United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
PB93-964103
EP A/ROD/R05-921192
March 1992
&EPA
Superfund
Record of Decision:
Twin Cities AF Reserve (SAR
Landfill), MN
u . S. Environmental ProtectGaJ'fi Ag~y
Region III Hazardous Waste
Technical Information Center
841 Chestnut Street, 9th Floor
Philadelphia. PA 19107
--- --- ~ --- -
EPA Report Collection
Information Resource Center
US EPA Region 3
Philadelphia. PA 19107
Hazardous Waste Cotrecfion
~nformation Resource Center
'US EP A Region 3
PhllQdelphla~ PA 19107
-------
. (,'
, .
NOTICE
The appendices listed in the index that are not found in this document have been removed at the request of
the issuing agency. They contain material which supplement, but adds no further applicable information to
the content of the document. All supplemental material is, however, contained in the administrative record
for this site.
/\
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50272-101
REPORT DOCUMENTATION ft. REPORTNO. 12.
PAGE EPA/ROD/R05-92/192
3. RedpIent'a ~ No.
4. TIlle end Sub1llle
SUPERFUND RECORD OF DECISION
Twin Cities AF Reserve (SAR Landfill), MN
First Remedial Action - Final
7. Author(a)
5. Report Date
03/31/92
6.
8. PerfonnIng 0rg8'I1mtion Rapt. No.
9. Performing Orgainlzallon Name and Addrea
to. Projec:tIT_klWork UnIt No.
t1. ConIr8cl(C)or GranI(G) No.
(C)
(G)
t 2. Sponaoring Org8'Ilzation Name and AddreIIs
U.S. Environmental Protection Agency
401 M Street, S.W.
washington, D.C. 20460
13. Type or Report A PerIod Covered
800/000
t4.
t5. Supplem8n18ry NoI88
PB93-964103
t 6. Ab8tr8ct (LImit 200 worda)
The 2-acre Twin Cities AF Reserve (SAR Landfill) site is a former disposal area for
U.s. Air Force (USAF) main Base refuse in Minneapolis, Hennepin County, Minnesota.
Land use in the area consists of a Small Arms Range, Minneapolis-St. Paul International
Airport, and Fort Snelling State park. The site is within the 100-year flood plain of
the Minnesota River, and a wetlands associated with the National wildlife Refuge is
located adjacent to the site. The Small Arms Range Landfill (SARL), acquired by the
USAF in 1955, was used for disposal of main Base refuse from 1963 to 1972. Industrial
wastes, which included paint sludge, paint filters, and leaded aviation gasoline
sludge, were buried at the landfill. The SARL was closed in 1972. In 1982 and 1983,
the state constructed a storm water retention and settling pond, serving Interstate
494, in the eastern part of the landfill. The landfill overlies two aquifer systems
that receive recharge from the stormwater retention areas. Additionally, the upper
aquifer has been shown to be connected hydraulically to the Minnesota River. In 1983,
the site was identified as a hazardous waste site, and in 1987, was placed on the NPL
list because of suspected contaminant release to ground water. Based on preliminary
investigations VOCs, metals, and other organics were detected in the soils, surface
(See Attached Page)
t7. Document AMyaia a. DeacrlpIDr8
Record of Decision - Twin Cities AF Reserve (SAR Landfill), MN
First Remedial Action - Final
Contaminated Media: gw
Key Contaminants: VOCs (benzene, toluene,TCE), other organics, metals (arsenic,
beryllium, cadmium, chromium)
b. IdentllleralOpen-endlld Tenna
c. COSATI Fiel6'Group
t8. AvailabiUty Stalement
t 9. Security aa. (1b1a Report)
None
20. SecurIty aa. (ThIa Page)
?\In,.,,,,
2t. No. of Pages
54
22. PrIce
(See ANSI-Z39. t8
See /nstIUcIIons on R-
272 (4-77)
(Formerly NT\So35)
Department or Commerce
-------
EPA/ROD/R05-92/192
Twin Cities AF Reserve (SAR Landfill), MN
First Remedial Action - Final
Abstract (continued)
water, and ground water. This ROD is the first and final action for the site and
addresses remediation of the ground water. The primary contaminants of concern affecting
the soil and surface water did not exceed ARARs and, therefore, are not considered a
threat since access restrictions addressed in this ROD will be implemented at the site.
The primary contaminants of concern affecting the ground water are VOCs, including
benzene, 2-butanone, toluene, and TCE; other organics, including di-n-butylphthalate; and
metals, including arsenic, beryllium, cadmium, and chromium.
The selected remedial action for this site includes natural attenuation of ground water
contamination; access restrictions, including fencing and implementation 'of deed
restrictions; site maintenance; and ground water and surface water monitoring to further
assess baseline conditions. Attenuation will occur due to adsorption, biodegradation,
physical/chemical degradation, and dispersion of the contaminated ground water. The
estimated present worth cost for the remedial action is $737,000, which includes a
capital cost of $53,000 and a present worth O&M cost of $684,000.
PERFORMANCE STANDARDS OR GOALS: The remediation goal is to reduce the levels of
contaminants in the ground water to below MCLs established under the SDWA and to ensure
that contaminant levels do not exceed federal or state Water Quality Criteria for
freshwater species or potential drinking water sources. The remediation will achieve a
carcinogenic risk level within EPA's target range for acceptable excess carcinogenic risk
of 10-4 to 10-6. Chemical-specific ground water clean-up goals are based on SDWA/MCLs or
Minnesota RALs, including arsenic 0.2 ug/l (RAL), beryllium 0.08 ug/l(RAL), cadmium
4 ug/l (RAL), lead 15 ug/l (SDWA), nickel 70 ug/l (RAL), selenium 10 ug/l (RAL), TCE
5 ug/l (SDWA), and vanadium 20 ug/l (RAL).
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AIR FORCE INSTAllATION RESTORATION PROGRAM
REMEDIAL INVESTIGATION I FEASIBiliTY STUDY
"
SMALL ARMS RANGE LANDFILL
MINNEAPOLIS-ST PAUL INTERNATIONAL AIRPORT
AIR FORCE RESERVE
RECORD OF DECISION
JANUARY 1992
Prepared for" ~"',',
HAZARDOUS WASTE REMEDIAL AcnONS PROGRAM
Oak Ridge, Tennessee 37831-7606
managed by
MAR,TlN MARIETI A ENERGY SYSTEMS, INC.
for the
U.S. DEPARTMENT OF ENERGY
under contract DE-AC05-840R21400
-------
ThIS "'POrt wa. prep. red on accounl of wOrt( Sponsored by an agency ot Ihe United
Siaies Govemment. Neither Ihe United States Governmenl nor any aO.ncy Ihereof,
nor any of Ihelr empIOy.e., nor any contractor or SubconlraCtor, ncr any of t/'leir
employ tis makes any warranty, eXj)"" or Implied, or "sumes any Itgall/ability or
r.soonsibillly for the accuracy, CO~lelent$$, or UMfulness ot any information, apparatus,
prOduct, or proc..s disClosed, or represents thai ils use would nOl/ntrlnge pr-iva:e/y
owned rights. Reference herein 10 any Specific commercial prOduct, process. or.
service by Irade name, trademart(. manufacturer, or olherwise, does not neceSSarily
cons lit ute or Imj)Iy Its endorumenl, recommendation, or favoring by the United
Slaies Govemment or any agency Ihereof. The views and opinions of authors
exprtlsed' herein do nOI neCessarily stile Or refleCt those' of Ihe Unit.d Siale.
Government or any agency theroof.
.', .
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AIR FORCE
INSTALLATION RESTORATION PROGRAM
REMEDIAL INVESTIGATION I FEASIBILITY STUDY
. SMALL ARMS RANGE LANDFILL
MINNEAPOLIS-ST. PAUL INTERNATIONAL AIRPORT AIR FORCE RESERVE
RECORD OF DECISION
JANUARY 1992
~j
Prepared By
ENGINEERING.SCIENCE, INC.
Atlanta, Georgia 30329
General Order No. 43B.99788C
Task Order K-ll
Submitted By
HAZARDOUS WASTE REMEDIAL ACTIONS PROGRAM
Oak Ridge, Tennessee 37831-7606
managed by
MARTIN MARIETI A ENERGY SYSTEMS, INC.
. for the
U.s. DEPARTMENT OF ENERGY
Under Contract DE-ACOS-840R21400 .
submitted to
U.S. AIR FORCE
HEADQUARTERS AIR FORCE RESERVFJDEPV
Robins Air Force Base, Georgia
~ATI81COVIlMCn'M4l111881
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RECORD OF DECISION
DECLARATION
Site Name and Location
Small Arms Range Landfill (SARL) .
Minneapolis-St. Paul International Airport (lAP) Air Force Reserve,
Minneapolis, Hennepin County, Minnesota
Statement of Basis And Purpose
This decision document presents the selected remedial action for the Small
Arms Range Landfill in Minneapolis, Minnesota, which was chosen in accordance'
with the Comprehensive Environmental Response, Compensation, and Liability Act
(CERClA), as amended by the Superfund Amendments and Reauthorization Act
(SARA), and, to the extent practicable, the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP). This decision is based on the admini~traqve
record for this site.
The State of Minnesota concurs with the selected remedy.
Assessmen~. 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 a potential future threat to public health, welfare, or the
environment.
Description of the Remedy
The selected remedial alternative will constitute the complete remedial action
for this site. The principal.threats posed by the constituents at the site include risk
to human~ and the environment from future groundwater usage or ingestion and
future contact with landfill contaminants. This alternative will use natural
attenuation of the existing low levels of groundwater contaminAnts to reduce risk to
public health and the environment from ~rt of contaminants to receiving
groundwater and groundwater and surface water bOdies. Acce~ restriction and site
maintenance are elements of the remedial action which will proteCt public health
and the environment by limiting contact with landfill contaminants.
AT661\91W29
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.'.1
The major components of the selected remedy include:
. The deed restrictions required by CERCLA, Section 120 (h) (3) will be
implemented at the time the property is place under the ownership of a
person or other entity of federal government because a deed does not
currently e~t for the property;
. Natural attenuation of low level groundwater contaminants through natural
processes such as biological/chemical and physical degradation, adsorption,
and dispersion;
. Restricted access through construction of a fence around the site; and
. Groundwater and surface water monitoring every-2 months for 2 years to
further assess the baseline condition and determine if and what future
sampling work may be required.
StatutoI)' Determinations
The selected remedy is protective of human health and the environment,
complies with Federal and State requirements that are legally applicable or relevant
and appropriate to the remedial action and is cost-effective. This remedy utilizes
permanent solutionS and alternative treatment (or resource recovery) technologies,
to the maximum extent practicable for this site. However, because treatment of the
principal threats of the site was not found to be practicable, this remedy does rtot
satisfy the statutory preference for treatment as a principal element. Because this
remedy will result in hazardous substances remaining on-site 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.
3 0 JAN 1992
~~d:o
Date
Name
Vu:c Commander
U.s. Air Force Rescne
. ~frl /%ZY
Datel /
'. . - .
An61\'1W2t
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TABLE OF CONTENTS
f!u
DECISION SUMMARY
1.0 Introduction
2.0 Site Name, Location, and Description
3.0 Site History and Enforcement Activities
4.0 Community Relations
5.0 Scope and Role of Response Action
6.0 Summary of Site Characteristics .
7.0 Summary Of Site Risks
8.0 Description Of Alternatives Analyzed In The Feasibility Study .
9.0 Summary Of Comparative Analysis Of Alternatives
10.0 Description Of The Selected Remedy
11.0 Statutory Requirements
1
1
5
6
6
7
19
28
32
36
38
RESPONSIVENESS SUMMARY
42
REFERENCES
45
. .. . .
A'n61/91W2t
i
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LIST OF FIGURES
Number Title Page
1 Location of Small Arms Landfill, Minneapolis St. Paul
InteI)1ational Airport, Air Force Reserve 2
2 Location of Small Arms Range Landfill in Area Designated as U.S.
Air Force Owned Property at the Minneapolis St. Paul
International Airport, Air Force Reserve 3
3 General Location of Small Arms Range Landfill 4
4 Media Sampling Locations and Numbers at the Small Arms Range
Landfill 11
5 Hydrogeologic Cross-Section Location Map 12
6 Hydrogeologic Cross-Section B-B' 13
7 Hydrogeologic Cross-Section C-C 14
8 Upper Aquifer (Water Table) Potentiometric Surface Map 16
9 Lower Aquifer Potentiometric Surface Map 18
'.I
LIST OF TABLES
Number
Title
Page
1
Applicable or Relevant and Appropriate Requirements for
Chemicals of Concern in Groundwater, Small Arms Range
Landfill Site
Chemicals of Concern in Surface Water, Small Arms Range
Landfill Site
Chemicals of Concern in Soils
. Contaminant Physical Characteristics
Toxicity Assessment of Chemicals of Concern for the
Small Arms Range Landfill
Potential Pathways For Human Exposure
Summary of Health Risks . - . .
Alternative Criteria Assessment and Comparison.
Compliance and Trigger Levels for Constituents Detected in
Groundwater Samples
8
2
3
4
S
9
10
20
6
7
8
9
21
.23
27
34
38
AT661/91W2P
ii
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AFR
ARAR
A VGAS
CAA
CERCLA
CFR
CLP
cm/s
CWA
DOT
EPA
FS
lAP
IRP
M
MCL
MCLG
MEK
~g/L
MPCA
MW
NCP
NPL
RAL
RCRA
RI
ROD
SAP
SARA
SARL
TBC
TCE
TCL
TMV
USAF
A1'661/911AJ29
ACRO~SANDABBRE~TIONS
Air Force Reserve
Applicable Relevant And Appropriate Requirement
Aviation Gasoline
Clean Air Act
Comprehensive Environmental Response, Compensation, and
Liability Act
Code of Federal Regulations
Contract Labortory Program
Centimeters per Second-
Clean Water Act
Department of Transportation
Environmental Protection Agency
Feasibility Study
International Airport
Installation Restoration Program
Million
Maximum Contaminant Level
Maximum Contaminant Level Goal
Methylethyl ketone
micrograms per liter
Minnesota Pollution Control Agency
Monitoring Well
National Oil and Hazardous Substances Pollution Contingency
Plan
National Priorities List
Recommended Allowable Limits
Resource Conservation and Recovery Act
Remedial Investigation
Record of Decision
Sampling and Analysis Plan
Superfund Amendments and Reauthorization Act of 1986
Small Arms Range Landfill
To Be Considered
Tricli1oroethylene
Target Compound List
Toxicity, mobility, and volume
U.S. Air Force
. - . .
ill
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DECISION SUMMARY
.
1.0 INTRODUcnON
This decision summary provides. an overview of the problems posed by the
conditions at the SARI., the remedial alternatives considered, and the analysis of
alternatives. This decision summary explains the rationale for the selection and how
the selected remedy meets statutory requirements. The Remedial
Investigation/Feasibility Study (RI/FS) for the site provided the majority of the
information presented.
~I
2.0 SITE NAME, LOCATION, AND DESCRIPTION
The SARL occupies approximately 2 acres near the Minneapolis-St. Paul
International Airport in Hennepin County, Minneapolis, Minnesota. Figs. 1, 2, and
3 depict the geographical location and the general layout of the site. The Small
Arms Range lies north of the landfill area and serves as the Air Force Reserve's
outdoor small arms firing range. The range is used by more than 25 other federal,
state, and local government organizations throughout the year.
The southern extent of the site is bounded by U.S. Highway 1-494. The
Minnesota River and Fort Snelling State Park extend from the south and southeast
of the site to the northeast. Further to the south and southwest of the site are
wetlands which serve as part of a National Wildlife Refuge in the area. A storm
water retention pond lies between the site and. the Minnesqta River. This pond is in
an area leased to the Minnesota Department of Transportation (DOT) and
Metropolitan Airport Comm;csion by the U.S. Air Force Reserve (AFR). The
Minneapolis-St. Paul International Airport lies to the northwest of the site. There
are no residential areas within a one mile radius of the site.
. .
The site is within the 100 year flood plain of the Minnesota River. Based on
historic flood data obtained from the Minnesota Department of Natural Resources,
the site haS been flooded in the past and is still p~one to flooding. The last flooding
of the landfill (highest known flood elevation on record) occu,rred in the area in
1965. Current ground surface elevations of the site (690 to 730 ft above sea level) .
are below this elevation.
Surface water resources at the site are limited to the storm water retention pond
and the Minnesota River. The pond discharges to the Minnesota River.
Hydrogeologic conditions at the site also indicate the pond acts as a recharge area
to the groundwater in the upper aquifer, in particular, when the pond receives
AT661\911Dm
1
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~
"'.OI8woOd
MINNESOTA
)
t
-N-
~
I
;1
~
o
SCALE I
4000
I FE
ES INQINEEIIIINQ -SCIENCE
Fig. 1. Location of Small Arms Range Landfill.
Minneapolis St. Paul International Airport. Air Force Reserve.
. 2
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o
sc..&.E
1CICID IDOO 3Il1O ~
FIEf
IJ
~
EXPLANATION
US,6F Owned Property
US,6F Leased Property
Fig. 2. Location of the Small Arms Range Landfill in area designated
as USAF owned property at the Minneapolis-St. Paullntemational
Airport, Air Force Reserve.
'3
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Concrete Diversion
Structure
Cyclone Fence
;f---)(-1J(--" k
/ ~.t
I Conlrol Ga1
~~ ~
+/
,// Storm.Water /1<
of Retention Pond I<
/ /
~ EM~y I
- (. DI"I~allon!
- ~~"1= ~-==,,---iI )....
Storm Sewer ":~ j
(Buried) "-
~-x
"
~
~
.!!
o
1
.S
~
II
1/
.I:-
J
'-N-
.~
EXPLANATION
~ Sludge Osposal Alea
~ Refuse Osposal AI~a
1.]mIJ Ref use Burn Pit
- '.494 Wes.bound
,.494 Eastbound --.
URCE: Modified From Phase II IRP Re rt
G882R 19
o
SCALE I
200
I FEET
Fig. 3. General location of Small Arms Range Landfill.
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discharge through the storm drain or from surface runoff. Groundwater resources
include the presence of major aquifers of regional importance in the area. These
aquifers are at considerable depths and include the St. Peter Aquifer, the Prairie du
Chien-Jordan Aquifer and the Franconia-Irontown-Galesville Aquifer. The depth
to shallow ground~ater at the site is approximately 22-25 ft below ground surface.
A survey of potable water wells in the area of the site indicates no current use of
shallow groundwater on-site or downgradient of the site.
~.t
3.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES
The SARL was acquired by the U.S. Air Force (USAF) in 1955 and served for
disposal of the main Base refuse from approximately 1963 to 1972. During its
period of use, general Base refuse and industrial wastes formed the bulk of waste
materials deposited at the site. The industrial wastes are believed to have included
approximately 100 gal of paint sludge (mainly paint thinners, paint removers, and
other miscellaneous paint wastes), 800 lb of paint filters, and 100 to 200 gal of
leaded aviation gasoline (A VGAS) sludge. . The A VGAS sludge was reportedly
weathered before it was buried at the landfill. The SARL was closed in 1972.
Native soil was used to cover the fill area. In 1982 and 83, the Minnesota
Department of Transportation constructed a storm water retention and .set~g pond
in the area immediately east of the landfill to receive runoff waters from the 1-494
right-of-way west of the landfill (Fig. 3). .
The site was first identified as a possible hazardous waste site in the Phase 1
Installation Restoration Program (IRP) Records Search report.in 1983 (CH2M Hill,
1983). Preliminary studies of the site (Weston, 1986) indicated low concentrations
of groundwater cont~min~nts were present and possibly migrating from the site.
The site was placed on the Environmental Protection Agency's (EP A) National
Priorities List (NPL) in 1987 because of a suspected release to the groundwater
based on results of these preHminary investigations. In 1988 and 1989, an RI was
conducted to confirm the release, further characterize the site, quantify contaminant
levels, evaluate risk, and obtain data necessary for evaluation of remedial
alternatives (ES, 199Oa). In addition, an evaluation of land uses in the study area
and an ecological assessment were conducted to apprise the potential effect/impact
of the site on surrounding lands, plants, and anima]".
These latter investigations were conducted under a F:ederal Facility Agreement
betWeen the U.S. Air Force Reserve and the E?~ Currently, the U.S. Air Force
and EP A are in compliance with this agreement .
Development of various remedial action alternatives, evaluation of these
. alternatives, and recommendation of a particular alternative were completed in an
. FS report in June 1991. Evaluation of these alternatives was in accordance with
criteria set forth in the National Contingency Plan (40 CFR 300). Subsequent to the
AT661\911OJ29
5
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completion of the FS, a Proposed Plan was prepared to summarize RI/FS efforts,
present the preferred remedial alternative, and solicit public review and comments.
4.0 COMMUNl1Y RELATIONS
The RI and FS Reports and the Proposed Plan were released to the public. The
RI Report was released in July 1990. The FS Report and the Proposed Plan were
released as separate documents in August 1991. These documents were made
available to the pubJ,ic in the admini~trative record and in information repositories
maintained at Southdale Public library in Edina, Minnesota and at the Public
Affairs Office at the Minneapolis-St. Paul lAP Air Force Reserve. A public meeting
was held on September 5, 1991 to present the remedial alternative for the site.
During the meeting, Air Force Reserve, EP A, and the Minnesota Pollution Control
Agency (MPCA) representatives presented the results of the RI/FS, presented the
Proposed Plan and answered questions about problems at the site and the remedial
alternatives under consideration. A response to the comments received during the
public comment period is included in the Responsiveness Summary, which is part of '
this ROD. A transcript of the public meeting is available for review at the Public
Affairs Office at the Air Force Reserve Base. The public comment period for the
Proposed Plan was completed on September 20, 1991.
5.0 SCOPE AND ROLE OF RESPONSE ACI'lON
The principal public health concerns associated with the site are potential
contact with contaminated landfill materials or ingestion of contaminated
groundwater. The principal environmental concerns are contact of local fauna with
contaminated landfill materials or degradation of ambient water quality in the
Minnesota River by runoff or groundwater discharge from the site. The objectives
for remediation of potentially adverse effects resulting from the low-level
contamination at the site are:
. To prevent risk to hnman~ or the e~viro~e~t through contact with landfill
conta.min~ts.
. To prevent risk to hum~ns or environmental receptor from contaminants in
groundwater.
For the first objective, specific risk levels are unknown,due to the diversity of
landfill materials that may be presented. Therefore, the remediation goals will be to
institute measures to mitigate the potential :'fQr any landfil1 components, but
primarily leaded A VGAS sludge, paint residues, and solvents, to be exposed directly
to potential human receptors or local fauna from erosional action by wind or surface
runoff. For,the second objective, the remediation goal will be to reduce the levels of
contaminants in the groundwater, which can potentially be used as a potable water
source at or in the vicinity of the site, to below Maximum Contaminant Levels
(MCUi) established under the Safe Drinking Water Act and to ensure groundwater
A T661 \911C1J29
6
-------
.
recharge from the landfill through the stormwater pond or directly to the Minnesota
River does not exceed federal or state Water Quality Criteria for freshwater species
or potential drinking water sources.
Table llists Applicable or Relevant and Appropriate Requirements (ARARs)
for chemicals or-concern in groundwater at the SARL Chemicals of concern in
surface water and soils at the site are provided in Tables 2 and 3, respectively.
Chemicals of concern in surface water were not included in the calculation of risks
associated with the site because pathways involving surface water are currently
incomplete. ARARs for drinking water con~min8-nts are provided in Table 2 only
for comparison to levels detected in.the pond water. nere are no ARARs for
chemicals of concern in the soils.
The selected remedy will address the response action objectives by limiting
contact with landfill contaminants through access restrictions and deed restrictions,
and reducing risks from groundwater contaminants through natural attenuation and
deed restrictions. Monitoring of groundwater and surface water will act as a check
on how well the responSe action is meeting objectives.
:1
6.0 SUMMARY OF SITE CHARACfERISTICS
The remedial investigation at the site was designed to determine the extent :of
contamination at the site, to determine potential impacts of the contaminants on
human health and the environment, and to develop data: for evaluating potential
remedial actions.
The assessment of the extent of contamination in the RI study was made
through evaluation of data collected through sampling of three media: soil,
groundwater and surface water. Media sampling locations are shown in Fig. 4. In
addition, a geophysical survey was performed to aid in defining the source and
possible extent of contamin9nt migration at the site. The results of this RI study
show that only low levels of some contamin3-nts, in particular, metals, are being
released from the landfill and are evident locally in the soils and groundwater.
In order to understand potential routes of migration for these contaminants at
the site, a general discussion of the site hydrogeologic conditions is necessary. To
evaluate hydrogeologic conditions beneath the site, water level measurements
obtained from monitoring wells, and other data gathered from boring logs during
drilling operations were used. The evaluation in4icated 'the surficial aquifer at the
site is comprised of an upper and lower aquifer:' Hydrogeologi~, cross-sections for
the site are presented in Figs. S, 6, and 7. The upper aquifer exists beneath the
landfill area and the area between the 1andfil1 and the Minnesota River.
The upper aquifer consists of a gravelly sand layer underlain by heterogeneous
unconsolidated materials comprised of silty sand, peat, clay, silty sandy clay, and
sandy clay which generally exhibit low permeability. These low permeability
materials combine to form a confining strata that separates the underlying aquifer
AT661\911QJ29
7
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Table I. Applicable or Relevant and Appropriate Requirements
For Chemicals of Concern in Groundwater
Small Arms Range Landlill Site
Indicator Chemicals
MlnDe50ta
RAUl)
(pg/L)
Proposed
MCL(Z) MCLG(Z) MCL(3,4)
(/Jg/L) (lJg/L) (/Jg/L)
50
5 0
1
Maximum
Groundwater
Concentration Detected
(IJK/L)
00
Arsenic
Benzene
BeryUium
2-Butanone
(methyletbyl ketone-MEK)
Cadmium
Chromium (total), Cr (VI)
Copper
di-n-butylphthalate
1,2-dichloroetbene
Lead
Mercury
Nickel.
Selenium
Silver
Toluene
Trichloroethene (TeE)
Vanadium
Zinc
4.0
100.0
1,000
700
70
20
1.0
70.0
10.0
10.0
1000.0
30.0
20.0
700.0
0.2
10.0
0.08
300.0
.'
10'
3
1.8'
71
5 5
100 100
1,3()()(5) 1,300
70 70
15(5) 0
2 2
100
50 50
1,000 1,000
5 0
5."
29.2
96.2
2
3
21.5'
0.28
143'
12.1'
7.6
1
6'
Well In Which Maxlmun
ConcentractioD 01
Contaminant was Detected
MWSA
MW9A
MW8B
MW4
MW2
MW7A
MW5
MW9B
MW2
MW7A
MWSA
MW2
MW9A
MW13
MW9A
MW3
MW9A
MW7A
56.1"
148
(1) Minnesota Department of Health, Section of Healtb Risk Assessment, Release No.3, "Recommended Allowable Limits for Drinking Water Contaminants;
(Janaury 19(1).
(2) EPA "Fad Sbeet: Drinking Water Regulations Under the Safe Drinking Water Act." January 1991,40 CPR 143.2.
(3) EPA "Fact Sheet: Drinking Water Regulations Under the Safe Drinking Water Act." May 1990, 55 FR 30370, July 25, 1990.
(4) To-De-Considered; Not ARARs. .
(5) Action Level.
. Exceeds ARARs.
-------
-
Table 2. Chemicals or Concern in Surface Water
Small Anns Range Landfill
Indicator Chemicals
Minnesota
RAL(I) MCL<2)
(pa/L) (pa/L)
1,000.0 1,000
.0.08
20 15(5)
10.0
20.0
700.0
Federal Water Quality Criteria(J) Mulmum
Fresh Water Minnesota Water Surface Water Surface Water Location
MCLG(2) Acute Concentration Standards(4) Concentration Detected Where DeteCted
(pg/L) (pg/L) (pgfL) ~L)' .
Toluene
Beryllium
Iron
Lead
Silver
Vanadium
Zinc
2 SWL3
0.77 SWL3
300 620 SWU
o 82 50 3.4 SWU
4.1 50 8.4 SWL3
6.6 SWL3
120 5,000 64.2 SWL2
\0
(1) Minnesota Depar(inent of Health, Section of Health Risk Assessment, Release No.3, RRecommended Allowable Umits for Drinking Water Contaminants;
(January 1991). " . .
(2) . EPA -Fad Sheet, Drinking Water Regulations Under the Safe Drinking Water Ad,R January 1991, 40 CPR 143.2.
(3) A.RARs Q's and A's. Compliance with Federal Water Quality Criteria, ROffice of Solid Waste and Emergency Response: U.S. EPA. June 1990.
(4) Minnesota Water Staiulards, -Specific Standards of Quality and Purity for Designated Classes of Waters or the stateR, 7050:2.20, November 1990.
(5) Action Level.
-------
Table 3. Chemicals of Concern in Soils
Small Arms Range Landfill
Maximum Soil Soil Sampling
Indicator Chemicals Concentration Detected ARARs Location Where Detected
(mg/Kg)
Antimony 26.4 Nonc' SB6 12' - 15'
Arscnic 12.7 Nonc SBS 16.5' - 19.5'
2-Butanone 2S Nonc SB6 12' - 15'
Magncsium 10,800 Nonc SBS 16.5' - 19.5'
Nickel 191 None SBS 16.5' . 19.5'
Selenium 161 Nonc SBS 7.5' - l0o?'
. .. . .
AT661/9110J29
10
-------
:.1
SMALL ARMS
FIRING RANGE
.....
\ I
....' I
. I
, /
..' /'
,..-MW11'
"", /
, '. ""
" J' ,'. /
i"(,~;ict~~'~~//
\:.::... ,-
,. ,
'. ..
ENERGY
DlSSIPlCT'lON
STRJCT\JAE
.. MW78
MW7 A '-- [SB4;f1
-~
I
,~f
r
~I
(I
r ; 1
, ~
S85.1
S85.2
INTERSTATE HIGHWAY 1-494 (Elevated)
100 0
SCALE ,.,..".~
EXPLANATION
100
200
J FEET.
landfill Area
Phase U Stage 1 Study Well and Number
AI Well and Number
. .. . .
. Surface Water Sampling Location
~83.1 Soil Sampling Location and Numbers
832
Surface Water Sample Number
* Indicates Background Sampling Location (Round 1 Sampling)
* lnclcates Background Sampling Location (Round 2 Sampling)
-,,- Fence
=} wen Cluster. Comprised of Shallow Well (A) and Deep Well (8)
Fig. 4. Media sampling locations and numbers at the Small Arms Range Landfill.
11
~tffl!1
~
MWI
.
-------
. ' ~
/' ~
! ,,1 ;
.. -- - ~~2 j ,./ N
~ , I ~
f; /' ~
\ .;'
'..--"
MW6
'\ ~ MW5 MW7rMW7B .,,~- MWSA .~B' ~
~ :..- ~ MW8B I
SOIL BORING 8T13 INTERSTATE HIGHWAY 1-494 (Elevated)
(MHO Leg) (3888)
SMALL ARMS
RRING RANGE
~'
I
1
,""'MW1~
,,;/ /
I~' /~
/ /...
~
,
100
SCALE
o
100
200
FEET
r-,
L_J
~
MWe
..
EXPLANATION
.
Landfill Area
Phase U Stage 1 Study Well and Number
AI Well and Number
Minnesota Highway Departmet:'t ~~D) Boring ,
Well Cluster. Comprised of Shallow Well (A) and Deep Well (8)
=}
Fig. 5 Hydrogeologic Cross Section Location Map___-
12
-------
730
710
::!
~
~ 700
L5
(/)
~ 690
o
~
1Ai680
W
~
-
z
S 670
~
W
~
Weeo
MW3
I
iI
i
I
i
720
-II
I!
650
~
~
~
rt!t]
~
~
~
Colluvium and .
Alluvium Deposita
(Post Glacial)
Bedrock
{D
B
B'
195'
MW2
t
...
MW 8B SA
1 r-125' II
. iI
i I
.
i
270'
133'
~
~~~
Xo~
o ii:
~t:Q
~~~
SCALE 0
100
.
200 FEET
EXPlANATION
Lithology Predominantly Sand
With Some/Trace Gravel
LlthoIogy'Predominantly Sand
With Some Silt and Some/Trace Gravel
Lithology Predominatly Sand
With Some Silt and Clay
MWS
Lithology Predominantly Clay
Lithology Predominantly Peat Uibroui) - . .
Lithology Predominantly Sandstone
. ~ ~aIiz8d DIr8ctIon of GromcMattr FIcM
\I8rtic8I ~atioI, - 10X
Fig. 6
FIGURE 6 Hydrogeologic Cross-Section 8-8'
13
I 730
! 720
...
I
710
....
j
700 ~
~
(/)
690~
g
~
6801Ai
~
-
Z
670 e
~
eeoW
650
640
Well Number
Toe of Well Casing
i
Water Tabie
(aa at 10/12/88)
Screened Intenia'
~ . Water Level in Deep Well
.. (as at 10/12/88)
Blank Casing
Total Hole Depth
-------
,C C'
MW3 MW1 MW9BSA
I- 270' I 125' rD' n n
t,.
..J I
j
740 740
730 a: 730
.... w
..J 2
~ a:
w 720 ~ 720
..J 0
~ (/)
Q W
rn z z
w 710 ~ z 710
~ ~
CD
«
tu 700 700
w
1;
Z
0 690 690
~
~
w
680 -- 680
670 670
..
680 660
650 650
640 6~.
SCALE 0
100
200 FEET
EXPlANATION
Colluvium and
Alluvium Deposits
(Post Glacial)
~
~
~
Lithology Predominantly Sand
With Some/Trace Gravel
Lithology Predominantly Sand
With Some Silt and Some/Trace Gra~ 0 ,--
Lithology Predominatly Sand
With Some Silt and Clay
MW8A
Well Number
Top 0' Well Casing
~
.~
Water Table
(as at 10/12/88)' .
Uthology Predominantly Clay
~
Uthology Predominantly Peat (fibrous)
,
Screened Interval
Water level in Deep Well
(as at 10/12/88) .
Bedrock
{
r:::3
Blank Casing
Lithology Predominantly Sandstone
Total Hole Depth
~ Q«*8IiZ8d Dir8ctiCIn of GrowdIat8r !=11M '
\W1IC8I ~atICIn - 10X
Fig. 7
Hydrogeologic Cross-Section C-C'
14
-------
:)
(lower aquifer) from the upper aquifer. Further review of subsurface conditions at
the site indicates a discontinuity in the lateral extent of the confining layer and
underlying materials to the west of the site. This discontinuity is due to the presence
of the bedrock (St. Peter Sandstone) at this portion of the study area.
Stratigraphically..,~he St. Peter Sandstone originally extended over the entire area
occupied by these sedimentary deposits. Subsequently, the Minnesota River eroded
a portion of the sandstone formation, resulting in a river valley which has filled to its
current datum mainl.y as a result of fluvial depositional processes. Based on this
evaluation, an unconformable contact is interpreted between the St. Peter
Sandstone and the overlying or adjac~nt sedimentary deposits. The deep wells at
the site indicate artesian conditions in the lower aquifer. This conclusion was made
because of the higher hydraulic heads in the wells penetrating the lower aquifer,
lower water levels in the sballow wells completed in the upper aquifer and tbe
characteristics of subsurface materials encountered during drilling for installation of
wells. These conditions further provide credence to the presence of low permeable
multilayered materials below the upper aquifer, in particular, in the landfill area
and area east of the landfill.
The groundwater in the upper aquifer may include water ac~ulated by
infiltration and groundwater from the surficial aquifer in upland areas adjacent to
the study area. Precipitation is probably the main source for groundwater rechaige
in upland areas adjacent to the study area, and probably contributes some amount at
the site. Groundwater moves vertically downward at a rapid rate through the
unconsolidated sand deposits, but this rapid movement is slowed as the groundwater
moves through sand with increasing silt and clay content, or the peat layer. This
assumption is valid because the pore spaces in these materials (silt, clay, and peat)
become extremely small and make movement of water difficult. When the site is
flooded, a rapid lateral movement of the flood water is expected at a shallow depth
(in the loose unconsolidated sand). Assumedly, a flushing effect can take place in
this layer during a flood.
Based on these hydrogeologic evaluations, it was determined that a hydrologic
relationship exists between the upper aquifer, the pond, and the Minnesota River..
As shown on Figs. 6 and 7, groundwater flows from areas of higher water levels, or
hydraulic heads, to areas of lower water leveis. The groundwater movement at the
site generally follows the dip of the sedimentary layers. The water in the retention
pond is recharged by both groundwater in the upper aqUifer and water discharged
'from the storm drain. The pond water rechargeS 'the groundwate~,beneath the pond
area, when discharge occurs from the storm drain. Subsequently, the groundwater
discharges into the Minnesota River.
,The shallow groundwater movement at the site was estimated from the shape of
the water table. Groundwater movement in the upper aquifer is generally from the
northwest to the east and southeast in the site vicinity as shown in Fig. 8. The water
in this unconfined upper aquifer probably moves in the silty sand layer beneath the
AT661\9111U29
15
-------
SMALL ARMS
FIRING RANGE
693.58
MW6
.
. ~ 683.
.,,-.~ ~/Mi8A
_..~ MW8B .
INTERSTATE HIGHWAY 1-494 (Elevated)
sCALE ~ . ~FEET
.~
WFC] landfill Ar-
w:a Phase II Stage 1 Study Well and Number
..,. AI Well and Number . ~ .'. .
- 690 - Groundwater Elevation Contour
693.58. Groundwater eleVation at Upper Aquifer Well
==} Well Cluater. Comprised of Shallow Well (A) and
Deep Well (8)
. Generalized Direction of Groundwater Flow
Note: Well MW3 was used because a portion of
the screen in the well is open to this aQUifer
Fig. 8 Upper aquifer (water table) potentiometric surface map.
16
-------
:.1
landfill and in the lower portion of the predominantly sandy layer between the
landfill and the pond. Between the pond and the river it appears groundwater
movement occurs through the upper portion of the fibrous peat layer and ultimately
discharges to the. Minnesota River. Groundwater movement in the lower aquifer is
estimated to be to .the southeast towards, but beneath, the Minnesota River (Fig. 9).
The water in this aquifer moves eastward from the St. Peter Sandstone Formation
through the adjacent or overlying unconsolidated sand layer beneath the confining
strata at the site. The lower aquifer does not discharge into the Minnesota River in
the site area; however, a negligible leakage may occur into the river through the
overlying confining strata.
The sources for the few contaminaf'ts with slightly elevated concentrations
detected at the Small Arms Range Landfill site are thought to be from within the
disposal area at the southwest portion of the landfill. Within this landfill, weathered
A VGAS sludge was reportedly buried in an area partially isolated from the main
landfill mass. The area regarded as the main landfill mass contains the paint wastes
and other industrial wastes. Contaminants evaluated are those likely related to
materials reportedly disposed of at the site. Of these, dissolved contaminants
include benzene, toluene and lead from A VGAS sludge; 2-butanone (MEK) and
chromium from paint waste; and 1,2-dichloroethene, and di-n-butylphthalate frQm
landfill related materials. Inorganics, in particular metals, which were detected' at
elevated levels include nickel, zinc, antimony, arsenic, beryllium, magnesium.,
selenium, vanadium, copper, mercury, cadmium, silver, lead and chromium.
Chemicals of concern as summarized from the analytical results of the RI effort are
presented in Tables 1, 2 and 3. The maximum detected concentrations of chemicals
and ARARs are also included in these tables.
Geophysical results were used to delineate the extent of the landfill area
depicted in Figs. 7, 8, and 9. The results indicated highly ferromagnetic objects are
present in the landfill and the depth of the landfill at the site is approximately 10 to
12 ft below ground surface. The water table beneath surficial materials immediately
adjacent to the Jandfil1 exists at 22 to 24 ft below ground surface. This indicates that
the landfill materials are not physically in contact with the groundwater beneath the
site. Physical and chemical processes within the unsaturated zone will include
infiltration and partial retention. Because of the physical state of the waste material
deposited at the site, it is expected that a major portion of the contaminant
coIistituents will initially sorb to surrounding ~~ij..materials until they are exhausted
or their movement is retarded in the absence of water. However, many of the
A VG~ sludge and paint waste contaminants are soluble to some extent. Those in
the source material will be dissolved by water moving through the source. The
source of the water for this purpose can only occur through three avenues; by water
infiltration from precipitation, by flooding of the area (as previously documented),
and by a rise in the water table due to a change in hydrology.
ATI61\911GJ29
17
-------
SMALL ARMS
ARiNG RANGE
CONCRETE
STRUCTURE
"
MW5
~'--.:. /" ~ MWSA
. Mae
~ 689.76
INTERSTATE HIGHWAY 1-494 (Elevated)
SCALE
~
Bmi Landfill Area
M~ Phase II Stage 1 Study Well and Number
~ RI Well and Number
. .. . .
- 690 - Groundwater Elevation Contour
MWBA} Well Cluster. Comprised of Shallow Well (A)
MW8B and Deep Well (a> . .
690.92 Groundwater Elevation at Lower Aquifer Well
. Generalized Direction of Groundwater Flow
Fig. 9 Lower aquifer potentiometric surface map.
18
-------
~ .{
The solubilities of the A VGAS sludge and paint wastes contaminants vary
largely, therefore, partitioning betWeen phases will vary from compound to
compound. When some of the compounds in the landfill become soluble, chemical
reactions will occur betWeen nonconservative compounds while some conservative
compounds will not react but tend to remain in solution. In general, many organic
compounds if present will be subject to biological degradation, oxidation, reduction,
reaction with other compounds and sorption.
Most migration- of contaminants from the landfill would be via shallow
groundwater to the Minnesota River and probably through the surficial aquifer in
the area immediately west of the landfill and beneath the landfill. Limited
migration may occur through the lower aquifer and possibly underneath the river.
However, because of the presence of low permeability materials in the upper
portion of the lower aquifer, significant downward migration of contaminants into
any underlying aquifers below the lower aquifer would not be expected, nor would
significant lateral migration northward or southward to wetlands or the wildlife
refuge. Migration of contamination from the site to any existing groundwater users
would not occur. Discharge of contaminants to the Minnesota River and
subsequent environmental or public health impacts to downstream users would be
negligible based on the dilution capacity of the river and the low levels of
contaminants found.
The physical characteristics of major contaminants expected in weathered
A VGAS are presented in Table 4. Toxicologic and carcinogenic concerns are
discussed under Snmmary of Site Risks in Section 7.
7.0 SUMMARY OF SITE RISKS
During the RI, an analysis was conducted to estimate the health or
environmental problems that could result if no remedial action is taken at the SARL
site. This analysis is commonly referred to as a baseline risk assessment. In the
baseline risk assessment, human health risks were estimated for current site
conditions and for future development scenarios. Environmental risks were
qualitatively assessed by performing an ecological assessment of biotic resources at
the site and within one mile of the site.
Human Health Risks
. The concentrations of contaminants of concern in 'each potential medium of .
exposure are presented in Tables 1, 2, and 03'.' Toxicity assessment of these
contaminants is provided in Table S. '
The risk assessment for current site conditions'indicated no pathways of human
exposure existed at the site, and therefore, no current risks exist. A complete
exposure pathway consists of (1) a source and mecbani!i:m for chemical release; (2)
an environmental transport medium; (3) an exposure point, and (4) a human
receptor and route of exposure at the exposure point An incomplete pathway
AT661\'1111J29
19
-------
Table 4. Contaminant Physical Characteristics
Small Arms Range Landfill Site
Solubility(a) Vapor Pressure(a)
Compound Pbase (mgJL) (mmHg)
Benzene Colorless 1780 @ WOC 60 @ 15°C
liquid 76 @ 20 ° C
118@30oC
Etylbenzene Colorless 140 @ ISoC 7 @ 20°C
liquid 152@WoC 12@30oC
206 @ 30°C
Toluene Colorless . 470@ 16°C 10@6.40C
liquid 515 @WoC 22@WoC
4O@31.SoC
N Xylenes:
0 175@WoC 5@WoC
o Colorless
liquid 9@30oC
m .Colorless 6@WoC
.,.liquid l1@30oC
p Colorless 198@25°C 6.5@WoC
liquid 12 @ 30°C
2-Butanone (MEK) Colorless 353,000 @ 10 ° C n.5 @WoC
liquid
Lead(Pb)(d) Bluisb-gray solid Insoluble
Chromium(Cr)(e) Steel-Gray solid Insoluble
Spec:inc
Gravity(a)
Chemical Half-life
in Water
Log K~
Values(C)
0.8786 @
4-WoC
O.71(b) yrs
2.13@woe(a)
0.867@4-woe
315@woe
0.867 @ 4-20 ° C
2.69@WoC
0.88 2.77 @WoC
0.864 3.W@WoC
0.86 3.15 @WoC
0.805 @ 4-20 ° C O.26@WoC
11.35 @woe N/A
7.20 @ 28° e(e) N/A
(a)
(b)
(c)
(d)
(e)
Vershueren, Karel, .Handbook of Bnvironmental Data on Organic Chemicals,. 2nd Bd., Van Nostrand Reinhold Company, New York, 1983.
USPHS, Benzene Toxicology Prorate.
Log Kow values are the log water-octanol particles coefficienl. The relatively high Kow values indicate lhat these compounds may sorb lo sedimenlary organic malerials.
USPHS, Lead Toxicity Profde, 1988 Draft.
USPHS, Toxicological Profde for Chromium, 1987 Draft.
AT661/911OJ29
-------
Table 5. Toxicity Assessment of Chemicals of Concern for the
Small Arms Range Landfill Site
Medium/Chemical
CAS Number
Toxicity
Class
Groundwater and Soils
Arsenic
2-butanone
Nickel
Selenium(l)
'.<
Soils On Iv
Antimony
Magnesium
Groundwater On Iv
Benzene(l)
Beryllium(l)
Cadmium
Chromium
Copper
1,2-dichloroethylene
Lead
Mercury
Silver(l)
Toluene(l)
Vanadium(l)
Zinc
7440-38-2 C
78-93-3 NC
7440-02-0 NC
7782-49-2 NC
7440-36-0 NC
7439-95-4 NC
71-43-2 C
7440-41-7 NC
7740-43-9 C,NC
7440-47-3 C
7440-50-8 NC
540-59-0 NC
7439-92-1 C
7439-97-6 NC
7440-22-4 NC
108-88-3 NC
7440-62-2 NC
7440-66-6 NC
(1) Also identified as potential indicator for surface water at the SARL Site; however, this
environmental media (surface water) was not quantitatively assessed because no complete
exposure pathways could be associated with it.
l':lC = noncarcinogen
C = carcinogen
. . .
AT661/9110J29
21
-------
would consist of one or some of these characteristics but not all. Air, soil;
groundwater, and surface water pathways are not complete because of the lack of
release of volatile organic compounds, lack of surficial soil cont~m;nation, the
location of the site within a semirestricted area, limited access to the stormwater
pond, no significa:n,t surface water contamination, and no current users of shallow
groundwaters on-site or downgradient of the site. In addition, contamination of the
Minnesota River is unlikely for three reasons: (1) contamination via runoff from
the site is unlikely due to the absence of surficial soil contamination (Table 3);
(2) groundwater seepage to the river is unlikely to contribute detectable
contamination due to the low concent(ation of compounds detected in groundwater
(Table 1); and (3) attenuation of the concentrations released to the river due to
mixing, natural degradation, and dispersion processes. Pathways involving the
consumption of fish, waterfowl, or mammals that inhabit local surface waters are
not considered to be complete because of the lack of significant surface water
contamination (Table 2). Table 6 S11mmarizes pathway analysis.
Baseline risks were also calculated for hypothetical future residential use of the
site. The risks for hypothetical (future) residents were calculated for incidental
ingestion of soils, inhalation of volatile compounds released during showering with
site groundwater, and the ingestion of drinking water obtained from the shallow
aquifer. Carcinogenic risks were calculated for arsenic and benzene exposure.
Noncarcinogenic risk and associated hazard indices were calculated for metals and
several organic chemicals detected at the site. For the specific risk calculation
procedure refer to the RI report.
Hazard Indices for noncarcinogenic health effects via groundwater ingestion
(i.e., maximum exposure for children and adults) and via soils ingestion (i.e.,
maximum exposure for children) exceeded one. A hazard index greater than one
indicates a potential hazard to human health. Thus, adverse health effects are a
possibility if maximum exposure does, in fact, occur.
Carcinogenic risks are expressed as excess cancer risk values. EP A's target
range for "acceptable" excess carcinogenic risk is 10'4 to 10'6. A 10'4 risk means that
1 additional person per 10,000 people has a chance of contracting cancer as a result
of long-term exposure to the contaminants in question. Similarly, 1()-6 means 1
additional person per 1,000,000 people has a chance of contracting cancer as a result
of ~ong-term exposure. During the risk assessment for the SARL site, the following
excess cancer risks were calculated for the indicated exposures (in the ~sence of
any site remediation). . .
. Hypothetical Groundwater Ingestion (Future Site Residents).
- Children - 5.9 excess cancer cases per 100,000 exposed (average), and 1.0
excess cancer cases per 10,000 exposed (maYimnm).
AT661\91111J29
22
-------
\.:
Table 6. Potential Pathways For Human Exposure
Associated With The Small Arms Range Landfill
Transport Source/Mechanism Potential Potential Primary Route(s) Probability of
Medium for Release Exposure Points Rec:eptor(s) Exposure PathwdY Completion
Current Pathways
Air Surface soils, surface On site; areas Base personnel, . Inhalation None: no significant concentrations of
water/volatilization downwind state DOT or volatile organic compounds were
contractor detected in site media
personnel, Small
Arms Range
users, trespassefs,
downwind
N residents
w
Soils/fugitive dust On site; areas Base personnel, Inhalation None: the landfill is vegetated and
, generation downwind state DOT or covered with natural soils; no surficial
contractor contamination was detected
personnel, Small
Arms Range
users, trespassers,
downwind
residents
Soils Disposed waste On site Base personnel, Oral, dermal None: the landfill is vegetated and
contammated trespassers covered with natural soils; no surficial,
, ,soils/leaching, runoff, contamination was detected; access to
. tracking. fugitive dust the landfill is restricted by fencing;
generation there are no residences within 1 mile of
the site
-------
Table 6. (Continued)
Traasport Source/Mechaalsm Potential
Medium ror Release Exposure Polats
Groundwater Contaminated soils/site Wells screened in
leaching the shallow
aquifer on site or
downgradient of
the site
Wells screened in
deep aquifers
downgradient of
the site
N Surface water Contaminated soils, Retention pond,
""
groundwater Isurface Minnesota River
runoff. groundwater
~page
"
'.
Minnesota River
Poteatial
Receptor(s)
Base personnel,
nearby residents
Base personnel,
nearby residents
Base personnel,
nearby residents
Nearby residents
using river water
as a drinking'
source
"
Primary Route(s)
Exposure
Oral, dermal,
inhalation
Oral, dermal,
inhalation
Oral, dermal
Oral, dermal,
inhalation
Probability or
Pathway Completion
None: the aforementioned potential
exposure points d~ not exist
None: There is no hydraulic
connection between the surficial and
deep aquifers either beneath or
downgradient of the site.
, None - very low: trace levels of.
contaminants were detected in
retention pond. However, access to the
retention pond is restricted by fencing,
making receptor contact highly
improbable. Due to the low levels of
contaminants detected in groundwater.
environmental degradative processes
and the large volume of mixing,
Minnesota River waters are not likely
to be impacted by groundwater
discharged from beneath the site
None - very low: contamination is
unlikely for reasons given above
-------
Table 6. (Continued)
'-
Transport
. Medium
Source/Mechanism
for Release
Potential
Exposure Points
Potential
Rec:eptor(s)
Primary Route(s)
Exposure
Probability or
Pathway Completion
Hypothetical Future
. Pathways
Soils
Groundwater
N
V1
Deep contamination/
excavation activities
Contaminated soils/site
leaching
..
On site
Wells screened in
the surficial
aquifer on site
Hypothetical
future residents
Hypothetical
future residents
Oral, dermal,
inhalation
Oral, dermal,
inhalation
Low: low levels of contaminants were
detected in deeper soils on site. U the
site were developed as a residence,
exposure could occur
Low: low levels of contaminants were
detected in shallow groundwater. U
. the site were developed as a residence,
it is unlikely that the shallow aquifer
. would be used as a drinking water
source. If it were, exposure could
occur if contaminants were still present
-------
- Adults - 2.8 excess cancer cases per 100,000 exposed (average), and 1.8
excess cancer cases per 10,000 exposed (maximum).
. Hypothetical Incidental Soils Ingestion (Future Site Residents).
- Children - 1.8 excess cancer cases per 1,000,000 exposed (average), and 9.2
excess cancer cases per 100,000 exposed (maximum).
- Adults - 5.0 excess cancer cases per 1,000,000,000 exposed (average), and
7.5 excess cancer cases per 100,000,000 exposed (maximum).
. Hypothetical Inhalation of a Volatile Compound Released During
Showering (Future Site Residents).
- Children - 3.3 excess cancer cases per 10,000,000 exposed (average), and
8.7 excess cancer cases per 10,000,000 exposed (maximum).
- Adults - 1.6 excess cancer cases per 10,000,000 exposed (average), and 1.5
excess cancer cases per 1,000,000 exposed ("1aYimum).
A summary of health risks associated with the site is presented in Table 7.
The calculated .risks associated with the site and hypothetical (future) residents
were considered conservative because:
. The location of the site within a flood plain and adjacent to a highway
overpass makes future residential development unlikely.
. The shallow aquifer is an unlikely groundwater resource since higher yield
aquifers are available.
. The risk from future/hypothetical ingestion of metals via groundwater was
based on total metals (unfiltered) whereas a portion of these metals would
remain on soil particles and not be available for consumption if groundwater
is developed for potable use.
. Persistence of even the currently low levels of volatile organic contamination
in the shallow aquifer is unlikely over the long term associated with risk
computations (70 years).
. Actual exposure durations would be much lower than values recommended
to be used in risk assessment computations because .cold temperatures and
snow coverage would limit potential exposure. activities for the winter
months. . - . .
The preferred alternative (Natur8.J. Attenuation, Maintenance, Access
Restriction, and Groundwater and Surface Water Monitoring) will eHminate the
possibility of future residents on this site. Thus, the potential for completion of the
exposure pathways included in the baseline risk assessment is eliminated, and it is
concluded that the preferred alternative will protect human health.
AT6U\911GJ29
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.10:
Table 7. Summary of Health Risks
Small Anns Range Landfill
Cbllclren
Ayerage Exposure Maximum Exposure
Ayerage Exposure
Adult
Maximum Exposure
Escas Urethoe Cueer Cua
Hypothetical Groundwater Ingestion 5.9/100.000(1) 1.0/10.000(1) 2.8/100,000(1) 1.8/10.000(1)
(Future Site Residents) (5.9E - 5}(2) (1.0 E - 4)(2) (2.8 E - 5)(2) (1.8 E - 4)(2)
Hypotheticallnc:idental Soils Ingestion 1.8/1.000.000(1) 9.2/100.000(1) 5.0/1.000.000,000(1) 7.5/100.000.000(1)
(Future Site Residents) (1.8 E - 6)(2) (9.2 E - 5}(2) (5.0 E - 9)(2) (7.5 E - 8)(2)
N Hypotbeticallnhalation of Volatile
..... Compounds Rele~ During Showering 3.3/10.000,000(1) 8.7/10.000.000(1) 1.6/10,ooo.000(~) 1.5/1,000.000(1)
(Future Site Residents) (3.3 E - 7}(2) (8.7 E _7)(2) (1.6 E _7)(2) (1.5 E - 6)(2)
NoacardD" """"Iam
Hypothetical Groundwater Ingestion 0:78(3) 2:2(3) 0.37<3) 1.1(3)
(Future Site Residents) (7.8 E - 1)(4) (2.2 E + 0)(4) (3.7 E - 1)(4) (1.1 E + 0)(4)
Hypotheticallnc:idental Soils Ingestion 0.44(3) 3.8(3) 0.051(3) 0.19<3)
(Future Site Residents) (4.4 E - 1)(4) (3.8 E + 0) (5.1 E - 2) (1.9 E - 1)(4)
Hypothcticallnhalation of Volatile
Compounds Released During Showering 0.038(3) 0.066(3) 0.018(3) 0.034(3)
(Future Site Residents) (3.8 E - 2)(4) (6.6 E - 2)(4) (1.8 E - 2)(4) (3.4 E - 2)(4)
(1) Number of expected ~ lifetime cancer cases per number of exposed populace.
(2) Exponential form for (1). above.
(3) Numerical value of total hazard index for indicated exposure.
(4) Exponential form for (3), above.
AT661/911OJ29
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Environmental Risks
Potential risks to the environment are primarily from contact by fauna with
landfill materials or transport of contaminants to receiving surface water bodies by
erosion or gro~dwater discharge. Ecological assessment at the site and within a
mile of the site mdicate no endangered species exist on the landfill site. Protected
flora are found in the Wildlife Refuge but not within a mile of the landfill site.
Protected fauna are found in Fort Snelling State Park. However, the presence of
species of concern (Blanding's Turtle, Eastern Milk Snake, Fox Snake, and Bell's
Vireo) have not been documented near the site. The remedy is expected to be
protective of flora and fauna, as well as human health.
8.0 DESCRIPTION OF ALTERNATIVES ANALYZED IN THE
FEASIBILI1Y STUDY
An array of alternatives for addressing the remedial objectives at the SARL site
was develope~ in the FS. The remedial alternatives were evaluated based on their
effectiveness in protecting human health and the environment; compliance with
federal and state environmental regulations, community acceptance, state
acceptance, short- and long-term effectiveness. and permanence, reduction of
toxicity, mobility, and volume; technical feasibility and implementability; and cost.
The remedial alternatives considered in the FS are briefly described below.'
Alternative 1: No Action
Under this alternative, no actions would be taken for soil, groundwater, or
surface water contamination. The site would be left in its current condition, and any
reduction of the low levels of contaminants would be a direct effect of natural
processes such as biological/chemical and physical degradation, adsorption and
dispersion. No costs would be aSsociated with Alternative 1.
Alternative 2: Natural Attenuation, Maintenance and Groundwater and Surface
Water Monitoring
In this alternative, contaminant reduction in groundwater would occur through
natural processes such as described for Alternative 1, a groundwater and surface
water monitoring plan would be implemented to monitor contaminant levels, and
site maintenance would be conducted on the landfill cover and monitoring system.
The elements of this alternative are as follows:
. Conducting sampling every two months fota minimum of~ yrs. of 11 existing
and 1 replacement (for MW3) groundwater monitoring wells and surface
water in the retention pond. Sampling would be conducted to evaluate
seasonal variation in groundwater quality. The samples obtained from
groundwater and surface water locations would be analyzed for volatile
organic compounds, semi-volatiles, and priority pollutant metals along with
vanadium. These parameters would include all compounds of concern at the
AT661\911AJ29
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'.I
SARL site as shown in Table 1. The volatile organic compounds analyzed
will include those on the Target Compound list (TCL). All analyses will be
conducted by Contract Laboratory Procedures (ClP) protocols. Field
measurements during the sampling work will include water levels in all wells,
pH and cQI!.ductivity. In accordance with the Federal Facility Agreement, the
specific parameters to be analyzed will be proposed in the Sampling and
Analysis Plan and negotiated between the USAF and EP A following
finalization o( the Record of Decision.
. Development of a Sampling and Analysis Plan (SAP) detailing sampling
methodology, quality assurance requirements, and training for sampling
personnel.
. Routine evaluation of monitoring results to determine future monitoring
requirements. After a year of sampling recommendations for the addition or
deletion of wells and parameters for sampling may be made.
The estimated capital cost and the present worth of O&M cost are $20,000 and
$684,000, respectively. The estimated total present worth for this alternative is
$704,000. The estimated time to complete would be determined by attenuation of
contaminants to compliance levels listed in Table 9.
Alternative 3: Natural Attenuation, Maintenance and Site Access Restrictions
Under this alternative, contamination reduction in groundwater would occur
through natural processes as described for Alternative 1 and, in addition, access to
the site would be restricted. Components of this alternative are the following:
. Deed restrictions on future development placed in the deed if the USAF
relinquishes the site and
. Restricted access through construction of a fence around the site.
The estimated total present worth of this alternative is S95,000. The estimated time
to complete would be determined by attenuation. of contaminants to compliance
levels listed in Table 9.
Alternative 4: Natural Attenuation, Maintenance, Site Access Restrictions and
Groundwater and Surface Water Monitoring .
A natural reduction of contaminants would occur in groundwater and
restrictions would be implemented as desaib~'under Alternative 3, above. In
addition to these access. restrictions, site mamtenance and a.' sumice water and
groundwater monitoring program would be implemented as .outlined in Alternative
2. The estimated capital cost and the present worth of O&M costs are S53,300 and
$684,000, respectively. The estimated total present worth for this alternative is
$737,000. The estimated time to complete would be determined by the attenuation
of contaminaJ1ts to compliance levels listed in Table 9.
A'n61\911OJ29
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Alternative sA: Multilayer Capping
In this alternative, a multilayer cap would be built over the landfill. The
components would be as follows:
. A three-layer cap, conforming to Resource Conservation and Recovery Act
(RCRA) performance standards in 40 CFR 264.310, would be constructed.
The cap would consist of a low permeability layer, a drainage layer, and an
upper vegetat!ve layer.
. The low permeability layer would be composed of a soil liner and a synthetic
liner placed directly over the landfill and extending beyond the boundary of
the landfill. The layer would be 2-ft thick and engineered to provide a
hydraulic conductivity of 10-7 cm/s or less.
. The drainage layer would be composed of coarse sand and be placed directly
over the low permeability layer. The thickness of the layer would be
dependent on the amount of settling expected and the volume of water
expected to infiltrate to the drainage layer (expected to be approximately I-ft
thick).
. The vegetative layer would be placed over a fabric filter above the drainage
layer. The vegetative layer would be approximately 6-ft thick; to
accommodate the maximum frost effect possible.
The estimated total present worth for this alternative is 51,331,000. The estimated
time to complete is 2 years.
Altemative 58: Capping (Asphalt Layer)
In th1s alternative, a single layer asphalt cap would be placed over the landfill.
The thickness of this cap would depend on the amount of anticipated settlement and
the local weather conditions. The cap would require inspection on a frequent basis.
The estimated total present worth for this alternative is $442,000. The estimated
time to complete would be 1 year.
Alternative 6A: Capping (Multilayered) and Groundwater and Surface Water
Monitoring
This alternative would involve capping as described in J.Uternative SA, with the
addition of groundwater and surface water monitoring. Two monitoring wells
(MWI and MW2) would be abandoned to ~CQD,UUodate the placement of the cap.
One new well will be installed dOWngradient to replace abandoned wells. In.
addition, the existing upgradient well (MW3) would be replaced to provide
necessary background groundwater quality data. Groundwater and surface water
monitoring would be conducted as in Alternative 2 except 11 monitoring wells
would be sampled. The estimated capital cost and the present worth of O&M costs
are $1,134,300 and $631,700, respectively The estimated total present worth for this
alternative is $1,766,000. The estimated time to complete construction is 2 years.
AT661\'1W2t
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~I
Alternative 68: Capping (Asphalt Layer) and Groundwater and Surface Water
Monitoring
This alternative would involve capping as described in Alternative 5B with
addition of groundwater and surface water monitoring. Eleven existing monitoring
wells and a replacement for MW3 would be sampled. Sampling would be conducted
as described in Alternative 2. The estimated capital cost and the present worth of
O&M costs are $370, 500 and $507,300, respectively. The estimated total present
worth for this alternative is $878,000. The estimated time to complete construction
is 1 year.
Alternative 7 A: In Situ Stabilization
This alternative would stabilize landfill materials inplace to immobilize
inorganic contaminants in a cementlike mass within the landfill. The components of
this alternative are as follows:
. Injection of polymerizing reagents and water into landfill soils, sludges, and
debris through use of an augering device consisting of cutting and mixing
blades. For large debris a backhoe would be used for mixing.
. Placement of a single layer asphalt cap (or other impermeable mateqal) over
the stabilized material. The thickness and dimensions of the cap would:be
determined after in-place stabilization because stabilization is expected to
increase the size and volume of the landfill.
The estimated total present worth of this alternative is $ 1,958,000. The estimated
time to complete is 1 year. .
Alternative 7B: In Situ Stabilization and Groundwater and Surface Water.
Monitoring
This alternative would involve in situ stabilization as described in Alternative
7 A with the addition of groundwater and surface water monitoring. Two monitoring
wells (MW1 and MW2) would be abandoned, and a new well would be installed, as
described in Alternative 6A. The upgradient monitoring well (MW3) would be
replaced. Monitoring wells and the surface water retention pond would be sampled.
as described in Alternative 2 except 11 wells would be sampled. The estimated
capital cost and the present worth of O&M costs are $1;958,500 and $435,600,
respectively. The estimated total present worth for this alternative is $2,394,000.
'The estimated time to complete stabilization is l'year.
Alternative 8: Excavation and Oft-Site Disposal
This alternative would involve excavation and off-site disposal of the contents of
. the landfill. The components of this alternative are as follows:
. Construct temporary erosion control measures to isolate the landfill area
from the pond and river.
An61\,nam
31
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. Excavate, segregate, and characterize landfill materials. Excavation. would
be accomplished by backhoe or similar equipment.
. Treat materials characterized as hazardous as required for disposal under
RCRA land disposal restrictions. Other excavated material will be directly
disposed of off-site in a commercial RCRA landfill.
. Backfill the excavated landfill, grade the area to meet surrounding slopes,
and revegetate the site.
. Abandon existing monitoring wells in accordance with regulatory
requirements. .
The estimated total present worth for this alternative is $10,492,000. The estimated
time to complete is 2 to 3 years.
SUMMARY OF COMPARATIVE ANALYSIS OF
ALTERNATIVES
The following nine evaluation criteria were used to evaluate alternatives in the
FS and select the preferred alternative for the SARL
-. Overall Protectiveness: A measure of how well an alternative protects
human health and the environment by eliminating, reducing, or controlling
exposures and unacceptable risks posed by hazardous substances.
. Compliance with ARARs: This criterion assesses whether an alternative
attains federal and state environmental and public health regulations. This
criterion also considers advisories or other guidelines that may pertain to
site-specific cases.
. Long-Term Effectiveness and Permanence: A measure .of the performance,
reliability, and management of an alternative long after the alternative is
constructed and in place and an assessment of achieving permanence through
treatment.
9.0
. Reduction of Toxicity, Mobility, or Volume: The degree to which an
alternative uses treatment technologies that reduce the toxicity, mobility, or
volume of the hazardous substances that pose the principal threats of the
site. .
. . Short-Term Effectiveness: Assesses the. .impacis to the local community,
environment, and workers during the consirUction and implementation of the
alternative. -
. Implementability: Addresses the technical and admini~trative feasibility of
an alternative. This criterion considers the availability, operation, and the
degree of difficulty of the technology and use of equipment.
AT661\91111J29 .
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. Cost: Assesses the capital, operation, and maintenance costs associated with
an alternative.
. State Acceptance: Relates the state's position and key concerns regarding
the preferred alternative and the application or waiver of state ARARs.
. Community Acceptance: Assesses the community's preference, concerns, or
support of the proposed alternative. This assessment cannot be completed
until after the community has commented on this proposed plan.
All alternatives in the FS were initially screened before detailed evaluation
against the nine criteria. Alternatives not including monitoring were eHminated in
screening since CERCLA requires that hazardous materials cannot be left in place
without monitoring. The alternatives eHminated at initial screening were
Alternatives 3, SA, SB, and 7A The remaining alternatives were then evaluated in
detail. An analysis of EP A criteria for the preferred alternative compared with the.
other alternatives that passed screening is provided below. A summary of the
criteria assessment for all alternatives passing initial screening is given in Table 8.
Overall Protectiveness
Alternative 1, No Action, may not provide adequate protection to human health
and the environment from groundwater usage in the future although current risks
are low and further reduction is expected due to attenuation. Additionally,
protection from future contact with landfill materials is limited. Alternative 2
provides for an assessment of future groundwater contaminant generation and
migration but does not address future exposure to site soils and surface water.
These alternatives can be ruled out from further consideration since they do not
provide measures for protection of human health and the environment into the
future. All the remaining alternatives are protective of human health and the
environment, although through different combinations of treatment, containment,
and institutional controls.
Compliance with ARARs
The site presently shows minimal health risks, and over a period of time through
natural attenuation, compliance with ARARs is expected for Alternatives 1, 2, and
4. Alternatives 6A, 6B, 7B, and 8 are likely to comply with ARARs after
implementation. Capping will reduce infiltration into the landfill thereby
JT1inimi7.ing leachate production and subsequent migration to groundwater.
Alternatives 7B and 8 will effectively immobilize or remove the contaminant source.
For Alternatives 6A, 6B, 7B, and 8, residual existing groundwater contamination will
migrate to the Minnesota River and attenuate with eventual compliance with
ARARs after implementation.
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------.-.
~---- .-.---.
Table 8. Alternative Criteria Assessment and Comparison
Small Arms Range Landfill
.usossmeat Fa
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Lona-Term ElrectiftDea ud Pel'lll8DeDce
Alternative 8 provides the greatest degree of long-term effectiveness and
permanence since it virtually removes all contamination sources present at the site.
The primary residual risk pmAtmnl would be residual groundwater contaminAtion
already present before excavation. This public health risk is low as found in the RI
baseline risk ~S5n'fl!ftt- Alternative 7B offers a high degree of long-term
effectiveness and permAnence by "immobilizing contaminAnts. The long-term
effectiveness of alternative 7B is dependant on the ability to mix stabilizer and
laDdfill material uniformly on-site. Alternatives 6A and 6B would offer a moderate
degree of long-term effectiveness by reducing infiltration and thereby reducing the
contact of water and contAminAnft However, infiltration of groundwater during
periods of high groundwater levels and flood could brina C01'ItaminAnt~ into contact
with groundwater with subsequent leaching out of contAminAnts as groUJ1dwater
levels or flood waters recede. Flooding could also cause erosion of the cap
materials; therefore, adequate maintenance would be required to ensure moderate
degrees of long term effectiveness. The effectiveness of Alternative 4 is dependent
on how effectively access restrictions can be enforced. Since the site is already
semirestricted and it is located in the floodplain, deed restriCtions and limiting site
access could provide a high degree of protection against future exposures to site
contAminAnts.
Reduction otToxidty, Mobility, ud Volume 1brough Treatment
Alternative 18 would reduce toxicity and mobility by treating (fixing) the
contRminRnts in cement; however, the total volume would increase. Alternatives 6A
and 6B would reduce the mobility of landfill CODtRminAnts by reducing leachate
generation, but would not employ treatm~t nor reduce toxicity or volume.
Alternatives 1, 2, and 4 would not use treatment to reduce the toxicity, mobility, and
volume (TMV) of the contAminants.
Short-Term Effectivenesl
Alternative 4 is probably the most effective in the short-term in that it can meet
the response objectives in 1 year considering natural attenuation effects with
minima1 adverse impacts resulting from implementation. Alternatives 6A, 6B, 18,
and 8 present greater short-term'risks since they involve varying amounts of landfill
cover disturbance, angering, excavation, and materials ft:tnd1ing These alternatives
present a risk of release of volatile organics and subsequent worker exposure.
These risks would be new risks not currently present at the site. Precautionary
measures may be needed to protect workers when handling laDdfill materials.
Implementabllity
All alternatives can be implemented. Alternatives 1, 2, and 4 would be the
easiest to implement since they require little or no site work (fence construction,
monitoring, and restrictions on property deeds at most). Capping alternatives may
AT661\91W2t
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require special flood design and surface water controls. Such controls could include
a flood wall to isolate the site from the l00-year flood level or placement of rip rap
on the periphery of the landfill to stabilize the slopes during the flood recession. A
flood wall can be constructed between the river and the landfill area since there is
evidence of approrimately 20 ft. of semi-permeable to impermeable materials
beneath the site and in the area between the site and the river to which the wall can
be tied. However, a rip rap stabilization approach would be much less costly and
could be effective. In situ ~~n (Alternative 7) may be diftic:ult dependiDs
on whether large objects are encountered in the landfill.
Cost
Alternative 8 is the most costly alternative at approximately SI0.sM followed by
Alternative 7B at S2.4M, Alternative 6A at SI.8M, Alternative 6B at SO.9M,
Alternative 4 at SO.1M, Alternative 2 at SO.1M, and Alternative 1 at no cost.
Although Alternatives 6A, 6B, 7B, and 8 provide containment, treatment, or off-site
disposal of landfill material, they do not l1t<:essarily represent a significant increase
in protectiveness. The risk ~5sment conducted during the RI indicated that the
site poses minimal current or future risk because of low contaminant levels and
incomplete or unlikely exposure. pathway completion.
State .uceptance
The MPCA has indicated that Alternative 4 is an acceptable remedial action for
the site.
Community Acceptance
A public meeting was held on September S, 1991 with one citizen attending. In
general, there was little public response to news releases and other information
made available to the public.
10.0 DESCRIPTION OF 111£ SELECl'ED REMEDY
The selected remedy at this site will consist of natural attenuation of
groundwater contamination, access restrictions, site maintenance and monitoring.
Natural attenuation of the low levels of groundwater contmninants would reduce
risk to public health from traDSpOrt of contaminSints to receiving surface water
bodies. Attenuation of contaminants would occur due to adsorption,
biodegradation, physical/chemical degradation and dispersion due to site
environmental characteristics. ~ restrictions and site maintenance will achieve
the objective of protecting public health and the environment from contact with
landfill contaminants. Site monitoring will assess the quality of groundwater and
surface water immediately downgradient of the landfill area and evaluate the
effectiveness of natural attenuation to further reduce the levels of contaminants
below health.based criteria and below levels that could impact ambient water
quality criteria.
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. .
The carcinogenic: risk level to attain will be within EP A's target range for
"ac:c:eptable" excess carcinogenic: risk; 1()-4 to 1()-6. The rationale for setting this goal
is to ensure that risks from future/bypothetic:al ingestion of CODtAminAn~ and
inhalation of a volatile compound are at a minimum
Acc:ess restrictions will include a physic:al barrier (fence) constructed around the
landfill to restrict public: access to the landfill surface. The barrier will also serve to
limit access by larger smimsd!: (e.g., deer) over the landfill area. Other restrictions to
be imposed will be institutional, such as deed restrictions limiting future
development of this site, if the property is reliDquisbed by the USAF, and deed
restrictions limiting future groundwater usage. These deed restrictions will be
imposed in the eventuality that USAF releases the property once a deed is
prepared. Additionally, all requirements of Section 120 of CERCLA for
notification and deed notation will be met. These requirements are imposed on
federal facilities relinquishing property on which hazardous substances were stored
for more than 1 year or wbere they were disposed of or released. Included in the
requirements is provision of a description of hazardous substances stored, disposed
of, or released, the general time frame of the activity, and the type and quantity of
materials. Any remedial action taken on the site is also to be described. The Air
Force must also warrant in the deed notatiOn that remedial action ne~ssuy to
protect public: health and the environment has been taken and any additional
remedial action found to be Dt~ssary in the future will be conducted by the federal
government
Site maintenance will be conducted to ensure the integrity of the existing soil
cover, the fence, and the monitoring system. A regularly scheduled maintenance
program will be implemented to inspect the pbysic:al property and ensure all of
these three systems are maintained in good repair. The maintf!nAnroe program will
be developed in a site operations and maintenance plan prepared as part of the
remedial design.
Site monitoring. will be conducted by periodic: sampling of the existing
groundwater monitoring well system and sampling of surface water in the
stormwater retention pond. The upgradient well, MW3, will be abandoned, in
ac:c:ordanc:e with Minnesota Department of Health procedures, and replac:ed by a
new well at the upgradient location. The new well will be constructed with a shoner
interval screen so that the root mass problem inherent with well MW3 will not
continue. At a minimnm sampling will be conducted every 2 months for 2 years to
gather additional data to suppon the assessment of the baseline condition. This
sampling period should cover a variety of meteorologic:al conditions. After the
initial sampling schedule, the analytic:al results will be reviewed to determine what
future sampling work may be required. The samples obtained from groundwater
and surface water locations will be analyzed for volatile organic: compounds, semi-
volatiles, and priority pollutant metals along with vanadium. Field measurements
will include water levels, pH, and conductivity. In accordance with the Federal
AT661\911Gm
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" .
Facility Agreement, the specific parameters to be analyzed will be proposed in the
Sampling and Analysis Plan and negotiated between the USAF and EP A following
the finalization of the Record of Decision. Site monitoring requirements and
procedures will be developed in a Sampling Plan and Quality Assurance Plan
developed during the remedial design. The effectiveness of the remedy will be
evaluated annually with the submittal of the annual monitoring report.
If groundwater contamination levels increase or do not show any sign of natural
attenuation to ARARs, the USAF in conjunction with U.S. EPA will review the
effectiveness of the preferred alternative and consider other remedial alternatives.
After the first year, changes in the frequency of monitoring for a given parameter
group may be proposed in the annual. monitoring report, based on the amount of
attenuation observed. .
Trigger levels will be used to evaluate the need for additional action. Trigger
levels in this case are established for confllminllnts of interest, ie., contaminants at
or above compliance levels. The trigger levels are set at two times the compliance
level for groundwater confllminants and are shown in Table 9.
Selection of the preferred alternative was based on meeting the requirements of
the National Contingency Plan for remedy selection. The two threshold criteria' of
overall protecUon of human health and the environment and compliance with
ARARs will be met by this alternative. Procedures will be in place to ensure
pathways involving contact with waste materials will not be completed. Monitoring
will be in place to evaluate the success of natural attenuation to achieve ARARs for
groundwater.
The five primary balancing criteria used in remedy selection ~er supponed
the preferred alternative over others that were considered. These criteria include
long term effectiveness and permanence; reduction of toxicity, mobility or volume
through treatment; shon term effectiveness; implementability and cost. The
effectiveness of this remedy in the shon and long term is adequate for the
protection of public health and the environment, primarily due to the'site location
and relatively low level of contamination detected. This alternative does not,
however, provide treatment to reduce toxicity, mobility and volume. The
importance of this criteria was diminished in remedy selection due to the low level
of detected contamination and limited migration seen at the site. Implementation
of this remedy would be relatively easy and require a shon time for all aspects
except monitoring. Access to the site is not a problem for constructing the fence
and follow-on monitoring and maintenance. Finally, the cost of this alternative is in
balance with the risks posed by the site.
11.0 STATUTORY REQUIREMENTS
The USAF and U.S. EPA have determined that this remedy satisfies the
statutory requirements of providing protection of human health and the
AT&61\9110129
38
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. . ~ . .
';,L"i...'
'. .: .'
, .. ~.
~
Table ,. Compliance ADd Trtaer Levels For CoutIhleDts
Detected In Gl'OlIDcJwater Samples
Small ArmI Ran. LucWl
Cadmium
CoIIIplllDcc TrIger
Leftl LeveI(1)
CJc/L) CJ4/L)
10 20
1.0 2
4.0 8
15 30
70 140
10 20
S 10
20 40
CoastItaeDt
Arsenic
Beryllium
Lead
NJdcel
Selenium
Tricbloroethene (TCE)
Vanadium
(1) Triger Lewd . 2. CompJiaDce Level
Note: If the IDOIIitoriIIg cIctccts (mOt""';..,,,," DOt prcvio1IsIy DOted; a trigcr IeYd for the c:ont"",m""t
will theD be detcrmiDCd at that lime.
AT661 \911QJ29
39
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"
. ..' ,
"
'.. 'of
environment, attaiDiDg ARARs, and being cost effective. Natural attenuation of the
low levels of groundwater contaminAnts would reduce risk to public health from
transport of contaminantt to surface water bodies. Therefore, preference for
treatment as a principal element in the remedy is not applicable. The remainder of
this section discusses how the statutoI)' requirements relate to this site.
Protection of Human Health and the Enwironment
The selec:ted re,medy of natural attenuation, site access and deed restrictions
and monitoring is protective of human health and the environment by preventing
completion of exposure pathways. The baseline risk ass-~ent indicated that air,
soil, groundwater, and surface pathways are currently not complete because of the
lack of release of voJatile organic compounds, Jack of surficial soil contamination,
the location of the site within a semi-restrlcted area, limited access to the storm
water pond, no significant surface water CODtaminJition, and no current users of
groundwater at the site or down-gradient of the site. The selected remedy will also
provide protection against future exposure through construction of a fence around
the site to limit access to the landfill and storm water pond, and deed restrictions
eliminating the possibility of future residents at the site.
Attabunent or CoDbllllln8nt-8pecU1.c ARARs
For water media, the.uSAF and USEPA considers drinking water Muimnm
ContaminAnt Levels, Federal Ambient Water Quality Criteria, and state
environmental standards to be contaminAnt-specific ARARs for ambient
concentration. The State of Minnesota considers State Recommended Allowable
limits (RAL) for drinking water contJlminJints as a State ARAR. The ARARs
considered for contJlminJition in the media at the SARL site are summarized in
Tables 1, 2, and 3. The remedy of the SARL site would eventually attain all
contAmin~nt specific ARARs through natural attenuation. Deed restrictions would
prevent use of the groundwater for drinking water and dilution of groundwater by
the Minnesota River would negate any effects on river quality.
Attainment of ~tiO..specUl.c ARARs
Location-specific ARARs are restrictions on remedial activities in especially
sensitive areas, such as wetlands, floodplains, or historic sites. The SARL site is
located within the 100 year flood plain of the Minnesota River. To the northeast
and east of the site is the Minnesota River and adjacent wet lands which serve as
part of the Minnesota Valley National Wildlife Refuge. The Minnesota River and
Fort Sne1ling State Historical Park extend from the south and southeast of the site
to the northeast.
An ecological assessment at the site and within one mile of the site indicate no
endangered species reside on the site. Protected flora are found in the Wildlife
Refuge and fauna in Fort Sne1ling State Park, but not within a mile of the site. The
selected remedy will cause no physical disturbance of protected habitats and limited
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on-site disturbance of existins conditions although protected habitats exist in the
area.
AttAinmeat ot Act1on-Spedtlc AltARs
Action-specific ARARs are enforceable state or federal requirements or
standards applicable to each remedial alternative. Federal statutes which apply are
as follows:
. Resource Conservation and Recovery Act - The provisions of these acts are
-applicable8 to remedial alternatives because they govern the remedial action
chosen, the disposal of Superfond wastes and future monitoring
requirements. RCRA requirements that are applicable to remedial
alternatives include mmim11m te("1m()logy standard, treatment standards,
monitoring requirements and prohibitions on l;Jndfi1ling of liquid and
specified solid hazardous wastes. If offsite treatment or disposal is chosen as
a remedial alternative. RCRA requirements for hazardous waste generators
and transporters as well as land disposal requirements and other
requirements for treatment. storage and disposal facilities must be met.
. Oem Water Act (CWA) - Remedial alternatives that require discharge to
waters oft'site must comply with provisions in the CWA Administrative
procedures for obtaining a permit for onsite discharge are DOt required. but
offsite discharge standards may be applicable.
. Oean Air Act (CAA) - This act may be applicable for those alternatives
where contaminants may be released to the air (such as strippiDg or
incineration). For onsite treatment alternatives administrative procedures
for obtaining a permit are not required. but offsite discharge Standards may
be applicable.
The above action specific ARARs are not applicable to this site because the
remedial action will not result in releases to air or water or produce RCRA wastes
for treatment or disposaL
To Be Considered CrIterIa
To be considered (TBC) criteria are those criteria, which although not required
by or based on federal statutes (as ARARs are). may be applicable to the site. No
TBCs were identified for the SARL
ARAR AttAinment
The seleded remedy is expected to meet ARARs through natural attenuation.
Groundwater monitoring would be performed in the remedy to track contaminant
concentrations against ARARs and trigger levels. If trigger levels are met or
exceeded the need for additional action will be evaluated.
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Cost Elrec:theDess
The USAFs and USEP A's selected remedy affords a high degree of overall
protectiveness by protecting the public against direct exposure to surfac:e soils,
surfac:e water and groundwater. The present worth estimated cost of USAFs and
USEP A's selected remedy is apprtWimSitely 5737,000 dollars. The selection remedy
affords overall ef£ectiveness proportioDal to these costs such that the remedy
represeJUS a reasonable value. When the relatfnn.cltip between cost and overall
effectiveness of the selected remedy is viewed in JiPt of the relationship between
cost and overall effectiveness afforded by the other altematives, the selected remedy
appears to be the most cost-effective.
Utill7--tioa olPena8IIeId Solutlou ad Altenlative Tr-tm-t Technologies or
Resoan:e ReccmIy TeduaoloPes to the MaxImum EDeat Pncdcable
The USAF and USEPA believes this remedy is the most appropriate cleanup
solution for the SARL site and provides the best balance among the evaluation
criteria for the remedial alternatives evaluated. This remedy provides effective
protection in both the short and long-term to potential human and enviroDJDfI!ntaJ
receptors, is readily implemented, is cost-ef£ective, and will reduce groundwater
contAminAnt concentrations through natural attenuation.
In-situ treatment. excavation and off-site disposal, and capping alternatives
would not significantly increase protection of human health and the environment
because the selected remedy will prevent exposure pathway completion as wen as
these alternatives. Excavation and in-situ treatment are more likely to cause
remedial action workers exposures aDd mayor may not result in attainment of
ARARs in a shorter time period than the selected remedy. The selected remedy
does not employ direct treatment or recovery technologies because the current risks
from the site are minimAl due to incomplete exposure pathways. Future risks are
minimi7cd by eliminAtion of hypothetical future residences at the site through deed
restrictions. The low risks currently present at the site coupled with implementation
of site access and deed restrictions, and groundwater monitoring, supports the use of
natural afU!mlAtion versus direct treatrl1ent of groundwater.
Prefereace for Treatmw IS . Prindpal Elemem
Natural attenuation of groundwater contAminAnts is a principle element of the
selected remedy. The 'baseline risk assessment for this site indicates the site
possesses minimAl risk to human health because exposure pathways are not
complete nor reasonably expected to be in the future. The selected remedy includes
site access and deed restrictions to prevent future exposure pathway completion.
The groundwater posses minimAl risk to the environment because of the dilution
capacity of the Minnesota River which will reduce contAminants to below ARARs if
the contaminAnts reach the river. For the reasons stated, use of natural attenuation
versus direct treatment is justified for the site.
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RESPONSIVENESS SUMMARY
The u.s. Air Force has gathered information on the types and extent of
contamination, evaluated remedial measures, and recommended remedial actions at
the Small Arms Range Landfill. A public meeting was held to explain the .intent of
the project, describe the results, and receive comments from the public. Public
participation in Superfund projects is required in the National Oil and Hazardous
Substances Contingency Plan. CommentS received from the public are considered
in the selection of the remedial action for the site.
This community relations responsiveness summary is divided into the fonowing
sections:
Backwound on Communi~ Involvement and Concerns - This section
provides a brief history of community interest and concerns raised during the
remedial planning activities at the SARL site.
Summ~ of Comments Received Durini the Public Comment Period
BACKGROUND ON COMMUNITY INVOLVEMENT
The Small Arms Range I.andfil1 was acquired by the U.S. Air Force in 1955 and
served as the main Base refuse from approximately 1963 to 1972. The site was
identified as a possible hazardous waste site in the Phase I IRP Records Search
report in 1983. In 1987 the site was placed on EPA's National Priorities List
because of a suspected release to groundwater. The Remedial Investigation and
Feasibility Study were conducted from 1988 to 1991. The proposed plan for the site
was completed in August 1991.
The U.S. Air Force issued press releases. following completion of the RI, FS,
and Proposed Plan. These releases summarized the content of the documents and
identified the repositories where the documents were available to the public for
review. A public meeting was announced for September 5. 1991, and 300 fact sheets
were sent to local newspapers, public interest groups, and lOcal politicians based on
a list compiled by the Minnesota Pollution Control Agency. The public meeting was
held on September 5. 1991 in Minneapolis-SL Paul.
Approximately 18 people attended the meeting with only one citizen attending.
The Air Force conducted the meeting and USEP A Region V and MPCA had
representatives in attendance.
SUMMARY OF COMMENTS RECEIVED
Only one written comment was received regarding the site. This comment was
received from the MPCA public affairs officer and was concerning the improvement
in the Air Force community relations efforts over the project life. No other
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comments were received. Thus, the selected remedy as presented in the proposed
plan bas not been modified for the ROD.
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REFERENCES
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REFERENCES
CH2M Hill, 1983. "Installation Restoration Program (IRP), Phase 1 - Records
Search for Twin Gties Air Force Reserve Base, Minnesota.. Prepared for Air
Force Engineering and Services Center, Tyndall Air Force Base, Florida.
Engineering-Science, Ine., 199Oa. "Fmal Remedial Investigation Report - Small
Arms Range I .sInrlfil1. Minneapolis-SL Paul lAP Air Force Reserve:
Engineering-Science, Ine., 199Ob. "Fmal Feasibility Study Report, Small Arms
Range I .sInrlfill, Minneapolis-SL Paul lAP Air Force Reserve:
Engineering-Science, Ine., 1991. "Final Proposed Plan, Small Arms Range Landfill,
Minneapolis-SL Paul lAP Air Force Reserve:
Weston, Roy F., Ine., 1986. "Installation Restoration Program Phase n -
Confirmation/Quantification, Stage 1: Minneapolis-SL Paul International
Airport, Hennepin County, Minnesota. Prepared for HQ AFRES/SGPB and
USAF OEHL.
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