PB98-964603
EPA 541-R98-052
October 1998
EPA Superfund
Record of Decision:
Vancouver Water Station #1
Contamination
Vancouver, WA
9/11/1998
-------
DECLARATION OF THE RECORD OF DECISION
SITE NAMI AND LOCATION
Vancouver Water Station 1
Vancouver, Washington
STATEMENT OF PURPOSE
This decision document presents the selected final remedial action for Vancouver Water Station 1 (WS1) in
Vancouver, Washington, which was developed in accordance with the Comprehensive Environmental Response,
Compensation, and Liability Act of 198C (CERCLA), as amended by the Superfund Amendments and
Reauthohzation Act of 1986 (SARA), and, to the extent practicable, the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP). This decision is based on the Administrative Record for the site.
The lead agency for this decision is the U.S. Environmental Protection Agency (EPA). The State of Washington
Department of Ecology concurs with the selected remedy.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from WS1, if not addressed by implementing the response
action selected in this Record of Decision (ROD), may present imminent and substantial danger to public health,
welfare, or the environment
DESCRIPTION OF THE SELECTED REMEDY
The City of Vancouver's public water supply wells at WS1 are contaminated with tetrachlorethene (PCE). No
source for the PCE in the groundwater has been identified; therefore a remedy that is limited to treatment of the
drinking water produced from WS1 has been determined to represent the maximum extent to which permanent
solutions and treatment technologies can be used in a cost-effective manner. Even without a source control
remedy, the concentration of PCE in groundwater at WS1 is expected to eventually decrease to a level below the
maximum contaminant level (MCL).
The selected remedy for both cleanup of the public water supply and groundwater at WS1 is air stripping. Air
stripping is a treatment technology in which the water to be treated trickles down through a tower in a packed
column that breaks up the flow of water to create as much surface area as possible. Large volumes of air are then
forced upward through the water, transferring the volatile contaminants from the surface of the water to the air
through the process of evaporation. The air to which the contaminants have been transferred is then treated by
forcing it through carbon filters, which adsorb the contaminants. The filters are then regenerated or treated and
disposed of as a hazardous waste.
The air stripping system at WS1 has been in operation since 1993, before the site was listed on the National
Priorities List. Use of air stripping has consistently reduced concentrations of PCE in treated water to below the
level of detection. This action addresses the principal threat to human healthcontamination of drinking water
with PCE.
62520V9808.030.wpd
-------
All water pumped from WS1 is treated by air stripping and distributed to customers as drinking water.
Groundwater is pumped from WS1 at a rate that varies between 8 and 19 million gallons per day, depending on the
time of year and customer demand. While the primary purpose of air stripping is cleanup of the water being
produced for distribution as drinking water, this action also serves as a pump-and-treat remedy that partially
addresses the contamination of the groundwater at the site (source removal is not part of the selected remedy.)
STATUTORY DETERMINATION
The selected remedial action protects human health and the environment, complies with federal and state
requirements that are legally applicable or relevant and appropriate to the remedial action, and is cost-effective.
This remedy utilizes permanent solutions and alternative treatment (or resource recovery) technologies to the
maximum extent practicable and satisfies the statutory preference for remedies that employ treatment that reduces
toxicity, mobility, or volume as a principal element. Because this remedy will result in hazardous substances
remaining on site above health-based levels, Water Station 1 will be subject to a 5-year review.
Chuck Clarke Date
Regional Administrator, Region 10
United States Environmental Protection Agency
62320\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page iii
EPA Region 10
CONTENTS
Section Page
ABBREVIATIONS AND ACRONYMS ' vii
1.0 INTRODUCTION 1
2.0 SITE NAME, LOCATION, AND DESCRIPTION ,. 1
3.0 SITE HISTORY AND ENFORCEMENT ACnvrTIES 3
4.0 COMMUNITY RELATIONS 7
4.1 CITY OF VANCOUVER COMMUNITY RELATIONS EFFORTS 7
4.2 EPA COMMUNITY RELATIONS EFFORTS 8
5.0 SCOPE AND ROLE OF RESPONSE ACTION 9
6.0 SUMMARY OF SITE CHARACTERISTICS 10
6.1 PHYSICAL CHARACTERISTICS . 10
6.1.1 Surface Features 10
6.1.2 Geology 11
6.1.3 Hydrogeology 12
6.2 NATURE AND EXTENT OF CONTAMINATION . . 12
6.2.1 Soil-Gas .12
6.2.2 Soil : : 13
6.2.3 Groundwater 14
7.0 SUMMARY OF SITE RISKS 17
7.1 HUMAN HEALTH RISK ASSESSMENT 18
7.1.1 Identification of Contaminants of Potential Concern . 18
7.1.2 Exposure Assessment 18
7.1.3 Toxicity Assessment '. 22
7.1.4 Risk Characterization 23
7.1.5 Uncertainty Assessment 25
7.2 ECOLOGICAL RISK EVALUATION 27
8.0 REMEDIAL ACTION OBJECTIVES 2fc
8.1 NEED FOR REMEDIAL ACTION 28
8.2 NO IDENTIFIED SOURCE 28
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page iv
EPA Region 10
CONTENTS (Continued)
Section
8.2.1 Potential Sources of Contamination 29
8.2.2 Transport of PCE to Water Station 1 30
8.2.3 Representativeness of Production Well PCE Concentrations 31
8.2.4 Conclusion 31
8.3 REMEDIAL ACTION OBJECTIVES 32
-r
9.0 DESCRIPTION OF ALTERNATIVES 32
9.1 THE OPERATING TREATMENT SYSTEM ALTERNATIVE 33
9.2 THE NO-ACTION ALTERNATIVE 33
10.0 COMPARATIVE ANALYSIS OF ALTERNATIVES 35
10.1 OVERALL PROTECTION OF HUMAN HEALTH AND
THE ENVIRONMENT 35
10.2 COMPLIANCE WITH ARARS ! .- 36
10.3 LONG-TERM EFFECTIVENESS AND PERMANENCE 36
10.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME THROUGH
TREATMENT .37
10.5 SHORT-TERM EFFECTIVENESS 37
10.6 IMPLEMENTABILITY 38
10.7 COST OF IMPLEMENTATION 38
10.8 STATE ACCEPTANCE 38
10.9 COMMUNITY ACCEPTANCE 39
11.0 THE SELECTED REMEDY 39
11.1 AIR STRIPPING 39
11.2 GROUNDWATER CLEANUP 40
11.3 GROUNDWATER MONITORING 40
12.0 STATUTORY DETERMINATIONS 41
12.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT 41
12.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND
APPROPRIATE REQUIREMENTS (ARARS) AND OTHER
CRITERIA AND GUIDANCE 41
12.2.1 ARARs 41
12.2.2 Other Criteria, Advisories, or Guidance To Be Considered
(TBCs) for This Remedial Action 43
62J20\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Pagev
EPA Region 10
CONTENTS (Continued)
Section Page
12.3 COST-EFFECTIVENESS 43
12.4 USE OF PERMANENT SOLUTIONS AND ALTERNATIVE
TREATMENT TECHNOLOGIES (OR RESOURCE RECOVERY
TECHNOLOGIES) TO THE MAXIMUM EXTENT PRACTICABLE 43
12.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT 44
13.0 DOCUMENTATION OF SIGNIFICANT CHANGES 44
APPENDK
A Responsiveness Summary
62520\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page vi
EPA Region 10
FIGURES
2-1 Site Location Map, Vancouver Water Station 1 2
2-2 City of Vancouver Production Well and Monitoring Well Locations .'. 4
7-1 Human Health Conceptual Site Model ...'. 20
9-1 Typical Air Stripper . .; 34
TABLES
6-1 Summary of PCE Concentrations in Production Wells at WS1
(6-19-91 Through 6-1-98) 15
6-2 Analytical Results for PCE and TCE in Groundwater Samples From MW1 -1
Through MW1-5 17
7-1 Summary of Cancer Risks Associated With PCE in Untreated Water 24
7-2 Summary of Noncancer Hazard Associated With PCE in Untreated Water 25
62520\9808.030.wpd
-------
VANCOUVER WATER STATION 1
FINAL RECORD OF DECISION
EPA Region 10
September 1998
Page vii
ABBREVIATIONS AND ACRONYMS
ARAR applicable or relevant and appropriate requirement
bgs below ground surface
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
CFR Code of Federal Regulations
COPC contaminant of potential concern
DNAPL dense nonaqueous-phase liquid
EPA U.S. Environmental Protection Agency
FS feasibility study
HHRA human health risk assessment
Ffl hazard index
HQ hazard quotient
IRIS Integrated Risk Information System
kg kilogram
MCL maximum contaminant level
fj.g microgram
mg milligram
MSL mean sea level
MTCA Model Toxics Control Act
NCEA National Center for Environmental Assessment
NCP National Contingency Plan
NPL National Priorities List
NTP National Toxicology Program
PCE tetrachloroethene (also known as perchloroethylene)
RAO remedial action objective
RBSC risk-based screening concentration
RCRA Resource Conservation and Recovery Act
RfD reference dose
Rl remedial investigation
RME reasonable maximum exposure
ROD Record of Decision
SARA Superftmd Amendments and Reauthorization Act
SDWA Safe Drinking Water Act
SF slope factor
TCA 1,1,1-trichloroethane
TCE trichloroethene
UCL95 95 percent upper confidence limit
62J20\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page viii
EPA Region 10
ABBREVIATIONS AND ACRONYMS (Continued)
VOC volatile organic compound
WDOH Washington State Department of Health
WS1 Vancouver Water Station 1
WS3 Vancouver Water Station 3
WS4 Vancouver Water Station 4
62320>S808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 1
EPA Region 10
DECISION SUMMARY
1.0 INTRODUCTION
In accordance with the Comprehensive Environmental Response, Compensation, and Liability Act
of 1980 (CERCLA) as amended by the Superfund Amendments and Reauthorization Act of 1986
(SARA), and, to the extent practicable, the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), the U.S. Environmental Protection Agency (EPA) is selecting under
CERCLA the existing air stripping treatment system to address environmental contamination at
Vancouver Water Station 1 (WS1) in the city of Vancouver, Washington. The selected treatment
system has been constructed and is operational.
The selected action has the concurrence of the Washington State Department of Ecology
(Ecology) and is responsive to the expressed concerns of the public. The selected action complies.
with applicable or relevant and appropriate requirements (ARARs) promulgated by Ecology,
EPA, and other state agencies.
2.0 SITE NAME, LOCATION, AND DESCRIPTION
WS1 lies within Waterworks Park in the city of Vancouver, Washington. Vancouver is located in
Clark County in the southwestern corner of Washington state, across the Columbia River from
the city of Portland, Oregon.
WS1 is near the center of the city, approximately 0.75 miles east of Interstate 5 and approximately
2 miles north of the Columbia River (Figure 2-1). The site is located on the southeast corner of
Fourth Plain Boulevard and Fort Vancouver Way, and is bounded on the west by Clark College,
and to the east by East X and Y Streets, and to the south by East 21st Street. It lies adjacent to a
commercial district and residential areas.
62J20\9808.030.wpd
-------
14
Lewis and Clark Hwy
I
J
CD
Hayflen
Island
Columbia River
Figure 2-1
Site Location Map
Vancouver Water Station 1
NORTH
1/2
Scale in Miles
EPA Region 10
Vancouver Water Station i
ROD
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 3
EPA Region 10
WS1 has 10 groundwater production wells and a holding reservoir used to provide storage
capacity to accommodate daily fluctuations in water demand (Figure 2-2). WS1 supplies drinking
water to approximately 150,000 residents, or about one-half of the drinking water for Vancouver.
The balance of drinking water is supplied by other similar wellfields in and around the city.
The aquifer from which WS 1 draws its water is known as the Troutdale Formation. The
Troutdale Formation, the upper portion of which is approximately 200 feet below ground surface,
supplies water to several municipal wellfields and an unknown number of private wells. All
known private wells are used for irrigation or filling swimming pools. None of the private wells
are known to be used for drinking water.
There are no wetlands, floodplains, threatened or endangered species, or properties on or eligible
for the National Registry of Historic Places on this site.
3.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES
The wellfield at WS 1 has been owned by the City of Vancouver for over 60 years. The reservoir
was constructed in 1936 and Production Well 1 was installed in 1937. Additional wells were
installed at the rate of approximately one per decade, with the most recent wells coming on line in
'1982. Water from WS1 is blended together with water from several other wellfields to provide
drinking water to the Vancouver region. The combined water supply system provides drinking
water to approximately 150,000 people throughout the Vancouver area. Approximately one-half
of the total water system production is supplied by WS1.
When the federal Safe Drinking Water Act (SDWA) was amended to require suppliers of public
drinking water to monitor for volatile organic compounds (VOCs), the City of Vancouver began
monitoring water from WS 1 and its other wellfields. Results of this monitoring, which began in
March 1988, indicated a persistent presence of tetrachloroethene (also known as
perchloroethylene, or PCE) in the water at WS1. In February 1989, in consultation with the
Washington State Department of Health (WDOH), the City notified the public of the presence of
PCE in the groundwater at both Water Station 4 (WS4) and WS 1. Because PCE concentrations
at WS 1 were much lower than those at WS4, the notice stated that WS 1 water was being blended
with WS4 water to reduce overall PCE concentrations.
In May of 1989, EPA proposed a maximum contaminant level (MCL) for PCE for public drinking
water systems of 5.0 micrograms per liter (fJ.g/L). Samples collected from the production wells in
62520'S808.030.wpd
-------
Roads, Sidewalks,
Driveways, Parking
"'" 'O City Production Well
M""JS Monitoring Well
Notes: ww;-2 was abandoned in 1997.
MW1-5 (located at East 13th arc i
East Z Streets) is approximately ]
one-third mile south of MW1-3. '
O
Figure 2-2
City of Vancouver
Production Well and
Monitoring Well Locations
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 5
EPA Region 10
July 1989 showed concentrations of PCE ranging from 0.3 to 3.7 //g/L, with an average
concentration of 0.95
In.July 1989, the City of Vancouver initiated field investigations to determine if there was a
source or sources of PCE or other VOCs near WSI. A soil-gas survey was conducted in the
WS1 area, and 19 soil-gas samples were collected and analyzed. In addition, groundwater
samples were collected from five existing private wells located within a 1 -mile radius of WSI.
There was no pattern in the soil or groundwater results that indicated a source of PCE.
In August 1989, EPA Region 10 began a study that included soil-gas surveys and groundwater
monitoring, in another attempt to identify potential sources of the PCE detected at WSI and
several other Vancouver water stations. Eight groundwater samples were collected from
production wells at WS 1 and Water Station 3 (WS3) (located approximately 1 mile northwest of
WS 1) and from private wells within approximately a 1-mile radius of WS 1 . A total of 194 soil-
gas samples were collected throughout the city of Vancouver during the Phase I study, with 20 of
the samples collected in the vicinity of WSI.
Phase n of this study focused on potential PCE sources within the vicinity of WSI by collecting
more than 100 additional soil-gas samples from 40 locations north and east of the site in February
and March of 1 990. To provide soil-gas depth profiles, multiple soil-gas samples were collected
from each sampling location and analyzed in the field for VOCs.
The results of both phases of the investigation failed to identify a potential source of the PCE
entering WS 1 . PCE was detected in soil gas samples collected just north of the WS 1 , although
the concentrations were not high enough to indicate that the area was responsible for the
contaminated groundwater at WSI . Groundwater monitoring wells in and adjacent to the
wellfield have never shown concentrations of PCE above the MCL. Because significant
concentrations of PCE have not been detected except in the production wells, it is not possible to
identify where the PCE originated (a source) or how it got to the well field (a plume).
EPA issued its final MCL for PCE (5.0 Mg/L) in January 1991, with an effective date of July 1992
(40 CFR Part 141).
In 1991 the City expanded the monitoring at WSI to include weekly PCE analyses for each of the
10 production wells. Because demand for water rarely required the output from all 10 wells, the
City was able to use results of the monitoring to determine which wells to use for production to
minimize the concentr .:ion of PCE in the water delivered to its customers. Water was drawn Prst
from wells with the lowest concentration of PCE. Wells with higher levels of PCE were used
only as necessary to meet peak demand. All of the water was mixed and stored in the reservoir
62320\9808 030 wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 6
EPA Region 10
prior to delivery to customers. Although the concentration of PCE in a few wells at WSl was
greater than the MCL, the combined output from WS1 (measured at the reservoir) was always
less than the MCL.
In the fall of 1992, EPA conducted a hydrogeologic assessment of the Vancouver area, and
installed five groundwater monitoring wells in the vicinity of WS 1 (see Figure 2-2). Depth-
specific groundwater samples were collected during drilling of these wells; PCE was detected in
groundwater samples from only one well (MW1-3) at depths between 260 and 280 feet below
ground surface (bgs). Lithologic soil sampling was conducted during construction of one-of the
wells (MW1-1); PCE was detected in soil samples at depths of between 30 to 60 feet bgs, and
again at approximately 80 feet bgs. Following well development, groundwater samples were
collected from all five of the monitoring wells, but PCE was detected in only one of the five wells
(MW1-3).
From 1991 through 1992, monitoring of the 10 production wells showed a trend of continuing,
and possibly increasing, concentrations of PCE in the groundwater at WSl. Although the PCE
concentration in the combined output at WSl, measured at the reservoir, remained below the
MCL, the concentrations in a few wells were consistently above the MCL. To ensure that city
drinking water was protected, in May 1993 the City of Vancouver installed five air stripping
towers at WSl to remove PCE from the drinking water produced by the wells. These towers are
still operating. Groundwater produced from the 10 wells is pumped to the towers for treatment,
' and the treated water is then transferred to the reservoir before distribution to water customers.
The air strippers have reduced PCE concentrations in public drinking water to nondetectable
levels. Following installation of the air stripping treatment system, the City changed the frequency
of its monitoring of the untreated water from weekly to monthly.
Although the air stripping system was effectively removing PCE from water that the City was
distributing for drinking water, Vancouver WS 1 was proposed for the National Priorities List
(NPL) in June 1993 because of the presence of PCE in the groundwater. The maximum detected
PCE concentration (30.0 /zg/L) was reported from Production Well 1 on June 28, 1993.
In 1993 EPA conducted a study to evaluate the WS 1 site for potential removal actions to mitigate
threats to public health. The study found that no immediate threats to public health existed from
WS 1 because appropriate action (air stripping) had already been implemented. However,
concentrations of PCE in groundwater continued to exceed the MCL, so in June of 1994 the site
was officially placed on the NPL.
As required under CERCLA, a preliminary health assessment was conducted by WDOH under
cooperative agreement with the U.S. Department of Health and Human Services' Agency for
6252
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 7
EPA Region 10
Toxic Substances and Disease Registry. Released for public comment in fall 1994, the
preliminary health assessment concluded that there was no apparent health hazard from exposure
to PCE in drinking water supplied by WS1, although WDOH did recommend further investigation
of PCE contamination in the ground water near WS1.
At about that time, funding constraints led to a decision by EPA to postpone further
investigations of WS1, saving EPA's limited funding for sites with greater risk.
«p»
In July 1997 EPA conducted groundwater sampling at all five of its monitoring wells at WS1
because monitoring well MW1-2 was scheduled for abandonment to facilitate construction of a
skateboard park by the City. Samples were collected using low-flow techniques and were
analyzed for VOCs. PCE was detected only at MW1-3 and MW1-5, with only the sample from
MW1-5 exceeding the MCL of 5.0 /zg/L.
In November 1997 EPA initiated a remedial investigation/feasibility study (RI/FS) and risk
assessment for WS1. EPA sampled all existing monitoring wells in March 1998. PCE was
detected only at MW1-3 and MW1-5, but neither sample exceeded the MCL. In July 1998 EPA
released the final RI/FS report for WS1. The results of the RI/FS report are summarized in this
ROD.
4.0 COMMUNITY RELATIONS
4.1 CITY OF VANCOUVER COMMUNITY RELATIONS EFFORTS
Most of the City's public information efforts regarding water quality at water production facilities
have focused on Water Station 4 (WS4). In February 1989 the City of Vancouver notified users
of public water that PCE had been detected in wells at WS4. However, because PCE
concentrations at WS1 were much lower than concentrations at WS4, the notice stated that the
City was reducing the amount of water pumped from WS4 and increasing the amount of water
pumped from WS1 to minimize the overall PCE concentrations. (In October 1989, the City took
WS4 out of service until a treatment system could be installed.)
Primarily in response to the water quality concerns at WS4, in 1989 the City began providing its
water customers with an annual water quality report that it included with each customer's March
billing statement. The contamination at WS4 was the subject of the first report.
62J20\9808 O30.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 8
EPA Region 10
AJso in response to the water quality concerns at WS4, in 1989 the City sponsored formation of
the Water Quality Advisory Committee, which includes medical and legal experts, members of the
community, state regulators, and representatives from the City's water department. The Advisory
Committee serves as a forum where the City disseminates technical information to the public and
receives input regarding the community's concerns: The Advisory Committee issues
recommendations to the City's Public Works Director and was instrumental in designing the
City's policy for notifying the public about water quality incidents.
4.2 EPA COMMUNITY RELATIONS EFFORTS
No formal Community Relations Plan has been developed for WS1. Most of EPA's public
information efforts have focused on WS4, with information regarding WS1 sometimes included in
Fact Sheets for WS4 distributed by EPA.
EPA issued a Fact Sheet in July 1992 entitled "Vancouver Water Station #4 Contamination
Superfund Site." This Fact Sheet contained a paragraph noting that EPA also planned to install
monitoring wells near WS1, and that the City was installing a treatment system at WS1 scheduled
to begin operation in 1993.
EPA issued a Fact Sheet dated February 1, 1993, that was devoted to the Community Relations
Plan for WS4 and did not mention WS 1. The Fact Sheet included a summary of concerns voiced
during EPA interviews with members of the community conducted on September 21 and 22,
1992. The comments summarized were either about WS4 or about general area-wide water
quality; none mentioned WS 1 specifically.
The September 6, 1994, Fact Sheet was entitled "Vancouver Water Stations #1 and #4
Contamination Sites." The discussion of WS1 noted that the air stripping system was removing
the contamination from the water at WS1 to below federal drinking water standards, and
announced that the site had been added to the NPL as of June 1994.
The most recent Fact Sheet was released June 18, 1998, and provided summaries of previous
activities at both WS1 and WS4. The Fact Sheet noted that the Proposed Plan for WSl was
expected to be issued in July 1998, with the Proposed Plan for WS4 following in early 1999.
The RI/FS report and Proposed Plan for WSl were released to the public in July 1998. These
two documents were made available to the public in the Administrative Record maintained at U.S.
EPA Region 10, 1200 Sixth Avenue, Seattle, Washington, and at the information repository
maintained at the Vancouver Public Library, Fort Vancouver Branch, 1007 E. Mill Plain
62320\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 9
EPA Region 10
Boulevard, Vancouver, Washington. The notice of availability of these two documents was
published in the Vancouver Columbian on July 22, 1998.
A public meeting for the proposed plan was not scheduled. A public comment period was held
from July 22, 1998, to August 21, 1998. Two coniments on the Proposed Plan were received
from the public. The community had an opportunity to request a public meeting during the public
comment period on the Proposed Plan, but no requests for a public meeting were received.
This decision document presents the selected remedial action for the WS1 site in Vancouver,
Washington, chosen in accordance with CERCLA, as amended by SARA, and, to the extent
practicable, the NCP. The decision for this site is based on the Administrative Record.
5.0 SCOPE AND ROLE OF RESPONSE ACTION
This site consists of one operable unit. The selected remedy is the final action at this site.
Several investigations spanning several years were previously conducted to identify the source of
PCE entering WS1, but neither a source nor a plume of PCE was ever identified. No additional
investigation into potential sources was conducted during the RI/FS because there were no areas
with sufficient potential as a source. No additional wells were installed to attempt to identify a
plume because (1) the concentrations of PCE in the wellfield were relatively low, (2) with no
suspected source areas to investigate, the locations of new wells would in effect be random, and
(3) there was a low probability that additional information would lead to a change in the operating
treatment system.
Because neither a source nor a plume of PCE entering the wellfield at WS1 has been identified,
the scope of the response action at WS 1 is limited to the following:
Ensuring that human health is protected by reducing the level of PCE in drinking
water produced from WS 1 to meet federal drinking water standards
Reducing the concentration of PCE in the groundwater at WS1 to below the MCL
ofS^g/L
Without a known or suspected source, no action can be taken to clean up the source of the TT
entering the wellfield. Without an identified plume of PCE, no action can be taken to treat
contaminated groundwater moving into the wellfield from off site. The response action is
62520v9S08.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 10
EPA Region 10
therefore limited to the groundwater at the wellfield and to drinking water produced by WS1 for
distribution to the public.
EPA's response action for WS1 is to select the continued treatment of drinking water produced
from WS1 by using the air stripping treatment system that is already in operation. Continued
operation of WS1 to provide drinking water will also serve as a treatment system for the
contaminated groundwater at the wellfield.
6.0 SUMMARY OF SITE CHARACTERISTICS
6.1 PHYSICAL CHARACTERISTICS
6.1.1 Surface Features
The Vancouver area is situated on a series of gentle terraces rising to the north from the Columbia
River. WS 1 is located near the edge of one of these terraces. Topography is flat in the northern
two-thirds of the site with a ridge running west-northwest to east-southeast in the southern third.
Vertical relief of this ridge is approximately 50 to 70 feet. Topography slopes gently to the south
from this ridge to the next terrace level.
Water Station 1 is located within the Waterworks City Park, which is landscaped with grass and
mature coniferous trees, as is the campus of Clark College, located approximately 1,500 feet to
the southwest. However, the vicinity also includes residential, light manufacturing, and
commercial businesses, resulting in large portions of paved or built-over areas. Paved areas are
typically equipped with stormwater drains, which are part of the city's stormwater system.
The site is located about 2 miles north of the Columbia River, on a terrace at an elevation of
approximately 160 to 230 feet above mean sea level (MSL). The site is generally flat in the
northern portion. A ridge trends northwest to southeast along the southern portion of the site
with a maximum south-to-north relief of approximately 70 feet. Most of the area is well drained
due to the underlying coarse alluvial deposits.
6.1.2 Geology
The geological setting of the Vancouver area consists of 2,000-foot thick Cenozoic-Age basaltic
basement rock overlain by Miocene to Pliocene Age sedimentary bedrock units (the Lower and
62J20\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 11
EPA Region 10
Upper Members of the Troutdale Formation), topped with Pleistocene to Holocene Age
unconsolidated alluvial sediments.
The sediments of the Upper Member of the Troutdale Formation contain a lower layer of coarse-
grained sandy gravel and an upper layer of cemented gravel. A period of erosion and weathering
followed deposition of the Troutdale Formation, resulting in a highly weathered zone at the top of
the Troutdale Formation and a thin soil horizon. The Pleistocene alluvium of the Orchards Gravel
overlies the Troutdale Formation. The Orchards Gravel is composed of coarse-grained sand and
gravel in the area of the Columbia River floodplain with finer-grained sands present as lenses
and/or stringers within the coarse-grained material in the terraced areas. The Orchards Gravel
contains variable amounts of silt in the area of WS1. The Orchards Gravel ranges from 75 feet
thick in the Columbia River floodplain to 120 feet thick at the top of the terrace.
The varying amounts of silt within the sand matrix at WS1 could result in decreased vertical and
horizontal permeability in local areas, which could also locally decrease "percolation" or vertical
migration rates of a contaminant. The boring log for MW1-1 identifies a silt layer with some sand
and trace clay from 80 to 82 feet bgs (99 to 97 feet above MSL). The boring log from MW1-2
identifies a silt with some sand from 66 to 70 feet bgs (110 to 106 feet above MSL). The boring
log from MW1-3 identifies silt with some clay tnterbedded with sand from 54 to 62 feet bgs (178
to 170 feet above MSL). The boring logs for MW1-4 and MW1-5 do not identify fine-grained
sediments in the explored column.
The occurrence of thin, fine-grained material at the WS1 site appears to either be laterally
discontinuous, or if continuous, sloping to the north. Regardless of the lateral continuity, it is
possible that localized pockets of pure PCE, referred to as dense nonaqueous phase liquid
(DNAPL), could exist in the fine-grained sediments. PCE concentrations in samples of these
sediments collected during the installation of MW1-1 were not high enough to suggest the
presence of DNAPL. (If DNAPL were present in the sediments, the concentrations of PCE
would probably be in the parts-per-million range, not in the parts-per-billion [ug/L] range
detected at MW1-1.) It is, however, possible that DNAPL is present in an unexplored portion of
the site or within the capture zone of WS1.
6.1.3 Hydrogeology
Groundwater in the Vancouver area is produced primarily from two formations, the Orchards
Gravel and the lower portion of the Upper Member of the Troutdale Formation. WS1 produces
groundwater from a gravel unit within the lower portion of the Upper Member of I lie Tronic!si:
Formation, which extends approximately 200 to 250 feet below ground surface.
62520V9808 030 wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 12
EPA Region 10
The hydraulic gradient is reported to be south-southwest toward the Columbia River in the
Orchards Gravel and Troutdale Formation. Specific capacities are reported to exceed 300 gallons
per minute per foot of drawdown, and the individual production well yields range from 1,000 to
3,400 gallons per minute.
Groundwater was reported at depths ranging from 175 to 228 feet below ground surface. The
apparent groundwater flow direction under static conditions is expected to be to the south or
southwest, but operation of the production wells at WS1 influences local groundwater flow
direction to the wellfield area. The estimated 30-year zone of capture for WS1 is approximately
10 square miles.
6.2 NATURE AND EXTENT OF CONTAMINATION
PCE is the primary chemical of concern, although trichloroethene (TCE), 1,1,1-trichloroethane
(TCA), and toluene have also been detected. Summaries of concentrations by medium are
presented in the following sections.
6.2.1 Soil-Gas
Soil-gas surveys were performed by both the City and EPA in an attempt to identify a source for
the PCE in groundwater. The data generally agree as to the distribution of PCE in soil-gas in the
WS1 area, with the highest concentrations in samples collected from near-surface soil (5 to
23 feet below ground surface) approximately 80 to 120 feet northwest of Production Well 1
(across Fourth Plain Boulevard from WS1). However, as discussed in Section 6.2.2, the detected
PCE soil-gas concentrations do not appear to be high enough to support the identification of a
contaminant source.
City of Vancouver Soil-Gas Survey Results
PCE was detected in 15 of the 19 soil-gas samples collected by the City, with concentrations
ranging from 0.003 //g/L-air to greater than 0.450 £ig/L-air. Four of the 19 soil-gas samples were
analyzed for TCE, with concentrations ranging from 0.013 to 0.060 /zg/L-air.
EPA Phase I Soil- Gas Survey Results
PCE, TCE, and TCA were detected during EPA's Phase I soil-gas survey. PCE was detected in
18 of 20 samples at concentrations ranging from 0.016 ^g/L-air to 11 jUg/L-air. TCE was
detected in 4 of 20 samples at concentrations ranging from 0.015 /^g/L-air to 0.11 /^g/L-air. TCA
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 13
EPA Region 10
was detected in 7 of 20 samples at concentrations ranging from 0.018 ^g/L-air to 2.5 /zg/L-air.
Toluene was detected in 19 of 20 samples, reported as an average concentration of 0.07 ^g/L-air.
EPA Phase II Soil-Gas Survey Results
PCE, TCE, TCA, and toluene were detected during EPA's Phase E soil-gas survey. PCE was
detected in 21 of 104 samples with an average reported concentration of 0.90 /ig/L-air and a
maximum concentration of 8 ^g/L-airrTCE was detected in 2 of 104 samples with an average
reported concentration of 0.033 /zg/L-air. TCA was detected in 8 of 104 samples with an average
reported concentration of 0.142 /ug/L-air. Toluene was reported in 27 of 104 samples with an
average reported concentration of 0.026 //g/L-air.
EPA soil gas survey results indicated that the highest TCE concentrations were located
approximately 115 feet north-northwest of the intersection of Fourth Plain Boulevard and the
Waterworks Park entrance. The highest TCA concentrations were located approximately
100 feet north-northwest of this same intersection. Sample depths ranged from 5 to 23 feet below
ground surface. :
6.2.2 Soil
Neither the measured nor the estimated concentrations of PCE in soil were indicative of a
significant source area as discussed in the following subsections.
Direct Measurements of PCE in Soil
Soil samples were collected during the installation of MW1-1 in the fall of 1992. Soil samples
collected from the MW1-1 boring were analyzed in the field using gas chromatography. PCE was
detected in soil samples collected from the MW1-1 boring at depths of 30 to 60 feet below
ground surface (bgs) and at approximately 80 feet bgs, with concentrations ranging from 0.0006
to 0.034 milligrams per kilogram (mg/kg). The highest PCE detection in soil (0.034 mg/kg) was
at a depth of 55 to 56.5 feet bgs. The soil samples collected from 60 to 61.5 feet bgs were
described in the boring log as wet, suggesting possible localized perched water conditions.
Toluene was detected at depths ranging from 20 to 116.5 feet bgs. However, toluene was
detected only in the field soil sample collected during well installation and was not detected in the
groundwater sample collected following well installation and development.
62320\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 14
EPA Region 10
Estimated Concentrations ofPCE in Soil
As noted in the preceding paragraph, the only data available on concentrations of PCE in soil in
the WS1 area come from one location, MW1-1. However, much more extensive information was
available in the form of soil-gas data. In an attempt to determine the location of a potential PCE
source area(s), an estimate of the maximum PCE concentration in soil was calculated from
soil-gas data. Estimated concentrations of PCE in the soil were extrapolated using a series of
assumptions regarding the characteristics of soil in the area and the highest documented soil-gas
PCE concentration of 11 /ug/L-air (measured by field analysis) as a conservative assumption. The
estimated concentration of PCE adsorbed to soil ranged from approximately 0.0062 mg/kg to
0.014 mg/kg. The estimated leachate concentration was thus approximately 3 //g/L. Dilution and
attenuation of this leachate during migration through approximately 175 feet of unsaturated soil,
mixing in groundwater, and groundwater transport to the wellfield, would result in much lower
concentrations of PCE than those measured at the wellfield. Because site-specific attenuation
data were not available for this area, the standard attenuation factor used by EPA for small sites is
applicable; this factor is 20. Using this standard (and most likely conservative) attenuation factor
would result in groundwater concentrations of PCE at the WS1 of approximately 0.2 ;/g/L.
6.2.3 Groundwater
PCE is the only VOC that has been detected in groundwater at concentrations greater than its
MCL at any production, monitoring, or private well in the vicinity of WS 1. Analytical results
from production well monitoring and groundwater monitoring show that PCE concentrations
appear to have decreased from a peak in the early 1990s. It should be noted, however, that PCE
is the only chemical that the City of Vancouver monitors for individual production wells at WS1.
Production well sampling results were the only data available to EPA on the condition of the
groundwater at WS 1. A full range of chemicals is analyzed for in samples collected from the
reservoir, but all samples collected from the reservoir since the air strippers were installed have
shown nondetectable levels of VOCs (as would be expected).
Screen intervals for production wells at WS1 range from 13 to 83 feet below mean sea level
(MSL) and screen intervals for monitoring wells MW1-1 through MW1-4 range from 5.5 to
59 feet below MSL.
Results of the various sampling programs are discussed in the following subsections.
62J20\9808.030.wpd
-------
VANCOUVER WATER STATION 1
FINAL RECORD OF DECISION
EPA Region 10
September 1998
Paee 15
Sampling of Production Wells
PCE has been detected in all 10 production wells. During the 6-year period summarized in
Table 6-1, average concentrations of PCE ranged from 1.1 /zg/L in Production Well 10 to
5.0 /zg/L in Production Well 5 and 5.3 /zg/L in Production Well 1. PCE concentrations in water
samples from the production wells appear to have decreased. The maximum detected PCE
concentration (30.0 /zg/L) was reported for a sample collected from Production Well 1, located
near the northern site boundary (Figure~2-2) on June 28, 1993.
Table 6-1
Summary of PCE Concentrations in Production Wells at WS1
(6-19-91 Through 6-1-98)
-" ~ ->~»
Weli;
ID
i
2
3
4
5
6
7
8
9
10
-1 Mm. '.:
FCE :
(UV/L)
30.0
5.7
15.0
12.0
18.0
9.6
9.3
5.9
5.8
5.4
~~i$« > - -v
r*,JHw "
-Dated)
06/28/93
12/30/91,
03/04/96
03/09/92,
04/13/92
04/13/92
04/13/92
03/06/95
04/06/98
03/06/95
08/02/93
04/06/98
Min.
,PCE':
(utfLY
0.2
0.4
0.4
0.4
0.4
0.4
0.4
0.2
0.0
0.0
=vfC\ ' t "- ~
Most Recent,
Mia, Date"
10/14/91
04/26/93
10/06/97
10/06/97
12/02/96
01/06/97
10/03/94
11/30/92
09/14/92
09/14/92
~~_~~~ - ."I" j£%
Numberof
Samples'
147
129
144
145
149
149
150
138
145
150
1.446
:Average =
"PCE-tn
(wrfL)'
5.3
2.1
4.8
4.5
5.0
2.6
2.3
2.1
1.5
1.1
3.2
-^z ,:.:,.- ,
5Stftridard::
DeviatKHi
3.7
1.0
3.0
2.4
2.8
1.8
1.2
1.2
1.1
0.7
2.7
~-2- *X1
Coefficient of
Variation
0.70
0.37
0.63
0.53
0.56
0.69
0.52
0.57
0.73
064
0.84
Values may be laboratory detection limits, indicating that PCE was not actually detected above these (presumed)
limits.
Notes:
Wells 1 through 10 (entire population)
Concentrations in micrograms per liter O^g/L) or parts per billion (ppb) equivalent
PCE - tetrachloroethene
62J20\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 16
EPA Region 10
Sampling of Private Wells
Ground water samples were collected from five private wells by the City of Vancouver. Two of
the five wells contained detectable concentrations of PCE, at concentrations of 0.9 ^g/L and
1.4 /zg/L, well below the MCL.
Sampling of Monitoring Wells During Installation
During installation of the five monitoring wells in the fall of 1992, groundwater samples were
collected and analyzed in the field. PCE was detected in the groundwater samples from only one
of the five monitoring wells, MW1-3, at depths of 260 feet bgs (3.0 //g/L) and 280 feet bgs
(0.9 A*g/L). Field analysis did not detect TCE, 1,1-dichloroethene, trans-1,2-dichloroethene,
benzene, chlorobenzene, or ethylbenzene at concentrations above detection limits at any of the
five monitoring wells. However, the field analysis did detect toluene (14.4 t^g/L) in one sample
collected from MW1-1 at a depth of 206.5 feet bgs.
Sampling of Monitoring Wells Following Installation
In addition to the field-analyzed samples collected during well installation, groundwater samples
have been collected from MW1-1 through MW1-5 on three different occasions: October 1992,
July 1997, and February 1998. As shown in Table 6-2, although PCE has been detected in all 10
of the production wells at WS1, it was detected in only 2 of the 5 monitoring wells (MW1-3 and
MW1-5), and only MW1-5 had PCE concentrations that exceeded the MCL (6.6 and 6.8 ^g/L).
MWI-5 is approximately one-third mile south of WS1 and is probably near the edge of the zone
of influence for WS1. TCE was reported at an estimated concentration below the detection limit.
Trichlorofluoromethane was the only other VOC positively detected in samples collected from the
monitoring wells, and it is probably a laboratory contaminant.
62J20\9808.030.wpd
-------
VANCOUVER WATER STATION 1
FINAL RECORD OF DECISION
EPA Region 10
September 1998
Page 17
Table 6-2
Analytical Results for PCE and TCE in Groundwater Samples
From MW1-1 Through MAV1-5
Weil ID
MW1-1
MW1-2
MW1-3
MWM
MW1-5
- - Sampling - £
~r- Date-- ---
10/92
7/97
3/98
10/92
7/97
3/98
10/92
7/97
3/98
10/92
7/97
3/98
10/92
7/97
3/98
*TJH^wJJ~J*iM« \**V Zzfes.' 1T»K;?
_"-3=i7 'UP/LA .".-is=<
~**-s£* "~\f*f,fM*f " * ""
0.9M
- 1U
1U
0.5M
1U
W/A
4.7
1.6
1.5
1U
1U
1U
6.8
6.6
3.5 _|
"Sr-*hsTCE
^- itee/L)
NA
1U
1U
NA
1U
W/A
NA
1U
1U
NA
1U
1U
NA
0.12J
1U
--- - Screen Interval - "--
-5.50 to -25.50 ft MSL
185.0 to 205.0 ft bgs
-38.70 to -58.70 ft MSL
2 15.0 to 235.0 ft bgs
W/A
-27.60 to -47.60 ft MSL
260.0 to 280.0 ft bgs
-28.20 to -48.20 ft MSL
250.0 to 270.0 ft bgs
-36. 10 to -56. 10 ft MSL
195.0 to 215.0 ft bgs '
Notes:
ft bgs - feet below ground surface
ft MSL - feet above mean sea level
J - estimated value
M - below detection limit
Mg/L - micrograms per liter or part per billion (ppb)
equivalent
NA - not analyzed or not reported
PCE - tetrachloroethene
TCE - trichloroethene
U - not detected above specified detection limit
W/A - well abandoned
7.0 SUMMARY OF SITE RISKS
Typically, a baseline risk assessment is conducted during the remedial investigation at an NPL.
site. A baseline risk assessment is an analysis of the potential adverse health effects caused by
hazardous substance release from a site in the absence of any actions to control or mitigate these
releases. WS1 differs from the typical NPL site in that remedial action (air stripping treatment of
drinking water produced from WS1) has already been implemented. Because of this, the human
health risk assessment (HHRA) for WS1 evaluates both an action alternative (treatment, of
62J20\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 18
EPA Region 10
by air stripping, the current situation) and a no-action alternative (a potential future scenario that
could occur if air stripping were to be discontinued). The HHRA is summarized in Section 7.1.
An ecological risk assessment is a process that evaluates the likelihood that adverse ecological
effects may occur or are occurring as a result of exposure to one or more stressors. At WS1, the
stressor consists of PCE in the groundwater, which occurs at a depth of about 200 feet below
ground surface. As discussed further in Section 7.2, no exposure pathway to PCE in groundwater
has been identified for ecological receptors.
7.1 HUMAN HEALTH RISK ASSESSMENT
An HHRA was performed to evaluate the risks to residents of Vancouver who use water
produced from WS 1 as their primary source of drinking water. The risk assessment consists of
four main components:
Identification of contaminants of potential concern (COPCs)
Exposure assessment
Toxicity assessment
Risk characterization
These components are summarized in Sections 7.1.1 through 7.1.4. The qualitative uncertainty
analysis is summarized in Section 7.1.5.
7.1.1 Identification of Contaminants of Potential Concern
In accordance with EPA Region 10 guidance, a risk-based screening approach was used to
identify contaminants of potential concern (COPCs) in drinking water at WS 1. The chemical
screening consisted of comparing concentrations of chemicals detected in groundwater at WS1 to
risk-based screening concentrations established by EPA. If the measured concentration of a
chemical at WS1 exceeded the risk-based concentration, the chemical was identified as a COPC.
Based on the screening procedure, the only COPC identified in untreated water produced from
WS 1 was PCE. No COPCs were identified in treated water.
7.1.2 Exposure Assessment
The exposure assessment identifies potential receptors and estimates the type and magnitude ^
exposures to the COPC (PCE) that was identified in Section 7.1.1. The results of the exposure
62520\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
.FINAL RECORD OF DECISION Page 19
EPA Region 10
assessment are then combined with the chemical-specific toxicity information (see Section 7.1.3)
to characterize potential risks (see Section 7.1.4).
The four steps in exposure assessment are characterization of the exposure setting and potential
receptors, identification of exposure pathways, development of exposure point concentrations,
and quantification of chemical intakes.
Characterization of Exposure Setting'and Receptors
Four groups of receptors were evaluated:
Public water supply users who are currently exposed to treated water
Public water supply users who could be exposed to untreated water in the future if
the air stripping treatment were to be discontinued or if private water supply wells
were to be used for drinking water
Site workers
Nearby residents and recreational visitors
Identification of Exposure Pathways
The primary medium through which exposure may occur is water. Potential exposure pathways
evaluated for WS1 are depicted in the human health conceptual site model shown in Figure 7-1.
Potential exposure pathways include ingestion of water, dermal contact with water, and inhalation
of PCE in air released during household use of water. Inhalation of PCE in fugitive air emissions
from the water treatment system was also evaluated.
Exposure via Treated Water. Exposure pathways for current public water supply users are
incomplete because no COPCs have been identified in treated water.
Exposure via Untreated Water. If water treatment were to be discontinued, or if private wells
near WS1 were to be used as a drinking water source, water users could be exposed to PCE in
drinking water. Potential exposure pathways for people using untreated water as a drinking water
source include ingestion of untreated water, inhalation of PCE in untreated water during
household use of water, and dermal contact with untreated water during bathing. Significant
dermal exposures to untreated water by site workers are not expected to occur. Water is
62520\9808.030.wpd
-------
Source
Release
Mechanisms
Secondary
Sources
Exposure Media
Exposure
Pathways
Receptors
Water
Supply
User with
Tf«atmen|
Water
Supply
Use» w/o
Tieatmem
Sue
Worker
Aiea
Resident/
Recreational
Visitor
Ingeslion
Inhalation
Dermal Contact
O
Q
O
O
O
O
Inhalation
O
O
O
i o I o i
-------
VANCOUVER WATER STATION 1 September J 998
FINAL RECORD OF DECISION Page 21
EPA Region 10
transported through the water station and treatment units via pipes, making direct contact with
untreated water by workers unlikely.
Exposure via PCE in Air. Potential exposures of nearby residents and site workers may occur
as a result of stack or fugitive emissions from the air strippers. According to the air permit issued
by the Southwest Air Pollution Control Authority in 1993, the combined air emissions of PCE
from the five air stripping columns will be controlled by^five granular activated carbon canisters,
and will not result in ambient air concentrations of PCE in excess of the applicable regulations.
The emissions from the carbon canisters are released through a stack at a height of at least 12 feet
above ground level. Therefore, although there will be some small release of PCE to the air,
potential exposures to site workers, nearby residents, or recreational visitors to Waterworks Park
are believed to be minimal.
Development of Exposure Point Concentrations
Exposure point concentrations are media-specific concentrations of a COPC that an individual
may plausibly come into contact with. Exposure point concentrations were developed for the
future residential scenario using PCE data collected between 1995 and 1997 from untreated water
from individual production wells at WS1. It is conservatively assumed that the chemical
concentrations remain constant over the assumed exposure period (i.e., 30 years).
EPA guidance states that "because groundwater is a very complex and dynamic medium with
characteristics that can change seasonally, it is likely that concentrations of a given contaminant in
each well will vary over time. Therefore, the concentration term is best described by an arithmetic
average [over time]..." Because of the uncertainty associated with estimating the true arithmetic
mean from a limited number of samples, a degree of conservatism is needed in calculating
exposure point concentrations. This conservatism is provided by using the 95 percent upper
confidence limit (UCL95) on the arithmetic mean, or the maximum detected value when the
variability in the sampling results in a UCL95 that exceeds the maximum detected value.
For this HHRA, the sources of VOC contamination have not been identified and limited data do
not allow a definition of a contaminated area within the capture zone of WS1. Therefore, the
arithmetic average concentration (as represented by the UCL95) of PCE in each production well
over time was used to characterize the range of potential future exposures to untreated water.
Although PCE concentrations in the production wells appeared to be increasing in the late 1980s
and early 1990s, concentrations have stabilized and have remained fairly constant or decreased
slightly since the mid-1990s. Therefore, data collected during the last 3 years (i.e., 1995 tlirougL
1997) were considered appropriate for use in this HHRA. This range of potential exposures
represented by the 10 production wells is believed to bound the actual exposures to users of the
62S:0'9g08.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 22
EPA Region 10
public water supply that would occur in the absence of treatment, because water from the
individual wells would be blended in the reservoir prior to distribution, as was done prior to
installation of the air strippers.
Quantification of Chemical Intakes
Chemical exposures, or intakes, were determined using exposure models that combine various
exposure parameters related to behavior and physiology, such as exposure frequency and body
weight, with exposure point concentrations. Reasonable maximum (or high end) exposures
(RMEs) were evaluated for this HHRA
The equations used to calculate intake from each exposure pathway are presented in the RI/FS
and are consistent with guidance from EPA Region 10. Exposures were calculated for adults
only. EPA default exposure parameters were used to quantify these models; sources for the
exposure parameters include EPA Region 10 supplemental guidance and EPA standard default
exposure factors. Exposure is averaged over a lifetime (70 years, or 25,550 days) for carcinogens
and over the exposure duration for noncarcinogens. A body weight of 70 kg was assumed for all
exposure pathways.
7.1.3 Toiicity Assessment
Carcinogenic Effects
PCE was found to produce liver cancer in male and female mice when administered orally by
gavage. Unpublished gavage studies in rats and mice performed by the National Toxicology
Program (NTP) showed hepatocellular carcinomas in mice and a slight, statistically insignificant
increase in a rare type of kidney tumor.
In evaluating cancer, the numeric descriptor of carcinogenic potency is termed a slope factor (SF).
The SF is defined as the UCL95 of the slope of the dose-response curve. The oral SF for PCE is
0.052 (mg/kg-day)'1; the inhalation SF is 0.00203 (mg/kg-day)'1. These slope factors are
provisional toxicity values from EPA's National Center for Environmental Assessment (NCEA).
Noncarcinogenic Effects
Renal toxicity and hepatotoxicity were noted following chronic inhalation exposure of rats to
PCE. During a subchronic inhalation study, exposure to PCE produced signs of central no vous
system depression. Oral exposure of mice to PCE in com oil resulted in depressed body weights
and liver toxicity.
62320\9808.030.wpd
-------
VANCOUVER WATER STATION 1 . September 1998
FINAL RECORD OF DECISION Page 23
EPA Region 10
For noncancer health effects, the toxicity values used in risk assessment are termed reference
doses (RfDs). These are route- and duration-specific estimates of the average daily intake that
can occur without appreciable risk of any adverse effect. The oral RfD for PCE is
0.01 mg/kg-day based on kidney toxicity. An uncertainty factor of 1,000 has been applied, and
the overall confidence in the oral RfD is medium. The oral RfD was obtained from EPA's
Integrated Risk Information System (IRIS) database. No inhalation RfD is available for PCE.
Dermal Toxicity Values
Calculation of risks from dermal exposures to groundwater requires dermal toxicity values.
Dermal toxicity values must be based on the absorbed dose (rather than the exposed or
administered dose), since dermal intakes are calculated as absorbed doses. Since EPA has not yet
established any dermal toxicity values, approximate toxicity values were derived by extrapolation
from oral toxicity values, assuming an oral absorption fraction of 1.
7.1.4 Risk Characterization
Risk characterization integrates the results of the exposure and toxicity assessments into a
quantitative description of potential cancer and noncancer risks. The method for risk
characterization used in the HHRA is consistent with EPA guidance.
The risk of cancer from exposure to a chemical is described in terms of the incremental probability
that an individual will develop cancer over his or her lifetime as a result of exposure to a potential
carcinogen. The resulting probabilities are expressed in numbers that indicate how many excess
cancer cases are likely for a specified population. For instance, an excess cancer risk of 1E-06
corresponds to one additional cancer case in a population of 1,000,000 people. Similarly, an
excess cancer risk of 1E-04 corresponds to one additional cancer case in a population of 10,000.
Excess cancer risks are summed across all COPCs and all exposure pathways that contribute to
exposure of an individual in a given population. Typically, remedial action is warranted when
total excess cancer risks to any population exceed EPA's acceptable risk range of 1E-06 to 1E-04
(40 CFR Part 300.430).
Cancer risks were calculated for current and future residents using WS1 as the primary drinking
water source. For current residents consuming treated water, no COPCs have been identified and
therefore no excess cancers are expected to occur. For hypothetical future residents consuming
untreated water (i.e., if treatment were to be discontinued), results are summarized in Table 7-1.
Due to the inherent uncertainty in cancer risk calculations, total cancer risk values are reporter1 *~
only one significant figure.
62J20\9808.030.»pd
-------
VANCOUVER WATER STATION 1
FINAL RECORD OF DECISION
EPA Region 10
September 1998
Page 24
Table 7-1
Summary of Cancer Risks
Associated With PCE in Untreated Water
'Production **
WeH
Well 1
Well 2
Well 3
Well 4
Well 5
Well 6
Well?
Well 8
Well 9
Well 10
; "v< ;"$>*,_#$?*-{ "*><> " Cancer Rifk \y-
-------
VANCOUVER WATER STATION 1
FINAL RECORD OF DECISION
EPA Region 10
September 1998
Page 25
in Table 7-2. Based on UCL95 exposure point concentrations of 1.0 to 5.7 y.g/L of PCE in the
production wells, the noncancer hazard to public water supply users ranges from an HI of 0.004
to 0.03. Since the total HI is less than 1, there is no appreciable risk that adverse noncancer
health effects will occur.
Table 7-2
Summary of Noncancer Hazard
Associated- With PCE in Untreated Water
<- -. ,.^.54-. -£*?,-. .,.«,,.. Wj
,, :-"&? ?£. -%-f:
..-,,, ^noausxaio.-^;^-
v. '^WeHID '<'7;-
. Welll
Well 2
Well 3
WelU
Well 5
Well 6
Well?
Well 8
Well 9
Well 10
.>/', :-»&. A-^r^iiH^^Ono^f^^f-^'-''"^7'^ ^
,-f , «v v S-J,'r,(&* s<^^"^^^^^^5J,lv^» , ^^ ''X'"''*' .V^**", v,'' ~ J r, ,f' i """ M *>
.- *''," .?*)&£'"-'"*'&
'" Injjestion r<^*~.
0.015
0.0068
0.0092
0.011
0.011
0.010
0.0065
0.0068
0.0035
0.0027
v *Xi^m^^ tt D ^ 1 8 TiOffi "$£>'£$*&
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
->frX-5-«Vx ~.v.4»w~sr*
n Dermal Contact «
0.0097
0.0043
0.0058
0.0068
0.0066
0.0063
0.0041
0.0043
0.0022
0.0017
.:X ,;.,'/,-'.. ->?, /;>'
'*$3i ' i X ~ £*'i>r~ >« ' .;'
1-,p, >>(ft.^.-'>«7,A -'V'
-Hazard Index "4
0.03
0.01
0.02
0.02
0.02
0.02
0.01
0.01
0.006
0.004
NA not applicable because no inhalation reference dose was available for PCE
7.1.5 Uncertainty Assessment
There are a number of factors that can introduce uncertainty into any exposure and risk estimate.
The key factors and assumptions that contribute to uncertainty in this risk assessment are
summarized below.
Water samples collected from the production wells were pulled from the turbine pumps and
therefore some VOCs may have volatilized during sample collection. EPA Superfund protocols
recommend sampling for VOCs under low-flow conditions to minimize loss of VOCs during
sampling. The effect of these sampling methods on concentrations of VOCs is not known;
however, they may result in an underestimate of VOC concentrations and the corresponding
human health risk.
62520 9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 26
EPA Region 10
Because reliable data on PCE concentrations in private wells were unavailable, untreated water
samples collected from the production wells at WS1 were assumed to be representative of
concentrations that would be found in hypothetical private water supply wells. However, because
the source (or sources) of PCE in the groundwater have not been defined, there is considerable
uncertainty associated with the potential PCE concentrations in off-site wells. Potential risks to
area residents who use private wells as a drinking water supply could be higher than those
presented in this HHRA.
The risk-based screening concentration (RBSC) comparison was designed to be conservative and
the elimination of chemicals is not likely to result in a significant underestimate of risk. The most
recent analytical results for a wide variety of analytes in untreated water are the contaminant
testing results for 1992, the year prior to installation of the air stripping towers. These data may
not reflect the current concentrations of organic and inorganic contaminants (other than PCE) in
untreated groundwater. To the extent that the 1992 data do not reflect current conditions (i.e., if
concentrations of contaminants other than PCE have increased), the COPC selection process may
have resulted in the elimination of chemicals that may currently be present at levels above the
RBSCs.
In some cases, analytical procedures were not sensitive enough to detect chemicals potentially
present at levels above RBSCs. For 1,1-dichloroethene and vinyl chloride, high sample
quantitation limits and their potential presence in the aquifer associated with WS1 may result in an
underestimate of risk.
The evaluation of human health risks used arithmetic average concentrations over a period of time
from 1995 through 1997. It is not known whether concentrations will decline over the long term
as natural attenuation processes degrade the COPCs, which would decrease risk, or whether input
from existing or potential future sources may result in an increase in concentrations of VOCs,
which would increase risk. Therefore, potential future risks may be over- or underestimated. The
magnitude of this potential over- or underestimate cannot be determined with available
information.
The daily intakes in this risk assessment were calculated using conservative exposure assumptions
(e.g., intake rate, exposure frequency, exposure duration). This may result in an overestimate of
risk.
Risks from dermal exposures were calculated based on dermal toxicity values extrapolated fioin
oral values using an absorption fraction of 1. Although organics are generally readily absorbed,
this assumption is associated with a small degree of uncertainty. Thus, actual risks may be slightly
underestimated.
62320\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 27
EPA Region 10
No EPA-approved cancer SFs exist for PCE. The oral and inhalation SFs used in this HHRA are
based on provisional values presented in NCEA memoranda, as presented in EPA Region 3
risk-based concentration tables. Therefore, there is a high degree of uncertainty associated with
the cancer toxicity of this compound, and the actual risks may be over- or underestimated.
*
Quantification of risk from exposure to a chemical cannot be accomplished in the absence of
reliable, appropriate toxicity values for all routes and exposure periods. PCE does not have an
inhalation RfD value. Thus no noncaneer health effects were calculated for inhalation of PCE.
Noncancer health effects from inhalation of PCE are likely to be underestimated. In summary,
estimates of exposure and risk are subject to a number of uncertainties that may lead to either an
overestimate or an underestimate of risk. In either case, however, the selected remedy will not
change.
7.2 ECOLOGICAL RISK EVALUATION
An ecological risk assessment is a process that evaluates the likelihood that adverse ecological .
effects may occur or are occurring as a result of exposure to one or more stressors. The EPA
framework consists of a three-step approach:
Problem formulation
Analysis
Risk characterization
Problem formulation is a formal process for generating and evaluating preliminary hypotheses
about why and how ecological effects may occur as a result of human activities. During problem
formulation, available information is collected about the sources of stressors, the characteristics of
the stressors, exposure to the stressors, the ecosystem potentially at risk, and ecological effects.
Assessment endpoints can then be identified, and a conceptual site model developed. During the
analysis phase, measures of exposure, effects, and ecosystem and receptor attributes are used to
evaluate questions and issues identified during problem formulation. During the risk
characterization phase, the results of the analysis phase are used to estimate risks to the
assessment endpoints.
The ecological evaluation performed for WS1 is qualitative in nature and does not extend beyond
the problem formulation phase. The stressor present at the site is PCE in the groundwater.
Groundwater occurs at a depth of about 200 feet below ground surface at the site. Most of WS 1
is located in a municipal park, and potential ecological receptors, including birds, small mamma!'
62520^808 030 wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 28
EPA Region 10
and invertebrates, may be present. However, no exposure pathways to contaminants in
groundwater have been identified for these receptors.
The aquifer that supplies raw water to WS1 (Orchards Gravel) is believed to discharge to the
Columbia River. Although the Columbia River sustains major fisheries, it transports vast
quantities of water; infiltration of groundwater from the Orchards Gravel would be unlikely to
result in a detectable impact on water quality.
Therefore, because no potentially complete and/or significant exposure pathways exist at WS1,
the potential ecological risk is considered minimal.
8.0 REMEDIAL ACTION OBJECTIVES
8.1 NEED FOR REMEDIAL ACTION
Even though the risks presented in the baseline risk assessment are within the NCP acceptable risk
range, it is necessary to take .an action at WS1 because groundwater has been shown to have
persistent concentrations of PCE above the MCL. EPA's 1991 guidance (Role of the Baseline
Risk Assessment in Super/and Remedy Selection Decisions) states that exceedances of the MCL
can trigger the need for action. In addition, the NCP requires that MCLs must be met in
groundwater, not just at the tap.
There are many uncertainties associated with this risk assessment. Even so, the fact that
groundwater at WS 1 exceeds MCLs from time to time is sufficient to require remedial action.
Actual or threatened releases of hazardous substances from WS 1, if not addressed by
implementing the response action selected in this ROD, may present imminent and substantial
danger to public health.
8.2 NO IDENTIFIED SOURCE
Although several investigations have been conducted, neither a source nor a plume of PCE
entering the wellfield has ever been identified. Soil-gas surveys conducted to the north of the
wellfield (in the immediate vicinity of MW1-1) detected the presence of PCE, TCE, TCA, air-
toluene. The concentrations of PCE detected in the area, however, were not high enough to
indicate a source of PCE that could be responsible for the contamination at the wellfield.
62320\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 29
EPA Region 10
Monitoring wells at and immediately adjacent to the wellfield have not shown concentrations of
PCE above the MCL.
8.2.1 Potential Sources of Contamination
Investigations have failed to identify a suspected source that could be responsible for the PCE
contamination measured in the wellfield. Historically, however, there were a number of dry
cleaners, auto repair shops, and othercommercial operations that may have used PCE in the area
near WS1, particularly during and following World War n. With a 30-year zone of capture
estimated at approximately 10 square miles, and a 50-year zone of capture even larger in size,
there are a large number of possible sources of a release of PCE. Because PCE is so persistent in
the subsurface environment and can travel large distances, a release (or releases) from 50 years
ago could be responsible for the contamination measured today. WS1 has been operating for
decades, and all groundwater within the wellfield's zone of capture will eventually be pulled into
the production wells.
Practices of solvent management in the past were considerably more casual than those of today.
Strict environmental laws and regulations have greatly reduced the release of chemicals such as
PCE to the environment. The results of past practices, however, can result in significant
environmental problems. The contamination at WS1 is very likely the result of past practices;
there is no evidence of a recent or continuing release.
Two scenarios could account for the PCE at WS1: (1) a single, relatively large release, perhaps
several decades ago, and (2) a number of smaller, separate releases from separate sources such as
dry cleaners. There is no known evidence of a single, large release in the vicinity of WSl, so the
second scenario is the most probable explanation for PCE contamination at WS 1. A contributing
factor may also be the fact that runoff captured in stormdrains is disposed of through dry wells
throughout the city of Vancouver, including the area around WSl. Any solvent allowed to drain
to a parking lot, street, or other paved area could eventually work its way into the groundwater.
Over decades, particularly with a large number of dry cleaners in the vicinity, this could lead to
the PCE contamination present in the groundwater at WSl.
Whatever the source and history of the release of PCE that is now contaminating WSl, it is
certain that the PCE was released at the surface and was transported to the groundwater as a
liquid or as a vapor. Calculations performed during the RI/FS process showed that it was
extremely unlikely that measured PCE as a vapor in the soil column would produce the
concentrations detected in groundwater at WSl. So it is reasonable to conclude that the PCE in
the groundwater was transported as either an aqueous solution (with a maximum concentration of
62520\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 30
EPA Region 10
1,100 mg/L), or as a dense, nonaqueous phase liquid (DNAPL), either as pure PCE or in a
solution of other oils and solvents.
8.2.2 Transport of PCE to Water Station 1
The majority of data available for this site are the water samples collected every week (or month)
from each of the 10 production wells. These samples are analyzed for PCE only. Since
monitoring began in June 1991, there have been approximately 80 weekly or monthly sampling
events, with a sample collected from most wells during each event. Approximately 1,500 -
production well samples from WSl have been analyzed for PCE since June 1991.
PCE has been detected in all 10 of the production wells at WSl. Within the wellfield, the area
with the highest concentration of PCE varies over time, although the well with the highest
concentration of PCE for any given sampling event is typically either at the north end of the site
or the south end. The maximum PCE concentration among the production wells for each weekly
or monthly sampling event has been routinely greater than the MCL. Approximately 50 percent
of these maximum PCE concentrations for a given week or month have occurred in Production
Well 1 at the north edge of the wellfield. The second highest percentage of period maximums is
in Production Well 5 (with slightly less than 20 percent) located at the southeast corner of the
wellfield. The remaining eight wells have each had the maximum weekly or monthly
concentration roughly 5 percent of the time or less.
Although PCE has been routinely measured in the wellfield, it has been detected in only one of the
four monitoring wells that roughly flank the wellfieldMW1-3, which is located in the southeast
comer near Production Wells 4, 5, and 6. (Monitoring well data are, however, quite limited; none
of the wells has been sampled more than three times.) The other three monitoring wells, located
to the north, west, and east of the site, have never had a detected concentration of PCE. The
concentrations of PCE in samples collected from MW1-3, all of which were below the MCL,
seem to correlate reasonably well with the concentrations in the three nearby production wells.
A fifth monitoring well, MW1-5, located approximately one-third mile to the south
(downgradient) of the wellfield, has had PCE detected in each of the three samples collected from
the well; only one sample, collected in 1992, exceeded the MCL. MW1-5 may be near the edge
of the capture zone for WSl.
The data from the production wells could indicate that PCE is entering the wellfield from separate
locations, one from the north and one from the south. There is, however, no indication of a
definable plume (or plumes) of PCE entering the wellfield. At the north end of the wellfield, for
example, monitoring well MW1-1 (located across the street from the wellfield and within about
6252Cm08.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 31
EPA Region 10
200 feet of Production Well 1) has never had a detectable concentration of PCE. Production
Well 7, located approximately 100 feet to the southeast of Production Well 1, has typically had
lower concentrations than Production Well 1, although the most recent sampling data show a
higher concentration in Production Well 7. At the southern end of the wellfield, Production
Wells 4 and 6, located close to Production Well 5, have had consistently and significantly lower
concentrations of PCE than Production Well 5, while monitoring well MW1-3, located in the
same general area, has never had a detection of PCE above the MCL.
The variation in maximum levels within the wellfield, together with the fact that none of the
monitoring wells in the vicinity of WS1 has ever had a detected concentration of PCE above the
MCL, indicate that there is not a definable plume of PCE entering the wellfield. The most
plausible explanation of PCE transport to the wellfield is that PCE is being pulled into the
production wells through one or more narrow "channels" of contamination originating outside the
wellfield. This explanation is consistent with experience at other sites with groundwater
contaminated by PCE and similar chemicals. Given a high probability that the PCE is entering the
wellfield through these narrow channels, it is possible that a much more extensive array of
monitoring wells would fail to identify a pathway of PCE into the wellfield. .
8.2.3 Representativeness of Production Well PCE Concentrations
During the remedial investigation, the issue arose concerning the representativeness of PCE
concentrations from samples pulled directly from the production wells. Typically, environmental
samples for VOCs are taken using low-flow techniques to minimize the volatilization of chemicals
being analyzed for. It is possible that the high flow rate in a production well reduces the
concentration of PCE in a sample taken from the well; that is, a sample taken from the same well
at the same time using a low-flow technique would show a higher concentration of PCE. Because
low-flow samples cannot be taken from any of the production wells, it is not possible to directly
compare the results of high-flow and low-flow sampling from the same well. The comparison of
samples taken at MW1-3 with samples collected at approximately the same time from nearby
production wejls could be a reasonable indication that PCE concentrations reported in production
well samples are not significantly under-reported.
8.2.4 Conclusion
In conclusion, the PCE contamination at WS1 is persistent and present at levels that require
continuing treatment to protect human health. (There are no complete pathways for ecological
receptors.) There is no suspected PCE source, and further investigation to identify sources would
be unlikely to affect the current status of continuing operation of the air stripping system.
Additional investigation into possible sources or channels into the wellfield would be very
62520\9808.030.upd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 32
EPA Region 10
expensive but would not necessarily identify either a source or a channel. Even if a source or a
channel were identified, it is likely that no additional action would be taken, given that
groundwater is 200 feet below ground surface. It is therefore appropriate to continue treating the
water from WS1, both to remove PCE from the drinking water supply and to reduce the
concentration of PCE in the groundwater. But further action to find either a source or a channel
of PCE entering the wellfield would not be cost-effective and would not further reduce risk.
8.3 REMEDIAL ACTION OBJECTIVES
Actual or threatened releases from the site, if not addressed by implementing the selected
response action, may present an imminent and substantial endangerment to human health and the
environment.
The primary remedial action objective for WS1 is to
Protect human health by reducing concentrations of PCE and other VOCs in
drinking water produced from WS1 to below the MCL specified in regulations
promulgated under the federal Safe Drinking Water Act (SDWA) and in the state
drinking water regulations
An additional remedial action objective for WS1 is to
Protect human health by reducing concentrations of PCE and other VOCs in
groundwater at WS1 to below the Method A cleanup level specified in the
Washington State Model Toxics Control Act (MTCA) regulations and below the
federal and state drinking water standards (MCLs)
The federal MCL and the state cleanup levels are both 5.0 /^g/L.
9.0 DESCRIPTION OF ALTERNATIVES
At WS 1 a treatment system consistent with EPA's presumptive remedy for VOCs in groundwater
(OSWER Directive 9283.1-12, October 1996) has been constructed and is operating effectively
Locating and removing the source of contamination is not feasible. Accordingly, the feaiitil.,.y
study was limited to evaluation of the operating creatment system alternative and the no-action
62320\5808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION ' Page 33
EPA Region 10
alternative. Evaluation of a no-action alternative is required under CERCLA to establish a
baseline for comparison.
As discussed in Section 8, the two remedial action objectives for WS1 are to treat the water to
achieve the MCL for PCE and other volatile compounds both at the tap and in groundwater.
9.1 THE OPERATING TREATMENT SYSTEM ALTERNATIVE
The operating treatment is air stripping. Air stripping is a treatment technology in which the
water to be treated trickles down through a tower in a "packed column" that breaks up the flow
of water to create as much surface area as possible, as illustrated in the drawing of a typical
packed tower configuration (Figure 9-1). Large volumes of air are then forced upward through
the water, transferring the volatile contaminants from the surface of the water to the air through
the process of evaporation. The air to which the contaminants have been transferred is in turn
treated by being forced through carbon filters, which adsorb the contaminants. The. filters are
then regenerated or treated and disposed of as a hazardous waste. This alternative includes
monitoring both the untreated and the treated water to ensure cleanup standards are met.
The air stripping system at WS1 consists of five packed towers, and has been operating since
1993. Use of air stripping has reduced concentrations of PCE (and other VOCs that may be
present) in treated water to below the level of detection.
9.2 THE NO-ACTION ALTERNATIVE
Under the no-action alternative, there would be no treatment of water to remove PCE. Although.
blending the output from all wells could reduce the PCE concentration to below the MCL, it is
likely that areas of the aquifer under WS1 would contain groundwater with PCE at concentrations
greater than the MCL. On-going monitoring of the water would continue under the no-action
alternative.
It should be noted, however, that the City of Vancouver has no plans to discontinue treatment and
would only do so if further investigations were conducted that demonstrate that no other VOCs
are present in the groundwater and that PCE concentrations in groundwater have fallen to below
the MCL.
62320\9808.030.wpd
-------
Air Out
Untreated
Water In
Water Distributor
Packing Restrainer
Random Packing
Water Redistributes
Packing Support
Air In
. Treated
Water Out
Figure 9-1
Typical Air Stripper
EPA Region 10
Vancouver Water Station
ROD
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 35
EPA Region 10
10.0 COMPARATIVE ANALYSIS OF ALTERNATIVES
EPA has established nine criteria for the evaluation of remedial alternatives:
1. Overall protection of human health and the environment
2. Compliance with ARARs
3. Long-term effectiveness and permanence
4. Reduction of toxicity, mobility, and volume through treatment
5. Short-term effectiveness
6. Implementability
7. Cost of implementation
8. State acceptance
9. Community acceptance
The following sections summarize the detailed evaluation of alternatives in regard to these nine
criteria. For the WS1 site, the evaluation of alternatives is limited to the operating treatment
system alternative and the no-action alternative.
10.1 OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
The operating treatment, air stripping, has been proven to be effective in removing VOCs from
water, based on operational data at this and other sites. It therefore meets the threshold criterion
of protecting human health. (There is minimal risk to the environment from this site because there
is no potentially complete and/or significant exposure pathway to untreated water for ecological
receptors.) If compared against other removal technologies or measures, air stripping would be
rated excellent for protecting human health.
The no-action alternative might not be protective of current human health because routine
monitoring of untreated water has shown occasional concentrations of PCE above the MCL.
Furthermore, because the samples taken from untreated water were analyzed only for PCE, it is
possible that other VOCs are present in the groundwater, which would increase risk. Given this
uncertainty, the no-action alternative may not be adequately protective of human health. The
no-action alternative will not be protective in the future because there would be no effort to
remove the contaminated groundwater; private wells may therefore be more exposed to risk.
62520\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 36
EPA Region 10
10.2 COMPLIANCE WITH ARARS
This criterion states that remedial alternatives will meet all applicable or relevant and appropriate
requirements (ARARs) of other federal and state environmental and public health laws or provide
justification for invoking a waiver. There are three'types of ARARs: chemical-specific, location-
specific, and action-specific.
The chemical-specific ARARs for this site are the following:
Federal and state Safe Drinking Water Act MCL of 5.0 //g/L
Washington State Model Toxics Control Act (MTCA) Method A level for PCE of
S.OyUg/L
The operating air stripping system as installed is compliant with chemical-specific, location-
specific, and action-specific ARARs. Moreover, if evaluated against other technologies or
remedial measures, air stripping would be rated excellent for compliance with state and federal .
ARARs.
Treatment or disposal of spent carbon from the strippers, if the spent carbon is determined to be
dangerous waste, must be compliant with Resource Conservation and Recovery Act (RCRA)
Subtitle C and Washington State dangerous waste regulations.
The no-action alternative might not be compliant with ARARs because concentrations in samples
of untreated water have occasionally exceeded the MCL. Under both the NCP and MTCA, the
. concentrations noted above must be met both at the tap and throughout the groundwater.
10.3 LONG-TERM EFFECTIVENESS AND PERMANENCE
Remedial alternatives are typically assessed for long-term effectiveness and permanence and the
degree of certainty that the alternative will prove successful in overall protection of human health
and the environment.
The operating treatment system, with continued operation and maintenance, is effective in
removing PCE (and other VOCs that may be present) from water. This treatment is permanent
and achieves a high degree of certainty of success.
62S20i9gOg.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OFDECISION Page 37
EPA Region 10
The no-action alternative would rate relatively low for long-term effectiveness and permanence
because there would be no removal of contaminants from water.
10.4 REDUCTION OF TOXICTTY, MOBILITY, OR VOLUME THROUGH
TREATMENT
This criterion assesses the degree to which the alternatives use active treatment to reduce toxicity,
mobility, and volume of the principal threats posed to the site and local environment. The
operating treatment system is very effective at removing VOCs from water, and therefore reduces
the toxicity and volume through treatment. The treatment is irreversible and leaves no detectable
concentrations of VOCs.
The no-action alternative would rely on natural degradation processes to reduce the toxicity,
mobility, and volume of PCE. These degradation processes are complicated, and have not been
examined in sufficient detail at this site. As such, the no-action alternative would rate very low
for this criterion.
10.5 SHORT-TERM EFFECTIVENESS
The alternatives were evaluated in terms of their effectiveness in protecting human health and the
environment during construction and implementation of the remedy and until the response
objectives have been met.
The operating treatment system has already been installed, so there are no short-term
effectiveness considerations for this site. Had the system been evaluated under this criterion
before a decision was made, however, air stripping would have rated highly effective because the
technology is well established and has proven to have relatively few short-term risks or potential
environmental impacts. The proven nature of the technology also means that a construction
schedule would have relatively few uncertainties.
r »
The no-action alternative would probably rate average for short-term effectiveness. Although
there are no impacts or risks for implementation of the no-action alternative, the time until
protection is achieved would be very long.
62520\9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 3 8
EPA Region 10
10.6 IMPLEMENTABELITY
The technical and administrative feasibility of the alternatives was evaluated.
The operating treatment system has a well-established history as an effective means of treating
water contaminated with VOCs. Air stripping systems are relatively simple to design and
straightforward to maintain. Start-up and shut-down can be accomplished quickly, and the
modular design makes air stripping easy to construct. Air stripping would rate high for
implementability in any comparison with other alternatives for water treatment.
The no-action alternative would be easily implementable, so it would also rate high for this
criterion.
10.7 COST OF IMPLEMENTATION
According to the City of Vancouver, the air stripping system at WS1 cost approximately
$4 million to design and build. Operating costs are estimated to be approximately $60,000 per
year, not including depreciation. Air stripping systems typically rate well in comparison to other,
equally effective treatment alternatives such as activated carbon or ultraviolet treatment of the
water. Because how long the system will be needed is unknown, operating costs (and possibly
replacement costs for a new system) could lead to a lower rating of air stripping for this criterion.
The no-action alternative would rate high for cost of implementation because there is no cost for
the no-action alternative.
10.8 STATE ACCEPTANCE
This criterion was evaluated following the receipt of state agency and public comments on the
RI/FS report and the Proposed Plan.
The Washington State Department of Ecology has reviewed the operating system alternative and
has accepted the remedy.
62320V9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 39
EPA Region 10
10.9 COMMUNITY ACCEPTANCE
The community was given the opportunity to review the Proposed Plan and to request a public
meeting if so desired. Two written comments were received. There was no request for a public
meeting and there were no objections to EPA's Proposed Plan.
11.0 THE SELECTED REMEDY
The selected remedy for cleanup of both groundwater and drinking water produced from WS1 is
air stripping. This remedial approach is consistent with EPA's presumptive remedy for
contaminated groundwater. It is protective of human health and the environment and provides
the best overall effectiveness proportional to its costs; the remedial approach includes treatment as
a principle element. The selected remedy also includes monitoring to evaluate system
effectiveness at removing PCE from both groundwater and drinking water produced from WS1.
11.1 AIR STRIPPING
Air stripping is a treatment technology in which the water to be treated trickles down through a
tower in a "packed column" that breaks up the flow of water to create as much surface area as
possible (Figure 9-1). Large volumes of air are then forced upward through the water,
transferring the volatile contaminants from the surface of the water to the air through the process
of evaporation.
The air to which the contaminants have been transferred is then treated by forcing it through
carbon filters, which adsorb the contaminants. The filters are then regenerated or treated and
disposed of as a hazardous waste.
The air stripping system at WS1 consists of five packed column towers, and has been operating
since 1993. Use of air stripping has reduced concentrations of PCE in production water to below
the level of detection.
The air stripping system is, and will continue to be, operated by the City of Vancouver. All
drinking water produced by WS 1 will be treated by the air stripping system until the City, the
Washington State Department of Ecology, and EPA agree that the remedial action objectives
have been met and the treatment can be terminated.
62520\9808.030.wpd
-------
VANCOUVER WATER STATION 1 ' September 1998
FINAL RECORD OF DECISION Page 40
EPA Region 10
Groundwater will be pumped from WS1 at a rate that varies between 8 and 19 million gallons per
day, depending on the time of year and customer demand. All water pumped by WS1 will be
treated and distributed to customers as drinking water. Estimated costs for this remedy are:
Capital costs: $4,000,000 *
Operating and Maintenance costs: $60,000 per year (includes monitoring but not depreciation)
11.2 GROUNDWATER CLEANUP
By extracting and treating large volumes of groundwater for drinking water, WS1 acts as a very
large pump-and-treat system for removing contaminants from the aquifer near WS 1. The capture
zone for WS 1 is estimated to be approximately 10 square miles over a 30-year period of time;
any contamination within this zone will eventually be pulled into the wellfield at WS 1. Although
the large capture zone has made it impractical to try to identify a source of the PCE, the high
pumping rates for the production wells provide an effective means of reducing the concentration
of PCE in the groundwater near WS1. Eventually, the extraction of groundwater will1 flush out
residual contaminants in the wellfield, although the time to achieve the remedial action objectives
is not known.
11.3 GROUNDWATER MONITORING
Periodic monitoring of the groundwater will be performed by both the City of Vancouver and
EPA to evaluate the effectiveness of and the need for continued operation of the treatment system
at \VS 1. Groundwater monitoring will consist of sampling production wells and monitoring wells
for PCE and other volatile organic compounds. The City of Vancouver will continue to monitor
the water at WS 1 and will take at least one sample each year from each operating production
well EPA will continue to review the City's data and will periodically, but no less often than
every 5 years, sample the available monitoring wells near WS 1.
The results of groundwater monitoring will be evaluated annually and at the 5-year review for
WS 1. Decisions on whether to continue and/or modify the monitoring program will be made by
EPA in conjunction with the City of Vancouver and the Washington Department of Ecology.
62.<:0 9808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 41
EPA Region 10
12.0 STATUTORY DETERMINATIONS
Under CERCLA Section 121, EPA must select remedies that are protective of human health and
the environment, comply with applicable or relevant and appropriate requirements (unless a
statutory waiver is justified), are cost-effective, and use permanent solutions and alternative
treatment technologies or resource recovery technologies to the maximum extent practicable. In
addition, CERCLA includes a preference for remedies that employ treatment that permanently and
significantly reduces the volume, toxicity, or mobility of hazardous wastes as their principal
element. The following sections discuss how the selected remedy meets these statutory
requirements.
12.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
The selected remedy protects human health through treatment of drinking water produced from
WS1 as well as groundwater by using air stripping to reduce PCE concentrations. The
contamination of groundwater at WS1 with PCE does not pose a threat to the environment
because the groundwater is 200 feet below ground surface.
Treatment of water produced from WS1 by air stripping reduces PCE concentrations to below
detectable levels and therefore there were no chemicals of potential concern identified in treated
water. There are no excess cancer or noncancer risks associated with ingestion, inhalation, or
dermal contact with chemicals of concern in treated water because no such chemicals were
identified.
Air emissions for the treatment system are in compliance with the permit issued by the Southwest
Air Pollution Control Authority.
12.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS (ARARS) AND OTHER CRITERIA AND GUIDANCE
12.2.1 ARARs
The selected remedy, treatment of drinking water produced from WS 1 by air stripping, will
comply with all applicable or relevant and appropriate requirements (ARARs) that have been
identified. The ARARs are presented below.
6252
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 42
EPA Region 10
National Primary Drinking Water Regulations (40 CFR Parts 141.50 and
141.60) and Washington State Maximum Contaminant Levels (MCLs)
(WAC Chapter 246-290-330). These regulations are applicable to water at the
tap. The federal MCL is relevant and appropriate to the groundwater of this
drinking water aquifer.
Washington State Model Toxics Control Act Geanup Regulations (WAC
Chapter 173-340-720). The groundwater cleanup levels established in the MTCA
cleanup regulations are applicable to the groundwater at this site.
RCRA Regulations (40 CFR Part 261) and Washington Dangerous Waste
Regulations (WAC Chapter 173-303). The City of Vancouver has designated
the spent activated carbon units from the air strippers as dangerous waste. The
units are sent off site for regeneration or disposal as dangerous waste, and as such
the requirements for manifesting and transport as a dangerous waste and treatment
or disposal at a permitted treatment, storage, or disposal RCRA Subtitle C facility
are applicable.
U.S. Department of Transportation (49 CFR Parts 171 through 180) and
Washington State Transportation of Hazardous Waste Materials (WAC
Chapter 446-50). If the spent activated carbon units contain hazardous waste,
these transportation requirements would be applicable.
Washington Minimum Functional Standards for Solid Waste Handling
(WAC Chapter 173-304); Washington Criteria for Municipal Solid Waste
Landfill (WAC Chapter 173-351); County Health District regulations. If
carbon filters are NOT dangerous waste then they will be disposed of off site as
solid waste under the applicable regulations.
General Regulations for Air Pollution Sources (Section 400), Southwest Air
Pollution Control Authority. The City of Vancouver submitted Notice of
Construction CL-948 to SWAPCA for installation of carbon filters to capture
volatile emissions from the air strippers. On October 21, 1993, the City was
granted Order of Approval SWAPCA 93-1499 to operate the air pollution control
equipment. Therefore, the requirements of the General Regulations and the Order
of Approval are applicable to the operation of the air strippers. Independent of
CERCLA, the requirements of this permit (Order of Approval) are the ai) >y i!ut;o
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION Page 43
EPA Region 10
12.2.2 Other Criteria, Advisories, or Guidance To Be Considered (TBCs) for This
Remedial Action
If the spent activated carbon used in treating the air stream at the air stripping system is disposed
or treated off site, the National Contingency Plan off-site disposal rule (58 FR 49200,
September 22, 1993) must be followed.
12.3 COST-EFFECTIVENESS
EPA believes this remedy eliminates the risks to human health. The system was designed and
installed in 1993 at an estimated cost of $4 million and has been operating successfully since then
at an estimated cost of approximately $60,000 a year for operation and maintenance and
monitoring but not including depreciation. Therefore the selected remedy provides an overall
effectiveness proportionate to its costs, such that it represents a reasonable value for the money.
The selected remedy ensures a high degree of certainty that the remedy will be effective in the
long term because of the significant reduction of the contamination in the water that has been
achieved to date through use of the existing air stripping system. No other treatment options
were evaluated because the existing system was already in operation when the site was listed on
the NPL and the technology has proven to be effective for removal of VOCs from water.
However, the cost for installing and operating an air stripping system compares well to other,
equally effective treatment alternatives such as activated carbon or ultraviolet treatment.
12.4 USE OF PERMANENT SOLUTIONS AND ALTERNATIVE TREATMENT
TECHNOLOGIES (OR RESOURCE RECOVERY TECHNOLOGIES) TO THE
MAXIMUM EXTENT PRACTICABLE
The selected remedy represents the maximum extent to which permanent solutions and treatment
technologies can be used in a cost-effective manner for final source control at WS1. No source
for the PCE in groundwater at WS1 has been identified within WS1, and numerous investigations
have failed to determine an off-site source or sources of the PCE in the groundwater at WS 1.
Therefore a remedy that is limited to treatment of the drinking water produced from WS1 has
been determined to represent the maximum extent to which permanent solutions and treatment
technologies can be used in a cost-effective manner.
Because air stripping was already in operation when WS 1 was listed on the NPL, it was the only
remedy evaluated. However, treatment of the water using air stripping has been proven to be
6252(T$808.030.wpd
-------
VANCOUVER WATER STATION 1 September 1998
FINAL RECORD OF DECISION . Page 44
EPA Region 10
protective of human health, and it complies with ARARs. EPA and the State of Washington have
determined that air stripping provides the best balance of trade-offs in terms of long-term
effectiveness and permanence; reduction in toxicity, mobility, or volume through treatment; short-
term effectiveness; implementability; and cost; while also considering the statutory preference for
treatment as a principal element and considering state and community acceptance.
Air stripping, the selected remedy, treats the principal threat posed by exposure to drinking water
produced from WS1 by reducing the concentration of PCE in treated water to below detectable
levels. This remedy provides a proven technology for removal of PCE from water and is cost-
effective. The selection of air stripping treatment of the contaminated water is consistent with
program expectations that indicate that contamination in water used for public drinking water
supply is a priority for treatment. The selection of air stripping treatment as EPA's remedy
ensures long-term effectiveness by requiring that the treatment system remain in operation as long
as necessary to reduce PCE concentrations in groundwater around WSl to less than 5.0 //g/L.
12.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT
Treatment by air stripping addresses the principal threat posed by drinking water produced from
WS1 through the use of a proven treatment technology. By using treatment as the sole remedy,
the statutory preference for remedies that employ treatment as a principal element is satisfied.
13.0 DOCUMENTATION OF SIGNIFICANT CHANGES
The Proposed Plan, released for public comment in July 1998, discussed remedial action
alternatives for WSl and identified air stripping as EPA's preferred alternative. No public
meeting was scheduled because no new alternatives were presented in the Proposed Plan. The
public comment period was July 22, 1998, to August 21, 1998. Two written public comments
were received.
EPA reviewed the written comments submitted during the comment period. Upon review of the
comments, it was determined that no significant changes to the remedy for WSl, as it was
originally identified in the Proposed Plan, were necessary to satisfy public concerns.
62520\9808.030 wpd
-------
APPENDIX A
Responsiveness Summary
-------
VANCOUVER WATER STATION 1 Appendix A
FINAL RECORD OF DECISION September 1998
EPA Region 10 Page A-l
APPENDIX A
Responsiveness Summary
This responsiveness summary addresses public comments on the Proposed Plan for remedial
action at Water Station 1 (WS1) at Vancouver, Washington.
The RI/FS report and Proposed Plan were released for public comment in July 1998. The two
documents were made available to the public in the Administrative Record maintained at U.S.
EPA Region 10, 1200 Sixth Avenue, Seattle, Washington, and at the information repository
maintained at the Vancouver Public Library, Fort Vancouver Branch, 1007 E. Mill Plain
Boulevard, Vancouver, Washington. The notice of availability of these two documents was
published in the Vancouver Columbian on July 22, 1998.
The public comment period was held from July 22, 1998, to August 21, 1998. Two written
comments were received.
No public meeting was scheduled. The public had an opportunity to request a public meeting.
No requests for a public meeting were received.
Comment 1: The commenter felt that the City of Vancouver should not limit its investigation of
potential sources of tetrachloroethene (PCE) to past uses by dry cleaners but should investigate
current use by plastics companies in the vicinity. Several potential sources were named
Response: The comment was more appropriate to Water Station 4, and EPA will be following
up on the information provided by the commenter regarding potential sources.
Comment 2: The commenter was concerned with the quality of Vancouver's drinking water and
felt that even 1 excess cancer per 1,000,000 people exposed was an unacceptable level of risk,
Response: EPA shares the commenter's concern with water quality. Excess cancer risks for a
chemical in water, in this case PCE, can only be calculated based on a detectable amount of the
chemical in water. The I in 1,000,000 risk that the commenter mentions was the low end of the
range of risks calculated for exposure to PCE in untreated water. EPA's selected remedy for
treatment of the PCE in drinking water at WS1 is air stripping, which removes PCE from water so
effectively that PCE cannot be detected in the treated water from WS1, even when using the most
sensitive laboratory tests. There is no risk from drinking treated water that can be quantified,
thus EPA believes the selected remedy is protective of human health.
625:o\9808.030.wpd
------- |