PB99-964002
EPA541-R99-020
1999
EPA Superfund
Record of Decision:
Savannah River Site (USDOE)
C Area Burning/Rubble Pit (131-C) (U)
Aiken, SC
12/23/1998
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Department of Energy
Savannah River Operations Office
P.O. Box A
Aiken, South Carolina 29802
01999
Mr. K. A. Collinsworth, Manager
Federal Facility Agreement Section
Division of Site Assessment and Remediation
Bureau of Land and Waste Management
South Carolina Department of Health and Environmental Control
2600 Bull Street
Columbia, SC 29201
Mr. J. L. Crane, Manager
SRS Remedial Project
Waste Management Division
United States Environmental Protection Agency, Region IV
61 Forsyth Street, SW
Atlanta, GA 30303
Dear Mr. Collinsworth and Mr. Crane:
SUBJECT: Submittal of the Record Copy of the Signed Interim Record Of Decision for
the C-Area Burning/Rubble Pit (131-C), WSRC-RP-98-4039, Revision. 1
Enclosed, please find a signed copy of the C-Area Burning/Rubble Pit Interim Record
of Decision for your records. SRS will make the distribution of the Administrative
Kecord file(s) and publish the notice of availability.
Please contact me at (803) 725-7032 if you have any questions.
Sincerely,
Brian T. Hennessey
Environmental Restoration Division
SRS Remedial Project Manager
BTH/HMH:kbs
OD-99-244
Enclosures
1. Interim Record of Decision for the C-Area Burning/Rubble Pit (131-C),
WSRC-RP-98-4039, Revision. 1
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MS/? 30
w -
c: A. B. Gould, DOE-ECD, 703-A
C. V. Anderson, DOE-ERD, 703-A
C. B. Warren, US EPA-IV
K. B. Feely, US EPA-IV*
J. K. Lindler, SCDHEC-Columbia
J. T. Litton, SCDHEC-Columbia
M. D. Sherritt, SCDHEC-Columbia
G. K. Taylor, SCDHEC-Columbia
SRS Administrative Record Files (Palmer, 730-2B, 1000)*
*w/enclosures
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c: A. B. Gould, DOE-ECD, 703-A
C. V. Anderson, DOE-ERD, 703-A
C. B. Warren, US EPA-IV
K. B. Feely, US EPA-IV*
J. K. Lindler, SCDHEC-Columbia
J. T. Litton, SCDHEC-Columbia
M. D. Sherritt, SCDHEC-Columbia
G. K. Taylor, SCDHEC-Columbia
SRS Administrative Record Files (Palmer, 730-2B, 1000)*
*w/enclosures
be: T. F. Heenan, 703-A
H. Thron, EM-421, DOE HQ
C. V. Anderson, 703-A
T. J. Temples, 703-A
J. J. Nelsen, 703-A
R. K. Cauthen, 730-2B
M. D. Dukes, 742-A
R. J. Steve, 730-2B
R. H. Sentelle, 730-2B
F. R. Falise, 730-2B
G. C. Blount, 730-2B
J. M. Bradley, 730-2B
M. R. Morgenstern, 730-2B
H. M. Hickey, 730-2B
T. W. Mickley, 730-2B
D. R. Earnhart, 730-2B
M. P. Wilson, 742-A
ERD Files, 730-2B, Rm. 1000*
EPD Files, 742-A (A. Odom)
*w/enclosures
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United States Department of Energy
Savannah River Site
00-31
Interim Record of Decision
Remedial Alternative Selection for the C-Area
Burning/Rubble Pit Operable Unit (131-C)(U)
WSRC-RP-98-4039
Revision 1
September 1998
SV
Westinghouse Savannah River Company *-^ =
Savannah River Site " SAVANNAH «1VE« SITE
Aiken, SC 29808
Prepared for U.S. Department of Energy Under Contract No. DE-AC09-96SK18500
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
DISCLAIMER
TTiis repon was prepared 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 service by trademark,
name, manufacturer or otherwise does not necessarily constitute or imply endorsement,'
recommendation, or favoring of same by Westinghouse Savannah River Company or by
the United States Government or any agency thereof.
Printed in the United States of America
Prepared for the
U. S. Department of Energy
by
Westinghouse Savannah River Company
Aiken, South Carolina
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INTERIM RECORD OF DECISION
REMEDIAL ALTERNATIVE SELECTION (U)
C-Area Burning/Rubble Pit Operable Unit (131-C) (U)
WSRC-RP-98-4039
Revision 1
September 1998
Savannah River Site
Aiken, 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
tOOOerwp doc MM/blb 09/18/98
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. i
September 1998 Declaration -' 1
DECLARATION FOR THE RECORD OF DECISION
Unit Name and Location
C-Area Burning/Rubble Pit Operable Unit 131-C (CBRP)
Savannah River Site
Aiken, South Carolina
The CBRP source control and groundwater 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) (FFA 1993) for the Savannah
River Site (SRS).
Statement of Basis and Purpose
This decision document presents the selected interim remedial action for the CBRP located at the SRS in Aiken. South
Carolina. The interim action was selected in accordance with CERCLA, as amended and, to the extent practicable, the
National Oil and Hazardous Substances Pollution Contingency Plan (KCP). This decision is based on the
Administrative Record File that includes all basis documents for this specific RCRA/CERCLA unit.
The proposed interim action will consist of a native soil over the CBRP pit and a vadose zone and groundwater
treatment system. The treatment system will be operated and evaluated for approximately 1 year with incorporation of
the results integrated into the final Corrective Measures Study/Feasibility Study (CMS/FS) which will include a detailed
review of remediation technologies for the final remedial action. A complete description of the action is provided in the
following sections.
This interim action, for the CBRP, is not a final action but is justified to minimize the impact of the CBRP on the
Fourmiie Branch watershed. It will be consistent with any planned future actions. A final Record of Decision (ROD)
will follow additional study by SRS, regulator approval, and public involvement and will document the final CERCLA
decision for the OU. Further, upon agreement among the U. S. Department of Energy (DOE), Environmental
Protection Agency (EPA), and the South Carolina Department of Health and Environmental Control (SCDHEC), on the
disposition of all source control and groundwater operable units within this watershed, a final comprehensive Record of
Decision (ROD) for the watershed will be pursued with further public involvement.
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Interim Record of Decision for the Remedial Alternative Selection for the WSRr-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (I31-C)(U) Savannah River Site " " R(,v i
September 1998 Declaration-'2
Assessment of the Site
Actual or threatened releases of hazardous substances from-this site, if not addressed by implementing the interim
response action scrected in this Intetfin Record* of Decision (IROD), may present an imminenl and substantial
endangcrment to public health, welfare, or the environment.
Description of the Selected Remedy
The DOE, EPA and SCDHEC have determined that an interim action principally designed to control the migration of
high concentrations of solvents, in the saturated zone, is appropriate for the CBRP. Specifically, this interim action has
two main objectives:
• Prevent direct contact with COC contaminated soils and reduce infiltration to minimize further migration of
CMCOCs to the groundwater from soils within and beneath the CBRP; and
• Treat the area in the vicinity of the pit, within the 25,000 ug/L VOC isoconcentration contour within the
groundwater, with an objective to reduce concentrations and control the migration of VOCs within the 25,000 ug/L
VOC contour.
The remedial action objectives for the interim action will be achieved by
• installing a soil cover over the source;
• performing soil vapor extraction (SVE) in the vadose zone beneath the pit; and
• performing air sparging (coupled with SVE) in the 25,000 ug/L contour of the groundwater plume
Specifically, the preferred alternatives for the Pit area at the CBRP OU arc: Alternative S-3: Native Soil Cover and
Alternative GW-3: In-Situ Air Sparging with Soil Vapor Extraction (AS/SVE). No final COCs were identified for the
Mounded Area and sofl adjacent to the-Drainage Ditch, therefore, no alternatives were developed for these areas.
The Native Soil Cover will address surficial exposure to low level threat wastes (i.e., low conceniration dioxin
contamination in the near surface pit soil and organic contamination in the deep soil) in the pit area. The alternative will
meet the sofl Interim Remedial Action Objectives (IRAOs) to prevent direct contact with final constituents of concern
• (COCs) in contaminated soils and reduce infiltration to minimize further migration of contaminant migration COCs (CMCOC)
IDOOnwp doc MM.trt> OW1ITO
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Interim Record or Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (I31-C) (U) Savannah River Site Rev. 1
September 1998 Declaration - 3
to the groundwater from soils within and beneath the CHRP. As part of the final ROD, the native soil cover would be
maintained and institutional controls will remain in place in perpetuity or until the waste no longer poses a threat to human
health or the environment.
AS/SVE will address principal threat wastes (i.e., highly concentrated TCE in the aquifer sediments immediately
adjacent to the pit in the upper zone of the water table aquifer) and VOC vadose zone contamination. AS/SVE will meet
the groundwater IRAOs to treat the principal threat area in the vicinity of the pit, within the 25,000 ug/L VOC isoconcentration
contour, with an objective to reduce concentrations and control the migration of VOCs within the 25,000 ug/L VOC contour.
Implementation of the preferred alternatives will require both near- and long-term actions. For the near term, surface
and subsurface soil contamination will be addressed by the installation of a native soil cover over the CHRP source unit.
The soil cover will be compacted to reduce infiltration, sloped to promote runoff, and will have a layer of vegetation to
prevent erosion. The soil cover will prevent future contact by workers, residents, and ecological receptors with the
dioxin contamination in the soil. The soil cover will also minimize further migration of contaminants from the soil to
the groundwater by reducing infiltration. In addition to continued inspection and maintenance of the cover, signs will be
posted at the CBRP to indicate that the area was used for the disposal of hazardous substances and existing SRS access
controls will be used to maintain the site for industrial use only.
Over a longer period of time, groundwater contamination will be addressed through controlled sparging of air into the
groundwater. The injected air will volatilize the organic compounds in the groundwater that will move into the vadose
zone and also volatilize the organic contaminants in the deep soil. Organic vapors from both the groundwater and deep
soil will be extracted from the soil above the shallow groundwater aquifer using vacuum wells connected to a soil vapor
extraction (SVE) system. The extracted soil vapors will be processed through a liquid-phase separator to remove
condensate. The offgas will then either be released into the atmosphere or treated to meet release requirements. Until
the IRAOs are achieved, groundwater monitoring will be performed.
The CBRP Corrective Measures Implementation/Remedial Design/Remedial Design Report/Remedial Action Work
Plan (CMI/RD/RDR/RAWP) post-IROD document was submitted to the regulatory agencies on June 19, 1998. The
CMI/RD/RDR/RAWP details the actions to be taken for implementing the soil cover and AS/SVE remedies including a
summary description of the scope of work for the remedial action design, monitoring requirements, a detailed
implementation/'submittal schedule for subsequent post-IROD documents, and an anticipated field activities start date.
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 Declaration - 4
Statutory Determinations
This interim action is protective of human health, and the environment and will reduce the principal threats posed by
the CBRP. Relative to its overall effectiveness with respect to the nine selection criteria established by the NCP, the
selected alternatives are cost effective. This interim action will not identify final remedial goals; but the selected
interim alternatives are consistent with the interim remedial action objectives and any final action. Pursuant to the EPA
IROD guidance (EPA 1989) and checklists, the alternative selection focused upon the key ARARs listed below which
apply to the limited scope of the interim action. The alternative selection also considered final action ARARs to ensure
the interim action is compatible. The final action will comply with Federal and State applicable or relevant and
appropriate requirements. Although this interim action is not intended to fully address the statutory mandate for
permanence and treatment to the maximum extent practicable, this interim action does utilize treatment and thus is a
furtherance of that statutory mandate.
• Fugitive Paniculate Emissions (40 CFR 50.6 and SC R61 -62.6, Section III)
• SCToxicAirPollutantregulations(SCR6I-62.1,SeaionII,paragraph3) IMl
• SC Well Construction regulations (SC R61-71)
Because this action does not constitute the final remedy for the CBRP, the statutory preference of remedies that employ
treatment that reduces toxicity, mobility, or volume as a principal element, although partially addressed in this remedy,
will be addressed by the final response action. Subsequent actions are planned to fully address the threats posed by the
conditions at the CBRP. This interim action is not designed or expected to be a final action for the groundwater, but the
selected remedy represents the best balance of tradeoffs among alternatives with respect of pertinent criteria, given the
limited scope of the action. The soil cover will likely be acceptable for the final action for soils at the unit.
SCHWMR R.61-79.124 and Section 117(a) of CERCLA, as amended, require advertisement of the draft permit
modification and the proposed plan, respectively. Because this is an interim remedial action, a permit modification is
not required to be included with this IROD. A final permit modification will include the final selection of remedial
alternatives under RCRA, will be sought for the entire CBRP OU with the final SB/PP and will include the necessary
public involvement and regulatory approvals. This IROD also satisfies the RCRA requirements for an Interim
Measures Work Plan.
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
Declaration - 5
Section 300.430 (f)(4)(ii) of the National Oil and Hazardous Substances Contingency Plan (NCP) requires that a five-
year review of a ROD be performed if hazardous substances, pollutants, or contaminants remain in the waste unit. The
SRS RCRA permit (SRS 1995 RCRA Renewal Permit, SCI 890 008 989) is reviewed every five years and was most
recently reviewed on September 5, 1995. Because this remedy will result in hazardous substances remaining on site
above health-based levels, a review will be conducted to ensure that the remedy continues to provide adequate
protection of human health and the environment within 5 years after commencement of the remedial action. Because
this is an interim action ROD, review of this site and of this remedy will be ongoing as SRS continues to develop final
remedial alternatives for the CBRP.
Date
Date
Date
Thomas F. Heenan
Assistant Manager for Environmental Quality
ergy, Savannah River Operations Office
Richard D. Green
Division Director
Waste Management Division
U. S. Environmental Protection Agency - Region IV.
R. Lewis Shaw
Deputy Commissioner
Environmental Quality Control
South Carolina Department of Health and Environmental Control
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Interim Record of Decision for the Remedial Alternative Selection for the .»-,UJ .
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 .^___ Declaration - 6
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INTERIM DECISION SUMMARY
REMEDIAL ALTERNATIVE SELECTION (U)
C-Area Burning/Rubble Pit Operable Unit (131-C) (U)
WSRC-RP-98-4039
Revision 1
September 1998
Savannah River Site
Aiken, 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
ICOOerwpdoc MM/blb 09/18/98
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-40.su
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site ncv i
September 1998
(This page was intentionally left blank)
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP 98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site n»v i
September 1998 _ .„
Page in of vi
Table of Conten^
Section _,
Page
DECLARATION FOR THE RECORD OF DECISION l
LIST OF FIGURES
LIST OF TABLES
LIST OF ACRONYMS AND ABREVIATIONS
I. SAVANNAH RIVER SITE AND OPERABLE UNIT NAME, LOCATION DESCRIPTION
AND PROCESS HISTORY ' ^"^ *""'
II. SITE AND OPERABLE UNIT COMPLIANCE HISTORY 3
III. HIGHLIGHTS OF COMMUNITY PARTICIPATION 6
IV. SCOPE AND ROLE OF THE OPERABLE UNIT WITHIN THE SITE STRATEGY 8
V. INTERIM ACTION OPERABLE UNIT CHARACTERISTICS 13
VI. SUMMARY OF INTERIM ACTION OPERABLE UNIT RISKS -. 22
VII. INTERIM REMEDIAL ACTION OBJECTIVES (IRAOS) AND DESCRIPTION OF THE
CONSIDERED ALTERNATIVES FOR THE CBRP OPERABLE 30
VIII. SUMMARY OF COMPARATIVE ANALYSIS OF THE INTERIM ALTERNATIVES 41
IX. THE SELECTED INTERIM REMEDY >,
""""**"**"""*"""""""••**•"••""••••""••«-•••••»•••••«•••• 43
X. STATUTORY DETERMINATIONS c,
"""•••••"••«-••• • *.......... 51
XI. EXPLANATION OF SIGNIFICANT CHANGES S2
XII. RESPONSIVENESS SUMMARY 52
XIII. POST-IROD DOCUMENT SCHEDULE S2
XIV. REFERENCES
" 56
APPENDIX A
• 58
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (I31-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
Page iv of vi
LIST OF FIGURES
Figure 1. Map of Savannah River Site Showing the Location of C-Area Burning/Rubble Pit . 2
Figure 2. Location of C-Area Burning/Rubble Pit 4
Figure 3. RCRA/CERCLA Logic and Documentation for the CBRP Interim Action 9
Figure 4. Revised Conceptual Site Model for the CBRP 14
Figure 5. CBRP Groundwater and Soil Sampling Locations ~ . j 6
Figure 6. CBRP TCE Plume in the Upper Water Table Aquifer , ...™ 19
Figure 7. C-Area Tritium and CBRP VOC Plumes in the Upper Water Table . 23
Figure 8. Conceptual CBRP Groundwater Remediation System . 33
Figure 9. CBRP AS/SVE Well locations and the Upper Water Table TCE Contours (ug/L)^ 47
Figure 10. CBRP Site Map Illustrating locations of Current and Proposed Monitoring Wells with
Respect to the 25,000 ug/L Contour and SVE/AS Treatment Zone . 48
Figure 11. CBRP Cross Section A-A.~ „„„........... . „.„ ........... . . ........... 49
Figure 12. Integrated Interim and Final Action Implementation Schedule 53
LIST OF TABLES
Table 1. Final Human Health and Ecological COCs and CMCOCs..
Table 2. Soil and Groundwater Interim Action Alternatives and Capital and Operations and
Maintenance (O&M) <"«»«*?*.,-.,........ .
.— 27
—.32
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
' Page v of vi
ARAR
AS
AS/SVE
bis
BRA
CBRP
CERCLA
cfm
CFR
CMCOC
CMI/RD/RDR/
RAWP
CMS/FS
coc
COPC
CPT
CRSB
CSM
DOE
DQO
EPA
FFA
FR
Ft
HpCDD
HQ
IAPP
IRAOs
IROD
M
MCL
NCP
NEPA
'NPDES
NPL
OCDD
LIST OF ACRONYMS AND ABREVIATIONS
applicable or relevant and appropriate requirement
Air Sparging
In-Situ Air Sparging/Soil Vapor Extraction
below land surface
Baseline Risk Assessment
C-Area Burning/Rubble Pit Operable Unit (131-C)
Comprehensive Environmental Response, Compensation, and Liability
Act
cubic feet per minute
Code of Federal Regulations
contaminant migration constituent of concern
Corrective Measures Implementation/Remedial Design/Remedial Design
Report/Remedial Action Work Plan
Corrective Measures Study/Feasibility Study
constituent of concern
constituent of potential concern
cone penetrometer technology
C-Reactor Seepage Basin
conceptual site model
U. S. Department of Energy
data quality objective
U. S. Environmental Protection Agency
Federal Facility Agreement
Federal Register
Feet
1,2,3,4,6,7,8 heptachlorodibenzo-p-dioxin
Hazard Quotient
Interim Action Proposed Plan
Interim Remedial Action Objectives
Interim Record of Decision
Meters
Maximum Contaminant Level
National Oil and Hazardous Substances Contingency Plan
National Environmental Policy Act
National Pollutant Discharge Elimination System
National Priorities List
octachlorodibenzo-p-dioxin
IGGOerwpdoc MM/b!b09/18/98
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
Pageviofyj
OSHA
OU
PAA
PCS
PCE
pCi/L
. pp
ppb
ppmv
RBC
RCRA
RFI
RPI/RJ/BRA
RGO
RI
ROD
SB
SCDHEC
SCHWMR
SRS
SVE
SVOC
TCDD
TCDF
TCE
TOHI
TMR
ug/Kg
«g/L
use
USSL
VOC
WSRC
LIST OF ACRONYMS AND ABRE VIATIONS
Occupational Safety and Health Administration
operable unit
Preliminary Alternatives Analysis
polychlorinated biphenyl
Tetrachlorpethylene
pico curies per liter
Proposed Plan
parts per billion
parts per million (by volume basis)
risk-based concentration
Resource Conservation and Recovery Act
RCRA Facility Investigation
RCRA Facility Investigation/Remedial Investigation Report with
Baseline Risk Assessment
Remedial Goal Option
Remedial Investigation
Record of Decision
Statement of Basis
South Carolina Department of Health and Environmental Control
South Carolina Hazardous Waste Management Regulation
Savannah River Site
soil vapor extraction
semivolatile organic compound
2,3,7,8 Tetrachlorodibenzo-p-dioxin
2,3,7,8 Tetrachlorodibenzo-p-furan
Trichloroethylene
total organ hazard index
Total Medium Risk
microgram per kilogram
microgram per liter
unit-specific constituent
unit-specific soil screening level
volatile organic compound
Westinghouse Savannah River Company
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 Page 1 of 59
I. SAVANNAH RIVER SITE AND OPERABLE UNIT NAME, LOCATION,
DESCRIPTION, AND PROCESS HISTORY
Savannah River Site Location, Description, and Process History
The Savannah River Site (SRS) occupies approximately 310 square miles of land adjacent to the Savannah River,
principally in Aiken and Bamwell counties of western South Carolina. SRS is a secured U.S. Government facility
with no permanent residents and is located approximately 25 miles southeast of Augusta, Georgia, and 20 miles
south of Aiken, South Carolina (Figure 1).
a
The Savannah River Site is owned by the U.S. Department of Energy (DOE). SRS has historically produced
tritium, plutonium, and other special nuclear materials for national defense and the space program. Chemical and
radioactive wastes are byproducts of nuclear material production processes.
Operable Unit Name, Location, Description, and Process History
The Federal Facility Agreement (FFA) (FFA 1993) for the SRS lists the C-Area Burning/Rubble Pit (CBRP),
131-C, as a Resource Conservation and Recovery Act (RCRA)/Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) unit. Consequently, the unit requires 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.
DOE is issuing this Interim Record of Decision (IROD). The DOE functions as the lead agency for SRS remedial
activities, with concurrence by the U.S. Environmental Protection Agency (EPA) and the South Carolina
Department of Health and Environmental Control (SCDHEC). The purpose of this IROD is to document the
preferred interim remedial actions for the CBRP which will consist of a native soil cover over the CBRP pit and a
vadose zone and groundwater treatment system. The cover and treatment system are detailed in Section IX.
The CBRP is located in the central pan of SRS. It is west of C-Area Reactor and north of Road A-7. Adjacent to
the road, there is a concrete Drainage Ditch. CBRP is in the Founmile Branch watershed on a ridge between two
unnamed tributaries of Fourmile Branch. At its closest point, one tributary is approximately 900 feet away.
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-Q (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
Page 2 of 59
Figure 1. Map of Savannah River Site Showing the Location of C-Area Burning/Rubble Pit
SRSBOWARt
SOUTH
CAROLINA
SOUTH
CAROLINA
GEORGIA
1. Map of Savannah River Site Showing the Location of the CBRP
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site RCV i
September 1998 Page 3 of 59
Fourmile Branch stream is located approximately 3,200 feet northwest of the CBRP and discharges into the
Savannah River fioodplain and associated swamps. Figure 1 shows the location of the CBRP in relation to other
facilities at SRS. Figure 2 shows the location of the CBRP in relation to C-Area reactor.
The CBRP was a shallow, unlined excavation (approximately 25 feet wide and 350 feet long) with depths of
approximately 8 to 12 feet. It had a volume of approximately 3,240 cubic yards. The CBRP was constructed in
1951 for use as a burning pit. During the operation of the pit, it served as a repository for organic materials (i.e.,
waste oils, wood, paper, plastics, and rubber) of unknown use or origin. Disposal records, including the chemical
composition, origin, use and volume of the disposed wastes, were not kept for this unit during its period of
operation. Disposal of combustible wastes in the pit was discontinued in 1973. At that time, the pit contents were
covered with a thin layer of soil. The pit was then used for the disposal of inert rubble and, when full, was
backfilled with soil and sediments to grade level. The pit is presently inactive (WSRC 1997a).
A Mounded Area, approximately 30 feet high, 270 feet wide, and 525 feet long, is located directly north of the
CBRP. This man-made mound contains soil and debris from the initial construction of the C-Area Reactor. It is
covered with native soils excavated to construct a large retention basin to the east of the CBRP. This Mounded
Area was not used for burning, and no known hazardous materials were disposed in this area. A Drainage Ditch
occurs to the south of the pit, paralleling Road A-7.
II. SITE AND OPERABLE UNIT COMPLIANCE HISTORY
SRS Operational History
The primary mission of SRS was to produce tritium, plutonium-239, and other special nuclear materials for U.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 to the
present. Chemical and radioactive wastes are byproducts 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.
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Interim Record oIDeoaoa for the Remedial Alternative SelectiaB far the
C-Area Bornint/Rnbble Pit Operable Unit (131-Q (U) Savannah River Site
September 1998
WSRC-RP-S8-403*
Rev.l
Page 4 of 5?
Fi jure 2. Location of C-Area Burnine/Rubble Fit
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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 SCDHEC; the permit was most
recently renewed on September 5, 1995. Part IV of the permit mandates corrective action requirements for
nonregulated solid waste management units subject to the requirements specified in Section 3004(u) of RCRA.
On December 21, 1989, SRS was included on the National Priorities List (NPL). 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 of CERCLA, DOE has negotiated a FFA (FFA, 1993) with EPA and
SCDHEC to coordinate remedial activities at SRS into a single comprehensive strategy which fulfills these dual
regulatory requirements.
Operable Unit Compliance History
As previously stated, the CBRP 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 a
Baseline Risk Assessment (BRA) were conducted for the unit berween 1994 and 1997 and the results presented in
the RFMRJ/BRA report. The RFI/RI/BRA, Rev. 1.1 (WSRC 1997a) report was submitted in accordance with the
FFA and the approved implementation schedule in December 1997. A final revision (Rev 1.3) is scheduled for
submittal in April 1999. Sufficient data has been collected to identify a high concentration (hot spot) source of
contamination under and adjacent the CBRP. Per EPA guidance, on presumptive response strategies for
ground water (EPA 1996), groundwater response actions should be implemented in a phased approach with
provisions for monitoring and evaluating their performance. Subsequently, SRS developed an SRS Early'Action
Strategy (10/21/97). Consistent with this EPA guidance and SRS's Early Action strategy, a CBRP interim action is
documented herein to install a soil cover and an In-Situ Air Sparging/Soil Vapor Extraction (AS/SVE) system to
remove principal threat wastes (i.e., high concentrations of trichloroethylene (TCE)).
An Interim Action Proposed Plan (IAPP) (WSRC 1998a) was submitted in accordance with the FFA and the
approved implementation schedule, and was approved by EPA and SCDHEC in April 1998. A presentation was
made to the Citizens Advisory Board at an open public meeting in May 1998, and the public comment period
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039 iflh
C-Area Burning/Rubble Pit Operable Unit (I31-C) (U) Savannah River Site Rev. i ^•^
September 1998 Page 6 of 59
ended in May 1998. The implementation of this interim action will be conducted concurrently with the pursuit of a
final remedial action.
HI. 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 113 and 117 of
CERCLA. These requirements include establishment of an Administrative Record File that documents the
investigation and selection of the remedial alternatives for addressing the CBRP soils and groundwater. The
Administrative Record File must be established at or near the facility at issue.
The SRS Public Involvement Plan POE 1994) is designed to facilitate public involvement in the decision-making
process for permitting, closure, and the selection of remedial alternatives. The SRS Public Involvement Plan
addresses the requirements of RCRA, CERCLA, and die National Environmental Policy Act, (NEPA 1969). The
lAPPfor the C-Area Burning/Rubble Pit (131-CJ (WSRC 1998a), which is pan of the Administrative Record File,
highlights key aspects of the investigation and identifies the preferred action for addressing the CBRP.
The FFA Administrative Record File, which contains the information pertaining to the selection of the response
•action, is available at the Atlanta EPA office and at the following locations:
U.S. Department of Energy
Public Reading Room
Gregg-Graniteville Library
University of South Carolina-Aiken
171 University Parkway
Aiken, South Carolina 29801
(803)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:
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
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September 1998 Page 7 of 59
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
SCHWMR R 61-79.124 and Section 117(a) of CERCLA, as amended, require advertisement of the draft permit
modification and any proposed remedial or interim action and an opportunity for the public to participate in the
selection of a remedial or interim action. Because this is an interim remedial action, a permit modification is
not required to be included with this IROD. The final permit modification will (1) include the final selection of
remedial alternatives under RCRA, (2) be sought for the entire CBRP Operable Unit with the final Statement of
Basis/Proposed Plan (SB/PP) and (3) will include the necessary public involvement and regulatory approvals.
This IROD also satisfies the RCRA requirements for an Interim Measures Work Plan.
The RCRA Administrative Record File for SCDHEC is available for review by the public at the following
locations:
The South Carolina Department of Health and Environmental Control
Bureau of Land and Waste Management
8901 Farrow Road
Columbia, South Carolina 29203
(803)896-4000
Lower Savannah District Environmental Quality Control Office
215 Beaufort Street, Northeast
Aiken, South Carolina 29802
(803) 648-9561
The public was notified of the public comment period through mailings of the SRS Environmental Bulletin, a
newsletter sent to citizens in South Carolina and Georgia, and through notices in \heAiken.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.
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interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
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The lAPP 30-day public comment period began on 4/17/98 and ended on 5/16/98. The lAPP was presented to the
Citizen Advisory Board in an open public meeting on 5/6/98. A Responsiveness Summary was prepared to
address comments received during the public comment period and the open public meeting on 5/6/98. The
Responsiveness Summary is provided in Appendix A of this Interim Record of Decision (IROD). It will also be
available in the final RCRA permit
IV. SCOPE AND ROLE OF THE OPERABLE UNIT WITHIN THE SITE
STRATEGY
RCRA/CERCLA Programs at SRS
RCRA/CERCLA units (including die CBRP) at SRS are subject to a multi-phase remedial investigation process
that integrates the requirements of RCRA and CERCLA as outlined in the RFI/RI Program Plan (WSRC 1993).
The RCRA/CERCLA processes are generically summarized in Figure 3. Figure 3 is consistent with the SRS ER
RI/FS Early Action Strategy (10/21/97) which was developed with regulatory concurrence.
The generic phases include (1) the investigation and characterization of potentially impacted environmental media
(such as soil, groundwater, and surface water) comprising the waste-site and surrounding areas; (2) the evaluation
of risk to human health and to the local ecological community; (3) the screening of possible remedial actions to
identify die selected technology which will protect human health and the environment; (4) implementation of die
selected alternative; (5) documentation that the remediation has been performed competently; and (6) the
evaluation of the effectiveness of the technology. The steps of this process are iterative in nature, and include
decision points which involve concurrence among the DOE (as owner/manager), the EPA and SCDHEC (as
regulatory oversight), and the public.
As outlined in Figure 3, and consistent with the above generic phases, the overall strategy for addressing the CBRP
is to (1) perform a RFI/RI to characterize the waste unit that will identify die nature and extent of contamination
and die media of concern; (2) perform a baseline risk assessment (BRA) to evaluate media of concern, constituents
of concern (COC), exposure pathways and characterize potential risks; (3) evaluate the possible remedial
alternatives and acquire community involvement in the remedial selection and document the process in die
Corrective Measures Study/Fcasibflity Study (CMS/FS) and Proposed Plan (PP); and (4) evaluate and perform a
final action to remediate, as needed, die identified media.
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Interim Record of Decision for the Remedial Alternative Selection for the
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September 1998
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Rev. 1
Page 9 of59
Figure 3. RCRA/CERCLA Logic and Documentation for the CBRP Interim Action
NO
Preliminary Evaluation '•"?•
*Unit Recorinaisarice1;?^-
. . RFI/RI Work Plan ,
',"•'.:.:'DevelopCSMvBffev.
•Develop Data Needs and \$
Quality Objective* <>«^1.
•Develop Sampling and ;J.
Analysis Plan '•'"-'
Corrective
Measures/Remedial
Action
Unit Closure/Remediation
per ROD
Unit Characterization
"Implement Work Plan .
• • Additional
Characterization
Characterization
> - Complete?
POST ROD DOCUMENTS
•Corrective Measures Design/Remedial Design Work Plan Report
•Corrective-Measures Design/Remedial Design Report
•Corrective Measures Implementation/Remedial Action Work Plan
•Post-Construction Report
I
RECORD OF
DECISION
•Select Remedy
'Document RI/FS Information
•Responsiveness Summary
•Final Permit Mods
No
Action
Remedy
Early
Action •".''
Needed?
PerSRS
RFI/RI Report
•Nature
•Extent
*Risk
*RGO/RAQ
Trealability Stud}
(If Needed)
^ Perform Early Action
•^•Interim Action Proposed Plan
**>>%-.•' 'Public Comment • .
•Interim Action ROD
•Interim Action Design
•Construction
'Operation
Statement of Basis/
Proposed Plan
•Preferred Alternative
•Draft Permit Mods.
•Public Comment
CMS/FS Report
• Identify: Response Actions,
•Technologies, Alternatives
Baseline Risk
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev j
September 1998 Page 10 of 59
The interim action described in this IROD was developed and planned concurrently with RFI/R1 process. Ficure 3
Slustrates the general decisions related to the recognition that an early action was appropriate. The following
sections succinctly describe the steps of the RFI/RI process. To date, the interim action has progressed through the
shaded areas of Figure 3 concluding with the "Perform Early Action" block.
RFI/RI Work Plan
Based on the data reviewed and collected during the unit'preliminary screening and process knowledge, a
conceptual site model (CSM) was developed to determine the contaminated media sources release mechanisms,
migration pathways, exposure routes, and potential human and ecological receptors. Section V provides the unit-
specific CSM for the CHRP OU and a summary of the characteristics of the primary and secondary sources and
release mechanisms for the units, consistent with RFI/RI Work Plan. The approved RFI/RI Work Plan for the
CBRP (WSRC 1994, WSRC 1998b) outlined the specific characterization activities for the CHRP.
Unit /Site Characterization (RFI/RI)
The primary need for the RFI/RI unit characterization is to establish unit-specific constituents (USCs) that pose
potential risk through various exposure routes and determine their distribution in source media associated with the
unit These characterization data provide the contaminant profile and mass information necessary to determine the
potential for contaminant migration to off-unit receptors. Even though characterization activities are ongoing at
CBRP, a good general understanding of the contamination is available. For a more complete discussion of the
present characterization, see Section V, and the latest revision to the RFI/RI/BRA (WSRC 1997a).
Baseline Risk Assessment
•
The intent of the BRA is to develop risk information necessary to assist in the decision-making process for
remedial sites. Because characterization is ongoing, a final risk assessment has not been completed. However, risk
can be quantified based upon known data, coupled with potential scenarios for current and future human and
ecological receptors through multiple exposure routes as identified in the CSM. A summary of the preliminary
findings of the latest revision of the BRA (WSRC 1997a) for the CBRP are presented in more detail in Section VI.
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Preliminary Alternatives Analysis (PAA)
A Preliminary Alternative Analysis (PAA) was conducted to support the development of a Corrective Measures
Study/Feasibility Study (CMS/FS) for the CBRP, which will be submitted in early 2001., The preliminary
alternative analysis was developed to eventually document the alternative selection process for a final remedial
remedy. Consequently, the preliminary alternative analysis is very complete with respect to the range of
alternatives and their consistency with final alternatives. The IAPP used the PAA as a basis for selecting
appropriate interim action alternatives for CBRP contaminated soil and groundwater. A summary of the results of
the PAA conducted for the CBRP is provided in Section VII, and a summary of the comparative analysis of the
alternatives is provided in more detail in Section VIII.
Interim Action Proposed Plan (IAPP)
The culmination of the interim response action selection process is the Interim Action Proposed Plan (IAPP). The
purpose of die IAPP 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 IAPP describes all remedial options
that were considered in detail in the PAA and explicitly identifies DOE's preliminary preferred alternative(s) for
remedial action and the rationale for the selection. The IAPP was subsequently approved by the regulatory
agencies. The basis for the selection and additional design and operational details for the approved remedy are
provided in Section IX.
Interim Record of Decision
The Interim Record of Decision (IROD) documents the interim remedial action plan for a unit and consists of three
basic components: a Declaration, the Decision Summary, and the 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 information document that provides the public with a consolidated
source of information about the history, characteristics, and risks posed by a unit, followed by a
summary/evaluation of the cleanup alternatives considered. The Responsiveness Summary presents comments
received during the public comment period (4/17/98 through 5/16/98) on the IAPP and a response to each
comment or criticism, whether submitted in writing or orally. The Responsiveness Summary for the CBRP is
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (I31-C)(U) Savannah River Site D-.. ,
September 1998 • _Pagel2of59
provided in Appendix A and an explanation of significant changes resulting from public comment is provided in
Section XI.
Records of Decision are typically accompanied with RCRA Permit modifications for SRS waste units. SRS has a
hazardous waste permit from SCDHEC (SRS 1995 RCRA Renewal Permit, SCI 890 008 989), which includes all
SRS RCRA waste units and is renewed every five years. The final ROD for the CBRP will include a RCRA
permit modification.
IROD Documentation
The post-IROD documentation consists primarily of the design documents required prior to initiating a remedial
action. Specific post-IROD documents include the Corrective Measure Implementation/Remedial
Design/Remedial Design Report/Remedial Action Work Plan, and the Post-Construction Report. A discussion of
the schedules that apply to these documents is provided in the IAPP and Section XIII of this IROD.
C-Area Interim Remedial Strategy
The CBRP is one of the OUs located within the Fourmile Branch watershed (Figure 2). Several source units within
this watershed will be evaluated to detennine impacts, if any, to associated streams and wetlands. It is the intent of
SRS, EPA, and the SCDHEC to manage these sources of contamination to minimize impact to the watershed.
During the CBRP characterization process, it was recognized that the highest concentrations of contaminants and
the contaminants with the highest risk were primarily associated with volatile organic compound (VOC)
groundwater contamination. However, it was also recognized that the full extent of the groundwater contamination
had not been completely characterized during the latest revision of the RCRA Facility Investigation/Remedial
- Investigation (RFI/RI) . Further, tritium groundwater contamination has also been identified in the vicinity" of the
CBRP but appears to be sourced from the C-Area Reactor Seepage Basin based on historical groundwater
monitoring of the C-Area Reactor Seepage Basin and the latest revision of the CBRP RFI/RI/BRA. Due to the
complexity of this unit and the current uncertainties with the hydrogeology (known tritium and VOC plumes),
farther characterization will be conducted concurrently with this interim action. In addition to the groundwater
characterization activities the potential impact to Fourmile Branch and Twin Lakes surface water and sediments
from the current release of unit contaminants is being investigated. The characterization results associated with the
CBRP will be included in the final RFI/RI/BRA Report.
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
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Concurrent with the final RFI/RI/BRA and final remedial selection remedial process, an interim action is planned
and is the subject of this document. The interim action is concordant with the SRS Early Action Strategy
(10/21/97), regulatory guidance on presumptive response strategies for groundwater (EPA 1996), and a preference
for treatment of principal threat waste.
The interim action will include the installation of an AS/SVE treatment system. The system will be operated and
evaluated for approximately 1 year with incorporation of the results into the final Corrective Measures
Study/Feasibility Study (CMS/FS) which wiil include a detailed review of remediation technologies for the final
.remedial action. A native soil cover will also be installed to act as a barrier to prevent soil exposure to future
human and ecological receptors and will also reduce precipitation infiltration to minimize the further migration of
TCE from the CBRP soils to the groundwater.
This interim action for the CBRP is not a final action but will be pursued to minimize the impact of the CBRP on
the Fourmile Branch watershed. The interim action will however be consistent with any planned future action. A
final ROD will follow additional study by SRS, regulator approval, and public involvement and will document the
final remedial decision for the OU. Further, upon agreement between the DOE, EPA, and SCDHEC, on the
disposition of all source control and groundwater operable units within this watershed, a final comprehensive ROD
for the watershed will be pursued with further public involvement.
V. INTERIM ACTION OPERABLE UNIT CHARACTERISTICS
A CSM was developed for the CBRP that identifies the primary sources, primary contaminated media, migration
pathways, exposure pathways, and potential receptors. The CSM for the CBRP is presented-in Figure 4 and is
based on the data presented in the RCRA/CERCLA documentation for these units and the latest characterization
data.
The Data Summary Reports (WSRC 1996, WSRC 1997b, WSRC 1997c) and the latest revision of the
RFI/RI/BRA Report (WSRC 1997a) contain detailed analytical data and interpretation of environmental impact for
all media samples taken in the characterization of the CBRP. The RFI/RI/BRA also includes the specific
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
4 of 59
Figure 4. Revised Conceptual Site Model for the CBRP
TRIMARY
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev i
September 1998 Page 15 of 59
methodologies for determining: Unit Specific Constituents (USCs) for nature and extent evaluations; preliminary
Contaminant Migration Constituents of Concern (CMCOCs) important for contaminant migration evaluations;
preliminary Constituents of Concern (COCs) for human health and ecological risk evaluations; and final COCs.
The data summary reports and RFI/RI/BRA are available in the Administrative Record File (See Section III).
The following sections provide a detailed discussion of the primary and secondary sources and release
mechanisms, the nature of contamination, and the extent of contamination in the vicinity of the pit. Section VI
provides a detailed discussion of operable unit risks.
Primary Sources and Release Mechanisms
The primary sources were organic liquids of unknown use and origin, waste oils, paper, plastics, and rubber
disposed in the pit during its operational history. Residual liquids are no longer present and the CBRP has been
filled to grade with nati\'e soils. The primary release mechanisms are deposition inside the CBRP and
infiltration/percolation to surface, subsurface and deep soil. There are no documented occurrences of CBRP
overflow. Disposal records, including composition, origin, and use of materials disposed were not kept for this
unit during its period of operation. These disposed materials are consistent with the constituents identified in pit
samples and visual observations made during die investigation.
Secondary Sources and Release Mechanisms
Secondary sources include surface and subsurface soil in the Pit Area. As illustrated in Figure 4, secondary release
mechanisms associated with these sources include volatilization from soil and water within the pit, fugitive dust
generation from exposed surface soil, bioric uptake, runoff and leaching to groundwater.
A detailed sampling and analysis plan was prepared and implemented to investigate these secondary sources. The
field investigations conducted from September 1994 to July 1997 included soil, groundwater, and associated
background sampling activities and provided data on the nature and extent of constituents present in soils and
groundwater. Soil and groundwater sample locations are illustrated in Figure 5. The sample analysis information
was grouped into Pit Area Soil and Groundwater (upper zone of the water table aquifer, and lower zone of the
water table aquifer). These characterization results are summarized below.
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (13I-Q (U) Savannah River Site
September 1998
Figure 5. CBRP Groundwater and Soil Sampling Locations
WSRC-RP-98-403
Rev. I
Pagel6of59
^RETENTION BASIN
* 9 * 90^-890
MOUNDED-v
AREA >^
CM ICROJNDVATER SA»«.EI
SOIL BCWIHC
ELECTRICAL LINES
SAV«HN/tN * IVEK S ITE
C-AREA BORN1WG/RUBBLE PIT
LOCATION WAP
SCALE IN FEET
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
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Pit Area Soil
To evaluate the potential effect of runoff from the CHRP, soil samples were collected from soil adjacent to the
Drainage Ditch that parallels RoadA-7 (See Figure 2). No significant contamination was identified in the
Mounded Area or the soil adjacent to the Drainage Ditch in the vicinity of the CBRP. Within the Pit Area, three
soil intervals were selected for analysis: the upper 1 foot (surface soil), the uppermost 4 feet (subsurface soil), and
from the surface to the depth of the deepest soil boring (all depths). The conclusions of these analyses indicate
soils within and beneath the pit are primarily contaminated with VOCs (principally TCE) and low concentrations
of dioxins and metals. A complete discussion of the final COCs for soils is provided in Section VI.
The pit contains a total of approximately 1,300 cubic yards of soils that are contaminated with varying
concentrations of VOCs, dioxins and metals. However, characterization data indicates that the western half of the
pit (approximately 650 cubic yards) is the area of highest TCE contamination. The maximum concentration of
TCE identified within the pit soils is 4.01 ug/L. The maximum concentration of TCE identified in soils beneath the
western portion of the pit is 286 ug/L.
The presence of TCE at higher concentration in the soils beneath the pit (compared to pit soils) indicates that
sampling did not intercept the highest concentration of TCE in pit soils. This situation is not unusual in highly
heterogeneous waste units like burning rubble pits. The presence of relatively high concentrations of TCE in the
vadose zone soils indicates that these soils may be a source of contaminants to the groundwater and should be
considered in contaminant migration modeling and probably the alternatives analysis. Because concentrations of
TCE in the vadose zone are likely to be highly variable it is difficult to estimate a volume of TCE laden soils within
the vadose zone.
Groundwater
The water table in the C Reactor Area can be subdivided into the upper and lower water table. The lower water
table is separated from the upper water table by a thin discontinuous stratigraphic unit of interbedded sands and
clayey sands. The upper water table in the vicinity of the CBRP is located approximately 60 feet below the land
surface and is approximately 20 feet thick. Sediments of the upper water table consist principally of interbedded
sand, silty sands, and clayey sands. The lower water table aquifer consists principally of less muddy sands with
higher potential rates of water flow (higher hydraulic permeabilities).
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP 98-4(m
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site •>„. ,
September 1998 ., „ •1
—*- , Page 18 of 59
Based on the results of seven groundwater sampling events between December 1995 and July 1997, several
constituents in the lower zone and the upper zone of the water table aquifer had a maximum concentration greater
than two times the average background concentration or equivalent to the Maximum Contaminant Level (MCL).
A complete list of these constituents are provided in the RFI/RI/BRA (WSRC 1997a). The characterization of the
groundwatcr in the vicinity of the pit indicates that the principal contaminants are PCE, TCE and tritium.
Figure 6 illustrates the contour of the TCE plume in the upper zone of the water table aquifer based on known well
and Cone Penetrometcr Techniques (CPT) data collected after the latest revision of the RFI/RI/BRA. The extent of
Ac plume to the northwest has not been fully characterized but is estimated based on hydraulic conductivity and
the groundwater gradients of the area. Assuming an average porosity of 0.2, the volume of impacted groundwater
depicted in Figure 6 is estimated to be 6.0 X 107gallons.
Among the contaminants in the upper zone of the water table aquifer, TCE is the most pervasive. It was measured
at a concentration of 1,660 ug/L in a monitoring well adjacent to the pit, and at concentrations as high as 130,000
ug.1. in CPT sampling locations adjacent to the pit The CPT data zn the upper zone of the xvater aquifer indicates
that maximum TCE concentrations are high enough to suggest a high probability of free phase (undissolved) TCE
in the upper water table aquifer. The free phase is likely present in the form of micro-droplets within the pore
spaces of the aquifer. In addition, the free phase TCE can be absorbed onto aquifer panicles.
Although the downgradiem extent has not been completely defined, sufficient data has however, been collected
identifying the hot spot source of contamination (e. g., >25,000 ug/L VOC). The volume of impacted >25.000
ug/L VOC groundwater is estimated to be 3.0 X Itfgallons. The hot spot source is driving an interim action while
characterization is finalized for the selection of a final ROD. The low concentrations of TCE measured
downgradiem in the lower water table aquifer well, in the vicinity of the pit, suggest that TCE has not migrated into
Hie lower zone of the water table aquifer.
The presence of a TCE plume beneath the CBRP is consistent with the soil sampling results. The presence of TCE
indicated by the elevated concentration in the vadose zone beneath the pit (at approximately 30 feet bis) indicates a
continuing potential source for TCE to migrate to the groundwater. Characterization information on the
froundwater VOC hotspot and distal plume is summarized as follows:
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Interim Record ofDecfsion for the Remedial Alternative Selection for fne '. WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. I
September 1998 Page 2i Of 59
__ . ^WMWMM. ^.^_»__.i .^—^^^
• Groundwatcr in the upper water table is contaminated with high concentrations of TCE, and lesser
amounts of tetrachlorocthylenc (PCE), dichloromcthane and tritium. TCE concentrations are hieh
enough to suggest a high probability of free-phase (undissolved) TCE in the upper water table.
• Figure 6 illustrates the distribution of TCE emanating from the Pit Area. The high concentrations arc
consistent with the presence of elevated TCE concentrations in vadose zone soils beneath the pit, as
described above.
• High groundwater TCE concentrations compared to the vadose zone maximum of 286 ug/1 indicates
free phase TCE is likely to be present in the vadose zone beneath the western end of the pit.
• Vertical migration of free-phase TCE to the lower water table is hindered by only a thin layer of
interbedded sands and clayey sands.
• Groundwater in the lower' water table is slightly contaminated with VOCs. However, the lower water
table is contaminated with relatively high activities of tritium from an upgradient source.
• Vinyl chloride (23 ug/L maximum) and chloroform (1.6 ug/L maximum) have been detected on a very
limited basis as part of ongoing CPT characterization of the distal portion of the plume. Vinyl chloride
and chloroform have not been identified in the groundwater adjacent to the pit and are therefore
probably the product of naturally occurring reductive dechlorination of TCE within the distal portion of
the plume.
Tritium detected in the groundwater at the CBRP is not consistent with contaminants found in CBRP soils above
the water table or the CSM (Figure 4). Therefore, other sources in the vicinity, such as the industrial activities in
C-Area, are thought to be contributing to groundwater contamination at the CBRP. Tritium is present at 19,400
picocuries per liter (pCi/L) in the upper zone of the water table aquifer upgradient to the Pit Area and at
significantly higher levels (94,400 pCi/L) in the lower zone of the water table aquifer at the same location. It is
also present at significantly higher levels upgradient of the Pit Area (94.400 pCi/L) than it is down-gradient of the
Pit Area, (52,800 pCi/L) in the lower zone of the water table aquifer. Side gradient (south) of the Pit Area, the
tritium concentration is 215,000 pCi/L. This indicates the tritium is from a source other than the CBRP, since the
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev 1
September 1998 . Page 22 of 59
concentrations generally decrease along the flow path and are higher in the deeper aquifer. Figure 7 illustrates the
known tritium and VOC contamination in the upper water table in the C Reactor Area.
Groundwater analytical data in general indicate an upgradient source of the tritium within the upper and lower
zones of the water table aquifer, such as the C-Arca Reactor Seepage Basin (CRSB) or C-Area industrial facilities.
Tritium activities are as high as 22,500,000 pCi/L immediately adjacent to the CRSB. As depicted in Figure 7, the
tritium plume emanating from the CRSB appears to migrate parallel to the CBRP VOC plume with a small lateral
separation between the two plumes in the vicinity of the CBRP. The two plumes converge approximately 400 feet
downgradient from the CBRP and ultimately overlap. Based on these observations, tritium in the groundwater is
not believed to be a result of past activities at the CBRP and, therefore, will not be addressed hereafter within this
IROD. The source of the tritium and its impact on the environment is, however, the subject of ongoing
characterizations (RFI/RI/BRA) of the C-Area Reactor and CBRP areas. A work plan to conduct additional
characterization of this source has been submitted. Field investigations at this unit are scheduled to begin on
June 30, 1998.
Fate and Transport Analysis
Predictive modeling techniques (i. e., SESOIL model) were used to determine whether chemicals present in the
soils of the waste unit could migrate to the groundwater at concentrations greater than the MCL or the risk-based
concentration (RBC) if no MCL is available. The predictive modeling runs were performed to simulate a potential
migration period of 1,000 years. If the potential contaminant was predicted to exceed the MCL or RBC, the
contaminant was considered a preliminary Contaminant Migration COC (CMCOC). Only TCE was retained as a
final CMCOC.
VI. SUMMARY OF INTERIM ACTION OPERABLE UNIT RISKS
As part of the unit investigation/assessment process a baseline risk assessment (BRA) was performed using data
generated during the assessment. The risk assessment was performed to: 1) systematically identify constituents of
potential concern (COPC), preliminary constituents of concern (PCOC), and final constituents of concern (COC);
and 2) assess the potential for adverse human health and ecological effects to occur from exposure to constituents
at the waste unit (without any institutional controls or remedial actions).
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
Page 23 of 59
Figure 7. C-Area Tritium and CHRP VOC Plumes in the Upper Water Table
WIOOO
N70SOO
N70000
M«00
W9000
WSSOO
N&JOCO
N67500 „
M57COO
KCSOO
WMOO
C-AREA TRITIUM AND CHRP VOC PLUMES IN THE UPPER WATER TABLE AQUIFER
LEGEND
VOC
—»oo 100 ppb VOC
—**— 20,000 ppb VOC
STREAM
-- :»— TOPOGRAPHIC CONTOUR
SEEP LINE
Tritium
—20— 20 pCi/ml Tritium
«<.ooo— 4.QOO pCi/ml Tritium
—20.000— 20.000 pCi/ml Tritium
0 TOO <00 600 BOO BOO
^ "'"• ' "'•>•*! i ~3>Z9?n
SCALE FEET
CAflVUl
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 ^ Page 24 of 59
Detailed information regarding the COC screening process, fate and transport constituents of concern (i.e.,
CMCOC), and the risk assessment process can be found in the latest revision of the RFI/RI/BRA report (WSRC
1997a). The latest version of the BRA does provide a realistic risk assessment with respect to most impacted
media; however, recent groundwater characterization data and surface water and sediment evaluations from
Fourmile Branch and Twin Lakes has not been assessed in the report. Sufficient characterization data and risk
information is, however, available to support this interim action. The human health and ecological risks for current
and future land use scenarios were evaluated and are presented below.
Human Health Risk Assessment
The human health risk assessment considered both current and future land uses and individuals likely to be
exposed. Current exposures were evaluated for an on-unit worker who may occasionally be in the area. Future
exposures were evaluated for a hypothetical industrial worker and residents. The resident scenario is the most
sensitive land use. The CBRP is located in an area that has been recommended for future industrial (nuclear) use.
(DOE 1996) Currently, .the industrial area nearest to the CBRP is the C-Area Reactor, located approximately 2,500
feet to the southeast.
Exposure parameters were based on unit-specific data and default values published by EPA. EPA methods were
used in conducting the risk assessment Soil was evaluated for ingestion, inhalation, dermal and external radiation.
Groundwater was evaluated for inhalation, ingestion and dermal contact, and produce was evaluated for ingestion.
Risks were quantified for adverse noncancer and cancer effects.
As part of the RI evaluation, if the level of a constituent in a given medium exceeds a state or federal chemical-
specific ARAR, that constituent is also included as a COC. For drinking water obtained from groundwater or
surface water, the MCL is the controlling ARAR. The preliminary COCs generated from the results of the human
health risk assessment for the Pit Area and the CBRP groundwater are detailed in the RFI/RI/BRA (WSRC 1997a).
Land Use
Current exposure was considered for the on-unit worker who may occasionally be in the area. Groundwater
exposures were not evaluated because the CBRP and surrounding area are undeveloped, and there are no drinking
water wells currently located in the surrounding area. Therefore, the risk assessment for current land use focused
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Interim Record of Decision for the Remedial Alternative Selection for the wsnr »P
C-Area Burning/Rubble Pit Operable Unit (131-C)(U) Savannah River Site **i--Kr-
jeptember 1998 Kev- *
only on soil at the Pit Area. There are no unacceptable risks for the on-unit worker. Risks for all exposure routes
are less than 1 x 10*. indicating that under current conditions carcinogenic risk from chemicals and rad,onuclides is
insignificant at the unit.
Future Use
Furore exposures were evaluated for the hypothetical industrial worker and resident. The resident scenario is the
most sensitive land use. The CBRP is located in an area that has been recommended for ruture industrial (nuclear)
use. Currently, the industrial area nearest to the CBRP is the C-Area Reactor, located approximately 2 500 feet to
the southeast Groundwater was included as pan of the risk assessment for the future land use seen,™, Soil and
the upper and lower zones of the water table aquifer were evaluated individually and are detailed below.
fit Area Snil
The characterization of the primary and secondary sources associated with the CBRP indicates the soils are
contaminated with inorganics, SVOCs, VOCs, pesticides, PCBs and radionuclides. Prelirninary COCs were
identified by comparing USCs with applicable or relevant and appropriate requirements (ARARs). analyzing for
fate and transport in the environmental setting, and assessing the human health and ecological risk. Details are
provided in the BRA portion of the latest revision of the RFI/R1-BRA (WSRC 1997a).
Upon completion of an analysis of uncertainties in the RFI/R1BRA, only the two dioxins (HpCDD and OCDD)
were retained as final COCs, for the unit resident scenario, at the Pit Area. TCE is not a risk-based COC in the
shallow soils (0 to 4 ft), but was detected in deeper soils as a contaminant migration constituent of concern
(CMCOC) (i.e.. soils contaminated with TCE at sufficient concentrations to continue to be a migration threat ,o
groundwater via precipitation infiltration). Those constituents retained as final COCs and CMCOCs and their risks
are listed in Table 1 and are detailed in the latest revision of the RFI/RI/BRA (WSRC 1997a).
Upper Zone of the Wa^r Tahle Aq»,-frr
The ongoing RFI/RI investigation determined the groundwater in both the upper and lower zones of the water table
aquifer at the CBRP is contaminated. For the upper zone of the water table aquifer, the human health risk
evaluation identified preliminary COCs for the hypothetica, ton on.Unit resident and for the hypothetical future
on-un,t mdustria. worker. Those groundwater constituents wh.ch were retard as preliminary COCs are detailed
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 Page 26 of 59
in the latest revision of the RFI/RI/BRA (WSRC 1997a). In the uncertainty analysis, PCE and TCE were retained
as final COCs for the future resident scenario. TCE was retained as a final COC for the future industrial worker
scenario. Dichloromethane was not identified as a human health COC but was retained as a final COC for
exceedance of the MCL. These final human health COCs and their risks are listed in Table 1.
Lower Zone of the Water Table Aquifer
The ongoing RFI/RI investigation determined the groundwater in both the upper and lower zones of the water table
aquifer at the CBRP is contaminated. For the lower zone of the water table aquifer, the human health risk
evaluation identified preliminary COCs for the hypothetical future on-unit resident and for the hypothetical future
on-unit industrial worker. Those groundwater constituents which were retained as preliminary COCs are detailed
in the latest revision of the RFI/RI/BRA (WSRC 1997a). Upon completion of the uncertainty analysis, only tritium
was retained as a final COC for the lower zone of the water table aquifer. However, as discussed in Section V, the
source of the tritium is upgradient of the CBRP and is believed to be from the C-Reactor Seepage Basins (CRSB).
Because tritium is not sourced from the CBRP, it is not a final COC for the CBRP. As no final COCs are sourced
from the CBRP. no remedial actions for the lower zone of the water table aquifer were recommended by the CBRP
Interim Action Proposed Plan (WSRC 1998a).
Ecological Risk Assessment
The ecological risk assessment defined the likelihood of harmful effects or the risk to ecological receptors from
exposure to contaminants at the CBRP. Receptors include both terrestrial plants and animals and their habitats.
Constituents in the upper 4 feet of soil were screened because this medium was the principal one resulting in
exposures to plants and animals. Based on characterization of the environmental setting and identification of
potential receptor organisms, a CSM was developed to determine the complete exposure pathways through which
ecological receptors could be exposed to COPCs.
The ecological risk assessment was completed for two scenarios. The current land use evaluated potential effects
only from exposure to the top 1-foot of soil in CBRP. Evaluation of the effects of the future land use scenario
considered the soil interval from the surface to a depth of 4 feet. Upon completion of the uncertainty analysis, only
HpCDD in the Pit Area was retained as a final ecological COC for shrews in surface soils.
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-403S
Rev. 1
Page 27 of 59
TABLE 1. FINAL HUMAN HEALTH AND ECOLOGICAL COCS AND CMCOCS
Media
Soil
Groundwater
Unit
Pit Area
Mounded Area
Soil adjacent to
Drainage Ditch
Jpper zone of the
water table aquifer
.o%verzone of the
water table aquifer
COCs*
TCE
OCDD ***
1,2,3,4,6,7,8-
HpCDD ***
None
None
TCE
PCE
Dichloromethane
^Jone
Basis/Receptor
Migration to groundwater
Risk to future resident
Risk to future resident
Ecological risk to small
burrowing animals (i.e., shrew)
NA
NA
R.isk to future resident;
risk to future worker;
exceedance of MCL
lisk to future resident;
exceedance of MCLs
Exceedance of MCL
NA
Risk/Hazard
Quotient
**
4x10-*
3xlO-6
NA/14.3
NA
NA
4x1 (r1 — /20
6x1 0-5 72.7
IxlO'6
*****
NA
NA « Not Applicable
•Note: Tritium was identified as a contaminant in the upper water table (up and sidegradient of the CBRPl but is not considered a COC
because it is not sourccd from the CBRP. Tritium and PCE were identified as contaminants in the lower water table (upgradient of the
CBRP) but are not considered COCs because they are not sourced from the CBRP.
"CMCOC. based upon exceedance of MCL. not risk-based.
•••Risk tor future industrial worker does not exceed 1 x 10"". The highest residential risk from either the surface of the subsurface soils is
listed above in Table 1. Risk for HpCDD in the subsurface soils (0-T) is 1.7 x 1Q-*. Risk for OCDD in the surface soils (0-1') is 3.4 x 10"
•—This table is based upon 1997 monitoring well data only. 1998 CPT data indicates maximum TCE concentrations are at 130,000
ug/L. Assuming this preliminary unvalidated CPT data would not be screened from risk protocols, a risk Of 3 x 10:: would be projected.
*»***COC due to exceedance of MCL, but not a risk-based COC.
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 Page 28 of 59
Risk Conclusions
The overall conclusions of the BRA include the following:
• Mounded Area soils and the soil adjacent to the Drainage Ditch do not pose a significant risk to
hypothetical human or ecological receptors, and, therefore, do not require remedial action. These areas
are, therefore, dropped from further discussion within this IROD.
• Low concentrations of dioxins in soils within and beneath the pit pose minimal human health and
ecological risks. Dioxin is a risk-based COC.
• TCE is not a risk-based COC in the shallow soils (0 to 4 feet), but was detected in deeper soils as a
contaminant migration constituent of concern (CMCOC) (i.e., soils contaminated with TCE at sufficient
concentrations which allow them to continue to be a migration threat to groundwater via precipitation
infiltration).
• Groundwater in the upper water table is sufficiently contaminated with VOCs so that it represents a
significant risk to human health, with TCE concentrations over 5,000-times the drinking water standard
andMCLof5ug/L.
Contaminant Threat Review
A review of the final human and ecological COCs present within the soils and groundwater at the CBRP indicate
that the wastes represent low-level and principal threat wastes. The contaminants within the soils and groundwater
can be categorized as follows:
• Low concentrations of dioxins and metals in surface soils are thought to be a low level threat waste
because the material represents relatively low risks to humans and moderate risks to the ecology, has a
low potential for migration, and is easily contained
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C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site »„,. i
September 1998 Page 29 of 59
• Based on current data presented in Table 1, the relatively low concentrations of VOCs in soils within
and beneath the pit appear to be low-level threat waste because they do not pose a risk to human or
ecological receptors, have a low potential for significant migration (based upon contaminant migration
modeling) and are easily contained. However, based upon high groundwater concentrations, principal
threat waste is probably present in the vadose zone which the proposed interim action should address.
• The highly concentrated TCE in the aquifer sediments immediately adjacent to the pit in the upper zone
of the water table aquifer arc thought to represent a principal threat. The risk to humans from TCE in
the groundwater is thought to be significantly higher than those presented in Table 1, which were based
on the then available 1997 monitoring well data. Preliminary unvalidated 1998 CPT data indicates
maximum TCE concentrations are at 130,000 ug/L versus the 1997 monitoring well data of 1,660 ug/L.
Assuming this preliminary unvalidated CPT data would not be screened from risk protocols, a
Significantly higher risk would be projected. The high concentrations of TCE (130,000 ug/L) are
thought to suggest the presence of free-phase TCE which is potentially mobile.
In conclusion, SRS believes that interim remedial actions should be considered for the >25,000 ug/L VOC areas of
the groundwater plume and vadose zone in an effort to minimize the further migration of this principal threat. A
thorough discussion of the specific remedial action objectives is provided in Section VII.
The actions suggested in this IROD (Section IX) are consistent with a bias for treatment of principal threat
materials because
• treatment technologies are feasible and available in a reasonable time frame;
• the small volume and simplicity of the site make implementation technically and economically
practicable;
• implementation of the treatment does not increase the risks to humans (includ.ng workers and the
surrounding community) or the environment; and
• implementation win not result in severe effects across environmental media.
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C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
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VII. INTERIM REMEDIAL ACTION OBJECTIVES (IRAOS) AND
DESCRIPTION OF THE CONSIDERED ALTERNATIVES FOR THE CBRP
OPERABLE
Interim Remedial Action Objectives
The IRAOs are specific early action goals developed to reduce risk to human health and the environment. These
interim goals are used to ensure that the selected interim remedial alternatives will impact exposure pathways and
media in a fashion that will reduce risk to human health and the environment. This IROD uses the interim
remedial action objectives to initially evaluate the applicability of the remedial alternatives. IRAOs specify unit-
specific contaminants, media of concern, potential exposure pathways, and remediation goals. The IRAOs are
based on the nature and extent of contamination, threatened resources, and the potential for human and
environmental exposure.
Based upon the human health, ecological, and contaminant migration risks (see Table 1) posed by the dioxins in
the subsurface soil and the TCE in the deep soil of the Pit Area, the general soil IRAQ is to:
• prevent direct contact with COC contaminated soils and reduce infiltration to minimize further
migration of CMCOCs to the groundwater from soils within and beneath the CBRP.
The largest contribution to groundwater hazards is from TCE in both the future resident and future industrial
worker scenarios (see Table 1). PCE poses significant risk in the future resident scenario only. Although
dichloromethane poses no significant risk to human health, it is a COC to be remediated because concentrations
in the shallow groundwater exceed the MCL. Based on the risks posed by these VOCs in the shallow
groundwater, the general groundwater IRAQ is to:
• treat the area in the vicinity of the pit, within the 25,000 ug/L VOC isoconcentration contour, with an
objective to reduce concentrations and control the migration of VOCs within the 25,000 ug/L VOC
contour.
As previously stated, this IROD is tailored to the limited scope and purpose of the interim action and does not
specify the final acceptable exposure levels for the site. Specifically, this IROD will not identify final remedial
goals; but the selected interim alternatives.will be consistent with the IRAOs and any final action. The interim
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action RAOs will be used to develop the final action RAOs as more information from the ongoing RF1/R1/BRA
and planned interim action operations concerning the unit and potential remedial technologies becomes available.
Remediation goals will ultimately be determiaed as part of the final remedial action determination and will
establish acceptable exposure levels that are protective of human health and the environment (CERCLA
300.430
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WSRC-RP-98-4039
Rev.l
Page 32 of S9
TABLE 2. SOIL AND GROUNDWATER INTERIM ACTION ALTERNATIVES AND CAPITAL
AND OPERATIONS AND MAINTENANCE (O&M) COSTS*
S-l
S-2
S-3
S-4
S-5
GW-1
GW-2
GW-3
GWJ
GW-5
ALTERNATIVES
CAPITAL COST
(SK)
O&MCOST
(SK)
SOIL
No Action
Institutional Controls
Native Soil Cover**
Thermal Desorption/Incineration
OfTsite Disposal
0
0
175
548
785
0
61
20
200
0
GROUNDWATER
No Acrion
Institutional Controls
In-Situ Air Sparging** (w«h SVE)
In-Sim Methane Biocegradarion (with SVE)
Ex Situ Air Snipping (pump and treat)
0
347
800
UOOO
500
0
60
UQO
1.500
700
TOTAL COST
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The No Action alternative would not be protective of human health or the environment, would not eliminate
potential future routes for human exposure, and would not be protective of human health because of the potential
for soil exposure to a worker, and would not provide control of leaching of contaminants to ground water. The No
Action alternative would require no construction and could, therefore, be implemented immediately. The
estimated cost associated with the No Action alternative is SO.
Alternative S-2: Institutional Controls
Institutional controls are administrative measures taken to minimize the potential for human exposure.
Administrative institutional controls consist of filing deed restrictions or notifications and performing 5-ycar
remedy reviews. Deed restrictions and notifications inform potential future buyers or developers of the hazardous
waste disposal activities previously conducted at the unit and limit the types of future activities that could be
conducted on the property (e.g., restrictions on excavation and land use).
Institutional controls arc effective in further minimizing the potential for human exposure to CBRP contaminants
and arc relatively easy to implement. In addition, costs associated with institutional controls are considered low
relative to other remedial responses. Institutional control costs include surveying, filing deed restrictions or
notifications, and preparation of 5-year remedy reviews. Five-year remedy reviews are required for any waste site
that has provisions that prevent unrestricted land use or leaves wastes in place. Under the alternative, the soils
within and below the pit would continue to be an ecological risk and a source of TCE groundwater contamination.
The estimated cost associated with the alternative is 561,300.
Alternative S-3: Native Soil Cover
This alternative consists of placing a layer of clean soil over the entire surface area of the CBRP. This additional
byer of soil will act as a barrier to prevent soil exposure to future human and ecological receptors and will also
reduce precipitation infiltration to minimize further migration of TCE from the CBRP soils to the groundwater.
Therefore, this alternative satisfies the remedial action objectives and would be protective of human health and the
environment by forming a physical barrier to prevent ingestion and direct exposure to contaminated soil.
A low permeability engineered cover would be sufficient to minimize infiltration, intrusion, and surface erosion.
"Re cover design would be approved by both EPA and SCDHEC prior to construction. The cover would include
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an area of approximately 0.6 acres (27,000 square feet). A soil cover is a performance-based engineering approach
since it does not reduce the total mass of COCs.
The thickness of the soil cover is determined by the contaminants present in the waste unit, the potential impact to
groundwater, and the future land use proposed for the waste unit. Subject to final design development and
approval, the soil cover will be a two-layer system consisting of a compacted sandy clay layer and a vegetative
layer placed on top. The vegetative layer would be maintained to prevent erosion from wind or rain. Thickness of
the sandy clay layer will be a minimum thickness of 2 feet.
Hydraulic conductivity will be approximately 1.0 x 10'5 cm/sec. The surface slope of the cover will be a minimum
of 3 percent and a maximum of 5 percent Side slopes will be no steeper than 4:1 (H:V). A minimum 6-in
vegetative layer will be added to minimize soil erosion of cover. Infiltration will be reduced by no less than 60
percent. The cover would greatly reduce the leaching of soil contaminants to the groundwater, where MCLs would
be exceeded; but the deep soils (4 to 60 feet) below the pit would continue to be a source of TCE groundwater
contamination. As part of the final ROD, the native soil cover would be maintained and institutional controls will
remain in place in perpetuity or until the %vaste no longer poses a threat to human health or the environment.
Costs associated with Alternative S-3 include labor and materials to install the earthen cover and to implement
institutional controls common to all soil alternatives. Costs also include operation and maintenance costs of the
cover and institutional controls. The estimated cost associated with this alternative is $ 194,800.
Alternative S-4; Thermal Desorption/Incinerarjon (with Compacted Backfill Covert
Dioxin risks were shown for the 0 to 1.2 m (0 to 4 feet) soil layer; thus, this layer would need to be remediated.
This option consists of removing the upper 1.2 m (4 feet) of soil, passing it through a rotary kiln to vaporize
' (desorb) the dioxins present. The vapor stream is sent through an incinerator that decomposes dioxins to harmless
materials. The remediated soil can be returned to the CBRP and the unit can be released for unrestricted use.
The compacted backfill would be sufficiently impervious to mitigate infiltration and promote runoff of surface
water. Two feet of native soil would be loosely placed over the compacted backfill. The Pit Area would be seeded
to revegetate the unit. Erosion control measures would be implemented until vegetation became established.
Administrative controls similar to those of Alternative S-3 would be implemented.
lOOOcrwp doc MM/blb W/18/98
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Interim Record of Decision for the Remedial Alternative Selection for the
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WSRC-RP-98-4039
Rev. 1
Page 35 of 59
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Altemanve S-5 wouM invo,ve exc^vaSon of con^-eo surf,,, and subsurfilce soi,s wnM, ,he Pi, Area and
Sh,pn,e»t oflsite to a ,ic™sed d.sposa, facfli^. The excavated soil »ou,d cite be phced di«c«v inK limi and
eovered hau, mcks or inu, hned »d seated c^taine. fo, ™spon. Tne soi, ma „ racarace(1 „ . „
fat The excavated a™ v^H be baited «* »a,ive soi, fton, a ,oca, bomiv pit C.nmrtn.^ „
»»n the e.xc,va«d , fee, depths . insipnHcan, „ „„,»„ ^ ana eco,ogica, .sfe howeve,. u«v do presen, a
leac U.S concern. To p«ven, sig.if.can, .caching of ^nunams ,o fte g™™,^, fte »ave soi, backfi,,
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 ' ^ Page 36 of 59
Alternative S-5 would be protective of human health and the environment. Virtually all of the contamination
present in Pit Area surface and subsurface soils to a depth of 4 feet would be permanently removed from the unit.
Removal of the Pit Area soil would eliminate the hazardous source material, thereby eliminating risk to future
residents and ecological receptors. Tne deep soils (4 to 60 feet) below the pit would continue to be a source of
TCE groundwater contamination.
Alternative S-5 is implementable. Construction would involve the use of available materials and conventional
earth-moving equipment. The cost for this alternative includes excavation, transportation, and waste disposal of
the contaminated soil (i.e., top 4 feet). Estimated present worth cost associated with Alternative S-5 is
prohibitively expensive at $785,400.
Groundwater Alternatives
Alternative GW-1; No Action
Under this alternative, no remedial efforts would be conducted to remove, treat, or otherwise lessen the toxicity,
mobility, or affected volume of contaminated media. This alternative assumes that the unit would potentially be
released for unrestricted use. The No Action alternative would not be protective of human health or the
environment and would not eliminate potential future routes for human exposure. Potential future releases are not
reduced or eliminated. The unit would continue to be a source of contaminated groundwater and would not
provide protection of the environment at points of exposure. The No Action alternative would require no
construction and could, therefore, be implemented immediately. The estimated cost associated with the No Action
alternative is SO.
Alternative GW-2: Institutional Controls
Under this alternative, a monitoring program for groundwater would be implemented. The monitoring program
would monitor the rate of attenuation of contamination at the site from natural processes such as degradation and
dispersion. The nearest point of exposure is determined to be at the nearest point of discharge to the surface
streams (a tributary of the Fourmile Branch). Monitoring would continue until contaminant concentrations reach
acceptable levels as defined by remediation goals.
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Interim Record of Decision for tbe Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. i
September 1998 Page 37 of 59
Existing SRS institutional controls would prevent exposure of environmental or human receptors to contaminants
by enforcing land use and groundxvater use restrictions. The existing SRS institutional controls would also restrict
access by the public to the area affected by the waste unit contamination.
Alternative GW-2 would be protective of human health and the environment. Over rime, as the VOCs decay and
concentrations lessen through dispersion, the risk to human health and the environment would decrease. However
as a stand-alone alternative, biodegradation, volatilization, and dispersion would potentially not decrease
contaminant levels to acceptable levels in a reasonable amount of time.
Alternative GW-2 would require no construction of groundwatcr monitoring wells other than the installation of the
six "point of compliance" wells. No specialized equipment or technical specialists would be required for
installation, and laboratories are readily available to perform the required analyses. The remedy coald be
implemented immediately. Costs associated with Alternative GW-2 include labor and materials to install the six
monitoring wells and conduct the required groundwater monitoring and associated administrative controls.
Although this alternative would be performed indefinitely, the costs arc estimated for 30 years. A 5-year remedy
review is required. The estimated cost associated with the alternative is S406.600.
Alternative GW-3: In-Situ Air Sparging (with Soil Vapor Extraction^
In-Situ Air Sparging (with Soil Vapor Extraction), conceptually depicted in Figure 8, would involve operation of
an air sparging system that -would inject air into the bottom of the contaminated groundwater plume. The
contaminants would then pass into the injected air, as it moves upward through the plume and, in turn, would flow
into the relatively dry sofl (vadose zone) above the water table. These volatilized groundwater VOCs would be
extracted via vacuum wells by a sofl vapor extraction (SVE) system as they rise into the vadose zone.
Additionally, VOCs residing in the vadose zone (see Figure 8) would also be extracted via these same vacuum
wells. The extracted soil vapors would be processed through a liquid-phase separator to remove condensate. The
offgas would then either be treated or released into the atmosphere in accordance with release requirements.
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98^039
Rev. 1
Page 38 of 59
Figure 8. Conceptual CBRP Groundwater Remediation System
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. I
September 1998 Page 39 of 59
Institutional controls would involve the installation and maintenance of long-term monitoring systems for
groundwatcr to monitor the rate of attenuation of organic contamination at the site. Monitoring would be similar to
that described for Alternative GW-2, except that soil vapor monitoring would be conducted as part of the SVE
system operation.
Alternative GW-3 would be protective of human health and the environment by removing VOCs from the shallow
groundwater. The estimate for this alternative assumes a 5-year period of operation of the in-Situ Air
Sparging/Soil Vapor Extraction (AS/SVE) system. Installation would involve straightforward construction
processes readily implementable in a relatively short time frame. Construction would involve the use of available
materials from commercial vendors and the use of conventional equipment In-situ AS/SVE has been commonly
used at other hazardous and mixed waste sites.
Installation of the AS/SVE system is targeted to remove high concentrations of TCE that could be in a free phase,
in the upper water table. The AS/SVE system will prevent rapid migration from the upper water table to the lower
table and will be consistent with the IRAOs. The use of AS/SVE to volatilize and extract the VOCs in the upper
water table will not result in significant releases of tritium to the environment or radiological hazards to workers
because the tritium activities are very low. The relatively high activities of tritium associated with me CRSB are
principally sidegradient of the CBRP and will not effect remedial operations.
Costs associated with Alternative GW-3 include labor and materials to install the extraction wells and injection
points, blowers, and an offgas control system. Also included is the cost for the operation and maintenance of the
AS'SVE system for a 5-year operation and maintenance period. The estimated cost associated with the alternative
is 52,000,000. A more thorough discussion of this alternative with respect to the interim action is provided in
Section IX.
Alternative GW-4; In-Situ Methane Biodegradation with fSoii Vapor Extraction!
Alternative GW-4 would involve operation of a faioremediatioa'SVE system and the installation of associated wells
in the Pit Area. Alternative GW-4 would be similar to Alternative GW-3 in that it would involve installing air
sparging points and SVE wells. The primary difference between the alternatives is that GW-4 would introduce a
methane and oxygen (air) mixture into the ground to enhance methanotrophic biological degradation of the
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
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—f- ; Page 40 of 59
chlorinated solvents by co-metabolism. This enhanced biodcgradation would accelerate remediation over natural
attenuation and AS/SVE by themselves.
Institutional controk would involve the installation and maintenance of long-term monitoring systems for
groundwater to monitor the rate of attenuation of organic contamination at the site. Monitoring would be similar to
that described for Alternative GW-2, except that soil vapor monitoring would be conducted as pan of the SVE
system operation.
Alternative GW-4 would protect human health by substantially reducing the volume of contaminants in
groundwater by degrading and removing fte VOCs. In-Situ Methane Biodegradation'SVE would involve
straightfom-ard construction processes leadfly implementable in a relatively shon time frame. Construction would
involve to use of avauable materials from commercial vendors and the use of conventional equipment (e.g, drill
rigs). The alternative may not be well soiled for an interim action. Specifically, In-Situ Methane Biodegradation
with SVE may not be effective on the free phase TCE, which is thought to be present in the upper water able. In
addition, the time required for biodegradation of the solvents is likely to be long (10 years) for an interim action.
Costs associated with Alternative GW-4 include labor and materials to install the extraction and injection wells.
blowers, and an ofigas control system. Also included in the cost for methane biodeeradatioa'SVE system is a 5-
year operation and maintenance period. The estimated cost associated with the ahemative is 32.500,000.
Alternative GW-S • Ev-Sir., Air Stripping
Alternative GW-5 would include a groundwater extraction system designed to capture VOC contaminated
groundwater between the pit and Fourmile Branch. Once extracted, the groundwater would be treated onsite using
air stripping follow,* by gianidar activated carbon adsor^ Oner treated, the
residual groundwater would be discharged directly to local surface water.
Alternative GW-5 would be protective of human health and the environment with respect to VOCs. and would
reduce the volume of VOCs in groundwater. If Ahemative GW-5 is employed, its groundwater extraction would
create a significant cone of depression (ie., lower the water table around each pumping well), which would
eventually cause migration of tritium bearing groundwater from the CRSB plume. Alternative GW-5 would
essentially cause mixing of VOCs and tritium in the upper water table. The operation of the air stripper would
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-9S-403 P
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev~ j
September 1998 • Page 41 of 59
result in significant atmospheric releases of tritium to the environment and potentially pose unnecessary health
risks to workers. Estimated present worth costs associated with Alternative GW-5 is S1.200,000.
VIII. SUMMARY OF COMPARATIVE ANALYSIS OF THE INTERIM
ALTERNATIVES
The previous section detailed the five alternatives for soils and five alternatives for groundwater. In the 1APP
(WSRC 1998a), each of these remedial alternatives was evaluated using nine criteria established by the NCP. The
criteria were derived from the statutory requirements of CERCLA Section 121. The NCP (40 CFR & 300.430 (e)
(9» sets forth nine evaluation criteria that provide the basis for evaluating alternatives and selecting a remedy. The
criteria are as follows:
• 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
• inplememabiliry
• cost
• state acceptance
• community acceptance
In selecting the preferred alternative, the above criteria are used to evaluate the alternatives developed. Seven of
Ac criteria are used to evaluate all the alternatives based on human health and environmental protection, cpst, and
feasibility issues. Comparative evaluations of all the remedial action alternatives against these seven criteria are
detailed in the IAPP and briefly summarized in the Comparative Alternative Analysis section below. The preferred
alternatives are further evaluated in the subsequent state acceptance and community acceptance sections below.
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 Page 42 of 59
Comparative Alternative Analysis
Alternative GW-3 would be protective of human health and the environment by removing VOCs from the shallow
groundwater. The removal of contamination would significantly reduce the risk from groundwater ingestion and
contact to future residents and workers. Alternative GW-3 involves active treatment commonly used at other
hazardous and mixed waste sites to volatilize the contaminants and remove them from the groundwater.
Installation, operation, and maintenance of the AS/SVE system could be readily implemented within a short time
period. Installation, operation, and maintenance of the system would present minor risk to the remedial worker,
which would be mitigated through the use of proper protective equipment and adherence to approved health and
safety procedures.
Alternative GW-3 is selected as the preferred alternative over Alternative GW-2 because in Alternative GW-2 it is
uncertain that groundwater concentrations would decrease below MCLs before reaching a point of exposure.
Alternative GW-3 is selected over Alternative GW-4 because it is less expensive with comparable results. Further,
Alternative GW-4 was not selected because "hot spot" concentrations of TCE in the groundwater beneath the Pit
Area are presently at levels that would likely poison the biological degradation process. Alternative GW-5 was not
selected because it would likely cause mixing of VOCs and the relatively high activities of tritium sidegradient of
the unit.
Pursuant to the EPA IROD guidance (EPA 1989) and checklists, the alternative selection focused upon the key
ARARs listed below which apply to the limited scope of the interim action. The alternative selection also
considered final action ARARs to ensure the interim action would be compatible.
• Fugitive Paniculate Emissions (40 CFR 50.6 and SC R61 -62.6, Section III)
• SC Toxic Air Pollutant regulations (SC R61-62.1, Section II, paragraph 3)
• SC Well Construction regulations (SC R61 -71)
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC RP 98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site " n«. T
September 1998 -, ,, , *
- e Page 43 of 59
State Acceptance
Per EPA guidance on presumptive response strategics for groundwatcr (EPA 1996), groundwater response actions
should be implemented in a phased approach with provisions for monitoring and evaluating their performance.
Consistent with this guidance, an interim action is documented herein to remove high concentrations of TCE from
» known source of VOC contamination.
State of South Carolina and EPA concurrence with the proposed interim action, detailed in Section IX, has been
received. Both alternatives are effective in protecting human health, are readily implementable, and are reasonably
priced for the benefit received.
Community Acceptance
Community acceptance of the preferred alternative is assessed by giving the public an opportunity to comment on
the IAPP. The public was notified of a public comment period through mailings of the SRS Environmental
Bulletin, the Aiken Standard, the AHendale Citizen Leader, the Bamwell People Sentine'., The State, and Augusta
Chronicle newspapers, and through announcements on local radio stations. In addition, the IAPP was presented to
the SRS Citizen Advisory Board in an open public meeting (May 6, 1998) during the public comment period.
Public comments concerning the proposed remedy are addressed in the Responsiveness Summary of this IROD.
IX. THE SELECTED INTERIM REMEDY
Based on the risks identified in Section VI, the CBRP Pit Area soil poses.a significant risk to human health.
Significant carcinogenic risks to the potential future worker or resident are driven by exposure from the Pit Area
soils contaminated with organic chemicals and shallow groundwater contaminated with VOCs. Significant
potential for contamination of groundwater exists from leaching of VOCs caused by rainwater infiltration. '
Based on the CERCLA evaluation criteria, the preferred alternatives that successfully address the IRAOs to prevent
or mitigate these hazards are Alternative S-3, Native Soil Cover, for Pit Area soils and Alternative GW-3, In-Situ
Air Sparging with SVE, for unit groundwater. Capital and O&M costs are listed in Table 2. The selected remedial
alternatives are consistent with EPA guidance and the NCP for sites that have relatively large volumes of waste
with low levels of contamination. They effectively represent the integration of IRAOs and risk management
principles.
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev. 1
September 1998 Page 44 of 59
Native Soil Cover
The preferred alternative for Pit Area soil, Alternative S-3, consists of placing a layer of clean soil over the entire
surface area of the CBRP. This additional layer of soil will act as a barrier to prevent soil exposure to future human
and ecological receptors and will also reduce precipitation infiltration to minimize the further migration of TCE from the
CBRP soils to the groundwater. Therefore, this alternative satisfies the remedial action objectives and reduces the
risk to humans and the environment.
The soil cover is consistent with present and future land use expectations, because the CBRP is located in an area
that has been recommended for industrial use by the SRS Citizens Advisory Board, and it is so designated by DOE.
In addition, the Savannah River Site Future Use Report Stakeholder Recommendations for SRS Land and Facilities
(DOE 1996) includes the recommendation that "residential uses of SRS land should be prohibited." Existing SRS
institutional controls would prevent exposure to the industrial worker by limiting activities in the vicinity of the
CBRP if the recommendations are upheld. However, in the event the property was ever transferred to nonfederal
ownership, land use restrictions and notifications would be filed as pan of the final ROD.
In conclusion, Alternative S-3 is selected as the preferred soil alternative because it is the least expensive
alternative that satisfies the IRAOs with comparable protection of human health, the ecosystem, and the
groundwater. Alternative S-3 is easily and quickly implementable because commercial, experienced resources are
readily available. The hazards to ,the workers are slight. Positive health and safety practices would minimize
inhalation of fugitive dust and standard industrial accidents.
AS/SVE
The selected groundwater remedy, In-Situ Air Sparging (with Soil Vapor Extraction), conceptually depicted in
Figure 8, would involve operation of an air sparging system that would inject air into die bottom of the
contaminated groundwater plume. The contaminants would then pass into the injected air, as it moves upward
through the plume and, in turn, would flow into the unsaturated soil (vadose zone) above the water table. These
volatilized groundwater VOCs would be extracted via vacuum wells by a soil vapor extraction (SVE) system as
they rise into the vadose zone. Additionally, VOCs residing in the vadose zone (see Figure 8) would also be
extracted via these same vacuum wells. The extracted soil vapors would be processed through a liquid-phase
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC «P
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September 1998 Kev- J
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separator to remove condensate. The olfgas would then either be treated or released into the atmosphere in
accordance with release requirements.
Insolation of the AS/SVE system is targeted to remove high concentrations of TCE in the upper water table that could be
in a free phase. Tne AS/SVE system, will prevent rapid migration from the upper water table to the lower water table and
wfll be consistent with the IRAOs.
As discussed in Section Vn, the primary difference between this alternative (GW-3) and biodegradation (GW-4) is
the injection of methane along with air. As the design and capnal costs are relatively low, the proposed Alternative
GW-3 will be designed, where cost effective, to allow the addition of methane or other nutrients as an injection
option.
Simultaneous institutional controls would involve the installation and maintenance of long-term monitoring
systems for groundwater, surface water, and biota to monitor the rate of attenuation of organic contamination at the
site. Monitoring would continue for an indefinite period until sampling indicated remediation is successful in
reducing groundwater contaminant levels below ARARs. Existing SRS access controls will be used to restrict the
public and limit utilization of the site to industrial workers.
The preferred alternative (GW-3: air sparging in conjunction with SVE) offers the following advantages:
• Air sparging induces volatilization of VOCs in the groundwater and also provides oxygen to the
groundwater, which is necessary for biodegradation and
• The injection points in the saturated zone could be used to introduce reagents that would assist in the
degradation of the solvent plume;
• SVE increases the volatility of Ac VOCs in the vadose zone and also ventilates the vadose zone to
facilitate removal of volatilized VOCs.
A groundwater concentration of 11,000 ug/L is typically thought to be reqmred to suspect a high probability for the
presence of free phase TCE. Figure 6 illustrates the area adjacent to the CHRP thought to have the highest
potential for free phase TCE in the upper water table (i.e, 25,000 ug/L contour). This IROD proposes treatment of
the 25.000 and 20,000 ug/L areas adjacent to the pit illustrated in the current contaminant contours depicted in
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site Rev i
September 1998 Page 46 of 59
Figure 6. As shown in Figure 9, sparging and extraction cells will be concentrated within the 25,000 ug/L TCE
zone, with fewer cells in the 20,000 to 25,000 ug/L'interval. The total AS design flow rate is 300 cfrn. To ensure
complete recovery of the sparged air, the total SVE design flow rate is slightly greater at 500 cfm. Catalytic
oxidation would be used for control of the SVE offgas because it is more cost-effective than carbon adsorption.
Per EPA guidance on presumptive response strategies for groundwater (EPA 1996), groundwater response actions
should be implemented in a phased approach with provisions for monitoring* and evaluating their performance. In
accordance with the phased approach provisions in this guidance, this interim action is documented herein to allow
the treatment system design to be evaluated and optimized. The goal of the interim system will be to treat the area
in the vicinity of the pit within the 25,000 ug/L VOC isoconcentration contour to reduce concentrations and
stabilize the migration of TCE within the 25,000 ug/L VOC contour. The criteria used to calibrate and evaluate the
remedial action will include, at a minimum, the following monitoring: groundwater VOC concentrations within
and adjacent to the treatment zone, AS radius of influence and SVE VOC air emissions rates.
Proposed monitoring well locations from the Corrective Measures Implementation/Remedial Design/Remedial
Design Report/Remedial Action Work Plan (CMI/RD/RDR/RAWP) Rev. 0 (WSRC-RP-98-4058) are illustrated in
Figure 10. Associated geologic, hydrogeologic, and hydraulic features are provided as Figure 11. The information
depicted in Figure 11 is described in the Phase IIRFI/RI Work Plan (WSRC 1998b).
Performance of the interim action will be assessed continuously. If it is determined during annual performance
reviews that the interim action is not effective, a decision will be made, in consultation with EPA and SCDHEC, on
whether to continue, modify, expand or discontinue this interim action. System modifications may include
• number, location and configuration of the cells may be changed to improve the performance of the
system;
• positive and negative air flow rates, temperatures, and pressures may be modified to improve
performance; and after the higher concentration areas targeted by this interim action become
remediated to concentrations amenable to bioremediation, nutrients may be added to the air sparging
system to enhance biodegradation.
• Air injection may be utilized in the vadose zone extraction points to promote VOC volatilization and
create pathway for extraction.
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Interim Record ofDecision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (I31-C) (U) Savannah River Site
September 1998
Figure 9.
WSRC-RP-9S-4039
Rev. i
Page 47 of 59
CBRP AS/SVE Well locations and the Upper Water Table TCE Contours (ug/L)
tfCflO
CBRP AS/SVE Well Locations and Upper Water Table TCE Contours (ppb)
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— - - - «tt mm amu M •••«••> •«.
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Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
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Rev. 1
Page 48 of 59
Figure 10. CBRP Site Map Illustrating locations of Current and Proposed Monitoring Wells with
Respect to the 25,000 ug/L Contour and SVE/AS Treatment Zone
68300
69200
0100
44100 44200 44300 44400 44500 44600 44700
Pit CERCLA Maricere
• Primary Wells
A Lateral Wells
e Up/Side Gradient Wells
+ Power Line ROW
• Proposed Monitoring Wells
43600 43700 43800 41800
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP 98-4039
C-Area Burning/Rubble Pit Operable Unit (131-C)(U) Savannah River Site Bpv i
September 1998 „ -, "l*
f _______ foge 51 of 59
The AS/SVE flow rates; monitoring criteria; system performance modifications; and soil cover specifications
provided in section V.B will be finalized with the approval of SCDHEC and EPA via the Corrective Measures
Implementation/Remedial Design/Remedial Design Report/Remedial Action Work Plan (CMI/RD/RDR/RAWP)
scheduled for December 22, 1998.
X. STATUTORY DETERMINATIONS
This interim action is protective of human health, and the environment and will reduce the principal threats posed by
the CHRP. Relative to its overall effectiveness with respect to the nine selection criteria established by the NCP, the
selected alternatives are cost effective. This interim action will not identify final remedial goals; but the selected
interim alternatives are consistent with the interim remedial action objectives and any final action. Pursuant to the
EPA IROD guidance (EPA 1989) and checklists, the alternative selection focused upon the key ARARs listed below
which apply to the limited scope of the interim action. The alternative selection also considered final action ARARs
to ensure the interim action and any final action is compatible. The final action will comply with Federal and State
applicable or relevant and appropriate requirements. Although this interim action is not intended to fully address the
statutory mandate for permanence and treatment to the maximum extent practicable, this interim action does utilize
treatment and thus is a furtherance of that statutory mandate.
/
Because this action does not constitute the final remedy for the CBRP, the statutory preference of remedies that
employ treatment that reduces toxicity, mobility, or volume as a principal element, although partially addressed in
this remedy, will be addressed by the final response action. Subsequent actions are planned to fully address the
threats posed by the conditions at the CBRP. This interim action is not designed or expected to be a final action for
the groundwater, but the selected remedy represents the best balance of tradeoffs among alternatives with respect
of pertinent criteria, given the limited scope of the action. The soil cover will likely be acceptable for the final
action for soils at the unit. The native soil cover will address low level threat wastes (i.e., low concentration dioxin
contamination in the Pit Area soil and organic contamination in the deep soil). In-Situ Air Sparging with Soil
Vapor Extraction will address principal threat wastes (i.e., highly concentrated TCE in the aquifer sediments
immediately adjacent to the pit in the upper zone of the water table aquifer) and VOC vadose zone contamination.
ICOOerap doc MM-1jlb09.'l8.">S
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (131-Q(U) Savannah River Site R.V i
September 1998 ^Page52ofS9
• Fugitive Paniculate Emissions (40 CFR 50.6 and SCR61-62.6, Section III)
• SC Toxic Air Pollutant regulations (SC R61 -62.1, Section II, paragraph 3)
• SC Well Construction regulations (SC R61 -71)
SCHWMR R.61-79.124 and Section 117(a) of CERCLA, as amended, require advertisement of the draft permit
modification and the proposed plan, respectively. Because this is an interim remedial action, a permit modification
is not required to be included with this IROD. A final permit modification will include the fina'J selection of
remedial alternatives under RCRA, will be sought for the entire CBRP OU with the final SB/PP and will include
the necessary public involvement and regulatory approvals. This IROD also satisfies the RCRA requirements for
an Interim Measures Work Plan.
XI. EXPLANATION OF SIGNIFICANT CHANGES
The IAPP provided for involvement with the community through a document review process and a public
comment period from April 17, 1998 through May 16, 1998. The IAPP was presented to the SRS Citizens
Advisory Board in an open public meeting which was advertised and held on May 6, 199S. Comments received
during the 30-day public comment period and the May 6. 1998 public meeting are addressed in Appendix A of this
IROD. No significant changes to the selected remedy resulted from public comments.
XII. RESPONSIVENESS SUMMARY
Comments received during the public comment period are discussed in the Responsiveness Summary (see
Appendix A) of this IROD.
XIII. POST-IROD DOCUMENT SCHEDULE
An integrated interim and final action implementation schedule is illustrated in Figure 12. A signed IROD is
scheduled for September 30, 1998. The interim CMI/RD/RDR/RAWP was submitted on June 19, 1998.
Construction of the interim action is scheduled to begin by January 22, 1999. A performance evaluation of the
interim action will be prepared and submitted to EPA and SCDHEC by October 27,2000.
lOOOCTwpdocMM/WbOWIMS
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Interim Record of Decision for the Remedial Alternative Selection for the WSRC-RP-98-4039
C-Area Burning/Rubble Pit Operable Unit (I3I-C)(U) Savannah River Site Rev 1
September 1998 Page S3 of 59
Figure 12. Integrated Interim and Final Action Implementation Schedule
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-------
Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
Figure 12. Integrated Interim and Final Action implementation Schedule
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-------
Interim Record of Decision for the Remedial Alternative Selection for the
C-Area Burning/Rubble Pit Operable Unit (131-C) (U) Savannah River Site
September 1998
WSRC-RP-98-4039
Rev. 1
Page 55 of 59
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