OSWER DIRECTIVE 9502.00-6C
    RCRA FACILITY INVESTIGATION (RFI) GUIDANCE
                 VOLUME II OF IV
SOIL, GROUND WATER AND S
AS RELEASES
          -^N.    NJJLY19I
          ^   \N/
             /ASTE MANAGEMENT DIVISION
               OFFICE OF SOLID WASTE
        U.S. ENVIRONMENTAL PROTECTION AGENCY
          REPRODUCED BY
          I I C r\CDA DTUCIUT r\r /Ny-ti

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                               ABSTRACT
   On November 8, 1984, Congress enacted the Hazardous and Solid Waste
Amendments (HSWA) to RCRA. Among the most significant provisions of HSWA are
3004(u), which requires corrective action for releases of hazardous waste or
constituents  from solid waste management units at hazardous waste treatment,
storage and  disposal facilities seeking final RCRA permits;  and  |30Q4(v), which
compels corrective action for releases that have migrated beyond the facility
property boundary.  EPA will be promulgating rules to implement the corrective
action provisions of HSWA, including requirements for release investigations and
corrective measures.

   This document, which is presented in four volumes, provides guidance to the
owner or operator of hazardous waste management facilities as to the conduct of
the second phase ot the RCRA Corrective Action Program, the RCRA Facility
Investigation (RFI). Instruction is provided for the development and performance of
an investigation based on determinations made by the regulatory agency as
expressed in the schedule of a permit or in  an  enforcement order issued under
HSWA3008(h). The purpose of the RFI is to obtain information to fully characterize
the nature and  extent of releases of hazardous waste or constituents.  This
information  will  be used to determine whether interim corrective measures or  a
Corrective Measures Study will be necessary.

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                               DISCLAIMER
     This Draft Report was prepared for the U.S. Environmental Protection Agency
by the NUS Corporation, Waste Management  Services Group, Gaithersburg, MO
20878, in fulfillment of Contract No, 68-01-7310, Work Assignment No.  5, and is
based on previous work performed by Alliance Technologies, Inc., under Contract
No. 6JJ-01-6871. The opinions, findings, and conclusions expressed herein are those
of the authors and not necessarily those  of the U.S.  Environmental Protection
Agency or the cooperating agencies. Mention of company or product names is not
to be considered an endorsement by the U.S. Environmental Protection Agency.

     This document is intended to assist Regional and State personnel in exercising
the discretion conferred by regulation in developing requirements for the conduct
of RCRA Facility Investigations (RFIs) pursuant to 40 CFR 264. Conformance with this
guidance is expected to result in the development of RFIs that meet the regulatory
standard of adequately detecting  and characterizing  the nature  and extent of
releases.  However, EPA will not necessarily limit acceptable RFIs to those that
comport with the guidance set forth herein. This document is not a regulation (i.e.,
it dots not establish a standard of conduct which has the force of law) and should
not be uitd as such.  Regional and State personnel must exercise their discretion in
using this guidance document as well as other relevant information in determining
whether an RFI mtets the regulatory standard.

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                          ACKNOWLEDGEMENTS


    This document was developed by the Waste Management Division of the
Office of Solid Waste (OSW). Mr. George Dixon was the EPA Work Assignment

Manager and Mr. Art Day was the Section Chief. Additional assistance was provided
by Ms. Lauris Davies and Mr Paul Cassidy.


    Guidance was also provided by the EPA ftFl Work Group, including;


         George Furst. Region              Janette Hansen, PSPD
         Andrew Bellina, Region fl          Lisa Feldt, HSCO
         William Smith, Region II            Stephen Botts, OECM
         Jack Potosnak, Region III           Chris DeRosa, OHEA
         Douglas McCurry, Region IV        James Durham, OAQPS
         Francine Norling, Region V         Mark Guilbertson, OWPE
         Lydia Boada Clista, Region VI       Nancy Hutzel, OGC
         Karen Flournoy, Region VII         Steve Golian, OERR
         Larry Wapensky, Region VIII        Dave Eberly, PSPO
         Julia Bussey, Region IX            Jackie Krieger, OPPI
         Melanie Field, Region IX           Lisa Lefferts, PSPD
         Jim Breitlow, Region IX            Florence Richardson, CAD
         Paul Day, Region X           *   Reva Rubenstein, CAD
         David Adler, OPPf                Steve Sisk, NEIC
         Joanne Bahura, WMD


    This document was prepared by the NUS Corporation, Tetra Tech,  Inc., and

Labat Anderson, Inc., and was based on  previous work performed by Alliance

Technologies, Inc. The principal authors included:


         Todd Kimmell, NUS               Tom Grieb, Tetra Tech
         Kyrt Sichelstiel, NUS                Kay Johnson, Tetra Tech
         William  Murray, NUS               Bill Mills, Tetra Tech
         Ron Stoner, NUS                   Nick Pangaro, Alliance
         John Gtorge, NUS                 Linda Marler, Alliance
         Ray Dever, NUS                    Andrea Mysliki, Labat Anderson
         Dave Navecky, NUS

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              RCHA FACILITY INVESTIGATION (RFI) GUIDANCE
                            VOLUME II
          SOIL, GROUND WATER AND SUBSURFACE GAS RELEASES

                        TASLE OF CONTENTS
SECTION                                                   PAGE

ABSTRACT                                                   i
DISCLAIMER                                                  ii
ACKNOWLEDGEMENTS                                         iii
TABLE OF CONTENTS                                           iv
TABLES                                                     xii
FIGURES                                                    xiii
LIST OF ACRONYMS                                            xv

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                               VOLUME II
            SOIL, GROUND WATER AND SUBSURFACE GAS RELEASES
                           TABLE OF CONTENTS
SECTION                                                          PAGE

9.0    SOIL                                                      9-1
   9.1  OVERVIEW                                                 9-1
   9.2  APPROACH FOR CHARACTERIZING RELEASES TO SOIL            9-2
       9.2.1     General Approach                                 9*2
       9.2 2     Inter-media Transport                              9-8
   9.3  CHARACTERIZATION OF THE CONTAMINANT SOURCE AND       9-9
       THE ENVIRONMENTAL SETTING
       9.3.1     Waste Characterization                            9-9
       9.3.2     Unit Characterization                    *          9-1?
            9.3.2.1   Unit Design and Operating Characteristics        9-17
            9.3.2.2   Release Type (Point or Non-Point Source)         9-17
            9.3,2.3   Depth of the Release                          9-20
            9.3.2.4   Magnitude of the Release                      9-22
            9.3.2.S   Timing of the Release                         9-23
       9.3.3     Characterization of the Environmental Setting         9-24
            9.3.3.1   Spatial Variability                             9-24
            9.3.3.2   Spatial and Temporal Fluctuations in Soil         9-25
                     Moisture Conent
            9.3.3.3   Soil, Liquid, and Gaseous Materials m            9-28
                     the Unsaturated Zone

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                     VOLUME II CONTENTS (Continued)
SECTION                                                          PAGE
     9.3.4     Sources of Existing Information                        9-38
         9.3.4.1    Geological and Climatologies! Data                9-38
         9.3.4.2    Facility Records and Site-Specific Investigations      9-39
9.4  DESIGN OF A MONITORING PROGRAM TO CHARACTERIZE           9-39
     RELEASES
     9.4.1     Objectives of the Monitoring Program                   9-39
     9.4.2     Monitoring Constituents and Indicator Parameters       9-41
     9.4.3     Monitoring Schedule                                  9-42
     9.4.4     Monitoring Locations                                 9-42
         9.4.4.1    Determine Study and Background Areas            9-42
         9.4.4.2    Determine Location and Number of Samples        9-43
         9.4.4.3    Predicting Mobility of Hazardous Constituents      9-46
                   in Soil
                   9.4.4.3.1   Constituent Mobility                    9-47
                   9.4.4.3.2   Estimating Impact on Ground-Water      9-49
                             Quality
9.5  DATA PRESENTATION                                          9-57
     9.5.1     Waste and Unit Characterization                       9-57
     9.5.2     Environmental Setting Characterization                9-57
     9.5.3     Characterization of the Release                        9-61
9.6  FIELD METHODS                                               9-61
     9.6.1     SurficiaI Sampling Techniques                         9-63
         9.6.1.1    Soil Punch                                      9-63
         9.6.1.2    Ring Samplers                                   9-63
         9.6.1.3    Shovels, Spatulas, and Scoops                     9-63
         9.6.1.4    Soil Probes (tube samplers)                       9-64

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                     VOLUME II CONTENTS (Continued)

SECTION                                                          PAGE
         9.6.1.5    Hand Augers                                   9-64
     9.6.2     Dttp Sampling Methods                              9-64
         9.6.2.1    Hollow-Stem Augers                             9-65
         9.6.2.2    Sol id-Stem Augers                               9-65
         9.6.2.3    Core Samplers                                  9-65
                   9.6.2.3.1  Thin-Walled Tube Samplers             9-65
                   9.6,2.3.2  Split-Spoon Samplers                   9-66
         9.6.2.4    Trenching                                      9-66
     9.6.3     Pore Water Sampling                                 9-66
9.7  CHECKLIST                                                   9-69
9.8  REFERENCES                                                  9-71

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                    VOLUME II CONTENTS (Continued)

SECTION                                                       PAGE
10.0 GROUND WATER                                           10-1
    10.1 OVERVIEW                                            10-1
    10.2 APPROACH FOR CHARACTERIZING RELEASES TO             10-2
         GROUND WATER
         10.2.1    General Approach                             10-2
         10,2.2    Inter-media Transport                          10-8
    103 CHARACTERIZATION OFTHi CONTAMINANT SOURCE        10-8
         AND THE ENVIRONMENTAL SETTING
         10.3.1    Waste Characterization                        10-8
         10.3.2    Unit Characterization                          10-11
         10.3.3    Characterization of the Environmental Setting     10-12
                  10.3.3.1   Subsurface Geology                   10-53
                  10.3.3.2   Flow Systems                         10-56
         10.3.4    Sources of Existing Information                   10-61
                  10.3.4.1   Geology                             1061
                  10.3.4.2   Climate                              10-62
                  1C.3.4.3   Ground-Water Hydrology              10-62
                  10.3.4.4   Aerial Photographs                    10-62
                  10.3.4.5   Other Sources                        10-63
    10.4 DESIGN OF A MONITORING PROGRAM TO CHARACTERIZE      10-63
         RELEASES
         10.4.1    Objectives of the Monitoring Program             10-63
         10.4.2    Monitoring Constituents and Indicator Parameters  10-66

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                     VOLUME I! CONTENTS (Continued)

SECTION                                                          PAGE
          10.4.3    Monitoring Schedule                             10-67
                   10.4.3.1   Monitoring Frequency                  10-67
                   10.4.3.2   Duration of Monitoring                 10-68
          10.4.4    Monitoring Locations                            10-69
                   10.4.4.1   Background and Dowmgradient Locations 10-73
                   10.4.4.2   Well Spacing                           10-74
                   10.4.4.3   Depth and Screened Intervals            10-78
     10.5  DATA PRESENTATION                                      10-82
          10.S, 1    Waste and Unit Characterization                  10-82
          10.5.2    Environmental Setting Characterization            10-83
          10.5.3    Characterization of the Release                   10-90
     10.6  FIELD METHODS                                          10-92
          10.6.1    Geophysical Techniques                          10-92
          10.6.2    Soil Boring and Monitoring Well Installation        10-93
                   10.6.2.1   Soil Borings                           10-93
                   10.6.2.2   Monitoring Well Installation             10-97
          10.6.3    Aquifer Characterization                         10-99
                   10.6.3.1   Hydraulic Conductivity Tests             10-99
                   10.6.3.2   Water Level Measurements              10-101
                   10.6.3.3   Dye Tracing                           10-103
          10.6.4    Ground-Water Sample Collection Techniques       10-103
     10.7  CHECKLIST                                               10-107
     10.8  REFERENCES                                             10-110

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                     VOLUME II CONTENTS (Continued)

SfCTION                                                          PAGE

11.0  SUBSURFACE GAS                                             11-1

     11.1 OVERVIEW                                              11-1
     11.2 APPROACH FOR CHARACTERIZING RELEASES OF              11-2
         SUBSURFACE GAS
         11.2.1     General Approach                               11 -2
         11.2.2     Inter-media Transport                           11 -7
     11.3 CHARACTERIZATION OF THE CONTAMINANT SOURCE         11-7
         AND THE ENVIRONMENTAL SETTING
         11.3.1     Waste Characterization                          11-10
                   11.3.1.1   Decomposition Process                 11-10
                        11.3.1.1.1  Biological Decomposition          11-11
                        11.3.1.1.2  Chemical Decomposition           11-12
                        11.3.1.1.3  Physical Decomposition            11-12
                   11.3.1.2   Presence of Constituents                11-13
                   11.3.1.3   Concentration                         11-14
                   11.3.1.4   Othtr Factors                         11-14
         11.3.2     Unit Characterization                            11-15
                   11.3.2.1   Landfills                              11-17
                   11.3.2.2   Units Closed as Landfills                 11-17
                   11.3.2.3   Underground Tanks                    11-17
         11.3.3     Characterization of the Environmental Setting      11-17
                   11.3.3.1   Natural and Engineered Barriers         11-17
                        11.3.3.1.1  Natural Barriers                    11-18
                        11.3.3.1,2 Engineered Barriers                11-18

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                     VOLUME II CONTENTS (Continued)

SECTION                                                         PAGE
                   11.3.3.2  Climate and Meteorological Conditions   11-19
                   11.3.3.3  Receptors                            11-20
     11.4 DESIGN OF A MONITORING PROGRAM TO CHARACTERIZE      11-20
         RELEASES
         11.4.1     Objectives of the Monitoring Program             11-22
         11.4.2     Monitoring Constituents and Indicator Parameters  11-23
         11.4,3     Monitoring Schedule                           11-24
         11.4.4     Monitoring Locations                           11 -24
                   11.4.4.1  Shallow Borehole Monitoring           11-24
                   11.4.4.2  Gas Monitoring Wells                  11-26
                   11.4.4.3  Monitoring in Buildings                11-28
                   11.4.4.4  Us of Predictive Models               11-29
     11.5 DATA PRESENTATION                                    11-30
         11.5.1     Waste and Unit Characterization                  11-30
         11.5.2     Environmental Setting Characterization           11-30
         11.5.3     Characterization of the Release                   11-31
     11.6 FIELD METHODS                                         11-31
         11.6.1     Above Ground Monitoring                       11-37
         11.6.2     Shallow Borehole Monitoring                     11 -38
         11.6.3     Gas Well Monitoring                            11-38
     11.7 CHICKUST                                              11-41
     11.8 REFERENCES                                             11-43

APPENDICES
Appendix C:    Geophysical Techniques
Appendix D:   Subsurface Gas Migration Model

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                                 TABLES
NUMBER                                                          PAGE
   f-1         Recommended Strategy for Characterizing Releases       9-3
              to Soil
   9-2         Release Characterization Tasks for Soils                  9-6
   9-3         Transformation/Transport Processes in Soil               9-10
   9-4         BODj/COD Ratios for Various Organic Compounds        9-14
   9-5         Potential Release Mechanisms for Various Unit Types      9-18
   9-6         Relative Mobility of Solutes                            9-52
   10-1        Recommended Strategy for Characterizing Releases to    10-4
              Ground Water
   10-2        Release Characterization Tasks for Ground Water         10-6
   10*3        Summary of Regional Flow Cells                        10-1?
   10-4        Default Values for Effective Porosity                    10-49
   10-5        Factors Influencing the Intervals Between Individual      10-75
              Monitoring Wells Within a Potential Migration Pathway
   10-6        Applications of Geophysical Methods to Hazardous       10-94
              Waste Sites
   10-7        Factors Influencing Density of Initial Boreholes           10-95
   11-1        Recommended Strategy for Characterizing Releases of    11-3
              Subsurface Gas
   11 -2        Release Characterization Tasks for Subsurface Gas        11 -6
   11-3        Summary of Selected Onsite Organic Screening           11-32
               Methodologies
   11-4        Summary of Candidate Methodologies for Quantification 11-33
               of Vapor Phase Organics
   11-5        Typical Commercially Available Screening Techniques for 11-36
              Organics in Air
   11-6        Subsurface Sampling Techniques                       11-39

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                                             FIGURES
            NUMBER                                                          PAGE
               9-1        Hydrogeologic Conditions Affecting Soil Moisture        9-27
                          Transport
               9-2        Soil Terms                                           9-29
               9-3        Hypothetical Adsorption Curves for A) Cations and 8)      9-54
                          Anions Showing Effect of pH and Organic Matter
               9-4        Fields of Stability for Aqueous Mercury at 25C           9-56
                          and Atmospheric Pressure
               9-5        Example of a Completed Boring Log                    9-59
               9-6        Typical Ceramic Cup Pressure/Vacuum Lysimeter          9-68
               10-1       Occurrence and Movement of Ground Water and         10-14
                          Contaminants Through (a) Porous Media, (b) Fractured
                          or Creviced Media, {cj Fractured Porous Media
               10-2       Ground Water Flow Paths in Some Different             10-15
                          Hydrogeologic Settings
               10-3       Western Mountain Ranges                            10-18
               10-4       Alluvial Basins                                       10-20
               10-5       Columbia Lava Plateau                                10-22
               10-6       Colorado Plateau                                     10-24
               10-7       High Plains                                          10-25
|              10-8       Non-glaciated Central                                10-27
               10-9       Glaciated Central                                     10-29
               10-10      Piedmont and Blue Ridge                             10-32
               10-11      Northeast and Superior Uplands                        10-33
 i              10-12      Atlantic and Gulf Coastal Plain                         10-35
 v
               10-13      Southeast Coastal Plain                               10-38
               10-14      Hawaiian Islands                                     10-41

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NUMBER
                           FIGURES (Continued)
                                                   PAGE
   10-15       Alaska                                              10-42
   10-16       Alluvial Valleys                                      10-43
   10-17       Monitoring Well Placementand Screen Lengths in a      10-52
              Mature Karst Terram/Fractured Bedrock Setting
   10-18       Monitoring Well Locations                            10-64
   10-19       Example of Using Soil Gas Analysis to Define Probable     10-71
              Location of Ground-water Release Containing Volatile
              Organics
   10-20       Vertical Well Cluster Placement                        10-79
   10-21       General Schematic of Multiphase Contamination In a     10-81
              Sand Aquifer
   10-22       Potentiometric Surface Showing Flow Direction          10-87
   10-23       Approximate Plow Net                               10-88
   11-1        Subsurface Gas Generation/Migration in a Landfill        11-8
   11-2        Subsurface Gas Generation/Migration from Tanks and    11-9
              Units Closed as Landfills
   11-3
Schematic of a Deep Subsurface Gas Monitoring Well
1-27

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                           LIST OF ACRONYMS
AA
Al
ASCS
ASTM
8CF
BOO
CAQ
CPF
CBI
CEC
CERCLA

CFR
CIR
CM
CMI
CMS
COD
COLIWASA
DNPH
DO
DOT
ICO
EM
EP
EPA
FEMA
FID
Foe
FWS
GC
GOMS
GPR
HE A
HliP
HPLC
H5WA
HWM
ICP
ID
Kd
Koc
Kow
LEI
MCL
MM5
MS/MS
NFIP
N1OSH
NPDES
OSHA
Atomic Absorption
Soil Adsorption Isotherm Test
Agricultural Stabilization and Conservation Service
American Society for Testing and Materials
Bioconcentration Factor
Biological Oxygen Demand
EPA Carcinogen Assessment Group
Carcinogen Potency Factor
Confidential Business Information
Cation Exchange Capacity
Comprehensive Environmental Response, Compensation, and
Lability Act
Code of Federal Regulations
Color Infrared
Corrective Measures
Corrective Measures Implementation
Corrective Measures Study
Chemical Oxygen Demand
Composite Liquid Waste Sampler
Dinitrophenyl Hydrazine
Dissolved Oxygen
Department of Transportation
Electron Capture Detector
Electromagnetic
Extraction Procedure
Environmental Protection Agency
Federal Emergency Management Agency
Flame lonization Detector
Fraction organic carbon in soil
U.S. Fish and Wildlife Service
Gas Chromatography
Gas Chromatography/Mass Spectroscopy
Ground Penetrating Radar
Health and Environmental Assessment
Health and Environmental Effects Profile
High Pressure Liquid Chromatography
Hazardous and Solid Waste Amendments (to RCRA)
Hazardous Waste Management
Inductively Coupled (Argon) Plasma
Infrared Detector
Soil/Water Partition Coefficient
Organic Carbon Absorption Coefficient
Octanol/Water Partition Coefficient
Lower Explosive Limit
Maximum Contaminant Level
Modified Method 5
Mass Spectroscopy/Mass Spectroscopy
National Flood Insurance Program
National Institute for Occupational Safety and Health
National Pollutant Discharge Elimination System
Occupational Safety and Health Administration

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                      LIST OF ACRONYMS (Continued)


OVA          -     Organic Vapor Analyzer
PID           -     Photo ionization Detector
pKa           -     Acid Dissociation Constant
ppb           -     parts per billion
ppm          -     parts per million
PUF           -     Polyurethane Foam
PVC           -     Polyvinyl Chloride
QA/QC        -     Quality Assurance/Quality Control
RCRA              Resource Conservation and Recovery Act
RFA           -     RCRA Facility Assessment
RfD                Reference Dose
RFI            -     RCRA Facility Investigation
RMCL         -     Recommended Maximum Contaminant Level
RSD           -     Risk Specific Dose
SASS          -     Source Assessment Sampling System
SCBA         -     Self Contained Breathing Apparatus
SCS           -     Soil Conservation Service
SOP           -     Standard Operating Procedure
SWMU        -     Solid Waste Management Unit
TCLP          -     Toxicity Characteristic Leaching Procedure
TEGD         -     Technical Enforcement Guidance Document (EPA, 1986)
TOC           -     Total Organic Carbon
TOT           -     Time of travel
TOX           -     Total Organic Halogen
USGS         -     United States Geologic Survey
USLE          -     Universal Soil Loss Equation
UV            -     Ultraviolet
VOST         -     Volatile Organic Sampling Train
VSP           -     Verticle Seismic Profiling
WQC         -     Water Quality Criteria

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                                SECTIONS

                                   SOU

9.1   Overview

     The objective of an investigation of a release to soil is to characterize the
nature, extent, and rate of migration or a  release of hazardous waste or
constituents to that medium.  This section provides:

        A recommended strategy for  characterizing  releases to soils, which
         includes characterization of the source and the environmental setting of
         the release, and conducting a monitoring program that will characterize
         the release,

     *   Recommendations for data organization and presentation;

     *   Appropriate field methods that may be used in the investigation; and

     *   A checklist of  information that may  be  needed for  release
         characterization.

     The exact type and amount of information  required for sufficient release
characterization will be site-specific and should be determined through interactions
between the regulatory agency and the facility owner or operator during the RFI
process.  This guidance does not define the specific data needed in all instances;
however, it identifies possible information that might be necessary to perform
release characterizations and methods for obtaining  this  information.  The RFI
Checklist, presented at the end of this section, provides a tool for planning and
tracking information for release characterization.  This list is not meant to be a list
of requirements for all releases to soil. Some release investigations will involve the
collection of only a subset of the items  listed, while others may involve the
collection of additional data.

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9.2  Approach for Characterizing Releases to Soil

9.2.1      General Approach

     Characterizing contaminant releases to soils may employ a phased approach.
Data collected during an initial phase can be evaluated to determine the need for or
scope of subsequent efforts.  For example, if a suspected release was identified by
the regulatory agency, the initial monitoring effort may be geared  to release
verification. Table 9-1 presents a recommended release characterization strategy.
The intensity and duration of the investigation will depend on the complexity of the
environmental setting and the nature  and magnitude (e.g., spatial extent and
concentrations) of the release.

     A preliminary task in any soil investigation should be to review existing site
information that might help to define the nature and magnitude of the release.
Information supplied by the regulatory agency in permit  conditions  or an
enforcement order will indicate known or suspected releases to soil from specific
units at the facility needing investigation; and may also indicate situations where
inter-media contaminant transfer should be investigated.

     The owner or operator should plan the initial characterization  effort with all
available information on the site, including wastes and soil characteristics. During
the initial phase, constituents of concern as well as indicator parameters should be
identified that can be used to characterize the release and  determine the
approximate extent and rate of migration of the release. Table 9-2  lists tasks that
can be  performed to characterize a release to soils and  displays the  associated
techniques and outputs from each of these tasks. Soil characteristics and  other
environmental factors include 1) surface features such as topography, erosion
potential, land-use capability, and vegetation; 2) stratigraphic/hydrologic features
such as soil profile, particle size distribution, hydraulic conductivity, pH,  porosity,
and cation exchange capacity; and 3) meteorological factors such as temperature,
precipitation, runoff, and evapotranspiration.  Soil physical and chemical properties
should be measured to determine the potential mobility of the contaminants in the

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                                 Table 9-1


          Recommended Strategy for Characterizing Releases to Soil*



                               INITIAL PHASE


1.    Collect and review preliminary information for use in formulating monitoring

     procedures:


         Waste characterization
         Unit characterization
         Surface features and topography
         Soil stratigraphy and hydrology
         Meteorological conditions


2.    Identify and collect additional information necessary to characterize release:


         Waste and unit information
         Soil characteristics and other environmental factors
         Monitoring data
         Inter-media transport
         Formulate conceptual model of release


3.    Develop monitoring procedures:


         Determine monitoring program objectives
         Select constituents and indicators to be monitored
         Plan  initial sampling based on site/waste/soil  characteristics and
         conceptual model
         Define study and background areas
         Determine sampling methods, locations, depths and numbers
         Sampling frequency
         Analytical plans
         QA/QC procedures

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                           Table i-1 (Continued)


           Recommended Strategy for Characterizing Releases to Soil*




4,    Conduct initial monitoring phase:


         Conduct initial soil sampling and field measurements
         Collect geologic data
         Analyze samples for selected constituents and indicators


5.    Collect, evaluate, and report results:


         Compare monitoring results to health and environmental criteria and
         identify and respond to emergency situations and identify priority
         situations  that may warrant interim corrective measures - Notify
         regulatory  agency
         Determine  completeness and adequacy of collected data
         Summarize and present data in an appropriate format
         Determine  if monitoring program objectives were met (e.g., monitoring
         locations, constituents and frequency were adequate to characterize
         release (nature, rate and extent)
         Report results to regulatory agency


                     SUBSEQUENT PHASES (if necessary)


1.    Identify additional information necessary to characterize release:


         Identify additional information needs
         Determine need  to exand or include further soil  stratigraphic and
         hydrologic sampling
         Evaluate potential for inter-media  contaminant transfer (e.g., leaching
         studies to evaluate potential for ground-water contamination)


2.    Expand initial monitoring as necessary


         Expand sampling area and/or density
         Add or delete constituents and parameters of concern
         Increase or decrease monitoring frequency

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                           Table 9-1 (Continued)


          Recommended Strategy for Characterizing Releases to Soil*



3.    Conduct subsequent monitoring phases:


         Perform expanded monitoring and field analyses
         Analyze samples for selected constituents and parameters


4,    Collect, evaluate, and report results/identify additional information necessary

     to characterize release:


         Compare results to health and environmental criteria and identify and
         respond to emergency situations and identify priority situations that
         warrant interm corrective measures - Notify regulatory agency
         Determine completeness and adequacy of collected data
         Summarize and present data in appropriate format
         Determine if monitoring program objectives were met
         Determine if monitoring locations, constituents, and frequency were
         adequate to characterize release (nature, extent, and rate)
         Determine need to expand monitoring system
         Evaluate potential for inter-media contaminant transfer
         Report results to regulatory agency
     The possibility for inter-media transport of contamination exists and should be
     anticipated throughout the investigation.

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                                     TABLE 9-2
                 RELEASE CHARACTERIZATION TASKS FOR SOILS
     investigatory Tasks
Investigatory Techniques
   Data Presentation
   Formats/Outputs
1.  Waste/Unit
   Characterization
Rtftr to Sectiom 3 and 7
Table of monitoring
constituents and their
chemical/physical properties

Table of unit ft stores
contributing to soil releases
2.  Environmental Setting
   Characterization

       Determ i ne su rf a
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soil.  Waste and soil properties should be  examined to formulate a  conceptual
model of the release.

     As monitoring  data become available, both within and at the conclusion of
discrete investigation phases, it should be  reported to the regulatory agency as
directed. The regulatory agency will compare the monitoring data to applicable
health and environmental criteria to determine the need for (1) interim corrective
measures; and (2) a Corrective Measures Study. In addition, the regulatory agency
will evaluate the monitoring data with respect to adequacy and completeness to
determine the  need for  any additional monitoring efforts.  The health and
environmental criteria and a general discussion of how the regulatory agency will
apply them are supplied in Section 8. A flow diagram illustrating RFI decision points
is provided in Section 3 (see Figure 3-2).

     Not withstanding the above process, the owner or operator has a continuing
responsibility to identify and respond to emergency situations and to define priority
situations that may  warrant interim corrective measures.  For such situations, the
owner or operator is directed to obtain and follow  the RCRA Contingency Plan
requirements under 40 CFR Part 264, Sub part D, and Part 265, Sub part 0.

     As indicated above, depending on the results of the initial phase, the need for
further characterization will be determined  by the regulatory agency.  Subsequent
phases, if necessary, may involve expansion of the sampling network, changes in the
study area, investigation of contaminant transfer to other media, or  other
objectives dictated by the initial findings. The owner or operator may propose to
use a mathematical model to aid in the choice of additional sampling locations or to
estimate mobility in soil.  The results of all  characterization efforts should be
organized and presented to the regulatory agency in a format appropriate to the
data.

     Case Study Numbers 1, 2,  3 and 17  in Volume IV (Case  Study Examples)
illustrate various aspects of soil investigations.

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9.2.2      Inter-media Transport

     As mentioned above, the potential for inter-media transfer of releases from
the soil medium to other media is significant. Contaminated soil can be a major
sojrce of contamination to ground water, air, subsurface gas and surface water
Hazardous wastes or constituents, particularly those having a moderate to high
degree of mobility, can leach from the soil to the ground water  Volatile wastes or
constituents can contribute to subsurface gas and releases to air.  Contaminated
soils can also contribute to surface water releases, especially through run-off during
heavy rains.  Application of the universal soil loss equation (See Section 13.6) can
indicate whether inter-media transport from soil to surface water as a result of
erosion can  act as a source of contamination.  The owner  or operator should
recognize the potential  for inter-media transport of releases to soil and should
communicate as appropriate with the regulatory agency when such transport is
suspected or identified during the investigation.

     Similarly  the potential for inter-media transport of constituents from other
media  to the soil also exists.  For example, hazardous waste or constituents may be
transported to the soil via atmospheric deposition (especially during rain or
snowfall events) through the air medium, and also through releases of subsurface
gas. The guidance provided in this section addresses characterization of releases to
soil from units and also can be used to characterize releases  to soil as a  result of
inter-media  transport through other  media. A key to  such characterization is
determining the nature of the contaminant source, which is described in Section 9.3.

     It is also important to recognize that where multiple media  appear to be
contaminated, the investigation  can be coordinated to  provide results that can
apply to more than one of the affected media. For example, soil-gas analysis (using
an organic vapor analyzer along with the subsurface investigation) can be used to
investigate releases to soil  and subsurface gas releases, and  may also provide
information concerning the spatial extent of contaminated ground water.

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9.3  Characterization of the Contaminant Source and the Environmental Setting

9.3.1     Waste Characterization

     The physical  and chemical properties of the waste or its constituents affect
their fatt and transport in soil; and, therefore affect the selection of sampling and
analytical methods.  Identification of monitoring constituents and the use of
indicator parameters  is discussed in  Section 3  and Aopendix S.  Sources of
information and sampling techniques for determining waste characteristics are
discussed in detail in Section 7,

     Chemicals  released to soil may undergo transformation  or degradation by
chemical or biological mechanisms, may  be  adsorbed onto soil particles, or may
volatilize into soil pore spaces or into the air. Table 9*3 summarizes various physical,
chemical, and biological transformation/transport processes that affect waste and
waste constituents in soil.

     The chemical properties of the contaminants of concern  also influence the
choice of sampling method. Important considerations include the water solubility
and volatility of the contaminants, and the  potential hazards to equipment and
operators during sampling. For example, water soluble compounds that are mobile
in soil water can be detected by pore water sampling and whole  soil sampling.
Volatile organic contaminants require specialized sampling and  sample storage
measures to prevent losses poo* to analysis.  Viscous substances require different
sampling techniques due to their physical properties

     Reactive, corrosive, or  explosive wastes may pose a potential hazard to
personnel during  sail  sampling.  High levels of  organic contamination may also
cause health problems due to toxicity. For example, landfills can produce methane
gas that can  explode  if ignited by sparks or heat from the drilling operation.
Corrosive, reactive, or explosive wastes can also damage soil sampling equipment or
cause fires and explosions. Appropriate precautions to prevent such incidents
include having an  adequate health and safety pian in place, using explosimeters or
organic vapor detectors as early-warning devices, and  employing  geophysical
techniques to help identify buried objects (e.g., to locate buried drums). All

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                TABLE 9*3
TRANSFORMATION/TRANSPORT PROCESSES IN SOIL
Process
Biodegradation
Photodcgradation
Hydrolysis
Oxidation/reduction
Volatilization
Adsorption
Dissolution
Key Factor
Waste degradability
Waste toxicity
Acclimation of microbial community
Aerobic/anaerobic conditions
pH
Temperature
Nutrient concentrations
Solar irradiation
Exposed surface area
Functional group of chemical
Soil pH and ouff ering capacity
Temperature
Chemical class of contaminant
Presence of oxidizing agents
Partial pressure
Henry's Law Constant
Soil diffusion
Temperature
Effective surface area of soil
Cation exchange capacity (CEC)
Fraction organic content (foe) of soil
Octanol/water partition coefficient (k0w)
Solubility
Soil oH and buffering capacity
Complex formation

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 contaminated soil samples should be handled as if they contain dangerous levels of
hazardous wastes or constituents.

     Identity and  composition of contaminants-The owner  or operator should
identify and provide approximate concentrations for any constituents of concern
found in the original waste and, if available, in leachate from any releasing unit.
Identification of other (non-hazardous) waste components that  may affect the
behavior of hazardous constituents or may be used as indicator parameters is also
recommended.  Such components may form a primary leachate causing transport
behavior different from water and may also mobilize hazardous constituents bound
to the soil. Estimations of transport behavior can help to focus the determination of
sampling locations.

     Physical state of cpntaminants-The physical state (solid, liquid, or gas) of the
contaminants in the waste and soil should be determined by inspection or from site
operating  records. Sampling can then be  performed  in locations most likely to
contain the contaminant.

     ViKO>ity-The viscosity of any bulk liquid wastes should be determined to
estimate potential mobility in soils.  A liquid with a lower viscosity will generally
travel faster than one of a higher viscosity.

     p_H--Bulk liquid pH may affect contaminant transport in at  least two ways:
(1) it may alter the chemical form of acids and bases, metaLsalls, and other metal
complexes, thereby altering their water solubility and soil sorption properties, and
(2) it may alter the soil chemical or physical makeup, leading to changes in sorptive
capacity or permeability. For example, release of acidic (low pH) wastes in a  karst
(e.g., limestone) environment can lead to the formation of solution channels.  See
Section 10.3 for more information on karst formations.

     Dissociation constant (pKa)-For  compounds that are  appreciably ionized
within the expected range of field pH values, the pKa of the compound should be
determined. Ionized compounds have either a positive or negative charge and are
often highly soluble in water; therefore, they are generally  more mobile than in
their neutral forms when dissolved.  Compounds that  may ionize include organic
and inorganic acids and bases, phenols, metal salts, and other inorganic complexes.

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Estimated  contaminant concentration  isopleths  can be  plotted with  this
information and can be used in determining sampling locations.

     Densitv-The density of major waste components should  be determined,
especially for liquid wastes. Components with a density greater than water, such as
some chlorinated solvents, may migrate through  soil  layers more quickly than
components less dense than water, such as gasoline.

     Water solubility-This chemical property influences constituent mobility and
sorption of chemicals to soil particle surfaces.  Highly water-soluble compounds are
generally very mobile in soil and ground water.  Liquid wastes that have low
solubility in water may form a distinct phase in the soil with flow behavior different
from that of water.  Additional sampling locations may be needed to characterize
releases of insoluble species.

     Henry's Law constant-This parameter indicates the partitioning ratio  of a
chemical between air and water phases at equilibrium.  The larger the value of a
constituent's  Henry's Law Constant, the greater is it's tendency to volatilize from
water surrounding soil particles into soil pore spaces or into above-ground air. The
Henry's Law Constant should be considered  in assessing the potential for inter-
media transport of constituents in soil gas to the air. Therefore, this topic is also
discussed in the Air and Subsurface Gas sections (Section 11 and 12, respectively).
Information on this parameter can help in determining which phases to sample in
the soil investigation.
     Octanol/Water partition coefficient (kftw)-The characteristic distribution of a
chemical between an aqueous phase and an organic phase (octanol) can be used to
predict the sorption of organic chemicals onto soils. It is frequently expressed as a
logarithm (log kow).  In transport models. (COM/ is frequently converted to koc. a
parameter that takes into account the organic content of the soil. The empirical
expression used to calculate koc is:  koc  0.63 kowfoo where foe is the fraction by
weight of organic carbon in the soil.  The higher the value of kow (or koc) the
greater  the tendency of  a constituent to adsorb to soils containing appreciable
orgar.i carbon. Consideration of this parameter will also help in determining which
phases to sample in the soil investigation.

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     BiodeQradabilitv--There is a wide variety of microorganisms that may be
present in the soil. Generally, soils that have significant amounts of organic matter
will contain a higher microbial  population, both  in density and in diversity.
Microorganisms are responsible for the decay and/or transformation  of organic
materials and thrive mostly m the "A* (uppermost) soil horizon  where carbon
content is generally highest and where  aerobic digestion occurs.  Since  some
contaminants can serve as organic nutrient sources that soil microorganisms will
digest as food, these contaminants will be  profoundly affected within organic soils.
Digestion may lead to complete decomposition, yielding carbon dioxide and water,
but more often resulting in partial decomposition and transformation into other
substances. Transformation products will likely have different physical, chemical or
toxicological characteristics than the original contaminants.  These products may
also be hazardous constituents and should therefore be considered in  developing
monitoring programs. The decomposition or degradation rate depends on various
factors, including:

     *   The molecular structure  of the contaminants.  Certain manmade
         compounds (e.g., PCBs and  chlorinated pesticides)  are  relatively
         nondegradable (or persistent), whereas others (e.g., methyl alcohol) are
         rapidly consumed by bacteria.  The owner or operator should consult
         published lists of compound degradability such as Table 9-4 to determine
         the persistence of waste constituents in soil. This table provides relative
         degradabilities for some organic compounds and can be used to identify
         appropriate monitoring constituents and  indicator parameters. It-may-
         be especially useful for older  releases where degradation may be a
         significant factor. For example, some of the parent compounds that are
         relatively degradable (see Table 9*4) may have been reduced to carbon
         dioxide and water or other decomposition products prior to sampling.
         Additional information on degradability  can be found in Elliott and
         Stevenson, 1977, Sims et al, 1984, and U.S. EPA. 1985.  See Section 9.8 for
         complete citations for these references.

         Moisture content Active biodegradation does not generally occur  in
          relatively dry soils or in some types of saturated soils, such as those that
          are saturated for long periods of time, as in a bog.

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TABLE 9-4. 8ODs/COD RATIOS FOR VARIOUS ORGANIC COMPOUNDS'
Compound
RELATIVELY UNOEGRADABLE
Butane
Butyln
Cartxin tttrachloride
Chloroform
1,4-Qioxane
Ethan*
Heptane
Hexane
Isobutant
isooutyiene
liquefied natural gas
Liquefied petroleum gas
Methane
Methyl bromide
Methyl chloride
Monochlorodiflueromethane
Nitrobenzene
Propane
Propylene
Propylene oxide
Tetrachloroethylene
Tetrahydronaphthalehe
1 Pentrene
Ethylene dichloride
lOctene
Morpholine
Ethyienediaminetetracetic acid
Triethanolamine
o-Xylene
m-Xylene
Ethylbenxene
MODERATELY OEGRAOABtE
Ethyl ether
Sodium alkylbenzenesulfonates
Monoisopropanol amine
Gas oil (cracked)
Gasoline* (various)
Ratio

-0
-0
~Q
-0
-0
-0
~o
~o
-.0
~9
~0
-0
~o
-0
-0
-0
-o
-o
-0
-0
-o
-o
< 0.002
0.002
>0.003
< 0.004
0.005
< 0.006
< 0.008
< 0.008
< 0.009

0012
~0.017
<0.02
-0.02
-0.02
Compound
MODERATELY DEGRAOA8LE
(CONTD)
Mineral spirits
Cyclohtxanol
Acrylomtriie
Nonanol
Undecanoi
Methylethylpyridine
1-Hexene
Methyl isobutyl ketone
Oiethanolamme
Formic acid
Styrene
Heptanol
sec-Butyl acetate
n-Butyl acetate
Methyl alcohol
Acetonttrtle
cthylene glycoJ
Ethylene glycol monoethyl ether
Sodium cyanide
Linear alcohols ( 1 2- 1 5 carbons)
Ally! alcohol
Oodecanol
RELATIVELY OEGRADABLE
Valeraldehyde
n-0eyl alcohbJ
p-Xylene
Urea
Toluene
Potawium cyanide
isopropyl acetate
Amyl acetate
Chlorobtmzene
let fuel! (various)
Kerosene
Range oil
Glycerin*
Adiponitnle
Ratio

-Q.02
0.03
0.031
>0.033
<0.04
0.04-075
< 0.044
< 0.044
<0049
0.05
>0.06
<0,07
0.07-0.23
0.07-024
0.07-0.73
0.079
0.081
<0.0f
<0.09
>0.09
0.091
0.097

<0.10
>0.10
<0.11
0.11
<0.?2
0.12
<0.13
0.13-0.34
0.15
-0.15
-0.15
-0.15
<016
017

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                              TABLE 9-4. (Continued)
Compound
RELATIVELY DEGRADA8UE
(cowro.)
Furfural
2-tthyt-3-propylacrolein
Methylethylpyndine
Vinyl acetate
Oiethylene glycol monomethyl
tthr
Napthalene (molten)
Oi butyl phthalate
Hexanol
Sovbean oil
?r raformaldehyde
n-Propyl alcohol
Methyl methacrylate
Acrylic acid
Sodium alkyl sulfates
Triethytene glyeol
Acetic acid
Acetic anhydride
Ethylenediamine
Formaldehyde solution
Cthyl acetate
Octanol
Sorbitol
Beniene
n-Butyl alcohol
Propionaldehyde
n-Butyraldehyde

Ratio

OJ7-C.46
<0.19
<0.20
<0.20
<0.20
<020
0.20
-0.20
~0.20
0.20
0.20-
0.63<0.24
<024
0.26
0.30
0.31
0.31-0.37
>0.32
<0.3S
0.35
<0.36
0.37
<0,3S
<0.3f
0.42-0,74
<0.43
<0.43

Compound
RELATIVELY DEGRADABLE
(CONTO.)
Ethyleneimme
Monoethanolamine
Pyndine
Dimethyl formamide
3extrose solution
Corn $ymp
Maleic anhydride
Propiomc acid
Acetone
Am lint
isopropyl alcohol
n-Amyl alcohol
itoamyl alcohol
Cresoli
Crotonaldehyde
Phthalic anhydride
Benialdehyde
Iwbutyl alcohol
2.4-Oichlorophenol
Tallow
Phenol
Senzek acid
Carbolic acid
Methyl ethyl ketone
Benxoyl chloride
Hydrazine
Oxalic acid
Ratio

0.46
0.46
0.46-O.Sa
0.48
0.50
~O.SQ
>051
0.52
0.55
356
0.56
O.S7
0.57
0.17-0.68
<0.58
0.58
0.62
0.63
0.78
-0.80
0.81
0.84
0.84
0.88
0.94
1.0
1.1
Source:   U.S. iPA 1985. Handbook: Remedial Action at Waste Disposal Sites (Revised).
          EPA/62S/6-85/006. NT IS P982-239054. Office of Emergency and Remedial Response.
          Washington, D.C 20460.

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        The  presence or absence of oxygen in the soil.  Most decjradable
         chemicals decompose more rapidly in aerobic (oxygenated)  soil.
         Although  unsaturated surficial  soils are generally aerobic, anaerobic
         conditions may exist  under landfills or other units.   Soils that are
         generally saturated year round are relatively anaerobic (e.g., as in a bog);
         however, most saturated soils contain enough oxygen to support active
         biodegradation.  Anaerobic biodegradation, however,  can  also  be
         significant in some cases. For example, DOT degrades more rapidly under
         anaerobic conditions than under aerobic conditions.

        Microbial adaptation or acclimation.  Biodegradation depends on the
         presence in the soil of organisms capable of metabolizing the waste
         constituents. The large and  varied population of microorganisms in soil
         is likely to have some potential for favorable growth using organic
         wastes and constituents as nutrients.  However, active metabolism
         usually requires a period of adaptation or acclimation  that can range
         from several hours to several  weeks  or months, depending on the
         constituent or waste properties and the microorganisms involved.

        The availability of contaminants to micro-organisms. Releases that occur
         below the upper 6 to 8 inches of soil are less likely to be affected since
         relatively  few organisms exist there.   In addition, compounds with
         greater aqueous solubilities are generally more  available  for
         degradation. However, high solubility also correlates  directly to the
         degree of mobility. If relatively permeable  soil conditions prevail and
         constituents migrate rapidly, they are  less likely to be retained long
         enough in the soil for biodegradation to occur.

        Other factors.   Activity of organisms is also dependent  on favorable
         temperature and pH conditions as well as the  availability  of  other
         organic and inorganic nutrients for metabolism

     Rates of  Hydrolysis. Photolysis, and  Oxidation-Chemical  and physical
transformation of the waste can also  affect the identity, amounts,  and  transport
behavior of the waste constituents. Photolysis is important primarily for  chemicals
on the land surface, whereas hydrolysis and oxidation can occur at various depths.

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Published literature sources should be consulted to determine whether individual
constituents are likely to degraded by these processes, but it should be recognized
that most literature values refer to aqueous systems. Relevant references include
Elliott and Stevenson, 1977; Sims et al. 1984; and U.S. EPA, 198S.  Chemical and
physical degradation will also be affected by soil characteristics such as pH, water
content, and soil type.

9.3.2      Unit Characterization

     Unit-related factors that may be important in characterizing a release include:

         Unit design and operating characteristics;

         Release type (point-source or nonpoint-source);

     *    Depth of the release;

     *    Magnitude of the release; and

         Ti mi n g of th e rel ease.

9.3.2.1    Unit Design and Operating Characteristics

     information on design and operating characteristics of a unit can be helpful in
characterizing a release. Table 9-5 presents important mechanisms of contaminant
release to soils for various unit types. This information can be used to identify areas
for initial soil monitoring.

9.3.2.2    Release Type (Point or Non-Point Source)

     The  owner or operator should establish whether the release involved a
localized (point) source or a non-point source. Units that are likely sources of

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                             TABLE 9-5
      POTENTIAL RELEASE MECHANISMS FOR VARIOUS UNIT TYPES
Unit Type
Surface Impoundment
Landfill
Waste Pile
Land Treatment Unit
Container Storage Area
Above-ground or
In-ground Tank
Incinerator
Oass l and IV Injection
Wells
Release Mechanisms
loading/unloading areas
Release* from overtopping
Seepage
Migration of releases outside the unit's runoff collection
and containment system
Migration of releases outside the containment area from
loading and unloading operations
Leakage through dikes or unlined portions to surrounding
soils
Migration of runoff outside the unit's runoff collection and
containment system
Migration of releases outside the containment area from
loading and unloading operations.
Seepage through underlying toils
Migration of runoff outside the containment area
Passage of leachate into the soil horizon
Migration of runoff outside the containment area
Loading/unloading areas
Leaking drums
Releases from overflow
Leaks through tank shell
Leakage from coupling/uncoupling operations
Leakage from cracked or corroded tanks
Rout ne releases from wane handling/preparation activities
Leakage due to mechanical failure
Leakage from waste handling operations at the well head
*  Waste transfer stations and waste recycling operations generally have mechanisms of
   release similar to tanks.

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localized releases to soil include container handling and storage areas, tanks, waste
piles, and bulk chemical transfer areas (e.g., loading docks, pipelines, and staging
areas).  Non-point sources may include airborne particulate contamination
originating from a land treatment unit and widespread  leachate seeps from a
landfill.  Land treatment can also result in widespread releases beyond the
treatment zone if such units are not properly designed and  operated; refer to EPA's
Permit Guidance Manual on Hazardous Waste Land Treatment Demonstration. July,
1986 (NT!S P886-229192) for additional information on determining contamination
from land treatment units. This manual  also discusses  use of the RITZ model
(Regulatory and Investigation  Treatment Zone Model), which may be particularly
useful for evaluating mobility and degradation within the treatment zone.  This
model is discussed in more detail in Section 9.4.4.2.

    The primary characteristic of a localized release is generally a limited area of
relatively high contaminant concentration  surrounded by  larger areas of relatively
clean soil. Therefore, the reiease characterization should focus on determining the
boundaries of the contaminated area to minimize  the analysis of numerous
uncontammated samples. Where appropriate, a survey of the area with an organic
vapor analyzer, surface geophysical instruments (see Appendix C), or other rapid
screening techniques may aid in narrowing the area under investigation. Stained
soil and stressed vegetation may provide additional indications of contamination.
However, even if the extent of contamination appears to be obvious, it is the
responsibility of the owner or operator to verify boundaries of the contamination
by analysis of samples from outside of the contaminated area.

    Non-point type releases to soil may also result from deposition of particulates
in the air, such as from an incinerator.  Such releases generally have a characteristic
distribution with concentrations often decreasing logarithmically away from the
source and generally having  low variability within a small area.  The  highest
contaminant concentrations tend to follow the prevailing wind directions (See also
Section 12 on Air).  Non-point releases occurring via other mechanisms (e.g., land
treatment)  may be distributed  more evenly over  the affected area.   In these
situations, a large area may need to be investigated in  order to determine the
extent of contamination.  However, the relative lack of "hot spots" may allow the
number of samples per unit area to be smaller than for a point source release.

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9.3.2.3   Depth of the Release

     The owner or operator should consider the original depth of the release to soil
and the depth to which contamination may have migrated since the release. Often,
releases occur at the soil surface as a result of spillage or leakage. Releases directly
to the subsurface can occur from leaking underground tanks, buried pipelines,
waste piles, impoundments, landfills, etc.

     Differentiating between deep and shallow soil  or surficial soil  can be
important in sampling and in determining potential impacts of contaminated soil.
Different methods to characterize releases within deep and surficial soils may be
used. For example, sampling  of surficial soil may involve the use of hand-driven
coring equipment, whereas deep-soil contamination usually requires the use of
power-driven equipment (see Section 9.6 for more information).  In addition, deep-
soil and surficial-soil contamination may be evaluated differently in the health and
environmental assessment process discussed  in Section 8. Assessment of surficial-
soil contamination  will  involve  assessing risk  from potential ingestion of the
contaminated soil as well as assessing potential impacts to ground water.  The
assessment of deep-soil contamination may be limited to determining the potential
for the soil to act as a continuing source of potential contamination to ground
water in the uppermost aquifer.

     For purposes of the RFI, surficial or shallow-zone soils may be defined as those
comprising the upper 2 feet of earth, although specific sites may exhibit surficial soil
extending to depths of up to 12 feet or more. Considerations foi determining the
depth of the shallow-soil zone may include:

        Meteorological conditions (e.g., precipitation, erosion due to high winds,
         evaporation of soil-pore gases);

        Potential for excessive s-rfice runoff, especially if runoff would result in
         gully formation;

        Transpiration, particularly from the root zone, and effects on vegetation
         and animals, including  livestock, that may feed on the vegetation; and

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         Land use, including potential for excavation/construction, use of the soil
          for fill material, installs* ,1  of utilities (e.g., sewer lines or electrical
          cables), and farnung activity.

     Deep-soil zones, for purposes of the rtKl, may be defined as those extending
from 2 feet below the land surface to the ground-water surface.  If deep-soil
contamination is already affecting ground water (through inter-media transport),
at a specific site consideration should be given to evaluating the potential for such
contamination to act as a continuing source of ground-water contamination.

     The depth to which a release may migrate depends on many factors, including
volume of waste released, amount of water infiltrating the soil, age of the release,
and chemical and physical properties  of the waste and soil (as addressed in the
previous section),  in a porous, homogeneous soil, contaminants tend  to move
directly downward within the unsaturated zone.  Lateral movement generally
occurs only through dispersion and diffusion. However, changes in soil structure or
composition with depth (stratification), and the presence of zones of seasonally
saturated  soil, fractures, and other features may cause contaminants to  spread
horizontally for some distance before migrating downward.  Careful examination
of soil cores and accurate measurement of physical properties and moisture content
of soil are therefore essential in estimating the potential for contaminant transport.

     Transport of chemicals in the soil is largely caused by diffusion and mass flow
Diffusion results from random thermal motion of molecules. Mass flow, also known
as convective flow, is transport by s flowing liquid or by a gaseous phase. Mass flow
is typically downward (due to gravity); however, mass flow could also be upward
due to capillary action (e.g.. if significant evaporation occurs at the surface).  Mass
flow is a much faster transport mechanism than is diffusion (Morrill et ai., 1J85).

     Other factors that can promote  downward contaminant  migration  include
turnover of soil by burrowing animals, freeze/thaw cycles, and plowing or other
human activities. All factors that may affect the depth of contamination should be
considered.  The owner or operator should use available information to estimate
the depth of contamination and should then conduct sampling at appropriate
depths to confirm these estimates.

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     Approaches to monitoring releases to soil will differ substantially depending
on the depth of contamination.  For investigations of both surficial- and deep-soil
contamination, a phased approach may be used. Initial characterization will often
necessitate a judgmental approach in which sampling depths are chosen based on
available information (e.g., topography, soil stratigraphy, and visual indication of a
release).  Information derived from this  initial  phase can  then  be used to  refine
estimates of contaminant distribution and transport.  This information will serve as
a basis for any subsequent monitoi ing that may  be necessary.

     Where the source or  precise location of  a suspected release  has  not been
clearly identified, screening sampling (See Section 9.6} may be necessary.
Subsurface contamination  can be detected by using  geophysical methods or
organic vapor probes.  Geophysical methods,  for example, can help in locating
buried drums.  Organic vapor analysis can be useful in estimating the lateral  extent
of soil contamination, but delineating the vertical extent of contamination may
necessitate an additional effort such as core sampling and analysis.   Sampling
approaches for locating and delineating subsurface contaminant sources include
systematic and random grid sampling. These approaches are discussed in Section 3.
Geophysical methods are discussed in Section 10 (Ground Water) and in Appendix C
                 iques).
9.3.2.4    Magnitude of the Release

     Information on the magnitude of the release can be estimated from site
operating records, unit design features, and other sources.  The quantity (mass) of
waste released to soil and the rate of release can affect the geographical extent and
nature of the contamination. Each soil type has a specific sorptive capacity to bind
contaminants. If the sorptive capacity  is exceeded, contaminants tend to migrate
through the soil toward the ground water. Therefore, a " minor" release may be, at
least temporarily, immobilized in shallow soils, whereas a "major* release is more
likely to result in ground-water contamination.  The  physical  processes of
volatilization and  dissolution in water are also affected  by contaminant
concentrations and should, therefore, be considered in assessing the potential for
inter-media transport. Section 9.4.4.3 provides additional guidance on estimating
the mobility of constituents within contaminated soils.

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9.3.2.S   Timing of the Release

     Time-related factors that should be considered in characteriiing a release
include:

        Age of the release;

     *   Duration of the release;

     *   Frequency of the release; and

     *   Season (time of year).

     The length of time that has  passed since a  release  occurred can affect the
extent of contamination, the chemical composition of the  contaminants present in
soil, and the potential for inter-media transport. Recent releases tend to be more
similar in composition to the parent waste material and may also be  more
concentrated within the original boundaries of the release.  If a recent release
occurred  at the land surface, contaminant volatilization  to air or dissolution in
overland  runoff may be important transport mechanisms.  Older releases are more
likely to have undergone extensive chemical or biological changes that altered their
original composition  and may have migrated a considerable distance from their
original location.  If the contaminants are relatively mobile in soil, transport to
ground water may be a concern; whereas soil-'oound contaminants may be more
likely affected by surface transport, such as runoff or wind. These factors should be
considered in the selection of monitoring constituents and sampling locations.

     The duration and frequency  of the release can affect the amounts of  waste
released to the soil and their distribution  in the soil. For example, a release that
consisted of a single episode, such as a ruptured tank, may  move as a discrete "slug"
of contamination through the soil. On the other hand, intermittent or continuous
releases may present a situation in which contaminants exist at different distances
from the source and/or have undergone considerable chemical and biological
decomposition. Therefore, the design of monitoring procedures and estimations of
contaminant fate and transport should consider release duration and frequency.

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     The time of year or season may also affect release fate and transport. Volatile
constituents are more likely to be released to the air or to migrate as subsurface gas
during the warmer summer months. During the colder winter months, releases may
be less mobile, especially if freezing occurs.

9.3.3      Characterization of the Environmental Setting

     The  nature and extent of contamination is  affected  by environmental
processes such as dispersion and degradation acting after the release has occurred.
Factors which should be considered include soil physical  and chemical properties,
subsurface geology and hydrology, and climatic or meteorologic patterns.  These
factors are discussed below.

     Characteristics of the soil medium which should be considered in order to
obtain representative samples for chemical or physical analysis include:

     *    The potentially  large spatial  variability of soil properties and
          contaminant distribution;

     *    Spatial and temporal fluctuations in soil moisture content; and

     *    The presence of solid, liquid, and gaseous  phases in the unsaturated
          zone.

9.3,3.1    Spatial Variability

     Spatial variability, or heterogeneity, can be defined as horizontal and vertical
differences  in soil properties occurring  within the scale of the  area under
consideration. Vertical discontinuities are found in most soil  profiles as a result of
climatic changes during soil formation, alterations  in topography or vegetative
cover, etc. Soil layers show wide differences in their tendency to sorb contaminants
or to transmit contaminants in a liquid form;  therefore, a monitoring program that
fails to consider vertical stratification will likely result in an inaccurate assessment of
contaminant distribution.  Variability in soil properties may also occur in the
horizontal plane as a result of factors such as drainage, slope, land use history, and
plant cover.

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     Soil and site maps will aid in designing sampling procedures by identifying
drainage patterns, areas of high or low surface permeability, and areas susceptible
to wind erosion and contaminant volatilization.  Maps of unconsolidated deposits
may be prepared from existing soil  core information, well drilling logs, or from
previous geological studies. Alternately, the information can be obtained from new
soil borings.  Since soil coring can be a resource-intensive activity, it is generally
more efficient to also obtain samples from these cores for preliminary chemical
analyses and to conduct such activity concurrent with investigation of releases to
other media (e.g., ground water).

     The number of cores necessary to characterize site soils depends on the site's
geological complexity and size, the potential areal extent of the release, and the
importance of defining small-scale discontinuities in surficial materials.  Another
consideration is the potential risk of spreading the contamination as a result of the
sampling effort. For example, an improperly installed well casing could lead to
leakage of contaminated water through formerly low permeability clay layer.  The
risks of disturbing the subsurface should be considered when determining the need
for obtaining more data.

     Chemical and physical measurements should be made for each distinct soil
layer, or boundary between layers,  that may be affected by a release.  During
drilling, the investigator should note on the drilling log the depths of soil horizons,
soil types and textures, and the presence of cracks, channels, and zones containing
plant roots or animal burrows. Soil variability, if apparent,  should  generally be
accounted for by increasing the number of sample points for measurement of soil
chemical and physical properties. Determination of the range and variability of
values for soil properties and parameters will allow more accurate prediction of the
mobility of contaminants in the soil.

9.3.3.2    Spatial and Temporal Fluctuations in Soil Moisture Content

     As described earlier in this section, there are several mechanisms for transport
of waste constituents in the soil. Release migration can be increased by the physical
disturbance of the soil during freeze/thaw cycles or by burrowing animals.
Movement can  also be influenced by microbial-induced transformations.  In
                                    9-25

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addition, movement can occur through diffusion and mass flow of gases and liquids.
Although all of these mechanisms exist, movement of  hazardous waste or
constituents through soil toward ground water occurs primarily  by aqueous
transport of dissolved chemicals in soil pore water.  Soil moisture content affects the
hydraulic conductivity of the soil and the transport of dissolved wastes through the
unsaturated zone. Therefore, characterizing the storage and flow of water in the
unsaturated zone is very important. Moisture in the unsaturated  zone is  in a
dynamic state and is constantly acted upon by competing physical forces.

     Water applied to the soil surface (primarily through precipitation) infiltrates
downward under the influence of gravity until the soil moisture content reaches
equilibrium with capillary forces. A zone of saturation (or wetting front) may occur
beneath the bottom of a unit (e.g., an unlined lagoon) if the unit is providing a
constant source of moisture. In a low porosity soil, such a saturation front  may
migrate downward through the unsaturated zone to the water table, and create a
ground-water or liquid "mound" (see  Figure 9-1).  In a higher porosity soil, the
saturation front may only extend a small distance below the unit, with liquid below
this distance then moving through the soil under unsaturated conditions toward
ground water  (see Figure 9-1).  In many cases,  this area will  remain partially
saturated  until the capillary fringe area is reached.  The  capillary fringe can be
defined as the zone immediately above the water table where the pressure is less
than atmospheric and where water and other liquids are held  within the  pore
spaces against the force of gravity by interracial  forces (attractive forces between
different molecules).

     In certain cases, soil  moisture characterization can also be affected  by the
presence of isolated zones of saturation  and fluctuations in the depth to ground
water, as illustrated in Figure 9-1. Where there is evidence of migration below the
soil surface, these factors should be considered  in the investigation by careful
characterization of subsurface geology and measurement of hydraulic conductivity
in each layer of soil that could be affected by subsurface contamination.

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              HAZARDOUS WASTE DISPOSAL IWOONDMEHT
                                                             ISOLATED SATURATION LAVEII
Figure 9*1. Hydrogeologic conditions affecting soil moisture transport

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9.3.3.3    Solid, Liquid, and Gaseous Materials in the Unsaturated Zone

     Soil in the unsaturated zone generally contains solid, liquid, and gaseous
phases. Depending upon the physical and chemical properties of the waste or its
constituents, contaminants of concern may be bound to the soil, dissolved in the
pore water, as a vapor within the soil pores or interstitial spaces, or as a distinct
liquid phase.  The investigation should therefore take into consideration the
predominant form of the contaminant in the soil.  For example, some whole-soil
sampling methods may lead to losses of volatile chemicals, whereas analysis of soil-
pore water may not be able to detect low solubility compounds such as PCBs that
remain primarily adsorbed in the solid phase. Release characterization procedures
should consider chemical and physical properties of both the soil and the waste
constituents to assist in determining the nature and extent of contamination.

     Soil classificationThe owner or operator should classify each soil  layer
potentially affected by the release.  One  or more of the classification systems
discussed below should be used, based on the objectives of the investigation.

     *    USD A Soil Classification system (USDA,  1975)--Pnmarily developed for
          agricultural purposes, the  USDA  system also provides information on
          tyoicalsoil profiles (e.g., 1-foot fine sandy loam over gravelly sand, depth
          to bedrock  12 feet), ranges of permeabilities for  each layer, and
          approximate particle size ranges. These values are not generally accurate
          enough for predictive purposes,  however, and should not be used to
          replace information collected on  site. Existing information on regional
          soil types is available but suitable for initial planning purposes only. U.S.
          Department of Agriculture (USDA) county soil surveys may be obtained
          for most areas.

     *    Unified Soil Classification Systems (USCS) (lambe and Whitman, 1979)- A
          procedure for qualitative field classification of soils according to ASTM
          D2487-69, this system should be used to identify materials in soil boring
          logs. The USCS is based on field determination of the percentages of
          gravel, sand and fines in the soil, and on the plasticity and compressibility
          of fine-grained soils.  Figure 9-2 displays the decision  matrix  used in
          classifying soils by this system.

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     The above classification systems are adequate for descriptive purposes and for
qualitative estimates of the  fluid transport properties of soil layers. Quantitative
estimation of fluid transport properties of soil layers requires determination of the
particle size distribution for each soil layer, as described below.

     Particle size distribution-A measurement of particle size distribution should
be  made for each  layer of soil  potentially affected  by the release.   The
recommended method for measurement of particle  size  distribution  is a
sieve/hydrometer analysis according to ASTM 0422 (ASTM, 1984).

     The particle size distribution has two major uses in  a  soils investigation;
(1) estimation of  the hydraulic conductivity of the soil by use of the Hazen (or
similar) formula, and (2) assessment of soil sorptive capacity.

     1.   The hydraulic conductivity(K) may be estimated from the particle size
          distribution using the Hazen formula:

                                 K - A (d)0)2

          where dig is equal to the effective grain size, which  is that grain-size
          diameter at which 10 percent by weight of the particles are finer and
          90 percent are coarser (Freeze and Cherry, 1979), The coefficient A is
          equal to 1.0 when K is in units of cm/sec and d 10 is in mm. Results should
          be verified with in-situ hydraulic conductivity techniques.

     2.   Particle size can affect sorptive capacity and, therefore, the potential for
          retardation of contaminants in the soil. Sandy soils generally have a low
          sorptive capacity whereas clays generally have a high affinity for heavy
          metals and some organic contaminants.  This is due in part to the fact
          that small clay particles have a larger surface area in relation to their
          volume than do larger sand particles. This larger surface area can result
          in stronger  interactions with waste molecules.  Clays may also bind
          contaminants due to the chemical structure of the clay matrix.

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     Porosity-Soil porosity is the percentage of the total soil volume not occupied
by solid particles (i.e., the volume of the voids),  In general, the greater the porosity,
the more readily fluids may flow through the soil. An exception is clayey soils that
tightly hold fluids by capillary forces. Porosity is usually measured by oven-drying an
undisturbed sample and weighing it. It is then saturated with liquid and weighed
again. Finally, the saturated sample is immersed in the same liquid, and the weight
of th*> displaced liquid is measured. Porosity is the weight of  liquid required to
saturate the sample  divided by the weight of liquid displaced, expressed as a
decimal fraction.

     Hydraulic conductivitv-An essential physical property affecting contaminant
mobility in soil is hydraulic conductivity. This property indicates the ease with which
water at the prevailing viscosity will flow through the soil and is dependent on the
porosity of the soil, grain size, degree of consolidation and cementation, and other
soil factors.

     Measurement of hydraulic conductivity in the saturated soil below the water
table is fairly routine.  Field and laboratory methods to determine saturated
conductivity are discussed in the section on ground-water investigations (Section
10).  Measurement of unsaturated conductivity is usually more difficult because the
value changes with changing soi! moisture content. Therefore, conductivities for a
range of moisture contents may need to be determined for each type of soil at the
facility.

     Techniques for determining saturated hydraulic conductivity are provided in
Method 9100 (Saturated Hydraulic Conductivity, Saturated Leach ate Conductivity,
and Intrinsic Permeability) from SW-846, Test Methods for Evaluating Solid Waste.
EPA. 3rd edition. September. 1986. Methods 9100 includes techniques for:

         Laboratory

               constant head methods; and
               falling head methods.

     *    Field

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               sample collection;
               well construction;
               well development;
               single well tests (slug tests); and
               references for multiple well (pumping tests).

     A detailed discussion of field  and laboratory methods  for determining
saturated and unsaturated hydraulic conductivity is also contained in Soil Properties
Classification and Hydraulic Conductivity Testing (U.S. EPA, 1984). In general, field
tests are recommended when the soil is heterogeneous, while laboratory tests may
suffice for a soil without stratigraphy changes. Estimation of hydraulic conductivity
from the particle size distribution may be used as a rough estimate for comparison
purposes and if precise values are  not needed

     Relative permeability-Trie hydraulic conductivity of a soil is usually established
using water as the infiltrating liquid. However, at sites where there is the likelihood
of a highly contaminated leachate  or a separate liquid waste phase, the owner or
operator should also consider determining conductivity with that liquid. The ratio
of the permeability of a soil to a non-aqueous solution and its permeability ic water
is known as relative permeability.

     The importance of determining this value is due to the potential effects ot
leachate on  soil hydraulic  properties. Changes in conductivity from infiltration of
leachate may result from differences in the viscosity or surface tension of the waste,
or the leachate may affect the soil structure so as to alter its permeability.  For
example, studies  of waste migration through landfill liners  made of clay have
demonstrated  that certain wastes  may cause shrinking or expansion of the clay
molecular structures, dissolve clays and organic matter,  clog soil pores with fine
particles, and cause other changes that affect permeability.

     Soil sorptive capacity and Soil-Water Partition Coefficient (Kd)-The mobility of
contaminants in soil depends not only on properties related to the physical structure
of the soil, but also on the extent to which the soil material will retain, or adsorb,
the hazardous constituents. The extent to which a constituent is adsorbed depends
on chemical properties of the  constituent and of the soil. Therefore, the sorptive
capacity must be determined with reference to particular constituent and soil pairs.

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The soil-water partition coefficient (Kg) is generally used to quantify soil sorption.

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     Cation  exchange capacity (CEC)--This parameter  represents the extent to
which the clay and humic fractions of the soil will retain charged species such as
metal ions.  The CEC is an important factor in evaluating transport of lead,
cadmium, and other toxic metals.  Soils with a high CEC will retain correspondingly
high levels of these inorganics.  Although hazardous constituents may  be
immobilized by such soils in the short-term, such conditions do not rule out the
possibility of future releases given certain  conditions (e.g., action  of additional
releases of low pH). A method for the determination of CEC is detailed in SW-846,
Method 9081 (U.S. EPA. !986c).

     Organic carbon content--The amount of natural organic material in a soil can
have a strong effect on retention of organic pollutants. The greater the fraction by
weight of organic carbon (F,x), the greater the  adsorption of organics.  Soil  F
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          q a volumetric flux/unit area, cm/day
          e  volumetric water content, dimensionless

     A simple approximation of volumetric flux (q) is to assume that it is equal to
percolation at the site. Percolation can be estimated by performing a water balance
as described below.  This approach for calculating pore-water velocity is limited by
simplifying assumptions; however, the method may  be used to develop an initial
estimate for time of travel of contaminants. More detailed methods, which account
for  unsteady flow and differences in moisture  content  are described in  the
following reference:

     U.S. EPA.  1986.  Criteria for identifying Areas of Vulnerable Hydroqeoloqy
     Under the Resource Conservation and Recovery Act. NTIS PB86-224953. Office
     of Solid Waste. Washington, D.C, 20460.

     Percolation (volumetric flux per unit area|--Movement of contaminants from
unsaturated soil to ground water occurs primarily via dissolution and transport with
percolating soil water. It is important, therefore, to determine the volume of water
passing through the soil.  The percolation rate, or volumetric flux, must be
determined in order to calculate pore water velocity through the unsaturated zone
The rate of percolation can be estimated from the water balance equation:

                             PER - P-ET-DR

where:    PER  *   Percolation/recharge to ground water
          P       Precipitation and irrigation
          ET      Evapotranspiration
          OR   *   Direct surface runoff

Annual averages for P, ET and OR should be obtained from existing local  sources.
Sources of information to estimate PER include:

         State or Regional water agencies;

         Federal water agencies (Geological Survey, Forest Service); and

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         National Weather Service stations.

It is recommended that site-specific ET and OR data be used if possible, since local
conditions can vary significantly from regional estimates.  More information on
percolation and ground-water recharge can be found in standard ground-water
texts such as Freeze and Cherry, 1979. Information on evapotransptration and direct
surface runoff may be found in the following references:

     U.S. EPA. 1975.  Use of  :he Water Balance Method for Predicting Leachate
     Generation from Solid Waste Disposal Sites. E PA/5 30/SW-168. Office of Solid
     Waste. Washington, D.C. 20460.

     U.S. Geological Survey. 1982. National Handbook of Recommended Methods
     for Water Oata Acquisition.

     Volumetric water  content-The volumetric water content is the  percent of
total soil volume that is filled  with water. It is equal to the amount of water lost
from the soil upon drying to constant weight at 105C, expressed as the volume of
water/bulk volume of  soil.  This parameter affects the  unsaturated hydraulic
conductivity and if required for calculation of pore-water velocity.  At saturation,
the volumetric water content is equal to the porosity of the soil.

     Additional soil conditionsAdditional soil conditions that may require special
consideration in investigating releases to soil are discussed below.

     *    In certain dense, cohesive soils, water may  move  primarily  through
          narrow solution channels or fracture zones rather than by permeating
          the bulk of the soil.  This condition can sometimes be recognized by dark-
          colored deposits indicating the fractures or by the tendency of soil cores
          to break apart at the discontinuity,

         Decomposed rock  (e.g., transitional soils) may  have a  low primary
          porosity but a high  secondary porosity due to relict joints or fractures or
          solution channels. Therefore, most flow may  occur through these cracks
          and channels rather than through the soil pores. As a result, the rate of
          fluid flow is likely to be high, and the low surface area within the joint or
                                    O.7C

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fracture system generally results in a low sorptive capacity.  Because field
conditions are highly variable, the characterization of soil structure
should be sufficiently detailed to identify such joints or fractures that
may provide contaminant pathways.

Certain clay soils known as vertisols, or expandable clays, may fracture
into large blocks when dry.   These cracks can be a direct route  for
ground-water contamination.  Soil surveys should  be consulted to
determine whether these soils are present at the site. They occur m, but
are not limited  to, eastern Mississippi and central and southern Texas
Other clay soils may also develop desiccation cracks to a lesser degree.  In
these  cases, it may be advisable to sample during both  wet and dry
seasons.

Sampling saturated soils may be accomplished with the  same drilling
techniques used for unsaturated soil sampling.  Particular care must be
taken to prevent contamination between soil layers.  Methods of
telescoping smaller diameter casing downward through larger diameter,
grouted casing  are useful for minimizing cross-contamination between
soil layers (See  Section 9.6 for additional information  on telescoping
methods).

Frequently, the choice of sampling technique is dictated by mechanical
factors.  Hard, rocky, or dense soils may prevent the use of manual tube
samplers or augers.  Power-driven auger drill rigs equipped with split-
spoon samplers can penetrate most soils. Power augers can penetrate
most unconsolidated materials, but will not drill through rock, for which
an air-driven rotary drill is the recommended method. Loose sandy soils
will fail to be retained in a tube simpler; therefore a sampler equipped
with a retaining device should be  used in such cases.  Core sampling
should generally be carried out under the supervision of an experienced
driller, in order to a void poor results or damaged equipment.

Where unfavorable soil conditions  interfere with a proposed sampling
location, the sampling point may have to be moved to a  nearby location.
                          9-37

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          In the event that such conditions are encountered, new locations should
          be chosen that are adequate to characterize the release

9.3.4     Sources of Existing Information

     Considerable information may already be available to assist in characterizing a
release.  Existing information should be reviewed to avoid duplication of previous
efforts and to aid in scoping the RFI.  Any existing information relating to releases
from the unit and to hydrogeological, meteorological, and environmental factors
that could influence the persistence, transport, or location of contaminants should
be reviewed. This information may aid in:

         Delineating the boundaries of the sampling area;

         Choosing sampling and analytical techniques; and

         Identifying information needs for later phases of the investigation, if
          necessary.

     Information may be obtained from readily available sources of geological and
meteorological data, waste characteristics, and facility operating records. (See also
Sections 2, 3.7 and Appendix A).

-9.3.4.1	Geological and Climatological Data

     The Federal government and most state governments compile geological data,
soil surveys, land use records, and  Climatological information. These sources should
be consulted for local geology, soil  types, historical precipitation, ground-water
elevation records, and other useful data.  Sources which may be consulted for soils
data include the Soil Conservation Service  (SCS),  Agricultural Stabilization and
Conservation Service (ASCS), the U.S. Geological Survey (USGS), state soils bureaus
and agricultural extension services, university soil science departments, and private
consultants.  Additional sources  of  geologic information  include geotechnical
boring'logs for foundation studies, well logs made during drilling of water supply
wells, and  previous hydrogeologic investigation monitoring wells.  These logs

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should indicate the depth, thickness, and character of geologic materials, and the
depth to the water table. Climate and weather information can be obtained from:

          National Climatic Center
          Department of Commerce
          Federal Building
          Asheville, North Carolina  28801
          Tel: (704)258-2850

8.3 4.2    Facility Records and Site Investigations

     The owner or operator should plan investigation activities by focusing on the
conditions specified in the permit  or  enforcement  order.  Facility records, the
facility's RCRA permit application,  and any previous site reports (e.g., the RFA
report) should also be examined for any other information on unit characteristics,
wastes produced at the facility, and other factors relevant to releases to soil.  Facility
operating records should have data on  wastes treated, stored, or disposed of at the
facility.  Wastes regulated under RCRA  are identified by a waste code that may also
aid in identifying constituents of concern (see 40 CFR Part 261).  Wastes originating
within the facility may be identified through analysis of process  control records.
Unit releases (e.g., losses from leaking tanks) can sometimes be  estimated  from
storage records.

9.4  Design of a Monitoring Program to Characterize Releases

9,4.1      Objectives of the Monitoring Program

     Monitoring procedures that specify locations, numbers, depths, and collection
techniques for soil samples should be prepared by the owner or operator prior to
each sampling effort. These procedures  should  provide the justification  for the
proposed  samples, in terms of their expected  contribution  to  the investigation.
Examples of soil monitoring objectives include.

         Describing soil contamination in a drainage channel where a release is
          known to have occurred;

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         Establishing a random or systematic grid sampling network to determine
          soil contamination concentrations in all zones of a large area affected by
          airbornedeposition, and

     *    Filling in data gaps concerning the transport of waste constituents within
          a permeable soil layer.

     In preparing soil monitoring procedures, the owner or operator should take
into consideration those factors discussed in Sections 9.3,1 through 9,3.4 that apply
to the facility.  Also see Section 9.4.4.3 (Predicting  Mobility of  Hazardous
Constituents in Soil).

     As discussed previously, the release characterization may  be conducted in
phases.  The objectives of the initial soil characterization are generally to verify
suspected releases or to begin characterizing known releases.  This characterization
should use relevant soil physical and chemical measurements and other information
as described earlier.  In developing the approach, the owner or operator should
determine the following:

     *    Constituents and indicator parameters to be monitored;

     *    Sampling methods;

     *    Approximate study and background areas;

     *    Sample locations (judgmental or systematic approach); and

     *    Number of samples to be collected.

     Depending on the outcome of the initial characterization effort, the owner or
operator may be required to obtain additional data to characterize the release. The
findings of the initial phase  will dictate the objectives of any -later phases.  Such
subsequent phrases will generally involve the following:

     *    Expanding the number of sampling locations to  a wider area and/or
          depth, or increasing sampling density where data are sparse;

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     *    Institution of a grid  sampling approach  to  further assess releases
          identified by judgmental sampling (see Section 3);

         Addition or deletion of specific monitoring constituent or indicator
          parameters; and

     *    Sampling  in areas of  interest based on previous sampling or model
          predictions to confirm the suspected extent of the release-

     There is no specified or recommended number of phases to complete a soil
investigation. The owner or operator should determine through consultation with
the regulatory agency whether the collected data  are sufficient to meet the
objectives of the investigation.

9.4.2      Monitoring Constituents and Indicator Parameters

     The owner or operator should propose hazardous constituents for monitoring
based on the composition of wastes known to be present  or released to soils at the
site (see Sections 3 and 7 and Appendix B). Additional measurements may include
nonhazardous chemicals that could serve as indicators of the presence of hazardous
constituents or that  could mobilize or otherwise affect the fate and transport of
hazardous constituents.  Chemical and physical properties of the soil that can  be
measured from soil samples should also be included in the list of parameters (see
Section 9.3.3.3).

     Justification of monitoring constituent selection may be provided through
detailed  facility  records or waste analyses, as explained in  Section 3.  If such
justification is inadequate,  it may be necessary to perform a broader analytical
program (SeeSection 3 and Appendix B).

     Afttr or during the selection  of monitoring constituents, the owner  or
operator should review guidance on compound-specific requirements for sampling
and sample preservation. The laboratory should use  EPA protocols and analytical
procedures when available,  and  accepted QA/QC practices. Guidance and specific
references in these areas are provided in Sections 2,3,4, and 7.

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9.4.3      Monitoring Schedule

     Monitoring frequency and duration determinations should be based primarily
on the type oi release to the soil  A single episode or intermittent release, as with
any release, would require monitoring until the nature and extent of contamination
has been characterized. This may be accomplished with one or two sample sets in
some  cases.  Longer-term releases wit' usually necessitate a greater duration of
sampling. Soi! pore liquid may require more frequent monitoring than in soil solids
since changes occur faster in these fluids. Frequency may also be adjusted generally
as sampling results become available.  As with single episode releases, longer-term
releases are monitored until the nature and extent of contamination has bean
adequately characterized.

9.4.4      Monitoring Locations

9.4.4.1        Determine Study and Background Areas

     Determination  of the area of  interest will depend  on the site layout,
topography, the  distribution of surface soils, soil stratigraphy, and information on
the nature and source of the release. The size and type of unit may affect the area
under consideration. For example, a landfill may only require monitoring of the
surrounding soil  whereas an inactive land treatment facility may require sampling
over the entire unit surface and beyond.	

     High variability in the  chemical composition of soils makes determination of
background levels  for the constituents of concern  essential.   This is particularly
important for quantification of metals, since toxic metals may occur naturally in soil.
Background areas not affected by any facility release should be selected based on
their similarity to the study area in terms of soil type, drainage, and other physical
factors.  Background soil samples should be taken from areas that are not near a
suspected source of contamination and from the same stratigraphy layer as the
study samples, if possible. Selection and sampling of appropriate background areas
may be  important  because verification of a release in a contaminated  area may
involve a comparison of study and background concentrations.
                                    Q-Jtt

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     The owner or operator could increase efficiency in the initial characterization
effort by using rapid-screening techniques or (e.g., HNu  or  OVA)  indicator
measurements to establish  the extent  of  the  study area.  Subsurface  soil
contamination can sometimes be identified by geophysical  techniques such as
electromagnetic and resistivity techniques (See  Section 10 and Appendix C).
Indicator parameters can also  be helpful in  establishing  the extent of the
monitoring  area.  For example, Total Organic Halogen (TQX) or Total Organic
Carbon (TOC) analysis may be used to detect total chlorinated solvents.  Such
parameters  may be used to characterize the  nature and extent  of a release but
should always be accompanied by specific constituent analyses.

     It is generally recommended that a sampling grid be developed for the site.
Gridding of the area to be  sampled prior to the sampling effort will aid in
determining appropriate sampling  locations  and in describing  these  locations.
Refer to Section 3.6 for additional information on gridding of a study site.

9.4.4.2   Determine Location and Number of Samples

     The owner or operator should  propose monitoring locations and the number
of samples to be collected and analyzed. Samples should be taken from the vicinity
of all units identified in the conditions of the permit or order as suspected or known
sources of so-! contamination.  The total number of samples necessary for the initial
investigation will depend on the extent of prior information, the suspected extent
and severity of the release, and the objectives of the characterization.  However, the
following general guidance should aid the owner or operator to sample efficiently.

     *   Sampling efficiency may be increased by use of a proportional sampling
         approach, which involves dividing the area of concern into zones, based
         on proximity to the release source and/or other factors. The number of
         samples taken in each zone should be proportional to the area of a zone.

     *   Use of  composite samples may be able to allow detection of
         contamination over  an  area of concern with a  smaller number of
         analyses. Compositing involves pooling and homogemzation of multiple
         soil samples. The composite is then analyzed to give an average value for
         soil contamination in  that area.   However, as discussed in Sections 3 and

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7, composites should have very limited application during the RF1 anc'
should always be accompanied by an appropriate number of individual
grab samples. The  following additional limitations on compositing
should be observed:

     Compositing is most useful when large numbers of soil samples can
     be easily collected (e.g., for surficial contamination).  In order to
     obtain the maximum information from deep soil coring, individual
     grab samples are preferred over composites.

     Compositing should not be used when analyzing soils for volatile
     organics because the constituents of interest may be lost during
     homogenization and sample handling.

The owner or operator should employ appropriate procedures for the
evaluation and reporting of monitoring data. These procedures can vary
in a  site-specific  manner but should result in determinations of the
nature, extent, and rate of migration of the release Where the release is
obvious and/or chemically simple, it  may be possible to characterize it
readily from a descriptive presentation of concentrations found.
However, where contamination is less obvious or the release is chemically
complex, a statistical inference approach may be proposed. The owner
or opertor should plan initially to take a descriptive approach to data
evaluation in order  to broadly delineate the extent of contamination.
Statistical comparisons of monitoring data among monitoring locations
and over time may  be appropriate if a descriptive approach does not
provide a clear characterization of the release. Further guidance on use
of statistical  methods in soil investigations is provided in the following
documents:

     Barth, D.S. and B.J. Mason.  1984.  Soil Sampling Quality Assurance
     User's  Guide    U.S.  EPA 600/4-84-043.   NTIS PB84-198621.
     Washington, D.C 20460.
                          9-44

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              Mason, BJ.  1983.  Preparation  of  a  Soil Sampling Protocol:
              Techniques and Strategies.  NTIS PB83-206979. U.S. EPA 600/4-83-
              020. Washington, DC. 20460.

     *   Characterization of contaminant distribution with depth necessitates
         sampling of each distinct soil layer that might be affected by the release
         and from boundaries between soil layers. If the soil profile contains thick
         layers of homogeneous soil, samples ;hc Jd be taken st regular intervals
         (e.g., every 5 feet). In addition, samples should be taken where borings
         intersect fracture  systems, at interfaces of zones of  high and  low
         permeability materials,  or at other features that could affect waste
         transport. The owner or operator should consider measurement of soil
         physical and hydraulic properties in each distinct soil layer. The objective
         of such measurements in the initial release characterization effort  is to
         identify properties that vary with depth. This  approach may indicate the
         use of stratified sampling in any future sampling phases.  Determination
         of soil  properties will also aid in  refining  conceptual models of
         contaminant transport and can be input for mathematical models of soil
         transport.

     Modeling-Prediction of contaminant  fate and  transport can range  from a
"conceptual" model of waste behavior in the soil to complex computer programs
requiring extensive input of soil and water budget  data.  The primary  uses of
predictive modeling  in  soil  investigations are to locate appropriate sampling
locations using site-specific input data and to estimate the future rate, extent, and
concentration of contaminant releases.

     Modeling of waste  transport in the unsaturateti  zone is often difficult due to
the generally high spatial variability  in soil physical  and hydraulic properties.
Therefore, modeling should  not be used to replace actual measured values (e.g.,
when establishing the limits of waste leaching or diffusion  in soil). However, if used
with caution, models can act as useful tools to guide sampling efforts by directing
sampling towards site areas identified as soil/water flowpaths (e.g., a permeable soil
layer). The owner or operator should discuss the use of  specific models with the
regulatory agency prior to use.

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     Numerous models,  including computer models,  hav5 been developed to
calculate water flow and contaminant transport under saturated and unsaturated
soil conditions. In using such models, site-specific data on soils and wastes should be
used. Ground water (saturated flow) models are discussed in Section 10. A U.S.
Nuclear Regulatory Commission Report (Oster, 1982) may be reviewed for
information on the applicability of 55 unsaturated flow  and transport models. Use
of the RITZ Model (U.S. EPA.  1986.  Permit Guidance  on Hazardous Waste land
Treatment Demonstration} may be particularly appropriate in certain situations.
The RITZ model describes a soil column, 1 meter square, with a depth equal to the
land treatment zone (usually  1.5 m).  The soil column consists  of a plow zone and
lower treatment zone that are made up of four phases:  soil grains,  pore water,
pore air, and pore oil.  Mobilization of constituents within the soil is accounted for
by dispersion, advection, and migration between phases. The constituent may also
be degraded by biochemical processes represented in the model. Output from the
model includes the concentration (C)  of a constituent  at the bottom of the
treatment zone,  and the time (T).required for a constituent  to travel a distance
equal to the treatment zone depth. Although the RITZ model was developed for
evaluating the effectiveness of land treatment units, the model may be used for
other applications, as appropriate (see above referenced document)

     Computer  models if proposed  for use in the RFI should (1) be  well-
documented, (2) have been peer reviewed; and (3) have undergone extensive field
testing.  As indicated previously, model documentation (e.g., model theory,
structure, use, and testing) should be provided to the regulatory agency for review
prior to use. Access to the relevant data sets should also be available upon request.
The regulatory agency may also recommend that a sensitivity analysis be performed
and that the results of the analysis be submitted with the model results. In selecting
a model, the owner or operator should consider its applicability, limitations, data
requirements, and resource requirements.

9.4.4.3    Predicting Mobility of Hazardous Constituents in Soil

     Predicting the mobility of hazardous constituents in soil may be necessary in
an RFI.  The prediction may then be  used to determine the  probable vertical or
lateral extent of contamination, which can be used to  identify potential sampling
locations.  Mobility predictions may also be used in determining potential inter-

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media  transfers from the soil to ground or surface water.  Finally,  mobility
predictions may  provide information  that can  be used during the Corrective
Measures Study to differentiate between contaminated soil that should be removed
from the site and that which may remain  at the site without adversely  affecting
human health or the environment. Predicting mobility of soil constituents may be
particularly relevant, as indicated in Section 8, for determining whether  deep-soil
contamination, or in some cases surficial-soil contamination, can lead  to ground-
water contamination at a level above health and environmental criteria (if such an
impact has not already occurred)

     There is no universally applicable, straightforward method for predicting the
mobility  of  alt hazardous constituents within soils under all  possible sets of
environmental conditions. Nor is there a universally applicable method of
estimating the impact of constituents  originating in the  unsaturated  zone on
ground-water quality.  To avoid unneeded efforts, the first question the  owner or
operator should address is whether this task is necessary.  For example, the
characterization of ground-water quality (conducted following the guidance in
Section 10) may provide information sufficient to describe the extent of the release
and to determine that a Corrective Measures Study is necessary; this should be true
where  the contaminated soils are within  the uppermost aquifer, or when the
hazardous constituents are very mobile. The ground-water impact characterization
may not, however, provide information on the future impact of contaminated soils
on ground water.

     This section presents some general approaches for predicting constituent
mobility in both saturated and unsaturated soils; it also discusses how to estimate
the impact on ground-water quality of the constituents leached from unsaturated
soils. The limitations of these methods are also reviewed.

9.4.4.3.1  Constituent Mobility

     There are several  means of investigating mobility, including a descriptive
approach (i.e., consideration of constituent and soil properties),  the use of
mathematical models, and the use of laboratory models or leaching tests, teaching
tests have the advantage of being the only approach that integrates soil and

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constituent properties in a single evaluation, providing a conservative (reasonable
worst case) estimate of the concentration within leachate of waste constituents that
may eventually impact  ground water   Leaching test results, coupled with site-
specific factors, (e.g., soil cation exchange capacity, ground-water pH, and depth to
ground water), can be used to design monitoring programs, determine potential for
inter-media impacts, and evaluate options for contaminated-soil  corrective
measures.

     The descriptive approach and the  use of mathematical models (such  as the
RITZ Model, discussed  previously} may be appropriate in those cases where
assumptions implicit in the use of leaching tests are not applicable. For example,
leaching  tests may be overpredictive of leachate concentrations where extensive
channeling (e.g., because of root zones) through the contaminated zone is present,
in this case, the  contact time between the leaching fluid (e.g.,  infiltrating
precipitation) and the soil as well as the surface area of the soil exposed to the fluid
would be less than that simulated by the leaching test. Leaching tests may also not
be applicable where low redox (reduction/oxidation) conditions  are  identified.
Consideration of redox conditions is particularly relevant for inorganics.

     Perhaps the most widely used of all leaching tests is the Extraction Procedure
(EP), which is presently used under 40 CFR Part 261.24 to determine whether wastes
pose a hazard because of their potential  to leach toxic constituents, primarily heavy
metals. However, EPA has proposed (51  FR 21648, June 13,1986) to replace the EP
with a new test known as the Toxicity  Characteristic Leaching Procedure  (TCLP).
which is designed to estimate  the concentrations of organic compounds (including
volatile organics)  and inorganic compounds in leachate.   The  TCLP was also
proposed and has since been finalized for use in the land disposal  restrictions rule
(51 FR 40572. November 7,1986).

     The owner or operator may use either of these leaching tests to predict the
mobility of soil constituents, depending  on the nature of the waste constituents of
concern,  subject to the limitations explained in this section. The TCLP is the
preferred procdure, however, if organic constituents are of concern, since the TCLP
was designed to primarily apply to organics. Other leaching tests, or modifications
of the EP or TCLP leaching tests, may be applied, as appropriate. For example, the
EP and TCLP leaching tests use a dilute acetic acid leaching fluid. If the potential is

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low for acidic conditions , neutral water (or local water, such as rain water) may be
used as the leaching fluid.  Because leaching of cyanide-containing waste under
acidic conditions may force the evolution of hydrogen cyanide (HCN), evaluation of
cyanide-containing wastes should be done with neutral water.  Additional
modifications may be appropriate in some cases.  The owner or operator should
review the procedures and test methods described in Sections 8 and 9 and Appendix
J of Petitions to Delist Hazardous Waste. 1986 (EPA/53Q-SW-85-OQ3), as well as Test
Methods for Evaluating Solid Wastes (EPA/SW-846, GPO No. 955-001-00000-1). to
determine what method, if any, is appropriate for evaluating  soil contaminant
levels based on actual conditions at the  site.

9.4.4.3.2   Estimating Impact on Ground-Water Quality

     As indicated above, leaching tests provide a conservative  (reasonable worst
case)  prediction or estimate of the concentration within leachate of constituents
that may impact ground water.  However, the owner or operator should evaluate
these results along with constituent properties and site-specific factors.  Important
constituent properties to consider include:

     *    Nature (e.g., organic, inorganic, ionic);
         Solubility;
         Octanol/water partition coefficient (Kow);
     *    Organic carbon absorption coefficient (Koc);
         Volatility (e.g., Henry's law constant);
     *    Dissociation constants (pK); and
     *    Degradation potential (e.g.,  hydrolysis, biodegradation).

     Site-specific environmental factors include;

     *    Depth to ground water;
     *    Cation exchange capacity;
         Soil pH and Eh;
     *    Clay content;
     *    Particle-size distribution;
     *    Hydraulic conductivity;
         Porosity;

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         Permeability;
     *    Sorptive capacity;
     *    Soil-water partition coefficient (Kd);
     *    Organic carbon content (Foe);
         Pore water velocity;
     *    Percolation (volumetric flux per unit area);
         Vol u metric wate r co ntent;
         Ground-water pH and Eh;
         Specific conductance; and
         Ground-water ionic and non-ionic species.

Refer to Section 9.3.2.3 for specific information regarding these factors,

     Both constituent and site-specific factors should be evaluated, together with
leaching test concentrations, to arrive at predictions of the potential impacts to
ground water.  For example, if the depth to ground water is great enough, and the
soil cation exchange capacity is high, the owner or operator may be able to predict
that  metal species would be adsorbed by the soil  before the soil leachate reaches
the ground water. Particular attention, in this example, would be needed to ensure
that  the cation  exchange capacity of *.he  soil could not be exceeded.  The
characteristics of the metal ions that are displaced from the exchange sites should
also be considered.

     As another example, the soil-water partition coefficient (Kd) is useful for
describing chemical mobility in the subsurface environment, and is widely used  in
studies of ground-water contamination.  For primarily  aqueous solutions, the
partitioning between the aqueous solution and the solid medium can be derived
from thermodynamic principles (Freeze and Cherry, 1979).

     More commonly, Kd is determined from  batch  experiments in which the
contaminated solution and geologic material of interest are brought into contact.
After a period of time has elapsed (e.g., 24-hours), the degree of partitioning of the
contaminant between the solution and the geologic material is determined.  The
partition coefficient is then calculated using the following equation;
                                   9-50

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               massof sorbed chemical/gram of solid

               mass of chemical/ml of solution

     The relative mobility of attenuated constituents in ground water can then be
estimated as follows (Mills, et al., 1985).
where
              1 +
where
     Va   -    average linerar velocity of attenuated constituent along center-line
               of plume, ft/day
     Vs   3    ground-water velocity, ft/day
     b    =    soil bulk density, g/cm3
     n    *    effective porosity, dimensionless
     K
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      TABLE 9-6   RELATIVE MOBILITY OF SOLUTES'
Group
Conservative




Slightly Attenuated
Moderately Attenuated
More Strongly
Attenuated
Example*
Total Dissolved
Solids
Chloride
Bromide
Nitrate
Sulfate
Boron
Tnehloro-
ethylene
Selenium
Arsenic
Benzene
Lead
Mercury
Penta-
chlorophenol
Matter Variables*
V
V
V
V, Redo* Conditions
V, Redo* Condition*
V pM, organic matter
V , organic matte*
V , pH. Iron hydroxides,
V , pH. Iron hydroxides,
V , organic matter
V,pH, Sulfate
V , pH, Chloride
V , organic matter
1  Under typical ground-water conditions (i ., neutral pH and
   oxidizing conditions). Under other conditions mobility may differ
   substantially. For example, acidic conditions can enhance the
   mobility of metais by several orders of magnitude.

2  Variables which strongly influence the fate of the indicated solute
   groups. Based on data from Mills ft_l., 1985 and Rat and Zachara,
   1984  (V * Average Linear velocity)
                            9-52

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 Adsorption
 fcy Jeil
Shift dut
to r*ftct
   M11 vrftnlc
ntter
Typical
iflto rfltlon
Oirvt for
                                                             . on  cl*i
                                                             |11U or
                                  curvt for
                                       *, an iil(e
                                  or iluMlfltf* i11lem
                                  uirfict cotd *1tn
                                  tall organft wttcr
             so -
                              pH af the Soil Solution

  a)  Gentr-aliied Htavjr f4etal Adsorp .icn Cyrvt  for Cationlc Speclts

                          (t.g,, CuOH*}
               100
 Ptrcent
 Adsorption     50
 (sy Soil
                       Typical  adsorption
                       curve  for heavy
                       metal  species, x,
                       on  iron  hydroxide

                   \

           ,SMft     \
           ^ due to   \
            i presence  \
             x  of soil  \
             v organic   \
              v  matter    \
                             pN of the Soil Solution

 b) Generalized Heavy  Hetal  Adsorption Curve for Anionic  Species
Figure 9-3.     Hypothetical Adsorption Curves for A Cations and
               S) Anions Showing Effect of pH and Organic Matter
               (Mills et at., 1985)
                                    9-53

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Eh-pH diagrams. These diagrams represent solution composition for specified
chemicals as a function of redox potential  (Eh) and of pH under equilibrium
conditions.

     Many  metals  of interest in ground-water contamination problems arc
influenced by redox conditions that result from changes in the oxidation state of
the metal or from nonmetallic elements with which the metal can form complexes.
Garrets and Christ (1965) present a comprehensive treatment of the subject and
provide numerous Eh-pH diagrams that can be used for analysis of geological
systems.

     For any particular point in  an Eh-pH diagram, a chemical reaction can be
written that describes the equilibrium between the solid and dissolved phases of a
particular constituent. The following equation represents the general form of the
equilibrium reaction:

                  aA * bB  cC + dD

where:            a, b, c, d * number of moles of constituent
                  A and B * reactants
                  C and D  products

At equilibrium, the solubility constant (K)  expresses the relation between the
reactants and the products following the law of mass action:
                            [A](B]b

     The brackets signify an effective concentration, or activity, that is reported as
molality (moles per liter).  Solubility constants for many reactions in water are
reported by Stumm and Morgan (1981). Alternatively, solubility constants can be
calculated  from thermodynamic data  (Gibbs  free energy)  for  products and
reactants.   Freeze and Cherry (1979) describe the use of thermodynamic data to

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calculate solubility constants for several constituents common in ground water.

     An example illustrating the use of Eh-pH diagrams and the influence of redo*
conditions on solution composition is shown for mercury (Hg) in Figure 9-4.  The
stability diagram shown in Figure 9-4 is constructed for mercury-contaminated
water that contains chloride (Cl)  and dissolved sulfur species. The solid lines in the
diagram represent the Eh-pH values at which the various phases are m equilibrium.
For pH values of less than about 7 and Eh values greater than O.S vc/lts  (strong
oxidizing conditions), HgCI2 is the dominant dissolved species.  For pH values
greater than 7, and at a high redox potential, Hg(OH)2 is the  dominant dissolved
species. The main equilibrium reaction in this Eh-pH environment is:

                   HgO t HjO  Hg (OH)2

     From the law of mass action, the  solubility relationship for this reaction is
written as follows:

                            [Hg(OH)2J
                             [HgOl [H2OJ

     At 25oC, the solubility constant (log K) for this reaction is -3.7 (Freeze and
Cherry, 1979). The activity coefficients for a solid (HgO) and H2O are assumed to be
one; therefore, the concentration of Hg(OH)2 in solution is calculated as follows:
[Hg(OH)2|  K  10-37 , i 995 x KH moles/1 > 47 mg/l (mol. wgt  235 g/mole)

     The Eh-pH diagram can be used to estimate the concentration of mercury in
solution *t any particular point in the diagram  if the solubility constant for the
appropriate equilibrium reaction is known.  For  lower redox conditions (pH * 6.0,
Eh =0.0), the  concentration of mercury in solution would be approximately 0.025
mg/l (Callahan et at., 1979).

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1.20
                                  10     12     14
   Figure 9-4. Fields of Stability for Aqueous Mercury at 25C
              and Atmospheric Pressure (Callahan et a)., 1979)

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     Several limitations are associated with the use of Eh-pH diagrams to predict
dissolved chemical  species, including the accuracy of thermodynamic data, the
assumption of equilibrium conditions,  and of other chemical processes such  as
adsorption that can maintain concentrations below those that would exist as a
result of only solubility constraints. However, the Fh-pH diagrams serve to illustrate
that solution composition depends on redox potential and that chemical mobility
within a ground-water system may vary from one zone to another.

9.S  Data Presentation

     The owner or operator will be required to report on the progress of the RFI at
appropriate intervals during the investigation.  The data should be reported in a
clear  and concise  manner, with interpretations supported  by the data.  The
following data presentation methods are suggested for soil investigations. Further
information is provided in Section 5.

9.5.1      Waste and Unit Characterization

     Waste and unit characteristics may be presented as:

     *    Tables of waste constituents and concentrations;

     *    Tables of  relevant physical  and  chemical properties of waste and
          constituents;

         Narrative description of unit operations; and

         Surface map and plan drawings of the facility and waste unit(s).

9.5.2      Environmental Setting Characterization

     Environmental characteristics may be presented as:

     *    A map and narrative description of soil classifications;

         Soil boring logs;
                                    9-57

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         Measurements of soil physical or hydrologic characteristics; and

         Onsite survey results (e.g., HNu'Photovac, geophysical techniques).

     Soil and site map(s)--ln addition to the required RCRA permit site topographic
map, the owner or operator  should prepare a map(s) displaying the location of
surface soil types (described  according to the appropriate classification system),
paved areas, areas of artificially compacted soil, fill or other disturbed soil, and
other features that could affect contaminant distribution. Specific guidance on the
use of maps and  other techniques such as aerial photographs and geophysical
surveys is provided in Appendices A and C.

     The owner or operator  should develop maps of unconsolidated geologic
materials at the site.  These  maps should identify the thicknesses,  depths, and
textures of soils, and the presence of saturated regions and other hydrogeological
features. Subsurface soils should be identified according to accepted methods for
description of soils (See Section 9.3.3.3). Figure 9-5 displays a typical soil boring log.

     Graphical  methods commonly used to display soil  boring  data are cross-
sections,  fence diagrams, and isopach maps.  Cross-sections are typically derived
from borings taken along a straight line through the site. Plotting the stratigraphy
of surficial deposits against horizontal distance between  sampling points gives a
vertical profile or transect.  Pence diagrams can depict the same type of information
between points that are not in a straight line.  An isopach map resembles a
topographic map, however, the  isopleth lines on an isopach map represent units of
thickness of a particular soil layer rather than elevations. For example, a map of clay
isopachs  may be used to show  the thickness in feet  of a low permeability layer
below a  waste  lagoon. Generally,  to verify lateral  continuity,  more than  one
transect through a site will be necessary. When it is important to indicate the area)
extent of a layer (e.g., where a clay lens is suspected to cause lateral transport in the
unsaturated zone) both vertical and horizontal  presentations may be necessary.
Graphical methods are discussed in detail in Section 5 (Data Management and
Presentation).

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Figure 9-5. Example of a completed boring log
                  9-59

-------

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9.5.3     Characterization of the Release

     Graphical displays of contaminant distributions in soil may include:

        Area/site maps with concentrations  indicated by numerica1  values,
         symbols, or isoconcentration lines,

        Three-dimensional isopleth plots of concentrations (including stack
         maps), such as are produced by computer graphics; and

        Vertical concentration contours (isopleths) plotted along a transect or
         fence diagram.

     All graphical displays  should be  accompanied by data tables showing
concentrations for each sampling location.

9.6   Field Methods

     Both soil and soil pore water sampling may be utilized in the investigation.
Chemical analysis of soil core samples may be used to characterize constituents of
concern that are adsorbed to the solid matrix,  (.ysimeters can  be installed in
boreholes created during core sampling to identify mobile constituents that may
migrate to ground water.

     Appropriate sample collection  and preservation techniques should be
specified.  When a soil sample is removed  from its surroundings, chemical tnd
physical changes can begin  immediately.  These changes include moisture  loss,
oxidation, gas exchange, loss of volatile components, increased or decreased
biological activity, and potential contamination of the sample. Therefore,
appropriate measures must be taken  to store and preserve samples to minimize
their degradation. Sampling techniques should not adversely affect  analytical
procedures and  hence results. For example, use of fluids other than water during
drilling can introduce organic  or inorganic contaminants that may make
quantification of the contaminants of concern impossible.  The practice of coating
metal parts of drilling equipment with oils or greases to prevent rust will have  a
similar effect.

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     Volatile compounds can sometimes be detected near the soil surface using
rapid screening methods (e.g., portable photoiomzation detector such as HNu or
Photo vac or an organic vapor analyzer (OVA)}, Organic vapors can also be detected
and measured  in shallow boreholes or in ground-water monitoring wells.  Vapor
sampling is especially usefu, for initial characterization because it is a rapid,
semiquantitative technique.  Benefitsof rapid screening techniques include:

         The  investigator can. in certain  cases,  quickly determine whether a
         sample is contaminated, thus, aiding in the identification of areas of
         concern;

         Samples that may undergo  chemical changes with storage can  be
         evaluated immediately; and

     *    These techniques can be used to investigate releases to several media
         simultaneously (e.g., subsurface gas, ground water and soil)

     However, there are drawbacks to rapid screening techniques:

     *    They are not always indicative of all constituents that may be present in
         the release; and

     *    Detection  limits may not  be low enough to detect  low level
         contamination, and additional analysis (e.g., GOMS) may be required.

     Soil sampling methods will vary with the depth of interest,  ror purposes of the
RFI, these methods are described as "surfkial* or "subsurface*. Surficial sampling in
the upper 20 on of soil can usually be accomplished with a simple tools, including
shovels, spatulas, soil punches, and ring samplers. Contaminants that have moved
further downward in the soil profile often  require tools such as tube samplers and
augers.  Manually operated tools  are commonly useful to about 1  to 2 meters in
depth, depending on the soil type. Below this depth, hydraulically or mechanically
driven equipment is  generally needed {See  Everett et al, 1984  for additional
information on soil sampling techniques, as well as Sections 3 and 7 of this Guidance
for discussions of additional sampling methods and references).

-------
     Methods to sample soil pore water or other fluids are presented in Section
9,6,3.

9,6.1      Surficial Sampling Techniques

     Surficial soils may also contain various materials, including rocks, vegetation,
and man-made items. The owner or operator should propose how these materials
will be treated (i.e., whether they will be discarded or analyzed separately).  Care
should be taken in choosing sampling equipment that will not adversely affect the
analytical objectives (e.g.,  painted or chrome/nickel plated  equipment may
adversely affect metals analyses). Some commonly used  Surficial  soil sampling
techniques are discussed below.

9.6.1.1    Soil Punch

     A soil punch is a thin-walled steel tube that is commonly 15 to 20 cm long and
1.3 cm to 5.1 cm in diameter.  The tube is driven into the ground with a wooden
mallet and twisted to free the sample. The punch is pulled out and the soil pushed
or shaken from the tube. This technique is rapid but is generally not useful in rocky
areas or in loose, granular soils that will not remain in the punch. Soil punching is
not useful for soil structure descriptions because the  method causes compaction
that destroys natural fractures.

9.6.1.2    Ring Samplers

     A ring sampler consists of a 15 to 30 cm diameter steel ring that is driven into
the ground. The soil is subsequently removed for analysis.  This technique is useful
when results are to be expressed on a unit area basis, because the soil ring contains
a known arta of soil. Ring samplers will generally not be useful in loose, sandy soils
or stiff clays.

9.6.1.3    Shovels, Spatulas, and Scoops

     Collection of grab samples by shovel, spatula, or scoop is not recommended if
sample area or volume determinations are required (the two previous methods are

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more accurate). The reproducibility of sample size is limited and subject to sample
bias. The principal advantages of grab sampling are the efficiency of collection and
the fact that samples may indicate the range of contaminant concentrations at the
site.

9.6.1.4   Soil Probes (tube samplers)

     Manual soil probes are designed  to obtain samples from the upper two meters
of the soil profile.  The soil probe is commonly a stainless-steel or brass tube that is
sharpened and beveled on one end  and fitted with a T-handle.  Soil probes are
common agricultural tools and can be obtained in several diameters. The probe is
pushed into the soil in 20 to 30 cm increments. At the desired depth, the tube is
pulled out and the soil sample extruded.   The sample  may  be considered
"disturbed" or "undisturbed* depending on whether it can be removed intact.  The
samples, however, are generally considered to be disturbed for the purposes of
engineering or physical measurements.  Loose soils will be difficult to sample with
this tool, and the borehole will tend to collapse when the tube is withdrawn to
obtain samples.

9.6.1.5   Hand Augers

     Augers have a spiral cutting Wade that transports soil cuttings  upwards. Hand-
operated augers are generally used to a depth of approximately 6 feet. Single flight
augers are pulled from the ground periodically and soil samples are taken from the
threads of the auger. Continuous flight augers transport the loosened soil  to the
top of the borehole, where it can be collected. Augers provide highly disturbed
samples.  Limited information can bt obtained on soil structure,  bulk density, or
permeability.  Cross-contamination between soil  layers  is likely and  depth
information on various soil layers is not reliable. Therefore, reliance on augermg as
a sole sampling technique if not recommended. Augering may be used, however, in
conjunction with tube sampling that obtains undisturbed samples.

9.6.2     DeepSampli g Methods

     The subject of deep drilling is discussed more extensive in the section on
ground-water sampling (see Section 10), since deep cores will generally be taken in
                                   9*64

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conjunction with drilling for monitoring well emplacement.  There are some
techniques that are of particular importance to soil sampling and, therefore, a brief
discussion is included here.  Procedures for sampling with split-spoon and thin-wall
tube corers and other equipment are presented in Section 7.

9.6.2.1     Hollow-Stem Augers

     Hollow-stem augers have a continuous flight-cutting blade around a hollow
metal cylinder.  A stem with a  plug is ordinarily  kept  inside the auger barrel to
prevent soil from entering.  When core samples are desired, the stem is withdrawn
and a tube sampler may be inserted to the bottom of  the borehole.  This drilling
method may be used for continuous soil sampling.  An additional advantage of
hollow-stem augers is that they do not require drilling fluids.

9.6.2.2    Solid-Stem Augers

     Solid-stem augers, as the name implies,.. i augers that do not have an inner
barrel. As with the manual variety, single-flight augers must be withdrawn each
time a sample is desired, or samples may be taken from the cuttings brought to the
surface by augers of the continuous flight type. Augers may be used in conjunction
with tube samplers by withdrawing the auger and obtaining a sample from the
bottom of the borehole. This sampling approach is only  useful with soils that do not
cave in or crumble after drilling.

9.6.2.3    Core Samplers

     Soil coring devices that may be used with hydraulically or mechanically- driven
drilling rigs include thin-walled Shelby tubes and split-spoon samplers. These are
two of the most common samplers and are discussed below

9.6.2.3.1   Thm-Walled Tube Samplers

     The Shelby tube is a metal cylinder with the end sharpened and beveled for
cutting into the soil. Common sizes used for field investigations are 1 to 3 inches in
diameter. The tube is pushed down into the soil with a smooth even motion by
applying downward pressure from a drilling rig or other apparatus.  Thin-walled
                                   9-65

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tubes produce high quality undisturbed cores that can be used for engineering and
hydraulics testing but are useful only in cohesive soils as loose soils may fall out of
the tube during removal. The soil must be extruded from the tube in a laboratory or
in a field extruding unit because core removal is generally difficult.  For rapid
characterization of the soil stratigraphy in the field, split-spoon  samplers  are
recommended.

9.6.2.3.2 Split-Spoon Samplers

     A split-spoon consists of a hollow steel cylinder split in half and screwed into
an "unsplit" outer tube and tip This assembly can be connected to drill rods. The
tube is commonly forced into the soil by applying a 140 pound sliding hammer,
dropping 30 inches along the drill rod (ASTM, 1986). The number of hammer blows
required to advance the sampler in six inch increments is recorded. The total blow
count number for the second and third increments is related to a standard
engineering parameter indicating soil density. After the tube  is pulled from the
soil, the cylinder is removed from the drill rod and opened, exposing the soil core.
Core samples may be used to determine stratigraphy, for chemical and grain-size
analysis, or for pore wate* extraction.  Split-spoons are the preferred method for
obtaining unconsolidated soil samples and may  alto be used to penetrate some
types of rock.

9.6.2.4   Trenching

     Trenches and test pits are useful  where detailed examination  of  soil
stratigraphy and geology is required. Trenching is generally limited for practicality
to the top eight feet of soil. Shallow trenches may be dug manually, but  in most
instances, a backhoe will be faster and easier.  Bulk soil samples may be obtained
with this method.

9.6.3     Pore Water Sampling

     When contaminants are suspected of migrating readily through the soii with
infiltrating water, monitoring of water or other fluids in the unsaturated zone may
be appropriate.  Sampling soil pore water before it reaches the water table can
provide an early warning of threats to ground water.

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     Compounds for which pore water sampling may be useful are those that are
moderately to highly water soluble and thus are not appreciably retained on soil
particles. Examples include poorly adsorbed inorganics such as cyanide or sulfate,
halogenated solvents such as TCE, and organic acids  Due to the mobility of these
compounds, pore water sampling will be most useful for current releases.

     A common pore water collection technique  uses a suction device called a
pressure vacuum lysimeter, which consists of a porous ceramic cup connected by
tubing to a collection flask and vacuum pump (Figure 9-6).  The lysimeter cup may
be permanently installed in a borehole of the appropriate depth, and if the hole is
properly backfilled. Suction from the pump works against soil suction to pull water
out of the  silica flour  surrounding the cup.  This method will not work well  in
relatively dry soils.

     An advantage of this method is that the installation is  * permanent," allowing
multiple samples from one spot to  measure changes in pore water quality  with
time. Limitations include:

        Measurements cannot be correlated accurately with soil concentrations
         because the sample is obtained from an unknown volume of soil;

     *   Lysimeters are subject to plugging and are difficult to install in fractured
         or rocky soils;

     *   Some organic and  inorganic constituents  may be  adsorbed  by the
         ceramic cup (Teflon porous suction lysimeter may overcome this
         problem); and

        Volatile organics will be lost unless a special organics trap is installed in
         the system.
                                   9-6?

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                       ACCESS  LINES
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     POROUS
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                                      POWDERED QUARTZ
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                      k" OIAMCTIR
Figy r i-6. Typical Cramic Cup Pressure/Vacuum Ly si meter

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9.7  Checklist
                              RF! Checklist - Soils
Site Name/Location	

Type of unit	

1,   Does waste characterization include the following information? (Y/N)
               Identity and composition of contaminants               	
               Physical state of contaminants                          	
               Viscosity                                              	

               pka                                                  ~^m
               Density                                              	
               Water Solubility                                       ~~~~~
               Henry's Law Constant                                  	

               Bioclegradability                                      ~~~"
               Rates of hydrolysis, photolysis and oxidation             	

     Does unit characterization include the following
     information?                                                   (Y/N)

               Age of unit                                           	
               Construction integrity                                 	
               Presence of liner (natural or synthetic)                   	
               Location relative to ground-water table
               or bedrock or otht; confining barriers                   	
               Unit operation data                                   	
               Presence of cover or other surface covering              	
               Presence of on/offsite buildings                         	
               Depth and dimensions of unit                          	
               Inspection records                                     	
               Operation logs                                       	
               Presence of natural or engineered barriers
               near unit                                             	

3.   Does environmental setting information include the following
     information?                                                   (Y/N)

               Site Soil Characteristics



               Surface soil distribution map                            _
               Soil moisture content                                   _
               Predominant soil phase to sample (solid, liquid, gaseous)   _
               Soil classification                                       _
               Particle size distribution
                                    9-69

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                         RFI Checklist -Soils
                            (Continued)
          Porosity                                              	
          Hydraulic conductivity (saturated and unsatu rated)       	
          Relative permeability                                  	
          Soil sorptive capacity                                   	
          Cation exchange capacity                              	
          Organic carbon content                                	
          Soil pH                                               	

          Unsatu rated Transport Characterization

         Depth to water table                                   	
         Pore water velocity                                    	
         Percolation                                           	
         Volumetric water content                              	

Have the following data on the initial phase of the release
characterization been collected?                                 (Y/N)

          Geological and ciimatological data                      	
          Facility records and site-specific investigations            	
          Area of contamination                                 	
          Distribution of contaminants within study area           	
          Depth of contamination                               	
          Chemistry of contaminants        '                    	
          Vertical rate of transport                               	
          Lateral rate of transport in each stratum                 	
          Persistence of contaminants in soil                      	
          Potential for release from surface soils to air              	
          Potential for release from surface soils to
          surface water                                         	
          Existing soil/ground-water monitoring data              	
          Evidence of vegetative stress                           	
          Potential for release to ground water                   	
          Potential receptors

Have the following data on the subsequent phase(s) of the
release characterization been collected?                           (Y/N)

         Further soil stratigraphic and hydrologic
          characterization data                                 	
         Expanded sampling data                              	
         Geophysical data on plume location                    	

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9.1  References

ASTM.  1984. Particle Size Analysis for Soils. Annual Book of ASTM Standards,
     Method 0422-63. Vol. 4.08. Philadelphia, PA.

ASTM.  1984. Standard Recommended Practice for Description of Soils. Annual
     Book of ASTM Standards, Method 02488-69. Vol. 4.08. Philadelphia, PA.

Barth, D. S., and B. J. Mason. 1984. Soil Sampling Quality Assurance User's Guide.
     EPA 600/4-84-043. NTISPB84-198621. U.S. EPA. Washington, D.C 20460.

Black, C. A. 1965. Methods of Soil Analysis. Part 2: Chemical and
     Microbiological Properties. American Society of Agronomy.
     Madison, Wisconsin.

Callahan.M.A., etal.  1979. Water-Related Environmental Fate of 129 Priority
     Pollutants.  Vol. 1 and 2. EPA 440/4-79-029a,  NTIS PB80-204373.  U.S. EPA. -
     Washington, D.C. 20460.

llliot, L F., and F. J. Stevenson.  1977. Soils for Management of Organic Wastes
     and Waste Waters.  Soil Science Society of  America,  American Society of
     Agronomy, Crop Science Society of America. Madison, Wisconsin.

Everett, L. G.. L G. Wilson, and . W. Hoylman. 1984. Vadose Zone Monitoring
     for Hazardous Waste Sites. Noyes Data Corporation.  Park Ridge. New Jersey.

Ford, P. J., et al. 1984. Characterization of Hazardous Waste Site - A Methods
     Manual. Vol. H. Available Sampling Methods. NTIS PB8S-168771.   U.S. EPA.
     EPA 600/4-84-076. Washington, D.C. 20460.

Freeie and Cherry. 1979. Ground Water. Prentice-Hall, Inc., Ertgltwood Cliffs,
     NJ.

Garrels, R.M. and C.L Christ.  1965. Solutions. Minerals, and Equilibria- Harper
     and Row, New York.
                                   9-71

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Lambe, T.W. and R.V. Whitman. 1979. Soil Mechanics. SI Version. John Wiley and
     Sons, Inc., New York. New York.

Lyman.WJ, Reehl.W. F. and D. H. Rosenblatt. 1981. Handbook cf Chemical
     Property Estimation Methods. McGraw Hill.

Mason, 8. J.  1983. Preparation of a Soil Sampling Protocol: Techniques and
     Strategies.  EPA/4-83-020,  NTIS PB83-206979.  U.S. EPA. Washington, D.C.
     20460.

Mills, W.B,,etal. 1985. Water Quality Assessment: A Screening Procedure for
     Toxic and Coventional Pollutants in Surface and Ground Water.  EPA/600/6-
     85/002a.b. e.  Vol. I, II and  III.  NTIS P886-12249*,  122504 and  162195.
     Washington, D.C. 20460.

Morrill, L G., L W. Reed, and K. S. K. Chinn. 1985. Toxic Chemicals in the Soil
     Environment. Volume 2:  Interactions of Some Toxic Chemicals/Chemical
     Warfare Agents and Soils. AD-A158-215. U.S. Army Ougway Proving Ground.
     Dugway, Utah.

Oster, C. A. 1982. Review of Ground Water Flow and Transport Models in the
     Unsaturated Zone.  PNL-4427,  Battelle Pacific Northwest Laboratory.
     Richland.WA.

Rai, 0. and J.M. Zachara. 1984. Chemical Attenuation Studies: Data
     Development and Use.  Presented at Second Technology Transfer Seminar:
     Solute Migration in Ground Water at  Utility Waste Disposal Sitts.  Held in
     Denver, Colorado. October 24-25,1985.  EPRl-EA-3356.

Sims, R. C., et al.  1184. Review of In-Place Treatment Techniques for
     Contaminated Surface Soils. Volume 2:  Background Information for In Situ
     Treatment.  EPA-540/7-84-0036  NTIS PB85-124899.  U.S. EPA. Washington,
     D.C. 20460.
                                  9-72

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Stumm, W, and J.J. Morgan, 1981. Aquatic Chemistry. An introduction
     Emphasizing Chemical Equilibria in Natural Waters. John Wiley and
     Sons. New York, IM.Y.

U.S.D.A. (U.S. Department of Agriculture). 1975. Soil Taxonomy:  A Basic System
     of Soil Classification for Making and Interpreting Soil Surveys.  Soil Survey
     Staff, Soil Conservation Service. Washington, D.C.

U.S. EPA. 1975. Use of the Water Balance Method for Predicting  Leachate
     Generation from Solid Waste Disposal Sites.  EPA/S30/SW-168. Office of Solid
     Waste. Washington, D.C. 20460.

U.S. EPA. 40CFR261.24. Extraction Procedure (EP) Toxicity Characteristic.

U.S. EPA. 1982. Sediment and Soil Adsorption Isotherm. Test Guideline No. CG-
     1710.  In:  Chemical Fate Test Guidelines.  EPA  56076-82-003   NTIS PB82-
     233008.  Office of Pesticide and Toxic Substances, Washington, O.C. 20460.

U.S. EPA. 1982. Sediment and Soil Adsorption Isotherm. Support Document No.
     CS-1710.  In: Chemical Fate Test Guidelines.  EPA 560/6-82-003. NTIS PB83-
     257709.  Off ice of Pesticide and Toxic Substances. Washington, D.C. 20460.

U.S. EPA, 1984. Soil Properties. Classification and Hydraulic Conductivity
     Testing.  EPA/SW-925. Off ice of Solid Waste. Washington, D.C. 20460.

U.S. EPA. 1985. Handbook: Remedial Action at Waste Disposal Sites (Revised).
     EPA7625/6-85/006   NTIS PB82-239054   Office of Emergency and  Remedial
     Response. Washington, D.C. 20460.

U.S. EPA. 1986. Criteria for Identifying Areas of Vulnerable Hydoqeoloqy Under the
     Resource Conservation gnd Recovery Act. NTIS PB86-224953. Office of Solid
     Waste. Washington, D.C. 20460.

U.S. EPA. 1986. Petitions to Delist Hazardous Wastes. EPA/530-SW-85-003. Office
     of Solid Waste. Washington, D.C. 20460.
                                   9-73

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U.S. EPA.  1986, Test Methods for Evaluating Solid Waste. EPA/SW-846. GPO No.
    95S-001-00000-1, Office of Solid Waste. Washington, DC  20460.

U.S. EPA.  June 13,1986.  Federal Register. Volume 51, Pg. 21648. TCLP Proposed
    Rule.

U.S. Geological Survey. 1982. National Handbook of Recommended Methods for
    Water Data Acquisition.
                                   9-74

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                               SICTION 10

                             GROUND WATER

10.1  Overview

     The objective  of an investigation  of  a release to  ground  water is to
characterize the nature, extent, and rate of migration of a release of hazardous
constituents to that medium. This section provides:

        A recommended strategy for characterizing releases to  ground water,
         which includes  characterization of  the source and the environmental
         setting of the release, and conducting a monitoring program which will
         characterize the release itself;

     *   Recommendations for data organization and presentation;

     *   Appropriate field methods which may be used in the investigation; and

        A checklist of information that may be  needed for release character-
         ization.

     The exact type and  amount of information required for sufficient  release
characterization will be site-specific and should be determined through interactions
between the regulatory agency and the facility owner or operator during the RFI
process. This guidance does not define the specific data needed in all instances;
however, it identifies possible information necessary  to perform release
characterizations and methods for obtaining  this information.  The RFI  Checklist,
presented at the end  of  this section, provides a tool for planning and tracking
information for  release  characterization.  This list is not meant as a  list of
requirements  for all releases to ground water.  Some release investigations will
involve the collection of only a subset of the items listed, while others may involve
the collection of additional data.
                                   10-1

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10.2 Approach for Characterizing Releases to Ground Water

10.2.1    General Approach

     The owner or operator should develop a monitoring program to determine
the nature, extent, and rate of migration of contaminant releases from SWMUs* to
ground water. 3-Oimensional characterization may be particularly important. The
initial monitoring phase should include a limited number of monitoring wells,
located and screened in such a way that they are capable of providing background
water quality and of intercepting any release. The regulatory agency will evaluate
the adequacy of an existing monitoring system, if proposed for use in the initial
monitoring phase.  The owner or operator may be required to install new wells if
the existing well system is found to be inadequate.

     Initial ground-water sampling and analysis may be conducted for a limited set
of monitoring constituents.  This set should include a subset of the hazardous
constituents of concern, and may also include indicator parameters (e.g., TOX).
Guidance regarding the selection of monitoring constituents and  indicator para-
meters is provided in Sections 3 and 7 and  in Appendix 8  Sampling frequency and
duration should also be proposed in the RFI Work Plan.

     Investigation of a suspected release may be terminated  based on results from
an initial monitc ring phase if these results show that an actual release has not,  in
fact, occurred. If, however, contamination is found, the release must be adequately
characterized through a subsequent monitoring phase(s).

     Subsequent characterization involves determining the detailed chemical
composition and the area! and vertical (i.e., three dimensional) extent of the
contaminant release, as well as its rate of  migration. This should be accomplished
through direct sampling and analysis and, when appropriate, can be supplemented
by indirect means such as geophysical methods (See Appendix C) and modeling
techniques.
     Guidan
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     Table 10-1 outlines a recommended strategy for characterizing release to
ground water. Table 10-2 lists the specific tasks which may be used in implementing
the strategy, and the corresponding data outputs.  The steps delineated in these
tables should generally be performed in sequential order, although some may be
accomplished concurrently.  For example, the site's hydrogeology may  be
investigated at the same time as waste and unit characterization; soil  borings
installed during hydrogeologic characterization may be converted into monitoring
wells; and additional wells may be installed to more accurately characterize a
release while a sampling and analysis program is in effect at existing wells.

     The specific tasks to be conducted for each release  will be determined on a
site-specific basis.  It should be noted that some of the characterization tasks may
have been previously  accomplished  in conjunction with  the 40  CFR Parts 264
and 265, Subpart F (ground-water monitoring) regulations.

     As monitoring data become available, both within  and at the conclusion of
discrete investigation phases, it  should be  reported to the regulatory agency as
directed.  The regulatory agency will compare the monitoring  data to applicable
health  and environmental criteria to determine the need for (1) interim corrective
measures; and (2) a Corrective Measures Study. In addition, the regulatory agency
will evaluate  the monitoring data with respect to adequacy and completeness to
determine the need for any additional monitoring efforts.   The health and
environmental criteria and a general discussion of how the regulatory agency will
apply them are supplied in Section 8.  A flow diagram illustrating  is provided in
Section 3  (See Figure 3-2).

     Not withstanding the above process, the owner or ope rater has a continuing
responsibility to identify and respond to emergency situations and to define priority
situations that may warrant interim corrective measures. For these  situations, the
owner or operator is directed to obtain and follow the RCRA Contingency Plan
under 40 CFR Part 264, Subpart D.

     Case Study numbers 5, 6,  7 and 22  in Volume IV (Case Study Examples)
illustrate the conduct of various aspects of ground-water investigations.
                                    10-3

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                                Table 10-1

                  Recommended Strategy For Characterizing
                         Releases to Ground Water'
                               INITIAL PHASE

1.    Collect and review preliminary information for use in formulating monitoring
     procedures:

         Waste  and unit information (including constituent identification and
         characterization)
         Site hydrog eology and other environmental factors
         Existing monitoring data
         Regional flow net information

2.    Identify and collect additional information necessary to characterize release:

         Waste and unit information
         Site hydrogeology and other environmental factors
         Geophysical investigations (See Appendix C)
         Conceptual model of release
         Monitoring data
         Inter-media transport

3,    Develop monitoring procedures:

         Select monitoring constituents and indicator parameters
         Identify QA/QC and analytical procedures
         Appropriate initial areal well locations (background and downgradient)
         Collection of additional hydrogeologic data (if necessary)
         Proper wtll screen interval selection
         Borehole testing and use of test pitting
         Sampling frequency and duration of monitoring
         Identification of data presentation and evaluation procedures

4.    Conduct initial monitoring phase:

         Collect samples and complete field analyses
         Analyze samples for selected parameters and constituents

S.    Collect, evaluate and report results:

         Compare monitoring results to health and environmental criteria and
         identify and respond  to emergency situations and identify priority
         situations that warrant interim corrective measures - Notify regulatory
         agency
         Determine completeness and adequacy of collected data
         Summarize and present data in appropriate format
         Determine if monitoring program objectives were met
         Determine if monitoring locations, constituents and frequency were
         adequate to characterize release (nature, rate, and extent)

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                           Table 10-1 (Continued)

                  Recommended Strategy For Characterizing
                         Releases to Ground Water1
                     SUBSEQUENT PHASES (If Necessary)

1.    Identify additional information necessary to characterize release:

         Identify additional information needs
         Perform further hydrogeologic characterization, if necessary
         Add and delete constituents or indicator parameters as appropriate
         Employ geophysical and other methods to estimate extent of release and
         to determine suitable new monitoring locations
         Inter-media transport

2.    Expand initial monitoring as necessary:

         Expand density of monitoring locations
         Expand monitoring locations to new areas
         Install new monitoring wells

3.    Conduct subsequent monitoring phases:

         Collect samples and complete field analysis
         Analyze samples for selected parameters and constituents

4.    Collect, evaluate, and report results/identify additional information necessary
     to characterize release:

         Compare monitoring results  to  health and environmental criteria and
         identify and respond to emergency situations and identify priority
         situations the  warrant interim corrective measures  Notify  regulatory
         agency
         Determine completeness and  adequacy of collected data
         Summarize and present data in appropriate format
         Determine if monitoring program objectives were met
         Determine if monitoring locations, constituents, and frequency were
         adequate to characterize release (nature, extent, and rate)
         Identify additional information needs
         Determine need to expand monitoring
         Evaluate potential role of inter-media impact
         Report results to regulatory agency
'The possibility for intermedia transport of contamination exists, and should be
anticipated throughout the investigation.

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                                            TABLE 10-2
                   RELEASE CHARACTERIZATION TASKS FOR GROUND WATER
         Inventory Tasks
  Investigatory Techniques
Data Pretentation Farmats/Out(
1.  Waste/Unit Characterization

       Identify waste properties
       (eg., pH, viscosity)
       Identify constituents of
       concern/possible indicator
       parameters

       Determine physical/chemical
       properties of constituent!

       Determine unit dimensions
       and other important design
       features and operational
       conditions

       Investigate possible unit
       release mechanisms to help
       determine flow
       characteristics
Review existing information and
conduct waste sampling if
necessary (See Sections 3 ft 7)

Review existing information and
conduct waste sampling if
necessary (See Sections 3 & 7)

Review existing information (See
Section 7)

Review existing information and
conduct unit examinations (See
Section 7)
Review existing information and
conduct unit examinations (See
Section 7]
   Tabular presentation (See
   Section 5)
   Tabular presentation (See
   Section 5)
   Tabular presentation (Se
   Section S)

   Tabular presentations, facility
   maps ft photographs & narrative
   discussion (See Section 5 and
   Appendix A)

   Facility maps i photographs &
   narrative discussions (See
   Appendix A)
   Environmental Setting
   Characterization

       Examine surface features ft
       topography for indications
       of subsurface conditions
       Define subsurface conditions
       ft materials, including soil
       and subsurface physical
       properties (e.g. porosity.
       cation exchange capacity)
Review existing information
facility maps, aerial ft other
photographs, site
history/conduct surface
geological surveys

Review of existing geologic
information

Soil borings and rock coring*

Soil I subsurface material
testing
                                      Geophysical technqiues($ee
                                      Appendix C)
   Facility map ft photographs/text
   discussion |See Appendix A ft Q
   Narrative discussions of geology
   Boring and coring logs

   Subsurface profiles, tansects &
   fence diagrams (See Appendix A
   A Section 5)

   Tabular presentations of soil ft
   subsurface physical & chemical
   properties

   Geologic cross sections ft
   geologic ft soil maps (See Section
   5*94 Appendix A)

   Structure contour maps (plar,
   view) of aquifer ft aquitards (See
   Section 5 ft Appendix A)

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                                         TABLE 10-2
         RELEASE CHARACTERIZATION TASKS FOR GROUND WATER (continued)
      Inventory Tasks
  investigatory Techniques
Data Presentation Formats/Outputs
Environmental Setting
Characterization (Continued)

   Identification of regional
   flow cells, ground-water
   flow paths A general
   hydrology, including
   hydraulic conductivities A
   aquifer interconnections
   Identification of potential
   receptors
Review of existing information

Installation of piezometers A
water level measurements at
different depths

Flow cell & flow net analyses
using measured heads

Pumping A slug tests A trace
studies

Geophysical techniques (See
Appendix C)
Review of existing information,
area maps, etc.
   Narrative descriptions of
   ground-water conditions, flow
   cells, flow nets, flow patterns,
   including flow rates 4 direction

   Water table or potentiomeiric
   maps (plan view) with flow lines
   (See Section 5)

   hydrologic cross sectional maps
   (See Sections)

   Flow nets for vertical &
   horizontal flow

   Tabular presentations of raw
   data & interpretive analysis

   Narrative discussion 8 area maps
Release Characterization

   Determine background
   levels A determine vertical
   and horizontal extent of
   release, including
   concentrations of
   eomtituents 4 determine
   rate A directions of release
   migration
Sampling A analysis of ground-
water samples from monitoring
system
Geophysical methods (See
Appendi C) for detecting A
tracking plume

Modeling to estimate extent of
plume A rate A direction of
plume migration
   Tabular presentations of
   constituent A indicator
   parameter analyses (See Section
   5)

   iso-concentrations maps of
   contamination (See Section S)
                                                                     Maps of rates of release
                                                                     migration A direction show ng
                                                                     locations of possible receptors
                                                                     (See Section 5)

                                                                     Narrative discussion A
                                                                     interpretations of tabular A
                                                                     graphical presentations

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10,2.2    Inter-media Transport

     Indirect releases (inter-media transfer) to ground water may occur as a result
of contaminant releases to soil and/or surface water that percolate or discharge to
ground water. These releases may be recurrent or intermittent in nature, as in the
case of overland run-off, and can vary considerably in area) extent.  Direct releases
to ground water may occur when waste materials are in direct contact with ground
water (e.g., when a landfill rests below the water table).

     Releases of  contaminated ground water to other media may also occur, for
example, in those cases  where ground and  surface waters are  hydraulically
connected.  It is important for the owner or operator to be aware of the potential
for  such occurrences, and to communicate these to the regulatory agency when
discovered.

     This section  provides guidance on  characterizing ground-water releases from
units, as well as those cases where inter-media transport has contaminated ground
water. The owner or operator should be aware that releases to several media can
often be investigated using concurrent techniques.  For example,  an organic vapor
analyzer (OVA) may help to characterize the extent of soil and subsurface gas
releases  and, at the same  time, be used to estimate the extent of a ground-water
release.

10.3 Characterization of the Contaminant Source and the Environmental Setting

10.3.1    Waste  Characterization

     Knowledge of the waste constituents (historical and current) and their
characteristics at the  units of concern is essential in selecting monitoring
constituents and well  locations.  Waste (source) information should include
identifying volumes and concentrations of hazardous waste or constituents present,
and their physical and chemical characteristics.

     Identification of hazardous constituents may be a relatively simple matter of
reviewing records of unit operations, but generally will require direct sampling and
analysisof the waste in the unit. Hazardous constituents may be grouped by similar

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chemical and physical properties to aid in developing a more focused monitoring
program. Knowledge of physical and chemical properties of hazardous constituents
can help to determine their mobility, and their ability to degrade or persist in the
environment. The mobility of chemicals in ground  water is related to their
solubility, volatility, sorption, partitioning, and density.

     Section 3 provides additional guidance  on  monitoring constituent selection
and  Section  7 provides additional guidance on waste  characterization.  The
following discussion describes several waste-related factors and properties which
can aid in developing ground-water monitoring procedures:

     *   The mobility of a waste is highly influenced  by its physical form. Solid
         and gaseous wastes are less likely to come in contact with ground water
         than liquid wastes, except in situations where the ground-water surface
         directly intersects the waste, or where infiltrating liquids are leaching
         through the unsaturated zone.

        The concentration of any constituent at the waste source may provide an
         indication of the concentration at which it may appear in the ground
         water.

     *   The chemical class (i.e., organic, inorganic, acid, base, etc.) provides an
         indication of how the waste might be detected in the ground water, and
         how the various components might react with the subsurface geologic
         materials, the ground water, and each other.

        The pH of a waste can provide an indication of the pH at which it would
         be expected to appear in the ground water.  A low pH waste could also
         be expected to cause dissolution of some subsurface geologic materials
         (e.g., limestone), causing channelization and differential ground-water
         flow, as in karst areas.

     *   The acid  dissociation constant of a chemical  (pKa) is a value which
         indicates its equilibrium potential in  water, and is equal to the pH at
         which the hydrogen ion is  in equilibrium with its associated base,  if
         direct pH measurements are not feasible, the  concentration of a waste in

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     combination with its pKa can be used to estimate the likely pH which will
     occur at equilibrium (in ground water), at a given temperature. Acid
     dissociation values can be found in most standard chemistry handbooks,
     and values for varying temperatures can be calculated using the Van't
     Hoff equation (Snoeyink and Jenkins, 1980).

    Viscosity is a measure of a liquid's resistance to  flow at  a given
     temperature.  The more viscous a fluid is, the more resistant it is to flow.
     Highly viscous wastes may travel  more slowly than the ground water,
     while low-viscosity wastes may travel more quickly than  the ground
     water.

    Water solubility describes the mass of a compound that dissolves in or is
     miscible with water at a given  temperature and pressure   Water
     solubility is important in assessing  the  fate and transport of the
     contaminants in ground water because it indicates the chemical's affinity
     for the aqueous medium.  High water solubility permits greater amounts
     of the hazardous constituent to enter the aqueous  phase, whereas low
     water solubility indicates that a contaminant can be present m ground
     water as a separate phase. Therefore, this parameter can be used to
     establish the  potential  for a constituent to enter  and remain in the
     hydrologic cycle.

*    The density of a substance (solid or liquid) is its weight per unit volume.
     The density of a waste will determine whether it sinks or floats when it
     encounters ground water, and will assist in locating well screen depths
     when attempting to monitor for specific hazardous constituents released
     to ground water.

*    The log of the octanol/water partition coefficient 00**) is a measure of
     the relative affinity of a constituent for the neutral organic and  inorganic
     phases represented by n-octano! and water, respectively. It is calculated
     from a ratio (P) of the equilibrium concentration* (C) of the constituent
     in each phase:

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                             .and K0.w = log P
          The KQW has been correlated to a number of factors for determining
          contaminant fate and transport.  These include adsorption onto soil
          organic matter, bioaccumulation, and biological uptake.  It also bears a
          relationship to aqueous solubility.

         The Henry's Law Constant of a constituent is the relative equilibrium
          ratio of a compound in air and water at a constant temperature.  It can
          be estimated from the equilibrium vapor pressure divided by the
          solubility in water and has the units of atm-m3/mole.  The Henry's Law
          Constant expresses the equilibrium distribution of the constituent
          between air and water and  indicates the relative ease with which the
          constituent may be removed from aqueous solution.

     *    Other influences of the  waste constituents should also be considered
          Constituents may react with soils, thereby altering the physical properties
          of the soil, most notably hydraulic conductivity.  Chemical interactions
          among waste constituents should also be considered.  Such interactions
          may affect mobility, reactivity, solubility, or toxicity of the constituents.
          The potential for wastes or reaction products to interact with  unit
	.  construction materials (e.g., synthetic liners) should also be considered.

     The references listed in Section 7 may be used to obtain information on the
 parameters discussed above. Other waste information may be found in facility
 records, permits, or permit applications.  It should be noted that mixtures of
 chemicals may exhibit characteristics different than those of any single chemical.

 10.3.2    Unit Characterization

     Unsound unit design and operating practices can allow waste to migrate from
 a unit and possibly mix with natural runoff.  Examples include surface impound-
 ments with insufficient freeboard allowing for periodic overtopping; leaking tanks
 or containers; or land based units above shallow, low permeability materials which.

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if not properly designed and operated, can fill up with water and spill over.  In
addition, precipitation falling on exposed wastes can dissolve and thereby mobilize
hazardous constituents. For example, at uncapped active or inactive waste piles and
landfills, precipitation and leachate are likely to mix at the toe of the active face or
the low point of the trench floor.

     Unit dimensions (e.g..depth  and surface area)  and configuration (e.g.,
rectangular, parallel trenches), as well as volume (e.g.capacity) should also  be
described, since these factors will have a bearing on predicting the extent of the
release and the development of a suitable monitoring network.

10.3,3     Characterization of the Environmental Setting

     Hydrogeologic conditions at the site to be monitored should be evaluated for
the potential impacts the setting may have on the development of a monitoring
program  and the quality of the resulting data. Several  hydrogeologic parameters
should be evaluated, including:

         Types and distribution of geologic materials;

     *    Occurrence and movement of ground water through these materials;

         Location of the facility with respect to the regional ground-water flow
          system;

     *    Relative permeability of the materials; and

     *    Potential interactions between contaminants and the geochemicjl
          parameters within the formation(s) of interest.

These conditions are interrelated and are therefore discussed collectively below.

     There are three basic types of geologic materials through which ground water
normally flows. These are:  (1) porous media; (2) fractured media; and (3) fractured
porous media.  In  porous  media (e.g., sand and gravels, silt, loess, clay,  till, and
sandstone), ground  water and  contaminants move through the pore spaces

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between individual grains.  In  fractured media (e.g., dolomites, some shales,
granites, and crystalline  rocks), ground water and  contaminants move through
cracks or solution crevices in otherwise relatively impermeable rock.  In fractured
porous media (e.g., fractured tills, fractured sandstone, and some fractured shales),
ground  water and  contaminants can move through both the mtergranular pore
spaces as well as cracks or crevices in the rock or soil. The occurrence and movement
of ground water through  pores and cracks or solution crevices depends on the
relative  effective porosity and degree of channeling occurring in cracks or crevices.
Figure 10-1 illustrates the occurrence and movement of ground water and contami-
nants in the three types of geologic materials presented above.

     The distribution of these three basic types of geologic materials is seldom
homogeneous or uniform.  In most settings, two or more types of materials will be
present. Even far one type of material at a given site, large differences  in
hydrologic characteristics may be encountered. The  heterogeneity of the materials
can play a significant role in  the rate of contaminant transport, as well as in
developing appropriate monitoring procedures for a site.

     Once the geologic setting is understood, the site  hydrology should be
va I LI a ted. The location of the site within the regional ground-water flow system, or
regional flow net, should be determined to evaluate the potential for contaminant
migration on the  regional scale.   Potentiometric surface data (water level
information)  for each applicable geologic formation at properly selected vertical
and horizontal locations is needed to determine the horizontal and vertical ground-
water flow paths (gradients)  at the site.  Figure I0-2(a)  and (b)  illustrate two
geohydrologic settings commonly encountered in  eastern  regions of the
United States, where ground water recharge exceeds evapotranspirational rates.
Figure 10-2(c) illustrates  a  common geohydrologic setting for the arid western
regions of the United States.  The potential dimensions of a contaminant release
would  depend on a number of factors including ground-water recharge and
discharge patterns, net precipitation, topography, surface water body locations,
and the regional geologic setting.

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                                  Ibl
Figure 10-1.   Occurrence and movement of ground water and contaminants
             through (a) porous media,  (b) fractured  or creviced media,
             (c) fractured porous media.

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          () LOCAL AND ItfGIONAl GROUND WATIB
            FLOW SYSTEMS IN HUMID fNVIftONMINTS
                (b) TIMTOAAftr ftfVIRUL 0' GBOUNO-*AT|B F10W OUC TO
                             FLOODING OP A NIVIR 0* STMf AM
                TYMCAI. CHOUNO-WATf A FLOW PATHS 1M AAiO tHVlMONMCNTS


Figure 10-2.  Ground-water flow paths in some different hydrogeologic settings.
                                      10-1 *i

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     Table 10-3 and Figures 10-3 through 10-16 illustrate regional, intermediate,
and local ground water regimes for the major ground-water regions in the United
States.  Generalized flow nets are shown superimposed on cross-sections of the
geological unir.  Much of the information presented in the figures and following
text descriptions were taken from Heath et al., 1984 (Ground Water Regions of the
U;S., U.S.G.S Water Supply Paper No. 2242). Following are descriptions of each of
the major ground-water regions illustrated in the Figures (Figures 10-3 through 10-
16).

     Ground-water flow  in the Western mountain Ranges region is influenced by
melting snow and rainfall at higher altitudes.  The thin soils and fractures in the
underlying bedrock  have a limited storage capacity and are quickly filled with
recharging ground water flowing from higher elevations (Se Figure 10-3).  The
remaining surface water runs overland to streams that may eventually recharge
other areas. Streams that recharge gound water are referred to as 'losing streams."
Figure  10-3 also shows local ground-water flow paths influenced  by  low
permeability bedrock located in intermountam valleys throughout the mountain
ranges.

     The Alluvial Basins region consists of deep, unconsolidated sediments adjacent
to mountain ranges.  Precipitation runs rapidly off the mountains and infiltrates
into the alluvium at the  valley margins. Tht water moves through the sand and
gravel layers toward the centers of the  basins (Figure  10-4),   True  presence  of
disjointed masses of bedrock in this region is crucial to the hydrogeological regime.
Low permeability igneous bedrock often isolates the ground water into individual
basins with minimal exchange of ground water. Where the bedrock is composed of
limestone or other highly permeable material, large  regional flow  systems
encompassing many basins can develop. Recharge area; hi this region are located in
upland areas; lowland stream beds carry water only when sufficient runoff from the
adjoining mountains occurs.  Figure 10-4 also shows an  example of a waste unit
located in thick alluvium overlying a structurally complex uppermost aquifer. In this
example, the localized  structural  geology  exerts the most influence over the
ground-water flow pattern.

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                                  TABU 10-3.  SUMMARY OF U.S GROUND WATER REGIONS
Region
t
2
3
4
5
6
7
8
9
10
11
12
13
Region Name
(Heath. 1984)
Western Mountain Ranges
Alluvial Basins
Columbia Lava Plateau
Colorado Plateau
High Plains
Non-glaciated central
Glaciated Central
Piedmont and Blue Midge
Northeast and Superior
Uplands
Atlantic & Gulf Coastal
Plain
Southeast Coastal Plain
Hawaiian Islands
Alaska
Recharge Area
infiltration in mountains
and mountain fronts
plateau uplands
surface infiltration
infiltration in plateau
uplands; infiltration from
surface waters
surface infiltration
upland infiltration
surface infiltration
surface infiltration
upland infiltration
-- j
infiltration In outcrop areas
i
infiltration in outcrop areas
i
surface infiltration
variable*
Discharge Area
streams and rivers
streams and rivers,
some enclosed basint,
localized springs and seeps
in steeper terrain
rivers and streams
seeps, springs, and surface
waters
rivers and streams, seeps
and springs along eastern
escarpments
springs, seeps, itreams and
rivers
springs, streams, rivers, and
lakes
springs, seeps, and surface
waters
surface water
surface water or subsea
leakage
surface water or subsea
leakage
springs, seeps, and surface
waters
variable*
Dimensions
(miles)
< 1-5 unconfirmed
5-60 con fined
< 1 -20 unconfined
5 80 confined
10-200 miles
s 80 miles
2 300 miles
< 1-40 miles
< 1-20 miles
< 1-5 miles
< 1-20 miles
10 ISO miles
1 -80 miles
<1 30 miles
variable*
Example
Wasatch Range. Utah
Nevada
Snake River Plain
Southeast Utah
Nebraska
Ohio Great Miami
Minnesota
West Virginia
Massachusetts
New Jersey
South Georgia
Oahu, Hawaii
North Slope
3
^
,1
         The recharge area, discharge area, and dimension* of the flow cells within Alaska are highly variable due to th wide range in topography
         and geology found in this region.

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WESTERN MOUNTAIN  RANGES
(Mountains with tMn  soils  over  fractured rocks,
alternating with  narrow  alluvial  and,  In  part,
giaciattd valleys)
                                                            I SWMMM
                                                            I CMrf**
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Recharge  Area
(Mountain Ranoe)
                                                         Recharge Area
                                                Losing Stream

                                    Gaining Stream
              ~^rs^ Granite and 'letanorphic  Rocks


              _	| ConsoH'late'l Sedinentary Rocks

              i^L-d^i  Alluvial  Deposits


                             earim Fractur?s
          Figure 10-3. Western Mountain Ranges (continued)

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ALLUVIAL  BASINS
(Thick alluvial  deposits in basins and valleys
bordered  5y mountains)
          Valley F111
          Alluvial  Deposit
Boundary Condition
                                                              j-~Sj Xttmorphlc Btdroek


                                                                           C1v
                                                                     Sinditont


                                                                     Llntstont
                                                         A*
                            Figure 10*4.  Alluvial Basins

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Example of an undetected structurally complex uppermost aquifer.
Elevation
M.S.L.
  700'
                               300'
 -600'
  500'
 -400'
Bore Hole    Waste Unit
Bore Hole
 L 300'
                                                                               Sand Zone
                                                                               Sandy  Si It
                                                                               Zone
                Scale
     100'   50'
         50'  .100'
                                          Sandstone

                                          Si 1tstone

                                          Dolomite
                                          Saturated

                                          Limestone
                       Figure 10-4.  Alluvial Basins (continued)
                                        10-21

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    COLUMBIA LAVA PLATEAU
    (Thick sequence of  lava  flows irregularly inter-
    bedded with thin unconsolidated deposits
    ami overlain by thin  soils)
 rSfff  Holoctnt-Plloctnt
_  Sedfwnti
I      I  B*Mlt
        Licco1'tn-8*U 01 kt
  "Sou n(j Svdfwnti

   '            Recks
                            Figure 10-5.  Columbia Lava Plateau

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                 Ground  Water Flow Path
                 (Mo  scale  intended)

                 Mote:   Assume  hydraulic heads increase
                 with depth.
    Interbed,
    Flow Top, "*"
    Flow Bottom

Dense Flow
Center with  "*"
Vertical  Joints
                 - High horizontal flow along flow tops
                 - Low vertical leakage through basalt interiors
             Figure 10-5.  Columbia Lava Plateau (continued)
                                 10-23

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                  Canyon
                          Extinct volcano**
                                                                     Dam*
Fault icarp
          CliH
                                                                              recto
                        Figure 10-6. Colorado Plateau

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   HIGH  PLAINS
   (Thick  allyvial deposits over fractured
   sedimentary  rocks)
                                              1  Paleovalley  Alluvial  Aquifers
                                              2  High Plains  Aquifer System
                                              3  Niobrara Sandstone Aquifer
                                              4  Herri Shale Aquitard
                                              5  Dakota Sandstone Aquifer
                                              6  Undlfferentfated Aquifers
                                                 in Cretaceous Rocks
                                              7  Undlfftrentiated Aquifers
                                                 in Paleozoic Rocks
Generalized local  ground water regime for site within the High Plains Region
                                 Figure 10-7. High Plains

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Ground water flow  in
sandstone and clay
lenses
                                                             flow Unt
                                                             Equipotential
                                                             Line
                                                             Sind tnd


                                                             S*nd


                                                             Cly


                                                              S*ndstsne
                       Generalized  Regional  Flow
                               Wtsttrn Texas
                       (lechirge centered  at pi ay as)
                      Figure 1 0-7 .  High Plains (continued)

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NONGLACIATED CENTRAL REGION
(Thin regoHth over fractured  sedimentary
rocks)
                                                                          Rtgollths


                                                                          Solution Civ1t1es


                                                                       ^ Kint Ltiwstant


                                                                       *3 Stndttont
                                                                          S*lt



                                                                          Frcturs
                          Figure 10-8. Non-glaciated Central
                                         1fl.-57

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                                  Surface
                                  Impoundments
             Stream
Alluvial
Deposit   \
                                                    Pittsburgh Coal
                              Sandstone
                                                   Flow line
                                             _     fqutpotentiil
                                               ~"~" line
           Figure 10-8.    Example of a surface impoundment site in Non-Glaciated Central
                          Region (continued)     I

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GLACIATED CENTRAL REGION
(Glacial deposits over fractured sedimentary rocks!
                                                                  CZ3
Said
                           >.i ^v^.tp^^.y Y.;,:.^
                                                                          Snd
                                                                          Lfntitont
                                                                          Flow Hue
                                                                          lint
                               Figure 10-9. Glaciated Central

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                                                                                      Clay 4 Silt Layer
                                                        Uaste Disposal  Unit
                                                                                                 Observed Ground
                                                                                                {  Water  Uvel
L100'
                                                         |     I'l'i'i'i     |     |  Scale
                                                         100'  50'   0'   50'   100'
                               Figure 10-9.  Glaciated Central (continued)

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Exanple of a ground-water reqime where till has a much lower hydraulic
conductivity than overlying deltaic deposits
 I Ml
 ii
 II
                                                                                                iii
                              Figure 10-9. Glaciated Central (continued)

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PIEDMONT BLUE RIDGE REGION
(Thick regolith over fractured crystalline and
metamorphosed sedimentary rocks)
                                                              j\ SprpHtc


                                                               .I Btdrock
                    Figure 10-10. Piedmont and Blue Ridge

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NORTHEAST AND SUPERIOR UPLANDS
(Glacial  deposits over fractured
crystal!int rocks)
                                                            riu*1l Vilify Trtln Otposits


                                                            Otlti Deposits


                                                            tiiif Ttrraet Deposits


                                                            Till OeposUi


                                                            Itkt-bottan Flnt-Sriined Sed-fu


                                                            IcJrock


                                                            Flew Lint

                                                            tqulpotent1*1
                                                            L1nt


                                                                        A'
              Figure 10-11.  Northeast and Superior Uplands

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                                                             8'
Generalized  local ground water regime within  the  Northeast and Superior
Uplands Region
       Figure 10-11.  Northeast and Superior Uplands (continued)

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            >*-	._ -,-.
10-12-  Atlan
lticandG Coastal Plain

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Landfill Site
                                              Losing Strean
         Gaining  Strean
                                                                   L-200
                 g^--.=j Sindy Shalt
Note:  Rei^onal 'Tow
       tils dianran.
                               on h^nh recharqe in bins which are not shown in
                Figure 10-12.  Atlantic and Gulf Coastal Plain (continued)

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 SI
 o
 
Q.
                                                                                      3

                                                                                      .
                                                                                      **
                                                                                      c
                                                                                      o
                                                                                      T5
                                                                                      Ml
                                                                                      IV
                                                                                      o
                                                                                      a
                                                                                      e
                                                                                      C
                                                                                      ffl
                                                                                      3
                                                                                      01

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 SOUTHEAST COASTAL  PLAIN
 (Thick layers of sand and clay over  semi
 consolidated carbonate rocks)
                                                         A'
                                Equ1potential
                            '"" Line
 Solution Limestone

Cross-section wfth highly generalized flow path lines and equipotential
lines.  Actual  condition in Karst terrain mav not  be  definable due to
fractures and solution channel  flow.
                                         Are*
                          Discharge Are*
                                             P1e1stoctn/Holoccne Sand
                    Sinkhole
lake
      Hawthorn
      ForMtlon
Mi/er Llnestone Spri ng
(Artesltn Condition)
                     Figure 10-13.  Southeast Coastal Plain


                                      10-38

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Swamp
Beaches and  Bars
                          i&i&!". .l.'.':'.'-.'.5igffi;'-*.-.i.:*.:.'.f ..";'i'.Ai.'.'
  Highly permeable due to water-washed sands.
  Sand deposits  serve as a source of recharge
  to the underlying unconsolldated coastal deposits.
    Figure 10-13.  Southeast Coastal Plain (continued)
                          10-39

-------
A qpneralized local ground water flow in Karst Limestone  terrain
Upqraifient
                                         Ground
                                 ^-nit Ground Mater

                                  1, 2   Ground Ui*r
                                        Monitor ^elli

                                 i I  ', i  I rrboiute Rock
                   Figure 10-13. Southeast Coastal Plain (continued)

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Burled SO
 UNSATVJRATED ROCK
           Figure 10-14.  Hawaiian Islands
                        10-41

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Figure 10-15.  Alaska

-------
10-16.

-------
             drum site
       .    ,     -  -..^ Prt-EttiMtlon
       kY / -." ".Prliwry "^^ Ground Surface
               '8rrl Pit  ^^
^^^^^Wi^t;^lii^^             1Brook
   1*00  2*00  3*00 4*00  5*00  6*00  7*00  8*00  9+00 10*00

              Horizontal D
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     Basaltic bedrock is the major source of ground water within the Columbia lava
Plateau region. Volcanic bedrock yields water mainly from zones that are at the
contacts of separate basalt flows. Permeability and hydraulic conductivity are much
higher in these zones at the edges of the flows than in the center of the flows  (See
Figure 10-5.) This is due, in part, to the rapid cooling and consequent fracturing of
the top of each basalt flow.

     The Colorado-Plateau region is underlain by fractured bedrock (See Figure 10-
6).  Tht main source of recharge  is upland filtration and  infiltration from  local
surf ace waters.

     The High Plains region is underlain by thick alluvial deposits that comprise a
productive and extensively developed aquifer system. The source of recharge to the
aquifer system is precipitation except in western Texas where recharge is centered
at playas (See Figure 10-7). In many areas, well discharge far exceeds recharge, and
water levels are declining. The dominant features influencing ground-water flow in
this region include the Ogalalla aquifer, the Pierre  Shale, and the complex
interbedded   sand and clay lenses. Figure 10-7 provides generalized regional flow
nets showing flow patterns through these features.

     Thin regolith over fractured sedimentary rocks typifies the nature of the
geology in the Nonqlaciated Central region. (See Figure 10-8.) This region extends
from the Rocky Mountains to the Appalachian Mountains.  Water is transmitted
primarily along horizontal fractures at bedding planes. Interconnected vertical
fractures also can store a large amount of the ground water. An example of a flow
net on a local scale is shown for ground-water flow through karst terrain. In karst
terrain, ground water moves rapidly through solution cavities in limestone and the
flow pathways are highly dependent on the configuration of fractures. Ground-
water flow in the  karst terrain does not follow Darcy's Law because the flow is
turbulent rather than laminar. Thus, the flow path lines shown are highly idealized.
An additional example of localized flow in this region is provided showing a surface
impoundment site in Pennsylvania. Notice that ground-water discharges to surface
water, a phenomenon typical of this region.

     The topography of the Glaciated Central region is characterized by rolling hills
and  mountains in the eastern  portion  and  flat to gently rolling terrain
                                   10-45

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ir, the western portion. Glacial deposits vary in thickness within the region and are
underlain by bedrock. Ground water occurs in the glacial deposits in pores between
the grains and in the bedrock, primarily along fractures.  Permeable   glacial
deposits range from extremely transmissive gravels to poorly sorted tills. Buried
valleys, till, deltas, kamts, and other glacial artifacts influence the transmission of
ground water within the region. Two examples of localized flow are presented in
Figure 10-9.  The first example shows a flow regime in an area where till has the
highest hydraulic conductivity relative to the other materials.  In the second
example, the till bed has a much  lower hydraulic conductivity than  the deltaic
outwash deposited above it.

     Thick regolith overlies fractured crystalline and metamprphic bedrock in most
of the Piedment and Blue Ridge region. The hydraulic conductivities of regolith and
fractured bedrock are similar. However, bedrock wells generally have much  larger
ground-water yields than regolith wells because, being deeper, they have available
a much larger drawdown. Fracture-controlled movement of ground water through
bedrock is illustrated  in Figure 10-10, as  is ground-water movement through
saprolite (weathered bedrock) and river alluvium.

     The Northeast and Superior Uplands region is characterized by folded and
faulted igneous and metamorphic bedrock overlain by glacial deposits.  The primary
difference in the ground-water environment between this region and the Piedmont
and Slue Ridge region is the presence of glacial material rather than regolith. The
different types of glacial material have vastly different storage capacities and
hydraulic conductivities. Examples of ground-water flow through till, delta, and
kame deposits, as well as a generalized  ground-water regime  with upward
gradients, are illustrated in Figure 10-11.

     Tht Atlantic and Gulf Coastal Plain region is underlain by unconsolidated
sediments that consist primarily of sand, silt, and clay.  The sediments are often
interbedded as a result of deposition on floodplains or deltas and  subsequent
reworking by ocean currents.  Recharge to the ground-water system occurs in the
inttrstream areas; most streams in this region are gaining streams. (See Figure 10-
12.)  Encroachment of salt water into well drawdown areas can be a problem in this
area if high rates of ground-water withdrawal occur. An example  (shown in Figure

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10-12) of a flow net for a waste disposal site in New Jersey shows how regional flow
may differ from the expected flow based on local topography Also shown in Figure
10-12 is a proposed landfill site in an area of high recharge near the Savannah River
in Georgia.

     Ground water in the Southeast Coastal Plain region lies  primarily within
semiconsolidated limestone. Sand, gravel, clay, and shell beds overlie the limestone
beds. Recharge in this region occurs by  infiltration of precipitation directly into
exposed limestone, and by seepage through the permeable soils that partly mantle
the limestone.  (See Figure 10-13.) Coastal environments such as  beaches and bars
and swamp areas have different ground-water regimes, shown in Figure 10-13,
Flow through solution channels and large fractures in limestone is often rapid and
thus the flow lines shown on the flow nets are highly idealized.

     The geohydrologic setting for the Hawaiin Islands and Alaska Regions are
provided in Figures 10-14 and tO-15, respectively.

     Alluvial Valleys occur throughout the United States and can supply water to
wells at moderate to high rates (See Figure 10-16). These valleys are underlain by
sand and gravel  deposited by streams carrying sediment-laden  melt water from
glaciation that occurred during the Pleistocene era. These valleys are considered a
distinct ground-water terrain. These valleys have thick sand and gravel deposits
that are in a clearly defined band and are in hydraulic contact with a perennial
stream. The sand and gravel deposits generally have a transmissivity on the order of
ten or  more times greater than that of the adjacent bedrock.  Silt and clay are
commonly found both above and below the sand and gravel channels in the Alluvial
Valley's as a result of overbank flooding of rivers.  Ground-water recharge is
predominantly by precipitation on the valleys, and also by ground water moving
from the adjacent and underlying aquifers, by overbank flooding of the streams,
and in some glacial valleys, by infiltration from tributary streams.  An example of a
flow net illustrating local ground-water movement beneath a waste disposal site in
Connecticut is also shown in Figure 10*16.

     In addition to determining the directions of ground-water flow, it is essential
to determine the approximate rates of ground-water movement to properly design
a monitoring program.  Hydraulic conductivity, hydraulic gradient, and  effective
                                   10-47

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porosity data are required to estimate the average linear velocity of ground water
and. therefore, assist in the determination of the rate of contaminant migration.
Hydraulic conductivity data can be determined using single well (slug) test data.
Several hydraulic conductivity measurements can be made on materials penetrated
by individual wells to provide data on the relative heterogeneity of the materials in
question. Measurements made in several wells also provide a comparison to check
for effects of poor well construction. Hydraulic conductivity can also be determined
from multiple-well (pumping)  tests.  A  multiple-well  test provides a hydraulic
conductivity value  for a larger portion of the  aquifer.  Hydraulic  conductivities
determined in the laboratory have been shown to vary by orders of magnitude from
values determined by field methods and are, therefore, not recommended for use in
the RFI.

     Porosity can  have an important controlling  influence on  hydraulic con-
ductivity. Materials with high  porosity values generally also  have high hydraulic
conductivities.  An exception is clayey geologic materials which, although possessing
high porosities, have low hydraulic conductivity values (resulting in low flow rates)
due to their molecular structure. All of the  pore spaces within geologic materials
are not available for water or solute flow. Dead-end pores and the portion of the
total porosity occupied by water held to soil particles by surface tension forces, do
not contribute to  effective porosity. Therefore, to determine average linear
velocities, the  effective porosity of the materials should be determined,  in  the
absence of measured values, the values provided in Table 10-4 should be used.
     Knowledge of the rates of ground-water flow is essential to determine if the
locations of the monitoring wells are within reasonable flow distances of the
contaminant sources.  Flow rate data can also be used to  calculate reasonable
sampling frequencies. This is particularly important when attempting to monitor
the potential migration of a intermittent contaminant release.

     Geochemical and biological properties of the aquifer matrix should  be
evaluated in terms of their potential interference with the goals of the monitoring
program.  For example, chemical reactions or biological transformations of the
monitoring constituents of concern may introduce artifacts into the results. Physical
and hydrologic conditions will determine whether or not information on  chemical

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          TABLE 10-4.   DEFAULT VALUES FOR EFFECTIVE POROSITY
                 Soil Textural Classes
 Effective
 Porosity of
Saturation^
 Unified Soil Classification System
   GC, GP, GM, GS
   SW, SP, SM, SC

   ML.MH
   CL.OL.CH.OH, PT
 USDA Soil Textural Classes
   Clays, si Ity days,
   sandy clays
   Silts, silt loams,
   Silty clay loams

   All others
 Rock Units Call)
    Porous media (nonfractured
    rocks such as sandstone and some carbonates)
    Fractured rocks (most carbonates, shales,
    granites, etc.)
   0.20
   (20%)

   0.15
   (15%)

   0.01
    0.01
    0.10
   (10%)

    0.20
   (20%)
    0.15
   (15%)

   0.0001
  (0.01%)
*  These values are estimates. There may be differences between similar units.
b  Assumes de minimus secondary porosity. If fractures or soil structure are
   present, effective porosity should be 0.001 (0.1%).
                                  10-49

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or biological interactions can be collected.  If the potential for these reactions or
transformations exists, consideration should be given to monitoring for likely
intermediate transformation or degradation products.

     The monitoring  system design  is influenced in many ways  by  a site's
hydrogeologic setting. Determination of the items noted in the stratigraphy and
flow systems discussions will aid in logical monitoring network configurations and
sampling activities. For example:

     *   Background and downgradient wells should be screened in the same
         stratigraphic horizon(s) to obtain comparable ground-water  quality
         data.  Hydraulic conductivities should be  determined to evaluate
         preferential flowpaths (which will require monitoring) and  to establish
         sampling frequencies.

        The distances between and  number of wells (well density) should be a
         function of the  spatial heterogeneity of a site's hydrogeology, as  is
         sampling  frequency.  For example, formations of unconsolidated
         deposits with numerous interbedded lenses of varying hydraulic
         conductivity or consolidated rock with numerous fracture traces will
         generally require a greater number of sampling locations to ensure that
         contaminant pathways are intercepted.

        The slope of the potentiometric surface and the slope of the aquitard-
         formation strongly influence the migration rates of light and dense
         immiscible compounds.

        The hydrogeology will strongly influence the  applicability of  various
         geophysical methods (Appendix C),  and should be used to establish
         boundary conditions for any modeling to be performed for the site.

     *   Analyses for contaminants of concern in the ground water monitoring
         program can  be influenced by the genera! water quality present.
         Naturally-occurring cations and anions can affect contaminant reactivity,
         solubility, and  mobility.

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    Sites with complex geology will generally require more hydrogeologic
     information to provide a reasonable assurance that well placements will
     intercept contaminant migration pathways.  For example, Figure 10-17
     illustrates 2 cross-sectional and plan view of a waste landfill located in a
     mature Karst environment.  This setting is characteristic of carbonate
     environments encountered in various parts of the country, but especially
     in the southeastern states.   An assessment of the geology of the site
     through the use of borings, geophysical surveys, aerial photography,
     tracer studies, and other geological investigatory techniques, identified a
     mature Karst geologic formation characterized by well  defined
     sinkholes,  solution channels and  extensive vertical and horizontal
     fracturing in an interbedded limestone/dolomite.  Using potentiometric
     data, ground-water flow was found to be in an easterly direction.

     Solution channels are formed by the flow of water through the  fractures.
     The chemical reaction between the carbonate rock and the ground-
     water flow in the fractures produces solution channels.  Through  time,
     these solution channels are enlarged to the point where the weight of
     the overlaying  rock is too  great to support, consequently causing a
     "roof" collapse and the formation of a sinkhole.  The location of thtse
     solution channels dictate the placement of monitoring wells. Note that
     in Figure 10-17 the placement of well No. 2 is offset SO feet from the
     perimeter  of the landfill.  The horizontal placement  of well No.  2.
     although not immediately adjacent to the landfill, is necessary in order to
     monitor all potential contaminant pathways.  The discrete nature  of
     these solution  channels dictate that each potential pathway  be
     monitored.

     The hei ght of the solution channels ranges from three to six feet directly
     beneath the sinkhole to one foot under the landfill. The vertical extent
     of the  cavities allow for full screening of the horizontal solution
     channels.  (Note the change in orientation of solution channels due  to
     the presence of the fossil hash layer).

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         Q  *CBMMJNWUNHMIMfMIWtll

           MMMMMAMINIMONMO*m<)*m

         H  tUKMIM

        _y_ MlmllOMf IMCMMf AC!

        -- . f IIACIUMM IHACf
       8
             ft IMttCO MMIHM.I
   Milt
                                  MU4 Mtlt
                         IPftOMCIIO IMfflll moMCIIPMMttl
                                                                 \
                     lAMOflll
           IXe riWNCIIVt -Mfllll
                                     OHCMINOMAIIN >!
                                        ooi et rAoi iro:
                                         -  f  .  -.-7^
                                                                                             * mm IMM
                                                                                             * W-
I.*M
Hit II
              Figure 10*17.   Monitoring well placement and screen lengths in a mature
                              karst terrain/fractured bedrock setting.

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     Chapter I of the RCRA..Ground. Water Monitoring Technical Enforcement
Guidance Document (TEGD) (U.S.  EPA, 1986) provides additional guidance in
characterization of site hydrogeology.  Various sections of the document will be
useful to the facility owner or operator in developing monitoring plans for RCRA
Facility Investigations.

     In order to further characterize a release to ground water, data should be
collected to assess subsurface stratigraphy and ground-water flow systems.  These
are discussed in the following subsections.

10.33.1  Subsurface Geology

     In order to adequately characterize the hydrologic setting of a site, an analysis
of site geology should first be completed. Geologic site characterization consists of
both a characterization of stratigraphy, which includes  unconsolidated  material
analysis, bedrock features such as lithology and structure, and depositional
information, which indicates the sequence of events which resulted in the present
subsurface configuration.

     Information that may be needed to characterize a  site's subsurface geology
includes:

        Grain size distribution and gradation;

        Hydraulic conductivity;

        Porosity;

     *   Discontinuities in soil strata; and

     *   Degree and orientation of subsurface stratification and bedding.

Rtfer to Section 9 (Soil) for further details.

     Gram size distribution and qradation-A measurement of the percentage of
sand, silt, and clay should be made for each distinct layer of the soil. Particle size can
                                   10-53

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affect contaminant transport through its impact on adsorption and hydraulic
conductivity.  Sandy soils generally have low sorptive capacity while clays tend to
have a high affinity for heavy metals and some organic contaminants. This is due in
part to the fact that small clay particles have a greater surface area in relation to
their volume than do  large sand particles.  Greater surface areas lead to stronger
interactions with contaminant molecules. Clays also bind contaminants due to the
chemical structure of the clay.  Methods for determination of sand/siit/ciay fractions
are available from ASTM, Standard Method No. D422-63 (ASTM, 1984).

     Hydraulic conductivity-This property represents the ease with which fluids can
flow through a formation, and is dependent on porosity, and grain size, as well as
on the viscosity of the fluid.  Hydraulic conductivity can be determined by the use of
field tests, as discussed in Section 10.6.

     Porosity-Soil porosity is the volume percentage of the total volume of the soil
not occupied by solid particles (i.e., the volume of the voids). In general, the greater
the porosity, the more readily fluids may flow through the soil, with the exception
of clays (high porosity), in which fluids are held tightly by capillary forces.

     Discontinuities in geological materials-Folds are layers of rock or soil that have
been naturally bent over geologic time. The size of a fold may vary from several
inches wide to several miles wide. In any case,  folding usually results in a complex
structural configuration of laytrs (Billings, 1972).

     Faults are ruptures in rock or soil formations along which the opposite walls of
the formation have moved past each other. Like folds, faults vary in size. The result
of faulting is the disruption of the continuity of structural layers.

     Folds and faults  may act as either barriers to or pathways for ground-water
(and contaminant) flow. Consequently, complex hydrogeologic conditions may be
exhibited. The existence of folds or faults can usually be determined by examining
geologic maps or surveys.  Aerial photographs can also  be  used to identify  the
existence of these features.  Where more detailed  information  is needed, field
methods (e.g., borings or geophysical methods)  may need to be employed.
                                    10-54

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     Joints are relatively smooth fracturts found in bedrock,  joints may be as long
as several hundred feet (Billings, 1972). Most joints are tight fractures, but because
of weathering, joints may be enlarged to open fissures. Joints result in a secondary
porosity in the bedrock which may be the major pathway of ground- water flow
through the formation (Sowers, 1981).

     Interconnected conduits between grains  may form during rock  formation
(Sowers, 1981).  The permeability  of a  bedrocic mass is often defined by the
degreeof jointing.   Ground water may travel  preferentially along  joints, which
usually governs the rate of flow through the bedrock. The degree and orientation
of joints and interconnected voids  is needed to determine if there will be any
vertical or  horizontal leakage through the formation. In some cases, bedrock acts as
an aquitard, limiting the ground-water flow in an  aquifer. In other cases, the
bedrock may be much more productive than overlying alluvial aquifers.

     Geologic maps available from the U5GS  (see Section 7)  may be useful in
obtaining  information on the degree and  orientation of jointing or interconnected
void forma*!on. Rock corings may also be used to identify these characteristics.

     Degree and orientation of subsurface stratification and peddinq-The owner
or operator should  develop  maps of the subsurface structure for the  areas of
concern.  These maps should identify the thickness and depth of formations, soil
types and  textures, the locations of saturated  regions and other hydrogeological
features.  For example, the existence of an  extensive, continuous, relatively
horizontal, shallow strata of low permeability  can provide a clue to contaminant
routing. In such cases, the contaminants may migrate at shallow depths, which are
above the regional aquifer.  Such contamination could discharge into nearby, low-
lying structures (e.g., seepage into residential basements). This basement seepage
pathway has  been demonstrated to be a significant migration channel in  many
cases. This pathway may result from migration of vapors in the vadose zone or
through lateral migration of contaminated ground water.  Basement seepage is
more likely to occur in locations with shallow ground water.

     A variety of direct and  indirect methods  are available to characterize  a site
geologically  with respect to the above geologic characteristics.  Direct  methods
utilize soil borings and rock core samples and subsequent lab analysis to evaluate
                                   10-55

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grain size, texture, uniformity, mineralogy, soil moisture content, bedrock lithology,
porosity, and structure. Combined, these data provide the basis for delineating the
geologic nature of the site and, in turn, provide the data necessary to evaluate the
hydro logic setting.

     Indirect methods of geologic investigation, such as geophysical techniques
(See Appendix C) and aerial photography (See Appendix A) can be  used to
supplement data gathered by direct field methods, through extrapolation  and
correlation of data on  surface and subsurface geologic features.  Borehole
geophysical techniques can be used to extrapolate direct data from soil borings and
bedrock cores.  Surface geophysical methods can provide indirect information on
depth, thickness, lateral  extent, and variation of subsurface futures that can be
used to extrapolate  information gained from direct methods.  Applicable surface
geophysical methods include  seismic  refraction,  electrical resistivity,  electro-
magnetics, magnetics, and ground penetrating radar.

103.3,2  Flow Systems

     In addition to characterizing the subsurface geology, the  owner or  operator
should adequately describe the ground-water flow system.  To adequately describe
the ground-water flow paths, the owner or operator should:

     *   Establish the direction of ground-water  flow (including horizontal and
         vertical components of flow);

     *   Establish the seasonal, temporal, and artificially induced (e.g., offsite
         production wtll pumping, agricultural use) variations in ground-water
         flow; and

     *   Determine the hydraulic conductivities of the hydrogeologic  units
         underlying the site.

     Hydrologic and hydraulic properties and other relevant information needed to
fully evaluate the ground-water flow system are listed and discussed below.

     *   Hydraulic conductivity;

                                   10-56

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         Hydraulic gradient (vertical and horizontal);

     *    Direction and rate of flow;

         Aquifer type/identification of aquifer boundaries;

         Specific yield (effective porosityVstorage coefficient;

         Depth to ground water;

     *    Identify uppermost aquifer;

     *    Identify recharge and discharge areas;

         Use of aquifer; and

     *    Aquitard type and location.

     Hydraulic conductivitv-ln addition to defining the direction of ground-water
flow in the vertical and horizontal directions, the owner or operator should identify
the distribution of  hydraulic conductivity within each formation. Variations in the
hydraulic conductivity  of subsurface materials can affect flow rates and alter
directions of ground-water flow paths.  Areas of high hydraulic conductivity
represent  areas of greater ground-water flow and zones of potential migration.
Therefore, information on  hydraulic conductivities is needed to make decisions
regarding well  placements.  Hydraulic conductivity measurement is described  in
Section 10.6,

     Hydraulic gradient-The hydraulic gradient is defined as the change in static
head per  unit distance in a given direction.  The hydraulic gradient defines the
direction of flow and may be expressed on maps of water level measurements taken
around the site. Ground-water velocity is directly related to hydraulic gradient.
Both vertical and horizontal gradients should be characterized.
                                   10-57

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     Direction and rate of flow-A thorough understanding of how ground water
flows beneath the facility will aid the owner or operator in locating wells to provide
suitable background and/or downgradient samples. Of particular importance is the
direction of ground-water flow and the impact that external factors (intermittent
well pumping, temporal variations in recharge patterns, tidal effects, etc.) may have
on ground-water flow patterns, in order to account for these factors,  monitoring
procedures should include precise water  level measurements in p;zometers  or
observation wells. These measurements should be made in a sufficient number of
wells and at a frequency sufficient to adequately gauge both seasonal average flow
directions and to show any seasonal or temporal fluctuations in flow directions.
Horizontal and vertical components of ground-water flow should be assessed.
Methods for determining vertical and horizontal components of flow are described
in Subsection 10.5.4.

     Identification of aquifer boundaries/aquifer type-Aquifer boundaries define
the flow limits and the degree of confinement of an aquifer. There are two major
types of aquifers: unconfined and confined.  An unconfined aquifer has a free
water surface at which the fluid pressure  is the same  as atmospheric.  A confined
aquifer is enclosed by retarding  geologic formations  and is, therefore, under
pressure greater than atmospheric.  A confining unit consists of consolidated or
unconsolidated earth materials that are substantially less permeable than aquifers.
Confining  units are called aquitards or aquiciudes.   Aquifer boundaries can  be
identified by consulting  geologic maps and  state geologic surveys.  Observation
wells and piezometers can be used to determine the degree of confinement of an
aquifer through analysis of water level data.

     Specific yield/storativity-Specific yield and ftorativity are both terms used to
characterize the amount of  water an  aquifer is capable of yielding.  In  an
unconfined system, the specific yield is the ratio of the drainable volume to the bulk
volume of the aquifer medium (some liquid will be retained in pore spaces). The
storativity of a confined aquifer is the volume of water released from a column of
unit area and height per unit decline of pressure head.  Specific yield or storativity
values may be necessary to perform complex ground-water modeling.

     Depth to ground water-The depth  to  ground water is the vertical distance
from the land's surface to the top of the saturated zone. A release from a unit not
                                   10-58

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in contact with the water table will first percolate through the umaturated zone
and  may, depending upon the  nature  of the geologic material, disperse
horizontally. Thus, a release of this nature may reach a deep water table with some
lateral spreading.  Depth to ground water can influence the selection of sampling
methods as well as geophysical methods.

     A shallow water table can also facilitate releases to other environments via
volatilization of some compounds into the unsaturated zone, seepage into base-
ments of buildings in contact with the saturated zone, or the transport of
contaminants into wetlands where the water table reaches the level of the ground
surface. Sufficient mapping of the water table with particular attention to these
features should provide an indication of where these interactions may exist.

     Identification of uppermost aquifer-As defined in 40 CRF 260.10, "aquifer"
means a geologic formation, group of formations, or part of a formation capable ot
yielding a significant amount of ground water to wells or springs. "Uppermost
aquifer," also defined in 40 CRF 260.10, means the geologic formation nearest the
natural  ground surface  that is an aquifer, as well as lower aquifers that are
hydraulically interconnected with this aquifer within the  facility's property
boundary. Chapter one of the Technical Enforcement Guidance Document (TEGD)
(U.S. EPA, 1986) elaborates on the uppermost aquifer definition. It states that the
identification of the confining layer or lower boundary is an essential facet of the
definition. There should be very limited interconnection, based on pumping tests,
between the uppermost and lower aquifers.  If zones of saturation capable of
yielding significant amounts of water are interconnected,  they all comprise the
uppermost aquifer. Identification of formations capable of "significant yield" must
be made on a case-by-case basis.

     There are saturated zones, such as low permeability clay, that may not yield a
significant amount of water, yet may act as pathways for contamination that can
migrate horizontally for some  distance before reaching a zone which yields a
significant amount of water. In other cases, there may be low yielding saturated
zones above the aquifer which can provide a pathway for contaminated ground
water to reach basements. If there is  reason to believe that a potential exists for
contamination to escape along such  pathways, the  owner  or operator should
monitor such zones.
                                   10-59

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     For furthtr information on  the suppermost aquifer definition,  including
examples illustrating the determination of hydraulic  interconnection in  various
geologic settings, see Chapter One of the TEGD.

     Identification of recharge and discharge areas-Ground-water recharge can be
defined as the entry into the saturated zone of water made available at the water
table surface, together with the associated flow away from the water table within
the saturated zone. Ground-water discharge can be defined as the removal of
water from the saturated  zone across the water table surface, together with the
associated flow toward the  water table within the saturated zone (Freeze and
Cherry, 1979)1 Ground-water recharge and discharge areas also represent areas of
potential inter-media transport.

     Recharge can  be derived from the infiltration of precipitation, inter-aquifer
leakage, inflow from streams or lakes, or inadvertently by leakage from lagoons,
sewer lines, landfills, etc.  Discharge occurs where ground water flows to springs,
streams, swamps, or lakes, or is removed by evapotranspiration or pumping  wells,
etc. Information on the source and location of aquifer recharge and discharge areas
may be obtained from state water resource  publications, geologic surveys, or
existing site information. Comparison of aquifer water levels with nearby surface
water levels may also provide an indication of the source and location  of aquifer
recharge and discharge areas.

     Flow nets can also be used to determine  areas of  aquifer recharge and
discharge. Section 10.5.2 describes the use of flow nets to  determine ground-water
flow patterns.

     Use of aquiferThe proximity and extent of local  ground-water use (e.g.,
pumping) may dramatically influence the rate and direction of ground-water flow
possibly causing seasonal or episodic variations. These factors should  be considered
when  designing  and implementing a  ground-water monitoring  system.
Information on local aquifer use  may be available from  the USGS, and state and
local water authorities.  Aquifer use for drinking water or other purposes may also
influence the location of ground-water monitoring wells, as it may be appropriate
to monitor at locations pertinent to receptors.

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     Aquitard type and locationAquitard type refers to the type of geologic
formation that serves to bound ground-water flow for a given aquifer.  Such
boundaries may be rock or may be an unconsolidated unit such as clay, shale, or
glacial till. The identification of such formations and their hydraulic characteristics
is essential in determining ground-water flow paths.  Aquitard locations can be
determined by consulting geologic maps and boring log information. Although
aquitards are substantially less permeable than aquifers, they are not totally
impermeable and can allow significant quantities of water to pass through them
overtime. The location of an aquitard should be used in determining monitoring
well depths.

10.3.4    Sources of Existing Information

     A complete  review of relevant existing information on  the facility is an
essential  part of the release characterization. This review can provide  valuable
knowledge and a basis for developing monitoring procedures.  Information that
may be available and useful for the investigation includes both site-specific studies
and regional surveys available from local, state, and Federal agencies.

     Information  from the  regulatory agency such as the  RFA report should be
thoroughly reviewed in developing monitoring procedures, and should serve as a
primary information  source. It may also  provide references to other sources of
mfo/mation. In addition, the facility's RCRA Permit Application may contain other
relevant information. These reports and all of the facility's RCRA compliance/permit
files will  provide an understanding of the current level of knowledge about the
facility, and will assist in identifying data gaps to be filled during the investigation.

     Public information is available from local, state, and Federal governments (see
Section 7) concerning the topics discussed below.

10.3.4.1   Geology

     Knowledge of local bedrock types and depths is important to the investigation
of a site. Sources of geologic information include United States Geological Survey
                                   10-61

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(USGS) reports, maps, and files; State geological  survey records; and local well
drilling logs. See also Section 9 (Soils),

10.3.4.2   Climate

     Climate is also an  important factor affecting the potential for contaminant
migration from a release source.  Mean values for precipitation, evaporation,
evapotranspiration, and estimated percolation will help determine the potential for
onsite and offsite contaminant transport. The investigator should consult monthly
or seasonal precipitation and evaporation (or temperature) records. Climate and
weather information can be obtained from:

          National Climatic Center
          Department of Commerce
          Federal Building
          Asheville, North Carolina 28801
          Tel:  (704)258-2850

10.3.4.3   Ground-Water Hydrology

     The owner or operator will need to acquire information on the ground-water
hydrology of a site and its surrounding environment. Ground-water use in the area
of the site should be thoroughly investigated to find the depths of local wells, and
their pumping  rates. Sources of such information include the USGS, state geological
surveys, local well drillers, and State and local water resources boards. A list of all
state and local cooperating offices is available from the USGS, Water Resources
Division in Reston, Virginia, 22092.  This list has also been  distributed to EPA
Regional Offices. Water quality data, including surface waters, is available through
the USGS via their automated NAVVDEX system. For further information, telephone
(703)860-6031.

10.3.4.4   Aerial Photographs

     Aerial reconnaissance can be an effective and economical tool for gathering
information on waste, management facilities.  For this application, aerial recon-
naissance includes  aerial photography and thermal infrared scanning.  See

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Appendix A for a detailed discussion of the usefulness of aerial photography in
release characterization and availability of aerial photographs.

10345  Other Sources

     Other sources of information for subsurface and release characterization
include:

        U.S. EPA files (e.g., CERCLA-rtlated reports);
     *   U.S. Geological Survey;
        U.S. Department of Agriculture Soil Conservation Service;
        U.S. Department  of Agriculture  Agricultural Stabilization and
         Conservation Service,
     *   U.S. Department of Interior -Bureau of Reclamation;
        State Environmental Protection or Public Health Agencies,
     *   State Geological Survey;
    . *   Local Planning Boards;
        County or City Health Departments;
     *   Local Library;
     *   Local Welt Drillers; and
     *   Regional Geologic and Hydrologic Publications.

10.4 Design of a Monitoring Program to Characterize Releases

     Information on waste, unit and environmental characterization can be used to
develop a conceptual model of the release, which can subsequently be used to
design a monitoring program to fully characterize the release.  The design of  a
monitoring program is discussed below.

10.4.1    Objectives of the Monitoring Program

     The objective of initial monitoring is to verify or to begin  characterizing
known or suspected contaminant releases to giuund water. To help accomplish  this
objective, the owner or operator should evaluate any existing monitoring wells to
determine if they are capable of providing samples representative of background
and downgradient ground-water quality for the unit(s) of concern. Figure 10-18
                                   10-63

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                  toes! available copy   HJ
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                                         Figure 10-18.
                                   Monitoring well locations

-------
illustrates three cases where existing well systems are evaluated with regard to their
horizontal location for use in a ground-water investigation. Adequacy is not only a
function of well location but also well construction.  Guidance on appropriate well
construction materials and methods can be found in the TEGD (EPA, 1986). If the
monitoring network is found to be inadequate for all or some of the units  of
concern, additional monitoring wells should be installed. Further characterization,
utilizing both direct and indirect investigative methods, of the site's hydrogeology
should be completed to identify appropriate locations for the new monitoring
wells.

     If initial monitoring verifies a suspected  contaminant release, the owner or
operator should extend the  monitoring program to determine the  vertical and
horizontal concentrations (e.g., 3- dimensions) of all hazardous constituents in the
release. The rate of contaminant migration should also be determined, A variety of
investigatory techniques are available for such monitoring programs.

     Monitoring procedures should include direct methods of obtaining  ground-
water quality information (e.g., sampling and analysis  of ground water from
monitoring wells).   Indirect  methods of investigation may be  used when
appropriate to aid in determining locations for monitoring  wells (i.e., through
geologic and/or geochemical interpretation of indirect data). For many cases, the
use of both direct and indirect methods may be the most efficient approach.

     Elements to be addressed in the ground-water monitoring program include:

     *    Indicator parameters and constituents to be monitored;

     *    Frequency and duration at which samples will betaken;

     *    Sampling  and analysis techniques to be used, including appropriate
          QA/QA procedures; and

         Monitoring locations.
                                   10-65

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     [Note:  Permit application regulations in 40 CFR 270.14(c)(2) require appli-
     cants to identify the uppermost aquifer and hydraulically interconnected
     aquifers beneath the facility property if the facility has any "regulated" units.
     The application must indicate ground-water flow directions and provide the
     basis for the  aquifer identification (e.g.. a report written by a qualified
     hydrogeologist on the hydrogeologic characteristics of the facility property
     supported by at least the well drilling logs and available professional
     literature).  However, some RCRA permit applications did not  require
     hydrogeologic characterizations (e.g.. storage only facilities) prior to the
     HSWA Amendments of 1984.  Now, such characterizations may be required
     according to RCRA Section 3004(u) when SWMU releases to ground water are
     suspected or known. The RCRA Ground Water Monitoring Technical Enforce
     ment Guidance Document (TEGD) (U.S. EPA, 1986), and the Permit Applicant's
     Guidance Manual for Hazardous Waste Land Treatment, Storage, and Disposal
     Facilities (U.S. EPA, 1984) should be consulted for further information on
     regulatory requirements.]

10.4.2    Monitoring Constituents and indicator Parameters

     Initial  monitoring should be focused on rapid, effective release character-
ization at the downgradient  limit of the waste management area.  Monitoring
constituents should include waste-specific subsets of hazardous constituents from
40 CFR Part 261, Appendix VIII (see Section 3 and the lists provided in Appendix S).
Indicator parameters (e.g., TQX, specific conductance) may also be proposed as
indicated in Section 3.  Such indicators alone may not be sufficient to characterize a
release of hazardous  constituents, since the  natural background variability of
indicator constituents can be quite high. Furthermore, indicator concentrations do
not precisely represent hazardous constituent concentrations, and the detection
limits for indicator analyses  are significantly  higher  than those for specific
constituents.

     In developing an initial  list of monitoring constituents  and indicator para-
meters, the following items should be considered:
                                   10-66

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     *   The nature of the wastes managed at the facility should be reviewed to
         determine which constituents (and any  chemical reaction products,  if
         appropriate) are relatively mobile and persistent,

     *   The effects of the unsaturated zone (if present) beneath the facility on
         the mobility, stability and persistence of the waste constituents; and

     *   The concentrations and related variability of the proposed constituents
         in background ground water.

     In the absence of detailed waste characterization  information, the owner  or
operator should review the guidance presented in Section 3, which discusses the use
of the monitoring constituent lists in Appendix 8. As discussed in Section 3, the use
of these lists is contingent upon the  level' of detail provided by  the waste
characterization.

     The owner or operator should consider monitoring for additional inorganic
indicators that characterize ths general  quality of water at the site (e.g., chloride,
iron, manganese, sodium, sulfate, calcium, magnesium, potassium, nitrate,
phosphate, silicate, ammonium, alkalinity and pH). Baseline data on such indicators
can be used for subsequent monitoring phases and in eventually selecting corrective
measures.  This  is also discussed in Section 3 and Appendix B.  For example,
information on  the major amons and cations that make up the bulk of dissolved
solids in water  can be used to determine reactivity and solubility of hazardous
constituents and therefore predict their mobility under actual site conditions,

10,4.3     Monitoring Schedu le

10.4.3.1   Monitoring frequency

     Monitoring frequency should be based on various factors, including:

         Ground-water flow rate and flow patterns;
                                   10-67

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     *   Adequacy of existing monitoring data, and

        Climatological characteristics (e.g., precipitation patterns).

     Generally, the greater the rate of ground-water flow, the greater  the
monitoring  frequency  needed.  For example, monitoring frequency  in an
intergranular porosity flow aquifer of low permeability materials would likely be
less than for a fracture or solution porosity flow aquifer with unpredictable  and
high flow rates.  In  the case of  a fracture or solution porosity flow aquifer,  it  is
possible that contaminants could migrate past the facility boundary in  a matter of
days, weeks, or months; thus requiring frequent monitoring.

     The adequacy of existing monitoring data can be a factor in determining the
monitoring schedule. For example, a  facility which has performed adequate
monitoring under interim status requirements may have a good data  base which
can be helpful in  evaluating initial monitoring results.  At the other end  of the
spectrum are facilities lacking hydrogeologic data and monitoring systems. Owners
or operators of these facilities will need to design and  install an adequate
monitoring system for the units of concern.  An accelerated monitoring program is
recommended at such facilities.

10.4.3.2       Duration of Monitoring

     The duration of the initial monitoring phase will vary with facility-specific
conditions (e.g., hydrogeology, wastes present) and should be determined through
consultation with the regulatory agency. The regulatory agency may evaluate
initial monitoring  results to determine how long monitoring should continue and to
determine the need for adjustments in th monitoring schedule, the  list of
monitoring constituents, and other aspects of the monitoring effort.  If the
regulatory agency determines that a release to ground water has not occurred, the
investigation process for that  release  can be terminated at its discretion.  If
contamination is  found  during initial monitoring,  further monitoring to  fully
characterize the release will generally be necessary.
                                   10-68

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10.5,2     Environmental Setting Characterization

     Environmental characteristics should be presented is follows:

     *    Tabular summaries of annual and monthly or seasonal relevant climatic
          inforamtion {e.g., temperature, precipitation);

     *    Narratives and maps of soil and relevant hydrogeological characteristics
          such as porosity, organic matter content and depth to ground water;

     *    Maps showing location of natural or man-made engineering barriers and
          likely migration routes; and

     *    Maps of geologic material at the site identifying the thickness, depth,
          and textures of soils, and  the presence of saturated  regions and other
          hydrogeological features.

     Flow nets should be  particularly useful for presenting environmental setting
information for the ground-water  medium.  A  flow  net  provides a graphical
technique for obtaining solutions to steady state ground-water flow. A properly
constructed flow net can be used to determine the distribution of heads, discharges,
areas of high (or low) velocities, and the general flow pattern (McWhorter and
Sunada, 1977).

     The Ground Water Flow Net/Flow line Technical Resource Document (TRD).
NTIS PB86-224979.  {U. S, EPA, 1985), provides detailed discussion and guidance in
the construction of flow  nets. Although the focus of this document is on the
construction of vertical flow nets, the same data requirements and theoretical
assumptions apply to horizontal flow nets. The fundamental difference between
vertical and horizontal flow nets is in  their application. A flow net in the horizontal
plane.may be used to identify suitable locations  for monitoring wells whereas a
flow net in the vertical plane would  aid in determining the screened interval of a
well.
                                   10-83

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     The following excerpts from the Flow Net Document (U.S. EPA, 1985} explain
data needs for flow net construction.  Several assumptions must  be made to
construct a flow net:

     *   Ground-water flow is steady state, which means flow is constant with
         time;

        The aquifer is completely saturated;

     *   No consolidation or expansion of the soil or water occurs;

     *   The same amount of recharge occurs across the system; and

     *   Flow is laminar and Darcy's Law is valid.

     Knowledge of the hydrologic parameters of the ground-water system is
required to properly construct a flow net. These parameters include:

        Head distribution, both horizontally and vertically;

     *   Hydraulic conductivity of the saturated zone;

     *   Saturated zone thickness, and

        Boundary conditions.

     The distribution of head can be determined using time equivalent water level
measurements obtained from piezometers and/or wells.  Plotting the water level
elevations on a base map and contouring these data will provide a potentiometric
surface. Contour lines representing equal head are called lines of equipotential.
Changes in hydraulic head, both horizontally and vertically within an  aquifer, must
be known for proper flow-net construction.  These changes can be delineated with
piezometers or monitoring wells installed at varying depths and spatially
distributed. The data must be time equivalent since water levels change over time.
Ground-water flow directions can be determined by drawing lines perpendicular to
                                   10-84

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the equipotential lines. Ground water flows from areas of high hydraulic head to
areas of low hydraulic head.

     The hydraulic conductivity of a material depends on the properties of the fluid
and the media.  Clayey materials generally have low hydraulic conductivities,
whereas sands and gravels have high conductivities (U.S EPA, 1985). Where flow
crosses a boundary between different homogeneous media the ground-water
flowlines refract and flow velocity changes due to an abrupt change in hydraulic
conductivity.  The higher permeability formation serves as a conduit to ground-
water flow. This is visually apparent in a properly constructed flow net, since flow
tubes are narrower in layers with higher conductivity because less area is necessary
to conduct the same volume of ground water. In media of lower conductivity, flow
tubes will be wider in order to conduct the same volume of flow (Cedergren, 1977),
Construction of flow nets for layered geologic settings (heterogeneous, isotropic
systems) are discussed in Section 2 of the flow net document (U.S. EPA, 1985).

     The boundary conditions of an aquifer  must also be known to properly
construct a flow net. These boundary conditions will establish the boundaries of the
flow net.  The three types of boundaries are:   1) impermeable boundaries;
2) constant head  boundaries; and 3) water table boundaries (Freeze and Cherry,
1979).  Ground water will not flow across an impermeable boundary; it flows
parallel to these boundaries. A boundary where the hydraulic head is constant is
termed a constant head boundary.   Ground-water  flow at a constant head
boundary is perpendicular to the boundary. Examples of constant head boundaries
are lakes, streams, and ponds. The water table  boundary is the upper boundary of
an unconfined aquifer, and is a line of known and variable head. Flow can be at any
angle in relation to the water table due to recharge and the regional ground-water
gradient The boundary conditions of an aquifer can be determined after a review
of the geohydrologic data for a site (U.S. EPA, 1985).

     Although a  complete  understanding of the mathematics of ground-water
flow is not necessary for proper flow-net construction by graphical methods, a
general understanding of the theory of ground-water flow is required. For a brief
discussion of ground-water flow theory as applied to flow nets, refer to Section 1 of
the flow net  document (U.S. EPA,  1985).   Detailed guidance on  graphical
construction of flow nets is given in Section 2 of that document.  Mathematical
                                  10-85

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techniques car. be used to construct flow nets although graphical techniques are the
simplest  and most  commonly used.  It is worth noting that flow  nets  are
dimension less.

     When a flow net has been constructed for a site, it may be possible to test the
adequacy of the flow net by installing additional piezometers at selected locations.
If the site hydrogeology is adequately characterized by the flow net, the head
values in  the new piezometer(s) will not vary significantly from those predicted by
the flow net.

     The number of new piezometers needed to check the adequacy  of the flow
net would  vary depending  on a number of factors including  size of the site,
complexity of the site hydrogeology. amount of data used to construct the flow net,
and the level of agreement between the site specific flow net and the regional flow
regime. For example, at a site with predominantly horizontal flow and well defined
stratigraphy, such as illustrated in Figure 10-22, a single new piezometer could test
the flow  net.  For a site with multiple, interconnected aquifers  and a significant
vertical component  of flow, such  as illustrated in Figure 10-23, several nested
piezometers might be necessary to test the flow net.

     In evaluating flow nets and the results of flow net tests, several factors should
be kept in mind.  The head measurements in a new piezometer may not exactly
match the values predicted by the flow net. Some variation is inherent in this type
of measurement.  The owner or operator should evaluate whether or not the
difference between measured and predicted values is significant in the context of
flow direction or flow velocity. A new value which reverses the direction of flow or
redirects flow towards potential receptors would obviously be significant. A change
in  flow velocity as indicated by a revised gradient might be significant if the
magnitude of the change is substantial or if an increased velocity suggests that the
characterization needs to be extended to a greater distance

     There are several situations in which extreme caution is needed in eva j a ting a
flow net  test.  In many cases, temporal  variations will alter the potentiometric
surface between the time the flow net  is constructed and a test piezometer is
installed.  Examples of this situation would include locations with large seasonal
variations in ground-water levels. Another situation that would introduce problems
                                   10-86

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Downgradient
                                                        Hazardous Waste
                                                        Land Applicat ion
                                                         Si te
                                             Upgradient
           100
Equipotential  lints
(in Mettrs)
Flow Lints
Wells with  Mell Nunbtrs
        Figurt 10-22.  Pottntiometric surfitt showifig flow dirtction
                                  10-87

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08
                                             BOUND ARIES
                                       OF THf PROPOSED FACILITY
                                               Blf
                                                                     743
                                                                                 80
                                                                                97.
                                                                                 672
                                                                    708 d
                                              ASSUME 100 =
                                                              H
                           Figure 10-23. Approximate flow net

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in interpretation would be a site that is adjacent to tidally influenced surface
waters.

     Construction of flow nets is not appropriate or valid in certain instances. As
discussed in the flow net document (U.S. EPA, 1985), these situations occur when
there is a lack of three-dimensional hydrologic data for a ground-water system, and
when ground- water flow in a system does not conform to the principles expressed
by and assumptions made in Darcy's Law. Scaling problems occur when the aquifer
and/or geologic layers associated with a particular ground-water system are thin in
relation to the length of the flow net. If a flow net is constructed for this situation,
the flow net will be made up of squares that are too small to work with unless the
scale is exaggerated. For sites where the assumption of steady-state flow is not
valid, the construction of flow nets is very difficult.  The flow net must be redrawn
each time the flow field changes to simulate the trans* .it conditions.

     Lack of three-dimensional hydrologic data or hydrologically equivalent data
for a ground-water flow system makes proper flow-net  construction impossible.
Hydrologic testing at various depths within an  aquifer and determination of the
vertical hydraulic conductivity of an aquifer are essential to provide the necessary
data. If these data are not available it will be necessary to obtain them before a
flow net can be constructed.

     There are three types of  ground-water systems in which the principles
expressed by Darcy's Law do not apply. The first is a system in which the flow is
through materials with  low hydraulic conductivities under extremely low gradients
(Freeze and Cherry, 1979). The second is a system in which a large amount of flow
passes through  materials with very high hydraulic conductivities.  The third is a
system in which the porous media assumption is not valid.  Darcy's Law expresses
linear relationships and requires that flow be laminar (flow in which stream lines
remain distinct from one another).  In a system with high hydraulic conductivity,
flow is often turbulent. Turbulent flow is characteristic  of karstic limestone and
dolomite, cavernous volcanics, and fractured rock systems.  Construction of flow
nets for areas of turbulent flow would not be valid. The use of Darcy's Law also
requires the assumption of porous media flow. This assumption may not be valid
for many fractured bedrock and karst environments where fractured flow is
dominant or large solution features are present.
                                   10-89

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10.5.3    Characterization of the Release

     The objective of monitoring is to estimate the nature, rate, and  extent (3-
Oimensional) of the release. Data are, therefore, collected from a set of monitoring
wells that will allow characterization of the dimensions and concentrations of
constituents in the plume, as well as the rate of flow.

     Subsequent monitoring phases will often  include the measurement of many
more constituents in a more extensive well network than initial monitoring. This
will often necessitate the collection of large amounts of data.  Sections 6.8 and 6.9
of the TIGD (US. EPA, 1986) provide useful guidance on organizing, evaluating,
and presenting monitoring data.  Section 4.7 of TEGD addresses evaluation of the
quality  of  ground-water data.  Specific data  presentation  and evaluation
procedures are presented below.

     Migration rates can be determined by using the concentration of monitoring
constituents over a period of time in wells aligned in the direction of flow. If these
wells are located both at the edge of the release and in the interior of the release,
subsequent analysis of the monitoring data can then provide an estimate of the rate
of migration both  of the contaminant front as a  whole  and of individual
constituents within the release.  This approach does not necessarily  provide  a
reliable  determination of the  migration rates that will occur as the contaminant
release  moves further away  from the facility,  due to potential changes in
geohydrologic conditions or degradation of the contaminants. More importantly,
this approach requires the collection of a time series of data of sufficient duration
and frequency to gauge the movement of contaminants.  Such a delay is normally
inappropriate during initial characterization of ground-water contamination since a
relatively quick determination of at least an estimate of migration rates is needed
to deduce  the impact of  ground-water contamination and to formulate an
appropriate reaction.

     Rapid estimates of  migration rates should be made from aquifer properties
obtained during the hydrogeologic investigation. The average linear velocity (v) of
the ground water should be calculated using the following form of Oarcy's law:
         -Ki
                                   10-20

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where (K) is hydraulic conductivity, (i)  is hydraulic gradient, and (n) is effective
porosity.  This assumes that contaminants flow at the same rate as ground water.
This equation can be used to roughly estimate the rate of migration, both of the
contaminant front as a whole, and of individual dissolved constituents within the
release.

     Rough estimates of migration rates beyond the facility property boundary can
be made based on aquifer properties obtained during the site hydrogeologic
characterization and knowledge of the physical and chemical properties of
contaminants known to be present.  By recognizing the various factors which can
affect the transport of monitoring constituents, the owner or operator can
determine approximate migration rates. Continued monitoring of the release over
time should be conducted to verify the rate(s) of migration. Information on rate(s)
of migration should be  used  in determining any additional  monitoring well
locations.

     More refined estimates of contaminant migration  rates  should consider
potential differential transport rates among various monitoring constituents.
Differencial transport rates are caused by several farters, including:

     *    Dispersion due to diffusion and mechanical mixing;

     *    Retardation due to adsorption and electrostatic interactions; and

         Transformation due to physical, chemical, and/or biological processes.

     Dispersion  results in the overall dilution of the contaminant; however,
chromatographic separation of the contaminant constituents  and differential
dispersion effects can result in a contaminant arriving at a particular location before
the arrival time computed solely on the average linear velocity of ground-  water
flow.  Alternately, retardation processes can delay the arrival of contaminants
beyond that calculated using average ground-water flow rate(s). Transformation of
waste constituents is a complex process which can be difficult to estimate.  While
some contaminants, such as radionuclides, decay at a constant rate over time, most
degradeable chemicals are influenced by a variety of factors and the interactions of
                                   10-91

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these factors are difficult or impossible to predict. Local geologic variations will also
affect constituent migration rates. Relating constituent migration rates to ground-
water flow rates is a reasonable and relatively quick way to estimate contaminant
flow rates. Where possible, contaminant- specific migration rates should also be
determined.

     Procedures for the evaluation of monitoring  data vary in a site-specific
manner, but should all result in determinations of the rate of migration, extent, and
composition of hazardous constituents of the release.  Where the release is obvious
and/or chemically simple, it may be possible to  characterize it readily from  a
descriptive presentation of concentrations found in monitoring wells and through
geophysical measurements. Where contamination is less obvious  or the release is
chemically complex, however, the owner or operator may employ a statistical
inference approach.  The owner or operator should  plan  initially to take  a
descriptive approach to data analysis in order to broadly delineate the extent of
contamination.  Statistical comparisons of monitoring data among wells and/or over
time may be  necessary, should  the descriptive approach provide no clear
determination of the rate of migration, extent, and hazardous constituent
composition of the release.

10.6 Field Methods

10.6.1     Geophysical Techniques

     During the past decade, extensive development of remote sensing geophysical
equipment, portable field instrumentation, field methods,  analytical techniques
and related computer processing have resulted in an improvement in the capability
to characterize hydrogeology and contaminant releases. Some of these geophysical
methods offer a means of detecting contaminant plumes and flow directions  in
both the saturated and unsaturated zones. Others offer a way to obtain detailed
information about subsurface soil and rock characteristics. This capability to rapidly
analyze subsurface conditions without disturbing the  site offers the benefit of low
cost and risk, and provides better overall understanding of complex site conditions.

     Various geophysical techniques, including electromagnetic, seismic refraction,
resistivity, ground penetrating radar, magnetic, and several borehole methods, are
                                   10-92

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applicable to RCRA Facility Investigations.   Table 10-6 suggests appropriate
applications for the various geophysical tools.  Appendix C provides additional
information.

10.6.2     Soil Boring and Monitoring Well Installation

10.6.2,1       Soil Borings

     Soil borings should be sufficient to characterize the subsurface geology below
the site. Section 1.2 of TEGD (U.S. EPA, 1986) provides criteria for adequate borings.
A summary of these criteria is presented below.

         Installation of initial boreholes at a density based on criteria described in
          Table  10-7 and sufficient to provide initial information upon which to
          determine the  scope of a more detailed evaluation of geology and
          potential pathways of contaminant migration.

     *    Initial  boreholes should be drilled into the first confining layer beneath
          the uppermost aquifer.  The portion of the borehole extending into the
          confining layer should be plugged properly after a sample is taken.

         Additional boreholes should be installed  in numbers and locations
          sufficient to characterize the geology btneath the site. The number and
          locations of additional boreholes should be based on data from initial
          borings and indirect investigation.

     *    Collection of samples of every significant stratigraphic contact and
          formation, especially the confining layer should be taken.  Continuous
          cores should be taken initially to ascertain the presence and distribution
          of small and large scale permeable  layers.  Once stratigraphic control is
          established, samples taken at regular, e.g., five foot intervals could be
          substituted for continuous cores.
                                   10-93

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                     TABLE 10-6.  APPLICATIONS OF GEOPHYSICAL METHODS TO
                                   HAZARDOUS WASTE SITES
APPLICATION
Mapping of Geohydrologk
features
Mapping of Conductive Leachatet
and Contaminant Plumes (ex.
Landfills. Acids. Basts)
Locations and Boundary
Definition of Buried Trenches
with Metal
Location and Boundary Definition
of Buried TreiKhes without Metal
Location and Definition of Buried
Metallic Objects (ex. Drums,
Ordinance)
RADAR
1
2
1
1
2
ELECTROMAGNETICS
I
1
1
1
2
RESISTIVITY
1
1
2
2

SEISMIC
1
'
2
2

METAL
DETECTOR
-
'
2
-
1
MAGNETOMETER

'
2
-
1
I.  Primary method - Indicates the most effective method
2.  Secondary method - Indicates an alternate approach
Source: EPA. 1982, Geophysical Techniques for Sensing Buried Waste and Waste Migration

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TABLE 10-7.  FACTORS INFIUENCING DENSITY OF INITIAL BOREHOLES
Factors That May Substantiate
Reduced Density of Boreholes:
 Simple geology (i.e., horizontal, thick,
homogeneous geologic strata that are
continuous across site that are
imfractured and are substantiated by
regional geologic information).
* Use of geophysical data to correlate
weii iog data.



Factors That May Substantiate
Increased Density of Boreholes:
* Fracture zones encountered during
drilling.
 Susptcteu pmchout zones (e.g.,
discontinuous areas across the site).
* Geologic formations that are tilted or
folded.
 Suspected zones of high permeability
that would not be defined by drilling
at 300-foot intervals.
* Laterally transitional geologic units
with irregular permeability (e.g.,
sedimentary facies changes).
                          10-95

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     *    Boreholes in which permanent wells are not constructed should  be
          sealed with materials at least an order of magnitude less permeable than
          the surrounding soil/sediment/rock in order to reduce the number of
          potential contaminant pathways.

     *    Samples should be logged  in the field by a qualified professional in
          geology.

     *    Sufficient laboratory analysis should be  performed to  provide
          information concerning petrologic variation, sorting (for unconsolidated
          sedimentary units), cementation (for consolidated sedimentary units),
          moisture content, and hydraulic conductivity of each significant geologic
          unit or soil zone above the confining layer/unit.

         Sufficient laboratory analysis should be performed to describe the
          mineralogy (X-ray diffraction), degree of compaction, moisture content,
          and other pertinent  characteristics of any clays or other fine- grained
          sediments held to be the confining unit/layer.  Coupled  with the
          examination of clay mineralogy and structural characteristics should be a
          preliminary analysis of the reactivity of the confining  layer in the
          presence of the wastes present.

     A5TM or equivalent methods should be used for soil classification, specifically:

     *    ASTM Method D422-63 for the particle size analysis of soils, which
          describes the quantitative determination of the distribution of particle
          sizes in soils; and

     *    ASTM Methods 02488-69, for the identification and  description of soils
          based on visual examination and simple manual tests.

     An adequate number of geologic cross-sections should be presented by  the
owner or operator. These cross-sections should adequately depict major geologic or
structural  trends and reflect geologic/structural features in  relation to ground-
water flow.  Additionally, an owner  or operator should provide a  surface topo-
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graphic map and aerial photograph of the site.  Details regarding the specific
requirements for the presentation of geologic data are presented in Section 5 and
insertion 1.2.3 of the TEGD (U.S. EPA, 1986).

10.6.2.2  Monitoring Well Installation

     Tht owner or operator is advised to consult Chapter Three of the TEGD (US.
EPA, 1986)  for guidance on monitoring well installation.  This chapter provides
information on the following topics:

     *   Drilling Methods  for Installing Wells-Section 3.1  (TEGD) discusses a
         variety of well drilling methods and corresponding applicability to the
         installation of RCRA monitoring wells. The selection of the actual drilling
         method that an owner or operator should use at a particular site is a
         function  of site-specific geologic conditions.  Of utmost importance is
         that the drilling method the owner or operator uses will minimize the
         disturbance of subsurface materials and will not cause contamination of
         the ground water.

     *   Monitoring Well Construction Materials-Section 3.2 (TEGD) discusses the
         selection of construction materials for RCRA monitoring wells which are
         durable enough to resist chemical and physical degradation, and do not
         interfere  with the quality of ground-water samples.  Specific well
         components that are of concern include well casings, well screens, filter
         packs, and annular seals.

     *   Design of Well Intakes-Section 3.3 (TEGD) discusses  the design and
         construction  of the intake of monitoring wells so as to:   (1) allow
         sufficient j -ound-water flow to the well for sampling; (2) minimize the
         passage of formation materials (turbidity) into the well; and (3) ensure
         sufficient structural integrity to  prevent the collapse  of the intake
         structure.

        Development of Wills-Section 3.4 (TEGD) discusses the requirements for
         proper development of the monitoring wells to ensure turbid-free
         ground water samples.
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Documentation of Well Construction Activity-Section 3.5 (TEGD) lists the
information required for the design and construction of wells as follows:

     date/time of construction;
     drilling method and drilling fluid used;
     well location {_*.0,5 ft);
     borehole diameter and well casing diameter;
     well depth (_t O.i ft);
     drilling and hthologiclogs;
     casing materials;
     screen materials and design;
     casing and screen joint type;
     screen slot size/length;
     filter pack material/size;
     filter pack volume calculations;
     filter pack placement method;
     sealant materials (percent bentonite);
     sealant volume (Ibs/gallon of cement);
     sea lant placement method;
     surface seal design/construction;
     well development procedure;
     type of protective well cap;
     ground surface elevation (.+.0.01 ft);
     top of casing elevation (.+_0.01 ft); and
     detailed drawing of well (including dimensions).

Specialized Well Design-Section 1.6 (TEGD) discusses two cases which
require special monitoring well design: (1) where dedicated pumps are
used to draw ground-water samples; and (2) where light and/or dense
phase immiscible layers are present.

Evaluation of Existing Wells-Section 3.7  (TEGD) discusses how to
evaluate the ability of existing wells to produce representative ground-
water samples.
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     Particular attention should be paid to the discussion in Section 3.2.1 regarding
well casing materials (TEGD).  it is imperative that well materials are nonreactive to
contaminants that may be present in the ground water.  In cases where the facility
has existing monitoring wells which could potentially be used in the RFI, the owner
or operator should evaluate whether these wells  are capable of producing
representative  ground water samples. A demonstration involving the installation
of new welt(s)  ntar existing wells and the analysis and comparison of samples for
the same parameters from both wells may  be necessary if  the existing  wells'
integrity is in question.

10.6.3    Aquifer Characterization

10.6.3.1    Hydraulic Conductivity Tests

     In addition to defining the direction of ground-water flow in the vertical and
horizontal direction, the owner or operator should identify areas of high and low
hydraulic  conductivity within each formation.  Variations in the hydraulic
conductivity of subsurface materials can create irregularities in ground-water flow
paths.  Areas of high hydraulic conductivity  represent areas of greater ground-
water flow and,  if contaminants are present, zones of potential migration.
Therefore, information on hydraulic conductivities is generally  required before the
owner or operator can make reasoned decisions regarding well placements.  It may
be beneficial to use analogy or laboratory methods to corroborate results of field
tests; however, only field methods provide direct information  that is adequate to
define the hydraulic conductivity.

     Hydraulic conductivity can be determined in the field using single well tests,
more commonly referred to as slug tests, which are performed  by suddenly adding
or removing a slug (known volume) of water from a well or piezometer and
observing the recovery of the water surface to its original level. Similar results can
be achieved by pressurizing  the  well casing, depressing the  water level, and
suddenly releasing the pressure to simulate removal of water from the well. Where
slug tests are not appropriate (e.g., in fractured flow aquifers),  hydraulic
conductivity can be determined by multiple well (pumping) tests.
                                   10-99

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     Slug  testing is applied by hydrogeologists in almost all field  situations.
Interpretation of the results requires some professional judgement, slug test
accuracy if reduced when dealing with extreme values of hydraulic conductivity.
Very low values (less than 10*6 cm/sec) are more accurately measured by a resurg
head test after bailing or pumping the well dry. High values (greater than 10-2
cm/sec) generally require fast response electronic measurement equipment. High
value cases in fractured rock or karst terrain may be misleading in that the slug test
is measuring the most permeable fractures or solution channels and may give an
artificially high value for the formation as a whole.

     When reviewing information obtained from slug tests, several criteria should
be considered. First, slug tests are run on one well  and, as such, the information
obtained from single well tests is limited in scope  to the geologic area directly
adjacent to the well. Second, the vertical extent of screening will control the part of
the geologic formation that is being tested during the slug test.  That part of the
column above or below the screened interval that has not been tested during the
slug test will not have been adequately tested for hydraulic conductivity. Third, the
methods used to collect the information obtained from slug tests should be
adequate to measure accurately parameters such as changing static water (prior to
initiation,  during, and following completion of slug test), the amount of water
added to, or removed from the well, and the elapsed time  of recovery.  This is
especially  important in highly  permeable formations where pressure transducers
and high speed recording equipment should be used. Lastly, interpretation of the
slug test data should be consistent with the existing geologic information (boring
log data).  It is, therefore, important that the program of slug testing ensure that
enough tests are run to provide representative measures of hydraulic conductivity,
and to document lateral and vertical variation of  hydraulic conductivity in the
h yd rogeologic subsurface below the site.

     It is important that hydraulic conductivity measurements define  hydraulic
conductivity both in a vertical and horizontal  manner across a site.  In assessing
hydraulic conductivity measurements, results from  the  boring program used to
characterize the site geology should be  onsidered.  Zones of high permeability or
fractures identified from drilling logs should be considered in the determinate  
-------
     Techniques for determining  hydraulic conductivity are specified in  Method
9100, Saturated Hydraulic Conductivity, Saturated Leachate Conductivity, and
Intrinsic Permeability; from SW-846, Test Methods for Evaluating Solid Waste. 3rd
edition, September, 1986. Method 9100 includes techniques for:

        Laboratory

              sample collection;
              constant head methods; and
              falling head methods.

     *   Field

              wet! construction;
              well development;
              single well tests (slug tests); and
              references for multiple well (pumping) tests.

     Cedergren, 1977 also  provides an excellent discussion  on aquifer tests,
including laboratory methods (constant head and falling head), multiple well
(pumping) tests (steady-state and nonsteady-state), and single well tests (open-end,
packer, and others).

10.6.3.2  Water Level Measurements

     Water level measurements are necessary for determining depth to the water
table and mapping ground-water contours to determine hydraulic gradients and
flow rates. Depths to water are normally measured with respect to the top of casing
as in well depth determinations.  Several methods are available including the
electric sounder and the chalked steel tape.

     The electric sounder,  although  not the  most  accurate method, is
recommended for initial site work because of the minimal potential for equipment
contamination and simplicity of use. Sounders usually consist of a conductivity cell
at the end  of a graduated wire,  and a  battery powered buzzer. When the cell
                                  10-101

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contacts the water the increased conductivity completes the circuit and allows
current to flow to the alarm buzzer The depth to water can then be read from the
graduations on the wire or the wire can be measured directly. This device may not
be suitable for use if  a potentially flammable or explosive layer (e.g., due  to
methane gas) is present in the well, unless it is an intrinsically safe device.

     The chalked steel tape is a more accurate device for measuring static water
levels. The lower 0.5 to 1.0 meters of a steel measuring tape is coated en either side
with either carpenter's chalk or any of the various indicating pastes.  A  weight is
attached to the lower end  to keep the tape taut and it is lowered into the center of
the well (condensate on the casing wall may prematurely wet the tape).  A hollow
"plopping" sound occurs when the weight reaches water, then the tape is lowered
very  slowly for at least another 15 cm, preferably to an even increment on the
measuring tape. Next, the tape is carefully withdrawn from the well; water depth is
determined by subtracting the wetted length of tape from the total length of tape
in the well. In small diameter wells, the volume of the weight may cause the water
to rise by displacement. In general, the use of indicating paste or chalk should  be
discouraged although they may not present a significant problem if water samples
are not collected. As with all depth measurement devices, the wetted section of the
tape and the weight  must  be thoroughly cleaned before reuse to avoid  cross
contamination.

     The following sections of the TEGD (U.S. EPA, 1986) should be consulted for
water level measurement requirements, and information on data interpretation:

        Ground-water level measurement (1.3.1.1);

         Interpretation of ground water level measurements (1.3.1.2);

         Establishing vertical components of ground water flow (1.3.1.3); and

         Interpr-iation of flow direction (1.3.1.4).
                                  10-102

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IU.D.J.J   uye (racing

     Dye tracing is a field method used to measure the velocity of ground water for
highly permeable strata (such as karst terrain and highly fractured rock media).
When the  velocity of flowing water and the hydraulic gradient at a common point
are known, the permeability can be estimated.  The hydraulic gradient (0 of an
existing water table can be estimated from wells in the area.  If not, observation
wells must be installed (Cedergren, 1977).

     The procedure used in dye tracing involves the insertion of a dye such as
fluorescein sodium into a test hole and observation of the time it takes to emerge in
a nearby test pit or on a bank from which seepage is emerging. The average linear
velocity, v, is determined by dividing the distance traveled, L, by the time of travel, t.
The effective porosity, n, is determined from test data  for the in-place soil; if no
tests are available, it is determined using the values in Table 10-4.  The hydraulic
conductivity is calculated from the equation:
     It should be noted that the time required for tracers to move even  short
distances can be very long unless the formations contain highly permeable strata
(Cedergren, 1977). As a result of the limitations of tracer techniques, this type of
study is applied only in highly specialized locations.  Uncertainties associated with
the flow path make interpretation of the results difficult. This technique has been
used effectively in conjunction with modeling in complex terrain with  the tracer
study serving to calibrate the model.

10.6.4    Ground Water Sample Collection Techniques

     The procedure for collecting a ground water sample involves the following
steps presented in Chapter 4 of TEGD (U.S. EPA, 1986):

     *    Measurement of static water level elevation (4.2.1);
                                   10-103

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     *    Monitoring of immiscible layers (4,2.2);

         Well evacustion (4.2.3);

     *    Sample withdrawal (4.2.4);

     *    In situ or field analyses (4.2.5);

     *    Sample preservation and handling (4.3); and

     *    Chain-of-custody procedures (4.4).

     Collection of static water level elevations on a continuing basis is important to
determine if horizontal and vertical flow gradients have changed since initial site
characterization, which could necessitate modification of the  ground-water
monitoring system.  Steps should be taken to monitor for the presence and/or
extent of  light and/or dense phase immiscible organic layers before the well  is
evacuated for conventional 'ampling if wastes of this type are  present at the
facility.

     The water standing in the well prior to sampling may not be representative of
m situ ground-water quality. Therefore, the owner or operator should remove the
standing water in the well so that water which is  representative of the formation
can replace the standing water. Purged water should be collected and screened
with photoioriization or organic vapor analyzers, pH, temperature, and conductivity
meters. If these parameters and facility backgro jnd data suggest that the water is
hazardous, it should be drummed and disposed of properly.

     The technique used to withdraw a ground-water sample from a well should be
selected based on a consideration of the parameters which will be  analyzed in the
sample. To ensure the ground-water sample is representative of the formation, it is
important to avoid  physically altering or chemically contaminating  the sample
during the withdrawal process.  In order to minimize the possibility of sample
contamination, the owner or operator should:
                                   10-104

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     (1)  Use only polytetrafluoroethylene (PTFE) or stainless steel sampling
         devices; and

     (2)  Use dedicated samplers for each well. (If a dedicated sampler is not
         available for each well, the sampler should be thoroughly cleaned
         between sampling events, and blanks should be taken and analyzed to
         ensure that cross contamination has not occurred.)

     Section 4.2.4 of TEGD (U.S. EPA, 1988) includes specific factors to take into
consideration regarding sample withdrawal.

     Some parameters are physically or chemically  unstable and must be tested
either in the borehole using a probe (in situ) or immediately after collection using a
field test kit. Examples of several unstable parameters include pH, red ox potential,
chlorine, dissolved oxygen, and temperature. Although specific conductivity
(analogous to electrical resistance) is relatively stable, it is recommended that this
characteristic also be determined in the  field.  Most conductivity instruments
require temperature compensation; therefore, temperatures of the samples should
be measured at the time conductivity is determined.

     Many of the  constituents and parameters that are included in ground-water
monitoring programs are not stable and, therefore, sample preservation may be
required. Refer to methods from EPA's Test Methods for Evaluating Solid Waste 
Physical Chemical Methods. 1986(EPA/SW-846GPO No. 955-001-00000-1) for sample
preservation procedures and sample container requirements.

     Improper sample handling may lead to sample contamination. Samples should
be transferred into their containers in such a way as to minimize any contamination.
Handling methods are analyte dependent.  Special handling considerations for
various analyte types are discussed in Section 4.3.3 of the TEGD (U.S. EPA, 1986).

     An adequate chain-of-custody program will allow for the tracing of possession
and  handling of individual  samples from the time of field collection through
laboratory analysis.   An  owner or operator's chain-of-custody  program
requirements are detailed in Section 4 (Quality Assurance and Quality Control).
                                  10-105

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     Chapter Four of the TEGD (U.S. EPA, 1986) may also consulted for sample
collection techniques as well as for analytical procedures, field and laboratory
QA/QC requirements, and suggestions for reporting of ground water data. Section
4 of this guidance presents a general discussion of QA/QC, In addition, the owner or
operator may also find the following publication useful for sampling information:

        U.S. EPA. September, 1987. Practical Guide for Ground Water Sampling.
         EPA/600/2-8S/104. NTISPB86-137304.  Washington.D.C. 20460.
                                  10-106

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10.7 Checklist

                         RFI Checklist - Ground Water
Site Name/Location.
Type of Unit	
1.    Does waste characterization include the following information?      (Y/N)
              Constituents of concern/supporting indicator parameters  	
          *    Concentrations of constituents
                                                                    ^B^wm^MM
              Physical form of waste                                 	
          *    Chemical properties of waste (organic, inorganic,
               acid, base) and constituents                            	
              PH                                                   	
              pka                                                  	
              Viscosity                                              	
              Water solubility                                       	
              Density                                               	
              kow                                                  	
              Henry's Law Constant                                  	
              Physical and chemical degradation (e.g., hydrolysis)       	

2.    Does unit characterizatio include the following information?        (Y/N)
              Age of unit                                           	
              Construction integrity                                 	
              Presence of liner (natural or synthetic)                   	
              Location relative to ground-water table or bedrock or     	
                other confining barriers
              Unit operation data                                   	
              Presence of covtr or other surface covering              	
              Presence of on/offsite buildings                         	
              Depth and dimensions of unit                          	
              Inspection records                                     	
          *    Operation logs                                        	
                                    10-107

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                   RFI Checklist- Ground Water (Continued)

              Past fire, explosion, or other complaint reports            	
              Existing ground-water monitoring data                  	
              Presence of natural or engineered barriers near unit      	

3.    Does environmental setting information include the following information?
                                                                    (Y/N)
     Site Soil Characteristics
              Grain size distribution and gradation                    	
              Hydraulic Conductivity                                 	
              Porosity                                              	
              Discontinuities in soil strata (e.g., faults)                 	
              Degree and orientation of subsurface stratification       	
               and bedding
     Ground Water Flow System Characterization                       (Y/N)
              Use of aquifer                                         	
              Regional flow cells and flow nets                         	
              Depth to water table                                  	
              Direction of flow                                      	
              Ratt of flow                                          	
              Hydraulic conductivity                                 	
              Storativity/specific yield (effective porosity)              	
              Aquifer type (confined or unconfined)                  	
              Aquifer characteristics (e.g., homogeneous, isotropic,     	
               leaky)
              Hydraulic gradient                                    	
              Identification of recharge and discharge areas            	
              Identification of aquifer boundaries (i.e., area! extent)    	
              Aquitard characteristics (depth, permeability degree of   	
               jointing, continuity;
                                    10-108

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                   RFI Checklist  Ground Water (Continued)

     Ground Water Quality Characteristics                             (Y/N)
            Presence of minerals and organics                      	
            Background water quality                             	
            Monitoring constituents and indicator parameters        	

4.    Have the following data on the initial phase of the release characterization
     been collected?                                               (Y/N)
            Extent                                              	
            Location                                            	
            Shape                                              	
            Hydraulic gradient across plume                        	
            Depth to plume                                      	
            Chemistry and concentration                           	
            Velocity                                             	
            Potential receptors                                   	

S.    Have the following data on the subsequent phase(s) of the release character-
     ization been collected?                                         (Y/N)
            Extent                                              	
         *   Location                                            __
            Shape                                              	
            Hydraulic gradient across plume                        ____
            Depth to plume                                      	
            Chemistry and concentration                          	
            Velocity                                             	
            Potential receptors                                   	
                                   10-109

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10.8 References

ASTM.  1984, Annual Book of ASTM Standards. Volume 4.08: Natural Building
     Stones;  Soil and Rock.  American  Society  for Testing  and Materials.
     Philadelphia. PA.

Salch, A. H., and W. W. Lee. 1984. Vertical Seismic Profiling Technique. Applications
     ap4Case Histories. DE83751260. International Human Resource Development
     Corp.

Billings. 1972. Structural Geology. 3rd Edition. Prentice-Hall, Inc. Englewood
     Cliffs, New Jersey.

Brady.  1974. The Nature and Properties of Soils. 8th Edition. MaeMillan
     Publishing Co., Inc. New York, N.Y.

Callahan.etal. 1979. Water-Related Environmental Fate of 129 Priority Pollutants.
     EPA-440/4-79-029. NTIS PB80-204373. Washington, D.C 20460.

Cedergren.  1977. Seepage. Drainage, and Flow Nets. 2nd Edition. John Wiley &
     Sons. New York, N.Y.

Freeze and Cherry. 1979. Ground water,  Prentice-Hall. Inc. Englewood Cliffs,
     Ntw Jersey.

Linsley, R.K., M.A. Kohler, and J. Paulhus.  1982. Hydrology for Engineers. Third
     Edition.  McGraw-Hill, Inc.  New York, N.Y.

McWhorterandSunada. 1977. Ground Water Hydrology and Hydraulics. Water
     Resources Publications. Litteton, Colorado.

Snoeyink and Jenkins.  1980. Water Chemistry. John Wiley & Sons. New York, N.Y.

Sowers, G. F. 1981. Rock Permeability or Hydraulic Conductivity - An Overview   in
     Permeability and Ground Water Transport. T. F. Zimmic and C. O. Riggs,  Eds.
     ASTM Special Technical Publication 746. Philadelphia, PA.
                                  10-110

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Technos.lnc 1982, Geophysical Techniques for Sensing Buried Wastes and Waste
     Migration. Environmental Monitoring Systems Laboratory. NT1SP884-198449.
     U.S. EPA. Washington, D.C. 20460,

U.S. Department of Agriculture. 1975. Soil Taxonomy: A Basic System of Soil
     Classification for Making and Interpreting Soil Surveys.  Soil Survey Staff, Soil
     Conservation Service. Washington, O.C.

U.S. Department of the Army. 1979. Geophysical Explorations. Army Corps of
     Engineers. Engineering Manual 1110-1-1802. May, 1979.

U.S. EPA. 1985. Characterization of Hazardous Waste Sites - A Methods Manual,
     Volume I - Site Investigations. EPA-600/4-84/075. NTIS PB85-215960. Off ice of
     Research and Development. Washington, D.C. 20460.

U.S EPA. 1984. Characterization of Hazardous Waste Sites - A Methods Manual:
     Volume II: Available Sampling Methods. 2nd Edition. EPA-600/4-84-076.  NTIS
     PB 85-168771. Office of Research and Development Washington, D.C. 20460

U.S. EPA. 1986. Ground Water Flow Net/Flow line Technical Resource  Document
     fTRD). Final P port.  NTIS P886-224979. Office of Solid Waste. Washington,
     D.C. 20460.

U.S. EPA. 1985. Guidance on Remedial Investigations Under CERCLA. NTIS PB85-
     238616.   Hazardous Waste Engineering Research Laboratory, Office of
     Research and Development. Cincinnati, OH 45268.

U.S. EPA. 1982. Handbook for Remedial Action at Waste Disposal Sites. EPA-625/6-
     82-006.  NTIS P882-239054.  Office of Emergency  and Remedial  Response
     Washington, D.C 20460.

U.S. I PA. 1984. Permit Applicant's Guidance Manual for Hazardous Waste  land
     Treatment. Storage, and  Disposal Facilities.   Office of Solid Waste.
     Washington, D.C 20460.
                                  10-111

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U.S. EPA,  1986. Permit Writers' Guidance Manual for the Location of Hazardous
     Waste Land Storage and Disposal Facilities  Phase II: Method for Evaluating
     the Vulnerability of Ground Water. NTISP886-125580. Office of Solid Waste
     Washington. D.C. 20460.

U.S. EPA.  1985. Practical Guide for Ground Water Sampling. EPA-600/2-85/104.
     NTISP886-137304. Washington, D.C, 20460.

U.S. EPA.  1985. RCRA Ground Water Monitoring Compliance Order Guidance
     (Final). Off JCt of Sol id Waste. Washington, DC  20460.

U.S. EPA.  1986. RCRA Ground Water Technical Enforcement Guidance Document.
     Office of Solid Waste. Washington, D.C. 20460.

U.S. Geological Service. 1984. Ground water Regions of the U.S. Health et, at,,
     Water Supply Paper No 2242.
                                  10-112

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                                SECTION 11

                             SUBSURFACE GAS
11.1  Overview

     This section applies to units with subsurface gas releases,  primarily landfills,
leaking underground tanks, and units containing putrescible organic matter, but
may include other units.

     The objective of an investigation of a subsurface gas release is to verify, if
necessary, that subsurface gas migration has occurred and to characterize the
nature, extent, and  rate  of migration  of the release of gaseous material or
constituents through the soil. Methane gas should be monitored because it poses a
hazard due to its explosive properties when it reaches high concentrations, and also
because it can serve as an indicator (i.e., carrier gas) for the migration of hazardous
constituents. Other gases (e.g., carbon dioxide and sulfur dioxide) may also serve as
indicators. This section provides:

         A recommended strategy for  characterizing subsurface gas releases,
          which includes characterization of the source and the environmental
          setting of the release, and conducting monitoring to  characterize the
          release itself,

     *    Recommendations for data organization and presentation;

         Appropriate field methods which may be used in the investigation; and

         A checklist  of information that may  be needed  for release
          characterization.

     The exact type and amount of infvrr.s^on required for sufficient release
characterization will be site-specific and should be determined through interactions
between the regulatory agency and the  facility owner or operator during the RFI
                                    11-1

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process. This guidance does not define the specific data required in all instances;
however, it  identifies possible information which may be necessary to perform
release characterizations and methods for obtaining this information. The RFI
Checklist, presented at the end of this section, provides a tool for planning and
tracking information for subsurface gas release characterizations.  This list is not
meant to serve as a list of requirement** for ail subsurface gas releases to soil. Some
releases will involve the collection of only a subset of the items listed.

     As indicated in the following sections, subsurface gas migrates along the path
of least resistance, and can accumulate in structures (primarily basements) on or off
the facility property. If this occurs, it is possible that an immediate hazard may exist
(especially if the structures are used or inhabited by  people) and that interim
corrective measures may be appropriate.  Where conditions warrant, the owner or
operator should  immediately  contact the regulatory agency and consider
immediate measures (e.g., evacuation of a structure).

     Case Study No. 8 in Volume IV (Case Study Examples) provides an example of a
subsurface gas investigation.

11.2 Approach for Characterizing Subsurface Gas Releases

11.2.1    General Approach

     Characterization of subsurface gas releases can be accomplished through a
phased monitoring approach.  A recommended strategy  for  characterizing
subsurface gas releases is shown in Table 11-1. The outlined strategy will provide an
acceptable technical approach to effectively characterize the nature and extent of
subsurface gas releases from units.

     The collection  and review  of information  for characterization of the
contaminant source and the environmental setting will be the primary basis for
development of a conceptual model of the release and subsequent development of
monitoring procedures used to characterize the release. This input data should
initially be  compiled from available sources.  Additional  data collection to
characterize the contaminant source and  environmental setiing maybe necessary.

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                                Table 1M

      Recommended Strategy for Characterizing Releases of Subsurface Gasl

                               INITIAL PHASE

1.    Collect and review preliminary information for use in formulating monitoring
     procedures:

         Characterization of the contaminant source
              Waste characterization
              Unit characterization
         Characterization of the environmental setting
              Natural and engineered barriers
              Climate and meteorological conditions
              Receptors

2.    Identify and collect additional information necessary to characterize release

         Spatial extent of release
         Release constituents present and concentration levels
         Inter-media transport
         Develop conceptual model of release

3.    Develop monitoring procedures:

         Determine monitoring constituent(s)
         Select indicator parameters)
         Sampling approach selection
         Sampling schedule
         Monitoring locations
         Analytical plans
         QA/QC procedures

4.    Conduct Initial Monitoring Phase:

         Use subsurface gas migration model to estimate release dimensions (plot
         1.0 and 0.25 lower explosion limit isopleths for methane),
         Monitor ambient air and shallow  boreholes around the site  using
         portable survey instruments to detect methane and other indicator
         parameters.
         Use results of above two steps to refine conceptual model and determine
         sampling locations and depths; conduct limited  well installation
         program. Monitor well gas and shallow soil boreholes for indicators and
         constituents.
         Monitor surrounding structures (e.g., buildings and engineered conduits)
         for other indicator constituents.

5.    Collect, evaluate and report results:

         Compare methane results with lowtr explosion limit (LEU and 0.25 III
         and  report results immediately to regulatory agency  if these values are
         exceeded.
         Determine completeness and adequacy of collected data

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                           Table 11-1 (Continued)

      Recommended Strategy for Characterizing Releases of Subsurface Gas1

          Summarize and present data in appropriate format
          Determine if monitoring program objectives were met
          Determine if data are adequate to describe nature, rate and extent of
          release
          Report results to regulatory agency

                     SUBSEQUENT PHASES (If Necessary)

1,    Identify additional information necessary to characterize release:

          Modify conceptual model and identify additional information needs
          Selection of monitoring constituents for subsequent phase
          Spatial extent of subsurface gas migration
          Concentration levels of methane and other indicators and additional
          monitoring constituents
          Evaluate potential role of inter-media transport

2.    Expand initial monitoring as necessary:

          Expand subsurface gas well monitoring network
          Add or delete constituents and parameters
          Expand number of structures subject to monitoring
          Increase or decrease monitoring frequency

3.    Conduct subsequent monitoring phases:

          Perform expanded monitoring  of area for methane and other indicator
          and specific monitoring constituents.
          Further monitoring of surrounding structures if warranted.

4.    Collect, evaluate and report results/identify additional information necessary
     to characterize release:

          Compare  monitoring results to health and environmental criteria  and
          identify/respond to emergency situations and identify priority situations
          that warrant interim corrective  measures - notify regulatory agency
          immediately
          Determine completeness and adequacy of collected data
          Summarize and present data in appropriate format
          Determine if monitoring program objectives were met
          Determine if data are adequate to describe nature, rate, and extent of
          release
          Identify additional information needs
          Determine need to expand monitoring system
          Evaluate potential role of inter-media transport
          Report results to regulatory agency

i~   me possibility  for inter-media transport of contamination exists, and should
     be anticipated throughout the investigation.

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The  subsurface pathway data collection effort should  be coordinated, as
appropriate, with similar efforts for other media investigations.

     Development of monitoring procedures  should include determining the
specific set of subsurface gas indicators and constituents for monitoring.  Methane
and carbon dioxide can be used to identify the presence of subsurface gas during
initial screening monitoring. Subsequent monitoring will generally involve these
gases, but may also involve various constituents. Development of the monitoring
procedures should also include selection of the appropriate field and analytical
methods.  Selection of these methods will be dependent on  site and unit specific
conditions.

     An initial monitoring phase  should be  implemented using screening
techniques and appropriate monitoring constituent(s).  A subsurface gas migration
model can be used, as applicable, as an  aid in selection of monitoring locations.
Subsequent monitoring will generally be necessary if subsurface  gas migration is
detected during the initial survey. This additional monitoring may include a wider
range of constituents.

     Characterization of a subsurface gas release can involve a number of tasks to
be completed throughout the course of the investigation. These tasks are listed in
Table 11 -2 with associated techniques and data outputs.

     As monitoring data become available, both within and at the conclusion of
discrete investigation phases, it should  be reported to the regulatory agency as
directed. The regulatory  agency will compare the monitoring data to applicable
health and environmental criteria to determine the need for (1) interim corrective
measures; and (2) a Corrective Measures Study.  In addition, the regulatory agency
will evaluate the monitoring data with respect to adequacy and  completeness to
determine the  need for any additional monitoring efforts.  The  health and
environmental criteria and a general discussion of how the regulatory agency will
apply them are supplied in Section 8.  A flow diagram illustrating RFI decision points
is provided in Section 3 (See Figure 3-2).

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                                           TA8LI11-2
                 RELEASE CHARACTERIZATION TASKS FOR SUBSURFACE GAS
        Investigatory Tasks
 Investigatory Techniques
Data Presentation Formats/Outputs
 t,  Waste/Unit Characterization

        Identification of waste
|        constituents of concern

i       identification of unit
{        characteristics which
I        promote a subsurface gas
I        release
See Sections 3, 7 and Appendix
B

See Section 7
   Listing of potential monitoring
   constituents

   Description of the unit, if
   active, and operational
   conditions concurrent with
   subsurface gas sampling
 2.  Environmental Setting
    Characterization

        Oefiniation of climate
        Definition of site-specific
        meteorological conditions
        Definition of soil conditions
        Definition of site-specific
        terrain

        Identification of subsurface
        gas migration pathways
        Identification and location
        of engineered conduits
        Identification and location
        of surrounding structures
Climate summaries for regional
National Weather Service
stations

Meteorological data from
regional National Weather
Service stations

See Section 9 (e.g.. porosity,
moisture content, organic
carbon content, etc.)

See Sections 7,9 and Appendix
A

Review of unit design and
environmental setting

Review of water level table

Examination of maps,
engineering diagrams, etc.

Ground penetrating radar (See
Appendix C)

Survey of surrounding area
   Tabular summaries for
   parameters of interest
    Tabular listing for parameters
    of interest concurrent with
    subsurface gas sampling

    Soil physical properties
    Topographic map of site area


    Identification of possible
    migration pathways

    Depth to water table

    Description of the examination


    Results of study


    Map with structures identified
 3.  Release Characterization

        Model extent of release
        Screening evaluation of
        subsurface gat release
        Measurement for specific
        constituents
Gas migration model (See?
Appendix 0)
Shallow borehole monitoring
and monitoring in surrounding
buildings for indicators and
specific constituent^)

Selected gas well installation
and monitoring
                                      Monitoring in surround
                                      buildings	
    Estimated methane
    concentration isopleths for LEL
    andOZSLIL

    Listing of concentrations levels
    Tables of concentrations

    Detailed assessment of extent
    and magnitude of releases

    Tables of concentrations

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     Not withstanding the above process, the owner or operator has a continuing
responsibility to identify and respond to emergency situations and to define priority
situations that may warrant interim corrective measures.  For these situations, the
owner or operator is directed to obtain and follow the RCRA Contingency Plan
requirements under 40 CFR Part 264. Sub part 0.

11,2.2         Inter-media Transport

     Contaminated ground water and contaminated soil can result in releases of
gaseous constituents via subsurface migration,  primarily due to volatilization of
organic constituents.   Information collected from ground-water  and  soil
investigations may provide useful input data  for the subsurface gas pathway
characterization.  It may also be more efficient to jointly conduct monitoring
programs for such related media (e.g., concurrent ground water and subsurface gas
migration monitoring programs).

     Subsurface gas migration also has the potential for inter-media transport (e.g.,
transfer of contamination from subsurface gas to the soil and air media). Therefore,
information from the subsurface gas migration investigation will also provide
useful input for assessing soil contamination and potential air emissions.

11.3 Characterization of the Contaminant Source and the Environmental Setting

     The type of waste managed in the unit will determine the conditions under
which the gas can be generated, and the type of unit and characteristics of the
surrounding environment {e.g., soil type and organic content) establishes potential
migration pathways.  Units which may be of particular concern for subsurface gas
releases contain putrescible organic material and generally include below grade
landfills,  units closed as landfills (e.g., surface impoundments), and underground
tanks. These types of units may have waste deposited or stored at such depths as to
allow for subsurface gas generation by volatilization or decomposition of organic
wastes and subsequent migration (see Figures 11-1 and 11-2).

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                             COVER StHL
                                  1 itt
                              MVi-tw  **>*||L.M t " I1 "" I I V * A V: :i '  
                                                                       UNSATURATED

                                                                         SOIL
                        GHOUNDWATER  TABLE
Figure 11-1.    Subsurface Gas Generation/Migration in a Landfill

              (Mote: Gas may also migrate slowly through cover soil.)

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                         UNDERGROUND TANK
                                              PAVING
                    U
VOLATILE

LIQUIDS
                        SURFACE IMPOUNDMENT CLOSED AS IANDFIU
                UNSATURATEO
                    SOIL
Figure 11-2.    Subsurface Gas Generation/Migration from Tanks and Units Closed
              as Landfills (Note: Gas may also migrate slowly through cover
              soil.)

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     The nature and extent of contamination are affected by environmental
processes such as dispersion, diffusion, and degradation, that can occur before and
after the release occurred.  Factors that should be considered include soil physical
and chemical properties, subsurface  geology and  hydrology, and in some cases,
climatic or meteorologic patterns.

     The principle components of "landfill gas" are generally methane and carbon
dioxide produced  by the anaerobic decomposition of organic materials in wastes.
Methane is of  particular concern due to its explosive/flammable  properties,
although other gases of concern  could be present.  The presence of  these other
gases in a unit is  primarily dependent upon the types of wastes managed,  the
volatilities of the waste  constituents, temperature,  and possible chemical
interactions within the waste. Previous studies (e.g., Hazardous Pollutants in Class II
landfills, 1986, South Coast Air Quality Management District, El Monte, California
and U.S. EPA. 198S. Technical Guidance for Corrective Measures - Subsurface Gas.
Washington, D.C.  20460) have indicated that the predominant  components of
landfill gas are methane and carbon dioxide.  Methane is generally of greater
concentration, however, carbon dioxide levels are generally also high, especially
during the early stages of the methane generation process.  Concentrations of
subsurface gas constituents which may accompany  methane/carbon dioxide  are
generally several  orders of  magnitude less than methane.  In some cases (e.g.,
associated with acidic refinery wastes) sulfur dioxide may be the primary subsurface
gas.

11,3.1         Waste Characterization

11.3.1.1        Decomposition Processes

     Subsurface gas generation occurs by biological, chemical,  and  physical
decomposition of disposed or stored wastes. Waste characteristics usually affect the
rate of decomposition.  The owner or operator  should review unit-specific
information (waste receipts, waste composition surveys,  and any other records of
wastes managed)  to determine waste type, quantities, location, dates of disposal,
waste moisture content, organic contend, etc.

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     The three decomposition processes known to occur in the production of
subsurface gases are  biological  decomposition, chemical decomposition, and
physical decomposition. These are discussed below:

1131.1.1      Biological Decomposition

     The extent of biological decomposition and subsequent gas generation from a
given waste is related to the type of unit. Biological decomposition, due primarily
to anaerobic microbial degradation, is significant in most landfills and units closed
as landfills which contain organic wastes. Generally, the amount of gas generated
in a landfill is directly related to the amount of organic matter present.

     Organic wastes such as food, sewage sludges, and garden wastes decompose
rapidly, resulting in gas generation shortly after burial, with high initial yields.
Much slower decomposing organic wastes include paper, cardboard, wood, leather,
some textiles and several other organic components. Inorganic and inert materials
such as plastics, man-made textiles, glass, ceramics, metals, ash, and rock do not
contribute to biological gas production.  At units closed as landfills, waste types that
undergo biological decomposition might include bulk  organic wastes,  food
processing sludges, treatment plant sludges, and composting waste.

     Waste characteristics can increase  or decrease the rate of  biological
decomposition.   Factors that enhance anaerobic decomposition include  high
moisture content, adequate  buffer capacity and  neutral pH, sufficient nutrients
(nitrogen and phosphorus), and moderate temperatures.  Characteristics that
generally decrease biological decomposition include the presence of acidic or basic
pH, sulfur, soluble metals and other microbial toxicants. The owner or operator
should review the waste characteristic information to document if biological
decomposition and subsequent gas generation may be occurring.

     Under anaerobic conditions, organic wastes are primarily converted by
microbial action into carbon dioxide and methane. Trace amounts of hydrogen,
ammonia, aromatic hydrocarbons, halogenated organics, and hydrogen sulfide may
also be present. With regard to subsurface  migration, the primary gases of concern
are methane (because of its explosive  properties) and constituents that may be
present in amounts hazardous to human health or the environment.

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11.3.1.1.2      Chemical Decomposition

     Gas production by chemical reaction can result from the disposal or storage of
incompatible wastes. Reactive or ignitable wastes can produce explosive or heat-
producing reactions, resulting in rapid production of gases, and increased pressures
and temperatures. Under acidic conditions, a strong oxidizing agent can react with
organic wastes to produce carbon dioxide and ammonia which can migrate from
the unit, possibly providing a transport mechanism for other gaseous components.

     Under typical  conditions, gas production from chemical reactions is not
expected to occur at landfills or jnits closed as landfills.  However, volatile liquids
stored in underground tanks may have a significant potential to create a release by
chemical reaction.   Good waste management practices, particularly the proper
design  and operation {e.g., pressure-relief valves and leak detection systems) of
underground tanks can minimize the potential for gas release.

11.3.1.1.3      Physical Decomposition

     Physical decomposition phenomena  include volatilization and combustion.
Volatilization can result in subsurface gas generation in underground tanks if there
is a leak or puncture. The greater a compound's vapor pressure, the greater will be
its potential to volatilize.  Maintenance of underground tanks (e.g., pressure-relief
valves and leak detection systems) can minimize volatilization.

     Combustion processes (e.g., underground fires) sometimes  occur at active
landfills and result in subsurface  gas release.  Combustion  can convert wastes to
byproducts such as carbon dioxide, carbon monoxide, and trace toxic components.
Combustion  processes can also accelerate chemical reaction rates and biological
decomposition, creating greater potential 'or future subsurface gas generation and
subsequent release.  The  owner or operator should review  facility records to
determine if combustion has occurred and when.

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11.3.1.2       Presence of Constituents

     Subsurface gas generation and migration of methane is of concern because of
its explosive properties. In addition, methane and other decomposition gases can
facilitate the migration of volatile organic constituents that may be of concern
because of potential toxic effects.  Subsurface gas migration due to leaks from
subsurface tanks may also be associated with  a  variety of  volatile organic
constituents.

     In determining the nature of a release, it may be necessary to determine the
specific waste constituents in the unit. Two means of obtaining these data are:

     (1)   Review of facility records.  Review of facility records may not provide
          adequate information (e.g., constituent concentrations) for RFI purposes.
          For example, facility records of waste  handled in  the unit  may only
          indicate generic wa*te information.    Knowledge of individual
          constituents and concentrations is generally needed for purposes of the
          RFI.

     (2)   Conducting waste sampling and analysis.  When facility records do not
          indicate the specific constituents of the waste which are likely  to be
          released  and  may migrate as  subsurface gas, direct waste
          characterization may be necessary. This effort, aimed  at providing
          compound specific data on the waste, can be  focused in terms of the
          constituents for which analysis should be performed through review of
          the waste types in the unit. In some cases, however,  the generic waste
          description (e.g., flammable liquids) will not give an indication of the
          specific constituents present, and analysis for  i of the constituents of
          concern as gaseous releases (See Appendix S, List 2) may be required.

     Additional guidance on identification of monitoring  constituents is presented
in Section 3.6. Section 7 provides guidance on waste characterization.
                                   11-13

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11.3.1.3       Concentration

     Determination of concentrations of the constituents of concern In the waste
may indicate those constituents which are of prime concern for monitoring. The
concentration of a constituent in a waste (in conjunction with its physical/chemical
properties and total quantity) provides an indication of the gross quantity  of
material that may be released in the gaseous form.

11.3.1.4       Other Factors

     fn addition to the factors described above, determination of the potential for
volatilization of the waste constituents will help determine if they may be released.
The parameters most important when assessing the potential for volatilization of a
constituent include the following;

     *   Water solubility.  The solubility in water  indicates the  maximum
         concentration at which a constituent can dissolve in water  at a given
         temperature.  This value can be used to estimate the distribution of a
         constituent between  the dissolved aqueous phase in the unit and the
         undissolved solid or immiscible liquid phase. Considered in combination
         with the constituent's vapor pressure, it can provide a relative assessment
         of the potential for volatilization.

     *   Vapor pressure. Vapor pressure refers to the pressure of vapor in
         equilibrium with a pjre liquid. It is best used in a relative sense;
         constituents with high vapor pressures are more likely to be  released in
         the gaseous form than those with  low vapor pressues, depending  on
         other factors such as relative solubility and concentration (i.e., at high
         concentrations releases can occur even though  a constituent's vapor
         pressure is relatively low).

        Qctanol/water  partition coefficient.  The  octanol/water partition
         coefficient indicates the tendency of an organic constituent to sorb to
         organic components of the soil or waste matrices of a unit. Constituents
         with high octanol/water partition coefficients will  adsorb readily to
         organic  carbon, rather than volatilizing to the atmosphere. This is

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         particularly important in landfills and land treatment units, where high
         organic carbon contents in soils or cover material can significantly reduce
         the release potential of vapor phase constituents.

     *   Partial pressure.  For constituents in a mixture, particularly in a solid
         matrix, the partial pressure of a constituent will be more significant than
         the pure vapor pressure. In general, the greater the partial pressure, the
         greater the  pottntial for  el ease.  Partial  pressures  will  be difficult  to
         obtain. However, when waste characterization data is available, partial
         pressuers can be estimated  using  methods commonly found  in
         engineering and environmental science handbooks.

        Henry's Law constant.  Henry's law constant is the  ratio of the vapor
         pressure of a constituent and its aqueous solubility (at equilibrium).  It
         can be used  to assess the relative ease with which the compound may  be
         removed from the aqueous  phase via vaporization.  It is accurate only
         when used in  evaluating low concentration wastes in aqueous solution,
         Thus it will  be most useful  when the unit being assessed is a surface
         impoundment or tank containing dilute  wastewaters.  As the value
         increases, the  potential for significant vaporization increases, and when
         it is greater than 0.001, rapid volatilization will generally occur.

     *   Raoult's law.   Raoult's Law  can  be used to predict  releases from
         concentrated  aqueous solutions (i.e.,  solutions over 10% solute).  This
         will be most useful when the unit contains concentrated waste streams.

11.3.2         Unit Characterization

     Unit design (e.g., waste depth, unit configuration, and cover materials) also
affects gas generation.  Generally, the amount of gas generated increases with
landfill volume and often with landfill depth. Deeper landfills have a proportionally
larger anaerobic zont, greater insulation and compaction, and are more likely to
confine gas production.  Deeper landfills, such as trench fills or canyon fills, can trap
gases along confining sidewalls  and bottom bedrock or ground water.  Daily,
interim, and final cover soils can confine gases within the landfill. This is particularly
true for  low permeability cover soils (e.g., clays)  which impede vertical gas

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migration. Conversely, mound or shallow landfills have large surface areas through
which gases can vent more easily.

     Unit operations, such as methods and procedures used to segregate and
isolate inert wastes, to prevent moisture infiltration, to compact and increase the
density of the waste, and to minimize or prevent mixing of waste types, can affect
resultant releases of subsurface gases.   Daily covering of the unit may  inhibit
decomposition and thus gas generation and subsequent migration.

     Certain units have a high potential for allowing the movement of subsurface
gas.  These units are those that receive and/or store large volumes of decomposable
wastes, volatile organic liquids or highly reactive  materials. Subsurface gas
migration may occur especially when major portions of a land-based unit are below
grade. Gas generated by these units can migrate vertically and laterally from the
unit, following the path of least resistance.

     Some units are operated above grade or in relatively shallow toils (e.g., surface
impoundments, iand treatment units).  The potential for subsurface gas migration
from such units is  usually low.  Gases generated by such units will generally  be
vented to the atmosphere unless  prevented  by a natural barrier (eg,  frozen
ground) or an engineered barrier (e.g., soil cover).

     Information on unit operations will therefore be important in assessing the
potential for subsurface gas migration. Unit operational data may also be required
concurrent with any subsurface gas sampling activities. It is particularly important
to obtain operational data on any gas collection system in use at the time of
sampling. These gas collection systems can significantly  affect subsurface gas
migration rates, patterns and constituent concentration levels.

     Generally, the units that  post the greatest potential for subsurface gas
migration include landfills, sites dosed as landfills, and underground storage tanks.
These are discussed below.

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11.3.2.1       Landfills

     Gas generated in landfills can vent vertically to the atmosphere and/or migrate
horizontally through permeable soil, as shown in Figure 11-1. Closure of the landfill
or periodic covering of cells or lifts with impermeable caps may impede the vertical
movement of the gases, forcing them to migrate laterally from the  unit.  Gas
migration  laterally through the subsurface (e.g., through underground utility line
channels or sand lenses) may accumulate in structures on or off the facility property.

11.3.2.2       Units Closed as Landfills

     Gas generation and subsequent migration is likely to occur at units closed as
landfills containing organic wastes, as previously discussed.  Although  surface
impoundments and waste piles may be closed as landfills, they tend to produce less
gas than  landfills because they generally contain  smaller quantities of
decomposable and volatile wastes and are generally at shallow depths. Closure of
such units with an impermeable cover will, however, increase the  potential for
lateral gas movement and accumulation in onsite and offsite structures (see Figure
11-2).

11.3.2.3       Underground Tanks

     Subsurface gas release and subsequent migration  may  occur if an
underground tank is leaking. Underground tanks frequently contain volatile liquids
that could enter the unsaturated zone should a leak occur (see Figure 11-2).

11.3.3        Characterization of the Environmental Setting

11.3.3.1       Natural and Engineered Barriers

     Subsurface conditions at the site should be evaluated to determine likely gas
migration  routes. Due to the inherent mobility of gases, special attention must be
paid to zones of high permeability created by man-made, biological, and physical
weathering action.  These zones include backfill around pipes, animal burrows,
solution channels, sand and/or gravel lenses, desiccation cracks, and  jointing  in

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bedrock. The presence of dead rodents, snakes and other burrowing animals is
usually a good indication of a potential subsurface gas pathway.

     Natural and engineered barriers can also affect gas migration, generally by
inhibiting migration pathways. Natural barriers to gas migration include surface
water, ground water, and geologic formations.  Engineered barriers include walls,
onsite structures, underground structures, caps, liners, and other design features.
On the other hand, preferred pathways for subsurface gas migration may result
from previous underground construction (e.g., underground utility lines) that can
facilitate gas flow. Natural and engineered barrier; are discussed in more detail
below.

11.3.3.1.1      Natural Barriers

     Surface water, ground water, and saturated soils can slow down or control the
direction of subsurface gas migration. Gases encountering these barriers will follow
the pathway of least resistance, usually through unsaturated porous soil.

     Geologic barriers can also impede or control the route of subsurface gas
migration.  For example, soil type is an important factor in gas migration. Gravels
and sands allow gas to migrate readily, particularly sand/gravel lenses, while clayey
gravels and sandy and organic clays tend to impede gas movement. Underground
utility trenches, backfill with granular materials, filled-in mine shafts, and tunnels or
natural caverns can also serve to channel subsurface gas flow.  Climatic conditions
such as precipitation or freezing can reduce the porosity of surface soils, thereby
impeding upward gas movement. Information regarding characterization of soils is
provided in Section 9 (Soils).

11.3.3.1.2     Engineered Barriers

     Landfills  and units closed as landfills may  use caps and liners to prevent
moisture infiltration and leachate  percolation to ground water.  Caps can
contribute to horizontal gas movement when upward migration to the surface is
restricted (as shown in Figure 11-1).   Liners tend to impede lateral migration into
the surrounding  unsaturated soils. The owner or operator should evaluate cap/liner
systems (type, age, location, etc.) to determine potential gas migration pathways.

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Similar to liners, slurry walls used to border landfill units can  retard lateral  gas
movement. With respect to underground tanks, caps and liners are not typically
used.  Tanks are often  placed into soils with sand or gravel backfill during
installation, followed by paving on the surface. Thus, any escaping gases from a
leaking underground tank may migrate laterally along the path of least resistance
adjacent to the units.  The owner or operator should evaluate  tank construction,
and agf, integrity, and location.

11.3.3.2       Climate and Meteorological Conditions

     The climate of the site should be defined to provide background information
for assessing the potential for subsurface gas migration, identifying migration
pathways, and designing the subsurface gas migration monitoring system.  Climatic
information, on an annual and monthly or seasonal basis, should be collected for
the following parameters:

     *    Temperature means/extremes and frost season (which  indicates the
          potential for impeding the upward migration of the subsurface gas, thus
          confining the gas within the ground),

     t    Precipitation means and snowfall (which  indicates the  potential for
          "trapping" as well as an indication of soil moisture conditions  which
          affect subsurface gas migration); and

         Atmospheric pressure means (which indicates the potential for gaseous
          releases to ambient air from a unit of concern).

     The primary source of climate information for the Unites States is the National
Climatic Data Center (Asheville, NC). The National Climatic Data Center can provide
climate summaries for the National Weather Service station nearest to the  site of
interest. Standard references for cl imatic information also include the following:

     Local Climatological  Data   Annual Summaries  with Comparative Data.
     published annually by the National Climatic Data Center;

     Climates of the States, National Climatic Data Center; and

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     Weather Atlas of the United States. National Climatic Data Center.

     Meteorological data for the above parameters should also  be obtained
concurrently with subsurface gas sampling activities. As previously discussed, these
meteorological conditions can influence  subsurface gas migration rates, patterns
and concentration levels.  Therefore, these data are necessary to properly interpret
subsurface gas sampling data. Concurrent meteorological data for  the sampling
period can  be obtained  from the National Climatic Data  Center  for National
Weather Service stations representative of the site area.  In some  cases, onsite
meteorological data will also be available from an existing monitoring program or
associated with an RFI characterization of the air media (See Section 12).

11.3.3.3       Receptors

     Receptor information needed to assess potential subsurface gas  exposures
includes the identification and location of surrounding buildings  and potential
sensitive receptors (e.g., residences, nursing homes, hospitals, schools, etc.). This
information should also be considered in the developing monitoring procedures.
Additional discussion of potential receptors is provided in Section 2.

11.4 Design of a Monitoring Program to Characterize Releases

     Existing data should help to indicate which units  have the potential to
generate methane or other gases or constituents of concern.  Such information can
be found in construction or design document;, permit and inspection reports,
records of waste disposal, unit design and operation records, and documentation of
past releases.

     Units of concern should be identified on the facility s topographic map.  The
location and area) extent of these  units can be determined from historical records,
aerial photographs, or field surveys. The depths and dimensions of underground
structures, locations of surrounding buildings, and waste-related information
should be identified.  Waste management records may provide information on
waste types, quantities  managed, location of waste units, and dates of waste
disposal. Waste receipts, waste composition surveys, and records of waste types

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(e.g., municipal refuse, bulk liquids, sludges, contaminated soils, industrial process
wastes or inert materials) should be reviewed. For underground tanks, liquid waste
compositions, quantities, and physical properties should be determined.

     Review of unit design and operation records  may provide  background
information on units of concern.  These records may include  engineering design
plans, inspection records, operations logs, damage or  nuisance litigation,  and
routine monitorng data. Also, for landfills and units closed as landfills, data  may
include the presence and thickness of a liner, ground-water elevations, waste
moisture contents, type and amount of daily cover, records of subsurface fires, and
in-place leachate and/or  gas collection systems.  Historical information on
underground tank integrity may be contained in construction and monitoring
records. Records of past  releases may provide information on problems, corrective
measures, and controls initiated.

     The owner or operator should review records of subsurface  conditions to
determine potential migration pathways. Aerial photographs or field observations
should identify surface water locations.  Infrared aerial photography or geological
surveys from the USGS can be used as preliminary aids  to  identify subsurface
geologic features and ground-water location.  In addition to obtaining  and
reviewing existing information, a field investigation may be necessary to confirm
the location of natural barriers. The local soil conservation service will often have
information describing soil characteristics (e.g., soil type, permeability, particle  size)
or a site specific investigation may need to be conducted. (Soil information sources
are discussed  in Section 9).  Climatic  summaries  (e.g., temperature, rainfall,
snowfall) can be obtained from the National Climatic Data Center for the National
Weather Service station nearest to the site of  interest (Specific climatic data
references are cited in  Section 12).  Historical  records of the site (prior  use,
construction, etc) should also be  reviewed to identify  any factors  affecting gas
migration routes.  The monitoring program should also address any engineered
structures affecting the migration pathway.

     in addition to the above, the owner or operator should examine the units and
surrounding area  for signs  of settlement, erosion, cracking of covers, stressed or
dead vegetation,  dead  rodents, snakes and  other burrowing  animals,
contamination of surface waters,  odors, elevated temperatures in any existing

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monitoring wells, and for venting of smoke or gases. The condition of any existing
gas monitoring systems and containment or  collection systems should also be
examined, as well as any structural defects in tanks or liners. Any overflow/alarm
shut off systems, subsurface  leak detection  systems, secondary containment
structures (e.g., concrete pads, dikes or curbs) or other safety systems for early
detection of potential gas releases should be checked.

     By reviewing all existing information, the owner or operator should be able to
develop a conceptual model of the release and design a monitoring program to
characterize the release.

11.4.1         Objectives of the Monitoring Program

     Characterization of subsurface gas releases can be accomplished through a
phased monitoring approach. The objective of initial monitoring should be to verify
suspected releases,  if necessary, or to begin characterizing  known releases.
Monitoring should include methane and other indicators such as carbon dioxide, as
well as  individual constituents if appropriate.  If initial  monitoring verifies a
suspected release, the owner or operator should expand the monitoring program to
determine the vertical and  horizontal extent of the release, as well  as  the
concentrations of all constituents of concern in the release.

     The full extent of the release can be determined through additional shallow
borehole and gas monitoring  well locations.  The goal  of this  further
characterization will be to identify the boundary of gas migration, including the
leading edge of the migration.

     A great deal of the effort conducted during any subsequent phase may involve
investigating anomalous areas where subsurface conditions are non-uniform. In
these situations, the gas migration characteristics may differ from surrounding
areas.   Consequently,  non-random sampling techniques are generally most
appropriate  to monitor these areas.  The location of additional  gas wells  and
shallow boreholes at the sites of subsurface  anomalies will provide information
regarding the migration pattern around these anomalous areas. Also, because gas
well installation may be conducted only to  a limited extent under the initial
monitoring phase, additional wells may need to be installed.

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     The monitoring program should also address the selection of constituents of
concern, sampling frequency and duration, and the monitoring system design.

11.4.2     Monitoring Constituents and Indicator Parameters

     As discussed above, the number  and  identity  of potential subsurface  gas
constituents will vary on a  site-specific basis.  Constituents to be included  for
monitoring depends primarily on the type of wastes received. For example, if an
underground storage tank contains specific constituents, they should be considered
during subsurface gas monitoring activities. The guidance provided in Section 3 and
the lists provided in Appendix 8 should be used to determine a select set of
constituents and indicator parameters far subsurface gas monitoring.

     Methane should be used as the primary indicator of subsurface gas migration
during the initial and any subsequent monitoring phases. Supplemental indicators
(e.g., carbon dioxide and sulfur dioxide) may also be used as appropriate. Field
screening equipment should be used to detect the presence of methane in terms of
the lower explosive limit (LEL). The LEL for methane is 5 percent by volume, which is
equivalent to 50,000 ppm.  Individual  constituents should also be monitored. !r>
addition, oxygen detectors  and nitrogen analyses  can be used to confirm  the
representativeness of all subsurface gas well samples obtained.  (The presence of
oxygen and nitrogen in well samples indicates the intrusion of ambient air into the
well during monitoring, Samples containing ambient  air would result in an
underestimate of methane  and other indicators as well as specific monitoring
constituents.)

     Methane concentrations observed during the initial monitoring phase which
exceed the LEL at the property boundary or 0.25 the  LEL at surrounding structures,
would warrant initiation  of subsequent monitoring phases and  possibly,
consideration of interim corrective measures. Similarly, the presence of individual
constituents would also trigger the need for subsequent monitorinc phases.

     Regardless of the degree to which monitoring constituents can  be limited by
site-specific data, analyses for all constituents identified as applicable in Appendix B

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(List  2) will generally be necessary for the subsurface gas medium at selected
monitoring locations.

11.4.3         Monitoring Schedule

     A monitoring schedule should be established and described in the RFI Work
Plan.  This schedule should describe the sampling frequency, the duration of the
sampling effort, and the conditions under which sampling should occur.

     During initial monitoring, bar punch probe (See jection 11-6) monitoring for
methane and appropriate constituents should be conducted at least twic over the
course of one week.  Monitoring the wells for methane and constituents should be
conducted at least once a week for one month. (Subsurface gas wells should not be
monitored for at least 24 hours after installation to allow time for equilibration.)
Surrounding buildings should be monitored at least once a week for one month.

     During any subsequent monitoring phases, more extensive sampling may be
needed to adequately characterize the nature and extent of the release. Monitoring
of wells and buildings for methane and constituents should be conducted  every
other day for a two week period to account for daily  fluctuations in gas
concentrations.

     Conditions for sampling should also be defined.  Sampling should generally
not be performed if conditions conducive to decreasing gas concentrations are
present (e.g.. subsurface  gas pressure at less than atmospheric  pressure).  In these
cases, sampling should be delayed until such conditions pass.   Subsurface  gas
pressures have a diurnal cycle and are generally at a maximum during  the
afternoon.

11.4.4        Monitoring Locations

11.4.4.1       Shallow Borehole Monitoring

     Areas identified for subsurface gas monitoring as a result of characterization
of the contaminant source and the environmental setting should be investigated for
concentrations of methane  and constituents during the initial monitoring phase.

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Shallow borehole mentoring using a bar punch probe method or equivalent (See
Section 11.6) is recommended. The bar punch is simply a steel or metal bar which is
hand-driven or hammered to depths of 6 feet. Once this hole is made it is covered
with a stopper or seal to confine the headspace in the hole.  The hole should be
allowed to equilibrate for -jp to an hour prior to sampling to provide sufficient time
for subsurface gas to replace the air in the hole. The ease of installation of bar
punch holes and the ability  to obtain real-time direct measurements from field
survey instruments combine to make this  task a relatively simple operation   It
should be recognized, however, that shallow borehole monitoring is a  rapid
screening method and therefore has its limitations. Two major limitations are that
negative findings cannot assure the absence of a release at a greater depth and that
air intrusions can dilute the sampling readings. See also Sections 9 (Soil) and 10
(Ground Water) for additional information.

     The number of locations to monitor will vary from site to site.  However, due
to the ease of this operation, it is recommended that many locations be surveyed
during the initial monitoring phase. Selection of locations along the perimeter of
the unit of concern and at intervals of approximately 100 feet is an adequate initial
approach. Individual site conditions and anomalies  should be considered to
determine whether the number of sampling  locations should be increased or
decreased.  A large site with homogeneous subsurface conditions  could require
fewer sampling locations  by  increasing the distance between sampling  points.  A
site with many subsurface anomalies, such as engineered barriers or varying soil
strata, would  require a greater number of sampling locations. In general, sampling
locations should be established where conditions are conducive to gas migration,
such as  in sands, gravels  and porous soils, and near engineered conduits (e.g.,
underground utility lints).  The appropriate precautions should be taken  when
sampling near engineered conduits so as not to damage such property and to assure
the safety of the investigative team and others.

     The distance from the unit at which to sample can best be determined through
consideration of site-specific characteristics (e.g., soil conditions), and can be aided
by the use of the gas concentration contour map generated by the predictive model
described in Appendix D.  The shallow borehole survey should be fairly extensive,
ranging from sampling locations very rear the unit to locations at the property
boundary and beyond.

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11.4.4.2       Gas Monitoring Wells

     Gas monitoring wells (Sec Section 11.6) should be installed to obtain data on
subsurface gas concentrations at depths greater than the depth accessible with a
bar punch probe. Wells should be installed to a depth equal to that of the unit.
Multiple probe depths may be installed at a single location as illustrated in Figure
11-3.  Where buried  material is fairly shallow (e.g.,  <1Q*feet), single depth gas
monitoring probes may be sufficient.  When buried material exceeds this depth
below ground, multiple depth probes should be installed.

     The location and depth of gas  monitoring wells should be based on the
presence of highly permeable zones (e.g., dry sand or gravel), alignment with offsite
structures, proximity of the waste deposit, areas where there is dead or unhealthy
vegetation (that may be due to gas migration), and any engineered channels which
would  promote the migration of a subsurface gas release (e.g., utility lines).  This
information should be gathered during  a  review of  subsurface  conditions, as
discussed previously.  At a minimum, a monitoring well should be installed at the
location(s) of expected maximum concentration (s), as determined or  estimated
during the initial monitoring phase.

     Gas monitoring  well installation usually requires the use of a drilling rig or
power auger.  Once  a borehole has been drilled to the desired  deptit, the gas
monitoring  probes can be installed as illustrated in Figure 11-3.  Additional
information concerning the installation  of subsurface gas monitoring  wells is
provided  in Section 10  (Ground Water)  and in Guidance  Manual for the
Classification of Solid Waste Disposal Facilities NTIS P881-218505 (U.S. EPA. 1981).

     Equilibration times of at least 24 hours should be allowed prior to collection of
subsurface gas samples for analysis after well installation and between subsequent
collection periods. Individual site characteristics or anomalies which can create
significantly different subsurface conditions will require an increased number of
wells to sufficiently determine the presence of gas migration. For  example, if the
predominant soil strata along one side of a unit changes from sandy  clay to gravel, a
well should be installed in both of these areas. Also, if the amount of gas producing

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                                                      duced tram
                                                      *vil*bl* copy
                   ASCUNO a
                   73 TJBE.
Figure 11-3. Schematic of a Deep Subsurface Gas Monitoring Weil
                           1 !_17

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waste buried at the site varies greatly from one area *o another, gas monitoring
wells should be installed near each area of concern.

     Subsurface gas monitoring may be done concurrently with ground-water
investigations (Section 10), because results of subsurface gas monitoring  may
provide useful information for identifying the overall extent of any ground-water
contamination.

11.4.4.3  Monitoring in Buildings

     Monitoring should also be conducted in surrounding structures near the areas
of concern, since methane and other subsurface gas constituents migrating through
the soil can accummulate in confined areas.  Use of an explosimeter for methane is
the recommended monitoring technique (See Section 11.6).

     Sampling should be conducted at times when the dilution of the indoor air is
minimized and  the concentration of soil gas is  expected to  be at its highest
concentration. Optimal sampling conditions would be after the building has been
closed for the weekend or overnight and when the soil surface outside the building
and over the unit of concern has been wet or frozen for several days. These
conditions will maximize the potential for lateral migration of gas into buildings
rather than vertically into  the ambient air.  Recommended sampling locations
within the building include basements, crawl spaces, and around subsurface utility
lines such as sewer or electrical connections. Access conduits such as manholes or
meter boxes are good sampling locations for water, sewer, or gas main connections.
Methane and, if appropriate, individual constituents should be monitored for.

     The threat of explosion  from accumulation of methane within a building
makes this monitoring activity important as well as dangerous. The monitoring of
gas concentrations within  buildings is a simple process involving a walk through
inspection of areas with portable field instruments (e.g., explosimiter).  Such
measurements should begin during the initial monitoring phase. The importance of
identifying potential releases to  buildings warrants a complete inspection of all
suspect areas. The inherent danger during these investigatons warrants adequate
health and safety procedures (See Section 6).

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     If significant concentrations of methane or constituents are  measured in
surrounding structures during initial monitoring, subsequent monitoring may need
to be expanded to include buildings at greater distances from the unit(s) of concern
and to include additional constituents of concern. In addition, interim corrective
measures should be considered.

     Background indoor air quality levels  may be  accounted for during the
collection and evaluation of the in-building sampling data. Background levels can
be accounted for by identifying potential indoor air emission sources (e.g., use of
natural gas as a fuel or wood paneling which has the potential for formaldehyde
emissions).  Further guidance on this subject is presented in the following reference:

     U.S. EPA.  1i83. Guidelines for Monitoring Indoor Air Quality.  EPA- 600/1-4
     83-066.   NTIS  PB83-264465   Office of Research  and  Development.
     Washington, D.C. 20460.

11.4.4,4  Use of Predictive  Models

     In addition to monitoring  potential gas releases using portable  survey
instruments, the owner or operator should consider the use of predictive models to
estimate the configuration and concentration of gas releases.  A subsurface gas
predictive model has been  developed by EPA to  estimate methane gas migration
from sanitary landfills.  This model is based on site soil conditions,  waste-related
data, and other environmental factors.

     As part of the initial monitoring phase, the model provided in Appendix D (or
another appropriate predictive  model after consultation with the regulatory
agency), should be used to estimate the extent of subsurface gas migration. Results
from this model can be used in determining appropriate monitoring locations. The
methane gas  migration model  presented in  Appendix 0 yields a  methane
concentration isopleth map of a release. The LEL and 0.25 LEL isopletns for methane
should be mapped for the RFI. Because predictive models may not be sensitive to
relevant site conditions, however, model results should be used cautiously for the
monitoring program design and to supplement actual field data.

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11,5 Data Presentation

     Subsurface gas data collected during the RFI should be presented in formats
that clearly define the composition and extent of the release. The use of tables and
graphs is highly recommended.  Section 52 provides a detailed discussion of data
presentation methods.

11.5.1     Waste and Unit Characterization

     Waste and unit characteristics should be presented as:

     *    Tables of waste constituents and concentrations;

     *    Tables  of relevant physical and chemical  properties of waste and
          potential contaminants;

         Narrative description of unit dimensions, operations, etc.; and

     *    Topographical map and plan drawings of facility and surrounding areas.

11.5,2     Environmental Setting Characterization

     Environmental characteristics should be presented as follows:

         Tabular summaries of annual and monthly or seasonal relevant climatic
          information (e.g., temperature, precipitation);

     *    Narratives and maps of soil and relevant hydrogeological characteristics
          such as porosity, organic matter content, and depth to ground water;

     *    Maps showing location of natural or man-made engineering barriers and
          likely migration routes; and

     *    Maps of geologic material at the site identifying the thickness, depth,
          and textures of soils, and the presence of saturated  regions and other
          hydrogeological features.

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11.5.3     Characterization of the Release

     In general, re leave data should  be initially presented in tabular form.  To
facilitate interpretation, graphs of concentrations of individual constituents plotted
against distance from the unit should  be used to identify migration pathways and
areas of elevated concentrations.  Concentration isopleth maps can also be drawn to
identify the direction, depths, and distances of gas migration, and concentrations of
constituents of concern.  Specific examples of  these and other data presentation
methods are provided in Section 5. Methane concentrations should be presented in
terms of  the  LEL and  0.25  LEL isopleths.  Specific monitoring  constituent
concentrations should also be presented.

11.6 Field Methods

     Field methods for subsurface gas investigations involve sample collection and
analysis.  Sample collection methods  are discussed to summarize the monitoring
techniques described above.  Since subsurface gas monitoring is similar to air
monitoring, the available methods for the collection and analysis of subsurface gas
samples are presented here only in tabular format with further discussion in the air
section of this document (Section  12).  Tables 11-3 through 11-5 summarize various
methodologies available to collect and analyze air samples. These methodologies
range from real-time analyzers (e.g.,  methane explosimeters) to the collection of
organic vapors on sorbents or whole  air samples with subsequent laboratory
analysis.

     A portable  gas chromatograph with a flame ionization detector (calibrated
with reference to methane) can be used to measure methane concentrations in the
field. Methane explosimeters (based on the principle of thermal conductivity) are
also available and provide direct readings of  LEL levels and/or percent methane
present by volume.
                                   11.

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                       TABLE 11-3
SUMMARY OF SELECTED ONSITE ORGANIC SCREENING METHODOLOGIES
Instrument or
detector
Century Series 100
or AID Model 500
(survey mode)
GfG Gas Etechomcs
(Methanometer)
National Mine Service
Company
Mine Safety
Appliances, Inc.
Measurable
parameters
Volatile organic
species
Methane explosion
potential
Methane explosion
potential
Methane explosion
potential
Low range of
detection
Low ppm
Low ppm
Low ppm
Low ppm
I
Comments
Uses Flame lonization
Detector (FID)
Sensitive to methane
Sensitive to methane
Sensitive to methane

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                                TABLE 11 -4
SUMMARY OF CANDIDATE METHODOLOGIES FOR QUANTIFICATION OF VAPOR PHASE ORGANICS
Collection Techniques
1. Sorption onto Tenax-GC
or carbon molecular
sieve packed cartridges
using low-volume pump
2. Sorption onto charcoal
packed cartridges using
low-volume pump
3. Sorption onto
pdyurethane foam (PUF)
using low-volume or
high-volume pump
Analytical Technique
Thermal Desporption into
GCorGC/MS
Oesorption with solvent-
analysis by GC or GOMS
Solvent extraction of PUF;
analysis by GC/MS
Applicability*
1
II
1. II, III
Positive Aspects
 adequate QA/QC data
base
 widely used on
investigations around
uncontrolled waste sites
 wide range of
applicability
e pg/mJ detection limits
 practicality for field use
 large data base for
various compounds
 wide use in industrial
applications
e practical for field use
 wide range >f
applicability
 easytopercleanand
extract
 very low blanks
 excellent collection and
retention efficiencies
 reusable u p to 1 0 ti mes
Negative Aspects
 possibility of
contamination
 artifact formation
problems
 rigorous cleanup needed
 no possibility of multiple
analysis
 low breakthrough
volumes for some
compounds
 problems with
irreversible adsorption of
some compounds
 high (mg/m3) detection
limits
 artifact formation
problems
 high humidity reduces
retention efficiency
 possibility of
contamination
 losses of more volatile
compounds may occur
during storage

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                            TABLE 11-4 (continued)
SUMMARY OF CANDIDATE METHODOLOGIES FOR QUANTIFICATION OF VAPOR PHASE OROANiCS
Collection Techniques
4 Sorption on passive
Dosimeters using Tenax
or charcoal as adsorbing
medium
5. Cryogenic trapping of
analytes in the field
6. Whole air sample taken
in glass or stainless steel
bottles
7. Whole air sample taken
in Tedlar* Bag
Analytical Technique
Analysis by chemical or
thermal desorption followed
byGCorGOMS
Oesorption into GC
Cryogenic trapping or direct
injection into GC or GC/MS
(onsite or laboratory)
Cryogenic trapping or
director injection into GC or
GC/MS (onsite or laboratory)
Applicability*
lor II
II, III
II, III
II, III
Positive Aspects
* Samplers are small.
portable, require no
pumps
e makes use of analytical
procedures of known
precision and accuracy
for a broad range of
compounds
* ug/m3 detection limits
e applicable to a wide
range of compounds
* artifact formation
minimized
* low blanks
* useful for grab sampling
* large data base
 excellent long-term
storage
e wide applicability
* allows multiple analyses
* grab or integrated
sampling
* wide applicability
e allows multiple analyses
Negative Aspects
* problems associated with
sampling using sorbents
(see t\ and II) are present
* uncertainty in volume of
air sampled makes
concentration
calculations difficult
* requires minimum
external mr flow rate
* requires field use of
liquid nitrogen or
oxygen
 sample is totally used in
one analysis-no
reanalysis possible
 samplers easily clogged
with water vapor
e no large data base on
precision or recoveries
 difficult to obtain
integrated samples
 low sensitivity if
preconcentration is not
used
* long-term stability
uncertain
 low sensitivity if
preconcentration is not
used
* adequate cleaning of
containers between
samples may be difficult
- - 	 ' 	 1

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                                              TABLE 11-4 (continued)

              SUMMARY OF CANDIDATE METHODOLOGIES FOR QUANTIFICATION OF VAPOR PHASE ORGANICS
Collection Techniques
8. DmitropheynJhydrazine
Liquid Imptnger
Sampling using low-
volume pump
9. Director introduction by
probe
Analytical Technique
HPLC/UV analysis
Mobile M VMS
Applicability*
IV
I, II. III. IV
Positive Aspects
* speci fie to aldehydei and
ketones
* good stability for
derivatued compounds
* low detection limits
* immediate results
* field identification of air
contaminants
* allows "real-time*
monitoring
* widest applicability of
any analytical method
Negative Aspects
 fragile equipment
* sensitivity limited by
reagent impurities
* problems with solvent
evaporation when long-
term sampling it
performed
 high instrument cost
($250K>
* requires highly trained
operators
e yrab samples only
* no large data base on
precision or accurac/
U1
     a  Applicability Code

     I   Volatile, nonpolar organics (e.g., aromatic hydrocarbons, chlorinated hydrocarbons) having boiling points in the
        range of 80 to 200 C
     II  Highly volatile, nonpolar organics (ie.g, vinyl chloride, vinyiidene chloride, benzene, toluene) having boiling points
        in the range of -15 to +120
-------
                            TABLE 11-5
TYPICAL COMMERCIALLY AVAILABLE SCREENING TECHNIQUES FOR ORGANICS IN AIR
Techniques
>as Detection Tubes
Continuous Flow Colorimeter
lolorimetric Tape Monitor
nf fared Analysis
ID (Total Hydrocarbon
knalyzer)
iOFID (portable)
ID and GOPID (portable)
1C/ECD (portable)
iC/FPD (portable)
Ihemiluminescent
Nitrogen Detector
Manufacturer
Draeger Matheson (Kitagawa)
CEA Instruments, Inc.
MDA Scientific
Foxboro/Wilkes
Beckman
MSA. Inc.
AID. Inc.
Foxboro/Century
AID. Inc.
HNU. Inc
AID. Inc
Photovac, Inc.
AID. Inc.
AID. Inc.
Antek. Inc.
Compounds Detected
Various organic' and inorganics
Acrylonitrile, Formaldehyde,
Phosgene, and
Toluene, diisocyanate. dinitro-
toiuene, phosgene, and various
inorganics
Most organic}
Most organics
Same as above except that polar
compounds may not elute from
the column
Most organic compounds can
be detected with the exception
of methane
Halogenated and nitro
substituted compounds
Sulfur or phosphorus-
containing compounds
Nitrogen-containing
compounds
Approximate
Detection
Limit
0. 1 to 1 ppmv
005 to 05
ppmx
0 OS-OS
ppmx
1-IOppmv
OSppmv
0 Sppmv
01 to 100
ppbv
0.1 to 100
ppbv
10- 100 ppbv
0. 1 ppmv (as
N)
Comment
Sensitivity and selectivity highly
dependend on components of
interest.
Sensitivity and selectivity similar
to detector tubes.
Sensitivity and selectivity similar
to detector tubes.
Some inorganic gases (H2). CO)
will be detected and therefore
are potential interferences.
Responds uniformly to most
organic compounds on a carbon
basis.
Qualitative as well as
quantitative information
obtained.
Selectivity can be adjusted by
selections of lamp energy
Aromatics most readily
detected.
Response various widely from
compound to compound
Both inorganic and organic
sulfur or phosphorus
compounds will be detected
Inorganic nitrogen compounds
will interfere.

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     Table  11*3 provides a list of organic screening methodologies suited for
detection of methane. Commercial monitoring equipment (direct reading) suitable
for screening application are also available specifically for carbon dioxide, and
sulfur dioxide. Similar field screening equipment are available for oxygen in order
to check for the potential for intrusion of ambient  air into the subsurface gas
monitoring well. These sere ening monitors are available from most major industrial
hygiene equipment vendors. Direct reading gas detection (e.g., draeger) tubes are
also available for methane  and other subsurface gas indicators  for screening
applications.

     It is important that all monitoring procedures be fully documented and
supported with adequate QA/QC  procedures.   Information should  include;
locations and depths of sampling points, methods used (including sketches and
photographs),  survey  instruments used,  date and time, atmospheric/soil
temperature, analytical  methods, and laboratory used, if any.  Also see Section 4
(Quality Assurance and Quality Control).

     The three basic monitoring techniques available for sampling subsurface gas;
above  ground air monitoring, shallow borehole monitoring,  and gas well
monitonng are summarized below.

11.6.1    Above Ground Monitoring

     This technique consists of the collection of samples of the subsurface gas after
it has migrated out of the soil or into engineered structures (e.g., within buildings
or along under-ground utility lines.).  Basically, there is no difference  in the
apparatus from that described for ambient air monitoring  (Section 12).  The
locations at which sampling is  conducted, however, are selected to  focus on areas
where  gases might accumulate. Sampling methods  can utilize various types and
brands of portable direct-reading survey instruments (see Table  11-5).  However,
since methane gas is frequently the  major component of the soil gas, those which
are most sensitive to  methane, such  as expiosimeters and  FID organic vapor
analyzers, are the preferred instruments. More selective air sampling  methods are
used, however, for constituent analyses (see Section 12 - Air Methods).
                                   11-37

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11.6.2    Shallow Borehole Monitoring

     Shallow borehole monitoring involves subsurface gas monitoring to depths of
up to 6 feet below the ground surface.  Bar punches or metal rods which can be
hand-driven or hammered into the ground are used to make boreholes from which
gas samples are removed.  Table 11-6 provides the basic procedure for shallow and
deep subsurface monitoring techniques. Sample collection should follow the same
methods employed during above ground monitoring.

     Shallow borehole monitoring, as previously discussed, is a rapid screening
method and, therefore, has its limitations. Two major limitations are that negative
findings cannot assure the absence of a release at a greater depth and that air
intrusion  can dilute the measured concentration levels  of the sample. Misleading
results can also be obtained if the surface soil layer is contaminated (e.g., due to a
spill).

11.6.3    Gas Well Monitoring

     Monitoring gas within wells will involve  either the lowering of a sampling
probe (made of a rtonsparking material) through a sealed cap on the top of the well
to designated depths, or the use of fixed-depth monitoring probes (see Figure 11 -3
and Table  11-6).  The probe  outlet is usually  connected to the desired gas
monitoring instrument. More information on  gas well monitoring is provided in
Sections 9 (Soil) and 10 (Ground Water).

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                                Table 11-6
                      Subsurface Sampling Techniques
SHALLOW (Up to 6 ft deep)

        Select sampling locations based on soil data and existing monitoring
         data.

     *   Penetrate soil to desired depth. A steel rod 1/2 to 3/4 inch diameter and a
         heavy hammer are sufficient.  A bar punch equipped with insulated
         handles is better for numerous holes. It is a small, hand operated pile
         driver with a sliding weight on the top. Hand augers may also be used.

        Insert inert (e.g.. Teflon) tubing to bottom of hole.  Tubing may be
         weighted or attached to a small diameter stick to assure that it gets to
         the bottom of the hole.  Tubing should lie perforated along bottom few
         inches to assure gas flew.

        Close top of hole around tubing using a gas impervious seal.

        Before sampling record well head pressure.

     *   Readings may be taken immediately after making the barhole.

     *   Attach meter or sampling pump and evacuate hole of air-diluted gases
         before recording gas concentrations or taking samples.

        When using a portable meter, begin with the most sensitive range (0-100
         percent by volume of the lower explosive limit (LED for methane). If
         meter is pegged, change to the next least sensitive range to determine
         actual gas concentration.

        Tubing shall be marked, sealed, and protected if sampling will be done
         later.
                                   11-39

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                          Table 11-6 (Continued)
                      Subsurface Sampling Techniques
     *   If results are erratic the hole should be plugged and further readings
         taken a few minutes later.

        Monitoring should be repeated a day or two after probe installation to
         verify readings.

DEEP (More Than 6 ft deep)

     *   Same general procedures as above.

     *   Use portable power augers or truck-mounted augers.

        For permanent monitoring points, use rigid tubing (e.g., Teflon) and the
         general construction techniques shown in Figure 11-4.

CAUTION

     *   When using hand  powered equipment, stop if any unusually high
         resistance is met. This resistance could be from P. gas pipe or an electrical
         cable.

        Before using powered  equipment, confirm  that there are  no
         underground utilities in  the location(s) selected (see  Appendix C -
         Geophysical Techniques).

     *   Use non-sparking equipment and procedures and monitor for methane
         explosive limits.

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11.7 Checklist

                        RFI Checklist- Subsurface Gas
Site Name/Location  	
Type of Unit        	
1.    Does waste characterization include the following information?      (Y/N)
            Physical form of waste                                 	
            Chemical composition and concentrations                	
            Presence of biodegr deable waste components           	
            Quantities managed and dates of receipt                 	
            Locatio n of wastes i n  u n it                               	
            Waste material moisture content and temperature        	
            Chemical and physical properties of constituents          	
              of concern

2.    Does unit characterization include the following information?       (Y/N)
            Age of unit                                           	
            Construction integrity                                 	
            Presence of liner (natural or synthetic)                   	
            Location relative to ground-water table or bedrock or     	
              other confining barriers
            Unit operation data                                   	
            Presence of cover or other surface covering to impede     	
              vertical gas migration
            Presence of gas collection system                        	
            Presence of surrounding structures such as buildings      	
              and utility conduits
            Depth and dimensions of unit                          _____
            Inspection records                                    	
            Operation logs                                       	
            Past fire, explosion, odor complaint reports              	

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                   RFI Checklist - Subsurface Gas (Continued)
            Existing gas/ground-water monitoring data
         *   Presence of natural or engineered barriers near unit
         *   Evidence of vegetative stress
3.    Does environmental setting information include the following
     information?                                                  (Y/N)
            Definition of regional climate                          	
            Definition of site-specific meteorological conditions       	
            Definition of soil conditions                            	
            Definition of site specific terrain                        	
            Identification of subsurface gas migration routes         	
            Identification of location of engineered conduits         	
         *   Identification of surrounding structures                 _____

4.    Have the following data on the initial phase of the release
     characterization been collected?                                 (Y/N)
            Extent and configuration of gas plume                  	
            Measured methane and gaseous constituent             	
              concentration levels in subsurface soil and
              surrounding structures
            Sampling locations and schedule                       	

5.    Have the following data on the subsequent phase(s) of the release   (Y/N)
     characterization been collected?
         *   Extent and configuration of gas plume                  	
         *   Measured methane and gaseous constituent
              concentration levels in subsurface soil and surrounding   	
              structures
            Sampling locations and schedule       .                	

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11.S References

National Climatic Data Center, local Climatoloqical Data - Annual Summaries
     with Comparative Data. National Oceanic and Atmospheric Administration.
     published annually. Asheville, N.C.

National Climatic Data Center. Climates of the States. National Oceanic
     and Atmospheric Administration. Asheville, N.C.

National Climatic Data Center. Weather Atlas of the United States.
     National Oceanic and Atmospheric Administration. Asheville, N.C.

South Coast Air Quality Management District.  1986. Hazardous Pollutants in
     Class II Landfills. El Monte, California.

U.S. EPA. October 1986.  RCRA Facility Assessment Guidance.  NTIS PB87-107769.
Office of Solid Waste. Washington, D.C. 20460.

U.S. EPA. 1983. Guidelines for Monitoring Indoor Air Quality.  EPA-60014-83-046.
     NITS PB83-264465.  Office of Research and Development.  Washington, D.C.
     20460.

U.S. EPA. January 1981. Guidance Manual for the Classification of Solid Waste
     Disposal Facilities.  NTIS P881 -218505. Office of Solid Waste. Washington, D.C.
     20460.

U.S. EPA. 185. Technical Guidance for Corrective Measures - Subsurface Gas.
     Office of Solid Waste. Washington, D.C  20460.
                                   11-43

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      APPENDIX C





GEOPHYSICAL TECHNIQUES

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                               APPENDIX C

                        GEOPHYSICAL TECHNIQUES

   The methods presented in this Appendix have been drawn primarily from two
sources. The first. Geophysical Techniques for Sensing Buried Wastes and Waste
Migration (Technos. Inc., 1982) was written specifically for application at hazardous
waste sites, and for an audience with  limited technical background.  All of the
surface geophysical methods discussed below can be found in this document. The
second, Geophysical Explorations (U.S. Army Corps  of Engineers, Engineering
Manual 1110-1-1802, 1979) Is a more generic application-oriented  manual which
contains the borehole methods described in this section.

   Caution  should be exercised in the  use of geophysical methods involving the
introduction or generation of an electrical current, particularly when contaminants
are known or suspected to be present which  have ignitable or explosive properties.
The borehole methods are of particular concern due to the possible build up of
large amounts of explosive or ignitable gases (e.g., methane).

ELECTROMAGNETIC SURVEYS

   The electromagnetic (EM)* method provides a means of measuring the electrical
conductivity of subsurface soil, rock, and ground water. Electrical conductivity is a
function of the type of soil and rock, its porosity, permeability, and the fluids which
fill the pore space. In most cases the conductivity (specific conductance) of the pore
fluids will dominate the measurement.  Accordingly, the EM method is applicable
both to assessment of natural geohydrologic conditions and to mapping of many
types of contaminant plumes. Additionally, trench boundaries, buried wastes and
drums, as well as metallic utility lines can be located with EM techniques.
*The term "electromagnetic" has been used  in contemporary literature as a
descriptive term for other geophysical methods, including ground penetrating
radar and metal detectors which are based on electromagnetic principles. However,
this document will use electromagnetic (EM) to specifically imply the measurement
of subsurface conductivities by low frequency electromagnetic induction. This is in
keeping with the traditional use of the term in the geophysical industry from which
the EM methods originated.

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   Natural variations in subsurface conductivity may be caused by changes in soil
moisutre content, ground water specific conductance, depth of soil cover over rock,
and thickness of soil and rock layers.  Changes in basic soil or rock types, and
structural  features such as fractures or voids may  also  produce changes in
conductivity. Localized deposits of natural organics, clay, sand, gravel, or salt- rich
zones will also affect subsurface conductivity.

   Many contaminants will produce an increase in free ion concentration when
introduced into the soil or ground water systems.  This increase over background
conductivity enables detection and mapping of contaminated soil and ground
water at hazardous waste sites. Urge amounts of organic fluids such as diesel fuel
can displace the normal soil moisture, causing a decrease in conductivity which may
also be mapped, although this is not commonly done. The mapping of a plume will
usually define  the local  flow  direction of contaminants. Contaminant migration
rates can be estimated by comparing measurements taken at different times.

   The absolute values of conductivity for geologic materials (and contaminants)
are not necessarily diagnostic in themselves, but the variations in conductivity,
laterally and with depth, art  significant.  It is these variations which  enable the
investigator to rapidly find anomalous conditions (See Figure C-1).

   At hazardous waste sites, applications of EM can provide:

       Assessment of natural geohydrologic conditions;

   *    Locating and mapping of burial trenches and pits containing drums and/or
        bulk wastes;

   *    Locating and mapping of plume boundaries;

   *    Determination of flow direction in both unsaturated and saturated zones;
                                    C-3

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Coil
                          FliLO
                  INOUCCO
                  CURRENT
                   LOOPS
                                               WOUND  SURFACE
 SECONDARY FIELDS
FROM CURRENT LOOPS
    SENSED BY
   RECEIVER COIL
 Figure C-1. Block diagram showing EM principle of operations.

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       R :t of plume movement by comparing measurements taken at  different
        times; and

   *    Locating and mapping of utility pipes and cables which may affect other
        geophysical measurements, or whose trench may provide a pathway for
        contaminant flow.

   Chapter V of Geophysical Techniques for Sensing Buried Wastes and Waste
Migration Q ethnos. Inc., 1982) should be consulted for further detail regarding use,
capabilities, ar.d limitations of electromagnetic surveys.

SEISMIC REFRACTION SURVEYS

   Seismic refraction techniques are used to determine the thickness and depth of
geologic layers  :nd the travel time or velocity of seismic waves within the layers.
Seismic refractior methods are often used to map depths to specific horizons such
as bedrock, clay is ten, and the water table.  In addition to mapping natural
features, other secondary applications of the seismic method include the locations
and definition of bu >al pits and trenches.

   Seismic waves transmitted into the subsurface travel at different velocities in
various types of soil and rock, and are refracted (or bent) at the interfaces between
layers.  This  refraction effects their path of travel.  An  array  of geophones
(transducers that respond to the motion of the ground} on the surface measures the
travel timt of the seismic waves from the source to the geophones at a number of
spacings.  The time required  tar the wave  to complete this path is measured,
permitting a determination to be made of the number of layers, the thicknesses of
the layers and their depths, as well a* the seismic velocity of each layer.  The wave
velocity in each layer is directly related to its material properties such as density and
hardness. Figure C-2 depicts the seismic refraction technique.

   Seismic refraction can be used to define natural geohydrologic conditions,
including thickness and depth of soil and rock layers, their composition and physical
properties, and depth to  bedrock or the water table. It can also be used for the
detection and location of anomalous features, such as pits and trenches and for
evaluation of the depth of burial sites or landfills.
                                    C-5

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                                                                                        Hammer
                                                                                         Some*
a*
             Figure C-2.  Filed layout of a 12-channel seismograph showing the path of direct
                         and refracted seismic waves in a two-layer soil/rock system

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   Specific details regarding the use of seismic  refraction surveys,  and the
capabilities and limitations of this method can be  found  in Chapter VII  of
Geophysical Techniques for Sensing Buried Wastes and Waste Migration (Technos,
Inc.. 1982).

RESISTIVITY SURVEYS

   The resistivity method is used to measure the electrical resistivity of the
geohydroiogic section which includes the soil, rock, and ground water. Accordingly,
the method may be used to assess lateral changes and vertical cross* sections of the
natural geohydroiogic settings. In addition, it can be used to evaluate contaminant
plumes and locate buried wastes at hazardous waste sites. Figure C-3 is a graphical
representation of the concept of a resistivity survey.

   Applications of the resistivity method at hazardous waste sites include:

       Locating and mapping contaminant plumes;

   *    Establishing direction and rate of flow of contaminant plumes;

   *    Defining burial sites by:
        -  locating trenches,
        -  defining trench boundaries, and
        -  determining the depths of trenches; and

   *    Defining natural geohydroiogic conditions such as:
        -  depth to water table or to water-bearing horizons; and
        -  depth to bedrock, thickness of soil, etc.

   Chapter VI of Geophysical Techniques for Sensing  Buried  Wastes and Waste
Migration (Technos. Inc.,  1982), discusses methods, use, capabilities, and limitations
of the resistivity method.
                                    C-7

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              Currtnt  Plow
             Through Earth
                                         Currtnt
                                         Voltaqt
                                                        Surf act
Figure C-3. Diagram showing basic concept of resistivity measurement.

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GROUND PENETRATING RADAR SURVEYS

   Ground penetrating radar (GPR)* uses high frequency radio waves to acquire
subsurface information.  From a small antenna which is moved slowly across the
surface of the ground, energy is radiated downward into the subsurface, then
reflected back to the receiving antenna, where variations in the return signal are
continuously recorded. This produces a continuous  cross-sectional "picture" or
profile of shallow subsurface conditions.  These responses are caused by radar wave
reflections from interfaces of materials Having different electrical properties. Such
reflections are often associated with  natural geohydrologic conditions such as
bedding, cementation, moisture and clay content, voids, fractures, and intrusions,
as welt as man-made objects. The radar method has been used at numerous sites to
evaluate natural soil and rock conditions, as well as to detect buried wastes. Figure
C-4 depicts the ground penetrating radar method.

   Radar responds to changes in soil and rock conditions. An interface between
two soil or rock layers having sufficiently different electrical properties will show up
in the radar profile. Buried pipes and other discrete objects will also be detected.

   Radar has effectively mapped soil layers, depth  of bedrock, buried  stream
channels, rock fractures, and cavities in natural settings. Radar applications include:

   *    Evaluation of the natural soil and geologic conditions;

   *    Location and delineation of buried waste materials, including both bulk
        and drummed wastes;
*GPR has been called by various names: ground piercing radar, ground probing
radar, and subsurface impulse radar. It is also known as an electromagnetic method
(which  in fact it is); however, since there are many other methods which are also
electromagnetic, the term GPR  has come into common use today, and is used
herein.
                                    c-i

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       ANTfNNA
                 5-300 Mt*r
                    Caw*
        0
        0
        0
        o
                     TAPf HfCOROEK
                                             iXOUND SURFACE
                            OIL
                    .ux
/r
                                    \
                          woe
Figure O4.  ilodi diagram of ground penetrating radar system.Radar waves art
           relfected from soil/rock interface.

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   *    Location and delineation of contaminant plume areas; and

       Location and mapping of buried utilities (both metallic and nonmetallic).

   In areas where sufficient ground penetration is achieved, the radar method
provides a powerful assessment tool.  Of the geophysical methods discussed in this
document, radar offers the highest resolution. Ground penetrating radar methods
are further detailed in Chapter IV of Geophysical Techniques for Sensing Buried
Wastes and Waste Migration (Technos, Inc., 1982), as are this method's capabilities
and limitations,

MAGNETOMETER SURVEYS

   Magnetic measurements are commonly used to map regional geologic structure
and to explore for minerals. They are also used to locate pipes and survey stakes or
to map archeological sites. In addition, they are commonly used to locate buried
drums and trenches.

   A magnetometer measures the intensity  of the earth's magnetic field.  The
presence of ferrous  metals creates variations in the local strength  of that field,
permitting their detection. A magnetometer's response is proportional to the mass
of the ferrous target. Typically, a single drum can be detected at distances up to 6
meters, while massive piles of drums can be detected at distances up to 20 meters or
more. Figure C 5 shows the use of a magnetometer in detecting a buried drum.

   Magnetometers may be used to:

   *    Locate buried drums;

   *    Define boundaries of trenches filled with ferrous containers;

   *    Locate ferrous underground utilities, such as iron pipes or tanks, and the
        permeable pathways often associated with them; and
                                   C-11

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Figure C-5.   Simplified block diagram of a magnetometer.  A magnetometer
            senses change in the earth's magnetic field due to buried iron drum.

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Electrical Surveys

   The two types of electrical subsurface surveys of geotechmcai interest, both of
which involve continuous logging with depth of the electrical characteristics of the
borehole walls, are the spontaneous potential log and the borehole resistivity log.

   The spontaneous potential log (also known as self potential) is a record of the
variation with depth of naturally occurring electrical potentials (voltages) between
an electrode at the depth in a fluid filled borehole and another at the surface.

   The known origins for spontaneous potentials arise frm the relative mobility and
concentrations of the different elemental ions dissolved in the borehole fluid and
the fluid in adjacent strata. The electrochemical activities of the minerals in the
strata also cause a component of the measured spontaneous potentials (Figure C-6).
The relative senses and magnitudes of the several causes from which spontaneous
potentials arise are affected by the  nature  of the borehole fluid,  by the
mineralogical characteristics of all the strata the borehole penetrates, and by the
dissolved solid concentration in the ground water in all potential layers,

   The second type of electric survey is the electrical resistivity log. The electrical
resistivity of strata is one of the  basic parameters that  correlates to lithology and
hydrology. Direct access to individual layers of the subsurface materials by means of
the borehole is the primary advantage of electrical resistivity logging over the more
indirect use of apparent electrical resistivity surveys from the surface.

   Electrical current can be passed through in situ earth materials between two
electrodes. Electric fields created within the three dimensional earth medium are
related  to the medium's structure and  the nature of the aqueous fluid in the
medium.  Figure C-? demonstrates the conceptual field  configuration for borehole
electrical resistivity survey.

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      1AMO

                                           VOLT
                                          MKTtft
                                          HUB
                                                HfTAMCK
                                               HKHSTAMCt
                                          VIV.THATI  MIST AMCC
Figure C-6.   Conceptual tquivalent drcuit for self-potential data (prepared by the
            Waterways Experiment Station, U.S.  Army Corps of Engineers.
            Vicksburg, Mississippi).

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             IMSULATO
Figure C-7.    Singl-point reststanc* log (prepared by the Waterways Experiment
             Station, U.S. Army Corps of Engineers, Vicksburg, Mississippi).
                                   C-16

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   Resistivity logging is a valuable tool in correlating  beds from borehole to
borehole. In addition, they can be used together with knowledge of ground water
and rock matrix resistivities (obtained from samples) to calculate porosities and/or
water saturations.  Also, if porosity is known  and a borehole temperature log is
available, contaminant concentrations can be inferred by electrical resistivity
variations.

Nuclear logging

   Nuclear borehole logging can be used quite effectively for borehole depths
ranging from 10 to more than 1,000 feet.  At  considerable depths, as for large
buried structures, nuclear logging is a very effective means of expanding a small
number of data  points obtained from direct  measurements on  core  samples to
continuous records of clay content, bulk density, water content, and/or porosity.
The logs are among the simplest to perform and interpret, but the  calibrations
required for meaningful quantitative interpretations must be meticulously
complete in attention to detail and consideration of all  factors affecting nuclear
radiation in earth materials.  Under favorable conditions, nuclear measurements
approach the precisions of direct density tests on rock cores. The gamma-gamma
density log and the neutron water content log require the use of isotopic sources of
nuclear radiation.  Potential radiation  hazards mandate thorough  training  of
personnel working around these sources. Strict compliance with U.S. NRC Title 10,
Part 20, as well as local safety regulations, is required. Additional information on
natural gamma, gamma-gamma, and neutron gamma methods is provided below.

   The natural gamma radiation tool is a passive device measuring the amount of
gamma radiation naturally occurring in the strata being logged. The primary
sources of radiation are trace amounts of the potassium isotope K*o and isotopes of
uranium and thorium.  K*o is most prevalent, by far, existing as an average of 0.012
percent by weight of all potassium.  Because potassium is part of the crystal lattices
of illites, micas, montmorillanites, and other clay materials, the engineering gamma
log is mainly a qualitative indication of the clay content of the strata.

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   The natural gamma log is  put to  its simplest and most frequently  used
applications in qualitative lithologic interpretation (specifically identification of
shale and clay layers) and bed correlations from hole to hole. Since clay fractions
frequently reduce the primary porosity and permeability of sediments, inferences as
to those parameters may sometimes be possible from the natural  gamma log
Environmentally based surveys may utilize the log for tracing radioactive pollutants.
If regulatory restrictions allow the use of radioactive tracers, the natural gamma log
can be used to locate ground water flow paths. The natural gamma radiation level
is also a correction factor to the gamma-gamma density log.

   In the gamma-gamma logging technique, a radioactive source and detector are
used to determine density variations in the borehole.  An isotopic source of gamma
radiation can be placed on the  gamma radiation  tool and shielded so that direct
paths of that radiation from source to detector are blocked.  The source radiation
then permeates the space and materials near itself.  As the gamma  photons pass
through the matter, they are affected by several factors among which is "Compton
scattering." Part of each photon's energy is lost to orbital electrons in the scattering
matt-rial.  The  amount of scattering is proportional to the  number of electrons
present. Therefore, if the portion of radiation able to escape through the logged
earth materials without being widely scattered and de-energized is measured, then
that is an inverse active measure of electron density, A schematic representation of
the borehole gamma-gamma tool is shown in Figure C-8.

   The neutron water detector logging method is much like the  gamma-gamma
technique in that it uses a radioactive source and detector. The difference is that
the neutron log measures  water content rather than density of the borehole
material.  A composite isotopic source of neutron radiation can  be placed on  a
probe together with a neutron detector.  A neutron has about the same mass and
diameter as a hydrogen nucleus and is much lighter and smaller than any other
geochemically  common nucleus.  Upon  collision with a hydrogen nucleus the
ntutron loses about half its kinetic energy to the nucleus and is slowed down as well
as scattered. Collision with one  of the larger nuclei scatters the  neutron  but
does not slow it. After a number of collisions with hydrogen nuclei, a neutron  is
slowed, or it is captured by a hydrogen atom and produces a secondary neutron
emission of thermal energy plus a secondary gamma photon.  Detectors can be
"tuned " to be sensitive to the epithermal (slowed) neutron or to the thermal
                                   C-18

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                     II
                   /\
Figure C-8.  Schematic of the borehole gamma-gamma density tool (prepared by
           the Waterways Experiment Station, U.S. Army Corps of Engineers,
           Vicksburg. Mississippi).

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neutron or to the gamma radiation. One of these detectors plus the neutron source
is then a device capable of measuring the amount of hydrogen in the vicinity of the
tool. In the geologic environment, hydrogen exists most commonly in water (H2O)
and in hydrocarbons.  If it can be safely assumed that hydrocarbons are not present
in appreciable amounts, then the neutron-epithermal neutron, the neutron-
thermal neutron, and the neutron-gamma  logs are  measures of the amount of
water present if the tool  is calibrated in terms of its response to saturated  rocks of
various porosities.

   The neutron log can  be used for hole to hole stratigraphic correlation. Its
designed purpose is to measure water quantities in the formation. Therefore, the
gamma-gamma density, the neutron water detector, the  natural gamma,  and the
caliper logs together form a "suite" of logs that, when taken together, can produce
continuous interpreted values of water content, bulk density, dry density, void ratio,
porosity, and pecent of water saturation.

Seismic Surveys

   The principles involved  in subsurface  seismic surveys are the same as  those
discussed earlier under surface seismic surveys. The travel  times for P- and S- waves
between source and detector are measured, and wave velocities are determined on
the basis of theoretical travel paths. These calculated wave velocities can  then be
used to  complement and supplement other geophysical surveys conducted in the
area of investigation.

   Three common types  of borehole seismic surveys are  discussed in this section.
They include Uphoie  and Down hole surveys, Crosshole Tests, and Vertical Seismic
Surveys. The applications and limitations are discussed for each of these methods.

   In the uphole and downhole seismic survey, a seismic signal travels between a
point in a borehole and a point on the ground near the hole. In an uphole survey
the energy source is in the borehole, and  the detector on the ground surface; in a
downhole survey, their positions are reversed. The raw data obtained are the travel
times for this signal and distances between the seismic source and the geophones.
A plot of travel time versus depth yields, from the slope of the curve, the average
                                   C-20

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wave propagation velocities at various intervals in the borehole. Figure C-9 depicts a
downhole seismic survey technique.

   Uphole and  downhole surveys are usually performed to complement other
seismic tests and provide redundancy in a geophysical test  program.   However,
because these surveys force the seismic signals to traverse all of the strata between
the source and detector, they provide a means of detecting features, such as a low
velocity layer underlying a higher velocity layer of a "blind" or  "hidden" zone (a
layer with insufficient thickness and  velocity contrast to be detected by surface
refraction).

   Crosshole tests are conducted to determine the P- and S-wave velocity of each
earth material or layer within the depth of interest through the measurement of
the arrival time  of a seismic signal that has traveled from a source in one borehole
to a detector in another. The crosshole test concept is shown in Figure C-10.

   In addition to providing true P- and S-wave velocities as a function of depth,
their companion purpose is to detect seismic anomalies, such as a lower velocity
zone underlying a  higher velocity zone or a layer with insufficient thickness and
velocity contrast to be detected by surface refraction seismic tests.

   The vertical seismic profiling technique involves the recording of seismic waves
at regular and closely spaced geophones in the borehole. The surface source can be
stationary or it can  be moved  to evaluate  seismic travel times to borehole
geophones, calculate velocities, and determine the nature of subsurface features in
the vicinity of the borehole.

   Vertical seismic profiling surveys are different  from downhole  surveys in that
they provide data on not only direct path seismic signals, but reflected signals as
well. By moving the surface source to discrete distances and azimuths from the
borehole, this method provides  a means of characterizing  the  nature  and con-
figuration of subsurface  interfaces (bedding, ground water table, faults), and
anomalous velocity zones around the borehole.

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           '**  ". ""^. .*    v  _>-iCis  ^TT
           r-   ^if-.*.<-^r^r- ,-**
Figure C-9.   Downhol* survey techniques far P-wav data (prepared by the
            Waterways Experiment Station. U.S. Army Corps of Engineers,
            Vickjfaurg, Mississippi).
                                 C-22

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                             ftlCOKOI*
        Y
        AX
! ! I  'sound
in
Figure C-10.  Basic crossholt test concept (prepared by the Waterways Experiment
           Station, U.S. Army Corps of Engineers, Vicksburg, Mississippi).
                               C-23

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   The interpretation of processed vertical seismic profiling data is used  in
conjunction with surface seismic surveys as well as other geophysical surveys in the
evaluation of subsurface lithology, stratigraphy, and structure.  Vertical seismic
profiling survey interpretations also provide a basis for correlation between
boreholes.

Sonic Borehole Surveys

   In this section, two types of continuous borehole  surveys involving high
frequency sound wave propagation are discussec.  Sound waves are physically
identical to seismic P-waves. The term sound wave is usually employed when the
frequencies include the audible range and the propagating medium is air to water.
Ultrasonic waves are also physically the same, except that the frequency range is
above the audible range.

   The Sonic borehole imagery log provides a record of the surface configuration of
the cylindrical wall of the borehole.  Pulses of high frequency sound are used in a
way similar to marine sonar to probe the wall of the borehole and, through
electronic and photographic means, to create a visual  image representing the
surface configuration of the borehole wall. The physical principle involved is wave
reflection from  a  high impedance surface, the same principle used  in reflection
seismic surveying and acoustic sub bottom profiling. The sonic borehole imagery
logging concept is depicted in Figure C-l \.

   The sonic borehole imagery log can be used to detect discontinuities in
competent rock lining the borehole. Varying lithologies, such as shale, sandstone,
and limestone,  can sometimes be distinguished on high quality  records by  ex-
perienced personnel.

   Another method of sonic borehole logging is referred to as the continuous sonic
velocity logging technique. The continuous sonic velocity togging device is used to
measure and record the transit time of seismic waves along  the borehole wall
between two transducers as it is moved up or down the hole. A diagram of the
continuous sonic velocity logging device is provided in Figure C-12.
                                   C-24

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                                            IMAOIMC OCVlCf
                                             o  o   o
                                         ABOVf "
                                         OM
                                         WITN
                                                   QlNCCTlOMS
Figure C-11.  Sonic imagery logger (prepared by th Wittrways Exptriment
            Station, U.S. Army Corp of Engineers, Vicksburg, Mississippi).

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              *MMtI{ IMIATM
                  ttdlVU
              Mllll* ril ,.._
                                            I
                                                   SI-
Figure C-12.  Diagram of three-dimensional velocity tool (courtesy of Seismograph
             Service Corporation, Birdwell Division).
                                     C-26

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   This subsurface logging method provides data on fractures and abrupt lithology
changes along the borehole wall that can be effective in characterizing the nature
of surrounding material as well as borehole correlation in lithology and structure.

Auxiliary Surveys

   An auxiliary survey is the direct measurement of some parameter of the
borehole or its contained fluid to provide information that will  either permit the
efficient evaluation of the lithology penetrated by the  boring or aid in the
interpretation or reduction of the data from other borehole logging operations. In
most instances, auxiliary logs are made where the property recorded is essential to
the quantitative evaluation of other geophysical logs. In some instances, however,
the auxiliary results can be interpreted and used directly to infer the existence of
certain lithologicor hydrologic conditions.

   Discussed here are three different auxiliary logs; fluid temperature, caliper, and
fluid resistivity, that are especially applicable to the  logging methods discussed in
this text. A description of each auxiliary log is presented below

   Temperature logs are the continuous records of the temperature encountered at
successive  elevations in a  borehole.  The two basic types of temperature logs are
standard (gradient) and differential. Both types of logs rely upon a downhole
probe, containing one or more temperature sensors (thermistors) and surface
electronics to monitor and  record the temperature changes encountered in a
borehole.   The standard temperature log is the result of  a  single thermistor
continuously sensing the thermal gradient of the fluid in the borehole as the sonde
is raised or lowered in the hole.  The  differential  temperature log depicts the
difference in temperature over a fixed interval of depth  in the borehole by
employing two thermistors spaced from one to several feet apart or through use of
a single thermistor and an electronic memory to compare the temperature at one
depth with that of a selected previous depth.
                                    C-27

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   Temperature logs provide useful information in both cased and uncased borings
and are necessary for correct interpretation of other geophysical logs (particularly
resistivity logs).  Temperature logs can also be used directly to indicate the source
and movement of water into a borehole, to identify aquifers, to locate zones of
potential recharge, to determine areas containing wastes discharged into the
ground, and to detect sources of thermal pollution.  The thermal conductivity and
permeability of  rock formations can be inferred from temperature fogs as can be
the location of grout behind casing by the presence of anomalous zones of heat
buildup due to the hydration of the setting cement.

   The caliper log is a record of the changes in  borehole casing or cavity size as
determined by a highly sensitive  borehole measuring device.  The record may be
presented in the form of a continuous vertical profile of the borehole or casing wall,
which  is obtained with normal  or standard  caliper logging systems, or as a
horizontal cross section at selected depths, used  for measuring voids or large
subsurface openings.  There are two basic methods of obtaining caliper logs. One
technique utilizes mechanically activated measuring arms or bown springs, and the
other employs  piezoelectric transducers for sending  and receiving a  focused
acoustic signal. The acoustic method requires that the hole be filled with water or
mud, but the mechanical method operates equally well in water,  mud, or air.
Reliable mechanically derived caliper logs can be  obtained in small (2 in.) diameter
exploratory borings as well as large {36 in.) inspection or access calyx-type borings.

   Caliper or borehole diameter logs represent one of the most useful and possibly
the simplest of all techniques employed  in borehole geophysics. They provide a
means  for determining in hole conditions and should be obtained in all borings in
which other geophysical logs are contemplated.  Borehole diameter logs provide
information on  subsurface lithology and rock quality.  Borehole diameter varies
with the hardnes*. fracture frequency, and cementation of the various beds
penetrated. Borehole diameter logs can be used  to accurately identify zones of
enlargement (washouts) or construction (swelling), or to aid in the structural
evaluation of an area by the accurate location of  fractures or solution openings,
particularly in borings where core loss has presented a problem.  Caliper logs also
are a means of identifying the more porous zones in a boring by locating the
intervals in which  excessive mud fitter cake  has built up on the walls of  the
borehole. One of the major uses of standard or borehole caliper logs is to provide
                                   C-28

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information by which other geophysically derived raw data logs can be corrected
for borehole diameter effects.  This is particularly true for such nonfocused iogs as
those obtained in radiation logging or the quantitative evaluation of flowmeter
logs or tracer and water quality work where inhole diameters must be considered.
Caliper logs also can be useful to evaluate inhole conditions for placement of water
well screens or for the selection of locations of packers for permeability testing.

   The fluid resistivity log is a continuous graphical record of the resistivity of the
fluid within a borehole.  Such  records are made by measuring the voltage drop
between two closely spaced electrodes enclosed within a downhole probe through
which a representative sample of the borehole fluid is channeled.  Some systems,
rather than recording in units of resistivity, are designed to provide a log of fluid
conductivity. As conductivity is merely the reciprocal of resistivity, either system can
be used to collect the information on inhole fluid  required for the correct
interpretation of other downhole logs.

   The primary use of fluid resistivity or conductivity logs is to provide information
for the correct interpretation of other borehole logs. The evaluation of nuclear and
most electrical logs requires corrections for salinity of the inhole fluids, particularly
when quantitative parameters are desired for determining porosity from formation
resistivity iogs.
                                    C-29

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             APPENDIX D

   SUiSURFACE GAS MIGRATION MODEL
           ADAPTED FROM
GUIDANCE MANUAL FOR THE CLASSIFICATION
   OF SOLID WASTE DISPOSAL FACILITIES
            U.S. EPA. 1981
                 0-1

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                               APPENDIX D

                   SUBSURFACE GAS MIGRATION MODEL

METHANE MIGRATION DISTANCE PREDICTION CHARTS

   Migration distance charts have been developed to estimate methane distances
and to plan the monitoring program. The  basic methane migration  distance
prediction chart and appropriate corrective factor charts were produced by
imposing a set of simplifying assumptions  on a general methane migration
computer model.  These charts are based on a number of assumptions that were
made to produce them. Case Study Number 9  (Volume IV) illustrates the use of the
Subsurface Gas Migration Model.

   To illustrate the use of the charts, an example landfill is shown  in Figure D-1
along with two cross-sections. Conditions along each side of the waste deposit are
typical conditions that could be encountered.  A similar sketch or plan of a facility
being evaluated should be prepared. The land use within 1/4-mile of the solid waste
limits, including offsite and facility structures, should be on the map. The property
boundaries and solid waste deposit limits should also be plotted, as has been done
in Figure D-1,

   Additional data needs are:

   1.    The age of the site from the initial deposit of organic waste in years;

   2.    The average elevation of the bottom of the solid waste;

   3.    Natural boundaries and topography around the site; and

   4.    The average elevation below the solid waste of a gas impervious boundary
        such as unf ractured rock.
                                   D-2

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                CS   23  53

                        A^
                                             Rptoducd from
                                             b .viilabU eopy
Figure D-1.  Example landfill (not to scale).
                   D-3

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   Two calculations of migration distance from the waste boundary are needed for
each side of the landfill:

   1.  The 5 percent (Lower  Explosion  Limit or LED distance for property
       boundaries.

   2.  The 1.25 percent (1/4 of the LEL) distance for onsite facility structures.

   After  preparation of the  sketch and  cross-sections,  the determination of the
estimated migration distances begins with the use of Figure D-2 for the 5 percent
methane (LEL) migration distance and for the 1.25 percent (1/4 LED distance. These
distances are then modified, if necessary, with the corrective factors for each depth
and surrounding soil surface permeability (Figures D-3 and D-4)  The final distances
of migration for each side of the landfill can then be plotted on the landfill sketch
for comparison to property boundary and structures locations.

UNCORRECTED MIGRATION DISTANCES

   The use of Figure D-2 requires the age of the site and the type of soil extending
out from each side of the solid waste deposit. The graph is entered with the site
age, moving up to the appropriate soil type and methane concentration (1.25 or 5
percent). Interpolations between the sand and clay lines on the graph can be made
for other soils, using the following general guidance:
Soil Name                  USCS Classification            Chart Use
Clear, (no fines)             GW, GP, SW, SP              Sand
gravels and sands
Silty gravels and sands,       GM,SM, ML, OL, MH          Interpolate
silt, silty and sandy
loam, organic silts
Clayey gravels and          GC, SC, CL, CH, OH            Clay
sands, lean, fat, and
organic clays

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Q
en


                                                                                            R*pro0uceo from"
                                                                                            best available copy
                              Figure D-2. Five Percent and 1.25 percent methane migration distance

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    at
    *

                                                       f
                                                            MTMtf'
                                                                                  IMAM 
                                                    U       "
                                               Hi AOi-VtAM
                                                                       l<        
                     Figure D-3. Correction factors for landfill depth below grade.

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Figure D-4. Correction factors for soil surface venting condition around landfill.

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   The uncorrected migration distance from the solid waste limit can then be read
on the left for the appropriate site age and soil type.

   if the soil along a given boundary is stratified and the variability extends from
the waste deposit to the property boundary, the most permeable umaturated
thickness should be used in entering the charts.  For example, if dry, clean sand
underlies surficial silty clays, the uncorrected migration distance should be obtained
using the sand line of the chart. If there are questions as to the extent of particular
soils along a  boundary, helpful  information might be obtained from  Soil
Conservation Services (SCS) Soil Survey Maps or the landfill  operator.   Field
inspection, SCS maps,  and permit boring information are sufficient. Additional
borings are not necessary as this is only a ranking procedure.  Where there is doubt,
use the most permeable soil group present.

   For the example landfill  in Figure 0-1, the uncorrected 5 percent methane
migration distances for a 10-year old landfill would be (Figure C- 2):

   Section A-A: East side, 10 years, sand * 165'
              West side, 10 years, sand  165'

   Section B-B: South side. 10 years, sand * 165'
              North side, 10 years, clay  130'

   The corresponding uncorrected distances  for the 1.25 percent methane
migration would be:

   Section A-A: East side, 10 years, sand * 225'
              West side, 10 years, sand - 135'

   Section B-B: South side, 10 years, sand  255'
               North side, 10 years, dsy  200'

   The depth to corrective mulitpliers for the example sites would be:

   Section A-A: East side, 10 years. 20'deep  1.0
               West side, 10 years, 20'deep * 1.0
                                    0-3

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   Section B-B: South side, 10 years, 10' deep = 0.95
              North side, 10 years, SO' deep * 1 4

VENTING CONDITIONS CORRECTION

   The corrective factors for the surrounding soil venting conditions are obtained
using the chart in  Figure D-4.  This chart  is based on the assumption that the
surrounding surficial soil is impervious 100 percent of the time. Thus, the value read
from the chart must be adjusted, based on the percentage of time the surrounding
surficial soil is saturated or frozen and the percentage of land along the path of gas
migration from which gas venting to the atmosphere is blocked all year (asphalt or
concrete roads or parking lots, shallow perched ground water, surface water bodies
not interconnected to ground water).  The totally impervious corrective factor is
only used when the landfill is entirely surrounded at ail times by these conditions.
Both time and area adjustments are necessary, and the  percentages are additive.
Estimates to the nearest 20 percent are sufficient.  An adjusted corrective factor is
obtained by entering the chart with site age and obtaining the totally impervious
corrective factor for the appropriate depth and soil type and then entering this
value in the following equation:

   Adjusted corrected factor  * [(Impervious corrective factor)-1)]
                             x [5 of impervious time or area] + 1

   When free venting conditions are prevalent most of the year, simply use 1.0 (no
correction).  For depths less than 25 feet  deep, use the 25 foot value.  For the
example site, the adjusted corrective factors for frozen or wet soil conditions 50
percent of the year are:

   Section A-A: East side (ignore narrow  - (2.1-1)(0.50)  + 1 =1.55
              road, sand 20' detp,
              10 years old)

              West side (sand 20'deep,  (2.1-1X0.50)  + 1  1.55
              10 years old)
                                    D-9

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   Section B-B: South side (sand, 10'deep,   = (2.1-0(0-50)  1   1.55
               10 years old)

               North side (day, 50'deep, (1.4-1)(0.50) + 1  1.2
               10 yean old)

   Once the surface venting factors have been tabulated as in Table  D-i, the
corrective distance can be obtained by multiplying across the chart for each side of
the landfill. These values can then be plotted on the scale plan to describe contours
of the 5 percent and 1.25 percent methane concentrations or simply compared to
the distance from the waste deposit to structures of concern (Figure D-5).
                                    D-10

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                      Table D-1. METHANE DISTANCE TABULATING FORM
Landfill
Side
E

W

s

N

Methane
Concentration
5%
1.25%
5%
1.25%
5%
1,25%
5%
1.25%
Uncorrected
Distance
165'
255'
165'
255'
165'
255'
130'
200'
Correction
for Depth
X1.0
X10
X1.0
X1.0
X0.9S
X0.95
X1.4
X1.4
Correction
for Venting
XI 55
X1.55
X1 55
X1.55
XI 55
XI 55
X1.2
X1.2
Corrected Distance
= 256'
a 395'
= 2S6'*(225' max.)
- 39S'*(225'max)
 243'*(22S' max.)
= 37S'*(225'max)
= 218'
= 336'
*  When these distances are plotted on the landfill sketch, they exceed the distance to the creek, which
   acts as a barrier to the gas migration.  Thus the distance to the creek is the maximum migration
   distance.

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}


   <

                                             I

                                      r'-l
                                    J     /
    Figure D-5. Example landfill methane conditions.
                      D-12

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