United States Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R10-92/048
September 1992
S-EPA Superfund
Record of Decision:
McChord AFB (Wash Rack
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()
NOTICE.
The appendices Hstedin the index that ant not found in this dOcument have been removed at the request of
the issuing agency. They contain materiaJ which supptement, but adds no .ful1t1er apptlcable informatiOn to
the content of the document. All supptementaJ material is, however. contained In the administrative record
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50272-101
REPORT DOCUMENTATION I 1. REPORT NO.. I ~ 3. Recipienfa AcC888ion No.
PAGE EPA/ROD/R10-92/048
1 4. Tide and Subtlde S. Report Date
SUPERFUND RECORD OF DECISION 09/28/92
McChord AFB (Wash/Rack Treatment), WA
6.
First Remedial Action - Final
7. Author(a) 8. Performing Organization Rept. No.
9. Performing Orglinlz8tion Nome and Addre.. 10. ProjectlTuklWork Unit No.
". ContnICI(C) or Grlnt(G) No.
(C)
(G)
12. Sponsoring Organizllion Name and Addr.... 13. Type 01 Report & Period Covered
U.S. Environmental Protection Agency 800/000
401 M Street, S.W.
Washington, D.C. 20460 14.
15. Supplementary Notes
PB93-964614
16. Abalract (Umlt: 200 worda)
The 4,600-acre McChord Air Force Base (AFB) is located in Pierce County, Washington.
The site contains a 22-acre parcel of land, referred to as the Site 54 Washrack
Treatment Area (WTA), which' contains weapon and aircraft maintenance facilities. Land
use in the area is associated with industrial and operational activities at the APB.
The WTA is located east of Clover Creek, a perennial stream that provides the only
surface water drainage for McChord AFB. There are no drinking water supply wells in
the immediate vicinity of the WTA. Site features included a former washrack, two leach
pits, an oil/water separator (skimmer), and storm drainage infiltration ditches. The
site has been utilized for airfield industrial activities, including draining fuel and
washing airplanes. In 1981, the Department of Defense Installation Restoration Program
was initiated onsite to identify the location and contents of past disposal sites.
Through both record searches and the use of aerial photographs dating from 1957 to
1985, several site areas, including Sites 54 and 60, were identified as waste spill and
disposal areas. Floating fuel was identified as underlying a 300,OOO-square-foot area
of the site, which resulted from unrecorded spills. This ROD addresses remediation of
the excavated soil and the NAPL-contaminated ground water at Site 54. The primary
(See Attached Page)
17. Document Analy"ia L Deacrlpto...
Record of Decision - McChord AFB (Wash/Rack Treatment), WA
First Remedial Action - Final
Contaminated Media: soil, gw
Key Contaminants: VOCs, other organics, metals (lead), oils
b. IdentifiersJOpen-Ended Terme
c. COSA 11 FleldJGroup
18. AvlllsbiUty Stllement 19. Secwity ClI.. (Thia Report) 21. No. 0' Pagea
I None 66
20. Secwity Cia.. (Thia Plge) 22. Price
None
(4-77)
(See ANSI Z39.18)
See In.fTucliOM on Reve-
(Fonnelly HTlS-35)
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EPA/ROD/R10-92/048
McChord AFB (Wash/Rack Treatment), WA
First Remedial Action - Final
Abstract (Continued)
contaminants of concern affecting the soil and ground water are VOCs; organics, including
oils; and metals, including lead.
The selected remedial action for this site includes excavating, consolidating, and
treating fuel-contaminated soil onsite with ex-situ bioremediation, then backfilling the
treated soil into an onsite trench; installing passive subsurface extraction trenches to
collect LNAPLs, with onsite separation using fuel skimmers (oil/water separator);
transporting the recovered fuel offsite in drums to either a recycling facility, if
specifications are met, or to a permitted disposal facility; conducting long-teDTI ground
water monitoring; and implementing institutional controls, including deed and ground
water use restrictions, as well as site physical controls. The estimated present worth
cost for this remedial action is $640,000, which includes an annual O&M cost of $54,000
for years 0-1, $23,000 for the years 3-5, and $22,000 for years 6-25 .
PERFORMANCE STANDARDS OR GOALS:
Chemical-specific ground water clean-up goals are based on SDWA MCLs, MTCA Method A, and
background levels, and include soil clean-up levels total petroleum hydrocarbons
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1.
II.
m.
IV.
V.
VI.
VII.
VITI.
IX.
X.
XI.
RECORD OF DECISION
for the
UNITED STATES AIR FORCE
WASHRACK TREATMENT AREA
McCHORD AIR FORCE BASE, W ASBINGTON
TABLE OF CONTENTS
Declaration of the Record of Decision
Decision Summary
Introduction
Page
1
Site Name, Location, and Description
Site History and Enforcement Activities
Community Relations
Scope and Role of Response Action Within Site Strategy
Summary of Site Characteristics
Summary of Site Risks
Description of Alternatives
-Summary of Comparative Analysis of Alternatives
The Selected Remedy
The Statutory Determinations
Documentation of Significant Changes
1
4
5
8
8
24
41
47
52
54
56
Actions Related to the State of Washington's Regulations
Responsiveness Summary
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DECLARATION OF THE RECORD OF DECISION
SITE NAME A..1W LOCATION
Washrack Treatment Area
McChord Air Force Base, Pierce County, Washington
STATEMENT OF BASIS AND PURPOSE
This record of decision presents the selected final remedial action for the Washrack
Treatment Area (WTA) at McChord Air Force Base, Washington, which was chosen in
accordance with the Comprehensive Environmental Response, Compensation, and Liability
Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act
of 1986, 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 WTA.
The state of Washington concurs with the selected remedy.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from this site to the groundwater, if
not addressed by implementing the response action selected in this Record of Decision
(ROD), present a potential endangerment to public health, welfare, or the environment for
future residents at the WT A.
DESCRIPTION OF mE SELECTED REMEDY
It has been determined that contaminant concentrations found in the soil do not pose an
unacceptable risk to human health or the environment, consistent with the NCP. Remedial
action under CERCLA is not necessary for source control to protect human health or
groundwater, surface water, or sediments.
The selected remedy (Alternative FF-5) for the WTA addresses the potential risks posed by
fuel-related contaminants in the groundwater by reducing site contamination to levels that are
protective of human health and the environment and comply with Applicable or Relevant and
Appropriate Requirements (ARARs).
The major components of the selected remedy under CERCLA include:
.
Install one or more extraction trenches capable of capturing the floating fuel in
the unconfmed aquifer.
.
Install on-site collection systems to contain fuel removed from the extraction
trench. .
.
Send extracted fuel to off-site recycler or appropriate disposal facility.
-------
.
Monitor the groundwater and the floating-fuel extraction/collection system during
fuel removal activities to ensure that groundwater remediation levels are achieved
throughout the site.
.
Construct soil piles on a low permeability surface for bioremediation of the
contaminated soil excavated during trench construction.
.
Backfill excavated trench with remediated soil after fuel removal is complete.
.
Implement administrative and institutional controls, such as restrictive covenants
and McChord Air Force Base command directives, that supplement engineering
controls and minimize exposure to releases of hazardous substances during
remediation.
Contaminants in exceedance of state levels of concern have been identified in the leach pit
soils. The leach pits will be monitored to ensure that these contaminants are not detrimental
to groundwater. Concerns under MTCA are attached to this ROD.
STATUTORY DETERMINATIONS
The selected remedy is protective of human health and the environment, it complies with
federal and state requirements that are legally applicable or relevant and appropriate to the
remediaJ action, and it is cost-effective. This remedy utilizes permanent solutions and
resource recovery technologies to the maximum extent practicable, and satisfies the statutory
preference for remedies that reduce toxicity, mobility, or volume as a principal element.
Because this remedy could result in hazardous substances remaining on-site in the
groundwater above health-based levels, a review will be conducted within five years after
commencement of remedial action to ensure that the remedy continues to provide adequate
protection of human health and the environment.
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Signature sheet for the foregoing McChord Air Force Base Record of Decision between the
United States Air Force and the U.S. Environmental Protection Agency, with concurrence by
the Washington State Department of Ecology.
=ARD~k~~NEL. USAF
Commander, 62d Airlift Wing
30 ¥ q,-
Date
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Signature sheet for the foregoing McChord Air Force Base Record of Decision between the
United States Air Force and the U.S. Environmental Protection Agency, with concurrence by
the Washington State Department of Ecology.
&A
-------
Signature sheet for the foregoing McChord Air Force Base Record of Decision between the
United States Air Force and the U.S. Environmental Protection Agency, with concurrence by
the Washington State Department of Ecology.
-~ /. J.J~.A/"J1-J
CAROL FLESKES, PROGRAM MANAGER
Toxies Cleanup Program
Washington State Department of Ecology
9,/:J slt;:l..
Date
QMf~ U. a~~/»1£Y~
1 Y. ACKERMAN
Assistmt Attorney General
State of Washington
Cf,/ 2'iflq ~
Date
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McChord AFB WT A ROD
Page 1
DECISION SUMMARY
INTRODUCTION
The McChord Air Force Base (AFB) Washrack Treatment Area (WTA, Site 54) was listed
on the National Priorities List (NPL) in 1987 under the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980 (CERCLA or Superfund), as amended
by the Superfund Amendments and Reauthorization Act of 1986 (SARA).
Pursuant to Executive Order 12580 (Superfund Implementation) and the National Oil and
Hazardous Substances Pollution Contingency PIan (NCP), the Air Force performed a
Remedial Investigation/Feasibility Study (RIfFS) for the WT A. The Remedial Investigation
(RI) (1992) characterized the nature and extent of contamination in the groundwater, soil,
surface water, and sediments. The RI also evaluated the nature and extent of a floating fuel
layer within the site. The Human Health Risk Assessment (1992) and the Ecological Risk
Assessment (1991) evaluated potential effects of the contamination on human health and the
environment. The Feasibility Study (FS) (1992) evaluated alternatives for remediation of the
contamination.
The Environmental Protection Agency Region 10 (EP A), the Washington Department of
Ecology (Ecology) and the Air Force have executed a Federal Facility Agreement (FFA)
under Section 120 of CERCLA. This agreement established a procedural framework and
schedule for developing, implementing and monitoring response actions at the WTA.
McChord Air Force is administering the Installation Restoration Program (IRP) at McChord
AFB. The Hazardous Waste Remedial Actions Program (HAZWRAP) of Martin Marietta
Energy Systems has been assigned responsibility by the Department of Energy (DOE) for
assisting the cleanup effort at McChord AFB.
I. SITE NAME, LOCATION, AND DESCRIPrlON
A. WTA
McChord AFB occupies an area of about 4,600 acres in Pierce County, Washington (Figure
1). The WT A is within the north industrial portion of the base along the western portion of
the instroment runway and is in the industrial and operational activity areas associated with
aircraft maintenance and flight operation. The WTA is an area where aiIplanes were washed
and drained of fuel. The study area as defined by the Air Force encompasses the area
between Air Mobility Command (AMC) Ramp C and Ramp D and includes a number of
buildings (see Figure 2). The C and D Ramps are large paved parking areas for aircraft.
The site includes a former washrack (now inactive), two leach pits (now backfilled), an
oil/water separator (skimmer), stonn drainage infIltration ditches (now backf1lled), and
floating fuel in the vicinity.
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Washrack Treatment Area
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McChord AFB WT A ROD
Page 4
B. Surface Water and Groundwater Resources
The WT A is located just east of Clover Creek, a perennial stream that provides the only
surface water drainage for McChord AFB. The creek generally flows southeast to northwest
across the base to Steilacoom Lake, which discharges into Puget Sound via Chambers Creek.
Clover Creek flows west beneath the main runway within a O.6-mile-long culvert upstream of
the WT A. After exiting this culvert, the creek flows north to northwest and borders the
WT A site through a redirected manmade channel. It then exits the base flowing westward
towards Steilacoom Lake within its natural channel. Adjacent to the WTA, Clover Creek
discharges to groundwater throughout the year.
There are no drinking water supply wells in the immediate vicinity of the WTA. The
shallow unconfined aquifer is not currently used for domestic or industrial purposes.
c. Current and Future Land Use
The WT A is a small 22 acre parcel of real estate located near the center of the McChord
airfield. It is bounded to the north and south by airfield parking aprons, to the east by an
airfield taxiway and to the west by a road and Clover Creek. Engine test stands and weapon
and aircraft maintenance organizational headquarters facilities are located on the site.
Additional industrial facilities are planned for construction on the site. Present and future
planning for the site is for airfield industrial activities. The WT A is anticipated to remain an
industrial site during U.S. Air Force tenancy.
McChord AFB is conterminous to the more than 85,000 acre U.S. Army Fort Lewis
Reservation. Neither of these installations were identified for closure in the recent two
rounds of military installation closures in the U.S. Both installations are currently spending
millions of dollars annually to integrate military units reassigned from closing bases as part
of the recent Base Realignment and Closure (BRAC) programs. .
TI. SITE HISTORY AND ENFORCEMENT ACTIVITIES
The Department of Defense (DOD) Installation Restoration Program (IRP) was initiated at
McChord AFB in March 1981. The purpose of the multi-phase program was to identify the
locations and contents of past disposal sites and to eliminate the hazards to public health in
an environmentally responsible manner. In 1982, the Phase I record search investigation
identified past and current potential waste disposal sites. Site 54, consisting of a waste spill
and disposal area adjacent to the old paved washrack and the industrial waste treatment
system (buried leach pits), was identified at this time. The Phase U investigation in 1983
measured low-level organic contamination at several of these sites across McChord AFB and
recommended further studies to confirm contaminant characteristics and distribution. The
EPA designated Site 54 as the Washrack/Treatment Area in 1984 and nominated it for
inclusion on the NPL following Hazard Ranking Scoring. In 1987 the WTA was placed on
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McChord AFB WTA ROD
Page 5
the NPL. In 1989 the Air Force entered into a three-party Federal Facility Agreement
(FFA).
Under the terms of the FFA, EPA and Ecology provided oversight of the remainder of the
RIfFS activities for the WT A. During scoping of the RI in 1989, Site 60 and its associated
floating fuel were included in the investigation due to the potential for commingled plumes
with Site 54. In accordance with CERCLA Section 120, the Air Force, the EPA, and
Washington State Department of Ecology are in agreement with the selection of the fmal
remedy in this Record of Decision (ROD).
A. Source Areas
Previous data and reports were reviewed in preparation for the WT A Remedial Investigation
(RI). In 1989, EPA Environmental Monitoring Systems Laboratory performed an analysis of
historical aerial photographs of the WT A site. The report documents physical conditions and
"potential environmental hazards" at the WTA site through time. Nine dates of photographs
collected over a 29-year period (1957 to 1985) were used to perform the analysis. From
these photographs and from information gathered during previous investigations, nine areas
of suspected contamination were identified for further investigation during the RI (Figure 3).
B. Groundwater
Floating petroleum hydrocarbons were detected in wells northwest of the washrack and
former leach pit locations during a Phase n IRP investigation (Figure 3). Because the
shallow unconfmed aquifer is not currently used as a drinking water source, it was not
necessary for the Air Force to take any preventative measures for immediate protection of
human health and the environment. Further investigation determined that the fuel layer was
not migrating off site.
m. COMMUNITY RELATIONS
A. Community Relations During the RI/FS
In accordance with 55 FR 8847, community interviews were conducted with local officials
and public interest groups to identify concerns and public infonnation needs, and to solicit
involvement in the Superfund process. The information gathered during the interviews
provided the basis for development of the site-specific Community Relations Plan (CRP).
Under the CRP, the following activities were undertaken to address community concerns and
interests.
.
Information repositories containing site information and documents on site activities
were established at the following four locations:
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1178
Page 6
1 = 22.396 Sq. Feet
2= 4,112
3 = 7,663
4= 2,134
5 = 1,584
6 = 9,401
7 = 1,121
8 = 1,570
9 = 19,392
.
Areas of Suspected
Contam ination
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............. ........ REFUELING HYDRANTS
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1197
McChord Air Force Base Washrack Treatment Area
Figure 3
Areas of Suspected Contamination
SCALE IN FEET
Note: Based on Historical Aerial Photographic Analysis
I
o
300
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McChord AFB wr A ROD
Page 7
Pierce County Library - Lakewood Branch
Pierce County Library - Tillicum Branch
McChord AFB - Library
McChord AFB - Public Affairs Office
.
One workshop was held to inform the public of the status and findings of the site
investigation on November 1, 1990 (announced the beginning of the RIfFS). One
factsheet and one press release were issued to correspond with this workshop.
Also, in accordance with Section 113 (k)(l) of CERCLA, an administrative record was
established to provide the basis for selection of the remedial action. The administrative
record is available for public review at the McChord AFB Environmental Engineering
Office.
In addition, a Citizen Advisory Committee (CAC) has been established to facilitate the
dissemination of information about the WT A site and another CERCLA site on McChord
AFB (Area D). The CAC is composed of 17 invited members, representing local business
leaders, elected officials, environmental organizations, state and federal agencies, and the
local school district. Members of the CAC inturn pass information received along to their
respective constituents.
To date, two CAC meetings have been conducted-the first on October 23, 1990, and the
second on November 25, 1991. The first meeting consisted of a presentation including such
information as site background, a description of the process for federal facilities, an
explanation of the purpose of the CAC, an overview of the Superfund process, a summary of
the Federal Facility Agreement between EP A, Ecology, and the Air Force, and an overview
of the WT A and Area D sites. Following the presentation, a question-and-answer session
was held. The second meeting provided an opportunity to update the CAC on activities at
both the wr A and Area D sites. It also concluded with a question-and-answer session.
B. Community Relations to Support Selection of a Remedy
In accordance with Sections 113 (k)(2)(B)(i-v) and 117 (a) and (b) of CERCLA, the public
was given the opportunity to participate in the process of selecting a remedy. A Proposed
Plan was prepared which summarized the alternatives evaluated and presented the preferred
alternative. This Proposed Plan was mailed to all members of the wrA mailing list in July,
1992. In addition, the Air Force provided notice in display ads in the Tacoma Morning
News Tribune arid the Lakewood Joumo.l explaining the Proposed Plan. A public meeting
was held on July 16, 1992. A news release was also provided to the local news media.
A 30-day public comment period on the Proposed Plan was held from July 3 to August 1,
1992. Approximately 20 people attended the public meeting held July 16, 1992 at Clover
Park High School in Lakewood, W A. There were no written comments received during the
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McChord AFB WT A ROD
Page 8
public comment period. Comments raised at the public meeting are included in the
Responsiveness Summary attached to this ROD.
IV. SCOPE AND ROLE OF RESPONSE ACTION WI11IIN SITE STRATEGY
The RI evaluated the nature and extent of contamination in all potentially affected media,
including groundwater, soil, surface water, and sediment. Results.from the RI and the
Baseline Risk Assessment indicate that no CERCLA remedial action is necessary for soil,
surface water, or sediments to ensure protection of human health or the environment. RI
results indicated benzene contamination of the shallow unconfmed aquifer as a result of the
floating fuel does exceed health-based levels and/or maximum contaminant levels (MCLs)
and will require remediation as outlined in this ROD. Therefore, the fInal remedial action
selected in this ROD addresses removal of the floating fuel. Groundwater will continue to be
monitored, and if continued contamination is identified, additional investigation and/or
remediation of the residual soil contamination may be required to remove any secondary
sources of benzene (and other contaminants of concern identified in the remedial action
objectives) to groundwater.
The fInal selected remedy under CERCLA includes: (I) removal of the floating fuel to
permanently and significantly reduce the volume and mobility of the hazardous substances
found within the saturated zone and (2) monitoring to evaluate the need for remediation of
the residual fuel in the soil, if it is found to be acting as a secondary source of contamination
to the shallow unconfIned aquifer.
Several metals were found in the leach pits which exceed state levels of concern but not in
groundwater downgradient of the site. The Air Force will install monitor wells around the
leach pits to determine if these metals will degrade the quality of the groundwater in the
future.
V. SUMMARY OF SITE CHARACTERISTICS
A. Site Geology and Hydrogeology
The WT A is situated on an extensive upland glacial drift plain that occupies much of central
Pierce County. The drift plain originated from glacial and glaciofluvial processes associated
with the Vashon Stade of the Fraser Glaciation (the most recent glacial advance). The WTA
is essentially flat ranging from 276 to 283 feet above msl.
Deposits from four glaciations have been recognized within the strata common to the region
(Figure 4). The typical sequence of glacial deposits includes advance outWash, till, and
recessional outwash. One or more of these deposits, representing each of the four
glaciations, along with alluvial and lacustrine interglacial sediments, have typically occurred
in the vicinity of the study area. This series of alternating glacial and nonglacial deposits
forms a complex system, funher complicated by discontinuities of some of the units.
-------
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BEND IJ SECTION
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McChord AFB WT A ROD
Page 11
Permeabilities vary between and within units, with both glacial and nonglacial units
exhibiting aquitard and aquifer properties. Horizontal permeabilities generally exceed
vertical permeabilities.
The uppermost stratigraphic unit, the Vashon Drift, consists of four basic types of glacial
deposits: Steilacoom Gravel, recessional outwash, till, and advance outwash. The
Steilacoom Gravel, a facies of recessional outwash, was deposited in channels caused by
torrential flood waters released by glacial Lake Puyallup. At the WT A, this deposit consists
of open-work coarse gravels and abundant cobbles. The Vashon Recessional Outwash
consists predominantly of sand and gravel at the WT A. This deposit varies in thickness from
15 to 30 feet and is underlain by the Vashon Till. This fine-grained unit is laterally
continuous at the WT A, with a thickness of up to 50 feet, and exhibits aquitard
characteristics. The Vashon Advance Outwash consists predominantly of sandy gravel with
lenses of gravelly sand and varying amounts of silt. Gravel deposits encountered at the
WT A range in thickness from 10 to 70 feet. G1acial outwash sand with layers of nonglacial
sand identified at the WTA is of post-Kitsap age and ranges from 15 to 50 feet in thickness.
The Kitsap Formation has been tentatively identified beneath the WT A and consists of non-
glacial alluvial and lacustrine deposits of silt, sand, and clay with scattered gravel lenses,
ash, wood, and peat. Relatively continuous, it generally occurs less than 150 feet above msl
and ranges in thickness from 20 to 75 feet beneath the WTA. The Kitsap Formation
represents a regional aquitard, although water-bearing layers were found within the unit at
the WTA.
The Salmon Springs glaciation at the WT A is an interbedded drift sequence consisting of
outwash and till. In the WTA, the Salmon Springs is on the order of 100 to 150 feet thick
and occurs below 100 feet msl. The Salmon Springs outwash consists of both recessional
and advance deposits of dense, predominantly stratified sandy gravel and gravelly sand, with
silt and clay lenses. The Salmon Springs Till is a compact deposit of gravelly, silty clay or
clayey, silty g~vel.
The Yashon outwash sequence is, for the most part, highly permeable and contains an
unconfined aquifer. The unconfined aquifer is continuous across the site. Depth to the water
table underlying the WTA is typically 10 feet below ground surface, The saturated thickness
of the unconfined aquifer is about 25 feet. Unconfined groundwater flow beneath the site is
generally towards the north. The gradient varies, across the site and by season, between 14
to 60 feet per mile. Groundwater flow velocities similarly vary from 59 to 113 feet per day,
with a median velocity of approximately 86 feet per day.
This unconfined aquifer is underlain by the Vashon Till. The confined aquifers below the till
layer are the Yashon Drift Confined Aquifer and the Upper and Lower Salmon Springs
Aquifers. The Yashon Drift Confined Aquifer is a shallow aquifer and consists of silty sand
to sandy gravel ranging from 60 to 90 feet thick, and in the southern portion of the WTA, up
to 35 feet of silty gravel of the Kitsap Formation, for a total aquifer thickness of
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McChord AFB wr A ROD
Page 12
approximately 60 to 125 feet. The Upper Salmon Springs Aquifer is a confined aquifer that
consists of silty sand to sandy gravel of the upper portion of the Salmon Springs Outwash.
The thickness of the Upper Salmon Springs Aquifer in the Area of the WTA ranges from 80
to 100 feet. The Lower Salmon Springs Aquifer is similar lithologically to the Upper
Salmon Springs Aquifer and it appears to be more than 75 feet thick.
In the underlying Salmon Springs confined aquifer, the flow direction varies from west to
northeast at a gradient of 8 to 17 feet per mile. The groundwater velocity, which is similar
to the unconfined aquifer, is 1.1 to 1.4 feet per day. Based on the results of the RI, there
appears to be a downward vertical gradient between the upper unconfined aquifer and the
lower Salmon Springs Aquifer.
B. Nature and Extent of Contamination
The WT A investigation evaluated the nature and extent of possible contamination of the soil
(surface and subsurface), groundwater (shallow unconfined aquifer and deeper confined
aquifers), surface water, and sediments within and adjacent to the WTA site. In addition,
investigation of a floating fuel layer within the area was conducted. Naturally occurring
(Le., "background") inorganic concentrations for groundwater and soils were derived from
samples which were collected from upgradient wells and sample locations located within
McChord Area D.
Quarterly sampling was conducted from 26 groundwater monitoring wells, and 3 surface
water/sediment locations within Clover creek. Soil samples were collected from 6 soil
borings and 8 additional surface locations. Preliminary remediation goals- were established
by identifying contaminant levels exceeding ARARS.
1. Soil
Surface soils were investigated in known areas of contamination (Site 54, two leach pits
comprising historical disposal areas for drainage from the wash rack) or in areas suspected of
contamination because of stains and/or spills (based on aerial photographic analysis of the
WTA). Subsurface soils were investigated in the two leach pits to a depth of approximately
25 feet. Four borings were sampled, one of an unpaved location thought to be upgradient of
the leach pits based on interpretation of the groundwater flow direction, one at a location
immediately downgradient of the leach pits, and two within the leach pits. Boundaries of the
leach pits were confmned using geophysical surveys, and surface and subsurface soil samples
were collected and analyzed for Target Compound List (TCL) organic compounds, Target
Analyte List (TAL) metals, and total petroleum hydrocarbons (TPH). Table 1 summarizes
compounds that were detected in the soil from the RI data.
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Page 13
Table 1. McChord AFB Washrack Treatment Area Soil Sampling Results.
Range of Mean of
Frequency of Concentration Concentration
Parameter Detection (ug/kg) (ug/kg)
Volatile Organics
1,2-Dichloroethene 1/10 220.00 220.00
Chlorobenzene 2/10 430-440 435.00
Ethylbenzene 4/10 160-2,700 1,145.00
Toluene 3/10 270-5,700 3,323.00
Total Xylenes 6/10 210-17,000 5,126.00
Semi volatile Or~anics and PAHs
1 ,2-Dichlorobenzene 3/23 440-33,000 11,780.00
1,3-Dichlorobenzene 2/23 510-10,000 5,255.00
1,4-Dichlorobenzene 1/23 870.00 870.00
Acenapthene 1/23 120.00 120.00
Bis(2- Ethylhexyl) phthalate 1 0/23 120-22,000 4,410.00
Butylbenzylphthalate 3/23 97-630 369.00
Chrysene 1/23 97.00 97.00
Di-n-Butylphthalate 2/23 83-150 117.00
Fluoranthene 2/23 100.00 100.00
Fluorene 1/23 90-100 95.00
N-N itrosodiphenylam ine 1/23 270.00 270.00
Naphthalene 3/23 2,000-16,000 6,733.00
Phenanthrene 5/23 100-980 502.00
Pyrene 3/23 91-150 110.00
TPH
Diesel 3/23 2,100,000-10,000,000 6,033,333.00
Ethylbenzene 6/23 0.08-1600 535.00
Ga; 5/23 140-55.000 11,300.00
Kerosene 7/23 100,000-7,700,000 3,324,286.00
Toluene 5/23 0.58-150 32.70
Total Xylenes 1 2/23 0.83-6200 2,350.00
Lube Oif 1/23 720,000.00 720,000.00
Pesticides/PCBs
Endosulfan sulfate 3/23 180-350 253.00
Inorganics
Aluminum 23/23 3,910-17,300 8,490.00
Antimony 7/23 1.8-3.1 2.30
Arsenic 23/23 1-110 7.80
Barium 23/23 17.1-139 46.50
Beryllium 11/23 0.1-2.6 0.47
Cadmium 1 0/23 1.1-23.8 5.50
Calcium 23/23 1,1'70-3,210 2,100.00
Chromium 23/23 6.3-62.3 23.40
Cobalt 23/23 1.6-29.6 6.40
-------
McChord AF8 Wash rack Treatment Area Soil Sampling Results.
Range of
Concentration
(ug/k g)
1.2-3
2,890-12,800
3.3-439
938-3.950
67.8-356
0.03-0.15
5.5-40.5
270-946
0.6-1.1
47.6-336
11.6-42.5
12.1-126
Table 1.
Parameter
Cyanide
Iron
Lead
Magnesium
Manganese
Mercury
Nickel
Potassium
Selenium
Sodium
Vanadium
Zinc
Frequency of
Detection
2/23
23/23
23/23
23/23
23/23
23/23
23/23
23/23
2/23
23/23
23/23
23/23
Page 14
Mean of
Concentration
(ug/kg)
2.10
9,070.00
59.30
2,782.80
170.20
0.08
16.10
498.00
0.85
138.50
21.00
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McChord AFB WT A ROD
Page 15
1.1 Contaminants Found in Surface Soils
Six organic compounds were reported as detections only once in the surface soil samples.
These six compounds included 4-chloroaniline, bis(2-ethylhexyl) phthalate, fluoranthene,
pyrene, gasoline, and lube oil. Of these compounds, the one detection of lube oil in sample
WB-3-1 was the only organic compound found at a level of concern. In general, the
inorganics results are consistent with other soils found in the region. One detection each of
arsenic (CW-29b), cobalt (WS-12), lead (WS-6), and selenium (WS-6) exceeded the
preliminary remediation goal level. These isolated occurrences would indicate a lack of
metals contamination present in the surface soils.
1.2 Contaminants Found in Subsurface Soils
Twenty-three organic compounds were detected in the subsurface soil samples, but only a
few compounds were reported with concentrations in exceedance of the preliminary
remediation goals. Two semivolatile compounds, bis(2-ethylhexyl) phthalate and napthalene,
were detected at elevated levels in two samples (WB-2-2 and WB-3-2). As discussed in the
CLP Statement of Work for organics (EPA 1988c) and the Functional Guidelines for
. Organics (EPA 1988c), bis(2-ethylhexyl) phthalate was determined to be a laboratory
contaminant. Only one carcinogenic PAH compound (chrysene) was detected in one sample
(WB-3-3) at an elevated level. Diesel was detected in three of the ten samples and kerosene
was detected in seven of the ten samples in exceedance of the preliminary remediation goal.
In general, the inorganic results are consistent with other soils found in the region, with a
few exceptions. Three out of ten samples (WB-3-2, WB-3-3, and WB-4-2) had elevated
cadmium levels. These samples were collected from the northernmost leach pit. Two
detections each of chromium (WB-3-2 and WB-3-3), and one detection each of copper (WB-
1-3) and lead (WB-3-2) were potential contaminants of concern. These isolated occurrences
indicate that metals contamination may be present within the leach pits but is not pervasive in
the other subsurface soils.
2. Groundwater
During the RI, 14 previously installed groundwater monitor wells and 12 new groundwater
monitor wells were sampled and analyzed on a quarterly basis to provide information on the
distribution and concentration of contaminants. The location of these wells are shown in
Figure 5. For the shallow, unconfined aquifer, fourteen existing and three new monitor
wells were sampled quarterly for four rounds. For the deeper, confined aquifers, nine new
monitor wells (three in each of the underlying confined aquifers) surrounding the site were
sampled quarterly for four rounds.
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McChord AFB WT A ROD
Page 17
New and existing wells were sampled for volatile organics, semivolatiles, pesticides,
polychlorinated biphenyls (PCBs), polynuclear aromatic hydrocarbons (pAHs), total
petroleum hydrocarbons (TPH), and Target Analyte List (TAL) inorganics. Table 2
summarizes compounds with detections from the RI groundwater sampling data for ten wells
located outside the floating fuel area.
Pesticides and PCBs were not detected in the groundwater. Elevated levels of inorganic
compounds were detected in many of the wells without a discernible pattern or apparent
plume. Samples were taken of both filtered and unfiltered metals, and exceedances of MCLs
were reported in the total metals samples of aluminum, antimony, arsenic, barium,
beryllium, cadmium, chromium, iron, lead, manganese, and vanadium. Based on
comparison with background data for McChord AFB, the presence of these inorganic
compounds was determined to be attributable to naturally occurring concentrations in the
glacial drift, which is generally present in the suspended sediment nonnally found in
monitonng wells screened in silty units.
Based on sampling results for groundwater within the area of floating fuel, benzene was the
only volatile compound for which the maximum concentration (7.6 ~g/l at well1W-9)
exceeded the preliminary remediation goal of 5 JLg/L However, the average value for
benzene was well below this criteria. No contaminant plume can be delineated from "the
benzene detections in the groundwater samples.
Groundwater results based on ten wells located outside the floating fuel area indicated
isolated occurrences of benzene, bis(2-ethylhexyl) phthalate, and P AHs above the preliminary
levels. Eight inorganic compounds were detected at levels above the remediation goal levels.
Interpretation of the data shows that no groundwater contamination plume is present at the
WTA, except for the floating fuel. Therefore, co-mingled plumes do not exist.
3.
Surface Water and Sediment
The WTA site is located east of and adjacent to Clover Creek, a perennial stream that
provides the only natural surface water drainage at McChord AFB. Clover Creek flows
northwest through the base and discharges into SteiJacoom Lake, which then drains through
Chambers Creek into Puget Sound. Surface drainage across the WTA is generally southwest
to northeast. No pennanent surface water features are present within the WTA boundaries.
Samples were obtained from the creek quarterly for three rounds, beginning with Round 2 of
groundwater sampling. Samples were analyzed for VOCs, semi-volatile organic compounds
including P AHs, TPH, and seven metals. Tables 3 and 4 summarize the compounds with
detections for the surface water/sediment data from the RI.
Five volatile organic compounds were detected in the surface water samples. These
compounds included benzene, tetrachloroethylene, bis(2-ethylhexyl) phthalate, butylbenzyl-
phthalate, and di-n-octyl-phthalate. Four of these five compounds occur as detections in only
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Page 18
Table 2. McChord AFB Washrack Treatment Area Groundwater Sampling Results.
Range of Mean of
Frequency of Concentration Concentration
Parameter Detection (ug/I) (ug/l)
Volatile Organics
1 ,1 Dichloroethene 6/40 0.1-0.5 0.20
1,1,1-TCA 2/30 0.3-0.5 0.40
1,1,1,2-TCA 4/30 0..1-1.5 0.75
1,1-DC? 3/40 0.1-0.3 0.20
1,2 DCE 3/40 0.1-7.6 3.10
1 ,2 Dichloroethane 1/40 0.80 0.80
1,2,3-Trichlorobenzene 4/40 0.1-0.2 0.13
1,2,3-Trichloropropane 1/40 0.10 0.10
1,2,4-Trichlorobenzene 5/40 0.1-0.4 0.18
1 ,2-DC? 1/40 0.20 0.20
1,2-Dibromo 3-chloropropane 2/40 3.7-23 13.35
1,2-Dichlorobenzene 3/40 0.1-2.0 0.96
1,3 DC? 2/20 0.3-0.7 0.50
1,3-Dichlorobenzene 2/20 0.2-4.5 2.35
2.Hexanone 2/22 2.2-2.4 2.30
Acetone 1/20 0.90 0.90
Ethylbenzene 6/20 2.1-6.6 5.50
M+p Xylenes 4/20 1.7-6.3 3.73
n-Propylbenzene 1/20 2.40 2.40
o Xylenes 2/20 32-35 33.50
Sec-butylbenzene 6/20 1.5-4.5 2.43
Styrene 1/20 0.60 0.60
Tert-butylbenzene 1/20 1.00 1.00
Toluene 2/20 1.6-2.3 1.95
trans-1,3 DCP 4/20 1.00-1.50 1.25
Trichlorofluromethan e 1/20 9.40 9.40
Semivolatile Organics
2,4,5- Trichloropropane 3/32 1.00-2.00 1.30
3.Nitro-Aniline 3/32 5.00-8.00 6.30
4-Chloro-Aniline 7/32 1.00-22.00 19.50
Be nzo(b) flu oranth en e 3/32 1 .00-2.00 1.30
Benzoic Acid 2/32 1.00 1.00
Bis(2-chloro)ether 1/32 1.00 1.00
Bis(2ch loro isopropyl)ethe r 5/32 1.00-2.00 1.75
Dibenzanthracene 4/32 1.00.2.00 1.25
Fluorene 1/32 1.00 1.00
N-Nitro-Di-n Propylamine 28/32 1.00-310.00 57.80
N- N itrosodiPhenylam ine 4/32 1.00-3.00 1.50
PAHs
Benzo(a)Anthracene 3/29 0.12-0.28 24.30
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Page 19
Table 2. McChord AFB Wash rack Treatment Area Groundwater Sampling Results.
Range of Mean of
Concentration Concentration
(ug/l) (ug/I)
0.17-0.63 0.40
0.074-0.29 0.18
0.064-0.4 0.28
0.093-0.20 0.15
0.072-0.34 0.24
Parameter
Benzo(b) Fluoranthene
Benzo(k) Fluoranthene
Chrysene
DiBenzo(ah)Anthracene
Indeno(123-cd)Pyrene
TPH
Benzene
Diesel
Ethylbenzene
Gasoline
Jet fuel
Kerosene
Lube oil
Toluene
Xylenes
Inorganics
Aluminum
Antimony
Arsenic
Barium
Beryllium
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Nickel
Potassium
Silver
Sodium
Thallium
Vanadium
Zinc
Frequency of
Detection
2/29
2/29
3/29
4/29
3/29
1/10
1/10
1/10
4/10
5/12
2/14
2/10
2/10
17/20
32/40
4140
26/40
28/40
5/40
9/40
40/40
22/40
14/40
16/40
35/40
32/40
40/40
39/40
7/40
21/40
33/40
1/40
37/40
2/40
23/40
31/40
0.66
1.90
15.00
4.10-16.00
800-43.000
930-2.200
560-2.400
420-550
33-8.200
63.1-231.000
9.7-16.4
1.1-49.00
5.2-1,710
1.4-9.00
2.20-7.00
9,990-71,800
3.4-415
1.8-107
6.2-350
32.5-245,000
1.4-85.9
3,710-69,200
4.5-4.930
0.11-1.4
6.4-335
1,100-18,900
11.00
5,110-23,100
1.1-1.4
3.5-463
4.4-9,520
0.66
1.90
15.00
10.90
14.626.00
1,565.00
1,480.00
485.00
1,086.00
27.413.00
13.80
10.00
280.10
4.76
3.80
19.693.00
87.00
30.90
96.00
24.687.00
23.20
11,098.00
524.00
0.45
115.40
3,455.30
11.00
8,290.00
1.25
88.25
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Page 20
Table 3.
McChord AFB Wash rack Treatment Area Surface Water Sampling Results.
Range of Mean of
Frequency of Concentration Concentration
Detection (~g/l) (~gil)
Parameter
Volatile Organics
Benzene
T etrachloroethene
Semi volatile Organics
Bis(2-Ethylhexyl) phthalate
Butylbenzylphthalate
D j- n-Octyl- Phthalate
PAHs
Benzo(b) Fluoranthene
Indeno-(123-cd) Pyrene
Dissolved Inorganics
Antimony
Arsenic
Cadmium
Chromium
Manganese
2/9 0.1 0.1
3/9 0.2 0.2
6/9 1 - 9 3.5
1/9 14 14
1/9 1 1
1/9 0.2 0.2
2/9 0.16-0.2 0.18
1/9 7 7
2/9 1.2-1.8 1.5
3/9 0.3-1.2 0.77
4/9 1 -1.3 1.08
3/9 3.2-3.9 3.57
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Page 21
Table 4. McChord AFB Wash rack Treatment Area Surface Sediment Sampling Results.
Range of Mean of
Frequency of Concentration Concentratio n
Parameter Detection (mg/kg) (mg/kg)
Volatile Organics
1, 1-Dichloroethene 4/10 0.002-0.015 0.009
1,2-Dichloroethane 6/10 0.002-9 1.581
1,2-Dichloropropane 2/10 0.031-0.044 0.038
Chlorobenzene 1/1 0 0.003 0.003
Total Xylenes 2/10 0.059-0.062 0.061
Semivolatile Organics
4- Bromophenyl-Ph e nylethe r 2/12 14 14
4-C h lorophenylphenylethe r 2/12 23 23
Benzo(ghi)perylene 3/12 0.015-0.24 0.09
Benzyl-Alcohol 1/12 0.007 0.007
Bis( 2-ch loro isopropyl) ethe r 6/12 0.094-0.3 0.164
8is(2-ethylhexyl) phthalate 7/12 0.008-0.23 0.048
Dibenzo-Furan 12/12 0.061-2.8 0.627
Diethylphthalate 8/12 0.011-0.38 0.092
Dimethyl-Phthalijl.te 3/12 0.39-0.48 0.427
Fluoranthene 12/12 0.2-2.8 0.728
Fluorene 12/12 0.037-3.9 0.711
Hexachlorobenzene 7/12 0.11-1.7 0.75
Indeno(123-cd) Pyrene 1 2/1 2 0.037-2.4 0.395
Isophorone 12/12 0.051-2.8 0.522
N-Nitro-Di-n Propylamine 9/12 0.17-3.1 0.806
N-Nitrosodi-Phenylam ine 1/1 2 0.86 0.86
Naphthalene 12/12 0.04-4.7 0.686
Nitro-Benzene 12/12 0.14-4.7 0.78
Pentachlorophenol 12/12 0.042-2.7 0.483
Phenanthrene 9/12 0.02-1.8 0.547
Phenol 3/12 0.054-0.89 0.365
Pyrene 6/12 0.001-0.04 0.02
PAHs
Benzo(a) Anthracene 6/9 0.016-2.2 1.139
Benzo(a) Pyrene 9/9 0.019-3 0.825
Benzo(b) Fluoranthene 6/9 0.052-4.2 1.587
Benzo(k) Fluoranthene 5/9 0.008-2 0.496
Chrysene 9/9 0.014-2.8 1.251
DiBenzo(ah) Anthracene 1/9 1.1 1.1
Indeno-(123-cd) Pyrene 6/9 0.012-1.8 0.579
TPHs
Total Hydrocarbons 6/9 70-1,000 265
Dissolved Inorganics
Antimony 3/9 0.35-2.6 1.817
Arsenic 9/9 1.2-6.8 4.222
Beryllium 8/9 0.19-0.74 0.404
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Table 4.
Page 22
McChord AFB Wash rack Treatment Area Surface Sediment Sampling Results.
Range of Mean of
Concentration Concentration
(mg/kg) (mg/kg)
17.3-107 48.33
5.8-9 7.167
131-289 217.3
Frequency of
Detection
9/9
9/9
9/9
Parameter
Chromium
Cobalt
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McChord AFB WT A ROD
Page 23
one round of sampling. The only compound detected in more than one round of sampling is
bis(2-ethylhexyl) phthalate. Bis(2-ethylhexyl)phthalate is a known laboratory contaminant
and is not believed to be present in the environmental samples.
Two P AH compounds were detected in the surface water. These included benzo(b)
fluoranthene and indeno(I23-cd)pyrene. They were detected in only one round of sampling.
PAR's do not dissolve in water and are believed to have been detected because of sediments
that may have been present in the samples.
There were no TPH detections reported during sampling. Five inorganics, including
antimony, arsenic, cadmium, chromium, and manganese were detected at low concentrations.
Only two of these five were detected in more than one round of sampling.
Five VOCs were detected in the surface sediment samples, with a maximum concentration
equal to 0.183 mg/kg for acetone. Of these five VOCs, only acetone was reported in more
than one round of sampling. Three of the remaining four compounds (2-butanone, toluene,
and 1,1,2,2-tetrachloroethane) were reported as a single detection, and methylene chloride
was reported only for the third round of sampling. Acetone and methylene chloride are
common laboratory contaminants. Additional semivolatile organic compounds were also
detected; the maximum concentrations were reported for bis(2-etbylhexyl) phthalate at 4.3
mg/kg. Bis(2-ethylhexyl) phthalate is also a common laboratory contaminant. Carcinogenic
P AH compounds were also reported at each of the sediment locations. The maximum
reported concentration was for benzo(b), fluoranthene, and benzo(k)fluoranthene at 5.1 ppm.
Laboratory reporting of TPH for Round 2 was separated into diesel and gasoline while
Rounds 3 and 4 data were reported as total hydrocarbons. One isolated detection of diesel
(250 mg/kg) was reported for Round 2 sediment samples, and maximum detections for
Rounds 3 and 4 ranged from 60 to 865 mg/kg. Sediment samples indicated the presence of
six of the seven analyzed metals (As, Be, Cd, Cr, Co, and Mn) in all three rounds.
Antimony was detected in two of the three rounds of sampling.
Direct surface water runoff pathways for transport of soil are not known to have existed
between the potential source areas and Clover Creek. Water levels obtained during the RI
indicate that Clover Creek recharges the shallow aquifer throughout the year. This would
indicate that any contamination potentially present in the soils or groundwater at the WT A
site should not affect the surface water in Clover Creek.
4.
Floatini Fuel
A hydrocarbon layer associated with Site 60, consisting of mixed A VGAS and diesel fuel
floats on the water table beneath the site. The source of this aged fuel layer is believed to be
from unrecorded spills that occurred over 20 years ago. No continuous source of fuel has
been identified at the WTA during this study.
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McChord AFB WT A ROD
Page 24
The nature and extent of this floating fuel layer were investigated during the RI, and a pilot
test was conducted on the removal of this product. Elevation and thickness levels of floating
product were measured in three existing wells and samples of the fuel were analyzed for
physical properties and chemical composition. Skimmer pumps were placed in the three
existing wells to test recovery of the product without removal of the groundwater.
Floating fuel has been identified underlying an area of approximately 300,000 fil. The
thickness of the floating fuel layer ranges from 0.065 to 0.58 feet, as observed in the three
wells during measurements taken in March, July, and August 1991. Mobility of the floating
fuel layer was demonstrated by the changes of fuel layer thickness within individual wells
between monitoring events. The fuel mobility is probably driven by seasonal fluctuations of
the groundwater table in the area. However, the fuel is not migrating beyond the immediate
area, based on observations from surrounding monitor wells screened at the water table, and
has remained in the same approximate location since first monitored in 1985 and 1986.
Physical analysis indicated that the fuel consists of Diesel No.2, or a mixture of diesel and
some lighter fuel, with small components of heavier oil. Semivolatile compounds normally
associated with diesel (Le., 2-methylnaphthalene, fluorene, and phenanthrene) were present
in trace amounts in all three wells. Compounds not normally associated with diesel but
detected in analyses for volatiles, semivolatiles, and metals include toluene, ethylbenzene,
4-methyl-2-pentanone, bis(2-ethylhexyl) phthalate, lead, chromium, and arsenic. .
VI. SUMMARY OF SITE RISKS
The baseline risk assessment considered both human health and ecological risks. The risk
evaluations were prepared in accordance with EP A's Risk Assessment Guidance for
Superfund (RAGS) and EPA Region 10 Exposure Parameters (EPA 1991). The results of
the human health risk assessment are discussed below.
A. Human Health Risks
Adverse effects resulting from exposure to chemical contaminants are identified as either
carcinogenic (Le., causing development of cancer in one or more tissues or organ systems)
or noncarcinogenic (Le., direct effects on organ systems, reproductive and developmental
effects). In the baseline risk assessment, risks have been evaluated for current and future
land use of the WTA. The human receptors considered included off-site residents, on-site
long- and short-term workers, on-site future residents, and off-site recreational visitors.
Exposure conditions for these receptors were assumed to correspond to a wide range of
activities, including residential, recreational, and industrial work. .
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McChord AFB WT A ROD
Page 25
1. Chemicals of Concern
Data collected during the RI were used to identify chemicals present at the site. Media
sampled included groundwater, soils, surface water and sediments. All chemicals were
included in the assessment unless a) they were not detected in any of the above media;
b) toxicity reference values (i.e., Reference dose [RID] or cancer slope factors [CPFs] have
not been developed for a chemical; or c) the chemical was identified as an essential nutrient.
The exception to the above criteria were chemicals that were detected in at least one media,
allowing for the possibility of migration between media. These chemicals were included in
the risk assessment at a concentration equal to half of their respective detection limits (RAGS
1989).
Of the 155 contaminants for which analysis was conducted in WT A exposure media, 12 were
determined by the risk assessment to be contaminants of concern (COC) based on a
reasonable maximum exposure (RME) scenario. In this case, COCs are defined as those
with potential exposures presenting a carcinogenic risk of greater than lE-Q6 and a
noncarcinogenic hazard index greater than a value of one. Based on average exposures, the
number of COCs is reduced to eight.
One of the COCs is a known carcinogen (arsenic); eight are probable carcinogens (beryllium,
benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene,
dibenz(a,h)anthracene, and indeno(1,2,3-cd)pyrene) and one is a possible human carcinogen
(l,4-dichlorobenzene). The remaining cac is a non-carcinogen (benzo(g,h,i)perylene). In
addition, benzene, a known human carcinogen, was found to pose a risk greater than lE-06
risk.
2. Exposure Assessment
a.
Exposed Populations: For this assessment, exposure pathways were evaluated for
four receptors: residents, long-term workers, short-term workers, and adult
recreational visitors. The exposure pathways evaluated for each population are
presented in Table 5. In addition, future on-site residents exposed to benezene in
groundwater were evaluated.
b.
Exposure Point Concentrations: Exposure point concentrations, including
averages and maxima, were derived for each medium of exposure (soils, surface
water, and sediments) for as many contaminants as were detected in each (see
Tables 6 through 9). Generally, a reasonable maximum exposure concentration
(RME, based on a 95 percent upper confidence limit on the arithmetic mean
contaminant concentration) could not be accurately computed; because of the
limited data, the RME was often found to be greater than the maximum value. In
these cases, the RME concentration was set equal to the highest (or in some
cases, the only) measured value. In the case of non-detections, if the detection
limit for a given chemical and medium was lower than the maximum detection
-------
Table 5. McChord WTA Exposure Matrix.
Resident" Worker Recreational II
Current Future Current Future Current Future
Long-term" Long-
Media/Pathway Off-base Off-base On-base Short-term term II Short -term Off-base Off-base
Air
Volatile Inhalation Yes Yes No Yes Yes Yes Yes No No
Soil
Particulate Inhalation Yes Yes No Yes Yes Yes Yes No No
Ingestion No No No Yes Yes Yes Yes No No
Dermal Contact No No No Yes Yes Yes Yes No No
Groundwater
Volatile Inhalation No No Yes No No No No No No
Ingestion No No Yes No No No No No 'No
Dermal Contact No No No No No No No No No
Surface Water
Volatile Inhalation No No No Yes No Yes No Yes Yes
Ingestion No No No No No No No Yes Yes
Dermal Contact No No No No No No No Yes Yes
Fish Ingestion No No No No No No No Yes Yes
Sediment
Ingestion No No No No No No No Yes Yes
Dermal Contact No No No No No No No Yes Yes
II Because exposure point concentrations are not assumed to be substantiaJly different, the current and future scenarios are the same for
this receptor.
MMES/9-IS-92/02S20T
~
~
IrQ
('II
t-..>
-------
Table 6. Soil Boring Exposure Point Concentrations.
Page 27
Page 1 of 2
CHEMICALS Average Concentration RME Concentration
INORGANICS (mg/kg)
Aluminum 7523.76 8016.06
Antimony 1.20 1.52
Arsenic 2.09 2.40
Barium 35.21 40.28
Beryllium 0.11 0.14
Cadmium 2.82 8.07
Chromium 27.26 42.72
Cobalt 5.68 6.16
Copper 40.91 58.67
Cyanide 0.42 0.71
Lead 33.45 67.09
Manganese 138.81 155.32
Mercury 0.07 0.09
Nickel 15.84 11.49
Selenium 0.15 0.15
Vanadium 21. 79 23.12
Zinc 45.92 61. 98
VOLATILE ORGANICS (pg/kg)
Chlorohenzene 354.45 377.91
Dichloroethene, 1,2- 220.00 220.00
Ethylbenzene 459.98 730.70
Toluene 562.11 1084.86
Xylenes. total 928.74 2365.58
SEMIVOL. ORGANICS (pg/kg)
Acenaphthene 120.00 120.00
Bis(2~thy Ihexyl) phthalate 3370.37 11075.90
Butylbenzylphthalate 309.55 599.80
Chrysene 97.00 97.00
Dibutylphthalate 111.58 150.00
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Table 6. Soil Boring Exposure Point Concentrations.
Page 28
Page 2 of 2
CHEMICALS Average Concentration RME Concentration
Dichlorobenzene, 1,2- 3469.96 11546.80
Dichlorobenzene, 1,3- 656.07 1979.99
Dichlorobenzene, 1,4- 417.15 618.76
Fluoranthene 100.00 100.00
FI uorene 270.00 270.00
Methylnaphthalene, 2- 6292.85 14564.80
Naphthalene 1210.43 4281.85
Nitrosodiphenylamine, n- 270.00 270.00
Phenanthrene 389.09 904.82
Pyrene 128.45 150.00
TPH (pg/kg)
Gas 23785.16 44882.00
Diesel 106450.12 556016.00
Kerosene 474968.07 1748461.00
Lube oil 40431.13 71996.90
PESTICIDES AND PCBs (pg/kg)
Endosulfan sulfate 111.40 160.59
-------
Table 7. Surface Soil Exposure Point Concentrations.
Page 29
Page 1 of 2
CHEMICALS Average Concentration RME Concentration
INORGANICS (mg/kg)
Aluminum 8455.55 10444.74
Antimony 1.79 2.19
Arsenic 3.79 6.97
Barium 42.76 57.27
Beryllium 0.27 0.38
Cadmium 0.32 0.52
Calcium 1750.45 NA
Chromium 11.48 13.62
Cobalt 5.15 6.89
Copper 8.93 13.60
Cyanide 0.26 0.26
Iron 7730.43 NA
Lead 22.46 45.29
Magnesium 2363.84 NA
Manganese 173.48 219.63
Mercury 0.06 0.09
Nickel 13.80 17.35
Potassium 434.74 NA
Selenium 0.27 0.36
Sodium 98.46 NA
Vanadium 18.83 22.06
Zinc 30.41 39.04
SEMIVOL. ORGANICS (pg/kg)
Bis(2-ethylhexyl) phthalate 284.23 240.00
Chloroaniline, 4- 160.00 160.00
Dichlorobenzene, 1,2- 337.23 344.52
Dichlorobenzene, 1,3- 337.23 344.52
Dichlorobenzene, 1,4- 337.23 344.52
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Table 7. Surface Soil Exposure Point Concentrations.
Page 30
Page 2 of 2
CHEMICALS Average Concentration RME Concentration
Fluoranthene 90.00 90.00
Methylnaphthalene, 2- 337.23 344.52
Naphthalene 337.23 344.52
Phenanthrene 337.23 344.52
Pyrene 91.00 91.00
PESTICIDES & PCBs (pglkg)
Endosulfan sulfate 25.40 35.59
TPH (pg/kg)
Gas 57.01 107.69
Diesel 12382.91 23451.00
Kerosene 12515.42 23031. 08
Lube oil 99005.73 266934.74
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Table 8. Surface Water Exposure Point Concentrations.
Page 31
Page 1 of 2
CHEMICALS Average Concentration RME Concentration
INORGANICS (pg1L)
Antimony 1.76 3.93
Arsenic 0.66 1.13
Beryllium 0.20 0.20
Cadmium 0.38 0.72
Chromium 0.73 0.90
Cobalt 16.92 16.92
Manganese 6.26 4.40
VOLA Tll.E ORGANICS (pglL)
Acetone 1.30 1.30
Benzene 0.10 0.10
Methylene chloride 0.14 0.33
Tetrachloroethene (pCE) 0.15 0.15
Tetrachloroethane, 1,1,2,2- 0.28 0.28
Toluene 0.13 0.13
SEMIVOL. ORGANICS (pg1L)
Acenaphthene 5.00 5.00
Anthracene 5.00 5.00
Benzo(a)anthracene 0.21 0.21
Benzo(a)pyrene 0.24 0.25
Benzo(b )t1uoranthene 0.22 0.23
Benzo(g,h,i)perylene 5.00 5.00
Benzo(k)t1uoranthene 0.22 0.23
Bis(2-ethylhexyl) phthalate 3.44 6.55
Butylbenzylphthalate 5.85 9.24
Chrysene 0.67 0.37
Dibenz(a,h)anthracene 0.27 0.27
Dibenzofuran 5.00 5.00
Dibutylphthalate 5.00 5.00
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Table 8. Surface Water Exposure Point Concentrations.
Page 32
Page 2 of 2
CHEMICALS Average Concentration RME Concentration
Dichlorobenzene, 1,2- 5.00 5.00
Dichlorobenzene, 1,4- 5.00 5.00
DiethylphthaIate 5.00 5.00
Dioctylphthalate 4.77 5.00
Fluoranthene 5.00 5.00
Fluorene 5.00 5.00
Indeno(1,2,3-cd)pyrene 0.23 0.36
Methylnaphthalene,2- 5.00 5.00
Naphthalene 5.00 5.00
Phenanthrene 5.00 5.00
Pyrene 5.00 5.00
TPH (pg/L)
Diesel 250.00 250.00
Hydrocarbons (fotal) 15.00 15.00
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Table 9. Sediment Exposure Point Concentrations.
Page 33
Page 1 of 2
CHEMICAlS Average Concentration RME Concentration
INORGANICS (pg/kg)
Antimony 1.52 2.29
Arsenic 4.33 12.04
Beryllium 0.39 0.47
Cadmium 2.36 7.80
Chromium 49.06 107.00
Cobalt 7.15 9.00
Manganese 207.87 238.88
VOLA Tll.E ORGANICS (pglkg)
2-Butanone 13.24 41. 20
Acetone 25.60 192.46
Benzene 9.01 27.79
Methylene chloride 5.31 11.55
Tetrachloroethene (PCE) 7.72 21. 25
Tetrachloroethane, 1,1,2,2- 9.01 27.79
Toluene 11.88 64.70
SEMIVOL. ORGANICS (pg/kg)
Acenaphthene 55.79 240.00
Anthracene 106.27 410.00
Benzo(a)anthracene 556.36 3000.00
Benzo(a)pyrene 769.46 2200.00
Benzo(b )fluoranthene 934.09 4200.00
Benzo(g,h,ijperylene 428.71 2000.00
Benzo(k)fluoranthene 230.04 1754.14
Bis(2-ethylhexyl) phthalate 771. 77 4849.49
Butylbenzylphthalate 373.33 770.00
Carbazole 45.06 211.81
Chrysene 579.71 2200.00
Dibenz(a,h)anthracene 211.33 949.46
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Table 9. Sediment Exposure Point Concentrations.
Page 34
Page 2 of 2
CHEMICAlS Average Concentration RME Concentration
Dibenzofuran 23.29 79.00
Dibutylphthalate 433.58 820.00
Dichlorobenzene, 1,2- 32.50 32.50
Dichlorobenzene, 1,4- 40.50 40.50
Diethylphthalate 173.88 300.00
Dioctylphthalate 456.51 860.00
Fluoranthene 546.66 3607.76
Auorene 39.61 230.00
Indeno( I, 2,3-cl)pyrene 392.37 2100.00
Methylnaphthalene, 2- 55.72 135.00
Naphthalene 39.24 110.00
Phenanthrene 383.72 2800.00
Pyrene 638.87 4200.00
TPH Vag/kg)
Diesel 33566.59 250000.00
Hydrocarbons (Total) 217058.38 100000o.00
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McChord AFB WT A ROD
Page 35
observed for that medium and chemical, the non-detection was assigned a value
equal to one-half the detection limit. If the detection limit exceeded the
maximum detection, the non-detection was discarded.
Assuming contaminants in soil, sediments, and surface water may enter the
atmosphere either by volatilization or through disturbances which suspend
particulate matter, air modeling was performed to develop ambient breathing level
contaminant concentrations. The air analysis was conducted in accordance with
the procedures outlined in the Air/Superfund National Technical Guidance Study
Series, Volumes 1-4 (EPA 1989).
For the current scenario, surface soil concentrations (0-6") were used to evaluate
direct soil exposure pathways for all receptors. Indirect vapor inhalation
pathways for all receptors were evaluated using exposure point concentrations
developed from the entire soil profile. Soil boring data at 0-6" intervals for the
current and future direct exposure scenario, and the total boring profile for the
current/future indirect exposure scenarios and future excavation were averaged
for each contaminant. The upper 95th percentile confidence interval was
selected. Duplicate samples from the same depth, or re-analysis of a sample,
were averaged prior to the overall averaging process.
Clover Creek is the only location of surface water/sediments close to the WTA
site. Three sites were sampled during the RI, including upstream, midstream,
and downstream of the site area. For the current exposure scenario, the
analytical results for each contaminant for all samples (rounds) all locations were
averaged. For the future scenario, the same concentrations as indicated above
were used based on hydrogeological information indicating that groundwater is
not flowing into the creek. Therefore, discharges into the creek are not
occurring.
Risk calculations for groundwater were based on a benzene exposure point
concentration (of 7.6 J'g/l) computed from one measurement in a downgradient
well outside of the area of the floating fuel product (see Appendix F to the WT A
Human Health Risk Assessment Report).
c.
Chemical Intake by Exposure Pathway: Chemical intakes (mg/kg-day) were
estimated for each exposure pathway using the exposure point concentrations and
other exposure parameters, such as soil and water ingestion rates, body weights,
and exposure frequencies and durations. Pathway-specific equations from the
RAGS guidance and EPA standard default equations were used to estimate
chemical intakes.
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McChord AFB WT A ROD
Page 36
3. Toxicity Assessment
For carcinogenic chemicals, slope factors are estimated using a conservative mathematical
model which estimates the relationship between experimental exposure (Le., doses) and the
development of cancer (i.e., response) that is derived from human or animal studies. Since
there is much uncertainty in the dose-response values generated using this procedure, the
upper 95 percent confidence limit of the slope of the dose-response curve is normally used in
deriving the slope factor.
For noncarcinogenic chemicals, the reference doses (RID) are used as benchmarks for toxic
endpoints of concern. The goal in developing a RID is to identify the highest
no-observed-adverse-effect level (NOAEL) or the lowest-observed-adverse-effect-Ievel
(LOAEL) from well-designed human or animal studies. One or more order-of-magnitude
uncertainty factors are incorporated to adjust this level based on the following considerations:
1) the duration of the experimental exposure, 2) effects elicited (if any), 3) extrapolation of
the data to other species (i.e., interspecies variability, such as extrapolation to humans), and
4) sensitive subgroups (i.e., intraspecies variability). Additional modifying factors varying
between a value of 1 and 10 may also be incorporated in the derivation of the RID if
additional considerations are necessary. RID and slope factors for the WT A risk assessment
were taken from EPA's computerized Integrated Risk Information System (IRIS); Health
Effects Assessment Summary Tables (HEAST); Drinking Water Health Advisories; or
personal communication with EPA Region 10 Risk Assessment staff.
4. Risk Characterization
a.
Cancer Risk:
Carcinogenic risk is estimated as the incremental probability of an individual
developing cancer above the normal background. population incidence over a
lifetime as a result of exposure to a chemical either known or suspected to cause
cancer. To estimate cancer risk, slope factors are combined with site exposure
information to estimate the incremental cancer risk, which represents a
probability of contracting cancer, and which is usually expressed in scientific
notation (e.g., lE-(4). An excess lifetime risk of lE-04 indicates that, as a
plausible upper bound, an individual has a one-in-ten-thousand chance of
developing cancer in a lifetime as a result of site-related exposure to a
carcinogen.
For known or suspected carcinogens, acceptable exposures are generally
concentration levels that represent an excess upper bound lifetime cancer risk to
an individual of between lE-04 and IE-06, using information on the relationship
between dose and response (NCP 1990).
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McChord AFB WT A ROD
Page 37
b.
Non-cancer Risk:
For 'non-carcinogens, the measure used to describe the potential for toxicity in an
individual is not expressed as a probability. The potential for noncarcinogenic
effects is evaluated by comparing an exposure level over a specific period (e.g.,
lifetime) with a reference dose derived for a similar exposure period. This ratio
of exposure to toxicity is called a Hazard Quotient. The Hazard Index (HI) is the
sum of more than one hazard quotient for multiple substances and/or multiple
exposure pathways. Potential noncarcinogenic effects may be of concern if the
HI exceeds unity (Le., HI> 1).
c.
Human Health Risk Characterization Summary:
A quantitative summary of the maximum risks for cancer risk and hazard indices
identified for COCs over all receptors, sites and land use scenarios is presented in
Tables 10 and 11, respectively. Critical receptors and associated sites are also
presented. The critical pathways identified were soil and sediment ingestion, fish
ingestion and the groundwater exposure pathways. The receptors at greatest risk
are the off-site recreational visitor, the on-site long-term worker and the on-site
future resident.
5. Uncertainty
Major components of the assessment which decreased the certainty of other results were 1)
the toxicity reference values used, and the lack of values for several chemicals; 2) limitations
in contaminant concentration data for soils, groundwater, and surface water; 3) the inclusion
of concentrations at a level one-half the detection limit for many chemicals; and 4) the use of
a number of assumptions to establish exposure parameters in computing chemical intakes.
Due to uncertainty in these and other areas, conservative assumptions were made in order to
ensure protection of human health. Cancer and non-cancer risk estimates must be carefully
interpreted, particularly when evaluating noncarcinogenic effects where uncertainty factors of
two to three orders of magnitude are used in dose-response assessments. For example, risks
in Table 10 for off-site recreational visitors are overly conservative. The fish ingestion
pathway is responsible for the inflated values of risk on the order of 10-3. the fish ingestion
pathway was calculated by assuming that benzo(b)fluoranthene, chrysene, and indeno(I,2,3-
cd)pyrene are also present in the surface waters at one-half the detection limit, even though
these chemicals were detected only in the sediments. This assumption is consistent with
EPA's RAGS guidance (1988).
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Page 38
Table 10. Maximum Estimated Cancer Risks for Contaminants of Concern in the Baseline
Human Health Risk Assessment.
Contaminant of Concern
Arsenic
Benzene
Beryllium **
1,4-dichlorobenzene**
Benzo(a)anthracene**
Benzo(a)pyrene**
Benzo(b )fluoranthene
Benzo(k)fluoranthene**
Chrysene**
Dibenz(a, h)anthracene**
Indeno(1,2,3-cd)pyrene
Target Population
Long- Term Worker/On-site
Soil ingestion
Resident/On-site
Drinking Water Ingestion
Vapor Inha1ation from Showering
Future
Recreational Visitor/ Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Recreational Visitor/Off-site
Fish Ingestion
Current/Future
Maximum Estimated
Cancer Risks
2.13E-06
1. 29E-05
4.26E-06
1.09E-06
6. 12E-05 .
1.92E-04
4.6GE-03
6.49B-03
6. 56E-03
2. 25E-06
9.71E-03
** Risks are based on calculations using one-half detection limit for this cae in surface
water (only). No detection of this cae occurred in surface water during RI sampling.
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Page 39
Table 11. Maximum Estimated Hazard Indices for Contaminants of Concern under the
Reasonable Maximum Exposure Scenario.
Maximum Estimated Hazard
Contaminant of Concern Target Population Indices
Benzo(g. h. i)peryleneal Recreational Visitor/Off-site Fish 12.40
Ingestion Current/Future
aI Risks are based on calculations using one-half detection limit for this COCo No detection of
this coe occurred in surface water during RI sampling.
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B. Environmental Risks
1. Chemicals of Concern
Clover Creek, a perennial stream located just west of the wr A, provides the only surface
water drainage for McChord AFB. The wr A site is an industrial and operational activity
area associated with aircraft maintenance and flight operation, and a potential source of
contaminants which could impact the biota of the area. The wr A risk assessment was
performed to evaluate the risk to aquatic and terrestrial biota at wr A from exposure to a
combination of contaminants from point and non-point sources.
Surface water and sediments were sampled and analyzed for 107 chemicals. Twelve
chemicals of concern were measured in surface waters and thirty-eight in sediments.
Other chemicals may exist at the site, but in concentrations below the detection limits of the
analytical techniques.
2. Exposure Asses'sment
The Ecological Risk Assessment evaluated the potential risk to the site's plant and animal
species from exposure to the contaminated surface waters and sediments. The assessment
was conducted in several phases as described below:
a)
Identification of potential exposure pathways of the contaminants to the biota.
b)
Identification of both the terrestrial and aquatic species possibly exposed to the
contaminant, including their potential level of exposure.
c)
A risk assessment including an initial screening of the primary chemicals of concern,
followed by a quantitattye risk assessment of the chemicals identified which pose a real
risk.
An evaluation identified eight species having a high exposure potential: the bullfrog, painted
turtle, Canada goose, mallard, American robin, river otter, muskrat and coyote. The high
rankings for these species were based on their diverse food habits, contact with sediments, or
duration of exposure to the site. '
3. Risk Characterization and Summary
For the risk assessment, a toxicity score (Toxicity Unit or TU) was derived for all 107
chemicals by comparing maximum concentrations of chemicals in surface water or in
sediment interstitial (pore) water (derived from equilibrium partitioning theory) with
concentrations known to cause a chronic effect. A conservative approach was taken for
chemicals below the detection limits, in which TU was calculated using one-half the detection
limit value.
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Chemicals in surface waters and sediments which posed a potential risk were identified based
on their ~culated TUs. Only cadmium and chromium met the criteria for full risk
assessment.
The risk to aquatic biota from chemical contamination at the wr A is relatively low.
Cadmium and chromium were detected only in sediments, not in surface waters. Interstitial
waters were high but would greatly overestimate the risk to most aquatic organisms. They
do approximate the exposure risks to benthic biota; benthic invertebrates may be at risk from
cadmium and chromium in Clover Creek. Terrestrial species would not be at significant risk
by direct exposure to contaminated sediments.
4. Uncertainty
Sources of uncertainty in the screening portion of the ecological risk assessment include the
chemical data, the estimates of interstitial water concentrations from whole sediment values,
and chronic toxicity values used to detennine the TU scores. In addition, sources of
uncertainty in the full risk assessment include water quality parameters (e.g., hardness),
sediment characteristics (e.g., particle size, acid volatile sulfides) and sediment ingestion
rates by wildlife. Because a reasonably conservative approach was used, the expected risks
are overestimated.
vu. DESCRIPTION OF ALTERNATIVES
A. Soil, Surface Water, and Sediment
Based on evaluation of the results of the Human Health and Ecological Baseline Risk
Assessment, it was detennined that no remedial action is necessary for soil, surface water,
or sediment to ensure protection of human health and the environment. Therefore, no
remedial alternatives were considered or developed for these media. However, floating fuel
in the groundwater does result in benzene contamination which poses an unacceptable risk to
future on-site residents at this site. Because benzene contamination was in exceedance of the
MCLs in one down gradient monitor well, remedial alternatives were evaluated in the
feasibility study for the removal of the floating fuel from the groundwater. A description of
these alternatives and of the applicable or relevant and appropriate requirements (ARARs) is
contained in the following section.
B. F10ating Fuel Alternatives
The remedial alternatives include the following common features:
(1)
Groundwater Monitoring: A long-tenn monitoring program would be instituted using
both existing and new wells to measure the effectiveness of the remedial action during
implementation. If contamination in the groundwater is found to present an
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unacceptable risk to human health and the environment, the Air Force will evaluate
alternatives for remediating the source of the contamination.
(2)
Institutional Controls: Administrative and institutional controls will include physical
controls to restrict access to contaminated media. In addition, appropriate controls
would be described in a restrictive covenant on the site property and would be recorded
with the register of deeds for Pierce County. This restrictive covenant would run with
the land and be binding on McChord's successors and assigns. Although the baseline
risk assessment determined that no unacceptable risk exists in the soil for future
residential use, McChord AFB directives would specifically prohibit future
development of the site for human residence as an added precaution. The McChord
AFB directives would restrict the uses of shallow groundwater within the site.
FF-t. No Action (monitoring only)
The NCP requires that the no action alternative be considered for every site to determine a
baseline against which other remedial alternatives can be measured. Under this alternative,
no remedial actions would be taken. Monitoring would be implemented only to evaluate
changes in the contamination.
FF-2. Institutional Controls
Under this option, no action would be taken to remove the floating fuel. Institutional
controls would be used to eliminate the potential for direct exposure to the fuel, including
physical controls (e.g. posting warning signs) to restrict access to contaminated media, and
legal and administrative measures to restrict land use at Site 60. A groundwater monitoring
program would be included to monitor any changes in contaminant concentrations.
The residual risk for this alternative is equivalent to the risk determined in the baseline risk
assessment, since this alternative does not remediate any of the contamination.
FF-3. Containment
This alternative prevents recharge to groundwater and thus minimizes the spread of the
floating layer. It consists of installing a concrete cap over the floating fuel area.
Institutional actions are also required to prevent disturbance of the cap. The purpose of the
cap would be to eliminate the potential for incidental contact with the floating fuel and to
minimize surface water infiltration. A concrete cap was chosen because of the proximity of
the contamination to the runway.
The concrete cap and drainage designs will be based on subsurface geophysical surveys,
hydrological surveys, and soil and groundwater testing. Site access will be assessed and
process areas designated.
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Final grading will be performed over the area of the floating fuel to complete drainage and
any berming that may be required. The cap will be tied into the existing concrete, currently
covering a portion of the area. The area of the installed cap is estimated to be 342,000
square feet. A base layer of approximately 4 inches of gravel will be placed over the area of
the floating fuel, followed by the concrete cap. The concrete will be compacted and finished
as required.
The residual risk for this alternative is equivalent to the risk determined in the baseline risk
assessment, since this alternative does not remediate any of the contamination.
FF-4. Active Removal or the Floating Fuel/Treatment/Groundwater Recharge/Orr-site
Fuel Recycle
This remediation alternative consists of the installation of a groundwater/fuel extraction
system, a treatment system to remove the floating fuel from the extracted groundwater, and
off-site recycling of recovered fuel. The intent of this alternative is to recover and dispose of
the floating fuel by using a groundwater extraction system that would cause the floating fuel
to flow to the extraction well. The water and oil recovered from the well would pass
through a treatment system to separate the oil from the water and chemically oxidize
oil/organic residues in the water prior to recharging the treated water to the aquifer.
A pump test will be necessary to obtain engineering data for the design of the extraction and
recharge system. The extraction system will consist of a single large-diameter extraction
well for removal of both the floating fuel and the groundwater. Groundwater will be
pumped to create the drawdown necessary to form a cone of depression that will extend over
the entire floating fuel area.
The groundwater treatment system will consist of an oil/water separator, a dissolved-air
flotation system, and a UV-enhanced chemical oxidation system. The oil/water separation
system will consist of two processing steps to separate the oil from the water. In the first
step, the extracted groundwater (which will consist of an oil/water mixture) enters a gravity
separator where the free-phased oil is separated from water with skimmers, weirs, and
coalescing filtration steps. The recovered oil will be pumped into a collection tank. The
second step in the oil/water separation consists of a dissolved air flotation cell. High-speed
pumps are used to aspirate air into the water. The aspirated air comes out of solution as it
rises through the tank and preferentially forms on suspended particles of oil. This causes the
fine oil particles to rise to the top of the internal compartments, where they are skimmed off.
The effluent from the oil/water separation process will pass through a chemical oxidation
process to remove any residual contamination. In this step, the contaminants are chemically
oxidized with oxygen to form carbon dioxide and water. The conversion efficiency can be
nearly 100 percent, depending on the contaminants and treatment conditions.
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A powerful oxidizing agent, such as hydrogen peroxide, is required to oxidize organic
contaminants at relatively dilute concentrations in waste water. It is necessary to convert
these oxidizing agents to hydroxyl radicals, which then attack the organic contaminants. A
widely used method for producing the hydroxyl radicals is to expose hydrogen peroxide to
ultraviolet (UV) light. With sufficient reaction time, organic contaminants can be converted
to carbon dioxide and water using the UV -enhanced oxidation process. The UV oxidation
system is expected to convert 99.7 percent of the organic contaminants to carbon dioxide.
The effluent from this system will be sampled to ensure that it meets discharge limits.
Recharge of the treated groundwater to the aquifer will enhance the artificial gradient in the
extraction system. Recharge can be accomplished by returning the water to the aquifer
through a shallow trench or trenches placed above the water table. The exact number of
trenches and the location of the recharge system will be determined during the design stage.
The fuel collected during the oil/water separation will be transported to a permitted off-site
recycling facility, which will test the fuel to make certain it meets acceptance requirements.
The facility will blend the fuel with other recycled stocks as required to create a blended fuel
oil which meets the specifications for use as a recycled fuel.
FF-S. Passive Fuel Removal/Off-site Fuel Recycle/BioremediatioD of Trench Soil/
Backfill
This remediation alternative consists of an excavated trench, passive fuel removal, off-site
recycling of recovered fuel, and ex situ bioremediation of the soil excavated from the trench.
The intent of this alternative is to recover the floating fuel without generating groundwater
that requires treatment. The recovered fuel will be recycled at an off-site facility.
For passive fuel collection, it will be necessary to excavate a trench on the downgradient
portion of the site from which the fuel will be skimmed. The construction of this trench will
include the excavation of soil contaminated with fuel. Uncontaminated overburden soils will
be excavated and stockpiled for backfill into the trench when the remediation is complete.
The contaminated soil will be remediated and also backfilled into the trench after
remediation.
The contaminated soil excavated during trench construction will be placed on a low
permeability surface and treated using bioremediation. An example of this process would be
injection of nutrients and microbes into the soil pile through a perforated pipe installed within
the pile. This creates the conditions necessary to allow biological activity to occur,
metabolizing the fuel contaminants and oxidizing them to create carbon dioxide and water.
Fuel skimmers (either stationary or traveling-this will be determined during design) will be
placed in the trenches. Recovered fuel will be placed directly into drums or large containers.
Initial fuel recovery is expected to be high but will decrease over the five year time frame
the extraction process is expected to be in operation.
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The fuel collected will be transported to a permitted off-site recycling facility which will test
the fuel to make certain it meets acceptance requirements. If the fuel fails the acceptance
requirements, it will be sent to a permitted disposal facility.
FF -6. In Situ Fuel and Soil Treatment
This remediation alternative consists of in situ bioremediation of the fuel and
fuel-contaminated soils which are located directly above the fuel layer. The intent of this
alternative is to treat the soil without excavation and to destroy the contaminants in the
groundwater with bioremediation.
This system will include a nutrient/oxygen mixing tank, a nutrient/oxygen feed pump, and
nutrient/oxygen injection wells. The mixing tanks are used to hydrate soils and groundwater,
and apply nutrients and oxygenating solutions through the injection wells. The feed pump
will transfer the mixture from the tank to a grid of injection wells.
Because of site-specific variances in biological activity and diverse implementation
technologies, both bench- and field-scale treatability studies will be performed. After these
. treatability studies, it may be necessary to perform a pilot-test over a small area of the
floating fuel. The construction necessary for the pilot-test will be incorporated into the
full-scale design. The construction of the nutrient mixing system and the spacing of the
injection wells will be determined during remedial design.
Alternatives FF-l, FF-2 and FF-3 do not reduce residual risks. Alternatives FF-4, FF-5 and
FF-6 for future on-site residents present a combined residual risk of 8.5E~06 (carcinogenic
risk) after achieving remediation goals of 5 j4g/l for benzene in the groundwater.
The goal of this remedial action is to restore useable groundwater (even though the water is
not currently being used as drinking water) at this site to its maximum beneficial use. Based
on information obtained during the remedial investigation, and the analysis of all remedial
alternatives, it is believed that the floating fuel remedies listed above can achieve this goal.
However, soils above the groundwater table have been saturated with fuel and may act as a
secondary source of contamination. The ability to achieve cleanup levels at all points
throughout the area of the floating fuel cannot be determined until the selected remedy has
been implemented and monitored over time to assess if cleanup level have been met. If the
selected remedy cannot meet the specified remediation levels at any or all of the monitoring
points during implementation, the contingency measures discussed in the next section will be
evaluated and considered along with other innovative technologies that are available at the
time. Technologies currently available which were examined are described below.
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c. Fuel-Contaminated Soil Alternatives
FS-l. No Action (monitoring only)
The NCP requires that the no action alternative be considered for every site to determine a
baseline against which other remedial alternatives can be measured. Under this alternative,
no remedial actions would be taken. Monitoring would be implemented only to evaluate
changes in the contamination.
FS-2. Institutional Controls
Under this option, no action would be taken to remove the fuel contaminated soil.
Institutional controls would be used to eliminate the potential for direct exposure to the fuel,
including physical controls (e.g., posting warning signs) to restrict access to contaminated
media, and legal and administrative measures to restrict land use of the site. A groundwater
monitoring program would be included to monitor any changes in contaminant
concentrations.
FS-3. Containment
This alternative consists of installing a concrete cap over the area of fuel contaminated soil.
Institutional actions are also required to prevent disturbance of the cap. The purposes of the
cap would be to eliminate the potential for incidental contact with the fuel contaminated soil
and to minimize surface water infiltration. A concrete cap was chosen because of the
proximity of the contamination to the runway.
The concrete cap and drainage designs will be based on subsurface geophysical surveys,
hydrological surveys, and soil and groundwater testing. Site access will be assessed and
process areas designated.
Final grading will be performed over the area of the floating fuel to complete drainage and
any berming that may be required. The cap will be tied into the existing concrete currently
covering a portion of the area. The area of the installed cap is estimated to be 342,000
square feet. A base layer of approximately 4 inches of gravel will be placed over the area of
the floating fuel, followed by the concrete cap. The concrete will be compacted and finished
as required.
FS-4. In Situ Bioremediation of the Soil
Under this alternative, an in situ bioremediation program would be initiated for the
contaminated soil remaining at the location of the former floating fuel layer . Bioremediation
is a process in which organisms capable of digesting fuel products are introduced into the
environment. It is anticipated that these organisms would remove from the soil any
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components harmful to humans and the environment. The intent of this alternative is to treat
the soil without excavation.
This treatment system will include a nutrient/oxygen mixing tank, a nutrient/oxygen feed
pump, and nutrient/oxygen injection wells. The mixing tanks are used to hydrate soils and
groundwater, and apply nutrients and oxygenating solutions through the injection wells. The
feed pump will transfer the mixture from the tank to a grid of injection wells.
Because of site-specific variances in biological activity and diverse implementation
technologies, both bench- and field-scale treatability studies will be performed. After these
treatability studies, it may be necessary to perform a pilot-test over a small area of the
floating fuel. The construction necessary for the pilot-test will be incorporated into the
full-scale design. The construction of the nutrient mixing system and the spacing of the
injection wells will be determined during remedial design.
FS-S. Excavation/Treatment/Disposal of the Soil
This alternative calls for the fuel-contaminated soil to be excavated and treated with a
soil-pile bioremediation system. Uncontaminated overburden soils will be excavated and
stockpiled for backfill into the excavation when the remediation is complete. The
contaminated soil will be remediated and backfilled into the excavation after remediation.
The contaminated soil will be treated using bioremediation. Soil piles will be constructed
into which nutrients and microbes are injected through perforated pipe installed within the
pile. This creates the conditions necessary to allow the biological activity to occur that will
metabolize the fuel contaminants and oxidize them, creating carbon dioxide and water.
vm. SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES
The remedial alternatives for the floating fuel at the McChord AFB WT A site were
compared according to nine criteria developed on the basis of statutory requirements of
CERCLA Section 121 and the NCP. The nine criteria are subdivided into three categories:
(1) threshold criteria which relate directly to statutory findings and must be satisfied by each
chosen alternative; (2) primary balancing criteria, which include technical factors such as the
long- and short-term effectiveness, implementability, reduction of toxicity, mobility, and
volume and cost; and (3) modifying criteria, which are measures of the acceptability of the
alternatives to state agencies and the community. The following sections summarize the
evaluation of the candidate remedial alternatives for the floating fuel according to these
criteria. Table 12 includes a summary of the comparative analysis, or relative ranking, of
the alternatives.
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Table U. Summary of Floating Fuel Remediation Alternative Analysis of
Balancing Criteria. Page 1 of 2
Alternative FF-l: Alternative FF-2: Alternative FF-3:
Criteria No Action Institutional Control Containment
Protection of Human Health
and Environment Low Medium High
Compliance with ARARs N/A No No
Long-Term Effectiveness Low Medium Medium
Reduction of Toxicity,
Mobility, and Volume Low Low Medium
Short-Term Effectiveness High High High
Implementability High High High
Capital Cost
Operating Costs
$71,000 $71,000 $992.100
$44,OOO/yr 1/ $45,000/yr 1/ $46,700/yr II
$22,000/yr'1J $23.000/yr'1J $24,700/yr '1J
$493,000 $511,000 $1,390,700
$317,000 $326,000 $1,193,100
Net Present Worth
(i=4%, n=30 yrs)
Net Present Worth
(i= 10%, n=30 yrs)
1/
2/
3/
4/
5/
6/
7/
8/
First 2 Years
Remaining 28 Years
Year 1
Year 2
Year 3
Remaining 27 Years
Year 4
Remaining 26 Years
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Table 12. Summary of Floating Fuel Remediation Alternative Analysis of Balancing
Criteria. Page 2 of 2
Criteria
Protection of Human
Health and Environment
Compliance with ARARs
Long-Term Effectiveness
Reduction of Toxicity ,
Mobility, and Volume
Short-Term Effectiveness
During Construction
Implementability
State Acceptance ..
Community Acceptance ..
Capital Cost
Operating Costs
Net Present Worth
(i=4%. n=30 yrs)
Net Present Worth
(i=10%. n=30 yrs)
11
21
31
41
51
61
71
81
91
101
First 2 Years
Remaining 28 Years
Year 1
Year 2
Year 3
Remain.ing 27 Years
Year 4
Remain.ing 26 Years
Third through Fifth Year
Remain.ing 25 Years
Alternative FF4: Alternative FF-5:
Active Fuel Removall Passive Fuel Removall Alternative FF-6:
Treatment of Fuel and Exca vationIT reatmentl In SitU Treatment
Groundwater Disposal of Trench Soil of Fuel and Soil
High High High
High High High
High High High
High High High
High High High
Medium High Medium
$1,523,100
$443,3OO/yr31
$44,ooo/yr41
S22,ooo/yr'
$205,400
$887,000
S377.000/yr3'
$215,OOO/yr4'
SI93,OOO/yr'
$193,OOO/yr71
$22,OOO/yr8'
$54.000/yr"
S23,OOO/yr9'
S22,000/yrO'
$2,328.900
$640,400
$2,085,000
$2,131,700
$462,900
S1,822,ooo
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A. Threshold Criteria
1. Overall Protection of Human Health and the Environment
This criterion measures how the alternative, as a whole, achieves and maintains protection of
human health and the environment.
Alternative FF-l (no action) does not change contaminant concentrations or exposure
potential; the residual risk is equivalent to the baseline risk. Alternative FF-2 does not
change contaminant concentrations; it provides a reduction in current exposure potential, but
not in future exposure potential. Alternative FF-3 provides a higher level of protection than
Alternative FF-2 by creating a physical barrier to the contamination. Alternatives FF-4,
FF-5 and FF-6 reduce the residual risks because they are designed to remove the floating
fuel.
2. Compliance with ARARs
Compliance with ARARs is a consideration of how the alternatives comply with other
regulations explicitly applicable to the site and with those sufficiently relevant and
appropriate to warrant inclusion. In some extenuating situations, waivers from selected
ARARs may be obtained.
Alternatives FF-l, FF-2, and FF-3 do not meet the chemical-specific ARARs identified for
this site. The floating fuel would remain in the aquifer, acting as a source of benzene
contamination to the groundwater. Additionally, alternatives FF-l and FF-2 do not require
action and; therefore, action-specific ARARs would not apply. FF-3 is consistent with
MCT A in as much as it protects human health and the environment. However, containment
is one of the least preferred options under MTCA. Alternatives FF-4, FF-5, and FF-6 do
provide similar compliance with ARARs. They equally meet the chemical-specific ARARs
because they would comply with the Safe Drinking Water Act by reducing the level of
benzene to below MCLs. These alternatives would also comply with MTCA by reducing the
levels of other contaminants of concerns to acceptable state leve1s. These alternatives would
also meet the state of Washington's requirements for hazardous waste operations conducted at
uncontrolled hazardous waste sites. One point of non-compliance is the injection of
biological agents into the sub-surface under Alternative FF-6 (bioremediation). The State of
Washington would need to approve this action. There were no location-specific ARARs
identified for the site.
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B. Primary Balancing Criteria
3. Long-term Effectiveness and Permanence
This criterion evaluates the long-term effectiveness of alternatives in maintaining protection
of human health and the environment after remedial action objectives have been met.
Alternative FF-l does not provide any long term protection. FF-2 and FF-3 provides limited
long-term protection by limited exposure. However, neither FF-2 nor FF-3 meet remedial
action objectives. Alternatives FF-4, FF-5, and FF-6 provide a high degree of long-term
effectiveness because the floating fuel will be removed or treated to eliminate risks.
4. Reduction of Toxicity. Mobility. or Volume through Treatment
Alternatives were also evaluated according to their ability to reduce, through treatment, the
toxicity, mobility, or volume of contaminants.
Alternatives FF-I, FF-2, and FF-3 do not take action to reduce the toxicity, mobility, or
volume of the contamination. Alternatives FF-4 and FF-5 reduces the volume of
contamination by removal of the floating fuel. FF-6 reduces the toxicity of the fuel by
treatment. FF-4, FF-5, and FF-6 are all effective in reducing the toxicity, mobility and/or
volume of contamination to the groundwater.
5 . Short-Term Effectiveness
This criterion addresses the effects of the alternatives during the construction and
implementation phase until remedial action objectives are met.
None of the floating fuel alternatives evaluated is expected to pose risks to human health
(e.g., workers) during construction or implementation. Any risks during construction can be
adequately regulated with engineering controls and standard health and safety practices.
Alternatives FF-4 and FF-6 provide greater short-term effectiveness by remediating the
groundwater at a significantly quicker rate than Alternatives FF-5.
6. Implementability
This criterion addresses the technical and administrative feasibility of implementing the
alternatives and the availability of services and materials required during implementation.
Alternatives FF-I, FF-2, FF-3, and FF-5 are readily implementable using available
technology. Construction requirements for each of these alternatives are not difficult to
meet, and equipment and specialists are readily available for these well-developed
technologies. Additionally, there should be no difficulty in obtaining any permits that may
be required during design and construction. Construction for Alternative FF-4 would be
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more difficult because of the treatment plant size necessary for the high groundwater
extraction rate. Alternative FF-6 includes a developing technology and will require a
treatability study to determine site-specific requirements.
7. Q;w
Cost is another criterion by which candidate alternatives are compared. Costs in this case
are measured as capital, operation and maintenance (O&M), and present worth costs. A
summary of costs for each of the alternatives is included in Table 14.
C. Modifying Criteria
Modifying criteria are used in the final evaluation of the remedial alternatives, and include
comment from Ecology and from the public.
8. State Ac~ptance
The state of Washington Department of Ecology (Ecology) concurs with the preferred
remedial alternative. Ecology has been involved with the development and review of the
Remedial Investigation, Feasibility Study, Proposed Plan, Record of Decision, and other
project activities (such as public meetings). Ecology's concerns regarding the leach pits are
attached to this ROD.
9. Community Acceptance
Based on verbal comments received during the public meeting held July 16, 1992 and written
comments received during the comment period ending August I, 1992, the community
appears to accept the preferred remedial alternative. Specific responses and comments to the
remedial alternatives may be found in the attached Responsiveness Summary.
IX. TIlE SELECTED REMEDY
Based on evaluation of the RI and the Baseline Risk Assessment, it was determined that no
remedial action under CERCLA is necessary for soil, surface water, or sediment to ensure
protection of human health and the environment.
The selected remedy for the contaminated groundwater is Alternative FF-5: Passive Fuel
Removal/Off-site Fuel RecyclelBioremediation of Trench Soil/Backfill and long-term
monitoring of the groundwater. This remedy addresses the risk posed by the contaminated
groundwater through removal of the floating fuel, which permanently and significantly
reduces the volume, toxicity, and mobility of the hazardous substances.
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A. Major Components of the Selected Remedy
The major components of the selected remedy include:
.
Install extraction trenches capable of capturing the floating fuel in the unconImed
aquifer. One extraction trench is estimated to be needed to achieve this goal.
.
Install on-site collection systems to contain fuel removed from the extraction trench.
.
Monitor the groundwater and the extraction/collection system during groundwater
remediation activities to ensure that groundwater remediation goals are achieved.
.
Construct soil piles for bioremediation of the contaminated soil excavated during trench
construction.
.
Implement administrative and institutional controls such as restrictive covenants and
McChord Air Force Base command directives to supplement engineering controls and
minimize exposure to releases of hazardous substances during remediation.
The goal of this remedial action is to remove the floating fuel and reduce the benzene
contamination in the groundwater associated with Site 60 to below 5 p.g/L.
The selected remedy will include removal of the floating fuel for an estimated period of five
years, during which the system's performance will be carefully monitored on a regular basis
and adjusted as warranted by the performance data collected during operation. Modification
may include installing additional extraction trenches to facilitate or accelerate removal of the
floating fuel. To ensure that cleanup levels are maintained, the aquifer will be monitored at
least annually at groundwater monitoring wells located throughout the site. Post-ROD
studies at least prior to remedial design may include a bench-scale treatability study to obtain
information for the bioremediation of the contaminated soils excavated during construction.
B. Remedial Action Objective/Remediation Level and Compliance Points
The risk assessment concluded that groundwater contamination from benzene (originating
from the floating fuel) presents a threat to human health for future on-site residents. The
objective of the remedial action is to remove the floating fuel from the groundwater,
resulting in a reduction of fuel-related contaminants to levels that are protective of human
health and the environment and are in compliance with ARARs. In accordance with the
NCP, remediation levels for groundwater shall generally be attained throughout the
contaminated plume, or at and beyond the edge of the waste management area when waste is
left in place. Thus for groundwater at the site, remediation levels will be met throughout the
area of the floating fuel. The remediation levels are present in Table 13.
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Table 13. Remedial Action Objectives for the Floating Fuel Area. Page 54
Remediation Level
Contaminant Media (}Lg/L) Basis
Benzene Groundwater 5 MCL
Toluene Groundwater 1000 MCL
Ethylbenzene Groundwater 700 MCL
Xylene Groundwater 10,000 MCL
TPH Groundwater 1000 MTCA Method A
Lead Groundwater 11 Background
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Residual risks from the benzene in the groundwater at tbe remediation level were evaluated
for future on-site residents following remediation. Relevant exposure pathways included
ingestion of drinking water, dermal contact, and inhalation of volatiles while showering. The
results of these analyses using EPA Region 10 exposure parameters and risk assessment
guidance present a total cancer risk of 8.5E-06.
Cancer risks for future on-site residents for groundwater ingestion, dermal contact, and
inhalation will be reduced by approximately 35 percent wben compared to risks calculated in
the Baseline Risk Assessment. Risks to any future on-site residents from groundwater
exposures will be funher mitigated through institutional controls and deed restrictions which
will be strictly enforced by the Air Force.
x. THE STATUTORY DETERMINATIONS
The selected remedy meets the statutory requirement of Section 121 of CERCLA, as
amended by SARA, and, to the extent practicable, the National Contingency Plan and the
state of Washington's MTCA.
. A. Protection of Human Health and the Environment
The selected remedy reduces the risk posed by the contaminated groundwater. The floating
fuel will be removed and the groundwater monitored for residual benzene contamination
above regulatory levels.
B. Attainment of Applicable or Relevant and Appropriate Requirements (ARARs)
ofEnvUomnen~ILaws
The selected remedy will comply with all applicable or relevant and appropriate requirements
(ARARs) of federal as well as more stringent, promulgated state environmental and public
health laws.
1. Ap,plicable or Relevant and Apj)ropriate Requirements
Action-Specific
State of Washington requirements for Water Well Construction (Chapter 18.104
RCW) as codified in Chapter 173-160 WAC.
State of Washington requirements for control of new sources of toxic air
pollutants (WAC 173-460).
State of Washington requirements for hazardous waste operations conducted at
uncontrolled hazardous waste sites as set forth in WAC 262-62 Part P (Hazardous
Waste Operations and Emergency Response).
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McChord AFB WT A ROD
Page 56
Chemical-Specific
Federal requirements of ~he Safe Drinking Water Act (40 USC 3(0) sets
standards for groundwater used as drinking water, as set forth in 40 CFR 141.
State of Washington Hazardous Waste Cleanup - Model Toxics Control Act
(Chapter 70.105D RCW) requirements for clean up of hazardous waste sites as
codified in Chapter 173-340 WAC.
Substantive water resource antidegradation fundamentals of the State of
W;iShington Pollution Control Act (Chapter 90.48 RCW).
Location-Specific
There are no location-specific ARARs identified for the WT A.
2. To-Be-Considered
State of Washington Department of Ecology - Guidance for Remediation of
Releases from Underground Storage Tanks.
C. Cost Effectiveness
The selected remedial action is cost-effective because it is protective of human health and the
environment and attains ARARs, and its effectiveness in meeting the objectives of the
selected remedial action is proportional to its costs.
D. Use of Permanent Solutions and Alternative Treatment Technologies or Resource
Recovery Technologies to Maximum Extent Practicable
The Air Force, EPA, and Ecology have detennined that the selected remedy represents the
maximum extent to which pennanent solutions and treatment technologies can be used in a
cost-effective manner for the site. The risk from the groundwater contamination is
permanently reduced through removal of the floating fuel to acceptable exposure levels for
benzene without transferring the risk to another medium (e.g., air). The selected remedy
provides the best balance of tradeoffs in terms of long-term effectiveness and permanence,
reduction in toxicity, mobility, or volume achieved through treatment, short-term
effectiveness, implementability, and cost. State and community acceptance was also
considered.
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McChord AFB WTA ROD
Page 57
E. Preference for Treatment as Principal Element
Although the selected remedial action does not include treatment as a component, removal of
the floating fuel pennanently and significantly reduces the volume, toxicity, or mobility of
the hazardous substances.
XI. DOCUMENTATION OF SIGNIFICANT CHANGES
The Proposed Plan for the WTA was released for public comment on July 3, 1992. The
Proposed Plan identified Alternative FF-5, passive removal of the floating fuel, as the
preferred alternative. Upon review of public comment, it was detennined that no significant
changes to the remedy, as originally identified in the Proposed Plan, were necessary.
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ACTIONS RELATED TO mE STATE OF WASHINGTON'S REGULATIONS
Contaminants were detected in the leach pit soil at concentrations above the "Model
Toxies Control Act" (MTCA) cleanup levels. These contaminants were not found to
present a risk to human health and the environment according to CERCLA guidance but
are at levels of concern according to the MTCA.
mE STATE'S CONCERN
The state is concerned with the potential mobilization to groundwater of the contaminants
found in the leach pit soil. These soil contaminants were found at levels above
background. and above conservative MTCA levels that are considered protective of
groundwater. See Table 1 for a list of the state's contaminants of concern.
PREFERRED ALTERNATIVE
No remedial action is required at this site under MTCA to remediate contaminants in the
leach pit soils at this time. A component of the preferred alternative is the requirement
to monitor the groundwater downgradient from and adjacent to the leach pits to ensure
that mobilization of soil contamination will not occur. If contaminants of concern
detected downgradient above the remedial action objectives (see Table 2) are determined
to be derived from the leach pit soils, then the need for implementation of one of the
other leach pit alternatives described in the Remedial Investigation/Feasibility Study will
be assessed. '
STATE CONCURRENCE
The State of Washington concurs with the Air Force's decision to monitor the
groundwater at the leach pits for the state's contaminants of concern. Any requirement
for further action will be assessed based on these monitoring results.
MMESf9-24-92/03370A
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Table 1. Soil Contaminants of Concern (mg/kg).
MTCA
Method C
Contaminant Soil Groupl/ UL Conc.2/ Background3/ Cleanup Level
Cadmium LP-2 23.8 1.8 1.7
LP-3 12.3 1.8 1.7
Chromium
LP-l
LP-2
14.6
140.0
25.0
25.0
5.0
5.0
LP-3
51.9
25.0
5.0
Copper
LP-3
170.5
31.0
100.0
Lead
LP-l 32.0 11.0 0.5
LP-2 148.2 11.0 0.5
LP-3 68.7 11.0 0.5
1/
LP-l - Soil sample interval of 0-6" in the Leach Pit borings.
LP-2 - Soil Sample interval of 12'-15' in the Leach Pit borings.
LP-3 - Soil sample interval of 15'-19.5' in the Leach Pit borings.
2/
95 percent upper confidence limit on the mean.
3/
90th percentile of background data.
MMES/9-25-92/03370A
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Table 2. Remedial Action Objectives for the Leach Pits
Remediation
Contaminant Media Level (}.Lg/l) Basis
Cadmium Groundwater 14 Background
Chromium Groundwater 50 MCL
Copper Groundwater 1000 MCL
Lead Groundwater 11 Background
MMESI9-14-92/03370A
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