W912DR18R0055_-_Attachment_V_-_OU_8_ERD_RAWP_20180718.docx

DRAFT

REMEDIAL ACTION WORK PLAN

OPERABLE UNIT 8

IN SITU BIOREMEDIATION

REMEDY OPTIMIZATION

DEFENSE SUPPLY CENTER RICHMOND

Prepared For

Defense Logistics Agency

And

Defense Supply Center Richmond

June 2018

DRAFT

REMEDIAL ACTION WORK PLAN

OPERABLE UNIT 8

IN SITU BIOREMEDIATION

REMEDY OPTIMIZATION

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

June 2018

REMEDIAL ACTION WORK PLAN OPERABLE UNIT 8

Christopher Spooner Technical Lead

Courtney Ingersoll Project Manager

In Situ Bioremediation Remedy Optimization

Prepared for:

Defense Supply Center Richmond and

Prepared by:

701 Town Center Drive Suite 600 Newport News Virginia 23606-4296 Tel 757 873 8700 Fax

Our Ref.:

02118201.0001

Date:

June 28uly 18, 2018

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.

Contents

TABLES

Table 2-1. 2018 PDI Soil Analytical Data Table 2-2. 2018 PDI Groundwater Analytical Data Table 4-1. ERD Performance Monitoring Plan

FIGURES

Figure 2-1. OU8 PCE Contours (UWBU) (Oct. 2017) Figure 2-2. OU8 TCE Contours (UWBU) (Oct. 2017) Figure 2-3. OU8 cis-1,2-DCE Contours (UWBU) (Oct. 2017) Figure 2-4. OU8 Vinyl Chloride Contours (UWBU) (Oct. 2017) Figure 2-5. Pre-Design Investigation Sampling Locations Figure 4-1. Proposed ERD Well Layout Figure 4-2. Proposed Performance Monitoring Well Network Figure 4-3. Proposed Injection Wellhead Construction Details

APPENDICES

Acronyms and Abbreviations

REMEDIAL ACTION WORK PLAN OPERABLE UNIT 8

In Situ Bioremediation Remedy Optimization arcadis.com https://arcadiso365.sharepoint.com/TEAMS/USACE_Bal_US_DSCR/Shared Documents/OU8 ERD/OU8 ERD WP/OU 8 ERD RAWP_20180620.docx iii

EXECUTIVE SUMMARY

This Remedial Action Work Plan (RAWP) addresses the planned remedies for two areas of concern at Operable Unit 8 (OU 8) at the Defense Supply Center of Richmond (DSCR). The primary source area is the chlorinated volatile organic compound (CVOC) source mass identified beneath Bay F of Warehouse 65. The secondary impacted area is downgradient (north) of this source mass and represents the migration of this source mass as a diffuse plume.

The remedial action objectives (RAO) for these remedies are based on the risks associated with elevated CVOC concentrations in groundwater and the ongoing migration of CVOCs from the source mass, and the sub-slab soil gas (Warehouse 65) at OU 8. If no corrective action is taken, the downgradient diffuse CVOC plume is at risk of migrating off-installation and impacting civilian populations. The remedies planned at each of the areas addressed in the RAWP include in-situ bioremediation via carbon-amended enhanced reductive dichlorination at both Warehouse 65 and downgradient in the diffuse CVOC plume.

Various soil and groundwater investigations have been completed in the OU 8 to date and have identified tetrachloroethene (PCE) and trichloroethene (TCE) as the principal constituents of concern (COCs) in addition to other degradation and breakdown (daughter) products.

The RAO tasks have been established for each of these remedies is as follows:

Task 1: Warehouse 65 (Source Mass):

Direct treatment of hot spot chlorinated solvent impacted groundwater concentrations of chlorinated solvents in the source mass identified and delineated during the pre-design investigation (PDI) in the vicinity of Warehouse 65 to (a) prevent potential exposure to nearby human populations (via vapor intrusion into new/existing buildings); and (b) mitigate further degradation of the groundwater due to continued contaminant migration from this source mass toward areas off-installation.

Task 2: Downgradient Plume:

Abate elevated mid-plume concentrations of CVOCs to prevent continued migration of elevated contaminants toward the DSCR property boundary where on-post monitoring wells are showing increasing contaminant concentration trends.

Injections of a soluble carbon donor source was selected for the source mass remedy (Warehouse 65) and a sparingly soluble carbon donor source was selected for the downgradient plume. Injections at Warehouse 65 will be completed using on group of injection wells installed inside and outside of Bay F of Warehouse 65. Bench testing was completed to determine the most effective carbon donor source.

arcadis.com https://arcadiso365.sharepoint.com/TEAMS/USACE_Bal_US_DSCR/Shared Documents/OU8 ERD/OU8 ERD WP/OU 8 ERD RAWP_20180620.docx ES-1 Introduction Arcadis U.S., Inc. (hereinafter referred to as Arcadis) has prepared this Operable Unit (OU) 8 Remedial Action Work Plan to document the planned activities, procedures, and analytical results for the Defense Logistics Agency (DLA) Restoration Program for the Defense Supply Center Richmond (DSCR), hereinafter referred to as the Site, located in Chesterfield County, Virginia. This document provides a description of the proposed activities, procedures, and required analysis to complete the enhanced reductive dechlorination (ERD) remedial strategies identified for the groundwater beneath F Bay of Warehouse 65 and further downgradient in the diffuse plume. The 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 Architect/Engineer Indefinite Delivery/Indefinite Quantity for Hazardous, Toxic, and Radioactive Waste and Military Munitions contract, Award No. W912DR-13-0019, 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 Work Plan is supported by a Quality Assurance Project Plan (QAPP) (Arcadis 2016a), Project Management Plan (Arcadis 2016b), Accident Prevention Plan (APP) and the Base Wide 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 Base Wide Monitoring Plan details the groundwater and surface water sampling activities and well gauging activities at the Site.

Background At the DSCR, DLA Installation Operations Richmond supports more than 1,300 major weapons 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 multiple military installations.

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; gas cylinder refurbishing and replenishing; firefighter training; and hazardous chemical storage, recoupment, and shipping. 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.

An initial assessment was completed in August 1981 and indicated potential soil impacts at six OUs and possible groundwater impacts at three OUs.

The acid neutralization pits (ANPs - OU 5) were investigated as the CVOC source area, and the groundwater plume associated with the soil impacts was identified as OU 8. The OU 8 groundwater focus is primarily in the Upper Water Bearing Unit (UWBU) in the northern area of the DSCR. The primary source contributing to groundwater impacts for OU 8 was the ANPs and operations supplying wastewater to the ANPs and resulting impacted soil located beneath Warehouse 65 and approximately 25 feet (ft) west of F Bay, 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 from 1958 through the 1990s. A secondary settling pit was added in the late 1970s, and the discharge from the secondary settling pit was to the sanitary sewer. The ANPs 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.

An initial field investigation was conducted in October 1986 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). The concentrations of CVOCs exceeding VDEQ Maximum Contaminant Levels for groundwater currently underlie F Bay and the outdoor pallet storage area on the north side of Warehouse 65. F Bay 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 likely the source of the CVOC plume designated as OU 8.

Conceptual Site model Summary of Existing Conditions Regional 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 and 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).

Most 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). The thickness of this formation ranges from 46 to 52 feet below ground surface (ft bgs) at the installation. Bedrock, defined as Petersburg Granite, occurs below this formation and is separated by weathered bedrock and saprolite of unknown thickness (Virginia Division of Mineral Resources).

Site Specific Geology Based on soil boring and geotechnical data collected at OU 8 from more than 80 soil boring locations, the general stratigraphy of the unconsolidated soils underlying OU 8 are described as follows (AECOM 2015):

· The UWBU consists of several layers of stratigraphic material. The top layer is shallow sediments from ground surface to depths ranging from approximately 12 to 30 ft bgs. The soil consists of silty sand, sandy silt, and silty or fat clay. There is also a sequence of poorly graded sand with gravel, interlayered with poorly graded gravel. The thickness of this layer is approximately 2 to 15 ft. The top of this layer is approximately 13 to 19 ft bgs, and the bottom of the layer is approximately 21 to 28 ft bgs. This layer is present throughout OU 8 except for the northern area where it is absent.

· The layer beneath the UWBU is a confining unit consisting of silty and/or fat clay. The thickness of this layer is approximately 5 to 10 ft. The top of the layer is approximately 21 to 28 ft bgs, and the bottom of the layer is approximately 26 to 36 ft bgs. This layer is absent in the northernmost part of the installation.

· The layer below the confining sequence is the lower water bearing unit (LWBU) consisting of poorly graded sand with gravel and silty sand, poorly graded sand with gravel, and/or poorly graded sand with gravel interlayered with poorly graded gravel. The thickness of this layer is approximately 10 to 25 ft. The top of the layer is approximately 26 to 36 ft bgs, and the bottom of the unit is approximately 46 to 52 ft bgs. This layer is present throughout OU 8.

The unconsolidated soils beneath OU 8 are underlain by saprolite weathered from the underlying Petersburg granite. The bedrock was not encountered in borings, and the thickness of saprolite and depth to bedrock is unknown. The top of the saprolite is the bottom of the groundwater flow system.

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

The potentiometric surface in the UWBU at the installation is typically encountered at depths ranging from 12 to 24 ft bgs. Groundwater movement primarily occurs in the coarse-grained materials of the UWBU. The saturated thickness is less than 5 to more than 20 ft in the UWBU. Regional groundwater flow in the UWBU at OU 8 is typically north to east-northeast; however, the local flow direction may vary locally from the effects of streams and sewers. Based on aquifer testing performed in 1995, hydraulic conductivity of the UWBU at OU 8 ranges from approximately 1.8 x 10-2 to 3.7 x 10-2 feet per minute (9.4 x 10-3 to 1.9 x 10-2 centimeters per second) (AECOM, 2012). The geometric mean hydraulic conductivity was approximately 2.4 x 10-2 feet per minute (1.2 x 10-2 centimeters per second). The potentiometric surface of the LWBU was encountered at depths ranging from 28 to 31 ft bgs. Groundwater elevations in LWBU wells were usually above the base of the confining unit (where present), indicating semi-confined conditions.

Source, Nature and Extent of Groundwater Contamination Numerous soil and groundwater investigations have been completed in OU 8 to date and have identified CVOCs as the primary constituents of concern. Semi-annual groundwater sampling was completed for OU 8 in October 2017. A total of 76 monitoring wells were sampled as part of the event in accordance with the OU 8 monitoring program (Arcadis, 2016c). Select groundwater results are presented as plume maps in Figures 2-1, 2-2, 2-3 and 2-4. The October 2017 groundwater data confirm data from recent groundwater samples (April 2017) indicating the CVOC plume had split because 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 from the larger diffuse impacts downgradient of the bioremediation treatment areas.

Summary of Site Data Initial Remedial Efforts Results of field activities and follow-on monitoring conducted between 2008 and 2011 indicated additional source areas (Warehouse 65, Warehouse 66, and former Warehouse 75) had contributed to the OU 8 UWBU groundwater contamination. In April/May of 2010, in situ bioremediation tests were conducted downgradient of the ANPs and in the Warehouse 65 source area. Approximately 6,700 gallons of 3% (volume/volume) edible oil emulsion was injected in this area to evaluate the effectiveness of organic carbon addition to the contaminant degradation processes at OU 8. Due to the relatively low permeability in this area, the injection rates were relatively slow (less than 1 gallon per minute). Subsequent groundwater monitoring results indicate that contaminant degradation via in situ biodegradation was occurring in the test area (AECOM, 2012).

These initial in situ bioremediation pilot tests were followed by full-scale in situ bioremediation via two events (July 2013 and April 2014) of emulsified vegetable oil (EVO) injections at four treatment areas in OU 8. Results of these injections showed general reductions in CVOC concentrations across OU 8, except for the southern lobe and a localized area north of Warehouse 65.

BDGR PDI Source Mass Investigation A pre-design investigation (PDI) for the Bio-enhanced Directed Groundwater Recirculation (BDGR) pilot system was conducted in 2016, to identify and ensure the appropriate placement of pilot test wells (injection wells specific to the BDGR pilot system). During this investigation Membrane Interface Hydraulic Profiling Tool (MiHPT) borings were conducted in F Bay. The presence of VOCs and CVOCs were measured at each boring using an electron capture detector (ECD), flame ionization detector (FID) and the photoionization detector (PID). During this investigation it was determined that the primary source of contamination in OU 8 is likely located beneath F Bay.

During the BDGR pilot system pre-design investigation conducted in 2016, four MiHPT borings were installed through the floor of F Bay. The borings were advanced to the bottom of the UWBU to a maximum depth of 28 ft bgs. One boring was installed near the former ANPs just outside F Bay west of the Warehouse (MiHPT-01) and the other three borings (MiHPT-02, MiHPT-03a, and MiHPT-04) were installed through the concrete floor near the south wall of F Bay (Figure 2-5). The presence of VOCs and CVOCs were measured at each boring using an ECD, FID, and a PID. Hydraulic profiling tool (HPT) and electrical conductivity (EC) were used to assess the relative permeability/hydraulic conductivity of the subsurface material at each boring location.

Based on the results from this BDGR pilot system PDI, two of the MiHPT boring locations (MiHPT-01 and MiHPT-04) showed the presence of CVOCs, but at relatively low concentrations (Appendix A). The relatively low ECD and PID responses at these borings indicated the presence of chlorinated alkenes in the vadose and saturated zones, but at relatively low concentrations. These borings were located on the western part of the F Bay (Figure 2-5).

Results from the other two boring locations (MiHPT-02 and MiHPT-03a) indicated the presence of relatively high chlorinated alkene mass in both the vadose zone and the saturated zone (Appendix A). The ECD responses at both locations fell at the lower clay encountered, suggesting the clay is acting as a confining unit. The PID responses at both boring locations suggest volatile impacts are present at and just below the water table. Based on a review of historical maps showing operational layout of the interior of Warehouse 65, there was a vitrified clay pipe (VCP) that served as a waste line from inside the Warehouse to the former ANPs outside the building. This VCP waste line is believed to be the source of the chlorinated alkenes at boring locations MiHPT-02 and MiHPT-03a which generated high ECD responses.

The HPT and EC logs at all four boring locations suggest the presence of an overlying less permeable silt/clay layer from ground surface to a depth ranging from 12 to 16 ft bgs; underlain by a permeable sand and gravel layer with a thickness of 8 to 11 ft, followed by a base clay layer separating the UWBU and LWBU. The base clay layer was determined to start at a depth of approximately 21 (at MiHPT-01) to 25 (at MiHPT-02) ft bgs. These results are consistent with the historical description of the site geology.

Source Mass Investigation In June 2018 and as part of the PDI, the additional characterization of the source mass beneath Bay F of Warehouse 65 was completed. This included 10 MiHPT borings (MiHPT-5, MiHPT-6, MiHPT-8, MiHPT-9, MiHPT-10, MiHPT-11, MiHPT-12, MiHPT-13, MiHPT-14, MiHPT-17), which were completed in F Bay and two MiHPT borings (MiHPT-15 and MiHPT-16) were completed outside Warehouse 65 under the canopy area north of F Bay (Figure 2-5). The borings were advanced to the bottom of the UWBU to a maximum depth of approximately 26 ft bgs, where the lower clay bed was encountered. The presence of VOCs and CVOCs were measured at each boring using an ECD, FID, and the PID.

MiHPT logs can be found in Appendix B. Based on the results from the MiHPT borings, the highest ECD, PID and FID responses were detected in the vadose zone in MiHPT-8 and MiHPT-9 indicating significant VOC and CVOC impacts near the central portion of the VCP, which runs adjacent to the southern wall of F Bay. MiHPT-5, MiHPT-11, MiHPT-15, MiHPT-16, and MiHPT-17 did not indicate significant impacts of VOCs and SVOCs. MiHPT-14 indicated significant impacts in the shallow soil and is located along the northwest wall near the location of former operation tanks. Based on the results of MiHPT-14, the contingent boring MiHPT-17 was advanced to the west of MiHPT-14 to identify the extent of the impacted area. ECD, PID and FID responses from MiHPT-17 indicate no significant VOC or CVOC mass is present. Based on the results of the MiHPT investigation the source area appears to be bounded to the east by MiHPT-5 and -11, west by MiHPT-4 and -17, south by the BDGR injection wells, and north by MiHPT-15 and -16.

Upon completion of the MiHPT investigation in F Bay five direct push technology (DPT) borings were advanced at MiHPT-5, MiHPT-8, MiHPT-9, MiHPT-12, and MiHPT-14. After screening with a PID, two soil samples were collected from each boring (10 total samples) by an Arcadis geologist and sent to lab for analysis. Samples that indicated the highest PID readings in the vadose zone and near the smear zone were collected and sent to TestAmerica Laboratories, Inc. in Savanah, Georgia for VOC analysis (USEPA method 8260). The soil analytical data are presented in Table 2-1. Two groundwater samples were taken from the saturated zone via a DPT Screen Point 16 groundwater sampling system at MiHPT-5, MiHPT-9, and MiHPT-12. Two groundwater samples were collected from the saturated zone using 1-inch temporary wells with 5-ft screen intervals at MiHPT-8 and MiHPT-14. Groundwater samples were screened for pH, conductivity, temperature, dissolved oxygen, oxidation reduction potential, and turbidity using a Horiba-U53 water quality meter. Groundwater samples were submitted to Test America Laboratories, Inc. for analysis of VOCs (USEPA method 8260). Additionally, groundwater samples will also be analyzed for anions [nitrate and sulfate] (SW9056), dissolved gases [ethane, ethene and methane] (USEPA Method RSK175), total organic carbon (SW9060), and alkalinity (as CaCO3) by Method SM2320B. The groundwater analytical data are presented in Table 2-2.

Soil and groundwater samples were collected from the target injection interval (sand and gravel layer) and sent to the Arcadis Treatability Laboratory in Raleigh, North Carolina. Testing included preparation of soil and groundwater microcosms to evaluate various pH and carbon amendments to achieve the optimal injection solution, reduce negative geochemical effects on the aquifer and carbon donor, and get complete dechlorination of CVOCs. The results of these treatability tests will be used to select the most appropriate carbon donor for each injection area described below. Laboratory reports are provided in Appendix C. Comment by UsaceAdmin: This section is part of a later comment. Just adding comment and highlight as a bookmark for quick reference.

OU 8 in situ bioremediation Remedial Design Basis Due to the recently identified source mass beneath F Bay of Warehouse 65 and the continued presence of elevated CVOC concentrations, additional optimization of the OU8 remedy is proposed. In situ bioremediation via ERD is proposed to address the source mass beneath F Bay proactively and aggressively and encourage degradation of the downgradient plume.

ERD is a process in which indigenous or augmented microorganisms degrade (metabolize) chlorinated organic compounds, converting them to innocuous end products. ERD is implemented by delivering an organic carbon source to the target in situ treatment area. Fermentation of the organic carbon yields electron donor (e.g., dissolved hydrogen) to drive terminal electron accepting processes, resulting in the depletion of naturally-occurring electron acceptors (e.g., oxygen, nitrate, ferric iron, and sulfate) and creates conditions in which the reductive dechlorination of chlorinated VOCs is energetically favorable. CVOCs are sequentially reduced through a series of two-electron transfer reactions, whereby a chlorine atom is removed and replaced with a hydrogen atom. For chlorinated ethenes, the sequential reduction of PCE will eventually produce ethene, a non-toxic end product via the following transformation steps:

PCE TCE cis-1,2-DCE VC ethene Reductive dechlorination of PCE and TCE generally results in production of cis-1,2-DCE, which is more energetically-favorable than production of other DCE isomers (i.e., trans-1,2-DCE and 1,1-DCE). The in-situ bioremediation of plume hot spotsgroundwater is intended to:

· Reduce the residual plume mass;

· Decrease contaminant flux from the highly concentrated plume source mass;

· Minimize downgradient plume migration;

· Minimize impact to the off-installation areas; and

· Generate biogeochemical conditions conducive to longer-term natural attenuation of remaining CVOC concentrations.

Proposed Treatment Areas For the purposes of this Remedial Action Work Plan, the remedial activities at OU 8 have been divided into two tasks each addressing a specific area, including: Warehouse 65; and the northern and downgradient portion of the contaminant plume. The identification of these areas was based on the presence of elevated concentrations of parent compounds and identification of mid-plume treatment zones to minimize the potential for downgradient contaminant migration. The remedial action for OU 8 is designed to target the dissolved phase impacts in these areas. The selected remedies for each area include the following:

· Task 1: Warehouse 65 –ERD of the CVOC hot spot beneath Bay F via soluble carbon substrate amendment injections through a suite of six new injection wells located inside Bay F.

· Task 2: Downgradient Remedy Optimization – ERD of the downgradient CVOC plume spine via injection of a semi-soluble carbon amendment across two existing parallel injection well tracts.

In situ Remedial Action Field Activities As identified in the approved Record of Decision (ROD), Arcadis will install injection well networks and inject remedial amendments to promote in situ bioremediation via ERD to reduce CVOC mass to the extent possible as identified in the approved ROD for: 1) the known source area beneath Warehouse 65, and 2) north (downgradient) of Warehouse 65 in the leading arm of the diffuse plume. As described in Section 3.1, ERD injections involve the addition of a carbon donor to the subsurface to facilitate the anaerobic biodegradation of target CVOCs. Carbon donors can include soluble (e.g., molasses, lactate, and corn syrup) reagents, semi-soluble (e.g., EVO) reagents, and combinations thereof (e.g., LactOil®). Each donor has advantages and disadvantages related to its solubility, reactivity, stability, and transport. Understanding the extent of the contamination and the state of the substrate is paramount to choosing the best donor for the application. During the PDI, substrate samples were collected from the contaminated interval and submitted to the Arcadis Treatability Lab for bench-scale testing. This testing is currently ongoing, and the results will be used to determine the optimal substrate-type, loading rate, injection volumes, and injection frequencies. Details on the system layout, design and operation are provided in the following sections.

Injection System Design and Implementation The following sections present the proposed design and implementation of the selected in situ remedy at the two areas at OU 8. The design elements in the following sections are subject to change during the adaptive implementation process. As-built drawings will be included in the injection summary report which will be provided following the initial injection and performance monitoring.

Warehouse 65 Source Remediation The overall objective of the Warehouse 65 ERD system is to reduce residual CVOC impacts in the most impacted areas beneath Warehouse 65 and prevent long-term mass flux to the downgradient plume. The specific technical objectives of the ERD implementation at Warehouse 65 include:

· Deliver excess electron donor throughout the target treatment area inside and immediately downgradient of Warehouse 65;

· Maintain geochemical conditions conducive to the reductive dechlorination of CVOCs in the treatment area; and

· Enhance the transformation of residual CVOCs such that downgradient mass flux is minimized.

Proposed Well Network The proposed ERD injection well network at Warehouse 65 is shown on Figure 4-1. The proposed injection network includes six new injection wells, divided into two transects of three wells. The two transects will be located inside Bay F of Warehouse 65. The injection wells will be spaced approximately 30-feet apart and will be screened from approximately 14 to 24 ft bgs to target the saturated zone with the highest VOC concentrations, as determined by MiHPT data collected during the PDI (Section 2.1.5). Final screen placement may be adjusted in the field based on geologic and site conditions encountered during drilling. Injection wells will be constructed of 2-inch diameter Schedule 80 polyvinyl chloride (PVC) with 20-slot wire-wrapped stainless-steel screens with prepacked filters to reduce flow restrictions in the well screens. Well installation methods are described in greater detail in Section 4.3.

The Warehouse 65 injection network will utilize the extraction wells and piping from the existing BDGR pilot system to supply water for injection and mix injection solution. Prior to installation of the injection wells, at least 10 (and up to 13) existing 1-inch DPT injection wells under the northern canopy of Warehouse 65 will be abandoned by grouting the wells to surface. Injectability of these wells is questionable, likely due to fouling from previous injections, and redevelopment is not possible. The performance monitoring well network at Warehouse 65 includes eight existing site wells around F Bay and three proposed monitoring wells to be installed inside Bay F (Figure 4-1). A more detailed summary of the performance monitoring program is provided in Section 5. Comment by UsaceAdmin: Utilize how? Need to elaborate.

Downgradient Remedy Optimization The overall objective of the downgradient ERD injections is to reduce residual CVOC impacts farther downgradient of Warehouse 65 and provide a barrier to prevent further migration of CVOC impacts. The specific technical objectives of the ERD implementation at the downgradient locations include:

· Deliver excess electron donor throughout the target treatment area downgradient of Warehouse 65;

· Maintain geochemical conditions conducive to the reductive dechlorination of CVOCs in the treatment area;

· Enhance the transformation of residual CVOCs such that downgradient mass flux is minimized.

Proposed Well Network The proposed ERD injection well network for the downgradient locations is shown on Figure 4-1. The injection network includes two transects consisting of six injection wells each. In each transect, three new injection wells will be installed and used with three existing injection wells that will be redeveloped for the proposed remedy optimization. The proposed injection well transects are located approximately 400 and 600 ft downgradient from the primary contaminant source beneath Warehouse 65 and will be positioned northwest to southeast, perpendicular to the contaminant plume. The transects will be located approximately 200 ft apart and will span approximately 150 ft, with injection wells spaced approximately 30-ft apart. The injection wells will target the entire thickness of the contaminant plume present in the sequence of poorly graded sand with gravel, interlayered with poorly graded gravel, estimated to be 14 to 24 ft bgs. Final screen placement will be adjusted in the field based on geologic conditions encountered during drilling. Injection wells will be constructed of 2-inch diameter Schedule 80 PVC with 20-slot wire-wrapped stainless-steel screens with prepacked filters to reduce flow restrictions in the well screens. Well installation methods are described in greater detail in Section 4.3. Comment by UsaceAdmin: This comment should extend to the building 65 new wells and existing wells. What are the development methods for the new wells and are we planning on rehabbing the old wells prior to injection, if not why do we feel that these wells are not potentially fouled like those under the canopy which are being abandoned? Comment by Spooner, Christopher: There are no existing injection wells being used Building 65. All wells will be new and developed post installation. Comment by UsaceAdmin: Can we specify the target Lithologic zone material, i.d. silty sand with gravel?

The performance monitoring well network for the downgradient transects includes six existing site wells (Table 4-1 and Figure 4-2). A more detailed summary of the performance monitoring program is provided in Section 5.

Injection Reagents For Warehouse 65, the selected carbon substrate will be a rapidly fermentable soluble substrate (e.g., molasses or lactate). The rapidly fermentable carbon substrate expedites the short-term biological growth response and the development of strongly-reducing conditions needed to facilitate reductive dechlorination.

For the downgradient injection transects, the selected carbon substrate will be a semi-soluble substrate (e.g., EVO). The semi-soluble carbon substrate will provide a longer-lasting source of electron donor to sustain reducing conditions and reductive dechlorination while necessitating fewer injection events.

The exact reagent will be selected based on results of bench-scale substrate testing. The carbon substrate will be mixed onsite using potable water collected from an on-site fire hydrant to a target carbon loading rate of approximately 1 to 5 percent by weight of total organic carbon (TOC). Prior to implementation, baseline sampling will be conducted to refine the starting injection dose based on pH buffering requirements, previously observed injection flow rates, and other design parameters. In addition, the distribution, utilization, and transport of injected solution observed following the initial injection will be used to confirm and/or modify the substrate strength and injection strength for subsequent injections. Additional carbon substrates may be utilized, with the primary decision criteria related to best matching the mechanism of carbon release and availability to the geologic and hydrogeologic conditions encountered. Given the need for adaptive management of any in situ remedial strategy, soluble, semi-soluble, and combined substrates are being included for future consideration over the course of implementation to optimize treatment performance. Comment by UsaceAdmin: Did we not do this already as described in section 2.1.5.3 last paragraph? How soon will these conclusions be made available for review prior to implementation? Comment by Spooner, Christopher: We selected the carbon donor type, but not the specific donor. Our treatability lab will be done with their evaluation this week and we will finalize donor selection. I’d like to use molasses in F Bay but want to make sure the testing doesn’t shows minimal pH depression. We will use straight EVO in the downgradient barriers. We just haven’t selected the vendor.

The pH in site groundwater has historically been less than 5. While reductive dechlorination can occur at sites where pH values are between 5 and 6, dechlorinating organisms most efficiently degrade contaminants at circumneutral pH (i.e., 6 to 8). The addition of a pH buffer is therefore recommended to raise the pH to support efficient reductive dechlorination for Warehouse 65 injections. During the PDI, soil and groundwater samples were collected and shipped to the Arcadis Treatability Lab in Durham, North Carolina. Microcosms were constructed using these materials to perform fermentation and titration experiments using various organic substrates and sodium hydroxide. The results of the microcosm experiments are pending and will be used to determine the dosing for successful pH adjustment during injection implementation.

The presence of intermediate dechlorination products (i.e., cis-1,2-DCE and VC) indicates that partial dechlorination is naturally occurring within the target treatment areas. Supplemental addition of organic carbon as part of the injection programs will accelerate this ongoing dechlorination activity. While the native microbial community has already demonstrated the capability to perform dechlorination, the addition of a bioaugmentation culture containing dechlorinating organisms can often accelerate early dechlorination rates and improve late-stage dechlorination to non-chlorinated end products. Bioaugmentation culture KB-1® Plus will be incorporated into the Warehouse 65 substrate injection program. This commercially available bioaugmentation culture contains microorganisms that can completely dechlorinate chlorinated ethenes; in addition, the microorganisms have been acclimated to lower-pH conditions. Bioaugmentation and pH adjustments are not necessary at the downgradient injection transects. Comment by UsaceAdmin: Will biological Assays be completed during performance monitoring on select wells to conclude viability of the bio augmentation? Comment by Spooner, Christopher: We did not plan to do any assays downgradient of in F bay. Siren does include several free assays when we procure the material. Our experience is the results are the best indicator rather than the assay which simply provides a microbial count.

Injection and Carbon Loading The proposed location of injection wells in the Warehouse 65 injection system are shown on Figure 4-1. The injection wells were located based on a target injection radius of influence (ROI) of 15-ft for each well. The volume of injection solution required to achieve a 15-ft ROI in the injection wells is calculated using the equation shown below. While this calculation provides an initial estimate for dosing purposes, an adaptive implementation approach will be used to validate these targets volumes and modify delivery based on actual conditions observed during field implementation to ensure technical objectives are met.

V = π * ROI2 * h * θm * 7.48 Where:

V = Volume of solution injected (gallons) ROI = target ROI (15 ft) h = thickness of treatment interval (10 ft) θm = mobile porosity (estimated range = 0.07-0.12)

7.48 = conversion from cubic feet to gallons The mobile porosity (or mobile fraction) is the portion of the subsurface that participates in advective groundwater flow. Ranges of these values are available for various soil types based on previous observations and a variety of injection tests (Payne et al. 2007), and the range identified above is consistent with that expected. Based on the range of expected mobile porosity values at the site, the expected injection volume for injection wells in the downgradient transects is between 3,700 and 6,300 gallons per well. The chart below shows injection well details and the proposed injection volume for each injection well during the initial injection event. The actual volume injected into each well will be determined in the field based on the well-specific injection rate and real-time monitoring at the dose-response wells. Injection volumes for subsequent events will be adjusted based on the results of the initial injection. Comment by UsaceAdmin: Are we proposing a potential to stop injection at a specific location regardless of whether or not target volumes or dose-responsiveness suggest incompleteness? Comment by Spooner, Christopher: If we see adequate dose response associated with a set of wells, we may elect to stop injection in those wells to focus injection solution into wells that may not have shown dose response. At the end of the day, we have a limited amount of carbon. If our volume assumptions are low and we run out of carbon, subsequent injection volumes will be increased until we confirm the appropriate volume. I expect the proposed volume below will be sufficient and we plan to inject all the carbon we order regardless of dose response during this initial event.

Chart 1: Proposed OU8 Injection Volumes

(ft bgs)

Notes:

Carbon substrate mass based on 2% (by weight) of injection volume.

Volume of carbon substrate will be determined based on chemical properties of the selected substrate Injection Procedure

Following mixing, the injection solution will be transferred to a piping manifold to split the flow to the injection wells and allow for the simultaneous injection of solution into multiple wells at one time. The injection manifold will be equipped with flow control valves, flow meters, and pressure gauges to monitor and control the flow rate and pressure to each injection well. In addition, each injection well will be equipped with a wellhead assembly that includes a local shutoff valve, local pressure gauge, and an air release valve to prevent air entrainment in the formation and prevent in-well air lock during the injection.