\,
,
'"
UrilBd Slates
EnvironmentaJ Protection
A9fK'q
Office of
Emergency and
Remedial Response
E PAlROOiROS-9Oi148
September 1990
Co?Y I
&EPA
Superfund
Record of Decision:
Hunts Disposal, WI
EPA Report Collection
Information Resource Center'
US EPA Region 3 I
Philadelphiee PA 19107 .
-------
,:> ~~~--'- ... Po"In,:> \
17. OOCunI8nl Analyal. .. 088crfplo"
Record of Decision - Hunts Disposal, WI
First Remedial Action - Final
Contaminated Media: soil, sediment, debris, gw
Key Contaminants: VOCs (benzene, TCE, xylenes),
metals (arsenic, chromium)
b. Idanllfl8ra1Opan-Endad T8m18
c. CooATI ReIdIGroup
18. Avail.bllty St8t8m8nt
18. S8cur1ty CI... (1111. Repor1)
None
20. SecurIty CI888 (11118 I'8ge)
None
21. No. 01 P.ge.
78
22. PrIce
(See ANSl-Z38.18)
SHlMtrvctlOM on~-
(FOI'III8fty NTlS.35)
~t of COIIIII'I8I'ce
-------
\i
BPA/ROD/R05-90/148
Hunts Disposal, WI
First Remedial Action - Final
Abstract (Continued)
migration. The primary contaminants of concern affecting the soil, sediment, debris,
and ground water are VOCs including benzene, TCE, and xylenes; acids; and metals
including arsenic and chromium.
Xhe selected remedial action for this site includes excavating and consolidating 5,300
cubic yards of onsite contaminated soil and sediment from outside the landfill area to
within the landfill, and filling excavated areas with clean soil; constructing a levee
to prevent erosion of the landfill during floods; capping the landfill with a
multi-layer clay and soil cover; installing an active landfill gas collection and
combustion system; constructing a slurry wall intersecting the cap and a subsurface
confining layer to hydraulically contain contaminated ground water; pumping and
offsite treatment of ground water, followed by offsite discharge; and implementing
institutional controls including land and ground water use and deed restrictions, and
site access restrictions such as fencing. The estimated present worth cost for this
remedial action is $17,454,000, which includes an annual O&M cost of $375,000.
PERFORMANCE STANDARDS OR GOALS: Ground water cleanup levels chosen for the site are
State Preventive Action Limits (PALs), which are equal to, or more stringent than
Federal MCLs. Ground water chemical-specific goals include benzene 1 ug/l, TCE
0.18 ug/l, xylenes 124 ug/l, arsenic 5 ug/l, and chromium 5 ug/l. Specific cleanup
standards for soil and sediment have not been set.
-------
o
~
RECORD OF DECISION
." ;
SELECTED REMEDIAL ACTION
site Name and Location
Hunts Qisposal Landfill Site
Town of' caledonia, wisconsin
statement of Basis and Purpose
This decision document presents the United states Environmental
Protection Agency's (U.S. EPA) selected remedial action for the
Hunts Disposal Landfill site, Caledonia, Wisconsin, which was
developed in accordance with the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980, as amended by
the Superfund Amendments and Reauthorization Act of 1986
(CERCLA), and, to the extent practicable, the National
contingency Plan (NCP). This decision is based on the
administrative record for this site.
The state of Wisconsin concurs with the selected remedy.
Assessment of the site
U.S. EPA has determined that actual and threatened releases of
hazardous substances, pollutants and contaminants from this site,
if not addressed by implementing the response action selected in
this Record of Decision, may present an imminent and substantial
endangerment to public health, welfare and the environment.
Description of the Selected Remedv
This remedial action is a source control action for the site.
This action addresses the principal known threats at the site by
containment of contaminated landfill materials, soils and
groundwater. The function of the remedy is to seal off the
Hunt's Disposal Landfill as a source of contamination and reduce
the risks associated with exposure to contaminated materials.
The major components of the selected remedy include:
Installation of a fence around the landfill site;
Consolidation of contaminated soil and sediment onto
the landfill;
Construction of a multilayer landfill cap over the
landfill and consolidated soil and sediment in
compliance with Resource Conservation and Recovery Act
Subtitle D requirements;
Construction of a full slurry wall around the
subsurface perimeter of the landfill;
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if
Performance of groundwater gradient control and
contaminated groundwater treatment via extraction and
offsite treatment;
Construction and installation of an active landfill gas
collection and destruction/treatment system;
Environmental monitoring to assure protectiveness and
effectiveness of the remedy;
Institutional controls governing groundwater use and
development of the landfill site;
Additional investigation and study to assist in design
of the remedial action; and
Additional investigation and study to supplement
remedial investigation and feasibility study
information, including potential off-site groundwater
contamination and the need for additional remedial
actions at the site.
statutory Determinations
The selected remedy is protective of human health, welfare 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 solution and alternative treatment technologies to the
maximum extent practicable at the site. However, because
treatment as a principal element was not considered practicable
at this site, this remedy does not satisfy the statutory
preference for treatment that reduces toxicity, mobility, or
volume as a principal element of the remedy. The size of the
landfill precludes a remedy in which contaminants could be
excavated and treated effectively. However, treatment is a
secondary element of this remedy in that landfill gases will be
destroyed and contaminated groundwater treated.
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 the remedial action to
ensure that the remedy continues to provide adequate protection
of human health and the environment.
Valdas V. Ada
Regional Adm'
;-
J~!tj)-19~{)
Date
-------
SUMMARY OF REMEDIAL ALTERNATIVE SELECTION
HUNTS DISPOSAL LANDFILL
CALEDONIA, WISCONSIN
I. Site.."Location and DescriDtion
The Hunts Disposal Landfill (HDL) (also known as the Waste
Management Inc.-Caledonia Landfill) is an inactive 35-acre
landfill which is a part of an 84-acre parcel (including a 25-
acre lake) located in southeastern Wisconsin. The landfill
reportedly accepted municipal and industrial wastes from 1959 to
1974. The parcel is currently owned by the Racine County Parks
Department and was originally purchased for inclusion in the
Racine County Root River Parkway System.
The site borders the Root River in a sparsely populated
agricultural area of Caledonia Township in Racine County. The
site is located immediately south of County Line Road (also known
as Eight Mile Road) and is approximately 1.5 miles west of
Highway 32 (see Figure 1). The chicago & North Western (C&NW)
Railroad tracks run north-south and are located just west of the
site.
The landfill is bordered on the west by a wetland located between
the landfill and the C&NW railroad tracks. To the southwest
between the landfill and the Root River is a narrow strip of
wooded wetland which varies from approximately 50 to 100 feet
wide. Wetlands also extend along the southern and eastern sides
of the site (see Figure 2). North of the site is a lake
approximately 25 acres in size. The lake was created during the
excavation of soil used to cover the landfill.'
, A wetlands assessment was conducted at the landfill from
September 10-12, 1990, by staff from the U.S. EPA Superfund
Technical Support Unit, in conjunction with the Wisconsin
Department of Natural Resources and the Southeast Wisconsin
Regional Planning Commission. According to the September 21,
1990, U.S. EPA report, at least 18 acres of wetlands (some of
which are forested) were delineated in the immediate vicinity of
the landfill.
The report found that these wetlands are important ecological
resources valuable in controlling erosional effects on the Root
River and in providing a habitat for numerous plant and animal
species. The report noted that several native plant species now
relatively rare in this region exist in the wetlands and
associated forest. Additionally, two State-endangered species,
blue-stemmed goldenrod (Solidaqo caesia) and hop-like sedge
(luDuliformis), were observed near the landfill.
-------
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SEVEN MILE RD,
LEGEND
-... - INTERMITTENT
STREAM
~~::.~.;--~ MARSH AREA
===== DIRT ACCESS
ROAD
SCALE
~' ~90'
DATE
APRIL 1990
REM V
HUNTS DISPOSAL LANDFILL SITE
CALEDONIA, WI
GENERAL SITE FEATURES
FIGU'
1
C.C.JOHNSON & MALHOTRA,P.C.
-------
-
"
i;
LEGEND
fZ]
- 100 -YR FLOOD
ZONE
-666- -100. YR FLOOD
ELEVATION
--- - 51TE BOUNDARY
SCALE
I" II 600'
DATE
MAY 1990
COUNry LINE ROAD
~
N
~
REM V
HUNTS DISPOSAL LANDFILL SITE
CALEDONIA, WI
AREAS SUBJECT TO FLOODING
. TO ROOT RIVER
FIGURE
2
... I ""'f"\:F1A,P.C.
E': . :~~,<1;.~" .""".-.'-'-'-- .
~ \..~:..:.:""(.."." , "<"""".'f-""
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t:.:.<.",.
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-------
i/
4
The site lies in the Root River watershed and much of the site is'
located within the 100-year floodplain of the Root River. The
Root River is a shallow meandering stream which is about 25 to 40
feet wide and abou~ 3 feet deep much of the year. The topography
of the area is flat, except for the landfill which is mounded
approximatelY'15 to 25 feet above the surrounding area.
Approximately 40 homes are located within 1/2 mile of the site.
One mile to the west is a rural community which includes the
Caddy vista School and approximately 150 homes. The community
uses local groundwater as a drinking water source.
II. site History
The HDL site was formerly an abandoned sand and gravel pit that
began operation as an open dump in 1959 following the issuance of
a permit to Harold Itzenhuiser by the Racine County Board of
Adjustments. Mr. Itzenhuiser operated the site until 1962. The
dump reportedly accepted a variety of municipal and chemical
wastes.
By 1961, garbage and rubbish burning in an open pit was observed
at the site. The site was purchased in 1962 by Clayton Hunt, who
operated the landfill until 1971.
In early 1971, the site was purchased by Elmer J. Lauer and
Joseph A. Magestro, Sr.. Shortly thereafter, HDL was renamed the
Caledonia Landfill, and operations were overseen by the Caledonia
Corporation. According to documentation in U.S. EPA and state
files, United Waste Systems and Waste Management of Wisconsin
appear to have participated in the management of the landfill.
In 197~, the Caledonia Town Board adopted a resolution that only
the southern portion of the landfill be utilized.
In 1974, the landfill operating license renewal request was
denied and the site was to have been closed and abandoned
pursuant to existing state regulations. In 1975, the deed to the
landfill property was transferred from Caledonia Corporation to
Boundary Corporation. Elmer Lauer and Joseph Magestro served as
officers in both the Caledonia and Boundary Corporations, and
apparently were also associated with United Waste Systems.
The Wisconsin Department of Natural Resources (WDNR) conducted
several site inspections from 1969 through 1982. During each
inspection, several violations were observed. WNDR made repeated
recommendations to improve landfill operations. WDNR held
several meetings with Waste Management of Wisconsin to discuss
the continuing problems associated with the site. However, the
violations were not remedied, and the license was not renewed in
1974.
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5
Racine County purchased the site in August 1976. The. issue of
proper closure was pursued by Wisconsin authorities from 1976-
1982, with no sucess. In 1982, the Racine County Parks
Department and Waste Management of Wisconsin, Inc. attempted to
cover and reseed portions of the site. These efforts were not
successful.
In 1984, the u.s. EPA field investigation team conducted a
preliminary inspection and site investigation (PA/SI).
Monitoring wells were installed at the site. Ground water,
surface water, soils and sediments were sampled and analyzed.
The results from this preliminary testing revealed that ground
water and soil contamination existed. In 1986, based on the
results of the PA/SI, the WDNR requested that the HDL site be
considered for inclusion on the National Priorities List (NPL).
The HDL site was placed on the NPL on July 21, 1987.
III. Enforcement History
In 1987, approximately eight (8) potentially responsible parties
(PRPs) were notified in writing of their status and were given
the opportunity to conduct a remedial investigation and
feasibility study (RI/FS) under u.s. EPA supervision. After the
PRPs failed to reach agreement with u.s. EPA, a federal-lead
RI/FS was commenced in the fall of 1988. The RI/FS was completed
in July 1990, and a plan outlining u.s. EPA's proposed source
control remedy for the landfill was issued on July 26, 1990.
In August 1990, U.S. EPA sent general notice letters to
approximately sixty (60) PRPs. The general notice letters
informed the PRPs of their potential liability, provided them
with copies of the u.s. EPA's proposed plan, and invited them to
an introductory meeting hosted by the u.s. EPA and the WDNR at
the WDNR's Milwaukee, Wisconsin offices. A number of the PRPs
attended the August 26, 1990, meeting, where they were given an
overview of the results of the RI/FS and the proposed source
control remedy for the site. The PRPs were encouraged by u.s.
EPA and the state to organize themselves and to appoint a
steering committee. 'u.s. EPA has made its files available and
has provided copies of documentation upon request to several
PRPs.
IV. Community Participation
Pursuant to Sections 113(k) and 117 of CERCLA, the Hunts Disposal
Landfill community has participated in the development of the
administrative record and in the remedy selection process, in
that:
-A press release was issued announcing a public "kick-off"
meeting held to inform the community as to u.s. EPA plans for the
RI/FS for the site;
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6
-The public "kickoff" meeting was held in October 1988,
announcing the initiation of the RI/FS;
-A fact sheet was developed and distributed in conjunction with
the October 1988 meeting;
-A fact.sheet was sent to the public and press, updating them on
the progress of the project in November 1989;
-A site information repository was established at the Caledonia
Town Hall to allow local access to site-related documents;
-An administrative record has been compiled, including the RI and
FS reports and other documents, and has been placed in the site
repository at the Caledonia Town Hall;
-A press release announcing the commencement of the public
comment period, the availability of the July 26, 1990, proposed
plan, and the time and place of the July 31, 1990, public meeting
was sent out to the local media and an advertisement was placed
in the Racine Journal Times, a local paper of general
circulation;
-The Proposed Plan for remedial action was released for public
comment and placed into the Administrative Record on July 26,
1990;
-A thirty (30) day comment period was established and scheduled
to end on August 25, 1990;
-A public meeting was held on July 31, 1990, at the Caledonia
Town Hall at which u.s. EPA and WDNR presented the Proposed Plan
to the community and received comments A transcript was kept of
the pUblic meeting and was made available to the public and
placed in the Administrative Record and site repositories;
-A fact sheet was developed and distributed in conjunction with
the July 31, 1990 meeting;
-General notice letters and a copy of the proposed plan were sent
to approximately sixty (60) potentially responsible parties
(PRPs) on August 16, 1990;
-An additional thirty (30) days were added to the comment period,
extending the closing date to September 24, 1990. Advertisements
were placed in the Racine Journal Times announcing the comment
period extension and notice, and notices were issued to the PRPs;
and
-u.s. EPA has received oral and written comments regarding the
RI/FS and Proposed Plan. Significant comments have been
addressed in the Responsiveness Summary as well as by this ROD.
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7
V. Scope of the Selected Remedy
The selected remedy is a source control remedial alternative to
be implemented at the Hunts Disposal Landfill site, encompassing
all currently identified areas of concern at the landfill. The
principal threats identified at the site are considered to be
ground~water contamination, contaminated soil, sediments and
exposed landfill waste materials. The selected remedy addresses
the landfill itself in order to mitigate the threat to human
health and the environment presented by the landfill as a
continuing source of ground-water contamination.
The selected remedy will also include additional investigations
and studies to assist in the design of the remedial action, to
verify hydrogeological and other conditions noted in the Remedial
Investigation, to assess and mitigate impacts of remediatipn
activities on the environment, to assess the nature and extent of
any off-site contaminant migration, and to evaluate the need for
and type of responses to off-site contamination.
VI. Summary of Site Characteristics-Remedial Investiqation
As noted above, the Hunts Disposal Landfill was used for the
disposal of various municipal and industrial wastes. Among the
many different types of municipal and industrial wastes which
were reportedly accepted at the HDL were: waste newspaper ink,
spent solvents, tannery wastes, chromic acids, arsenic acid and
beryllium.
Based upon previous investigations bY the WDNR and the U.S. EPA
and upon available site records, the Remedial Investigation (RI)
was directed at determining the source, nature and extent of
contamination at the site and adjacent areas including:
Surface and subsurface soil and sediments;
Local groundwater; and
Adjacent surface water bodies, the Root River and an
unnamed lake.
The RI consisted of a program of monitoring well installation and
sampling, soil sampling, radiological investigation and surface
water and sediment sampling. site geology and groundwater flow
patterns were examined. The conditions observed are discussed
below.
A. Hvdroqeoloqy
Two aquifers exist in the area of the landfill. The landfill is
situated in an upper sand and gravel aquifer, which extends
approximately 25 to 35 feet below ground surface. A second
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8
aquifer, comprised of
formation, is located
limestone unit serves
area residents.
dolomitic limestone of the "Niagara"
beneath the sand and gravel unit. This
as the source of drinking water for local
Region~lly, the two aquifers have been found to be hydraulically
connect~d. However, a fine grained clay-till-silt layer has been
noted between the upper and lower aquifers in certain localities,
including in the area of the landfill. This clay-till layer may
serve as a barrier to groundwater flow from the upper. to the
lower unit. Based upon the RI, this clay-till layer appears to
be present beneath the landfill, althou~h its continuity must be
confirmed for the entire landfill area.
Based on observed hydraulic gradients in the upper aquifer in the
vicinity of the landfill, ground water appears to flow towards
the southwest, and discharges from the landfill to the Root
River. Groundwater flow in the limestone aquifer was not
delineated in the RI. Groundwater on the other side of the Root
River also appears to flow into the river.
B.
Source and Nature of Contamination
/ \
The total landfill volume is estimated at 788,000 cubic yards.
The total waste volume is estimated at 620,000 cubic yards. Of
this, it is estimated that 168,000 cubic yards of waste are below
the water table.
The landfill has been and is currently acting as a source of
contamination to the ground water, surface water, sediments and
soil around the landfill. Water level measurements indicate that
some of the wastes in the landfill are below the water table,
thus providing a continuing source of ground water contamination.
Ground water is the primary migration pathway for contaminants at
the site. Leachate is produced by precipitation infiltrating
through the eroded cap of the landfill, as well as by groundwater
passing through the wastes located beneath the water table,
causing contaminants to be released from the waste mass into the
ground water. Leachate also migrates from the waste mass to
2 The existence and continuity of the clay-till-silt layer
is an essential component of the selected remedy, since, if
continuous, it would serve as a barrier to leachate miqration
from the upper to the lower aquifer. The continuity of the
layer, as well as the interaction between the Root River and
qroundwater flow direction/reqime, potential contaminant plumes,
and other conditions, will be assessed and verified durinq
investiqations and studies to be conducted as part of the
selected remedy.
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9
adjacent surface soils, sediments and water bodies, especially
during periods of high precipitation and flooding.
Particulate contaminants derived from exposed wastes may be blown
by the wind or carried by runoff into surrounding soils and
sedime~ts. Additionally, landfill gases such as methane and
vinyl chloride are being generated within the landfill waste
mass.
C'::;;1'...c..;;.i1~a.nt.i:;o ~c;"i:;.;;';'...<;;;~ ~;"~:'::'1'~ :':'he RI inclu.u.t: 'vu~,n:.il~ organic
compounds (VOCs), semivolatile organics (including polycyclic
aromatic hydrocarbons [PAHs] and polychlorinated biphenyls
[PCBs]) and inorganics (metals). The highest concentrations of
soil and sediment contamination detected outside the landfill are
located between the southwest edge of the landfill and Root
River, at the southern tip of the landfill and at the northern
edge of the landfill, adjacent to the lake.
The highest degree of ground water contamination was found
between the landfill and the Root River and along the southern
tip of the landfill. Based upon the RI and as noted above, it is
assumed that this contaminated ground water flows into the Root
River and is diluted below levels of concern.
A total of seventeen private wells were sampled as part of the
RI. The locations of the private wells are shown in Figure 3.
Based on the results of the RI, private residential wells do not
appear to be affected by contaminants from the landfill.3
i. Inorganic contaminants
The predominant inorganic contaminants of concern include
arsenic, chromium, barium, manganese and nickel, based upon
potential impacts to human health and the environment.
Concentration ranges for these chemicals in the various
environmental media are presented in Table 1.
ii. Organic Contaminants
The predominant organic contaminants of concern include vinyl
chloride, trichloroethene, 1,1-dichloroethane, 1,1-
dichloroethene, 1,2-dichloroethane, benzene, napthalene and
xylenes, based upon potential impacts to human health and the
environment. Concentration ranges for these chemicals in the
various environmental media are given in Table 1.
3 Monitoring of residential wells will be conducted as part
of the selected remedy to provide continuing verification of
these results.
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8 RW-9
14~'
. - RESIDENTIAL WELL
lOCATION AND WELL
DEPTH
'.
RW~I ..
220 RW-2
145'
COUNTY LINE RD,
. RW-6
150'
.#
z
- .8RW-8
~ 220'
o
r
en
o
z
~
N
~
::u . RW-II
o 8 RW.IO
. MAPLE DR. 200
RW-13.
100'
~
r
r
~
::u
o
"'II
o
r
JTI
~
.
RW-17
. RW- 3, 127'
. RW"'14, 182'
. RW-12, 196'
. RW-16
8 RW- 4, 100'
o
:u
:u
o . RW-7
. 110'
,m
,m
SEVEN MILE RD.
DATE
APR'l
REM V
HUNTS DISPOSAL LANDF'LL SITE
CALEDONIA, WI .
FIGURE
SCALE
o' I pori
I I
3
30
RESIDENTIAL WE'
'SAMPLE
LOCATIONS
C.C.JQJ-tNSON & MALHOTRA.P.C.
-------
uq/kq
51-1500
Trichloroethene 3-140 .5-39 4-5
1,1-dichloro- 0.7-15 390
ethane
1,1-dichloro- 8
ethene
1,2-dichloro- 62-630 3-80 .3-18
ethene
Benzene 0.8-15 13-41
Naphthalene 1-50
Xylene 49-290
v
ComDound
Inorqanics
Arsenic
Chromium
Barium
Manganese
Nickel
Orqanics
Vinyl
Chloride
11
TABLE 1
ANALYTICAL RESULTS-CONCENTRATION RANGES OF
PRIMARY CONTAMINANTS OF CONCERN
Sediments
ua/l
Surface Subsur-
Soil face Soil
ma/kg ma/ka
GW
ua/l
SW
mg/ka
ND-19.0 1.7-8.5 1.1-25.3 1.2-14.4
ND-22.6 14.5-18.4 .7-165 3.4-22.8
121-2460 21. 5-296 9.8-441
17-7870 12.3-6670 83.7-1390
ND-40.5 15.6-19.1 5.7-129 4.4-36.6
0.9-21.2
4.5-38.0
5.1-37.3
uq/l
0.7-120
uq/l
uq/kq
uq/kq
2-100
50-100
GW-Groundwater
SW-Surface Water
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12
VII. SUMMARY OF SITE RISKS
Pursuant to CERCLA and the NCP, a baseline risk assessment was
performed based on unaltered conditions at the site, as
contemplated by the no-action alternative (see Section 5 of the
RIReport). The no-action alternative assumes that no corrective
action "will take place and that no site use restrictions, such as
fencing, zoning and drinking water restrictions will be imposed.
The risk assessment then determines actual or potential risks or
toxic effects posed by the chemical contaminants at the site
under current and feasible future land-use assumptions. As
described in the RI report, the following baseline assumptions
were made for determination of current risk:
No remedial actions will be taken;
No development of the landfill itself will occur due to
State restrictions (CH. NR 506.08(5), WAC);
No potential industrial, commercial or residential
development will occur on site; and
Groundwater contaminant concentrations will not
decrease significantly over time as continual
contaminant loading to the groundwater would occur, due
to the continued leaching of contaminants from the
waste mass into the groundwater and surrounding areas.
A. Chemicals of Concern and Toxicitv Assessment
Water, soil and sediment samples were analyzed for chemicals on
the u.s. EPA Target Compound List (TCL) and Target Analyte List
(TAL). As discussed in the RI Report, the risk assessment
identified a number of indicator chemicals of concern (see
section 6 of the RI report for a complete list of chemicals of
concern). The primary contaminants of concern are listed above
in Table 1.
The inclusion of each chemical of concern was based on its
relative concentration, frequency of detection, and toxic
effects, as well as whether an environmental standard or criteria
(such as Federal drinking-water standards) exists for the
chemical. Inclusion of a compound on the list of chemicals of
concern indicates remedial controls that may be applied to a site
should mitigate migration and exposure to the compound from
contact with groundwater, soil, surface water and sediments.
The chemicals of concern are classified as non-carcinogens, or as
potential or known human carcinogens (cancer-causing agents) .
Additionally, acute (short-term at high concentrations) or
chronic (long-term at low concentrations) exposure to each of the
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v
13
chemicals of concern can lead to various toxic effects (see
Section 6.4 of the RI Report).
B. Human Health Exposure Pathways
The following exposure pathways have been identified as being
potential or actual exposure pathways of primary concern for
protection of human health at the Hunts Disposal Landfill site:
Inhalation, ingestion/and or dermal contact with
surface waters, soils, sediments, or exposed wastes due
to.persons accessing the site, the Root River and on-
site lake;
Inhalation of landfill gases by persons accessing the
site; and
Use of contaminated groundwater for drinking, bathing,
and other household uses.
1. Groundwater Use
As noted above, the intermediate dolomite or "Niagara Aquifer",
is the primary water source for private wells including private
residential wells near the HDL site. A total of 17 residential
wells, using water from the dolomite aquifer for drinking water,
were sampled during the RI. The locations of these wells are
given in Figure 3. The closest residential wells are located
cross-gradient to the movement of groundwater in the immediate
vicinity of the HDL site. The sampling results do not indicate
contamination of the residential well supply that can be
attributed to the landfill.
The dolomite aquifer lies beneath the water table aquifer. It is
unlikely that the dolomite aquifer would be adversely affected by
landfill contaminants, based on the assumption that the low
permeability clay-rich silt-till layer continuously underlies the
water table aquifer. If so, vertical migration of contaminants
to the dolomite aquifer would not be expected to be significant.
A lower sandstone aquifer is an important regional source of
groundwater. A shale aquitard forms a barrier that impedes flow
between the dolomite aquifer and the underlying sandstone
aquifer.
2. Landfill Waste Materials
The highly permeable nature and erosion of the original cover
material aid in groundwater contamination by providing conduits
for infiltration of precipitation into the landfill mass.
Precipitation filters through the landfill waste materials and
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14
causes contaminants to leach out of the waste and into soils,
surface waters and groundwater.
The airborne pathway is not expected to be of concern off-site
due to atmospheric dispersion prior to reaching the nearest
residence (1000 feet away). However, the potential for
significant on-site risk due to inhalation of airborne
particulate soils/waste exists. Given the current rate of
erosion, it is possible that waste materials and/or contaminants
would be exposed in the future, contributing to increase loading
to the airborne pathway.
3. Surface Water
The local surface water bodies associated with the site represent
potential routes for contaminant migration from the site.
Contaminants which are discharging via groundwater and/or surface
runoff into the river have the potential to migrate off-site and
possibly reach populated areas. There is also indication that
contaminants from the landfill are migrating, through the
groundwater or surface runoff, into the on-site lake and
surrounding wetlands. After reaching the lake, contaminants
could potentially flow into the Root River through the culvert
which drains the lake.
C. Risk Pathwavs and Calculations for Human Health Exposure
Using data generated during the RI, U.S. EPA conducted a site-
specific baseline risk assessment to characterize the current and
potential threats to human health and the environment posed by
site contaminants. Generally, the individual and cumulative
threats posed by contaminant migration into groundwater, air,
soil, surface water or bioaccumulation in the food chain are
evaluated in the risk assessment. The results of the risk
assessment establish acceptable exposure levels for the Chemicals
of Concern, which are then used to develop remedial alternatives
in the FS.
Toxic substances may pose certain types of hazards to human
and/or animal populations. Typically, hazards to human health
are expressed as carcinogenic ri~ks and non-carcinogenic toxic
effects.
Carcinogenic risk, numerically presented as an exponential factor.
(e.g., 1 x 10-6), is the increased chance a person may have in
contracting cancer in his or her lifetime due to exposure to a
Chemical of Concern over his or her lifetime. For example, a 1 x
10-6 risk due to a lifetime of drinking water with a Chemical of
Concern in it means that a person's chance of contracting cancer
due to drinking the water over his/her lifetime is increased by 1
in 1 million. The U.S. EPA attempts to reduce risks at Superfund
sites to a range of 1 x 10-4 to 1 X 10-6 (1 in 10,000 to 1 in 1
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u
15
million), with an emphasis on the lower end (1 x 10-6) of the
scale.
The Hazard Index, an expression of non-carcinogenic toxic
effects, measures whether a person is being exposed to adverse
levels of non-carc'inogens. Any hazard index value greater than
1.0 suggests that a non-carcinogen potentially presents an
unacceptable toxic effect.
1. Groundwater
Current exposure to groundwater contamination is not expected to
occur, since residential wells are located upgradient or in areas
most likely not affected by site conditions and the contaminated
groundwater appears to discharge from the landfill to the nearby
Root River. However, risks from future exposure to site-affected
groundwater do exist, and thus were determined for potential
future land use.
The standard risk assessment assumption that an individual,
weighing 70 kilograms (154 pounds) and ingesting contaminated
groundwater at the rate of 2 liters per day for his or her 70-
year lifetime was used to determine the potential risks. The
total carcinogenic risk for adults for future use of site-
affected groundwater is 1 x 10-3. The lifetime excess
carcinogenic risk (LECR) for inhalation, ingestion and dermal
contact are 3 x 10.4, 1 X 10-3 and 3 x 10.6 respectively.
Thus, the groundwater contamination is a principal threat, since
the potential total future carcinogenic risk at the site from
groundwater contamination (1 x 10.3) exceeds the target
carcinogenic risk range that the NCP considers to be adequately
protective (1 X 10-4 to 1 x 10-6) . Table 2 lists contaminants
that exceeded an LECR of 1 x 10.6 and the associated risks due to
exposure.
2. Soils and Landfill Waste Materials
The risks posed by ingestion of contaminated soil or the landfill
waste materials were calculated based on standard ingestion rates
for soil: over a 30-year time period a 70-kg individual may visit
the site once per week and accidentally ingest 0.1 grams of soil
per visit. Dermal absorption of contaminants from soil was based
on standard dermal exposure for soil.,: over a 30-year time period
a 70-kg individual visits the site 170 days out of a year and
dermal contact with the soil is made with the hands. Inhalation
risks were calculated based on the standard model: over a 30-year
time period a 70-kg adult visits the site 110 days of the year
for a 2 hour period each visit. The risks from exposure to soil
and landfill waste were calculated for the on-site area as a
whole.
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16
Inhalation of exposed landfill waste materials and contaminated
soils poses the principal soil/waste current threat. Cap erosion
could expose additional landfill waste materials and soils which
would pose greater unacceptable hazards to human health and/or
the environment in the future.
Under the present exposure scenario for surface soil and exposed
waste, periodic trespass on-site was assumed, which resulted in a
carcinogenic risk of 3 x 10-4 and a Hazard Index of 3.64. Based
on this risk, it has been determined that waste and contaminated
soil are media of concern. Table 3 lists the waste/soil risks
present at the site.
Table 2
Summary of Groundwater Risks
Hunts Disposal Landfill
Excess
Carcinoqenic Hazard
Contaminant Exposure Risk Index
vinyl ingestion 1 x 10-3
chlorideq inhalation 2 x 10-4
dermal 2 x 10-6
chromium inhalation 2 x 10-5
arsenic inhalation 2 x 10-5
ingestion 0.11
nickel inhalation 1 x 10-5
ingestion 0.29
1,1- inhalation 1 x 10-5
dichloro- ingestion 4 x 10-6 0.34
ethene
trichloro- inhalation 4 x 10-6
ethene ingestion 3 x 10-6
benzene inhalation 4 x 10-6
ingestion 3 x 10-6
1,1- ingestion 4 x 10-6 less than
dichloro- 0.1
ethane
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17
Table 3
Summary of Soil and Landfill Waste Materials Risks
Hunts Disposal Landfill
contaminant Exposure
Chromium inhalation
Arsenic inhalation
Nickel inhalation
Cadium inhalation
Manganese inhalation
Excess
Carcinoqenic
Risk
2 x 10'4
Hazard
Index
6 x 10-5
4 X 10'6
1 X 10.6
3.2
Surface Water and Sediments
3.
The groundwater in the vicinity of the landfill is apparently
discharging to the Root River. It also appears that contaminants
from the landfill are migrating into the on-site lake through
groundwater. contaminants are also released to the surface water
bodies through surface runoff and from leachate.
Under the present exposure scenario for surface water and
sediment, periodic trespass on-site was assumed, which resulted
in an excess carcinogenic risk of 6 x 10-6 and a Hazard Index of
0.08. Surface water and sediments at the site are thus
considered a low-level threat to humans.
D. Environmental/Ecoloqical Analvsis
A qualitative environmental/ecological assessment for the
Disposal Landfill site was prepared. The site is located
near agricultural fields, small tracts of hardwood forest
wetlands, the Root River and a lake.
Hunts
on and
land,
An exposure pathway determined to be of significance to the
environmental risk analysis was to aquatic life which is actually
or potentially exposed to the chemicals detected in soils and
surface water. Potentially exposed populations identified in the
environmental/ecological assessment are identified below.
1. Terrestrial Plants
Terrestrial plants may be exposed to contaminants in the surface
soils. Chemical concentrations found at the site could be high
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18
enough to cause sublethal effects (e.g. reduced growth)
plants or death in sensitive species.
in some
2. Terrestrial Wildlife
The evaluation of potential exposures is limited to an evaluation
of potential impacts associated with ingestion of surface water
and contaminated food. The on-site lake, wetlands and Root River
could be used as a drinking water source by some terrestrial
species. At least one species likely to be exposed via drinking
water is deer. The occasional use of surface waters ~or drinking
water by other species is not expected to result in significant
exposure. 4
To evaluate potential impacts in deer, it is assumed that a deer
obtains one-third of its drinking water from surface water on or
downgradient of the site. Drinking water limits for deer were
estimated using recommended drinki~g water limits for livestock
reported by the National Academy of Sciences in 1974, as
described in the RI report. Surface water concentrations are
below the drinking water limits. Therefore, it appears that deer
are not presently at an increased risk.
Of the chemicals detected at the site, PCBs and DDE are known to
accumulate to a significant degree in plants or animals. PCBs
and DDE can cause a variety of sublethal toxic effects in
wildlife species. Because the size of the area contaminated with
these compounds appears to be small, significant impacts to the
wildlife community would not be expected under present
conditions.
3. Aquatic Life
Risks to aquatic life in the on-site lake, wetlands and the Root
River were evaluated based on exposure through direct contact
with contaminated water and sediments.
Surface water impacts were evaluated by comparing estimated
exposure concentrations with Wisconsin State aquatic life
toxicity criteria and U.S. EPA ambient water quality criteria for
the protection of aquatic life, as described in the RI report.
4 It is unclear whether barren areas noted on the landfill
are attributable to erosion or due to contaminant or landfill gas
stress. Furthermore, unquantified effects on individual plant
species could be occurring. Several native plants now uncommon
to the region have been noted in the immediate vicinity of the
landfill, as well as two endangered plant species. Further
investigation and study of the site impacts and the remedy's
impacts on terrestrial plants may be required as part of the
selected remedy.
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19
Several chemicals in on-site surface water and located in surface
water downgradient of the site exceed one or more of these
standards. Of the contaminants of concern at the site, estimated
surface water concentrations of copper, lead, chromium and zinc
exceed the state and/or federal standards both in on-site waters
and downgradient waters (see RI surface water data and table 6-18
of the-F-S).
Estimated groundwater concentrations of cyanide, PCBs and nickel
exceed chronic aquatic life toxicity criteria (see RI groundwater
data and table 6-19 of FS). The release of these three compounds
from groundwater to surface water is not currently thought to be
causing significant impacts to aquatic life due to the limited
known occurrence of the three compounds and dilution effects.
A comparison of the concentrations with the standards indicate
that aquatic life may be adversely affected by chemicals in the
surface water and groundwater at the site. Chemicals released
through surface runoff or in leachate are a significant source of
surface water contamination. Aquatic life impacts are likely to
be greatest in the shallow wetlands adjacent to the landfill and
in the near-shore areas of the lake and river where the dilution
of chemicals is limited.
State or federal standards similar to State and federal surface
water quality criteria have not been developed for sediments.
Therefore, potential impacts associated with sediment
contaminants at the site were assessed by comparing measured
concentrations with sediment toxicity information derived from
laboratory and/or field studies. Based on comparisons to limited
information derived from sediment toxicity literature, the RI
found that no significant adverse impacts to aquatic life from
sediment appear to be occurring from PAHs, copper, lead or zinc.
Literature on other contaminants of concern could not be located
or does not exist.
VIII. Rationale for Action
The u.S. EPA considers several sources of information in
determining whether or not to take action at a site. Based on
the data gathered in the RI, the u.S. EPA performs a risk
assessment to determine if adverse health conditions currently or
potentially threaten human health and/or the environment. The
u.S. EPA also evaluates site conditions in relation to Federal
and State environmental statutes and policies, in addition to the
statutory mandates promulgated in CERCLA and the goals and
expectations identified in the NCP. The primary criteria with
respect to the Hunts Disposal Landfill site are presented below.
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20
A. Risk Summary
Total lifetime excess carcinogenic risk by exposure route are
estimated to be:
ingestion - 1 x 10.3
inhalation - 6 x 10-4
dermal contact - 9 x 10-6
The two major environmental media contributing to the total
excess carcinogenic risk are:
groundwater - 1. 3 X 10-3
surface soil and exposed waste - 3.6 X 10-4
These potential risks exceed the acceptable risk range of. 1 x 10.
4 to 1 X 10-6, and thus present unacceptable potential risks to
human health. .
Hazard indices for contaminants of concern are listed in Tables 2
and 3 of this ROD. The total current HI for the HDL site is
estimated to be greater than 1. The total future use HI is also
estimated to be greater than 1. U.S. EPA considers HI's above 1
to be unacceptable.5
B. Environmental Standards Not Met at the Site
In addition to posing unacceptable risks to receptors, the Hunts
Disposal Landfill does not meet certain applicable or relevant
and appropriate Federal or State environmental standards at this
time.
1. Cap
The existing landfill cap does not meet the requirements of Ch.
NR 506.08 and Ch. NR 504.07, WAC, the current state solid waste
landfill closure requirements which have been determined to be
ARARs for the site.
2. Groundwater
The shallow groundwater zone under the landfill contains levels
of volatile organics and metals exceeding ARARs, including State
groundwater quality standards and Federal drinking-water
standards. The locations and concentrations of contaminants
exceeding groundwater standards are shown on Figure 4.
5 The total chronic non-carcinogenic adult current HI is
1.14; the future use HI is 5.3 for groundwater. Sub-chronic
non-carcinogenic risk for adult groundwater future use is 3.2;
for children it is 11.4.
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21
C. Summary
Actual or threatened releases of hazardous substances are
occurring from this site. If not addressed, these releases may
present an imminent and substantial endangerment to public
health, welfare or the environment. Thus, it is necessary that
corrective and mitigative action be taken to address the threats
posed by the releases.
A Feasibility study (FS) was performed to develope alternatives
to address the principal and low-level threats at the site. The
FS report documents the evaluation of the magnitude of site
risks, site-specific applicable or relevant and appropriate
requirements (ARARs) and the requirements of CERCLA and the NCP.
In summary, the goals of the proposed remedial alternatives were
to:6
1)
Reduce precipitation and groundwater infiltration and
movement through the landfill and landfill wastes,
which would reduce leaching of contaminants into the
groundwater;
2)
Reduce the levels of hazardous contaminants migrating
from the landfill waste and discharging to surrounding
soils and surface waters, including the Root River, the
lake and nearby wetlands; and
3)
Reduce potential exposures to contaminated soil and
sediments.
IX. Description of Alternatives
This response action addresses the landfill area and adjacent
contaminated areas. Groundwater contamination, the landfill
wastes, and contaminated soils are the principal threats at the
site. Different remedial alternatives were evaluated to address
the principal and low-level threats at the site. The
alternatives passing the initial screening and considered for
detailed analysis in the FS are presented below.
Although the NCP reaffirms CERCLA's preference for permanent
solutions to Superfund site problems through the use of treatment
technologies, the preamble to the NCP contemplates that many
remedial alternatives may be impractical for certain sites due to
severe implementability problems or prohibitive costs. In the
case of HDL, excavation and treatment of the contents of such a
large, heterogeneous landfill would be impractical. The
6 See Chapter 2 of the FS for a discussion and listing of
the remedial action goals.
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22
Feasibility study (FS) was thus directed
containment and/or removal and treatment
groundwater rather than treatment of the
alternatives analyzed were as follows:7
at studying options for
of contaminated
landfill contents. The
-1:
No Action;
-3:
Multilayer cap and groundwater monitoring;
-4a: Multimedia cap, full slurry wall, excavate and
consolidate contaminated soil and sediment, off-site
groundwater treatment and groundwater monitoring, gas
extraction and treatment;
-4b: Multilayer cap, full slurry wall, excavate and
consolidate contaminated soil and sediment, groundwater
monitoring and off-site treatment, gas extraction and
treatment; .
-5a: Multimedia cap, partial slurry wall, excavate and
consolidate contaminated soil and sediment, on-site
groundwater treatment and groundwater monitoring, gas
extraction and treatment; and
-5b: Multilayer cap, partial slurry wall, excavate and
consolidate contaminated soil and sediment, on-site
groundwater treatment and groundwater monitoring, gas
extraction and treatment.
Components Common to All Alternatives
Each of the alternatives analyzed, with the exception of the no-
action alternative, include fencing and administrative and
institutional controls. A galvanized steel chain-link type of
fence would be installed around the perimeter of the property.
Institutional controls would include deed restrictions and/or
other mechanisms to limit the use of the HDL property, such as
prohibitions on well installation and construction.
Each of alternatives 3-5b include a landfill cap. The entire
Hunts Disposal site, except the top portion of the landfill, lies
within a lOO-year floodplain. Therefore, the selected remedy
7 Alternative 2 (Minimal Controls): Under this
alternative, only fence installation, groundwater monitoring, and
deed restrictions would be implemented. Since, at the outset,
this does not meet ARARs and remedial action goals, it was
eliminated from further consideration and was not analyzed. only
those alternatives which underwent detailed analysis are included
in this discussion.
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~
C(~J ~~~
.\
.'" ,.v: . ,..1.1
~~&:.;".:~:...
1~ ew.......,....... (let'"
..."'..--
1-
'" 01"''''..'''..
SCAL.E
o 300'
.. ~
REM V
HUNTS DISPOSAL LANDFILL SITE
CALEDONIA, WI
LOCATIONS WHERE GROUNDWATER
CONTAMINANTS EXCEED ARARs
OATE
MAY 1990
I
...........
.~
FIGURE
4
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24
will include measures to protect the cap and the other
of the remedy from the potentially damaging velocities
effects of the Root River flood waters both during and
construction.
components
and
after
Such measures must, at a minimum, be sufficient to prevent
erosion.'- and disruption of the cap. This would consist of
construction of a low permeability barrier, such as a clay levee,
around the perimeter of the cap. Clay material would be used as
fill to bring the levee to two feet above the 100-year floodplain
elevation. The top of the levee would be approximately 20 feet
wide to provide a level working surface for construction
activities. The side slopes of the levee would be overlain by a
geotextile mat to limit soil erosion. The mat would be overlain
by one foot of rip-rap to reduce the velocity effects of the
flood waters. The design of the low permeability barrier will
take into account potential detrimental effects on integrity of
the cap and impacts on the floodplain, wetlands, woods and
surrounding areas.
An active landfill gas collection system would be included for
each of the alternatives which includes a cap. The purpose of
the system would be to maintain the integrity of the cap by
relieving gas pressures from within the landfill and to extract
methane and other gases being emitted from the landfill for
treatment. The system would consist of the installation of gas
collection wells in the landfill to a depth of about twenty feet.
The gases would be extracted from the landfill and combusted to
form carbon dioxide and water vapor. The actual number of gas
collection wells and the size of the combustion facility would be
determined during remedial design.
In Alternatives 4a-Sb, the groundwater extraction and treatment
systems would be operated until MCLs or Wisconsin Groundwater
Quality Standards are met. The total time estimated required to
meet this goal would be a minimum of 30 years.
A description of the components of the alternatives is provided
below.
A. Alternative 1: No action
Under the no action alternative, no active response would occur.
This alternative does nothing to protect public health and the
environment. Under present conditions, the landfill will
continue to deteriorate because the landfill slopes are eroded
and are releasing contaminants to the surface and subsurface
environments. Rates of contaminant release are likely to
increase in the future. Future health risks would
correspondingly increase. The no action alternative serves as a
baseline against which all other alternatives are compared.
There are no costs associated with this alternative.
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25
B. Alternative 3: Multilaver Cap and Groundwater Monitorinq
Under Alternative 3, a new multilayer cap which meets the
requirements of Ch. NR 504.07, WAC would be installed over the
landfill. The total area of the proposed cap would be
approximately 35 acres. The multilayer cap would consist of
(from bottom to top) a minimum 2-foot compacted clay barrier
layer, and a frost-protection layer consisting of a
2 foot soil layer, and a minimum 6-inch topsoil layer with
surface vegetation. The estimated volume of wastes under the cap
would be 788,000 cubic yards. Approximately 60 million gallons
of contaminated groundwater would remain under the site.
Additionally, groundwater would continue to move through the
wastes and become contaminated.
The current risks associated with landfill contaminant exposure
would be reduced relative to Alternative 1. The multilayer cap
is projected to reduce the rate of precipitation by at least 50
to 70 percent in comparison to Alternative 1, reducing the
potential for migration of contaminants towards the groundwater.
site operation and maintenance would consist of grass cutting,
regular inspections and repair of damaged areas of the cap.
Alternative 3 would take approximately 7 months to construct.
The capital cost is $6,582,000 and the Operation and Maintenance
cost is $84,300 per year. The present worth cost is projected at
$7,452,000.
C. Alternative 4a: Multimedia Cap. Full Slurry Wall. Excavate
and Consolidate contaminated Soil and Sediment. Off-site
Groundwater Treatment. Groundwater Monitorinq
Under Alternative 4a, the contaminant sources contributing to the
groundwater contamination would be contained by a full slurry
wall and multimedia cap. A cement-bentonite slurry wall would
encircle the landfill, tieing into the surface cap above the
landfill and the silt and clay layer beneath the site.
Groundwater outside of the slurry wall, which is apparently
discharging to the Root River at present, would be allowed to
continue to discharge at acceptable levels (i.e. below one or
more of: Water Quality Criteria (WQC), drinking water standards
(MCLs), and/or groundwater quality standards-see section XII(B».
The cap is constructed of the same components as in Alternative 3
with the addition of a synthetic membrane located between the
clay layer and the cover soil layer. The synthetic membrane
serves as an added barrier to infiltration, reducing it by nearly
90 percent relative to Alternative 1, thereby reducing the
continued leaching of contaminants to the groundwater.
Approximately 60 million gallons of contaminated groundwater are
contained within and beneath the landfill. A groundwater
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26
extraction system consisting of gradient control wells would be
installed inside the landfill/slurry wall area. The gradient
control wells would establish an inward flow of water into the
landfill and provide for the extraction and treatment of
groundwater from within the landfill. The extraction wells would
extract approximately 3 gallons per minute (GPM) of contaminated
groundwater from within the landfill, the equivalent of 3800
gallons per day. Extracted water would be treated and disposed
of at an off-site facility. Treatment will be to the appropriate
Federal or state standards, depending on the location and type of
the off-site treatment facility.
Risks due to the potential ingestion of contaminated groundwater
located beneath the landfill are not projected to decrease as
continual contaminant loading to the groundwater under the
landfill would occur, since the source of groundwater
contamination would remain in place. Thus, the groundwater
extraction system would be operational until groundwater under
the landfill meets groundwater cleanup standards (Chap. NR 140
Wisconsin Groundwater Quality standards or Federal drinking water
standards) .
soil along the west, south and east perimeter of the landfill and
sediments in two ditches flowing south from the landfill to the
Root River (see Figure 5) containing concentrations of
contaminants in excess of 10-6 carcinogenic rate concentrations,
exceeding background concentrations, or exceeding yet to-be-
determined clean-up levels (based on consideration of risk levels
and background concentrations), would be excavated and
consolidated on the landfill prior to capping.
The volume of soil and sediment to be consolidated would be
approximately 5300 cubic yards. Any wetlands areas destroyed as
a result of the remedial action would be replaced in a suitable
location. The excavated areas, outside the wetlands, would be
backfilled with suitable off-site material and vegetated.
Wetland areas southeast and south of the landfill would be
impacted during the slurry wall construction phase.
Approximately 3.3 acres of wetlands could potentially be
destroyed by slurry wall construction. The wetland area would
either have to be restored to its original condition or replaced
with additional enhanced wetland areas in suitable locations.
Alternative 4a would take up to 2 years to construct the cap and
slurry wall. The capital cost is $15,964,000 and the Operation
and Maintenance cost is $375,000 per year. The present worth
cost is projected to be $19,494,000.
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~
N
\
LAKE
66
)
LEGEND
REA OF SOIL /
SEDIMEHTS TO BE
REMEDIATED *
- - -LANDFILL BOUNDARY*
--- PROPERTY BOUNDARY*
*Approximated
'.
I SCALE,
9 2~
DATE
JULY 1990
REM V
HUNTS DisPOSAL LANDFill SITE
CALEDON lA, WI
APPRoxYtaAtED AREA OF SOIL /
SEDIMENTS TO BE REMEDIATED
MALHOTRA,P.C.
FIGURE
5
,.. ,.. ''"'1-1'''<::1''1'''' A
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28
D.
Alternative 4b: Multilayer Cap. Full Slurry Wa11. Excavate
and Consolidate Contaminated Soil and Sediment. Off-site
Groundwater Treatment and Groundwater Monitoring
This alternative is identical to Alternative 4a except that under
Altern~t~ve 4b, a new multilayer cap would be constructed instead
of the multimedia cap in 4a. The multilayer cap would meet Ch.
NR 504.07, WAC requirements. The cap would be constructed of the
same materials as described in Alternative 3. As above, the rate
of precipitation infiltration would be reduced by at ~east 50 to
70 percent in comparison to the No Action Alternative. The
multilayer cap would allow more infiltration. to enter the
landfill. Due to the greater infiltration, slightly more
groundwater would need to be pumped in order to maintain inward
groundwater gradients. Accordingly, a greater volume of
groundwater would also need to be treated. However, significant
cost savings would be realized due to the elimination of the
synthetic membrane.
This alternative is estimated to take two years for construction
of the cap and slurry wall. The capital cost is $13,924,000 with
Operation and Maintenance costs of $375,000 per year. The
projected present worth cost is $17,454,000.
E.
Alternative 5a: MUltimedia Cap. Partial Slurry Wall.
Excavate Consolidate Contaminated Soil and Sediment. On-site
Groundwater Treatment and Monitoring
Under Alternative 5a, groundwater extraction wells would be
stationed along the downgradient edge of a partial slurry wall.
The open portion of the slurry wall would be located between the
southeast corner of the lake extending approximately 1000 feet
south. The extraction wells would pull the groundwater from the
upgradient (open portion of the slurry wall) end of the landfill
and pull this water through the waste material. Extracted
groundwater would be treated on-site. Treated groundwater would
be discharged to the Root River.
A series of extraction wells would be constructed to remove
contaminated groundwater at an approximate rate of 420 GPM from
beneath the landfill. Since the quantity of groundwater pumped
would be much greater than in Alternative 4a or 4b, the
groundwater treatment system would be built on-site. Treatment
of the contaminated water would consist of equalization,
flocculation and filtration, air stripping and carbon adsorption
prior to discharge to the Root River in compliance with the
substantive requirements of an WPDES permit, in accordance with
Chaps. NR 105 and 106, WAC. Sludge produced from the treatment
process would be disposed of at an appropriate facility.
Alternative 5a would take two years for the construction of the
cap and partial slurry wall. The capital cost is $15,596,000 and
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29
the Operation and Maintenance cost is $536,000 per year.
total present worth cost is projected to be $20,656,000.
The
F.
Alternative 5b: Multilayer CaD. Partial Slurry Wall.
Excavate and Consolidate Contaminated Soil and Sediment,
On-site Groundwater Treatment and Groundwater Monitorinq
Alternative 5b is identical to 5a except that a multilayer cap
will be used instead of a multimedia cap described in 5a. The
groundwater extraction and treatment system and partial slurry
wall described in 5a would be implemented.
Alternative 5b would require 7 months for construction of the
partial slurry wall and 2 years for cap construction. The
capital cost is $13,581,000 and the Operation and Maintenance
cost is $536,000 per year. The present worth is projected to be
$18,641,000.
X. ComDarative Analysis of Alternatives: The Nine criteria
In accordance with the NCP, the relative performance of each
alternative is evaluated using the nine criteria (Section
300.430(e) (9) (iii) as a basis for comparison. An alternative
providing the "best balance" of tradeoffs with respect to the
nine criteria is determined from this evaluation.
A. Threshold criteria
1. Overall Protection of Human Health and the Environment
Overall protection of human health and the environment addresses
whether a remedy eliminates, reduces or controls threats to human
health and the environment through treatment, engineering methods
or institutional controls. The major exposure pathways of
concern at the Hunts Disposal Landfill site are contaminated
groundwater and inhalation of particulate matter from soil and
waste at the site. Based on these pathways of concern, the
alternatives were evaluated on their ability to:
Reduce precipitation and groundwater infiltration and
movement through the landfill and landfill wastes,
which would reduce the leaching of contaminants into
the groundwater;
Reduce the levels of hazardous contaminants migrating
from the landfill waste and discharging to surrounding
soils and surface waters, including the Root River, the
lake and nearby wetlands; and
Reduce potential exposures to contaminated soil and
sediments.
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30
Alternative 1, No Action, does not provide adequate protection of
human health and the environment since, under existing
conditions, the landfill would continue to deteriorate and the
rates of contaminant release are projected to increase with time.
Presently, there are deficiencies in the final cover and top soil
depths, severe gully erosion on some of the slopes, an absence of
vegetative cover over portions of the landfill, and landfill
wastes are exposed.
The present landfill cover is constructed of a high permeability
soil. The maintenance of a low permeability cap over time is
critical with respect to both direct contact exposure of wastes
by human and environmental receptors, as well as protection of
the groundwater through minimization of precipitation
infiltration through the landfill. with diminished cap
integrity, contaminants detected in the landfill wastes would
continue to be carried to the groundwater at unacceptable rates.
Alternatives 3, 4b and 5b provide for a cap which provides a
barrier to direct contact and which would decrease the rate of
precipitation infiltration by at least 50 to 70 percent.
Contaminant migration through surface water runoff to shallow
wetland and low lying near shore areas would be mitigated. The
cap decreases the direct conduits for precipitation infiltration
through the landfill and thereby decreases the rate of
contaminant leaching from the waste mass into the groundwater.
Wear and damage to the cap's clay barrier layer can be minimized
with the addition of the frost-protection layer.
Alternatives 4a and Sa utilize a multimedia cap. The multimedia
cap is similar to the multilayer cap used in Alternatives 3, 4b
and 5b with the addition of a geotextile membrane. The rate of
precipitation infiltration would be decreased by approximately 90
percent. The geomembrane cap is less tolerant of well
installation, settling and subsidence than is the clay cap.
Additionally, installation, operation and maintenance of the well
extraction system is more difficult due to the presence of the
geomembrane.
Alternative 3 is not protective of human health and the
environment. Alternative 3 does not provide a contaminated
groundwater barrier or groundwater treatment, thus allowing
continued migration of leachate and contaminated groundwater.
Continued impacts on the quality of surface water and the low-
lying wetlands due to contaminated groundwater discharge would be
expected. Contaminated soils and sediments, exhibiting
unacceptable risks, would remain in place.
Alternatives 4a through 5b include containment and treatment of
the contaminated groundwater. Contaminated soils and sediments
surrounding the landfill would be consolidated within the
landfill. Landfill gases will be extracted and treated.
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31
Alternatives 4a through 5b provide for long term protection of
human health and the environment.
2.
Compliance with Applicable or Relevant and Appropriate
Requirements ARARs
This criterion evaluates whether an alternative meets applicable
or relevant and appropriate requirements set forth in Federal or
more stringent state environmental standards pertaining to the
site or proposed actions. (The statutory determinations section
(Section XII) discusses ARARs for the site). This section only
notes those ARARs not addressed, if any, by an alternative.
Alternative 1 does not meet the current Ch. NR 504.07, WAC
landfill requirements for solid waste landfill closure, which
have been determined to be an ARAR for this site. Alternatives 3
through 5b would meet the Ch. NR 504.07, WAC requirements.
Alternatives 1 and 3 may not comply with Ch. NR 140, WAC in that
they may not prevent the continued release of contaminants at
levels exceeding standards at the point of standards application.
In addition, these alternatives would not result in compliance
with water quality criteria in surface water. Thus, these
alternatives would not comply with Groundwater Cleanup standards.
Alternatives 4a through 5b would comply with Groundwater Cleanup
standards as well as with water quality criteria for surface
water within a certain period of time.
B. primarv Balancinq criteria
3. Lonq-Term Effectiveness and Permanence
This criterion evaluates long-term effectiveness and permanence
each alternative affords along with the degree of certainity that
the alternative will prove successful. This includes assessment
of the expected residual risk and the ability of an alternative
to maintain reliable protection of human health and the
environment over time, once clean up levels are achieved.
Alternative 1 provides no long-term effectiveness or permanence
since low permeability layers were not used for the present cap.
Rapid cap deterioration, which leads to an increased rate of
precipitation infiltration, will occur, as demonstrated by the
performance of the current cap. Alternative 1 does not provide
protection to the wetlands environment.
Alternatives 1 and 3 do not provide adequate protection from
exposure to surface soil and sediment with excess cancer risk of
greater than 1 x 10-6. These alternatives do not- provide
adequate protection from contaminated groundwater. Alternatives
1 and 3 do not provide protection over the long-term of the
surface water.
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32
Under Alternatives 4a, 4b, 5a and 5b, potential exposure to
contaminated groundwater and surface water, soil, exposed waste
and sediment would be reduced to less than 1 x 10-6 excess
carcinogenic risk and hazard indices less than 1 for all media.
Alternatives 4a, 4b, 5a and 5b, would provide a similar degree of
long-term effectiveness in reducing the amount of water
infiltration into the landfill, with Sa and 4a being slightly
more effective than 4a and 4b.
Contaminated groundwater
significantly reduced by
Contaminated groundwater
through Sb.
would be contained and migration
the slurry wall in 4a and 4b.
is extracted and treated under 4a
Contaminated soil and sediments exceeding cleanup standards would
be excavated and consolidated under the landfill caps under 4a
through Sb, minimizing potential exposure. Proper maintenance is
requ~red to maintain the effectiveness of the cap and slurry wall
in order to maintain adequate protection of human health and the
environment.
Alternative Sa has the same difficulties as 4a with respect to
the geotextile membrane layer of the cap. Under alternatives Sa
and 5b, the pumping and treating on-site of large amounts of
groundwater for an indefinite amount of time would be required.
4.
Reduction of Toxicitv. Mobilitv or Volume Throuqh Treatment
This criterion evaluates treatment technology performance in the
reduction of chemical toxicity, mobility or volume.
As described above, the stated programmatic goal of the U.S. EPA,
as expressed in the NCP, is to select remedies that are
protective over time and "minimize untreated waste" (Section
300.430(a) (1) (i». The NCP contemplates that the U.S. EPA will
use "treatment to address the principal threats at a site,
wherever practicable" (Section 300.430(a) (1) (iii) (A)).
Alternatives 1 and 3 would provide no reduction of toxicity,
mobility or volume through treatment. Alternatives 4a through Sb
provide secondary treatment which reduces the toxicity, mobility
or volume of contaminated groundwater and landfill gases.
Treatment to reduce the toxicity, mobility or volume of waste in
the landfill is not contemplated in any alternative, since the
large volume of landfill waste makes treatment of the waste
technically impracticable.
5. Short-Term Effectiveness
Short-term effectiveness considers the time to reach cleanup
objectives, and the risks an alternative may pose to site
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33
workers, the community and the environment during remedy
implementation. This criterion also considers the reliability
and effectiveness of any mitigative measures taken during remedy
implementation to control those short-term risks.
Alternatives 4a through 5b are of similar short term-
effectiveness. Construction would be completed for Alternatives
4a through 5b in 2 years. Groundwater treatment for these
alternatives would begin approximately 15 months after the
initiation of work and would continue for a minimum of 30 years.
Clean up objectives would not be achieved by Alternatives 1 and
3. Alternative 1 would continue to discharge contaminants to the
wetlands and surrounding area through surface water runoff.
Alternatives 1 and 3 would continue to discharge contaminants to
the Root River and other water bodies.
Alternatives 4a through 5b, in providing more measures for site
remediation than Alternatives 1 and 3, impose more relative risks
to workers, the community and the environment. Noise, dust and
construction activities may pose short-term risks to site
workers, the community or the environment during construction
activities. 5a and 5b impose slightly more environmental risks
than 4a and 4b due to the need to construct the treatment
facility in the Root River floodplain.
Capping, excavation, and slurry wall construction are standard
engineering processes and standard safety precautions will be
undertaken to reduce the likelihood of accidents. Dust controls
will reduce the short-term impacts to site workers and residents.
The use of erosion control measures will mitigate some of the
short-term effects impacting the environment. Actions would be
taken to minimize and/or reverse adverse environmental impacts
during and after construction activities to the greatest extent
possible.
6. Implementabilitv
This criterion considers the technical and administrative
feasibility of implementing an alternative.
No significant implementation problems are associated with cap or
slurry wall construction in Alternatives 3, 4b or 5b. Cap
materials are expected to be obtainable from nearby sources and
construction methods are straightforward. Under Alternatives 4a
and Sa, the difficulty associated with the installation of gas
extraction wells through the geotextile membrane of the
multimedia cap could pose problems with implementation of these
alternatives.
Under Alternatives 5a and 5b, pumping and treating on-site of
large amounts of groundwater would be required. Construction of
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34
an on-site treatment plant in a floodplain would be required.
Plant discharge would need to meet the substantive requirements
of a WPDES permit.
7. Cost
Table 6 '''compares the capital, Operation and Maintenance, and
present worth costs of implementing the various alternatives at
the site.
Table 6
Estimated Costs of Remedial Action
Hunts Disposal Landfill
Alternative
Capital Cost
o & M
Present Worth
1
3
4a
4b
5a
5b
$0
$6,582,000
$15,964,000
$13,924,000
$15,596,000
$13,581,000
$0
$93,000
$375,000
$375,000
$536,000
$536,000
$0
$7,452,000
$19,494,000
$17,454,000
$20,656,000
$18,641,000
C. Modifvinq Criteria
8. state AcceDtance
The state of Wisconsin is in agreement with the u.s. EPA's
analyses and recommendation presented in the RIfFS and the
Proposed Plan. The State concurs with the selected alternative
presented in Section XI below.
9. Community AcceDtance
Community reaction to the proposed plan is mixed. Generally,
those that think some other form of remedial action should be
implemented believe that the waste at the site should be
excavated and incinerated or excavated and disposed of off-site,
rather than being left in place. Additionally, some residents
question the long-term effectiveness of the slurry wall. These
concerns are addressed in the Responsiveness Summary.
XI. Selected Remedv
As provided in CERCLA and the NCP, based upon the evaluation of
the RIfFS and the nine criteria, and in consultation with the
State, the u.S. EPA has selected Alternative 4b as the method
providing overall effectiveness in adequately protect human
health and the environment against currently identified threats
at the site. Additionally, u.S. EPA has determined that
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35
additional investigations and studies will be conducted as part
of the selected remedy.
Under Alternative 4b, a multilayer cap shall be placed on the
landfill (see Figure 6) in compliance with Ch. NR 504.07, WAC.
The cap shall consist of a minimum 2 foot clay layer, compacted
to a pe~eability of 10-7 cm/s or less, a 2 foot common borrow
zone to protect the cap and a minimum of 6 inches of topsoil with
vegetation. The main purposes of the cap are to reduce the rate
of precipitation infiltration through the landfilled wastes to
the groundwater, reducing the amounts of contaminants "leaching
from the landfill and to minimize exposure to contaminated soil
and exposed landfill waste.
A full slurry wall shall be constructed to encircle the landfill,
tieing into the surface cap above the landfill and the silt and
clay layer beneath the site. The full slurry wall will contain
the contaminated groundwater.8
A groundwater extraction system consisting of gradient control
wells shall be installed inside the landfill. Groundwater shall
be extracted until Federal Maximum contaminant Levels or
Wisconsin Groundwater Quality standards (Chapter 160 wis. stats.
and Chap NR 140 Wis. Admin. Code), depending on which are more
stringent for each of the contaminants of concern detected, are
met. The extracted groundwater would be treated at an off-site
facility to the appropriate Federal or state standard. The
extraction system will establish an inward flow of groundwater
into the landfill.9
Areas of the site containing contaminated soil and sediment in
concentrations greater than 10-6 risk, greater than background
concentrations, or greater than yet to-be-determined cleanup
levels (based on consideration of risk levels and background
concentrations) will be excavated and consolidated in the
8 TheFS used a cement-bentonite slurry wall in the
description and costing of alternatives. However, it is possible
that equivalent effectiveness could be provided by some other
type of slurry wall, such as a soil-bentonite wall. Additional
studies will be performed during the design phase of the selected
remedy to investigate options for the type of slurry wall.
9 If adverse levels (i.e. exceeding one or more of: Federal
drinking water standards, WQC and/or groundwater quality
standards) of site contaminants are found to be discharging to
the River or are found outside the slurry wall, additional
remedial action may be required.
-------
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I I
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& ~ N
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~ i
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. '*
I
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L.AK!
&
.
.
a.
LEGEND
. I~D PROPOSED
WE LL.
.
SUJRRY W AL.L
o
"
GRAOIENT CONTROL wELL
SCALE
,II . 500'
DATE
JULY 1990
~
FIGURE
REM V
HUNTS DISPOSAL LANDFILL SITE
CALEDONIA, WI
6
PLAN VI EW OF AL TERNATIYE
IVb
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37
landfill. The volume of contaminated soil and sediment to be
excavated is estimated at approximately 5300 cubic yards.'o
An active gas collection system shall be installed in the
landfill. The system will consist of the installation of gas
collection wells in the landfill to a depth of about twenty feet.
The gases will be extracted from the landfill and combusted to
form carbon dioxide and water vapor. The purpose of the gas
collection and combustion system will be to maintain the
integrity of the cap by relieving gas pressures from within the
landfill and to extract and destroy or treat methane and other
gases being emitted from the landfill.
Long-term monitoring programs shall be established and
implemented to provide information on the performance of the
remedy and local conditions. Such monitoring programs shall be
designed to provide information on: potential and actual'
contaminant migration in groundwater, surface water, and other
media; the performance of the groundwater and gas extraction
systems, the slurry wall and the cap; and on residential wells in
the area.
Institutional controls will be relied on to provide additional
effectiveness to the remedy. Deed and use restrictions will be
implemented to prohibit excavation, construction or other
activities on or near the landfill which could interfere with the
remedy.
A galvanized chain link fence will be installed and maintained
around the perimeter of the site to ~educe trespassing.
As noted above, the selected remedy also includes additional
investigations and studies. These may include investigations and
studies required to:
1)
2)
. 3)
4)
Assist in the design of the selected remedy;
Verifv backaround conditions;
Verify hydrogeological conditions;
Assess and evaluate the impact of remedial activities
on the surrounding environment, including wetlands,
animal and plant life, the Root River, and the
floodplain; and
10 Purther investiqation, study and evaluation will be
conducted to delineate the actual amounts of soil to be
excavated. Furthermore, as noted previously, impacts resultinq
from the remedial action as a whole will be assessed, and
mitiqative, restorative and other measures will be studied and
implemented to minimize, reduce and reverse the impact of
excavatioa and other remedial activities on surroundinq ar~...
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38
Minimize, mitigate and reverse any adverse impacts to
the environment caused by the remedial activities.
Determine the nature and extent of any off-site
contaminant migration, and evaluate appropriate
remedial alternatives which may be required.
The invastigations and studies shall be conducted as directed by
U.S. EPA, in consultation with the State. Based on the results
of the additional investigations and studies and available data,
U.S. EPA, in consultation with the state, will consi~er if
additional remedial action is necessary and if this ROD should be
amended.
5)
6)
XII. Statutorv Determinations
The selected remedy must satisfy the requirements of Section 121
of CERCLA to:
A. Protect human health and the environment;
B. Comply with ARARs
C. Be cost-effective;
D. Utilize permanent solutions and alternate treatment
technologies to the maximum extent practicable; and
E. Satisfy the preference for treatment as a principle
element of the remedy.
The implementation of Alternative 4b at the Hunts Disposal
Landfill site satisfies the requirements of CERCLA as detailed
below:
A. Protection of Human Health and the Environment
Implementation of the selected alternative will reduce and
control potential risks to human health posed by exposure to
contaminated groundwater, soil and sediments. The selected
remedy will reduce potential exposure to contaminated groundwater
to less than 1.0 x 10.6 and a Hazard Index less than 1.0. The
selected remedy also protects the environment by reducing the
potential risks posed by site chemicals discharging to
groundwater, the Root River, the on-site lake, and surrounding
soils, sediments and wetlands.
Institutional controls will be implemented to provide against the
drinking of contaminated groundwater at the site.
Capping the landfill, in addition to reducing the potential risk
posed by exposure to landfill contaminants and contaminated
surface water runoff, will reduce precipitation infiltration
through the cap. Groundwater contaminant loading would then be
reduced.
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39
Gas extraction and destruction will reduce the volume of
contaminants in the landfill waste and will reduce potential
risks'due to landfill gases.
Excavation and consolidation, under the landfill cap, of
contaminated soil and sediments will reduce the excess cancer
risk due to exposure to soil and sediments to less than
1.0 x 10.6 and a Hazard Index less than 1.0.
The slurry wall will provide a barrier to impede contaminant
migration from under the landfill to adjacent areas, including
the on-site lake and the Root River. The slurry wall and cap,
along with the presumed clay-till underlayer, will serve to
isolate the wastes from the environment.
No unacceptable short-term risks will be caused by implementation
of the remedy. The nearby community, and site workers, may be
exposed to noise and dirt nuisances during construction.
standard safety measures should manage any short-term risks.
Dust control measures would mitigate risks as well. Mitigative
measures will be taken to prevent and address adverse
environmental impacts.
B. Compliance with ARARs
with respect to any hazardous substances, pollutants or
contaminants that will remain on-site, CERCLA (Section 121(2) (A»
requires the u.S. EPA to select a remedial action which complies
with legally applicable or relevant and appropriate standards,
requirements, criteria or limitations(ARARs). The selected
remedy will comply with the Federal and/or State ARARs where more
stringent. ARARs for Alternative 4b are listed below:
1. Chemical-specific ARARs
Chemical-specific ARARs regulate the release to the environment
of specific substances having certain chemical characteristics.
Chemical-specific ARARs typically define the extent of cleanup at
a site.
a. Soils/Sediments
No chemical-specific standards exist for soils and sediments.
However, calculations can be made for organic contaminant
concentrations for sediments based on surface water quality
criteria (under Ch. NR 105, WAC) and for soils based on
groundwater quality standards (under Chap. NR 140, WAC), to
ensure protectiveness of the environment. The results of the
calculations yield chemical-specific cleanup goals for the soils
and sediments that are factors "to be considered" in designing a
protective remedy at this site.
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40
b. Groundwater
i. Federal ARARs
Maximum contaminant Levels (MCLs), and to a certain extent,
Maximum Contaminant Level Goals (MCLGs), the Federal drinking
water s~andards promulgated under the Safe Drinking Water Act
(SDWA), are ARARs for the site. MCLGs are relevant and
appropriate when the standard is set at a level greater than zero
(noncarcinogens), otherwise MCLs are relevant and appropriate.
At the HDL site, MCLs and MCLGs are not applicable, but are
relevant and appropriate, since the groundwater in the upper
aquifer could potentially be used as a drinking water supply.
The NCP, Section 300.430(f) (5) (iii) (A), states that performance
of the remedy shall be measured at appropriate locations in the
groundwater, surface water, soils, air and other affected.media.
The point of standard applications (point of compliance) for
groundwater ARARs is discussed further at 55 FR 8753, and is
generally one of the following: all points throughout a
contaminant plume; at and beyond the edge of the waste management
area; or at some alternative point (e.g. in order to address
several distinct sources which are located in close geographic
proximity as a whole).
ii. State ARARs
The state of Wisconsin is authorized to administer the
implementation of the Federal SDWA. The State has also
promulgated groundwater quality standards promulgated under Ch.
NR 140, WAC. The statute (Chap. 160, Wis. Stats.) directs the
WDNR to take action to prevent the continual release of
contaminants at levels exceeding standards at the point of
standards application.
The Wisconsin Groundwater Quality Standards (WQS) promulgated
under Ch. NR 140, WAC, under Ch. 160, Wisconsin statutes, are
listed for major contaminants of concern in Table 7. WQS are
generally equivalent or more stringent than corresponding Federal
standards and, therefore, are ARARs to groundwater cleanup
conducted at the site.
Consistent with the exemption criteria of section NR 140.28, WAC
a (Wisconsin) alternative concentration limit (WACL) may be
established to modify the preventive action limit (PAL) if it is
determined that it is not technically and economically feasible
to achieve the PAL for a specific substance." Except where
11 A determination of technical or economic infeasibility
may be made after five years of operation of the ground water
extraction system if it becomes apparent that the contaminant
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41
the background concentration of a compound exceeds the
enforcement standard (ES) and consistent with the criteria in
section NR 140.28(4) (B), the WACL that is established may not
exceed the ES for that compound.
The implementation of the selected remedy at the HDL site will be
in compliance' with Ch. NR 140, WAC, in that preventative action
limits (PALs) will be met unless (Wisconsin) alternative
concentration limits (WACLs) are established pursuant to the
criteria in section NR 140.28, WAC, in which case the WACLs will
be met.
Table 7
Wisconsin Groundwater Quality
Enforcement Standard
Compound of Concern
uq/l
Standards
Preventative
Limit
uq/l
Action
Arsenic
Barium
Benzene
Cadmium
Chromium
Cyanide
1,2-dichloroethane
1,2-dichloroethene
Lead
Methylene Chloride
Toluene
Trichloroethene
Vinyl Chloride
Xylene
50
1mg/l
0.67
10
50
460
850
0.24
50
150
343
1.8
0.015
620
5
0.2mg/l
1
1
5
92
85
0.024
5
15
68.6
0.18
0.0015
124
c. Surface Water
i.. Federal ARARs
CERCLA section 121(2) (B) requires the U.S. EPA to consider
whether surface water quality standards for human health and
aquatic life protection developed under the Clean Water Act (CWA)
Section 304 would be relevant and appropriate considering the
designated or potential use of groundwater or surface water, the
environmental media affected, the purposes for which such
criteria were developed, and the latest information available.
level has ceased to decline over time and is remaining constant
at a statistically significant level above the PAL (or any WACL
established due to high background concentrations) in a discrete
portion of the area of attainment, as verified by multiple
monitor wells.
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42
Federal Ambient Water Quality Act Criteria (AWQC) are non-
enforceable guidelines that set pollutant concentration limits to
protect surface waters that are applicable to point source
discharges, such as from industrial or municipal wastewater
streams. At a Sup~rfund site, the Federal AWQC would not be
applicable except for pretreatment requirements for discharge of
treated.'water'to a Publicly Operated Treatment Works (POTW).
Since the HDL discharges to the Root River, the AWQC for
protection of freshwater aquatic organisms are relevant and
appropriate to any point source discharge into the Root River.
ii. State ARARs
Section 303 of the CWA requires the State to promulgate state
water quality standards for surface water bodies, based on the
designated uses of the surface water bodies. The State has
promulgated Wisconsin Water Quality Criteria (WWQC) under Ch. NR
105, WAC, based on the Federal AWQC developed by u.S. EPA. The
Surface Water Quality Criteria for Toxic and Organoleptic
Substances under Ch. NR 105, WAC, are applicable to the
maintenance of surface water quality impacted by the discharge to
the Root River of groundwater from the site.
The Root River is designated as a warm water sport fish community
and recreational use under Ch. NR 104, WAC. The warm water sport
fish WWQC are therefore applicable to the discharge of
groundwater from the site.
In addition, Ch. NR 102, WAC establishes an anti-degradation
policy for all waters of the State and it establishes water
quality standards for use classifications. Chapter NR 102, WAC
would be applicable to actions that involve discharges to the
Root River in that discharges must meet water quality standards.
Ch. NR 106, WAC, provide for water quality based discharge limits
for discharges to the Root River containing toxic or organoleptic
substances. Ch. NR 106, WAC is applicable to at ions involving
discharge to surface water bodies, and is applicable to this
site.
2. Location SDecific ARARs
Location-specific ARARs are those requirements that relate to the
geographical position of a site. These include:
a. Federal ARARs
Executive Order 11988 - Protection of Flood Plains, is an ARAR
for the site due to its location within the mapped 100-year flood
plain (666 feet above mean sea level) of the Root River.
Executive Order 111988 would require that all remedial activities
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43
proposed within the floodplain avoid adverse impacts of
development in the floodplain.
Executive Order 11990 - Protection of Wetlands is an ARAR for the
site to protect against the loss or degradation of wetlands. As
presented above, Alternative 4b will have an adverse impact on
the wetYands. . Executive Order 11990 requires that activities in
a wetland be conducted so as to minimize adverse impacts on the
wetlands.
The Scenic Rivers Act (16 USC 1271, section 7(a» is an ARAR for
the site. Since the Root River is designated for recreational
use, this provision requires that the selected remedy should
avoid taking or assisting in any action that will have an adverse
effect on the scenic river.
b. State ARARs
Chapter NR 112, WAC, which requires that no drinking water wells
be located within 1200 feet of a landfill, unless a variance is
obtained from the WDNR, is an ARAR for the site.
section 29.415, wis. stats. and Chapter NR 27, WAC, are State
Endangered and Threatened Species resource laws which protect
against the "taking" or harming of endangered or threatened
wildlife resources in the area. These are ARARs for the remedial
action, due to that the potential for poisoning of endangered or
threatened species by site contaminants exists, including at
least two endangered plant species found at the site.
3. Action-specific ARARs
Action-specific ARARs are requirements that define acceptable
treatment and disposal procedures for hazardous substances.
a. Federal ARARs
Since the Hunts Disposal Landfill was closed prior to
November 1980 (in 1974), RCRA hazardous waste requirements are
not applicable unless RCRA-listed or characteristic hazardous
wastes are excavated and managed (treated, disposed and stored),
as defined by RCRA, during the cleanup. There is no actual
documentation (e.g. manifests) to indicate that RCRA-1isted
hazardous or characteristic wastes were disposed of at the site.
Therefore, RCRA Subtitle C hazardous waste landfill requirements
are not applicable. Since hazardous substances in the landfill
are sufficiently similar to RCRA listed or characteristic wastes,
these requirements are relevant. However, they are not
considered appropriate at the HDL site since a portion of the
landfill waste is below the water table. Thus, the additional
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44
precipitation infiltration reduction achieved by a subtitle C
geomembrane cap (versus a clay cap) will not significantly affect
the contaminant loading caused by the immersed waste.
Land Disposal Restrictions ("LDR" or "Land Ban") would not be
applicable because no placement of RCRA hazardous wates will
occur and no l.isted wastes are documented at the site. LDR is
not relevant or appropriate because the remedy addresses soil and
debris.12
b. state ARARs
The state of Wisconsin is authorized to implement the subtitle D
solid waste requirements of RCRA. Chaps. NR 504, 506, 508, 514
and 516, WAC, which regulate solid waste landfill activities, are
ARARs for this site. Additional state action-specific ARARs are
found in the FS.
C. Cost-effectiveness
Cost-effectiveness is determined by evaluating the following
three of the five balancing criteria to determine overall
effectiveness: long-term effectiveness and permanence, reduction
of toxicity, mobility or volume through treatment and short-term
effectiveness. Overall effectiveness is then compared to cost to
ensure that the remedy is cost-effective.
Alternative 4b, the selected remedy, provides overall cost-
effectiveness because it provides adequate long-term
effectiveness and permanence. Secondary reduction in toxicity,
mObility.and volume is accomplished through treatment of the
groundwater and landfill gases. No unacceptable short-term risks
will be caused by implementation of the remedy. The selected
remedy can be implemented at a lower cost than Alternatives 4a,
5a and 5b.
D.
utilization of Permanent Solutions and Alternative Treatment
Technoloaies or Resource Recoverv Technoloaies to the
Maximum Extent Practicable
The selected remedy utilizes permanent solutions and alternative
treatment technologies to the maximum extent practicable ("MEP").
This finding was made after evaluation of the protective and
ARAR-compliant alternatives for the Hunts Disposal Landfill site
remedial action and comparison of the "trade-offs" (advantages
12 The U.S. EPA is currently undertaking a rulemaking that
will specifically apply to soil and debris. Until such
rulemaking is complete, U.S. EPA does not consider LDR to be
relevant or appropriate at this site as to soil and debris.
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45
vs. disadvantages) among the remedial alternatives with respect
to the five balancing criteria (see discussion above).
E.
Preference for Treatment as a Principal Element
The principal threats at the Hunts Disposal Landfill site are the
contaminated groundwater and the contaminated soil and landfill
waste. Alternative 4b, the selected remedy, uses treatment as a
seondary element of the remedy through extraction and treatment
of contaminated groundwater under the landfill and extraction and
treatment of landfill gas. As noted above, treatment-of the
landfill waste would be technically impracticable.
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RESPONSIVENESS SUMMARY
This Responsiveness Summary has been prepared to meet the
requirements of Sections l13(k) (2) (B) (iv) and l17(b) of the
Comprehensive Environmental Response, Compensation and Liability
Act of 1980 as amended by the Superfund Amendments and
Reauthorization Act of 1986 (CERCLA), which requires the United
States Environmental Protection Agency (U.S. EPA) to respond
"... to each of the significant comments, criticisms and new data
submitted in written or oral presentations" on a proposed plan
for remedial action. The Responsiveness Summary addresses
concerns expressed by the public, potentially responsible parties
(PRPs) and governmental bodies in the written and oral comments
received by the U.S. EPA and the State regarding the proposed
remedy for the Hunts Disposal Landfill site.
A. OVERVIEW
1.
Backaround/PrODosed Plan
The Hunts Disposal Landfill site is an inactive 35-acre landfill
which is part of an 84-acre parcel located in the Township of
Caledonia in Racine County, Wisconsin. The site borders the Root
River and includes several wetland areas and a 25-acre lake.
The Remedial Investigation eRI) identified several areas of
concern at the site: two principal threatsl which are the
groundwater contamination and the contaminated soil, sediments
and exposed landfill waste materials. The landfill itself is
considered to be a low-level, long-term threat2 to human health
and the environment. The Feasibility Study (FS) evaluated six
cleanup alternatives in order to address the areas of concern.
The proposed plan for remedial action included:
Construction of a multilayer landfill cap in compliance
with NR 504.07, Wisconsin Administrative Code (WAC)
landfill closure requirements:
- Construction of a full slurry wall around the perimeter of
the landfill:
lprincipal threats are characterized by waste that cannot be
reliably controlled in place, such as liquids, highly mobile
materials (e.g., solvents), and high concentrations of toxic
compounds (e.g., several orders of magnitude above levels that
allow for unrestricted use and unlimited exposure(55 Fed. Reg.
8703)
2The landfill contains a large volume of waste material (55 Fed.
Reg. 8703)
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2
- Consolidation of contaminated soil and sediment under the
landfill cap;
- Groundwater gradient control through extraction and off-
site treatment of contaminated groundwater;
- Installation of an active landfill gas collection and
treatment system.
Institutional controls governing the use of groundwater and the
development of the landfill would be implemented and engineering
controls (i.e., fencing) would aid in the prevention of the
ingestion of contaminated groundwater and exposure to
contaminated soil, sediments and landfill waste materials.
Groundwater monitoring would also be implemented.
2.
Public Comment Period
A public comment period was held from July 26, 1990 to September
24, 1990 to allow interested parties to comment on the Proposed
Plan, in accordance with section 117 of CERCLA. On July 31,
1990, a public hearing was held in Caledonia, Wisconsin, at which
the U.S. EPA and the Wisconsin Department of Natural Resources
(WDNR) presented the Proposed Plan, answered questions and
accepted comments from the public. During the comment period,
the U.S. EPA received written and several verbal comments
concerning the Proposed Plan.
sections Band C contain responses to significant verbal and
written comments.
B. COMMUNITY INVOLVEMENT
Public interest regarding the site has been moderate.
areas of concern expressed are as follows:
Several
COMMENT: Local officials and residents have expressed concern
over the possibility of airborne contamination, especially the
potential impacts to nearby residences.
RESPONSE: The risk due to air-borne contamination is greatest
when you are directly on top of the landfill. Due to dispersion,
it is not expected that this is a significant exposure pathway
for nearby residences. During construction of the remedial
action, dust control measures will be taken.
COMMENT: The site is closed to the public.
Signs were posted
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3
and the site gate was locked to prevent and discourage the
public's access to the property. However, in spite of these
attempts, trespassing on the property continues. Actions should
be taken to improve site security.
RESPONSE: As part of the remedial action, the site will be
fenced and institutional/administrative controls implemented.
COMMENT: Concerns were expressed that a highway is proposed for
the area which would cross the western edge of the landfill.
RESPONSE: Institutional controls will be implemented which will
preclude development of the landfill.
COMMENT: "Perhaps because of the superficial treatment of
aquatic impacts, the Feasibility Study does not appear to
evaluate the desirability of removal and/or treatment of
contaminated sediments in the Root River. This is a serious
flaw, one which must be redressed." .
RESPONSE: The Risk Assessment evaluated potential impacts of
sediments on aquatic life. Based on a comparison of the
estimated sediment exposure concentrations from on-site and
downgradient locations with sediment toxicity data from
literature, none of the estimated concentrations exceed the
sediment values from literature. Based on this, chemicals in
sediment are probably not impacting aquatic life.
COMMENT 1: The commentor asked that a fence be installed around
the entire property to deter the trespassing that occurs almost
daily.
RESPONSE: U. S. EPA and the state are aware that there is
frequent trespassing occurring at the HDL site. It is for this
reason that the ROD includes the construction of a chain link
fence around the entire site.
COMMENT 2: The commentor asks that samples be taken along the
access roadway to determine if contaminants are present, and
whether any contaminants present are leaching into the lake
and/or the pond.
RESPONSE: During the design phase it is expected that
additional environmental samples be taken on and around the HDL
site. This sampling effort will be designed to determine the
degree of contamination in other areas around the landfill, and
to better characterize background conditions. It is likely that
the access roadway and other areas around the site will be
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4
included in this sampling effort.
COMMENT 3: The commentor requests that the Town of Caledonia be
ordered to raise the elevation of County Line Road so that it is
in comp;iance with floodplain zoning (i.e., the road is 2.5 feet
above the floodplain).
RESPONSE: The elevation of County Line Road does not have
direct relevance to the issues being considered as a part of the
action at the HDL site.
COMMENT 4: The commentor requests that activities take place at
the site so that the site's access road also complies with the
floodplain zoning requirement listed above (i.e., the road is 2.5
feet above the floodplain).
RESPONSE: The U.S.EPA and the State recognize the fact that the
HDL area is periodically subjected to flooding. The remedial
alternatives developed for the HDL site address the problems
which may result from this flooding. One of the important tasks
of the design phase will be to consider the potential for
periodic flood conditions in the design. The site's access road
is an important element of the remedy. Therefore, the site's
access road, (and all other elements of the remedy), will be
designed and constructed in a manner which is both functional and
in compliance with all local, state and federal
standards/guidance.
COMMENT 5: The comment or requests that "flapper gates" be
installed on the 12 inch and 36 inch culverts under the HDL
access roadway to prevent Root River floodwaters from raising the
levels of the lake and pond.
RESPONSE:
See the response to the previous comment.
COMMENT 6: The commentor
located north and east of
analyzed for contaminants
encroaching flood waters.
requests that soil from the properties
the lake and/or pond be sampled and
which may have deposited there by
RESPONSE:
See the response to Comment 2 above.
COMMENT 7: The commentor requests that area residents who had
their private water wells tested be provided with a signed
affidavit from the test laboratory indicating that their water is
safe and healthy for human consumption.
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5
RESPONSE: U.S. EPA and the State have each performed sampling
of the residential wells in the vicinjty of the HDL site. For
each well sampled, the resident was provided with a summary of
the analytical results of the laboratory analysis perf9rmed on
their drinking water sample. These residents were also provided
with ihformation indicating that there was no contamination in
their drinking water which could be associated with the landfill.
We encourage any residents who have questions on these results to
call U.S. EPA or WDNR.
C. roI'ENTIALLY RESPONSIBLE PARTIES
Comments were received from CH2M Hill on behalf of a PRP. . CH2M
Hill provided both general and specific comments, based on their
overview of the RIfFS. In general, if comments were addressed as
specific comments, they are not included in the general overview,
but are addressed in the sections below.
1.
General ResDonses
COMMENT 1: The commentor noted that fl. . . the risk posed by
the site was incorrectly based on the human exposure pathway of -
development of the site with residential use of the groundwater
beneath the site for drinking water. This exposure pathway does
not exist now and will not develop in the future. . . "
Consequently, the comment or believes that, fl. . . because the
residential exposure setting is invalid, the reestimated
potential carcinogenic and noncarcinogenic risks are reduced by
approximately 99 percent. . ."
RESPONSE 1: The risk posed by the ground water at HDL was
determined by U.S. EPA to be 1 x 10-3 under a future use
scenario, as documented in the ROD. This risk clearly exceeds
the acceptable risk range under the criteria set forth in the
NCP. The NCP states that, "In the Superfund program, the
exposure assessment involves developing reasonable maximum
estimates of exposure for both current land use conditions and
potential future land use conditions at each site. . . The
Superfund program has always designed its remedies to be
protective of all individuals and environmental receptors that
may be exposed at a site; consequently, EPA believes it is
important to include all reasonably expected exposures in its
risk assessments."
The risk posed by the site, however, is not the only factor used
in determining to what extent remedial action is warranted.
Health-based chemical specific ARARs are also used to determine
whether a release constitutes an unacceptable risk to human
health or the environment and if action under Sections 104 and
106 of CERCLA is warranted, as is the case with HDL. The NCP
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6
states that, ". . . ARARs should be addressed consistently in
the baseline risk assessment, the RIfFS and remedy selection. .
"
.
For ground water actions, MCLs and non-zero MCLGs will generally
be used" to gauge whether remedial action is warranted. Levels of
contamination at HDL were found to be greater than MCLs and State
standards, thereby providing additional basis for remedial action
and the trigger of 121 cleanup standards at HDL.
In response to the commentors reference to the use of the water
beneath the site, Section 300.430 (f) (5) (iii) (A) of the NCP
states that performance shall be measured at appropriate
locations in the ground water. EPA believes that remediation
levels should generally be attained at or beyond the edge of the
waste management area, when waste is left in place. At HDL,
performance is not being measured beneath the site: rather, the
point of compliance at HDL is at the edge of the slurry wall.
The remedial action will meet this objective at its completion
through a combination of natural attenuation of the southwest
contaminant plume, construction of a slurry wall and gradient
control system.
COMMENT 2: The commentor noted that, ". . . even if the site's
groundwater contaminant levels exceed drinking water standards or
state preventative action limits, there is no potential for
groundwater use, these standards or limits should not be
ARARs . . ."
RESPONSE 2: U.S. EPA believes that there is a potential for use
of the ground water and that drinking water standards and state
standards are ARARs at HDL.
In accordance with the provisions of the NCP, EPA's Superfund
program uses EPA's Ground-Water Protection strategy as guidance
when determining the appropriate remediation for contaminated
ground water at CERCLA sites. EPA's Ground-Water Protection
strategy establishes different degrees of protection for ground
waters based on many factors, including their vulnerability, use
and value. The goal of EPA's Superfund approach is to return
usable ground waters to their beneficial uses.
The ground water at HDL is considered "usable" by the NCP
definition. The NCP notes that ground water is "unusable" only
if it is ". . . unsuitable for human consumption - due to high
salinity or widespread contamination that is not related to a
specific contamination source - and that does not have the
potential to affect drinkable or environmentally significant
ground water)" and that for unusable ground water, "drinking
water standards are not ARARs and will not be used to determine
prelimin~ry remediation goals. . ." The ground water at HDL
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7
clearly does not meet the NCP's definition of "unusable." For
usable ground water, the NCP $tates that, "preliminary
remediation goals are generally set at standards promulgated
under the Safe Drinking Water Act or more stringent State
standards."
The U.S. EPA believes that the remedial action for the ground
water was selected in accordance with the expectations set forth
in the NCP. The NCP states that, " . . . It is EPA's policy to
consider the beneficial use of the water and to protect against
current and future exposures. Ground water is considered a
valuable resource and should be protected and restored if
necessary and practicable. Ground water that is not currently
used may be a drinking water supply in the future. ..n The
NCP indicates that ". . . when ground-water restoration is not
practicable, remedial action will focus on plume containment to
prevent contaminant migration and further contamination of the
ground water, prevention of exposures, and evaluation of further
risk reduction. . ." The major component of the ground water
remedy at HDL is containment of the plume.
COMMENT 3: The commentor has raised a number of technical points
or flaws with the risk assessment, including, It. . . the
contaminants of concern that were used as the basis for the risk
assessment have been improperly selected. . ." The commentor
points out that ". . . chemicals which were detected in the
background samples as well as at the site were included as
contaminants of concern. . ." and should not be included. In
addition, chemicals found to be lab contaminants It. . . should
not have been included as contaminants of concern in the Risk
Assessment. . ." Finally, the commentor questions the
identification of potential contaminants of concern without
regard for frequency of detection which ". . . is not consistent
with current u.s. EPA guidance. . ."
RESPONSE 3: U.S. EPA guidance indeed recommends procedures which
should be used to identify chemicals of concern. U.S. EPA has
evaluated the discrepancies with guidance and has looked at the
concerns of the commentor. U.S. EPA has determined that the
reasons for proceeding with the selected action are sound despite
minor discrepancies with guidance in technical points concerning
risk characterization. U.S. EPA has found risk levels in excess
of the acceptable range established in the NCP and levels of
contamination in the ground water that exceed relevant and
appropriate standards for the ground water and feels that, based
on the provisions of the NCP, the selected action is appropriate
and justified both quantitatively and qualitatively. In
addition, in the interest of protection of the public, U.S. EPA
believes that it should be conservative in its approach to
remedial action at HDL based on the fact that several of the
contaminants detected at the site are known human carcinogens.
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8
Many factors, such as uncertainties related to the risk
assessment, may cause even greater conservativeness in the risk
management decision-making process.
Summary of Comments received from The Earth TechnoloQV
Corporation (TECT)
COMMENT Tl: TETC noted that quantification of risk based on a
future use scenario of groundwater ingestion and inhalation was
unrealistic and inappropriate.
RESPONSE Tl:
See Response 1 to Comment 1 from CH2M-Hill.
COMMENT T2: TECT has raised a number of discrepancies or flaws
in the baseline risk assessment including improper selection of
contaminants of concern in all media based on errors in: blank
screening criteria; comparison with background concentrations;
accounting for frequency of detection; using maximum
concentrations in the reasonable worst case scenario; and,
improper dose and risk estimation based on errors in exposure
frequency and absorption factors. Consequently, TECT feels that
". . . risk based remedial action objectives will likely change
for the site. . ."
RESPONSE T2: In addition to the reasons stated above in the
response to Comment 3 from CH2M-Hill concerning discrepancies in
the risk assessment, exceedances of federal and state has
provided additional cause for taking action (i.e., in addition to
unacceptable site risk) and has provided the basis for the
selection of the remedial action objectives for the site.
2.
Hvdroqeoloqy Review
COMMENT: Vertical Gradients in the Landfill "The data on
vertical gradients are basically inconclusive, with the exception
of well nest MW-7s, which shows strong downward gradients.
However there is not enough data to evaluate the direction of
vertical gradients across the landfill and for the area in
general."
RESPONSE: We agree that the vertical gradients are generally
inconclusive. However, information regarding vertical gradients
was not necessary to select a preferred alternative. While the
results for some of the measurements produced varying
information, we believe that the vertical gradient information
which has been collected for the HDL is adequate to provide
support the selection of a remedial alternative for the site.
While a more extensive investigation could be performed to
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9
further characterize vertical gradients in the area, it is not
believed that the results of such an investigation would have any
substantive effect on the sel~ction of a remedy for the site.
COMMENT: Groundwater Moundinq on the Landfill "There was not
sufficient data obtained to evaluate whether there is groundwater
mounding at the landfill. Surface water which infiltrates the
cover of the landfill could be mounding up as it moves through
the landfill due to the presence of low permeability materials
such as daily cover. This water would then [be] discharged form
the bottom of the landfill radially, irrespective of the
direction of groundwater flow in the area. The contractor had
three wells in the landfill, however, insufficient rounds of
water levels were taken to be able to assess if there are
mounding effects within the landfill."
RESPONSE: We agree that groundwater mounding could cause radial
flow of leachate from the landfill. We also agree that
additional information should be collected during remedial
design in order to assess mounding effects. If radial flow is
occurring due to mounding effects, the full slurry wall will
serve to capture those contaminants driven out radially,
including those driven in the (normally) upgradient direction.
COMMENTS: Thickness of Underlvinq Clav/Silt Laver and Qualitv of
Aauifer Below "The thickness of the underlaying [sic] silt/clay
layer under the landfill was not investigated. In addition,
there were no wells placed in the aquifer below the silt/clay
layer to evaluate if it had been impacted by the landfill. This
missing information would have a direct effect on the evaluation
of migration potential from the landfill."
RESPONSE: We agree with the commentor that prior to the final
implementation of a remedial action at the site, it would be
useful to investigate the silt/clay layer and the bedrock beneath
the landfill. We believe that this can be best accomplished as a
part of remedial design activities. The installation of
additional bedrock wells would be an important element of such an
investigation. It is important, however, that these wells be
installed using techniques which prevent cross contamination
between the upper and lower aquifers. .
COMMENT: "The data on vertical gradients are basically
inconclusive, with the exception of well nest MW-7s, which shows
strong downward gradients. However there is no enough data to
evaluate the direction of vertical gradients across the landfill
and for the area in general."
RESPONSE:
We agree that vertical gradient information obtained
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10
from the several well nests installed at the site shows
inconclusive results.~'
3.
RI General Comments
COMMENT 1: "A major comment with the RI is that many
contaminants in nearly all media were found in background samples
at levels similar to those found on-site or downgradient...It
appears that many non-site related contaminants were. included in
the risk assessment..."
RESPONSE 1: A complete discussion of the selected contaminants
of concern is presented in a response to CH2H Hill comments on
the Risk Assessment.
COMMENT 2: Exposure to site related contaminated groundwater
does not appear to be a reasonable exposure scenario. It is not
reasonable to assume that the landfill itself will not be
developed, but the land immediately surrounding it will be
developed.
RESPONSE 2: The total carcinogenic risk for adults for future use
of site-affected groundwater is 1 x 10-3. It is entirely
appropriate for U.S. EPA to consider current and potential risk
due to exposure to contaminated groundwater from the site.
The u.S. EPA risk calculations presented in the RI/FS comply
Agency policy and guidance on risk assessment and resolve
ambiguities in favor of protecting human health and the
environment.
with
The NCP details that the Superfund program shall achieve an
adequate level of protectiveness at Superfund sites. This
adequate level has been defined as a lifetime carcinogenic risk
range of 1 in 10,000 to 1 in 1,000,000 (1 x 10-4 to 1 x 10-6).
The potential risk associated with the ingestion of contaminated
groundwater from the site is 1 in 1,000 (1 x 10-3), which is an
unacceptable risk. In addition, the U.S. EPA must protect the
environment, which the commentor did not address. The Agencies
are concerned with the long-term impacts posed by site
contaminants to the Root River, the on-site lake and the
wetlands.
The Agencies have determined that the alternative proposed is the
best way to achieve protection of human health and the
environment.
COMMENT 3: "...The probability of DNAPLs disposal is an
important factor in deciding the need for additional monitoring
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11
wells. Depending on this evaluation it may be prudent to install
at least .three monitoring wells in the underlying aquifer to
evaluate contamination in the lower aquifer."
RESPONSE 3: U.S. .EPA agrees that monitoring of the bedrock
aquifer would be prudent. This work should be performed, at a
minimum~ as part of the Remedial Design phase.
4.
RI Specific Comments - CH2M Hill
COMMENT 1: "...Typically if clean cover soils are used, surficial
soil sampling is not appropriate."
RESPONSE: The origin of the soil used for the landfill cover is
uncertain. Surface soil samples (from the top 2 inches of soil)
were collected from four general areas: background locations,
cover material, erosion areas and areas at the base of the
landfill.
It is entirely appropriate that surficial soils were sampled.
Waste material in the landfill has been exposed due to erosion of
the cover and, during seasons of high precipitation, leachate has
seeped through the sides of the landfill into the low-lying areas
around the landfill. Therefore, it is important that surface
soil samples were taken in order to characterize risks from
exposed waste materials and from contaminants that have migrated
due to surface runoff.
COMMENT 2: Page 2-11, background surface water and sediment
samples to determine the contamination resulting from the
railroad were not taken. Railroad ties are preserved either
solutions of pentachlorophenol or creosote.
with
RESPONSE: It is agreed that the use of pentachlorophenol and
creosote on the railroad tracks may represent another source of
phenolic and PAR compounds. And while it is possible that
railroad activities could be responsible for some of the
substances identified in surface water sample SW-1, our knowledge
of the site leads us to believe that some other site may be
responsible for the contamination found at this sampling
location. The wetland area to the north from the associated
with the line could be responsible for the materials not shown on
the Figure 2-6
COMMENT 3: Pages 2-11, concerning the type of water used by
the residents...
RESPONSE: Within Region V, surface water samples are typically
not filtered prior to shipping to the laboratory. Thus it is
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12
appropriate that these samples were not filtered. It is true
that the acid preservative, would tend to dissolve the naturally
occurring inorganics from the suspended sediment. However,
aquatic life and persons using. the surface water bodies for full
. contact recreational purposes will also be exposed to the
surface water, its suspended sediment, and any inorganics which
may be "adsorbed onto the surface of the suspended organic.
COMMENT 4: "... Groundwater samples were not analyzed for
conventional pollutants..."
RESPONSE: The groundwater samples were analyzed for Target
Compound List (TCL) organics, Target Analyte List (TAL)
inorganics and total dissolved solids (TDS). Analyses for BOD,
COD, TOC, chloride and alkalinity are typically not performed as
a part of RIfFS. .
COMMENT 5: "Pages 3-10, groundwater flow directions for the
second set of water level measurements taken October 12, 1989
were not plotted or discussed. A plot of water table contours
for this date show a similar southwest flow direction but the
mounding near LW-3 is gone and a mound near LW-2 occurs. Further
water level measurements should be taken if a groundwater
collection system is the selected remedy."
RESPONSE: Refer to section 2, Hvdroqeoloqy Review.
COMMENT 6: "..Toluene is found at nearly all locations including
background. Since it is a likely lab contaminant, it should have
been deleted from the risk assessment."
RESPONSE 6: U.S. EPA disagrees. The high concentrations of
toluene detected are not indicative of laboratory contamination
and indicate that there is toluene contamination at the site.
COMMENT 7: "The surficial soil contaminants causing
unacceptable risk (i.e., >1 x 10-6) are As, Ba, Cr, Mn. The
exposure concentration used (upper 95 percent confidence limit of
the arithmetic mean) was in all cases lower than corresponding
background concentration (also the upper 95 percent confidence
limit). Because inorganic background concentrations typically
exhibit a wide variation, the upper 95 percent confidence limit
of background is the appropriate measure of background. As a
result, unacceptable risks from surface soils (i.e., > 1 x 10-6
or HI>l) are not documented to be occurring. This would be
expected if uncontaminated cover soils were used.
RESPONSE 7:
u.S. EPA disagrees that unacceptable risks from
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13
surface soils are not documented to be occurring. Application of
statistical analysis (calculation of the upper 95 percent
confidence limit) to the background sample data is not a valid
method for determination of background concentrations, due to the
small background sample size. In addition, refer to the above
discussion on surface soil contamination.
. .
Comment 8: "Unacceptable risks from exposure to surface water
were not documented other than...resulting from one surface water
sample..."
Response 8: "As shown in the risk assessment, surface water
quality criteria were exceeded at on-site and downstream
locations. Impacts to aquatic life could potentially be expected
resulting from these exceedances. As stated in the ROD, there is
the potential for aquatic life impacts.
Comment 9: "An unacceptable risk from exposure to sediment was
caused by only 1 sample...Remediation of sediment should be
limited to that area unless further data is obtained..."
Response 9: As stated in the ROD, additional sediment quality
data will be obtained during the remedial design to further
define the areas of sediment needing remediation.
Comment 10: Risks from exposure to groundwater ...were
documented for numerous organic and inorganic contaminants." A
detailed review of background related contaminants would reduce
the calculated risks lightly. "The overall conclusion of
unacceptable risk in the unlikely future event of use of this
groundwater would not change."
Response 10: U.S. EPA and the State acknowledge this comment.
As discussed throughout the responsiveness summary, adjusting the
risk assessment to account for minor errors would not
significantly reduce the groundwater risk levels.
Comment 11: Aquatic life environmental threats were limited to
exposure to chromium, copper, lead, and zinc. Background
concentrations were higher than downstream concentrations for
all parameters but chromium, which was slightly higher than
background. "Chromium exists in surface waters in
the...trivalent state."
RESPONSE 11: It is unclear what data the commentor is referring
to. Background concentrations were not higher than on-site and
downstream concentrations. For example, at background sampling
locations SW-15 and SW-16, chromium was not detected in Phase 2
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14
sampling, whereas SW-11 had a concentration of 65.2 ug/l and SW
19A had a concentration of 48.3 ug/l. A conservative assumption
was made regarding the hexavalent state of the chromium.
CH2M Hill FS General Comments
5~
. .
COMMENT 2a: "The RI did not document risks to public health and
the environment caused by the site..." "Four of the final six
alternatives address risks from groundwater ingestion through
institutional controls."
RESPONSE 2a: This comment has been addressed in another
response. While included as portions of the selected remedy,
institutional controls, in and of themselves, are not sufficient
to meet the expectations of the NCP. The NCP maintains the
expectation that groundwater be restored to its beneficial use,
and that institutional controls should not substitute for active
response measures as the sole remedy..."
COMMENT 2b: The primary objective of the slurry wall included in
alternatives 4a and 4b is to prevent discharge to surface water.
RESPONSE 2b: Alternatives 4a and 4b include the slurry wall in
order to prevent discharge to surface water and to prevent
continued contamination of groundwater. The primary objective of .
the slurry wall is to control the source of contaminants,
therefore preventing further contamination of groundwater and
subsequently, surface water contamination.
COMMENT 2c: Exceedances of Federal drinking water standards and
Wisconsin groundwater standards does not mean that groundwater
remediation must be undertaken. WDNR could require other
remedial actions, such as capping, which would eventually result
in meeting Wisconsin standards.
RESPONSE 2c: If Wisconsin groundwater quality standards are
exceeded, Chapter NR 140, Wisc. Adm. Code, requires that
responses be implemented such that the facility regains and
maintains compliance with the groundwater quality standards.
More than one response, or remedial action, may be required in
order to regain and maintain compliance with the groundwater
quality standards. Wisconsin groundwater quality standards are
exceeded at HDL, therefore, responses must be implemented. The
selected alternative includes a cap to limit infiltration through
the waste mass, thereby reducing contaminant loading to the
groundwater. However, since waste was disposed within the
groundwater, this waste will act as a continued source of
groundwater contamination after the cap is placed. U.S. EPA and
the State believe that a cap alone will not be sufficient to
-------
15
reduce groundwater contamination to below groundwater quality
standards, and that additional remedial actions are necessary.
COMMENT 3: Renovating the existing cover may meet remedial
objectives. "The basic objective of renovation would be to prevent
erosio~.and exposure or overland transport of landfill wastes.
Whether RCRA is an ARAR should be evaluated. The NR 504 cap
requirements should be "contingent on exceedance of a groundwater
'action level' designed to be protective of surface water."
RESPONSE 3: The objective of the cap in the selected alternative
is to limit infiltration through the waste mass, reducing
contaminant loading to the groundwater. A secondary objective is
to prevent erosion and direct contact exposure to the landfill
contents and contaminated surface soils. NR 504 states that "all
final cover systems shall be designed to minimize leachate
generation. . ." NR 506 states that the final cover system of NR
594 may be required if "this type of final cover system is
necessary to prevent or abate attainment or exceedance of the
groundwater standards contained in ch. NR 140." Although surface
water protection is a goal of the selected remedy, groundwater
standards are not dependent on surface water protection. NR 504
also states that "all final cover systems shall be designed to
minimize leachate generation". Chapters NR 504 and 506 are ARARs
at the HDL site. RCRA Subtitle C is not considered an ARAR at HDL.
COMMENT 4: "The advantages of a "multimedia cap" were not
quantified in the FS...lf a cap is required by the agencies, the
lower cost "multilayer" cap would likely meet objectives and be
cost effective in light of the overall low risks from the site.
RESPONSE 4: U.S. EPA agrees that the multilayer cap is a component
of the remedy that will meet remedial objectives. However, a cap
alone will not meet all established remedial objectives and will
not attain ARARs. As described in the NCP, remediation goals shall
establish acceptable exposure levels that are protective of human
health and the environment.
Comment Sa: "The FS did not sufficiently document the rationale
for the groundwater treatment system included in Alternatives 5a
and 5b." Conventional pollutants were not analyzed for.
Response 5a: At the time of sampling, the guidance was followed
for selection of parameters to include in the sampling regime (i.e.
TAL, TCL). The compounds mentioned, BOD, COD, TOC, are normal
parameters when sampling leachate generated from a lined landfill,
but are not standard parameters for groundwater. The
concentrations of specific parameters can be used as a general
guideline whether more rigorous treatment methods are necessary
(i.e. biological treatment).
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16
COMMENT 5b: "Typically, an FS will evaluate the tradeoffs between
high capital cost of slurry walls with resulting low groundwater
treatment annual costs versus no slurry wall and higher annual
groundwater treatment costs."
RESPONS~' 5b: The HDL FS did evaluate between alternatives 4a and
4b versus 5a and 5b using this tradeoff. Alternatives 4a and 4b
were shown to be less costly. CH2M Hill response 6 of this
section, CH2M Hill FS Specific Comment 15, and TETC FS Response
III also respond to this comment.
COMMENT 6: "Alternative 6 included recycle of groundwater back to
the landfill to promote degradation of wastes". This alternative
"could provide early stabilization of the landfill waste as well as
offer material cost savings".
RESPONSE 6: Chapter NR 112 WAC prohibits injection of waste waters
or surface waters. Once the groundwater is pumped out, it is
considered a waste water. After treatment, the effluent is
considered surface water. Also, chapter NR 504 requires that "All
final cover systems shall be designed to minimize leachate
generation by limiting the amount of percolation through the cap
system. . . " U.S. EPA and WDNR are not aware of any situations
where liquid recycling through landfills resulted in ~tabilization
of the landfill such that groundwater quality standards could be
met.
6.
CH2M Hill FS SDecific Comments
COMMENT 1: "section 1 requires significant changes for the RI
review comments."
RESPONSE 1:
U.S. EPA disagrees.
COMMENT 2: "... arsenic and beryllium are mentioned as
contaminants causing unacceptable risk in sediment. This could not
be found in the RI Risk Assessment. The vinyl chloride in SD-7 was
not mentioned on page 1-13."
RESPONSE 2: U.S. EPA feels confident that risks at the site were
adequately characterized.
COMMENT 3: "Also, many objectives are stated in terms of meeting a
1 x 10-6 excess cancer risk. EPA guidance is that 1 x 10-6 is a
"point of departure" but that risks as high as 5 x 10-1, can be
considered.
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17
RESPONSE 3: The NCP explains how the point of departure is to be
used. Where remediation goals are not determined by ARARs,
u. S. EPA uses a 10-6 risk level as a point of departure for
establishing preliminary remediation goals. This means that a
cumulative risk level of 10-6 is used as a starting point for
determin~ng th~ most appropriate risk level that remedial actions
should be designed to obtain. The use of 10-6 expresses
U.S. EPA's preference for actions that result in risks at the more
protective end of the risk range.
COMMENT 4:
site..."
"The discussion of ARARs lacks specificity to the
RESPONSE 4: There is an adequate discussion of ARARs in the FS and
the ROD.
Comment 5: Background estimates were performed using an arithmetic
mean rather than a 95 percent confidence limit.
ResDonse 5: U. S. EPA acknowledge this comment. Addi tional
background sampling will be performed during remedial design.
Background estimates will be re-evaluated at that time.
COMMENT 6: "NR 506.08 regulations for active gas control are not
retroactive to closed landfills. The relevancy and appropriateness
of this requirement must be judged based on the specifics of this
site."
RESPONSE 6: NR 506.08 requires that "All solid waste disposal
facilities which have a design capacity of greater than 500,000
cubic yards and have accepted municipal solid waste shall install
. a system to efficiently collect and combust hazardous air
contaminants emitted by the facility". WDNR applies this
requirement retroactively to closed landfills. The HDL site is a
solid waste disposal facility with an estimated waste volume of
788,000 cubic yards. The site accepted municipal solid waste.
This requirement is an ARAR for the HDL site.
COMMENT 10: The low permeability levee encircling the cap may not
be necessary. "Rip rap along the side slopes of the cap may. . .
provide the same protection."
RESPONSE 10: Adequate protection from floodwater must be provided
for the cap, the gas extraction system, and the groundwater pumping
system. The cap must not only be protected from erosional damage,
but increased infiltration due to flood
COMMENT 11:
"The need for a more expensive cement-bentonite slurry
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18
wall instead of a soil-bentonite slurry wall needs further review."
RESPONSE 11: As noted in the ROD, different types of slurry walls
will be evaluated during remedial design in order to select the
better option.
COMMENT 12: "The actual risk after capping is not reduced. The
risk from background natural arsenic levels in soils is about
1 x 10-t., based on Table 2-6. As a result, any soil used in
capping would not be expected to change the existing natural
background risk. Thus, no justification is offered for the
multimedia cap."
RESPONSE 12: Once it is determined that remedial action is
necessary at a site, U. S. EPA must choose a remedy that meets
ARA~s. A multilayer "cap will meet ARARs for landfill closure. The
main purpose of the cap is to reduce precipitation infiltration
through the landfilled wastes to the groundwater, reducing the
amounts of contaminants leaching from the landfill and to minimize
exposure to contaminated soil and exposed landfill waste. Soil to
be used in cap construction will contain only naturally occurring
levels of chemicals.
Background samples will be obtained during the design phase to
refine background concentrations of contaminants determined in the
RIfFS.
COMMENT 13:
appears too
should be a
head on the
The percent reduction given for a multilayer cap
low. "1 foot of the 2-foot cover soil above the clay
sand to provide drainage, thus reducing the hydraulic
clay and lowering the amount of infiltration.
RESPONSE 13: The percent reduction in infiltration given for a
multilayer cap is conservatively estimated. Higher percent
reductions may be possible. Given the relatively long flow
distances, a sand drainage layer may not be effective in reducing
infiltration. A saturated sand layer at the toe of the side slopes
may lead to slope failure. Should design calculations show that a
1 foot sand drainage layer above the clay would effectively reduce
infiltration, and that slopes would be stable, U.S. EPA and the
State would consider its inclusion as the lower foot of the 2-foot
cover layer.
Comment 14: "Consolidation of the "contaminated soil and sediment"
was not described in alternatives 4a, 4b, Sa, and 5b, and costs
were not included in the cost estimates."
Response 14: U. S. EPA and the State acknowledge this comment.
Costs for this item will be included in the cost estimates. This
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19
omission does not affect selection of the selected remedy.
COMMENT 15a: An alternative should be analyzed which includes
groundwater collection with recycle to the landfill to promote in
situ biodegradation, and more rapid landfill stabilization.
Infiltration trenches would be used for recycle, with capping "in
the future only if contaminants no longer decreasing, were above
Wisconsin standards, and groundwater collection could be
terminated."
RESPONSE 15a: As stated in the response to CH2M Hill General
Comment 6, injection wells are prohibited by chapter NR 112, WAC.
Final cover systems must be designed to minimize leachate
generation. If contaminant concentrations are above groundwater
standards and no longer decreasing, additional remedial actions may
be required in order to meet standards. The time frame necessary
for stabilization of a landfill through in situ biodegradation
would be extremely long. U.S. EPA and the state can not select an
alternative which is not protective or will not meet ARARs within
a reasonable time frame. Additionally, biodegradation remedies
often involve injection of oxygen in order to maintain aerobic
conditions in the "bioreactor", thus increasing the rate at which
stabilization occurs. Injection of oxygen into a landfill is
technically suspect due to the possibility of uncontrolled landfill
fires.
Comment 15b: If a cap is placed in the future, "its reliability
would be substantially better since'the cap failures associated
with landfill differential settlement would be nearly eliminated.
Cost savings would be realized..."
. Response 15b: As stated elsewhere in this responsiveness summary,
NR 506 and NR 504 require that all final cover systems be designed
to minimize leachate generation by limiting the amount of
percolation through the cap system. Landfill differential
settlement is believed to continue until the entire waste mass has
stabilized, i.e., decomposition is complete. The time frame
necessary for this to occur may be extremely lengthy. The NCP
expresses an expectation that groundwater be restored within a
timeframe that is reasonable.
Comment 15c: The rationale for elimination of Alternative 6 are
not convincing.
Response 15c: Alternative 6 included a mUltilayer,cap, full slurry
wall, groundwater treatment, consol idation of CSS, and in-situ
flushing of the landfill. This al ternati ve is essentially the
selected remedy with the addition of in-situ flushing. As stated
elsewhere, the time frame needed to accomplish stabilization
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20
through flushing is expected to be lengthy. The additional costs
over those of Al ternati ve 4b necessary to install the flushing
system do not seem warranted given the lengthy time frame that
flushing would be necessary. There are additional technical
considerations mentioned elsewhere in this responsiveness summary
which would also need to be resolved.
COMMENT 16: The discussion of ARARs is inadequate. In particular,
stating that no action does not meet ARARs without r~ferring to
which ARARs, provides no useful information.
RESPONSE 16: u.s. EPA disagrees. There is an adequate discussion
of ARARs in the RI/FS and the ROD.
Comment 17: Placing a levee around the landfill for flood
protection "may allow a substantial upward gradient on the cap to
occur. It "Also, the levee would substantially affect the flood
plain."
Response 17: The levee, in conjunction with the slurry wall,
should prevent sudden buildup of hydrostatic pressures within the
landfill. Consideration will be given for this potential situation
during remedial design, as well as flood plain effects.
Comment 18: "Two inches of infiltration through a cap with two low
permeability layers appears excessive. Also, 2 inches over 3 acres
result in 1.9 million gallons per year, not the 1.3 million used in
the cost estimate.
Response 18: The cap in the selected alternative 4b will have one
low permeability layer of clay. The expected infiltration rate
through this cap was addressed in Response 13, above.
Comment 19: "Two inches of infiltration appears excessive also for
a clay cap."
Response 19: The expected infiltration rate through this cap was
addressed in Response 13, above.
Comment 20: "Calculations of groundwater
Alternatives Sa and Sb were not presented."
flow
rate
for
Response 20: The omission of these groundwater calculations is not
considered significant.
COMMENT 21:
relied on
In general, the detailed evaluation of alternatives
aualitative discussions based on faulty remedial
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21
objectives. Very little effort was made in the FS to quantify the
real benefits to pUblic health and the environment. This section
must be completely redone to serve as a basis for remedy selection.
RESPONSE 21: U.S. EPA disagrees. Levels of contamination in the
groundwater were found that exceed relevant and appropriate
standards and, based on the provisions of the NCP, the selected
action is appropriate and justified both qualitatively and
quantitatively. In order to protect public health, U.S. EPA is
conservative in its approach to the remedial action at the HDL
site, since some of the contaminants detected at the site are human
carcinogens.
7.
Ch2M Hill Comments on Risk Assessment
COMMENT: "Contaminants detected in less than 10 percent of
samples or in some instances only once per media are retained for
assessment of risk."
COMMENT: "Potential contaminants of concern identified for one
environmental media ... were characterized "without exception" for
all environmental media irrespective to the stated criteria for
selection of contaminants.
RESPONSE: Several comments were made that infrequently detected
chemicals were retained for evaluation in the risk assessment.
This r~sponse addresses each of those comments. If a chemical was
not detected in a medium, it was eliminated from the risk
assessment for that particular medium. For chemicals that were
detected, but infrequently, a conservative approach was used in
retaining these chemicals for the risk assessment. This is in
accordance with u.S. EPA guidance, Risk Assessment Guidance for
Superfund, Volume 1; Human Health Evaluation Manual, December 1989.
The infrequent detection of a chemical at a site does not imply
that its presence should be ignored. Infrequent detection can be
the result of practical limitations on the number of samples taken;
care needs to be used not to eliminate chemicals that may be
present at toxicologically significant concentrations. For this
site, however, the impact of infrequently detected chemicals on
total site risk is minimal. For example:
( 1)
1,1-dichloroethene was detected in groundwater in lout of 26
samples and in sediment in lout of 14 samples; the
carcinogenic risk of 1.5 x 10-5 in both environmental media is
less than 1% of the total carcinogenic risk for the site;
( 2 )
Bis(2-ethylhexyl)phthalate was detected in surface water at 1
out of 27 samples and in groundwater in 8 out of 26 samples;
the carcinogenic risk of 2 x 10-5 is approximately 1.2% of the
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22
total carcinogenic risk for the site.
COMMENT: "Organic contaminants were not considered as natural
substances in any media therefore, they were not compared to the
backgrouryd and thus attributed as site contaminants for estimation
of potential risk. However, numerous organics quantified in the
risk assessment may in fact be attributable to laboratory
contamination or non-site related sources of contaminants."
RESPONSE: Background sampling stations were chosen based on site
specific geographical and assumed hydrogeological characteristics
at each sampling station; stations thought "least likely to be
affected by the site" were chosen. However, in some instances,
selected background areas may be impacted by a site. The presence
of organic chemicals in these soil samples may be the result of
contamination from the site. These chemicals may not be
attributable to blank contamination as suggested by the cornmentor
(see Section 6.2.2 of the RI report). An additional investigation
of background conditions will be performed as part of the selected
remedy.
COMMENT: "There is no discussion as to how data was combined from
various site investigation activities... In the absence of any
explanation, the accuracy of the statistical reduction of site
sampling data cannot be verified... At a minimum, such errors, if
present, would require reanalysis of the existing data and a new
discussion of the results."
COMMENT: "...residential wells are not influenced by site
conditions and have thus "been excluded from the quantitative risk
assessment. II Therefore, it is incorrect to include analytes
detected in such residential wells in the listing of potential site
related contaminants of concern..."
RESPONSE: Data used for the quantitative risk assessment was
collected during phase I and II of the RI activities and are
tabulated in the Appendix to the RI report. All samples were
analyzed by a U.S. EPA certified contract laboratory.
Data for residential well sampling was not used in the quantitative
risk assessment and was not considered during the selection of
contaminants of concern for other media. However, in order to
maintain consistency with the RI report, they were included on
Table 6-1 of the Risk Assessment.
COMMENT: "There is no discussion of how sample data was
statistically reduced by calculation of geometric or arithmetic
means. .. This question requires. clarification before the mean
values can be considered accurate."
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23
RESPONSE: The 95% confidence limit of the arithmetic ~ean was used
to establish the exposure concentration for risk calculation. The
equation used was:
L=Y+ (to.Sen-')
x s)/n'/2
. .
where
L=95% confidence limit
Y=arithmetic mean
s=standard deviation
n=sample size
to.Sen-1>=t statistic from t table with 95% confidence limit
There are two methods presented in Risk Assessment Guidance for
Superfund, Volume 1; Human Health Evaluation Manual, December 1989,
for calculating the 95th percent confidence limit on the arithmetic
mean. The method used for this assessment assumes that the data
are normally distributed; the other method assumes the data are
log-normally distributed. The method used in this report is less
conservative in that it results in lower risks.
8.
EXDosure Pathway
COMMENT: "Future residential development. and subsequent use of
affected groundwater from beneath the landfill would not be
feasible..."
RESPONSE: The groundwater risk assessment was included in the
report in accordance with U. S. EPA guidance for baseline risk
assessments. The Baseline Risk Assessment is to address potential
risks from the site under both current and alternate future land
use conditions. Since groundwater is used in the
area, the potential exists for exposure to contaminated groundwater
from the site.
The NCP states that a baseline risk assessment is an assessment of
risks from the site in the absence of remedial alternatives which
include institutional controls such as deed and zoning
restrictions.
9.
Toxicoloqical criteria
COMMENT: The comm.entor noted that "The lengthy review of potential
toxic effects, primarily drawn from animal studies, provides little
information regarding potential human health effects from the
hypothetical de minimus exposures to humans,
"The slope factors do not contain all available IRIS/HEAST values
and thereby raise questions as to the adequacy of the estimated
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24
risk values.
RESPONSE: Toxicity data bases ,for most chemicals lack sufficient
information on toxic effects on humans. In such cases, U.S. EPA
may infer the potential for the substance to cause an adverse
effect in humans from toxicity information drawn from experiments
conducted on non-human mammals, such as the rat, mouse, rabbit,
guinea pig, dog or monkey. The inference that humans and animals
(mammals) are similar, on average, in intrinsic susceptibility to
toxic chemicals, and that data from animals can in many cases be
used as a surrogate for data from humans is a basic premise of
modern toxicology. This concept is particularly important in the
regulation of toxic chemicals. There are occasions, however, in
which observations in animals may be of uncertain relevance to
humans. U.S. EPA considers the likelihood that the agent will have
adverse effects in humans to increase as similar results are
observed across sexes, strains, species and routes of exposure in
animal studies.
The slope factors listed in Table 6-3 were accurate when the risk
assessment was prepared. The addition of the most recent values
would not affect the remedy selection process.
Risk Characterization
10.
COMMENT 1: "The presumption that the estimated lifetime cancer
risk is a rate is not correct...There is no known epidemiological
data for this site, and there is no identified known human
population at risk."
RESPONSE 1: u.S. EPA did not intend to use the term "rate". The
use of the term "lifetime excess cancer rate" is not meant to imply
that human health effects are known to have resulted from the site.
It refers to the possibility of such effects.
COMMENT 2: "Use of chronic oral RfDs for hypothetical subchronic
exposures may result in an overestimate of risk for noncarcinogenic
health effects...."
RESPONSE 2: The use of chronic oral RfDs as a substitute for
subchronic oral RfDs could lead to overestimates of the Hazard
Index (HI). However, without subchronic RfDs for cadmium, silver,
acetone, carbon disulfide and heptachlor epoxide, the subchronic
effects of these chemicals cannot be assessed. This leads to
underestimates of the total HI. In order to maintain a conservative
quantitative risk estimate, the chronic oral RfDs should be used to
evaluate the subchronic effects.
COMMENT 3:
"The discussion of estimated noncarcinogenic risk
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25
arbitrarily highlights several risks less than unity... u.s. EPA
considers a HI of 1 to be a reference point...The discussion of
potential noncarcinogenic risk in the Risk Characterization
requires revision to state that the HI estimate for no individual
site contaminant exceeds a HI of 1, and that cumulative HIs summed
by targ~~ organ are less than one. Therefore, exposure and intake
of noncarcinogenic contaminants...do not appear to be a problem at
the site."
RESPONSE 3: When the total HI for an exposed individual or group
of individuals exceeds unity, there is concern for potential
noncarcinogenic health effects. For multiple exposure pathways,
the HI can exceed unity even if no single exposure pathway exceeds
unity. If the total HI exceeds unity and if combining exposure
pathways result in combining HIs based on different chemicals,
segregating the contributions of the different chemicals according
to major effect (U.S. EPA 12/89) may need to be considered.
Risk estimates that are less than one for an individual contaminant
are NOT considered to be insignificant. Instead, risk estimates
that are less than one for total contaminants are considered to be
insignificant. Therefore, individual contaminants having an HI
less than 1.0 need to be included in the report for discussion.
COMMENT 4: The site may not pose an unacceptable risk to public
heal th. . . the hypothetical future residential exposure setting. .. is
not valid...".
RESPONSE:
above.
See response to comment for exposure pathway section
11.
Earth Technoloqy General Feasibilitv study Comments (TETC)
COMMENT l: "Background for arsenic and chromium provided the basis
for soil removal...It is apparent that the actual amount of soil
could vary widely, even assuming that the background values
established for arsenic and chromium are representative."
RESPONSE l: Additional background sampling will be conducted
during the design phase in order to refine background
concentrations. The volume of soil and sediment presented in the
FS was an estimate. The actual amount of soil and sediment to be
excavated will be determined during the remedial design.
12.
Overview of the Remedial Investiqation Report (TETC)
COMMENT IA: Data summary sheets were compared in Appendix H were
compared with summary tables presented in Section 4 of the RI.
variations were noted in Tables 1-1 through 1-4 of the TETC
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26
comments. This lack of quality control may have resulted in a.
flawed characterization of the site risk. The analytical reports
from the laboratory were not included, therefore, TETC could not
determine which data set was valid.
RESPONSE IA: U.S. EPA and the State recognize that discrepancies
exist between' the referenced summary tables. However, for the
substances noted in the tables, the noted discrepancies do not
significantly affect the calculated risk levels. The laboratory
analytical reports were available for review, as TETC was informed
during the comment period.
COMMENT IB: The number and type of quality control
obtained during the remedial investigation were not
performed in accordance with the QAPP.
samples
always
RESPONSE IB: U.S. EPA and the State recognize that the number of
quality control samples obtained were not in accordance with the
QAPP in every situation. However, U. S. EPA and the State are
confident that the laboratory data substantially reflects field
conditions and is reliable data since an adequate number of blanks
were taken overall.
COMMENT IC: The absence of the laboratory's analytical reporting
sheets and the noted errors "undermine the credibility of the
report". The risks, remedial action objectives, and conclusions of
the FS and Proposed Plan "are not adequately supported by reliable
data."
RESPONSE IC: As noted in responses IA and IB, u.S. EPA and the
State recognize that some discrepancies exist. The data, as a
whole, reflects field conditions and are considered a reliable
basis for the risk assessment, remedial action objectives, and
conclusions of the FS and Proposed Plan.
13.
Review of Baseline Risk Assessment (TETC)
COMMENT II: The "majority of the risks are attributable to a
future. . scenario. and the ingestion and inhalation of
associated contaminants." "The current risks. . . are primarily
due to the inhalation of contaminated soil particulates by on-site
trespassers."
RESPONSE II: U.S. EPA and the State acknowledge this comment.
NCP directs U.S. EPA to consider actual and potential risks.
The
COMMENT IIA: Inappropriate data evaluation and selection of
contaminants of concern were used to generate "an unrealistic worst
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27
case list of contaminants
concentrations."
of
concern,
as
well
as
exposure
RESPONSE IIA: U. S. EPA guidance documents were followed to
evaluate data and select contaminants of concern. Appropriate
methodolpgy was used to generate a conservative list of
contamiriants of concern and conservative exposure concentrations.
COMMENT IIAl: Field and laboratory screening criteria were not
followed in selecting contaminants of concern. This "resulted in
improper selection of contaminants of concern in all media."
RESPONSE IIAl: The sample data were evaluated against the quality
control blank data according to u.S. EPA guidelines. The
evaluation included surface water and groundwater samples. This
data was rechecked and found to be consistent with this guidance.
For those data where field QC blanks were not available, a
conservative evaluation was made and all of these sample data were
'retained for further risk characterization.
COMMENT IIA2: "Failure to properly compare analytical results with
background concentrations resulted in improper selection of
contaminants of concern."
RESPONSE IIA2: Background sampling stations were chosen based on
site specific geographical and hydrogeological characteristics at
each sampling station. Stations least likely to be affected by the
site were chosen. Accordingly, the presence of organic chemicals
in background samples was not considered sufficient reason to
eliminate those detected at the site from evaluation in the
quantitative risk assessment, since their presence could be the
result of site contaminants. These chemicals were not attributable
to blank contamination as suggested, since a screening step was
employed using standard EPA data validation criteria (see Section
6.2.2) .
COMMENT IIB: The commentor expressed concerns over the pathway
exposure dose and risk estimation models and parameter values used
in the Risk Assessment.
RESPONSE IIB: U.S. EPA feels confident that risks at the site were
adequately characterized in the Risk Assessment. Reference should
be made to general Risk Assessment comments and responses and to
CH2M Hill Risk Assessment comments and responses.
COMMENT IIIB:
characterization.
The
commentor
expressed
concern
over
risk
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28
RESPONSE IIIB: Please refer to response lIB.
14.
Feasibilitv study Review (TETC)
COMMENT. IlIA: ."Background levels for arsenic and chromium provided
the basis for soil removal. The levels were establ ished. . . by
calculating the 95% confidence level mean, for a sample population
of two". The basis for calculating soils volumes was "an arbitrary
depth of one foot, and an extrapolation to determine the horizontal
extent of the contamination." Volumes could vary widely.
RESPONSE IlIA: Background levels were chosen to estimate clean-up
levels for chromium and arsenic because soil concentrations
corresponding to health risks of 10-6 are below background soil
concentrations. The sample population for determining background
levels is based on the best available information to date. A depth
of one foot was used to calculate soil volume because it is
believed that existing health risks due to exposure to surface soil
are limited to approximately one foot. The horizontal extent of
contamination was determined by use of existing RI data which is
the best available information to date. Additional information
will be collected during the remedial design phase to verify the
extent of soil removal.
COMMENT IIIB: The FS report had errors regarding the utility of
barrier walls. Sheetpiling was rejected "because interlocking
edges limit the ability form a good seal." with a pressure
gradient, sheetpiling can be effective. "Joints can be
grouted...and/or a natural sediment seal may be formed over time.
Advantages of sheetpiling include: "that it would be less
destructive of the wetlands,...a levee would not have to be built
around the site,...(it) would not require the construction of a
working platform around the site,...(it) could provide for
protection from an 100 year flood" and it would be less costly.
RESPONSE IIIB: A slurry wall was selected instead of sheetpiling
because the permeability of a slurry wall is lower by at least a
factor of ten. In addition, the presence of large rocks and
boulders can limit the seal between sheets and may cause
deflections during driving. Also, it is difficult to determine
when the sheet piles have penetrated the silt and clay layer below
the aquifer. The intended pressure gradient included in the
selected alternative 4b will be minimal, only enough to prevent
groundwater from flowing outward through the wall. In order to
provide protection from a 100-year flood event, additional
structural support would be necessary, which would increase costs.
COMMENT IIIC:
"Conceptually, a barrier wall would inhibit the flow
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of materials through the shallow aquifer in and around the waste
mass, thus slowing or preventing the migration of material away'
from the site." The slurry. wall would reduce the hydraulic
conductivity to 10-6 or 10-7. "If contaminant recovery is the
objective of the barrier/well system, then the lost gradients would
have tq be made up by increased pumping... leading to a loss in
efficiency of' the recovery system." "A well field could be
designed to keep contaminants from escaping to the Root River,
saving the cost of installing a slurry wall...the damage to the
wetlands, and the adverse effects on the groundwater cleanup time.
RESPONSE IIIC: The slurry wall is intended to prevent the flow of
contaminants through the shallow aquifer in and around the waste
mass and to prevent the migration of the contaminants away from the
site. The barrier wall also provides additional protection should
the pumping system fail or need to be temporarily shut down. The
pumping system within the barrier wall is intended to create inward
gradients into the landfill. The pumping rate will be sufficient
to create inward gradients, but is not intended to flush the
landfill. Groundwater pumping, with much denser well placement,
could potentially be used to prevent contaminated groundwater from
migrating away from the landfill. Since the groundwater volumes
pumped would be high, an on-site treatment plant would be
necessary. The treatment plant would most likely need to be
constructed within the floodplain and may adversely affect the area
wetlands. The pumping system would have to be carefully designed
in order to provide contaminant capture during high water
condi tions. This groundwater pumping system would also have
adverse effects on the wetlands due to the high rate of groundwater
extraction necessary to capture all contaminants. Protection to
the site wetlands and to the Root River to prevent these adverse
effects would be necessary. Groundwater cleanup time for this
system would also be expected to be extremely long.
COMMENT IIID: The proposed plan "indicates an off-site treatment
alternative for the extracted groundwater". No further information
regarding the specifics of the implementability of this option were
provided in Section 3 or 4. Implementability of this treatment
option is not substantiated in the FS.
RESPONSE IIID: The most cost-effective option for off-site
treatment of extracted groundwater in the area would be the Oak
Creek treatment facility, which is connected to a manhole located
within one mile of the site. There are other wastewater treatment
facilities in the area which have available capacity.
COMMENT IIIE: "The recommended remedy... includes an active gas
venting system. ... Prior to requiring an active gas abatement
system, justification should be provided that there is a risk
associated with the gas emissions."
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RESPONSE IIIE: The response to Comment 6 of the CH2M Hill Specific
Comments responds to this concern.
COMMENT IIIF: Information in the FS was insufficient to reproduce
the sustainable yield value of 42 gpm.
RESPONSE IIIF: The sustainable yield estimate of 42 gpm is based
on the best available information as a result of the RI. The FS
states that the actual number of wells, spacing, pumping rates, and
drawdown would be determined by pump testing conducted "during the
design phase. The hydraulic conductivity, which is usually the
most critical factor in determining well flow, was checked against
resul ts of other values from the same aquifer. A pump test will be
conducted during the design to refine this'estimate.
COMMENT IVA: TETC personnel inspected the HDL site and "concluded
the wetlands were more extensive than previously anticipated." "It
appears that the state wetlands maps underestimated the actual
extent of wetlands that would meet the unified Federal criteria."
RESPONSE IVA: A wetlands assessment was conducted at the landfill
by U.S. EPA in conjunction with the State and the Southeast
Wisconsin Regional Planning Commission. This assessment is
discussed in the ROD. The assessment generally concurred with the
previous wetland mapping. U.S. EPA and the state are confident
that this assessment represents the actual extent of wetlands that
meet Federal criteria.
COMMENT IVB: This comment references the Federal Manual For
Identifvinq and Delineatinq Jurisdictional Wetlands and summarizes
the technical criteria mandatory for an area to be identified as
wetlands.
RESPONSE IVB:
This information is noted.
COMMENT IVC1:
TETC performed their own wetlands determination.
RESPONSE IVC1: U.S. EPA and the State acknowledge that TETC
accessed the site and surveyed the area for wetland
characteristics, although without U.S. EPA authorization or
supervision. Thus, U.S. EPA cannot independently verify TETC's
results.
COMMENT IVC3: "Installation of a full slurry wall...will greatly
disturb the wetlands surrounding the landfill as well as the Root
River." A summary of regulatory concerns regarding wetland impacts
is provided.
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RESPONSE IVC3: The HDL ROD recognizes that installation of a full
slurry wall will have impacts on the wetlands. The ROD states that
wetland impacts will be minimized to the extent possible and that
unavoidable impacts will be compensated for by the enhancement of
existing wetlands or the creation of new wetlands.
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