EPA/625/R-95/005

July, 1996

Pump-and-Treat Ground-Water Remediation

A Guide for Decision Makers and Practitioners

Prepared by

Eastern Research Group, Inc.

110 Hartwell Avenue

Lexington, MA

U.S. Environmental Protection Agency

Office of Research and Development

National Risk Management Research Laboratory

Center for Environmental Research Information

Cincinnati, Ohio
ii

Notice

The information in this document has been

funded wholly, or in part, by the U.S. Environmental

Protection Agency (EPA). This document has been

subjected to EPA’s peer and administrative review

and has been approved for publication as an EPA

document. Mention of trade names or commercial

products does not constitute endorsement or recommendation for use.

 In September, 1995 the Office of Research and Development completed a reorganization of its Laboratories and

Centers. The former Risk Reduction Engineering Laboratory located in Cincinnati, Ohio, the Robert S. Kerr

Research Laboratory located in Ada, Oklahoma, the Air and Energy Research Laboratory, located in Research

Triangle Park, North Carolina, and the Center for Environmental Research Information located in Cincinnati, Ohio,

were merged into the National Risk Management Research Laboratory. No physical relocations were involved. The

documents referenced in this guide were published prior to the reorganization: therefore former laboratory/center

names are shown as they were at the time of publication.
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Foreword

The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation's land,

air, and water resources. Under a mandate of national environmental laws, the Agency strives to formulate

and implement actions leading to a compatible balance between human activities and the ability of natural

systems to support and nurture life. To meet this mandate, EPA's research program is providing data and

technical support for solving environmental problems today and building a science knowledge base necessary to manage our ecological resources wisely, understand how pollutants affect our health, and prevent or

reduce environmental risks in the future.

The National Risk Management Research Laboratory is the Agency's center for investigation of

technological and management approaches for reducing risks from threats to human health and the environment. The focus of the Laboratory's research program is on methods for the prevention and control of

pollution to air, land, water and subsurface resources; protection of water quality in public water systems;

remediation of contaminated sites and ground water; and prevention and control of indoor air pollution. The

goal of this research effort is to catalyze development and implementation of innovative, cost-effective

environmental technologies; develop scientific and engineering information needed by EPA to support

regulatory and policy decisions; and provide technical support and information transfer to ensure effective

implementation of environmental regulations and strategies.

This publication has been produced as part of the Laboratory's strategic long-term research plan. It is

published and made available by EPA's Office of Research and Development to assist the user community

and to link researchers with their clients.

E. Timothy Oppelt, Director

National Risk Management Research Laboratory
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Contents

List of Figures ........................................................................................................................... v

List of Tables ............................................................................................................................ xi

Acronyms and Abbreviations .................................................................................................. xii

Acknowledgments.................................................................................................................. xiii

1. Introduction to Pump-and-Treat Remediation.................................................................... 1

2. Appropriate Use of Pump-and-Treat Technology .............................................................. 3

3. Smart Pump-and-Treat Techniques .................................................................................... 5

3.1. Contaminant Removal/Control ................................................................................. 5

3.2. Thorough Site Characterization ................................................................................ 5

3.3. Dynamic Management of the Well Extraction Field ................................................ 7

3.4. Realistic Cleanup Goals ......................................................................................... 10

4. Anticipating Tailing and Rebound Problems ................................................................... 19

4.1. Effects of Tailing and Rebound on Remediation Efforts ........................................ 19

4.2. Contributing Factors ............................................................................................... 19

4.2.1. Non-Aqueous Phase Liquids (NAPLs)...................................................... 19

4.2.2. Contaminant Desorption............................................................................ 20

4.2.3. Precipitate Dissolution............................................................................... 23

4.2.4. Matrix Diffusion ........................................................................................ 24

4.2.5. Ground-Water Velocity Variation .............................................................. 24

4.3. Assessing the Significance of Tailing and Rebound at a Site ................................. 26
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Contents (continued)

5. Effective Hydraulic Containment ..................................................................................... 28

5.1. Ground-Water Barriers and Flow Control .............................................................. 28

5.1.1. Horizontal and Vertical Capture Zones...................................................... 28

5.1.2. Pressure Ridge Systems............................................................................. 31

5.1.3. Physical Barriers........................................................................................ 31

5.2. Hydraulic Containment: Other Special Considerations.......................................... 32

5.2.1. Effects of Anisotropy ................................................................................. 32

5.2.2. Drawdown Limitations .............................................................................. 32

5.2.3. Stagnation Zones ....................................................................................... 33

6. Pump-and-Treat System Design and Operation ............................................................... 36

6.1. Capture Zone Analysis and Optimization Modeling .............................................. 36

6.2. Efficient Pumping Operations ................................................................................ 40

6.3. Treating Contaminated Ground Water .................................................................... 42

6.4. Monitoring Performance ........................................................................................ 43

6.4.1. Hydraulic Head Monitoring for Containment ........................................... 43

6.4.2. Ground-Water Quality Monitoring for Containment................................. 44

6.4.3. Aquifer Restoration Monitoring ................................................................ 48

6.5. Evaluating Restoration Success and Closure.......................................................... 50

7. Variations and Alternatives to Conventional Pump-and-Treat Methods .......................... 53

7.1. Alternative Methods for Fluid Delivery and Recovery .......................................... 53

7.2. Vadose Zone Source Control .................................................................................. 54

7.3. Physical and Chemical Enhancements ................................................................... 54

7.3.1. Physical Enhancements ............................................................................. 59

7.3.2. Chemical Enhancements ........................................................................... 59

7.4. Biological Enhancements ....................................................................................... 59

7.5. Alternatives to the Pump-and-Treat Approach ....................................................... 61

7.5.1. Intrinsic Bioremediation ............................................................................ 63

7.5.2. In Situ Reactive Barriers ............................................................................ 63
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8. References ........................................................................................................................ 66

9. EPA Publications Providing Further Information ............................................................ 70

List of Sidebars

1 Changing Expectations for the Pump-and-Treat Approach ............................... 2

2 Major Types of Hydrogeologic Settings .......................................................... 11

3 Computer Graphics as a Site Characterization Tool ........................................ 13

4 The Effect of NAPL Phases on Ground-Water Contamination ....................... 16

5 Computer Modeling of Well Patterns Versus Hydrogeologic Conditions........ 38

Contents (continued)
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Figures

1. Examples of hydraulic containment in a plan view and cross section using

pump-and-treat technology: (a) pump well, (b) drain, and (c) well within a

barrier wall system (after Cohen et al., 1994). ................................................................... 4

2. Contaminant plumes as a function of density and miscibility with ground water:

(a) light liquids (gasoline and methanol) create contaminant plumes that tend to

flow in the upper portions of an aquifer; (b) dense liquids (perchloroethylene

[PCE] and ethylene glycol) create a plume that contaminates the full thickness

of an aquifer (adapted from Gorelick et al., 1993). ............................................................ 6

3. This hollow-stem auger is fitted with a 5-foot sampling tube that collects a

continuous core as the auger advances, allowing detailed and accurate

observation of subsurface lithology. When drilling is completed, a monitoring

well also can be installed. ................................................................................................... 8

4. Hydraulic or vibratory direct-push rigs can be installed on vans, small trucks,

all-terrain vehicles, or trailers and allow collection of continuous soil cores and

depth-specific ground-water samples for detailed subsurface mapping if

contaminants are generally confined to depths of less than 15 meters.

(Photo courtesy of Geoprobe Systems.) ............................................................................. 9

5. Conceptual diagram of Dense Non-Aqueous Phase Liquid (DNAPL) Trichloroethylene (TCE) based on soil and ground-water sampling in a heterogeneous sand

and gravel aquifer. The extreme difficulty in cleaning up this site, which includes

five distinct forms of TCE (vapors and residual product in the vadose zone; pooled,

residual, and dissolved product in the ground water) led to modification of the

pump-and-treat system for hydraulic containment rather than restoration

(adapted from Clausen and Solomon, 1994). ................................................................... 10
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Figures (continued)

6. GEOS computer screen showing organic contaminant plume in relation

to subsurface stratigraphy. ................................................................................................ 12

7. EPA’s SITE3D software, under development at the Ada, Oklahoma,

laboratory, helps visualize in three dimensions a TCE contaminant plume at a

Superfund Site. Yellows and reds indicate zone with highest concentrations of

TCE in ground water. ....................................................................................................... 14

8. Dark NAPL (Soltrol) and water in a homogenous micromodel after (a) the

displacement of water by NAPL and then (b) the displacement of NAPL

by water, with NAPL at residual saturation (Wilson et al., 1990). ................................... 17

9. Photomicrographs of (a) a single blob occupying one pore body, and

(b) a doublet blob occupying two pore bodies and a pore throat

(Wilson et al., 1990). ........................................................................................................ 18

10. Concentration versus pumping duration or volume showing

tailing and rebound effects (Cohen et al., 1994). ............................................................. 20

11. Contaminants are mobilized when ground water that is undersaturated

with a contaminant comes in contact with a NAPL (a) or contaminant sorbed

on an organic carbon or mineral surface (b). High ground-water velocities

and short contact times will result in low contaminant concentrations, and

low velocities and long contact times will result in high contaminant

concentrations (c) (adapted from Gorelick et al., 1993)................................................... 21

12. Laboratory model of the transport of DNAPL contaminant through

an aquifer with varying permeability; note the concentration of

downward movement in fingers and the DNAPL pools above the lowpermeability zones (the horizontal discs).

(Source: U.S. EPA National Risk Management Research Laboratory.)........................... 22

13. Dissolved contaminant concentration in ground water pumped from a

recovery well versus time in a formation that contains a solid-phase

contaminant precipitate (Palmer and Fish, 1992). ............................................................ 23
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Figures (continued)

14. Changes in average relative trichloroethene (TCE) concentrations

in clay lenses of varying thickness as a function of time (NRC, 1994). .......................... 24

15. Tailing resulting from ground-water velocity variations: (a) horizontal

variations in the velocity of ground water moving toward a pumping well

(Keely, 1989) lead to (b) tailing as higher concentrations of ground water

in slower pathlines mix with lower concentrations in faster pathlines (Palmer

and Fish, 1992); (c) in a stratified sand and gravel aquifer, tailing occurs

at t1 when clean water from the upper gravel strata mixes with stillcontaminated ground water in the lower sand strata (Cohen et al., 1994). ...................... 25

16. Zone of residuals created in former cone of depression after cessation of

LNAPL recovery system (Gorelick et al., 1993). ............................................................. 27

17. Plan view of a mixed containment-restoration strategy. A pump-and-treat

system is used with barrier walls to contain the ground-water contamination

source areas (e.g., where NAPL or waste may be present) and then collect

and treat the dissolved contaminant plume (Cohen et al., 1994). .................................... 29

18. In an isotropic aquifer, ground-water flow lines (b) are perpendicular

to hydraulic head contours (a). Pumping causes drawdowns and a new

steady-state potentiometric surface within the well’s zone of influence

(c). Following the modified hydraulic gradients, ground water within

the shaded capture zone flows to the pumping well (d).

(Cohen et al., 1994, adapted from Gorelick et al., 1993). ................................................ 30

19. Cross section showing equipotential contours and the vertical capture zone

associated with ground-water withdrawal from a partially penetrating well

in isotropic media (Cohen et al., 1994). ........................................................................... 31

20. Effect of fracture anisotropy on the orientation of the zone of contribution

(capture zone) to a pumping well (Bradbury et al., 1991)................................................ 33
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Figures (continued)

21. Capture zone simulation of three pumping wells for an isotropic aquifer

(a) and anisotropy ratio of 10:1 (b) using the EPA Well Head Protection Area

(WHPA) code. .................................................................................................................. 34

22. Examples of stagnation zones (shaded where ground-water velocity is less than

4 L/T): (a) single pumping well and (b) four extraction wells with an injection

well in the center (Cohen et al., 1994). ............................................................................ 35

23. Major types of pumping/injection well patterns (Satkin and Bedient, 1988). ................. 39

24. Ground-water flow line in the vicinity of conceptual pumping centers at

Lawrence Livermore National Laboratory superimposed on an

isoconcentration contour map and showing areas of potential stagnation

(Cohen et al., 1994, after Hoffman, 1993). ...................................................................... 41

25. Effect of adaptive pumping on cleanup time at Lawrence Livermore

National Laboratory Superfund site (Cohen et al., 1994, after Hoffman, 1993).............. 42

26. The pulsed pumping concept (Cohen et al., 1994, after Keely, 1989). ............................ 43

27. Nested piezometer hydrograph for 1992 at the Chem-Dyne Superfund site

(Cohen et al., 1994, after Papadopulos & Associates, 1993). .......................................... 46

28. Ground-water flow between and beyond the extraction wells, resulting

even though hydraulic heads throughout the mapped aquifer are higher

than the pumping level (Cohen et al., 1994). ................................................................... 47

29. Example display of ground-water flow directions and hydraulic

gradients determined between three observation wells (Cohen et al., 1994). .................. 48

30. Influent and effluent VOC concentrations (mg/L) at the Chem-Dyne

treatment plant from 1987 to 1992

(Cohen et al., 1994, after Papadopulos & Associates, 1993). .......................................... 49

31. Cumulative mass of VOCs removed from the aquifer at the Chem-Dyne

site from 1987 to 1992 (Cohen et al., 1994, after Papadopulos & Associates, 1993). ..... 50
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Figures (continued)

32. Determining the success and/or timeliness of closure of a pump-and-treat

system (Cohen et al., 1994). ............................................................................................. 51

33. Stages of remediation in relation to example contaminant concentrations

in a well at a pump-and-treat site (U.S. EPA, 1992). ....................................................... 52

34. Some applications of horizontal wells: (a) intersecting flat-lying layers,

(b) intercepting plume elongated by regional gradient, (c) intersecting

vertical fractures, and (d) access beneath structures (U.S. EPA, 1994). .......................... 55

35. Two approaches using trenches or horizontal wells to intercept

contaminant plumes (U.S. EPA, 1994). ............................................................................ 58

36. Process diagram for air sparging with (a) vertical wells, and (b) horizontal wells

[after National Research Council (NRC), 1994]. ............................................................. 60

37. Schematic of chemical enhancement of a pump-and-treat system. Key areas of

concern are shown in boxes. In some cases, the reactive agent will be recovered

and reused (Palmer and Fish, 1992). ................................................................................ 61

38. Two types of aerobic in situ bioremediation systems: (a) injection well with sparger,

(b) infiltration gallery (Sims et al., 1992, after Thomas and Ward, 1989). ...................... 62

39. Alternative ground-water plume management options: (a) pump-and-treat system,

(b) intrinsic bioremediation, (c) in situ reaction curtain, (d) funnel-and-gate system

(adapted from Starr and Cherry, 1994). ............................................................................ 64

40. Funnel-and-gate configurations (Starr and Cherry, 1994). ............................................... 65
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Tables

1. Categories of Sites for Technical Infeasibility Determinations (NRC, 1994) .................. 15

2. Data Requirements for Pump-and-Treat Systems (Adapted from U.S. EPA, 1991) ........ 37

3. Applicability of Treatment Technologies to Contaminated

Ground Water (U.S. EPA, 1991) ...................................................................................... 45

4. Issues Affecting Application of Alternative Methods for Delivery or Recovery

(U.S. EPA, 1994) .............................................................................................................. 56
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 Acronyms and Abbreviations

ACL Alternate concentration limit

CZAEM Capture Zone Analytic Element Model

DNAPL Dense non-aqueous phase liquid

DOD/ETTC Department of Defense Environmental Technology Transfer Committee

EPA Environmental Protection Agency

GAEP Geographic Analytic Element Preprocessor

LNAPL Light non-aqueous phase liquid

LLNL Lawrence Livermore National Laboratory

MCL Maximum contaminant level

MCLG Maximum contaminant level goal

NAPL Non-aqueous phase liquid

NRC National Research Council

NTIS National Technical Information Service

ORD Office of Research and Development

OSWER Office of Solid Waste and Emergency Response

PCB Polychlorinated biphenyl

PCE Perchloroethylene

RCRA Resource Conservation and Recovery Act

SVE Soil vapor extraction

TCE Trichloroethylene

TI Technical impracticality

VOC Volatile organic compound

WHPA Well Head Protection Area
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Acknowledgments

This document was prepared under Contract No.

68-C3-0315, Work Assignment No. 1-33, by Eastern

Research Group, Inc. (ERG), and under the sponsorship of the U.S. Environmental Protection Agency.