Hazard Ranking System Issue Analysis:
            Geohydrology
                MITRE

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Hazard Ranking  System Issue Analysis:
                  Geohydrology
                    Robert E. Gerstein
                     November 1986
                       MTR-86W62
                        SPONSOR:
                 U.S. Environmental Protection Agency
                      CONTRACT NO.:
                       EPA-68-01-7054
                    The MITRE Corporation
                       Metrek Division
                      7525 Colshire Drive
                    McLean, Virginia 22102-3481

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 Department Approval:  '
MITRE Project Approval:
^Lb\^
            ii

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                              ABSTRACT
     Three principal hydrogeologic issues have been raised in public
comments on the National Contingency Plan and the National
Priorities List.  All three issues relate to the identification, in
the EPA Hazard Ranking System (HRS), of the target population
potentially affected by a release of hazardous substances to ground
water.  The three issues are that:

     •  Ground water flow directions need to be considered in the
        HRS.

     •  The three-mile radius currently used to define the target
        area in the HRS overestimates (or underestimates) the
        distance contaminants can migrate.

     •  The interconnection (or separation) of aquifers needs to be
        defined in the HRS.

     This study examines each of these issues and the requirements
involved in addressing the issues in the HRS.  The requirements
examined include data needs, data acquisition costs, and data
uncertainties.  Detailed hydrogeologic investigations would be
needed at every site to provide the necessary data.  The cost and
time required to obtain the necessary data would be high relative to
that of current site inspections.  Due to uncertainties inherent in
the data, the use of the data would introduce different types of
uncertainties than those currently present in the HRS.

     In the course of this study, three additional issues were also
identified and examined.  These are the influence of topography on
ground water flow, the behavior of ground water in karst terranes,
and the estimation of the future use of ground water supplies.
These issues focus on ground water conditions which are extremely
site specific and not consistently predictable on a national basis.
It does not appear feasible to develop quantitative, generic rating
factors to account for these issues in the HRS.

Suggested Keywords:  Superfund, Hazard ranking, Hazardous waste,
Ground water, Hydrogeology.
                                 iii

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                          TABLE OF CONTENTS

                                                                 Page

LIST OF ILLUSTRATIONS                                             ix

1.0  INTRODUCTION                                                  1

1.1  Background                                                    1
1.2  Geohydrologic Issues Identified During the Rulemaking         3
     Process
1.3  Organization of This Report                                   5

2.0  DEFINITION OF HYDROLOGIC TERMS                                7

2.1  Underground Water                                             7
2.2  Aquifers and Confining Beds                                   7
2.3  Heads and Gradients                                           9
2.4  Hydraulic Conductivity                                       11
2.5  Transmissivity and Storativity                               15

3.0  GEOHYDROLOGIC DATA ELEMENTS IN THE HAZARD RANKING SYSTEM     17

3.1  Overview of the HRS Requirements Pertaining to the           17
     Ground Water Migration Route
3.2  Depth to the Aquifer of Concern                              18
3.3  Permeability                                                 21
3.4  Ground Water Use                                             23
3.5  Distance to the Nearest Well                                 24
3.6  Population Potentially Threatened                            25
3.7  Summary                                                      26

4.0  DETERMINING THE DIRECTION OF GROUND WATER FLOW               27

4.1  Overview of the Issue                                        27
4.2  General Considerations                                       27
4.3  Measuring Hydraulic Potential                                28

     4.3.1  Data Requirements                                     28
     4.3.2  Data Density                                          29
     4.3.3  Data Constraints                                      31

4.4  Measuring Hydraulic Conductivity                             34

     4.4.1  Piezometer Tests                                      34
     4.4.2  Pumping Tests                                         38
     4.4.3  Data Constraints                                      40

4.5  Findings                                                     41

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                    TABLE OF CONTENTS (Continued)

                                                                  Page

5.0  AQUIFER INTERCONNECTION                                       45

5.1  Overview of the Issue                                         45
5.2  Data Requirements                                             45
5.3  Findings                                                      47

6.0  THE THREE-MILE RADIUS                                         49

6.1  Overview of the Issue                                         49
6.2  Data Related to Migration Distance                            49

     6.2.1  Survey of Contaminant Plume Geometries                 49
     6.2.2  Additional Illustrations of Contaminant  Plume  Size    50

6.3  Flow Velocity and Migration Distance                          53

     6.3.1  Darcy's Law                                            53
     6.3.2  Data Requirements                                      54
     6.3.3  Findings                                               55

6.4  Conclusions                                                   56

7.0  OTHER RELATED ISSUES                                          59

7.1  Topography                                                    59
7.2  Karst Terranes                                                61
7.3  Future Use of Ground Water Supplies                           64

8.0  SUMMARY AND CONCLUSIONS                                       69

8.1  Direction and Velocity of Ground Water Migration             69
8.2  Aquifer Interconnection                                       70
8.3  The Three-Mile Radius                                         71
8.4  Related Issues:  Topography, Karst Terranes, and the          72
     Future Use of Ground Water Supplies

9.0  BIBLIOGRAPHY                                                  75
                                 vi

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                    TABLE  OF  CONTENTS  (Concluded)
APPENDIX A - GLOSSARY OF SELECTED TERMS                           77

APPENDIX B - DETERMINING THE DIRECTION OF GROUND WATER FLOW       83

APPENDIX C - CORRELATION BETWEEN CONTAMINANT PLUME LENGTH         87
             AND HYDRAULIC GRADIENT

APPENDIX D - ESTIMATED COST AND TIME REQUIREMENTS FOR             93
             GEOTECHNICAL FIELD WORK
                                 vii

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                        LIST OF ILLUSTRATIONS

Figure Number                                                    Page

     2-1        Aquifer Types and Associated Terms                10

     2-2        Components Used to Determine Total Head           12
                and Hydraulic Gradient

     4-1        Possible Flow Path of Contaminants More           35
                Dense versus Less Dense than Water
                                 ix

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1.0  INTRODUCTION
1.1  Background
     The Comprehensive Environmental Response, Compensation, and
Liability Act  of 1980  (CEROA)  (PL  96-510) requires the President to
identify national priorities for  remedial action among releases or
threatened  releases of hazardous  substances.  These releases are to
be identified  based on criteria promulgated in the National
Contingency Plan (NCP).  On July 16, 1982, EPA promulgated the
Hazard Ranking System (HRS) as Appendix A to the NCP (40 CFR 300;
47 FR 31180).  The HRS comprises the criteria required under CERCLA
and is used by EPA to estimate the relative potential hazard posed
by releases or threatened releases of hazardous substances.
     The HRS is a means for applying uniform technical judgment
regarding the  potential hazards presented by a release relative to
other releases.  The HRS is used in identifying releases as national
priorities for further investigation and possible remedial action by
assigning numerical values (according to prescribed guidelines) to
factors that characterize the potential of any given release to
cause harm.  The values are manipulated mathematically to yield a
single score that is designed to indicate the potential hazard posed
by each release relative to other releases.   This score is one of
the criteria used by EPA in determining whether the release should
be placed on the National Priorities List (NPL).

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     During the original NCP rulemaking  process and the subsequent

application of the HRS to specific releases,  a number of technical

issues have been raised regarding the HRS.  These issues concern the

desire for modifications to the HRS to further improve its

capability to estimate the relative potential hazard of releases.

The issues include:

     •  Review of other existing  ranking systems suitable for
        ranking hazardous waste sites for the NPL.

     •  Feasibility of considering ground water flow direction and
        distance, as well as defining "aquifer of concernt" in
        determining potentially affected targets.

     •  Development of a human food chain exposure evaluation
        methodology.

     •  Development of a potential for air release factor category
        in the HRS air pathway.

     •  Review of the adequacy of the target  distance specified in
        the air pathway.

     •  Feasibility of considering the accumulation of hazardous
        substances in indoor environments.

     •  Feasibility of developing factors to  account for
        environmental attenuation of hazardous substances In ground
        and surface water.

     •  Feasibility of developing a more discriminating toxicity
        factor.

     •  Refinement of the definition of  "significance" as it relates
        to observed releases.

     •  Suitability of the  current HRS default value for an unknown
        waste  quantity.

     •  Feasibility of determining and using  hazardous substance
        concentration data.

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     •  Feasibility of evaluating waste quantity on a hazardous
        constituent basis.

     •  Review of the adequacy of the target distance specified in
        the surface water pathway.

     •  Development of a sensitive environment evaluation
        methodology.

     •  Feasibility of revising the containment factors to increase
        discrimination among facilities.

     •  Review of the potential for future changes in laboratory
        detection limits to affect the types of sites considered for
        the NPL.


     Each technical issue is the subject of one or more separate but

related reports.  These reports, although providing background,

analysis, conclusions and recommendations regarding the technical

issue, will not directly affect the HRS.  Rather, these reports will

be used by an EPA working group that will assess and integrate the

results and prepare recommendations to EPA management regarding

future changes to the HRS.  Any changes will then be proposed in

Federal notice and comment rulemaking as formal changes to the NCP.

The following section describes the specific issue that is the

subject of this report.

1.2  Geohydrologic Issues Identified During the Rulemaking Process

     The Hazard Ranking System and the National Priorities List have

been promulgated using the Federal notice and comment rulemaking

procedures.  These procedures include a public review and comment

period during which comments and concerns were expressed by the

public regarding the HRS and how it affects the evaluation of sites

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for NPL listing.  Those commenters who focused on geohydrologlc



issues identified three principal areas of concern.



     One of these issues is that the ground water gradient is not



considered in the HRS.  The commenters implied that gradient data



could be used to determine the direction of ground water flow, and



thus the direction of contaminant migration, so as to more



accurately define potential targets.  Another implied use Is to



determine the speed of contaminant migration.



     Secondly, several commenters cited the three-mile radius used



in the HRS as another major concern.  The HRS uses a three-mile



radius to define the target area potentially affected by a site.



Commenters suggested that the three-mile radius overestimates the



distance contaminants can migrate and that, similar to the first



issue, the circular target area defined by the three-mile radius



ignores the direction of ground water flow.



     A third hydrologlc issue is that the separation of hydrologic



units is undefined in the HRS.  Commenters have suggested that



criteria need to be established which could be used to determine the



degree of interconnection between stratigraphlc units so that the



likelihood of vertical migration of contaminants, from a waste site



into one or more aquifers, can be evaluated.  This issue involves




both defining the aquifer of concern and, in turn, identifying the



target population.

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1-3  Organization of This Report




     In order to provide a basic ground water vocabulary, Chapter 2




contains definitions and explanations of some of the fundamental




principles and concepts that are important in the study of




geohydrology.  A detailed glossary is provided in Appendix A.




     Chapter 3 describes the geohydrologic data elements currently




in the HRS.  This establishes a frame of reference for describing




the geohydrologic parameters which are being evaluated in this




report for possible inclusion in the Hazard Ranking System.



     Chapter 4 addresses the issue of ground water flow direction.




Data collection and analysis schemes are described and their




inherent uncertainties are highlighted.




     Chapter 5 discusses the aquifer interconnection issue.  The




concepts and criteria for establishing interconnection are also



discussed.




     Chapter 6 presents an evaluation of the three-mile radius




currently used in the HRS to delineate the potential target area.




In addition, case histories are used to provide examples of typical




ground water contamination plumes.




     Chapter 7 describes three additional issues that have been




identified in the process of conducting this study.  These issues




are:  the influence of topography on ground water flow, the




specialized regime represented by karst terrane, and the future use




of ground water supplies.

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     A summary of the findings and recommendations of this study is




presented in Chapter 8.  Hie bibliography is presented in Chapter 9.




     Appendix A contains the glossary.  Appendix B provides an




illustration of how field data can be used to determine the direction




of ground water flow.  Appendix C presents an analysis of the



correlation between the length of ground water plumes and their




respective hydraulic gradients.  Appendix D provides estimates of




the cost and time requirements associated with hydrogeologic




investigations of hazardous waste sites.

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2.0  DEFINITION OF HYDROLOGIC TERMS




     In order to address the issues which are the subject of this




report, a basic hydrologic vocabulary needs to be introduced.  The




definitions presented here are summaries of more detailed discussions




in Heath (1983) and the Ground Water Manual published by the U.S.




Department of the Interior (1981).  A detailed glossary is provided in




Appendix A.




2.1  Underground Water




     Underground water is the term applied to all water beneath the land




surface.  It occurs in two different zones, the unsaturated zone and




the saturated zone.  The unsaturated zone contains both water and air



and it occurs at and immediately below the land surface.  Beneath the




unsaturated zone is the saturated zone in which all interconnected




openings are full of water.  The water table is the level in the



saturated zone at which the upward pressure exerted by the water is




equal to the downward pressure exerted by the atmosphere (i.e., the




level at which the hydraulic pressure is equal to atmospheric pressure).




Usually it can be thought of as the point below which all geologic




materials are saturated.  Water in the saturated zone is the only




underground water that is available to supply wells and springs.  It is



the only water to which the term ground water is correctly applied.




2.2  Aquifers and Confining Beds




     All saturated geologic materials can be classified either as




aquifers or as confining beds.  An aquifer is a geologic unit that

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will yield water in a usable quantity  to a well or spring.  A




confining bed  is a geologic unit having low  hydraulic conductivity,




relative to adjacent aquifers,  that  restricts  the movement  of  ground




water  either  into or out of the adjacent aquifers.




     Aquifers  are classified as being  either confined or




unconfined.  An unconfined aquifer is  one  that does  not have a




confining layer overlying it.   Its upper boundary is the  water table




and  for  this  reason it  is often referred to  as a free or  water table




aquifer  or  as  being under water table  conditions.  Water  at the




upper  surface  of an unconfined  aquifer is  in direct  contact with the




atmosphere  through the  open pore  spaces of the unsaturated  zone.  At




 the  water  table the upward pressure exerted  by the water  in the




aquifer  is  in balance with atmospheric pressure.  Typically, the




movement of the ground  water  in an unconfined  aquifer is  in direct




 response to gravity.




      A confined or artesian aquifer has an overlying confining layer




 of lower hydraulic conductivity than the aquifer and has  only  an




 indirect or distant connection  with the atmosphere.   In an  artesian




 aquifer, the water  is  under pressure such  that when  the aquifer is




 penetrated  by a  tightly cased well or  piezometer, the water will




 rise above  the bottom  of the  confining bed  to  an elevation  at  which




 it is in balance with  the atmospheric  pressure and which  reflects




 the  pressure in  the aquifer at  the point of  penetration.   If the




water level in an artesian well stands above the land  surface, the

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well is a flowing artesian well.  The  imaginary  surface which



conforms to the elevations to which water will rise in wells



penetrating artesian aquifers is known as the potentiometrie surface.




     Special local  conditions may exist within a hydrologlc regime



which give rise to  a perched aquifer and perched water table.  Above



the regional water  table  in some areas, hydrologic units with



relatively low hydraulic  conductivities (e.g., silt, clay,



unfractured rock) may be  surrounded by higher conductivity



material.  Downward percolating water  may be interrupted by the low



conductivity material forming a saturated zone of limited areal



extent.  This  saturated zone is a perched aquifer and its upper



surface is a perched water table.  Unsaturated material lies between



the bottom of  the saturated zone and the top of  the regional water



table.  A perched water table may be permanent or seasonal depending



upon the climatic conditions or overlying land use.




     The types of aquifers and the terms associated with the ground



water regime are illustrated in Figure 2-1.



2.3  Heads and Gradients



     Ground water moves from regions of higher potential energy to



regions of lower potential energy.  In fluid mechanics the term head



describes the potential energy stored, in a fluid.  Total head is



defined as the sum  of the potential energy in a  fluid which can be



attributed to the elevation, pressure, and velocity of the fluid.

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                                                                            Well in
                                                                           Unconfirmed
                                                                            Aquifer

                                                                               V
 Non-flowing Well
in Confined Aquifer
Potentiometric Surface

             Flowing Well
           in Confined Aquifer
                                                          Confined Aquifer


                                                    Bedrock
                                                                                              Confining Layer
Source: Adapted from US. Department ot the Interior, 1981.
                                            FIGURE 2-1
                          AQUIFER TYPES AND ASSOCIATED TERMS

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In ground water studies velocity head can be ignored because ground
water moves relatively slowly (Heath, 1983).  The total head at a
well, then, is the sum of two components, elevation head and pressure
head.  The total head can be determined by subtracting the depth to
water in a non-flowing well from the altitude of the measuring point.
Alternatively, the equation for total head (h ) is:
                           ht = Z + hp
where Z, the elevation head, is the distance from an arbitrarily
chosen datum plane (e.g., sea level) to the point where the pressure
head, h  . is determined.  This point usually corresponds to the
bottom of the well bore or the depth of the well screen.  Figure 2-2
illustrates the components used to determine total head and hydraulic
gradient in an unconfined aquifer.
     If all other factors remain constant, the rate of ground water
movement depends on the hydraulic gradient.  The hydraulic gradient
(dh/dl) is the change in total head (also known as the head loss)
per unit of distance (1) in a given direction.  Referring to
Figure 2-2 it may be expressed as:
                                           = htl ~ ht2
                Hydraulic Gradient (dh/dl)
                                                 1
2.4  Hydraulic Conductivity
     In the 1850's a systematic study of the movement of water
through a porous medium led Henry Darcy to conclude that the rate of
water flow through a filter bed of a given nature is proportional to
the difference in the height of the water between the two ends of

                                 11

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         Well 1
                                                    Well 2
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  Source: Heath, 1983.
     (National Geodetic Vertical
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                                FIGURE 2-2
COMPONENTS USED TO DETERMINE TOTAL HEAD AND HYDRAULIC GRADIENT
                                    12

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the filter bed and inversely proportional to the length of the flow

path.  He also determined that the quantity of flow is proportional

to a coefficient, K, which is dependent upon the nature of the

porous media.  The flow was also found to be proportional to the

cross-sectional area of the test bed.  These relationships have come

to be known as Darcy's law and are shown symbolically as:

                  Q . KA (ha ~ V  or Q - KA(dbYdl)
                            1
where:

     Q  « quantity of flow or discharge expressed as a volume per
          unit time (L3/T)

     A  " cross-sectional area (L^)

     ha = total head at well a (L)
      eft

     ht - total head at well b (L)

     1  • distance between the two wells (L)

     K  ^ coefficient of proportionality (the hydraulic
          conductivity) (L/T)

     dh " hydraulic gradient (L/L)
     dl

     The above equations can be rearranged to solve for K, the

hydraulic conductivity:

                             K      Q
                                 A(dh/dl)

Dimensional analysis shows that hydraulic conductivity is expressed

in units of velocity (or distance divided by time):
                                 13

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         [Q]    ,  when expressed in units of length (L) and time (T)
     [A][dh/dl]   equals

              ,  which reduces to L/T.
     [L2][L/L]

     The factors involved in the definition of hydraulic

conductivity include the volume of water that will move in a unit

time under a unit hydraulic gradient through a unit area.  Using a

unit gradient to express the value of hydraulic conductivity (rather

than an actual gradient at some particular point in the aquifer)

allows for easy comparison of hydraulic conductivity for different

types of rocks.

     The hydraulic conductivity of rocks ranges through 12 orders of

magnitude (Freeze and Cherry, 1979; Heath, 1983).  Not only is it

different for different types of rocks but the hydraulic

conductivity may vary from place to place in the same rock.  When

hydraulic conductivity is variable within an aquifer, then the

aquifer is said to be heterogeneous .  Alternatively, if it is

essentially the same in all areas, then the aquifer is termed

homogeneous.

     Also, at any place within an aquifer, the hydraulic

conductivity may be different in different directions.  Under these

conditions the aquifer is termed anisotropic.  If the hydraulic

conductivity is essentially the same in all directions, the aquifer

is said to be isotropic.
                                 14

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     In USGS Water Supply Paper 2220, Heath (1983) makes the

following statement:

     Although it is convenient in many mathematical analyses
     of ground water flow to assume that aquifers are both
     homogeneous and isotropic, such aquifers are rare, if they
     exist at all.  The condition most commonly encountered is
     for hydraulic conductivity in most rocks and especially in
     unconsolidated deposits and in flat-lying consolidated
     sedimentary rocks to be larger in the horizontal direction
     than it is in the vertical direction.

Hydraulic conductivity, then, is a very site specific variable in

the flow equation.

2.5  Transmissivity and Storativity

     Heath (1983) defines the transmissivity of an aquifer as the

rate at which water is transmitted through a unit width of an

aquifer under a unit hydraulic gradient.  It equals the hydraulic

conductivity multiplied by the aquifer thickness.

     Storativity (the storage coefficient) is a dimensionless number

which represents the volume of water released from storage in a unit

prism of an aquifer when the head is lowered a unit distance.

According to Heath (1983), for confined aquifers the storage

coefficient ranges between 0.00001 to 0.001.  For unconfined

aquifers the range is from 0.1 to about 0.3.

     Both of these factors are important in the analysis of data

from pumping tests (see Section 4.4.2) and are used to determine the

hydraulic conductivity of the aquifer being tested.
                                 15

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3.0  GEOHYDROLOGIC DATA ELEMENTS IN THE HAZARD RANKING SYSTEM

3.1  Overview of the HRS Requirements Pertaining to the Ground Water
     Migration Route

     A complete description of the HRS appears as Appendix A to the

National Contingency Plan  (40 CFR 300) as published in the Federal

Register on July 16, 1982  (47 FR 31219).  The HRS assigns three

scores to a site:  migration, fire and explosion, and direct contact.

The ranking of sites as national priorities for further investigation

and possible remedial action is based primarily on the site migration

score.  The scores for fire and explosion and direct contact are

used in identifying sites  requiring emergency attention.

     The site migration score reflects the potential for harm to

public health, welfare, or the environment by the migration of

hazardous substances away  from the site.  It is a composite of three

separate scores for three  possible migration routes:  ground water,

surface water, and air.  A migration score for each applicable route

is first calculated by evaluating the site with respect to a number

of factors that characterize (a) the hazardous substances at the

site, (b) the containment  of the hazardous substances, (c) the

potential for migration of the hazardous substances from the site by

that route, and (d) the presence and proximity of targets (i.e.,

human populations or sensitive ecological systems or environments).

The individual route scores are then combined to give an overall HRS

site migration score.  The scoring system is structured so that HRS

site migration score can range from 0 to a maximum of 100.  The
                                 17

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higher the score the higher the relative threat ascribed to the site.

Under present policy, sites eligible for the National Priorities List

that have HRS scores greater than or equal to 28.50 are included on

the National Priorities List.

     This study focuses on the ground water migration route and

particularly on those factors that pertain to ground water route

characteristics and targets.  Three current HRS rating factors are

based on the geologic or hydrogeologic conditions at the site and

are used to evaluate the likelihood of contaminant migration via the

ground water route.  These factors are as follows:

     •  The depth to the aquifer of concern.

     •  The permeability of the unsaturated zone or the intervening
        geologic material.

     •  The distance to the nearest well that draws water from the
        aquifer of concern.

Other ground water related factors considered in the evaluation of

a  site are the use of ground water (e.g., drinking, Industrial,

irrigation) and the population potentially threatened through regular

use of ground water.  Each of these factors has unique informational

or data requirements as described in the following sections.

3.2  Depth to the Aquifer of Concern

     When the ground water migration path is evaluated on the basis

of route characteristics, the depth to the aquifer of concern is one

of the principal scoring factors.  The depth to the aquifer of

concern is defined as the distance between the lowest known point at
                                 18

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which contaminants are present at the site and the top of the aquifer



which serves as a source of water for the target(s).



     The key term is "aquifer of concern" which, for the purpose of



the HRS, is the aquifer which yields the highest HRS score for the



ground water pathway.  At many sites, more than one aquifer is



present and potentially may be affected by releases from the site.



A common condition at a site is to observe a release of contaminants



to a surficial aquifer which serves as a source of supply for a




relatively small number of private wells.  Often a deeper aquifer,



which serves as a source of supply for several community wells, is



also present in the site area and has the potential to be



contaminated by pollutants migrating through the intervening geologic



material.  Therefore, data on both aquifers (in some cases it may



be three or more aquifers) and the intervening geologic material



needs to be evaluated separately in order to determine which of



these aquifers yields the highest HRS ground water route score for



the site.  This is described more fully in Section 3.2, and is



illustrated in Figure 3 of Appendix A to the NCP (40 CFR 300;



47 FR 31226; July 16, 1982).



     Identifying the aquifer of concern, and thus determining



the depth to the aquifer of concern, frequently requires more



hydrogeologic information than any other migration factor in the



ground water pathway.  The data needed to clearly identify the



aquifer of concern at most hazardous waste sites are similar to the
                                 19

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data needed for a complete hydrogeologic site characterization as




described by Freeze and Cherry, 1979; the Office of Technology




Assessment, 1984; and the U.S. Environmental Protection Agency,




1985a, among others.



     Identification of the aquifer of concern begins with the




collection and examination of available reports, maps, and data.




Geologic maps and reports indicate the geologic formations in the




site area, together with their stratigraphic (i.e., the number and




types of rock units present) and structural relationships.




Topographic maps along with soils or surflclal geology maps provide




information on the genesis and distribution of unconsolidated




deposits and landforms.  Hydrogeologic maps usually provide an




interpretation of the ground water flow characteristics, considering




the topographic, geologic, hydrogeologic, geochemical and water




resource data available for the area.




     Air photo interpretation may also be used to prepare maps of




landforms, soils, land use, vegetation, and drainage in the vicinity




of a site.  Each of these environmental features leads to Inferences




about the natural ground water flow systems and/or the presence of



potential aquifers.




     The information described in the previous paragraphs relate for




the most part to surface geology.  However, in order to identify the




ground water regime in the vicinity of a site (i.e., in order to




identify all potentially affected aquifers), it is also necessary to
                                 20

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compile information on the subsurface geology.  Ideally, on-site




boring logs would be used to depict the subsurface stratigraphic




relationships.  The more usual case in the application of the HRS to




a site is to first use available records rather than boring logs.




Published geologic maps and available well log records can be used




to determine the local lithology (i.e., the physical characteristics




of the rock units), stratigraphy, and structure.  Similar information




on a regional scale can help establish the context in which the local




geology is interpreted.  Depending upon the availability of the data,



it may be possible to produce a wide variety of visual aids to




characterize a site.  These could include stratigraphic cross




sections, geologic fence diagrams, isopach maps of overburden or




formation thickness, and lithofacies maps.  Hydrogeologic information




might include water table contours and isopachs of saturated




thickness of unconfined aquifers.




     The identification of the aquifer(s) of concern is of critical




importance to the HRS evaluation of the ground water migration route.




From the above discussion, it is apparent that initially a site




inspection needs to draw on a considerable amount of existing




information in order to characterize the surface and subsurface




geological conditions.




3.3  Permeability




     In the HRS, permeability is another factor which is used when




the ground water migration path is being evaluated on the basis of
                                 21

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route characteristics.   As explained in Appendix A to the NCP




(40 CFR 300; 47 FR 31224, July 16, 1982), the permeability being




evaluated is either that of the unsaturated zone (when the aquifer




of concern is the uppermost aquifer) or that of the intervening




geological formations (when the aquifer of concern is a deeper,




confined aquifer).  This factor is used as an indicator of the speed




at which a contaminant could migrate from a site.  It is assigned a




value based on the least permeable continuous layer below the site.




     A table entitled "Permeability of Geologic Materials" (Table 2




in Appendix A to the NCP) is used to select a rating value which




corresponds to the type of material beneath the site and its




approximate range of hydraulic conductivity.  This table was derived




from Davis (1969) and Freeze and Cherry (1979).  In this table the




terms "permeability" and "hydraulic conductivity" are used



interchangeably.  The hydraulic conductivity depends upon the size




and arrangement of the fluid transmitting openings within the




geologic media (its specific or intrinsic permeability) and on the




dynamic characteristics of the ground water (i.e., kinematic




viscosity, density, and the strength of the gravitational field).




     Usually, for HRS scoring purposes, qualitative data gathered




during a site inspection are used to define the stratigraphic




sequence at a site.  Typically, the lithology is described based on




well logs from local or regional hydrologic studies.  It is these




descriptions that form the basis for the evaluation of the hydraulic
                                 22

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conductivity of the least permeable continuous layer which is used

to assign a value to the HRS permeability factor.

3.4  Ground Water Use

     This rating factor indicates the use made of ground water

drawn, within three miles of the site boundary,* from the aquifer of

concern.  A value of zero is assigned if the ground water is

evaluated as being unusable (e.g., a saline aquifer, or extremely

low yield).  Intermediate factor values include both non-drinking

use (e.g., commercial, industrial, or irrigation) and drinking water

use with unthreatened alternate supplies readily available.  A

maximum value is assigned to this factor when the aquifer of concern

is the only source of supply for drinking water.

     In those cases where several separate aquifers exist beneath a

site, each aquifer must be evaluated separately on the basis of the

information that pertains to the particular aquifer.  For example,

if two separate aquifers are present beneath a site, the HRS

precludes evaluating the ground water use based on one aquifer if

the other scoring factors are going to be based on a different

aquifer.  This is explained more fully in Appendix A to the NCP

(40 CFR 300; 47 FR 31189, July 16, 1982).

     Also, ground water use is evaluated in the HRS as it existed

prior to the occurrence of any remedial actions at the site and as
*The site boundary is the term used here to describe the edge of the
 area of known contamination attributable to the site (Section 3.5
 of Appendix A to the NCP, 40 CFR 300; 47 FR 31230, July 16, 1982).


                                 23

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it existed before the effects of pollution attributable to the site




may have caused changes in usage patterns.  For example, a domestic




well, abandoned because of contamination from the waste site, would




still receive the maximum ground water use score If it was a sole



source of supply prior to being contaminated and abandoned.




3.5  Distance to the Nearest Well



     The distance to the nearest well factor is used In the HRS




as a measure of the likelihood of exposure of a population (see




Section 3.6) to contaminated ground water.  The distance is measured




from the site boundary (i.e., the edge of the area of known




contamination attributable to the site) to the nearest well drawing




drinking or irrigation water from the aquifer of concern.  There are




five distance intervals associated with this factor.  The intervals




are ordered so that the factor value decreases as the distance




increases.  The decreasing value of the factor serves as a surrogate




for attenuation of contaminants in ground water as it migrates to a




potential target.  The highest value is assigned if the well is




within 2000 feet of the site boundary.  The next highest value Is




assigned for a distance interval of 2001 feet to one mile.  The




scoring values decline to zero as the distance increases, in one



mile increments, to over three miles.




     In order to evaluate this factor it is necessary to identify




the nearest well to the site drawing drinking and/or irrigation




water from each aquifer.  The depth of each well should be documented
                                 24

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to show that it is actually completed in the aquifer to which it is




assigned.  This factor is used in combination with another factor,




the population potentially threatened.




3.6  Population Potentially Threatened




     This factor is used in the HRS to indicate the population




potentially threatened by regular use of ground water drawn from the




aquifer of concern.  It includes residents, workers, and students.




Transient populations, such as customers or travelers passing




through an area, are excluded.



     The potentially threatened population is that population using




water drawn from wells within three miles of the site boundary.




Detailed information about well locations, well construction, and




the water distribution system is needed in order to evaluate this




factor.  Depending upon the nature of the water distribution system,




the population being counted may itself be in areas beyond the




three-mile limit, providing the water used by the population is




drawn from wells within the three-mile limit.  Similarly, people




within three miles of the site boundary who do not use water from




the aquifer of concern are not counted.  Six population ranges are




used to evaluate this factor with a population of greater than




10,000 individuals receiving a maximum value.




     The distance to the nearest well and the population potentially




threatened are combined into a single factor which is used as a




measure of the risk to public health presented by the migration of
                                 25

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contaminated ground water.  The combined factor assesses the




likelihood of exposure and the number of people who might be exposed.




A complete description of the use of the combined factor appears in




Section 3.5 of Appendix A to the NCP (40 CFR 300; 47 PR 31230,



July 16, 1982).




3.7  Summary



     The migration of contaminants via ground water is one of the




principal areas of concern in the HRS.  In evaluating the ground




water migration route, several geohydrologic factors are




considered.  These include identification of the aquifer of concern




and a determination of its use for drinking or non-drinking




purposes.  The distance from the known extent of contamination to




the nearest point of withdrawal is also determined, as is the



population that would regularly use ground water derived from the




aquifer of concern within three miles of the site boundary.




Depending upon which aquifer is the aquifer of concern, the




hydraulic conductivity of the unsaturated zone or of intervening




geologic formations is also evaluated.  The data used to evaluate




these factors are derived from existing information and the results




of field studies performed during site Inspections.
                                 26

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4.0  DETERMINING THE DIRECTION OF GROUND WATER FLOW




4.1  Overview of the Issue




     Determining the ground water flow regime in the vicinity of a




hazardous waste site has been cited as being important for the




identification of the target area potentially threatened by the




site.  This chapter describes the methodology generally used for




determining the direction of ground water flow and identifies




important sources of uncertainty in the determination.




4.2  General Considerations



     An isotropic aquifer provides the simplest example for




determining the direction of ground water flow.  Under isotropic




conditions, flow is parallel to the direction of the greatest




decrease in the potential field (i.e., total head).  The direction




of ground water movement and the hydraulic gradient can be determined




if the following data are available for three wells located in any




triangular arrangement in the area of study (Heath, 1983):




     •  The relative geographic position of the wells.




     •  The distance between the wells.




     •  The total head at each well.




An illustrative example of how the data are used is provided in




Appendix B.  As mentioned previously, however, isotropic aquifers




are rarely, if ever, encountered.  Anisotropic aquifers are the more




common condition, and in these aquifers ground water flow is usually




not parallel to the hydraulic gradient.
                                 27

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     Fetter (1981)  points out that in the majority of field




situations, the direction of ground water movement is a function of




two variables.   The first is the potential field of the ground water




flow system and the second is the degree of anisotropy and the




orientation of the axes of permeability.




     Therefore, directional hydraulic conductivity and hydraulic




potential (i.e., hydraulic head) are the principal parameters which




must be measured in the field in order to determine the direction of




flow in anisotropic aquifers.




4.3  Measuring Hydraulic Potential




     4.3.1  Data Requirements




     The direction of ground water flow is a function of both




horizontal and vertical components.  Fetter (1981) describes the



procedure for resolving the directional components of ground water




flow.  Similar to the example shown in Appendix B, the horizontal




components can be determined from three tightly cased boreholes.




These boreholes need to be located in the same aquifer in such a




manner that they form a right triangle, and they must all be




completed to the same elevation above a horizontal datum (usually




mean sea level).  For the vertical component, a fourth borehole,




located adjacent to the borehole at the right angle of the triangle}




needs to be constructed and completed to a deeper part of the same




aquifer.  The three components can then be resolved into a resultant
                                 28

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vector.  Fetter suggests that a typical horizontal  spacing would be




100 feet for each leg of the triangle.




     A single determination of ground water flow direction at a




single location and at a single point in time, then, requires some




prior knowledge of the hydrogeology of the site.  This is necessary




for completing the three shallow piezometers at the same depth in




the same aquifer and is especially necessary for setting the vertical




piezometer within the same aquifer.  Similarly, the locations of the




piezometers need to be accurately surveyed, including an indication




of the elevation of the measuring point (usually the top of the




casing).  Water level measurements need to be taken simultaneously




(or as nearly as possible).  Depending upon the nature of the




measuring and recording devices, water level measurement accuracies




of one hundredth of a foot are achievable (Everett, 1980, among




others).




     4.3.2  Data Density




     The direction of ground water flow can best be determined by




compiling a map of the potentiometric surface in an aquifer.  Where




multiple aquifers are present, a potentiometric map will be needed




for each.  Perhaps the single most important issue  is the number of




data points needed to accurately characterize the potentiometric




surface at a site.




     The scheme described by Fetter (1981) employs a 100-foot




horizontal spacing to derive one data point from a  5,000 square-foot
                                 29

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area.  At this level of detail, as many as nine data points could be

required per acre.  (There are 640 acres per square mile.)  An

alternative scheme has been suggested in the draft version of the

RCRA Ground Water Monitoring Technical Enforcement Guidance Document

(U.S. Environmental Protection Agency, 1985b).  In this report an

initial 300-foot spacing is suggested; this spacing may be decreased

depending upon preliminary results and the need for greater detail.

According to this guidance, then, the number of boreholes needed at

a site could range between one and three per acre.  R.W. deary

(personal communication, 1985) suggests that a 5 to 10 acre site

would require as many as 10 to 20 wells to characterize the flow

regime.  This well density is comparable to the range specified by

the U.S. Environmental Protection Agency (1985b).

     Appendix D provides estimates of the cost and time requirements

for installation of ground water wells and for collection and

analysis of data to determine the direction of ground water flow.

For a field program consisting of ten wells, representative total

cost for well installation and for data collection and analysis are

estimated to be $21,000 for 20-foot wells, $50,500 for 100-foot

wells, and $92,000 for 200-foot wells (see Table D-2 of Appendix D).*

Representative total time requirements for well installation and
*Based on the data presented in Table D-l of Appendix D, the
 estimated range of total costs is $6,600 to $54,000 for 20-foot
 wells, $20,000 to $329,000 for 100-foot wells, and $29,000 to
 $635,000 for 200-foot wells.
                                 30

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for data collection and analysis are estimated to be 4 weeks for




20-foot wells, 6 weeks for 100-foot wells, and 16 weeks for 200-foot




wells.  It should be noted that wells installed for determining the




direction of flow could also be used for other purposes such as the




collection of ground water samples and the determination of




hydraulic conductivities (see Section 4.4).  When this is done,




there would not be additional well installation costs for these




other activities.




     4.3.3  Data Constraints




     Fetter (1981), the Office of Technology Assessment (1984), and




the U.S. Environmental Protection Agency (1985a) cite several sources




of uncertainty associated with the determination of the direction of




ground water flow.  One of these is the frequency with which ground




water level measurements are taken.  The ground water flow regime is




subject to seasonal and temporal forces which may produce either




short-term or long-term variations in ground water levels and flow




patterns.  The sources of these variations may include on-site or




off-site well pumping, intermittent natural processes such as tidal




processes or changes in river stage, and changes in land use




patterns.  At any particular site, then, a one-time determination of




ground water levels is not likely to provide a reliable picture of




the ground water regime because any seasonal or temporal variations




would not be detected.  For this reason, local conditions must




dictate the frequency of water level measurements.
                                 31

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     Another data constraint concerns measurement uncertainties




related to whether a site is in an area of recharge or discharge.




In such areas there can be erroneous interpretations of ground water




level measurements as described below.




     A recharge area is defined by decreasing hydraulic head with




depth indicating downward flow.  In an open (i.e., uncased) borehole




in a recharge area, ground water is free to move into the borehole




from any of the upper (higher hydraulic head) pores or joints above




the bottom of the borehole and then to move into regions of lower




hydraulic head within the borehole.  In a cased borehole (e.g.,




piezometer), ground water is not free to move into the borehole from




the upper pores or joints and then to move to regions of lower




hydraulic head within the borehole; ground water can only move into




the borehole at the point at which the screen is set.  Water levels




in an open borehole will therefore be higher than water levels in a




piezometer completed to a discrete, but the same, depth in a recharge




area.




     Similarly, a discharge area is defined by an increasing




hydraulic head with depth.  If piezometers set at different depths




within an aquifer indicate increasing heads with depth, then an




upward flow condition exists.  In an open borehole in a discharge




area, ground water will move up the bore and out of the borehole




through pores or Joints having a lower hydraulic potential.  Hie




artesian head will be relieved in the open borehole and the composite
                                 32

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water level will be lower than in a cased borehole (e.g., piezometer)




completed at the same depth as the open borehole because the water




cannot move out of the cased borehole.




     Ground water table or potentiometric surface maps based on




erroneous interpretations of ground water level measurements in



recharge or discharge areas can thus lead to misinterpretations of




the ground water flow regime in the area potentially affected by a




waste site.




     Another source of measurement uncertainty has been described by



Saines (1981) as a back water effect in a discharge area.  According




to this theory, sudden increases in water levels in piezometers in a




river valley after heavy rains and a rise in river stage have been




incorrectly ascribed to infiltration of rain water or flood water,




even though some of the piezometers may be over 330 feet deep.  In




many cases the increase in the water levels in the piezometers is




due to the increased pressurization on the system caused by the




increased elevation of the discharge point.  Again, this is a




temporal effect.




     At some sites, the characteristics of the hazardous substances




themselves cause uncertainty regarding the direction of contaminant




migration.  Hazardous substances (including leachate) which are more




dense or less dense than water may not follow the same flow path as




ground water.  Their movement may instead be more controlled by




geology and gravity.  For these contaminants, analysis of water level
                                 33

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and piezometric data cannot adequately predict their transport




direction because the analysis assumes a single density fluid which




moves in the direction of ground water flow.  Dense contaminants




may, however, move at an angle to the normal ground water flow



direction or vertically downward until they encounter a relatively




impermeable layer.  At that point, they may move by gravity along




the contact between the aquifer and the impermeable material.  Ihis




may be either in the general direction of ground water flow or




opposite to the ground water flow direction.  Contaminants that are




less dense than water may "float" on top of ground water and move



randomly along the interface between the saturated and unsaturated




zone.  Figure 4-1 illustrates a possible migration path for




contaminants more dense and less dense than water.




4.4  Measuring Hydraulic Conductivity




     There are two types of field tests which can be used to measure




hydraulic conductivity:  piezometer tests and pumping tests.




     4.4.1  Piezometer Tests




     Hydraulic conductivity values can be determined in the field by




means of tests carried out in a single piezometer.  The water level




in the piezometer is suddenly changed by either introducing water (a




slug test) or removing water (a bail test) in the water column.  The




recovery of the water level with time is then observed.  The same




effect can be created by suddenly introducing or removing a solid




cylinder of known volume from the water column.  According to the
                                 34

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                        Source of Contaminant
                      (Greater Density Than Water)
  Source of Contaminant
(Lesser Density Than Water)
 Unsaturated
    Zone
	• •	Waterjab|e_
              Direction
         of Ground Water Flow
            . Flow of Dissolved
               Contaminant
  Saturated
   Zone
     Source: Adapted from Office of Technology Assessment, 1984.
                               FIGURE 4-1
              POSSIBLE FLOW PATH OF CONTAMINANTS
          MORE DENSE VERSUS LESS  DENSE THAN WATER
                                   35

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Practical Guide to Ground Water Monitoring (U.S. Environmental




Protection Agency, 1985a), another technique exists in which the




water level is depressed by pressurizing the well casing.  The




pressure is rapidly released, and the recovery of the water level is




observed.




     Slug/bail tests are suitable for relatively low conductivity




settings where the resultant changes in water levels take place




slowly and measurements accurate to one hundreth of a foot can be




made.  For a slug test, water of a different quality than that in




the aquifer may be introduced into the system.  This water must be




removed prior to any sampling of water quality in the well.  For a




bail test, in a well where hazardous constituents are suspected to




be present, water removed from the well needs to be managed in an




environmentally protective manner.  A single slug/ball test in a




30-foot thick confined aquifer, approximately 100 feet below the




surface, is estimated to cost between $300 and $1,600 (exclusive of




drilling costs) and to take between 3 and 18 hours (see Table D-3 of



Appendix D).




     A significant limitation of slug and bail tests is that they




are heavily dependent on a high quality piezometer intake.  Corroded




or clogged intakes may yield highly inaccurate measurements.




Alternatively, if the piezometer was developed by surging or




backwashing prior to testing, the values may reflect artificially




induced increased conductivities.
                                 36

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     The pressurization technique minimizes the disturbance of the




well, and it has the least potential for compromising the integrity




of water quality samples.  It can also be used for conducting tests




on wells with very high hydraulic conductivities when pressure




transducers are used for the water level measurements.  A single




pressurization test in a 30 foot aquifer, approximately 100 feet




below the surface, is estimated to cost $500 to $2,200 (exclusive




of drilling costs) and to take 4 to 18 hours (see Table D-3 of




Appendix D).




     Freeze and Cherry (1979) describe two methods for analyzing and




interpreting the water level versus time data that arise from slug




or bail tests.  The simplest interpretation is that of Hvorslev which




is applicable for tests in a point piezometer (i.e., a piezometer




open only at one point).  For a bail test Hvorslev reasoned that the




rate of inflow at the piezometer tip at any time is proportional to




the hydraulic conductivity of the geologic media and the unrecovered




head difference.  A detailed description of the method of analysis




can be found in Freeze and Cherry (1979).  According to these




authors, Hvorslev also developed formulas for anisotropic conditions




and for special conditions affecting the physical placement of the




piezometer openings.




     The second test interpretation procedure described by Freeze




and Cherry (1979) applies to piezometers that are open over the




entire thickness of a confined aquifer.  It assumes that the aquifer
                                 37

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is horizontal,  confined between impermeable formations, infinite in




horizontal extent, of constant thickness, and that hydrogeologically




it is homogeneous and isotropic.  A graphical curve matching procedure



is used to determine the aquifer parameters of transmissivity and




storativity.  Ihe hydraulic conductivity can then be determined by




dividing the transmissivity by the thickness of the aquifer.




     4.4.2  Pumping Tests



     A pumping test is made by pumping a well for a period of time




and observing the change in hydraulic head in the aquifer.  These




tests are specifically well suited to determining the transmissivity




and storativity in confined and unconfined aquifers.  Pumping tests




provide in-situ measurements that are averaged over a large aquifer




volume.




     The mathematical principles behind pumping tests have been



described by Freeze and Cherry (1979), Bouwer (1978), Fetter (1980),




and Heath (1983), among others.  For a given pumping rate, if the




transmissivity and storativity of an aquifer are known, it is possible




to calculate the time rate of drawdown (i.e., change in potential




level versus time) at any point in the aquifer.  This response




depends solely on the values of transmissivity and storativity.




Therefore, measured values of drawdown versus time, at some




observational point in an aquifer, can be used to work backwards




through the equations to determine the values of transmissivity and




storativity.  The hydraulic conductivity at the observation point can
                                 38

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then be calculated from the transmissivity by dividing the




transmissivity by the aquifer thickness.




     Freeze and Cherry (1979) point out that a single pumping test




can provide information on both the hydraulic conductivity and




storage properties of an aquifer.  Also, important leakage properties




of an aquifer system can be investigated if observations are made in




both the aquifers and the potential confining layers.




     The same authors, however, indicate that there are two major




disadvantages to conducting pumping tests.  The principal technical




concern is that the interpretation of pumping test results is not




unique.  Freeze and Cherry (1979, p. 376) illustrate that there is a




marked similarity in the time-drawdown response that can arise from




leaky, unconfined, and bounded systems.  The authors state that "The




fact that a theoretical curve can be matched by pumping test data in




no way proves that the aquifer fits the assumptions on which the




curve is based."




     Similarly, Driscoll (1986, pp. 559-579) presents several




examples of pumping tests set in different types of environments.




Driscoll draws alternative conclusions for each of these examples to




illustrate that pumping test data can be interpreted in more than




one way.




     The second disadvantage which is cited is that pumping tests




are expensive.  As shown in Appendix D (Table D-3), a single pumping




test for a 30-foot thick confined aquifer, approximately 100 feet
                                 39

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below the surface, Is estimated to cost between $10,000 and $15,000




if drilling is not necessary and to take 10 to 15 days.  If drilling




is necessary, the costs of pumping test is estimated to be about




$40,000.  The costs associated with site security, drilling spoils




and pumped water disposal, and increased contractor costs for working



in a potentially hazardous environment are not included in the cost




estimate.  The cost to test a two aquifer system is estimated to




range between $13,000 and $29,000 if drilling is not necessary and




to take 20 to 25 days (see Table D-3 of Appendix D).  If drilling is




necessary, the total cost of the test is estimated to range between




$68,000 and $110,000.




     Freeze and Cherry suggest that pumping tests should be used only




in cases where it is anticipated that the aquifer will be developed




for water supply purposes.  They further state that it is usually




inappropriate to use pumping tests for geotechnical applications,




contamination studies, or regional flow analyses.




     A third disadvantage is that the construction and placement of




pumping and observation/monitoring wells must be done with extreme




care.  Driscoll (1986) notes that even under non-pumping conditions




poorly constructed or abandoned wells may serve as conduits for



contaminant migration.




     4.4.3  Data Constraints




     The limitations of slug and bail tests and the advantages




and disadvantages of pumping tests have already been described.
                                 40

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Furthermore, as part of this study, a representative sample of the




data submitted to EPA in support of RCRA Part B permit applications




was reviewed.  The data showed that even within one stratigraphic




unit the range of reported values of hydraulic conductivity could be



several orders of magnitude.  Other sources of uncertainty in the




data reviewed included average values outside the range of reported




measured values and standard deviations as great as the range of




values presented in the field data.  It would appear, then, that




field determinations of hydraulic conductivity are at present costly,




unreliable, and subject to reporting and/or interpretive errors.




4.5  Findings




     As it is presently designed, the Hazard Ranking System relies




on a large amount of existing data to characterize the hydrogeologic




regime at hazardous waste sites.  The additional data that are needed




to address the issues that have been raised concerning direction of




ground water flow are primarily field measurements of potential head




and hydraulic conductivity.




     In order to evaluate the ground water regime in the area




potentially affected by the site, the data requirements imply a




significantly increased field effort, in terms of cost and time




requirements, compared to the current site inspection program.  The




increased field effort is needed both to evaluate the ground water




regime at any one point in time and to account for time dependent




changes in the ground water regime.  Typically, a one year cycle of
                                 41

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water level measurements may be necessary to adequately characterize




flow conditions at a site.



     Sections 4.3 and 4.4 discuss the increased cost and time




requirements associated with measurements of potential head and




hydraulic conductivity.  As indicated, representative costs for a




ten well program for measuring the potential head are estimated to




range from $21,000 (for 20-foot wells) to $92,000 (for 200-foot



wells).  Representative time requirements for well installation and




data collection and analysis are estimated to range from 4 weeks




(for 20-foot wells) to 16 weeks (for 200-foot wells).  Hydraulic




conductivity testing is estimated to cost an additional $300 to




$2,200 for a single slug/bail test or pressurizatlon test (assuming




no additional wells need to be installed) and to take an additional




3 to 18 hours.  If a pumping test is done instead to evaluate




hydraulic conductivity, the additional cost for a single pumping




test is $10,000 to $15,000 for a single aquifer and $13,000 to




$29,000 for a two aquifer system (assuming no additional wells need




to be installed).  A pumping test is estimated to require 1.5 to




2 weeks in the former case and 3 to 3.5 weeks in the latter case.




     Furthermore, the increased data collection effort does not




necessarily always translate into more accurate knowledge about




conditions at the site.  Each of the additional data elements




needed to assess the direction of ground water flow has attendant




uncertainties as described in detail in Sections 4.3 and 4.4.
                                 42

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Consequently, the use of these data elements in evaluating the



direction of ground water flow at a site would introduce different



types of uncertainties into the HRS process than those that are



currently present as a result of the direction of flow not being



considered.  The primary concern would be in underestimating the




target area potentially threatened by the site.  The extend to which



this could be a significant problem would depend upon site specific



conditions, the amount of data collected both temporally and



spatially, and the uncertainties inherent in the measurement methods.



In addition to the data reliability issues, these uncertainties also



create an added quality control/quality assurance burden because



judgments need to be made based on interpretations of the data.
                                 43

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5.0  AQUIFER INTERCONNECTION




5.1  Overview of the Issue




     Commenters have noted that the separation (or, conversely, the




connection) of hydrologic units is not defined in the HRS.  EPA




personnel, contractors, and commenters have suggested that a




definition is needed so that a judgment can be made as to when two or




more water bearing units function as a single hydrologic unit.  This




issue focuses on the vertical migration of contaminated ground water.




As discussed in Chapter 3, both the definition of the aquifer of



concern and the identification of the target population are affected




by the number of hydrologic units that are present in the vicinity of




a disposal site and the degree of connection between multiple water




bearing units.




5.2  Data Requirements




     A primary piece of information needed to evaluate the connection




(or lack of connection) between two or more water bearing units is




the areal extent of confining layers beneath a disposal site.  As




described in Chapter 3, evaluation of the ground water migration




pathway generally requires that a large body of existing information




be collected and analyzed in order to define the hydrogeologic




environment at the site under investigation.  The collected




hydrogeologic information should help define both the lateral and




vertical extent of potential confining layers.
                                 45

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     A second key data element needed to determine the degree of




aquifer connection is the hydraulic conductivity of adjacent




strata.  Fetter (1981) illustrates how the direction of ground water



flow is affected by the degree of anisotropy in the aquifer.  Ratios



of horizontal to vertical hydraulic conductivity on the order of 100




or less require that the lateral, transverse, and vertical components




of flow be resolved into a resultant vector.  As he points out in his




1980 textbook (Fetter, 1980), differences of more than two orders of




magnitude between horizontal and vertical hydraulic conductivity are




not uncommon.  This finding was reiterated by Heath (1983).  Under




these conditions the direction of flow would be in the direction of




greatest hydraulic conductivity.




     This criterion is used at the U.S. Environmental Protection




Agency's Robert S. Kerr Environmental Laboratory when the placement




of injection wells is being evaluated (Thornhill, personal




communication, 1985).  A real difference of two orders of magnitude




or more in the hydraulic conductivities of two successive strata is




considered sufficient to retard vertical migration.  As mentioned in




Section 4.4, however, there are several uncertainties associated




with the direct measurement of hydraulic conductivity.  These




include unreliable pumping test design and implementation, variable




interpretations of test results, and reporting errors.  Field




determinations of hydraulic conductivity may be of questionable




value for making comparisons between different strata for reasons



discussed in Section 4.4.




                                 46

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5.3  Findings




     On the subject of aquifer interconnection, guidance can be




developed that can be incorporated into a revised HRS.  The guidance




could establish that the hydrogeology of the site, and/or




contrasting values of hydraulic conductivity, should be used for




determining the degree of interconnection between aquifers.  In so




doing, a decision would need to be made regarding the requirements




to determine hydraulic conductivity.  Field determinations of this




parameter are both time consuming and costly (see Section 4.4), and




uncertainties are introduced at all levels of data aquisition,




analysis and interpretation.  If the HRS continues to serve as a




screening tool intended to use only limited data, then qualitative




assessments of the hydraulic conductivity, based on descriptions of




the geologic units, are the recommended requirement.
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6.0  THE THREE-MILE RADIUS

6.1  Overview of the Issue

     During public review and comment on both the HRS and the

National Priorities List, comments were received regarding the

three-mile radius used in the HRS to evaluate ground water targets.

Some commenters indicated that three miles is an overestimate of the

potential migration distance of contaminants from hazardous waste

sites while other commenters stated that it is not far enough.

     In order to address this issue, data related to contaminant

plume size were collected from the open literature and other

available sources.  Also, a general range of ground water velocities

was used to estimate annual migration distances.  The following

sections describe the available data.

6.2  Data Related to Migration Distance

     6.2.1  Survey of Contaminant Plume Geometries

     As part of a 1985 study for the U.S. EPA Office of Ground Water

Protection, the consulting firm of Geraghty and Miller, Inc. prepared

a survey of 50 contaminant plumes and their geometries (i.e., length,

width, depth).  The raw data is reproduced in Appendix C.  Analysis

of the plume survey data has led to the following conclusions:

     •  As of the time of observation, the average plume length is
        greater than 2,800 feet and the maximum reported length is
        18,000 feet.

     •  There is little correlation in the reported data between
        plume length and gradient (see Appendix C).
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      •   Over  ten percent of the  plumes appear  to  be  circular or
         semi-circular  (i.e., length equals width).

      •   Data  gaps limit further  meaningful study  of  these plumes;
         details of their age, content, and the nature  of  the source
         (continuous or intermittent) are not provided.

 The data does not show which plumes have stablized,  nor does it

 indicate which plumes discharge  to surface water.  The survey,

 however, illustrates that plume  geometries are highly variable and

 site-specific.

      6.2.2  Additional Illustrations of Contaminant  Plume  Size

      In  their 1974 paper "Leachate Plumes in a Highly Permeable

 Aquifer," Kimmel and Braids present an Investigation of a  landfill

 located  on sand and gravel on Long Island, New York.  They delineated

 a leachate plume which is more than 10,000 feet long and has reached

 a depth  of more than 160 feet.

      In  their chapter on ground water contamination, Freeze  and Cherry

 (1979) cite the example of a landfill located on a moderately

 permeable, glaciodeltaic sand aquifer.  A large plume of leachate

 contaminated water has penetrated deep into the aquifer (approximately

 65 feet) and has moved laterally one to two thousand feet  in the

 direction of ground water flow.   They point out that contamination  in

 this landfill developed over a period of 35 years and that leachate

will continue to be produced as  water infiltrates through  the

landfill.  The zone of contamination is expected to expand.

     In a 1984 report prepared for the U.S. Environmental  Protection

Agency, Geraghty and Miller,  Inc. evaluated a number of surface
                                 50

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impoundments and their effects on ground water quality.  Several case




histories are cited below to illustrate certain unique characteristics




of ground water contamination.




     At a site in Oregon, timber and wood products wastes were



disposed in a shallow alluvial sand and gravel deposit which supplied




nearby domestic wells.  In August 1972, "only a few weeks after




disposal operation began," a plume of contaminated ground water had




migrated 1,000 feet downgradient and had contaminated 11 domestic




wells.  The affected area covered about 4 acres.  By January 1973,




the plume had advanced to a point about 1,500 feet from the disposal




pit and the affected area had increased to about 15 acres.




     In the Las Vegas-Henderson area of Nevada, the case history data




provides a comprehensive picture of a long-term, multi-source




contamination problem.  Much of the contamination in the ground water




is derived by seepage from industrial waste impoundments and, to some




extent, from municipal waste impoundments.  The waste generating




facilities include a major industrial complex housing several




companies engaged chiefly in metal refining and the manufacture of




chemical products.  The other waste generating facilities in the area




include four sewage treatment plants.  The companies at the industrial




complex began operation in 1946 after the U.S. Army ceased using the




area for disposal of wastes from the manufacture of magnesium




products.  In 1971, a plume of nitrate-rich ground water in the near-




surface aquifer extended downgradient to a distance of 3 to 4 miles.
                                 51

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     In yet another example, between 1953 and 1959 a pulp and paper




mill at Brokaw, Wisconsin, discharged sulfite waste liquors into a




six-acre percolation pond on an island in the Wisconsin River.




Migration in the aquifer was reported by the company to be 3,300 feet




downgradient in 11 years (equivalent to 0.8 feet per day).  The




contaminant plume, which was composed of spent liquor of high




specific gravity, migrated beneath the Wisconsin River to contaminate




supply wells southeast of the percolation ponds.  Barrier wells were




constructed in the mid to late 1960's to prevent further migration



of the plume and to remove the spent liquors from the aquifer.




     A case history from Long Island, New York,  describes the growth




of a contaminant plume since the early 1940's.  In 1942, plating




wastes from an aircraft manufacturing plant in South Farmlngdale




were observed in the water table aquifer.  By 1948, a domestic well




1,500 feet from the disposal basin was found to be contaminated (a




migration rate of 0.7 feet per day).   In 1962 the plume was about




4,200 feet long, with an average width of 750 feet.  In this latter




phase the longitudinal migration rate had diminished somewhat to



0.53 feet per day.




     Migration rates for contaminant plumes range between 0.5 and




1.0 foot per day for these latter four case histories reported by




Geraghty and Miller.  Further,  the case histories show a range of




plume lengths from a few hundred feet to beyond three miles.  Also,
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based on these limited data, it appears that the age of the disposal




facility may be related to the length of the plume.




6.3  Flow Velocity and Migration Distance




     Over the course of several NPL notice and comment rulemaking



cycles, several commenters have stated that hydraulic gradient data




could be used to determine ground water migration velocities which,




in turn, could be used to calculate expected migration distances at




specific sites.  In this section the governing equations are defined




and the data needs are identified.




     6.3.1  Darcy's Law




     As described in Section 2.4, Henry Darcy developed, from




empirical data, an expression for the factors controlling ground




water movement.  He found that the total flow is proportional to the




cross-sectional area perpendicular to the direction of flow,




multiplied by the hydraulic gradient in the aquifer, and by the




hydraulic conductivity of the aquifer.  Algebraically Darcy's law is




written as:



                          Q = KA (dh/dl)




     where:




                          Q = total flow




                          K = hydraulic conductivity




                          A = cross-sectional area




                      dh/dl = hydraulic gradient
                                 53

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Similarly, as shown in Heath (1983), the velocity equation of




classical hydraulics states that the total flow (Q) is a product of




cross-sectional area and velocity (V).  Written algebraically:



                               Q - AV



The two equations can be combined to yield an expression known as




the Darcy (or discharge) velocity in an aquifer:



                            V - K  (dh/dl)




     Fetter (1980) notes that the discharge velocity "is an apparent




velocity, representing the velocity at which water would move through



an aquifer if the aquifer were an open conduit."  To determine the




actual velocity of ground water through a porous medium, the




hydraulic conductivity is divided by a dimenslonless porosity term




(n) to account for the actual open space available for flow.  The




equation for velocity becomes:




                           V - K/n (dh/dl)




Multiplying the velocity by an appropriate time factor yields the



migration distance:




                               D - Vt




     6.3.2  Data Requirements




     As shown above, the velocity equation is dependent on three




field parameters:  the hydraulic conductivity, the hydraulic




gradient, and the porosity.  The data requirements, constraints, and




costs for both hydraulic gradient and hydraulic conductivity have
                                 54

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been described in Sections 4.3 and 4.4, respectively.  The porosity




parameter presents a special problem in determining flow velocity.




     Traditionally, porosity is defined as the ratio of the volume




of openings in a rock to the total volume of the rock.  In evaluating




the flow of ground water through porous media, it is necessary to




account for surface adhesion which will fill some of the available




pore space.  The net result, then, is that the effective porosity




for flow (n ) is somewhat less than the total porosity.  Rigorous




solutions to the flow equation would require that the effective



porosity be used to calculate ground water flow velocities.  As




stated in the Practical Guide to Ground Water Sampling (U.S.




Environmental Protection Agency, 1985a), methods are still being




developed by which effective porosity can be measured.  In order to




solve the Darcian flow equation, it is necessary to use surrogate




values for the effective porosity of the geologic material being




investigated.




     6.3.3  Findings




     The parameters needed to evaluate ground water migration




velocity and distance include hydraulic conductivity, hydraulic




gradient, and effective porosity.  The uncertainities associated




with field measurement of these parameters have been previously




discussed and include non-unique interpretations of analytical




results, reporting errors, extensive data collection requirements




(some with associated long time requirements) and the inability  (as
                                 55

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yet) to measure effective porosity in the field.  The costs




associated with the field determination of some of these parameters




are described in detail in Appendix D and have been summarized in




Chapter 4.




     The costs and uncertainties which surround the parameters




needed to evaluate migration velocity and distance suggest that, if




the HRS continues to serve as a screening tool, it is not feasible




to require a distance/velocity analysis at each site.  Also, the




hydrologic literature (e.g., Princeton Associates, 1985) generally



cites a velocity range of 5 feet per day to 5 feet per year as being




typical of ground water flow.  These values imply that on an annual




basis, ground water can migrate as little as 5 feet or as much as




1,800 feet.  Consequently, for hazardous wastes sites, which may




have a history of disposal that spans several decades, it is not




surprising that some migration distances are found to approach or go



beyond three miles.




6.4  Conclusions




     Plume geometries and case histories have been used to study




the three-mile radius issue.  Complete data sets describing the




hydrogeologic conditions at each site reviewed are not available.




Therefore, analytical studies have not been performed to verify the




plume geometries and to establish age and migration rate



relationships.
                                 56

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     The empirical data from the plume survey and the case histories,




and the generally accepted rate of ground water migration, indicate




that, in general, ground water contamination plumes are less than




four miles in length.  Of the fifty-seven plumes examined, 93 percent




(53 of 57) are less than three miles in length, 86 percent (49 of 57)




are less than two miles in length, and 82 percent (47 of 57) are



less than one mile in length.




     In selecting a distance to define a zone of influence around a




hazardous waste site, the Agency needs to consider to what extent an




overestimate (or underestimate) of the potentially exposed targets




is undesirable.  For example, using the data on fifty-seven plumes,




a decision to use a four-mile radius will rarely underestimate the




potential targets, but will overestimate (compared to, for example,




a three-mile radius) in up to 93 percent of the cases examined.




Likewise, a three-mile radius overestimates in up to 86 percent of




the cases and underestimates in about 7 percent of the cases.




Similarly, a two-mile radius overestimates the potentially exposed




targets in up to 82 percent of the cases and underestimates in




14 percent of the cases.  Additionally, the available data indicate




that the current HRS practice for measuring the three-mile radius




(i.e., starting the measurement from the furthest point of known




contamination attributable to a site rather than from the source of




the contamination) is likely to add to overestimates of the potential




targets at many sites.  In practical terms, an overestimate of the
                                 57

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potentially exposed targets may result in a site being included on




the NPL whereas an underestimate may result in a site not being




listed.  Thus, the decision as to what distance is appropriate for



inclusion in the HRS needs to take into consideration the objectives



of the Agency in preparing the NPL.  It is recommended that whatever




distance is selected, the current HRS practice for dealing with




aquifer discontinuities be retained (i.e., not counting populations




within the target distance limit that are beyond an aquifer




discontinuity).
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7.0  OTHER RELATED ISSUES




     This study originated, in large part, in response to issues and




concerns raised by the public during review and comment cycles of




NPL and NCP rulemaking.  In the course of conducting this study,




additional issues have been identified which are worthy of some



consideration.  These include the influence of topography on ground




water flow regimes, the movement of ground water in karst terranes,




and the future use of ground water supplies.




7.1  Topography




     The authors already cited in this report (e.g., Freeze and




Cherry, Fetter, and Heath) generally agree that in unconfined




aquifers the water table is a subdued expression of the surface




topography.  In confined aquifers stratigraphic, structural, and



hydraulic controls are the dominant influence.   Beyond the general




statement about topography, no relationship is established that




defines the effect of topography on the direction of ground water




flow.  The overriding principle is that ground water will flow from




an area of high potential head to an area of low potential.




     The explanation for this uncertainty about the influence of




topography on the direction of ground water flow is related to the




primary purpose of the study of hydrogeology.  For the most part




that purpose has been to explore and evaluate ground water resources




with an aim towards developing sources of water supplies.  As an
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analogy, in the petroleum or gas industries, traditional exploration




schemes begin with research and reconnaissance.  This is followed by




exploratory drilling which in turn leads to test drilling.  If test




drilling proves successful and there appears to be sufficient yield



from the oil or gas reservoir, development proceeds.   Development




continues by step-out drilling (new wells located no more than one




mile from successful development wells) until yields decrease to




uneconomic levels.



     So it is with ground water resource development.  General




knowledge of an area may be assembled from reconnaissance and



preliminary research studies.  However, the specific conditions



which define the hydrogeologic regime in a particular area cannot be




described until exploratory wells are drilled and field data are




collected and analyzed.




     Because the primary purpose of the study of hydrogeology has




been to develop water supplies, there has been a heavy emphasis on




the use of field data.  This reliance on empirical information has



obviated the need for lengthy explanations or theoretical




discussions of the relationship between topography and the direction




of ground water flow.  For this reason, no scales or mechanisms have



been developed specifically to define the relationship between




topography and ground water flow.  As a result, then, it appears




that there is presently no quantitative way to incorporate




topography into the MRS.






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7.2  Karst Terranes




     Karst terranes have also been included as part of this study.




The following discussion defines karst terranes and explains why




generic HRS rating factors cannot be developed for facilities located




in these areas.




     Karst terranes (named for the Karst Region of Yugoslavia) are




characterized by a landscape which exhibits irregularities in surface




form caused by rock dissolution.  This landscape usually occurs in




limestone (a rock composed of calcium carbonate) although it may also




form in dolomite (a rock in which some of the calcium in the limestone




has been replaced by magnesium), or in areas of gypsum (calcium




sulfate) or rock salt  (sodium chloride).  Dissolution may occur along




joints, bedding planes or other openings.  If the limestone beds are




horizontal or dip at a low angle, the land surface develops sinkholes




and solution valleys.  In addition, large networks of interconnected




caves may form.  Freeze and Cherry (1979) state that "in major karst




regions thousands of kilometers of caves exist . . . ."  According to




Quinlan and Ewers (1986), about 20 percent of the United States is




underlain by carbonate rock.  At least half of this rock is "maturely




karsted" (i.e., it contains a well developed, integrated conduit




system).  Examples which indicate the wide geographic distribution of




these features include Luray Caverns in Virginia, Howe Caverns in New




York, Mammoth Caves in Kentucky, Carlsbad Caverns in New Mexico, Wind




Cave in South Dakota, Wyandotte Cave in Indiana, and Manama Caverns




in Florida.



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     In the  context  of  evaluating  hazardous waste sites located in

karst terranes, Quinlan and Ewers  (1986) point out that pollutant and

ground water flow in most karst aquifers is not described by the

dispersive Darcian flow characteristics of granular aquifers.

Restricting their comments to "maturely karsted carbonate rocks," they

state that most pollutant and ground water flow is analogous to flow

in surface stream networks.  Flow  is turbulent; it occurs in conduits;

it commonly has velocities of 30 to 1,500 feet per hour; and it

terminates in springs.

     From the site inspection perspective, however,  karst terranes

present special problems.  Quinlan and Ewers state that "the

probability of a single well Intercepting a conduit near a typical

site, where the approximate flow direction is known, is about 1 in

2,600."  These authors  suggest a strategy for establishing a

monitoring network at hazardous waste sites located in karst terranes.

This strategy can be adapted to serve site inspection purposes and

includes the following  steps:

     •  Locate all springs, streams in sinkhole bottoms, and major
        streams in caves.

     •  Establish connections between the site, springs, and
        underground streams using  dye-tracing techniques.

     •  Sample the connected points.

     •  Determine the background values by sampling one geochemically
        similar spring  which was shown by dye-tracing not to be
        connected to the site.
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     As Indicated In the steps outlined above, dye-tracing techniques



play an important role in the investigation of a ground water basin




in karst terrane.  Quinlan and Ewers suggest that dye-tracing would




have to be carried out under both base flow and flood conditions.




This, they explain, is because during flood flow, cave streams may




occupy alternate high-level routes which lead to springs other than




those delineated during base flow conditions.  In some situations it




may also be desirable to use dye-tracing to determine the boundaries




of the ground water basin.



     Quinlan and Ewers also address the issues of off-site




investigations and sampling frequency.  Because the network of




conduits in a karst terrane may be very large, they suggest that the




area that must be evaluated for any particular site might extend to




a radius of five miles or more.  And, because the flow velocity can




range between 30 and 1,500 feet per hour, they point out that




quarterly sampling may completely miss discharge events.  At the




other extreme, continuous monitoring may be wholly impractical.




Quinlan and Ewers candidly admit that the issue of determining the




proper sampling frequency in karst terrane is still an open question.




     In practice, then, a site monitoring strategy described by




Quinlan and Ewers (and modified for site inspection) would be very




site-specific and time consuming.  Although they do not specifically




address cost considerations, they imply that because of the time




involved (generally an annual cycle) and the number of samples
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required, an adequate site inspection is quite costly.  Because the




hydrogeologic settings of karst terrenes are highly variable and




because sites can only be characterized by site-specific studies, it




does not appear feasible to develop a meaningful, generic HRS




scoring factor applicable to sites located in these areas.




     With regard to selecting a distance to use in estimating the




potential targets that may be affected by the migration of



contaminants in karst terranes, it is necessary to consider the




extent to which inherent overestimates or underestimates of potential




targets is undesirable.  For example, Qulnlan and Ewers state that a




radius of investigation may extend to five miles or more.  A decision




to extend the HRS ground water radius needs to consider not only the




fact that contaminants may migrate greater distances in karst



terrane, but also that this migration is more localized.  Therefore,




an expansion of the radius would tend to greatly overestimate the




potential targets, except in the situation where the bulk of the




potential targets are centrally located (e.g., a municipal well)




and are drawing from a solution channel containing water with




contaminants from the site.  Also, potential targets may not be




overestimated in those areas where solution channels are generally



well connected (e.g., portions of Florida).




7.3  Future Use of Ground Water Supplies




     Another related issue is the feasibility of assessing the




future use of potentially affected aquifers.  As discussed in
                                 64

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Driscoll (1986), Fetter (1980), and Freeze and Cherry (1979), among




others, both geologic and socio-economic factors need to be



considered when discussing the projected use of ground water.  Fetter




(1980) has synthesized from several sources a definition for the




"safe yield" of an aquifer that incorporates both the geologic and




socio-economic concerns which need to be considered in evaluating an




aquifer:  the "safe yield is the amount of naturally occurring ground




water that can be withdrawn from an aquifer on a sustained basis,




economically and legally, without impairing the native ground water



quality or creating an undesirable effect such as environmental




damage."




     The principal geologic factor which needs to be determined is




the volume of water in the aquifer.  This can be calculated by




multiplying the thickness and areal extent of the aquifer by its




specific yield.  The specific yield is the ratio of the volume of




water that drains from a rock (under the influence of gravity) to the




total volume of the rock.  This ratio is expressed as a percentage




and ranges from an average value of 2 percent for clay to 27 percent




for coarse sand (Fetter, 1980).




     The data requirements and constraints associated with the




determination of thickness and areal extent of an aquifer have




already been described in Sections 3.2 and 5.2.  Specific yield may




be determined by both laboratory and field methods.
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     In the laboratory, a sediment column is flooded from the bottom




driving out all the air.  This creates a known volume of fully




saturated sediment.  Water is then drained from the column in such a




manner so as to avoid evaporation losses.  The drainage period




required for the column to reach equilibrium can be as long as




several months.  The ratio of the volume of water drained to the




volume of the soil column is the specific yield.  To express the




specific yield as a percentage the ratio is multiplied by 100.




     The specific yield of sediments and rocks can also be determined




in the field from pumping tests.  Water wells are pumped and the




rate at which water level falls in nearby wells is measured.  A more




detailed discussion of pumping tests and their data requirements and




constraints appears in Section 4.4.2.




     To estimate the volume of water available from an aquifer would




thus require a significant commitment of time and resources.  A




field program of hydraulic conductivity testing would be required.




The costs associated with hydraulic conductivity testing and, if




necessary, drilling are described in Sections 4.3.2 and 4.4.2.




Also, as previously discussed, there are significant uncertainties




associated with the determination of the key parameters needed to




estimate the volume of water available from an aquifer.




     Furthermore, from the socio-economic perspective, several




additional issues have been discussed in the literature already




cited.   Aside from geologic concerns, Fetter's definition of safe
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yield refers to legal, as well as economic, constraints.  One major




concern is the variation in State water laws.  Each State has its




own body of water law which encompasses both ownership and




appropriation of water.  Although generally concerned with surface




water, many States consider ground water to be the source of some




part of their surface water resources.  Rules governing ownership of




water rights and appropriation of the resource are very complex and




State specific.  These differences make it very difficult to




consistently estimate national trends or even local trends in the




future use of ground water resources.




     Similarly, other socio-economic factors which affect projections




of ground water use cannot be consistently estimated on a national




basis.  Two such socio-economic factors are regional economic growth




(or contraction) and population increases (or decreases).
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8.0  SUMMARY AND CONCLUSIONS




     This study has examined the feasibility of developing additional




scoring factors for the HRS related to the geohydrology of hazardous




wastes sites.  Of particular interest was the direction and velocity




of ground water movement.  Associated with this issue was the use of




a three-mile radius circle to delineate the area of concern around a




hazardous waste site.  Another major issue that was investigated for




this study was the criteria for determining the interconnection of




aquifers.  During the course of this research, some related issues




were identified and investigated.  The principal findings of these




collected studies are summarized in the following sections.




8.1  Direction and Velocity of Ground Water Migration




     In fractured or cavernous aquifers (typified by aquifers in




karst, as discussed in Section 7.2), the direction and velocity of




ground water flow is largely unpredictable.  In granular aquifers,




however, laminar flow predominates.  The direction of ground water




flow, the migration distance, and the flow velocity are all related




through Darcy's Law and the basic flow equation of hydraulics.  These




are empirical relationships and, because of this, they rely on




actual field data.  The required data elements include hydraulic




conductivity, effective porosity, and the hydraulic gradient as




determined from measuring both the total hydraulic head in




observation/monitoring wells and the distance between the wells.
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     Regarding the field data, there are considerable uncertainties




attached to determining values of hydraulic conductivity in the field.




Laboratory determinations of hydraulic conductivity yield results  that




are not equivalent to field values.  Similarly, the effective porosity




for flow has been recognized as being significantly different (i.e.,




10 to 20 percent less) from the bulk porosity of an aquifer.  This is




an active research area and, for the moment, surrogate values are being




used to solve flow equations.  Although relatively straight-forward, the




determination of hydraulic gradient in the area around a hazardous waste




site requires a large amount of data.  Well locations, elevations, and



head measurements must all be accurately determined.  Temporal factors




such as base flow and flood flow must also be considered.




     As described in Sections 4.3 and 4.4, the level of effort and the




associated costs needed to collect the field data are very high




compared to those of current site inspections.  The use of these data,




furthermore, would not necessarily always translate into more accurate




knowledge about conditions at the site.  Use of the data would introduce




different types of uncertainties into the HRS process than those that




are currently present as a result of the direction of flow not being




considered.  The primary concern would be in underestimating the target



area potentially threatened by the site.




8.2  Aquifer Interconnection




     To evaluate the connection (or lack of connection) between two or




more water bearing units, information is needed on the areal extent of
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confining layers beneath a site.  In addition to the hydrogeologic




characterization of the site, the primary data element on which to




base a decision would be the hydraulic conductivity of adjacent rock




units.  Other site specific conditions, such as poorly cased or




abandoned wells and channels left by decayed root material, could




also have a local influence on aquifer interconnection.  As described




in Section 4.4, field determinations of hydraulic conductivity are




generally unreliable and costly.  Developing a rating factor which




would require these field data is not recommended, assuming the HRS




remains a screening tool intended to use only limited data.




8.3  The Three-Mile Radius




     A three-mile radius, measured from the furthest point of known




contamination attributable to a site, is currently used in the HRS




to evaluate ground water targets.  Data from case histories and a




plume survey have been used to examine the likely areal extent of




ground water plumes.  This data, along with data on generally




accepted ground water migration velocities, indicate that plumes




are typically less than four miles in length.  The data further




indicate that the use of target distances less than four miles will




overestimate potential targets at some sites and underestimate




potential targets at other sites.  The greater the target distance




used, the greater the potential for overestimating target




populations.  On the other hand, the lesser the target distance used,




the greater the potential for underestimating target populations.
                                 71

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Therefore, the objectives of the Agency, with regard  to  the  NPL,

need to be considered in reaching a decision as to the appropriate

distance to be used in identifying a zone of influence around  a

hazardous waste site.

8.4  Related Issues;  Topography, Karst Terranes, and the Future  Use
     of Ground Water Supplies

     Three related issues that have been identified in the course of

this study have also been examined.  The influence of topography  on

ground water movement is not rigorously described in the ground water

literature.  Because of this, no quantitative way of Incorporating

topographic influences into the HRS can be developed.

     In karst terranes (e.g., cavernous limestone), ground water  flow

is wholly unpredictable and site-specific.  Consequently, it Is not

feasible to develop a meaningful, generic, rating factor applicable

to such areas.

     Future use of ground water supplies depends upon both geologic

and socio-economic factors.   The principal geologic factor Is the

volume of water in the aquifer.  As previously discussed, estimation

of the volume of water available is costly and time consuming

compared to the time and cost of current site inspections.  There

are also significant uncertainties associated with the determination

of the key parameters needed to make the estimate.  Furthermore,

water supplies, water laws and other socio-economic factors which

affect the future use of ground water supplies exhibit a high degree
                                 72

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of local variability.  Consequently, it is not possible to




consistently predict changes related to these factors on a national




basis.
                                 73

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9.0  BIBLIOGRAPHY

American Geological Institute, Dictionary of Geological Terms,
Anchor Press, Garden City, 1976.

Bouwer, H., Groundwater Hydrology, McGraw-Hill, New York, 1978.

Cleary, R.W., Personal Communication, Princeton Associates, July
1985.

Davis, S.N., "Porosity and Permeability of Natural Materials" in
Flow Through Porous Media, R.J.M. DeWeist (ed.), Academic Press,
pp. 54-89, New York, 1969.

Driscoll, F.G., Groundwater and Wells, 2nd ed., Johnson Division,
St. Paul, 1986.

Ecology and Environment, memorandum to the U.S. Environmental
Protection Agency, TDD No. HQ-8608-06, September 3, 1986.

Everett, L.G., Groundwater Monitoring, General Electric Co.,
Schenectady, NY, 1980.

Fetter, C.W., Applied Hydrogeology, Charles E. Merrill Co., Columbus,
OH, 1980.

Fetter, C.W., "Determining the Direction of Ground Water Flow", in
Ground Water Monitoring Review, Vol. 1, No. 3, 1981.

Fetter, C.W., "Potential Sources of Contamination in Ground Water
Monitoring", in Ground Water Monitoring Review, Vol. 3, No. 2, 1983.

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

Geraghty and Miller, Inc., letter report to the U.S. Environmental
Protection Agency Office of Ground Water Protection, November 1985,

Heath, R.C., Basic Ground Water Hydrology, USGS Water Supply Paper
2220, Reston, VA, 1983.

Keely, J.F., "Optimizing Pumping Strategies for Contaminant Studies
and Remedial Actions", in Ground Water Monitoring Review, Vol. 4,
No. 3, 1984.

Kimmel, G. and O.C. Braids, "Leachate Plumes in a Highly Permeable
Aquifer", Ground Water, Vol. 12, pp. 388-393, 1974.
                                 75

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NUS Corporation, letter report to the U.S. Environmental Protection
Agency, C582-9-6-18, September 3, 1966.

Office of Technology Assessment, Protecting the Nation's Groundwater
from Contamination. OTA-0-233, Washington, DC, 1984.

Princeton Associates, Groundwater Pollution and Hydrology, Course
Notes, July 1985.

Quinlan, R. and A. Ewers, "Ground Water Monitoring in Karst
Terranes", Guest editorial in Ground Water Monitoring Review,
Vol. 6, No. 1, 1986.

Saines, M., "Errors in Interpretation of Ground Water Level Data",
in Ground Water Monitoring Review, Vol. 1, No. 1, 1981.

Scalf, M.R. et al., Manual of Ground Water Quality Sampling
Procedures, National Water Well Association, Worthington, OH, 1981.

Thornhill, J.T., Personal Communication, U.S. Environmental
Protection Agency, Robert S. Kerr Environmental Laboratory, Ada, OK,
November 1985.

U.S. Code of Federal Regulations—40 CFR Part 300, The National Oil
and Hazardous Substances Contingency Plan; Appendix A;  Uncontrolled
Hazardous Waste Site Ranking System - A User's Manual, 47 FR 31219,
July 16, 1982.

U.S. Department of the Interior—Water and Power Resources Service,
Ground Water Manual, Washington, DC, 1981.

U.S. Environmental Protection Agency, National Surface Impoundment
Assessment Report, January 1984.

U.S. Environmental Protection Agency, Practical Guide for Ground
Water Sampling. EPA/600/2-85/104, 1985a.

U.S. Environmental Protection Agency, RCRA Ground Water Monitoring
Technical Enforcement Guidance Document - Draft, 1985b.

Walton, W.C., Groundwater Resource Evaluation, McGraw-Hill Book Co.,
New York, 1970.

Ward, C.H. et al. (ed.), Ground Water Quality. John Wiley & Sons,
Inc., New York, 1985.

Zuras,  A.D. et al., "The National Priorities List Process", in
conference proceedings, Management of Uncontrolled Hazardous Waste
Sites,  HMCRI, Silver Spring, MD, November 1985.

                                 76

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                             APPENDIX A

                     GLOSSARY OF SELECTED TERMS

            (Adapted from Fetter, 1980; Heath, 1983; and
              the American Geological Institute, 1976)
Anisotropy
Aquifer
Aquifer, Confined
Aquifer, Unconfined
Bedrock
Confining Bed
Datum Plane
Density
The condition under which one or more of the
hydraulic properties of an aquifer vary
according to the direction of flow.

Rock or sediment in a formation, group of
formations, or part of a formation which is
saturated and sufficiently permeable to
transmit usable quantities of water to wells
and springs.

An aquifer that is overlain by a confining bed.
The confining bed has a significantly lower
hydraulic conductivity than the aquifer.

An aquifer in which there are no confining beds
between the zone of saturation and the surface.
There will be a water table in an unconfined
aquifer.  Water-table aquifer is a synonym.

A general term for the consolidated (solid) rock
that underlies soils or other unconsolidated
surficial material.

A body of material that is stratigraphically
adjacent to one or more aquifers and that has a
low hydraulic conductivity relative to the
adjacent aquifers.  It may lie above or below
the aquifer.

An arbitrary surface (or plane) used in the
measurement of ground water heads.  The datum
most commonly used is the National Geodetic
Vertical Datum of 1929, which closely
approximates sea level.

The mass or quantity of a substance per unit
volume.  Units are kilograms per cubic meter or
grams per cubic centimeter.
                                 77

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Discharge Area
Discharge Velocity
Dynamic Viscosity

Effective Porosity
Equipotential Line
 Equipotential
 Surface
Fence Diagrams
Ground Water
Ground Water,
Confined
Ground Water Flow
An area in which there are upward components of
hydraulic head in the aquifer.  Ground water is
flowing toward the surface in a discharge area
and may escape as a spring, seep, or baseflow,
or by evaporation and transpiration.

An apparent velocity, calculated from Darcy's
law, which represents the flow rate at which
water would move through an aquifer if the
aquifer were an open conduit.  Also called
specific discharge.

See Viscosity.

The amount of interconnected pore space through
which fluids can pass, expressed as a percent
of bulk volume.  Part of the total porosity
will be occupied by static fluid being held to
the mineral surface by surface tension, so
effective porosity will be less than total
porosity.

A line in a two-dimensional ground water flow
field such that the total hydraulic head is the
same for all points along the line.

A surface in a three-dimensional ground water
flow field such that the total hydraulic head
is the same everywhere on the surface.

Three or more geologic cross-sections showing
the relationship of wells or outcrop sections
to formations.

The water contained in interconnected pores
located below the water table in an unconfined
aquifer or located in a confined aquifer.

The water contained in a confined aquifer.
Pore-water pressure is greater than atmospheric
at the top of the confined aquifer.

The movement of water through openings in
sediment and rock which occurs in the zone of
saturation.
                                 78

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Ground Water,
Perched
Ground Water,
Unconfined

Head, Total
Heterogeneous
Hydraulic
Conductivity
Hydraulic Gradient
Isopach
Isotropy
Kinematic Viscosity
Lithofacies Map
Lithology
The water in an isolated, saturated zone located
in the zone of aeration.  It is the result of
the presence of a layer of material of low
hydraulic conductivity, called a perching bed.
Perched ground water will have a perched water
table.

The water in an aquifer where there is a water
table.

The sum of the potential energy that can be
attributed to the elevation, pressure, and
velocity of the ground water at a given point
in an aquifer.

Pertaining to a substance having different
characteristics in different locations.  A
synonym is non-uniform.

A coefficient of proportionality describing the
rate at which water can move through a permeable
medium.  The density and kinematic viscosity of
the water must be considered in determining
hydraulic conductivity.  Also referred to as
permeability.

The change in total head with a change in
distance in a given direction.  The direction
is that which yields a maximum rate of decrease
in head.

A line on a map drawn through points of equal
thickness of a designated unit.

The condition in which hydraulic properties of
the aquifer are equal in all directions.

The ratio of dynamic viscosity to mass density.
It is obtained by dividing dynamic viscosity by
the fluid density.  Units of kinematic viscosity
are square meters per second.

A map showing the areal variation in overall
physical characteristics of a stratigraphic
unit.

The physical character of a rock (e.g., grain
size, color, mineral constituents).
                                 79

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Observation Well
Permeability

Piezometer
 Pore Space


 Porosity
 Potentiometric
 Surface
 Pumping  Test
 Recharge Area
Rock
A nonpumping well used to observe the elevation
of the water table or the potentiometric
surface.  An observation well is generally of
larger diameter than a piezometer and typically
is screened or slotted throughout the thickness
of the aquifer.

See Hydraulic Conductivity.

A nonpumping well, generally of small diameter,
which is used to measure the elevation of the
water table or potentiometric surface.  A
piezometer generally has a short well screen
through which water can enter.

The volume between mineral grains in a porous
medium.

The ratio of the volume of void spaces in a
rock or sediment to the total volume of the
rock or sediment.

A surface that represents the level to which
water will rise in tightly cased wells.  If the
head varies significantly with depth in the
aquifer, then there may be more than one
potentiometric surface.  The water table is a
particular potentiometric surface for an
unconfined aquifer.

A test made by pumping a well for a period of
time and observing the change in hydraulic head
in the aquifer.  A pumping test may be used to
determine the capacity of the well and the
hydraulic characteristics of the aquifer.  Also
called aquifer test.

An area in which there are downward components
of hydraulic head in the aquifer.  Infiltration
moves downward into the deeper parts of an
aquifer in a recharge area.

Any naturally formed, consolidated or
unconsolidated, material (but not soil)
consisting of two or more minerals.
                                 80

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Safe Yield
Saturated Zone
Seepage Velocity


Slug Test
Soil


Specific Retention



Specific Yield




Storage, Specific



Storativity
The amount of naturally occurring ground water
which can be economically and legally withdrawn
from an aquifer on a sustained basis without
impairing the native ground water quality or
creating an undesirable effect, such as
environmental damage.  It cannot exceed the
increase in recharge or leakage from adjacent
strata plus the reduction in discharge, which
is due to the decline in head caused by pumping.

The zone in which the voids in the rock or soil
are filled with water at a pressure greater than
atmospheric.  The water table is the top of the
saturated zone in an unconfined aquifer.

The actual rate of movement of fluid particles
through porous media.

An aquifer test made by either pouring a small
instantaneous charge of water into a well or by
withdrawing a slug of water from the well.  A
synonym for this test, when a slug of water is
removed from the well, is a bail-down test.

The layer of material at the land surface that
supports plant growth.

The ratio of the volume of water the rock or
sediment will retain against the pull of gravity
to the total volume of the rock or sediment.

The ratio of the volume of water a rock or soil
will yield by gravity drainage to the volume of
the rock or soil.  Gravity drainage may take
many months to occur.

The amount of water released from or taken into
storage per unit volume of a porous medium per
unit change in head.

The volume of water an aquifer releases from or
takes into storage per unit surface area of the
aquifer per unit change in head.  It is equal
to the product of specific storage and aquifer
thickness.  In an unconfined aquifer, the
storativity is equivalent to the specific yield.
Also called storage coefficient.
                                 81

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Stratification

Stratigraphic Unit



Transmissivity
Unsaturated Zone
The layered structure of sedimentary rocks.

A unit consisting of stratified, mainly
sedimentary rocks, grouped for description,
mapping, or correlation.

The rate at which water of a prevailing density
and viscosity is transmitted through a unit
width of an aquifer or confining bed under a
unit hydraulic gradient.  It is a function of
properties of the liquid, the porous media, and
the thickness of the porous media.

The zone between the land surface and the water
table.  It includes the root zone, intermediate
zone, and capillary fringe.  The pore spaces
contain water at less than atmospheric pressure,
as well as air and other gases.  Saturated
bodies, such as perched ground water, may exist
in the unsaturated zone.
Viscosity
Water Table
Well, Full
Penetrating
Well, Partially
Penetrating
Zone of Aeration
The property of a fluid describing its
resistance to flow.  Units of viscosity are
newton-seconds per meter squared or pascal-
seconds.  Viscosity is also known as dynamic
viscosity.

The surface in an unconfined aquifer or
confining bed at which the pore water pressure
is atmospheric.  It can be measured by
installing shallow wells extending a few feet
into the zone of saturation and then measuring
the water level in those wells.

A well drilled to the bottom of an aquifer,
constructed in such a way that it withdraws
water from the entire thickness of the aquifer.

A well constructed in such a way that it draws
water directly from a fractional part of the
total thickness of the aquifer.  The fractional
part may be located at the top or the bottom or
at any point in between in the aquifer.

See Unsaturated Zone.
                                 82

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                             APPENDIX B

           DETERMINING THE DIRECTION OF GROUND WATER FLOW


     This appendix illustrates how field data from three piezometers

can be analyzed to indicate the direction of ground water flow.

This problem is similar to a three-point problem in structural

geology wherein it is sometimes necessary to determine the attitude

of various strata at depth, given only stratigraphic logs.

     In order to determine the direction of ground water flow from

piezometer data, a uniform aquifer is assumed.  Beyond this

assumption, there are three basic data requirements.  The relative

geographic position of the wells must be known along with the

distance between the wells.  Also the total hydraulic head at each

well is required data.  For this illustrative example, the following

information is given:

     •  The total head at well 1 is 26.26 feet.

     •  Well 2 is 165 feet southwest of well 1.  The total head at
        well 2 is 26.20 feet.

     •  Well 3 is south-southeast of Well 1 and southeast of
        well 2.  The intervening distances are:

            1 to 3 - 215 feet
            2 to 3 - 150 feet

     •  The total head at well 3 is 26.07 feet.

Figure B-l is a schematic representation of the raw data.

     The following steps, and the accompanying Figure B-2, outline

the solution to this example problem:
                                 83

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                             Well 1
                         (Head, 26.26 ft.)
   Well 2
(Head, 26.20 ft.)
    25
50
                  100 feet
   Well 3
(Head, 26.07 ft.)
                     FIGURE B-1
        RAW DATA FOR EXAMPLE PROBLEM

-------
                                    26.26 ft.
(A) Well 2
W.L = 26.20 ft.
(B)  (26.26-26.20)  _  (26.26-26.07)
(E) 26.2-26.07
      133
                     215
          0.13 ft.
          133ft
                               Direction of
                               Ground Water
                               Movement
                                                 26.07 ft.
0.001
                        FIGURE B-2
           SOLUTION TO EXAMPLE PROBLEM
                              85

-------
A.  Identify the well with the intermediate value of total head
    (i.e., well 2).

B.  Locate, along the line connecting the wells with the highest
    and lowest heads, the point at which the head is the same
    as the intermediate value.  This is done by interpolation.

C.  Draw a straight line from the intermediate well to the point
    identified in the previous step.  This segment represents a
    water level contour of equal total head.

D.  A line perpendicular to the water level contour and through
    either the well with highest or lowest head parallels the
    direction of flow.

E.  The difference between the head of the well intersected by
    the line and that of the contour divided by the distance
    between them is the hydraulic gradient.
                           86

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                             APPENDIX C


            CORRELATION BETWEEN CONTAMINANT PLUME LENGTH
                       AND HYDRAULIC GRADIENT
     Analysis of the correlation between the length of the contaminant


plumes and their respective hydraulic gradients was performed on the


data from the contaminant plume survey.  The plume survey data are


shown in Table C-l.  As shown in Table C-2, gradient information was


not available for many of the contaminant plumes.  Table C-2 lists


the plumes for which both data points (i.e., the plume length and the


hydraulic gradient) are available.  The results of the correlation


analysis are shown at the bottom of the table.  The analysis


demonstrates that for the plumes identified in the survey there is


little correlation between length and gradient (i.e., the coefficient

                   2
of determination, r , is only about 18 percent).
                                 87

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              TABLE C-l




SURVEY OF CONTAMINANT  PLUME GEOMETRIES
Case
1
3
4
6
7
8
9
10
11
12
14
18
19
20
21
22
25
26
27
Length
(feet)
18,000
1,000
5,000
700
3,000
1,300
2,200
8,000
4,300
7,000
1,000
2,200
1,600
4,400
1,000
1,800
500
3,600
2,000
Width
(feet)
4,000
600
5,000
100
1,600
1,300
1,300
6,000
1,000
4,500
800
256
715
2,500
1,000
700
300
1,800
700
Depth Transmissivity
(feet) (gpd/ft)*
30 —
—
75 —
80 2,000-400,000
60-70 —
—
60 —
20 —
55-140 —
100 —
50 —
15 —
30 40,000
50 20,000
20 —
40 —
30 —
80 40,000
20
Gradient
(feet /mile)
14
—
—
—
6.6
29
10.5
—
—
1-19.6
—
63
21
42
—
—
370
—
•VHK
                 88

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TABLE C-l (Continued)
Case
28
29
30
31
32
33
34
37
38
39
40
41
43
46
47
48
50
51
52
53
Length
(feet)
1,000
800
1,600
10,600
5,000
9,800
2,000
450
400
1,000
3,000
3,000
1,000
—
700
4,000
2,500
1,400
450
400
Width
(feet)
400
500
1,200
2,000
1,000
3,600
1,500
120
150
250
1,000
600
1,000
—
700
2,000
700
900
200
240
Depth
(feet)
—
15
60
70
170
135
180
16
60
50
50
80
150
20
25
40

95

25
Transmissivity
(gpd/ft)*

24,000
—
140,000
340,000
110,000
—
—
—
—
—
—
3,000
40,000
—
—
160,000
200,000
2,000
—
Gradient
(feet /mile)
—
422
—
—
—
5.3
264
316.8
316.8
—
—
15.84
31.7
—
—
13.2
—
—
158
—
         89

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                        TABLE C-l (Concluded)
Case
54
55
56
57
58
60
62
65
66
67
68
Length
(feet)
1,100
5,000
1,600
1,000
600
350
2,000
400
1,500
6,000
700
Width
(feet)
800
2,300
800
700
200
100
450
200
400
2,500
400
Depth
(feet)
70
165
120
26
110
40
100
50
30
50
90
Transml ss 1 vity
(gpd/ft)*
46,000
71,000
—
—
—
—
—
66, 000
—
—
270,000
Gradient
(feet /mile)
—
—
—
158
—
—
—
—
—
—
—
*gpd/ft = Gallons per day per foot.




Source:  Geraghty and Miller, 1985.
                                 90

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                       TABLE C-2

DATA USED FOR CORRELATION ANALYSIS BETWEEN PLUME LENGTH
        AND HYDRAULIC GRADIENT (from Table C-l)
Case
1
7
8
9
18
19
20
25
29
33
34
37
38
41
43
48
52
57
Results of

Length (feet)
18, 000
3,000
1,300
2,200
2,200
1,600
4,400
500
800
9,800
2,000
450
400
3,000
1,000
4,000
450
1,000
the Correlation Analysis:
Length
Mean Value 3116.67
Standard Deviation 4338.2
Gradient (feet /mile)
14
6.6
29
10.5
63
21
42
370
422
5.3
264
316.8
316.8
15.84
31.7
13.2
158
158

Gradient
125.43
145. 72
     Correlation Coefficient (r)  = -0.429
                           91

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                             APPENDIX D

                ESTIMATED COST AND TIME REQUIREMENTS
                     FOR GEOTECHNICAL FIELD WORK
     This appendix provides estimates of the current cost and time

requirements associated with a hydrogeologic investigation of a

hazardous substance release site.  In particular the estimates are

for the costs associated with addressing the principal issues cited

in this report (i.e., the direction of ground water flow, aquifer

interconnection, and the three-mile radius).  The data presented in

this appendix are 1986 estimates developed by the EPA Field

Investigation Teams (FIT) as follows:  NUS Corporation (estimates

for FIT-Zone I, EPA Regions I-IV) and Ecology and Environment

(estimates for FIT-Zone II, EPA Regions V-X).

     Tables D-l and D-2 present cost and time estimates for well

drilling and for the collection and analysis of water level data.

Table D-l shows the estimated range of cost and time requirements

for the two FIT Zones.  The table also indicates representative cost

and time requirements; the representative values are based upon the

data provided for the individual EPA Regions within the two FIT

Zones.  Table D-2 provides representative cost and time estimates

for a field program consisting of the installation of ten wells and

the collection and analysis of water level data from those wells.
                                 93

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                  TABLE D-l

COST AND TIME ESTIMATES FOR WELL DRILLING AND
COLLECTION AND ANALYSIS OF WATER LEVEL DATAa
Cost Factors
(dollars)
Mobilization0
Drilling cost (per
single 4" well)
20 Foot Depth
100 Foot Depth
200 Foot Depth
Data Collection and
Analysis (assumes
10 well drilling
program)^
20 Foot Depth
100 Foot Depth
200 Foot Depth
FIT
Zone Ib
1,500-20,000


850-3,000
1,500-30,000
2,500-60,000




3,500-4,000
3,500-9,000
2,500-15,000
Time Requirement for
A Ten Well Drilling FIT
Program (weeks)
Drilling
20 Foot Depth
100 Foot Depth
200 Foot Depth
Data Collection and
20 Foot Depth
100 Foot Depth
200 Foot Depth
Total Representative
20 Foot Depth
100 Foot Depth
200 Foot Depth
Zone Ib

2-5
2-12
4-16
Analysis^
2-3
7
11
Timee»f
-
-
-
FIT
Zone IIb
1,000-6,000


400-1,300
2,000-4,000
4,000-7,000




1,600-2,400
2,400-3,200
3,200-4,000
Representative
Cost
6,000


1,200
4,000
8,000




3,000
4,500
6,000
FIT Representative
Zone IIb

2-3
6-10
4-16

1
1
1-2

-
-
-
Time

3
8
12

2
4
6

4
10
16
                     94

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                        TABLE D-l (Concluded)


aCost estimates do not include costs associated with site security
 or disposal of drill spoils, or increased costs associated with
 working in a potentially hazardous environment.
"The indicated range represents the range of estimates provided
 for each EPA Region within the FIT Zone.
cMobilization costs include contract administration, rig
 outfitting, and initial transportation to site.
dIncludes water level measurements, well description, and water
 level contour mapping.
^Assumes some data analysis occurs concurrently with the latter
 phase of drilling.
^Additional time would be required for mobilization.  Mobilization
 time includes time for such activities as contract bidding, contract
 negotiation, rig outfitting, and transportation to the site.

Source:  U.S. Environmental  Protection Agency Field Investigation
         Teams (FIT), Zones I and II, 1986, unpublished data.
                                  95

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                              TABLE D-2

             REPRESENTATIVE COST AND TIME ESTIMATES FOR
              A FIELD PROGRAM CONSISTING OF TEN WELLS3
Cost
(dollars)13
Mobilization0
Drilling
Data Collection
and Analysis^
Total Cost

Time (weeks)
Drilling
Data Collection
and Analysis"
Total Time6
20-Foot
Wells
6,000
12,000
3,000
21,000
20-Foot
Wells
3
2
4
100-Foot
Wells
6,000
40,000
4,500
50, 500
100 -Foot
Wells
8
4
6
100-Foot
Wells
6,000
80, 000
6,000
92,000
100-Foot
Wells
12
6
16
Representative estimates are based upon Table D-l.
bCost estimates do not include costs associated with site security
 or disposal of drill spoils, or increased costs associated with
 working in a potentially hazardous environment.
cMobillzation costs include contract administration, rig outfitting,
 and initial transportation to site.
dIncludes water level measurements, well descriptions, and water
 level contour mapping.
eAssumes some data analysis occurs concurrently with the latter phase
 of drilling.

Source:  U.S. Environmental Protection Agency Field Investigation Teams
         (FIT), Zones I and II, 1986, unpublished data.
                                 96

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     Table D-3 presents cost and time estimates for determining




hydraulic conductivities.  The data are for slug/bail tests,




pressurization tests, and pumping tests.  The assumptions behind the




estimates are indicated on the table.  If well installation is




necessary, the installation costs would be those shown in Tables D-l




and D-2.  However, wells previously installed for water level




measurements could also be used for determining hydraulic




conductivities, providing the wells are properly installed.  If such




existing wells were used, there would be no additional cost for well



installation.




     Geophysical surveying techniques may also be used to supplement




conductivity testing and well drilling.  These surveys are used




either to characterize the stratigraphy beneath a release site or to




locate the actual areas of waste deposition (e.g., buried drums may




be located by a magnetometer survey).  Because each site and each




site inspection may be different, it is not possible to generalize




the exact nature of the additional field work that could be conducted




at any given site.  For information purposes, however, representative




costs and time requirements of various geophysical field surveys are




presented in Table D-4.
                                 97

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                                TABLE D-3

     COST AND TIME ESTIMATES FOR DETERMINING HYDRAULIC CONDUCTIVITY
                                                                 Time
                                   Cost Factors3             Requirements3
                         	(dollars)	     (days)
                               FIT                FIT            FIT
Type of Field Test	Zone I	Zone II	Zone IIb

Slug/Bail Test              270-1,600d          300-1,500d       3-18d»e
  (single well)c

Pressurization Test         500-l,100d          530-2,200d       4-l8d»e
  (single well)c

Pumping Test If            10,000d»8          9,800-15,000d»8   10-15d
  (single aquifer)0      38,000-43,000h

Pumping Test II1.          12,700d>8         19,600-29,200d     20-25d
  (two aquifers)J        68,000-110,000h


aThe indicated range represents the range of estimates provided for
 each EPA Region within the FIT Zone, except where otherwise noted.
^Estimates not available for FIT Zone I.
cAssumes 90 feet of overburden above a 30-foot thick aquifer.
dEstimate does not include drilling costs and drilling time.
eTime in hours,  not days.
*Test is intended to determine hydraulic conductivity.
^Estimate for Zone I, Region I only.
hEstimate for Zone I, Region II only; includes drilling costs.
^Test is intended to determine hydraulic conductivities and degree of
 aquifer interconnection.
JAssumes two aquifers:  one is 30 feet thick and begins 90 feet below
 the ground surface; the other is 50 feet thick and begins 200 feet below
 the ground surface.

Source:   U.S.  Environmental Protection Agency Field Investigation Teams
         (FIT),  Zones I and II, 1986, unpublished data.
                                 98

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                              TABLE D-4

          COST AND TIME ESTIMATES FOR GEOPHYSICAL SURVEYS3
ELECTRICAL EARTH RESISTIVITY

  FIT Zone I

    Cost Factorsb:
      Cost Per 100 Linear Feet                           $    42
      Survey Line Spacing                                    300 feet
      Survey Line Length                           approx. 1,500 feet
      Total Survey Length                          approx. 7,500 feet
      Survey Cost (does not include labor costs)         $ 3,150
      Field Team Labor Cost                              $24,000
      Data Analysis                                      $ 1,120
      Total Estimated Cost                               $28,270

    Time Requirement:
      Daily Coverage                                         200 feet
      Time for 7,500 Foot Survey                       approx. 6 weeks
      Time for Data Analysis                                   1 week
      Total Time                                               7 weeks

  FIT Zone II

    Cost Factorsb:
      Cost Per 100 Linear Feet                           $   250
      Survey Line Spacing                                    100 feet
      Survey Line Length                                   1,500 feet
      Total Survey Length                                 22,500 feet
      Survey Cost                                        456,250
      Data Analysis                                $2,600-$5,200
      Total Estimated Cost                       approx. $60,000

    Time Requirement:
      Daily Coverage                                 1,000-2,000 feet
      Time for 22,500 Foot Survey                              3 weeks
        (use 1,500 feet/day) (15 days)
      Time for Data Analysis                                 2-3 weeks
      Total Estimated Time                                   5-6 weeks
                                  99

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                       TABLE D-4  (Continued)
ELECTROMAGNETIC TERRAIN CONDUCTIVITY

  FIT Zone I
    Subcontract Cost in 1983 for a 15,000                $27,000
      Foot Survey15

  FIT Zone II

    Cost Factors15:
      Cost Per 100 Linear Feet                           $10-$50
      Survey Line Spacing                                      25 feet
      Survey Line Length                                  90,000 feet
      Survey Cost (based on $30/100 feet)                $27,000
      Data Analysis                                      1 1,800
      Total Estimated Cost                               $28,800

    Time Requirement:
      Daily Coverage                                 2,000-5,000 feet
      Time for 90,000 Foot Survey                      approx. 4 weeks
        (based on 4,000 feet/day)
      Time for Data Analysis                                   1 week
      Total Estimated Time                                     5 weeks

SEISMIC SURVEY
  FIT Zone I

    Subcontract Cost (1983-1985) for a                   $20,700
      9,000 Foot Survey15

  FIT Zone II

    Cost Factors15:
      Cost Per 100 Linear Feet                         $200-$350
      Survey Line Length (assumed)                         9,000 feet
      Survey Cost                                $18,000-$31,500
      Data Analysis                                      $ 1,800
      Total Estimated Cost                       Jl9,800-$33,300

    Time Requirement:
      Daily Coverage                                     200-500 feet
      Time for 9,000 Foot Survey                       approx. 6 weeks
        (based on 350 feet/day)
      Time for Data Analysis                                   1 week
      Total Estimated Time                                     7 weeks
                                 100

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                        TABLE D-4 (Continued)
PROTON MAGNETOMETER SURVEY

  FIT Zone I

    Cost Factorsb:
      Cost Per 100 Linear Feet                           $    60
      Survey Line Spacing                                     10 feet
      Survey Line Length (assume 25 percent       approx. 60,000 feet
        of the site area needs this detailed
        survey)
      Survey Cost                                        $36,000
      Data Analysis                                      $ 4,200
      Total Estimated Cost                               $40,200

    Time Requirement:
      Daily Coverage                                 1,000-2,000 feet
      Time for 60,000 Foot Survey                      approx. 8 weeks
        (assume 1,500 feet/day)
      Time for Data Analysis                                   3 weeks
      Total Estimated Time                                    11 weeks

  FIT Zone II

    Cost Factors15:
      Cost Per 100 Linear Feet                           $20-fc30
      Survey Line Spacing                                     10 feet
      Survey Line Length (assume 25 percent       approx. 60,000 feet
        of the site area needs this detailed
        survey)
      Survey Cost (based on $25/100 feet)                $15,000
      Data Analysis                                      $ 1,800
      Total Estimated Cost                               $16,800

    Time Requirement:
      Daily Coverage                                 2,000-3,000 feet
      Time for 60,000 Foot Survey                      approx. 5 weeks
        (assume 2,500 feet/day)
      Time for Data Analysis                                   1 week
      Total Estimated Time                                     6 weeks
                                 101

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                        TABLE  D-4  (Concluded)
GROUND PENETRATING RADAR SURVEY

  FIT Zone I

    Cost Factorsb:
      Subcontract Cost for 1983 for a 5,000
        Foot Survey
      Data Analysis
      Total Estimated Cost

    Time Requirement:
      Daily Coverage
      Time for 5,000 Foot Survey
      Time for Data Analysis
      Total Estimated Time

  FIT Zone II

    Cost Factorsb:
      Cost Per 100 Linear Feet
      Survey Line Length (assume 5,000 foot
        survey)
      Survey Cost (assume $400/100 feet)
      Data Analysis
      Total Estimated Cost

    Time Requirement:
      Daily Coverage
      Time for 5,000 Foot Survey
        (assume 400 feet/day)
      Time for Data Analysis
      Total Estimated Time
                                                         $14,000

                                                         $   560
                                                         $14,560
                                                           5,000 feet
                                                               1 day
                                                               2 days
                                                               3 days
                                                       $200-$600
                                                           5,000 feet

                                                         $20,000
                                                         $ 2,800
                                                         $22,800
                                                         200-600 feet
                                                       approx. 3 weeks

                                                       approz. 2 weeks
                                                               5 weeks
aFor all these estimates,  a 50-acre survey is assumed, unless
 otherwise noted.
bSurvey costs include labor cost unless otherwise noted.

Source:  U.S. Environmental Protection Agency Field Investigation
         Teams (FIT), Zones I and II, 1986, unpublished data.
                                102

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