United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EP AlRODIR08-91/04 7
June 1991
CO!Y (
I
PE Of?. ~16
-------
50272-101
REPORT DOCUMENTATION 11. REPORT NO. I ~ 3. Recipient'a Acce88ion No.
PAGE EPA/ROD/R08-91/047
4. Title and Subtitle 5. Report Date
SUPERFUND RECORD OF DECISION 06/27/91
Chemical Sales (New Location) (Operable Unit 3), CO
6.
Third Remedial Action - Final
7. Author(a) 8. Perfonnlng Organization Rept No.
D. Perfonnlng Orgalnlzatlon Name and A!ldru.. 10. ProjectITa8k/Work Unit No.
11. Conlt8ct(C) or Granl(G) No.
(C)
(G)
1~ Sponaoring Organlz8\lon Name and Addre.. 13. Type 01 Repor1 & Pertod Covered
U.S. Environmental Protection Agency
401 M Street, S.W. 800/000
Washington, D.C. 20460 14.
15. SUpplementary Notee
16. Abelrec1 (Utnlt: 200 worda)
The Chemical Sales (New Location) (Operable Unit 3) site is an active chemical sales
and storage facility in Commerce City, Adams County, Colorado. Land use in the area
is predominantly industrial. This area is part of a 4-square-mile area, which
consists of single and multifamily residences, small businesses, municipal facilities,
and agricultural and undeveloped land. An estimated 30,000 residents near the site
use the alluvial aquifer as the principal source of drinking water. Since 1976,
Chemical Sales (CS) has used the site to store and sell a variety of organic chemicals
and acids. Onsite features include a warehouse, a tank farm, and an associated system
of underground storage tanks and pipelines. Between 1985 and 1990, three onsite
chemical releases of hazardous substances into the soil and ground water from the CS
facility were documented. First, in 1985, approximately 200 gallons of methylene
chloride were released during an onsite chemical transfer. Second, in 1986,
VOC-contaminated rain water was discharged into a nearby drainage ditch. And third,
in 1990, approximately 3,700 gallons of methanol were spilled on the the ground
surface near the CS tank farm. EPA investigations confirmed the release of hazardous
substances into ground water from the CS property. This site has been divided into
three operable units (OUs) for remediation. Two previous 1991 Records of Decision
(See Attached Paqe)
17. Document AnalyaJe L Deecrlptors
Record of Decision - Chemical Sales (New Location) (Operable Unit 3), CO
Third Remedial Action - F ina 1
Contaminated Medium: gw
Key Contaminants: VOCs (benzene, PCE, TCE)
b. Identifle,8I0pen-Ended Tenna
c. COSA TI FleldlG,oup
18. AvoJlebilty Statement 1 D. Sec..ity CIa.. (Thie Report) 21. No. o' pegea
None 194
20. Security CIa.. (Thia Page) ~ Price
Nonp
See ANSl-Z3D.18 See InalrucUon. on ~v.- (4.77)
(Formerly NTIS-35)
Depertment o' Commerce
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EPA/ROD/R08-91/047
Chemical Sales (New Location)
Third Remedial Action - Final
(Operable Unit 3), CO
Abstract (Continued)
(RODs) have addressed soil and ground water contamination as OUl and OU2. This ROD
addresses OU3, residential exposure to site contaminants through domestic use of the
underlying alluvial aquifer. The primary contaminants of concern affecting the ground
water are VOCs including benzene, PCE, and TCE.
The selected remedial action for this site includes connecting residences currently
using alluvial wells for domestic water supply to the South Adams County Water Supply
District (SACWSD); installing home-activated carbon units in homes not readily
accessible to SACWSD; implementing ground water monitoring for benzene; and providing
public notification of the potential health threat from the contaminated ground water.
The estimated present worth cost for this remedial action is $157,000, which includes an
annual O&M cost of $5,520 for 30 years. Future costs for activated carbon treatment
units have not been estimated, and residents may be expected to pay small annual O&M
costs.
PERFORMANCE STANDARDS OR GOALS:
Chemical-specific goals were not provided.
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CHEMICAL
RECORD OF DECISION
SALES COMPANY SUPERFUND
OPERABLE UNIT 3
DECLARATION STATEMENT
SITE
SITE NAME AND LOCATION
Chemical Sales Company Site
Adams County, Colorado
Operable Unit 3 - Residential Exposure to Contaminated Ground Water
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial action for
the Chemical Sales Company (CSC) Site, Operable Unit (OU) 3 located
in Adams County, Colorado.
This remedy was chosen in accordance with the Comprehensive
Environmental Response, Compensation and Liability Act of 1980
(CERCLA) , as amended by the Superfund Amendments and Re-
authorization Act of 1986 (SARA) and the National oil and Hazardous
Substances Pollution Contingency Plan (NCP).
This decision document explains the basis for selecting the remedy
for this OU. The information that forms the basis of this remedial
action decision is contained in the Administrative Record for this
Site and is summarized in the attached decision summary.
The State of Colorado concurs with the selected remedy for OU3.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from this
site, if not addressed by implementing the response action selected
in this Record of Decision (ROD), may present an imminent and
substantial endangerment to public health, welfare, or the
environment.
DESCRIPTION OF SELECTED REMEDY
The CSC site has been divided into three operable units: Leyden st.
location (OU1): Volatile Organic Compound (VOC) ground-water
contamination north of Sand Creek (OU2); and residential exposure
to contaminated ground water (OU3). Contaminated soil located on
the CSC property and ground-water contamination located south of
Sand Creek make up the area known as OU1. Remedial action
objectives for OUl include the control of migration of contaminated
ground water from OU1 into OU2. A separate ROD will be prepared
for the remediation of OU1. The selected remedy presented in the
ROD for OU2 addresses ground water that has been contaminated by
sources within and outside of OU2. The remedy addresses both the
tetrachloroethylene (PCE) plume which originates in the vicinity of
56th Avenue and Quebec Street and a residual plume comprised of
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several volatile organic compounds, primarily trichloroethylene
(TCE) whose source is primarily the CSC property (OU!). The ROD
sUI!h~laries for both OU2 and OU3 have been incorporated into one
document. This document is attached to this Declaration Statement.
The selected remedy for OU3 addresses residential exposure to
contaminated ground water through use of private alluvial wells.
The major components of the selected remedy for OU3 include:
*
Connection of private alluvial well users to the SACWSD
Water system;
*
For residences located in rural areas without reasonable
access to SACWSD water lines, provision of individual
home activated treatment units; and
*
Notification of potential health risks associated with
contaminated ground water, upon request for an alluvial
well permit within the CSC Site.
'STATUTORY DETERMINATIONS
The selected remedy for OU3 is protective of human health and the
environment, complies with federal and State requirements that are
legally applicable or relevant and appropriate to the remedial
action, and are cost-effective. These remedies utilize permanent
solutions and alternative treatment technologies to the maximum
~xtent practicable. No principal threat exists for OU3.
~9t~..
Jame Schere
Regional Adminis~rator
EPA Region VIII
~-'~
~
r f t I
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RECORD OF DECISION
CHEMICAL SALES COMPANY SUPERFUND SITE
OPERABLE UNIT 2 - GROUND-WATER CONTAMINATION
OPERABLE UNIT 3 - RESIDENTIAL EXPOSURE
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Section
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
TABLE OF CONTENTS
Paqe
SITE HISTORY AND ENFORCEMENT ACTIVITIES
SITE NAME, LOCATION, AND DESCRIPTION. . . . . . . . . 3
. . . . .
HIGHLIGHTS OF COMMUNITY INVOLVEMENT
........
SCOPE AND ROLE OF OPERABLE UNIT WITHIN SITE STRATEGY
SITE CHARACTERISTICS.
. . . . .
. . . .
SUMMARY OF SITE RISKS
. . . .
. . . . .
SUMMARY OF ALTERNATIVES
...........
SUMMARY OF THE COMPARATIVE ANALYSIS OF ALTERNATIVES
SELECTED REMEDY
. . . . .
. . . .
. . . . . .
STATUTORY DETERMINATIONS
. . . . .
DOCUMENTATION OF SIGNIFICANT CHANGES.
. . . .
REFERENCES
.......... ..... .... .....
APPENDICES
APPENDIX A.
ARARs
APPENDIX B.
RESPONSIVENESS SUMMARY
APPENDIX C.
STATE CONCURRENCE
1 of 91
. . 7
11
13
14
27
43
66
77
86
89
91
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FIGURES
1-
c.. 2.
3 .
4.
5.
6.
7.
TABLES
1-
2.
3.
4.
5.
6.
7.
8.
9.
10.
Paqe
CSC Site Location Map. .
........
. . . . . . . 4
SACWSD Wells and Wells of Residences Not
Connected to the SACWSD System. . . . .
. . . . .
Alluvial Aquifer Water Table Elevation
. . . . . . .
Bedrock Surface Elevation. . . . .
Saturated Thickness of Aquifer
. . . .
. . . .
TCE Plume.
. . . . .
. . . .
. . . . . .
PCE Plume
. . . . .
. . . . .
.........
Reference Doses and Cancer Potency Factors
for CSC OU2 COCs . . . . . . . . . .
. . . . .
Chemical Concentrations Used to Calculate
Case 1 Exposure Point Concentrations. . . . . . . .
Case 2 (Well SAC-18) Exposure Point Concentrations
Exposure Estimates for Case 1
Exposure Estimates for Case 2
. . . . . .
OU2, Chronic Hazard Index Estimates, Excess
Cancer Risk Estimates, Case 1 . . . . . . .
. . . . .
OU2, Chronic Hazard Index Estimates, Excess
Cancer Risk Estimates, Case 2 . . . . . .
Remediation Levels for CSC OU2
. . . . .
Costs of Remedial Alternatives, OU2
Costs of Remedial Alternatives, OU3 .
........
2 of 91
. . 5
17
18
19
22
23
32
35
37
38
40
41
42
47
74
76
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I.
SITE NAME, LOCATION, AND DESCRIPTION
The Chemical Sales Company (CSC) Superfund site is located in
Commerce City and in north Denver, Colorado, approximately
five miles northeast of downtown Denver, Colorado. The Site
is divided into three operable units, Operable Unit No. 1
(OUl) and Operable Unit No.2 (OU2), which are separated by
Sand Creek (see Figure l), and Operable Unit No.3 (OU3),
which addresses residential exposure to contaminated ground
water through use of private alluvial wells. OUl
investigations address source control/source removal of
contamination identified on, adjacent to, and downgradient of
the CSC facility, and OU2 investigations address VOC ground-
water contamination north of Sand Creek. The subject of this
decision summary is OU2 and OU3. OU2 addresses volatile
organic compound ground-water contamination north of Sand
Creek. OU3 addresses residential exposure to contaminated
ground water within the OU2 area.
OU2 is located north and hydrogeologically downgradient of
OUl, extending from Quebec Street to the east, Holly Street to
the west, Sand Creek to the south, and East 86th Avenue to the
north (Figure 1). These boundaries have been defined by the
approximate extent of volatile organic ground-water
contamination extending northward from Sand Creek. Existing
and potential residential exposure addressed in OU3 occurs
t.hrough use of private alluvial wells in OU2. Figure 2
describes the location of residences that are dependant on
private alluvial wells as their sole source of water for
indoor use. OU2 and OU3 are located wi thin Adams County,
Colorado, and are mostly contained within Commerce City. A
Remedial Investigation (RI) and Feasibility Study (FS) were
ini tiated by EPA for OU2 in June 1989. The OU3 FS was
initiated in January 1991. site characterization data used
for the OU3 FS were based on information collected for the OU2
RIo
3 of 91
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SITE
LOCATION - ,
.
COLORADO
--
I
1
I
1
__I
ROCK Y MOUNTAIN
ARSENAL
~
o
....
\D
.....
~
r- I 8,.
ST APlETON ~ C
INTERNATIONAL , 'I1~~1(
AIRPORT -,
,--'
~-~
COLFAX AVE.
~
~
Sc8Ie
0 t t S 4
. '
MI88
a..I08I ..... Co8IPMr ... RW8
CSC 918 Location Map
c- -..... -. 8IC.
,.....
1
COM
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SAC-47
o
SAC-21
E 86t
.
«
:J
I
«
o
SAC~3 8 SAC-17
00 I
SAC~2 SAC~5
o KLEIN WATER
TREATMENT PLANT
.
SAC-16
o
.
.
.
SAC-14
o
.
ROCKY
MOUNTAIN
ARSENAL
N
A
SCALE
o '.000 2.000 3.000
FEET
LEGEND
SAC-oS SACWSD ALLUVIAL
o MUNICIPAL .t.ELL
KNOWN
. WELLS BEL0"1GING
TO RESIDENCES
NOT CONNECTED
TO SACWSD
FIGURE 2
SACWSD "'ELLS AND WELLS OF RESIDENCES
NOT CONNECTED TO THE SAC\-VSD SYSTEM
5 of 91
, -
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levels. This scenario provides an estimate of potential
health risks if the SAC-1S water were to be used directly.
The two routes or exposure pathways evaluated quantitatively
were:
1-
2.
inqestion of the water during normal residential use, and
inhalation of volatiles during showering.
Basement VOC exposure was not evaluated for two reasons: (1)
a validated basement exposure model was not available at the
time the risk assessment was prepared and (2) ground-water
concentrations were so low within OU2 that the contribution of
the pathway was judged to not contribute significantly to the
overall risks at the Site. Such potential risks will be
reevaluated during the 5 year review to ensure the remedies
selected are protective.
Representative exposure point concentrations were developed
from the sampling data for the contaminants of concern. For
Case 1, the concentrations of individual contaminants in
ground water at the hypothetical well were set equal to the
ari thmetic average of the highest concentrations from 3-5
validated samples from the 1989 sampling for each contaminant
of concern. A range of sample numbers was used because there
were different numbers of validated samples for each compound.
This approach was selected to obtain a RME estimate that
reflects potential mixing of different contaminants from
various sources wi thin the alluvial aquifer of OU2. Wells
with the highest concentrations of individual contaminants and
average contaminant concentrations calculated for the Case 1
scenario are presented in Table 2. The best approximation of
the RME for Case 1 assumes that all contaminants of concern
could be present in a single location but that their
respective concentrations would not likely exceed an average
34 of 91
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TABLE 2
CHEMICAL SALES COrtPAHT OU2 RA
CHEMICAL CONCENTRATIONS (ug/L) USED TO CALCULATE CASE 1 EXPOSURE POINT CONCENTRATIONS
VeU ID
PCB
TCE
TCA
DCA
1,I-DCE
1,2-DCB
8.nz.ne
Vinyl
Chlol'1d.
0\1-004
DII-029
D\I-030
0\1-051
011-062
011-073
0\1-076
0\1-104
0\1-106
SAC-02
SAC-H\I-02
SAC-H~J8
SAC-14
NH\I-09
FIT-IH-HV-02
FIT -IH-\lP-OI
FlT-IH-\lP-02
FIT -IH-\lP-03
37
100
47
9
8
12
16 J
13
11 J
'J
9
6
19
23
18
2 J-C
2 J-C
2 J-C
3 J
55
8
2 J
37
73
31
28
. ~4
6
28
17
4 J
11
Ad th..etic Hean
of Highest 3-5
Values
58
48
9.3
13
7.5
21
2
3
Note: Values used are fro. COM fall 1989 s88pllng. The type of analysis Is Routine Analytical
Services (RAS) through the IPA Contract Laboratory Pro,r.. (CLF). All results used have been
validated. Qualifiers are explained In Table 5-1C.
. Not validated so not Included In average
J - The associated nu.erical value is an esti.ated quantity bee au.. the &8ount
detection 11.1t. or becau.. quality control criteria were not ..t.
C - The value vas esU.ated due to h.stru.ent calibration proble.s.
detected h below the requlrecl
-
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Contaminated soil located on and adjacent to the CSC property
and ground-water contamination located south of Sand Creek
make up the area known as OUI. OUI is also known as the
Leyden Street location. It is approximately bounded by Forest
Street to the west, I-70 to the south, Quebec Street to the
east, and Sand Creek to the north. The CSC Site was first
developed in 1962 when a warehouse was constructed on the
property. CSC purchased the property in 1976 and began
installing both above and below ground chemical storage tanks
ranging in size from 5,000 to 15,000 gallons and containing a
variety of organic chemicals and acids. The CSC facility has
been identified as a source of contamination to ground water
in OU2 as a result of both documented and undocumented spills
related to handling and storage of chemicals. A RI/FS has
been conducted for the OUI Site by the Chemical Sales Company
under an EPA Administrative Order on Consent (CERCLA-VIII-90-
03, signed September 29, 1989).
CSC OU2 and OU3 comprise approximately four square miles and
consist of single and multi-family residences, small
businesses, and municipal facilities. Several truck transport
operations and light industrial facilities are located in the
southern part of the study area. The northern part of the
study area contains areas of irrigated agricultural land and
undeveloped land. The Site is underlain by an alluvial
aquifer which serves as a major water. supply.
CSC OU2 and aU3 are located in the piedmont, at the juncture
of the Rocky Mountain and High Plains physiographic provinces.
The study area for these operable units is contained within
the South Platte River Basin. The topography is characterized
by low relief with elevations ranging from approximately 5,200
feet at Sand Creek at the southern end of the study area to
5,120 feet at the northwest corner of the study area.
6 of 91
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Extensive ground-water contamination by VOCs has been observed
in the shallow alluvial aquifer beneath the site. Most of the
SACWSD municipal water supply is developed from this aquifer.
The SACWSD supplies about 30,000 customers with water derived
from wells. A total of six alluvial aquifer production wells
are currently in use within OU2. All of these wells except
one, SACWSD Well No. 18, are treated through activated carbon
at a permanent treatment facility selected via the EPA Off-
post Rocky Moutain Arsenal OUI ROD.
II.
SITE HISTORY AND ENFORCEMENT ACTIVITIES
The history of ground-water contaminant investigations and
remediation within CSC OU2 and the surrounding area is very
complex. The first contaminant study in the area began in the
1950s, and numerous studies have been conducted since 1980.
Boundaries of these various studies have often overlapped and
results from one investigation have often led to the
initiation of another. Commerce City and adjacent areas grew
in response to the rapid post-war proliferation of industry
north and east of the city of Denver. A special governmental
district, SACWSD was created in 1953 to provide a water supply
and sewage treatment to the residents and businesses. The
SACWSD supplies approximately 30,000 customers with water from
wells completed in alluvium and bedrbck. Approximately 85
percent of its water supply is derived from the alluvial
aquifer. A total of six SACWSD alluvial production wells are
currently in use within the CSC OU2 boundaries (SAC-14, 2, 3,
5,17, and 18).
In 1981, EPA conducted a random national survey of drinking
water systems. Several organic chemicals were detected in
SACWSD wells. Additional sampling in 1982 and 1985 confirmed
these results. As a result of these findings, EPA began a
7 of 91
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RI/FS of an area called !tEPA's Off-Post Rocky Mountain Arsenal
(RMA) OU1". This area was larger than CSC OU2, extending from
Sand Creek to the south, East 80th Avenue to the north, and
from the South Platte River to the west to the western border
of the RMA to the east. The RI/FS was completed in December
1986. The RI results consistently indicated widespread
contamination by volatile organic compounds in ground water
along the eastern portion of the study area. The selected
alternative was a permanent water treatment system for SACWSD
water. This system, the Klein Water Treatment Plant, began
operating in October 1989. It is located near the SACWSD
municipal water supply center at East 77th Avenue and Quebec
Street. The purpose of the Klein Water Treatment Plant is to
treat contaminated alluvial ground water prior to distribution
to the community, thereby protecting the health of municipal
water supply users. The majority of residents in the area are
provided with treated water from the Klein Water Treatment
Plant. Concurrent with the RI/FS in 1986, some 400 residents
using private wells were connected to the SACWSD municipal
water supply under an EPA removal action.
Following completion of the RI/FS for EPA's Off-Post RMA OU1,
a second au was defined with slightly different boundaries.
Additional ground-water sampling was conducted in 1987 as part
of this continuing investigation. More wells were installed
in 1988 and additional ground-water ~mpling was undertaken.
The adjacent RMA was suspected as one of the potential sources
of contaminants in the EPA's Off-Post Rocky Mountain Arsenal
Study Area because of the history of waste disposal practices
on that site. Further investigation by EPA's Field
Investigation Team (FIT) indicated that additional source
areas were potentially contributing to ground-water
contamination detected within the study area. An EPA soil gas
survey conducted in April 1986 of an area near 48th Avenue and
8 of 91
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Leyden Street indicated elevated TCE ion flux values in the
vicinity of the CSC facility. Ground-water investigations
were also undertaken by EPA in August/September 1986 at 48th
Avenue and Leyden Street and at East 50th Avenue and Ivy
Street, and revealed the presence of volatile organic
contaminants in the vicinity of the CSC facility. A soil gas
survey conducted by the Chemical Sales Company in August 1987
confirmed the presence of TCE and other chlorinated
hydrocarbons near the CSC facility. Ground-water monitoring
wells installed on the CSC property have since confirmed CSC
as a source of ground-water contamination.
Based on the additional work by EPA to define source areas,
the CSC Site was proposed for listing on the National
Priorities List (NPL) in June 1988. Responsibility for the
RI/FS was then transferred from the EPA Off-post Rocky
Mountain Arsenal Study Area to the CSC site studies. The
listing was made final in August 1990.
On August 1, 1989, EPA issued CSC a Special Notice Letter
requesting CSC to conduct an RI/FS for the entire CSC Site.
CSC notified EPA that the company would elect not to conduct
an RI/FS for the entire CSC Site. In June 1989, EPA
subdivided the ground-water RI/FS activities into two separate
OUs for the CSC Site (OU1 and OU2). As a result of this
subdivision, EPA initiated RI/FS activities for OU2 and
requested that CSC conduct an RI/FS for OUl. On September 9,
1989, EPA and CSC entered into an Administrative Order on
Consent requiring CSC to conduct an RI/FS for CSC OUl.
EPA initiated the RI/FS
for CSC OU2
in June
1989.
The
objectives of the RI were to:
*
identify the nature
contamination at the
and
-...ite;
extent
of ground-water
9 of 91
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.
identify existing and potential receptors of the
contc..mination;
.
assess the potential risks to public health and the
environment; and
.
evaluate potential
the QU2 area.
contaminant sources
impacting
To meet these objectives, soil borings were drilled, a
comprehensive sampling of monitoring of private wells was
undertaken, a risk assessment was performed, a laboratory
investigation of the fate and transport of the contaminants
was conducted, and a ground-water flow and transport model was
developed. The FS was then conducted to develop and evaluate
remedial al ternati ves that would effectively minimize the
threat to, and provide adequate protection of, public health
and the environment from contaminated ground water in QU2.
In order to assess existing and potential receptors to the
observed ground-water contamination, a study was conducted by
the Colorado Department of Health and Tri-County Health
Department to determine the water source of residents
potentially at risk from exposure to contaminated ground
water. Results of this survey indicate that 12 known
residents within the CSC QU2 area are solely dependant on
domestic alluvial wells for their principal source of water.
In addition, Tri-County Health Department, under direction of
EPA, conducted a similar survey within CSC QUI. Although many
residents within the QUI area had domestic wells located on
their property, all residents within QUI were provided treated
water from the SACWSD system.
The nearest untreated SACWSD well to the SACWSD pumping center
at 77th Avenue and Quebec street is Well 18, located north of
the SACWSD pumping center (Figure 2). Some organic compounds,
most notably TCE, have been detected sporadically in this
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well. The maximum concentration of TCE that has been detected
in Well 18 is 12 ~g/l. Average concentrations of TCE range
from approximately 4 ~g/l to 6 ~g/l. Although concentrations
of TCE fluctuate dramatically, there appears to be an upward
trend in concentration. Well 18 is not connected to the Klein
Water Treatment Plant, and it is always blended with water
that has been treated at the plant before it is put into the
SACWSD distribution system. Assuming an average TCE
concentration of 3 ~g/l from the Klein Water Treatment
Facility effluent, the maximum concentration of TCE that can
be tolerated in Well No. 18 is 5.7 ~g/l in order not to exceed
the MCLs. Well 18 is located down gradient of the other
SACWSD supply wells. The presence of VOCs in Well 18 water
implies that either the current SACWSD municipal supply wells
are not capturing the entire plume or the contamination is
migrating to Well 18 from other parts of the aquifer. While
remediation of Well 18 is not contemplated at this time, EPA
will evaluate additional data subsequent to issuance of the
RODs for the Site, and if necessary, identify and evaluate
alternatives to address Well 18 ground water contamination.
III. HIGHLIGHTS OF COMMUNITY INVOLVEMENT
Communi ty interest in ground-water contamination in south
Adams County was very intense in 1985 and early 1986 when the
problem first became public. Initially the Rocky Mountain
Arsenal, which is adjacent to the contaminated public water
supply area and already receiving significant media attention,
was thought to be the source. Local citizens formed a very
vocal group, Citizens Against Cont~mination (CAC), which held
a number of well attended public meetings (o,~r 600 people
attended the March 6, 1986 meeting). CAC kept the issue in
the press and in the attention of local, State, and federal
politicians. EPA and the Army responded to numerous public and
11 of 91
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media inquiries, issued press releases for new developments,
and attended the public meetings. Community relations
activities were coordinated among the EPA, the Army, and the
SACWSD. The State conducted a separate program.
Public interest subsided in mid-1986 after a temporary water
treatment system funded by the Army and the EPA came into
operation at SACWSD and treated water was thus made available
to the affected residences. In the fall of 1986, EPA named
the Chemical Sales site as a source of ground-water
contamination. EPA has since issued a number of fact sheets
discussing the progress of the investigation and activities at
the Site. The Chemical Sales Site was also included in joint
community relations activities with several other south Adams
County superfund sites.
The
Proposed
Plan
for
OU2
was
issued
to
the
public
concurrently with proposed plans for OUl and OU3 on
February 25, 1991. The proposed plan and RIfFS reports were
made available to the public in the Administrative Record
maintained at the EPA Region VIII Superfund Records Center in
Denver, Colorado. A notice of availability for these
documents was published in the Denver Post and Rocky Mountain
News on February 28, 1991; in the Commerce City Beacon on
February 27, 1991; and in the Commerce City Express on
March 5, 1991. The public comment period was open from
February 28 to April 1, 1991. The public meeting was held
March 14, 1991 at the Commerce City Recreation Center and was
attended by 50-75 people. A transcript of the public meeting
is included in the Administrative Record. At this meeting,
EPA representatives answered questions about the Site and
discussed the remedial alternatives under consideration.
Details of community involvement throughout the RIfFS are
included in the Responsiveness Summary section of this ROD.
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In addition, responses to comments received during the pubic
comment period on the proposed plan are presented in the
Responsiveness Summary.
IV.
SCOPE AND ROLE OF OPERABLE UNITS WITHIN SITE STRATEGY
The CSC site has been divided into three operable units: OU1,
which addresses contaminated soil located on and adjacent to
the CSC property and ground-water contamination south of Sand
Creek; OU2, the subject of this ROD, which addresses ground
water contamination by volatile organic compounds north of
Sand Creek; and OU3, also the subject of this ROD, which
addresses exposure to contaminated ground water through use of
private alluvial wells located within OU2. OU1 and OU2 are
separated by Sand Creek. OU2 is located north and generally
down gradient of OU1. The boundaries of OU2 have been defined
by the approximate extent of ground-water contamination north
of Sand Creek.
EPA is selecting remedies for OU1 concurrently with the
remedies for OU2 and OU3. Contaminated soil and ground water
within OU1 provide a major source of contamination to ground
water located in OU2. The principal risk at the OU1 Site is
ingestion, direct contact and inhalation of ground-water
contaminants and direct contact and inhalation of soil
contaminants. Contaminated soil is also a principal source of
ground-water contamination.
It is assumed that source control of contaminated ground water
in CSC OU1 will be undertaken as part of the remedial
activities planned for the CSC OU1 Site. Remedial action
objectives for the CSC OUI Site are: 1) to prevent the
migration of contaminated ground water into CSC OU2; 2) to
restore the ground water in CSC OU1 to concentrations meeting
13 of 91
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v.
drinking water standards and carcinogenic risk within 10-' to
10"6; 3) to prevent contaminants in the soil from leaching into
ground water resulting in the non-attainment of the remedial
action objectives for ground water; and 4) prevent inhalation,
ingestion and direct contact with soils resulting in a cancer
risk in excess of 10"6. Since aU2 is located directly
downgradient of aUl, successful attainment of these objectives
will result in the reduction of contaminant concentrations in
ground water within aU2.
The objective of aU2 is to restore alluvial aquifer to
acceptable contaminant levels for indoor use. aU2 addresses
the downgradient portion of the TCE ground-water plume and the
entire PCE plume.
The objective of aU3 is to ensure that all residents within
the CSC Site are provided suitable water for domestic
purposes. Currently, 12 properties within the OU2 Site have
not been connected to the SACWSD municipal water supply system
and rely on their alluvial wells for indoor use. The primary
function of this operable unit is to evaluate remedial
alternatives which will reduce the risk posed through
residential use of domestic water. Remedial alternatives
evaluated under aU3 would reduce exposure to contaminated
ground water for residents using alluvial wells during the
time period required to remediate the aquifer underlying aUl
and aU2.
SITE CHARACTERISTICS
Geoloqy
The Site is located within the Denver Basin, a structural
depression extending from the Front Range eastward to the
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Kansas border, and from Pueblo, Colorado, northward to
the Hartville uplift of Wyoming. At least 12,000 feet of
sedimentary rocks overlie Precambrian basement rock
within the basin, which has undergone episodes of
tectonic movement throughout geologic time. The bedrock
stratum of interest is the Denver Formation of the Dawson
Group, of Upper Cretaceous to Paleocene age. The bedrock
strata are overlain by unconsolidated alluvial and eolian
deposits of variable thickness.
The Denver Formation is comprised of 600 to 1,000 feet of
interbedded shale, claystone, siltstone and sandstone,
with abundant fossil remains and coal seams. Surficial
deposits which overlie the bedrock Denver formation in
the vicinity of the Site consist of alluvial material
deposited by the South Platte River system and windblo~n
sand, silt and clay. The thickness of these
unconsolidated deposits is variable, ranging from less
than 10 feet to over 100 feet in several paleochannel
features eroded into the upper surface of the Denver
Formation by the ancestral South Platte River and its
tributaries. The entire thickness of the unconsolidated
sands, gravels, silts, and clays is considered to be a
single water-bearing unit throughout the Site. In some
areas, the alluvial material may be hydraulically
connected with the underlying Denver Formation.
Hydrogeology
The principal migration pathway for the organic
contaminants is ground-water flow within the alluvial
aquifer. This aquifer is the primary drinking water
source for area residents via SACWSD municipal wells.
Extensive ground-water contamination by volatile organic
compounds has been observed in the alluvium.
15 of 91
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Ground water in the alluvial aquifer beneath OU2
generally flows north to northwest toward the South
Platte River (Figure 3). The water table in OU2 varies
from a few feet below ground surface adj acent to the
South Platte River to about 50 feet below ground surface
at the eastern boundary of the OU2 Site. The
potentiometric surface is characterized by a lower
gradient in OU2 and near the South Platte River, and a
steeper gradient south and east of OU2. The
potentiometric surface configuration is influenced by the
location of bedrock paleochannels (Figure 4) and pumpage
of SACWSD municipal wells (Figure 2), the RMA Irondale
Boundary System and to a lesser extent, private,
commercial, and agricultural wells. Ground-water flow
converges in the vicinity of the SACWSD pumping center at
77th Avenue and Quebec street from southeast to
southwest, because of convergence of paleochannels in
this area. These paleochannels influence the migration
of contaminants, and are important with respect to
contamination of SACWSD municipal wells, since several of
the municipal wells are located in or near paleochannels.
The vertical hydraulic gradient within the alluvium is
generally downward. The vertical gradient between the
underlying bedrock and the alluvium varies from upward to
downward across the Site and is generally considered to
be insignificant in magnitude.
The saturated thickness of the alluvial aquifer varies
widely from localized unsaturated zones to saturated
thicknesses of over sixty feet. Depth to the saturated
zone ranges from a few feet near the South Platte River
to over fifty feet further away from the river (Figure
5). Flow dominates in paleochannels, which contain larger
saturated thicknesses and sand and gravel deposits with
a relatively higher hydraulic conductivity.
16 of 91
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NOTE:
,. ~ - -l1li II\CI. DArA -
MUrnCIof ,. ~ .. ID'T
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LEGEND
'w'ATER
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£LEVATION
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FIGURE 3
N
O DE:I'RtSSION
CONTOUR
t
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ruT
CSC SITE OtJ2 RIm STtroY
.ul.UVl.U. AQ U1FER
WATER TABLE ELEVATION
t:~ n-...n . WArn ntc:..
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17 of 91
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18 of 91
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1.£CE:>'D
."" T"'I:<~i:SS
SATvgA'L~ c
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19 of 91
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The shallow alluvial aquifer is highly transmissive.
Ground-water flow velocity is variable within CSC OU2
(approximately 5 to 12 feet/day), and is locally
influenced by the hydraulic gradient, the hydraulic
conductivity and the effective porosity of the aquifer.
Depending on these factors, travel time from East 48th
Avenue to the SACWSD pumping center ranges from 4.8 to
12.1 years. Actual contaminant velocities will be lower
due to compound retardation.
Nature and Extent of contamination
The results of the CSC OU2 RI showed extensive ground
water contamination by volatile organic compounds in the
study area. Contaminants were not detected in other
media. The chemicals of concern in ground water are:
l,l-dichloroethane (DCA)
l,l-dichloroethylene (DCE)
Total 1,2-dichloroethylene (total 1,2-DCE)
sum of the trans and cis isomers)
l,l,l-trichloromethane (TCA)
Trichloroethylene (TCE)
Tetrachloroethylene (PCE)
Benzene (BZ)
Vinyl Chloride (VC)
(the
This group of contaminants is generally mobile in ground
water. Most of the compounds are central nervous system
depressants and either liver or kidney toxins at high
doses. Six of the compounds are known to cause
carcinogenic effects in animal studies, and of the six,
vinyl chloride and benzene are classified by EPA as Class
A - Human Carcinogens.
Maximum contaminant Levels (MCLs) or proposed MCLs were
exceeded for five of the eight compounds of concern in
CSC OU2 wells during sampling conducted in October 1989.
These compounds are PCE, TCE, DCA, DCE and VC. In
20 of 91
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general, concentrations of contaminants in wells
upgradient (south and east) of OU2 are higher than
concentrations in wells within OU2. Contaminant
concentrations generally decrease from south to north
within OU2. North of the East 77th Avenue SACWSD pumping
center, most contaminant concentrations are below the
MCLs. Maps showing the distributions and concentrations
of contaminants and discussions of temporal trends in
contaminants may be found in the final RI Report.
PCE contamination is pervasive throughout the alluvial
aquifer in CSC OU2. Mean 1989 concentrations ranged from
a high of 110 ug/l north of Sand Creek near 60th Avenue
and Quebec street to less than 10 ug/l near the SACWSD
pumping center at 77th Avenue and Quebec street. High
concentrations of PCE found south of 56th Avenue between
Holly and Monaco Streets within OU2 appear to be directly
related to high concentrations of PCE found south of Sand
Creek within OUI. An unidentified source of PCE
contamination is believed to be present near 56th Avenue
and Quebec Street, where relatively high PCE
concentrations have also been identified in ground water.
TCE contamination is also widespread in CSC OU2. In
1989, mean concentrations ranged from below detection to
53 ug/l within OU2. Relatively high concentrations (10-
50 ug/l) are distributed from Sand Creek to the SACWSD
pumping center.
The TCE and PCE ground-water data summarized above were
hand-contoured to illustrate the major plumes of ground-
water contamination in CSC OU2. These plumes are
presented in Figures 6 and 7. The maps were developed to
show general trends in the present contaminant
distribution in CSC OU2. Potential sources and temporal
21 of 91
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t ..~
t aoT}4
~
~
..
5
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ROCKY MOUNTAIN
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ex ~IITI ouz RIm STUDT
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BASED ON DATA rROW
12/88 TO 11 88
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*Plurne not shown south of Sand Creek
22 of 91
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C lOTI"
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ROCKY MOUNTAIN
ARSENAL
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FIGURE 7
£ 48~
csc ,m OUt m;n STUDY
PCE PLU1a *
BASED ON DATA now
12 aa TO 11 &8
1-70
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........-
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*Plume not shown south of Sand Creek
23 of ql
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trends were not considered in development of these maps,
and as such, they can be subject to uncertainty and open
to other interpretations.
A distinct plume of ground-water contamination emanating
from the CSC facility flows northward from OU1 into OU2.
This plume is characterized primarily by relatively high
levels of TCE in mean concentrations ranging from greater
than 50 ug/l in the upgradient area (south of Sand Creek)
to below detection limits in downgradient areas within
OU2. PCE, TCA, and 1,2-DCE also occur within the area of
this plume. The areal distribution of these contaminants
is indicative of a continuous plume from the CSC property
in OU1 to north of Sand Creek in OU2. Concentrations
decrease steadily downgradient of the CSC property, which
is believed to be due to dilution, dispersion,
adsorption, and biodegradation. This plume (referred to
as the TCE Plume) has migrated northward through most of
the CSC OU2 Site, as shown in Figure 6.
The presence of
the plume was detected as early as 1985, and the Klein
Water Treatment Plant was constructed to treat
contaminated ground water that was extracted from the
aqui fer before it was added to the municipal water
system.
The second plume begins at approximately East 56th Avenue
and Quebec Street (Figure 7), and is characterized
primarily by PCE, at a mean concentration of up to 110
ug/1. Monitoring at SACWSD Monitoring Well 08, located
on the northwest corner of the intersection of 56th
Avenue and Quebec Street, has shown high concentrations
of PCE. The source of the PCE plume was not located in
csc OU2 during the RI. EPA Field Investigation Team
(FIT) investigations were conducted up-gradient of
Monitoring Well 08 on the Denver Engineering Operations
24 of 91
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Center (DEOC) property to the southeast of 56th Avenue
and Quebec street. Monitoring wells were installed and
a soil gas survey was performed, but the PCE source was
not found. Resul ts of the CSC OU2 RI and the FIT
investigations indicated that another potential source
area for the PCE plume may be located directly south of
Monitoring Well 08. Well 08 is located on the northwest
corner of the 56th Avenue and Quebec intersection. This
was not expected during the previous investigations
because the regional ground-water gradient in this area
is to the northwest. However, local directions of ground
water flow may be different due to local influence from
a north-trending paleochannel located along Quebec St.
This paleochannel may cause ground water to flow in a
more northerly direction.
For the purposes of the FS, a degrading source was
assumed because true continuing sources are relatively
rare, and a continuing source could not be located during
field investigations. If future monitoring indicates
that significant source material remains, EPA will again
attempt to identify this source and remediate it as
quickly as possible.
Both of the plumes described above follow ground-water
flow paths which converge upgradient (south) of the
SACWSD pumping center at East 77th Avenue and Quebec
street. The future migration of these plumes depends on
the major transport and fate processes of dispersion,
adsorption, biodegration, and hydrolysis (TCA only) and
on the potential for plume interception by the high-
discharge SACWSD wells.
In addition to the TCE and PCE plumes located in CSC OU2,
a plume consisting of dibromochloropropane (DBCP) and
25 of 91
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other volatile organic compounds (VOCs), referred to as
the "contamination on the western tier of the Arsenal",
is present to the east of CSC OU2 on the RMA property.
This contamination was detected in Irondale community
wells in 1980 and was traced back to the western tier of
RMA. A ground-water interception system, known as the
Irondale System, was installed at the RMA boundary in
December 1981 to prevent this contamination from
migrating off of RMA. This system uses wells to extract
and inject the ground water and activated carbon to
remove the VOC contamination.
Behavior of the contamination on the western tier of the
Arsenal is influenced by ground-water extraction
practices and schedules in CSC OU2. During normal
operations, SACWSD pumps considerably more water from the
aquifer during the summer than at other times of the
year.
There
is concern that during periods of high
ground-water
flow may be
western tier
extraction, the direction of ground-water
altered, causing the contamination on the
of the Arsenal to deflect to the south and
partially bypass the Irondale System. However, DBCP has
not been detected in CSC OU2 in the vicinity of the
Irondale system. Improvements to the Irondale System, to
ensure that the entire contamination on the western tier
of the Arsenal is being captured at all times, are
currently being evaluated under CERCLA at the RMA site.
Until those improvements are implemented, the amount of
contamination that may periodically bypass the Irondale
System is considered to be insignificant compared to the
contamination corning from other sources into CSC OU2, and
requires no different remedy than that selected for the
TCE/PCE plumes.
26 of 91
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One of the contaminants detected in the CSC OU2 RI was
vinyl chloride. This compound is believed to be a
breakdown product of other chlorinated hydrocarbons
detected at the Site, such as all forms of DCE. It was
detected only sporadically with respect to location and
concentration, and it did not appear to define a
continuous plume. The focus of this ROD is on the known
plumes of chlorinated VOCs, although the remedial actions
were also evaluated based on their ability to remove
vinyl chloride if it is present. The previous ROD
provides the ability to remove vinyl chloride from the
SACWSD water supply if it becomes a health threat.
VI.
SUMMARY OF SITE RISKS
Actual or threatened releases of hazardous substances from
both OU2 and OU3, if not addressed by implementing the
response action selected in this ROD, may present an imminent
and substantial endangerment to public health, welfare and the
environment.
CERCLA mandates that EPA select remedies that protect human
health and the environment from current and potential
exposures to hazardous substances. Therefore, EPA has
conducted a Baseline Risk Assessment (BRA) to evaluate the
risk posed by the presence of contaminants at CSC OU2.
The
risk analysis resulting from EPA's BRA is used for the CSC OU2
and OU3 FS and for this ROD. This BRA was carried out to
characterize the current and potential threats to human health
and the environment which exist for these OUs in the absence
of any remedial action.
The major
associated
potential health risk to area residents is
wi th the use of ground water contaminated by
27 of 91
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volatile organic compounds. The maj ori ty of ground water from
contaminated municipal wells is currently treated prior to
distribution to the community. One untreated well, SACWSD
Well No. 18 is located within the CSC Site and is currently
impacted from contamination at the Site. Approximately 12
remaining residents within the CSC site are solely dependant
on private alluvial wells for indoor use. Environmental risks
were not considered except as they pertain to restoring the
ground water. Environmental risks for both OU2 and OU3 were
not considered because there are no identified exposure
pathways by which significant exposure to environmental
receptors could occur.
Eight contaminants were identified as chemicals of concern
(COCs) based on their toxicity, widespread occurrence, or
concentration. These compounds are PCE, TCE, TCA, DCA, DCE,
1,2-DCE, VC and benzene. These contaminants are judged to
represent the major potential health risks at the site for
both OU2 and OU3.
The selection criteria used to identify COCs followed the most
recent guidance from EPA (Risk Assessment Guidance for
Superfund (RAGS), Volume I, Human Health Evaluation Manual
(Part A) Interim Final EPA/540/1-89/002, December 1989). A
list of all chemicals detected during the 1989 RAS sampling
was compiled. The list was reviewed and chemicals were
eliminated from further consideration based on QA/QC criteria,
laboratory or field blank contamination, or frequency of
detection. A detection frequency of less than 10 percent was
used in the RA to el iminate chemicals not bel ieved to be
representative of site contaminants. Although a 5% detection
frequency is recommended by RAGS referenced above, this
recommendation allows for professional judgement and
modification for specific sites and conditions. In the case
of OU2, several years of sampling information consistently
28 of 91
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detected the chemicals selected as COCs. Other chemicals have
been sporadically detected at low concentrations in these
sampling efforts, but the eight COCs selected for OU2 are
representative of historical and current Site contamination.
Furthermore, the chemicals detected at 5-10% frequency, even
if they were included in the RA, would have only a marginal
effect on the magnitude of potential health risks at the site.
l/
The eight chemicals remaining after this preliminary review
were clearly relevant to the RA based on toxicology,
widespread occurrence, or concentration. Therefore, no
further selection criteria were applied. Vinyl chloride is
included as a chemical of concern even though it was only
detected in five percent of the wells because vinyl chloride
is a potent human carcinogen and reliability of the sampling
results for vinyl chloride is uncertain.
Toxicity Assessment
The COCs are a diverse group of volatile halogenated
hydrocarbons and sol vents. Most of the COCs are central
nervous system depressants and either liver or kidney toxins
at high doses. Benzene is toxic to the blood forming system.
six of the COCs (PCE, TCE, DCE, DCA, VC and Benzene) are known
to cause carcinogenic effec~s in animal studies. Of the six,
vinyl chloride and benzene are both classified by EPA as Class
A - Human Carcinogens based on the weight-of-evidence for
carcinogenicity.
Non-carcinogenic Effects - TCE is a central nervous system
depressant in humans. Inhalation and oral exposure studies in
animals indicate that bone marrow, central nervous system,
liver, and kidney are the target organs. The principal toxic
effects of PCE in humans and animals are central nervous
29 of 91
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system depress ion and liver and kidney damage. TCA is a
central nervous system depressant at high concentrations and
adverse effects on the cardiovascular system have also been
reported. Exposure to high concentrations of DCA has been
reported to cause cardiac arrhythmia and liver damage in
humans. DCE can induce neurotoxicity after short-term
inhalation exposure, and DCE is possibly associated with liver
and kidney toxicity after repeated, low-level exposure in
humans. Benzene has demonstrated toxic effects on the central
nervous system, blood-forming system, and immune system in
both animals and humans. Long-term inhalation of vinyl
chloride by workers is associated with liver damage, central
nervous system disturbances, pulmonary insufficiency,
cardiovascular toxicity, and osteolysis.
carcinoqenic Effects TCE is classified as a Group B2
carcinogen (a probable human carcinogen). PCE and DCA are
also classified as Group B carcinogens. DCE is classified as
a Group C carcinogen (a possible human carcinogen). Benzene
and vinyl chloride have been classified as human carcinogens
(Group A). Classification into this category means that there
is sufficient evidence from epidemiologic studies to support
a causal association between the compound and human cancer.
Risk Characterization for OU2 and OU3
Both carcinogenic and non-carcinogenic health risks were
characterized for two exposure scenarios. Case 1 represents
the maximum range of health risks likely to be encountered by
an individual using untreated ground water as a primary
domestic water source (OU2). Case 2 is a current estimate of
potential health risks associated with an untreated well
located at the periphery of the contaminated ground-water
plume (OU3). Risks were calculated for each chemical of
concern for the two exposure pathways.
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Non-Carcinoqenic Risks - The potential for non-carcinogenic
effects is evaluated by comparing the. estimated chemical
exposure to the appropriate reference dose (RfD). The RfD is
an estimate of a daily exposure level for an individual that
is likely to be without an appreciable risk of
deleteriouseffects during a lifetime. RfDs for CSC OU2 and
OU3 COCs are presented in Table 1. The ratio of exposure to
a toxicity value is defined as a hazard index (HI). The
hazard index is based on the assumption that there is a level
of exposure, the RfD, below which it is unlikely for adverse
health effects to occur. If the exposure exceeds the RfD (the
HI exceeds 1.0), there may be a concern for potential non-
cancer health effects.
Carcinoqenic Risks Potential excess cancer risks are
estimated by multiplying an exposure estimate by a cancer
potency factor (CPF), which has been derived from either human
epidemiology studies or experimental animal studies with the
specific chemical under consideration. The CPF for CSC OU2
and OU3 COCs is presented in Table 1. Generally, cancer risks
are assumed to be additive, as long as the exposures are for
the same individuals and time period. Carcinogenic risks are
presented as a probability value, i.e., the increased chance
of contracting some form of cancer over a lifetime.
In the risk characterization, the aggregate carcinogenic risk
due to indicator contaminants at the site is compared to an
acceptable target risk.
Carcinogenic effects are evaluated
based on a calculated increase in the risk of contracting
cancer that is a direct result of exposure to the COCs at a
Site. The EPA has defined an increased risk, exceeding the
10-4 to 10-6 range, due to exposures at a site as being
unacceptable regarding the protection of public heal th and the
environment. Remediation action objectives are established
based on ARARs (i.e. MCLs and MCLG) and acceptable risk levels
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TABLE 1
Reference Doses and Cancer Potency Factors
for Chemicals of Concern
CSC OU2
Reference Dose, RFD Cancer
(mg/kg/day) Potency Fact~r
(mg/kg-day) .
Oral Inhalation Oral Inhalation
PCE 0.018 0.0518 O. 0033c
TCE NDb 0.0118 0.01 7c
TCA 0.098 0.38 Nod NOd
DCA 0.18 0.18 0.091 e 0.0918
OCE 0.0098 0.608 1. 28
1 2-0CE 0.028 Nod NOd
VC NDb 2.308 0.2958
Benzene NDb 0.0298 0.0298
8 IRIS - EPA's Integrated Risk Information System, March 1990.
b None determined - No RFD currently avaiable from EPA.
c Cancer slope factors have been withdrawn from IRIS pending EPA
review.
d None determined - No cancer Potency Factor available from EPA.
e Oral slope factor used for inhalation risk estimates.
32 of 91
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(i. e. 10-6), while ARARs and the 10-6 cancer risk point of
departure are used as the basis for developing preliminary
. remediation goals. The chance of one person developing cancer
per one million people (or 10.6) is used as a target value or
point of departure above which carcinogenic risks may be
considered unacceptable. The 10-6 point of departure is used
for determining remediation goals when ARARs are not available
(i. e., no MCLs or proposed MCLs exist for the indicator
contaminant) or are not sufficiently protective of human
health and the environment because of the existance of
mul tiple contaminants at a site or multiple pathways of
exposure.
Exposure Assessment
Only pathways associated with ground water uses were evaluated
in the risk assessment, as it is the only contaminated medium
at the Site. Two exposure scenarios were developed to
describe a range of potential health risks. For Case 1, a
Reasonable Maximum Estimate (RME) was developed by calculating
exposures from use of a hypothetical private well in OU2
placed wi thin a mixing zone for the existing ground-water
plumes. This hypothetical well was assumed to be contaminated
with all eight chemicals of concern. The second exposure
scenario (Case 2) was developed to provide information
regarding the potential health risks associated with SACWSD
production well SAC-lB. This well is located at the periphery
of the ground-water plume and is currently used as a seasonal
source of domestic water for part of the community. TCE has
been detected at SAC-lB. Average concentrations of TCE range
from 4 ~g/l to 6 ~g/l. The maximum concentration of TCE that
has been detected at SAC-18 is 12 ~g/l. Water from SAC-18 is
currently blended with treated water from the Klein Water
Treatment Plant to ensure -hat any potential contaminant
concentrations in the untreated water are diluted to safe
33 of 91
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of the highest detected values. Contaminant concentrations
used for calculating Case 2 exposures are presented in Table
3. These are 1989 concentrations measured in Well 18.
Calculations of exposure from ingestion of ground water and
inhalation of volatiles were based on standard EPA guidance
(Risk Assessment Guidance for Superfund (RAGS), Volume I,
Human Health Evaluation Manual (Part A) Interim Final
EPA/540/1-89/002, December 1989) and theoretical models.
Exposures were
concentrations,
exposure route:
calculated based onexposure
and the following assumptions for
point
each
Ingestion of ground water:
Ingestion rate = 2 liters/day
Exposure frequency = 365 day/year
Exposure duration = 30 years
Body weight = 70 kilograms
Inhalation during showering:
ventilation rate = 15 liters/minute
Body weight = 70 kilograms
Air exchange rate = 0.008333 minutes.'
Shower duration = 15 minutes
Total time in shower room = 20 minutes
Exposure frequency = 365 days/year
Exposure duration = 30 years
Adsorption rate across lungs = 100%
Exposure estimates for the Case 1 scenario for both exposure
routes are summarized in Table 4. The highest chemical
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TABLE 3
CHEMICAL SALBS COMPANY OU2 RA
CASE 2 (VELL SAC-18) EXPOSURE POINT CONCENTRATIONS.
Chemical
of
Concern
Concentration
(~g/L)
Type of
-\nalys is
PCE
TCE
TCA
0.87 J-C
3.1
3.6
0.61 J-C
0.03 J-C
0.49
b
1.00 UJ-C
1 J-C
SAS
SAS
SI.S
SAS
SAS
SAS
SAS
RAS
OCA
DCB
1,2-DCE
Vinyl chloride
Benzene
a Values used are from CDM Fall 1989 sampling only. RAS indicates Routine
Analytical Services vhile SAS indicates Special Analytical Services under
the EPA Contract Laboratory Progra..
b A concentratl0n of 0.5 ug/L (one-half the estimated detection li8it) vas
used for the exposure assessment calculations)
U - The -aterial vas analyzed for, but vas not detected. The associated
numerical value is the estimated detection li8it.
J - The associated numerical value is an estimated quantity because the
amount detected is below the required detection li.its or because
quality control criteria vere not .et.
C - The value vas estiaated due to instrument calibration problems.
37 of 91
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TABLE 4
EXPOSURE ESTIMATES FOR CASE 1
CHEMICAL SALES COMPANY OU2 RAa
Exposure Pathvays (mg/ke/day)
Che.ieal Il\gestion Shover Total
DCA 3.7 x 10-4 3.6 x 10-4 7.3 x 10-4
-4 2.3 x 10-4 4.6 x 10-4
DeE 2.3 x 10
1,2 OCE: 6.0 x 10-4 5.9 )( 10-4 1.2 x 10-3
-4 2.5 x 10-4 5.4 x 10-4
TCA 2.9 x 10
TCE 1.4 x 10-3 1. 2 x 10-3 .L6 x 10-3
PCE 1. 7 x 10-3 1. 3 x 10-3 3.0 x 10-3
5.7 x 10-5 -5 1.2 x 10-4
Benzene 6.0 x 10
Vinyl chloride 8.6 ']I: 10-5 1.0 x 10-4 1.9 x 10-4
'Daily exposure during 30 year exposure.
.-
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exposures for both routes were from PCE and TCE.
estimates for the Case 2 scenario are presented in
The highest exposures were due to TCA and TCE.
Exposure
Table 5.
Results
The chronic HI estimates for Case 1 indicated a very low
potential for non-cancer health effects. The HI for each
contaminant of concern was less than 1.0. The HI for PCE,
however, was considerably higher than for the
othercontaminants. This reflects the higher concentration of
PCE in ground water. Addition of HIs for specific exposure
routes still resulted in a HI of less than 1.0 for each
exposure route, with the largest component of the HI for each
route due to PCE. The chronic HI estimates for Case 2
indicated an extremely low potential for non-carcinogenic
adverse health effects. The aggregate HI for all exposure
routes was also summed and did not exceed 1.0. The HIs for
individual contaminants were nearly two orders of magnitude
lower than for Case 1. The individual and aggregate HI for
CSC OU2 COCs is presented in Table 6.
The Risk Assessment revealed that DCE, VC, and TCE pose the
most significant carcinogenic risks to human health. For the
Case 1 exposure scenario (RME) as shown in Table 6, the total
excess cancer risk estimate for all chemicals via ingestion
and inhalation while showering was 3.6 X 10.'. For the Case
2 exposure scenario (Well 18) as shown in Table 7, the total
excess cancer risk estimate for all chemicals via both
exposure pathway routes was 2.0 X 10-5.
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TABLE 5
EXPOSURE ESTIMATES FOR CASE 2
CHEMICAL SALES COMPANY OU2 RAa
Exposure Pathways (lIIg/kg/day)
Chelllical In~estion ~h()\Jer Tot31
-5 1. 7 x 10-5 3.4 x 10-5
DCA 1.7:1e 10
DCE 8.6 x 10-7 8.6 x 10-7 1. 7 x 10-6
1,2 DCE 1.4 :< 10-5 1.4 x 10-5 2.8 x 10-5
TCA 1.0 x 10-4 1.0 x 10-4 2.0 x 10-4
8.9 x 10-5 ~ 10-4
TCE 7.8 x 10-~ 1. i :.<
PCE 2.5 x 10-5 2.0 x 10-5 4.5 :: 10-S
Benzene 2.9 x 10-5 3.0 x 10-5 5.9 x 10-5
vt~:'l c~lf)rid'! 1... x 10-5 1. 7 x 10-5 3.1 x 10-5
'Daily exposure during 30 year exposure.
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TABLE 6
CHEMICAL SALES COMPANY OU2 RA
CHRONIC HAZARD INDEX ESTIMATESa - CASE 1
Exposure Route
Inhalation
Chemical Ingestion SholJer Total
PCE 0.2 0.1 0.3
TCA 0.003 0.0008 0.004
DCA 0.003 0.004 0.007
DCE 0.03 0.03 0.06
1,2-DCE 0.03 0.03 0.06
Combined Total 0.27 0.16 O. '.'oJ
a Bazard index calculated by dividing exposure by the RfD.
CHEMICAL SALES COMPANY OU2 RA
EXCESS CANCER RISK ESTIMATES - CASE 1
Exposure Route
Inftalation
Chemical Ingestion SholJer Total
3.6 x 10-5 1.8 x 10-6 -5
PCE 3.8 x 10
TCE 6.5 x 10-5 8.8 x 10-6 7.4 x 10-5
DCA 1.5 x 10-5 1.4 x 10-5 2.9 x 10-5
DCE 5.9 x 10-5 1. 2 x 10-4 1.8 x 10-4
Vinyl Chloride 8.5 x 10-5 1. 3 x 10-5 9.8 x 10-5
7.1 x 10-7 7.5 x 10-7 -6
Benzene 1. 5 x 10
Combined Total -4 -4 -4
2.0 x 10 1. 6 x 10 3.6 x 10
-------
TABLE 7
CHEMICAL SALES COMPANY OU2 RA
CHRONIC HAZARD INDEX ESTIMATESa - CASE 2
Exposure Route
Inhalation
Chemical Ingestion Shover Total
PCE 0.002 0.002 0.004
TCA 0.001 0.0003 0.001
DCA 0.0002 0.0002 0.0004
DCE 0.0001 0.0001 0.0002
1,2-DCE 0.0007 0.0007 0.001
Combined Total 0.004 0.004 0.008
a Hazard index calculated by dividing exposure by the RfD.
CHEMICAL SALES COMPANY OU2 RA
EXCESS CANCER RISK ESTIMATES - CASE 2
Exposure Route
I11balation
Chemical Ingestion . Sho....er Total
-7 -8 -7
PCE 5.5 x 10 2.8 x 10 5.8 x 10.
TCE 4.2 x 10-7 5.7 x 10-7 9.9 x 10-7
DCA 6.6 x 10-7 6.6 x 10-7 1. 3 x 10-6
DCE 2.2 x 10-7 4.4 x 10-7 6.6 x 10-7
Vinyl Chloride 1.4 x 10-5 2.2 x 10-6 1. 6 x 10-5
Benzene 3.6 x 10-7 3.7 x 10-7 7.3 x 10-7
-5 -6 -5
Combined Total 1. 6 x 10 4.3 x 10 2.0 x 10
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VII. SUMMARY OF ALTERNATIVES
The OU2 FS and OU3 FS were conducted to develop and evaluate
remedial alternatives that would effectively minimize threats
to and provide adequate protection of public health and the
environment from contaminated ground water located within the
operable unit" boundaries. The OU2 FS and OU3 FS were
conducted in three phases: Phase I, development of
alternatives; Phase II, screening of alternatives; and Phase
III, detailed analysis of alternatives. In Phase I,
remedialalternatives were assembled from applicable remedial
technology process options. These alternatives were initially
evaluated for effectiveness, implementability, and cost in
Phase II. The favorable alternatives were then evaluated in
detail in Phase III with respect to the following criteria
specified in the National Contingency Plan (NCP):
Overall protection of human health and
environment
Compliance with ARARs
Long-term effectiveness and permanence
Reduction of toxicity, mobility, or volume
Short-term effectiveness
Implementability
Cost
State acceptance
Community acceptance
the
In addition to the remedial alternatives, the NCP requires
that a no-action alternative be considered at every site. The
no-action alternative serves primarily
comparison for other alternatives.
as
a
point
of
A ground-water model was developed for the CSC OU2 Site as a
tool to aid in determining the relative effectiveness of the
remedial action alternatives. This model was developed to
allow comparison of the different alternatives, rather than to
define exact aquifer characteristics at future times. The
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model was not calibrated, and many simplifications were made
dur ing its development. The model takes into account
contaminant transport by advection, sorption, and dispersion.
Contaminant degradation from such processes as biological and
chemical breakdown are not accounted for by the model. Output
from the model is useful to give a general idea of contaminant
transport and removal rates resulting from remedial actions
within CSC OU2. This information has been used to compare the
effectiveness of the various treatment alternatives. The
predicted aquifer restoration time periods derived for the
various alternatives evaluated in the OU2 FS were used to
estimate duration of residential exposure evaluated in the OU3
FS.
Remedial Action objectives and Goals
Remedial action objectives for establishing acceptable ground-
water remediation and exposure levels were developed from
applicable or relevant and appropriate requirements (ARARs)
and from risk-based considerations. The standards,
requirements, limitations, and criteria that were considered
to be applicable or relevant and appropriate for remediation
at CSC OU2 and CSC OU3 include chemical, location, and action-
specific requirements.
Chemical-specific ARARs pertaining to water quality include
requirements from the federal Safe Drinking Water Act (SDWA)
and Resource Conservation and Recovery Act (RCRA). State laws
that were considered are the State Primary Drinking Water
Regulations and the Colorado Water Quality Control Act.
Acceptable concentration limits have been established pursuant
to these laws and are relevant and appropriate in establishing
acceptable concentration levels for the alluvial aquifer in
CSC OU2 in order that the aquifer will be restored to a
quality that will allow its future beneficial use. These
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levels are also used in establishing acceptable" levels of
exposure for indoor use for aU3. The levels established under
the SDWA are referred to as Maximum Contaminant Levels (MCLs).
MCLs are enforceable drinking water standards that regulate
publ ic drinking water supply systems. "Maximum contaminant
level goals (MCLGs), established under the Safe Drinking Water
Act, that are set at levels above zero, shall be attained by
remedial actions for ground or surface waters that are current
or potential sources of drinking water, where the MCLGs are
relevant and appropriate under the circumstances of the
release based on the factors in ~ 300.400(g) (2). If an MCLG
is determined not to be relevant and appropriate, the
corresponding maximum contaminant level (MCL) shall be
attained where relevant and appropriate to the circumstances
of the release. Where the MCLG for a contaminant has been set
at a level of zero, the MCL promulgated for that contaminant
under the Safe Drinking Water Act shall be attained by
remedial actions for ground or surface waters that are current
or potential sources of drinking water, where the MCL is
relevant and appropriate under the circumstances of the
release based on the factors in S 300.400(g) (2). In cases
involving multiple contaminants or pathways where attainment
of chemical-specific ARARs will result in cumulative risk in
excess of 10.", criteria in paragraph 9 300.400(e) (2) (i) (A) of
this section may also be considered when determining the
cleanup level to be attained." (40 C.F.R. 300.430
(e) (2) (i) (8». Under the SDWA, MCLs have been established for
DCE, TCA, TCE, benzene and vinyl chloride. Cumulative
carcinogenic risk for these compounds associated with the
remediation levels through ingestion and inhalation during
showering is estimated at 1 X 10.". Since this risk is
considered to be protective, MCLs for these chemicals are used
for establishing acceptable remediation and exposure levels.
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If no ARAR covers a particular situation, or if an ARAR is not
sufficient to protect public health or the environment,
proposed standards, criteria, guidance and advisories are Used
as "to be considered" or TBCs to provide a standard or goal.
Proposed MCLs under the SDWA are considered to be TBCs in
establishing acceptable concentration levels for those
compounds without a promulgated MCL or state standard. For
those contaminants without TBCs, acceptable levels may be
derived based on the 10-6 risk level. Because clean-up can
only be verified down to the laboratory analytical detection
1 imi t, it is important that detection 1 imi ts are either
equivalent to or less than the remediation levels for the
COCs. For this Site, it was assumed that samples will be
analyzed under the Contract Laboratory Program (CLP) using
either Routine Analytical Services (RAS) or Special Analytical
Services (SAS) protocols, and that method detection limits as
suggested by EPA methods will be attainable. Acceptable
remediation and exposure levels and appropriate analytical
methods and their detection limits for the COCs at this Site
are presented in Table 8 along with the governing ARAR (if
available) .
The following remedial action objectives were identified for
both CSC OU2 and OU3:
1.
Prevent the ingestion and inhalation through showering of
chemicals of concern in excess of levels specified in
Table 8 and a total carcinogenic risk in excess of 10-~
to 10-6. This remedial action objective will be
addressed under CSC OU3.
2.
Restore the alluvial aquifer for chemicals of concern to
levels specified in Table 8 and to levels which pose a
10-~ to 10-6 total excess cancer risk. This remedial
action objective is addressed under CSC OU2.
3.
Prevent migration of contaminants in excess of
levels specified in Table 8. This remedial action
objective is addressed under CSC OU2.
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TABLE 8
REMEDIATION LEVELS FOR CSC OU2
Analytical
Remediation Analytical Detection
Chemical Level Method Limit Comments
(J~g/ 1 ) ( ~g/ 1 )
DCA 5 RAS 5 10-6 risk level
l,l-DCE 7 RAS 5 MCL (40 CFR 141)
TCA 200 RAS .5 MCL (40 CFR 141)
PCE 5 RAS 5 MCL (56 FR, No.
20, 1/30/91)
TCE 5 RAS 5 MCL (4 0 CFR 141)
1,2-DCE 70 RAS 5 Colorado Basic
(cis and Standard for
trans) Ground Water,
effective 9/30/89
Benzene 5 RAS 5 MCL (40 CFR 141)
Vinyl 2 SAS 2 MCL (40 CFR 141)
Chloride
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Remedial Alternatives
Operable unit 2 - VOC Ground-water Plume
For Operable Unit 2, three remedial alternatives were
considered for detailed evaluation and are described below.
All alternatives pertain to ground-water remediation. Three
different treatment technologies were evaluated under these
al ternati ves for treating contaminated ground water associated
with the PCE plume. In evaluating these alternatives, it was
assumed that remedial action objectives for OUl and OU3 would
be met. These objectives include preventing the migration of
contaminated ground water from OU1 into OU2, and protecting
residents currently using shallow alluvial wells from
exposures to contaminated ground water.
Ground-water contamination in CSC OU2 can be viewed as three
separate problems: 1) TCE and other VOCs entering the Site
from a source to the south, 2) a PCE plume and unknown source
near 56th Avenue and Quebec Street, and 3) contamination
currently existing in the aquifer. TCE entering the site from
the south will be addressed by the CSC OUl ROD. It has been
assumed in this ROD that the TCE will be prevented from
entering the CSC OU2 site through remedial activities at the
CSC OU1 site. Remedial alternatives that have been identified
in the CSC OU1 FS to achieve this objective involve the
installation of ground water pump and treat systems at or near
the CSC property and at Sand Creek. Because these activities
will be conducted under another ROD, alternatives developed in
this ROD do not include TCE treatment as it enters the CSC OU2
site.
The second problem, the PCE plume and unknown source near 56th
Avenue and Quebec Street, is addressed by this ROD.
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The final problem, remediation of the existing plume in CSC
OU2, is already being addressed, in part, by operation of the
Klein Water Treatment Plant. Ground water from SACWSD supply
wells is pumped to the Klein Water Treatment Plant for
treatment before it enters the municipal distribution system.
SACWSD supplies nearly all of the residences in CSC OU2 with
domestic water and represents by far the largest demand on the
aquifer at this Site. To meet the water demand, SACWSD
extraction wells have been located in highly transmissive
areas of the aquifer, most notably the paleochannel that runs
north approximately beneath Quebec Street. Because
contaminant plumes in the aquifer will tend to migrate most
quickly through these highly transmissive portions of the
aquifer, the SACWSD extraction wells are fortuitously
optimally located to capture contaminated ground water as
well. It would be difficult to locate additional extraction
wells throughout CSC OU2 to achieve better contaminant capture
than what is currently being done by the SACWSD wells. The
Klein plant is also large enough (12 million gallons per day,
maximum capacity) that construction of additional treatment
facilities will not provide significantly more effective or
quicker remediation. Therefore, options for remediating the
plume center on increased pumping of SACWSD wells that feed
the Klein Water Treatment Plant.
Each
remedial
alternative
includes
the
following
common
elements:
Continued operation of the Klein Water Treatment
Plant to protect municipal water users in CSC OU2.
The Klein Water Treatment Plant is an activated
carbon system that was installed specifically to
removed chlorinated hydrocarbons from ground water
that is extracted by SACWSD for municipal use.
Monitoring of selected wells to ensure that the
remedial action is effective and to determine when
the remedial action can be discontinued based on
recovery of the aquifer and elimination of
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contaminant migration into QU2.
with the exception of the no-action alternative, each
alternative further includes the following common elements:
Abandonment of bedrock wells. If any bedrock well
is determined to cause contamination to flow from
the alluvial to the bedrock aquifer, the well would
be properly abandoned provided that permission is
granted by the well owner. The criteria for
bedrock well abandonment will be established in RD.
Alternative I - No Action
A no-action remedial alternative is required by the NCP and is
used as a baseline for comparison of other alternatives. The
no action alternative assumes that no remedial activities will
be undertaken beyond activities currently being conducted or
currently planned within and outside of CSC QU2. Activities
currently being conducted within CSC QU2 include operation of
the Klein Water Treatment Plant at its current rate of
operation to protect municipal water users in CSC QU2i
monitoring of selected wells by SACWSD; and providing
alternate water supplies to private alluvial well users in CSC
QU2. Ground-water monitoring would continue at a minimum of
an annual basis at approximately 15 wells in QU2. Measured
concentrations would be used to update the prediction of
contaminant migration patterns and impacts on the SACWSD
municipal water supply system.
This alternative assumes that remedial action objectives will
be met for CSC QU1 and CSC QU3. The CSC QUI remedial action
objectives include preventing contaminated ground water from
migrating into CSC QU2 from QUI. It is assumed that this
objective will be met and the source of TCE entering CSC QU2
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from the south will be remediatedby 1993. This allows
adequate time for remedial activities to be implemented in
OUl. The remedial action objective for CSC OU3 is to reduce
risk to acceptable levels posed by domestic use of
contaminated ground water from private alluvial wells. It is
assumed that this objective will also be met and that
residences in CSC OU2 that are currently dependent on shallow
alluvial wells will be protected from exposures to
contaminated ground water by CSC OU3 remedial actions. This
alternative also assumes that the PCE source at 56th Aven
and Quebec street is a degrading source and will not 1:
remediated.
Under the no action
alternative,
natural
attenuation and
ground-water flow aided by normal pumping of the aquifer by
SACWSD and operation of the Klein Water Treatment Plant would
be the primary means of restoring the aquifer. A portion of
the residual contamination in the aquifer would be captured by
the SACWSD withdrawals. This water would then be treated at
the Klein Water Treatment Plant prior to entering the
municipal water supply system.
The model results showed that by the years 2010/2011, 53
percent of the TCE plume and 49 percent of the PCE plume would
be captured and remediated before moving out of range of the
SACWSD wells feeding the Klein Water Treatment Plant. Model
results predicted that TCE and PCE concentrations would be
reduced to remediation levels by the year 2015, when the plume
would have moved out of the modeled area. Costs for this
alternative are summarized below and include annual sampling
of 15 existing wells. The life of this alternative was
assumed to be approximately 20 years because this is the
estimated time required for the plume to reach remediation
levels within the modeled area.
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Assumed life of the alternative:
20 years
capital Costs:
Annual Costs (sampling & analysis):
Present Worth of Annual Costs:
Total Capital Cost and Present Worth:
$2,600
$27,000
$261.000
$263,600
To determine present worth of annual costs, please use the
following formula where i is the interest rate in decimals and
n is the number of years.
Present Worth Factor
=
[ ( 1 + i) "-1] / [ i ( 1 + i) "]
Alternative 2 - PCE Plume Treatment with Hvdraulic containment
and Standard Pumpinq of SACWSD Wells
This
alternative
includes the
extraction
of
contaminated
ground water, treatment of the ground water, and reinjection
of the treated water. This alternative also includes the
existing and planned activities described in Alternative 1
plus the option to initiate bedrock well abandonment programs.
The extraction system would be installed to extract the
maximum amount of the PCE plume possible. Ground-water
extraction and reinjection would be accomplished through a
series of pumping and injection wells whose configuration
would be determined during remedial design. The pumped water
would be collected in a header pipe and transported to the
treatment system, treated to health based levels, as specified
in Table 1, and transported to the reinjection wells. The
treated ground water would be reinjected into the alluvial
aquifer upgradient to enhance flushing of contaminated ground
water. This alternative would be operational until the PCE
plume was reduced to remediation levels identified for this
Site in Table 6. For the purposes of the FS evaluation, and
based on model results, it was assumed that the PCE source
would be remediated within eight years. Therefore, the life
of this pump and treat system was assumed to be eight years.
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The model results showed that by the year 2006, 84 percent of
the PCE plume would be captured. At this time, the model
predicted that PCE concentrations would be below remediation
levels for the OU2 Site.
The treated ground water would be sampled as necessary to
substantively comply with Underground Injection Control (UIC)
requirements (40 CFR 144, and 146, RCRA requirement section
3020 and Colorado Regulations 5 CCR 1002-2, 6.1.0; 5 CCR 1002-
3 sec. 10.1. 0 and 6 CCR 1007-3 section 100.21 (b» . Under
these requirements, reinjected ground water must be treated to
health based levels (i.e. MCLGs, MCLs, proposed MCLs and 10.6
excess cancer risk levels).
The Hazardous and Solid Waste Amendments (HSWA) include
specific provisions restricting the land disposal of RCRA
hazardous wastes. These land disposal restrictions (LDRs)
were adopted to minimize the potential of future risk to human
health and the environment by requiring hazardous waste
treatment before land disposal. The only on-site portion of
the remedial action which would potentially constitute land
disposal or "placement" is the discharge of treated water to
the injection trench. However, EPA policy (Applicability of
Land Disposal Restrictions to RCRA and CERCLA Ground Water
Treatment Injection Superfund Management Review:
Recommendation No. 26 OSWER Directive No. 9234.1-06, December
27, 1989) is that UIC rules take precedence over LDRs for
injection of hazardous waste into the ground water.
Therefore, for injection of the treated water, the LDRs are
not relevant and appropriate. However, as noted previously,
UIC regulations are applicable to this action.
Costs
for
this
alternative
include
monitoring and the
Because this system
the treatment options
extraction and injection systems only.
will be used in conjunction with one of
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described below, the cost of the extraction and injection
system has been included with the costs for the individual
treatment options. These treatment options are presented in
the following sub-alternatives. Costs for the extraction and
injection system are based on four extraction wells and six
injection wells, all approximately 70 feet deep.
Alternative 2A - PCE Plume Treatment Usinq Carbon Adsorption
In this alternative, activated carbon would be used to treat
contaminated ground water. Influent from the extraction wells
would be collected in a surge/inlet tank, and then filtered
prior to entering the activated carbon contactors. Treated
water exiting the contactors would be sent to a pressurized
storage tank and then piped to the injection wells. Carbon in
the contactors would require regeneration approximately every
nine months at an off-site location. The life of this
treatment system was estimated to be eight years.
This type of treatment is effective in treating contaminated
ground water to health based levels as presented in Table 8
for all CSC OU2 COCs except vinyl chloride. vinyl chloride
does not readily adsorb to activated carbon.
Costs associated with this alternative are summarized below.
Costs for the monitoring activities are shown separately,
while the cost of the carbon adsorption system includes the
ground-water extraction and injection system.
The capital costs for the carbon treatment system include a
packaged Granular Activated Carbon (GAC) system with
associated filters, tanks, and pumps: construction equipment
and labor: land and site development: building and utilities:
contractor's costs: and engineering and design. Annual and
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periodic costs include operation and maintenance and carbon
change-outs. The costs of the monitoring program and the
carbon adsorption program are listed below.
Assumed life of the alternative:
20 years
Monitoring Program (20 years)
capital Costs:
Annual Costs (sampling and analysis):
Present Worth of Annual Costs:
Total Present Worth and Capital Costs:
$27,000
$2,600
$261,000
$263,600
Carbon Adsorption Program (8 years)
Capital Costs:
Annual and Periodic Costs: $62,000
Present Worth of Annual and Periodic
Total Present Worth and Capital Costs:
$1,910,000
Costs:
$1.230.000
$3,140,000
Alternative 2B - PCE Plume Treatment Using UV-Oxidation
In this alternative, contaminated ground water would be
treated by UV-Oxidation. Influent from the extraction wells
would be collected in a surge/inlet tank. Hydrogen peroxide
would be added to the inlet stream, which would then be
filtered prior to entering the treatment vessel. Ozone would
be generated from atmospheric air and bubbled through the
treatment vessel, and UV lamps would be inserted into the
water being treated. Treated water would be routed to a
storage tank and then pumped to the injection wells.
Excess
ozone from the treatment vessel would be sent through an ozone
decomposer prior to being discharged to the atmosphere. This
type of technology is capable of treating all CSC OU2 COCs to
heal th based levels. Extensi ve testing, however, would be
required to determine appropriate adjustments prior to final
design and construction of the system.
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Costs
Costs
associated with this alternative are summarized below.
for the monitoring activities are shown separately,
the cost of the uv-oxidation system includes the ground-
extraction and injection system.
while
water
The capital costs for the UV-oxidation treatment system
include UV-oxidation units with associated filters, tanks, and
pumps; construction equipment and labor; land and site
development; building and utilities; contractor's costs; and
engineering design. Annual costs cover operation and
maintenance, including power requirements for operation of the
UV lights and ozone generation. The costs of the monitoring
program and the UV-oxidation program are listed below.
Assumed life of the alternative:
20 years
Monitoring Program (20 years)
capital Costs:
Annual costs (sampling and analysis):
Present Worth of Annual Costs:
Total Present Worth and Capital Costs:
$2,600
$27,000
261.000
$263,600
UV-Oxidation Program (8 years)
Capital Costs:
Annual and Periodic Costs: $277,000
Present Worth of Annual and Periodic
Total Present Worth and Capital Costs:
$1,950,000
Costs:
1. 310.000
$3,260,000
Alternative 2C - PCE Plume Treatment Usinq Air Strippinq
This al ternati ve involves treatment of contaminated ground
water by air stripping. Influent from the extraction wells
would be collected in a surge/ inlet tank. Extracted water
would be filtered prior to entering two air stripping towers
in parallel, where it would flow down the packing by gravity.
Treated water would be collected in a storage tank and then
pumped to the injection wells. Air would be forced upwards
through the columns with an air blower and would be discharged
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to the atmosphere from the top of the columns.
The CSC OU2 Site is located in an OZone non-attainment area.
EPA policy (Control of Air Emissions from Superfund Air
Strippers at Superfund Ground-water Sites, OSWER Directive
9355.0-28) recommends controls for air emissions exceeding 3
pounds per hour, 15 pounds per day and 10 tons per year. The
maximum uncontrolled Volatile Organic Compound (VOC) emissions
rate from an air stripping unit in CSC OU2 is estimated to be
0.03 pounds per hour or about 0.79 pounds per day.
Colorado Air Quality Regulations Nos. 1,2,3,7 and 8 are
applicable requirements for this action. The specific
ci tations of these regulations and their purpose are as
follows: (a) 5 CCR 1001-5, Reg. 3, requires air pollution
emission notices (APENs); (b) 5 CCR 1001-5 Sec. IVD, Reg.3,
regulates the attainment and maintenance of any National
Ambient Air Quality Standards (NAAQS); (c) 5 CCR 1001-9, Reg.
7, regulates emissions of volatile compounds, requires a
Reasonable Available Control Technology (RACT) evaluation for
sources emitting greater than one pound per day; (d) 5 CCR
1001-10, Reg. 8, regulates vinyl chloride emissions; and (e)
5 CCR 1001-4, Reg. 2, requires that the design provide for an
odor-free operation. Federal ARARs pertaining to this action
include National Emission Standards for Hazardous Air
Pollutants for regulating vinyl chloride emissions (40 CFR
61). Air emission controls have not been planned for this
action as the total VOC emissions are calculated to be less
than acceptable emission rate levels allowed by federal and
State requirements. However, air emission monitoring will be
conducted to verify that emissions do not exceed the
standards.
Costs
Costs associated with this alternative are summarized below.
for the monitoring acti vi ties are shown separately,
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while the cost of the air stripping system
ground-water extraction and injection system.
incl udes the
The capital costs for the air stripping system include two air
stripping towers with associated filters, tanks and pumps;
construction equipment and labor; land and site development;
building and utilities; contractor's costs; and engineering
and design. Annual and periodic costs include operation and
maintenance of the system. The costs of the monitoring
program and the air stripping program are listed below:
Assumed life of the alternative:
20 years
Monitoring Program (20 years)
Capital Costs:
Annual costs (sampling and analysis):
Present Worth of Annual Costs:
Total Present Worth and Capital Costs:
$27,000
$2,600
Air Stripping Program (8 years)
Capital Costs:
Annual and Periodic Costs: $223,000
Present Worth of Annual and Periodic
Total Present Worth and Capital Costs:
261.000
$263,600
$1,410,000
Costs:
1. 010.000
$2,420,000
Alternative 5 - PCE Plume Treatment plus Increased Pumpinq of
SACWSD Wells
This al ternati ve combines PCE source treatment (AI ternati ve 2)
and increased pumping of SACWSD wells. Under this
alternative, contaminated ground water would be extracted to
capture the PCE plume, treated by air stripping, and
reinjected, as described in Alternative 2C. The existing and
planned activities described in Alternative 1 are also assumed
in this alternative plus the option to initiate bedrock well
abandonment programs. Pumping of the SACWSD production wells
presently connected to the Klein Water Treatment Plant would
be increased as part of this alternative, thereby accelerating
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the flushing of contaminants from the aquifer. The extra
water would be reinjected in the southern portion of CSC OU2.
The Klein Water Treatment Plant has the capacity to treat 12
million gallons per day (MGD). This capacity is only
approached during the summer months (when water demand is
high) and is significantly more than what is needed during the
fall, winter, and spring. The average annual flow through the
Klein Water Treatment Plant is 3.8 MGD. This alternative is
based on an increase of the average annual flow to 4.7 MGD.
This flow rate represents the maximum pumping capacity of the
alluvial aquifer based on ground-water modeling. The
increased pumping of the SACWSD wells would be limited to
those portions of the fall, winter, and spring months when
water demand is low.
During increased pumping periods, all of the extracted water
would be treated at the Klein Water Treatment Plant and the
extra water would be reinjected in the southern (upgradient)
portion of CSC OU2. Reinjection of clean water at this
location would aid in flushing contaminated ground water
toward the SACWSD extraction wells. Ground-water reinjection
would be accomplished by multiple injection wells located to
avoid depletion of the aqui fer. Treated water would be
transported to the injection area via existing SACWSD water
mains in the southern portion of CSC OU2. ARARs pertaining to
reinjection of contaminated ground water are identical to
those identified in Alternative No.2.
Some problems inherent with this alternative include impacts
on the RMA contamination on the western tier of the Arsenal
(possible diversion of the plumes around the Irondale System
containment), possible depletion of the water supply in the
aquifer, the variability of SACWSD pumping rates, and
administrative constraints with respect to water rights.
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As noted in section 5.3 of this ROD, contamination on the
western tier of the Arsenal is present to the east of CSC OU2
on RMA and is being captured and treated by the Irondale
System. There is concern that increased pumping of the SACWSD
wells during the summer may temporarily alter the direction of
ground-water flow and cause this plume to deflect to the south
and partially bypass the Irondale System. Increased pumping
of the SACWSD wells during other times of the year may cause
the contamination on the western tier of the Arsenal to bypass
the Irondale System on a more consistent basis and thereby
cause increased contamination of the aquifer in CSC OU2. This
si tuation would be detrimental, rather than beneficial to
aquifer remediation efforts.
Possible depletion of the aquifer under this alternative is
also of concern. It is believed that current SACWSD pumping
rates stress the aquifer to such a degree that the lower
pumping rates in fall, winter, and spring are necessary to
allow the aquifer to recover from the high summer pumping
rates. Increased pumping during low demand periods may not
allow sufficient aquifer recovery, even with reinjection of
the surplus water upgradient of the extraction wells.
Aquifer depletion could also occur if injection points are not
correctly located to return surplus extracted water to the
area of the aquifer from which it carne. Determination of
injection point locations would be extremely difficult due to
the presence of paleochannels and variations in the
permeability of the alluvial aquifer.
The increased pumping rate of 4.7 MGD was developed with the
ground-water model. When the model was run using an average
annual extraction rate of 5.4 MGD, it predicted that some
areas of the aquifer would become dry. The model was then run
at decreasing extraction rates until all portions of the
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aquifer remained saturated for a period of 15 years. The
highest pumping rate that could be maintained without
significantly depleting the aquifer was 4.7 MGD. It should be
noted that this analysis was based on average annual pumping
rates. Daily fluctuations of SACWSD pumping rates may make it
difficult to extract and inject surplus water.
A final consideration for this alternative is the impact of
water rights. Increased extraction and subsequent injection
of surplus water would require a revision of SACWSD's
augmentation plan. These revisions must be made through the
state of Colorado water court and can become quite lengthy and
costly, requiring a minimum of three years to accomplish.
The model was used to evaluate the relative benefits of
increasing the pumping rate of SACWSD supply wells when demand
is low. The model results showed that by 2010, 66 percent of
the TCE plume would be remediated, and concentrations would be
reduced to ground-water remediation levels given in Table 8,
before moving out of the SACWSD wells area of influence.
Increased pumping would also pull the PCE plume through the
aquifer faster than with standard SACWSD pumping. Modeling
results indicated that PCE concentrations would be reduced to
below remediation levels by the year 2007.
Increased pumping also reduces the maximum concentrations of
TCE by approximately 5 ~g/l, although it has little impact on
the time required to reduce the concentration to ground-water
remediation levels.
Costs associated with this alternative are summarized below.
Increased Pumping of the Klein Water Treatment Plant
Capital Costs: $880,000
Annual and Periodic Costs: $602,000
Present Worth of Annual and periodic Costs: $2.700,000
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Total Present Worth and Capital Costs:
$3,580,000
Total Present Worth of Air stripping (8 years)
and Increased Pumping of the Klein Plant (20 years)
(No Monitoring): $6,000,000
ODerable unit 3 - Residential Exposure To Contaminated Ground
Water
For aU3, three alternatives were evaluated during the detailed
analysis phase of the aU3 FS. All of these alternatives
address direct exposure to contaminated ground water through
ingestion and inhalation during showering. In the OU3 FS,
these al ternati ves assumed that residents already on the
SACWSD system were provided with domestic water at
concentrations below health-based levels (i.e. MCLs, and
proposed MCLs). This assumption was based on data collected
by EPA and information provided by SACWSD. However, other
residents still directly use untreated ground water and
therefore are at risk. Upon request for a well permit within
the CSC Site area, the resident would be notified by the
Colorado state Engineering Office of the potential health risk
associated with the contaminated ground water until ground
water is cleaned up to federal and State standards.
Alternative 1 - No Action
The no-action remedial alternative is required by the NCP and
is used as a baseline for comparison of other alternatives.
This alternative requires no further action beyond that which
has already been planned. Activities currently planned
include treatment of contaminated soil and ground water within
CSC aUl to acceptable levels for domestic use, prevention of
migration of contaminated ground water from aU1 into aU2, and
restoration of contaminated ground water to acceptable levels
for domestic use within OU2.
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Under this alternative, residences with private alluvial wells
as the sole source of domestic water will be sampled and
analyzed for chemicals of
monitor levels of exposure.
concern on an annual basis to
Cost associated with this alternative are summarized below:
No Action
capital Costs:
Annual Operation & Maintenance Costs:
Total (30-Year Present Worth) Costs:
None
$21,600
$332.000
Alternative 2 - Connection of Homes to the SACWSD Public Water
Svstem, and Installation of Horne Activated Treatment Units for
Homes Not Readilv Accessible to SACWSD Water Mains.
This alterative involves connecting private alluvial well
users to the SACWSD water system. This activity would entail
connecting a service line from the home to the water main and
acquiring a tap from SACWSD. A fee would be required to
purchase the tap. This fee is used by SACWSD for purchase,
treatment, and distribution of water and the installation of
a meter and shutoff valve. Currently, all private alluvial
well users within the CSC Site boundaries are located within
the SACWSD water district and have easy access to SACWSD water
mains.
Based on ground-water modeling conducted in the OU2 FS,
ground-water contamination within the CSC Site has the
potential to continue to actively migrate northward past the
current boundaries of the CSC site. If ground water continues
to migrate northward, many residents outside the current site
boundaries may be exposed to contaminated water. Results from
the ground-water modeling indicate that approximately 20 years
would be required for the last of the ground-water
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contaminants in OU2 to migrate north/northwest of the current
Site boundaries. Many residents outside the current Site
boundaries may not be able to be readily connected to the
SACWSD system due to unavailabil i ty of water mains. The
unavailability of water mains may be attributed to the sparse
population of residential homes north and northwest of the
current CSC boundaries.
If private wells become contaminated in areas where it is not
practical to connect users to the SACWSD system due to the
sparse population and lack of accessibility to SACWSD water,
it is likely that activated carbon treatment units would be
installed to treat the contaminated ground water.
This alternative would be effective in preventing private
alluvial well users from being exposed to contaminated grouhd
water. This alternative would comply with chemical-specific
ARARs. Residents would be provided water from the SACWSD
system which is required to comply with federal and State
regulation under the Safe Drinking Water Act (SDWA) and the
previous EPA ROD. This alternative is considered to be a
permanent remedy. It is technically and administratively
feasible. Since all existing private alluvial well users with
contamination are located near existing water mains,
connection to the SACWSD system can be quickly and easily
accomplished.
Costs for this alternative include the acquisition of a tap,
installation of a service line from the home to the water
main, installation of a shut-off valve, and interior plumbing
for 12 known residences.
Costs associated with this alternative are summarized below:
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Connection of Residences to the SACWSD Water System
Capital Costs:
Annual Operation & Maintenance Costs: $5,520*
Total (30-Year Present Worth) Costs:
Total Present Worth and Capital Costs:
*EPA expects the residents to pay these expenses.
**Future costs for activated carbon treatment units have not
been estimated.
$36,000
$121. 000
$157,000**
Alternative 3 -
units
Individual Home Activated Carbon Treatment
This alternative involves the installation of individual home
activated carbon treatment units for residences dependant on
alluvial wells for domestic purposes. Domestic water used for
drinking, cooking, and showering would be treated. It is
estimated that the carbon would be required to be replaced
approximately three times a year.
The activated carbon treatment units would effectively treat
the chemicals of concern except for vinyl chloride. Vinyl
chloride has been detected sporadically throughout the CSC OU2
Site. Many of the chemicals of concern for the Site may
degrade to vinyl chloride under anaerobic conditions.
Due to the potential for biodegradation of Site contaminants
to vinyl chloride and to ensure that units are being replaced
in a timely manner, water quality monitoring would be required
on a yearly basis. This alternative would not meet chemical-
specific ARARs related to vinyl chloride as promulgated under
the SDWA.
Individual Home Activated Carbon Treatment
Capital Costs:
Annual Operation & Maintenance Costs:
Total (30-Year Present Worth) Costs:
Total Present Worth and Capital Costs:
units
$24,000
$30,600
$370.000
$394,000
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VIII. SUMMARY OF THE COMPARATIVE ANALYSIS OF ALTERNATIVES
The remedial alternatives developed in the OU2 FS and OU3 FS
were analyzed in detail using the nine evaluation criteria of
the NCP. The resulting strengths and weaknesses of the
alternatives were then weighed to identify the alternative for
each OU which would provide the best balance among the nine
criteria. These criteria are: 1) overall protection of human
health and the environment: 2) compliance with applicable or
relevant and appropriate requirements (ARARs): 3) reduction of
toxicity, mobility, or volume through treatment: 4) long-term
effectiveness and permanence: 5) short-term effectiveness: 6)
implementabilitYi 7) cost: 8) state acceptancei and 9)
community acceptance. Each of these criteria is described and
evaluated below.
Overall
Protection
of
Human
Health
and
the
Environment
addresses whether or not a remedy provides adequate protection
and describes how risks posed through each pathway are
eliminated, reduced or controlled.
O~erable unit 2. Overall protection of human health would be
achieved for all alternatives except Alternative 1 (no
action) . Al though operation of the Klein Water Treatment
Plant and remedial acti vi ties undertaken in CSC OU3 will
ensure that all residents in CSC OU2 are protected from
contaminated ground water, there are currently no
institutional controls to prohibit future use of the aquifer.
Based on an assessment of a Reasonable Maximum Exposure
scenario, unacceptable cancer risk of 3 X 10 -4 ~~ posed to
site residents. In addition, Alternative 1 does .: protect
the environment because it does not control, remediate and
prevent the PCE plume from migrating further into and beyond
CSC OU2 and becoming more dispersed in the aquifer.
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Alternative 5 incorporates the most aggressive steps to
remediate both the TCE and the PCE plumes, but in the process
may cause the contamination on the western tier of the RMA
site to move into CSC OU2. The resulting movement of the
contamination on the western tier of the Arsenal would
increase the areal extent of the contamination, thereby
increasing the potential risks to site residents and
disrupting the remedial actions being taken on the RMA site.
This alternative may also deplete the aquifer by extracting
water at such a rate that the aquifer may recover very slowly.
Because of these considerations this alternative may not be
protective of the environment.
Alternative 2 is protective of the public health and the
environment. This alternative addresses the PCE plume without
the possibility of influencing the contamination on the
western tier of the Arsenal, and therefore represents the most
advantageous approach. All the treatment options under
consideration are protective and recognize that vinyl chloride
will not be removed by Alternative 2A, should it become a
problem.
Ground-water contamination associated with the CSC plume (also
referred to as the TCE plume) south of Sand Creek will be
remediated by activities undertaken in CSC OUl. Subsequent to
implementation of remedial action at OUI, ground water
migrating into OU2 from OUI will be below levels cited in
Table 8. All of the alternatives for CSC OU2 adequately
address remediation of the TCE that currently exists in CSC
OU2.
Operable Unit 3. Alternative 2 is protective of public
health. This alternative achieves the remedial action
objectives established for OU) for all chemicals of concern.
Alternative 1 is not protective of public health. The
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resultant risk associated with this alternative under a RME
scenario is 3 X 10-4. Al ternative 3 is not as protective
because the carbon filtration units will not effectively treat
vinyl chloride.
.0
Compliance with ARARs addresses whether or not a remedy will
meet all Federal and State environmental laws and/or provide
grounds for a waiver.
ODerable Unit 2. Chemical- and action-specific ARARs for CSC
OU2 include requirements of the Safe Drinking Water Act, the
Underground Injection Control Program, the State of Colorado
Water Quality Control Act, and the State of Colorado Air
Quality Act. These ARARs require that the aquifer be restored
to drinking water quality. Alternative 1 does not comply with
these ARARs because the PCE concentrations in the aquifer will
increase above proposed federal standards (i.e. the proposed
MCL for PCE) in many portions of the aquifer because the PCE
plume will continue to migrate northward. As the no action
alternative does not include treatment controls, it provides
no reduction in risk and would not comply with ARARs.
Therefore, it will not be discussed further with regard to
Operable Unit 2. Al ternatives utilizing air stripping
(AI ternati ve 2C) , the Klein Water Treatment Facil i ty
(Alternative 5) and UV-oxidation (Alterative 2B) are capable
of removing all COCs to health based levels and, therefore,
would be in compliance with federal and State Underground
Injection Control ARARs. Alternative 2A would not comply with
these requirements for vinyl chloride. Carbon adsorption
(Alternative 2A) cannot effectively treat vinyl chloride to
health based levels.
ODerable Unit 3. Alternative 2 complies with ARARs for all
chemicals of concern based on existing site conditions.
Alternative 3 would not comply with SDWA standards for vinyl
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chloride. Alternative 1 would not comply with ARARs for all
chemicals of concern. As the no action alternative
(A~ternative 1) does not reduce Site risks to acceptable
levels and does not comply with ARARs for chemicals of
concern, it will not be discussed further for aU3.
Long-term Effectiveness and Permanence refers to the ability
of a remedy to provide reliable protection of human health and
the environment over time.
operable Unit 2. Alternatives 2A, 2B, and 2C provide
permanent remedies for the PCE plume. These alternatives all
provide reliable protection of human health and the
environment of the TCE and PCE plumes and minimal residual
risk. Ground-water treatment through activated carbon
(Alternative 2A) would result in residual waste management of
contaminants adsorbed to the spent carbon filters but poses a
minimal residual risk. UV oxidation would result in no
treatment residual. Risks associated with emissions from air
stripping under Alternative 2C would not pose an unacceptable
risk to the public (i.e. greater than 1 X 10-6). Alternative
5 results in approximately 5 ~g/l reduction in TCE in
comparison to Alternative 2. This alternative, however, may
result in the migration of the contamination on the western
tier of the Arsenal onto CSC aU2, resulting in an increased
risk from this plume.
operable unit 3.
Alternative 2 would result in a permanent
remedy. Once residences are connected to SACWSD, no
additional activities would be required. Alternative 3 is not
a very reliable alternative. Carbon filters would be required
to be replaced approximately three times per year.
Reduction of Toxicity, Mobility, or Volume Through Treatment
refers to the preference for a remedy that reduces health
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hazards, the movement of contaminants,
contaminants at the Site.
or the quantity of
Operable unit 2. The toxicity, mobility and volume of
contaminants will decrease under most alternatives as a result
of operation of the Klein Water Treatment Plant and the PCE
treatment system. Alternative 5 removes the greatest mass of
contamination, closely followed by Alternatives 2A, 2B, and
2C. Under Alternatives 2C and 5 (air stripping), the
contaminants removed from the ground water would be emitted to
the atmosphere at acceptable emission rates although the
toxicity, mobility and volume would not be reduced. The
mobility of contaminants treated through activated carbon
(Alternative 2A and 5) would be reduced to near zero during
treatment. All alternatives include activated carbon
treatment because of operation of the Klein Water Treatment
Plant, and Alternative 2A includes an additional carbon
treatment system to treat the PCE plume. The mobility of the
removed contamination is reduced to near zero when it is
adsorbed by the carbon and subsequently destroyed during
carbon regeneration. The mobility of contamination drops to
zero in the UV-oxidation process (Alternative 2B) because
contaminants are actually destroyed rather than transferred to
another medium.
Operable Unit 3.
The treatment of contaminated ground water
is documented in the CSC OUI and OU2 RODs.
Short-term Effectiveness addresses the period of time needed
to complete the remedy, and any adverse effects to human
heal th and the environment that may be caused during the
construction and implementation of the remedy.
Operable unit 2. All treatment alternatives promote
remediation of the aqui fer to some degree. Al ternati ve 5
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would remediate the aquifer most quickly and would remove the
greatest mass of contamination (92 percent of the PCE) by
remediating the PCE plume and increasing the amount of ground
water being treated by the Klein Water Treatment Plant. It is
estimated that the PCE plume would be remediated in 17 years
and the TCE plume would approach remediation levels in 25
years. This alternative, however, has the potential to induce
migration of the contamination on the western tier of RMA into
CSC OU2, which would have a detrimental effect on ground-water
quality in CSC OU2. In addition, Alternative 5 may result in
aquifer depletion, which is unacceptable because this aquifer
is the principal source of water for Commerce city.
Alternatives 2A and 2C provide the greatest degree of short-
term effectiveness. Despite the fact that these alternatives
require slightly more time to remediate the aquifer than
Alternative 5, they will not impact water availabilities or
the contamination on the western tier of RMA. Alternative 2B
would require conducting pilot and treatability tests to
optimize treatment. This would result in a delay in
finalizing remedial design plans and initiating remedial
action. Approximately 86 percent of the PCE plume would be
removed by Alternatives 2A, 2B, and 2C and remediation times
are estimated to be 20 years for PCE and 30 years for TCE.
Field and construction activities associated with all of these
alternatives would not impact human health or the environment
during alternative implementation. The adverse impact from
emissions to the atmosphere of Alternatives 2C and 5 is judged
acceptable by federal and state requirements and EPA policy.
Operable Unit 3. Both Alternative 2 and Alternative 3 can
be implemented very quickly (i.e., less than 30 days).
Implementability refers to the technical and administrative
feasibility of a remedy. This includes the availability of
materials and services needed to carry out a remedy. It also
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includes coordination of federal, state, and local governments
to clean up the Site.
\~
ODerab1e unit 2. Alternative 2 is the easiest to implement as
installation of pump and treat systems is commonly performed
on similar Sites. Within the treatment options, carbon
adsorption and air stripping will be easier to implement than
UV-oxidation, which would require extensive treatability and
pilot testing. Finally, Alternative 5 is the most difficult
to implement because SACWSD would be required to revise its
water augmentation plan and to request approval from the State
of Colorado water court, which would require at a minimum 3
years. In addition, technical considerations, ~~imarily
depletion of the aquifer, may prevent this alternative from
being technically implementable. Increased pumping of the
SACWSD extraction wells and the potential for misplaced
reinjection points could result in aquifer depletion.
Therefore this alternative is also difficult to implement from
a technical standpoint.
ODerab1e unit 3.
implementable.
Alternative 2 and Alternative 3 are readily
Cost evaluates the estimated capital and operation and
maintenance costs of each alternative in comparison to other
equally protective alternatives.
Operable Unit 2. The alternative with the greatest capital
cost is Alternative 5 ($3,290,000), PCE Plume Treatment with
Increased Pumping of the SACWSD Wells. The treatment option
with the greatest capital cost is UV-oxidation ($1,950,000),
followed by carbon adsorption ($1,910,00) (Alternative 28 and
2A respectively). Alternative 2C, air stripping has the
lowest capital costs ($1,410,000). The alternative with the
greatest operation and maintenance (O&M) costs is also
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Al ternative 5, and O&M costs are also greatest for UV-
oxidation, followed by carbon adsorption, and air stripping
(Alternatives 2B, 2A, and 2C, respectively). The present
worth of the alternatives varies in the same manner as capital
and O&M costs. Specific capital, 0 & M, and present worth
costs for Alternatives 2A, 2B, 2C and 5 are presented in Table
9.
Operable unit 3. Based on present worth cost calculations,
Alternative 2 is approximately three times less costly
thanAI ternative 3 because additional monitoring would be
required for Alternative 3. The capital costs for Alternative
2 are approximately $36,000. The capital cost for Alternative
3 is sl ightly less at $24,000. Al ternative 2, however,
requires no 0 & M costs, compared to $30,000 per year under
Al ternati ve 3, since monitoring would not be required for
Alternative 2.
Specific capital, 0 & M and present worth
Alternative 2 and Alternative 3 are presented in
costs
for
Table 10.
state Acceptance indicates whether the State agrees with,
opposes, or has no comment on the preferred alternative.
Operable unit 2. EPA has involved the Colorado Department of
Health (CDH) throughout the RI/FS and remedy selection
process. CDH was provided the opportunity to comment on the
RI/FS document and the Proposed Plan and took part in the
public meeting held to inform the public of the Proposed Plan.
CDH submitted formal comments to EPA during the public comment
period for OU2. In these comments, CDH identified additional
State ARARs which were not included in the OU2 FS. Prior to
public release of the OU2 proposed plan, the State of Colorado
(CDH) informed EPA in writing that the State concurs with
EPA's preferred alternative, Alternative 2C. Appendix C
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2C.
5.
ALTERNATIVE
1.
No Action
2A.
PCE Plume Treatment, Hydraulic
Containment 0' PCE Plume,
Activated Carbon Treatment 0'
Extracted Water
28.
UV-Oxidation
Extracted Water
Treatment
Air Stripping
Extracted Water
Treatment
PCE Plume Treatment, Hydraulic
ContaiM)80t 0' PCE Plume,
Increased Pumping 0' South
Adams County Water and
Sanitation District Wells
TABLE 9
COSTS OF REMEDIAL ALTERNATIVES
OPERABLE U~irr 2
CAPITAL
~
$2.600
$1,910.000
0'
$1,950,000
0'
$1,410,000
$3,290,000
ANNUAL OPERATION
AND MAINTENANCE COST
YEARS 1-8* YEARS 8-20*
$27,000
$262,000
$27,000
$277,000
$27,000
$223,000
$27,000
$825,000
$27,000
TZ'-C08026-Ix~
TOTAL CAPITAL COST
AND PRESENT WORTH
$263,600
$3,400,000
$3,520,000
$2,420,000
$6,260,000
-------
contains the state's letter of concurrence with these RODs.
Operable unit 3. Similar to Operable Unit 2, CDH was provided
the opportunity to comment on the RI/FS document and Proposed
Plan for Operable Unit 3. CDH submitted formal comments to
EPA during the public comment period for OU3. In these
comments, CDH requested clarification regarding the
identification of specific residences requiring connection to
SACWSD. Responses to these specific concerns are provided in
the Responsiveness Summary section of the ROD. Prior to
public release of the OU3 proposed plan, the State of Colorado
informed EPA in writing that the State concurs with EPA's
preferred alternative, Alternative 2. Appendix C contains the
State's letter of concurrence with these RODs.
community Acceptance includes determining which components of
the alternatives interested persons in the community support,
have reservations about, or oppose.
Operable unit 2. EPA solicited input from the community on
the cleanup methods proposed for ground water at CSC OU2. One
citizens' group, citizens Against Contamination (CAC),
submitted formal comments to EPA during the public comment
period. In their comments, they indicated that they were
opposed to the lack of emission controls on the air stripping
unit proposed under Alternative 2C. This concern is addressed
in the Responsiveness Summary section of this ROD.
Operable Unit 3. Concerns were raised by the South Adams
County Water and Sanitation District (SACWSD) regarding the
acceptability of water from Well #18. SACWSD provided EPA
with additional data on the water quality for Well #18. These
data indicated that concentrations of TCE routinely fluctuated
above the MCL of 5 ~g/l. The highest reading of TCE was 12
~g/l. SACWSD would prefer that the selected remedy include
75 of 91
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AL TERNA TIVE
1.
No Action
2.
Connection of Residences to the
SACWSO Water System
3.
Individual Home Activated Carbon
Treatment Unites
TABLE 10
COSTS OF REMEDIAL ALTERNATIVES
OPERABLE UNIT 3
CAPITAL
COST
ANNUAL OPERATION
AND MAINTENANCE COST
None
$21.600
$36.000
$5.520
$24.000
$30.600
TZ~-05842
TOTAL CAPITAl COST
AND PRESENT WORTH
$332.000
$121.000
$370.000
-------
IX.
provisions for treatment of water from Well *18.
concerns are addressed in the Responsiveness Summary.
These
SELECTED REMEDY
EPA has selected CSC OU2 Alternative 2C, PCE Plume Treatment
by Air Stripping with Hydraulic containment and Standard
Pumping of SACWSD Wells, and CSC OU3 Alternative 2,
connection of homes to the SACWSD water system as the remedies
for Chemical Sales Operable Unit 2 and Operable unit 3. The
remedy assumes continued operation of the Klein Treatment
Plant.
The remedy for Operable unit 2 is made up of the following
components:
extraction of
extraction wells
contaminated
ground
water
by
treatment
stripping
of
contaminated
ground
by
air
water
reinjection of
injection wells
treated water to the aquifer by
This remedy also includes:
monitoring of approximately 15 wells on at least an
annual basis
voluntary abandonment of bedrock wells for which
criteria will be established in RD
The ground water extraction system will be installed to
extract the maximum amount of the PCE plume possible. The
configuration of the extraction and injection wells will be
determined during remedial design. The system will operate
until contaminant concentrations are reduced to site
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remediation levels cited in Table 8.
This alternative assumes that the remedial action objectives
for CSC OUI and CSC OU3 will be met. Thus, contaminated
ground water will be prevented from entering OU2 from OUI, and
users of shallow alluvial wells in OU2 will be protected.
Estimated cost for the selected remedy is $2,683,600 (includes
cost of monitoring).
()
The remedy for Operable Unit 3 consists of the following
components:
Connection of Residences currently using alluvial
wells for domestic water to the SACWSD. Currently,
all known site residences can be readily connected
to SACWSD water.
Installation of home activated carbon units for
-homes not readily accessible to SACWSD. Monitor
for vinyl chloride to ensure protection of remedy.
Notification of potential health treat.
The selection of these remedies is based upon the comparative
analysis of alternatives presented in the previous section.
These remedies provide the best balance with respect to the
nine evaluation criteria, are prot:::tive of both human health
and the environment, and will comply with all identified State
and federal ARARs.
Operable Unit 2
The selected remedial alternative (Alternative 2C) for
Operable Unit 2 addresses the PCE plume without influencing
the contamination on the western tier of RMA. Air stripping
technology is the most effective and implementable technology
for removing all the COCs identified for OU2. VOC emissions
resulting from air stripping operations will result in minimal
risk (i.e. less than 1 X 10-6 risk level). The source of the
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Chemical Sales Co. plume (also referred to as the TCE Plume)
will be remediated by activities undertaken in CSC OU1. These
activities will result in a significant reduction in the mass
of alluvial aquifer contamination within OU1. In addition,
ground-water contaminants within OU1 will be prevented from
migrating into OU2. These actions are considered to be
sufficient with regard to addressing ground-water
contamination emanating from the CSC facility.
Alternative
2C
was
and
selected
technical
over
Alternative
5
due
to
administrative
implementability problems
These concerns include: (1) a
associated with Alternative 5.
delay in initiating remedial action resulting from
administrative difficulties in obtaining the Colorado State
Engineer's Office approval for SACWSD water augmentation plan
revision; (2) potential depletion of the alluvial aquifer
which is the primary source of water to the residents of
Commerce City; and, (3) possible migration of the RMA
contamination on the western tier of the Arsenal into OU2.
Although Alternative 5 would restore the alluvial aquifer
within OU2 faster than Alternative 2, Alternative 5 was not
selected due to the implementability concerns listed above.
Air stripping was selected as the most appropriate treatment
technology because it is the most effective technology to
treat CSC OU2 COCs, is readily implementable and is the least
costly treatment technology. Despi te the fact that uv-
oxidation reduces the mobil i ty of contaminants more
effectively than air stripping and is permanent, this
technology is more costly than air stripping and would require
extensive testing to determine appropriate adjustments for
treatment.
Under Alternative 2C, the toxicity and volume of contaminants
will decrease as a result of operating the Klein Water
79 of 91
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Treatment Plant and the PCE treatment system. Approximately
86 percent of the PCE plume will be removed by this
alternative. Remediation times are estimated to be 20 years
for PCE and 30 years for TCE. This alternative will not
result in unacceptable risks to the community during
implementation.
The selection of this alterative (Alternative 2C) is in
keeping with EPA policy to act quickly and capture as much of
the plume as possible, before it dilutes and disperses in the
aquifer. Experience has shown that preventing further
migration of contamination is an essential objective for any
aquifer remediation effort. The monitoring portion of this
al ternative further reflects EPA I s policy that data should
continue to be collected at a Site to assess contaminant
movement and predict the likely response to extraction. This
alternative will meet the remedial action goals and objectives
for ground water in CSC OU2 outlined in Section VII of this
ROD.
Remediation Goals and Performance Standards tor Ground Water
Remedial Action Ob;ectives. Remedial action objectives for
this site are presented in Table 8
Area of Attainment. The area of attainment for the ground
water remediation shall be the CSC OU2 plumes exceeding ground
water remediation levels for all COCs. Low-level
contamination not captured by the SACWSD pumping wells will be
allowed to flow to the north and northwest, and any users of
water exceeding acceptable contaminant concentration levels as
defined in Table 8, will be provided with alternate water
under OU3. The estimated area that currently exceeds
remediation levels is shown on Figures 6 and 7. The TCE and
PCE plume areas shown in Figures 6 and 7 currently include all
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areas where other COCs exceed their respective remediation
levels. This, area may be revised based on water quality
sampling during RD/RA.
Restoration Time Frame. The restoration time frame for this
remedial action is estimated to be approximately 20 years for
the PCE plume and 30 years for the TCE plume.
Performance standards. Specific performance standards, used
to ensure attainment of the remedial action objectives for
ground water are:
1)
Reduce contaminant concentrations in ground water
wi thin the area of attainment to the remediation
levels specified in Table 8 and to levels which
present a total carcinogenic risk of less than 10-4
to 10-6.
2)
Ensure capture of the PCE plume within the area of
attainment. Verify that plume movement is being
controlled by measuring hydraulic gradient within
and outside of the plume, and demonstrating that
the gradient is inward toward the pumping wells.
3)
Meet all
identified
in
this
ROD
for the
ARARs
remediation of ground water, including
for air emissions monitoring and UIC
for reinjection of ground water.
requirements
requirements
4)
The remedial action shall be considered complete
after the remediation levels have been maintained
in all compliance monitoring wells for four years.
The extraction system shall continue to operate until
remediation levels have been maintained in all compliance
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monitoring
sampling.
wells
for
four
consecutive
quarters
of
After that time, ground water extraction may be
terminated upon approval by EPA. The remediation levels
must then be met for three additional years (with a
sampling frequency to be determined during RD/RA, but
expected to be quarterly), after which the remedial
action may be considered complete. After the remedial
action is complete, there may be additional monitoring
conducted by EPA. If any excedence of the performance
standards occurs in any of the compliance monitoring
wells during this three-year period, the extraction and
treatment system shall be restarted and operated until
performance standards are again attained in all
compliance monitoring wells. This cycle shall continue
until quarterly monitoring for one year demonstrates no
excedence of performance standards in the compliance
monitoring wells.
The wells to be used for compliance monitoring for water
quality and water levels will be approved by EPA during
review of the 60% Remedial Design completion report, and
will, at a minimum, include wells upgradient of the
plumes, within the plumes, around the plumes, and
downgradient of the plumes. Any statistical methods to
average well concentrations shall be specified during
RD/RA.
The first remedial action objective, stated above, is to
restore ground water to its beneficial use as a drinking
water aquifer. Based on information obtained during the
Remedial Investigation and a careful analysis of all
remedial al ternati ves, EPA and the state of Colorado
believe that the selected remedy will achieve this
82 of 91
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objective. It may become. apparent, however, during
implementation or operation of the ground water
extraction systems and their modifications, that
contaminant levels have ceased to decline or are
remaining constant at levels higher than the remediation
goal over some portion of the contaminated plumes. In
such a case, either or both of the extraction systems'
performance standards and/or remedy may be reevaluated.
If new extraction or remediation technologies become
available in the future which would significantly improve
the remediation process (allow attainment of remediation
levels which were not previously attainable, or expedite
the cleanup), the remedy will be reevaluated in light of
the new information.
The selected remedy will include ground water extraction
for an estimated period of approximately 20 years for the
PCE plume and 30 years for the TCE plume, during which
time the two systems' performance will be carefully
monitored on a regular basis and adjusted as warranted by
the performance data collected during operation.
Modifications may include any or all of the following:
a)
at individual wells where cleanup goals have
been attained, pumping may be discontinued;
b)
alternating pumping
stagnation points;
at
wells
to
eliminate
c)
pulse pumping to allow aquifer equilibration
and to allow adsorbed contaminants to
partition into ground water; and
d)
installing
facilitate
additional
extraction
wells
or
accelerate
cleanup
of
to
the
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contaminant plume.
To ensure that remediation levels are maintained at those
wells where pumping has ceased, those wells will be
monitored every year following discontinuation of ground-
water extraction, until the remedial action is completed.
"
Performance and Compl iance Sampl inq Program. A sampl ing
program for monitoring the remedial action performance and for
determining compliance with the performance standards shall be
implemented during the remedial action. This program will be
developed during remedial design and shall include, at a
minimum, the following: locations of performance and
compliance monitoring wells for water quality sampling,
frequency of monitoring of performance and compliance wells,
analytical parameters (focusing on COCs with possible use of
indicator chemicals), sampling field methods, water level
measurement frequency, analytical methods for chemical
analysis (with possible use of non-CLP analysis), locations
and methods for water level measurement, and statistical
methods for evaluating data. The performance and compliance
sampling program will be specified in the RA Workplan and may
be modified during the RA.
The performance monitoring system will be designed to provide
information that can be used to evaluate the effectiveness of
the remedial action with respect to the following:
horizontal and vertical extent of
contaminant concentration gradients,
balance calculation, if possible
the plume and
including a mass
rate and direction of contaminant migration
84 of 91
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changes in contaminant concentrations or distribution
over time
effects of any modifications to the original remedial
action.
other items to be specified in the performance monitoring plan
include:
monitoring of concentrations of influent and effluent to
the PCE plume air stripper (influent water concentration,
and effluent water and air concentrations), so as to meet
air emission standards.
concentrations of contaminants in ground water to be
reinjected, so as to comply with UIC requirements for
reinjected ground water.
methods to monitor possible migration of contaminants to
the north and northwest of the main SACWSD pumping
center.
Operable unit 3
For CSC OU3, continued operation of the Klein Water Treatment
Plant (KWTP) and connection of alluvial well users to the
SACWSD water system will ensure that all residents in CSC OU2
are protected from exposure to contaminated ground water.
Alternative 2 was selected over Alternative 3 because it
represents a permanent remedy, is less costly than Alternative
3, and is protective of human health for all COCs.
Alternative 3 requires that home carbon filters be changed
about three times a year and would not be effective in
treating vinyl chloride.
85 of 91
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Vinyl chloride has not been detected in ground water extracted
by the SACWSD municipal supply wells. If vinyl chloride is
detected at the Klein Water Treatement Facility, it will be
treated through air stripping under the provisions of the EPA
Off-post RMA OUI Record of Decision.
x.
STATUTORY DETERMINATIONS
EPA's primary responsibility at CERCLA sites is to select
remedial actions that are protective of human health and the
environment. CERCLA also requires that the selected remedial
action for the site comply with applicable or relevant and
appropriate environmental standards established under federal
and state environmental laws, unless a waiver is granted. The
selected remedy must also be cost-effective and utilize
permanent treatment technologies or resource recovery
technologies to the maximum extent practicable. The statute
also contains a preference for remedies that include treatment
as a principal element. The following sections discuss how
the selected remedies for CSC aU2 and CSC aU3 meet these
statutory requirements.
Protection of Human Health and the Environment
Operable Unit 2. In order to meet the remedial objectives
outlined in the previous section, the risk associated with
exposure to the contaminated ground water must fall within the
acceptable risk for carcinogens. Attainment of MCLs and
proposed MCLs will assure Site risk falls within this range.
The selected remedy protects human health and the environment
by reducing levels of contaminants in the ground water through
extraction and treatment.
86 of 91
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EPA expects that the aquifer will be completely remediated in
20 to 30 years. The PCE treatment system, together with
activities conducted in OUl and OU3 and operation of the Klein
Water Treatment Plant, will reduce to acceptable levels,
threats of exposure posed to residents and the environment
from contaminated ground water in OU2. The selected
al ternati ve provides the best protection to human health
without significant adverse impact to the environment.
Remedial action objectives and goals will be met.
Implementation of the selected remedy will not pose
unacceptable short-term risks or cross-media impacts.
Operable Unit 3. During the period of time required to
restore the OU2 alluvial aquifer to acceptable levels, a
potential exists for residents to be exposed to contaminated
ground water. The remedy selected for Operable Unit 3
addresses this exposure. Alternative 2 provides protection to
human health by ensuring that residents within the CSC Site
are provided with water containing acceptable levels of
contaminants, as defined in Table 7. No unacceptable short-
term risks or cross-media impacts would be caused by
implementing this remedy.
Attainment
of
Applicable
or
Relevant
and
Appropriate
Requirements
All ARARs would be met by the selected remedy.
OU2 were discussed in Section VII of this ROD.
ARARs for CSC
Cost Effectiveness
EPA believes the selected remedies are cost-effective in
mitigating the principal risk posed by contaminated ground
water within a reasonable period of time. Section
300.430(f) (ii) (D) of the NCP requires EPA to evaluate cost-
87 of 91
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effectiveness by comparing all the alternatives which meet the
threshold criteria, protection of human health and the
environment, against three additional balancing criteria:
long-term effectiveness and permanence; reduction of toxicity,
mobility or volume through treatment; and short-term
effectiveness. The selected remedies meet these criteria and
produce the best overall effectiveness in proportion to their
cost. The estimated costs for the selected remedies are
$2,420,000 for CSC aU2 and $121,000 for CSC aU3.
utilization of Permanent Solutions and Alternative Treatment
Technologies or Resource Recovery Technologies to the Maximum
Extent Practicable
EPA believes the selected remedies represent the maximum
extent to which permanent solutions and treatment technologies
can be utilized in a cost-effective manner for CSC aU2 and CSC
aU3. af those alternatives that are protective of human
health and the environment and comply with ARARs, EPA has
determined that the selected remedies provide the best balance
of trade-offs in terms of long-term effectiveness and
permanence; reduction in toxicity, mobility or volume achieved
through treatment; short-term effectiveness; implementability;
and cost, and also considering the statutory preference for
treatment as a principal element and considering state and
community acceptance.
Operable Unit 2.
The selected alternative (Alternative 2C)
provides a permanent, long-term remedy for the PCE plume.
Although Alternative 5 would restore the alluvial aquifer to
acceptable levels slightly quicker than the Alternative 2C,
this alternative potentially is administratively infeasible,
and may result in migration of the contamination on the
western tier of the RMA onto CSC aU2 and the depletion of a
major source of water to the residents of Commerce City.
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XI.
Toxicity and volume of contaminants will be reduced by the
selected alternative as a result of operating the PCE
treatment system and the Klein Water Treatment Plant.
Alternative 1 is the least effective in providing this
reduction. The selected alternative will not impact the
contamination on the western tier of the Arsenal or deplete
the aquifer, thus provides the greatest degree of short-term
effectiveness. The selected alternative was the least costly
of alternatives meeting the threshold criteria.
Air stripping was determined to be most the most appropriate
treatment technology because it is the most effective
treatment for CSC OU2 COCs, the least costly and easiest to
implement.
Operable unit 3. The selected alternative (Alternative 2)
provides a permanent remedy at minimal costs. No additional
activities will be required subsequent to connection of
residences to the Klein Water Treatment facility. The
selective remedy was the least costly alternative.
The state of Colorado concurs with selection of Alterative 2C
(OU2) and Alternative 2 (OU3). Appendix C contains the
state's letter of concurrence with these RODs.
Preference for Treatment as a Principal Element
The selected remedies satisfy the statutory preference for
treatment as a principal element. No principal threat exists
for either CSC OU2 or CSC OU3.
DOCUMENTATION OF SIGNIFICANT CHANGES
The Proposed Plans for CSC OU2 and CSC OU3 were released for
89 of 91
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public comment on February 28, 1991. The CSC OU2 Proposed
Plan identified Alternative 2C, PCE plume treatment/ hydraulic
containment of PCE plume/ air stripping treatment of extracted
water, as the Preferred Alternative. The CSC OU) Proposed
Plan identified Alternative 2, connection of residences to
SACWSD Water system, as the Preferred Alternative. EPA
reviewed all written and verbal comments submitted during the
public comment period. No significant changes have been made
to the CSC QU2 or au) Preferred Alternatives, Alternative 2C,
and Alternative 2.
90 of 91
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REFERENCES
ARAR's Q's & A's, General Policy, u.s. EPA Superfund Fact Sheet,
May 1989.
Chemical Sales Company, EPA Administrative Order on Consent
(CERCLA-VIII-90-03, Signed September 29, 1989).
Control of Air Emissions from Superfund Air Strippers at Superfund
Ground-water sites, OSWER Directive 9355.0-28.
Guidance for Conducting Remedial Investigations and Feasibility
Studies under CERCLA, Interim Final, u.S. EPA/540/G-89/004,
October 1988.
Risk Assessment Guidance for Superfund, Volume I, Human Health
Evaluation Manual (Part A) Interim Final; u.S. EPA/540/1-
89/002, December 1989.
Role of the Baseline Risk Assessment in Superfund Remedy Selection
Decisions, OSWER Directive 9355.0-30.
Final Remedial Investigation Report, Chemical
Operable Unit 2, Chlorinated Hydrocarbon
October 19, 1990.
Sales Company site,
Ground Water Plume,
Feasibility Study Report, Chemical Sales Company Site, Operable
unit 2, March 1991.
91 of 91
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APPENDIX A
-------
CHEMICAL SPECIPIC ARARs./(1)
Citation Requirement Evaluation
Groundwater - Volatile Organic Compounds (TCE, Carbon tetrachloride, 1,2-
DCE, l,l,l-TCA, l,l-DCE, Vinyl Chloride)
42 V.S.C. ~300g Safe Drinking Water Act
40 CFR 141 National Primary Drinking The alluvial aquifer is
5 CCR 1003-1 Water Standards - used a public drinking
establishes health-based water source. Regulation
standards for public is applicable.
water systems (maximum
contaminants levels
(MCLs)) and Colorado
Primary Drinking Water
Regulations.
Pub.L. No. 94-580 Resource Conservation and
as amended Recovery Act (RCRA)
40 CFR Class IV Injection Wells: Land disposal restriction
144.13 (c) addresses waste injection may be waived if the
as part of RCRA and reinjected water is
CERCLA~ remediation treated to substantially
reduce hazardous
constituents and is
protective of human
health and the
environment. Regulation
is applicable.
5 CCR 1002-8 Colorado Groundwater The alluvial aquifer is
Sec. 3.11.0 Standards: establishes used as a public drinking
water quality standards water source, therefore
to protect existing and the regulation is
potential beneficial applicable.
qroundwater users.
A-I
-------
CHEMICAL SPECIFIC ARAR.w
(continued)
Citation Requirement Evaluation
Soil - Volatile Organic Compounds (PCE, TCE, 1, 1-DCE)
40 CFR 148 Land Disposal Variance can be
Restrictions: prohibits granted on site-
land disposal of certain specific basis.
contaminated soil and Regulation is relevant
debris. and applicable to
contaminated soils.
40 CFR 261 Identification and Regulation is relevant
Listing of Hazardous and appropriate,
Waste: specifies establishing maximum
Toxicity Characteristic soil concentrations of
Leaching Procedure (TCLP) leachable compounds to
and establishes meet HCLs.
regulatory levels for
organic chemicals.
CRS-25-7-101-512 Colorado Air Quality Regulation is
Control Act: sets applicable to vapor
ambient air standards and extraction and
air emissions volatile emissions.
requlations.
5 CCR 1001-14 Colorado Ambient Air Applicable to vapor
Quality Standards extraction and
volatile emissions.
CRS-30-20-101 through Colorado Solid Waste Applicable to any non-
118 Disposal Act: regulates hazardous solid waste
the management of solid regulated under this
waste. act. Regulation is
relevant and
appropriate to
management of all
solid waste.
40 CFR Part 60, Performance Standards Regulation is relevant
Subpart Kb and appropriate to
volatile liquids
storaqe.
Air
5 CCR 1001-10 Hazardous Air Pollutants: These requirements are
Reg. 8 Regulate emission of applicable to vinyl
seven specific chemicals. chloride.
A-2
-------
ACTION SPECIFIC ARARs8'
Citation Requirement Evaluation
29 U.S.C. Occupational Safety and Applicable to
H65l-678 Health Act: regulates worker response actions.
health and safety.
49 CFR 107, 171-177 Hazardous Materials These requirements
Transportation: regulates are applicable to any
transportation of hazardous transportation of
materials. hazardous materials.
40 CFR 260-270 Resource Conservation and These requirements
Recovery Act: regulates are relevant and
generation, treatment, appropriate to
storage and disposal of disposal of soil or
hazardous waste. treatment residue.
S CCR 1002-2 Regulation for state Sets forth applicable
discharge permit regulations for land
treatment and
disposal
40 CFR 144-147 Underground Injection Control These reqUirements
Program: regulates are applicable to
underground injection wells. reinjection of
treated aroundwater.
4 CCR 723-18, HMT 1- 9 Rules and Regulations These requirements
Governing the Transportation are applicable to the
of Hazardous Materials Within transport of
Colorado: establishes hazardous waste.
specific requirements for the
transportation of hazardous
materials within the state.
6 CCR 1007-3 Colorado Hazardous Waste These requirements
~260 and 270 Regulations: regulates are applicable to
dis~osal of hazardous waste, onsite disposal of
TSD' facilities, and treatment residue,
treatment of residue. and may apply to
offsite disposal.
S CCR 1002-8 Colorado Water Quality These requirements
~3.1.0-3.1.11, Control Act: regulates are relevant and
3.11.0 discharge to state waters. appropriate to
discharges to surface
water.
'\-3
-------
ACTION SPECIFIC ARAR.~
(continued)
Citation Requirement Evaluation
~25-12-103, C.R.S. Colorado Noise Abatement: These requirements apply
establishes standards for to construction
controlling noise. activities.
37-91-104, 106, 110 Water Well Construction These requirements apply
C.R.S. and Pump Installation: to well construction and
Regulates water wells, groundwater withdrawal.
test holes, and pump
installation.
33 u.s.c ~ 1251-1376 Clean Water Act
40 CFR 230, 231, Dredge or Fill (section A small area may be a
33 CFR 323 404): Requires permit to wetland. A permit will
discharge dredged or fill not be required pursuant
material into navigable to Section 121 (e) of
waters or wetlands. CERCLA, but the
substantive requirements
may be appropriate for
activities involving
dredge and fill.
Executive Order No. Protection of Wetlands: Regulations may be
11990, 40 CFR 6.302(b) requires action to avoid relevant and appropriate
adverse effects, minimize to a small wetland area.
potential harm and
preserve and enhance
wetlands.
5 CCR 1001-5 Colorado Air Pollution CERCLA Section 121(e)
Reg. 3 Control Regulations: exempts onsite response
requires air pollution actions from obtaining
emission notices (APEN) permits, but requires
and permits. compliance with
substantive provisions
and filing of APEN.
Regulations are
applicable.
A-4
-------
5 CCR 1001-9
Reg. 7
LOCATION SPECIFIC ARAR.~
Volatile Organic
Compounds: regulates
emissions of volatile
compounds.
5 CCR 1001-)
Reg. 1
Fugitive Dust Emissions:
regulates fugitive dust
emissions and opacity
limitations. Requires
that particulate emissions
be minimized, that opacity
limitations be observed,
and that a particulate
emission control plan be
filed.
5 CCR 1002-3, S 10.1.0
Discharge of effluent to
qroundwater
Stationary Emissions:
regulates attainment and
maintenance of any
NAAQS. dl Also requires
air impact analyses for
toxic pollutants, and the
attainment and maintenance
of State standards.
5 CCR 1001-5
Sec. IVD, Reg. 3
5 CCR 1001-4
Reg. 2
Odor-Free Operation:
requires design action to
provide odor-free
operation.
.. AAAAs . Applicable or Relevant and Appropriate Requirements.
01 CERCLA. Comprehensive EnvironmenlaJ Fleapon.., Compensation, and
Liabiht\i Act.
c! TSD . Treatment, storage. and disposal.
a. NMOS. National ambient air quality standard..
e. RACT = Reasonable, available OCntroltechnique.
(1) Remediation levels are presented in Table 8 01 1M ROO te.1.
A-5
"
<'
RACT81 . 1 .
1S app 1cable and
is required to control
emissions in ozone non-
attainment area.
These regulations would
apply to construction,
excavation and haul
roads.
Applicable to treated
water discharqe.
The Operable Unit is in
a non-attainment area.
The regulations are
applicable.
These are applicable in
order to limit nuisance
conditions from emission
sources.
-------
APPENDIX B
-------
CHEMICAL SALES COMPANY OU2 AND OU3
Responsiveness Summary
Backqround of community Involvement
SUMMARY OF COMMUNITY RELATIONS ACTIVITIES
CHEMICAL SALES COMPANY
Community interest in the ground-water contamination in south
Adams County was very intense in 1985 and 1986 when the problem
first became known, and persisted until the permanent water
treatment plant started operation in October of 1989. Initially
the Rocky Mountain Arsenal, which was adjacent to the
contaminated public water supply area was thought to be the
source. EPA and the Army responded to numerous public and media
inquiries, issued press releases and attended public meetings.
Community relations activities were coordinated among the EPA,
the Army, and the South Adams County Water and Sanitation
District (SACWSD). The State conducted a separate program.
In 1984 and 1985, local newspapers were printing stories almost
daily concerning the Arsenal cleanup process and ground-water
contamination. At least 10 articles were published in July of
1985 regarding TCE found in ground water west of the Arsenal.
EPA personnel responded to numerous questions from reporters and
the public.
In September of 1985, a local citizen's group, Citizens Against
contamination (CAC), held a meeting at which 100 to 200 people
attended, including EPA, Colorado Department of Health (CDH),
Army, and SACWSD officials, and local elected officials. The
meeting was covered by at least KUSA TV, Channel 9.
On November 13, 1985, the Army issued a press release announcing
the detection of TCE in wells on the Arsenal property. A public
meeting was held on November 25, 1985 at which the Army reported
ASC2/BSPL/062691
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the results of the sampling. The Army stated that they planned
to locate the source of the TCE found in the Arsenal wells and
discussed the next steps. They maintained that the available
information was not sufficient to determine if the Arsenal was a
source of the TCE found in the SACWSD wells.
u
On December 19, 1985, EPA issued a press release stating that
they were seeking Superfund money for cleanup of the south Adams
County water. At least 22 articles appeared in the Denver Post
and the Rocky Mountain News in December and January 1985. The
articles focused on EPA's attempts to obtain funding and the
Arsenal as a suspected source. On January 24, 1986, EPA met with
CAC and promised to answer their questions, implement
suggestions, and provide copies of documents.
CAC arranged a public meeting on February 13, 1986 with speakers
from the EPA, the Army, SACWSD, and CDH. The Army offered
technical assistance and funding for an interim solution. The
EPA passed out a fact sheet listing contacts for information on
various topics. There were at least 15 newspaper articles in
February concerning the citizens concerns and the Army's role.
The State of Colorado was threatening to sue the Army for the
groundwater contamination. The Army issued a press release on
February 6, 1986, stating that CDH had agreed to withdraw the
State suit.
CDH issued a health advisory on February 27, 1986, recommending
that residents using shallow private wells in a specified area
boil their drinking water or use bottled water (the advisory was
updated by a second release on March 4 clarifying the boundaries
of the affected area). The advisory resulted in a flurry of
newspaper articles. The agencies were again flooded with calls
from the public, the press, and politicians. A major concern was
access to bottled water for children at school. The Army agreed
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to provide bottled water to schools in the area in March.
also donated bottled water.
Coors
EPA held a press conference on March 4, 1986 and issued a press
release on March 5, 1986 reporting levels of TCE in three private
wells that were much higher than levels found in water provided
by SACWSD. EPA issued an additional press release on March 5
stating that EPA and the Army had agreed in concept to enter into
an agreement to transfer funds from the Army to EPA to pay for
water treatment. A number of newspaper articles followed.
CAC held another public meeting March 6, 1986, which was attended
by more than 600 people, including representatives of the EPA,
the Army, CDH, Tri-County Health (TCH) and SACWSD. Questions
centered on the health effects and the advisory. CDH passed out
a summary of the health advisory with clarifications. Residents
using contaminated private wells were urged to connect to the
public water system. EPA stated that their goal was to have an
interim water treatment system in place in four to twelve months
(this was reiterated by SACWSD). EPA also said they hoped to
have an agreement with the Army and SACWSD to transfer funds from
the Army to SACWSD for the interim system. The Army passed out a
letter explaining that the evidence was still insufficient to
substantiate the Arsenal as a contributor or the sole source of
the TCE contamination.
Heavy newspaper coverage continued following the meeting. A
press release issued March 20, 1986 announced an agreement to
transfer $1 million from the Army to the EPA. On April 7, 1986,
the Army, EPA, the state, and SACWSD signed a cooperative
agreement to provided funding for the water treatment. The
agreement transferred the funds to SACWSD. Press coverage
followed.
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On April 23, 1986, EPA presented an award to CAC for their
efforts. Also in the spring of 1986, EPA prepared and widely
distributed a videotape that answered common questions residents
had regarding the TCE in their water.
On May 1, 1986, EPA issued a press release reporting new data on
private wells. The new data gave a clearer indication that
sources of TCE in addition to the Arsenal were involved. In May
of 1986, six Colorado members of Congress wrote EPA's
Administrator requesting he make funds available for the cleanup.
CAC held another public meeting on May 22, 1986, at which CAC,
the Army, and EPA presented updates. EPA passed out a statement
describing progress. EPA was ready to fund the connection of
private wells to SACWSD. The meeting was attended by a number pf
State, local and federal elected officials.
The Summer 1986 issue of SACWSD's newsletter "The Waterspout"
announced the installation of the temporary carbon filtration
system (May 30, 1986) and urged residents with shallow wells in
the area to apply for free hookups. EPA issued a press release
offering the free hookups. A questionnaire was also sent to
individual well owners.
Media and public interest subsided in the fall of 1986 after 200
private well owners were hooked up to a temporary water treatment
system. EPA issued a fact sheet in August of 1986 containing
information about the site (referred to as EPA's Rocky Mountain
Arsenal Off-Post Study Area) and a summary of activities in
progress. A press release September 11, 1986 announced that the
Army had transferred $6 million to EPA to fund a permanent
treatment facility.
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In an October 23, 1986 press conference, EPA specifically named
the Chemical Sales site as a source of ground-water contamination
in south Adams County.
In December of 1986, EPA issued another fact sheet discussing the
findings of an initial remedial investigation in the EPA Off-Post
Arsenal Study Area. Remedial alternatives were presented and a
public comment period from December 12, 1986 to January 7, 1987
was announced. Notice of the opportunity to comment was also
published in the newspaper on December 10, 1986. Comments were
received from CAC, CDH, SACWSD (and consultant), TCH, the City of
Commerce City, the Adams County Commission, Adams County School
District No. 14, Holme Roberts and Owen, the Army (and
contractor), and a number of residents. The majority of
commentors supported EPA's preferred alternative, a granular
activated carbon filtration system.
In June of 1987, EPA issued a Record of Decision (ROD) for the
selected remedial alternative, a permanent water treatment plant
with a granular activated carbon filtration system. In October
of 1987, the Army and the EPA agreed to pay to construct the
Klein Water Treatment Plant and operate it for 25 years. The
Klein Water Treatment Plant opened on November 17, 1989.
EPA issued a fact sheet for the EPA Off-Post Arsenal Study Area
in April of 1988 announcing further field activities for
investigation of the contamination. EPA prepared a Community
Relations Plan for the Chemical Sales site in December of 1988.
In August of 1989, EPA issued a fact sheet stating that the
Chemical Sales site had been proposed for inclusion on the
National Priorities List (NPL).
EPA issued a fact sheet in April of 1990 concerning TCE
contamination in the Commerce City Area. The fact sheet
discussed the background and the status of the site. In May of
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1990, EPA issued an additional fact sheet covering the status of
four south Adams County Superfund Sites, including Chemical
Sales.
.,
In May of 1990, EPA's Community Involvement Coordinator took
approximately 40 EPA management personnel and officials on a tour
of the south Adams County Superfund sites. In June of 1990, EPA
gave two presentations to brief City, County, and State officials
on the Superfund process and sites in south Adams County.
EPA mailed out Proposed Plans for the three Operable Units at the
Chemical Sales site February 28, 1991. The Proposed Plans
discussed remedial action alternatives for the source and the
ground-water contamination, and announced the public comment
period from February 28, 1991 to April 1, 1991. Notice of the
public comment period also appeared in four local newspapers
between February 27, 1991 and March 5, 1991. A public meeting
held March 14, 1991 was attended by 50 to 75 people.
Comments and Responses
Comments on the CSC OU2 RIjFS report were received from South
Adams County Water and Sanitation District, Department of the
Army, Colorado Department of Health, Chemical Sales Company, and
Citizens Against Contamination. No written comments were
received from individual citizens. The full text of all comments
received is included as Exhibit A.
A letter received from SACWSD stated that SACWSD supported EPA's
efforts to remediate the aquifer in CSC OU2 and generally agreed
with the preferred alternative, although some concerns remained.
The concerl'': focused on the future impact of SACWSD supply Well
18, the predicted operation and maintenance of the Klein Water
Treatment Plant, and potential impacts from the proposed remedial
activities on SACWSD performance.
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~
The Department of the Army submitted the most extensive comments.
These addressed all phases of the RI/FS, including the RI report,
the Risk Assessment, the FS report, and the Modeling report.
"
Colorado Department of Health (CDH) submitted three comments, all
of which dealt with the identification and selection of ARARs.
No other topics were addressed by CDH.
citizens Against Contamination is an organized citizens' group
that has been closely following activities at hazardous waste
sites in the Commerce city area. They submitted only one comment
and it was regarding the air stripper.
Comments received from the Chemical Sales Company (CSC) all
focused on the RI report. Concerns were raised that insufficient
data exist or that the existing data were misinterpreted to
identify CSC as a principle responsible party for the CSC OU2
site.
Responses to all comments have been prepared and are presented in
this section. The comments have been grouped by topic and, in
some cases, have been combined if several comments address a
common concern. The topics are: Responses to Citizen Comments,
the RI, the Risk Assessment, the FS, the modeling report, ARARs,
and Operable unit 3. Within each topic the comments are
generally grouped by author, although there is some overlap when
comments from different sources address the same concern. The
actual text of the comments has been paraphrased for the purpose
of this section of the ROD.
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TOPIC I: RESPONSE TO CITIZEN CONCERNS
1. Citizens Against Contamination Comment
Department of the Army, General Comment 7.
These comments address the need for emission controls on the
air stripper that is included in the preferred alternative.
EPA Response. It is assumed that "air stripper controls"
refers to air emission controls on the air stripper. Both
the federal and state governments have regulations that
specify maximum allowable emissions into the atmosphere of
chemicals such as the chemicals of concern at the CSC OU2
site. The air stripper that will be built for this site
will be in compliance with both federal and state standards.
It is anticipated that air emission controls will not be
needed for the air stripper because the ground water plume
being treated in CSC OU2 is fairly dilute. The air stripper
will be monitored during operation to ensure that the
emissions do not exceed state and federal standards. If
monitoring indicates that air emission controls are needed
for the air stripper, they will be added at that time. In
comparison, the air stripper for CSC OUl will include air
emission controls because the plume in OUl is much more
concentrated and the resulting air emissions would exceed
state and federal regulations without the controls.
TOPIC II:
RI REPORT
2 .
Department of the Army, Specific Comment la, p. 1-2.
It seems inappropriate to define remedial action objectives
(RAOs) in the RI. RAOs should be developed in the FS.
EPA Response. The identification of preliminary RAOs during
the RI is consistent with EPA RI/FS guidance. The purpose
of this identification is to focus and streamline data
ASC2/BSPL/062691
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--
collection activities conducted during the RI. The
preliminary RAOs identified in the RI were formulated based
on data collected during the earlier EPA RMA Off-Post RI/FS
for Operable unit 1 and Operable Unit 2 and EPA's Field
Investigation Team (FIT) during various site investigations.
The amount of data was sufficient to identify COCs for the
operable unit. The preliminary RAOs presented helped to
focus the remedial investigation data collection by
identifying data needs required to address the proposed
objectives. The preliminary RAOs were re-evaluated during
the CSC OU2 FS.
3.
Department of the Army, Specific Comment 1b, p. 1-2.
EPA should clarify what is meant by "...important chemicals
detected in the shallow aquifer..." And should present
criteria used in establishing the "important chemicals."
EPA Response. The term "important chemicals" is used to
provide an overview of the site characteristics during the
summarization of existing site information. The intent of
using this term is to provide the reader a general
understanding of the nature of ground-water contamination
at OU2. The term "important chemicals" is not synonymous
with COCs. COCs were originally identified based on a
comprehensive evaluation process conducted during the EPA
Off-Post Arsenal RI/FS and confirmed in the OU2 RA.
In section 1.2.3, Chemicals of Concern in CSC OU2 were
listed and it was stated that "A Risk Assessment was
performed as part of the RI, resulting in selection of
eight chemicals of concern for the site." The COCs
identified in the RA were a confirmation of the COCs
identified in the EPA RMA Off-Post RI/FS, with minor
additions. The identification of CSC OU2 COCs is
ASC2/BSPL/062691
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discussed
regarding
Assessment
in the RA, and the responses to comments
COC selection are given under Topic II:
(comments 70-81) of this document.
Risk
4 .
Department of the Army, specific Comment 2, p. 1-16.
The text in the last paragraph
indicate that the CSC property
source of contamination to the
potential source.
should be modified to
has been identified as a
alluvial aquifer, not as a
EPA Response. EPA considers the CSC property a source of
contamination in ground water at OU2. Ground-water
contamination emanating from the CSC facility migrates
northward beneath Sand Creek and continues to migrate
northward where it impacts SACWSD municipal water supply
wells. This interpretation is based on the potentiometric
surface maps, water quality data and assessment of the
distribution of chemicals (i.e. PCE/TCE ratios) presented in
the CSC OU2 RI.
5.
Department of the Army specific Comment 3&, p. 1-20.
Significant additional discussion is warranted regarding the
scope and status of the RMA off-post activities, which are
currently underway.
EPA Response. The Army RMA Off-Post Site north of CSC OU2
is not believed to impact CSC OU2 directly. Additional
discussion is not considered to be necessary for the OU2 FS
report, although EPA is willing to discuss the RMA off-post
activities with concerned parties.
ASC2/BSPL/062691
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~
c
6.
Department of the Army Specific Comment 3b, p. 1-20.
Chemicals of Concern (COCs) are identified in this section
of the report. This seems premature and results in
eliminating any discussion on the nature and extent of a
number of other contaminants detected in OU1 and OU2 ground
water. This report does not appear to fully discuss the
nature and extent of contaminants.
EPA Response. An exhaustive analysis of potential COCs was
performed for the OU2 Risk Assessment (RA), and the site
COCs were identified as part of this evaluation. The
identification of COCs utilized all analytical data
available within CSC OU2. The RA is the appropriate place
for discussing the selection of the identified COCs, and
responses to comments regarding the RA are given under Topic
II: Risk Assessment (comments 70-81).
The RI evaluation of the nature and extent of contamination
is based on the COCs identified in the earlier EPA Off-Post
RMA RIjFS. OUl contamination is a separate RIjFS, and
contaminants found in OU1 that do not impact OU2 are not
relevant to OU2. EPA disagrees with the comment that the RI
report "does not fully discuss the nature and extent of
contamination." The nature and extent of contaminants were
evaluated in the EPA RMA Off-Post RI, and were refined in
the CSC OU2 RI.
7 .
Department of the Army specific Comment 4, p. 1-22.
Because of other possible cleanup goals at the site (e.g.,
risk-based standards), it appears that this section should
be retitled and refocussed to indicate that the discussion
simply presents ARARs. It seems premature for the RI to be
discussing tI... what concentrations of contaminants are
ASC2/BSPL/062691
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likely to be of concern for the CSC OU2." These issues
cannot be developed without fully considering the results of
the RA and FS. Additionally it is not clear why ARARs for
non-COCs are presented.
o
EPA Response.
The section is introduced with a statement
that specific cleanup levels would be determined in the FS,
based on a number of factors including ARARs and protection
of human health and the environment. This section is meant
only as a brief introduction of factors affecting the
determination of cleanup levels. Preliminary ARARs are
discussed more fully in the FS. Potential ARARs are
presented in this section to give the reader a basis for
comparison when evaluating the nature and extent of
contamination relative to drinking water standards. ARARs
for potential COCs were presented in Table 1-1. These
included several analytes that were detected within or near
CSC OU2, but were determined to not be compounds of concern
during the RA. This table was meant to be a comprehensive
listing of potential COCs based on evaluation of site
analytical data. The table was used to ensure ~hat
laboratory detection limits were lower than potential
remediation levels. Each of these analytes was evaluated
during the RA to confirm the list of COCs identified in the
earlier Off-Post RMA RIfFS.
8 .
Department of the Army specific Comment 5, p. 2-8.
The report continually implies that RMA is a possible source
of contaminants to the CSC OU2 ground water. Plume maps
presented in the OU3 FS and EPA's proposed plan for OU2
clearly show that plumes migrating north from the CSC site
or from other sources off-post of RMA are flowing onto the
western boundary of RMA. Additionally, the FS indicates
that the ground water plumes in OU2 are principally
ASC2/BSPL/062691
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associated with OU2 or other non-RMA sources. The findings
of the OU2 RI indicate that RMA is not a significant source
of contaminants to ground water in the OU2 study area,
except in the extreme northeastern part of OU2 where low-
level ground water contamination may be attributable to RMA
sources.
EPA Response. Section 2.2 presents contaminant source
investigations potentially relevant to CSC OU2. This
section does not apportion sources for contamination in CSC
OU2, but summarizes previous investigations. EPA sees no
implied apportionment of sources in this section. Section
4.5 evaluates contaminant sources potentially impacting CSC
OU2, including RMA. In Section 4.5.1.2, the RMA and the
49th and Havana Street site are evaluated. This section
concluded that a portion of the contamination at the SACWSD
pumping center at East 77th Avenue and Quebec Street could
be attributable to ground water from RMA, and that the RMA
appeared to be a very minor source of contamination in CSC
OU2. This is not in conflict wit~ the Army comment.
Ground-water contamination associated with the CSC "referred
to as TCE Plume in OU2 FS," and PCE plume may potentially
impact the extreme western edge of the Rocky Mountain
Arsenal.
9.
Department of the Army Specific Comment 6, p. 2-17.
EPA should conduct a reasonable number of long-term (e.g.
24-hour or greater) aquifer pumping tests to adequately
characterize the range of hydraulic conductivities for the
alluvial aquifer.
EPA Response. EPA considers the hydraulic conductivity
values presented in the FS sufficient to adequately
characterize the site and evaluate the effectiveness of the
ASC2/BSPL/062691
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various remedial alternatives identified in the OU2 FS. EPA
recognizes that hydraulic conductivities cover a range of
values over the site, however EPA does not agree that the
time and expense required for additional aquifer evaluation
is necessary to complete the OU2 FS. EPA agrees that the
site data suggest that paleochannel features have
substantially higher transmissivities than areas outside of
the channels. Previously conducted pump tests at production
wells located in paleochannels are believed adequate for
characterizing ranges of hydraulic conductivities in these
features. outside of the paleochannels, the aquifer
saturated thicknesses are much less and hydraulic
conductivities are lower than inside the paleochannels.
Evaluation of borehole geologic logs showed that lithologies
away from the paleochannels are very heterogeneous, and
therefore a large number of pump tests would be required to
approximate hydraulic conductivities. Instead of this time-
consuming and expensive process, EPA opted to utilize
existing pump test data and literature ranges for sa~urated
lithologies based on evaluation of geologic logs.
EPA may require that additional aquifer testing be conducted
during remedial design to provide information regarding the
number, location and rate of extraction wells that will be
installed.
10.
Department of the Army specific Comment 7, p. 2-20.
The basis for the frequency of ground water monitoring (e.g.
approximately every 14 to 16 months) is not discussed. It
would be useful to identify the criteria used to develop
this monitoring plan and cite the sampling plan that
presents the rationale.
ASC2/BSPL/062691
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EPA Response. Routine ground water monitoring was not
conducted by EPA as such for the CSC OU2 RI/FS; a discrete
ground water sampling episode was conducted in 1990 as EPA
determined that additional data were needed. The EPA RMA
Off-Post RI/FS included a phased sampling approach, and the
basis for the sampling interval is given in the EPA RMA Off-
Post RI.
11.
Department of the Army Specific Comment 8, p. 2-26.
The Army agrees that it is important to assess the behavior
of contaminants in the ground water. However the RI
eliminates some chemicals detected in the ground water, so
that the assessment of fate and transport issues does not
completely consider all compounds detected. The fate and
transport discussion could be expanded to include other
chemicals that have been detected, particularly if they fall
into classes whose behavior is substantially different from
the currently identified COCs.
EPA Response. Environmental fate and transport issues were
considered during the selection of the COCs in the RA. EPA
RI/FS guidance recommends the evaluation of existing data to
focus and streamline data collection activities. Although
the use of indicator chemicals serves to focus and
streamline the assessment on those chemicals that are likely
to be of greatest concern, a final check will be made during
remedy selection and the remedial action phase to ensure
that the waste management strategy being implemented
addresses risks posed by the range of contaminants found at
the site. The previous EPA RMA Off-post RI/FS gave a
"baseline" characterization of ground water contamination in
CSC OU2. It is both prudent and valid to conduct the RI/FS
ASCZ/BSPL/06Z691
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process utilizing all previous investigation results to
narrow the scope of investigation.
u
12.
Department of the Army Specific Comment 8&, p. 2-46.
There is no explanation for zero values in the database.
EPA Response. The zeros in the site analytical database
indicate that the sample was not analyzed for that analyte,
or that no usable data exist for that analyte for the given
sample. The site database is formatted in DBASE III+ which
replaces all blank numeric fields with zeros. Further
distributions of the site database will include a statement
explaining this feature.
13.
Department of the Army specific Comment 8b, p. 2-46.
There are gross inconsistencies between various tables in
the report and various appendices. It is not clear why
chloroform data contained in Appendix 2D are not also
presented in Table 3-10. Additionally, the statistical
summary for DCA for well 03002 shown in Appendix 4A is
inconsistent with the number of samples and range of values
from Appendix 2D.
EPA Response. The confusion over chloroform relates to the
types of analytical results presented. EPA studies included
the analysis of data under Routine Analytical Services (RAS)
and Special Analytical Services (SAS) requests through the
EPA's contract lab program. SAS results often have lower
detection limits for the analyzed compounds. Due to
laboratory problems, many of the SAS results were rejected
or were considered suspect. Accordingly, SAS analytical
results are found in the database but many are not reported
in Table 3-10. These SAS database records are flagged in
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the database with a field identifying SAS data. Data
confidence was considered higher with RAS data than with SAS
data, and only RAS data are reported in Table 3-10. The
statistical summary in Appendix 4A which includes DCA
results for onpost well 03002 was also only for RAS data.
14.
Department of the Army specific Comment 9, p. 3-1.
The first paragraph states that the purpose of the
investigation is to "...gather information regarding fate
and transport of the volatile organic contaminants..." This
raises the issue of the overall objectives of the RI and the
definition of the COCs. It is our understanding that an RI
should not involve focusing on the basis of RA results.
EPA Response. The document clearly states that "the
investigations" refer to activities described in section
2.0, which includes refining EPA's understanding of the
ground water flow systems and the contaminants migrating
within it. These are clearly appropriate as objectives for
an RI. The other purpose of the investigations, cited in
the comment, should have been less specific to include non-
halogenated as well as halogenated volatile organic
compounds. The previous EPA RI/FS identified volatile
organic contaminants in the aquifer, of which one (benzene)
is non-halogenated. As listed in section 1.2.3, all of the
COC's are volatile organic compounds.
The RI and RA activities interact in an iterative manner
throughout the site characterization process. In fact, the
RA is included as a section of the OU2 RI. As stated
previously, EPA considers it appropriate to refine data
collection activities and site characterization based on the
identification of COCs in the RA.
ASC2/BSPL/062691
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15.
Department of the Aray Specific Comment 9., p. 3-21.
Figure 3-5 is referenced on this page. All wells identified
on the map should be labelled with the well name, otherwise
the figure may be useless to the reader not having intimate
knowledge of the site.
EPA response. The wells in Figure 3-5 are identified in
Figure 2-9, "SACWSD Municipal and Monitoring Wells".
Future reproduction of this figure will identify well names.
16.
Department of the Army specific Comment 9b, p. 3-21.
It is not clear how the database for constructing the water
level maps, Figures 3-7 and 3-8, was developed. The text
indicates that measurements were taken between 1986 and 1989
(for the potentiometric surface map). This...may not be
appropriate.
EPA Response. The database used for the generation of the
potentiometric surface map was discussed in Section 2.6.3,
"Water Level Elevation Database". As discussed in Section
2.6.3, all SACWSD and CDM well hydrographs were analyzed to
assess the effect of mixing water level data from different
years and/or seasons for generating the potentiometric
surface map. No annual variation was apparent, and effects
of hydrologic features (such as Sand Creek and the SACWSD
pumping wells) were considered. Seasonal variation in the
aquifer (due to seasonal pumping of the SACWSD wells) was
determined to be much more significant than annual
variation. The proximity to wells and Sand Creek was
considered in the use of all data points. A calculation
brief is available in the Administrative Record which
presents the rationale for including various wells and the
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17.
18.
thought process for constructing the potentiometric surface
map.
Department of the Army Specific Comment 10, p. 3-22.
It is not clear why the configuration of the water table as
depicted in Figure 3-7 needs to be reinterpreted and why it
is to be presented in the FS.
EPA Response. Additional field borings and water level
measurements collected by the EPA FIT and by csc provided
additional data in the vicinity of Sand Creek. This data
became available too late to be included in maps presented
in the CSC OU2 RI report. The new data were presented in a
FIT report (FIT, 1990) that is included in the
Administrative Record.
Department of the Army specific Comment 11&, p. 3-23.
It is not clear if Figure 3-10 was constructed using only
the data points shown on the figure. If so, the figure
should be modified to permit an assessment of the drawdown
off-post of RMA.
EPA Response. Figure 3-10 was modified from the u.s. Army
Western study Area Report, and EPA assumes that the Army
used only the data control points shown. EPA inadvertently
left out a reference in this figure, and apologizes for this
oversight. EPA considers this figure adequate for
characterization of the drawdown cone caused by the SACWSD
pumping center at East 77th Avenue and Quebec street due to
the higher density of control points On-Post in this area,
and the larger number of seasonal measurements taken
compared to data available in the off-post area.
ASC2/BSPL/062691
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19.
Department of the Army Specific Comment 11b, p. 3-23.
o
The effects of the Irondale containment System and SACWSD
supply wells are apparently not assessed in the RI. It
appears appropriate to consider these influences.
EPA Response. The effects Irondale Containment System and
SACWSD supply wells were considered for both the RI and the
FS. The Irondale Containment System was mentioned in
Section 3.1.2.2, potentiometric surface, and in Section
4.5.1.2. Discharge and recharge at this barrier system was
evaluated during the development of the ground water model
presented in the FS. The effects of the SACWSD wells on the
aquifer were addressed in detail in several sections of the
RI, including on page 3-23. It is unclear why the Army
considers these as "not assessed".
20.
Department of the Army specific Comment 12 p. 3-32.
While it is recognized that the ground water flow velocities
are certainly variable within the study area, it is not
clear where the assumed values were obtained (e.g.
references), nor why those numbers were justified.
Additionally, a sensitivity analysis should be conducted to
ascertain how much variability would be/could be expected
given the uncertainty in parameters. It seems inappropriate
to present velocity values to two or three significant
figures when the uncertainty could be as much as "...an
order of magnitude..." as indicated on page 3-32.
EPA Response. Section 3.1.2.7 is entitled "Ground Water
Velocity Estimates" and addresses this topic in detail.
This section contains a discussion of how each variable for
the calculation of particle velocity was obtained. The
values obtained by reference were hydraulic conductivity and
ASC2/BSPL/062691
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effective porosity. The hydraulic conductivity values used
were obtained as discussed in Section 3.1.2.6. Numerous
literature sources were evaluated for ranges of hydraulic
conductivities for lithologies found at the site. For
hydraulic conductivity, the references for various
lithologies are given in Table 3-4 (Freeze and Cherry
(1979), McWhorter and Sunada (1981) and Walton (1984».
Considering the aquifer testing done at or near the site,
and the heterogeneities of the alluvial aquifer as discussed
in comment and response No.8, a range of hydraulic
conductivities was estimated. An average literature value
of 0.25 for sandy unconsolidated deposits was considered a
reasonable value for effective porosity. No literature
references are deemed necessary for effective porosity as
standard hydrogeologic sources give similar estimated values
for this parameter.
EPA does agree that a sensitivity analysis is useful to show
the possible range of particle velocities at the site. The
effects of varied average hydraulic conductivities on
particle velocity and travel time were presented, indicating
a possible range of travel times from 48th Avenue to the
pumping center of 4.8 to 12.1 years. The number of
significant figures presented for average flow velocities
are in excess of what is warranted by the data used and
should be rounded to one significant figure. The range of
uncertainty, however, based on the highly uncertain
hydraulic conductivity is clearly given.
21.
Department of the Army specific Comment 13 p. 3-50.
The text would be improved by the inclusion of a discussion
of the data quality objectives, which were apparently
developed in the CSC OU2 Work Plan. It would be helpful if
the report also discussed why some of the data were not
ASC2/BSPL/062691
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validated and clearly identify what, if any, limitations may
be appropriate to the use of the data. CUrrently it appears
that no use-limitations were imposed for non-validated data,
except that they were not considered in the RA.
EPA ResDonse. As stated in Section 3.2.4, non-validated
data were considered to be DQO Level III, and were
acceptable for the preparation of point maps and for all
data interpretation. The selection of data to be validated
was discussed in the EPA RMA Off-Post RI, and in the CSC OU2
Workplan.
Not all data collected during the CSC OU2 RI were validated
because several rounds of sampling and analysis had been
conducted during the earlier EPA RMA Off-post RIfFS. It was
determined that the data collected during the CSC OU2 RIfFS
could be compared to the previous data, which had been
validated and to determine whether the data was consistent
with previous results for the same wells. Based on EPA DQO
guidance, a decision was made that Level IV and V data were
required for use in the OU2 RA and hence only validated CLP
data were used to assess risk.
22.
Department of the Army specific Comment 14a p. 4-1.
The first paragraph indicates that the section provides an
interpretation of ground water quality data from the
regional database, contained in Appendix 2D; however, much
of the data contained in that appendix are not discussed
because of the identification of COCs from the RA. The
report would be improved if it were modified to include a
discussion of non-COC data.
EPA Response. The CSC OU2 RI report presents the results of
a focussed investigation and is the culmination of studies
ASC2/BSPL/062691
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conducted since 1984 by EPA and others to evaluate the
extent of contamination in the area. Previous reports,
including the EPA's RMA Offpost RI (December, 1986)
presented and discussed ground water quality results for all
detected compounds. As many of the non-volatile organic
compounds have been detected at low levels, in sporadic
areal distributions and have been found to pose no
unacceptable risk to human health or the environment, it was
deemed unnecessary to present a discussion of non-COC
compounds in the current RI.
~
23.
Department of the Army Specific Comment 14b p. 4-1.
Please clarify why the distribution of contaminants in the
ground water are discussed relative to Safe Drinking Water
Act (SDWA) levels. This seems premature because SDWA mayor
may not be the selected action level.
EPA ResDonse. SDWA standards are relevant and appropriate
requirements for establishing ground-water remediation
levels at the site (see U.s. EPA, 1991; U.S. EPA, 1989a).
SDWA standards are generally used as ground water
remediation levels provided they are cumulative within the
risk range. Although these standards may not represent the
final remediation level, they provide a preliminary target
to focus data collection, identify potentially impacted
receptors, characterize the extent of ground-water
contamination, initiate the evaluation of remedial
alternatives and establish detection limit requirements.
24.
Department of the Army Specific Comment 15 p. 4-6.
The RI report should present a discussion and show
distribution maps for non-COC chemicals to permit a separate
ASC2/BSPL/062691
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25.
26.
assessment of the adequacy of the report and
interpretations.
EPA Response.
See Specific Comment Response 22.
Department of the Army specific Comment 16 p. 4-6 to 4-26.
A limited review of these sections and figures was
conducted. In general, it was difficult to assess the
distributions because plumes were not presented. Instead,
only point plots were included in the report. This
significantly increases the level of effort necessary to
evaluate the information.
EPA Response.
EPA considers the review of the areal
distribution of contaminants in the CSC OU2 RI to be
adequate for the purposes of the FS. Specific comments
regarding areal distributions of contaminants will be
reviewed. As CSC OU2 covers a large area with a
heterogeneous alluvial aquifer and a limited dataset, it was
deemed inappropriate to generate isoconcentration (plume)
maps. Point maps show laboratory data in an areal context,
and allow the readers to make their own interpretations in
defining plume configurations. Plume maps at a small scale
(large area) are subject to interpretation and debate.
Point maps are not.
Department of the Army specific Comment 17 p. 4-26.
The statistical assessment of the relationships between
concentration and distance seems questionable. Although
high correlation coefficients were derived, the approach
followed and the assumptions made in conducting this
assessment were not fully presented. Additional backup for
the statistical procedures used would improve this report.
ASC2/BSPl/062691
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For example, the use of a T-test requires certain
characteristics of the data set (e.g. normality), but no
discussion of this requirement was found in this report.
EPA Response. The linear regression relationships discussed
in section 4.2.9 were undertaken as part of an effort to
relate voc compound concentrations along an assumed ground
water flow path. The general form of the linear regression
equation given on page 4-32 indicated the transformations
and other assumptions applied to the data. The transformed
data used in the T-tests generally fit the requirements of
normality based on an evaluation of probability plots.
Omission of this background information from the text was an
oversight.
27.
Department of the Army specific Comment 18 p. 4-35.
In general, too little data appears available and too much
averaging was conducted to permit much interpretation of the
average concentration map. Only three sampling events have
been conducted and do not necessarily support a detailed
assessment of temporal changes in data, beyond some obvious
and dramatic changes.
EPA Response. More than three sampling events were used for
the evaluation of time trends, as is apparent in reviewing
the time trend plots 4-11a through 4-11h. In addition to
data collected by EPA for the EPA RMA Off-Post RIfFS and the
CSC OU2 RIfFS, data were also collected by SACWSD, the
Army, and EPA FIT. All of these data were used as
appropriate. The use of the term "significant" trend was
included to mean only obvious or dramatic changes. EPA does
not agree with the Army's assertion that too little data
appear available and too much averaging was conducted.
ASC2/BSPL/062691
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28.
Department of the Army specific Comm.nt 19 p. 4-60.
The source of PCE in the southeast corner of OU2 may be
appropriate for further characterization. Such additional
characterization could be conducted in the remedial design/
remedial action (RD/RA) phases of site remediation.
EPA Response. EPA agrees that further characterization of
the source of contamination in this area may be necessary
during remedial design.
29.
Department of the Army specific Comment 20, Appendix 2A- PIT
Investigation of B 56th Ave and Quebec street Site.
This appendix reports on the oversight activities performed
by Ecology-and Environment, Inc. (E&E) Field Investigation
Team (FIT) during drilling and well installation conducted
within OU2. The appendix generally only presents how
drilling and other field activities were conducted and does
not discuss major interpretations of the data, except for a
general description of possible paleochannels, no comments
have been included.
EPA ResponSE. The investigation of the area near East 56th
Ave and Quebec Street by FIT was being conducted concurrent
to the writing of the CSC OU2 RI report. Further evaluation
of this area may be contained in subsequent FIT reports
which are part of the CSC OU2 Administrative Record. EPA
utilized and incorporated some of the FIT findings in maps
and discussions presented in the CSC OU2 RI and FS reports,
including water quality results, boring logs, and saturated
thickness maps.
ASC2/BSPL/062691
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30.
31.
Department of the Aray specific Comment 21,Appendiz 2B-
Geophysical Inve.tiqation Methods and Result..
This appendix reports on the geophysical investigation
conducted by E&E and COM. It is not clear if additional
seismic surveys were conducted as recommended.
EPA response. Depth to bedrock interpretations derived from
the geophysical investigations were confirmed by the
drilling of several boreholes in this area. No additional
seismic surveys were undertaken as part of the OU2
investigations.
Department of the Army specific Comment 22, Appendix 2C-
Borehole Loqs and Well Completion Diaqrams for CDM-600
Series Wells.
This appendix appears to be a photocopy of a final report
entitled Monitoring Well Installation Report, RMA Off-Post
Site, prepared by Geoscience Consultants, Ltd. for COM dated
August 31, 1988. However, appendices identified in the
table of contents are not included in this appendix. This
appendix was only briefly reviewed because the results
section contained only general conclusions and appeared
reasonable.
EPA Response. The appendices to the above mentioned report
are available for review in the Administrative Record,
however they were not deemed necessary for inclusion in the
RI.
ASC2/BSPl/062691
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32.
Department of the Aray Specific Comment 22, Appendiz 2D-
Reqional South Ad... County Database., Bedrock Blevation,
Water Table Blevation, and Water Quality.
These data were printed and compared to the list of COCs.
As discussed previously, much of the data contained in this
appendix were only sparingly discussed and presented in the
report. There are detections reported in these databases
for chemicals that are not COCs. EPA may want to consider
issuing a revised RIfFS report.
EPA Response. Please refer to previous responses regarding
COCs. EPA considers the evaluation conducted in the RI as
adequate in that it represents continued investigations of a
former RIfFS site. EPA does not consider issuing a revised
RIfFS report to discuss non-COC compounds to be necessary,
given the low concentrations and sporadic occurrences of
these compounds.
33.
Department of the Army specific Comment 23a, Appendix 4A-
Summary Statistics of Selected VOCs in Ground Water.
Statistics, consisting of the number of samples, number of
detections, maximum concentration, and arithmetic mean, are
presented only for COCs introduced in Section 1.0 of the RI
report.
EPA Response. Please refer to previous responses regarding
COCs. EPA considers the evaluation conducted in the RI to
be adequate.
34.
Department of the Army specific Comment 23b, Appendix 4A-
Summary Statistics of Selected VOCs in Ground Water.
From a statistical standpoint, the number of samples, which
generally appears to be in the range of 1 to 3, seems too
ASC2/BSPL/062691
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few to permit much use of the statistical values. It seems
clearly appropriate that the standard deviation of the mean
or the variance should also be presented. Further, the
method for handling non-detections in the calculations
should be discussed. A footnote at the bottom of the Table
in Appendix 4A indicates that the method for calculating the
sample mean is discussed in the text; however the table of
contents does not note a section for discussing statistical
calculations and such a discussion could not be located
during a reasonable level-of-effort scan of the document.
EPA Response. As both the arithmetic mean and maximum
detection were reported, EPA does not consider the variance
or standard deviation to be very useful for these summary
statistics. This is especially true considering the low
number of analyses used (which could result in
uncharacteristically large or small variance and standard
deviation values that could be misleading), and the use of
non-detections in generating the arithmetic mean. The
statistics presented in Appendix 4A were from the database
used to generate the point maps in the RI, and the methods
used in averaging data are discussed in Section 2.6.1,
Ground Water Quality Database (pages 2-48 to 2-49). The use
of non-detections is also discussed in that section.
Appendix 4A is not meant to present a detailed statistical
analysis of the data; rather it presents a summary of the
contaminant vital statistics as presented in the point
concentration maps in Section 4.0 of the RI.
35.
Department .of the Army specific Comment 23c, Appendix 4A-
summary statistics of Selected VOCs in Ground Water.
It is not clear why the appendix reports statistics for all
COCs between 1986 and 1989, but only considers the 1989 data
set for identification of the COCs. This approach to data
ASC2/BSPL/062691
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assessment and COC identification seems inconsistent and
modification appears appropriate. For example, if the 1989
data set is considered more representative of current site
conditions, then the basis for including the earlier data
should be discussed. Additionally, the statistics presented
provide little useful information regarding trends in the
data, which might allow the adequacy of the 1989 data set,
or may indicate that earlier data may need to be considered,
and, therefore, additional chemicals might be appropriate
for inclusion in the list of COCs.
EPA ResDonse. Comments regarding selection of COCs are
considered under Topic II: Risk Assessment (comments 71-
82). The data sets from different years actually show very
little difference in terms of detected contaminants. As
stated before, the data in Appendix 4A summarizes data
presented in the point concentration maps. Trends in data,
both areally and temporally are discussed in other Sections
of the RI.
Appendix 4A-1 was intended to show the variation in
contaminant concentration over time, with all results for a
given well plotted versus time. The 1989 results were
considered the most representative and not highly variable
from previous results.
36.
Department of the Army Specific Comment 24, Appendix 4A-1-
CSC OU2 1990 Ground Water Data summary.
This appendix presents plume maps for five chemicals. It is
not clear why only these data were presented, and other data
excluded. Additionally it is not clear why the actual data
were not presented in the appendix for all chemicals in
which analyses were performed. It appears that if plume
maps can be prepared and included in this report, that the
ASC2/BSPL/062691
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actual data should also be available and included.
EPA Response. The actual title of this appendix is "CSC QUI
RI/FS 1990 Ground Water Data". This appendix was not meant
to provide all QUI ground water data, but to give the reader
a brief overview of QUI data. The appendix includes the
title page from the report from which the plume maps were
obtained. The reader can use this reference to obtain more
data pertaining to CSC QUI. A more appropriate appendix
title could be: "Selected CSC QUI RI/FS Ground Water Plume
Maps".
37.
Department of the Army specific Comment 25, Appendix 4B-
Time Trend Plots for Selected SACWSD Production Wells and
Private Domestic Wells.
Except for a number of the SACWSD production wells, most of
the time trend plots have only two data points and provide
little useful information. These plots are discussed in
Section 4.3.2.1. However, it appears that the plots for the
monitoring wells actually are of extremely limited value
because the results from only two sampling events were
available at the time. A discussion of the significance of
these plots starts on page 4-42; however, it appears that
the use of these plots for assessing temporal changes or
evaluating chemical fingerprinting is extremely limited.
with only two data points for most of these wells, it seems
inappropriate to draw any conclusions regarding the
monitoring well data based on the methods contained in this
appendix.
EPA Response. As discussed in Section 4.3.2.1, temporal
plots with only two data points were used only to assess
gross trends, such as the relative proportions of the
volatile chlorinated compounds. These plots are meant to be
ASC2/BSPl/062691
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a visual tool for evaluating the data, and not for
statistical analysis of the data. EPA considers these plots
useful for evaluating gross trends when comparing them in an
areal context. The plots were also used to see if the 1989
data were comparable to previous data and therefore
representative for use in the RA.
38.
Department of the Army Specific Comment 26, Appendix 4C-
Water Quality Results for Bedrock and Alluvial Well Hests on
the RMA and Sand Creek Industrial Site.
Page 4-52 of the report and the title of the table in the
appendix suggests that this appendix contains Denver
Formation water quality information. However, the appendix
title suggests that alluvial data are also included, while
the table-title indicates only Denver Fm water quality is
included. These inconsistencies should be remedied.
EPA Response. Water quality results from alluvial aquifer
completions are included for comparison purposes in this
table. The text clearly states, "Contaminant concentrations
in SACWSD alluvial wells located nearest some of the bedrock
w~lls are also shown on this table for comparison purposes."
The table includes a heading entitled "Aquifer" which
identifies the zone that each well was completed in, so no
confusion should occur over what data are presented.
39.
Chemical Sales Company (CSC), Specific Comment 1, p. 1.
Page 1. CSC questions the statement, "OUI has been
identified as a potential source of contamination as a
result of both documented and undocumented spills from the
chemical storage tanks." This statement has been repeated
in the OU2 Feasibility study. As presented in the OUI
documents, CSC has provided all available information with
ASC2/BSPl/062691
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'..1'" .,*.--~.
respect to leaks and spills from its operation. No evidence
for "undocumented spills" has ever been discovered, except
for the presence of contaminated soil and ground water in
QUI. The tank inventories and tank testing conducted as
part of the QUI RI did not support the contention that the
csc tanks were the source of contamination. The documented
releases from the Chemical Sales facility are insufficient
to explain the extent of contamination in QUI and QU2. The
evidence presented in the QU2 documents in support of
contamination extending from the CSC property to East 77th
Avenue is hypothetical, and is based on average migration
rates and technical assumptions.
EPA Response. The use of the phrase "undocumented spills"
was meant to include all activities that could have resulted
in ground water contamination at the CSC property. As
pointed out by the Interstate Distribution Center Associates
(IDCA), a number of releases occurred on the CSC property
during the course of the RI which were not documented in the
CSC QUI RI. In addition, the EPA admits that spills could
have occurred from other sources than the chemical tanks
such as from unloading rail tanker cars. Surfical soil
contamination has been detected on the CSC property,
unrelated to documented releases, indicating releases of
hazardous substances during handling or storage of chemical
waste. The State of Colorado has also provided notification
under RCRA authority to CSC that the company is
inappropriately storing hazardous waste on the site. Based
on this information and data collected during the QUI RI,
EPA has determined that releases have occurred on the CSC
property which have not been previously documented.
40. Chemical Sales Company (CSC), Specific Comment 2, p. 8.
Page 8. CSC objects to the following statements, "Assuming
ground water flows at a rate of 5 feet per day, and assuming
a travel time of 13 years (based on information that CSC
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- ~ .-.' ,.... '.~ . -.. ','
began site operations in 1976), a particle of ground water
could have traveled at least 4.5 miles from the CSC site, or
to north of East 80th Avenue, to date." and "Based on these
conservative flow rates and contaminant migration estimates,
the CSC facility could account for contamination at the
SACWSD pumping center at East 77th Avenue and Quebec
street." The text should note that an estimate based on
these assumptions does not prove, in fact, that CSC is the
source. The inherent assumptions, not mentioned in this
analysis, are: 1) there is a continuous and downgradient
flowpath between the CSC site and East 77th Avenue; 2) the
migration rate of 0.58 feet per day for the documented 1985
release of methylene chloride from the CSC site, as
discussed in the OU1 RI/FS, the contaminants would only
migrate 0.5 mile in the 13 year period. This estimate is
based on actual release and plume data, whereas the estimate
described in the OU2 RI is based on regional studies
performed outside the scope of the OU2 RI/FS. The rate of
migration estimated by the OU2 RI is just that rate
necessary to link CSc to the contamination at East 77th
Avenue.
EPA Response.
The use of the word "could" is used to
indicate that using conservative assumptions and estimates,
the CSC facility could account for at least a portion of
ground water contamination at the SACWSD pumping center at
East 77th Avenue and Quebec street. The conservative
assumptions included low estimates of hydraulic
conductivity, not only from area pump tests but also
evaluation of borehole lithologies and literature hydraulic
conductivity ranges. The hydraulic conductivities in OU2
are considerably greater than those values derived for QUl
south of East 48th Avenue. The EPA considers the VOC
distributions sufficient to establish a link between OU2
ground water contamination and the CSC facility area.
ASC2/BSPL/062691
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41.
Chemical Sal.. Company (CSC), Specific Comment 3, p. 1-6.
Page 1-6. Section 1.2.1.3. states, "The southern portion of
the study area contains several truck transport operations
and light industrial facilities." Such facilities commonly
use solvents such as those contaminating OU2, and often have
less stringent handling and disposal procedures than
chemical distributors. No evidence is provided to show why
these facilities could not be sources of OU2 contamination.
EPA should specifically identify these facilities, and
investigate the use of compounds of concern at these
locations.
EPA Response. No statement was made to conclude that the
several truck transport operations and light industrial
facilities are not potential sources of ground water
contamination. One of these type of facilities may be
responsible for the observed PCE Plume in OU2. None of
these facilities, however, are believed to contribute to the
observed TCE contamination within OU2.
42.
chemical Sales company (CSC), specific Comment 4, p. 1-11.
Page 1-11, top paragraph. The sentence "Ground water
monitoring wells installed on the CSC property have since
confirmed CSC as a source of ground water contamination." is
misleading in that it implies an incorrect assumption. The
ground water results for the CSC property show that the
property is contaminated. They do not prove that CSC itself
is the source of the groundwater contamination.
EPA Response. The relatively high detections of
contaminants of concern in ground water and soil at the CSC
property indicate that a source of contamination is on the
CSC property. The text, however, does not state that CSC is
the only source of contamination in the area. For example,
the EPA is aware that a monitoring well upgradient of CSC
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contains several VOC's, and that contaminated soils and
ground water exist on the adjacent IDeA property.
43.
Chemical Sa18. Company (CSC), Specific Comment 5, p. 1-17.
Page 1-17, second paragraph. The reference to the "an
unidentified solvent" in the CSC underground tank farm is a
statement in the OU1 RI/FS work plan. Documents submitted
to EPA since that time have identified all tank contents,
and EPA has been provided with Material Safety Data Sheets
for specific compounds. This statement is misleading
because it implies compounds of concern may have been stored
underground at the CSC facility. None of the chemicals of
concern were stored in the CSC underground tank farm.
EPA Response. EPA acknowledges that contamination on the
CSC property might not have originated from CSC's
underground tanks. However, it is clear that solvent
contamination did occur from the CSC property, regardless of
the original source. Records show that the CSC company did
distribute several of the COCs, even if none were stored in
the underground tank farm. In addition, the State of
Colorado under RCRA authority has issued CSC a Notice of
Violation regarding the storage of hazardous substances.
44.
Chemical Sales Company (CaC), Specific Comment 6, p. 1-17.
Page 1-17, last paragraph.
several reported spills on
large number of incidents.
state that there have been
which L /01 ved PCE or TCE.
The statement, "There have been
the CSC property." implies a
It would be more appropriate to
three reported spills, none of
EPA Response.
The EPA is aware of at least five releases
which have occurred on the CSC property since February 1990,
that wer' .ot reported in the QU1 RI and may have remained
unreported. This number of releases within a one year time
ASC2/BSPL/062691
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45.
period suggests operational practices which, if comparable
to past practices, could have potentially resulted in a
large number of incidents over time. EPA does agree,
however, that it would be more precise to state that there
have now been eight documented releases between 1985 and
1991, none of which involved PCE or TCE.
Chemical Sales Company (CSC), specific Comment 7, p. 1-22.
Page 1-22, third full paragraph. CSC agrees with the
statement, "CUrrent data suggest that the chemicals of
concern have entered the ground water at several locations
upgradient of OU2 and have migrated in the aqueous phase in
the alluvium."
EPA Response.
No response is required.
46.
Chemical Sales Company (CSC), specific Comment 8, p. 3-9.
Page 3-9, Drilling Near Quebec street and East 56th Avenue.
The text states, "The soil gas survey results were largely
inconclusive in that no suspected source was located."
However, from Appendix B of Appendix 2A, CSC questions the
validity of those results, given the method used. The
samples were collected with a split spoon sampler,
transferred to sample containers, delivered to the
laboratory, and analyzed about one week later. Based on the
experience in OUI, the lack of soil detections from these
analyses is not surprising. Although CLP holding times were
met, the OU1 investigation showed that those holding times
are inappropriate, and VOC's are lost during the interim.
EPA required CSC to conduct additional soil analyses in OUl
because this method resulted in non-detects. The second set
of samples, analyzed within 24 hours, detected high
concentrations of VOCs, where none had been detected in
previous laboratory analyses. Although the text on page 3.9
notes that the results are inconclusive, CSC does not
ASC2/BSPL/062691
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believe that a source at 56th & Quebec can be ruled out on
the basis of these results. The methodology used may
explain why no source was determined.
u
EPA Response. EPA disagrees with this statement. Soil
vapor concentrations were analyzed on a daily basis by the
FIT Field Analytical Support Program (FASP) laboratory,
ensuring that volatile loss was minimal.
47.
Chemical Sales Company (CSC), specific Comment 9, p. 3-13.
Page 3-13, middle paragraph. The statement, "Simplified
sections E2, E3, and E4 (Figures 3-2c through 3-2e) show a
similar trend of decreasing clay and increasing sand from
east to west, toward the South Platte River." would
indicate that the preferred ground water flow direction
would also be east to west along East 56th Avenue. Based on
this discussion and these figures, flow from the East 48th
Avenue and Monaco area would be toward the northwest, not
northeastward toward the bedrock high near East 56th &
Quebec.
EPA Response. The direction of ground water flow is not
dictated by hydraulic conductivity alone, but by a
combination of factors including hydraulic gradient,
saturated thickness, and hydraulic conductivity. Ground
water flows perpendicular to the potentiometric surface.
A
detailed evaluation of the potentiometric surface indicates
that flow diverges north of the CSC facility in the vicinity
of East 58th Avenue, with a portion going to the northwest,
and a portion going to the northeast. The Sand Creek oil
plume located north of Sand Creek in that area indicates
that flow from the CSC facility would be oriented to the
northeast, north of Sand Creek.
ASC2/BSPL/062691
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48.
Chemical 8a18. Company (CSC), Specific Comment 10, p. 3-18.
Page 3-18, third paragraph and Figure 3-4. As a general
note, it would have been very helpful if all figures had
been plotted for the same time interval or if better
landmarks had been provided, in order to compare one figure
to another. However, comparing Figure 3-4 with Figure 3.7
of the QU1 RI (attached to this report) shows that the
paleochannel extending northward from the CSC property
corresponds to the paleochannel discussed in this paragraph.
This paragraph states, "A second major paleochannel
originates near the southwest corner of CSC QU2, near
approximately Holly and East 56th Avenue, and trends in a
southwest direction south of Sand Creek. The effect of this
paleochannel on ground water flow within CSC QU2 is
minimal". While agreeing that flow from this channel into
QU2 is minimal, CSC believes more should be said. Figure 3-
4 actually shows this channel to have two southern
tributaries originating near 50th & Ivy and 50th & Holly.
The eastern tributary (near 50th & Ivy) matches the
paleochannel shown on the QUl RI Figure 3.7. These two
tributaries meet near Sand Creek & Holly, and flow west.
The CSC paleochannel is shown on Figure 3-4 to flow north to
about East 56th & Holly, then meander southwest to Sand
Creek, where it joins the other tributary. Based on Figure
3-4, the contaminant flow from QUl should flow generally
north to near Holly & East 56th Avenue, and then west
approximately parallel to East 56th Avenue. This could
account for. the contaminant patterns in this area, as shown
on the maps in Section 4 of the QU2 RI, which show
contamination from QUl migrating to about East 56th Avenue
and disappearing. It appears from these that the
contaminants from aUl are following this paleochannel
meander.
EPA Response. Though paleochannel features will certainly
effect flow, they will not determine the direction of flow.
ASC2/BSPL/062691
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As previously stated, ground water flows perpendicular to
the potentiometric surface. Ground water in the vicinity of
East 56th Avenue and Holly does not flow to the west based
on evaluation of potentiometric surface maps. EPA does not
agree with the conclusion that contamination from CUl turns
to the west in the vicinity of East 56th Avenue and Holly
Street, then disappears.
49.
Chemical Sales Company (CSC), Specific Comment 11, p. 3-22.
Page 3-22. The first paragraph states, "The potentiometric
surface map was constructed for a large area and the data
point spacing was extremely variable, so confidence in the
surface configuration should be directly proportional to
data point density. Local variation the potentiometric
surface could significantly affect ground water flow."
Based on this discussion, and the high density of data
points in the area of the CUI plume, the flow lines on
Figure 3-9 may be oversimplified. Although correct in large
scale, the pattern made by smaller and more concentrated
flow lines in that area show the bulk of the flow from CUI
to be northwestward toward an intersection with the Platte
River where the 5080-foot contour crosses the river on
Figure 3-9. Such a flow pattern is generally consistent
with the paleochannel map (Figure 3-4). It should be noted
that this area has the highest density of data points on
Figure 3-8, and therefore the greatest interpretive
confidence.
EPA Response. Though flow does appear to go to the
northeast from the CSC facility to Sand Creek the
potentiometric surface map indicates that it arcs to the
north-northeast north of Sand Creek. This is supported by a
relatively high number of data points. An evaluation of
flow lines suggests that by skewing flow either slightly
east or west, flow from the CSC could either go to the
northwest and out of CSC CU2, or to the northeast and to the
ASC2/BSPL/062691
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50.
SACWSD pumping center at East 77th Avenue and Quebec street.
It is not inconceivable that flow could vary between these
directions with seasonal effects of SACWSD pumping wells.
The potentiometric surface was constructed from time periods
when the SACWSD pumping wells would have the least effect on
ground water flow. A greater curvature of flow towards the
wells would be expected later in the pumping season.
chemical Sales Company (CSC), specific Comment 12, p. 3-23.
Page 3-23, second paragraph. This paragraph states, "Flow
converges in the vicinity of East 77th Avenue and Quebec
street from the southeast to southwest, because of
convergence of paleochannels in this area. Several
contaminant plumes also appear to converge in this area, and
are discussed in section 4.0." These several plumes and
their sources did not appear to be clearly identified in
section 4, but should be thoroughly investigated by EPA.
EPA Response. Potential contaminant plumes converging at
the pumping center at east 77th Avenue and Quebec Street
consist of the plume in the vicinity of Holly Avenue
suspected of at least partially originating in OUI, the
plume in the vicinity of 56th Avenue and Quebec Street, and
contamination in the Western Study Area of the RMA. Each of
these apparent plumes are discussed in Section 4.0 of the
report.
51.
Chemical Sales Company (CSC), specific Comment 13, p. 3-24.
Page 3-24, second paragraph. It states, "One unsaturated
zone was identified in the vicinity of East 56th Avenue and
Quebec Street. This unsaturated zone, located just east of
Quebec Street, is potentially important due to the suspected
presence of a contaminant source in the vicinity." From
ASC2/BSPl/062691
41
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this it appears that ground water flow from the OU1 plume is
not reaching that area. This would be consistent with the
flow direction discussed under the comment to page 3-18.
EPA Response.
required.
The comment is noted and no response is
52.
Chemical Sale8 Company (CSC), Specific Comment 14, p. 3-31.
Page 3-31. It is stated on this page, "Table 3-4 presents
hydraulic conductivities obtained from various studies
conducted in the area and from values cited in the
literature that might be expected based on the lithologic
units present.", and "Three zones were selected to initially
represent the hydraulic conductivities of the saturated
alluvial lithologies contained in the CSC OU2 study area for
the ground water model (Table 3-4)." Given the
heterogeneity of the alluvial aquifer and the generic value
of these hydraulic conductivities, CSC questions the
accuracy of the contaminant migration rate based on these
values, especially for the purpose of implicating CSC in the
contaminant plume that extends to East 77th Avenue.
EPA Response. Hydraulic conductivities are inherently
variable in a heterogeneous aquifer, therefore a
conservative range of values was used in transport
calculations. The hydraulic conductivity values used in the
models were all based on site-specific aquifer pumping test
results conducted in the region and on numerical modeling
calibration and sensitivity analyses.
53.
Chemical Sa1e8 Company (CSC), Specific Comment 15, p. 3-31.
Page 3-31, third full paragraph. "Slug tests conducted as
part of the csc OU2 RI effort on several wells in the CDM
600-well series proved to be inconclusive. Hydraulic
conductivities ranged from 7 to 44 feet/day (Appendix 2E). .
ASC2/BSPL/062691
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These are one to three orders of magnitude lower than
hydraulic conductivities derived from other studies
conducted in the area, and are not thought to reflect actual
field conditions. Instead, they appear to be measurements
of the permeability of the sand pack placed in the screened
intervals of the wells." It is unclear why the values from
previous investigations summarized on Table 3-5 (ranging
from 310 ft/day to 5,626 ft/day) should be more conclusive
than the specific tests conducted as part of the OU2
investigation (ranging from 7 ft/day to 44 ft/day). It
should be noted that the discounted results all show
significantly lower hydraulic conductivities than those used
to make the contaminant travel time estimates from the CSC
property. CSC could not find an adequate discussion of the
reasons for discounting the slug test results, or why the
sand pack should have a much lower hydraulic conductivity
than the geologic formation. Normally, the opposite is the
case. If the slug test values are used in the travel time
estimates a totally different picture would emerge, relative
to contaminant migration from the CSC property.
EPA Response. Slug tests are inherently less accurate than
the results presented in Table 3-5, which are of pump tests
using observation wells conducted in or adjacent to CSC OU2.
Slug tests can give lower hydraulic conductivities than the
actual aquifer hydraulic conductivity due to the order-of-
magnitude accuracies typical of such tests. EPA agrees that
the sand pack may not have a lower hydraulic conductivity
than the aquifer although this potential exists. Based on
evaluation of pump tests in the area, borehole lithologies,
and literature ranges of hydraulic conductivities for
selected lithologies, EPA considers the slug test-derived
hydraulic conductivity values to be lower than actual
aquifer hydraulic conductivities.
ASCZ/BSPL/062691
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54.
Chemical S8l.. Co.pany (CSC), Specifio Co...nt 16, p. 3-35.
.
Page 3-35, Section 3.1.2.8. This section states "Despite
previous studies indicating that ground water from QUI flows
beneath Sand Creek (CDM 1988b), the results of the ground
water surface water interaction study described in Section
2.3.3 were largely inconclusive." Page 3-36 states "An
apparent net increase in flow was observed in Sand Creek
between the upstream and downstream locations." However the
increase was determined to be not statistically significant.
This seems to leave open the possibility that QUI
contamination is migrating into Sand Creek instead of into
QU2. It seems that this issue, which was a major contention
of the HRS score, remains unresolved.
EPA Response. EPA agrees that a undetectable amount of the
contamination from QUI may be entering Sand Creek (Sand
Creek Industrial RIjFS, 1988) during certain portions of the
year. Most of the VQC contamination, however, does continue
across Sand Creek. This interpretation is based on the
detection of contaminants related to releases from the CSC
facility in monitoring wells located near the south and
north banks of Sand Creek.
55.
Chemical Sales Company (CSC), specific Comment 17, p. 3-36.
Page 3-36, second paragraph. "Transmissivities derived from
.i, -2 2
slug tests showed a range of 3.4 x 10 to 5.1 x 10 ft jsec.
The large range in values indicates considerable
heterogeneity of the alluvial sediments." Two things are
apparent from these sentences. First, these slug test
results do not appear to be as "inconclusive" here as was
indicated earlier in the document (see comment to page 3-
31). Second, the considerable heterogeneity of the alluvium
places serious limitations on use of one average hydraulic
conductivity to estimate travel time from the CSC property
to East 77th Avenue.
ASC2/BSPL/062691
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56.
EPA Response. EPA agrees that these statements appear to be
inconsistent with a previous statement that the slug test
results were inconclusive. The slug test results discussed
on page 3-36 are of piezometers installed as part of the
surface water-ground water interaction study, and are
different from slug test results discussed as inconclusive
on page 3-31. EPA maintains that the slug tests conducted
on monitoring wells within OU2 and discussed on page 3-31
were indeed inconclusive, and therefore the given
transmissivity values are of limited use. EPA considered
aquifer heterogeneity in transport calculations, and a range
of results was given based on the uncertainty of hydraulic
conductivity in the aquifer.
Chemical Sa18s company (CSC), Specific comment 18, p. 4-4.
Page 4-4. This entire discussion presents the limits on the
amount of natural biodegradation that is taking place in OU1
or OU2. This consistent with our interpretation.
EPA Response.
No response required.
57.
Chemical Sales Company (CSC), specific Comment 19, p. 4-10.
Page 4-10, fourth full paragraph. It states "It is
difficult to determine whether the 10 ~g/L concentration at
64th and Monaco is related to high concentrations of PCE
just north of Sand Creek (from OUI) or whether it is related
to the PCE plume apparently emanating from the vicinity of
56th Avenue and Quebec Street." CSC believes the 10 ppb
detection of PCE near 64th & Monaco can be directly
attributed to the source near 56th & Quebec. The PCE
concentrations migrating into OU2 from OUI clearly decrease
to less than MCL a short distance north of Sand Creek, and
several monitoring points directly between 64th & Monaco and
the OUI plume show decreased concentrations. On the other
ASC2/BSPL/062691
45
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hand, 64th & Monaco is clearly downgradient from the 56th'
Quebec source, with two points between showing similar
concentrations (8.5 and 9.3 ppb). It is apparent from this
that the PCE concentrations throughout most of QU2 can be
related to a source near 56th & Quebec, with a possible
secondary source near 64th & Quebec.
D
EPA ResDonse. EPA does not fully agree with CSC's assertion
that contamination from QUI clearly decreases to below MCL
north of Sand Creek. The elevated concentration near East
64th and Monaco could be indicative of an earlier pUlse of
contamination that has migrated downgradient to the north.
Though EPA does agree that at least part of the PCE
contamination at the pumping center at East 77th Avenue and
Quebec Street is believed to come from the vicinity of East
56th Avenue and Quebec Street, EPA also concludes that a
portion of the PCE contamination at the pumping center could
be attributable to QUI contamination.
58.
Chemical Sales Company (CSC), Specific Comment 20, p. 4-11.
Page 4-11, third paragraph. We do not understand the last
sentence in this paragraph, which states, "These data
confirm the PCE distribution just described, indicating the
plume is slightly more extensive." More extensive than
what? The same comment applies to Section 4.2.2.2 on page
4-13, and throughout this section.
EPA ResDonse.
Review of the
stating that
EPA agrees that this sentence is unclear.
previous paragraphs show that the sentence is
PCE contamination in QUI was slightly more
1990 data than in 1989 data.
extensive in
59.
Chemical Sales Company (CSC), Specific Comment 21, p. 4-12.
Page 4-12, last sentence. This sentence says, "The location
of the TCE contamination is consistent with a source of TCE
ASC2/BSPL/062691
46
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in QU1, the paleochannels, and ground water flow
directions." CSC disagrees with this interpretation, and
believes it is unreasonable to attribute the prevalent TCE
contamination throughout QU2 to the QU1 plume. Such an
interpretation fails to explain how the TCE concentration
can increase from 14 ppb at 56th & Monaco to 43 and 53 ppb
near 64th & Monaco. The PCE/TCE pattern for QU2 differs
considerably from that in QU1. The TCE pattern is
consistent with a source near East 56th & Quebec. The
prevalent TCE contamination may also be associated with the
general use of the compound by the types of industries
located within QU2. The EPA interpretation is not
consistent with the gradient and paleochannel flow paths,
which would indicate the QU1 plume would migrate northwest
toward the Platte River, as discussed earlier in this
report. Comparing Figure 4-2b with Figure 3-4 shows the TCE
plume somewhat west of the paleochannel but directly
downgradient of East 56th & Quebec, with a bedrock ridge
between this plume and the QU1 plume.
EPA Response. Though EPA agrees that other minor sources of
TCE contamination could exist in QU2, the continuity of
contamination from QU1 into QU2 is apparent. As discussed
in the RI, the decreasing ratio of PCE to TCE can be
explained by the higher retardation of PCE. The apparent
decrease in TCE concentration between East 56th Avenue and
East 64th Avenue can be explained by the data gap discussed
in the response to Comment 57 above. The direction of flow
was discus~ed in the response to Comment 49 above.
60.
Chemical Sales Company (CSC), specific Comment 22, Figure 4-
2b.
Figure 4-2b. From this map there appear to
distinct sources of TCE: (1) the QUI plume
about 2,000 to 3,000 feet into the southern
(2) an apparent source in the 64th & Monaco
be three
which extends
portion of QU2;
area extends to
ASC2/BSPL/062691
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about East 77th Avenue; and (3) a third source appears to be
at about East 64th Avenue east of Quebec.
EPA Response. EPA disagrees with this interpretation.
Concentration levels and distribution of contaminants
detected in the vicinity of 64th and Monaco are consistent
with the ground-water contaminants emanating from the CSC
facility. Although contaminant concentrations of TCE
increase north of 56th and Monaco, these increases are
considered to be relatively' small and are most likely
related to variations within the alluvial ground-water
system.
61.
Chemical Sales Company (CSC), specific Comment 23, p. 4-27.
Figure 4-27, top paragraph. The statement, "Figures 4-2b
and 4-8b suggest a contaminant plume which trends
approximately perpendicular to the potentiometric surface
contour lines from near the CSC property to at least as far
north as the East 77th Avenue SACWSD municipal pumping
center." is misleading, and gives the impression that csc
was responsible for all of the contamination in OU2. It
would be more correct to state that there are at least three
contaminant plumes extending from near the CSC property to
East 77th Avenue. Figures 4b and 8b suggest that the OUl
plume ends near East 56th Avenue, as discussed earlier. The
main paleochannel, which is admittedly "approximately"
perpendicular to the potentiometric surface lines in that
area, is not aligned with the gradient in the area of the
OUl plume.
EPA Response. As stated, "It should be noted that this
flowpath was selected only for purposes of evaluating fate
processes and relationships amongst the COCs." EPA reads no
preconceived interpretation in this methodology. The
purpose of this evaluation was to assess the transport and
fate of contaminants migrating from OUl into OU2. EPA RI/FS
ASC2/BSPL/062691
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62.
guidance emphasizes the importance of assessing the
interaction between various operable units within a given
site. Results of this assessment indicate that ground-water
contamination associated with releases in the vicinity of
the CSC facility appeared to have migrated northward into
OU2 and, given the limited areal data, appear to be a likely
source of TCE and other select compounds which have had an
impact on the SACWSD supply wells. The flowline used was
believed to approximate a continuous path. This analysis
showed no data to contradict this interpretation.
Chemical Sales company (CSC), specific Comment 24, p. 4-27.
Page 4-27, middle paragraph. The sentences, "The flowpath
selected for this evaluation extends from the CSC propertr
(well ES-MW-06) north to the SACWSD municipal pumping center
at East 77th Avenue and Pontiac street (wells SAC-02 and
SAC-03). It should be noted that this flowpath was selected
only for purposes of evaluating fate processes and
relationships amongst the COCs." suggest a preconceived
interpretation based on certain assumptions, rather than an
unbiased scientific analysis. It is not stated that this
flow path may, in fact, be discontinuous. This assumed
flowpath is presented in a manner that leads the reader to
believe such a flowpath does actually exist.
EPA Response. The EPA feels that the flowpath selected
for the subject evaluation is a continuous flowpath.
63.
Chemical Sales company (cac), specific Comment 25, Page 4-
28.
Page 4-28, top paragraph. "The ethanes (TCA and DCA) and
benzene were not included on these plots in order to express
more clearly the evident relationships due to biodegration."
This concept of biodegration should be more fully explained
in light of the limited conditions of the aquifer to support
ASC2/BSPl/062691
49
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biodegration, as discussed in Section 4.1.2.1. CSC is not
convinced that significant biodegration is occurring in OUl
or aU2.
EPA Response. EPA believes that biodegradation was
sUfficiently discussed in the RI. The anaerobic
dehalogenation of the chlorinated solvents could play an
important role in fate and transport of contaminants in
ground water in OU2. Though most of the aquifer is believed
to be aerobic, localized anaerobic zones could cause
dehalogenation transformations. Detection of vinyl chloride
in the aUl and OU2 alluvial aquifer indicate that certain
portions of the aquifer are under anaerobic conditions.
64.
Chemical Sales Company (CSC), Specific Comment 26, Section
4.3.2.1.
Section 4.3.2.1 Although this section is interesting, it
really does not determine anything of significance. It
implies that CSC could have caused the OU2 contamination,
but also states that it could be caused by other sources.
This is clear form the last two sentences in this section,
"The changes in contaminant proportions moving downgradient
from the CSC facility can be explained by fate processes
such as adsorption, biodegradation, and for TCA, hydrolysis.
This does not discount the possibility of additional sources
in the area, however." In fact, the greater rate of
attenuation downgradient would seem to argue against the
higher concentrations near 56th & Quebec being related to
the aUl plume.
EPA Response.
This section is not meant to "determine
anything of significance", but to present the data in such a
way that readers can draw their own conclusions. EPA has
previously stated that contaminants at East 56th Avenue and
Quebec Street are probably unrelated to the aUl plume.
ASC2/BSPL/062691
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65.
66.
Chemical Sal.. Company (CSC), specific Comment 27, p. 4-59.
Page 4-59, section 4.5.1.3. From the statement, "CSC is an
unlikely source of ground water contamination detected near
East 56th Avenue and Quebec street, since that area is
located cross gradient from the CSC property." it appears
that EPA agrees with our interpretation that a source exists
near East 56th Avenue & Quebec.
EPA Response.
No response required.
Chemical Sa18. Company (CSC), specific Comment 28, p. 4-60.
Page 4-60, third paragraph. "The drilling results showed
that the area just southeast of the intersection of 56th
Avenue and Quebec Street (DEOC area) is generally
unsaturated. This indicates that the source area may be to
the southwest of the intersection of 56th Avenue and Quebec
street, and not from either the DEOC or the DBMC." It is
unclear why DEOC or DBMC cannot be sources just because the
alluvium beneath those sites is unsaturated. Contaminants
could have flowed downgradient through unsaturated materials
to ground water, especially in view of the statement, "The
FIT investigation determined that both facilities used
products containing PCE." EPA seems to have assumed that
the contamination had to be associated with ground water
from an upgradient source.
EPA Response.
The statement that the area was unsaturated
is meant to indicate that localized high bedrock elevations
in the area have no saturated alluvium on top. In such
cases, dense non-aqueous phase liquid (DNAPL) transport of
the contaminants of concern in this area would be required
for the contaminants to reach the adjacent saturated zones.
EPA has seen no evidence of DNAPLs in this area, however
this possibility cannot be entirely discounted. EPA does
not assume that contamination had to be associated with
ASC2/BSPL/062691
51
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ground water from an upgradient source. EPA will consider
further evaluation to locate the source of this
contamination.
67.
Chemical Sal.. Coapany (CSC), Specific Comment 29, p. 4-60.
Page 4-60, Section 4.5.2. CSC fails to see the point of the
last sentence on this page, "None of these other potential
source areas have shown concentrations in ground water
comparable to those concentrations detected at the CSC
facility." This statement implies that any area having
lower contaminant concentrations than CSC cannot be a
source.
EPA Response. The statement in question does not imply that
there are no other sources of contamination than the CSC
facility. It states the fact that no ground water analyses
in OU2 have shown contaminant concentration of the same
order of magnitude as at the CSC facility.
68.
Chemical Sales Company (CSC), Specific Comment 30, p. 4-62.
4-62, last paragraph. The theory of clay sorbing and
desorbing, stated as "Organic contaminants which entered the
ground water at an upgradient location may have sorbed onto
the clayey materials in the vicinity of East 62nd Avenue and
Monaco Street, and may now be desorbing into the ground
water, resulting in the observed contamination." seems to be
stretching .a point. A separate source in this area would
appear to be a more reasonable interpretation. The evidence
discussed in this paragraph appears to strongly support such
an interpretation, without resorting to the clay hypothesis.
Although CSC acknowledges the hypothesis that clays can act
essentially as capacitors for organic compounds, it is
difficult to imagine contaminants desorbing at such
concentrations as are found in that area. This theory also
fails to explain why clay in this area should behave in this
ASC2/BSPl/062691
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69.
70.
manner, when such behavior is not observed in similar clays
elsewhere in OU1 and OU2.
EPA ResDonse. As previously stated, a separate source,
though possible, is not necessary to explain contamination
found in the vicinity of East 62nd Avenue and Monaco street
due to the data gap in that area. The "clay hypothesis"
was used to explain the possibility of increased anaerobic
dehalogenation, as a clay rich environment could be oxygen
depleted, and adsorption could facilitate anaerobic
dehalogenation transformations. Localized higher organic
contents could also contribute to localized anaerobic zones.
A combination of adsorption, desorption, and
biotransformations could reasonably explain the contaminant
distributions found in this area. The subject text also
suggests the possibility of separate sources.
Chemical Sales Company (CSC), specific Comment 31, p. 6-1.
Page 6-1. Although the second conclusion is true, the
statement is misleading. It states "Concentrations of
chemicals of concern in wells upgradient (to the south and
generally east) of OU2 are higher than concentrations in
wells within OU2." This again implies that csc is one
(south) source of OU2 contamination, simply because that
property has higher contaminant concentrations.
EPA ResDonse. The CSC facility is upgradient of OU2 and has
ground water contamination of up to three orders of
magnitude higher than any contamination found in OU2. As
flow path analysis and contaminant distributions indicate,
the CSC facility is a major source of ground water
contamination in OU2. EPA considers discussion of other
potential source areas affecting OU2 to be adequate.
Chemical Sales company (CSC), specific Comment 32, p. 6-2.
ASC2/BSPL/062691
53
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Page 6-2, item 7. This states "The Chemical Sales Company
property appears to be a major source of contaminants
affecting ground water quality in the southern portion of
CSC OU2." All other possible sources are qualified, and it
is unclear why CSC was not, especially since the OU2 study
did not include investigation of the CSC property. However,
it could follow from this that CSC is not a major source of
contamination elsewhere in OU2. It would be more correct to
state that OU1 appears to be a source of contaminants in the
southwestern portion of OU2.
EPA ResDonse. Based on analysis of the areal extent of
contaminants and ground water flow, EPA considers the CSC
facility to be a significant source of ground water
contamination in OU2.
TOPIC III:
RISK ASSESSMENT
71.
Department of the Army, Appendix 5 - Risk Assessment,
Section 4, Page 4-1.
This comments requests justification for use of validated
data in risk assessment (RA) and use of both validated and
nonvalidated data in the Remedial Investigation (RI). Use
of RAS data for Case 1 and SAS data for Case 2 is also
questioned.
EPA Response. As discussed in Risk Assessment Guidance for
Superfund (USEPA, 1989b) and Guidance for Data Useability in
Risk Assessment (USEPA, 1990), the use of validated data is
preferred for quantitative risk assessment wherever
possible. Due to the generally low and sporadic extent of
ground water contamination in OU2, as well as budgetary and
time constraints, only a necessary portion of the
environmental sampling data were validated. Validation
efforts were primarily directed at the samples indicating
the highest concentrations, which resulted in protective
ASC2/BSPL/062691
54
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estimates of ground water concentrations. This protective
approach is appropriate for the size of the operable unit
and the wide range in contaminant concentrations.
Both validated and unvalidated data were used for the RI to
provide a thorough characterization of the extent of
contamination, and because data quality objectives are less
stringent for the RI than for the RA.
The RAS data for OU2 were selected for use rather than the
SAS data because of laboratory difficulties with sample
quantitation limits when SAS methods were used, particularly
in the case of vinyl chloride. Nevertheless, the SAS data
were used for the special instance of Case 2, where the
closest well to the contaminant ground water plume was
identified for the purpose of evaluating current potential
health risks from a nearby, untreated well. In this case,
the SAS data were the most recent data available and most
appropriate for the specific objectives of this risk
assessment.
72.
Department ot the Army, Appendix 5 - Risk Assessment,
section 4, Page 4-3.
Justification is requested for use of a 10% detection
frequency rather than 5% to select potential chemicals of
concern (COCs).
EPA Response.
Although a 5% detection level is recommended
by RAGS, this recommendation allows for professional
judgment and modification for specific sites and conditions.
In the case of OU2, several years of sampling information
have consistently detected the chemicals selected as COCs.
Other chemicals have been sporadically detected at low
concentrations in these sampling efforts, but clearly the
eight COCs selected for OU2 are representative of historical
and current site contamination. Furthermore, the chemicals
ASC2/BSPL/062691
55
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detected at 5-10%, even if they were
would have only a marginal effect on
potential health risks at the site.
included in the RA,
the magnitude of
73.
Department of the Army, Appendix 5 - Risk Assessment,
Section 4, paq. 4-4.
This comment questions the validity of excluding xylene and
chloromethane from the COC list on the basis of them being
laboratory contaminants.
EPA Response. Both xylene and chloromethane were detected
in blanks, so for this site these two chemicals were
considered laboratory contaminants. As mentioned previously,
the inclusion of these chemicals as COCs would have no
significant impact on the potential health risks calculated
at the site.
The "most recent guidance from EPA" reference is to Risk
Assessment Guidance for Superfund (RAGS) EPA 540/1-89/002
(USEPA, 1989b).
74.
Department of the Army, Appendix 5 - Risk Assessment,
Section 5, paqe 5-1.
This comment requests further discussion of soil gas survey
results. Further explanation of the statement "no basement
exposure model has been validated with empirical data" on p.
5-10 is also requested.
EPA Response. Soil gas surveying was carefully considered
for OU2. A soil gas survey was never actually performed at
OU2, because, based upon experience gained from OUI, ground
water concentrations were judged to be too low to produce
significant soil gas concentrations.
ASC2/BSPL/062691
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The statement regarding exposure models and empirical data
was true at the time that the RA was prepared. Since that
time, basement exposure models have been developed for radon
at Oak Ridge and Lawrence Berkeley Laboratories. However,
it is still true that no basement exposure models based on
empirical data have been validated for VOCs.
75.
Department of the Army, Appendix 5 - Risk Assessment,
section 5, paq. 5-2.
This comment requests justification of the exposure point
concentrations used for Case 1.
EPA Response. The exposure point concentrations for Case 1
were developed to obtain an RME for OU2. The area showed
wide temporal and spatial variations in COC presence and
concentration. No single collection of well data appeared
to provide a reasonable maximum exposure to all COCs.
Furthermore, ground water modeling data were not available
to predict future concentrations at specific receptor points
within the OU2 area. In order to develop an RME, the
highest 3-5 validated values from the 1989 sampling round
were used to calculate reasonable maximum exposure point
concentrations. The maximum values were used without regard
to their location or presence with other COCs. This is a
protective but reasonable assumption; the area under
consideration is large and ground water migration parameters
are not fully understood. The selection of 3-5 values was a
professional judgment based on the pattern of the data and
the size of the validated database. If non-detects were
included, the averages or 95% confidence limits would have
yielded lower values than this method. Because so few data
points were available, no statistical treatment of the data
is warranted.
ASC2/BSPL/062691
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76.
Department of the Aray, Appendix 5 -Risk Assessment,
Section 5, paqe 5-4.
This comment questions the use of estimated data over
nonestimated data for Case 1 exposure point concentration
calculations.
EPA Response.
Only validated data were used in the RA.
77.
Department of the Army, Appendix 5 - Risk Assessment,
Section 5, paqe 5-5.
Clarification is requested regarding whether water from SAC-
18 is always or usuallY blended with treated water.
EPA Response. Water from SAC-18 is always blended
treated water. The statement that SAC-18 water is
blended with treated water is not correct.
with
usually
78.
Department of the Army, Appendix 5 - Risk Assessment,
Section 5, paqe 5-8.
This comment questions how a value for S (indoor VOC
generation rate) is obtained for use in the shower exposure
formula.
EPA Response. The formula for calculation of S is described
in the work by Foster and Chrostowski (Foster & Chrostowski,
1987).
79.
Department of the Army, Appendix 5 - Risk Assessment,
Section 5, paqe 5-15.
This comment addresses VOC inhalation in basements and
questions whether thi~ has been addressed.
EPA Response. Basement VOC exposure was not eyaluated in
OU2 for two reasons; 1) a validated basement exposure model
ASC2/BSPL/062691
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80.
81.
was not available at the time the risk assessment was
prepared, and 2) ground water concentrations were so low
within OU2 that the contribution of the basement exposure
pathway was judged to not contribute significantly to the
overall risks at the site. Such potential risks will be
reevaluated during the 5-year review to ensure that the
selected remedies are protective.
Department of the Army, Appendix 5 - Risk Assessment,
section 6, Paqe 6-2.
This comment asks for an explanation of why the oral slope
factor was used to calculate inhalation exposure risks when
this is inconsistent with EPA guidance (RAGS).
EPA Response. The toxicity assessment was prepared in
consultation with USEPA Region VIII toxicologists and USEPA
Environmental criteria Assessment Office, Cincinnati, OH
(ECAO). ECAO recommended the cancer slope factors used in
the risk assessment because information for the inhalation
pathway was not available.
Department of the Army, Appendix 5 - Risk Assessment,
section 6, Paqe 6-8.
This comment questions the applicability of oral reference
doses for calculating noncarinogenic inhalation risks.
EPA Response. The oral reference doses for PCE, DCE, and
1,2-DCE were used to calculate inhalation hazard indices.
This is a reasonable assumption based on the toxicology of
the chemicals involved. Since the lung is not the target
organ, pharmacodynamics are unlikely to cause a shift in
target organ, and there is no reason to believe that
toxification or detoxification mechanisms are substantially
different as a function of the exposure route.
ASC2/BSPL/062691
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82.
Department of th. Army, Appendix 5 -Risk Assessment,
Section 8, paq. 8-1.
The decision not to validate all data, particularly those
for vinyl chloride is questioned.
EPA Response. There was no compelling reason to validate
the nondetect samples. Due to the method used to derive the
maximum exposure point concentrations, (hypothetical well
scenario), additional validation would only have lowered the
maximum concentrations calculated and thus produced a less
conservative scenario. Although there is uncertainty
associated with the hypothetical well approach, it is
nevertheless a reasonable surrogate for a maximum exposure
point concentration.
TOPIC IV:
FEASIBILITY STUDY
83.
SACWSD Comment '1
Tl. - comment notes that trichlorofluoromethane (TCFM) has
been detected at a maximum concentration of 3.2 ug/l in
SACWSD Shallow Wells 3 and 14, and Monitoring Well 5,
beginning in 1990. The comment also states that an MCL does
not exist for TCFM, so an action level should be developed
based on health risks. Two action levels, based on EPA
documents, are presented (0.14 ug/l and 2000 ug/l) and EPA
is requested to identify the appropriate concentration to
use as a clean up level at the Klein Water Treatment
Facility (KWTF). Because TCFM is poorly adsorbed by carbon,
SACWSD is concerned that a need to remove TCFM at the KWTF
will dramatically increase carbon usage. SACWSD then
suggests that a program be initiated to establish funding,
design, and construction criteria for the addition of air
strippers to the KWTF to remove weakly adsorbed compounds
such as TCFM and vinyl chloride.
ASC2/BSPl/062691
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84.
85.
EPA ReSDonse. The acceptable level for TCFM is 2000 ug/l,
in accordance with the EPA health advisory, published in
November, 1990 (USEPA, 1990b). This action level should not
adversely affect carbon usage at KWTF. A program to install
air strippers will be undertaken if continued monitoring
indicates that such equipment is needed, as was provided for
in the 1987 EPA ROD.
SACWSD Comment '2
The average concentrations of 1,1-DCE, l,2-DCE, and 1,1-DCA
recorded in the KWTF influent during 1990 and 1991 ranged
between 1-3 ug/l, 1-7 ug/l and 1-7 ug/l, respectively. On
page 1-15, the report states that "1,2-DCE may be a useful
indicator in predicting VC generation within CSC-OU2". The
document should be revised to state that 1,1-DCE, 1,2-DCE
and 1,1-DCA may all be useful indicators in predicting VC
generation within CSC-OU2 since, as correctly shown on page
1-18, all three chemicals can potentially biodegrade into
vinyl chloride.
EPA Response. As stated on page 1-16 of the report, 1,2-DCE
is the primary parent compound of vinyl chloride. The
diagram on page 1-18 was configured to indicate that 1,2-DCE
is the most likely precursor to vinyl chloride. 1,1-DCA is
not likely to degrade to vinyl chloride because it would
require creation of a double bond between the carbons where
only a single bond exists in 1,1-DCA.
SACWSD Comment '3:
This comment focuses on the PCE source near 56th Avenue and
Quebec street and the source's potential impacts on the
KWTF. Concern is expressed that the source is not
identified and characterized, and that existing TCE and PCE
plumes will continue to degrade into 1,1-DCE, 1,2-DCE, and
l,l-DCA. Because these compounds are only weakly adsorbed
ASC2/BSPl/062691
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by carbon, SACWSD is again concerned that the carbon usage
rate at the KWTF will exceed the planned usage rate and
thereby drive up operating costs for the plant. It is
stated that the report should address provision for
additional funding of KWTF if changing aquifer conditions
cause operating costs to increase. The possible need for
air stripping towers at KWTF to remove vinyl chloride is
ag in presented and identification of a funding mechanism
for this addition is requested.
EPA Response.
It is true that the actual source of the PCE
plume at 56th Avenue and Quebec street has not been
identified. As stated in the report, in March and April of
1990 a FIT investigation was undertaken upgradient of the
plume in an attempt to identify the source. This
investigation included a soil gas survey (49 samples) ground
water sampling (3 wells), and soil borings (3 borings).
Although the source was not identified, concentrations of
PCE in SACWSD Monitoring Well 08 have shown a slight
decreasing trend and the source has been assumed to be a
degrading source. Plume monitoring will continue and EPA
will make further attempts to identify the source, as
possible.
The purpose of the remedial activities in CSC OU2 is to
remove as much contamination from the aquifer as is
practical. The concern that existing TCE and PCE plumes
will degrade into l,2-DCE, l,l-DCE and l,l-DCA and
consequently overburden the KWTF is based on the assumption
that the pump and treat system will be located at 56th
Avenue and Quebec street. As noted in the description of
Alternative 2 (see pages 4-7, 5-10, and 5-11), the actual
location and configuration of the extraction system will be
determined during remedial design. The system will be
designed to capture as much of the existing plume as
possible. Some possible design schemes that will be
considered include locating the system north of 56th Avenue
ASC2/BSPL/062691
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(near the leading edge of the plume), or installing the
extraction and injection wells in a line down the center of
the plume. By maximizing plume capture, the amount of
contamination remaining in the aquifer is minimized and
future loading on the KWTF will remain near expected levels.
If continued monitoring indicates that need for air
strippers at KWTF, funding will be obtained at that time.
86.
SACWSD Comment '4
Department of the
Department ot the
Department of the
Department ot the
Department ot the
A~y,
Army,
A~y,
A~y,
A~y,
specific Comment Page 3-3
specific Comment Page 3-4
specific Comment Page 5-6
OU3 General Comment 1
OU3 specific Comment, section 4.2
These comments address SACWSD supply Well 18. SACWSD points
out that the maximum measured TCE concentration in Well 18
as presented in the report is incorrect and that water from
Well 18 should be treated to allow efficient use of water
resources in the CSC OU2 area.
The Army suggests that a remedial alternative addressing VOC
contamination in Well 18 is needed. Concerns are raised
that portions of the PCE and TCE plumes that are
downgradient of the SACWSD pumping center at 77th Avenue and
Quebec street are not addressed.
EPA Response. Based on additional information submitted to
EPA by SACWSD during the public comment period, levels of
TCE have been detected in Well 18 and are higher than those
used in the RIjFS. EPA will evaluate additional information
and, if necessary, identify alternatives to address
contamination associated with Well 18 in a separate action.
One of the alternatives will likely include connecting Well
18 to the KWTF to ensure that residents are provided with
water suitable for domestic uses (i.e. showering and
drinking). Funding of projects is not a topic that is
ASCZ/BSPL/06Z691
63
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addressed by an RIjFS.
parties to ensure that
activities.
EPA will work with appropriate
funding is available for remedial
87.
SACWSD Comment '5
The report indicates that it will take 20-30 years for the
proposed remedy to remove the bulk of the PCE. The report
should therefore address and resolve the 0 & M funding
deficiency that will occur if the proposed remedies for
whatever reason fail to prevent substantial additional
influent concentrations of PCE and related compounds at KWTF
beyond what was contemplated in the 1987 SSjPSA as a basis
for estimating long-term 0 & M costs.
EPA Response. Funding of projects is not a topic that is
addressed by the Record of Decision. EPA will be happy to
discuss this topic in a different forum.
The proposed pump and treat system is intended specifically
to reduce the amount of PCE in the aquifer upgradient of the
KWTF and will be designed to meet this objective. It is
anticipated that the pump and treat system will operate for
approximately 20 to 30 years and during that time will
reduce the amount of contamination reaching the KWTF from
this portion of the aquifer. continued monitoring will
indicate if the system is operating satisfactorily.
Remedial actions are re-evaluated every five years and
modifications to improve system performance can be made at
those times, if needed. Installation and operation of the
pump and treat system should ensure that carbon usage at
KWTF is not adversely affected.
ASC2/BSPL/062691
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88.
SACWSD Comment .,
Based on the District's understanding that Alternative 2 is
the most feasible plan, the District remains concerned that
the implementation of the alternative be thoroughly
investigated, discussed, and coordinated with the District.
The primary issue to be considered is that the alternative
not affect the District's water rights. Specific design
issues include the location and scheduling of the extraction
and injection wells with respect to the location and
scheduling of the District's supply wells, changes in water
quality due to treatment that may affect the aquifer's
geochemistry and hydraulic properties, and the methods to be
used for the long-term monitoring and evaluation of
impacts on the District's ground water supply.
EPA Response. It is EPA's intention to work closely with
SACWSD during design and implementation of this remedial
action so that the municipal water supply and distribution
are not adversely impacted. It is also realized that SACWSD
has an extensive working knowledge of this aquifer and may
provide valuable input during design and implementation of
this remedial action.
89.
Department
Department
Department
Department
of the
of the
of the
of the
Army,
Army,
Army,
Army,
General Comment 4
General Comment 8
Specific Comment Page
specific Comment Page
4-2
4-10
These comments discuss the need for additional remedial
alternatives for treating the TCE plume. Specifically, the
following options were suggested: (1) no action, (2)
partial containment with limited extraction, (3) partial
containment with enhanced extraction, (4) plume capture with
extraction, and (5) plume capture with enhanced extraction.
Concerns are raised that the SACWSD wells are not located
advantageously for extraction of contaminated ground water.
ASC2/BSPL/062691
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EPA ResDonse.
been adequately
the FS. Twelve
Plume remediation at the CSC OU2 site has
addressed by the alternatives presented in
remedial alternatives were evaluated in the
CSC OU1 and OU2 FSs to address the TCE ground-water
contamination. These alternatives represent a wide range of
hazardous waste management strategies including no action
(Alternative 1), partial containment and limited extraction
(Alternative 2 - OU1 FS), partial containment with enhanced
extraction (Alternatives 3, 4, and 5 - OU1 FS), plume
capture with extraction (Alternative 4 and 5 - OU2 FS), and
plume capture with enhanced extraction (Alternatives 3, 4, 5
- OU1 FS, combined with Alternative 5 - OU2 FS). These
alternatives meet NCP requirements cited in 40 CFR Section
300.430(e) (4).
Ground water extraction is most effectively accomplished in
regions of high ground water flow because these areas
accommodate the bulk of the ground water that is moving
through the aquifer. Plume movement is most pronounced in
these areas, therefore, these are the areas that would be
targeted for a pump and treat system to maximize the
remedial effect. These are also the areas that are targeted
for water supply wells to ensure that water is available to
meet customer demand. In both cases, extraction well
locations are chosen for the same reason (high ground water
flow) but for different purposes (aquifer remediation versus
municipal water supply). SACWSD supply wells are currently
located in areas of high flow and, as stated in the FS
report, it.would be difficult to design a system to do a
better job of extracting contaminated water than the SACWSD
wells are currently doing. EPA agrees that it was incorrect
to have stated that KWTF was constructed for the purpose of
remediating the aquifer. The statement would have been
correct if it had stated that the SACWSD wells feeding the
KWTF are located advantageously for aquifer remediation.
ASC2/BSPl/062691
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TCE plume remediation was addressed in the QU1 and QU2 FSs
through the evaluation of twelve alternatives. As shown in
Figure 1-10 of the FS, the only part of the TCE plume that
was not addressed by a pro-active treatment system is the
small portion of the plume north of the SACWSD pumping
center at 77th Avenue and Quebec street and south of 80th
Avenue. In addition, low concentrations (below action
levels) of TCE have been detected north of 80th Avenue as is
shown on the TCE point map (Figure 1-9 of the FS). The
plume is quite dispersed north of the extraction wells at
77th Avenue and would therefore require an extensive (and
correspondingly expensive) extraction and injection system
to provide significant TCE removal.
Development of an alternative to treat the limited northern
portion of the TCE plume, such as a pump and treat system
along 80th Avenue, was not considered to be appropriate
because of the high cost and minimal benefits of such a
system. A qualitative discussion of why this alternative
was not developed is presented below and is based on the
nine criteria used in the detailed screening of
alternatives.
Treatment of the TCE plume north of 77th Avenue would be
protective of human health and the environment, although it
would not improve protection of human health beyond the
protection offered by the other alternatives developed for
the FS. Human health is protected by operation of the KWTF
and by activities planned for CSC QU3 remediation. The
environment would also be protected to the same extent as it
is under the alternatives presented in the FS, although
restoration of the aquifer would occur somewhat sooner with
additional treatment.
An additional TCE treatment system would be subject to the
same ARARs as the other alternatives presented in the FS.
ASC2/BSPL/062691
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The long-term effectiveness and permanence of additional TCE
treatment would be the same as other alternatives presented
in the FS. Use of the KWTF will treat the bulk of the TCE
plume. The small amount of TCE remaining north of the
pumping center is estimated by modeling to reach action
levels in approximately 30 years through natural processes.
During the recovery period, the water will not be used for
domestic purposes unless it is extracted and distributed by
the SACWSD system. Water supplied by SACWSD is carefully
monitored and managed to ensure that it is in compliance
with drinking water quality standards before it is
distributed. An additional TCE treatment system would not
change the long-term effect of using natural processes and
SACWSD wells and the KWTF to remove contaminants from the
aquifer; it would, however, accelerate the process. EPA
will collect additional groundwater monitoring data for the
duration of RD/RA activities and if necessary, identify and
evaluate alternatives to address the remaining TCE plume in
a separate action. Since any future receptors will be
protected through either the OU3 remedy or separate, future
actions, there is no advantage to speeding up the
remediation.
The toxicity, mobility, and volume of contamination in the
aquifer would be reduced slightly by the addition of a TCE
treatment system. However, as noted by EPA (U.S. EPA,
1989c), as ground water plumes become more dilute,
contaminant removal systems become less successful. Because
the TCE plume north of 77th Avenue is dilute, the total mass
of contamination removed would be a smaller percentage of
the plume than where a plume is more concentrated.
The short-term effectiveness of an additional TCE treatment
system would be the same as for the alternatives presented
in the FS. Any receptors of contaminated ground water will
be protected by either the OU3 remedy or by separate future
actions. The aquifer would be remediated more quickly with
ASC2/BSPL/062691
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the additional TCE treatment, but there would be no tangible
benefit to accelerating the clean-up.
An additional treatment system would be implementable from a
technical as well as an administrative standpoint. However,
the larger the system, the more difficult it is to
implement, technically and administratively. A system to
capture the entire dilute TCE plume at about 80th Avenue
would have to be approximately one-half to one mile wide.
Acquisition of access to many private properties for the
location of the numerous extraction wells, and the extensive
piping and pumping that would be required, would increase
the difficulty of implementation.
The cost to install such a TCE treatment system was not
determined. However, because of the width of the TCE plume,
the extraction system (e.g., row of pumping wells), would
have to be three to four times as long as the proposed PCE
treatment system. The costs would escalate roughly
proportionately. As noted above, the benefit of treating
the entire TCE plume, in terms of mass of contamination
removed and additional protection of public health, would
not be significant.
The final two criteria, state acceptance and community
acceptance, are expected to be similar to acceptance of the
proposed PCE treatment system.
Based on all of the considerations noted above, an
alternative to capture the northern fringe of the TCE plume
was not considered to be appropriate and was not developed.
EPA will collect additional groundwater monitoring data for
the duration of CSC OU2 RD/RA activities and if necessary,
will address the remaining plume in a separate action.
ASC2/BSPL/062691
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90.
Department of the Aray, General Comment 5
Department of the Aray, General Comment'
These comments address the level of detail presented in the
FS report. Costing information during the preliminary
screening of alternatives and the extent of system design
for the detailed screening of alternatives are specifically
cited as needing more development.
EPA Response. The FS was written to be consistent with EPA
guidance (Guidance for Conducting Remedial Investigations
and Feasibility Studies under CERCLA: USEPA, 1988). costing
for the preliminary screening of alternatives is only
developed in enough detail to allow relative comparison
between alternatives. At this stage an alternative would
only be screened out based on cost if the other two
screening criteria (effectiveness and implementability) are
equal for the alternatives being considered. The cost
criterion was used to eliminate Alternative 3 during the
preliminary screening of alternatives. In a similar manner,
the level of detail developed for the remedial alternatives
was sufficient to choose an appropriate remedial action.
91.
Department of the Army, General Comment 9
Department of the Army, specific Comment Page 1-15
These comments raise concerns about the interaction between
the alluvial aquifer and the bedrock aquifer. The Army
feels that .the potential impact on the alluvial system from
pumping SACWSD bedrock wells has not been adequately
addressed and the conclusion that the vertical gradient
between these units varies from upward to downward across
the site is questioned.
EPA Response. The SACWSD bedrock wells are all completed in
either the Arapahoe or the Laramie-Fox Hills formations:
none are completed in the Denver formation. The Denver
ASC2/BSPL/062691
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~
formation, which has been observed to be made up primarily
of shale, acts as a confining layer between the alluvium and
the Arapaho and Laramie-Fox Hills formations. Therefore,
pumping the SACWSD bedrock wells at the current pumping rate
is not expected to impact the alluvial aquifer, and
contamination in the alluvial aquifer will not be pulled
downward into the bedrock as a result of this pumping.
92.
Department of the Army, specific Comment Page ES-3
This comment questions whether the annual monitoring
included in the no action alternative is sufficient to track
contaminant movement and possible impacts on the SACWSD
system.
EPA Response. Annual monitoring conducted by EPA and
ongoing SACWSD monitoring of supply wells on a quarterly
basis will be sufficient to track contaminant movement.
SACWSD conducts a separate, on-going monitoring program of
water supply wells to track contamination in the aquifer and
the potential impact on the supply system. This program
will be continued to ensure that the supply system is in
compliance with drinking water standards. SACWSD provides
EPA with all acquired data.
93.
Department of the Army, Specific Comment Page 3-2.
This comment points out that the PCE source near 56th Avenue
and Quebec street has not been identified, but that an
assumption has been made that contamination will not enter
the CSC QU2 site from CSC QUI. The validity of this
assumption is questioned.
EPA Response. EPA has attempted to identify the source of
the PCE plume but has not been successful to date. Further
attempts to locate the source will be undertaken if
continued monitoring indicates that the source is not a
ASC2/BSPL/062691
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degrading source, as has been assumed. EPA has determined
that the PCE plume does not originate in QUI. EPA has
selected Alternative 5 of the QUI FS. Successful
performance of this alternative will assure that
contamination from QUI will not impact QU2.
~
The assumption that contamination will not migrate northward
from CSC QUI into CSC QU2 addresses the TCE, rather than the
PCE plume. This assumption is based on the remedial
activities planned for the CSC QUI site, which include a
PL } and treat system at the boundary between CSC QUI and
CSC QU2. It is assumed that this system will be effective
in removing TCE from the aquifer before it enters CSC QU2.
94.
Department of the Army, specific Comment Page 5-6.
Please explain how Figures 5-1 and 5-2 are appropriate in
comparison to Figures 1-10 and 1-11 in assessing the plumes
predicted by the model versus the actual plumes present
since the time frames are different.
EPA Response. Figures 5-1 and 5-2 were incorrectly chosen
in the FS report. A better comparison can be made between
Figures 1-10 and A-3a (in Appendix B) and Figures 1-11 and
A-5a (in Appendix B).
95.
Department of the Army, specific Comment Page 6-11.
This comment requests clarification of EPA's policy
regarding attenuation processes versus pro-active capture
actions with respect to dilute contaminant plumes
downgradient of source-removal activities. Alternative 2,
PCE Plume Treatment with Hydraulic containment and Standard
Pumping of SACWSD Wells, is specifically cited as relying on
natural attenuation and degradation to remediate portions of
ASC2/BSPL/062691
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the TCE and PCE plumes that are beyond the influence of the
planned remedial activities.
~
EPA Response. EPA's policy is to act quickly to treat as
much of the plume as possible. Alternative 2 includes
remediation of the PCE plume that enters CSC OU2 near 56th
Avenue and Quebec street before the plume becomes dispersed.
Reliance on the SACWSD extraction wells to capture
contamination downgradient of the PCE treatment system is a
pro-active approach to plume capture at this site. A more
aggressive approach, increased pumping of the SACWSD system,
was also considered but was determined to be detrimental to
the SACWSD supply system. The alternatives that included
the more aggressive use of the SACWSD wells were screened
out on both technical and administrative implementability.
standard pumping of the SACWSD wells was therefore
determined to be the most active, but still feasible,
approach to aquifer remediation.
TOPIC V:
FS MODELING REPORT
96. Department of the Army, specific Comment, Page 6
Department of the Army, specific Comment, Page 9, First
Paragraph
Department of the Army, Specific comment, page 9, First
Paragraph
Department of the Army, Specific Comment, Page 10
Department of the Army, specific Comment, Page 17
Department of the Army, specific Comment, page 29 and 30
These comments raise concerns regarding the lack of model
calibration and use of the model in transient, rather than
steady state mode. It is stated repeatedly that the model
should have been calibrated, regardless of the lack of data
in some areas of the aquifer. It is felt that without
proper calibration the model did not properly simulate
phenomena such as flow rates and capture zones. In
addition, the decision to run the model in transient mode is
questioned because it is felt that the aquifer generally
ASC2/BSPL/062691
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responds to pumping as a confined system with storativities
that are orders of magnitude less than the 0.25 that was
used in this study.
EPA Response. The objective of the modeling effort must be
kept in mind. The model was developed to provide a basis
for comparing the effectiveness of the remedial alternatives
developed in the FS. In accordance with this approach,
modeling results were not used to exactly determine aquifer
characteristics at some future time, but rather to evaluate
the relative effectiveness of the alternatives in general
terms. For example, one alternative appeared to remediate
the aquifer more quickly than others, or one alternative
removed a greater quantity of contamination from the aquifer
than others. Total remediation times for the alternatives
were based on model results, but as stated in the text,
these times were considered to be rough estimates. Given
the intended purpose of the model, the fact that it is not
calibrated does not detrimentally affect the results.
In response to concerns that the model should have been run
in steady state mode, it should be noted that initial
attempts to run the model were done in steady state mode.
The model was equilibrated in steady state mode, a process
in which piezometric head values are assigned to the nodes
along the perimeter of the model area and the model then
generates head values at the internal nodes. Considerable
effort was then expended in an attempt to calibrate the
model. As a result of this effort it was found that
unacceptably large mass balance errors were generated in the
process. At that point it was decided that it would be more
appropriate to run the model in transient mode rather than
steady state. This was appropriate because steady state
mode most closely models a confined aquifer with
correspondingly low specific yield, while transient mode
most closely models an unconfined aquifer with higher
specific yield. The aquifer in CSC OU2 is an unconfined
ASC2/BSPL/062691
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aquifer and in addition is subject to extreme pumping
particularly in the summer. It is felt that these
considerations justify running the model in transient mode.
While running the model in this mode it was found that it
took at least 12 to 15 years to reach steady state.
Two other ground water modeling studies were cited in the
comments as examples of similar models being run in steady
state model. The referenced report by Ebasco (Ebasco, 1989)
was not reviewed. The referenced report by Morrison-Knudson
Engineers (MKE, 1989) stated that their model, which
included the western tier of RMA, was run in steady state
mode, however, it did not include pumping effects of either
the SACWSD extraction wells or the Irondale Boundary System
(IBS) wells. These pumping activities were later imposed on
the model to determine their effects on flow paths near the
IBS. In contrast, the CSC OU2 model included pumping
effects in the baseline scenario.
One final point that should be made regarding the MKE model
is that the aquifer was modeled as an unconfined system
(contrary to statements made in the comments pertaining to
pages 6 and 17). Results from this study that most closely
modeled actual conditions in the aquifer were obtained when
specific yields of 0.2 to 0.3 were used (MKE, 1989, pp 67-
69). Specific yields in this range correspond to unconfined
aquifers and are in agreement with the value of 0.25 that
was used in the CSC OU2 model.
97.
Department of
paragraph
Department of
paragraph
the Army, specific Comment Page 9, last
the Army, specific Comment Paqe 9, last
These questions address the TCE contaminant distribution in
CSC OU2. It is stated that the TCE distribution can be
partially explained by ground water moving northward under
Sand Creek. vertical variations in permeability are not
ASC2/BSPL/062691
75
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considered to adequately explain theTCE plume being
oriented obliquely to the ground water level contours.
is also stated that vertical variations in hydraulic
conductivity can be accounted for in a two-dimensional
through vertical averaging.
It
model
EPA Response. EPA agrees that the water table map indicates
that ground water moves northward under Sand Creek.
However, in the area north of the creek, it is maintained
that vertical variations in permeability are the most likely
cause of contaminant transport in a more northerly direction
than the hydraulic gradient. Vertical averaging is not an
acceptable method to represent vertical variation in
permeability because a layer of very high permeability, such
"~ a gravel channel, will provide a nearly unobstructed
pathway for contaminated ground water to flow. In this
case, flow volume and direction will most closely be
determined by the highly permeable channel, not by a
hypothetical channel of averaged permeability. Evidence of
a gravel bed at the base of the aquifer has been found in
other parts of the aquifer, such as north of the SACWSD
pumping center at 77th Avenue and Quebec street. It is
likely that similar conditions exist in the aquifer just
north of Sand Creek, and that these conditions cause the TCE
to migrate in a northerly direction.
98.
Department of the Army, specific Comment, page 11, Table A-1
Department of the Army, Specific Comment, Page 22
These comments are primarily concerned with the source
loading rates for TCE and PCE. The equations used to arrive
at the source loading rates are questioned, as well as
discharge at the gravel pits and the units on the TCE and
PCE distribution coefficients.
EPA Response. For the purposes of the modeling effort, the
TCE and PCE sources were modeled as water sources that
ASC2/BSPl/062691
76
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'"
contained an elevated concentration of either TCE or PCE.
The concentration of TCE and PCE in their respective sources
was assumed to be approximately equal to the maximum
concentration that has been detected in the aquifer for each
contaminant between 11/85 and 11/89. The source loading
rate, i.e., the rate at which the contaminated water was
injected into the aquifer, was calculated from a simple mass
balance. First, the total mass of TCE and PCE present in
the aquifer was calculated. Second, the number of years
that the sources were active was estimated, based on
historical data. Finally, the rate at which the contaminant
sources had to be injected was calculated based on the total
mass of TCE and PCE in the aquifer, the assumed source
concentrations, and the period of time they were active.
The equations on page 20 and 23 characterize this approach
although the rate equation on page 22 became disarranged
during production of the report. The equation should read:
RATE =
TOTKG
TIMYR (SECPYR)
6
(10 uq/kq)
CONCs (3.79 L/gal) (7.48 gal/Ft3)
Regarding discharge to the gravel pits, it may be true that
locally the aquifer discharges to the pits, however, the
general trend is for recharge. In order to simplify the
model it was assumed that the pits recharge the aquifer
through the length of the canal.
The TCE and PCE distribution coefficients have units of
milliliters per gram (ml/g).
99.
Department of the Army, specific Comment, Page 13
This comment states that a native recharge rate of 1.48
inches/year appears to be too high and a recharge rate of
0.25 inches/year is suggested. The appropriateness of the
EPA HELP model to predict the recharge rate is questioned.
ASC2/BSPL/062691
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EPA ResDonse. The EPA feels that the recharge rate of 1.48
inches/year is appropriate. This value was predicted by the
HELP model and is in close agreement with the 1.54
inches/year used by Konikow (Konikow, 1977).
100. Department of the Ar.ay, Specific Comment, paqe 14
This comment states that while the longitudinal dispersivity
is in agreement with Konikow's value, the transverse
dispersivity is much less than that used by Konikow.
EPA ResDonse. In the data set that is distributed with MaC,
Konikow makes it clear that DLTRAT = 0.30, where DLTRAT is
the ratio of transverse to longitudinal dispersivity. This
data set was developed by Konikow (Knoikow, 1977) for the.
adjacent Rocky Mountain Arsenal and was considered to be
ar~ropriate for CSC OU2.
101. Department of the Army, specific Comment, paqe lS
"The units of the Kd values are not given."
EP~ ResDonse.
(m~/g).
The units of Kd are milliliters per gram
102. Department of the Army, specific Comment, Page 19
This comment states that initial contaminant distributions
can be input directly into the MaC model and that this would
have been a more accurate approach than the one that was
taken. Concern is also expressed that the study was
determentally affected by the fact that the source areas for
the plumes may not lie within the model boundaries.
EPA ResDonse. A sincere effort was made to insert initial
contaminant concentrations into the MaC model. The model
was tested using this approach and it was found that the
ASC2/BSPL/062691
78
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~
model tried to maintain the concentrations at these nodes as
background contamination, and the mass of the contaminant
increased over time, resulting in a large error. At that
point it was decided that a source loading rate would be a
more appropriate approach. The equations on pages 20-23
were used to calculate realistic injection rates.
It is agreed that uncertainties regarding source location
and characteristics add to the uncertainty of the results,
however, the purpose of the model should be remembered.
This model was developed to allow comparison of the
effectiveness of the remedial alternatives; it was not
intended to be a detailed, calibrated, regional ground water
model.
103. Department of the Army, specific Comment, Page 23
Concerns regarding the relationship between desorption times
and hydraulic conductivity are raised. It is felt that this
topic was not adequately discussed in the text.
EPA Response. Zones of low hydraulic conductivity are
associated with longer desorption times for both of the
reasons noted in the comment. organic content is usually
higher in zones of low conductivity than in zones of high
conductivity, resulting in greater adsorption of organic
contaminants. This prolongs the desorption process because
of the large mass of contaminants that are adsorbed and
because of their affinity for organic material.
The same effect can be seen from a mass flow perspective.
Areas of low hydraulic conductivity tend to have a large
proportion of dead pore space than areas of high hydraulic
conductivity. contaminants then enter dead pore space by
diffusion and then adsorb and desorb to the surrounding
matrix. Once the contaminants diffuse into the dead pore
ASC2/BSPL/062691
79
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spaces they must also exit by diffusion. This is a slower
process than that occurring in the open pore spaces where
contaminants that have desorbed then migrate as a result of
advection rather than diffusion.
104. Department of the Aray, Specific Comment, Page 24
Clarification of the term "interior nodes" and the
assignment of fixed heads to these nodes is requested.
EPA Response. The interior nodes referred to in the text
are the nodes immediately interior to the nodes that run
along the boundaries of the modeled area (the outside
nodes). The MOC model requires that all outside nodes are
no flow boundaries. The nodes just interior to these
outside nodes were used to set the boundary conditions,
which included assigning fixed heads.
TOPIC VI:
ARARS
105. Colorado Department of Health, Comment '1
Colorado Department of Health, Comment '3
These comments cite regulations and standards that were
omitted from the RI/FS reports. These are:
o
Colorado Air Quality Regulations 1, 2, and 3.
o
Regulations for the state Discharge Permit, 5 CCR 1002-
2, 6.1.0.
EPA Response. EPA concurs with these comments. The
regulations and standards have been added to the ARARs
section in the Record of Decision.
ASC2/BSPL/062691
80
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106. Colorado Departaent of Health, Comment '2
This comment states that Practical Quantification Limits are
not state standards and, therefore, are not ARARs.
u
EPA Response.
EPA concurs with this comment.
Topic VII:
OPERABLE UNIT 3
107. Colorado Department of Health Disease Control Environmental
Epidemioloqy Division (DCEED), Comment '1
Colorado Department of Health (DCEED), Comment '3
Colorado Department of Health (DCEED), Comment '5
DCEED recommended a door-to-door survey within CSC OU2 to
identify all residences where exposure might occur and that
additional efforts be made to communicate risk concerns to
site residents.
EPA Response. EPA will determine whether any additional
survey is required during Remedial Design. EPA will consult
with DCEED before any decision is finalized. The
appropriateness of connecting businesses will also be
determined at this time. EPA agrees that a substantial
effort should be made to communicate potential risks to site
residents during RD/RA for OU3.
108. Colorado Department of Health (DCEED), Comment '4.
DCEED requested clarification regarding whether residents
outside the current CSC boundary are covered in the OU3
proposed plan and recommended that if possible, residences
outside the current CSC boundary should be connected to
SACWSD.
ASC2/BSPL/062691 .
81
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EPA ResDonse: The Site boundaries of CSC OU2 and OU3 are
defined by the areal extent of ground-water contamination.
If ground contaminants continue to migrate northward, the
boundaries of the site will correspondingly expand. EPA
agrees that, if practicable, residences with contamination
should be connected to the SACWSD system. Installation of
carbon treatment units was included in the OU3 ROD to ensure
protection of residences in rural areas where connection to
system is not practicable.
109.
Colorado Department of Health (DCEED), Comment .,
Colorado Department of Health (DCEED), Comment '7
DCEED requested clarification regarding the inclusion of
provisions prohibiting the installation of alluvial wells.
EPA ResDonse: As part of the OU3 remedy, individuals
requesting well permits to install alluvial aquifer wells
within the CSC Site will be notified by the State Engineers
Office of potential health risks related to use of the
contaminated ground water. Due to water rights
considerations, EPA determined that prohibiting use of
domestic alluvial wells was not appropriate for CSC OU3
since EPA does not have authority to approve well use
permits.
110. Colorado Department of Health (DCEED), Comment '8
DCEED requested information regarding a plan to treat vinyl
chloride if it is detected at the KWTF.
EPA ResDonse: If vinyl chloride is detected at the KWTF,
the air stripping will be used to treat this contaminant.
This provision is documented in the EPA Off-Post Arsenal,
Operable Unit 1, Record of Decision.
ASC2/BSPL/062691
82
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111. Department of Azay, General Comment '2
u
This comment states that residents not presently hooked up
to the SACWSD municipal water supply and using alluvial
wells should be provided an alternative water supply in the
interim period before the remedy is implemented.
EPA Response: It is unnecessary tO,provide an alternative
water supply for residents not presently hooked up to the
SACWSD municipal water supply and using alluvial wells
during the interim period before the remedy is implemented.
The risks associated with this contaminated ground water are
based on chronic, long term exposure. EPA expects to
complete this remedy within 1 year of signing this ROD.
Exposure to contaminated ground water during this time
period will not significantly increase the risks.
112. Department of Army, Specific Comment section 2.0, Page 9
Department of Army, Specific Comment Page 12-13
Department of Army, Section 5.2
These comments address the CDH/TCH well survey. It was
requested that an explanation concerning (1) why residents
on systems were not included in developing the list of
people potentially at risk, (2) why potentially affected
residents were included in this list and (3) the
inconsistencies between Figures 2 and 3 in the OU3 FS and
Figures 1-10 and 1-11 in the OU2 FS.
EPA Response: Potentially exposed residents were identified
based on a list of those residents who are connected to the
SACWSD sewage system but not to the SACWSD water system.
EPA will evaluate the adequacy of this survey during OU3
Remedial Design. Since ground-water contamination is
actively migrating, it is necessary to include potentially
affected residents to be connected to the SACWSD system.
Figures 2 and 3 in the OU3 FS are based on Figures 1-10 and
ASC2/BSPl/062691
83
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1-11 in the OU2 FS. Figure 1-11 of the OU2 FS speculates
that PCE contamination from the CSC plume may commingle with
the PCE plume. This speculation was not depicted in Figure
3 of the OU3 FS.
113. Department of Aray, specific Comment section 5.2
This comment requests clarification of EPA's position on
presenting all potentially applicable technologies (drilling
of deep wells) in the first level of screening in an FS. In
addition, the comment stated that it is inappropriate to
select an alternative that does not protect public health
without accounting for exposure to contaminants outside the
current site boundaries.
EPA Response: All potentially applicable technologies
should be considered for the first level screening of an FS.
Drilling of deep wells was not considered to be potentially
applicable due to concerns associated with cross
contamination. CSC Site boundaries are based on the areal
extent of ground-water contamination. If contaminated
ground water continues to migrate to the north, the Site
boundaries will correspondingly expand. Residents will be
prevented from exposure to contaminated ground water even
though they may be located outside the current Site
boundaries since these boundaries are dependant on the areal
extent of contamination.
ASC2/BSPL/062691
84
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References
Camp, Dresser and McKee (CDM), 1988. Remedial Investigation and
Site Characterization Report, Sand Creek Industrial Site.
Commerce City, Colorado. March 4, 1988. Document No. 203-
RI1-RT-ESDW-1.
FIT, 1990. Ecology and Environment, Inc. Report of Sampling
Activities, Denver Engineering and Operations Center
(Chemical Sales, Operable Unit 2). Field Investigation Team
Zone II. EPA ID COD007431620. May, 1990.
Foster, S.A. and P.C. Chrostowski, 1987. Inhalation Exposure to
Volatile organic Contaminants in the Shower. Presentation
at the 80th Annual Meeting of the Air Pollution control
Association, June 21-26, 1987. New York, N.Y.
Freeze, R.A., and J.A. Cherry, 1979. Ground Water.
Hall, Inc., Englewood Cliffs, New Jersey.
Prentice-
Konikow, L.F., 1977. "Modeling Chloride Movement in the Alluvial
Aquifer at the Rocky Mountain Arsenal, Colorado." U.S.
Geological Survey Water-Supply Paper 2044, 43 pp.
McWhorter, David B., and O.K. Sunada, 1981. Ground-Water
Hydrology and Hydraulics, Water Resources Publications.
Collins, Colorado.
Ft.
Morrison-Knudsen Engineers, Inc. (MKE) , 1989. Impacts of
Municipal Well-Field Development on the Operation of the
Irondale boundary System at the Rocky Mountain Arsenal.
Draft Report. Project 1680, WP-15593. March 7, 1989.
SHELL 4834.
RT
United States Environmental Protection Agency (U.S. EPA), 1991.
"Role of the Baseline Risk Assessment in Superfund Remedy
Selection Decisions." OSWER Directive 9355.0-30, April 22,
1991.
U.S. EPA 1990a. Guidance for Data Useability in Risk Assessment.
Interim Final. OERR Directive: 9285.7-05, October 1990.
EPA/540/G-90/008.
U.S. EPA, 1990b.
Advisories.
Drinking Water Regulations and Health
Office of Drinking Water. November 1990.
U.S. EPA, 1989a. "ARARs Questions and Answers."
9234.2, May, 1989.
OERR Fact Sheet
U.S. EPA, 1989b. Risk Assessment Guidance for Superfund, Volume
I, Human Health Evaluation Manual (Part A). Interim Final.
OERR. December 1989. EPA/540/1-89/002.
ASC2/BSPL/062691
85
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u.s. EPA, 1989c. Considerations in Ground Water Remediation at
Superfund sites. OSWER Directive 9355.4-03. October, 1989.
u.s. EPA, 1988. Guidance for Conducting Remedial Investigations
and Feasibility studies Under CERCLA. LSWER Directive
9355.3-01, october, 1988. EPA/540/G-89/004..
U.S. EPA, 1986. Remedial Investigation for the First Operable
Unit, Rocky Mountain Arsenal Off-Post RI/FS site. December
1986. Document No. 198-RI1-RT-DRLM-1.
Walton, William C. 1984.
MOdeling, NWWA.
Practical Aspects of Ground Water
ASC2/BSPl/062691
86
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(..',
Time
DAY ONE
9:00 - 9:15
9:15 - 9:45
9:45 - 10:30
10:30 - 10:45
10:45 - 12:00
12:00 - 1:00
1:00 - 2:00
2:00 - 3:30
3:30 - 3:45
3:45 - 4:30
DAY TWO
9:00 - 10:30
10:30 - 10:45
10:45 - 12:00
12:00 - 1:00
1:00 - 2:00
2:00 - 3:00
3:00 - 3:15
INTRODUCTION TO SUPERFUND ENFORCEMENT
July 30-31, 1991
Washington, D.C.
AGENDA
Session
Opening Remarks
Expectations/Agenda
overview of Enforcement
Programmatic Goals,
Objectives, Mandates
and History
BREAK
Integrated Timeline
Exercise
LUNCHAPPENDIX C
PRP Liability
PRP Search
BREAK
Negotiations - Intro
Negotiations - Tools
and Outcomes
BREAK
PRP Oversight
LUNCH
Admin Record
Cost Recovery
Closing Remarks
Staff Lead
Debby Thomas
Monica Lamote
Walter Mugdan
Renee Wynn
----.
, .
Waler " Mugdan
'S-teve Suprun
Debby Thomas
Tony Diecidue
Debby Thomas
Steve Spiegel
Frank Biros
Debby Thomas
-------
DEI' ..\ f{ T .\1 E :\ T
OF.AJlE:\LTH
ROY ROMER
Governor
JOEL KOlc-l
loterim El~Utivt Dire.:tor
Grand Junction R"1!ionaJ Office
222 S. 6th Street, Room 232
Grand JunCtion, Colorado 81S01.2768
Teld.. Nunm.r:
(303) 248.7198
@ pt'VUrd 0111 "C)d~d ptJIH,.
June 25, 1991
Mr. James J. Scherer
Regional Administrator
U.S. Environmental Protection
Region VIII
One Denver Place
999 18th Street, Suite 500
Denver, Colorado 80202-2405
Agency
Re:
State of Colorado Concurrence on Chemical Sales,
Operable Units 2 and 3 - Records of Decision
Dear Mr.~~r:
The State of Colorado concurs with the Records of Decision (RODS)
for Operable Units 2 and 3 of Chemical Sales. However, an
additional issue has been raised by the State Engineer's Office
that may apply to the project. A ground water augmentation plan
may be required for water loss due to evaporation from the air'
stripping operation. This issue will need to be pursued during
the Remedial Design phase.
We would like to congratulate EPA on the speedy and competent
manner in which the RI/FSs and RODs for the site were developed.
We look forward to a continued good working relatio~ship with EPA
during the Remedial Design and Remedial Action phases for the
cleanup of this source cf pollution to the alluvial aquifer.
Sincerely,
~k-I~-
Thomas P. LOObY/
Assistant Director for Health and
Environmental Protection
Colorado Department of Health
TPL:nr
cc:
Ron Cattany
Dave Shelton
John Leary
Charlotte Robinson
Robert Eber
Vickie Peters
Hal Simpson
Nancy Chick
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