopes around  clay pipe call for
a minimum of 12 inches of gravel envelope above the pipe for structural
support.  The horizontal thickness of envelopes varies according to design
considerations, as discussed previously.

     When fine grained soils are encountered, a dual layered aggregate gravel
envelope can be installed.  To install the dual layered envelope, fine
aggregate is placed to form the bottom of the outer envelope.  A narrow strip
of coarse aggregate is then placed to form the bottom of the inner envelope.
After the drainage pipe is installed, the sides and tops of the two layer
system are then completed.
                                                                   t^f,f- ^
     Costs for placing gravel fill are $8.60 and $10.10 per cubic jfpot, for
bank run and screened gravel, respectively (Godfrey, 1981).

     If the existing soil hydraulic conductivity is sufficient, the existing
soil may be backfilled as the envelope material.  This practice is commonly
used in agricultural drainage, however, a greater degree of control is desired
for drainage at waste disposal sites.  Therefore, for leachate plume control,
envelope materials should consist of a hydraulic conductivity significantly
higher than the surrounding strata.

          6.4.2.4  Filter Fabrics

     Filter fabrics are sometimes installed around the gravel envelope to
prevent fines from clogging the envelope and drain pipe.  Fabrics function by
                                     6-87

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creating a graded soil filter against the fabric.  Non-woven  filter  fabrics
can be used successfully in sand and gravel base materials  containing  little
or no silt or clay, i.e., up to 1 percent (Wolbert-Master,  Inc.,  1982).   When
soils contain substantial percentages of silt or clay, the  non-woven fabric
eventually forms a filter cake and prevents the groundwater from  entering the
envelope.  Woven fabrics can be used in strata with  significant concentrations
of silt, i.e., 5 to 10 percent (Wolbert-Master, 1982).

     When constructing a drain using a fabric filter wrapping, the  fabric is
installed first, followed by the bedding, the pipe,  and  the envelope in  that
order.  The fabric filter is then wrapped around the top of the envelope prior
to backfilling with soil.  A schematic of an installed pipe drain with filter
fabric is shown in Figure 6-28.  Fabric filters can  be installed  manually or
by machine.
                                  FIGURE 6-28.
                         PIPE DRAIN WITH FILTER FABRIC
                     Perforated
                      Pipe
                                                Backfill
                                                Envelope

                                                 Geotextile
                                                Fabric Filter
     The costs for  installing geotextile  fabrics  vary somewhat depending on
the difficulty of installation.   Material  costs  are typically $0.75 to $0.85
per square yard of  fabric  for non-woven,  spun  bound synthetics, and about
                                      6-88

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$1.60 to $2.70 for the heavier, traditional woven-type fabric (Wolbert-Master,
Inc., 1982).  Costs for simple installations are typically $0.10 to $0.15 per
square yard of material.  In deep trenches, where installation is more
difficult, rolls of material may have to be sewn together and installation
costs have been known to range from $2.00 to $5.00 per square yard
(Wolbert-Master, Inc., 1982).

          6.4.2.5  Backfilling

     After the gravel envelope has been installed, the trench must be back-
filled to the original grade.  Almost any type of excavation equipment can be
used to backfill trenches.   In addition to the previously mentioned excavation
equipment, bulldozers, bucket loaders, scrapers, or front end loaders can be
used.  Many times a backhoe combined with a front end loader will be used on
the job site, with excavation being done by the hoe end (i.e., the back end)
and loading or backfilling being done by the front end.  Backfilling is done
simultaneously in some continuous trenchers.  The use of a geotextile fabric
on the top of the envelope may be advisable to prevent siltation of the
envelope from the backfill material.  In order to prevent settling of the
backfill after construction, periodic compaction of soil  lifts is also
required.   This may be accomplished using air tamping, or a vibrating or
sheepsfoot compactor.  An additional compaction technique developed for
agricultural  drainage is called puddling.   Puddling involves inundating a soil
lift with water to cause compaction.  Dams are built across the trench every
200 feet to provide suitable conditions for puddling (Van Schilfgaarde, 1979).
Puddling may not be advisable because the water applied may contact contam-
inated water or soil  near the trench and thus require treatment.

     The top two feet of trench should be backfilled with topsoil (if origi-
nally present) to reestablish the ambient vegetation.  Estimated costs and
daily outputs for backfilling by dozer with and without compaction is given in
Table 6-16.
                                     6-89

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                                  TABLE  6-16
             ESTIMATED COSTS AND OUTPUTS  FOR  BACKFILLING  BY  DOZER
                                (Godfrey,  1981)
Item
Dozer backfilling in trench,
up to 300 foot haul , no
compaction
Air tamped
Compacted Backfill, 6" to
12" lifts, vibrating roller
Sheepsfoot roller
Daily Output (yd3)
825
235
460
410
Cost/yd3
$1.09
$4.92
$2.11
$2.39
          6.4.2.6  Manholes and Wet Wells

     Manholes are used in subsurface drainage systems to serve as junction
boxes between drains, silt and sand traps, observation wells, and access
points for pipe location, inspection, and maintenance.  Manholes should be
located at junction points, changes in alignment or grade, and other
designated points.  There is not a set criteria for manhole spacing.

     A manhole should extend from 12 to 24 inches above the ground surface for
ease of location.  The base of the manhole should be a minimum of 18 inches
below the lowest pipe to provide a trap for sediments.  Manholes are typically
designed to have a drop in elevation between the inlet and outlet pipes, to
compensate for head losses in the manhole (Bureau of Reclamation, 1978).  A
typical manhole design is shown in Figure 6-29.

     A manhole is not required for the upper end of a drainage line, however,
the end should be plugged to prevent debris from entering.  Riser pipes may be
put at the upper end of a drainage pipe for cleanout purposes.  These should
be installed at an angle enabling access for pipe cleaning equipment.  Costs
for the installation of concrete manholes is given in Table 6-17.
                                    6-90

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                                FIGURE 6-29.
    TYPICAL MANHOLE  DESIGN FOR  A CLOSED  DRAIN
                 (BUREAU OF RECLAMATION, 1978)
                                            M Bars « 12"
                                            OC  Both Ways
                                            Onter of Cover


                                            Handle - M Bar
     Note  Use chain or other locking
          device between handles

               Plan
                                                                Cover
                               '- }t£j&w^
f)
                                             12" Mm
                                             24" Max
                              Ground Surface

                             36" Mm for dram pipe up
                             to and including 12" diameter
                             Manholes receiving three
                             or more large size pipe and
                             all boxes receiving larger
                             than 12" pipe should have
                             a dimension of 42"
                             Standard Precast Unrein-
                             forced Concrete Pipe
                                           M Bars O 12"
                                           O.C  Both Ways
                                           Canter of Base
                                                       Loops, if us«d, should be placed J
                                                       close to trwde of manhole
                                                                 Base
Break tower section of manhote in the
fiekJ so that rough circular opening is
formed to receive pipe After sections are
fitted in place, grout carefully to bring
pipe to grade and place gravel  packing
around pipe as directed

         Vertical  Section
     Concrete Base. Precast or
     Cast in Place, Square or
     Round
                                   6-91

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                            TABLE 6-17

                    INSTALLED COSTS FOR MANHOLES
                           (Godfrey, 1981)
        Item
                         Cost ($)
Concrete slab, cast in place,
 8" thick,
 6' deep
 8' deep
12' deep
16' deep
20' deep
Precast concrete riser pipe,
                     4' inside diameter,
                               6' deep
                               8' deep
                              12' deep
                              16' deep
                              20' deep

                     6' inside diameter,
                               6' deep
                               8' deep
                              12' deep
                              16' deep
                              20' deep
Slab tops, precast,  8" thick,
                               4'  diameter
                               5'  diameter
                               6'  diameter
Frames and covers,
                     watertight,
                              24" diameter
                              32" diameter

                     light traffic,
                              24" diameter
                              36" diameter
                                                         630
                                                         865
                                                       1,345
                                                       1,825
                                                       2,305
                           510
                           690
                           781
                           872
                           963
                         1,075
                         1,475
                         1,665
                         1,855
                         2,045
                           122
                           136
                           170
                           310
                           405
                           185
                           355
                                  6-92

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     Manholes are also used as wetwells and as silt traps in conjunction with

a wetwell, so that pumps can be protected from abrasive sediments.  A typical

design of a combined sediment trap and wet well for pumping collected

groundwater to the surface is shown in Figure 6-30.
                                 FIGURE 6-30.
                TYPICAL DESIGN OF SEDIMENT TRAP AND WETWELL
                                   • Pump
              Pump
              Screen
     6.4.3  Inspection and Maintenance


     Proper and frequent inspection of the subsurface drain during construc-

tion will often uncover potential problems that might otherwise remain

undetected for years.  The following items should be checked during

construction:


     o  Quality of tile, tubing, pipe and other materials

     o  Alignment, depth, and grade of drain and bedding, (although minor
        variations are acceptable, there should never be a reverse grade)
                                     6-93

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     •  Trench width at the top of the drain
     o  Spacing of tile joints and integrity of other connections
     •  Bedding, filter, and envelope materials and installation
     •  Backfilling and compaction
     0  Auxiliary structures including manholes, cleanout riser pipes,
        sediment traps and wet wells, and pumps and piping.

     After all components of the drain are in place the drain should be tested
for obstructions.  This can be done visually by shining a high powered flash-
light through a drain from one manhole and observing the beam in another.  If
an unobstructed view cannot be obtained by this method because of an actual
obstruction, slight misalignment, or great distance, an air filled rubber
ball or plug about one inch less than the drain diameter should be flushed
or pulled through the drain (Bureau of Reclamation, 1978).  Only a moderate
amount of water pressure or pulling force should be used so as not to deform
the ball.  Any obstruction which causes the floating ball to stop or which
significantly increases the pulling force (greater than 25 Ibs; Van
Schilfgaarde, 1979) will justify digging up and replacing the pipe, removing
the obstruction, or taking some other corrective action.  In large diameter
drains, TV-camera inspection can be used after construction and periodically
during operation.

     Manholes and silt traps should be checked frequently for the first year
or two of operation for sediment buildup.  Less frequent inspection is
required as the system ages.

     Piezometers may be installed in the various parts of the drainage system
to identify operational  problems with the filter,  envelope, pipe, or other
components of the system.  Piezometers can measure the loss of head through a
medium, and thus, can identify obstructions to flow, such as a clogged
envelope or filter.
                                     6-94

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     There are a number of problems that can develop  in drainage systems that
will require maintenance or corrective action, including:

     •  Clogging by sediment build-up in manholes or  drains
     •  Root clogging of tile drains
     •  Clogging by build-up of chemical compounds
     •  Sinkholes developing in the soil above the drain.

Problems caused by the above conditions are usually apparent at the surface
above the drain.  Inspection of the area will reveal  soft or ponded surface
conditions, areas of subsidence, and areas of accelerated vegetative growth.

     Sediments that enter the system will usually be  scoured through the drain
to the manhole where they collect.  If manholes are not cleaned out periodi-
cally, sediments can build-up to the point of clogging the drains.  Drains can
also clog because of breaking or partial collapse of  pipe, a partial obstruc-
tion, or an adverse change in alignment caused by settling in a poorly
compacted soil or inadequately installed bedding.

     Subsurface drainage pipes can also be clogged by plant roots, particu-
larly trees and shrubs.  The roots of a single plant  may extend over a
distance of several meters in a drainage pipe, given  the right conditions.
Cottonwoods and willows are particularly troublesome.

     The build-up of chemical compounds may also occur in a drain pipe.  Iron
and manganese can form insoluble precipitates with sulfur via microbial oxida-
tion.  If drains are located in areas with high deposits of reduced iron and
manganese and the flow to the drains is sufficiently  constant for a long
period of time, these compounds can build-up to the point of clogging the
drain.

     Sinkholes, or blowouts, may also develop over the drain.  These may be
caused by improper spacing of tile drains, pipe breakage, insufficient cover
material, or high pressures within the drain.
                                     6-95

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     Clogged drainage pipe can be corrected by either hydraulic jetting or
mechanically scraping the drain.  Flushing methods use high pressure water
jetting equipment that can travel inside the drain pipe.  The water jets  can
remove sediment and chemical compounds from the walls as well as from perfor-
ation in the drainage pipe.  Specially designed water jets can cut through
dead roots up to one-half inch in diameter (Winger, 1979).  Some water jetting
apparatus also contain special, closed-cage, rotating root cutters for cutting
larger roots.  Cleaning speed by water jetting is about 1,000 feet per hour,
with few roots, to 800 feet per hour, with a moderate number of roots,
(Winger, 1979).

     Mechanical scraping removes deposits from the pipe wall using such tools
as augers, pull or push blades, brushes, and hollow pipe bailers.  Costs  for
mechanical and hydraulic pipe cleaning were about $2.00 per foot in 1980
(USEPA, 1982).

     Chemical means are often used for removing iron and manganese deposits
where hydraulic or mechanical methods are ineffective.  Usually, sulfur
dioxide gas or a solution composed mainly of sulfuric acid is used to soften
the deposit to the point where hydraulic jetting can be used.  Non-corrosive
sulfuric acid pellets have recently been developed which prevent the initial
formation of iron and manganese compounds when added to the gravel envelope.

     In cases where there is a structural problem, such as drain breakage or
improper drain spacing causing a sinkhole, the drain must be dug up and the
condition corrected.  Malfunctioning perforated pipe drains located near  root
systems should be dug up and replaced with non-perforated pipe (or in the case
of tiles, sections of cemented joints).
                                     6-96

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                                   CHAPTER 7
                           LOW PERMEABILITY BARRIERS


     Low permeability barriers can be used to divert groundwater flow  away
from a waste disposal site or to contain groundwater contaminated by a waste
site.  There are two major types of low permeability barriers which find
application in leachate plume control — slurry walls and grout curtains.  A
slurry wall is a subsurface barrier that is formed through the excavation of  a
trench using a high density slurry, typically bentonite and water, to  support
the sides.  The trench is then backfilled with materials  having  lower  perme-
ability than the surrounding soil.  This backfilled trench or slurry wall
reduces or redirects the flow of qroundwater.  A grout curtain is a subsurface
barrier formed through the pressure injection of one of a variety of special
fluids known as grouts into a rock or soil body to seal and strengthen  it.
Once in place, these fluids set or gel in the rock or soil voids to greatly
reduce the permeability of and impart increased mechanical strength to  the
grouted mass.  Because a grout curtain can be three times as costly as  a
slurry wall and is  incapable of achieving uniformly low permeability,  it  is
rarely used when groundwater has to be controlled  in loose overburden.  Grouts
are primarily used  to seal voids  in porous or fractured rock when other
methods of controlling groundwater flow are impractical.

     Impeded groundwater flow may cause an increase in the upgradient
hydraulic head, which may in turn affect the rate  of vertical movement  of the
water.  Therefore,  the probable effects of a locally heightened  water  table
should be carefully considered before deciding to  apply a barrier wall.   Also,
unless measures are taken to reduce  infiltration,  a site  surrounded by a
barrier wall could  easily fill up in the so-called "bathtub effect."
                                      7-1

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      Several  types  and  variations  of  slurry wall  and  grout implacement methods
can be used to control  or  reverse  leachate  plume  migration.   The  following
sections describe the applications  and  limitations, the  theory, the design and
construction, and the cost of  slurry  walls  and  grouts.

7.1   Slurry Walls

      Slurry walls are formed through  a  slurry trench  construction  process.
Slurry trenching is a means of placing  a  low permeability,  subsurface  cut-off
or wall near  a polluting waste source in  order  to capture  or  contain  leachate
plumes.  A trench is excavated through  or under a slurry of bentonite  clay and
water.  The trench  is then backfilled with  an engineered mixture  of earth
materials having the desired permeability properties.  The  width  of slurry
trenches vary, but  are  typically from two to five feet (D'Appolonia,  1979).

     Slurry trenches are usually excavated  down to and often  into  a natural
low permeability layer  (called an aquiclude) in order to shut off  groundwater
flow.   However,  when only lowering the  water table is required, the trench may
not have to be keyed into an impervious layer.

     7.1.1  Applications and Limitations

     Slurry walls are classified by the materials of which  they are composed
and by the position in  which they are placed with respect to the  pollution
source.  Slurry wall material and configuration determine the applications  and
limitations of different slurry wall  alternatives for leachate plume
management.

     There are three major types of slurry  walls  that are categorized
according to the material used to backfill  the trench.  These three types  are:

     •  Soil-bentonite
     •  Cement-bentonite
     t  Diaphragms.
                                     7-2

-------
     Soil-bentonite walls are composed of soil materials  (often the trench
spoils) mixed with small amounts of the bentonite slurry.  Cement-bentonite
cut-off walls are excavated using a slurry of Portland cement  and  bentonite
which is left to set or harden to form the final wall.  Diaphragm  walls  are
composed of pre-cast or cast-in-place reinforced concrete  panels (diaphragms)
installed using slurry trenching techniques.  Each  of these,  as well  as
hybrids of the three, has different characteristics  and applications.

     In general, soil-bentonite walls can be expected to  have  the  lowest
permeability, the widest range of waste compatibilities,  and the lowest
installation cost.  They also offer the least structural  strength  (highest
compressibility), usually require the largest work  area,  and are restricted  to
sites that can be graded nearly level.

     Cement-bentonite walls can be installed at sites where there  is
insufficient work area to mix and place soil-bentonite backfill.   Also,  by
allowing wall sections to harden and then continuing the  wall  at a higher or
lower elevation, they are more adaptable to an extreme topography.  Although
cement-bentonite walls are stronger than soil-bentonite walls, they are  at
least an order of magnitude more permeable, resistant to  fewer chemicals, and
more costly.

     Diaphragm walls are the strongest of the three  types  as well  as  the most
costly.  Provided the joints between panels are installed  correctly,  diaphragm
walls have lower permeability and about the same chemical  compatibilities as
cement-bentonite walls.  Because of the higher expense of  diaphragm walls and
the rarity of a need for a high strength barrier, they are seldom  used  for
pollution control, thus they will not be treated in  detail here.

     Combinations of these three major backfill types may be  included within
the same wall.  For example, a soil-bentonite backfill may be  used for  the
majority of a wall with cement-bentonite being used  for a portion, such  as  a
road or rail crossing that requires greater strength.  Being  able  to  combine
                                      7-3

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the various types of walls makes this technique adaptable to  a wider  range  of
site characteristics.

     The vertical and horizontal positioning of a slurry wall with  respect  to
the location of the pollution source and groundwater flow characteristics  is
known as configuration.  There are two types of configurations--vertica1  and
horizontal.  Wall configuration, combined with associated remedial  measures,
determine  in theory how effective a slurry wall will be in controlling
leachate migration.  Although configuration depends greatly on geologic  and
topographic setting, waste characteristics, and the nature of the environ-
mental problems caused by the site, generalizations on the applications  of
different  slurry walls can be useful in understanding and evaluating  a slurry
wall as a  part of a remedial action.

           7.1.1.1  Vertical Configuration

     Vertical  configuration refers to the depth of the slurry wall  with
respect to both geologic formations and the water table.  Based on  vertical
positioning, walls are either "keyed" into a low permeability formation  below
an aquifer or placed to intercept only the upper portion of the aquifer.  This
latter type is commonly referred to as a "hanging" slurry wall.

     Keyed-in slurry walls are excavated to a confining layer below,  to
contain contaminants that mix with groundwater or sink to the bottom  of  the
aquifer.  This layer may be a low permeability formation such as a  clay  or
silty clay or may be the underlying bedrock (Figure 7-1).   In either  case,  the
connection between the wall and the low permeability zone is critical to the
overall  effectiveness of the wall.  If the low permeability zone is some
easily excavated material, such as a clay layer or weathered rock,  basic
construction quality control should be sufficient to ensure a good  key-in.  In
cases were the low permeability zone is hard bedrock, however, the  excavation
process may be much more complicated and costly.
                                     7-4

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                                   FIGURE 7-1.
                    HANGING SLURRY WALL (SPOONER et al., 1984)
     Hanging  slurry  walls  are  not  keyed  into a low permeability layer.  This
configuration  is  used  to control contaminants,  such as petroleum products,
which do not mix  with  the  groundwater  but  float on top of it.   In such cases,
the slurry wall need only  extend into  the  water table  to  intercept the
contaminants  (Figure 7-2).   The exact  depth  of  the wall will  depend on the
thickness of the  floating  contaminant  layer  and the lowest  water table
elevation.  Other considerations include the extent to which  the weight of the
contaminant might have depressed the water table  and the  effect  removal  of the
contaminants would have on the water table.

          7.1.1.2  Horizontal Configuration

     Horizontal configuration refers to the  positioning of  the wall  relative
to the location of the pollution to be controlled  and  the direction  of  ground-
water flow.   Depending on desired horizontal  configuration, slurry walls may
                                     7-5

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                                   FIGURE 7-2.
                   HANGING SLURRY WALL (SPOONER et al., 1984}
                                    Leaky
                                  • Fuel Tank
                                             Extraction  Traffic
We!!
Cap
L-
                   Water
                   Table
                                     Floating
                                    Contaminants
         Slurry
          Wall
               »%»" **" •  - - *   f *
               ;-/.; Bedrock :^W::
completely surround the polluted area or be placed upgradient or downgradient
from it.

     Circumferential placement refers to placing  a slurry  wall  completely
around a contaminated area (Figure 7-3).  Although this requires a greater
wall length than either upgradient or downgradient placement alone,  it  does
offer many advantages and is a common practice.   A circumferential slurry
wall, when used with a surface infiltration barrier (cap), can  greatly  reduce
both leachate movement and generation.   If a leachate  collection system is
used, the surrounded area can be virtually dewatered.   This offers the
advantages of vastly reduced leachate amounts and can  help increase  the
longevity of the wall by reducing the amount of leachate and wall contact.   As
shown in Figure 7-4, groundwater levels can be adjusted to maintain  the
direction of groundwater flow inward, and thus, prevent the escape of
contaminants.
                                     7-6

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                 FIGURE 7-3.
 PLAN OF CIRCUMFERENTIAL WALL PLACEMENT
             (SPOONER et al., 1984)
                                     Slurry Wall
                                  Extraction Wells
                 FIGURE 7-4.
CUT-AWAY CROSS-SECTION OF CIRCUMFERENTIAL
    WALL PLACEMENT (SPOONER et al., 1984)
                7-7

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     Upgradient placement refers to the positioning of a wall  on the
groundwater source side of a leachate source.   This type of placement can be
used where there is a relatively steep gradient across the site such that
groundwater flow can be diverted around the wastes.  In such cases, leachate
generation is reduced.   As can be seen by Figures 7-5 and 7-6,  a high water
table gradient is required for upgradient placement to be effective.
Depending on the site setting and the contaminants involved, an upgradient
wall may be keyed-in or left hanging.  In either case, drainage and diversion
structures are likely to be needed to successfully alter the flow of clean
groundwater.  The use of upgradient barrier walls is not common.

     Placement of a slurry wall  at a site on the side opposite  the groundwater
source is referred to as downgradient placement. This placement configuration
does nothing to limit the amount of groundwater entering the site and is
practical only in situations where there is a  limited amount of groundwater
flow, such as near drainage divides (Figures 7-7 and 7-8).  This positioning
does not reduce the amount of leachate being generated, but acts as a barrier
to contain the leachate so it can be recovered.  Although this  placement may
be used as a keyed-in wall for miscible or sinking contaminants, it is most
often used to contain and recover floating contaminants.  In either case, the
compatibility between the leachate and the wall backfill is important because
of contact between the two.  In addition, care must be taken in designing a
downgradient wall installation to ensure that  contaminated groundwater does
not overtop the wall.

     As outlined above, slurry walls can be applied to a plume  migration
problem in several ways.  The possible combinations of configurations and
their typical uses are summarized in Table 7-1.

     7.1.2  Theory

     During construction of slurry walls, a slurry containing bentonite is
placed in the open trench to support the trench walls.  After excavation is
completed, a mixture of bentonite slurry and soil, or a mixture of cement,
bentonite, and water is placed in the trench to form the completed wall.  This
                                     7-8

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                FIGURE 7-5.
PLAN OF UPGRAOIENT PLACEMENT WITH DRAIN
           (SPOONER et al.. 1984)
                FIGURE 7-6.
   CUT-AWAY CROSS-SECTION OF UPGRADIENT
 PLACEMENT WITH DRAIN (SPOONER et al., 1984)
                    7-9

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                  FIGURE 7-7.
     PLAN OF DOWNGRADIENT PLACEMENT
             (SPOONER et al., 1984)
Groundwater Divide
                                   «- Extraction Welte
                                         Slurry Wall
                  FIGURE 7-8.
 CUT-AWAY CROSS-SECTION OF DOWNGRADIENT
       PLACEMENT  {SPOONER et al., 1984)
                           To Treatment
                                -^*
                                Extraction Wall
                   7-10

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   TABLE 7-1.  SUMMARY OF SLURRY WALL CONFIGURATIONS (Spooner et al., 1984)
  Vertical
Configuration
                     Horizontal Configuration
                   Ci rcumferential
                    Upgradient
                    Downgradient
Keyed-in
Most common and
expensive use
                   Most complete
                   containment
                   Vastly reduced
                   leachate
                   generation
Hanging
Used for floating
contaminants
moving in more
than one direction
(such as on a
groundwater divide)
Not common
Used to divert
groundwater
around site in
high gradient
situations

Can reduce
leachate
generation but
not movement

Compatibil ity
not critical

Not common
                                       May temporarily
                                       lower  water  table
                                       behind it
                                       Can  stagnate
                                       leachate  but
                                       halt  flow
                                 not
Used to capture
miscibl e or sinking
contaminants for
treatment

Inflow not
restricted, may
raise water table
                                        Compatibility
                                        very important
Used to capture
floating contami-
nants for treatment
                    Infl ow not
                    restricted,  may
                    raise  water  table

                    Compatibility very
                    important
                                    7-11

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 section presents the current-held theories on the mechanisms by which the
 slurry and the backfill perform this function.
 7.1.2.1  Slurry Materials and Functions

     To properly construct a barrier wall for pollution migration control, a
 high quality slurry is necessary which:

     o  Has a high viscosity when allowed to stand and a low viscosity when
        agitated (termed thixotrophy)
     o  Forms a low permeability layer called a filter cake on the trench
        sides
     o  Has a density that is lower than that of the backfill.

 Slurry specifications, along with ranges normally encountered during
 construction, are presented in Table 7-2.

               7.1.2.1.1  Clay

     Both soil-bentonite and cement-bentonite slurries rely on bentonite clay
 to maintain the required slurry properties.   Bentonite is a soft, soapy-
 feeling deposit composed primarily of the clay mineral montmorillonite and
 about 10 percent  impurities, such as iron oxides and native sediments (Boyes,
 1975).   Montmorillonite's  structure and chemical composition give bentonite
 its unique properties.

     Crystals of  montmorillonite are composed of three distinct  layers.   The
outer layers consist of a  tetrahedral  arrangement of silicon and oxygen
molecules.  Some  of the silicon atoms in these layers have been  replaced by
 aluminum.   Sandwiched between the silica layers  is a layer of aluminum atoms
 surrounded by six hydroxyls or oxygen atoms  in an octahedral configuration.
 Some of the aluminum atoms in this layer have been replaced by magnesium.
 Because of the substitutions in the three layers, unsatisfied bonds  exist
within  the crystal, resulting in a net negative  charge.  To satisfy  this
charge, cations and water  molecules are adsorbed onto the internal and
 external  surfaces of the clay crystals.  These surfaces comprise the exchange
                                     7-12

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 TABLE  7-2.   SPECIFIED PROPERTIES OF BENTONITE AND CEMENT BENTONITE  SLURRIES (Spooner et al.,  1984)
Parameter
Density (g/cm )
(p.s.f.)
Viscosity, apparent
(Seconds Marsh)
(centipoise)
Viscosity, plastic
Filtrate Loss, ml
PH
Fluid Content, %
of Total Wt.
Bentonite Content, %
Other Ingredients, %
by weight
Gel Strengths
10 seconds, Pascals
10 minutes, Pascals
10 minutes,,
lb/100 ft* 7
(24-72 dynes/cnr)
Bentonite Slurry
Fresh-Hydrated
1.01-1.04
65
38-45
15
<20*
<30
range 15-30
7.5 to 12
93-97
4-7
sand <1*
solids 2
7-30
5-15
During Excavation
1.10-1.24
69-84
38-68

range 15-70
apparent average
40-60
10.5-12
78-82
6
sand <5*
solids 3-16
20-40
Cement-Bentonite Slurry
Fresh-Hydrated
1.03 to 1.4
40-45
15
9
100-300
12-13
76
3-6
cement 18
solids 15-30
15
18
During Excavation

38-80
>130
30-50


55-70
3-6
30-45
10
22
*Specification for  construction of tremied concrete diaphragm walls.

Adapted from Case,  1982;  Xanthakos, 1979; Millet and Perez, 1981; U.S.  Army  Corps  of  Engineers,  1976;
Guertin and McTigue,  1982b; Boyes, 1975; Jefferis, 1981a; Ryan, 1976

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complex of the clay.  The types of cations adsorbed  on  the exchange complex
have a great influence on the properties of the  clay (Brady,  1974).

     There are two major types of montmorillonites;  sodium-saturated  and
calcium-saturated.  Sodium montmorillonites are  preferable to calcium mont-
morillonites because sodium montmorillonites swell more and flocculate less
than calcium montmorillonites when exposed to water.  Not all  of the
bentonites used for slurry trench construction,  however, consist chiefly  of
sodium montmorillonites because there are limited quantities  of natural  sodium
bentonites.  In some cases, calciim bentonites are  used after being exposed  to
sodiim-containing materials such as sodium hydroxide to force some of the
calcium ions off of the exchange complex of the  montmorillonite and then
replace them with sodium ions (Grim, 1968).

     Where high concentrations of calcium salts  occur  in the  soil  or
groundwater and where cement-bentonite is used,  calcium ions  can easily
displace sodium ions on the clay.  The ease of replacement of sodium  by
calcium increases as the concentration of calcium in the solution and on  the
clay exchange site increases.   Once about 30 percent of the exchange  sites
become occupied by calcium, the clay acts like calcium  montmorillonite rather
than the sodium variety (Grim, 1968).

     Clays other than montmorillonite have occasionally been  used in  slurries
to maintain trench stability,  particularly in areas  where bentonite is
difficult to obtain.  Table 7-3 lists several  properties of montmorillonite  as
compared to other common clay minerals.   The primary drawback  to the  use  of
other clays in the slurry during trench  construction is the inability of  these
clays to form a filter cake under relatively low hydraulic heads and  short
formation times.

     An exception to this general  rule concerns  situations where a high
concentration of salts in the  slurry trench construction area  is anticipated.
When sodium bentonite is exposed to salt water,  undesirable property  changes
occur; the slurry begins to flocculate,  viscosity decreases,  fluid loss
                                     7-14

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                          TABLE  7-3.   COMPARISON OF SELECTED PROPERTIES OF  CLAYS (Spooner et al.,  1984)
I
I—"
en
Parameter
Volume change
caused by hydration
Hydration rate
Particle shape
Theoretical
specific surface
area, m /g
Cation Exchange
Capacity,
meg/lOOg
Liquid limit
Plastic limit
Montmorlllonite Kaolinlte 11 lite
2-11 cm3/g
Water sorption
continues for
about 1 week
thin, flat, irregular irregular, flat
plates hexagonal s
700-800 5-20 100-200
60-150 3-15 10-40
150-700 29-75 59-90
65-97 26-35 34-43
Other Clays or
Sheet Silicates
vermiculite >montmorillonite
>beidellite >kaolinite
>ha Hoy site
water sorption for
most colloidal clays is
complete in 1 to 3 days
attapul gi te-f 1 brous ,
sepiolite-fibrous,
most others irregular
and flat
vermiculite 300-500
vermiculite 100-150,
attapulgite/sepiolite
3-15
--
Continued
                    Adapted from Baver, Gardner and Gardner,  1972; Grim, 1968;  Grim and Guven,  1978; Xanthakos,  1979; Spangler and

                    Handy, 1973

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                                                          TABLE  7-3   (continued)
                     Parameter
                        Montmorillonite
Kaolinite
Illlte
Other Clays or
Sheet Silicates
en
Percentage of clay          5.5-12
  by weight In
  water to produce
  a 15 centlpolse
  colloidal suspension

Approximate                 0.5-1.3
  negative charge
  per formula
  unit
                                                                                           1.2-2.0
                                                                                                          25-36 for typical
                                                                                                          native clays
                                                                                                          attapulgite-same  as
                                                                                                          montimorillonite
                                   vermiculite 1.2-1.8,
                                   muscovite 2.0
                     Density2of chacge
                       meq/m  x 10"

                     Layer thickness
                       in angstroms
                     Particle density,
                       g/cnr
                            1.1-1.9
                        expansive  >10
                        air dry  15
                        2.5 Wyoming  bentonite
                        2.2 Japanese bentonite
6-7.5


7.15
1.0-2.0        vermiculite 3.0-3.3
10             vermiculite 14,
               muscovite 10,
               biotite 10,
               halloysite 10,

               mica 2.8-3.2
                     Adapted from Baver, Gardner and Gardner,  1972; Grim,  1968;  Grim and  Guven,  1978;  Xanthakos,  1979;  Spangler  and
                     Handy, 1973

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increases, and the slurry may gel  completely and  lose  its  thixotropic
properties (Xanthakos, 1979).  In  these situations,  a  type of clay called
attapulgite has been used.

     Attapulgite is not composed of plates as is  montmoril lonite.   Instead,
the attapulgite crystals are composed  of linked  silica chains that form  a
fibrous structure; chains of water molecules fill  voids between  the
tetrahedral and octahedral silica  layers (Grim,  1968).  Attapulgite is
apparently not negatively affected by  the electrolyte  concentration in the
water to which it is added and does not require  any  initial  hydration  time as
does montmoril lonite.

     Wyoming bentonites are the most commonly used bentonites for  slurry
trench construction.  They contain about 60 percent  sodium and 40  percent
calcium and magnesium cations on the exchange complex  of the clay  (Connybear,
1982).  These bentonites are mixed at  a rate of  4 to 7 percent bentonite in  93
to 96 percent water (Boyes, 1975).

               7.1.2.1.2  Filter Cake

     When trench excavation is initiated, the slurry is pumped into the  trench
to maintain a slurry level at or near  the initial  ground level (Millet and
Perez, 1981).  As the slurry is introduced into  the  trench, it flows into
pores in the strata through which  the  trench is  cut.  Leakage of slurry  into
these voids continues until the flat clay particles  in the slurry  begin  to
accumulate in layers, which grow large enough to bridge the gaps between the
soil particles or until gelation of the slurry within  the  pores occurs.
Figure 7-9 illustrates the relatively  rapid initial  slurry loss, followed by a
reduction  in the rate of loss.  This reduction is caused by the formation of a
layer of clay particles "plastered" on the trench sides, which reduces lateral
liquid flow out of the trench and  into the adjacent  soil.   This layer  is
called a filter cake.
                                     7-17

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                                  FIGURE 7-9.
                   FLUID LOSS DURING FILTER CAKE FORMATION
             (HUTCHINSON et al., 1983 AS CITED BY SPOONER et al., 1984)
            I
            s
            a
                                            Time for Initial Cake Formation
                                     (TimeT)V4
     The filter cake is a thin membrane composed  of  plate-like  bentonite
particles (Case, 1982).  The solids content of the newly  formed  filter  cake
ranges from 10 to 50 percent, with higher solids  contents  found  in  filter
cakes from calcium than from sodium bentonites (Grim and  Guven,  1978).  The
filter cake from a slurry containing 5 percent bentonite  typically  contains  15
percent bentonite (Hutchinson et al . , 1975).  During active excavation, the
filter cake is usually less than three millimeters thick.  This  thick layer  of
clay is, however, an effective barrier to water movement as the  permeability
of the filter cake can be as low as 10~6 ft/day (Xanthakos, 1979).

     Formation of the filter cake is of critical   importance in  slurry trench
construction.  This membrane performs numerous functions  including:

     0  Minimization of slurry loss into surrounding soils
     •  Stabilization of the soil that is in contact with the slurry by
        gelling in the soil  pores and by plastering the particles against the
        trench wall s
                                     7-1!

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     0  Providing a plane on each trench wall  against which the  hydraulic
        pressure and dead weight of the slurry can act to stabilize the
        excavation.

     Desirable characteristics of filter cakes include rapid formation and
reformation when necessary, resistance to shearing, and low permeability.
Experience has shown that a thin filter cake is an indication of a tough,
impermeable membrane, but a thick "flabby" filter cake is likely to allow high
fluid losses (Boyes, 1975).

     Filter cakes must be formed rapidly when the initial soil  contact occurs
in order to avoid excessive slurry losses.  These membranes must resist
mechanical disruption by the backhoe bucket or clamshell  during  trench
excavation.  If inadvertently scraped off the trench wall during excavation,
the slurry must be of such composition as to allow rapid formation of a new
filter cake to avoid possible collapse of the trench.

     A high gel strength is desirable in the filter cake because the gel
structure contributes to shear strength, and the filter cake must resist
shearing forces from both the excavation equipment agitated slurry and the
soil  comprising the trench wall.  In addition, high gel  strength indicates
rapid formation of a gel structure.  When the slurry penetrates  soil pores,
rapid gelation assists in restricting further slurry flow and thus minimizes
slurry losses (Xanthakos, 1979).

     A final desirable filter cake characteristic is low permeability.  The
movement of water through the filter cake should be minimized to:

     o  Avoid wetting and thus softening and lubricating unstable layers  that
        may be present in the soil  surrounding the trench (Boyes, 1975)
     •  Avoid increasing pore water pressure, because this increases the  total
        stress on the system and reduces the angle of friction  in the soil
        surrounding the trench (Hutchinson et al., 1975).
     •  Maintain the slurry level  in the trench well  above the groundwater
        level.  This sustains the thrust of the slurry on the trench side
        walls by restricting the pressure losses caused by filter cake leakage
        (Xanthakos, 1979).
                                     7-19

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               7.1.2.1.3  Cement-Bentonite


     Cement-bentonite (CB)  slurries normally contain  less  than  6  percent  by

weight bentonite, 18 percent ordinary  Portland  cement (o.p.c.), and  76  percent
water (Jefferis, 1981b).  Typical  ranges of CB  slurry contents  are presented
in Tabl e 7-4.
         TABLE 7-4.   TYPICAL COMPOSITIONS  OF  CEMENT-BENTONITE  SLURRIES
                     (Jefferis,  1981b  as cited  by  Spooner  et al.,  1984)
     Constituent                                  Amount  of  Slurry
                                                 (Percent by weight)
Bentonite                                              4-7

Water                                                 68-88

Cement
  without replacements                                 8-25
  when blast furnace slag added,  minimums               1-3
  when fly ash added, minimums                         2-7

Blast furnace slag, maximums                           7-22
  (not commonly available in U.S.)

Fly ash, maximums, if used                             6-18
     When bentonite slurries are compared  to  CB  slurries,  the  differences
become evident.   Most of these differences are caused  in  part  by  the effects
of the calcium from the cement on the  sodium  montmorillonite  in the bentonite.
The three most important differences between  the  properties of CB slurries  and
bentonite slurries are:


     •  Physical  properties, including  viscosity and  filter cake  formation
     •  Setting  times
     •  Filter cake permeability.
                                     7-20

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     Because of the calcium in the cement, the properties of the sodium
bentonite in CB slurries are permanently altered.  For example, the initial
viscosity is somewhat higher because of the flocculation of the slurry and the
higher solids concentration; 15 to 30 percent in CB slurry, opposed to about 6
percent in bentonite slurries (Millet and Perez, 1981; Jefferis, 1981b).  The
results of the filtrate loss test are also higher.  This indicates that the
time required for filter cake formation is longer and the permeability of the
cake formed is higher (Hutchinson et al., 1975; Millet and Perez, 1981).

     The primary differences betwen CB and soil-bentonite (SB) slurries that
is of practical  importance in slurry trench construction is the fact that CB
slurries begin to harden within two to three hours after mixing, while
bentonite slurries do not set (Case, 1982).  This often necessitates the use
of construction techniques different from those used during construction of SB
walls, as described below.

     CB walls may be constructed in a series of panels but are more commonly
installed as a continuous trench.  When CB panels are constructed, alternate
panels are excavated under a CB slurry, then allowed to partially set.  When
they have obtained a sufficient shear strength, the intervening panels are
excavated also under a slurry.  A portion of the initial  panel ends are
removed during this second stage to ensure continuity between  the initial
panels and the intervening ones.  This technique is used only  for very deep
installations.

          7.1.2.2  Backfill  Materials and Functions

     Two major types of backfill  have been used in barrier walls:  soil-
bentonite and cement-bentonite.  Soil-bentonite (SB)  backfills are composed of
bentonite slurry and soil  materials, often the  spoils excavated from the
trench.  Cement-bentonite (CB)  backfills are the result of the in-place
hardening of cement-bentonite slurries.   The design  factors  affecting  the
permeability of completed cement-bentonite and  soil-bentonite  walls are
backfill  composition and  slurry properties.
                                     7-21

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                7.1.2.2.1   Soil-Bentonite Walls

      Soil-bentonite walls  are excavated under a bentonite slurry in a
continuous trench.  The trench is then backfilled with a soil-bentonite
mixture having  the desired properties.

      Two primary components make up the backfill:  the bentonite slurry and a
suitable soil mixture.  The soil mixture used in backfilling is often soil
material from the trench excavation, augmented with selected soil from a
suitable borrow source.  Regardless of the source, the soil  material must meet
three requirements:

     •  Must be free of deleterious materials
     •  Must have a suitable particle size distribution
     •  Must mix with the  slurry to form a more-or-less homogeneous paste.

     The backfill  should not contain materials that would react with the
pollutants being contained.  For example, calcium-containing materials
(gypsum, chalk, or caliche) should  not be used in walls intended to contain
highly acidic groundwater.

     Another requirement for backfill material is that it contain a suitable
particle size distribution.  To  ensure a low permeability, the backfill  must
have from 20 to 40 percent fine  particles, preferably plastic fines.  As shown
in Figure 7-10, backfill  permeability will  be lower when the backfill  material
contains a higher proportion of  fines (D'Appol onia, 1980).  Fine particles,
particularly clays, contribute to low permeability by assisting in  bridging
the pores between larger particles.

     A final  requirement of the  soil material used in the backfill  is that it
be mixed with the  slurry to form a  more-or-less  homogeneous  paste.   This is
largely a function of water content and blending technique.   According to
D'Appolonia (1980), this requirement is relatively easy to meet as  a wide
variety of materials have been successful ly mixed at slurry  trench  construc-
tion  sites.   In general, clayey  soils will  require a greater blending  effort
and higher water content than  more  coarse materials.
                                     7-22

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                                  FIGURE 7-10.
                   RELATIONSHIP BETWEEN PERMEABILITY AND
                 QUANTITY OF BENTONITE ADDED TO SB BACKFILL
               (D'APPOLONIA, 1980 AS CITED BY SPOONER et al., 1984)
                10
                 -2
                10
                10-
                 -3
                10
                 -5
                10
                 -6
                10
                 -7
                10
                 -9  '
Well Graded
Coarse Gradations
(30-70% + 20 Sieve)
w/10 to 25% NP Fines
       Poorly Graded
       SitySand
       w/30-50% NP Fines
                       Clayey Saty Sand
                       w/30 to 50% Fines
                              1234

                             % Bentonite by Dry Weight of SB Backfill
     Once the  backfill  material  has been selected,  it  is mixed with the slurry
until the slurry  attains the necessary slump.   The  slump of the backfill is
the vertical distance  a cone-shaped mass of concrete or  other  plastic material
will settle  and  is  a measure of the backfill's  shear strength.  The slump
should range from two  to seven inches on the ASTM C143-74 "Slump of Portland
Concrete" Test (D'Appolonia, 1980).  The shear  strength  of the backfill
mixture, as  indicated  by the slump cone test, should be  high enough that the
backfill easily displaces the slurry, but not so high  that it  folds over
itself rather  than  flowing into  the trench.  The density of the backfill
should be at least  15  pounds per cubic foot (240 kilograms per cubic meter)
greater than that of the slurry  in the trench (D1Appolonia, 1980).   Prefer-
ably, the shear  strength should  be lower than that  of  the filter cake, yet
high enough to allow it to stand on a 5:1 to 10:1 slope  (Millet and Perez,
1981).
                                      7-23

-------
     The primary requirement of a slurry wall  for  controlling  leachate plumes
is low permeability.  Permeabilities of completed  soil-bentonite walls can be
as low as 1.5 x 10   ft/day, although  higher  permeabilities are more common
(Xanthakos, 1979).  Several factors affect the  permeability of the completed
wall  including:

     •  Quality of the filter cake
     •  Fines content of the backfill
     t  Bentonite concentration of the backfill
     •  Plasticity of the  fines in the backfill
     0  Voids ratio of the backfill.

     D'Appolonia (1980) found that plastic  fines  inhibit water movement more
effectively than non-plastic fines.  This is  logical  since the plastic fines
are composed mostly of clays, which  are less  pervious than the non-plastic
fines, which are primarily silts.  Since bentonite has a very  small  particle
size, it also contributes  to reduced permeability.  The effect of plastic and
non-plastic fines on backfill permeability is shown  in Figure  7-11.
                                   FIGURE 7-11.
                    EFFECT OF PLASTIC AND NON-PLASTIC FINES
                CONTENT ON SOIL-BENTONITE BACKFILL PERMEABILITY
                (D'APPOLONIA. 1980 AS CITED BY SPOONER et al., 1984)
               80

               70

               60

               SO

               40

               30

               20

               10
                0
O Non-Ptottic or Low
    Plasticity Fines
            i  o
                 0  10~9     10-*      10-7     10-«      10-8

                               SB Backfill Permeability, cm/sec.
                    10-*
                                      7-24

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     The void ratio of a soil  material  is dependent on pore size and  particle
size.  Small  particle sizes and a low void ratio (high packing  density)  will
yield low permeability.

               7.1.2.2.2  Cement-Bentonite Walls

     In contrast to soil-bentonite walls, cement-bentonite walls are  normally
used where strength, rather than low permeability is the primary consideration
(Guertin and McTigue, 1982).  The requirements for cement-bentonite wall
performance are the same as for soil-bentonite walls.

     Cement-bentonite wall  strength is designed to be slightly greater than
that of the surrounding ground and is typically comparable in strength to
stiff clay (Jefferis, 1981a; Millet and Perez, 1981).  Although strengths of
cement-bentonite walls can range from 10 to 100 pounds per square inch,
ultimate strengths are generally about 5 to 20 pounds per square inch and are
achieved after 90 days (Xanthakos, 1979; Case, 1982).

     Cement-bentonite walls can usually withstand compressive strains of about
2 percent without cracking.  This is because they are not as brittle as
typical concrete walls (Ryan, 1976).  Moreover, they can withstand relatively
high hydraulic gradients and are basically non-erodable.  A cement-bentonite
wall only 2 to 3 feet wide can satisfactorily withstand at least 100 feet of
hydrostatic  head because of its cohesive nature (Millet and Perez, 1981).
Despite the fact that cement-bentonite walls are both non-brittle and
cohesive, they are not indestructable and hydro fracturing has been reported
(Millet and Perez, 1981).

     The continuity of cement-bentonite walls is an especially important
factor when these walls are constructed in panels rather than in a continuous
trench.  Thus, there  is a  possibility for gaps to remain between the panels
which can allow for leachate escape.  The time required for cement-bentonite
walls to harden depends on the presence of set time retarders and cement
replacements, among other  factors.  The speed of set time is of interest when
panel  construction techniques  are employed.
                                     7-25

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                                                                     •5
     The permeability of cement-bentonite  walls  is  normally  about  10    ft/day
(Case, 1982).   This can be decreased  slightly  by adding  blast  furnace  slag  or
additional  bentonite.  Jefferis (1981a)  reports  that  the  permeability  can  also
be decreased as much as an order  of magnitude  because of  consolidation  of  the
completed wall.  This, however, can be  deleterious  as it  is  accompanied by
cracking.

     There are many factors which affect the  performance  of  cement-bentonite
walls including:

     •  Slurry contents
     t  Mixing methods
     •  Use of additives
     •  Cement content
     •  Bentonite content
     •  Use of cement replacements.

     As the cement content in the backfill  is  increased,  a  stronger, more
brittle wall is formed (Millet and Perez,  1981).  Higher  cement  contents,
however, may allow higher wall permeabilities  because of consolidation
cracking.  The ultimate strength of cement-bentonite  walls  is  low, on  the
order of 15 to 20 pounds per square inch,  and  the permeability is  relatively
high, usually around 10"3 ft/day (Case,  1982).

     The ratio of the water to cement in the  slurry also  affects the
characteristics of cement-bentonite walls.   Generally, higher  ratios  produce
weaker walls.  Typical water-cement ratios range from 3:1 to 5:1.   These are
much higher than the ratios found in  concrete  mixes.   The cement is  kept in
suspension while the slurry is liquid because  of the  presence  of the  bentonite
in the mixture.  The bentonite content  in  the  cement-bentonite slurry  walls
contributes to their low permeability and  resistance  to chemical attack.
Where very low permeability or resistance  to  aggressive chemicals  are
required, the bentonite content of the  slurry  can be  increased (Jefferis,
1981a).  However, as the bentonite content is  increased,  the viscosity goes
up, and the slurry becomes unworkable.
                                     7-26

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     Cement replacements, such as blast furnace slag or fly ash, can be used
to replace up to one-third of the cement in the slurry (Jefferis, 1981a).
Typical  percentages of these constituents in cement-bentonite slurries are
shown in Table 7-4.  Cement replacements have several  effects on the
characteristics of the completed wall.  The most significant effect is the
reduction in the rate at which water separates from the cement mixture before
and during hardening (bleeding rate).

     When conventional cement-bentonite walls or walls with fly ash repl ace-
                                                                  _3
ment are allowed to set for seven days, permeabilities of 2.8 x 10   to 1.4 x
10~2 ft/day (1 to 5 x 10~6 cm/sec) result.  In contrast, cement-bentonite
walls containing from 2.5 to 7.5 percent blast furnace slag exhibited
permeabilities of about 2.8 x 10"4 ft/day (10   cm/sec) after seven days of
hardening (Jefferis, 1981a).  Fly ash replacements, on the other hand, can
effectively increase a wall's chemical  resistance while blast furnace  slag
replacements cannot (Jefferis, 1981a).

               7.1.2.2.3  Diaphragm Walls

     Precast concrete panels and cast-in-pl ace concrete walls are known as
diaphragm walls.  Unlike soil-bentonite and cement-bentonite walls, these
walls develop a great deal  of strength  over time and can be used as structural
components.

     Precast concrete panel walls are cast offsite  in segments from 1 to 3
feet wide, from 10 to 20 feet long, and from 30 to  50 feet deep.  The  panels
are lowered into a trench containing bentonite slurry and secured in place.
Because of their dimensional limitations, concrete  panel walls are usually
only employed where depths of 50 feet or less are required (Guertin and
McTigue, 1982).  An exception to this general  rule  occurs where a cement-
bentonite slurry that remains in place  is allowed to set up around the panel.
Using this technique, the trench can be extended lower than 50 feet and the
panel suspended in the cement-bentonite slurry.  The slurry then forms a
cut-off both below the panel and on either side of  it.
                                     7-27

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     Cast-in-place concrete walls are constructed by excavating a short trench
(or slot) under  a bentonite slurry.   The maximum allowable  slurry density is
75 pounds per square inch and the maximum allowable sand content is 5 percent
(Millet and Perez, 1981).  Once the  density and  the sand content of the slurry
in the trench are appropriate, the reinforcing  bars are lowered into place.
Concrete is then tremied into place  using a funnel-like apparatus that directs
the concrete to  the trench bottom.  The apparatus is raised as the concrete
level  rises.  Slurry is pumped out as the concrete is tremied in and then
filtered and used for the next panel.  When set, the wall  is composed of a
concrete panel  sandwiched between two bentonite  filter cakes.  One side of the
wall is normally excavated during later construction thus  destroying one of
the filter cakes.  The other side, however, retains its filter cake which
serves as a low permeability seal (Guertin and  McTigue, 1982).

     Diaphragm walls are not normally used for  pollution migration control
because of their susceptibility to leakage through panel connections and their
greater expense.

          7.1.2.3  Failure Mechanisms

     There are several mechanisms or processes  that can affect the construc-
tion or functioning of slurry walls and cause failure.  These failures may be
the result of excavation and installation procedures or subsurface conditions.

     The failure may occur during excavation and installation thus requiring
re-excavation of the slurry trench.  Once the wall is in place, a variety of
factors can affect the integrity of the wall and its impermeability.

     One failure mechanism  is trench collapse caused by the loss of stability
in the trench walls during excavation and before backfilling or cement-
bentonite  slurry hardening.  Direct causes of trench collapse are (U.S. Corps
of  Engineers, 1978; Duguid et al., 1971;  Nash and Jones, 1963).:

     •   Insufficient  slurry  head  above  groundwater
     •   Sudden or rapid  loss of  slurry  caused by contact with gravel , large
         pores, or  fissures
                                     7-28

-------
     •  Vibrations
     •  Surface runoff into open cracks
     •  Surcharges
     •  Insufficient agitation of the  slurry.

     A number of mechanisms can cause  failure  of  the  completed  wall.   Among
these fail ure mechanisms are:

     •  Cracking
     •  Hydrofracturing
     •  Tunnelling
     •  Piping
     •  Chemical disruption.

Each of these mechanisms is discussed  below.

     Soils containing an appreciable concentration  of clay can  shrink  when
allowed to dry, forming cracks.  Even  cement  bentonite walls  can  crack
"drastically" when allowed to dry (Jefferis,  1981b).   Some soils  can,  however,
shrink and crack even when nearly fluid  enough to flow.   Nash (1976) and
Tavenas et al. (1975) noted the formation of  cracks in silty  clay soil
mixtures only slightly dry of their liquid limits.

     These cracks can be caused by several processes, including:

     •  Consolidation
     •  Hydraulic fracturing
     •  Syneresis
     •  Tunnelling and piping
     •  Chemical disruption.

               7.1.2.3.1  Consolidation

     Consol idaton of soils occurs when water  is squeezed  from the soil  pores
(Hirschfeld, 1979).   This process is accompanied  by a decrease  in the  volume
                                     7-29

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of the soil mass caused by a decrease in the volume of voids in the soil
(Baver, Baver and Gardner, 1972).  The amount of consolidation is maximal in
fine-textured soils and minimal  in coarse-textured materials.  The rate of
consolidation depends on the soil  permeability, the thickness of the layer
being loaded and the magnitude of the volume decrease.  In fine textured
soils, consolidation occurs at a much slower rate than in coarse tex.tured
ones.  Most consolidation occurs rather quickly, however, fine textured soils
can continue slow minor consolidation for several months (Hirschfeld, 1979).
The soil-bentonite backfill  in slurry walls has been found to continue
consolidating for about 6 months, with minimal  decreases in volume thereafter
(Xanthakos, 1979).

     The amount of consolidation in slurry walls is limited by the backfill's
arching action along the trench  walls and by grain to grain contact in the
backfill (Xanthakos, 1979; D'Appolonia, 1980).   The amount of slurry wall
consolidation depends on trench  width as well  as on the amount of fines in the
backfill.   As the fines content  increases, consolidation increases because
fine particles are more compressible  than coarse ones (Mitchell,  1976).  Wider
trenches have been found to consolidate more than narrow ones.  An eight-foot
wide trench, for example, was reported by Xanthankos (1979) to have
consolidated from one to six inches during the  first few months after
construction.  In contrast to soil-bentonite walls, cement-bentonite walls
consolidate very rapidly (Ryan,  1976).

     The process of consolidation in  soil-bentonite walls can produce many
small  cracks along shear zones in  the soil  mass (Mitchell, 1976).   Horizontal
cracks that extend through the backfill  can also be produced by the arching
action mentioned earlier (Nash,  1976).  This cracking can occur even when the
backfill is still quite fluid.  Normally, the  backfill  contains from 25 to 30
percent water.  This moisture content is slightly more than the liquid limit
of the backfill  (D'Appolonia, 1980a).  When soil  is at its liquid limit, it
contains so much water that it will  flow under  the influence of an applied
stress (Baver, Baver and Gardner,  1972).  Even  so, Nash (1976) observed the
formation  of horizontal  cracks in  a  silty clay  backfill  that was  only slightly
below its  1iquid limit.
                                     7-30

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     The arching that accompanies consolidation can also lead to the  formation
of another type of cracking called hydrofracturing.  The relationship between
hydrofracturing and consolidation is described below.

               7.1.2.3.2  Hydrofracturing

     When soils or rocks are  subjected to excessive hydraulic pressures,
cracks may form through which the excess water can flow.  The pressure at
which this cracking occurs can be less than the effective overburden  pressure
on the rock or soil  in situ.  This phenomenon has been used by petroleum
geologists to fracture petroleum-containing strata and thereby increase the
yield of oil wells (Bjerrum et al., 1972).

     The amount of pressure required to  induce fracturing depends on  the depth
of the point receiving the pressure and  the ratio of vertical  to horizontal
pressures at that point.  Other  factors  are also likely involved.  Values  used
by petroleum geologists are 1 psi per foot of depth where the vertical
pressures are less than the horizontal  pressures, and 0.64 psi per foot of
depth where the vertical  pressures are greater than the horizontal  pressures
(Bjerrum et al., 1972).

     The cracks caused by this pressure  extend vertically where the vertical
pressures are greatest and horizontally  where the horizontal pressures are
greatest (Tavenas et al., 1975).  These  cracks can continue to increase in
length as long as the excess  head is applied until  they reach an area having
greater permeability (Bjerrum et al., 1972).  When the pressure is decreased,
the cracks will  partially close but  will  reopen when the pressure is  again
increased (Tavenas et al., 1975).

     The effects of hydrofracturing on the functioning of a slurry wall can be
severe.  Where the vertical  pressure exceeds the horizontal  pressure  (which is
normally the case) the pressure exerted  on the aquielude can cause it to
fracture.  The vertical  cracks will  be  immediately filled with slurry if this
occurs during construction.   Continued fracturing can, however, occur during
backfilling.  The backfill  is less likely than the slurry to completely flow
                                     7-31

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in and fill  the cracks in the aquiclude, and the aquiclude's permeabil ity may
thus be increased.  The overall effect of this type of fracturing may be
minimal  except at sites where the aquiclude is thin or overlies a very
permeable strata or both.

     A more detrimental effect of hydrofracturing may occur where the
horizontal  pressures on the wall  are greater than the vertical  pressures.  If
more than 1 psi of pressure per foot of depth is applied to the wall,
horizontal  cracks may form.  These could allow significant amounts of water or
leachate to flow through the wall.  Hydrofracturing has been reported in both
soil-bentonite and cement-bentonite walls (Bjerrum et al ., 1972; Millet and
Perez, 1981).

     The likelihood of slurry wall damage caused by hydraulic fracturing is
highest where:

     •  Significant amounts of consolidation occur
     t  Piezometers are installed in the wall  to monitor the wall's
        permeability using constant head tests
     •  Large vertical loads are applied to the soils on either side of the
        trench
     •  Large  hydraulic gradients are allowed to develop across the wall.

     When a great deal of consolidation and subsequent arching  occur after
backfilling, the vertical loadings on the wall can be reduced to levels less
than the horizontal loadings.  This allows the wall  to become susceptible to
horizontal  cracking (Bjerrum et a!., 1972).  The amount of consolidation can
be minimized by reducing the content of fine particles in  the backfill
(Mitchell, 1976).  However, when additional coarse material is included  in the
backfill, the  wall's permeability is likely to be increased (D"Appolonia,
1980b).  The amount of permeability increase expected because of the inclusion
of additional  coarse material in the backfill  should be weighed against the
risk of hydrofracturing caused by the anticipated pressure differential  across
the trench.
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     Where piezometers are placed in the wall to test the wall's permeability,
hydrofracturing may be induced when the excess head is applied.  Hydro-
fracturing caused by use of piezometers occurred when permeability tests were
being conducted on a series of dikes with soil-bentonite cores that were
installed in Israel.  The constant head permeability tests were designed so
that the maximum head applied did not exceed the effective weight of the soil
above the piezometer.  However, even at very low hydraulic pressures,
hydrofracturing occurred.  This fracturing resulted in a thousand-fold
                                                    -4
increase in the measured permeability, i.e., from 10   ft/day initially to
10"1 ft/day after fracturing (Bjerrum et al., 1972).

     Tests on an in situ, normally consolidated clay were conducted to see if
hydrofracturing was caused by arching along the walls of the soil bentonite
cores.  The normally consolidated clay that was not influenced by arching
along trench walls also fractured under the influence of an applied hydraulic
pressure that was less than the effective overburden pressure (Bjerrum et al.,
1972).  This indicates that the occurrence of hydrofracturing is not dependent
upon arching (and consolidation) along the walls of slurry trenches.

     When large vertical loads are applied along the trench walls, the
horizontal stresses on the slurry wall can be greatly increased.  The vertical
loading can occur because of placement of stockpiles or heavy equipment along
the  sides of the trench.  Depending on the other stresses acting on the wall
at the site, the horizontal stress may become greater than the vertical
stress, thus making the wall susceptible to horizontal hydrofracturing.

     A fourth potential cause of hydrofracturing is the presence of an exces-
sive hydraulic gradient across the wall.  If the pressure on the upgradient
wall exceeds 1 psi per foot of depth and the horizontal pressures acting on
the wall are greater than the vertical pressures, horizontal fracturing of the
wall could occur.  Excessively high hydraulic gradients could be induced by:

     •  Failing to provide subsurface drains or extraction wells upgradient of
        the wall
     •  Installing extraction or injection wells too close to the wall
                                     7-33

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     •  Dewatering a site without deflecting groundwater around the site and
        away from the wall (via drains, ditches, or extraction  wells).

For this reason, the proper use and placement of auxil iary measures, such as
wells, should receive careful  attention during the wall's design  stages.

               7.1.2.3.3  Syneresis

     Another process that can  result in the formation of cracks in  a slurry
wall  is syneresis.  . According to Mitchell  (1976), syneresis  is a "mutual
attraction between clay particles"  that causes the particles  "to  form  closely
knit aggregates with fissures  between."  Contractions that occur  in the gel
result in the extrusion of liquid (water).   Syneresis is often  observed in
gelatin after aging (Mitchell, 1976).   Syneresis may take place in  slurry
walls, however, the extent to  which this phenomenon affects the performance of
slurry walls is not known.

               7.1.2.3.4  Tunnelling and Piping

     Two processes that can result  in  extensive breaching of  a  slurry  wall  are
tunnelling and piping.   Both of these  processes involve the formation  of
channels through the wall.  However, the causes and solutions for the  two
problems are different.

     Several dams have failed  because  of the formation  of very  large pores
that extend completely  through the  dam from the upstream to the downstream
face.  These failures occurred where the earthen dams were constructed of low
to medium plasticity native clays that contained appreciable  amounts of sodium
montmorillonite (Mitchell, 1976).  The process by which the failures occurred
is termed tunnelling and can be described as a series of interrelated  steps,
as are listed below (Mitchell, 1976):

     1.  Differential  consolidation of the  wet and dry  portions of  several
         earthen dams led to the formation  of stress cracks below the  water
         1 ine.
                                     7-34

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     2.  Water that contained  calciun ions  flowed  into the cracks.
     3.  Calcium ions from the water replaced sodiun ions to the  exchange
         complexes of the clay particles in  the dam.
     4.  The calcium ions caused the clay particles to decrease  in  size
         (shrink)  and to  form  packets or "floes."
     5.  As the clay particles formed floes, they  became less dispersed  and
         the space formerly occupied by the  dispersed  clay particles became
         filled with water.
     6.  As the sizes of water-filled spaces (pores) increased,  the rate of
         water movement in the pores increased.
     7.  The increased rate of water movement allowed  the water  to  carry more
         particles in suspension.
     8.  As the particle-carrying capacity of the  water increased,  the number
         of clay particles eroded by the flowing water increased.
     9.  As the number of clay particles eroded from the dams increased, the
         sizes of the pores in the dams increased.
    10.  As the pore space size increased,  the speed of the tunnelling process
         increased until  extensive tunnelling had  occurred.

     This tunnelling process has been found to take place in earthen dams and
                                                         P
embankments that had initial  permeabilities as low as  10"  ft/day.   One method
that has been used to reduce the likelihood  of tunnelling is to  mix the  soil
with lime prior to dam construction.  This causes  the  clay particles to  shrink
and become less easily dispersed before any cracking or particle erosion can
occur (Mitchell , 1976).
     The risk of tunnelling failures in slurry walls is greatest where ground-
waters contain high concentrations of calcium.  At these sites the  calcium
ions from the groundwater can  disrupt the soil bentonite backfill and cause
tunnelling failures that are similar to the ones experienced with the earthen
dams described  above.  High calciun concentrations in  groundwater are most
commonly found  in sedimentary  aquifers, particularly limestone ones.  Water
from these aquifers can contain over 50 ppm dissolved  calcium (Freeze and
Cherry, 1979).
                                     7-35

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     The presence of stress cracks, high hydraulic gradients, and permeable
backfills are not prerequisites for the tunnelling process, but these factors
are likely to speed failure rate considerably.  The causes of stress cracking
were described previously.  The hydraulic gradients across slurry walls at
hazardous waste sites are not normally as high as the gradients across dams,
so the rate of tunnelling in slurry walls should be much slower than in
earthen dams.  Another factor that operates in favor of slurry walls is their
low permeability, which is normally one to three orders of magnitude less than
the minimum permeability of the materials through which tunnelling had been
reported (Mitchell, 1976; D'Appolonia, 1980b).  This low permeability
indicates that the initial rate of water movement through a slurry wall will
be much less than through the earthen dams, consequently the particle carrying
capacity will also be severely restricted and the erosion rate will  be
minimal.

     Despite the fact that tunnelling failures, if they occur in a soil-
bentonite wall, are expected to require long time periods to develop, the
potential for slurry wall disruption caused by the presence of calcium ions
should be kept in mind when evaluating the feasibility and design criteria for
a slurry wall installation at a particular site.

     On the other hand, piping begins at the downstream face and proceeds
toward the upstream face (Mitchell, 1976).  Piping occurs because of the use
of improper backfill materials or procedures.  Variable wall thicknesses,
poorly mixed backfill, or extensive quantities of coarse materials in the
backfill  can all contribute to piping failure.

     Piping occurs where a high hydraulic gradient causes the rate of water
movement through the wall to increase as the water nears the downgradient side
of the wall.  If the water movement is rapid enough, the water could
conceivably force the downstream filter cake into the pores in the soil along
the trench wall.  As the rate of water movement out of the wall increases, the
water can begin to erode the easily-dispersed backfill, creating even larger
pores and allowing the water movement rate to increase further (Anderson and
Brown, 1980).  To avoid piping failures, the quality of the filter cake should
                                     7-36

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be maximized, the backfill materials should be properly selected and mixed,
the backfill should be carefully placed to avoid fold-overs and permeable
areas, and the hydraulic gradient across the wall should be monitored and kept
within designed levels.

               7.1.2.3.5  Chemical  Disruption

     Chemical substances in soil and groundwater can affect the durability of
the slurry wall once it is in place.  Chemical destruction can affect the
cement in cement bentonite slurry walls as well as the bentonite in cement
bentonite and soil bentonite walls.  The effects of alkali salts on bentonite
slurries were described previously.

     The action of the chemicals on cement or bentonite are similar to that of
the tunnelling process.  The cement may become slurry solubilized and the
bentonite may become entrained  in the solution as the chemicals eventually
create a solution channel  through the wall into surrounding soil.  Thus,
chemical destruction processes may create, as well as accelerate, the
tunnelling process.  Chemicals may also prevent the slurry from forming an
adequate filter cake along the  sides of the slurry trench by interfering  in
the slurry gelation process.

     7.1.3  Design and Construction

     This section discusses design and construction considerations for
pollution control slurry walls.  The section also shows how the design must
consider site-specific factors  and discusses design components.  Construction
techniques for soil- and cement-bentonite and diaphragm walls are also
covered.

          7.1.3.1  Design Procedures and Considerations

     The process of designing a slurry wall requires assessment of site-
specific data and consideration of numerous design variables to determine the
feasibility of a slurry wall and to select the most appropriate wall type for
use at the site.  This section  describes these processes.
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                     7.1.3.1.1  Feasibility Determination

      Using the data  from the site investigations, the designer must determine
 the  feasibility  and  applicability of  installing a slurry wall at the site.
 Factors to consider  include:

      •  Potential waste incompatibility
      t  Anticipated  hydraulic gradients and maximum allowable permeability in
        the completed wall
      •  Aquiclude characteristics, e.g., depth, permeability, continuity, and
        hardness
      •  Wall placement relative to wastes and leachates
      •  Cost and time considerations.

 Each  of these factors is discussed below.

      Waste and leachate compatibility with proposed slurry wall  backfill
mixtures can be determined using laboratory tests.  Where long-term
permeability is crucial, clay mineralogy and geochemical  testing is advisable.
These tests provide  an indication of which proposed backfill  mixtures show the
greatest resistance to long- and short-term permeation by the pollutants at
the site.

      Data on the anticipated hydraulic pressures on either side of the  wall
indicate the range of hydraulic  gradients to which the wall may be exposed.
When  projected permeabilities and wall areas are known, the  rate of subsurface
movement through the wall  can be determined using  Darcy's Law.   Darcy's Law
states that

                                    Q = KIA
where Q is the volume of water flowing through the wall,  K is the hydraulic
conductivity of the wall, I is the hydraulic gradient, and A is the
cross-sectional wall  area.
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     To illustrate how Darcy's Law can be used to estimate a slurry wall's
effects on groundwater flow at a site, consider the following hypothetical
situation:  a proposed slurry wall  is designed to be 164 feet (50 meters)
long, 81 feet (25 meters) deep, and 3.2 feet (1 meter) thick.  The hydraulic
gradient at the site is estimated at 2, and the wall's hydraulic conductivity
is designed to be less than 2.12 x 10"  gpd/ft (1 x 10" cm/sec).  According to
Darcy's Law, the amount of water that will move through the wall  is 57 gpd
        2
(0.216 m /day).  Before the slurry wall was installed, the hydraulic
                                                   2        -4
conductivity of the same area was about 2.12 gpd/ft   (1 x 10   cm/sec), a low
permeability for undisturbed soils.  The amount of water flowing through the
                                                                     2
area each day prior to slurry wall  installation was 57,000 gpd (216 m /day).
Thus, this particular slurry wall would reduce the volume of water flow
through this area by 99.9 percent.   In areas having higher initial  hydraulic
conductivity the effect of the slurry wall would be even greater.

     Another factor to consider when evaluating the feasibility of a slurry
wall is the aquiclude at the site.   Ideally, the aquiclude should be thick,
impermeable, and unfractured, and should be soft enough for a backhoe or
clamshell to excavate a 1- to 3-foot key-in to prevent seepage under the
slurry wall.  In areas where aquicludes are very hard, either slurry walls
will be more expensive to install or the aquiclude wall union will  be less
certain.  Where the aquiclude is thin, discontinuous, or fractured, slurry
walls can be expected to be less efficient in pollution migration control
because of seepage through the aquiclude.  Consequently, other remedial
measures may be called for.

     An early assessment of possible wall locations and configurations can
indicate the overall  amount of wall  exposure to wastes and leachates, the
types and placements of auxiliary measures, and the actual  length and depth of
wall required.   These factors, along with an estimate of the necessary wall
durability, can assist designers in projecting the cost of the construction
effort.

     The need for rapid response at some sites necessitates an evaluation of
the construction time required. According to Miller (1979), soil-bentonite
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slurry walls are normally installed at a rate of 25 to 100 linear feet per
day.  Thus, the wall described previously could be installed in 2 to 7 days,
assuming the work is accomplished in a nonhazardous environment.  Hazardous
conditions can more than double on-site work time.

               7.1.3.1.2  Selection of Slurry Wall Type

     If a slurry wall  is determined feasible, the type of wall  (soil- or
cement-bentonite) that is required should be established.  To decide whether a
soil- or cement-bentonite cut-off wall should be installed at a particular
site, several  factors  need to be considered. The following factors affect the
suitability of soil- and bentonite-cement walls:

     •    Required permeability and hydraulic pressure
     •    Leachate characteristics
     •    Availability of backfill material
     •    Required wall  strength
     •    Aquicl ude depth
     •    Site terrain
     •    Cost.

These factors are discussed below.

     Where low permeability is required, soil-bentonite walls are used and the
wall  width is determined by the hydraulic head across the trench.  Case (1982)
recommends that the trench should "have a width of 0.5 feet to 0.75 feet per
10 feet of hydrostatic head on the wall.  Thus, for a 100-foot  head loss, wall
thickness should range from 5 to 7.5 feet."   In comparison, a cement-bentonite
wall  only 2 to 3 feet  thick will  stand up to the same hydrostatic force (i.e.,
100 feet).  Deeper walls are generally wider then shallower ones because
larger excavation equipment is used for deep walls, and this equipment
generally digs a wider trench (Millet and Perez, 1981).  Generally, cement-
bentonite walls are designed to be narrower  than soil-bentonite walls because
of the greater shear strength and the higher cost of cement-bentonite walls
(Millet and Perez, 1981; Ryan, 1976).
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     Soil-bentonite walls exhibit a lower permeability and a greater
resistance to chemical attack, particularly to acids, than cement-bentonite
walls.  For this reason, soil-bentonite walls are favored for use as pollution
migration cut-offs (Jefferis, 1982b; Xanthakos, 1979).  Where floating rather
than sinking contaminants are encountered, the slurry wall does not have to be
extended down into the aquiclude.   Instead, a "hanging" wall is installed.
These walls are usually soil-bentonite types.

     In some sites, the material  excavated from the trench is contaminated
because of contact with polluted groundwater.  This contaminated soil  may be
unsuitable for use in the backfill.  Samples of this material should be mixed
with bentonite slurry and tested to determine the effects of the contaminants
on the soil-bentonite wall permeability.  In some cases, the contaminants will
increase the permeability of the completed wall , but the increase may be less
than the increase that could be caused by the sudden exposure of the wall
to the polluted groundwater.  At these sites, use of the contaminated material
in the backfill may be advisable, providing the gradation is adequate
(D'Appolonia, 1980b).  If, however, the contaminated soil is discovered to be
inappropriate for use as backfill material, a suitable borrow area should be
found.  Where such a borrow area is not available nearby, cement-bentonite
walls may be more appropriate.

     Generally, cement-bentonite walls are used where heavy vertical loadings
are anticipated and large lateral earth movements are not expected.  This is
because cement-bentonite walls have a higher shear strength and lower
compressibility than soil-bentonite walls.  Cement-bentonite walls are,
however, more likely to crack than  relatively plastic soil-bentonite (Millet
and Perez, 1981).  If the wall must be extended beneath roads, rail tracks, or
in close proximity to existing foundations, cement-bentonite walls can be
used.  In addition, cement-bentonite walls can be used in localized areas
requiring strength and tied into soil-bentonite walls for the rest of the
trench di stance.

     Cement-bentonite walls are more expensive than soil-bentonite walls
because of the cost of the cement.  For this reason, cement-bentonite walls
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are not generally used where the aquielude is deep or where very long  cut-off
walls are required (Ryan 1977).

     At sites where slopes are steep,  the areas for backfill  mixing  are
limited or non-existent, and low permeability is  not critical,  cement-
bentonite walls may be preferred. In general, soil-bentonite  walls are limited
to areas where the maximum slope along the trench line is  on  the order of
2 percent or less.  At many sites, hills can  be leveled and depressions
backfilled with compacted soil  prior to trench construction.   The lack of
sufficient backfil 1 .mixing areas can be overcome  by hauling trench spoils to a
central backfill mixing area, then hauling mixed  backfill  back  to the  trench.
Pug mills can also be used for backfill mixing.  These operations, site
leveling use of pug mills and central  backfill mixing, result in slower
construction rates and higher costs.

     In contrast to soil-bentonite walls, cement-bentonite walls can be
constructed in areas of steeper terrain by utilizing the cement-bentonite
panel construction technique described later  in this section.

     As mentioned earlier, a cement-bentonite wall  is typically more expensive
than a  soil-bentonite wall of the same volume because of the  cost of the
cement.  Where thick or deep walls are planned, cement-bentonite walls will,
in most cases, be more expensive than soil-bentonite walls.  Where wall
thickness can be minimized and very low permeability is not essential,
cement-bentonite walls can be considered.

          7.1.3.2   Soil Bentonite Wall Construction

     Following award of the construction contract, the selected firm will
proceed with construction of the slurry wall.  The major activities include:

     •    Reconstruction assessment and mobilization
     •    Site preparation
     •    Slurry  preparation and control
     •    Slurry mixing and hydration
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     t    Slurry placement
     •    Trench excavation
     •    Backfill  preparation
     •    Backfill  placement
     •    Site cleanup and demobilization.

Discussions of these activities follow.

               7.1.3.2.1  Reconstruction Assessment and Mobilization

     Three major activities occur during the mobilization  phase  of slurry
trench construction.  These are:

     •  Layout of the site plan
     •  Determination of the the equipment, type, amounts  of materials,  and
        facilities  required.
     •  Determination of the number and source of personnel  required.

These three activities are discussed below.

     A preliminary  layout is prepared based on drawings supplied by the
engineer.   Once the preliminary layout is developed, a  close examination of
the proposed construction site must be performed in  order  to ensure that all
details of the plan are practical.  After the on-site examination, a final
layout of the worksite can be prepared.  A diagram of a typical  slurry wall
construction site is shown in Figure 7-12.

     The specifications and drawings, test boring records, subsurface explora-
tion reports, and records of utility lines are the first sources of informa-
tion for determining equipment, materials and facilities needs.   In addition,
an on-site inspection may be required to gain the detailed understanding
needed for planning the construction activities.
                                     7-43

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                                         FIGURE 7-12.
                       TYPICAL SLURRY WALL CONSTRUCTION SITE
                                          Bemonite
                                           Storage
                                                                  Backhoe
                                                      Area of Active
                                                        Excavation
Propoaed Line
of Excavation


Hydration
Pond



\
Slurry
Storage
Pond
                                                                         Slurry
                                                                        Pumps
                                                        Slurry
                                                      Preparation
                                                      Equipment
                                          Bentonite
                                           Storage
                                                                      ooo
   Water Tanks
Access
 Road
                                              7-44

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     The major work elements and equipment and facilities typically associated

with each work element are:
     t  Excavation
           hydraulic backhoe
        -  mechanically operated clamshell
        -  hydraul ically operated kelly-mounted clamshell

     •  Slurry preparation and control
           high speed colloidal batch mixer for small  projects
        -  flash mixer for large projects
        -  pumps, valves, pipes, and tools
        -  hydration ponds
        -  desanders, hydrocyl ones, or screens

     o  Slurry placement
           pumps
           placement hoses and piping

     •  Backfill  preparation
           dozer or grader

     •  Backfill  placement
        -  dozer
        -  mechanically operated clamshell
        -  trucks and trough

     •  Supervision and quality assurance
           shed or trailer
        -  Marsh funnel
        -  mud balance
        -  standard sieves.


     Numerous factors influence the types of equipment required as well  as the

final plan layout and the relative difficulty of construction activities.
Some of these factors, along with their potential  effects on slurry trench

construction operations are listed in Table 7-5.


     Determining the correct equipment applications for a particular project
is based upon construction requirements and the constraints imposed by the job

site.  For example, choice of excavation equipment depends upon the depth of

the slurry wall  and the soil  in which the wall  is  placed.   The maximum excava-

tion depth for a standard backhoe is about 50 feet, but larger, extended

models are available to reach up to 80 feet in  depth (D'Appolonia, 1980a).

Both clamshell excavation systems will reach depths of more than 150 feet,
                                     7-45

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                                                         TABLE  7-5.
                        TYPES OF  PHYSICAL CONSTRAINTS AND THEIR  EFFECTS ON SLURRY WALL  CONSTRUCTION
                             (Ryan,  1980a; U.S.  Army Corps of Engineers, 1978; Xanthakos,  1979;
                                    Wetzel, 1982; Tamaro, 1980; Ryan,  1980b; Namy, 1980)
            Physical  Constraints
 Possible Affected Areas
Approach Required
            Topography:   Irregular contours       • Necessary equipment
                         Steeply sloping terrain
                                                 • Site access and work  space

                                                 • Type of wall  selected
Ol
            Site Access  Site congestion/
              and Work    traffic
              Space:     Steep terrain
                         Dense vegetation
                         Lack of head room
                         Insufficient space
                          for mixing
• Extent of site prepara-
  tion and pre-construction

• Type of equipment selected

• Type of wall  selected

• Wall construction process
                              •  Selection  of  equipment capable of
                                operating  in  site specific terrain

                              •  Extensive  site  preparatory work  -
                                leveling of areas for site entry and
                                work  space

                              •  Use of  cement-bentonite wall in  panels
                                or diaphragm  wal 1
 Special equipment needs; construction
 of access  road; leveling of working
 area; clearing of dense vegetation

 Amount of  head room affects type of
 equipment  selected or needed to
 relocate obstruction

 Amount of  work space affects wall type
 selected;  soil-bentonite wall requires
 space for  mixing; cement-bentonite
 wall requires less area for opera-
 tions, but is more expensive; soil-
 bentonite  can be mixed away from
 trench but this approach may mean
 cement-bentonite is cheaper for the
 site
                                                                                                            (continued)

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                                        TABLE 7-5.  (Continued)
Physical  Constraints
                         Possible  Affected Areas
                             Approach  Required
Site Access
  and Work
  Space:
  (continued)
                                                     • Extra time needed for site prepara-
                                                       tion and construction

                                                     t Appropriate easement clearances
Utilities:    Abandoned sewers
              Pipelines
              Leakage from water
                mains, sewers
              Power/telephone cables
                         •  Equipment  selection

                         t  Construction  process
                           (operations)

                         •  Problem control  methods

                         •  Sudden  slurry loss and
                           possible trench  collapse
                           if  unanticipated pervious
                           zone,  i.e., sewer piping
                           is  entountered and
                           ruptured
                             • Special  equipment  necessary  for
                               excavation  around  piping and  sewer
                               lines,  or need  for manual  excavation

                             • Sequence of trench segment excava-
                               tion  may change if utility discovered;
                               excavate other  areas  first

                             • Watermain or sewer leakage may cause
                               slurry  contamination  and loss of
                               trench  stability;  a control  plan
                               necessary at outset of  project

                             t Sudden  slurry loss requires  immediate
                               placement of solid materials (soil,
                               debris)  into trench
Cultural
  Features:
Old foundations
Nearby structures
Overhead structures
• Equipment selection

• Construction process
  (operations)

• Problem control methods
• Foundation penetration to isolate site

• Excavation around foundations, or
  incorporate foundation into wall; if
  foundation support needed cement
  bentonite or diagraphm may be required
                                                                                                 (continued)

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                                                   TABLE 7-5.  (Continued)
             Physical  Constraints
Possible Affected Areas
Approach Required
-J

00
             Cultural  Features:
               (continued)
• Headroom
            Other:       Availability  of  water
                         Time  of year; water
                           table  fluctuations,
                           temperature
                         Subsurface geology;
                           large  subsurface
                           bounders
                         Type  of wall  backfill
• Equipment selection

• Slurry mixing

• Time needed and available
  for project completion
                                                 • Site preparation

                                                 • Problem control methods
• Special equipment needed if breaking
  old foundations

• Tall equipment may be restricted,
  e.g., cranes

• More time may be necessary for
  operations

• Experienced problem control personnel
  necessary
• Equipment selection for boulder
  destruction or excavation

• Site may need de-watering system if
  water table is high or is expected
  to rise

• Soil-bentonite backfill cannot be
  mixed in subfreezing temperatures

t Cement-bentonite  will  not set in
  certain temperature ranges

t Experienced problem control-personnel
  necessary
                                                                               • Transport of water to site if none
                                                                                 available

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with the hydraulic model  sometimes  preferred  in  more  difficult  digging
conditions (Guertin and McTigue, 1982).  Table 7-6  lists  the  typical  equipment
used for slurry trench construction.


     Consideration must also be given to site access  and  obstructions.   Access

road's might limit the size equipment that can be brought  to the site, while
obstructions at the site might preclude the use  of  some types of equipment.
                                   TABLE 7-6
           EXCAVATION EQUIPMENT USED FOR SLURRY TRENCH CONSTRUCTION
  (Case, 1982; D'Appolonia, 1980; Guertin and McTigue, 1982;  Shallard,  1983)
Type
Trench Width
   (feet)
Trench Depth
   (feet)
Comments
Standard
backhoe
Modi fied
backhoe
Cl amshel 1
Dragline
Rotary drill ,
percussion
drill or large
chisel
     1-5
     2-5
     1-5
     4-10
      50       Most rapid and  least  costly
               excavation method
      80       Uses an extended dipper stick,
               modified engine & counter-
               weighted frame; is also rapid
               and  relatively low cost

    >150       Attached to  a  kelly bar or
               crane; needs >_ 18 ton crane;
               can  be mechanical  or hydraulic

    >120       Primarily used for wide, deep
               soil-bentonite trenches

               Used to break  up boulders and
               to key into  hard rock
               aquicludes.   Can slow construc-
               tion and result in irregular
               trench walls
                                     7-49

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     When determining the sources of personnel  for use at slurry trench
construction site, two choices face the construction firm.  The firm can send
their own equipment and personnel  to the construction site or they can rent
equipment and hire personnel  locally.  Most firms will  use varying combina-
tions of each approach.  For larger jobs and critical small  jobs, equipment
and personnel are more frequently sent directly from the construction firm.
Small  jobs can often be handled effectively by  using only specialized
company-owned equipment, such as an extended backhoe arm, accompanied by
supervisory personnel.  Other equipment such as bulldozers,  cranes, clam-
shells, and large ba'ckhoes can be rented near the job site.   Laborers and
certain equipment operators can be hired locally for the specific job.  How-
ever, there are not set rules and each construction contractor will tailor his
approach on a site-by-site basis.

     Slurry trench construction contractors are best able to judge appropriate
equipment and personnel  needed at the job site.  However, site owners and
their representatives should be aware of the approach to be  taken by the
construction contractor and should be satisfied that appropriate equipment and
personnel are available at the job site.

7.1.3.2.2  Pre-excavation Site Preparation

     Once site planning has been completed, necessary permits and clearances
have been obtained, and required utility, water, and other services have been
arranged, preparation of the  construction site  can proceed.   The work site can
then be cleared if necessary, security fences erected,  utility and water
hook-ups made, equipment and  facilities brought in and  set-up, and construc-
tion materials delivered.  At this time, work can proceed to move or remove
obstructions if necessary.

     7.1.3.2.3  Slurry Preparation and Control

     Before excavation begins, the slurry must  be prepared.   To do this,
bentonite and water quality must be tested, hydration ponds  must be con-
structed, lines laid, pumps placed, and the mixing area  prepared.  The slurry
                                     7-50

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is then mixed in a venturi or paddle mixer and allowed to hydrate fully prior
to placement in the trench for soil-bentonite slurry trench cut-off construc-
tion or mixing with cement for cement-bentonite cut-off construction.

     Bentonite quality is critical  to the quality of the slurry.  Bentonite is
usually shipped to the job site accompanied by laboratory test results showing
that it meets quality criteria.  These criteria include physical and chemical
purity, pH, gel strength, dry fineness (percent passing the number 200 sieve)
and filtrate loss.  At the job site, these criteria are checked frequently,
such as by testing every truckload of bentonite delivered.  Requiring field
testing of delivered bentonite is important for the site owner because
deliveries are occasionally rejected by field testing.  At a minimum, testing
of pH, viscosity, and fluid loss should be conducted in the field for
bentonite delivered to the site.

     Slurry quality decreases significantly if the quality of make-up water is
poor.  Make-up water should be relatively low in hardness, near neutral  or
slightly higher pH, and low in dissolved salts.  Water suitable for drinking
is not necessarily suitable for mixing with bentonite.  Water of inadequate
quality will result in higher bentonite consumption and a lumpy slurry that is
difficult to mix and contains above average amounts of free water.  In some
instances, poor quality water can be chemically treated to make it suitable
for mixing (Ryan, 1977).

     Two types of mixing systems are most frequently used.  These are batch
mixing and flash mixing.  In the batch system, specified quantities of water
and bentonite are placed in a tank and mixed at high speeds with a circulation
pump or paddle mixer.  Mixing continues until  hydration is complete and  the
batch is ready for use in the trench.  Hydration is usually complete in  a
matter of minutes for the two- to five-cubic-yard batch produced by this
system.  Because of the low output of the batch system, its use is limited to
small jobs.

     The second type of mixing system is the flash or venturi mixer.  For this
system, bentonite is fed at a predetermined rate into a metered water stream
                                     7-51

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as it is forced through a nozzle at a constant  rate.   The  slurry  is  subjected
to high shear mixing for only a fraction of a second,  which is  not always
adequate for hydration.  Therefore, the  slurry  is  often  stored  until  hydration
is complete.  This is determined by periodically measuring  the  Marsh Funnel
vi scosity.

     When Marsh Funnel  viscosity readings stabilize,  hydration  is considered
complete.  Flash mixing is a process that can be operated  at  high production
rates.  Because a majority of cut-off walls require  continuous  production of
large amounts of slurry, flash mixing is the more  common of the two  mixing
methods (Ryan, 1977).  The type of mixing system used  has  been  found to affect
the quality of the slurry produced.  High shear (or  high speed  batch mixers)
produce slurries with higher gel strengths (Xanthakos, 1979).

     The grade of bentonite dictates the percent needed  for a given  slurry and
hydration time.  For example, a grade 90 (bbl/ton) bentonite  may  have to be
mixed at a 6.3 percent concentration, while a grade  125  would require 4.5
percent concentration for an equivalent  slurry.  Hydration times  for higher
grades are likewise lower, which may result in  higher  slurry  production rates
for a given slurry preparation facility (Ryan,  1977).   However, the  higher
cost of the higher grade bentonites requires that  the  selection of bentonite
grade be made on a site-by-site basis.  Frequently a mud balance  test is run
on slurry from the hydration pond as a quality  control check of the  bentonite
content.  Viscosity and pH are also checked frequently (Cavalli,  1982).

               7.1.3.2.4  Slurry Placement

     From the hydration pond, slurry is pumped  on an as-needed  basis to the
excavated slurry trench.  Slurry level in the trench must  be maintained at
least several feet above the water table and normally within  a  foot or two of
ground level.  This slurry level is maintained  to provide  the hydrostatic
pressure necessary to  hold  open the trench.

     Once a slurry trench installation is under way, backfill and excavation
are being performed simultaneously, with a minimum amount of trench remaining
                                     7-52

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open under the slurry.  Figure 7-13 illustrates  the  excavation  and  backfill
placement operations.  The amount of trench remaining  open  at  any one  time
depends on the properties of the backfill  material  and  the  characteristics of
the excavation equipment, which are discussed in the following  sections.
Samples removed from the trench for QC checks must  be  representative,  that is,
they should not be taken only from the top surface  of  the slurry but should  be
taken at various depths in the trench.  The slurry, designed to keep the
trench open during excavation and backfilling, must also allow displacement  by
the backfill material.  That is the reason for stipulating  maximum  and minimum
values for  parameters such as density, viscosity, and  sand  content.  Those
requirements are listed in Table 7-7.  During the excavation operation, some
of the spoil becomes incorporated in the slurry.  This increases slurry
density and sand content.  A high sand content indicates a  high density and  a
likelihood  of problems with eventual displacement of the slurry by  the
backfill  (D'Appolonia and Ryan, 1979).
                                  FIGURE 7-13.
                   CROSS-SECTION OF SLURRY TRENCH, SHOWING
                    EXCAVATION AND BACKFILLING OPERATIONS
                                     7-53

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                                              TABLE  7-7.
           MATERIALS  QUALITY CONTROL  PROGRAM  FOR  SOIL-BENTONITE  WALLS
           (Federal  Bentonite,  1981  as  cited  by  Spooner  et  al.,  1984}
Duality Subject Standard Name
Control Item
Materials Water
Type of Test
-pH
-Total hardness
Frequency
Per water source
or as changes
occur
Specified Values
As required to properly
hydrate bentonite with
approved additives.
Determined by slurry
viscosity and gel strength
tests
Slurry
              Additives
              Bentonite
              Backfill
                soils
Prepared
for place-
ment Into
the trench
              In Trench
                         API Std 13:
                         Standard Procedure
                         for Testing
                         Drilling Fluids
Backfill
 Mix
              At  Trench
API  Std 13:
Standard Procedure
for  Testing
Drilling Fluids
                         API Std 13B1:
                         Standard Procedure
                         for Testing
                         Drilling Fluids
           ASTM C 143
           Slump Cone Test
                             Manufacturer certificate
                             of compliance with
                             stated characteristics

                             Manufacturer certificate
                             of compliance
Selected soils obtained
from a borrow area
approved by the engineer

Roll  to 1/8" thread

- Unit Weight

- Viscosity
                                                                  1 set per shift or
                                                                  per batch (pond)
                                           - Filtrate  Loss
                             -  pH

                             -  Unit Weight
                             - Slump

                             - Gradation
                                          1 set per shift at
                                          point of trenching

                                          1 set per 200 cu
                                          yds
                                                                                      As approved  by engineer
                                                             Premium grade sodium cation
                                                             montmorlllonite
                                                                        65  to 100% passing 3/8"  Sieve
                                                                        35  to 85% passing 120 Sieve
                                                                        15  to 35% passing 1200 Sieve
Unit  Weight = 1.03 gm/cc

v = 15 centipose  of
    40 sec-Marsh  8 6°F

Loss  = 15 cc to 25 cc 1n
      30 min 3 100 psi

pH = 8

unit  weight = 1.03 to 1.36
      gm/cc

Slump 2 to 6 inches

65 to 100% passing 2/8"  Sieve
35 to 85% passing #20 Sieve
15 to 35% passing 1200 Sieve

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               7.1.3.2.5  Trench Excavation

     Excavation of a slurry trench parallels standard trench excavation
procedure except that only the portion of the trench above slurry level  can be
visually inspected for continuity.  Trench excavation is usually accomplished
with backhoes with appropriate boom length and bucket capacity.   Frequently,
boom lengths are extended by construction contractors to meet the needs of the
trench installation.  Counterweights are often required to offset the movement
created by the long boom lifting a full bucket from the trench.   The backhoe
is the favored means of excavating a slurry trench because it is much faster
than other equipment, such as the crane and clamshell.  However, boom lengths
are currently limited to 70 to 90 feet.  For greater depths, the crane and
clamshell are normally used.  Drag lines have been used in the past, but have
been used rarely for recent installations (D' Appolonia, 1982).

     Trench continuity is critical to a successful installation.  For checking
continuity of slurry trenches, several approaches have been used.  All  of them
may be employed at a given site to ensure that the trenching is continuous
from the ground surface to the aquiclude key-in.

     The field inspector should have boring logs and a cross-sectional  drawing
of the trench so that visual inspection of the excavated material and the
degree of extension of the backhoe boom will indicate approximate depth and
whether the aquiclude has been reached.  Soil boring data can also be used to
quantify the aquiclude key-in.  By watching excavated material for a change in
color or texture, construction personnel can determine when the  subsurface
layer which is to be keyed into is reached.

     Sounding of depth with a weighted line or a rod should be performed
frequently to ensure an even trench bottom and to detect any irregularities.
Finished trench depths should be recorded for preparation of a drawing showing
trench cross section.
                                     7-55

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               7.1.3.2.6  Backfill Preparation

     Standard practice during backfill preparation for soil  bentonite walls is
to use excavated material  mixed with slurry from the trench  for backfill.  In
this case, the slurry provides moisture necessary for backfill  mixing.  When
trench spoils are used, the material  excavated from the trench  is usually
placed nearby, slurry is added, and a bulldozer is used to track and blade the
material  until it is thoroughly mixed.

     A relatively level working surface is needed for backfill  mixing.  At
sites that are too steep, backfill mixing  areas can be excavated.  These
should be at least as wide as the width of the excavating equipment track.
Where backfill mixing areas are not available, batch mixers  or  pugmills can be
used, although these are slower than using a bulldozer for backfill mixing.

     A number of quality control  checks are necessary for backfill  preparation
activities.  These include tests of the:

     •  Fines content
     •  SI ump
     •  Wet density
     •  Presence of contaminants.

     A key parameter in the design of a backfill  is the sieve analysis and
particularly the amount of fines.  The content of fines in the  backfill  is
directly related to the permeability of the finished soil-bentonite wall and
its ability to withstand chemical  attack.   A standard practice  is to perform
permeability testing in the pre-construction phase to define the range of
acceptable grain size distributions that  will  provide the design permeability.
During construction, frequent grain size  distributions and less frequent
permeability testing is performed on the  backfill  material to ensure that the
design permeability requirements will  be met by the completed slurry trench.
Grain size distributions can be performed  in a field laboratory and are much
less expensive to run than permeability tests, which are usually run in a
1aboratory.
                                     7-56

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      Slump cone testing  should be  performed  frequently on backfill material
after mixing  to make  sure  that backfill  is wet  enough to  slump  in  the  trench
without trapping pockets of  slurry, yet dry  enough to displace  the slurry
easily.   High  slump also  indicates  a gentler slope of backfill  in  the  trench,
which would require keeping more of the trench  open.  A slump of 2 to  6  inches
is adequate (D'Appolonia ,  1980).

      Mud  balance testing  should be  performed frequently on  the  backfill  before
it is placed  in the trench.  Mud balance tests  indicate the wet density  of the
backfill.  This shows  for  certain  that the backfill will  or will not readily
displace  the  slurry.   The  wet backfill sample used for the mud  balance test
can be dried  and reweighed to determine the  water content.  A very high  water
content can result in  excess water  infiltration  into the  trench walls  and
excess settlement of the backfill.  The separation of water from an exces-
sively wet backfill can also dilute the slurry  in the trench.

               7.1.3.2.7   Backfill  Placement

      Once trench excavation has proceeded for a distance that will  not result
in backfill material being re-excavated, backfill placement can begin.   First,
samples of slurry at the base of the trench  are collected and tested for wet
density.  The  slurry should be at  least 15 pcf  less dense than  the backfill
mixture (D'Appolonia,  1980b).  If the slurry is too dense, it will  not be
displaced properly during  backfill  placement.   The dense  slurry or coarse
material   on the trench bottom must be removed via airlift pumps, a clamshell
bucket or other method.  This slurry can be  used for backfill  mixing or  be
desanded  via desanders, hydrocycl ones, or screens, and returned to the trench.

     To place the initial  layer of backfill, a  clamshell   is often used.  The
backfill  must not be allowed to drop freely through the slurry, as this may
cause segregation of the backfill  particles  or  entrapment of slurry pockets
within the backfill.   For this reason, the clamshell  lowers the initial
grabfull   of backfill to the trench bottom.   The next grabfull  is placed  on top
of the first, and so on until  the  backfill  is visible at  the ground surface.
Thereafter, the backfill is pushed into the  trench by bulldozers or graders.
                                     7-57

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 The  point  of trench backfilling progresses  toward  the area of active
 excavation (D'Appolonia  and Ryan,  1979).

      The  slope  of the  emplaced  backfill  is  normally 5:1  to 10:1.   The distance
 to be maintained  between  the  toe of  the backfill and  the area of  active
 excavation varies greatly,  depending on  soil  types and  backfill  slopes.
 Ideally this distance  is  kept to a minimum  to  avert  trench stabil ity problems
 (D'Appolonia, 1980b).   Some specifications  have  set  the  distance  at  from 30 to
 200  feet  (U.S.  Army Corps of  Engineers, 1975;  Ryan,  1976).

     Soundings  of the  placed  backfill  should  be  taken to show the  slope at
 which the  backfill  is  coming to  rest  and to indicate  possible problems  with
 trench wall  collapse and  entrapment  of pockets of  slurry.   Depths  should be
 recorded and plotted on a cross-sectional drawing  of  the  trench.   Trench
 excavation  and  backfilling  progress  can also  be  recorded  in  this manner.

     When a  slurry  wall is  constructed to entirely surround  a waste  site, the
 excavation  must end with enough  overlap to  ensure  that all material  designated
 for excavation  is  removed.  The  inspector must determine  that the  backhoe
 bucket is  removing  backfill materials  from  the full trench depth to  verify
 that the trench is  continuous for its  entire length.

                7.1.3.2.8  Capping

     To protect the finished soil-bentonite wall, either  a dessication  cap  or
 a traffic cap is generally applied to  the slurry wall surface.

     Once backfill  has been completed, cracking  is soon observed on  the  top of
 the slurry wall  unless it stays wet.    To complete the installation,  the top  1
 to 3 feet of  wall   is removed to eliminate the cracks  and  a high quality
 backfill  material  replaces it.  The material used is  usually  required to have
 a high clay content and to be compacted in lifts over the  trench.  This  forms
a low permeability cap to protect the cut-off  wall  from excessive dessication
 (U.S. Army Corps of Engineers, 1976).  This is followed by topsoil  and  seeding
or a  gravel layer  to prevent water  and wind  erosion.
                                     7-58

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     Where traffic over the wall  is anticipated, a traffic cap can be con-
structed to reduce the load on the completed cut-off.  To do this, lifts of
compacted clay are interspersed with geotextile layers.  Gravel  can be used
over the final geotextile layer at the surface.  At one facility where a soil
bentonite cut-off wall was close to a heavily traveled gravel  road, the cap
consisted of an 18-inch thick compacted clay lift topped by a geotextile
sheet.  This was overlain by another 18-inch thick compacted clay layer topped
by another geotextile sheet.  Several inches of gravel were placed over the
final  sheet of geotextile to distribute the weight and bear the load of the
vehicles (Coneybear, 1982).

               7.1.3.2.9  Cleanup Activities

     After wall construction is complete, the excess slurry and mixed backfill
must be disposed of in a manner that avoids erosion and disruption of sewer
lines.  The slurry should not be allowed to enter sanitary or storm sewer
lines because of the potential for pipe blockage from the slurry.  Excess
slurry also should not be left as a thick layer on the soil  surface, as this
may result in excessive ponding of surface water.  One method of slurry
disposal would be to mix the slurry with dry, coarse soil  to produce as dry a
mixture as possible.  This material could then be either buried or spread in a
thin layer over disturbed areas, then fertilized and seeded.  Any contaminated
soil from the excavation must be disposed of in accordance with site require-
ments.  All disturbed areas should be stabilized and site maintenance
procedures should be instituted.

     There are a number of differences in construction activities that vary
with construction materials.  The following is a brief summary of cement
bentonite and diaphragm wall construction techniques.

          7.1.3.3  Cement Bentonite Wall Construction

     The discussion presented above is an outline of a soil-bentonite cut-off
wall construction.  Modifications to the construction specifications are
                                     7-59

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necessary when constructing a cement-bentonite cut-off wall.  These
modifications include the following:

     0  The requirement for backfill materials are eliminated
     •  A description of the standards for cement and cement storage is added
        in the materials section
     •  A description of the cement-bentonite slurry requirements and the
        cement/water (c/w) ratio to be maintained for desired compressive
        strength is added to the materials section
     •  The methods to be used for tie in of adjacent cement-bentonite panels
        (if used) are addressed in the performance section
     •  Under the Quality Control  section, a requirement is added for the
        manufacturer's certification of the cement and the testing of
        cement/water ratio for each batch of mix is required.

     Cement bentonite slurry walls involve the use of a slurry consisting of
water, bentonite, and cement.   The advantages of cement-bentonite walls are
that backfill  material  is not needed and they exhibit some structural
strength.   In  addition, by excavating one section (panel)  at a time, a
cement-bentonite wall can be installed on a site with more extreme topography.

     Two types of cement-bentonite walls are being used.  The in-place method
involves simply excavating under a cement-bentonite slurry and leaving the
slurry in  place.  The slurry eventually sets to  provide some structural
strength.   For the replacement method, excavation takes place under a
bentonite  slurry.  After excavation of the section of wall  is complete, the
bentonite  slurry is pumped out of the trench and the cement-bentonite slurry
is pumped  in and allowed to set.  The replacement method is used only when
setting of the cement-bentonite slurry could possibly occur while excavation
is being completed.

     Cement-bentonite slurries begin to set within 2 to 3  hours after the
cement and slurry are mixed.  If the slurries are agitated for over 48 hours,
they lose  their ability to set (Jefferis, 1981b).  For this reason, when it
appears that the excavation of a single cement-bentonite panel  will  take
longer than a day or so to complete, cement retarders are  added to the slurry
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or the replacement method is used.  Examples of this situation would be very
deep excavations, when rock is encountered in the excavation or when keying
the trench into bedrock.

     Quality control  procedures for cement-bentonite walls are identical  to
those for soil  bentonite walls.  However, composition of the cement-bentonite
slurry is more critical, therefore, care must be taken when weighing and
mixing components of the slurry.  This is because the calcium in the cement
causes an irreversible decrease in slurry quality.  Table 7-8 shows typical
materials quality control standards for cement-bentonite cut-off walls.

          7.1.3.4  Diaphragm Wai 1  Construction

     Construction of diaphragm walls also involves the use of bentonite or
cement-bentonite slurries, although these walls are not normally used for
pollution migration cut-offs, except where high strength is required.
Diaphragm walls are composed of either precast concrete panels or cast-in-
place concrete sections.  Unlike soil-bentonite and cement-bentonite walls,
these walls develop a great deal of strength over time and can be used as
structural components.  A brief description of the techniques used for
construction of diaphragm walls is given in Section 7.1.2.2.3.

     7.1.4  Completed Wall Costs

     Contractors have provided average costs for completed slurry cut-off wall
construction and installation.  These estimates may vary widely, however, as
they are  based upon a number of site-specific factors.  Some of these factors
include the following:

     •  Type of backfill (either cement- or soil-bentonite)
     t  Distance materials must be transported
     •  Presence of contamination or high salt content in groundwater
        requiring special bentonite and excavation procedures
     •  Health and safety considerations
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                                                           TABLE 7-8.
                                 MATERIALS QUALITY  CONTROL PROGRAM FOR  CEMENT-BENTONITE WALLS
                                   (Federal Bentonite,  1981 as cited  by  Spooner et al., 1984)
                 Subject
Standard
Type of Test
Frequency
Specified Values
            Water
-^1

CT)
            Materials   Bentonite    API STD 13A
                        Cement
ASTM C 150
              - pH
              - Total  hardness
                (Ca  &  Mg)
Manufacturer
certificate of
compliance

Manufacturer
certificate of
compliance
                   Per water source
                   or as changes
                   occur
                                                                                           As  required  to  properly
                                                                                           hydrate  bentonite with
                                                                                           approved additives.
                                                                                           Determined by slurry
                                                                                           viscosity and gel strength
                                                                                           tests.
                                                      Unaltered sodium cation
                                                      montmorillonite
                     Portland, Type  1  (Type  V or
                     Type  II  for certain applica-
                     tions)
            Bentonite   Prior to     API STD 13B
             Slurry     addition of
                        cement
              -  Viscosity
                   1 set per shift  or
                   per batch (pond)
                    v =  34 sec-Marsh @ 68°F
                    pH = 8
Cement -
Bentonite
Slurry
Upon
introduc-
tion in
the trench
API STD 13B
API STD 10B
- C/W ratio
- Viscosity
Each batch
5 per shift
                                                                                          C/W = 0.20
                                                                                          v = 40 to 50 sec-Marsh

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     •  Type of overburden being excavated
     •  Depth of excavation
     t  Presence of physical  constraints upon working area (i.e., buildings or
        other structures which must be worked around)
     •  Suitability of native materials for use as backfill  constituents.

     Ressi  di Cervia (1980) developed a chart (Table 7-9) which relates
cut-off wall construction costs to type of backfill  used, depth of excavation,
and soil  type present.   Costs are given in terms of  square foot of wall since
the width of the excavation is generally determined  by the excavation
equi pment.

7.2  GROUTING

     Grouting is a process in which a fluid material is injected into a soil
or rock mass in order to reduce water movement or to impart  increased strength
to the formation.  Once in place within the formation voids, the fluids
solidify or gel  thus greatly reducing the permeability and imparting increased
mechanical   strength to the grouted mass (JRB, 1982;  Herndon  and Lenahan ,
1976a & b).

     Grout  barriers can be many times as costly as slurry walls and are
generally incapable of attaining truly low permeabilities in unconsolidated
materials.   Therefore, they are rarely used when groundwater control in
unconsolidated materials is desired.  The primary use of grouting is to seal
voids in porous or fractured rock when other groundwater control methods are
not practical.  The installation of grout barriers has not been as common a
practice for controlling leachate plume migration from hazardous waste sites
as has slurry wall  installation.  Hence, there is not a great deal  of
information available on the application of grouting techniques at hazardous
waste sites for controlling leachate plume migration.

     Grouting is the most practical and efficient method for sealing fissures,
solution channels, and other voids in rock.  Where rock voids allow the
passage of  large volumes of water, a grout can often be formulated to set with
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                                   TABLE 7-9
             RELATION OF SLURRY CUT-OFF WALL COSTS PER SQUARE FOOT
                       AS A FUNCTION OF MEDIUM AND DEPTH
           (Ressi  di  Cervia, 1980 as cited  by Spooner et al., 1984)
Geologic Material
  Slurry Trench Prices
    in 1979 Dollars
Soil  Bentonite Backfill
 (Dollars/Square Foot)
Unreinforced Slurry Wall
 Prices in 1979 Dollars
Cement Bentonite Backfill
  (Dollars/Square Foot)
Depth Depth Depth
30 30-75 75-120
Feet Feet Feet
Soft to Medium Soil
N 40 2-4 4-8 8-10
Hard Soil
N = 40 - 200 4-7 5-10 10-20
Occasional Boulders 4-8 5-8 8-25
Soft to Medium Rock
N 200 Sandstone, Shale 6-12 10-20 20-50
Boulder Strata 15-25 15-25 50-80
Hard Rock
Granite, Gneiss, Schist* — — —
Depth Depth
60 60-150
Feet Feet

15-20 20-30

25-30 30-40
20-30 30-40

50-60 60-85
30-40 40-95

95-140 140-175
Depth
> 150
Feet

30-75

40-95
40-85

85-175
95-210

175-235
Notes:
     N is standard penetration value in number of blows of the hammer per foot
     of penetration (ASTM D1586-67)

*Normal Penetration Only

     For standard reinforcement add  $8.00 per sq. ft.
     For construction in urban environment add 25% to 50% of price.
     Costs do not reflect work in a  contaminated environment.
                                     7-64

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sufficient speed to shut off the flow.  In theory, placement of a grout
curtain upgradient or downgradient from, or beneath, a hazardous waste site is
possible.  In practice, however, this can be a very difficult task to
accomplish successfully.

     As with slurry walls, placing a grout barrier upgradient from a waste
site can redirect the flow so that groundwater does not flow through the
wastes that are creating the hazardous leachate.  Given normal  groundwater
chemistry, most grouts could be expected to function well  in this capacity.

     Placement of a grout barrier downgradient from or beneath a hazardous
waste site is quite another matter.  A variety of problems typically occur
when attempting to grout in the presence of leachate or very impure ground-
water.  In many instances, controlling the set time, and consequently,
ensuring a barrier of reliable integrity is difficult or impossible.  Little
information exists in the literature on the resistance of grouts to chemical
attack.  Should a case arise where a grout might contact leachate or very
impure groundwater, extensive testing must be conducted to determine possible
effects on the grout.  Additional problems occur in attempting to grout a
horizontal curtain or layer beneath a waste site.  In order to inject grout in
such a case, injection holes must be drilled either directionally from the
site perimeter or through the wastes.  The first situation can be very
difficult and expensive and the second could be very dangerous.  In either
case, effective barrier placement is very difficult and virtually impossible
to ensure (JRB, 1982).

     7.2.1  Theory

     Successful  grouting depends on the selection of the proper grouting
material for the specific area to be grouted.  Thus, the physical  and chemical
characteristics, the geology and hydrology, and the groundwater chemistry of
the site must be evaluated.  The factors that will  determine the groutability
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of the site include (Bowen, 1981; Sommerer and Kitchens, 1980; Herndon and
Lenahan, 1976a & b):


     •  Soil and rock physical  characteristics:   The permeability, porosity,
        particle distribution,  and pore size distribution of the  formation
        will control  the physical properties, such as viscosity and particle
        size, that the grout must possess as well  as the quantity of grout
        that will be  needed.

     •  Groundwater characteristics:  The hydrology and contaminants contained
        in the groundwater will  determine the chemical  properties such as  set
        time and structure, that the grout must  possess.

     •  Soil and rock chemical  characteristics:   The contaminants contained  in
        the soil and  rock structure will  control  the chemical  properties that
        the grout must possess.


     Based on these factors, an  appropriate grout  can be selected from
(Guertin and McTigue, 1982; Bowen, 1981):


     •  Bituminous grouts:  These grouts, either  as emulsions or  asphalts, can
        be used to waterproof soils or rock cavities.

     •  Suspension grouts:  These are the most common types of grout and
        include coarse grouts which contain particles in suspension such as
        cement, clay  and cement-clay.  These materials are usually the more
        viscous of the available grouting materials as  well  as having  the
        largest particle size.   Thus, these grouts are best used  in the
        grouting of rock or coarse material.

     •  Chemical grouts:  These  grouts rely on chemical  reactions to form
        gels.  They initially have low viscosities and  thus can be used in
        finer-grained cohesionless soils  and as  a  secondary treatment  for
        grouting coarse soils and rock fissures.   The common  types of  chemical
        grouts include silicates, acryl amides, and various polymers.


     The following sections discuss the chemical composition  and  reaction

theory of the major types of grout.


          7.2.1.1  Bitumen Grouts
     Bitumen or asphalt emulsions consist  of bitumen,  water,  and  an  emulsi-

fier.  Bitumens are viscoelastic materials containing  high molecular weight
hydrocarbons (Kirk-Othmer, 1978a).  When dispersed  in  water,  bitumens yield  an
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emulsion with a low viscosity suitable for injection (Tallard and Caron,
1977a).  The viscosity of the emulsion is controlled by adjusting the ratio of
bitumen to water.  Typical  emulsions include bitumens;  bitumen, soap, and
casein; and bitumen with a filler such as clay (Bowen,  1981).

     Emulsions are stabilized by the emulsifiers, which delay mol ecular
aggregation and increase viscosity (Ki rk-Othmer, 1978a).  The emulsifiers are
polar and determine whether the resulting emulsion is cationic or anionic
(Bowen, 1981).  For example, amine chains are often used as acid emulsifiers
to yield cationic emulsions (Bowen, 1981; Kirk-Othmer,  1978a).  Emulsifiers
should be water soluble and have properly balanced hydrophilic and lipophilic
properties (Koehmstedt, Hartley and Davis, 1977).

     Bitumen emulsions break up upon contact with earth materials so that the
more viscous emulsion components settle out and fill  the pores and fissures of
the earth material.  The breakdown of bitumen emulsions can occur through
direct breakdown, the addition of destabilizing agents, or  the adsorption of
emulsifying water.  In direct breakdown, a stabilizing  agent is eliminated
through decomposition or absorption by fine soil  material.   Direct breakdown
is difficult to control and often occurs too quickly or too slowly (Tallard
and Caron, 1977a).  A second method involves adding destabilizing  agents
(electrolytes or hydrolyzable esters)  to the emulsion either before or after
the emulsion is injected to promote breakdown and flocculation of the emulsion
(Bowen, 1981; Tallard and Caron, 1977a).  When destabilizing agents are added,
a one-step method (addition of additives prior to injection) is preferable
(Tallard and Caron, 1977a).

     The set time of bitumen grout will  vary depending  on the method used to
achieve a breakdown of the  emulsion.   Set time is further controlled by the
emulsifier present in the grout (Koehmstedt, Hartley and Davis, 1977).

     Bitumen grout is known to have long term stability (Tallard  and Caron,
1977a).  Oxidation and aqueous leaching  of oxidation products are  the primary
causes of degradation.  Oxidative processes include microbial  action and
sunlight.  There is little  evidence of anaerobic  bacterial  oxidation (Hartley,
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et al., 1981).  Upon aging,  viscous  bitumen material  can develop an  internal
structure and the viscosity  may  increase  (Kirk-Othmer, 1978a).

     The bitumen used as grout typically  consists of  a coal tar or asphalt
base (Tallard and Caron, 1977a).   These materials consist of complex hydro-
carbons which can be toxic if leached.

          7.2.1.2  Cement Grouts

     Cement grout consists of Portland  cement  and water.   Several types of
Portland cement are available.   The  types most often  used  in soil grouting
include Type I (ordinary Portland  cement), Type  II  (modified Portland cement,
moderate sulfate resistance), and  Type  V  (low  alumina, sulfate resistant).
Fillers such as clay, sand,  or pozzolans, and  additives  such as chemical
polymers may be added to the cement  to  vary the  characteristics of the grout
and  improve its resistance to deleterious chemicals (Littl ejohn, 1982; Bowen,
1981).

     Portland cement is made from  limestone, clay,  and iron oxide and consists
chiefly of tricalcium silicate (45 percent), dicalcium silicate  (27  percent),
tricalcium aluminate, tetracalcium al umino-ferrite, magnesium oxide, and other
minor constituents (Littlejohn,  1982;  Ingles and Metcalf,  1973).  The calcium
silicates are the major cementation  compounds  in cement  (Neville, 1973).

     Various materials (organic  and  inorganic) may  be added to cement grout to
achieve special characteristics  or to  control  grout properties.  Special
additives include anti-bleed agents, accelerators,  retarders, and expansion
agents (Littlejohn, 1982).  Latexes or water-soluble  polymers may be added  to
achieve special properties (Kirk-Othmer,  1979).  Calcium chloride may be added
as an accelerator, however,  calcium chloride may cause increased shrinkage
upon drying  (Littlejohn, 1982).   Sand  may be added  so that cement grouts may
be used to treat coarse materials  (Bowen, 1981).  Clays  can be added to
stabilize the cement while pozzolans or clay may be added  to  improve alkali
resistance (Littlejohn, 1982; Bowen, 1981).  Polyhydric  alcohols can be added
to provide acid-resistance (Farkas and Szwere, 1949).  Colloids such as
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gelatin, agar, and ammonium stearate may be  added  as  stabilizers  (Bowen,
1981).

     Upon addition of water, the silicates and  aluminates  in  cement  form
hydration products which have low solubilities  in  water (Neville,  1973).   The
calcium silicates form gels of mono- and di-calcium  silicate  hydrate  (Ingles
and Metcalf, 1973).  The insoluble calcium silicate  hydrate crystallizes  to
form a matrix within which the remaining hydration products  form  (Ingles  and
Metcalf, 1973; Neville, 1973).  The resulting cement  gel is considered  to be a
fine physical mixture of copolymers of hydrates (Neville,  1973).

     The properties of fresh and cured concrete depend  primarily  upon the
water-cement ratio and the degree of hydration  of  the cement  (Kirk-Othmer,
1979).  Excess water will  result in poor durability,  increased  shrinkage, and
bleeding (Littlejohn, 1982).  High water-cement ratios also  cause  large
numbers of capillary spaces in the matrix (Kirk-Othmer, 1979).

     The viscosity of cement grouts depends on  the amount  of  water added  to
the cement.  As the water-cement ratio increases from 0.4  to  0.7,  the
viscosity decreases from 5,000 to 500 centipoise.   The viscosity  can  also be
reduced through the addition of certain organic admixtures (Kirk-Othmer,
1979).

     The setting  process occurs in two stages.   First, fluidity of the  grout
decreases until it is not pumpabl e--this is called the  set time.   Second, the
grout  hardens and increases in strength--thi s is called the  hardening time
(Littlejohn, 1982).  The various components of  cement grouts  set  at  different
rates.  These rates vary from a "flash set" (tricalciim aluminate) to several
hours  (tricalcium silicate and dicalcium silicate) (Littlejohn, 1982).
Complete setting  takes approximately six hours  (Kirk-Othmer,  1979).

     The set time may be increased by the action of  a number  of substances
including:  organic materials, silt, clay, coal, lignite,  sulfates,  sodium
salts, metals, sugar, and tartaric acid (Fung,  1980;  Littlejohn,  1982;
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 Thompson, Mai one and Jones, 1980).  Increasing the water-cement ratio will
 also  increase the set time.

     While concrete is durable under normal conditions, concrete is subject to
 deterioration as a result of deficiencies in grout quality, chemical  attack,
 drying, and temperature fluctuations (Littlejohn, 1982).  Increasing the
 water-to-cement ratio can greatly increase the permeability of the concrete
 through an increase in the number of capillary spaces which permit penetration
 of solutions (ACI Committee 515, 1979; Kirk-Othmer,  1979).   Furthermore, all
 cement grouts expel  bleed water which can lead to accumulations of water and a
 decrease in strength and lateral  impermeability (Bowen, 1981).  Cement may
 also shrink causing the formation of microfi ssures and cracks unless it is
moist-cured (Littlejohn, 1982).

     Concrete is vulnerable to chemical  attack because of its alkalinity,
 reactivity, and permeability.   Penetration of fluids may be accompanied by
 chemical reactions between the fluid and concrete constitutents (ACI Committee
 515, 1979).  Concrete will deteriorate because of sul fates, chemical  wastes,
 and organic acids (Tomlinson,  1980).  Furthermore, cement hydration compounds
may leach from the matrix and  this can also cause deterioration (ACI Committee
 515, 1979).

     The basic components of cement grouts are lime, silica, alumina, iron
oxide and water, which are all  nontoxic.  However, substances such as chemical
 polymers (e.g., acryl amide)  may be added to the grout to modify its
 properties, and these materials may be toxic.

          7.2.1.3  Clay Grouts

     Clay grouts are composed  primarily of bentonite.  The  basic reaction
theory and  chemical  composition of bentonite is described in section 7.1.2.1.

     Bentonite grouts will start to set  as soon as the injection pressure is
decreased.   Once this  process  starts,  the viscosity  and then the gel  formation
and strength will  increase with time.   The final  strength of the gel  will
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depend on the setting time, colloid concentration,  and the  composition  of the
suspending fluid (Xanthakos, 1979).  The  final  strength obtained,  though, is
very low compared to other grouts (Talland and  Caron, 1977b).   The set  time
can be controlled through the addition of silicates to the  bentonite  grout,
resulting in set times from a few minutes to five hours (Bowen,  1981).

     The basic ingredient in this type of group, bentonite, is  essentially
nontoxic.  The toxicity of most of the additives, such as sodium silicate, are
also low, although agents used to gel  the sodium silicate could  pose  a  risk
(Tallard and Caron, 1977b).

     The presence of organic or inorganic compounds in the  groundwater  can
have a detrimental  effect on the ability  of bentonite grouts to  contain
pollutants.  These chemicals can affect the physical  and chemical  properties
of the bentonite, result in fl occulation, reduce swelling of the bentonite, or
destroy the bentonite's crystalline structures.

     If the bentonite is injected into groundwater  which contains  high  con-
centrations of electrolytes, such as sodium, calcium, and heavy  metals,  the
bentonite could flocculate.  This will  result in particles  that  can exceed
10 microns in diameter, thus hampering the grout's  ability  to  penetrate  into
the soil  structure (Tallard and Caron, 1977b; Matrecon, Inc.,  1980; Alt her,
1981b).

     Various organic and inorganic compounds can cause a change  in the  amount
of swelling that bentonite particles undergo (Alther, 1981b).   This can  lead
to increased porosities and permeabilities.  Strong organic and  inorganic
acids and bases can dissolve alumina and  silica or  alter the bentonite,  and
also lead to large permeability increases (D'Appolonia and  Ryan, 1979; Alther,
1981b).  Undiluted alcohols increase grout permeability by  extracting water
from the clay interlayers, thus reducing  the amount of particle  swelling.
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           7.2.1.4  Silicate Grouts

     Silicate grouts consist of alkali silicates, water, a gelling or setting
agent, and sometimes an accelerator.  Typically, sodium silicate is used in
the grout  although potassium silicate may be used instead.  The gelling or
setting agent used varies depending on the desired properties of the gel.   In
general, acids, acid-forming compounds, polyvalent cations, and some organics
may be used as setting or gelling agents (Kirk-Othmer, 1979; Hurley and
Thornburn, 1971).  Accelerators include chlorides, aluminates, or bicarbonates
(Johnson,  1979).  Other substances, such as organic  esters, may be added to
delay gelling time (Bowen, 1981).  Grout compositions can vary considerably
with the grouting method and are often proprietary (Herndon and Lenahan,
1976a).

     The viscosity of sodium silicate grouts varies  from 1.5 to 50 centipoise
and may be as high as 260 centipoise (Sommerer  and Kitchens, 1980; Tall and and
Caron, 1977a).  The viscosity of the grout depends on the ratio of SiO_ to
Na20.   The higher the ratio of silica to  sodium, the lower the viscosity.   The
set time of silicate  grouts varies from less than a  minute to several  hours.
Factors affecting the set time include silicate concentrations, setting agent
concentrations, and temperature.  Increasing any of  these three factors will
decrease the set time (Tall and and Caron, 1977a).  The accelerator concentra-
tions may  also be varied to control  set time.  Soil  conditions can also affect
the set time with acid soils reducing gel  time  and alkaline soils  potentially
preventing gel formation (Office of the Chief of Engineers, 1973).

     Tallard and Caron (1977a) report that silicate  grout is quite durable.
However, long-term strength and impermeability are of concern because  silicate
grouts are subject to deterioration via syneresis (water expulsion),  shrinkage
(dessication), and solution erosion by groundwater (Hurley and Thornburn,
1971).

     Sodium silicate  grouts are essentially nontoxic.  The set grout  has a
toxicity (oral)  of 15 g/kg, while  sodium  silicate has a  toxicity (oral)  of 1.1
g/kg.   Anides frequently used in formulating the grout are skin irritants
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(Tallard and Caron, 1977b).  Other organic  substances,  such as  formamide, are
toxic, possibly carcinogenic, and  require  special  precautions when  preparing
and injecting the grout (Karol ,  1982a;  Ki rk-Othmer,  1979;  Tallard  and  Caron,
1977a).  Heavy metal  salts, which  may be  used  as  gelling  agents, are also
toxic and could potentially be leached  from  the gel.   In  addition,  sodium
salts may be expelled from the grout and  under certain  circumstances they may
be an environmental hazard (Karol, 1982a).

          7.2.1.5  Organic Polymer Grouts

     Organic polymer grouts represent only  a small  fraction of  the  grouts in
use.  These grouts consist of organic materials  (monomers) that  polymerize  and
cross-link to form an insoluble gel.  This  section  addresses acryl amide,
phenolic, urethane, urea-formaldehyde,  epoxy,  and polyester grouts  and  their
properties.

               7.2.1.5.1  Acryl amide Grouts

     Acryl amide grouts consist of  a base  material (typically a  monomer  or
mixture of monomers), a cross-linking agent, an  initiator or catalyst,  and  an
accelerator or activator.  Persul fates  or  peroxides,  typically  ammonium
persulfate, are used as an initiator.  Accelerators  or  activators  include
dimethyl aminopropionitrile , diethyl aminopropionitrile,  or triethanolamine
(Tallard and Caron, 1977a).  The substances  used  vary with the  particular
product.  Gel time may be controlled through the  addition of a  reaction
inhibitor, typically potassium ferricyanide (Karol,  1982a; Tallard  and  Caron,
1977a).  Buffers may be required to maintain the  pH  of  the grout solution
around 8.

     The set time of acryl amide grouts  can  vary  from  a  few seconds  to  several
days (Karol, 1982a; Cues, Inc.,  1982; Tallard  and Caron,  1977a;  Office  of the
Chief of Engineers, 1973).  The primary factors  controlling set time are
concentrations of reaction inhibitors,  catalysts, and activators (Karol,
1982a; Ki rk-Othmer, 1979; Tallard  and Caron, 1977a).   An  acidic grout  solution
or acidic grouting conditions (groundwater  or  earth material) can lengthen  the
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 set  time  and may even prevent gelation (Office of the Chief of Engineers,
 1973).   The  set time may be shortened through the action of metals, tri-
 ethanol amine, or ammonium persulfate by increasing the pH, or by increasing
 the  dry matter  in the grout (Clarke, 1982; Avanti International, 1982;  Tallard
 and  Caron, 1977a; Office of the Chief of Engineers, 1973).

      Once an acryl amide grout is set, it is fairly stable chemically and is
 not  subject to  slow deterioration or syneresis (Karol, 1982a; Berry, 1982;
 Avanti International, 1981; Tallard and Caron, 1977a).  Over time,  however,
 the  grout may shrink or some salts, unreacted materials, and hydrolysis
 products may leach out (Karol, 1982a; Tallard and Caron, 1977a).

                7.2.1.5.2  Phenolic Grouts

     Phenolic grouts, commonly referred to as phenoplasts, are polycondensates
of phenols and aldehydes (Sommerer and Kitchens,  1980; Tallard and  Caron,
 1977a).  Atypical  phenolic grout consists of a  phenol,  an aldehyde, water,
 and  a catalyst.   Formaldehyde  is  used exclusively because of its reactivity
 (Billmeyer, 1971).   Sodium hydroxide or other alkaline materials (hydroxides,
carbonates, phosphates)  are typically used as catalysts, although acids can
 al so be used.

     Phenolic grouts may be mixed in a one or two solution system.   The
proportions of phenol, formaldehyde, and  catalyst are  fixed  by reaction
requirements so  the  only variable is the  amount of water added (Tallard and
Caron, 1977a).   Polymerization  begins as  soon  as  the  solutions or grout
components are mixed.  In  general, polyvalent cations  from the alkali catalyst
initiate  and promote polymerization (Chung,  1973).   The  polymerization
(polycondensation)  process results in  the  formation  of a three dimensional
network of polymer  chains  that  are joined  and  cross-linked by  formaldehyde
(Karol, 1982a; Bowen, 1981;  Tallard and  Caron, 1977a).   The  catalyst  is also
attached  to  the  polymer  resin  and may form secondary linkages  within  the  resin
network or bond  with soil.   The  resulting  resin is  insoluble and  retains  all
constituent material s (Tallard  and Caron,  1977a).
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      Phenolic grouts made with resorcinol and formaldehyde have viscosities
between  1.2 and 3.0 centipoise (Karol , 1982a; Tallard and Caron, 1977b).
Commercial products consisting of tannin or polyphenols typically have higher
viscosities:  "Geoseal"  ranges from 2 to 12 centipoise, "Terranier" ranges
from  4 to 10 centipoise, "Rocagil" ranges from 5 to 10 centipoise (Bowen,
1981; Tallard and Caron, 1977a; Tallard  and Caron, 1977b).  The viscosity of
resorcinol-formaldehyde grouts, like acryl amides, remains constant until
gelation occurs.  In tannin-based grouts, the viscosity gradually increases
after the components are mixed (Karol, 1982a; Tall ard and Caron, 1977b).

      The gel or set time of phenolic grouts is proportional  to the solution
diluteness and may vary  from several minutes to several  hours (Bowen, 1981;
Karol, 1982a; Tallard and Caron, 1977a).  With very dilute solutions, the gel
time  increases so much that gelation never occurs and the grout becomes
unusable (Tallard and Caron, 1977a).  If all other factors remain constant,
the choice of catalyst will  affect the set time because different bases have
different reactivities.  Sodium hydroxide, the most common catalyst,  provides
approximately a 20 minute gel  time as do some carbonates and calcium
hydroxide.  Other bases  (hydroxides and  carbonates) provide longer set times
(Tallard and Caron, 1977b).

      The length of set time affects the  strength of the grout.  Short set
times give strong gels while long set times give weak gels.   Strong grouts are
not critical to waterproofing, but short set times are often important (Karol.,
1982a).  To decrease the set time, phenolic grouts may be combined with
another grout such as a  silicate that has a shorter set time.   This grout will
set first and provide a "false set."  The phenolic grout is  retained  in the
grout matrix and sets at its normal  rate.  The final  properties of the grout
mixtures are determined by the phenolic grout (Tallard and  Caron, 1977a).

      Wet cured phenolic grouts (under groundwater) are generally durable,
however, there may be a slight weakening  over time potentially caused by  the
gradual swelling of the resin  (Tallard and  Caron, 1977b).  After setting  is
complete, the phenolic resin contains water  that is not  chemically bound  in
the matrix.   Under dry conditions, this water can evaporate  and the gel may
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shrink and crack (Sommerer  and  Kitchens,  1980;  Tall ard  and  Caron,  1977a;
Tallard and Caron,  1977b).   Unlike  acryl amides  and  silicates,  this dehydration
is irreversible and  can  lead  to disintegration  of the gel  (Karol ,  1982a;
Tallard and Caron,  1977a).

     Proper proportioning of phenol  and  formaldehyde in  the  grout  will  produce
a complete reaction  and  the resulting  gel  is  insoluble  and  inert  (Tall ard  and
Caron, 1977a; Tallard and Caron; 1977b).   If  the materials  are not properly
proportioned, excess materials  may  leach  out  of the resin.   In either  case,
some of the catalyst may remain partially soluble and leach  out of the  matrix
(Karol, 1982a; Tallard  and  Caron, 1977a;  Tallard and Caron,  1977b).

               7.2.1.5.3  Urethane  Grouts

     Urethane, or polyurethane  , grout  consists  primarily of  a  polyi socyanate
and a polyol  or other hydroxy compound such as  a  polyether,  polyester,  or
glycol (Karol, 1982a; Vinson  and Mitchell, 1972).   A dii socyanate  is often
                                         ®
used (Vinson and Mitchell,  1972).   RokLok , a polyurethane  grout,  consists of
polymethylene polyphenyl  isocyanate (containing diphenylmethane diisocyanate)
and poly(oxyal kyl ene) polyether polyol  resin  (Mobay Chemical  Corporation,
1982).  Other substances such as catalysts, surfactants, dilution  agents,
pi asticizers, and stabilizers may be added to control  the reaction of  the
grout and its properties before and after setting.

     Urethane grouts set through a  polymerization  process.   The initial
reaction occurs between  excess isocyanate and the  polyol  compound  to  form  a
polyurethane prepolymer (Jiacai, et al.,  1982;  Karol, 1982a).   The reaction
may be stopped at this step and be  completed later.  To complete  the  reaction
sequence, the prepolymer is reacted with  water, carboxylic  acid,  or other
hydroxyl-containing compounds to form polyurethane  foam (Karol , 1982a;  Vinson
and Mitchell, 1972).  This foam consists  of cross-linked polyurethane  chains
with the cross-linking occurring through  the formation  of urea linkages and
the generation of carbon dioxide gas (Vinson and  Mitchell,  1972;  Billmeyer,
1971).
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     Additional materials may be added to the grout.   Catalysts  such as
tertiary amines (triethylamine, triethanolamine, triethylenediamine) or tin
salt may be added to control  the rate of gellation and foaming (Karol ,  1982a;
Jiacai, et al., 1982).  Stabilizers and surfactants may be added to control
the surface tension of the grout as well  as the size  of the bubbles (Karol,
1982a; Jiacai, et al., 1982).  Since the prepolymer has a  high viscosity, the
grout may be diluted with acetone, xylene,  ethyl acetate, or dichl oroethane.
Plasticizers such as dibutyl phthal ate may also serve  as dilution agents
(Jiacai , et al., 1982).

     The set time varies from several seconds to several minutes or hours
(McCabe, 1982; Avanti International, 1982;  Tall and and Caron,  1977a).   The set
time can be shortened by increasing the water content, moving  from a primary
to a secondary or tertiary alcohol, or increasing the catalyst (amine)  content
(Vinson and Mitchell, 1972; Tallard and Caron, 1977a) .  The set  time can  be
lengthened by decreasing the  size of the polyol  or by adding acid (Sommerer
and Kitchens, 1980; Vinson and Mitchell, 1972).

               7.2.1.5.4  Urea-Formaldehyde Grouts

     Urea-form aldehyde resin  grouts consist of urea,  formaldehyde, catalyst,
and water.  The urea-formaldehyde mixture may be in monomer or prepolymer
form.  The catalyst is an organic acid, inorganic acid, or acid  salt.

     The urea-formaldehyde resin is formed  in a two-step reaction  process.
First, the urea and formaldehyde monomers react through methyl ol ation or
hydroxymethylation to form low molecular weight polymers.   This  reaction  may
be either acid or base catalyzed (Kirk-Othmer, 1978b).  Second,  further
polymerization occurs through condensation  of the polymers  with  water being
generated.  This reaction will only occur with an acid catalyst  (Kirk-Othmer,
1978b; Billmeyer, 1971).  The resulting resin is a stable  network  of cross-
linked urea-formaldehyde polymers (Tallard  and Caron, 1977a).

     There are two mechanisms for achieving this reaction  sequence.   Where the
grout mixture uses urea and formaldehyde monomers, the two  reactions occur
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 rapidly and  the overall  reaction  is difficult to control (Karol , 1982a).  The
 second mechanism involves stopping the reaction sequence after methyl ol ation.
 At this point, precondensates or  prepolymers have formed that are soluble in
 water and are prevented  from further reaction by the use of inhibitors or by
 pH control (Karol, 1982a; Tallard and Caron, 1977a).  Commercially, the
 methyl ol ation reaction is base catalyzed (Kirk-Othmer, 1978b; Tallard and
 Caron, 1977a).  The second reaction, polymerization, may occur later by
 lowering the pH of the prepolymer solution.  By introducing an intermediate
 stage in the reaction, better gel time control  is achieved and sudden setting
 of the grout may be avoided (Karol, 1982a;  Tallard  and Caron, 1977a).

     In either case, an  acid medium is required for  final  polymerization to
 occur.  Urea-formaldehyde resins cannot be  used in  alkaline media because the
 acid catalyst would react with the media and be destroyed  before it could
 react with the grout (Sommerer and Kitchens, 1980;  Tallard  and Caron, 1977a;
 Rensvold, 1968).  In addition to pH control, the urea-formaldehyde reaction is
 also controlled by the mole ratio of the reactants  and  the  dilution of the
mixture (Kirk-Othmer,  1978b;  Tallard and Caron, 1977a).

     Urea-formaldehyde grouts have a low vi scosity.   Urea  solutions
 (unpolymerized) have viscosities similar to acryl amides  and phenol ics (Karol,
1982a).   Solutions of  urea-formaldehyde prepolymers  are  more viscous, having
typical  viscosities of 10 to  13 centipoise  (Karol,  1982a;  Sommerer  and
 Kitchens,  1980).

     The set time varies with the type of grout formulation and  the type of
catalyst.   Monomer grouts have a very short  set time because  the  reaction  is
 abrupt.   To  achieve more control  over the set time,  prepolymer grouts are
used, however,  this increases the viscosity of  the grout and  makes  the grout
unsuitable for fine soils.  Depending on the catalyst, the  set time, may  vary
from several  minutes (hydrochloric acid)  to  almost an  hour  (sulfuric  acid).
The proportion  of the  catalyst and the  dilution of the grout  will  also affect
the set  time (Tallard  and Caron, 1977a).
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     For urea-formaldehyde grouts there is both a gel  time and  a cure  time.
The gel time refers to the time required to form a soft gel  similar to
acryl amide.  Following gellation, the grout cures to  a sti f f er  consistency.
This occurs over a few hours to as long as a day depending on the gel  time
(Karol  , 1982a).   The setting of urea-formaldehyde grouts may be slowed by
organic solvents and oils (Malone, Jones and Larson,  1980).   Cement will
prevent the setting of these grouts (Kirk-Othmer, 1979).  In general,  alkaline
materials will inhibit the polymerization reaction through destruction of the
acid catalyst.

               7.2.1.5.5  Epoxy Grouts

     Epoxy grouts are resins that consist of an epoxide, a hydroxy compound,
and a  hardener.   The epoxide is typically epichl orohydrin while the hydroxy
compound is typically bis-phenol-(2,2-bis(4-hydroxyphenol )propane (Modern
Plastics Encyclopedia, 1981; Tallard and Caron, 1977a; Billmeyer, 1971).

     Epoxies are generally cured through the addition of a hardener (Tallard
and Caron, 1977a).   These hardeners are cross-linking agents that react with
epoxy and hydroxyl  groups (Modern Plastics Encyclopedia, 1981).  The resulting
epoxy resins are polyethers (Billmeyer, 1971).   A number of  hardeners  may be
used, typically, amines, polycarboxyl ic anhydrides, or monocarboxyl ic  acids.
Each hardener reacts differently and imparts different properties to the
resin.   Different proportions between the resin and the hardener will  also
provide different types of resins.  However, the resin-hardener ratio  cannot
be varied greatly (Tallard and Caron, 1977a).

     As a result of the amine hardening process, amine-terminated polyamide
resins are generated.  These resins replace water on  wet surfaces creating a
water-free interface between the resin and the  material  covered (Engineering
News-Record, 1965).  For this reason, epoxy resins are useful  in applications
in wet  areas or  under water.

     The viscosity of epoxy grouts varies with  the molecular weight
(Billmeyer, 1971).   The most fluid of these resins has a viscosity of  at  least
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400 centipoise.  This viscosity may be lowered to 100 centipoise by adding a
fluid hardener (Tallard and Caron, 1977a).   Organic  solvents  and reactive
dilution substances may also be used to change the viscosity  (Sommerer and
Kitchens, 1980; Tallard and Caron, 1977a).   Ethers such as  butyl  glycidyl
ether can decrease the viscosity of epoxy grouts to  20 centipoise (Tallard and
Caron, 1977a).

     The set time of epoxy grouts varies depending on the  choice of hardener.
In general, the set time is difficult to regulate (Tallard  and Caron,  1977a).

               7.2.1.5.6  Polyester Grouts

     Polyester grouts consist of a resin base and a  catalyst  (Office of the
Chief of Engineers, 1973).  The resin is unsaturated and consists of a
polyester produced from the reaction of a polyacid and a polyalcohol.
Typically, this reaction involves the condensation of an unsaturated diacid
(maleic acid or fumaric acid) with a dialcohol.   In  commercial  products, a
reticulant is included with the polyester resin.  These products may contain
30 to 40 percent reticulant, typically styrene (Tallard and Caron,  1977a;
Billmeyer, 1971).

     Polymerization is achieved through the addition of the catalyst which is
generally a peroxide.  The catalyst causes  the polyester resin  to polymerize
as well as copolymerize with the reticulant.  A gel  forms  which eventually
hardens to a solid material (Tallard and Caron,  1977a; Office of the Chief of
Engineers, 1973).  The hardening process is accompanied by  shrinkage of the
resin by as much as 10 percent (Office of the Chief  of Engineers, 1973).

     Accelerators may be added to speed up the setting by  facilitating the
decomposition of the catalyst into free radicals (Tallard  and Caron, 1977a;
Office of the Chief of Engineers, 1973).  Accelerators include cobalt,
manganese, or vanadium salts, mercaptans, tertiary amines,  and quaternary
ammonium salts (Tallard and Caron, 1977a).
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     The quantity and type of polyester, reticulant, and catalyst may each be
varied.  Each variation will  produce different resins with different
characteristics (Tallard and  Caron, 1977a).

     Commercial polyesters vary in viscosity from several  hundred to several
thousand centipoise.  The minimum viscosity  is between 200 to 250 centipoise,
however, this is too high to  grout fine earth materials such as sand.  By
adding reactive diluent, the  viscosity may be reduced to 10 to 50 centipoise
(Tallard and Caron, 1977a).

     The set time of polyester grouts varies from a few minutes to several
days.  The resins may contain volatile compounds that make long set  times
uncertain (Tallard and Caron, 1977a).  The  set time is dependent on  resin
volume, ambient temperature,  catalyst selection, and heat dissipation
(polymerization is exothermic).  In addition, excessive moisture may inhibit
the setting of polyester grouts (Office of  the Chief of Engineers, 1973).

     7.2.2  Design and Construction

          7.2.2.1  Types of Grouts

     Different types of grouts are currently available including emulsion,
polymers, and particle suspensions.  These grouts are generally water
solutions with low viscosity  which allow for easy penetration of formation
voids.  There are five major  grout types:

     •  Bitumen grouts
     •  Cement grouts
     t  Cl ay grouts
     t  Silicate grouts
     •  Organic polymer grouts.

     The most common grouts in use are cement and clay, constituting
approximately 95 percent of all  grouts used.   Silicates represent the majority
of the remaining 5 percent.  Bitumen and organic polymer grouts are  of
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relatively limited use in plume management.   A brief description  of  these
different grout types and their applications follows.

               7.2.2.1.1  Bitumen Grouts

     Bitumen or asphalt emulsions are direct emulsions  in  which water  is  the
continuous phase.   These emulsions have a  variety  of uses  including  surface
and subsurface waterproofing applications.  Emulsions are  typically  used  for
fine materials such as sand or in finely fissured  materials.   Hot bitumen
grout has been used in coarse soil formations, however,  it is  difficult to
handle (Tallard and Caron, 1977a).  Bitumenous materials appear to have
1imited use as grouts.

     Bitumen or asphalt is resistant to most chemicals.   Inorganic chemicals
(except concentrated acids), dilute acids, simple  alcohols, glycols, and
aldehydes will not affect bitumen (Puzinaurkas, 1982).   ASPEMIX®, an asphalt-
based slurry used  in vibrating beam constructed slurry  walls,  has been  found
in the short term  to be resistant to paint thinner and  hazardous  waste  site
leachate containing chemicals or brine (Slurry Systems,  1982).   In particular,
ASPEMIX appears to be a resistant coal  tar,  which  contains dimethyl-
naphthalene, methyl naphthalene, and pyrene (Drozda,  1981).

     Asphalt is not compatible with concentrated mineral acids.  Most  polar
and nonpolar solvents will dissolve asphalt  as will  chlorinated,  aliphatic,
and aromatic hydrocarbons.  Ketones and phenols may also slowly degrade
asphalt (Puzinaurkas, 1982).  Salts and organic matter  in  the  earth materials
will prevent proper formation of a seal between bitumen or asphalt and  soil.
In addition, some  salts will cause bitumen to effloresce (Ingles and Metcalf,
1973).

     Some liners  for hazardous waste sites consist of an emulsified asphalt
membrane.  These membranes are not compatible with nitric  acid or oils.  In
general, materials reported to be detrimental to emulsified asphal t membranes
include organic substances, highly ionic wastes, and waste containing  salts,
strong acids, or  strong bases (Haxo, 1980).
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     The primary area of bitumen grout usage is for reducing the permeability
of fine sands, fine soils (e.g., clayey sands), or finely fissured  rock.   This
type of grout is not generally suitable for coarse soils because a  poorly
gelled grout may draw away from the coarse material  resulting in an
ineffective seal (Tall and and Caron, 1977a).  Bitumen grout may be  applied in
combination with cement (Bowen, 1981).

               7.2.2.1.2  Cement Grouts

     Cement has probably been used longer than any other type for grouting
applications (Bowen, 1981).   Cement grouts utilize hydraulic cement which
sets, hardens, and does not disintegrate in water (Kirk-Othmer, 1979).
Because of their large particle size, cement grouts are more suitable for rock
than for soil  applications (Bowen, 1981).  However, the addition of clay  or
chemical polymers can improve the range of usage.  Cement grouts have been
used for both soil  consolidation and water cut-off applications, but their use
is primarily restricted to more open soils.  Typically, cement grouts cannot
be used in fine-grained soils with cracks less than 0.1 millimeter  wide
(Bowen, 1981).

     Cement grout may be applied to fractured rock (w'ith voids of sufficient
size to ensure penetration of the grout) for underpinning and constructing a
variety of structures (Bowen, 1981; Ki rk-Othmer, 1979).  Type I Portland
cement may be used for materials with large voids.  Resin and gypsum cements
are used by the oil well cementing industry for rapid water seal-off
applications (Bowen, 1981).

     Materials may be added to cement grouts to improve their applicability.
Sand may be added to portl and cement to create a grout suitable for coarse
materials (Bowen, 1981).  Bentonite may be added to improve the penetration of
cement in alluvial  soils (Sol entanche, no date).
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               7.2.2.1.3  Clay Grouts

     Clays have been widely used as grouts, either  alone or in  formulations
because they are inexpensive (Guertin  and  McTigue,  1982).   Only certain  types
of clay minerals, however, possess the physical  and chemical  characteristics
favorable for use in grouting.  These  characteristics  include the  ability  to
swell in the presence of water and to  form a gel  structure at low  solution
concentrations.  These properties are  possessed most markedly by the
montmoril lonites.  Other types of clay mineral s,  such  as kaolinite and illite,
can be used as fillers in grout formulations, such  as  clay-cement  mixtures
(Greenwood and Raffle, 1963).

     Local deposits of clay will contain a mixture  of  clay minerals which,
depending on their proportions, can be utilized  as  a grout material  either
directly or in mixtures.  Many local  clays require  some type of treatment  in
order to remove large particles that would reduce the  effective distance that
the clay could penetrate into a formation.  Instead of using locally derived
material, pure montmorillonite or bentonite can  be  utilized.

     Bentonite grouts alone can be used as void  sealers in coarse  sands with
a permeability of more than 10  ft/day (10   cm/sec).   Bentonite-chemical
                                                                         2
grouts can be  used on medium to fine sands with  a permeability  between 10
ft/day (10"1 cm/sec) and 1 ft/day (10    cm/sec).   Both of these grout types
can  also be utilized to seal  small rock fissures (Guertin and  McTigue, 1982).
Because of their low gel strengths, bentonite grouts are not able  to support
structures and therefore can only be used  as void sealers (Tallard and Caron,
1977b).

               7.2.2.1.4  Silicate Grouts

     Alkali silicates are the largest and most widely used type of chemical
grouts.   Sodium, potassium, and lithium silicates are available with sodium
silicates being  used most frequently.   Chemical  grouts  (i.e., silicates and
organic  polymers) constitute  less than 5 percent by volume of the grouts  used
in the United  States although they represent almost 50  percent  in Europe
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(Kirk-Othmer, 1979).   In  addition  to  their  use  as  a  grout,  sodium  silicates
may be used as additives  to other  grouts, such  as  Portland  cement,  to  improve
strength and durability (Hurley and Thornburn,  1971).

     Silicate grouts are  used for  both soil  consolidation and  void  sealing
applications.  These grouts are suitable for subsurface applications  in  soils
                                               2
with a permeability of less than 10 ft/day (10    cm/sec).  Silicate grouts  are
not suitable for open fissures or  highly permeable materials,  because  of
syneresis, unless they are preceded by cement grouting (Karol , 1982a;  Sommerer
and Kitchens, 1980).  Furthermore, tests conducted by  the Waterways Experiment
Station found silicate grouts to be ineffective in waterproofing  fine-grained
soils (Hurley and Thronburn, 1971).

     Silicate grouts are  resistant to moderate  amounts of acids or alkalies
(Kirk-Othmer, 1979).  These grouts are also resistant  to  high  concentrations
of chromic, nitric, and sulfuric acid (Boova, 1977).  Organic  esters  have
little effect on silicate grout (Bowen, 1981).   Sil icate mortar is  similar  to
silicate grout but contains fillers such as silica,  quartz, or ganister.  This
mortar is resistant to most acids  (except hydrofluoric acid) as well  as
neutral salt solutions (ASTM, 1982).

     Silicate grouts gel  through the action of acids or acid salts.  Hurley
and Thornburn (1971) and  Karol  (1982a) report that the setting time of
silicate grouts may be significantly decreased  in  the  presence of soils  or
groundwater with appreciable salt  contents.  These effects may be mitigated by
using the groundwater to mix the grout.  Acidic soils  may also decrease  the
gel time (Karol  , 1982a).

     Silicate grouts are not compatible with a  number  of materials.  Gel time
and grout strength may be affected by large amounts  of acid or alkali  (Kirk-
Othmer, 1979).  Additionally, organic materials and  high concentrations  of
some metals will slow the setting  time (Malone, et al  ., 1980).
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               7.2.2.1.5  Organic Polymer Grouts

     Organic polymer grouts represent only a small  fraction  of the  grouts in
use.  These grouts consist of organic materials (monomers) that  polymerize and
cross-link to form an insoluble gel.   The organic  polymer grouts include:

     •  Acryl amide grouts
     t  Phenolic grouts
     •  Urethane grouts
     t  Urea-formaldehyde grouts
     •  Epoxy grouts
     •  Polyester grouts.

     Acryl amide Grouts--Ac ryl amide grouts have been in  use  for about  30  years,
and were the first of the organic chemical  polymer  grouts to be  developed.
Acryl amide grouts have the largest use among the  organic  polymer grouts  and
are the second most widely used chemical  grouts (Karol , 1982a).   They may be
used alone or in combination with other grouts such as  silicates, bitumens,
clay, or cement (Tallard and Caron, 1977a).

     AM-9® was the first acryl amide grout developed,  however, it was  removed
from the market in 1978 because of the toxicity of  one of its components
(Karol, 1982a).  There are only a few acryl amide  or acryl amide-based  grout
products available and a number of them are imported.   These grouts include
acryl ates, polyacryl amides, and acryl amide derivates.   Some  grouts, such as
Rocagil 1295®, are not used in  the United States  (Karol,  1982a).  Although
AM-9 was removed from the market, it has been used  as  recently as 1980 in
water cut-off applications (Berry, 1982).  A number of  acryl amide grouts that
were similar to AM-9, have been imported and marketed  after  AM-9's  removal
(Karol, 1982a).  AM-9 is probably the most studied  of  the acryl amide  grouts
and because of the similarity of the materials and  the  reaction  mechanisms,
much of the AM-9 data is valid  to other acryl amide  grouts (Karol, 1982a).

     The use of acryl amide and  acryl amide-based grouts  is greater in  the
United States than in Europe where phenolic grouts  are more  common.  Acrylic
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and polyacryl amide grouts are typically used in ground surface  treatment,
ground treatment for oil  well drilling, and subsurface applications (e.g.,
waterproof concrete structures).  Acryl ate grouts are more commonly used  for
ground surface treatment than for soil  injection where acryl amide grouts  are
more frequently used.  Acryl amide applications include structural  support  and
seepage control for mines, soil  consolidation for foundations of structures
and dams, and water control  and soil  consolidation for tunnels, wells, and
mines (Tallard and Caron, 1977a).  Specific applications include grout
curtains, loose sand stabilization, artesian flow shut-off, and water seepage
control  in jointed and fissured rock (Office of the Chief of Engineers, 1973).
Based on AM-9 applications, acryl amide grouts may be used in  a  variety of  soil
materials such as fine gravel; coarse, medium, or fine sand;  coarse silt;  and
some clays (Herndon and Lenahan, 1976b).

     All of the acryl amide grout formulations contain substances that are
toxic and require special handling (Berry, 1982; Geochemical  Corporation,
1982; Tallard and Caron, 1977a).  While the gelled grouts or polymerized
acrylamides are reported to be non-toxic, unreacted toxic monomer or other
substances can leach from the grout matrix if the polymerization process  is
not complete (Tallard and Caron, 1977a).

     Many groundwater contaminants (e.g., acids, alkalies, salts)  will have
little effect on acryl amide grouts, particularly if dilute and  the groundwater
is  used to mix the grout (Clarke, 1982; Avanti International, 1981; Kirk-
Othmer, 1979).  Acryl amide grouts are impermeable to gases and  hydrocarbon
solvents such as kerosenes (Office of the Chief of Engineers, 1973).  Toluene,
heptane, and dilute hydrochloric acid (2 percent) also do not have effect  on
acryl amide grouts (Berry, 1982).  They are also unaffected by 10 percent
solutions of alcohols, ketones, hydrocarbons, acids, and metal  salts (Clarke,
1982).

     Some salts and pH will affect the setting time of acryl amide grouts
(Caron, 1963).  Low pH conditions (less than 6.5) can prevent acryl amide
grouts from setting.  Polymerization inhibitors such as sodium  nitrates and
metallic salts can also delay gelation (Avanti International, 1981; Office  of
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the Chief of Engineers, 1973).  Alkaline conditions or metal  ions,  such as
iron, copper, zinc, or tin can shorten the gelation time (Avanti  Inter-
national, 1981; Tallard and Caron, 1977a).  Other gel  time accelerators
include hydrogen sulfide and soluble salts such as Nad , CaCl  ,  sul fates, and
phosphates (Karol , 1982a; Office of the Chief of Engineers,  1973).

     The durability of acryl amide grout is affected by highly  alkaline  media.
Such media can promote saponi fication of the grout, particularly  the monomer
(Sommerer and Kitchens, 1980;  Tallard and Caron, 1977a), which will  affect  the
performance of the grout (Tallard and Caron, 1977a).   Herndon  and Lenahan
(1976b) report that sul fides affect AM-9 grout, but the  effect is not
specified.  Strong or concentrated hydrating and dehydrating  agents  will  have
the greatest impact on acryl amide grouts.  For example,  acryl amide grouts will
swell  in the presence of sulfuric acid, sodi in chloride, sodium  sulfite,
sodiun hydroxide,  and laundry  detergent.  Alcohols and glycols will  cause the
grout to shrink by drawing out the water (Berry, 1982).

     Phenolic Grouts—The use  of phenolic resin grouts in  underground  and
foundation construction began  in the 1960's (Kirk-Othmer,  1979;  Tallard and
Caron, 1977a).  These grouts may be used in fine soils and sands  for a  variety
of water control  and ground treatment applications.   However,  phenolic  grouts
are not widely used aTone but  are typically used in conjunction  with other
grouts (Tallard and Caron, 1977a).  Phenolic resin mortars are recommended  for
use with organic acids, wet gases (reducing), nonoxidizing and nonreducing
gases, and nonoxidizing mineral  acids except hydrofluoric  acid and  highly
concentrated sulfuric acid.  These recommendations are based  on  immersion of
the mortar (ASTM,  1982).

     Phenolic resins are not resistant to alkali (Boova, 1977).   Both  strong
acids and bases will  attack phenol-formaldehyde resins (Billmeyer,  1971).
Phenolic resin mortars are not recommended for use with  bleaches  or  wet gases
(oxidizing), but they are recommended for limited use with oxidizing mineral
acids, inorganic alkali, and organic solvents (ASTM,  1982).   Phenol-
formaldehyde resins are resistant to most organic solvents (Billmeyer,  1971).
                                     7-88

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     Phenolic grouts are used in soils of high permeability such as fine
gravel  and coarse, medium, and fine sand (Sommerer and Kitchens, 1980;  Herndon
and Lenahan, 1976b).  These grouts have been  used to stop leaks in  railway
tunnels and for ground surface treatment (Flatau, Brockett and Brown, 1972;
Tall ard and Caron, 1977a).  Phenolic grouts find their greatest use in
combination with silicate grouts in treating  fine sands and silts (Tallard and
Caron, 1977a).

     Different phenolic grout products have been formulated to meet different
needs.  For example, Geoseal MQ-4® was designed for resistance to saline
groundwater, Geoseal MQ-14 was designed for treating low permeability
materials, and Terranier C® was designed for  silts (Bowen, 1981).

     Phenolic grouts are limited however in that they contain toxic and
caustic materials which require special handling (Karol , 1982a; Tallard and
Caron, 1977b).

     Urethane Grouts--Urethane grouts are the second most commonly used type
of organic polymer grout  (Jacques, 1981).  Urethane grouts were developed in
Germany for consolidation applications and are now used  in Europe, South
Africa, Australia, and Japan  (Sommerer and Kitchens, 1980).  These grouts are
used for water and soil applications and can penetrate finely fissured
material.

     If properly formulated,  urethane grouts resist most chemical and other
degradative processes.  Urethane grouts are reported to  have good resistance
to oxidation, shrinkage from  drying, and biological agents, although some
shrinkage of the grout may  occur in response to water table fluctuations
(Avanti International,  1982;  Billmeyer, 1971).

     While the prepolymer used  in urethane grouts is flammable, this type of
grout  is relatively nontoxic  (Berry, 1982; Avanti International, 1982; Mobay
Chemical Corporation, 1982).  Most of the grouting formulations contain some
free toluene diisocyanate,  hence, special  handling and protective equipment
                                     7-89

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are needed when working with the grout materials because they are eye, skin,
and respiratory irritants (Berry, 1982; Avanti International, 1982).

     Urethane grouts have been used for a number of water and soils applica-
tions.  Some formulations have been used for consolidation in coal  mines and
railroad tunnels (Mobay Chemical  Corporation, 1982).  Other formulations are
primarily used for sewer grouting and pipe sealing (Avanti International,
1982).  CR-250® has been used for potable water applications as well as for
soil sealing and waterproofing applications (Jacques, 1981).

     TACSS®, a urethane grout produced in Japan, has been used for  treating
rivulets in karstic materials and for consolidating and waterproofing ground
through which large volumes of water circulate (Tallard and Caron,  1977a).
Because of the high viscosity of this formulation (and by analogy,  other
urethane grouts), TACSS cannot be used to treat fine-grained soils  (Karol ,
1982a).

     Urea-Formaldehyde Grouts--Urea-formaldehyde resins are frequently
referred to as aminoplasts.   The idea for the use of these resins as grouts
came from their use as glue in the oil  industry (Tallard and Caron, 1977a).
Although urea-formaldehyde grouts have been available since the 1960's, they
have found limited usage (Karol, 1982b;  Sommerer and Kitchens, 1980).  These
grouts can only set-up in an acid environment, therefore, they cannot be used
in basic formations.

     Urea-formaldehyde grouts are considered to have good stability (Karol,
1982a).  If the grout is properly formulated and a good polycondensation
reaction is achieved, the resulting resin should be inert and insoluble to
most solvents although it will  contain some free formaldehyde (Karol, 1982a;
Tallard and Caron, 1977a).  However, these grouts may quickly break down when
subjected to cyclic wet and dry or freeze and thaw cycles (Karol, 1982a).
Fung (1980) reports that some urea-formal dehyd e resins are also biodegradable.

     Solutions of urea-formaldehyde grout are both toxic and corrosive because
they contain formaldehyde and an acid catalyst.  However, solutions using
                                     7-90

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prepolymers have less free formaldehyde (Karol ,  1982a; Tall ard  and Caron,
1977a).  The cured resin has low toxicity and considered inert, but it does
contain some unreacted formaldehyde (Kirk-Othmer, 1978b; Tall ard and Caron,
1977a).

     Because of the acidity requirements, urea-formal dehyde grouts have under-
gone little development (Tall ard and Caron, 1977a).   They have  been used for
ground stabilization and for sealing coal  mines but  long-term applications
have not been reported (Karol, 1982a; Tall ard and Caron, 1977a).  These grouts
can generally be used only in ground and groundwater with a pH  less than 7.
Their development has been further limited because of their toxic constituents
and the production of ammonia during condensation (Sommerer and Kitchens,
1980).

     Most of the descriptions of urea-formal dehyde grout applications come
from Eastern Europe, the USSR, and Japan.  Products  containing  prepolymers
have been used in Poland and Hungary.  Injection of an acid solution to
destroy carbonates before grouting has been used in  the USSR to minimize high
pH media problems.  However, this technique is not used widely  because it  is
costly and increases the size of soil voids.  Further, more soil imbalances
may be created through the destruction of soil  components (Tallard and Caron,
1977a).

     Epoxy Grouts--Epoxy grouts and other glue-like  grouts have been in use
since 1960.  These grouts have had limited use in soil grouting primarily
because of their high cost (Tall ard and Caron, 1977a).  Most of the applica-
tions reported in the literature involve the use of  epoxy resins in mortars
and for sealing cracks.  Epoxy resins can adhere to  and seal  submerged
concrete, steel, or wood surfaces and are useful  in  water applications
(Engineering News-Record, 1965).  They have been used for grouting cracked
concrete for structural repairs and grouting fractured rock to  improve its
strength (Office of the Chief of Engineers, 1973).

     Epoxy grouts exhibit good durability.   In the ground, their properties
are similar to those of polyester grouts in that they may be subject to
                                     7-91

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hydrolysis (Tallard and Caron, 1977a).   Epoxy mortars  tend  to  have  little
shrinkage and limited water absorption  (U.S.  Grout  Corporation,  1981;  Boova,
1977).

     Epoxy grouts consist of substances requiring  special  handling  precau-
tions.  If the grouts are properly formulated, the  set  resin  should  incor-
porate all of the materials such that the  toxicity  of  the  gel  or  its
components is minimized (Tallard and  Caron, 1977a).

     Polyester Grouts—Polyester grouts have  been  in  use  since the  1960's.
They have been used in a variety of construction applications, principally  to
treat cracks in buildings and structures (Tallard  and  Caron,  1977a).   These
grouts have also been used in mines as  well as to  stabilize and  strengthen
porous and fissured rock (Tallard and Caron,  1977a; Office of the Chief of
Engineers, 1973).  Polyester grouts have been  used  infrequently  to  treat sand
(Tallard and Caron, 1977a).

     The long-term behavior of polyester grouts is  reported to be good,
but there is a long-term risk of hydrolysis particularly  in alkaline media
(Tallard and Caron, 1977a).  Furthermore,  these gels  shrink as much as
10 percent during curing (Office of the Chief  of Engineers, 1973).

     The components of the polyester  grouts are toxic  and  often  require
special  handling during grout preparation.  After  polymerization, the  risks
are lower although unreacted grout constituents may leach  out  (Tallard and
Caron, 1977a).

               7.2.2.1.6  Other Grouts

     There are several other grout types that  have  limited  application in
soil  and rock.  The two major types are lignochrome and furan  grouts.

     Lignochrome grouts are also referred  to  as 1 ignosul fonate or chrome! ignin
grouts.   This type of grout consists  of a  1 ignin-containing material  and a
hexavalent chromium salt (Kirk-Othmer,  1979;  Ingles and Metcalf,  1973).
                                     7-92

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Calcium 1 ignosul fates provide better waterproofing and stability than  sodium
1 ignosul fates (Rogo shews ki , et al., 1980).   Ammonium 1 ignosul fonate  is also
used occasionally (Sommerer and Kitchens, 1980).  Potassium dichromate may be
used as the hexavalent chrome salt (Ingles  and Metcalf,  1973).

     Lignochrome grouts typically have low  viscosity (2  to  15 centipoise)  and
moderately short setting times -(3 to 300 minutes).  The  durability of  these
grouts is questionable.  Their strength generally decreases over time  in
water-saturated environments (Kirk-Othmer,  1979).  Also, chromium can  be
leached from the set grout depending on the age of the grout, the chrome-
lignin ratio, the acidity (pH), and the curing time (Sommerer and Kitchens,
1980; Office of the Chief of Engineers, 1973).

     The application of 1 ignochrome grouts  is limited because the chromium
salts used in 1 ignochrome grouts are toxic  and the lignin materials  can cause
skin irritation.  Lignochrome grouts should not be used  with Portland  cement
because the pH of the materials conflict (Kirk-Othmer, 1979).  Furthermore,
1 ignochrome grouts are not compatible with  fly ash because  the  fly ash's
alkalinity can cause trivalent chromiun to  precipitate from the dichromate
catalyst (Chung, 1973).

     Lignochrome grouts have been used primarily for water  cut-off and
consolidation of fine, granular soils (Office of Chief of Engineers, 1973).
However, they can be used in sands with a permeability between  102 to  1 ft/day
   -1      -3
(10   to 10   cm/sec) (Sommerer and Kitchens, 1980).  Although, 1 ignochrome
grouts had been used in water cut-off applications for dams, their use is  rare
and they are not manufactured in the U.S. (Engineering News Record,  1953).

     Furan grouts consist of simple polymers of furfuryl  alcohol  dissolved in
excess furfuryl  alcohol.  They are used primarily as mortars in which  the
liquid resin is mixed with an inert powder  filler (usually  carbon) containing
an acid catalyst.  This catalyst promotes further polymerization  to  form a
cross-linked, infusible material  (Boova, 1977).  Furan mortar grouts have
excellent resistance to a broad  range of chemicals including organic and
inorganic acids, alkalies, salts, greases,  and solvents  (Boova, 1977).
                                     7-93

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However, in general  they are not recommended for use  with oxidizing  acids or
with chromic acid (20%), nitric acid,  sodium hypochlorite (10%),  or
concentrated sulfuric acid (Boova,  1977;  ASTM,  1982).

     Furan resin grouts are used primarily in applications  where  resistance to
corrosive media is important.  They are also used  for  polymer  concrete,  in
which alkali-free aggregate (silica or  quartz)  is  bonded  with  furan  resins and
cured with an acidic catalyst.   This concrete is resistant  to  acids,  salts,
solvents, and bases (Modern Plastics Encyclopedia,  1981).

     Several other types of grouts  have been referenced with regard  to  soil
applications, the majority of which are polymers.   One such grout, Polythixon
FRD®, is an oil-based unsaturated fatty acid polymer.  Polythixon  FRD has low
viscosity (10 to 80 centi poise) and a  gel  time  of  25 to 360 minutes.  This
grout is recommended for high strength  consolidation  rather than  waterproofing
applications (Neelands and James, 1963).

     Another polymer grout is PWG®  sealant,  a polymerized cross-linked  gel of
an unspecified polymer.  This grout has a very  low viscosity (1.5  centi poise)
and a very short set time (several  seconds to a few minutes).   The  set  gel is
insoluble in water,  kerosene, and oil,  and impermeable to water, oil, and gas.
If the gel  dehydrates, it can rehydrate in the  presence of  water  to  regain its
original  size.  In addition, this gel may undergo  "wicking," i.e., if one face
of the gel  dehydrates, moisture can move from the  hydrated  face to the
dehydrated face (Lenahan, 1973).

     Anil ine-furfural  resins may be used  for the stabilization of cohesion-
less sand.   These resins are catalyzed  by pentachl orophenol or ferric chloride
(Bowen, 1981).  Emulsions such  as latex and  salt water, styrene butadiene
latex, and pitch polyurethane mixtures  may also be  used as  grouts  (Bowen,
1981).  Base-cured materials have been  investigated for use as grouts,
however, these materials do not have low viscosities or other  characteristics
that lend them to pumping or injection  at pressures (Rensvold, 1968).
                                     7-94

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          7.2.2.2  Grouting Preparation

     This section discusses some of the considerations that must be addressed
prior to actual grout injection.  Because grouting is seldom considered for
restricting leachate flow in unconsol idated materials, particular emphasis is
placed on preparation for rock grouting.  Many of these concerns also apply to
soil grouting.

     As with other types of barrier construction, the ultimate success of a
grouting project depends on thorough site characterization.  The ability to
seal water bearing voids or zones is dependent on being able to locate them.
In many remedial grouting operations, only a small portion of the rock mass
will transport water and must be sealed.  Consequently, the exploratory
investigation must be very thorough.  Detailed geologic mapping of the site,
aided by ranote sensing techniques and extensive  rock coring, is required.
Even with extensive investigation, the complexity of groundwater flow in
fractured and fissured bedrock can make a grouting project impossible to plan
in advance.

     Based on the background and ex pi oratory data, the location for a pattern
of primary injection holes is chosen and injection at one or more zones is
identified.  The  first few primary holes are then drilled and pressure washed
with water and air (Millet and Engelhardt, 1982).  This step removes drill
cuttings and other debris from the hole to allow better grout penetration.
Each hole is then pressure tested, often using a  non-setting fluid of the same
viscosity as the  grout to be used.  These tests are used to determine the
initial grout mixture and are often conducted using the grout plant and other
equipment to be used for the actual grouting (Millet and Engelhardt, 1982;
Karol , 1982).

     Each zone within each primary hole is then injected with the grout
mixture until a predetermined amount is pumped (grout take), or a
predetermined  flow rate at maximum allowable pressure is reached.  Maximum
allowable pressure is typically around 1 pound per square inch (psi) per foot
of overburden  (Millet and Engelhardt, 1982).  Data from the drilling and
                                     7-95

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injection of the first primary holes is analyzed,  and  if necessary,  the  grout
mixture or injection pressure modi fied before completing the remaining  primary
holes.  Following completion of the primary hole grouting,  the  program  is
again analyzed, necessary changes made, and  a pattern  of more closely  spaced
secondary holes drilled and injected.

     The analysis and evaluation of the completed  grouting  becomes,  in
essence, another pressure test.   Close quality control  during drilling  and
grouting identifies areas that require tertiary hole grouting to  complete
sealing.  Such areas are identified by faster than expected drilling  rates  and
higher than expected grout takes (Millet and Engelhardt, 1982).   For a
successful grouting program, each hole series (i.e., primary, secondary)  will
have lower grout takes than the  previous one.  Many projects will  require that
proof holes be drilled and injected.   A very low grout take on  tertiary  or
proof holes indicates that most  voids  are grout filled and  the  grouting
program was successful.

     A variety of methods are in use for actual  grout  injection,  and many
types of grout are in use.  The  following sections describe grout injection
techniques and selection techniques.

          7.2.2.3  Grout Injection

     Grouting methods combine two processes—mixing and injection.   Chemical
grouts are prepared by either batch mixing or by continuous mixing  systems
based on metering or  proportioning  pumps.  Continuous mixing systems permit
better control over the injection process since short gel  times can  be  used.
Typical gel times used with batch systems are several  hours, whereas gel  times
used with continuously mixed systems are usually 10 to 20 minutes.   Thus, the
formation of large  pools of ungelled grout in the ground is avoided.
Additionally, long gel time grouts can become diluted and wash  away before
gellation occurs.   Batch mixing can probably be used without difficulty in
most soil grouting projects, but greater control  is afforded by the  use of
short gel times (Hayward Baker et al., 1980).  Mixing methods are dependent
upon the  size of the  project in relationship to the grouting materials  used
                                     7-96

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and the equipment available.  A larger project would most likely require a
continuous mixing system as opposed to a batch system to ensure that correct
grout specifications are met throughout the site in a relatively short period
of time.

     Construction of a grout barrier is accomplished by pressure injecting the
grouting material through a pipe into the strata to be waterproofed.  The
injection points are usually arranged in a triple line of primary and
secondary grout holes (Figure 7-14).  A predetermined quantity of grout is
pumped into the primary holes.  After the grout in the primary holes has had
time to gel , the secondary holes are injected.  The secondary grout holes are
intended to fill in any gaps left by the primary grout injection (Hayward
Baker et al ., 1980).  The primary holes are typically spaced at 20- to 40-foot
intervals (Guertin and McTigue, 1982).

     There are  several basic techniques that are utilized to form the grout
wall.  These include (Hayward Baker et al., 1980; Guertin and McTigue, 1982):

     t  Stage-up method
     •  Stage-down method
     •  Grout-port method
     0  Vibrating beam method.

In the stage-up method, the borehole is drilled to the full  depth of the wall
prior to grout  injection.  The drill is withdrawn one "stage," leaving several
feet of borehole exposed.  Grout is then injected into this  length of open
borehole until   the desired volume has been injected.  When injection is
complete the drill is withdrawn further and the next stage is injected
(Hayward Baker et al ., 1980).

     Stage-down grouting differs from stage-up grouting in that the injections
are made from the top down.  Thus, the borehole is drilled through the first
zone that is to be grouted, the drill is withdrawn, and the  grout injected.
Upon completion of the injection, the borehole is redrilled  through the
                                     7-97

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                                                       FIGURE 7-14.

                               GROUTING PIPE LAYOUT FOR CONSTRUCTING A BARRIER WALL

                              (HAYWARD BAKER et al., 1980 AS CITED BY SPOONER et al, 1984b)
i
10
CO
                                                                                     o-—^
                                                                                       Basic Cell
                                                                                                 Primary Grout Pipe
                                                                                                          o
                         o
                                                                                              Secondary Grout Pipe
                                Secondary Grout Ball
Primary Grout Ball

-------
grouted layer into the next zone to be grouted and the process is repeated
(Guertin and McTigue, 1982).

     The grout-port method utilizes a slotted injection pipe that has been
sealed into the borehole with a brittle Portland cement and clay mortar
jacket.  Rubber sleeves cover the outside of each slit (or port) permitting
grout to flow only out of the pipe.  The injection process begins by isolating
the grout port in the zone to be injected using a double packer.  A brief
pulse of high pressure water is injected into the port to rupture the mortar
jacket.  Grout which is pumped between the double packers, passes through the
ports in the pipe, under the rubber sleeve, and out through the cracked mortar
jacket into the soil  (Guertin and McTigue, 1982).  This grouting process is
illustrated in Figure 7-15 and a detailed diagram of the double packer is
shown in Figure 7-16.

     The vibrating beam method is not an injection technique as described
above, but instead is a way of placing grout in such a way as to generate a
wall.  In this method, an I-beam is vibrated into the soil  to the desired
depth and then raised at a controlled rate.  As the beam is raised, grout is
pumped through a set of nozzles mounted in the beam's base filling the newly
formed cavity.  When the cavity is completely filled, the beam is moved along
the direction of the wall, leaving a suitable overlap to ensure continuity
(Harr, Diamond and Schmednecht, unpublished).  Figure 7-17 shows the steps
involved in forming a vibrating beam cut-off wall.

          7.2.2.4  Grout Selection

     The physical and chemical properties of grouts that determine the type
that should be used at a specific site include (Herndon and Lenahan, 1976a):

     •  Viscosity
     •  Setting time
     •  Permeability
     •  Strength
                                     7-99

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                     FIGURE 7-15.
    STAGE-UP GROUT-PORT INJECTION PROCESS
            (HAYWARD BAKER et al., 1980)
                                            Grout Rod
Grout Pipe
(PVC Pipe
with Grout
Ports)
                                           Double Packer
                                           on Grout Rod
                                                   Mortar Jacket
                                                Rubber
                                                Sleeves
                                                over Grout
                                                Ports on
                                                Grout Pipe
                         7-100

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                FIGURE 7-16.
DIAGRAM OF A DOUBLE PACKER USED IN
         GROUT PORT INJECTION
      (GUERTIN AND McTIGUE, 1982)
                                   Double Packer
                                   Wall of Grout Hole
                                   Semi-plastic Sealing
                                   Sheath
                                   Pipe Sealed into Hole


                                   Rubber "Manchette"


                                   Grouting Orifice


                                   Grouting Pipe


                                   Double-Packer
                      7-101

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                                  FIGURE 7-17.
                VIBRATING BEAM GROUP PLACEMENT PROCESS
            (BOYES, 1971, AS CITED BY GUERTIN AND McTIGUE,  1982)
Grouted .
Sections
(shaded)

1
1

1
1
— *
1 r
'Q^sXXV
fc
r
P
^
w\ w\\\\\. \
y
i
' (typ.)
                      Tfa&fr
                         a. Insertion of Single Injection Beam
                                                               10-12 cm
     Extracting
     Last Beam

Grouted
 Zone
(shaded)
1-
 Inserting
Lead Beam

                         b. Use of Multiple Injection Beams
                                                                         Grout Tubes
                       LZIiq^tJMHMH
                                                          Grouted
                                                           Zone
                                    Inserted Clutch
                                      of Piles
                                      7-102

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     •  Stability
     t  Toxicity.

     The viscosity of a grout will control  its ability to penetrate the voids
in the soil  or rock structure (Tall and and Caron, 19775).  Grout viscosity can
also contribute to the effectiveness of the groundwater cut-off wall.  For
example, if the initial viscosity is too low, all of the soil  or rock voids
may not be completely filled and holes in the wall may develop.  Conversely,
if the viscosity is too high, the grout may not be able to penetrate all  of
the strata, potentially resulting in wall openings (Tallard and Caron, 1977b).
Low viscosity grouts, such as chemical grouts, can be used in  fine soils
                                      ?            c
having a permeability greater than 10   ft/day (10   cm/sec).   High viscosity
grouts can generally only be used in coarse-grained soils or in fractured rock
                                                               _2
having a coefficient of permeability greater than 10 ft/day (10   cm/sec)
(Sommerer and Kitchens, 1980).

     After a grout is mixed, its viscosity will generally increase with time
until  it gels or solidifies.  This change in viscosity will control both the
time period during which the grout can be pumped  and the distance which the
grout can travel through the soil or rock formation.  If the setting time of
the grout is too short, it will  be too viscous to move far enough into the
soil or rock structure.  Conversely, if the grout has too long a setting time,
the grout may filter down past the target zone (Tallard  and Caron, 1977b).
For suspension grouts, the setting time is a function of the water to
particulate ratio and the temperature.  As the water to  particul ate ratio is
increased, the grout viscosity,  set time, and pumpabil ity will  also increase.
For chemical grouts, the set time will be a function of  the ratio of chemicals
used and the temperature (Sommerer and Kitchens, 1980).

     Grout strength can determine the long term mechanical stability of a
grout cut-off wall.  The grouted soil or rock mass must  have enough strength
to  resist hydrostatic  forces (Tallard and Caron,  1977b).  The long-term
durability of the wall is critical if the groundwater barrier is to be
maintained over extended periods of time.  Any chemicals contained within the
soil mass or in the groundwater must not affect the grout's set time or its
                                     7-103

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ability to set fully.   If the set time is varied, the  finished wall  may not be
continuous or will  contain weak spots.  Also, the grout must be able to
withstand long-term contact with chemicals in the groundwater without any
deterioration (Sommerer and Kitchens, 1980).

     Since grouts used to form waterproof barriers come in contact  with
groundwater, the toxic properties of their ingredients should be considered.
The toxicity of the grout has to be examined from two  aspects—the  toxicity of
the grout's components and the toxicity of the hardened grout (Sommerer and
Kitchens, 1980; Tallard and Caron, 1977b).  If the compounds contained in the
grout do not react fully, they can contaminate the groundwater.  This happened
in Japan in 1974 when  groundwater was contaminated by  acryl amide monomer from
a chemical grout used  in the construction of a sewer system.  This  contami-
nation led to subacute poisoning of local  inhabitants  (Ando and Makita, 1977).
Hardened grout can also release potentially toxic compounds through syneresis
of the grout (Sommerer and Kitchens, 1980).

     The selection of the proper grout will depend not only on the  physical
and chemical properties of the soil or rock strata but also on such factors as
grout availability, costs, local experience, and groundwater flow and
chemistry (Guertin and McTigue, 1982).  Thus, grout selection is a  very site
specific process.  In  the selection of a grout to be used at hazardous waste
disposal sites, the most important factor to be considered is its
compatabil ity with chemicals found in the groundwater  and in the soil at the
disposal site.

     7.2.3  Grouting Costs

     The drawbacks to grout usage  stem from the fact that grouting  is
conducted by a limited number of firms in the United States and involves
special techniques and equipment.  In most cases, a substantial equipment
mobilization fee must be paid.  Equally important is the cost of
characterization and testing that must be  performed to ensure effective
grouting.  A final consideration is the cost of the grout itself.  Approximate
costs of grouts are found  in Table 7-10.
                                     7-104

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                                 TABLE 7-10
             APPROXIMATE COSTS OF GROUTS (Spooner et al ., 1984)
               Grout type                 Approximate cost
                                  $/gallon of solution (1979)
               Portland  cement                  0.95
               Bentonite                        1.25
               Silicate  -  20%                   1.25
                        -  30%                   2.10
                        -  40%                   2.75
               Epoxy                          $30.00
               Acryl amide                       6.65
               Urea  formaldehyde                5.70
     Individual  grout  costs  can  show  a  wide  variation, whereas, grout costs
for a complete job show much less  variation.   This  is because  the cheaper,
particulate grouts are used  to  seal large  voids,  thus using more grout, while
the more expensive, chemical  grouts are commonly  used to  seal  small voids.
                                     7-105

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                                   CHAPTER 8
                             INNOVATIVE TECHNOLOGIES
8.1   Introduction

      The techniques presented in this chapter are relatively new or novel
ideas that have seen limited use at hazardous waste sites with contaminated
groundwaters, hence the use of the term "innovative technologies."  The
innovative technologies presented in this chapter include bioreclamation, in
situ  chemical treatment (e.g., soil flushing, polymerization, permeable
treatment beds), and block displacement.  Because this group of technologies
has not been widely used or accepted, the amount of information available for
each  varies widely.  Therefore, attempts have not been made to make the
contents of this chapter parallel the other technology volumes (Chapters 5, 6,
and 7).  The reader is advised that because these technologies are relatively
untested and unproven compared to the more established techniques presented
previously, they will require more extensive research and development before
they  can be confidently implemented at hazardous waste sites.

      Most of the techniques presented originated as methods to treat con-
taminated surface waters or spill sites, and have been modified for the in
situ  treatment of groundwater.  In general, these technologies have many
limitations associated with their use, and they may be most useful in the
treatment of groundwater residuals and in cases where a prevalence of one type
of contaminant exists, such as a biodegradable organic compound or a toxic
metal.

      Although bioreclamation techniques may be the furthest along in develop-
ment  and testing to fulfill this need, using any one of these innovative
techniques as a sole method to control  or mitigate the migration  of a leachate
                                     8-1

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plume probably is not warranted at this time.  Most of these technologies
could be used with one of the more accepted technologies to enhance or
accelerate contaminant recovery.  The result of the combined technologies
could be faster cleanups at lowered costs.  Even within the group of
innovative technologies, a combination of these technologies nay prove to be
more effective than a single technology alone.  For example, oxidation (a
chemical treatment) may be used to break down high molecular weight organic
compounds so that they are more readily biodegraded.

     This chapter is divided into three main sections:  Bioreclamation,
Chemical Treatment, and Block Displacement.  Bioreclamation, presented first
because it appears to have the greatest potential  for treating contaminant
plumes, is stirring the most interest and controversy, and is furthest along
in development and testing.

     The bioreclamation process involves the addition of nutrients and oxygen
to the contaminated groundwater so that either the naturally occurring soil
bacteria or introduced mutant species are provided with an optimized environ-
ment for the biodegradation of the contaminants in the plume.  Bioreclamation
techniques for cleaning up contaminated groundwaters originated with work
performed to clean up gasoline.  Since then, the technique has been used at
numerous sites with gasoline contaminated groundwaters with varying degrees of
success.  With the discovery of naturally occurring microorganisms that are
capable of degrading refractory chlorinated organics and the advent of
genetically engineered microorganisms developed for specific compounds and
chemical classes, bioreclamation is expected to see increasing applications to
hazardous waste site cleanups and spills.

     The second section of the chapter deals with  those techniques that
require the injection of a specific chemical or chemicals into the plume to
either degrade, immobilize, or increase the mobility of the contaminants.  The
techniques reviewed include soil flushing (solution mining), oxidation/
reduction, precipitation/polymerization, neutralization/hydrolysis, and
permeable treatment beds.
                                     8-2

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     Soil flushing or solution mining is a technique used to remove residual
contamination from soils.  The method involves the  introduction of a  solvent
to the soil to solubilize substances adsorbed to the soil surface.  Solvents
that can be used are water, water plus a surfactant, dilute acids or  bases,
and complexing agents.  Soil flushing has the potential to be  used at
hazardous waste sites in the removal of organics and metals from soils.
Because soil flushing is used for removing residual contaminants from  soils
rather than from groundwater, it is not a true leachate plume  control
technique.

     The remaining techniques--oxidation/reduction, precipitation/
polymerization, neutralization/hydrolysis, and permeable treatment beds--
involve injecting or placing specific chemicals  in  the groundwater to,  in
theory, destroy or otherwise render harmless contaminants in the plume.  They
are applicable only to specific chemical contaminants  and have been proposed
mainly for hazardous substance spill cleanup.  Actual  use of these chemical
techniques at hazardous waste sites with contaminated  groundwater has  been
rare.

     Oxidation/reduction involves the injection  of  an  oxidizing or reducing
substance  into the contaminated groundwater.  The oxidizing agent may  alter
the oxidation state of a metal or decompose an organic to a less toxic, more
soluble, or more biodegradable form.  Reducing agents  alter the oxidation
state of metals to a less toxic or soluble form, and they may  cause a
precipitate to be formed.

     Precipitation involves the introduction of  a substance which will  form an
insoluble precipitate with the contaminant substance (usually  a metal), there-
by removing the substance from the groundwater flow regime.  Similarly,
polymerization involves injection of a catalyst  into a groundwater plume to
cause polymerization of an organic monomer.  The polymerization reaction
transforms the once fluid substance into a gel-like, non-mobile mass.

     Neutralization/hydrolysis involves injecting acids or bases into  the
groundwater plume to adjust the pH of the groundwater.  This method may be
                                     8-3

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useful as a preliminary treatment for bioreclamation, as a means to degrade
organic chemicals, as a means to prevent toxic gas formation  (such as
cyanide), as a preparation for other chemical treatments (polymerization  under
acid conditions), or as a post-treatment technique to restore natural
groundwater pH.

     Permeable treatment beds are essentially excavated trenches placed
perpendicular to groundwater flow and filled with an appropriate material to
treat the plume as it flows through the material.  Some of the materials  that
may be used in the treatment bed are limestone, crushed shell, activated
carbon, glauconitic greensands, and synthetic ion exchange resins.  Permeable
treatment beds have the potential to reduce the quantities of contaminants
present in leachate plumes.

     The final section in this chapter deals with a relatively new technique
that had its origin in mining:  block displacement.  This technique involves
vertically lifting a large mass of earth and isolating the mass completely
from the groundwater flow regime using a physical barrier.  The barrier  is
formed by pumping slurry into a series of notched injection holes which  are
physically connected underground.  As the slurry is pumped in, the soil mass
is displaced upward resulting in the block's displacement.

     Prior to discussing the individual in situ treatment techniques,  a
general presentation of the types of wastes that are found at hazardous waste
sites and the potentially useful in situ treatments that could be utilized may
aid the reader.  A survey of the 114 top priority Superfund sites (EPA, 1981)
was performed by Ellis, et al. (1982) to determine the contaminants that  are
likely to be found and be amenable to in situ treatment.  Table 8-1 presents
the results of this survey.  The occurrence of heavy metals,  acids, alkalis,
aromatics, phenols, PCB's, and other halogenated hydrocarbons is widespread
among sites.

     Ellis, et al. (1982) went further and suggested potential in situ
treatments for each of the chemical groups based on available literature.
This information is presented in Table 8-2.  The table lists  the five
                                     8-4

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                                  TABLE 8-1.

     HAZARDOUS SOIL CONTAMINANTS AT SUPERFUND SITES (Ellis,  et  al.,  1982)
Contaminants
Heavy Metal Wastes
Chromium
Arsenic
Lead
Zinc
Cadmium
Iron
Copper
Mercury
Selenium
Nickel
Vanadium
Fly ash
Plating wastes
Other Inorganics
Cyanides
Acids
Alkalis
Radioactive wastes
Number of Total Examples
Sites Sites
47
9
8
7
5
4
3
2
2
2
1
1
1
2
26
6
7 sulfuric acid
6 lime, ammonia
3 uranium mining and purifica-
   Miscellaneous
Hydrophobic Organics

   Polychlorinated biphenyls    15
   Oil,  grease                  11
   Volatile hydrocarbons         6
   Chlorinated hydrocarbon        5
     pesticides
   Polynuclear aromatics         1
        tion wastes,  radium,  tritium
      beryllium,  boron  hydride,
        sulfides, asbestos
38
      Varsol,  hexane
      endrin,  lindane,
      diel drin
DDT, 2,4,5-T,
                                                                   (Continued)
                                     8-5

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                            TABLE 8-1.   (continued)
   Contaminants
Number of
  Sites
Total
Sites
Examples
Slightly Water Soluble Organics

   Aromatics
      Benzene                    9
      Toluene                    8
      Xylene                     5
      Other aromatics            3

   Halogenated hydrocarbons
      Trichloroethylene         11
      Ethylene dichloride        6
      Vinyl chloride             4
      Methylene chloride         3
      Other halogenated         15
        hydrocarbons
Hydrophilic Organics

   Alcohols                      4
   Phenols                      12

   Other hydrophilics            4
Organic solvents (unspecified)
   and other organics
              64
                    styrene, napthalene
              20
              30
                    chloroform, trichloroethane,
                      tetrachloroethylene,
                      trichlorofluoromethane
        methyl, isopropyl, butyl
        picric acid, pentachloro-
          phenol, creosote
        dioxane,  bis(2-chloroethyl)
          ether,  urethane, rocket fuel

        dioxin, dioxane, dyes,
        pigments, inks, paints,
          nitrobenzene
                                     8-6

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                                                                         TABLE 8-2.

                                     POTENTIAL  USEFUL  SOIL  IN SITU TREATMENT  PROCESSES  (Ellis,  et al.,  1982)
                    Hazardous Waste
                    Heavy metals
oo
i
                    Hydrophobia organics
 In Situ Treatment
•  Sulfide precipitation
                                                 •   Fixation with municipal refuse
•  Aqueous leaching to dissolve and/or
   flush with injection/recovery system
•  Water injection/recovery system  with:

     Surfactants

     Oxidizing reactants (NaOCl,  H-CL)

     Micellar-polymer,  e.g.,  petroleum
     sulfonates and polyacrylamides

     Solvents


•  Sodium polyethylene  glycol  reactant

•  Clay immobilization:   injection/
   fixation process
Selected References
Pohland, et al.  (1981,  1982)
U.S. EPA (1979)
Huibregtse and  Kastman  (1978)

Myers,  et al.  (1980)
Phunq,  et al.  (1982)
Kinman, et al.  (1982)
Jones and Malone (1982)

Epstein, et al.  (1978)
Fuller  and Korte (1976)
Huibregtse et  al.  (1978)
                                                                                                Hill,  et al.  (1973)

                                                                                                Chou,  et al.  (1982)

                                                                                                Klins, et al.  (1976)
                                                                                                Anderson,  et al.  (1982)
                                                                                                Griffin and  Chou  (1980)

                                                                                                Pytlewski, et  al.  (1980)
                                                                                                                           (continued)

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                                                                 TABLE  8-2.   (continued)
                    Hazardous  Waste
                              In  Situ  Treatment
Selected References
oo
i
oo
                    Hydrophobic  organics
                      (continued)
                              •   Biostimulation
Slightly water-soluble        •   Water  injection/recovery  system
organics (e.g., benzene,         with surfactants
toluene., trichloroethylene)
                              •   Chemical  and  aerobic  oxidation
                    Hydrophilic  organics
                    (e.g.,  aniline,  phenol)
                              •   Anaerobic  oxidation

                              t   Water  injection/recovery system  with:
                                 pH adjustment  (buffering)

                              •   Biostimulation
Wilkinson, et al.  (1978)
Kobayashi and Rittman (1982)
Zitrides (1982)

Texas Research Institute (1979, 1982b)
                                                                                                Dragun and Helling (1982)
                                                                                                Texas Research Institute (1982a)
                                                                                                Kinman, et al. (1982)
Laguros and Robertson (1978)
                                                                                                Wilkinson (1978), Kobayashi and
                                                                                                Rittmann (1982), Zitrides (1982)

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categories of hazardous waste materials previously  identified  as significant,
several potential in situ treatment techniques for  each hazardous waste
category, and key citations to the source of  information.  These information
sources should be referred to for elucidation of the processes  and  situations
under which they were utilized.

8.2  Bioreclamation

     Bioreclamation is an in situ groundwater treatment technique based  on  the
concept of enhancing microbial activity by altering the physical or chemical
environment of the aquifer.  Methods currently under investigation  include
aeration and the addition of nutrients to accelerate the biodegradation  of
groundwater contaminants.  Typically, in bioreclamation, groundwater  extrac-
tion wells are strategically placed downgradient to control the migration of
the contaminant plume.  Contaminated groundwater pumped to the  surface  is
mixed with nutrients needed for organism growth, and the treated contaminated
groundwater is reinjected upgradient.  Specialized  microorganisms may be
injected along with the nutrients, or the indigenous soil bacteria may  be
stimulated with nutrients to adapt to the groundwater contaminants.   The
groundwater is aerated above ground by in-line injection or underground  using
a series of wells.  A simplified view of the  process is shown  in Figure  8-1.

     The bioreclamation process, as described above, results in aerobic
decomposition of groundwater contaminants in  the subsurface.   Bioreclamation
claims a number of advantages such as low capital costs, minimal worker  safety
and air pollution control requirements, and contaminant destruction rather
than containment.

     The bioreclamation technique has been used by  a number of  specialized
firms to treat contaminated groundwater plumes resulting from  underground
gasoline and hydrocarbon leaks.  The technique has  not yet been demonstrated
for groundwater treatment at an uncontrolled  hazardous waste site.  However,
bioreclamation1s potential to treat organics  which  are or can be made
biodegradable in contaminated groundwaters establishes it as a viable
technique.
                                     8-9

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                                   FIGURE 8-1.
         SIMPLIFIED VIEW OF GROUNDWATER BIORECLAMATIOIM
                                         Subsurface Aeration Wells
   Injection Well
                                                                    Extraction Well
                                                            Direction of Groundwater Flow
       Nutrients c
         In-line
Injection
  Well
                                                 Aeration Zone

                               Direction of Groundwater Flow '—^
                                                                              Extraction Well
                                         8-10

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     8.2.1  Applications and Limitations

     Bioreel amat ion techniques are applicable to leachate plumes which contain
biodegradable organics.  Relative biodegradabilities of selected compounds
have been reported based on ratios of laboratory parameters associated with
the oxygen requirement for decomposition.  These include 5-day or 21-day
biochemical oxygen demand (BODr, BOD^i), chemical oxygen demand (COD), and
ultimate oxygen demand (UOD).  Table 8-3 presents relative biodegradabilities
by adapted sludge cultures of various compounds in terms of a BODr/COD ratio.
A higher BOO,-/COD means a higher relative biodegradability.  Table 8-4
presents relative biodegradabilities  in terms of an alternate ratio, i.e.,
the BOD?,/UOD ratio, termed refractory index (RI).  Again, the higher the RI,
the more biodegradable.  The data presented in Tables 8-3 and 8-4 provide a
general guideline for determining the biodegradability of certain compounds,
but do not preclude the need for a laboratory treatability study.  The
degradative capability of different microbial populations can vary
considerably; and so, to accurately predict the treatability of a specific
leachate plume, site-specific laboratory treatability studies are essential.
Additionally, many compounds previously thought to be refractory have been
found to be degraded by certain naturally-occurring bacteria as well as
constructed strains.

     In addition to the biodegradability of the leachate plume components, the
applicability of bioreclamation also depends on groundwater temperature. The
temperature range for optimal organism growth in aerobic biological wastewater
treatment processes has been found to range from 68°F to 99°F (20°C to 37°C).
Figure 8-2 gives groundwater temperatures throughout the United States.  A
comparison of Figure 8-2 to the optimal temperature ranges for aerobic
biological wastewater treatment processes suggests that only the southern
portion of the country is within the optimal range.  In areas of the country
where the groundwater temperatures are below optimum, slower rates of
biodegradation should be expected.  Studies of 2,4-D breakdown in surface
water indicated that a 75 percent reduction in degradation rates occurred when
temperature was reduced by 64CF (Lyman, et al., 1982).   This reduction in
degradation rates may be attributable to a drop in temperature from that which
                                     8-11

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TABLE 8-3.   BOD../COD RATIOS FOR VARIOUS ORGANIC COMPOUNDS
                  9    (Lyman, et  al.,  1982)
                                                                  1
Compound

Relatively Non-degradable
Butane
Butyl ene
Carbon tetrachlonde
Chloroform
1,4-01 oxane
Ethane
Heptane
Hexane
Isobutane
Isobutylene
Liquefied natural gas
Liquefied petroleum gas
Methane
Methyl bromide
Methyl chloride
Monochlorodifluoromethane
Nitrobenzene
Propane
Propylene
Propylene oxide
Tet rachl oroethyl ene
Tetrahydronaphthalene
1-Pentene
Ethyl ene d1 chloride
1-Octene
Morpholine
Ethylened1am1netetracet1c acid
Triet Hanoi ami ne
o-Hylene
m-Xylene
Ethyl benzene

Moderately degradable
Ethyl ether
Sodium alkylbenxenesulfonates
Monoisopropanoalmine
Gas oil (cracked)
Gasolines (various)
Mineral spirits
Cyclohexanol
Acrylonitrile
Nonanol
Undecanol
Methyltthylpyrldine
1 -Hexane
Methyl IsobutyUetone
01 ethanol ami ne
Formic add
Styrene
Heptanol
sec -Butyl acetate
n -Butyl acetate
Methyl alcohol
AcetonltMle
Ethyl ene glycol
Ethyl ene glycol monothyl ether
Sodium cyanide
Linear alcohols (12-15 carbons)
Allyl alcohol
Dodecanol

Relatively Degradable
Valeraldenyde
n-Decyl alcohol
p-Hylene
Urea
Toluene
Ratio
Compound
Ratio
Relatively Degradable (continued)

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
<0.002
0.002
>0.003
<0.004
0.005
<0.006
<0.008
<0.008
<0.009


0.012
0.017
<0.02
0.02
0.02
0.02
0.03
0.031
>0.033
<0.04
0.04-0.75
<0.044
<0.044
<0.049
0.05
>0.06
<0.07
0.07-0.23
0.07-0.24
0.07-0.73
0.079
0.081
<0.09
<0.09
>0.09
0.091
0.097


<0.10
>0.10
<0.11
0.11
<0.12
Potassium cyanide
Isopropyl acetate
Amyl acetate
Chlorobenzene
Jet fuels (various)
Kerosene
Range oil
Glycerine
Mlponitrile
Furfural
2-Ethyl -3-propylacrole1n
Methylethylpyrldine
Vinyl acetate
Diethylene glycol
monomethyl ether
Naphthalene (molten)
D1 butyl phthalate
Hexanol
Soybean oil
Paraformaldehyde
n-Propyl alcohol
Methyl methacrylate
Acrylic acid
Sodium alkyl sulfates
Triethylene glycol
Acetic acid
Acetic anhydride
Ethyl enedi ami ne
Formaldehyde solution
Ethyl acetate
Octanol
SorbHol
Benzene
n-Butyl alcohol
Propionaldehyde
n-Butyraldehyde
Ethyleneimine
Monoethanolamine
Pyridine
D1 methyl formamide
Dextrose solution
Corn syrup
Maleic anhydride
Proplonic add
Acetone
Aniline
Isopropyl alcohol
n-Amyl alcohol
Isoamyl alcohol
Cresols
Crotonaldehyde
Phthallc anhydride
Benzaldehyde
Isobutyl alcohol
2,4-D1ch1orophenol
Tallow
Phenol
Benzole add
Carbolic acid
Methyl ethyl ketone
Benzoyl chloride
Hydrazine
Oxalic acid





0.12
<0.13
0.13-0.34
0.15
0.15
0.15
0.15
<0.16
0.17
0.17-0.46
<0.19
<0.20
<0.20

<0.20
<0.20
0.20
0.20
0.20
0.20
0.20-0.63
<0.24
0.26
0.30
0.31
0.31-0.37
>0.32
<0.35
0.35
<0.36
0.37
<0.38
<0.39
0.42-0.74
<0.43
<0.43
0.46
0.46
0.46-0.58
0.48
0.50
0.50
>0.51
0.52
0.55
0.56
0.56
0.57
0.57
0.57-0.68
<0.58
0.58
0.62
0.63
0.78
0.80
0.81
0.84
0.84
0.88
0.94
1.0
1.1





BODj values were not measured under the same conditions for all chemicals
                               8-12

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                   TABLE 8-4.

REFRACTORY INDICES FOR VARIOUS ORGANIC COMPOUNDS
       (Adapted from Lyman, et al., 1982)
      Compound                      RI
      High Degradability

      Biphenyl                      1.14
      Antifreeze                    1.12
      Sevin                         1.0
      d-Glutamic acid               1.00
      d-Glucose                     0.93
      1-Valine                      0.93
      Acetone                       0.93, 0.71
      Phenol                        0.87
      Sodium butyrate               0.84
      1-Aspartic acid               0.81
      Sodium prop ionate             0.80
      Propylene glycol              0.78, 0.52
      Ethylene glycol               0.76
      Medium-High Degradability

      Potato Starch                 0.72, 0.64
      1-Arginine                    0.65
      Acetic acid                   0.61
      Aniline                       0.58
      Soluble starch                0.54
      1-Histidine                   0.52
      1-Lysine                      0.52
      Hydroquinone                  0.41

      Low Degradability

      Benzene                       0.23
      Gasoline                      0.21
      Adenine                       0.14, 0.12
      Vinyl chloride                0
      Carboxymethyl
      cellulose                     0
      Humics                        0
      DDT with carrier              0
      p-Chlorophenol                0
      Dichlorophenol                0
      Bipyridine                    0
      Chloroform                    0
      Cyanuric Acid                 0
                      8-13

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00
                                    47°
                         52°
                             62°
                                67° 72°
                                                   FIGURE 8-2.
                             TYPICAL GROUNOWATER TEMPERATURES <°F) AT 100 FT. DEPTH
                             IN THE CONTERMINOUS UNITED STATES (JOHNSON DIVISION,
                                                  UOP INC., 1975)

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The organism is accustomed.  Ladd, et al. (1982) reported high heterotrophic
activities in groundwater samples from Alberta, Canada.  Therefore,
biorecTarnation may not be as applicable to sites in the extreme north because
of reduced biodegradation rates caused by low groundwater temperatures.
However, organisms adapted to cold water will still grow and metabolize at
appreciable rates if stimulated with oxygen and nutrients.

     Site geology is also an important factor that may affect the feasibility
of using the bioreclamation process.  Optimum geologic conditions for bio-
reclamation require substrata with moderate to high hydraulic conductivities.
Substrate materials with the above hydraulic conductivity characteristics may
include gravels, coarse sands, sandstones, and highly fractured rocks.

     Other factors may also limit the applicability of bioreclamation.  The pH
of the  leachate plume is one such factor.  Microbial growth can occur within a
relatively wide pH range, about 5.0 to 9.0.  However, optimum growth occurs
within  a pH range of about 6.0 to 8.0, with slightly alkaline conditions being
more favorable.  Leachate plumes having pH values outside this range may not
provide suitable conditions for rapid biodegradation of contaminants.  How-
ever, in some cases adjusting pH in the process may be possible.

     The availability of oxygen and nutrients for aerobic decomposition
enhances to the bioreclamation process, and if not present, would limit
biodegradation.  Introducing enough soluble oxygen into the groundwater has
been the major challenge in applying bioreclamation to leachate plumes.  This
is because the demand for oxygen is high in this process and the solubility of
oxygen  in groundwater is relatively low.  The problem  is compounded by the
difficulty of distributing the gas within the substrate.  The design section
of this chapter presents several approaches to solving the oxygen availability
problem.

     8.2.2  Theory

     The bioreclamation process is based on the capability of many species of
bacteria to degrade a wide variety of organic compounds.  Species have been
                                     8-15

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 isolated which  are  capable of  degrading  hydrocarbons,  aromatics,  and
 halogenated  aliphatics  and aromatics.  Naturally  occurring  species  of
 Pseudomonas  and Arthrobacter have  been associated with  the  biodegradation  of
 gasoline contaminated groundwater  (Raymond, et  al.,  1976).   Other major  genera
 known to attack organic contaminants  include Achromobacterium, Flavobacterium,
 and Nocardia (Kincannon,  1972).  In general, more rapid  and  more  complete
 biodegradation  is carried out  by microorganisms in an  aerobic  (oxygenated)
 environment.  However,  for certain compounds, most notably  the halogenated
 alkanes and  certain pesticides such as DDT, more  rapid  breakdown  occurs  in
 anaerobic  (oxygen-free) environments  (Suflita,  et al.,  1982; Bouwer and
 McCarty, 1983).

     In the  aerobic decomposition  of  organic matter,  bacteria respire  oxygen
 while catabolizing the  organic compound, producing metabolic by-products,  cell
 biomass, carbon dioxide,  and water.   The generalized  process is given  by the
 following  equation:

 Bacteria + 02 + Organics + Nutrients	•-CCL  + hLO  + Byproducts + Cell Biomass

 Approximately 5 to 50 percent  of the  organic material metabolized will be
 transformed  into cell biomass.  The more refractive  a  compound, the less
 carbon there  is available for  cell growth.  Therefore,  an increase  in  cell
 number is  directly related to  the  biodegradability of  the compound.

     Inorganic nutrients such  as nitrogen, phosphorus, and trace elements  are
 required for proper cell respiration, growth, and reproduction.  Oxygen  serves
 as the terminal electron acceptor  in  aerobic cell  respiration, and thus, must
 be present for aerobic  biodegradation.  The organic matter,  known as the
 substrate, is the organic carbon containing energy for the microorganisms.

          8.2.2.1  Nlicrobial  Populations

     In bioreclamation, specialized microbial populations are promoted to
degrade the  organic materials  contaminating the groundwater.  The total
microbial  population may originate from naturally occurring species in the
                                     8-16

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environment, enriched strains, or genetically manipulated organisms developed
in the laboratory.  Supporting evidence is available that naturally occurring
species of bacteria survive in the soil subsurface and that these can be
stimulated to proliferate with the introduction of oxygen and a suitable
substrate.  Also, introduced strains, developed in the laboratory, have been
shown to be able to survive in the subsurface environment.

     Many types of bacteria have been isolated from soil cores, subsurface
oil, and water from deep wells (Dunlap and McNabb, 1973).  The data suggest
that subsurface microbial colonization may occur down to several thousand
feet, however, the studies did not take into account the possibility of
contamination from the surface during sampling.  A number of other studies
identified microbial populations in the lower unsaturated zone and in upper
regions of the groundwater table.  Sulfate-reducing bacteria were found in
concentrations of 10  to 10  organisms per milliliter in well waters in
Montana (Dockins, et al., 1980).  Nitrate-reducing bacteria were found to
depths of 120 feet (40 meters) in the unsaturated zone of the Chalk Formation
in Great Britain in a concentration of 10  to 10  organisms per gram of soil
(Whitelaw and Edwards, 1980). In other studies of two water table aquifers  in
Oklahoma, a variety of bacteria were found with typical concentrations of 10
to 10  cells per gram of soil.  The bacteria were relatively small, with both
gram-negative and gram-positive forms being present.  Many double cells were
found suggesting that the bacteria were in the process of cell division
(Ghiorse and Balkwell, 1981).  The movement of bacteria through considerable
distances of soil, particularly during saturated flow conditions, has been
well established (Hagedorn, et al., 1981).  Thus, there is strong evidence
that the subsurface and  water table aquifers are constantly inoculated with
organisms from the surface during recharge events.  Also, subsurface
sedimentary formations may contain bacteria that were once surface organisms
which have maintained significant populations.

     Some species of these naturally occurring bacteria have the ability to
feed on hydrocarbons and other organics, as evidenced by the studies of McKee
(as cited by Litchfield  and Clark, 1973), and Litchfield and Clark (1973).
                                     8-17

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McKee found that high bacterial populations of Pseudomonas;  and Arthrobacter
were associated with gasoline contaminated groundwater, while  low  counts  of
bacteria were associated with odor-free water  (Raymond, et  al.,  1976).
Litchfield and Clark (1973) confirmed that significant  populations  of  bacteria
were present in groundwater contaminated with gasoline, fuel oil,  and  other
petroleum products.  They found that waters containing  less than 10 parts  per
million (ppm) of hydrocarbons generally had populations of  less  than 103
organisms per milliliter, while hydrocarbon concentrations  in  excess of 10 ppm
generally supported populations of 10  organisms per milliliter.   Species  were
identified as belonging mostly to the genera Pseudomonas  and Arthrobacter.
     Firms specializing in the bioreclamation process have found that  the
naturally occurring organisms in the subsurface can,  in fact, be stimulated  by
adding nutrients and oxygen to produce a thriving colony which uses the
groundwater contaminants as substrates for growth (Williams, 1982).  Alterna-
tively, mutant strains developed for the treatment of industrial wastewaters
have been used in the bioreclamation process.  In this method, a thriving
microbial colony, acclimated to the contaminants, is  introduced rather than
developed, and the time requirement for adaption of a microbial population  is
significantly reduced or eliminated (Thibault and Elliot, 1980).

     The simplified selective adaptation and mutation process is illustrated
in Figure 8-3.  Original strains are collected from industrial or
environmental sources, such as an oil well, coke oven, or contaminated
aquifer, where natural populations have been exposed to the compound of
interest.  Adaptation can, sometimes, be accelerated by irradiation-induced
mutation and growth on selective media.  In the bioreclamation process,  the
mutant bacteria can be cultured with contaminated groundwater in a surface
holding pond and then inoculated into the subsurface via spraying or injection
wells.

          8.2.2.2  Nutrient Requirements

     Besides the carbon-containing substrate, inorganic nutrients are  also
required for proper cell growth and therefore are essential elements of  the
                                     8-18

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                                                 (Pure Culturesl
Long-term
 Storage
 Vacuum
  Vials
                                                          Nutrients
    (Pure Cultures)
Isolated Adapted Mutants
Growth and
 Selection
                                                      Scale Up
                           Shake Flasks
                                FIGURE 8-3.
           SIMPLIFIED SELECTIVE  ADAPTION/MUTATION PROCESS
                          (MCDOWELL, et ai., 1982)
                                                                         A.4
                                                                            Radiation
                                                Dry
                                               Blend
                                               Store
                                     8-19

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bioreel amat ion process.  Cell nutrients include nitrogen, phosphorus,  and
potassium.  Trace elements are also required and  include  sulfur,  sodium,
calcium, magnesium, iron, and copper (Rogoshewski, 1977).  Nitrogen  and phos-
phorus are needed in the greatest quantities for  cell growth  and  can  limit
cell growth if they are not present at sufficient levels.  Trace  elements
usually are present in sufficient quantities in groundwater environments.

     The quantity of phosphorus occurring naturally in groundwater usually  is
controlled by the presence and solubility of the  mineral  apatite.  Phosphorus
concentrations in solution rarely exceed 0.1 milligrams per liter  (mg/1)
(Bouwer, 1978).  Bacteria contain about one percent phosphorus  on  a  dry-weight
basis (Doetsch and Cook, 1973), suggesting that groundwater containing 0.1
mg/1 of phosphorus could support a maximum bacterial population of 10  mg/1.
Assuming a 50 percent conversion efficiency, contaminant  plumes of concen-
trations greater than 20 mg/1 of substrate may become phosphorus  deficient  and
require the addition of phosphate.

     Similarly, bacteria were found to contain about 10 percent nitrogen on  a
dry-weight basis, while normal groundwater contains from  0.1  to 10.0 mg/1
(Doetsch and Cook, 1973; Davis and DeWiest, 1966).  These concentrations would
permit degradation of 2 to 200 mg/1 of substrate, assuming a  50 percent
conversion of nitrogen-free organic matter to new cells.  Chemical analysis  of
nitrogen in groundwater should provide a reasonable estimate  of the  amount of
organic contamination that can be degraded according to the above relation-
ships.  This has been confirmed in a study by Kappler and Wuhrman  (1978) in
which 0.17 mg/1 of bound nitrogen in groundwater  permitted degradation of only
2.0 to 2.1 mg/1 of water soluble organics.  When  ammonium chloride was added,
further degradation took place.  The relationships observed in this  study
indicate that organic concentrations in groundwater above 120 mg/1 probably
will require additional nitrogen.  This addition  of nutrients may cause
problems by further contaminating the aquifer.  Therefore, only the amount
needed to sustain biological  activity should be added.
                                     8-20

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          8.2.2.3  Oxygen Requirements

     Theoretical quantities for the amount of oxygen required to degrade
organic chemicals can be determined from stoichiometric analysis.  The major
assumption in this approach is that all organic materials  break down  into
carbon dioxide and water.  Degradation of 1.0 mg of a  simple organic  acid,
such as acetic acid, theoretically would require only  1.1  mg of oxygen, while
a fully saturated aliphatic hydrocarbon would require  about 3.4 mg.   Thus,
groundwater with an organic contaminant concentration  of 100 mg/1 may require
oxygen concentrations .as high as 340 mg/1 if saturated organics are  involved.

     Dissolved oxygen concentrations in groundwater are generally considered
to be quite low for aerobic degradation of compounds.  This presumes  that any
dissolved oxygen in water that percolates through the  soil column is  used up
by microbial oxidation of soil organics (Johnson Division, UOP Inc.,  1975).
Therefore, oxygen generally must be added to support biodegradation  of
organics in a contaminated groundwater plume.  Different techniques  of adding
oxygen and the various advantages and disadvantages of each system are
discussed in Section 8.2.3.3:  Oxygen Supply.

          8.2.2.4  Substrate Characteristics

     The key to the success of bioreclamation of contaminated groundwaters  is
the ability of the microorganisms to use the pollutants as substrates or food
for their metabolism and growth.  Previously mentioned bioreclamation studies
of groundwater contaminated with gasoline and fuel oil have shown that many
hydrocarbons can be biodegraded.  However, in a leachate plume associated with
a hazardous waste site, many toxic compounds with different biodegradability
rates may be present.   In determining whether bioreclamation can be  a viable
process for treating a specific leachate plume, consideration must be given to
the biodegradabilities of all substances present, their concentrations in the
plume, and the interactive effects of the contaminants on  the microbial
community.
                                     8-21

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     The biodegradability of a specific substance can be related to  its
chemical structure.  However, there is much disagreement centered around the
development of generalized structure/biodegradability relationships  for
predictive purposes (JRB Associates, 1982).  Empirical approaches have been
developed in which the relative biodegradability of specific chemical sub-
stances is obtained from laboratory measurements.  One such approach uses the
ratio of the five day biochemical oxygen demand (600^) to chemical oxygen
demand (COD).  Compounds with a BODg/COD ratio of less than 0.01 are defined
as relatively nondegradable, whereas compounds with a BODg/COD ratio of 0.01
or greater are defined as relatively degradable.  BOD,-/COD ratios for specific
chemicals have been given previously in Table 8-3.  A second empirical
approach involves the use of a ratio of ultimate biochemical oxygen  demand
(BODU) to ultimate oxygen demand (UOD).  This ratio is known as the  refractory
index (RI).  An RI over 0.5 indicates that a compound biodegrades readily to
carbon dioxide, water, and other associated mineralization products.
Compounds with an RI value of 0.0 to 0.5 are considered to be of low to
moderate biodegradability.  Table 8-4 gives refractory indices for a number of
organic substances.

     The classification of a substance as having a moderate or low biode-
gradability does not mean it cannot be biodegraded.  Gasoline, which is listed
as moderately biodegradable in Table 8-3 and only slightly biodegradable in
Table 8-4, has been the substance most frequently treated successfully by the
bioreclamation process.  Studies indicate that certain bacterial species can
degrade compounds considered to be fairly refractory (Vandenbergh, et al.,
1981).  Also, pretreating a compound of low biodegradability may be  possible
with ozone for example, to partially oxidize it to a more biodegradable form.

     In leachate plumes consisting of many components which are biodegradable,
organisms may preferentially degrade one compound before another (SCS
Engineers, 1979).  The following generalizations apply concerning these
preferences:

     •  Non-aromatics are biodegraded preferentially over aromatics
     t  Substances with unsaturated bonds are biodegraded preferentially over
        substances with saturated bonds
                                     8-22

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     •  Straight chain compounds are biodegraded preferentially over branched
        isomers and complex, polymeric substances
     •  Soluble compounds are usually more biodegradable than insoluble
        compounds
     0  The presence of various functional groups affects biodegradability:
        i.e., alcohols, aldehydes, acids, esters, amides, and amino acids are
        more biodegradable than corresponding alkanes, olefins, ketones,
        dicarboxylic acids, nitriles, and chloroalkanes (Lyman, et al., 1982)
     •  Halogen substituents generally make a compound more biorefractory.

     Concentrations of substances present in the leachate plume can also
affect biodegradability.  When substances are present at levels below  0.1
mg/1, the assimilative processes of microorganisms are sometimes not stimu-
lated, thus adaption to the particular substrate will not occur and the
substance will generally not be degraded  (SCS Engineers, 1979).  Conversely,
high concentrations of organic substances may cause  inhibition of normal
microbial processes because of their toxic nature, and thus may appear to be
of low biodegradability.  Table 8-5 presents a list  of compounds that  have
been found to be problematic in this respect during  industrial wastewater
treatment.  Problem concentrations are listed for two conditions:  substrate
limiting—in which the subject compound is the sole  source of microorganism
food; and non-substrate limiting--in which other carbon substrates are
present.  In a leachate plume of mixed organics, the non-substrate limiting
condition would be expected to prevail.   If the  leachate plume contains
inhibiting concentrations of organics, the bioreclamation process can  be
designed to treat a diluted portion of the contaminated groundwater to
circumvent inhibitory effects.

8.2.3  Design and Operation

     The design of an in situ groundwater bioreclamation system must take into
account biodegradation kinetics, hydraulic design, oxygen supply, and  the need
for nutrient addition.  In the past, bioreclamation  projects have been con-
ducted largely on a trial and error basis.  Even though the basic scientific
principles of the system may be fairly well understood, the application of
these elements for cleanup at a hazardous waste  disposal site is not yet fully
                                     8-23

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                                  TABLE 8-5.
                 PROBLEM CONCENTRATIONS OF SELECTED CHEMICALS
                             (SCS Engineers, 1979)
Chemical
   Problem Concentration (mg/1)
                                      Substrate
                                      Limiting
                     Non-Substrate
                       Limiting
n-Butanol
sec-Butanol
t-Butanol
Allyl  alcohol
2-Ethyl-l-hexanol

Formaldehyde
Crotonaldehyde
Acrol ein

Acetone
Methyl  isobutyl ketone
Isophorone

Di ethyl amine
Ethyl enediamine
Acrylonitril e
2-Methyl-5-ethylpyridine
N,N-dimethylaniline
phenol

Ethyl  benzene
Ethyl  acrylate

Sod i im ac ryl ate
Dodecane
Dextrose
Ethyl  acetate
Ethyl ene glycol
Diethylene glycol
Tetralin
Kerosene
Cobalt chl oride
>1000

 500-1000


 200
>1000
>1000
>1000
>1000
>1000
>1000

>1000
 600-1000
>1000
>1000
>1000
>1000

>1000
>1000
>1000
>1000
>1000
 50-100
 50-100
>1000
 100-300
 300-1000
 100-300
 100
 100

 300-1000
 300-600

>500

XLOOO

>900
>1000

>500
>1000
                                     8-24

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developed.  Furthermore, most private companies specializing  in bioreclamation
of polluted groundwater have not always been willing to disclose  information
about bioreclamation technology for fear of revealing trade secrets.  Never-
theless, enough design  information for the bioreclamation process  is  available
for adopting reliable bioreclamation treatment at hazardous waste  sites.  The
following sections describe biodegradation kinetics, hydraulic design,  oxygen
supply, nutrient addition, and other design aspects.

          8.2.3.1  Biodegradation Kinetics

     In situ bioreclamation of highly contaminated groundwater (i.e., over
100 mg/1) generally involves aerobic microbial degradation at ambient tempera-
tures.   In this case, the rate equation describing biodegradation  of  organic
material in the aqueous environment is based on Monod kinetics (Lyman,  et al.,
1982):

                     - d[C]/dt = (Um)(Cm)(C)/Yd(Cu/2 + C)

  where:      d[C]/dt = the rate of disappearance of substrate
              U  = maximum growth rate of the microorganism
              C  = the concentration of microorganisms
              C = concentration of the substrate
              C i2 = concentration of the substrate supporting a half-maximum
                     growth rate (Um/2); can be assumed to range from 0.1 to
                     10 mg/1  for most substances
              Yj = the yield coefficient, which is -dCm/dC, can be assumed to
                     be 0.5 for non-dilute systems.

     The equation is a variable order rate equation, however, it can  be
simplified to first and second order approximations for two conditions—when
C is much greater than C  ,„ and when C is much less than C /,,.  At the  start
of bioreclamation of contaminated groundwater, the first condition will apply
because substrate concentrations will  be substantial.  However, when  the
concentration of contaminating substance has been lowered by bioreclamation to
a residual level, the second condition will apply.
                                     8-25

-------
     When C is much greater than Cu/2, the expression (Cu/2+C)  is approx-
imately equal  to C.  By substituting C for (Cu/2+C) and the expression 0.5C+C
for C  (which is derived from integrating the yield coefficient equation YJ  =
0.5 + -dC /dC), the equation reduces via integration to a first order
equation:


where:        C,: = final concentration
              C- = initial concentration
              t = time
              U  = maximum growth rate of microorganisms; equal  to  the  first
                   order rate constant k
              e = base of natural logarithms.
     This equation is applicable only for  large values of C  in relation  to
C  /2.  If C is at least ten times C,2,  less than  a 10 percent error  in  the
calculated final concentration can be expected.

     In a residual concentration, when C is much less than C/2,  the  value
C  /?+C is approximately equal to C  /2 and  the equation reduces to the second
order expression:

               - d[C]/dt = f(Cm)(C),

where:         f = WCu/2>-

     When the substrate concentration is of the same order as the C /2 value,
the rate expression  is a hybrid between  first and  second order.

     Biodegradation  rates  in  groundwater can be calculated more  accurately if
sorption/desorption  effects of the earth material  comprising the  aquifer are
taken into account.   In this  case, the rate order  constant (k)  can be related
                                      8-26

-------
to an apparent constant (k   ) by the partition coefficient of the substrate
(k )  and the earth-to-water mass ratio (p) as (Maki, et al., 1980):

               kapp ' k/<1+Pkp'

     Unfortunately, much of the data compiled on biodegradation rate constants
are not generally useful for assessing compound degradation in an  in situ
groundwater bioreclamation situation because the data have been developed for
river die-away predictions based on concentrations of organics which are too
dilute.  Some rate data have been developed based on aerobic biodegradation of
organic materials by an adapted activated sludge process, in which the rate is
expressed in mg of COD degraded per mass of the microbial inoculum per unit
time (Pitter, 1976). However, these rate data may not be directly  applicable
to assessing in situ biodegradation rates for a combination of organics
because of synergistic and antagonistic effects such as preferential bio-
degradation and co-metabolism.

     In properly assessing the applicability of bioreclamation as  a means of
treating contaminated groundwater, bench and pilot  scale testing should be
conducted to obtain the necessary values of the variables described in the
above equations. Test results for in situ biodegradation studies may prove to
be more accurate if they are conducted in a system mimicking the groundwater
system to be treated (i.e., physical and chemical properties).

     Degradation rates obtained from controlled bench and pilot scale  studies
can be extrapolated to ambient temperature rates by using the Arrhenius
equation (Lyman, et al., 1982):
                   Rt = R.e-        a

where:             R. = temperature-corrected  reaction  rate
                   R. = initial rate of reaction
                   E  = activation  energy
                    a
                   R  = gas constant
                   T_ = absolute temperature
                    a
                   e  = base of natural logarithms.

                                     8-27

-------
     This equation also demonstrates the relationship  between  temperature  and
reaction rate (i.e., lower temperatures result  in  lower reaction  rates  and
higher temperatures result in higher reaction rates).

          8.2.3.2  Hydraulic Design

     Hydraulic design is an essential element of the bioreclamation  process
pertaining to the collection and containment of the groundwater plume.   Proper
design of groundwater injection systems is  important for the prevention  of
pollutant migration away from treatment areas.  In addition, hydraulic  design
relates to placement of the extraction system to collect contaminated ground-
water .

     Injection and extraction of contaminated groundwater may  be  accomplished
by using either a pumping system (Chapter 5) or a  subsurface drainage system
(Chapter 6).  In either case, the groundwater extraction and injection  system
must be properly designed to contain the groundwater plume and minimize  back-
flow as a result of groundwater reinjection.

     A subsurface trench was used to reinject treated  groundwater during the
cleanup of an underground spill in Waldwick, N.J.  (Jhaveri and Mazzacca,
1983). In this case, the bioreclamation process was augmented  by  surface
biological treatment.  A diagram of the injection  trench is shown in
Figure 8-4. The trench is 10 feet deep by 4 feet wide  by 100 feet long.  The
trench has a 15 mil plastic liner installed on the bottom, back,  ends,  and top
such that reinjected water can only flow out of the front (downgradient) face
of the trench.  About 40 feet of slotted steel pipe is installed  horizontally
in the trench to carry reinjected water into the trench system.   As  water
flows into the injection trench, the water  is forced to exit only from  the
front face.  Back flow is minimized by this design feature. Barriers can also
be used behind the trench and extended to a point  where backflow  is  further
minimized. In extreme cases, total control of backflow and plume  containment
can be obtained by installing a circumferential barrier wall.
                                     8-28

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CO
 i
ro
               Plane View
                                                                              FIGURE 8-4.
                                                           CONFIGURATION OF REINJECTION TRENCHES
                                                           (JHAVERI AND MAZZACCA, 1983 AS CITED BY
                                                                        COCHRAN, et al., 1984)
                                                                                  Edge of Earth Mound
                                                                                                           2" Well
               Front View
                                                            4" Diameter Washed Stone
                                                                                         2" Diameter Well
                                                                                          Hand Slotted
4" Diameter Plastic
Well Hand Slotted
    Plastic Liner
(Overlapped 1-3 Times)
                                                                                                     4" Diameter
                                                                                                   r Washed Stone
                          i*.V--vft - ?"/ •.••{•••-••/MvYf-• -:• •••- v- •-;• ••.• •H-: "tf-\v •>V":--:--:Y! frT-yft -^-!
                          ^i^::-S«ty.:/r.^)^^
                                                                            6"  ^i»i\.•.-.'...y:.'.'"iV-
                                                                           .71  ~ sv-J !•' *•>:*»• ?• • •:."'
              Approx 10' ^
                        ^\
                                                                                                      Grade

                                                                                                  Plastic Liner
                                                                                                  (Overlapped 2-3 Times)

                                                                                                   4" Diameter
                                                                                                  Washed Stone
                                                                 Plastic Liner
                                                                Sand Base
                                                                 on Top
                                                                 of Liner
                                                                    Sand Base
                                                                   Below Liner
                                                                (Approx.  1 Ft. Thick
                                                                 No Less Than 6")
               Note: Treated water exits only from one side of the trench.

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          8.2.3.3  Oxygen  Supply

     The supply of oxygen  to  subsurface  microorganisms  is  essential  to the
effectiveness of the bioreclamation  process.   Oxygen  can be  supplied in a
number of ways, including  aeration,  oxygenation,  and  the use of hydrogen
peroxide and other oxygen  containing compounds.

               8.2.3.3.1   Aeration

     Air has been used for many years  in conventional wastewater  treatment to
provide the necessary oxygen  for microbial activity and growth.   In  an in situ
bioreclamation process, air can either be added to the extracted  groundwater
before reinjection or injected directly  into the  contaminated  plume.   The
first method involves adding  the air into the  pipeline and mixing  it with a
static mixer (Figure 8-5).  The aerated water  can then be  reinjected to the
subsurface.  Air injection can provide a maximum  of about  10 mg/1  of dissolved
oxygen at a temperature sufficient to carry out bioreclamation  (15°C).   Table
8-6 shows saturated dissolved oxygen concentrations in equilibrium with air
for other temperatures.

       A higher oxygen concentration can be attained  in a  pressurized  line or
a confined aquifer.  The equilibrium oxygen concentration  in water increases
with increased air pressure according to Henry's Law  (Sawyer and McCarty,
1967):

                   CL -  « PHk
where:             CL = concentration of oxygen in liquid  (mg/1)
                   a  = volume fraction (0.21  for 02  in air)
                   P  = air pressure (atm)
                   H^ = Henry's Law Constant for oxygen.

     The value of Henry's Law constant is 43.8 mg/1-atmosphere  at  68DF  (20°C).
Pressure increases with groundwater depth at the rate of 0.0294 atmospheres
per foot.
                                     8-30

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                                FIGURE 8-5.
                       CONFIGURATION OF STATIC MIXER
               Air
     Flow
TABLE 8-6.  SOLUBILITIES OF OXYGEN  IN WATER  AT  SELECTED  TEMPERATURES
                   (After Davis and DeWiest,  1966)
Temperature °F (°C)
Dissolved Oxygen Concentration (mg/1)
     in Equilibrium with the
          Air at 760 mm
32 (0)
50 (10)
68 (20)
96 (30)
122 (50)
15
11
9
8
6
                                8-31

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          Oxygen solubility in a non-polar organic compound, such  as hexane,
is approximately ten times higher than the solubility of oxygen  in water
(Texas Research Institute, 1982b).  Therefore, in leachate plumes  consisting
of an aqueous phase and a non-aqueous organic phase, concentrations of
dissolved oxygen may be higher than that attainable with ordinary  water.

     The theoretical amount of oxygen required to degrade 1 mg/1 of hydro-
carbon substrate can be calculated by performing a stoichiometric  analysis for
the given substance, as shown by the following equation:

                   CxHy + (x+(y/4))02	^x C02 + (y/2)H20
     Usually, about 3 to 4 mg/1 of oxygen is required to degrade 1 mg/1 of a
medium-length hydrocarbon compound.  If 50 percent of the organic material is
converted to bacterial cell matter and the other half oxidized to carbon
dioxide and water, only 4 to 6 mg/1 of organic material can be converted  and
oxidized under oxygen saturation conditions.  Thus, for contaminated ground-
waters having organic concentrations significantly higher than the above
values, in-line aeration prior to injection is insufficient, because only
about 10 mg/1 dissolved oxygen can be attained on a single pass, and the
reinjected groundwater will use up all  available oxygen in a very short period
of time.

     The use of in situ aeration wells is a much more feasible approach to
treating highly contaminated leachate plumes.  A bank of aeration wells can be
installed to provide a zone of continuous aeration through which the contam-
inated groundwater would flow.  Oxygen saturation conditions can be maintained
for degrading organics during the residence time of groundwater flow through
the aerated zone.   The required time for aeration can be derived from bench
scale studies.  Residence time (t ) through the aerated zone can be calculated
                                     8-32

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from Darcy's equation (Freeze and Cherry, 1979) using groundwater elevations
(i.e., head) and hydraulic conductivity as follows:

                    tr = (La)2/K(hrh2)

where:              t  = residence time
                    K  = hydraulic conductivity
                    L  = length of aerated zone
                     a
                    K, = groundwater elevation at beginning
                         of aerated zone
                    h2 = groundwater elevation at end of  aerated  zone

      In the design of an in situ aeration well zone system, the zone must  be
wide  enough to allow the total plume to pass through.  The flow of  air must be
sufficient to give a substantial radius of aeration while small enough not to
cause an air barrier to the flow of groundwater.

      Data based on de-icing of waste lagoons by bubbling  has shown  that  a
ratio of about 1:1 exists between the depth of aeration and the diameter of
the zone of aeration (Rothman, 1983).  Based on this logic, an aeration  well
20 feet into pure water would give a radius of aeration of about  10 feet.
However, the effect of aeration wells in a geological formation is  not known
and the effect on the zone of aeration is not well understood but would
probably be less than in water.  Pilot studies would be necessary to determine
the relationship accurately.

      At greater groundwater depths, greater pressure is present (2  atms) at
33 feet) and oxygen solubility and mass transfer is increased.  A possible
configuration for an aeration well bank is given in Figure 8-6.   Much of the
information presented needs further bench and pilot scale investigation  to
determine optimum design criteria.
                                     8-33

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                                 FIGURE 8-6
      POSSIBLE CONFIGURATION OF IN SITU AERATION WELL BANK
Surface Contours-
                                                              Zone of Aeration
                                                                               Plane View
                                                                 Direction of Groundwater Flow
                                                           . Air Injection Wells
h~'/2d*
1 »««•..

*eO '.
d V
1
V
1 \1

• * • •
• 9
'•'."•
*.' 0 0
' ',* o .
e o •
tt ^

• *» *
/ •';•;"

* •
0 0 °
-/ ^

<>'»•' ''•
«'• o • *
• • *. '
'.' '* .'*
•* * V
ff ^

• • 0 0
•••"/
• o • r*
* 0 ^ 
-------
     A blower can be used to provide the flow rate and pressure for aeration.
At the groundwater bioreclamation project in Waldwick, N.J., 5 pounds per
square inch pressure was maintained in nine 10-foot aeration wells, each with
an air flow of 5 cubic feet per minute (Groundwater Decontamination Systems,
Inc., 1983).

               8.2.3.3.2  Oxygenation

     Oxygenation systems, either in-line or in situ can also be installed to
supply oxygen to the bioreclamation process.  Their advantage over conven-
tional aeration is that higher oxygen solubilities can be attained and hence,
more efficient oxygen transfer to the microorganisms. Oxygen solubilities in
water in equilibrium with gaseous oxygen at one atmosphere  are given in
Table 8-7.
          TABLE 8-7.  OXYGEN SOLUBILITY IN WATER IN EQUILIBRIUM WITH
         OXYGEN GAS AT ONE ATMOSPHERE (After Davis and DeWiest, 1966)
     Temperature (°F) (°C)                   Oxygen Solubility (mg/1)

             32 (0)                                    70
             50 (10)                                   54
             68 (20)                                   44
             86 (30)                                   37
            122 (50)                                   27
     Solubilities of oxygen in various liquids are four to five times higher
under pure oxygen systems than with conventional aeration.  Therefore,  in-line
injection of pure oxygen will provide sufficient dissolved oxygen to degrade
20 to 30 mg/1 of organic material, assuming 50 percent cell conversion.  This
value is still probably insufficient for treating contaminant plumes with
higher levels of contamination, since many recyclings would be required.
However, according to Henry's Law, oxygen solubilities will significantly
                                     8-35

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increase at groundwater  depths  greater  than 30 feet or in pressurized
aquifers.

     As with aeration,  in  situ  wells  can  be installed to provide pure oxygen
to the groundwater.  The higher  oxygen  solubilities may provide some flexi-
bility in the design of  cell  banks, especially at greater pressures, since the
oxygen may not be used  up  immediately,  as  with aeration,   well distances
parallel to groundwater  flow  may then be  designed on the basis of time for
oxygen consumption if groundwater  flow  rates  are compatible.  Configuration of
an in situ oxygenation  well system may  be  similar to Figure 8-7.
                                  FIGURE 8-7.
              CONFIGURATION OF IN SITU OXYGENATION WELL SYSTEM
                 AND DISSOLVED OXYGEN CONCENTRATIONS AS A
                       FUNCTION OF DISTANCE FROM WELL
           GROUNDWATER
             FLOW
                                                      OXYGENATED ZONE
                                                      OXYGEN WELLS
                50 •
             'm  40

                20 -
                10 -
                 0 -1
                                                           A - AERATED ZONE
                                                           R - RESIDUAL ZONE
                                     8-36

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     Pure oxygen systems are expensive.  Two types of systems are available:
stored liquid oxygen and on-site generation.  Costs for the stored system are
about $100,000 for a 45 ton storage installation and supply costs are about
$100/ton within a 50 mile radius of the supplier (additional $16 for each
50 mile increment).  An on-site oxygen generation plant costs about $2.5 mil-
lion for a 30 ton per day (tpd) plant  and about $1.5 million for a 10 tpd
plant.  Power and operation and maintenance (O&M) costs are about $55 -to $75
per ton, respectively (Lamparella, 1983).

     For a temporary installation such as bioreclamation, the stored system is
recommended over the on-site generation system because of lower costs.  A
typical installation may be a bank of  50 aeration wells, supplying 5 cubic
feet per minute at 1 bar or 250 cubic  feet per minute.  This converts to 12
tons of oxygen per day using a conversion factor of 24,000 cubic feet per ton
of oxygen (Lamparella, 1983).  Supply  costs for oxygen would run about $1,200
per day.

               8.2.3.3.3  Hydrogen Peroxide

     Classically, hydrogen peroxide (H?0?) has been used as a bactericide in
medicine and as a chemical oxidant in  industrial wastewater treatment.  How-
ever, in dilute concentrations, H202 may be feasible to use as a source of
oxygen for the microorganisms associated with bioreclamation.  Bacterial cells
normally produce H?0? during respiration, and though H^Op is cytotoxic at
higher concentrations (3%), bacteria have developed enzymatic defenses against
H202 toxicity, known as hydroperoxidases (Texas Research Institute, 1982a).
This phenomena suggests that a threshold concentration exists below which
microorganisms can tolerate hydrogen peroxide.  The cells may then be free to
use the oxygen provided by the decomposition of H^Op to aerobically degrade
organic material.

     Studies conducted in flasks indicate that toxicity threshold levels for
hydrogen peroxide are dependent on cell populations.  H202 concentrations
higher than 1000 mg/1 have not been found to elicit a toxic response from
established microbial populations.  In fact, maximum cell mass was measured at
                                     8-37

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concentrations of about 1000 mg/1 H202 (Texas Research Institute, 1982a).  A
much lower toxicity threshold of 100 mg/1 H202 was exhibited with non-
established, smaller populations.  Measurements were not conducted on hydro-
carbon utilization rates.

     A major concern in the use of hydrogen peroxide as an oxygen source  is
that it may be completely decomposed in a matter of hours, thereby releasing
oxygen all at once instead of under more controlled conditions.  Then, oxygen
may bubble out of the system instead of being available for areas farther
downgradient in the aquifer.

     Decomposition of H^ can be catalyzed either biologically or chemically.
Enzymatic decomposition by hydroperoxidases (catalases and peroxidases) is the
defense mechanism of bacteria mentioned earlier.  The reactions are as follows
(Texas Research Institute, 1982a):

                                 catalase
                                 peroxidase
                           H202 + XH2 - ^2H20 + X

where X is reduced nicotinamide adenine dinucleotide (NADH), glutathione or
another biochemical reductant.
     Enzymatic decomposition of H202 to oxygen would occur only with catalases
and not with peroxidases.  Decomposition of hLO^ to oxygen also is catalyzed
by metal salts, particularly ferrous iron.  The mixture of HLO,, and ferrous
salts is called Fentons reagent, and has been widely used as a hydroxylation
reagent (Texas Research Institute, 1982a).  Reduced iron present in the
substrata may catalyze the decomposition reaction and cause immediate
decomposition and release of 0?.  Similarly, an alkaline pH will also
accelerate decomposition of the H202 molecule.
                                     8-38

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      Decomposition of H202 may be slowed by the addition of mineral acid,
dissolution in an acidic solution, or addition of a stabilizing agent,
such as acetanilide or sodium pyrophosphate (Texas Research Institute, 1982a).
However, the effect of stabilizing agents is limited to conditions of  low
metal contamination (FMC Corporation).  Introduction of H202 to soil would
cause contact with metals and thus probably catalyze the decomposition
reaction.  Other stabilizers, which slow the rate down considerably, may be
developed  .  Studies to measure decomposition rates and dissolved oxygen
retention  are required to properly assess the feasibility of H202.

     Hydrogen peroxide is available commercially for industrial uses in
35 percent, 50 percent, and 70 percent solutions (FMC Corporation).  A highly
stabilized product mix is recommended for bioreclamation; however, even this
may not be adequate because of the high susceptibility to catalytic decom-
position when in contact with metal-containing substances,  such as soils.  An
H202 storage and metering facility is required for use.  Drum or tank  storage
may be used.   Drum storage has inherent labor costs associated with it, while
a tank facility would  incur large capital costs.  Since H202 is a powerful
oxidizer,  only specific materials of construction can be used such as
aluminium  alloys, white chemical porcelain, pyrex, teflon,  and Kel- F® 81
resin (FMC Corporation). Polyethylene, stainless steel, and polyvinyl  chloride
also can be used for limited contact application.

               8.2.3.3.5  Other Oxygen Sources

     Other oxygen containing compounds have been proposed,  including potassium
permanganate, barium and strontium peroxides, and urea-peroxide (Texas
Research Institute, 1982b).  All but the latter introduce undesirable metals
into the system.  Urea-peroxide has been used in conjunction with phosphate
solutions  to treat plants suffering from oxygen starvation  in the root zone
(Texas Research Institute, 1982b).
                                      8-39

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          8.2.3.4  Pretreatment by Ozone of Other Chemical Oxidants

     In some cases, improving the biodegradability of refractory substances in
the leachate plume may be possible by pretreating with ozone or other chemical
oxidants prior to nutrient addition, reinjection, and aeration.  The role of
an oxidative pretreatment step would be to partially oxidize the refractory
compounds to a form more usable-by microorganisms.  Oxidative pretreatment, if
conducted at excessively high oxidant concentrations, could destroy bacteria
in the pumped leachate feed stream.  Also, residual concentrations of oxidant
could linger in the pretreatment effluent at levels toxic to the micro-
organisms.  However, such deleterious effects are lessened by two factors:

     •  Much of the active bacterial population will remain in the substrata
        attached to or filtered by earth materials, and thus will not be
        carried off in the pumped leachate and destroyed by pretreatment
     *  Groundwater will dilute reinjected water containing oxidant residuals,
        and thus will  help to bring down oxidant concentrations below toxic
        levels.

These factors suggest that oxidative pretreatment could be carried out in a
bioreclamation scheme without significant adverse effects on the active
microbial population.   Any deleterious effects could be further attenuated by
conducting pretreatment at subtoxic oxidant levels (to be determined by
laboratory studies), providing a retention or aeration basin to remove
residuals, or by pretreating at a lower flow rate, so that the dilution effect
of groundwater is more pronounced.

     Potential chemical oxidants include ozone, hydrogen peroxide (^Og),
ozone and HLOp mixes and other free radical forming mixtures, potassium
permanganate, and chlorine dioxide.

     Classically, ozone has been used for disinfection and chemical oxidation
of organics in water and wastewater treatment.  In commercially available
ozone-from-air generators, ozone is produced at a concentration of one to
two percent in air  (Nezgod, 1983).  In bioreclamation, this ozone-in-air
mixture could be contacted with pumped leachate using in-line  injection and
                                     8-40

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static mixing or using a bubble contact tank.  A dosage of 1 to 3 mg/1  of
ozone can be used to attain chemical  oxidation (Nezgod, 1983).  However,
German research on ozone pretreatment of contaminated drinking waters
indicates that the maximum ozone dosage should not be greater than 1 mg/1 of
ozone per mg/1 total organic carbon.   Higher concentrations may cause
deleterious effects to microorganisms (Rice, 1983).  Contact with the ozone-
in-air mixture will increase the dissolved oxygen in the leachate stream,
similar to in-line aeration.  However, additional aeration may be required,
depending on the concentration of organic material in the leachate (refer to
Section 8.2.3.3.1)..  Partial oxidation should be noted as only causing  an
increase in biodegradability of a substance.  Partial oxidation does not
decrease the amount of substance present in the leachate.

     Estimated costs for ozone pre-treatment, based on an ozone-from-air
generator and an air preparation unit to remove moisture, are shown in  Table
8-8 as a function of flow rate.  Power requirements and average power costs
for ozone-from-air systems are shown  for different size units in Table  8-9.

                 TABLE 8-8.  CAPITAL  COSTS FOR OZONE TREATMENT
                                (Nezgod, 1983)
Gas Flow Rate
Cost ($)
scfm1 m3/s2
0.5 2 x 10"4
7.0 3 x 10"3
25 0.01
250 0.1
7,090
28,000
65,000
290,000
 scfm = standard cubic feet  per minute
 m /s = cubic meter per second
                                     8-41

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00
I
ro
                                                         TABLE 8-9.
                                   POWER  COSTS  FOR  OZONE  GENERATOR SYSTEM (Nezgod, 1983)
Gas Flow Rate
scfm
0.5
7.0
25
250
m3/s
2 x 10"4
3 x 10"3
0.01
0.1
Ozone
Ibs/day
1
14
50
500
Rate
kg/day
2.2
31
110
1,100
Power Requirements
KWhr/lb 03
27.5
16.5
9.7
3.5
KWhr/kg 03
12.5
7.5
4.5
1.6
Cost
Dollars per day at
$0.08/KWhr
2.2
18.5
38.8
740

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     Hydrogen peroxide, previously discussed in section 8.2.3.3.3, can also be
used in higher concentrations as a chemical oxidant.  Hydrogen peroxide can
partially oxidize a limited number of substances including alcohols, alde-
hydes,  secondary amines, acryl chlorides, nitriles, dicarboxylic acids,
polynuclear hydrocarbons, and various unsaturated compounds.  A weight ratio
of two  to four units of H^CL per unit of organic has been recommended for com-
plete oxidation to carbon dioxide and water (FMC, 1978).  Partial oxidation
would most likely require a lesser concentration.

     Hydrogen peroxide can also be used  in combination with ozone or ferrous
salts to produce hydroxyl (OH-) free radicals which will attack a greater
number  of substances (Rice, 1983).  Incorporating these combined treatments to
partially oxidize the more refractory compounds may be possible.

     Other oxidants, such as potassium permanganate and chlorine dioxide, may
also be considered for use in an oxidative pretreatment.  However, the use of
such chemicals introduces undesirable substances to the groundwater.

     Potassium permanganate introduces manganese to the groundwater, which
besides being a contaminant, may clog well screens and soil pores upon
precipitation.

          8.2.3.5  Nutrients and Other Additives

     Nitrogen and phosphorus are usually the limiting nutrients in biodegrada-
tion processes and must be added if not  present  in sufficient quantities to
support an active microbial population.  Analysis of cell protoplasm indicate
that the carbon: nitrogen: phosphorus weight ratio  is 100:15:3  (Thibault and
Elliot, 1980).  The total amount of nitrogen and phosphorus required could be
calculated if the following were known:

     •  The total volume of contaminated water to be treated
     •  The amount of elemental carbon available in the organic compounds
        present
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     •  Nitrogen and phosphorus  associated  with  the  organic  compounds  present
        in the  leachate plume.

     Usually the above quantities  are not known, therefore nutrient  levels
cannot be accurately calculated.   Determining the optimum amount  of  these
nutrients should be based on previous research from  similar  projects and
treatability studies conducted  in-the laboratory, if available.   Other
nutrients required for sustaining  microbial  populations  include potassium,
sulfur, sodium, calcium, magnesium,  iron, and manganese.  With the exception
of potassium, most of these substances  are  present in  sufficient  quantities
in the groundwater and need not  be supplemented.  As  with nitrogen and
phosphorus, potassium supplements  will  most  likely need  to be added  to the
leachate plume.

     In previous bioreclamation  projects not utilizing  in situ methods,
required levels of nutrients have  been  derived empirically through plate
counts and shaker studies.  Growth studies  conducted  by  Suntech Inc. on  a
gasoline-contaminated groundwater  incorporated a basal salts medium.
Composition of the medium is given in Table  8-10 (Jamison, et al., 1976).

     Once microbial activity was established, Suntech,  Inc.  applied  bulk
quantities of ammonium sulfate [(NH4)2S04],  disodium  phosphate (Na2HP04),  and
monosodium phosphate (NaH2P04) to  the groundwater in  the form of  a 30% con-
centrate in water which was metered  into test wells.  They determined  that
other nutrient substances were present  in sufficient  quantities in the aquifer
and did not need to be added.  The solution  was made  up  in a 2200 gallon tank
truck and contained 1.7 tons (NH4)2S04, 0.5  tons) Na2HP04, and 0.4 tons
NaH2P04 (Raymond, et al., 1976).   Suntech Inc.,  in flask studies, found that
the forms of nitrogen and phosphorus were not critical.  However, they did
find from this initial investigation that diammonium  phosphate could not be
used because of excessive precipitatio-n (Jamison, et  al., 1976).

     Groundwater Decontamination Systems (CDS) Inc.  used a variation of the
basal salt medium in a combined  surface and  in situ microbial degradation
system.  Concentrations of nutrients added  to the surface biotreatment system
are given in Table 8-11.  GDS Inc. (1982) has also used  the  Davis medium,
                                     8-44

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 TABLE 8-10.  COMPOSITION OF BASAL SALTS MEDIUM
            (Jamison, et al., 1976)
Salt Type
KH2P04
N cl/-» n r U H
r A-
(NH4)N03
MgS04.7H20
Na2C03
CaCl2.2H20
MnS04.H20
FeS04.7H20
Concentration (mg/1)
400
600
10
200
100
10
20
5
TABLE 8-11.  BASAL SALT MEDIUM USED BY GDS INC,
  (Groundwater Decontamination Systems,  Inc.,
      1983 as cited Cochran, et al., 1984)
Salt
NH4C1
KH2P04
K2HP04
MgS04
Na2C03
CaCl9
2
MnSO.
4
FeS04
Concentration (mg/1)
500
270
410
1.4
9
0.9

1.8

0.45
                      8-45

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which contains citrate to hold trace metals in solution, for growth  studies.
Adding citrate if alkaline groundwater  is encountered may be advisable when
metals would tend to precipitate.  Exact composition of the nutrient mix may
be varied to accommodate pH adjustment  and buffering capabilities.

     Adding low concentrations of readily metabolized protein-type compounds
(such as peptone, yeast extract, nicotinamide, riboflavin, pyridoxine, and
thiamine) have been found to often promote biodegradation of other target
organics.  However, high concentrations of these substances may hinder
degradation of the target hydrocarbons  (Texas Research  Institute, 1982b).  Use
of these protein sources may become important when low  levels of target
organics are reached and some substrate is required to  sustain an active
microbial population.

     The use of biodegradable emulsifiers to "pseudo-solubilize" hydrocarbons
also has been proposed to increase the  availability of  the nonsolubles to the
microorganisms (Thibault and Elliot, 1980).  However, emulsifiers have been
found to cause foaming in aeration wells, which may present mechanical
problems.  This is especially true if surfactant emulsifiers are to  be used
(Raymond, et al., 1976).  Non-toxic and biodegradable anti-foaming agents
possibly may be added to control this.

     As mentioned earlier, pH control can be attained by adjusting the
nutrient salt composition to produce a  specific pH (around 7) and serve as a
buffer to maintain this pH.  Also, mineral acids (preferably nitric  or
phosphoric) and alkaline substances (sodium hydroxide or lime solutions) can
be used for pH control.  Acid conditions (pH 6 to 7) should be maintained if
hydrogen peroxide is being proposed as  the oxygen supply to retard catalytic
decomposition.  Biological systems are  vulnerable to sudden changes  in
environment and addition of nutrients,  additives, and pH control reagents
should be performed gradually.   In operations, batch and slug doses  should be
avoided to prevent toxic, osmotic, and  pH shock conditions, especially if the
more susceptible engineered microorganisms are used.  Since nutrient additions
may be potentially contaminating the groundwater, consideration should be
given to minimize the applied concentrations.
                                     8-46

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          8.2.3.6  Other Design Aspects

     Optimum extraction and injection flow rates will many times be pre-
determined by aquifer yield limits or hydraulic design for plume containment.
The factors affecting aquifer flow rates are described in Chapter 5,
Groundwater Pumping.

     Aquifer flow rates should be sufficiently high  so that the  aquifer  is
flushed several times over the period of operation.  Thus, if the cleanup
occurs over a three-year period, flow rates between  injection and extraction
wells should be such that a residence time of one-half year or less occurs
between the well pairs.  This corresponds to six or  more flushes.  Several
recycles would cause flushing of soils containing organics, preventing the
clogging caused by microorganism build-up (because of  increased  flow  rate);
more even distribution of nutrients and organic concentration within  the
plume; and better and more controlled degradation.   Flow rates and the number
of recycles should not be high enough to incur excessive pumping costs,  loss
of hydraulic containment efficiency because of turbulent conditions,  or  cause
corrosion, excessive deposition on system components,  flooding,  or well  blow
out.  The operating period will depend on the field  biodegradation rate  of  the
contaminants in the plume and the number of recycles.  If the period  of
operation is excessively long, for example more than 5 years, the operating
costs of bioreclamation may outweigh the capital costs of another remedial
alternative.

          8.2.3.7  Operation  and Maintenance

     Operation and maintenance of a bioreclamation process involve aspects  of
the hydraulic  system as well  as the biological system.  The hydraulic aspects
relate to pumps, extraction wells, injection wells,  and  injection trenches,
which have been discussed previously in Chapters 5 and 6.

     In a biological system,  pH should be maintained in a range  between  6  and
8 and concentrations of both  nutrients and organics  should be kept as uniform
as possible to protect against shock loading.  Dissolved oxygen  should be
                                     8-47

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maintained above the critical concentration for the promotion of aerobic
activity, which ranges from 0.2 to 2.0 mg/1, with the most common being
0.5 mg/1 (Hammer, 1975).

     Clogging of the aquifer, injection wells or trenches, and extraction
wells by microbiological sludge is a possibility.  GDS Inc. installed two
wells in each of their injection trenches in case flushing was ever required
to remove sludge.  After 1-1/2 years of operation clogging had not occurred
(Groundwater Decontamination Systems Inc., 1982).  Microorganisms growing on
toxic organics have characteristically low growth rates compared to those
growing on other substrate systems.  Therefore, they are not expected to
produce much sludge (Wilson, et al., 1982).  The above suggests that clogging
may not be a usual occurrence in bioreclamation of aquifers contaminated with
toxic organics.

     Maintenance of the bacterial population at their optimal