PB99-964603
EPA541-R99-056
1999
EPA Superfund
Record of Decision:
Vancouver Water Station #4
Contamination Site
Vancouver, WA
9/1/1999
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FINAL RECORD OF DECISION Page iii
Vancouver Water Station 4
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 ACTIVITIES 4
3.1 INITIAL RESPONSE 4
3.2 INVESTIGATIONS 5
3.2.1 Results of Investigations 6
3.2.2 Sources ofPCE 6
3.3 INSTALLATION OF THE AIR STRIPPING SYSTEM 9
3.4 ENFORCEMENT 9
4.0 COMMUNITY RELATIONS 10
4.1 CITY OF VANCOUVER COMMUNITY RELATIONS EFFORTS 10
4.2 EPA COMMUNITY RELATIONS EFFORTS 11
5.0 SCOPE AND ROLE OF RESPONSE ACTION ..12
6.0 SUMMARY OF SITE CHARACTERISTICS 13
6.1 PHYSICAL CHARACTERISTICS 13
6.1.1 Surface Features 13
6.1.2 Geology 13
6.1.3 Hydrogeology 14
6.2 NATURE AND EXTENT OF CONTAMINATION 16
6.2.1 Chemicals of Potential Concern 16
6.2.2 Acetone Detections . . . 17.
6.2.3 PCE Concentrations 18
7.0 SUMMARY OF SITE RISKS 22
7.1 HUMAN HEALTH RISK ASSESSMENT 22
7.1.1 Identification of Chemicals of Potential Concern 23
7.1.2 Exposure Assessment 23
7.1.3 Toxicity Assessment 27
7.1.4 Risk Characterization 28
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CONTENTS (Continued)
7.1.5 Uncertainty Assessment ... -,-,
7.2 ECOLOGICAL EVALUATION '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'. 33
8.0 REMEDIAL ACTION OBJECTIVES
34
8.1 NEED FOR REMEDIAL ACTION -J
8.2 POTENTIAL SOURCES *
8.3 TRANSPORT OF PCE TO WATER STATION 4 .'.'.".''.'.. 35
8.3.1 Mill Plain Release Scenario 36
8.3.2 Flowpaths to WS4 .....'...'. 35
8.3.3 Preferential Pathways '. ' 37
8.3.4 Degradation of PCE in Groundwater -27
8.4 CONCLUSIONS " " '
8.5 REMEDIAL ACTION OBJECTIVES . . . . '...........'.['. .'.'." 38
9.0 DESCRIPTION OF ALTERNATIVES 3g
9.1 THE OPERATING TREATMENT SYSTEM ALTERNATIVE 30
9.2 THE NO-ACTION ALTERNATIVE ...'.'.'.'.'.'.'.'.'." 39
10.0 COMPARATIVE ANALYSIS OF ALTERNATIVES . 39
10.1 OVERALL PROTECTION OF HUMAN HEALTH AND THE
ENVIRONMENT
10.2 COMPLIANCE WITH ARARS "4
10.3 LONG-TERM EFFECTIVENESS AND PERMANENCE 49
10.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME THROUGH
TREATMENT 4?
10.5 SHORT-TERM EFFECTIVENESS 4?
10.6 IMPLEMENTABILITY ?~
10.7 COST OF IMPLEMENTATION " " A
10.8 STATE ACCEPTANCE . T!
10.9 COMMUNITY ACCEPTANCE ........ .....'.'.'.'.\\\ 44
11.0 THE SELECTED REMEDY
11.1 AIR STRIPPING *
11.2 GROUNDWATER CLEANUP " ^-
11.3 GROUNDWATER MONITORING " " Al
4o
12.0 STATUTORY DETERMINATIONS
12.1 PROTECTION OF HUMAN HEALTH AND THE' ENVIRONMENT .' .' \ 47
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CONTENTS (Continued)
.12.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS (ARARS) AND OTHER CRITERIA AND GUIDANCE 47
12.2.1 ARARs 47
12.2.2 Other Criteria, Advisories, or Guidance to Be Considered (TBCs) for
This Remedial Action 48
12.3 COST-EFFECTIVENESS 48
12.4 USE OF PERMANENT SOLUTIONS AND ALTERNATIVE TREATMENT
TECHNOLOGIES (OR RESOURCE RECOVERY TECHNOLOGIES) TO
THE MAXIMUM EXTENT PRACTICABLE 49
12.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT : 50
13.0 DOCUMENTATION OF SIGNIFICANT CHANGES 50
APPENDIX
A Responsiveness Summary
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FIGURES
2-1 Site Location Map ..... ................. .-,
2-2 Site Map .......................... ............ 3
3-1 Well Locations ........... ....................... .................. 7
6-1 Physical Conceptual Site Model ........... ........... ..'..' ............ 15
7-1 Human Health Conceptual Site Model ...... '. ................ .."..'. ...... 25
9-1 Typical Air Stripper ................ • ...............
TABLES
6-1 Summary of PCE Detections in Groundwater (1988-1998) .............. . 20
7-1 Summary of Cancer Risks, Future User of Untreated Public Water Supply ........ . . 29
7-2 Summary of Cancer Risks, Future Private Water Supply User ......... . . 29
7-3 Summary of Cancer Risks, Current Private Water Supply User ....... ....... ^ .. ^ 30
7-4 Summary of Noncancer Hazard, Future User of Untreated Public Water Supply '.'.'.'.'.'. 30
7-5 Summary of Noncancer Hazard, Future Private Water Supply User ............... 31
7-6 Summary of Noncancer Hazard, Current Private Water Supply User ............ 31
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FINAL
DECLARATION OF THE RECORD OF DECISION
SITE NAME AND LOCATION
Vancouver Water Station 4
Vancouver, Washington
STATEMENT OF PURPOSE
This decision document presents the selected final remedial action for Vancouver Water Station 4 (WS4) in
Vancouver. Washington, which was developed in accordance with the Comprehensive Environmental Response,
Compensadon, and Liability Act of 1980 (CERCLA), as amended, 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 Washington State
Department of Ecology concurs with the selected remedy.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from WS4, 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 WS4 are contaminated with tetrachloroethene (PCE). No
ongoing source for the PCE in the groundwater has been identified for which cleanup acdon could be taken.
Therefore a remedy that focuses on treatment of the drinking water produced from WS4 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 WS4 is
expected to eventually decrease to a level below the maximum contaminant level (MCL).
The selected remedy for cleanup of both the public water supply and groundwater at WS4 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 now of water to create as much surface area as possible. Large volumes of air are then
forced upward dirough 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 WS4 has been in operation since January 1992. 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 acdon addresses the principal threat to human health—contamination of
drinking water widi PCE.
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DATA CERTIFICATION CHECKLIST
H Chemicals of concern (COCs) and their respective concentrations (Table 6-1; Section 7. 1. 1;
BI Baseline risk represented by the COCs (Section 7)
H Cleanup levels established for the COCs and the bases for the levels (Section 8.5)
H Land and groundwater use that will be available at the site as a result of the selected remedy
a^sult iff
r Operati°n and maintenance (O&M) costs (Section 10.7); total present
worth costs. Ascount rate, and the number of years over which the remedy cos estimates are
™™™
erating costs)
H Decisive fector(s) that led to selecting the remedy (Section 8.4)
STATUTORY DETERMINATim*
/^ Chuck Clarke, Regional Administrator
LsJLS. EPA Region 10
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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
COC chemical of concern
COPC chemical of potential concern
DNAPL dense nonaqueous-phase liquid
EPA U.S. Environmental Protection Agency
HHRA human health risk assessment
HI hazard index
HQ hazard quotient
IRIS Integrated Risk Information System
kg kilogram
MCL maximum contaminant level
/"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
RI/FS remedial investigation/feasibility study
RME reasonable maximum exposure
ROD Record of Decision
SDWA Safe Drinking Water Act
SF slope factor
TC A 1,1,1 -trichloroethane
TCE trichloroethene
UCL95 95 percent upper confidence limit
VOC volatile organic compound
WDOH Washington State Department of Health
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ABBREVIATIONS AND ACRONYMS (Continued)
WS1 Vancouver Water Station 1
WS4 Vancouver Water Station 4
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DECISION SUMMARY
1.0 INTRODUCTION
In accordance with the Comprehensive Environmental Response, Compensation, and Liability Act
of 1980 (CERCLA), as amended, 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 4 (WS4) in the city of Vancouver, Washington. The
selected treatment system has been constructed and is operational.
EPA is the lead agency for overseeing the implementation of the selected remedy. The selected
action has the concurrence of the Washington State Department of Ecology and is responsive to
the expressed concerns of the public. The selected action complies with applicable or relevant
and appropriate requirements promulgated by EPA, Ecology, and other state agencies.
2.0 SITE NAME, LOCATION, AND DESCRIPTION
WS4, a public water supply station operated by the City of Vancouver, is located approximately
'/2 mile north of the Columbia River at the intersection of East Fifth Street and Blandford Drive in
the city of Vancouver, Washington (Figure 2-1). Vancouver is located in Clark County in the
southwestern corner of Washington state, across the Columbia River from the city of Portland,
Oregon. The site is located on a river terrace north of Lewis and Clark Highway (SR-14),
adjacent to a commercial district and residential areas.
The Superfimd site (CERCLIS ID No. WAD 988475158) was listed on the National Priorities
List (NPL) in October 1992. The site is defined as the wellfield, which encompasses
approximately '/2 acre and includes several support buildings, six production wells, two air
stripping towers, and one capped well (Figure 2-2). Until the discovery that the groundwater was
contaminated with tetrachloroethene (also known as perchloroethylene, or PCE), WS4 provided
about 25 percent of the public water supply for the city of Vancouver. Only two of the
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Washington
vancoiiver
Lewis and Clark Hwy
Columblaniver
Figure 2-1
Site Location Map
54-52-OJ3C
Vancouver Water Station 4
RECORD OF DECISION
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&EPA
REGION 10
p i 50-100
SCALE IN FEET
Figure 2-2
Site Map
54-52-OJ3C
Vancouver Water Station 4
RECORD OF DECISION
FILENAME T-\voncouver\«s-«Vod\2-2 d»g
EDIT OMC- 04/19/99 AI l7-56
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Vancouver Water Station 4
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Page 4
wells—the two with the lowest average concentration of contamination—have been used since
1989. Most drinking water for the city of Vancouver is supplied by other wellfields- WS4 is used
primarily to meet peak demands for water, with the largest volumes pumped during the summer.
WS4 pumps water from an alluvial zone in hydraulic communication with the Troutdale
Formation, a deep aquifer from which several municipal wellfields and an unknown number of
private wells draw water. Investigations into potential sources of PCE contamination at WS4
have shown the persistent and widespread presence of PCE in this deep groundwater. PCE is
routinely measured in monitoring and private wells at levels near (and often above) the maximum
contaminant level (MCL) of 5.0 micrograms per liter (ug/L). In some cases, private wells located
outside of, but in the vicinity of, the defined Superfiind site have been measured with much higher
levels of PCE. None of the private wells in the vicinity of WS4 are known to be used for
domestic purposes. All known private wells within approximately 1 mile of WS4 are on
properties that are connected to city water for domestic water use. Property owners with known
private wells in the vicinity of WS4 have been notified of the presence of PCE in groundwater
they have been told that their private wells should not be used to supply domestic water (for
drinking or bathing) but can be used for activities such as irrigation and washing cars. At this
time the EPA does not intend to include the wider contamination by PCE throughout the aquifer
as part of the Superfund site.
There are no wetlands, flood plains, 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 WS4 has been owned by the City of Vancouver for over 50 years The
production wells at WS4 were installed during World War II to provide water for workers at the
Vancouver Shipyards. Water from WS4 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 Water '
trom WS4 is primarily used to meet peak demand, particularly in the summer
3.1 INITIAL RESPONSE
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
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Vancouver Water Station 4
EPA Region 10
monitoring water from WS4 and its other wellfields. Results of this monitoring, which began in
March 1988, indicated a persistent presence of PCE in the water at WS4. 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 1 (WSI) and WS4.
Because PCE concentrations at WSI were much lower than those at WS4, the notice stated that
WS1 water was being blended with WS4 water to reduce overall PCE concentrations.
In April of 1989, the four WS4 wells with the higher PCE concentrations were taken out of
service. In May of 1989, EPA proposed an MCL for PCE for public drinking water systems of
5.0 ug/L. EPA issued the final MCL for PCE (5.0 ug/L) in January 1991, with an effective date
of July 1992 (40 CFR Part 141). Samples collected from the production wells in the spring of
1989 showed concentrations of PCE ranging from approximately 3 to 10 ug/L,
3.2 INVESTIGATIONS
Several investigations into the source or sources of PCE at WS4 have been conducted by the City
of Vancouver and EPA since PCE was detected at WS4 in 1988. The investigations began in
1989 by sampling private wells, surface water sources, and industrial sumps in the vicinity of
WS4. Early investigations focused on dry cleaning operations on the Mill Plain plateau to the
north (and upgradient) of WS4. PCE is commonly used as a solvent in dry cleaning, and dry
cleaners are routinely considered in most investigations of an unknown source of PCE in
groundwater.
Investigations of potential sources of PCE at WS4 included conducting soil-gas surveys, installing
monitoring wells, and taking samples from monitoring and private wells in the vicinity of WS4.
From 1989 through 1992 over 300 soil-gas samples were collected from hundreds of locations
within the expected capture zone of WS4. The soil-gas results were inconclusive and although
they did not identify any specific "hotspots," they were used to locate monitoring wells.
In 1990 the City of Vancouver installed seven monitoring wells at locations including Hamey
School, Dubois Park, East Fifth Street, and the Park Hill Cemetery. In 1992 EPA installed an
additional eight monitoring wells and collected samples from the new wells and several existing
monitoring wells. (The new wells were installed at locations covering a wide area to the north
and northwest of WS4.) Between 1993 and 1997 the City of Vancouver installed and collected
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EPA Region 10
samples from another eight wells on the Mill Plain plateau. Two additional wells were installed by
S'iSuW^ remedial inVeStigati°n " 1998' Figure 3-' Shows the ***»"• of wells in
I-1"6 Ci,to0°/ Vanco"ver has also routinely collected samples from the production wells at WS4
bmce 1988, more than 1,500 weekly samples have been collected and analyzed for PCE (The
product,on weH samples have been analyzed only for PCE, but all monitoring well samples have
been analyzed for the full suite of VOCs.)
3.2.1 Results of Investigations ,
The groundwater data clearly indicate that a pulse, or concentrated volume, of PCE passed
through the wellfield over a period of several years beginning in 1992. PCE concentrations
suddenly increased in 1992, peaked in about 1993, and decreased over the next several years to
the current level (,n the range of 20 to 40 ug/L). Concentrations of PCE at WS4 have ranged
from a low of less than 1 ug/L to a maximum of 520 ug/L. Although PCE has been measured in
A ™l/n° °n ' highest average concentrations have measured in WS4-1 WS4-4B
and WM-9. These production wells are located at the northern portion of the wellfield
Production wells WS4-2B and WS4-5B, both on the southern portion of the wellfield have the
lowest average concentrations. (These are the only two wells that have been used for water
production since 1989.) WS4-3B, located in approximately the middle of the wellfield, shows a
concentration trend over time that is higher than the two southern wells but lower than the three
northern wells.
A similar pulse of PCE passed through PW-2, a private well located approximately 200 yards
northeast (and upgradient) of the wellfield. The highest concentrations of PCE measured in this
investigation were in PW-2 (concentrations of over 1,000 ug/L were routinely measured in PW-2
«!l?r8, A 1992)' 1?e City °f Vancouver PumPed PW-2 for several years (disposing of the
water to the sewer system) m an effort to reduce the PCE entering the WS4 wellfield
3.2.2 Sources of PCE
of PCE may be present in the area. (PCE has
co»-ntrations of PCE measured a°WS4
to cleanup or other source control measures. Using this definition no primary
ongomg source of the PCE in WS4 was ever identified. Howevef, the significant reducS
or
or
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PCE concentration over the last several years strongly supports the conclusion that there is not an
ongoing source of PCE contamination in the area.
3.3 INSTALLATION OF THE AIR STRIPPING SYSTEM
In October 1988, the City began weekly monitoring of the water at each of the six wells at WS4.
The City used the results to determine which wells to use for drinking water production to ensure
that the concentration of PCE in the drinking water delivered to its customers was as low as
possible. In November 1989, the City removed WS4 from service.
To regain full use of WS4, the City installed an air stripping system to remove PCE from the
groundwater pumped by the station. During the initial design of the air strippers, the
concentration of PCE at WS4 was consistently in the range of 5 to 20 ug/L, so the stripper design
was based on a maximum expected concentration of 100 ug/L. During 1991, however, the
concentration of PCE in PW-2 rapidly increased to over 1,000 ug/L. This upgradient well was
being sampled weekly to provide an "early warning" of possible increasing concentrations of PCE
at WS4. Because of this increase, the City modified the design of the treatment system to
accommodate an input concentration of more than 100 ug/L. The two stripping towers,
originally designed to run in parallel and to treat 8,000 gallons per minute (gpm), were '
re-configured to run in series. This design change reduced the total flow to 4,000 gpm, but
enabled the system to remove much higher concentrations of PCE.
The redesigned treatment system was put into operation in January 1992, and has reduced
concentrations of PCE in treated water to below detectable levels. Only two of the six wells at
the water station—the two with the lowest average concentrations of PCE—have been used since
the station resumed service in 1992.
Following installation of the air stripping treatment system, the City changed the frequency of its
monitoring of the untreated water from weekly to monthly.
3.4 ENFORCEMENT
Although the air stripping system was effectively removing PCE from water that the City was
distributing for drinking water, Vancouver WS4 was listed on the NPL in October 1992 because
of the presence of PCE in the groundwater. The maximum detected PCE concentration reported
from a production well was 520 ug/L, reported on July 6, 1993 from WS4-9
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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
Toxic Substances and Disease Registry. Released for public comment in April 1993, the
preliminary health assessment evaluated only the effects of exposure to untreated PCE-
contaminated water. The assessment identified one community health concern: the risk of cancer
from drinking water contaminated with PCE. However, at the time that the assessment was
prepared, the carcinogenicity of PCE was still under review by EPA and the assessment could
state only that the likelihood of developing cancer as a result of lifetime exposure to PCE-
contaminated water associated with WS4 could not be estimated. The assessment also concluded
that the site posed no apparent public health hazard to the known exposed population as a result
of short-term exposure to elevated PCE concentrations in water.
In September 1993, federal funding constraints led to a decision by EPA to postpone further
investigations of WS4, saving EPA's limited funding for sites with greater risk. (The threat to
human health had been eliminated by the treatment system, which was fully operational in 1992.)
In November 1997, EPA resumed work on the investigation of WS4. In March 1998, EPA
collected samples from existing monitoring wells and private well PW-2. In September 1998,
EPA installed two additional monitoring wells and collected samples from monitoring and private
wells in the vicinity of WS4. Samples were collected using low-flow techniques and were
analyzed for the full suite of VOCs. PCE concentrations ranged from 1.1 to 19 9 ug/L in the
March 1998 sampling and from 1.1 to 25.6 ug/L in the September sampling. Eighteen wells were
sampled on both occasions; concentrations in 7 of these wells did not significantly vary from
March to September, concentrations increased in 7 wells, and concentrations decreased in 4 wells.
In 1999, EPA released the final remedial investigation and feasibility study (RI/FS) report for
WS4. The results of the RI/FS report are summarized in this Record of Decision (ROD).
4.0 COMMUNITY RELATIONS
4.1 CITY OF VANCOUVER COMMUNITY RELATIONS EFFORTS
In February 1989 the City of Vancouver notified users of public water that PCE had been
detected in wells 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 reduce the
concentration of PCE in water delivered to its customers. In November 1989, the City took WS4
out of service until a treatment system could be installed.
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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.
Also 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 through which 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
EPA issued a fact sheet in July 1992 entitled "Vancouver Water Station #4 Contamination
Superfund Site." This fact sheet described the startup of the air stripping system and announced
plans to install monitoring wells in the vicinity of WS4 and to begin scoping for the remedial
investigation.
In October 1992, EPA issued a news release announcing that WS4 had been added to the NPL as
a Superfund site.
EPA's "Superfund Community Relations Plan" for the WS4 Superfund site was released to the
public on February 1, 1993. The plan noted that 32,000 copies of the July 1992 fact sheet had
been distributed and that EPA had met with members of the community on September 21 and 22,
1992. The plan also announced establishment of an information repository at the Fort Vancouver
Regional Library and stated that many Vancouver neighborhood associations and other local
organizations had been placed on EPA's mailing list.
In September 1993, EPA distributed another fact sheet entitled "Vancouver Water Station #4
Contamination Superfund Site," announcing the postponement of the investigation of WS4 to
give funding priority to other sites with more immediate health risks and noting that monitoring
would continue while the investigation was on hold.
In September 1994, EPA released another fact sheet, entitled "Vancouver Water Stations #1 and
#4 Contamination Sites," reiterating the postponement of the investigation at WS4 and noting that
the investigation at WS1 was also on hold.
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The most recent fact sheet was released June 18, 1998, and provided summaries of previous
activit.es at both WS1 and WS4. The fact sheet noted that the Proposed Plan for WS1 was
expected to be issued in July 1998, with the Proposed Plan for WS4 "to be developed early" in
The RI/FS report for WS4 was released in May 1999 and made available to the public in the
Administrative Record maintained at 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 Proposed Plan for WS4 was
published on May 5, 1999. The notice of availability of these two documents was published in the
Vancouver Columbian on May 5,1999.
The public comment period was held from May 5, 1999, to June 3, 1999. Written comments on
the Proposed Plan and RI/FS report were received from two individuals and the City of
Vancouver. 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 WS4 site in Vancouver
Washington chosen in accordance with CERCLA, as amended, and, to the extent practicable the
INUF. 1 he 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.
The City of Vancouver and EPA conducted numerous investigations prior to the remedial
investigation, spanning a period of 10 years, to identify the source of PCE entering WS4 but an
ongoing source (or sources) of the PCE contamination for which cleanup action could be taken
was never identified. Although it appears that a pulse of higher-concentration PCE passed
through the water station, a definitive PCE plume has not been delineated No additional
investigation into potential sources was conducted during the remedial investigation because
concentrations at WS4 had decreased substantially and there was no evidence of an ongoing
source area where cleanup action could be taken.
The response action is therefore focused on the groundwater at the wellfield and on ensuring that
the dnnlcing water distributed by WS4 meets the standards that are protective of human health
The scope of the response action at WS4 is the following:
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• Ensuring that human health is protected by reducing the level of PCE in drinking
water produced from WS4 to meet federal drinking water standards
• Reducing the concentration of PCE in the groundwater at WS4 to below the MCL
of 5
EPA's response action for WS4 is to select the continued treatment of drinking water produced
from WS4 by using the air stripping treatment system that is already in operation Continued
operation of the air stripping treatment system at WS4 to provide clean 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. WS4 is located about '/2 mile north of the Columbia River, near the first terrace above the
Columbia River flood plain at an elevation of approximately 100 to 1 10 feet above mean sea level
(msl). Topography is flat with a gentle slope to the west. South of the site, the ground surface
slopes down to the flood plain, which is at an elevation of approximately 30 feet above msl
North of the site, the ground surface slopes steeply upward to elevations of approximately 250 to
300 feet above msl at the top of the second terrace north of the Columbia River This terrace is
located roughly at Mill Plain Boulevard and is referred to as the Mill Plain plateau.
Water, Station 4 is located within a fenced area in a neighborhood that also includes single and
multifamily residences and small commercial businesses to the west, north, and east The Lewis
and Clark Highway is south of the site. Paved areas are typically equipped with stormwater
drains, which are part of the city's stormwater system.
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
Upper Members of the Troutdale Formation), topped with Pleistocene to Holocene Age
unconsohdated alluvial sediments.
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FINAL RECORD OF DECISION . p ,,
Vancouver Water Station 4 g
EPA Region 10
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 flood plain with finer-grained sands present as lenses
and/or stringers within the coarse-grained material in the terraced areas.
Lithology in the wider vicinity around WS4 is dependent upon location. Boring logs for wells in
the Mill Plain plateau describe sand with variable amounts of silt and gravel (Orchards Gravel) to
depths ranging from approximately 130 to 140 beet below ground surface (bgs). A 3- to 7-foot-
thick, low-permeability, sandy silt/clay with gravel is present below the sand that represents the
weathered top of the Troutdale. Gravel with variable amounts of sand and silt is present beneath
the silt/clay unit to depths in excess of 300 feet bgs.
Boring logs for wells in the immediate area of WS4 describe silty sand with minor amounts of
gravel to depths of approximately 80 feet bgs. A gravelly silt to clay is present from
approximately 80 to 130 feet bgs in the western portion of the area (data from MW4-6) that thins
to the east (data from MW4-4). These sediments are assumed to be alluvial deposits from the
Columbia. The Troutdale is observed below the alluvial sediments. The weathered top of the
Troutdale does not appear to be present in the lower elevations (i.e., elevations similar to those of
WS4) at the base of the Mill Plain bluff.
The physical conceptual site model (Figure 6-1) is based on an interpretation of the geological
data that concludes that the weathered top of the Troutdale was eroded in the area between WS4
and the top of the Mill Plain plateau by the Columbia River prior to the deposition of the
Orchards Gravel. Wells installed in the Mill Plain plateau to the north of WS4 provide strong
support for the conclusion that the Orchards Gravel is prominent on the plateau, but not present
at the lower terrace occupied by WS4.
6.1.3 Hydrogeology
Groundwater in the Vancouver area is produced primarily from two formations the Orchards
Gravel (also referred to as the shallow groundwater zone) and the lower portion of the Upper
Member of the Troutdale Formation (referred to as the deep groundwater zone). Production
wells at WS4 are screened in the deep groundwater from either the Troutdale Formation or
alluvium in direct hydraulic communication with the Troutdale Formation.
WS4 produces groundwater from a gravel unit within the lower portion of the Upper Member of
the Troutdale Format.on. This deeper groundwater formation extends approximately from 200 to
-------
Representative
Shallow Monitoring Well
Representative
Deep Monitoring Well
Representative
Private Well
Mill Plain Plateau^
i&iinifr^.-..?-.-^T"- l&nttl..-— - Tl""
Hypothetical Ckintaminanl/Groundwater Migration Routes
Groundwater Aquifer Surface
Hypothetical Contaminant Plume
Wellfield-
Water Station 4
REGION 10
Figure 6-1
Physical Conceptual Site Model
54-52-OJ3C
Vancouver Water Station 4
RECORD OF DECISION
41F006252030-2M41499
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Vancouver Water Station 4 Pa£e 16
EPA Region 10
250 feet bgs and is known to be present below the Mill Plain plateau, with a hydraulic gradient to
the south-southwest toward the Columbia River. Specific capacities are reported to exceed 300
gallons per minute per foot of drawdown, and the individual production well yields range from
600 to 2,000 gallons per minute.
-r Shall°W Sroundwater z°ne >s ™t known, although it is known to exist in
the Mill Plam plateau, specifically in the area of the Tower Mall shopping center The shallow
groundwater zone is found at a depth of about 120 feet bgs and is generally about 10 to 20 feet
thick Apparent groundwater flow in this perched zone is to the west. Based on boring logs
developed during s.te investigation activities, the Orchards Gravel does not appear to provide a
potential for significant water resources in the immediate area of WS4.
6.2 NATURE AND EXTENT OF CONTAMINATION
PCE is the primary chemical of concern, although acetone and bromoform have also been
detected.
6.2.1 Chemicals of Potential Concern
PCE is the only chemical of potential concern (COPC) identified in untreated water from
production wells, monitoring wells, or private wells in the vicinity of WS4 because it is the most
frequently detected chemical and is detected at concentrations significantly greater than the risk-
based screening concentration (RBSC). The RBSC is equal to \x\0~6, using EPA standard
exposure assumptions for drinking water use. Other detected chemicals, as well as chemicals that
were not detected but that had sample quantitation limits greater than the RBSCs, were eliminated
from further evaluation for one or more of the following reasons:
• The chemical was infrequently detected or not detected in any sample (e g
bromoform in production wells; 1,1,1-trichloroethane in deep wells; and acetone in
shallow wells). Numerous volatile organic compounds were analyzed for in
samples collected but were never detected.
• The chemical was detected at concentrations less than the RBSCs (e g
bromoform in production wells; 1,1,1-trichloroethane in deep wells acetone in
shallow wells).
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EPA Region 10
• The chemical was detected at concentrations greater than the RBSCs, but the
magnitude of the exceedance was not great, or the concentration has decreased to
less than the RBSCs during recent sampling events (e.g., chloroform in deep wells;
benzene in shallow wells).
• Available data from prior to 1996 may not be representative of current conditions
because of changing groundwater conditions over time.
6.2.2 Acetone Detections
Although PCE was the only COPC for the WS4 site, acetone was recently detected at elevated
concentrations in the groundwater beneath the Mill Plain plateau. In September 1998, acetone
was detected in samples from five wells (MW4-DP1, MW4-DP2, MW4-5S, MW4-14S, and
MW4-PHC). At four of these five wells, the detected concentrations of acetone were much less
than the RBSC of 3,650 ug/L. (An MCL for acetone has not been established.) In MW4-PHC
however, the reported concentration of acetone was 42,600J ug/L. Because acetone had not
previously been detected in this well, and had never been detected at any elevated concentration in
a monitoring well in the vicinity of WS4, MW4-PHC was resampled in January 1999 The
concentration of the sample collected in January was 930 ug/L, less than the RBSC but still higher
than any other detected concentration of acetone in wells near WS4. The elevated concentrations
of acetone in MW4-PHC are too high to have been caused by laboratory contamination.
(Acetone is commonly used as a solvent in laboratory extractions, so low levels of acetone
detected in environmental samples are often attributed to laboratory contamination.) Accordingly
these concentrations are probably representative of actual groundwater conditions.
The City of Vancouver has been notified about the detected concentrations of acetone in
groundwater at the Mill Plain plateau. The City has indicated that it will begin monitoring for
acetone in samples routinely collected from production wells at WS4. (The current practice is to
analyze these samples only for PCE). Further investigation into the acetone detected in MW4-
PHC is not being pursued under EPA's investigation of the PCE contamination at WS4 for the
following reasons: (1) acetone was detected only recently and has no apparent relationship to the
historical releases of PCE, (2) acetone was detected in the Mill Plain area only at low
concentrations (except for MW4-PHC), (3) MW4-PHC has shown a significant decrease in
acetone over a 4-month period, and (4) acetone is both miscible in water and readily
biodegradable, and therefore is unlikely to reach WS4 in concentrations approaching the RBSC of
Therefore, PCE is the only chemical evaluated in the remedial investigation.
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FINAL RECORD OF DECISION page 18
Vancouver Water Station 4
EPA Region 10
6.2.3 PCE Concentrations
Summaries of PCE concentrations are presented by medium in the following paragraphs.
Soil-Gas
Soil-gas sampling was conducted in early investigations to identify PCE "hotspots," particularly
near the existing and former dry cleaning facilities on the Mill Plain plateau. When the
concentrations of PCE began to increase at WS4 productions wells and at PW-2, additional soil-
gas sampling was conducted in the PW-2 area. The results were useful in helping locate potential
sites for monitoring well installation, even though none of the concentrations were considered
indicative of an ongoing PCE source area for which cleanup action could be taken.
Soil
Approximately 100 soil samples were collected from a range of depths during installation of six
monitoring wells in the vicinity of WS4. Additionally, surface soil samples were collected from
five locations in the vicinity of the dry cleaning businesses on the plateau. Relatively few soil
samples were collected so the lateral coverage of soil data across the area is therefore limited.
However, laboratory-reported analytical results from these samples do not show significant
detections of PCE or degradation products.
Groundwater
To evaluate the extent of PCE contamination, existing groundwater data for the site were
separated into the following three data sets based on well location and the groundwater formation
in which the well is screened:
• WS4 production wells
• Wells completed in the deep aquifer (Troutdale Formation)
• Wells completed in the shallow aquifer (Orchards Gravel)
Results for these three groups of wells are discussed in the following subsections.
Production Wells. WS4 consists of six active production wells and one inactive well. The six
active wells, which are all screened at approximately the same depth, are dispersed over a large
portion of the well field. Two of the active production wells (WS4-2B and WS4-5B), both
located in the southern portion of the well field, have had historically the lowest concentrations of
PCE. These are the only wells from which water has been produced by WS4 since 1989. PCE
concentrations in the four remaining active wells (WS4-1, WS4-3B, WS4-4B, and WS4-9) have
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FINAL RECORD OF DECISION Pace 19
Vancouver Water Station 4
EPA Region 10
varied over time, but are generally consistent with the overall wellfield pattern of sudden increase
and gradual decrease in PCE concentrations.
It is not known to what extent the pattern of higher concentrations of PCE in the northern portion
of the wellfield (and lower concentrations in the southern portion) are related to the location of
the release(s) of PCE responsible for contamination at WS4. Although an ongoing source for
which cleanup actions could be taken has not been identified, the concentration of PCE in every
production well has significantly decreased over the last several years.
A summary of PCE detections in WS4 production wells, including maximum and minimum
concentrations and the total number of samples compared to the number of samples exceeding the
MCL of 5.0 ug/L, is provided in Table 6-1.
Deep Wells. Concentrations of PCE in the 16 deep monitoring wells and 4 deep private wells in
the vicinity of WS4 vary considerably over time and by location. Low concentrations of PCE (but
still above the MCL of 5.0 ^ig/L) appear to be widespread in the deep groundwater; PCE has been
detected in every deep well in the vicinity of WS4 and has been measured in concentrations above
the MCL in 17 of the 20 wells used in this evaluation.
The highest concentration of PCE measured in any well during the investigations was 1,600 ug/L
at PW-2, a deep private well located about 200 yards upgradient of the wellfield. The next
highest concentration in a deep well was 145 ug/L, at private well PW-9 about '/2 mile northwest
of WS4. The highest concentration of PCE measured in a deep well on the Mill Plain plateau was
66.7 ug/L, at MW4-DP2.
These maximum concentrations do not appear to be part of any common plume. Two deep
monitoring wells were installed near PW-2. MW4-7, located a few hundred feet east of PW-2,
had the highest detected concentration of PCE in any of the monitoring wells sampled during the
investigations (100 ug/L in 1992). However, concentrations in MW4-1, located a few hundred
feet west of PW-2, have all been below the MCL. This is strong evidence that a high-
concentration PCE plume was not widespread and was limited to a relatively narrow channel that
was intercepted by PW-2.
A summary of PCE detections in the deep-zone wells, including maximum and minimum
concentrations and the total number of samples compared to the number of samples exceeding the
MCL of 5.0 ug/L, is provided in Table 6-1.
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Page 20
Table 6-1
Summary of PCE Detections in Groundwater (1988-1998)
Minimum
Detected
PCE
Maximum
Detected
PCE
Detections/
Total
Samples
Exceedances/
Total
Samnles
Date
Detected
Date
Detected
Production Wells
II WS4-I
WS4-2B
WS4-3B
WS4-4B
WS4-5B
WS4-9
Deep Wells
MW4-1
MW4-2
MW4-3
MW4-4
MW4-5
II MW4-6
MW4-7
MW4-8D
MW4-8I
MW4-DP1
MW4-DP2
MW4-FS1
MW4-FS2
MW4-HS1
MW4-HS2
MW4-PHC
PW-2
j_ PW-7
PW-8
PW-9
1 Shallow Wells
| MW4-3S
1 MW4-5S
' MW4-8S
5.2
0.98
3.6
15.9
0.24
8
0.6
0.6
12.1
11
19.9
2
1.3
8.6
0.7
0.37
2.2
3.99
2.01
0.9
0.61
1.45
0.2
7.9
11.6
0.77
3.2
5.5
1.6
1989
1990
1989
1997
1990
1998
1997
1997
1998
1989
1998
1998
1997
1998
1996
1990
1998
1990
1990
1990
1990
1990
1989
1990
1998
1990
1998
1998
1996
370
380
450
390
501
520
1.8 J
1.3
17
11
50
5.7
100
8.6
1.1
9.8
66.7
18.8
7.2
7.45
5.71
5.5
1,600
93
55
145
55
5.5
23
1992
1993
1992
1992
1993
1993
1998
1992
1997
1992
1992
1992
1992
1998
1997
1998
1990
1992
1998
1992
1991
1991
1992
1992
1989
1992
"" • '•
1992
1998
1997
290a
287*
258"
294a
293"
276"
5/5
3/5
4/5
1/2
5/5
3/3
5/5
1/6
5/6
7/10
18/18
7/7
6/6
14/15
4/6
9/11
262b
7/7
5/5
5/5
5/5
1/1
8/8
290/290
287/287
258/258
291/294
292/294 1
271/276
J f^ J
0/5 [
0/5 j
4/5
1/2 '
5/5
1/3
4/5
1/6
0/6
2/10
17/18
4,7"
2/6 1
9/15
2/6
1/11
205/262
7/7
5/5
4/5
..-,:,,:^,:,
3/5
~~^I
— —
5/8 \
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Vancouver Water Station 4
EI'A Region 10
Page 21
Table 6-1 (Continued)
Summary of PCE Detections in Groundwater (1988-1998)
Well ID*
MW4-9S
Minimum
Detected
PCE i
Date
Defected
Maximum
Detected
FCEl
Date
Detected
Detections/
TotaJ
Samples
Exceedances/
Total
Samples
"Well locations are shown in Figure 3-1.
"Number of samples in provided data set. Documentation not provided to evaluate nondetects.
Notes:
Exceedance - equal to or greater than 5 ug/L
ug/L - micrograms per liter or part per billion (ppb) equivalent
ND - not detected
PCE - tetrachloroethene
Shallow Wells. Nine monitoring wells have been installed in the shallow groundwater zone at
locations near or downgradient from former and current dry cleaning operations on the Mill Plain
plateau (including four installed during 1998). These wells were installed in an attempt to identify
the shallow groundwater plume of PCE that would have first materialized if a surface release of
PCE was moving down through the soil column.
The maximum PCE concentration (55 ug/L) was observed in a water sample collected from
shallow well MW4-3S in October 1992. The well is located directly downgradient from current
and historical dry cleaning facilities in or near the Tower Mall. Concentrations of PCE in this well
have steadily decreased over the last 6 years and in 1998 were below the MCL.
PCE concentrations exceeding the MCL (23 ug/L at MW4-8S and just under 10 ug/L at
MW4-9S) had been observed in 1997, but at both locations concentrations were below the MCL
in the 1998 sampling. Only one of the four remaining wells has had a detection of PCE that
slightly exceeded the MCL (5.5 ug/L at MW4-5S). PCE concentrations detected during the
September 1998 sampling at newer wells MW4-13S and MW4-14S were 2 5 and 2 8 us/L
respectively. '
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FINAL RECORD OF DECISION Paee22
Vancouver Water Station 4 g
EPA Region 10
i
A summary of PCE detections in the shallow-zone wells, including maximum and minimum
concentrations and the total number of samples compared to the number of samples exceeding the
MCL of 5.0 ug/L, is provided in Table 6-1.
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 releases from a site in the absence of any actions to control or mitigate these
releases. WS4 differs from the typical NPL site in that remedial action (air stripping treatment of
drinking water produced from WS4) has already been implemented. Because of this the human
health risk assessment (HHRA) for WS4 evaluates both an action alternative (treatment of water
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 WS4, 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 risks to residents of Vancouver who use water produced
from WS4 as their primary source of drinking water. The risk assessment consists of four main
components:
• Identification of 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.
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FINAL RECORD OF DECISION p 23
Vancouver Water Station 4
EPA Region 10
7.1.1 Identification of Chemicals of Potential Concern
In accordance with EPA Region 10 guidance, a risk-based screening approach was used to
identify COPCs in drinking water at WS4. The chemical screening consisted of comparing
concentrations of chemicals detected in groundwater at WS4 to risk-based screening
concentrations established by EPA. In untreated water from production wells, monitoring wells,
or private wells, PCE was identified as the only COPC because it is the most frequently detected
chemical and is detected at concentrations significantly greater than the risk-based screening
concentration (RBSC). No COPCs were identified in treated water.
7.1.2 Exposure Assessment
The exposure assessment identifies potential receptors and estimates the type and magnitude of
exposures to the COPC (PCE) that was identified in Section 7.1.1. The results of the exposure
assessment are then combined with the chemical-specific toxicity information (Section 7.1.3) to
characterize potential risks (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 the Exposure Setting and Receptors
Three groups of receptors were evaluated:
Future public water supply users
Future private water supply users
Current private water supply users
Identification of Exposure Pathways
,The primary medium to which exposure may occur is groundwater. WS4 is one of several water
stations that supply drinking water to people in the city of Vancouver and surrounding Clark
County. Although there is a potential exposure pathway for current public water supply users
(i.e., people using treated water produced by WS4), PCE has not been identified in the treated
water and therefore the exposure pathway to these receptors is incomplete.
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FINAL RECORD OF DECISION
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EPA Region 10
Page 24
Three potentially complete exposure pathways (Figure 7-1) were evaluated:
• Future public use of untreated water from the production wells if treatment
to be discontinued
were
• Future private use of untreated groundwater from shallow or deep wells installed
in the area around WS4 (represented by shallow and deep monitoring wells in this
nsk assessment)
• Current private use of untreated water from private wells near WS4 as a drinking
water source
Potential exposure pathways for area residents using untreated water as a drinking water source
include ingestion of PCE in untreated water, inhalation of PCE in untreated water during
household use of water, and dermal contact with PCE in untreated water during bathing.
Significant exposures to untreated water by on-site workers are not expected to occur
(Figure 7-1). Water is transported through the water station and treatment units via pipes
making direct contact with untreated water by workers unlikely. '
Potential exposures to PCE in air may occur as a result of stack or fugitive emissions from the air
stoppers. According to the Order of Authorization to Operate issued by the Southwest Air
?2S?!l Ol Authority in 1997 (Authorization No. 95CL-512), the combined air emissions
of PCE from two air stripping columns will be controlled by four granular activated carbon
canisters, and will not result in ambient air concentrations of PCE in excess of the applicable
Small Quantity Emission Rates as provided in Washington Administrative Code (WAC) 173-460
The granular activated carbon canisters are designed to achieve better than 95 percent removal of
PCE from the vapor phase. 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 som? small
release of PCE to the air, potential exposures to site workers or area residents 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 scenarios using PCE data collected between 1996 and 1998 from untreated
water from individual production wells at WS4 and monitoring wells installed in the vicinity
during source investigations. Exposure point concentrations were developed for the current
residential scenario using PCE data collected in 1998 from untreated water from private wells It
-------
Receptors
Source
••
Unknown
Sourcefs)
•
Release
Mechanisms
Direct
— * Discharge to
Soil
Spills/Leaks to
Soil
Discharge to
^""^ DryWell
Leaching
k
t"
teaching
Leac
ling
Secondary
Sources
— »
L
WS4 Treatment -
System
Exposure Media
•M
mmm
1
-*•
*
L
Private
Water
Supply Well
Stack/Fugitive
Air Emissions
Public Water
Supply
Exposure
Pathways
u
i
Currant
Water
Supply
ler Without
reatment
Future
Water
Supply
Jser Without
Treatment
X \
Ingestion
— > Inhalation
Dermal Contact
•
•
•
O
o
o
Site
Worker
/
O
o
o
k-*j Inhalation
O
Ingestion
-* Inhalation
Dermal Contact
o
o
o
o
9 <
•
•
%
O (
O (
O (
Future
Area
tesldentlal
User
/
0
Q
•
D
:>
D
3
•
3
O
Potentially complete exposure pathway
Potentially complete but less significant;
will not be quantified
Exposure pathway incomplete or no
COPCs identified
c/EPA
REGION 10
Figure 7-1
Human Health Conceptual Site Model
54-52-OJ3C
Vancouver Water Station 4
RECORD OF DECISION
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FINAL RECORD OF DECISION
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EPA Region 10
is conservatively assumed that the chemical concentrations remain constant over the assumed
exposure periods (i.e., up to 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 by using the maximum detected value when
the variability in the sampling results in a UCL95 that exceeds the maximum detected value The
methodology used to calculate exposure point concentrations for each of the three exposure
pathways is described below.
Future Public Water Supply Users. An area of high PCE concentrations within the capture
zone of WS4 was not identified. 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 groundwater from the production wells. Although PCE
concentrations in the production wells appeared to be increasing in the late 1980s and early
1990s, concentrations have decreased significantly since the mid-1990s. Therefore, data collected
during the previous 2 years (i.e., September 1996 through October 1998) were considered
appropriate for use in this HHRA.
Future Private Water Supply Users. The available 1996 to 1998 data for monitoring wells
installed in the shallow and deep aquifers at WS4 were used to estimate hypothetical future
exposure concentrations for potential future users of untreated shallow aquifer and deep aquifer
water. Maximum detected concentrations as reported from the 1996 or 1998 sampling events for
the two location groups (shallow and deep) were used as exposure point concentrations.
Current Private Water Supply User. The available 1998 data for the four private wells located
near WS4 were used to estimate current exposure concentrations for private well users Specific
uses of area private wells are unknown (e.g., drinking water, irrigation, industrial uses); therefore -
the same exposure pathways assumed for the production well source were assumed for the private
InfCilS
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
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FINAL RECORD OF DECISION Page 27
Vancouver Water Station 4
EPA Region 10
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
report 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 Toxicity Assessment
Carcinogenic Effects
Chronic inhalation exposure of mice and rats to concentrations of PCE resulted in liver cell
carcinomas in male and female mice, an increased incidence of mononuclear cell leukemia in male
and female rats, and an increase of renal tubular cell tumors in male rats. No evidence of skin
tumors was observed in a mouse skin initiation-promotion assay and no studies were located
regarding cancer in humans after dermal exposure to PCE.
In evaluating cancer, the numeric descriptor of carcinogenic potency is termed a slope factor (SF).
The slope factors for PCE are not available on the EPA Integrated Risk Information System
(IRIS) database, although they are reported in EPA's Risk Assessment Issue Paper for:
Carcinogenicity Information for Tetrachloroethylene. The oral slope factor as listed was 0.052
(mg/kg-dy1 and the inhalation slope factor was 0.002 (mg/kg-d)"1 for PCE. The IRIS database is
typically selected as the primary source of toxicity criteria when evaluating health risks or setting
health-based cleanup goals because of the extensive research effort and scientific review.
However, the National Center for Environmental Assessment (NCEA) serves as an adequate
source if toxicity criteria are not available in IRIS.
Noncarcinogenic Effects
Chronic exposure to concentrations of PCE in air caused abnormal hepatic function,
lightheadedness, headache, malaise, and dizziness in humans. Chronic occupational'exposure to
PCE in air causes significantly impaired functioning on neurobehavioral tests as compared to
controls. In another study, dry cleaning workers exposed primarily to PCE in air exhibited minor
liver and kidney changes. No studies on humans were found in the literature regarding chronic
oral exposure to PCE.
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Page 28
mrn r US6d in risk assessment are tenned reference
(RfDs) These are route- and duration-specific estimates of the average daily intake that
can occur without appreciable risk of any adverse effects.
The chronic oral reference dose of 0.01 mg/kg-day for PCE was derived based on a 6-week
fcE accl± 'f mC? reSUltCd ^ liV6r tOXidty- ThC Uncertain* factor of 1.°°° ^signed to
PCE accounts for '"traspecjes variability and extrapolation of a subchronic effect level to Jts
chronic equivalent The RfD confidence level is considered medium. Assuming a 100 percent
oral-to-dermal adjustment factor, the dermal RfD value is the same as the oral SfD value The
inhalation RfD of 0. 4 mg/kg-day used in the risk assessment was reported in EPA Region 9s
preliminary remediation goal tables. region y s
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 '
~tT? ? f X T6 de™al intakes are calculated M absorbed doses. Since EPA has not yet
established any dermal toxicity values, approximate toxicity values were derived by extrapolation
from oral toxic.ty values, assuming an oral absorption fraction of 1 . *poiauon
7.1.4 Risk Characterization
rCSUltS °f the exposure and toxidty assessments into a
description of potential cancer and noncancer risks. The method for risk
characterization used in this HHRA is consistent with EPA guidance.
cancer nsk of 1E-06 (or 1 x 10"6) corresponds to one additional cancer case in an exoosed
population of 1,000,000 people. Similarly, an excess cancer risk of lE-oT(o^Tx 10°
corresponds to one additional cancer case in an exposed population of 10 000 Excess cancer
^<^=^^^
°f IE-"6 '<> 1E-04 (40
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For current residents consuming treated water, no COPCs have been identified and therefore no
excess cancers are expected to occur. Therefore no chemicals were identified as chemicals of
concern (COCs) in treated water.
Cancer risks were calculated for residents using untreated water as the primary drinking water
source. Results are summarized in Tables 7-1 through 7-3. Due to the inherent uncertainty in
cancer risk calculations, total cancer risk values are reported to only one significant figure
Potential cancer risks to residents using untreated water range from 2E-05 to 5E-06 The cancer
risks are attributed primarily to water ingestion and dermal contact with water Even thoush
these risks are within the NCP acceptable risk range, it is necessary to take an action at WS4
because groundwater has been shown to have persistent concentrations of PCE above the MCL.
Table 7-1
Summary of Cancer Risks
Future User of Untreated Public Water Supply
Table 7-2
Summary of Cancer Risks
Future Private Water Supply User
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Table 7-3
Summary of Cancer Risks
Current Private Water Supply User
Location kH>~ 'Ifrr*!
PW-2
PW-7
PW-8
PW-9
•-^IfffJSSi^
^rffinSkon?^
2.6E-06
1.1E-05
7.1E-06
7.4E-06
•fJEittliiligi'^S
3.8E-07
1.6E-06
l.OE-06
1.1E-06
:^OermSi^MitAA' '?
1.6E-06
6.8E-06
4.4E-06
4.7E-06
^S^l^P^-'-' ^
5E-06
2E-05
1E-05
1E-05
The potential for noncancer health effects from exposure to a chemical is evaluated by comparing
the estimated intake of a chemical over a specific time period with the RfDs for that chemical
derived for a similar exposure period. This comparison results in a noncancer hazard quotient
(HQ). Since exposure to PCE may occur simultaneously by more than one exposure pathway,
HQ values are summed to obtain a hazard index (HI). If the total HI is equal to or less than 1, it
is believed that there is no appreciable risk that adverse noncancer health effects will occur. If an
HI exceeds 1, there is some possibility that adverse noncancer effects could occur, although an HI
above 1 does not indicate an effect will definitely occur.
Potential noncancer hazard to residents using untreated water ranges from an HI of 0.02 to an HI
of 0.2. Results are summarized in Tables 7-4 through 7-6. Since the total HI is less than 1 for all
pathways evaluated, there is no appreciable risk that adverse noncancer health effects will occur.
Table 7-4
Summary of Noncancer Hazard
Future User of Untreated Public Water Supply
* ' X ' ,'„ „' X » ^?"
Location ID • '-
WS4-1
WS4-2B
WS4-3B
WS4-4B
WS4-5B
WS4-9
• ^;^'->?f f
•''•'l^e&iMfM
0.089
0.080
0.12
0.12
0.045
0.065
0.024
0.022
0.032
0.031
0.012
0.018
' -i''-"--"^'^-,^-,. '1^-"-,:
"- Dennal €&ata£t*
0.056
0.051
0.076
0.072
0.028
0.041
0.2
0.2
0.2
0.2
0.09
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Table 7-5
Summary of Noncancer Hazard
Future Private Water Supply User
Table 7-6
Summary of Noncancer Hazard
Current Private Water Supply User
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 in the following discussion.
The estimates of risk in this assessment were based on the results of analytical data from several
separate sampling rounds. Although different analytical laboratories may have been used, it is
assumed that they used standard methods and followed similar quality control measures. '
Although the possibility exists for interlaboratory differences in measuring contaminant
concentrations, this uncertainty is not expected to be large.
Water samples collected from the production wells were pulled from the turbine pumps and
therefore some PCE 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 PCE is not known;
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however, they may result in an underestimate of PCE concentrations and the corresponding
human health risk. °
Because an ongoing source (or sources) of PCE in the groundwater for which cleanup action
could be taken have not been defined, there is considerable uncertainty associated with the
potential PCE concentrations in off-site wells. It is possible that areas or pockets of groundwater
with higher concentrations of PCE exist. If water from a private well in or near one of these areas
was used for domestic water purposes, the potential risk to users of the water from these wells
could be higher than those presented in the HHRA.
The RBSC comparison was designed to be conservative and the elimination of chemicals is not
likely to result in a significant underestimate of risk. All data available from sampling of untreated
water in 1989 through 1998 were used to determine COPCs. Due to the limited set of avaiSe
data (the City of Vancouver tested regularly only for PCE at WS4), these data may not reflect the
current concentrations of organic and inorganic contaminants other than PCE in untreated water.
In some cases, analytical procedures were not sensitive enough to detect chemicals potentially
present at concentrations greater than RBSCs. For 1, 1-dichloroethylene and vinyl chloride high
sample quantitation limits and their potential presence in the aquifer associated with WS4 may
result in an underestimate of risk. y
The evaluation of human health risks for the future resident used arithmetic average
concentrations in untreated water over a period of time from 1996 through 1998. It is not known
whether concentrations will decline over the long term as natural attenuation processes reduce the
concentrations of the COPCs, which would decrease risk, or whether input from existing or
potential future sources may result in an increase in water concentrations of VOCs which would
increase risk. Therefore, potential future risks may be over- or underestimated. The magnitude
of this over- or underestimate cannot be determined with available information (although the data
the PCE contamination at WS4 peaked in the eariy 1990s and has
The daily intakes in this risk assessment were calculated in a very conservative manner
Conservative exposure parameters (e.g., intake rate, exposure frequency, and exposure duration) '
were used to calculate daily intakes. This may result in an overestimation of risk In add-on
there is significant uncertainty in the volatilization factor that predicts the concentration of VOCs
in indoor HIT.
Risks from dermal exposures were calculated based on dermal toxicity values extrapolated from
oral values using an absorption fraction of 1 . Because organics are readily absorbed, the degrS
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of uncertainty associated with this assumption is believed to be small. Thus, actual risks are likely
to be slightly underestimated.
No EPA-approved cancer SFs for PCE are available on the EPA IRIS database. The oral and
inhalation SFs used in this risk assessment are reported in EPA's draft document Risk Assessment
Issue Paper for: Carcinogenicity Information for Tetrachloroethylene. 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.
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. While the magnitude and direction of these
uncertainties is largely unknown, it is most likely that risks estimated in this assessment have been
overestimated as a result of the conservative assumptions contained in the various steps of the
assessment. In either case the selected remedy would still be appropriate and protective and
would not change.
7.2 ECOLOGICAL 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-phased 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, stressor
characteristics, exposure, the ecosystem potentially at risk, and ecological effects. Assessment
endpoints can then be identified, and a conceptual site model developed. The conceptual site
model describes the predicted relationships between ecological entities and the stressors to which
they may be exposed. A complete exposure pathway from the stressor source to an ecological
receptor must exist for the risk assessment to proceed.
A qualitative ecological risk assessment was performed for WS4 that consists of the conceptual
site model portion of the problem formulation phase. The stressor present at the site (i e the
wellfield) is PCE in the groundwater. WS4 is located in a primarily undeveloped area with open
fields nearby where ecological receptors such as birds, small mammals, and invertebrates forage
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and live However these receptors are not exposed to contaminated groundwater, which occurs
at a depth of about 50 feet below ground surface.
The aquifer that supplies raw water to WS4 (Troutdale Formation) is believed to discharge to the
Columbia River approximately 3,500 feet downgradient from WS4. Although the Columbia River
sustains major fisheries, it transports vast quantities of water, and infiltration of contaminated
groundwater from WS4 would be unlikely to have a detectable effect on water quality in the
Columbia River.
Because there are no potentially complete exposure pathways at WS4, there is no ecological risk.
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, lt ,s necessary to take an action at WS4 because groundwater has been shown to have
persistent concentrations of PCE above the MCL. EPA's 1991 guidance (Role of the Baseline
Risk Assessment ,n Superfimd 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.
Although there are many uncertainties associated with this risk assessment and PCE
2SST* ^ 8™"dwT ^ WS4 ^ bee" deCreasing Since ™d-19'93' Concentrations
during 1998 were still from 2 to 8 times the MCL.
Actual or threatened releases of hazardous substances from WS4, if not addressed by
action selected in this ROD' may present imminent
8.2 POTENTIAL SOURCES
n^StiSations h^e been conducted and 25 monitoring wells have been
been iden *** " °ng°ing ^ ** wWch deanup action could be taken h- **
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Dry cleaning facilities on the Mill Plain plateau, approximately 1 mile north/northeast of WS4
were identified early in the investigations as a probable source of the PCE at WS4. However'
these investigations were largely completed by 1992, before the sudden increase in PCE
concentration at WS4 and nearby PW-2. Although 17 monitoring wells have been installed in the
vicinity of the dry cleaning facilities, PCE has been detected in these wells at only a fraction of the
concentrations measured in WS4 wells. While it is therefore difficult to conclude that the dry
cleaners are the primary source of PCE at WS4, it is probable that they contributed to the
contamination. Elevated concentrations of PCE have been measured in both the shallow and deep
ground water zones in the plateau area. The capture zone of WS4, although not well defined,
almost certainly includes deep ground water from the plateau area.
The extent of the high-concentration PCE plume is not known, but the significant reduction in
concentration in production wells, monitoring wells, and private wells over the last several years
indicates that there is not an ongoing source of PCE contamination in the area.
Other potential primary sources of PCE at WS4 are speculative. The sharp increase and relatively
fast decrease in PCE concentrations are consistent with a large, sudden release in the immediate
vicinity of the wellfield, perhaps from illegal dumping. There is no direct evidence of this
however, and the identity of the source or sources primarily responsible for the observed PCE
contamination at WS4 remain unknown. Because the PCE concentrations at WS4 have been
steadily declining, and the treatment system at WS4 is effective and reliable, further investigation
into source identification does not appear to be warranted. Given the extensive area in which the
release could have occurred, and the improbability of identifying the source even with a larger
investigation, the cost of additional investigation was determined to be disproportionate to the
benefit. The concentration of PCE at the source or sources has almost certainly decreased
significantly during the last 10 years and it is unlikely that an effective cleanup could be
completed, given the high probability that PCE has moved via groundwater and sorbed onto soil
over a large area. A fully effective cleanup of the source would not, in itself, immediately
eliminate the need for continued treatment at WS4.
8.3 TRANSPORT OF PCE TO WATER STATION 4
A pulse of groundwater with high concentrations of PCE moved through the WS4 wellfield and
immediate vicinity from about 1991 through 1993. The highest concentrations of PCE
(approximately 500 to 1,600 ug/L) were measured at the production wells and a single nearby
private well (PW-2). ' 3
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8.3.1 Mill Plain Release Scenario
If dry cleaners on the Mill Plain plateau were the primary source of PCE at WS4 it seems likely
that hundreds of gallons of PCE (and perhaps much more) would have had to have been released
in a relatively short time to account for the spike in concentrations that began in 1992 More than
200 gallons of PCE have been removed to date by the air stripping system at WS4, so the primary
source of PCE would have had to have been at least several times that volume (or even more if
the release point was as far away as the Mill Plain plateau).
If such a large release had occurred in the Mill Plain area, it would have almost certainly caused a
high-concentration plume of PCE in the shallow groundwater zone. Any PCE that was released
at the surface on the plateau would have migrated through the soil column and dissolved into the
shaHow aquifer. A steady, long-term release would have gradually increased the concentration of
PCE in the surrounding shallow groundwater. A sudden, large release could have resulted in
free-phase PCE settling onto the aquitard at the bottom of the shallow groundwater zone (This
would only occur if the release of PCE was large and sudden enough to overcome the solubility
limit in water, approximately 150,000 ug/L.) The resulting plume of PCE would have spread
with groundwater flow (towards the west). Although such a plume could have been relatively
narrow, it seems highly unlikely that it would be undetected by any of the shallow monitoring
wells in the area.
8.3.2 Flowpaths to WS4
To reach WS4, the plume of PCE in shallow groundwater (or, if present, free-phase PCE) would
next have had to move through the aquitard at the bottom of the shallow groundwater zone
through an unsaturated zone above the deep groundwater, and finally into the deep groundwater
being drawn towards WS4. Even if most of the PCE moved through a large hole in the aquitard
a plume of PCE in the shallow groundwater should still be identifiable. But investigations to date
have not indicated the existence of such a plume; concentrations of PCE measured in shallow
groundwater at the Mill Plain plateau have exceeded 25 ug/L only three times.
The next highest concentrations of PCE in groundwater (approximately 50 to 150 ug/L) have
been measured in several locations in the vicinity of WS4 (mostly in deep wells), but they do not
form an apparent pattern or indicate a common plume of PCE contamination. It is possible that
these areas are related, although the available data are not sufficient to establish relationship It is
more likely, however, that the PCE contamination in groundwater near WS4 is the result of
multiple, independent releases or sources; PCE has been detected over too large an area to be
accounted for by a single point release. It is also likely that one or more of those releases was
relatively large and sudden, given the sudden increase and relatively fast decrease in PCE
concentrations at WS4 production wells.
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Of more than 30 production, monitoring, and private wells sampled in various investigations over
the last 10 years, only monitoring well MW4-3, a deep well on the plateau, has not shown a
significant trend of decreasing PCE concentrations since 1992. Concentrations at MW4-3 have
remained relatively consistent at 10 to 20 ug/L.
8.3.3 Preferential Pathways
Controlled studies have shown that PCE can travel in narrow, preferential pathways, particularly
through the unsaturated soil column. Although it is possible that such preferential pathways have
transported PCE to WS4, it is not likely that a large volume of PCE could have moved through
two groundwater formations and an intermediate aquitard without being detected by an array of
shallow and deep monitoring wells between the presumed source (Mill Plain plateau) and WS4.
8.3.4 Degradation of PCE in Groundwater
PCE will eventually degrade into less complex molecules, leaving a chemical chain of breakdown
products that includes TCE and DCA. The conditions that lead to chemical degradation can be
complex, but degradation is generally thought to best occur under anaerobic conditions. A
comprehensive study of PCE degradation was not conducted at WS4 because a primary, ongoing
source was never identified and the treatment system is effective and reliable. However, primary
degradation products of PCE (including DCA and TCE) were analyzed for in all monitoring well
samples. Although these compounds were occasionally detected, they were not found in
sufficient concentrations to indicate that chemical degradation of PCE was a significant factor in
the trend of decreasing PCE concentrations in groundwater near WS4.
8.4 CONCLUSIONS
The PCE contamination at WS4 is persistent and present at levels that require continuing
treatment to protect human health. (There are no complete pathways for ecological receptors and
therefore there is no ecological risk.) There is no suspected ongoing PCE source for which
cleanup action could be taken, and additional investigations into possible sources or channels
would not be cost-effective. Such investigations would be cost prohibitive because the area to be
covered is extensive. It is probable that even an exhaustive investigation would fail to provide
significant additional information about potential sources. If a potential primary source were
identified, it is probable that no direct action would be feasible. Even if further remedial action
were feasible, it is likely that continuing operation of the treatment system at WS4 would be
required. It is therefore appropriate to continue treating the water from WS4, both to remove
PCE from the drinking water supply and to reduce the concentration of PCE in the groundwater.
-------
Air Out
Untreated
Water In
«EPA
REGION 10
Water Distributor
Packing Restrainer
Random Packing
Water Redistributor
Packing Support
Air In
- Treated
Water Out
Figure 9-1
Typical Air Stripper
54-52-OJ3C
Vancouver Water Station 4
RECORD OF DECISION
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Vancouver Water Station 4
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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 WS4 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,
including PCE, 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 would not be protective of current human health because routine
monitoring of untreated water has shown consistent concentrations of PCE above the MCL.
Furthermore, because most of the samples taken from untreated water were analyzed only for
PCE, it is possible that other VOCs are present in the groundwater. Exposure to other VOCs in
the groundwater, together with exposure to PCE, could increase the risk. Given this uncertainty,
the no-action alternative would not be adequately protective of human health. The no-action
alternative would not be protective in the future because users of water drawn from WS4 would
be exposed to unacceptably high concentrations of PCE.
10.2 COMPLIANCE WITH ARARS
This criterion states that remedial alternatives will meet all ARARs of other federal and state
environmental and public health laws or provide justification for invoking a waiver.
The most significant ARARs for this site are the following:
• Federal and state Safe Drinking Water Act MCL for PCE of 5.0 ug/L
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Washington State Model Toxics Control Act (MTCA) Method A level for PCE of
5.0 jig/L; if other chemicals of concern are found in future monitoring, the cleanup
level for those chemicals shall be determined by the ARARs listed in Section
1 J~* • ^. I .
The operating air stripping system as installed is compliant with all ARARs Moreover if
— a* — —" be —'
waste' so tre^ent or
carbon from the strippers must be compliant with Resource Conservation and
Recovery Act (RCRA) Subtitle C and Washington State dangerous waste regulaSonl
mn^rf TIteT ^ W°Uld n0t bC C°mpliant With ARARs because PCE concentrations in
samples of untreated water consistently exceed the MCL. Under both the NCP and MTCA, the
5.0 ug/L concentrate of PCE 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
81 '
vn vnr , is effective in
nH ^h 8 ,an Oter V9Cs that may be Present> from water. This treatment is permanent
and achieves a high degree of certainty of success. permanent
The no-action alternative would rate relatively low for long-term effectiveness and permanence
because there would be no removal of contaminants from water. permanence
^^
s~s
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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. Accordingly, 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.
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.
10.6 IMPLEMENTABDLITY
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 an air stripping system 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.
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Page 44
10.7 COST OF IMPLEMENTATION
t , ir Stripping system at WS4 cost approximately
ion to des.gn and build (including approximately $2 million to build a pumping station and
cnn0^6 ^ City'S Water SyStCm With°ut WS4 until the Batmen' sys'tem a WS4 was
complete ). Operating costs are estimated to be approximately $230,000 per year not ncludinT
-
"* **
Because there is no cost for
10.8 STATE ACCEPTANCE
of state agency
10.9 COMMUNITY ACCEPTANCE
The community was given the opportunity to review the Proposed Plan and to request a
S°
Vaoerrnm
Vancouver All comments were supportive of the selected remedy. A detailed response to
comments ,s provided in the Responsiveness Summary (Appendix A) Tlw,Wno^ir fn
public meeting and there were no objections to EPA'Tproposed Plan q "
1 1.0 THE SELECTED REMEDY
contaminated groundwater.
protective of human health anS the environment, provides the
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EPA Region 10
best overall effectiveness proportional to its costs, and includes treatment as a principal element
The selected remedy also includes monitoring to evaluate system effectiveness at removing PCE
from both groundwater and drinking water produced from WS4.
ll.f 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. K
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 WS4 consists of two packed columns operating in series and has been
operating since January 1992. 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 and paid for by the City of
Vancouver. All drinking water produced by WS4 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.
.Groundwater will be pumped from WS4 at a rate that varies, depending on the time of year and
customer demand. All water pumped by WS4 will be treated and distributed to customers as
drinking water. Estimated costs for this remedy are:
Capital costs: $5,000,000 (construction completed in 1993)
Operation and maintenance costs: $230,000 per year (includes monitoring but not
depreciation)
11.2 GROUNDWATER CLEANUP
By extracting and treating large volumes of groundwater for drinking water, WS4 acts as a very
large pump-and-treat system for removing contaminants from the aquifer near WS4. The captun
zone for WS4 is estimated to be approximately 5 square miles over a 30-year period of time any
ture
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Vancouver Water Station 4
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contamination within this zone will eventually be pulled into the wellfield at WS4. Although the
large capture zone has made it impractical to try to identify an ongoing source of PCE for which
cleanup action could be taken, the high pumping rates for the production wells provide an
effective means of reducing the concentration of PCE in the groundwater near WS4. Eventually,
the extraction of groundwater will flush out residual contaminants in the wellfield, although the
time to achieve the remedial action objectives is not known. Any decision to stop operating the
treatment system must be made with the concurrence of EPA and the Washington State
Department of Energy. *
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 WS4. Groundwater monitoring will consist of sampling production wells and monitoring wells
for PCE and other VOCs. The City of Vancouver will continue to monitor the water at WS4 and
will take at least one sample each year from each active production well. EPA will continue to
review the City's data annually and will periodically, but no less often than every 5 years, sample
the available monitoring wells near WS4.
The results of groundwater monitoring will be evaluated annually and at the 5-year review for
WS4. 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 State Department of
Ecology.
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 treatments that permanently
and significantly reduce the volume, toxicity, or mobility of hazardous wastes as their principal
element. The following sections discuss how the selected remedy meets these statutory
requirements.
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Vancouver Water Station 4
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12.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
The selected remedy protects human health through treatment of drinking water produced from
WS4 as well as groundwater by using air stripping to reduce PCE concentrations. The
contamination of groundwater at WS4 with PCE does not pose a threat to the environment
because the groundwater is 50 feet below ground surface.
Treatment of water produced from WS4 by air stripping reduces PCE concentrations to below
detectable levels, and therefore there were no COPCs identified in treated water. There are no
excess cancer or noncancer risks associated with ingestion, inhalation, or dermal contact with
COCs 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 WS4 by air stripping, complies
with all applicable or relevant and appropriate requirements (ARARs) that have been identified.
The chemical-, location-, and action-specific ARARs are presented below.
• 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, established under the Safe
Drinking Water Act, 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 Cleanup 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
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Vancouver Water Station 4
EPA Region 10
the requirements for manifesting and transport as dangerous waste and treatment
or disposal at a permitted RCRA Subtitle C treatment, storage, or disposal 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. On November 11, 1997, the City was granted
Order of Authorization to Operate SWAPCA 95-CL-512 to operate the air
pollution control equipment. Therefore, the requirements of the General
Regulations and the Order of Authorization to Operate are applicable to the
operation of the air strippers. Independent of CERCLA, the requirements of this
permit (Order of Authorization to Operate) are the air pollution control
requirements.
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
of or treated off site, the NCP 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 1992 at an estimated cost of $5 million. It has been operating successfully since then
at an estimated cost of approximately $230,000 a year for operation and maintenance and
monitoring (depreciation not included). Therefore the selected remedy provides an overall
effectiveness proportionate to its costs, such that it represents a reasonable value for the money.
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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 WS4. No ongoing
source for the PCE in groundwater at WS4 has been identified within WS4, and numerous
investigations have failed to determine an ongoing off-site source or sources of the PCE in the
groundwater at WS4 for which cleanup action could be taken. Therefore a remedy that is focused
on treatment of the drinking water produced from WS4 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 WS4 was listed on the NPL, it was the only
remedy evaluated. However, treatment of the water using air stripping has been proven to be
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 WS4 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 WS4 to less than 5.0 ug/L
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12.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT
Treatment by air stripping addresses the principal threat posed by drinking water produced from
WS4 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 May 1999, discussed remedial action
alternatives for WS4 and identified air stripping as EPA's preferred alternative. No public
meeting was scheduled. The public comment period was May 5, 1999, to June 3, 1999. Written
comments on the Proposed Plan and RI/FS report were received from two individuals and the
City of Vancouver.
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 WS4, as it was
originally identified in the Proposed Plan, were necessary to satisfy public concerns.
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APPENDIX A
Responsiveness Summary
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Vancouver Water Station 4 Appendix A
EPA Region 10 Page A-1
APPENDIX A
Responsiveness Summary
This responsiveness summary will address public comments on the Proposed Plan for remedial
action at Water Station 4 (WS4) at Vancouver, Washington, upon completion of the public
comment period.
The remedial investigation/feasibility study (RI/FS) report and Proposed Plan were released for
public comment in May 1999. 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 May 5, 1999.
Opportunity for Public Comment
The public comment period was held from May 5, 1999, to June 3, 1999. Written comments on
the Proposed Plan were received from two individuals and the City of Vancouver during the
comment period. Comments on the draft RI/FS report that were received from the City of
Vancouver during the comment period for the Proposed Plan are also included in this
Responsiveness Summary.
Opportunity for Public Meeting
The public had an opportunity to request a public meeting. No requests for a public meeting were
received. ,
This responsiveness summary does not reproduce the original comments, but instead presents
compilations of related comments that address the same concern. Original comments that relate
to several different portions of the RI/FS report or the Proposed Plan have been combined and
one response is given. Comments have been numbered to facilitate reference. The complete text -
ot the written comments is available in the Administrative Record file.
Comments on the Draft Final RI/FS Report Received From the City of Vancouver
During the Public Comment Period for the Proposed Plan
Comment 1: While u.s true that no exclusive source of the PCE contamination at WS4 has been
identified, and that EPA has not identified any specific sources that currently require source
control remedial actions at the source location, it is not the case that no source has been
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Page A-2 ^^
EPA Region 10
identified. PCE concentrations measured in groimdwater samples collected immediately
downgradient of Griff ee 's Cleaners and the Town Plaza strongly indicate that those dry cleaning
operations are sources of PCE contamination. We suggest that all statements to the effect that
no sources have been identified be rephrased to state that no sources have been identified that
currently require source control remedial actions at the source location.
Response 1 : This commenter is correct that the term "source" as used in the RI/FS report and
Proposed Plan needs clarification. As used in the RI/FS report and Proposed Plan, the term
"source" was intended to describe a source that could be either (1) primarily responsible for the
sustained high concentrations of PCE measured at WS4, or (2) subject to cleanup or other source
control measures. The maximum PCE concentrations detected downgradient of Griffee's
Cleaners and the Town Plaza were 1/1 Oth of the average concentration of PCE measured at the
wellfield in 1992 (and less than l/20th of the concentration measured at PW-2, immediately
upgradient of the wellfield.) Although the dry cleaners on the Mill Plain plateau may have
contributed to the PCE contamination at WS4 to some extent (as stated in the RI/FS report), the
data indicate that another source or sources were primarily responsible for the sustained high
concentration of PCE measured at WS4.
To more precisely bound the definition of "source," that term in the Record of Decision (ROD)
has been clarified by wording such as "no ongoing source of PCE contamination for which
cleanup action could be taken."
Comment 2: EPA should clarify that although source control remedial actions may not be
currently required at potential sources, those potential sources "may still be liable for remedial
action costs" associated with the investigation and groundwater remediation.
Response 2: This commenter is correct that whether or not source control remedial actions are
required for potential sources, those potential sources are not necessarily ruled out from potential
liability for remedial action costs. Such liability issues are not addressed in these documents. The
purpose of the RI/FS report is to assess the nature and extent of contamination and to analyze the
range of cleanup alternatives for the site. The purpose of the Proposed Plan is to present EPA's
proposed remedy for public comment. The purpose of the ROD is to document the final decision .
regarding the remedial action selected for the site and to explain why that remedy was selected.
Issues of liability are not addressed in the RI/FS report, the Proposed Plan, or the ROD. These
are technical documents that address matters related to the selection of the remedy.
Comment 3: Section 2.6 should state that the hydrogeologic unit in the WS4 area most likely
consists of recent alluvium and Orchards Gravel, not the Troutdale Formation.
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Similarly, in Section 4.2, the following wording is suggested for the seventh bullet on page 4-4:
"WS4 wells pump from the alluvium in hydraulic communication with the deep zone. "
Response 3: The commenter appears to be making the assumption that the Orchards Gravel
extends from the Mill Plain plateau to the WS4 wellfield and therefore that there is a hydraulic
connection between the shallow groundwater region at the Mill Plain plateau and the groundwater
from which WS4 draws its water. The shallow aquifer beneath the Mill Plain plateau is known as
the Orchards Gravel. The deeper groundwater zone is known as the Troutdale Formation. The
alluvium is material near WS4 that could be hydraulically connected to either of these
groundwater formations.
Based on a review of boring logs for the site, the Orchards Gravel does not extend to the base of
the bluff where WS4 is located. The bluff itself likely represents an erosional surface where the
Orchards Gravel was eroded by the Columbia River. The erosional surface somewhat increases
geologic complexity and resultant subsurface uncertainty. However, it appears reasonably clear
that the WS4 wells are screened either in the Troutdale Formation or in recently deposited
alluvium in direct hydraulic communication with the Troutdale Formation.
Comment 4: Only March and September 1998 groundwater elevation data are presented. The
text lacks discussion of seasonal variations in groundwater elevations, groundwater flow
direction, and hydraulic gradient, which would affect fate and transport processes, particularly
migration pathways from potential source areas to WS4.
Response 4: Groundwater Elevations. This commenter is correct that the RI/FS report does
not include data showing seasonal variations in groundwater data. Seasonal variations in
groundwater elevations, groundwater flow direction, and hydraulic gradient were not discussed
for two reasons: (1) a full dataset for groundwater elevations was available only for March and
September of 1998, and (2) those data did not indicate a significant difference that would affect
the conclusions of the RI/FS report or the decision to continue operating the treatment system at
WS4. A table showing the available seasonal groundwater surface elevations has been provided as
an addendum to the final RI/FS report and is also attached to this responsiveness summary. Data
from the entire study area are available only from two dry season dates (October 1992 and
September 1998) and one wet season date (March 1998) because EPA had suspended the
investigation. The time gap (almost 6 years) between October 1992 to September 1998
confounds comparison of these two data sets. The limited temporal data from the entire study
area limits the evaluation of seasonal groundwater surface elevation fluctuations and therefore
seasonal influences on contaminant fate and transport. However, the data do not indicate
significant effects to fate and transport processes, including migration pathways.
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Seasonal Fluctuations. Groundwater surface elevations in the shallow zone decreased in every
measured well from March 1998 to September 1998. These decreases ranged from approximately
0.5 to 1 foot, with an average decrease of approximately 0.7 feet. This is an expected seasonal
fluctuation from the wet season (March) to the dry season (September).
Groundwater surface elevations in the deep zone decreased in all but one of the wells from March
1998 to September 1998. The decreases ranged from approximately 0.25 to 4 feet, with an
average decrease of approximately 2.9 feet. This is an expected seasonal fluctuation from the wet
season (March) to the dry season (September).
Groundwater Flow Direction. The RI/FS report states that "groundwater flow in the deep zone
is to the south-southwest across most of the study area." The two comprehensive data sets
(March and September 1998) suggest that some seasonal fluctuation in the groundwater surface
elevation occurs. However, the same general flow pattern was observed at both times. These
limited observations indicate (1) that seasonal fluctuation of the groundwater surface elevations
do not result in seasonal variation of contaminant fate and transport, and (2) that generally, PCE
in deep zone groundwater will migrate to the south-southwest in the study area regardless of the
season.
Comment 5: The apparent deep zone groundwater divide indicated in Figures A-3 andA-4
likely does not exist. MW4-PHC is deeper than other wells in the Troutdale Formation and the
lower groundwater elevation at this well was used, in part, to create the figures, which resulted
in the apparent divide. A more reasonable groundwater elevation map would indicate a
southerly groundwater flow for the entire Mill Plain plateau.
Response 5: Given the limited deep zone data available in the area, the existence of a
groundwater flow divide in the Parkhill Cemetery area cannot be conclusively confirmed or ruled
out. The available data (without consideration of data collected from MW4-PHC) do suggest
that groundwater flow in this area does have an easterly component. Inclusion of MW4-PHC
suggests an even greater easterly component to flow. The gradient from MW4-3 to MW4-8I
suggests an easterly component to flow. The gradient from MW4-2 to MW4-8I suggests a
southeasterly component to flow. However, the gradient is much shallower in this area than from.
the Tower Mall to WS4. The shallow nature of the hydraulic gradient in this area introduces
uncertainty that precludes drawing a high-confidence conclusion with respect to interpretation of
groundwater flow.
Comment 6: The text does not discuss the hydraulic connection between the shallow and deep
groundwater zones or compare horizontal flow to vertical flow in the shallow groundwater zone
Groundwater in the shallow zone flows to the west and also discharges vertically into the deep
groundwater system. This connection is the primary pathway for contaminant migration frc
rom
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Vancouver Water Station 4 page
potential sources on the surface in the Mill Plain plateau to WS4. The aquitard separating the
two zones likely is a former weathered surface that was subsequently covered by the Orchards
Gravel. The deposition of the younger gravel likely incised channels into and through the
aquitard, which would have created vertical migration pathways. The detection ofPCE in the
deeper groundwater strongly indicates vertical contaminant migration through the aquitard.
Accordingly, we suggest the following wording for the 10th bullet on page 4-4: "Pumping from
WS4 wells captures groundwater over a large area from both the shallow and deep zones to the
north. "
Further, the statement that a large sudden release of PCE probably did not occur on the Mill
Plain plateau is refuted by the indications of vertical flow discussed above. Vertical flow
through the unsaturated zone, the thin shallow groundwater zone, and the aquitard, and/or a
flushing event that released residual PCE in soil in the Mill Plain plateau are entirely plausible
scenarios for the pulse detected in WS4.
Response 6: The competence of the aquitard and the presence of the unsaturated zone directly
beneath the aquitard suggests that there is no significant direct hydraulic connection between the
shallow zone (Orchards Gravel) and the deep zone (Troutdale Formation). That is, contaminant
migration from the Orchards Gravel to the Troutdale Formation is likely to be limited to leakage
from the Orchards Gravel through the aquitard. This leakage is probably dominated by
percolation of groundwater through the aquitard at a rate controlled by the permeability of the
aquitard material (orders of magnitude lower than the Orchards Gravel). In the absence of any
direct evidence, the presence or absence of "incised channels," cracks, windows, or any other
preferential vertical migration pathway in the aquitard can only be speculative. The existing
evidence also cannot rule out a preferential vertical migration pathway through the aquitard.
Hydraulic communication between WS4 and the shallow zone (Orchards Gravel) is limited to the
groundwater that percolates through the aquitard and reaches the saturated portion of the deep
zone (Troutdale Formation) within the capture zone of WS4. The aquitard is competent enough
to create the shallow saturated zone that is relatively areally extensive. This suggests that the
effective average permeability of the aquitard is orders of magnitude lower than the Orchards
Gravel. In addition, blow counts of the aquitard material range as high as 50 blows per 2 inches
of penetration. This indicates that the aquitard material is very hard and not readily eroded.
In the Mill Plain area, the aquitard ranges from 4 to 8 feet in thickness, with the base of the
aquitard at approximately 140 to 125 feet msl. Deep zone groundwater surface elevations
average approximately 110 feet msl. These observations indicate that an unsaturated zone of soil
that ranges from 15 to 30 feet in thickness is present beneath the aquitard.
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Vancouver Water Station 4 Appendix A
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Pumping from WS4 wells captures groundwater over a large area from the deep zone (Troutdale)
and/or alluvium. However, the WS4 wells are screened at elevations between 150 to 200 feet
below the base of the Orchards Gravel. The unsaturated zone between the bottom of the aquitard
and the top of saturation in the Troutdale Formation precludes any sort of direct communication
between the two formations or direct influence of WS4 pumping on the shallow zone. Given (1)
the lack of direct hydraulic connection between the Orchards Gravel and the Troutdale
Formation, (2) the differences in groundwater flow direction between these two units, and (3) the
vertical separation between the intake screens and the bottom of the Orchard Gravel WS4 wells
will capture groundwater from the Orchards Gravel only to the extent that it percolates through
the aquitard to the underlying WS4 capture zone.
The detection of PCE in the Troutdale could suggest that PCE has migrated vertically through the
aquitard and into the deep zone. However, detected PCE concentrations are generally lower in
the shallow zone than in the deep zone (excluding WS4 sample results). Under these geologic
and hydrogeologic conditions, and given available data, it is difficult to develop a scenario in
which a PCE release from the Mill Plain area would result in concentrations in the deep zone that
are greater than concentrations in the shallow zone. It is more likely that the PCE concentrations
in the deep zone are a result of a release from an area outside of the Mill Plain area with
contribution from the Mill Plain area via percolation through the aquitard.
Comment 7: The statement that degradation products of PCE include trichloroethane (TCA)
and dichloroethane (DCA) is inaccurate. TCA is a primary chlorinated hydrocarbon compound
used for industrial purposes, andDCA is a degradation product of TCA. The presence of TCA
indicates a source of chlorinated hydrocarbons that may or may not be related to the potential
sources of PCE.
The presence of TCA andDCA does not indicate degradation of PCE, which would occur under
specific geochemical conditions that are not present in the area of WS4. PCE degradation likely
is not occurring because of the lack of organic carbon required for microbial metabolism, and
the presence of elevated dissolved oxygen concentrations, which limit PCE degradatl
non.
Response 7: The RI/FS report did mistakenly include TCA as a degradation product of PCE
TCA is not a degradation product. However, there is evidence that dichloroethane (DCA) can be
a breakdown product of PCE (although a minor one). As stated in the RI/FS report there is very
little evidence of degradation products of PCE in groundwater in the area of WS4 The lack of
PCE degradation products could be either the result of specific geochemical conditions (as noted
in the comment) or relatively low concentrations of PCE. Determining whether the very low level
of DCA detected in groundwater was the result of PCE degradation or a release of DCA to the
environment was beyond the scope of the investigation and would not have affected the selected
remedy.
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Comment 8: Groundwater results indicate the presence ofPCE at WS4 both before and after the
pulse ofPCE in 1991. This indicates that the 1991 pulse was not the only release event that
impacted the wellfield. PCE was likely released from multiple sources and multiple events. The
distribution and migration pathways of PCE are unknown and no data exist that preclude
another pulse of PCE entering WS4 in the future.
Response 8: The high concentrations of PCE measured at WS4 beginning in 1991 (the "pulse of
PCE") may or may not be associated with the lower concentrations measured prior to that time.
Data presented in the RI/FS report indicate that multiple sources of PCE probably contributed to
the contamination at WS4. However, this conclusion is better supported by the high
concentrations measured at PW-7, PW-8, and PW-9 than by the sudden increase at WS4 in 1991;
it is likely that low concentrations of PCE would both precede and follow a higher-concentration'
pulse regardless of the initial source or sources.
We agree that no data exist that preclude another pulse of PCE entering WS4 in the future. It is
inherently impossible to preclude that no future pulses of contamination will occur. Even if the
past and current source or sources of PCE at WS4 were known, there is always the possibility of
new future sources, particularly given the fact that surface stormwater runoff is routinely disposed
of through dry wells in the area around WS4.
Comment 9: The pattern of decreasing concentrations applies only to the pulse of
contamination. Continuous detections of PCE upgradient of WS4 indicate persistent
contaminant migration, and a steady release of PCE to grovndwater. Releases of PCE at the
surface may have ceased, but residual PCE in soil may be slowly releasing PCE to groundwater
especially at MW4-3S, MW4-8S, and MW4-9S.
Response 9: The commentor is correct that residual PCE in soil may be slowly releasing PCE to
groundwater; residual PCE in soil could be responsible for the PCE measured at both WS4 and
monitoring wells in the vicinity. However, the data presented in the RI/FS report clearly show a
pattern of decreasing concentrations of PCE in wells throughout the area of WS4 (of 29
monitoring and private wells, all but 3 showed decreasing concentrations of PCE from 1992
through 1998.) The continuing detections of PCE, both at WS4 and in wells throughout the area, -
clearly indicate that PCE remains in the environment. Whether these detections are the result of '
residual PCE in soil or in groundwater (or both) was beyond the scope of the investigation, and
would not have changed either the conclusions or the selected remedy.
Comment 10: The distribution of PCE in the area north of WS4 indicates potential sources at
Griffee 's Cleaners and the Town Plaza. Although PCE concentrations may be lower than
concentrations at or near the wellfield, this does not preclude them from being contributors of
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EPA Region 10
PCE to the wel/field. As staled in the text, groundwater may flow in narrow channels, especially
mar sources where dispersion effects are small.
Response 10: Data presented in the RI/FS report indicate that dry cleaning operations at the Mill
Plain plateau could have contributed to the PCE contamination at WS4. Although PCE plumes
can flow in narrow channels, it is unlikely that a large (or steady, longer-term) surface release of
PCE on the plateau could be the primary source of PCE contamination at WS4 (measured at
hundreds of ug/L) without being detected at similar concentrations between the plateau and WS4.
Comment 11: The PCE concentrations in PW-7, PW-8, andPW-9 northwest of the wellfield are
similar to those in the Mill Plain area, indicating that both areas contributed to the PCE at the
•wellfield. .
Response 11: The concentrations of PCE measured at PW-7, PW-8, and PW-9 were higher than
any concentration detected in the Mill Plain area. (The maximum measured concentration in these
three private wells was almost three times the maximum concentration measured in any
monitoring well in the Mill Plain area.) The groundwater flow patterns (both shallow and deep) in
the area do not support a link between these two areas. It is reasonable to conclude that there
probably are multiple sources of PCE in the area of WS4 as stated in the RI/FS report and the
Proposed Plan.
Comment 12: Figure 4-1 suggests northerly groundwater flow in the shallow zone. All data
indicate shallow groundwater flow is to the west.
Response 12: Figure 4-1 was not intended to show directional flow; it is a highly simplified
illustration of the features affecting potential contaminant transport in the vicinity of WS4. As a
two-dimensional representation of a three-dimensional condition, some simplification was
necessary, and the groundwater flow direction arrow referred to in the comment was intended to
represent flow out of the page. Directional headings are meaningless on this type of a simplified
drawing. Calculated directional flows for both the shallow and deep groundwater zones are
shown in Appendix A of the RI/FS report.
Comment 13: The soil-gas concentrations may be too low to indicate an exact location of a
release of PCE, but do indicate at least a proximity to a source area, because PCE is a
manmade chemical used for specific purposes and is not expected to occur widely in the
environment. In addition, PCE is relatively volatile, and will not remain in the soil unless
released in more than trace quantities. Soil-gas results should be considered as indicators of
either a nearby source, or an old source that has substantially volatilized.
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Response 13: As the comment notes, PCE is relatively volatile. Indeed, studies have shown that
gas-phase PCE can travel relatively long distances through soil. Measurement of PCE in soil-gas
may or may not indicate proximity to a source. Soil-gas data alone are insufficient to quantify the
proximity, age, or size of the source.
City of Vancouver Comments on the Proposed Plan
Comment 14: The following statements in the Proposed Plan should be rephrased:
Introduction, page 1 ("no source of the PCE contamination has been positively identified
for possible cleanup")
Background, page 2 ("no source of the PCE contamination at WS4 was definitively
identified")
Results of Previous Investigations, page 3 ("neither the source nor the extent of the high-
concentration PCE plume is known")
Recommended Remedy, page 4 ("no PCE source has been identified")
PCE concentrations in groundwater samples collected immediately downgradient ofGriffee 's
Cleaners and the Town Plaza strongly implicate those dry cleaning operations as potential
sources of PCE to groundwater. PCE concentrations at WS4 have not decreased to below
detection limits, indicating that residual PCE sources remaining in soil continue to release PCE
into groundwater. Potential PCE sources have been identified, but may not presently be
amenable to direct cleanup.
We suggest that the following language be used on page 4 of the Proposed Plan: "No single
PCE source of all contamination at WS4 has been identified. Multiple releases of PCE in the
area of groundwater capture are likely responsible for PCE contamination at WS4. Recent
groundwater test results suggest that source control/treatment is not called for, and that
groundwater treatment at the water station is the preferred remedial action. "
Response 14: The Proposed Plan for WS4 is final and its language will not be rephrased. The
purpose of the Proposed Plan was to briefly summarize the information used to select the
proposed remedy (continued air stripping at WS4), not to present a complete, detailed
explanation of the more complex question of specific sources. The Proposed Plan stated that
"Neither the source nor the extent of the high-concentration PCE plume is known." As noted in
the responses to previous comments on the RI/FS report, this is a reasonable conclusion to draw
from the available facts.
-------
FINAL RECORD OF DECISION Appendix A
Vancouver Water Station 4 Page A-10
EPA Region 10
Comment 15: Page 2 of the Proposed Plan states that "Both the City and EPA continued these
investigations. " The City of Vancouver is currently continuing to pursue identification of
possible sources ofPCE.
Response 15: Comment noted.
Comment 16: Page 3 of the Proposed Plan states that "the significant reduction in PCE
concentration over the last several years strongly supports the conclusion that there is not an
ongoing source of PCE contamination in the area. " However, PCE concentrations have not
decreased to below detection limits at WS4. indicating the persistence of PCE sources in soil.
Historical operations at dry cleaners typically did not manage wastes as rigorously as current
industry practices. It is likely that multiple releases of PCE occurred in the groundwater capture
area of WS4 in the past. These sources have the potential to continue to release PCE into
ground\vater that will migrate to WS4.
Response 16: As noted in both the RJ/FS report and responses to previous comments, it is likely
that residual PCE in soil will continue to release PCE into the groundwater that is eventually
pumped from WS4. This residual PCE could be the result of one or more releases, as stated in
the RI/FS report. Indeed, the high probability that PCE will continue to be present in the
groundwater near WS4 was a major factor in EPA's decision to select continued air stripping as
the remedy for this site.
Comment 17: Recent sampling results several thousand feet upgradient of WS4 indicate
measurable PCE concentrations in groundwater. No data exist suggesting that another pulse of
high-concentration PCE from an unidentified source will not move through the wellfieldin the
future.
Response 17: As stated in the RI/FS report, PCE has been routinely measured in groundwater
throughout the area upgradient of WS4; 21 out of 29 monitoring and private wells sampled during
the WS4 investigations had detections of PCE above the MCL.
EPA agrees that no data exist suggesting that another high-concentration pulse of PCE from an
unidentified source will not move through the wellfield in the future. In fact, it is impossible to
provide such data. The practice of disposing of surface stormwater runoff to dry wells in the
vicinity of WS4 only complicates the question of whether concentrations of PCE will decrease,
stay steady, or increase. In any case, the selected remedy will be sufficient to protect against any
likely future increases in PCE concentrations at WS4.
Comment 18: Page 3 the Proposed Plan states that "this deep groundwater is the source of
water pumped from WS4. "' However, we believe that WS4 captures both shallow and deeper
-------
FINAL RECORD OF DECISION A dix A
Vancouver Water Station 4 p-0- A ,,
EPA Region 10 Page A-11
groundwater from a 5-square-mile area. Shallow groundwater within the capture area migrates
vertically downward into the deep groundwater through a leaky aquitard.
Response 18: As stated in previous responses to comments on the RI/FS report, there are no data
supporting a direct connection between the shallow groundwater (from the Mill Plain plateau) and
the groundwater from which WS4 draws. The shallow groundwater appears to be largely
independent of the deeper groundwater zone. The extent of "leakage" through the aquitard has
not been estimated, but the available data indicate that the aquitard is effective in preventing
significant communication between the two groundwater zones.
Private Individuals' Comments on the Proposed Plan
Comment 19: I was offended when I found out mywater was "not proper water." I contacted
the city and a representative visited my home and instructed me now to treat the water from my
taps so that it would be potable. I installed a water cleaning system and am now having no
difficulties. I appreciate your efforts. I have recently been trying to use the water without my
cleaning system and have found it acceptable. The result is that I believe that the means you are
using to make the water acceptable are effective.
Response: It is unclear whether the water from this commenter's tap was from a private well or
supplied by the City of Vancouver. Further, the nature of the difficulties with the commenter's
tap water is unknown. If the commenter is using water from a private well, the air stripping
system being used to treat City of Vancouver water from WS4 is not treating this water and the
quality of the commenter's private well water, with or without use of an in-home cleaning system,
is unknown.
If the commenter's water is being supplied by the City of Vancouver, it meets all EPA drinking
water standards, and use of in-home water filtering would be based purely on personal preference
for improved taste or odor but would not be required for health or safety reasons.
Comment 20: Thank you for the update. You appear to have done a thorough job in containing
the risks from the pulse ofPCE that entered the system. If the pulse has in fact passed, I would
be interested in a discussion of the need to treat water compared to the value of monitoring, the
cost of treatment compared to monitoring, and the possibility of using the savings [from
monitoring instead of treating], if any, for other sites.
Response 20: Both monitoring and treatment need to be continued at WS4. PCE concentrations
have dropped significantly; however, the concentrations of PCE in untreated water still exceed the
maximum contaminant level (MCL) set by EPA for safe drinking water. Treatment will continue
to ensure that PCE concentrations in the drinking water are reduced to levels that are below safe
-------
FINAL RECORD OF DECISION Appendix A
Vancouver Water Station 4 Page A-12
EPA Region 10
drinking water standards before the water is distributed to citizens for domestic uses. Monitoring
will keep us informed as to the effectiveness of the treatment and will alert us if PCE
concentrations rise to a level that would require increased treatment or other appropriate action.
-------
FINAL RECORD OF DECISION
Vancouver Water Station 4
EPA Region 10
Appendix A
Page A-13
Table A-l
Summary of Depth-to-Water Measurements and Groundwater Surface Elevations
Vancouver Water Station 4
-li'r-'&ii
il?8
Shallow Wells
MW4-3S
MW4-5S
MW4-8S
MW4-8I
MW4-9S
MW4-10S
MW4-11S
MW4-12S
MW4-13S
MW4-14S
»eeiWeifs>f'
MW4-1
MW4-2
MW4-3
MW4-4
MW4-5
MW4-6
W'-f :«fl
I1SI
tfl^'Mt^
293.57
285.46
297.97
297.41
299.38
294.11
302.59
293
292.64
291.74
'/• • . •'»-, -•• ;
132.66
291.56
293.68
30.56
283.51
139.04
•'' X &<.•'*£. 4$
• ,;- Screen;-:^
•^It^Wl
151 to 171
153 to 163
153 to 173
120 to 125
150 to 170
144 to 164
151 to 171
148 to 168
153 to 173
153 to 163
;-«-, - ' :• ,,/.
1310-17
92 to 1 12
89 to 109
-44 to -64
84 to 104
-41 to -61
'.**?• i**
^•jftejpthto,,
^VWjjtej* '
>t4l;^-ff/
129.02
NI
NI
NI
NI
NI
NI
NI
NI
NI
' - y';-;^ ' ,
126.84
175.55
178.53
27.42
167.01
134.36
•?>•:••' '*•$•-,
Grounttwater , ;
.',^ferla'<:«Jlcv.*
,h:<<-;v|!B -^
164.55
NI
NI
NI
NI
NI
NI
NI
NI
NI
•f • '
5.82
116.01
115.15
3.14
116.5
4.68
.. 1 INI, ,,n..|,. mi !••.
flSS
127.34
NI
121.3
NA
122.51
115.84
123.85
NI
NI
NI
f: • ,
120.51
172.98
175.75
164.46
129.17
=====
: Groundwater
>.^;v%'iV-r~
166.23
NI
176.67
NA
176.87
178.27
178.74
NI
NI
NI
12.15
118.58
117.93
Well
Abandoned
119.05
9.87
— - _!!_•••••• __
'V-^Septeia
Jieptli to
*t: (ftb^i,,..
"' j' ' ' * >NC *'*'' '(
127.78
121.47
121.93
121.47
123.13
116.55
124.75
126.64
125.65
126.42
t '•••
124.98
173.22
176.05
164.3
113.23
!—••— •••
»cr i998 / '-}. \ '
Groundwater
'StJjfaceiiev,
_;,_|-''(ftiMsD^
"" \ ' * ''•-.* ' *"
165 79
163.99
17604
17594
17625
17756
17784
16636
166 99
165 32
7 68
11834
11763
119.21
5.81
-------
FINAL RECORD OF DECISION
Vancouver Water Station 4
EPA Region 10
Appendix A
Page A-14
Wel
MD .
Table A-l (Continued)
Summary of Depth-to-Water Measurements and Groundwater Surface Elevations
Vancouver Water Station 4
^Screen/
'f~" Interval
Depth to
Watli*
' (ft-btoc)
Groundwater
Depth to
Water
Grarao&water
SurfaceEIev,
Depth to
Witerf
Gmrndwater
Surface EFev.
- ffttfili) :
MW4-7
156.55
-23 to -43
148.57
7.98
142.36
14.19
146.36
10.19
MW4-8D
297.25
91 to 101
NI
NI
194.68
102.57
198.45
98.8
MW4-DP1
284.38
45 to 65
205.55
78.83
181.18
103.2
182.17
102.21
MW4-DP2
284.34
5 to -5
174.33
110.01
NA
NA
201
NA
MW4-FS1
38.97
7 to -8
NI
NI
29.82
9.15
33.94
5.03
MW4-FS2
38.75
-42 to -52
NI
NI
NI
NI
33.68
507
MW4-HS1
138.95
lto-9
134.75
4.2
129.71
9.24
133.88
5.07
MW4-PHC
292.12
62 to 72
"Source: R.F. Weston 1993
Notes:
ft btoc - feet below top of casing
ft tnsl - feet above mean sea level
NA - not available
NI - well not installed on specified measurement date
198.12
94
193.94
98.18
199.46
92.66
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