United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EP AIRODIR08-91/049
September 1991
e892-961161~
&EPA
Superfund
Record of Decision:
Hill Air Force Base, UT
'. f'c~fP~ iM@J)(Q;~ C@~~@cr:~ffO!1l-
~~~~~~ti~itm ResGurce Center
. us EPA Region 3
fdUadelphia. PA 19107
Hazardous WaateColectiOn-
InfOl'mOtion Resourc.-een --
USEPA RegIon 3 '. ~
Philadelphia.. PA 19107
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502"/2.101
I REPORT DOCUMENTATION 1'. REPORTNO.
PAGE EPA/ROD/R08-91/049
TItle and Subdue
SUPERFUND RECORD OF DECISION
Hill Air Force Base, UT
First Remedial Action
I ~
3. RecIpient'. AcceMion No.
5. Report Date
09/30/91
I.
7. Aulhor(a)
a. Performing Organlzadon Repl No.
II. PIIrformlng Orgalnlzadon Nam8 and Add-
10. ProJectlTuklWort Unit No.
11. Contr8ct(C) or GrIU1t(G) No.
(C)
(G)
12. Sponaorlng Organization Nam8 and Addr888
U.S. Environmental Protection
401 M Street, S.W.
Washington, D.C. 20460
13. Type 01 Report. Period Covered
Agency
800/000
14.
15. Supplementary Note.
16. Abatract (Umlt: 200 worda)
The 6,700-acre Hill Air Force Base (Hill AFB) site is an active military facility
situated between the cities of Ogden and Salt Lake City, covering portions of Davis and
Weber Counties, Utah. This Record of Decision (ROD) addresses part of Operable Unit 2
(OU2), which consists of two unlined disposal trenches, seeps, and springs, and
confined and unconfined aquifers. Land use in the area is mainly agricultural and
residential. Both South Weber and Hill AFB obtain drinking water from deep wells in
confined aquifers. Because the base covers a large area, the Air Force has grouped
geographically adjacent contaminated preas into seven OUs. From 1967 to 1975, Hill AFB
disposed of waste solvents and sludge from degreasing operations in the onsite disposal
trenches. It is estimated that 100,000 to 1,000,000 gallons of TCE bottoms from the
solvent recovery unit, sludge from vapor degreasers, and plating-tank sludge bottoms
were disposed of in these trenches. Federal investigations from 1983 to 1986
identified VOC contamination in onsite and offsite ground water. As a result of these
investigations, Hill AFB began collection and treatment of contaminated ground water
from seeps and springs in 1986. In addition, an alternate water supply was provided to
five properties to prevent the use of contaminated ground water from seeps and springs.
(See Attached Page)
17. Document Analyal. L De.crlptora
Record of Decision - Hill Air Force Base, UT
First Remedial Action
Contaminated Media: soil, gw
Key Contaminants: VOCs (PCE, TCE, toluene, xylenes)
b. Idendller8l0pen-EndecI T811118
Co COSA TI FleIdlGro!4)
Av8llabIUty Statement
111. s.a.lty CI... (nile Reportj
None
211. Secwlty CI... (nile Page)
NnnA
21. No. 01 Pagea
32
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22. PrIce
(See ANSI Z3B.1S)
&Ie 1lu11Ucll- on Re-
212 (4-17)
(Formerly NTlS-35)
Department 01 Commerce
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EPA/RODl/R08-91/049
Hill Air Force Base, UT
~irst Remedial Action
Abstract (Continued)
This ROD addresses the interim remediation of OU2 subsurface soil and ground water by
removing a DNAPL source and thus preventing contaminants from reaching aquifers currently
used as drinking water sources. A subsequent ROD will provide a final remedy for OU2
soil, ground water, surface water, and air. The primary contaminants of concern
affecting the soil and ground water are VOCs including PCE, TCE, toluene, and xylenes.
The selected remedial action for this interim remedy includes installing and maintaining
a source recovery system to remove DNAPL contamination from the subsurface; pumping
DNAPL-contaminated ground water, with onsite discharge to a pretreatment facility to
separate DNAPL from ground water using a steam stripper; temporarily storing the DNAPL
onsite in steel tanks, followed by transporting the waste offsite for incineration;
installing a pipeline from the site to the base Industrial Wastewater Treatment Plant
(IWTP); treating the pretreated ground water at the IWTP using air stripping, followed by
carbon adsorption; discharging the treated water offsite to a publicly owned treatment
works (POTW); and monitoring DNAPL collection and treatment during remediation
activities. The estimated present worth cost for this remedial action is $3,710,000,
which includes an annual O&M cost of $1,000,000 for 2 years.
PERFORMANCE STANDARDS OR GOALS:
in a future ROD.
Actual chemical-specific standards or goals will be set
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Hill Air Force Base, Utah
Final
Record of Decision for Interim
Action at Operable Unit 2
August 1991
Environmental Management Directorate
~ Ogden Air Logistics Center
.~ HiIIAFB. Utah
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RECORD OF DECISION FOR
INTERIM ACTION AT
OPERABLE UNIT 2
Site WP07 - Chemical Disposal Pit 3
Hill Air Force Base, Utah
August 1991
Prepared by:
,
Captain Edward Heyse, P.E.
W. Robert James, PhD, P.E.
Jo Anne Summers
Environmental Restoration Division
Environmental Management Directorate
Hill AFB, Utah 84056
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1.0
2.0
3.0
4.0
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TABLE OF CONTENTS
DECLARATION FOR THE RECORD OF DECISION. . . . . . . . .
1.1 Site Name and Location. . . . . . . . . . . . . .
1.2 Statement and Basis of Purpose. . . .
1.3 Assessment of the Site. . . . . . . . . . . . . .
1.4 Description of Selected Remedy. . . . . . . . . .
1.5 Statutory Determination. . . . . . . . . . . . . .
1.6 Signature and Support Agency Acceptance of the
Remedy . . . . . . . . . . . . .
DECISION S~Y . . . '. . . . . . . . . . . . . . . . .
2.1 Site Name,- Location and Description. . . . . . . .
2.2 Site History and Enforcement Activities. . . . . .
2.3 Highlights of Community Participation. . . . . . .
2.4 Scope and Role of Response Action. '....
2.5 Site Characteristics . . . . . . . .
2.6 Summary of Site Risks. . . . . . . . . . . . . .
2.7 Description of Alternatives. . . . . . . . . . .
2.8 Summary of Comparative Analysis of Alternatives.
2.9 Selected Remedy. . . . . . . . . . . . . . . . .
2.10 .Statutory Determinations. . . . . . . . . . . .
RESPONSIVENESS SUMMARY. . . . . . . . . . . . . . . .
3.1 Responsiveness Summary Overview. . . . . . . . .
3.2 Oral Comments Received During the Public Comment
Period, and t,he Hill AFB Response to These
Commen t s .............. . . . . . .
3.3 Written Comments Received During the Public Comment
Period, and the Hill AFB Response to These
Commen t s . . . . . . . . . . . . . . . . .
BIBLIOGRAPHY.
. . . . . .
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9
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15
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1.0
DECLARATION FOR THE RECORD OF DECISION
1.1
Site Name and Location
Operable Unit 2
(Chemical Disposal Pit 3, Site WP07)
Hill Air Force Base (AFB), Davis and Weber Counties, Utah
1.2
Statement and Basis of Purpose
This decision document represents the selected interim remedial
action for Operable. Unit. 2 (OU2), developed by Hill AFB (the Base)
in accordance with the Comprehensive Environmental Response,
Compensation and Liability Act of 1980 (CERCLA), as amended by the
Superfund Amendments and Reauthorization Act of 1986 (SARA), and,
to the extent practicable, the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP).
This decision is based upon the contents of the Administrative
Record for OU2, Hill AFB.
..
The United States Environmental Protection Agency and the Utah
Department of Environmental Quality concur with the selected
interim remedy. References will be made in portions of this
document to both The Utah Department of Health (UDOH) and the Utah
Department of Environmental Quality (UDEQ). Both names refer to
the same State agency responsible for CERCLA response actions. The
name changed with agency reorganization during the period in which
this document was developed.
1.3
Assessment of the Site
Actual or threatened releases of hazardous substances from this
site, if not addressed by implementing the response action selected
in this Record of Decision (ROD), may present an imminent and
substantial endangerment to public health, welfare, or the
environment.
1.4
Description of Selected Remedy
This interim remedy addresses removal of a source of contamination
in the subsurface soils and ground water and reduction of threat of
contamination of aquifers currently used as a source of drinking
water by eliminating or reducing the risks posed by the site
through treatment. The contamination addressed by this interim
action is dense, non-aqueous phase liquid (DNAPL). The DNAPL is a
free-phase organic liquid composed mainly of-solvent compounds and
acts as a source for high concentrations of toxic or suspected
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carcinogenic contaminants. High concentrations of contaminants
have been detected in ground water samples from areas immediately
adjacent to the DNAPL areas.
This interim action is consistent with any future actions to
complete clean up of the entire operable unit, and is a logical
first step in the clean up process. Future clean up actions
addressing final remedies for all contaminated media (soil, ground
water, surface water, air) will be detailed in a subsequent record
of decision (ROD).
No changes have been made to the selected remedy originally
presented in the proposed plan. The major components of the
selected remedy include:
Installation and maintenance of a source recovery system
capable of removing DNAPL contamination from the subsurface.
Installation and maintenance of an on-site ground water and
DNAPL pretreatment facility to separate DNAPL from ground
water and to treat contaminated ground water to levels which
can be discharged to the Base industrial waste water treatment
plant (IWTP).
Disposal of DNAPL off-site by incineration in accordance with
the Re~ource Conservation and Recovery Act (RCRA).
Installation and maintenance of a double-walled pipeline from
the site to the Base IWTP capable of transporting pretreated
ground water.
Treatment and discharge of the pretreated ground water with
other Base industrial waste waters at the IWTP and discharge
to the North Davis County Sewer District's Publicly Owned
Treatment Plant in accordance with the Base's industrial
- pretreatment discharge permit.
Monitoring the DNAPL collection and treatment system during
remediation activities.
1.5
statutory Determination
The interim action is protective of human health and the
environment, complies with Federal and State applicable or relevant
and appropriate requirements for this limited-scope action, and is
cost-effective. Although this interim action is not intended to
address fully the statutory mandate for permanence and treatment to
the maximum extent practicable, this -interim action does utilize
treatment and thus is in furtherance of that statutory mandate.
Because this action does not constitute a final remedy for the
operable unit, the statutory preference for remedies that employ
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treatment that reduces toxicity, mobility, or volume as a principal
element, although partially addressed in this remedy, will be
addressed by the final response action. Subsequent actions are
planned to address fully the threats posed by the conditions at
this operable unit. Because this remedy will result in hazardous
substances remaining on-site above health-based levels, a review
will be conducted to ensure that the remedy continues to provide
adequate protection of human health and the environment within five
years after commencement of the remedial action. . Because this is
an interim action ROD, review of this site and of this remedy will
be ongoing as the Air Force continues to develop final remedial
alternates for the operable unit.
1.6
Signature and Support ~ency Acceptance of 1:I1e Remedy
,;J.tf k!T' q I
DATE
BY:
Major General Dale W. Th son
Commander, Ogden Air Logistics
Hill Air Force Base, Utah
Center
,
QUALITY
BY:
KennE;:!th . A k m
Executive Director, Utah
Environmental Quality
~rti¥q(
DATE'
Department of
BY:
Jack W
Actin
Regio
PROTECTION AGENCY ~--
'p 9/
DATE
Administrator
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2.0
2.1
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DECISION SUMMARY
Site Name, Location and Description
Hill AFB is located in north-central Utah, covering portions of
Davis and Weber Counties (Figure 1). The Base is topographically
situated on a plateau formed by the ancient Weber Delta and is
approximately 300 feet above the adjacent Great Salt Lake basin.
Land surrounding the Base is generally level or slopes gently
westward toward the basin.
Located on the northeastern boundary of Hill AFB (Figure 1),
Operable Unit 2 (OU2) is described in earlier documents as Chemical
Disposal pit 3 and/or Site 7. For environmental response actions,
OU2 consists of two disposal trenches used in the past,
contaminated soils, surface water (seeps and springs) the DNAPL,
and contaminated ground water in the vicinity of the disposal
trenches. There are no buildings or facilities in the immediate
area. The access route, Perimeter Road, carries little traffic.
Land adjacent to OU2 that is off the Base is in the town of South
Weber (approximate population of 1500). Land use is mainly for
agriculture. Natural resource use in the general area includes
mining of" gravel and sand. No mining has occurred in the
contaminated area of OU2.
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The town and the Base both obtain their drinking water from deep
wells in the general vicinity of OU2. For the purpose of this
document, "deep" wells are defined as those completed at depths
greater than 150 feet in confined aquifers that are part of the
Delta or Sunset aquifer systems. Based on established use and
EPA's classification method, the water quality in these aquifers is
IIA, currently used for drinking. The nearest municipal well,
which supplies about 1500 people in the town of South Weber, is
located about three-quarters of a mile from OU2. Approximately
20,000 people, whose drinking water is supplied by a separate and
deeper well (approximately one mile away and hydrologically
downgradient), work or live on the Base. No evidence of
contamination has been detected to date in samples taken from these
wells.
"Shallow" wells refer to those completed in the uppermost,.
unconfined aquifer materials, generally at depths of 50 feet or
less. Generally this water is suitable for use as drinking water,
and the water quality would be class IIA or lIB (potentially
available) under EPA's classification method. The near surface
ground water qualifies as potential drinking water under Utah's
Ground Water Protection Rules. While the yield of the shallow
aquifer is sufficient for domestic wells, it is probably too low to
be a likely source for municipal water supply.
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NORTH
".
WEBER COUNTY
DAVIS COUNTY
hiLL
AIR FORCE
BASE
.
South
Gote
~.:
Cna.t Solt Lake
SoJt City
LaJc.
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MILE
OD
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Figure 1.
Location Map of Hill Air Force Base and Operable Unit 2
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Between the deep and shallow aquifer materials is a sequence of
clays and silty clays with interbedded sand units. The interbedded
sand units are typically thin and discontinuous, but are locally as
thick as 15 feet. While no evidence of contamination has been
detected in deeper wells, a pathway may exist for migration and
communication between these zones.
Approximately 20 residences are located within a one-half mile
radius of OU2. Most are located northerly of OU2, in the down-
gradient direction of shallow ground water flow. Some of these
home-owners have chosen to use water from private shallow wells,
although they are connected to a municipal water system supplied by
deep wells. None of the shallow wells are immediately threatened
by contamination from OU2.
A system of seeps and springs along the hillside north of the Base
constitute the surface water of Ou2. These have been used in the
past as supplies for drinking and irrigation water. Present use is
restricted mainly to irrigation. Contamination of this water,
where used, has been addressed by the Air Force by interception and
treatment or by providing alternate water supplies.
..
The Davis-Weber Canal runs along the perimeter of the Base and is
about 500 feet from the Base boundary in the vicinity of OU2.
Because the base of the canal is above the ground water level, no
contamination from ground water affects the water in the canal.
The canal is also a water source for irrigation.
2.2
Site History and Enforcement Activities
Chemical Disposal pit 3 consisted of two unlined, north-northwest-
trending trenches (Figure 2) that were used from 1967 to 1975 for
disposal of waste solvents and sludges from degreasing operations
on Base. Unknown quantities of trichloroethene (TCE) bottoms from
the solvent recovery unit, sludge from vapor degreasers, and
plating-tank sludge bottoms were disposed of in these trenches.
The amount of waste solvents disposed at this site has been
estimated to range from 100,000 to 1,000,000 gallons.
Reports identified in the bibliography provide detailed information
on the investigative activities at OU2 that are summarized here.
Investigative activities are currently under way to address all
contaminated media at the site. All documents listed in the
bibliography are part of the Administrative Record. These
documents are available for public review at the Davis County
Library, Central Branch, Layton, Utah.
Volatile organic compounds (VOCs) were first identified at OU2 in
1983. TCE is a relatively mobile and frequently detected VOC. The
distribution of TCE approximately coincides with the distribution
of other contaminants. For these reasons, TCE has been used as the
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80
IJORTH
D..
T .
R@
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Lys;meter.
Borehole Location
Piezometer
Test Well
Recovery Well
Dense Nonaqueous
Phase Liquid (DNAPl)
NOTE:
Only locations used to define
extent of DNAPL shown.
o
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FENCE
8-10
8-2'b
P-3.
A
P-4
o
8-27
DISPOSAL
TRENCEES
CP3T-2
.
P-9 9-12
~O
.P-8
8-41
C~T-12 \A
Figure 2.
100
I
FEET
Scale: 1" = 1 00'
200
I
G1J32
RADIAN
co.....,.....
,
)(
H
~t
or
.Approximate Lateral Extent of DNAPL Contamination in the Provo
and Alpine Formations
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primary indicator parameter for contamination from vapor degreasing
wastes and sludges from the solvent recovery unit. Investigations
have been inconclusive in identifying plating-tank sludge
contaminants in the ground water.
High levels of VOCs dissolved in shallow ground water near the Base
boundary were confirmed in 1986. A survey of off-Base water rights
was conducted. Sampling of off-Base waters included wells, seeps
and springs, and agricultural ponds in the area. Contaminants were
found in several springs, some more than 1500 feet from the
trenches. In general, the VOC concentrations are greatest near the
trench area and decrease as distance increases away from the
trenches. The maximum TCE concentration detected off-Base is
11,000 micrograms per liter (ug/l).
Hill AFB has collected and treated contaminated water from seeps
and springs adjacent to OU2 since 1986. In addition, two homes
below the site (which had used springs as a water supply) were
connected to the municipal water supply, and three farms (which had
used seeps and springs as sources of irrigation water) were
supplied with alternate sources of irrigation water. These limited
response actions have successfully prevented short-term exposure,
but do not collect all of the potential contaminants migrating from
the Base.
..
Subsurface conditions and delineation of the lateral and vertical
extent of the DNAPL are based on:
Information acquired from soil samples and field observations
during drilling of one hundred and eight soil bore holes in
the OU2 area;
Thirty-six of the soil bore holes were converted to monitoring
wells, recovery wells, or piezometers for ground water samples
and water level information;
Pumping tests of the aquifer were conducted in 1988 to
determine properties of the shallow aquifer. An emulsion of
water and approximately four percent DNAPL by volume was
recovered. Samples were taken to determine the approximate
composition of the DNAPL and VOC concentrations in the water
phase; and .
Geophysical investigations that included seismic refraction,
self potential, electro-magnetic conductivity,~nd resistivity
methods to supplement and support the soil bore hole and
analytical data.
All investigations and actions at this site have been conducted by
the United States Air Force as the lead agency under the
Installation Restoration Program (IRP). The IRP was established in
1980 as the program by which military facilities will conduct
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environmental investigation and response actions to comply with
CERCLA and the NCP. A Hazard Ranking System score for Hill AFB was
developed that led to the inclusion of the Base on the
Environmental Protection Agency's National Priorities List on 1
July 1987.
Hill AFB, the U.S. Environmental Protection Agency (EPA), and the
Utah Department of Healthy (UDOH) signed a Federal Facilities
Agreement (FFA) on 10 April 1991. The FFA is required pursuant to
CERCLA Section 120, as amended by the Superfund Amendments and
Reauthorization Act (SARA) of 1986. Subject to a 45-day public
comment period that ended 2 June 1991, the FFA became effective as
written. The FFA sets forth the process for conducting CERCLA
response actions at the Base. The Air Force is a responsible party
with respect to present and past releases at the Base.
Responsibility for oversight of activities performed under the FFA
will be shared by EPA and the State.
2.3
High~ights o~ Community Participation
Community participation requirements in CERCLA Sections
117(k) (2) (B) (i-v) and 117 have been met for this interim action.
"
Community participation in actions at OU2 began in 1986, when
contaminants were discovered to be migrating off-Base. Meetings
. with the South Weber City Council and the public were held on 13
May 1986 to report results of off-Base water sampling, and in
November 1986 to report results of the off-Base soil gas
investigation. The results of off-Base water sampling are reported
to property owners by letter on an annual basis.
A Community Relations Plan for the Base hazardous waste sites was
produced in December 1990 and is being reviewed by the EPA and the
Utah Department of Environmental Quality. This document lists
contacts and interested parties throughout government and the local
community. It . also identifies effective ways to disseminate
pertinent information. The focused remedial investigation/
feasibility study (RI/FS) and the proposed Plan for Interim Action
were released to the public in February 1991. All of these
documents were made available in both the administrative record and
an information repository maintained at the Davis County Library-
Central Branch. The proposed plan was mailed to property owners on
the mailing list accompanied by a letter that encouraged their
participation and comment. .
A public comment period was held from 19 February 1991 through 20
March 1991. Advertisements announcing the public comment period
and public meeting were published in the Ogden Standard Examiner
and the Salt Lake Tribune on 19 February 1991. News releases
announcing the public comment period and public meeting were sent
to local newspapers and radio and television stations. The Ogden
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Standard Examiner also published two articles indicating the public
comment period (4 and 17 February 1991). A public meeting was held
on 5. March 1991 to present the results of and solicit public
comments on the RIfFS and the alternatives as presented in the
Proposed Plan for the operable unit. Twenty-five people attended
the 5 March public meeting which was held at South Weber Elementary
School. Additional copies of the proposed plan and fact sheets
describing the Installation Restoration Program (IRP), its history
and the history of the Base were made available to the public at
the public meeting. All comments which were received by Hill AFB
prior to the end of the public comment period, including those
expressed verbally at the public meeting, are addressed in the
Responsiveness Summary which is Section '3.0 of this Record of
Decision.
2.4
Scope and Ro~e of Response Action
Hill AFB covers 6,700 acres, and has several areas where past
disposal practices and spills have contaminated soil and ground
water. Because the Base covers a large area, the Air Force decided
to group geographically adjacent contaminated areas into operable
units, each to be addressed under separate but concurrent
investigations. Operable Unit 2, part of which is the subject of
this Record of Decision for Interim Action, is one of seven
operable units under investigation at Hill AFB.
..
Several response actions have already been taken at OU2 resulting
from the discovery of off-Base ground water contamination in 1986.
Five properties were provided alternate water sources to prevent
them from using contaminated ground water supplied from seeps and
. springs. Residents at two of the properties had not been drinking
contaminated water, but were at risk of having their drinking water
source contaminated in the future. These residents were provided
municipal drinking water. The other three properties were provided
alternate sources of irrigation water. Water from several
contaminated seeps and springs along the hillside has been
diverted, treated with activated carbon, and then returned to the
original channel. All of these actions have been in force since
1987 to prevent residents of off-Base properties from being exposed
to contaminants in the shallow ground water.
In this ROD, the Air Force is selecting an interim. action to
prevent contaminants from reaching aquifers currently used as a
source for drinking water. This interim action focuses on removal
and off-site destruction of Dense, Non~Aqueous Phase Liquid (DNAPL)
present in the subsurface at OU2.
The DNAPL is considered a principal threat waste and is a
concentrated source of contaminants for soil and ground water. It
is considered the major source of VOCs which are polluting the
shallow ground water. The Air Force has elected to address this
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contamination problem because the DNAPL is chemically altering and
dissolving protective clay layers and will, if unabated or
uncontrolled, eventually contaminate the deeper aquifers currently
used as a primary source of drinking water for the communities of
north Davis County. Addressing the problem now will help protect
the water supplies of the deeper aquifer systems by reducing the
volume and mobility of the DNAPL. The mobility and volume of the
dissolved VOCs in the shallow aquifer will also be reduced.
A future ROD, scheduled for August 1993, will address all remaining
media at OU2, including contamination of soil, ground water,
surface water, and air. The remedy selected in this ROD for
interim action is the first step in the process to clean up of all
contaminated media at OU2, and will be consistent with planned
future actions to the extent possible.
2.5
Site Characteristics
The contaminant media of concern for this ROD, the DNAPL, is
composed mostly of volatile chlorinated solvents, primarily TCE,
with lesser amounts of other volatile and non-volatile organics.
Table 1 summarizes the analytical results of two samples taken from
the DNAPL. Some of these VOCs are suspected carcinogens. Several
VOCs in the shallow ground water exceed the national primary
drinking water standards (maximum contaminant levels or MCLs) as
established by the Safe Drinking Water Act. Other constituents are
likely to be petroleum products, such as oil and grease.
The highest concentrations of VOCs dissolved in ground water are
from samples adjacent to the DNAPL and in the water phase of the
recovered emulsions. These data are presented in Table 2. Due to
mixing during pumping, the VOC concentrations in the water phase of
recovered emulsions are probably higher than concentrations would
be in static equilibrium conditions. The data probably represent
worst-case concentrations.
~
The site-specific subsurface geology has limited the migration and
caused the DNAPL to accumulate. Further detail on the geological
conditions summarized here are in "Hill Air Force Base, Utah; Draft
Site Characterization Summary for Operable Unit 2 {4 volumes),"
August 1990 and "Hill Air Force Base, Utah; Final Focused'
Feasibility Study for Operable Unit 2," February 1991.-
DNAPLs move downward due to gravity through permeable materials,
such as sands and gravels. Because the DNAPL is heavier than
water, it continues to migrate downward through ground water
contained in the permeable materials. Migration is slowed or
halted when a less permeable material,. such as a clay, is
encountered. The DNAPL will then move "downhill" along the top
surface of the less-permeabl~ layer and accumulate in depressions
in this surface.
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TABLE 1.
CONSTITUENT CHEMICALS OF DENSE, NON-AQUEOUS PHASE LIQUID
(DNAPL) AT OPERABLE UNIT 2.
Contaminant
Percent
Methylene Chloride
Trichloroethene
Tetrachloroethene .
1,1,1-Trichloroethane
1,1,2-Trichloro 1,2,?-trifluoroethane
Toluene
Xylene
Other (non-volatile)
< 1
78 - 90
2 - 5
< 1
1 - 4
< 0.1
< 0.1
7 - 12
TABLE 2.
,
HIGHEST CONCEN~RATION OF DISSOLVED VOLATILE ORGANIC
COMPOUNDS IN THE WATER PHASE AT OPERABLE UNIT 2.
Contaminant
Concentration
(ug/L)
MCL
(ug/L)
Methylene Chloride
Chloroform
Trichloroethene
Tetrachloroethene
1, 1, 1-Trichloroethane
1,1,2-Trichloroethane
1,1,2-Trichloro 1,2,2-trifluoroethane
Toluene
Acetone
200,000
16,000
1,700,000
130,000
220,000
13,000
140,000
12,000.
7,000
100
5
5
200
3*
2000
*Non-zero MCLG (Maximum Contaminant Level Goal)
12
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,
Such a situation exists at OU2 where the uppermost geologic
materials, in which the disposal trenches were excavated, consist
primarily of sands and gravels of the Provo Formation (Figures 2
and 3). Beneath the sands and gravels is the Alpine Formation, the
uppermost part of which is primarily clays and silts with some
localized sand units. The sand units in the Alpine Formation are
typically thin and discontinuous, but vary in thickness and areal
extent.
The subsurface contact between the Provo Formation sands and
gravels, and the underlying Alpine Formation clays, is irregular.
A curved trough in the top surface of the Alpine Formation clays
has been defined beneath the disposal trenches from which the spent
solvent materials comprising the DNAPL migrated. This trough
appears to have slowed the vertical"DNAPL migration and guided the
DNAPL migration laterally. Some DNAPL has accumulated in the
bottom of this trough and is in the lower, ground water-bearing
Provo sands and gravels.
Most of the DNAPL has been found in the Alpine Formation, mainly in
one of the localized, discontinuous sand units, which has been
designated the "second sand". The second sand underlies the clay
trough, fol.lows its shape, and is estimated to range between 2 feet
and 15 feet in thickness. The second sand seems to be
approximately 75 feet wide in the area of the disposal trenches;
the extent of the second sand to the west and south are undefined.
Low areas of the second sand seem to be near wells CP3T-1 and R-1,
and in the south branch near boring B-40. DNAPL should tend to
accumulate in these low areas, and has been detected at these
locations. If the second sand is saturated with DNAPL between well
R-1 and boring B-40, over 250,000 gallons of DNAPL could be present
in this part of the site.
,
Figure 2 illustrates the approximate areal extent, about one third
of an acre, of the DNAPL in both the Provo and Alpine Formations.
The DNAPL is all on-Base. The DNAPL is located at depth varying
between 40 to 60 feet below the ground surface. Figure 3
illustrates the approximate vertical extent of DNAPL in both the
Provo and Alpine Formations.
The fate and transport of contaminants associated with the DNAPL is
governed by two mechanisms: (1) continued vertical migration of
the DNAPL, and (2) dissolved VOCs that migrate within the shallow
ground water.
Clay samples taken from the upper portions of the Alpine Formation
in contact with the DNAPL appeared to be altered. The alteration
is presumed to be a chemical degradation of the clay materials,
suggesting the potential for the DNAPL to ~'eat" downward into the
clay. Most of the alteration appears .to be within the uppermost
several feet of clays. In one soil boring (B-40), the depth of
alteration was over 20 feet below the top of the Alpine Formation.
13
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"DO
A
lIOII'"
O-JI(!)
PROVO
R-.0
-
g
Q ..10
~
1-
~
1-
..10
---
---
-
--
AlPINE
" . _.._.._.._.._.._.:==.:.:.~~:!'!'~Hn='::;~:=
........ '-'~IUiiaimii~milgima
"-t......... .Ii~ iii ;-iiis:li;;ii=;
.. -.. -" ...----"11==1 ... 1:1:"'1""'::
'~
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,
Some uncertainty in the depth of alteration exists at this location
due to poor recovery of well cuttings from boring B-40.
Some of the soil bore holes penetrated 85 feet into the Alpine
Formation clay materials below the Provo sands and gravels,
establishing this as an approximate minimum thickness for the clay
materials at the site. In addition, geologic logs of subsurface
strata from wells about a mile away suggest that the deeper Delta
Aquifer is about 500 to 600 feet below ground surface. The
materials between the investigation depth and the aquifer depth are
. predominantly Alpine Formation clays and silts, but localized sand
units may exist and act as preferential pathways for contaminant
migration. Migration of theDNAPL into the Alpine second sand may
be due to alteration of clays or through thin, localized sand
units. Continued migration offers a threat to the quality of the
water in the aquifers currently used as a source of drinking water,
such as the Delta Aquifer.
Not only is the DNAPL a contaminant, it also acts as a source of
dissol ved VOCs in the shallow ground water. Components of the
DNAPL have limited solubilities in ground water. Unconfined ground
water within the Provo Formation flows northeasterly. The seeps
and springs are discharge areas for some of this ground water.
VOCs have been detected in monitoring wells as far as 1400 feet
from the disposal area.
,
2.6
Summary of Site Risks
The VOCs detected are suspected human carcinogens. The most common
VOC is trichloroethene (TCE), a suspected human carcinogen.
Several VOCs in the shallow ground water exceed the national
primary drinking water standards (MCLs or non-zero MCLGs) as
establ~shed by the Safe Drinking Water Act (see Table 2). Trans
1,2-dichloroethene, a product of anaerobic biodegradation of TCE,
was recently found in seeps which are used to water stock animals.
As the degradation process continues, chloroethene (vinyl
chloride), a known human carcinogen, can be formed. Chloroethene
has not been detected in samples to date.
Unless the DNAPL is extracted or separated from the shallow ground
water, dissolved contaminant concentrations in ground water
downgradient of OU2 are likely to increase to levels where they
will pose a health risk at seeps, springs, and existing wells. The
actions taken to date have served to collect migrating contaminants
only locally at potential exposure points. The VOC contaminated
water is subirrigating crops used as animal feed. Some of the
homes in South Weber below OU2 have private drinking water wells
completed in the shallow aquifer which could eventually be
contaminated.
15
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. .
,
Children have played in some of the seep or spring areas with low-
level contamination. The contaminant concentration is well below
safe drinking water standards, so no access restrictions have been
necessary. These areas are monitored by Hill AFB on a monthly to
quarterly frequency.
The chemical degradation of the Alpine Formation uppermost clays,
that slowed the contaminant movement between the shallow and deeper
ground water, raises the concern that the DNAPL could reach the
deeper Delta aquifer and subsequently contaminate drinking water
wells. The nearest municipal well, which supplies about 1500
people in the town of South Weber, is located about three-quarters
of a mile from OU2. Approximately 20,000 people, whose drinking
water is supplied by a separate and deeper well (approximately one
mile away and hydrologically downgradient), work or live on the
Base.
At the rate of migration suggested by alteration of the Alpine
Formation clays, an immediate threat to the quality of water in the
deeper aquifer is not perceived. However, a longer-term risk is
possible. The materials between the investigation depth and the
aquifer depth are predominantly Alpine Formation clays and silts,
but localized sand units may exist and act as conduits and increase
the rate of migration.
..
,
No complete exposure route exists between the DNAPL and human
receptors. Such a route can occur only in the situation that no
action is taken and land use changes allow for water supply wells
to use the shallow ground water for domestic purposes, or if future
activities would include excavation in the area of OU2.
No environmental risks, such as adverse effects of contamination on
critical habitats or endangered species, are apparent at this site.
No critical habitats have been identified in the area. No
endangered species inhabit the area, but the range of some
endangered birds in the vicinity (bald eagles and peregrine
falcons) may include portions of the Base.
A risk assessment to quantitatively evaluate current and potential
future risks will be completed as part of the process for
determining the final remedy (ies) at Operable .Unit 2. The more
specific findings of the baseline risk assessment, which will help
establish the ultimate clean up objectives, will be included in the
subsequent final action ROD for the operable unit. Shallow ground
water contamination in concentrations exceeding health based limits
(drinking water standards) and potential deep ground water
contamination associated with the DNAPL are items of sufficient
concern that USAF recommends initiating remedial actions as soon as
practicable.
Actual or threatened releases of hazardous substances from this
site, if not addressed by implementing the response action selected
16
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"
in this ROD, may present an imminent and substantial endangerment
to public health, welfare, or the environment.
2.7
Description of ~ternatives
Media-specific actions consistent with the remedial. action.
objectives include any combination of treatment, containment,
excavation, extraction, disposal, institutional controls, and no
action. A full range of alternatives will be considered for the
final remedy(ies), but for an interim action for the DNAPL at OU2,
only two will be discussed:
No action.
Extraction and treatment of the DNAPL
contaminated ground water (Pump and Treat) .
and
associated
Several alternatives, including physical containment, excavation,
and in-situ treatment were briefly considered, but were judged to
be inappropriate for this interim action. A brief discussion of
these alternatives is contained in "Hill Air Force Base, Utah,
Focused Feasibility Study for Operable Unit 2," February 1991.
Alternatives that include these response actions will be addressed
in the evaluation for final remedy selection.
2.7.1 H.Q Action (Alternative.l.L:. The no action alternative
evaluated here refers only to taking no further action until the
final remedy(ies) are selected and embodied in a Record of Decision
(ROD) for OU2. This is expected to be in August 1993. Ongoing
remedial investigation and feasibility study activities will
provide information for the final selection. The present worth of
this alternative is $163,000 assuming a 3 year life (same time
frame as alternative 2).
2.7. 2 ~ ~ Treat (Alternative 2.Li.. This alternative is
schematically illustrated by Figure 4. This system will take
approximately one year to build, and is expected to operate for
approximately two years or until the final remedy is determined.
Assuming a 2 year operating life until final remedy (ies) are
enacted, the present worth is estimated to be $3.71 million.
This alternative includes recovering as much DNAPL as practicable
with a series of pumping wells. Wells are the preferred extraction
technology since they are generally less costly to install than
subsurface drains and the subsurface materials containing the DNAPL
appear to have adequate permeability (ies) on the basis of pump
tests. In the event of fouling or scaling, wells can be
reconditioned more easily than a subsurface drain system.
The pumped liquid, probably an emulsion, will be placed in batch
settlers to separate DNAPL and the associated water into separate
17
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CONDENSER
CONTAMINATED
STEAM
./
RECOVERY
WELLS
CONTAMINATED
WATER
STEAM
STRIPPER
DNAPL
PHASE
PRETREATED
WATER
STEAM
BOILER
BASE INDUSTRIAL
WASTE WATER
TREATMENT
PLANT
DNAPL TRUCKED OFF SITE
TO PERMITTED INCINERATOR
DISCHARGE TO
SANITARY SEWER
Figure 4. Treatment Process for Rlternatiue 2
,
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,
phases. The amount of DNAPL recovered can only be guessed at this
time, but over 200,000,000 gallons of contaminated ground water and
DNAPL may be recovered and treated during the expected two year
life of this interim action. DNAPL recovered cannot exceed what
was disposed at the site, estimated to range between 100,000 to
1,000,000 gallons. DNAPL will be temporarily stored on site in
steel tanks with secondary containment until sufficient amounts
(approximately 5,000 gallons) accumulate for off-site transport.
Storage at any other location on Base will be in accordance with
the conditions of Hill AFB's existing (or as modified) hazardous
waste storage permit. The DNAPL will be transported in compliance
with the Resource Conservation and Recovery Act (RCRA) and
Department of Transportation (DOT) regulations to an incineration
facility operating in compliance with RCRA.
The aqueous phase is expected to contain high concentrations of
dissolved VOCs and will require pretreatment prior to disposal. An
evaluation of the pretreatment alternatives is contained in the
report "Hill Air Force Base, Utah; Final Conceptual Design Report;
Source Recovery and Ground water Pre-Treatment System at Operable
Unit 2; June, 1990." On-site pretreatment will be in two phases:
(1) stearn stripping in a unit at the site; then (2) final
pretreatment in the Base Industrial Waste Treatment plant (IWTP).
The maximum pumping rate of pretreated water to the IWTP will be
about 20 gallons per minute. The treatment process in the IWTP
includes air stripping and carbon absorption to remove VOCs.
..
Treated effluent from the IWTP must be of low enough concentrations
to meet pretreatment standards before being discharged to the North
Davis County Sewer District treatment works. This discharge will
be regulated under the conditions of a UPDES (Utah Pollution
Discharge Elimination System) permit.
2.8
Summary of Comparative Analysis of Alternatives
Provisions of the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP) require that a limited number of
alternatives that represent viable alternatives be evaluated
against nine criteria in 40 CFR 300.430(e) (9). The alternatives
are evaluated against each of these criteria and then against each
other to determine the preferred alternative. .
2.8.1 Criteria ll.
Environment
Overall protection Q! Human Health ~ ~
This criteria addresses whether or not a remedy provides adequate
protection and describes how risks posed through exposure pathways
are eliminated, reduced, or controlled.
Alternative 1 (no-action) does nothing to alleviate threats and
potential threats to' human health and the environment until the
19
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. .
,
final remedy (ies) are enacted. Unacceptable risks may occur if
shallow ground water in the vicinity of the DNAPL is used as a
water supply. If not removed, the DNAPL will potentially migrate
through the upper aquifer system and contaminate deeper aquifers
currently used as pqtable water supplies by the Base and by
surrounding municipalities.
Alternative 2 (pump and treat) provides for removal of as much
DNAPL from the subsurface as practicable, resulting in a permanent
reduction in the volume of DNAPL that acts as a source of
contaminants in shallow ground water used for irrigation and
domestic use. Vertical and lateral migration of the DNAPL would be
inhibited. Pumping should also slow the rate at which dissolved
contaminants can migrate off-Base in the shallow ground water. For
the final remedial action, attainment of exposure levels within the
acceptable risk range for carcinogens in the shallow ground water
is unlikely without extracting as much of the DNAPL as practicable.
2.8.2
Criteria 2....:..
Compliance ~ ARARs
ARARs are applicable or relevant and appropriate requirements.
Applicable requirements are cleanup standards, standards of
control, .and other substantive environmental protection
requirements, criteria, or limitations promulgated under Federal or
State law that specifically address a hazardous substance,
pollutant, contaminant, remedial action, location or other
circumstance at a CERCLA site. Relevant and appropriate
requirements address problems or situations sufficiently similar to
those encountered at the CERCLA site that their use is well suited
to the environmental and technical factors at a particular site.
ARARs are grouped into three categories:
~
Chemica~-specific ARARs are health- or risk-based numerical
values or methodologies which, when applied to site-specific
conditions, result in the establishment of the amount or
concentration of a chemical that may be found in, or
discharged to the environment (soil, water, or air) .
Location-specific ARARs restrict the concentration of
hazardous substances or the conduct of activities solely
because they are in specific locations, such as flood plains,
wetlands, historic places, and sensitive ecosystems or
habitats.
Action-specific ARARs are usually technology or activity-based
requirements or limitations on actions taken with respect to
hazardous wastes. The largest number of action-specific
requirements are generally provided by RCRA.
The analysis of ARARs has been limited ~o the scope of the interim
action. Other ARARs may be invoked in enacting final remedy (ies) .
20
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. ,
Alternative 1 (no-action) delays
remedy(~es) are implemented.
meeting ARARs
until the final
Alternative 2
in achieving
water. These
are selected.
(pump and treat) represents a only preliminary step
chemical-specific ARARs for the shallow ground
ARARs will be addressed when the final remedy(ies)
No location-specific ARARs have been identified. The site and
any treatment facilities that would be constructed are not
located within a 100-year flood plain, wetland, historical site,
or sensitive ecosystem or habitat.
Potential action-specific ARARs that will ,be met include:
Design of the treatment plant equipment to meet the
substantive requirements of RCRA (40 CFR Part 264) that may
include secondary containment for tanks and pipelines,
release detection, pressure contiols, safety cutoffs and
bypass systems. Operation of the treatment plant will meet
RCRA waste handling requirements. RCRA is also an ARAR for
storage of hazardous waste (40 CFR Parts 260, 264) awaiting
transport to the disposal facility. RCRA is administered by
the State of Utah. State provisions parallel to those
federa~ provisions cited in this' paragraph are found at
U.A.C. R450-8.
,
Design and operation of the treatment plant at OU2 to meet
the applicable requirements of various air quality
regulations, including National Ambient Air Quality Standards
(U.A.C. R446-l-3, 40 CFR Parts 50 and 61), use of Best
Available Control Technology (U.A.C. R446-1-3.1.8, 40 CFR
Parts 50 and 61), and emergency closure (U.A.C. R446-1-5.1).
Fugitive dust control requirements (U.A.C. R446-1-4.S) will
be met during construction. No visible air emissions are
expected. Any air emissions from the IWTP will be comply
with existing Utah Bureau of Air Quality permits for that
facility.
Treatment of the effluent at the IWTP and discharge to the
North Davis County Sewer District (NDSCD)' treatment works
must comply with the applicable laws, regulations, and permit
requirements (U.A.C. R448-8-8, 40 CFR Part 403, local POTW
regulations). A modification to the Base's pretreatment
discharge permit with NDCSD will be necessary prior to
discharge under this alternative. A corresponding
modification to the NDCSD's UPDES permit is also likely to be
required. EPA guidance documents on discharge to POTWs will
be utilized as actions that are to be considered (TEC).
Similar compounds are treated and discharged on a daily
basis. Other alternatives will be evaluated if discharge to
the NDCSD is not permitted. .
21
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,
Compliance with federal (29 CFR 1910.120) and Utah (U.A.C.
R500) regulations concerning occupational safety and health
standards for workers at hazardous waste sites.
Construction and abandonment of wells to meet applicable
portions of Utah water well drilling regulations, including
provisions to prevent further contamination of the
environment (U.A.C. R625-4).
Land disposal is not expected to occur, so the RCRA land
disposal restrictions (40 CFR Part 268) are generally not
applicable or relevant and appropriate. Any residual ash
from incineration of the DNAPL will be disposed in accordance
with the LDRs.
Regulations for off-site disposal pertaining to manifesting,
transport, destruction of the DNAPL and any residuals will be
met. CERCLA Section 121(d)(3) requires that hazardous
substances, pollutants, or contaminants may be transported
off-Site only to facilities operating in compliance with RCRA
Sections 3004 and 3005 and other applicable laws and
regulations.
,
2.8.3 Criteria 3:
Long-term Effectiveness and Permanence.
Long-term effectiveness and permanence refers to the ability of a
remedy to provide reliable protection of human health and the
environment over time.
Alternative 1
selected and
permanence.
delays any
is unlikely
action until final remedy(ies) are
to provide long-term effectiveness and
Alternative 2 will permanently remove most of the DNAPL. Due to
uncertainties in hydrogeological characteristics of the shallow
aquifer, the physical and chemical nature of the DNAPL, and
extraction system design parameters, complete extraction is not
~.ikely. The threat of contamination migrating to the deeper
ground water currently used as a source of drinking water will be
substantially reduced. Data collected and analyzed during the
operation of the system will be used to evaluate long-term
effectiveness and permanence of the final remedy(ies). No
residuals are expected to be land disposed and all wastes will be
treated to meet applicable or relevant ~nd appropriate
requirements of federal and state environmental and siting laws.
If there is residual ash from incineration of the DNAPL, it will
be disposed in accordance with the land disposal restrictions.
22
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'\
2.8.4
Criteria.i..:.. Reduction.Q.f. Toxicity. Mobility. .and Volume
Through Treatment
Reduction of toxicity, mobility, or volume through treatment refers
to the preference for a remedy that reduces health hazards, the
movement of contaminants, or the quantity of contaminants at the
site.
Alternative 1 delays reduction of toxicity, mobility, and volume
since no treatment would be taking place. Contaminants may migrate
further into the environment, resulting in a greater volume of
contaminated materials.
Alternative 2 utilizes established treatment technology to address
the pr{ncipal threats posed by the DNAPL. The volume of the DNAPL
in the subsurface will be permanently reduced and mobility will be
inhibited. On the basis of experience with similar recoveries and
uncertainties discussed above, some residuals will probably remain
in place unless recovery enhancement techniques can be feasibly
used. A reduction of the amount of DNAPL results in less material
available to contaminate shallow ground water. All of the
recovered DNAPL will be destroyed by the incineration process. Any
associated. contaminated water effluent will be treated to meet
discharge requirements from the IWTP. The steam stripping
treatment system will have a performance specification of 99
percent removal of VOCs. No residuals from the treatment will
remain on the site.
~
2.8.5 Criteria.5...;.
Short-term Effectiveness
This criteria addresses the period of time needed to complete the
remedy, and any adverse effects to human health and the environment
that may be caused during the construction and implementation of
the remedy.
Alternative 1 offers no immediate risks to the community.
Potential immediate risks have been addressed with the actions
already taken. If the final ROD for this operable unit involves
clean up, Alternative 1 probably only delays any short-term risks.
Alternative 2 will involve some short-term risks to workers on the
site during the construction phase of the system (one yeai
estimated duration). No adverse impacts on the co~unity are
anticipated. Potential risks include exposure of site workers to
contaminated water and soil, volatile organic vapors, or extracted
DNAPL; and air emissions from any part of the operating facility.
Dust control techniques will be employed to control exposure to
chemicals from fugitive dust during construction. Alternative 2
will be designed to protect the community and workers during
operation of remedial actions (two year estimated duration).
Worker protection will be consistent with the OSHA requirements
(U.A.C. R500, 29 CFR 1910.120), the site Health and Safety Plan,
23
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:'
,
and Contingency Plan during construction and operation. All tanks
and pipelines installed will have secondary containment systems or
double walls to collect accidental spills or leaks. All tanks will
be fitted with emissions control devices to prevent contaminants
from entering the air. The recovered DNAPL product will be hauled
by a qualified contractor to a permitted incinerator for
destruction. Transporting hazardous wastes off site will involve
risks of accidental spills and traffic "accidents, however, over
1,000 tons of hazardous waste are already trucked off of Hill AFB
every year. Truck traffic is expected to be infrequent or sporadic
and should not present any noise or traffic problems for the
community. No adverse environmental impacts are expected from
implementation of Alternative 2.
2.8.6 Criteria.2..&.
ImDIementability
rmplementability refers to the technical and administrative
feasibility of a remedy. This includes the availability of
materials and services needed to carry out a remedy. It also
includes coordination of Federal, State, and Local government
efforts to clean up the site.
,
Alternativ~ 1 offers no implementability concerns since it is
technically and administratively feasible and does not rely on the
availability of services and materials.
Alternative 2 will utilize proven "off-the-shelf" technology,
standard construction met~ods, and existing facilities. Adequate
treatment, storage capacity, and disposal services are available.
Off-site incineration services are readily available and can be
implemented immediately. The equipment for on-site pretreatment is
commercially available.
Access to the site is available through existing roadways and the
site topography allows access for drilling equipment. Road
construction will be necessary only to install treatment facilities
and provide access for the trucks hauling the recovered product.
The action is administratively feasible. Discharge of the treated
water effluent from the IWTP to the North Davis County Sewer
District will require agreement and coordination with the district.
Notification and possible permitting of air" discharge may be
required through the State of Utah (U.A.C. R446-1-3.1), depending
on the final emissions control system. Off-site disposal of the
product will require a manifesting system (U .A.C. R4S0-4) and
possibly a modification of the existing State-issued permit for
Hill AFB under the Resource Conservation and Recovery Act (RCRA)
(U.A.C. R450-8) in terms of storage location and amounts of wastes
to be disposed.
24
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~
2.8.7
,
Criteria 1..l.
~
Cost evaluates the estimated captial, operation, and maintenance
costs of each alternative in comparison to other equally protective
alternatives.
Alternative 1 does not involve any indirect or capital costs.
Annual Operations and Maintenarice (O&M) costs on the existing seep
treatment system and water supplies provided to residences is
estimated to be $60,000. The present worth of this alternative is
$163,000 assuming a 3 year life (same time frame as alternative 2).
Alternative 2 is estimated to cost $2 million in capital costs to
install the necessary facilities and to cost $1 million per year to
operate. Assuming a 2 year operating life until final remedy(ies)
are enacted, the present worth is estimated to be $3.71 million.
2.8.8
Criteria ~
State AcceDtance
State acceptance describes whether the State agrees with, opposes,
or has no comment on the preferred alternative.
,
The Utah Department of Environmental Quality (UDEQ) and the
Environmental Protection Agency Region VIII concur with the Air
Force's selected remedy for interim action at OU2. The UDEQ
response to the alternatives is presented in the responsiveness
summary (Section 3.0). While UDEQ supports this interim action, it
does not necessarily agree with all descriptions of site
hydrogeology found in this ROD, especially as they relate to
aquifer systems at the site.
2.8.9 Criteria ~
Community Acceptance
Community acceptance includes determining which components of the
alternatives which interested persons in the community support,
have reservations about, or oppose.
The community response to the alternatives is presented in the
responsiveness summary (Section 3.0) which addresses comments
received during the public comment period. Community members were
generally concerned about health effects of chemicals in ground
water and seeps on private property. No comments opposing this.
interim action were received from the community.
2.9
Selected Remedy
Based on the comparative analysis of the nine .criteria, alternative
2 (pump and treat) is preferable, and is the selected remedy for
interim action. The selected remedy. involves pumping wells to
remove DNAPL and contaminated ground water from the subsurface. An
on-site treatment plant will separate the DNAPL and aqueous phases,
25
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~.
,
then pretreat the recovered ground water by means of a steam
stripper. All actions involved in this interim action will occur
on Base at the actual dump site. Pretreated ground water will be
discharged to the Base IWTP and then to the North Davis County
Sewer District's sanitary sewer. DNAPL will be disposed of in an
off-site, RCRA-permitted incinerator. The present worth of this
remedy is estimated to be $3.71 million as discussed in section
2.8.7.
Alternative 1 (no-action) is more easily implemented and of lower
cost (criteria 6 & 7) than alternative 2. In all. of the other
criteria, alternative 2 provides greater overall protection of
human health and the environment with active progress towards clean
up. Other benefits of alternative 2 are that it: provides for
rapid response; will reduce contaminant loading on any future
actions; and will inhibit contaminant migration.
This alternative calls for the design and implementation of an
interim remedial action to protect human health and the
environment. The goals of this remedial action are to:
Remove as much of the DNAPL as
reducing the volume and mobility;
practicable,
permanently
Reduce the rate of dissolved contaminant migration and reduce
contaminant loading for future response actions.
Collect data on aquifer and contaminant response to
remediation measures that will be useful in the selection and
design of final response actions.
This remedial action will be monitored carefully to determine the
feasibility of reducing contamination with this method and to
ensure that control of the DNAPL is maintained. After the time
necessary to arrive at a final decision for the site, a final ROD
will be prepared. This ROD will address the final remedy and
anticipated remediation time-frame. Upon completion of the RI/FS
for operable unit 2, this interim system may be incorporated into
the design of the site remedy specified in the final action ROD.
Specific points of compliance will not be defined for this interim
action, but will be appropriately designated for the final response
action. In general, the area of attainment is the general area of
DNAPL accumulation with the primary objective of removing as much
of the DNAPL as practicable. . .
The system will use the most cost-effective of equivalent treatment
systems available and will meet best engineering practices and
technology.
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2.10
,
Statutory Determinations
The selected remedy meets the statutory requirements of Section 121
of CERCLA as amended by SARA. These statutory requirements include
protection of human health and the environment, compliance with
ARARs, cost effectiveness, utilization of permanent solutions and
alternative treatment technologies to the maximum extent
practicable, and preference for treatment as a principal element.
The manner in which the selected remedy for this interim action
. meets each of these requirements is presented in the following
discussion. The statutory determinations for the preferred remedy
for soils, ground water, surface water, and air will be discussed
in a separate Record of Decision that will be prepared following
the initiation of this interim action and the collection and
analysis of additional monitoring data.
2.10.1
Protection Qf Human Health ~ ~ Environment
This interim action is protective of human health and the
environment from the threat being addressed and the waste being
managed (DNAPL). The interim action will remove DNAPL from the
environment and destroy it by incineration. The risks posed by the
threat of DNAPL contaminating deeper drinking waters will be
substantially reduced. Also, by removing DNAPL, a major source of
shallow ground water cont~mination will be removed.
2.10.2 Attainment Qf ApDlicable .Q£ Relevant .a.n.Q. A'pproDriate
Requirements Qf Environmental ~
No chemical-specific ARARs will be met with this interim action.
However, without the removal of DNAPL, it is unlikely that any
chemical-specific ARARs will be met as the result of any remedial
action. Therefore this interim action is the first step in
ultimately achieving chemical-specific ARARs for this site.
Potential action-specific ARARs that will be met include:
Design of the treatment plant equipment to meet the
substantive requirements of RCRA (40 CFR Part 264) that may
include secondary containment for tanks and pipelines, release
detection, pressure controls, safety cutoffs and bypass
systems. Operation of the treatment plant will meet RCRA.
waste handling requirements. RCRA is also an ARAR for storage
of hazardous waste (40 CFR Parts 260, 264) awaiting transport
to the disposal facility. RCRA is administered by the State
of Utah. State provisions parallel to those federal
provisions cited in this paragraph are found at U.A.C. R450-8.
Design and operation of the treatment plant at OU2 to meet the
applicable requirements of various Utah air quality
regulations, including National Ambient Air Quality Standards
(U.A.C. R446-1-3, 40 CFR Parts 50 and 61), use of Best
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.
.
,
Available Control Technology (U.A.C. R446-1-3.1.8, 40 CFR
Parts 50 and 61), and emergency closure (U.A.C. R446-1-5.1).
Fugitive dust control requirements (U.A.C. R446-1-4.S) will be
met during construction. No visible air emissions are
expected. Any air emissions from the IWTP will be comply with
existing Utah Bureau of Air Quality permits for that facility.
Treatment of the effluent at the IWTP and discharge to the
North Davis County Sewer District (NDSCD) treatment works must
comply with the applicable laws, regulations, and permit
requirements (U.A.C. R448-8-8, 40 CFR Sec. 403, local POTW
regulations) . A modification to the Base's pretreatment
discharge permit with -NDCSD will be necessary prior to
discharge under this alternative. A corresponding
modification to the NDCSD's UPDES permit may also be required.
EPA guidance documents on discharge to POTWs will be utilized
as actions that are to be considered (TBC). Similar compounds
are treated and discharged on a daily basis. Other
alternatives will be evaluated if discharge to the NDCSD is
not permitted.
,
Compliance with federal (29 CFR 1910.120) and Utah (U.A.C.
RSOO) -regulations concerning occupational safety and health
standards for workers at hazardous waste sites.
Construction and abandonment of wells to meet applicable
portions of Utah water well drilling regulations, including
provisions to prevent further contamination of the environment
(U .A. C. R625-4).
Land disposal is not expected to occur, so the RCRA land
disposal restrictions (40 CFR Part 268) are generally not
applicable or relevant and appropriate. Any residual ash from
incineration of the DNAPL will be disposed in accordance with
the LDRs.
Regulations for off-site disposal pertaining to manifesting,
transport, destruction of the DNAPL and any residuals will be
met. CERCLA Section 121(d) (3) requires that hazardous
substances, pollutants, or contaminants may be transported
off-Site only to facilities operating in compliance with RCRA
Sections 3304 and 3005 and other applicable laws and
regulations.
2.10.3
~ Effectiveness
The no action alternative initially appears to be the most cost
effective alternative. However, the alternative is defined as no
further action until ~ final BQQ. If the interim action is not
taken now, contamination will migrate further into the environment,
probably increasing ultimate clean up costs for OU2. Therefore the
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selected remedy is cost effective in terms of reduction in threat
to public health and the environment per dollars expended when
remediation of the entire site is considered. The interim action
makes use of existing facilities to the extent practicable.
2.10.4 Utilization Q! Permanent Solutions ~ Alternative
Treatment Technologies QL Resource Recovery Technologies ~ ~
Maximum Extent Practicable
As this is an interim action, it is not designed or expected to be
final. However, the selected remedy represents the best ~alance of
tradeoffs with respect to pertinent criteria given the limited
scope of the action. The interim action involves removing and
destroying DNAPL a permanent reduction in the volume of
contamination. Once removed and destroyed, the DNAPL can no longer
threaten the drinking water aquifers or contribute to the
contamination of shallow ground water. As removal technology is
not 100 percent effective, some residuals may remain in the
subsurface. This residual DNAPL will represent a reduced threat to
the drinking water and shallow aquifers because the amount of DNAPL
will be permanently reduced and the mobility of the DNAPL will be
inhibited. The interim action meets this statutory requirement.
,
2.10.5
Preference ~ Treatment ~ ~ Principal Element
This interim action does employ treatment as a principal element,
and is therefore in furtherance of meeting this statutory
requirement. The preference for treatment as a principal element
will be addressed in the final ROD for this operable unit.
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