U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5112

Prepared in cooperation with the

Directorate of Public Works,

Environmental Management Division

Aberdeen Proving Ground, Maryland

Design and Performance of an Enhanced 

Bioremediation Pilot Test in a Tidal Wetland

Seep, West Branch Canal Creek, Aberdeen

Proving Ground, Maryand
Cover. Photographs showing site preparation and sediment excavation for the installation of a reactive mat pilot test at seep area 

3-4W, West Branch Canal Creek, Aberdeen Proving Ground, Maryland. (Photographs by U.S. Geological Survey.)
Design and Performance of an Enhanced 

Bioremediation Pilot Test in a Tidal 

Wetland Seep, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland

By Emily H. Majcher2, Michelle M. Lorah1, Daniel J. Phelan1, and 

Angela L. McGinty3

1 U.S. Geological Survey, Baltimore, Maryland.

2

 Geosyntec Consultants, Inc., formerly of the U.S. Geological Survey.

3

 EA Engineering, Science, and Technology, Inc., formerly of the U.S. Geological Survey.

Prepared in cooperation with the

Directorate of Public Works,

Environmental Management Division

Aberdeen Proving Ground, Maryland

Scientific Investigations Report 2009–5112

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Majcher, E.H., Lorah, M.M., Phelan, D.J., and McGinty, A.L., 2009, Design and performance of an enhanced 

bioremediation pilot test in a tidal wetland seep, West Branch Canal Creek, Aberdeen Proving Ground, Maryland: 

U.S. Geological Survey Scientific Investigations Report 2009–5112, 70 p. plus appendixes.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................5

Description of Study Area ..................................................................................................................5

Background on Reactive Mat Technology Development...............................................................7

Basis in Existing Technologies ..................................................................................................8

Reactive Mat Laboratory Tests................................................................................................10

Design Methods and Data Analysis .........................................................................................................11

Optimizing Degradation ....................................................................................................................11

Maintaining Compatibility with the Wetland System....................................................................11

Geotechnical Investigations and Analysis ............................................................................11

Hydraulic Investigations and Analysis...................................................................................13

Geochemistry and Water Quality ............................................................................................13

Performance Methods and Data Analysis ..............................................................................................14

Groundwater Sampling......................................................................................................................14

Drive-Point Piezometers...........................................................................................................14

Continuous Multi-Channel Tubing Piezometers....................................................................14

Mini-Porewater Samplers........................................................................................................14

Multi-Level Diffusion Samplers ...............................................................................................19

Surface-Water Sampling...................................................................................................................20

Groundwater and Surface-Water Analysis....................................................................................20

Reactive Mat Matrix Sampling and Analysis.................................................................................21

Determination of Hydraulic and Geotechnical Compatibility ......................................................21

Design of a Reactive Mat for Enhanced Bioremediation......................................................................22

Degradation Efficiency ......................................................................................................................22

Consideration of Compatibility With the Wetland System...........................................................23

Bearing Capacity and Settlement ...........................................................................................23

Hydraulic Design........................................................................................................................27

Geochemistry and Water Quality ............................................................................................28

Reactive Mat Design Summary for Seep 3-4W ............................................................................29

Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation .........................................31

Pre-Installation Conditions................................................................................................................31

Assessment of Volatile Organic Compound Degradation............................................................33

Establishment of Conditions Favorable for Anaerobic Degradation.................................33

Volatile Organic Compound Distribution and Mass Removal.............................................43

Assessment of Compatibility with the Wetland System...............................................................47

Geotechnical Integrity ..............................................................................................................47

Hydraulics ...................................................................................................................................47

Effects on Surrounding Hydrologic Conditions............................................................47

In-Mat Flow........................................................................................................................52

Volatile Organic Compounds in Shallow Porewater as Tracers in Seep Areas ....54

Water Quality..............................................................................................................................58
iv

Summary and Conclusions.........................................................................................................................64

Acknowledgments.......................................................................................................................................66

References Cited..........................................................................................................................................66

Appendix 1A. Field Measurements, and Concentrations of Reduction-Oxidation (Redox)-

Sensitive Constituents and Nutrients from Groundwater Samples, 

Seep 3-4W Reactive Mat Pilot Test Area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, August 2004–January 2005 .............. available online

Appendix 1B. Field Measurements, and Reduction-Oxidation (Redox)-Sensitive 

Constituents from Groundwater Samples, Seep 3-4W Reactive Mat Pilot 

Test Area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, March–October 2005......................................................................... available online

Appendix 2A. Field Measurements and Concentrations of Inorganic Constituents 

from Groundwater and Surface-Water Samples, Seep 3-4W Reactive Mat 

Pilot Test Area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, August 2004–January 2005............................................................... available online

Appendix 2B. Field Measurements and Concentrations of Inorganic Constituents 

from Groundwater and Surface-Water Samples, Seep 3-4W Reactive Mat 

Pilot Test Area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, February–August 2005....................................................................... available online

Appendix 3A. Organic Constituents from Groundwater and Surface-Water 

Samples from Seep 3-4W Reactive Mat Pilot Test Area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, 

August 2004–January 2005 .................................................................................. available online

Appendix 3B. Organic Constituents from Groundwater and Surface-Water 

Samples from Seep 3-4W Reactive Mat Pilot Test Area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, 

February–September 2005................................................................................... available online

Appendix 4. Quality Assurance for Volatile Organic Compound, Methane, and 

Inorganic Analyses ............................................................................................... available online

Appendix 5A. Sequential Extraction Procedure Analysis of Wetland Sediment 

Sample GT34W-5, Seep 3-4W Reactive Mat Pilot Test Area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland ........................................ available online

Appendix 5B. Sequential Extraction Procedure Analysis of Wetland Sediment 

Sample GT34W-14, Seep 3-4W Reactive Mat Pilot Test Area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland ........................................ available online

Appendix 5C. Sequential Extraction Procedure Analysis of Organic Mix with 

BionSoil Compost, Seep 3-4W Reactive Mat Pilot Test Area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland ........................................ available online

Appendix 5D. Sequential Extraction Procedure Analysis of Organic Mix with 

Chesapeake Blue Compost, Seep 3-4W Reactive Mat Pilot Test Area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland................ available online

Appendix 5E. Sequential Extraction Procedure Analysis of Organic Mix with 

Leafgro Compost, Seep 3-4W Reactive Mat Pilot Test Area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland ........................................ available online

Appendix 6A. Hydrograph Showing Water Levels in Upland Monitoring Well 

CC27A, August 2004–05, West Branch Canal Creek, Aberdeen Proving 

Ground, Maryland.................................................................................................. available online

Appendix 6B. Hydrograph Showing Water Levels in Piezometer Pair PTZ4, 

Seep 3-4W Reactive Mat Pilot Test Area, September 2004–05, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland ........................................ available online
v

Figures

1a–1b. Maps showing—

1a. Location of the West Branch Canal Creek study area, Aberdeen 

Proving Ground, Maryland .................................................................................................3

1b. Location of pilot-test seep and natural attenuation study areas, 

West Branch Canal Creek, Aberdeen Proving Ground,Maryland...............................4

2a–2b. Diagrams showing—

2a. Anaerobic degradation pathways for tetrachloroethene, trichloroethene, 

hexachlororethane, and 1,1,2,2-tetrachloroethane .......................................................6

2b. Anaerobic and aerobic degradation pathways for carbon tetrachloride..................7

3. Graphs and maps showing lines of section N-N' and M-M' showing slope of 

wetland surface along two transects within seep area 3-4W, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, (A) location 

of lines of section, (B) transect N-N', and (C) transect M-M'...............................................9

4. Diagram showing conceptual model of a reactive mat .......................................................10

5a–5b. Maps showing—

5a. Seep 3-4W piezometer network, location of reactive mat, and 

lines of section D-D', E-E', Y-Y', and Z-Z' at pilot-test study area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland............................15

5b. Location of multi-level diffusion samplers (PTBs) and mini-porewater 

samplers (PTNs) at the pilot-test study area, West Branch Canal 

Creek, Aberdeen Proving Ground, Maryland................................................................16

6. Photographs showing multi-level diffusion samplers (PTBs) in the reactive 

mat (A) construction, (B) assembly, and (C) deployment at seep 3-4W, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland.....................................21

7. Graphs showing concentrations of major chlorinated volatile organic 

compounds predicted by BioChlor in a simulated reactive mat 

(A) chlorinated ethenes and ethanes [tetrachloroethene (PCE), 

trichloroethene (TCE), 1,1,2,2-tetrachloroethane (TeCA), 

1,2-dichloroethene (DCE), and vinyl chloride (VC)], and 

(B) chlorinated methanes [carbon tetrachloride (CT), 

chloroform (CF), and methylene chloride (MeCl)].................................................................25

8. Diagram showing reactive mat schematic for seep 3-4W, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland (A) cross-sectional 

view, and (B) plan view..............................................................................................................27

9. Photographs showing installation of a reactive mat pilot test at seep 3-4W, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

(A) site preparation, (B) sediment excavation, (C) reactive material 

placement, and (D) bioaugmentation with WBC-2................................................................32

10. Maps showing distribution of selected volatile organic compounds in 

shallow porewater, seep location 3-4W, April (DS163–DS176) and 

December (DS317–DS332) 2003 in relation to the reactive mat pilot test, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

(A) chloroform (CF), (B) tetrachloroethene (PCE), and 

(C) cis-1,2-dichloroethene (cis-1,2-DCE).................................................................................33

11. Graph showing vertical distribution of selected chlorinated volatile 

organic compunds at seep location 3-4W, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, August 2003..............................................................34
vi

12. Maps showing baseline distribution of total chlorinated volatile organic 

compounds at (A) the top of the Canal Creek aquifer, and (B) in wetland 

sediments beneath the seep 3-4W reactive mat pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

August–September 2004............................................................................................................35

13–14. Diagrams showing—

13. Section D-D' showing baseline mean hydraulic head distribution 

at the seep 3-4W reactive mat pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, 

August–September 2004, (A) low tide and (B) high tide..............................................38

14. Section E-E' showing baseline mean hydraulic head distribution 

at the seep 3-4W reactive mat pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, 

August–September 2004, (A) low tide and (B) high tide..............................................39

15. Map showing baseline planar distribution of hydraulic head in the 

upper wetland sediments at low tide, seep 3-4W reactive mat pilot 

test area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, September 2004 .......................................................................................................40

16–17. Diagrams showing—

16. Baseline distribution of chlorinated volatile organic compounds 

in section Y-Y' at the seep 3-4W reactive mat pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, August–September 2004, (A) chloromethanes and 

(B) chloroethenes plus chloroethanes...........................................................................41

17. Baseline distribution of chlorinated volatile organic compounds 

in section Z-Z' at the seep 3-4W reactive mat pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, August–September 2004, (A) chloromethanes and 

(B) chloroethenes plus chloroethanes...........................................................................42

18–20. Graphs showing—

18. Methane concentrations in the reactive mat pilot test at seep 

area 3-4W, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, (A) PTBC level, (B) PTBB level, and 

(C) in profile at PTB7/PTC4 ...............................................................................................44

19. Concentrations of 1,1,2,2-tetrachloroethane (TeCA), 

1,1,2-trichloroethane (TCA), trichloroethene (TCE), 

trans-1,2-dichloroethene (trans-1,2-DCE), and 

cis-1,2-dichloroethene (cis-1,2-DCE) in activity tests from the 

reactive mat pilot test at seep area 3-4W, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, 

(A) November 2004 and (B) March 2005 ........................................................................45

20. Concentrations of total volatile organic compounds at various 

depths in reactive mat porewater, seep 3-4W reactive mat pilot 

test area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, (A) top of Canal Creek aquifer, (B) wetland sediments 

5 feet below land surface, (C) immediately below the reactive 

mat (PTN), (D) top of the zero-valent-iron (ZVI) -organic (PTBC) zone 

within the reactive mat, and (E) middle of the organic (PTBB) zone 

within the reactive mat.....................................................................................................46
vii

21–22. Maps showing—

21. Planar distribution of chlorinated methanes below and within the 

reactive mat at the seep 3-4W pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, August 2005, 

(A) aquifer, (B) wetland sediments 8 feet below land surface, 

(C) wetland sediments 5 feet below land surface, (D) PTN level, 

(E) PTBC level, and (F) PTBB level ..................................................................................48

22. Planar distribution of chlorinated ethenes and ethanes below and 

within the reactive mat at the seep 3-4W pilot test area, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

August 2005, (A) wetland sediments 5 feet below land surface, 

(B) PTN level, and (C) PTBB level ...................................................................................50

23–25. Graphs showing—

23. Vertical distribution of total chlorinated volatile organic compounds 

below and within the reactive mat at the seep 3-4W pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

August 2004–September 2005, (A) PTC4 (southwest corner), 

(B) PTC2 (northeast corner), and (C) PTC5 (southeast corner)..................................51

24. Total chlorinated volatile organic compounds in selected perimeter 

piezometers at the seep 3-4W pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, (A) south and 

(B) north of reactive mat...................................................................................................52

25. Vertical distribution of selected chlorinated volatile organic 

compounds below and within the reactive mat in the spring and 

summer at the seep 3-4W pilot test area site PTC4/PTB7, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

(A) chloroethenes and chloroethanes, March 2005, 

(B) chloromethanes, March 2005, (C) chloroethenes and 

chloroethanes, June 2005, and (D) chloromethanes, June 2005 ...............................53

26. Maps showing surface elevations of reactive mat and surrounding 

area at seep 3-4W reactive mat pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, (A) October 2004 

and (B) March 2005 ....................................................................................................................55

27. Graphs showing vertical distribution of mean head elevation at low 

tide along two lines of section after reactive mat installation, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

(A) D-D’ and (B) E-E’ ...................................................................................................................56

28a. Photograph showing thermal infrared image of the seep 3-4W reactive 

mat pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, 2005 ............................................................................................................................58

28b. Map showing total volatile organic compound concentrations detected 

in passive diffusion samplers installed following thermal infrared 

imaging of the seep 3-4W reactive mat pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, 2005....................................................59

29–30. Diagrams showing—

29. Vertical distribution of chloromethanes along line of section Z-Z’, 

seep 3-4W reactive mat pilot test area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, August 2005.....................................................60

30. Vertical distribution of chloromethanes along line of section Y-Y’, 

seep 3-4W reactive mat pilot test area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, August 2005.....................................................60
viii

Tables

1. Piezometer and sampler screen depths from the seep 3-4W reactive 

mat pilot test area, West Branch Canal Creek, Aberdeen Proving 

Ground, Maryland.......................................................................................................................17

2. Groundwater and surface-water sampling at the seep 3-4W reactive 

mat pilot test area, West Branch Canal Creek, Aberdeen Proving 

Ground, Maryland, August 2004–September 2005 ................................................................20

3. BioChlor input values for chloromethane, chloroethane, and 

chloroethene degradation in a model reactive mat..............................................................24

4. Calculated reactive mat tolerable thicknesses based on laboratory and 

field-determined unconfined shear strength of wetland sediments at 

seep 3-4W, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland ......................................................................................................................................26

5. Sediment properties from reported successful in situ capping projects 

and wetland sediments at seep 3-4W, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland .....................................................................................26

6. Comparison of metal concentrations in native wetland sediment samples 

from seep 3-4W, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, and in compost mixtures to consensus-based probable effect 

concentrations ............................................................................................................................30

7. Nutrient and organic matter content of composts used in this study ...............................31

31–33. Graphs showing—

31. Concentrations of total volatile organic compounds detected in 

perimeter piezometers, seep 3-4W reactive mat pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

August 2004–September 2005, (A) west of reactive mat and 

(B) south of reactive mat..................................................................................................61

32. Quality of wetland sediment porewater, seep 3-4W reactive mat 

pilot test area, West Branch Canal Creek, Aberdeen Proving 

Ground, Maryland, September 2004–05, (A) pH in perimeter 

piezometers, (B) pH in under-mat samplers, (C) specific 

conductance in perimeter piezometers, and (D) specific 

conductance in under-mat samplers ............................................................................62

33. Selected volatile organic compounds in surface water at the 

seep 3-4W reactive mat pilot test area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, (A) August 2004, 

(B) February 2005, and (C) June 2005 .............................................................................63
ix

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

square foot (ft2) 0.09290 square meter (m2)

foot per day (ft/d) 0.0003048 centimeter per second (cm/s)

foot per year (ft/yr) 0.3048 meter per year (m/yr)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

gallon (gal) 3.785 liter (L)

pound, avoirdupois (lb) 0.4536 kilogram (kg)

pound per cubic foot (lb/ft3) 0.0160 gram per cubic centimeter (g/cm3)

Other abbreviated units of measure: Water temperature, chemical concentrations, and other 

chemical and physical properties of constituents are given in metric units. 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

 °F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

 °C=(°F-32)/1.8

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L), 

micrograms per liter (μg/L), or micromoles per liter (μM/L).

Conversion Factors and Abbreviations

8. Concentrations of methane and hydrogen from in-mat diffusion samplers, 

seep 3-4W reactive mat pilot test area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, December 2004–October 2005..............................36

9. Estimated mass removal of chloromethanes and the sum of chloroethanes 

and chloroethenes through the zero-valent iron (ZVI) mix and organic-mix 

zones in the seep 3-4W reactive mat pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland, 

November 2004–August 2005....................................................................................................54

10. Comparison of water-level elevations at low and high tide in selected 

piezometers before deployment of the reactive mat (August–September 2004) 

to the mean water-level elevations measured after deployment 

(November 2004–September 2005), seep 3-4W pilot test area, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland..............................................................57

Design and Performance of an Enhanced Bioremediation 

Pilot Test in a Tidal Wetland Seep, West Branch Canal 

Creek, Aberdeen Proving Ground, Maryland

by Emily H. Majcher, Michelle M. Lorah, Daniel J. Phelan, and Angela L. McGinty

Abstract

Because of a lack of available in situ remediation 

methods for sensitive wetland environments where contaminated groundwater discharges, the U.S. Geological Survey, in 

cooperation with the U.S. Army Garrison, Aberdeen Proving 

Ground, Maryland, conceived, designed, and pilot tested a 

permeable reactive mat that can be placed horizontally at the 

groundwater/surface-water interface. Development of the 

reactive mat was part of an enhanced bioremediation study 

in a tidal wetland area along West Branch Canal Creek at 

Aberdeen Proving Ground, where localized areas of preferential discharge (seeps) transport groundwater contaminated 

with carbon tetrachloride, chloroform, tetrachloroethene, 

trichloroethene, and 1,1,2,2-tetrachloroethane from the Canal 

Creek aquifer to land surface. The reactive mat consisted of a 

mixture of commercially available organic- and nutrient-rich 

peat and compost that was bioaugmented with a dechlorinating 

microbial consortium, WBC-2, developed for this study. Due 

to elevated chlorinated methane concentrations in the pilot 

test site, a layer of zero-valent iron mixed with the peat and 

compost was added at the base of the reactive mat to promote 

simultaneous abiotic and biotic degradation.

The reactive mat for the pilot test area was designed to 

optimize chlorinated volatile organic compound degradation 

efficiency without altering the geotechnical and hydraulic 

characteristics, or creating undesirable water quality in the 

surrounding wetland area, which is referred to in this report as 

achieving geotechnical, hydraulic, and water-quality compatibility. Optimization of degradation efficiency was achieved 

through the selection of a sustainable organic reactive matrix, 

electron donor, and bioaugmentation method. Consideration 

of geotechnical compatibility through design calculations of 

bearing capacity, settlement, and geotextile selection showed 

that a 2- to 3-feet tolerable thickness of the mat was possible, 

with 0.17 feet settlement predicted for unconsolidated sediments between 1.5 and 6 years following installation of the 

reactive mat. To ensure hydraulic compatibility in the mat 

design, mat materials that had a hydraulic conductivity greater 

than the surrounding wetland sediments were selected, and the 

mixture was optimized to consist of 1.5 parts compost, 

1.5 parts peat and 1 part sand as a safeguard against fluidization. Sediment and matrix properties also indicated that a 

nonwoven geotextile with a cross-plane flow greater than that 

of the native sediments was suitable as the base of the reactive 

mat. Another nonwoven geotextile was selected for installation 

between the iron mix and organic zones of the mat to create 

more laminar flow conditions within the mat. Total metals 

and sequential extraction procedure analyses of mat materials, 

which were conducted to evaluate water-quality compatibility 

of the mat materials, showed that concentrations of metals in 

the compost ranged from one-half to one order of magnitude 

below consensus-based probable effect concentrations in 

sediment. 

A 22-inch-thick reactive mat, containing 0.5 percent 

WBC-2 by volume, was constructed at seep area 3-4W and 

monitored from October 2004 through October 2005 for the 

pilot test. No local, immediate failure of the mat or of wetland 

sediments was observed during mat installation, indicating 

that design estimates of bearing capacity and geotextile textile 

selection ensured the integrity of the mat and wetland sediments during and following installation. Measurements of surface elevation of the mat showed an average settlement of the 

mat surface of approximately 0.25 feet after 10 months, which 

was near the predicted settlement for unconsolidated sediment. 

Monitoring showed rapid establishment and sustainment 

throughout the year of methanogenic conditions conducive to 

anaerobic biodegradation and efficient dechlorination activity 

by WBC-2. The median mass removal of chloromethanes 

and total chloroethenes and ethane during the performance 

monitoring period was 98 and 94 percent, respectively, within 

the 1.5-feet-thick zone between the base of the mat and the 

middle of the organic zone, whereas no mass removal was 

observed within the underlying 12–15-feet-thick wetland 

sediment in the seep area. Following mat installation, transient 

appearance of daughter volatile organic compounds, including 

trichloroethene, cis-1,2-dichloroethene, vinyl chloride, and 

methylene chloride, was observed in groundwater in the mat 

in association with decreasing concentrations of parent volatile 

organic compounds. In some areas of the mat, the non-toxic 

end products of ethene and ethane were consistently detected 
2 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

throughout the monitoring period. An apparent decrease in 

volatile organic compound degradation and methane production occurred in late winter to early spring, consistent with a 

decline in microbial activity during the colder months. Waterquality monitoring for pH, specific conductance, nutrients, 

major ions, and metals indicated that the mat had no adverse 

effect on the groundwater quality in the wetland sediments 

surrounding the reactive mat, nor on nearby surface-water 

quality. 

Hydraulic head gradients (0.20 to 0.26 feet/feet) in 

and around the reactive mat remained dominantly vertically 

upward following mat installation, consistent with pre-installation calculations. Horizontal hydraulic gradients remained 

at least one to two orders of magnitude lower than the vertical 

hydraulic head gradients. Despite the dominantly vertically 

upward head gradients in the mat, an aerial thermal infrared 

flight during winter 2005 showed that the reactive mat was not 

warmer than surrounding wetland sediments, as observed on 

flights over the seep area prior to mat installation. Observed 

seep areas in the vicinity of seep 3-4W were consistent with 

previous flight imagery, however, and porewater sampling 

indicated that transport of volatile organic compounds had not 

shifted to these nearby seep areas as a result of the mat installation. This indicates that the design goal of normalizing flow 

across the mat area without affecting flow in the surrounding 

wetland was achieved. 

Overall, the pilot test showed that the design goal of at 

least 90 percent mass removal of total chlorinated volatile 

organic compounds was achieved and maintained for 1 year 

in the reactive mat without any undesired geotechnical, 

hydraulic, or water-quality effects on the wetland and tidal 

creek. Additional monitoring, however, would be necessary 

to evaluate long-term sustainability of enhanced biodegradation in the mat. Future applications would benefit from either 

deeper placement within the native sediments or a thinner mat 

to minimize final elevation of the mat above land surface.

Introduction

A study of the design of a reactive mat for enhanced 

bioremediation at the groundwater/surface-water interface and 

demonstration of its performance in a pilot test was completed 

by the U.S. Geological Survey (USGS), in cooperation with 

the U.S. Army Garrison, Aberdeen Proving Ground (APG). 

The West Branch Canal Creek study area, the location of the 

performance pilot test demonstration, is the focus of ongoing 

Remedial Investigation and Feasibility Study efforts for the 

Installation Restoration Program (IRP) at APG, in accordance 

with the U.S. Environmental Protection Agency (USEPA) 

Superfund Program (fig. 1a).

Wetlands are a natural transition zone between groundwater and surface water (Winter and others, 1998; Mitsch and 

Gosselink, 1993). Wetland sediments have been shown to 

have the ability to efficiently naturally attenuate chlorinated 

solvents in porewater (Lorah and others, 1997; Lorah and 

Olsen, 1999; CFR Technical Services, 2005) when acting as 

receptors of contaminated groundwater discharge. In heterogeneous wetland systems, discrete pathways for solute transport 

to surface water can occur by preferential flow in the form of 

springs or seeps (Harvey and others, 1995; Portnoy and others, 

1998; Winter and others, 1998; Conant and others, 2004). In 

cases where underlying groundwater is contaminated, seeps 

can provide a route for contaminants to migrate into surface 

water (Conant and others, 2004; Majcher and others, 2007) 

and reach human and ecological receptors. 

Where chlorinated volatile organic compound (VOC) 

plumes discharge to the West Branch Canal Creek bottom 

sediments and wetlands from an aerobic, sand and gravel aquifer, natural attenuation in anaerobic wetland sediments appears 

to efficiently reduce concentrations in most of the wetland area 

throughout the year (Lorah and others, 1997, 2003; Lorah, 

Spencer, and McGinty, 2005; Majcher and others, 2007). Seep 

areas have been identified, however, where natural attenuation 

of chlorinated solvents by anaerobic biodegradation is hindered by the increase in vertical seepage flux and the resulting 

decrease in residence time in the wetland sediments (Majcher 

and others, 2007) (fig. 1b). This hydrologic occurrence results 

in more oxidizing conditions, an accumulation of chlorinated 

VOCs, and in some cases, a change in the microbial community in wetland porewater (Majcher and others, 2007). 

Although seeps of contaminated porewater to surface water 

are limited to approximately 1 percent of the total discharge 

area along the West Branch Canal Creek, they contribute 

approximately 20 percent of the total volume discharge of 

groundwater to surface water and contain up to 35 ppm (parts 

per million) of total chlorinated VOCs near the groundwater/

surface-water interface (Majcher and others, 2007). 

Chlorinated VOCs in groundwater in the West Branch 

Canal Creek study area include 1,1,2,2, tetrachloroethane 

(TeCA), hexachloroethane (HCA), pentachloroethane (PCA), 

trichloroethene (TCE), carbon tetrachloride (CT), chloroform 

(CF), and tetrachloroethene (PCE) from historical use and 

disposal during military manufacturing and research activities 

in the area (Nemeth, 1989; Lorah and Clark, 1996). These 

compounds, many of which are common to other industrial 

and military sites, can be converted to non-toxic compounds 

by abiotic and microbially mediated degradation reactions 

under anaerobic conditions (figs. 2a,b). 

In cases where sources of chlorinated VOCs are near or 

beneath the existing wetland sediments, traditional remediation technologies become infeasible due to logistical constraints, particularly if a complementary goal of the remediation is compatibility, defined in this report as having minimal 

adverse effect on the surrounding wetland ecosystem. Some 

approaches used for chlorinated VOC remediation such as 

pump-and-treat and chemical oxidation, have the potential 

to adversely impact the downgradient wetland ecosystem. 

For this USGS study, enhanced bioremediation approaches 

were investigated, with the goal of duplicating the previously 

documented natural processes in other areas of the wetland in 
Introduction 3

the seep areas. Two enhanced bioremediation methods, both of 

which involved biostimulation [addition of a favored electrondonor substrate and (or) nutrients] with or without bioaugmentation (addition of degrading microorganisms), were studied 

first in laboratory experiments—direct injection into the 

wetland sediments and the installation of a permeable reactive 

mat (Lorah and others, 2008). If logistical constraints such as 

delivery of amendments to the subsurface and site access can 

be overcome, enhanced bioremediation is a desirable treatment 

method for seep areas. 

This study developed the methods for and demonstrated 

in situ remediation with the reactive mat at a chlorinated 

VOC-contaminated seep area along West Branch Canal Creek. 

USGS conceptualized and developed a permeable, biologically 

reactive mat to be placed horizontally at the seep surface and 

create a zone of enhanced degradation for the upward-flowing 

groundwater before the contaminants reach the surface water. 

The components of the reactive mat, selected during the laboratory investigation, included commercially available compost 

and peat that were bioaugmented with a newly developed 

Figure 1a. Location of the West Branch Canal Creek study area, Aberdeen Proving Ground, Maryland (modified from Phelan and 

others, 2002).
4 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 1b. Location of pilot-test seep and natural attenuation study areas, West Branch Canal Creek, Aberdeen Proving 

Ground,Maryland (modified from Majcher and others, 2007).
Introduction 5

microbial consortium, WBC-2, capable of dechlorinating the 

suite of chlorinated VOCs in this wetland environment (Jones 

and others, 2006; Lorah and others, 2008). The objectives of 

this study were to (1) develop the site-specific design of the 

reactive mat at a contaminated seep area along West Branch 

Canal Creek, (2) implement a pilot-scale demonstration of the 

reactive mat at the seep area, and (3) evaluate the performance 

of the pilot-scale demonstration over 1 year. 

Purpose and Scope 

The purpose of this report is to describe the design and 

performance of an enhanced bioremediation pilot test at seep 

area 3-4W along West Branch Canal Creek (fig. 1b). The 

overall design framework and performance metrics at seep 

3-4W are presented. Field and laboratory investigations that 

were conducted in support of the primary design objectives, 

degradation optimization, and determination of compatibility 

with the hydraulic, geotechnical, and water-quality characteristics of the wetland are described. The synthesis of results 

from these investigations is discussed and presented in a 

site-specific design. Specifically, results of hydraulic, geotechnical, and water-quality investigations were used to estimate 

the allowable thickness and reactive matrix composition to 

maximize removal of VOCs as they passed through the mat. 

Performance was evaluated using specially designed monitoring devices to measure various performance parameters in and 

around the reactive mat. Results that describe the reactive mat 

degradation efficiency and compatibility also are presented. 

The reactive mat design for seep 3-4W was finalized 

using an iterative design process in which a maximum tolerable thickness was calculated based on the hydraulic, geotechnical, and water-quality constraints for the site and the 

ability to remove chlorinated VOCs. Degradation rates of 

parent compounds, transient removal of daughter compounds, 

and the optimal conditions for survival of the bioaugmented 

microbial consortium, WBC-2, were evaluated to predict the 

mass removal of VOCs reaching surface water in the seep area 

using a one-dimensional model. An analysis of bearing capacity and primary settlement are presented as part of the design 

based on an investigation conducted in spring 2004. 

The overall performance of the reactive mat at seep 

3-4W from October 2004 through October 2005 is discussed 

relative to the design goals. Sampling results for VOCs below 

and within the mat are presented and mass removal of VOCs 

reaching surface water is discussed. Oxidation-reduction 

(redox) conditions within the mat and their impact on WBC-2 

activity also are discussed. Analysis of the potentiometric 

surface surrounding the reactive mat, vertical gradients, and 

aerial thermal infrared (TIR) analysis of the pilot test area 

were used to assess hydraulic compatibility. Planar surface 

elevations of the mat were compared to predicted settlement 

over time to evaluate the geotechnical compatibility of the 

reactive mat. Finally, sampling results for VOCs, metals, 

and nutrients were used to evaluate the overall impact of the 

reactive mat on native porewater surrounding the mat and on 

surface-water quality. 

Description of Study Area 

The pilot test was conducted within the USGS seep study 

area (Majcher and others, 2007) in the northwest section of 

the Edgewood Peninsula of APG near the northwest reaches 

of the Chesapeake Bay at seep 3-4W, on the western perimeter 

of the West Branch Canal Creek (figs. 1a, b). The USGS study 

areas (including the pilot test) are wholly encompassed by the 

APG IRP-designated West Canal Creek Study Area (Weston 

Solutions, 2005). The main industrial part of the West Canal 

Creek study area was located to the east of the creek and is 

considered the likely source of chlorinated solvent groundwater contamination detected in the underlying aquifer and the 

downgradient freshwater, tidal wetlands (Lorah and Clark, 

1996), including seep 3-4W. The pilot test area was located 

downstream of previous USGS investigations of natural 

attenuation processes (natural attenuation study area, fig. 1b). 

The regional geology of the USGS study areas was previously characterized and described (Oliveros and Vroblesky, 

1989; Lorah and others, 1997; Weston Solutions, 2005). The 

Canal Creek aquifer of the Patapsco Formation is largely 

unconfined near the West Branch Canal Creek wetland and 

stream. Soft, organic-rich sediments comprise the wetland 

and stream bottom. Physical and chemical characteristics of 

these sediments have also been described previously (Lorah 

and others, 1997; Olsen and others, 1997; Phelan, Senus, and 

Olsen, 2001; Majcher and others, 2007). 

Preferential seepage of contaminated groundwater from 

the aquifer to West Branch Canal Creek was identified as 

the major transport mechanism of VOCs to surface water 

(Majcher and others, 2007). Generally, porewater in seep 

areas contaminated with chlorinated VOCs had less reducing 

conditions and greater VOC concentrations than porewater in 

non-seep wetland sediments. Seep locations characterized as 

focused seeps contained the highest concentrations of chlorinated parent compounds, relatively low concentrations of 

chlorinated daughter compounds, and insignificant concentrations of methane in shallow porewater samples. These seeps 

were primarily along the creek edge or formed a dendritic-like 

pattern between the wetland and creek channel. In contrast, 

seep locations characterized as diffuse seeps contained relatively high concentrations of chlorinated daughter compounds 

(or a mixture of daughter and parent compounds) and detectable methane concentrations in shallow porewater samples. 

These seeps were primarily along the wetland boundary 

(Majcher and others, 2007). 

The USGS identified site characteristics that were desirable for the pilot test on the basis of the seep investigation 

that helped define hydrologic and redox characteristics, and 

VOC distribution in sediments within seep 3-4W (Majcher and 

others, 2007). Seep 3-4W was characterized as a focused discharge seep, with a seepage flux up to a maximum of 34 ft/yr 

(feet per year), during mid- to low-tidal range, which is about 

37 times greater than flux estimates in the non-seep areas of 

the wetland (Lorah and others, 1997). The geometric mean of 

multiple measurements during various tidal ranges was 
6 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 2a. Anaerobic degradation pathways for tetrachloroethene, trichloroethene, hexachlororethane, and 

1,1,2,2-tetrachloroethane (modified from Lorah and others, 1997). 
Introduction 7

Figure 2b. Anaerobic and aerobic degradation pathways for 

carbon tetrachloride (modified from Majcher and others, 2007).

19 ft/yr, or about 20 times greater than the non-seep area estimates. Similarly, estimates of vertical hydraulic conductivity 

were calculated to be at least two orders of magnitude greater 

than non-seep sediments, averaging 66 ft/yr (to a maximum of 

88 ft/yr). In situ estimates of horizontal hydraulic conductivity 

ranged from 0.33 to 15 ft/yr (Majcher and others, 2007).

The depth to the Canal Creek aquifer in the vicinity of 

seep 3-4W was consistent with depths reported previously in 

nearby HP05 and HP11 (Phelan, Senus, and Olsen, 2001). The 

depth to the aquifer varied from the north to the south, ranging 

from about 12 to 15 ft (Majcher and others, 2007). Lithologic 

descriptions of organic sediments within seep 3-4W were 

consistent with those described elsewhere in West Branch 

Canal Creek (Olsen and others, 1997; Phelan, Senus, and 

Olsen, 2001). There was no visible evidence of preferential 

flowpaths. Similarly, other physical properties of the seep sediments (total organic carbon, grain size) were not indicative of 

preferential flowpaths (Majcher and others, 2007).

The hydrologic occurrence of rapid or focused discharge 

at seep 3-4W influenced anaerobic biodegradation of the 

various chlorinated solvents present in the wetland porewater 

(Majcher and others, 2007). Whereas anaerobic conditions 

were present, sulfide and methane were not detected in substantial quantities in the upper 2 to 4 ft of wetland sediments. 

Rather, seep 3-4W supported predominantly iron-reducing 

conditions in the upper sediments and also accumulated 

ammonia. Both lateral and vertical delineation of chlorinated 

VOCs indicated that under these redox conditions, minimal 

anaerobic biodegradation occurs (Majcher and others, 2007). 

Concentrations of parent VOC compounds CF, CT, and PCE 

occupy a similar spatial footprint (approximately 1,000 square 

feet), in which concentrations of individual contaminants 

range from 15,000 to less than 100 μg/L (micrograms per liter) 

over as little as 10 ft (feet) (and not greater than 20 ft) within 

the seep footprint. The increased velocity and corresponding 

decreased residence time in the wetland seep sediments results 

in a lack of anaerobic biodegradation, as indicated by the conservation of CF, CT, and PCE contaminant mass along vertical 

flowpaths in the wetland sediments. In some cases, an accumulation of mass is apparent with decreasing depth bls (below 

land surface), indicating that flow may not be entirely vertical 

in this area and that the seep may accumulate VOCs from the 

surrounding area. Discharge of the accumlated chlorinated 

VOCs and a lack of biodegradation results in an increased 

contaminant mass flux to surface water compared to non-seep 

wetland sediments (Majcher and others, 2007).

 The overall land-surface slope of the seep 3-4W area 

was evaluated along two transects (N-N' and M-M') from the 

area of maximum seepage and contamination and across the 

main channel of West Branch Canal Creek. The slope profiles, 

which extend from west to east across the creek, are shown in 

figure 3. The area is relatively flat (minimally sloped) and is 

offset from the center of the channel, providing some 

protection from erosive forces.

Background on Reactive Mat Technology 

Development

A diagram showing the conceptual model for the receptor-targeted, reactive mat technology is presented in figure 4. 

This conceptual model incorporated principles of existing 

technologies including anaerobic bioremediation, in situ capping, and constructed or restored wetlands. The similarities 

and differences of these existing technologies to the reactive 

mat are summarized in this section. In addition, background 

microbial consortium development and bench tests for the 

reactive mat technology reported elsewhere (Jones and others, 

2006; Lorah and others, 2008) also are summarized. 
8 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Basis in Existing Technologies 

Anaerobic, engineered bioremediation has become 

a widely accepted practice for in situ aquifer remediation 

of particular chlorinated solvents (Air Force Center for 

Environmental Excellence, 2004; Environmental Security 

Technology Certification Program, 2005). Biostimulation, or 

the addition of organic substrate or nutrients to the subsurface, 

facilitates conditions favorable to reductive dechlorination 

of these compounds. Numerous organic substrates in both 

liquid (such as lactate) and solid (such as chitin) forms are 

widely available (Lorah and others, 2008). Addition of these 

substrates typically creates a highly reducing environment that 

encourages the growth of native microorganisms capable of 

reductive dechlorination. In addition to promoting the abiotic 

reduction of various chlorinated compounds, zero-valent iron 

(ZVI) can generate hydrogen to support the anaerobic biodegradation of some chlorinated VOCs (Novak and others, 1998; 

Weathers and others, 1997). 

Under some circumstances, biostimulation alone does 

not appear to facilitate the complete dechlorination to nonchlorinated end-products, resulting in accumulation of cis-1,2-

dichloroethene (cis-1,2-DCE) or other chlorinated daughter 

products. Similarly, there may be instances where there is a 

need to increase rates of dechlorination beyond those achieved 

with biostimulation. In these cases, bioaugmentation, or the 

addition of a known dechlorinating consortium to the subsurface, may be considered in combination with biostimulation. Currently, there are at least four commercially available 

mixed cultures capable of degrading PCE or TCE by reductive 

dechlorination at various stages of maturity in the presence 

of a preferred organic substrate (Environmental Security 

Technology Certification Program, 2005). Dehalococcoides

bacteria, known to degrade vinyl chloride (VC) to ethene, are 

contained in each of these commercially available consortia and are strictly anaerobic. These cultures do not readily 

degrade chlorinated ethanes or methanes, although there is 

a commercially available culture that will degrade 1,1,2-trichloroethane (1,1,2-TCA) and 1,2-dichloroethane(1,2-DCA) 

(Environmental Security Technology Certification Program, 

2005). Mixtures of ethane or methane compounds with ethenes typically inhibit the degradation activity of these various 

cultures, however (Bagley and others, 2000; Weathers and 

Parkin, 2000). 

Preferential discharge of contaminated groundwater in 

seeps results in high concentrations near the groundwater/

surface-water interface. Maximum contaminant mass removal 

within a minimal barrier thickness is desirable. The use of 

non-native materials and the desire for rapid rates of degradation required inclusion of a mixed culture capable of complete 

dechlorination of mixed chlorinated methanes, ethanes, and 

ethenes near the wetland surface. Due to the lack of a commercially available culture for this application at the time of the 

pilot test, a culture was specifically developed as part of this 

study (see next section on Reactive Mat Laboratory Tests). 

On the basis of earlier natural attenuation studies conducted at West Branch Canal Creek wetlands (Lorah and 

others, 1997; Lorah and Olsen, 1999), interest in constructed 

and restored wetlands for treatment of chlorinated VOCs grew 

(Pardue, 2002; Kassenga and others, 2003; Richard and others, 

2001) due to the wetlands’ inherent abilities to generate conditions favorable to anaerobic biodegradation. Using commercially available organic materials mixed with sand, Kassenga 

and others (2003) and Pardue (2002) demonstrated effective 

treatment of chlorinated VOCs with constructed wetland material in column tests. On the basis of VOC degradation rates 

measured in the columns and adjusted for potential decline in 

rates due to temporal changes, a required sediment thickness 

of more than 6 ft was estimated for a constructed treatment 

wetland to meet drinking-water standards (Kassenga and 

others, 2003). Subsequent studies by CFR Technical Services 

(2005) and Kassenga and others (2004) indicated that the 

long-term circulation of groundwater and site contaminants to 

the column matrix resulted in enrichment of a mixed culture 

containing Dehalococcoides-related organisms, increasing the 

rate of removal of TeCA, TCE, cis-1,2DCE, and 1,2-DCA in 

this matrix. These constructed wetland matrices were desirable 

for application in a reactive mat due to their similarity to 

natural wetland sediments (including high organic matter 

content). In addition, because biodegradation was desired over 

as minimal a thickness as possible and with minimal delay 

after installation of the mat, bioaugmentation of the matrix 

was required.

Richard and others (2001) reported a more empirical 

approach to wetland restoration for chlorinated VOC remediation at a preferential flowpath in a small, dredged channel 

of a lake. Using degradation rates reported elsewhere, they 

encompassed the dredged channel into a nearby, existing wetland. In addition, constructed wetland cells have been reported 

for chlorinated VOC remediation, although VOC removal 

processes were not documented (Haberl and others, 2003; 

Clemmer, 2003).

Subaqueous, passive, and active caps have recently been 

utilized as an in-place containment alternative for ex situ sediment remediation alternatives such as dredging (Palermo and 

others, 1998). Active caps contain a reactive media, as does 

the reactive mat for this study, but are typically targeted to 

contain (or treat) hydrophobic contaminants associated with 

sediment such as metals, polychlorinated biphenyls (PCBs), 

and polyaromatic hydrocarbons (PAHs) (Palermo and others, 

1998). Bench tests and field demonstrations of various active 

capping materials (AquaBlock, apatite, coke, ZVI, activated 

carbon, and sorbents) have been conducted (Reible and others, 

2006). Geotechnical guidance developed for in situ capping 

was utilized for the reactive mat since the two technologies 

have similar design challenges in that they both require placing non-native material on soft, often subaqueous contaminated sediments that possess low shear strength and are in a 

possible high energy (such as a tidal) environment (Palermo 

and others, 1998). 
Introduction 9

Figure 3. Lines of section N-N' and M-M' showing slope of wetland surface along two transects within seep area 3-4W, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, (A) location of lines of section, (B) transect N-N', and (C) transect M-M'.
10 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Microbial mats, comprised of self-associating bacteria 

that do not require the use of a solid support matrix, also 

have been tested at the bench and pilot scale for biosorption 

and degradation of PCE and TCE (O’Niell and others, 1999). 

The commercially available “Biomats” (“microbial aquatic 

treatment systems”) have been suggested for use in aqueous 

(such as ponds or bioreactors) as well as non-aqueous systems 

(Planteco Environmental Consultants, written commun., 2005; 

O’Niell and others, 1999). The microbial community in the 

“Biomats” is reported to be self-sustaining so that continual 

addition of microorganisms is not needed for long-term 

contaminant treatment. Ideally, inoculation of the reactive mat 

matrix will only be required at installation. 

Reactive Mat Laboratory Tests

Results from a series of bench scale tests (Lorah and 

others, 2008; Geosyntec Consultants, Inc., 2004, 2007; Jones 

and others, 2006) contributed to the development of the reactive mat technology used at seep 3-4W and are summarized 

in this section. The need to bioaugment the reactive mat 

was predicated by the need to maximize chlorinated solvent 

mass removal while minimizing mat thickness. As described 

previously, no known commercially available consortia were 

capable of achieving these goals. A microbial consortium 

(WBC-2) was developed by the USGS using enrichment techniques from wetland sediments collected from West Branch 

Canal Creek (Jones and others, 2006; Lorah and others, 2008). 

WBC-2 can completely dechlorinate TeCA and its chlorinated 

daughter products, including 1,1,2-TCA, cis-1,2-DCE, and 

VC (fig. 2a). In collaboration with the USGS, larger quantities of the WBC-2 were grown for the pilot test by SiREM 

Laboratory (Guelph, Ontario), a division of Geosyntec 

Consultants (Geosyntec Consultants, Inc., 2007). 

Physiological characteristics of WBC-2 that were 

important for the reactive mat application were determined in 

batch tests, including electron donor and pH preference and 

oxygen tolerance (Geosyntec Consultants, Inc., 2007; Lorah 

and others, 2005a, 2005b). Testing with various commercially 

available electron donors showed that dechlorination rates 

were most rapid with chitin, which is a relatively insoluble 

donor comprised of crushed shells, and the soluble donors 

ethanol and lactate (Geosyntec Consultants, Inc., 2007; Lorah 

and others, 2005a). The enhancement of dechlorination rates 

with both insoluble and soluble donors provides flexibility 

for applications of the reactive mat. The wetland porewater at 

seep 3-4W is acidic, with pH typically less than 5 (Majcher 

and others, 2007), but the organic matrix tested for the reactive 

mat was thought likely to cause an increase in pH. WBC-2 

was able to maintain complete dechlorination of added TeCA, 

1,1,2-TCA, and cis-1,2-DCE under acidic (pH 5) to alkaline (pH 9) conditions (Lorah and others, 2005b; Geosyntec 

Consultants, Inc., 2007), indicating that the mat could be 

effective over a wide range of operational conditions.

Typically, microorganisms capable of reductive dechlorination (specifically Dehalococcoides-related organisms) 

are highly sensitive to the presence of oxygen, making the 

reactive mat inoculation and viability at the groundwater/

surface water interface a challenge. Oxygen sensitivity of 

WBC-2 was tested by bubbling ambient air through an aliquot 

for designated timeframes. Following timed exposures to 

ambient air, culture media was purged with anaerobic gas 

and dechlorination of TeCA, 1,1,2-TCA, and cis-1,2-DCE 

was evaluated. Dechlorination after 20 minutes of exposure 

was comparable to culture with no exposure to oxygen at all, 

while after 60 minutes, activity was temporarily inhibited 

before proceeding to completion (Lorah and others, 2005b; 

Geosyntec Consultants, Inc., 2007).

Concurrent with the characterization of the culture, 

bench scale tests were completed with wetland sediments 

and reactive matrices to evaluate dechlorination ability using 

biostimulation and bioaugmentation (Lorah and others, 2008). 

Bioaugmentation with WBC-2 increased degradation rates of 

chlorinated ethanes in wetland sediments at least two-fold in 

microcosms conducted with sediment collected during different seasons. This same enhancement of the degradation rate 

was not observed when biostimulation (addition of nutrients or 

soluble organic substrates) was tested without the addition of 

WBC-2 (Lorah and others, 2008).

Mixtures of peat, various compost types, and sand were 

evaluated as an organic matrix for the reactive mat in anaerobic laboratory microcosms and columns (Lorah and others, 

2008). The first mixture that was evaluated was based on 

extensive laboratory testing reported on materials used in 

constructed wetlands by Kassenga and others (2003), although 

the proportions of peat, compost, and sand were adjusted to 

make hydraulic properties compatible with the field conditions 

at seep 3-4W. Peat combined with crab compost (Chesapeake 

Blue), leaf compost (LeafGro), or organic dairy compost 

(BionSoil) facilitated reductive dechlorination of TeCA and 

its daughter products by WBC-2 when mixed with wetland 

porewater from West Branch Canal Creek. Several other 

dairy-derived composts were tested but were not effective in 

Figure 4. Conceptual model of a reactive mat.
Design Methods and Data Analysis 11

enhancing degradation rates, underlining the importance of 

reactive material selection (Lorah and others, 2008).

In addition to the organic matrix, the incorporation 

of iron filings (-8/50 mesh size) into the reactive mat was 

explored to facilitate abiotic dechlorination of chlorinated 

methanes (CT and CF), which are present in high concentrations at some seep sites and are common microbial inhibitors 

(Lorah and others, 2008). Rapid reductive dechlorination 

of the chlorinated methanes at various concentrations was 

observed with the addition of ZVI in batch tests (Lorah and 

others, 2008). Degradation of TeCA, CT, and CF also was 

compared in two flow-through columns that were bioaugmented with the culture—one constructed with only the 

organic matrix (peat-compost-sand) and one with the organic 

matrix overlying a zone of ZVI mixed with the organic matrix 

(Lorah and others, 2008). TeCA, CT, and CF and all associated 

daughter compounds were typically removed within half of 

the column length (15 in./ inches) with or without the presence 

of the ZVI layer, although a lower transient accumulation of 

methylene chloride was measured in the ZVI-organic matrix 

column. Rapid TeCA degradation was maintained in both 

column matrices when various co-contaminants, including 

PCE, TCE, CT, and CF were added. Complete degradation of 

the chloroethene and chloromethane co-contaminants and their 

associated daughter compounds also was observed.

Design Methods and Data Analysis

The design of the reactive mat was based on two primary 

objectives: (1) optimize degradation of chlorinated VOCs; 

and (2) maintain compatibility with the existing wetland ecosystem. Design methods and data analysis were selected on the 

basis of existing technologies and are presented here according 

to the primary objectives.

Optimizing Degradation

Results from hydrologic investigations and bench scale 

testing reported in Majcher and others (2007) and Lorah and 

others (2008) were used to conduct one-dimensional modeling 

of chlorinated VOC degradation through the reactive mat. 

BioChlor (U.S. Environmental Protection Agency, 2002) is a 

one-dimensional, sequential, first-order reaction rate model 

developed by the USEPA for screening the biodegradation of 

chlorinated solvent plumes in groundwater. The model was 

modified for chlorinated methanes and ethanes and used to 

predict concentrations in the field through the reactive mat. 

Model results were then used to estimate the overall mass 

removal of chlorinated ethenes, ethanes, and methanes for a 

given mat thickness:

(1 - [∑CEf+∑CAf+∑CMf]/[∑CEi+∑CAi+∑CMi]) x 100 = 

percent removal (1)

where

 ∑CEf and ∑CEi = the sum of final and initial mass 

of chloroethenes, respectively;

 ∑CAf and ∑CAi = the sum of final and initial mass 

of chloroethanes, respectively; and

 ∑CMf and ∑CMi = the sum of final and initial mass 

of chloromethanes, respectively.

Maximum mass removal estimates were compared to 

reactive mat thicknesses that were compatible with the geotechnical, hydrologic, and water quality-conditions described 

in the following sections.

Maintaining Compatibility with the Wetland 

System

In addition to enabling a reduction in the overall mass 

loading of VOCs to surface water, the reactive mat was also 

designed to be compatible with the existing tidal wetland environment in which the seep areas were located. Geotechnical, 

hydraulic, and water-quality compatibility is discussed in the 

following sections.

Geotechnical Investigations and Analysis

Geotechnical tests were performed during the investigation phase to determine the shear strength and consolidation behaviors of the subaqueous sediments in the seep area. 

These tests helped predict the maximum thickness of the mat 

required to avoid failure of the soft contaminated sediment 

immediately after the mat material was placed, as well as during long-term performance. In addition, the incorporation of 

geosynthetic fabric into the mat design for additional strength 

was evaluated. Geosynthetics, which include woven or nonwoven fabrics, are used for filtration, drainage, separation, 

and reinforcement of soils (Koerner, 1998). Site-specific data 

were compared to properties of published, successful in situ

subaqueous caps. 

Three continuous cores were collected along the perimeter of seep area 3-4W in schedule 80 polyvinylchloride 

(PVC) casing and sealed at both ends for laboratory analysis 

(Majcher and others, 2007). The standard test method for the 

unconsolidated-undrained (UU) triaxial compression test on 

cohesive soils (American Society for Testing and Materials, 

2003) was performed to obtain data on the shear strength 

and stress-strain relationship of the native sediment. Results 

of the UU test were then used to perform bearing capacity 

calculations. The standard test method for one-dimensional 

consolidation properties of soils (American Society for Testing 

and Materials, 2001) also was performed and provided data 

to evaluate the magnitude of load-induced primary settlement of the wetland soil and calculate a time rate of primary 

settlement. A total of 17 samples from the three cores were 

then analyzed for Atterberg limits and water content. These 
12 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

engineering properties of the sediments allowed for an evaluation of the physical-chemical properties of the fine fraction 

and provided general information on minimum strength. 

In addition to laboratory tests, in situ tests were 

performed using an electronic piezocone cone penetrometer 

(CPT) to obtain additional information on shear strength with 

depth bls. A CPT test was performed at two locations at seep 

3-4W, the north and south ends, as described in Majcher and 

others (2007). A steel cone tip, a pore pressure transducer, and 

sensors attached to a friction sleeve were pushed into the wetland sediment using a vibracore drill on a floating platform. 

As the piezocone was pushed into the sediment, tip resistance, 

sleeve friction, and porewater pressure were continuously 

recorded. These data were used to calculate bearing capacity. 

The tolerable thickness of the mat was determined on 

the basis of geotechnical criteria of strength of the underlying 

sediments and the depth below grade where it was placed. The 

evaluation of bearing capacity was based on shallow foundation analysis for square footings in local failure (since the 

depth-to-width ratio is less than 4 and the length-to-width ratio 

is less than 5) (Das, 2002). Similar applications of empirical 

bearing capacity theory have been used for assessment of the 

tolerable thickness of in situ sand caps (Palermo and others, 

1998). 

The values of ultimate shear strength, Cu, were generated 

from the UU laboratory tests from the three continuous cores 

and the in situ CPT data (average and maximum). These values of ultimate shear strength were then used to calculate ultimate bearing capacity, qu

, under local (not immediate) failure 

conditions, according to the following empirical relation based 

on Terzaghi’s equations (Das, 2002):

qu = 7.1Cu + q (2) 

where

q = γs Df;

γs = unit weight of the sediment; and 

Df = depth of the mat below grade.

The allowable bearing capacity, qa, was calculated based 

on a conservative factor of safety (FS):

qa = qu / FS (3)

Finally, the tolerable thickness T1 for this allowable bearing capacity was estimated using the method from Das (2002):

T1 < qa / γr (4)

where

γr = saturated unit weight of the reactive matrix.

Whereas bearing capacity calculations address questions 

regarding the stability of a structure before excess porewater 

has dissipated from the foundation material, settlement calculations answer questions about consolidation in the long term 

while porewater is dissipating and the volume of the foundation is decreasing over time (Das, 2002). For clay-sized particles like those found in the mat matrix, settlement may take 

a long time (Das, 2002). The settlement caused by primary 

consolidation as well as the time to settlement was calculated 

with the data obtained from laboratory consolidation tests. 

Lab curves with incremental applied pressure loads (σ) versus 

void ratio (e) were generated by the testing laboratory after 

the consolidation tests were performed. In geotechnical terms, 

the void ratio is the difference in the height of the sediment 

specimen before and after a load is added (Das, 2002). 

Preconsolidation pressure (Pc or σ’p ), or the maximum effective past pressure that the soil was subjected to, was reported 

with the laboratory results. Additionally, time-deformation 

readings were reported by the laboratory for selected samples. 

For each applied load, the height of the sample was plotted 

against time for a specified duration. From this graph, the time 

for which 50-percent consolidation occurred at each load is 

called the “t

50” value. This value was then used in calculations 

to determine time to settlement.

The first step in accurately evaluating the magnitude of 

settlement when a given load is applied is the correction to and 

an evaluation of sample consolidation curves. A comparison of 

the initial vertical effective stress (σ’vo ) was compared to the 

preconsolidation pressure (σ’p ) to determine if the sample was 

overconsolidated. The initial vertical effective stress (before 

a load is applied) was calculated with the following equation 

from Coduto (1999):

σ’vo= γz - uo (5)

where

γ = bulk density of the soil;

z = depth of the sample; and 

uo = porewater pressure at depth z, which is the 

pressure of the water within the soil voids. 

If σ’vo< σ’p , then the samples are overconsolidated (Das, 

2002). This means that the soil is presently not at its maximum 

historical stress and the pressure or stress on the soil has been 

relaxed over time. If σ’vo= σ’p , the soil has been normally 

consolidated and the soil is experiencing its maximum stress at 

the time of collection (Das, 2002). If overconsolidation occurs, 

field virgin (corrected) consolidation curves are typically 

constructed from the lab curves before further calculations are 

made (Schmertmann, 1953).

The amount of primary settlement (Sc ) and time to 

primary settlement (t

field ) were the focus of further calculations. The amount of settlement due to the various anticipated 
Design Methods and Data Analysis 13

reactive mat loads was calculated from corrected consolidation curves using adjusted void ratios (Schmertmann, 1953) to 

obtain a range of settlement values using the following equation from Das (2002):

S H

e e

e c field

f = −

+

o

o 1 (6)

where 

Hfield = sediment depth over which the load is 

observed;

eo = initial void ratio; and

ef = void ratio at a specific applied pressure.

Both eo and ef were taken from the corrected (field virgin) 

pressure versus void ratio curves to give a value of settlement 

for any specified pressure. 

Calculation of t

field depends largely on the coefficient of 

consolidation (cv ). Values of cv were reported by the lab from 

the time-deformation readings for six samples (Das, 2002):

c

H

t v lab = 0 197 2

50

. *

(7)

where

Hlab = height of the sediment sample used in the 

lab test; and 

t

50 = time for 50 percent of the sample to deform 

at a specific load.

The cv values were then used to determine t

field with the 

following equation from Das (2002): 

t

H

c field

field

v

=

1 781 2 . *

(8)

Hydraulic Investigations and Analysis

Hydraulic compatibility was investigated by comparing 

the hydraulic properties of the potential reactive mat materials with the native seep sediments. Hydraulic properties of 

the components of the reactive mat were determined in the 

laboratory and from previously reported values in the literature 

(Kassenga and others, 2003; Gillham and O’Hanessin, 1994). 

Flex-wall permeability tests of organic mixtures were conducted in a laboratory under 3 psi (pounds per square inch) of 

pressure at a specified saturated density of 78 lbs/ft3 (pounds 

per cubic foot).

A force balance was completed to assess the likelihood 

of fluidization of the reactive mat materials when placed in 

the field at the pilot test site. Using the approach outlined in 

Kassenga and others (2003) for constructed wetland systems, 

the effective stress from the saturated weight of the reactive 

mat materials was compared to the stress from the upward 

moving porewater in the wetland sediments to ensure that 

the gravitational forces of the reactive mat exceeded the pore 

pressure in the seep area. According to Kassenga and others 

(2003), with an effective stress equal to zero, a critical gradient (icr) can be calculated for the specific materials under a 

given pore pressure according to the following equation:

i

cr = (γsat– γw) / γw (9)

where

γsat = saturated unit weight of the mat materials; 

and

γw = unit weight of water.

Geochemistry and Water Quality

In the design phase, water-quality compatibility of the 

reactive mat was assessed by analyzing the potential for metal 

transport from the mat materials and surrounding wetland 

sediments. Both total metals and Sequential Extraction 

Procedure (SEP) analyses were performed on the reactive 

mat materials and wetland sediment samples to evaluate the 

potential release of metals into solution with geochemical 

changes, such as a change in the redox conditions or pH level. 

Although the mat was not designed for metals treatment, the 

design may alter metal solubility and may be engineered to 

treat metals by immobilizing them in low solubility, immobile, 

non-bioavailable phases.

SEP analysis separates metals in the soil into seven 

geochemical phases—an exchangeable phase that includes 

metal that is reversibly sorbed to soil minerals and six additional phases (from most to least bioavailable) that are known 

as carbonate, organic-bound, non-crystalline materials, metal 

hydroxide, acid/sulfide, and residual. These six phases quantify the amount of metal that either is irreversibly sorbed under 

ambient conditions, or exists as a separate mineral or immobile complex (Schultz and others, 1996; Brady and others, 

2003). 

SEP analyses were performed on three native wetland 

sediment samples from the seep 3-4W area and five organic 

mixes (mixes were comprised of 40/40/20 by volume compost, peat, and sand, respectively). The variable component 

of the mixes is the compost fraction, which included three 

dairy waste-derived composts (BionSoil, PayGro, and TLC), 

a crab-derived compost (Chesapeake Blue), and a leaf-derived 

compost (Leafgro).
14 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Performance Methods and Data 

Analysis

 Several different methods were used to collect samples 

for the reactive mat pilot test, some of which were designed by 

project personnel to solve unique technical problems presented 

by the design of the mat. The following sections describe the 

methods used to collect and analyze samples from the site to 

evaluate the performance of the reactive mat between October 

2004 and September 2005.

Groundwater Sampling

The groundwater sampling network was primarily within 

the area of seep 3-4W (figs. 1 and 5a,b; table 1) and consisted 

of Solinst 1.5-in.-diameter continuous multi-channel tubing 

(CMT) piezometers flushmounted beneath and around the 

perimeter of the reactive mat, drive-point piezometers installed 

around the entire seep area from both sides of the creek, 

mini-porewater samplers installed directly beneath the base of 

the reactive mat, and multi-level diffusion samplers set in the 

reactive mat. 

All piezometers and most sample names begin with the 

letters “PT,” designating that they are located at the “pilottest” area (tables 1 and 2). The name of the shallowest piezometer in a nest ends with the letter “A,” while the next deeper 

piezometer at the same site name ends in the letter “B,” and so 

forth.

Drive-Point Piezometers

Most drive-point piezometers (identified with the prefix 

PTZ) were installed to monitor only groundwater levels, 

although some piezometers were used for both water-quality 

sampling and groundwater levels. The shallow piezometers 

screened in the wetland sediments were installed either by 

pushing the casings in by hand or by using a slide hammer. 

Piezometers screened in the aquifer were installed using a 

portable vibracore drill rig mounted on floating pontoons. 

Most piezometers screened in the wetland sediments were 

constructed of 0.75-in. and 2-in. Schedule 40 PVC, whereas 

the piezometers screened in the aquifer were constructed of 

0.75-in.-diameter stainless steel.

For sampling, dedicated 0.25-in.-diameter Teflon tubing 

was inserted in each piezometer to the top of the screened 

interval. Approximately 1-ft sections of dedicated tygon peristaltic pump tubing were attached to the top of the Teflon tubing to use in peristaltic pumps. Each piezometer was pumped 

slowly. Field parameters (specific conductance, pH, and 

temperature) were measured at least twice, and the sample was 

collected after one casing volume of water was purged. This 

sampling technique was used to prevent drawing porewater 

from sediments in surrounding areas and temporarily changing flow characteristics of the seep. Some piezometers with 

low casing volumes or low recovery rates were sampled using 

dedicated 60-mL (milliliter) syringes connected to dedicated 

3-way luer-lock valves attached to the 0.25-in. tubing. 

Continuous Multi-Channel Tubing Piezometers

CMT piezometers (identified with the prefix PTC) were 

installed with a portable vibracore rig. These piezometers 

consisted of three to six channels, each with a screened interval and sand pack approximately 6 in. long, within the same 

borehole. Coated bentonite pellets were placed in a protective 

mesh to seal the annulus space between screened intervals. 

A temporary outer casing of 3-in.-diameter PVC with a PVC 

“knock-out point” on the bottom was advanced to the top 

of the aquifer or base of the wetland sediments and then the 

1.5-in.-diameter CMT assembly was inserted. The outer casing 

was immediately removed to prevent the bentonite from locking the casing in place. Expansion plugs designed specifically 

for the chambers were used to isolate the sample intervals.

Five of the CMT piezometers were installed within 

the footprint of the reactive mat prior to its construction. 

Immediately following sediment excavation and prior to construction of the reactive mat, the channels of each CMT were 

cut off below grade, and fitted with flow-through adaptors and 

elbows so that Teflon tubing could run horizontally underneath 

and beyond the reactive mat boundaries to allow for sampling. 

The horizontal tubing was required to avoid penetration of the 

two layers of geosynthetic fabric in the reactive mat. Eight 

additional CMT piezometers were installed around the perimeter of the mat (two on each side, fig. 5a).

As with the drive-point piezometers, dedicated 0.25-in.-

diameter Teflon tubing was installed in each sample chamber 

to reach the top of the 3-in.-long screened interval. Dedicated 

tygon tubing was attached to the Teflon tubing and attached 

to peristaltic pumps for sample collection. Each chamber was 

pumped slowly, field parameters were measured, and samples 

were collected after one casing volume of water was purged 

(included the lateral tubing volume). Some CMT piezometers 

with low casing volumes or low recovery rates were sampled 

using dedicated 60-mL syringes instead of peristaltic pumps.

Mini-Porewater Samplers

Nine mini-porewater samplers (identified with the prefix 

PTN, fig. 5b) were placed directly below the base of the 

reactive mat following sediment excavation. These samplers 

allowed the collection of water samples from the wetland 

sediments just below the bottom membrane of the reactive 

mat. Each sampler provided a discrete sampling point and was 

approximately 1 in. long, and 0.5 in. in diameter. The sampler 

consisted of a 0.25-in. screen placed inside a clean cotton bag 

that was filled with a clean sandpack. The screen was attached 

on the end of 0.25-in.-diameter Teflon tubing. The tubing ran 

horizontally for the length of and slightly beyond the reactive 

mat boundaries to allow access for sample collection.
Performance Methods and Data Analysis 15

Figure 5a. Seep 3-4W piezometer network, location of reactive mat, and lines of section D-D', E-E', Y-Y', and Z-Z' at pilot-test 

study area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland. (Refer to fig. 5b for rest of monitoring network.) WEST BRANCH CANAL CREEK

PTZ4A-C

PTZ3A,B

PTZ5A,B

PTZ9A,B

PTZ1A-D

PTZ8A,B

PTZ10A,B

PTZ11A,B

PTZ13A,B

PTZ12A,B

PTZ

2A-E

PTZ6A-C

PTC11A-E

PTC9A-E

PTC8A-E

PTC

1A-C

PTC

4A-C

PTC7A-D PTC6A-E

GT34W-5

GT34W-8

GT34W-14

PTC5A-C

PTC2A-C

PTC3A-C

PTC13A-C

PTC12A-B

PTC10A-E

PTZ7A,B

N

E

S

W

E

E'

D

Y

Z

Z'

Y'

D'

REACTIVE

MAT

WETLAND

WETLAND

Floating walkway

Floating walkway

Floating walkway

GT34W-14

0 5 10 FEET

0 1.5 3 METERS

EXPLANATION

SURFACE-WATER 

SAMPLER INTAKE

PTZ5A,B

PTC7A-D CONTINUOUS MULTI-CHANNEL TUBING

(CMT) PIEZOMETER AND IDENTIFIER

SEDIMENT SAMPLING LOCATION AND

IDENTIFIER

PIEZOMETER NEST FOR WATER-LEVEL

MEASUREMENT AND IDENTIFIER

REACTIVE MAT

WETLAND AREA

HIGHLY SATURATED AREA

Seep area

3-4W
16 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 5b. Location of multi-level diffusion samplers (PTBs) and mini-porewater samplers (PTNs) at the pilot-test study area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland.
Performance Methods and Data Analysis 17

Table 1. Piezometer and sampler screen depths from the seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen 

Proving Ground, Maryland.—Continued

[ft bls, feet below land surface; DS, diffusion sampler, Mini, mini-porewater sampler; PVC, polyvinyl chloride; PZ, piezometer; SS, stainless steel piezometer 

with inner Teflon tubing; CMT, continuous multi-channel tubing; ", inch]

Device identifier Device type Hydrogeologic unit Depth, screened interval (ft bls)

Multi-level diffusion samplers

[depths given are above (-) and below original land surface, and are the midpoints of a 0.33-foot-long screen]

PTB1B DS in mat -0.35

PTB1C DS in mat 0.01

PTB2B DS in mat -0.35

PTB2C DS in mat 0.01

PTB3B DS in mat -0.35

PTB3C DS in mat 0.01

PTB4A DS in mat -0.7

PTB4B DS in mat -0.35

PTB4C DS in mat 0.01

PTB5A DS in mat -0.7

PTB5B DS in mat -0.35

PTB5C DS in mat 0.01

PTB6B DS in mat -0.35

PTB6C DS in mat 0.01

PTB7A DS in mat -0.7

PTB7B DS in mat -0.35

PTB7C DS in mat 0.01

PTB8A DS in mat -0.7

PTB8B DS in mat -0.35

PTB8C DS in mat 0.01

PTB9B DS in mat -0.35

PTB9C DS in mat 0.01

Mini-porewater samplers

PTN1 Mini Wetland 1.0

PTN2 Mini Wetland 1.0

PTN3 Mini Wetland 1.0

PTN4 Mini Wetland 1.0

PTN5 Mini Wetland 1.0

PTN6 Mini Wetland 1.0

PTN7 Mini Wetland 1.0

PTN8 Mini Wetland 1.0

PTN9 Mini Wetland 1.0

Drive-point piezometers

PTZ1A 3/4" PVC PZ Wetland 3.5-4.5

PTZ1B 3/4" PVC PZ Aquifer 7.5-8.5

PTZ1C 3/4" SS PZ Aquifer 13-14

PTZ1D 3/4" SS PZ Aquifer 24.7-25.7

PTZ1E 3/4" SS PZ Aquifer 35-36

PTZ2A 3/4" PVC PZ Wetland 6-7
18 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Table 1. Piezometer and sampler screen depths from the seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen 

Proving Ground, Maryland.—Continued

[ft bls, feet below land surface; DS, diffusion sampler, Mini, mini-porewater sampler; PVC, polyvinyl chloride; PZ, piezometer; SS, stainless steel piezometer 

with inner Teflon tubing; CMT, continuous multi-channel tubing; ", inch]

Device identifier Device type Hydrogeologic unit Depth, screened interval (ft bls)

PTZ2B 3/4" PVC PZ Wetland 12-13

PTZ2C 3/4" SS PZ Aquifer 20-21

PTZ2D 3/4" SS PZ Aquifer 29.5-30.5

PTZ2E 3/4" SS PZ Aquifer 37.7-38.7

PTZ4A 2" PVC Wetland 6.5-7.5

PTZ4B 2" PVC Wetland 9-10

PTZ4C 2" PVC Aquifer 11.6-12.6

PTZ13A 2" PVC Wetland 5-6

PTZ13B 2" PVC Aquifer 14-15

PTZ14A 2" PVC Wetland 4.3-5.3

Continuous multi-channel tubing piezometers [modified, under mat]

PTC1A CMT Wetland 4.8-5.2

PTC1B CMT Wetland 7.8-8.2

PTC1C CMT Aquifer 11.3-11.5

PTC2A CMT Wetland 4.8-5.2

PTC2B CMT Wetland 7.8-8.2

PTC2C CMT Aquifer 11.8-12.0

PTC3A CMT Wetland 4.4-4.8

PTC3B CMT Wetland 7.4-7.8

PTC3C CMT Aquifer 13.1-13.3

PTC4A CMT Wetland 4.8-5.2

PTC4B CMT Wetland 7.8-8.2

PTC4C CMT Aquifer 11.8-12.0

PTC5A CMT Wetland 4.8-5.2

PTC5B CMT Wetland 7.8-8.3

PTC5C CMT Aquifer 11.8-12.0

Continuous multi-channel tubing piezometers [outside mat]

PTC6A CMT Wetland 2.8-3.2

PTC6B CMT Wetland 4.8-5.2

PTC6C CMT Wetland 7.8-8.2

PTC6D CMT Wetland 9.8-10.2

PTC6E CMT Aquifer 11.8-12.0

PTC7A CMT Wetland 2.8-3.2

PTC7B CMT Wetland 4.8-5.2

PTC7C CMT Wetland 7.8-8.2

PTC7D CMT Wetland 10.3-10.5

PTC8A CMT Wetland 2.8-3.2

PTC8B CMT Wetland 4.8-5.2

PTC8C CMT Wetland 7.8-8.2

PTC8D CMT Wetland 9.8-10.2

PTC8E CMT Aquifer 11.8-12.0
Performance Methods and Data Analysis 19

Each PTN device was purged and sampled with a 

dedicated 60-mL plastic syringe, fitted with a 3-way stopcock 

and tubing that extended to the top of the screen. This allowed 

samples to be collected slowly without aerating the sample. 

As with the piezometers, only one casing volume (including 

lateral tubing volume) was removed before collecting the 

samples.

Multi-Level Diffusion Samplers

Multi-level diffusion samplers (identified with the prefix 

PTB) were constructed to characterize the in-mat porewater at 

up to three depths above the middle geotextile membrane. The 

samplers consisted of two to three 4-in.-long, 1-in.-diameter 

PVC screens with 0.010-in. slots stacked together with internal 

plugs to isolate each screen (figs. 6a-c). The samplers were 

placed at nine locations within the top section of the reactive 

mat to the maximum depth of the geosynthetic fabric 

(generally up to 1 ft deep) and directly above the locations of 

the PTN samplers (fig. 5b).

The number of screens in the PTB samplers was determined by the thickness of the upper section of the reactive 

mat. Initially, three sections of the samplers were used. The 

sampler locations were labeled PTB1 through PTB9, with the 

top section designated “A,” the middle designated “B,” and 

the bottom designated “C” (for example, PTB1C). Following 

initial settlement of the reactive mat, the “A” screen was no 

longer used because the sample would have been exposed 

to air and surface water above land surface. The remaining 

screens were designated “B” and “C” levels since the orientation to the middle geosynthetic fabric did not change after 

settlement of the reactive mat.

Table 1. Piezometer and sampler screen depths from the seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen 

Proving Ground, Maryland.—Continued

[ft bls, feet below land surface; DS, diffusion sampler, Mini, mini-porewater sampler; PVC, polyvinyl chloride; PZ, piezometer; SS, stainless steel piezometer 

with inner Teflon tubing; CMT, continuous multi-channel tubing; ", inch]

Device identifier Device type Hydrogeologic unit Depth, screened interval (ft bls)

Continuous multi-channel tubing piezometers [outside mat—Continued]

PTC9A CMT Wetland 2.8-3.2

PTC9B CMT Wetland 4.8-5.2

PTC9D CMT Wetland 9.8-10.2

PTC9E CMT Aquifer 12.1-12.3

PTC10A CMT Wetland 2.4-2.8

PTC10B CMT Wetland 4.4-4.8

PTC10C CMT Wetland 7.4-7.8

PTC10D CMT Wetland 9.4-9.8

PTC10E CMT Aquifer 12.6-12.8

PTC11A CMT Wetland 1.8-2.2

PTC11B CMT Wetland 4.8-5.2

PTC11C CMT Wetland 7.8-8.2

PTC11D CMT Wetland 9.8-10.2

PTC11E CMT Wetland 11.8-12.2

PTC11F CMT Aquifer 14-14.2

PTC12A CMT Wetland 2.8-3.2

PTC12B CMT Wetland 4.8-5.2

PTC12C CMT Wetland 7.8-8.2

PTC12D CMT Wetland 9.8-10.2

PTC12E CMT Aquifer 11.8-12.2

PTC12F CMT Aquifer 15.2-15.4

PTC13A CMT Wetland 2.8-3.2

PTC13B CMT Wetland 4.8-5.2

PTC13C CMT Wetland 7.8-8.2

PTC13D CMT Wetland 9.8-10.2
20 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Generally, the PTB samplers were first deployed with 

sample vials for VOC and hydrogen analysis, allowed to equilibrate for 2 weeks before sample retrieval, and then deployed 

again with vials for analysis of redox constituents (methane, 

iron, sulfide, and ammonia). Each time one set of samplers 

was removed, the alternate group of samplers was set in place 

and allowed to equilibrate until the next sampling round. For 

VOC and hydrogen samples, respectively, 8- and 6-mL vials 

were filled with deionized water and covered with porous 

polyethylene (secured with viton o-rings) that was previously 

used in passive diffusion samplers throughout the West Branch 

Canal Creek study area (Spencer and others, 2002). For redox 

constituents, a 20-mL glass vial was filled with deionized 

water and covered with a 0.2-micron filter paper (HT Tuffryn) 

that was used previously for diffusion samplers called “peepers” (Lorah and others, 1997; Spencer and others, 2002). All 

samplers were submerged in deionized water for at least 24 

hours, bubbled with nitrogen overnight prior to installation, 

and again purged for at least a half hour in the field prior to 

placement to displace dissolved oxygen from the sample vials.

Surface-Water Sampling

Surface-water samples for both inorganic and organic 

analyses were collected using automated samplers approximately monthly during the performance evaluation (table 2). 

An ISCO model 3700 autosampler was used to collect surface 

water for inorganic analyses every 4 hours for 48 hours during 

each sampling event. A refrigerated autosampler (ISCO model 

6100) was used to collect VOC samples every 2 hours for 48 

hours. Each sampler unit was staged on the floating walkways 

near the southeast edge of the seep area during sample collection. Intake screens for the two autosamplers were placed 

together along the west bank of the creek near the southeast 

edge of the reactive mat, where the intakes remained below 

the water surface under most tidal conditions (figs. 5a,b). The 

placement of the intake screens was designed to collect water 

from the creek near the discharge from the reactive mat area, 

and was not designed to collect samples from a representative 

cross section of the creek.

Groundwater and Surface-Water Analysis

Groundwater samples were analyzed for field parameters (specific conductance, pH, and temperature), alkalinity, 

redox-sensitive constituents, nutrients, major inorganic 

constituents and trace metals, and VOCs (Appendixes 1–3). 

Redox constituents and nutrients analyzed for most groundwater samples included ferrous iron, methane, sulfide, ammonia, 

phosphate, and nitrate. Phosphate and nitrate were generally 

not analyzed in low-volume samples such as those collected 

with the PTB diffusion samplers. Unfiltered samples were 

collected for sulfide, ammonia, phosphate, and nitrate analysis 

in the field immediately after collection (Majcher and others, 

2007). Methane and iron samples (0.2-micron filtered) were 

preserved in the field and analyzed in the USGS MarylandDelaware-D.C. Water Science Center (MD-DE-DC WSC) 

research laboratory (Majcher and others, 2007). Groundwater 

Table 2. Groundwater and surface-water sampling at the seep 3-4W reactive mat pilot test area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, August 2004–September 2005. 

[VOC, volatile organic compound; redox, oxidation-reduction constituents; CMT, continuous multi-channel tubing] 

Sample type Sampling dates

Groundwater samples

Multi-level diffusion VOC or redox samples 

(PTB)

November and December 2004

January, March, May, June, August, September 2005

Mini-porewater VOC samples 

(PTN)

August-September, November 2004 

March, May, June, August, September 2005

CMT and drive-point piezometer VOC samples 

(PTC and PTZ) 

August-September, November 2004,

March, May, June, August, September 2005

CMT and drive-point piezometer inorganic samples 

(PTC and PTZ)

August 2004 

March, August 2005

Creek-channel passive diffusion samplers 

(PDS) April 2005

Continuous surface-water samples

Inorganic samples 

(PTV)

2004: August 21–22, October 25–27, December 2–3 

2005: February 8–10, March 30–April 1, June 14–15, August 2–4

Organic samples 

(PTV)

2004: August 25–27, October 25–27, November 11–12, November 30–December 2 

2005: January 11–13, February 8–10, March 30–April 1, June 14–16, August 2–4
Performance Methods and Data Analysis 21

and surface-water samples also were analyzed for VOCs at the 

USGS MD-DE-DC WSC research laboratory using a purgeand-trap capillary gas chromatograph with a mass-selective 

detector (GC/MSD) (Majcher and others, 2007). 

Appendix 4 gives quality-assurance data for the VOC and 

methane analyses conducted in the USGS MD-DE-DC WSC 

research laboratory.

The USGS National Water-Quality Laboratory performed 

the inorganic and trace metal analyses of groundwater and 

surface-water samples using methods detailed in Fishman 

(1993) and Fishman and Friedman (1989). In-mat samples 

were analyzed for hydrogen by SiREM Laboratory (Guelph, 

Ontario). Hydrogen samples were capped with Viton septa 

upon removal from the multi-level passive diffusion sampler 

and shipped on ice for analysis (Geosyntec Consultants, Inc., 

2007).

Reactive Mat Matrix Sampling and Analysis

During the November 2004 and March 2005 sampling 

events, small samples of the reactive mat matrix were collected for microbial activity testing. A small, stainless steel 

scoopula was used to scrape the mat matrix from the inside 

wall formed by the recovery of the PTB7 multi-level diffusion 

sampler. These samples were placed into a nitrogen-purged 

40-mL VOC vial and shipped immediately to the USGS 

microbiology laboratory (Reston, Virginia). Sediment samples 

were collected soon after installation and following the winter 

months to assess the viability of the dechlorinating abilities 

of WBC-2 in the mat matrix. WBC-2 activity was tested by 

placing the sediment in anaerobic culture media, amending 

with TeCA, and measuring its degradation along with the 

production and degradation of daughter products over time, as 

described for previous activity tests with WBC-2 (Jones and 

others, 2006).

Determination of Hydraulic and Geotechnical 

Compatibility

During the performance monitoring, the hydraulic and 

geotechnical compatibility of the reactive mat was assessed 

by observing the pilot test area for generation of new seep 

areas around the mat, measurement of hydraulic gradients and 

groundwater-flow rates, and monitoring of the settlement rate 

of the reactive mat. In February 2005, the USGS conducted 

a high resolution, low altitude (100 to 200 ft), aerial thermal 

infrared (TIR) survey of the pilot test area to compare to predeployment images from 2002–04 and determine whether seep 

areas were generated around the mat. Methods used during the 

2002–04 flights were described in Majcher and others (2007) 

and were also used during 2005. Following TIR observation 

of the pilot test area, 30 polyethylene bag passive diffusion 

samplers (Vroblesky, 2001) were installed in the creek channel 

for one-time measurements in April 2005 to determine VOC 

concentrations in shallow groundwater in and around the 

Figure 6. Multi-level diffusion samplers (PTBs) in the 

reactive mat (A) construction, (B) assembly, and (C)

deployment at seep 3-4W, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland. (Photographs by 

Mastin Mount, U.S. Geological Survey.)
22 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

pilot test area. This method was used successfully during the 

investigation by Majcher and others (2007) to locate areas of 

preferential flow.

Groundwater-level monitoring was performed using 

both continuous and synoptic methods to evaluate changes 

in hydraulic head surrounding the reactive mat. Continuous 

water-level data were collected using 0.375-in.-diameter 

Druck pressure transducers in up to 12 piezometers (fig. 5a). 

Data were recorded in 1-hr (hour) intervals by Campbell 

Scientific CR10x data loggers. Synoptic groundwater levels 

were measured in up to 37 piezometers in the pilot test area 

(fig. 5a). Synoptic groundwater levels were collected 11 times 

between August 2004 and September 2005. Five of the 11 

synoptic measurements included measurements on the same 

day at both high and low tide. Measurements were taken using 

steel tapes with chalk applied to the tape to indicate the water 

levels.

The difference in hydraulic head between shallow 

groundwater and surface water was measured at several locations in the seep area and within the reactive mat (at PTB5) by 

use of a potentiomanometer to quantify the pressure gradient 

between the interstitial water in the shallow sediments and 

the constantly changing tidal fluctuations. The instrument 

was used by placing one screen in the creek channel and 

one screen in the shallow wetland sediments or reactive mat 

matrix. Suction was placed on both screens to draw the water 

from each into a chamber where the difference between both 

levels could be compared. The chamber is described in detail 

by Winter and others (1988). Comparisons between the two 

levels were recorded over times ranging from 2.5 to 4.5 hours 

as tides were changing.

Seepage meters were deployed at up to six seep locations 

over multiple days at different stages of the tidal cycle. 

Seepage meters were placed at various locations inside and 

outside the mat boundary during July-August 2005 to compare 

groundwater discharge rates in and around the reactive mat. 

Each seepage meter used during this investigation was made 

from the closed-end section of a 55-gallon steel drum that was 

inserted open-end down into the sediment, as described in 

Majcher and others (2007).

Seepage flux was estimated from the seepage meters by 

use of equation 10:

qv = Q / A (10)

v = qv / n (11)

where

qv = seepage flux (or specific discharge);

Q = the volume of seepage into or from the 

meter bag divided by the time interval; 

A = the cross-sectional area of the meter;

v = interstitial velocity; and 

n = effective porosity.

Seepage was considered to be positive for groundwater 

discharge and negative in cases where surface water flowed to 

groundwater. 

Settlement of the reactive mat and underlying sediments 

was measured and compared to the settlement estimated during the design phase. The amount of settlement was determined by periodically surveying the elevation of the top of 

the mat at the same 111 locations along 2 diagonal (southwest 

to northeast, and southeast to northwest), 3 east-west, and 3 

north-south transects. Elevations were surveyed on the day 

that the mat installation was completed on October 8, 2004, 

and during November 2004, and January, March, June, and 

July 2005. 

Design of a Reactive Mat for Enhanced 

Bioremediation

The design of the reactive mat specific to seep 3-4W is 

described in this section; however, the approach and application of the design procedures would generally be applicable to 

other groundwater/surface-water interface applications. Effects 

such as the influence of tidal energy and fluctuations, seasonal 

changes in microbial activity, and variable hydraulic discharge 

rates could not be simulated in the laboratory, and were tested 

in the field during the pilot-scale technology demonstration. 

Laboratory-derived design parameters related to geotechnical, 

hydraulic, and water-quality characteristics were verified during the field pilot test. In this section, the two major design 

components—consideration of degradation efficiency and 

wetland compatibility—also are discussed.

Degradation Efficiency

The primary objective of the reactive mat pilot test 

design was to optimize degradation efficiency of the mixed 

chlorinated VOCs within the mat at seep 3-4W through the 

selection of sustainable reactive materials, electron donors, 

and a method for bioaugmentation with WBC-2. Degradation 

rates from previous laboratory investigations, including 

flow-through column experiments (Lorah and others, 2008; 

Geosyntec Consultants, Inc., 2007), were used to estimate 

the reactive materials thickness required to achieve a mass 

removal goal of at least 90 percent for total mixed chlorinated 

VOCs.

The reactive mat was designed with two reactive zones—

a lower (hereafter referred to as ZVI-organic) zone, designed 

to enhance abiotic and biotic degradation of chlorinated 

methanes, and an upper (hereafter referred to as organic) 

zone, designed to enhance biodegradation of the remaining 

chlorinated methanes, ethanes, and ethenes. Although use of 

the organic matrix alone resulted in effective dechlorination 

in the laboratory tests, this dual-zoned approach was used in 
Design of a Reactive Mat for Enhanced Bioremediation 23

the mat design for seep 3-4W for several reasons. In the field, 

shallow porewater at the site would immediately be exposed to 

high concentrations of chloroemethanes (CT and CF), whereas 

chloroemethane concentrations were gradually increased in 

the column experiments for the reactive mat (Majcher and 

others, 2007; Lorah and others, 2008). Inclusion of ZVI also 

could provide a safeguard against any possible temperaturedependent rate reduction over the winter months. Therefore, 

the selected design for the pilot test included a lower zone 

comprised of a mixture of ZVI filings combined with the 

organic matrix. The upper zone was comprised of the organic 

matrix bioagumented with WBC-2. 

The selected organic matrix was a combination of commercially available compost, reed sedge peat, and sand. Of a 

variety of composts tested (Lorah and others, 2008), a crab 

compost (Chesapeake Blue) was selected for use in the pilot 

test at seep 3-4W because of the material’s consistency and the 

minimal transportation cost from the nearby supplier.

On the basis of its successful use in batch tests 

(Geosyntec Consultants, Inc., 2007), chitin (supplied by JRW 

Bioremediation, Lenexa, KS) was selected as a long-term electron donor to be included in the mat materials. Commercially 

available irrigation drip-tubing was incorporated into the 

design as five laterals between the two zones of the reactive 

mat, through which lactate or other liquid amendments could 

be injected if necessary. 

Because laboratory tests showed that WBC-2 had a high 

tolerance to oxygen exposure, direct application of WBC-2 

from anaerobic culture vessels was determined to be appropriate to inoculate the reactive matrix using a standard garden 

sprayer hose attachment (Geosyntec Consultants, Inc., 2007). 

A specified volume of 24 L was sprayed based on a calibrated 

rate of application. Although previous bioaugmentation pilot 

tests conducted in aquifers (Ellis and others, 2000; Major and 

others, 2002) were used to provide some guidance for the 

quantity of mixed culture to add to in the field, volume adjustments were made since WBC-2 was not added to groundwater 

as in those demonstrations, but rather to an unsaturated, solid 

matrix over a wider area. The volume of WBC-2 added was 

0.5 percent of the total material volume (plus a contingency 

volume of 20 percent), or approximately 24 L of culture. 

 On the basis of model results using input values summarized in table 3, the mass removal of chlorinated ethenes and 

ethanes was predicted to be near 90 percent, with degradation 

occurring in both the ZVI-organic and organic zones from 

total reactive mat thicknesses ranging from 1 to 2 ft 

(fig. 7). The mass removal of the chlorinated methanes is more 

difficult to predict because of multiple degradation pathways, 

but is estimated to be greater than 80 percent when the total 

thicknesses ranged from 1.5 to 2 ft. Sustained mass removal 

efficiency occurred for at least 8 months in the column 

experiments. Sustainment in the field would be correlated to 

methanogenic conditions in the reactive mat matrix, and the 

ability of WBC-2 to maintain activity under changing 

environmental conditions.

Consideration of Compatibility With the Wetland 

System

In addition to VOC mass removal, compatibility of the 

reactive mat with its surroundings was considered in the 

design. Results of investigations and design calculations for 

geotechnical, hydraulic, and water-quality considerations are 

presented in this section and are discussed relevant to the mass 

removal goals presented in the previous section. A summary of 

the site-specific design for seep 3-4W also is presented. 

Bearing Capacity and Settlement

As part of the reactive mat design, geotechnical compatibility of the reactive mat with the native wetland was 

considered by evaluating the bearing capacity and settlement 

of the native sediments, and identifying criteria for a suitable 

geotextile to reinforce and separate the mat from the native 

sediments. Bearing capacity of the sediments was calculated 

(equation 2) for a range in saturated unit weights of the anticipated matrix materials that should yield the desired VOC mass 

removal. A factor of safety of three was applied to the allowable load (qa ) estimate. The saturated unit weight of the native 

sediment was assumed to be 76 lbs/ft3 on the basis of physical 

property analysis of sediments reported in Majcher and others 

(2007). Tolerable thickness values for the reactive mat ranged 

from 0.93 ft to 5.3 ft (table 4), based on a 60/40 ZVI-organic/

organic zone ratio, by volume. In these calculations, equal 

thicknesses were assumed for the ZVI-organic and organic 

zone. The minimum tolerable thickness values (0.93, 1.60 ft) 

were estimated using a Cu from the uppermost zone of both 

CPT locations within seep 3-4W. The thickness of the mat 

based on VOC mass removal goals exceeded the lower end of 

the minimum thickness range. To minimize bearing capacity 

issues and the height of the mat above the original land surface, some excavation of surface sediments was incorporated 

into the design. 

Field- and laboratory-determined shear strength results 

and other physical properties from West Branch Canal Creek 

sediments were compared to published results of installed, in 

situ sand caps on soft sediments (table 5). Physical properties 

of the West Branch Canal Creek sediments (such as Atterberg 

limits and water content) were within the range of other 

reported sediments on which in situ sand caps were placed, 

although the undrained shear strength values at West Branch 

Canal Creek are in the upper range of those reported for sediments elsewhere (table 5). The resulting tolerable thickness 

values calculated for the Canal Creek sediments are within the 

range of those reported as successful in situ caps.

Load-induced primary settlement and time to settlement 

of native sediments underlying the proposed reactive mat 

area within seep area 3-4W were calculated from results of 

laboratory one-dimensional consolidation tests. Samples 

from cores at seep 3-4W revealed that σ’vo< σ’p (after σ’vo

was calculated from equation 5) indicating that samples were 
24 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD Table 3. BioChlor1 input values for chloromethane, chloroethane, and chloroethene degradation in a model reactive mat. [ZVI, zero valent iron; ft/yr, feet per year; ft/ft, foot per foot; g/cm3, grams per cubic centimeter; CT, carbon tetrachloride; CF, chloroform; MeCl, methylene chloride; Koc, organic carbon partitioning coef- ficient; yr, year; ft, feet; mg/L, milligrams per liter; TeCA, 1,1,2,2-tetrachloroethane; PCE, tetrachloroethene; TCE, trichloroethene; DCE, 1,2-dichloroethene; VC, vinyl chloride; -- no data] Zone 2–2 ZVI-organic mix Seepage velocity (ft/yr) Hydraulic gradient (ft/ft) Porosity Bulk density (g/cm3

)

Fraction 

organic 

carbon

CT 

K

oc

CF 

K

oc

MeCl 

K

oc

CT to 

CF 

(yr-1)

CF to 

MeCl 

(yr-1)

Methanes 63.2 0.25 0.5 1.3 0.055 174 40 -- 999 124

Zone 2–

ZVI-organic 

mix 

Simulation 

time 

(yr)

Model 

width 

(ft)

Model 

length 

(ft)

Zone 2 

length 

(ft)

Source 

thickness 

(ft)

Source 

width 

(ft)

Input 

CT 

(mg/L)

Input 

CF 

(mg/L)

Input 

MeCl 

(mg/L)

Methanes 0.2 12 1 1 1 12 12 14 0

Zone 1–

organic mix

Seepage 

velocity 

(ft/yr)

Hydraulic 

gradient 

(ft/ft)

Porosity 

Bulk 

density 

(g/cm3

)

Fraction 

organic 

carbon

TeCA 

K

oc

DCE 

K

oc

VC 

K

oc

Ethene 

K

oc

TeCA to 

DCE 

(yr-1)

PCE to 

TCE 

(yr-1)

TCE to 

DCE 

(yr-1)

DCE to 

VC 

(yr-1)

VC to 

Ethene 

(yr-1)

CF to 

MeCl 

(yr-1)

MeCl 

(yr-1)

Ethanes 77.6 0.2 0.5 0.55 0.055 79 125 30 302 700.8 -- -- 307 204 -- --Ethenes 77.6 0.2 0.5 0.55 0.055 79 125 30 302 -- 606 885 306 204 -- --

Methanes 77.6 0.2 0.5 1.25 0.055 -- -- -- -- -- -- -- -- -- 150 205

Zone 1–

organic mix

Simulation 

time (yr)

Model 

width 

(ft)

Model 

length 

(ft)

Zone 1 

length 

(ft)

Source 

thickness 

(ft)

Source 

width 

(ft)

Input 

TeCA 

(mg/L)

Input 

PCE 

(mg/L)

Input 

TCE 

(mg/L)

Input 

DCE 

(mg/L)

Input 

CF 

(mg/L)

Input 

MeCl 

(mg/L)

Ethanes 0.3 12 1.5 1.5 12 12 0.1 -- -- 0.7 -- --Ethenes 1 12 1 1.7 12 12 -- 3 1 0.7 -- --

Methanes 1 12 1 0.8 12 12 -- -- -- -- 6.46

1 U.S. Environmental Protection Agency, 2002.2 Zone 2 is the lower of the two zones.
Design of a Reactive Mat for Enhanced Bioremediation 25

overconsolidated. On the basis of these results, field virgin (or 

corrected) consolidation curves were constructed for the overconsolidated sediment and used for subsequent calculations.

The magnitude of settlement was calculated from the 

laboratory odeometer tests based on load intervals equal to 

twice the reactive mat load (factor of safety of 2) determined 

in the bearing capacity calculations and a thickness range of 

2 to 3 ft. Since percent total organic carbon in the wetland 

sediments was negatively correlated with depth bls (Majcher 

and others, 2007), two representative one-dimensional consolidation test results from different depths were used for the 

settlement calculations. The field virgin curves (developed on 

the basis of overconsolidation of sediments) consistently gave 

lower values of settlement ranging from 0.12 to 0.37 ft (equation 6). Calculations using the lab curve predicted settlement 

of 0.97 to 1.4 ft.

A range in time of primary settlement was calculated 

by estimating an appropriate coefficient of consolidation 

(cv ) using laboratory and empirical methods. The range of 

cv values estimated by the laboratory from time-deformation 

readings at loads greater than the anticipated load from the 

reactive mat was 0.01 to 0.03 ft2/d (square feet per day). These 

laboratory estimates of cv were compared to values determined 

from empirical relations between cv and liquid limit (Naval 

Facilities Engineering Command, 1986) and cv and organic silt 

(Holtz and Kovacs, 1981), respectively, which give cv values 

ranging from 0.016 to 0.017 ft2/d and 0.018 to 0.088 ft2/d. 

Using the median cv value of 0.017 ft2/d and equation 8, the 

calculated time for settlement was 1.5 years within the upper 

5 ft of wetland sediment.

In order to provide filtration, separate the native sediment 

from the two reactive zones, and account for an overestimate 

of shear strength, a geotextile material was included at the 

base of the reactive mat (fig. 8). Hydraulic properties considered in filtration design were porosity (ratio of void volume 

to total fabric volume), apparent opening size (AOS) or the 

sieve size restricted by the fabric, and cross-plane permeability 

(flow through the fabric). The porosity and permeability of the 

geotextile needed to be greater than the porosity of the native 

sediment and the reactive matrices to avoid any impediment 

to flow. More than 50 percent of the site sediment passed 

through the No. 200 sieve, and since the wetland sediment 

is predominantly clay and silt, a No. 70 AOS was selected 

(Koerner, 1998), combined with a fabric porosity greater than 

the porosity of the native sediment (estimated to be 0.4 based 

on the void ratio). Finally, to prevent any impediment of the 

seepage flow, the permeability of the fabric was selected to be 

greater than the maximum vertical hydraulic conductivity at 

seep 3-4W, which was calculated to be 0.34 ft/d, or feet per 

day (1.2x10-4 cm/s, or centimeters per second) (Majcher and 

others, 2007). The sediment and matrix properties indicated 

that the selection of a nonwoven, polypropylene geotextile 

(GSE Inc., Houston, TX) was adequate for the site-specific 

application (see following Hydraulic Design section). When 

installed, the nonwoven geotextile material was keyed into the 

surrounding sediment to anchor it in place during installation.

Figure 7. Concentrations of major chlorinated volatile organic compounds predicted by BioChlor (U.S. Environmental Protection 

Agency, 2002) in a simulated reactive mat (A) chlorinated ethenes and ethanes [tetrachloroethene (PCE), trichloroethene (TCE), 

1,1,2,2-tetrachloroethane (TeCA), 1,2-dichloroethene (DCE), and vinyl chloride (VC)], and (B) chlorinated methanes [carbon tetrachloride 

(CT), chloroform (CF), and methylene chloride (MeCl)].
26 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Table 4. Calculated reactive mat tolerable thicknesses based on laboratory and field-determined unconfined shear strength of 

wetland sediments at seep 3-4W, West Branch Canal Creek, Aberdeen Proving Ground, Maryland.

[CPT, cone penetrometer; Cu, unconfined shear strength; Df, foundation depth below land surface; γ, unit weight; qu, ultimate bearing capacity; qa, allowable 

bearing capacity; lbs/ft2, pounds per square foot; ft, feet; lbs/ft3, pounds per cubic foot] 

Location Cu

(lbs/ft2)

Df

(ft)

Sediment γ

(lbs/ft3)

qu

(lbs/ft2)

Factor of 

safety

qa

(lbs/ft2)

Reactive 

Mat γ

(lbs/ft3)

Tolerable

thickness 

(ft) 

North core – 

Laboratory 

140 1 76 768 3 256 98 2.61

South core – 

Laboratory 

300 1 76 1,558 3 519 98 5.30

North CPT, 

average

240 1 76 1,262 3 421 98 4.29

North CPT, 

minimum 

40 1 76 274 3 91 98 0.93

South CPT, 

average

200 1 76 1,064 3 355 98 3.62

South CPT, 

minimum 

80 1 76 471 3 157 98 1.60

Table 5. Sediment properties from reported successful in situ capping projects and wetland sediments at seep 3-4W, West Branch 

Canal Creek, Aberdeen Proving Ground, Maryland.

[LL, liquid limit; PI, plasticity index; lbs/ft2, pounds per square foot; %, percent, CPT, cone penetrometer; >, greater than; <, less than; NR, not reported; 

ND, not determined; NA, not applicable; APG, Aberdeen Proving Ground]

Location 

Atterberg limits Undrained 

shear strength 

(lbs/ft2)

Water

content 

(%)

Cap thickness 

(ft) 

LL PI (sand size)

KPC Ward Cove sediment remediation, 

Alaska

NR NR 3-100 415 (average) 0.5-1 (fine) 

Dredge material placement, Los Angeles 

harbor

53-76 22-41 7.5-13 140-183 2.5-3

Cap material placement, Los Angeles 

harbor

38-51 7-20 5-22 98-134 5 (medium) 

Matsushima Bay, Japan 160-175 115-130 5-35 200-375 1 (fine) 

Soda Lake Capping, Wyoming 91-155 > 50 < 280 161-455 3 (medium) 

Hiroshima Bay, Japan 60-75 22-38 20-85 80-100 1-1.6 

SLRIDT, Duluth, Minnesota 48-96 9-54 15-300 36-284 3 (medium) 

Lake Biwa, Japan 70-135 40-70 20-190 95-150 0.7 (medium) 

G-P Log Pond, Washington 65-170 36-79 65-277 97-175 0.5-0.7 (medium) 

West Waterway, Seattle, Washington 73 (average) 39 (average) NR 91 (average) 2

3-4W North core, APG (Laboratory) 72-81 27-40 140 138-308 NA

 (CPT) NA NA 40-500 NA NA

3-4W South core, APG (Laboratory) 53-77 24-38 300 129-373 NA

WB35, APG (Laboratory) 48-86 22-34 ND 200-230 NA

(modified from Palermo and others, 1998) 
Design of a Reactive Mat for Enhanced Bioremediation 27

Hydraulic Design 

Hydraulic properties of the components of the reactive 

matrix were measured in the laboratory permeability tests and 

from previously reported values in the literature; conductivity 

values of a similar compost-peat-sand mixture ranged from 

0.37 to 0.85 ft/d (1.3x10-4 to 3x10-4 cm/s) at a saturated density of 78 lbs/ft3

 (1.25 g/cm3, or grams per cubic centimeter) 

(Kassenga and others, 2003). Similarly, laboratory results from 

two composts were near the range reported in the literature 

(0.57 to 1.13 ft/d). Given this range of vertical conductivity 

values, an average organic matrix vertical hydraulic conductivity of 0.57 ft/d (2x10-4 cm/s) was conservatively estimated. 

The conductivity of a 100-percent ZVI zone using the -8/50 

mesh size was estimated to be 1,700 ft/d (0.6 cm/s), using 

particle size data analysis (Majcher and others, 2007). In combination with the 40/40/20 organic mixture, hydraulic conductivity increased when compared to the mixture alone, even at a 

low volumetric proportion (such as 20 percent), as confirmed 

with laboratory estimates. In general, at a saturated density 

greater than that of water, 62 lbs/ft3, all materials used in the 

reactive mat matrix have a hydraulic conductivity greater than 

the surrounding sediments reported previously for the seep 

area (Majcher and others, 2007). 

A force balance was completed to assess the likelihood 

of fluidization of the reactive mat materials when placed in 

the field, under artesian conditions at the seep site. Using the 

approach outlined in Kassenga and others (2003) for constructed wetland systems, the effective stress from the saturated weight of the reactive mat materials was compared to 

the stress from the upward moving porewater in the wetland 

sediments. From this pressure balance, a critical gradient and 

resulting critical flow were estimated above which fluidization 

of the reactive mat materials may occur. Due to the high saturated density of the ZVI zone, only the organic mixture zone 

was used to assess fluidization. The calculated critical gradient 

Figure 8. Reactive mat schematic for seep 3-4W, West Branch Canal Creek, Aberdeen Proving 

Ground, Maryland (A) cross-sectional view, and (B) plan view.
28 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

of 0.3 ft/ft (feet per foot) was in the range of the maximum 

vertical hydraulic gradients measured at seep 3-4W. Using the 

average vertical hydraulic conductivity of the organic mix, the 

critical flow (0.18 ft/d) was estimated near the measured maximum seepage velocity (Majcher and others, 2007). Therefore, 

using a factor of safety of 2, with the measured seepage 

velocity from the site equal to the critical flow, an optimized 

saturated density of materials was estimated. A mixture of 1.5 

parts compost, 1.5 parts peat, and 1 part sand (37.5/37.5/25 by 

volume) achieved the required increase in saturated density.

This optimized mixture was conservative in that it 

assumed all seepage velocity in the pilot test area exceeded the 

critical flow of the materials. Majcher and others (2007), however, reported that seepage actually varied spatially within the 

boundaries of the pilot test area and therefore, only the maximum was used in the fluidization estimate. The high transmissivity (or inter-planar flow) of the nonwoven geotextile that 

was selected for installation between the ZVI zone and the 

organic zone was expected to normalize flow conditions in the 

treatment area. For ease of installation, the same nonwoven 

geotextile material selected for the base filtration was used.

The strong, vertical hydraulic gradients and increased 

vertical hydraulic conductivity in the seep sediments at 3-4W 

result in artesian conditions at the pilot test area. The hydraulic gradient (or overall change in head) in the regional area 

is a result of the recharge in the upland area (pressure head) 

and overall elevation differences between the uplands and the 

wetlands (elevation head) as described by Bernoulli’s equation. At seep 3-4W, this gradient is strongly upward (Majcher 

and others, 2007). The addition of materials to a maximum of 

10 in. above the current wetland surface elevation is a minimal 

change in the overall regional flowpath and is only an addition 

of approximately 5 percent of the overall thickness to the local 

wetland sediments; therefore, this addition was not anticipated 

to impact the gradient. On the local scale, the static water level 

height (pressure head) in piezometers screened in the wetland 

and aquifer sediments along the perimeter of the pilot test area 

was 1 to 3 ft above the baseline wetland surface elevation. 

These pressure heads appeared to be adequate to maintain 

upward flow through the reactive mat.

Given the estimated hydraulic properties of the reactive 

mat matrix materials and the hydraulic gradient at the site, a 

hydraulic residence time (HRT) within the reactive mat was 

estimated for various reactive mat thicknesses, hydraulic 

gradients, and effective porosities. A higher hydraulic conductivity than that of natural sediments combined with the natural 

vertical gradient would promote flow into the porespace of 

the reactive zones of the reactive mat, according to Darcy’s 

Law. For a 22-in.-thick reactive mat, with an effective porosity 

between 0.4 and 0.6 and a vertical hydraulic gradient of 0.3, 

the HRT within the reactive mat was predicted to range from 

approximately 8 to 14 days, assuming a predominantly vertical 

flowpath. Therefore, a sampling frequency of every 2 weeks 

was used to provide adequate time for a pore volume exchange 

through the reactive mat.

Geochemistry and Water Quality 

Although the overall objective of the reactive mat was 

to reduce mass loading of chlorinated VOCs to surface water 

from seeps, it was critical that actions taken to remediate the 

VOCs did not create a secondary water-quality problem due 

to soluble metals or nutrients. Changing redox conditions 

and pH have been shown to mobilize metals in some in situ

bioremediation applications in aquifers. In addition, nutrient 

runoff into surface water can cause negative water-quality 

effects, including depressed dissolved oxygen and increased 

submerged aquatic vegetation. Due to the sensitive nature of 

wetlands, care was taken to evaluate the potential to mobilize 

both metals and nutrients from the reactive mat materials 

prior to placement in the wetland. Existing soil criteria, which 

are based on human health and drinking-water standards for 

unsaturated sediment, are not applicable to assess the impact 

of the placement of materials into wetlands. Therefore, 

alternate sediment criteria were selected to evaluate the use 

of the reactive mat matrix materials in a freshwater environment, and evaluate the potential to mobilize any contaminants 

during sediment excavation. MacDonald and others (2000) 

developed consensus-based sediment-quality guidelines 

(SQGs) to be used as predictors of sediment-quality conditions 

in freshwater systems, and these were used for reference in the 

design of the reactive mat. The probable effect concentrations 

(PECs) derived by MacDonald and others (2000) are levels 

above which adverse biological effects are expected to occur. 

These values, developed from data across North America, can 

predict adverse effects on a regional basis (Ingersoll and others, 2000). The predictive ability of the consensus-based PEC 

values can be used to assess the potential effects of contaminated sediment on sediment-dwelling organisms (Ingersoll and 

others, 2000; Ingersoll and MacDonald, 2002), and were used 

as a screening tool for native sediment and the reactive mat 

materials.

 Total metals concentrations in the three native sediment 

samples showed that arsenic, lead, mercury, nickel, and zinc 

concentrations were greater than consensus-based PECs for 

these metals (table 6). Subsequent SEP analyses indicated that 

these metals were bound mostly in the organic, carbonate, 

non-crystalline, or metal hydroxide fractions 

(Appendixes 5A,B). The low pH present at the site and the 

desire to decrease the redox potential from iron-reducing to 

methanogenic conditions has the potential to increase the 

solubility of those metals bound in the carbonate and hydroxide fractions; however, the metals bound to the organic and 

non-crystalline fractions were considered fairly stable in the 

sediment.

Metals for which PECs do not exist were also qualitatively assessed for current and future levels in the wetland 

sediment and porewater. Aluminum, iron, manganese, and 

nickel were detected in elevated concentrations in sediment, 

but were primarily bound tightly in the residual phase 

(Appendixes 5A,B). The less dominant, metal hydroxide 

bound fraction of iron and manganese may become more 
Design of a Reactive Mat for Enhanced Bioremediation 29

mobile under more highly reduced redox conditions. Zinc, 

which is predominantly found in the non-crystalline and 

residual fractions, also was found with concentrations in the 

more loosely bound metal hydroxide and carbonate fractions.

SQG-derived PECs also were used to assess the metals 

detected in a variety of composts, including those derived 

from dairy, leaf, and crab wastes. Copper concentrations in the 

three dairy-derived compost samples were greater than those 

in the consensus-based PECs. Copper was bound mostly in the 

organic fraction for each dairy compost sample and therefore 

was not readily available. Copper sulfate is used at dairy farms 

to prevent foot disease in cattle, which may explain its detection in all three compost samples. The two alternative composts were not dairy farm-derived and did not contain copper 

above the PEC.

The results of the Chesapeake Blue and Leafgro analysis 

showed concentrations that ranged from one-half to one order 

of magnitude below the consensus-based PECs for all eight 

metals. The remaining metals have been compared to the 

SEP results of the three native sediment samples, which were 

viewed as background concentrations (Appendixes 5C-E). 

With the exception of calcium (Chesapeake Blue and Leafgro) 

and manganese (Leafgro only), all of the remaining metals 

were found in concentrations less than or equal to concentrations found in the native sediment. Calcium concentrations in 

Chesapeake Blue and Leafgro were one-half to one order of 

magnitude greater than values found at one native sediment 

sampling location (GT34W-5), and greater than one order of 

magnitude at the two remaining native sediment sampling 

locations (GT34W-8, GT34W-14; fig. 5a). The Chesapeake 

Blue compost has calcium bound in the exchangeable, organic, 

carbonate, and metal hydroxide fractions. For the Leafgro 

compost, the majority of the calcium was bound in the 

exchangeable and organic fractions. The presence of calcium 

in the exchangeable phase may indicate an expected increase 

in nearby surface-water concentrations of calcium. Currently, 

no Maryland or Federal surface-water criteria for calcium 

exist.

Organic compost products are frequently used as a source 

of nutrients to soils. Therefore, their use in the reactive mat 

could increase loading of nutrients to West Branch Canal 

Creek. The nutrient (nitrogen and phosphorus) content of 

native sediments at the pilot test site was compared to reported 

nutrient content in the composts (table 7). The phosphorus 

content of the compost mixtures was an order of magnitude 

greater than that measured in the native sediments, but nitrogen was within the range of the nitrogen content for sediment. 

In laboratory column tests conducted with the mat materials, 

an increase in soluble nitrogen and phosphate was detected 

(Lorah and others, 2008). It is difficult to predict the behavior 

of these nutrients in the field, their ultimate fate in the environment, and their impact on surface water, since laboratory tests 

do not take into account nutrient cycling that will occur in the 

natural environment. These results indicate that periodic nutrient monitoring (ammonia, nitrate-nitrite, and phosphate) of 

the reactive mat porewater and the nearby surface water was 

needed to evaluate their potential impacts.

Reactive Mat Design Summary for Seep 3-4W

The area selected for placement of the reactive mat at 

seep 3-4W was flat, and more than 10 ft from the west bank of 

West Branch Canal Creek (figs. 5a,b). The mat encompassed 

a 12-ft by 13-ft area that had the maximum discharge and 

VOC concentrations at the seep (Majcher and others, 2007). 

The overall tolerable thickness of the two zones, including 

the geotextile materials, was approximately 2 ft with safety 

factors included; however, the ZVI-organic zone was limited 

to a maximum of 10 in. and the subsequent organic zone was 

limited to a maximum of 12 in. at the mat center for a total 

maximum thickness of 22 in. The reactive mat was placed 

1 ft below grade to minimize stability concerns. Although the 

reactive mat would initially extend above the natural wetland 

surface, it was estimated that the final topography of the seep 

area would be closer to the original topography after predicted 

settlement.

The ZVI-organic zone was comprised of ZVI filings 

(aggregate-size -8+50, Peerless Metal Powders & Abrasives, 

Detroit, MI) and the organic mixture. This organic mixture 

consisted of 1.5/1.5/1/0.25 parts compost (Chesapeake Blue, 

Cambridge, MD), peat (New Plant Life, Newbury, IN), #1 

drilling sand (Toney Drilling, Baltimore, MD), and chitin 

(JRW Bioremediation, Lenexa, KS). The ZVI and organic 

materials were combined in a variable volume ratio ranging 

from 60 to 40 percent ZVI and 40 to 60 percent organic mixture (fig. 8a), with a part of the northeast quadrant of the reactive mat consisting of 15 percent ZVI and 85 percent organic 

mixture. The upper reactive zone was comprised entirely of 

the organic mixture in a consistent volumetric ratio of 

1.5 parts compost, 1.5 parts peat-chitin mixture, and 1 part 

sand (fig. 8a). The reactive mat was covered with a fine layer 

of pea gravel to anchor fines during initial settling and possible 

storm events.

At the base of the reactive mat and between the ZVIorganic and organic zones, a recycled, nonwoven geotextile 

was placed to facilitate filtration, normalize flow, and provide 

a safety factor for bearing capacity. Between the two reactive 

zones, separated by the non-woven geotextile, a delivery 

system consisting of small diameter, commercially available 

irrigation tubing was installed to deliver soluble electron donor 

or, if rebioaugmentation was required, WBC-2 culture (fig. 8). 

The delivery system was comprised of 5 laterals of 10-ft, 

0.25-in. (outer diameter) polyethylene tubing with built-in 

emitters spaced 6 in. apart along each lateral (Dripworks, 

Willets, CA). 

Following site preparation (fig. 9a) and sediment excavation (fig. 9b), the reactive mat was constructed in shallow, 2 ft3

lifts (fig. 9c) until it reached the desired thickness. The organic 

zone was bioaugmented with WBC-2, as shown in figure 9d. A 

total of 24 L of the mixed culture, WBC-2, was added in liquid 

to the reactive mat. All VOCs were purged from the culture 

media before the culture was applied to the reactive matrix. 
30 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD Table 6. Comparison of metal concentrations in native wetland sediment samples from seep 3-4W, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, and in compost mixtures to consensus-based probable effect concentrations. [Units are milligrams per kilogram dry weight; *, probable effect concentrations (PECs) from MacDonald and others, 2000; compost mix indicates 40 percent compost, 40 percent peat, 20 percent sand; BOLD indicates value exceeds the PEC; Italics indicates value exceeds native sediment value for same metal; --, no data; U, not detected [the associated number indicates the method detection limit for the analyte.]; B, estimated result [the result reported is less than the reporting limit for the analyte.]; J, method blank contamination [the associated method blank contains the target analyte at a reportable level.] Total metals from sequential extraction procedure (SEP) analysis Metals Consensus- based PEC* Native sediment GT34W-14 Native sediment GT34W-5 Native sediment GT34W-8 Dairy compost mix (1) Dairy compost mix (2) Dairy compost mix (3) Leafgro compost mix Chesapeake Blue compost mix Aluminum -- 41,700 J 101,000 J 38,500 J 9,680 J 7,380 J 9,010 J 13,500 13,200 Antimony -- 5.3

B 15.3

U 6.4

B 2.6

B 1.5

B 2.4

B 2.9

B 2.7

B

Arsenic 33 29.6 39.3 35.9 5.1 1.9 1.8 3.7 3.8Barium -- 203 408 256 156 77 80 139 204Beryllium -- 2.6 J 9.0 B J 5.4 J 0.47 J 0.27 B, J 0.31 B, J 0.32

B 0.17

B

Cadmium 4.98 2.1 1.5

U 4.4 0.32

B 0.22

B 0.22

B 0.25

B 0.23

B

Calcium -- 409 B, J 2,420 B, J 827 B, J 6,170

J 6,700

J 15,200

J 10,100

J 24,400

J

Chromium 111 70.6 85.0 94.2 14.3 7.9 9.8 12.4 9.6Cobalt -- 48.0 52.6

B 59.2 2.6

B 1.7

B 1.9

B 2.2

B 1.1

B

Copper 149 109 124 153 189 172 171 12.4 13.0Iron -- 21,100 J 34,800 J 36,900 J 8,560 J 4,510 J 4,700 J 6,010 5,190Lead 128 157 205 247 8.7 4.7 7.4 9.5 7.2Magnesium -- 1,820 6,610

B 1,810 1,310 2,140 1,970 1,250 1,200

Manganese -- 160 304 300 169 141 143 216 101Mercury 1.06 4.0 4.7 -- -- 0.055

U 0.052

U 0.077

U 0.072

U

Nickel 48.6 58 59

B 72 12 7.8 8.6 11.2 J 8.6 J

Potassium -- 10,700 J 10,700 B, J 12,700 J 5,960 J 5,420 J 6,360 J 3,820 J 5,190 JSelenium -- 1.5 3.9

U 2.1 0.90 0.55 0.60 1.2 J 1.5 J

Silver -- 1.8 1.5

B 1.6

B 0.26

U 0.21

U 0.20

U 0.29

U 0.40

B

Sodium -- 2,240 2,520

B 2,840 1,820 2,080 2,530 1,100 1,150

Thallium -- 7.3 24

B 11 1.7 0.69

B 2.3 2.2 2.9

Vanadium -- 105 115

B 121 26 12 14 20.3 18.4

Zinc 459 1,020 J 683 J 1,050 J 76 J 77 J 103 J 47.5 41.8
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 31

Performance of a Reactive Mat Pilot 

Test for Enhanced Bioremediation

After measurement of baseline conditions in August 

and September 2004, and installation of the reactive mat in 

October 2004 at seep area 3-4W, monitoring was conducted 

through October 2005 to evaluate the performance of the 

pilot test to determine whether the design objectives outlined 

in the previous sections were met. Seep 3-4W represented a 

highly contaminated seep area with mixed chlorinated ethenes, 

ethanes, and methanes. A successful pilot test would demonstrate a new remedial solution for mixed, chlorinated VOCs 

near the groundwater/surface-water interface.

Pre-Installation Conditions

On the basis of results from PDSs, peepers, seepage 

meters, and CPT data at seep 3-4W (Majcher and others, 

2007), the reactive mat was placed over the area with the 

greatest concentrations of parent chlorinated VOCs and the 

greatest point of discharge to surface water for the primary 

contaminants within the seep area, including CT, CF (fig. 10a 

shows CF distribution; CT distribution was similar to CF), 

and PCE (fig. 10b). It was known that the placement did not 

encompass all of the contaminated part of the seep area, especially the pre-existing chlorinated daughter compounds, such 

as cis-1,2-DCE (fig. 10c). Vertical profiles of VOC distribution 

within this area indicated that mass increased with decreasing 

depth bls (fig. 11), and that porewater was largely in ironreducing conditions, with no detections of methane (Majcher 

and others, 2007).

After multi-level monitoring points were installed below 

and surrounding the seep area in August 2004, a broader and 

more defined areal and vertical baseline of VOC distribution 

and hydrologic behavior could be assessed. Total VOC 

concentrations at the top of the Canal Creek aquifer (depth of 

12 ft) were greatest at PTC4C, and extended laterally beyond 

the proposed southern boundary of the mat footprint 

(fig. 12a). At 5 ft bls within the wetland sediments, concentrations in the southwestern boundary were approximately the 

same as at the top of the aquifer, but an additional hotspot was 

apparent at PTC6, an area to the northeast of the mat boundary 

in the wetland sediments (fig. 12b) near a previous peeper 

sampling location and an area of high seepage (Majcher and 

others, 2007). This distribution is consistent with PDS results 

and indicates an expansion of the overall VOC distribution 

near land surface. Although an order of magnitude less, the 

chlorinated ethenes and ethanes also were found in the highest 

concentrations along the southern boundary area and followed 

a similar pattern with decreasing depths. More than 99 percent 

of the total measured VOC mass was comprised of parent 

compounds (CT, CF, PCE, TCE, TeCA, hexachloroethane, 

and pentachloroethane), with no apparent degradation in the 

vertical profile from the aquifer to land surface. Methane was 

not detected (less than 2 μM, or micromolar) in this area, 

except at a few isolated locations where it was detected below 

the threshold concentration for methanogenic conditions 

(Appendix 1, table 8).

Regional hydrologic characterization of the area indicated that groundwater discharges in a generally vertical 

direction from the underlying aquifer toward the central area 

of the wetlands from the west and east (Lorah and others, 

1997; Lorah, Spencer, and McGinty, 2005; Phelan and others, 

2002; Weston Solutions, 2005; General Physics Corporation, 

2005). In the area of seep 3-4W, discharge was focused on the 

western boundary of the creek channel at very discrete points 

(Majcher and others, 2007). Along line of section D-D' (fig. 

5a) that spans the creek channel from west to east and bisects 

the mat location, upward groundwater discharge in this localized area was evident in the low and high tide potentiometric 

surfaces (figs. 13a,b). The seep boundaries were not apparent. The pre-installation potentiometric surface along a north 

to south line of section E-E' (fig. 14) was consistent with the 

west to east section, indicative of vertical flow at both low and 

high tides (fig. 14). The planar potentiometric surface in the 

wetland sediments 3 to 5 ft bls that was obtained with the finescale monitoring network at the pilot test area showed gradual 

flow towards the creek, which was slightly greater at low tide 

when water levels are mainly contained within the creek channel (fig. 15). The magnitude of change in the potentiometric 

surface (gradient) was substantially lower in the horizontal 

direction compared to the vertical direction. Vertical hydraulic 

Table 7. Nutrient and organic matter content of composts used 

in this study.

[%, percent; mg/kg, milligrams per kilogram; BET, Bion Environmental 

Technologies, Inc.; MES, Maryland Environmental Services; NR, not 

reported; <, less than].

Nutrients and

organic matter

Units

(dry)

BET 

BionSoil

organic 

dairy

New Earth

Chesapeake 

Blue crab

MES

Leafgro

leaf

Total Nitrogen (N) % 1 0.66 1.5

NH4-Nitrogen mg/kg NR <100 175

NO3-NO2 Nitrogen mg/kg NR 184 NR

NO3-Nitrogen mg/kg NR NR 41

Organic Nitrogen % NR 0.66 1.5

Phosphorus (P) % 0.5 0.82 NR

Phosphorus (P2O5) % NR NR 0.53

Potassium (K) % 0.5 0.03 NR

mg/kg NR NR 6,837

Potassium (K2O) % NR NR 0.82

Organic Matter % 40 NR 51

Carbon:Nitrogen ratio NR 12 18
32 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

gradients from the underlying aquifer into the overlying wetland sediments in the pilot test area were consistent at low and 

high tides, ranging from 0.12 to 0.25 across the area. These 

gradients are consistent with or slightly lower than vertical 

gradients reported in Majcher and others (2007) for the seep 

area, and Lorah, Spencer, and McGinty (2005) in the wetland 

study area, and are at least an order of magnitude greater than 

horizontal gradients in the area.

The baseline distributions of chlorinated VOCs are 

shown in two dimensions along west-east (Y-Y') and southnorth (Z-Z') cross sections through the southern and western 

edges of the reactive mat, respectively (fig. 5a; figs. 16, 

17). Isoconcentrations of chloromethanes indicate that the 

greatest mass of these contaminants was immediately below 

the southwest corner of the mat location, near the top of 

the aquifer sediments (12 ft bls) (figs. 16a, 17a). Therefore, 

some contamination appeared to extend beyond the western 

boundary of the mat toward PTC9 and to the east towards 

PTC12 in the upper parts of the wetland sediments (fig. 16a). 

Along the south-north cross section on the western plane 

of the reactive mat location, maximum contamination was 

centered at PTC4, and contaminants appeared to extend 

beyond the mat boundary to the south (fig. 17a). Chlorinated 

ethenes and ethanes follow similar patterns as the chlorinated 

methanes, spreading in a lateral direction with decreasing 

depths bls along the two sections (figs. 16b, 17b). Cross 

sections along the eastern and northern planes (data not 

shown) indicated a secondary hotspot (also evident in the 

planar distribution in figs. 10 and 12b) that extended beyond 

the northeast boundary of the mat, and was not adequately 

captured within the mat footprint. Although contaminant 

distribution exceeded the proposed mat boundaries, consistent 

contaminant transport primarily in the vertical direction from 

the aquifer through the upper wetland sediments provided 

sufficient opportunity to show effectiveness of the reactive mat 

within the placement area.

Figure 9. Installation of a reactive mat pilot test at seep 3-4W, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, (A) site preparation, (B) sediment excavation, (C) reactive material placement, and (D) bioaugmentation with WBC-2. 

(Photographs by Michelle Lorah, U.S. Geological Survey.)
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 33

Assessment of Volatile Organic Compound 

Degradation

Degradation of chlorinated VOCs by WBC-2 requires 

anaerobic conditions in the subsurface. In this section, the 

establishment of conditions favorable for anaerobic degradation of these contaminants is discussed. The distribution and 

removal of VOCs were assessed to evaluate the degradation 

efficiency of the reactive mat pilot test at seep 3-4W. 

Establishment of Conditions Favorable for 

Anaerobic Degradation

Throughout the monitoring period, the mat was evaluated 

for conditions that would facilitate anaerobic degradation 

(primarily biodegradation) of chlorinated VOCs. Redoxsensitive constituents (ammonia, iron, sulfide, methane), 

hydrogen, and WBC-2 activity were analyzed to evaluate a 

change from iron-reducing to methanogenic conditions that 

Figure 10. Distribution of selected volatile organic compounds in shallow porewater, seep location 3-4W, April (DS163–DS176) 

and December (DS317–DS332) 2003 in relation to the reactive mat pilot test, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, (A) chloroform (CF), (B) tetrachloroethene (PCE), and (C) cis-1,2-dichloroethene (cis-1,2-DCE) (modified from Majcher and 

others, 2007).
34 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

are favored by WBC-2 (Jones and others, 2006; Lorah and 

others, 2008). Consistent with results from previous investigations, the amount of methane in samples proved to be the most 

valuable indicator for appropriate conditions (Lorah, Spencer, 

and McGinty, 2005; Lorah and others, 2008). Methane could 

be used alone (or in combination with iron) in future applications for a more streamlined analytical program to evaluate 

mat redox conditions.

Ammonia concentrations measured in the reactive 

mat over the monitoring period were greater than ammonia 

concentrations in underlying and surrounding native sediment 

(Appendix 1). Increased ammonia concentrations were likely 

due to the nitrogen introduced with the compost contained in 

the reactive mat. Maximum concentrations of ammonia were 

detected in May 2005 (15 mg/L, or milligrams per liter; or 

0.8 mM, or millimolar). Ammonia concentrations decreased 

in July (5.5 mg/L or 0.31 mM) and August 2005 (less than 

0.7 mg/L or 0.04 mM). A subsequent increase was measured 

in September 2005, which resulted in a more evenly distributed concentration from 5 to 8 mg/L (0.3 to 0.4 mM). These 

fluctuations may be attributed to the invasion and growth of 

non-native vegetation in the reactive mat during the summer 

months, followed by removal of plant biomass in early 

September 2005. Ammonia concentrations did not correlate 

well with the other redox constituents, and the presence of 

ammonia did not appear to have an adverse effect on the 

production of methane. The presence of ammonia also may 

be indicative of favorable conditions for the degradation of 

chlorinated methanes, which can occur under denitrifying 

conditions (Bouwer and McCarty, 1983).

Soluble ferrous iron and sulfide were both detected in 

minimal concentrations within the reactive mat throughout 

the monitoring period (Appendixes 1A and 1B), similar to 

observations in the laboratory column tests (Lorah and others, 

2008). Sulfide was commonly detected at concentrations less 

than 0.1 to less than 0.25 mg/L (1.6x10-3 to 3.9x10-3 mM). 

Ferrous iron consistently decreased by one to two orders of 

magnitude from 1 to 3 ft below the reactive mat to within the 

reactive mat (Appendixes 1A and 1B), despite the generation 

of ferrous iron from the ZVI zone. The lack of both iron and 

sulfide within the mat may indicate iron sulfide precipitation 

in the mat. Precipitated iron sulfide has been observed within 

ZVI barriers (Vikesland and others, 2003).

The immediate dosing of electron donor within the 

organic matrix (crab compost and chitin) resulted in a rapid 

establishment in methane concentrations throughout the mat 

with relatively high concentrations detected during the first 

monitoring event in November-December 2004 (table 8, figs. 

18a,b). Methanogenic conditions were maintained, especially 

immediately above the ZVI-organic zone (PTBC), throughout 

the monitoring period (fig. 18a). A decline in methane concentrations was observed over the winter months in sampling 

points nearest to land surface in the organic zone (PTBB and 

PTBC), as evident in the decreased concentrations between 

November 2004 and March 2005 (figs. 18a,b). Between May 

and September 2005, methane concentrations increased again.

Concentrations of methane detected in native sediments 

deeper than 3 ft bls underneath and surrounding the reactive 

mat were consistent with pre-installation concentrations 

(Appendix 1). Immediately below the reactive mat, from 

1 ft to approximately 3 ft bls (PTN and PTCA levels, 

respectively), methane concentrations gradually increased 

consistent with the in-mat fluctuations, particularly between 

May and September 2005, as shown by the data from the 

PTB7/PTC4 monitoring location (fig. 18c). Increased methane 

concentrations in these underlying wetland sediments may 

indicate downward transport of WBC-2 from the mat and its 

subsequent growth and methane production, or downward 

transport of methane itself with tidal recharge of groundwater 

and surface water within these sediments.

Hydrogen previously has been used as an indicator of 

dechlorination activity in aquifers as a result of its metabolic 

use by dehalorespiring bacteria (Maymó-Gattel and others, 

1997). Hydrogen distribution within the reactive mat did not 

Figure 11. Vertical distribution of selected chlorinated 

volatile organic compunds at seep location 3-4W, 

West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, August 2003 (modified from Majcher and 

others, 2007).
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 35

Figure 12. Baseline distribution of total chlorinated volatile organic compounds at (A) the top of the Canal Creek aquifer, 

and (B) in wetland sediments beneath the seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen 

Proving Ground, Maryland, August–September 2004.
36 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD Table 8. Concentrations of methane and hydrogen from in-mat diffusion samplers, seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, December 2004–October 2005.—Continued [+, measurable hydrogen detected, with ++ and +++ indicating relatively higher concentrations detected; --, negligible hydrogen detected; μM, micromolar concentration; nM, nanomolar concentration; NC, not collected; <, less than] Sample name Date collected Methane (μM) Hydrogen (nM) Date collected Methane (μM) Date collected Methane (μM) Hydrogen (nM) Date collected Methane (μM) Hydrogen (nM) PTB1B December 2004 921 -- January 2005 305 March 2005 1.5 NC May 2005 99.4 6.1 PTB1C-1 December 2004 1,006 NC January 2005 574 March 2005 172 < 0.4 May 2005 550 <0.4 PTB1C-2 December 2004 1,001 NC January 2005 571 March 2005 218 NC May 2005 NC NC PTB2B December 2004 1,268 -- January 2005 NC March 2005 NC NC May 2005 1.5 11 PTB2C December 2004 1,101 -- January 2005 1,074 March 2005 183 20 May 2005 562 57 PTB3B December 2004 871 -- January 2005 52.9 March 2005 NC NC May 2005 1.5 < 0.4 PTB3C December 2004 1,204 ++ January 2005 1,289 March 2005 2.8 < 0.4 May 2005 84.3 4.9 PTB4A December 2004 371 +++ January 2005 3.5 March 2005 NC NC May 2005 NC NC PTB4B December 2004 909 -- January 2005 192 March 2005 1.4 < 0.4 May 2005 158 41 PTB4C December 2004 731 -- January 2005 359 March 2005 238 21 May 2005 231 5.2 PTB5A December 2004 52.1 -- January 2005 14.8 March 2005 NC NC May 2005 NC NC PTB5B December 2004 1,079 -- January 2005 454 March 2005 1.5 NC May 2005 23.6 < 0.4 PTB5C December 2004 1,015 -- January 2005 1,142 March 2005 66.8 47 May 2005 772 23 PTB6B December 2004 1,151 -- January 2005 409 March 2005 1.5 NC May 2005 20.0 NC PTB6C December 2004 967 -- January 2005 1,211 March 2005 196 < 0.4 May 2005 442 < 0.4 PTB7A December 2004 NC -- January 2005 17.5 March 2005 NC NC May 2005 NC NC PTB7B December 2004 83.4 -- January 2005 243 March 2005 7.1 NC May 2005 27.5 9.7 PTB7C December 2004 79.5 +++ January 2005 271 March 2005 69.0 15 May 2005 107 < 0.4 PTB8A December 2004 18.2 -- January 2005 18.3 March 2005 NC NC May 2005 NC NC PTB8B December 2004 763 -- January 2005 746 March 2005 1.5 NC May 2005 253 < 0.4 PTB8C December 2004 608 -- January 2005 928 March 2005 235 4.6 May 2005 503 12 PTB9B December 2004 3.7 -- January 2005 195 March 2005 NC NC May 2005 1.4 NC PTB9C December 2004 883 -- January 2005 429 March 2005 153 1.9 May 2005 436 6.6
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 37

Table 8. Concentrations of methane and hydrogen from in-mat diffusion samplers, seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, December 2004–October 2005.—Continued[+, measurable hydrogen detected, with ++ and +++ indicating relatively higher concentrations detected; --, negligible hydrogen detected; μM, micromolar concentration; nM, nanomolar concentration; NC, not collected; <, less than]

Sample 

name

Date 

collected

Methane 

(μM)

Hydrogen 

(nM)

Date 

collected

Methane 

(μM)

Hydrogen 

(nM)

Date 

collected

Methane 

(μM)

Hydrogen 

(nM)

PTB1B July 2005 499 85 August 2005 884 6.5 October 2005 658 36

PTB1C-1 July 2005 587 6.1 August 2005 NC 14 October 2005 745 5.3PTB1C-2 July 2005 NC NC August 2005 NC NC October 2005 NC NC

PTB2B July 2005 NC 20 August 2005 1.2 35 October 2005 41 1.5PTB2C July 2005 661 21 August 2005 847 28 October 2005 621 30PTB3B July 2005 NC 1.4 August 2005 7.3 11 October 2005 2.8 33PTB3C July 2005 378 < 0.4 August 2005 709 16 October 2005 992 33PTB4A July 2005 NC NC August 2005 NC NC October 2005 NC NCPTB4B July 2005 404 < 0.4 August 2005 718 NC October 2005 NC NCPTB4C July 2005 506 < 0.4 August 2005 954 82 October 2005 907 14PTB5A July 2005 NC NC August 2005 NC NC October 2005 NC NCPTB5B July 2005 62 121 August 2005 1.4 139 October 2005 NC 12PTB5C July 2005 536 15 August 2005 886 16 October 2005 88 15PTB6B July 2005 NC 10 August 2005 1.4 4.4 October 2005 NC 10PTB6C July 2005 506 37 August 2005 893 56 October 2005 1085 39PTB7A July 2005 NC NC August 2005 NC NC October 2005 NC NCPTB7B July 2005 341 615 August 2005 565 46 October 2005 234 45PTB7C July 2005 491 1180 August 2005 866 22 October 2005 262 30PTB8A July 2005 NC NC August 2005 NC NC October 2005 NC NCPTB8B July 2005 449 40 August 2005 601 56 October 2005 24 1500PTB8C July 2005 520 < 0.4 August 2005 917 35 October 2005 715 31PTB9B July 2005 NC 19 August 2005 1.5 20 October 2005 NC 40PTB9C July 2005 600 118 August 2005 407 NC October 2005 912 38
38 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 13. Section D-D' showing baseline mean hydraulic head distribution at the seep 3-4W reactive mat pilot test area, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, August–September 2004, (A) low tide and (B) high tide.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 39

Figure 14. Section E-E' showing baseline mean hydraulic head distribution at the seep 3-4W reactive mat pilot test area, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, August–September 2004, (A) low tide and (B) high tide.
40 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 15. Baseline planar distribution of hydraulic head in the upper wetland sediments at low 

tide, seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, September 2004.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 41

Figure 16. Baseline distribution of chlorinated volatile organic compounds in section Y-Y' at the seep 3-4W reactive mat pilot test 

area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, August–September 2004, (A) chloromethanes and 

(B) chloroethenes plus chloroethanes.
42 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 17. Baseline distribution of chlorinated volatile organic compounds in section Z-Z' at the seep 3-4W reactive mat pilot test 

area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, August–September 2004, (A) chloromethanes and 

(B) chloroethenes plus chloroethanes.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 43

consistently correlate with methane concentrations, particularly prior to May 2005 (table 8). The hydrogen concentrations 

detected also were quite variable, and in some cases, ranged 

from two to three orders of magnitude, with maximum 

hydrogen concentrations occurring in both the presence of and 

absence of methane (table 8). Hydrogen detection did correspond to degradation of chlorinated VOCs, particularly after 

March 2005, and possibly indicated the growth of the dechlorinating bacteria in the reactive mat during this timeframe.

In addition to evaluating redox indicators for favorable 

biodegradation conditions for VOCs, microbial community 

activity tests were conducted periodically to assess the dechlorinating ability of the microorganisms established in the reactive mat, which were assumed to be WBC-2. When TeCA was 

added to a subsample of reactive mat matrix collected from 

PTB7 in November 2004, removal of TeCA and all its associated daughter compounds occurred within 20 days (fig. 19a). 

Following the winter months, the activity test was repeated in 

the same areas of the reactive mat. Although the March 2005 

removal rates were lower than those in November 2004, all 

added TeCA and its daughter compounds were subsequently 

removed, even in the presence of PCE (fig. 19b). These results 

indicated that microbial activity, stimulated at least in part 

by the WBC-2 bioaugmentation within the reactive mat, was 

sufficient to maintain dechlorination activity even following 

the winter months, and that no additional bioaugmentation or 

biostimulation was required.

Volatile Organic Compound Distribution and 

Mass Removal

The distribution of total VOC concentrations in the top 

of the aquifer and the wetland sediments (5 ft and 1 ft bls) 

below the reactive mat (figs. 20a,b), and in piezometer PTZ2 

on the eastern side of the creek (fig. 5a; Appendix 3) was used 

to evaluate changes to VOC input to the reactive mat during 

the monitoring period. Whereas some variations of VOCs in 

the aquifer were noted in the footprint of the mat, the overall 

distribution of underlying VOCs was largely consistent with 

pre-installation concentrations (figs. 20a,b). Maximum VOC 

concentrations were typically detected during the spring at 

all depths. Total VOC concentrations in piezometer PTZ2E 

(screened at approximately 38 ft bls) reached a maximum of 

18 mg/L (125 μM) during March 2005, decreased to 11 mg/L 

(79 μM) in May 2005, and ranged from only 0.73 to 1.9 mg/L 

(5.2 to 8.8 μM) during other sampling periods (Appendix 3). 

The total VOC concentrations at the top of the Canal Creek 

aquifer in the central and southwestern parts of the mat area 

reached a maximum in May 2005, with a 40- to 70-μM 

increase compared to March 2005 (fig. 20a), indicating the 

possible transport of a slug of contaminants from this deep 

zone at PTZ2E to the reactive mat between March and May 

2005. Variations in VOC concentrations observed within the 

reactive mat (figs. 20d,e) were consistent with VOC loading 

from underlying depths (though the overall concentrations 

were much lower), and were focused in the southwest corner. 

At the base of the organic zone (PTBB level), total VOC concentrations were highest in January and March 2005, consistent with the decrease in methane concentration described in 

the previous section (fig. 20e). Overall, VOC distribution was 

temporally consistent within the mat during the monitoring 

period (figs. 20d,e). Therefore, further comparisons between 

pre- and post-installation concentrations are presented for the 

August 2005 monitoring event as a representative month during the monitoring period.

To evaluate VOC distribution and reduction, VOC 

concentrations within the mat area are shown in planar twodimensional isoconcentrations at various depths within the 

underlying wetland sediments and reactive mat (figs. 21a-f 

and 22a-c), and in vertical VOC concentration profiles at 

given monitoring locations (figs. 23a-c). Despite the large 

difference in concentration between chloromethanes and 

chloroethenes and chloroethanes, the distribution of the three 

contaminant groups within the reactive mat was fairly consistent. Maximum concentrations at all depths during all seasons 

occurred primarily in the southwestern-western area of the mat 

footprint. The highest concentrations were located along the 

southwest boundary and extended beyond the boundaries in all 

directions below the mat (figs. 21a,b and 22a,b). In most cases, 

little to no change in the overall distribution and concentration 

of chlorinated compounds was observed between the aquifer 

and 1 ft bls in the wetland sediments (figs. 21a,d). This spatial 

distribution was consistent with pre-installation conditions of 

the aquifer (figs. 16a,b and 17a,b) and in various depths within 

the wetland sediments (figs. 21a-f and 22a-c). The decrease in 

VOC concentrations from just below the reactive mat (PTN) 

to immediately above the ZVI-organic zone (PTBC) was 

typically at least an order of magnitude. Further removal was 

frequently observed between the ZVI-organic (PTBC) and 

organic (PTBB) zones. Variation between the isoconcentrations within the reactive mat (figs. 21e,f, and fig. 22c) was 

generally small despite significant concentration gradients 

observed at deeper depths within the same area, which is 

indicative of substantial mass removal over the narrow mat 

thickness.

The distribution of total VOCs in the untreated seep area 

outside of the reactive mat was relatively consistent over the 

monitoring period up to the most shallow monitoring depth 

of 3 ft bls for total VOCs, particularly along the southwestern 

mat perimeter (fig. 24a). Greater variation was apparent in the 

northeastern perimeter wells (fig. 24b). Increased porewater 

concentrations of chloromethanes in May 2005 near PTC6 and 

PTC13 at this shallow depth corresponded to the increased 

VOC concentrations observed on the eastern side of the creek 

channel in piezometer PTZ2.

Chloromethanes typically decreased from west to east 

through both reactive mat zones (figs. 21d,e), consistent with 

the distribution within the wetland sediments immediately 

below the mat, and therefore, with the loading from these sediments (fig. 21c). The consistent, increased loading of chloromethanes to the southwestern corner of the mat appeared to 
44 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

slightly decrease the degradation efficiency of chloroethenes 

and ethanes in both mat zones in this area (fig. 22c). This measured co-contaminant effect was similar to observations made 

in laboratory column tests, where degradation of TeCA was 

slightly reduced with long-term loading of CT and CF (Lorah 

and others, 2008).

Chloromethanes were detected at more sampling locations in the ZVI-organic (PTBC) zone of the mat in January 

and March 2005 than were detected during warmer months 

(fig. 20d), likely, in part, due to the low temperature at shallow 

depths during the winter months. Methane concentrations 

also declined throughout this treatment zone during the winter 

months (fig. 18a), and decreased VOC degradation efficiency 

was affirmed by the activity tests that showed reduced 

removal rates in March 2005 compared to November 2004 

(figs. 19a,b). 

In addition to the effects of temperature on biodegradation efficiency, the reactive mat received different VOC 

loading amounts during the pilot test that likely decreased the 

biodegradation efficiency within the mat. Increased loading 

from the aquifer was observed particularly in May 2005, as 

described at the beginning of this section (fig. 20c). In spite of 

the increased loading, methanogenic conditions were maintained during May 2005 and the thickness of the mat appeared 

to be adequate to facilitate a decline in overall concentrations 

through the organic zone (fig. 20e). The decrease in loading 

observed during later sampling events appeared to improve the 

degradation efficiency of chloromethanes (fig. 21f) and chloroethane and chloroethenes (fig. 22c) in the ZVI-organic zone.

Vertical profiles of total VOC concentrations below and 

within the mat were consistent over the monitoring period 

(fig. 23) and indicated that the primary source of VOCs to the 

Figure 18. Methane concentrations in the reactive mat pilot test at seep area 3-4W, West Branch Canal Creek, Aberdeen Proving 

Ground, Maryland, (A) PTBC level, (B) PTBB level, and (C) in profile at PTB7/PTC4.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 45

reactive mat was likely in the aquifer in the southwest corner 

(fig. 23a). Profiles of compound concentrations were relatively 

consistent over the monitoring period throughout the mat area 

compared to concentration profiles prior to mat installation 

(figs. 23a-c). In the southwest corner, total VOCs decreased 

with shallower depths and were completely removed within 

the reactive mat (fig. 23a). In the northeast and southeast 

corners of the reactive mat, maximum concentrations of 

VOCs were detected at shallower depths within the wetland 

sediments compared to the southwest corner (figs. 23b,c).

Vertical contaminant profiles of individual VOCs (both 

parent and daughter compounds) were examined to assess 

VOC mass removal (complete degradation to non-toxic endproducts) through the mat. Since concentrations were consistent over the monitoring period (figs. 23a-c), results are only 

shown for March and June 2005, in the southwest (PTC4) 

area of maximum concentration from the aquifer upwards 

through the reactive mat (figs. 25a-d). In the vertical profile 

with depth within the wetland sediments, parent compounds 

CT, CF, PCE, TCE, and TeCA were conserved in the vertical 

direction to a depth of 5 ft bls (figs. 25a,b; location PTC4), 

similar to parent compounds found in the PDS investigations 

in the upper 2 ft prior to mat installation (Majcher and others, 

2007; fig. 11). A decline in CT was apparent between 5 ft and 

1 ft bls of wetland sediment, but substantial CF mass remained 

immediately below the reactive mat with lower concentrations 

of PCE, TCE, TeCA, and HCA during the entire monitoring 

period. Through the mat itself, transient appearance of 

daughter compounds TCE, cis-1,2-DCE, VC, and methylene 

chloride was observed, but mass balances of parent and 

daughter compounds were poor over the narrow thickness of 

the mat (figs. 25a-d). These transient daughter compounds also 

were detected in areas of efficient natural attenuation, often 

with poor mass balances (Lorah and others, 1997). Ethene 

and ethane were detected in the two reactive zones, indicative 

of complete dechlorination (figs. 25a,c). Incomplete removal 

of CF, methylene chloride, and TCE was apparent during the 

March sampling event (figs. 25a,b). Removal of these contaminants improved through the summer, however, with the 

reappearance of ethene and ethane end-products (fig. 25c). 

Overall, these results are significantly different from the 

pre-installation results (fig. 10), where little to no removal of 

parent VOCs was observed in the upper sediments.

Estimates of mass removal over time between the base 

of the mat (PTN) and the middle of the organic zone (PTBB) 

were made over the monitoring period to compare to the 

design goal of 90-percent removal of total VOCs (table 9). 

These estimates were based on a reactive mat divided into 

nine sections, with porespace equal to 0.5, and concentrations 

equalized in each section based on its center monitoring point. 

Applying these conservative assumptions, the reactive mat 

appeared to reach the design goal during the performance 

period. The median mass removal of chloromethanes and chloroethenes plus chloroethanes during the entire performance 

monitoring period was 98 and 94 percent, respectively. The 

minimum removal in the PTBC level occurred in March 2005, 

likely due to the colder temperatures. The minimum removal 

in the PTBB level occurred during May 2005 (table 9), likely 

due to increased loading.

Figure 19. Concentrations of 1,1,2,2-tetrachloroethane (TeCA), and daughter compounds 1,1,2-trichloroethane (TCA), 

trichloroethene (TCE), trans-1,2-dichloroethene (trans-1,2-DCE), and cis-1,2-dichloroethene (cis-1,2-DCE) in activity tests from the 

reactive mat pilot test at seep area 3-4W, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, (A) November 2004 and 

(B) March 2005. [Note: Tetrachloroethene (PCE) was present in mat sample in March 2005.]
46 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 20. Concentrations of total volatile organic compounds at various depths in reactive mat porewater, seep 3-4W reactive mat 

pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, (A) top of Canal Creek aquifer, (B) wetland sediments 5 

feet below land surface, (C) immediately below the reactive mat (PTN), (D) top of the zero-valent-iron (ZVI) -organic (PTBC) zone within 

the reactive mat, and (E) middle of the organic (PTBB) zone within the reactive mat.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 47

Assessment of Compatibility with the Wetland 

System

A secondary objective of the reactive mat design was 

to maintain compatibility with the wetland in which it was 

placed. The reactive mat performance was effective in 

removing VOCs, based on the design. A discussion of compatibility with the native environment is presented in this section 

based on hydraulic, geotechnical, and water-quality monitoring and performance metrics.

Geotechnical Integrity

No local, immediate failure (such as collapse or caving) 

of the mat or of surrounding wetland sediments was observed 

during or following mat installation. This indicated that the 

bearing capacity estimates, and sediment excavation, combined with the subsurface non-woven geotextile used at the 

base, maintained the integrity of the sediment surface during 

and following installation. Similarly, the pea gravel appeared 

to hold fines from the mat surface in place for at least 1 year.

Measurements of surface elevation of the mat between 

October 2004 and July 2005 showed an average settlement 

of the mat surface of approximately 0.25 ft. Settlement rates 

were fairly uniformly distributed over the mat surface, with 

a maximum in the northeast corner of 0.38 ft (closest to the 

creek), and a minimum of 0.07 ft about 5 ft to the west of the 

northeast corner. This magnitude of settlement was near the 

range of settlement predicted for the virgin sediment curves 

(see Geotechnical Integrity section), confirming that the 

collected sediments were overconsolidated. The majority of 

settlement was observed between October 2004 (fig. 26a) and 

March 2005 (fig. 26b).

Data-collection methods used during this pilot test did 

not distinguish between settlement of the mat materials and 

underlying sediment. Measured settlement was likely a combination of both, on the basis of the exposure of the uppermost sampling level (PTBB) of multi-level diffusion samplers 

within the mat over the monitoring period. This was also indicated by the fact that this apparent settlement within the mat 

materials was not equal to the total change measured in elevation over time. Future applications of the reactive mat would 

benefit from the collection of a core of materials periodically 

throughout the monitoring period to assess settlement and any 

subsequent reduction in permeability of the mat materials.

The reactive mat maintained its integrity through all 

seasons, even after the removal of shoring walls in December 

2004. The shoring and silt fencing used during construction 

and as safety mechanisms in the case of failure were removed 

with the anticipation of the winter freeze-thaw events. While 

non-native vegetation invaded the reactive mat in summer 

2005, which increased the stability of the mat, plants did not 

appear to be a critical component in its strength based on its 

stability prior to plant growth. To prevent the invasion of 

non-native species in the wetland, future applications of the 

reactive mat would benefit from being seeded with native, 

wetland plants.

Hydraulics

In order to assess the hydrologic compatibility of the 

reactive mat with the wetland, hydrologic monitoring was 

conducted around the mat throughout the monitoring period. 

VOCs, which were shown to be good tracers in seep areas 

(Majcher and others, 2007), also were used to assess the 

advective transport of contaminated groundwater in wetland 

sediments below and surrounding the mat. Whereas the incorporation of a geotextile in the reactive mat prohibited hydrologic monitoring across the wetland-mat interface, isolated 

hydraulic measurements were conducted within the reactive 

mat during individual monitoring events and are presented in 

the following section.

Effects on Surrounding Hydrologic Conditions

During the monitoring period, no atypical hydrologic 

occurrences were observed in the broader West Canal Creek 

study area, as evidenced by the upgradient groundwater elevations (in monitoring well CC27A) and upstream tide gage fluctuations. Groundwater elevation in monitoring well CC27A 

(Appendix 6A), located near the probable VOC source area 

in the eastern uplands of Canal Creek, was consistent with 

previous investigations that spanned multiple years (Lorah, 

Spencer, and McGinty, 2005). The tide gage, considered to be 

representative of the West Branch Canal Creek, recorded tidal 

fluctuation over the monitoring period ranging from -0.3 ft to 

3.7 ft, consistent with previous investigations (Phelan, Olsen, 

and others, 2001). 

Continuous water levels in selected piezometers indicated 

a relatively consistent fluctuation over the tidal cycle in the 

wetland sediments, with decreasing variation with increasing 

depth bls, as illustrated by piezometer PTZ4 (Appendix 6B). 

Groundwater discharge along cross-sections D-D' and E-E' 

remained predominantly vertical following mat installation, 

the subsequent monitoring period, and during high and low 

tide as indicated by the potentiometric surface (figs. 27a,b, 

low tide shown) based on measurements during 11 individual 

groundwater elevation synoptic events of piezometers to the 

north, south, east, and west of the mat throughout the monitoring period. The potentiometric surface along the two cross 

sections was generated using mean groundwater elevations at 

high (n=7) and low (n=6) tides. Groundwater-level variation 

was consistent in both direction and magnitude with preinstallation conditions previously described at each tidal stage 

(figs. 13, 14, 27). Variation between post-installation high and 

low tides was largely encompassed by the standard deviation 

among the post-installation synoptic measurements 

(figs. 27a,b, low tide shown). 

Any impacts from the installation of the reactive mat 

(such as a possible redirection of flow) would be reflected in 

increased groundwater elevations in piezometers screened in 

the upper wetland sediments surrounding the reactive mat and 

a corresponding increase in vertical hydraulic gradients from 

the aquifer to wetland sediments. At low tide after installation 
48 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 21. Planar distribution of chlorinated methanes below and within the reactive mat at the seep 3-4W pilot test area, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, August 2005, (A) aquifer, (B) wetland sediments 8 feet below land surface, 

(C) wetland sediments 5 feet below land surface, (D) PTN level, (E) PTBC level, and (F) PTBB level.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 49

Figure 21. Planar distribution of chlorinated methanes below and within the reactive mat at the seep 3-4W pilot test area, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, August 2005, (A) aquifer, (B) wetland sediments 8 feet below land surface, 

(C) wetland sediments 5 feet below land surface, (D) PTN level, (E) PTBC level, and (F) PTBB level.—Continued
50 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 22. Planar distribution of chlorinated ethenes and ethanes below and within the reactive mat at the seep 3-4W pilot test 

area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, August 2005, (A) wetland sediments 5 feet below land surface, 

(B) PTN level, and (C) PTBB level.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 51

Figure 23. Vertical distribution of total chlorinated volatile organic compounds below and within the reactive 

mat at the seep 3-4W pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

August 2004–September 2005, (A) PTC4 (southwest corner), (B) PTC2 (northeast corner), and 

(C) PTC5 (southeast corner).
52 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

of the mat, median groundwater elevation in piezometers 

screened in wetland sediments from 3 to 5 ft bls showed a 

slight decrease to no change (table 10) when compared to preinstallation groundwater elevations. The variation between the 

values was largely within the standard deviation of groundwater elevation measurements (table 10). Similarly, at high tide, 

median values were slightly greater than pre-installation values; however, the standard deviation was consistently greater 

at high tide encompassing much of the observable variation in 

the median values (table 10).

Both vertical and horizontal hydraulic gradients in the 

vicinity of the reactive mat were estimated using groundwaterlevel data and then compared to pre-installation conditions in 

the same area. Vertical hydraulic gradients were calculated for 

seven piezometer clusters screened in the top of the aquifer 

and shallow (3 to 5 ft bls) wetland sediments. No variation in 

vertical hydraulic gradients was observed between low and 

high tides, with mean vertical hydraulic gradients ranging 

from 0.20 to 0.26 ft/ft, which is consistent with pre-installation 

calculations and those reported in Majcher and others (2007). 

Horizontal hydraulic gradients remained at least one to two 

orders of magnitude lower than those calculated in the vertical 

direction. The lack of an observable increase in groundwater 

elevation in shallow wetland piezometers and vertical gradients surrounding the mat indicated that the mat installation 

did not result in increased hydraulic pressure in the perimeter 

wells.

In-Mat Flow

The presence of a geotextile layer prevented the installation of piezometers through and below the reactive mat. 

Alternate methods used to assess and quantify flow through 

the mat included a potentiomanometer, seepage meters, and 

TIR imaging.

In December 2004, a potentiomanometer was used to 

assess the difference in hydraulic head between the surface 

water and porewater within the reactive mat (at location 

PTB5), and northeast of the mat boundary within the wetland 

sediments at similar depths and tide stages. The hydraulic 

head measured in the mat materials was greater than surfacewater elevation and increased with decreasing surface-water 

stage. The magnitude of hydraulic head difference between 

porewater and surface water was greater in the mat materials 

compared to the wetland sediments outside the mat at the 

same tidal stage. These measurements indicated a preferential 

flow through the mat compared with flow through the wetland 

sediments outside the mat boundary.

In July–August 2005, groundwater discharge within and 

outside of the mat was measured using a series of seepage 

meters to confirm vertical discharge through the mat during 

various stages of the tidal cycle, and to compare discharge 

with pre-installation conditions described in Majcher and 

others (2007). Meters were seated and measurements made 

within surrounding wetland sediments immediately to the 

north of the mat and along the former west and east shoring 

walls (mat boundary) toward the southern edge of the mat. 

Seepage flux to the north and west of the mat was similar, 

with some periods of recharge (negative seepage flux into 

sediments) and discharge (positive seepage flux out of the 

sediments). In these areas, the magnitude of seepage (about 

2 ft/yr) was an order of magnitude less than the geometric 

mean flux of 19 ft/yr for seep 3-4W and was comparable to 

the minimum values of seepage detected within seep 3-4W 

(Majcher and others, 2007). The values were still greater, 

however, than reported seepage flux of 0.3 to 0.9 ft/yr that was 

Figure 24. Total chlorinated volatile organic compounds in 

selected perimeter piezometers at the seep 3-4W pilot test 

area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, (A) south and (B) north of reactive mat.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 53

Figure 25. Vertical distribution of selected chlorinated volatile organic compounds below and within the reactive mat 

in the spring and summer at the seep 3-4W pilot test area site PTC4/PTB7, West Branch Canal Creek, Aberdeen Proving 

Ground, Maryland, (A) chloroethenes and chloroethanes, March 2005, (B) chloromethanes, March 2005, 

(C) chloroethenes and chloroethanes, June 2005, and (D) chloromethanes, June 2005.
54 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

typical of non-seep areas of the wetland (Majcher and others, 

2007). Seepage flux along the eastern mat boundary (37 ft/yr) 

was similar to or greater than seepage flux measured in areas 

of maximum discharge prior to mat installation, a ten-fold 

increase over the areas to the north and west.

Within the mat, meters were positioned in the southwest 

and east-central areas. Seepage measurements in both areas 

were highly variable, with periods of recharge and discharge. 

Measurements of seepage discharge within the mat were similar to measurements along the north and west areas surrounding the mat, with a geometric mean flux ranging from 0.8 to 

1.4 ft/yr.

Measurements of seepage recorded along the southeast 

boundary of the reactive mat and decreased seepage flux 

within the mat area may be attributable to a combination 

of several factors. First, one design goal of the geotextile 

was to create laminar flow throughout the treatment area. 

Normalization of flow appears to have occurred, resulting 

in an overall reduction in flux. Second, the range of seepage 

measured in most meters was near the method detection limit, 

thus reducing accuracy and sensitivity. Finally, the observed 

reduction in flux and increase in recharge may also have 

resulted from the increased head requirement to reach the top 

of the mat, which was constructed about 10 in. above land surface in the mat center. Whereas the hydraulic head differences 

appeared to be substantial enough for flow to reach the surface 

prior to installation of the mat, it is possible that the normalization of flow throughout the mat footprint may have reduced 

the head difference enough to inhibit constant discharge under 

all tidal conditions. Due to the gradual slope of the area and 

the gradual horizontal gradient in the direction of the creek, 

some part of flow from the above-grade section of the reactive 

mat may be directed horizontally to the eastern boundary of 

the mat area.

Further evidence of more normalized flow was apparent 

in the aerial TIR flight of the seep area conducted during winter 2004. The reactive mat area did not appear to be warmer 

than surrounding sediments as it had in previous flights, prior 

to installation (fig. 28a). No new seep areas were apparent in 

the wetland sediments surrounding the mat (fig. 28a); however, previously observed seep areas in the vicinity of 3-4W 

were consistent with previous flights (Majcher and others, 

2007). Consistency with previous studies and the lack of 

thermal contrast in the mat area indicated groundwater was not 

bypassing the reactive mat, at least at the time of observation. 

The seepage and TIR results implied that the area of maximum 

seepage at 3-4W was largely encompassed by the footprint of 

the mat. The possible reduction in flux and slight discharge 

towards the eastern boundary during low tide in areas above 

grade would result in a beneficially longer residence 

(treatment) time in the reactive mat.

Due to the high dosing of chitin and compost in the 

reactive mat, methane concentrations had increased substantially by the first monitoring event in November 2004 and 

may have impacted the mat hydraulics. The sharp concentration gradient of methane over a narrow thickness may have 

delayed the establishment of more homogeneous hydrologic 

conditions due to the biogenic gas generated immediately 

following installation of the mat (Beckwith and Baird, 2001; 

Himmelheber and others, 2007). At the time of installation, the 

mat pore space was not entirely saturated with wetland sediment porewater, but likely contained a mixture of porewater, 

biogenic gas, and surface water. The immediate production 

of biogenic gas may have resulted in a reduction of hydraulic 

conductivity (Beckwith and Baird, 2001). A reduction in 

methane concentration following the winter months resulted in 

a more gradual increase in methane concentration, and likely 

more consistent hydrologic conditions in the reactive mat. A 

better understanding of the effects of biogenic gas in the mat 

would be gained from the collection of intact cores.

Volatile Organic Compounds in Shallow Porewater as 

Tracers in Seep Areas

In focused seep areas such as seep 3-4W, VOCs were 

shown to be largely conserved from near sources in the aquifer 

to the wetland surface, making them useful tracers of advective groundwater flow (Majcher and others, 2007). PDSs were 

shown to be effective, economical tools to identify contaminated seeps through the presence or absence of VOCs and 

methane in the upper wetland sediments (Majcher and others, 

2007). Sediments in seep areas nearby the mat were characterized in April 2005 using PDSs and these results were used to 

assess the possible divergence of flow (and contaminants) to 

these pre-existing seeps. The PDS investigation included the 

coves along the western bank north of the reactive mat pilot 

Table 9. Estimated mass removal of chloromethanes and 

the sum of chloroethanes and chloroethenes through the 

zero-valent iron (ZVI) mix and organic mix zones in the seep 

3-4W reactive mat pilot test area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, November 2004–August 

2005.

Sampling 

event

Percent mass removal 

of chloromethanes 

PTBC1

Chloroethanes plus 

chloroethenes 

PTBB2

November 2004 97.9/98 99.9/99.6

March 2005 82.1/88.1 98.1/98.5

May 2005 90.8/85 93.7/87.1

June 2005 99.4/90.1 99.4/92.6

August 2005 92.5/67.4 98.2/94

1

 top of ZVI-organic zone

2

 middle of organic zone
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 55

test, the creek channel to the east of seep 3-4W, and previously 

identified seep area 3-3E (Majcher and others, 2007) 

(fig. 1b). VOCs were found in concentrations below their 

detection limits in northern inlet areas on the western side of 

the creek channel and in a seep along the eastern creek bank 

(3-3E), consistent with previous investigations of these areas 

(Majcher and others, 2007). 

Any local shift in contaminant transport likely would be 

most apparent within the untreated parts of seep 3-4W. PDS 

samples that were collected immediately north, south, and 

along the boundary of the reactive mat had VOC concentrations similar to those measured during fall 2002, fall 2003, and 

spring 2004 (Majcher and others, 2007) in wetland sediments 

along the western bank of the creek (fig. 28b). VOCs were 

detected between the western bank and the center of the creek 

channel; however, these VOCs were primarily daughter compounds including TCE, cis-1,2DCE, VC, and CF and methylene chloride. The presence of these daughter compounds is 

consistent with the deeper transport of parent VOCs within the 

aquifer to the western side of the creek with an upward and 

slight easterly migration of VOCs in the upper wetland sediments (Majcher and others, 2007).

Vertical cross sections of chloromethane VOC isoconcentrations, which span the western vertical plane from south 

to north (Y-Y') and the southern vertical plane from west to 

east (Z-Z'), were used to assess advective flow below and 

surrounding the reactive mat (figs. 5a, 29, and 30). In areas 

where the greatest discharge occurs, advection or macropore 

flow will control the transport of the VOCs, whereas in areas 

of lesser discharge, a combination of advection and diffusion 

across a steep concentration gradient will control VOC transport (Lorah, Spencer, and McGinty, 2005; Majcher and others, 

2007). Along cross-section Z-Z', a decline in concentrations 

of chloromethanes was observed to the north and south of the 

PTC4 profile (fig. 29), where the maximum concentrations of 

chloromethanes were mainly focused during all monitoring 

events (Appendixes 3A,B). A greater proportion of the chloromethane mass appears to be conserved in a vertical direction 

directly below the mat, as evident in the steeper concentration 

gradient in the lateral direction compared to the vertical 

direction (fig. 29). The concentration gradient did not appear 

to increase with time from mat installation at a depth of 3 ft 

bls, except during August-September 2005, when increased 

concentrations also were detected in nearby PTC1 to the north. 

A corresponding increase in total VOCs is apparent in the 

northwest perimeter piezometer PTC7 during this timeframe, 

predominantly due to an increase in chloromethanes 

(figs. 29, 31a). More variability immediately below the reactive mat was observed for chloroethenes and ethanes over time 

along section Z-Z'; however, the general VOC isoconcentration pattern, particularly from PTC4 to PTN7, was similar to 

the pattern for chloromethanes.

Along cross-section Y-Y', chloromethane concentrations 

decreased laterally from a maximum concentration along the 

wetland/aquifer boundary at PTC4 to the west and east, where 

isoconcentrations extended beyond the western and eastern 

Figure 26. Surface elevations of reactive mat and 

surrounding area at seep 3-4W reactive mat pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, (A) October 2004 and (B) March 2005.
56 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 27. Vertical distribution of mean head elevation at low tide along two lines of section after reactive mat installation, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, (A) D-D' and (B) E-E'.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 57

Table 10. Comparison of water-level elevations at low and high tide in selected piezometers before deployment of the reactive mat 

(August–September 2004) to the mean water-level elevations measured after deployment (November 2004–September 2005), seep 

3-4W pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland.

[ft, feet; --, not measured]

Piezometer

Water-level elevation (ft above mean sea level) 

September 2004 

low tide

Mean post 

deployment 

low tide

Standard 

deviation 

August 2004 

high tide

Mean post 

deployment 

high tide 

Standard 

deviation 

Wetland piezometers 

PTZ1A 1.43 1.29 0.06 1.52 1.85 0.38

PTZ2A 1.63 1.24 0.23 1.56 1.76 0.34

PTZ3A -- 1.03 0.10 -- 1.86 0.34

PTZ4A 1.39 1.17 0.12 1.48 1.82 0.40

PTZ5A -- 1.26 0.08 -- 1.68 0.39

PTZ6A 1.20 1.21 0.10 1.6 1.91 0.36

PTZ7A 1.12 0.76 0.26 1.46 1.78 0.28

PTZ8A 1.45 1.39 0.15 1.5 1.91 0.37

PTZ9A 1.44 1.37 0.04 1.63 2.01 0.35

PTZ10A 1.60 1.25 0.08 1.47 1.71 0.32

PTZ11A -- 1.51 0.35 -- 1.72 0.29

PTZ12A 1.62 1.36 0.15 1.54 1.74 0.40

PTZ13A 1.65 1.41 0.19 1.66 1.76 0.30

PTZ14A 1.00 1.01 0.38 1.32 1.89 0.38

Aquifer piezometers

PTZ1C 3.46 3.84 0.24 3.8 4.29 0.47

PTZ2C 4.00 4.00 0.29 4.1 4.46 0.40

PTZ4C 2.84 2.70 0.15 2.98 3.27 0.29

PTZ6D 3.81 3.76 0.22 3.86 4.27 0.39

PTZ9B 3.32 3.79 0.23 3.54 4.01 0.49

PTZ10B 3.67 3.80 0.23 3.67 3.71 0.91

PTZ11B 3.94 4.06 0.10 3.98 3.42 1.13
58 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

mat boundary during all monitoring events as evident in 

August 2005 (fig. 30); and this was consistent with conditions 

prior to the installation of the mat. Similar to the Z-Z' cross 

section, isoconcentrations indicated a more rapid decrease in 

VOC concentrations in the lateral direction compared to the 

vertical direction, consistent with the apparent differences 

in rates of flow in these two directions. Observations of 

total VOCs over time (including prior to mat installation) 

in perimeter wells PTC9 (to the west) and PTC12 (to the 

east) from 3 to 5 ft bls indicated that the mat did not redirect 

contaminated porewater outside of the mat area (fig. 31b). The 

lack of increased VOC concentrations in porewater to the east 

of the mat (PTC12A), despite increased seepage in this area, 

indicated no bypassing of water under the mat in an easterly 

direction.

Water Quality

Groundwater and surface water were sampled throughout 

the monitoring period to determine if the reactive mat had any 

measurable effects on water quality. Groundwater and wetland 

porewater immediately below and at shallow depths surrounding the reactive mat were sampled during the monitoring 

period for pH, specific conductance, nutrients, major ions, and 

dissolved metals. Porewater from within the reactive mat was 

not sampled due to the passive nature of sampling devices and 

resulting small volumes available from these samplers.

pH ranged from 3.6 to 4.0 throughout the monitoring 

period in both perimeter and under-mat piezometers at 3 ft bls 

(fig. 32a). The pH in under-mat piezometers from 1 to 3 ft bls 

was more variable than the perimeter piezometers, particularly at the 1 ft bls level, ranging from 3.3 to 5.8 (fig. 32b). At 

1 ft bls, a slight overall increase in pH was measured, likely 

due to the close proximity to the ZVI zone of the reactive 

mat. Specific conductance followed a similar pattern with pH 

(figs. 32c,d). Below the reactive mat, the specific conductance 

was more variable than what was observed in the perimeter 

piezometers; however, most monitoring points followed similar patterns over the monitoring period. Values of specific conductance were within the range of those reported historically 

at West Branch Canal Creek (Lorah, Spencer, and McGinty, 

2005). Variability in specific conductance is likely attributable 

to temporal changes rather than a change in water type as a 

result of mat installation.

Nutrients, ammonia, o-phosphate (as PO4), and nitrate 

(N as NO3), consistently were near or below the detection 

limits prior to and throughout the monitoring period in the 

uppermost sampling interval of perimeter piezometers and 

under-mat piezometers following mat installation 

(Appendix 1). Some isolated detections of o-phosphate and 

nitrate were found under the reactive mat (PTC3A in March 

2005 and PTC2A in May 2005), but these detections showed 

no spatial or temporal trends. These detections also may be a 

result of the warming of the sediments following the winter 

months, which results in increased microbial activity and 

possibly, increased nutrients in porewater (Lorah, Spencer, and 

McGinty, 2005). Similarly, some isolated detections of nutrients were measured in perimeter piezometers during various 

sampling events with maximum concentrations of ammonia, 

o-phosphate, and nitrate detected at 1.05, 5.1, and 0.75 mg/L, 

respectively, during different sampling events from different 

piezometers.

Some dissolved metals and ions had the potential to 

increase nearby groundwater concentrations following mat 

installation due to pH or redox changes, as indicated by preinstallation SEP analysis. A slight increase in dissolved calcium concentrations was observed in the uppermost sampling 

interval of PTC3, possibly as a result of the elevated concentration of calcium found in the crab compost fraction of the 

reactive mat. Perimeter piezometers indicated variable concentrations of calcium, increasing over time in PTC6, PTC8, and 

PTC10, but remaining steady in PTC12. A slight increase also 

was observed in sodium concentrations from PTC3, PTC6, 

and PTC12 over the monitoring period.

Immediately below the reactive mat (PTC3A), arsenic, 

lead, and zinc slightly increased over the monitoring period, 

while mercury and nickel remained steady or decreased 

over time when compared to pre-installation concentrations 

(Appendix 2). Perimeter piezometers had stable to declining 

concentrations of dissolved metals. Aluminum and manganese, 

two metals without PECs, generally increased in concentration 

over time both below and around the reactive mat.

Figure 28a. Thermal infrared image of the seep 3-4W 

reactive mat pilot test area, West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland, 2005.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 59

Figure 28b. Total volatile organic compound concentrations detected in passive diffusion samplers installed following thermal infrared 

imaging of the seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, 2005.
60 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 29. Vertical distribution of chloromethanes along line of section Z-Z', seep 3-4W reactive mat pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, August 2005.

Figure 30. Vertical distribution of chloromethanes along line of section Y-Y', seep 3-4W reactive mat pilot test area, 

West Branch Canal Creek, Aberdeen Proving Ground, Maryland, August 2005.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 61

Monthly surface-water-quality sampling (pH, specific 

conductance, nutrients, dissolved metals, and VOCs) in the 

creek channel next to the reactive mat was conducted and 

results were compared to pre-installation water quality to 

assess seasonal variations. A slight decrease in pH was noted 

after the reactive mat was installed, however, seasonally pH 

values were consistent, with median values ranging from 7.6 

(August 2004) to 7.0 (February 2005). Similarly, specific 

conductance was consistent during pre- and post-installation 

conditions; however, a reduction in specific conductance was 

observed in December 2004, likely due to the freezing of 

surface water. Nutrient concentration variability appeared to 

be highly dependent on season, masking any minimal impact 

of the mat materials. Ammonia, o-phosphate, and nitrate 

plus nitrite were consistently higher during winter and spring 

sampling events compared to summer events, likely due to the 

growing season in the wetland. During the growing season, 

wetland plants appeared to utilize excess nutrients in porewater. Baseline conditions were sampled in August 2004, and 

concentrations appeared to increase following installation 

and then decreased again during the post-installation summer 

monitoring events. Nutrients from the reactive mat appeared to 

be inconsequential in the natural nutrient cycling observed in 

the creek.

Of the several dissolved metals sampled before and after 

installation of the mat, seven metals (aluminum, arsenic, 

copper, iron, selenium, mercury, and silver) were consistently 

observed before and after deployment and with minor seasonal 

variation in concentration (Appendix 2). Concentrations of 

cadmium, lead, cobalt, manganese, and zinc increased in 

surface water following mat installation. Maximum concentrations of these metals were detected at low tidal stage, indicating that the increase in surface water may be due to increases 

in base-flow concentrations. Increases in the concentrations 

of three of these metals corresponded to increases observed in 

groundwater (lead, manganese, and zinc), despite the lack of 

change in pH or redox conditions surrounding the mat. Except 

for one isolated detection of copper in surface water, concentrations in all samples were substantially lower than USEPA 

established ambient water-quality criteria (U.S. Environmental 

Protection Agency, 2006).

Surface-water samples collected along the western 

part of the creek channel showed little change in total VOC 

concentrations following deployment of the reactive mat. 

Comparisons of surface-water concentrations collected 

monthly following deployment with baseline conditions 

in August 2004 and previous surface-water investigations 

(Majcher and others, 2007) indicate a similar range in concentrations before (fig. 33a) and after installation of the mat 

(figs. 33b,c). Surface-water VOCs were dominated by CF 

and CT, two of the main parent VOCs found at seep 3-4W. 

Maximum concentrations were detected during the winter 

months, when surface-water mixing was inhibited by ice 

(fig. 33b). Concentrations detected in surface water were 

affected by tidal stage throughout the monitoring period, with 

maximum concentrations typically detected during low tidal 

stage and minimum concentrations detected during times of 

higher tidal stage (figs. 33b,c).

Overall, results indicated that the installation of the reactive mat had a negligible effect on the quality of groundwater 

in wetland sediments below and surrounding the reactive mat 

and on surface water near the pilot test area. Future applications of the reactive mat would benefit from the evaluation 

of in-mat porewater using dialysis samplers if small volume 

analysis could be performed.

Figure 31. Concentrations of total volatile organic compounds 

detected in perimeter piezometers, seep 3-4W reactive mat pilot 

test area, West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, August 2004–September 2005, (A) west of reactive 

mat and (B) south of reactive mat.
62 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Figure 32. Quality of wetland sediment porewater, seep 3-4W reactive mat pilot test area, West Branch Canal Creek, Aberdeen 

Proving Ground, Maryland, September 2004–05, (A) pH in perimeter piezometers, (B) pH in under-mat samplers, (C) specific 

conductance in perimeter piezometers, and (D) specific conductance in under-mat samplers.
Performance of a Reactive Mat Pilot Test for Enhanced Bioremediation 63

Figure 33. Selected volatile organic compounds in surface water at the seep 3-4W reactive mat pilot test 

area, West Branch Canal Creek, Aberdeen Proving Ground, Maryland, (A) August 2004, (B) February 2005, 

and (C) June 2005.
64 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Summary and Conclusions

Localized preferential discharge areas (seeps) transport 

groundwater contaminated with carbon tetrachloride, chloroform, tetrachloroethene, trichloroethene, and 1,1,2,2-tetrachloroethane from the Canal Creek aquifer to land surface 

of a tidal wetland and stream at West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland. Due to the lack of in 

situ remediation methods for sensitive wetland environments 

and the suite of contaminants found in these seep areas, the 

U.S. Geological Survey, in cooperation with the U.S. Army 

Garrison, Aberdeen Proving Ground, Maryland, conceived and 

designed a permeable reactive mat that was placed horizontally at the seep surface to provide a zone of enhanced degradation for groundwater contaminants flowing upward to the 

groundwater/surface-water interface. The reactive mat concept 

was pilot tested at seep area 3-4W along West Branch Canal 

Creek and monitored from October 2004 through October 

2005. The reactive mat consisted primarily of a mixture of 

commercially available organic- and nutrient-rich peat and 

compost that was bioaugmented with a dechlorinating microbial consortium, WBC-2, developed for this enhanced bioremediation study. A layer of zero-valent iron (ZVI) mixed with 

the peat and compost was added to the base of the reactive mat 

because of the elevated chlorinated methane concentrations in 

the seep selected for the pilot test.

The reactive mat for seep area 3-4W was designed to 

optimize chlorinated volatile organic compound degradation 

efficiency without altering the geotechnical and hydraulic 

characteristics, or creating undesirable water quality, in the 

surrounding wetland area, which is described in this report as 

achieving geotechnical, hydraulic, and water-quality compatibility. Optimization of degradation efficiency was achieved 

through the selection of a sustainable reactive matrix, electron 

donor, and bioaugmentation method for WBC-2. The reactive 

mat was comprised of two primary reactive zones—a lower 

zone designed to enhance abiotic and biotic degradation of 

chlorinated methanes, and an upper zone designed to enhance 

biodegradation of the remaining chlorinated methanes, 

ethanes, and ethenes. The lower zone (termed the ZVI-organic 

zone) was comprised of ZVI filings combined with an organic 

matrix that consisted of a mixture of commercially available 

crab-derived compost, reed sedge peat, and sand. The upper 

zone (organic zone) was comprised of the compost-peat-sand 

mixture bioagumented with WBC-2. Chitin was also added to 

this mixture as a persistent electron donor.

During the design phase, geotechnical compatibility 

was considered through the evaluation of bearing capacity, 

settlement, and geotextile selection. Tolerable thickness based 

on bearing capacity calculations ranged from 2 to 3 feet. 

Predicted settlement ranged from 0.17 to 1.4 feet for unconsolidated and consolidated sediments, respectively, and was 

calculated to occur between 1.5 and 6 years following installation of the reactive mat. The sediment and matrix properties 

indicated that a nonwoven geotextile with a cross-plane flow 

greater than that of the native sediments was suitable as the 

base of the reactive mat. At the time of installation, the mat 

measured 22 inches in thickness above land surface.

Hydraulic compatibility was considered in the design 

phase by comparing the hydrologic properties of the seep 

sediments to the expected properties of the reactive matrix 

and evaluating the potential for fluidization of the reactive mat 

materials in the artesian conditions at the seep area. Each of 

the reactive mat materials had a hydraulic conductivity greater 

than the surrounding wetland sediments, and the mat mixture 

was optimized to consist of 1.5 parts compost, 1.5 parts peat, 

and 1 part sand as a safeguard against fluidization. In addition, 

a nonwoven geotextile was selected for installation between 

the iron mix zone and the organic zone to create more laminar 

flow conditions within the mat.

 Water-quality compatibility was considered in the design 

phase by total metals and sequential extraction procedure 

analysis of native sediments and matrix materials. Results of 

total metals analysis from three native seep sediment samples 

revealed that arsenic, lead, mercury, nickel, and zinc concentrations were greater than consensus-based probable effect 

concentrations for metals in sediment. These metals were 

bound mostly in the organic, carbonate, non-crystalline, or 

metal hydroxide fractions, which could be solubilized at low 

pH and under the highly reducing conditions that would be 

generated in the reactive mat. Analysis of the compost used in 

the pilot test showed concentrations that ranged from one-half 

to one order of magnitude below consensus-based probable 

effect concentrations for all metals in sediment.

In October 2004, installation of a reactive mat pilot test 

was completed at a part of seep area 3-4W along West Branch 

Canal Creek, and its performance relative to the design objectives was monitored through October 2005. Throughout the 

monitoring period the mat was assessed for conditions that 

would facilitate anaerobic degradation (primarly biodegradation) of chlorinated volatile organic compounds. Redoxsensitive constituents (ammonia, iron, sulfide, methane), 

hydrogen, and WBC-2 activity were assessed to evaluate a 

change from iron-reducing to methanogenic conditions that 

are favored by WBC-2. Consistent with results from previous 

investigations, the amount of methane in samples proved to be 

the most valuable indicator for appropriate redox conditions. 

Methane could be used alone (or in combination with iron) in 

future applications for a more streamlined analytical program 

to evaluate mat redox conditions.

The immediate dosing of electron donor within the 

organic matrix (crab compost and chitin) resulted in a rapid 

establishment in methane concentrations throughout the mat, 

with relatively high concentrations detected by the first monitoring event in November 2004. Methanogenic conditions 

were maintained, particularly just above the ZVI-organic zone, 

throughout the entire monitoring period. A decline in methane concentrations was observed over the winter months at 

sampling points closest to land surface in the organic zone, as 

indicated by the decreased concentrations between November 

2004 and March 2005. Between May and September 2005, 

methane concentrations correlated with volatile organic compound concentrations in the reactive mat, particularly at the 

top of the ZVI-organic zone.
Summary and Conclusions 65

Results of reactive mat material microbial activity tests 

indicated that microbial activity, stimulated at least in part 

by the WBC-2 bioaugmentation within the reactive mat, was 

sufficient to maintain dechlorinated activity even following 

the winter months, and that no additional bioaugmentation or 

biostimulation was required.

Maximum concentrations of volatile organic compounds 

were typically detected in the spring at all depths. Variation 

in concentrations within the reactive mat was consistent with 

volatile organic compound loading from underlying depths 

and was largely concentrated in the southwest corner of the 

mat. Maximum concentrations of chloromethanes, chloroethenes, and chloroethanes at all depths during all seasons of the 

monitoring period occurred primarily in the southwesternwestern area of the mat footprint. Maximum concentrations 

were detected in monitoring points along the southwest 

boundary and extended beyond the boundaries of the mat in all 

directions. Concentration reduction from immediately below 

the reactive mat to immediately above the ZVI-organic zone 

was typically at least an order of magnitude. Further removal 

was frequently observed between the ZVI-organic and organic 

zones. Variation between the concentrations within the reactive mat was generally small in spite of significant concentration gradients observed at deeper depths within the same 

area, reflective of substantial mass removal of volatile organic 

compounds over the narrow mat thickness.

Estimates of mass removal between the base of the mat 

and the middle of the organic zone were made during the 

monitoring period to compare to the design goal of 90-percent 

removal of total volatile organic compounds. The median mass 

removal of chloromethanes and chloroethenes plus chloroethanes during the entire performance monitoring period 

was 98 and 94 percent, respectively. The minimum removal 

in the ZVI-organic level occurred in March 2005. The minimum removal in the upper organic level occurred during May 

2005, corresponding to the increased loading from underlying 

sediment.

An analysis of individual volatile organic compounds 

indicated that during baseline conditions and throughout the 

monitoring period in the southwest corner of the mat, parent 

compounds carbon tetrachloride, chloroform, tetrachloroethene, trichloroethene, and 1,1,2,2-tetrachloroethane were 

conserved in the vertical direction through the wetland sediments to a depth of 5 feet below land surface. Following mat 

installation, transient appearance of primarily trichloroethene, 

cis-1,2-dichloroethene, vinyl chloride, and methylene chloride 

was observed in the southwest part of the mat itself. Ethene 

and ethane were consistently detected in the mat. Overall, 

these results contrast with pre-installation results, which 

showed little to no removal of parent volatile organic compounds in the upper sediments.

During the monitoring period, no atypical hydrologic 

occurrences were observed in the broader West Canal Creek 

study area. Groundwater discharge remained predominantly 

vertical following mat installation and during the monitoring 

period over high and low tides to the north, south, east, and 

west of the reactive mat. No variation in vertical hydraulic 

gradients was observed between low and high tide, with mean 

vertical gradients ranging from 0.20 to 0.26 feet/feet, which is 

consistent with pre-installation calculations and those reported 

in an earlier study. Horizontal hydraulic gradients remained 

at least one to two orders of magnitude lower than those 

calculated in the vertical direction. The lack of an observable 

increase in vertical gradient surrounding the mat indicates that 

its installation did not result in increased hydraulic pressure in 

nearby wells.

Within the reactive mat itself, the magnitude of hydraulic 

head difference between porewater and surface water was 

greater in the mat materials compared to the wetland 

sediments surrounding the mat at the same tide stage. These 

measurements indicated a preferential flow through the mat 

materials along the southeast boundary compared to wetland 

sediments outside the mat boundary.

Evidence of the more laminar flow conditions was 

apparent in the aerial thermal infrared flight of the seep area 

conducted during winter 2005. The seep area treated with 

the reactive mat did not appear to be thermally warmer than 

surrounding sediments as it had in previous flights prior to 

installation. No new seep areas were apparent in the wetland 

sediments surrounding the mat either to the west or east of the 

creek channel; however, previously observed seep areas near 

3-4W were consistent with previous flights. Passive sampling 

of the porewater of these nearby seep areas indicated that 

transport of volatile organic compounds had not shifted as a 

result of the reactive mat installation.

No local, immediate failure of the mat or of underlying 

wetland sediments was observed during mat installation. 

Measurements of surface elevation of the mat between 

October 2004 and July 2005 indicated an average settlement 

of the mat surface of approximately 0.25 feet. This magnitude 

of settlement was near the range of settlement predicted for 

the virgin sediment curves (which predicted a range in settlement of 0.12 to 0.37 feet), confirming that the sediments were 

overconsolidated. Future applications of the reactive mat 

would benefit from either deeper placement within the native 

sediments or a thinner mat (if concentrations were lower) to 

minimize final elevation above land surface.

Results of water-quality sampling for pH, specific conductance, metals, major ions, and nutrients indicated that the 

installation of the reactive mat had a negligible effect on the 

quality of groundwater in wetland sediments below and in 

shallow sediments surrounding the reactive mat and surface 

water near the pilot test area. Future applications of the reactive mat would benefit from the evaluation of in-mat porewater using dialysis samplers if small volume analysis could be 

performed.

Overall, the reactive mat showed promise as a lowimpact, high contaminant mass removal approach to remediation of mixed chlorinated volatile organic compounds near 

the groundwater/surface-water interface. In sensitive environments such as wetlands where existing technologies are not 

feasible, the reactive mat has been shown to be a positive 

alternative. During the demonstration, mass removal goals 

were consistently achieved while compatibility with the surrounding wetland ecosystem was maintained.
66 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Acknowledgments

The authors thank the following people and agencies 

for their contributions to this study. John Wrobel, U.S. Army 

Environmental Management Division at APG, and Allison 

O’Brien, Lisa Myers, and Amy Burgess, contractors for the 

U.S. Army Environmental Management Division are thanked 

for their support. Heather Hilton, Walter Vuncannon, and the 

staff of the APG range support program provided logistical 

support during the planning and installation of the reactive 

mat. William Kriner of the U.S. Army Corps of Engineers, 

Baltimore District, loaned the drilling equipment, and William 

Smithson of the U.S. Army Center for Health and Promotion 

and Preventive Medicine, Ground Water and Solid Waste 

Program, Edgewood Area, APG, loaned soil-sampling equipment. James Agiuar and assistant personnel from the Aberdeen 

Test Center, International Imaging Center assisted with the 

aerial thermal infrared survey, and Aberdeen Test Center Tech 

Escort personnel provided unexploded ordnance clearance. 

Eric Jensen, Paul Botek, Aaron Krasnopoler, Lisa Smith, 

and Duane Graves from Geosyntec Consultants helped with 

construction, installation, and performance monitoring of 

the reactive mat. Sandra Dworatzek, Greg Dreidger, and Jeff 

Roberts of SiREM Laboratory assisted with maintenance and 

field application of the WBC-2 consortium. Donna Fennell 

(Rutgers University), Craig Benson (University of Wisconsin), 

William Schneider (Weston Solutions), and Jack Lendvay 

(University of San Francisco) provided technical review and 

input on the reactive mat design prior to installation. Thanks 

also are given to colleagues Mastin Mount (USGS, Baltimore, 

Maryland) and Joseph Beman (USGS, New Mexico) for 

assistance with field investigation preparation, sample collection, and chemical analyses, Betsy Marchand (USGS, 

Baltimore, Maryland) for volatile organic compound analyses, 

Michael Hansen (formerly of USGS, Baltimore, Maryland) for 

methane analyses, Lisa Olsen (USGS, Sacramento, California) 

and Tom Imbrigiotta (USGS, West Trenton, New Jersey) for 

data quality-assurance of volatile organic compound analyses, 

and Mary Voytek and Elizabeth Jones (USGS Reston, 

Virginia) for microbial analyses.

References Cited

Air Force Center for Environmental Excellence, 2004, 

Principles and practices of enhanced anaerobic bioremediation: Prepared under AFCEE, Contract F41624–

00–D–8024, August 2004, accessed December 9, 2008 at 

http://costperformance.org/remediation/pdf/principles_and_

practices_bioremediation.pdf.

American Society for Testing and Materials, 2001, D 2435, 

Standard test method for one-dimensional consolidation 

properties of soils, in Annual Book of ASTM Standards: 

West Conshohocken, PA, ASTM International, p. 237–245. 

American Society for Testing and Materials, 2003, D 2850, 

Standard test method for unconsolidated-undrained triaxial 

compression test on cohesive soils, in Annual Book of 

ASTM Standards: West Conshohocken, PA, ASTM 

International, p. 300–305. 

Bagley, D.M., Lalonde, M., Kaseros, V., Stasiuk, K.E., and 

Sleep, B.E., 2000, Acclimation of anaerobic systems to 

biodegrade tetrachloroethene in the presence of carbon 

tetrachloride and chloroform: Water Research, v. 34, no. 1, 

p. 171–178.

Beckwith, C.W., and Baird, A.J., 2001, Effect of biogenic gas 

bubbles on water flow through poorly decomposed peat 

blanket: Water Resources Research, v. 37, no. 3, 

p. 551–558. 

Bouwer, E.J., and McCarty, P.L., 1983, Transformation of 

halogenated organic compounds under denitrification conditions: Applied and Environmental Microbiology, v. 45, 

no. 4, p. 1,295–1,299.

Brady, W.D., Eick, M.J., Grossl, P.R., and Brady, P.V., 2003, 

A site-specific approach for the evaluation of natural 

attenuation at metals-impacted sites: Soil and Sediment 

Contamination, v. 14, no. 4, p. 541–564.

CFR Technical Services, 2005, Treatability study, 1,1,2,2-tetrachloroethane and inoculation procedure, Aberdeen 

Proving Ground: Edgewood, MD, Produced for General 

Physics, GP–R–123E05016, March 2003, 48 p. 

Clemmer, N.D., 2003, Characterization of chlorinated solvent 

degradation in a constructed wetland: Wright-Patterson Air 

Force Base, Ohio, Air Force Institute of Technology 

(Air University), M.S. Thesis, 146 p.

Coduto, D.P., 1999, Geotechnical engineering: Principles and 

practices (1st ed.): India, Pearson Education, Inc., 759 p. 
References Cited 67

Conant, B.J., Cherry, J.A., and Gillham, R.W., 2004, A PCE 

groundwater plume discharging to a river: Influence of the 

streambed and near-river zone on contaminant distributions: 

Journal of Contaminant Hydrology, v. 73, nos. 1–4, 

p. 249–279.

Das, B.M., 2002, Principles of geotechnical engineering 

(7th ed.): Pacific Grove, CA, Brooks/Cole, 589 p. 

Ellis, D.E., Lutz, E.J., Odom, J.M., Buchanan, R.J., Jr., 

Bartlett, C.L., Lee, M.D., Harkness, M.R., and Deweerd, 

K.A., 2000, Bioaugmentation for accelerated in situ

anaerobic bioremediation: Environmental Science and 

Technology, v. 34, no. 11, p. 2,254–2,260.

Environmental Security Technology Certification Program, 

2005, Bioaugmentation for remediation of chlorinated solvents: Technology development, status, and research needs: 

October 2005, accessed October 26, 2009 at http://www.

clu-in.org/download/remed/bioaug2005.pdf

Fishman M.J., ed., 1993, Methods of analysis by the U.S. 

Geological Survey National Water-Quality Laboratory—

Determination of inorganic and organic constituents in 

water and fluvial sediments: U.S. Geological Survey OpenFile Report 93–125, 217 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

General Physics Corporation, 2005, Remedial investigation 

report, Westwood study area, Aberdeen Proving Ground, 

Maryland: Edgewood, MD, [variously paged.]

Geosyntec Consultants, Inc., 2004, Interim technical status 

report: Microbial consortium growth and characterization: Knoxville, TN, Geosyntec Consultants, Inc., Project 

Number KE0008, 45 p.

Geosyntec Consultants, Inc., 2007, Final technical status 

report: Microbial consortium growth and characterization: Knoxville, TN, Geosyntec Consultants, Inc., Project 

Number KE0008, [variously paged.]

Gillham, R.W., and O’Hannesin, S.F., 1994, Enhanced 

degradation of halogenated aliphatics by zero-valent iron: 

Ground Water, v. 32, no. 6, p. 958–967.

Haberl, R., Grego, S., Langergraber, G., Kadlec, R.H., 

Cicalini, A.-R., Dias, S.M., Novais, J.M., Aubert, S., Gerth, 

A., Thomas, H., and Hebner, A., 2003, Constructed wetlands for the treatment of organic pollutants: Journal of 

Soils and Sediments, v. 3, no. 2, p. 109–124.

Harvey, J.W., Chambers, R.M., and Hoelscher, J.R., 1995, 

Preferential flow and segregation of porewater solutes in 

wetland sediment: Estuaries, v. 18, no. 4, p. 568–578.

Himmelheber, D.W., Pennell, K.D., and Hughes, J.B., 2007, 

Natural attenuation processes during in situ capping: 

Environmental Science and Technology, v. 41, no. 15, 

p. 5,306–5,313. 

Holtz, R.D., and Kovacs, W.D., 1981, Introduction to geotechnical engineering: Prentice Hall, 733 p. 

Ingersoll, C.G., MacDonald, D.D., Wang, N., Crane, J.L., 

Field, L.J., Haverland, P.S., Kemble, N.E., Lindskoog, 

R.A., Severn, C., and Smorong, D.E., 2000, Prediction of 

sediment toxicity using consensus-based freshwater sediment quality guidelines: Chicago, IL, U.S. Environmental 

Protection Agency Great Lakes National Program Office, 

EPA 905/R-00/007, 33 p., accessed December 9, 2008 at 

http://www.cerc.usgs.gov/pubs/center/pdfdocs/91126.pdf.

Jones, E.J.J., Voytek, M.A., Lorah, M.M., and Kirshstein, J.D., 

2006, Characterization of a microbial consortium capable 

of rapid and simultaneous dechlorination of 1,1,2,2-tetrachloroethane and ethane and ethene intermediates: 

Bioremediation Journal, v. 10, no. 4, p. 153–168. 

Kassenga, G.R., Pardue, J.H., Blair, S., and Ferraro, T., 2003, 

Treatment of chlorinated volatile organic compounds in 

upflow wetland mesocosms: Ecological Engineering, v. 19, 

no. 5, p. 305–323.

Kassenga, G., Pardue, J.H., Moe, W.M., and Bowman, K.S., 

2004, Hydrogen thresholds as indicators of dehalorespiration in constructed treatment wetlands: Environmental 

Science and Technology, v. 38, no. 4, p. 1,024–1,030.

Koerner, R.M., 1998, Designing with Geosynthetics (4th ed.): 

Upper Saddle River, NJ, Prentice-Hall, Inc., 761 p. 

Lorah, M.M., and Clark, J.S., 1996, Contamination of ground 

water, surface water, and soil, and evaluation of selected 

ground-water pumping alternatives in the Canal Creek area 

of Aberdeen Proving Ground, Maryland: U.S. Geological 

Survey Open-File Report 95–282, 318 p.

Lorah, M.M., Majcher, E.H., Jones, E.J., Dreidger, G., 

Dworatzek, S., and Graves, D., 2005a, Electron donor 

preference of reductive dechlorinating consortium 

in Alleman, B.C., and Kelley, M.E. eds., In Situ and 

On-Site Bioremediation—2005, Proceedings of the 

Eighth International In Situ and On-Site Bioremediation 

Symposium, Baltimore, Maryland, June 6–9, 2005.

Lorah, M.M., Majcher, E.H., Jones, E.J., Dreidger, G., 

Dworatzek, S., and Graves, D., 2005b, Physiological characterization of a broad spectrum reductively dechlorinating 

consortium in Alleman, B.C., and Kelley, M.E. eds., In Situ

and On-Site Bioremediation—2005, Proceedings of the 

Eighth International In Situ and On-Site Bioremediation 

Symposium, Baltimore, Maryland, June 6–9, 2005.
68 Design and Performance of an Enhanced Bioremediation Pilot Test in a Tidal Wetland Seep, APG, MD

Lorah, M.M, Majcher, E.H., Jones, E.J., and Voytek, M.A., 

2008, Microbial consortia development, batch microcosms, 

and column experiments for enhanced bioremediation of 

chlorinated volatile organic compounds, West Branch Canal 

Creek wetland area, Aberdeen Proving Ground, Maryland: 

U.S. Geological Survey Scientific Investigations Report 

2007–5165, accessed December 9, 2008 at http://md.water.

usgs.gov/publications/sir-2007-5165/index.html.

Lorah, M.M., and Olsen, L.D., 1999, Degradation of 

1,1,2,2-tetrachloroethane in a freshwater tidal wetland: 

Field and laboratory evidence: Environmental Science and 

Technology, v. 33, no. 2, p. 227–234.

Lorah, M.M., Olsen, L.D., Smith, B.L., Johnson, M.A., and 

Fleck, W.B., 1997, Natural attenuation of chlorinated 

volatile organic compounds in a freshwater tidal wetland, 

Aberdeen Proving Ground, Maryland: U.S. Geological 

Survey Water-Resources Investigations Report 97–4171, 

95 p. 

Lorah, M.M., Spencer, T.A. and McGinty, A.L., 2005, 

Temporal changes in indicators of natural attenuation and 

physical controlling factors for a freshwater tidal wetland 

contaminated with chlorinated volatile organic compounds, 

West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, 1995–2001: U.S. Geological Survey Scientific 

Investigations Report 2005–5057, 64 p.

Lorah, M.M., Voytek, M.A., Kirshtein, J.D., and (Phillips) 

Jones, E.J., 2003, Anaerobic degradation of 1,1,2,2-tetrachloroethane and association with microbial communities 

in a freshwater tidal wetland, Aberdeen Proving Ground, 

Maryland: Laboratory experiments and comparisons 

to field data: U.S. Geological Survey Water-Resources 

Investigations Report 02–4157, 64 p.

MacDonald, D.D., and Ingersoll, C.G., 2002, A guidance 

manual to support the assessment of contaminated sediment in freshwater ecosystems, Volume III—Interpretation 

of the results of sediment quality investigations: Chicago, 

IL, U.S. Environmental Protection Agency Great Lakes 

National Program Office, EPA–905–B02–001–C, accessed 

December 9, 2008 at http://www.cerc.usgs.gov/pubs/sedtox/

VolumeIII.pdf.

MacDonald, D.D., Ingersoll, C.G., and Berger, T., 2000, 

Development and evaluation of consensus-based sediment 

quality guidelines for freshwater ecosystems: Archives of 

Environmental Contamination and Toxicology, v. 39, 

p. 20–31.

Majcher, E.H., Phelan, D.J., Lorah, M.M., and McGinty, A.L., 

2007, Characterization of preferential ground-water seepage from a chlorinated hydrocarbon-contaminated aquifer 

to West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, 2002–04: U.S. Geological Survey Scientific 

Investigations Report 2006–5233, accessed December 9, 

2008, at http://pubs.usgs.gov/sir/2006/5233/.

Major, D.W., McMaster, M.L., Cox, E.E., Edwards, E.A., 

Dworatzek, S.A., Hendrickson, E.R., Starr, M.G., Payne, 

J.A., and Buonamici, L.W., 2002, Field demonstration of 

successful bioaugmentation to achieve dechlorination of 

tetrachloroethene to ethene: Environmental Science and 

Technology, v. 36, no. 23, p. 5,106–5,116.

Maymó-Gatell, X., Chien, Y.-T., Gossett, J.M., and Zinder, 

S.H., 1997, Isolation of a bacterium that reductively 

dechlorinates tetrachloroethene to ethene: Science, v. 276, 

p. 1,568–1,571.

Mitsch, W.J., and Gosselink, J.G., 1993, Wetlands: (2d ed.): 

New York, Van Nostrand Reinhold, 722 p. 

Naval Facilities Engineering Command, 1986, Soil mechanics design manual 7.01: Alexandria, VA, Naval Facilities 

Engineering Command, [variously paged.]

Nemeth, G., 1989, RCRA facility assessment report, 

Edgwood Area, Aberdeen Proving Ground, Maryland: 

U.S. Army Environmental Hygiene Agency, Waste 

Disposal Engineering Division, Aberdeen Proving Ground, 

Maryland, Project 38–26–0490–90, 929 p.

Novak, P.J., Daniels, L., and Parkin, G.F., 1998, Rapid dechlorination of carbon tetrachloride and chloroform by extracellular agents in cultures of Methanosarcina thermophila: 

Environmental Science and Technology, v. 32, no. 20, 

p. 3,132–3,136.

Oliveros, J.P., and Vroblesky, D.A., 1989, Hydrogeology of 

the Canal Creek area, Aberdeen Proving Ground, Maryland: 

U.S. Geological Survey Water-Resources Investigations 

Report 89–4021, 71 p.

Olsen, L.D., Lorah, M.M., Marchand, E.H., Smith, B.L., and 

Johnson, M.A., 1997, Hydrogeologic, water-quality, and 

sediment-quality data for a freshwater tidal wetland, West 

Branch Canal Creek, Aberdeen Proving Ground, Maryland, 

1992–96: U.S. Geological Survey Open-File Report 

97–560, 267 p.

O’Niell, W.L., Nzengung, V.A., Noakes, J.E., Bender, J., and 

Phillips, P.C., 1999, Biosorption and transformation of tetrachloroethylene and trichloroethylene using mixed-species 

microbial mats: Journal of Hazardous Substance Research, 

v. 2, p. 2–1 to 2–16. 
References Cited 69

Palermo, M., Maynord, S., Miller, J., and Reible, D., 1998, 

Guidance for in-situ subaqueous capping of contaminated 

sediments: Chicago, IL, U.S. Environmental Protection 

Agency Great Lakes National Program Office, EPA 905–

B96–004, [variously paged.]

Pardue, J.H., 2002, Remediating chlorinated solvents in wetlands: Natural processes or an active approach? in Wetlands 

and Remediation II, Proceedings of the Second International 

Conference on Wetlands & Remediation, September 5–6, 

2001: Burlington, Vermont, Battelle Press, Columbus, 

Ohio, p. 1–8.

Phelan, D.J., Fleck, W.B., Lorah, M.M., and Olsen, L.D., 

2002, Changes in ground-water quality in the Canal Creek 

aquifer between 1995 and 2000–2001, West Branch Canal 

Creek Area, Aberdeen Proving Ground, Maryland: U.S. 

Geological Survey Water-Resources Investigations Report 

02–4076, 42 p. 

Phelan, D.J., Olsen, L.D., Senus, M.P., and Spencer, T.A., 

2001, Assessment of volatile organic compounds in surface 

water at Canal Creek, Aberdeen Proving Ground, Maryland, 

November 1999–September 2000: U.S. Geological Survey 

Water-Resources Investigations Report 01–292, 49 p.

Phelan, D.J., Senus, M.P., and Olsen, L.D., 2001, Lithologic 

and ground-water-quality data collected using hoverprobe 

drilling techniques at the West Branch Canal Creek, 

Aberdeen Proving Ground, Maryland: U.S. Geological 

Survey Open-File Report 00–446, 43 p.

Portnoy, J.W., Nowicki, B.L., Roman, C.T., and Urish, D.W., 

1998, The discharge of nitrate-contaminated groundwater 

from developed shoreline to marsh-fringed estuary: Water 

Resources Research, v. 34, no. 11, p. 3,095–3,104. 

Reible, D., Lampert, D., Constant, D., Mutch, R.D., Jr., 

and Zhu, Y., 2006, Active capping demonstration in the 

Anacostia River, Washington, D.C.: Remediation Journal, 

v. 17, no. 1, p. 39–53.

Richard, D.E., Connell, D., Berns, J.J., and Hirl, P.J., 2001, 

Assessment of a reconstructed wetland for remediation of 

chlorinated solvents, in Second International Conference on 

Wetlands & Remediation, September 5–6, 2001, Burlington, 

Vermont: Columbus, OH, Battelle Press, p. 117–124.

Schmertmann, J.H., 1953, Estimating the true consolidation 

behavior of clay from laboratory test results: ASCE Journal 

of the Soil Mechanics and Foundations Division, v. 79, 

p. 1–26. 

Schultz, M.K., Burnett, W.C., Inn, K.G.W., Thomas, 

J.W.L., and Lin, Z., 1996, Conference report by the NIST 

Speciation Workshop: Journal of Research of the National 

Institute of Standards and Technology, v. 101, no. 5, 

p. 707–715.

Spencer, T.A., Phelan, D.J., Olsen, L.D., and Lorah, M.M., 

2002, Water-quality data for a freshwater tidal wetland, 

West Branch Canal Creek, Aberdeen Proving Ground, 

Maryland, November 1999 through May 2000: U.S. 

Geological Survey Open-File Report 01–420, 302 p.

U.S. Army Corps of Engineers, 1990, Engineering and design: 

Settlement analysis: 1990, Department of the Army: Army 

Corps of Engineers: Washington, D.C., Engineering 

Manual No. 1110–1–1904, accessed October 26, 2009 at 

http://140.194.76.129/publications/eng-manuals/em1110-1-

1904/entire.pdf

U.S. Environmental Protection Agency, 2002, Biochlor version 2.2, accessed December 9, 2008 at http://www.epa.gov/

ada/csmos/models/biochlor.html.

U.S. Environmental Protection Agency, 2006, National recommended water quality criteria: Office of Water, accessed 

December 9, 2008 at http://www.epa.gov/waterscience/

criteria/wqctable/.

Vikesland, P.J., Klausen, J., Zimmerman, H., Roberts, A.L., 

and Ball, W.P., 2003, Longevity of granular iron in groundwater treatment processes: changes in solute transport properties over time: Journal of Contaminant Hydrology, 

v. 64, nos. 1 and 2, p. 3–33.

Vroblesky, D.A., 2001, User’s guide for polyethylene-based 

passive diffusion bag samplers to obtain volatile organic 

compound concentrations in wells, Part 1: Deployment, 

recovery, data interpretation and quality control and 

assurance: U.S. Geological Survey Water-Resources 

Investigations Report 01–4060, 18 p.

Weathers, L.J., and Parkin, G.F., 2000, Toxicity of chloroform 

biotransformation to methanogenic bacteria: Environmental 

Science and Technology, v. 34, no. 13, p. 2,764–2,767.

Weathers, L.J., Parkin, G.F., and Alvarez, P.J., 1997, 

Utilization of cathodic hydrogen as electron donor for chloroform cometabolism by a mixed, methanogenic culture: 

Environmental Science and Technology, v. 31, no. 3, 

p. 880–885.

Weston Solutions (Weston), 2005, Canal Creek Study Area, 

Remedial investigation report—volume 1, West Canal 

Creek aquifer and Building E-5188 site, draft, [variously 

paged.] 

Winter, T.C., Harvey, J.W., Franke, O.L., and Alley, W.M. 

1998, Ground water and surface water, a single resource: 

U.S. Geological Survey Circular 1139, 79 p. 

Winter, T.C., LaBaugh, J.W., and Rosenberry, D.O., 1988, 

The design and use of a hydraulic potentiomanometer 

for direct measurement of differences in hydraulic head 

between groundwater and surface water: Limnology and 

Oceanography, v. 33, no. 5, p. 1,209–1,214.

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