W912DR18R0055_-_Attachment_AA_-_DSCR_OU8_BDGR_Work_Plan_1-18-2017_track_changes.pdf

FINAL

PILOT TEST DESIGN

OPERABLE UNIT 8

BIO-ENHANCED DIRECTED GROUNDWATER

RECIRCULATION

DEFENSE SUPPLY CENTER RICHMOND

Prepared For

Defense Logistics Agency

And

Defense Supply Center Richmond

February 2017 arcadis.com i

FINAL

OPERABLE UNIT 8

BIO-ENHANCED DIRECTED GROUNDWATER

RECIRCULATION

DEFENSE SUPPLY CENTER RICHMOND

Prepared For:

Defense Supply Center Richmond

Prepared By:

Arcadis U.S., Inc.

Contract No. W912DR-13-D-0019

Delivery Order 0005 arcadis.com ii

Defense Supply Center Richmond Operable Unit 8 Bio-enhanced Directed Groundwater Recirculation

Prepared for:

Defense Supply Center Richmond and

Prepared by:

Arcadis U.S., Inc.

701 Town Center Drive

Suite 600

Newport News

Virginia 23606-4296

Tel 757 873 8700

Fax 757 873 8723

Our Ref.:

02118201.0000

Date:

This document is intended only for the use of the individual or entity for which it was prepared and may contain information that is privileged, confidential and exempt from disclosure under applicable law. Any dissemination, distribution or copying of this document is strictly prohibited.

Christopher Spooner, P.E.

Senior Engineer

Scott Potter, P.E., P.G.

Principal Hydrogeologist

Courtney Ingersoll

Project Manager arcadis.com iii

CONTENTS

Acronyms and Abbreviations ....................................................................................................................... vii

Executive Summary

1 Introduction .......................................................................................................................................... 1-1

1.1 Background .................................................................................................................................. 1-1

1.2 Purpose and Objectives ............................................................................................................... 1-3

1.3 Technology Overview .................................................................................................................. 1-4

1.4 Work Plan Organization ............................................................................................................... 1-5

2 Conceptual Site Model ......................................................................................................................... 2-1

2.1 Summary of Existing Conditions .................................................................................................. 2-1

2.1.1 Geology ............................................................................................................................ 2-1

2.1.2 Hydrogeology ................................................................................................................... 2-1

2.1.3 Summary of Dissolved Phase Constituents Nature and Extent ....................................... 2-2

2.2 Overview of Previous Site Investigations and Pilot Studies ........................................................ 2-2

2.2.1 Initial Discovery ................................................................................................................ 2-2

2.2.2 Initial Field Investigation ................................................................................................... 2-2

2.2.3 Remedial Investigation and Additional Field Investigations ............................................. 2-3

2.2.4 Focused Feasibility Study ................................................................................................ 2-3

2.2.5 Pilot Test of the Vapor Vacuum Extraction and Treatability Study of the Dual Phase Extraction System .......................................................................................................................... 2-4

2.2.6 Additional Site Investigations and Revised FFS .............................................................. 2-5

2.2.7 Pilot Test of In-situ Bioremediation and Chemical Oxidation ........................................... 2-5

2.3 Summary of Site Data .................................................................................................................. 2-6

2.3.1 Soil Borings and Geotechnical Data................................................................................. 2-6

2.3.2 Hydraulic Testing .............................................................................................................. 2-7

2.3.3 Data Gaps ........................................................................................................................ 2-7

3 Design Criteria ..................................................................................................................................... 3-1

3.1 Summary of Pre-Design Investigation ......................................................................................... 3-1

3.1.1 Pump Testing ................................................................................................................... 3-1

3.1.2 MiHPT Investigation ......................................................................................................... 3-1 arcadis.com iv

3.2 Treatment Areas and Depths ....................................................................................................... 3-2

3.3 System Performance Requirements ............................................................................................ 3-2

3.3.1 Directed Groundwater Recirculation ................................................................................ 3-2

3.3.2 Enhanced Bioremediation (Anaerobic)............................................................................. 3-3

3.3.3 Groundwater Treatment ................................................................................................... 3-3

3.4 Implementation Strategy .............................................................................................................. 3-4

3.4.1 Design and System Installation Implementation .............................................................. 3-4

3.4.1.1 Project Management and Meetings ........................................................................ 3-4

3.4.1.2 Site Security and Communication .......................................................................... 3-4

3.4.1.3 Health and Safety ................................................................................................... 3-5

3.5 Permitting ..................................................................................................................................... 3-5

3.5.1 Drilling and Subsurface Installations ................................................................................ 3-5

3.5.2 Subsurface Injections ....................................................................................................... 3-5

3.5.3 VPDES Permit .................................................................................................................. 3-6

4 Directed Groundwater Recirculation Design ........................................................................................ 4-1

4.1 Recirculation System Layout ....................................................................................................... 4-1

4.1.1 Well Design and Installation ............................................................................................. 4-2

4.1.1.1 Utility Clearance ...................................................................................................... 4-2

4.1.1.2 Drilling and Well Installation ................................................................................... 4-2

4.1.1.3 Well Development and Completion ........................................................................ 4-3

4.1.1.4 Well Survey ............................................................................................................. 4-3

4.1.2 Piping and Trenching ....................................................................................................... 4-3

4.2 BDGR System Design ................................................................................................................. 4-4

4.2.1 System Description........................................................................................................... 4-4

4.2.2 System Operation ............................................................................................................. 4-6

4.3 Effluent Treatment and Discharge ............................................................................................... 4-8

5 Directed Groundwater Recirculation Implementation .......................................................................... 5-1

5.1 Performance Metrics .................................................................................................................... 5-2

5.1.1 Recirculation System Operational Performance Metrics.................................................. 5-2

5.1.2 Recirculation System Treatment Metrics.......................................................................... 5-3 arcadis.com v

5.2 Operational Sequence ................................................................................................................. 5-3

5.3 Recirculation System Start-up ..................................................................................................... 5-4

5.3.1 Start-up Period ................................................................................................................. 5-4

5.3.2 Start-up Monitoring ........................................................................................................... 5-5

5.3.3 Dye Tracer Testing ........................................................................................................... 5-5

5.3.3.1 Tracer Test Design ................................................................................................. 5-5

5.3.3.2 Tracer Chemicals .................................................................................................... 5-6

5.3.3.3 Tracer Test Completion .......................................................................................... 5-6

5.3.3.4 Monitoring Sampling and Analysis ......................................................................... 5-6

5.3.3.5 Data Evaluation and System Monitoring ................................................................ 5-7

5.4 Recirculation System Operation .................................................................................................. 5-7

5.4.1 Operational Performance and System Operation Period ................................................. 5-7

5.4.2 Performance Monitoring ................................................................................................... 5-7

5.4.2.1 Analytical Samples ................................................................................................. 5-8

5.4.2.2 Post-Amendment Injection Monitoring.................................................................... 5-8

5.4.2.3 Groundwater Treatment System Performance Monitoring ..................................... 5-9

5.5 Pilot Test Evaluation .................................................................................................................... 5-9

6 Reporting .............................................................................................................................................. 6-1

6.1 Recirculation System Implementation Summary Report ............................................................. 6-1

6.2 Annual Operation, Optimization and Maintenance Reporting ..................................................... 6-1

7 References ........................................................................................................................................... 7-1

TABLES

Table 2-1 – March 2016 OU8 Water Levels

Table 2-2 – March 2016 OU8 Groundwater Analytical Results

Table 3-1 – BDGR Effluent Treatment Requirements

Table 5-1 – BDGR Baseline Performance Monitoring

Table 5-2 – BDGR Dye Tracer Sampling

Table 5-3 – BDGR Performance Monitoring arcadis.com vi

FIGURES

Figure 1-1 – Site Location

Figure 1-2 – Site Layout

Figure 1-3 – Process Flow Diagram

Figure 2-1 – OU8 PCE Isoconcentration Contours (April 2016)

Figure 2-2 – OU8 TCE Isoconcentration Contours (April 2016)

Figure 2-3 – OU8 cis-1,2-DCE Isoconcentration Contours (April 2016)

Figure 2-4 – OU8 VC Isoconcentration Contours (April 2016)

Figure 3-1 – MiHPT Locations

APPENDIX

A MiHPT Logs

B Pilot Test Design Drawing Package

C BDGR System Control Narrative arcadis.com vii

ACRONYMS AND ABBREVIATIONS

1,2-DCE 1,2-Dichloroethene (total) cis-1,2-DCE cis-1,2-Dichloroethene

ANP Acid Neutralization Pit

APP Accident Prevention Plan

BDGR Bio-enhanced Directed Groundwater Recirculation bgs Below Ground Surface

BNA Base Neutral and Acid Extractable Compound cm/sec Centimeters Per Second

COC Compound of Concern

CVOC Chlorinated Volatile Organic Compound

DLA Defense Logistics Agency

DO Dissolved Oxygen

DOD Department of Defense

DPE Dual-Phase Extraction

DSCR Defense Supply Center Richmond

EC Electric Conductivity

ECD Electron Capture Detector

ELAP Environmental Laboratory Accreditation Program

FFS Focused Feasibility Study

FID Flame Ionization Detector

FTA Fire Training Area gpm Gallons Per Minute

HPT Hydraulic Profiling Tool

ID Inner-diameter

ISCO In-situ Chemical Oxidation

MCL Maximum Contaminant Level mg/L Milligrams Per Liter

MiHPT Membrane Interface Probe / Hydraulic Profiling Tool

MNA Monitored Natural Attenuation arcadis.com viii

ORP Oxidation Reduction Potential

OU Operable Unit

O&M Operation and Maintenance

PCE Tetrachloroethene

PID Photoionization Detector

PM Project Management

PVC Polyvinyl Chloride

QAPP Quality Assurance Project Plan

RI Remedial Investigation

ROD Record of Decision

ROI Radius of Influence

SSO Site Safety Officer

SSDS Sub-slab Depressurization System

S.U. Standard Units

TCE Trichloroethene

TOC Total Organic Carbon

U.S. United States

UIC Underground Injection Control

USACE United States Army Corp of Engineers

USEPA United Stated Environmental Protection Agency

UWBU Upper Water Bearing Unit

VCP Vitrified Clay Pipe

VDEQ Virginia Department of Environmental Quality

VOC Volatile Organic Compound

VPDES Virginia Pollutant Elimination Discharge System

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EXECUTIVE SUMMARY

The Defense Supply Center Richmond (DSCR), also known as Defense Logistics Agency (DLA) Aviation, supports more than 1,300 major weapon systems as the military's primary source for more than 1.3 million repair parts and operating supply items. Past industrial operations at the installation have resulted in the use, storage, management, inadvertent release, and/or disposal of hazardous materials, such as chlorinated volatile organic compounds (CVOCs), petroleum products, and wastewater treatment sludge.

In addition, past storage operations at the installation have led to the accidental release of these and other hazardous materials, such as polycyclic aromatic hydrocarbons, pesticides, petroleum hydrocarbons, polychlorinated biphenyls, and metals.

Operable Unit (OU)-8 is designated as the volatile organic compound (VOC) groundwater area located in the northern part of DSCR. The primary source of the OU-8 was the Acid Neutralization Pits (ANPs) that consisted of two former concrete settling pits that received wastewater from Warehouse 65 and the former conveyance pipes under Warehouse 65 that delivered the waste to the ANPs and the surrounding impacted soil located near Warehouse 65. The ANPs and the surrounding impacted soil are designated as OU-5. Based on past investigation and remedial work, it has been identified that very little source mass remains around the ANP areas. Recent investigation indicates the majority of the dissolved phase CVOC mass is located in the Bay F area on the north side of Warehouse 65, which is the former acid dipping and metal cleaning tanks. The bio-enhanced directed groundwater recirculation (BDGR) pilot study will be implemented beneath portions of OU-5 and Bay F of Warehouse 65 to provide both hydraulic control of the dissolved-phase VOC impacts, and establish a groundwater recirculation cell to deliver organic carbon in support of enhanced anaerobic degradation of the dissolved-phase VOC impacts.

This BDGR Pilot Test Design for OU-8 was prepared to document the activities, procedures and metrics by which monitoring, operations and maintenance, and optimization activities for the DLA Restoration Program will be conducted for DSCR. These metrics are detailed in the scope of work dated 22 June, 2015 from the United States (U.S.) Army Corps of Engineers (USACE) Baltimore District, and all amendments and question and answer sets under the Multiple Award Environmental Services contract, Award No. W912DR-13-D-0019, Delivery Order 0005, awarded 25 September, 2015. The BDGR Pilot Study Design is supported by a Quality Assurance Project Plan (QAPP), Project Management Plan, and the Basewide Monitoring Plan. The Design provides basis for the pilot study, presents the BDGR design criteria and details of the system design and outlines the planned BDGR implementation.

The dissolved phase VOC impacts at OU-8 are found within the unconfined upper water bearing unit (UWBU) of the surficial aquifer. The UWBU at OU-8 consists of a layer of silty sand, sandy silt and silty clay underlain by a layer of poorly graded sand with gravel, interlayered with poorly graded gravel. The UWBU is underlain by a confining unit with an approximate thickness of 5 to 10 feet. The water table is approximately 9 to 13 feet below ground surface and the more permeable sand and gravel layer of the UWBU where a significant portion of the VOC plume is present is approximately 2 to 19 feet thick. The primary organic constituents in the dissolved phase are tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dichloroehtene (cis-1,2-DCE) and vinyl chloride (VC). These organic constituents have not been detected in the lower water bearing unit or beneath the confining unit underlying the UWBU.

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Multiple pilot and treatability study remedies have been implemented to remediate the dissolved phase impacts at OU-8. However, nearly all of these studies has shown limited effectiveness because, in most cases, the remediation focused on the diffuse portion of the plume rather than directly remediating the highest dissolved phase concentrations under Bay F of Warehouse 65. The diffuse nature of the downgradient plume combined with the overall horizontal extent suggests engineering hydraulic gradients can effectively remediate the source of the diffuse groundwater plume. Through the use of BDGR, groundwater recirculation can be used to effectively engineer a dynamic flushing process that can both remove COCs from the aquifer (via extraction) and increase the overall extent of in-situ COC treatment through enhanced anaerobic biodegradation (via re-injection of a carbon amended water).

Past site data have shown the aquifer pH to be naturally low, which can inhibit complete reductive dechlorination to ethene and ethane. Although historic site remediation has shown the occurrence of complete dechlorination with introduction and distribution of organic carbon, the recirculation system can be utilized to support appropriate pH adjustments of the extracted groundwater prior to reinjection if performance data indicates the need for pH adjustment. The flexibility of the groundwater recirculation system that allows the reconfiguring of the system at the surface to allow a range of amendments to be applied during a full-scale remedy is one advantage of the BDGR technology.

Hydraulic control of the groundwater containing organic compounds is inherent in the application of groundwater recirculation. To maintain hydraulic control of the plume while delivering organic carbon, a balanced circulation rate is proposed with approximately equal volume of the extracted water re-injected.

The BDGR treatment cell will be installed in the Warehouse 65 area and is anticipated to create a recirculation cell over an area of approximately 1.2 acres to treat the UWBU (Appendix B, Sheet C1), which is where the majority of the dissolved-phase mass is present.

Performance metrics will be evaluated to assess the overall effectiveness of the BDGR pilot system.

These will be evaluated based on the following:

• Operational run time

• Overall hydraulic control of the dissolved phase plume

• Effectiveness in enhancing biodegradation of the dissolved phase plume within the treatment area

• Effectiveness in reducing dissolved phase VOC concentrations downgradient of the enhanced biodegradation treatment area

• Effectiveness of the groundwater treatment system to meet the required effluent standards if the

BDGR system is unbalanced.

The system is anticipated to begin showing results towards meeting the performance metrics within 12 months, but it is estimated to take up to 3 years to meet all pilot study objectives.

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1 INTRODUCTION

Arcadis U.S., Inc. (hereinafter referred to as Arcadis) has prepared this Operable Unit (OU) 8 Bio- Enhanced Directed Groundwater Recirculation (BDGR) Pilot Test Design to document the activities, procedures, and metrics by which monitoring, operations and maintenance, and optimization activities for the Defense Logistics Agency (DLA) Restoration Program will be conducted for the Defense Supply Center Richmond (DSCR), hereinafter referred to as the Site, located in Chesterfield County, Virginia.

These metrics are detailed in the scope of work dated 22 June, 2015 from the United States (U.S.) Army Corps of Engineers (USACE) Baltimore District, and all amendments and question and answer sets under the Multiple Award Environmental Services contract, Award No. W912DR-13-D-0019, Delivery Order 0005, awarded 25 September, 2015. Work will be conducted pursuant to the approval of, and coordination with, DLA, the United States Environmental Protection Agency (USEPA) Region 3, and the Virginia Department of Environmental Quality (VDEQ) for Comprehensive Environmental Response, Compensation and Liability Act activity at the Site.

This Design is supported by a Quality Assurance Project Plan (QAPP) (Arcadis, 2016a), Project Management Plan (Arcadis, 2016b), Accident Prevention Plan (APP) and the Basewide Monitoring Plan (Arcadis, 2016c). The QAPP contains both field and laboratory standard operating procedures. The Project Management Plan details the specific management, administrative, and technical details of work execution, including project organization, staffing, status reporting, deliverables, and schedule. The Basewide Monitoring Plan details the groundwater and surface water sampling activities and well gauging activities at the Site.

1.1 Background

The DSCR, also known as DLA Aviation, supports more than 1,300 major weapon systems as the military's primary source for more than 1.3 million repair parts and operating supply items. In addition, DLA Aviation manages supply, storage and distribution operations alongside its military customers at Robins Air Force Base, Georgia; Tinker Air Force Base, Oklahoma; Hill Air Force Base, Utah; Marine Corps Air Station Cherry Point, North Carolina; Naval Air Station North Island, California; and Naval Air Station Jacksonville, Florida. DLA Aviation also manages depot-level reparable procurement operations at Robins, Tinker and Hill Air Force Bases; Navy Inventory Control Point Philadelphia; and Redstone Army Arsenal in Huntsville, Alabama.

The U.S. government purchased the land from private owners in 1941, and construction activities began in September of that year. The installation was activated as the Richmond Quartermaster Depot on 1 January 1942. In 1943, the installation became the Richmond Armed Service Forces Depot. The Quartermaster Branch Depot was established on-site in 1949, followed by the U.S. Army General Supply Center in 1958. DLA began overseeing operations in 1962, when the installation became known as the Defense General Supply Center. In 1996, the installation was renamed the Defense Supply Center Richmond.

Past operations at the installation have encompassed a variety of industrial operations including the following: tent, refrigerator, and parachute repair; military vehicle and equipment overhauling; automotive engine repair and rebuilding; sanitary and industrial waste treatment and disposal; helmet refurbishing;

arcadis.com 1-2 gas cylinder refurbishing and replenishing; firefighter training; and hazardous chemical storage, recoupment, and shipping.

Current missions at the installation include:

• Managing, controlling, storing, and distributing general military, administrative, and other supplies worldwide for DLA

• Recovering industrial chemicals

• Refurbishing and refilling chemical gas cylinders

• Storing and supplying operational and maintenance parts for military aircraft

• Disposing of excess inventory

• Maintaining and storing military and government vehicles

• Storing and distributing maps to Department of Defense (DOD) installations and other government agencies worldwide

• Providing professional development and training opportunities for Government supply and inventory specialists

• Maintaining the U.S. Army’s National Technical Information System for hazardous substances.

Past industrial operations at the installation have resulted in the use, storage, management, inadvertent release, and/or disposal of hazardous materials, such as chlorinated volatile organic compounds (CVOCs), petroleum products, and wastewater treatment sludge. In addition, past storage operations at the installation have led to the accidental release of these and other hazardous materials, such as polycyclic aromatic hydrocarbons, pesticides, petroleum hydrocarbons, polychlorinated biphenyls, and metals.

An initial assessment was completed in August 1981, and indicated potential soil impacts at six OUs and possible groundwater impacts at three OUs. In 1982, the U.S. Army Environmental Hygiene Agency investigated the hydrogeologic setting, and identified two areas of significant groundwater impacts associated with the Area 50 landfill and the former Fire Training Area (FTA), and installed monitoring wells in the vicinity of the most impacted areas.

Based on the results of these investigations, the installation was officially placed on the National Priorities List in 1987 with a Hazard Ranking System score of 33.85 due to CVOCs in on-site groundwater, potential off-site migration of CVOC-contaminated groundwater, and groundwater discharge into surface water. In 1990, USEPA, VDEQ, and Defense General Supply Center (now DSCR) entered into a Federal Facilities Agreement to continue monitoring the installation, and develop and implement remedial action plans. Thirteen OUs were ultimately defined for the Installation Restoration Program.

A Remedial Investigation was initiated in 1986 to characterize the nature and extent of CVOCs in soil at four OUs:

• Open Storage Area - OU 1

• Area 50 Landfill - OU 2

• National Guard Area-OU3

• Former FTA-OU4

The acid neutralization pits (ANPs - OU 5) were investigated as a possible CVOC source area.

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The groundwater plumes associated with soil impacts were considered separately from the soil OUs:

• Open Storage Area /Area 50/NGA groundwater – OU-6

• Former FTA groundwater – OU-7

• ANP groundwater- OU-8

An installation wide pesticide monitoring study was completed in 1986 by U.S. Army Environmental Hygiene Agency and identified three additional possible areas of concern:

• Former Building 68 – OU-10

• Former Building 202 – OU-11

• Former Building 112 - OU-12

The OU-8 groundwater focus is primarily in the Upper Water Bearing Unit (UWBU) in the northern area of the DSCR (Figure 1-1). The primary source contributing to groundwater impacts for OU-8 was the ANPs and surrounding impacted soil located approximately 25 feet northwest of Warehouse 65, designated as OU-5. The ANPs consist of two former concrete settling pits that received wastewater from Warehouse

65. Historical operations at Warehouse 65 included metal cleaning operations, which included the use of chlorinated solvents. Wastewater from the operations was discharged from the primary settling pit into the storm sewer between 1958 through the 1990s. A secondary settling pit was added in the late 1970s, and the discharge was to the sanitary sewer (AECOM, 2014).

The concentrations of CVOCs exceeding USEPA Maximum Contaminant Levels (MCLs) for groundwater underlie Bay F and the outdoor pallet storage area on the north side of Warehouse 65. Bay F was the location of former acid dipping and metal cleaning tanks used to prepare World War II combat helmets, cylinders and other metal parts for repainting. Based on concentrations of volatile organic compounds (VOCs) in groundwater, this is considered to be the source of the CVOC plume designated as OU-8 (AECOM, 2014). The presence of underground utilities (storm and sanitary sewers) near the ANPs and across OU-8 area may have historically acted as preferential pathways for migration of CVOCs which would exacerbate the promulgation of CVOCs throughout OU-8 and create a large diffuse plume.

Because Warehouse 65 directly overlies the UWBU groundwater impacts, a sub-slab depressurization system (SSDS) was installed to address potential vapor intrusion concerns. Soil gases are extracted from eight vapor extraction points. Figure 1-2 provides a site layout that shows locations of extraction points, vapor monitoring points and indoor air sampling locations.

1.2 Purpose and Objectives

Multiple pilot and treatability study remedies have been implemented to remediate the dissolved phase impacts at OU8 including dual-phase extraction (DPE) with air injection, in-situ bioremediation, and in-situ chemical oxidation (ISCO). While in most cases these technologies focused on the diffuse portion of the plume rather than directly remediating the highest dissolved phase concentrations under Bay F of Warehouse 65, the diffuse nature of the downgradient plume combined with the overall horizontal extent suggests engineering hydraulic gradients can effectively remediate the source area of the diffuse groundwater plume. Groundwater recirculation can be an effective means of engineering a dynamic flushing program that will sweep both COCs from the aquifer (via extraction) and increase the overall extent of carbon treatment (via enhanced distribution of organic carbon).

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The BDGR pilot test will be implemented to enhance biodegradation of the dissolved-phase plume beneath portions of OU-5 and Bay F of Warehouse 65. This will be achieved by delivering organic carbon to the subsurface beneath specific areas of the plume and utilizing directed groundwater recirculation to enhance distribution of organic carbon while maintaining downgradient capture and also enhancing pore volume flushing through the source. Groundwater extraction will be used to prevent further migration of the dissolved phase compounds of concern (COCs) along the plume periphery, and will serve as a source of water for carbon reagent mixing. The combined carbon injection and groundwater extraction strategy will be used to establish an enhanced biological treatment zone near the historic source areas that can be advanced within the subsurface via engineered groundwater gradients outward towards the plume periphery. Treatment within the recirculation area will be achieved via biological mechanisms (where carbon is present) and physical mechanisms (where carbon is absent). Performance monitoring activities completed over the course of operation will be used to confirm adequate anaerobic treatment conditions have been established, guide the timing of reagent introductions, and tailor the operational recirculation approach (e.g., changes in injection/extraction rates, changes in specific wells in operation).

To achieve this purpose, the pilot test objectives are as follows:

• Sustain anaerobic and reducing geochemical conditions in groundwater within and immediately downgradient of the ANPs, Bay F of Warehouse 65, and portions of the pallet storage area;

• Maintain hydraulic control of the targeted dissolved phase plume, thereby preventing further migration of the dissolved phase COCs along the targeted plume periphery;

• Evaluate the effectiveness of BDGR for degradation of COCs and decreasing dissolved phase VOC concentrations; and

• Quantify the concentrations or VOC mass that can remain in the aquifer for treatment via natural attenuation processes.

1.3 Technology Overview

A process flow diagram of the proposed groundwater recirculation system is shown on Figure 1-3. This groundwater recirculation system consists of upgradient injection wells to deliver carbon amended water to the subsurface, and downgradient extraction wells to provide capture of impacted groundwater in the treatment zone and enhance carbon transport. The recirculation cell increases the hydraulic gradient and groundwater velocity through the treatment zone and the number of pore volumes that would otherwise be flushed or treated passively or with standard pump and treat technology. While the effect on the hydraulic gradient will be exaggerated around the injection and extraction wells, the recirculation cell is not designed or anticipated to significantly increase the overall groundwater gradient across the treatment area. The extracted water is treated ex-situ, typically via granular activated carbon (GAC), and delivered back to the upgradient injection wells for re-injection at which point a carbon amendment (e.g. sodium lactate, molasses, or emulsified vegetable oil) or other compounds used to enhance biological treatment can be introduced (e.g., sodium hydroxide or bicarbonate for pH modification, bioaugmentation), as necessary.

A primary benefit of groundwater recirculation is the ability to deliver in-situ remedial measures, such as:

• ISCO, including permanganate or persulfate;

• Bioaugmentation, through addition of exogenous microorganisms to enhance degradation of

COCs; and, arcadis.com 1-5

• Enhanced biodegradation through addition of nutrients and electron donors (anaerobic), or dissolved oxygen (DO) to enhance biodegradation.

The flexibility of the groundwater recirculation system allows it to be reconfigured at the surface to allow a range of amendment applications during a full-scale remedy. In addition, dye tracer compounds may also be added, alone or in conjunction with remedial amendments, to aid in evaluating the effectiveness of the recirculation system to transport the amendments throughout the treatment zone.

Re-injection of the groundwater is often balanced, where the volume of re-injected water (or water and amendments) equals the amount of water being extracted. However, the recirculation system may also be unbalanced, where additional water is added or removed so that the injection and extraction rates are not equal. This strategy can maintain hydraulic control of the treatment zone and prevent plume migration.

The result is that the recirculation system will reduce dissolved-phase COCs in a three-fold manner through both groundwater extraction with ex-situ treatment, through in situ treatment delivered through re-injection, and enhanced pore flushing. In slow moving hydraulic systems, groundwater recirculation is a more efficient delivery method than stand-alone injection events as the recirculation cell will allow greater spreading and contact with both the immobile and mobile portions of the groundwater COCs throughout the treatment zone. By taking advantage of the induced hydraulic gradients, which can also be rotated or adjusted through the course of the project, fewer wells are needed versus a traditional batch injection strategy The additional benefits of the groundwater recirculation system include controlling groundwater gradients, increasing pore water flushing, and enabling better management of system performance.

1.4 Work Plan Organization

The remainder of this Design is organized as follows:

• Section 2 provides the basis for the pilot study, including a brief summary of existing site conditions, an overview of previous site investigations, and a summary of current site data.

• Section 3 provides a discussion of the design criteria for the BDGR System, including the planned implementation strategy and BDGR system performance requirements.

• Section 4 provides details of the BDGR system design, including the system layout and system controls.

• Section 5 outlines the planned BDGR implementation, including details for the operational sequence, system operation, maintenance and monitoring, system shutdown, and final decommissioning and demobilization.

• Section 6 details the reporting requirements for the BDGR system.

• Section 7 provides the references cited in this Design.

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2 CONCEPTUAL SITE MODEL

2.1 Summary of Existing Conditions

2.1.1 Geology

The Site lies very close to and directly east of the Fall Line, which separates the Atlantic Coastal Plain physiographic province to the east from the Piedmont physiographic province to the west. The Fall Line is a geomorphic and hydrologic feature that marks the boundary between the resistant bedrock of the Piedmont to the west and the unconsolidated sediments of the Coastal Plain to the east. The Coastal Plain is an eastward-thickening wedge of stratified, undeformed, and unconsolidated sediments that overlie a mixed assemblage of metamorphic rock with igneous intrusions (MACTEC, 2006).

The majority of the near-surface sediments at the Site consist of the upper Pliocene Bacons Castle Formation sand and gravels. This unit is consistent with deposition in fluvial, nearshore and strandline environments and is subdivided into two members: 1) a thick bedded pebble and gravel grading upward into a pebbly sand and sand and clayey silt and 2) a thin bedded clayey silt and silty fine sand (MACTEC, 2006). Piedmont bedrock beneath the installation is the Petersburg granite, at an elevation of approximately 90 feet above National Geodetic Vertical Datum (U.S. Geological Survey PP1731).

2.1.2 Hydrogeology

McFarland and Bruce (McFarland, E.R., and Bruce, T.S., 2006) classified the local and regional aforementioned Coastal Plain sedimentary sequence into a hydrogeologic framework of interbedded WBUs and confining units. In Chesterfield County, the Coastal Plain water bearing unit (WBU) is the surficial aquifer present within sediments associated with the Bacons Castle Formation. At the Site, the surficial aquifer is locally divided into two hydrostratigrapyhic units: an unconfined UWBU and a deeper semi-confined lower WBU separated by a confining unit typically 10 feet thick or less. The lower WBU overlies saprolite associated with the Petersburg granite bedrock.

The potentiometric surface in the upper WBU at the installation is typically encountered at depths ranging from 1 foot to 20 feet below ground surface (bgs). Groundwater levels from the April 2016 groundwater sampling event for select wells are presented in Table 2-1. Groundwater movement primarily occurs in the coarse-grained materials of the UWBU. The saturated thickness of the UWBU is less than 5 to more than 20 feet. In the UWBU, historical activities, including remedial activities and pilot testing, have shown well yields ranging from approximately 0.5 to 10 gallons per minute (gpm). Regional groundwater flow in the UWBU at OU-8 is east-northeast, however local flow direction may be influenced by subsurface utilities. The potentiometric surface of the lower WBU was encountered at depths ranging from 5 to 46 feet bgs. Groundwater elevations in lower WBU wells were usually above the base of the confining unit (where present), indicating semi-confined conditions. The lower WBU is 10 to 40 feet thick and is fully saturated. Therefore, the saturated thickness of the lower WBU is 10 to 40 feet (MACTEC, 2006).

Based on data from OUs within the installation, confining units separate the upper and lower WBUs, and the lower and saprolite WBUs. The thickness of these confining units at the OUs (OU-6 and OU-7) can arcadis.com 2-2 range from 3 to 27 feet. The horizontal hydraulic conductivity of the confining unit at OU-8 was estimated to be approximately 1.8 x 10-6 centimeters per second (cm/sec). The vertical hydraulic conductivity was approximately 9.7 x 10-8 to 1.8 x 10-6 cm/sec. The confining unit at OU-8 is considered leaky where the thickness of the unit is small and/or the hydraulic conductivity is in the high end of the measured ranges

(MACTEC, 2006).

2.1.3 Summary of Dissolved Phase Constituents Nature and Extent Annual groundwater sampling was completed for OU8 in April 2016. A total of 85 monitor wells were sampled as part of the event in accordance with the OU8 monitoring program (Arcadis, 2016c). Select groundwater results are presented in Table 2-2 and shown on Figures 2-1, 2-2, 2-3 and 2-4. The included data represents a sub-set of the wells sampled focusing on the pilot study area. A complete evaluation of the groundwater data will be provided in an annual report following the next semi-annual sampling event. The April 2016 groundwater data confirm data from recent groundwater samples (October 2015) indicating the CVOC plume has bifurcated as a result of the implementation of the contingency remedy (bioremediation) between July 2013 and April 2014. Implementation of bioremediation has resulted in conversion of tetrachloroethene (PCE) and trichloroethene (TCE) via reductive dechlorination to cis-1,2-dichlroethene (cis-1,2-DCE), vinyl chloride (VC), and ethene. The bioremediation appears to have successfully isolated the groundwater impacts associated with the ANPs and Warehouse 65 from the larger diffuse impacts downgradient of the bioremediation treatment areas.

2.2 Overview of Previous Site Investigations and Pilot Studies

2.2.1 Initial Discovery

The ANP area, which is designated as OU-5 was identified in 1981 during Phase 1 activities at DSCR, which included a record search and site assessment study to determine the existence of toxic and hazardous materials and related contamination. Emphasis was placed on the compounds posing a potential for migration beyond the installation boundary. The ANP area is a site of two former concrete settling tanks which received wastewater from metal cleaning operations conducted in Bay F of Warehouse 65. It was identified as an area of industrial waste treatment consisting of acid neutralization, sludge settling, and discharge of waste water to the sanitary sewer system. However, emphasis was not placed on the area as being a major source of contamination until 1986. The tanks were removed from service and filled with soil in 1985. During this time, cracks and holes were discovered in the concrete sides and bottoms, which were considered to potentially provide migration pathways for the release of hazardous constituents to the environment.

2.2.2 Initial Field Investigation

An Initial field investigation was conducted in October1986 to January 1987 to determine if the ANP area was a potential source of groundwater contamination. Soil and groundwater samples were collected from soil borings and groundwater monitoring wells. Based on the results from the soil and groundwater analyses, the ANP area was identified as a potential source of soil and groundwater contamination and subsequently identified as OU-5 (soil) and OU-8 (groundwater).

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2.2.3 Remedial Investigation and Additional Field Investigations Additional field investigations were conducted as part of a Remedial Investigation (RI) for the ANP area to assess the potential location, magnitude, and extent of groundwater and/or soil contamination (Dames & Moore, 1989). The initial RI field investigation included soil gas sampling used to provide a preliminary assessment of the potential presence of a groundwater contamination plume. The soil gas sampling was conducted in October 1987, and, based on the results, additional groundwater wells including piezometers and soil borings were installed to determine the extent of contamination. A monitoring program was established as part of the RI and soil and groundwater samples were collected quarterly in 1987 and 1988. Results of the RI sampling program for the ANP area indicated constituents detected in soil and groundwater included metals, VOCs and base neutral and acid extractable semi-volatile compounds (BNAs). However, only the VOCs and BNAs detected in soils were determined to be potentially significant. These constituents in soil were localized around the ANPs. The highest concentrations (1,500 micrograms/kilogram of PCE) were detected in the soil sample from the secondary acid pit boring. Although metals were present in groundwater from the ANP area, elevated levels were not detected in downgradient wells relative to upgradient concentrations. VOCs observed in the soil were also present in the groundwater and their concentrations were determined to increase in wells downgradient of the pits. For example, groundwater samples collected in November 1988 from monitor wells DMW-24A (within the ANP area) and DMW-30A (downgradient of the ANPs) contained PCE concentrations of 1,700 and 3,700 micrograms per liter, respectively. PCE, TCE, 1,2-dichloroethane, and 1,2-dichloroethene (1,2-DCE) (total) were identified in wells. The presence of BNA contamination in the groundwater was not a significant concern because of the small number of compounds detected, the low concentrations, infrequent occurrence and sporadic distribution, which was primarily limited to the vicinity of the pits.

The soil and groundwater data indicated the potential for the soils in the vicinity of the acid pits to be sources of the contamination detected in the groundwater. Based on the occurrence and distribution of constituents in the monitoring wells, it was concluded that COCs were migrating into the groundwater of the UWBU from the acid pits and appeared to be transported along the general direction of groundwater to the northeast (Dames & Moore, 1989).

Additional RI investigations were conducted in 1992 (LAW, 1995) where 10 groundwater samples were collected at the ANP area and analyzed. Other soil and groundwater sampling efforts at the ANP area were completed: 1) during and after a pilot study conducted for a vacuum extraction system in 1995; 2) prior to the initiation of a dual phase extraction system treatability study in 1995; and 3) post the initiation of the dual phase extraction treatment system during six months of operation in 1997-1998.

2.2.4 Focused Feasibility Study

Based on the RI conducted for the ANP area, a Focused Feasibility Study (FFS) was completed for the soil contamination at the site (LAW, 1991). Based on soil and groundwater data collected, it was believed the source of contamination for the soil was the soil beneath the tanks. A set of remedial alternatives were evaluated for the primary constituents identified at the ANP site that included PCE, TCE and 1,2-dichloroethane. Five remedial alternatives were identified for detailed analysis. As a result of the evaluation of the five potential remedial alternatives based on Comprehensive Environmental Response, arcadis.com 2-4

Compensation, and Liability Act evaluation criteria and discussions with federal and state agencies, vacuum extraction was identified as the preferred alternative for the ANP soil contamination.

A separate FFS was completed for the contaminated groundwater designated as OU-8 (LAW, 1998).

The FFS was based on the results of six months operation of a dual phase extraction system treatability study and information from two sets of RIs (LAW, 1995; Dames & Moore, 1989). The main objective for groundwater remediation at OU-8 was to prevent human contact with contaminated groundwater exceeding MCLs. Remedial technologies were identified and screened, and combined into alternatives to address the site remedial goals. Five favorable alternatives were retained for detailed analysis. The five alternatives were evaluated based on six different criteria in accordance with the National Contingency Plan. The final alternative selection was based on a consensus between all parties involved with the site, including state and federal regulators, representatives of the DSCR and DLA. The recommended remedial technology was groundwater extraction/soil vapor extraction (Dual Phase Extraction), air injection, air stripping, and surface water discharge of treated groundwater.

2.2.5 Pilot Test of the Vapor Vacuum Extraction and Treatability Study of the Dual Phase Extraction System

A pilot test was conducted for the dual extraction system that was recommended as the preferred remedial alternative for the ANP soil contamination in the final FFS (LAW, 1996). The objective of the pilot testing at the site was to collect site-specific parameters needed to further assess and design a full scale DPE system. The test was limited to a single extraction well and a combined total of five days of system operation. Based on the results from the pilot test, it was recommended to perform a larger scale treatability study in order to evaluate more aggressive aquifer dewatering that would allow for increased portions of the aquifer to be exposed to air flow.

Based on the soil analytical results obtained after completion of the pilot testing, the maximum detected soil concentrations were below the soil action levels in the OU-5 Record of Decision (ROD). This data indicated the OU-5 soils did not pose an unacceptable risk to human health or the environment, and were no longer considered a source of groundwater contamination.