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DOE/OR/01-2539&D2

Explanation of Significant Differences for the Record of Decision for Phase I Interim

Source Control Actions in the Upper East Fork Poplar Creek Characterization Area,

Oak Ridge, Tennessee

This dcxajment has received the appropiiate reviews for release to tlie public.

Larry Sparks

DOE Oak Ridge Office Classification Officer

July 18, 2012

Date

Signatu le fr )c # .03,032,0677

[SD 3/2 to.

IC U

DOE/OR/01-2539&D2

Explanation of Significant Differences for the Record of Decision for Phase I Interim

Source Control Actions in the Upper East Fork Poplar Creek Characterization Area,

Oak Ridge, Tennessee

Date Issued — August 2012

U.S. DEPARTMENT OF ENERGY

Oak Ridge Office of Environmental Management

DOE/OR/01-2539&D2

Table of Contents

1.0 Introduction 1 2.0 Summary of Site History, Contamination Problems Requiring Remediation, and Selected Remedy 3

2.1 Site History 3 2.2 Summary of Remedy Selected in UEFPC Phase I ROD 5

3.0 Description of the Significant Diff«*ences and the Basis for Those Differences.... ll 3.1. Description of Remedy Changes 11 3.2 Cost & Schedule Impacts 15

4.0 Agency Comments 16 5.0 Public Participation 16 6.0 Affirmation of Statutory Determinations 17 7.0 References 18

List of Tables

Principal Actions for the Selected Remedy (Alternative 3A) in the Phase I ROD for the UEFPC CA (from DOE 2002, Table 2.21) 6 Land Use Controls for the Selected Remedy (Alternative 3A} in the Phase I ROD for the UEFPC CA (from DOE 2002, Table 2.23) 7 Side-by-Side Comparison of the Original and Proposed Remedy Components for the Selected Remedy (Alternative 3A) in the Phase I ROD for the UEFPC CA 12

List of Figures

1 Locations of asphalt caps over unpaved areas at West End Mercury Area selected in the UEFPC Phase I ROD (DOE 2002) and eliminated under this ESD (i.e., the asphalt caps depicted in this Figure are eliminated under this ESD) 8

ill

DOli/OR/01-2539&D2

ACRONYMS

ARAR applicable or relevant and appropriate requirement AWQC ambient water quality criteria CA characterization area CERCLA Comprehensive Environmental Response, Compensation, and

Liability Act of 1980 CFR Code of Federal Regulations D&D decontamination/decommissioning and demolition DOE U.S. Department of Energy EFPC East Fork Poplar Creek (upper and lower segments) ESD Explanation of Significant Differences EU Exposure Unit EMWMF Environmental Management Waste Management Facility EPA U.S. Environmental Protection Agency FFA Federal Facility Agreement FS feasibility study LUC land use control LUCAP Land Use Control Assurance Plan NOP National Oil and Hazardous Substances Pollution Contingency Plan NEPA National Environmental Policy Act of 1969 NNSA National Nuclear Security Administration NPDES National Pollutant Discharge Elimination System NPL National Priorities List ORR Oak Ridge Reservation ppt pai-ts per trillion RA remedial action RAO remedial action objective RCRA Resource Conservation and Recovery Act of 1976 RI remedial investigation ROD Record of D«:ision TCLP toxicity characteristic leaching procedure TDEC Tennessee Department of Environment and Conservation UEFPC Upper East Fork Poplar Creek VOC volatile organic compound WAC waste acceptance criteria WEMA West End Mercury Area Y-I2 Y-12 National Security Complex

IV

nOe/01U01-2539&D2

1.0 Introduction

This Explanation of Significant Differences for the Record of Decmon for Phase I Interim Source Control Actions in the Upper East Fork Poplar Creek Characterization Area, Oak Ridge, Tennessee was prepared in accordance with requirements of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 [CERCLA §117(c) and National Contingency Plan (NCP), 40 CFR 300.435(c)(2)(i)]. This document updates the selected remedy for environmental remediation of contaminated areas within the Upper East Fork Poplar Creek (UEFPC) characterization area (CA) at the U. S. Department of Energy (DOE) Y-12 National Security Complex (Y-12) in Oak Ridge, Tennessee, as provided in the UEFPC Phase 1 Record of Decision (ROD) signed in May 2002 (DOE 2002).

Remediation of the UEFPC CA is designed to be conducted in stages using a phased approach, The actions selected in the UEFPC Phase I ROD constitute an initial phase, tbcusing on interim source control actions for remediation of mercury-contaminated soils, sediments, and groundwater that c»ntribute contamination to surface water. These actbns address the most significant sources of mercury contamination in UEFPC for which sufficient data exist to allow appropriate remedy-selection decisions under the CERCLA fiamework. Subsequent phases of remediation will address additwnal contaminated soils and sediments, groundwater, and buildings in futuro CERCLA decision documents. The UEFPC Phase II ROD (DOE 2006) was issued in 2006 and selected additional actions for Y-12 soils and scrapyards.

The puipose of this Explanation of Significant Differences (ESD) is to document changes to components of the remedy selected in the UEFPC Phase I ROD (DOE 2002). Over the past several years, DOE has conducted ongoing work for the identificatbn of major sources of mercury contamination in UEFPC and has completed actions outlined in the UEFPC Phase 1 ROD. These actions, additional data collection efforts, and the planning for future work at the Y-12 site have resulted in the need for changes to some of the actions selected in the UEFPC Phase I ROD. The proposed changes described in this ESD are designed to be consistent with the new remediatbn strategy developed for the UEFPC CA to conduct remedial actions for UEFPC generally in an upgradient-to-downgradient sequence in order to reduce the potential for r«x)ntamination. Tliis remediation strategy for UEFPC results in conducting remedial actions in a sequence consistent with the approach outlined in the UEFPC Phase II ROD (DOE 2006) and with the conceptual model of primary mercury sources developed as a result of ongoing data collection efforts.

This ESD documents the affirmation by the DOE as the lead agency for this action, and the Tennessee Department of Environment and Conservation (TDEC) and the U.S. Environmental Protectbn Agency (EPA), as support agencira, that these changes to the selected remedy remain protective of human health and the environment, are compliant with the established applicable or relevant and appropriate requirements (ARARs), and are cost-effective. The remedy will continue to be implemented with an effort to minimizing disruption of the continuing mission of the Y-12 National Security Complex (fomierly the Oak Ridge Y-12 Plant). This ESD is based on the Administrative Record file for this project, including, but not limited to, the following:

DOri/OR/()l-2539&D2

Report on the Remedial Investigation of the Upper East Fork Poplar Creek Characterization Area at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, DOE/OR/01-1641/V1-V4&D2 (DOE 1998);

Feasibility Study for the Upper East Fork Poplar Characterization Area at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, DOE/OR/OM747&D2 (DOE 1999);

Addendum to the Feasibility Study for the Upper East Fork Poplar Creek Characterization Area at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, DOE/OR/01-1747&D3/A3 (DOE 2000);

Proposed Plan for Interim Source Control Actions for Contaminated Soils, Sediments, and Groundwater (Outfall 51) which Contribute Mercury and PCB-Contamination to Surface Water in the Upper East Fork Poplar Creek Characterization Area, Oak Ridge, Tennessee, DOE/OR/01-1839&D3 (DOE 2001);

Record of Decision for Phase I Interim Source Control Actions in the Upper East Fork Poplar Creek Characterization Area, Oak Ridge, Tennessee, DOE/OII/01-1951&D3 (DOE 2002);

Record of Decision for Phase H Interim Remedial Actions for Contaminated Soils and Scrapyard in Upper East Fork Poplar Creek, Oak Ridge, Tennessee, DOE/OR/01 -2229&D3 (DOE 2006); and

Characterization Report for the 81-10 Area in the Upper East Fork Poplar Creek Area at the Oak Ridge Y-12 National Security Complex, Oak Ridge, Tennessee, DOE/OR/01-

.2485&D2 (DOE 2010),

This ESD will become part of the Administrative Reconl file as required by the NCP, 40 CFR 300.825(a)(2). This document and other inlbnnation supporting the selected remedial action can be found in the Administrative Record file at the DOE information resource center:

U.S. Department of Energy InfoiTTiation Center 1 Science.Gov Way

Oak Ridge, Tennessee 37830 Office Hours: 8:00 am.-5;00 p.m. (Monday through Friday)

(865) 241-4780

DOE is the lead agency for implementing all aspects of the UEFPC cleanup program pursuant to Section 120 of CERCLA, with EPA and TDEC providing oversight.

DOE/OR/01-2539&D2

2.0 Summaty of Site History, Contamination Problems Requiring Remediation, and Selected Remedy

This section provides an overview of the site and the original remedy selection in the UEFPC Phase I ROD (DOE 2002).

2.1 Site History

The 34,000-acre DOE Oak Ridge Reservation (ORR) is located within and adjacent to the corporate limits of the city of Oak Ridge, Tennessee, in Roane and Anderson counties. The ORR is bounded to the east and north by the developed portion of the city of Oak Ridge. The ORR hosts three major industrial research and production facilities originally constructed as part of the World War ll-era Manhattan Project: East Tennessee Technology Park (formerly the K-25 Site), Oak Ridge National Laboratory (ORNL, formerly X-10), and the Y-12 National Security Complex (Y-12, formerly the Oak Ridge Y-12 Plant). UEFPC CA is tocated within the Y-12 National Security Complex.

The UEFPC CA (approximately 1,170 acres) includes the East Fork Poplar Creek Watershed upstream of the point where flow leaves the ORR (Station 17) and the industrialized areas of Y-12. The characterization area lies within Bear Creek Valley and is bounded by Pine Ridge to the north, Chratnut Ridge to the south, the Bear Creek CA to the west, and the DOE ORR boundary (Scarboro Road) to the east. The UEFPC CA also includes a contaminated groundwater plume [Y-12 Plant East End Volatile Organic Compound (VOC) Plume] that extends beyond the ORR boundary to the east into Union Valley.

Historic processes, programs, and waste management practices associated with the Y-12 mission have contaminated soil, surface water, sediment, and groundwater. These processes included chemical separation tojhniques; weapons manufacturing; rraearch and development; waste storage, management, and disposal; and physical plant maintenance activities. These processes and practices released contaminants into the environment at concentrations exc^ing risk-based criteria. The pervasiveness of contamination within the industrialized portions of Y-12, and the widespread application of selected chemicals (i.e., chlorinated solvents) in different source areas, complicate the definition of distinct contaminant plumes and areas of contamination. Current (and historical) contaminant relies fiom the UEFPC CA exit the ORR via surface water (UEFPC at Station 17) and groundwater (east into Union Valley).

Y-12 is an active manufacturing and developmental engineering facility. The main opCTating plant occupies approximately 800 acres within Bear Creek Valley near the northeast comer of the ORR, adjacent to the city of Oak Ridge. Built in 1943 by the U.S. Army Corps of Engineers as part of the World War Il-era Manhattan Project, Y-12's original missfon was to chemically separate and produce fissile ^^^U from ^'®U using an electromagnetic separation process (alpha process) and to manufacture weapon components as part of the national effort to produce the atomic bomb. As other uranium enrichment precedes were devebped and implemented at other installations, the role of Y-12 expanded to include weapon components manufacturing and precision machining, research and development, lithium isotope separation, and special nuclear materials storage and management. The current mission of the installation is multifaceted and includes the following National Nuclear Security Administration (NNSA)

DOB/OR/01-2539&D2

assignments: manufacturing and reworking nuclear weapons components, dismantling nuclear weapons armponents, serving as tiKS nation's stockpile for special nuclear materials, and providing special production support to other programs. In addition, Y-12 applies its unique expertise, initially developed for militaiy purposes, to a wide range of manufacturing applications through the Oak Ridge Center for Manufacturing Technology.

Historical missions of Y-12 resulted in the release of contaminants to the environment. A diverse legacy of contaminated inactive facilities, waste disposal areas, and secondarily contaminated media are potentid candidates for remediation. These include the following:

buildings and other facilities, above- and below-grade tanks, buried waste (burial trenches and fonxier surface impoundments), above-ground and underground process pipelines, drain and storm sewer lines, contaminated surface and subsurface soil, contaminated surface water and sediment, and contaminated groundwater.

Because of these contaminant releases, in 1989 the ORR was placed on the EPA National Priorities List (NPL) established under CERCLA. DOE, EPA, and TDEC signed a Federal Facilities Agr^ment (FFA) govoning CERCLA based cleanup efforts at the ORR in 1992. Ongoing monitoring of surface waters and sediments at the site is conducted to meet the requirements of National Pollutant Discharge Elimination System (NPDES) permits.

The Remedial Invest^ation (Rl) (DOE 1998) and Feasibility Study (FS) documents (DOE 1999, 2000) for the UEFPC CA focused on potential source units (i.e., areas of soil contamination or groundwater plumes) that potentially contribute to the fate and transport of contaminants within and from the chai-acterization area. Appendices A and D of the RI report list and briefly describe each source unit investigated. Specific areas identified in the RI, draft FS, FS Addendum (DOE 2000), and proposed plan (DOE 2001), as contributors to unacceptable risk, are the focus of proposed cleanup actions outlined in the UEFPC CA Phase 1 ROD (DOE 2002).

In accordance with CERCLA Section 120 and 40 Code of Feda-al Regulations (CFR) 300.430(0(4) and the Federal Facilities Agreement (FFA), DOE is acting as the lead agency for remedial actions. TDEC and EPA, as parties to the FFA, provide oversight and approval of the remedy selection and related cleanup decisions as supporting agencies.

DOli/OR/01-2539&D2

2.2 Summary of Remedy Selected in UEFPC Phase I ROD

The selected remedy presented in UEFPC Phase 1 ROD (DOE 2002) was designed to meet interim goals established by the FFA parties for surface water quality and to make substantial progress toward attainment of the long-term water quality goal. It constitutes the initial phase of the phased approach to remediation of the entii'e UEFPC CA, focusing on interim source control actions for remediation of mercury-contaminated soils, sediments, and groundwater that contribute contamination to surface water. The selected remedy (Alternative 3A, which also was selected as the preferred alternative in the proposed plan) includes principal actions described below. Principal actions associated with the selected remaiy are summarized in Table 1 and land use controls (LUCs) are summarized in Table 2.

I. Hydraulic Isolation of the West End Mercury Area: Hydraulic isolation actions in the West End Mercury Area (WEMA) were selected in the Phase 1 ROD to protect recreational human surface water users and to reduce contaminant levels in fish by reducing the release of mercury to UEFPC. Hydraulic isolation actions selected in the Phase I ROD to reduce the flux of mercury to UEFPC included: installation of asphalt caps over unpaved aieas with mercury-contaminated soil and gravel; flushing of contaminated sediments from storm sewers; and refining or replacement of stonn sewers as needed. A third hydraulic isolation component, the installation of a horizontal groundwater capture well to lower the water table, also was identified for a treatability study (see item 5a below) but any implementation decision was deferred to a subsequent CERCLA document. Mercury-contaminated water collected from WEMA building sumps, dewateied soil and sediment from the WEMA storm sewer cleaning and repair, and other WEMA sources would be treated at the Central Mercury Treatment System (CMTS) and/or East End Mercury Treatment System (EEMTS) until the hydraulic isolation actions are complete and their effectiveness verified.

a) Approximately 3.5 acres of unpaved areas with mercury contaminated soils and gravel were identified for construction of asphalt caps (Figure 1) to reduce mercury contamination in surface runoff; these unpaval areas would be excavatal to a depth of approximately 8 inches, and subsequently filled with a 4-inch base of crushed stone and 4 inches of asphalt.

b) Approximately 11,500 linear teet of storm sewec lines were identified for flushing using high-pressure water jets to remove accumulated sediments in both unrepaired and previously cleans! and refined storm sewers.

c) Approximately 2,650 linear feet of storm sewer lines were identified to be refined or repaired in place through: (1) slip-lining or insertion of another pipe within the damaged section of storni sewer; (2) fonning a linei' using injected plastic resins around an inflatable mold; or (3) repairing leaks and bre^s at specific points along the pipe.

Unit Type Unit Remedial Acdons Protectioii Goals Expected Outcomes and Demonstradon of Effecdveoess

Performnce Sfandards

Mercury-contaminated areas

WBMA Hydraulic isolation • Asphalt caps • Sewer flushing/relining

Protect recreational surface water users

Reduction by --50% of mercuiy flux in WEMA outfalls. Current mercury flux in the WEMA area is 1.8 g/day as measured at Outfalls 169,163,160, and 150, Reduction will be monitored in outfalls and is anticipated within 1 year of remediation.

Lining to reduce infiltration is complete when: • size, frequency of visible cracks {<0.5 mm

width, <l crack per fl) Sediment removal is complete when: • 95% volume removal • <0.01 ft thickness of residual sediment Capping to reduce infiltradon/pcrcolation is complete when: • rates are <0.0015 in/hr over 100 m~ area.

Sediments UEFPC and Lake Reality

Remove contaminated sediment/soil

Protect recreational surfece water users

Reduction of 70% of Station 8 area un^ugpd mercury flux and up to 100% of ungauged mercury flux boween Stations 8 and 17. Current Station 8 area mercury flux is 4.5 g/day and 1.4 g/day at Station 17, Reduction will be monittx-ed at Station 8 and Station 17 and is anticipated within I year of remediation.

Removal of sediments in Lake Reality is complete w^hen: • 95% volume removal • <0.1 ft thickness of residual sediment Removal of sediments in UEFPC is complete when: • 95% vol ume removal

Surface water UEFPC Monitor effectiveness of source control and removal actions

Protect recreational surface water users

Attainment of200 ppt interim mercury goal in UEFPC at Station 17. Current mercury flux at Station 17 is 11.2 g/day (330 ppt). Reduction is anticipated within 2 years of remediation. Station 17 is the compliance point for all control actions.

Attainment ofsuriace water goal when: • 200 ppt total mercury concentration at

Station 17

Surface water/ Groundwater

WEMA and Bldg 9201-2

Temporary water treatment at CMTS and EEMTS

Proiea recreational surface water users

Meet NPDES requirement of 200 ppt mercury at Station 17, continuation of monitoring and current effluent compliance throughout operation.

Water tieatment to allow discharge is complete when: • <NPDES discharge limits for all

constituents except mercury, which is 200 ppt

Surfece water/ Groundwater

BIdg. 9201-2 Treatment of dis(±arge from Outfall 51

Protect recreational surface water users

Meet NPDES requirement of200 ppl mercury in effluent (95% reduction in flux) and TDEDCAA air polluhon emission standards. Effluent from the water treatment system and emissions from the air stripper will be monit<»-cd. Compliance with effluent limitation is anticipated after construction and startup.

Water treatment to allow discharge is complete when: • <NPDES discharge limits for all

constituents except mercury, which is 200 ' ppt

CA — characterization area CAA " Oean Air Act of 1970 CMTS = Central Mercury Treatment System

EEMTS - East End Mercury Treatment System NPDES = National Pollutant Discharge Elimination System TDEC == Tennessee Department of Environment and Conservation

UEFPC Upper East Fork Poplar Creek WT-MA = West End Mercury Area

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Type of Cootrol Purpose of Control Buratioa Implementatioii Affected Areas (after remediatiofl)

Property Record Restrictions ®

- Land use

- Groundwater

Restrict use of property by imposing limitations.

Prohibit uses of groundwater.

Indefinitely Restrictions to be drafted and implemented by DOE upon transfer of affected areas; and recorded by DOE in accordance with state law at County Register of Deeds office.

WEMA mercury-contaminated areas

Property Record Notices ^ Provide notice to anyone searching records about the existence and location of contaminated areas.

Indefinitely Initial notice recorded by DOE in accordance with state law at County Register of Deeds office: (1) as soon as practicable after signing of the ROD; (2) upon transfer of affected areas; and (3) final notice upon completion of all remedial actions.

WEMA mercury-contaminated areas

Zoning Notices ^ Provide notice to city about existence and location of waste disposal and residual contamination areas for zoning/planning purposes.

Indeflniteiy Initial property notice filed by DOE with County Register of Deeds office and City Planning Commission as soon as practicable after signing of the ROD; and survey plat upon completion of remedial actions.

WEMA mercury-con taniinaied areas

Excavation/Porcttnation Pennit Program

Provide notice to worker/developer (i.e., pennit requestor) on extent of contamination and prohibit or limit excavation/penetration activity.

As long as the prt^erty remains under DOE control.

Excavation/penetration pennit program to be implemented by DOE and its contractors. Initiated by pennit request.

WEMA mercury-contaminated areas

Si^s^ Provide notice or warning to prevent unauthorized access.

Indefinitely Signage maintained by DOE. UEFPC

Surveillance Patrols Control and monitor access by . workers and'or public.

Indefinitely Surveillance patrols established and maintained by DOE. Necessity of patrols evaluated upon completion of remedial actions.

UEFPC

Properly Record Restrictions - Includes conditions and/or covenants that restrict or prohibit certain uses of real property and are recorded along w ith original property' acquisition records of DOE and its predecessor agencies.

Property Record Notices - Refers to any non-enforceable, purely informational document recorded along with the original property acquisition records of DOE and its predecessor agencies that alerts anyone searching property records to imponant information about residual contamination/waste disposal areas of the property.

Zoning Notices - Includes information on the location of waste disposal areas and residual contaminanon depicted on a survey plat, which ts provided to a zoning authority (i.e., City Planning Commission) for consideration in appropriate zoning decisions for non-DOE property.

Excavation/Penetration Permit Program - Rcfa-s to the internal DOE/DOE-contractor administrative program(s) that require the pennit requester to c^tain authorization, usually in the form of a permit, before beginning any excavation/peneiraiion activity <c.g., well drilling) for the purpose of ensuring that the proposed activity will not affect underground utilities/structures, or in the case of contaminated soil or groundwater, will not disturb the affected area without the appropriate precautions and safeguards.

Signs - posted command, warning or direction. OA characteriaation area ROD record of decision WEM A - West End IVJercuiy Area DOE = U.S. Dq>artment of Energy UEFPC ~ Upper East Fork Poplar Creek

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PRMMY ROMS SECONDWY HMOS

FENCE ASPHULT C«>S

=tauw ouffAas

looaiani of vphdi caps owr ooiatVMM

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Figure L Locations of asphalt caps over impaved areas at West End Mercury Area selected in the UEFPC Phase I ROD (DOE 2002) and eliminated under this ESD (i.e., the asphalt caps depicted in this Figure are eliminated under this ESD).

S lb U> VO

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DOIM)R/OI-2539&D2

2. Removal of Contaminated Soil and Sediment; Contaminated.sediments and bank soils in UEFPC and Lake Reality were identified for removal to protect recreational surface water users and reduce mercury levels in fish tissue.

a) Mercury-contaminated soil and sediment was identified for removal from approximately 4,750 ft of stream bed in UEFPC. Creek bank soils identified to be a source of inercuiy flux to UEFPC also would be removed and the creek channel restored. An estimated volume of 7,900 yd^ of contaminated material would be removed for disposal at EMWMF or an otfoite disposal facility. The removal of contaminated sediment and soil from UEFPC was expected to reduce the flux of ungauged mercury at Station 8 by up to 70%, and over time to reduce the concentration of mercury in fish tissue. Administrative land use controls also were specified to prevent the consumption of fish from UEFPC.

b) Approximately 1 ft of contaminated sediment (approximately 4,035 yd^) was identified for removal from Lake Reality, using remotely operated dredging equipment fitted with a vacuum suction unit to prevent damage to the hypalon liner, for disposal at EMWMF or an offsite disposal facility. The removal of contaminated sediments from Lake Reality was designed to eliminate the risk from contaminated sediment to industrial workers and recreational users.

3. Building 9201-2 Water Treatment System: A 300-gallon/minute water treatment system was selected for construction to remove mercury from the discharge from Outfall 51 and groundwater collected in dewatering sumps at Building 9201-2. This water treatment system was specified to be designed using best available technology with a goal to reduce mercury to 200 ppt or less in the system effluent.

4. Surface Water Monitoring: Conduct surface water monitoring to evaluate reductions in contaminant concentrations and flux, with a goal to reduce mercury to 20O ppt or less at Station 17. Station 17 is the compliance point for all source control actions.

5. Short-Term Studies: Conduct short-term characterization and/or treatability studies to address uncertainties identified with potential additional components of the selected remedy.

a) Conduct a treatability study to evaluate the technical feasibility of using a horizontal groundwater capture well as part of hydraulic isolation of WEMA. As noted in item 1 above, the Phase I ROD mentioned this as a potential additional hydraulic isolation action, but deferred any implementation decision to a subsequent CERCLA document.

b) Conduct a characterization study to better define the depth and mobility of contamination at the Building 81-10 area, and conduct a treatability study to evaluate alternative technologies for in situ stabilization of mercury soil contamination at this site.

I)Ol'yOU/01-2539&D2

c) Conduct a study to evaluate treatment and disposal options for excavated soil and sediment failing to meet EMWMF waste acceptance criteria for onsite disposal, and evaluate onsite and offsite treatment and disposal options.

6. Long-Term Studies: Longer-term studies also were specified in the selected remedy.

a) Conduct groundwater studies to facilitate better understanding of dynamics of groundwater plural underlying the UEFPC CA.

b) Conduct studies to evaluate the viability of large-scale treatment of mercury-contaminated surface water in UEFPC.

7. Land Use Controls; Land use controls were specified in the selected remedy to limit the use of and/or exposure to areas of the UEFPC CA, including water resources, as required to ensure that the remedy remains protective of human health and the environment. The LUCs identified in the Phase I ROD were developed in accordance with the Memorandum of Understanding for the Land Use Control Assurance Plan (LUCAP) developed by DOE, EPA, and TDEC (DOE, EPA and TDEC 1999). LUCs specified in tlie selected remedy are summarized in Table 2 and include: property record restrictions, property record notices, zoning notices, excavation/penetration permit program requirements, signs, and surveillance patrols.

In addition, ongoing maintenance and monitoring ro^uirements were identified to assure proper implementation of the above outlined principal actions.

Remediation of the entire UEFPC CA has been planned to be conducted in stages using a phased approach. The remedial actions noted above constitute an initial phase, focusing on interim source control actions for remediation of mercury-contaminated soils, sediments, and groundwater that contribute contamination to surface water. These actions address the most significant sources of mercury contamination in UEFPC for which sufficient data exist to allow appropriate remedy-selection decisions under the CERCLA firameworlc. Subsequent phases of remediation will address additional contaminated soils and sediments, groundwater, and buildings in future CERCLA decision documents. A Phase 11 ROD (DOE 2006) has also been issued addrrasing soils and scrapyards.

The Phase 1 selected remedy was designed to fit into the overall DOE-ORR cleanup strategy by removing and disposing of contaminated media to the extent practicable. The remedial actions implementtxJ under the Phase I ROD are to be completed, evaluated, and used as the basis for deteraiining what, if any, additional remedial actions may be necessary to meet final goals. Decisions regarding final land use and final goals for surface water, groundwater, and soils are to be determined in future decision documents.

10

DOE/ORy01-2539&D2

3.0 Description of the Significant Differences and the Basis for Those Differences

The significant differences between the selected remedy presented in the Phase 1 ROD (DOE 2002) and the proposed remedy change are describ^ below. DOE followed the requirements of CERCLA § i 17(c) and NOP 40 CFR 300.435(c)(2)(i) and 40 CFR 300.825(a)(2) in evaluating the need for this ESD. The differences noted betow include changes to both field remedy implementation as well as the special studies outlinai in the ROD.

The purpose of this ESD is to outline significant differences for implementing the actions outlined in the Phase 1 ROD (DOE 2002), Over the past several years, DOE has conducted ongoing work for the identificatbn of major sources of mercury contamination in UEFPC and has completed some of the actions outlined in the Phase I ROD. These actions, additional data collection efforts, and the planning for future work have eliminated the need for, or warrant changes to, some of the actions selected in the Phase I ROD. The proposed changes described in this ESD are designed to be more consistent with the new remediation strate^ developai by DOE, EPA, and TDEC to conduct remedial actions for UEFPC in a generally upgradient-to-downgradient sojuence. This remediation strategy for UEFPC results in performing (decontamination/decommissioning and demolition) D&D of buildings and subsequent remediation of environmental media as needed consistent with the exposure unit (EU) approach outlined in the Phase II ROD (DOE 2006), as well as with the conceptual model of primary mercury sources developed as a rrauli of ongoing data collection efforts.

3.1. Description of Remedy Changes

Changes to the selected rmiedy in the Phase I ROD are described bdow, along with the basis for each change. For purposes of clarity, the numbering system used in Section 2.2 is also used here to describe each change; this numbing system does nc* appear in the Phase I ROD and is not intended to denote any type of hierarchy or implementation sequence in the remedy, but is used here only for purpcses of clarity. These changes are also summarized in Table 3.

I. Hydraulic Isolation of the West End Mercury Area

a) Asphalt Capping of Unpaved Areas - The construction of asphalt caps over approximately 3.5 acres of unpaved areas with mercury contaminated soils and gravel (see Figure 1), and associated excavation to enable placement of the asphalt caps, is eliminated. At the time the Phase I ROD was issued, demolition of WEMA buildings was not expected to occur for many years, so the capping of unpaved areas was selected as a component of a plan to hydraulically isolate mercury contaminated soils in the WEMA to reduce mercury migration. However, the schedule for demolition of these buildings has been accelerate, so that mercury contaminated soils in th^e areas will be accessible for excavation under the Phase II ROD much sooner than previously anticipated. Therefore, the capping of these areas to support hydraulic isolation is no longer needed. Mercury-contaminated water collected from the WEMA building sumps, dewatered soil and sediment from the WEMA storm sewer cleaning and repafr, and other WEMA sources will continue to be treated at the CMTS until remedial actions at WEMA are complete and their effectivenras verified through ongoing monitoring. Elimination of the asphalt

11

Table 3. Side^by-Side Comparison of the Original and Proposed Remedy Components

Unit Type Unit Component of Selected Remedy (Alternative 3a) in Pliase I ROD

Proposed Remedy Components Under this ESD

Mercury-contaminated areas

WEMA Hydraulic isolation • Asphalt caps

• Sewer flushing/relining

Eliminate construcnon of asphalt caps over approximately 3.5 acres of unpaved areas with mercury contaminated soil and gravel. The construction of large-scale asphalt caps as a component of hydraulic isolation t)r WEMA soils is no longer needed as the schedule for demolition of WEMA buildings has been accelerated, making contaminated soils in these areas accessible for excavation, where appropriate, under the Phase 11 ROD. No change.

Sediments UEFPC and Lake Reality

Remove contaminated sediment/soil Change implementation schedule/construction logic for consistency with UEFPC upgradient-to-downgr^tent remediation strategy. No change to actions.

Surface water UEFPC Monitor effectiveness of source control and removal actions

No change - continue surfece water monitoring to evaluate reductions in contaminant concentrations and flux, relative to the goal of rediK:ing mercury to 200 ppt or less at Station 17 compliance point.

Surfece water/ Groundwater

WEMA and Bldg920i.2

Temporary water treatment at CMTS and EEMTS

No change - continue temporary treatment of mercury-contaminated storm water and groundwater at CMTS and EEMTS with respea to the goal of reducing mercury to 200 ppt or less in the system effluent.

Bldg- 9201-2 Treatment of discharge from Outfell 51 Ho change - continue treatment of mefcury-contaminaied storm water and groundwater at the Building 9201-2 water treatment system relative to goal of reducing mercury to 200 ppt or less in the system effluent.

NA NA Short-Term Studies • Technical feasibility of horizontal

groundwater capture well for hydraulic isolation at WEMA

« Characterization study and treatability study for 81 -10 Area soils.

• Treatment and disposal options for mercury-contaminated excavated soil

Eiiminate feasibility study for horizontal well The potential use of a horizontal well as part of a hydraulic isolation remedy for WEMA soils is no longer needed, as the schedule for demolition of WEMA buildings has been accelo-ated, making contaminated soils in these areas accessible for excavation, where appropriate, under the Phase 11 ROD.

Retain chamcierization study, which is now complete, but eliminate treatability study, which is no longer needed based on results of the characterization study (DOE 2010); 81-10 Area soils have not been found to be RCRA-characteristic and do not appear to be an important source of mercury migration to UEFPC

No change. NA NA Long-Term Studies

• Dynamics of groundwater plumes at VEFPC

• Viabi Hty of large-scale treatment of mercurv-contaminated surfece water

No change.

No change.

Land Use CcmtroU UEFPC CA 1 UEFPC CA 1 Land Use Controls 1 No substantive change. Minor change in description of Zoning Nonce land use controls. CMTS Central Mercury Treatment System EEMTS - East End Mercury Treatment System

NPDES - National Pollutant Discharge Elimination System UEFPC = RCRA Resource Conservation and Recovery Act WEMA- West End Mercury Area

0

S s

1 K> iy» u> "O s o K>

D01i/0K/()1-2539&D2

caps over unpavcd areas represents only six percent (6%) of the total scope of the selected remedy in terms capital cost {$1.8M / $29.6!V1) and only two percent (2%) of the annual operation and maintenance cost ($0.9M / $43.4M).

b) Storm Sewer Line Flushing - No change.

c) Storm Sewer Line Relining and Repair - No change.

2. Removal of Contaminated Soil and Sediment from UEFPC and Lake Reality

a) Removal of contaminated sediments ajid soil from UEFPC - Retain actions but revise implementation schedule for these actions for consistency with the UEFPC remediatbn strategy of working in a generally upgradient-to-downgradient sequence to address tire contaminants of concern associated with UEFPC. To improve cost efficiency and to prevent rccontamination of remediated areas, contaminated sediment removal will be sequenced to coincide with upstream D&D and soils remediation.

b) Removal of contaminated sediments from Lake Reality Retain actions but revise implementation schedule for these actions for consistency with the UEFPC remediation strategy of working in a generally upgradient-to-downgradient direction to address the contaminants of concern associated with UEFPC. To improve cost efficiency and to prevent recontamination of remediated areas, contaminated sediment removal will be sequenced to coincide with upstream D&D and soils remediation.

3. Building 9201 -2 Water Treatment System

No change. Continue treatment of mercury-contaminated storm water and groundwater at the Building 9201-2 water treatment system and other existing NPDES pemiitted treatment systems, relative to goal of reducing mercury to 200 ppt or less in the system effluent.

4. Surface Water Monitoring

No change. Continue surface water monitoring to evaluate reductions in contaminant concentrations and flux, relative to the goal of reducing mCTCury to 200 ppt or less at Station 17 ajmpliance point.

5. Short-Term Studies

a) Eliminate treatability study to evaluate the technical feasibility of using a horizontal groundwater capture well as part of hydraulic isolation of WEMA. The Pliase I ROD identified the potential use of a horizontal well to lower the water table to be evaluated in a future decision document. At the time the Phase 1 ROD was issued, demolition of WEMA buildings was not expectal to occur for many years, so the hydraulic isolation of mercury contaminated soils in these aieas was selects! to reduce mercuiy migration. However, the schedule for demolition of these buildings has been accelerated, so that mercury contaminated soils in these areas will be accessible for excavation under the

13

DOli'OR/01-2539&D2

Phase 11 UEFPC ROD much sooner than previously anticipated. Therefore, the potential use of a Ixtrizontal well as part of a hydraulic isolation remedy is no longer needed.

b) Retain characta ization study to better define the depth and mobility of contamination at the Building 81-10 Area, but eliminate treatability study to evaluate alternative technologies for in situ stabilization of mercury contamination in soils at this site. The selection of a remedy for the 81-10 source area was deteired pending the results of ongoing characterization studies to address uncertainties in the extent of contamination and the connection to UEFPC and a treatability study to determine the etTcctiveness of in-situ stabilization to immobilize mercury in these .soils. The potential ne«i tor a treatability study was based on the assumption that mercury contaminated soils in the 81-10 Area might be Resource Conservation and Recovery Act (RCRA)-cliaracteristic, and that mercury contamination may be migrating trom the 81-10 Area to UEFPC. The characterization study has been completed (DOE 2010) and has determined that the 81-10 Area soils meet toxicity characteristic leaching procedure (TCLP) criteria for mercury. Based on the results of the characterization study, the mercury-contaminated soils in this area have not been found to be RCRA-characteristic and may be a less important contributor to mercury contamination in UEFPC that previously suspected. A treatability study, therefore, is no longer needed.

c) Conduct study to evaluate treatment and disposal options for excavated soil and sediment failing to meet EMWMF waste acceptance criteria for onsite disposal, and evaluate onsite and ofFsite treatment and disposal options - No change.

6. Long-Term Studies

a) Conduct groundwater studies to facilitate better undemtanding of dynamics of groundwater plumes underlying the UEFPC CA - No change.

b) Conduct studies to evaluate the viability of laige-scale treatment of mercury-contaminated surface water in UEFPC - No change.

7. Land Use Controls

As described in Table 2 above, one of the types of land use controls specified in the selected remedy in the Phase I ROD is Zoning Notices. The City of Oak Ridge Planning Commission has indicated that zoning notices from DOE are of no value to them unless the land is made available for placement on the City tax roles. The city will not retain DOE-provided zoning records prior to this occurrence. Therefore, the entries in Table 2 regarding Zoning Notices are revised as follows, consistent with recent land use control descriptions for other ORR CERCLA documents:

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DOB/OI^01-2539&D2

Revisions to Table 2, Land Use Controls, regarding Zoning Notices, type of Control

Purpose of Control Duration Implementation Affected Areas (after remediation)

Zoning N«i(x:s Provide notice to City Planning • Comiiiis.sion about the existence and I<x:alim of waste disposal and/or contarninatcd areas and providing use limitation.s information for zoning/planning purposes if/whai UEFPC areas are transferred out of l>OE federal control.

Indellnitcly Zoning notice, use limitations information, and taundary survey plat wilt be filed with the City Planning Commission if/when areas arc to be transferred out of DOE teileral control.

WEMA nicrcury-containlnatcd areas

3.2 Cost & Schedule Impacts

As noted in the FS Addendum (DOE 2000), Proposed Plan (DOE 2001), and Phase I ROD (DOE 2002), the implementation cost of the selected remedy had a present worth value (in yeai- 2000 dollars) of about $38.3M and had an estimated timeframe for completion of nearly 10 years. The actual schedule and cost of remedy implementation, including that at the UEFPC CA, is dependent on annual funding appropriated to DOE by Congress, as well as the prioritization of remedial actions throughout the ORR to achieve risk reduction.

This BSD has minimal impart on the cost aiKl schedule contemplated in the original remedy analysis. A summary of specific cost/schedule impacts is discussed below.

• Eliminating the asphalt caps and associated excavation will reduce the capital cost of the original ROD by less than 6% (about $2!VI).

• Change to the special studies and land use controls result in virtually no cost/schedule impact to the original remedy.

• Resequencing work to be consistent with overall UEFPC cleanup strategy of conducting remediation in a generally upgi-adient-to-downgradient direction does not yield any cost impacts, but the schedule contemplated in the original ROD will likely take longer" when considering Phase I only. However, because resequencing of work reduces the potential for recontamination, both schedule and cost may be lower in the long teim because rework and additional remediatkm will be eliminated.

Overall, the cost impact as a result of this ESD is expected to be less than 10% with respect to that originally estimated in the ROD. The schedule impact is negligible when considering the full litecycle cost of both Phase I and Phase II UEFPC remediation efforts.

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DOE/OR/01-2539&D2

4.0 Agency Comments

DOE and its subcontractors have worked closely with EPA and TDEC through the UEFPC Core Team to tmild consensus prbr to formal regulatory review and approval Facility regulators reviewed a previous version of this ESD, and these comments have been incorporated in the current version of this document. Through signature of this document, EPA and TDEC concur with this ESD and with this change to the UEFPC Phase I ROD.

5.0 Public Participation DOE will publish a notice of availability and a brief description of this ESD in the local

newspapers to meet the requirements of 40 CFR 300.435(c)(2)(i)(B). An Information Sheet that presents a summary of this ESD is also available and was announced to the public through local newspapers and to advisory groups through direct mailings. The Oak Ridge Site Specific Advisory Board (ORSSAB) assisted in the development of this Information Shert through their review and comment. Additional information can be obtained from:

David Adler, FFA Manager U.S. Department of Energy

Oak Ridge Office of Environmental Management P.O. Box 2001

Oak Ridge, Tennessee 37831 (865) 576-4094

In addition, this approved ESD will be placed in the Administrative Record file per the requirements of the NCP, 40 CFR 300.435(c)(2)(i)(A) and 300.825(a)(2), and made available to the public at:

U.S. Department of Energy Information Center 1 Science.Gov Way

Oak Ridge, Tennessee 37830 Office Hours: 8:00 a.m.-5:00 p.m. (Monday through Friday)

(865) 241-4780

There will be no formal public comment period. If requested by stakeholder groups, specific review sessions will be provided. These briefings will be consistent with requirements of NCP, 40 CFR 300.825(b).

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DOB/OR/01-2539&D2

6.0 Affirmation of Statutory Determinations

Under CERCLA § 121, the selected remoiy must be protoitive of human health and the environment, comply with ARARs (unless a statutory waiver is justified and granted), be cost ctTective, and utilize permanent solutions and alternative treatment technologies or resource recovery to the maximum extent practicable. With the changes desciibed in this ESD to the selected remedy in the UEFPC CA Phase 1 ROD, the remedy remains protective and continues to meet ARARs as required by the NCP, 40 CFR 300.430(t)(l)(ii)(B)(l) and (2). There are negligible cost and schedule impacts to remedy implementation in the UEFPC characterization area as result of the remedy changes described in this ESD. In addition, these changes do not alter impacts to National Environmental Policy Act (NEPA) values discussed in the Phase I ROD.

This ESD proposes no cliangcs in the ARARs identified in the UEFPC Phase 1 ROD. Under Tennessee water quality regulations, streams may be designated for multiple u.se classifications (TDEC 1200-04-04), and different Ambient Water Quality Criteiia (AWQC) may be specified for each use classification (TDEC 1200-04-03). The entire length of East Fork Poplar Creek is currently designated for four use classifications: Fish and Aquatic Life, Recreation, Livestock Watering and Wildlife, and Irrigation. Among these four designated use classifications. Recreation has the most stringent criterion with respect to mercury at 0.051 pg/L. The Phase I ROD states that the response actions under the selected remedy are not expected to attain this criterion for mercury in UEFPC, aiKi that a waiver will be invoked under CERCLA 121(d)(4)(A). Under the NCP at 40 CFR 300.430(fi(l)(ii)(C)(l), an alternative that does not meet an ARAR may be selectal with the alternative is an interim measure and the the ARAR will be attained or waived as part of a total (i.e., final) remedial action. On completion of the Phase I source control actions, a risk-based surface water remediation goal for mercury of 200 pg/L is expected to be met at Station 17 in the interim. This ESD proposes no changes in these ARARs.

Considering the new information and the changra that will be made to the selected remedy, the DOE, EPA, and TDEC believe that the remedy remains protective of human health and the environment, complies with Federal and State requirements identifial in the ROD as applicable or relevant and appropriate to this remedial action, and is cost effective. In addition, the revised remedy utilizes permanent solutions and alternative treatment technologies to the maximum extent practicable for this site. The selected remedy with the changes described in this ESD satisfies the requirements of CERCLA §121.

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DOli/Oli/01-2539&D2

7.0 References

40 CFR 300, 2004, "National Oil and Hazardous Substances Pollution Contingency Plan," Code of Federal Regulations, Ofticc of the Federal Register, October 4, 2004.

42 use 9601 et seq., 1980, "Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA/Supertund)," United States Code, December 11, 1980.

U.S. Department of Energy, U.S. Environmental Protection Agency, and Tennessee Department of Conservation and Environment (DOE, EPA, and TDEC 1999), Memorandum of Understanding for Implementation of a Land Use Control Assurance Plan (LUCAP) for the United States Department of Energy Oak Ridge Resen>ation, 1999.

U.S. Department of Eno-gy (DOE 1998), Report on the Remedial Investigation of the Upper East Fork Poplar Creek Characterization Area at the Oak Ridge Y-12 Plant, Oak Ridge, Tennes.see, DOE/ORy01-l641A^l-V4&D2, August 1998.

U.S. Department of Energy (DOE 1999), Feasibility Study for the Upper East Fork Poplar Characterization Area at the Oak Ridge Y-12 Plant, Oak Ridge. Tennessee, DOE/OR/01-1747&D2, 1999.

U.S. Department of Energy (DOE 2000) Addendum to the Feasibility Study for the Upper East Fork Poplar Creek Characterization Area at the Oak Ridge Y-12 Plant. Oak Ridge, Tennessee, DOE/OR/OU1747&D3/A3, April 2000.

U.S. Department of Energy (DOE 2001), Proposed Plan for Interim Source Control Actions for Contaminated Soils, Sediments, and Groundwater (Outfall 51) which Contribute Mercury and PCB-Contamination to Surface Water in the Upper East Fork Poplar Creek Characterization Area, Oak Ridge, Tennessee, DOE/OR/OI-1839&D3, January 2001.

U.S. Department of Energy (DOE 2002), Record of Decision for Phase I Interim Source Control Actions in the Upper East Fork Poplar Creek Characterization Area, Oak Ridge, Tennessee, DOE/OR/01 -1951 &D3, May 2002.

U.S. Department of Energy (DOE 2006), Record of Decision for Phase II Interim Remedial Actions for Contaminated Soils and Scrapyard in Upper East Fork Poplar Creek, Oak Ridge, Tennessee. DOE/OR/01-2229&D3, March 2006.

U.S. Department of Enei"gy (DOE 2010), Characterization Report for the 81-10 Area in the Upper East Fork Poplar Creek Area at the Oak Ridge Y-12 National Security Complex, Oak Ridge, Tennessee, DOE/OR/01-2485&D2, September 2010.

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APPROVALS

Explanation of Significant Differences for the Record of Decision for Phase I Interim Source Control Actions in the

Upper East Fork Poplar Creek Characterization Area, Oak Ridge, Tennessee

August 2012

itney, ManafflsJ Marie Whitn^, Mana^ Oak Ridge Office of Environmental Management U. S. Department of Energy

Director, Superfund Division U.S. Environmental Protection Agency, Region TV

Owsley A

John Qwsl^ Director, DOE Oversight Tennessee Department of Environment & Conservation

Date

DOli/'OR/Ol -2539&D2

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