PB95-964006
EPA/ROD/R04-95/202
December 1994
EPA Superfund
Record of Decision:
Savannah River (USDOE), TNX Area,
Groundwater Operable Unit, Aiken, SC
11/9/1994
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WSRC-TR-94-0375
Rev 1
October 1994
Interim Action Record of Decision Remedial Alternative
Selection—TNX Area Groundwater Operable Unit(U)
Westinghouse Savannah River Company
Savannah River Site +•* %>
Aiken, SC 29808 £ £ n £ %
SAVANNAH RIVER SITf
Prepared for the U.S. Department of Energy under contract no. DE-AC09-89SR18035
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Interim Action Record or Decision
WSRC-TR-94-0375 Remedial Alternative Selection
Contents
Declaration for the Record of Decision 1
Unit Name and Location 1
Statement of Basis and Purpose 1
Assessment of the Unit 1
Description of the Selected Remedy 1
Recirculatioii Wells 2
Extraction Wells with an Air Stripper 2
Declaration Statement • 3
Section I Site and Operable Unit Names, Locations, and Descriptions 4
Section II Operable Unit History and Compliance History 7
Operable Unit History 7
Compliance History 7
Section III Highlights of Community Participation 8
Section IV Scope and Role of Operable Unit within the Site Strategy 10
Section V Summary of Operable Unit Characteristics 11
Section VI Summary of Operable Unit Risks 20
Comtaminated Media 20
Contaminants of Concern 20
Interim Risks 20
Section VII Description of Alternatives 21
Alternative 1—No Interim Action, Invoke Institutional Controls 21
Treatment Components 21
Engineering Controls 21
Institutional Controls 21
Implementation Requirements 21
Estimated Construction and Operation and Maintenance Costs 21
ARARs Associated with the Considered Alternative 22
Alternative 2—Hybrid Groundwater Corrective Action 22
Engineering Controls 22
Institutional Controls 24
Implementation Requirements 24
Estimated Construction and Operation and Maintenance Costs 24
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Interim Action Record or Decision
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ARARs Associated with the Considered Alternative 24
Section VIII Summary of Comparative Analysis of Alternatives 30
Description of Nine Evaluation Criteria 30
Section IX Selected Remedy 32
Section X Statutory Determination 33
Section XI Explanation of Significant Changes 34
References 35
Appendix A Responsiveness Summary 36
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Interim Action Record of Decision
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List of Figures
1 Location of the TNX Area Groundwater Operable Unit CERCLA unit at SRS 5
2 Topographic Map of the TNX Area and Local Surroundings 6
3 Geophysical and Lithologic Log Showing Units and Hydrogeologic Section of the TNX Area 14
4 TNX Water Table Map (Average Elevation for 1991) 15
5 Trichloroethylene (u,g/L) 4Q90 Data 16
6 Nitrate as N (u,g/L) 4Q90 Data 1 7
7 4Q90 Field pH Mercury Posting Map for Water Table Wells at TNX 18
8 4Q90 Gross Alpha and Total Radium Posting for Water Table Wells at TNX 19
9 Sources of Risk to Onsite Worker 25
10 Risks for Different Exposure Scenarios 25
11 Flow Patterns for a Recirculation Well System 26
12 Capture Zone of a Hypothetical Hybrid Groundwater Corrective Action for TNX 27
List of Tables
1 List of Constituents Detected Above the Primary Drinking Water Standard
in Groundwater at TNX Area from 3Q88 to 1Q92 12
2 Applicable or Relevant and Appropriate Requirements for the Hybrid Groundwater
Corrective Action 28
3 Evaluation of Interim Response Actions 31
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Interim Action Record of Decision
WSRC-TR-94-0375 Remedial Alternative Selection
Declaration for the Record of Decision
Unit Name and Location
TNX Area Groundwater Operable Unit CERCLA Unit
Savannah River Site
Aiken County, South Carolina
Appendix C of the Federal Facility Agreement (FFA) lists this Comprehensive Environmen-
tal Response, Compensation, and Liability Act (CERCLA) unit as Groundwater, TNX.
Statement of Basis and Purpose
This document presents the selected interim remedial action for the TNX Area Groundwater
Operable Unit at the Savannah River Site (SRS), which was developed in accordance with
CERCLA of 1980, as amended by the Superfund Amendments and Reauthorization Act
(SARA) of 1986, and to the extent practicable, the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP). This decision is based on the Administrative Record
File for this specific CERCLA unit
The State of South Carolina concurs with the selected interim action remedy.
Assessment of the Unit
The TNX Area is a pilot scale test facility for the Savannah River Technology Center
(SRTC). The pilot scale facilities are used to provide technical support to various SRS pro-
duction areas. From 1953 to August 1988, wastewater generated by research performed in
the TNX Area was disposed of in seepage basins. In August 1988. wastewater was rerouted
to the TNX Effluent Treatment Facility.
In 1980, the first series of groundwater monitoring wells were installed in the TNX Area.
The first series of monitoring wells were determined to be inadequate and were abandoned
and replaced in 1984. The groundwater sampling data from the new wells indicated that
seepage from the unlined basins, leakage from the process sewers, and leachate from other
activities in the area resulted in soil and groundwater contamination throughout the TNX
Area. Analysis of surface water samples collected from the swamp adjacent to the Savannah
River indicate that groundwater contaminated with Chlorinated Volatile Organic Com-
pounds (CVOCs) is outcropping in the swamp before it reaches the river. No contaminants
from the plume were detected in the Savannah River. Actual or threatened releases from this
site, if not addressed by implementing the response action selected in this Record of Deci-
sion (ROD), could present an endangerment to public health, welfare, or the environment.
Description of the Selected Remedy
The TNX Area groundwater and the source areas contributing to contamination of the
groundwater are in various stages of the CERCLA investigation and remedy selection pro-
cess. This groundwater interim action will serve to mitigate the further migration of the
groundwater plume hotspot while also removing contaminants from the groundwater. Fol-
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Interim Action Record or Decision
WSRC-TR-94-03 75 Remedial Alternative Selection
lowing investigation and remedy selection for the source units in the TNX Area, the ground-
water unit will be reassessed and appropriate final remedial alternatives will be developed.
The selected alternative to achieve the interim action goals is Alternative 2. Hybrid Ground-
water Corrective Action (HGCA). The HGCA includes one recirculation well and a series of
groundwater extraction wells with an air stripper. The conceptual design for the extraction
system has three to five groundwater extraction wells with a combined flow rate of up to 60
gallons per minute. The target treatment level for tricholorethylene (TCE) in the extracted
groundwater will be 5 ug/L prior to discharge to a NPDES outfall. The actual design of the
remedial system will be addressed through the remedial design process.
Recirculation Wells
Recirculation wells are an emerging technology for in situ cleanup of CVOC contaminated
groundwater. In recirculation wells, air is injected into a groundwater well. As the air rises
to the surface in the well, it removes CVOCs from the water in the well by air stripping.
Additionally, the air causes groundwater to flow upward in the well establishing a circula-
tion system where water is drawn into the bottom of the well and discharged at the water
table. The air is collected by a vacuum at the surface for treatment. The vacuum also recov-
ers soil vapor from the unsaturated zone resulting in additional cleanup.
Extraction Wells with an Air Stripper
The migration of the contaminated groundwater plume hotspot will be intercepted by a
series of water wells known as extraction wells. The extraction wells are used to drawdown
the water table and collect contaminated groundwater. Drawdown from the extraction wells
produces a capture zone that prevents the further migration of contamination from the site.
The contaminated groundwater that is collected by the extraction wells will be treated by an
air stripper. Treated groundwater will be discharged to a permitted outfall. The air stripper
can also be used to treat contaminated water from other cleanup activities, such as ground-
water sampling. Air emission from the air stripper and recirculation well will be treated as
necessary to comply with South Carolina Department of Health and Environmental Control
(SCDHEC) air pollution regulations.
In addition to TCE, the main contaminant of concern, CVOCs, mercury, gross alpha, and
nitrate will be monitored in the effluent from the treatment system to ensure that they do not
exceed discharge limits. If they begin to exceed discharge limits, the well causing the
exceedance will be identified through sampling, and discharges from that well will be
treated using methods similar to ion exchange or reverse osmosis.
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WSRC-TR-94-0375
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Remedial Alternative Selection
Declaration Statement
This interim action is protective of human health and the environment, complies with (or
waives) Federal and South Carolina applicable or relevant and appropriate requirements
(ARARs) for this limited scope action, and is cost-effective. ARARs pertaining to aquifer
restoration to Safe Drinking Water Act (SDWA) Maximum Contaminant Levels (MCLs) do
not apply to this action because this limited scope interim action is pan of an overall remedy
that will attain (or waive) all ARARs for the final action. Although this interim action is not
intended to fully address the statutory mandate for permanence and treatment to the maxi-
mum extent practicable, this interim action utilizes treatment and. accordingly, is in further-
ance of that statutory mandate. Since this action does not constitute the final remedy for the
TNX Area Groundwater Operable Unit, the statutory preference for remedies that employ
treatment that reduces toxicity, mobility, or volume as a principal element, although par-
tially 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 this unit. Because
this remedy will result in hazardous substances remaining onsite above health-based levels.
a review will be conducted to ensure that the remedy continues to provide adequate protec-
tion of human health and the environment within five years after commencement of the
remedial action. Since this is an Interim Action Record of Decision, review of this unit and
this remedy will be ongoing as the Department of Energy (DOE) continues to develop final
remedial alternatives for the TNX Area Groundwater Operable Unit.
Date
Thomas F. Heenan
Assistant Manager for Environmental
Restoration and Waste Management
U.S. Department of Energy
Date
/*\
John H. Hankinson, Jr.
Regional Administrator
U.S. Environmental Protection Agency
Region IV
Date
R. Lewis Shaw
Deputy Commissioner
Environmental Quality Control
South Carolina Department of Health and
Environmental Control
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Interim Action Record or Decision
WSRC-TR-94-0375 Remedial Alternative Selection
Site and Operable Unit Names, Locations, and
Descriptions
The Savannah River Site (SRS) occupies approximately 300 square miles adjacent to the
Savannah River, principally in Aiken and Barnwell counties of South Carolina (Figure 1).
SRS is a secured facility with no permanent residents. The Site is approximately 25 miles
southeast of Augusta, Georgia and 20 miles south of Aiken. South Carolina. According to
1990 census data, the average population densities (in people/square mile) for the surround-
ing South Carolina counties are 111 for Aiken County, 36 for Barnwell County, and 28 for
Ailendale County and for the surrounding Georgia counties, 228 for Columbia County. 524
for Richmond County, 25 for Burke County, and 21 for Screven County. The population
within a 50-mile radius of SRS is 634,784 people.
SRS is owned by the U.S. Department of Energy (DOE). Wesdnghouse Savannah River
Company (WSRC) provides management and operating services for DOE. SRS has histori-
cally produced tritium, plutonium, and other special nuclear materials for national defense.
The Site has also provided nuclear materials for the space program and medical, industrial.
and research efforts. Chemical and radioactive waste are by-products of nuclear material
production processes. Hazardous substances, as defined by the Comprehensive Environ-
mental Response, Compensation, and Liability Act (CERCLA). are present in the environ-
ment at SRS. Appendix C, RCRA/CERCLA Units List, of the Federal Facility Agreement
(FFA, 1993) lists the TNX Area Groundwater Operable Unit.
The TNX Area is located adjacent to the Savannah River in the southwestern portion of SRS
(see Figure 1). Pilot-scale testing and evaluation of chemical processes in the TNX Area
included support of the Defense Waste Processing Facility, separations areas, and fuel and
target manufacturing areas. Wastewater generated during support of the previously identi-
fied initiatives was discharged to unlined earthen basins through a network of process sew-
ers.
The TNX Area is one quarter of a mile east of the Savannah River, between Upper Three
Runs Creek to the north and Fourmile Creek to the south, at an elevation of 150 feet above
mean sea level (MSL). Local topography is relatively flat with a slope toward the east, away
from the Savannah River.
Immediately west of the TNX Area is a swamp adjacent to the Savannah River at 95 feet
above MSL (see Figure 2). A small terrace divides the swamp and serves as the bank of the
river during high stages. The terrace in the swamp is covered by bottomland hardwoods, and
the swamp west of the terrace has stands of cypress and tupelo typical of Savannah River
swamps. Typical fauna for bottomland hardwood forests includes, but is not limited to, sala-
manders, frogs, snakes, bats, squirrels, raccoons, skunks, weasels, and foxes. Large mam-
mals include white-tailed deer and feral pigs. No endangered or threatened species have
been identified in the vicinity of the TNX facility from previous surveys, nor do habita
exist there for the American alligator, red-cockaded woodpecker, the wood stork, or th
short-nosed sturgeon.
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WSRC-TR-94-0375
n^.'im Action Record ot Decision
Remedial Alternative Selection
North Carolina
• Charlotte
Greenville
•
50 100
x^ South Carolina
Scale in Miles Savannah River
Atlanta
~\
Tinkir Creek
Upper Three Rum
1
Tim Branch
Upper Three Rum .
McQueenA
Branch
Branch
(Par Pond SOUth
V Carolina North
Pen Branch
Georgia
Lower Three Rum Creefc
Scale in Miles
Savannah River
Figure 1. Location of the TUX Area Groundwater Operable Unit CERCLA unit at SRS.
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Environmental Sciences Seclioi
LEGEND
• WELL
TNX SEEPAGE BASIN
WELL CLUSTER
SURFACE WATER ELEVATION
—— TNX FENCE
SEEPMEA
TNX BURYING GROUND
FIGURE2:
TOPOGRAPHIC MAP OF THE
TNX AREA AND LOCAL
SURROUNDINGS
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Interim Action Record of Decision
WSRC-TR-94-0375 Remedial Alternative Selection
II. Operable Unit History and Compliance History
Operable Unit History
The TNX Area is a pilot scale test facility for the SRTC. The pilot scale facilities are used to
provide technical support to various SRS production areas. From 1953 to August 1988.
wastewater generated by research performed in the TNX Area was disposed of in seepage
basins. In August 1988, wastewater was rerouted to the TNX Effluent Treatment Facility.
In 1980, the first series of groundwater monitoring wells was installed in the TNX Area. The
first series of monitoring wells was determined to be inadequate and were abandoned and
replaced in 1984. The groundwater sampling data from the new wells indicated that seepage
from the unlined basins, leakage from the process sewers, and leachate from other activities
in the area resulted in soil and groundwater contamination throughout the TNX Area. Anal-
ysis of surface water samples collected from the swamp adjacent to the Savannah River indi-
cates that groundwater contaminated with CVOCs is outcropping in the swamp before it
reaches the river. No contaminants from the plume were detected in the Savannah River. An
environmental impact statement addressing groundwater contamination caused by site oper-
ations was submitted for public comment in 1987 (DOE, 1987).
Compliance History
On December 21, 1989. SRS was placed on the National Priorities List (NPL). A site placed
on the NPL comes under the jurisdiction of CERCLA. In accordance with Section 120 of
CERCLA, DOE negotiated a Federal Facility Agreement (FFA, 1993) with the U.S. Envi-
ronmental Protection Agency (EPA) and SCDHEC to coordinate cleanup activities at SRS
into one comprehensive strategy that fulfills Resource Conservation Recovery Act (RCRA)
Section 3004(u) and CERCLA assessment, investigation, and response action requirements.
The FFA lists the TNX Area Groundwater Operable Unit as a CERLCA unit requiring fur-
ther evaluation using the CERCLA Remedial Investigation (RI) process to determine the
actual or potential impact to human health and/or the environment.
Public participation requirements are listed in Sections 113 and 117 of CERCLA. These
requirements include the establishment of an Administrative Record File which documents
the selection of cleanup alternatives and provides for review and comment by the public.
The SRS Public Involvement Plan (PIP)(WSRC, 1991) is designed to facilitate public
involvement in the decision making processes for permitting, closure, and selection of reme-
dial alternatives. The PIP addresses the requirements of RCRA. CERCLA, and the National
Environmental Policy Act (NEPA). Section 117(a) of CERCLA. 1980. as amended by the
Superfund Amendments and Reauthorization Act (SARA) of 1986. requires the preparation
of a proposed plan as part of the site remedial process. The Interim Action Proposed Plan
for the TNX Area Ground-water Operable Unit, which is part of the Administrative Record
File, highlights key aspects of the assessment and investigation phases of the remediation
process and identifies the preferred interim action alternative for remediation of the TNX
Area Groundwater Operable Unit.
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Interim Action Record of Decision
WSRC-TR-94-0375 Remedial Alternative Selection
III. Highlights of Community Participation
•The Administrative Record File, which contains the information upon which the selection of
the response action was made, is available 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 29802
(803) 777-4866
Similar information is available through the following repositories:
Reese Library
Augusta College
2500 Walton Way
Augusta, Georgia 30910
(404) 737-1744
Asa H. Gordon Library
Savannah State College
Tompkins Road
Savannah, Georgia 31404
(912)356-2183
The public was notified about the comment period for the TNX Area Groundwater Operable
Unit through mailings of the SRS Environmental Bulletin, a newsletter sent to more than
1400 citizens in South Carolina and Georgia, and through notices in the Aiken Standard, the
AUendale Citizen Leader, the Barnwell County Banner, the Bamwell People-Sentinel, the
North Augusta Post, The State, and The Augusta Chronicle newspapers.
The 30-day public comment period began on August 15, 1994, for the Interim Action Pro-
posed Plan for the TNX Area Groundwater Operable Unit. Responses to comments are dis-
cussed in the Responsive Summary (see Appendix A). The proposed plan included a means
for requesting a public meeting to discuss the TNX Area and the proposed interim action. A
public hearing was requested during the initial public comment period. As a result of the
request for a public hearing, the public comment period was extended to October 13. 1994,
and a public hearing was held on October 11, 1994.
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Interim Action Recorder Decision
WSRC-TR-94-0375 Remedial Alternative Selection
Two written comments were received on the LAPP. One of the comments only requested a
public hearing, and the other comment pertained to permitting issues for the treatment sys-
tem.
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Interim Action Record or Decision
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IV. Scope and Role of Operable Unit within the Site
Strategy
Past operations within the TNX Area led to the contamination of the area's groundwater.
Several source units have been identified in the TNX Area which contributed to the ground-
water contamination. These units include the Old TNX Seepage Basin, the New TNX Seep-
age Basin, and the TNX Burying Ground. Operations associated with these units, as well as
leakage from process sewers and leachate from other site activities, contributed to the
groundwater contamination.
The areas contributing to the groundwater contamination will be investigated pursuant to the
requirements of the NCP and the FFA. Following investigation of these areas, appropriate
cleanup alternatives will be developed.
The groundwater system in the TNX Area has been adequately characterized to identify the
need for a limited scale action and support the design and implementation of a system to
begin controlling and remediating groundwater contamination. Final cleanup alternatives
for the groundwater will be developed following remedy selection for the source units.
A limited scale interim action is desired to control the further migration of the groundwater
contamination hotspot, prevent the further degradation of the groundwater system, and
begin contaminant mass removal from the groundwater contamination hotspot. An interim
action addressing the most contaminated groundwater at the TNX Area through plume sta-
bilization and contaminant removal will be protective of human health and the environment.
will not be inconsistent with potential future cleanup activities, and reduce the scope of
future final actions.
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V. Summary of Operable Unit Characteristics
-TNX is underlain by two aquifer systems—a deep aquifer system and a shallow aquifer sys-
tem. The systems are separated by a thick layer of clay and silt with thin sand lenses approx-
imately 50-feet thick (see Figure 3). The clay and silt layer greatly reduces flow between the
aquifer systems. An upward gradient between the deep aquifer system and the shallow aqui-
fer system equals about 55 feet of water (24 psi). The upward gradient results in upward
groundwatcr flow from the deep aquifer system to the shallow aquifer system. Domestic and
process water for the TNX Area is produced from the deep aquifer system. Lateral ground-
water flow in the deep and shallow aquifers beneath TNX is to the west-northwest direction
towards the Savannah River.
The shallow aquifer system is composed of a water table aquifer and a semi-confined aqui-
fer. Depth to the water table varies from zero to 50 feet in the area of groundwatcr contami-
nation. Groundwater flow in the shallow aquifer system is toward the Savannah River. The
water table aquifer crops out in the swamp between the Savannah River and the TNX Area
(see Figure 4). Groundwater contamination at TNX was detected only in the water table
aquifer in the shallow aquifer system.
Groundwater monitoring wells in the TNX Area are sampled and analyzed for a wide range
of parameters. The parameters analyzed include indicators of water quality (pH, alkalinity.
specific conductivity, gross alpha, nonvolatile beta, etc.) and specific chemical constituents.
The chemical constituents include organic compounds, specific radionuclides. and non-
radiological inorganic species. Shallow groundwater at TNX has low ionic strength, is
slightly to moderately acidic, aerobic, and has a small amount of total dissolved solids. This
general groundwater chemistry is consistent with the local aquifer materials, specifically,
highly leached sand with some silt and lesser amounts of clay. The groundwater contamina-
tion can be divided into two categories, organic and inorganic contamination.
The water table aquifer at TNX is contaminated with CVOCs, primarily trichloroethylene
(TCE), tetrachloroethylene (PCE), and carbon tetrachloride (see Table 1). The CVOC con-
tamination underlays eight acres, has a maximum thickness of 20 feet, and contains approx-
imately six gallons of TCE. Trans- 1.2-dichloroethylene, a product of natural aerobic
biodegradation of TCE and PCE, has been measured in some of the wells with TCE. The
absence of vinyl chloride in the groundwater suggests that the biodegradation is following
an aerobic pathway. A concentration map for TCE illustrates the lateral extent of CVOC
migration (see Figure 5). 1,1,1-trichloroethane and chloroform were also detected in ele-
vated concentrations, but did not exceed Primary Drinking Water Standards (PDWS).
At one time, benzene was detected above the PDWS. A replicate analysis by the same labo-
ratory yielded a result of 3 u,g/L, and both results from a replicate analysis performed by an
independent laboratory on a split sample were below detection of 1 ng/L. The replicate and
duplicate analyses provide strong evidence to suggest that the one reported value, which
exceeds the PDWS, was not representative of the field conditions.
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Table LList of Constituents Detected Above the Primary Drinking Water Standard in Groundwater at TNX Area from
3Q88tolQ92
Constituent
Trichloroethylene
Tetrachloroethylene
Carbon Tetrachloride
Chloroform
Benzene
Lindane
Endrin
Mercury
Gross Alpha (pCi/L)
Nitrate as Nitrogen
Lead
Chromium
Primary Drinking
Water Standard Value
5
5
5
100"
5
0.2
0.2
2
15
10000
15
100
Maximum
Result
4800
110
750
221
97
0.28b
0.63b
4.39
80
98600
37.5C
197*1
Wei]
TBG5
XSB1D
TBG4
XSB1D
TBG7
TNX2D
TNX2D
TBG4
TBG3
TBG4
XSB5A
XSB2D
Date
9/18/90
3/27/89
7/3/89
3/27/89
12/5/89
3/7/91
3/7/91
9/9/89
6/14/89
12/10/90
3/6/90
3/11/90
Most Current
Result (e>
1100
5.25
270
LT1
LT1
LT 0.005
LT 0.006
3.7
5.70
43200
10.2
LT4
Date
3/16/91
2/5/92
3/15/91
2/5/92
2/3/92
2/5/92
2/5/92
3/15/91
9/4/91
3/15/91
2/3/92
2/4/92
AH units are ug/L unless noted otherwise.
a The level for trihalomethanes is set as 100 ug/L. Because brominated methane is rarely detected in SRS groundwater. it is presumed
that most of the trihalomethanes present are chloroform.
b An insufficient number-of detected results is available to determine if this is a representative value.
c Values have not been above PDWS since 1Q91.
d This value is not believed to be representative of the maximum concentration because of laboratory error. Historical groundwater
monitoring data confirms that chromium is not present at levels that exceed PDWS.
LT = less than
e Most current result for well in "Maximum" Summary.
Five inorganic constituents have been detected above PDWS: nitrate, mercury, gross alpha.
lead, and chromium. Results from groundwater monitoring analyses show that nitrate is
present in concentrations that exceed PDWS in several wells at TNX. Large quantities of
industrial-grade nitric acid were used in the operations at TNX. Nitric acid dissociates into
hydrogen and nitrate ions in water. Since nitrate is stable in aerobic groundwater, relatively
mobile in groundwater. and was used throughout the TNX Area, it can be used as an indica-
tor of the extent of groundwater contamination at TNX. Figure 6 is a concentration map for
nitrate.
Mercury concentrations from monitoring well TBG4 consistently exceed PDWS. Very low
pH (<4.2) and high nitrate concentrations have also been observed at well TBG4. indicating
that the mercury was probably pan of a spent nitric acid solvent solution disposed of at
TNX. A solvent containing nitric acid and mercury was used at TNX in research on the
chemical separations processes used at SRS.
Groundwater from monitoring well TBG4 also has elevated calcium, magnesium, and silica.
which are the result of the dissolution of clay minerals in the sediments by very low pH
water. The dissolution of clay minerals buffers the low pH water and is a natural chemical
response to the addition of acid. The low pH conditions in the immediate vicinity of moni-
toring well TBG4 increase the solubility of mercury and reduce the number of sites avail-
able for mercury adsorption by occupying them with hydrogen ions. Since the groundwater
h aerobic and contains chloride, the dissolved mercury is probably in the form of chloride
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complexes. As groundwater migrates downgradient away from the low pH mercury source-
term, the concentration of mercury complexes is diluted and the groundwater pH increases.
As the mercury complexes are diluted, they become unstable and break down, setting free
the ionized mercury for adsorption to the soil. Soil downgradient of TBG4 has more sites
available for mercury adsorption because of the increased pH. The groundwater monitoring
data suggest that these natural processes prevent mercury from migrating very far from the
source-term (see Figure 7).
Gross alpha, an indicator of contamination by alpha-emitting radionuclides. is persistently
elevated in two monitoring wells, TBG3 and TBG4, located immediately downgradient of
the TNX Burying Ground (see Figure 8). Specific alpha emitters in the groundwater were
identified by alpha spectroscopy; they were Ra-226, Th-228,230. and 232. U-233.234. 235.
and 238, Pu-238. 239, 240, and 242, Am-241 and 243. and Cm-242. 243. 244. and 246. Iso-
topes of radium (Ra) and thorium (Th) are natural decay products of uranium (U). which is
also naturally present in sediments. U is a raw material used in several processes at SRS. but
it occurs as a natural constituent in sediments as well. Plutonium (Pu). americum (Am), and
curium (Cm), commonly referred to as transuranics, do not occur naturally and are the result
of artificial nuclear reactions such as the ones used at SRS. Ra-226 is the main contributor to
gross alpha in groundwater throughout the TNX Area (see Figure 8).
Monitoring well XSB5A is the only well that has had lead concentrations that exceed
PDWS. Lead concentrations have been steadily decreasing at this well and have not
exceeded PDWS since the beginning of 1991. The lead probably comes from the galvanized
steel screen in well XSB5, which is located less than ten feet upgradient of well XSBSA.
The low pH (<5) of the groundwater in the vicinity of these wells leached lead from the gal-
vanized screen when well XSB5 was active. The decreasing lead concentrations may indi-
cate that the lead source was reduced by the abandonment of well XSB5.
Chromium (Cr) concentrations that exceeded PDWS at TNX were reported during one quar-
ter of analysis and were not elevated prior to or following the quarter of suspect data. The
suspect chromium analyses were conducted by the same laboratory and analyst.
Endrin and lindane (pesticides) have been occasionally (<50% of the time) above the PDWS
at TNX.
Groundwater samples from the semiconfined aquifer at TNX have not exceeded the PDWS.
The relative amounts of major ions in the semiconfined aquifer are different from the uncon-
fined aquifer: iron, magnesium, calcium, sulfate. and HCO3 concentrations are higher in the
semiconfined aquifer, and sodium, chloride, and NO3 are lower.
Tritium is below detection limits in the semiconfined aquifer as compared to the overlying
unconfined aquifer, which has 2-4 pCi/mL. (Average tritium levels in rainfall at TNX are
2-4 pCi/mL (Murphy, et. al., 1993): the PDWS for tritium is 20 pCi/mL.) The low tritium
levels in the semiconfined aquifer at TNX indicate that groundwater in the unconfined aqui-
fer is not migrating into or impacting the semiconfined aquifer (Nichols, 1992).
94X04198fmk 13
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WSRC-TR-94-0375
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Remedial Alternative Selection
TNX-SB1
Gamma Ray Log
(API-GR Units)
0 250 500
50
75
100
125
150
200
225
Roststivrty L
(Ohm-M)
500 1000
50
75
100
e
a.
&
125
150
175
200
225
V)
£
I
s
2L
CO
s
I
o
u>
V)
Q.
$
o
I I
CO §
I s
^ s
a a
Figure 3. Geophysical and Littaologic Log Showing Units and Hydrogeologic Section of the TNX Area
94X04198fmk
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Environmental Sciences Section
LEGEND
WELL
TNX SEEPAGE BASIN
WELL CLUSTER
TNX FENCE
SURFACE WATER ELEVATION
SEEP AREA
TNX BURYING GROUND
NOTE: THE NUMBER BY THE
SYMBOL IS WATER ELEVA TION
IN FEET ABOVE MSL
FIGURE 4:
WATER TABLE MAP
(AVERAGE ELEVATION FOR 1991)
CONTOUR INTERVAL IS 1 FOOT
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A
*
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Environmental Sciences Secl/o»|
LEGEND
• WELL
"< TNX SEEPAGE BASIN
WELL CLUSTER
SURFACE WATER ELEVATION
TNX FENCE
SEEP AREA
TNX BURYING GROUND
FIGURE 6:
NITRATE AS N (ug/L)
4090 DAT A '
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Environmental Sciences Section
LEGEND
• WELL
TNX SEEPAGE BASIN
* WELL CLUSTER
SURFACE WATER ELEVATION
5.3 pH (pH UNITS)
<0.2 MERCURY (figIL)
—— TNX FENCE
ilHl SEEP AREA
TNX BURYING GROUND
FIGURE?:
4090 FIELD pH
MERCURY POSTING MAP FOR
WATER TABLE WELLS AT TNX
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Environmental Sciences Section
LEGEND
• WELL
TNX SEEPAGE BASIN
WELL CLUSTER
SURFACE WATER ELfVATIOM
GROSS ALPHA (pCi/L)
TOTAL RADIUM (pd/n
TNX FENCE
WX BURYING GROUND
FIGURES:
4Q90 GROSS ALPHA AND TOTAL
RADIUM POSTING MAP FOR
WATER TABLE WELLS AT TNX
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Interim Action Record oi Decision
WSRC-TR-94-0375 Remedial Alternative Selection
VI. Summary of Operable Unit Risks
•This interim action will serve an incremental step in addressing contamination in the TNX
Area and is not intended as a final action. As required by CERCLA, development and selec-
tion of final cleanup activities will depend upon the extent of vadose zone contamination.
the effectiveness of this interim action, and the results of the Baseline Risk Assessment. The
Baseline Risk Assessment will evaluate the current and potential risks to human health and
the environment from contamination in the TNX Area. Based upon the results of that assess-
ment, appropriate cleanup alternatives will be developed to fully address site risks.
Contaminated Media
Contaminated media at the TNX Area includes ground water, surface water, and the soil
above the water table. The focus of this interim action is the contaminated groundwater.
Contaminants of Concern
Interim Risks
As reflected in Table 1, a number of contaminants have been detected in the groundwater
system at levels exceeding health-based standards. The primary contaminant of concern for
this interim action is TCE. While carbon tetrachloride and nitrates also appear to be migrat-
ing offsite, the plume distributions of TCE and carbon tetrachloride coincide, but the con-
centrations of carbon tetrachloride are significantly lower than TCE concentrations. The
concentration of nitrates leaving the TNX Area is at or slightly exceeds health-based stan-
dards and does not pose as significant a threat as TCE. The chemicals of concern will con-
tinue to be evaluated for this unit as this interim action is implemented and further
investigations in the TNX Fundamental Study Area are conducted.
The TNX Groundwater Interim Risk Evaluation (IRE) was performed to determine current
risks to human health and the environment and to determine if the risk was high enough
(greater than 1 x 1O4) to require immediate remedial action. Results of the IRE indicate that
the contaminant responsible for the largest portion of the risk to the onsite worker is TCE
(see Figure 9). The largest risk to the onsite worker is through contact with contaminated
soil and water at the groundwater outcrop in the swamp during sampling. The IRE shows
that under current conditions, the onsite worker is not exposed to contaminants at concentra-
tions that will produce an unacceptable risk to human health (see Figure 10).
While the contaminants in the groundwater system exceed SDWA drinking water standards.
the contaminated groundwater is not being used, nor is it planned to be used while the site is
controlled by DOE. Use of this groundwater as a drinking water source would present unac-
ceptable risk levels. The goals of this action are to mitigate the migration of contaminants
and prevent the further degradation of the groundwater system. These goals are consistent
with the expectations of the NCP and EPA guidance on addressing groundwater contamina-
tion.
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Interim Action Record of Decision
WSRC-TR-94-0375 Remedial Alternative Selection
VII. Description of Alternatives
• Interim action alternatives developed for the TNX Area Groundwater Operable Unit
include:
Alternative 1
No Interim Action, Maintain Existing Institutional Controls
Alternative 2
Hybrid Groundwater Corrective Action, the hybrid groundwater corrective action includes
groundwater extraction wells with an air stripper and a recirculation well.
Alternative 1—No Interim Action, Maintain Existing Institutional Controls
Alternative 1 would include no interim cleanup activities. Under the no action alternative,
existing groundwater contamination would gradually be reduced with time and distance
through attenuation processes, such as biodegradation or dispersion. Contaminated ground-
water would continue to migrate west toward the swamp and the Savannah River.
Treatment Components
No treatment would be implemented under Alternative 1.
Engineering Controls
No engineering controls would be executed under this alternative.
Institutional Controls
Access to SRS is controlled at primary roads by continuously manned barricades. Other
roads entering the site are closed to traffic by gates or barriers. The entire SRS facility is sur-
rounded by an exclusion security fence, except along the Savannah River. SRS is posted
against trespassing under Federal and state statutes.
Implementation Requirements
This alternative is readily implementable.
Estimated Construction and Operation and Maintenance Costs
Costs associated with Alternative 1 include groundwater monitoring and annual reporting.
Groundwater monitoring and reporting is estimated to be $20,000/year.
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Interim Action Record of Dec. i .
WSRC-TR-94-0375 Remedial Alternative Selection
ARARs Associated with the Considered Alternative
Applicable or Relevant and Appropriate Requirements (ARARs) are Federal and state envi-
ronmental regulations that establish standards that remedial actions must meet. There are
three types of ARARs:
• chemical-specific
• location-specific
• action-specific
No Action-specific ARARs are associated with Alternative 1. The only potential location-
specific ARAR associated with Alternative 1 is related to the Clean Water Act.
Alternative 2-Hybrid Groundwater Corrective Action
Alternative 2, the Hybrid Groundwater Corrective Action, includes groundwater extraction
wells with an air stripper and a recirculation well. The extraction wells and air stripper
would be used to remove and treat the groundwater exceeding the cleanup goal in the TNX
Area Groundwater Operable Unit A recirculation well installed upgradient of the extraction
wells would provide in situ treatment of contaminated groundwater and may stimulate the
natural soil bacteria to degrade some of the contamination while in the aquifer. Air emis-
sions from the air stripper and recirculation well will be treated as necessary to comply with
SCDHEC air pollution regulations.
Treatment/Engineering Controls
Recirculation Weils
Recirculation wells are an emerging technology for in situ cleanup of CVOC contaminated
groundwater. In recirculation wells, air is injected into a groundwater well. As the air rises
to the surface in the well, it removes CVOCs from the water by air stripping. Additionally.
the air causes groundwater to flow upward in the well establishing a circulation system
where water is drawn into the bottom and discharged at the water table. The air is collected
by a vacuum at the surface for treatment (see Figure 11). The vacuum also recovers soil
vapor from the unsaturated zone resulting in additional cleanup.
Extraction Wells with an Air Stripper
The flow of contaminated groundwater is intercepted by a series of water wells known as
extraction wells. The extraction wells are used to drawdown the water table and collect con-
taminated groundwater. Drawdown from the extraction wells produces a capture zone that
prevents the further migration of contamination from the site (see Figure 12). The contami-
nated groundwater that is collected by the extraction wells will be treated by an air stripper.
Treated groundwater will be discharged to a permitted outfall. The air stripper can also be
used to treat contaminated water from other cleanup activities such as groundwater sam-
pling. Air emission from the air stripper and recirculation well will be treated as necessary
to comply with SCDHEC air pollution regulations.
Mercury, gross alpha, and nitrate will be monitored in the effluent from the treatment system
to ensure that they do not exceed discharge limits. If they begin to exceed discharge limits.
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Interim Action Record of Decision
WSRC-TR-94-0375 Remedial Alternative Selection
the well causing the exceedance will be identified through sampling, and discharges from
that well will be treated using methods similar to ion exchange or reverse osmosis.
Performance Objectives
The performance objectives of the interim action are to:
• Stabilize the operable unit and prevent the further degradation of the ground water system
by containing the portion of the plume with >500 ng/L TCE. This concentration level
was selected based upon calculations performed associated with the IRE and technical
considerations for well placement and system performance. Controlling the portion of
the plume with >500 u,g/L TCE will also control and treat the area with the highest con-
centrations of other CVOCs and nitrates.
• Maintain risks associated with potential exposure pathways within acceptable limits.
• Implement an action that will not be inconsistent with and facilitate potential future
cleanup efforts.
The interim action cleanup goal was developed using a risk-based approach to protect
humans in the interim exposure scenario with the highest risk of cancer, the onsite worker.
In the IRE. the onsite worker was exposed to 930 u,g/L of TCE in the groundwater outcrop.
The cleanup goal of the interim action is to reduce the maximum TCE concentration in the
plume to £500 u,g/L ensuring that the concentrations at the seep do not present a risk to
human health and the environment. The 500 (J-g/L concentration for TCE was selected based
on the results of the IRE and the concentration of TCE that is admissable in a solid waste
(TCLP level) before it is considered a hazardous waste. This remedy will provide protection
of human health by ensuring that the most highly exposed person in the IRE does not
receive a dose of TCE that results in an unacceptable cancer risk. CVOC concentration in
the recovery wells, TNX monitoring wells, air stripper influent and effluent, and air stripper
offgas will be monitored to evaluate system performance.
Benefits
In the Hybrid Groundwater Corrective Action, the advantages of one technology addresses
the disadvantages of the other resulting in a robust cleanup system. The benefits of the
Hybrid Groundwater Corrective Action are listed below.
Recirculation Well
• in situ treatment of contaminated groundwater
• in situ biodegradation reduces cleanup times
• conserves groundwater resources during cleanup
• potential for cleaning up the unsarurated zone using soil vapor extraction
Pump and Treat
• stops migration of contaminated water exceeding interim cleanup goals
• collects and treats contaminated water
• provides infrastructure for handling secondary waste associated with cleanup
• enhances transport of nutrients from recirculation well for in situ cleanup
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Interim Action Record of Decision
WSRC-TR-94-u375 Remedial Alternative Selection
Institutional Controls
Public access to SRS is controlled by existing security personnel and security equipment, as
discussed under Alternative 1. The existing SRS security controls will be maintained as pan
of normal SRS operations.
Implementation Requirements
The implementation requirements for the Hybrid Groundwater Corrective Action will
include the following:
• installing groundwater recovery wells to capture the portion of the plume with >500 ug/L
TCE
• constructing the air stripper to treat the TCE and other CVOCs in the recovered ground-
water
• installing a recircularion well to enhance the natural in situ biocegradation of TCE and
other CVOCs in the groundwater
Standard drilling techniques for unconsolidated sediments will be used when possible. The
recirculation well uses a larger than normal borehole and may require special materials to
drill the well. The air stripper and components of the recirculation well are standard indus-
trial equipment and are readily available. The air lift recirculation well is a relatively new
remediation technique and will require some startup testing to evaluate the optimal operat-
ing conditions.
Estimated Construction and Operation and Maintenance Costs
The costs for Alternative 2 are estimated to be $600,000. Costs include construction, moni-
toring, and maintenance of the recirculation well and pump and treat system.
ARARs Associated with the Considered Alternative
The ARARs for the Hybrid Groundwater Corrective Action are listed in Table 2. The
National Primary Drinking Water Standards (MCL/MCLGs) will not be ARARs because
they are beyond the scope of the interim action.
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Remedial Alternative Selection
038%
• CNonfem. 0.18%
• MMhytm CMandt. 0.02%
£3 CMan T«ncMMd*. 27.77%
Figure 9. Sources of Risk to Onshe Worker
Exposure Scenario
Figure 10. Risks for Different Exposure Scenarios
25
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Remedial Alternative Selection
Flow patterns for a Retirculation Well System
Alrk^aefion
O&gas recovery
Figure 11. Flow Patterns for a Recirculaiion Well System
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interim Action Record of Decision
Remedial Alternative Selection
ZomeT
by
The Hybrid Groundwater Corrective Action is designed to stabilize the groundwater contamination through containment
of the most contaminated groundwater. Containment of the portion of the plume with >500 ug/L TCE will be accom-
plished using 3-5 recovery wells cumulatively pumping up to 30 gallons per minute. A recirculation well will be installed
in the most contaminated portion of the groundwater being contained by the recovery wells to accelerate the reduction of
contamination levels. The bottom of the recirculation well recovers groundwater and the top of the recirculation recharges
the contaminated aquifer with treated groundwater containing nutrients to stimulate in situ cleanup of the contamination
downgndient of the recirculation well. As the water rises in the recirculation well, the nutrients in the air. used to treat the
contaminants, dissolve into the water (see Figure 11). The recovery wells can be used to direct the recharge from the recir-
culation well to expand the zone of in situ cleanup. The hypothetical capture zone above was developed using a simplified
model of the groundwater flow at TNX based on data from monitoring wells and pumping tests.
Figure 12. Capture Zone of a Hypothetical Hybrid Groundwater Corrective Action for TNX
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Table 2. Applicable or Relevant and Appropriate Requirements (ARARs) and Guidance for the Hydraulic Contain-
ment of Offsite Groundwater
Actions
Requirements
Prerequisites
Federal citation
South Caro-
lina Code of
Laws
CHEMICAL-SPECIFIC
Treatment of con-
taminated
groundwater
Air Stripping
Protection of the
general public
from all sources
of radiation
Protection of the
general public
from all sources
of air emissions
Worker protection
Discharge must not exceed
DCGs for radionuclides: dis-
charge of radionuclides must not
exceed 1 rad/day for protection
of aquatic organisms
Environmental Permits to con-
struct and operate
The general public must not
receive an effective dose equiva-
lent greater than 100 mrem/year
All releases of radioactive mate-
rial must be "as low as reason-
ably achievable" (ALARA)
No member of the general public
shall receive an effective dose
equivalent greater than 10 mrenV
year
Maintain worker exposures to
ALARA
Maximum exposure to occupa-
tional workers: 5 rem/year (sto-
chastic); 50 rem/year
(nonstochastic) effective dose
equivalent
Direct discharge of groundwater to
a surface water body - TBC guid-
ance
Discharge of toxic air pollutants
(trichloroethylene and tetrachoro-
ethylene) - Substantive require-
ments an applicable
Dose received by the general pub-
lic from all sources of radiation
exposure at a DOE facility - TBC
guidance
Releases of radioactive material
from DOE activities - TBC guid-
ance
Emissions of radionuclides to the
ambient air from DOE facilities -
Applicable
Internal and external sources of
continuous exposure to occupa-
tional workers at a DOE facility -
TBC guidance
Internal and external sources of
continuous exposure to occupa-
tional workers at a DOE facility -
TBC guidance
DOE Order 5400.5
DOE Order 5400.5
DOE Order 5400.5
40 CFR 6 1.92: DOE
Order 5400.5
DOE Order 5480. 11
DOE Order 5480. 11
SC-R. 61-62.1.
SC-R. 61-62.5.
Standard Number
8
ACTION-SPECIFIC
Erosion Control
Well Construction
Develop a plan for erosion sedi-
ment control
Construction by a certified driller
is required
Standards for construction, main-
tenance, and operation of all
wells
Standards for construction of
injection wells
Land disturbing activities - Appli-
cable
Drilling water wells - Applicable
Drilling water wells - Applicable
Construction injection well (recir-
culating wells) - Applicable
40 CFR 144-147
SC 72-300
SCR.61-71
SCR.61-71
SCR.61-87
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Table 2. Applicable or Relevant and Appropriate Requirements (ARARs) and Guidance for the Hydraulic Contain-
ment of Offsite Groundwater
Actions
Discharge of
treated groundwa-
ter to stream
Air Stripping
Requirements
Discharge must comply with the
effluent limitation of the NPDES
permit SC 0000175
Discharges to streams must meet
the established water quality
standards
State of S.C. requires a permit to
build and operate a wastewater
facility
A NESHAP evaluation to deter-
mine if source of radionuclide
emission requires EPA approval
Prerequisites
Point sources discharge to waters
of the United States - Applicable
Discharges to surface waters of the
State - Applicable
Construction and operation of an
industrial wastewater treatment
facility - Substantive require-
ments and applicable
Radionuclides other than radon
from DOE facilities - Substantive
requirements are applicable
Federal citation
40CFR 122
40 CFR 61.96
South Caro-
lina Code of
Laws
SCR.61-9
SCR.61-68
S.C. Pollution
Control Act Title
48-1-110
Acronyms used in Table 2
TBC = to be considered
DCGs = derived concentration guide
CFR = Code of Federal Regulations
DOE = Department of Energy
EPA = Environmental Protection Agency
NPDES = National Pollutant Discharge Elimination System
NESHAP = National Emissions Standards for Hazardous Air Pollutants
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VIII. Summary of Comparative Analysis of Alternatives
•Each interim response alternative was evaluated using nine criteria developed by the EPA.
The criteria were derived from statutory requirements of CERCLA. Section 121. The results
of the evaluation are presented in Table 3.
Descriptions of Nine Evaluation Criteria
• Overall Protection of Human Health and the Environment. This addresses whether a
remedy provides adequate protection and describes how risks posed through each path-
way are eliminated, reduced, or controlled through treatment, engineering controls, or
institutional controls.
• Long-Term Effectiveness and Permanence. This refers to the magnitude of residual risk
and the ability of a remedy to maintain reliable protection of human health and the envi-
ronment over time once cleanup goals are met.
• Shan-Term Effectiveness. This refers to the speed with which the remedy achieves pro-
tection, as well as the potential for a remedy to create adverse effects on human health
and the environment that may result during the construction and implementation period.
• Reduction ofToxicity, Mobility, or Volume through Treatment. The remedial alternatives
are assessed based on the degree to which they employ treatment that reduces toxicity.
mobility, or volume, including how treatment is used to address the principal threats
posed by a media-specific operable unit.
• tmplementability. This refers to the technical and administrative feasibility of a remedy.
including the availability of materials and services that may be used to implement the
chosen solution.
• Compliance with Applicable or Relevant and Appropriate Requirements (ARARs). This
criterion addresses whether a remedy will meet the ARARs of other Federal and state
environmental statutes.
• Cost. This includes capital, operation, and maintenance costs.
• State Acceptance. Based on its review of the proposed interim action, this indicates
whether the state concurs with, opposes, or has no comment on the preferred alternative.
• Community Acceptance. Acceptance by the surrounding community will be assessed in
the Record of Decision following a review of the public comments received on the pro-
posed interim actions.
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Table. 3
Evaluation of Interim Response Actions
Evaluation Criteria
Overall Protection of Human
Health and the Environment
Compliance with ARARs
Long-term effectiveness and
permanence
Reduction of toxicity, mobil-
ity, or volume through treat-
ment
Short-term effectiveness
Implementability
Cost (for comparison only)
State acceptance
Community acceptance
Alternatives
(1) No action
Minimal
This alternative will not be in compliance
with the Safe Drinking Water Act in the
following areas:
• contaminant concentrations in the
groundwater and local surface water
exceeds PDWS
• surface water concentrations in local
seeps do not meet NPDES require-
ments
This evaluation criterion does not apply to
Interim Actions.
None
This alternative does not provide a short-
term remedy for preventing discharges of
contaminated groundwater to the swamp.
This alternative is already in place.
Capita] Cost: $0
Operation and Maintenance (O&M)
Costs: approximately $20,000 per year
Months to Implement: already in place
This alternative is not acceptable to
SCDHEC.
See responsiveness summary.
(2) Hybrid Groundwater Corrective
Action
High
The water treatment plant (air stripper) will
be constructed and operated in full compli-
ance with wastewater treatment plant regu-
lations. Treated groundwater will meet
NPDES requirements and offgas from the
treatment system will meet Clean Air Act
regulations.
Same as no action.
Air stripping removes the contaminants
from the recovered groundwater, reducing
its toxicity. Volume of groundwater that
may pose a risk to onsite workers will be
reduced through reduction of contaminant
mass in the portion of the plume exceeding
the interim goal.
Groundwater recovery will immediately
begin to reduce the amount of contaminant
remaining in the subsurface and control the
migration of contaminated groundwater
into the swamp.
All of the technologies in this alternative
are currently available. Air stripping is
extremely efficient and requires minimal
maintenance. This system has a wide range
of operating conditions and as result, reme-
diation system upgrades can be easily
incorporated.
Capital Cost: $600.000
Operation and Maintenance (O&M)
Costs: approximately $ 100,000
Months to Implement: 18-24
This alternative is acceptable to SCDHEC.
See responsiveness summary.
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IX. Selected Remedy
• Alternative 2 is the selected alternative for this interim action. This alternative will provide
the best balance between the need for prompt action for groundwater remedial actions and
the current site conditions and exposure scenarios. The hybrid groundwater corrective action
will achieve the goals highlighted for this action and will serve as an incremental step in
addressing environmental contamination within the TNX Fundamental Study Area and
SRS.
The hybrid groundwater corrective action system will stabilize the portion of the piume with
>500 |ig/L TCE as it is generally depicted in Figure 5. However, if the area containing TCE
levels exceeding 500 \ig/L has expanded, the area that will be intercepted will be expanded
accordingly. Samples from existing monitoring wells as well as samples from the influent
and effluent from the air strippers, air emissions from the air stripper, and the recirculation
well will be used to monitor the performance of the interim action. The details of the moni-
toring will be discussed in the operating and maintenance plan for the hybrid groundwater
corrective action system.
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X. Statutory Determination
- The National Contingency Plan (40 CFR 300.430(e)(9)) sets forth nine evaluation criteria
that provide the basis for evaluating alternatives and subsequent selection of a remedy. The
selected alternative. Alternative 2. was evaluated with respect to the five statutory findings.
as required for interim actions under CERCLA. The results of the evaluation are as follows:
Protection of Human Health and the Environment. Alternative 2 will mitigate the risks of
exposure to contaminated surface water by stopping the migration of groundwater contain-
ing CVOCs above the interim cleanup goal before it reaches the swamp and utilizing exist-
ing administrative controls. Additionally, removing CVOC-contaminated groundwater will
reduce the future risk of exposure to contaminated groundwater through ingestion.
Attainment ofARARs. All ARARs pertaining to the treatment and disposal of contaminated
groundwater will be met by the selected alternative (Table 2). The selected alternative will
clean up the contaminated groundwater to meet the interim cleanup goals.
Cost Effectiveness. The recovery well system is a cost- effective method of providing
hydraulic containment of the groundwater contamination beneath an operating facility
where physical barriers are not practical. The recovery system also provides an advantage
over the physical barriers due to the benefits of contaminant removal. Air stripping is an effi-
cient method for removing CVOCs from groundwater and is a well established treatment
method for contaminated groundwater.
Recirculation wells are new technology for cleaning up CVOCs and there is little data on the
cost-effectiveness of the technology. Cost-effective methods such as air lift pumping and air
stripping play a major role in recirculation wells. The cost-effective components along with
potential for in situ groundwater cleanup indicate that recirculation wells will be economi-
cally feasible.
Utilization of Permanent Solutions and Alternative Treatment Technologies or Resource
Recovery Technologies to the Maximum Extent Practicable. The proposed alternative relies
heavily on treatment technologies to remove CVOCs from the groundwater. Treatment is a
principal element of this interim action and is achieved through enhanced in situ biodegra-
dation and air stripping of groundwater contaminated with VOCs. However, this action is an
interim action and is not designed or expected to be final. The selected remedy represents
the best balance of tradeoffs with respect to pertinent criteria given the limited scope of the
action.
Preference for Treatment as a Principal Element. The principal threat in the TNX Ground-
water Operable Unit is trichoroethylene. The selected alternative uses treatment as a princi-
pal element of the Hybrid Groundwater Remediation System. Specifically, the selected
alternative uses air stripping and in situ bioremediation to treat the principal threat. Further-
more, the selected alternative does not include any element that requires storage of waste.
Although this statutory preference is partially addressed in this remedy, the preference for
treatment as a principal element will be addressed by the final response action for this unit.
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XI. Explanation of Significant Changes
• There were no significant changes to the LAPP as a result of the public comments.
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XII. References
•DOE (U. S. Department of Energy), 1987, Final Environmental Impact Statement—Waste
Management Activities for Groundwater Protection Savannah River Plant. Aiken.
South Carolina. DOE/EIS-0120, Savannah River Plant Operations. Aiken, SC 29808.
FFA, Federal Facility Agreement for the Savannah River Site. Administrative Docket No.
09-05-FF, Effective Date: August 16. 1993.
Nichols, R. L-, 1992, Characterization of Shallow Groundwater at TNX (U). WSRC-TR-92-
508, Rev. 0.
WSRC, 1991b, SRS Public Involvement Plan. WSRC-RP-91-445. Rev 2. September 8.
1992, Westinghouse Savannah River Site, Aiken, SC 29802.
WSRC, Assessment of Tritium in the Savannah River Site Environment (U). WSRC-TR-93-
214. October 1993, Westinghouse Savannah River Site, Aiken. SC 29802.
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Interim Action Record of Decision
WSRC-TR-94-0375 Remedial Alternative Selection
Appendix A
Responsiveness Summary
General Response
During the 30 day comment period, a request for a public meeting was received. The public
comment period was extended an additional 30 days so the public meeting could be held.
The public information meeting was held on October 11, 1994. in Aiken. South Carolina.
The public meeting was divided into three main segments: a general introduction section, a
discussion about the proposed TNX groundwater interim action, and a discussion about the
proposed D-Area Oil Seepage Basin interim action. The TNX discussion was broken into a
general information and background segment, a discussion and question/answer session
about the proposed interim action, and finally, an opportunity for formal commenting. No
formal comments were received at the public meeting.
During the public comment period, limited written comments were received. In general.
comments concerning the proposed action for the TNX groundwater unit addressed techni-
cal details regarding treatment of the extracted groundwater. No comments were received
which opposed the proposed action. During the public information meeting, several ques-
tions were raised regarding selection of the interim action goals and general information on
the contaminants present at the site. No comments were received which opposed the pro-
posed action. The minutes of the public meeting are available in the administrative record
file.
During the public information meeting, suggestions were received from the Energy
Research Foundation on potential improvements to the meeting format. These comments
will be evaluated, and to the extent possible, the recommendations will be followed.
Written comments were received from members of the public and the Energy Research
Foundation.
Specific Comments
Comment
A series of public meetings should be held.
Response
A public meeting was held on October 11, 1994, in Aiken, SC, to discuss the proposed
interim action. In general, the Department of Energy plans to conduct periodic public infor-
mation meetings to review the general status of significant cleanup operations, solicit public
input on specific remedial actions, and provide an opportunity for the public to discuss
cleanup issues with DOE and the regulators.
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Interim Action Record of Decision
WSRC-TR-94-0375 Remedial Alternative Selection
Comment
Energy Research Foundation
Columbia, SC
... The phrase "treated as necessary" on page 11 begs further definition as to whether the air
will be routinely treated, or whether it will be treated only when it goes above a certain
monitoring threshold. If so, what is the threshold, and is it consistent with the State and Fed-
eral regulations? However, air emissions will be monitored to ensure compliance with appli-
cable regulations.
Response
The treatment threshold is set by the State and Federal air regulations. Discussions with the
State and Federal regulators about the anticipated air emissions from the TNX treatment
system indicate that no treatment of air emissions will be required.
Comment
Energy Research Foundation
Columbia, SC
Further, SRS should certify that it has the treatment capability for each of the contaminants
that may be present in groundwater that is pumped to the surface for treatment and dis-
charge via the "permitted outfall." The permitted outfall is, presumably, to be a NPDES per-
mitted stream. NPDES permits don't include radioactive materials though, and it's not clear
what "discharge limits" SRS will apply. Any surface water discharge that exceeds Federal
drinking water standards would not be acceptable - not because it wouldn't be illegal, but
because it is probably increasing the risk to the public.
Response
A wastewater construction permit must be issued by the SCDHEC before the construction
of the wastewater treatment plant can begin. All chemical constituents in the groundwater
that require treatment prior to discharge at a permitted NPDES outfall in the TNX area will
be addressed by the treatment system. SCDHEC does not issue water construction permits
unless all necessary treatment is provided for in the permit application. SRS will meet dis-
charge requirements for radionuclides in compliance with DOE Order 5400.5. which is soon
to be 10CFR 834. The contaminant of concern in the interim has been identified in the
lAPPas trichloroethylene. Stabilization and remediation of the portion of the plume with
the highest concentrations of TCE will also address the portion of the plume with the high-
est concentrations of other contaminants that do not pose an unacceptable health risk during
the interim remediation period.
Comment
Energy Research Foundation
Columbia, SC
Questions about the combined effects of pumping, treating, and releasing contaminated
groundwater should be answered before a decision is made.
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Interim Action Record ot uc\.i
WSRC-TR-94-0375 Remedial Alternative Selection
Response
All questions pertaining to the combined effects of pumping, treating, and releasing contam-
inated groundwater were answered in the public hearing. Specifically, a question to the
mobilization of mercury as a result of pumping was asked. The mobile form of mercury is
not stable in groundwater at TNX. and as a result the mercury contamination is highly
localized
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