u
United States
Environmental Protection
Ag~
Office of
Emergency and
Remedial Response
P894-964122
IIInlllllllllllllm mllll~1 mil 11111 111111111111111111
EPAlRODJR05-931242
June 1993
PB94-964122
(J
&EPA
Superfund
Record of Decision:
Oakhue Sanitary La.ndfill, MN
"~ ' ..' ,",-':;' :~,.;'"
Hazardous Wasf.C~/';r
information Resource ,oenter., " '.
US EPA Reg'Ion 3 .
Philadelphia, PA19107
EP A Report Collection
Information Resource Center
US EP A Region 3
Philadelphia, PA 19107
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50272-101
REPORT DOCUMENTATION 11. REPORT NO.
PAGE EPA/ROD/R05-93/242
2.
3. Reclplenfs Acc:8sslon No.
4.
TItle and Subthle
SUPERFUND RECORD OF DECISION
Dakhue Sanitary Landfill, MN
Second Remedial Action - Final
Author(a)
s.
Report Date
06/30/93
6.
7.
8.
Performing Organization Repl No.
9.
Parformlng Organization Nama and Add-
10 Project TalclWot1c Un" No.
,J
11. Contract(C) or Grant(G) No.
(C)
(G)
12. Sponsoring Organization Nama and Ad~
U.S. Environmental Protection
401 M Street, S.W.
Washington, D.C. 20460
13. Type of Report a Period Covar8d
Agency
800/800
14.
1 S. Supplementary Nat-
PB94-964122
16. Abstract (Umh: 200 words)
The 80-acre Dakhue Sanitary Landfill site is an inactive sanitary waste municipal
landfill located in Hampton Township, Dakota County, Minnesota. Land use in the area is
predominantly agricultural and residential. A gravel surficial aquifer, that is not a
drinking water source, extends downgradient of the site. Mos~ residents obtain their
drinking water supply from nearby wells and/or a municipal water supply well located
over-3 miles south of the site, both of which extract ground water from a deeper
aquifer. The surficial and deep aquifers .underlying the Dakhue site are thought to be
hydraulically connected. From 1971, Dakhue Sanitary Landfill, Inc. owned and operated
the landfill, and accepted mixed municipal and commercial waste and small amounts of
industrial waste. Site operations ceased in 1988, but the landfill never received a
final cover as part of the closure activities. State investigations conducted between
1983 and 1989 identified a variety of contaminants onsite in soil and ground water.
EPA investigations identified elevated levels of VOCs, other organics, and inorganics
in the surficial onsite aquifer, and it has been determined that the source of
contamination is related to the improper disposal of municipal, industrial, and
commercial waste in the landfill. The site has been divided into two OUs for
remediation. A 1991 ROD addressed the source of the contamination and provided for
(See Attached Page)
17. Document Analyals a. Descriptors
Record of Decision - Dakhue Sanitary Landfill, MN
Second Remedial Action - Final
Contaminated Medium: gw
Key Contaminants: VOCs (benzene, PCE, TCE, toluene), metals (lead)
b.
IdantifierslOpan-End8c:I T..ms
c.
COSA TI FleldlGroup
18. Avallabllhy Statemant
19. S8c:urIty Class (this Report)
None
20. S8c:urhy Class (This Page)
None
21. No. of Pages
44
22. Price
(See ANSI..z39.18)
S../nstructions on R.lfflfSB
OPTIONAL FORM 272 (4-77)
(Formerly NTIWS)
Department of Co-
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EPA/ROD/ROS-93/242
Dakhue Sanitary Landfill, MN
Second Remedial Action - Final
Abstract (Continued)
capping of the landfill with a final cover, as OU1. This ROD provides
the site and addresses onsite ground water contamination, as OU2. The
contaminants of concern affecting the ground water are VOCs, including
and toluene; and metals, including lead.
a final remedy for
primary
benzene, PCE, TCE,
The selected remedial action for this site includes allowing ground water to naturally
attenuate; providing for a contingent remedy to initiate a corrective action, if
monitoring results indicate that ground water downgradient of the site exceeds the surface
water standards set as ~trigger levels" for certain contaminants; monitoring ground water;
and implementing institutional controls, including ground water use restrictions. The
estimated present worth cost for this remedial action is $360,000.
PERFORMANCE STANDARDS OR GOALS:
Chemical-specific ground water cleanup goals are based on SDWA MCLs, and include benzene 5
ug/l; bis(2-ethylhexyl)phthalate 6 ug/l; 1,2-DCA 5 ug/l; 1,2-DCE 70 ug/l; 1,2-
dichloropropane 5 ug/l; methylene chloride 5 ug/l (proposed MCL); 1,1,2-TCA 5 ug/l; TCE 5
ug/l; and vinyl chloride 2 ug/l. Trigger levels for the ground water contingent remedy
are based on surface water exceeding the following levels, and include aluminum 87 ug/l;
chromium 11 ug/l; cyanide 5.2 ug/l; iron 221 ug/l; manganese 572 ug/l; silver 0.12 ug/l;
and zinc 191 ug/l.
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p
.
Hampton
Declaration
Record of Decision
Dakhue sanitary Landfill
Township, Dakota County, Minnesota
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial action for
the Dakhue sanitary Landfill in Cannon Falls, Minnesota, chosen
in accordance with the Comprehensive Environmental Response,
compensation, and Liability Act of 1980 (CERCLA), as amended by
the Superfund Amendments and Reauthorization Act of 1986 (SARA),
and to the extent practicable, the National Contingency Plan
(NCP). The decision is based on the Administrative Record for
the Dakhue Sanitary Landfill. The attached index identifies the
items which comprise the administrative record upon which the
selection of the remedial action is based.
The u.S. Environmental Protection Agency has been consulted and
concurs with the selected remedial action.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from this
site, if not addressed by implementing the remedial action
selected in this Record of Decision, may present an imminent and
substantial endangerment to public health, welfare, or the
environment.
DESCRIPTION OF SELECTED REMEDY
This operable unit is the second for the site. The first
operable unit involved capping the landfill to mitigate leachate
formation. This operable unit includes the following major
components:
Institutional Controls contained in Dakota County Ordinance
No. 114 and Minnesota Rules 4725.2000 and 4725.4300 which
restrict well development: and
Long term groundwater monitoring program to: (1) determine
the migration of contamination: (2) assess trends in water
quality in the Sand and Gravel aquifer: (3) verify that the
deep aquifer is not affected: and (4) monitor contaminant
levels in Judicial Ditch no. 1.
STATUTORY DETERMINATIONS
Consistent with CERCLA and, to the extent practicable, the NCP,
40 C.F.R. Part 300, the selected remedial action 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. The
remedy utilizes permanent solutions and alternative treatment
-------
"
"
-2-
technologies to the maximum extent practicable. This remedy does
not satisfy the statutory preference for treatment as a principle
element of the remedy. Natural attenuation of groundwater
contaminants will take only slightly longer than an active
treatment system and will cost less. Because this remedy will
reSU1~i hazardous substances remaining on-site above health
based 1 vels, the ve year review provisions of CERCLA will
apply 0 thitct' n.
. ~
~ . . JkltL30, Iff~ .
/
Valdas V. d s Date
Regio . istrator
June 29, 1993
Date
Control
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u
'J
I.
II.
III.
IV.
V.
VI.
VII.
Record of Decision
Dakhue sanitary Landfill
Hampton Township, Dakota County, Minnesota
**********
TABLE OF CONTENTS
SITE NAME,
LOCATION AND DESCRIPTION..................... 1
SITE
HISTORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2
COMMUNITY
RELATION HISTORY.............................. 3
SCOPE AND ROLE OF REMEDIAL ACTIVITIES................... 3
SUMMARY OF SITE CHARACTERISTICS......................... 4
DESCRIPTION OF
ALTERNATIVES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
SUMMARY OF THE COMPARATIVE ANALYSIS OF ALTERNATIVES..... 11
THE REMEDY............................... 15
VIII. DESCRIPTION OF
STATUTORY DETERMINATION SUMMARY......................... 16
IX.
x.
DOCUMENTATION OF SIGNIFICANT CHANGES.................... 20
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"
.
SUMMARY OF REMEDIAL ALTERNATIVE SELECTION
Dakhue sanitary Landfill
Hampton_Township, Dakota County, Minnesota
I.
SITE NAME, LOCATION, AND DESCRIPTION
Location
The Dakhue sanitary Landfill (DSLF) is located in Hampton
Township, Dakota County, Mirinesota (Figure 1), off Hogan
Avenue as shown in Figure 2. The Dakhue Sanitary Landfill
is approximately 30 miles south of st. Paul, the state
capital.
site DescriDtion
The DSLF is located in southeastern Dakota County, within
the Rochester Till Plain Physiography region of Minnesota.
The area of the landfill is associated with ~ topographic
ridge trending northwest-southeast across the site. At the
southern edge of the landfill the topographic ridge ends
abruptly forming a series of gullies which drain into a dry
creek bed. Farther to the east and south of the landfill
the terrain is relatively flat, composed of open and
cultivated fields. .
The adjacent land is used primarily for agriculture with
some residential plots intermixed.
The Dakhue sanitary Landfill is developed over a sand and
gravel water table aquifer which is present throughout the
site and extends downgradient of the site. Only the bottom
20 to 30 feet of the glacial drift is saturated.
Based on well logs from residential and irrigation wells in
the area, and on resistivity values from the 1985
hydrogeologic investigation, Bruce A. Liesch Associates
(Liesch) (1985) concluded that there appears to be no
hydraulic barrier between the drift aquifer and the
underlying prairie du Chien aquifer. This lack of hydraulic
barrier is substantiated by the similar variations of
groundwater elevations in wells MW-2 and BAL-1, both
screened in the sand and gravel aquifer, and Well MW-l, open
hole in the prairie du Chien aquifer (Figure 3). Figure 3
was drawn using groundwater elevations published in the
Evaluation Report (1987).
Based on groundwater elevations measured in Wells .MW-1, MW-2
and BAL-l Liesch (1987) concluded that groundwater flows in
a southeasterly to southwesterly direction with a hydraulic
gradient of 0.008 feet/foot.
1
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D
~
II.
SITE HISTORY
The DSLF is owned and was operated by Dakhue Sanitary
Landfill, Inc., a Minnesota corporation. The DSLF is
located in southern Dakota County approximately 3 miles
north of Cannon Falls, Minnesota. The location of the
landfill is shown on Figures 1 and 2. Dakhue Sanitary
Landfill, Inc. purchased the property in 1971 for the
purpose of developing a sanitary landfill.
Prior to 1971, the land within the site boundary was
primarily undeveloped. On October 1, 1971, the Minnesota
Pollution Control Agency (MPCA) issued a Solid Waste
Disposal Facility Permit SW-50 (permit number) for an 80
acre operation at the Dakhue site to Dakhue sanitary
Landfill, Inc. As part of this permit requirement, Dakhue
Sanitary Landfill, Inc. installed two on-site monitoring
wells in October 1971. Monitoring Well MW-1 was installed
upgradient, and Monitoring Well MW-2 was installed
downgradient of the refuse area.
The landfill was initially open on a part-time basis (three
days a week) until 1973, when the landfill extended its
operation to six days a week. DSLF received an updated or
amended permit from the MPCA on July 25, 1983.
DSLF operated until May 31, 1988, at which time waste
disposal activities ceased. From October 1971 to May
the landfill was utilized for the disposal of mixed
municipal and commercial waste, and small amounts of
industrial waste.
1988,
In a letter dated July 22, 1988, representatives of the
landfill owners stated that Dakhue sanitary Landfill, Inc.
was financially unable to undertake closure and post closure
activities necessary at the landfill. On October 11, 1988,
Dakhue Sanitary Landfill, Inc. filed for Chapter 11
bankruptcy.
The facility was originally scored using the Hazardous
Ranking System (HRS) on September 29, 1985. On June 23,
1987, the permittee, signed a Response Order by Consent with
the MPCA. The HRS scoring package was amended on May 23,
1988, and in March 1989. The facility is currently on the
State's Permanent List of Priorities and is on the u.S.
Environmental Protection Agency's (U.S. EPA) National
Priority List with a score of 42.
Additional information can be found in the Evaluation Report
(Liesch, 1987).
2
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~
~
A final cover consisting of a gas drainage layer, synthetic
membranes, water drainage layer, and topsoil was installed
during the 1992 construction season as part of the Source
Control Operable unit. The Remedial Investigation (RI)
Report for the Groundwater Migration Operable Unit was
completed in August 1992 and the Feasibility Study (FS)
Report was completed in December 1992. Both contain
additional information pertinent to this Record of Decision.
III. COMMUNITY RELATIONS HISTORY
Following completion of the RIfFS the State of Minnesota
published a Proposed Plan for remedial action on January 28,
1993. The RIfFS Report and Proposed Plan for remedial
action are located at the Cannon Falls Public Library and at
MPCA, and in the Administrative Record located at the u.s.
EPA in Region 5. consistent with Section 113 of CERCLA, the
Administrative Record includes all documents such as the
work plan, data analyses, public comments, transcripts, and
other relevant information used in developing remedial
alternatives for the site. These documents were made
available for public review and copying at the Cannon Falls
Public Library and MPCA.
To encourage public participation in the remedy selection
process consistent with section 117 of CERCLA, the U.s. EPA
initially set a 30 day public comment period from January
28, 1993 through March 1, 1993, for the Proposed Plan. A
formal public hearing was held on February 11, 1993, to
accept verbal public comment on the Proposed Plan.
Interested parties provided comments on the alternatives
presented in the Proposed Plan and elaborated upon in the
FS. The remedy for the DSLF site described herein was
selected after a detailed review of public comments
received. The attached Responsiveness summary addresses
those public comments received.
IV.
SCOPE AND ROLE OF REMEDIAL ACTIVITIES
The U.S. EPA and MPCA agreed to divide the project into two
operable units in order to facilitate progress toward
remedial action at this site. The two operable units are
for source control and groundwater migration management.
Source Control ODerable Unit
The DSLF never received final cover when the landfill
closed. In October 1992, the installation of a final cover
for the site was completed to prevent further infiltration
of precipitation and subsequent leachate generation.
Operable Unit One's Record of Decision was signed June 28,
1991.
3
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"
Groundwater Miaration Manaaement ODerable Unit
The FS identified two remedial objectives for the DSLF site
based on the data obtained by the Remedial Investigation and
the potential exposure ratio identified in the health and
ecological risk assessments. The objectives of the
Groundwater Migration Management FS are:
1.
To eliminate or mitigate risks associated with human
water supply use of groundwater from the sand and
gravel or bedrock aquifer resulting in exposure to
contaminants which exceed MCLs, have a total excess
lifetime cancer risk greater than the range of
protectiveness designated by U.s. EPA (10-6_10-4), or
have a hazard index which exceeds one; and
To provide adequate protection to aquatic life in
Judicial ditch No.1 from adverse effects resulting
from possible discharge of contaminated groundwater.
Ten actions were identified by the FS to satisfy the
remedial action objectives. These potential actions were
combined to formulate an array of remedial alternatives.
These alternatives were screened and compared to each other
and the remedial objectives to determine their ability to
achieve the objectives.
2.
Further evaluation of the FS array of remedial alternatives
resulted in eight remedial alternatives that would satisfy
the objective of the FS, meet health based cleanup levels
and meet the statutory requirements of CERCLA. Table 1
lists the eight remedial alternatives that would satisfy the
objectives of the FS.
The remedial action selected in this Record of Decision for
the DSLF site will eliminate the threats associated with
direct contact with contaminated media. It is anticipated
that no further action will be necessary at the Site. The
monitoring of groundwater will be conducted to assure that
degradation of residual groundwater contamination is
occurring. since hazardous substances above health based
levels will remain in fill material at the Site, five year
reviews will be necessary.
v.
SUMMARY OF SITE CHARACTERISTICS
A).
Site Characteristics
There is no discrete source of contamination other than
mixed municipal waste at the DSLF. Most of the waste
disposed of at the landfill was household trash and garbage.
A small quantity of industrial, commercial waste was
4
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~
TABLE 1
Alternatives Summary
Groundwater Migration Control Operable Unit
Dakhue Sanitary Landfill Site
Alternative 1: No Action
Alternative 2: Monitoring, Water Supply Cost Participation
Alternative 3A:
Monitoring, Extraction Wells to Contain Future
contaminant Migration from the Landfill, Air
Stripping, Iron and Manganese Removal, Discharge
to Stormwater Retention Basin
Alternative 3B: Monitoring, Extraction Wells to Remediate Entire
Plume, Air Stripping, Discharge to Stormwater
Retention Basin
Alternative 4A:
Monitoring, Extraction Wells to Contain Future
contaminant Migration from the Landfill, Carbon
Adsorption, Iron and Manganese Removal, Discharge
to Stormwater Retention Basin
Alternative 4B: Monitoring, Extraction Wells to Remediate Entire
Plume, Carbon Adsorption, Discharge to Stormwater
Retention Basin
Alternative SA:
Monitoring, Extraction Wells to Contain Future
contaminant Migration from the Landfill,
Photolysis/Chemical Oxidation, Iron and Manganese
Removal, Discharge to stormwater Retention Basin
Alternative SB: Monitoring, Extraction Wells to Remediate Entire
Plume, Photolysis/Chemical oxidation, Discharge
to Stormwater Retention Basin
4A
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disposed of at this site.
Twenty-two VOCs were detected in groundwater samples
collected during the RI investigation. The RI discovered
1,2 Dichloropropane, 1,2 dichloroethylene,
trichloroethylene, tetrachloroethylene, vinyl chloride and
benzene on-site. These levels exceeded groundwater quality
standards discussed below and more fully in the Feasibility
study Report (FS). In addition, groundwater quality
standards for vinyl chloride, tetrachloroethylene and
trichloroethylene were exceeded off-site. Table 2
summarizes the highest detected concentrations water quality
data for the DSLF. Figure 4 depicts the present and
potential future extent of impacted ground~ater in the sand
and gravel aquifer. No VOCs were found in groundwater
samples from the prairie du Chien aquifer.
Groundwater quality standards which were considered during
the FS included u.s. EPA Maximum Contaminant Levels (MCLs)
and Maximum Contaminant Level Goals (MCLGs) provided for
under the Safe Drinking Water Act. Proposed MCLs and MCLGs,
u.s. EPA Office of Drinking Water Health Advisories, and
Minnesota Recommended Allowable Limits also were considered
as potential groundwater quality standards. .
The human health risk assessment (HHRA) for the Groundwater
Migration Management O.U. characterized the potential human
health risks posed by the site if no additional remedial
actions occurred. There are no known current exposures of
people to chemicals associated with the site. The major
risks for the site are associated with the future
installation of residential water supply wells into areas of
contaminated groundwater. The primary human health risk is
cancer. The primary chemicals of concern are chlorinated
ethenes and ethanes, especially vinyl chloride.
Potential exposure pathways were identified and evaluated
(Table 3). The following potential future exposure pathways
were identified by the HHRA: .
.
Exposure of people if a residential (potable water)
well is installed in a contaminated portion of the Sand
and Gravel aquifer;
exposure of people if a residential well is installed
in the bedrock aquifer and the pumping of the well
draws in contaminated groundwater from the Sand and
Gravel aquifer;
.
exposure of people, directly or indirectly, if an
agricultural water supply is installed in the bedrock
aquifer and the pumping of the well draws in
5
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.0
TABLE 2
SUMMARY 0: HIGHEST ~ETEC~D C~NCENTRATIONS
WATER QUALITY DATA
DAKRUE SANITARY LANDFILL
(Concen~ra~ions in ~g/L)
Potassium
3ighes~ Moni~oring Well
Detec~ed wi~h Highes~
Concen~ra~ion Concen~ra1:ion
215 MW-8B
12.5 MW-10A( 1)
182 MW-3A(1)
0.56 MW-12A( 1)
2.1 MW-10A(2)
219.000 MW-5A( 1)
15.3 MW-9A(1)
8.6 MW-5A( 1)
9.2 MW-10A( 1)
17,200 MW-5A( 1)
7.5 MW-8A( 1)
70,900 MW-SA( 1)
2,590 MW-10A( 1)
46 MW-5A( 1)
16,000 MW-llA( 1 )
2.2 MW-llA( 1)
9.2 MW-10A( 1)
62,500 MW-9A( 1)
829 MW-10B
28.8 MW-llA( 1 )
Compound
INORGANICS
Aluminum
Arsenic
Barium
Beryllium
Cadmi W'I1
c:alciu::1
Chromium
Cobal1:
copper
Iron
Lead
Magnesium
Manqanese
Nickel
Selenium
Silver
Sodium
Zinc
Cyanide
VOLATnE ORGANICS
Cbloromethane
1.1-Dicbloroethylene
1 MW-SA( 1)
35 KW-SA( 1)
8 MW-5A( 1 )
9 MW-5A( 1)
13 MW-8A( 1)
2 MW-SA( 1)
vinyl Cbloride
Cbloroethane
Methylene Chloride
. .
Trichlorofluoromethane
23\19\182\DAXKOERI.RPT\XMB
SA
-------
TABLE 2 (CONT)
SUMMARY OF HIGHEST DETEC~D CONCENTRATIONS
WATER QUALITY DATA
DAXRUE SANITARY ~DFII.L
.'
(Concen~ra~ions in ~q/L)
1,1-Dichloroe~hane
1,2-Dichloroethylene
Hic;hes~ Monitoring Well
Detec~ed with Hic;hes~
Concentration Concentra~ion
39 MW-SA(l)
86 MW-SA( 1)
1 MW-SA(l)
6 MW-9A( 1 )
190 MW-SA( i )
19 MW-SA(l)
8 MW-SA( 1 )
62 MW-SA( 1)
10 MW-9A(1)
9 MW-SA( 1)
8 MW-SA(l)
110 MW-SA( 1)
33 MW-10A( 1)
2 MW-9A(1)
14 MW-SA( 1 )
49 MW-9A( 1 )
Compound
Chloroform
1,2-Dichloroethane
Methyl E~hyl Ketone
1.1,1-Trichloroe~hane
1,2-Dichloropropane
Trichloroethylene
1,1,2-Trichloroethane
Benzene
Methyl Isobutyl Ketone
Tetrachloroethylene
Toluene
Chlorobenzene
Xylenes
Tetrahydrofuran
SEM:IVOLAT:ILES
Phenol
Diethyl phthalate
Di-n-butyl phthalate
Bis(2-ethylhexyl)phthalate
,
3 MW..SA( 1) .
r
12 MW-9A(,1)
28 MW-'S~'( l)
4 MW-SA(l)
2 MW-8B
8' . MW-4A(1)
p-Cresol
Benzoic Acid
TENTATIVELY IDENTIFIED COMPOUNDS
Dichlorofluoromethane
75
MW-5A(1)
23\19\182\D~.RPT\KHB
SB
-------
.
:
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..
, '
.... .--.'
"J
7S' "....:" -...
."
"'-","-
_u./
; ."-.
, '.7J
~~--_.._._--
~ '.35
o
Q
2000
11000
~CONZEMIJS -- . "
----':0----- --
.
.
Scale in Feet
/
()
Residential Well Owner and MGS Unique
Well Number if available
I rrigation Well Owner and MGS Unique
Well Number
PRESENT AND POTENTIAL
FUTURE EXTENT OF
IMPACTED GROUNDWATER
IN THE SAND AND
GRAVEL AQUIFER
Dakhue SanitaTy Landfill
~
. FIGURE 4
<$
Present Extent of Impacted Groundwater
in the Sand and Gravel Aquifer
////
~////~
/--:,=/,
Potential Future Extent of Impacted
Groundwater in the Sand Aquifer
5C
-------
TABLE 3
EVALUATION OF POTENTIAL EXPOSURE PATHWAYS
GROUNDWATER OPERABLE UNIT
DARHUE SANITARY LANDFILL
U1
t::I
Migration Pathway Exposure Point Exposure Route Exposed population likelihood of Exposure
Migration In aand and gravel DOWIgradlent relldentlal Ingestion Residential well users No currently exposed population.
aquifer well. Icreened In .and and Dermal absorption Existing wells would not be
lrevel .qulfer Inhalet Ion 1"Plcted by contamination In the
future. Exposure could only
occur if new wells are installed
In the contaminant plume. land
use practices and MDN
prohibition on sand and 9r~vel
wells limit likelihood of
exposure.
Mllratlon frC8 Iind .nd DCM1IIradlent r..ldentlal Ingestion Residential well users No currently exposed population.
Ireve' equUer to bedrock ...U. Icreened In bedrock Der..l Ibsorptlon future exposure limited by
aqulf.r .. e relult of Inhalet Ion existing land uses (I.e.,
DlinDlna of bedrock w.' I egrlcuUural).
Migration In sand and gravel DCM1IIradlent Irrlgatlonl Uptake by crops . cons~tlon Farm families and crop No currently exposed population.
aquifer agricultura' wells 0' 'ood crops cons~rs Future exposure limited by well
prohibitions. l Imi ted ablll ty
Uptake by cattle Ingesting of plants to take up chemlcels.
..ater - conlUll'flt I on 0' beef or Farm families and beef/dairy Chemicals likely to be lost by
d.lry product. c:onslJll8r1 volatilization during use of
water.
Migration In Iind end gravel DCM1IIradlent Irrlgatlonl Volatilization of ch~lcell Agricultural workers and No currently exposed population.
aqul fer agrlcultura' we"1 fro. Irrigation water nearby residents future exposures limited by well
prl!hibitlons. DHutlon of
.." tile compounds with ambient
air reduces magnitude of
exposure.
Discharia of groundwater to Judicia' Ditch No.1 Bloconcentrat I onl Consumers of fish limited habitat for sport fish.
Judlcle' Ditch No.1 bloaccumu'atlon by fish - limited access to ditch by
conlumption of fllh by people people to fllh. Chemicals are
volatile end may leave water
phase. Chemicals have
relatively low bloconcentration
potential.
DI.charge 0' groundwater to Judlcl.' Ditch No.1 Denne I absorption People wading In ditch Chemicals are volatile and may
Judicia' Ditch No.1 Inhalation leave water phase. Ditch is
shallow, limiting dermal
exposure. Dilution of volatile
compounds with ambient air
reduces lllagnitude of exposure.
limited access to ditch.
23\19\lB2\HHRA.TAB\PLS
, .
. .
-------
-
2
contaminated groundwater from the Sand and Gravel
aquifer:
exposure of people, directly or indirectly, if
chemicals migrate to existing agricultural wells
currently not contaminated;
exposure of people, directly or indirectly, if
contaminated groundwater discharges to Judicial Ditch
No. 1.
Analysis and evaluation of the exposure pathways indicated
that the primary exposure pathways of concern involve
residential use of contaminated groundwater. The exposure
routes associated with the groundwater use pathways are
ingestion, dermal absorption during bathing, and inhalation
of volatile compounds released to the household air. The
other potential exposure pathways (e.g., agricultural water
use) are not significant contributors of risk.
Minnesota Department of Health (MDH) rules currently
prohibit the installation of a residential potable water
well in the Sand and Gravel aquifer and prairie du Chien
aquifer. In addition, while the installation of a well in
the Jordan Sandstone aquifer is not prohibited, a change in
the current land use from agricultural to residential in the
zone of potential groundwater impacts would be required.
The main potential risk to human health at the Dakhue
Sanitary Landfill is through future use of the shallow sand
and gravel aquifer. Installation of a residential well in
the sand and gravel aquifer and within the contaminated
plume would pose a greater than 10-4 risk to human health.
As stated above, Minnesota Department of Health rules
prohibit the development of such a well downgradient of a
landfill.
A preliminary screening of ecological risks was conducted
for the Groundwater Migration Management O.U. The primary
objective of the ecological risk screening was to
qualitatively assess the potential ecological impacts of
groundwater contamination on aquatic habitats associated
with discharge to Judicial Ditch No.1 surface water. The
results are summarized in Table 4.
The potential for future ecological impacts was assessed by
estimating the future discharge concentrations of
contaminants from the groundwater plume to Judicial Ditch
No.1. Discharge concentration estimates were made by
utilizing the highest groundwater concentrations detected
during the Remedial Investigation and factoring in
concentration reductions through dispersion. A two-
6
-------
TABLE 4
POTENTIAL FOR ECOLOGICAL EFFECTS
DAKBtJE SANITARY LANDFILL SITE
POTENTIAL FOR I
_... ECOLOGICAL
CONTAMINANT OF CONCERN EFFECTS EXPLANATION
INORGANICS
Aluminum Yes Exceeds chronic standard
Arsenic No Below standards and criteria
Barium No Below NOEC
Bervllium No Below LREL
Cadmium No Below standards
Chromium Yes Exceeds chronic standard
Cobalt Yes Exceeds state chronic criterion
Coooer No Below standards and criteria
I Iron Yes Exceeds state criteria
Lead No Below standards and criteria
Manaanese Yes Exceeds state chronic criterion
Nickel No Below standards and criteria
Selenium No Below standards and criteria
Silver Yes Exceeds chronic and maximum standards
Zinc Yes Exceeds standards and criteria
Cyanide Yes Exceeds chronic and maximum standards
and federal criteria
VOLATILE ORGANICS
.
Chloromethane No Below LREL
Vinvl Chloride No Below chronic standard
Methvlene Chloride No Below standards and criterion
1 I-Dichloroethvlene No Below LREL
1 2-Dichloroethvlene No Below LREL
Chloroform No Below standards. criterion and LREL
1 2-Dichloroethane No Below standards criterion. and LREL
Methvl Ethvl Ketone No Below NOEC
1 1 l-Trichloroethane No Below standards and LREL
1 2-Dichloro~ro~ane No Below LREL
Trichloroethvlene No Below standards. criterion. and LREL
1 1 2-Trichloroethane No Below LREL
Benzene No Below standards. criterion and LREL
Methvl Isobutvl Ketone No Below NOEC
6A
23\19\182\DAEBCER%.RPT\EMB
-------
".
q
TABLE 4 (COXT.)
POTENT~ FOR ECOLOGXCAL E:FECTS
DAKBUE SANXTARY LANDFXLL S!TE
POTENTIAL FOR
ECOLOGXCAL
CONTAMINANT OF CONCERN 'EF!'ECTS EXPLANATXON
Tetracnloroe~hylene No Exceeds chronic s~andard which is
human health based. but is below
chronic criterion which is aqua~ic
life based. and is a150 below o~her
standards and LREL
Toluene No Below standards and LREL
Chlorobenzene No Below s~andards and LREL I
xvlenes No Below standards
Tetrahvdrofuran No Below HOEC
SEMIVOLATILE ORGANICS I
phenol Ho Below 8~andards and LREL
D-Cresol No Below HOEC
Benzoic Acid No Below HOEC
Diethvl Phthalate No Below HOEC
Di-n-butvl Dhthalate No Below NOEC
Bist2-ethvlhexvl)Dhthalate No Below cnronic standard
23\19\182\~.RPT\EHB
6B
-------
dimensional solute transport model (MYGAT Version 2) was
employed for these calculations. This model is considered
quite conservative because it does not take other reduction
mechanisms into account such as retardation through reaction
with aquifer components. Estimated future discharge
concentrations were then compared with Federal and state
surface water quality standards and criteria for the
protection of aquatic life, lowest reported effect levels
(LRELs), and no observable effect concentrations (NOECs).
Contaminants of concern that were determined to have the
potential for affecting the aquatic communities within
Judicial Ditch No.1 consist of the following inorganic
compounds: aluminum, chromium, cobalt, iron, manganese,
silver, zinc and cyanide. Concentrations of the other
inorganic compounds, VOCs, and semivolatiles were below the
standards, criteria, LRELs, and NOECs. At present, there
are no contaminants being discharged to Judicial Ditch No.1.
B) .
Hvdroqeoloqy
The first aquifer beneath the refuse area is the Sand and
Gravel aquifer (Figure 5). Groundwater in this aquifer
occurs mostly under unconfined conditions and flows in a
south to southeasterly direction (Figure 6). Downgradient
of the landfill, the hydraulic gradient is estimated at 1.3
x 10-3 feet/foot. The geometric mean of all hydraulic
conductivities measured in the Sand and Gravel monitoring
wells is estimated at 15 feet/day. However, downgradient of
the landfill where the VOC plumes are migrating, the
geometric mean of the hydraulic conductivities is
approximately 50 feet/year. Based on the hydraulic
conductivity and hydraulic gradient measured downgradient of
the landfill, the average groundwater flow velocity in that
area is estimated to be 94 feet/year.
The Sand and Gravel aquifer is in direct hydraulic
connection with Judicial Ditch No.1. only a small portion
of the groundwater from the Sand and Gravel aquifer is
expected to discharge to Judicial Ditch No.1, because of
the shallow depth of the ditch (1 to 3 feet) as compared to
the saturated thickness of the aquifer at the location
(approximately 36 feet). The majority of groundwater in the
Sand and Gravel aquifer is expected to bypass the ditch and
continue to flow to the south-southeast, discharging
ultimately to the regional discharge zone, the Cannon river.
The prairie du Chien/Jordan Aquifer lies directly beneath
the Sand and Gravel aquifer. The prairie du Chien/Jordan
Aquifer is composed of two units: the prairie du Chien
Group, and the Jordan Sandstone. The prairie du Chien group
is a thin-to-thick bedded sandy dolomite in which flow
occurs primarily in joint, fractures, and bedding planes.
7
-------
D
D
- I
01
°1
c::
w
Cl..
GEOLOGIC UNIT
c
. 0
u
>
o
~
~
o
Ice Contact
Stratified Drift of the
River rails Formation
~
°
c:
i ~ I
~
o
Orin of the River
Falls Formation
Outwash of the
River Falls Formation
Old .Gray Ouh(ash
.Horizon N~. '" .
FIGURE 5
SAND
u
o
:0
-...J
,01-,
.w-'
I~ZI
I O::J I
e:: I
o I
>- I
:I: I
.!
.0
en
I)
c:
o
<
I)
..
o
"0
°
>
~- ~
VU
"0>:::
c:0::l
oCs~
en
CI
C
--
c.-
-=c:
c::;)
o
U
........
c:
I)
.:::.
(,)C
o
::1"0
"0"
o
tI~
"t:
C
~
Q..
DISCONTINUOUS CONFINING LAYERS
TYPICAL STRATIGRAPHIC SECTION
Dakhue Sanitary Landfill Site
7A
-------
.'. ~.
,/
---~i - ,
~ . ---
..\ " . --\...
.' . - _1" '-c. . '-'
':- --
" \ ~_.
, ' :, ..- " \~:\, ,'-
.
.~
~ ::.
/ ,;.
!1
'Gra~S~j~tij:. .
-- ~Qo'
, ,._~,,":,.,-:::.::--:
, ~ , J""- -"
: ' :..:::::=:---""
-...
,
'.
.~._-_.
A
-
"
.i ".
..1 "
, "
..'
. -... .
'. ,
'" .
,-.
SW-1
... ~
88Uf
c
- .. - - -
MW-10A(1)
. Surficial Water Table Monitoring Well
MW-10A(2)
... Deep Water Monitoring Well
MW-1 B
.
'. .
Prairie du Chien Monitoring Well
- 870- Croundwater Elevation Contour. ft. MSL
(Contour Interval 2 feet)
.---..'
BtJ7.8B
Croundwater L.evel Elevation. ft. MSL
(Measured on 11/8/91)
SW-1
X
Surface Water Monitoring Location
o
I
1000
I
Scale in Feet
2000
I
FIGURE 6
WATER TABLE ELEVATION CONTOUR MAP
(November 1991)
Dakhue Sanitary Landfill Site
Q
7B
-------
.
G
The flow in the Jordan Sandstone is primarily intergranular.
Although the nature of flow is fundamentally different in
the two units, these two geologic units are considered to
act as a single hydrogeologic unit as no confining bed
separates them. It was determined during the Remedial
Investigation that the irrigation wells screened in the
Jordan aquifer would not result in vertical migration of the
plume into the Jordan aquifer.
At the site, the Sand and Gravel aquifer is directly
underlain by the prairie du Chien (Figure 5). Groundwater
in the prairie du chien aquifer flows in a south to
southwesterly direction. Downgradient of the landfill, the
average groundwater flow velocity in the prairie du Chien
aquifer is estimated to be 6 feet/year.
The prairie du Chien aquifer is in direct hydraulic
connection with the Sand and Gravel aquifer. Hydraulic
gradients between these two aquifers are very small (in the
10-4 to 10-3 range). Some reversed gradients were even
observed in two nests of wells. These low hydraulic
gradients indicate that the flow in the Sand and Gavel.
aquifer is mainly horizontal, and that the Sand and Gravel
and the prairie du Chien aquifers act as a single aquifer
near the site.
VI.
DESCRIPTION OF ALTERNATIVES
The major objective of the FS and the Proposed Plan was to
evaluate remedial alternatives using a cost-effective
approach consistent with the goals and objectives of CERCLA,
as amended by SARA.
Alternative 1: No further Action
As a basis for comparison to other alternatives, the
National contingency Plan (40 CPR 300.430 (e) (6» requires
full evaluation of the no action alternative. No action for
the GroundwateF Migration Management O.U. incorporates the
construction of a cap to control the source of
contamination. The cap is expected to reduce infiltration
to less than ~.5 percent of the precipitation. For the
purposes of this evaluation, no action would be taken to
control the migration of contaminated groundwater toward
Judicial Ditch No.1. Long-term impacts of the no action
alternative would be as identified in the risk assessment.
Alternative 2: Monitoring, Water supply Cost participation
This alternative incorporates groundwater monitoring, and
provides cost participation for potable water source in the
area affected by the Groundwater Migration Management O.U.
8
-------
o
Cost participation refers to the difference in cost between
a well developed in the Sand and Gravel aquifer and the
Jordan aquifer. The plume is expected to attenuate
naturally. MPCA will monitor the plume upgradient of the
judicial ditch to insure that attenuation is occurring.
Water quality monitoring would consist of periodic sampling
of selected existing and new monitoring wells and surface
water. The samples would be analyzed for the appropriate
parameters. The monitoring data would be used to: (1)
determine the migration of contamination: (2) assess trends
in water quality in the Sand and Gravel aquifer: (3) verify
that the deep aquifer is not being affected: and (4) monitor
contaminant levels in Judicial Ditch No.1. Corrective
action for surface water will be triggered if levels in the
new wells installed downgradient exceed the surface water
standards for iron (221 ug/l), manganese (572 ug/l),
aluminum (87 ug/l), chromium (11 ug/l), silver (.12 ug/l),
zinc (191 ug/1), and cyanide (5.2 ug/1).
The State will strictly enforce restrictions contained in
Dakota County Ordinance No. 114 and MN. Rules 4725.2000 and
4725.4300. If potable water wells are constructed in the
area affected by the Groundwater Migration Management O.U.,
they would be double cased at least 70 feet into the prairie
du Chien and screened at least 15 feet into the Jordan
Sandstone aquifer.
Alternative 3A: Monitorinq, Extraction Wells to contain Future
contaminant Miqration From the Landfill, Air strippinq, Iron and
Manqanese Removal, Discharqe to stormwater Retention Basin
This alternative combines groundwater monitoring, collection
of contaminated groundwater, treatment to remove the
contaminants and discharge of treated water. Monitoring
activities are as described in Alternative 2.
The groundwater extraction system would be designed to
capture groundwater that contains contaminant concentrations
above drinking water or other health-risk based criteria at
the landfill boundary. Treated water would be discharged to
an on-site stormwater retention basin in accordance with a
State Disposal System (SDS) discharge permit. The air
stripping system would be designed and operated to meet the
discharge limitation established in the discharge permit.
Since the organic contaminants are emitted to the
atmosphere, off-gas controls may be required for this
alternative. The air system has the potential to remove
manganese through oxidation, adsorption and sedimentation.
9
-------
Alternative 3B: Monitoring Extraction Wells to Remediate Entire
Plume, Air stripping, Discharge to stormwater Retention Basin
This alternative incorporates the monitoring, discharge
location and treatment system from Alternative 3A. The
groundwater extraction system would be designed to capture
the entire contaminant plume. The extraction system would
be located at the landfill and between Judicial Ditch No.1
and MW-12a(1). Although manganese removal is not required
to meet the discharge standards, the air stripping system
has the potential to remove manganese through oxidation,
adsorption, and sedimentation.
Alternative 4A: Monitoring, Extraction Wells to contain Future
contaminant Migration from the Landfill, Iron and Manganese
Removal, Carbon Adsorption, Discharge to stormwater Retention
Basin
This alternative incorporates the monitoring, extraction
system and discharge location from Alternative 3A. An iron
and manganese removal system would be installed in series
with a carbon adsorption system. The iron and manganese
removal system would consist of chemical oxidation followed
by filtration. The carbon adsorption system would remove
the volatile organic compounds, except vinyl chloride.
vinyl chloride will rapidly volatilize to the atmosphere
after discharge to the stormwater retention basin. Spent
carbon would be regenerated under controlled conditions at a
permitted facility.
Alternative 4B: Monitoring, Extraction Wells to Remediate Entire
Plume, Carbon Adsorption, Discharge to stormwater Retention Basin
Same as Alternative 4A, except the groundwater extraction
system is designed to capture the entire contaminant plume.
The influent manganese concentration is expected to be below
the assumed discharge limitation. Therefore, iron and
manganese removal is not required with this alternative.
Alternative SA: Monitoring, Extraction Wells to contain Future
contaminant Miqration from the Landfill, Iron and Manqanese
Removal, Photolysis/Chemical Oxidation, Discharge to stormwater
Retention Basin
Same as Alternative 3A, except Photolysis/Chemical Oxidation
replaces air stripping. Photolysis/Chemical Oxidation
technology oxidizes the contaminants to C02' H~O, and other
oxidation products. This technology is espec~ally effective
for treating chlorinated organic compounds. Iron and
manganese removal is required to limit scaling on the
interior of the reaction vessel. Additional pretreatment
may be required based on water chemistry which would
10
-------
o
increase the cost for this alternative. The capital and
maintenance costs for this alternative are higher than other
alternatives.
Alternative SB: Monitoring, Extraction Wells to Remediate Entire
Plume, Iron and Manganese Removal, Photolysis/Chemical oxidation,
Discharge to stormwater Retention Basin
Same as Alternative 5A, except groundwater extraction system
is designed to capture the entire contaminant plume. Iron
and Manganese removal is required to limit scaling on the
interior of the reaction chamber. Additional pretreatment
may be required based on water chemistry which would
increase the cost for this alternative.
VII. SUMMARY OF THE COMPARATIVE ANALYSIS OF ALTERNATIVE
The NCP and Section 121 of the Superfund Amendments and
Reauthorization Act of 1986 (SARA) form the regulatory and
statutory basis for the nine evaluation criteria utilized in
determining the appropriate remedial action at a CERCLA
site. Specifically, Section 121 of SARA requires that the
selected remedy is to be protective of human health and the
environment, cost-effective, and use permanent solutions and
alternative treatment technologies or resource recovery
technologies to the maximum extent practicable.
Alternatives were evaluated using current u.S. EPA guidance,
including "Guidance for Conducting Remedial Investigations
and Feasibility Studies under CERCLA", OSWER Directive
9355.3-01, October 1988; II A Guide to Selecting Superfund
Remedial Action, "OSWER Directive 9355.)-27FS, April 1990;
and" Streamlining the RI/FS for CERCLA Municipal Landfill
sites," OSWER Directive 9355.ll-llFS, September 1990. The
nine evaluation criteria, referenced in the first two
guidance documents above, are as follows:
2)
Long Term Effectiveness - The analysis under this
criterion focuses on any residual risk remaining at the
site after the completion of the remedial action. This
analysis included consideration of the degree of threat
posed by the hazardous substances remaining at the
site, the adequacy of any controls (e.g., engineering
or institutional control) used to manage the hazardous
substances at the site, and the reliability of controls
against possible failure.
Reduction of Toxicity, Mobility, and Volume - This
evaluation criterion addresses the statutory preference
for selecting remedial actions that employ treatment
technologies that permanently and significantly reduce
the toxicity, mobility, and volume of hazardous
1)
11
-------
8)
9)
3)
substances as a principal element.
Short-Term Effectiveness - This evaluation criterion
addresses ~he effects of the alternative during the
construction and implementation phase until the
remedial response objectives are met. Under this
criterion alternatives are evaluated with respect to
their effects on human health and the environment
during the implementation of the remedial action.
4)
Implementability - The implementability criterion
addresses the technical and administrative feasibility
of implementing an alternative and the availability of
various services and material required during its
implementation.
5)
Cost- The estimated capital, annual maintenance and
monitoring, and present worth value costs are evaluated
under this criterion. Present worth costs are
calculated using a ten percent discount rate over a 50
year period of operation.
6)
Overall Protection of Human Health and the Environment.
This evaluation criterion draws on the results of the
above evaluation criteria to describe whether, and how,
each alternative provides protection of human health
and the environment.
7)
compliance with ARARs - This evaluation criterion is
used to determine whether each alternative will meet
all of- its federal and state ARARs (as defined in
CERCLA 121). The detailed analysis should summarize
which requirements are applicable or relevant and
appropriate to an alternative and describe how the
alternative meets those requirements. When an ARAR is
not met, the detailed analysis should discuss whether
one of the six waivers allowed under CERCLA may be
appropriate.
Community Acceptance - This criterion refers to the
community's comments on the remedial alternatives under
consideration. These comments are presented in the
Responsiveness Summary which is included as an
attachment to this Record of Decision.
state Acceptance - The State of Minnesota (MPCA) is the
lead ~gency for this site.
12
-------
Q
~
COMPARATIVE ANALYSIS OF ALTERNATIVES
This section provides a summary of the relative performance of
the alternatives with respect to each of the nine criteria.
Table 5 present a comparison of the nine criteria for each
alternative.
1.
OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
All alternatives are considered protective of human health
and the environment. All alternatives incorporate the
access/use restrictions contained in Dakota County Ordinance
No. 114 which prohibits the use of the contaminated aquifer
for potable water and in MN Rules 4725.2000 and 4725.4300.
If left unattended, future groundwater discharge to the
judicial ditch might exceed surface water quality standards
for some metals. MPCA will monitor groundwater levels
upgradient of the judicial ditch, and take further action if
necessary to meet water quality standards or to be
protective of human health.
2.
LONG-TERM EFFECTIVENESS AND PERMANENCE
All alternatives under consideration involve long term
response actions. The active pump and treat system will
restore the contaminated plume to potable quality in an
estimated 45 years. The groundwater is expected to reach
potable quality in 55 years after natural attenuation
occurs. The residual risk following these time frames is
expected to be well below the U.S. EPA's point of departure
for groundwater ingestion, provided the landfill cap
integrity is maintained. The landfill cap will be
maintained under an operation and maintenance program
administered by the MPCA. Institutional access/use
restrictions of the site groundwater will be strictly
enforced by MPCA. Long term monitoring will identify
whether discharge standards are being exceeded.
Time to reach the MCLS for PCE is as follows:
ALTERNATIVES PCE
1,2 55 Years
3A, 4A, 5A 45 Years
3B, 4B, 5B 45 Years
3. SHORT - TERM EFFECTIVENESS
Since there are no current complete exposure pathways,
Alternative land 2 are more effective. The other
alternatives have the potential to expose people to
13
-------
contaminants during remediation activities. In addition,
the treatment alternatives do not substantially reduce the
time required to clean-up the contaminated plume.
4 .
COMPLIANCE WITH STATE AND FEDERAL REGULATIONS CARARS)
Alternatives 1, 2, 3a, 3b, 4a, 4b, Sa and Sb meet ARARs for
groundwater, but vary in the amount of time within which
they will meet revised Preliminary Remediation Goals (PRGs)
for groundwater. The revised PRGs for groundwater are set
forth in Table 7 and the method through which they were
derived is set forth in the FS. Briefly, if an ARAR-based
level for a contaminant was available, namely MCLs, it was
selected to be the revised PRG for groundwater for that
contaminant. If an ARAR-based PRG for groundwater was not
available for a contaminant, a risk-based PRG served as the
basis for the revised PRG. Alternatives 3b, 4b, and 5b
comply with all ARARs. Currently, no contamination is
discharging to surface water. Under Alternatives 1, 2, 3a,
4a, and Sa, some metals, most notably Iron, do have the
potential to exceed at a future date surface water quality
criteria and standards under the Federal Water Pollution
Control Act and MN Rule 7050 for the protection of aquatic
life. MPCA will monitor the groundwater plume upgradient of
the ditch as stated above. This monitoring will include
trigger levels for further action specified below (set at
the surface water quality standards and criteria.)
5.
Additional ARARs were presented in the FS for the Ground
Water Migration Management Operable Unit.
REDUCTION OF TOXICITY. MOBILITY. OR VOLUME THROUGH TREATMENT
Alternatives 1 and 2 do not reduce the toxicity, mobility,
or volume of the contaminants beyond that due to natural
degradation. Alternatives 4A, 4B, SA, and SB reduce the
toxicity of organic compounds. Alternatives 3A, 3B, 4A, 4B,
SA, and 5B reduce the mobility of iron and manganese through
treatment.
6.
IMPLEMENTABILITY
The no action alter~ative requires no implementation.
Alternative 2 is the easiest to implement of the remaining
alternatives. Alternatives 3A and 3B are more easily
implemented than the other alternatives that involve
groundwater treatment. Alternatives 3B, 4B, and 5B require
an easement for construction of extraction wells and
pipelines on farm land south of the landfill. All the
alternatives rely on future enforcement (long-term or short-
term) of Dakota County water well restrictions and Minnesota
Rules. Such enforcement is subject to funding levels and
14
-------
o
~
priorities.
7 .
COST
Alternative 2 has an estimated cost of $360,000. Earlier
cost estimates indicated the cost of Alternative 2 was
higher. The Proposed Plan estimated its cost at $450,000.
The difference in cost is based on elimination of the cost
participation portion of the alternative. Alternative 2 has
the lowest cost except for Alternative 1, the No Action
Alternative, when compared to the remaining alternatives.
See Table 5.
8.
STATE ACCEPTANCE
MPCA and u.S. EPA concur on the remedy.
9.
COMMUNITY ACCEPTANCE
Community acceptance has been assessed in the Responsiveness
Summary following a review of the public comments received
on the RI/FS Report and Proposed Plan. The selected remedy
is a modification of the preferred alternative presented in
the Proposed Plan and was modified to reflect comments
received during the Public Comment Period. There does not
appear to be any local opposition to the selected remedy.
VXXX.DESCRXPTXON OF THE REMEDY
The U.S. EPA and MPCA select a modification of Alternative 2
which constitutes a limited action involving continued water
quality monitoring. Cost participation has been eliminated
as a component of this alternative. This limited action
alternative relies on the integrity of the composite cap
which was installed on the landfill pursuant to the Source
Control o.u. Record of Decision. The composite cap is
expected to be 98.5 percent efficient in reducing
infiltration through the waste material at the Site. In
addition, current regulations restrict the use of the Sand
and Gravel, and the prairie du Chien aquifers in the area
downgradient of the landfill. These aquifers are currently
impacted or have the potential to be impacted in the future.
MPCA and the County will enforce regulations, Dakota County
Ordinance No. 114 and MN. Rules 4725.2000 and 4725.4300,
restricting installation of wells in the future through well
permit requirements.
It is anticipated that no further action will be required to
mitigate the migration of contaminants already present in
the aquifer. Since the leachate from the landfill is
significantly reduced by the installation of the composite
cap, the concentration in groundwater should decrease over
15
-------
CRITERIA
o.erel1 'roteotion
at Hu..n aeeltb end
tbe In"iroD.eDt
Long-Una
Eft.cth.n.e. .nd
'.r..n.Dc.
Reeidu.l ri.k tro.
untr..t.d ..a.t.
and treat.88at
n.iduah
Adequ.cl .nd
nlhbi it, at
ooatrol.
....
In
>
Sbort-t.ra
Iff.cU".D...
CoapliaDO. ..itb.
uu. .ad 'rIC.
ALTIRNATIIIJ:
I
prot.cti". at
hu..n he.lth.
'ot.Dthl
.cological
i.p.ct..
1I..tdct.d u.. of
BaDd and Gr.".l
aquiter
dOV1lgradi.nt of
landfill.
Depend. of
.nforceDlDnt..
No ..po.ura to
co_unit, or
..or.er.. 'ri.. to
reacb .IIG. for
'CE in 55 y..n.
.IIG for lroD 18
Dot ..t ..ith
pr.UDt c.p
d..ign. 'otential
.cologlcal
i.p.cta.
HCL. for drinklng
..at.r .r.
..c..d.d in the
S.nd and Gra".l
aquihr.
I.t i..ted to
r.acb MCLa after
55 y.an.
.ntanthl to
ellc.ad ...rface
..atar .t.ndard.
or crit.ri..
2
s.- .. 1.
5... .. I.
S... a. I.
5.81. .. I.
Sa.. a. I.
23\19\182\STUDY.RPT\PLS
TABLE 5
COMPARATIVE ANALYSIS SUMMARY
MIGRATION CONTROL OPERABLE UNI'r
DAKHUE SANITARY LANDFILL SITE
JA
Protecti"a at
human health.
Poten tJ.I
ecologic81
impacta.
Sallie aa I.
Traat.ant
ra.id...l. handled
under 50S per.it.
Same as 1.
vac elllie.ion. .ra
below SEll..
Eati.ated 10 years
npention. Ti.e
to reech PRGe for
PCE end iron i. 15
end 71 yeer.,
re.pecHvely.
Reach MCL. dter
IS yean. Air
e.ieeion. ere
likel, belo.. SERe.
Treeted ..eter
diecherged in
accordenca with
.505 per.it. Iron'
.angane.e aludg.
.anage.ent. would
compl, wit.h ARAlIa.
]8
Prot.ectiv. of
human heelth and
envlronment.
Treatlllent.
re.iduel. handled
under SDS per.it.
L.rger "nlu.e
treated.
No long-term
cant role.
vac emi..ion. ere
below SER..
Eatt.atad >]0
yaer. operation.
Time to reecb PRGa
.for PCE end iron
in IS end to
yan.,
re.pectively.
R..ch HCL. efter
IS yean. Air
..i..ione are
likely b.lo.. SERe.
Treated ...t.er
dincherged in
eccord,nce ..ith
50S per.it. Iron
, .angane.e eludge
.an.galllent would
co.ply with ARARe.
4A
Same 88 )A. Le..
pl"otective if
vinyl chlor ide h
preaent.
Same ao ]A and
generation of
epent carbon.
Same ail 1.
Esti.ated 10 yeara
operetion. Tl.e
to reach PRG. for
PCE and iron i. 15
and 71 yean,
reepectivelr'
Vinyl chlor de
emi..ions are
below SER.
Reach HCLa after
15 ye~rs. Treated
..eter diachelg.d
in eccordance with
50S permit. Spent
carbon management
would comply with
ARAII.. Iron'
mang.n.a. eludge
menagement would
comply with ARAlIa.
tB
Same .. )8. LeaD
protective if
vinyl chloride ie
pre.ent.
Same as ]8 end
g.neration of
.pent carbon.
Same 88 38.
Eetilllated >30
y.ar. operetion.
TIllie to reach PRGa
for PCE .nd iron
in .5 end 10
v.ar.,
re.pectively.
Vinyl chloride
elllle.ion. ar.
below SEll.
Reach HCLe after
I~ year.. Treated
...ter diecharg.d
In .ccordance with
50S permit. Spent
cerbon management
would comply with
AIIARe. J ron'
lIIanganeee aludge
managelllent would
comply with AIIARo.
~A
Same 88 JA.
Same DS JA.
Same 88 1.
Eetimated 10 yeare
operation. Time
to reach PRGe for
PCE and iron I. I~
and 11 yeare.
reepectively
Reach HCLs efter
15 yeare. Treat".1
water diecharged
in accordance wLth
50S permit. Iron
, lIIanganeee aludge
management would
comply wlth ARARe.
~B
Same 88 )8.
--
Same au Ht
Same all )8
t;"UlDaled »0
yeara
operat. ion
Time to .ead.
PRGe fOI PCE
and Iron ie .~
and .0 y"ar a,
re."ectively.
~--- . ...-
Reach
after
yeare
water
dlechaltJ"d In
accordance
with 50S
pecmit. J,un
, 1h4n9an,~a~
elud
-------
~ v
.~D
TABLE 5
(CONT)
COMPARATIVE ANALYSIS SUMMARY
MIGRATION CONTROL OPERABLE UN] 'I'
DAKHUE SANITARY LANDFILL SITE
......
VI
~
ALUMII'rlVE
CRITERIA I 2 JA )8 4A tB 510 5B
- .-._"
.eduatlaD of No reductlaD S_e .e I. Mobility of Iron Mobillty of Iron Reducea toxicity Reduce. toxicity Reducee toxicity Reduclis
Ta.lclty, Mobility, other tb.. end mangeneae I. end mlnganeae I. through treltment. through treatment. through treatment toxiclty
or Valu.. tbraugb D.tur.l reduc.d. reduced. MobiUty of Iron Mobillty ot lron through
'fr..t...t prac...... and manganeae la and manganeae le t t"eatment ""
reduced. reduced. atmoephel ic
emis8ion..
Mobi I lty "I
iron and
manqaneel! 'II
reduced.
.-
l.pla.aDtablllty aaadUy S... a. I. lIeadily Hore lapact on SalDe aa )/1. Same aa )8. Same 88 )/1. Same 118 lB.
lath..nt.ble. iaple...ntable. agricultural hnof DiU Icult Difficult DiU ieul.
a. h. aD tutura dovDgradlant ot operation. operation. opelatinn.
.Dtarc...Dt of hndfill than Additional additional
MDI cad.. IIltanative )11. pretreatment may pretreatmenl
be required. may ba
required.
Ca.t,
Capital fO $0 $150,000 $280,000 $180,000 $270,000 $))0,000 $460,000
Pra.aDt Worth '0 U10,OOO $600,000 "10,000 $960,000 $1.550,000 $910.000 $1.610,000
'fotal to 1510,000 $150,000 $1,200,000 $1,100,000 $1,800,000 $1,)00,000 $2,100,000
Support "'..0)' Nil Nil Nil Nil Nt. Ht. Nt. NA
IIccaptance
HA - Hot applicable to State-lead Dakhue aite.
23\19\182\STUDY.RPT\PLS
-------
IX.
time due to dilution, biodegradation and other natural
processes. Water quality monitoring will be conducted to
monitor contaminant migration and to assess water quality in
the Sand and Gravel aquifer, the deep aquifer and Judicial
Ditch No.1. Total cost for monitoring the site is
estimated to be $360,000 with the installation of two
additional monitoring wells. The preferred alternative
provides the best balance of tradeoffs among alternatives
with respect to the criteria used to evaluate the remedies.
Corrective action will be initiated if monitoring results
indicate that the cover system is ineffective in reducing
concentrations in the Sand and Gravel aquifer or that
Judicial Ditch No.1 will be negatively impacted.
Corrective action for surface water will be triggered if
levels in the new wells installed downgradient exceed the
surface water standards for iron (221 ug/1), manganese (572
ug/1), aluminum (87 ug/l) , chromium (11 ug/l), silver (.12
ug/l), zinc (191 ug/l) , and cyanide (5.2 ug/l).
CERCLA provides for the establishment of Alternative
Concentration Limits (ACLs) for groundwater pursuant to
CERCLA Section 121 (d) (2) (B) (ii) under certain limited
situations. The statutory prerequisites for the
establishment of ACLs include 1) there are known and
projected points of entry of groundwater into surface water,
2) on the basis of measurements or projections, there is or
will be no statistically significant increase of such
constituents from such groundwater in such surface water at
the point of entry where there is reason to believe
accumulation of constituents may occur downstream, and 3)
the remedial action includes enforceable measures that
preclude human exposure to contaminated groundwater at any
point between the facility and all known or projected points
of entry of groundwater into surface water then the assumed
point of human exposure may be at such known and projected
points of entry. Consideration may be given to setting ACLs
if groundwater contamination is not attenuating as projected
and the prerequisites are satisfied.
STATUTORY DETERMINATION SUMMARY
The selected remedy must satisfy the requirements of Section
121 (a-e) of CERCLA, as amended by SARA, to:
a.
b.
Protect human health and the environment;
Comply with ARARs;
Be cost-effective;
Utilize permanent solutions and alternative
treatment technologies to the maximum extent
practicable; and,
Satisfy the preference for treatment as a
c.
d.
e.
16
-------
\
~
principal element or provide an explanation as to
why this preference is not satisfied.
The implementation of modified Alternative 2 at the DSLF
site satisfies the requirements of CERCLA, as amended by
SARA, as detailed below:
a.
Overall Protection of Human Health and the Environment
This alternative is considered protective of human
health. There are no known complete exposure pathways
under current site conditions (Barr, August 1992). The
only possible mechanism for exposure to occur would be
for someone to install a potable water well in a
location where contaminated groundwater may be
withdrawn. The installation of new surficial aquifer
drinking water wells is legally prohibited and is,
therefore, unlikely. The groundwater MCLs for TCE,
PCE, vinyl chloride and benzene will be met after
approximately 55 years due to natural attenuation.
Absent an active groundwater extraction and treatment
system for the contaminated plume; Aluminum, Chromium,
Cobalt, Silver, Zinc and cyanide all have the potential
to exceed their surface water quality standards as
groundwater discharges to Judicial Ditch No.1.
Exposure point concentrations for the above metals were
modelled using a two-dimensional solute transport mode
(MYGAT Version 2.0) and the contaminant source was
assumed to be equal to the highest concentrations
observed. The model estimates reductions in
concentration based only upon dispersion. Other
chemical fate processes such as retardation through
reaction with aquifer components were not evaluated.
In addition, dilution effects due to mass flow in
Judicial ditch No.1 were not considered. Therefore
the model is considered a very conservative worst case
scenario, and the actual concentrations are likely to
be significantly lower. Notwithstanding this, MPCA
will monitor the groundwater plume upgradient of
Judicial Ditch No.1 and will implement measures to
ensure that surface water quality standards and
criteria are met.
b.
Compliance with ARARs
This remedy will attain all applicable or relevant and
appropriate Federal and/or State requirements which are
more stringent.
Revised PRGs for groundwater will be met under this
remedy. As stated earlier, the revised PRGs set forth
17
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~
in Table 7 are either ARAR-based, MCLs, or risk-based
levels. Now that the landfill cap has been installed,
contaminant concentration in the Sand and Gravel
aquifer is expected to slowly decrease over time due to
natural attenuation processes. It is expected that the
MCL for PCE, which has the longest half-life and
highest concentration of the chemicals of concern, will
be attained in approximately 55 years. The MCLs for
other chemicals of concern will be met more quickly.
The State and the County will enforce well placement
restrictions under MN Rules 4725.2000 and 4725.4300,
and Dakota County Ordinance No. 114 to ensure that no
residential wells are developed in the area
downgradient of the landfill.
The selected remedy will attain ARARs for surface water
as well. At the present time, surface water standards
under Minnesota Rule 7050 and Federal Ambient Water
Quality Criteria promulgated under the Federal Water
Pollution Control Act are not exceeded. There,
however, is a possibility that they may be exceeded in
the future using extremely conservative groundwater
models. Long term monitoring will be conducted on-site
to ensure that inorganic concentrations in discharges
to Judicial Ditch No.1 do not exceed these surface
water standards and criteria. Trigger levels have been
specified above so that if groundwater monitoring
indicates that the surface water standards and criteria
are going to be exceeded, further action will be taken
to address these discharges.
c.
Cost - Effectiveness
The cost to install two additional monitoring wells and
monitor the site over the next 30 years is estimated at
$360,000. (Table 6) This is cost effective when
compared to the cost of the treatment remedial
alternatives which are significantly more expensive
with only a marginal increase in their effectiveness in
attaining the revised PRGs.
d.
utilization of Permanent Solutions and Alternative
Treatment Technologies or Resource Recovery
Technologies to the Maximum Extent Practicable.
u.S. EPA and the State of Minnesota believe the
selected remedy meets the statutory requirement to
utilize permanent solutions and treatment technologies
to the maximum extent practicable. Of the alternatives
that are protective of human health and the environment
and comply with ARARs, u.S. EPA and the State have
18
-------
,\
."
TABLE 6
Preferred Alternative
Groundwater Migration Control Operable Unit
Dakhue Sanitary Landfill Site
Quantity/
Unit
Unit
Cost
Cost
1.
SITE HONITORING
2 Each
1 L.S.
3,300
2,200
6,600
2,200
5,400
4,860
756
6,000
$19,200
3,840
$23,040
Install Monitoring Wells
Sample Collection
Analysis:
VOC
Metals
Cyanide
Review and Reporting
Contingencies (20%)
18 Each
18 Each
18 Each
1 L.S.
300
270
42
6,000
SUSTOTAL:
subtotal:
PRESENT WORTH:
Site Monitoring (30 yrs @ 5%)
$350,000
SUBTOTAL:
site Monitoring
18A
$360,000
-------
TABLE 7
REVISED PRELIMINARY REMEDIATION GOALS
GROUNDWATER-DRINKING WATER USE
DAKHUE SANITARY LANDFILL SITE
(concen~ra~ion in ~g/L)
I CHEMICAL I PRG I BASIS I
VOLATILE ORGANIC COMPOUNDS
! Benzene 5 MCL
,
, Chlorobenzene 100 MCL
I Chloroe~hane 29 Risk-based (10-')
!
I
I Chloroform 100 MCL
I Chlorome~hane 1.4 Risk-based (10-')
I
i
I 1.1-Dichloroe~hane 1,000 Risk-based (HQ)
:.2-Dichloroe~hane 5 MCL
: 1.1-Dichloroe~hylene 7 MCL
I
1.2-Dichloroe~hvlene 70 MCL
1.2-Dichloropropane 5 Met.
Methvlene Chloride 11 (5). Risk-based (10-')
Methyl Ethyl Ketone 570 Risk-based (HQ)
Methyl Isobutvl Ketone 200 Risk-based (HQ)
Tetrachloroe~hylene 5 Met.
1. 1. 1-Trichloroethane 200 Met.
1.1.2-Trichloroethane 5 Met.
Trichloroe~hvlene 5 MCL
I
I Trichlorofluoromethane 1,700 Risk-based (HQ)
Vinyl Chloride 2 Met.
Xylenes 10,000 Met.
SEMIVOLATILES
Benzoic Acid 150,000 Risk-based (HQ)
Bis(2-ethvlhexvl)~hthalate 6 Met.
Cresol 1,800 Risk-based (HQ)
Diethvl phthalate 29,000 Risk-based (RO)
Phenol 22,000 Risk-based (RO)
INORGANICS
Aluminum 36,000 Risk-based (HO)
Arsenic 50 Met.
23 \19 \182\STUDY.RPT\PLS
laB
-------
'\
(>
'"
Q
TABLE 7 (CONT)
REVISED PRELIMINARY REMED~TION GOALS
GROUNDWATER-DRINKING WATER USE
DAKBUE SANITARY LANDFILL SITE
(concen~ra~ion in ~q/L)
:I CHEMICAL ! PRG ! BASIS I
,
! Barium 2,000 MCL
,
Cadmium 5 MCL
Chromium 100 MCL
Cooper 1.300 MCL
cyanide 730 (200)D Risk-based (HQ)
Manaanese 3,600 Risk-based (HQ)
i Nickel 100 MCL
!
! Selenium 50 MCL
I Zinc 7,300 Risk-based (HQ)
Basis of Revised PRG:
MCL - maximum cont~nant level
Risk-based (10~) - based on cancer risk at lO~ risk
Risk-based (8Q) - based on noncarcinoqenic risk
level
Q
Proposed MCL in parenthesis.
23\19\182\STODY.RPT\PLS
l8C
-------
\,
.,
;:,
~
determined that the selected remedy provides the best
balance of tradeoffs in terms of long-term
effectiveness and permanence, reduction of toxicity,
mobility or volume through treatment, short-term
effectiveness, implementability, cost and state and
community acceptance. The selected remedy can be
implemented more quickly, with less difficulty, with no
short-term exposure pathways, and at less cost than the
active groundwater treatment alternatives.
The human health risk assessment indicates that the
risks associated with the Groundwater Migration
Management o.u. fall within acceptable guidelines as
long as no potable water wells are screened in the Sand
and Gravel aquifer downgradient of the landfill.
Dakota County Ordinance No. 114 prohibits constructing
a potable water well screened in the Sand and Gravel
aquifer (Minn. Rules 4725.2000) and prairie du Chien
aquifer (Minn. Rules 4725.4300) in this area. In
addition, the ordinance restricts the use of the Sand
and Gravel aquifer due to elevated nitrate
concentrations. These risks are controlled when these
restrictions are enforced.
If a potable water well is required in the Groundwater
Migration Management o.u. affected area, the well would
be screened in the Jordan Sandstone aquifer. The human
health-risk assessment indicates this aquifer would
provide a safe potable water source (Barr, August
1992) .
In addition, the Source Control O.U. is expected to
significantly reduce migration of contaminants from the
DSLF site.
The selected remedy represents the maximum extent to
which permanent solutions and treatment can be
practicably utilized for this action taking into
account the site conditions, the Source Control O.U.
and the comparative analysis of the alternatives
considered.
e.
Preference for Treatment as a Principal Element
Because treatment of the groundwater at the site was
not found to be practicable, the remedy does not
satisfy the statutory preference for treatment as a
principle element of the remedy. As was stated above,
it is expected that the Source control o.u. is expected
to significantly reduce groundwater contaminants
travelling off-site. In addition, based on the
comparative analysis of the alternatives, it has been
19
-------
determined that active groundwater treatment does not
provide a significant benefit proportional to its cost.
x.
DOCUMENTATION OF SIGNIFICANT CHANGES
The Proposed Plan for the DSLF Groundwater Migration
Management O.U. was released for public comment in January
1993. The Proposed Plan identified a modification of
Alternative 1 with monitoring as the preferred alternative.
After review of the public comments, the selected remedy has
been changed to a modification of Alternative 2 which calls
for groundwater monitoring with provision for additional
action should trigger levels be met. In addition, cost
participation for potable water sources in the area effected
by the o.u. was eliminated from the selected remedy.
20
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