OSWER DIRECTIVE 9502.00-6D
              INTERIM FINAL

RCRA FACILITY INVESTIGATION (RFI) GUIDANCE

             VOLUME II OF IV
        SOIL, GROUND WATER AND
        SUBSURFACE GAS RELEASES
            EPA 530/SW-89-031
                 MAY 1989
         WASTE MANAGEMENT DIVISION
            OFFICE OF SOLID WASTE
     U.S. ENVIRONMENTAL PROTECTION AGENCY

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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  §3004(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
regulatory agency personnel on overseeing owners or  operators  of hazardous waste
management facilities in the conduct of the  second phase of the RCRA Corrective
Action  Program, the  RCRA Facility Investigation (RFI).  Guidance is provided for the
development and  performance of an investigation by  the facility  owner  or operator
based  on determinations  made  by the regulatory agency  as  expressed  in  the
schedule of  a permit or  in an  enforcement  order  issued  under  §3008(h),  §7003,
and/or  §3013.  The purpose of the RFI is to obtain information to fully characterize
the nature,  extent  and rate of migration  of releases  of  hazardous waste  or
constituents  and  to interpret  this  information  to  determine  whether  interim
corrective measures and/or a Corrective Measures Study may be necessary.

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                                  DISCLAIMER
     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 does not establish a standard  of conduct  which has the force of  law) and should
not be used 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 meets the regulatory standard.

     Mention  of company  or  product  names  in this  document   should  not  be
considered as an endorsement by the  U.S. Environmental Protection  Agency.

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               RCRA FACILITY INVESTIGATION (RFI) GUIDANCE
                             VOLUME II
           SOIL, GROUND WATER AND SUBSURFACE GAS RELEASES
                         TABLE OF CONTENTS
SECTION
ABSTRACT                                                           i
DISCLAIMER                                                        M
TABLE OF CONTENTS                                                 m
TABLES                                                           xii
FIGURES                                                          xiii
LIST OF ACRONYMS

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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                               9-17

               9.3.2.1      Unit  Design  and Operating Characteristics      9-17

               9.3.2.2     Release  Type  (Point  or Non-Point  Source)       9-19

               9.3.2.3     Depth  of the Release                          9-20

               9.3.2.4     Magnitude  of  the  Release                      9-22

               9.3.2.5     Timing of the  Release                          9-23

          9.3.3      Characterization  of the Environmental  Setting       9-24

               9.3.3.1      Spatial  Variability                             9-25

               9.3.3.2     Spatial and Temporal Fluctuations  in Soil       9-26
                          Moisture Content

               9.3.3.3     Soil,  Liquid, and Gaseous Materials in           9-28
                          the  Unsaturated  Zone
                                       IV

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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  Climatological  Data                 9-38

          9.3.4.2    Facility  Records and  Site-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        9-43

     9.4.3      Monitoring Schedule                                    9-43

     944      Monitoring Locations                                   9-44

          9.4.4.1     Determine  Study and  Background Areas             9-44

          9.4.4.2    Determine  Location and  Number  of  Samples         9-45

          9.4.4.3    Predicting  Mobility of  Hazardous  Constituents       9-48
                    in Soil

                    9.4.4.3.1 Constituent Mobility                     9-49

                    9.4.4.3.2  Estimating  Impact  on   Ground-Water      9-51
                               Quality

9.5  DATA PRESENTATION                                              9-60

     9.5.1      Waste and Unit Characterization                         9-60

     9.5.2      Environmental Setting  Characterization                  9-60

     9.5.3      Characterization of  the  Release                          9-61

9.6  FIELD METHODS                                                   9-64

     9.6.1      Surficial Sampling  Techniques                           9-66

          9.6.1.1     Soil Punch                                         9-66

          9.6.1.2    Ring Samplers                                     9-66

          9.6.1.3    Shovels,  Spatulas,  and  Scoops                       9-67

          9.6.1.4    Soil Probes (tube  samplers)                          9-67

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                      VOLUME II CONTENTS (Continued)








SECTION                                                             PAGE






          9.6.1.5    Hand  Augers                                      9-67



     9.6.2      Deep  Sampling Methods                                9-68



          9.6.2.1     Hollow-Stem Augers                               9-68



          9.6.2.2    Solid-Stem Augers                                 9-68



          9.6.2.3    Core Samplers                                     9-68



                    9.6.2.3.1  Thin-Walled  Tube  Samplers               9-69



                    9.6.2.3.2  Split-Spoon  Samplers                    9-69



          9.6.2.4    Trenching                                        9-69



     9.6.3      Pore Water Sampling                                   9-70



9.7  SITE  REMEDIATION                                               9-72



9.8  CHECKLIST                                                      9-73



9.9  REFERENCES                                                     9-75

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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
     10.3 CHARACTERIZATION OF THE CONTAMINANT SOURCE          10-9
         AND THE ENVIRONMENTAL SETTING
         10.3.1     Waste Characterization                           10-9
         10.3.2     Unit Characterization                             10-12
         10.3.3     Characterization of the Environmental Setting       10-13
                   10.3.3.1  Subsurface  Geology                     10-55
                   10.3.3.2  Flow Systems                           10-58
         10.3.4     Sources of Existing Information                    10-63
                   10.3.4.1   Geology                               10-64
                   10.3.4.2  Climate                                10-64
                   10.3.4.3   Ground-Water  Hydrology                10-64
                   10.3.4.4  Aerial Photographs                      10-65
                   10.3.4.5  Other  Sources                           10-65
     10.4  DESIGN OF A MONITORING PROGRAM TO CHARACTERIZE       10-65
         RELEASES
         10.4.1     Objectives of the Monitoring Program               10-66
         10.4.2     Monitoring Constituents  and Indicator Parameters    10-68

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                      VOLUME II CONTENTS (Continued)

SECTION                                                             PAGE
          10.4.3     Monitoring Schedule                              10-69
                    10.4.3.1  Monitoring  Frequency                    10-69
                    10.4.3.2  Duration  of  Monitoring                   10-70
          10.4.4     Monitoring Locations                              10-71
                    10.4.4.1 Background and  Downgradient  Wells      10-75
                    10.4.4.2 Well  Spacing                             10-76
                    10.4.4.3 Depth and  Screened  Intervals             10-79
     10.5 DATA PRESENTATION                                        10-84
          10.5.1     Waste and Unit Characterization                    10-84
          10.5.2     Environmental Setting Characterization             10-85
          10.5.3    Characterization of the Release                     10-92
     10.6 FIELD METHODS                                             10-94
          10.6.1     Geophysical Techniques                            10-94
          10.6.2    Soil Boring and Monitoring Well Installation          10-95
                    10.6.2.1 Soil  Borings                              10-95
                    10.6.2.2 Monitoring  Well  Installation               10-99
          10.6.3    Aquifer Characterization                            10-101
                    10.6.3.1  Hydraulic Conductivity Tests               10-101
                    10.6.3.2 Water Level Measurements               10-103
                    10.6.3.3 Dye  Tracing                              10-105
          10.6.4    Ground-Water Sample Collection Techniques         10-105
     10.7 SITE REMEDIATION                                          10-108
     10.8 CHECKLIST                                                  10-110
     10.9 REFERENCES                                                10-113
                                    viii

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                       VOLUME II CONTENTS (Continued)



SECTION                                                              PAGE


11.0  SUBSURFACE GAS                                                 11-1


     11.1  OVERVIEW                                                  11-1

     11.2 APPROACH FOR CHARACTERIZING  RELEASES OF                n_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                             11-11

                    11.3.1.1    Decomposition  Process                    11-11

                         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  Other  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
                                     ix

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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                              11-25

                    11.4.4.1  Shallow  Borehole  Monitoring            11-25

                    11.4.4.2  Gas  Monitoring Wells                    11-26

                    11.4.4.3  Monitoring  in  Buildings                  11-28

                    11.4.4.4  Use 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 SITE REMEDIATION                                          11-38

     11.8 CHECKLIST                                                   11-42

     11.9 REFERENCES                                                  11-44

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                       VOLUME II CONTENTS (Continued)
SECTION

APPENDICES

Appendix C:

Appendix D:

Appendix E:



Appendix F:
Geophysical Techniques

Subsurface  Gas  Migration  Model

Estimation  of Basement Air  Contaminant
Concentrations  Due  to  Volatile Components in
Ground Water Seeped Into the Basement

Method  1312: Synthetic  Precipitation  Leach Test
for Soils
PAGE



C-1

D-1

E-1



F-1
                                     xi

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                                TABLES (Volume II)
NUMBER                                                                  PAGE

   9-1           Example  Strategy  for  Characterizing  Releases              9.3
                to  Soil

   9-2           Release Characterization  Tasks for Soils                    9-7

   9-3           Transformation/Transport  Processes  in  Soil                 9-10

   9-4           BODs/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                                9-55

   10-1          Example  Strategy for Characterizing Releases  to            10-4
                Ground Water

   10-2          Release Characterization Tasks for  Ground  Water          10-6

   10-3          Summary of  U.S.  Ground-Water  Regions                   10-17

   10-4          Default Values  for Effective  Porosity                       10-51

   10-5          Factors  Influencing  the  Intervals  Between  Individual        10-77
                Monitoring  Wells Within a  Potential  Migration Pathway

   10-6          Applications  of Geophysical  Methods  to  Hazardous        10-96
                Waste Sites

   10-7          Factors  Influencing  Density  of Initial  Boreholes             10-97

   11-1          Example Strategy for Characterizing Releases  of            11-4
                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
                                        XII

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                               FIGURES (Volume II

NUMBER                                                                 PAGE


   9-1           Hydrogeologic Conditions Affecting  Soil  Moisture         9-27
                Transport

   9-2           Soil Terms                                                9-30

   9-3           Hypothetical  Adsorption Curves  for A)  Cations  and B)      9-56
                Anions  Showing  Effect of pH and Organic Matter

   9-4           Fields of Stability for  Aqueous Mercury  at 25°C            9-59
                and Atmospheric  Pressure

   9-5           Example  of  a  Completed  Boring Log                       9-62

   9-6           Typical  Ceramic  Cup  Pressure/Vacuum  Lysimeter           9-71

   10-1          Occurrence  and  Movement of Ground  Water  and          10-15
                Contaminants Through  (a) Porous  Media,  (b)  Fractured
                or  Creviced  Media, (c) Fractured Porous Media

   10-2         Ground-Water  Flow  Paths in Some  Different               10-16
                Hydrogeologic Settings

   10-3         Western  Mountain Ranges                                10-18

   10-4         Alluvial   Basins                                            10-20

   10-5         Columbia Lava  Plateau                                    10-21

   10-6         Colorado Plateau                                         10-23

   10-7         High Plains                                               10-24

   10-8         Non-glaciated  Central                                    10-26

   10-9         Glaciated Central                                         10-28

   10-10        Piedmont and  Blue  Ridge                                 10-31

   10-11        Northeast and Superior  Uplands                           10-32

   10-12        Atlantic  and  Gulf  Coastal  Plain                             10-34

   10-13        Southeast Coastal Plain                                   10-37

   10-14        Hawaiian Islands                                         10-39

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                          FIGURES (Volume n-Continued)

NUMBER                                                                 PAGE


   10-15       Alaska                                                    10-41

   10-16       Alluvial Valleys                                           10-43

   10-17       Monitoring Well Placement  and Screen  Lengths  in  a        10-54
               Mature  Karst  Terrain/Fractured Bedrock Setting

   10-18       Monitoring  Well  Locations                                10-67

   10-19       Example of Using Soil Gas Analysis to  Define Probable      10-73
               Location  of  Ground-water  Release Containing Volatile
               Organics

   10-20       Vertical Well  Cluster  Placement                           10-81

   10-21        General Schematic of Multi  phase Contamination  In a      10-83
               Sand Aquifer

    10-22       Potentiometric Surface Showing  Flow  Direction            10-89

    10-23       Approximate  Flow Net                                    10-90

   11-1         Subsurface  Gas  Generation/Migration  in a  Landfill         11-9

   11-2        Subsurface  Gas  Generation/Migration  from  Tanks and      11-10
               Units Closed as  Landfills

   11-3        Schematic  of  a Deep Subsurface  Gas  Monitoring  Well      11-27
                                       X IV

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                              LIST OF ACRONYMS
AA          Atomic  Absorption
Al           Soil  Adsorption  Isotherm  Test
ASCS         Agricultural  Stabilization  and  Conservation  Service
ASTM        American Society  for Testing  and Materials
BCF          Bioconcentration  Factor
BOD         Biological  Oxygen  Demand
CAG         EPA Carcinogen Assessment Group
CPF          Carcinogen  Potency  Factor
CBI          Confidential  Business  Information
CEC          Cation  Exchange  Capacity
CERCLA      Comprehensive  Environmental  Response,  Compensation, and  Lability
             Act
CFR          Code of Federal Regulations
CIR          Color Infrared
CM          Corrective Measures
CMI          Corrective Measures  Implementation
CMS         Corrective Measures  Study
COD         Chemical Oxygen  Demand
COLIWASA   Composite  Liquid Waste Sampler
DNPH        Dinitrophenyl  Hydrazine
DO          Dissolved  Oxygen
DOT         Department  of  Transportation
ECD         Electron Capture  Detector
EM          Electromagnetic
EP           Extraction Procedure
EPA         Environmental  Protection  Agency
FEMA        Federal Emergency Management Agency
FID          Flame  lonization  Detector
             Fraction organic carbon in soil
             us  Fish and wildlife Service
G C         Gas Chromatography
GC/MS       Gas chromatography/Mass  Spectroscopy
GPR         Ground  Penetrating  Radar
HEA         Health  and  Environmental Assessment
HEEP         Health  and  Environmental Effects Profile
HPLC         High  Pressure  Liquid Chromatography
HSWA       Hazardous and  Solid Waste Amendments  (to RCRA)
HWM        Hazardous  Waste Management
ICP          Inductively Coupled  (Argon)  Plasma
ID           Infrared  Detector
Kd           Soil/Water  Partition  Coefficient
Koc          Organic  Carbon Absorption  Coefficient
Kow         Octanol/Water  Partition  Coefficient
LEL          Lower  Explosive Limit
MCL         Maximum Contaminant  Level
MM5         Modified Method  5
MS/MS       Mass Spectroscopy/Mass  Spectroscopy
NFIP         National  Flood  Insurance  Program
NIOSH       National  Institute  for Occupational  Safety  and Health
NPDES       National  Pollutant  Discharge  Elimination  System
OSHA        Occupational  Safety and  Health Administration
foe
FWS
                                      xv

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                        LIST OF ACRONYMS (Continued)
OVA         Organic Vapor  Analyzer
PID          Photo  lonization  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
                                      XVI

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                                   SECTION 9

                                      SOIL

9.1         Overview

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

     •    An example 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.

     •    Formats for data organization and  presentation;

     •    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.
                                      9-1

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 9.2        Approach for Characterizing Releases to Soil

 9.2.1       General Approach

      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.

      A conceptual  model  of the release should  be formulated  using  all available
 information on the waste,  unit characteristics,  environmental setting,  and  any
 existing  monitoring data.  This  model  (not  a computer or numerical  simulation
 model)  should  provide a  working hypothesis  of the release mechanism, transport
 pathway/mechanism,  and  exposure   route  (if any).  The  model  should  be
 testable/verifiable  and  flexible  enough to be modified  as  new  data  become
 available.   For  soil  investigations, this model should  account for the  ability of the
 waste to  be dissolved by infiltrating precipitation, its affinity  for soil particles  (i.e.,
 sorption),  its  degradability  (biological  and   chemical),  and   its  decomposition
 products.   Unit-specific factors  affecting  the  magnitude  and  configuration of the
 release should also be  incorporated  (e.g., large  area  releases from  land treatment
 versus  more localized  releases  from small  drum storage  areas).  The conceptual
 model should  also  address the  potential for  transfer  of contaminants in  soil  to  other
 environmental   media  (e.g., overland  runoff  to  surface  water,  leaching to  ground
 water, and  volatilization  to the  atmosphere).

      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 an example of  a 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.
                                      9-2

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                                  TABLE 9-1


         EXAMPLE STRATEGY FOR CHARACTERIZING RELEASES TO SOIL*



                                 INITIAL PHASE


1-     Collect and  review existing information on:


           Waste
           Unit
           Environmental   setting
           Releases, including inter-media transport


 2.    Identify additional information necessary to fully characterize  release.


           Waste
           Unit
           Environmental   setting
           Releases, including inter-media transport

 3.    Develop  monitoring  procedures:
           Formulate conceptual  model of release
           Determine  monitoring  program objectives
           Select  constituents and indicators  to be  monitored
           Plan  initial sampling based  on unit/waste/environmental  setting
           characteristics  and conceptual model.  May include  field screening
           methods,  if appropriate.
           Define  study and  background areas
           Determine sampling methods,  locations,  depths  and numbers
           Sampling  frequency
           Analytical  methods
           QA/QC procedures
                                     9-3

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                            TABLE 9-1 (continued)

         EXAMPLE STRATEGY FOR CHARACTERIZING RELEASES TO SOIL*




 4.    Conduct initial  monitoring  phase:


           Employ field screening  methods,  if appropriate
           Conduct  initial  soil  sampling  and  other  appropriate  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
           Evaluate  potential  for inter-media contaminant transfer
           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:


           Determine need to  expand or include further soil stratigraphic and
           hydrologic  sampling
           Information  needed  to  evaluate  potential for inter-media
           contaminant transfer (e.g., leaching  studies  to evaluate potential  for
          ground-water  contamination)


2.    Expand monitoring network as necessary:


           Expand area of field screening,  if  appropriate
           Expand sampling area and/or increase density
          Add or delete constituents and parameters of  concern
           Increase or  decrease  monitoring frequency
                                    9-4

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                            TABLE 9-1 (Continued)


        EXAMPLE 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 interim  corrective  measures -  Notify  regulatory agency
          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,  including  results of inter-media
          •transfer evaluation, if  applicable.
     The  possibility  for inter-media  transfer of  contamination  should  be
     anticipated throughout the  investigation.
                                    9-5

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      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.  Relevant soil  physical  and  chemical
 properties  should be measured and  related  to waste properties to  determine  the
 potential mobility of the contaminants in  the  soil.

      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/or  (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).

      Notwithstanding 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, Subpart D, and Part 265, Subpart D.

     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
                                       9-6

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

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

       Determine surface
       features and
       topography

       Characterize soil
       stratigraphy and
       hydrology
Aerial photography  or
mapping (See Appendix A
Soil core examination

Measurement of soil
properties
       Meteprological
       Conditions
On-site  meteorological
monitoring
- Soil survey  map
    Topographic map
    Photographs

- Soil  boring  logs

- Soil  profNe,  transect, or
    fence  diagram

    Particle size distribution

    Table  of unsaturated
    hydraulic  conductivities for
    each soil layer

    Table  of soil chemistry and
    structure (e.g., pH, porosity)
    for each soil type

- Temperature charts

    Tables of monthly and
    annual precipitation,
    runoff, and  evapo-
    transplration
3.  Release  Characterization
Field Screening
                                Sampling  and  Analysis
                                Soil Transport  Modeling
    Maps and tables showing
    results of soil gas surveys

    Tables and graphs showing
    results of chemical analyses
    performed in the field

    Map of sampling points

    Table of constituent
    concentrations  measured at
    each  sampling  point

    Area and profile maps of
    site,  shown  distribution of
    contaminants

    Table of input values,
    boundary conditions,
    output values, and
    modeling assumptions

    Maps of resent or future
    extent of contamination
                                          9-7

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 objectives  dictated by  the  initial  findings.  The owner or operator may propose to
 use mathematical models (e.g., chemical,  physical)  to aid in  the choice of additional
 sampling  locations or  to estimate  contaminant 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 2, 3, 15, 16 and 17 in Volume IV  (Case Study Examples)
 illustrate various aspects of soil investigations.

 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
 source  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
                                      9-8

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apply to more than  one of the affected media. For example,  soil-gas analysis  (e.g.,
using  a portable gas chromatography  during  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

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  fate 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  Appendix  B.  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  may  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 volubility
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  may  be detected  by  pore-water sampling  and  whole soil  sampling.
Volatile  organic  contaminants require specialized  sampling and sample storage
measures to prevent losses  prior 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  soil  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,
                                      9-9

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                TABLE 9-3
TRANSFORMATION/TRANSPORT PROCESSES IN SOIL
Process
Biodegradation
Photodegradation
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 buffering capacity
Temperature
Chemical class of contaminant
Presence of oxidizing agents
Partial pressure
Henry's Law Constant
Soil porosity
Temperature
Effective surface area of soil
Cation exchange capacity (CEC)
Fraction organic content (Foc) of soil
Octanol/water partition coefficient (Kow)
Solubility
Soil pH and buffering capacity
Complex formation
                  9-10

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 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 plan 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
 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 contaminants-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  at  locations  most  likely to
 contain the contaminant.

     Viscosity--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.

     pH  -Bulk liquid  pH  may  affect  contaminant  transport in at least two ways:
 (1)  it may  alter the chemical form of acids and bases, metal salts, and other metal
complexes, thereby  altering  their water  volubility  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.
                                      9-11

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

      Density   --The  density  of major waste components should  be determined,
especially for  liquid wastes. Components with a density greater than water, such as
carbon  tetrachloride,  may migrate  through  soil layers  more quickly  than
components  less  dense than water, such  as toluene,  assuming viscosity to be
negligible.  Density  differences become  more  significant  when  contaminants reach
the saturated zone.  Here they may  sink, float,  or be dissolved in the ground water.
Some fraction of a "sinker" or "floater" may also  be dissolved in  the ground  water.

      Water volubility-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
volubility 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 the tendency of the constituent
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 Subsurface Gas and Air sections  (Sections  11  and
12, respectively).  Information  on  this  parameter  can help  in  determining  which
phases to sample in  the  soil investigation.

     Octanol/Water  partition  coefficient  (K^J  -The characteristic distribution of a
chemical between an  aqueous phase and an  organic phase (octanol) can be used to
                                     9-12

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predict the sorption of organic chemicals  onto  soils. It is frequently  expressed as a
logarithm  (log  Kow). In transport models,  Kowis frequently  converted to  Koc, a
parameter  that  takes into  account the organic  content of the  soil. The empirical
expression used to calculate  Kocis:  Koc= 0.63  Kowf0cwhere  focis 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
organic carbon.  Consideration of this parameter will also help  in  determining which
phases to sample in the  soil investigation.

     Biodegradability --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  in  the  "A"  (uppermost)  soil horizon where  carbon
content is  generally highest and  where  aerobic  digestion occurs.  Because 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  results 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 (some  with  higher toxicities)  and should  therefore
be  considered  in  developing   monitoring   programs.  The  decomposition  or
degradation rate depends on various  factors, including:

     t    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 estimate
          the  persistence of waste constituents in soil. This table provides relative
          degradabilities for  some   organic compounds  and  can  be an  aid  to
          identifying  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
                                     9-13

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TABLE 9-4. BODs/COD  RATIOS  FOR VARIOUS ORGANIC COMPOUNDS*
Compound
RELATIVELY UNDEGRADABLE
Butane
Butylene
Carbon tetrachloride
Chloroform
1,4-Dioxane
Ethane
Heptane
Hexane
Isobutane
Isobutylene
Liquefied natural gas
Liquefied petroleum gas
Methane
Methyl bromide
Methyl chloride
Monochlorodifluoromethane
Nitrobenzene
Propane
Propylene
Propylene oxide
Tetrachloroethylene
Tetrahydronaphthalene
1 Pentrene
Ethylene dichloride
1 Octene
Morpholine
Ethylenediaminetetracetic acid
Triethanolamine
o-Xylene
m-Xylene
Ethyl benzene
MODERATELY DEGRADABLE
Ethyl ether
sodium alkylbenzenesulfonat.es
Monoisopropanol amine
Gas oil (cracked)
Gasolines (various)
Ratio

~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
~0
<0.002
0.002
>0.003
<0.004
0.005
<0.006
<0.008
<0.008
<0.009

0.012
-0.017
<0.02
-0.02
-0.02
Compound
MODERATELY DEGRADABLE
(CONT'D)
Mineral spirits
Cyclohexanol
Acrylonitrile
Nonanol
Undecanol
Methylethylpyridine
1-Hexene
Methyl isobutyl ketone
Diethanolamine
Formic acid
Styrene
Heptanol
sec-Butyl acetate
n-Butyl acetate
Methyl alcohol
Acetonitrile
Ethylene glycol
Ethylene glycol monoethyl ether
Sodium cyanide
Linear alcohols (12-1 5 carbons)
Allyl alcohol
Dodecanol
RELATIVELY DEGRADABLE
Valeraldehyde
n-Decyl alcohol
p-Xylene
Urea
Toluene
Potassium cyanide
Isopropyl acetate
Amyl acetate
Chlorobenzene
Jet fuels (various)
Kerosene
Range oil
Glycerine
Adiponitrile
Ratio

-0.02
0.03
0.031
>0.033
<0.04
0.04-0.75
<0.044
<0.044
<0.049
0.05
>0.06
<0.07
0.07-0.23
0.07-0.24
0.07-0.73
0.079
0.081
<0.09
<0.09
>0.09
0.091
0.097

<0.10
>0.10
<0.11
0.11
<0.12
0.12
<0.13
0.13-0.34
0.15
-0.15
-0.15
-0.15
<0.16
0.17
                         9-14

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                              TABLE 9-4. (Continued)
Compound
RELATIVELY DEGRADABLE
(CONT'D.)
Furfural
2-Ethyl-3-propylacrolein
Methylethylpyridine
Vinyl acetate
Diethylene glycol monomethyl
ether
Napthalene (molten)
Dibutyl phthalate
Hexanol
Soybean oil
Paraformaldehyde
n-Propyl alcohol
Methyl methacrylate
Acrylic acid
Sodium alkyl sulfates
Triethylene glycol
Acetic acid
Acetic anhydride
Ethylenediamine
Formaldehyde solution
Ethyl acetate
Octanol
Sorbitol
Benzene
n-Butyl alcohol
Propionaldehyde
n-Butyraldehyde

Ratio

0.17-0.46
<0.19
<0.20
<0.20
<0.20
<0.20
0.20
-0.20
-0.20
0.20
0.20-
0.63<0.24
<0.24
0.26
0.30
0.31
0.31-0.37
>0.32
<0.35
0.35
<0.36
0.37
<0.38
<0.39
0.42-0.74
<0.43
<0.43

Compound
RELATIVELY DEGRADABLE
(CONT'D.)
Ethyleneimine
Monoethanolamine
Pyridine
Dimethylformamide
Dextrose solution
Corn syrup
Maleic anhydride
Propionic acid
Acetone
Aniline
Isopropyl alcohol
n-Amyl alcohol
Isoamyl alcohol
Cresols
Crotonaldehyde
Phthalic anhydride
Benzaldehyde
Isobutyl alcohol
2,4-Dichlorophenol
Tallow
Phenol
Benzole acid
Carbolic acid
Methyl ethyl ketone
Benzoyl chloride
Hydrazine
Oxalic acid
Ratio

0.46
0.46
0.46-0.58
0.48
0.50
-0.50
>0.51
0.52
0.55
0.56
0.56
0.57
0.57
0.57-0.68
<0.58
0.58
0.62
0.63
0.78
-0.80
0.81
0.84
0.84
0.88
0.94
1.0
1.1
*Source:    U.S. EPA 1985. Handbook: Remedial Action at Waste Disposal Sites (Revised).
          EPA/625/6-85/006. NTIS PB82-239054. Office of Emergency and Remedial Response.
          Washington, D.C. 20460.
                                        9-15

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     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.

•    The  presence or absence  of  oxygen in the  soil. Most degradable
     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, DDT 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 because
     fewer micro-organisms  exist  there. In addition,  compounds  with greater
     aqueous  solubilities are  generally  more available  for  degradation.
     However,  high volubility 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.
                                9-16

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     •    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.
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,  1985.  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

     •    Timing of the release.

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.
                                      9-17

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                                  TABLE 9-5
      POTENTIAL RELEASE MECHANISMS FOR VARIOUS UNIT TYPES
     Unit  Type
                 Release  Mechanisms
Surface Impoundment
Loading/unloading  areas
Releases from overtopping

Seepage
Landfill
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
Waste Pile
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 soils
Land Treatment Unit
Migration of runoff outside the containment area

Passage of leachate into the soil horizon
Container Storage Area
Migration of runoff outside the containment area
Loading/unloading  areas
Leaking drums
Above-ground  or
In-ground Tank
Releases from overflow

Leaks through tank shell

Leakage  from coupling/uncoupling  operations

Leakage from cracked or corroded tanks
Incinerator
Routine  releases from waste  handling/preparation  activities

Leakage due to mechanical failure
Class I and IV Injection
Wells
Leakage from waste handling operations at the well head
Waste transfer Stations and waste  recycling operations generally have  mechanisms  of
  release similar to tanks.
                                     9-18

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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
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 (NTIS  PB86-229192) 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  release characterization should  focus on  determining  the
boundaries of  the  contaminated  area  to minimize  the  analysis  of numerous
uncontaminated  samples.  Where  appropriate,  a  survey of the area with an organic
vapor analyzer,  portable gas  chromatography, 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  both inside  and outside of
the contaminated  area.

     Non-point type  releases to  soil  may also  result from deposition of particulate
carried in the air, such as from  incinerator "fallout".  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
                                      9-19

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(e-g.,  land  treatment) may  be distributed  more  evenly  over the  affected area.  In
these  situations,  a large area  may  need to reinvestigated  in order to determine the
extent of contamination.  However,  the  relative  lack of  "hots  pots"  may  allow the
number of samples per unit area to  be smaller than for a point source type release.

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 shovels or 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.

     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 for 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);
                                      9-20

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     •     Potential for excessive surface  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

     •     Land use,  including potential for  excavation/construction,  use of the soil
           for fill  material, installation  of utilities (e.g.,  sewer  lines or  electrical
           cables), and farming  activities.

     Land use that  involves housing developments is an  example  of  when the
surficial soil depth may extend to 12 feet  because foundation excavation may result
in deep  contaminated soils  being  moved  to the  surface.  Deep-soil  zones, for
purposes  of the RFI,  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
primarily  downward  within the  unsaturated  zone.   Lateral movement  generally
occurs only through  dispersion and diffusion. However,  changes in soil structure or
composition  with depth   (e.  g., 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 a flowing liquid or by a gaseous  phase.  Mass flow
is  typically downward  (due to gravity); however,  mass  flow  could  also be upward
                                      9-21

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due to capillary action (e.g.,  if significant evaporation  occurs at  the  surface).  Mass
flow is a much faster transport mechanism than is diffusion (Merrill et al.,  1985).

      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.

      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  monitoring that may be necessary.

      Where the source or precise  location  of a  suspected  release  has  not  been
clearly identified, field  screening  methods  (See  Section 9.6)  may  be  appropriate.
Subsurface  contamination can be  detected by using geophysical methods  or soil gas
surveying  equipment  (e.g., organic  vapor  analyzers).  Geophysical  methods,  for
example,  can  help in  locating  buried  drums.   Soil gas  surveys can  be useful  in
estimating  the  lateral  and  vertical extent of soil contamination.  Further  delineation
of 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 (Geophysical  Techniques).

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
                                      9-22

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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.

9.3.2.5    Timing of the Release

     Time-related  factors  that  should  be considered in characterizing  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-bound contaminants may  be more
likely  affected  by surface transport,  such as overland  runoff  or  wind  action. These
                                      9-23

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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  its 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.

     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.
                                      9-24

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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.

      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. Because 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 a 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  joints, channels,  and  zones containing
                                       9-25

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 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
 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).
                                      9-26

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                                         HAZARDOUS WASTE DISPOSAL IMPOUNDMENT

                 UNSATURATED

                     ZONE      I
                                                                                      SATURATION FRONT


                                                                                              ISOLATED SATURATION LAYER
NJ
                                              SEEPAGE

                                                  PATH
I
I     i

                                                                          CLAY LENS
                                                                    MOUNDING /S[[[^    CAPILLARY
                                                                                                              FRINGE
                                  WATER TABLE

                SATURATED ZONE


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      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.

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 volubility 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 classification--The  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.

     •     USDA  Soil  Classification System  (USDA,  1975)-Primarily  developed  for
          agricultural  purposes,  the  USDA  system  also  provides information  on
          typical soil  profiles (e.g., l-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.
                                      9-28

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           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-g rained  soils.   Figure  9-2 displays  the decision matrix used in
           classifying soils  by this system.

     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 D422 (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 (dj2

           where  d10is  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 d10is 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
                                       9-29

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                                                                                Figure 9-2. Soil Terms
UNIFIED SOIL CLASSIFICATION ( USCS )
COARSE GRAINED SOILS
More lhan half ol material Is LARGER than No 200 sieve size
FIELD IDENTIFICATION PROCEDURES
(Excluding particles large' lhan 3" & basing tractions
on estimated weights)
GRAVELS
50*O)> 1/4* »
«•
•
*r
*
CLEAN
GRAVE-LS
Low %
tirws
3«*
>5£»
!S«
G =; *s
z £S!
< "-.?£
w » I"~
Wide range in grain size and substantial
amounts ol all Intermediate particle sizes
Predominantly one size or a range ol sizes
with some intermediate sizes missing
Non-plastic lines (lor Identification
procedures see ML)
Plastic lines (lor Identification procedures
see CL)
Wide range In grain size and substantial
amounts of all Intermediate panicle sizes
Predominantly one size or a range of sizes
with some intermediate sizes missing
Non-plastic lines (for identification
procedures see ML)
Plastic lines (tor Idenlllicallon procedures
see CL)
GROUP
SYM -
BOLS
GW
GP
GM
GC
SW
SP
SM
SC
TYPICAL NAMES
Well graded gravels, gravel-sand mixtures.
little or no fines
Poorly graded gravels, gravel-sand
mixtures, little or no fines
Silly gravels, poorly graded gravel-sand-
slll mixtures
Clayey gravels, poorly graded gravel-
sand-clay mixtures
Well graded sand, gravelly sands, lillle or
no lines
Poorly graded sands, gravelly sands, little
or no fines
Sllty sands, poorly graded land-sill
mixtures
Clayey sands, poorly graded sand-clay
mixtures
FINE GRAINED SOILS
More lhan hall ol malarial Is SMALLER than No. 200 sieve size
FIELD IDENTIFICATION PROCEDURES
(Excluding particles larger than 3" & basing fractions
on estimated weights)
Idenlillcallon procedures on fraction smallor than No. 40 stove size
to o
5 v
S !
I \


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           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.

      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  the  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  soil within the  saturated  zone  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  soil 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. Method  9100 includes techniques  for:

      •     Laboratory
                                       9-31

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                constant head  methods; and
                falling  head  methods.
           Field
                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 significant strati  graphic 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--The 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 to water
is known  as relative  permeability.

     The  importance  of determining this  value is due  to  the potential effects of
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.
                                       9-32

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      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.
The soil-water  partition  coefficient (Kd) is generally used to quantify  soil sorption.
Kd is  the  ratio of the  adsorbed contaminant  concentration to  the  dissolved
concentration, at equilibrium.

     There are two  basic  approaches to  determining Kd:  (1) soil  adsorption
laboratory  tests, and  (2) prediction from soil and  constituent properties. The Soil
Adsorption Isotherm (Al) test is widely  used  to  estimate the extent of  adsorption of
a  chemical  (i. e.,  constituent) in soil  systems.  Adsorption is  measured by
equilibrating  aqueous  solutions  containing varying  concentrations  of the test
chemical with  a known  quantity of  uncontaminated soil.  After  equilibrium  is
reached,  the  distribution of the  chemical  between  the  soil  and water (Kd) is
measured by  a suitable  analytical  method.

     The Al  test has  several  desirable features.   Adsorption  results are  highly
reproducible.   The  test  provides excellent quantitative  data  that  are  readily
amenable to statistical  analysis. In addition,  it has  relatively  modest reagent,  soils,
laboratory space and equipment requirements. The ease of performing this test will
depend on  the physical/chemical  properties of the  contaminant  and the  availability
of suitable analytical techniques to measure the  chemical.

     The Al test can  be used  to  determine  the soil adsorption  potential  of slightly
water soluble  to infinitely water soluble chemicals.  In general, a chemical having a
water volubility of less than  0.5 mg/l  is not tested with this  method  because  these
chemicals are relatively immobile in soil. The U.S. EPA Office of Pesticides  and  Toxic
Substances  (U.S. EPA 1982a, 1982b)  has compiled information on  the use of the Al
test, including  a detailed  discussion   of apparatus,  procedures, sources of  error,
statistical  requirements, calculation methods,  and limitations of the test.

     A second approach for determining Kd is to estimate the value from soil and
waste  properties.  Soil properties that  should  be considered  when  using this
                                      9-33

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approach  are particle  size  distribution, cation  exchange  capacity, and  soil  organic
carbon content.  The  waste  properties that  should  be determined  will  vary
depending  on the type  of  waste.  Lyman et al.  (1981) discuss several  methods for
estimating  Kdfrom  chemical  properties  of the constituent  (e.g.,  Kowand water
volubility)  and the soil  organic content.  Data collection needs for waste  properties
were discussed earlier in this section.

     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  inorganic.   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, 1986).

     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  (Foe),  the greater the  adsorption  of  organics.  Soil  Foc
ranges from under 2 percent for many subsurface soils  to over 20 percent for a peat
soil. An estimate of  Focshould be made based on literature  values for similar soils if
site-specific  information  is  not  available.

     Soil  pH-Soil  pH  affects  the  mobility  of  potentially ionized  organic and
inorganic  chemicals  in  the  soil.  Compounds in  these  groups include  organic  and
inorganic acids and bases, and metals.

     Depth  to ground water -The thickness  of the unsaturated zone may  affect the
attenuation capacity  of  the  soil  and  the time taken for contaminants to migrate  to
ground water.  If  significant, seasonal  fluctuations  in  ground-water elevations
should  be identified  as  well as elevation  changes  due  to pumping  or other factors
(e.g., tidal influences).

     Pore-water velocity-Pore water  velocity  affects  the time of travel  of
contaminants in  unsaturated soil  to ground water. For steady state flow and a unit
                                      9-34

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 hydraulic gradient  (i.e.,  moisture  content  does  not  change  with  depth), the pore-
 water velocity can  be calculated by the following equation:

                                     V = q/e

 where:     V = pore water velocity, cm/day
           q = 'volumetric flux/unit area, cm/day
           e = volumetric  water content, dimensionless

     A  simple approximation of volumetric flux (q)  can be made by assuming 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
           DR   =    Direct surface  runoff
                                      9-35

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Annual  averages for P, ET and DR 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

      •    National Weather Service stations.

It is recommended that site-specific ET and  DR data be used if possible, because 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  evapotranspiration  and
direct surface runoff may  be found in  the  following  references:

      U.S. EPA.  1975.  Use  of the Water  Balance  Method for  Predicting  Leachate
      Generation from Solid Waste  Disposal Sites.  EPA/530/SW-168.  Office  of Solid
      Waste.  Washington,  D.C. 20460.

      U.S. Geological Survey. 1982. National  Handbook of Recommended  Methods
      for Water Data  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 105°C,  expressed as the volume of
water/bulk volume  of  soil. This  parameter affects  the unsaturated hydraulic
conductivity  and  is  required  for calculation of pore-water velocity.  At saturation,
the volumetric water content  is equal to the porosity of the soil.

     Additional soil  conditions-Additional  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-
                                     9-36

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   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
   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 in, 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
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           will  fail to be  retained in a tube sampler; 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 avoid  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.
           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
                                      9-38

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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
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

9.3.4.2     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
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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;

     •     Establishing  a random  or systematic grid sampling network to determine
          soil  contamination concentrations  in all  zones  of a large area affected by
          airborne deposition;  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. I  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;

     •    Role of field  screening methods, if any;

     •    Sampling  methods;

     •    Approximate  study  and background areas;

     •    Sampling locations  and approach  (e.g., judgmental or systematic); and

     •    Number of samples to be collected.
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      The owner or operator may propose the use of field  screening methods to aid
 in  delineating  the  zone  affected by  a contaminant  release  to  soil  and/or ground
 water. Such methods  may  be  applied just  below the  land  surface  or at greater
 depths,  as  within soil  bore holes.  An increasingly used method to  detect organic
 vapors is generally known as a  soil gas  survey. Such a survey can yield qualitative
 and  relative quantitative  data  on  volatile constituents present in the  soil  gas,
 depending  on   the  instrumentation  used.  For  example,  a  total  photoionization
 detector  will provide  an integrated value  for the volatile organics present;  whereas
 a  portable  gas  chromatography can  identify  and quantitate specific  compounds
 present  in the  soil vapor. Field screening  can also include  chemical analyses of soil
 samples performed onsite in  mobile  laboratories.

      When  conducting a soil gas survey,  it should be  realized that any measured soil
 vapor concentrations of specific  compounds cannot be directly  correlated  with  their
 actual concentrations in the soil  zone  of  concern. The concentrations in soil vapor
 resulting from   a soil  with given  volatile contaminant concentrations will  vary,
 depending  on  several  factors,   including  barometric  pressure,  relative  humidity  in
 the  soil,  weather conditions  (e.g.,  precipitation events, soil  inhomogeneities,  and
 temperature). Therefore, the  results  of a  soil  gas survey can  reveal  the  relative
 abundances  of volatile  compounds  in  the soil   gas, but not  their  actual
 concentrations  in the soil.

      The soil gas survey technique may also be applied when  drilling boreholes  to
 characterize site geology or when  drilling  to install  ground-water monitoring wells.
 Soil samples taken at various depths within the  borehole can  be placed  in separate
 sample bottles  with septums.

      A sample  of the gas  in the headspace  can then be  withdrawn with a  syringe
 and injected into a  portable  gas chromatography  to  identify the presence  and
 relative abundances of specific volatile compounds in  the  soil gas. Analysis of drill
 cuttings  in the  open air is not as effective  as the headspace technique in  detecting
volatile organic  compounds; therefore, the  headspace  method is preferred.

     Additional  information  on  soil gas  monitoring  may be  obtained from  the
following  reference:
                                      9-41

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      U.S.  EPA.  1987.  Soil  Gas  Monitoring Techniques  Videotape.  National Audio
      Visual Center.  Capital Heights, Maryland  20743.

      Screening  methods  may help to reduce  the  number of soil  and/or  ground-
water  samples needed  to characterize a release by  better delineating  the  area  of
concern  in  a relatively rapid manner.  However,  due to limitations  (e.g., relatively
high   detection  limits and  inability  to  identify   all  the  potential  hazardous
constituents of concern),  some  screening methods  may  not  be adequate to verify
the absence of  a release.  For  such  verification, an appropriate  number  of  soil
samples would  need to  be  analyzed  in the  laboratory. Additional  information  on
field screening methods is presented later in this section and  in the Compendium  of
Field  Operations Methods, (EPA, 1987).

      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 phases 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;

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

     •    Addition or  deletion  of specific monitoring  constituents 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.
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 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 or  suspected  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 (See Section 3 and Appendix B).

      During or  after 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.

9.4.3      Monitoring Schedule

      Monitoring frequency and  duration  determinations  should  be based primarily
on  the type of 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  will  usually necessitate a  greater duration of
sampling. Soil-pore  liquid  may require more frequent  monitoring than  in  soil  solids
because changes  generally occur faster  in these fluids.  Frequency may also be
adjusted,  if appropriate,  as  sampling  results  become available.  As  with  single
episode releases, longer-term  releases are  monitored  until the  nature and extent of
contamination  has been  adequately  characterized.
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 9.4.4      Monitoring Locations

 9.4.4.1     Determine Study and Background Areas

      Determination  of the  area  of  interest will  depend  on  the facility  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  small  land-fill 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 toxic metals,  because  such metals  commonly 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
 stratigraphic layer as the  study area 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.

     The  owner  or  operator  may  increase  efficiency  in the  initial  characterization
 effort by using rapid, field-screening methods (e.g., soil gas surveys using HNu, OVA
 or portable  gas chromatography)  or through indicator  parameter 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  (TOX) or Total Organic Carbon  (TOC)  analysis may  be useful  in
detecting  total  chlorinated and  nonchlorinated organic  solvents. Such parameters
 may be used to characterize the nature and extent of a release but should always be
verified  by an  adequate number of  specific constituent analyses.
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     it  is generally recommended that  a sampling grid  be developed for the  site,
even  for  judgmental  sampling.   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 soil 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  oroperator 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  homogenization   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
          7,  composites should  have very  limited application  during the RFI  and
          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.
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     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  operator 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.

     Mason, B.J.   1983.  Preparation  of a  Soil  Sampling   Protocol:
     Techniques and Strategies. NTIS PB83-206979.  U.S. EPA 600/4-83-
     020.  Washington,  D.C. 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 should be taken at 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
contaminant transport.   The owner  or operator should  consider
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           remeasurement 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 contaminant  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 contaminant  transport  in  the  unsaturated 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  preferred 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.

      Numerous  models,  including  computer models,   have   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 (found in U.S. EPA. 1986. Permit  Guidance  Manual  on  Hazardous
Waste Land Treatment Demonstration.    NTIS  PB86-229192)  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
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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).

     EPA is in the process of developing a more sophisticated version of the RITZ
model, known as the RITZ-VIP model. The VIP version differs in that it is designed to
provide information for multiple waste  loadings in  a land treatment  situation.  The
initial  version  of  the  RITZ  model  only  applies where the waste  or material  in
question  is applied  to the  land  once.   The   RITZ-VIP  version  is  currently  in  the
review/verification  process.  More  information   on this model may  be obtained by
writing to  EPA at the following address:

     U.S.  Environmental  Protection  Agency
     Robert S. Kerr  Environmental Research Laboratory/0RD
     P.O. Box1198
     Ada,  Oklahoma 74820

     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 estimate the probable vertical or  lateral
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extent  of contamination,  which  can  be  used to  identify potential  sampling
locations.  Mobility predictions  may  also  be  used  in  determining  potential inter-
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  accepted,  straightforward  method  for predicting  the
mobility  of all  hazardous constituents within  soils  under  all  possible  sets  of
environmental  conditions.  Nor is  there  a fully tested method of  estimating  the
impact  of constituents  originating  in the unsaturated  zone  on ground-water
quality.  Therefore, 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
in soils as well, and to determine that a  Corrective Measures Study is  necessary. This
may be the case in situations where contaminated soils  are located solely within the
ground  water  and  when  the  contaminants  are  relatively mobile.  The most recent
ground-water impact  characterization data  may not,  however,  provide  information
on  the future  impact  of  contaminated soils  on ground water  (e.g., due  to  different
leaching  rates for different contaminants).

     This section  presents various 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
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mathematical models, and the  use of  laboratory  models or leaching tests. Leaching
tests have  the advantage of being  the  only  approach  that  integrates soil  and
constituent properties in  a single evaluation. They  may, in  certain  cases,  provide a
conservative  (reasonable  worst case)  estimate of the concentration within  leachate
of waste constituents  that  may  eventually  impact ground  water.  Leaching  test
results  must  be  coupled with site-specific  factors,  (e.g.,  soil cation exchange
capacity,  ground-water  pH,  and  depth to  ground  water) when  used to design
monitoring programs,  determine  potential  for  inter-media impacts, and evaluate
options for contaminated-soil  corrective  measures.  When  assessing  leach  test
results,  specific hazardous constituent  concentrations in  the  leachate will  be
compared  with the health  and  environmental criteria concentrations for  water
described in Section 8.

     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 may  not  be  applicable.  For
example,  leaching  tests  may  be  overpredictive of leachate  concentrations where
extensive channeling  (e.  g.,  because  of root  zone or  joints) 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 inorganic.

     The  Agency  has  devised  a soils/waste mixture leaching procedure, known as
the Synthetic Precipitation  Leach Test  (Method 1312) that  it generally believes may
be  appropriate for evaluating the potential  impact  of  contaminated  soils on
ground-water  quality.   (See  Appendix  F for  a  description  of  this   procedure).
Although neither Method  1312 nor  any other leaching test  (such  as   the Toxicity
Characteristic Leaching Procedure  (Method 1311) have  been validated for use on  a
wide range of contaminated-soil types,  the Agency believes that Method 1312 may
have the broadest  applicability.   Method   1312 may  be  particularly   appropriate
when no  future waste  management or other  industrial activities likely  to  produce
an acidic leaching medium  are likely  to  be conducted at  the site of the release.
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     However, other leaching  tests may be appropriate under certain case-specific
circumstances. For example, a  test such as Method  1311  may be  appropriate at a
release site that will be used for management of municipal refuse or a similar waste
in the  future,  because  the  refuse  could  produce an  acidic leaching medium,  which
Method  1311  has been  designed  to  simulate.  The  evaluation  of  leaching  from
cyanide-containing  soils should  be performed with  neutral  water,  rather  than  an
acidic  leaching medium, because leaching  of cyanide-containing waste under acidic
conditions may result  in  the  formation  of toxic  hydrogen cyanide gas.  Other
leaching  test variations may  be  necessary  if interactive effects  on mobility  are
caused by  non-aqueous  solvents,  for example,  or if an  aqueous  phase  leaching
medium  may underpredict  potential  mobility  due  to  site  and  waste  constituent
characteristics.

9.4.4.3.2  Estimating  Impact on  Ground-Water  Quality

     In  evaluating  results  obtained  using  the  leach  test for  the  evaluation of
contaminants  of concern at a specific release site, the Agency will consider relevant
hazardous constituent properties, the  physical and chemical  characteristics  of the
soil/waste matrix at the site, and  local  climatological factors.  Factors that will  be
considered include the following:

     •    Chemical structure,  classification,  and  bonding  (organic  vs.  inorganic,
          ionic vs. covalent, etc);

     •    Volubility  of  the  constituents;

     •    Octanol/water or  other  partitioning  coefficients;

     •    Density;

     •    organic   carbon  adsorption   coefficient;

     •     Volatility (e.g., Henry's Law constant);

     •     Dissociation constants (Pk);
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      •    Degradation  potential  (hydrolysis,  biodegradation);

      •    Soil/waste  matrix characteristics;

      •    Cation exchange capacity;

      •    Soil pH and Eh;

      •    Soil classification (e.g.,  clay,  silt,  and sand content);

      •    Particle-size  distribution;

      •    Porosity;

      •    Unsaturated  hydraulic  conductivity;

      •    Climatological   characteristics;

      •    Precipitation patterns (volume, frequency, etc.); and

      •    pH  of local or  regional precipitation.

      The results  obtained from a  specific leach  test  must  be supported by  an
analysis of the relevant factors, such as those listed above, and considering the likely
future use of the site (industrial, waste management, residential, etc.).

      As  an alternative   approach  to  the use of  a  leach test  for  evaluating
contaminated soil, the owner or operator  may propose to perform an analysis of the
waste,  soil,  and  Climatological  conditions,  considering  such factors as  are  listed
above, to demonstrate  that  the  expected  concentrations of  any constituents that
could  leach from any contaminated section  of  the subsurface soils would not  exceed
the action levels  for  ground-water.  This analysis,  which would  require  appropriate
technical  justification and  should  rely  as much  as  possible on  data (such  as the
results of published  field  studies  conducted under environmental  conditions similar
to those at  the release site),  must be  based on  conservative assumptions related to
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 future changes  in environmental  conditions and land use  (e.g., the use of the site
 for future  non-hazardous waste  management).

      At the present time, studies are  being designed to more fully examine various
 methods  for  evaluating  leaching of hazardous  constituents from  contaminated
 soils. Further  guidance will be  provided  by the Agency  upon  completion  of these
 studies.  It  is  recommended that the  owner or  operator review the procedures and
 methods described in  Sections 8 and 9  and Appendix J  of Petitions  to  Delist
 Hazardous waste, EPA/530-SW-85-003, as well  as SW-846, to assist in determining
 the  appropriateness  of  any  particular  leaching  procedures for  evaluating
 contaminated  soils.  Until  more  definitive guidance  is  available,  the owner or
 operator may  propose  what he believes to  be the most  appropriate   leaching
 procedure,  and provide technical justification  to  support  the  proposed procedure
 based on site  and waste conditions at the time of the investigation. For additional
 assistance  on  selection  of a leaching procedure, the owner or operator may contact
 the Technical  Assessment Branch of the Office  of Solid Waste  in Washington, D.C.
 (202/382-4764).

     As  indicated  above,   waste 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 the  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.
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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:

                mass of sorbed chemical/gram of solid
      K d =    	
                mass of chemical/ml  of solution

     The relative mobility of attenuated constituents in ground  water can  then  be
estimated as follows (after Mills, et al., 1985):

                                 (1  + Kdb)/ne
where

     v     =    average  linear  velocity  of attenuated  constituent along  centerline
                of plume,  distance/time;
     Vs    =    ground-water velocity, distance/time;
     b     =    soil bulk density, mass/volume;
     ne    =    effective  porosity, dimensionless; and
     Kd    =    soil-water  partition  coefficient,  volume/mass.
     The  relative  mobility  of  selected  constituents,  based  on  typical partition
coefficients,  is  shown in  Table 9-6. It is important to  note that Kd is  a simplified
measure  of  the  relative  affinity of a  chemical for the  solution  and the  soil.  Kdis
highly  site-specific, varying as a function of pH, redox conditions, soil characteristics,
and  the availability of alternate solution  phases (organic and  inorganic  liquids, or
colloidal  solids).  The  general  effect of pH  and  organic matter content on  partition
coefficients for metals is shown in Figure 9-3.

     The Kd value  selected for use in  estimating chemical mobility should  reflect the
predominant  chemical  species  in  solution.  One  approach to  estimating  solution
composition  is to  use  thermodynamic stability  diagrams,  commonly  illustrated  as
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       TABLE 9-6 RELATIVE MOBILITY OF SOLUTES1
Group
Conservative




Slightly Attenuated
Moderately Attenuated
More Strongly
Attenuated
Examples
Total Dissolved
Solids
Chloride
Bromide
Nitrate
Sulfate
Boron
Trichloro-
ethylene
Selenium
Arsenic
Benzene
Lead
Mercury
Penta-
chlorophenol
Master Variables2
V
V
V
V, Redox Conditions
V, Redox Conditions
V, pH, organic matter
V, organic matter
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.e., neutral pH and
   oxidizing conditions). Under other conditions mobility may differ
   substantially. For example, acidic conditions can enhance the
   mobility of metals by several orders of magnitude.

2 Variables which strongly influence the fate of the indicated solute
   groups. Based on data from Mills et al., 1985 and Rai and Zachara,
   1984.  (V= Average Linear Velocity)
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             100
 •Percent
 Adsorption
 by Soil
              50
                I          Shift due
                          to presence
                '          of soil organic
               I          natter

               I

               .^-Typical adsorption
               '  '  curve for heavy
               I    netal x, on silica
              I    or aluminum silicate
                   surface coated with
              /     soil organic matter
Typical
Adsorption
curve for
heavy metal
x. on a clear
silica or
aluminum
silicate
surface
                                pH of the  Soil  Solution

  a) Generalized Heavy Metal  Adsorption  Curve for  Cationic Species

                            (e.g., CuOH*)
                100  --
 Percent
 Adsorption
 by Soil
50  -

X

•
Typical adsorption
curve for heavy
metal species, K,
on iron hydroxide







C "N
%
\
\
V «
\ -A
\Shift \
x due to \
\ presence \
\ of soil \
* organic \
N matter \
\
                              pH of  the Soil Solution


 b) Generalized Heavy  Metal  Adsorption Curve for  Anionic Species
                                      i
                           (e.g.,
Figure 9-3.      Hypothetical Adsorption Curves for A) Cations and

                B) Anions Showing Effect of pH and Organic Matter

                (Mil Is eta I., 1985)
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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  are
 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.
 Garrels 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  volubility constant  (K)  expresses the relation  between  the
reactants and  the products following the  law of mass action:

                    K=       [C]c[D]d
                               [A]a[B]b

     The  brackets signify an effective concentration,  or activity, that  is reported  as
molality (moles  per liter).   Volubility constants  for  many  reactions  in water  are
reported  by Stumm  and  Morgan  (1981). Alternatively, volubility 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
calculate  volubility  constants for several constituents common  in ground water.
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     An example  illustrating  the  use of Eh-pH diagrams and the influence of redox
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 in equilibrium.
For  pH  values of less than  about  7  and Eh  values  greater than 0.5 volts  (strong
oxidizing  conditions),   HgCIJs  the dominant dissolved species.  For  pH  values
greater than 7,  and  at  a  high  redox potential,  Hg(OH)2is the dominant  dissolved
species.  The main equilibrium reaction in this Eh-pH environment is:

                     HgO + H20 = Hg  (OH)2

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

                               [Hg(OH)2]
                     K —
                               [HgO] [H20]

     At 25°C,  the  volubility  constant  (log K) for this reaction  is  -3.7 (Freeze and
Cherry,  1979). The  activity coefficients for a solid (HgO)  and H20 are assumed to  be
one; therefore, the  concentration of Hg(OH)2in  solution  is calculated  as  follows:

[Hg(OH)2] = K = 10'37= 1.995 x KTmoles/l = 47 mg/l (mol. wgt. = 235 g/mole)

     The  Eh-pH diagram can be  used to estimate the  concentration of  mercury in
solution at  any particular point in  the  diagram  if the  volubility  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 al., 1979).

     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 volubility constraints.  However, the Eh-pH  diagrams  serve  to  illustrate
                                      9-58

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1.20
1.00
          2      4     6      8      10     12     14
   Figure 9-4. Fields of Stability for Aqueous Mercury at 25°C
               and Atmospheric Pressure (Callahan et al., 1979)
                             9-59

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that  solution composition  depends  on redox  potential  and  that  chemical  mobility
within a ground-water system  may vary from one  zone to  another.

9.5        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;

     •     Measurements of soil physical  or hydrologic characteristics; and

     •     Onsite  survey  results  (e.  g.,  OVA,  portable  gas  chromatography,
           geophysical techniques).

                                      9-60

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     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.  Fence  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 areal
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).

9.5.3      Characterization  of  the  Release

     Graphical  displays of contaminant  distributions in soil may include:
                                      9-61

-------
                BORING   L06
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                     Figure 9-5.  Example of a completed boring log
                                            9-62

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               BORING  L06
            — 9




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                                Figure 9-5 (Continued)
                                          9-63

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     •    Area/site  maps  with  concentrations indicated by  numerical 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.   Lysimeters  can be installed  in
boreholes created during core sampling  to  identify  mobile  constituents  that  may
migrate to ground water. In addition, field screening methods may be  used to  help
determine the presence  and extent of releases.

     Appropriate sample  collection  and  preservation  techniques should  be
specified.  When  a soil sample is removed from  its  surroundings,  chemical  and
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.

     Volatile  compounds can sometimes be detected  near the soil  surface  using
rapid, field screening  methods (e.g., portable photoionization detector  such as HNu
                                     9-64

-------
or Photovac 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 useful  for initial  characterization because  it is a  rapid,
semi-quantitative technique. Benefits of field  screening methods 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  limitations  in  using field screening methods, including:

      •   They cannot always  account for all  constituents that  may  be present in
          the release;

      •   They may not be able to quantify  concentrations of specific constituents
          of concern; and

      •   Constituents  may be  present at levels below detection capability.

Field-screening  methods  are described  in the Compendium of  Field  Operations
Methods (EPA, 1987).

      Soil sampling  methods  will  commonly  vary  with the  depth  of  interest.  For
purposes of the  RFI, these methods  are  described  as "surficial"  or  "subsurface".
Surficial sampling in  the upper 20 cm of soil can usually be  accomplished with 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
                                      9-65

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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 area of soil. Ring samplers will  generally  not be useful  in loose,  sandy soils
or stiff clays.
                                      9-66

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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
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 blade  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  be 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 augering as
a sole sampling  technique  is not  recommended. Augering may  be used, however, in
conjunction with tube sampling that obtains undisturbed  samples.
                                      9-67

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9.6.2      Deep Sampling Methods

     The subject  of  deep drilling is discussed more extensively in the section  on
ground-water sampling (see Section  10), because  deep cores will generally be taken
in  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, are  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.
                                      9-68

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 9.6.2.3.1  Thin-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
 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 water  extraction.  Split-spoons are the  preferred  method for
 obtaining  unconsolidated soil  samples  and  may also  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.
                                      9-69

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9.6.3      Pore Water Sampling

     When contaminants are suspected  of migrating readily  through  the  soil 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.

     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  inorganic 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 lysimeters  may  overcome this
           problem); and
                                      9-70

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       PRESSURE-VACUUM
         ACCESS TUBE
          BENTONITE
    BENTONITE
       POROUS
       CERAMIC
        TIP
                              ACCESS L/NES
                             'POLYETHYLENE
                                TUBING)
   DISCHARGE TUBE
                                            BACKFILL
POWDERED QUARTZ
                                       BENTONITE
                      AUGERED HOLE
                       *" DIAMETER
Figbre 9-6. Typical Ceramic Cup Pressure/Vacuum Lysimeter
                         9-71

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     •    Volatile organics  will  be lost unless  a special organics trap is  installed in
          the system.

9.7  Site Remediation

     Although the  RFI  Guidance is  not  intended  to  provide  detailed  guidance on
site remediation,  it  should  be recognized  that certain  data  collection activities that
may be necessary for a Corrective Measures Study may be collected  during the RFI.
EPA has developed a  practical  guide  for assessing and  remediating contaminated
sites that directs users  toward  technical  support,  potential  data requirements and
technologies that may be applicable to EPA programs  such as RCRA and CERCLA.
The reference for this guide is provided below.

     U.S. EPA.  1988.  Practical  Guide for Assessing and Remediating Contaminated
     Sites.  Office  of Solid Waste and Emergency Response. Washington, D.C.
     20460.

     The  guide  is  designed to  address releases to ground water as  well as soil,
surface  water and  air. A  short  description of the guide is provided  in  Section  1.2
(Overall  RCRA  Corrective  Action Process), under the  discussion of  Corrective
Measures Study.
                                     9-72

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9.8  Checklist
                               RFI 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                                                   	
                PH
                pKa
                Density                                                    	
                Water Volubility                                           	
                Henry's  Law  Constant                                     	
                                                                          __
                "^o w                                                       	
                Biodegradability                                           	
                Rates of hydrolysis, photolysis and  oxidation               	

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                                          	
                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
                                       9-73

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                          RFI CHECKLIST- SOILS
                               (Continued)
           Porosity
           Hydraulic conductivity  (saturated  and  unsaturated)
           Relative  permeability
           Soil  sorptive capacity
           Cation  exchange capacity
           Organic carbon  content
           Soil pH
           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?

           Geological  and  climatoiogical  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?

     •     Further soil  stratigraphic and hydrologic
          characterization  data
     •     Expanded  sampling data
     •    Geophysical  data  on release  location
 (Y/N)
(Y/N)
                                 9-74

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9.9  References

ASTM.  1984. Particle  Size Analysis for Soils. Annual Book of ASTM  Standards,
     Method D422-63. Vol.  4.08.  Philadelphia,  PA.

ASTM. 1984. Standard Recommended  Practice  for Description of Soils.  Annual
     Book of ASTM  Standards, Method D2488-69. 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. NTIS PB84-198621.  U.S. EPA. Las Vegas, Nevada.

Black,  C.  A. 1965. Methods of Soil Analysis, Part2: Chemical and  Microbiological
     Properties.  American  Society  of Agronomy.  Madison,  Wisconsin.

Callahan,  M. A.,  et al. 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.

Elliot, 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 E. 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.II,  Available  Sampling  Methods.  NTIS  PB85-168771. U.S.  EPA.
     EPA 600/4-84-076. Las Vegas, Nevada.

Freeze and  Cherry.  1979. Ground Water. Prentice-Hall,  Inc.,  Englewood  Cliffs,
     N.J.

Garrels, R.M. and  C.L. Christ. 1965. Solutions, Minerals, and  Eguilibria.  Harper
     and Row, New York.
                                     9-75

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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, W. J. Reehl, W. F. and D. H. Rosenblatt. 1981  Handbook of  Chemical
      Property Estimation Methods. McGraw Hill.

 Mason, B. J. 1983. Preparation  of a Soil Sampling Protocol: Techniques and
      Strategies. NTIS PB83-206979. U.S. EPA.  Las Vegas, Nevada.

 Mills, W. B., et al.  1985. Water Quality Assessment: A Screening Procedure for
      Toxic and  Conventional Pollutants in  Surface and  Ground Water. EPA/600/6-
      85/002a,b,  c.   Vol.  I, II  and  III. NTIS  PB86-122494,  122504 and   162195.
      Washington,  D.C. 20460.

 Merrill, 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 Dugway  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,  D. 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 Sites.  Held in
      Denver,  Colorado. October 24-25,1985. EPRI-EA-3356.

Sims, R. C., et al. 1984. Review of In-Place Treatment Techniques for
     Contaminated  Surface  Soils,  Volume  2:  Background  Information  for  In  Situ
     Treatment.  EPA-540/2  -84-003b.  NTIS PB85-1 24899.  U.S. EPA. Washington,
      D.C. 20460.

Stumm, W, and J.J. Morgan. 1981. Aquatic Chemistry. An  Introduction
     Emphasizing Chemical  Equilibria in Natural Waters. John Wiley and
     Sons.  New York, N.Y.
                                    9-76

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 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 Prediciting Leachate
     Generation from  Solid Waste  Disposal Sites. EPA/530/SW-I 68. Office  of Solid
     Waste. Washington, D.C.  20460.

 U.S. EPA.  1982. Sediment and Soil Adsorption Isotherm. Test Guideline No.  CG-
     1710. ITL Chemical  Fate Test Guidelines.  EPA 560/6-82-003.  NTIS PB82-
     233008. Office of Pesticide and Toxic Substances. Washington, D.C. 20460.

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

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

 U.S. EPA. 1985.  Handbook: Remedial Action at Waste Disposal Sites (Revised).
     EPA/625/6-85/006. NTIS  PB82-239054.  Office  of Emergency and  Remedial
     Response. Washington,  D.C. 20460.

 U.S. EPA.  1986.  Criteria for  Identifying  Areas of Vulnerable  Hydrogeoloqy Under
     the  Resource  Conservation and 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. NTIS PB
     85-194488.  Office of Solid Waste. Washington, D.C. 20460.

U.S. EPA. 1986. Test Methods for Evaluating Solid Waste. EPA/SW-846. GPO No.
     955-001-00000-1.  Office of Solid Waste. Washington, D.C. 20460.

U.S. EPA. June 13, 1986. Federal Register. Volume 51, Pg. 21648. TCLP Proposed
     Rule.
                                    9-77

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U. S. EPA. 1986. Permit Guidance Manual on Hazardous Waste Land Treatment
     Demonstration. NTIS PB86-229192.  Office of Solid Waste. Washington, D.C.
     20460.
U.S. EPA. 1987. Soil Gas Monitoring Techniques Videotape. National Audio Visual
     Center. Capital Heights,  Maryland 20743.

U.S. Geological Survey. 1982. National Handbook of Recommended Methods  for
    Water Data Acquisition.
                                  9-78

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                                   SECTION 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
 waste  or constituents to that medium.  This  section provides:

     •    An example  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;

     •    Formats for  data  organization  and  presentation;

     •    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

     A  conceptual  model  of  the release  should  be formulated  using all available
information  on  the  waste,  unit characteristics,  environmental  setting,  and  any
existing  monitoring  data.   This model  (not  a computer or numerical  simulation
model)  should  provide  a working hypothesis of the release mechanism, transport
pathway/mechanism,  and  exposure  route  (if  any).  The  model  should  be
testable/verifiable and  flexible  enough  to  be modified  as new  data become
available.

     For  ground-water  investigations,  this model  should account for the ability  of
the waste to  be dissolved or  to appear as a distinct  phase (i.e.,  "sinkers"  and
"floaters"), as  well  as  geologic and  hydrologic factors which  affect the release
pathway.  Both  the  regional and site-specific  ground-water flow regimes should be
considered  in  determining  the potential magnitude  of the  release, migration
pathways and  possible exposure  routes.  Exposure  routes of  concern  include
ingestion  of ground  water  as  drinking  water  and near-surface flow of contaminated
ground  water  into basements of residences  or other structures  (see Appendix E).
This "basement  seepage" pathway  can  pose  threats through  direct contact,
inhalation of toxic vapors and through fires and explosions if the contaminants are
flammable. The model  should consider  the  degradability  (chemical  and biological)
of the  waste  and its  decomposition  products.  The  conceptual model should  also
address  the  potential  for  the  transfer of contaminants  in  ground  water to  other
environmental  media (e.g., discharge to surface water  and volatilization  to the
atmosphere).

     Based on the  conceptual  model,  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.  Three-dimensional
characterization  is  particularly  important. The  initial monitoring  phase  should
  * Guidance in this section applies to releases from all solid waste management units, except
     releases to ground water from "regulated units" as defined under 40 CFR pan 264.NW).
     Releases to ground water from "regulated units" must be addressed according to the
     requirements of 40 CFR Parts 264.91 thorugh 264.100 for purposes of detection,
     characterization  and  appropriate response.
                                      10-2

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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 B. 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 monitoring 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  areal  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.

     Table  10-1 outlines  an example  of  strategy for characterizing releases  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.
                                      10-3

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                                  TABLE 10-1

                   EXAMPLE STRATEGY FOR CHARACTERIZING
                         RELEASES TO GROUND WATER1
                                  INITIAL PHASE

1.    Collect and  review existing  information  on:

          Waste
          Unit
          Environmental  setting
          Contaminant  releases,  including  inter-media transport

2.    Identify  any  additional  information necessary to fully  characterize  release:

          Waste
          Unit
          Environmental  setting
          Contaminant  releases,  including  inter-media transport

3.    Develop  monitoring  procedures:

          Formulate conceptual model of release
          Determine monitoring  program  objectives
          Plan field screening if appropriate (e.g., geophysical investigations - see
          Appendix  C)
          Select  monitoring  constituents  and indicator parameters
          Identify  QA/QC and analytical procedures
          Appropriate  initial  area well locations  (background  and  downgradient)
          Collection of additional  hydrogeologic data (if necessary)
          Proper well  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:

          Conduct field  screening, if  appropraite
          Collect  samples and  perform  appropriate field  measurements
          Analyze samples  for selected  parameters and constituents

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  warrant interim corrective  measures  -  Notify  regulatory
          agency
          Determine completeness and adequacy of collected data
          Summarize and present data in appropriate  format
                                      10-4

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                            TABLE 10-1 (Continued)

                   EXAMPLE STRATEGY FOR CHARACTERIZING
                         RELEASES TO GROUND WATER'
                           INITIAL PHASE (Continued)

          Determine  if monitoring  program objectives were  met
          Determine  if monitoring locations,  constituents  and frequency were
          adequate to characterize release (nature, rate, and extent)

                       SUBSEQUENT PHASES (If Necessary)

1.    Identify  additional  information  necessary to characterize release:

          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 monitoring network  as necessary:

          Increase 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
          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
     1 The possibility for  inter-media transport of  contamination  should  be
     anticipated throughout  the  investigation.
                                      10-5

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                                              TABLE 10-2
                    RELEASE CHARACTERIZATION TASKS FOR GROUND WATER
        Investigatory Tasks
     Investigatory  Techniques
Data Presentation  Formats/Outputs
1.  Waste/Unit  Characterization

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

   -  Determine  physical/chemical
       properties  of constituents

   -   Determine  unit dimensions
       and other  important design
       features and operational
       conditions

   -  Investigate  possible uni
       release mechanisms to help
       determine  flow
       characteristics
  Review existing information and
   conduct waste sampling if
   necessary (See Sections 3 &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  am
   conduct unit examinations (See
   Section 7)
  Tabular  presentation  (See
   Section 5)
  Tabular  presentation  (See
   Section 5)
  Tabular  presentation  (See
   Section 5)

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

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

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

-   Review  of  existing  geologi
   information

-   Soil  borings  and  rock  coring

-  Soil & subsurface material
   testing
                                      Geophysical  technqiues  (Sec
                                      Appendix C)
   Facility map  & photographs/text
   discussion (See Appendix A &C)
-  Narrative discussions of geology
- Boring and coring logs

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

- Tabular presentations  of soil &
  subsurface physical & chemical
  properties

- Geologic cross sections &
  geologic & soil  maps (See Section
  5 & 9 & Appendix A)

- Structure contour maps (plan
  view) of aquifer & aquitards (See
  Section 5 & Appendix A)
                                                 10-6

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

  -  Identification   of  regional
       flow  ceils,  ground-water
       flow paths & general
       hydrology,  including
       hydraulic conductivities  &
       aquifer  interconnections
  Review of existing  information

  Installation of piezometers  &
 water level measurements at
 different depths

Flow cell & flow net  analyses
  using measured heads

Pumping & slug tests&  tracer
 studies

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

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

  hydrologic cross sectional maps
   (See Section 5)

   Flow nets for vertical &
   horizontal  flow

   Tabular presentations of raw
   data & interpretive analysis

   Narrative discussion & area maps
3. Release  Characterization

       Determine    background
       levels & determine vertical
       and  horizontal extent of
       release, including
       concentrations of
       constituents & determine
       rate  & directions of release
       migration
 Sampling  & analysis of ground-
 water samples  from  monitoring
 system
 Geophysical  methods  (See
 Appendix C)  for detect!ng&
 tracking  plume

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

  Iso-concentrations maps of
  contamination (See Section 5)
                                                                           Maps of rates of release
                                                                           migration  &direction showing
                                                                           locations of possible receptors
                                                                           (See Section 5)

                                                                           Narrative discussion  &
                                                                           interpretations of tabular&
                                                                           graphical  presentations
                                                  10-7

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     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/or  (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).

     Notwithstanding 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
under 40 CFR  Part 264, Subpart D.

     Case Study  numbers  10,  18,  19,  20,  21 and  22  in Volume IV (Case  Study
Examples) illustrate  the  conduct of various aspects  of ground-water  investigations.

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 areal  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
                                      10-8

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connected.   Volatilization  of  contaminated  ground water to  the  air  within
residential and other structures  may  occur via the  basement  seepage pathway, as
described previously. 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,  soil gas  surveys
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.  Further
guidance on the use of soil  gas surveys for investigating releases  to soil and ground
water are presented  in the Soil Section (Section 9).

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
analysis of the waste in the unit. Hazardous constituents may be  grouped by similar
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  commonly  related  to
their volubility,  volatility,  sorption, partitioning, and  density.

     Section 3  provides  additional guidance on  monitoring  constituent selection
and  Section  7  provides  additional  guidance  on waste  characterization.  The
                                      10-9

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following discussion describes  several  waste-related factors  and  properties which
can  aid  in  developing  ground-water monitoring  procedures:

     t    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
          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.
                                      10-10

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     Highly viscous wastes may travel  more slowly than  the  ground water,
     while low-viscosity  wastes  may  travel  more  quickly than  the ground
     water.

•    Water volubility describes the mass  of a compound  that dissolves in  or  is
     miscible  with  water  at a given  temperature  and pressure.  Water
     volubility 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  volubility permits greater amounts
     of the hazardous  constituent to  enter  the  aqueous phase, whereas low
     water volubility indicates  that  a  contaminant can  be  present  in 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
     ground  water.

•    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  (Kow) is a measure of
     the relative  affinity  of  a  constituent  for the neutral  organic and inorganic
     phases  represented  by n-octanol and water, respectively.  It is  calculated
     from  a  ratio (P)  of  the  equilibrium  concentrations  (C) of the constituent
     in each phase:
          P =  Coctano1    and Kow = log P
               Cwater
     The  Kowhas 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 volubility.
                                 10-11

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     •     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
           volubility in water and has the units  of atm-mVmole.  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, volubility,   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,
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
                                      10-12

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described, because 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  geochemical
          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
between  individual grains.   In  fractured  media (e.g.,  dolomites,  some  shales,
granites, and  crystalline  rocks),  ground water and  contaminants move
predominantly 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 intergranular 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
                                     10-13

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channeling occurring in  cracks or crevices. Figure 10-1 illustrates the occurrence and
movement  of  ground  water and contaminants  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  for  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
evaluated.  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 10-2(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.

     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.  Ground-water flow paths, and where possible, generalized  flow nets are
shown  superimposed  on  cross-sections  of  the  geological units.  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
                                     10-14

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       (a)
(b)
(O
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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         (a) LOCAL AND REGIONAL GROUND WATER
            FLOW SYSTEMS IN HUMID ENVIRONMENTS
                (b) TEMPORARY REVERSAL OF IMOUND-WATER FLOW DUE TO
                             FLOODING OF A RIVER OR STREAM
               (c) TYPICAL GROUND-WATER FLOW PATHS IN ARID ENVIRONMENTS
Figure 10-2. Ground-water flow paths in some different hydrogeologic settings.
                                     10-16

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                         TABLE 10-3.  SUMMARY OF U.S GROUND WATER  REGIONS
Region
I
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 Ridge
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
surf ace infiltration
surface infiltration
upland infiltration
infiltration in outcrop areas
infiltration in outcrop areas
surface infiltration
variable*
Discharge Area
streams and rivers
streams and rivers,
some enclosed basins,
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, streams 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 unconfined
5-60 confined
<1-20 unconfined
5-80 confined
10-200 miles
5-80 miles
2-300 miles
<1-40 miles
<1-20 miles
<1-5 miles
<1-20 miles
10-150 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
The recharge area, discharge area, and dimensions of the flow cells within Alaska are highly variable due to the wide range in topography
and geology found in this region.

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    WESTERN MOUNTAIN RANGES
    (Mountains with thin soils over fractured rocks,
   alternating with narrow alluvial and, in part,
   glaciatad valleys)
                  A
    Potenfometric Surface
    of Lower Aquifer
          I
Confined
Bed
                                                                    Silty Clay

                          Figure 10-3. Western  Mountain Ranges
                                               10-18

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 Recharge Area
(Mountain Range)
                                                                           Recharge Area
                       Granite


                      Weathered Bedrock

                      Clay


                 iiJ  Alluvial Deposits
              ,0-3.  Western Moun,ainRanges(eontJnued)

-------
ALLUVIAL BASINS
(Thick alluvial deposits in basins and valleys
bordered by mountains)
                                                A1
       Vally Fill
       Alluvial Deposit
                                                      Boundary condition
                                                                                                  Alluvial
                                                                                                  Deposit
                                                                                   Limes tone
                         Figure 10-4. Alluvial Basins     A
                                        10-20

-------
              COLUMBIA LAVA PLATEAU
              Thick sequence of laval flows irregulary intebdded
              with thin unconsolidated deposits and overlain by thin soils)
           ^consolidated
           Holocene-Piiocene
          Sediments
          Basalt
 - •  J
rk0JH  interbedded Basalt
         and Sediments
 1^-ij  Basement Rocks
                                 Figure 10-5. Columbia Lava Plateau
                                                   10-21

-------
               Schematic Diagram of
               Ground Water Flow Regime Through a Saturated Cross Section

               Note: Assume hydraulic heads increase with depth.
 Interbed,
 Row Top,  —^
 Row 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)
                                   10-22

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COLORADO PLATEAU AND

WYOMING  BASIN
(This soils over consolidated sedimentary
rocks)
        Fault scarp
                 Cliff.
                         Canyon   Extinct v°'<»noes
Ridges
                                                                          Dome
                                                                             Metamorphic
                                                                               rocks
                     Figure 10-6. Colorado Plateau


                                  10-23

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 HIGH PLAINS
(Thick Alluvial deposits over fractured
sedimentary rocks
                                                                    1. Paleovalley Alluvial Aquifers

                                                                    2. High Plains Aquifer System

                                                                    3. Niobrara Sandstone Aquifer


                                                                    4. Pierre Shale Aquitard

                                                                    5. Dakota sandstone Aquifer

                                                                     6. Undifferentiated Aquifers
                                                                       in Crataceous Rocks
                Generalized local ground water regime for site within the
                High plains Region
                                   Figure 10-7.  High Plains
                                                10-24

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  Ground water flow in
  sandstone and clay lenses
B
 plow Line



 Equipotential Line


 Gravel


Sand
                                                                            Sandsto
                                                                                  ne
                               Losing Stream
                              Generalized Regional Flow
              Withdrawal Well
                                     Playa
                              Western Texas.
                              (Recharge centered at playas)
                    Figure 10-7. High Plains (continued)
                                     10-25

-------
NONGLACIAED CENTRAL REGION
(Thin regolith over fractured sedimentary rocks)
                                                                                if' Sandstone

                                                                        r"  —J
                                                                        L     J Saltwater
                                                                                 Fractures


                                                                                Clay So/Is
                                                                         Solution Enlarged

                                                                             ts and Fractures and
                                                                                  ne Disolution
                     Figure 10-8.  Non-glaciated Central
                                    10-26

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                                     Surface Impoundments
                Stream
                                                                                          Fill berm
Alluvial Deposits
              " "i Y.V'l ••' "~
            Figure 10-8.
                                Shale

                               Sandstone

                               Clay Stone
                            Pittsburgh Coal
                           Limestone
                           Flow Line

                                ntial Line
Example of a surface impoundment site in  Non-Glaciated Central
Region (continued)

-------
GLACIATED  CENTRAL REGION
(Glacaial deposits over fractured sedimenary rocks)
                                                                               ^~~-3  Shale
                                                                                       Sand

                                                                                      °UtWaShed ^Posits and
                                                 A1
                       Figure 10-9. Glaciated Central
                                                                                     Sandstone


                                                                                    F'ow Line


                                                                                   £9U'Poten6alLine
                                     IO-28

-------
     600'
                                                                                     Waste Disposal Unit
    500"   JE
   400'
200'
          TJII >  k xx,
          ""    Clay and Silt
                                                                              100-     so-
                                                                                               0'
                                                                                                       50"     tOO-

-------
PIEDMONT BLUE RIDGE  REGION
(Thick regolith over fractured crystalline and
metamorphosed sedimentary rocks)
                                                                     V-I--T--T-
            Bedrock outcrops
                                                                                          Fractures
                                                                                  sfo  Saprolite
                                                                                [::;X-:-X'.j Crystalline Bedrock
 Note: In areas of fractured bedrock, flow through fractures is often greater than flow through the bedrock matrix. Flow through these frac-
 tures may not conform to Darcy's Law. The above flow lines represent generalized flow paths rather than quantitative flow lines used in
 a flow net.
                            Figure  10-10.  Piedmont  and  Blue  Ridge
                                                 10-31

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NORTHEAST AND SUPERIOR UPLANDS
(Glacial Deposits Over Fractured
Crystalline rocks)
                                                                        Fractures
                                                                        Glacio-Fluvial Sand and Gravel
                                                                    jig]  Fluvial Valley Train Deposits


                                                                        Delta Deposits


                                                                        Kame Terrace Deposits
                                                               -^ri.-^-—I  Glacio-lacustrine Fine-grained sediments
                                                               -'//.','/\   Bedrock
                                                              - — — —  Equipotential Line

                                                                  A'
                                                                         Note:  Flow component along
                                                                                axis of valley, although
                                                                                not shown in this
                                                                                cross-section can often
                                                                                be important.
                    Figure  10-11.  Northeast  and Superior  Uplands

                                             10-32

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                                 Discharge Area
B
                                                                                    Water Table
             Generalized local ground water regime within the Northeast and
             Superior Uplands Region showing a confining layer of till.
   Figure  10-11.  Northeast and  Superior Uplands  (continued)
                                   10-33

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ATLANTIC AND GULF COASTAL PLAIN
(Complexly interbedded sand, silt, and day)
                                                                                  &  Clay

                                                                                      Sand
                                                                               '  i  ' I Limestone
                         Figure  10-12.  Atlantic and Gulf Coastal Plain
                                                10-34

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                                           Losing Stream
   '••Q'*:'*•';] Alluvial Deposits
                                                                    200
                                            *4_>L~?-^^^^5Sfet — Sea Level
                                            ^"~T ~ ~~^^>r~~^-r-~-
                                                                 L_ -200
            Sandy Shale
   Note: Regional flow based on high recharge in hills which are
      not shown in this diagram.
Figure 10-12. Atlantic and Gulf Coastal Plain (continued)
                              10-35

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                 Landfill site near the Savannah River in Georgia.
                West
                                                                                                                               East
UJ
                                                                                                                        -*"*»-*-^
                                                                                                                  h=107
                                        Figure 10-12. Atlantic and Gulf Coastal Plain (continued)

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 SOUTHEAST COASTAL PLAIN
 (Thick layers of sand and day over semiconsolidated
 carbonate rocks)
                                                                                          Row Line
                                                                        A"      - — — — Equipotential Line
Solution Limestone

Cross-section with highly generalized flow path lines and equipotential
lines. Actual condition in Karst terrain may not be definable due to
fractures and solution channel flow.
Recharge Area
                                                                                   Discharge Area
                        Sinkhole
                Pteistocene/Holocene Sand        *
               k             /
       Lake    ^             /      Limestone Spring
                                    (Artesian Condition)
      Hawthorn   g>-:->:-"•..  rr:>: j^g
                           Figure *\ 0-13.  Southeast Coastal Plain
                                               10-37

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-Highly permeable due to water-washed sands.
                  a 8ourc8 °' recha^
 to «r» underlying uncorwolidated coastal deposits.
     Figure 10-13. Southeast Coastal  Plain (continued)
                             10-38

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                                                                  •9C
HAWAIIAN  ISLANDS
(Lava flows segmented in part by dikes,
interbedded with ash deposits, and partly
overlain by alluvium)
.8-
                                                                      HAWAIIAN
                                                                      • , ISIANO

                                                               PACIFIC  |0 C £ A
                 Buried s
                  UNSATURATED ROCK
                                     •jj c^^^c? •-•**• ™ ^
                                     i coastal deposits
                     Figure 10-13. Southeast Coastal Plain (continued)

-------
                            159*30'
                                            159*20'
                                                                             1&8W
     Keuei
22"
10'
22"
00'
   Kekeh?
                                   10M4LES
                    0    5   10   IS KILOMETERS
            J56-30'
                        156-20'      15Fl6'
                                              156W
                       5    10    IS MILES
                  0
                  I  I 'l  .'   I  '  •
                  0  5  10  IS  20KILOMETERS
                                                        21'
                                                        40'
                                                        21'
                                                        30'
                                                        21'
                                                        20'
                                                                                          157-SO'
                                                                                                       157'40'
                                                           156*00'
                                                        20-
                                                        00'
                                                        30'
                                                        00'
                O»hu
                                                                    BartMr* Point
S    10 MILES
I	I
0
h
0   S   10  IS KILOMETERS

   155TO'	  155W
                                                                                              Hmraii
                                                                                              20 MILES
                                                                                       10  20 30 KILOMETERS
                                21'
                                10'
                                                                                                                21'
                                                                                                                00'
                                                                                                                20-
                                                                                                                SO'
                                                                                                                                         ismo'
                                                                                                                                                      1CTSO'
                                                                                                                                                         ~
                                                                                                                                 10 MILES
                                                                                                                     0   5  10  IS KILOMETERS
                                        ^^^      .   EXPLANATION
                                        Ullllllj Ground water  impounded  by dikM or
                                              other Mructur**

                                        11 i | i | i | Af>«  underlain by geologic  structure*
                                              •uiteble for impounding ground weter

                                        I    I Ground water perched on Boil or esh
                                              layera

                                        |    JBeeel ground water floeting  on Mline
                                              ground weler

                                        [    ) Brecki*h betel ground weter
                                       Approximate outline  of [he  different  ground-water areas  on the principal Hawaiian  islands. (From  Takasaki,  1977  )
                                                     Figure  10-14.  Hawaiian Islands (Continued)

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ALASKA

(Glacial and Alluvial Deposits, Occupied in
Part by Permafrost, and Overlying Crystalline,
Metamorphic, and Sedimentary Rocks)
                                                                                          Water

                                                                                          Permafrost
                                        Figure 10-15.  Alaska
                                                   10-41

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                                                                             EXPLANATION


                                                                            Continuous permafrost


                                                                            Discontinuous permsfrosi


                                                                            No permafrost
                                                                       Losing
                                                                       Stream
Alluvium
•°''^V,'::'7r^^v:^
•^^^^Vv^-^X: -Tf-; .if- V
                                                                ^

                                    Figure 10-15. Alaska (Continued)


                                                    10-42
                                                                                                     Permafrost
                                                                                                    Fluvial
                                                                                                    Deposits
                                                                                                     Till
                                                                                                     Alluvial
                                                                                                     Deposits

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ALLUVIAL VALLEYS

Thick sand and gravel deposits beneath floodplains and terraces
of  strams)
                                                               MISSISSIPPI RIVER
                                                         \\.v\\v^
                                                       Naturall^ee
                                                                                               Gravel

                                                                                               Sand

                                                                                               Silt and clay

                                                                                          i   i] Limeatone
                                  Figure 10-16. Alluvial Valleys
                                                 10-43

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                   Buried drum site
           Existing Ground Surface.
                                      Pre-Excavation Ground Surface
                        £ Fine Sand, Trace   ^  Lake Deposits

1+00    2-fOO     3+00    4+00     5+00    6+00     7+00    8+00     9+00    10+00
                            Horizontal  Distance
    Stratified Drift
        Figure 10-16. Alluvial  Valleys (continued)
                               10-44

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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  present in
the underlying bedrock have  a limited storage capacity  and are filled  quickly with
recharging  ground water  flowing from higher elevations  (see Figure  10-3). The
remaining  surface  water runs overland  to  streams that eventually  may recharge
other  areas.  Streams  that  recharge ground water are referred  to  as "losing
streams."   Figure 10-3  also shows local  ground-water flow paths influenced  by low
permeability bedrock  located in intermountain  valleys throughout  the  mountain
ranges.

     The  Alluvial Basins region consists of deep,  unconsolidated sediments adjacent
to mountain  ranges.   Precipitation  often  runs  rapidly off the  mountains and
infiltrates  into the  alluvium at the  valley margins. The water  moves  through the
sand  and  gravel layers  toward the centers of the basins (Figure 10-4). The presence
of disjointed  masses  of  bedrock in  this region  is  crucial  to the  hydrogeological
regime. Low  permeability  igneous  bedrock often isolates the ground-water  regime
into  individual basins with minimal exchange of  ground  water. Where  the  bedrock
is composed of limestone  or  other highly permeable formations, large regional flow
systems can develop, encompassing many basins. Recharge areas in  this  region are
located in  upland  areas;  lowland stream beds  only  carry  water when  sufficient
runoff from the  adjoining mountains  occurs.

      Basaltic bedrock is the major source of ground water within the Columbia Lava
Plateau region. Volcanic bedrock yields water mainly from zones at the contacts of
separate basalt flows.  The  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 caused partially by the  rapid cooling and consequent fracturing  of the
top of each basalt flow.

     The  Colorado  Plateau  and Wyoming  Basin region is a large plateau  consisting
principally  of  sandstones,  shales,  and limestones.  These  sedimentary  rocks  are
generally  horizontal but have  been  modified by  basins and domes in  some  areas
(see  Figure 10-6).  Sandstones have significant primary porosity and  are  the  major
                                      10-45

-------
water-bearing  units in this  region.   Recharge  occurs where the sandstones are
exposed.  Intermittent  losing  streams  created by  sudden  summer  storms provide
some recharge, but most recharge is caused  by snowmelt.

     Generally, ground water is unconfined  in the  recharge  areas and  confined in
the lower reaches  of  the  aquifers.  The storage coefficients  and transmissivities in
the confined portions of the  aquifers are small, causing extensive drawdown during
even  minor  pumping.  Saline ground  water  is  characteristic of this  region  and is
caused by the  existence of gypsum and halide in  the sedimentary deposits.

     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 discharges far exceed 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
interbedding  of sand and clay  lenses.  Figure  10-7 provides generalized flow  nets,
showing flow patterns  through these features.

     Thin regolith  over  fractured sedimentary  rocks  typifies the  nature  of the
geology in the Nonqiaciated  Central  region  (see  Figure 10-8). This  region extends
from the  Rocky  Mountains  to  the Appalachian  Mountains.  Water is  transmitted
primarily  along fractures  developed  at  bedding  planes.  Interconnected vertical
fractures also can store a  large portion of  the ground  water. An example of ground-
water flow on  a  local  scale  is shown for  karst terrain,  where  ground  water moves
rapidly  through solution  cavities  and fractures  in  limestone  and  where  the  flow
pathways  are  closely  associated  with the configuration of  fractures.  Ground-water
flow  in  the  karst regime does  not usually follow  Darcy's  law because most of the
flow goes  through large channels  rather than  the  pores  in  the  rock. Thus,
construction   of a flow  net may  not  be appropriate in  some  cases.  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 of  the region  and  by  flat to  gently rolling
                                      10-46

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terrain in the  western portion of the  region.  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.
Permeability of glacial  deposits ranges from extremely transmissive in gravels to low
transmissivity  in poorly sorted tills.  The presence of buried valleys,  till,  deltas,
kames,  and  other glacial artifacts highly influences  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 formations.  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 metamorphic bedrock in  most
of the Piedmont 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  a much
larger available  drawdown.   Fracture-controlled movement  of  ground water
through  bedrock is  illustrated  by  generalized  flow paths  rather than  quantitative
flow lines used in  a flow  net in Figure 10-10, as is ground-water  movement through
saproiite  (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  Blue  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.

     The  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  of  subsequent
reworking  by ocean currents. Recharge  to the ground-water  system occurs in the
interstream 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
                                      10-47

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area if  high rates of ground-water withdrawal occur. An  example of a regional  flow
net  based on high  recharge  in  hills  shows how regional  flow may differ  from
localized flow based on  local  topography.  Also shown in Figure 10-12 is a landfill
located  in a recharge area 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  precipitation infiltrating  directly  into
exposed limestone  and  by seepage  through the  permeable soils  that  partially
mantle the  limestone  (see Figure  10-13). Coastal environments, such as beaches and
bars, and  swamp areas  have  different  ground-water  regimes,  which are shown in
Figure  10-13. Flow through solution channels  and  large fractures  in  limestone is
often rapid, similar to the situation  shown in Figure  10-8.

     The Hawaiian Islands  region consists  of many distinct and separate  lava flows
that  repeatedly  issued  from several  eruption centers forming  mountainous islands.
Lava extruded below sea level  is  relatively impermeable; lava extruded above  sea
level  is  much more  permeable,  having  interconnected  cavities,  faults,  and joints.
Ground-water  flow  in this region is similar  to that of the Columbia  Plateau  region,
with  the central parts  of thick  lava flows being  less  permeable  and  the  major
portion  of  ground-water flow  in  these  thick  beds  occurring  at  the edges  and
contacts of the  different  lava flows.  Alluvium overlies the lava in  the valleys  and
portions  of the coastal plains.

     Ground  water  in  this  region  can  be  characterized  by  one of three  ground-
water flow  regimes. The first flow regime  consists of ground  water impounded in
vertical  compartments by dikes  in  the  higher elevations near the eruption  centers.
The  second flow regime  consists of fresh  water  floating  on  salt water in the  lava
deposits that  flank the  eruption  centers. This ground  water is  referred to  as basal
ground water  and makes up the  major aquifers in  the  region.  In  some areas of the
coastal  plain,  basal  ground water  is  confined  by overlying  alluvium, which  may
restrain  seaward migration  of fresh water.  The third  flow  regime is where  ground
water is perched  on soils,  ash,  or thick impermeable lava flows above  the basal
ground  water.   Figure  10-14  illustrates  examples of  ground-water flow  in  this
region.
                                      10-48

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     The Alaska region  comprises several  distinct  flow regimes that can  be
categorized  by ground-water regions in  the  lower  48 States. For  example, Alaska's
Pacific  Mountain  System  is similar to  the  Western Mountain  Range and  Alluvial
Basin  regions described  previously.  The  major  variable  causing Alaska  to  be
classified as a separate region is its climate  and the existence of  permafrost over
most of  the region.

     Permafrost  has a major  effect on the hydraulic conductivity of most geologic
deposits. Hydraulic conductivity  declines as  temperatures  drop below  0°C. This
effect can be  severe, causing a deposit that would  be an aquifer in  another  area to
become  a low-permeability aquitard in  an area  of permafrost. In  Alaska, ground-
water supplies are drawn  from  deposits that underlie the permafrost or from areas
where the permafrost is not continuous.  See Figure 10-15.

     Most recharge in this region occurs  in large alluvial deposits,  such  as alluvial
fans, which  streams cross and discharge to.  Although  the  volume  of  interstream
surface  water is  large during  periods of snow  melt, these  interstream areas do not
act as recharge areas because they are usually frozen during the snow melts.

     The Alluvial  Valley  region consists of valleys underlain  by  sand  and  gravel
deposited  by  streams carrying  sediment-laden  melt  water  from   glaciation that
occurred  during  the Pleistocene.   These valleys  are considered to be  a  distinct
ground-water  terrain.  They  occur  throughout the  United  States and  can supply
water to  wells at  moderate to high rates  (see Figure 10-16). 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  of  10  or more  times greater  than  that of the adjacent bedrock. Silt
and clay commonly  are found  both  above and  below the sand and  gravel channels
in the Alluvial Valley  region  as  a result of  overbank flooding  of  rivers.  Ground-
water recharge in this  region  is  predominantly  by precipitation on  the  valleys,  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
                                      10-49

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streams.  An example  of  a flow  net illustrating  local ground-water  movement
beneath a waste disposal site in Connecticut also is 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
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.
                                      10-50

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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, silty clays,
    sandy clays

    Silts, silt loams,
    Silty clay loams

    All others
  Rock Units (all)
    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.
"Assumes de minimus secondary porosity. If fractures or soil  structure  are
   present, effective porosity should be 0.001 (0.1 %).
                                    10-51

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     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
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.
                                     10-52

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

•    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 a 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 sinkholes,  solution
     channels  and  extensive  vertical   and  horizontal  fracturing  in  an
     interbedded  limestone/dolomite.   Using  potentiometric  data,  ground-
     water flow was found to be predominantly 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 these
     solution  channels  should guide  the  placement  of  monitoring wells.
     Note that in  Figure  10-17 the  placement of well No. 2  is offset 50  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 height of the solution channels  ranges  from three to  six feet  directly
     beneath  the  sinkhole to one  foot under the  landfill except for the 40-
                                10-53

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l/l
                  WELL 2
                  (PROJECTED 100 FEET)
                  1.120
                  1.100
                  1,080-
                  1.060
                  1.040-
                  1.020
                  FEET
                          A   BACKGROUND/UPGRADIENTWELL


                              DOWNGRADIENT MONITORING WELL
                              WELL SCREEN

                              POTENTIOMETRIC SURFACE

                              FRACTURE TRACE


                              OUTLINE OF CAVERN (PLAN VIEW)

                              PLUGGED BOREHOLE
WELL 4              WELLS
(PROJECTED 155 FEETI  (PROJECTED 50 FEET)
                                         LANDFILL
                                   (PROJECTED 5 - 50 FEET)
    SOLUTION CHANNEL
    LIMESTONE
    K=5.0x10  cm/iec
                                                                                                                        REGOLITH
                                                                                                                        K=10"3 cm/sec
                                                                                                                        FOSSIL HASH
                                                                                                                        K=10'* cm/sec
                             100
                                      150
                                                       250
                                                                300
                                                                        350
                                                                                400
                                                                                        450
                                                                                                 500
                                                                                                        550
                                                                                                                 600
                              Figure 10-17.    Monitoring well  placement and  screen lengths in  a mature
                                                karst terrain/fractured bedrock  setting.

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foot deep cavern.  This  limited vertical extent of the cavities allows 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).

     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  strati  graphy and ground-water flow systems.  These
are discussed in the following subsections.

10.3.3.1  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.
                                      10-55

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Refer to Section  9  (Soil) for further details.

     Grain  size  distribution  and gradation-A  measurement  of  the percentage  of
sand, silt, and clay  should  be  made for each distinct layer of the soil. Particle size can
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  the larger  sand  particles.  Greater  surface  areas allow for
increased  interactions  with  contaminant molecules.   Clays may  also bind
contaminants  due  to the  chemical structure  of the  clay. Methods for determination
of sand/silt/clay  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  layers (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
                                      10-56

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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.

     Joints are  relatively smooth fractures 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  bedrock mass is often defined by the degree
of 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 USGS (see Section  7)  may be  useful  in
obtaining  information  on the  degree and orientation  of jointing  or  interconnected
void  formation. Rock corings may also  be used to identify these characteristics.

     Degree and orientation  of subsurface  stratification  and   bedding-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  method  for
                                     10-57

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 estimating basement air  contaminant concentrations due to volatile  components  in
 ground-water seeped into basements appears in Appendix  E.

     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
 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
 hydrologic 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  features  that can  be
 used to extrapolate  information  gained from  direct  methods,   Applicable surface
 geophysical  methods  include seismic refraction,  electrical  resistivity,  electro-
 magnetic, magnetics,  and ground penetrating  radar.

 10.3.3.2  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  well  pumping,  agricultural  use) variations  in  ground-water
          flow;  and
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     •     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;

     •     Hydraulic  gradient (vertical  and  horizontal);

     •     Direction and rate of flow;

     •     Aquifer  type/identification  of  aquifer  boundaries;

     •     Specific  yield (effective porosity)/storage coefficient;

     •     Depth to  ground water;

     •     Identify  uppermost  aquifer;

     •     Identify  recharge and discharge areas;

     •     Use of aquifer; and

     •     Aquitard  type and location.

     Hydraulic  conductivity-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.
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     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  maybe 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.

     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  piezometers 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  aquicludes.  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 vield/storativity --Specific  yield and  storativity 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
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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
in contact with  the water  table will first percolate through  the unsaturated 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
limited  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 CFR  §260.10,  "aquifer"
means a geologic formation, group  of formations, or part of a formation  capable of
yielding  a significant  amount  of ground  water  to wells  or springs. "Uppermost
aquifer,  " also defined in 40 CFR §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
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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.

      For further information  on  the  uppermost  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).  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 aquifer-The proximity  and  extent of local ground-water use  (e.g.,
pumping)  may  dramatically influence  the  rate  and direction of  ground-water flow
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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.

     Aquitard  type  and  location-Aquitard  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
over time. 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
information.  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.
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 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
 (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 NAWDEX system. For  further information,  telephone
(703)860-6031.
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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
Appendix  A for  a  more detailed discussion of the usefulness of aerial photography
in release  characterization  and availability of  aerial photographs.

10.3.4.5 Other  Sources

     Other  sources  of  information for subsurface  and  release  characterization
include:

     •    U.S. EPA files (e.g., CERCLA-related 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  Well 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.
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 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  ground  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
 illustrates  three possible  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 (i.e.,  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  also  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:

      •    Monitoring  constituents   and  indicator parameters;

      •    Frequency  and duration at which samples will  be taken;
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                Case One
                   WMA
                                   	1
    l_
          No new wells may be needed
          for SWMU if all units are
          closely spaced.
                                                              Case Two
Wells for RUs not adequate
for SWMU due to geographic
remoteness.
                                                                                                         Case Three
                                                                                                  WMA
                                                                                                                       WMA
                                                                                                                    I	I
New wells needed for SWMU
due to presence of a ground-
water divide.
                                               KEY:
          SWMU -  Solid Waste Management Unit

             RU -  Regulated Unit

           WMA -  Waste Management Area

              O -  Background Monitoring Well
          - Downgradient Monitoring Well
            Ground-Water Flow Direction
Note: Drawings not to scale.

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

     •    Monitoring  locations.

     [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,  Storaqe.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 B).
Indicator parameters (e.g., TOX,  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,  because  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.
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     In developing  an  initial  list of monitoring  constituents and  indicator  para-
meters, the following items should be considered:

     •    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 B. 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 the 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 for selecting corrective measures
(e.g.,  in assessing ground-water  treatment alternatives).  This  is also  discussed  in
Section 3 and Appendix B. Information on the  major anions and cations that  make
up the  bulk  of dissolved  solids in  water can  be used to  determine  reactivity and
volubility  of   hazardous  constituents and therefore  predict  their mobility   under
actual  site conditions.

10.4.3     Monitoring Schedule

10.4.3.1  Monitoring Frequency

     Monitoring frequency should be based on various factors, including:
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     •     Ground-water flow rate  and flow  patterns;

     •     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  RCRA 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.,  hydrogeoiogy, wastes present) and  should  be determined through
consultation with  the  regulatory   agency. The regulatory agency will  evaluate initial
monitoring  results to  determine  how  long  monitoring  should  continue and  to
determine  the need  for  adjustments  in the  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.
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10.4.4     Monitoring Locations

     If  there  is no  existing  monitoring  system or if  the  system is inadequate to
effectively characterize  ground-water  contamination, the owner or  operator should
design and  install  a well  system  capable of intercepting the suspected contaminant
plume(s).  The system  should  also be  used  for  obtaining relevant  hydrogeologic
data.  The  monitoring  well  network configuration  should  be  based  on  the site's
hydrogeoiogy,  the  layout  of  the  facility  and the  units of concern,  the location of
receptors, and should  reflect a  consideration  of  any information available  on the
nature and  source of  the release.  It is important to  recognize  that the potential
pathways of  contaminant  migration  are three  dimensional.  Consequently,  the
design of a monitoring  network which intercepts  these potential pathways  requires
a three dimensional  approach.

     in many cases, the  initial  monitoring system will need  to be  expanded  for
subsequent  phases.  Additional  downgradient  wells will often  be needed  to
determine the extent of the  contaminant plume.  A greater  number of background
wells  may also be needed to account for spatial variability in ground-water quality.

     Prior to the  installation  of additional  downgradient monitoring  wells,  a
conceptual  model of the release  should  be made from a  review of waste and unit
information  and  current  and  past site characterization  information. Additional
hydrogeologic investigations may  also  be appropriate.  For example,  piezometer
readings surrounding  the  well(s)  showing a  release,  should be  used to  determine
the current  hydraulic  gradient(s). These values should  be  compared  to  the
potentiometric surface   map  developed  for  the site  hydrogeologic  characterization
to better describe the direction(s)  of  release  migration. Seasonal (natural  or
induced) or regional  fluctuations  should  be  considered during  this  comparison.  A
re-evaluation of  the facility's subsurface  geologic  information should  be  performed
to identify  preferential  pathways  of contaminant  migration.  In  many  situations,  it
may  be appropriate to  develop  ground-water flow nets  to  show vertical and
horizontal components  of flow. Guidance on  construction  of flow nets is provided
in Section 10.5.2 and in the  Ground Water Flow Net/Flow Line Technical Resource
Document.  NTIS   PB86-224979.  (EPA,  1985).  The  installation of additional
piezometers may be necessary to verify  the accuracy of the flow nets and assist in
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determining  whether or  not the  site  hydrogeology  has been  adequately
characterized.

     At  facilities where  it  is  known or likely that volatile  organics have  been
released to the  ground water, organic vapor analysis of soil  gas from shallow bore
holes  may  provide an  initial indication of  the  areal  extent  of the release
(Figure 10-19).  An  organic vapor  analyzer  (OVA)  may be  used  to measure  the
volatile  organic constituents  in  shallow  hand-augered  holes.  Alternatively, a
sample of  soil gas  may be  extracted  from  a shallow hole and  analyzed  in the field
using  a  portable gas chromatography. These techniques  are  limited to situations
where  volatile organics are  present.   As discussed  previously, it  is recommended
that, where  possible, concurrent  investigations of  more  than one contaminated
media be  conducted.   Further,  the presence  of intervening,  saturated,  low
permeability sediments strongly  interferes with the ability to  extract a gas sample.
Although it  is not necessarily a limitation,  optimal gas chromatography  results  are
obtained  when the  analyte is matched with the highest resolution  technique,  (e.g.,
electron  capture for halogenated  species).   The effectiveness  of  this  approach
should be evaluated  by initial OVA sampling in the vicinity of any wells known  to be
contaminated.

     Other  direct  methods  that may  be used  to define the  extent  of  a  release
include sampling of  seeps and  springs.  Seeps  and  springs  occur  where the local
ground-water surface intersects  the  land  surface  resulting in  ground-water
discharge into a  stream, lake,  or other surface water body. Seeps and springs may
be observed near marshes, at road  cuts,  or near streams. As  discharges from seeps
and  springs reflect the height  of the potentiometric  surface, they  are likely to be
most abundant during a wet season.

     To  minimize the  installation of new wells, the  use of applicable  geophysical
and  modeling methods  may  be proposed  to  describe geologic  conditions  and
contaminant  release  geometry/characteristics.   Such methods  can also aid  in  the
placement  of  new monitoring  wells.
                                     10-72

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o

CO
                                               / LANDFILL ICONIAININO VOLAf lit ODGANICSl
                                    (Plan  View)
                                                                                      LEGEND
                                                                                           Monitoring Well
                                                                                           (No Contaminant Detection)

                                                                                           Soil Gas Analysis Probe Point

                                                                                           Monitoring Well
                                                                                           (Contaminant Detected)
                                                                                      	 Extent of  Contaminated Soil

                                                                                      ^_^ Extent of  Ground-Water Contamination
                                                                                           Plume
                      Figure 10-19.   Example of using soil gas analysis to define probable location of
                                      ground-water release containing volatile organics.

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     A variety of indirect geophysical methods  are  currently available to aid in
characterizing  geologic  conditions and ground-water  contamination.  Geophysical
methods do not  provide detailed,  constituent-specific  data;  however, they can  be
useful in investigating  geologic conditions and  in  estimating  the  general  areal
extent of a  release.  This may reduce speculation involved  in  determining  new well
locations. Details  on the use of geophysical  methods are presented in  Section 10.6
and in Appendix C.

      Mathematical and/or  computer modeling  results  may  be used  in  conjunction
with  the  results of geophysical investigations to assist  in well  placement decisions.
The  owner  or operator should not,  however,  depend  solely on  such models to
determine  the placement of  new monitoring wells.  Because models  may  not
accurately  account  for the high  spatial and temporal  variability  of conditions
encountered in the field, modeling  results should be limited to estimating the  aerial
extent of a  release,  and in determining placement of new  monitoring  wells.

     In  order  to estimate  the potential  extent of a  release in  the  direction of
ground-water flow, Darcy's law should  be applied, if appropriate, to  determine the
average  linear  ground-water velocity (see  Section  10.5.3). This velocity  should  then
be multiplied by the  age of the unit of concern (assuming the unit began  releasing
immediately) to  estimate  the potential distance  of  contaminant migration.  This
distance  should  be  used as  a "yardstick" in  determining  well  locations.  More
complex  modeling  (e.g., solute  transport),  may be  proposed  by  the  owner  or
operator to assist  in  locating additional  monitoring  wells.  However,  modeling
results should  not be used in lieu of field monitoring data.

     The International  Ground  Water  Modeling Center  supported largely by  the
U.S.  Environmental   Protection  Agency,  operates a clearing-house  for ground-water
modeling software, organizes  and conducts short courses  and seminars, and carries
out a research  program  supporting the  Center's  technology  transfer  and
educational  activities. Two major functions of  the Center  are  the  dissemination of
information  regarding  ground-water  models  and the  distribution of  modeling
software. The Center maintains  computerized  data bases, including  updated
computer codes and  test files,  and descriptions of a large  number of ground-water
models.  By  means  of  a  search  and retrieval  procedure, this  information  is easily
                                     10-74

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inaccessible  and readily  available. The Center  can  be contacted  at  the following
address:

           International  Ground  Water Modeling  Center
           Holcomb Research  Institute
           Butler  University
           Indianapolis,  Indiana  46208
           Telephone: (317)283-9458

The Center  will   send,  upon  request and  free  of charge,  a listing  of available
publications,  and  a copy of its  Newsletter.

     In selecting  and applying models, it  is important  to remember that a model is
an  artificial representation of a physical system  used to characterize a  site. A model
cannot  replace field data, nor  can it be more accurate than the  available site data.
In  addition,  the   use of  computer models requires  special expertise.  Time  and
experience are needed  to  select the appropriate code  and subsequent  calibration, if
these resources  are  not  available,  modeling should not be attempted.  Models  are
used  in conjunction  with scientific  and  engineering  judgment; they are  an  aid to,
not a surrogate for, a skilled analyst.

     If  a model  is  proposed  in the  monitoring procedures, the  owner or operator
should describe all assumptions used in applying the  model to the site in question. A
sensitivity analysis of the  model  should be run  to determine which  input parameters
have the most influence on  model results,  and the  model's  results should  be  verified
by field sampling.  The owner or operator should clear the use of any and all  models
through  the   regulatory agency prior to use.   Section  3 provides  additional
information on the use of models.

10.4.4.1 Background and  Downgradient  Wells

     Background   wells  (preferably upgradient)  may  be installed  to obtain samples
that  are not   affected by  the facility,  if the owner or operator believes  that other
sources are contributing to the  releases of concern. These wells should  be screened
at the  same  stratigraphic horizon(s) as the downgradient  wells.  Background wells,
                                      10-75

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if  installed, should  be sufficient  in  number to.  account for any  heterogeneity in
background  ground-water quality.

      Downgradient wells  should  be located and  constructed to  provide  samples of
ground  water containing  any releases  of hazardous  constituents from  the  units of
concern.  Determination of the appropriate number of wells to  be  included  in an
initial monitoring system should be based  on  various factors, including unit size and
the  complexity of  the  hydrogeologic  setting  (e.g.,  degree  of fracturing and
variation  in  hydraulic  conductivity).  Downgradient  monitoring wells  should be
located  at the  limit  of the waste  management  area of the  units of concern  and at
other downgradient locations, as appropriate.  For example,  "old" releases may
show higher constituent  concentrations at locations  downgradient of the  unit.  In
such  cases,  flow  nets may  be  useful  in determining additional downgradient well
locations (See Section 10.5.2).

10.4.4.2  Well  Spacing

     The horizontal  spacing  between wells should  be a design  consideration. Site
specific  factors as listed in Table 10-5  should be considered when determining the
horizontal distances  between  initial monitoring system wells.  These factors cover a
variety  of physical and  operational  aspects  relating to  the facility  including
hydrogeologic  setting,  dispersivity,  ground-water  velocity,  facility design,  and
waste characteristics.  In  the less  common  homogeneous  geologic  setting  where
simple flow patterns are  identified, a  more  regular  well spacing  pattern may be
appropriate. Further guidance  on  the  consideration  of  site specific conditions  to
evaluate well spacing is described  in Chapter Two of the TEGD (U.S. EPA,  1986).

     Subsequent phase monitoring systems  should be  capable of identifying  the
full extent of  the  contaminant  release and  establishing the concentration  of
individual  constituents throughout  the  release.  Well installation  and  monitoring
should concentrate on  defining those areas that  have been affected by the release.
A  well cluster network should be  installed in  and around the release to define the
horizontal and  vertical  extent of  contamination. Networks  of monitoring  wells  will
vary  from  site  to site, depending  upon hydrogeological complexity  and
contaminant characteristics. Surface geophysical techniques  and  modeling may also
                                     10-76

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     TABLE 10-5.  FACTORS INFLUENCING THE INTERVALS BETWEEN INDIVIDUAL

               MONITORING WELLS WITHIN A POTENTIAL MIGRATION PATHWAY
         Wells intervals May Be
            Closer If the Site:
                                               Wells  Intervals  May  be
                                                  Wider  If the  Site:
  Manages or has managed liquid waste
  Is very small (i.e., the d?wngradient
  perimeter of the site is less than 1 so
 feet)
 as waste incompatible with liner
 materials
 as fill material near the waste
 management  units  (where  preferential
flow might occur)
Has buried pipes, utility trenches, etc.,
where  a  point-source leak might occur
Has complicated geology
-  closely spaced fractures
- faults
- tight folds
•solution channej^
•discontinuous structures

as heterogeneous conditions
-  variable hydraulic  conductivity
- variable lithology

ocated in or neara  recharge  zone


 a high (steep) or variablp  nydraulic
client                   e

 dispersivity

  average linear velocity
                                        Has simple geology
                                       - no fractures
                                       -no  faults
                                       - no folds
                                       -no solution  channels
                                       -continuous  structures

                                      Has homogeneous conditions
                                      -uniform  hydraulic  conductivity
                                      -uniform  lithology
                                         a low (flat) and constant hydraulic
                                     gradient
                                     High dispersivity
                                     Low
                                         average linear velocity
                             10-77

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 be used,  where appropriate, to help facilitate release definition.  The well  density or
 amount  of  sampling  undertaken  to  completely identify the  extent  of  migration
 should be determined by the variability  in  subsurface  geology  present  at the site.
 Formations  such as  unconsolidated  deposits with numerous interbedded  lenses of
 varying  permeability,  or consolidated  rock with numerous  fracture  traces,  will
 generally require  more  extensive  monitoring  to  ensure  that contamination is
 appropriately  characterized.

      Monitoring should  be  performed  to  characterize the  interior portion(s) of a
 release.  This  is important because constituents  can migrate at differing  rates and
 may  have been released at different times.  Monitoring only  at  the  periphery of  the
 release may not identify all  the  constituents  in the release,  and the concentration of
 monitoring  constituents  measured at the periphery  of  the  release  may  be
 significantly  less  than  in  the  interior  portion(s).  Patterns in  concentrations  of
 individual constituents can  be  established  throughout  the release  by  sampling
 along several lines  that  perpendicularly  transect  the  release. The number of
 transects  and  the  spacing  between  sampling points  should be  based on  the waste
 characteristics, the  size  of  the  release,  and variability in geology observed at  the
 site.  Sampling locations should also be selected so  as  to  identify those areas of
 maximum contamination  within the  release.  In addition to the  expected hazardous
 constituents,  the  release  may  contain  degradation  and  reaction products, which
 may also be hazardous.

      Results  of geophysical  methods  may be correlated with  data  from  the
 monitoring  well  network.  The monitoring  program  should  be flexible  so  that
 adjustments can be made to reflect  release  migration and changes in direction.

     The  spacing  between  initial  downgradient  monitoring wells should ensure  the
 measurement  of releases near the unit(s) of concern.  However,  it is possible  that  the
 initial spacings between wells will only provide for measurements in the  peripheral
 portion of a  release.  This might result in  water quality measurements  that do  not
 reflect the  maximum  concentration of contaminants in the  release. Therefore,
additional downgradient wells  may be  needed  adjacent to the units  of concern
during subsequent  monitoring phases.
                                     10-78

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     A similar effect  may  be  observed,  even  with  a  closely  spaced initial
downgradient  monitoring network, if a  narrow,  localized  release  migrates  past  the
limit of the waste  management area.  Such a  plume may  originate from a small  leak
in a liner and/or from  a  leak located close to  the downgradient  limit of the waste
management  area,  thereby  limiting the  amount  of  dispersion occurring  in  the
release prior  to  its  passing the  monitoring wells.  Consequently,  if relatively wide
spacing exists between  wells or there is reason to  expect a narrow, localized  release,
the installation of additional monitoring wells may  be  necessary in the immediate
vicinity of those wells in which a release has  been measured. Such  an expansion of
the monitoring  network  is  recommended when a release has been measured  in  only
one  or two  monitoring  wells, indicating  a localized plume.

10.4.4.3 Depth and  Screened  Intervals

     The  depth and  screened  intervals for initial  phase monitoring  wells should be
based  on: (1) geologic factors  influencing the  potential  contaminant  pathways  of
migration  to  ground  water;  (2)  physical/chemical  characteristics of  the  contaminant
controlling its likely movement  and distribution  in the ground  water;  and  (3)
hydrologic factors  likely  to have  an  impact  on  contaminant  movement. The
consideration  of these  factors in evaluating  the  design of monitoring  systems  is
described  in the TEGD  (U.S. EPA, 1986),  including  examples of placement in some
common geologic  environments.  Subsection 10.6 provides guidance on borings  and
monitoring well construction.

     In order to  establish vertical concentration gradients  of  hazardous
constituents  in the release  during subsequent  monitoring phases,  well clusters or
multi-depth  monitoring  wells should be  installed.  The first well  in  a cluster  (or
initial  sampling interval  in a  multi-depth well)  should be screened at the horizon in
which  contamination  was initially  discovered.  Additional  wells in a  cluster should
be  screened,  where appropriate, above  and  below the  initial  well's  sampling
interval  until the margins of  the release  are established.

     Several  wells should  be placed at the fringes  of the release to define its vertical
margins,  and  several  wells should  be  placed  within  the release  to  identify
constituents  and  concentrations.  Care  must  be  taken in placing contiguously
screened wells close together because one well's  drawdown  may  influence  the next
                                     10-79

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and thus change  the  horizon  from  which its samples are drawn. Alternating lower
and higher screens should reduce this effect (see Figure 10-20).

     The specifications of sampling depths  should clearly identify the  interval over
which  each sample will be  taken. It  is  important that these  sampling intervals  be
sufficiently  discrete  to allow  vertical  profiling  of constituent  concentrations  in
ground water at each  sampling location.  Sampling will  only  provide  measurements
of the average  contaminant  concentration over the interval from  which that sample
is taken.  Samples  taken  from  wells screened  over a large vertical interval  may  be
subject to  dilution effects from  uncontaminated  ground water lying  outside  the
plume limits.  The  proposed screened  interval  should  reflect  the expected vertical
concentration  gradients within  the release.

     At those facilities where  immiscible contaminants  have  been  released and
have migrated as a separate phase  (see Figure  10-21),  specific techniques will  be
necessary to  evaluate their migration.  The detection  and  sampling of  immiscible
layers  requires  specialized equipment  that  must be  used before  the  well  is
evacuated  for conventional sampling.   Chapter  4 of the TEGD (U.S. EPA,  1986)
contains a  discussion  of ground-water monitoring  techniques  that can  be  used  to
sample multi-phased  contamination. These sampling  techniques  vary according  to
whether the immiscible phase is  lighter than  water (i.e., floats) or denser than water
(i.e., sinks),  and is also dependent on the thickness  of the layer.

     The formation   of  separate  phases  of  immiscible contaminants in the
subsurface  is largely controlled by  the rate  of infiltration  of the  immiscible
contaminant and  the  solubility  of that  contaminant in  ground  water.  Immiscible
contaminants  generally have limited volubility in water. Thus,  some  amount of  the
immiscible contaminant released from  a  unit(s) will dissolve  in  the ground  water
and  thus  migrate  in  solution.  However,  if the  amount  of  immiscible  contaminant
reaching ground water exceeds  the ability of  ground water to dissolve  it (i.e.,  the
constituent  water  solubility),  the ground  water in the upper  portion of  the  water
table aquifer  will  become saturated  and the contaminant  will form  a separate
immiscible phase.  Hence, the contaminant will  be  present in the  ground water at a
concentration  approaching  its water volubility,  as  well as in  a separate  immiscible
phase.  If cosolvents  are present,  the  concentration of the  contaminant  in the
ground  water can  exceed the contaminant's  water volubility,  whether  or not a
separate immiscible phase is  present.
                                      10-80

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                                       UECENO
                                           ANOSCflMN






                                  10-  SCfltCN tINGTM






                                 Illll* WATCA TAiLI
        Figure  10-20
Vertical Well Cluster Placement
            10-81

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     At this  point,  the  behavior and migration  of an  immiscible contaminant  will  be
strongly influenced  by its density relative  to  ground water.  If the  immiscible  is less
dense than  ground  water,  it will tend to form a separate immiscible layer and
migrate on top  of the ground water. If the density  of the immiscible contaminant is
similar to  that of ground water,  it will tend to  mix and  flow as a  separate  phase with
the ground water, creating  a condition of multiphase  flow.

     If the density  of the immiscible constituent is  greater than  ground water, it will
tend to sink  in  the aquifer  (see  Figure  10-21). As the immiscible  layer sinks and
reaches  unaffected  ground  water in a deeper  portion of  the aquifer,  more  of the
immiscible contaminant will  tend  to  enter into  solution in ground  water and  begin
to migrate as a  dissolved constituent.  However, if  enough  of the dense immiscible
contaminants are present,  some portion of these contaminants  will  continue to sink
as a separate immiscible phase until a geologic formation of reduced permeability is
reached.  At  this point,  these  dense contaminants will tend to form  a layer that
migrates  along  the  geologic formation (boundary).

     Immiscible  phase contaminants may migrate at rates different  than that  of
ground water.   In  addition,  immiscible  contaminants  may  not flow  in the  same
direction  as  ground  water.   However, it  is  important to  re-emphasize  that  some
fraction of these contaminants may  dissolve  in ground  water and migrate  away
from the facility  as  dissolved  constituents.

     Light immiscible  contaminants tend  to migrate  downgradient as a floating
layer above the  saturated zone (see  Figure 10-21).  The hydraulic gradient is a major
factor  in  the movement of this  light  immiscible  layer.  Other  important factors
involved  in the  migration  rate of  a light immiscible phase include  the intrinsic
permeability  of  the  medium,  and the density   and viscosity of the  contaminants.
Oftentimes, an  ellipsoidal  plume will develop  over the  saturated  zone as depicted in
Figure 10-21. While it may  be possible to analyze  the behavior  of a light immiscible
layer  using  analytical  or  numerical  models,  the  most  practical approach for
determining  the  rate  and direction  of migration of such  a  layer  is to observe  its
behavior  overtime  with  appropriately located monitoring  wells.
                                      10-82

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                   CONTAMINATION
                      SOURCE
                                                                                          SAND
                                                                                         AQUIFER
AOUITARO
LEGfNO
      LICMI IMMISCIULE PLUME


      MAIN PLUME


      HEAVY IMMISCIBLE PLUME
           Figure 10-21.   General schematic of multiphase contamination in a sand aquifer.

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     The migration  of  a layer  of  dense  immiscibles resting  on a  low permeability
geologic formation  may be strongly  influenced by  gravity.  Depending  on the slope
of the  retarding  formation, the  immiscible  layer may  move  with  or in a  different
direction from  the  flow of the  ground  water.  Consequently,  the evaluation of the
rate and direction  of  migration of  a  dense immiscible  layer  should  include  a
determination  of  the  configuration of  the  retarding  formation  on  which  the
immiscible layer  is migrating. The  direction  of migration and  estimates  of migration
rates of  dense  immiscibles  can then  be  obtained  by  including  the  gravitational
forces  induced by  the slope of the retarding formation in the gradients  used to
calculate contaminant  flow rates.  If a dense immiscible  layer(s) is expected or
known,  the monitoring  plan  should  include  procedures to verify  its direction  and
rate of  flow.

10.5 Data Presentation

     Section 5 of this guidance describes data presentation methods with examples.
In addition  to  sorted data tables,  the methods described  for contaminant  isopleth
maps,   geologic  cross-sections,  cross-sectional  concentration  contours,  and  fence
diagrams should  be  useful for presenting ground-water  investigation findings.  The
following  presents specific data presentation methods that may  be  particularly
useful  for presenting  ground-water  investigation  data.

10.5.1     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
          constituents;

     •    Narrative description  of  unit dimensions,  operations etc.;  and

     •    Topographical map and  plan  drawings  of facility  and surrounding  areas.
                                      10-84

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10.5.2     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.

      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.
                                      10-85

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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  because water  levels change  over
time.   Ground-water  flow directions  can  be  determined   by   drawing  lines
                                     10-86

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 perpendicular  to the equipotential  lines.  Ground water flows from areas  of higher
 hydraulic head to areas of lower 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,  because
 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
                                     10-87

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construction  of  flow  nets is  given in Section  2  of that document.  Mathematical
techniques can be used to construct flow nets although graphical  techniques are the
simplest  and  most  commonly  used.   It  is  worth  noting that  flow  nets  are
dimensionless.

     When  a flow  net has been constructed  for a  site,  it  is advisable  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 evaluating 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
                                      10-88

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                                                    IN
DOWNGRADIENT
                                                   3.5-
                                      UPGRADIENT
                                                               HAZARDOUS WASTE
                                                               LAND APPLICATION
                                                               SITES
    0      50    100

       Scale, Meters
                                          Key:
Equipotential Lines
(in Meters)

Flow Lines

Wells with Well Numbers
    Figure 10-22, Potentiometric  surface  showing  flow  direction
                                 10-89

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            805.8
10
o
 ^—-»
         BOUNDARIES

  OF THE PROPOSED FACILITY
                         —•—




  .WATEHTABLE
          rv
                                                                                   743
                          <*' ^Tja.2 -7fl9 /I79
                                                                                  f  '     ' /
                                                                                 /   /   / / /

                                                                              '-'   I  ///•
                                                                              x   /  /  /  i
                                                                                              888
866
                                                          827.3*  \
                                             ' 872
                                                                                   708.8
                                                            ASSUME  100 =
                                        Figure 10-23. Approximate flow net

-------
variations  in ground-water  levels.  Another situation that would  introduce  problems
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 transient 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.
                                      10-91

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10.5.3    Characterization of the Release

     The objective  of  monitoring is to estimate the  nature,  rate,  and extent (3-
dimensional)  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 may  include the  measurement  of  additional
constituents  in  a more extensive well network than initial  monitoring.  This will
necessitate careful data management. Sections 6.8 and 6.9 of the TEGD (U.S. EPA,
1986)  provide  useful  guidance  on  organizing,  evaluating,  and  presenting
monitoring data.  Section  4.7  of the  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
because 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  Darcy's law:
          -Ki
          ne
                                     10-92

-------
where  (K) is hydraulic conductivity, (i) is hydraulic gradient,  and (ne) is the  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.
Differential transport rates are caused by several factors,  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
degradable chemicals  are  influenced  by a variety  of factors  and  the interactions of
                                      10-93

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these factors can be extremely difficult 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 may  provide  a  better
overall  understanding of complex site conditions,  with relatively  low risk to the
investigative  team.
                                     10-94

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     Various  geophysical  techniques,  including electromagnetic,  seismic refraction,
electrical  resistivity,  ground  penetrating  radar,  magnetic, and several  borehole
methods,  can  be applicable  to  RCRA  Facility  Investigations.  Table  10-6  suggests
appropriate  applications  for the various geophysical methods.  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 beneath  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 intervals (e.g., five foot)  could be
          substituted for continuous cores.
                                      10-95

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10
                                 TABLE 10-6. APPLICATIONS OF GEOPHYSICAL METHODS TO
                                                HAZARDOUS  WASTE SITES
APPLICATION
Mapping of Geohydrologic
Features
Mapping of Conductive Leachates
and Contaminant Plumes (e.g.,
Landfills, Acids, Bases)
Locations and Boundary
Definition of Buried Trenches
with Metal
Location and Boundary Definition
of Buried Trenches without Metal
Location and Definition of Buried
Metallic Objects (e.g., Drums,
Ordinance)
RADAR
1
2
1
1
2
ELECTROMAGNETICS
1
1
1
1
2
RESISTIVITY
1
1
2
2

SEISMIC
1

2
2

METAL
DETECTOR


2

1
MAGNETOMETER


2

1
            1. 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 INFLUENCING 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
unfractured and are substantiated by
regional geologic information).
• Use of geophysical data to correlate
well log data.



Factors That May Substantiate
Increased Density of Boreholes:
• Fracture zones encountered during
drilling.
•Suspected pinchout zones (e.g.,
discontinuous areas across the site).
• Geologic formations that are tilted or
folded.
•Suspected zones of high permeability
that would not defined by drilling
at 300-foot intervals.
• Laterally transitional geologic units
with irregular permeability (e.g.,
sedimentary facies changes).
                          10-97

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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
          geologist.

     •    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.

     ASTM  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  D2488-69,  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-
                                     10-98

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graphic map  and aerial photograph of the site.  Details  regarding specific means for
the presentation of geologic data are  presented  in Section  5 and in  Section 1.2.3 of
the TEGD (U.S.  EPA, 1986).

10.6.2.2 Monitoring  Well  Installation

     The owner or operator is advised to consult Chapter  Three of the TEGD  (U.S.
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  ground-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 Wells-Section 3.4 (TEGD)  discusses  the requirements for
          proper development  of  the  monitoring  wells to  ensure  turbid-free
          ground water samples.
                                     10-99

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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  (± 0.1 ft);
          drilling  and lithologic  logs;
          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);
          sealant  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 3.6 (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.
                                10-100

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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 well(s)  near existing wells and the analysis  and comparison  of samples for
the same monitoring constituents 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.
                                     10-101

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     Slug  testing  is  applied  by  hydrogeologists in  many  field  situations.
Interpretation  of  the results  requires some  professional  judgement.  Slug test
accuracy  is  reduced when dealing with extreme values of hydraulic conductivity.
Very low values (e.g., less than 10-6 cm/see)  are  more accurately  measured  by a
resurg head  test after bailing or pumping the well  dry.  High values (e. g.,  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 if
the slug test is measuring the most permeable  fractures or solution  channels.  In
such cases,  the test results may be misinterpreted  to 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 (e.g.,
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 geologic materials 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  considered.  Zones  of  expected  high
permeability  or fractures identified  from  drilling logs  should  generally  be included
in the  determination  of hydraulic  conductivity.  Additionally,  information from
                                     10-102

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coring  logs can  be used to refine the data generated by slug tests (TEGD, Section
1.3.3).

     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. 1986. Method  9100 includes techniques for:

     •    Laboratory

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

     •    Field

               well  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 the
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
                                     10-103

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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
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 on 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

     •    Interpretation  of flow direction  (1.3.1.4).
                                     10-104

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10.6.3.3  Dye  Tracing

     Dye tracing  is a field method which can be  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 (i)  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,  ne,  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);
                                      10-105

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     •     Monitoring of immiscible  layers (4.2.2);

     •     Well evacuation (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  sampling if wastes  of this  type  are  present at  the
facility.

     The water standing in the well  prior to sampling may not be representative of
in 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  photoionization or  organic vapor analyzers,  pH,  temperature,  and conductivity
meters.   If these parameters and facility background data  suggest that  the water
may be 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:
                                     10-106

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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, 1986)  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, redox 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-846 GPO 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).
                                    10-107

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     Chapter Four of the TEGD (U.S. EPA,  1986)  may also be 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/600/2-85/104. NTIS  PB86-137304. Washington,  D.C. 20460.

10.7 Site Remediation

     Although  the RFI  Guidance is not  intended  to provide  detailed guidance on
site  remediation,  it  should  be  recognized that  certain  data collection activities that
may be necessary for a Corrective Measures Study may be collected  during the RFI.
EPA has developed a  practical guide for  assessing and  remediating contaminated
sites that directs users toward technical  support,  potential data requirements and
technologies that  may be applicable to EPA  programs such as RCRA and CERCLA.
The  reference  for this guide is provided below.

     U.S. EPA. 1988. Practical Guide for Assessing and Remediating Contaminated
     Sites.  Office  of  Solid Waste  and  Emergency Response.  Washington,  D.C.
     20460.

     This guide  is  designed  to address  releases  to ground  water as well  as soil,
surface  water  and air. A short  description of the  guide  is provided  in  Section 1.2
(Overall  RCRA  Corrective  Action  Process),  under the  discussion  of Corrective
Measures  Study.

     In  addition  to the above  described  reference,  several ground-water computer
modeling  programs  are available to  assist in  designing  ground-water  remediation
systems, such  as the one  referenced below. Application of such  models should be
based  on site-specific  considerations, as most models  are  not applicable to all
situations.

     U.S. EPA.  1987. Zone  of Capture  for Ground Water Corrective Action.  IBM
     Compatible  Computer Program and Users Guide.  Federal  Computer  Products
                                    10-108

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Center,  National  Technical  Information Service.  Springfield, VA 22161.
                               10-109

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10.8 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
           •    Physical form of waste
           •    Chemical properties  of waste (organic, inorganic,
                acid, base)  and constituents
           •    pH
           •    pKa
           •    Viscosity
           •    Water  volubility
           •    Density
           *    KOW
           •    Henry's Law Constant
           •    Physical and chemical degradation  (e.g., hydrolysis)
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
           •    Presence of on/offsite buildings
           •    Depth and dimensions of unit
           •    Inspection records
           •    Operation logs
                                      10-110

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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
          •    Rate 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.,  areal  extent)
          •     Aquitard  characteristics (depth,  permeability degree of
                jointing,   continuity)
                                      10-111

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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
5.    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
                                    10-112

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10.9 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.

Balch,  A. H., and W. W. Lee. 1984.  Vertical Seismic  Profilin  Technique,  Applications
     and Case 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.  MacMillan
     Publishing Co., Inc. New York,  N.Y.

Callahan, et al. 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,
     New Jersey.

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

McWhorter  and Sunada. 1977.  Ground  Water Hydrology and  Hydraulics. Water
     Resources  Publications. Littleton,  Colorado.

OkirD.S.  and  T.W.  Giambelluca,  "DBCP,  EDB, and  TCP  Contamination  of  Ground
     Water in  Hawaii, " Ground Water. Vol. 25, No. 6, November/December 1987.

Snoeyink and Jenkins.  1980. Water  Chemistry. John  Wiley&  Sons.  New York, N.Y.
                                    10-113

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Sowers, G. F. 1981.  Rock  Permeability or  Hydraulic Conductivity  - An  Overview in
     Permeability and  Ground  Water Transport. F.  Zimmic and C. 0.  Riggs,   Eds.
     ASTM Special Technical Publication 746. Philadelphia, PA.

Sun, R. J., Editor.  1986. Regional Aauifer-Svstem  Analysis  Program  of the  U.S.
     Geological  Survey.  Summary of Projects.  1978-1984. U.S.G.S.  Circular  1002.
     U.S. Geological  Survey. Denver, CO.

Technos, Inc.  1982. Geophysical Techniques for Sensing Buried Wastes  and Waste
     Migration.  Environmental Monitoring  Systems  Laboratory. NTIS  PB84-198449.
     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, D.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. Office 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
     (TRD^ Final Report.  NTIS PB86-224979.  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.
                                   10-114

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U.S. EPA. 1982.  Handbook for Remedial Action at Waste Disposal Sites. EPA-625/6-
     82-006.  NTIS  PB82-239054.  Office  of Emergency and  Remedial  Response.
     Washington,  D.C. 20460.

U.S. EPA. 1984. Permit Applicant's Guidance Manual for Hazardous Waste - Land
     Treatment.   Storage,  and  Disposal  Facilities.    Office of  Solid  Waste.
     Washington,  D.C. 20460.

U.S.  EPA. 1985.   DRASTIC:  A Standardized System for  Evaluating  Ground-water
     Pollution  Potential Using Hvdroaeoloaic Settings. EPA/600/2-88/018.  Robert  S.
     Kerr Environmental  Research  Laboratory. Ada, OK.

U.S. EPA. 1986.  Guidance Criteria  for Identifying  Areas  of Vulnerable Hydrogeology
     Under  the   Resource  Conservation  and  Recovery  ActJnterim  Final.
     Washington,  D.C. 20460

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. NTIS P886-125580. Office  of Solid Waste.
     Washington,  D.C. 20460.

U.S. EPA. 1985.  Practical  Guide for Ground Water Sampling.  EPA-600/2-85/104.
     NTIS PB86-137304. Washington,  D.C. 20460.

U.S. EPA. 1985.  RCRA Ground-Water Monitoring Compliance Order  Guidance
     (Final).  Office of Solid  Waste.  Washington, D.C. 20460.

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

U.S. EPA. 1987.  Zone of  Capture for Ground Water Corrective Action. IBM
     Compatible  Computer Program and  Users  Guide.  Federal Computer Products
     Center,  National Technical  Information  Service.  Springfield, VA 22161.
                                   10-115

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U.S. EPA. 1988. Practical Guide for Assessing and Remediating Contaminated
     Ground  Water.  Office  of Emergency and  Remedial  Response.  Washington,
     D.C. 20460.

U.S. Geological  Survey. 1984. Ground water Regions of the U.S. Heath et. al.,
     Water Supply Paper No  2242. Washington, D.C.
                                 10-116

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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:

     •    An  example  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;

     •     Formats for data organization and  presentation;

     •     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  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 required  in all instances;
                                      11-1

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however,  it identifies  possible  information which may be  necessary  to  perform
release characterizations  and  methods  for  obtaining  this  information.  The  RF
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 requirements for all 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 Numbers 23 and 24  in Volume IV (Case Study Examples)  provide
examples  of subsurface gas investigations.

11.2 Approach for Characterizing Subsurface Gas  Releases

11.2.1     General Approach

     The  collection  and review of  existing  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  to characterize the release.  A conceptual  model  of the
release should  be formulated  using  all  available information  on the  waste,  unit
characteristics,  environmental   setting, and  any  existing  monitoring  data.  This
model  (not a  computer  or numerical  simulation model) should  provide  a  working
hypothesis of  the  release  mechanism, transport pathway/mechanism, and  exposure
route (if any).  The model should be  testable/verifiable  and flexible  enough  to be
modified as new data become available.
                                      11-2

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     The conceptual model  for  subsurface  gas should consider the ability  of  the
waste to  generate  gaseous  constituents, the  conditions which would  favor
subsurface migration of the gaseous release, and the likelihood of such a release to
reach  and accumulate within structures (e.g., residential basements)  at explosive or
toxic  concentrations.

     Additional  data  collection  to characterize  the contaminant  source  and
environmental  setting  may  be  necessary  prior to implementing the  monitoring
procedures. The subsurface  pathway  data collection  effort  should  be coordinated,
as  appropriate,  with similar efforts for other media  investigations.

     Characterization of subsurface gas  releases  can be  accomplished through a
phased  monitoring  approach.   An  example  of  a  strategy  for  characterizing
subsurface gas releases is shown in Table 11-1.

     Development  of  monitoring  procedures  should  include determining  the
specific set of subsurface gas indicators  and constituents for monitoring. Methane,
carbon dioxide,  and site-specific volatile organics (e.g., vinyl chloride), can  be used
to  identify the  presence  of  subsurface  gas during initial   monitoring.  Subsequent
monitoring will generally  involve these gases, but  may also involve various  other
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.
                                      11-3

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                                  TABLE 11-1

   EXAMPLE STRATEGY FOR CHARACTERIZING RELEASES OF SUBSURFACE GAS1

                                 INITIAL PHASE

1.    Collect and  review existing information  on:

          Waste
          Unit
          Environmental  setting
          Contaminant  releases,  including  inter-media transport

2.    Identify any  additional information necessary to fully  characterize release:

          Waste
          Unit
          Environmental setting
          Contaminant  releases,  including  inter-media transport

3.    Develop  monitoring  procedures:

          Formulate conceptual model of release
          Determine  monitoring program  objectives
          Determine  monitoring constituents  and  indicator parameters
          Sampling approach  selection
          Sampling schedule
          Monitoring   locations
          Analytical  methods
          QA/QC procedures

4.    Conduct  Initial Monitoring:

          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 parameters  and constituents

5.    Collect, evaluate and report results:

          Compare methane results with lower explosion limit (LEL) and 0.25  LEL
          and report  results  immediately to regulatory agency if these  values  are
          exceeded
                                     11-4

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                             TABLE 11-1 (Continued)

    EXAMPLE 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:

          Perform  expanded  monitoring of area  for  methane  and other  indicator
          parameters  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
          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
     The  possibility  for  inter-media  transport of  contamination  should be
     anticipated throughout  the  investigation.
                                      11-5

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                                             TABLE 11-2
                  RELEASE  CHARACTERIZATION  TASKS FOR SUBSURFACE GAS
        Investigatory Tasks
  Investigatory Techniques
Data Presentation Formats/Outputs
1.  Waste/Unit  Characterization

       Identification  of waste
       constituents of concern

       Identification  of unit
       characteristics which
       promote a subsurface gas
       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

       Definition  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
measurements

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
1. Release  Characterization

       Model extent of release
       Screening evaluation of
       subsurface gas release
       Measurement for specific
       constituents
Gas migration model (See
Appendix  D)
Shallow  borehole  monitoring
 and monitoring in  surrounding
buildings for indicators and
specific constituent(s)

Selected gas well installation
and  monitoring
                                      Monitoring  in  surrounding
                                      buildings	
   Estimated methane
   concentration isopleths for LEL
   and 0.25 LEL

   Listing of concentrations levels
   Tables of concentrations

   Detailed assessment of extent
   and magnitude of releases

   Tables of concentrations
                                                 11-6

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     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/or  (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).

      Notwithstanding 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, Subpart D.

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
                                      11-7

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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).

     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. 1985. 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.
                                      11-8

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                                                                UNSATURATED
                      GROUNDWATER  TABLE
Figure 11-1.


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                         UNDERGROUND TANK
                                               PAVING
                                                              file
                       VOLATILE

                       LIQUIDS
                        SURFACE IMPOUNDMENT CLOSED AS LANDFILL
                               LIQUIDS/SLUDGES
                UNSATURATED
                    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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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 content, etc.

     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:

11.3.1.1.1      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 comporting 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
                                     11-11

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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.

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  units  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.
                                     11-12

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      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  for future  subsurface  gas generation  and
 subsequent release.  The  owner  or  operator should  review facility  records to
 determine if combustion has occurred  and when.

 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  waste   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
                                     11-13

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           specific  constituents present,  and  analysis for ail of the  constituents  of
           concern  as gaseous releases (See Appendix B,  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.

11.3.1.3         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

     In 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  volubility  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 pure  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  volubility and concentration  (i.  e.,  at high
           concentrations  releases  can  occur even though a constituent's vapor
           pressure is relatively low).
                                      11-14

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     •     Octanol/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
           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  potential  for release.  Partial pressures  will  be  difficult  to
           obtain.  However,  when  waste  characterization data is  available,  partial
           pressures  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  volubility (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
                                      H-15

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 landfill  volume and often  with  landfill  depth.  Deeper  landfills  have a  proportionally
 larger anaerobic zone,  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
 migration. Conversely,  mounds 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 soils  (e.g., surface
 impoundments,  land  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 (e.  g.,  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.
                                      11-16

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

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
                                      11-17

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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
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  barriers  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
                                      11-18

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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.
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  age,  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);

     •     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  climatic  information also include  the following:
                                      11-19

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     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

     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  developing the 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 documents, 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 areal extent of these units can be determined from historical records,
aerial  photographs,  or field  surveys. The  depths and dimensions of underground
                                      11-20

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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
(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  monitoring 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.
                                      11-21

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      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
 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
                                     11-22

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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.

     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 B  should be used  to  determine  a select set  of
constituents and  indicator  parameters  for 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.  In
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  within  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  monitoring phases.
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     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
(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  Section 11-6) monitoring  for
methane and appropriate constituents  should be conducted  at least twice  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.
                                     11-24

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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.
Shallow borehole  monitoring  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 up  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  lines).  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.
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     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 near  the  unit  to  locations  at  the  property
boundary  and  beyond.

11.4.4.2         Gas  Monitoring Wells

     Gas monitoring wells (See 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.,  <10-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  depth, 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 PB81 -218505 (U.S. EPA, 1981).
                                      11-26

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                   1/2 DIA, SCH. 40
                   PVC PIPE
                      1/8" DIA.
                      PERFORATIONS
                      FIBERGLASS
                      SCREENING TO
                      BE WRAPPED
                      AROUND a TAPED
                      TO TUBE.
MONITORING PROSE  DETAIL
                                MONITORNG
                                PROBE
   1/2" DIA. SCH. 40
   PVC  PIPE
                                                        SOIL BACKFILL
   '-2' 3ENTONITE
   PLUG
       BACKFILL

    PEA GRAVEL
  SOIL BACKFILL


   '-2' BENIONITE
  PLUG

  SOIL BACKFILL


  2' PEA  GRAVEL
  SOIL BACKFILL


  '-2' BEiNTONITE
  PLUG

  SOIL BACKFILL


— 21 PEA GRAVEL
       Figure 11-3. Schematic of a Deep Subsurface Gas Monitoring Well
                               11-27

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      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
waste buried at the  site varies  greatly from  one area  to 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  accumulate 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
                                     11-28

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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).

      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.  1983.  Guidelines  for  Monitoring Indoor Air  Quality.  EPA-  600/1-4
     83-046.  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
                                     11-29

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methane  gas  migration  model  presented in  Appendix  D  yields a  methane
concentration isopleth map  of a release. The  LEL and 0.25  LEL isopleths for methane
should be  mapped for  the RFI when appropriate. 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.

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  5.2  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;
                                     11-30

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     •     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.

11.5.3      Characterization of the  Release

     In  general,  release  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.  Because 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 chromatography  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
                                      11-31

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                                                              TABLE 11-4

                 SUMMARY OF CANDIDATE METHODOLOGIES FOR QUANTIFICATION  OF VAPOR PHASE ORGANICS
          Collection Techniques
    Analytical Technique
Applicability
Positive Aspects
Negative Aspects
        . Sorption onto Tenax-GC
          or carbon molecular
          sieve packed cartridges
          using low-volume pump
Thermal Resorption into GC
or GC/MS
               •  adequate QA/QC data
                  base
               •  widely used on
                  investigations around
                  uncontroNteoti waste sites
               •  wide range of
                  applicability
               •  |jg/m3 detection limits
               • practicality for field use
                     •  possibility of
                        contamination
                     •  artifact formation
                        problems
                     t  rigorous cleanup needed
                     •  no possibility of multiple
                        analysis
                     t  low breakthrough
                        volumes for some
                        compounds
u>
U)
       2. Sorption  onto charcoal
          packed cartridges using
          low-volume pump
Resorption with solvent-
analysis by GC or GC/MS
               • large data base for
                  various compounds
               •  wide use in industrial
                  applications
               • practical for field use
                     t  problems with
                         irreversible adsorption of
                         some compounds
                     • high (mg/m3)  detection
                         limits
                     •   artifact formation
                         problems
                     t high humidity  reduces
                         retention
       J.  Sorption onto
          polyurethane foam (PUF)
          using low-volume or
          high-volume pump
Solvent extraction of PUF;
analysis by GC/MS
               •  wide range of
                  applicability
               •  easy to preclean and
                  extract
               •  very low blanks
               •  excellent collection and
                  retention efficiencies
               •  reusable up to 10 times
                     •  possibility of
                         contamination
                     t 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 ORGANICS
          Collection Techniques
    Analytical  Technique
Applicability
       Positive  Aspects
      Negative  Aspects
       1. Sorption  on  passive
          dosimeters using  Tenax
          or charcoal  as  adsorbing
          medium
Analysis by chemical  or
thermal resorption followed
by GC or GUMS
    I  or
• Samplers  are  small,
    portable,  require no
    pumps
•   makes use of analytical
    procedures  of  known
    precision  and accuracy
    for a  broad range of
    compounds
•   ug/m3detection  limits
• problems   associated   with
    sampling  using  sorbents
    (see #l  and II) are present
•   uncertainty  in volume of
    air sampled  makes
    concentration
    calculations  difficult
•   requires  minimum
    external  air flow rate
Ul
       5. Cryogenic  trapping of
          analytes  in the field
Resorption  into GC
                •   applicable to  a wide
                    range of compounds
                •   artifact  formation
                    minimized
                •    low blanks
                              •  requires field use of
                                 liquid  nitrogen  or
                                 oxygen
                              •  sample is  totally used in
                                 one  analysis-no
                                 reanalysis possible
                              • samplers easily  clogged
                                 with  water  vapor
                              •  no large data base on
                                 precision  or recoveries
       6. Whole air sample  taken
           in glass or stainless steel
           bottles
Cryogenic trapping  or  direct
injection into GC or GC/MS
(onsite  or  laboratory)
                •   useful  for grab sampling
                •   large data base
                •   excellent  long-term
                    storage
                   wide  applicability
                •   allows  multiple analyses
                              •  difficult to obtain
                                 integrated samples
                              • low  sensitivity if
                                 preconcentration  is  not
                                 used
       7. Whole  air sample  taken
           in TedlareBag
Cryogenic trapping  or  direct
injection into GC or GC/MS
(onsite  or  laboratory)
                 • grab or  integrated
                    sampling
                 •  wide  applicability
                 •  allows multiple analyses
                              • long-term  stability
                                  uncertain
                              • low sensitivity if
                                  preconcentration  is  not
                                  used
                              •   adequate  cleaning  of
                                  containers between
                                  samples may  be  difficult

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                                                  TABLE 11-4 (continued)

           SUMMARY  OF  CANDIDATE METHODOLOGIES FOR QUANTIFICATION OF VAPOR PHASE ORGANICS
    Collection Techniques
   Analytical Technique
Applicability
   Positive Aspects
                                 Negative Aspects
 8. Dinitropheynlhydrazine
    liquid  Impinger sampling
    using  low-volume pump
HPLC/UV  analysis
     IV
 specific to aldehydes and
 ketones
 good stability for
 derivatized compounds
low detection limits
                               fragile equipment
                              sensitivity  limited by
                               reagent  impurities
                              problems  with  solvent
                               evaporation when  long-
                               term sampling  is
                               performed
 9.  Direct introduction by
    probe
Mobile MS/MS
  I,II, III, IV
•   immediate results
• field identification  of  air
    contaminants
•   allows "real-time"
    monitoring
• widest  applicability of
    any analytical method
                           high  instrument cost
                            requires highly trained
                            operators
                           grab  samples only
                            no large data base on
                            precision or accuracy
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  (e.g.,  vinyl  chloride,  vinylidene  chloride,  benzene,  toluene)  having  boiling   points
    in the  range of -15 to + 120° C.
Ill Semivolatile  organic  chemicals  (e.g.,  organochlorine  pesticides  and  PCBs).
IV  Aldehydes and  ketones.

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                               TABLE 11-5
TYPICAL COMMERCIALLY AVAILABLE SCREENING TECHNIQUES FOR ORGANICS IN AIR
Techniques
Gas Detection Tubes
Continuous Flow Calorimeter
Calorimetric Tape Monitor
Infrared Analysis
FID (Total Hydrocarbon
Analyzer)
GC/FID (portable)
PID and GC/PID (portable)
GC/ECD (portable)
GC/FPD (portable)
Chemiluminescent
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 organics and inorganic
Acrylonitrile, formaldehyde,
phosgene
Toluene, diisocyanate, dinitro-
toluene, phosgene, and various
inorganic
Most organics
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
0.005 to 0.5
ppmv
0.05-0.5
ppmv
1-10ppmv
0.5 ppmv
0.5 ppmv
0.1 to loo
ppbv
0.1 to loo
ppbv
10-100 ppbv
0.1 ppmv (as
N)
Comment
Sensitivity and selectivity highly
dependent 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 varies 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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also available  and provide  direct readings of LEL  levels and/or percent methane
present by volume.

     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  screening 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
monitoring 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,
because methane gas  is frequently  the  major  component  of the  soil gas,  those
which are  most sensitive to  methane, such as explosimeters  and  FID organic vapor
                                     11-37

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analyzers,  are the preferred  instruments.  More  selective  air sampling methods  are
used, however, for constituent analyses (see Section 12- Air Methods).

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 nonsparking material) through  a sealed  capon 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).

11.7 Site Remediation

     Although the  RFI  Guidance is  not  intended  to provide  detailed guidance  on
sites  remediation,  it should be recognized that  certain data collection activities  that
may be necessary for a Corrective Measures Study  may  be collected during the RFI.
EPA  has  developed a  practical  guide for assessing  and  remediating contaminated
site  that directs  users  toward technical  support,  potential  data  requirements and
                                     11-38

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                                  TABLE 11-6
                     SUBSURFACE SAMPLING TECHNIQUES
SHALLOW (Up to 6 ft deep)

     t    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  be perforated along bottom  few
          inches to assure gas flow.

     •    Close top of hole  around tubing using  a  gas impervious seal.

     t    Before sampling record well head pressure.

     •    Readings may be taken immediately after making  the barhole.

     t    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  (LEL) for  methane).  If
          meter is  pegged,  change  to the next least sensitive  range  to  determine
          actual gas  concentration.

     t     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 reading
          taken a few minutes later.

     •    Monitoring should be  repeated a  day or two after  probe  installation t
          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 a gas pipe or an electrica
          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.
                                    11-40

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technologies that may be applicable to EPA programs such  as RCRA and CERCLA.
The reference for this guide  is provided below.

     U.S. EPA.  1988. Practical Guide for AssessinG and Remediating  Contaminated
     Sites.  Office of Solid  Waste and  Emergency Response. Washington,  D.C.
     20460.

     The  guide  is designed to address  releases to  ground water as well  as soil,
surface  water and air. A  short description  of the guide  is  provided in Section 1.2
(Overall  RCRA  Corrective  Action  Process), under the discussion of Corrective
Measures  Study.
                                     11-41

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11.8 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  biodegradable  waste  components
          •    Quantities managed and  dates  of receipt
          •    Location of wastes in unit
          •    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
                                      11-42

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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  and  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
                                      11-43

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11.9 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-600 14-83-046.
     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 PB81-218505.  Office of Solid Waste. Washington, D.C.
     20460.

U.S. EPA. 1985. Technical Guidance for Corrective Measures - Subsurface Gas.
     Office of Solid Waste. Washington, D.C. 20460.
                                     11-44

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      APPENDIX C





GEOPHYSICAL TECHNIQUES
         C-1

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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
 *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.
                                     C-2

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boundaries, buried wastes  and drums, as well as  metallic utility lines can be located
with  EM techniques.

     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. Large 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,  are 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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                                         Phos«
                                        Sensing
                                        Circuits
                                                              Chort
                                                              Mog Tap*
                                                              Recorders
                  RANSMITTER
                                                    GROUND SURFACE
                     INDUCED
                     CURRENT
                      LOOPS
 SECONDARY FIELDS
PROM CURRENT LOOPS
    SENSED BY
   RECEIVER COIL
Figure C-l. Block diagram showing EM principle of operations.
                           C-4

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     •     Rate of plume movement by  comparing  measurements taken  at dif-
           ferent 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  (Technos,  Inc.,  1982)  should  be consulted for further detail regarding use,
capabilities, and  limitations  of electromagnetic surveys.

SEISMIC  REFRACTION SURVEYS

     Seismic refraction techniques are used  to determine  the  thickness and depth
of geologic layers and the travel time or velocity of seismic waves within the layers.
Seismic refraction methods  are  often used to map depths  to specific horizons  such
as  bedrock,  clay  layers,  and the  water table.  In addition  to mapping  natural
features,  other secondary applications of the seismic  method  include the  locations
and  definition of  burial 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  affects  their path  of travel. An array  of  geophones
(transducers  that respond to the motion of the ground) on the surface measures the
travel time of the  seismic waves from the source  to the geophones  at a number of
spacings.   The time  required for  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 as 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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n
                                                                                              Hammer
                                                                                               Source
                                                                            -i-'  i  •-,-T.in: Bedrock
              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
geohydrologic 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  geohydrologic  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  geohydrologic 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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                                            -Current  Meter
                                                               Surface
                 Current  Flow
                Through Earth
                                            Current

                                            Voltage
Figure C-3. Diagram showing basic concept of resistivity measurement.
                            C-8

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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 well 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-9

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                                                         GRAPHIC RECORDER
         ANTENNA
                                  CONTROLLER
                                                            TAPE RECORDER
                                                             00
Figure C-4.    Block diagram of ground penetrating radar system. Radar waves are
             relfected from soil/rock interface.
                                     C-10

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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-ll

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                                    Amplifiers
                                       and
                                     Counter
                                     Circuits
                                                             Chart and
                                                             Mag Tap*
                                                             Rtcordart
                                                     Ground Surface
Figure C-5.   Simplified  block  diagram  of  a  magnetometer.  A  magnetometer
             senses change in the earth's magnetic field due to buried iron drum.
                                      C-12

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     •    Aid  in  selecting drilling locations that  are clear  of  buried drums,

          underground utilities,  and other obstructions.


     The  use,  capabilities,  and  limitations of magnetometer surveys  at  hazardous

waste sites are provided in  chapter IX of Geophysical  Techniques for Sensing Buried

Wastes and  Waste Migration (Technos, Inc., 1982).


BOREHOLE GEOPHYSICAL METHODS


     There are several different types of borehole  geophysical  methods used  in the

evaluation of  subsurface lithology,  stratigraphy, and structure.  Much  of  the  data

collected in  boreholes is  analyzed  in conjunction  with  surface geophysical data to

develop a  more  detailed  description of subsurface  features.  In this  section,  the

major  and most  applicable types  of borehole geophysical methods  are  identified

and briefly discussed.  They include:

     I.    Electrical Surveys
          a. Spontaneous  Potential
          b. Resistivity

     II.    Nuclear  Logging
          a. Natural  Gamma
          b. Gamma  Gamma
          c. Neutron

     III.   Seismic  Surveys
          a. Up and  Down Hole
          b. Crosshole Tests
          c.  Vertical  Seismic Profiling

     IV.   Sonic Borehole Surveys
          a. Sonic Borehole Imagery
          b. Sonic Velocity

     v.    Auxiliary Surveys
          a. Temperature
          b. Caliper
          c.  Fluid Resistivity


     All of the  borehole  methods presented in this section  are  detailed in the Army

Corps  of Engineers  Geophysical Explorations  Manual (Engineering Manual 1110-1-

1802,  1979),  with the  exception  of  vertical seismic  profiling. This  method is

relatively new and  further information can  be found  in  Batch and Lee,  1984.
                                      C-13

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 Electrical Surveys

      The two  types of  electrical subsurface surveys  of geotechnical 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 from 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-7  demonstrates  the conceptual  field   configuration for  borehole
electrical  resistivity survey.
                                       C-14

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                                          E, » BOREHOLE-FORMATION
                                              FLUID POTENTIAL
                                          E$ * SMALE-SAND.POTENTIAL.
                                          E. * MUD FILTRATE-FORMATION
                                           B   FLUID POTENTIAL
                                          im * BOREHOLE FLUID RESISTANCE
                                          t,h s SHALE RESISTANCE
                                          r,, « SAND RESISTANCE
                                          rb » FILTRATE RESISTANCE
Figure C-6.    Conceptual equivalent circuit for self-potential data (prepared by the
             Waterways  Experiment  Station,  U.S.  Army Corps of  Engineers,
             Vicksburg, Mississippi).
                                    C-15

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                                                              ANO
                                                           RECORDER
                INSULATED
                SHE A VC
> s'DHAWWQKKS
co r.S
W
i" 	
*esis-
TANCE
IS

                                                                        ELECTROOC
                                     L.INCX OF
                                     ELCCTMtCAl.
                                     CURRENT
Figure C-7.   Single-point resistance log (preparedly 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 precision 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  K40and  isotopes of
uranium  and thorium.  K40is most prevalent, by far, existing as an  average of 0.012
percent by  weight of ail  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.

     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
                                      C-17

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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 gammea  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 material.  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
neutron 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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                                                       I
                                                      I
                                                      I
                                             PHOTONS
                                             o F«OM
                                       ISOTOPIC SOURCS
                                                         I
I
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).
                                  C-19

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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  (H20)
 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 Uphole and Downhole 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.
                                      C-21

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Figure C-9.   Downhole survey  techniques  for  P-wave data (prepared by  the
            waterways Experiment Station, U.S. Army Corps  of Engineers,
            Vicksburg, Mississippi).
                                 C-22

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                                   RECORDER
                                     ITiMCRI
                       SOURCE
                                                        RECEIVER
Figure C-IO. Basic crosshole 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  discussed.  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  subbottom  profiling.  The  sonic borehole imagery
logging concept is depicted in  Figure C-11.

     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 logging  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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                                               POWER SUPPLY AND
                                                 IMAGING DEVICE
    COMPASS OK
    DIRECTION
    SENSOR
                                                 COO
    ULTRASONIC
    ACOUSTIC
ROTATING
PIEZOELECTRIC
TRANSDUCER
                                              N    C   S    W   N
                                             RECORD SHOWING
                                             AZIMUTMAL DIRECTIONS
                                             ABOVE "UNWRAPPED"
                                             BOREHOLE IMAGE
                                             WITH IMAGES OF
                                             TWO DIPPING PLANES
Figure  C-ll.  Sonic  imagery  logger (prepared  by  the Waterways Experiment
             Station,  U.S. Army Corp of Engineers, Vicksburg, Mississippi).
                                     C-25

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                ACOUSTIC ISOLATOft
                    UCtlVtK
                ORIIIINC FLUIO _

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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  lithologic  or  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  logs 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 inhole  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  hardness, 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  filter 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  logs  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 logs.
                                       C-29

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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 24 (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 unfractured rock.
                                     D-2

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                     FIGURE D-1. EXAMPLE  LANDFILL
                                 D-3

-------
     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 LEL)  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 LEL) 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
Clean (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
                                       D-4

-------
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-------
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-------
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-------
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-------
      The  unconnected  mignation distance fnom  the  solid waste  limit can  then  be
 nead  on the left fon the appnopniate site age and soil type.

      If the soil along  a given  boundany is  stnatified and  the vaniability extends fnom
 the waste  deposit  to the  pnopenty  boundany,  the  most  penmeable  unsatunated
 thickness should be  used in entening  the  chants.  Fon example,  if dny,  clean  sand
 undenlies sunficial  silty clays, the unconnected mignation distance should  be obtained
 using the sand  line of the chant. If thene ane  questions as to the  extent of panticulan
 soils  along  a boundany,  helpful  infonmation  might  be  obtained  fnom  Soil
 Consenvation  Senvices  (SCS)  Soil Sunvey Maps on  the  landfill openaton.    Field
 inspection,  SCS  maps,  and  penmit  boning  infonmation  ane  sufficient.  Additional
 bonings ane not necessany as this  is only a  nanking pnocedune.  Whene  thene is doubt,
 use the most  penmeable soil  gnoup pnesent.

      Fon  the  example landfill  in  Figune D-1, the unconnected 5 pencent methane
 mignation  distances fon a  10-yean old landfill would be (Figune C-2):

      Section A-A:     East side, 10 yeans, sand   = 165'
                      West side, 10 yeans, sand = 165'

     Section B-B:    South side, 10 yeans, sand = 165'
                      North side, 10 yeans, clay =  130'

     The  connesponding unconnected  distances fon  the  1.25  pencent methane
mignation  would be:

     Section A-A:    East side, 10 yeans, sand = 225'
                     West side, 10 yeans, sand = 135'

     Section B-B:    South side, 10 yeans, sand = 255'
                     North side, 10 yeans, clay = 200'

    The depth to  connective  mulitpliens  fon the example sites would be:

    Section A-A:    East side,  10 yeans, 20' deep = 1.0
                     West side, 10 yeans, 20' deep =  1.0
                                      D-8

-------
      Section  B-B:     South side, 10 years, 10' deep = 0.95
                       North side, 10 years, 50' 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  char-t  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  so
 percent  of the year are:

      Section A-A:     East  side  (ignore narrow = (2.1-1)(0.50) +  1  = 1.55
                       road, sand 20' deep,
                       10 years old)

                      West side  (sand 20' deep, = (2.1-1)(0.50) + 1 = 1.55
                       10 years old)
                                       D-9

-------
     Section B-B:    South  side (sand, 10' deep,  = (2.1-1)(0.50) + 1 = 1.55
                       10 years old)

                       North side (clay, 50' deep, = (i .4-1 )(0.50) + 1 = 1.2
                       10 years old)

     Once  the  surface venting  factors  have been tabulated as  in Table D-1, 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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                        APPENDIX E

ESTIMATION OF BASEMENT AIR CONTAMINANT CONCENTRATIONS DUE TO
VOLATILE COMPONENTS IN GROUND WATER SEEPED INTO THE BASEMENT
                           E-1

-------
                                 APPENDIX E

    ESTIMATION OF BASEMENT AIR CONTAMINANT CONCENTRATIONS DUE TO
    VOLATILE COMPONENTS IN GROUND WATER SEEPED INTO THE BASEMENT
     Ground water can reach the basement  and the walls of a house in  several
ways.  If ground water is  contaminated  by volatile components,  there  are  several
possibilities that  the  indoor  ambient air  can be affected  by these constituents.
There  are  several  methods which  can  be  applied  to estimating the  ambient  air
concentrations in  the basement into  which  the  contaminants  are  volatilized  from
ground water. The manner in  which and the extent to which  the  ground water
reaches the basement or the walls will dictate the  choice of a method.

     Two cases are considered as  example  scenarios:  Case  1)  Ground water is
seeped inside the basement  completely wetting  the  basement,  with  a visual
indication of water  on  the floor, Case 2)  The basement  is partially  wetted  without
a visual indication of liquid on the floor. This latter case can be subdivided into two
subcases: Subcase  1)  involving a  damp floor evident on the surface;  Subcase  2)
involving a  floor without observable  dampness on the floor surface but with  ground
water  underneath  the concrete  floor.

     The way  the emission rates are estimated will be different for the three cases.
If the emission flux rate per unit square area of the exposed surface is denoted  by E
(g/m2day), then in all cases the  air concentration,  C  (ug/m3), in the basement  can be
estimated  from:

                    C (ug/m3) = Ex106AteA/B                              (1)

where          A   = basement floor and wall area  exposed to ground water,  m2

               VB = volume of the basement,  m3, and

               te    = air exchange time for the basement, days.
                                     E-2

-------
      The air exchange  time should be  determined on  a site-specific or situation-
 specific basis. The tight  room will have a longer time per air exchange in the room,
 and the room with an exhaust fan will  have a  shorter time per air exchange.  The
 default value for a typical house  could be te= 0.05 days.

      The emission rates in Eq. (1)  can  be estimated for the various case scenarios
 illustrated  above.

      Case 1.    Wet basement with visible liquid,

      The volatilization is  a mass  transfer  phenomenon  from the liquid phase  of
 ground  water on the  floor  to the basement air.  Emission flux rate can be estimated
 from:

                               E = KOL(CL-CL*)                              (2)

 where  KOL  = overall  mass  transfer  coefficient in the liquid phase unit,  m/day, CL =
 concentration  of contaminant in  water, g/m3, and CL* =  liquid  phase  concentration
 in  equilibrium  concentration with  the basement air,  g/m3.  The  equilibrium
 concentration  C* could be  assumed to be approaching a small  value compared  to
 the ground  water  contaminant  concentration  when  the air exchange rate  is  high,  or
 when the time per air exchange is small.  But this assumption would not be valid  at a
 low air exchange rate  or at a longer time for a  room air exchange. In this case, the
 emission flux rate should be estimated by a trial and error method using Equation
 (2) in combination with Equation  (1), and  Henry's Law constant.

      It  is a well-established scientific principle  to  use the two-resistance theory  to
 obtain the overall  mass transfer coefficient, KOL, as  follows:
                       KOL=   -±—  +   -J—                          (3)
                                  KL         Hckq
where KL and  kg =  individual  mass transfer  coefficients in  liquid  and gas  phases,
respectively,  m/day,  and He  = dimensionless Henry's  Law  constant  obtained  from
                                      E-3

-------
 reconcentration  units for gas  and liquid  phase concentrations.  The numerical value
 for Hccan  be calculated  from  Henry's  Law  constant given in atm/g-mol.m3by
 multiplying by 41. Default values for the individual mass transfer  coefficients  can be
 estimated  from:
                                        1
           kL = 3       cm  .  /..44  \  2  /  24       M        hr \
                        hr    1  MW  I     \   100      cm      day  I       (4)
           kg = 3000  -^m—  |—^—l        24       M       	
                        hr    I  MW  I     I  100      cm      dav  I       (5)
where  MW =  molecular  weight  of the contaminant.

     Case 2.   Basement partially wetted  with  no visual indication  of liquid.

     (a)  Subcase  1.   Dampness evident on  the  floor  or  wall  surface.  The
volatilization  process can be treated  as  a  diffusional  process  from  the air  at  the
water-air interface  through the  air pores in the basement floor material and into
the basement air.   The  diffusional  process  can  be  solved  using  the  approach
described  in  the  EPA report  Development of Advisory  Levels  for  Polychlorinated
Biphenyls  (PCBS) Cleanup (PB86-232774).  The final  result  needed for emission flux
estimation would be:
                      e =    	e
                             'V    iraT
                                     E-4

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            APPENDIX F

METHOD 1312: SYNTHETIC PRECIPITATION
        LEACH TEST FOR SOILS

-------
                         METHOD 1312

         SYNTHETIC PRECIPITATION LEACH  TEST FOR SOILS

 1.0  SCOPE AND  APPLICATION

      1.1 Method 1312  is  designed to determine  the  mobility of
both  organic  and inorganic contaminants present  in  soils.

      1.2 If  a  total  analysis  of the soil  demonstrates that in-
dividual  contaminants  are  not  present  in the  soil,  or that they
are present but at such low concentrations that the appropriate
regulatory thresholds  could not possibly be  exceeded,  Method
 1312  need not be  run.

 2 . 0  SUMMARY  OF METHOD

      2.1 The  particle  size of   the  soil  is  reduced (if necessary)
and is  extracted  with an amount of extraction  fluid equal  to 20
times the weight  of  the soil.   The extraction  fluid employed is
a function of the region of the country where  the  soil site is
located.  A special  extractor vessel is used  when  testing for
volatiles.  Following extraction,  the  liquid  extract is separated
from  the soil by 0.6-0.8 urn glass fiber filter.

 3.0   INTERFERENCES

      3.1 Potential  interferences that may be encountered during
analysis  are  discussed  in the  individual analytical  methods.

4 . 0  APPARATUS  AND MATERIALS

      4.1 Agitation  apparatus  - an acceptable  agitation apparatus
is one  which  is capable of rotating  the extraction  vessel  in an
end-over-end fashion at  30  ±  2 rpm (see Figure  1) .   Suitable
devices  known to  EPA  are identified  in Table 2.

      4.2  Extraction  vessel - acceptable extraction vessels are
those that are  listed  below:

          4.2.1  Zero  Headspace  Extraction Vessel  (ZHE)  -  This
     device is  for use only when the soil  is  being  tested  for the
     mobility of  volatile  constituents  (see Table 1) .   The ZHE is an
     extraction vessel  that allows for liquid/solid separation within
     the  device and  which effectively  precludes  headspace  (as depicted
      in  Figure  3).   This type of vessel allows  for initial liquid/solid
     separation,  extraction,  and final extract  filtration  without
     having to  open  the  vessel (see  Step 4.3.1).   These vessels shall
     have an internal  volume of  500  to 600 mL and be equipped to
     accommodate a 90-mm  filter.   Suitable ZHE  devices  known to EPA
     are  identified in  Table 3.   These devices  contain viton 0-rings
     which should  be  replaced  frequently.   For  the  ZHE to be acceptable
     for  use,  the  piston within the  ZHE should be able  to  be moved

                              1312-1                     Revision 0
                                                        December 1988

-------
     with  approximately  15 psi or less.   if it takes more pressure
     to  move the piston,  the  0-rinqs  in  the device should be replaced.
     If  this does not solve the  problem,  the ZHE is unacceptable  for
     1312  analyses and the manufacturer  should  be contacted.   The ZHE
     should  be  checked after  every extraction.    if the device con-
     tains  a built-in pressure gauge,  pressurize  the  device to
     50  psi,  allow it to  stand unattended  for  1 hour,  and recheck
     the pressure.   If  the device does not have a built-in pressure
     gauge,  pressurize the device to  50  psi,  submerge  it in water
     and check  for the presence  of air bubbles  escaping from any
     of  the  fittings.    If pressure is  lost,  check all  fittinqs and
     inspect  and replace 0-rings, if  necessary.   Retest the device.
     If  leakage problems cannot  be solved,  the  manufacturer should
     be  contacted.

         4.2.2  When the  soil  is  being evaluated  for  other than
     volatile contaminants,  an extraction vessel  that  does not pre-
     clude  headspace  (ea. a  2-liter  bottle) is used.   Suitable
     extraction  vessels  include bottles made from various materials,
     depending  on the  contaminants to  be analyzed and  the nature of the
     waste  (see Step  4.3.3)0    It  is  recommended that  borosilicate
     glass bottles be  used over  other  types of  glass,  especially
     when  inorganic are  of  concern.    Plastic bottles  may be used
     only  if inorganic  are to be investigated.   Bottles are available
     from  a  number of  laboratory suppliers.  When this type of ex-
     traction vessel  is  used,  the filtration device discussed in
     Step  4.3.2 is used  for initial  liquid/solid  separation and final
     extract  filtration.

         4.2.3  Some ZHEs  use  gas pressure  to actuate  the  ZHE piston,
     while others  use  mechanical  pressure  (see  Table 3).   Whereas
     the volatiles procedure   (see Step 7.4)  refers to  pounds-per-
     square  inch (psi),  for the  mechanically actuated  piston,  the
     pressure applied  is measured in  torque- inch-pounds.   Refer to
     the manufacturer's  instructions  as to  the proper conversion.

     4.3  Filtration  devices   - It is  recommended  that  all filtrations
be performed in  a  hood.

         4.3.1   Zero-Headspace  Extractor Vessel  (see  Figure  3)-
     When the waste is being  evaluated for  volatiles,  the zero-
     headspace  extraction vessel  is  used for filtration.   The device
     shall be capable  of supporting  and keeping in place  the fiber
     filter, and be able to withstand  the  pressure needed to accomplish
     separation  (50 psi).

         NOTE:  When is it suspected that the glass fiber filter
                has been  ruptured, an  in-line glass fiber  filter  may be
                used to filter  the material within  the  ZHE.

          4.3.2  Filter  holder - when  the  soil  is being evaluated
     for other  than volatile  compounds, a  filter  holder capable  of


                               1312-2                     Revision  0
                                                        December 1988

-------
      supporting a glass fiber  filter  and able to withstand 50 psi
      or more of pressure shall be used.   These devices shall  have  a
      minimum internal volume of 300 mL and be  equipped  to  accommodate
      a minimum filter size  of  47  mm (filter holders having an
      internal capacity of 1.5  liters  or greater are recommended).

          4.3.3 Materials  of construction  -  filtration devices  shall
      be made of inert materials which will not leach or absorb  soil
      components.  Glass,  polytetrafluoroethylene  (PTFE)  or type  316
      stainless steel equipment may  be  used when evaluating the  mobility
      of both organic and inorganic  components.   Devices made  of hiqh
      density polyethylene (HDPE), polypropylene,  or polyvinyl  chloride
      may be used only when  evaluating  the  mobility of metals.   Boro-
      silicate glass  bottles  are  recommended  for use over other types
      of glass bottles,  especially  when  inorganic  are  constituents
      of concern.

      4.4  Filters  -  filters  shall be  made of borosilicate glass
 fiber,  shall  have  an effective  pore  size of 0.6 - 0.8 urn and
 shall  contain no binder materials.  Filters  known  to EPA to meet
 these  requirements are identified in  Table  5.  When evaluating the
 mobility of metals,  filters  should  be  acid-washed  prior to use
 by  rinsing with 1. ON nitric  acid  followed by three consecutive  rinses
 with  deionized distilled water (a minimum  of  1-liter per rinse  is
 recommended).   Glass fiber  filters  are fragile and should be  handled
 with care.

      4.5 pH  meters   - any of  the  commmonly available pH meters  are
 acceptable.

      4.6 ZHE  extract  collection  devices - TEDLAR  bags, glass,  stain-
 less  steel  or PTFE gas tight syringes  are  used to  collect the volatile
 extract.

      4.7 Laboratory  balance - any  laboratory balance accurate  to
within  +  0.01 g may be used  (all weight  measurements are to be  within
 + 0.1 g).

      4.8 ZHE extraction fluid  transfer devices  -  any device  capable
of  transferring  the  extraction fluid into  the  ZHE  without changing
 the nature  of the  extraction fluid  is  recommended.

 5 . 0  REAGENTS

      5.1 Reagent water - reagent water  is  defined  as water in
which  an  interferent  is  not  observed at  or above the method
detection limit of the analyte(s)  of interest.   For non-volatile
extractions,  ASTM  Type  II  water,  or equivalent  meets the definition
of  reagent  water.   For volatile extractions,  it  is recommended
 that reagent  water be generated by any of  the  following methods.
Reagent  water should be  monitored periodically  for impurities.
                              1312-3                    Revision 0
                                                        December 1988

-------
          5.1.1 Reagent  water for volatile  extractions  may be
      generated by passing tap water  through a carbon filter bed
      containing about 500 g  of  activated  carbon (Calgon Corp.,
      Filtrasorb 300 or equivalent).

          5.1.2 A  water  purification system  (Millipore  Super-Q or
      equivalent)  may also be used to generate reagent water for
      volatile  extractions.

          5.1.3 Reagent  water for volatile  extractions  may also
      be  prepared by boiling water for  15  minutes.   Subsequently,
      while  maintaining the  water temperature  at  90  +  5°C,  bubble
      a  contaminant-free  inert gas (e.g. nitrogen)  through the
      water  for 1  hour.   While still  hot,  transfer the water to a
      narrow-mouth screw-cap bottle under  zero headspace and seal
      with a Teflon lined septum and  cap.

      5.2 Sulfuric  acid\nitric  acid   (60/40  weight  percent mixture)
H2S04/HN03.    Cautiously mix  60  g  of  concentrated sulfuric acid with
40  g  of  concentrated nitric acid.

      5.3 Extraction  fluids:

          5.3.1 Extraction  fluid #1   -  this  fluid is made by adding
      the 60/40 weight percent mixture  of  sulfuric  and nitric acids
      to  reagent water until the pH is  4.20  ±0.05.

          5.3.2 Extraction  fluid #2   -  this  fluid is made by adding
      the 60/40 weight percent mixture  of  sulfuric  and nitric acids
      to  reagent water until  the pH is  5.00  ±0.05.

          5.3.3 Extraction  fluid #3   -  this  fluid is reagent water
      (ASTM  Type II water, or equivalent)  used to determine cyanide
      leachability.

      Note:   It is  suggested  that  these extraction  fluids  be moni-
             tored frequently for impurities.   The  pH should be
             checked prior to use to  ensure  that  these fluids are
             made  up accurately.

      5.4  Analytical standards shall  be prepared according  to  the
appropriate  analytical method.

6.0 SAMPLE  COLLECTION,  PRESERVATION, AND HANDLING

      6.1 All samples shall be  collected using  an  appropriate
sampling plan.

      6.2  At  least  two   separate  representative  samples of a  soil
should be collected.   The first sample  is used  to  determine if the
soil  requires  particle-size  reduction and,  if desired,  the  percent
solids of the  soil.   The second sample  is used  for extraction
of volatiles and  non-volatiles.


                               1312-4                    Revision 0
                                                        December 1988

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      6.3 Preservatives shall  not  be added  to  samples.

      6.4 Samples shall be refrigerated to  minimize loss of  volatile
organics  and to retard biological  activity.

      6.5 When the  soil  is to be  evaluated  for volatile contaminants,
care  should  be  taken to minimize  the loss of  volatiles.   Samples
shall be taken  and stored in a manner  to  prevent  the loss of
volatile  contaminants.    If possible,  it is  recommended that  any
necessary particle-size  reduction be conducted  as  the sample is
being taken.

      6.6.  1312  extracts should be prepared  for analysis and
analyzed  as  soon as possible following  extraction.   if they  need
to be stored,  even for a  short period  of  time,  storage shall be at
4°C,   and samples for volatiles analysis shall  not  be allowed to
come  into contact  with the atmosphere  (i.e.  no headspace) .  See
Section  8.0  (Quality Control) for acceptable  sample and extract
holding  times.

7 . 0   PROCEDURE

      7.1 The preliminary  1312 evaluations are  performed on a mini-
mum 100g representative sample  of soil  that will  not  actually under-
go 1312  extraction  (designated as the first sample  in Step  6.2).

          7.1.1  Determine  whether  the soil  requires particle-size
      reduction.   If the soil passes  through a  9.5  mm (0.375-inch)
      standard  sieve,  particle-size reduction is  not required
      (proceed to Step 7.2) .   If portions  of the sample do not
     pass through  the sieve,  then the  oversize portion of the
      soil will  have to be prepared  for  extraction  by crushing
      the soil  to pass the 9.5 mm  sieve.

          7.1.2  Determine  the  percent solids if  desired.

      7.2  Procedure when volatiles are  not  involved -  Enough
solids should be  generated for extraction such  that the volume
of 1312  extract  will  be  sufficient to support  all  of the analyses
required.  However,  a minimum  sample size  of  100  grams shall
be used.   If the amount of extract generated by a  single 1312
extract  will not be sufficient  to perform all  of the analyses,
it is recommended  that  more than  one extraction be performed and
the extracts be  combined  and then aliquoted for  analysis.

          7.2.1  Weigh out  a  representative subsample of  the  soil  and
     transfer to  the filter holder extractor vessel.

          7.2.2  Determine   the  appropriate  extraction fluid to use.
      If  the  soil  is from  a site that is east of the Mississippi
     River,   extraction  fluid  #1  should be used.   If the soil is
     from a  site that is   west of  the Mississippi  River,  extraction
     fluid #2 should be used.   If the soil  is  to be tested  for
     cyanide leachability,  extraction fluid  #3 should be  used.

                              1312-5                    Revision 0
                                                        December 1988

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Note:   Extraction fluid #3  (reagent  water)  must be used
when  evaluating cyanide-containing soils  because leaching
of  cyanide-containing soils under  acidic  conditions may
result  in the formation of hydrogen  cyanide  gas.

     7.2.3 Determine  the  amount  of extraction  fluid to add
based on the following formula:

     amount  of extraction fluid  (mL)  =  20  x  weight of soil (q)

Slowly  add  the amount of appropriate extraction fluid to the
extractor vessel.   Close the  extractor bottle tightly  (it
is  recommended that Teflon tape be used to  ensure a tight
seal),  secure in rotary extractor device, and rotate at 30
+ 2  rpm for 18+2 hours.   Ambient temperature (i.e. temper-
ature of room in which extraction is to take place) shall
be  maintained at 22 + 3°C during  the extraction period.

Note:   As agitation continues, pressure may  build up within  the
        extractor bottle for some  types  of soil (e.g. limed or
        calcium carbonate containing  soil  may evolve gases such as
        carbon dioxide).   To relieve  excess  pressure, the extractor
        bottle may be periodically opened  (e.g.  after 15 minutes,
        30 minutes, and 1 hour) and vented into  a  hood.

     7.2.4 Following  the  18  ±2  hour  extraction,  the material in
the  extractor vessel  is separated into  its  component liquid  and
solid phases  by filtering through a  glass fiber filter.

     7.2.5 Following collection of  the 1312  extract  it  is re-
commended that  the pH of the extract be recorded.   The extract
should  be immediately aliquoted for  analysis and properly
preserved  (metals  aliquots  must be acidified with nitric
acid to  pH  <  2;  all other aliquots must be  stored under
refrigeration  (4°C)  until  analyzed) .    The 1312 extract
shall be prepared and analyzed according  to  appropriate
analytical  methods.   1312 extracts to  be  analyzed for metals,
other than  mercury,  shall  be acid digested.

     7.2.6  The contaminant concentrations  in the  1312  extract are
compared  to  thresholds  in  the  clean  closure  guidance manual.
Refer to  Section 8.0  for Quality Control  requirements.

7.3  Procedure  when volatiles are involved:

     7.3.1 The  ZHE device is used to  obtain  1312 extracts for
volatile  analysis  only.   Extract resulting from the use of the
ZHE  shall not  be used to evaluate the  mobility of non-volatile
analytes  (e.g.  metals,  pesticides,  etc.).    The ZHE  device
has  approximately a 500 mL  internal   capacity.   Although a minimum
sample size of  100 g  was required in the  Step  7.2 procedure,  the
ZHE can  only  accommodate  a  maximum of 25  g of  solid ,  due to the
need to  add an amount of extraction  fluid equal  to  20  times  the

                         1312-6                    Revision 0
                                                   December 1988

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weight  of  the soil.   The  ZHE  is  charged with sample only once  and
the  device is not opened  until the  final extract has been  col-
lected.   Although the  following  procedure allows for particle-
size  reduction during the conduct of  the procedure,  this could
result  in  the loss of  volatile compounds.   if possible  particle-
size  reduction (see  Step  7.1.1)  should  be conducted on  the
sample  as  it is being  taken  (e.g.,  particle-size may be reduced
by crumbling).   If necessary  particle-size  reduction may be
conducted  during  the  procedure.   in carrying out the following
steps,  do  not allow the soil  to  be  exposed to the atmosphere for
any  more  time than is  absolutely necessary.   Any manipulation of
these  materials  should be done when  cold (4°C)  to minimize the
loss  of volatiles.   Pre-weigh  the ejaculated container  which
will  receive the  filtrate  (see Step 4.6), and  set  aside.   If
using  a TEDLAR°bag,  all air  must be expressed  from  the device.

     7.3.2  Place  the  ZHE  piston within the  body of the ZHE  (it
may be  helpful  firs-t  to moisten  the piston 0-rings  slightly with
extraction  fluid).   Adjust the piston within  the ZHE body to a
height  that  will  minimize the distance  the  piston will  have to
move once  it is  charged with sample.  Secure  the gas inlet/outlet
flange  (bottom flange)  onto the  ZHE  body in accordance  with the
manufacturer's  instructions.   Secure  the glass  fiber filter
between the  support  screens and  set aside.   Set liquid  inlet/out-
let  flange  (top  flange) aside.

     7.3.3  Quantitatively transfer 25  g  of soil  to  the  ZHE.
Secure  the  filter and support screens into  the  top  flange of the
device  and  secure  the  top flange  to  the ZHE  body in accordance
with  the  manufacturer's instructions.   Tighten  all  ZHE  fittings
and place  the device in the vertical  position (gas  inlet/outlet
flange  on  the  bottom).   DO not attach the extraction collection
device  to  the  top  plate.   Attach a  gas  line  to  the gas  inlet/out-
let valve  (bottom flanqe)  and, with  the liquid  inlet/outlet
valve  (top  flange)  open,  begin applying gentle  pressure of 1-10
psi to  a maximum  of  50 psi to force  most of  the headspace out of
the device.

     7.3.4  With the ZHE in the vertical  position, attach a
line  from  the extraction fluid reservoir to  the liquid  inlet/
outlet  valve.   The line used  shall  contain  fresh extraction
fluid  and  should  be  preflushed with  fluid  to  eliminate  any air
pockets in the line.   Release qas pressure on the ZHE  piston
 (from  the  gas inlet/outlet valve), open the  liquid  inlet/
outlet  valve,  and begin transferring  extraction  fluid  (by
pumping or similar means)  into the ZHE.    Continue  pumping
extraction fluid  into  the  ZHE until  the appropriate  amount  of
fluid has been introduced  into the device.

    7.3.5  After  the extraction fluid has been  added,  immediately
close  the  inlet/outlet  valve and  disconnect  the  extraction fluid
line.    Check the  ZHE  to ensure that all valves  are  in  their closed
positions.    Physically rotate the device  in  an  end-over-end fashion


                        1312-7                     Revision 0
                                                   December 1988

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      2  or  3  times.   Reposition the ZHE  in  the vertical position with
      the liquid  inlet/outlet  valve on top.    Put 5-10 psi behind the
     piston  (if  nesessary)  and slowly open  the liquid inlet/outlet
     valve to  bleed out any headspace  (into  a hood)  that may have
     been  introduced  due  to the addition of  extraction fluid.
     This  bleeding  shall  be done quickly and shall  be stopped at the
      first appearance  of  liquid from the valve.   Re-pressurize the
      ZHE with  5-10  psi and check all ZHE fittings  to ensure that
      they  are  closed.

         7.3.6  Place the ZHE  in the rotary  extractor apparatus (if
      it is not  already there)  and rotate the  ZHE at  30 + 2 rpm for
      18 ±  2  hours.   Ambient temperature (i.e.  temperature of the room
      in which  extraction  is to occur) shall  be  maintained at 22 +_ 3°C
     during  agitation.

         7.3.7  Following  the  18+2  hour agitation  period,  check
     the pressure behind  the ZHE piston by  quickly opening and closing
     the gas inlet/outlet valve and noting the  escape  of  gas.   If the
     pressure has not  been  maintained (i.e.  no  gas  release observed),
      the device  is  leaking.   Check the  ZHE  for  leaking and redo the
     extraction with a  new  sample  of  soil.    If  the pressure within
     the device  has been  maintained,  the material  in the extractor
     vessel  is  separated  into its component  liquid  and solid phases.

         7.3.8  Attach  the  evacuated  pre-weighed filtrate collection
     container to the  liquid  inlet/outlet  valve and  open  the valve.
     Begin applying gentle  pressure  of  1-10 psi to  force  the liquid
     phase into  the  filtrate  collection container.    If no additional
     liquid  has  passed through the filter in  any 2  minute interval,
     slowly  increase  the  pressure  in 10-psi  increments  to a maximum of
     50 psi.   After  each  incremental  increase of 10  psi,  if no additional
     liquid  has  passed through the filter in  any 2  minute interval,
     proceed to  the next  10  psi increment.    When liquid flow has
     ceased  such that  continued pressure filtration  at  50 psi  does
     not result  in  any additional  filtrate  within any  2  minute  period,
     filtration  is  stopped.   Close the  inlet/outlet  valve,  discontinue
     pressure to the piston,  and disconnect  the filtration collection
     container.

         NOTE :   Instantaneous  application of high pressure can
               degrade  the  glass fiber  filter and may  cause
               premature  plugging.

         7.3.9  Following  collection of  the  1312 extract,  the  extract
     should be immediately  aliguoted  for analysis and  stored with
     minimal  headspace  at 4°C  until  analyzed.   The  1312  extract will  be
     prepared and analyzed  according  to the  appropriate  analytical
     methods.

8.0  QUALITY  CONTROL

     8.1 All data,   including quality assurance data,  should be


                              1312-8                     Revision  0
                                                        December  1988

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maintained and  available  for reference or  inspection.

      8.2  A minimum of one blank (extraction fluid #  1)  for every
10  extractions  that  have  been conducted in  an  extraction vessel
shall be  employed  as  a check to determine  if any  memory effects
from  the  extraction  equipment are occurring.

      8.3  For each analytical batch  (up to twenty samples),  it is
recommended  that a matrix spike be performed.  Addition of matrix
spikes should occur  once  the 1312 extract has  been generated
 (i.e.  should not  occur prior to performance of the 1312 procedure).
The purpose  of  the matrix spike is to monitor  the adequacy of the
analytical methods used on  the  1312  extract and for  determining
if  matrix interferences exist in analyte detection.

      8.4  All quality control measures described in the appropriate
analytical methods shall  be  followed.

      8.5  The method of standard addition shall be employed for
each analyte if:   1)  recovery of the  compound  from the  1312
extract is not  between  50 and 150%,  or 2)  if the  concentration of
the constituent measured  in  the extract is within 20% of  the
appropriate  regulatory  threshold.   If more  than one  extraction is
being run on samples  of the  same waste (up to  twenty  samples) ,
the method of standard  addition need  be applied only  once  and the
percent recoveries applied on the remainder of the extractions.

      8.6  Samples  must undergo  1312 extraction within the  following
time period  after  sample  receipt:   Volatiles,   14 days;  Semi-
Volatiles, 40 days;  Mercury,  28 days;  and other Metals,   180  days.
1312  extracts shall  be analyzed after generation  and  preservation
within the following  periods:   Volatiles,  14 days; Semi-Volatiles,
40 days; Mercury,   28  days;  and  other  Metals, 180  days.

9.0 METHOD PERFORMANCE

      9.1  None available.

10.0  REFERENCES

      10.  1  None available.
                              1312-9                    Revision 0
                                                       December 1988

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TABLE 1.   --  VOLATILE CONTAMINANTS
Compounds
Acetone 	
Ac rrylonitzrile 	 - 	
Benzene 	

Carbon disulf ide 	

Chlorobenzene


1 1 Dichloroethylene 	
Ethyl acetate 	

Ethyl either 	
Isobutanol 	

Methylene chloride 	


1112 -Tetrachloroethane 	 • 	

Tetrachloroethylene 	 	
Tolulene 	 	 	 	

1,1, 2 -Trichloroethane 	

Trichlorofluoromethane 	
l,l,2-Trichloro-l,2,2-trifluoroethane 	

Xylene 	

CAS No.
67-64-1
m-13-1
71-43-2
71-36-6
75-15-0
56-23-5
108-90-7
67-66-3
107-06-2
75-35-4
141-78-6
100 41 4
60-29-7
78-83-1
67-56-1
75-09-2
78-93-3
108-10-1
630-20-6
79-34-5
127-18-4
108-88-3
71-55-6
79-00-5
79-01-6
75-69-4
76-13-1
75-01-7
1330-20-7

              1312-10
Revision 0
December 1988

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              TABLE 2. -- SUITABLE ROTARY AGITATION  APPARATUS1
     Company
Location
Model
Analytical  Testing and
  Consulting  Services,  Inc.

Associated  Design and
  Manufacturing  Company

Environmental  Machine
  and Design,  Inc.

IRA Machine Shop and
  Laboratory

Lars Lande  Manufacturing
Millipore  Corp.
REXNORD
Warrington,  PA
   (215)  343-4490

Alexandria,  VA
   (703)  549-5999

Lynchburg, VA
   (804)  845-6424

Santurce,  PR
   (809)  752-4004

Whitmore Lake, MI
   (313)  449-4116

Bedford, MA
   (800)  225-3384
Milwaukee, WI
   (414)  643-2850
 4-vessel device
 4-vessel device,
 6-vessel device

 4-vessel device,
 6-vessel device

16-vessel device
10-vessel device
 5-vessel device

 4-vessel ZHE  device
 or 4-one litter
 bottle extractor
 device

 6-vessel device
'Any device that  rotates the extraction  vessel  in an end-over-end
 fashion  at 30  ±  2 rpm is acceptable.
      TABLE  3.  -- SUITABLE  ZERO-HEADSPACE  EXTRACTOR VESSELS
        Company
    Location
   Model No.
Analytical Testing  & Con-
 sulting  Services,  Inc.

Associated Design  & Manu-
 facturing Co.

Lars Lande Mfg.
Millipore Corp.
Barrington, PA,
  (215)  343-4490

Alexandria, VA
  (703)  549-5999

Whitmore Lake, MI
  (313)  449-4116

Bedford, MA,
  (800)  225-33.84
   C102, Mechanical
    Pressure Device

   3740-ZHB, Gas
    Pressure Device

   Gas Pressure
    Device

   SD1 P581 C5, Gas
    Pressure Device
                               1312-11
                          Revision 0
                          December 1988

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              TABLE  4.  --  SUITABLE ZHE FILTER HOLDERS1
Company
Micro Filtration Systems
Millipore Corp.
Nuc 1 eopor e Corp .
Location
Dublin, CA
(415) 828-6010
Bedford, MA
(800) 225-3384
Pleasanton, CA
(800) 882-7711
Model
302400
YT30142HW
XX1004700
425910
410400
Size
142 mm
142 mm
47 mm
142 mm
47 mm
'Any device capable of separating  the  liquid from the solid phase  of
 the soil is suitable, providing that  it is chemically  compatible  with
 the soil  and  the constituents  to be  analyzed.   Plastic  devices  (not
 listed above)  may  be used when only  inorganic contaminants are of con-
 cern.   The 142 mm  size  filter holder  is recommended.
                TABLE 5.  --  SUITABLE FILTER MEDIA
Company
Millipore Corp.
Nuc 1 eopor e Corp .
Whatman Laboratory
Products, Inc.
Location
Bedford, MA
(800) 225-3384
Pleasanton, CA
(415) 463-2530
Clifton, NJ
(201) 773-5800
Model
AP40
211625
GFF
Size!
0.7
0.7
0.7
'Nominal  pore size
                              1312-12
Revision 0
December 1988

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Figure 1.   Rotary Agitation
   Motor

(30 * 2 rpra)
             Extraction Vess«l Holder
        1312-13
                                   Revision  O
                                   December 1988

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Figure 2.   Zero-Headspace  Extraction  Vessel
        liquid inlet/outlet valve
                  f
                filter—
           waste and
            extraction
             fluid
              piston
                                         top  flange
                                      -V body
                                        VITON 0-rings
                                    >• bottom  flange
 pressurizing gas  inlet/outlet  valve
              1312-14
                                          Revision 0
                                          December 1988

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