PB98-964027
                             EPA541-R98-114
                             March 1999
EPA Superfund
      Record of Decision:
      Savannah River Site (USDOE)
      D-Area Oil Seepage Basin (631-G)
      Aiken, SC
      8/14/1998

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"United States Department of Energy
Savannah River Site
Record of Decision
Remedial Alternative Selection
for the
D-Area Oil Seepage Basin (631-G) (U)
WSRC-RP-97-402
Revision 1, Final
August 1998
*V/estinghouse Savannah River Company
   tannah River Site
   en, South Carolina 29808
                                                       SAVANNAH R ! V £ r
  SPARED FOR THE U.S. DEPARTMENT OF ENERGY UNDER CONTRACT DE-AC09-96-SR18500

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                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                                       REGION 4
                                ATLANTA FEDERAL CENTER
                                 61 FORSYTH STREET. SW
                               ATLANTA. GEORGIA 30303-8909

                                    AUO 1 4  1998
 CERTIFIED MAIL
 RETURN RECEIPT REQUESTED
 4WD-FFB
 Mr. Brian T. Hennessey, FFA Project Manager
 Environmental Restoration Division
 SRS Project Manager
 U.S. Department of Energy
 Savannah River Operations Office
 P.O. Box A
 Aiken, South Carolina 29802

 SUBJ: Record of Decision
       Remedial Alternative Selection for the
       D-Area Oil Seepage Basin ,
       Rev. 1 (WSRC-RP-97-402), dated August 1998
Dear Mr. Hennessey:

The Environmental Protection Agency (EPA) has completed its review of the subject document and has
no additional comments. Accordingly, this letter provides EPA approval of the Rev. 1  Record of
Decision for the D-Area Oil Seepage Basin operable unit.

If you have any questions regarding this matter, please contact me at (404) 562-8547.

                                         Sincerely,
                                         Julie L. Corkran, RPM
                                         DOE Remedial Section
                                         Federal Facilities Branch
                                         Waste Management Division
cc:     Keith Collinsworth, SCDHEC
       Ben Gould, DOE-SRS
       Sandra Carrol, ERD-WSRC (Signed Original)
           R*cycl*d/R*cyct*bl« • Printed with Vegetable Oil Based Inks on 100% Recycled Paper (40% Posloonsumer)

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be:    Julie Corkran, FFB
       Peter Raack, HAD
jlc/JCORKRAN/4WD-FFB:28547/08-13-98/c:\...\rodapprvl
CORKRAN         CRANE            .WAF
RAACK

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United States Department of Energy
Savannah River Site
Record of Decision
Remedial Alternative Selection for the
D-Area Oil Seepage Basin (631-G) (U)
 WSRC-RP-97-402
 Revision 1, Final
 August 1998
 Westinghouse Savannah River Company
 Savannah River Site
 Aiken. SC 29808	
 Prepared for tn« U. S. Department of Energy under Contract No. O£-AC09-96SFM 8500

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Record of Decision for the
D-Area Oil Seepage Basin (6J1-G) (U)
Savannah River Site	
 WSRC-RP-97-402
  Revision 1. Final
	Aurust 1998
                                            DISCLAIMER
                  This report  was prepared  by Westinghouse  Savannah  River  Company
                  (WSRC) for the United States Department of Energy under Contract No.
                  DE-AC09-96SR18500 and is  an account of work performed under that
                  contract. Reference herein to any specific commercial product, process, or
                  services  by  trademark, name,  manufacturer or  otherwise  does  not
                  necessarily constitute or imply endorsement, recommendation, or favoring
                  of same  by  WSRC  or by the United States Government or any agency
                  thereof.
                                  Printed in the United States of America
                                              Prepared for
                                       U. S. Department of Energy
                                                  By
                                  Westinghouse Savannah River Company
                                          Aiken. South Carolina

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               RECORD OF DECISION
      REMEDIAL ALTERNATIVE SELECTION (U)
            D-Area Oil Seepage Basin (631-G)
                  WSRC-RP-97-402
                   Revision 1, Final
                     August 1998
                  Savannah River Site
                 Aiken, South Carolina
                      Prepared by:
           Wesiinghouse Savannah River Company
                        for the
U. S. Department of Energy Under Contract DE-AC09-96SR18500
             Savannah River Operations Office
                  Aiken, South Carolina

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Record of Decision for the                                                                 \VSRC-RP-9T-40:
D-Area Oil Seepage Basin (6J1-G) (L")                                                         Revision 1. Final
Savannah River Site	.	August 1998
DECLARATION FOR THE RECORD OF DECISION

Unit .\'ame and Location

D-.Area Oil Seepage Basin (Building Number 631-G)
Savannah River Site
Aiken. South Carolina

The D-Area Oil  Seepage Basin (D-Area OSB) Operable  Unit  (OU) is listed  as  a  Resource Conservation and
Recovery Act  (RCRA)  3004(u)  Solid  Waste  Management  Unit/Comprehensive  Environmental  Response.
Compensation, and Liability Act (CERCLA) unit in Appendix C of the Federal Facility Agreement (FFA) for the
Savannah River Site (SRS).

Statement of Basis and Purpose

This decision document  presents the selected remedial alternative for the D-Area  OSB located at SRS  south of
Aiken. South Carolina. The selected alternative was developed in accordance with CERCLA, as amended, RCRA.
and to the extent practicable, the National Oil and Hazardous Substances Contingency Plan (NCP).  This decision :s
based on the Administrative Record File for this specific RCRA/CERCLA unit.

Assessment of the Site

Actual or threatened releases of hazardous substances  from  this site, if not addressed by implementing the  respond
action selected in this Record of Decision (ROD), may present an imminent and substantial endangermem  to pubi:-
health, welfare, or the environment.

Description of the Selected Remedy

 Since remedial action objectives (RAOs) for deep soils have been achieved by the interim remedial action (IRA) ar.J
 biovent testing. No Further Action is the selected remedy for this medium (WSRC, 1997b, c, d. and e). No  Action .i
 the selected remedy for shallow soil, surface water and sediment, because no constituents of concern (COCs) -Acre
 identified  for them in  the RCRA Facility Investigation/  Remedial  Investigation/  Baseline  Risk  Assessment
 (RFI/RI/BRA).  For these reasons, development of remedial alternatives for these media is not warranted.
                                              Declaration • 1

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Record of Decision for the                                                                   WSRC-RP-97-J02
D-Area Oil Seepage Basin (631-G) (LI                                                          Revision 1. Final
Savannah Rjver Site	 _	August 1998
The selected remedy for D-Area OSB groundwater is Alternative GW-2: Natural Attenuation/Groundwater Mix:r.-2
Zone (GWMZ) -with  Institutional  Controls.   Under  this  remedy, natural  attenuation mechanisms  such as
biodegradation.  flushing,  volatilization,  adsorption,  and  hydrolysis  would  continue  to  reduce  contaminant
concentrations in the groundwater to acceptable levels. Results from a bioventing study, conducted after the IRA at
the unit, indicate that the source of groundwater contamination (i.e., the D-Area OSB soil) was abated  as a result of
the combined IRA and biovent test and no longer contributes to groundwater contamination.  Evidence indicating
that natural  attenuation processes are occurring in the D-Area OSB groundwater was presented in the  RFI/RI/BRA
Report CWSRC. I997a) for the unit.   This evidence included:   (1) decreased dissolved  oxygen  levels  in  the
ground water, indicating that microorganisms are utilizing the contaminants as a carbon source and the oxygen within
the groundwater to produce energy, (2) elevated chemicaJ oxygen demand, chloride, and sulfate levels downgradiem.
(3) depressed pH levels in contaminated areas, and (4) presence of breakdown products.

Herbert et al., 1984, report that natural attenuation is selected as a preferred remedial  option when the following site-
specific conditions exist:

     Groundwater is unsuitable for consumptive use.
•    Contaminants degrade quickly or are not at highly toxic concentrations.
•    There is low potential for exposure.
•    Active restoration  is not feasible due to complex hydrogeologic conditions.
•    There is low projected demand for future groundwater use.
•    The unit is in close proximity to a surface water discharge area, with dilution  to levels that are  protective of
     human  health and the environment.

Based on the information presented in the RFI/RI/BRA report for the D-Area  OSB, the conditions at the D-Area
OSB would be  conducive to natural attenuation. Specific findings from that report include:

•    The source of contamination at the D-Area OSB was removed during the IRA  in  conjunction with the bio^eni
     testing and is no longer contributing to groundwater contamination.
•    Naturally occurring mechanisms will continue to reduce contaminant concentrations.
•    There are no receptors of groundwater at the D-Area OSB; therefore,  the potential for exposure is low.
•    The aquifer is limited in thickness and yield and the groundwater it contains is not targeted for  residential or
     commercial use; therefore, projected demand for future groundwater use is low.
 •    Modeling  indicates that contaminant concentrations in the D-Area OSB groundwater would be reduced to below
     maximum contaminant levels  (MCLs) prior to reaching Fourmile Branch; therefore dilution  in the surface water
     body is not necessary to achieve MCLs.
                                                Declaration - 2

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Record of Decision for the                                                                    WSRC-RP-97-402
D-Area Oil Seepage Basin (6J1-G) (TO                                                          Revision 1. Final
Savannah River Site	__^_^	.   	August 1998
The  time  required to degrade the  unit-specific contaminants was  conservatively  estimated  through grour.dwaier
modeling. The modeling indicates that all contaminant concentrations in groundwater would be reduced  below their
respective MCLs  within approximately 10 years, which is well within the time-frame that the U.S.  Department of
Energy (DOE) plans to maintain control of the SRS.

A GWMZ application, defined under South Carolina Regulations R.61-68. has been approved by the SCDHEC as
pan  of this alternative.  Based on area characteristics and evidence presented in the GWMZ Application vWSRC.
1998c). a GWMZ variance for the D-Area OSB is an appropriate pan of natural attenuation remedies.

Mixing zones are appropriate for situations where the source of groundwater contamination has been removed and
where contaminant concentrations are  being  reduced by natural processes.  Under these regulations,  certajn
concentration limits above MCLs. known as mixing zone  concentration limits (MZCLs),  will be established within
the designated mixing zone, where the plume will migrate  while it dissipates.  MCLs. which are protective limits for
drinking water, will be established at the compliance boundary downgradient of the plume. Plume monitoring wells
will  be  installed  within the plume and at the compliance  boundary, and would be  sampled periodically to monitor
compliance with permitted MCLs and  MZCLs.  Intermediate wells will be installed at other locations within the
mixing zone to monitor plume behavior between the plume wells and compliance boundary wells as an early warning
mechanism if plume behavior does not match predictions.

The  mixing zone application has demonstrated that RAOs will be met, MZCLs will be achieved  throughout the
groundwater aquifer, and MCLs will be achieved at the compliance boundary as described in the approved GWMZ
application. Implementation of this alternative will  involve installation of nine new wells and monitoring of a total
of 12 groundwater wells, as described in the GWMZ application.

The D-Area OSB is in an industrial use zone, as identified in Figure 3.3 of the SRS FFA Implementation Plan
(WSRC, 1996e),  for both current and anticipated future land use.  Although the remediation  decisions  for this unit
were based on the industrial use scenario, the groundwater remedy will achieve the more protective residential use
scenario.  The D-Area  OSB currently meets unrestricted land use criteria for soils, sediment and surface water.
Groundwater  beneath the unit exceeds  the MCLs.  Although  institutional  controls are included in all  of the
alternatives (except the no-action alternative), the DOE has recommended that residential use of SRS land  in the
 vicinity of D Area be prohibited (DOE. 1996); therefore,  future residential use and potential residential  water usage
 in this area is unlikely.  Modeling of groundwater transport processes as pan of the evaluation of the remedial
 alternatives indicates that MCLs for  the contaminants of  concern will be achieved in all areas of the D-Area OSB
 groundwater after approximately 10 years.  Upon confirmation  that MCLs have been achieved, institutional controls
 at the unit will no longer be required.
                                               Declaration - 3

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Record of Decision for the                                                                  \VSRC-RP-97-40:
D-Area Oil Seepage Basin (631-G) (L~)                                                        Revision ). Final
Savannah River Site	     August 1998
Per the EPA Region-FV Land Use Controls (LUCs) Policy, a LUC Assurance Plan (LL'CAP) for SRS and a LUC
Implementation P4an (LUCIP) for the D-Area OSB will be developed and submitted to the regulators tor appro'-a!.
The LL'CAP will be submitted under separate cover, whereas the LUCIP will be submitted with the Remedial Design
Work Plan/Remedial Design Report/Remedial Action Work Plan (RDWP/RDR/RAWP) in accordance with the posi-
ROD document schedule provided in Figure IS. The LUCIP details how SRS will implement, maintain, and monitor
the land use control elements of the D-Area OSB ROD to insure that the remedy remains protective of human health.

The LUC objective necessary to ensure the protectiveness of the preferred alternative is:

•   Prevent unauthorized access to the D-Area OSB  contaminated groundwater plume.

The  institutional controls required to prevent unauthorized exposure to the contaminated media at the D-Area OSB
include the following:

•   controlled  access to the D-Area OSB through  existing SRS security gates and perimeter fences and the  sue
    use/site clearance programs
    signs posted in  the area to  indicate that groundwater in the vicinity of the  unit has  been contaminated by
    hazardous materials
•    notification of groundwater contamination to any future landowner through deed notification, as required under
     CERCLA Section 120(h)

A certified survey plat of the site will be prepared by a registered land surveyor and will be included with the post-
ROD documents.  If D-Area OSB is transferred to non-FederaJ ownership prior to remediation of  the groundwater to
the MCLs for the COCs, reevaluation of the  need  for deed restncuons would  be  performed through an amended
 ROD with Environmental Protection Agency (EPA) and South Carolina Department of Health (SCDHEC) approval
The survey plat will be reviewed and updated, as necessary, at the time the site is transferred and  will be recorded
 with the appropriate county recording agency.  The D-Area OSB  is located in Aiken County.

 This selected remedy is intended to be the final action for the D-Area OSB. and is intended to be permanent and
 effective in both the long and short terms. This remedy is considered to be the least cost option that is still protective
 of human health and the environment.  The  state regulatory authority, the SCDHEC, will modify the SRS RCRA
 permit to incorporate the selected remedy.

 The Rev. 0 of the post-ROD document, the combined  RDWP/RDR/RAWP. will be submitted to the U.S. EPA and
 SCDHEC within  approximately ISO calendar days after the issuance of the ROD. The RDWP/RDR/RAWP will
                                               Declaration - •

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Record of Decision for the                                                                  WSRC-RP-97-402
D-Area Oil Seepage Basin (631-G) CL~)                                                          Revision I, Final
Savannah River Site	                      August 1998
contain a conceptual Corrective Action Plan Strategy, a summary description of the scope of work for the remedial
action design, an implementation/ submJttai schedule for subsequent post-ROD documents, and an anticipated field
activities start date. The regulatory review period. SRS revision period,  and final regulatory review and  approval
period will be 90. 60. and 30 calendar days, respectively.

Statutory Determinations

Based on the D-Area OSB RFI/RJ Report and BRA fWSRC. I997a.i, D-Area OSB groundwater poses no significant
n>k to the environment but  poses significant  risk to human health.   Therefore, monitoring of the existing
groundwater constituents, consistent with the GWMZ application, is necessary.

The selected remedy  is protective of human  health and  the  environment, complies  with federal  and state
requirements that are legally applicable or relevant and appropriate to the remedial action, and is cost-effective. This
remedy utilizes permanent  solutions and alternative treatment (or resource recovery) technology  to the  maximum
extent practicable  and satisfies the statutory preference for remedies that employ  treatment to reduce toxicity.
mobility, or volume as a principal element. Section 300.430(f)(4)(ii) of the NCP requires that a five-year review of
the ROD be performed  if  hazardous substances, pollutants, or contaminants remain  at the waste unit.   Since
hazardous  substances will  remain at the unit above  health-based standards during the  remediation time  frame
indicated in the groundwater mixing zone application (approximately  10 years), the three  FFA Parties below have
determined that a five-year review of the ROD for the D-Area OSB will be performed  to ensure continued protection
of human health and the environment until the MCLs are attained in the sroundwater.
 Date                        T. F. Heenan: Assistant Manager for Environmental Quality
                             U. S. Department of Energy, Savannah River Operations Office
 Date                        Richard D. Green; Division Director
                             Waste Management Division
                             U. S. Environmental Protection Agency - Region IV
 Date                        R. Lewis Shaw; Deputy Commissioner
                             Environmental Quality Control
                             South Carolina Department of Health and Environmental Control
                                               Declaration - 5

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                DECISION SUMMARY
      REMEDIAL ALTERNATIVE SELECTION (U)
            D-Area Oil Seepage Basin (631-G)
                   WSRC.RP-97-402
                   Revision 1, Final
                     August 1998
                  Savannah River Site
                 Alken, South Carolina
                      Prepared by:
          Westinghouse Savannah River Company
                        for the
U. S. Department of Energy Under Contract DE-AC09-96SR18500
             Savannah River Operations Office
                  Aiken. South Carolina

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Record of Decision for the                                                                WSRC-RP.9"-40:
D-Area Oil Seepage Basin (631-G) ft")                                                       Revision I. Final
Savannah River Site	August 1998
                —           DECISION SUMMARY TABLE OF CONTENTS



Section                                                                                          Page

I.       Savannah River Site (SRS) and Operable Unit (OU) Name. Location. Description, and Process History	I

II.      Site and OU Compliance History	1 I

III.     Highlights of Community Participation	12

IV.     Scope and Role of the OU Within the Site Strategy	U

V.      OU Characteristics	26

VI.     Summary of OU Risks	4"

VII.    RAOs and Description of Considered Alternatives for the D-Area OSB OU	6"

VIII.   Summary of Comparative Analysis of the Alternatives	~9

IX.     The Selected Remedy	3?

X.      Statutory Determinations	92

XI.     Explanation of Significant Changes	92

XII.    Responsiveness Summary	92

XJH.   Post-ROD Document Schedule	9}

XTV.   References	9"

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Record of Decision for the
D-Area Oil Seepage Basin T631-G) (IT)
Savannah River Site	
 WSRC.RP-97.402
  Revision 1. Final
	August 1998
List of Figures
Figure I:      Location of the D-Arca OSB at the SRS	3
Figure 2:      Topography of the .Area Surrounding the D-Area 053	5
Figure 3:      Site Plan of the D-Area OSB	~
Figure 4:      Current Photograph of the D-Area OSB (May 1993,	9
Figure 5:      RCRA/CERCLA Logic and Documentation	\5
Figure 6:      Response Action Selection Process	23
Figure 7a:     CSM for the D-Area OSB	29
              Showing Potential Human Receptors and Exposure Pathways
Figure 7b:     CSM for the D-Area OSB	31
              Showing Potential Ecological Receptors and Exposure Pathways
Figure 8:      TCE in the Shallow Portion of the Water Table Aquifer	37
Figure 9:      TCE in the Deeper Portion of the Water Table Aquifer	39
Figure 10:     Cross Section of TCE in Groundwater	J1
Figure 11:     Master Legend for Maps and Cross Sections	43
Figure 12:     Risk-based COCs  for  the Current On-Unit Worker, by  Pathway	57
              after the Uncertainty Analysis
Figure 13:     Risk-based COCs  for  the Future On-Unit Worker, without	59
              Excavation of Soils, by Pathway, after the L'ncertainry Analysis
Figure 14:     Risk-based COCs for the Future On-Unit Worker. with	61
              Excavation of Soils, by Pathway, after the Uncertainty Analysis
Figure 15:     Risk-based COCs for the Future Resident, without	63
              Excavation of Soils, by Pathway, after the Lncerjmtv Analysis
Figure 16:     Risk-based COCs for the Future Resident, with	65
               Excavation of Soils, by  Pathway, after the Uncertainty .Analysis
Figure 17:      Proposed GWMZ with Monitoring Well Locations	73
 Figure 18:     Post-ROD Schedule  	95

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Record of Decision for the
D-Area Oil Seepage Basin (631-G) (L*)
Savannah River Site	
 WSRC-RP-97-40:
  Revision 1. Final
	August 1998
List of Tables

Table 1       USCs for all Media	33

Table 2      Summary of Risk-Based PCOCs. Grouped by Exposure Route	49

Table 3      Summary of PCOCs	54

Table 4      Uncertainty Matrix for COCs	55

Table 5      Final COCs. with Selected RGOs	69

Table 6      Comparative Analysis of Groundwater Alternatives	80

Table 7      MZCLs and MCLs for COCs	:	91









Appendix

A.            Responsiveness Summary	99
                                                  in

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Record of Decision for the
D-Arva Oil Seepage Basin (631-G) (U)
Savannah River Site	
 WSRC-RP-97-402
  Revision 1. Final
	August 1998
                            LIST OF ACRONYMS AND ABBREVIATIONS
ARAR          applicable or relevant and appropriate requirement
BRA           Baseline Risk Assessment
CAB           Citizen's Advisory Board
CERCLA       Comprehensive Environmental Response, Compensation, and Liability Act
CFR            Code of Federal Regulations
CMS           Corrective Measures Study
COC           constituent of concern
COPC          constituent of potential concern
CSM           conceptual site model
D-Area OSB     D-Area Oil Seepage Basin
DCE           dichloroethene
DOE           U.S. Department of Energy
DQO           Data Quality Objectives
DRO           diesel range organics
EPA            U.S. Environmental Protection Agency
ERA           Ecological Risk Assessment
ER&WM       Environmental Remediation and Waste Management
ESC            Expedited Site Characterization
FFA            Federal Facility Agreement
FRR            Final Remediation Report
FS             Feasibility Study
ft   ;           feet/foot
GWMZ         Groundwater Mixing Zone
Hc             Henry's Law coefficient
HI             hazard index
HQ            hazard quotient
IRA            interim remedial action
LUC           land use control
LUCAP        land use control assurance plan
LUCIP         land use control implementation plan
km            kilometer
m              meter

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Record of Decision for the
D-Area Oil Seepage Basin (631-G) (U)
Savannah River Site	
 WSRC-RP-97-40:
  Revision I. Final
	August 1998
MCL           maximum contaminant level
MEPAS        -Multimedia Environmental Pollutant Assessment System
ma              mile
Mg/fcg           micrograms per kilogram
Mg/1            rrucrogram per liter
MLSSL         mass-limited soil screening level
msl             mean sea level
MZCL          mixing zone concentration limit
NCP           National Oil and Hazardous Substances Contingency Plan
NPDES         National Pollutant Discharge Elimination System
NPL           National Priorities List
OU            Operable Unit
PCE           tetrachloroethene
PCOC          Preliminary COC
PCR           post-construction repon
PP             Proposed Plan
RAO           Remedial Action Objective
RAWP         Remedial Action Work Plan
RBC           risk-based concentration
RCRA          Resource Conservation and Recovery Act
RDR           Remedial Design Repon
RDWP         Remedial Design Work Plan
RFI            RCRA Facility Investigation
RGO           remedial goal option
RI             CERCLA Remedial Investigation
RME           Reasonable Maximum Exposure
ROD           Record of Decision
SAFER         Streamlined Approach for Environmental Restoration
SB            Statement of Basis
SCDHEC       South Carolina Department of Health and Environmental Control
 SCHWMR      South Carolina Hazardous Waste Management Regulations
 SRS           Savannah River Site
 SSL           soil screening level
 TCE           trichloroethene
 TPH           total petroleum hydrocarbons

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Record of Decision for the                                                                 WSRC-RP-97-402
D-Area Oil Seepage Basin (631-G) (V)                                                        Revision 1, FinaJ
Savannah River Site	August 1998
USC            unit-specific constituent
V'OC           volatile organic compound
WSRC          Westinghouse Savannah River Company
                                                    VI

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Record of Decision for the                                                             WSRC-RP-97-402
D-Area Oil Seepage Basin (631-G) (V)                                                     Revision 1. Final
Savannah River Site	August 1998
                       THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                VII

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Record of Decision for the                                                                WSRC-RP-97-402
D-Area Oil Seepage Basin (631-G) (U)                                                        Revision 1. FinaJ
Savannah River Site	   August 1998
I.       SAVANNAH RJVER SITE (SRS) AND OPERABLE UMT (OL ) NAME, LOCATION,
        DESCRIPTION, AND PROCESS HISTORY

SRS Location, Description, and Process History

The SRS  occupies approximately 777 square kilometers (km) [310 square miles (mi)] of land  adjacent to the
Savannah  River, principally in Aiken and Barnwell counties of South Carolina (Figure  1). SRS is a secured U.S.
Government facility with  no  permanent  residents.  SRS is located  approximately 40  km (25 mi) southeast of
Augusta, Georgia,  and 32 km (20 mi) south of Aiken, South Carolina.

SRS is  owned by  the U.S. Department of Energy  (DOE).  Management and operating services are provided by
Westinghouse Savannah River Company (WSRC).  SRS has  historically produced tritium, plutonium,  and other
special nuclear materials for national defense. Chemical and radioactive wastes are by-products of nuclear material
production processes.

OU Name, Location, Description, and Process History

The Federal Facility Agreement (FFA) (WSRC,  1993a) lists the D-Area Oil Seepage Basin (D-Area OSB), Building
Number  631-G,  as  a  Resource Conservation  and  Recovery Act   (RCRA)/Comprehensive  Environmental
Compensation and Liability  Act (CERCLA) unit  requiring further evaluation  using an investigation/assessment
process that integrates and combines the RCRA Facility Investigation (RFI) process with the CERCLA Remedial
Investigation (RI) to determine  the actual or potential impact  to human  health  and the environment.  Information
regarding the D-Area OSB can be found in the RFURJ Report and Baseline  Risk Assessment (BRA) fWSRC.
 1997a), the Corrective Measures Study/Feasibility  Study Report (CMS/FS) (WSRC. 1998a), and the Statement of
 Basis/Proposed Plan (SB/PP) (WSRC,  1998b).

 The D-Area OSB  is located within SRS, in a clearing between  roads A-t.4 and A-4.5, approximately 1.6 km (1  mi)
 north of the coal-fired D-Area Powerhouse, and approximately 3.1 km (1.9 mi) from the  nearest SRS boundary
 (Figures 2 and 3). The D-Area OSB is on the Ellenton Plain along the Savannah River at an elevation of 46 meters
 (m) [150 feet (ft)] above  mean sea level (msl).  The water table ranges from approximately 1 to 5 m (4 to 16 ft)
 below ground surface in the  area of the D-Area OSB.  Surface drainage  is to the southwest, toward the Savannah
 River, which is at an elevation of 26 m (85 ft) msl [20 m (65 ft) below the basin elevation].

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Record of Decision for the                                                                    WSRC-RP-97-402
O-Area Oil Seepage Basin (631-G) (l~>                                                          Revision 1. Final
Savannah River Site	August 1998
The  D-Area OSB is designated as Building Number 631-G and has the approximate dimensions of I i" m (333 fti
long by 33 m (.10S"rt) wide and 2.5 m (3 ft) deep. During an interim remedial action iIRA) conducted at the unit, the
trenches were found to be  continuous, without noticeable  berms. and were constructed as  a  sene> of adjacent
trenches along the back half of the clearing (Figure 3).

The  D-Area OSB unit is located in a cleared, rectangular-shaped area adjacent to an  unimproved road in D Area
(Figure 4). The location of the former seepage basin is currently not discernible because the unit has been backfilled
and leveled. The only evidence of the unit's prior existence is the four orange balls marking the comers of the unit, a
perimeter fence, and the presence of multiple monitoring wells  and piezometers  located at or near the unit. The
terrain is flat, with no discernible slope or relief, and is surrounded by  a mature forest of hardwoods and softwoods.
The  forested conditions provide dense cover for wildlife, and,  in combination with the boggy conditions prevailing in
the adjacent wetlands, create access problems for equipment and personnel involved in unit investigation activities.

The  closest surface water feature is a Carolina bay, a  natural wetland  located adjacent to the unit to the west. The
Carolina bay appears to be dry during the summer  months or periods of little or no precipitation, but  may contain
surface water during wet seasons.  Unimproved dirt road A-4.4, located immediately north of the waste unit,  bisects
the Carolina bay. Aerial photographs indicate that the road was in existence during the early 1950s. Other wetlands
exist approximately 76 m (250 ft) to the south of the unit, beyond din road A-4.5.

The  major local surface water drainage system is the Savannah River and associated swamps, located approximately
2.6 km (1.6 mi) to the west of the basin. Upper Three Runs Creek, a tributary to the Savannah River,  is located  2.7
km (1.7 mi) to the north-northwest, and Fourmile Branch, another tributary, is 2.7 km (1.7 mi) to the south-southeast
(Figure 1).  The local surface drainage at the unit is to the south-southwest, toward a wetland area and  runoff ditch.
These wetlands discharge into another unnamed ditch, which traverses D Area and eventually leads to  the Savannah
River.

The D-Area OSB was constructed in  1952 as a series  of unlined trenches for disposal of waste oil products, from D
 Area and other areas at SRS, which  were unacceptable for incineration in the 400-D powerhouse boilers.  As the
 trenches filled, the waste oils along with general office and cafeteria waste were occasionally  ignited.   The practice
 of open burning was a common practice at  SRS until 1973 when  it was stopped  site-wide. In  1975 the basin was
 removed from service and was backfilled with soil.

 The basin remained inactive and covered with natural  vegetation, including bushes and grasses, until 1996. when an
 IRA was implemented.  During the IRA, the trench area was excavated and drums and debris were removed along
 with any obviously contaminated soils.  The  remaining soils were returned to the excavation in "last out first in" order.

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Record of Decision for the
D-Area Oil Seepage Basin (631-C) (U)
Savannah River Site	
                                                  WSRC-RP-97-402
                                                   Revision 1, Final
                                                 	August 1998
          SOUTH
        CAROLINA
      D-AREA OIL
        SEEPAGE
           BASIN
                                                SOUTH
                                              CAROLINA
                    GEORGIA
Figure 1.
Location of the D-Area OSB at the SRS

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Record of Decision for the                                                            \VSRC-RP-97-402
[>-Area Oil Seepage Basin (631-G) (U)                                                    Revision 1. Final
Savannah River Site	August 1993
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 Record of Decision for the
 D-Area Oil Seepage Basin (631-G) (U>
 Savannah River Site	
                                                                       WSRC-RP.97-402
                                                                         Revision 1, Final
                SERIES i
Figure 2.
Sire  *ott»
•curu
  \l

     K
                                                   23CO
Topography of the Area Surrounding the D-A/ea OSB
                                                                  200C
                                                                    SCALE IN FEET
                                                                                                 iCOO

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Record of Decision for the                                                            \VSRC-RP-;>7-H>;
D-Area Oil Seepage Basic i631-G) fU)                                                   Revisioo I, Final
Savaooah River Site	      August 1993
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Record of Decision for the
D-Area Oil Seepage Basin (631-G) (LI
Savannah Rjver Site	
 WSRC-RP-97-402
  Revision 1, Final
	August 1998
                        300
       ORIGIN*!. -CUP
               C "ILLS
                                                                                                T£ UNIT
Figure 3.         Site Plan of the D-Area OSB

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Record of Decision for the                                                             WSRC-RP-97-402
D-.*r*a Oil Seepage Basin (631-G) (L")                                                    Revision 1. Final
Savannah Rjver Site	August 1993
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Record of Decision for the
D-Area Oil Seepage Busin (6JI-C» (U)
Savannah River Site	
WSRC-RP-97.40'
  Revision I. Final
	.August 1998
 Figure 4.         Current Photograph of the D-Area OSB (May 1993)

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Record *r Decision for the
D-Area Oil Seepage Basin 3l-G> .LI                                                     Revbion I, Final
Savannah River Site	August
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                                                10

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Record of Decision for the                                                                  VVSRC-RP-97-402
D-Area Oil Seepage Basin (631-G) (U)                                                         Revision 1. Final
Savannah River Site	August 1998
At :he close of the IRA, the contractor installed two horizontally oriented, perforated pipes along the length of the
former waste unit for technology testing (biovenung; purposes.  These pipes were used to force fresh air. nutnenti
and tracers into the soils at a depth of about 2.4 m (3 ft) in order to volatilize the constituents in the soil, enhance the
aerobic degradation of the  constituents in  both the soil and groundwater, and monitor  the effectiveness of the
treatment program (WSRC. 1997b, c, d. e).

n.       SITE AND OU COMPLIANCE HISTORY

SRS Operational History
                                                                                         ^
The primary mission of SRS  has been to produce  tritium (3H),  plutonium-239 (-39Pu).  and other special nuclear
materials for  our  nation's  defense programs.   Production of nuclear  materials  for  the defense  programs was
discontinued in 1988.  SRS has provided nuclear materials for the space program, as well as for medical, industrial.
and research efforts up to the present. Chemical and radioactive wastes are by-products  of nuclear  material
production processes.  These  wastes have been treated, stored, and in some cases, disposed at SRS.  Past disposal
practices have resulted in soil and groundwater contamination.

SRS Compliance History

Waste materials handled at SRS are regulated and managed under RCRA. a comprehensive law requiring responsible
management of hazardous waste.   Certain  SRS activities have required federal operating or  post-closure permits
under RCRA.   SRS  received a hazardous  waste  permit  from the South Carolina  Department  of Health and
Environmental Control (SCDHEQ; the permit was most recently renewed on  September 5, 1995.  Pan IV of the
permit mandates that SRS establish and implement an RFI Program to fulfill the requirements specified in Section
30O4(u) of the federal permit.

On December 21, 1989, SRS was  included on the National Priorities List (NPL).  Sites  included on the NPL fail
under the  jurisdiction of CERCLA.  This inclusion created a need to integrate the established  RFI Program with
 CERCLA  requirements to provide for  a focused environmental program.   In accordance with Section 120 or"
 CERCLA. DOE has negotiated a FFA (WSRC,  1993a) with the U.S. Environmental Protection Agency (EPA) and
 SCDHEC to coordinate remedial activities at SRS into one comprehensive strategy that fulfills  these dual regulatory
 requirements.
                                                    11

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Record of Decision for the                                                                 '.VSRC-FIP-97.-02
D-Area Oil Seepage Basin i.5Jl-G) iL~)                                                        Revision 1, Finjl
Savannah River >itt	.	August
OL" Compliance History

As previously stated, the D-Area OSB is listed in the FFA as a RCRA/CERCLA unit requiring further evaluation to
determine the actual or potential impact to human health and the environment. An RFI/RI characterization and BRA
were conducted for the unit between 1995 and 1996.  The results of the RFI/RI and BRA were presented in the
RFI/RI Report and  BRA (\VSRC. 1997a).  The RFI/RI Report and BRA were submitted in accordance with the-flFA
and the approved  implementation schedule,  and were approved by EPA  and SCDHEC in  August 1997.  SRS
submitted the Si'.-isian  0 In:;nm Acr.on Proposed Pkn for the D-A.---.1 OSB.  ^nich E?A and SCDHEC received
November 16, 1993. Tie three Parties issued the Initrim Ac:ion Record of Dtc:j:on in March 1995.  SRS prepared
and submitted the D-Area OSB  Interim Action Post-Cons:rucrion Repon 10 E?A and SCDHEC on  November 8,
1996. SCDHEC approved the report on January 7,  1997, and EPA approved it on February 27, 1997.  The CMS/FS
(WSRC,  1998a), SB/PP  O'SRC,  1998b), and Groundnater  Mixing Zone  Application  (WSRC,  1998c) were
submitted to EPA and SCDHEC in accordance with the FFA and the approved implementation schedule, and were
approved by them on April 1. 1998.

ILL     HIGHLIGHTS OF COMMUNITY  PARTICIPATION

Both RCRA and CERCLA require that the public be given an opportunity to review and comment on the draft permit
modification  and proposed  remedial alternative.   Public participation requirements are  listed  in South Carolina
Hazardous Waste Management Regulation (SCHWMR) R.61-79.124 and Sections 113and 117 of CERCLA.  These
requirements include establishment of an Administrative Record File to document the investigation and selection of
the remedial alternatives for addressing the D-Area OSB soils and groundwater. The Administrative Record File
must be established at or near the fc.-ility at issue.  The SRS Public Involvement Plan (DOE, 1994) is designed to
facilitate public involvement in the  decision-making process for permitting, closure, and  the selection of remedial
alternatives. Tne SRS  Public Involvement Plan addresses the requirements of RCRA, CERCLA. and the National
Environmental Policy Act (N"E?A;.  SCHWMR R.61-79.124 and Section 117(2. of CERCLA. as amended, require
advertisement of the draft permit modification  and notice of any proposed remedial action and provide the public an
opportunity to participate in the selection of the remedial action.  Tne Staremant of Basis/7roposed Plan for ;he D-
Arta Oil Sitpa%e  Basin (WSRC. 1993b). a pan of the Administrative Record File, highlights  key aspects of the
investigation and identifies the preferred action for addressing the D-Area OSB. The Administrative Record File is
available at the  EPA office and at the following locations:

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Record of Decision for the                                                                 WSRC-RP-97-J02
D-Area Oil Seepage Basin (631-G) (U)                                                        Revision 1, Final
Savannah River Site	August 1998


U. S. Department of Energy
Public Reading Room
Gregg-Graniteville Library
University of SouuTCarolina-Aiken
171 University Parkway
Aiken, South Carolina 29801
(303)641-3465


Thomas Cooper Library
Government Documents Department
University of South Carolina
Columbia. South Carolina 29208
(803) 777-4866


Similar information is available through the repositories listed below:


Reese Library
Augusta State University
2500 Walton Way
Augusta. Georgia 30910
(706)737-1744


Asa H. Gordon Library
Savannah State University
Tompkins Road
Savannah, Georgia 31404
(912)356-2183


The public  was notified of the public comment period through  mailings of the SRS Environmental  Bulletin, a

newsletter sent to approximately 3500 citizens in South Carolina and Georgia, through notices in the Aiken Standard.

the Allendale Citizen Leader, the Augusta Chronicle, the Bamwell People-Sentinel, and The State newspapers.  The

public comment period was also announced on local radio stations.


The 45-day public comment  period began on May 1, 1998 and ended on June  14, 1998.  However, no public

comments were received during this period. The Environmental Remediation  and Waste Management  (ER&\VM>

 Program subcommittee  of  the SRS  Citizen's  Advisory Board  (CAB)  was given a briefing on the preferred

 alternatives on May 6.  1998.  The ER&WM subcommittee was supportive of the preferred alternative and made a

 motion to the  full CAB at the May 18, 1998 meeting to accept the preferred alternative.  This motion was  accepted

 with no opposition. The subcommittee also commended the site's successful use of the bioventilation system in the

 remediation of the unit's subsurface soil.  The Responsiveness Summary, provided in Appendix A of this Record of

 Decision (ROD), and the final RCRA permit will indicate that no comments were received.
                                                   13

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Record of Decision for the                                                                  \VSRC-RP-9~-402
D-Area Oil Seepage Basin i631-G) (U)                                                        Revision 1. Final
Savannah Rjver Site  	        	                                         	A-jf^st :"•*><
FV.     SCOPE AND ROLE OF THE OL \\ITHCS THE SITE STRATEGY

RCRA/CERCLA Programs at  SRS

RCR.VCERCLA units (including the D-Area OSB) at SRS  are  subject to  a  multi-stage  remedial investigation
process that integrates the requirements of RCRA and CERCLA as outlined in  the RFl/RI Program Plan (WSRC,
1993b).  The RCRA/CERCLA  processes are summarized on  Figure 5.  Figure 5 illustrates the investigation and
characterization  of potentially   impacted  environmental  media  vsuch  as soil, sediment,  surface  water,  and
zroundwater) comprising the waste unit and surrounding areas; the evaluation  of risk to human health and the local
ecological community; the screening of possible remedial actions to identify the selected technology that will protect
human health and the environment; implementation  of the selected alternative; documentation that the remediation
has been performed competently; and evaluation of the effectiveness of the technology.  The steps of this process are
iterative in nature, and include decision points that involve concurrence between DOE (as owner/manager). EPA and
SCDHEC (as regulatory oversight), and the public.  The RCRA/CERCLA process as applied to the D-Area OSB is
outlined below.

RFI/RJ Work Plan

Prior experience in the  Superfund program has identified a strong need for streamlining the remediation process
(EPA, 19S9a).  To address this need. DOE has developed the Streamlined Approach for Environmental Restoration
(SAFER) (Daily  et  al.,  1992).   DOE  Headquarters  identified  the D-Area  OSB  as  a p:lot  project for the
implementation of SAFER and elected to design the D-Area OSB RFI/RI Work Plan using SAFER methodologies.

The SAFER program  combines elements of two  recognized processes developed  for  managing uncertainty at
different points in the environmental restoration process:  the data  quality objectives (DQO) process, developed by
the Quality Assurance Management  Staff of EPA (Neptune et  al., 1990) and the  Observational Approach (OA),
which is rooted in management of uncertainty in traditional geotechnical engineering applications 'vPeck, 1969).  The
OA provides a framework for  managing uncertainty throughout the environmental restoration process,  while :he
DQO process focuses on establishing the quality and quantity of  data required to  help make decisions at various
points in the environmental restoration process.  Description of the DQO process  is found in Data Quality Objecti-.es
Process for Superfund. Interim Final (EPA, 1993).
                                                    14

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Record of Decision for the
D-Area Oil Seepage Basin (631-G) (U)
Savannah River Site	
                                                                 VVSRC-RP-97-402
                                                                   Revision 1, Final
                                                                 	August 1998
                       SRS RCRA/CERCLA UNIT
                     PRELIMINARY EVALUATION

                     •  Unit Reconnaisance
                     •  Unit Screening
                          RFI/TU WORK PLAN

                  Develop Conceptual Site Model (CSM)
                  Identify Data Needs
                  Develop Data Quality Objectives and
                  Decision Logic
                  Detailed Sampling and Analysis Plan
                   UNIT/SITE CHARACTERIZATION

                   • Implement Rfl/RI
                   • Data Evaluation vs. DQO's
                   • Re-Evaluate CSM
                           Characterization
                              Complete?
                                            Additional
                                          Characterization
                                                          Characterization
                                                             Complete?
                        DATA EVALUATION
                          Validation
                          Verification
  Figure 5.
RCRA/CERCLA Logic and Documentation

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Record of Decision for the                                                             '.V5RC-S?-'>"-i02
D-Area Oil Seepage Basin .631-G) (U)                                                     Revision 1. Final
Savannah Rjvtr Site	August 1998
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                                                 16

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Record or Decision for (he
D-Area Oil Seepage Basin (631-G) (U)
Savannah River Site	
                                                                   WSRC-RP-97-402
                                                                    Revision 1, Final
                                                                  	August 1998
      Treatability Studies
        (as necessary)
     NO ACTION REMEDY
                                            0
                         RFI/RJ REPORT

                    • Document Results of RF1/RI
                                          CMS/FS Report
                                   • Establish RAOs
                                   • Identify Response Actions
                                   • Identify Technologies
                                   • Alternatives Development
                                   • Alternatives Screening
                                   • Detailed Analysis
                                           SB/PP

                                    Preferred Alternative
                                    Draft Permit Modification
                                    Public Comment
                                    RECORD OF DECISION

                                    • Select Remedy
                                    • Responsiveness Summary
                                    • Final Permit Modification
                                   CORRECTIVE MEASURE/
                                     REMEDIAL ACTION

                                   • Unit Closure
                                   • Post Closure Documentation
                                    (Post Construction Report)
Baseline Risk Assessment

  • Determine Unit Risk
  • Develop RGOs
                                                          POST ROD
                                                      DOCUMENTATION

                                                      • Remedial Design
                                                       Workplan/Report
                                                      • Remedial Action
                                                       Workplan/Repon
 Figure 5.
(continued) RCRA/CERCLA Logic and Documentation
                                               17

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Record of Decision for the
D-A.-ea Oil Seepage Basin i631-G) (U)                                                      Revision 1. Finiil
Savannah SJver Site	                	        	Vjaust :r'°j
                         THIS PAGE WAS LNTENTIONALLY LEFT BLANK.
                                                   IS

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Record at Decision for the                                                                   WSRC-RP-97-J02
D-Area Oil Seepage Basin (631-G) (ID                                                           Revision 1. Final
Savannah Rjver Site	.	August 1998
The SAFER method incorporates the DQO and OA processes to achieve the following:

    enhanced emphasis on planning
    linkage of data collection to decision-making needs
    explicit recognition and management of uncertainty
•   direct and efficient application of information gained as planning and remediation proceed
•   early convergence on a remedy
•   informing and soliciting input from key stakeholders (regulators and public)

SAFER emphasizes the  use of decision  rules to quantitatively define data adequacy in the RFI/RI process.  Each
decision rule  provides  a  quantitative statement defining  what quantity and quality  of data provide adequate
information upon which decisions can be based.  Inherent in the idea of the  decision rule is the understanding that
there  will be uncertainty  in ihe decision-making process.   The goal is to identify data adequacy that provides
acceptable  uncertainty in making decisions while managing the residual uncertainty.  The objective of the decision
rule is to establish the linkage between the problem at the unit, its remedial objective, and data requirements. This
will be done iterauvely, first based on preliminary understanding and then modified as more information is obtained.

Federal, state,  and  local  regulatory agencies  are recognized  as  key stakeholders  within  the SAFER process.
Continuing concurrence with regulatory  requirements  is  an implicit  SAFER objective.    Data from previous
environmental  investigations, performed under the existing phased investigation  approach,  are included  in  the
SAFER design.  SAFER'S iterative  approach allows regulatory concurrence  as the investigation  proceeds.  The
SAFER process was implemented at  the D-Area OSB as an  Expedited Site Characterization (ESC) field effort that
sought to accomplish project objectives in a rapid fashion while maintaining data quality.

The initial step in  the  SAFER  process consists of  identifying probable conditions  at  the investigation site and
developing a conceptual site model (CSM) based on those conditions. This conceptual model is used to  concentrate
 the unit investigation on the processes,  medium(s). constituents, exposure pathways, and potential receptors most
 likely to be found during the investigation. With the model in mind, a more  focused work plan can be developed to
 fully address each item identified in the model.

 Section V provides the unit-specific CSM for  the D-Area OSB OU and a summary of the  characteristics of the
 primary and secondary sources and release mechanisms for the unit as determined in the RFI/RJ.
                                                     19

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Record of Decision for the                                                                   vv SRC-RP-<>7-JO:
CX-Area Oil Seepase Basin :631-Gi iV)                                                         Revision 1. Final
Savannah Rjver Site	Auyjst 1'>?S
Bised on Lu.e CSM  for ihe D-Area OSS. a  *et;iiied  sampling ar.d ir.ahsis plan  '-MS ~r;?are-J and imp'.err.erid
(\VSRC. 1995a. b; 1996ai. The unit assessment plan and confirmation sampling plans were designed to characterize
the following sources and  release mechanisms:

    primary source:  disposal trenches comprising the D-Area OSB
•    primary release mechanisms:  deposition and infiltration/percolation
•    source media (primary media impacted):  surface soil and subsurface soil
•    secondary  release  mechanisms:  fugitive  dust generation, volatilization, vege'.aii'-e 'biotici  '_p:ake, storm^-aier
    runoff, and leaching into Jie groundwater
•    exposure media (secondary media impacted):  air, produce, surface water, sediment, and groundwater

RFI/RI Characterization Report

The primary  purpose of the RFT/RJ is to establish unit-specific constituents (USCs) that pose potential risk through
various exposure routes and to determine their distribution in the media associated with the unit. As an indicator of
unit-specific  contamination, the results of the analysis of soil, surface water, and sediment samples at the unit were
compared to  2x mean background concentrations, and the groundwater analytical results were compared with EPA
primary  maximum contaminant levels (MCLs) or 2x mean  background concentrations where  no MCL exists.
Compounds that exceed these comparison levels are called USCs and their nature and extent were evaluated in detail
in the RFI/RI.

To address the identified sources and  release mechanisms in the CSM, the following RFI/RI unit characterization
objectives were identified for the D-Area OSB (WSRC, 1995a):

    enhance and refine the liihologic and hydrogeologic characterization of the subsurface in the vicinity of the D-
    Area OSB unit
•   establish background concentrations of potential contaminants in soil, groundwater. surface \oter, and sediment
    to determine the impact on :hese media associated specifically with the operation of the D-Area OSB unit
    determine the USCs.  if any. released to the various environmental media related to the D-Area OSB
•   address  aspects of the CSM related to sources, release mechanisms, and exposure media, and/or refine the CSM
    based on the data collected
    define the horizontal  and vertical extent of contaminants in the impacted media
    assist in determining the feasibility of potential remedial alternatives through  the  collection of preliminary soil
    engineering parameters
                                                     20

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Record of Decision for the                                                                    WSRC-RP-97-402
D-Area Oil Seepage Basin (6J1-C) (U)                                                          Revision 1. Final
Savannah River Site	August 1998
    confirm groundwater analytical data generated by the onsite lab during the SAFER process, with anaKses for
    USCs generated by a conventional, offsite laboratory data

ERA

The purpose  of a BRA  is to develop risk information to assist in the decision-making process for remedial sites
(EPA. I989b).  This risk assessment follows the EPA Risk Assessment Guidance for Superfund (EPA.  1989b. o.
According to EPA. 1989b. a BRA should provide the following:

•   an analysis of baseline risks and help determine whether there is a need for remedial action
•   a basis for determining levels of chemical and radiological constituents that can remain in-sim, on-unit and that
    will be adequately protective of human health and the environment
    a basis for comparing potential human health and ecological impacts of various remedial alternatives
    a consistent process for evaluating and documenting risk to public health and the environment

The BRA assesses risks  that may result from a release of, and exposure to, chemical contaminants under  reasonable
maximum exposure (RME) conditions.  The assessment uses current and hypothetical  future land use scenarios and
associated receptors with the assumption that constituent  concentrations remain the same as reported in the RFI/RJ.
The RME represents the highest exposure that is reasonably expected to occur at the unit.

During the development of a BRA, risk from the unit is quantified, based on unit-specific data, for current and future
human  and ecological receptors, through the multiple exposure routes identified in the CSM.  Carcinogenic  nsk at
or above 1.0  x 10^ (one  excess human cancer in a population of one million) is considered significant.  In  addition, if
the hazard index (HI) is  greater than 1.0 for noncarcinogenic constituents, there is concern that adverse health effects
can occur.
 The information from the BRA supports identification of those areas where no further action or selected  re
 actions are warranted. The BRA also provides the basts for deriving nsk-based constituent levels that are protectr-e
 of human health and environment [remedial goal options (RGOs)J for use in consideration of remedial alternatives
 A summary of the results of the BRA for the D-Area OSB is presented in Section VI.

 CMS/FS

 The results  of the RFI/RI Report and  the BRA provide the basis for establishing unit-specific remedial action
 objectives  (RAOs)  in  the CMS/FS.   RAOs for the  D-Area  OSB  were  developed to  address: unit-specific
                                                    21

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Record of Decision for the                                                                   WSRC-RP-97-402
D-Area Gil Seepage Basin '631-Gi (V)                                                          Revision 1. Final
Savannah Rivgr Site	August 19C'8
ccntarrup.ar.ts. rr.ecia of concert-.. poter.;ial ixposurj path-Ax.s. and remediation ^oais.  . r.s RAOs -^ers based on the
nature and extent of contamination,  threatened resources, human and  environmental  risk information, and  the
potential for human and environmental exposure. In addition, the preliminary remediation goals for the D-Area OSB
were developed based upon applicable or relevant and appropriate requirements (ARARs) or other information from
the RFI/RJ Report and the BRA.

The methodologies used to identify and  screen relevant technologies for the  remediation of the waste unit followed
an established remedy selec'Jon process developed by  the  EPA.  The goal of this process is to select  corrective
measures/remedial actions that are protective of human health and the environment, that maintain protection over
time,  and that minimize contaminant (or waste) mobility,  toxicity, or volume through treatment. when possible
[CERCLA 300.430 (a)(l)'(!)].  The selection of a response action for the D-Area waste unit proceeded in a series of
steps, as defined in the National Oil and Hazardous Substances Contingency  Plan (NCP) of November 20, 19S5  (50
FR 47973).  and as outlined in Figure 6.  In addition, the remedial alternatives were further evaluated against the
following nine selection criteria established by the NCP:

•   overall protection of human health and the environment
•   compliance with ARARs
•   long-term effectiveness and permanence
•   reduction of toxicity. mobility, or volume through treatment
•   short-term effectiveness
•   implementability
•   cost
•   state acceptance
•   .community acceptance

The results  of the CMS/FS conducted for the D-Area OSB are summarized in Section VII. and a summary of the
comparative anaKsis of the alternatives is provided in Section VIII.

SB/PP

The culmination of the response action selection process is the SB/PP.  Tne  purpose  of the SB/PP is to facilitate
 public participation in the remedy selection process through the solicitation of public review and  comment on all the
 remedial alternatives described.  The SB/PP presents the lead agency's preliminary recommendation(s) concerning
 ho1*  best to undertake  a  remedial action  at a  particular w -ste unit.  The SB/PP describes all remedial options that

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Record of Decision for the
D-Area Oil Seepage Basin (631-G) iU)
Savannah River Site	
                                                                               WSRC.RP-97~IO:
                                                                                Revision 1, Final
                                                                              	August 1998
                                            Establish  Remedial  Action  Objectives
                                                  Develop  General  Response
                                                 Actions Describing Areas or
                                                 Volumes of Media to Which
                                                 Containment, Treatment, or
                                              Removal  Actions  May Be Applied
                                               Identify Potential Treatment sod
                                                  Disposal  Tecbnologies  and
                                                  Screen Based on  Technical
                                                       Iraplemenlability
                                             Evaluate  Process  Options Based on
                                            Effectiveness,  Implementability,  and
                                                  Relative  Cost,  to Select a
                                               Representative Process  for each
                                                       Technology  Type
                                                                                                 Response  Action
                                                                                                 Selection  Process
        Repeat Previous Scoping Steps:
         - Determine New Data Needs
         • Develop Sampling Strategies
       and Analytical Support to Acquire
              Additional Data
          • Repeal Steps in RI Site
              Chasaaehzacoo
Combine Media-Specific
Technologies into
Alternatives
1
r
                                                        Detailed Anal/is
                                                         of Alternatives
     Scores: EPA. I988i
 Fisure 6.
Response Action Selection Process

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Record of Decision for the                                                             \\snr SP o-  -n->
D-Area Oil Seepage Basin ,631-C) iU)                                                   %\?  -   J r  1
Savsnnah aiv^r Sit>	   '                                                     Rev,noa 1. Final
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                                              24

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Record of Decision for the                                                                  WSRC-RP-97-402
D-Area Oil Seepage Basin (631-G) (U)                                                         Revision 1, Final
Savannah River Site	August 1998
were considered in detail in the CMS/FS. and explicitly identifies both the preferred alternative for a remedial action
at a waste unit and_the preference rationale for that alternative.

The  SB/PP directs the public to the RFI/RJ,  BRA,  and CMS/FS reports as the primary sources of detailed,  unit-
specific information and information on the remedial alternatives analyzed.  It also provides information on how the
public can be involved in the remedy selection process. The public is notified of a public comment period through
mailings of the SRS Environmental Bulletin, through  notices in the Aiken Standard, the Allendale Citizen Leader, the
Barnwell  People - Sentinel,  The State, and Augusta Chronicle  newspapers, and through announcements on  locoJ
radio stations.
ROD
The ROD documents the remedial action  plan  for  a  waste  unit and  consists of three basic components:   a
Declaration, a Decision Summary, a Responsiveness Summary.  The purpose of the Declaration is to certify that the
remedy selection process was carried out in  accordance with  the requirements of CERCLA and, to the extent
practicable, the NCP. The Decision Summary is a technical and informational document that provides the public
with a consolidated source of information about the history, characteristics, and risks posed by the unit, and includes
a summary/evaluation of the  cleanup alternatives and the considerations  that led to the selected remedy.  The
Responsiveness  Summary presents comments received  during  the public  comment period on the SB/PP.  and a
response to each comment or criticism that was submitted in writing or orally.  The Responsiveness Summary for the
D-Area OSB is provided in Appendix A and an explanation of significant changes resulting from public comment on
the SB/PP for the unit is provided in Section XI.

SRS received a RCRA hazardous waste permit from SCDHEC. which is renewed every five years. The D-Area OSB
is a Solid Waste Management Unit (SWMU) listed on the SRS  RCRA Permit because the unit received hazardous
substances. Thus, the remedial decision for this SWMU requires a RCRA Permit Modification. No comments \vere
received during the public comment period on the proposed remedial action and the associated draft RCRA permit
modification  (May  I through June 14,  1998).  This is indicated in the Responsiveness Summary of this  ROD
(Appendix A) and in the final RCRA Permit. The final RCRA Permit and this ROD document the final decision for
 this OU.

 Post-ROD Documentation

 The  post-ROD documentation consists primarily  of  the design documents that  are required  prior to initiating a
 remedial action.  Specific post-ROD documents  include the  combined Remedial Design Work Plan/ Remedial
                                                    25

-------
Record of Decision for the                                                                  WSRC-RP-97-402
D-Area Oil Seepage Basin '.631-Gi .U)                                                          Revision !. Final
Savannah River Site	              \ur:st 1 '^S
Design Report/ and Remedial Action Work Plan iRDV,'?'RDR/RA'.V?; and the corr.bir.ed ?os;-Ccnstr-.;c-.ion Report
and Final Remediation Report t?CR/FRR). A discussion of the schedules thai apply to these documents is provided
in the SB/PP and in Section XIII of this ROD.
            »•

D-Ar«a OSB Remedial Strategy

The RF1/RI process provides a method of managing the steps that lead to1 the ultimate remediation of a specific waste
unit. An operable  unit (OU) usually consists of the contaminj'.-d  rredia ^sources, soil.  gTC'jrsdwater.  sediments.
surface water, and  air) specific to a waste unit  and the proposed actions related to their characterization and ultimate
remediation, and/or the timing of those actions.

The overall strategy for addressing the D-Area OSB was to: (1) characterize the waste unit by delineating the nature
and extent of contamination  and identifying the media of concern (perform the RFI/RI); (2) perform a BRA to
evaluate media of concern, constituents of concern (COCs), and exposure pathways, and to characterize potential
risks; and (3) evaluate and perform a final action to remediate, as needed, the identified media of concern.

The D-Area OSB  is an OU located within the Savannah River Floodplain Sw-amp watershed. Several OUs within
this watershed will be evaluated to determine impacts, if any, to associated streams and wetlands.  SRS will manage
ail OUs to minimize  impact to the watershed.  Based on characterization and BRA information, the D-Area  OSB
does  not  significantly  impact the watershed.   Upon disposition  of all   OUs  within  this watershed, a  final,
comprehensive evaluation of the watershed will  be conducted to  determine whether any additional actions are
necessary.  Based  on the BRA  and vadose zone modeling after the IRA and  biovent testing, the  soils at the unit do
not warrant further remediation. Additionally, results of the BRA  indicated  that surface water and  sediment at the
unit do not require remediation. Groundwater is the only medium identified  in the BRA that requires evaluation of
remedial alternatives. The D-Area OSB investigation considered  all  unit-specific ground'-vater.   Based on the
investigation of the groundwater. the contamination in the water table aquifer  is apparently attributable to the D-Area
OSB  elites.  The proposed  action for the D-Area OSB groundwater, soil,  sediment, and surface  water is a final
action.

V.      OU CHARACTERISTICS

A CSM was  developed  for the D-Area  OSB that  identifies  the  primary  source, primary  contaminated media,
migration  pathways,  exposure  pathways, and potential receptors for the unit.  The CSM for the  D-Area OSB is
presented m TMgures 7j and 7b and is based on the data that ore presented in the RCRA/CERCLA documentation for
this unit.  The d^ta summary reports (WSRC. 1996b. c,  d.  e) and the combined  RCfU  Facility Investigation/

-------
Record of Decision for the                                                                   WSRC-RP-97-402
D-Area Oil Seepage Basin (631-C) (U)                                                          Revision 1, Final
Savannah River Site	August 1998

Remedial Investigation Report and Baseline Risk Assessment for the D-Area Oil Seepage Basin (U'SRC. 1997ai
contain detailed analytical  data for all of the environmental media samples  taken in the characterization of the
D-Area OSB.  These documents are available in the Administrative Record File (see Section III).

The primary data used for the RF1/RI and BRA were collected during the ESC Phase I, Phase II,  confirmation phase
(Phase III), Phase FV, and the post IRA soil sampling conducted during 1995 and 1996. All samples were analyzed
in accordance  with EPA-approved protocols.

As an indicator of unit-specific contamination, the soil, surface water, and sediment results were compared to 2.x
mean background concentrations, and the groundwater results were compared with EPA Primary MCLs or 2x mean
background concentrations, where  no MCL exists.  Compounds which exceed these comparison levels are  called
USCs (Table 1) and their nature and extent are evaluated in detail in the RFI/RI and BRA Report.

For the analysis of the nature and extent of contamination, soil sample results were grouped into three depth intervals
for both the unit and the background borings in conformance with the depth intervals evaluated  in the BRA.  These
depth intervals are 0.0 to 0.3 m (0-1 ft), and 0.0 to 1.2 m (0-4 ft) which covered the exposures from surface soil and
subsurface soil, respectively, as evaluated in the BRA.  Analyses were also conducted on samples from a deep soil
interval, extending below 1.2 m (4 ft) to evaluate the nature and extent of contamination in the deep soil for the unit.
All groundwater samples collected and analyzed were  taken from the uppermost aquifer and were evaluated as  a
single group.  Additional physical  and hydraulic analyses regarding the effects of the local weak aquiurds on the
movement of groundwater and contaminants were also conducted.

Primary Sources and Release Mechanisms

The primary source for the contamination of the various media is waste oils disposed in the D-Area OSB. a  series of
unlined trenches constructed to a depth of 1.2 to 3.7 m (4 to 12 ft) (Figure 3).  These wastes were deposited directly
into the deeper soil, greater than 1.2 m (4 ft) deep,  and even into the locaJ groundwater, when  the water table was
close to the surface.  The waste oils disposed of in the D-Area OSB originated in D .Area and other areas at SRS. and
were disposed of  in the D-Area OSB because they were unacceptable for incineration  in the  400-D powerhouse
boilers. The D-Area OSB has been out of service since 1975. when it was backfilled with soil.

The  primary  release  mechanisms  are  deposition  (contaminants  deposited  directly  into the  soils)  and
 infiltration/percolation (contaminants migrating vertically and laterally into the pore spaces of the soils).
                                                     27

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Record of Decision for the                                                                   WSRC-RP-97-402
D-Area Oil Seepage 3jsm ..631-Gi i.U)                                                         Revision 1. Final
Savannah River Jite	August
Secondary Sources and Release Mechanisms

Secondary source media impacted  by waste disposal  activities  at  ;he D-Area OSB  include surface soils and
subsurface soils within the basin and the basin perimcier.  Secondary release mechanisms for surface soil include:
fugitive dust generation, volatilization, biotic uptake, and stormwawr runoff. Respective secondary media impacted
for these release mechanisms are: air (dust), air (vapor), biota, and surface water.  The secondary release  mechanism
for subsurface soil is leaching.  The exposure medium tor contaminants that leach frcm sell is  grour.dwater. which
may  in  turn discharge to and undergo potentiaJ cherr.ical constituent exchange with biota.  stream  sediment, and
surface  water.  A detailed sampling and analysis plan was prepared and implemented to investigate these secondary
sources and a complete description of the sampling methods and  protocols is provided in the RFI/RI  Report and
BRACWSRC. 1997a).

Media sampled for investigation of this unit included soil (at multiple .depths),  groundwater (from  the uppermost
aquifer), surface water, and sediment (Carolina bay and the adjacent wetland).

Seventy-five  compounds were detected at least once above screening  levels in the soil, groundwater, surface water,
and  sediment associated with the D-Area OSB and have been designated  as USCs, as listed  on Table 1.  Those
compounds detected  in  soils were  23 metals, 15  volatile organic compounds (VOCs), 3 semi-volatile  organic
compounds (SVOCs), 11 pesticides/polychlorinated biphenyis (PCBs). and  5 ligands. The groundwater  beneath the
basin and as far downgradient as 320 m (1.050 ft) in the shallow aquifer  contained USCs including 15 metals, 4
ligands. 16 VOCs, 4 SVOCs. 5 pesticides/PCBs, and total petroleum hydrocarbons  (TPHs).  Sediment  and surface
water in the  Carolina bay and  wetlands contained USCs comprised of 3 VOCs. 2  SVOCs. 4  pesticides/PCBs, 15
metals, 1 ligand. and diesel range organics (DROs) and TPHs.

A large fraction of the anantical results above detection limits for Lhis report are estimated '."T'-flagzed) values, with
concentrations below the sample quantitation levels.  The majority of sample results that exceed the quantitation
level exceed  it by less than an order of magnitude. Therefore, the 'au set for this :r.'.es::za'.ion contains mainly low-
level detections of compounds in both soil and groundwater.

-------
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    -------
    Record of Decision for the                                                              \VSRC-RP-9T-40.2
    D-Area Oil Se«paee Basin .631-G) -U)                                                     Revision 1, Find
    Savannah River Site	Auyi« 19«»S
                             THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                      30
    

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    -------
    Record of Decision for the                                          '                    \VSRC-RP-9T-40:
    D-Area Oil Seepage Basin (631-G) it)                                                     Revision 1, Final
    Savannah River Site	.	Xugust IJ^S
                             THIS PAGE WAS INTENTIONALLY LEFT BLANK.
    

    -------
    Record or Decision for the
    D-Ar«a Oil Seepage Basin (631-G) fU)
    Savannah River Site	
    WSRC-RP-97-40:
     Revision 1. Final
         August 1998
                                                     Table 1
                                               USCs for all Media
    
    
    
    Volatile;
    Acetone
    Jenzene
    Jromo methane
    Batonone, 2-(MEK)
    Carbon Oisulfide
    Carbon Tetrachlonde
    Chioro benzene
    Chloroe thane
    Chloroform
    >ichloroethane. 1.1-
    )ichloroethene. 1.2 - (total)
    >ichloroethene. 1 .2 - cis
    ithylbenzene
    Methylene chloride (Dichloromethane)
    Styrene
    Tetrachloroethene (PCE)
    'oluene
    "richloroethene (TCE)
    Tichlorofluoromethane
    Vinyl Chloride (Chloroethene)
    Xylenes
    Semivolatiles
    Jis(2-ethylhexyl) phthalate
    ienzoic acid
    iutylbenzylphthalate
    )i-n-butyl phthalate
    Dichlorobenzene, 1.2-
    Dichlorobenzene. 1 .4-
    Petroleura Indicators
    Diesel range organics
    Total petroleum hydrocarbons (purgeable)
    (C4-C12)
    Pesticides/PCBs
    AJpha-BHC
    Beta-BHC
    ODD. 4.41-
    DDE. 4.4'-
    DDT. 4.4'-
    Delta-BHC
    Dieldnn
    Endosulfan I
    Endrin
    Endrin ketone
    Surface
    Soil
    (Post IRA)
    
    6/14
    2/14
    
    . 1/14
    
    
    1/14
    
    1/14
    
    
    
    
    14/14
    
    9/14
    
    4/14
    
    
    
    
    
    2/14
    
    
    
    
    
    
    
    
    
    1/14
    1/14
    
    7/14
    3/14
    
    
    
    1/14
    
    Subsurface
    Soil
    (Post IRA)
    
    11/28
    5/23
    
    4/23
    
    
    1/23
    
    1/28
    
    
    
    1/28
    28/28
    1/23
    16/28
    
    7/28
    
    
    1/28
    
    
    2/23
    
    
    
    
    
    
    
    
    
    1/23
    1/28
    
    12/23
    8/28
    
    1/23
    
    1/28
    
    Deep
    Soil
    fPost IRA)
    
    13/30
    9/30
    
    1 6/30
    5/30
    
    1/30
    
    
    
    5/30
    
    12/30
    26/30
    1/30
    
    19/30
    5/30
    
    1/30
    15/30
    
    2/30
    
    
    2/30
    
    
    
    
    
    
    
    1/30
    
    1/30
    4/30
    3/30
    1/30
    4/30
    
    1/30
    
    Ground-
    water
    (Pre IRA)
    
    31/75
    2/79
    2/79
    4/75
    9/75
    6/79
    6/79
    1/79
    
    1/79
    
    2/218
    
    1/79
    
    22/223
    
    35/223
    2/48
    24/223
    
    
    3/26
    
    
    15/26
    1/26
    1/26
    
    
    1/14
    
    
    3/80
    
    
    
    
    1/26
    
    
    2/26
    
    Surface
    Water
    (Pre IRA)
    
    5/5
    1/5
    
    
    
    
    
    
    
    
    5/5
    
    
    
    
    1/5
    
    4/5
    
    2/5
    
    
    
    
    
    2/5
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    1
    Sediment
    (Pre IRA>
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    7/8
    
    2/8
    
    
    
    
    
    
    
    2/8
    
    
    
    
    3/8
    2/8
    
    
    
    
    1.3
    
    1/3
    
    
    1/8
    
    1/8
                                                  (Table page I  of 2)
                                                        33
    

    -------
    Record of Decision for ihe
    D-Area Oil Seepage Basin i6Jl-G) (U)
    Savannah River Site     	
                                                                                               \VSRC-RP-97-402
                                                                                                 Revision 1, Final
                                                                                                    August 1993
                                                 Table 1 (continued)
                                                 USCs for alJ Media
    
    •
    Pesticides/PCBs (continued)
    Gamrnj-chlordane
    ^ptachior ipo.xnie
    _inJane
    PCS- 1 254
    PCB-1260
    Metals
    Aluminum
    Antimony
    Arsenic
    Barium
    Beryllium
    Cadmium
    lalcium
    Chromium
    Cobalt
    Copper
    iron
    _«ad
    Magnesium
    Manganese
    Vtercury
    Nickel
    Potassium
    Selenium
    Silver
    Sodium
    Thallium
    Vanadium
    Zinc
    Ligands
    Chemical oxygen demand
    Cyanide
    Nitrate as nitrogen
    Nitroeen bv Kjeido.-il method
    PH
    Suifate
    Total organic carbon
    Total Organic Halogens
    Total chosohates is P)
    Surface
    SoU (
    (Post IRA)
    . .
    
    
    1/14
    
    3/14
    
    » <
    
    
    
    
    5/14
    2/14
    6/14
    
    6/14
    4/14
    7/14
    3/14
    
    7/14
    1/14
    
    6/14
    
    
    3/14
    8/14
    6/14
    
    
    1/14
    10/14
    14/14
    
    8/14
    
    
    14/14
    Subsurface
    Soil •
    (Post IRA)
    
    
    
    1/23
    
    5/23
    
    
    
    2/23
    
    
    12/28
    6/28
    13/28
    
    12/23 '
    3/28
    22/28
    7/2S
    
    14/28
    3/23
    1/23
    6/2S
    
    
    5/28
    7/23
    8/28
    
    
    3/23
    19/23
    2S/23
    
    1 7/23
    
    
    23/23
    Deep
    /Soil
    (Post IRA)
    
    
    
    
    1/30.
    J/30
    
    1/30
    5/30
    9/30
    12/30
    29/30
    . 10/30
    30/30
    2/30
    23/30
    • 13/30
    
    13/30
    30/30
    19/30
    16/50
    28/30
    30/30
    8/30
    3/30
    22/30
    2/30
    
    13/30
    
    
    7.30
    10/13
    13/13
    
    10/13
    
    
    13/13
    Ground-
    water
    (Pre [RA)
    
    l.'SO
    1,26
    
    
    
    
    13/29
    
    
    
    4/154
    3/154
    15/29
    
    7/154
    
    142/154
    
    20/29
    42/154
    
    1/154
    7/29
    
    15/154
    8/29
    1/29
    2/154
    11/29
    
    4/12
    
    
    
    3/12
    
    4.'-l
    1'4
    5/12
    Surface
    Water
    (Pre [RA)
    
    
    
    
    
    
    
    2/5
    
    
    1/5
    
    
    
    2/5
    1/5
    1/5
    
    3/5
    
    
    
    1/5
    
    
    
    
    2/5
    4/5
    1/5
    
    
    2/5
    
    
    
    
    
    
    
    
    Sediment
    (Pre IRA)
    
    
    
    
    
    
    
    
    1/8
    1/8
    1/8
    
    
    1/8
    
    
    
    1/8
    
    
    3/8
    
    
    
    
    
    
    
    
    1/8
    
    
    
    
    
    
    
    
    
    
    Note:    The numocrs on this table reflect the number of samples exceeding the
             number of samples collected.
                                                                                -ipecific ic:iir.:ng value over the total
                                                    (Table page 2 of 2)
    

    -------
    Record of Decision for the                                                                   W SRC-RP-97-402
    D-Area Oil Seepage Basin r6Jl-G) (U>                                                          Revision 1. FinaJ
    Savannah River Site	August 1998
    Soil
    The analytical data indicate that there has been minimal impact to the surface and subsurface soil media [down to 1.2
    m (4.0 ft)] from past disposal activity at the D-Area OSB. This conclusion is supported by the historical record for
    the unit.  The trenches that received the waste oils and other debris *ere constructed to a depch of 1.2 to 3.7 m (4-12
    ft), which resulted in waste placement beneath, rather than into, the shallower soils.  The wastes were deposited  onto
    the deeper soil, and even  into the locaJ groundwater when  the water table was close to  the  surface. The greatest
    impact is to the deep >1.2 m (>4 ft) soils into which the waste was deposited.
    
    The  principal  VOC  constituents  impacting  soil  quality  at  the  basin   are  the  chlorinated hydrocarbons
    [tetrachlorocthene (PCE). trichloroethene (TCE), 1,2-dichloroethene (1,2-DCE), and vinyl chloride], which probably
    represent a degradation series starting with the PCE and TCE deposited in  the basin  with  waste  oils and grease
    (Table 1).  The  aromatic  compounds benzene, toluene, ethylbenzene, and xylene (BTEX),  which are commonly
    associated with petroleum  products like  gasoline, are  also found in the vadose zone soils, but appear to be of
    secondary importance to the chlorinated  hydrocarbons. Three  other VOCs  (acetone,  2-butanone. and methylene
    chJoride) also appear to be related to waste disposal actions in the basin.  The metals chromium, iron, lead, mercury
    and zinc are distributed throughout the D-Area OSB in a fashion similar to the VOCs and appear to have elevated
    concentrations within the soils of the trenches, primarily below the surface and subsurface soil  horizons.
    
    Groundwater
    
    The principal contaminants found to exceed their respective  screening levels in the groundwater (MCLs, where they
    have  been established, and 2x mean background, where no MCL exists) are listed on Table 1 and include compounds
    from all 7 analyte  groups, except dioxins/furans.  The pattern developed from a review of the data set is  generally
    consistent with a source of contaminants  in the basin and with a plume in the groundwater migrating downgradient
    from the basin to the south and southwest in the uppermost aquifer.
    
    Three chlorinated hydrocarbons (TCE, PCE, and vinyl chloride)  were the most common VOCs detected and  had the
    highest concentrations.  The uppermost aquifer contaminant plume outlined by these compounds is at least 320 m
    (1,050 ft) long by  100 m (300 ft) wide and extends vertically from the water table surface  down to at least 12 m (40
    ft) in depth.  The "green clay" occurs  at 12 m (40 ft) bis and is expected  to provide a barrier  against deeper  vertical
    migration of contaminants. The vertical geometry of the TCE plume is typical of dissolved organic compounds  in an
    aquifer with an internal downward  vertical gradient.   The source area contains the highest concentrations and
     narrowest lateral extent with concentrations decreasing and the cross-sectional area increasing with distance from the
     source.  In general, with  the exception of a small portion  of the aquifer in the immediate  vicinity of the former
    

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    Record of Decision for the                                                                  \VSRC-RP-97-402
    D-Area Oil Seepage Basin '.631-G» (U)                                                         Revision 1, Rnal
    Savannah River 5ite	^	August 1998
    trenches. V'CCs in the groundwater were found at concentrations ceirr.v 100 u-il. A small area jailed the "hoi spot",
    having an  approximate diameter of 6 m (20 ft), contained the highest total concentrations of TCE (1.151  ug/1)
    detected during the investigation.
    
    TCE was the compound detected most frequently above the screening levels (Figures 8 to 11). It was found from the
    water table  aquifer down to the  "green clay" (Figure  10).  TCE was also the compound  detected  farthest
    do'ATtgradient [3.11 ug/1 (micrograms per liter)]  215 m (TOO ft) southwest of the basin.  Concentrations detected in
    the sa-Tiples ranged from non-detect up  to 1.151 ug/l. *ith an average  of 3.0 ug/1.  These data indicate that this
    compound  is present in groundwater in a volume approximately 565 m (1.2CO ft; long by ICO m (300 ft) wide and
    from the w-ater table surface to 12 m (40 ft) in depth.
    
    PCE was the -;econd most frequently detected VOC at concentrations above screening levels. Concentrations of this
    compound  ranged from below the detection limit up to 34.95 ug/1. with an average of 2.1 ug/1. The PCE plume is
    smaller than, and wholly contained within, the TCE plume.
    
    The third most frequently detected VOC above its screening level was vinyl chloride.  It was found throughout trie
    same  aquifer zones as the two preceding compounds ind is a degradation product of them because it was never used
    at SRS. The concentrations of vinyl chloride ranged from below the detection limit up to 52.0 ug/1, with an average
    of 1.1 ug/1. Like the PCE plume, the vinyl chloride plume is contained within the TCE plume.
    
    The isomers of DCE were the fourth most frequently detected  VOC above screening levels.  This compound can be
    found in groundwater over a volume approximately 260 m (850 ft) long by  100 m (300 ft) wide and from the surface
    to 12 m (40 ft) in depth.  The lateral extent of this compound is  the smallest of the four most commonly detected
    VOCs and lies within the TCE plume shown on Figures 8 to 10.
    
    Benzene was detected in only 13 of 97 groundwater samples (16^;'. with concentrations ranging from non-detect to
    6.2 jJZ/1.   Only  two of the analyses exceeded the  primary MCL (5.0 pg/lj.  The  distribution of this constituent is
    primarily localized in the shallow portion of the aquifer immediately beneath the  basin.
    
    The SVOCs detected  in groundwater samples were primarily bis(2-ethylhe.v«T) phthalate and di-n-butyl phthalate.
    Because the concentrations of these compounds were  lower in the vicinity of the basin, it appears that the  detected
    SVOCs do not originate at the D-Area  OSB. but  may be a result of sampling  or analytical bias.  Only one  of 14
    groundwater samples analyzed for DROs/TPHs contained detectable concentrations, and this sample was from the
    western-most disturbed soil  area.   No  dioxins/funns v.ere  detected  in  the  26 samples analyzed, and only  5
    pestictdes/PCBs  were detected at concentrations above their MCLs.
    

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    Record of Decision for the
    D-Area Oil Seepage Basin (631-G) (U)
    Savannah River Site	
                WSRC-RP-97-402
                  Revision 1. Final
               	Aueust 1998
                                                                                     \\
                                                                                        \\
                                                                                          \\
                                                                                                \
                                                                                               \\
           Units = |ig/l
    MCL = 5 |ag/l
                             300
                                         See Figure 11  for Master Legend
    Figure S.        TCE in the Shallow Portion of the Water Table Aquifer
    

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    Record of Decision for the                                                              \VSRC-RP-97-402
    D-Area Oil Seepage Basin •6J1-G) iU)                                                     Revision I. Final
    Savannah River Site	    \ugust 1998
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     Record of Decision for the
     D-Area Oil Seepage Basin (6JI-G) (L">
     Savannah River Site
    WSRC.RP-97-402
     Revision 1, Final
                                                                                                   -I   • fc* 100
                                               SCALE  IN  r££T
    
                                         See Figure 11 for Master Legend
    Figure 9.        TCE in the Deeper Portion of the Water Table Aquifer
    

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    Record of Decision for the                                                             WSRC-RP-9T-402
    D-Ar«a Oil Seepage Basin (631-G) iU)                                                     Revision 1. Final
    Savannah RJver Site	\unsi l»)3
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                                                                     a
    
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                                   Sec I igure 11 for Miisler Legciul
    

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    Record of Decision for the                                                            »0SRC:RP;97-4°2
    D-Area Oil Seepage Basin -631-G) (U)                                                    Revision 1. Final
    Savannah RJver Site		Auyjst 1908
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    j	Ml I.ill I
                          CHOSS SECTION  LOCATION MAP
    MAPS
                                                                                    O ••--	-
                                                                      LEGEND TOR Cf?OUNDWATEn
                                                                         CROSS SECTIONS
    
                                    «.r»i t IM n f i
    

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                                                                                                                  HI*.it-tit:
                                                                                                                 >	 l.lm.l
    THIS PACK «'AS INTKNTKINAI.I.V I.EKT IlLANK.
    

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    Record of Decision Tor the
    D-Arta Oil Seepage Basin (631-G) (U)
    Savannah River Site	
                                     VVSRC-RP-97-402
                                      Revision 1. Final
                                    	August 1998
    Groundwater samples  were analyzed for metals and 22  were detected at least once at concentrations above their
    
    quamitation limits. Generally, the meiaJ concentrations are low when compared with background and are within an
    
    order of magnitude of the screening levels.  The exceptions are  iron and manganese, which have their maximum
    
    concentrations (392.300 \izf[ iron and 66,400 pg/l manganese) in the upper portion of the aquifer immediately below
    
    the former trenches.  Elevated concentrations of these two metals continue to the southwest of the unit.
    
    Surface Water
    
    
    Surface water was sampled in  the wetlands located downgradient of the D-Area OSB.  Six VOCs, 1 SVOC. 10
    
    metals,  and cyanide were detected at  very low or estimated  ("J"-qualified) concentrations.   The impact  of the
    
    detected compounds is not significant when compared to background.
    
    Sediment
    
    
    Sediment at the unit was sampled from ihe Carolina bay to the west of the basin and from wetlands to the south.  The
    concentrations of all detected compounds were estimated ("J"-qualifiers) or low when compared to background, and
    
    there were no apparent patterns to indicate the source for  any of the detected constituents.
    
    Fate and Transport Assessment
    
    The conditions at the  D-Area OSB appear to be favorable to the natural breakdown  of the organic contaminants
    
    through the action of the in-situ bacterial population in the subsurface. Evidence of the degradation of contaminants
    
    in both the soil and groundwater are shown below:
                              SOIL
              GROUNDWATER
                Elevated carbon dioxide and methane in
                soil gas
                Depressed oxygen in soil gas
                Location of the soil gas anomalies in close
                proximity to the most contaminated
                location
                Depressed pH levels in contaminated areas
                Bacterial "slime" and noxious odors in one
                sample
                Presence of breakdown products (DCE and
                vinyl chloride)
    depressed dissolved oxygen downgradient
    
    Enhanced mobility of iron and manganese
    Elevated chemical oxygen demand, chloride
    and sulfate levels downgradient
    
    Depressed pH levels in contaminated areas
    Presence of breakdown products (DCE and
    vinyl chloride)
                                                        45
    

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    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) fU)                                                         Revision 1, Final
    Savannah River Site	                        	August 1998
    Soil Leachability Analysis
    
    The soil data set was subjected to analysis by the soil screening level (SSL) process and Multimedia Environmental
                                                                          *
    Pollutant Assessment System (MEPAS) computer model runs to evaluate -the potential for constituents in the soil to
    migrate to the groundwater at levels exceeding their  MCLs or risk-based concentrations (RBCs).  Twenty-four
    constituents failed the  SSL screening process (7 VOCs. 4 pesticides, and 13  melab) and were considered to be.^
    potentially leachable from the soil to the groundwater.
    
    Following  the SSL evaluation, two types of MEPAS computer simulations were conducted: a unit-wide evaluation
    for all  20 compounds and a  "hot-spot" evaluation  of the  three  constituents  (antimony,  methylene  chloride
    (dichloromethane). and dieldhn) that failed the unit-wide test.  All three of the  remaining constituents failed the
    second  series of "hot spot"  runs, indicating that they have the potential to leach to the groundwater at concentrations
    exceeding  the MCL or  RBC, even after removing the sources from the most contaminated area of the trench.
    
    After completion of the RFI/RI report, a supplemental calculation for a  mass-limited SSL (MLSSL) was completed
    for methylene chloride.   This supplemental  calculation raised  the  target remediation  concentration  from 1.0
    microzram per kilogram  (ug/kg)  (the  SSL)  to 41  ug/kg (the  MLSSL).   This  is well  below the maximum
    concentration in the  RFI/RI (2,400  ug/kg) but exceeds the current (post-biovent test) sample results (4 ug/kg) by a
    factor of 10 (WSRC, 1997b, c).  The biovent test cycle has been extremely effective in removing methylene chloride
    from  the basin soils.
    
    Groundwater Transport Analysis
    The area in the vicinity of the D-Area OSB is currently listed as industrial future land use (DOE, 1996). Therefore,
    the potential for utilization of the shallow water table aquifer for potable  water uses is minimal, and the only valid
    exposure scenario to unit groundw-ater is through the discharge of grour.dwater from the water table aquifer to the
    Savannah  River or Fourmile Branch.
    
    The estimated flow  rates in the aquifer beneath the unit indicate that constituents in  the groundwatir could have
    traveled up to 2.350 m (7.700 ft) since the unit  was opened in 1952. and up to 1,120 m (3.630 ft) since the basin was
    closed  in  1975 (WSRC, 1997a). The fact that the largest plume in the groundwater (TCE) extends only 365.8 m
    (1.200  ft) from the source  area (1/3 to 1/6 the distance predicted  by groundwater flow) indicates  that degradation,
    volatilization, retardation and other factors are working to reduce the impact of the basin disposal practices on the
    local groundwater.
                                                         46
    

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    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-C) (U)                                                          Revision 1, Final
    Savannah River Site	___	August 1998
    VI.     SUMMARY OF OU RISKS
    
    As pan of the D-Area OSB  RFI/RI process, a BRA was prepared to evaluate the potentiaJ risk to human health and
    the environment from chemical contaminants identified in investigations at the D-Area OSB.  The following sections
    outline the results of the  human health risk characterization and the ecological risk characterization.  A complete
    discussion of the risk assessment methodology, receptor analysis, risk characterizations, and uncertainty within the
    characterizations can be found in the RFI/RI Report and BRA (WSRC, 1997a).
    
    Unit-specific data from the RFI/RI were  used  to  identify  and screen constituents of potential concern (COPCs;.
    Exposure point concentrations were  calculated  and used to estimate potentiaJ exposures  and  risks to humans and
    wildlife.  Carcinogenic risks and hazard indices (His), based on a combination of exposure scenarios, locations, and
    receptors identified  in the CSM,  were calculated and then  compared to EPA risk guidelines [i.e., 1E-04 to IE-06
    carcinogenic risk, HI > 1, and Ecological Effects Quotient (EEQ) > 1]. COPCs were selected as preliminary COCs
    (PCOCs) and designated as  primary or secondary COCs, based on their individual contribution  to total media risk or
    hazard.
    
    Human Health Risk Assessment
    
    To evaluate the risk to human receptors due to the contamination at the D-Area OSB, unit-specific analytical data are
    used to identify  COPCs.  Exposure  point concentrations are determined for  each COPC to estimate the potential
    exposure for various receptors and exposure scenarios.  Receptors were selected based on the current land use and
    two potential future land uses.  Receptors include a current known on-unit worker (researchers and samplers), a
    hypothetical future on-unit industrial worker, and a hypothetical future on-unit resident (Figure 7a). Environmental
    media evaluated in the BRA include  surface soil, excavated/subsurface soil, "hot spot" soil, surface water (wetland).
    sediment (wetland and Carolina bay), and groundwater (Figure 7b).
    
    Following the selection of human receptors for evaluation, the cancer risk and the noncancer health hazard were
    estimated for each COPC and for each pathway/receptor combination, based on EPA guidance (EPA, I989b).
    
    Carcinogenic risk is defined as the incremental probability of an individual developing cancer over a lifetime as a
    result of pathway-specific exposure to cancer-causing contaminants (carcinogens).  The risk to an individual
    resulting from exposure to  non-radioactive chemical carcinogens is expressed as the increased  probability of cancer
     occurring over the course of a 70-year lifetime.  At NPL sites incremental cancer risk is compared to the EPA target
     risk range of one in ten thousand  (IE-04) to one in  one million (IE-06).
                                                        47
    

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    Record of Decision for the                                                                   WSRC-RP-97-4D2
    D-Area Oil Seepage Basin v6Jl-G) CO                                                         Revision 1, Final
    Savannah River Site	                            	    August 1998
    Noncarcinogenic hazards ire also evaluated to identity a level  at which  iher;  may  be  concern for potential
    noncarcinogenic health effects. The hazard quotient (HQ), which is the ratio of the exposure dose to the reference
    dose, is calculated for each contaminant. HQs are summed for each exposure pathway to determine the specific HI
    for each exposure scenario. If the HI exceeds unity (1.0), there is concern that adversc-health hazards mi^ru exist.
    Current Land Use - Carcinogenic Risks
                                                                                                    f
    Under the current land use scenario, human health risks were characterized for the current on-unit worker. Estimated
    cancer risks from surface soil ingestion, dermal contact, and particular inhalation were less than 1E-06, indicating r.o
    concern for carcinogenic health effects (Table 2).
    
    Future Land Use -  Carcinogenic  Risks
    The  hypothetical future on-unit worker scenario has two exposure  routes with carcinogenic  risks within the target
    range of IE-CM to 1E-06 (Table 2).  Ingestion of excavated soil has  a risk of I E-06 primarily  due to the ingestion of
    arsenic and PCB-1260, and ingestion of groundwater has an estimated risk of 5E-05 primarily due to the ingestion of
    beryllium. bis(2-ethylhexyl)phthaJate, and vinyl chloride. The risks for the future worker from all other pathways are
    less  than the  EPA point of departure (IE-06),
    
    Several pathways for the future on-unit resident have estimated risks within the target range (Table 2).  Ingestion of
    surface soil and excavated soil have risk values  of 1E-06 and IE-OS, respectively.  The primary contributor to risk
    for ingestion of surface soil is PCB-1260. The primary contributors  to risk for ingestion of excavated soil are arsenic
    and  PCB-1260. Ingestion of leafy, tuberous,  and fruit produce grown in excavated soil has estimated risk values of
    2E-06, 1 E-06. and 3E-06, respectively.  The primary contributor to  risk  for all of these pathways is arsenic.  Dermal
    contact (3E-06) with ground water and inhalation of  VOCs (1E-05) in groundwater during showering also have
    estimated  risks between 1E-06 and  1E-04.   The risk  for hypothetical residential  exposure  to groundwater by
    ingestion (2E-04) is the  only pathway to exceed the target risk  range.  Beryllium,  bis(2-ethylhexyl) phihalate. and
    vinyl  chloride are  the primary contributors  to  the risks from ingestion and dermal contact, while  groundwater
    inhalation risk is due to 1,1-DCE. cis-l,2-DCE. and vinyl chloride.
    
    Current Land Use - \oncjrcinoytnic Hazards
    The BRA shows that potential adverse noncarcinogenic health effects are not likely to occur  because the sum of the
    His for the current  on-unit worker scenario do not exceed a value of 1.0 (Table 2).
    
    Future Land Use - Moncarcinogenic Hazards
    No r.c arc i no genie His for the hypothetical future  on-unit worker  do not exceed 1.0 for any of  the pathways evaluated
    (TaBTe?).
    

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    Record of Decision for the
    D-Area Oil Seepage Basin (631-C) fU)
    Savannah River Site	
                                         WSRC-RP-97-402
                                          Revision 1. Final
                                        	August 1998
                                                    Table 2
    
                                             Summary of Risk-Based
    
                                      PCOCs, Grouped by Exposure Route
    Receptor *
    Current Known On-Unit
    Worker
    Hypothetical Future
    Worker
    
    Hypothetical Future
    Resident
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    Exposure Route/
    Pathway
    None
    
    Ingestion of Excavated
    Soil
    [ngestion of Groundwater
    Ingestion of Surface Soil
    
    Ingestion of Excavated
    Soil
    
    Ingestion of Homegrown
    Produce Using Excavated
    Soil
    Leafy vegetables
    Tuberous vegetables
    Fruits
    Ingestion of Groundwater
    
    
    
    Dermal Contact with
    Groundwater
    Inhalation of
    Groundwater
    
    Preliminary
    COCs
    None
    
    PCB-1260. As
    
    Be. BEHP. Vinvl Chloride
    PCB-1260
    
    PCB-1260. As
    
    Fe, Tl. As
    
    
    
    As
    .As
    As
    Be. BEHP. Vinvl Chloride,
    1.1-DCE. PCE
    Mn. Tl, Fe. BEHP.
    1.2-DCE (mixture)
    Be, BEHP
    
    1,1-DCE, cis-1 .2-DCE.
    
    Vinvl Chloride
    Carcinogenic
    Risks
    
    
    l.E-06
    
    5.E-05
    l.E-06
    
    l.E-05
    
    
    
    
    
    2E-06
    1E-06
    3E-06
    2.E-04
    
    
    
    3.E-06
    
    l.E-05
    
    
    Hazard
    Index
    
    
    
    
    
    
    
    
    
    1.13
    
    
    
    
    
    
    
    
    4
    
    
    
    
    
    
       No Ecological Receptors were identified as being impacted by Unit-Specific Chemicals.
      PCB = polychlorinated biphenyls
      As = arsenic
      Be = beryllium
      BEHP = bis(2-ethylhexyl)phthalate
      Fe = iron
      BOLD = FINAL Risk-Based Constituents of
               Concern.
    Tl = thallium
    Mn = manganese
    DCE = dichloroethene
    PCE = tetrachloroethene
                                                       49
    

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    Record of Decision for the                                                                    WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) ft,")                                                          Revision 1. Final
    Savannah River Site	                                         	August 1998
    The His tor hypothetical future resider.: exposures equal or exceed 1.0 for the tngesticn of excavated soil a.-.d for the
    ingestion of groundwater (Table 2).   The HI  for ingestion  of excavated soil  is slightly  greater than one and is
    primarily a result of thallium, iron, and arsenic concentrations. The HI for groundwater ingestion during childhood
    is 4 and the HI for groundwater ingestion during childhood through adulthood is 2.  These hazards are due primarily
    to thallium and manganese.
    
    Total Pjf/txav Risks and Ha-ard Indices
    Carcinogenic risks  and noncarcinogenic hazards associated with the individual exposure  pathways for surface soil
    (0-1 ft;, excavated soil (0-4 ft), surface water, sediment and groundwater have been summed to obtain total pathway
    risks and His for each receptor (worker and resident). The total risk from surface soil (0-1 foot) and excavated soil
    (0-4 ft)  were summed with the total risk from surface  water, sediment,  and  groundwater for a total risk from all
    exposure pathways  across all media for each receptor.
    
    The total pathway risk values for the current known  on-unit worker, hypothetical  future on-unit  worker, and
    hypothetical future  on-unit resident are 6E-09,  5E-05, and 2E-04, respectively.  The risk values that exceeded the
    EPA point of departure (1E-06) for the future receptors are a result of exposure to constituents in groundwater.
    
    Total pathway  His exceeded 1.0 for the future on-unit resident. These His were 5 [for pathways excluding excavated
    soil (0-4 ft)] and 6 [for pathways excluding surface soil (0-1 ft)].  The noncarcinogenic hazards for the future on-unit
    resident were a result of exposure to chemicals in groundwater and exposure to arsenic in excavated soil.
    
    Ecological  Risk Assessment (ERA)
    
    The.purpose of the ERA component of the BRA is to evaluate  the likelihood  that  adverse  ecological  effects are
    occurring or may occur as a result of exposure of biological  organisms to unit-specific chemical constituents. The
    specific methodology followed in the ERA for the D-Area OSB consists of a two-tiered evaluation. The  first tier of
    the process is the selection of ecological COPCs through a screening evaluation.  Any analytes that fail the screening
    are classified as COPCs and are evaluated in the second tier of the process, the ERA.  The ERA is based on more
    unit-specific  and realistic  assumptions than  the consistently conservative assumptions used  in the  screening.
    Accordingly, the ERA assesses whether COPCs, identified as having a  potential to  pose  ecological risk in  a very
    conservative screening, are actually likely to pose risk to assessment endpoints under existing or future conditions  at
    the unit.
    
    COPCs art; identified following qualification and evaluation of data, and screening of inorganics against unit-specific
    background levels.  Unit-specific soil  wus grouped into exposure groups in three exposure areas: (! .1 the area of the
                                                          50
    

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    Record of Decision for the                                                                    WSRC-RP-97.402
    D-Area Oil Seepage Basin (631-G) (V)                                                           Revision 1. Final
    Savannah River Site	August 1998
    former basin. (2) the Carolina bay to the west, and (3) the wetland area to the south. Soil data from a depth of 0-0 3
    m (0-1 ft; are used to estimate COPC exposure point concentrations under current land  use conditions at the basin.
    Subsurface soil samples from a depih of 0-1.3 m (0-4 ft) are used  to evaluate future risk, under the assumption of
    future excavation activity in the basin area associated with a hypothetical future human residential land use scsnano.
    Croundwater data collected at  the  unit are evaluated  under the future scenario  by conservatively assuming  thai
    current  groundwater concentrations of COPCs will discharge  to surface  water  without  attenuation or  dilution.
    Sediment data from the Carolina bay and the wetland and surface water data from the wetland are assumed to remain
    unchanged under future conditions.
    
    Exposure point concentrations  for  COPC  selection are based on the maximum  detected concentration  for each
    exposure group.  Exposure point concentrations  for the ERA are based  on the  RME concentration, the highest
    concentration to which a receptor may reasonably be exposed.  In selecting COPCs, those analytes that pass to.xicity.
    background, and frequency of detection screenings but  have  an aquatic bioconcentration factor greater than 300 are
    re-included as COPCs due to their potential to pose risk through bioaccumulation and/or  biomagnification.
    
    The ecological study area at the  D-Area OSB includes a variety of  habitats, both terrestrial and wetland. No known
    endangered, threatened, or special concern species exist in the study area. The basin area has been highly impacted
    physically by previous activities  at the unit, and the habitat (mowed field) is  low in  diversity and productivity. Areas
    adjacent to the unit include a  mesic  pine/hardwood forest, a Carolina bay wetland,  and a blackgum/sweetgum
    wetland.
    
    Following the identification of ecological COPCs and the characterization of the ecological communities of  the study
    area, ecological assessment endpoints are selected so as to determine whether relevant policy goals (protection of the
    environment under CERCLA and protection of wetland surface waters under the Clean Water Act) are being attained
    at the OU. Ecological risk from unit-specific COPCs is assessed on the basis of the potential for adverse effects on
    the  assessment endpoints:  (1) survival and reproduction of terrestrial wildlife populations at the unit, including
    herbivores and predators; and (2)  survival and reproduction of populations of aquatic species and of  terrestrial
     wildlife species that prey on aquatic  species in the wetland near the unit.  Effects on assessment endpomts are
    predicted from measurement endpoints (e.g., levels of COPCs  that have been shown  to  produce toxic  effects  m
     animal studies).  Decision rules by  which the potential  for effects on assessment endpoints  are decided are stated  in
     terms of the measurement endpoints and are based on the calculation of HQs.
    
     In order to evaluate potential effects on the assessment endpoints, multiple ecological receptor species are chosen  to
     represent the multiple  trophic  levels of the ecological communities present within the study area.  The  receptors
     evaluated include: (I) aquatic organisms directly exposed to surface  water and sediment;  (2) a herbivorous rodent
                                                         51
    

    -------
    Record of Decision for the                                                                   \\ SRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) fU)                                                          Revision 1, Final
    Savannah River Site	                                 	August 1998
    (meadow vole) directly exposed to soil,  sediment, and surfac; water, as well as biotic uptake of COPCs:  and (3)
    predators  (mink  and  green-backed heron) that are directly exposed  to environmental  media  as  well as to
    bioaccumulative COPCs in the food chain.
    
    Risks to each of these  receptors from the exposure groups ai the OU are estimated on the basis of calculated HQs.
    COPCs with an HQ greater  than on* are designated as PCOCs. Risk is estimated for both  current conOWons and
    hypothetical future conditions  (i.e.. assuming wildlife exposures  to subsurface soil  that may be excavated,  and
    assuming exposure of aquatic organisms to current groundwater concentrations of COPCs). PCOCs ar« individuaHy
    evaluated  based on their chemical  and lexicological characteristics and the  uncertainty  associated with their°HQ
    value.  Those PCOCs that  are estimated to have a significant potential to cause adverse  ecological  effects are
    summarized for each  combination of exposure area, receptor, and medium.  This  subset of  COPCs is further
    evaluated  based  on  uncertainty  in the  risk  assessment, confidence  in the risk estimates, and  the  ecological
    significance of the risk estimated to be posed by these PCOCs. This evaluation of ecological  significance ultimately
    determines whether each PCOC actually poses significant ecological risk and warrants designation as a final COC.
    
    The ecological receptors identified as having a significant potential for lexicological effects at the D-Area OSB are
    aquatic, semi-aquatic,  and benthic organisms living  in the Carolina  bay and the wed and.  The community of
    aquatic/semi-aquatic  organisms that can be  supported by the Carolina bay is inherently restricted in diversity and
    abundance of organisms due to the  intermittent character of the inundation of the bay and its hydrological isolation.
    The ERA  found that there may be significant potential for adverse effects from DRO on the more sensitive members
    of the aquatic community during chronic, long-term exposures. However, such exposures are unlikely due to (be
    frequent dry periods during  which the aquatic animal  community is essentially absent. DRO at the concentrations
    detected in sediment is unlikely to significantly affect populations  of aquatic  species at the Carolina bay, therefore.
    the ecological risk posed by  DRO is considered insignificant, and it is not a final COC.
    
    The aquatic community in the arm  of the wetland that extends to the south of the OU  also is subject to intermittent
    desiccation, though it  appears to be a more diverse  and  productive community than  that of the Carolina  bay.  A
    potential for adverse ecological effects on this community  is indicated by the measured concentrations of aluminum
    and barium in surface water  and of DRO  and  TPH in sediment.  Chronic exposure of aquatic organisms (e.g..
    invertebrates,  fish, and amphibians) to these contaminants at RME levels could reduce reproduction and/or  increase
    mortality  among  sensitive individuals sufficiently to cause a reduction  in population size.  However, if such effects
    are  limited to the small  area evaluated, the larger ecological community  of the wetland system is  unlikely to
    experience significant  effects, such as a loss of species. Therefore, aluminum and barium in  surface water and DRO
    and TPH in sediment of the wetland are unlikely to pose significant ecological risk to the  wetland  assessment
    endpoint (the biodiversity of the aquatic community), and they ore not considered to be ecological final COCs.
                                                         52
    

    -------
    Record of Decision for the                                                                  VVSRC-RP-97-lo:
    D-Area Oil Seepage Basin (6J1-G) 0.")                                                         Revision I. Final
    Savannah River Site	.	         August 1998
    In summary, the assessment of ecological risk at the D-Area OSB indicates that the COPCs and environmental media
    in the exposure areas evaluated do not pose significant risk to ecological assessment endpoints. and policy goals for
    the OU are achieved under baseline conditions. There is essentially no Iik±lihood of unit-specific chemicals causing
    significant impacts to the community of species in the vicinity of the unit.  Based on their toxicity at their current
    concentration, none of the COPCs identified in soil, sediment, or surface water at the D-Area OSB are estimated to
    pose significant ecological risk.
    
    COCs
    
    PCOCs.  which include primary and secondary COCs, were selected for the D-Area OSB  because they exceed
    ARARs,  because they exceed risk-based criteria in the BRA, or because they are projected to have the potential to
    leach to the groundwater at levels exceeding an MCL or RBC.  Primary COCs are defined in the human health nsk
    assessment as constituents that contribute a chemical-specific risk of more than IE-06 or an HQ of greater than 0.1 to
    any media risk estimate that exceeds a 1E-04 risk  or an HI of 3.  Secondary COCs are defined as those constituents
    in each medium contributing a chemical-specific risk greater than IE-06 or an HQ of at least 0.1 to a media with a
    risk greater than IE-06. but not more than 1E-04 or an HI of one or greater, but not more than three.  Table 3 lists all
    PCOCs and the basis for their qualification as PCOCs.
    
    The final risk-based COCs are presented by potential receptor scenario, pathway, and exposure route in Figures 12
    through 16.
    
    Final COCs were selected from the PCOCs by evaluating  the uncertainty associated with each chemical during each
    phase of the  RF1/RI/BRA (Table 4).  Eight groundwater  PCOCs [1,1-DCE; cis-l.2-DCE, total  1,2-DCE; benzene.
    dichloromethane (methylene chloride); PCE: TCE; and vinyl chloride] were judged to be  USCs and, therefore, final
    COCs. One soil PCOC [dichloromethane (methylene chloride)] was judged to be a USC and. therefore, a final COC
    

    -------
    Record of Decision Tor the
    D-Area Oil Seepage Basin (631-G) (U)
    Savannah River Site	
    WSRC-RP-97-402
      Rerision 1, Final
          August 1998
                                                                   Table 3
                                                            Summary of PCOC»
    
    PCOC Name
    
    
    1.1- Dichloroethene
    
    1 .2-Dichloroethene (cis-)
    i. 2-Dichloroethene (mixed)
    
    Antimony
    
    Benzene
    Beryllium
    Bis(2-ethylhexyl)phthalate
    
    
    
    Dichloramethane
    Iron
    
    Manganese
    
    Tetrachloroethene
    
    Thallium
    
    
    Trichloroethene
    Vinyl chloride
    
    
    l.l-Dichk>roe(hene
    1 .2-Dichloroethene (cis-)
    Beryllium
    
    
    B i$< 2 -ethyihexy 1 Iphthalate
    
    
    Vinyl chloride
    
    
    Antimony
    Dichloro me thane
    Dicldrin
    Thallium
    
    Arvenic
    
    
    Iron
    PCB-1260
    
    Thallium
    Risk or
    Basis Hazard Pathways
    Value
    PRIMARY GROtNDWATER COC* '
    exceeds risk criterion 2E-06 resident (childhood through adulthood) ingesa'oa
    4E-06 resident (childhood through adulthood) inhalation
    exceeds MO.'
    exceeds hazard criterion 0.27 / 0.49 resident (childhood through adulthood / childhood
    only) ingQncn
    exceeds hazard criterion 0.1/0.26 resident ; childhood :hrough adulthood /childhood
    only) ingesticn
    exceeds MCL1
    exceeds risk criterion 2E-04 resident I childhood through adulthood) ingestion
    exceeds risk criterion IE -05 resident (childhood through adulthood) ingesnon
    exceeds MCL1
    exceeds hazard criterion 0. 1 / 0.2 resident (childhood through adulthood / childhood
    only) tngestioft
    exceeds .M€tJ
    exceeds hazard criterion 0.3 / 0.6" resident (childhood through adulthood / childhood
    only) ingesrion
    exceeds hazard criterion 0.4/0.77 resident (childhood through adulthood / childnoed
    only) ingesnon
    exceeds risk criterion 2E-06 resident (childhood through adulthood) ingesnon
    exceeds MCL1
    exceeds hazard criterion 0.9 / 1 .7 resident (childhood through adult / childhood oiii)*
    ingestion
    exceeds MCI'
    exceeds MCL1
    exceeds risk criterion- 2E-05 resident (childhood through adulthood) ingesQoa
    exceeds MCI?
    SECONDARY GROUND WATER COO J
    exceeds risk criterion 4E-06 resident (childhood through adulthood) inhalation
    exceeds risk criterion 4E-06 resident (childhood throogh adulthood) inhalation
    exceeds risk criterion 4E-OS industrial worker \nfatHf
    exceeds risk criterion I E-06 resident (childhood through adulthood) dermal
    contact
    exceeds risk criterion 3E-06 industrial worker ingestion
    exceeds risk criterion 1E-06 resident (childhood through adulthood) dermal
    contact
    exceeds risk criterion 5E-06 industrial worker ingestion
    exceeds risk criterion 4E-06 resident (childhood through adulthood) inhalation
    PRIMARY SOIL COO '•
    Projected to leach to groundwaier in excess of MCL or RBC
    Projected to leach to groundwater in excess of MCL or RBC
    Projected to leach :o groundnut: in excess of MCL at RBC
    Projected to leach to groundwater in enctss of MCL or RBC
    SECONDARY SOIL COO '-
    exceeds nsk criterion IE -06 industrial worker ingestion fioil 0- 1 .2 m)
    exceeds nsk criterion 9E-06 resident ingesucn and produce ingestion (0-1 .2 m)
    exceeds hazard cnterion 0.2 resident (childhood only; ingestion (soil 0-1.2 m)
    exceeds hazard criterion 0.2 resident (childhood only) ingestion (soil 0-1.2 m)
    exceeds risk criterion 1 E-06 resident (childhood through adulthood) ingestion
    (soil 0-0.3 m)
    exceeds hazard criterion 0.7 resident (childhood onM ineesdon (soil 0-1.2 m)
          Primary COCi *re Je fiord u COPO whcft rontnbuu upufciftiiy •'cterrjciVtpec-/r rak of n !eui : E-«>S or checmciJ-tpec-jic haunJ ofO I) to i pathway
          (uw| > toul ruk if greater than IE-0* or HI puier ifuwi three, of *hc.t ire pro«rnl :o leva to {rounrtwiur u concrmniioru :ueeJifl| in MCI. or RBC
          Secondary COC i ire Jc fined u COPCi ihii ^I»T ichcmcii-ipcr/c nr»-c: r^ic ;ruvr u*un IE 06. IT i .-
          huifd of 0 1 -*tac3«orunbui£* to * p«h»iy *\uard pznti '^^n o^t.
          Sod COO w« it>
          Sec Tick *- 1 * '*SRC. I990a
                                                                      54
    

    -------
                                                                           Table 4
    
    
                                                               Uncertainly Matrix for C'OCs
    
    Constituent Name
    Gruuntlwater COCs
    Antimony
    Benmnc
    Dcryllium
    ms(2-clhylhexyl)phlhalate
    Dichloroethenc, (ck-) 1,2-
    Dicliloroelliene.(mL\-eti-)l,2-
    nichlorotlhene, 1.1-
    Dii'hloroHiellmiiit (ntelliylene clilurltle)
    tun
    Manganese
    Ttlnwhlurueilmnt
    1 hallium
    Trii-hluroethene
    Vinyl chloride
    Soil C0(\
    Antimony
    Arsenic
    Duiiloronielliane (mtlhylene i-liltiriilt)
    Dicldrin
    Iron
    PCU-1260
    I'liallium
    CATEGORY UNCERTAINTY LEVELS «
    Unit
    History
    
    high
    LOW
    high
    high
    LOW
    LOW
    LOW
    high
    high
    high
    LOW
    high
    LOW
    LOW
    
    high
    high
    LOW
    high
    high
    unknown
    high
    Background
    Comparison
    
    LOW
    LOW
    high
    LOW
    LOW
    LOW
    LOW
    .OW
    .OW
    .OW
    .OW
    .OW
    LOW
    LOW
    
    high
    high
    LOW
    high
    LOW
    LOW
    high
    Analytical
    
    high
    LOW
    LOW
    LOW
    LOW
    LOW
    LOW
    high
    LOW
    LOW
    LOW
    high
    LOW
    LOW
    
    high
    high
    LOW
    high
    LOW
    LOW
    LOW
    Unit-Related
    Distribution
    
    high
    LOW
    high
    high
    LOW
    LOW
    LOW
    LOW
    LOW
    LOW
    LOW
    high
    LOW
    LOW
    
    LOW
    high
    LOW
    high
    LOW
    high
    high
    Toxicity
    
    high
    LOW
    LOW
    LOW
    LOW
    LOW
    high
    LOW
    high
    high
    LOW
    high
    high
    LOW
    
    NA
    LOW
    NA
    NA
    high
    high
    high
    Risk
    Assessment
    
    high
    high
    LOW
    LOW
    LOW
    LOW
    LOW
    high
    high
    high
    LOW
    LOW
    high
    LOW
    
    NA
    high
    NA
    NA
    high
    high
    high
    Exceeds
    ARAR?
    
    high
    LOW
    high
    LOW
    LOW
    LOW
    LOW
    LOW
    high
    high
    LOW
    LOW
    LOW
    LOW
    
    high
    high
    high
    high
    high
    high
    high
    	 , 	 _l_ ^
    Overall
    Level of
    Uncertainty
    
    high
    LOW
    high
    high
    LOW
    LOW
    LOW
    LOW
    high
    high
    LOW
    high
    LOW
    LOW
    
    high
    high
    LOW
    high
    high
    high
    high
    Retain as
    linal
    COC?
    
    no
    YES
    no
    no
    YES
    YLS
    YES
    YES
    nu
    no
    )/:.V
    no
    YES
    YES
    
    no
    no
    YES
    no
    no
    no
    no
    Uncertainty = "LOW" indicates that this analyle could be a llnal COC based solely on the indicated category.
    
    Uncertainly = "high" indicates thai this analyle could noi be a final COC based solely on the indicated category.
    
    NA '- Category docs not ;i|>|>ly because this compound was added to this list based on its potential lo leach to groundwatcr.
                                                                                                                                                          < > 0
                                                                                                                                                          u :, o
                                                                                                                                                          3 n -i
                                                                                                                                                          3 O O.
                                                                                                                                                          |> « -•
                                                                                                                                                          i -o a.
                                                                                                                                                            a ;
    
                                                                                                                                                            ff\
                                                                                                                                                            o
    
                                                                                                                                                            r.
    -•"IT
       '
    

    -------
    Record of Decision for the                                                            WSRC-RP-97-402
    D-Area CHI Seepage Basin (631-G) (U)                                                    Revision 1. Final
    Savannah River Site	August 1998
                            THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                    56
    

    -------
    31
    c
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    •i4Clltt«l ItUMMII ICiC|'lulft
                luve been ouuiicJ
            "*  llltul«IIUII iW VtX'l JUIIII| ttUUKlluUI UK Ul
            NC'  Nul Ctlculiied due tu » >Kk uf loxu ily il4U
            NA  Nu ft^lickblc
            NU  Nu itau weie ivtiUtlc Im llu» iicdiuin
                                                                                                                                                      Cuclwigciik MUk COCi
                                                                                                                                                              HoCOC,
                                                                                                                                                              H» ClK'i
                                                                                                                                                              NoCOC.
    
    
    
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                                                                                                                                                              NuClX'i
    
    
    
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                                                                                                                                                                NA
    
    
                                                                                                                                                                NA
    
    
    
    
    NC
    
    No I'OCi
    NufLK',
    NA
    NA
    NA
    NA
    N.iCIH't
    N..CCX'|
    Nil
    Nil
    N..C.LH,
    N..(ln'>
    NA
    NA
    NA
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    3 ra n
    3 U O.
    S-92.
    < » f?
    3-35:
    j!»0 3
    3 n
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    "»
    - o' yg
    *O ti ®
    oo ri u
    

    -------
    Record of Decision for the                                                              WSRC-RP-97.402
    D-Area Oil Seepage Basin (631-G) (U)                                                      Revision 1. Final
    Savannah River Site	.	August 1998
                             THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                      58
    

    -------
        T1
    
       (TO
      -  7i
    n  Z'
    
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    D  cr
    n  u
    
    3  »
    3  Q.
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                   liavc been unuilcJ
    
               **  lnhal«lioa ul VlK'l Juniif huulclttitj ukc ul
               NT Not Clkuliuj due lu I l<>.li ul lull, lly Jiu
    
               NA Nul .ptilK.blt
    
    
               Nl> Nudtfi weic •vaiUble fm (hit litcdluin
                                                                                                                                                            C.rclnojcMk Hbk CUCi
    N.I cxx:«
    
    
    
    
    
    
    
    
    NofUC'.
    
    
    
    
    
    
    
    Nu C'CX'i
    
    
    
    
    
    (In COO
    
    
    
    
    
    
      NA
    
    
    
    
    
      NA
    
    
    
    
    
      NA
    
    
    
    
    
      NA
    
    
    
    
    
       NA
    
    
    
    
    
    
    
    
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      Nil
    
    
    
    
    
      Nl)
    
    
    
    
    
    
      NA
    
    
    
    
    
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      NA
    
    
    
    
      NA
    
    
    IU»rd Old
    1
    Nl'
    N.i('(H'>
    NullX'i
    N,. (XX'.
    NA
    NA
    NA
    NA
    NA
    NA
    NA
    Nil
    Nil
    NA
    IIA
    N.,1 l« ,
    II f:
    NA
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    u i, o
    3 i» 2
    3 M Q.
    f Decision for the
    XI Seepage Basin (6
    h River Site
    O
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    <^
    I-n
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    ^ 3 ^
    ^ r™ so
    CfO — 1 J
    

    -------
    Record of Decision for the                                                            WSRC-RP-97-40"*
    D-Ar*a Oil Seepage Basin (631-G) (U)                                                     Revision 1. Final
    Savannah River Site	Aueust 1998
                            THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                    60
    

    -------
        •n
       00
        c
    c  y
    
    S  r
    2  °"
    > n
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       c
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    '  Pilli«t)» wiUUMt pouinul tiuiiun rcccpuxi
    
         v< beco tMiililcd
    
    •*  lolulMJwi o/ VUCl Juilii| IwuuhuU UK of
    
    
    C.nl.u,..!. Mbk CUfi
    -.«*
    
    N.CWi
    N-l'UCt
    N. UA'I
    NA
    NA
    NA
    NA
    NA
    NA
    NA
    NU
    NU
    NA
    NA
    V.,IIU.U<
    NA
    NA
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
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    I 	
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    Nxt'UCi
    N..CO,.
    NA
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    NA
    NA
    NA
    tM
    NA
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    Nit
    MA
    NA
    N.. 1 M i
    NA
    NA
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
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    S-22.
    ?-S s:
    ^
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                                                                                                                                                                                                       ' 4.
                                                                                                                                                                                                        O
    

    -------
    Record of Decision for the                                                             WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                    Revision 1, Final
    Savannah River Site	_	^^___	August 1998
                            THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                   62
    

    -------
    00
     c
                                                                                                                                                                                                                         > 0
     2  or
     u  u
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    ^  Q.
     •^ n
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                  •    Hailiwtyi wiiliuui (MMcinul liuinaii ict;e|iluff
                       tuvc been uttuucd
                  ••   liiluliliuii ul VIH't Juiinf luuulivlil ux u)
                       giuunjwttei
                  "•  H«i«iJ viluo nc lot ililljhu>»l »|uiuic
                       tcclUM (hckc viluek MIC lti|ltci lluit
                       valucl (of Uic clilld Uuuu|lt aJ
                       CKpuiuie
                  NC  Nu4 ttliullltJ tlue lo l Ink ul luuuly dm
                  Nl)  Nuiliu wcic aoilible loi ihu uicJlviih
                  IX'E • Juhlwucllicnc
                  HL't - uutclUwucdiciie
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                                                                                                                                                         CucliMi|Ciik KUk COC'i
                                                                                                                                                                No C'CX'.
    
    
                                                                                                                                                                No ClX'l
    
                                                                                                                                                                Nil 1 LH'i
    
    
                                                                                                                                                                   NC
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             Nil
    
    
             NU
    
    
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       VC. I.I IM t. fft
    
    
          NoCOCl
    
    I.I K'E.m  1.1 IX't. VC
    
    NriT.',doV«".k
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    Nol'lK.
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    :a Oil Seepage Basin
    mah River Site
    Ov
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    50^
    f JO
    f = ^
    ; •"" >o
    

    -------
    Record of Decision for the                                                               WSRC-RP-97-10:
    D-Area Oil Seepage Basin (631-G) (U)                                                      Revision 1, Final
    Savannah River Site	.	August 1998
                            THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                     64
    

    -------
    Figure 16. Risk-based COCs for the Future Resident, with E.x
    Uncertainty Analysis
    u
    5'
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    Record of Decision for the                                                           WSRC RP 97 •10''
    D-Area Oil Seepage Basin (631-G) (U)                                                    Revision 1. Final
    Savannah River Site	August 1998
                            THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                    66
    

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    Record of Decision for the                                                                  WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                         Revision 1, FinaJ
    Savannah River Site             	August 1998
    VII.    RAOS AND DESCRIPTION OF CONSIDERED ALTERNATIVES FOR THE D-AREA OSB OL
    RAOs
    RAOs address unit-specific contaminants, media of concern, potential exposure pathways, and remediation goals.
    The RAOs are based on the nature and extent of contamination, threatened resources, and the potential for human
    and  environmental exposure.  Initially, preliminary remediation goals are developed based upon ARARi or other
    information from the RFI/RI Report and BRA.  These goals should be modified, as necessary, as more information
    concerning  the unit and potential remedial technologies  becomes  available.  Final remediation goals  will be
    determined when the remedy is selected and shall establish  acceptable exposure levels protective of human health
    and the environment.
    
    ARARs are those cleanup standards, standards of control, and other substantive requirements, criteria, or limitations
    promulgated under federal, state,  or  local environmental  law  that specifically  address a  hazardous substance.
    pollutant, contaminant, remedial action, location, or other circumstance at a  CERCLA site.   The following three
    types of ARARs have been developed to simplify identification and compliance with environmental requirements:
    
    •    Action-specific requirements - set controls on the design, performance, and other aspects of implementation of
         specific remedial activities.
    •    Chemical-specific requirements - are media-specific and health-based concentration limits developed  for site-
         specific levels of constituents in specific media. There are two general sources of chemical-specific RGOs: (1;
         concentrations based on ARARs,  and (2) concentrations based on risk.
    •    Location-specific  requirements  must  consider   federal,  state, and  local   requirements  that  reflect the
         physiographical and environmental characteristics of the unit or the immediate area.
    
    Action-specific and location-specific  ARARs are addressed as pan of die remedial alternatives developed for the
    D-Area OSB groundwater. Only MCLs (as identified in  South Carolina R.61-58.5 State Primary Drinking Water
    Regulations and Federal 40 Code of Federal Regulations (CFR) 14] National  Primary Drinking Water  Regulations)
    have been  identified as  chemical-specific  ARARs.  The groundwater is not a current source of drinking uater.
    however, all groundwater in South Carolina is classified as GB under South Carolina R.61-68 Water Classification
    and Standards and, as such, is required to be addressed in some manner (State of South Carolina groundwaters must
    undergo active remediation to achieve MCLs unless a groundwater mixing zone (GWMZ) is granted). MCLs will be
     the clean-up standard for groundwater contaminants.
                                                        67
    

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    Record of Decision for the                                                                 W'SRC-RP-97-402
    D-Area Oil Seepage Basin (631 -G) (II)                                                        Revision 1. Final
    Savannah River Site	August 1998
    The RFI/RI and BRA identified the following COCs for zroundwater at the D-Area OSB:  PCE; TCE: 1.1-DCE:
    1,2-DCE: cis-1,2-DCE; vinyl chloride: benzene; and methylene chloride.
    
    Two of these contaminants (1,1 -DCE and 1,2-DCE) became COCs based on risk calculations. However, neither 1.1-
    DCE nor 1.2-DCE were detected  in  the D-Area OSB  groundwater at concentrations  exceeding their respective
    MCLs.  MCLs  are drinking water standards developed to be protective of human health and obtainable by current
    treatment methods.  Because these contaminants do not exceed the levels determined  to be protective of human
    health and  safe for drinking water  purposes,  1,1-DCE and  1,2-DCE will not be addressed in D-Area  OSB
    groundwater remediation. However, the remedial alternatives developed for the D-Area OSB groundwater include
    groundwater monitoring of VOCs (with the exception of no action) that will be inclusive of 1,1-DCE and 1.2-DCE.
    These VOCs are degradation products  of TCE and require evaluation during remediation.
    
    The primary chemical-specific ARAR for soil is an EPA SSL for methylene chloride (EPA. 1994).  The screening
    level limits  the concentration  of  methylene chloride in soil to 1.0 ug/kg based on its potential  to  leach to
    groundwater. A second screening level, the MLSSL (EPA,  1996), has been calculated to be 41 Mg/kg based on unit
    specific conditions.  Following biovent testing, methylene  chloride concentrations were below the MLSSL of 41
    ug/kg.  Therefore, because methylene chloride concentrations in the soil have  been reduced to levels  that cannot
    leach to the  groundwater above the MCL (WSRC,  1998 a) remediation of deep soils is  not warranted and it is not
    addressed further in this document.
    
    Based on ARARs and BRA results, the RAOs developed for the groundwater at the D-Arca OSB OU are to:
    •    reduce risks to human health  associated with dermal contact and  ingestion of groundwater, and inhalation of
         groundwater vapor
    •    restore groundwater to achieve ARARs and RGOs
    
     RGOs for groundwater COCs will be equivalent to their respective MCL values.  The groundwater contaminants ihat
     will be addressed at the D-Area OSB and their corresponding MCLs are provided in Table 5.
    
     At the close of the IRA. the  contractor installed two horizontally oriented, perforated pipes along the length of the
     former waste unit for treatability (biovent) study purposes. These pipes were used to force fresh air, nutrients and
     tracers into  the soils at a depth of about 8  ft in order to volatilize the constituents in the soil, enhance the aerobic
     degradation of the constituents in both the soil and groundwater, and monitor  the effectiveness of a potential soil
     treatment program (WSRC. 1997b, c. d, e).
                                                        63
    

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    Record of Decision for the
    D-Area Oil Seepage Basin (6J1-G) fU)
    Savannah River Site	
     WSRC-RP-97-402
      Revision 1, Final
    	August 1998
                                                      Table 5
    
                                         Final COCs, with Selected RGOs
    FINAL
    COCs
    Tetrachloroethene
    Trichlorocthene
    cis- 1 ,2-Dichloroethenc
    total- 1 .2-Dichloroethene
    1.1-Dichloroethenc
    Vinyl Chloride
    Benzene
    Dichloromethane
    (Meihylcnc Chloride)
    Basis for Becoming Final COC
    Excess
    Risk
    X
    
    
    X
    X
    X
    
    
    Excess
    Hazard
    
    
    
    X
    
    
    
    
    Leach
    toGW
    
    
    
    
    
    
    
    X
    Exceeds
    MCL
    X
    X
    X
    
    
    X
    X
    X
    Maximum
    Concentration
    Detected
    (ng/i)
    85
    1151
    457
    68.6
    0.84
    52
    6.2
    9.5
    Average
    Concentration
    in
    Groundwater
    2.1
    8.0
    4.88
    21.24
    0.399
    1.1
    0.22
    0.16
    Selected
    RGO
    (pg/1)
    5.0
    5.0
    70.0
    70.0
    7.0
    2.0
    5.0
    5.0
    Basis
    for
    RGO
    MCL
    MCL
    MCL
    MCL
    MCL
    MCL
    MCL
    MCL
                                                         69
    

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    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                         Revision 1. Final
    Savannah River Site	      	                       	August 1998
    Secondary Source Alternatives
    
    A3 pan of the investigation/assessment process for the D-Area OSB waste unit, a CMS/FS was performed using data
    generated during the assessment phase.  Detailed information regarding the development and evaluation of remedial
    alternatives  can be found in the Corrective Measures Study/Feasibility Study for the  D-Area Oil Seepage  Basin
    (631-G) (U) (WSRC, I998a). The RF1/RI and BRA indicate that D-Area OSB  groundwater poses a risk to human
    health.  Risk associated with ingestion. dermal contact, and inhalation of groundwater for the future on-unit worker
    and resident result in risk greater than the EPA's target risk range for future use scenarios. Therefore, a CMS/FS was
    conducted, which includes detailed analyses and groundwater alternatives.  Concerning other environmental media.
    the no further action alternative was selected for soil, and no action is required for surface water and sediment.
    
    Remedial alternatives  were not developed for  soil, surface water, or sediment at the unit.  Remediation  of these
    media is not warranted based on the evaluation of federal and state standards and the risk assessment.  As discussed
    above,  the interim action and  the biovent test cycle  performed on unit soil adequately eliminated the source of
    groundwater contamination.   Six  alternatives were  evaluated  for remedial  action  of  the  D-Area OSB OU
    groundwater. Each alternative is described below.
    
    Alternative GW-1 • No Action
    Under  this alternative, no remedial efforts would  be conducted  to remove, treat, or otherwise reduce the toxicity.
    mobility, or  affected volume of contaminated media.  An ERA and biovent test have been conducted for unit soils.
    These  reduced contaminant concentrations to acceptable  levels.   Biovent  testing  appears to have also reduced
    groundwater contaminant concentrations in the vicinity of the testing. However, under the no-action alternative, no
    further remedial efforts would be made to monitor or treat unit groundwater.
    
    The semi-confining unit ("tan clay") lying within  the uppermost, water table aquifer is not continuous  and has not
    prevented contaminant migration. However, the next confining layer ("green clay") provides an adequate barrier.
    which  prevents the migration of COCs to lower aquifers (Figure 10).  Additionally, modeling results indicate that
     under most scenarios, contaminant plumes have already largely reached their maximum extent down gradient and will
     not migrate significantly further.  Therefore, both the  horizontal and vertical migration of contaminants appears to
     have largely stopped. However,  the no-action alternative would not provide a mechanism to monitor the migration
     of contaminants in the future  and confirm that  further migration is  not occurring.   Additionally, the no-action
     alternative would not  guarantee that access to contaminated groundwater would be restricted.
    
     If no  action  were implemented, no action would be  taken  to reduce  or monitor  contaminant  concentrations.
     Transport modeling of the D-Area OSB DCE, PCE. TCE. and vinyl chloride contaminant plumes indicates that
                                                          70
    

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    Record of Decision for the                    N                                                WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) fU)                                                          Revision 1. Final
    Savannah River Site	                                                           August 1998
    without degradation concentrations would be reduced to below MCLs within 35 years. (Model runs that included
    degradation indicated that the maximum time required for contaminants to reach their MCLs was only approximately
    10 years.) For the purpose of cost estimating, the maximum length of time to be evaluated is 30 years, as determined
    by EPA guidance.  Therefore, the cost of this alternative would include a review of remedy every five years for 30
    years and would total 5278,000.
    
    Alternative GW-2 • Natural Anenuation/GWMZ with institutional Controls
    Under this alternative, natural subsurface processes, such as flushing, volatilization, biodegradation. adsorption, and
    chemical reaction with subsurface materials, would be allowed to continue to reduce contaminant concentrations in
    the groundwater to acceptable levels.  A  GWMZ  application has been approved by the SCDHEC  under  South
    Carolina Regulations R.61-68 as part of this alternative. This GWMZ creates a specific area at the unit that would
    be  required to meet mixing  zone concentration  limits  (MZCLs) at  plume  monitoring  wells.   Downgradient
    compliance boundary wells would be installed.  Groundwater at this compliance boundary would be required to meet
    RGOs (equivalent to MCLs).  Between the compliance boundary wells and the plume wells, intermediate wells will
    be monitored and compared to concentrations predicted by the fate and transport models. The well locations for the
    approved GWMZ are illustrated  in Figure  17.  In addition to groundwater monitoring, institutional controls will be
    maintained to restrict access to groundwater until RGOs are met in all areas of the plume.  Institutional controls
    would include:
    
    •    controlled access to SRS through existing security gates and perimeter fences
    •    signs posted in the area to indicate that  groundwater in the  vicinity of the unit has been  contaminated by
         hazardous materials
    •    deed notification to any future landowner of groundwater contamination, as required under CERCLA Section
         120(h)
    
    Although institutional controls are inclusive of the alternatives (except  the no-action alternative), the  DOE  has
    recommended that residential use of SRS land in the vicinity of D Area be prohibited (DOE, 1996); therefore, future
    residential use and potential residential water usage in this area is unlikely.   Modeling of groundwater alternatives.
    indicates that MCLs for the contaminants of concern will be  met in the D-Area OSB groundwater in approximately
     10 years. Upon confirmation that  RGOs have  been  achieved, neither the institutional controls at the unit nor the 5-
     year ROD reviews will be required any longer.
    
     Natural attenuation could effectively treat D-Area OSB groundwater. Results from bioventing testing indicate  that
     the source of groundwater contamination (the D-Area OSB soil) is abated and no longer contributes to groundwater
                                                         71
    

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    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) fU)                                                          Revision 1, Final
    SaTannah River Site	August 1998
    
    contamination.  Evidence presented in the RFI/RJ and BRA indicated that natural degradation is occurring in D-A/ea
    OSB  groundwater.   Herbert et al..  1984. report that  natural attenuation  can be selected as  a  preferred remedial
    option when the following site-specific conditions exist:
    
    •   Groundwater is unsuitable for consumptive use.
    •   Contaminants degrade quickly or are not at highly toxic concentrations.
    •   There is low potential for exposure.
    •   Active restoration is not feasible due to complex hydrogeologic conditions.
    •   There is low projected demand for future groundwater use.
    •   The unit is in close proximity to a  surface water  discharge area, with dilution to levels  that are protective of
        human health and the  environment.
    
    The RFI/RI conducted at the D-Area OSB revealed the  following:
    
    •   The source of contamination  at  the D-Area  OSB was removed  during  IRA  in conjunction with  the biovent
        testing and no longer contributes to groundwater contamination.
    •   Naturally occurring mechanisms will continue to reduce contaminant concentrations.
    •   There are no receptors of groundwater at the D-Area OSB; therefore, there is low potential for exposure.
    •   The aquifer is limited in  thickness  and  yield and is not targeted for  residential or commercial use; therefore.
        projected demand for future groundwater use is low.
    •   Modeling indicates that contaminant concentrations in the D-Area OSB groundwater would be reduced to below
        MCLs prior to discharging to  Founru'le  Branch; therefore dilution in the surface water body is not necessary to
        achieve MCLs.
    
     Based on this information the contaminants in the D-Area OSB would  be conducive to natural attenuation.
    
     Howard (1990) reports that the half-lives for PCE range from one to  two  years, for TCE range from 1.5 months to
     4.5 years, for cis-l,2-DCE range from eight  weeks to eight years, for  vinyl chloride range from eight weeks to eight
     years, and for methylene chloride range from 14 days to eight weeks. The groundwater  modeling  effort utilized
     contaminant degradation rates from the higher limit  (slower degradation)  of the range of  half-lives for each
     contaminant.  Therefore, degradation times in the  model output were  conservatively estimated to be longer than
     expected in the field.   These model  results indicate that all contaminants should  be below their respective MCLs
     within approximately 10 years. The primary conclusions of the groundwater modeling effort include the following:
    
     1.   Degradation is more  effective at removing contaminant mass than the simulated extraction wells.
    

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    Record of Decision for the                                                            WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                    Revision 1. Final
    Savannah River Site	              	August 1998
                            THIS PAGE WAS INTENTIONALLY LEFT BLANK.
                                                   74
    

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    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                         Revision 1. Final
    Savannah River Site		Auexist 1998
    2.  None of the contaminants simulated  (DCE, TCE, PCE,  and  vinyl chloride; ever reached Fournule  Branch.
        regardless of the modeled scenario.
    
    3.  Model runs that included degradation indicated that the maximum time required for contaminants to reach
        MCLs was approximately 10 years.
    
    4.  Under most scenarios  modeled (pumping, non-pumping, degradation, and no degradation), plumes  do not
        migrate beyond their current extent.
    
    According to the Ground-Water Mixing Zone Guidance Document (SCDHEC. 1997). a GWMZ application must
    demonstrate that the unit will meet the following four criteria:
    
    1.  "reasonable measures  have  been taken  or  binding commitments are made (o minimize the addition  of
        contaminants to groundwater and/or control the migration of contaminants in groundwater";
    
    2.  "the groundwater in question is confined  to a shallow geologic unit that has little or no potential of being an
        Underground Source of Drinking Water, and discharges or will discharge to surface waters without contravening
        the surface water standards set forth in this regulation";
    
    3.  "the contaminant(s) in question occurs on the property of the  applicant, and there is minimum possibility  for
        groundwater withdrawals (present or future) to create drawdown such that contaminants would flow off-site";
    
    4.  "the contaminants or combination of contaminants in question are not dangerously toxic, mobile, or persistent."
    
     A GWMZ application has been  approved by the SCDHEC that demonstrates how D-Area OSB meets these four
     criteria. Based on area characteristics and evidence presented in the GWMZ Application, a GWMZ for the D-Area
     OSB is an appropriate part of natural attenuation remedies.
    
     Based on data from monitoring wells around the D-Area OSB and groundwater transport modeling (WSRC.  1997b,
     Appendix B), remedial goal objectives  will be met and MCLs will not be exceeded beyond the  GWMZ.  This
     alternative will reduce the risks  associated with groundwater ingestion. dermal contact, and inhalation by ensuring
     that through natural GWMZ processes, the nearest groundwater receptor is not exposed to groundwater contaminated
     above MCLs.
    

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    Record of Decision for the                                                                    WSRC-RP-97-402
    D-Area Oil Seepage Basin (6J1-G) (V)                                                            Revision 1. Final
    Savannah River Site	.	August 1998
    Capital costs associated with natural attenuation would include the installation of nine new monitoring wells.  Wells
    would be sampled quarterly the first year  and semiannually thereafter.  Operation and maintenance costs  would
    include groundwater monitoring, maintenance of institutional controls, and a review of remedy every five years until
    contaminant concentrations are reduced to below their MCLs within the mixing zone. Transport modeling of DCE,
    PCE. TCE. and vinyl chloride indicates that this will be achieved  in approximately 10 years.  The total estimated
    cost associated with natural attenuation is $391,OCX).
    
    Alternative GW-3 • Bio remediation with Institutional Controls
    Under this alternative,  groundwater  would be extracted from  the leading edge of the plume, oxygen  and other
    nutrients would be added, and  then the supplemented water would be injected back into  the plume  area via injection
    wells. Institutional controls would be maintained as part of this alternative  to prohibit access to  unit groundwater
    (i.e.,  SRS security, sign posting, and deed notifications).   Groundwater monitoring would also be conducted  to
    monitor contaminant concentrations and any migration.
    
    This alternative would utilize the same natural  processes as natural attenuation, discussed in the previous subsection.
    Bioremediation would  involve the injection of oxygen and nutrients into the  subsurface, which should expedite
    natural biodegradation processes. Based on unit conditions and modeling results, bioremediation could effectively
    reduce contaminant concentrations in less than  ten years.
    
    Following addition of nutrients and oxygen, groundwater would be  injected into the aquifer. Injection would require
    a variance to inject water exceeding MCLs.
    
    Components of Alternative GW-3 include installation of new monitoring wells, a groundwater extraction system,  an
    oxygen/nutrient addition system,  and wells through which the treated groundwater would be reinjected.  Operation
    and  maintenance costs associated  with this alternative  would  include  nutrients, operation,  and  groundwater
    monitoring (quarterly the first year and semiannually thereafter). It is estimated that this remedy will take less than
    ten years to reach MCLs.  A review of remedy would be required  at five and ten years. Estimated costs associated
    with Alternative GW-3 total SI, 102.000.
    
    Alternative CW-4g - Air Sparging Hot Spot Areas/GWMZ with Institutional Controls
     Alternative GW-4a includes air sparging at the hot spot areas within the contaminant plume.  COC concentrations in
     the hot spot areas  would reduce rapidly,  allowing natural subsurface  processes, such as flushing, volatilization,
     biodegradation. adsorption, and chemical reaction with subsurface  materials  to reduce contaminant concentrations in
     the remaining contaminant plume.  Based on  physical  properties of unit contaminants, air  sparging would provide
                                                         76
    

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    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                           Revision 1, Finj»J
    Savannah River Site	August 1998
    effective treatment.  A  GWMZ would be applied for  under South Carolina Regulations  R.61-68 as pan of this
    alternative.  This would  create a specific area at the unit that would be required to meet MZCLs at plume monitoring
    wells.   Downgradient compliance wells would be installed.   Groundwater at this compliance boundary  would be
    required to  meet RGOs (equivalent to MCLs).   Between the compliance boundary wells and  the  plume wells,
    intermediate wells will  be monitored and compared to concentrations predicted by the fate and  transport models.
    Vadose zone soils and  groundwater would  be  monitored to determine contaminant removal  rates.   Institutional
    controls to restrict access to unit groundwater would be  maintained as a component of Alternative  GW-4a (i.e., SRS
    security, sign posting, and deed  notifications). Groundwater contaminant concentrations would also be monitored to
    ensure that concentrations decrease as a result of treatment and contaminants do not migrate.
    
    Costs associated with Alternative GW-4a include the labor and materials needed to construct the sparging system.
    Also included in the costs is operation and maintenance of the system and a remedy review every five years until
    clean-up levels are met. It is estimated that contaminant concentrations would be sufficiently reduced through air
    sparging in less than 10 years. Operation and maintenance would include air, soil, and groundwater monitoring, and
    operation.   Groundwater would be  sampled quarterly the first year and semiannually thereafter.  Estimated costs
    associated with Alternative GW-4a total SI.080,000.
    
    Alternative GW-4b • Air Sparging with Institutional Controls
    Air sparging would involve the injection of air into a series of wells in the area of the groundwater plume.  The air
    would migrate upward through the aquifer in the form of bubbles. The air would volatilize VOCs  and carry them up
    through and out of the aquifer, through the vadose zone, and into the atmosphere where they could be degraded (e.g..
    by photolysis).  Vadose zone soils,  as  well  as groundwater. would  be  monitored to determine contaminant removal
    rates.   Nine additional monitoring wells  would be installed as pan of  this alternative  to monitor contaminant
    concentrations in groundwater.  Institutional controls would be maintained to prevent access to  unit groundwater.
    Based on physical properties of unit contaminants, air sparging would provide effective treatment.
    
    Costs associated with Alternative GW-4b include the labor and materials needed to construct the sparging system.
    Also included in the costs is operation and  maintenance  of the system and a remedy review every five years until
    clean-up levels  are met. It is estimated that contaminant concentrations would be sufficiently reduced through air
    sparging in less than 10 years.  Operation and maintenance would include air, soil, and groundwater monitoring, and
    operation.  Groundwater would be sampled quarterly  the first year  and semiannually thereafter.  Estimated costs
     associated with Alternative GW-4b total 51,144,000.
                                                         77
    

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    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                          Revision 1, Final
    Savannah River Site	August 1998
    Alternative G^-5^_Extraciion/Strippim/Discharye with Institutional Controls
    This alternative would generally require three components: an extraction system, a treatment system, and a discharge
    system.  Institutional controls and  groundwater monitoring would also  be implemented  and  maintained  as  a
    component of this alternative.
    
                                                 Extraction Svstem
    Contaminated groundwater would be extracted using either extraction wells or interceptor trenches.  For purposes of
    this document, extraction wells will be considered the preferred extraction  technique. Selection of the appropriate
    extraction system would be determined during Corrective Measures/Remedial Design.  The objective  of extraction
    would be to capture groundwater contaminants.  Based on groundwater quality data from  the RI,  contaminants are
    limited to the upper two aquifers, which are  both located above the "green clay"  confining unit  (Figure 10).  An
    extraction system would, therefore, have wells that are screened in the upper two aquifers.
    
    Modeling of groundwater extraction indicated that  two extraction wells would be necessary downgradient of the
    plume. The extraction well located in the upper aquifer would be pumped at approximately 3 gallons per minute and
    the lower well would be pumped at approximately 2 gallons per minute. As pan of this alternative, new monitoring
    wells would be installed to confirm reduction in concentrations of contaminants.
    
    Groundwater extraction has been proven effective in containing groundwater plumes. Based on the high hydraulic
    conductivity in the impacted area of the aquifer, extraction wells would be effective at this  unit. Modeling indicates
    that clean-up levels could be reached in 9 years (with degradation) to 25 years (without degradation).
    
                                                   Air Stripping
    Air stripping is a physical process in  which volatile compounds in groundwater  are transferred  to an air stream.
    typically using a packed  tower.  Compounds with a Henry's Law Coefficient (Hc) greater than 0.01 are readily
    stripped. 1,2-DCE (cis and trans), methylene chloride, PCE, TCE, and vinyl chloride have Hcs of 0.29. 0.13. 1.08.
    0.38, and 3.4, respectively. Therefore. DCE.  methylene chloride. PCE, TCE, and vinyl chloride would  be effectively
     removed through air stripping. Air stripping would effectively treat contaminated groundwater at the D-Area OSB.
    
                                                      Discharge
     Under this  alternative, treated groundwater would  be discharged to  an existing National  Pollutant Discharge
     Elimination System (NPDES) permitted outfall  or to infiltration  galleries.   For  purposes of ihis document, it is
     assumed that treated groundwater would be discharged at the nearest existing NPDES  outfall.   Selection of the
     preferred discharge option would be conducted during Corrective Measures/Remedial Design.
                                                         73
    

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    Record of Decision for ihe                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) fU)                                                          Revision 1. Final
    Savannah River Site	August 1998
    An NPDES permit places a restriction or effluent limitation on the quantities, discharge rates, and/or concentrations
    of pollutants that may be discharged into surface waters.  Therefore, the effluent limitations specified in the existing
    NPDES permit would determine the type and extent of treatment required prior to a discharge.
    
    Costs associated with this alternative would  include the labor and materials needed to construct new monitoring
    wells, an extraction system (assumed extraction wells), an air stripping system, a discharge  line to the NPDES
    outfall, and modification  of an existing NPDES permit. Operation and maintenance costs for the system  include
    operation of the system, groundwater monitoring, maintenance of institutional controls, and a remedy review at five
    years, which is the estimated time required to meet RAOs. The estimated costs associated with  this alternative total
    SI.309.000.
    
    Vm.   SUMMARY OF COMPARATIVE ANALYSIS OF THE ALTERNATIVES
    
    Each of the remedial alternatives was evaluated using the nine criteria established by the NCP [40 CFR § 300.430 (e)
    (9)].  The criteria were derived from the statutory requirements of CERCLA Section 121, to provide the basis for
    evaluating alternatives and selecting a remedy. The nine criteria are listed below:
    
    •    overall protection of human health and the environment
    •    compliance with ARARs
    •    long-term effectiveness and permanence
    •    reduction of toxicity, mobility, or volume through treatment
    •    short-term effectiveness
    ••   implementability
    •    cost
    •    state acceptance
    •    community acceptance
    
    In selecting the preferred  alternative, the above mentioned  criteria were used to evaluate the alternatives  developed
    in the Corrective Measures Study/Feasibility Study for the D-Area Oil Seepage Basin (631-G) (U) fWSRC, 1998a).
     Seven of the criteria are  used to evaluate all the alternatives based on human health and environmental protection.
     cost, and feasibility issues.  The  preferred  alternative  is  further evaluated  based  on  the  final  two  criteria,  state
     acceptance and community acceptance.  The comparative  analysis for the five groundwater alternatives, using the
     first seven criteria, is presented in Table 6.  Brief descriptions of the nine criteria are provided below,  followed by a
     brief comparison of soil and groundwater alternatives based on the criteria.
                                                         79
    

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                                                               Table 6
                                           Comparative Analysis of Ground water Alternatives
    CA>
    O
    Criterion
    ti&tfftSlf
    Human Health
    Hnvironinent
    1 \ .-«• •' . •-,•• v. •.:•
    Compliance with AV
    Chcinicul-Specil'ic
    Luculion- Specific
    Action-Specific
    
    Magnitude of
    Rcsiiluul Risks
    Alternative GW-1
    No Action
    jJ^^}^V;^!' '-1 3SfiSH
    Protective
    Protective
    Sffl&Sfr' -^v
    Will meet MCLs
    following treatment
    Wetland Protection
    Slate air
    requirements
    NPDI-S
    modification
    IJHKBISf.''
    Contaminants
    would be removed;
    minimal residual
    risk
      Z 3.
    5-52,
                                                                                                                               •> o
                                                                                                                               »  a
                                                              Page
    

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                                                                    Table 6
                                           Comparative Analysis ol'Croumlwaler Alternatives
    ecord o
                                                                                                                                                      30  C3
                                                                                                                                                      "?!r
        Criterion
     AllcniutiveCW-l
        No Action
    Alternative CYV-2
         Natural
    Attenuation /GW
    Mixing Zone with
       Institutional
         Controls
    Alternative GVV-3
     Uioremediation
    with Institutional
        Controls
       Alternative
         GW-4a
    Air Sparging Hot
    Spols/GW Mixing
        Zone with
       Institutional
        Controls
       Alternative
         GW-4L
    Air Sparging with
       Institutional
        Controls
    Alternative GW-S
      Kxlraclioli/Air
        Stripping/
     Discharge with
       Institutional
        Controls
    r the
    W
      Adequacy of
        Controls
     No controls would
        be provided
        Institutional
       Controls and
       groundwater
        monitoring
       Institutional
        Controls,
       groundwater
       monitoring.
     process controls,
     and conventional
        equipment
        requiring
       maintenance
       Institutional
        Controls,
       groundwater
       monitoring,
     process controls,
     and conventional
        equipment
        requiring
       maintenance
       Institutional
        Controls,
       groundwaler
       monitoring,
     process controls,
     and conventional
        equipment
        requiring
       maintenance
       Institutional
        Controls.
       groundwater
       monitoring,
     process controls,
     and conventional
        equipment
        requiring
       maintenance
        1'uxicily
    No active treatment
    Reduced by natural
      attenuation; no
     active treatment
       Reduced by
      biodegradation
       Reduced by
       volatilization
       Reduced by
       volatilization
       Reduced by
      extraction and
        treatment
        Mobility
    No active treatment
    Reduced by natural
      attenuation; no
     active treatment
       Reduced by
     biodegradalion
       Reduced by
      volatilization
       Reduced by
      volatilization
       Reduced by
      extraction and
        treatment
        Volume
    No active treatment
    Reduced by natural
      attenuation; no
      active treatment
       Reduced by
     biodegradation
       Reduced by
      volatilization
       Reduced by
      volatilization
       Reduced by
      extraction and
        treatment
    Risk lo Remedial
        Workers
          None
     Minimal; workers
      protected  under
     health and safety
           plan
    Minimal; workers
     protected under
     health and safely
          plan
    Minimal; workers
     protected under
     health and safely
          plan
    Minimal; workers
     protected under
     health and safety
          plan
    Minimal; workers
     protected under
    health and safely
          plan
                                                                   I'age 2 of 3
    

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                        Table 6
    
    Comparative Analysis of Groundwater Alternatives
    Criterion
    Risk lo Community
    Risk to
    linvironmenl
    Time lo Achieve
    Remediation Goals
    Allernalive GW-1
    No Action
    i
    None
    None
    35 years
    Alternative GVV-2
    Natural
    Attenuation /GW
    Mixing Zone with
    Institutional
    Controls
    None
    Minimal;
    precautions would
    be taken
    10 years
    Alternative GVV-3
    Dioremediation
    with Institutional
    Controls
    None
    Minimal;
    precautions would
    be taken
    Less than 10 years
    Alternative
    GW-4a
    Air Sparging Hot
    Spots/GW Mixing
    Zone with
    Institutional
    Controls
    Minimal risk from
    air emissions
    Minimal;
    precautions would
    be taken
    Less than 10 years
    Alternative
    GW-4b
    Air Sparging with
    Institutional
    Controls
    Minimal risk from
    air emissions
    Minimal;
    precautions would
    be taken
    Less than 10 years
    Alternative OW-5
    Extraction/Air
    Stripping/
    Discharge with
    Institutional
    Controls
    Minimal risk from
    air emissions
    Minimal;
    precautions would
    be taken
    9 years
    1 ITCTHHrnTffiIfflP"iililllM 7 ' . v ^^'SSSSI?Sf SKI
    Ahilily iti C'onslnicl
    ami Opciiilc
    Ability lo Obtain
    Approval
    •x-^sV^i-i/^Jiaa
    Cosl^- .-•: /j!: '*>;*
    Capital Costs
    O&M Costs
    Hslinuted Years of
    O&M
    Total I'icseni Worth
    Costs
    No implementation
    ic«|iiiicil
    May cause
    regulatory or public
    concern
    mmmm
    .
    $278.000
    35
    $278,000
    Readily
    Implemented
    No concerns
    ^^HHB^^^^^^^^flBIB
    •FinVMravfTCHicnnK
    $142,000
    $299.000
    10
    $391.000
    Readily
    constructed, hut
    effectiveness during
    operation limited
    May be difficult lo
    obtain approval for
    reinjeclion
    ^ujflwm^nH^^^Q2|n
    BI^^^^B^^^^^^^^il^HEI^RSi
    ^^^•••••^•^^^Bnunj
    $594,000
    $508.000
    
                                                                                         .>o
    
                                                                                         .•"if*
                                                                                         5' i.
                                                                                         g O
                                                                                         —IJ
    

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    Record of Decision for the                                                                    \VSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                          Revision 1. Final
    Savannah River Site    	.	August 1998
    Overall Protection of Human Health and the Environment
    
    The remedial alternatives are assessed to determine the degree to which each alternative eliminates,  reduces, or
    controls  threats to human health and the environment through treatment, engineering methods, or institutional
    controls.
    
    All groundwater alternatives, except no action, would be protective of human health and the environment because
    they result in a decrease of contaminant concentrations and include institutional controls to restrict access to  unit
    groundwater. The alternatives also include monitoring to verify that contaminants do  not exceed target levels at
    compliance  boundaries  (if  applicable)  and  that  contaminant concentrations  are decreasing.  As  contaminant
    concentrations decrease,  risks to  human health  associated  with ingestion, dermal  contact, and  inhalation of
    groundwater would be prevented. The BRA determined that groundwater contaminants do not pose a significant risk
    to ecological receptors. Additionally, modeling results indicate that the nearest surface water body downgradient of
    D-Area OSB  will not receive groundwater contaminants at concentrations exceeding MCLs.   Therefore,  all
    alternatives are protective of the environment.
    
    Compliance with ARARs
    
    ARARs are federal and state environmental regulations that  establish standards  that remedial actions must meet.
    There are three types of ARARs:  (I) chemical-specific, (2) location-specific, and (3) action-specific.
    
    Chemical-specific ARARs are usually health- or risk-based  levels  or  methodologies  that,  when applied to unit-
    specific conditions, result in the establishment of numerical values. Often these numerical values are promulgated in
    federal or state regulations.
    
    Location-specific ARARs are restrictions placed on the concentration  of hazardous substances or the conduct of
    activities solely  because they are in specific  locations.  Some examples of specific locations include  floodphms.
    wetlands, historic places, and sensitive ecosystems or habitats.
    
    Action-specific ARARs are usually technology-  or remedial  activity-based requirements or limitations on actions
    taken with  respect to hazardous substances  or unit-specific conditions. These requirements are triggered  by the
    particular remedial activities that are selected to accomplish a remedy.
                                                         83
    

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    Record of Decision for the                                                                   WSRC-Rp.97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                         Revision 1. FioaJ
    Savannah River Site	                                    	August 1998
    In addition to complying with ARARs. other criteria, guidance, or proposed standards are "to be considered" even
    though they are not legally binding, because they may provide useful information or recommended procedures, when
    setting remedial objectives.
    
    Under all groundwater alternatives, contaminant concentrations in groundwater would remain above current MCLs
    (chemical-specific ARARs) for the near future, but would meet  MCLs following remediation.  However, the  no-
    action alternative would not provide monitoring to confirm when MCLs are reached.
    
    No action-specific  ARARs are associated with Alternative GW-1. Alternatives GW-2  and GW-4a would require
    compliance with  the GWMZ. Alternative GW-3 would require a variance to inject groundwater exceeding MCLs
    Such a variance may be difficult to obtain.  State air quality regulations would apply to emissions from Alternatives
    GW-4a,  GW-4b, and Alternative  GW-5, but should not be difficult to meet. Alternative GW-5 may also require an
    NPDES  permit modification, which should not be difficult to obtain.  Alternatives GW-3, GW-4a, GW-4b,  and
    GW-5 would also require construction permits, which should not be difficult to obtain.
    
    No  location-specific ARARs are associated  with  Alternative  GW-1.   The potential  location-specific  ARAR
    associated with Alternatives  GW-2, GW-3, GW-4a,  GW-4b,  and GW-5  would require  protection of  the nearby
    wetlands.
    
    Long-Term Effectiveness  and Permanence
    
    The remedial alternatives are assessed based on their ability to maintain reliable protection of human health and the
    environment after implementation.
    
     All alternatives except the no-action alternative would result  in a permanent reduction of contaminants to below
     remediation goals (MCLs) by an effective means  of treatment.  The  no-action alternative would not provide
     treatment to  reduce contaminant  concentrations  and  would result in contaminants  remaining at the  unit above
     regulatory limits.
    
     Process controls are available for Alternatives GW-3, GW-4a, GW-4b, and GW-5 that could adequately and reliably
     control each system.  Alternative GW-2 would not require any process controls.  All alternatives except no action
     would  also utilize institutional  controls and groundwater monitoring to restrict access to unit groundwater  and
     monitor treatment effectiveness, respectively.  The no-action alternative would  provide no control over existing
     groundwater contamination.
                                                          84
    

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    Record of Decision for the                                                                  WSRC-RP-97-402
    D-Arca Oil Seepage Basin (631-G) (U)                                                          Revisioo 1. Final
    Savannah River Site	                             Aueust 1998
    Reduction ofToxicitv. Mobility, or Volume Through Treatment
    
    The remedial alternatives are assessed based on the degree to which they employ treatment that reduces toxicity (the
    harmful nature of the contaminants), mobility (ability  of the contaminants  to move through the environment), or
    volume of contaminants associated with the unit.
    
    Alternative GW-1  would provide no treatment of groundwater contaminants.  Alternative GW-2 would involve
    passive treatment through natural  attenuation  processes and  would result in decreases in  contaminant toxicity.
    mobility, and volume.  Alternative GW-4a includes natural  attenuation as pan of the  active treatment alternative.
    Alternatives GW-3. GW-ia, GW-4b, and GW-5 would provide active treatment of unit contaminants to reduce the
    toxiciry, mobility, and volume of groundwater contaminants.  Each alternative would result in reaching MCLs; the
    time frames required to reach MCLs are provided in the following section.
    
    Short-Term Effectiveness
    
    The remedial alternatives are assessed  considering factors relevant to  implementation of the remedial action.
    including risks to the community during implementation,  impacts on workers, potential  environmental impacts (e.g..
    air emissions), and the time required to achieve protection.
    
    Remedial goals (MCLs) would be  met  by each alternative in the  following time periods  based on groundwater
    modeling (WSRC, 1998a, Appendix B), and professional  experience:
    
          Alternative GW-1              35  years
      •   Alternative GW-2              10 years
          Alternative GW-3             <10 years
          Alternative GW-4a           < 10 years
      •   Alternative GW-4b           <10 years
      •   Alternative GW-5              9 years
    
     Alternative GW-1 would not require any remedial actions and would, therefore, not result in any risk to remedial
     workers.  Of the remaining alternatives. Alternative GW-2  would result  in the least risk to  remedial workers and
     Alternative GW-5 would result in the most. However,  no significant risks are associated with any of the alternatives
     and compliance with the health and safety plan should protect remedial workers during implementation.
                                                        35
    

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    Record of Decision for the                                                                    WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                           Revision 1, Final
    Savannah River Site	August 1998
    Construction andjmplementaiion activities would not endanger the community for any of the aJternatives.  However.
    a minimal  risk would be associated with Alternatives GW-la. GW-4b. and GW-5 due  to air emissions from the
    treatment systems. However, compliance with air regulations would provide protection to  the community.
    
    All aJternatives except no action would involve some disturbance to the environment. This  disturbance would be
    least for Alternative GW-2 and  greatest for Alternative  GW-5. However, precautions  would be taken to minimize
    disturbance.
    
    Implementabilifv
    
    The remedial alternatives are assessed  by considering the  difficulty of  implementing the  alternative including
    technical feasibility, constructabiliry, reliability of technology, ease of undertaking additional remedial actions (if
    required), monitoring considerations, administrative feasibility (regulatory requirements), and availability of services
    and materials.
    
    All alternatives could be readily implemented with no difficulty obtaining materials or equipment.  All alternatives
    except  the no action alternative would  provide an effective means of treatment and groundwater monitoring to
    evaluate treatment effectiveness. The added effectiveness provided by injecting nutrients under Alternative GW-3
    would likely be limited  due to subsurface heterogeneities and preferential  pathways that would develop.   It would
    also be difficult  to  evaluate overall performance  because the areas of preferential pathways will have increased
    bioactivity.  None of the alternatives would preclude any further  remedial action, should it be deemed necessary in
    the future. All alternatives except no action would require approval of permits or variances.  Obtaining approval is
    not anticipated to be difficult for any of these alternatives except Alternative GW-3, which would require a variance
    to  inject  groundwater  exceeding  MCLs.    However,  obtaining  such  a variance would not  likely prevent
    implementation of the alternative.
    
    Cost
    
    The evaluation of remedial alternatives must include capital, operational, and maintenance costs. Present value costs
     are estimated within +50/-30 percent, per EPA  guidance. The cost estimates given with each alternative are  prepared
     from information available at the time of the estimate.  The final costs of the project will  depend on actual labor and
     material costs, actual site conditions, productivity, competitive market conditions, final project scope, final project
     schedule,  and other variable factors. As a result, the final project costs  may vary from the estimates presented
     herein.
                                                          86
    

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    Record of Decision for the                                                                  WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-C) (U)                                                         Revision 1. Final
    Savannah River Site  	                                                            Auzust 1998
    For ease of comparison, the total estimated present worth costs for each alternative are listed below:
    
     Alternative GW-1             5278,000
     Alternative GW-2             $391,000
     Alternative GW-3            SI,102,000
     Alternative GW^ta           SI.080,000
     Alternative GW-4b           51.144,000
     Alternative GW-5            $1.309,000
    
    State Acceptance
    
    In accordance with the FFA, the state is required to comment on and approve the RFI/RI Report and BRA, the
    CMS/FS, and the SB/PP.  State acceptance of previous documentation as listed above has been obtained. Also, state
    acceptance of the GWMZ application has been obtained, as well.
    
    Community Acceptance
    
    Community acceptance of the preferred alternative is assessed by giving  the public an opportunity to comment on the
    remedy selection process. A public comment  period was held from May 1,  1998 to June 14, 1998 during which
    comment was invited from the general public. No comments were received during this time. The ER&WM Program
    subcommittee of the  SRS CAB was given a briefing on the preferred alternatives on May 6, 1998. The ER&WM
    subcommittee was supportive of the preferred alternative and made a motion  to the full CAB at the May 18,  1998
    meeting to accept the preferred alternative.  This motion was accepted  with no opposition.  The subcommittee also
    commended the site's successful use of the bioventilation system in the remediation of the unit's subsurface soil.
    
    
    K.    THE SELECTED REMEDY
    
    The selected remedy for  the D-Area OSB deep soils is No Further Action, since RAOs have been achieved by the
     IRA and biovent testing.
    
     The selected remedy for  shallow soil, surface  water, and sediment is No Action, because no COCs in those media
     were identified in the RFI/R1/BRA.
    

    -------
    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                          Revision 1, Final
    Savannah River Site	^	August 1998
    The selected  remedy  for  D-Area  OSB groundwater  is Alternative  GW-2: Natural Attenuation/  GWMZ with
    Institutional Controls.   Under this  alternative, natural attenuation mechanisms such as biodegradation. flushing.
    volatilization,  adsorption, and hydrolysis would continue to reduce contaminant concentrations in the groundwater to
    acceptable levels. Results from the bioventing study, conducted as pan of the interim action, indicate that the source
    of groundwater contamination (i.e., the D-Area OSB soil) was abated as a result of the combined interim action and
    biovent test, and no longer contributes to groundwater contamination.  Evidence indicating that natural attenuation
    processes are occurring in the D-Area OSB groundwater was presented  in the RFI/RI Report and BRA and included:
    (1) decreased  dissolved  oxygen levels in  groundwater,  which indicates  that  microorganisms are utilizing a
    combination of the contaminants as a carbon source and oxygen within the groundwater as an oxygen  source to
    produce energy, (2) elevated chemical oxygen demand, chloride,  and sulfate levels downgradient. (3) depressed  pH
    levels in contaminated  areas, and (4) presence of breakdown products.
    
    Researchers report that natural  attenuation is appropriate for sites with certain  characteristics and emphasis on  the
    removal of the contaminant source and the ability of the specific contaminants to  naturally degrade.  Herbert et  al..
     1984, report that natural attenuation can be selected as a preferred remedial option when the following site-specific
    conditions exist:
    
         Groundwater is unsuitable for consumptive use.
    •    Contaminants degrade quickly or are not at highly toxic concentrations.
    •    There is low potential for exposure.
    •    Active restoration is not feasible due to complex hydrogeologic conditions.
     •    There is low projected demand  for future groundwater use.
     •    The unit  is in close proximity  to a surface water discharge  area,  with dilution to levels that  are protective, of
         human health and  the environment.
    
     The RFI/RJ conducted at the D-Area OSB revealed the following:
    
     •   The  source of contamination at the D-Area OSB  was removed  during FRA in conjunction  with the biovent
         testing and no longer contributes to groundwater contamination.
     •   Naturally occurring mechanisms will continue to reduce contaminant concentrations.
     •   There are no receptors of groundwater at the D-Area OSB; therefore, there is low potential for exposure.
     •   The aquifer is limited in thickness and  yield  and is not targeted  for  residential  or commercial  use; therefore,
         projected demand for future groundwater use is low.
    

    -------
    Record of Decision for the                                                                   WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) fU)                                                          Revision 1, FinaJ
    Savannah Pjyer Site	August 1998
    •   Modeling indicates that contaminant concentrations in the D-Area OSB groundwater would be reduced to below
        MCLs prior to_discharging to Fourmile Branch: therefore dilution in the surface water body is not necessary to
        achieve MCLs.
    
    Based on this information the contaminants in the D-Area OSB would be conducive to natural attenuation.
    
    The  time  required to degrade the unit-specific contaminants  was conservatively estimated through groundwater
    modeling.  The modeling indicates that all contaminants in  groundwater would be reduced below their respective
    MCLs within approximately 10 years, which is well within the time-frame that DOE plans to maintain control of the
    SRS.
    
    A GWMZ application, defined under the South Carolina Regulations R.61-68, has been approved by the  SCDHEC
    as pan of this alternative (Figure  17). Mixing  zones are considered in situations where the source of groundwater
    contamination has been removed and contaminant concentrations  are decreasing by natural  processes.  This
    alternative will  demonstrate  through  monitoring  that RAOs  will  be met,  MZCLs  (Table 7) will be achieved
    throughout the aquifer, MCLs will be achieved at the compliance boundary, and predicted concentrations will be
    achieved at intermediate wells, as described in the approved GWMZ application.  Implementation of this alternative
    involves installation of nine new wells  and monitoring of a  total  of 12 groundwater  wells.  Based on  area
    characteristics and evidence presented in the  GWMZ Application, a GWMZ for the D-Area OSB is an appropriate
    pan of a natural attenuation remedy and has been approved by the SCDHEC.
    
    The D-Area OSB is in  an industrial use zone, as identified in  Figure  3.3 of the SRS FFA Implementation  Plan
    (WSRC. 1996e), for both current and anticipated future land use.  Although  the remediation decisions for this unit
    were, based  on the industrial use scenario, the groundwater remedy will  achieve the more protective residential use
    scenario.  The  D-Area  OSB  currently meets unrestricted land use criteria for soils, sediment and  surface water.
    Groundwater beneath the unit exceeds the  MCLs.   Although institutional controls  are  included in all  of the
    alternatives (except the  no-action alternative),  the DOE has recommended that residential use of SRS land in the
    vicinity of D Area be prohibited (DOE, 1996);  therefore, future residential use and potential residential water usage
    in this area is unlikely.  Modeling of groundwater transport  processes as pan  of the evaluation of the remedial
    alternatives indicates that MCLs for the contaminants of concern will be achieved in all areas of the D-Area OSB
     groundwater after approximately 10 years. Upon confirmation that MCLs have been achieved, institutional controls
     at the unit will no longer be required.
    
     Per the EPA Region-IV LUCs Policy, a LUCAP for SRS and a LUCIP  for the D-Area OSB will be developed and
     submitted to the regulators for approval.  The LUCAP will be submitted under separate cover, whereas the LUCIP
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    Record of Decision for the                                                                  WSRC-RP-97-402
    D-Area Oil Seepage Basin (6J1-G) (U)                                                         Revision 1. Final
    Savannah River Site	                                               	August 1998
    will be submitted_wilh the RDWP/ RDR/ RAWP in accordance with the posi-ROD document schedule provided m
    Figure 13.  The LUCIP details how SRS will implement, maintain, and monitor the land use control elements of the
    D-Area OSB ROD to insure that the remedy remains protective of human health.
    
    The LUC objective necessary to ensure the protectiveness of the preferred alternative is:
    
    •   Prevent unauthorized access to the D-Area OSB contaminated zroundwater plume.
    
    The institutional controls required to prevent unauthorized exposure to the contaminated media at the D-Area OSB
    include the following:
    
    •   controlled access to the  D-Area OSB through existing SRS security gates and perimeter fences and the  site
        use/site clearance programs
    •   signs posted in  the area to indicate that groundwater  in the  vicinity of the unit has been contaminated by
        hazardous materials
    •   notification of groundwater contamination to any future landowner through deed notification, as required under
        CERCLA Section 120(h)
    
    A certified survey plat of the site  will be prepared by a registered land surveyor and will be included with the post-
     ROD documents. If D-Area OSB is transferred to non-Federal ownership prior to remediation of  the groundwater to
     the MCLs for the COCs, reevaluation of the need for deed restrictions would  be performed through an amended
     ROD with EPA and SCDHEC approval. The survey plat will be reviewed and updated, as necessary, at the time the
     site is transferred and will be recorded with the appropriate counry recording agency. The D-Area OSB is located in
     Aiken Counry.
    
     Along with the institutional controls  identified above, implementation of  the selected  remedy  will  involve  the
     placement of compliance boundary monitoring wells between the  basin and the downgradient stream and periodic
     monitoring of these compliance wells against the MCLs.  This alternative will meet RAOs.  MZCLs will be achieved
     throughout the  aquifer and MCLs will be achieved at the compliance point as described  in the approved GWMZ
     application. All monitoring, compliance, and reporting requirements to satisfy the GWMZ demonstration should be
     met in accordance with Section 5 of the approved GWMZ application.
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    Record of Decision for the
    D-Area OU Seepage Basin (631-G) (IT)
    Savannah River Site	
     WSRC-RP-97-402
      Revision 1, Final
    	August 1998
                                                     Table 7
    
                                           MZCLs and MCLs for COCs
    Constituent of Concern
    Tetrachloroethene
    Trichloroethene
    Cis- 1 .2-Dichloroethene
    1,1-Dichloroethene
    Total- 1 ,2-Dichloroethene
    Vinyl Chloride
    Benzene
    Methylene Chloride
    MZCL
    (Mg/1)
    85
    1150
    457
    7.0
    70.0
    32
    6.2
    9.5
    MCL
    (Mg/l)
    5.0
    5.0
    70.0
    7.0
    70.0
    2.0
    5.0
    5.0
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    Record of Decision for the                                                                 WSRC-RP-97--102
    D-Area Oil Seepage Basin (631-G) (IT)                                                        Revision 1. Final
    Savannah River Site	^	August 1998
    X.      STATUTORY DETERMINATIONS
    
    The selected remedy for the D-Area OSB deep soils is No Further Action, since RAOs have been achieved by ihe
    IRA and biovent testing.
    
    The selected remedy for shallow soil, surface water, and sediment is No Action, because no COCs in those media
    were identified in the R5I/R1/BRA.
    
    Based  on the findings of the D-Area OSB RI and BRA, groundwaier contaminants present a risk to human health
    through ingestion, dermal contact, and inhalation. Modeling of unit groundwater indicates that naturally occurring
    processes,  such  as  flushing,  volatilization, biodegradation, adsorption, and chemical reaction  with subsurface
    materials, would effectively reduce contaminant concentrations in groundwater to target levels within approximately
    10 years. Monitoring wells would be used to verify that MCLs are not exceeded at compliance boundaries and that
    MZCLs would not be exceeded in the area of the contaminant plumes. Institutional controls would be maintained to
    limit access to unit groundwater until MCLs are  satisfied. Natural attenuation is the most cost effective remedy for
    D-Area OSB unit groundwater.
    
    The selected remedies for all media are protective of human health and the environment, complies with federal and
    state requirements that are legally applicable or relevant and appropriate to the remedial action, and is cost-effective.
    These remedies can be easily implemented  with  minimal risk  to remedial workers,  the community,  and the
    environment. These remedies would also provide a permanent solution  to unit contamination that would not require
    any future remedial actions and satisfy the statutory preference  for remedies that employ treatment that reduces
    toxicity, mobility, or volume as a principal element.
    
    XI.     EXPLANATION OF SIGNIFICANT  CHANGES
    
    The SB/PP provides for involvement with the community through a document review process and a public comment
     period.  No comments were received during  the 45-day public comment period.  Therefore, there have been no
     significant changes to the selected remedy as a result of public comments.
    
     XII.    RESPONSIVENESS SUMMARY
    
     No comments were received during the public comment  period (May 1 to June 14, 1998).  This is indicated  in the
     Responsiveness Summary (Appendix A).
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    Record of Decision for the                                                               WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                       Revision 1, Final
    Savannah River Site	       	August 1998
    XIII.    POST-ROD DOCUMENT SCHEDULE
    
    The post-ROD document schedule, based on calendar days, is listed below and is illustrated in Figure 13.
    
    1.  The combined Revision 0 RDWP/RDR/RAWP Report for the D-Area OSB will be scoped 45 days after the
        ROD is approved, if determined by all three panics to be necessary.
    2.  RDWP/RDR/RAWP Report will be submitted to EPA and SCDHEC within 180 days of approval of the ROD.
        This report will contain the LUCIP. as pan of the submittal.
    3.  EPA and SCDHEC review of the  D-Area OSB RDWP/RDR/RAWP Revision 0 Report will be completed 90
        days from submirtaJ of the document.
    4.  SRS revision of the D-Area OSB RDWP/RDR/RAWP Report will  be completed 60 days after receipt of all
        regulatory comments.
    5.  EPA and SCDHEC fmaJ review and approval of the D-Area OSB RDWP/RDR/RAWP Revision 1 Report will
        extend to 30 days after receipt of the Rev. 1.0 document.
    6.  D-Area  OSB Remedial Action Field Stan will begin on September 3. 1999.  following  EPA and SCDHEC
        approval of the Rev 1.0 RDWP/RDR/RAWP Report.
    7.  D-Area OSB PCR/FRR Revision 0 will be submitted to EPA and SCDHEC 90 calendar days after completion
        of the remedial action.
    8.  EPA and SCDHEC review of the D-Area OSB PCR/FRR will last 90 calendar days.
    9.  SRS revision of the D-Area OSB  PCR/FRR will be completed 60 calendar days after receipt of all regulatory
        comments.
     10. EPA and SCDHEC final review and approval  of the Revision 1 PCR/FRR will  last 30 calendar days.
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    Record of Decision for the                                                           WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (IT)                                                    Revision 1, Final
    Savannah River Site	                                  	  August 1998
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    OQ
    "O
    s
    O
    a
    Q.
    c_
    n
             EPA/ SCOHEC IMM ROD
             RDWP/nOR/RAWP Rpf
                SRS 0«v»top R«v 0 ROWP/RDRAUWP Rpl
                Scop* ROWP/ROR/RAWP Rpt. (II n**d«d)
    SRS Submit R«v 0 RDWP/RDR^AWP Rpl
                EPA / SCOHEC fUvtow Rm 0 Rpl
                SRS D«v»k» Rev 1 ROWP/RDR/RAWP Rpl
                SRS SuUrtt R«v 1 ROWP/ROR/RAWP Rpl
                EPA / SCOHEC Review R«v 1.0 Rpl
                EPA/ SCOHEC Approve R«v 1.0 Rpl
             Construction Activities
                Const Activities (during, well Inst....)
                HA Field Completion
            Post-Conslr Rpl / Flnel Rem Rpl
                SRS Develop Rev 0 PCR/FRR
                SRS Submit Rev 0 PCR/FRR
                EPA/SCOHEC Review
                SRS Develop Rev 1 PCR/FRR
                SRS Submit Rev 1 PCR/FRR
                EPA/SCOHEC Review
                EPA/SCOHEC Apptovel
         ' Includes Ihe Conceplutl Conecllve Action Slielegy end UM LUCIP
                                                                                                                                                §22.
                                                                                                                                                S-22.
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    Record of Decision for the                                                            WSRC-RP-97-402
    D-Arca Oil Seepage Basin (631-G) (U)                                                    Revision 1. FinaJ
    Savannah River Site	.	                                      August 1998
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    Record of Decision for the                                                                WSRC-RP-97-402
    D-Area Oil Seepage Basin (6J1-G) (U)                                                        Revision 1, FinaJ
    Savannah River Site	                                      Aueust 1998
    XIV.    REFERENCES
    
    
    DOE, 1994. Public Involvement. A Plan for Savannah River Site.  Savannah River Operations Office, Aiken. SC.
    
    DOE, 1996.  Savannah River Site:  Future Use Project Report. Stakeholder Recommendations for SRS Land and
        Facilities. January  1996.   Cover letter:   Fiori,  Mario P..  "SRS  Future Use Project  Report  (Reference:
        Transmitial  of FinaJ Draft "Forging the Missing  Link:  A  Resource Document  for Identifying  Future  Use
        Options," Crumbly/Pearlrnan letter,  1-12-94),  USDOE  Letter EB-96-015. Savannah River Site,  Aiken.  SC.
        January 29.  1996.
    
    Daily. R.C.. D. Smith, and D. Lillian. 1992.  Streamlining Approach for Environmental Restoration (SAFER): An
        Overview.  In 1992 Waste Management and Environmental Sciences Conference, April 9-11, 1992, San Juan,
        Puerto Rico. (In Press).
    
    EPA, I989a. RI/FS Streamlining. OSWER Directive No. 9355.3-06, Washington, DC.
    
    EPA, 1989b. Risk Assessment Guidance for Superfund (RAGS) Volume I. Human Health Evaluation Manual (Pan
        A), EPA/540/1-89/002, Office of Emergency and Remedial Response, Washington, DC.
    
    EPA,  1989c.  Risk Assessment Guidance for Superfund (RAGS) Volume II. Environmental Evaluation  Manual.
        EPA/540/1-89/001. Office of Emergency and Remedial Response, Washington, DC.
    
    EPA.  1993.  Data  Quality  Objectives  Process for Superfund, Interim  Final.   Guidance, EPA540/R/93-071,
        Washington. DC.
    
    EPA, 1994. Technical Background Document for Soil Screening Guidance. EPA/540/R-94/106, Washington. D.C.
    
    EPA, 1996. Soil Screening Guidance:  Technical Bacground Document. EPA/540/R-95/128, Washington,  D.C.
    
    Herbert, R.L.. Sczurko, J.J.. and Lewis, R.A., 1984. A Case Study of Factors Favoring Natural Attenuation as the
        Preferred Alternative for Aquifer Restoration.  E. C. Jordan Company, Portland, ME.
    
    Howard, P.M.. 1990. Handbook of Environmental Fate and Exposure  Data for Organic Chemicals, Volume II
        Solvents. Lewis Publishers, Chelsea, MI.
    
    Neptune, D. et  al.. 1990.  Quantitative Decision Making in  Superfund:  A Data Quality Objectives  Case Study.
        Hazardous Materials Control. May/June 1990.
    
    Peck, R.B., 1969. North Rankinc Lecture, Advantages and Limitations of the Observational Method in Applied Soil
        Mechanics. Geotechnique 19, No. 2, pp. 171-187.
    
    SCDHEC, 1997. Ground-Water Mixing Zone Guidance Document. May 1997.
    
    •WSRC, 1993a.   Federal Facility Agreement for the Savannah River Site. Administrative Docket No. 89-05-FF.
        WSRC-RP-94-42. Westinghouse Savannah River Company. Savannah River Site, Aiken, SC.
    
    WSRC,  1993b.   RCRA Facility Investigation/RJ Program Plan.  WSRC-RP-89-994.  Rev. 1. Westinghouse
        Savannah River Company. Savannah River Site, Aiken, SC.
    
    WSRC.  1995a.   Phase  II  RFl/Rl Work Plan.  D-Area  Oil  Seepage Basin,  WSRC-RP-94-l 175, Rev.  l.l.
        Westinghouse Savannah River Company. Savannah River Site. Aiken, SC.
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    Record of Decision for the                                                                WSRC-RP-97-402
    D-Area Oil Seepage Basic (631-G) (U)                                                       Revision 1. Final
    Savannah River Site	                                    August 1998
    WSRC. 1995b.  Confirmatory  Sampling Plan for D-Area  Oil  Seepage Basin,  tt'estinghouse  Savannah River
        Company, Savannah River Site, Aiken. SC.
    
    WSRC, 1996a. Phase IV Groundwater and Soil Sampling Plan for D-Area Oil Seepage  Basin. Addendum to
        WSRC-RP-96-169, Rev.  I.I.  WSRC-RP-96-169. Westinghouse Savannah River Company.  Savannah River
        Site, Aiken. SC.
    
    WSRC, 1996b. Quality Assurance/Quality Control Summary Report for the RFI/RI Assessment of the D-Area Oil
        Seepage Basin, Phase III Soil and Croundwater Sampling Events. ESH-EMS-960002, Westinghouse Savannah
        River Company, Savannah River Site. Aiken. SC.
    
    WSRC, 1996c. Preliminary Quality Assurance/Quality Control Summary Report of the Groundwater Volatile
        Organics Analyses for the  RFI/RI Assessment of the D-Area Oil  Seepage  Basin. Phase II Expedited Site
        Characterization. Westinghouse'Savannah River Company, Savannah River Site, .Aiken, SC.
    
    WSRC, 1996d. Quality Control Summary Report for the D-Area Oil Seepage Basin Interim Remedial Action Plan.
        ESH-EMS-96-0391. Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.
    
    WSRC. 1996c. Data Summary Report for the RFI/RI Assessment of the  D-Area Oil Seepage Basin. Phase IV (U).
        ESH-EMS-96-0503, Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.
    
    WSRC. 1996f. Savannah River Site Federal Facility Agreement Implementation Plan.  WSRC-RP-94-1200, Rev 0.
        Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.
    
    WSRC, 1997a. RCRA Facility Investigation/Remedial Investigation Report and the Baseline Risk Assessment for the
        D-Area Oil Seepage Basin (631-G) (U).  WSRC-RP-96-00154, Rev.  1.1,  Westinghouse  Savannah Rjver
        Company. Savannah  River Site, Aiken, SC.
    
    WSRC, 1997b. Air Flow Evaluation Report for D-Area Bioventing Optimization Test (Phase  2). Environment
        Restoration Support, WSRC-TR-97-0104, Draft  Copy,  Wcstinghouse Savannah River Company. Savannah
        River Site, Aiken, SC.
    
    WSRC, 1997c. TEP Injection Campaign Report for D-Area Bioventing Optimization Test (Phase 2). Environmental
        Restoration Support.  WSRC-TR-97-0146. Westinghouse Savannah River Company, Savannah  River  Site,
        Aiken. SC.
    
    WSRC, I997d. Evaluation of D-Area Oil Seepage Basin Bioventing Optimization Test Sediment Samples Data.
        WSRC-TR-97-00399. Final Copy. Westinghouse  Savannah River Company, Aiken, SC.
    
    WSRC. 1997e. Post-Construction Report for D-Area Oil Seepage Basin Interim Action (IT).  WSRC-RP-96-00859.
        Rev. 1.0.  Westinghouse Savannah River Company. Aiken. SC.
    
     WSRC.  1998a.   Corrective Measures Study/Feasibility Study for the  D-Area Oil Seepage Basin (631-G) (U>.
         WSRC-RP-97-167, Rev. 1.1. Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.
    
     WSRC. I998b. Statement of Basis/Proposed Plan for the D-Area Oil Seepage Basin (632-G) (U).  WSRC-RP-97-401.
         Rev. 1.1, Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.
    
     WSRC.  1998c. Groundwater Mixing Zone Application for the D-Area Oil Seepage Basin (63J-G)(U). WSRC-RP-97-
         422, Rev. 1.1, Westinghouse Savannah River Company, Savannah River Site, Aiken, SC.
    

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    Record of Decision for the                                                            WSRC-RP-97-402
    D-Area Oil Seepage Basin (631-G) (U)                                                    Revision 1. Final
    Savannah River Site	                               August 1998
                                              APPENDIX A
                                      RESPONSIVENESS SUMMARY
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    Record of Decision for the                                                             WSRC-RP-97-402
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    Savannah River Site    		August 1998
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    Record of Decision for the                                                                WSRC-RP-97-402
    D-Area O<| Seepage Basin (631-G) (U)                                                        Revision 1. Final
    Savannah River Site        	        	   	               August 1998
                                        RESPONSIVENESS SUMMARY
    
    The public was notified of the public comment period through mailings of the SRS Environmental Bulletin,  a
    newsletter sent to approximately 3500 citizens in South Carolina and Georgia, through notices in the Aiken Standard.
    the Allendale Citizen Leader, the Augusta Chronicle, the Barnwell People-Sentinel, and The State newspapers. The
    public comment period was also announced on local radio stations.
    
    The 45-day public comment period began on May 1, 1998 and ended on June 14, 1998. However, no public
    comments were received during this period.
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