GROUND WATER CONTAMINATION STUDIES
Handbook
Presented to:
I U. S. ENVIRONMENTAL PROTECTION AGENCY
* Region VI, Dallas, Texas
October 26th-28th, 1987
Presented by:
INTERNATIONAL TECHNOLOGY CORPORATION
Austin, Texas
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GROUND WATER CONTAMINATION STUDIES
Short Course Handbook
Presented to
U. S. Environmental Protection Agency
Region VI
October 26, 27, and 28, 1987
Prepared by
International Technology Corporation
October 1987
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TABLE OF CONTENTS
PAGE
LIST OF TABLES vi
LIST OF FIGURES viii
INTRODUCTION xiii
ACKNOWLEDGEMENTS xvi
1.0 GROUND WATER HYDROLOGY 1-1
1.1 HYDROLOGIC CYCLE 1-5
1.2 HYDROLOGIC PROCESSES OF GROUND WATER FLOW 1-5
1.2.1 Principles of Ground Water Flow 1-10
1.2.1.1 Darcy's Law 1-12
1.2.1.2 General Ground Water Flow Direction 1-14
1.2.2 Aquifer, Aquitards, and Aquicludes 1-15
1.2.2.1 The Aquifer, the Matrix in which
Ground Water Flows 1-15
1.2.2.2 Aquicludes and Aquitards 1-22
1.3 GROUND WATER RESOURCES 1-23
1.3.1 Description of Major Aquifer Systems in EPA
Region VI States 1-23
1.3.1.1 Arkansas 1-23
1.3.1.2 Louisiana 1-26
1.3.1.3 New Mexico 1-29
1.3.1.4 Oklahoma 1-32
1.3.1.5 Texas 1-36
1.3.2 Ground Water Use 1-40
1.4 WELLHEAD PROTECTION REQUIREMENTS 1-41
1.4.1 Wellhead Protection Area Method Development 1-41
1.4.2 Protection From Spills (Immediate Zone) 1-42
1.4.3 Well Construction Standards 1-42
1.4.3.1 Well Casings and Grouting 1-42
1.4.3.2 Casing Installation 1-44
1.4.3.3 PVC Casing 1-44
1.4.4 Well Plugging Procedures 1-46
1.4.5 Buffer Zone 1-46
1.4.6 Protection From Bacteria 1-46
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TABLE OF CONTENTS (Continued)
PAGE
1.4.7 Protection From Contamination by Naturally Occurring
or Synthetically Derived Organic Compounds 1-48
1.4.8 Wellhead Protection Area Delineation Methods 1-49
1.4.8.1 Arbitrary or Calculated Fixed Radii 1-49
1.4.8.2 Simplified Variable Shapes 1-49
1.4.8.3 Analytical Methods 1-53
1.4.8.4 Hydrogeologic Mapping 1-53
1.4.8.5 Numerical Flow/Transport Models 1-53
1.4.8.6 Conclusion 1-53
2.0 GROUND WATER CHEMISTRY 2-1
2.1 CONSTITUENTS IN GROUND WATER 2-1
2.1.1 Inorganic Constituents 2-4
2.1.2 Organic Constituents 2-7
2.2 SIGNIFICANCE OF LOW CONCENTRATIONS OF ORGANIC AND INORGANIC
COMPOUNDS 2-14
3.0 INVESTIGATIVE TECHNIQUES 3-1
3.1 BACKGROUND DATA 3-1
3.1.1 Soil Data 3-2
3.1.2 Boring Inventory 3-3
3.1.3 Geology 3-4
3.1.4 Ground Water Data 3-5
3.1.5 Aerial Photos 3-6
3.1.6 Landsat Image Data 3-6
3.1.7 Additional Sources 3-7
3.2 FIELD INVESTIGATIVE TECHNIQUES 3-7
3.2.1 Geophysical Methods 3-7
3.2.1.1 Earth Electrical Resistivity Surveys 3-8
3.2.1.2 Ground Penetrating Radar 3-18
3.2.1.3 Magnetic Surveys 3-20
3.2.2 Exploratory Drilling 3-25
3.2.2.1 Drilling Methods 3-28
3.2.2.2 Logging Techniques 3-31
3.2.3 Monitor Wells 3-41
3.2.3.1 Well Location 3-41
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TABLE OF CONTENTS (Continued)
PAGE
3.2.3.2 Screen Placement 3-46
3.2.3.3 Installation Methods 3-46
3.2.3.4 Materials of Construction 3-54
3.2.3.5 Well Development Methods 3-58
3.2.4 Lysimeters 3-63
3.2.4.1 Installation and Operation of
Suction Lysimeters 3-63
3.2.4.2 Installation and Operation of
Pan Lysimeters 3-73
3.2.4.3 Other Information on Lysimeters 3-74
3.2.5 Tensiometers 3-74
3.2.6 Cone Penetrometer Surveys 3-75
3.2.6.1 Description 3-76
3.2.6.2 Cone Penetrometer Log Correlation 3-80
3.2.6.3 Other Uses 3-80
3.2.7 Soil Gas/Vapor Monitoring 3-83
3.2.7.1 Liquids and Gases as Flow Media 3-84
3.2.7.2 Soil Vapor Sampling 3-84
3.2.7.3 Sample Analysis 3-85
4.0 MIGRATION OF CONTAMINANTS/AQUIFER CHARACTERIZATION 4-1
4.1 UNSATURATED ZONE 4-1
4.1.1 Effect of Thickness 4-1
4.1.2 Effect of Composition 4-3
4.1.3 Effect of Unsaturated Permeability 4-5
4.2 SATURATED ZONE 4-7
4.2.1 Direction and Rate of Ground Water Flow 4-7
4.2.2 Permeability 4-9
4.2.3 Density of Contaminant Plume 4-13
4.2.4 Chemical Reactions 4-16
4.3 AQUIFER CHARACTERIZATION TESTS 4-19
4.3.1 Field Tests 4-19
4.3.1.1 Aquifer Characteristics Definitions 4-19
4.3.1.2 Steady State (Equilibrium) Method 4-21
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TABLE OF CONTENTS (Continued)
PAGE
4.3.1.3 Transient (Non-Equilibrium, Non-Steady)
Methods 4-29
4.3.1.4 Conducting An Aquifer Characteristics Test 4-38
4.3.1.5 Test Design and Analysis 4-40
4.3.1.6 Slug Tests 4-45
4.3.1.7 Field Permeameter Test 4-53
4.3.2 Laboratory Tests 4-53
4.3.2.1 Index Tests 4-56
4.3.2.2 Permeability Tests 4-60
5.0 HEALTH AND SAFETY WITH RESPECT TO GROUND WATER INVESTIGATIONS 5-1
5.1 JOB-SPECIFIC HEALTH AND SAFETY PLANS 5-1
5.1.1 Assignment of Responsibilities 5-1
5.1.2 Employee Training and Information 5-2
5.1.3 Employee Decontamination 5-2
5.1.4 Personal Protective Equipment and Procedures 5-2
5.1.5 Regulated Areas 5-4
5.2 GENERAL WORK PRACTICES 5-4
5.2.1 Personal and Ambient Air Monitoring 5-4
5.2.2 Emergency Procedures 5-4
5.3 PROBLEMS ASSOCIATED WITH HEALTH AND SAFETY PROGRAMS 5-5
6.0 SAMPLE INTEGRITY 6-1
6.1 SAMPLE COLLECTION AND HANDLING 6-1
6.1.1 Decontamination and Sampling Procedures for Soils 6-1
6.1.2 Collection of Ground Water Samples ' 6-3
6.1.2.1 Static Water Level Measurements 6-3
6.1.2.2 Detection of Immiscible Layers 6-4
6.1.2.3 Well Purging 6-5
6.1.2.4 Sampling Devices 6-6
6.1.3 Proper Handling of Samples 6-9
6.1.3.1 Sample Preservation 6-9
6.1.3.2 Chain-of-Custody 6-15
6.1.3.3 Preparation, Packaging, Handling
and Shipping 6-17
IV
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TABLE OF CONTENTS (Continued)
PAGE
6.1.3.4 Sample Storage 6-17
6.1.4 RCRA Sampling Versus Real World Sampling 6-18
6.2 SAMPLE ANALYSIS AND DATA INTERPRETATION 6-19
6.2.1 Use of Blanks 6-20
6.2.2 Choice of Analytical Parameters 6-20
6.2.3 Detection Limits 6-24
6.2.4 Analytical Precision and Matrix Effects 6-33
6.2.5 Sources of Contamination in the Laboratory 6-35
6.2.6 Adsorption of Air Emissions 6-36
6.2.7 Sources of Sample Contamination in the Field 6-36
6.2.8 Physical and Chemical Concerns 6-40
7.0 GROUND WATER MODELING 7-1
7.1 FLOW MODELS 7-1
7.2 MASS TRANSPORT MODELS 7-3
7.3 GUIDELINES TO CHOOSING AND USING A MODEL 7-4
7.4 USE OF MODELS IN CONTAMINATION STUDIES 7-5
7.5 AVAILABILITY OF MODELS 7-6
8.0 BIBLIOGRAPHY 8-1
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LIST OF TABLES
TABLE NO. TITLE PAGE
1-1 Contamination of Major Aquifers 1-2
1-2 Contamination of Shallow Aquifers 1-3
1-3 Comparison of Contaminated vs. Uncontaminated
Ground Water 1-4
1-4 Permeability 1-11
1-5 Aquifer Definitions 1-17
1-6 Methods of Management of the Immediate Area 1-43
1-7 Wellhead Protection Area Delineation Methods 1-50
2-1 Distribution of Chemical Constituents in
Natural Waters 2-2
2-2 Texas and EPA Standards for Drinking Water 2-3
2-3 Trace Metal Concentrations: Range in Coal, Ash
Bedrock, Soil, and Plants 2-8
2-4 Occurrence of Metals 2-9
2-5 EPA Hazardous List Compounds Found in Coal 2-13
2-6 National Urban Runoff Program (NURP) Priority
Pollutant Sampling Results 2-15
2-7 Range of Chemical Constituents Found in 20
Peat Samples from Three Canadian Bogs 2-18
2-8 Chemical Analysis of Water Samples From Peat
Bogs in Canada 2-19
3-1 Resistivities of Different Rock and Sediment Type 3-9
3-2 Resistivity Values for Selected Sediments 3-10
3-3 Drilling Methods 3-29
3-4 Unified Soil Classification System 3-33
3-5 Field Identification Procedures for Fine-grained
Soils or Fractions 3-35
3-6 Well Casing and Screen Materials 3-56
3-7 Leachate Analysis of #200 Novacite 3-68
3-8 Physical and Chemical Data on Novacite 3-68
4-1 Sample Field Permeability Calculation 4-54
6-1 Addition of Acidic Preservative Prior to Filtering 6-12
6-2 Travel and Field Blank Results 6-21
VI
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LIST OF TABLES (Continued)
TABLE NO. TITLE PAGE
6-3 Results of Organic Analysis of Laboratory Blanks
Oklahoma State Department of Health Laboratory
(Matrix Unknown) 6-22
6-4 Results of Organic Analysis of Laboratory Blanks
Gulf South Research Institute, New Orleans, LA 6-22
6-5 Organic Compounds Found in Method Blank Analysis 6-23
6-6 Volatile Hazardous Substance List Compounds 6-25
6-7 Acid Extractable Hazardous Substance List Compounds 6-28
6-8 Base/Neutral Extractable Hazardous Substance
List Compounds 6-29
6-9 QC Limits for Water and Soil 6-34
6-10 Organic Analyses of Well Water and Corresponding
Field Blanks - 2,4-Oinitrotoluene,
2,6-Dinitrotoluene 6-37
vii
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
1-1 Hydrologic Cycle 1-6
1-2 Flow in Porous Sediments 1-8
1-3 Diagram Depicting Aquifer Terms 1-9
1-4 Darcy Tube 1-13
1-5 Approximate Altitude of Water Levels in Wells
Completed in the Goliad Sand, 1977-1978 1-16
1-6 Plots of Permeability Versus Porosity 1-19
1-7 Plot of Permeability Versus Grain Size 1-20
1-8 Principal Aquifers in Arkansas 1-24
1-9 Principal Aquifers in Louisiana 1-27
1-10 Principal Aquifers in New Mexico 1-30
1-11 Principal Aquifers in Oklahoma 1-33
1-12 Major Aquifers in Texas 1-37
1-13 Minor Aquifers in Texas 1-38
1-14 Well Casing and Completion Methods 1-45
1-15 Fixed Radius Method for WHPA Delineation 1-51
1-16 Variable Shapes for WHPA Delineations 1-52
1-17 Analytical Method for WHPA Determination 1-54
1-18 Hydrogeologic Mapping for WHPA Determination 1-55
1-19 WHPA Comparison for Three Methods 1-56
3-1 Electrical Resistivity Electrode Configuration 3-12
3-2 Resistivity Data Sheet 3-14
3-3 Resistivity Sounding 3-16
3-4 Resistivity Survey of a Salt Water Disposal Pond 3-17
3-5 Electrical Resistivity Sounding 3-19
3-6 Block Diagram of Fluxgate Magnetometer 3-22
3-7 Example of Typical Magnetic Anomaly 3-24
3-8 Magnetic Survey Results 3-26
3-9 Magnetic Contour Map of a Superfund Site in
Arkansas 3-27
3-10 Comparison of Geophysical and Geologic Log 3-37
3-11 Example of a Gamma Ray Log Compared to the
Stratigraphic Log Determined by the Driller 3-39
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LIST OF FIGURES (Continued)
FIGURE NO. TITLE PAGE
3-12 Delineation of Confining Zone by Gamma Log
Which Were Not Apparent in Grab Samples of the
Mud Rotary Cuttings 3-40
3-13 Cross Section A-A' Based on Drillers Log Description 3-42
3-14 Cross Section A-A' Based on Natural Gamma Ray Logs 3-43
3-15 Potential Paths for Subsurface Migration of Waste 3-45
3-16 Cluster Well Completions 3-47
3-17 Completion of a Monitor Well Using Mud Rotary
Drilling 3-50
3-18 Manganese Concentrations vs. Time of Pumping-Data
from Well Shown in Figure 3-15 3-52
3-19 Monitor Well Installation Diagram 3-53
3-20 Monitor Well Surface Completion 3-55
3-21 G. C. Scan Water Sample from Monitor Well
Constructed with PVC Pipe and Glue 3-59
3-22 G. C. Scan - PVC Pipe and Glue in Distilled Water 3-60
3-23 Lysimeter Vacuum 3-64
3-24 Pressure-vacuum Lysimeter 3-65
3-25 Modified Pressure-vacuum Lysimeter 3-66
3-26 Sampling and Installation of Pressure-vacuum
Lysimeters 3-69
3-27 Sampling and Installation of Vacuum Lysimeters 3-70
3-28 Alternate Lysimeter Installation 3-71
3-29 Cone Penetrometer and Instrument Log 3-77
3-30 Soil Classification Chart for Standard Electric
Friction Cone (After Douglas and 01 sen, 1981) 3-78
3-31 Comparison of Soil Boring, Electric Logs, and
Cone Penetrometer Logs 3-79
3-32 Cross-Section from Cone Penetrometer Logs 3-81
3-33 Isopach Map of Stratigraphic Zone "A" 3-82
4-1 Schematic Diagram of Contaminant Flow in an
Unconfined Homogeneous Aquifer 4-2
4-2 Effects of Unsaturated Zone Lithology on
Contaminant Migration 4-4
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LIST OF FIGURES (Continued)
FIGURE NO. TITLE PAGE
4-3 Suction and Permeability Versus Degree of
Saturation for Compacted Fine Clay (Olson and
Daniel, 1979) 4-6
4-4 Schematic Diagram of Flowlines in the Vicinity
of a Potentiometric Mound 4-8
4-5 Effect of Differences in Transverse Dispersivity
on Shapes of Contamination Plumes (Miller, 1980) 4-10
4-6 Altitude of Water Levels, Deep Aquifer, Showing
Mounded Water Surface Under a Cooling Lake Near
Corpus Christi, Texas, April 14, 1981 4-11
4-7 Potentiometric Surface Map Before and After
Ground-Water Mounding 4-12
4-8 Migration of Contaminant Plume with Density
Equal to Ground Water 4-14
4-9A Contaminant Plume with Density Greater than
Ground Water 4-15
4-9B Contaminant Plume with Density Less than the
Ground Water 4-15
4-10 Cross Section of Disposal Site on the Texas
Gulf Coast 4-17
4-11 Graphical Concepts of the Hydraulic Conductivity
and Transmissivity 4-20
4-12 Graphical Concepts of Hydraulic Gradient 4-22
4-13 Graphical Concept of Storage Coefficient and
Storativity (After Heath, 1983) 4-23
4-14 Various Terms Used in the Equilibrium Equation
for a Confined Aquifer 4-26
4-15 Various Terms Used in the Equilibrium Equation
for an Unconfined Aquifer 4-27
4-16 Graphic Depiction of Cone of Depression as Defined
by Observations in Three Wells 4-28
4-17 Theis Method of Superposition for Solution of the
Nonequilibrium Equation Using a Reverse Type Curve 4-32
4-18 Type Curves for Analysis of Pumping Test Data to
Evaluate Storage Coefficient and Transmissivity
of Leaky Aquifers 4-34
4-19 Graphic Depiction of the Jacobs Straight Line
Method for Analyzing Aquifer Test Data 4-35
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LIST OF FIGURES (Continued)
FIGURE NO. TITLE PAGE
4-20 Semilog Plot of Data from Three Observation Wells for
Distance Drawdown Analysis (After Driscoll, 1986) 4-37
4-21 Time-drawdown Plot for a Well Discharging 2,700
gpm (After Driscoll, 1986) 4-42
4-22 Drawdown Data for 6-in. (152-mm) Test Well in
Brewster, Minnesota (After Driscoll, 1986) 4-42
4-23 Drawdown Data Showing Barometric Effects (After
Hall Southwest, 1983) 4-43
4-24 Recovery Data Showing Effects of Nearby
Intermittently Pumping Wells 4-44
4-25 Well Into Which a Volume, V, of Water is Suddenly
Injected for a Slug Test of a Confined Aquifer 4-47
4-26 Type Curves for Slug Test in a Well of Finite
Diameter 4-48
4-27 Geometry and Symbols of Partially Penetrating
Partially Perforated Well in Unconfined Aquifer
with Gravel Pack or Developed Zone Around Perforated
Section (Bouwer and Rice, 1976) 4-50
4-28 Curves Relating Coefficients A, B and C to
L/rw (From Bouwer and Rice, 1976) 4-51
4-29 Field Permeameter Installation 4-55
4-30 Plasticity Chart 4-58
4-31 Permeameter Cell 4-62
4-32 Pressure Board 4-63
4-33 Influence of Using Distilled Water (from
Wilkinson, 1969) 4-65
4-34 Effect of Temperature on Permeability 4-66
5-1 Tailgate Safety Meeting Form 5-3
5-2 Emergency Numbers Form 5-6
6-1 Concentrations of Chemical Parameters vs.
Pumping Time 6-7
6-2 Field Refrigeration of Samples Using Water Ice 6-13
6-3 Bottles Placed in Crushed Ice Chilled to 40°C,
and Transferred to Ice Chest Pre-Chilled with
Blue Ice 6-13
6-4 Field Refrigeration of Sample Using Blue Ice 6-14
6-5 Chain-of-Custody Record 6-16
XI
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LIST OF FIGURES (Continued)
FIGURE NO. TITLE PAGE
6-6 Flow Behavior of Leachate from a Surface
Impoundment 6-44
XII
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INTRODUCTION
PURPOSE OF SEMINAR
The Southwest is blessed with an abundance of ground water. This abundance of
water, the fact that the Sunbelt has always been an attractive location for
industry, and the general lack of understanding of ground water systems have
resulted in numerous occurrences of ground water contamination. The purpose
of this seminar is to acquaint the regulatory staff with the potential for
pollution from man's activities and to demonstrate study techniques that will
enable them to determine the extent of ground water problems at individual
sites.
Recent federal and state regulatory programs have had an effect on future
siting and construction of waste facilities. New construction standards
should reduce the incidences of ground water pollution in the future. How-
ever, the extent of contamination from existing and closed facilities must be
addressed if we are to have sufficient, good quality water for future economic
growth and to meet the legislated goals for the environment.
This seminar does not pretend to be a state-of-the-art course as the state of
the art changes each minute. Advances in knowledge about contaminant migra-
tion are occurring at a tremendous pace. However, regardless of the state of
knowledge, unless regulators understand the procedures by which investigations
are conducted, and how they can be conducted, then reports from industry
cannot be properly evaluated.
At the conclusion of this seminar, the participant should be able to review
reports from industry and/or their consultants and determine if adequate
information has been developed to determine the pollution potential of new or
existing disposal sites. The participants should be able to take the raw data
presented in these reports and develop their own conclusions about the site.
The seminar should also assist those who will be required to conduct field
evaluations of facilities regulated under the Resource Conservation and Recov-
ery Act (RCRA).
xn i
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This course and other similar ones have been presented to regulatory agencies
several times. One common concern about such courses is the problem of regu-
lators requiring a company or consultant to "do something" because of what
they have "just learned in a short course." What are we striving to promote
in this course is the ability to think through data with an understanding of
how the data was obtained, which allows the individuals to reach independent
professional opinions. We are not presenting the right way or the only way,
but instead are presenting only one way.
INTRODUCTION TO SPEAKERS
Bob Kent is a certified ground water professional and professional geological
scientist with over 13 years of experience in the area of ground water
management. His experience has been obtained by working for administrative
agencies, private industry, and municipal and federal governments. Mr. Kent's
major areas of experience are related to ground water contamination studies,
subsurface injection systems, waste management techniques, and ground water
resource evaluations.
Typical ground water contamination projects undertaken by Mr. Kent include the
development and supervision of a ground water contamination study of a large
regional aquifer in the Texas Panhandle, and the performance of field investi-
gations of ground water contamination from waste disposal sites. Mr. Kent is
the author of numerous papers on injection systems, ground water recovery
systems, and waste management.
Ed Fendley is the acting supervisor of the engineering staff of IT
Corporation's Austin office. Mr. Fendley is a project engineer and manages
projects concerned with the design of hazardous waste treatment and disposal
facilities, site assessment, and site remediation. His experience includes
the design of hazardous waste land disposal units, closure alternatives for
hazardous units, ground water recovery systems, and permitting assistance.
Representative ground water contamination and recovery projects include
conceptual design, feasibility studies, and installation.
Mark Katterjohn is a project geologist with seven years of experience in
geology, geophysics, and chemistry. His experience in ground water and
xiv
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subsurface geology has been gained through working for technical consulting
firms and state agencies. Over the last few years, Mr. Katterjohn has
evaluated subsurface conditions related to ground water occurrence, quality,
usage, and contamination as well as injection well practices. His experience
includes evaluation of the hydrology and geology of single and multiple
aquifer systems of regional and site specific scope in the United States and
abroad. Mr. Katterjohn has prepared and presented several courses on ground
water sampling and data interpretation and ground water contamination studies.
EXPLANATION OF SEMINAR HANDBOOK
The seminar is primarily a series of lectures by speakers who are relating
their practical knowledge and experience in the subjects covered. This
handbook is not a textbook to be reiterated during the course, but is provided
as a supplementary material to the content of the lectures. While the
lectures are geared toward the overall content of the handbook, they may not
follow the text and substantial additional information will be presented in
the lectures.
xv
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ACKNOWLEDGMENTS
This seminar handbook was prepared by International Technology Corporation. A
large portion of the book has been adapted from previous course books prepared
by Underground Resource Management, Inc. A number of past and current employ-
ees of these firms have contributed time to assemble the information presented
here and in the course presentation. It is not possible to list all the indi-
viduals here. Major contributions that have not been previously presented
have been made to this new book. The contributors of this new information
are: Mark Katterjohn, Bob Krasko, Perry Mann, Ed Fendley, and Phil Bullock.
Additional staff members who have worked in the preparation of this course
are: Charlie Mauldin, Kathy Payne, Terry Moody, Jene Thomas, and Elaine
AlIan.
xvi
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SECTION 1.0
GROUND WATER HYDROLOGY
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1.0 GROUND WATER HYDROLOGY
The term "ground water" refers to water occupying the voids within a geologic
stratum. This saturated zone is distinguished from the unsaturated zone where
the voids are filled with both water and air. The water-bearing formations of
the earth's crust act as conduits for the transmission of and as reservoirs
for the storage of water.
Over the years, various agencies and consultants have conducted investigations
into the quality and quantity of ground water in the region. These investiga-
tions have documented numerous site-specific examples of ground water pollu-
tion. Regional water quality contamination is not indicated, although in some
areas of the state, over 1,500 acres of ground water have been affected from a
single evaporation pond.
The areas of the region where major ground water contamination is most likely
to occur corresponds to the outcrop area of major and minor aquifers. Fortu-
nately, many of these areas are not heavily industrialized and although numer-
ous cases of ground water contamination have occurred, the effects are primar-
ily local. Table 1-1 is a listing of several cases of ground water contamina-
tion where the contaminated aquifer is the only ground water source in the
area. Table 1-2 is a list of occurrences of shallow aquifer contamination
where the aquifer is not a source of drinking water. These cases are primar-
ily in the Texas Gulf Coast area where numerous shallow sands exist in an
otherwise clay soil environment. Generally, this type of contamination is
restricted to the general vicinity of the plant.
Frequently, the waste streams contain greater concentrations of naturally
occurring substances than the native ground water. Table 1-3 is a comparison
of water quality data of several wells before and after contamination. Data
presented in other sections of this seminar handbook demonstrate the diffi-
culty of determining if an aquifer is contaminated. Frequently, contamination
can be identified by analysis for the normal ground water constituents, which
exist in different concentrations than in the wastewater. In order to evalu-
ate sites which may contribute to ground water problems, an understanding of
the hydrology is required.
1-1
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1-2
-------
TABLE 1-2
Contamination of Shallow Aquifers
INDUSTRY TYPE
Petrochemical**
Power plant
Petrochemical**
Petrochemical**
Steel Pipe
Manufacturer
Chemical
Iron and Plastic
Pipe Manufacturer
POLLUTION SOURCE
Abandoned disposal
site
Cooling lake
Lagoons
Lagoons
Effluent Ponds, Sludge
Drying Basins
Effluent Ponds
Sludge Drying Lagoons
CONTAMINANTS FOUND
IN GROUND WATER
High TDS, arsenic,
phenols
High TDS*
Phenols, chlorin-
ated hydrocarbons
High TDS*
High TDS*, Iron (1460mg/l)
High TDS*, Cadmium,
Chromium, Lead, Nickel,
Silver, Barium, Selenium
High TDS*, F
EFFECTS OF
CONTAMINANTS
shallow unused jquifei
no damage to deeper
regional aquifer -
some discharge to
surface water
some surface damage,
shallow aquifer in
plant contaminated,
slight leakage Uu u
aquitard and some
effect on the region-
al aquifer
local effects in
plant area on
shallow sands - no
danger- to regional
system - possible
migration off
plant along pipe-
lines, drainage
ditches, etc.
Local effects in plant
area on shallow
sands - future possi-
bility of migr at ion
to local water wells
Local effects in
plant area on shallow
sands - future possi-
bility of migrat ion
to local water wells
Minimal local con-
tamination of
shallow aquifer-.
Negligible chance of
migration of contami-
nants to deeper
aquifers
*Chemical analysis in Table 1-3.
**More than one documented case.
1-3
-------
TABLE 1-3
Comparison of Contaminated vs. Uncontamlnated Ground Water
Domestic well before and
after contamination by cooling
tower blowdown
Domestic well before and after
contamination by sewage disposal
ponds
Domestic well before and after
contamination by effluent from
magnesium plant
Monitor well before and after
contamination by salt water
pond
Monitor well before and after
initial influence of cooling
reservoirs
Monitor well before and after
contamination by leachate
from disposal site
An uncontaminated shallow
monitor well and a monitor
well completed at the same
depth, contaminated by pond
effluent
An uncontaminated shallow
monitor well and a monitor
well, completed at the same
depth, contaminated by pond
effluent
An uncontaminated shallow
monitor well and a monitor
well, completed at the same
depth, contaminated by pond
effluent
An uncontaminated area well
compared to a contaminated
monitor well
An uncontaminated area well
compared to a contaminated
monitor well
B
A
B
A
B
A
B
A
B
A
B
A
UC
C
UC
C
UC
C
UC
C
UC
C
Ca
27
224
55
111
86
478
56
808
90
177
95
190
98.2
714
127
545
2.0
120.0
90
474.4
41
43
Mg
30
268
56
92
28
222
32
538
23
49
20
100
65.7
1950
28
119
2.6
255.2
37
196.9
1
4.6
Na
40
799
57
192
28
152
161
3550
319
561
370
725
2040
2560
110
310
25.9
14,948
400
1439.0
2
32
HC03
265
203
284
395
378
310
189
49
165
317
575
465
6940
372.3
120.5
-
1.5
376
322.6
123
103
So4
17
1388
90
299
31
311
250
7680
24
159
155
1590
1150
415
285
3856
21.6
8489.5
400
1703.2
<4
66
Cl
6
1210
118
246
37
1318
110
1116
605
1020
355
305
2400
9470
64
303.9
34.0
18,694.2
380
1733.5
5
26
No 3
5
162
<4
123
--
—
~
—
—
—
1
0.5
10.2
25
7
5.1
0.4
1200.7
3.1
35.4
2.1
2.0
TOS
340
4310
560
1320
396
2630
798
13,856
1226
2283
1285
2960
5876
47,355
816
8874
144
45,350
1560
6338
124
318
TOC
119
12,962
14.8
338
B-Before
A-After
C-Contaminated
UC-Uncontaminated
Al1 analysis in mg/1
1-4
-------
1.1 HYDROLOGIC CYCLE
Ground water is part of an endless cycle of water recirculating from the earth
to the atmosphere and back by evaporation and transpiration and then precipi-
tation. Water on the earth exists either as lakes, rivers, icecaps, shallow
fresh ground water, deep saline ground water, or oceans (Figure 1-1). The
latter two categories, deep saline waters and the ocean, comprise the bulk of
the water. Deep saline ground waters, in general, have been isolated from the
biosphere for thousands to millions of years. Some fresh meteoric ground
water may have been isolated for hundreds or thousands of years. Isolation of
this ground water attaches a much longer time element to the hydrologic cycle
than is normally considered. This point is important in understanding the
role of hydrology in geology.
Ground water and surface water do not occur as separately and distinctly as
they are commonly treated. Man is most familiar with surface water because he
can directly observe it everywhere. Anyone can be aware of the variation in
quantity and quality of surface water. The problems of development and con-
servation of surface water can be readily appreciated by laymen. However,
ground water passes out of direct contact with man's senses. Partly because
of specialization and partly because of the large differences between surface
water and ground water environments, the two are often treated as separate and
distinct. However, they are one hydrologically interconnected system.
The part of the hydrologic cycle which is the primary concern of this section
is the fresh meteoric ground water component. It is this component that
furnishes potable water, and is the component most easily polluted .by man's
disposal activities.
1.2 HYDROLOGIC PROCESSES OF GROUND WATER FLOW
Ground water flow in an aquifer is controlled by the physical laws of fluid
flow and the geology of the aquifer within which flow occurs. For simplifi-
cation, this section addresses the movement of fluid in an ideal aquifer
rather than a real, heterogeneous, anisotropic geologic system.
An aquifer is a water-bearing unit having a porous or fissured framework that
permits water to move through it under natural conditions. In this section,
1-5
-------
For motion water from
sediment compaction
Figure 1-1. Hydrologic Cycle. Nearly all water on or in the Earth
is being recycled, whether it be in surface water bodies,
meteoric ground waters, or deep formation waters (Modified
from Brown and Others, 1975).
1-6
-------
the primary focus will be on formations that have a porous, rather than a
fissure matrix, as most aquifers in the region are sedimentary formations
which have predominately intergranular ground water flow rather than fracture
flow (Figure 1-2).
Geologic units that typically have intergranular flow or a porous matrix are
generally comprised of a sand sized matrix. These sands were deposited in
fluvial, arid or humid fans, intermontane, deltaic marine, terrace-gravel, or
glacial sedimentary environments. When these sands are consolidated (ce-
mented), the term sandstone is used.
Formations that typically have fracture or joint flow are limestones, basalts,
granites, metamorphic rocks, and consolidated sedimentary rocks that have been
fractured. In jointed units, primary porosity was either never present (as in
granite), or diagenesis (cementation) or subsequent deformation has eliminated
most of the porous framework (as in a consolidated sedimentary rock).
A necessary feature in the hydrologic cycle is recharge and discharge to the
system. Without recharge, the aquifer becomes drained of water. Without
discharge, the system becomes pressurized to the point that the hydraulic head
of the aquifer is higher than the hydraulic head of recharge waters and no
fresh water can be taken into the system.
A recharge zone is the area in which the aquifer receives water. The hydrau-
lic head of the recharge water must be greater than that of the water in the
aquifer (see Section 1.2.1.1). Often this zone represents a topographically
higher section of the aquifer. Recharge is either by infiltration of surface
waters such as rivers and lakes or percolation of precipitation through a soil
profile. In the case of soil percolation of recharge water, water moves
through an unsaturated zone (Figure 1-3). This mode of recharge represents a
common method of recharging an aquifer.
1-7
-------
(d)
Ground-water flow in sand or sandstone aquifers is generally
intergranular (a) rather than through fracture porosity (d).
Permeability in the granular medium decreases where the sediments
are poorly sorted (b) or have been cemented (c) (modified from
Meinzer, 1923).
Figure 1-2. Flow in Porous Sediments
-------
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1-9
-------
Discharge zones are areas where ground water is lost from the aquifer; that
is, they represent the areas of lowest hydraulic head. Discharge can be
either to the land surface via rivers, lakes, springs, and seeps, to the
oceans (e.g., submarine springs in Florida and Hawaii) or to other aquifers
with lower heads.
1.2.1 Principles of Ground Water Flow
Porosity (0) is the percent void space or pore volume in a rock, sediment or
soil and is defined by the equation:
0 =
Volume of the void space
Volume of the total porous medium
Total porosity is a measurement of the total void space, regardless of whether
the void spaces are interconnected or whether they are totally isolated.
Porosity is generally expressed as a percent.
Effective Porosity (ne)is the measurement of the interconnected pore space.
It is a more realistic measure of the pore space that can be utilized in
ground water flow. Porosity varies with sediment type, degree of sorting,
degree of compaction, and degree of cementation. In most unconsolidated sand
aquifers, effective porosity and total porosity are approximately equal.
Hydraulic Conductivity (or permeability) is the ability of a medium (rock,
sediment or soil) to transmit a fluid. Permeability (k) is dependent on the
properties of the medium (pore size, stratification, sediment size, packing,
size distribution, and porosity). Ground water hydrologists, however, common-
P
ly use either Meinzer units (gpd/ft ) or cm/sec for permeability units.
Typically, values of Meinzer units are determined by field aquifer tests.
Field tests measure transmissivity, which is permeability multiplied by the
thickness of the producing interval of the aquifer. Regardless of the methods
of determining coefficients of permeability, the unit represents a rate (dis-
o
tance/time). The range of k varies widely; measured values vary from 10
cm/sec for some clays to 10 cm/sec or less for well-sorted gravels (Table 1-
4).
1-10
-------
TABLE 1-4
PERMEABILITY
105
10 8
10 4 10 3 10 2
1 1 1
10' 1 10-'
1 I 1
10 5 1Q4 TO 3
10 4 10 3 10 2
1 1 1
1,0 ^ 1,0 e 1,0 5
1,0 i 1 1,0-1
1,0
10-2
i
1,0 '
IP 1
1,04
1,0-2
FT./DAY
I 1
FT./MIN.
TO'3
10-'
io-4
GAL./DAY/FT.
1.0 i 1
M/OAY
1
FT./YR.
1,0 3
CM/ SEC.
1,0-3
1,0-1
1.02
1.0-4
1,0-2
TO'5
10-1
10-2
1,0 i
1,0-5
10-3 10-4 10-5
ID'6 lO-^ 10-8
10 -2 1p-3 1p-4
ID'3 1Q-4 10-5
1 1.0 -1 1,0 "2
1,0-e 1,0-7 irj-a
RELATIVE PERMEABILITY
VERY HIGH HIGH
MODERATE
LOW
VERY LOW
REPRESENTATIVE MATERIALS
CLEAN SAND
CLEAN GRAVEL AND SANO
AND GRAVEL
FINE SAND
SILT. CLAY AND
MIXTURES OF SAND.
SILT AND CLAY
MASSIVE CLAY
POROSITY %
30-40 30-40
30-35
40-50
45-55
REPRESENTATIVE MATERIALS
VESICULAR AND SCORIACEOUS
BASALT AND CAVERNOUS
LIMESTONE AND DOLOMITE
CLEAN SANDSTONE AND
FRACTURED IGNEOUS
AND METAMORPHIC
ROCKS
LAMINATED SANDSTONE,
SHALE. MUDSTONE
MASSIVE
IGNEOUS AND
METAMORPHIC
ROCKS
POROSITY %
1-50
< 20
< 10
< 5
-COMPARISON OF PERMEABILITY AND REPRESENTATIVE AQUIFER MATERIALS.
1-11
-------
1.2.1.1 Darcy's Law
Ground water flows from areas of higher head to areas of lower head. The
total head is a summation of its gravitation, pressure, and kinetic (velocity)
energy. In most ground water systems, the rate of flow is sufficiently slow
so that the kinetic component is negligible and, therefore, not considered.
The total head (h) in an aquifer represents the height to which a column of
water will rise in a well screened within the aquifer.
This difference in head (Ah) represents a loss of energy to friction in the
system. Darcy, in 1856, observed that ground water flow (q) through a unit
area (A) was proportional to the energy loss (Ah), and to the coefficient of
permeability (k), but inversely proportional to the distance between head
measurements (length of flow path, AL). This relationship is known as Darcy's
Law and is represented quantitatively as:
q = kA Ah
AL
Figure 1-4 graphically demonstrates this relationship.
Nearly all other ground water flow equations are based on this basic flow
equation. The equation does have certain limitations or constraints that need
to be mentioned. Darcy's Law is valid only for low velocity, laminar ground
water flow. Laminar flow can be characterized as the movement of water parti-
cles along parallel, non-intersecting flow paths. Ground water flow in a
sedimentary, porous rock is generally laminar and not turbulent. Turbulent
flow (high-velocity flow with erratic flow velocities, flow directions, and
intersecting flow paths) can occur in highly permeable, fractured rocks (e.g.,
karstic limestones) or in close proximity to high-discharge water wells where
head differentials are extreme. Darcy's Law is not applicable under turbulent
flow conditions or higher laminar flow velocities (Davis and Deweist, 1966).
Turbulent flow, and non-Darcian laminar flow would not be expected in sedimen-
tary media with intergranular porous flow.
The average velocity of a ground water particle in an aquifer can be deter-
mined by the equation:
1-12
-------
Datum Z = 0
Figure 1-4. Darcy Tube. Ground water flows from areas of
higher head to areas of lower head and conforms
to Darcy's Law
(Q = KA
Ah
1-13
-------
V = q/Ane = Ki/ne
where:
V = average velocity
i = Ah/Al
ne = effective porosity as a decimal fraction
This equation (Lohman, 1972) is derived by dividing Darcy's Equation by the
cross sectional area (A) and the effective porosity (ne). Though dividing
Darcy's equation by (A) alone will give a dimensionally correct answer (L/T)
for velocity (Darcian velocity), it will not give the correct average flow
velocity until effective porosity is divided through the equation. An example
will illustrate the need to account for porosity. Flow through a porous media
is comparable to flow through a pipe or conduit. If, for a given discharge, q
the available flow is reduced, then the velocity of the fluid will increase.
This can be seen mathematically as:
V = q/Ae
where: Ae = available flow area
For ground water; Ae is analogous to Ane (the effective cross-sectional flow
area). Flow velocities may be needed to calculate mass transport over geolog-
ic time or to calculate the rate of possible contaminant migration from dis-
posal sites.
1.2.1.2 General Ground Water Flow Direction
Steady-state ground water flow must follow the principle of the conservation
of mass. If we consider ground water flow through a unit element in an aqui-
fer, then the mass inflow rate must equal the mass outflow rate, plus any
change in mass storage capacity. A change in mass storage capacity results
from the compressibility of the aquifer matrix and the water. If the storage
term is negligible, then flow into and out of an element has to remain con-
stant. As stated earlier, ground water flows from areas of high hydraulic
potential to areas of lower hydraulic potential. In the Darcy tube (Figure 1-
1-14
-------
4), the focus of points of equal head result in equipotential contours (in two
dimensions) or equipotential surface (in three dimensions). Under isotropic
conditions, ground water flows perpendicular to this equipotential line or
surface. By knowing the shape of potentiometric surface, the direction of
ground water flow can be determined. Potentiometric surface maps are a com-
monly used tool by hydrogeologists for determining direction and rates of
movement of ground water in a geologic unit. Figure 1-5 is a potentiometric
surface map for the Goliad Sand in South Texas.
1.2.2 Aquifer, Aquitards, and Aquicludes
1.2.2.1 The Aquifer, the Matrix in which Ground Water Flows
Permeability and transmissivity control both rate and direction of ground
water flow. The geology controls these parameters at several different
scales. Table 1-5 presents the definitions of terms applicable to aquifers.
Ground water flow between recharge and discharge zones will be either under
unconfined conditions (water table), under confined conditions (artesian), or
under semiconfined conditions (Figure 1-3). For an unconfined aquifer, the
upper boundary of the saturated zone is the water table. The water table is
defined as a free surface over which pressure is zero (atmospheric pressure);
therefore, the hydraulic head of the water table is equal to the elevation of
the table. Below the water table, pressures are greater than zero, while
above it (in the unsaturated zone), pressures can be less than zero. In the
case of an unconfined aquifer, the elevation of the water table and subsequent
changes in head are commonly controlled by the topography. The water table
often mimics the topography in a subdued fashion; therefore, ground water
tends to follow the topography. Recharge occurs at the high points and dis-
charge at the low points.
In a confined system (an artesian aquifer), the hydraulic head is a summation
of the gravity head and the pressure head. The potentiometric surface (as
measured in a well penetrating the aquifer) is above the elevation of the top
of the aquifer. The potentiometric surface and the subsequent ground water
flow does not necessarily follow the overlying topography but rather is con-
trolled by the stratigraphic dip of the aquifer.
1-15
-------
Number indicates altitude of water level
Water level contour
Datum mean sea level
Figure 1-5. Approximate Altitude of Water Levels in Wells Completed
in the Goliad Sand, 1977-1978
1-16
-------
TABLE 1-5
AQUIFER DEFINITIONS
AQUICLUDE OR CONFINING LAYER - a geologic unit or layer that forms an upper or
lower boundary to a ground water flow system through which only significant
ground water flow occurs.
AQUIFER - a geologic unit that can store and transmit water.
AQUITARD OR LEAKY CONFINING LAYER - a geologic unit or layer that can store
ground water and also transmit it slowly from one aquifer to another.
CAPILLARY FRINGE - the zone at the bottom of the vadose zone and immediately
above the water table surface, where water is drawn upward by capillary
forces.
CONFINED OR ARTESIAN AQUIFER - an aquifer that is overlain by a confining
layer and, if the overlain aquifer is saturated, then the water in the aquifer
is under artesian pressure.
PERCHED AQUIFER - an aquifer that is usually not very large and exists as a
lens of saturated sediments resting on an impermeable layer located above the
main water table.
POTENTIOMETRIC LEVEL - the level to which water would rise in a tightly cased
well from a given point in an aquifer. This level varies vertically through-
out an aquifer because it is the response to the sum of the forces acting on
the system including gravitational, overlying pressure heads, and confining
pressure heads.
POTENTIOMETRIC SURFACE - an imaginary surface representing the ground water
head in a confined aquifer which is expressed by the level to which water
rises in a tightly cased well. The term "piezometric" was used in the past
although potentiometric is now preferable.
SATURATED ZONE - the portion of the geologic media in which the voids are
filled with water at greater than atmospheric pressures.
UNCONFINED OR WATER-TABLE AQUIFER - an aquifer that does not have an upper
confining layer and extends from the ground surface to a lower confining
layer, or in which the potentiometric surface is below any overlying confining
bed.
UNSATURATED OR VADOSE ZONE - the portion of the geologic media in which the
voids are filled with water at less than atmospheric pressures and air.
WATER-TABLE - a special potentiometric surface which occurs in unconfined
aquifers and represents the upper surface of the ground water in the saturated
zone. The pressure at this surface is equal to that of the atmosphere.
1-17
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The aquifer is confined by overlying and underlying lower permeability beds
(aquitards). It is important to note that even though the aquitard causes the
artesian conditions, it can transmit significant quantities of water if the
bed is relatively thin, has a large cross sectional area, and has a signifi-
cant head differential across the bed. For example, a clay with a thickness
of 100 feet and a permeability of 0.1 millidarcy and a hydraulic head of
differential of 10 feet will transmit 1.84 x 10° gallons of water each year
for each square mile of aquitard (David and DeWiest, 1967). In the Houston,
Texas area, Jorgensen (1975) estimated that up to 22 percent of the 500 mil-
lion gallons of ground water produced daily resulted from clay drainage. Even
though clay has a low permeability, the total flow may be quite large because
of the large cross sectional area in which flow occurs. This concept is
important in recharge-discharge relationships for an aquifer and where thin
clay units separate large waste lagoons from an aquifer.
Permeability of Sediments
The permeability of sediments is particularly dependent on (1) porosity, (2)
grain size, and (3) sorting of the component grains. Figure 1-6 shows the
relationship between permeability and porosity. Permeability trends plotted
against natural grain-size populations are compiled in Figure 1-7. Though
there is considerable spread, sand populations with a median in the very fine
sand size have permeabilities of tens of meinzers, and permeability increases
logarithmically to thousands of meinzers for very coarse sand populations.
Other factors, including horizontal stratification and depositional environ-
ment, can also affect permeability.
Sand-Body Geometry
Geologic formations too often are thought of as being either aquifers or
aquitards. A geologic formation, however, represents a mixture of lithologic
units that are genetically related. A fluvial system is composed of channel
sands, crevasses, sands and silts, and overbank muds. A deltaic system may
consist of several sand and mud units from different modes of deposition.
Because of this heterogeneous nature of a formation, an aquifer may often have
an internal geometric framework of high-permeability sands within low-
permeability muds. This concept is important in determining potential pollu-
tion migration in many aquifers.
1-18
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TEXTURE
10000 1 r
5OOO
IOOO
5OO
f_ IOO
Ij
03 50
Ul
a:
LiJ
O, 10
O
O.I
DOGGER
BETA
'X;
IOOO
500
100
50
I
0.5
O.I
0.05
0 5 10 15
0.01
UPPER
CARBONIFEROUS
20 25 30 05 10
POROSITY (PERCENT)
is 20 25 30
Figure 1-6- Plots of Permeability Versus Porosity
(From Fuchtbauer, 1967)
1-19
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10,000
1000
o
£
x VERDIGRIS a VALLEY (OKLA)
+ ARKANSAS R. VALLEY(OKLA)
• MISSISSIPPI R. VALLEY (ARK)
o LABORATORY SAMPLES
a LOWER MISSISSIPPI R VALLEY
sty vf
sd * jrov
GRAIN SIZE (0)
Figure 1-7. Plot of Permeability Versus Grain Size
(Raw Data from Bjorklund & Brown, 1957;
Newcome & Page, 1962; Smith & Others, 1964,
Sniegocki, 1964)
1-20
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The geometry of the aquifer can be predicted by the depositional model. The
initial deposition of the genetically related unit will dictate the orienta-
tion of the sand and mud bodies. Fluvial sands and distributary channel sands
characteristically will be dip-oriented. Strandplain, delta-front sands or
barrier-bar sands characteristically will be strike-oriented. Braided stream
and fan deposits will form more continuous sand sheets in comparison with mix-
load meandering stream channel or deltaic distributary channel fills.
In the Houston area, major dip-oriented sand trends in Plio-Pleistocene depos-
its stack one on top of the other. Similarly, the strike-oriented sands along
the Coast from land surface to the base of the Alta Loma Sand (1,000 feet
below land surface) are also stacked (Kreitler and others, 1977). Fisher and
McGowen (1967) observed a similar phenomena in the deep Wilcox Group. This
stacking of sands offers a different model for an aquifer. It is possible
that there is better vertical continuity through a number of overlying forma-
tions than there is horizontal continuity within one horizontal formation.
The geometry of sands and muds in a stratigraphic package can result in com-
plex, large scale aquifer heterogeneities.
Structural Features
Faults are another type of boundary that control the. geometry of an aquifer.
The effectiveness of a fault as a low-flow zone is dependent on the ratio of
sand thickness to fault displacement and the presence of fault gouge within
the fault zone. A fault with small displacement in a thick sand will be a
less effective barrier than that same fault completely displacing several
thinner sands. Fault gouge may reduce permeability within the fault and cause
the fault to act as a low-permeability boundary, even though the fault-
displacement/sand-thickness ratio is relatively small. Bed displacement
results in a change in transmissivity, whereas fault gouge results in a change
in permeability.
The impact of faulting on the aquifer hydrology is dependent on the geologic
style of the area. Faults in the Gulf Coast region are typically growth
faults formed syngenetically with deposition. Density of faults may be very
high in this region where thin sand beds are intercalated with muds. Faults
1-21
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in these sediments easily offset sand beds, and the higher mud content may
form a gouge along the faults. In the western interior basins, such as the
Paradox or the San Juan Basins, the faults are basement-derived and, in gener-
al, post-depositional. Fault displacements are greater than in the shallow
Gulf Coast sequences, but sand beds are thicker and percent displacements are
probably less. Faulted sands are cleaner, with more sand and less mud; there-
fore, they probably have less fault-gouge developed in the fault zone. Faults
in Gulf Coast aquifers may act as better low-flow boundaries than faults in
interior basins of the arid West. Faulting contemporaneous with deposition,
such as Tertiary growth faults in the Gulf Coast or faulting in the Pennsylva-
nian section of north Texas, can cause thickening of sands on the down-thrown
side (increase of transmissivity) or cause different facies to be deposited on
either side of the fault (differences in permeability). In most instances,
faulting in the Texas Gulf Coast area is not an important consideration in
pollution migration since faults usually do not displace the thick clay units
which protect the regional aquifer. However, in the competent rock areas, for
example in the Balcones Fault zone in Texas, pollution migration along fault
zones has been documented. In these areas, the permeability of the fault zone
has been increased by percolating surface water, and contaminant transport is
rapid.
1.2.2.2 Aquicludes and Aquitards
Perhaps the single most common error that the uninitiated make in relation to
ground water hydrology is related to aquicludes and aquitards. An aquiclude
is a theoretical body that acts as a perfect no-flow barrier (i.e., it pre-
cludes the transmission of water or pressure). An aquiclude is a useful tool
in the initial analysis of a ground water system in that it allows the inves-
tigator to make simplifying assumptions for his ground water model. It must
be realized that such a perfect barrier is unlikely to exist in any area under
investigation. An aquitard is the realistic unit that limits or retards
movement of ground water or transmission of pressure in a given direction.
Once the theoretical model has been constructed and the field testing phase of
a project has been completed, the aquiclude must be modified to represent the
conditions found in the field and becomes an aquitard model.
1-22
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1.3 GROUND WATER RESOURCES
According to the United States Geological Survey (USGS; 1970), the United
States used 1.4 x 10* itr/day of water. Of this total, 57 percent was used
industrially and 35 percent for irrigation. For the entire country, 81 per-
cent of the water came from surface supplies, and 19 percent from the
ground. However, in the 17 western states, 46 percent of all public water
supplies came from the ground. In EPA Region VI, the following percentages of
public water supplies coming from ground water are: over 40 percent in Okla-
homa, over 50 percent in Arkansas, over 70 percent in Louisiana, over 80
percent in Texas, and over 90 percent in New Mexico.
1.3.1 Description of Major Aquifer Systems in EPA Region VI States
The following information, most of which is summarized from the National Water
Summary (USGS,1984), briefly discusses the aquifers of each state and their
characteristics.
1.3.1.1 Arkansas
Six major aquifers supply most of the ground water used in Arkansas (Figure 1-
8). The aquifers are (1) Alluvial aquifers, (2) Cockfield aquifer, (3) Sparta
Sand aquifer, (4) Wilcox aquifer, (5) Nacatoch Sand aquifer, and (6) the Ozark
aquifer system.
Alluvium
The alluvial deposits, which are the principal source of water for irrigation,
blanket much of eastern Arkansas, the Red River Valley in southwestern Arkan-
sas, and isolated areas along the Arkansas River in the interior Highlands.
The alluvium is composed of coarse sand and gravel at the base that grades
upward to silt and clay near the surface. Recharge is from stream loss and
local precipitation. In parts of Chicot, Desha, Lincoln, Monroe, and White
Counties, the water contains as much as 3,750 mg/1 of dissolved solids, which
makes it unsuitable for irrigation. The saline water is believed to have
migrated upward from underlying, saline water-bearing beds through faults or
abandoned oil test wells. A similar problem exists in the Red River alluvium
in parts of Miller and Lafayette Counties.
1-23
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EXPLANATION
fci;^j Alluvial aquifers
j^jfl Cockfield aquifer
^^ Sparta Sand aquifer
f"j| Wilcox aquifer
^^J Nacatoch Sand aquifer
I Not a principal aquifer
Ozark aquifer system - Present only in
the subsurface in Arkansas
50
i
100 MILES
(Adapted from U.S.G.S.. 1985)
Figure 1-8. Principle Aquifers in Arkansas
1-24
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Cockfield
The Cockfield aquifer is at or near the surface of the Coastal Plain of south-
eastern Arkansas. The aquifer, which consists of interbedded fine to medium
sand, clay, and lignite, is as much as 400 feet thick in Chicot and Desha
Counties. The water generally is suitable for most municipal and industrial
uses.
Sparta Sand
The Sparta Sand aquifer is the principal source of water for public and indus-
trial supplies in much of southern and southeastern Arkansas. The aquifer also
is being tapped increasingly for irrigation in Arkansas County. The Sparta is
composed of massive fine to medium sands that contain interbedded clay lenses,
and is as much as 800 feet thick. North of about latitude 35°N, the Sparta
Sand becomes part of a thick sand sequence known as the Memphis Sand. The
Memphis Sand commonly is not used in Arkansas as a source of water because the
water generally contains high concentrations of iron.
WiIcox
The Wilcox aquifer occurs throughout most of the Coastal Plain in Arkansas but
is a major source of water only in northeastern Arkansas where it is known as
the "1,400-foot sand." It is primarily used for public and industrial sup-
plies. In southwestern Arkansas, the unit is composed of fine sand and silt
and does not yield significant amounts of water. The Wilcox aquifer contains
fresh water to a depth of 1,500 feet below land surface in Crittenden County.
Nacatoch Sand
The Nacatoch Sand aquifer underlies the Gulf Coastal Plain part of Arkansas
but contains fresh water only in parts of the northeast and southwest. It is
used primarily for public and industrial supplies in Clay, Greene, Randolph,
and Lawrence Counties in the northeast and in Nevada, Hempstead, and Little
River Counties in the southwest. However, water-level declines of more than
40 feet have been noted at Prescott in Nevada County as a result of large
municipal withdrawals.
1-25
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Ozark
The Ozark aquifer consists primarily of dolomite, sandy dolomite, and sand-
stone and is the only significant aquifer system, except for the Arkansas
River alluvium in the Interior Highlands. It is used in northern Arkansas in
an area from Benton and Washington Counties to Randolph and Lawrence Coun-
ties. The system includes the Roubidoux Formation and the Gunter Sandstone
Member of the Van Buren Formation, which do not crop out in Arkansas. These
strata are the principal source of ground water in the northern part of the
state. The Roubidoux is 100 to 250 feet thick and is present at depths rang-
ing from 600 feet at the Arkansas-Missouri state line to about 2,300 feet at
the southern limits of the area of use. The Gunter Sandstone Member is about
50 feet thick and is 300 to 600 feet below the "Roubidoux Formation. The
massive dolomites between these aquifers do not yield water.
1.3.1.2 Louisiana
The principal aquifers in Louisiana, as shown in Figure 1-9, are (1) Alluvial
aquifers, (2) Pleistocene aquifers, (3) Pliocene-Miocene aquifers, (4) Cock-
field and Sparta aquifers, and (5) the Wilcox-Carrizo aquifer.
A1luvium
The alluvial aquifers underlie the floodplains of the Mississippi, Red, and
Ouachita River valleys. The alluvial deposits typically consist of a confin-
ing layer of clay and silt that overlies sand and gravel. The aquifers gener-
ally thicken southward; the base of the aquifer is about 100 feet below land
surface in the north to 250 to 450 feet below land surface in the south. The
Mississippi River alluvial aquifer is the largest yielding unit. The alluvial
aquifers are not developed extensively, but the water is ideal for irriga-
tion. Slightly saline water in local areas in the Red and Mississippi River
valleys may be the result of pollution by oil-field brines.
Pleistocene Aquifers
The Pleistocene aquifers are principal sources of fresh water in central,
southwestern, and southeastern Louisiana. In central Louisiana, the terrace
aquifers are important, though of limited potential. The aquifers range in
depth from 50 to 200 feet.
1-26
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EXPLANATION
|i::i:3 Alluvial aquifers
Pleistocene aquifers
Pliocene-Miocene aquifers
Cockfield and Sparta aquifers
Wilcox-Carrizo aquifer
Areas where no freshwater
occurs at any depth
(Adapted from U.S.G.S.. 1985)
Figure 1-9.
£>p
!Xv*"»
a&:
50
100 MILES
Principal Aquifers in Louisiana
1-27
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The Pleistocene Chicot aquifer, which is the principal aquifer in southwestern
Louisiana and is the most intensively pumped aquifer, provides over 50 percent
of the total ground water withdrawals in Louisiana. Aquifer depths range from
about 50 feet in northern outcrop areas to 800 to 1,000 feet in total coastal
area. To the north, the water is hard but is suitable for irrigation; to the
south, deeper sands yield soft water of excellent quality for public-supply
use.
In southeastern Louisiana, the Pleistocene aquifers range in depth from a few
hundred feet to more than 1,000 feet and contain freshwater to depths of 700
to 800 feet in the southern part of the area. Principal individual aquifers
are the "400-foot" and "600-foot" sands at Baton Rouge, the Gonzales-New
Orleans aquifer (principal source in New Orleans), and the upper Ponchatoula
aquifer.
Principal problems with the Pleistocene aquifers are (1) the limited produc-
tion capacity of the terrace aquifers locally, (2) local saltwater problems in
the Chicot aquifer, and (3) saltwater encroachment (in the "600-foot" sand at
Baton Rouge and in the Gonzales-New Orleans aquifer).
Pliocene-Miocene Aquifers
The Pliocene-Miocene aquifers form part of a large artesian basin in the west-
ern part of the Gulf Coastal Plain and supply potable water to many towns and
cities. The Pliocene-Miocene aquifers include the Evangeline, Jasper, and
Catahoula aquifers of central and southwestern Louisiana; the sands below the
"600-foot" aquifer in the Baton Rouge area; and deeper sands in southeastern
Louisiana.
In the Evangeline aquifer in southwestern Louisiana, freshwater extends to a
maximum depth of about 2,200 feet; in the underlying Jasper aquifer, fresh-
water extends to about 3,400 feet. The total sand thickness available for
development ranges from about 100 to 1,000 feet. In southeastern Louisiana,
individual sands tend to be thicker and average yields greater than in other
areas. Depth to the base of the freshwater section in southeastern Louisiana
ranges from about 2,000 to 3,400 feet.
1-28
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The principal problems pertaining to Pliocene-Miocene aquifers are locally
high fluoride concentrations (greater than 2 mg/1), dark color, depletion of
artesian head in intensively pumped areas, and local saltwater encroachment.
Cockfield and Sparta
The Cockfield and Sparta are important aquifers in northern Louisiana - the
Cockfield principally in the northeastern and the Sparta in the north-central
parts of the state. In much of the area where the Cockfield contains fresh
water, it underlies the alluvial aquifer and generally yields softer water
than that yielded by the alluvium. Water in the Cockfield typically has a
color level that may be objectionable for public supply.
The areally extensive Sparta aquifer is the principal source of supply in
north-central Louisiana, where it is as much as 700 feet thick. Fresh water
in the Sparta aquifer is present to depths ranging from a few hundred feet to
about 1,000 feet. The water generally is soft, and iron concentrations are
typically less than 0.3 mg/1 in the deeper sand units. The principal problems
of the Sparta are declining water levels (annual declines range from 1 to 3
feet), and saltwater encroachment (in the Monroe area).
Wilcox-Carizzo
The Wilcox-Carizzo is the most important and areally extensive aquifer in
northwestern Louisiana. However, the aquifer sands are typically thin and
fine, which restricts well yields. Water quality is somewhat variable but
generally suitable for domestic and public-supply use.
1.3.1.3 New Mexico
New Mexico's most important aquifers include (1) Valley-fill aquifers, (2)
Basin-fill aquifers, (3) Sandstone aquifers, and (4) Limestone aquifers.
Their areal distribution is depicted on Figure 1-10.
Valley-Fill Aquifers
The valley-fill aquifers consist mostly of alluvial and terrace deposits that
border the major rivers in the state. The most important are located along
the Rio Grande, which flows north-south through the center of the New Mexico,
Rio Chama in the north, the San Juan River in the northwest, and the Pecos
1-29
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EXPLANATION
p*jj Valley-fill aquifers
||||i| Basin-fill aquifers
[;.;.vj Sandstone aquifers
yffl( Limestone aquifers
Not a principal aquifer
CAdapted from US.G-S, 1985}
Figure 1-10.
50
100 MILES
Principal Aquifers in New Mexico
1-30
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River in the southeast. These aquifers generally are less than 200 feet
thick. The valley fill along the Rio Grande and Pecos River provides large
quantities of water to wells. Wells drilled in these areas commonly penetrate
deeper aquifers to increase yields. The water generally is fresh, although
slightly saline water may be encountered locally in the aquifers. Water is
discharged from the aquifers by wells, spring flow, evapotranspiration, and
seepage to the rivers.
Basin-Fill Aquifers
The basin-fill aquifers are comprised mostly of materials that have been
eroded from the mountainous areas and transported by either streams or wind
into structural or topographic basins. Two very distinct basin-fill areas
occur in New Mexico. One is the deep troughs and intermontane valleys of the
Basin and Range province (filled with material commonly called bolson depos-
its), and the other is in the Great Plains province where a broad expanse of
alluvial fans and other stream and wind-blown deposits collectively comprise
the High Plains aquifer. The thickness of basin-fill deposits in the Rio
Grande valley may be as much as 20,000 feet, but in most areas, the deposits
range in thickness from only a few hundred feet to 2,000 feet. The water
contains more than 1,000 mg/1 dissolved solids generally below a depth of
3,000 feet. The High Plains aquifer, located along the eastern border of the
state, has a maximum thickness of about 400 feet and an average thickness of
about 200 feet. Water from this aquifer generally contains less than 1,000
mg/1 dissolved solids. Discharge from the basin-fill aquifers occurs mostly
as a result of pumpage for irrigation and municipal supplies, of infiltration
to the valley-fill aquifers, and of underflow to Texas.
Sandstone Aquifers
The sandstone aquifers are located in the San Juan Basin part of the Colorado
Plateau province. The total of sedimentary rocks in the basin probably is
more than 15,000 feet; these aquifers are a series of hydraulically intercon-
nected sandstones. The series of sandstones are exposed around the perimeter
of the basin and are recharged by precipitation and ephemeral streams. The
quality of the water in the sandstone generally is fresh near outcrop areas
and for some distance down the flow path but may deteriorate with depth as it
flows toward discharge areas in the northwestern part of the basin. Some of
1-31
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the ground water in the aquifers discharges to the San Juan River, some evapo-
rates, and some discharges to the Rio Grande. Much of the water in the lower
sandstones may move upward through partially impermeable confining layers to
other aquifers or to the land surface in the central part of the basin where
it evaporates or is used by plants. Water is also withdrawn for industrial,
public, agricultural, and rural supplies.
Limestone Aquifers
The limestone aquifers are a major source of water in the southeastern and
central parts of New Mexico near the Pecos River and in the western part of
the state near the Rio San Jose. The aquifers are productive in these areas
because of the secondary solution and fracture permeability that has developed
in the rock. Primary recharge to these aquifers is from infiltration of
precipitation, from surface water from tributaries of the Pecos River, and
from the Rio San Jose. Discharge from the aquifers is mainly from wells and
springs.
1.3.1.4 Oklahoma
Figure 1-11 shows the principal aquifers in Oklahoma. These include (1)
Alluvial/terrace deposits, (2) High Plains aquifer, (3) Antlers aquifer, (4)
Rush Springs aquifer, (5) Dog Creek-Blaine aquifer, (6) Garber-Wellington
aquifer, (7) Vamoosa-Ada aquifer, (8) Keokuk-Reeds Spring (Boone) aquifer, (9)
Roubidoux aquifer, (10) Arbuckle-Simpson aquifer, and (11) Arbuckle-Timbered
Hills aquifer.
A1 luvium
The alluvial aquifers consist of alluvium and terrace deposits of Quaternary
and Tertiary age along the major rivers - the Arkansas (including the Salt
Fork Arkansas), the Cimarron, the North Canadian, the Canadian, the Washita,
and the North Fork Red Rivers. These deposits generally extend from 1 mile to
as much as 15 miles from the rivers, and their thickness ranges from a few
feet to about 300 feet. The alluvium and terrace deposits are generally
unconfined and consist of sand, silt, clay, and gravel. In some areas, over-
lying dune sand forms a part of the aquifer.
1-32
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EXPLANATION
Alluvium and terrace deposits along major streams
High Plains aquifer
Antlers and Rush Springs aquifers L
Dog Creek - Blaine aquifer
Garber - Wellington and Vamoosa • Ada aquifers
Keokuk • Reeds Spring (Boone) aquifers
Roubidoux aquifer
£$£ Arbuckle - Simpson and Arbuckle - Timbered Hills aquifers
Not a principal aquifer
Boundary of aquifer uncertain
(Adapted from US.G.S, 1985)
Figure 1-11. Principal Aquifers in Oklahoma
1-33
50
100 MILES
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High Plains Aquifer
The single largest source of ground water in Oklahoma is the High Plains
aquifer, which consists of the Tertiary Ogallala Formation and associated
Quaternary alluvium and terrace deposits. Saturated thickness of this aquifer
ranges from a few feet to more than 500 feet. This aquifer consists mostly of
fine sand and silt with lesser quantities of clay, gravel, and minor beds of
limestone and caliche. Most of the water from the High Plains aquifer is used
for irrigation, but it also is the principal source of domestic and industrial
supply in the High Plains of Oklahoma. The water is suitable for most uses.
Antlers
The Antlers aquifer in southeastern Oklahoma contains large quantities of
water. Due to the greater precipitation and the resulting availability of
surface water in the southeastern part of the state, this aquifer is not used
to its full potential. The water generally is suitable for all uses but may
be saline at depth.
Rush Springs
The Rush Springs aquifer, a fine-grained sandstone in the west-central section
of the state, is used extensively for irrigation. Water generally is suitable
for all uses. In areas of intensive irrigation pumpage, water levels have
declined as much as 50 feet.
Dog Creek-Blaine
The Dog Creek-Blaine aquifer in extreme southwestern Oklahoma contains water
in solution openings in gypsum. The water is used extensively for irrigation
but it contains excessive quantities of calcium sulfate (gypsum) in solution
that renders it unsuitable for drinking. During the pumping season, drawdowns
may be as much as 50 feet, but the aquifer is recharged rapidly by surface
runoff that flows into sinkholes and solution openings.
Garber-Wellington
In central Oklahoma, the Garber-Wellington aquifer is the principal water
supply for several of the Oklahoma City suburbs. The aquifer generally con-
sists of fine-grained sandstone, shale, and siltstone with a maximum thickness
of 900 feet. Several water-yielding zones, which become confined with depth,
1-34
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are present in the aquifer. Water quality generally is suitable for all
uses. Local areas of intensive pumpage have caused drawdowns of 100 to 200
feet. Excessive pumpage may cause upwelling of brine, which is present at
depth.
Vamoosa-Ada
The Vamoosa-Ada extends in a band from north to south in east-central Okla-
homa. Aggregate thickness of water-yielding sandstone ranges from 100 to 550
feet. Where it is near the land surface, the aquifer is unconfined, but down-
dip (to the west) the aquifer is confined. Most withdrawals from this rela-
tively undeveloped aquifer are for public supply and industrial use. The
water quality generally is suitable for all uses in the upper part of the
aquifer but becomes increasingly saline near the interface between the potable
and saline water in the deeper confined part of the aquifer. Excessive pump-
age may cause upwelling of this saline water. Oil-field brines and wastes
resulting from past operations have caused some local contamination.
Keokuk-Reeds Spring (Boone)
In northeastern Oklahoma, the Keokuk-Reeds Spring (Boone) aquifer is a depend-
able source of water where it is near the land surface. The Keokuk-Reeds
Spring aquifer consists of residual chert and cherty limestone. The small
yields from wells preclude any large-scale development of the aquifer for
other than domestic purposes. The water generally is suitable for most uses
but is hard to very hard. Because of interconnecting sinkholes and cavern
development, the Boone has the potential to be readily contaminated by surface
sources.
Roubidoux
Underlying part of the Keokuk-Reeds Spring aquifer is the Roubidoux aquifer,
which consists of fractured dolomite that contains several sandy zones and is
not exposed at the surface in Oklahoma. The water is moderately hard and is
the principal public and industrial water supply in Ottawa County in extreme
northeastern Oklahoma.
Arbuckle-Simpson
In the Arbuckle Mountain area in south-central Oklahoma, limestone, dolomite,
1-35
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and sandstone units from 5,000 to 9,000 feet thick form the Arbuckle-Simpson
aquifer. The aquifer is largely undeveloped and contains an estimated 9
million acre-feet of generally very hard water in storage.
Arbuckle-Timbered Hills
The Arbuckle-Timbered hills aquifer in southwestern Oklahoma underlies the
Lawton area. Fluoride concentrations of up to 35 mg/1 effectively prevent any
widespread use of the water for public supply.
1.3.1.5 Texas
Seven major aquifers supply most of the ground water used in Texas (Figure 1-
12). The aquifers are (1) Alluvium, (2) the Carrizo-Wilcox, (3) the Edwards-
Trinity Plateau, (4) the Edwards Balcones Fault zone, (5) the Gulf Coast
aquifer, (6) the Ogallala, and (7) the Trinity Group. There are also numerous
other minor aquifers located throughout the state (Figure 1-13) which are
important sources of water for industries and municipalities in those regions.
Alluvium
The alluvial deposits which are considered major aquifers in Texas are the
unconsolidated deposits in structural troughs in Crane and Walker Counties and
the Seymour aquifer in North Central Texas. These deposits generally consist
of interconnected, lenticular deposits of sand and gravel interbedded with
clay and silt. Recharge is from stream loss and local precipitation. In West
Texas, ground water movement is toward the Pecos River Basin. This area is
susceptible to pollution from oil and gas industries in the area. In the
Seymour aquifer, ground water movement is generally to the southeast. The
aquifer is susceptible to pollution from oil and gas activities, industrial
facilities, and agricultural practices.
Carrizo-WiIcox
The Carrizo Formation and the Wilcox Group are two separate geologic units,
yet they are frequently considered as one aquifer. Generally, the Carrizo
consists of well-sorted quartz sand. In some areas, it is poorly cemented and
contains thin beds of shale. The Wilcox Group consists mainly of interbedded
sand, silt and clay, with minor amounts of lignite. The sands are typically
gray and most are relatively thin-bedded and silty; individual beds generally
1-36
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Major Aquifers in Texas
MAJOR AQUIFERS
qMHIH'H at MMV in larf* ana of tin Stow
AHuvkn and Bollon OcpoUti
EHwoMt-Trlnltr (Pmng)
&JWOT* (Mam Rmll z«w)
TMr*, Gow,
(Texas Hater Commission)
Figure 1-12. Major Aquifers in Texas
1-37
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Minor Aquifers
rffilNlTY •
OHIGH..BLA1NS1
7v>;-.:- r™i. ''"""^(yvNTA Rn'S'A-/ ' :
•HICKORY \. ^ -,-.:.„;- . /- - V^J"';•'••-•
ELLENBURGER- SAN - SABA
;*••!» T j,« -osc- j »*O(H! r" / (
(Texas Water Commission)
Figure 1-13. Minor Aquifers in Texas
1-38
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cannot be correlated. The principal source of recharge to the Carrizo-WiIcox
is rainfall on the outcrop along the western edge of the aquifer. Additional
recharge is from the numerous streams which cross the outcrop. Generally,
ground water movement is to the south-southeast. Oil and gas production is
the major industry situated on the recharge zone. The aquifer is susceptible
to pollution on the outcrop.
Edwards-Trinity Group
The Edwards-Trinity Group is the principal source of water in the Edwards
Plateau Region of Texas. This group consists of Georgetown, Edwards, Com-
manche Peak, Trinity Sand and Glen Rose Formations. These formations are
composed of medium to thick-bedded limestone frequently containing fractures
and vugular porosity. Recharge is from precipitation, runoff and stream
loss. Generally, ground water moves from north to south or from northwest to
southeast. Several cases of ground water contamination have been documented
associated with septic tanks and animal feedyards.
Gulf Coast Aquifer
The Gulf Coast aquifer includes a broad belt of sediments along the entire
coastal plain from the shoreline to approximately 100 miles inland. For the
most part, the geologic formations included in the Gulf Coast aquifer are
composed of sand, clay, silts, gravels, and some tuff and volcanic ash. These
sediments dip toward the coast and ground water occurs under both unconfined
and artesian conditions. Recharge is from precipitation and stream losses on
the outcrop. The Texas Gulf Coast area is one of the most heavily industrial-
ized zones in the United States, and the potential for ground water pollution
is great.
Ogallala
The Ogallala occurs at the surface in most of the Texas Panhandle area. The
Ogallala is composed of clay, silt, fine to coarse sand, gravel and caliche.
Generally, individual beds, lenses, sand, or gravel cannot be traced over long
distances. The formation ranges in thickness from 0 to 500 feet. Ground
water occurs under unconfined conditions and generally moves toward the south-
east at a rate of 50 to 150 feet per year. Recharge is from precipitation on
the outcrop and underflow from the Ogallala in New Mexico. The Ogallala is
1-39
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probably the aquifer with the greatest potential for ground water pollution.
The generally unconsolidated nature of the aquifer and the occurrence of
numerous industrial complexes and oil fields have resulted in many documented
cases of ground water contamination.
Trinity Group
Frequently called the Trinity Sands, this formation is the major aquifer for
North Central Texas. In the north, the Trinity can usually be divided into
two zones, the Paluxy Sand and the Travis Peak Formations. In the southern
area, these units are separated by the Glen Rose Formation. Generally, the
Paluxy consists of fine-grained quartz sand and the Travis Peak is composed of
fine-grained sand interfingered with shale, clay, and limestone. Recharge is
from rainfall and stream losses on the outcrop. Water generally moves east
and southeast and occurs under both confined and unconfined conditions. Very
few cases of ground water contamination are known in this aquifer, and most
are associated with septic tanks or other small scale sources.
Edwards-Balcones Fault Zone
The Edwards-Balcones Fault Zone aquifer is a limestone aquifer, and flow
exists primarily in solution channels. Recharge to the aquifer is from pre-
cipitation on the outcrop and stream losses. On the outcrop, the aquifer is
very susceptible to pollution because of the thin soil mantle and rapid infil-
tration. This aquifer has been declared a sole source aquifer by the EPA.
Because of the stringent controls which exist over this aquifer, and the
general lack of industry in the area, little, if any, significant pollution is
expected, although numerous localized effects from septic tanks have been
documented.
1.3.2 Ground Water Use
The demand for renewable water resources is increasing at a rapid pace. In
many aquifers the annual withdrawal of water is greater than the annual re-
charge. The net effect is a depletion, or "mining," of underground storage
reservoirs.
When more water is withdrawn from an aquifer than is recharged to that aqui-
fer, the lowered water level results in lowered well yield. To meet increased
1-40
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water demands, pumps must be set deeper and larger pump motors installed. In
some cases, existing well development is inadequate, so new wells are added to
meet increased demands. Adding new wells and lowering the yield of existing
wells causes operating costs to increase as' water levels decline further.
Besides reduced well yields, the dewatering of aquifers can reduce the aqui-
fers' ability to transmit water, can cause saline-water to move into heavily
pumped fresh water aquifers, and can cause the land surface to subside. As
the ground water resources decline, it becomes more and more important to
protect the resources we have in order to ensure a sufficient supply for the
future.
1.4 WELLHEAD PROTECTION REQUIREMENTS
Recent amendments to the Safe Drinking Water Act (SDWA), require states to
develop programs to protect wellhead areas of public water supply well(s) from
contaminants. The programs developed by the states are required to identify
all potential anthropogenic sources of contaminants within each wellhead
protection area. One major task required by the amendments is the
determination of the size and shape and area to be protected. These areas are
referred to as Wellhead Protection Areas (WHPA's) and are defined as "the
surface and subsurface area surrounding a water well or well field, supplying
a public water system, through which contaminants are reasonably likely to
move toward and reach such water well or well fields."
The June 1986 amendments to the SDWA authorized two new programs for protec-
tion of ground water. One of these is the Wellhead Protection Program
(WHPP). The intent of Section 1428 of the amendment is to establish a state
program. Unlike other programs authorized by the SDWA, the EPA is not author-
ized to establish a federal program if states elect not to develop rules and
regulations. However, if states do not develop and submit programs to EPA for
approval within three years of the enactment of the amendments, the EPA may
withhold grant monies to the state. The only mandated EPA action is to de-
velop and issue technical guidance to the states for development of WHPP's.
1.4.1 Wellhead Protection Area Method Development
In order to prepare a method for actual determination of the area which will
be included in the WHPA, criteria for establishing protection must be devel-
1-41
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oped. The criteria developed by each state will probably be a combination of
both technical and non-technical (political or administrative). The technical
criteria are those activities that would reduce the contaminants to acceptable
levels. The EPA has identified five types of technical criteria that could be
utilized. They are:
• Distance from source to wellhead
Radius of drawdown of pumping wells
• Time of potential contaminant travel
• Aquifer flow boundaries
• Assimilative capacity of the aquifer.
The purpose of the WHPP is to protect the well fields from pollution. Three
major targets, which are discussed below, are:
• Prevention of Direct Introduction of Contaminants
around the Well Casing.
• Prevention of Contamination by Bacteria and Viruses.
• Prevention of Contamination by Naturally Occurring or
Synthetically Derived Organic Compounds.
1.4.2 Protection From Spills (Immediate Zone)
Many domestic, industrial and municipal supply wells have become contaminated
because of poor well construction practices or by lack of sanitary control at
or near to the wellhead. Prevention of contamination of the well as opposed
to the aquifer has generally been dependent upon construction or operating
standards. Table 1-6 lists several management methods that have been used,
and these are discussed in the following sections.
1.4.3 Well Construction Standards
1.4.3.1 Well Casings and Grouting
Casings, normally steel or PVC, are required in almost all water wells to pro-
vide a base for the pumping unit and to prevent the geologic formation from
caving into the borehole. However, when the wells are completed in hard rocks
such as limestone, granites, sandstones, etc., casing may not be needed for
structural support of the borehole. In many domestic wells, casing may extend
only 5 or 10 feet into the borehole and there may be several hundred feet of
1-42
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TABLE 1-6
METHODS OF MANAGEMENT OF THE IMMEDIATE AREA
Standards for
Well Casing
Grouting
Housing
Grading
Establishment of
Buffer Zones
Well Plugging Procedures
1-43
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open borehole before the water table is encountered. This type of completion
can allow a "short circuit" for nearby sources of pollution to enter the well
or aquifer. For municipal water supply wells, casings should extend to the
top of the water table or production zone and should be cemented. The in-
stallation of casing without grout can still provide an avenue of migration in
the casing-well bore annulus. Figure 1-14 indicates several different comple-
tion methods and potential problems. Although most public water supply sys-
tems will have adequate casing and cementing, the following discussions demon-
strate the potential problems that can exist at wellheads and well completion.
1.4.3.2 Casing Installation
Steel casing installed in water wells is either thread and collar or plain end
that is welded. Plain end casing is cheaper and can be run in a smaller hole;
because of this, it is the most common type used in water well systems. Many
early well drillers cut holes in the casings to support the casing on a cable
as it was lowered into the hole. After the next joint of pipe was welded to
that joint, the holes were welded closed. Frequently, these holes if not
adequately welded are weak spots in the casing and can allow contaminants to
enter the wells. Downhole television pictures of wells at Kelly Air Force
Base in San Antonio, Texas and at Green Pasture Water Supply System near
Austin, Texas have documented the entrance of clay and shales into water wells
through casing patches. When steel casings are utilized, corrosion can occur.
This is especially true where casings penetrate alternating layers of rocks
with different lithologies, especially sand and clay or limestone and clay.
It has been noted that frequently, at the contacts of these two layers, corro-
sion of casing will occur and contaminants can enter. In San Antonio, down-
hole television photographs demonstrated the entrance of gasoline into water
wells at the contact between the Buda limestone, and the underlying Del Rio
clay. The casing was poorly cemented in this zone, possibly because of lost
circulation in the Buda limestone or poor well cementing procedures.
1.4.3.3 PVC Casing
Within the last several years, PVC casing has been approved for use in public
water supply system water wells. The use of PVC has been especially prevalent
in areas where corrosion and iron bacteria have been a problem. However, the
use of PVC has created two potential problems for water supply systems. Where
1-44
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d
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o z
cc O
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Z> °
2: o
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1-45
-------
static water levels are deep (200 - 300 feet), the heat of cement setting up
has resulted in the weakening and collapse of PVC pipe above the water
table. These circumstances require that the well be abandoned or the casing
be milled out slightly to accept the pumping equipment, thus creating a weak
spot which could potentially fail, allowing contamination to enter the well-
bore. An additional problem is the fact that "bell jointed" PVC well casing,
which is glued together, is frequently used. Glued joints can leach MEK,
toluene and hydrotetrafluor into the water.
Contamination of the well by pumping equipment is also possible. Many water
supply systems use lineshaft turbine pumps. Lineshaft turbine pumps are
either water lubricated or oil lubricated. Oil lubricated pumps are subject
to leaks and it is not uncommon to find several feet of hydrocarbons floating
on the water inside a water well. This refined oil can result in low levels
of dissolved organics being detected in the water from the well.
1.4.4 Well Plugging Procedures
Although there are generally procedures developed for plugging and abandoning
public water supply wells, most domestic water wells are abandoned and not
plugged. Since these private wells are often completed in the same aquifer
that supplies public water supply systems, they provide an avenue of contami-
nation entrance into the aquifer if not properly plugged. In addition, these
domestic wells are generally not cemented or cased in the same manner as are
public supply systems. Accordingly, in wellhead protection zones, procedures
should be developed to properly plug and abandon domestic water supply wells.
1.4.5 Buffer Zone
Most public water supply systems have established buffer zones or sanitary
easements around their wells. The minimum requirement for most water utility
companies in Texas is generally a 150-foot radius as a sanitary easement. If
other wellhead protection measures are taken, such as proper site grading,
concrete pads, etc., this 150-foot distance should be sufficient for immediate
area protection from spills of materials that would contaminate a well.
1.4.6 Protection From Bacteria
The protection of drinking water from pathogenic organisms has been practiced
1-46
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for many decades. The connection between polluted water and diseases was not
fully appreciated until the late 1800's and in some areas of underdeveloped
countries it is still not recognized. However, even after the recognition of
these facts, ground water was considered to be free of pathogens and the earth
was considered to be a "natural filter." This was based upon early work using
sand filtration of pathogenic organisms for surface water supplies. The
actual "elimination" of bacteria and viruses from ground water involves more
than filtration, although this is an important factor in sand aquifers. The
concept of minimum distances from bacteriologic sources and water supply wells
has been established by many states. Texas, for example, requires a minimum
of 150 feet sanitary easement around public water supply systems. This also
follows the general recommendation of the American Water Works Association
(AWWA). Early experiments in California with the injection of sewage in a
sand and gravel aquifer suggested this distance was sufficient for the removal
of bacteria.
In addition to filtration, elimination of pathogens in ground water is the
result of the chemical conditions in the aquifer, including the effect of
oxygen concentrations, temperature and pH.
Various studies on the survival of viruses and bacteria have been conducted by
many authors (Keswick and Gerha, 1980; Yates, et a!., 1985; etc.). Based upon
these studies and case histories, residence time in aquifers has been devel-
oped in European countries. Residence time is the time it takes for an in-
jected fluid to reach the point of production, with the aquifer providing
physiochemical treatment. Residence times from two months to one year have
been recommended. Regardless of minimum residence times, these pathogenic
sources should also be prohibited within a certain minimum distance, such as
150 feet for the AWWA or 100 meters (325 feet) recommended by Matthess (EPA,
1987). Artificial recharge with treated sewage effluent is practiced in
several areas of the world. In one major effort in El Paso, Texas, residence
times in excess of two years are predicted and the distance from injector
wells to production wells is over one mile.
Since the source of pathogens can be non-point source such as feces from
animals, polluted streams, etc., it will be difficult to regulate or develop a
1-47
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WHPA based upon area of influence. It is probable that most programs will
rely upon a fixed radius concept for protection against bacteria and viruses.
1.4.7 Protection from Contamination by Naturally Occurring or Synthetically
Derived Organic Compounds
With the rise of industrial development since the early 1900's, inorganic and
organic chemicals began to appear in our drinking water supplies. Prior to
this, contamination of supplies was generally biologic in nature. Because of
the diverse sources of these chemicals, they are currently present throughout
the earth; that is, traces of industrial pollution can be found in all areas
of the earth as a result of transport by wind, rivers, and oceans. Small
quantities of inorganic and organic chemicals have been detected in ground
water systems far removed from modern industrial societies. For instance,
ground water can be dated in any area of the world based upon the trittium
contributed to the atmosphere by nuclear weapons testing. Trash and chemicals
dumped into the ocean are carried significant distances by currents, resulting
in contaminants being present in areas that do not generate these contami-
nants. The protection of ground water supplies from such diffuse sources of
pollution is probably not possible, especially since some of these problems
are global in scope.
The intent of the 1986 amendments was to establish protection measures against
the more obvious source of contaminants, that is, an identifiable point source
or practice within the WHPA developed for each well or well field. All poten-
tial sources must be identified and control strategies developed to prevent
release of a contaminant from a source to the aquifer. The WHPP's are the
responsibility of individual states. Protection from contaminant sources will
depend upon dilution and dispersion and the consideration that the concentra-
tions that ultimately reach wells and are produced will be of such low concen-
trations that they will not be a hazard to human health. (This assumes that
some concentration above absolute zero is acceptable for human health).
In the development of the size of the WHPA, the states are required to look at
the mobility and persistence of the contaminants. Since many of the organic
and inorganic contaminants are very persistent, wellhead protection areas
could be exceedingly large. In cities that use ground water as a source of
1-48
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drinking water and have large cones of ground water depression, wellhead
protection areas will be quite large.
1.4.8 Wellhead Protection Area Delineation Methods
Although the concept of requiring a buffer zone or sanitary easement around a
wellhead has been in existence for some time, the concept of protecting a
water source to the point of where the water originates is a new concept. The
EPA has identified several methods for developing a WHPA. These methods are
listed in Table 1-7. The methods range from simple, inexpensive and probably
politically acceptable to the complex, expensive and politically contro-
versial. The main focus of the EPA programs will be the delineation of areas
that impose and use control to protect water supply wells. Using hydro-
geologic concepts versus fixed radii will result in larger areas being desig-
nated and will affect the price of land; thus, the potential for political
pressure will increase.
1.4.8.1 Arbitrary or Calculated Fixed Radii
There is very little difference in the arbitrary or calculated fixed radii.
Both methods result from drawing a circle around the wellhead or well field
with the well being at the center of the circle. The calculated radii include
the concept of time of travel (TOT) or volume pumped over certain times.
Figure 1-15 shows these two methods. The major problem with this method is
the assumption that the aquifer is homogeneous and that the piezometric sur-
face is flat. The method generally overestimates the downgradient area and
underestimates the upgradient area.
1.4.8.2 Simplified Variable Shapes
The concept of variable shapes includes components of both the calculated
radius and analytical methods. This concept normally results in an elliptical
shape, elongated in an upgradient direction. The standardized form is ori-
ented around the pumping well and aligned with the flow direction. The up-
gradient extent is calculated using a TOT criteria; Figure 1-16 illustrates
this concept.
1-49
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TABLE 1-7
WELLHEAD PROTECTION AREA DELINEATION METHODS
Arbitrary and Calculated Fixed Radii
Simplified Variable Shapes
Analytical Methods
Hydrogeologic Mapping
Numerical Flow/Transport Models
1-50
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.H
in
C TJ
O O
v= em
a> ~O
J 3
ii
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01
-------
S
_*
tr>
0.5
Natural Springs
T
in
r-
U«-1.0km-»-
Pumping Rate <5 Ml/d
Pumping Rate 5 to 15 Ml/d
LEGEND:
• Pumping Well
in
pg
-1.5km-
Pumping Rate >15MI/d
DIRECTION OF GROUND WATER FLOW
I
SOURCE: EPA.1987
Figure 1-16. Variable Shapes for WHPA Delineations
1-52
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1.4.8.3 Analytical Methods
In order to calculate the WHPA using analytical techniques, values of various
hydrogeologic parameters are required as input into the formulas. Using these
values and standard ground water flow equations, the WHPA can be determined
based upon time of travel or flow boundaries. An example of this method is
shown in Figure 1-17.
1.4.8.4 Hydrogeologic Mapping
Standard geologic mapping techniques can be utilized to determine the WHPA.
The flow boundaries or aquifer boundaries frequently coincide with geologic
contact. Aerial photographs, satellite images and both surface and subsurface
geophysical techniques are useful. Figure 1-18 indicates two examples of WHPA
determination using geologic methods.
1.4.8.5 Numerical Flow/Transport Models
Where aquifer boundaries are complex or where numerous recharge - discharge
points exist, the determination of WHPA becomes complex. These complex prob-
lems are better suited for computer solution. Numerous ground water flow
models exist that can be run on either a prime or a micro computer. Input
data requirements for most flow/transport models are extensive and include but
are not limited to permeability, porosity, thickness, recharge rates, and
recharge location. Where these data are available, numerical flow models are
probably one of the better methods of determining WHPAs. However, if little
data exist, it is probably more desirable to use an analytical or hydrologic
solution.
1.4.8.6 Conclusion
A review of the methods available for determining the WHPA was conducted by
EPA for several hypothetical areas. Figure 1-19 is an example of the areas
determined using three different methods and assuming a 25-year time of
travel. This same general shape was established in most of the comparisons;
that is, the analytical and numerical model give similar shapes and both
identify those areas that should receive protection from pollutants. The
calculated fixed radii give somewhat similar answers only in those instances
of flat water tables and low times of travel. If states adopt the more com-
plex method of analytical and numerical modeling, most state agencies will be
1-53
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GROUNDWATER
DIVIDE
A'
LAND SURFACE
PREPUMPING
WATER LEVEL
BEDROCK
A) VERTICAL PROFILE
(B) PLAN VIEW
LEGEND:
V Water table
» Ground-water Flow Direction
• Pumping Well
ZOI Zone of Influence
ZOC Zone of Contribution
Figure 1-17. Analytical Method for WHPA Determination
1-54
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1-55
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WILDLIFE
MA.VGMEST AREA
C* Cranberry
Boj •>. .
• • . Waqiioit Village
•' ' -
EXPLANATION
NUMERICAL MODEL
ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
SOURCE: EPA, 1987
Figure 1-19. WHPA Comparison for Three Methods
1-56
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required to increase their staffs. The new staff members will have to be
experienced ground water hydro legists, who at the present time command sig-
nificant salaries.
1-57
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SECTION 2.0
GROUKD WATER CHEMISTRY
-------
2.0 GROUND WATER CHEMISTRY
The most important sources of dissolved substances in ground water are the
minerals in the soil, in near-surface sediments, and in the sediments of the
aquifer which contain the ground water. The chemical quality of the recharge
also influences the quality of the water in the aquifers. As rain falls
through the atmosphere, natural gases such as carbon dioxide, sulphur dioxide,
nitrogen and oxygen, and man-made airborne pollutants are dissolved into the
rain. As a result of the solution of the atmospheric gases, the pH of most
precipitation is acidic (less than 7) and rainwater is slightly corrosive.
Upon reaching the surface of the earth, the water may increase its corrosive
character by picking up organic acids from soils, when the water percolates
through the subsurface toward the water table, the water dissolves the miner-
als in the sediments and rocks. The amount and character of the mineral ions
entering the ground water depend on: 1) the chemical composition of the
water; 2) the mineralogical and physical structure of the rocks in contact
with the water; 3) the temperature and pressure at which the solution occurs;
and 4) the amount of time the water stays in contact with rocks and sedi-
ments. Nearly every element may be present in ground water, and the mineral
content can vary from aquifer to aquifer. Table 2-1 demonstrates the varia-
tions in common dissolved inorganic compounds that can be expected in natural
water. Table 2-2 lists the Texas and EPA Standards for Drinking Water. In
many areas in the state, the natural ground water cannot meet these stan-
dards.
2.1 CONSTITUENTS IN GROUND WATER
Many organic and inorganic compounds in ground water, that might also be
present in industrial wastes, occur naturally. Thus, it is important to
establish, as best possible, whether a specific constituent can occur natural-
ly and what the natural concentration might be or actually is. Frequently,
the occurrence of metals or organic compounds in ground water and/or soils are
viewed only as contamination. The following discussion provides an overview
of the source and significance of chemical constituents frequently found in
ground water.
2-1
-------
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2-2
-------
TABLE 2-2
Texas and EPA Standards for Drinking Water
EPA-Interim Pri-
mary and Proposed
Texas State Health Secondary Drink-
Dept. Primary and ing Water
Secondary Standards Standards
Ca * *
Mg * *
Na + K * *
HC03 * *
S04 300 250
Cl 300 250
Fe 0.3 0.3
F 1.4-1.8 1.4-2.4
N03 45 45
pH >7 6.5-8.5
TDS 1000 500
Mn 0.05 0.05
As 0.05 0.05
Cd 0.010 0.010
Cr 0.05 0.05
Pb 0.05 0.05
Cu 1.0 1.0
Zn 5.0 5.0
Phenols .01-.10 .01-.10
Hg 0.002 *
Ba 1.0 1.0
Sn 0.01 0.01
Ag *.05 .05
Chlorinated Hydrocarbons:
Endrine 0.0002 0.0002
Lindane 0.004 0.004
Methoxychlor 0.1 0.1
Toxaphene 0.005 0.005
Chlorophenoxys:
2, 4-D 0.1 0.1
2, 4, 5-TP Silvex 0.01 0.01
All units in mg/L, except pH
*No standards established.
2-3
-------
2.1.1 Inorganic Constituents
Silica
Silica is usually reported in water analyses as SiC^, although it is believed
to occur as monomeric silica acid, H4Si04, at the normal temperature and pH
ranges of natural water. The natural accumulation of residual quartz and clay
minerals attests to the relatively slow rate of solution of certain silicate
minerals. The moderately rapid disintegration of other silicate minerals,
notably in volcanic and igneous rocks, releases sufficient silica in a soluble
form to account for the concentrations found in natural waters. The concen-
tration commonly ranges from 5 to 40 mg/L silica in natural ground waters.
Dissolved silica forms a hard scale in pipes and boilers and on the blades of
turbines.
Calcium and Magnesium
Subsurface waters in contact with sedimentary rocks of marine origin derive
most of their calcium and magnesium from the solution of calcite, aragonite,
dolomite, anhydrite and gypsum. Large quantities of both ions can be present
in some brines. The most commonly noted effect of these ions in water is
their tendency to react with soap to form a precipitate called soap curd.
This soap neutralizing power is called water hardness.
Sodium
All natural waters contain measurable amounts of sodium. In ground waters,
the primary source is the weathering of both igneous and sedimentary rocks.
High concentrations combine with chloride to give a salty taste to water and
may limit the use of water for irrigation. However, moderate concentrations
have little effect on water quality.
Potassium
The weathering of minerals in igneous and metamorphic rocks produces most of
the potassium in ground waters. In areas with extensive evaporite deposits,
waters may dissolve large amounts of potassium. Potassium commonly has one-
tenth the concentration in water as sodium, because potassium is incorporated
into clays and plants more readily.
2-4
-------
Iron
Abundant sources of iron exist in the earth's crust. The weathering of many
minerals releases large quantities of iron which are usually converted to
insoluble and stable iron oxides. Concentrations are, therefore, low in
natural waters. Upon exposure to air, iron oxidizes to a reddish brown pre-
cipitate, making a concentration greater than 0.3 mg/L objectionable for food
processing, beverages, ice manufacturing, brewing, and textile manufactur-
ing. Concentrations above 0.3 mg/L will result in fixture staining.
Bicarbonate
Most bicarbonate ions in ground water result from the carbon dixoide in the
atmosphere, carbon dixoide in the soil, and the solution of carbonate rocks
such as limestones and dolomite. Ground water usually contains more than 10
mg/L but less than 800 mg/L bicarbonate. Only rarely does ground water have
pH less than 4.5, causing bicarbonate to convert to carbonic acid, or more
than 8.2, where bicarbonate will dissociate to carbonate. Alkalinity is a
measurement of bicarbonate. In combination with calcium and magnesium, bicar-
bonate causes hardness. Under high temperature conditions such as in steam
boilers and hot water heaters, a calcium-magnesium carbonate scale will form.
Sulfate
Most sulfate found in ground water results from the dissolution of rocks and
soils containing gypsum, iron sulfides, and other sulfur compounds. Atmo-
spheric sulfur dixoide, from natural and man-made sources, causes sulfate to
be one of the major dissolved constituents of rain and snow. Sulfate is also
commonly present in industrial wastewaters. Natural concentrations range from
0.2 mg/L in rain to 100,000 mg/L in magnesium sulfate brines. High sulfate
waters have a bitter taste and form a scale in steam boilers. The federal and
state limits for sulfate in drinking water are 250 mg/L and 300 mg/L, respec-
tively. Consumption of water with high sulfate and magnesium concentrations
may have laxative effects.
Chloride
Most chloride in ground water conies from: 1) the solution of evaporite miner-
als, 2) concentration of evaporation of chloride in rain and snow, and 3)
2-5
-------
ancient seawater entrapped in sediments. Chloride is also present in sewage,
oil field brines, seawater, and industrial waste streams. Once chloride
enters ground water, it is difficult to remove by natural processes. Concen-
trations range from 0.1 mg/L in snow to 150,000 mg/L in brines. Large amounts
combined with sodium give water a salty taste and can increase the corrosive-
ness of water. The federal and state limits in drinking water are 250 mg/L
and 300 mg/L, respectively.
Nitrate
Nitrate comes from decaying plant and animal matter, nitrogen fertilizer,
return flow of irrigation water, barnyard and feedlot leachate, sewage, and
natural soil nitrogen. Nitrate is highly soluble, and can be removed from
ground water through the activity of plants and bacteria. Waters with high
concentrations of nitrate can cause a fatal disease in infants called methemo-
globinemia. Such waters may be linked with gastric cancer as well. The
federal and state limits in drinking water are 45 mg/L as nitrate or 10 mg/L
as nitrogen.
Fluoride
Fluoride is dissolved in small quantities from most rocks and soils. Many
municipal water supplies add it to their distribution systems. When the
concentration approaches the optimum value, from 0.7 to 1.2 mg/L, fluoride
reduces the incidence of tooth decay in children. Excessive amounts in drink-
ing water can mottle teeth, depending on the age of the child, the concen-
tration of fluoride, the amount of water drunk, and the susceptibility of the
individual. Both state and federal limits exist for fluoride concentration in
drinking water.
Metals
Samples of ground water and frequently "soil samples" from the unsaturated
zone are collected and analyzed for metals. Soil, in most places, is a natu-
ral residuum developed by prolonged weathering of the bedrock. In contamina-
tion studies, samples of soil (upper 1 to 3 feet) are normally not taken since
waste migration from lagoons, etc. generally occurs at a deeper depth. There-
fore, samples collected for chemical analysis during waste site investigations
are normally geologic materials, not soils. Since the geologic material is
2-6
-------
not as uniform as soils, one would expect a wide potential range of naturally
occurring compounds within any set of samples.
Data presented in Table 2-3 demonstrates the wide range of concentrations of
metals in naturally occurring substances including soil and bedrock. This
list was compiled from 11 sources. Given sufficient time, the ranges shown
here could certainly be expanded. Accordingly, one must be careful in making
assumptions about the source of metals when conducting contamination
studies. A discussion on the possible natural and man-made sources of metals
is contained in Table 2-4.
2.1.2 Organic Constituents
The occurrence of elevated concentrations of certain organic compounds and
frequently, ratios or concentrations of common inorganic compounds is, in most
situations, an indication of contamination related to disposal activities.
Although it might be presumed that all detected organic compounds are derived
from the wastes at a site, this is not the case, as numerous organic compounds
occur naturally or occur as nonpoint sources of pollution.
Lignite is very common in many areas of east and south central Texas. In
these areas, low concentrations of naturally occurring organics may be diffi-
cult to distinguish from contamination by man. Table 2-5 presents a list of
organics frequently found in coal.
Coal is a heterogeneous solid originating from plant material, but also con-
taining inorganic sedimentary material, i.e., sand, silt, clay, that accumu-
lated with the plant material. The principal elemental composition of coal is
carbon, hydrogen, nitrogen, and sulphur, with carbon predominating. Coal has
a structure similar to cross linked polymers. The main organic functionali-
ties are carbonyl, hydroxyl, aromatic, and heterocylic. Alkyl side chains are
common, especially one and two member aromatic rings, e.g., benzene and
naphthalene.
When coal is oxidized, polynuclear aromatic hydrocarbons (PNAs) are generated,
along with the phenols and cresols. Similar compounds are found in liquified
coal. PNAs are also common constituents in coal tars and cresol tars. Com-
2-7
-------
TABLE 2-3
TRACE METAL CONCENTRATIONS: RANGE IN COAL, ASH, BEDROCK, SOIL, AND PLANTS"
Elements
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Nickel
Selenium
Silver
Thalium
Tin
Vanadium
Zinc
RANGE IN COAL
REF 1,2,4,5,9
0.04
0.10
20 -
0.1 -
0.01
0.25
0.05
0.13
1,800 -
0.37
100 -
0.75 -
0.01
0.32
0.02
0.02
<0.2
0.04
4 -
1.0 -
- 43
- 420
3,000
1,000
- 170
- 220
- 930
- 300
100,000
- 590
20,000
3,500
- 33
- 580
- 150
- 2
- 8
- 51
300
5,350
RANGE IN COAL ASH
REF 1,3,5,7
5.6
2.8
96 -
1
1 -
10 -
10 -
10 -
78,000
20 -
11,900
10 -
0.1
3 -
0.77
1
0 -
10 -
6 -
50 -
- 100
- 200
13,900
- 60
100
1,000
10,000
3,020
- 480,000
1,500
- 79,300
10,000
- 18
10,000
- 40
- 60
17.1
4,250
5,000
1,200
RANGE IN BEDROCK*
REF 6,8,10
0.1 - 1
<1 - 39
<1 - 7,500
<1 - 12
<1 - 12
<1 - 700
0.01 - 71
<1 - 400
<500 - > 100,000
<3 - 7,000
<60 - 98,000
0.5 - 10,000
0.05 - 1500
<2 - 420
<0.1 - 12
<0.2 - 10
0.3 - 3
<10 - 20
<2 - >1,100
6 - 2,300
RANGE IN SOIL
REF 2,6,8,10,11
<150 - 500
<0.1 - 183
15 - 5,000
<1 - 7
0.01 - 11
1 - 4,000
.05 - 300
<1 - 5,000
100 - 123,000
2 - 1,200
50 - 100,000
<2 - >20,000
<10 - 4600
<5 - 5,000
0.03 - 10
<0.5 - 30
0.02 - 5
1-100
<5 - 500
<5 - 2,000
RANGE IN PLANTS
REF 2,8,10,11
-
0.2 - 30
5 - 50,000
<2 - 7
<0.2 - 60
0.01 - 150
0.05 - 10,000
4 - 7,000
100 - 20,000
0.1 - 3000
4,000 - 240,000
15 - 50,000
<0.1 - 50
1 - 1,300
<0.01 - 4.8
<0.4 - 20
<2
<15 - 30
0.1 - 700
15 - 10,000
* Sandstone, shale, mudstone, siltstone, limestone
REF - References
- No references on concentrations found
" all numbers are expressed in ppm
1) Bush and Colton, 1983
2) Lisk, 1972
3) Torrey, 1978
4) Swaine, 1977
5) Valkovic, 1968
6) Aubert and Pinta, 1977
7) Sauchelli, 1969
8) Conner and Shacklette, 1975
9) Ruch, Gluskoter, Shimp, 1974
10) Smith and Carson, 1977
11) Brown, 1980
NOTE: This table was compiled by combining information from various documents and references. Many authors stated a range in or
average value of concentrations, without stating the number of samples tested or the locality from which the samples were taken.
For this reason, there is no feasible manner in which to ascertain the number of samples from which the table was compiled. Also,
there is no direct relation between the values in the various columns.
2-8
-------
METAL
Antimony
Arsenic
Barium
Beryl!ium
Cadmium
TABLE 2-4
OCCURRENCE OF METALS
USE
Industrial Occurrence: medicinal agents, on safety
matches, in vulcanizing rubber, as a pigmenting agent in
glass and porcelain, the bronzing of steel, and as a
caustic in medicine
Natural Occurrence:
particles
as the mineral stibnite, fly-ash
Industrial Occurrence: insecticides, herbicides, pesti-
cides, pigment production, manufacture of glass, manufac-
ture of Pharmaceuticals, textile printing, tanning,
taxidermy, and in lubricating oils to control sludge
formation
Natural Occurrence:
arsenic
yellow arsenic (III) sulfide, gray
Industrial Occurrence: insulator for electrical appara-
tus, alloy constituent in automobile spark plugs, addi-
tive to increase the weight of drilling fluids; in medi-
cine, it is given to patients when X-ray photographs are
to be taken of the gastrointestinal tract because it
absorbs X-rays so well
Natural Occurrence: as the minerals barite and witherite
Industrial Occurrence: primary use is as an additive in
structural metal alloys, also in electrical contacts,
springs, nonsparking tools, and X-ray tubes, electrical
applications in televisions, computers, and beryllium
alloys in personal body armor
Natural Occurrence:
cles
in the mineral beryl, fly-ash parti-
Industrial Occurrence: electrolytically deposited coat-
ing on metals, solder, photographic chemicals, manufac-
ture of fireworks, rubber, fluorescent paints, glass and
porcelain, smelting and plating operations, and litho-
graphy.
Natural Occurrence: found associated with lead, copper,
and zinc ores; leaves of tobacco plants; fly-ash parti-
cles
2-9
-------
TABLE 2-4
OCCURRENCE OF METALS (Continued)
METAL
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
USE
Industrial Occurrence: the most common use of chromium
is in the production of metallic products; pigmenting
agents in paints, photographic processes, tanning, corro-
sion inhibitors, and fungicides
Natural Occurrence:
particles
metallic ore, chromite; fly-ash
Industrial Occurrence: alloy in metals in the electri-
cal, automobile, aircraft, and tool steel industries;
pigments in enamels, glazes, paints and in the glass,
pottery, and electroplating industries
Natural Occurrence: as arsenides, sulfides, and oxidized
mineral forms; coal fly-ash particles
Industrial Occurrence: electrical circuitry, castings,
rods, tubing, water and gas piping, cooking utensils, and
coninage; insecticides, algicides, plant fungicides,
pigments and in fertilizers as a copper supplement for
pastures
Natural Occurrence: copper ores such as malachite,
cuprite, chalcopyrite, emitted as fumes in the coal
combustion process
Industrial Occurrence: wrought iron, cast iron, and
steel; galvanized sheeting and electromagnets
Natural Occurrence: as the minerals hematite, hoethite,
magnetite, siderite, and limonite; fly-ash particles
derived from coal
Industrial Occurrence: lead plates in sotrage batteries,
electrical cables, as lining material in pipes, tanks,
and X-ray apparatus; glass manufacture, drier in oils and
varnishes, pigmenting agents in paints, and as a gasoline
additive
Natural Occurrence: galena, the ore of lead; leaves of
tobacco plants; fumes in the combustion of coal
Industrial Occurrence: castings for airplane parts and
varied metallurgical applications; optical instruments,
photographic flashlight powders, incendiary bombs, as a
medicinal agent in the product known as "Epsom Salt"
2-10
-------
TABLE 2-4
OCCURRENCE OF METALS (Continued)
METAL
Manganese
USE
Mercury
Nickel
Selenium
Silver
Natural Occurrence:
site
in the minerals dolomite and magne-
Industrial Occurrence: iron and steel industry as an
agent used to reduce oxygen and sulfur content of molten
steel; manufacture of dry cell batteries, paints, var-
nishes, inks, dyes, matches and fireworks, as a fertil-
izer, disinfectant, bleaching agent, and as a coloring
agent in the glass and ceramics industry
Natural
ashes
Occurrence: the mineral pyrolusite, in coal
Industrial Occurrence: thermometers and other scientific
apparatus, vacuum pumps, barometers, switches, electric
rectifiers; common antiseptics, pigments, electrodes,
fungicides
Natural Occurrence:
cles
the mineral cinnabar, fly-ash parti-
Industrial Occurrence: metallurigcal alloys, coinage,
smelting, electroplating, nickle-cadmium batteries,
nickel soaps in crankcase oils, colored ceramics and
glass
Natural Occurrence: as the minerals garniete, millerite,
niceo lite, pent 1 andite, and pyrrhotite; leaves of tobacco
plants
Industrial Occurrence: photoelectric devices, as a
coloring agent in glasses and enamels, additives to
vulcanized rubber, insecticides; and in medicines used to
treat dandruff, acne, exzema, seborrheic dermatitis, and
other maladies; printing paper and xerography
Natural Occurrence: as an amorphous mass called vitreous
selenium, lustrous crystals called metallic selenium
Industrial Occurrence: jewelry, tableware, coinage,
various medicinal applications, photographic processes,
smelting and plating operations
Natural Occurrence: as the ores cerargyrite, pyrargy-
rite, sylvanite, and argentite; fly-ash particles associ-
ated with coal combustion
2-11
-------
TABLE 2-4
OCCURRENCE OF METALS (Continued)
METAL
Thai "Hum
Tin
Vanadium
Zinc
USE
Industrial Occurrence: rodenticides, fungicides, in-
secticides, bromoiodide crystals for lenses, plates, and
prisms in infrared optical instruments
Natural Occurrence: occurs in combination with pyrites,
zinc blende, and hematite; leaves of tobacco plants; coal
fly-ash particles
Industrial Occurrence: various utensils, cups, plates;
metallic alloys, protective metals coatings, heat stabi-
lizers in chemical processes, catalysts, wood preserva-
tives, and in textiles as biocides
Natural Occurrence:
tinstone
as the minerals cassiterite or
Industrial Occurrence: metallic alloys, manufacture of
sulfuric acid, photographic developers, as reducing
agents, and as drying agents in various paints
Natural Occurrence: as the minerals roscoelite, vanadi-
nite, and carnotite; coal fly-ash particles
Industrial Occurrence: protective coating for iron and
steel; paint pigment, filler in rubber tires, antiseptic
ointment, wood preservative, and soldering fluid
Natural Occurrence:
and smithsonite
the principle ores are sphalerite
2-12
-------
TABLE 2-5
EPA HAZARDOUS LIST COMPOUNDS FOUND IN COAL1
VOLATILES EXTRACTABLES TYPE
Benzene Naphthalene pna3
Toluene 2-Methylnaphtalene pna
Ethyl benzene Fluorene pna
Xylenes Phenanthrene pna
Anthracene pna
Fluoranthene pna
Pyrene pna
Chrysene pna
HAZARDOUS SUBSTANCE LIST ORGANICS RELEASED INTO ENVIRONMENT FROM COAL COMBUS-
TION/
VOLATILES EXTRACTABLES TYPE
Benzene Benzole Acid
Toluene Aniline
Xylene Benzidene
Carbon Disulfide Phenol
Cresol
Benzo (A) Pyrene pna
Dibenz (ah) Anthracene pna
Chrysene pna
Ideno (123cd) Pyrene pna
Pyrene pna
Acenaphthene pna
Acepahthylene pna
Fluorene pna
Anthracene pna
JvALKOVIC, VLADO, TRACE ELEMENTS IN COAL VOL. I
^TORREY, S. (ED), TRACE CONTAMINANTS FROM COAL
°pna = polynuclear aromatic
2-L'
-------
pounds found include several volatiles as well as extractables, which are
mostly PNAs.
Potential concentrations of these organic compounds in coal are not known, but
presumed to be low. Table 2-5 also contains a list of hazardous substance
organics released into the environment from the combustion of coal. In areas
where lignite or coal power plants exist, these compounds may also occur in
the air.
2.2 SIGNIFICANCE OF LOU CONCENTRATIONS OF ORGANIC AND INORGANIC COMPOUNDS
The tendency in conducting investigations is to review chemical analysis of
soils, ground water, and surface wastewater in order to determine what is
present and what the relationship is to a waste site. Frequently, anything
found, no matter how far away from the site, is attributed to the site. This
is often in error and fails to realize the multitude of compounds which are
now in the environment as a result of many industrialized activities. These
compounds are frequently referred to as non-point source contaminants.
Examples of these non-point source contaminants can be found in the volumes of
data collected as part of the National Urban Runoff Program (NURP). Table 2-6
contains data from the Austin program and demonstrates the wide range of
pollutants that can be found in urban settings that cannot be related to any
particular point source of pollution.
While inorganic and organic compounds can naturally occur in soil and aquifer
matrices, very little data have been presented in the literature which docu-
ment that naturally occurring metals and organic substances would be dissolved
in ground water. However, our theory of the origin of dissolved substances in
ground water would suggest that they could. A 1983 Canadian study also sug-
gests that it is possible. Table 2-7 lists the concentration range of chemi-
cals found in peat in three peat bogs in Canada. Table 2-8 is the result of
analysis of waters from these bogs, indicating that both metals and organics
were found. Although these data are from Canada, many areas in the Gulf Coast
are "swampy" and buried plant and wood detrital matter are very common.
2-14
-------
TABLE 2-6
NATIONAL URBAN RUNOFF PROGRAM (NURP)
PRIORITY POLLUTANT SAMPLING RESULTS
(AIL SAMPLE RESULTS ARE IN ug/l UNLESS NOTED)
Range of Pollutant Concentrations
in NURP* Storm Water
Samples That Were Above
Pollutant Detection Limit (U9/D
Metals and Inorganics
Antimony 2
Arsenic 3.3-37
Bery 1 1 ium
Cadmi um
Chromium 2-61
Copper 2-110
Cyanide 2-33
Lead 37.6-460
Mercury
Nickel
Selenium 0-225
Si Iver
Thai 1 ium
Zinc 10-546
Pesticides
Acrolein
Aldrin
Chlordane 0.01
DDO
DOE 0.35
DOT 0.008-0.1
Dieldrin 0.2
EndosuHan and Endosulfan Sulfate
Polycyclic Aromatic Hydrocarbons
Acenaphthene
Acenaphthylene
F luorene
Naphthalene 1-13
Anthracene '-7
Fluoranthane 0.3-15
Phenanthrene 0.3-7
Benzolalanthracene 1-3
Benzo(b) f 1 uoranthene 2
Benzo(k) f 1 uoranthene 4
Chrysene 0.6-6
Pyrene 0.3-13
Benzo ( gh i ) pery 1 ene
Benzo(a)pyrene 1-2
D i benzol a, h) anthracene
1 denot 1 ,2.3-cd)pyrene
Halogenated Ethers
Bislchloromethyl lether
Bis(2-chloroethyl lether
Bis(2-ch loroisopropy 1 )ether
2-chloroethy I vinyl ether
4-chloropheny 1 phenytether
4-bromopheny 1 pheny)etner
Bis (2-chloroethoxy)methane
Phthaiate Esters
Dimethyl Phthalale
Number ot All NURP* Samples
That Reported Values
Above Detection Limit/
Number of Samples
Analyzed for Compound
1/28
16/28
18/28
26/28
7/27
26/28
6/28
26/28
0/42
0/42
1/42
0/42
1/42
2/42
1/42
0/42
0/42
0/41
0/41
0/41
4/41
4/41
5/41
7/41
2/41
1/41
1/41
4/41
5/41
0/41
2/41
0/41
0/41
0/41
0/41
0/41
0/41
0/41
0/41
0/41
0/41
2-15
-------
TABLE 2-6 (Continued)
NATIONAL URBAN RUNOFF PROGRAM (NURP)
PRIORITY POLLUTANT SAMPLING RESULTS
Range of Pollutant Concentrations
in NURP" Storm Water
Samples That Were Above
Pollutant Detection Limit (ug/l)
Diethly Phthaiate 1-5
Di-n-butyl Phthaiate 3-11
Di-n-octyl Phthaiate 1-3
Bis(2-ethylhexy)Phthalate 1-42
N-butyl Benzyl Phthaiate
Pol ychlori nated Bipnenyls and
Related Compounds
PCB-1016
Aroclor 1221
Aroclor 1232
Aroclor 1242
Aroclor 1248
Arcolor 1254
Arcolor 1260 0.03
2-ch 1 oroanaph tha 1 ene
Nitrosamines and Other N Compounds
Dimethyl Ni trosami ne»
Dimethyl Nitrosamine
Di-n-propyl Nitrosamine
Benzidl ne
3 ,3-d i ch lorobenz i di ne
1 ,2-dipheny I hydrazine
Aery Ion 1 tr i le
Halogenated Aliphatic Hydrocarbons
Chloromethane (Methyl Chloride)
Dich loromethane
(Methyiene Chloride) 5-1,645
Trochloromethane (Chloro(orm) 0.2-8
Tetrachorome thane
(Carbon Trachloride) 1-4
Chloroethane (Ethyl Chloride)
1 ,1-dichloroethane (Ehty 1 i dine Chlor ide) 1-5
1 ,2-dtchloroethane (Ethylene Chloride) 4
1 , 1 , 1 -tr i ch 1 oroethane
(Methyl Chloroform) t-23
1 ,1 ,2-trichloroethane 1-3
1 ,1 ,2,2-tetracnloroethane 1/3
Hexach 1 oroethane
Chloroethene (Vinyl Chloride)
1 , 1 -d i ch loroethene
(Vinyl idine Chloride) 1-4
1 ,2-trans-dichloroethene '-3
Tr ichloroethene '-3
Tetrach loroethene 4-43
1 ,2-dich loropropane 3
1 ,3-dichlorpropane 1-2
Hexach lorobut ad i ene
Hexach lorocycl open tad i ene
Bromomethane (Methyl Bromide)
Bromodichlorometnane 2
Olbromochlorom«tnen« 2
Tr i bomomethane (Bromoform) 1
Dichlorodi f 1 uorome thane
Tr ichlorof 1 uoromethane 1-5
Number of All NURP" Samples
That Reported Values
Above Detection Limit/
Number of Samples
Analyzed for Compound
4/41
6/41
2/41
16/41
0/41
0/42
0/42
0/42
0/42
0/42
0/42
1/42
0/42
0/41
0/41
0/41
0/41
0/41
0/41
0/41
0/40
19/40
12/40
4/40
0/40
5/40
1/40
17/40
5/40
6/40
0/40
0/40
2/40
6/40
7/40
6/40
1/40
2/40
0/40
0/40
0/40
1/40
1/40
1/40
0/40
4/40
2-16
-------
TABLE 2-6 (Continued)
NATIONAL URBAN RUNOFF PROGRAM (NURP)
PRIORITY POLLUTANT SAMPLING RESULTS
Pollutant
Range of Pollutant Concentrations
In NURP* Storm Water
Samples That Were Above
Detection Limit (ug/t)
Number of All NURP1 Samples
That Reported Values
Above Detection Limit/
Number of Samples
Analyzed for Compound
Monocyclic Aromatic Hydrocarbons
Benzene
Chlorobenzene
I,2-dichlorobenzene
1,3-d i chIorobenzene
1 ,4-d i chIorobenzene
1,2,4-trichIorobenzene
HexachIorobenzene
Ethyl benzene
Ni trobenzene
To Iuene
2,4-dint trotoluene
2,6-dini trotoluene
Phenol
2-chlorophenol
2,4-dichiorophenol
2,4,6-tr ichlorophenol
Pentach I oropheno I
2-ni trophenol
4-n i trophenol
2,4-dini trophenol
2,4-dimethyl phenol
p-chIoro-m-cresoI
4,6-d i n i tro-o-cresoI
1-13
1-3
1-3
6-9
2-8
2-22
10
3-H5
1-19
1-2
17/41
5/41
0/41
0/41
0/41
0/41
0/41
8/41
0/41
16/41
0/41
0/41
4/41
2/41
1/41
0/41
11/41
0/41
4/41
0/41
0/41
2/41
0/41
2-17
-------
TABLE 2-7
RANGE OF CHEMICAL CONSTITUENTS
FOUND IN 20 PEAT SAMPLES
FROM THREE CANADIAN BOGS
PARAMETER
UNITS
RANGE
Sample Moisture
METALS (total)
aluminum (Al)
antimony (Sb)
arsenic (As)
barium (Ba)
beryllium (Be)
boron (B)
cadmium (Dc)
chromium (Cr)
cobalt (Co)
copper (Cu)
iron (Fe)
lead (Pb)
lithium (Li)
mercury (Hg)
molybdenum (Mo)
nickel (Ni)
potassium (K)
selenium (Se)
strontium (Sr)
thallium (Tl)
thorium (Th)
titanium (Ti)
uranium (U)
vanadium (V)
zinc (Zn)
zirconium (Zr)
NON-METALS
carbon (C)
nitrogen (N)
phosphorus (P)
sulphur (S)
phenol
phenanthrene
pyrene
triphenylene
fluoranthene
benzo(g,h,i)perylene
benzo(a)pyrene
benzo(e)pyrene
chrysene
benzo(k)f1uoranthene
benzo(b)fluoranthene
ideno(l,2,3-c,d)pyrene
benzo(a)anthracene
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppb
ppm
ppm
ppm
ppm
ppm
ppm
ppm
%
ppm
ppm
ppm
ppm
yg/L
ug/L
ug/L
yg/L
yg/L
yg/L
yg/L
yg/L
yg/L
yg/L
yg/L
yg/L
yg/L
700-4800
<1
<2
<15
.1-.3
7-25
.3-1
5-37
<1
1.5-13
408-3575
4-81
.1-1.4
.5-105
<1
1-6.5
84-1025
1-6
14-80
<.5
1-10
.01-.21
1-2
<2-9
6-74
9-66
38-55
.6-1.54
.016-.066
.1-.4
.89-600
Not detected
Not detected
Not detected
.0041-.13
.0066-.09
.033-.044
.012-.066
.029-.031
.030-.058
<.04-.054
.0050-.092
Not detected
2-18
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-------
It is assumed that many of the compounds found in the Canadian study could
also be found to occur naturally in EPA Region VI. Frequently, waste disposal
sites are located in low areas which could be considered "swampy." This is
particularly true along the Texas and Louisiana Gulf Coast. Monitor wells
completed in these shallow zones may produce water that is not typical of most
ground water supplies.
Another potential source of low concentrations of constituents is from air
pollution. Industrial societies generate large volumes of products. During
the manufacturing process, chemicals and/or chemical compounds escape into the
atmosphere. If an odor exists, then the chemical is either dissolved in the
air or is suspended as a mist or attached to a dust particle. Rain falling
through the atmosphere can adsorb these chemicals directly, or can settle the
dust out of the atmosphere to the ground surface where further leaching by
rain can occur. The fact that water can absorb chemicals from discharges to
the atmosphere has been known for decades. In the latter 1870's, the Louisi-
ana Board of Health reported that cistern water in New Orleans was contami-
nated with ammonia that was escaping from the vents of pit privies. More
recently, analysis of travel blanks collected in odoriferous parts of petro-
chemical plants has detected chemicals produced at the plant. Laboratory
blank results, especially for methylene chloride, suggest that vapors in the
air can be readily absorbed into water. Acid rain is another good example.
Accordingly, when one finds volatile chemicals in low concentrations in the
shallow ground water in industrial areas, there may be more than one possible
answer as to their source.
2-21
-------
SECTION 3.0 INVESTIGATIVE TECHNIQUES
-------
3.0 INVESTIGATIVE TECHNIQUES
The purpose of investigating both inactive and active waste disposal sites
includes (1) the assessment of the potential environmental hazards, (2) the
determination of how much environmental damage has occurred, and (3) the
development of corrective measures and/or changes in site management prac-
tices. Each waste disposal site must be evaluated individually because of the
geologic and hydrologic variations and the variety of the wastes they con-
tain. Although no one standard investigative approach is applicable in all
instances, some general procedures can be followed.
Initially it is useful to assemble all the available data about the particular
waste disposal site, including:
1. Physical location and boundaries of the site from
plats, aerial photographs and topographic maps, and
interviews with employees of the plant.
2. Type of site, i.e., landfill, surface impoundment,
landfarm and chemical analysis of the waste.
3. Area and depth of site
4. Length of time the site was active
5. Original design characteristics of the site
6. Method of site closure, if inactive
7. Existing environmental monitoring system.
The investigation of an active site will be greatly aided by any available
knowledge about the nature, variety, and quantity of wastes disposed in the
site, the physical and chemical characteristics of each waste, and the methods
of disposal. Abandoned sites where waste types and quantities are unknown
create additional problems for the investigator.
3.1 BACKGROUND DATA
Before beginning a field investigation, all available background data should
be collected and reviewed. The following is a partial breakdown of available
data and sources.
3-1
-------
3.1.1 Soil Data
A good source of soils data is the U. S. Soil Conservation Service (SCS), a
federal agency with offices in each county and a main office for each state.
Published soil reports exist for numerous counties in Region VI. These
reports, which provide maps, textural, drainage, and other information for
each area are available from the SCS at the address below:
U. S. Soil Conservation Service
Soil Scientist Department
101 South Main Street
Temple, Texas 76501
Phone: (817) 774-1261
U. S. Soil Conservation Service
Soil Scientist Department
Room 5423, Federal Office Building
700 W. Capital Street
Little Rock, Arkansas 72201
Phone: (501) 378-5410
U. S. Soil Conservation Service
Soil Scientist Department
3737 Government Street
Alexandria, Louisiana 71302
Phone: (318) 473-7757
U. S. Soil Conservation Service
Soil Scientist Department
USDA Agricultural Center Building
Stillwater, Oklahoma 74074
Phone: (405) 624-4448
U. S. Soil Conservation Service
Soil Scientist Department
517 Gold Avenue SW, Room 3301
Albuquerque, New Mexico 87102-3157
Phone: (508) 766-1844
Most of these reports are also available for viewing at each state's agricul-
tural departments. The local county Agricultural Extension Agent's office
also keeps soils reports for the county in which they are located. For those
areas for which soils reports are not published, soil groups have usually been
mapped on aerial photos. These are generally available at the local SCS
office and can be traced or reproduced.
3-2
-------
Another source of soils data is the Agronomy or Soils Departments of the
agricultural schools in each state. Access to this data can usually be ob-
tained by contacting the department head or by contacting the State Coopera-
tive Extension Services office located on the campus of the university.
County and State Engineering Offices, the Department of Transportation of
Highway Departments of each state, and local drillers that have worked on
construction projects, or have drilled water wells in the area, can often
provide information on the soils and also on sources of information about an
area.
Soils data may not be directly applicable to ground water studies; however,
they generally give some clue as to the underlying geology.
3.1.2 Boring Inventory
In most industrial complexes, numerous soil foundation borings have been
performed. A contractor seldom constructs a building without substantial
soils data. Although soil samples from these borings may not have been tested
for permeability and other desired parameters, at least the borings will help
determine the shallow stratigraphy. This data is normally on file in the
plant office, or copies can be obtained from either the soil testing firm or
the construction contractor. For large structures, borings to 100 feet may be
avai Table.
Soil borings were conducted prior to construction of many existing waste
storage or disposal units. For a landfarm, soil borings may have been con-
ducted to determine the shallow stratigraphy and to classify soil types. Soil
borings may have been conducted for areas now covered by tanks or a drum
storage area. For landfills, borings may have been conducted to determine
stratigraphy or to sample the soil to determine its bearing capacity, perme-
ability, and so forth.
For roads, bridges, overpasses, or riverways bordering the site of interest,
boring records should be on file at the city or county engineer's office or
highway department office.
3-3
-------
3.1.3 Geology
The state geological agencies have numerous geologic maps, at several scales,
available for purchase. They also carry published reports on specific geo-
graphic areas, with more detailed information concerning the geological,
hydrological, and other aspects of those areas. Their phone numbers and
mailing addresses to use when ordering publications are listed below:
Arkansas Geological Commission
3815 W. Roosevelt
Little Rock, Arkansas 72204
Phone: (501) 663-9714
Louisiana Geological Survey
P. 0. Box G
Baton Rouge, Louisiana 70893
Phone: (504) 342-6754
New Mexico State Bureau of Mines and Mineral Resources
Socorro, New Mexico 87801
Phone: (505) 835-5011
Oklahoma Geologic Survey
830 Van Vleet Oval, Room 163
Norman, Oklahoma 73019
Phone: (405) 271-2555
Bureau of Economic Geology
Box X, University Station
Austin, Texas 78713-7508
Phone: (512) 471-7721
In addition, local geologic societies, universities and the 11. S. Geological
Survey have available data on local geologic conditions. The U. S. Geological
Survey offices frequently contain unpublished reports or geologic/hydrologic
observations made by employees. These are frequently filed by the county. To
gain access to these files you must travel to the USGS offices and review them
as they are NOT cataloged.
Another source to consider for regional and site-specific geologic information
is the geologic report submitted to regulatory agencies, as part of a permit
application or other reports, by industries which may be near the site of
interest. As an example, there are three refineries in El Paso, Texas that
are adjacent to each other. Information available for any two of three sites
3-4
-------
could be extrapolated to the third site to give a general overview of the
geologic and hydrologic conditions which could be expected to occur at that
site. In fact, all three sites have conducted numerous geologic and hydro-
logic investigations, and the sharing of some information, such as water
levels or boring logs, has enabled each company to achieve a better under-
standing of the hydrogeologic conditions in the area. In addition to geologic
reports on industrial complexes which may be located nearby, the state health
departments maintain permit applications for sanitary landfills. These per-
mits have geologic/hydrologic reports that frequently cover large areas.
3.1.4 Ground Water Data
The state water regulatory agencies have numerous publications concerning the
availability and quality of ground water. All water related reports and
general information are available upon request at each agency. Their
telephone numbers and addresses are listed below:
Arkansas Department of Pollution Control and Ecology
8001 National Drive
P. 0. Box 9583
Little Rock, Arkansas 72209
Phone: (501) 562-7444
Louisiana Department of Environmental Quality
Office of Water Resources
P. 0. Box 44091
Baton Rouge, Louisiana 70804-4091
Phone: (504) 342-6363
New Mexico State Engineer
Baton Memorial Building, State Capital
Santa Fe, New Mexico 87503
Phone: (505) 827-6110
Oklahoma Water Resource Board
100 N. E. 10th Street
P. 0. Box 53585
Oklahoma City, Oklahoma 73152
Phone: (405) 271-2555
Texas Water Commission
P. 0. Box 13087, Capitol Station
Austin, Texas 78711
Phone: (512) 463-7834
3-5
-------
Data on public water supply wells can frequently be obtained from the State
Health Departments. In some areas, underground water districts have been
formed. Where applicable, these agencies have large volumes of data on ground
water resources.
Another valuable source of ground water data is the data supplied by facili-
ties which have filed permit applications with various regulatory agencies,
which are located near the site of interest. This data is often public
information. One good source for permit applications and related files is the
central records room of each agency.
3.1.5 Aerial Photos
Aerial photos are helpful aids for locating faults and describing both soil
and geologic conditions. They are also useful for preparing base maps. The
yellow pages of most city phone books list aerial photographs for sale in the
area.
Aerial photographs can be used to review a site history with time.
Frequently, photographs are available for a number of years, occasionally
predating the site itself. In one instance in the Texas Gulf Coast, a
windmill was obvious from an old photograph. A later photograph shows an acid
pit had been constructed on top of the old well.
3.1.6 Landsat Image Data
When available, Landsat images can be surveyed for a regionwide assessment of
possible structural controls on ground water flow. The method employed in
this assessment is to view the images repeatedly for through-going, straight
linear features. These features, termed lineaments, are defined as being of
endogenetic origin (that is, structurally controlled) and consist of a natural
pattern of tones, textures, and contours that are straight, linear, and more
or less continuous, have definable end points and lateral boundaries (high
length/width ratio), and hence a discernible azimuth.
3-6
-------
Lineaments viewed on Landsat images provide a perspective not gained from low-
altitude aerial photography or on-ground surveys of structural grain. This is
because of the synoptic overview provided by the satellite image, whereby a
standard 29-inch' image allows one to survey an area of more than 30,000 square
kilometers at one time. Such an overview allows features to be seen that are
not discernible at a larger scale. Used in concert with more detailed, low-
altitude surveys and ground investigations, the structural grain of an area
may be characterized. The use of Landsat or air photographs for possible
controls on ground water flow works best in those areas where competent rocks
crop out at the ground surface. Contamination studies in limestone terrains
such as the Central Texas Edwards limestone cannot be conducted without them.
3.1.7 Additional Sources
In addition to the above list, local universities, Councils of Government, and
the U.S. Geological Survey have large volumes of data available to the pub-
lic. Details on specific waste handling and disposal units and their history
can often be obtained by conversations with plant personnel.
3.2 FIELD INVESTIGATIVE TECHNIQUES
Once background data have been accumulated, site-specific information is
needed to properly assess the problem. The data needed includes: depth to
water; types and permeabilities of soils; the type, depth, and thickness of
water-bearing material; direction and velocity of ground water flow; and
chemical quality of the ground water. This information can be obtained by a
variety of field investigative techniques.
3.2.1 Geophysical Methods
Several geophysical methods can be employed to assess subsurface conditions.
While there are numerous geophysical tools used in exploratory investigations,
the most common are resistivity and electromagnetics. These methods are used
in conjunction with exploratory methods of direct observation and measurement
such as exploratory drilling, monitor wells and lysimeters, tensiometers, cone
penetrometers, and soil gas/vapor monitoring.
3-7
-------
3.2.1.1 Earth Electrical Resistivity Surveys
Resistivity surveys can be utilized in a number of applications in hydrogeo-
logic investigations. They are most useful in shallow applications where
preliminary data are required on subsurface stratigraphy or shallow water
quality. They can also be utilized to supplement data obtained from existing
soil borings or monitor wells.
Resistivity is a fundamental property of material and can frequently be used
to characterize that material. The success of the electrical resistivity
method for subsurface investigations rests on the fact that earth materials
are good conductors of current in proportion to their content of (1) water or
moisture and (2) dissolved ions. Thus, massive rock formations, such as
basalt or dolerite, are poor conductors (show high resistivity) because they
contain little moisture. Clean sands and clean gravels are also poor conduc-
tors because even when saturated with water, the water tends to be relatively
low in dissolved ions. In contrast, moist clays and clay soils contain both
water and dissolved ions, and they are good conductors (low resistivity ma-
terials) .
Electrical resistivity of various rocks and sediments exhibits great varia-
tion. Tables 3-1 and 3-2 list characteristic resistivities for various ma-
terials. If the quality of water in the zone of saturation is not constant,
or if it is highly conductive, then these values may vary greatly from those
shown.
Resistivity surveying is performed by introducing a direct current into the
ground via two electrodes. Low frequency (<1 Hz) current is typically used to
minimize undesirable interferences (i.e., electronic noise) caused by small
variations in earth resistivity near the ground surface. The change in poten-
tial is measured between another pair of electrodes. If the four electrodes
are arranged in any of several possible configurations or patterns, the cur-
rent and potential measurements can be used to compute the resistivity associ-
ated with a given configuration. By changing the distances among the four
electrodes within a given configuration, or by relocating the entire electrode
array at another ground position, a series of resistivity measurements are
made to complete a survey.
3-8
-------
TABLE 3-1
RESISTIVITIES OF DIFFERENT ROCK AND
SEDIMENT TYPES
Rock Type
Igneous and Metamorphic Rocks
Granite
Diorite
Dacite
Diabase
Lavas
Gabbro
Basalt
Schists
Tuffs
Graphite shcist
Slates
Gneiss
Marble
Skarn
Quartzites
Sedimentary Rocks
Consolidated shales
Argil lites
Conglomerates
Sandstones
Limestones
Unconsolidated wet clay
Marls
Clays
Alluvium and Sands
Resistivity
3 x 102
104
2 x 104 (wet)
20
102
103
10
20
2 x 103
10
6 x 102
7 x 104
102
3 x 102
10
20
10
2 x 103
1
50
20
3
1
10
Range (ohm-m)
106
106
5 x
5 x
106
107
104
105
102
4 x
3 x
2 x
3 x
2 x
2 x
8 x
104
6 x
- 107
200
70
100
800
107
104
107
106
108
108
108
103
102
108
Source: (Telford et al., 1976)
3-9
-------
TABLE 3-2
Resistivity Values for Selected Sediments
SEDIMENT TYPE
Resistivity (ohm-cms)
0 200 1000 2000 3000 30,000 100,000 300,000
Sediment Type
Clay Marl (CH)
SiHy/Sandy Clay (Cl)
Sandy Soils (Sm), (Sc)
Gravels
Dry Sand or Gravel
Fractured Bedrock
Massive Bedrock
Very Dry Sand or Gravel
3-10
-------
If the measurement of resistivity is made over a semi-infinite space of homo-
geneous and isotropic earth, then a value for true resistivity is obtained.
Practically, however, no measurement of the geologic environment meets this
ideal case, and heterogeneous and anisotropic conditions are normally encoun-
tered. Hence, the value computed is more appropriately termed apparent resis-
tivity. Apparent resistivity is a function of the electrode configuration;
the distances between electrodes; true resistivities; topographic irregular-
ities; and subsurface characteristics, such as strata thickness, angle of dip,
and anisotropic properties.
Electrode Configurations
In principle, any electrode configuration could be used; however, only about
six patterns are known to be in common use, since computations and data inter-
pretations are otherwise difficult. Two electrode configurations commonly
used to conduct electrical resistivity surveying are the Schlumberger and
Wenner arrays (Figure 3-1). In both arrays, the four electrodes are placed
along a straight line on the ground surface, as shown. With the Schlumberger
array, the four electrodes are again placed in a straight line in the order
AMNB, but with distance AB > 5 MM.
The Wenner Array is particularly well suited for soil and pollution investiga-
tions. The Wenner electrode configuration utilizes equal electrode separation
(A) between potential electrodes (M-N) and opposing current and potential
electrodes (A-M and N-B). Current (I) is introduced into the subsurface at
electrodes A and B and forms a potential field perpendicular to the current
flow. Voltage drop (V) is measured by electrodes M and N. The apparent
resistivity at each electrode spacing can be calculated by the following
formula:
Pa =
where:
Pa = apparent resistivity in ohms/feet
V = voltage drip measured at M and N in millivolts
I = current applied at A and B in mi Hi amperes
A = electrode spacing in feet
3-11
-------
M
/ ////////// 7 /
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I
(o) SCHLUMBERGER ELECTRODE CONFIGURATIONS
////// /7V /77////////////
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Figure 3-1. Electrical Resistivity Electrode Configuration
3-12
-------
Resistivity Survey Types
The two types of resistivity surveys used for exploration are vertical
electrical soundings and horizontal profiling. The Wenner and Schlumberger
arrays are particularly suited to sounding investigations. Soundings are
conducted by incrementally expanding the electrode array about a fixed central
station, while maintaining the proper distance relationships among the elec-
trodes. The voltage drop and current are measured at each increment. Loga-
rithmic increments are typically used, and the measured apparent resistivity
values are graphed as a function of electrode spacing on logarithmic coordi-
nate paper as a sounding curve. The expanding spread is best suited for the
detection of horizontal or gently dipping strata of different resistivities.
By increasing the separating distance between the current and potential elec-
trodes, measured resistivities relate to increasingly greater depths. Hence
the method is useful in determining the approximate true resistivities of
sedimentary strata, as well as their thickness. Soundings can often be com-
pleted more rapidly if the Wenner array is used rather than the Schlumberger.
In electrical profiling, a fixed electrode spacing is chosen, and the entire
array is moved laterally along a ground traverse. Resistivity measurements
are made at regular intervals along the traverse. The field resistivity
values are plotted as a function of the distance of each value from the start
of the traverse. Either the Wenner or Schlumberger arrays is suited to pro-
filing, as the survey method seeks to detect anomalous resistivities that
exist along the traverse. Profiling is best suited to detection of steeply
dipping or vertical contacts, faults, or dikes of contrasting resistivity.
Data Interpretation
Interpretation of the resistivity profile curves is largely subjective and
consists of recognizing deflections in the curve which are representative of
lateral discontinuities or changes in subsurface conditions. The procedures
developed to interpret resistivity data using Wenner or Lee electrode arrays
can be grouped into two categories: theoretical and empirical. Using theore-
tical methods, the field data (Figure 3-2) are plotted for comparison to
specially prepared type curves developed for numbers of resistivity layers
with definite ratios of resistivity and thickness. For the purposes of many
3-13
-------
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Investigations, two empirical methods, Moore's Cumulative and Barnes1 Layer
Method are utilized (Figure 3-3).
The Barnes1 Layer Method of interpretation assumes that the subsurface sedi-
ments act as a set of horizontal layers in which the thickness of each is
equal to the increment in electrode spacing. Using Moore's Method, the elec-
trode spacing is multiplied by the apparent resistivity value and the cumula-
tive values are plotted. Slope changes in the lines connecting the cumulative
values generally indicate depth to subsurface sediment changes or changes in
the quality of the ground water. Soil borings in the vicinity of the
soundings graphically displayed in Figure 3-3 revealed a fairly consistent
clay strata with a high moisture content at approximately 15 feet.
Earth resistivity surveys are particulary useful in determining lateral migra-
tion from liquid waste disposal sites constructed in alluvium sediments.
Figure 3-4 was constructed using resistivity values obtained at a constant
electrode spacing of 18 feet. The survey indicates that saltwater is migrat-
ing from the pond in a southeasterly direction.
There are many sites where resistivity surveys are not suitable. In areas
where the quality of the liquid waste or leachate is of similar quality to
natural ground water (in terms of conductivity), then it is difficult to
determine waste fronts. In many industrial complexes, the occurrence of
underground pipelines, overhead electrical lines, and paved areas decreases
the efficiency of resistivity surveys. In addition, where the subsurface
strata is not uniform, the method has major limitations.
Interpretation of the Schlumberger sounding survey can be accomplished through
the use of a computer program that employs linear filter theory to compute a
theoretical apparent resistivity curve for an initial set of user defined
layer thicknesses and resistivities. Marquardt's algorithm is then applied to
the user defined model, modifying the model iteratively until it produces a
match with the field curve. The procedure assumes that the earth model is an
infinite half-space divided into horizontal layers, each electrically homo-
geneous and isotropic. The model parameters include the resistivity and the
thickness of each layer. The bottom or deepest layer is assumed to have
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3-16
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3-17
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infinite thickness. Figure 3-5 shows an example of a field data curve (solid
line) generated by hand, and the computer modeled curve (dashed line) gener-
ated for the same data.
3.2.1.2 Ground Penetrating Radar
Ground Penetrating Radar (GPR) is the electromagnetic equivalent of seismic
profiling used for oil exploration, except on a more reduced scale. This non-
destructive geophysical test is a fast, relatively inexpensive way to find and
outline subsurface feature configuration. The system provides a continuous
graphic cross-section of the subsurface. GPR components are portable and the
instrumentation fits into a station wagon, pickup or van.
The power converter is energized by a 12-volt car battery or AC generator and
powers the pulse generator in the control unit. This generates a two nano-
second pulse, 50,000 times per second, transmitted into the ground by the an-
tenna.
After transmission, the antenna "listens" for 200 nanoseconds as it detects
and amplifies signals reflected from the boundaries between media with con-
trasting electrical properties. The greater the electrical contrast, the
higher amplitude of the reflected signals.
As the antenna is towed along the ground, a continuous stream of reflections
is printed on the graphic recorder and stored on magnetic tape.
Some uses for the GPR include:
• Subsurface void detection
Profile the depth to bedrock
Establish soil horizon continuity along a route to
minimize expensive drilling operations
• Measure the thickness of weathered bedrock in mountain-
ous terrain.
• Locate buried utilities, e.g., pipelines, sewers and
electrical conduits.
3-18
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3-19
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Horizontal survey control is required. Each time the GPR antenna crosses a
known location, the operator electronically marks the radar profile. The
marks are permanent references to ground control and the distance between
marks is interpolated. On a smooth, level ground surface, these marks may.be
200 feet apart. On rough roads or cross country, where the survey vehicle
speed may vary, more closely spaced control is needed.
The GPR antenna scans a path about 16 inches wide. With no data between the
lines, subsurface configuration can be approximated only by straight line
correlation between profiles. Large features which do not intersect adjacent
profiles can cause significant errors in subsurface feature interpretation.
This technique, as with resistivity, has restricted use in petrochemical
plants and other areas where numerous surface and buried structures exist.
3.2.1.3 Magnetic Surveys
It has been known for more than three centuries that the earth behaves as a
large and somewhat irregular magnet. The geomagnetic field is composed of
three parts, so far as exploration geophysics is concerned:
1. The main field which, although not constant in time,
varies relatively slowly, and is of internal origin.
2. The external field, a small fraction of the main field,
which varies rather rapidly, partly cyclically, and
partly randomly, and which originates outside of the
earth.
3. Variation of the main field, usually much smaller than
the main field, relatively constant in time and place,
and caused by local magnetic anomalies in the near-
surface crust of the earth. These variations are the
targets in magnetic surveys.
Magnetic anomalies are caused by the amount of magnetic minerals contained in
the rocks, i.e., magnetite, pyrrhotite, and a few others. Although in many
cases the magnetization of rocks depends mainly upon the present strength of
the ambient geomagnetic field and the magnetic mineral content, in general
this is not true. In practice, residual magnetism, or normal remnant magneti-
zation, often contributes to the total magnetization in rocks, both in ampli-
tude and direction. This fact is very important, particularly in the areas
where several intrusive and extrusive rock types of different age occur.
3-20
-------
The degree of magnetization, I, of rocks for induced polarization is the
product of the susceptibility, k, and the magnetizing field, H. That is:
I = k*H.
The polarization produced by magnetization in the earth's geomagnetic field,
H, has an intensity range of about 30,000 gammas to 60,000 gammas, with a
common value of about 50,000 gammas.
To the extent that the magnetization of the rock is caused by simple induced
magnetization by the earth field in its present direction, anomalies caused by
such magnetization will have variation with latitude. Polarization and polar-
ization contrast among rocks control the magnitude of magnetic anomalies. The
susceptibility of rocks is a measure of their magnetite (FejO^) content.
Magnetite is highly ferromagnetic and by far the most common of the magnetic
minerals in rocks.
The magnetic field survey entails the measurement of variations in the earth's
geomagnetic field. The survey is carried out by taking measurement of the
magnetic intensity, usually in straight lines where possible, across areas
previously selected by the interpretation of the aerial or satellite photo-
graphs or on a survey grid across waste disposal sites. A magnetometer is
used for magnetic surveys. This instrument measures the vertical component of
the total magnetic field in gamma units. A block diagram showing a fluxgate
magnetometer is shown in Figure 3-6.
The points of measurement (magnetic stations) are distributed along each
traverse or grid line at regular intervals, i.e., 10 to 30 feet. The station
interval will depend either on the magnitude of the magnetic anomaly to be
investigated, or on the degree of accuracy required. The magnetic intensity,
gamma, is plotted against distance traversed. The resulting magnetic profile
is examined for anomalies on the earth's geomagnetic field.
The magnetic profile is qualitatively interpreted by examining the relative
locations and amplitudes of the positive and negative portions of the curve,
3-21
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and by inspecting the sharpness of any anomalies produced (Figure 3-7). A
magnetic anomaly may be created by variations in the magnetic susceptibility
of the subsurface material, or by a change in the relief of the magnetic
basement.
Various rock types possess very different magnetic susceptibilities, and are
thus easily distinguished by using the magnetic method. For example, sedimen-
tary rocks generally create a magnetic field of relatively low and constant
magnetic intensity. Dolerite (dikes and sheets) produces a magnetic field
which, due to the distribution of magnetite, can be of high intensity and
variable direction. The magnetic field created by extrusive basalt is gener-
ally lower than that of dolerite, but much higher than the magnetic field
created by sedimentary rocks. The magnetic intensity created by rock can be
reduced by destroying the magnetite content of this rock. Magnetite can be
destroyed by weathering processes of the rock.
In order to measure the daily variations of the magnetic field, a monitoring
base station should be established. The maximum daily variation of the verti-
cal component of the total magnetic field should be measured and recorded.
Corrections to the field data for these daily variations are not necessary, if
the anomalies of interest are considerably larger than the maximum recorded
daily variation.
Besides the daily variations of the magnetic field associated with electric
current generated in the ionized layers of the outer atmpsphere, the following
variations of the magnetic field take place:
1. A secular variation (long term variation, on the scale
of years, of main magnetic field);
2. A short term regular periodic variation of external
field; and
3. Irregular transient fluctuations (magnetic storms).
3-23
-------
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FROM SEVAN (1983)
Figure 3-7. Example of Typical Magnetic Anomaly
3-24
-------
Interpretation of Data
The end result of a magnetic survey is a set of magnetic profiles. The pro-
files are plotted at a scale and vertical exaggeration suitable for inter-
pretation. The method of interpretation involves matching field anomalies
with simple geometrical shapes. These anomalies can be displayed as single
traverse profiles, as magnetic contour maps or as three dimensional plots
(Figure 3-8). Although magnetic exploration techniques are most useful for
ore body determination, or ground water exploration in basement rock com-
plexes, they have been adapted in recent years to contamination studies at
waste disposal sites where drums of waste are suspected to have been buried.
Magnetic surveys at waste sites are normally conducted similar to geologic
exploration. The site is normally laid out in traverses and readings taken at
regular intervals. The data are then used to construct contour maps of magne-
tic intensities. Figure 3-9 is a magnetic contour map which was prepared for
a Superfund site in Arkansas. The magnetic high on the north side of the site
corresponded to an old strip mine which had been filled with trash and indus-
trial waste. The area in the middle of the site corresponded to the southern
edge of an old evaporation pond which had been located by using air photo-
graphs. These magnetic highs were later targeted for exploration. Numerous
trenches were excavated in both areas. In the northern area, numerous drums
of solid industrial waste were found along with typical municipal metals such
as refrigerators and appliances. At the southern location, numerous crushed
drums were found which at one time contained liquid solvents and other waste
organics. In areas of the site where no magnetic anomalies were detected,
very little waste was found.
3.2.2 Exploratory Dri11 ing
Exploratory drilling is key to the characterization of the site. The drilling
program seeks to define the geology beneath the site which, in turn, identi-
fies ground water flow paths. This definition is obtained from the collection
of subsurface soil samples for visual classification and laboratory analysis
or obtained from running downhole geophysical logs. Additional means to help
define the subsurface would include drilling observations such as changes in
drilling rates, rig chatter, lost circulation, etc. The drilling program
ultimately provides information on the correlation of the subsurface units
3-25
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between boreholes, identification and physical properties of the confining
beds and permeable zones, and lithologic changes within a given unit.
An exploratory drilling program usually is a phased process. In areas where
the subsurface conditions are unknown, several phases of drilling may be
required. The initial number of boreholes should be sufficient to provide
enough information so a more detailed drilling program can be devised. The
overall geologic picture must be evaluated to determine this number. The
total number and depth of subsequent borings will be better defined once the
drilling program begins.
The number of boreholes required to define the subsurface conditions are
dependent upon the site conditions. A simple geologic environment with thick,
relatively continuous, horizontal beds can be characterized with relatively
few boreholes. However, in areas with dipping strata or in coastal areas with
numerous facies changes and lithologic zones of varying materials, the number
will be larger.
3.2.2.1 Drilling Methods
A variety of drilling methods have been successfully applied to exploratory
drilling as well as monitor well installation. Table 3-3 lists the advantages
and disadvantages of the most commonly used methods.
The most suitable drilling method for any situation requires a site specific
evaluation and selection. Several factors relating to the investigation
objectives and site conditions require consideration.
- The type of formation material to be drilled through.
- The total depth of the drilling operation.
- Depth to water table.
- The type of contaminants expected.
- The surface conditions at the drilling site.
- The design and depth of screen placement of the monitor
well, if it is to be installed.
3-28
-------
TABLE 3-3
DRILLING METHODS
TYPE
ADVANTAGES DISADVANTAGES
Hoi low-stem • NoDrillingfluidis used, eliminat i ng
auger contamination by drilling fluid additives
• Formation waters can De sampled during
dri I I ing by using a screened auger or
advancing a well point ahead of the augers
• Formation samples taken by split-spoon
or core-barrel methods are highly accurate
• Natural gamma-ray logging can be done
inside the augers
• Hole caving can be overcome by setting
the screen and casing before the augers
are removed
• Fast
• Rigs are highly mobile and can reach
most dr i I I i ng si tes
Can be used only in unconsol idated
materials
Limited to depths of 100 to 150 ft (30.5
to 45.7 m)
Possible problems in controlling
heaving sands
May not be able to run a complete suite
of geophysical logs
Direct rotary • Can be used in both unconsol idated and
consolidated formations
• Capable of drilling to any depth
• Core samples can be collected
• A complete suite of geophysical logs can
be obtained in the open hole
• Casing is not required during drilling
Many options for well construction
• Fast
• Smaller rigs can reach most driI I ing sites
• Relatively inexpensive
• Formation samples taken by split-spoon,
Shelby tube or cores are very accurate
and fast
Drilling fluid is required and
contaminations are circulated with the
fluid
Dr iI I i ng fIu fd mi xes with the format i on
water, invades the formation and is
sometimes difficult to remove
Organic fluids may interfere with
bacterial analyses and/or organic-related
parameters
During drilling, no information can be
obtained on the location of the water
table and only limited information
on water-producing zones
3-29
-------
TABLE 3-3
DRILLING METHOD (Continued)
TYPE
ADVANTAGES
DISADVANTAGES
Air rotary • No water-based drilling fluid is used
• Capable of drilling to any depth
» Formation sampling by cuttings is excellent
in hard, dry formations
" Formation water blown out of the hole
makes it possible to determine when the
first water-bearing zone is encountered
• Field analysis of water blown from the
hole can provide information regarding
changes for some basic water-quality
parameters such as chlorides
• Fast
Casing is required to keep the hole open
when drilling in soft, caving formations
below the water table
When more than one water-bearing zone
is encountered and hydrostatic pressures
are different, flow between zones occurs
during the time drilling is being
completed and before the borehole can be
cased and grouted properly
Air must be filtered to prevent blowing oil
in the hole
Can only be used in consolidated formations
Cab Ie too I • On I y smaI I amounts of dr iI Ii ng fluid are
required (generally water with no
add i t i ves)
• Can be used in both unconsol idated and
consolidated formations; well suited for
extremely permeable formations
• Can drill to depths required for most
mon itor i ng we I Is
• Highly representative formation samples
can be obtained by an experienced driller
• Changes in water level can be observed
• Relative permeabilities for different
zones can be determined by skilled drillers
• Rigs can reach most drilling sites
• Relatively inexpensive
Minimum casing size is 4 in. (102 mm)
Steel casing must be used
Cannot run a complete suite of
geophysical logs
Usually a screen must be set before a
water sample can be taken
Slow
Cannot cement upper casing although
seals are usually good
Adapted from Manufacturer's Literature Provided by Johnson
Mon i tor ing Wei Is
Screens, Materials Selection for Ground Water
3-30
-------
Regardless of the drilling method chosen, good sediment samples should be
obtained. Although cuttings can be used, undisturbed samples are preferred.
The choice of drilling method is contingent upon a number of factors including
depth, ' materials of construction of the well, preferred water sampling
methods, sediment type, and others. Each method has its applications, and as
long as the advantages and limitations of each method are understood, there is
no inherent, preferred method.
3.2.2.2 Logging Techniques
The logging of boreholes enables the site to be characterized by describing
the lithology and correlating the stratigraphy of one borehole with another.
The subsurface can be logged in several ways. The subsurface can be visually
described from grab samples of the drilling mud returns or from extracted
samples using Shelby tubes, split-spoon samplers, or rock coring devices.
Alternatively, indirect means of classifying the subsurface can be accom-
plished with downhole geophysical logs.
Lithologic Logging
Lithologic sampling and logging should be performed by a qualified geologist
during the drilling of a borehole. The aim of the geologist is to classify
the subsurface soils and identify the major confining and permeable units.
Subsurface samples can be obtained by several means. Cohesive soils, such as
silts, clays, and clayey or silty sands, can be sampled with a Shelby tube.
This provides an "undisturbed" soil sample which can be used for laboratory
determinations of permeability. Non-cohesive soils, such as sands and
gravels, can be collected using a split-spoon sampler. Harder consolidated
sediments such as sandstone and limestones can be sampled with a rock corer.
Although not as precise or suitable for laboratory analysis, grab samples are
often taken from the mud or cutting returns.
The sampling frequency is site specific. In areas of unknown geology or
contamination, continuous sampling would best establish control of the subsur-
face. For most exploratory programs, undisturbed samples collected at 3-foot
intervals for the upper 20 feet and at 5-foot intervals thereafter are gener-
ally sufficient for site stratigraphy and permeability determinations. Once
3-31
-------
the overall geologic picture is determined and the major units defined,
samples from subsequent boreholes can be taken at regular 5-foot or 10-foot
intervals depending on the complexity of the environment.
The lithology is described in the field by the supervising geologist. The
geologist will classify the soil or rock type and augment the classification
with a description of the color, plasticity, cohesiveness, degree of weather-
ing, moisture content, and indications of potential contamination, such as
organic content and odor. Notations on the presence of fractures, bedding,
vugs, or cavitities, and water bearing zones are also made. This classifica-
tion and associated descriptions are included on the driller's log.
Several soil classification systems exist, e.g., the Unified, Wentworth,
AASHTO and USDA. The predominant system is the Unified Classification Sys-
tem. However, the Wentworth Classification System is commonly used by geolo-
gists. The Unified System is outlined in Table 3-4. The criteria for classi-
fication in Table 3-4 are arranged in such a manner that identification can be
performed in the field by visual inspection and simple manual tests. This
field method is described in detail in ASTM D 2488-84. A numerical version of
the system (ASTM D 2487-83), based on particle-size and Atterberg limit tests,
is used in the laboratory to more accurately classify selected samples and to
check the field identification.
Field identification procedures will generally concentrate on estimating
gradation and plasticity, which are the fundamental criteria for grouping
soils in the Unified System. Classification of coarse-grained soils is based
on the gradation, while the classification of fine-grained soils is based on
plasticity. Gradation is used to further divided soils into groups of clean
and "dirty" (soils with fines). The clean soils are further divided into well
graded and poorly graded. The "dirty" soils are divided based on plasticity.
Visually determining whether the soil is fine-grained or coarse-grained can be
difficult, particularly if the coarse-grained portion is fine to medium sand,
and the percent passing the No. 200 sieve (fine-grained fraction) is near 50
percent. In this instance, the soil will be classified with a modifier such
as silty or clayey sand or sandy clay or silt. In marginal cases, it is best
3-32
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to classify it as a silty or clayey sand as this will be conservative with
respect to permeability characteristics and, hence, pollution migration.
Whether the modifier is "silty" or "clayey" will be based on plasticity
characteristics.
For a coarse-grained soil which is predominantly clean, the determination of
whether it is well or poorly graded is relatively easily determined by visual
examination and feel. The sample can be spread across a flat surface and the
gravel-size particles can be felt and moved aside. A well-graded soil will
have a wide range in grain sizes with substantial amounts of intermediate
particle sizes.
A poorly graded sand can be identified, in many instances, by its feel as well
as its appearance. When a wetted, poorly graded sand sample is packed by the
fingertips into the cupped palm of the hand, it will not cease deforming and
moving out ahead of the probing fingers. Treated similarly, a well graded
sand can be felt to densify, stiffen, and resist penetration by the fingers.
The determination of whether a sample is a silt or a clay or a silty or clayey
sand is subjective to the geologist performing the classification. Since the
difference between silt and clay is not visible to the naked eye, field
methods of identifying the plasticity and classification of fine-grained soils
are best described by referring to Table 3-5. Even with these field methods,
classification between silts and clays generally can only be determined with
laboratory testing.
Trying to correlate gradational units across a site with a differentiation
between a clay and silt based upon field determination only is not practi-
cal. Even with laboratory data to corroborate field data, correlating these
units from one borehole to the next is suspect. It is best to correlate the
subsurface stratigraphy on a broader determination of relative permeability.
In other words, differentiate between low permeability soils such as silt and
clay and higher permeability soils such as silty sand, clayey sand, and sand.
3-34
-------
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3-35
-------
Downhole Geophysical Logging
Another means of determining and correlating subsurface units is through the
use of downhole geophysical logging. Geophysical logging is generally used in
conjunction with a field sampling program. In ground water investigations,
the logs are generally used for correlation and determination of bed thickness
but can also be used for determination of porosity and water saturation.
The most commonly used logs are resistivity, natural gamma, and spontaneous
potential (SP). In some cases, a neutron density log is run. Figure 3-10
shows an example of these types of downhole geophysical logs compared to the
geologic log for a site in Oklahoma.
Resistivity logs measure the electrical resistivity of the formation by pass-
ing an electric current out into the formation. The resulting logs help
define the contact between resistive geologic units such as limestone and
sandstone and conductive units such as clays and shales. If the lithology has
been well defined from the boring program, it is sometimes possible to evalu-
ate the water content and salinity of a given formation. A formation which is
either saturated with fresh water, or unsaturated, will be more resistive than
the same formation saturated with saline water.
Spontaneous potential or SP logs are a measurement of the electrical potential
between a point in the borehole and a grounded electrode at the surface. This
potential is caused by electromagnetic forces in porous or permeable zones.
The SP can be used to define geologic contacts, detect permeable units, and
give qualitative indications of the clay content within sands. In impermeable
sediments, the SP will not respond and results in what is known as the shale
baseline. Deviation from this baseline is an indication of permeability.
Natural gamma tools measure the natural radiation within the formation. Since
clays usually contain radioactive isotopes of potassium, the clayey formations
are indicated by a maximum gamma value. Sands or carbonaceous formations
generally have little or no radioactivity and are differentiated from the
clays. Therefore, the gamma is a useful tool for delineating the depth and
thickness of aquitards.
3-36
-------
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3-37
-------
Not as commonly used as natural gamma, the neutron density tool measures the
hydrogen content of the formation. Since clays contain interstitial water,
the neutron density log responds to the formation. This tool is generally
used in conjunction with the natural gamma as a delineator of clay and shale
zones.
At certain sites where the stratigraphy is well defined, a borehole can be
drilled using mud rotary techniques and logged from the grab samples of the
cuttings within the mud returns. These samples can be collected every 10 feet
until the approximate depth of the target formation is reached. While this
technique provides reasonable accuracy in delineating, for example, the con-
fining zone overlying a permeable saturated zone, the process of circulating
mud from the bottom of the hole to the surface introduces certain errors.
One problem is the lag time between the penetration of the stratigraphic unit
by the bit and when the cuttings reach the surface. Another problem is the
classification of grab samples below a formation which caves into the hole as
a deeper formation is being penetrated. This will tend to give an indication
of a gradation within the subsurface when in fact the units may be well de-
fined. For example, a clay zone underlying a sand can appear at the surface
as a sandy clay because portions of the overlying sand were either stripped by
the mud or sluffed into the hole.
Downhole geophysical logs are useful for delineating different lithologic
units in the subsurface. Figures 3-11 and 3-12 show examples of the drillers
log compared to the natural gamma log. Figure 3-11 shows the depth determina-
tions of lithologic units from the cuttings were more accurately defined by
the gamma log. (Note the silt zone indicated by the driller to be from 125 to
135 is really located between 110 to 125). The borehole shown in Figure 3-12
was drilled for a monitor well installation. The screened interval was to be
placed just below a clay zone known to occur at about 230 feet below the
surface. The driller's log constructed from the cuttings from the hole did
not clearly indicate the depth or existence of the confining zone. The natu-
ral gamma log, however, clearly defined the unit and allowed the bentonite
seal to be placed within the confining zone.
3-38
-------
WELL CONSTRUCTION
GAMMA RAY LOG
FEET
BG
20
40
60
80
100
120
140
160
180
200
220-
240
260l-
— 12 1/4" BOREHOLE
85/8-TCSTEEL
CASING
CEMENT/BENTONITE
GROUT
BENTONITE PELLETS
4" ID FJT sch. 40 PVC
CASING
7 7/8" BOREHOLE
BENTONITE PELLETS
NO. 1 SAND
4-ID.010-SLOT
sch. 40 PVC SCREEN
COLLAPSE
CPS
50
100
GENERAL
STRATAGRAPHIC
LOG
FEET
BG
SAND
CLAYEY SILT
SAND
SILTY CLAY
SAND
CLAYEY SILT
SILTY CLAY
SAND
SILT
SAND
SAND
ffl
20
40
Figure 3-11. Example of a Gamma Ray Log Compared to the
Stratigraphic Log Determined by the Driller
80
100
120
140
160
180
200
220
210
260
3-3°
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3-40
-------
Geophysical logs also aid in the correlation of subsurface stratigraphic
units. Figures 3-13 and 3-14 show the difference between correlating
driller's logs units and downhole geophysical logs. While the driller's logs
indicate a relatively non-uniform environment with units of varying thickness
and depth, the natural gamma logs show the subsurface consists of broad,
relatively uniform, permeable zones that can be correlated over larger areas.
3.2.3 Monitor Wells
Monitor wells are the preferred method for determining the concentration and
movement of chemical constituents in the saturated zone. They can be used
either to determine the natural chemistry of the ground water (as in back-
ground wells) or to monitor the movement and concentration of contaminants in
the ground water downgradient of a source (as in downgradient wells).
Monitor wells are primarily used to:
• Provide access to ground water for collecting water
quality samples,
• Determine the ground water chemistry,
• Detect contaminants in the subsurface soils and water
bearing formations,
• Determine the area! and vertical extent of contami-
nants,
• Monitor the movement of contaminants in the water bear-
ing formation,
• Determine water levels in the aquifer, and
• Perform aquifer testing for aquifer properties.
In order to accomplish these objectives a monitoring system must be designed
to take into account and incorporate a variety of criteria including the
location of the well, the placement of the screen, the installation procedures
used, and the design of the well.
3.2.3.1 Well Location
Selection of monitor well locations is dependent upon ground water flow and
hydrogeologic conditions although site access and drilling capabilities must
be considered and often direct the ultimate decisions.
3-41
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3-43
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The initial purpose of monitoring wells is to determine if a waste facility is
leaking. Later purposes include determining the quality and perhaps quantity
of leakage, and the direction and rate of movement of the contaminants. There
is no set number of wells which should be required around a facility. If the
facility is a pond or lagoon with a shallow water table it is likely that the
leakage could be detected with one well.
In over-simplistic terms, the shallow ground water table is often a subdued
replica of the surface topography, and normally, shallow monitor wells can be
properly placed using a site topographic map. Following this concept, many
early wells were installed at the lower surface elevation at a facility. This
concept was widely used in the late 1970's and early 1980's when monitor wells
were first being installed throughout the country. History indicated that
this logic was right in over 90 percent of the cases as verified by construct-
ing water table maps after the wells were installed. Another concern that has
been "voiced" is the placement of the well screen. Recent guidance has sug-
gested that screen lengths should be small in order to measure discrete inter-
vals and that long screen intervals would dilute discrete plumes. The vast
majority of monitor wells that were installed without benefit of subsurface
control and with varying screen lengths functioned as they were planned, and
most old facilities were demonstrated to have leaked.
Where the primary purpose of monitor wells is to determine the extent of
contamination migration, additional monitor wells are usually required. These
monitor wells are generally placed at further distances from the source both
in the horizontal and vertical plane.
Ideally, leachate from a landfill or leakage from a lagoon moves downward
until it intersects the water table. Movement and dispersion is then con-
trolled by gradient, sediment-waste reactions, quantity of the waste, and the
hydrogeology of the area. At existing sites where little is known about the
underlying sediments or direction of ground water movement, several wells
should be installed around each potential source. Selected wells may also be
completed at different depths. Figure 3-15 is a hypothetical cross section
indicating potential migration paths and indicates the need for detailed
information prior to monitor well placement.
3-44
-------
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3.2.3.2 Screen Placement
The screened interval for a monitor well should be placed to monitor a dis-
crete interval of the water bearing information or a segregated water bearing
unit that has minimal interaction with other units. Admittedly these are
ideal conditions that do not always exist, although the placement of seals,
both upper and lower, have been used effectively to segregate the screened
unit.
Determination of the proper screen placement is dependent on site hydrogeology
and the physical characteristics of the parameters being monitored for. One
concern is over the proper placement of well screens when sampling is to be
conducted for chemical constituents that are lighter than water. In uncon-
fined formations the screen must be placed to extend from a few feet above to
a few feet below the range of seasonal fluctuation anticipated for the water
table. Under confined to semi-confined conditions the screen must extend to
above the top of the formation so that water quality analyses will be repre-
sentative of the light fraction constituents present at the top of the water
bearing formation. In many contamination studies, cluster wells are frequent-
ly installed to insure the screen(s) are properly placed to detect a contami-
nant (Figure 3-16).
3.2.3.3 Installation Methods
The choice of drilling method for installing monitor wells is contingent upon
a number of factors including depth, sediment type, well construcion materi-
als, preferred water sampling methods, and others. As previously discussed,
the most commonly used drilling methods are hollow-stem auger, mud rotary, air
rotary, and cable tool.
The most prevalent method of installing wells without drilling fluids is the
hollow-stem continuous-flight auger method. The augers allow determination of
depth to initial saturated zone and does not introduce drilling fluids into
the borehole. This drilling method may, however, allow fluids from an upper
zone to come in contact with those of a lower zone. Generally the auger
method is restricted to depths of less than 150 feet.
3-46
-------
MW-101 MW-102 MW-103 MW-104 Qamma Ray Neutron
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3-47
-------
Hollow-stem augers come in several sizes with perhaps the most useful having
8-inch and 10-3/4 inch outer diameters (OD). The inner diameters of these
hollow stems are 3-3/8 inch and 6-inch, repsectively. Both 2-inch and 4-inch
monitor wells are commonly installed with these augers.
To install a monitor well using the hollow-stem augers, the borehole is
drilled and the sediments sampled continuously or at intervals of 3 to 10 feet
depending on the degree of subsurface data needed. The borehole is advanced
until the desired monitoring zone is reached. With the augers still in the
borehole, a water sample can be collected for preliminary assessment of water
quality by inserting a bailer through the hollow stem of the auger.
The well casing and screen can either be lowered through the augers or in-
stalled after the augers are pulled from the hole. Generally, if the sedi-
ments are unconsolidated, there is a tendency for the walls of the hole to
collapse as the augers are removed. For this reason, the casing is installed
through the hollow stem of the augers before removing them from the hole.
Under these conditions, however, it is difficult to place the gravel pack and
to ensure a bentonite seal in the annul us. If the sediments will remain open
after the augers are removed, then the casing and screen can be assembled and
inserted in the borehole after removal of the augers. A gravel pack can then
be installed and the annulus sealed with bentonite or cement grout back to the
surface.
In recent years, the hollow-stem auger has been highly touted as a preferred
installation technique because additional fluids are not introduced into the
ground water and because representative samples are more easily collected and
interpreted. Although for shallow, water table aquifers this may be the best
method, there are limitations to the method. One of the most severe limita-
tions is the possible migration of contaminants down the annulus if the well
is completed in a deeper horizon than the lowest contaminated zone. For
multi-layered systems, the deeper zones should probably be drilled with mud
rotary or with a surface casing set through the contaminated zone.
In cases where the water table is deep and the sediments are competent to
moderately competent, air rotary methods may be used. Like the auger tech-
3-48
-------
nique, this method has the advantage of introducing no liquids into the forma-
tion. It has the disadvantage that wells cannot be completed very far below
the water table because the hole will not remain open when air circulation is
stopped. In hard rock areas, air rotary drilling can be conducted well below
the water table and has several advantages over other methods (see Table 3-3).
In many instances, effective stratigraphic sampling and well installation
requires the use of drilling fluids. Unfortunately, circulating drilling
fluids tend to invade the permeable zones. This lost fluid may impair well
performance and/or complicate interpretation of chemical analyses from the
monitor well.
Since the exact amount of fluid loss may not be known, the amount of subse-
quent pumpage required to remove all drilling water prior to obtaining a valid
sample of in situ formation water may be difficult to determine. Tracers
placed in the drilling fluid may help to indicate when all introduced fluid
has been removed. One example of a tracer is lithium bromide. In a test
using this tracer, over five times as much fluid was produced as was lost
before all of the tracer was recovered, due to mixing of insitu and introduced
fluids.
The primary advantage of the mud rotary method is that hole stability allows
removal of drill pipe and installation of casing large enough to accommodate a
submersible pump. Prior to removing the drill pipe, a clean up trip of the
borehole is made by running the drill bit from the surface to the total
depth. Generally the borehole is flushed with potable water to thin out the
drilling fluids and to facilitate the installation of the casing.
In mud rotary drilling, potential crossflow between formations is difficult to
detect prior to completion. In fact, recognizing water-saturated formations
at all may be difficult. As a result, gravel packs may be installed at the
wrong elevations, allowing crossflow between layers or migration down the
annulus from masses of perched water above the water table.
Figure 3-17 indicates an example of a mud-rotary installation where it was not
know that a thin zone of contaminated water was perched on a thin clay above
3-49
-------
100
200
a
a
300
Elev. 3286.4'
400
Static W.L.
at 391'
500
Generalized
Stratigraphy
Sllty Clay
• 12" dla. reamed
hole to 520'
•Cement to 350'
•6 5/8" dla.
ataal eaalng
blank to 380'
Clayey Sand
and
Sand Layers
9
i
•1 1/4" dla.
galvanized
discharge pipe
•Gravel pack
350' to 520'
•Top of 1 1/2 HP
pump at 420'
-Screen
380' to 520'
6 5/8" dla.
carbon steel
Mill slot w/
0.05" wide
at 34/ft.
Sandy Clay
and
Sand Layers
V Perched
~ Contaminated
Water
Clay
Sand
Clay Shale
(Red Bed)
Figure 3- 17. Completion of a Monitor Well
Using Mud Rotary Drilling
3-50
-------
the regional water table. The clay zone was not discovered in cuttings or
undisturbed sediment samples. The gravel pack extended above the screen,
which is normally done to ensure sampling the top of the zone of saturation.
In this case, however, the gravel pack location allowed the perched water to
migrate down the annulus.
These conditions are somewhat analogous to a multi-layered aquifer. Here, if
only one or two casing volumes are bailer or pumped, the samples may seem to
indicate that the lower zone is contaminated. Figure 3-18 illustrates the
concentration versus volume pumped for such a well and demonstrates that, in
this case, the lower aquifer was not contaminated. Other instances of mis-
leading monitor well data are common.
Collection of multiple samples as shown in Figure 3-18 can be a valuable aid
in explaining anomalous data. This data, combined with the completion records
of the well shown in Figure 3-15, gave the first indication that contamination
had traveled as deep as the perched layer, but no further.
Once the drilling method has been chosen and the borehole drilled, the well
casing and screen are lowered into the borehole. Figure 3-19 shows the con-
struction of a typical shallow monitor well. The monitor well screen is
surrounded by a gravel pack generally consisting of a graded sand which
matches the screen slot size. The gravel pack usually extends a few feet
above the screened interval in order to prevent the overlying annular bento-
nite seal from being drawn into the gravel pack during puming or bailing of
the well.
The annulus is sealed with a bentonite plug consisting of 2 to 5 feet of
granular or pelletized bentonite. The seal prevents the migration of fluids
from overlying zones from entering the monitoring zones through the borehole
annulus. This seal is most effective when located opposite the overyling
confining zone or aquitard.
The remaining borehole is grouted back to the surface with grout, bentonite,
or a combination of both. The grout is best pumped through a small diameter
pipe inserted into the annulus and placed a few feet above the bentonite
3-51
-------
Z.3 -
2.2 -
2.1 -
2.0 -
1.9 -
1.8 -
1.7 —
1-81—
1.S
a 1.4
o»
I '•'
o
0.8
a?
a.e
o.s
0.4
0.3
0.2
o.i
PUOID si «rt•fl-
0.0
10/80
11/90
12/80
1/81
Dlyi
1/21/61
1/22/81
Hour*
1/23/81
Figure 3-18. Manganese Concentrations vs. Time
of Pumping-Data From Well Shown
in Figure 3-15
3-5;
-------
'•^
Var
1
^^S^^V/^^Xy%21P|
30
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able ~T
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-^: Locate in most Impermeable
zone above monitoring zone
J
' 2. Static Water Table
Screen
Natural material
or gravel pack
(as required)
Figure 3-19. Monitor Well Installation Diagram
3-53
-------
seal. However, grout can be poured from the surface but the placement should
be verified with a trimie pipe.
A concrete well pad should be placed around the well which will direct runoff
away for the well. For ease in sampling and to minimize the potential for
mixing of waters between wells, each monitor well can be supplied with its own
(i.e., a "dedicated") bailer or pump. In some instances, a barrier post may
be installed with the monitor well. This post serves the dual function of
protecting the monitor well from off-road machinery and securing the well
against tampering. All locks at a given facility can be keyed alike to pre-
vent subsequent complications (Figure 3-20).
3.2.3.4 Materials of Construction
There are numerous factors to consider when selecting the materials for a
monitor well. In the past, steel or plastic materials have been utilized
because they are readily available off the shelf. Because costs associated
with well installation and materials are often insignificantly small with
respect to the long term costs associated with sampling and analysis, it is
important to place greater emphasis on the proper selection of well construc-
tion materials.
It is often practical to compromise between cost and ideal construction ma-
terials because the effective life expectancy of a monitor well is as yet
unknown and highly dependent on the levels and types of ground water contami-
nants. Furthermore, a consideration of site specific contaminants may indi-
cate that less expensive materials will enable reliable collection of ground
water samples for selective parameters. Table 3-6 list the advantages and
disadvantages of the major types of materials available for monitor well
construction.
Most liquid wastes are corrosive, and many environments, both subsurface and
surface, are also corrosive. In the Gulf Coast area, many steel monitor wells
have deteriorated on the surface to the point that caps and fittings may be
corroded in place. In the Gulf Coast area, shallow sands (+20 feet)
frequently contain saline water, especially if the land surface elevation is
below 15 feet. In these areas, steel casing and screens deteriorate rapidly.
3-54
-------
1) SINGLE CASED WELL
^ "
U-
3'X3'X6' CONCRETE PAD
APPROX 2'
6" SQUARE PROTECTIVE POST
WITH LOCKING CAP
» 4 «
, » »
fc 4 4
4' PVC WELL CASING WITH SLIP
.- CAP AND HANDLE
»
1 LV/-
APPROX. 3'
"
CEMENT/BENTONITE GROUT
8' BOREHOLE
2) DOUBLE CASED WELL
3'X3'X6' CONCRETE PAD
12" BOREHOLE '
CEMENT/BENTONITE
GROUT
4" WELL CASING WITH
SLIP CAP AND HANDLE
6' PROTECTIVE POST
WELDED TO 8* STEEL
SURFACE CASING
APPROX. 3'
Figure 3-20. Monitor Hell Surface Completion
3-55
-------
TABLE 3-6
WELL CASING AND SCREEN MATERIALS
TYPE
ADVANTAGES
DISADVANTAGES
PVC (Polyvinyl-
chlori de)
L i ghtwe i ght
Excellent chemical resistance to weak
alkalies, alcohols, aliphatic hydrocarbons
and oils
Good chemical resistance to strong
minerals acids, concentrated oxidizing
acids, and strong alkalies
Weaker, less rigid, and more temperature
sensitive than metallic materials
May adsorb some constituents from
ground water
May react with and leach some
constituents from ground water
Read i Iy ava i IabIe
Poor chemical resistance to ketones,
esters, and aromatic hydrocarbons
PoIypropyIene
TefIon
Low priced compared to stainless steel
and TefIon
L ightwe ight
Excellent chemical resistance to mineral
aci ds
Good to excellent chemical resistance to
alkalies, alcohols, ketones, and esters
Good chemical resistance to oils
Fair chemical resistance to concentrated
oxidizing acids aliphatic hydrocarbons,
and aromatic hydrocarbons
Low priced compared to stainless steel
and tefIon
L ightweight
High impact strength
Outstanding resistance to chemical
attack; insoluble in alI organics except a
few exotic fluorinated solvents
Weaker, less rigid, and more temperature
sensitive than metallic materials
May react with and leach some
constituents into ground water
Poor machinabi I ity - it cannot be
slotted because it melts rather than cuts
Tensile strength and wear resistance low
compared to other engineering plastics
Slots may compress with time.
Expensive relative to other plastics and
stainless steel
Difficult to install and keep it straight
in the hole
3-56
-------
TABLE 3-6
WELL CASING AND SCREEN MATERIALS (Continued)
TYPE
ADVANTAGES
DISADVANTAGES
Kynar
Mild steel
Stainless steel
Greater strength and water resistance
than TefIon
Resistant to most chemicals and solvents
Lower priced than Teflon
Strong, rigid; temperature sensitivity not
a problem
Read!Iy aval I able
Low priced relative to stainless steel and
TefIon
High strength at a great range of
temperatures
Excellent resistance to corrosion and
ox i dat ion
Readi Iy ava i I able
Moderate price for casing
• Not readily available
• Poor chemical resistance to ketones,
acetone
• Heavier than plastics
• May react with and leach some
constituents into ground water
0 Not as chemically resistant as
stainless steel
• Heavier than plastics
« May corrode and leach some chromium
in highly acidic waters
• May react as a catalyst in some organic
reactions
• Screens are higher priced than plastic
screens
Adapted from Manufacterer's Literature Provided by Johnson Screens, Material Selection for Ground Water
Mon itor i ng Wei I s
3-57
-------
In most ground water investigations, PVC materials can be utilized. PVC is
resistant to most chemicals except aromatic organics such as ketones, esters,
etc. However, the concentration of contamination will normally be small and
should have no significant effect on the integrity of the casing. Where
adsorption of contaminants on the PVC casing is of concern, a more inert
material, e.g., stainless steel or teflon, can be used.
The most significant problem to be solved with selection of materials of
construction is possible sample contamination. The use of PVC glue to weld
casings to screens can result in sample contamination. Figure 3-21 is a gas
chromatograph scan of a sample of water collected from a monitor well con-
structed with PVC pipe and glue. Figure 3-22 is a scan of PVC glue in dis-
tilled water. Later gas chromotography/mass spectroscopy analysis identified
some of these peaks as methylethyl ketone, toluene, and tetrahydrofuran. PVC
could still be utilized in this investigation by using threaded coupling.
In addition to pipe and casing materials, the gravel pack and grouting materi-
als should be selected to minimize sample contamination. Gravel pack sand
should contain no chemical additives. Bentonite pellets, which are normally
used in sealing the producing zone have been mixed with distilled water, and
TOC values in excess of 6,000 mg/L have been found. In addition, bentonite
supplied by typical drilling mud suppliers may contain some organic polymers
in order to meet American Petroleum Institute standards for drilling fluids.
3.2.3.5 Well Development Methods
All drilling methods alter the formation hydraulic properties in the vicinity
of the wellbore, although to differing degrees depending on the formation
materials. These well bore damage effects are greatest in unconsolidated
sediments where development techniques are required in order to achieve repre-
sentative ground water results from the wells. Well development serves the
following purposes:
- Remove the filter cake (drilling fluid film that develops on the
borehole wall) and enable water to flow easily into the well.
- Remove any solids or liquids that have invaded the formation
during drilling.
3-58
-------
Figure 3-21.
G. C. Scan Water Sample from Monitor Well
Constructed with PVC Pipe and Glue
3-59
-------
Figure 3-22. G. C. Scan - PVC Pipe and Glue in
Distilled Water
3-60
-------
- Remove the finer particles and create a graded particle zone
around the well which increases the porosity and permeability of
the formation near the well and reduces the production of fine-
grained material by the well.
A few of the development methods used in the water well industry have been
adapted for use in developing monitor wells because they cause the least
detrimental effects to the subsequent ground water data collected.
Ba i1i ng
A hollow cylinder of smaller diameter than the well and with a trap bottom to
prevent water from flowing back into the well is used to repeatedly remove
water from the well. This method is commonly used for developing 4-inch or
larger wells when a drilling rig or other hydraulic hoisting equipment is
available to perform the bailing process and create a high velocity flow into
the well. False bailing is especially useful in developing wells. In this
method, a "full" bailer is hoisted to above the water level and then "dropped
back" into the well. This creates a surge at the screen/formation zone and
assists with removing fines.
Pumping
Submersible pumps are commonly used to develop 4-inch monitor wells with
surging as a complimentary technique. Many 2-inch wells have been success-
fully developed using jet pumps which can develop high velocity flow into the
well. With the exception of 2-inch submersible pumps (which are expensive and
inefficient in pumping sediment particles), most other pumps (i.e., bladder
pumps, peristaltic pumps) fitting 2-inch wells do not develop adequate flow
velocities to develop monitor wells.
Surging
Surging is a technique used in conjunction with other methods to develop
monitor wells and prevent the filter pack material from bridging as a result
of one directional flow. Bridging may result in future well flow problems
requiring redevelopment or premature replacement of the well. Surging is
performed in several manners including false bailing or plunging the bailer
without removing it from the well, raising and lowering a submersible pump
3-61
-------
while pumping, allowing developed water to surge back into the well, (prefer-
ably without actually removing the water from the well casing) or with the use
of a surge block.
Water Jetting
Water jetting is a practice often used to break up the filter cake on the
borehole wall and also to backwash the filter pack through the screen. This
can be a very important development technique when drilling additives are
required to keep the borehole open during drilling. This method can result in
drilling fluids being forced into the formation and therefore it must be used
in conjunction with extensive evacuation type development to ensure that all
drilling fluids are withdrawn from the formation.
Air Development
Monitor wells can be developed using air compressors with an eductor type
system which enables water to flow out of the well along with the flow of
air. This method is not often recommended for developing monitor wells be-
cause it can result in air being forced into the formation. The often power-
ful surges of water ejected from the well may create containment as well as
health and safety problems if the ground water is heavily contaminated. Used
with proper safeguards, air is an effective development tool.
Measuring Development
The sensitive nature of water quality analyses from monitor wells has caused
an increased concern over development practices. As a result, a number of
parameters are regularly used to measure the adequacy of monitor well develop-
ment. These parameters include turbidity, pH, and conductivity.
Turbidity is a commonly used indicator of well development although it is not
the best. Reducing the turbidity does not necessarily mean that the wellbore
area of influence is adequately developed to provide representative samples.
On the other hand turbidity may cause greater unreliability in sampling for
certain parameters (i.e., metals) and therefore may be an indicator of the
need for additional development when monitoring for these parameters.
3-62
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The pH of the ground water is often affected by drilling practices and can be
used to determine when the affected fluids have been removed. This parameter
is also useful in determining if the bentonite seal thickness is adequate to
prevent grout contamination of the filter pack which, if containing cement,
would increase the pH and possibly affect water quality analyses.
The conductivity of the ground water is another parameter used for determining
when the well has been developed sufficiently to provide water quality samples
that are representative of the aquifer. As the well is developed, the conduc-
tivity should stabilize.
3.2.4 Lysimeters
Lysimeters have been used with some success in obtaining water samples from
both saturated and unsaturated sediments. In most ground water contamination
investigations, monitor wells are better suited for sampling or monitoring in
the saturated zone. In the unsaturated zone, the normal monitor well will not
collect sufficient fluid. Lysimeters are frequently able to detect leachate
or surface infiltration in the unsaturated zone, and can be used in a leak
detection system to sample soil-pore water.
The most commonly used lysimeters, suction lysimeters, are of two general
types, vacuum and pressure-vacuum lysimeters. Vacuum lysimeters utilize
vacuum only and are limited to approximately 15 feet in depth (over 15 feet,
the pressure type is recommended). Pressure-vacuum lysimeters can be in-
stalled to a depth of approximately 50 feet. Below 50 feet, a modified pres-
sure-vacuum lysimeter can be utilized. Figures 3-23, 3-24, and 3-25 are
schematic drawings of each general type. Pan lysimeters are also briefly
discussed.
3.2.4.1 Installation and Operation of Suction Lysimeters
Generally, lysimeters should be installed prior to construction of the land-
fill, pond, lagoon, or landfarm operation. In this way, background samples
can be obtained prior to operation. Holes are drilled to the desired depth by
using a hollow-stem auger or hand auger. The hole should then be cleaned as
well as possible. In order to provide an appropriate medium to move soil
moisture under capillary pressure, the porous cup should be in contact with
3-63
-------
MALE CONNECTOR
PVC CEMENT
VACUUM DISCHARGE LINE
TO THE SURFACE
PVC CAP
PVC PIPE
1/4" POLYETHYLENE
TUBING
PVC CEMENT
POROUS CUP
Figure 3-23. Lysimeter Vacumm
3-64
-------
MALE CONNECTORS
EPOXY CEMENT
1/4" POLYETHYLENE TUBING
(DISCHARGE LINE)
TUBING TO THE SURFACE
PVC CAP
1/4" POLYETHYLENE
VACUUM-PRESSURE LINE
PVC PIPE
PVC CEMENT
POROUS CUP
Figure 3-24. Pressure-vacuum Lysimeter
3-65
-------
PVC CEMENT
POLYETHYLENE TUBING
BRANCH "T"
CONNECTORS
POROUS CUP
TUBING TO SURFACE
MALE CONNECTORS
PVC PIPE CAP
PVC PIPE
FEMALE ELBOW
POPPET CHECK VALVE
EPOXY CEMENT
POLYETHYLENE TUBING
Figure 3-25. Modified Pressure-vacuum Lysimeter
3-66
-------
material that is as fine as, or finer grained than, the native sediments.
Several commercial products are available including Super Sil and Novacite,
both of which are relatively inert. Table 3-7 gives a leachate analysis of
Grade 100-C Novacite (finer than 200 mesh silica powder) and Table 3-8
contains physical and chemical data on Novacite.
Many existing lysimeters have been installed by the following method and have
subsequently produced samples of sufficient quantity for sampling. Approxi-
mately six inches of Novacite is placed in the bottom of an augered hole (See
Figure 3-26 and 3-27). The lysimeter tip assembly is then lowered into the
hole, and Novacite is added until the lysimeter cup is covered by approximate-
ly six inches. Native soil, which was removed from the borehole, is used to
backfill the hole for approximately two feet and then three feet of bentom'te
(pellets, granular, or powder) is added to prevent infiltration down the
borehole, the rest of the hole is then filled with native material up to 2 to
3 feet below ground surface where another bentonite seal is installed.
Another alternative for lysimeter installation (shown in Figure 3-28) involves
digging a narrow trench, about 2 to 3 feet deep, from the location of the
control box to the point where the lysimeter tip assembly will be located.
From the intersection of the end wall of the trench and its bottom, a hole is
then dug with a hand auger or post hole digger. This hole is generally 2 to 3
feet deep, and angled downward from and extending away from the end of the
trench.
Novacite or a Novacite and water slurry is placed in the far end of the
augered hole. The porous cup of the lysimeter tip assembly is placed on the
Novacite at a depth of approximately 5.5 feet below the ground surface. Dry
Novacite or Novacite slurry is then placed in the hole to cover the tip and
about 12 inches of the lysimeter tube. A 3- to 6-inch plug of bentonite
pellets is placed over the lysimeter and Novacite. Because the augered hole
is at an angle, the bentonite will not be directly above, and therefore would
not obstruct surface water percolation through, the soil which immediately
overlies to the lysimeter tip assembly. The tubing bundle is then connected
to the existing tubing in the trench and the trench backfilled to the surface.
3-67
-------
TABLE 3-7
Leachate Analysis of /200 Novacite
Metal
Ag
As
Ba
Cd
Cr
Hg
Pb
Se
Units
ppb
ppb
ppb
ppb
ppb
ppb
ppb
ppb
1-A
<3.0
<2.0
61
<1.0
<5.0
<1.0
<10.0
<5.0
1-B
<3.0
<2.0
104
<1.0
5.9
<1.0
<10.0
<5.0
1-C
<3.0
<2.0
89
<1.0
<5.0
<1.0
<1CLO
<5.0
TABLE 3-8
Physical and Chemical Data on Novacite
Typical Chemical Composition
Si02 99.12%
Fe203 0.04%
Ti02 0.015%
CaO 0.0%
MgO 0.0%
A1203 0.61
True specific gravity at 70°F, 2.650
pH in distilled wter 6.0 to 6.3.
3-68
-------
Vacuum Gauge
Vacuum-pressure Line (Black)
Discharge Line (Clear)
Sample Bottle
SOIL BACKFILLED TRENCH
SOIL BACKFILL
VACUUM PRESSURE LINE
0'-
V p.'
8ENTONITE SEAL
SOIL BACKFILL
NOVACITE
-• o-
.3; .
'•p''.
'£>.
•k^
DISCHARGE LINE
Figure 3-26. Sampling and Installation of Pressure-vacuum Lysimeters
3-69
-------
Vacuum Gauge
Vacuum-pressure Line (Black)
Discharge Line (Clear)
Sample Bottle
, .o. - >
••n • •«• O. •'«"*••'••.*>•• o-
t>-° \^°.: • ~ -o.--.' «>.• -o •••:
SOIL BACKFILL IRECOMPACTEDl
NOVACITE
Figure 3-27- Sampling and Installation of Vacuum Lysimeters
3-70
-------
o
4->
(O
na
a>
+->
CD
(/I
>,
01
+J
ro
£=
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CO
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ro
-------
Other options are available for the completion of the hole after the lysimeter
is installed. These include the sole use of native materials and the use of
varying amounts and combinations of crushed silica-sand and bentonite and are
largely dictated by the type of soil concerned and the tools available. As
long as the primary objective of creating a thorough contact between the
porous ceramic cup of the sampler and the soil in the borehole is achieved,
varying alternatives can be utilized. In most types of installations, the
vacuum and/or pressure-vacuum and discharge lines are buried in a trench and
routed outside the pond, landfarm, or landfill area to a central location for
sampling (see Figure 3-26 and 3-27).
Soil-pore water (soil moisture) is stored in the small capillary spaces be-
tween soil particles and on the surfaces of the soil particles. In unsatu-
rated soil, moisture is held at pressures below atmospheric pressure (under
suction). To remove this moisture, a negative pressure (vacuum) must be
developed in order to pull the moisture from the soil particles. The amount
of vacuum required to remove this soil moisture is the soil suction. In wet
soils the soil suction is low, and the soil moisture can be removed fairly
easily. In dry soils, the soil suction is high, and it is difficult to remove
the soil moisture.
Vacuum is applied to lysimeters by means of a pump. Either a hand operated or
electrical vacuum pump can be used. For field work, a hand pump is desira-
ble. Figure 3-27 is a typical set-up for a vacuum system. A vacuum is placed
on the system and valve "A" is closed. This vacuum should be maintained for
at least eight hours (if the lysimeter integrity has been breeched, the lysim-
eter may lose its vacuum in a significantly shorter time, usually within
minutes). If soil moisture or leachate is present, liquid will be collected
in the flask. After the vacuum is applied and the valve closed, the pump can
be removed and used to sample other lysimeters. For permanent pump installa-
tions, more elaborate automatic sampling equipment can be utilized.
Figure 3-28 is an example of one alternative for a more permanent installation
set-up for a pressure-vacuum lysimeter. The system is equipped with a monitor
box which provides a permanent, continuous means of observing the behavior of
the lysimeter. The vacuum pressure and discharge lines from the lysimeter
3-72
-------
each enter the box through a bulkhead union located at the base of the box.
The black colored, vacuum-pressure line is connected to valve "B" mounted on
the right side of the panel board, and penetrates the board just above the
valve. The clear discharge line is connected to the tubulature of 250-ml
sample flask by a short piece of neoprene tubing. The discharge line then
passes through a flask stopper and is connected to a tee fitting. One branch
of the tee is attached directly to the vacuum gauge, and the second branch is
connected to the "A" valve by a short length of polyethlene tubing. The
discharge line then penetrates the panel above the "A" valve.
The valves used in the system provide a fast, sure means of access to the
vacuum-pressure and discharge lines to apply a vacuum or evacuate fluid. The
vacuum gauge allows continuous visual monitoring of the system. All compo-
nents are housed in a weather resistant box. A plexiglass front panel pro-
vides visibility and weather resistance.
A similar installation set-up can be utilized in the case of the modified
pressure-vacuum lysimeter, which is useful in monitoring soils at depths
greater than 50 feet. However, the internal sampling procedure for this type
of lysimeter is slightly different, in that a separate upper chamber for water
storage is utilized. Two check valves permit the flow of water from the
porous cup into the upper chamber when a vacuum is applied. When pressure is
subsequently applied, the collected sample is removed from the chamber to the
surface. This procedure prevents the high pressure (necessary to bring water
to the surface) from reaching the porous ceramic cup chamber, where it would
force much of the collected water back into the soil.
3.2.4.2 Installation and Operation of Pan Lysimeters
Pan lysimeters (free drainage type lysimeters) can be constructed and used to
sample macropore or fracture flow. They can be used in conjunction with
suction lysimeters. A pan lysimeter can be constructed of any non-porous
material (e.g., sheet metal, glass brick) which will not interact with the
leachate, possibly jeopardizing the validity of the sampling effort.
The operating principle of a pan lysimeter is simple. Water draining freely
through the soil macropores will collect in the soil just above the pan cavi-
3-73
-------
ty. When the tension in the collecting water reaches zero, dripping will
initiate and the pan will funnel the leachate into a sampling bottle. The use
of a tension plate or a fine sand packing reduces the extent of capillary
perching at the cavity face and promotes free water flow into the pan (EPA,
1986).
3.2.4.3 Other Information on Lysimeters
Recent EPA guidance documents which discuss unsaturated zone monitoring in-
clude:
Hazardous Waste Land Treatment (SW-846, EPA, 1983).
Permit Guidance Document on Unsaturated Zone Monitoring
for Hazardous Waste Land Treatment Units (EPA/530-SW-86-
040, 1986).
Permit Guidance Manual on Hazardous Waste Land Treatment
Demonstrations (U.S. EPA Office of Solid Waste, 1986).
RCRA Guidance Document Land Treatment Units (EPA, 1983).
Test Methods for Evaluating Solid Waste (SW-874, EPA,
1986).
Vadose Zone Monitoring for Hazardous Waste Sites (Everett
et al., 1983).
3.2.5 Tensiometers
Tensiometers can be used at proposed or existing lysimeter locations to deter-
mine whether the soil suction values of those locations are within the operat-
ing range of the lysimeters. Tensiometers can be used at the same locations
and depths as the proposed active area and background lysimeter tip assemblies
in order to determine soil suction values.
A tensiometer consists of a porous ceramic cup, a fluid reservoir, and a
vacuum gauge. The porous ceramic cup is designed so that the pores in the cup
are finer than the pores in the surrounding soil matrix. This is required so
that the water in the tensiometer will experience the same negative pressures
as the water in the soil. The fluid reservoir provides a continuous liquid
medium to transport the negative pressures from the porous cup to the vacuum
gauge. This liquid is normally water that has been deaired as much as is
3-74
-------
practical and has had an herbicide added to inhibit algal growth in the ten-
siometer. During construction of the tensiometer, the reservoir is filled
with water and the tensiometer allowed to stand open so that the porous cup
becomes saturated. After the porous cup is saturated, the reservoir is re-
filled, the tensiometer sealed and the porous cup enclosed in plastic to
prevent water loss. The plastic is removed prior to installation.
The installation of tensiometers into the soil is relatively simple. First, a
hole is cored in the soil to desired depth. The tensiometer is then installed
into the cored hole. Care should be taken that the tensiometer fits snugly
into the hole; this can be accomplished by using a soil corer available
through the tensiometer manufacturer.
After installation, the tensiometer is monitored simply by reading the value
shown on the face of the vacuum gauge. The gauge should be monitored on a
schedule similar to that used for well testing. A recommended schedule is 1,
2, 4, 8, 15, 30, 60, 120, 230, 480 and 1440 minutes. This information will
allow the determination of when the tensiometer has stabilized, and what the
true value is. After the tensiometer has been stabilized, the value of soil
suction is simply read from the gauge. If the soil suction value is success-
fully obtained by the tensiometer, this value will represent the negative
pressure which must be exceeded by a lysimeter in order to retrieve a sample
of the unsaturated zone pore water. A tensiometer, or a lysimeter, is only
functional to approximately 0.9 atmospheres of negative pore water pressure.
If a lysimeter does not yield a sample during several consecutive sampling
events, tensiometer testing can be performed at its location. If it is deter-
mined that there is sufficient moisture and yet the lysimeter is not collect-
ing water, the lysimeter may not be functioning properly. It can then be
repaired or replaced.
3.2.6 Cone Penetrometer Surveys
Cone penetrometer testing has existed within the United States for the last 20
years. In the Netherlands, where the technology was developed, the cone
penetrometer has been in use for almost 50 years. The original cones, common-
ly referred to as the "Dutch cone" were mechanical and very unsophisticated.
3-75
-------
Significant advancements in micro computer technology in the last 5-10 years
have led to the development of the computerized or "electric" cone which has
greatly increased the tool's popularity as an in situ test method for usage in
site investigations and geotechnical design. Its practical use as a geophysi-
cal logging tool, for determining underlying stratigraphy, is just beginning
to be appreciated.
3.2.6.1 Description
The cone penetrometer (Figure 3-29) is a cone shaped instrument which contains
sensitive strain gauges which transmit continuous electronic measurements of
both the resistance of the cone's tip to penetrating (qc), and the interface
friction between the penetrated soils and the outside of the cone or friction
sleeve (f$). The instrument is hydraulically advanced into the soil by the
addition of hollow steel rods, which house the coaxial cable that connects the
cone to an on-board digital computer. The computer first formats the data and
then sends it to an on-board printer producing a three line trace log similar
to electric logs used in oil field exploration (Figure 3-29). From left to
right, the line traces are the friction sleeve, tip resistance, and then the
friction ratio (fr) which is the calculated value of qc divided by f$.
When the cone penetrates sediments with different bearing and shear strengths,
which are directly related to grain size, sorting, etc., unique line-trace
"signatures" result. In Robertson and Campanela (1983), and Douglas and Olsen
(1981), soil classification charts were developed to directly relate the line-
trace signatures to soil types. (See example in Figure 3-30). Both classifi-
cation charts rely primarily on the friction ratio (fr) to provide the means
for identifying soil types.
Field experience with various sites in different geological settings (e.g.,
unconsolidated Gulf Coast alluvial sediments, over-consolidated East Texas -
Louisiana sediments, glacial outwash and ground moraine sediments in south-
eastern Illinois) has demonstrated that total reliance on these charts is not
prudent. Empirical data, such as soil samples from continuously sampled
borings placed adjacent to several cone penetrometer tests (CRT) locations
within a large survey, provide a more reliable means of "calibrating" the
tool's response to site specific soils. Figure 3-31 shows the correlations
3-76
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3-78
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between a cone penetrometer test and a continuously sampled boring drilled 5-
feet away. The borehole was also geophysically logged with a conventional
electric logging tool.
3.2.6.2 Cone Penetrometer Log Correlation
Litho-stratigraphic correlation between CRT's are interpreted in a similar
manner to the e-logs which have been used for over 40 years in oils explora-
tion. Figure 3-32 is an example of a cross section interpreted from a cone
penetrometer survey. Figure 3-33 is an isopach map interpreted from the same
cone penetrometer survey located in Louisiana. A total of 57 CRT's with an
average depth of 55-feet were conducted over a nine day period (an average of
350 feet per day). Continuous soil sampled were collected and described from
5 borings located adjacent to 5 CRT locations for calibration. In addition,
soil samples were selected and tested for grain size (sieve and hydrometer) to
directly correlate the soil classifications to tool responses. (Note: The
soil types identified in the figures have been described using the Wentworth
classification system.)
The cone penetrometer can be a useful tool for delineating subtle variations
in lithologies with high levels of confidence. Its many advantages include
its speed as compared with conventional drilling methods, its costs, and the
level of accuracy it can provide when the data are interpreted by an experi-
enced professional. Some of its disadvantages lie in the fact that the tool
has limited use in unindurated sediments (clays, silts, sands, some gravels)
only; it cannot penetrate through fissle shales, thick lignites or coals,
sandstones, or carbonates. The total penetration depth of the tool is limited
by the underlying lithologies. Thick dense sands cannot be fully penetrated
nor thick low plasticity clays. A 200-foot penetrating depth is the maximum
depth to be expected in ideal geologic settings such as deltas in southern
Louisiana. In the Gulf Coastal sediments, the depth of penetration generally
averages between 30 to 125 feet, depending on site specific conditions.
3.2.6.3 Other Uses
Cone penetrometer surveys can be used for several purposes including standard
penetration test (SPT), cyclic stress ratios, shears modulus data, undrained
strengths (suu) of clays (bearing capacity), and foundation or liner design.
3-80
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More recent advancements in the technology have been significantly influenced
by the ground water (contamination) assessment related industry. Some of
these are listed and briefly described below:
• Piezo-Cone - measures soil pore pressure response; can
be used to obtain ambient pore pressures which can be
related to hydraulic conductivity
• Resistivity (or conductivity) Cone - measures electri-
cal resistance (or conductance) of soil; can be used to
trace contaminant plumes of a resistant or conductive
nature (e.g., metals, brine salts)
• Thermal Cone - measures soil thermal response to me-
chanical penetration; can be used to determine ambient
in-situ soil temperatures
• Seismic cone - measures soil response to surface seis-
mic excitation
• Fluid/Gas Vapor Sampling Cone - provides the acquisi-
tion of select or continuous samples of in-situ liquids
or gases, can be used in combination with in-field
testing such a as OVA, HNU, portable gas chromatro-
graphy unit.
3.2.7 Soil Gas/Vapor Monitoring
Soil vapor surveys are useful in contaminant investigations of volatile con-
stituents in the subsurface media. The pore spaces between the particulate
grains of a soil or sediment media are filled with matter in one of the three
elementary forms: solid, liquid or gas. In-filling with solid matter results
in reduced porosities and flow pathways. Liquids and gases on the other hand
are mobile forms of matter which are able to move through porous media and
even increase the porosity.
The objective of soil vapor monitoring is to delineate the extent of soil
contamination and to characterize the contaminants. Given the proper subsur-
face conditions, soil vapor surveys can be inexpensive to conduct and can
provide data from a large area over a short period of time. Because soil
vapor sampling is an indirect method of detecting subsurface contamination, it
is considered a screening technique to be used to aid in the design of a more
focused sampling plan which would most likely include detailed soil sampling
and monitor wells installation. That is, information obtained during an
3-83
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initial investigation can then be used to develop an effective follow-up study
which would include the thorough delineation of soil and ground water contami-
nation with soil borings and monitor wells.
3.2.7.1 Liquids and Gases as Flow Media
In saturated sediments, the pore spaces are predominantly filled with liquids
while a mixture of liquids and gases fill the unsaturated sediment voids. As
sediments become drained, a liquid film is retained on the soil particles by
adsorption and capillary forces while the remainder of the pore spaces become
filled with gases. If connected, the pore spaces provide a pathway for vapor
(a mixture of matter diffused in air) migration.
Several factors are of importance in considering migration rates and direc-
tions with respect to the following media:
a. Gases are generally less viscous than liquids and
therefore are less subject to frictional retardation.
b. The flow of gases and liquids are both dependent on
thermodynamic factors although gases generally exhibit
greater changes than liquids in response to these
forces.
c. Both gases and liquids can be either lighter or heavi-
er than their standards (air and water) although their
potential for vertical migration versus horizontal
migration is significantly different. Volatile gases
can migrate vertically up through unsaturated zones
from the water table while light fraction liquids can
migrate to the top of the saturated zone and then
follow the horizontal flow direction dictated by the
gradient.
3.2.7.2 Soil Vapor Sampling
A variety of equipment has been modified and created for sampling the vapor
present in the unsaturated sediments at contamination sites including monitor
wells, well points, cone penetrometers, lysimeters and soil gas probes. Most
involve the use of a vacuum or suction to collect a sample of the gas.
The depth of sample collection is directly related to the investigation objec-
tives and location of the contaminant sources. Shallow investigations can be
performed to evaluate lateral migration from near surface facilities and also
3-84
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to delineate the boundaries of deeper ground water contamination plumes if the
overlying sediments are permeable to the gases enabling their vertical migra-
tion toward the surface. Deeper soil vapor sampling has been used to deline-
ate three dimensional vapor plumes and thereby identify potential sources and
the migration direction of discrete vapor plumes.
Another factor affecting the sampling methodology is the volatility or affini-
ty for the vapor phase of the constituents. Constituents with a greater
affinity for water (highly soluble) are not good candidates for this type of
technology because they would be harder to detect and would be present in
decreasing concentrations the farther away the sampling point is from the
source.
3.2.7.3 Sample Analysis
Depending upon the objectives of the investigation a variety of analytical
methods can be used. Simple field methods and equipment such as cork bore
samples in 40 ml septum bottles and photoiom'zation detectors can be used as
screening techniques for gross detection of volatile contaminants. In more
sophisticated investigations where contaminant plume tracking or pathway
identification are the objectives, more precise sampling techniques and analy-
sis equipment (specialized sampling probes and gas analyzers or gas chromato-
graphs) may be required.
A two part soil vapor survey is commonly conducted in order to determine the
dimensions and gross chemical characteristics of the area(s) of soil contami-
nation. The first part of the survey would utilize a photoiom'zation field
detection instrument (PID) capable of detecting relative units of total con-
tamination concentration at each soil vapor sampling location. Part two of
the survey would utilize a field gas chromatograph (GC) to gain more specific
data with regard to the major chemical constituents present at strategic
locations within the contaminated area. The GC data will also indicate
whether significant biodegradation of the contaminants has occurred at the
site. In addition, this instrument is capable of detecting lower contaminant
concentrations than the PID unit used in the first part. In some cases, it
may also be possible to utilize GC equipment which is already on-site in the
facility's own laboratory, which could result in a savings for the facility.
3-85
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The data from both parts of the survey can then be used to delineate the
potential boundaries of a contaminant plume and areas within the plume where
the contamination exhibits differences in its chemical composition. The data
can also indirectly indicate the degree of biological activity at the site,
which is useful in assessing the feasibility of in situ biological remediation
of the contamination should it be necessary.
3-86
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4.0 MIGRATION OF CONTAMINANTS/AQUIFER CHARACTERIZATION
-------
4.0 MIGRATION OF CONTAMINANTS/AQUIFER CHARACTERIZATION
Regional ground water flow has been described in a previous section. We must
now be concerned with the introduction of a contaminant into an aquifer and
describe how that contaminant moves away from its source. It is an under-
standing of these processes which will provide the background necessary to
design monitoring systems for disposal sites and to determine the extent of
contamination.
Figure 4-1 shows a generalized picture of how contaminants are transported
from their source (lagoon, landfill, etc.) through the unsaturated zone to the
water table, creating a contaminated ground water mound below the disposal
sites and then flowing down the ground water gradient.
4.1 UNSATURATED ZONE
In the unsaturated section, the prime considerations are its thickness, compo-
sition and permeability.
4.1.1 Effect of Thickness
The thicker the unsaturated section, ttie longer it will take for a contaminant
to percolate downward to the water table. Solid waste disposal sites in arid
environments are generally considered to generate fewer .problems than those in
humid areas. Two reasons for this are: (1) the unsaturated section has a
greater thickness, and (2) less rainfall percolates through the disposal site,
and less water and/or leachate is available for recharge. With no or limited
water moving through a landfill, there is very .limited water to percolate to
the ground water. Most of the water that does move into the unsaturated
section will either evaporate or be absorbed into the soil moisture. However,
with liquid waste disposal, an unlimited water supply is available to the site
which, with percolation, can create a localized saturated section from the
surface to the deep water table. In the High Plains of Texas, holding ponds
have contaminated ground water after passing through 200 feet of unsaturated
deposits. A thick, unsaturated section in an arid climatic region is a retar-
dant to contamination transport, but not necessarily an absolute barrier.
4-1
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4.1.2 Effect of Composition
The composition (i.e., stratigraphy and minerology) of the unsaturated zone
will strongly influence the fate of a contaminant migrating from a waste
unit.' The path that the migrating fluid must follow is dependent upon the
stratigraphic profile which underlies the waste unit. Two different strati-
graphic profiles underlying similar units (Figure 4-2) will result in widely
varying arrival times and concentrations for the same waste. Fluids migrating
through a predominately sand environment (Figure 4-2A) will tend to migrate
vertically through the sediments until the water table is impacted. As the
fluid migrates through the sand body any in situ pore water will be displaced
and mixed with the migrating waste front, which will result in a longer time
until the undiluted waste reaches the water table. Fluids migrating through a
mixed environment (Figure 4-2B) such as those normally found in the Coastal
Plain areas (and other deltaic areas) must follow a longer, more tortuous path
before reaching the ground water. This path, while it will not prevent ground
water impact, allows a greater chance for the waste constituents to be oxi-
dized or adsorbed by the unsaturated sediments.
The lithologic composition of the unsaturated sediments will determine whether
the waste constituents are attenuated-or degraded prior to reaching the water
table. Sediments which contain significant quantities of clay minerals
(illite, montomorillinite, etc.) have the ability to adsorb and degrade a wide
variety of waste constituents. Wastes which contain metals will realize
significant immobilization of the metals as they pass through the clay-rich
sediments. So long as the pH of the sediments remains neutral to mildly basic
the metals will be adsorbed onto the clay matrix and not be available for
transport into the ground water. The clay-rich sediments also provide good
opportunity for biodegration of organics by containing existing colonies of
micro-organisms. The biodegradation of the organic wastes again will reduce
the volume of the waste constituents available for transport to the ground
water. A third consideration of the lithologic composition is the water
retention capacity of fine grain sediments. A general rule is that the finer
the particle size of the sediments, the higher the water holding capacity of
the sediments.
4-3
-------
DEFINED
DOWNGRADIENT
Figure 4-2a. Unsaturated Zone Predominately Sand
DESIGNATED AS
DOWNGRADIENT
RELATIVE
TO AQUIFER IMPACT
LINES OF
SEEPAGE
DEFINED
DOWNGRADItNT
Figure 4-2b. Unsaturated Zone Typical of Amarillo Area
Figure 4-2. Effects of Unsaturated Zone Lithology on Contam-
ination Migration.
4-4
-------
4.1.3 Effect of Unsaturated Permeability
In the unsaturated zone, permeability is also an important parameter for
transport beneath landfills and lagoons. The lower the permeability, the
slower the velocity of contaminant transport. A decrease in the permeability
by an order of magnitude, will cause the rate of contaminant transport to
decrease by about an order of magnitude. Instead of a hypothetical travel
time of 10 years, the lower permeability material would have a travel time of
100 years.
Permeability of the underlying sediments becomes more important as the thick-
ness of the unsaturated sections thins. It must be realized that the
permeability of unsaturated sediments change as water is introduced into the
matrix. The term unsaturated permeability of soils is widely misunderstood to
indicate that the sediment will always have this permeability. As shown in
Figure 4-3, as the moisture content of the sediments increases and approaches
saturation the permeability of the sediments increases dramatically. This
increase in moisture content can easily be extrapolated to the situation of a
liquid waste front passing through the unsaturated zone. As illustrated, this
increase in permeability can easily exceed 3 to 4 orders of magnitude.
Monitoring the permeability of in situ soils near a waste management unit
requires a combination of laboratory and field testing. Determination of the
unsaturated permeability of soils over a variety of moisture contents is
necessary to estimate the permeability of the fine grained sediments under the
waste management unit under changing conditions. The unsaturated permeability
can be measured by a variety of methods including steady state methods, in-
stantaneous profile methods and pressure plate methods. These techniques are
described in detail by Roy E. Olson and David E. Daniel ("Measurement of the
Permeability of Fine Grained Soils," ASTM Symposium on Permeability and Ground
Water Contaminant Transport, June 21, 1979, Philadelphia, Pennyslvania). Use
of these methods requires that the investigator be familiar with the in-place
conditions of the site and have the ability to monitor the conditions at the
site to detect changes in the water content of the sediments.
4-5
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100F
0 20 40 60 80 100
Degree of Saturation, %
Figure 4-3. Suction and Permeability Versus Degree of
Saturation for Compacted Fine Clay.
(Olson and Daniel , 1979)
4-6
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Several methods are available to track the water content of the subsurface
soils. Of these methods, tensiometers are the most commonly used. A tensio-
meter measures the negative pore water pressures that develop when a- soil is
partially saturated. This pore water pressure must be calibrated in the
laboratory to each sediment type that underlies the waste management unit over
a range of water contents. Unfortunately, the tensiometer is limited to
approximately 0.9 atmospheres of negative pore water pressure that it can
monitor under ideal conditions, and in most cases this represents a saturation
of the sediments in excess of 90 percent (Figure 4-3). A more flexible method
with a wider range is the use of a neutron backscatter probe to measure the
water content of the soils. This method must be calibrated to laboratory
results of permeability versus moisture content and can be used over a much
wider range of correlated permeabilities.
4.2 SATURATED ZONE
Once the contaminant has reached the water table, several additional parame-
ters have to be considered: (1) direction and gradient of ground water flow,
(2) permeability of the aquifer, (3) density of the contaminant in comparison
to the ground water, and (4) the chemical reactivity of the fluids and native
ground water.
4.2.1 Direction and Rate of Ground Water Flow
Calculations of direction and rate of ground water flow from a pollutant
source are essentially the same as those described for the regional ground
water flow systems. In general, contaminants enter the ground water system
and are transported along flow lines (Figure 4-4). Since flow lines are
parallel and do not cross, theoretically there is no dilution. However, in
real aquifers, there is a dilution of the contaminant, and the average concen-
tration of the contaminant will be less than its initial input. This results
from the mechanical phenomenon known as longitudinal and transverse disper-
sion. Dispersion is the mechanical mixing of waters on the microscopic
level. On the macroscopic level, flow is considered laminar and, therefore,
flow lines do not cross. On the microscopic level, however, flow lines con-
verge and diverge and actual velocities will be greater or slower than the
average velocity. The contaminant plume from a single, one-time injection of
a contaminant is an ellipse with concentrations increasing toward the
4-7
-------
Flowlines
Zone of
Contamination
Plan View
Figure 4-4. Schematic Diagram of Flowlines in the Vicinity
of a Potentiometric f'ound
4-8
-------
center. In Figure 4-5(a), a contaminant plume from Idaho Falls, Idaho, is
wider than it is long. However, the longitudinal radius of a contaminant
plume (down the hydraulic gradient) is generally much longer than the trans-
verse radius (perpendicular to the gradient) as shown in Figure 4-5(b). The
ratio of longitudinal to transverse dispersion is quite different for these
two cases. An important controlling parameter of the shape of the contaminant
plumes is the heterogeneous and anisotropic nature of the aquifer.
The recharge from a contaminant source creates a "recharge mound." The in-
crease in water moving to the water table causes this surface to rise and
create a bulge on what had been previously a gently dipping, planar surface.
Therefore, the ground water gradient at the mound is greater than the normal
local gradient, and ground water will flow out from the mound at a faster rate
than the normal ground water flow rates in the area. Figure 4-6 shows the
effect on the potentiometric surface of a recharge mound and diagrams the
profile through the mound. Similarly, Figure 4-7 shows a potentiometric
surface before and after seepage from settling ponds began to impact the
ground water. As previously described, ground water flows down the hydraulic
gradient. In the case of the recharge from the hypothetical pollutant source,
ground water flows down the recharge-mound in all directions. A pollutant,
therefore, can migrate up the regional hydraulic gradient. How far the pollu-
tant migrates up the regional gradient is dependent on the height and slope of
the mound and slope of the regional water table. Pollutants can therefore be
expected hydrologically up-dip from the waste disposal site and it cannot be
assumed that the pollutant will only be evident down-gradient. Similarly, the
plume will widen and decrease in concentration down-dip. In some documented
cases, the plume became as wide as it was long for a very gently sloping
ground water surface.
4.2.2 Permeability
The rate, direction, and degree of dispersion of our hypothetical waste plume
is controlled by the permeability of the sediments as well as the shape of the
potentiometric surface. As has been described in the regional ground water
flow section and the unsaturated flow of contaminant section, flow velocity is
proportional to permeability. Decreased permeability by an order of magnitude
will lead to transit time decreased by the same amount.
4-9
-------
DIRECTION OF
GROUND-WATER FLOW
DISPOSAL
a) CHLORIDE PLUME, INEL, IDAHO
Transverse dispersivity '. 450 feet
Time ! 16 years
DIRECTION OF
GROUND-WATER FLOW
O
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1000 ft
— J
b) CHROMIUM PLUME , LONG ISLAND
Transverse dispersivity ", 14 feet
Time " 13 years
Figure 4-5. Effect of Differences in Transverse
Dispersivity on Shapes of Contamination
Plumes (Miller, 1980)
4-10
-------
N
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2000
4000
6000
8000
Distance, feet
10,000
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14.000 ie.000
Figure 4-6.
Altitude of Water Levels, Deep Aquifer, Showing Mounded Water
Surface Under a Cooling Lake Near Corpus Christi, Texas, April
14, 1981.
4-11
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Permeability in sedimentary deposits is heterogeneous. All sands and muds
associated with fluvial and deltaic depositional episodes are heterogenous
because of the varying water energy that carried the sediment to its point of
deposition. The Beaumont Clay, which is the surficial formation in most of
the Texas coastal zone, is an ancient delta plain. Though it is predominantly
mud, it is interlaced with sands channels. This heterogeneity affects our
hypothetical contaminant plume in two ways: (1) pollutants will move more
rapidly through the highly permeable materials, since flow lines will be
concentrated in the highly permeable materials (needless to say, monitoring
wells should be located in the sands and not the muds), and (2) the heteroge-
neity causes lateral dispersion of the plume (the more the fabric or aniso-
tropic nature of the deposits are perpendicular to flow, the more the plume
will spread laterally).
4.2.3 Density of Contaminant Plume
The flow of the contaminant in the regional ground water flow system is depen-
dent on the density of the contaminant in comparison to the density of the
ground water (density (p) of water = 1.0). If the contaminant density is
about equivalent to the density of the ground water, the entire saturated
section would be affected (Figure 4-8)-. However, if the contaminant plume is
heavier than the ground water (pp]ume > 1.0), it will tend to sink to the
bottom of the aquifer. Generally, the more concentrated the contaminant
solution, the higher the density. Brine from oil and gas production is a
typical example of a dense concentrated fluid, as is the waste from many
petrochemical facilities. Figure 4-9A is a hypothetical cross section of a
disposal site in the Texas Gulf Coast area showing a denser fluid migrating to
the bottom of the aquifer.
In contrast, contaminants less dense than the ambient ground water (Pp-|ume
<1.0) will float on top of the ground water (Figure 4-9B). Hydrocarbons and,
specifically, gasoline contaminant plumes float on top of the ground water.
Gasoline moves at the water table and in the capillary fringe above the water
table.
In the case of a heavy leachate (Ppiume >^' monitor wells completed only in
the upper portion of the water table may miss the contamination or at least
4-13
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IMPOUNDMENT
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Figure 4-9A.
Contaminant Plume with Density Greater than Ground
Water
IMPOUNDMENT
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Figure 4-9B. Contaminant Plume with Density Less the Ground Water
4-15
-------
indicated lower concentrations of pollutants. When P < 1, monitor wells
completed in the base of an aquifer might completely miss the contamination.
Figure 4-10 is an example of shallow monitor wells missing the contaminant and
the deeper wells' indicating contamination.
4.2.4 Chemical Reactions
So far, the discussion of the contaminant plume, its shape and movement, has
been based on physical aspects of the system, flow rates, permeability, and
densities. The chemical reactivity of the contaminant is another important
factor in determining where and how far the plume migrates. Similarly, the
geochemical environment of the aquifer is an equally important factor. Both
these factors are important in both the saturated and unsaturated sections of
the aquifer.
Contaminants can be either reactive or nonreactive. Nonreactive contaminants
are extremely soluble anions or small non-ionic organic molecules which move
through the systems at approximately the same velocity as the ground water.
For example, chloride (leaking from a brine disposal pond) is a nonreactive
anion. A contaminant plume of chloride will not be retarded by chemical
reactions. Because of this, chloride-and bromide (similar to chloride) have
commonly been used as tracers in ground water flow experiments.
Reactive contaminants are retarded in an aquifer in several different
fashions, depending on the type of reaction involved. Examples of reactive
species would be the divalent cations Ca"1"*" and Ba"1"1", ammonium (NH^4^), trace
metals, and acidity. Cations such as NH4+ react with clays by a process known
as cation-exchange. Clay particles carry negative charges on their sur-
faces. In a natural systems, the negative charge points are occupied by
cations. If an ammonium solution flowed through these clays, the ammonium
would replace some of the other cations already in the clay. There would be a
loss of ammonium from the contaminant plume. The problem with this type of
retardation of a contaminant is that the reaction is reversible. Once the
ammonium plume had flowed past the clay particle, the particle would release
some of the ammonium to bring it into equilibrium with the new solution. This
type of reaction retards the movement of a contaminant but does not completely
eliminate the contaminant.
4-16
-------
a
MW-1
EXPLANATION
MW-1 d Monitor wel
22 Contour of water table
——^^"» Direction of contaminated
groundwater flow
Total Dissolved Solids content
of samples from monitor wells
WELL
MW-1
MW-2
MW-7
MW-8
MW-9
MW-10
DEPTH
45
25
48
30
30
48
IDS
330
450
95.000
4,300
3,900
78,000
MW-1
MW-2
MW-8
MW-7
Fine silty sand
KS1 x 10 ~2
cm./sec.
Dense leachate
density > 1
Note: A recharge mound is not indicated.
The site wai drained & capped prior
to monitor wel inetalation.
Zone of gravimetric
separation
Stiff clay
K s 1 x 10 ~* cm./sec.
Figure 4-10. Cross Section of Disposal Site on the Texas Gulf Coast
4-17
-------
Adsorption of trace metals on the aquifer matrix is another process of
leachate attenuation. This process differs from cation-exchange in that (1)
adsorption is not dependent on clays with high cation exchange capacities, (2)
an ion is not released for every metal ion adsorbed, and (3) the reactions may
or may not be reversible. Examples of metals that are adsorbed are chromium
and copper. In one Texas Gulf Coast disposal site, leachates contained 5 mg/1
of copper. However, in nearby contaminated monitor well (approximately 10
feet from the disposal site), only .064 mg/1 of copper was detected in water
samples. Similarly, in a disposal site located in the northern High Plains,
suspected contamination of a site water well by leachates occurred. Despite
high levels of chromium and lead in the plant leachates, the contaminated well
water showed negligible levels of these constituents, which has apparently
been attenuated by the uppermost soils.
Acidity in a contaminant plume is altered in an aquifer by reaction of the
hydrogen with the carbonate minerals in the aquifer matrix. Acidity will
react with calcite to form bicarbonate. An increase in bicarbonate in an
aquifer is generally not considered a problem. If the aquifer lacks the
carbonate minerals, then acid plumes ean continue. Acid mine drainage occurs
in the northeastern United States because the rocks in which the acid water
flow are very low in carbonate minerals.
Many contaminants will precipitate out of solution, because specific ions
become oversaturated either by reacting with the aquifer or by changes in the
pH in the redox environment of the aquifer. Iron is very soluble in acidic,
reducing waters as the ferrous ion fe . Oxidation of the iron solution will
lead to the shifting of the ferrous ion to ferric iron (fe ), which is ex-
tremely insoluble and will precipitate as an iron hydroxide.
Although the preceding discussion indicates leachate migration is a complex
subject, in most ground water contamination studies, some estimates of the
lateral extent of contamination must be made. Generally, insufficient funds
and little time are available for comprehensive investigations. Therefore,
estimates of lateral migration are made on the basis of Darcy's Law.
4-18
-------
4.3 AQUIFER CHARACTERIZATION TESTS
In order to assess the various hydraulic parameters which affect contaminant
migration, a variety of tests can be performed. These tests consist of field
tests which measure and determine aquifer characteristics and consist of
laboratory testing of soil samples and aquifer matrix.
4.3.1 Field Tests
Aquifer characterization tests conducted in the field (pumping, aquifer,
drillstem, etc.) are generally considered to be more reliable than laboratory
tests used for determining hydraulic characteristics of aquifers. These tests
generally involve the removal of water from an aquifer by pumping a well while
the subsequent reaction of the aquifer to this imposed stress is observed
simultaneously.
There are two different types of analyses used in the determination of hy-
draulic characteristics; steady state (equilibrium) and transient (nonequili-
brium). Both of these types of analyses are described in Section 4.3.1.2 and
4.3.1.3 respectively. Section 4.3.1.1 is a list of the definitions of some of
the terms frequently used in these sections.
4.3.1.1 Aquifer Characteristics Definitions
ANISOTROPY - is the condition under which one or more of the hydraulic proper-
ties of an aquifer vary with respect to the direction within the aquifer.
HEAD (TOTAL) - is the sum of head resulting from elevation, pressure and
velocity at a given point in an aquifer.
HYDRAULIC CONDUCTIVITY - is the capacity of media (sediments or rock) to
transmit water of a prevailing density and viscosity through a unit cross-
sectional area of an aquifer. Hydraulic conductivity is equal to transmissiv-
ity divided by the aquifer thickness (Figure 4-11). The term "coefficient of
permeability" was used in the past although hydraulic conductivity is now
preferable. This has resulted in some confusion with respect to the use of
the term permeability.
4-19
-------
msm
I ^Sro pg^-^f
4-20
-------
HYDRAULIC GRADIENT - is the change in total head for a change in some unit of
distance in the direction of maximum decrease in head (Figure 4-12).
ISOTROPY - is the condition in which the hydraulic properties of an aqufier
are equal in all directions.
SPECIFIC CAPACITY - is the yield of a well per unit of drawdown.
SPECIFIC RETENTION - is the ratio of the volume of water retained in a porous
media sample after gravity drainage has occurred.
SPECIFIC YIELD - is the ratio of the volume of water that will drain under the
influence of gravity to the saturated media sample.
STORAGE COEFFICIENT - is the volume of water released from storage in a unit
volume of an unconfined quifer by lowering the head a unit distance. In
unconfined aquifers the storage coefficient equals the specific yield because
water is released from storage. The release of water per unit decline in head
is much greater for unconfined aquifers than for confined aquifers where other
properties are similar (Figure 4-13).
STORATIVITY - is the volume of water released from storage per unit volume of
a confined aquifer per unit change in head. In confined aquifers, water is
released from the aquifer's pore spaces from the compression of the grains
within the aquifer (Figure 4-13)
TRANSMISSIVITY - is the rate at which water of a prevailing density and vis-
cosity is transmitted through a unit width of the fully saturated thickness of
an aquifer under a unit hydraulic gradient. It is a function of properties of
the liquid, the porous media, and the thickness of the porous media. Trans-
missivity is equal to the hydraulic conductivity multiplied by the aquifer
thickness. The term "transmissibility" was used in the past and has almost
completely been replaced by transmissivity in literature (Figure 4-11).
4.3.1.2 Steady State (Equilibrium) Method
The steady state method was the first method developed for aquifer test analy-
4-21
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sis. For this method, the test must remain in progress until the aquifer
reaches equililibrium from the imposed stress (pumping). This requires a
relatively long testing period (until equilibrium is reached). In reality,
equilibrium may not be an achievable goal if one or more the ideal aquifer
assumptions are not met.
STEADY STATE ASSUMPTIONS
The use of steady state equations is based upon the following assumptions:
- The formation is homogenous (characteristics are uni-
form areally), isotropic (hydraulic properties are
equal in all directions), and of uniform thickness.
- Hydraulic characteristics of the formation and any
confining layers are constant at all times and at all
locations within the area of influence of the well.
- The formation is not stratified.
- The discharging well is screened over the entire thick-
ness of the formation.
- Flow to the well is horizontal (i.e., the slope of the
water table or piezometric surface is relatively flat),
radial and laminar (fluid particle flow paths are
smooth, straight and parallel) within the radius of
influence of the well.
- The rate of discharge from the well (or imposed stress
to the aquifer) is constant.
- The pumping well is 100 percent efficient.
- The cone of depression has reached equilibrium and will
not expand with continued pumping.
4-24
-------
In addition, the method requires the use of two or more observation wells at
different radial distances from the pumping well for water level measure-
ments. Figures 4-14, 4-15, and 4-16 provide an illustrative definition for
various terms used in equilibrium methods.
STEADY STATE (EQUILIBRIUM, OR THIEM) EQUATION METHOD
The equilibrium method can be employed to evaluate the aquifer characteristics
around a pumping well. This method is accurate for determining transmissivity
(T) and/or hydraulic conductivity (k) but not storativity or specific yield,
which are both designated as (S).
The appropriate form of the equation used in the analysis of unconfined (water
table) aquifers is:
English Engineering Units
1055 Q log (r2/r1)
k=
(h2
International System of Units
k=
Q log (r2/r1)
1.366 (h22- t^
where:
Q = well yield or pumping rate, in gpm
k = hydraulic conductivity of the water
•)
bearing formation, in gpd/ft
r-^ = distance to the nearest observation
well, in ft
r2 = distance to the farthest observation
well, in ft
h2 = saturated thickness, in ft, at the
farthest observation well
h-^ = saturated thickness, in ft, at the
nearest observation well
Q
K
rl
r2
ho
= well yield or pumping rate, in gpm
= hydraulic conductivity of the Water-
's o
bearing formation, in nr/day/m
(m/day)
= distance to the nearest observation
we!1, in m
= distance to the farthest
observation well, in m
= saturated thickness, in m, at the
farthest observation well
= saturated thickness, in m, at the
nearest observation well
4-25
-------
Ground surface
Impermeable
'/X////////////////////
Impermeable
CARTER TODD, 1976D
Radius of weil-^
fl
f*- Radius of influence-
^^ ^ Cone of
"\^ depression
X
Drawdown curve^ \
(potentiometric surtacer
^mp^o^str^gmX
b
Thickness of
water-bearing
formatjon
T
w
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i
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=
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s
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f Depth to static
potentiometric surface
'Draw
/ in v
/ H
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down
veil.
h
•
• i
CAFTER DRISCOLL, 1986)
Figure 4-14. Various Terms Used in the Equilibrium
Equation for a Confined Aquifer
4-26
-------
Ground surface
permeable
CAFTER TODD. 19763
CAFTER DRISCOLL. 1986}
Figure 4-15. Various Terms Used in the Equilibrium
Equation for an Unconfined Aquifer
4-27
-------
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and for confined (artesian) aquifers:
English Engineering Units
International System of Units
T = kb =
where:
528 Q log (r2/r1)
(h2 -
all terms except the following are
the same as for unconfined aquifers
b = thickness of the aquifer, in ft
head, in ft, at the farthest
observation well, measured
from the bottom of the aquifer
head, in ft, at the nearest
observation well, measured
from the bottom of the aquifer
ho =
hl =
T = kb =
Q log (r2/r1)
2.73 (h2 -
all terms except for the following are
the same as for unconfined aquifers
b = thickness of an aquifer, in m
h2 = head, in m, at the farthest obser-
vation well, measured from
the bottom of the aquifer
h^ = head, in m, at the nearest obser-
vation well, measured from
the bottom of the aquifer
4.3.1.3 Transient (Non-Equilibrium, Non-Steady) Methods
The transient methods differ from the steady state methods in that the expand-
ing cone of depression does not have to reach equilibrium in order to evaluate
the data determining aquifer characteristics.
Specific Capacity Method (Modified Thiem Formula)
A modification of the Thiem equilibrium formula enables a rapid approximation
of transmissivity. This method uses the pumping test parameters, discharge
(Q) and maximum drawdown (Sw), to determine specific capacity from which a
value of transmissivity can be derived. The transmissivity of the aquifer is
calculated using the following formulas:
T = specific capacity x a constant
where: Specific Capacity =
Sw
4-29
-------
and:
T = transmissivity in gallons/day/foot (gpd/ft)
Q = discharge during pumping in gallons per minute (gpm)
Sw = maximum drawdown in the well in feet
Constant = a number in the general range of 1,700 to 2,000
TRANSIENT ASSUMPTIONS
The following assumptions apply to the transient methods.
- The formation is homogeneous (characteristics are uni-
form areally), isotropic (hydraulic properties are
equal in all directions), of uniform thickness and of
infinite areal extent.
- Hydraulic characteristics of the formation and any
confining layers are constant at all times and at all
locations within the area of influence of the well.
- The discharging well is of infinitesimal diameter and
is screened over the entire thickness of the formation
- Flow to the well is horizontal (slope of water table or
piezometric surface is relatively flat), radial and
laminar (fluid particle flow paths are smooth, straight
and parallel) within the radius of influence of the
well.
- All water is released from storage instantaneously with
the lowering of the head and there is no delay in the
reaction observed.
- The formation has no points of discharge or recharge
within the area of influence.
THEIS GRAPHIC NONEQUILIBRIUM METHOD
Theis developed the nonequlibrium well equation based upon the analogy between
the flow of water in a confined aquifer and heat flow in a thermal conduc-
tor. This equation was the first to take into account the effect of pumping
time and, thus, provided for the determination of transmissivity and hydraulic
conductivity from early stages of pumping, without ever reaching equlibrium.
4-30
-------
Theis' method utilizes a graphical solution which involves matching a plot of
actual field data with a theoretical type curve (See example, Figure 4-17).
1. Obtain an existing type curve, or plot a type curve to
a convenient scale on logarithmic paper.
2. Plot field data (also on logarithmic paper).
Drawdown (hQ - h) vs t.
Note: For observation wells^with differing distances
from the pumping well, use t/r^
Solutions for transmissivity, (T) are as follows:
English Engineering Units
International System of Units
T =
114.6 Q W(u)
h0 - h
T =
1 Q W(u)
(h0 - h)
where:
h - h =
drawdown, in ft, at any
point in the vicinity of a well
discharging at a constant rate
Q = pumping rate, in gpm
T = coefficient of transmissivity
of the aquifer, in gpd/ft
W(u) = is read "well function of u"
and represents an exponential
integral
h - h =
drawdown, in m, at any point
in the vicinity of a well
discharging at a constant rate
pumping rate, in m /day
coefficient of transmissivity
of the aquifer, in m /day
W(u) = is read "well function of u"
and represents an exponential
integral
Q
T
Solutions for the coefficient of storage (S) are as follows:
English Engineering Units
uTt
International System of Units
4uTt
S =
where:
r = distance, in ft, from the center of a
pumped well to a point where the
drawdown is measured
S = coefficient of storage
(dimensionless)
S =
r = distance, in m, from the center of a
pumped well to a point where
the drawdown is measured
S = coefficient of storage
(dimensionless)
4-31
-------
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4-32
-------
T = coefficient of transmissivity, in T = coefficient of transmissivity
gpd/ft in m /day
t = time since pumping started, in days t = time since pumping started, in days
Numerous - adaptations and modifications of this method have been derived for
specific situations including type curves for leaky aquifers (Figure 4-18) and
developed yielding aquifers.
JACOB'S STRAIGHT LINE METHOD
It was postulated by Jacob that, after steady state conditions had been
reached, higher values in the infinite series become negligible; thus, a more
simple equation, could be utilized to achieve approximately the same value as
Theis' equation.
Jacob's solution to the Theis equation also utilizes a graphical solution
except the slope of a line intercept is used instead of the matching of field
data to a type curve (See Figure 4-19). The Jacob method applies, however,
only when the well radius (r) is small with respect to time (t).
Steps:
1. Plot drawdown against time on semi logarithmic paper.
2. Draw a straight line through plotted field-data points.
3. Extend line to the zero-drawdown axis and note the
value of tQ
4. Measure value of drawdown per log cycle.
The aquifer characteristics of transmissivity and storage coefficient can be
calculated using the following equations:
Solutions for transmissivity (T) are as follows:
English Engineering Units International System of Units
264Q
T = T = 2.3 q_ = 0.183 Q
AS 4ir AS AS
4-33
-------
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4-35
-------
where:
T = coefficient of transmissivity, in
gpd/ft
Q = pumping rate, in gpm
AS = (read "delta s") slope of the time
drawdown graph expressed as the
change in drawdown in ft over one
low cycle
T = coefficient of transmissivity, in
or/day
Q = pumping rate in nr/day
AS = (read "delta s") slope of the time
drawdown graph expressed as the
change in drawdown in m over one
log cycle
Solutions for the storage coefficient (S) are as follows:
English Engineering Units
International System of Units
S =
T =
2°25
where:
S = storage coefficient
T = coefficient of transmissivity, in
gpd/ft
t0 = intercept of the straight line at
zero drawdown, in days
r = distance, in ft, from the pumped
well to the observation well where
the drawdown measurements were made
S = storage coefficient
T = coefficient of transmissity, in
nr/day
tQ = intercept of the straight line at
zero drawdown, in days
r = distance, in m, from the pumped
well to the observation well where
the drawdown measurements were made
DISTANCE DRAWDOWN METHOD
The distance drawdown method utilizes the simultaneous observations of draw-
down in three or more observation wells (See example, Figure 4-20).
Steps:
1. Plot drawdown on arithmetic scale as a function of
distance from the pumping well on logarithmic scale
2. Draw a line through data points for the wells close to
the pumping well and extend it to intercept the zero-
drawdown line.
3. Measure the drawdown per log cycle as before i.e., A(h
-h).
4-36
-------
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4-37
-------
The following equations can then be used to determine the aquifer characteris-
tics:
English Engineering Units
International System of Units
T = 528_
AS
T = 0.366 Q
AS
where:
where:
T = coefficient of transmissivity, in
gpd/ft
Q = pumping rate, in gpm
AS = slope of the distance drawdown
graph expressed as the change in
drawdown, in ft, over one log cycle
T = coefficient of transmissivity, in
m2/day
Q = pumping rate in nr/day
AS = slope of the distance drawdown
graph expressed as the change in
drawdown, in m, over one log cycle
and
S = 0.3 Tt
= 2.25 Tt
where:
where:
S = coefficient of storage S
T = coefficient of transmissivity, in T
gpd/ft
t = time since pumping started, in days t =
rQ = intercept of extended straight line rQ =
at zero drawdown, in ft
= coefficient of storage
= coefficient of transmissivity, in
m2/day
time since pumping started, in days
intercept of extended straight
line at zero drawdown, in m
4.3.1.4 Conducting An Aquifer Characteristics Test
There are three stages to conducting an aquifer characterization test:
a. Pre-test stage: Check equipment and measure the re-
sponse and efficiency of the wells. The optional pump-
ing rate is determined in this stage.
4-38
-------
bo Drawdown (pumping) test stage: Maintain constant pump-
ing rate over a long period of time and measure draw-
down.
c. Recovery (post-pumping) stage: Stop the pump and mea-
sure recovery of water levels.
Test Requirements:
• A reliable pumping system must be used.
• All wells must be designed for measuring water levels
in the unit of interest.
• Pumped water must be discharged at a sufficient dis-
tance that it does not recharge the aquifer in an area
which may affect test results.
• All measurements must be referenced to a fixed point
(e.g., the top of each well casing).
Observation Prior to Test: Water levels in all wells should be measured prior
to the test to establish any water level anomalies (e.g., tidal influences
etc.).
Length of Test: The length of the pumping test depends on both aquifer and
recharge conditons (e.g., stream recharge). Artesian aquifers are generally
pumped for a minimum of 24 hours and water table aquifers, for a minimum of 72
hours.
Frequency of Readings: The most common schedule for measuring drawdown begins
with readings taken at 30-second intervals for the first 10 minutes of the
test (one-minute is maximum interval). Subsequent measurements should be such
that an even spread of drawdown data points are obtained on a log scale plot.
Staffing: The test should be run by a qualified hydrogeologist experienced in
dealing with problems which can be encountered during field testing.
End of Test: At the end of the test (after recovery data has been obtained)
all wells should be sounded and these data compared with pre-test soundings to
determine if anomalies have affected static conditions.
4-39
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4.3.1.5 Test Design and Analysis
The field procedures used to perform aquifer tests and the methods used to
analyze the data were derived in response to the need for evaluating ground
water supplies for domestic, agricultural and industrial use. Therefore, the
tests were often performed on a large scale. With the growing interest in
ground water contamination investigations and hazardous waste migration
studies, the use of these tests has been adapted to a smaller scale.
Quite often the water bearing formation of interest in environmental studies
does not fit the scientific definition of an aquifer but rather the regulatory
definition of the word. As a result, these low to poorly yielding water
bearing units might be considered aquitards in relation to major aquifers by
water well industry standards, while the environmental community would con-
sider them aquifers.
As the scale of the test is reduced, deviations from the assumptions of an
ideal aquifer become increasingly significant, making it even more important
that we realize that these methods only provide approximate answers. Objec-
tives must be achievable within the constraint of the situation, and the test
design must be appropriate to fulfill these objectives. In designing aquifer
tests and evaluating the results, a number of factors should be considered
with respect to the scale and objectives of the test:
- Can an appropriate set of materials and equipment be
assembled to perform the test?
- Can the test be performed so as to yield adequate data
for reasonably accurate evaluations or are too many of
the assumptions invalidated?
- How will the test be analyzed?
- Can all or any of the objectives be fulfilled by the
test, which ones, and is this adequate?
While many methods of analysis have been developed, the evaluation of pumping
test data may not always be straightforward. As a result, pumping test data
can be interpreted in more than one way such that several factors must be kept
in mind during data interpretation. These factors include errors in data
4-40
-------
collection, well design and construction details, hydrogeologic characteris-
tics of the tested aquifer, accuracy of pumping rates and potential environ-
mental influences such as barometric effects, highway and railroad traffic,
and tides.
The calculation of an aquifer's transmissivity using Jacob's straight line
method is based upon the determination of a straight line slope through the
field data. In some pumping test data, more than one slope can be determined
over the period of the aquifer test. Figure 4-21 represents the time-drawdown
plot for a well discharging 2,700 gpm. The early time data is attributed to
wellbore storage and is not used in the analysis for transmissivity even
though the data may yield a straight line. On the other hand, drawdown data
yielding two separate straight line portions (Figure 4-22) can be used to
indicate important physical characteristics of the aquifer. Figure 4-22
indicates the boundary effects within an aquifer caused by variable lithology
within a glacial outwash deposit.
Pumping test data can also be affected by sources uncontrolled by the per-
former of the pumping test. The influence of these outside sources needs to
be understood before an accurate assessment of the data can be made. Figure
4-23 represents a plot of drawdown data collected from an observation well
during a pumping test. Because of the small drawdown in the observation well,
it was necessary to evaluate the barometric efficiency of the aquifer and make
adjustments to the water level data. While the actual data collected during
the test is erratic, the corrected data permits a straight line to be drawn
through the latter time data. Changes in water levels due to barometric
effects sometimes exceed the changes in water levels expected from a nearby
pumping well. In these cases, the barometric effects mask the test results
and make the data uninterpretable.
The test data can also be influenced by surrounding pumping wells in areas of
uncontrolled pumpage of the tested aquifer. Figure 4-24 presents the recovery
data for a Travis County, Texas well. The changes in the slope of the recov-
ery data result from several nearby wells being intermittently turned on and
off during the pumping test.
4-41
-------
Early data
40 affected by
casing storage
60
80
100
120
140
160
Q = 2,700 gpm_
—
<= 158i40pgpd/ft
10 100 1,000
Time since pumping began, minutes
10,000
(After Driscoll, 1986)
Figure 4-21. Time-drawdown Plot for a Well
Discharging 2,700 gpm
20
~- 30 E
£ 40
Q
50
60
70
10 100 1,000
Time since pumping began, minutes
(After Driscoll, 1986;
Figure 4-22. Drawdown Data for 6-in.(152-mm) Test
Well in Brewster, Minnesota
4-42
-------
^- -
oo
co
l/l
4->
O
Ol
01
o
S-
CQ
01
c
o
-o
03
O
QJ
i-
CD c\J
0 i
_J O
_l |_
LU <
i g
Q- $
5: <
T CO
T 8
O
00
S-
01
10
6
4-43
-------
Water
Level
(FU
144
145
146
147
148
149
150
151
50
100 150
TIME. MINUTES
200
250
Figure 4-24.
Recovery Data Showing Effects of Nearby
Interim'ttantly Pumping Wells
4-44
-------
Real world aquifers do not meet the assumptions made in establishing well-
hydraulics methodology. Some deviation is to be expected from "idealized"
type curves. Calculated properties should be regarded as being approxima-
tions. Therefore, aquifer test data should be analyzed by a qualified pro-
fessional who is experienced in determining the quality and validity of the
results.
4.3.1.6 Slug Tests
Slug tests are often used as an alternative or supplement to conventional
pumping tests for the determination of aquifer characteristics (e.g., transmi-
ssivity, storativity, hydraulic conductivity). As in the case of pumping
tests, aquifer characteristics are determined from the data. Certain assump-
tions about the aquifer's characteristics are necessary, and the physical
constraints posed by the testing method must be considered. In most analytic
methodologies utilizing slug tests, the assumptions concerning the aquifer are
that it is:
Homogeneous
Isotropic
Areally extensive and
Uniform in thickness
There are several different approaches to analyzing slug test data. In most
ground water related texts on the subject, the following three are the most
commonly referenced methods:
• Cooper, Bredehoeft, and Papadopulos (1967; 1973)
• Bouwer and Rice (1976)
• Hvorslev (1951)
Another noteworthy method that is not as prevalently known is the method
described by Nguyen and Finder (1981).
The Cooper et al. method (1967; 1973) is used to analyze confined (artesian)
aquifers, exclusively. Bouwer and Rice's method (1976) is primarily used for
unconfined (water table) or semi-confined aquifers, although the authors
maintain it can provide accurate results in confined aquifers as well.
Hvorslev's method (1951) is appropriately used where specially designed piezo-
4-45
-------
meters have been installed. Hvorslev's method is useful in determining the
hydraulic conductivity (k) of fine grained materials such as clays and silts
(i.e., aquitards) rather than coarser grained water-bearing formations. Since
the emphasis of this section is toward aquifer characterization, the Hvorslev
method will not be discussed in any detail.
Testing Procedure
Although there are many different analytic methods for slug tests, the actual
testing procedures are basically the same. Test procedures involve either the
injection into, or withdrawal of a slug of water of known volume from, a
well. The change in water level in the well in response to the addition or
removal of the slug is measured over time with either an electric line, chalk
line, or transducer. The rate of this response is primarily controlled by the
characteristics of the screened aquifer. At first, the rate of the response
is very fast and then slowly decays with time until equilibrium is reached.
For this reason, water levels are collected initially at very short time
intervals, e.g., every 10 seconds. As the response decays, this interval can
be lengthened to 20 seconds, 30 seconds, 60 seconds, 2 minutes, 5 minutes,
etc. These data (change in water level vs. time) are then plotted on semi-
logarithemic paper for analysis using the appropriately selected method.
Description of Methods
Cooper, Bredehoeft, and Papadopulos Method
Cooper, et al. ( 1967 and 1973) described a method for
analyzing slug test data based on non-steady flow. This
method utilizes the plot of the ratio of the measured head
to the head after displacement by the slug (H/HQ) over the
function of time. (See Figure 4-25). The ratio H/Hg and
time are plotted on arithmetic and logarithmic scales,
respectively, on semi logarithmic graph paper. The result-
ing curve plot will look similar to the theoretical type
curves shown in Figure 4-26. A transparent (same scale)
copy of the type curve is placed over the field data plot
until an appropriate match of the curve has been
achieved. The transmissivity (T) of a confined aquifer
can then be determined from the formula:
T = 1.0rc2
4-46
-------
Water level immediately
after injection
Water level at time t
Head in aquifer
^.Initial head
in aquifer
Well casing
Well screen or
wall of open hole'
[Source: H. H. Cooper, Jr., J. D. Bredehoeft, and S. S. Papa-
dopulus, '-later Resources Research, 3 (1967) :263-69)
Figure 4-25. Well Into Which a Volume, V, of Water is Suddenly
Injected for a Slug Test of a Confined Aquifer.
-------
^Source: S. S. Papadopulos, J. D. Bredehoeft, and H. H. Cooper,
'jr., Water Resources Research, 9 (1973):1087-89.
Fiqure 4-26.
Type Curves for Slug Test in a ;'ell of Finite
Diameter.
4-48
-------
Where r is the radius of the well casing, and ti is the
value of time on the field data jjlot intercepted by the
matched vertical axis where Tt/r^ = 1 on the chosen type
curve. The storativity (S) of the aquifer can also be
obtained using the value of the y-curve matched with the
field data from the formula:
Where r is the radius of the well casing and r. is the
radius of the borehole annulus or well screen. The use of
this method in the determination of storativity has been
described by the authors as having "questionable relia-
bility;" the accuracy can be expected to be within two
orders of magnitude of the actual value.
Bouwer and Rice Method
The slug test method described by Bouwer and Rice (1976)
is based on steady state flow theory and is applicable to
both fully or partially penetrating wells in unconf ined
(water table) aquifers (Figure 4-27). The field data are
collected in the same manner as previously described. The
solutions for characteristics are similar to open auger
hole techniques which measure hydraulic conductivity (k,
coefficient of permeability). The empirical equation,
which takes in account the geometry of the well (or piezo-
meter), and is used in determining k from the water dis-
placement by a slug, is:
k = rc2 1n
2L
yt
The effective radius term, R , is the equivalent radial
distance over which the head loss y is dissipated through
the system during the test. Rg is dependent upon the geo-
metry of the flow system. The value of Re, which is used
in the previous formula as Re/i"w» must be derived using
the following equation for a partially penetrating well
(i.e., D>H):
In R0/r
e w 1.1 + A + B In [(D-H/r )
ln(H/rw)
Where A and B are dimensionless coefficients that are
functions of L/r , as shown in Figure 4-28.
W
If the well being tested is fully penetrating (i.e., D =
H) then the previous formula should be modified to
4-49
-------
/"•
2rc
I
y
T t
1
VXV»WW/X/^
f/SXJ//.
WATER TABLE
^.
•J'
H
IMPERMEABLE
Figure 4-27.
Geometry and Symbols of Partially Penetrating,
Partially Perforated Well in Unconfined Aquifer
with Gravel Pack or Developed Zone Around Per-
forated Section (From Bouwer and Rice, 1976)
-------
14
12
A
AND
C
10
10
50 100
LJ J 0
500 1000 5000
<-e/rw
Figure 4-28. Curves Relatinq Coefficients A, B and C to
(From Bouwer and Rice, 1976)'.
w
4-51
-------
In Re/rw
ln(H/rw) L/rw
Where C is a dimensionless coefficient that is a fraction
of L/rw. Using these equations for deriving the effective
radius, Re, the authors point out the calculated values of
In Rp/rw are within 10 percent of the actual value if
L>0.4H and within 25 percent if L«H.
The solution for hydraulic conductivity (k) is made by
first plotting the recovery of the water level after dis-
placement by a slug (yt) against time (t) on logarithmic
and arithmetic scales, respectively. A straight-line is
extrapolated through the straight-line portion of the
resulting curve, which is the valid part of the readings,
and is then extended to the time axis. A point along the
extended line is arbitrarily selected, and then values of
y.£ and t are determined from the intersections with this
point. The term y0 represents the displacement of water,
in distance, which is derived from the value at the inter-
cept of the extrapolated straight line with the yt axis.
After all the terms are identified, the hydraulic conduc-
tivity (k) can be solved for by the following equation:
k = rc2 ln(Re/rw) 1 In y0
21 t yt
Transmissi vity (T) can be solved for by multiplying the
hydraulic conductivity (k) by the thickness of the aquifer
(D).
Slug tests provide a useful alternative to conventional pumping tests which
are generally more time-consuming and costly. However, the use of slug tests
is limited to aquifers (or aquitards) with relatively low permeability.
Determination of storativity (S) from slug tests is not considered to be
reliable. However, transmissivity and hydraulic conductivity can be deter-
mined with relatively high confidence so long as it is recognized that these
values are representative of the aquifer within extremely close proximity to
the well. It is also important to evaluate other factors which may signifi-
cantly bias the test results with respect to this problem of limited test
proximity, such as:
4-52
-------
• grain size, sorting of sand pack material installed
around the screen
• ratio of the effective volume of the borehole annulus
to the well casing
• ratio of the volume of the slug to the effective volume
of the well casing and borehole annulus
• well development, i.e., well efficiency.
These factors cannot be filtered analytically from the results and should,
therefore, be considered when anomalous results are produced. Nevertheless,
with sufficient planning, test design and interpretation, slug tests can be
utilized to determine aquifer characteristics with relative confidence.
4.3.1.7 Field Permeameter Test
The field permeameter test is an adaption of the basic falling head perme-
ability test. Water percolates into the formation from a surface reservoir,
such as a 55-gallon drum. A sight glass or pipette indicates the flow of
water, and measurements, at intervals, can be used to determine a flow rate.
Once the flow rate has reached equilibrium (indicating saturation of the
surrounding sediments), the value for the constant rate of flow can be used in
conjunction with well construction specifications to calculate a permeability
value for the formation. The sample calculation in Table 4-1 illustrates the
equation and method used to calculate the permeabilities. Figure 4-29 shows a
typical setup for field permeameter.
4.3.2 Laboratory Tests
The scope of the geotechnical testing program for most ground water contamina-
tion and waste migration evaluations is generally limited. In most instances,
the variety and number of laboratory tests performed is small. The primary
purpose of the laboratory testing program is to determine the permeability of
the soils. The testing program should also obtain enough soil indices to
allow for classification of the project site soils. With sufficient soil
classification tests, laboratory permeability data can be extrapolated across
the site. It should be noted here that most geotechnical laboratories are not
equipped to handle hazardous waste samples and some test methods require
direct skin contact.
4-53
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TABLE 4-1
Sample Field Permeability Calculation
Field Permeability
K = d2- • In (2L/D) t H-,
8 • L • (t2 - i) F£
K = Permeability, in./min
D = Diameter of test hole = 9.0 in.
d = Diameter of standpipe .= 22.1
(reservoir diameter = 4 in. and barrel diameter = 22 in,
(42 = 222)^ = 22.4 in.)
L = Length of test hole = 62.0 in.
HI = Piezometric head at time = t^
\\2 = Piezometric head at time = t£
K = (22. 4)2 In (2 x 62/9) In 13.60 = 5.8 x 10'3
8 x 62 x 50 12.23
= 5.8 x 10'3 in./min = 2.4 10"4 cm/sec
4-54
-------
22" diameter
55 Gallon Barrel
Siphon Hose
2' Long *Sightglass'
4" diameter Reservoir Pipe
Concrete Plug
2" diameter Riser Pipe
Native Soil Backfill
Granular Bentonite
2" X 5' Slotted Well Screen
C0.008" Slots)
No.2 Blast Sand
TO
Figure 4- 29. Field Permeater Installation
4-55
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4.3.2.1 Index Tests
The following table lists common soil index and classification tests with the
corresponding ASTM test method. Although there are other test methods, for
the purpose of this discussion only ASTM test methods are referenced.
INDEX/CLASSIFICATION TEST
Test Method for Liquid Limit,
Plastic Limit, and Plasticity
Index of Soils
Method for Laboratory
Determination of Water
(Moisture) Content of
Soil, Rock, and Soil-
Aggregate Mixtures
Method for Particle-Size
Analysis of Soils
Test Method for Amount of
Material in Soils Finer
Than the No. 200 (75-uM)
Sieve
COMMON USAGE
Atterberg limits
Moisture Content
Gradation Analysis
Minus 200
ASTM TEST METHOD
D 4318-84
D 2216-80
D 422-63
D 1140-54
A visual inspection of the soil sample can help to determine which index/
classification tests to perform. In general, fine-grained materials (i.e.,
clay and silts) are classified according to plasticity, and coarse-grained
materials (i.e., sands and gravels) are classified by gradation. If the soil
sample is a clay, or primarily clayey or silty in composition, an Atterberg
limit test and minus 200 mesh-sieve test will be sufficient in most instances
to classify the sample. The natural moisture content will be determined in
the Atterberg limit test. However, if the soil sample contains appreciable
material of various particle sizes, or is primarily sandy or gravelly in
composition, a complete gradation analysis (includes No. 200 sieve) will be
required for proper classification of the sample. In these cases, a separate
natural moisture content test will need to be performed. As most soils are
composed of materials with differing particle sizes, judgement needs to be
exercised in the selection of index/classification tests. In instances where
there is a question about which tests to select, an Atterberg limit test and
complete gradation analysis should be performed.
4-56
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For projects involving construction of new facilities, additional laboratory
testing will be required to provide the necessary geotechnical design parame-
ters. Additional testing might include compaction, shear strength, and con-
solidation tests. This discussion will be limited to the index/classification
and permeability tests generally associated with initial ground water investi-
gations.
Atterberg Limits
Atterberg limits were first developed in 1911 by a Swedish soil scientist,
Albert Atterberg, for the purpose of evaluating plasticity of soils. From
Atterberg1s original work, three sets of limits were adopted for use in foun-
dation engineering.
NAME OF LIMIT SOIL CONSISTENCY
Liquid limit fluid
Plastic limit plastic
Shrinkage limit semi-solid to solid
Natural soil moisture content is normally between the liquid limit and shrink-
age limit; however, many soils are in the more restrictive range between the
liquid and plastic limits.
The original limits were qualitative and, later, Terzaghi (1926, 1927) and
Casagrande (1932) arbitrarily quantified the plastic limit and liquid limit,
respectively (Figure 4-30). In recent years, the Atterberg limit test has
been used as one indication of the suitability of soils for waste disposal
sites. Both TWC and TDH have established guidelines for Atterberg limits.
Standard specifications, such as ASTM D4318-84, are available for standarizing
preparation of the soil sample for the Atterberg limit test. Details of the
standard specifications will not be presented; however, a critique of the
standard procedures will be presented. (It should be noted that ASTM D2217-
66, Procedure B, presents a wet preparation method which avoids the problems
associated with ASTM D4318-84).
The Atterberg limit test is performed on the soil fraction which passes the
No. 40 sieve. Thereafter, to facilitate sieving the soil, some standard
4-57
-------
\
X
o
\
\
^
\i
A
\
V
\
\
~ O
00 '
A
X
O
\
\
ly Plastic
1*-
u_
O
CO
o
-------
methods (i.e., dry preparation) recommend drying the soil prior to sieving.
The air- or oven-dried soil is then pulverized using a mortar and rubber-
tipped pestle. Several problems which exist with this method are discussed
below.
Large reductions may occur in the liquid limit as a result of oven drying and
somewhat smaller changes occur in the plastic limit. As the plasticity index
is the numerical difference between the liquid limit and plastic limit, the
plasticity index may decrease by a rather large amount. Data published by
Eden (1959) on a wider range in soil types indicated an increase in liquid
limit of some shales upon air drying and a decrease on oven drying. It may be
that air drying produces a more thorough breakdown of the structure of the
shales. Oven drying apparently resulted in irreversible dehydration of the
shale.
If the soil is dried prior to performing the Atterberg limit, it may take some
time for the soil to rehydrate. Generally, as the "tempering time" increases,
the liquid limit will decrease until finally leveling off at a constant
value. For most plastic clays, the tempering time may take up to 16 hours.
Air drying or oven drying tends to make highly plastic soils extremely hard.
Therefore, when an overall soil sample is pulverized, the less plastic materi-
al breaks down first. As pulverizing the soil by hand is difficult, as soon
as sufficient material has been ground past the No. 40 sieve, the test will
proceed. Because the less plastic material breaks down last, it tends to be
selected out of the sample.
As can be seen from the above discussions, the results of the Atterberg-1imit
tests are dependent upon test methods and the techniques of the operators.
Therefore, test results can vary considerably between testing laboratories.
It should also"be noted that due to the high degree of disturbance inherent in
Atterberg limit testing, in situ physical properties of the soil may be
different. Atterberg limits are, however, a good indicator of soil physical
properties.
4-59
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4.3.2.2 Permeability Tests
As discussed in Section 1.2, flow in saturated soils is governed by Darcy's
Law:
q = kiA
where:
q = rate of flow
k = hydraulic conductivity
i = Ahi = hydraulic gradient
AL
Ah = difference in heads at the two ends of soil sample
AL = length of soil sample in direction of flow
A = total cross-sectional area of soil sample
Theoretically, Darcy's Law says that seepage is proportional to the hydraulic
gradient for a unit area with the constant of proportionality being the hy-
draulic conductivity (coefficient of permeability).
The hydraulic conductivity for a given soil is dependent upon a large number
of variables such as particle size, grain size distribution and orientation,
and density. The best way to determine the permeability of a soil is by
conducting the permeability test on a soil sample having:
1. The same particle size,
2. The same void ratio,
3. The same composition,
4. The same structural arrangement of particles, and
5. The same degree of saturation.
While it is impossible to reconstruct conditions in the laboratory which match
all the conditions of the in situ natural soil, use of a relatively undis-
turbed soil sample in the permeability test is a step in the right direc-
tion. Obtaining an undisturbed sample which is representative of the in situ
soil conditions is in itself very difficult.
Measurement of the permeability of the soil is done by constructing a test
arrangement which measures a flow rate through a soil sample of a known degree
4-60
-------
of saturation under a known hydraulic gradient. The coefficient of perme-
ability (k) is then back-calculated from these measurements. Two standard
test methods, the constant head test and the falling head test, are typically
utilized in conducting the permeability tests.
In the constant head test, the hydraulic gradient is maintained at a constant
value throughout the test, and a total volume of flow, q, is measured during a
time period, t. The problem with the constant head test is that at low values
of head in fine-grained soils, the volume of flow may be so small that it
becomes difficult to reliably measure.
Usually, for fine-grained soils, a falling head test method is used in which
the change in head in a volumetric tube is measured for a time period, t. The
volumetric tube will have a small cross sectional area; therefore, a relative-
ly small change in volume and flow quantity will result in a significant
change in the position of the water level in the tube. Even in a falling head
test, the testing time may become lengthy under small heads. The testing time
may be increased by superimposing an air pressure on top of the water thus
increasing the hydraulic gradient. Figures 4-31 and 4-32 show a permeameter
cell and pressure board for performing permeability tests.
A state-of-the-art paper written by 01 sen and Daniel (1979) presents a de-
tailed discussion of the effects of various test procedures on the measured
value of the coefficient of permeability. Material for the following discus-
sion comes primarily from this reference.
As indicated previously, it is difficult to obtain an undisturbed sample which
is representative of the mass in situ soil conditions. The field sampling
process typically imparts a major degree of disturbance as does sample
handling in the laboratory. Unrepresentative sampling and sample selection
represents the largest source of error in laboratory tests. Natural, in situ
soil characteristics such as fissures, roots, sand lenses, etc., which con-
tribute greatly to the overall mass permeability characteristics of the
strata, also cause the most difficulty in sample preparation for the labora-
tory tests. The least difficult samples to prepare are the intact, cohesive
samples, which are also the most impervious. In the setting of a commercial
4-61
-------
Quick-Connect
Top Plata
Clamping
Rod
Baaa Lag
Flow Out to Call
Praaaura Board
Call Wall
Flow Out
Pluggad
Figure 4-31. Permeameter Cell
4-62
-------
PRESSURE BOARD
To Cell Pressure Port
or Cell Flow-In Port
or Cell Flow-out Port
Figure 4-32. Pressure Board.
To Pressure
Regulator
4-63
-------
testing laboratory, the tendency to select the "easiest" sample to trim tends
to selectively limit the testing to the impervious samples. In addition to
the selectivity of lab testing, other errors introduced in the sample pro-
cedure are:
1. Voids created at the sides of the samples, and
2. Smear zones created on the face of the sample.
Changes in laboratory permeability can occur with differences in the permeant
which is used. The use of distilled water can alter the pore water chemistry
of clay samples, resulting in induced swelling and reduced permeability.
Figure 4-33 indicates the effect of distilled water. The most reliable test
results can be achieved by permeating either the natural ground water, or
representative samples of the expected waste liquid through the sample. If
these alternatives prove to be impractical, then tap water should be utilized.
As the test methods presented in this discussion address saturated sample
conditions, the presence of air in the sample can have an effect on the test
results. Air bubbles in the sample effectively reduce the void space that can
be occupied by water and thus reduce permeability. As air bubbles are pushed
out of the sample, the permeability can increase significantly.
An increased hydraulic gradient to decrease testing times can affect some
samples. Although theoretically, the coefficient of permeability is a con-
stant, some researchers have found that k increased as the gradient increased
(Schwartzerdruber, 1963).
Many laboratory test results are corrected to a standard temperature to
account for viscosity changes in the pore fluid. The effect of temperature
can be seen in Figure 4-34. For the typical range in temperatures expected in
a normal laboratory or field setting, this correction is not absolutely neces-
sary.
The orientation of the sample can significantly affect the test result. The
in situ horizontal permeability, kh, will, in many cases, be much higher than
the vertical permeability, kv. Measurement of horizontal permeabilities can
be very difficult, therefore, most laboratories measure only kv.
4-64
-------
o
0)
E
o
03
(D
E
i_
CD
CL
Permeant: Distilled Water
Sample No. 2
Permeant ••
Natural Pore Water
Sample No. 7
20 40 60 80
Cumulative Inflow, cc
100
Figure 4-33. Influence of Using Distilled Water
(From Wilkinson, 1969)
4-65
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KT=21°
0
20
KEY
• Taylor Marl
-t- Kaolini te
* Tokyo Silt
Relationship Predicted
by Viscosity Correction
Average Measured
Curve
_L
30 40 50
Temperature (°C)
60
Figure 4-34 .
Effect of Temperature on Permeability. Permeabilities
at temperature t (Kj) are normalized with respect to
the measured permeability at 25°C. (Colson & Daniel,
1979)
4-66
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At best, laboratory test results are qualitative indicators of soil perme-
ability. Provided reasonable test procedures are followed, the typical labo-
ratory tests will indicate the order of magnitude of the permeability. As
typical soil waste migration rates are small magnitudes to begin with, an
order of magnitude accuracy in the laboratory test results is normally suffi-
cient for prediction of migration rates to a suitable accuracy. If field
investigations reveal that a site is located in unconsolidated, sandy depos-
its, then laboratory permeability testing should be supplemented with field
permeability testing.
4-67
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5.0 HEALTH AND SAFETY WITH RESPECT TO GROUND WATER INVESTIGATIONS
-------
5.0 HEALTH AND SAFETY WITH RESPECT TO GROUND WATER INVESTIGATIONS
A fundamental policy of all ground water contamination investigations is to
provide a safe and healthful work environment for all personnel involved.
It is both a moral obligation and sound business practice to prevent accidents
(in that accidents can cause personal injuries or illnesses and property
damage). No phase of operations or administration should be of greater im-
portance than injury and illness prevention. Safety should take precedence
over expendiency or short cuts. Every attempt should be made to reduce the
possibility of accident occurrence. Safety, good industrial hygiene prac-
tices, and loss prevention are the direct responsibility of all levels of
management.
The statements above express a general attitude towards Health and Safety that
should be implemented by all personnel involved in ground water investiga-
tions. The issue of Health and Safety should be taken much further than this
general concept. Detailed, job-specific, Health and Safety procedural plans
should be devised for all major undertakings.
Inherent problems arise from the requirement of job-specific Health and Safety
plans. There is often little site-specific information available, and plans
are frequently written which are too complex for the site being studied. The
following discussion is presented to illustrate the need for good Health and
Safety programs as well as discuss some of the problems created by Health and
Safety plans.
5.1 JOB-SPECIFIC HEALTH AND SAFETY PLANS
Job-specific Health and Safety plans generally include discussions on both
universal safety practices as well as specific job-related practices. Several
items are briefly described below as they relate to field investigations.
5.1.1 Assignment of Responsibilities
Specific duties and responsibilities are designated to the individuals direct-
ly involved in the job. Generally, a Health and Safety Supervisor is directly
involved in writing the Health and Safety plan prior to job start-up and is
5-1
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on-site during job start-up and during critical functions through comple-
tion. Enforcement of all other daily on-site Health and Safety procedures are
the responsibility of assigned field personnel including Technicians, Project
and Site Managers and Field Engineers/Scientists. Normally, Health and Safety
specialists are not utilized in areas where the staff is fully familiar with
the site and its potential hazards.
5.1.2 Employee Training and Information
Personnel directly involved in potentially hazardous on-site activities should
be required to complete some approved form of site specific Health and Safety
training. Site-specific training and information generally includes about
four hours of safety training conducted in the field by the Health and Safety
Supervisor at the beginning of the job. In addition, abbreviated safety
meetings (tailgate safety meetings) are then conducted by the appointed field
safety supervisor prior to the beginning of (each days) activities. Figure 5-
1 is a typical form used to record safety meeting participation. All persons
involved in hazardous waste work should also have completed a minimum of 40
hours of non-site specific Health and Safety training and should be enrolled
in a medical monitoring program.
5.1.3 Employee Decontamination
Generally, on-site decontamination facilities will include decontamination
line facilities consisting of separate wash tubs for hands, face and boot
cleansing, waste containers for soiled tyveks and gloves, and a storage area
for equipment. Emergency eye wash/shower facilities are sometimes set up at
small sites but at those sites where the potential contamination is low, they
are not usually utilized.
5.1.4 Personal Protective Equipment and Procedures
When working in hazardous or potentially hazardous areas, the minimum required
equipment includes disposable tyveks, protective gloves, and safety glasses.
Where working around heavy equipment, hard hats and protective steel toe boots
are also necessary. When atmospheric exposure levels exceed recommended
breathing levels, respiratory protection is required. Respiratory protection
is provided primarily through the use of half-face or full-face forced air
respirators with applicable filter cartridges. "Positive-pressure" filter
5-2
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Division/Subsidiary
Date
Customer
Specific Location
Type of Work
Chemicals Used
Facility
Time_
Job Number
-Address:.
Protective Clothing/Equipment.
SAFETY TOPICS PRESENTED
Chemical Hazards-
Physical Hazards-
Emergency Procedures.
Hospital / Clinic
Hospital Address
Special Equipment
Phone (
Paramedic Phone ( )
Other
ATTENDEES
NAME PRINTED
Meeting conducted by:
Supervisor
NAME PRINTED
SIGNATURE
SIGNATURE
Manager.
Figure 5-1. Tailgate Safety Meeting Form
5-3
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respirators such as the RACAL units are also used. Although less frequently
needed, the use of self-contained breathing apparatus can also be required if
exposure levels are excessive.
5.1.5 Regulated Areas
To prevent the spread of contamination and limit personal exposure, potential-
ly hazardous ground water investigation sites are generally divided into three
delineated zones.
1. Contaminated Zone - This zone includes the actual
areas of contamination and has the highest potential
for contaminant exposure.
2. Contamination Reduction Zone - This zone includes the
areas immediately surrounding the Contamination
Zone. It is in this area that the decontamination
facilities are installed.
3. Clean Zone - This zone covers all area outside of the
contamination reduction zone.
5.2 GENERAL WORK PRACTICES
Safe and healthy work practices are extremely important during field investi-
gations. Through past experiences and training, the personnel designated for
field activities should become very familiar with general safe and healthy
work practices.
5.2.1 Personal and Ambient Air Monitoring
Air monitoring equipment generally used on-site includes such devices as the
HMD photoionization meter, draeger tubes, and explosimeter. The HNU is usual-
ly the primary means for determining atmospheric exposure to on-site organic
contaminants. HNU readings are recorded periodically during field activities,
generally by the Field Engineer/Scientist.
5.2.2 Emergency Procedures
A general description of supplemental emergency response procedures is usually
included in the Health and Safety plan. Procedures are outlined for specific
situations such as fires, spills, worker injury, etc. Emergency procedures
are discussed in the field prior to job start-up. Emergency phone numbers,
hospital locations, first aid kits, fire extinguishers and other safety equip-
5-4
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ment are obtained and located in a readily accessible location. Figure 5-2 is
a typical form posted at locations where site work is in progress.
5.3 PROBLEMS ASSOCIATED WITH HEALTH AND SAFETY PROGRAMS
The following section discusses some of the problems that seem to be inherent
to the process of writing a Health and Safety plan which is realistically
implementable in the field.
A major problem associated with Health and Safety plans is the fact that the
plan writer's perspective is different from the perspective of the people
involved in job plan implementation. Each year clients place more and more
emphasis on a potential contractors Health and Safety program as a measure of
the companies qualification for certain jobs. In addition to this, many
companies' Health and Safety programs have become very "liability" oriented.
This increased "political" attention and liability concern has resulted in an
attempt by Health and Safety plan writers to become as thorough and as de-
tailed as possible, attempting to address and provide procedural requirements
for every possible health and safety hazard that may be encountered on-site.
Theoretically this is fine, however, in reality what frequently happens is the
Health and Safety plan becomes so rigid, time consuming, costly, and compli-
cated that it can no longer be effectively implemented in the field.
Field personnel generally do not posses the "political" or "liability" per-
spective towards the Health and Safety issue. These people are simply con-
cerned with getting the job done safely and efficiently. As stated earlier,
the people designated for field work should be Health and Safety qualified
through experience and training. In addition to enforcement of prescribed
Health and Safety procedures, decisions concerning day to day activities
should also be the responsibility of the field personnel. Health and Safety
plans should be written to provide Health and Safety procedures for known
and/or expected hazards but should also allow for easy amendment by qualified
field supervisors.
A second problem occurring with respect to job-specific Health and Safety
programs is one of insufficient time. Generally, a somewhat "generic" Health
and Safety plan is drawn up and submitted with the work plan when a job pro-
5-5
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EMERGENCY NUMBERS
Ambulance...
Doctor...
Hospital[[[
Fire Dept......................................... ...........!................
Police ......................................'...................................
Sheriff
U.S. EPA (24 Hour Hotline) ........800-424-8802
Chemtrec. ......................800-424-9300
National Poison
Control Center 404-588-4400
UTILITY NUMBERS
Electric Co ...........
Water Co '......
Gas Co
-------
posal is written. A more detailed, job-specific Health and Safety plan is
written up only after the job has been secured. This often creates a problem
with respect to devising a complete, job-specific Health and Safety plan
before the work begins. For this reason, Health and Safety plans often become
"cut and paste" versions of plans previously written for other jobs. Admit-
tedly, there is abundant "general" health and safety information and even some
job-specific information that can be transferred from one job to the next,
however, unnecessary procedures often end up being transferred. Once entered
into the Health and Safety plan, it is then the burden of the field personnel
to implement them.
The final problem discussed here is the fact that often the people involved in
writing the Health and Safety plan have very little knowledge of actual field
operations. Many times procedures are outlined in Health and Safety plans
that unnecessarily hinder field activities and can even create dangerous
situations. An example of this can be taken from a health and safety plan
that required all personnel involved in field activities to wear goggles for
eye protection rather than regular OSHA approved safety glasses. Goggles
restrict vision more than regular safety glasses and fog up easily during hot
weather. There may not have been a hazard at the site that justified the use
of goggles instead of safety glasses, yet the difference between a full day in
goggles compared to a full day in glasses in enormous. Obviously the person
writing the plan had not spent many days drilling in 95 degree weather in
goggles. Again, to prevent problems such as these from occurring, Health and
Safety plans should be written in such a manner as to address and provide
information and procedures for any known and/or expected hazards, but the
responsibility of day to day health and safety decisions should be placed on
qualified field supervisors.
5-7
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6.0 SAMPLE INTEGRITY
-------
6.0 SAMPLE INTEGRITY
The integrity of samples collected for the purpose of chemical analysis is
extremely important to the validity of the analysis obtained. When proper
procedures are followed during sampling, storing and transporting of samples,
their integrity can be preserved. This section discusses procedures that
should be followed during these events.
6.1 SAMPLE COLLECTION AND HANDLING
6.1.1 Decontamination and Sampling Procedures for Soils
The prevention of cross-contamination between samples is of critical impor-
tance during soil sampling operations. The sampling procedures followed must
allow samples to be collected without coming into contact with outside contam-
inant sources. Recommended decontamination and sampling procedures are dis-
cussed below:
1. Prior to drilling, all drilling equipment should be
checked for possible contaminant sources such as oil
or grease leaks, hydraulic fluid line leaks, and pos-
sible air compressor oil emissions. Any problem areas
should be repaired.
2. Prior to drilling, all equipment including drill bits,
drill rods, augers, hand tools, and sampling equipment
should be cleaned, preferably with a high temperature,
high pressure soapy water, then rinsed with high
temperature, high pressure clean water. In addition,
all sampling equipment should be rinsed successively
with distilled water, methanol or hexane, and finally
with distilled water or deionized water again. Alter-
nate methods may be required based on site-specific
conditions.
3. After cleaning, all sampling equipment should be
stored in a clean area to reduce the possibility of
contamination prior to use. All decontaminated sam-
pling equipment should be handled in such a manner as
to preserve cleanliness (i.e., don't handle equipment
while wearing gloves used to change drill rig oil or
add hydraulic fluid, etc.).
4. After obtaining a sample, the sample should be ex-
truded from the sampling device into a sample collec-
tion tray with minimal handling. Personnel handling
the samples should wear clean, disposable gloves such
6-1
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as latex surgical gloves. Job-specific analytical
requirements may not necessitate replacement of the
disposable gloves between each sample collected to
minimize possible cross-contamination between samples,
however, it is a good practice. As a minimum, the
gloves should be changed between drill locations.
5. Select portions of the sample should be retained in
containers compatible with the intended analysis.
Site specific requirements may necessitate the use of
teflon lined lids and/or other preservative measures
and the samples should be collected in accordance with
these requirements. The sample jars should be ade-
quately marked for identification at the time of col-
lection. Marking should be on a tag or label attached
to the sample container and should include as a mini-
mum:
• Project name and number
• Unique sample number
• Sample location (e.g., boring, depth or sampling
interval, and field coordinates)
• Sampling date
Individual performing the sampling
• Preservation or conditioning employed
6. After sample collection, the used sample tubes, col-
lection trays and other sampling equipment should be
stored in a separate area prior to reuse until decon-
tamination has been performed.
In some investigations, such elaborate decontamination may not be required.
For instance, samples collected in Shelby tubes are approximately 18 inches
long by 2 inches diameter. If the sample was collected in a "dirty" sampling
tube only the outside edges of the core would be "dirty" or potentially con-
taminated. The outside areas could be cut or trimmed off. In addition, such
tools as cork borers can be utilized to obtain samples from the interior of
the core. In any event, field investigators should take care in collecting
samples to prevent cross contamination.
6-2
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6.1.2 Collection of Ground Water Samples
The importance of proper sampling of monitor wells cannot be overemphasized.
Even though the well being sampled may be correctly located and constructed,
precautions must be taken to ensure that the sample taken from that well is
representative of the ground water at that location and that the sample is
neither altered nor contaminated by the sampling and handling procedure.
6.1.2.1 Static Water Level Measurements
A static water level should be taken in each well prior to evacuation. This
data is necessary to construct piezometric surfaces to determine the direction
of ground water flow at a given time. The accuracy and precision with which
these measurements are taken are dependent upon the hydrology of the site.
Those areas with relatively horizontal piezometric surfaces demand more accu-
rate and precise measurements. Detailed records of the time and conditions
during measurement are necessary due to potential environmental influences.
Tides (in coastal areas), barometric pressure, and highway or railroad traf-
fic, among others, can cause measurable differences in water levels. In areas
of low hydraulic gradients, these differences can result in projecting wrong
directions of flow. Tapes or carpenter's rules capable of measuring accu-
rately to 0.01 foot should be used. Values should be read in a consistent
manner off of electric lines (E-lines). For instance, depths should consis-
tently be taken from the bottom of the lowest colored band on the Olympic E-
line during the first event (if they were measured from this point on). A
surveyed mark or groove at the top of the casing should be used as a reference
point to eliminate errors due to unevenly cut casing tops. Finally, the
measurement should be taken more than once while at the well to determine
reproducibility. In areas with high gradients, ascertaining reproducibility
and noting possible influences is not as critical.
Decontamination of E-lines between wells may not be necessary because the
minute amount of contaminant introduced into the well should be removed during
purging. However, they should be wiped off with disposal towels dampened with
distilled water. If the water level probe is coated with visible residue, it
should be sufficiently cleaned to remove the visible contamination. This may
include using a non-phospate detergent or an organic solvent followed by a
rinsing of distilled water. The TEGD suggests a more thorough decontamination
6-3
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procedure. In order to further minimize the transmission of contaminants
between wells, measurements can be taken in the least contaminated wells
first.
E-lines are also used to sound the bottom of the wells, primarily to determine
if silting has occurred which may influence the thickness of the unit yielding
water to the well. Enough weight should be on the probe at bottom to keep the
line vertical. Olympic E-lines have weights that can be added to the probe
for this purpose. Brainard-Kilman well probes are heavy enough that they hang
plumb. Where dedicated permanent pumps have been installed, sounding well
bottoms with E-lines may not be prudent. The time and effort required to
remove the pump is not warranted in all cases. Instead, careful attention
should be paid to the turbidity of the water purged from the wells prior to
sampling. If turbidity is increasing compared to earlier sampling events, the
removal of the pump may be called for to confirm that the well is silting up.
6.1.2.2 Detection of Immiscible Layers
Immiscible ''ayers are those with densities less than or greater than ground
water. RCRA suggests that testing for immiscible layers be included as the
initial step in any water sampling plan.
For "floating" immiscible layers to be intercepted and detected in a well, the
well screen must extend above the top of the ground water and into the zone of
the aquifer containing the immiscible layers. To capture sinking layers, the
screen must extend into the aquitard. It should be remembered that the slots
on most PVC screens begin 6 inches from the end of each joint. Care should be
taken in well construction so that the slots actually intersect the horizon of
interest.
Hydrocarbon indicating paste on an E-line can be used to measure the thickness
of a floating immiscible layer. An interface probe may also be used if the
well is accessible for the larger probe. If a permanent pump is installed,
there may not be a large enough port on the well cover to allow access. In
addition, there is probably not enough clearance around the pump to take
readings on sinking layers.
6-4
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If an immiscible layer is detected, a sample should be taken for analysis. A
top-filling bailer or sampling device is the easiest method for collecting a
floating layer. A bottom filling bailer can be used to sample a sinking layer
provided the well is not completed with a permanent submersible pump or suf-
ficient room exists to allow the bailer to pass. In areas where sinking
immiscible fluids are suspected, a sample can be collected within a few min-
utes of turning on the submersible pump is the submersible pump is located
near the bottom of the well.
6.1.2.3 Well Purging
The purpose of well purging is to eliminate stagnant water in the wellbore and
adjacent sand pack which may have undergone chemical alteration, thus allowing
the collection of a sample that is representative of the in situ quality of
ground water near a particular well.
Various methods for determining the necessary extent of well purging have been
recommended. The U.S. Geologic Survey (USGS) has recommended pumping the well
until temperature, pH and specific conductance are constant (USGS, 1976).
Schuller and others recommend calculation of the percent aquifer water pumped
versus time based upon drawdown in the well (Schuller, 1981). The Environmen-
tal Protection Agency (EPA) recommends removal of three well casing volumes
prior to sampling.
The extent of well purging will vary with the hydraulic properties of the
water-bearing unit being monitored. Without proper consideration of the flow
characteristics of the monitored unit, the integrity of the sample collected
after purging could be compromised. Giddings indicates that emptying the
wellbore of a well screened in a low yield unconsolidated aquifer can result
in a steep hydraulic gradient in the sand pack (Giddings, 1984). This steep
hydraulic gradient, in turn, can lead to the addition of clays and silts to
the produced water, turbulent flow into the well, and with turbulent flow into
the well, a possible loss of volatile organics in the produced water. Simi-
larly, wells screened in very low-yield bedrock with fracture flow may also be
bailed dry. If the water-bearing fractures or higher permeable zone is lo-
cated near the static water table, the water will refill the well by cascading
into the wellbore, which will result in the loss of volatile compounds from
the water.
6-5
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Purging of a high yield aquifer that has major water-producing fractures or a
highly permeable unit at the bottom of a screened section in an unconsolidated
aquifer may result in limited purging of water higher up in the wellbore and,
in the case that any monitored species has a specific gravity less than the
formation water, it is likely that it will be detected at "lower levels than
exist in the aquifer.
Removal of stagnant water from the well bore before sampling is necessary to
ensure that a representative sample is obtained. However, equally important
are the hydraulic processes resulting from well purging. In order to minimize
turbulent flow and sample alteration, it is recommended that, prior to prepar-
ing a sampling program, each monitor well be tested to determine the necessary
extent and the appropriate rate of well purging. Determination of the neces-
sary extent of well purging can be based upon equilibration of ground water
indicator parameters during well evacuation. Figure 6-1 indicates changes in
nine analytical parameters with pumping in a well that had been idle for six
months prior to pumping. When pumping began, the partially reduced water
surrounding the pump was discharged first. As pumping continued, formation
waters were drawn into the wellbore and the rate of change in the concentra-
tion of the chemical parameters decreased. Because of the low discharge rate
of this well, the mixing of wellbore water and formation water continued for
45 minutes (Chapin, 1981). In order to obtain a representative sample, the
QA/QC sampling protocol for this well would specify a minimum period of well
evacuation of 45 minutes prior to collection of the sample when using the
existing pump run at the same flow rate used in the test.
6.1.2.4 Sampling Devices
Commonly used sampling devices include electrical submersible pumps, positive
displacement bladder pumps, bailers and suction lift pumps. Choosing a sam-
pling device is dependent upon site-specific criteria including compatibility
of the rate of well purging with well yield, well diameter, limitations in the
lift capability of the device, and the sensitivity of selected monitoring
species to the mechanism of sampling delivery.
It is important to recognize that aeration or degassing of a sample can occur
during withdrawal of a sample from a monitoring well. The introduction or
6-6
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30 45
TIME CMINUTES)
70
(Chap-in, 1981)
Figure 6-1. Concentrations of Chemical Parameters vs. Pumping Time
6-7
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loss of volatile organic compounds or gases (02, ^ CC^, and CH4) in the
ground water sample can affect the ground water solution chemistry of the
sample, and result in the further speciation of both volatile organics and
other analyses of interest. The degree of aeration and/or degassing of the
ground water has been shown to vary with the type of sampling device employed.
A field evaluation of sampling devices was conducted in association with
ongoing remedial action at the Savannah River Plant, Aiken, South Carolina
(Muska, et al., 1986). The electric submersible pump was chosen over various
modified bailers, the bladder pump, and others because of its accuracy, pre-
cision, reliability, its ability to evacuate a well, and its moderate cost.
However, levels of organics at the Savannah River Plant range up to 200,000
ppb. In this case, detection of organics near analytical detection limits (1
to 10 ppb) was not a criteria for choosing a sampling device. Where detection
of organics at low levels is desired, a closer evaluation of the sampling
devices potential for altering the sample may need to be conducted.
Bailers are commonly used both for purging and sampling water from small
diameter, shallow wells due to their relative low cost, portability and ease
of maintenance. A disadvantage of the bailer as a sampling device is the
potential aeration and/or degassing of the sample during sample collection.
The aeration is the result of repeated submergence and removal of the bailer
during sampling, which may result in turbulent flow of water in the well-
bore. Further aeration can occur as a result of pouring the collected sample
out the top of the bailer into the sample bottles. Aeration of a sample when
using a bailer can be minimized by gently lowering the bailer into the water
when collecting the sample. Aeration/degassing can be further reduced by
utilizing a bailer modified to include a bottom draw valve. The device allows
emptying of the bailer at a slow controlled rate, thus avoiding aeration of
the sample, which occurs during decanting. Improvements in sample representa-
tiveness between conventional bailers and bottom draw bailers have been docu-
mented by Barcelona (1984).
Field and laboratory testing of suction lift and gas displacement pumps
indicates that these pumps are consistently below average in terms of the
accuracy of the sample delivered when compared to other devices (Nielsen and
6-8
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Yeates, 1985; Schuller et al., 1981; Barcelona et al., 1984). The suction
lift pump employs application of a negative pressure which can cause degassing
of the water sample. Gas displacement pumps, typically air or nitrogen lift,
can cause gas stripping of carbon dioxide (which results in a change in in-
itial pH of the sample), or gas stripping of volatiles.
6.1.3 Proper Handling of Samples
6.1.3.1 Sample Preservation
Water samples may undergo change with regard to their physical, chemical, and
biological state during transport and storage. In order to preserve the
integrity of a sample after collection, the samples are generally refrigerated
and/or preserved by the addition of acid or alkaline solutions.
In spite of these practices of stabilizing samples, there is a potential for
alteration of a sample during transport and storage. Particular practices and
areas of disparity that may contribute to the variance of water quality during
the sample holding period are:
1. Delaying filtering and preserving of samples until
samples reach the laboratory.
2. Aeration of the sample during filtration.
3. Failure to filter samples prior to the addition of acid
for preservation.
4. The lack of necessary temperature reduction for suc-
cessful stabilization of the sample during transport.
A field experiment has shown that the delay of preservation of samples can
lead to variation in water quality analyses (Schuller, et al., 1981). In the
experiment, multiple samples were collected from one monitoring well installed
at an anaerobic lagoon and one monitoring well installed at an inactive sani-
tary landfill. Once collected, the samples were divided into four sets, the
first set being preserved immediately and the remaining sets preserved 7, 24
and 48 hours after collection, by the addition of acid. Each of the collected
samples were analyzed for calcium, iron, potassium, magnesium, manganese,
sodium and zinc, within the EPA prescribed holding times specified for each of
6-9
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the parameters. Iron showed the most dramatic change in concentration. Seven
hours after collection, the measured concentration of iron in the sample
collected from the well located at the lagoon was .33 mg/1; the concentration
of iron in the sample collected from the same well and preserved immediately
was 11.6 mg/1. The change in iron concentration from the sample collected at
the landfill showed a change in iron concentration from 5.74 to <.08 mg/1
between zero and seven hours after collection and before preservation. Sig-
nificant changes were also noted for magnesium, manganese and zinc.
One possible explanation for the sample alteration is the aeration of the
sample during transfer from the sampling device to the sample bottle or from
the sampling device to a holding vessel prior to filtration, and prior to
fixation of the metals by the addition of acid. Where ground water is in a
reduced state, the addition of oxygen via aeration can cause oxidation of
ferrous iron to ferric iron and subsequent precipitation as ferric hydrox-
ide. Once allowed to form, much of the ferric hydroxide will be removed by
filtering prior to analyses.
A recent laboratory experiment measures the precipitation of iron from a col-
lected sample using different filtration methods and different sampling de-
vices. The filtration methods tested included on-line filtration, vacuum
filtration following transfer from a holding vessel, and the same vacuum
filtration procedure after a 10-minute holding time. Sampling mechanisms used
included a bailer, peristaltic pump, bladder pump, air and nitrogen lift
pumps, and a submersible electrical pump. With each sample mechanism used,
the samples handled by on-line filtration exhibited higher dissolved iron
concentrations than samples transferred to holding containers prior to filtra-
tion. The 10-minute holding period appeared to have no consistent effect on
the concentration of measured iron as compared to immediate filtration from
the holding vessel (Stolzenburg, et a!., 1986). The study indicates that the
turbulence and associated aeration of the sample during filtering can signifi-
cantly alter sample quality. In fact, the study indicates that aeration of
the sample during filtration has at least as much impact on sample quality as
the sampling device itself.
6-10
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Many monitor wells are completed in low yield, clay rich sediments. It is
impractical and in some instances impossible to complete these wells in such a
fashion that water samples can be collected free of sediment. EPA recommends
field acidification of samples collected for metals analysis to a pH less than
2 (EPA, 1982). Acidification of unfiltered samples can lead to dissolution of
minerals from clays in the suspended solids. Table 6-1 indicates that the
measured concentrations of calcium and magnesium in samples acidified prior to
filtration are directly related to the concentration of suspended solids. On
the other hand, concentrations of calcium and magnesium in unacidified samples
show no correlation to dissolved solids (Kent, et al, 1985). This is not to
say that samples should not be acidified, but rather that samples should be
filtered prior to acidification. Otherwise, constituents of interest that may
occur naturally in the formation matrix may be dissolved when acidified re-
sulting in a sample that is not representative of the water contained in the
aquifer.
EPA states the preservation of samples by refrigeration requires that the
temperature of collected water samples be adjusted to a temperature of 4
degrees Celsius immediately after collection and during shipment. In order to
observe the effectiveness of different types of ice in cooling samples and in
order to determine the effort required to maintain sample bottles at 4 degrees
Celsius, the cooling rates of water samples chilled by ice and the temperature
maintenance ability of frozen blue ice were recorded. Ten 250 ml bottles and
twelve 500 ml bottles were filled with tap water. The initial temperatures of
the samples were recorded. Thermisters (electronic thermometers) were in-
serted through small holes drilled in the center of each sample bottle lid.
The bottles were placed in a 48 quart cooler, covered with two (ten pound)
bags of ice, and their temperatures monitored. Readings were taken every 10
minutes until the monitored bottles reached their desired temperature of 4
degrees Celsius. These bottles were transferred to a pre-cooled ice chest
filled with blue ice. As indicated in Figure 6-2, the temperature of the
samples dropped to 4 degrees Celsius within 3 hours. As shown in Figure 6-3,
the blue ice was successful in maintaining the bottles below 4 degrees Celsius
for 24 hours. In contrast, when ambient temperature samples were placed in a
48 quart cooler and covered only with blue ice, the samples did not reach 4
degrees Celsius (Figure 6-4).
6-11
-------
TABLE 6-1. Addition of Acidic Preservative Prior to Filtering
Sample Turbidity
1
2
3
4
5
6
7
8
9
22,000
18,500
9,700
8,600
5,200
3,400
3,100
2,200
1,900
Ca
2,442
1,980
1,452
1,452
915
827
704
453
286
Acidified
Mq
55
54
34
36
33
47
27
33
18
Unacidified
Ca
44
73
95
78
134
284
101
134
78
Mq
18
16
13
15
20
36
19
27
13
All analysis are in ing/l
6-12
-------
25
LU
Q
£20
O
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O
w10
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LU
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0 1.5 3 5 7 9 11 15 18
TIME (HOURS)
24
Figure 6-2. Field Refrigeration of Samples Using Water Ice
T
8 12 16 20
TIME CHOURSD
24 28
Figure 6-3. Bottles Placed in Crushed Ice Chilled to 40°C,
and Transferred to Ice Chest Pre-ChilUd with
Blue Ice.
6-13
-------
25
20
O
o
<» 15
co
^
0
a 10
12
24
Time ChrsJ
36
48
Figure 6-4. Field Refrigeration of Sample Using Blue Ice
6-14
-------
This experiment suggests that when using blue ice to refrigerate, the samples
must be initially chilled using wet ice. Samples can then be transported to
the laboratory in either blue ice or wet ice. However, when using wet ice for
an extended period, additional ice may need to be added to the ice chest to
maintain the recommended 4 degrees Celsius temperature.
In conclusion to this section covering sampling strategy, there are multiple
avenues for sample alteration during collection including the method of well
purging, the device used to sample the wells, and the method of sample preser-
vation. It has been demonstrated that the alteration of a sample that occurs
during sampling may be more or less quantified by collecting replicate samples
a few days apart, i.e., collecting samples from the monitoring system on
Monday and collecting another set of samples on Thursday, and comparing the
variability in analytical data between the two sets. When the variation is
significant, the well sampling protocol should be tested in the field, e.g.,
comparing variations in analyses resulting from different methods of filtra-
tion, to determine the source or sources of sample alteration.
6.1.3.2 Chain-of-Custody
One consideration for data resulting from chemical analyses is the ability to
demonstrate that the samples were obtained from the locations stated and that
they were not tampered with before they reached the laboratory. Evidence of
collection, shipment, laboratory receipt, and laboratory custody until dispos-
al must be documented to accomplish this. Documentation should be accom-
plished through a chain-of-custody form (Figure 6-5) that lists each sample
and the individuals responsible for sample collection, shipment, and
receipt. A sample is considered "in custody" if it is:
• In a person's actual possession
• In view, after being in physical possession
• Locked so that no one can tamper with it, after having
been in physical custody
• In a secured area, restricted to authorized personnel.
The chain-of-custody form should be signed by each individual who has the
samples in their possession.
6-15
-------
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6-16
-------
Multipart chain-of-custody forms may be used so that a copy can be retained by
the individual shipping the sample.
6.1.3.3 Preparation, Packaging, Handling and Shipping
Samples should be placed in containers compatible with the intended analysis
and properly preserved. Also, control of samples must consider the time
interval between acquiring the sample and analysis (holding time) so that the
sample is representative.
Samples to be shipped off site for chemical analysis are normally placed in
ice chests and packed to prevent breakage during shipment. The ice chest
should be sealed, addressed, identified, and placarded as appropriate.
To provide necessary information to the laboratory, a Request for Analysis
form should be completed by the field personnel, or other project personnel if
appropriate, and included with the chain-of-custody record. It is imperative
that the Request for Analysis be provided so that analytical requirements are
defined and sample holding times are not exceeded.
Transportation should enable samples to arrive at the laboratory in time to
permit testing in accordance with established sample holding time and project
schedule.
In many investigations, the samples may be transported in private vehicles by
the person collecting the samples. At other times, samples may be sent by
common carriers. Frequently, commercial airlines or bus companies will not
accept samples for shipment. Most samples should be shipped by Federal Ex-
press, Purolator, or other non-passenger earring transports.
6.1.3.4 Sample Storage
In general, storage of sample should be adequate to prevent damage, loss, or
unacceptable deterioration. Soil samples collected for chemical analysis may
require specific preservation measures to insure sample integrity. Samples
should be stored in a manner which fulfills the sample-specific preservation
requirements. This may require use of teflon lined lids, certain sample
6-17
-------
temperatures, attention to holding times, and use of chemical preservatives.
Samples should not be subjected to excessive amounts of moisture or large
temperature variations. The samples should not be allowed to freeze if in
situ characteristics to be determined by testing could be affected. Indoor
storage should be employed, where possible, to provide a controlled environ-
ment.
6.1.4 RCRA Sampling versus Real World Sampling
After examining a monitor well sampling plan or reading through the RCRA
guidance document on sampling and analysis, it appears that following the
careful path established by the EPA provides an appropriate procedure to
achieve accurate analytical results. This is the intention of RCRA, but when
the procedures are put into action in the field, the scientist or engineer
involved comes to a new understanding of what is possible and what is neces-
sary to assure that the samples collected accurately represent the conditions
of the water in the sampled aquifer. The preceding sections have addressed
specifics involved in a sampling program. A few more examples from actual
sampling situations follow in order to briefly ellaborate.
RCRA specifies that soil should be prevented from contaminating the sampling
equipment or from entering the monitor well. Basically this may be impossible
to accomplish. Wind and rain are the two major factors which create problems
in this area. If the field personnel has to hike through mud or the wind
keeps blowing dirt through the air around the sampling site, it is impossible
to eliminate the entrance of dirt into the well or the sample. The placement
of a drop sheet to prevent contamination of the equipment from the ground
around the well may not be very effective. To begin with, the sheet must be
anchored down. Simple tasks like this become very difficult when considering
the location of most monitor wells. If enough rocks or heavy objects are
found to prevent the drop cloth from blowing away, then it is difficult to
prevent soil from getting on top of the drop cloth. If it is raining or has
rained recently, it is easy to understand that this goal becomes difficult or
impossible.
Once the drop cloth is in place, the next obstacle is to measure the water
levels and then decontaminate the equipment involved. The decontamination
6-18
-------
procedures outlined in RCRA guidance are unrealistic given that most sampling
programs only require one person in order to accomplish all of the other
procedures involved. Two people are normally required to accomplish the tasks
required to comply with the RCRA decontamination guidelines. The intentions
of these procedures are obvious, but their impracticality and cost outmeasures
their effect on the outcome of the analytical results. In most wells only
about 1 foot of the E-line will actually enter the water. After purging three
casing volumes of water from the well, the effects of any slight cross-
contamination should be undetectable.
Disposal of the water purged from a monitor well creates a great problem.
RCRA guidelines recommends disposal of purged water in 55-gallon drums. The
acquisition of large storage drums, their transportation, and their eventual
disposal is a major task to accomplish. If purging involves hand bailing, the
weight of the bailer creates another problem. Not only are stainless steel
bailers expensive, they are heavy. Larger bailers for large diameter wells
are also heavy.
6.2 SAMPLE ANALYSIS AND DATA INTERPRETATION
During the past several years, hundreds of thousands of ground water samples
have been collected from ground water monitoring wells and the results re-
ported to the regulatory agencies. The results of these analyses are most
frequently interpreted by individuals other than those who performed the
analysis. Many of these people have not been inside an analytical laboratory
and may not understand the limitations of the equipment and/or methods used to
analyze the water. Hence, they do not have the education or experience to
understand the limitations of the analysis. One method that has been utilized
is a statistics approach to try to view data strictly from an "objective
approach." Unfortunately, most geologists and engineers do not have an ade-
quate knowledge of statistics; therefore, this approach has limitations.
The basis for interpreting analytical results must include a knowledge of
monitor well construction, geohydrology, geochemistry, and analytical tech-
niques. Also important is an understanding of the factors affecting the
validity of a set of data and the limitations on data interpretation.
6-19
-------
6.2.1 Use of Blanks
In addition to the problem of equipment limitation, other factors can influ-
ence the results of lab analysis. One way of attempting to determine these
effects is with the use of travel blanks, field blanks and method blanks.
Travel blanks are samples of distilled water placed in bottles and sealed and
sent to the sample location and returned to the laboratory unopened. These
are then analyzed for selected compounds. Those found are generally common
laboratory chemicals used in the laboratory. Table 6-2 shows the results from
a recent Arkansas investigation.
Another QA/QC technique is the use of field blanks. Distilled water is taken
in a sealed bottle to the field and during a routine sampling event is de-
canted into another bottle. This provides an indication of possible effects
of adsorption from the air or the existence of sample handling problems.
Table 6-2 also contains the results for field blanks for the Arkansas Investi-
gation.
Method blanks are used to determine if there are errors caused by the labora-
tory method and/or if the chemicals used in the method contain items of inter-
est. Tables 6-3 and 6-4 show the results from two separate laboratories
working on the same project. Many compounds are commonly found in analyses of
this type. Some more of the frequently detected compounds in method blank
analysis are indicated in Table 6-5.
6.2.2 Choice of Analytical Parameters
When conducting a contamination study, decisions must be made as to what
parameters will be analyzed for in the laboratory testing program. For the
most part, a laboratory only reports to you the value for compounds for which
you ask and/or pay. For example, if an analysis for benzene, toluene, and
ethylbenzene was requested, the lab may only report values for these compounds
and not report the presence of other chemicals that may have been found during
the analysis for the requested items. During the early 1980's, many companies
conducting contamination studies would ask for priority pollutants analysis of
the ground water and would frequently obtain laboratory analysis reports which
stated that none were detected. It was frequently concluded that the site was
6-20
-------
TABLE 6-2
TRAVEL AND FIELD BLANK RESULTS
ARKANSAS SUPERFUND SITE
Travel Blank
Methylene Chloride
Acetone
2-butanone
Field Blank
Methyl ene Chloride
Acetone
2-butanone
Chlorotom
Range
(ug/1)
1-3
4
1
2
3-4
2
1
No. Of
Samples
3
3
3
3
3
3
3
No. of Positive
Results
3
2
1
1
2
1
2
6-21
-------
TABLE 6-3
RESULTS OF ORGANIC ANALYSIS OF LABORATORY BLANKS
OKLAHOMA STATE DEPARTMENT OF HEALTH
LABORATORY (MATRIX UNKNOWN)
Compounds Found
Di-N-butylphthalate
Bis (2-Ethylhexyl) phthalate
2,4,6-Trichlorophenol
Methylene Chloride
Trichloroethane
Toluene
Chloroform
1,1,1-Trichloroethane
Range
yg/1 (ppb)
1.8-170
440-10,000
150
3.1-22
2.3-17
3.1-4.7
6.3-7.1
3.4-6.5
No. of
Analysis
8
8
8
11
11
11
11
11
No. of Positive
Results
2
2
1
11
10
3
8
2
TABLE 6-4
RESULTS OF ORGANIC ANALYSIS OF LABORATORY BLANKS*
GULF SOUTH RESEARCH INSTITUTE
NEW ORLEANS, LOUISIANA
Compounds Found
Methylene chloride
Acetone
Chloroform
2-Butanone
Di-N-butylphthalate
Acetom'trile
Bis(2-Ethylhexyl) pthalate
Hexane
Range
ug/Kg (ppb)
1,600-10,000
3,500-7,300
3,100-3,300
2,300-7,700
7,800
2,000-10,000
3,600-3,800
5,000
No. of
Analysis
11
11
11
11
4
11
4
11
No. of Positive
Results
7
9
2
7
1
11
2
2
* Matrix Methanol
6-22
-------
TABLE 6-5
ORGANIC COMPOUNDS FOUND IN METHOD BLANK ANALYSIS
Di-N-butylphthalate
2,5-dimethylfuran
Acetic acid, 1-methylethyl ester
Heptane, 2,3-dimethyl octane
Hexadecanoic acid
Butyl benzylphthalate
Bis (2-ethylhexyl) phthalate
2-hexanone
Phosphoric acid, 2 ethylhexyl-diphenylester
2-butanone
Squalene
N-nitrosodiphenylamine
Methylene chloride
Chloroform
6-23
-------
not leaking because no priority pollutants were found in the ground water.
Later studies that have concentrated on waste-specific chemical analyses have
found the waste-related compounds to be present in ground water systems which
were previously thought to be "clean." Those parameters were not previously
requested, therefore, were not reported.
In recent times, regulatory agencies have begun to ask for Appendix VIII or
IX, Skinner list, or other more comprehensive lists of analyses. Although
this is certainly a step in the right direction, the absolute application of
these "guidelines" can waste tremendous amounts of money. In a recent inves-
tigation in Arkansas, over 145 samples of soil, waste and ground water were
collected and analyzed for hazardous substance lists of volatile organics, and
acid and base/neutral (ABN) extractables. Of these analyses, only four major
volatile organics and three ABN extractables were detected on a routine
basis. A review of the profiles of waste buried at the site, and/or collec-
tion of several samples of the waste and performance of a comprehensive analy-
sis could have lead to the identification of the major contaminants. Over
$81,000 worth of analyses could have been saved, by having only selected
analyses performed. Tables 6-6, 6-7, and 6-8 list the major organic compounds
frequently analyzed for during hazardous waste site studies. The tables also
list the general sources of these organics. A review of these tables and
suspected wastes can lead to a significant reduction in anlaytical cost.
6.2.3 Detection Limits
Over the last several years, analytical methods have improved and where con-
centrations of chemicals or ions were reported in parts per million, they are
now reported in parts per billion. Parts per trillion analysis is currently
possible for many elements and compounds. However, detection limits are also
a function of the amount of time that one has to analyze samples. Most
analytical work today for ground water contamination is performed at
commercial laboratories. Hundreds of samples are analyzed on a daily basis.
The labs do not charge sufficiently for each analysis to treat routine samples
as individual research projects. Most major laboratories today are EPA
certified or certified by a state agency. These laboratories follow general
QA/QC programs that meet state and federal standards and routinely analyze
blanks, duplicates and spikes as part of their programs. However, samples
6-24
-------
TABLE 6-6
VOLATILE HAZARDOUS SUBSTANCE LIST COMPOUNDS
**acetone - paints, varnishes, lacquers, sealants, adhesives, cellulose ace-
tate solvent; natural microcomponent in blood and urine; common laboratory
solvent used to extract solid waste samples, and dry glassware.
benzene - motor fuels; solvent for fats, inks, oils, paints, plastics, and
rubber; photogravure printing; mfg. of detergents, explosives, Pharmaceuti-
cals, and dye-stuffs.
*benzo (a) pyrene - by-product of combustion; sources: coal refuse piles,
outcrops, abandoned coal mines, coke mfg., external combustion of anthra-
cite coal.
bromomethane (methylbromide) - soil and space fumigant; organic synthesis.
2-butanone (methy ethyl ketone or MEK) - resin solvent; paint strippers; wax
production; cements; adhesives; cleaning fluids.
*carbon disulfide - mfg. rayon, cellophane, carbon tetrachloride, rubber
chemicals, soil disinfectants, electronic vacuum tubes; solvent (phor-
phorus, sulfur, bromine, selenium, fats, resins, rubbers); mfg. grain
fumigants, soil conditioners, herbicides; paper mfg.; pharmaceutical mfg.
carbon tetrachloride - fire extinguisher mfg.; dry cleaning operations; mfg.
of refigerants, aerosols and propellants; mfg. of chlorofluoromethanes;
extractant, solvent; veterinary medicine; metal degreasing.
bromodichloromethane - fire-extinguisher fluid ingredient; solvent (fats,
waxes, resins); synthesis intermediate; heavy liquid for mineral and salt
separations.
bromoform - pharmaceutical mfg.; ingredient in fire-resistant chms.; gage
fluid; heavy liquid in solid separations based on differences in specific
gravity; geological assaying; solvent for waxes, greases and oils.
chlorobenzene - solvent recovery plants; intermediate in dyestuffs mfg.; mfg.
aniline, insecticide, phenol, chloronitrobenzene.
chloroethane (ethyl chloride) - mfg. of TEL and ethylcellulose; anesthetic;
organic synthesis; alkylating agent; refrigeration; analytical reagent;
solvent.
2-chloroethylvinylether - mfg. of anesthetics, sedatives, and cellulose
ethers.
chloroform - mfg. of refrigerant and plastics; solvent.
chloromethane (methylchloride) - mfg. silicones, tetraethyllead, synthetic
rubber and methyl cellulose; refrigerant mfg.; mfg. fumigants; low tempera-
ture solvent; catalyst carrier in polymerization; medicine; extractant;
propellant; herbicide.
6-25
-------
TABLE 6-6
Continued
cis-l,3-dichloropropene - soil fumigant; nematocide.
dibromochloromethane - mfg. fire extinguishing agents; mfg. aerosol propel-
lants; mfg. refrigerants; mfg. pesticides; organic synthesis.
1,1-dichloroethane - vinylchloride; chlorinated solvent intermediate; coupling
agent in gasoline; paint, varnish and finish removers; metal degreasing;
ore flotation.
1,1-dichloroethene (1,1-dichloroethylene) - adhesives; component of synthetic
fibers.
1,2-dichloroethane (ethylenedichloride) - mfg. of vinyl chloride; mfg. of
tetraethyllead; intermediate insecticide fumigant; tobacco flavoring;
constituent in paint, varnish and finish removers; metal degreaser; ore
flotation.
1,2-dichloropropane - intermediate for perchloro-ethylene and carbon tetra-
chloride; lead scavenger for antiknock fluids; solvent; soil fumigant for
nematodes.
ethylbenzene - styrene mfg.; solvent, asphalt, gasoline, and naphtha constitu-
ent.
2-hexanone (methylbutylketone) - solvent.
methylene chloride - paint stripping; degreasing; aerosols; synthetic fibers
mfg.; refrigerant; textiles; coatings; blowing agent; common laboratory
solvent used extensively in extraction of sample for GC/MS.
4-methyl-2-pentanone (MIBK or methylisobutylketone) - solvent for paints,
varnishes, nitrocellulose lacquers; mfg. of methylamylalcohol; denaturant
for alcohol.
styrene - mfg. styrene, polystyrene; mfg. synthetic rubber; ABS plastics mfg.;
mfg. resins, insulators; mfg. protective coatings (styrene-butadiene latex,
alkyds).
1,1,2,2-tetrachloroethane - mfg. 1,1-dichloroethylene; solvent for chlorinated
rubber and other organic materials; insecticide mfg.; bleach mfg.; paint,
varnish, rust remover mfg., soil fumigant; cleansing and degreasing metals;
herbicide; alcohol denaturant.
tetrachloroethylene (tetrachloroethene) - organic chemical mfg.; dry cleaning
operations; metal degreasing; solvents for fats, greases, rubber, gums;
mfg. paint removers, printing inks; mfg. of fluorocarbons.
trans-l,2-dichloroethylene (trans-l,2-dichloroethene) - solvent for fats and
phenols; rubber mfg.; dyes and lacquers; perfumes; thermoplastics.
trans-l,3-dichloropropene - soil fumigant; nematocide.
1,1,1-trichloroethane (methylchloroform or chloroethene) - degreaser; dry-
cleaning agent; vapor degreasing agent; propellant.
6-26
-------
TABLE 6-6
Continued
1,1,2-trichloroethane - mfg. 1,1-dichloroethylene; solvent for chlorinated
rubber and various organic materials (fats, oils, resins, etc.).
trichloroethene (trichloroethylene or TCE) - solvent; dry-cleaning agent;
chemical intermediate in the production of pesticides, waxes, gums, resins,
tars, paints, and varnishes.
*toluene - mfg. of benzene derivatives; caprolactam mfg.; saccharin mfg.;
perfumes; component of gasoline; paint and coatings solvent; adhesives
solvent; asphalt and naphtha constituent.
vinyl acetate - used in polymerization processes to produce polyvinyl acetate,
polyvinyl alcohol, and vinyl acetate copolymer. Polymers are used in
adhesives, paints, paper coatings and textile finishes.
vinyl chloride - vinyl monomer in the manufacture of polyvinyl chloride and
other resins; solvent; chemical intermediate.
*xylene - petroleum distillation; coal tar distillation; mfg. terepthalic acid
for polyester; solvent recovery plants; mfg. isophthalic acid, aviation
gasoline; protective coatings mfg.; solvent for alkyd resins, lacquers,
enamels, rubber cement; insecticide mfg.; pharmaceutical mfg.
*Can also occur naturally or associated with coal or coal combustion. Can
also occur naturally or associated with organic deposits such as coal, lig-
nite, peat, etc. Also found in waters associated with these deposits.
**Common laboratory contaminant or lab chemical.
OCommon name appears in parenthesis following compound.
Source: Handbook of Environmental Data on Organic Chemicals, Verschueren, K.
Mass Spectrometry of Priority Pollutants, Middleditch, B., Missler,
S., and Nines, H.
The Merck Index, Windholz, Budavari, Stroumtsos and Fertig
6-27
-------
TABLE 6-7
ACID EXTRACTABLE HAZARDOUS SUBSTANCE LIST COMPOUNDS
benzole acid - food preservative; pharmaceutical and cosmetic preparations;
mfg. of alkly resins; intermediate in the synthesis of dyestuffs and phar-
maceuticals; production of phenol and caprolactam; plasticizer mfg.
4-chloro-3-methylphenol (p-chloro-m-cresol) - external germicide; preservative
for glues, gums, inks, textile and leather goods
2-chlorophenol - organic synthesis
2,4-dichlorophenol - organic synthesis
2,4-dimethylphenol (2,4-xylenol) - intermediate in mfg. of phenolic antioxi-
dants; pharmaceutical mfg.; plastics and resins mfg.; disinfectant mfg.;
solvent mfg.; insecticides and fungicides; rubber chemicals; mfg. poly-
phenylene oxide; wetting agent; dyestuffs; cresylic acid constituent
4,6-dinitro-2-methyphenol - dormant ovicidal spray for fruit trees
2,4-dinitrophenol- used in the manufacturing of dyestuff intermediates, wood
preservatives, pesticides, herbicides, explosives, chemical indicators,
photographic developers, and also in chemical synthesis
2-methylphenol(cresol) - disinfectanct; foot antioxidant; perform mfg.; dyed
mfg.; plastics and resins mfg/ herbicide mfg.; ore floatation; textile
scouring agent; organic intermediate; mfg. of slaicycladehyde; surfactant
4-methylphenol(cresol) - disinfectant; ore floatation agent; intermediate in
the manufacture of chemicals, dyes, plastics, and antioxidants
2-nitrophenol - intermediate in organic synthesis; indicator
4-nitrophenol - intermediate in organic synthesis; production of parathion;
fungicide for leather
pentachlorophenol - mfg. insecticides, algicides, herbicides, and fungicides;
preservation of wood and wood products; mfg. of sodium pentachlorophenate
phenol (carbolic acid, phenic acid) - mfg. of explosives, fertilizer, coke,
illuminating gas, lampblack, paints, paint removers, rubber, asbestos
goods, wood preservatives, synthetic resins, textiles, drugs, pharmaceuti-
cal preparations, perfumes, bakelite, and other plastics; as a disfinfec-
tant in the petroleum, leather, dye and agricultural industries
2,4,5-trichlorophenol - fungicide; bactericide
2,4,6-trichlorophenol - organic chemical industry; pesticide mfg.; mfg. anti-
septics, bactericides, fungicides, germicides; mfg. wood and glue preserva-
tives; used as anti-mildew agent for textiles
() common name appears in parentheses following compound
Sources: Handbook of Environmental Data on Organic Chemicals, Verschueren,
K., Handbook of Toxic and Hazardous Chemicals and Carcinogens.
Sittig, M., The Merck Index, Windholz, Budavari, Stroumtsos and
Fertig
6-28
-------
TABLE 6-8
BASE/NEUTRAL EXTRACTABLE HAZARDOUS SUBSTANCE LIST COMPOUNDS
acenaphthene - coal tar, dye intermediate; mfg. of plastics, insecticide and
fungicide
acenaphthylene - in soots generated by the combustion of aromatic hydrocarbon
fuel doped with pyridine; coal refuse heaps; coke ovens
anthracene - used in dyes
benzo (a) anthracene - gasoline, bitumen, crude oil; asphalt hot-mix emission
benzo (a) pyrene - by-product of combustion; coal refuse piles, outcrops,
abandoned coal mines; coke mfg; external combustion of anthracite coal
*benzo (b) fluoranthene - petroleum based fuel, gasoline, diesel, etc.; coal
refuse heaps; coke ovens
benzo (g,h,i) perylene - coal tar, pitch distillate
benzo (k) flouranthene - petroleum based fuels, bitumen, crude oil
benzyl butyl phthalate - plasticizers, vacuum pump fluids
benzyl alcohol - perfumes and flavors; solvent; intermediate; inks; surfactant
bis (2-chloroethoxy) methane - selective solvent; textile mfg. and cleaning
bis (2-chloroethyl) ether - fumigants; processing fats, waxes, greases, cellu-
lose esters; general solvent; insecticide mfg.; textile mfg. (scour tex-
tiles) and cleaning; mfg. butadien, medicinals and Pharmaceuticals; selec-
tive solvent; constituent in paints, lacquers, varnishes
bis (2-ethylhexyl) phthalate (dioctyl phthalate) - plasticizer for resins;
mfg. of organic pump fluids; frequently found in lab blanks
4-bromophenyl phenyl ether (methyl ethyl ketone) - chlorinated insecticides
4-chloraniline - dye intermediate; Pharmaceuticals; agricultural chemicals
2-chloronaphthalene - production of electric condensers, insulation of elec-
tric cables and wires; additives to extreme pressure lubricants; supports
for storage batteries; coating in foundry use
4-chlorophenyl phenyl ether - selective solvent; nonsystemic insecticide
chrysene - high octane gasoline motor-oils; bitumen; crude oil
dibenzo(a,h) anthracene - used in wood preservatives; gasoline additive; found
in coal tar
dibenzofuran - (coumarone) - mfg. of coumarone-indene resins
6-29
-------
TABLE 6-8
Continued
di-n-butyl phthalate - plasticizer; cosmetics (fingernail polish); safety
glass; insecticides; printing inks; paper coatings; adhesives; textile
lubricating agent
1,2-dichlorobenzene - mfg of solvent; dye mfg.; fumigant and insecticide;
metal polishes; industrial odor control
1,3-dichlorobenzene - mfg. of solvent; dye mfg.; fumigant and insecticide;
metal polishes; industrial odor control
1,4-dichlorobenzene - mfg. moth repellants; mfg. air deodorizers; mfg. dyes
and intermediates; Pharmaceuticals mfg.; soil fumigant; pesticide
3,3'-dichlorobenzidine - intermediate in the manufacture of azo pigments;
curing agent for isocyanate terminated resins, for urethane resins
diethylphthalate - plasticizer mfg.; plastics mfg. and processing; explosive
(propellant) component; dye application agent; wetting agent; camphor
substitute; perfumery; alcohol denaturant; mosquito repellant
dimethyl pthalate - plasticizer for cellulose ester plastics; insect repellent
2,4-dinitrotoluene - mfg. TNT, urethane polymers, flexible and rigid forams
and surface coatings, dyes; organic synthesis
2,6-dinitrotoluene - mfg. TNT; urethane polymers, flexible and rigid foams and
surface coatings, dyes; organic synthesis
di-n-octyl phthalate - plasticizer mfg.; plastics mfg. and recycling, process-
ing; organic pump fluid
*fluoranthene - crude oil, coal tar, wood preservatives, motor-oils; coke
ovens; coal refuse heaps
fluorene - coal tar; wood preservative; coke oven emissions
hexachlorobenzene - mfg. of pentachlorophenol, wood preservative; fungicide,
seed treatment; used in production of aromatic fluorocarbons; organic
synthesis, impregnation of paper; in technical pentachlorophenol; herbi-
cides, pesticides
hexachlorobutadien - solvent for natural rubber, synthetic rubber and other
polymers; heat transfer liquid, transformer liquid, and hydraulic fluid;
washing liquor for removing hydrocarbons
hexachloroclopentadiene - key intermediate in the synthesis of stable chlori-
nated cyclodiene insecticides including aldrin, dieldrin, endrin, endosul-
fan, heptachlor, chlordane, isodrin, and mirex; mfg. of nonflammable resins
and shock proof plastics, acids, esters, ketones and fluorocarbons
6-30
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TABLE 6-8
Continued
hexchloroethane - mfg. smoke candles and grenades; by-product of industrial
chlorination processes; plasticizer for cellulose esters; minor use in
rubber and insecticidal formulations; medicinal mfg.; moth repellant;
retardant in fermentation process; fire extinguishing fluids mfg.; camphor
substitute in nitro cellulose solvent
indeno (l,2,3-c,d) pyrene - gasoline; motor-oil; coke oven emissions
isophorone - solvent; intermediate for alcohols, raw material for 3,5-dimethy-
laniline; solvent for polyvinyl and nitrocellulose resins; lacquers,
finishes mfg.; pesticide mfg.
2-methylnaphthalene - coal tar pitch, coal processing
naphthalene - mfg. source: petroleum refining; coal tar distillation in
commercial coal tar; moth ball mfg.; mfg. pesticides, fungicides, dyes,
detergents and wetting agents, synthetic resins, celluloids, lampblack,
solvent; lubricants; motor fuel mfg.
2-nitroaniline - intermediate for dyes and antioxidants; gasoline gum inhibi-
tors; medicinals for poultry; corrosion inhibitor
3-nitroani1ine - intermediate in the manufacture of dyes, antioxidants, phar-
maceuticals, and pesticides
4-nitroaniline - intermediate for dyes and antioxidants; gasoline gum inhibi-
tors; medicinals for poultry; corrosion inhibitor
nitrobenzene - mfg. aniline and dyestuffs; solvent recovery plants; mfg.
rubber chemicals, drugs, photographic chemicals; refining lubricants oils;
solvent in TNT production; solvent for cellulose ethers; cellulose acetate
mfg.; constituent in metal polish and shoe polish formation
n-nitroso-di-n-propylamine - contaminant of herbicide Treflan (Trifluralin) in
concentrations up to 150 ppm
n-nitrosodiphenylamine - gasoline additive; analytical chemistry in the deter-
mination of cobalt; an accelerator in vulcanizing rubber. It decomposes in
GC analysis to be come diphenylamine, and is detected as diphenylamine, so
is essentially inseparable from it by normal GC methods
*phenanthrene - dyestuffs; explosives; synthesis of drugs; biochemical re-
search
*pyrene - gasoline, coal tar, wood preservative sludge, motor-oil
1,2,4-trichlorobenzene - solvent in chemical manufacturing dyes and intermedi-
ates; dielectric fluids; synthetic transformer oils; lubricants; insecti-
cides
* can also occur naturally or associated with coal or coal combustion
** common laboratory contaminant of lab chemical
() common name appears in parenthesis following compound
6-31
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TABLE 6-8
Continued
Sources: Handbook of Environmental Data on Organic Chemicals, Verschueren, K.
Mass Spectrometry of Priority Pollutants, Middleditch, B., Missler,
S., and Nines, H.
The Merck Index, Windholz, Budavari, Stroumtsos and Fertig
6-32
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that have matrix problems or samples that are heavily contaminated can cause
extreme scheduling problems in laboratories unless the samples are diluted.
When a sample is diluted prior to being analyzed, the detection limit rises
proportionally to the dilution factor. This practice makes it difficult for
an investigator to compare results from one analysis to another analysis in
absolute terms and in fact can lead to incorrect determinations concerning the
presence or absence of contaminants.
6.2.4 Analytical Precision and Matrix Effects
Most analytical techniques were developed to look for impurities or to isolate
chemical species. However, in contamination studies we frequently have mix-
tures of waste with water and soil material. Individuals interpreting results
of analysis should be aware of equipment and operator limitations. In running
a common analytical method, for instance GC/MS, looking for large numbers of
compounds at a single run, sample matrix effects may occur. For example, if
one compound exists at a high concentration and another at a very low level,
then the analytical precision is not the same for both compounds. In addi-
tion, many of the techniques are qualitative and not quantitative methods.
When dealing with organic compounds, extreme care must be exercised when
accepting reported concentrations as being a "fact." Most chemists have
recognized this and there are ranges for QA/QC that they are willing to
accept. Table 6-9 contains the U. S. Environmental Protection Agency (EPA) QC
limits for matrix spike/matrix spike duplicate recovery results for water
samples and (soil/waste/sludge) samples.
Extreme care should be used in interpreting relative concentrations of organic
compounds when comparing up-dip to down-dip monitor wells. For instance, if a
lab reported concentrations of benzene in ground water downgradient of a site
to be 125 ppb and upgradient to be 76 ppb, one might infer a direction of flow
from the chemical analysis alone. However, a review of Table 6-9 shows that
this range of values is within our QA/QC and any value reported between these
ranges may in fact be the same number. A review of 77 soil surrogate percent
recovery analyses for volatiles analysis performed during a recent investiga-
tion indicated 11 analyses were outside the QC limits for Toluene-DB (81-117),
four analyses were outside the limits for BFB (74-121), and all were within
6-33
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TABLE 6-9
QC LIMITS FOR WATER AND SOIL
Fraction
Volatiles
Base/Neutrals
Acids
Pesticides
Compound
1,1-Dichloroethene
Trichloroethene
Chlorobenzene
Toluene
Benzene
1,2,4-Trichlorobenzene
Acenaphthene
2,4-Dinitrotoluene
Di-n-butylphthalate
Pyrene
N-nitrosodi-n-propylamine
1,4-Dichlorobenzene
Pentachlorophenol
Phenol
2-Chlorophenol
4-Chloro-3-methylphenol
4-Nitrophenol
Lindane
Heptachlor
Aldrin
Dieldrin
Endrin
4,4'-DDT
Water Samples
QC Limits
Recovery
61-145
71-120
75-130
76-125
76-127
39- 98
46-118
24- 96
11-117
26-127
41-116
36- 97
9- 103
12- 89
27-123
23- 97
10- 80
56-123
40-131
40-120
52-126
56-121
38-127
Soil Samples
QC Limits
Recovery
59-172
62-137
60-133
59-139
66-142
38-107
31-137
28- 89
29-135
35-142
41-126
28-104
17-109
26- 90
25-102
26-103
11-114
46-127
35-130
34-132
31-134
42-139
23-134
6-34
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the limits (70-121) for 1,2-dichloroethane D4. The chemist reports that 6 of
the 11 samples that failed the QC test were strongly affected by the matrix
(in other words, somethi-ng else in the sample was interfering with the
results). For the 77 samples discussed, only four samples were outside the QC
limits for semi-volatile compounds. One should note here that the QC window
for semi-volatile compounds is generally larger than for the volatile QC.
A review of 50 water surrogate percent recoveries for the same investigation
indicated only two samples were out of QA/QC limits for toluene-DB (88-110).
However, out of 35 water surrogate results for semi-volatile analysis, over
half were out of limits for at least one compound.
6.2.5 Sources of Contamination in the Laboratory
As discussed earlier, there are other sources for chemicals identified in
laboratory reports. The following table lists the possible sources of com-
pounds recently found in analysis of laboratory blanks for a particular
project.
Common Solvent Artifacts Dirty Glassware
Lab or Natural or
Compound Contaminant Impurities Products Syringe
di-N-butylphthalate
butylbenzylphthalate
bis(1-ethylhexyl)phthalate
2,5-dimethyl-furan
4-methyI-octane
hexadeconic acid
squaIene
methylene chloride
chrysene
6-35
-------
The chrysene found in the laboratory blanks is probably the result of the
laboratory not adequately washing out glassware or syringes because it is
known that chrysene was found in samples analyzed on that day,
6.2.6 Adsorption of Air Emissions
Even when the greatest care is exercised in the field, the possibility exists
for contamination by absorption of air emissions. In many chemical/
petrochemical complexes there are odors. This leads to the conclusion that
there are concentrations of chemicals in the air. Recent data indicate that
organics may be absorbed from the atmosphere into the water sample when de-
canting from the bailer to the sample bottle. In one case, eleven monitoring
wells were sampled to determine the lateral and vertical extent of nitrotolu-
ene and dinitrotoluene isomers relative to surface impoundments containing DNT
and DNT process by-products. During collection of the samples, corresponding
field blanks were collected at each monitor well to monitor potential absorp-
tion of organics from the air by the collected water sample. The field blanks
consisted of distilled water; the water passed between two glass sample
bottles approximately six times at the well site prior to collection of the
well water sample. Water quality results for both the well sample and the
field sample blank are included in Table 6-10. The average percent variation
in concentration of 2,4-DNT and 2,6-DNT in the well water, excluding outside
values, as measured by the field blank, is 6 and 7 percent, respectively. The
percent variation presents the potential DNT available for absorption, as
indicated by concentrations measured in each corresponding field blank.
6.2.7 Sources of Sample Contamination in the Field
There is an abundance of literature about the development of pristine drilling
and sampling procedures for monitoring disposal site. In practice, these
conditons are extremely hard to meet. Some sources of self-contamination of
monitor wells include pipe dope applied to the joints of drill pipes, leaking
hydraulic fluid from the drilling rig, and foreign material on the drill
pipe. Under the adverse drilling conditions of most waste sites, pristine
drilling is almost impossible. Each investigation should be planned and
carried out to minimize self-contamination, and/or sufficient data should be
developed to document the influence of completion procedures.
6-36
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TABLE 6-10
Organic Analyses of Well Water and Corresponding Field
Blanks - 2,4-Oinitrotoluene, 2,6-Oinitrotoluene
Well No.
1
2
3
4
5
6
7
8
9
10
11
Parameter
2,4-DNT
2,6-ONT
2, 4-0 NT
2,6-ONT
2,4-DNT
2,6-ONT
2,4-DNT
2,6-DNT
£,4-DNT
2,6-ONT
2,4-ONT
2,6-DNT
2,4-ONT
2,6-DNT
2,4-DNT
2,6-DNT
2,4-ONT
2,6-ONT
2,4-ONT
2,6-ONT
2,4-ONT
2,6-DNT
Concentration
Well Samole
ND
NO
1.88
3.77
0.017
0.024
0.098
0.356
0.001
0.003
0.306
0.188
0.011
0.083
0.050
0.356
0.004
0.050
ND
ND
ND
ND
Field
Blank
ND
NO
0.014
0.008
0.019
0.013
0.002
0.001
ND
ND
0.001
ND
ND
ND
0.001
0.001
0.002
0.001
ND
ND
0.006
ND
Percent
Variation
0
0
.01
0.2
112.0
54.0
2.0
0.3
0
0
0.3
0
0
0
2.0
0.3
50.0
2.0
0
0.6
0
0
All analyses are in mg/L
6-37
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An example of probable sample contamination due to materials of construction
occurred in 1980. Nine monitor wells were installed at a chemical plant which
produces no chlorinated products or wastes. Presented below are the results
of the analyses for Total Organic Halogen of water samples from the wells.
Total Organic Halogen (ug/1)
Monitor Well S1 S2 S3 S4
1 <10 13
2 30 21 30
3 28 25 23 14
4
5
6
7
10
64
26
34
66
<10
67
40
56
30
<10
56
35
28
21
40
68
75
75
42
The only difference in the nine wells is that wells 1 through 4 were installed
using screen from a different supplier than wells 5 through 9. It is probable
that the second supplier used a chlorinated degreasing solvent to clean the
well screens. Another possible explanation for the presence of halogenated
organics in these wells is leaching of vinyl chloride monomers and polymers
from the PVC casing itself.
A third possibility for explaining the anomalous data is that there is a
naturally occurring background level of halogenated organics in the ground
water system. It has been shown that natural background concentrations of
both chloroform and carbon tetrachloride are present in both the atmosphere
and surface waters. However, given the low concentrations of halogenated
organics in both local wells and in Monitor Wells 1 through 4, it is unlikely
that the high levels in Monitor Wells 5 through 9 can be attributed to natural
causes.
Obviously, another source for the presence of these compounds in Wells 5
through 9, because they were sampled on a different date from Wells 1 through
4, is contaminated sample containers. The containers may have inititally been
contaminated or may have become contaminated during sampling.
6-38
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Contamination can also be caused by sampling equipment and by components used
during manufacturing of the sampling devices. High pressure liquid chroma-
tography grade water was poured over a fresh pair of gloves while the gloves
were being worn. The water was collected directly into a 1 liter amber glass
jar, placed on ice and transported to the laboratory for analysis. The sample
was analyzed by GC/MS for phthalates plus any significant peaks. The analysis
detected 2,6-dimethyl-2,5-heptadiene-4-one at 5 ppb, and isophorone at 4.9
ppb. These two compounds were not detected in equipment blanks of PVC bailers
used to sample the wells, trip or field blanks, or the laboratory blank.
Based upon the whole of the data, the source of these compounds appeared to be
directly attributable to the surgical gloves.
Another example of contamination caused by sampling devices concerned work at
a land treatment facility on the Texas Gulf Coast. Analysis of water samples
collected from ground water monitoring wells located at the perimeter of the
active portion of the Land Treatment Unit measured tetrachoroethylene, and
1,1,1-trichoroethane at 13 to 66 ppb in select samples. The samples were
collected using a dedicated bladder pump. Previous to the sampling event that
detected the compounds, notification of pump contamination by chlorinated
hydrocarbons had been sent to owners by the manufacturer. Water extraction
testing of pump parts by the manufacturer had identified a food grade Teflon
lubricant used during final assembly of the pumps as the source of the chlori-
nated hydrocarbons.
In order to identify whether or not the contaminants detected at the Texas
facility were related to the pumps, an in situ time series sampling of the
pumps was completed at the site. The time series sampling consisted of col-
lecting three discrete samples of water resident in the pump tubing and body
from each of two wells where the contaminants had previously been detected,
namely Well A and Well B. Identification of the sample was based upon calcu-
lated volumes of water in the discharge hose and the known volume of water in
the pump body itself. The first collected sample consists of water which has
been residing in the discharge hose of the pumps. The second sample approxi-
mately represents water residing in the body of the pump. The third sample
represents water from the well sand pack and the aquifer itself. Previous to
6-39
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the time series sampling, the pumps had not been operated for approximately 3
months. Once the three samples had been collected using the bladder pump, the
pump was removed and the well was purged using a rigid PVC bailer. A fourth
sample was then collected for analysis using a new dedicated PVC bafler.
The samples collected using the bladder pump showed significant levels of
1,1,1-trichloroethane, tetrachloroethylene and 1,1 dichloroethylene. Of the
three samples collected using the bladder pump, the highest levels of the
compounds occurred in water which had been residing within the body of the
pump. Samples A-4 and B-4, collected using the PVC bailer after the bladder
pump was removed, contained no detectable (<10 ppb) levels of the chlorinated
hydrocarbons.
Wells C and D were sampled in the same manner as Wells A and B, in order to
identify any contribution of phthalate organics to collected samples by the
bladder pump. The primary organics detected were bis-2-ethylhexyl phthalate
and 2 ethyl hexanol. As with the chlorinated hydrocarbons, the highest con-
centration of the contaminants were in the sample of water that was residing
in the body of the pump. Samples collected subsequent to removal of the pumps
showed a significant decrease or absence of the organics. Detection of bis-2-
ethylhexyl phthalate was attributed to laboratory contaminants.
6.2.8 Physical and Chemical Concerns
Interpreting the results from a sampling event also requires a thorough know-
ledge of the lithology of the aquifer, the directions and velocity of ground
water flow and the spatial, temporal and chemical variations of ground water
quality. This section gives examples of ways in which these characteristics
can affect conclusions on analytical results.
The lithology of uppermost sediments along the southern Gulf Coast of the
United States consists of interbedded, discontinuous strata of interdeltaic
silts, clays, and sands. In the course of monitoring a hazardous waste facil-
ity, one well may be within the facility monitoring system screened in a
coarse sand and another well in the same monitoring system screened in a
clayey sand, where both wells monitor the uppermost permeable unit underlying
the Resource Conservation and Recovery Act (RCRA) regulated facility. Water
6-40
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samples collected from such wells have been shown to exhibit a significant
variation in concentration of inorganic monitoring parameters as a result of
the naturally occurring variations in lithology of the permeable zone. Where
the variations in sediments within a monitored zone include variations in
carbon content, significant variations may occur in the amount of adhesion of
any organic waste constituents present in the monitored zone to the aquifer
sediment. Furthermore, where variations in lithology exist, significant
variations in seepage velocities of the ground water may occur and result in
preferential flow paths of monitored species. Proper documentation of litho-
logic variations within a monitored zone is crucial to the correct interpreta-
tion of sample analytical data.
Variations in the permeability of the aquifer have been demonstrated to affect
the quality of the ground water sample collected from the monitoring well.
Wells of similar construction and design screened in variable lithologies may
exhibit variations in recovery rates subsequent to purging due to the innate
variations in permeability of the monitored unit. As a result, the concentra-
tions of monitored species, both organic and inorganic, may vary between wells
because of variations in aeration or chemical reduction of the sample in the
wellbore, which may occur during the recovery period. For example, a monitor
well completed in a well-sorted coarse sand may be sufficiently purged within
15 minutes; thus, prompt collection of a water sample is allowed. On the
other hand, a monitor well that is completed in a sandy silt may take several
hours to recover sufficient water to collect a sample. Where the recovery
rate of a well is believed to affect water quality results, the suspected
influence should be verified by sampling the slowly recovering well. The
degree of influence may then be more or less quantified and considered in the
overall interpretation of the water quality data.
The occurrence of vertical gradients of flow between permeable strata within
an aquifer system, if not properly accounted for, may result in the monitoring
of water quality in multiple zones within one well. The upper aquifer is
contaminated, but the lower aquifer is not. Under static conditions, the
lower aquifer has a higher hydraulic head than the upper aquifer, and vertical
cross flow in the well occurs from the lower aquifer to the upper aquifer.
Assuming that the transmissivities of the aquifers are 2,000 gallons/day/foot
6-41
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and the storage coefficient is 0.0003, over 40 days of pumping this well at a
rate of 15 gallons/minute would be required before a sample of the contami-
nated water in the upper aquifer could be obtained. To avoid cross flow
between permeable strata, the screen section of any one monitoring well should
be set to monitor one discrete permeable stratum. Identification of vertical
components of flow in the aquifer system can be made with clustered or nested
wells, which are a group of wells installed in the same immediate vicinity and
screened at variable depths.
In addition to defining the hydraulic characteristics, the chemistry of the
monitored zone(s) should be thoroughly defined prior to interpreting sample
analytical data obtained as part of a RCRA monitoring program. A naturally
occurring spatial variation in the salinity of connate waters is commonly
found along the Texas Gulf Coast. During the coarse of monitoring a regulated
waste facility in the Gulf Coast area, total dissolved solids were measured at
30,000 mg/1 in one well. Water quality in wells located at the other end of
the facility showed total dissolved solids of approximately 500 to 800 mg/L.
On the basis of a statistical comparison of the concentrations of chromium
between wells, the well yielding saline-quality water was interpreted to have
been affected by the waste management unit. Monitoring wells were later
installed at points between the freshwater and saline wells. A measurement of
specific cations and anions, total dissolved solids, and specific conductivity
revealed a clear spatial trend from freshwater to saline-quality water in the
region, in contrast to any plume of contamination originating from the waste
management unit.
The degree of alteration in the chemistry of the ground water sample during
sample collection (e.g., oxidation, precipitation, and adsorption) has been
shown to be influenced by the initial chemistry of the ground water (e.g.,
initial Eh, pH, redox buffering capacity, and pH buffering capacity, and pH
buffering capacity). Through laboratory simulation of sampling from a very
shallow water table (less than 18 feet below ground), the amount of iron
precipitation due to aeration of the sample during collection has been demon-
strated to be significantly reduced in waters with a lower initial pH. Mixing
of well water with the atmosphere causes aeration and oxidation of ferrous
iron to ferric iron. Ferric iron rapidly precipitates as iron hydroxide and
6-42
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can adsorb other monitoring constituents including arsenic, cadmium, lead, and
vanadium. Therefore, aside from the amount of aeration that may occur as a
result of the sample collection procedure, the amount of iron precipitation
resulting from aeration is dependent upon the innate quality of the ground
water.
In addition to considering the hydrologic and geochemical controls of the
aquifer upon the ground water sample, the flow behavior of the monitored
species should be taken into consideration when designing the monitoring
well. Figure 6-6 shows a cross section of a surface impoundment containing
soluble salts. As indicated by chemical analysis of ground water from shallow
and deep cluster wells, the flow of leachate originating from the surface
impoundment was concentrated along the bottom of the aquifer because of the
greater density of the leachate relative to the density of the unaffected
ground waters. Without consideration of the flow behavior of the leachate and
without investigation of the vertical extent of the aquifer, the contaminants
may have gone undetected.
6-43
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MW-1 MW-2
JL JL
K31 x 10-2
cm./sec.
Approximate Boundary of
Surface Impoundment used
for Disposal of Soluble Salts
o MW-7
Fine """ -y
Silty 4
Saiid.r
^ Leacnate with
Specific Gravity >1.0
Stiff Clay
K 31 x 10-6 cm./sec.
Zone of
Gravimetric
Separation
Total Dissolved Solids content
of samples from monitor wells
WELL
MW-1
MW-2
MW-7
MW-8
MW-9
MW-10
DEPTH
45
25
48
30
30
48
TDS
830
450
95.000
4,300
3,900
78,000
PLAN VIEW
MW-1
Approximate
Boundary of
Abandoned
Disposal Site
MW-4
MW-12 MW-11
'/MW-9
MVV-10
Explanation
Monitor V/ell
•Direction of
Ground Water
Flow
Figure 6-6. Flow Behavior of Leachate from a
Surface Impoundment
6-44
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7.0 GROUND WATER MODELING
-------
7.0 GROUND WATER MODELING
In general terms, a model can be described as a simplification, or abstrac-
tion, of the complex physical reality and the processes in it (Bear 1979). A
model of ground water contamination may consist of contours on a map repre-
senting lines of equal concentration of chloride in the monitored zone, or a
three dimensional picture of contaminant plume migration, taking into account
adsorption and radioactive decay of the monitored species.
Modeling ground water contamination is just one application of one type of
ground water model. There are four general types of ground water models.
They are prediction models which simulate the response of the flow system to
stress; resource management models which integrate hydrologic prediction with
management decision; identification models which determine input parameters
for both of the above; and data manipulation and storage procedures which
process and manage input data for all of the above. Prediction models may be
subdivided into four major categories: flow, and mass transport models,
described below; subsidence models used to describe the phenomenon of land
subsidence resulting from ground water withdrawal, and heat transport which
couples the flow of heat with water or steam for problems where thermal ef-
fects are important, i.e. storage of nuclear waste, geothermal reservoirs.
Modeling of ground water contamination consists of solving mathematical equa-
tions described by flow and mass transport type predictive models. Following
is a brief overview of the flow and mass transport models, the method of
mathematical solution of the models, and general guidelines for applying such
models.
7.1 FLOW MODELS
Flow models are utilized to solve partial differential equations used to
quantify aspects of ground water flow including change in water level, the
direction and rate of flow, stream-aquifer interaction and interference ef-
fects of production wells. The models together with appropriate boundary and
intial conditions express conservation of mass, momentum, and energy. The
basic rule of conservation for the fluid in the volume of aquifer is:
7-1
-------
rate of change of rate of flow of rate of flow of
mass of fluid in = fluid mass into - fluid mass out
a volume with time the volume of the volume
In order to solve the equations describing ground water flow the following
elements must be completely described:
1. The distribution of the parameters through the space of
interest,
2. Initial conditions for fluid pressure, composition, and
temperature,
3. The sources and sinks of interest and their variation
with time, and
4. The boundary conditions at the margins of the space of
interest.
There are two widely used methods of solution of flow models -- the analytical
and numerical method. The analytical method utilizes functional relationships
which can be expressed in closed form with fixed parameters. Analytical
solutions to problems of ground water flow are generally applied to uniformly
porous aquifers and aquitards which are homogeneous, infinite in area! extent,
and of the same thickness throughout. Except in the case of flowing wells,
the discharge or recharge of production or injection wells is assumed to be
constant. Both fully and partially penetrating wells are considered.
Numerical models approximate partial differential equations describing ground
water flow for each node of a grid designed over the aquifer area of inter-
est. All nodes are combined to form a matrix equation. The numerical ap-
proach computes new values of the variables involved (head potentials) at each
node, for each time step adopted.
Because of the large number of calculations involved, numerical models employ
computer capability. By 1977 about 200 predictive numerical computer models
had been developed throughout the world (Walton, 1984). 69 percent of these
models are flow models and 19 percent are mass transport models. One example
is the Prickett Lonquist Aquifer Simulation Model (PLASM), which models non-
steady state two dimensional flow in a heterogeneous, isotropic, artesian
ground water system with internal sources and sinks.
7-2
-------
Ground water scientists and engineers typically depend upon commercially
generated software for ground water modelling. Most computer models are
written in BASIC or FORTRAN. Software is available for purchase at minimum
cost ($50.00 to $5,000.00) for both micro and mainframe computers. The Inter-
national Ground Water Modeling Center (IGWMC) associated with Butler Univer-
sity in Indianapolis, Indiana, serves as an informational clearinghouse for
ground water modeling software.
7.2 MASS TRANSPORT MODELS
The mass transport model is used to describe the spread of mass in the subsur-
face under the influence of physical, chemical and biological processes. The
model has, as its basis, the conservation of a chemical species. The equation
may be written in words as
the rate of the rate of transport the net rate at
change of mass = of mass into and out +/- which species
of species A of the system A is produced
in a volume in the volume
with time by chemical
reaction.
As shown in the equation, the mass transport model contains a flow submodel
which provides flow direction and velocities. The submodel utilizes these
velocities to simulate adyective transport, allowing for dispersion. Methods
of transformation of the solute include adsorption, biodegradation, radioac-
tive decay, and ion exchange.
Analytical solutions to mass transport simulate advection and dispersions from
a solute injection well in uniformly porous, non-leaky artesian aquifer which
is homogeneous, isotropic, and infinite in area! extent. The models are based
on assumptions of one dimensional flow and dispersion in one, two, or three
dimensions. (Ogata and Banks, 1961; Wilson and Miller, 1978; Domenico and
Robbins, 1985, respectively).
There are serious limitations associated with the numerical methods for solu-
tion of mass transport equations, including overshoot, undershoot and numeri-
cal dispersion, especially when transport is dominated by advection (Hitchon,
7-3
-------
Trudell, 1985). In most applications these probelms are manageable through
appropriate modifications to the grid or through algorithmic treatment of high
gradients at the fronts of plumes*
7.3 GUIDELINES TO CHOOSING AND USING A MODEL
In deciding whether or not to employ a model, it should be decided whether the
model is necessary to the field study, and what level of sophistication of
modeling is required.
Applying a model to a field site can be useful in several ways. Application
of a model gives the hydrogeologist a perspective as to what processes are
important in the flow and/or mass transport. Modeling provides a precise
framework for the kinds of measurement which need to be made. Where there are
complex and multiple interacting effects, the model serves to integrate the
field data.
Modeling, depending upon the level of complexity, can be a time expensive
endeavor. There are several steps in completing a model: 1) definition of
the problem to be addressed; 2) accumulation of the data base; 3) design of a
conceptual model; 4) formulation of the model; 5) programming the model; 6)
specification of the dimensions, internal parameters, along with the initial
conditions and boundary conditions; 7) testing the sensitivity of the model;
8) calibration of the model; 9) design and execution of simulation experiments
directed toward solution of the problem; 10) analysis of simulation data; and
11) conclusions. Though modelling today is well aided by computer brainpower,
there are time outlays involved in testing .and calibrating the model and
documenting the assumptions and limitations of the model.
Once it has been decided to employ a model, the required level of sophistica-
tion should be decided. Model input may include the following: the geology
of the system including geometry and lithologic composistion of the strata,
the aquifer characteristics including the piezometric surface through time,
hydraulic conductivity, porosity, dispersivity, leakage, historical and pro-
jected pumpage; knowledge of surface water features including stream and
reservoir elevations, precipitation, evapotranspiration; knowledge of the
chemical and biological behavior of the solute species in the flow system
7-4
-------
including the degree of adsorption, and biodegration of the chemical species
in the flow system.
The ground water model is only as good as the data used in the model; the
sophistication of the model should not exceed the reliability and accuracy of
the data. Adequate acknowledgement of data base limitations should accompany
every completed simulation. Most models are easily simplified to take into
account fewer variables in the system.
Alternatively, the model should incorporate all available data on the
physical/chemical system. All known boundary conditions must be accounted for
in the flow model. The mechanisms of chemical transformation of the contami-
nant must be identified in the mass transport model. The geology, observed
patterns of flow, and the distribution of contaminants should fit together to
form a consistent hydrogeologic picture.
7.4 USE OF MODELS IN CONTAMINATION STUDIES
Contamination studies in themselves can range from the simple to the com-
plex. Contamination from small ponds and lagoons or landfills where the water
table is very shallow (less than 25 to 35 feet) generally gain very little
from the initial use of modeling. That is, if the question is how far has the
waste migrated vertically and/or horizontally, the answer can be best derived
from field studies such as installing monitoring wells. Once the zone of
contamination has been defined, models may become useful depending upon the
solution proposed to the problem. For instance, if any industry proposed to
do nothing about a contaminated plume by claiming that the contaminants would
be diluted by the time it reached a pumping water well, then the use of some
type of model would be advisable. Several such models would be advisable.
Several such models are readily available. If, however, the contaminant is to
be enclosed by a slurry wall, then modeling may not be necessary or desirable.
If a recovery program is proposed, a model may be used to give some initial
indication of the number of wells required and the length of time they may
require. However, the better approach here would be to track the volume
recovered and the water levels to determine if the recovery system was per-
forming as predicted. A model is not necessary to do this.
7-5
-------
Models are most useful when the underlying geology is very complex. In many
Gulf Coast areas, there are multiple sands and clays underlying disposal
sites. In these areas, where the contamination has migrated into multiple
layers, modeling may be required and may result in substantial savings.
Models are also useful when large areas of aquifers have been impacted. If
sufficient geologic and hydrologic data can be developed for the model, future
monitor well locations can be predicted and different recovery scenerios
developed.
•7.5 AVAILABILITY OF MODELS
Numerous ground water models are commercially available for use on most com-
puters. Many early models were developed to run on main frame computers,
although today most models can be run on IBM PC, XT or AT and compatibles and
many are available for Macintosh systems.
7-6
-------
8.0 BIBLIOGRAPHY
-------
8.0 BIBLIOGRAPHY
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3-1
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8-2
-------
Johnson Division, 1975, Ground-water and wells, 4th printing: St. Paul,
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P-
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3-3
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8-4
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8-5
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8-6
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GROUND WATER CONTAMINATION STUDIES
OCTOBER 26, 27, 28, 1987
Dallas, Texas
Monday. October 26. 1987 Instructor
8:00 - 8:30 Registration and Introduction
8:30 - 9:00 "Wellhead Protection Requirements" R. Kent
9:00 - 10:15 "Introduction to Ground Water Hydrology" R. Kent
10:15 - 10:30 Break
10:30 - 11:30 "Investigative Techniques for Ground Water E. Fendley
Contaminations Studies"
11:30 - 1:00 Lunch
1:00 - 2:00 "Ground Water Monitoring Systems Design E. Fendley
and Installation"
2:00 - 2:15 Break
2:15 - 3:15 "Ground Water Sampling Techniques" M. Katterjohn
3:15 - 3:30 Break
3:30 - 4:30 "Ground Water Flow and Aquifer M. Katterjohn
Characterization"
4:30 - 5:00 "Practical Approaches to Ground Water M. Katterjohn
Contamination Studies"
5:00 Adjourn for Day
Tuesday. October 27. 1987
8:00 - 8:30 Leave for Field Site
8:30 - 10:00 Demonstration of Drilling and Soil Sampling Techniques
Hollow Stem Auger
10:00 -10:30 Slug Test Set-Up
10:30 - Noon Demonstration of Mud Rotary Drilling, Monitor Well
Installation, and Grouting
Noon - 1:00 Lunch
1:00 - 2:00 Slug Test Demonstration
2:00 - 3:30 Sampling Demonstration
3:30 - 4:00 Return to Classroom
4:00 - 4:30 Field Demonstration Overview - Question and Answer
4:30 Adjourn for Day
-------
Wednesday. October 28. 1987 Instructor
8:00 - 8:30 Coffee
8:30 - 9:30 "Ground Water Chemistry and Significance R. Kent
of Organic and Inorganic Constituents in
Ground Water"
9:30 - 10:00 Break
10:00 - 10:45 "Ground Water Contamination Studies Data R. Kent
Analysis and Evaluation"
10:45 - 11:30 "Practical Problems in Ground Water M. Katterjohn
Contamination Studies"
11:30 - 1:00. Lunch
1:00 - 2:30 "Designing a Ground Water Contamination All
Study"
2:30 - 3:00 Break
3:00 - 4:00 "Designing a Ground Water Contamination All
Study"
4:00 Course Critique
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GROUND WATER CONTAMINATION STUDIES
OCTOBER 26-28, 1987 DALLAS, TEXAS
COURSE CRITIQUE
COURSE EXCELLENT AVERAGE VERY POOR
RATINGS: 10 987654321
MEETING ROOM FACILITIES: 10987654321
AUDIO/VISUAL AIDS: 10 987654321
COURSE MANUAL CONTENT: 10987654321
LECTURE CONTENT: 10987654321
COMMENTS:
WHAT DID YOU LIKE ABOUT THIS COURSE ?
WHAT DID YOU LEARN FROM THIS COURSE WHICH WILL BE USEFUL TO YOU IN THE FUTURE ?
WHAT DID YOU NOT LIKE ABOUT THE COURSE ?
SUGGESTIONS ON WAYS TO IMPROVE THIS COURSE AND/OR GENERAL COMMENTS ?
-------
-------
CLASS PROBLEMS
1. Using Figures 1 and 2 and the well construction information in Table 1,
construct a water table contour map and determine the direction of ground
water flow.
2. Using the information in the text book, the graph paper provided, the
slug test data from Table 2, and the monitor well construction diagram of
Figure 3, calculate the hydraulic conductivity (using the Bouwer and Rice
Method) of the formation in gpd/ft, cm/sec and ft/day, assuming the base
of the aquifer corresponds with the base of the well, (i.e., h = D).
3. Using the calculated hydraulic conductivity and the water table contour
map calculated in Item 1, calculate the rate of apparent movement in the
aquifer.
4. Using the information contained in 1, 2 and 3 above, what volume of water
is moving underneath the pond in Figure 1, assuming the pond is 200 feet
wide and 400 feet long? What affect will this volume have on any
potential leakage from the impoundment?
5. A shut-down refinery along the Gulf Coast has a series of waste
treatment/disposal facilities. Figure 4 shows the plant map. The owners
are concerned that their two disposal sites, a landfarm and a waste water
treatment lagoon, may be impacting the ground water. Only limited
chemical analysis is available for the landfarm or lagoon (Table 3).
There are no existing monitor wells and only a limited number of on-site
soil borings (attached). The plant asked you to design and carry out a
ground water investigation to determine if the facility is leaking.
Prepare an investigative plan for conducting the investigation.
-------
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-------
TABLE 2
Slug Test #1 of Monitor Well MW-7
Project Name
Project Number
Test Date
Well Number
Casing Radius
Static Water Level - BTOC
Test Start - 17:10
Time
(seconds)
1 5
25
45
65
85
105
135
155
195
225
255
285
315
345
375
41 0
450
495
520
555
645
735
820
915
1215
BTOC
Water Level
(feet below top
of casing)
23.06
22.66
22.38
22.28
22.20
22.15
22.06
22.00
21.93
21.87
21.84
21.78
21.75
21.73
21.70
21.68
21.65
21.63
21.62
21.61
21.59
21.58
21.57
21.56
21.55
GenFac, USA
100-01 1
April 30 1987
Monitor Well MW-7
.17 feet
21.54 feet
Test End - 17:30
Y(t)
(feet)
1.52
1.12
0.84
0.74
0.66
0.61
0.52
0.46
0.39
0.33
0.30
0.24
0.21
0.19
0.16
0.14
0.11
0.09
0.08
0.07
0.05
0.04
0.03
0.02
0.01
-------
V
1 *
1
Water Table
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1
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L
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r$H J |'T£
%A|5§^aJ
\ ^ Concrete Well Pad
]
2" Schedule 40 PVC Casing
or Bentonlte Slurry
^ b buf ehole
Filter Sand
PVC
Clay
FIGURE 3
MONITOR WELL MW-7 CONSTRUCTION DIAGRAM
BAILER PERMEABILITY TEST
-------
FIGURE 4
X
B-1
f
PROPERTY LINE
LAND
TREATMENT
UNIT
X
B-7
ROADS
X
TANK B-6
FARM
TANK
FARM
ROADS
'B-4
ROADS
OFFICE
X
B-8
PARKING
ROADS
T
GATE
SCALE (ft)
0
I I
100 200
-------
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-------
BORING LOG
BORING NO. B-l
DATE DRILLED 7/2/75
TOTAL DEPTH 45'
SURFACE ELEVATION 64.2'
Description of Stratum
5 -5
10
Topsoil
CLAY, slightly silty, slightly calcareous,
dark gray, moist (CH)
CLAY, silty, slightly calcareous, light
gray, moist (CL)
-very calcareous, very silty, trace of
sand, wet
CLAYEY SAND, fine to medium, 30% clay,
light gray, saturated (SC)
CLAY, stiff, iron-stained, tan with black,
~moTst (CH)
CLAY, 30% fine sand, calcareous, light
gray, saturated (CL)
SAND, fine to medium, 10« clay, black and
\tan, saturated (SP/SC)
CLAY, stiff, iron-stained, oxidized roots,
tan, moist (CH)
-very stiff @ 29'
CLAYEY SAND, fine to medium, 45% clay,
gray, wet (SC)
-30% clay (a 40 ft.
CLAY, stiff, calcareous, light brown,
moist (CH)
T.D. 45'
-------
BORING LOG
BORING NO. B-2
DATE DRILLED 7/2/75
TOTAL DEPTH 40'
SURFACE ELEVATION 54.4'
>-
CO
DESCRIPTION OF STRATUM
6
9
12
15
18
21
CH
CL
ML
CH
Clay, slightly organic, dark gray, moist.
Clay, very calcareous, slightly silty, light
tan, moist
Wet
Silt, clayey, 20% fine-grained sand, light
tan, saturated
Clay, slightly silty, trace of calcareous
nodules, red/tan, moist
24
27
Tan and gray
30
33
SC Sand, clayey, 60% fine to medium-grained,
light tan, saturated
36
39
42
CL Clay, sandy, light tan, moist
T.D. 40'
-------
BORING LOG
BORING NO. B-3
DATE DRILLED 7/7/75
TOTAL DEPTH 50'
SURFACE ELEVATION 58.9'
a
a
a
o
.a
c.
a
Sample Description
5 -
CH
5ILTY CUY. highly plastic, 5-lOt very f1n« sand, 35-451 fines,
firm, very moist, grey mottled with white and black, very
strong reaction HC1. odor, gooey
10 -4
SP "is SAND, poorly graded, f1n« to very fine, 0-101 fines, loose,
saturated, tan to grey, very strong odor
15 -
20 —
CL HHS 5ILTY CUY. moderately plastic, 5-15X very fine sand, 20-301
silt, stiff, moist-damp, tan to grey, very strong reaction
to HC1. odnr
CH
CH
30 —
CH
CUY. highly plastic, 0-lOt very fine sand, stiff, moist, tan,
very strong reaction HC1, odor
CUY. similar to above, except very stiff, no odor
CUY. similar to above except mottled tan and very light green
35 -
40 -
45 —
CH
CH
CL
P
SANDY CUY. highly plastic, 15-25J very fine sand, firm (cru*.
bles), moist, grey, moderate reaction to HC1
SANDY CUY. similar to above except 30-40t very fine sand,
stiff, strong reaction to HC1
SANDY CUY, similar to above, except sllghtly-moderately
plastic, 40-501 very fine sand, very moist
50 -
SP/
CH
1
SAND i SANDY CUY LAYERS-
SAND, poorly graded, fine to very fine. 0-51 fines, loose.
moist, tan to grey, slight reaction to HC1
I SANDY CLAY, similar to above, except varying plasticity and/
\ sandy content ^hrouohout I
iotal ueoth at 50 ft.
-------
BORING LOG
BORING NO. B-4
DATE DRILLED 7/8/75
TOTAL DEPTH 46'
SURFACE ELEVATION 56.4'
-C
a
0
a
t
-
_
5 -
"j
15 —
_
20-
25 —
-
30 —
J
-1
— 1
J
45 —
-
50 _
j
~~;
"o
.a
1
i'
•I
1
CH 'f
1
"\
y
MH
CH ^
CH V
\
t.
sw '••:•:
c
a
a
a Samole Description
•3
7>
0 Oik
H 4
\
/ CLAY, soorly graded, 10-151 silt, 30X clay, very plastic, hard
/, Tpp-3.5). saturated, tan color, root mottles
A SIL7Y CLAY, poorly graded, 10-151 fine sand. 30-35? silt, SOS
ty clay, some minor caliche, very highly plastic, very Hard
^ (pp «.5), saturated, tan matrix with areas of red reduction,
y| wnlte caliche and black organics. root mottles, worn burrows
/. SANOY CLAY, poorly graded, 20-30S fine sand, 10-20^ silt,
'/ 50", cUy, minor caliche, highly oiastic, hard (pp-3.0),
A saturated, same color >.s samole ?t 10' . root nnttlps
f
: SAHOY SILT, soorly graded, 5-101 medium sand, 20-30* fine sand,
i JO--OJ siit, 10-151 clay, hignly oiastic. hard (pp«3.0),
! saturated, tan matrix, black organic spots
] SANOY CLAYEY SILT. ;oorly graded. 23-lQr, fins to m»di,,.-n 5;1nH,
1 50; snt, lO-JO^ clay, hignly oiastic. hard (pp*3.3),
' saturated, tan with black organic spots, good ripple develop-
ment
/
/ CLAY, poorly graded, 5-151 fine sand, 70-80X clay, highly
',, plastic, hard (pp-3.5), saturated, tan matrix, red reduction
/ spots, black organics, ripples, root mottles
A
/
', CLAY, same as sample at 30'
A
A
/
/ SANDY CLAY, poorly graded, 20-30J fine sand, 50-60* clay, 10S
/ organtcs, hignly plastic, hard (pp-3.0), saturated, tan
..;i SANO, well graded. 20-251 medium arained. 60-70! Hn. nr.in.H
i \ sard, in.isi clay or silt, non-olast1c, comoact, saturated /
! \ tan /
| Total Depth at 16'
-------
BORING LOG
BORING NO. B-5
DATE DRILLED 7/8/75
TOTAL DEPTH 38'
SURFACE ELEVATION 49.6'
>•
CO
DESCRIPTION OF STRATUM
9
12.
15
18
21
24
27
30.
33_
36.
39
CH/
CL
SM
CH
SC
CL
Clay, slightly organic, slightly silty, dark
brown, moist
Slightly calcareous
Sand, silty, slightly clayey, 60% fine to
medium-grained, light gray, saturated
Clay, slightly calcareous, red/tan, moist
Stiff, light tan with gray
Highly calcareous
Sand, silty, clayey, 60% fine-grained, light
tan, wet
Saturated
Clay, calcareous, sandy, light tan, wet
T.D. 38'
-------
BORING LOG
BORING NO. B-6
DATE DRILLED 7/27/76
TOTAL DEPTH 50*
SURFACE ELEVATION
£
a
o
O
5-
-
_
10-
~
15-
20—
.
25—
_
30—
35—
-
_
40—
-
—
45 —
—
"o
a
CO
CL
SP
sc
CL
CH
SP
CL
CL
CL
SP
JC
a
ia
w
a
a
CO
1
^
•*/•'.-
•::•:
M
1
\
/
•
>\
1
1
^
ft
fy
//
'/
/
'/,
Sample Description
CLAY, moderately plastic. 2-3% f1n« sand, stiff, moist, red
with black dendrltes, root mottles, no odor
SANO, poorly graded, mostly fine sand. 1-3X fines, very lonte.
saturated, tan to buff, silts In partings, root mottles, no
ndnr*
CLAYEY SAND, similar to above only 1% caliche gravel and
5-81 fines
SANDY CLAY, moderately plastic. 1-2X caliche gravel. 10-151
fine sand, tan to reddish brown, root mottles, no odor
S.ILTY.CLAY, similar to above only no sand and Is highly
"plastic
CLAYEY SANO. poorly graded, mostly fine sand, 201 fines, com-
pact, saturated, buff colored, root mottles, clay partings.
CLAY, slightly plastic. IS caliche pellets. 1-31 fine sand.
hard, saturated, light green, root mottles, no odor
CLAY, similar to above
CLAY, similar to above
SANO, poorly graded, mostly fine sand, loose, saturated, tan
\ to buff, root mottles, no odor /
Total Depth at 50 ft.
-------
BORING LOG
BORING NO. B-7
DATE DRILLED 3/21/76
TOTAL DEPTH 50'
SURFACE ELEVATION 59.3'
a
o
a
o
a
>.
CO
Sample Description
5 -
SP
CLAYEY SAMO. poorly graded. 801 mostly fine sand. 20t fines,
stiff (pp-3.0), damp, tan, dens*, root mottles, reduction
spots, no odor
CH
10 —
/
X
CLAY, highly plastic, 3-4X very fine sand, hard (pp 4.5),
moist, tan, root mottles, reduction spots, no odor
IS —
SANO, poorly graded, 971 mostly fine sand. Z-31 fines, loose,
moist, tan, reduction soots, no odor
20 —
CL
X
SANOY CLAY, moderately plastic, 301 mostly medium sand, firm
lpp-2.75), moist, tan, reduction spots, sand appears 1n
Dockets
CL
X
/.
X
CLAY, moderate plasticity, Z-31 fine sand, hard (pp 4.5). moist
tan, reduction spots
SC
CLAYCY SANO. poorly graded, 601 medlm to fine sand. 40X fines.
very dense, moist, tan, reduction spots, root mottles, no odor
35 -
40 -
45 -
CH
CH
CH
CH
CLAY, high plasticity, 3-4% very fine sand, dense (pp 4.5).
saturated, tan, reduction spots, no odor
CLAY, similar to above
SANOY CLAY, similar to above only 10-15S mostly fine sand
CLAY, similar to above only 3-4X very fine sand
Total Depth at 50 ft.
-------
BORING LOG
BORING NO. B-8
DATE DRILLED 3/22/76
TOTAL DEPTH 44'
SURFACE ELEVATION 54,5-
.c
Q.
0>
Q
5_
10 -
15
20 -
?C _,
30 -J
35 -
40 -
45 H
-
o
JO
E
>>
(0
\vv
^VO
1
1
Ir
1
r
•x::::::
:|:j:j:j:;
Description of Stratum
Tnncni 1
CLAY, slightly silty, slightly calcareous,
dark gray, moist (CH)
CLAY, silty, calcareous", light gray, moist
ICL)
-very calcareous, small nodules •
-light tan, calcareous, saturated @ 11 ft,
-trace of sand, tan and red, moist
•.cl i nhtl \/ ^al c* A v*ennc
CLAY , firm, slightly silty, large crystals
of calcite, tan with red and black, moist
VlCH/CL)
SILT. 30% clay, 20% very fine sand, light
tan, saturated (ML)
CLAY. 25* silt, 15% very fine sand, cal-
careous, tan and red, moist (CL)
v CLAY, slightly calcareous, tan and red,
\- moist fcfl^
\CLAYEY SAND saturated - no returns (SC)
\uLAY_, 20% very fine sand, abundant crys-
tals and nodules of calcite, gray, moist
(CL/CH)
-moderately stiff
SAND, fine, 30% clay, light tan, satura-
X ted (SC)
\ CLAY, stiff, slightly calcareous, tan and
\ red, moist (CH) -
T.D. 44'
-------
|