PB94-964127
EPA/ROD/R05-94/253
September 1994
EPA Superfund
Record of Decision:
Sauk County Landfill Site,
Excelsior, WI,
3/24/1994
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PROPOSED RECORD OF DECISION
REMEDIAL ACTION FOR THE SOURCE CONTROL OPERABLE UNIT
Site Name and Location
Sauk County Landfill
The Sauk County landfill is located in the in the Town of Excelsior, Sauk
County, Wisconsin (approximately 6 miles east of the City of Reedsburg and
approximately 9 miles west and north of the City of Baraboo), SE 1/4 of
Section 15, Township 12 North, Range 5 East.
Statement of Basis and Purpose
This decision document represents the selected source control remedial action
for the Sauk County Landfill in the Town of Excelsior, Sauk City, Wisconsin,
developed in accordance with CERCLA, as amended by SARA, and to the extent
practicable, the National Contingency Plan. The attached Summary of Remedial
Alternatives identifies the information contained in the administrative record
for this site upon which the selection of the remedial action is based.
Assessment of the Site
Actual or threatened releases of hazardous substances from the site, if not
addressed by implementing the remedial action selected in this Record of
Decision ("ROD"), may present an imminent and substantial danger to public
health, welfare, or the environment.
Description of the Selected Source Control Remedv
The selected source control remedy is Alternative B, Construction of a Gas
Extraction System, as listed in the Focused Feasibility Study. The selected
remedy is an operable unit that meets the solid waste disposal requirements of
NR 500 to 520, Wis. Adm. Code. The specific components of the source control
remedy include:
*
continued monitoring of the groundwater at on-site groundwater
monitoring wells and offsite private wells
regrading of the landfill surface to promote drainage off of the
landfill cover
fencing the landfill
installation of a gas extraction system to efficiently collect and
combust landfill gases
placing a deed restriction on the property to prohibit the disturbance
of the surface of the landfill cap in the future
future maintenance of the landfill cap to prevent erosion and
differential settlement
a contingency which requires a composite landfill cover system if
groundwater quality preventive action limits are not achieved in the
future
*
*
*
*
*
*
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Statutory Determinations
This source control remedy is protective of human health and the environment,
complies with Federal and State requirements that are legally applicable or
relevant and appropriate requirements ("ARARs") for this action, and is cost
effective. This remedy satisfies the stutory preference for remedies that
employ treatment that reduces the toxicity, mobility or volume as a principal
element because it includes the collection and treatment of landfill gas.
Because this remedy will result in hazardous substances remaining on site, a
review will be conducted to ensure that the remedy continues to provide
adequate protection of human health and. the environment within 5 years after
the commencement of this source control remedial action.
A review of the remedy and groundwater quality will be conducted every five
years. This review shall concentrate on whether the remedy is continuing to
prevent and abate groundwater quality standards, and whether the standards in
NR 140, Wis. Adm. Code are being met. If the VOC concentrations on
groundwater start to increase, then additional source control measures will be
taken, including the installation of a composite landfill cover.
A second operable unit for groundwater ~ill be issued after the remedial
~nvestigation and feasibility study have been completed. This source control
operable unit will be consistent with the final groundwater operable unit ROD
for the site.
~ - Zt{--~'f
Date
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SUMMARY OF REMEDIAL ALTERNATIVES SELECTION
SOURCE CONTROL REMEDY
SAUK COUNTY LANDFILL
Findinas of Fact
The following findings of fact summarize the information contained in the
administrative record for the saukCounty Landfill site. The selected source
control remedy is based upon the information contained in the site's
administrative record.
The Wisconsin Department of Natural Resources ("WDNR") finds that:
I.
SITE NAME. LOCATION AND DESCRIPTION
The Sauk County Landfill was listed on the National Priorities List
the U.S. Environmental Protection Agency (EPA) in October of 1989.
does not include the active Sauk County.landfill which is located a
~undred feet north of the closed Sauk county Landfill.
(NPL) by
This site
few
The Sauk County Landfill is located in the northeastern part of the county
between Reedsburg and Baraboo, south of Hwy 33. The landfill is 14 acres in
size and is part of a 320 acre parcel containing both the closed and active
landfills in the Southeast 1/4 of Section 15, Township 12 North, Range 5 East,
Town of Excelsior, Sauk County, Wisconsin. The location is depicted on Map 1.
The landfill is unfenced. Vehicle access is limited by a gate across the road
entering the landfill property.
The Sauk County landfill accepted municipal and industrial waste from Sauk
County between the years 1973 and 1983. The site was designed as a natural
attenuation landfill. This means it has no liner or leachate collection
system designed into modern landfills. It has a volume of about 750,000 cubic
yards. The landfill accepted large quantities of foundry sand, municipal
wastes and industrial wastes from homes and businesses located within the
county.
II.
SITE HISTORY AND ENFORCEMENT ACTIVITIES
Sauk County operated this landfill between 1973 and 1983. During operations,
the site accepted municipal, commercial and industrial wastes, including over
200,000 tons of foundry sand. The foundry sand was used primarily in berms on
the edge of the refuse. The site was closed in 1983 with a cover system
consisting of 2' of clay on the landfill surface, l' of clay on the sidewalls
and 6" of topsoil over the entire site. The topsoil was vegetated. The site
has been maintained by Sauk County since closure.
After reviewing groundwater
recommended to EPA that the
(NPL). The site was listed
quality data from this landfill, the WDNR
site be included on the National Priorities List
on the NPL in 1989. In September, 1991, sauk
1
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/l14/ /
SAUK COUNTY LANDFILL
REEDSBURG
BARABOO
j
N
MADISON
SITE LOCATION MAP
SAUK COUNTY LANDFILL
33
Not to Scale
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County entered into a contract with WDNR to perform a remedial investigation
and feasibility study ("RI/FS") pursuant to s. 144.442, Wisconsin Statutes and
the Comprehensive Response, Compensation and Liability Act ("CERCLA). Under
terms of the contract, Sauk County also agreed to complete a Source Control
Operable Unit. Since that time, Sauk County has been completing the RI.
In December, 1992 WDNR and Sauk County agreed to move ahead with a source
control operable unit while completing the RI. The goal was to speed up the
process and implement a source control action prior to completing the full
RI/FS. Sauk County submitted the Alternatives Array Document in April, 1993
and the Focused Feasibility Study of Source Control Alternatives in August,
1993.
The WDNR issued a proposed plan in September, 1993. The proposed plan
selected Alternative E, Construction of a composite Landfill Cover and Gas
Extraction System as the source control remedy. Data submitted during the
public comment period caused WDNR to reconsider the proposed plan. Based upon
the additional data, WDNR now believes that a modified Alternative B,
Construction of a Gas Extraction System with a contingency plan is the best
source control remedy for the site. Factors considered by WDNR in making it's
decision are listed in section III, Highlights of Community Participation.
~II.
HIGHLIGHTS OF THE COMMUNITY PARTICIPATION
An information repository has been established at the Reedsburg Public
Library, 345 Vine Street, Reedsburg, Wisconsin. The administrative record is
made available to the public at the Baraboo Public Library, 230 Fourth Street,
Baraboo, Wisconsin.
In September, 1992 WDNR issued a Superfund Fact Sheet which provided a summary
of the site history, explained the Superfund process and delineated the
approved RI work plan. On September 29, 1992 the WDNR and the Wisconsin
Department of Health and Social Services (WDHSS) held a public informational
meeting at 7:00 p.m. in the Rock Springs Community Center. The meeting was
held to discuss the landfill and to explain the RI field work which was about
to start. Approximately 30 residents attended the meeting.
Residents living near the iandfill created the Evergreen Property OWners
Association. On November 11, 1992 the Property Owners Association organized a
meeting attended by WDNR, WDHSS and Simon Hydro-Search (consultant to Sauk
county) to answer questions from residents living near the landfil~.
Approximately 100 persons attended this meeting.
,
In March, 1993 WDNR issued a Superfund Fact Sheet containing a summary of the
RI data up to that point in time. This fact sheet contained information on:
*
groundwater
groundwater
preliminary
stress, and
a timeline for installing new monitoring wells at the
quality from site monitoring wells
quality from houses surrounding the landfill
results from a vegetation survey designed to detect methane
*
*
*
site.
2
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2.
In May, 1993 the Evergreen Property Owners Association was awarded a Technical
Assistance Grant from EPA. The purpose of the grant is to allow persons
affected by Superfund sites to retain their own technical staff to explain the
Superfund process and the data generated during the RI.
In September, 1993 the WDNR issued another Superfund Fact Sheet.
sheet also contained a summary of the RI data.
This fact
The Proposed Plan for the source control operable unit was made available for
public comment on September 8, 1993. Notices announcing the availability of
the proposed plan were published in the Reedsburg Time Press and the Wisconsin
State Journal on September 2, 1993. A public meeting to explain the Proposed
Plan, and to receive public comments was held on September 21, 1993.
Approximately 40 persons attended the meeting. The public comment period was
held between September 8, and November 9, 1992. Comments received from the
public and WDNR's response to those comments are included in the attached
Responsiveness Summary, which is part of this ROD.
In the Proposed Plan, WDNR had selected Alternative E, Construction of a
Geosynthetic membrane as the preferred remedy. Based upon comments received
during the public comment period, and i~formation contained in Technical Memo
~3, WDNR has changed it's decision as to the best source control remedy for
the site. WDNR has selected and modified Alternative B, Construction of a Gas
Extraction System with a contingency plan, as the best source control remedy.
Reasons for this include:
1.
Sauk County presented groundwater quality data from TW-25 and TW-26A.
Both of these wells have historical VOC data dating back to 1985 and
1987 respectively. When the entire total VOC data set is graphed as
concentration vs. time, both data sets indicate a strong downward trend
in the VOC concentrations. Capping is the only remedial action that has
taken place on the landfill since closure in 1983. Thus, the cap that
is on the site is having beneficial effects towards stopping the further
release of contaminants to groundwater. The data from TW-25 and TW-26A
are depicted on Figures 1 and 2, respectively.
Sauk County commented that the decrease in total VOCs at TW-25 and
TW-26A can be explained using the exponential decay equation. This
equation assumes that the source decays at a constant rate. Decay rates
are often measured in half-lives, or the amount of time necessary for
the concentration to decay (or decrease) to one-half of it's original
concentration. The analysis presented by Simon Hydro-Search indicates
that:
*
the half-life based upon data from TW-25 and TW-26A are the same
and are approximately 1 year
the semi-log graph of data vs time has a straight line for both
wells. This indicates the decay rate is constant and that there
is not additional input of VOCs from the landfill.
a comparison of the two semi-log graphs shows that they have
similar slopes. This indicates that the same process of releasing
*
*
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Years
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SAUK COUNTY LANDFILL
SAUK COUNTY, WISCONSIN
Brookfield Lakes Corporate Center XII
175 N. Corporate Drive, Suite 100
Brookfield, Wisconsin 53045
Apprv. by:
09/20/93
TOTAL VOCs IN
TW-25
DRAWING: 3037-a3
I FIGURE: 1
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SAUK COUNTY LANDFLL
SAUK COUNTY, WISCONSIN
Brookfield Lakes Corporate Center XU
175 N. Corp~rate Drive, Slite 100
Brookfield, WIsconsin 53045
TOTAL VOCs IN
TW-26A
Dsgn. by:
PRO.ECT:
DRA WING: 3037-a6
FIGURE: 2
-------
3.
4.
~
*
VOCs from the aquifer matrix is occurring at both locations. See
Figures 3 and 4.
should the decreasing trend in VOC concentrations continue, NR
140, Wis. Adm. Code preventive action limits should be met for all
parameters within two years
WDNR agrees that VOC concentrations in groundwater are decreasing and
exponential decay is probably playing a part in the decrease. However,
other factors such as minimizing inputs to groundwater and dilution are
also contributing to the decreasing VOC concentrations. .
A graph comparing total VOC concentrations at TW-25 and the
precipitation at Baraboo indicates that high precipitation years don't
produce flushing events from the landfill. This means that the existing
landfill cap has been successful in reducing percolation of water into
the landfill. See Figure 5.
An analysis of the groundwater data indicates that the existing landfill
cover is decreasing the amount of contamination entering groundwater.
Since 1985, VOC concentrations have been declining. Installing the cap
and maintaining it are the only a~tions that have taken place on the
landfill since it closed. The existing cap must be helping to improve
groundwater quality by reducing the amount of contamination entering
groundwater.
5.
Groundwater quality data from monitoring wells located next to the
-landfill show improving groundwater quality at this time. To address
possible future releases from the s.ite, the remedy includes a
contingency plan which requires that if preventive action limits are not
achieved in the future, a composite landfill cover must be placed on the
landfill.
6.
Residents living near the landfill utilize a sandstone formation~beneath
the area as their water supply source. VOC monitoring of homes in the
area has detected VOCs in one home at concentrations far below drinking
water standards. To address residential concerns about their wa~er
supply, the remedy includes monitoring of private homes for VOCs.
WDNR originally selected Alternative E, a composite cap as the best source
control remedy for this landfill. However, based on the improving groundwater
quality, WDNR has decided that the additional reduction of water into the
landfill provided by the composite cap over the existing landfill cover is not
necessary at this time. Should the results of future groundwater monitoring
indicate that groundwater quality starts to degrade, other source control
actions will be taken at that time.
These were the primary factors used by WDNR to select Alternative B,
Construction of a Gas Extraction System as the source control remedy for this
site.
The public participation requirements of s. 144.442(6)(f), Wisconsin
Statutes, and the community relations requirements in the National contingency
4
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Dsgn. by: Chk. by:
PRO.ECT: 302073037
SAUK COUNTY LANDFR..L
SAUK COUNTY, WISCONSIN
SEMI-LOGARITHMIC
PLOT OF
TOTAL VOCs IN TW-25
DRAWING: 3037-a4
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SAUK COUNTY LANDFILL
SAUK COUNTY, WISCONSIN
SEMI-LOGARITHMIC
PLOT OF
TOT AL VOCs IN TW-26A
RSI SlmDn [H]1fIDJ[pJ(Q)Q~{ffi[pJ~[}{]
Brookfield Lakes Corporate Center XU
175 N. Corp~rate Drive, Suite 100
Brookfield, Wisconsin 53045
DRA WING: 3037 -a 7
FIGURE: 3
-------
100,000
:1
;
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SEMI-LOGARITHMIC
PLOT OF
TOTAL. VOCs IN TW-25
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(Baraboo, Wisconsin)
-------
Plan at 40 CFR s. 300.430(f) (3) have been met in this source control remedy
selection process.
IV.
SCOPE OF THE SOURCE CONTROL REMEDY
As with many Superfund sites, the hydrogeologic conditions at the landfill are
complex. Because of this, and a desire to speed up the process, WDNR and Sauk
County chose to complete work on the source control remedy while also
completing the RI. Remedial actions at the site have been divided into two
activities or "operable units". The first operable unit, or source control
operable unit involves remedial actions taken to control the source of
contamination to groundwater. For landfills, source control options primarily
involve landfill caps or cover systems. This ROD addresses source control
actions. The second, or groundwater operable unit involves remedial actions
necessary to clean up groundwater and achieve compliance with established
groundwater quality standards.
Because this is a source control operable unit, Sauk County has continued to
work on the RI/FS work plan, in order to develop and evaluate final
groundwater remedial alternatives for the site. WDNR has determined that this
source control remedy will be consistent with the groundwater operable unit
Femedy for the site.
An expedited source control remedy is desirable from a public health
standpoint. Taking action now rather than waiting for completion of the RI
has shortened the time required to eliminate the potential for the public to
be exposed to methane and volatile organic compounds which may have migrated
from the site through soil or air. Direct contact with the waste is not
possible because the site is capped with a soil cover. Gas migration will be
controlled through a gas extraction and flaring system. Fencing the site will
also reduce exposure by keeping trespassers off the landfill and away from the
gas extraction system. In addition, adding soil to promote drainage off of
the landfill cap will help to reduce the infiltration of rain and snow into
the waste, reducing the potential for leachate generation. Maintaining the
vegetative cover will continue to reduce infiltration through transpiration.
V.
SUMMARY OF SITE CHARACTERISTICS
A.
Topography
The Sauk County landfill is located along the eastern margin of the
unglaciated area. Topography in the site vicinity is gently sloping to
somewhat hilly. The landfill is located in an east-west trending valley
bounded to the north and south by sandstone bedrock ridges. Elevations on the
ridges are approximately 1200 feet above mean sea level. The valley is gently
sloping to the west with elevations near the fill ranging from 1010 to 960
msl.
B.
Geology/Hydrogeology
The geology near the landfill consists of approximately 50 feet of
unconsolidated material, primarily sand with some silt and gravel layers
5
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present. The color of the sand is predominantly brownish yellow. Below the
unconsolidated material three different bedrock units were identified.
The top of the bedrock is a poorly lithified weathered sandstone. This is the
Mazomanie Formation. It is medium grained and brown to yellow in color. It
ranges in thickness from approximately 40' east of the landfill to only 5' at
the western edge of the County property.
The next bedrock unit is the Lone Rock Formation. This unit consists of
siltstone, shale and very fine grained sandstone. It ranges in thickness
30' to over 50'. This unit acts as asemi~confining unit between. the
sandstone units above and below.
from
Below the Lone Rock Formation is the Wonewoc Formation. It is a medium
grained sandstone that is brown, reddish brown to yellow in color. The entire
thickness of the Wonewoc was not penetrated by monitoring wells, but it is at
least 65' thick near the landfill. The Wonewoc Formation acts as a water
supply aquifer for homes located to the west of the landfill.
Within the unconsolidated deposits, shallow groundwater at or near the water
table flows west, southwest towards the ~araboo River. This upper flow system
~as an average horizontal gradient of 0.015 ft/ft west of the landfill. Near
the base of the unconsolidated deposits and within the weathered sandstone
(Mazomanie Fm) groundwater also flows west, southwest with a horizontal
gradient ranging from 0.010 to 0.013 ft/ft. These groundwater. flow directions
are a result of the natural slope of the upper bedrock surface.
Directly beneath the siltstone and shale semi-confining layer (Lone Rock Fro),
groundwater flows southeast with a gradient of 0.006 to 0.007 ft/ft. Deeper
within the Wonewoc Formation groundwater flows to the east. This is
consistent with the regional flow towards the Wisconsin River. The horizontal
gradient in the deeper Wonewoc is approximately 0.0012 ft/ft.
All vertical gradients wer~ downward and ranged from 0.02 to 0.76 ft/ft. The
highest vertical gradient was noted to the east of the landfill where the
semi-confining layer is thickest. Thickness of the confining layer as well as
the lithology and competence of the Lone Rock Formation are likely to affect
vertical gradients.
C.
Groundwater Contamination
Based upon data collected as part of the RI, a total of 18 volatile organic
compounds (VOCS) were detected in groundwater monitoring wells. The most
common VOCs detected are 1,1-DCA which was found in 13 wells and 1,1,1-TCA
which was found in 8 wells. Of the 18 VOCs detected, only two exceeded
enforcement standards found in NR 140, Wis. Adm. Code during sampling events
in 1993. Tetrachloroethylene (PCE) and vinyl chloride were detected in
concentrations attaining or exceeding enforcement standards. Five additional
VOCs exceeded NR 140, Wis. Adm. Code preventive action limits.
A total of 18 private wells surrounding the landfill have been tested for
VOCs. A home located approximately 3000 feet west-southwest of the landfill
6
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has detected VOCs. l,l-dichloroethane (l,l-DCA) has been detected on two
occasions and l,l,l-trichloroethane (l,l,l-TCA) has been detected three times.
These samples were taken in 1992, 1993 and 1994. In all three sampling
events, the concentrations of these two compounds was far below their .
respective drinking water standards. A second home had detections of l,l-DCA
and l,l,l-TCA the first time it was sampled. These detections were also far
below the drinking water standards. Subsequent sampling of the well has
failed to detect any vocs. None of the other 16 wells tested have had VOCs
detected.
D.
Landfill Gas
Three of the gas probes and one well located within the waste had landfill gas
samples collected and analyzed for VOCs. Nineteen VOCs were detected with the
highest concentration of total VOCs occurring in the gas probe on the east
side of the landfill. The VOCs with the highest concentration (at any
sampling point) are methyl ethyl ketone, toluene, vinyl chloride, total
xylenes and l,l-DCA.
In addition, the gas probes, two wells screened within the waste, and a
background location were measured for m~thane, oxygen and carbon dioxide.
packground sample was not a soil gas sample, but was an ambient air sample
near the access gate to the landfill. It can only be used for comparative
purposes. All methane measurements except the background location and the
gas probe on the southern edge of the landfill indicated combustible
concentrations of methane.
The
VI.
SUMMARY OF SITE RISKS
A qualitative risk assessment was completed for the Sauk County landfill
Superfund site. The purpose of the assessment was to identify human health
hazards posed by environmental contamination from the site. The qualitative
risk assessment evaluates current as well as future potential exposures to
site related contamination. sample results from the remedial investigation
were used to evaluate all environmental pathways with potential human exposure
routes.
The reasons that a qualitative, rather than a quantitative risk assessment was
completed include:
*
state standards for air and water quality are protective of human health
and the environment
the remedy must comply with state standards
EPA guidance documents state that exceedances of state standards, as
opposed to the site representing an unacceptable risk, are a cause for
action at Superfund municipal landfill sites.
*
*
A copy of the qualitative assessment is found in the administrative record.
Presented below is a brief summary of the assessment and it's conclusions.
The groundwater, surface soil/sediment, and air pathways were evaluated as
possible exposure routes for contaminants. The groundwater data came from on
7
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~:
site monitoring wells and off site private water supply wells. No surface
water bodies are present on the site. The sediment samples were collected
from areas which runoff water, when present, would settle out and deposit
sediment. Soil gas samples and one ambient air sample were collected and used
in the evaluation of the air pathway.
Groundwater Pathwav
The following compounds were identified as contaminants of concern:
benzene
chrysene
tetrachloroethylene
vinyl chloride
l,l-dichloroethylene
- barium
iron
manganese
.. benzoic acid
diethylphthalate
2,4-dimethyl phenol
The compounds listed in the first column represent are probable carcinogens.
The qualitative health assessment concludes that persons who drink groundwater
every day, over a lifetime, with the highest concentration of these
contaminants detected in on site monitoring wells are at an increased
getting cancer. This does not represen~ a present use scenario since
~ells containing these concentrations are on Sauk County property and
water is not being used for water supply purposes. This represents a
possible, though not probable future use scenario. The future use scenario is
not probable since NR 112, Wis. Adm. Code on private water supplies requires a
minimum setback distance of 1200 feet from landfills.
risk of
the
this
The compounds listed in the second and third columns are not carcinogens, but
were evaluated for non-carcinogenic health effects. The qualitative risk
assessment concludes that there are no adverse health effects associated with
exposure to these compounds at the highest concentrations detected in on site
groundwater monitoring wells.
Two additional compounds were detected in monitoring of private wells around
the landfill. l,l,l-trichloroethane and l,l-dichloroethane were detected in
two private wells. The concentrations detected are far below the drinking
water standards for these compounds. The qualitative risk assessment
concludes that there are no adverse health effects expected from exposure to
these compounds in the private wells.
Surface Soil and Sediment Pathway
Because~here are no surface water bodies at the site, the surface soil and
sediment data were evaluated together. The following compounds were identified
as contaminants of concern for surface soils:
arsenic
lead
beryllium
manganese
polyaromatic hydrocarbons (PABS)
Arsenic and beryllium are probable carcinogens. The concentrations of these
metals in surface soils are at concentrations that could cause an increased
8
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risk of cancer if they were ingested at a rate of 100 mgjday for a lifetime.
This exposure is only appropriate for assessing exposures in urban areas or in
residential yards. Because the location of the surface soil contamination is
in a rural area that has restricted access, no increased cancer risk would be
expected from incidental exposures to the highest concentrations of arsenic
and beryllium.
PAHs were detected in samples of surface soils on site. PAHs are created from
the incomplete combustion of fossil fuels. They are often associated with
vehicle emissions and/or oil and grease spills. Individual PAHs are rarely
identified in the absence of others. The health effects of the individual
PAHs may not be exactly alike. However, the coincident detection of a number
of these compounds makes it difficult to isolate health effects for individual
PAHs. For this reason the toxicity of these PAHs is evaluated as a group.
There are over one hundred different PAR compounds. Long term exposure to
some PAH compounds has been shown to cause cancer in humans exposed through
inhalation and dermal absorption. These PAHs were detected in soils at
concentrations that could cause an increased cancer risk if they were ingested
at a rate of 100 mgjday for a lifetime. This exposure scenario is only
appropriate for assessing surface soil exposures in urban areas or residential
yards. Because the location of the sur~ace soil contamination is in a rural
~rea with restricted access, no increased cancer risk would be expected from
"incidental exposures to the highest concentrations of PAHs at the site.
Arsenic, beryllium, lead and manganese
carcinogenic health effects.. Exposure
compounds detected in the surface soil
adverse health effects.
were also evaluated for non-
to the highest concentrations of these
samples are not expected to cause
Air pathwav
Gas samples collected as part of the investigation were primarily soil gas and
not ambient air. Samples of soil gas are not indicative of ambient air
quality. It is expected that concentrations in ambient air would be
considerably less than those detected in soil gas. Because the data collected
were for soil gas and not for ambient air, the qualitative risk assessment
does not include estimates of potential exposure concentrations. The
following compounds were identified as contaminants of concern for the air
pathway:
benzene
1,1-dichloroethylene
methylene chloride
tetrachloroethylene
vinyl chloride
freon
acetone
methyl ethyl ketone
toluene
xylene
1,2-dichloroethylene
Those compounds listed in the first column are probable carcinogens and were
detected in soil gas at concentrations above that considered to pose a health
concern in ambient air.
9
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Compounds listed in the second column were evaluated for non-carcinogenic
health effects. The highest concentration of these compounds detected in soil
gas were below levels that would be expected to cause adverse health effects.
In addition to carcinogenic and non-carcinogenic health effects, landfill gas
also represents another hazard. Methane generated by decomposing refuse, when
mixed with oxygen in the right concentration, is an explosion hazard. Soil
gas probes around the landfill detected methane at high enough concentrations
to represent an explosion and fire hazard.
To control the methane and other landfill gases listed above, the.selected
remedy has an active gas collection and treatment system. The gas will be
collected through a series of wells and piping. The gas is then routed to a
flare where it is destroyed by controlled combustion.
VII.
ENVIRONMENTAL STANDARDS NOT MET AT THE SITE
The Sauk County landfill does not meet the following applicable State
environmental standards:
NR 504.05(7), Wis. Adm. Code
Administrative code that requires facilities accepting
generate explosive gases must prevent the migration of
landfill currently has no gas extraction system.
waste which may
the gas. The old
NR 504.05(8), Wis. Adm. Code
Administrative code that requires facilities accepting
waste to efficiently collect and combust hazardous air
generated by waste decomposition.
municipal solid
contaminants
NR 506.08(3), Wis. Adm. Code
Administrative code that
surface water runoff and
2\ slope.
requires that landfills must be sloped to allow
that the landfill surface must have at least a
NR 506.08(6), Wis. Adm. Code
Administrative code that
than 500,000 cubic yards
contaminants.
requires all facilities which accepted greater
of waste to collect and combust hazardous air
NR 445, Wis. Adm. Code
Administrative code
.contaminants
which regulates the discharge of hazardous air
NR 140, Wis. Adm. Code
Administrative code which regulates groundwater quality and actions
taken to restore groundwater quality. Tables 5 and 6 within NR 140
lists potential actions to be taken when preventive action limits and
enforcement standards are exceeded. One potential action listed in both
Tables includes a change in the design or construction of a facility.
10
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Once the gas collection and flaring system part of the source control remedy
is installed and properly operating, the Sauk County landfill will achieve
compliance with the NR 445 and NR 500 series codes listed above. Regrading of
the site to promote drainage from the landfill surface, and the gas extraction
system will help to achieve compliance with NR 140.
VIII. Description of the Remedial Alternatives
A.
Source Control Remedial Action Objectives
Remedial action objectives were developed for this site to address the source
of contamination, to provide short and long term protection of human health
and the environment, and to meet applicable or relevant and appropriate
requirements. The site specific source control remedial objectives for this
landfill are to:
1-
2.
3.
4.
Prevent direct contact with the landfill wastes
Reduce contaminant leaching to groundwater
Control surface water runoff and erosion of the
Control and destroy landfill gas.
landf ill cap
B.
Development of Alternatives
The source control remedial action objectives for this site involve limiting
the potential for exposure to contaminants via inhalation, ingestion, and
dermal absorption pathways, and controlling landfill gas emission and
migration.
The remedial alternatives were assembled from applicable remedial technology
options. The alternatives surviving the initial screening were evaluated and
compared with respect to the nine criteria set forth in the National
Contingency Plan ("NCP"). In addition to the remedial action alternatives,
the NCP requires that a no-action alternative also be considered for the site.
The no action alternative serves primarily as a point of comparison for the
other alternatives.
C.
Source Control Alternatives
Alternative A - No Action
Alternative B - Construction of a Gas Extraction System
Alternative C - Side Slope Enhancement
Alternative D - Construction of a Soil Protective Layer
Alternative E - Construction of a Geosynthetic Membrane
Alternative G - Construction of a composite Cover Over the Entire
Landfill
Alternative H - Construction of a Composite Cover on the Landfill Top
Only
A complete description of the various alternatives is provided in the Focused
Feasibility Study. A brief narrative description of each alternative is
provided below:
11
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Alternative A:
No Action
The No Action alternative is developed to act as a baseline to compare all
other alternatives against. This alternative consists of continued monitoring
of groundwater, regrading the site to eliminate low spots and promote positive
drainage from the landfill, provide for proper surface water drainage, fencing
the landfill and obtaining deed restrictions on the future use of this
disposal area. Maintenance of the site includes inspection, mowing to prevent
tree growth, filling low areas resulting from settling of the wastes and
repairing any erosional problems.
Alternative B: Construction of a Gas Extraction System Only
As with Alternative A, groundwater monitoring, regrading as needed, fencing,
deed restrictions and cap maintenance would be provided. In addition, an
active gas collection system would be installed. The system would consist of
eight extraction wells located as two rows of four in a north-south
orientation in the landfill. The landfill gas would be collected in the wells
and then sent to a flare using subsurface piping. The flare would then burn
the gas, destroying the contaminants pr~sent in the gas. Condensate from the
9as system will be treated as leachate.
The Evergreen Property Owners Association commented that they are concerned
with contamination of the groundwater since all of the residents in the area
use groundwater as their water source. VOCs are present in one home near the
landfill. The concentrations of these VOCs are very low and are below
drinking water standards. WDNR has included monitoring of some private homes
as part of the remedy in order to make sure that the groundwater at private
wells is safe. In addition, WDNR has created a contingency remedy. Should
groundwater data from monitoring wells located next to the landfill indicate
that groundwater quality should start getting worse, then additional source
control measures, such as a new landfill cap are required to be placed on the
landfill. WDNR will review the data at 5 year increments to determine if the
remedy is still protective, or whether additional source control measures need
to be taken.
Alternative c:
Side Slope Enhancement
Clay thickness on the side slopes of the landfill averages about 12". Under
this alternative, the topsoil would be removed and the clay would be compacted
on the side slopes to provide a minimum clay thickness of 24". The top
surface of the landfill already has a clay thickness of approximately 24".
All of the provisions of Alternative B are also part of this alternative.
Alternative D:
Construction of a Soil Protective Layer
The existing landfill does not have a frost protection and plant
layer. Under this alternative, the topsoil would be removed and
As under Alternative C, compacted clay would be added to provide
clay layer on the side slopes. An 18"-30" soil protective layer
rooting zone
stockpiled.
a minimum 24"
would then be
12
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constructed over the entire landfill. The purpose of this layer is to provide
a plant rooting soil for the surface vegetation and to protect the clay layer
from freezing and desiccation. The topsoil would then be replaced and the
site re-vegetated.
As under Alternatives B & C, an active gas recovery system would be installed,
the site would be fenced, and groundwater monitoring and site maintenance
provided.
Alternative E:
Construction of a GeosyntheticMembrane
This alternative is identical to Alternative D except for the addition of
geosynthetic membrane placed immediately above the clay layer. A 40-60 mil
plastic geomembrane and drainage layer are placed on top the clay layer, and
geotextile fabric is placed on top of the drainage layer. The purpose of the
geotextile is to prevent soil from moving into the drainage layer and
decreasing it's ability to drain water off the geomembrane. The 18"-30"
protective layer and topsoil will be placed above the geotextile.
This alternative also has a gas extraction system as part of the remedy.
Alternative F:
Construction of a Soil Cover
This alternative consists of constructing a soil cover in conformance with
NR 504.07, Wis. Adm. Code. Specifically this alternative includes removing
the topsoil and stockpiling it for re-use. The low spots on the cap would
then be filled in and the site re-graded to promote surface water runoff.
landfill cover consists of (from the surface downward):
The
A topsoil layer of at least 6" that will sustain plant growth,
reduce erosion and promote drainage.
An 18" to 30" frost protection and plant rooting layer.
A low permeability clay layer that is at least 24 inches thick.
A minimum 6" grading layer to attain a stable base and meet
minimum slope requirements for the cover system.
A gas collection and combustion system are included with this alternative.
The site would be fenced, deed restrictions on future property use,
groundwater monitoring and maintenance of the cap are also part of this
alternative.
Alternative G:
Construction of a Composite Cover Over the Entire Landfill
This alternative consists of the construction of a composite cover over the
entire landfill. A composite cover is one which has both soil and geomembrane
components. The composite cover is identical to the soil cover described in
Alternative F, with the addition of a geomembrane and drainage layer on top of
the clay layer, and geotextile fabric placed on top of the drainage layer.
The entire landfill is then covered with topsoil and seeded.
13
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A gas extraction system is also part of this alternative.
Alternative H:
Construction of a Composite Cover on the Landfill Top Only
This alternative is identical to Alternative G except that
described in Alternative G would only be placed on the top
landfill. The soil cover described on Alternative F would
the side slopes of the landfill.
the composite cover
surface of the
be constructed on
IX.
SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES
A.
Introduction
U.S. EPA has established in the NCP nine criteria that balance health,
technical, and cost considerations to determine the most appropriate remedial
alternative. The criteria are designed to select a remedy that will be
protective of human health and the environment, attain ARARs, utilize
permanent solutions and treatment technologies to the maximum extent
practicable, and to be cost effective. The relative performance of each of
the remedial alternatives listed above pas been evaluated using the nine
.criteria set forth in the NCP at 40 CFR 300.430(e)(9)(iii) as the basis of
'comparison. These nine criteria are summarized as follows:
THRESHOLD CRITERIA - The selected remedy must meet the threshold criteria.
1.
Overall Protection of Human Health and the Environment
A remedy must provide adequate protection and describe how risks are
eliminated, reduced or controlled through treatment, engineering
controls or institutional controls.
Compliance with Applicable or Relevant and Appropriate Requirements
(ARARs)
A remedy must meet all applicable or relevant and requirements of
federal/state laws. If not, a waiver may apply.
2.
PRIMARY BALANCING CRITERIA are used to compare the effectiveness of the
remedies.
3.
Long-term Effectiveness and Permanence
Once clean up goals have been met, this refers to expected residual risk
and the ability of a remedy to maintain reliable protection of human
health and the environment over time.
Reduction of Toxicity, Mobility or Volume Through Treatment
The purpose of this criteria is to anticipate the performance of the
treatment technologies that may be employed.
Short-term Effectiveness
This refers to how fast a remedy achieves protection. Also, it weighs
potential adverse impacts on human health and the environment during the
construction and implementation period.
Implementability
4.
s.
6.
14
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7.
This criteria requires consi~ration of the technical and administrative
feasibility of a remedy, including whether needed services and materials
are available. .
Cost
capital, operation and maintenance, and 30 year present worth costs are
addressed.
MODIFYING CRITERIA deal with support agency and community response to the
alternatives.
8.
State Acceptance
After review of the Focused Feasibility Study and the Proposed Plan,
support agency's concurrence or objections are taken into consideration.
community Acceptance
This criteria summarizes the public's response to the alternative
remedies after the public comment period. The comments from the public
are addressed in the Responsiveness Summary attached to this ROD.
9.
B.
Evaluation of the Remedial Alternatives for Source Control
.1.
Threshold Criteria
The threshold criteria are CERCLA statutory requirements that must be
satisfied by any alternative in order for it to be eligible for selection
CERcLA-quality remedy. These. two criteria are discussed below:
as a
a.
Overall Protection of Human Health and the Environment
All of the alternatives provide a soil barrier which eliminates the direct
exposure to the waste within the landfill. Fencing of the landfill will also
eliminate potential exposure pathways by keeping persons from trespassing on
to the landfill surface. The gas collection and combustion system proposed as
part of Alternatives B through H will eliminate the exposure to landfill gas.
Alternative A - Because this alternative fails to control the migration of
landfill gas, persons working near or on the landfill, and persons who
trespass on the landfill may be exposed to the contaminants and explosive
hazard of landfill gas. This alternative is not protective of human health
and the environment.
Alternative B - This alternative will efficiently collect and burn the
landfill gas, eliminating the exposure to persons entering the site.
Collecting landfill gas will capture some VOCs so they are unable to
contaminate the groundwater. Regrading of the site will promote drainage from
the landfill so that precipitation is able to run off rather than flow into
the surface depressions currently present on the landfill surface.
Alternatives C,D,E,F,G and H all provide improved barriers to the
precipitation into the waste. However, the efficiency of each of
alternatives in reducing infiltration is variable.
movement of
the
15
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b.
Compliance with Applicable or Relevant and Appropriate Requirements
(ARARs)
Alternative A - Administrative Rules relating to landfills require that
landfills over 50Q,000 cubic yards must efficiently collect and burn landfill
gas. This alternative fails to provide for the collection and combustion of
landfill gas, and therefore does not comply with state laws and will not be
evaluated further.
Alternatives S,C,D,E,F,G and H all propose gas collection and combustion
systems and comply with state laws requiring these.systems. .Emissions from
the gas system must comply with NR 445, Wis. Adm. Code.
Alternatives S,C,D - These alternatives will comply with the landfill capping
requirements of NR 506.08(3), Wis. Adm. Code.
Alternatives E,F,G,H - These alternatives comply or exceed (on a performance
basis) the solid waste capping requirements for landfills in NR 504.07, Wis.
Adm. Code.
2.
Primary Salancing Criteria
Alternatives which satisfy the two threshold criteria are then evaluated
according to the five primary balancing criteria.
a.
Long-term Effectiveness and Permanence
Alternatives S,C,D, & F - The long-term effectiveness and permanence of any of
the landfill capping options is highly dependent upon how well the cap is
maintained with time. These alternatives are multi-layer soil designs. All
of these remedies have a maintenance component. With proper maintenance,
these remedies will provide a landfill cap that is protective of human health
and the environment with time.
Alternatives E,G & H - These remedies entail composite designs. This means
that they have both soil and plastic components in the landfill cap. These
types of landfill caps also need to be properly maintained. However, the
presence of the plastic membrane will generally give these caps a higher
degree of long-term effectiveness and permanence.
b.
Reductior in Toxicity, Mobility or Volume Through Treatment
The gas extraction system proposed as
will reduce the toxicity and mobility
and destroying it rather than letting
part of Alternatives S,C,D,E,F,G & H
of the landfill gas by capturing the gas
the gas diffuse from the landfill.
The toxicity, mobility or volume of the landfilled waste is not affected by
any of the proposed alternatives. Instead, the alternatives eliminate the
exposure to the waste and reduce the amount of contamination that can leave
the waste and affect groundwater. This approach is consistent with EPA
Guidance.
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c.
Short-term Effectiveness
All of the alternatives, S,C,D,E,F,G & H, will reduce the amount of
contamination coming from the landfill by reducing infiltration and capturing
the landfill gas. These benefits will occur immediately after the systems are
in place. All of these alternatives should be operational within a single
construction season.
Potential short term adverse impacts on human health include drilling into the
landfill. Methane, an explosive gas, is generated by decomposing refuse.
Installation of gas extraction wells will require that special precau~ions be
taken by the drilling firm in order to protect the safety of their workers.
Another short term adverse impact of all the alternatives is damage to the
vegetation currently on the landfill. Vegetation removes water from the soil
and transpires it back to the atmosphere. Until the vegetation has been
restored, there is a potential for additional leachate generation. Another
short term impact may be additional erosion of soil from the landfill cover
until the vegetation is re-established.
d.
Implementability
"Installation of the gas extraction system common to all of the alternatives is
easily implemented using established engineering and construction techniques.
Alternatives B,C,D & F are easily implemented using common earth moving and
compaction equipment. In addition, because soil landfill caps have been used
in this state for the past several years, there are many firms available with
the expertise to construct a soil cap.
Alternatives E,G & H involve a plastic geomembrane. The sheets of membrane
must be seamed together to eliminate leaks. Placing and seaming a geomembrane
is more difficult than constructing a soil cover. However, these types of
caps are becoming more common and there are many firms available with the
expertise to construct this type of cap.
e.
Costs
Alternative B
capital Costs - 5444,000
Annual Costs - $28,200
Present Worth - $832,000
Alternative C
Capital Costs - $737,600
Annual Costs - $28,200
Present Worth - 51,126,000
Alternative D
Capital Costs -
Annual Costs-
Present worth -
$1,063,000
$28,200
$1,452,000
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Alternative E
Capital Costs -
Annual Costs-
Present Worth -
$1,720,000
$28,200
$2,109,000
Alternative F
Capital Costs -
Annual Costs-
Present Worth -
$1,799,000
$28,200
$2,187,000
Alternative G
Capital Costs -
Annual Costs-
Present Worth -
$2,456,000
$28,200
$2,844,000
Alternative H
Capital Costs -
Annual Costs-
Present Worth -
$2,149,000
$28,200
$2,537,000
The cost of each remedial alternative ~enerally increases as the amount of
.material and construction required to implement the remedy increases.
3.
Modifying Criteria
a.
State Acceptance
The WDNR is the lead agency on this case and authors 'this ROD.
b.
Community Acceptance
Comments by the Evergreen Property OWners Association supported Alternative E
as was listed in the Proposed Plan issued by WDNR. A Sauk County property
owner and Sauk County officials submitted comments and data which support
Alternative B as the best source control remedial action. All of the comments
indicated that they want the solution to be cost effective. The substantive
comments received by WDNR are listed in the attached Responsiveness Summary.
c.
Summary
With the exception of Alternative A, all of
alternatives meet the threshold criteria of
with applicable or relevant and appropriate
the source control remedial
being protective and complying
. requirements.
A decision as to che best source control remedy is based upon an analysis of.
the balancing criteria. The criteria of Reduction in Toxicity, Mobility or
Volume, Short-term Effectiveness, and Implementability are all equally met by
each of the alternatives. The primary factors in the decision are Long-Term
Effectiveness and Permanence, and Cost.
As stated earlier, the Long-term Effectiveness and Permanence is strongly
controlled by how well the landfill cap is maintained. Proper maintenance of
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the landfill cover is part of this remedy. Annual reports
maintenance are also required. WDNR also has the right to
landfill to see that it is properly maintained. Long term
permanence are also addressed through the contingency plan
possible changes in groundwater quality.
detailing the
inspect the
effectiveness and
which monitors
The data and analysis provided by Sauk county in Technical Memo #3, and in
comments submitted during the public comment period show that the existing
landfill cap is having a beneficial effect on groundwater quality. A gas
extraction system and regrading of the landfill are necessary to comply with
ARARs,. and to. reduce or eliminate exposure pathways. These are. .the ..most .
substantive parts of Alternative B.
Alternative B is also the least costly of the alternatives that comply with
ARARs. Since it meets the threshold criteria and other balancing criteria,
cost becomes that final factor to consider. Alternative B is a cost effective
source control remedy.
CONCLUSIONS OF LAW
Alternative B will protect human health-and the environment from exposure
:pathways identified in the Summary of Site Risk section of this ROD, complies
with all legally applicable, or relevant and appropriate requirements for this
final source control remedy, and is cost effective.
A.
Protection of Human Health and the Environment
The selected remedy provides protection of human health
through capping to contain wastes, which will alleviate
contact and minimize leachate generation. It will also
extraction of VOCs and other landfill gases.
and the environment
threats from direct
provide active gas
B.
Attainment of ARARs
The selected remedy will
appropriate requirements
the Sauk County landfill
exemption is available.
remedy must be obtained
will be achieved by the
be designed to meet all applicable, or relevant and
under federal and state environmental laws. Since
is a state lead cleanup, no CERCLA on site permit
All permits and approvals required to implement the
and strictly complied with. The primary ARARS that
selected alternative are:
1.
Action specific ARARs
Wisconsin Statutes, section 114.43 to 144.47
Wis. Adm. Codes, ss. NR 504.05(7), NR 504.07(3), NR 506.08(6)
Landfill gas control. Standards for landfill gas control and
practices. These requirements are applicable to the landfill
system at the site.
and NR 508.04 -
monitoring
gas collection
Wis. Adm. Codes, ss. NR 504.08(3), NR 514.07 and NR 516 - Landfill Closure
Requirements. Substantive requirements for the design, construction,
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upgrading, maintenance and documentation of
construction, maintenance and documentation
requirements.
landfill caps. cap design,
must comply with these applicable
Wis. Adm. Codes, ss NR 508.04 and NR 140 - Groundwater monitoring
requirements. Substantive requirements for groundwater monitoring
meet these applicable requirements.
plans must
Wis. Adm. Code, NR 600 series - Hazardous waste requirements. This code was
enacted to regulate the transportation, storage and disposal of hazardous
waste. This code is neither applicable, nor relevant and appropriate -for this
site.
RCRA, Subtitle C - Hazardous waste requirements. Subtitle C are the
regulations enacted for hazardous waste. Hazardous waste was placed
landfill, however, the disposal took place prior to promulgation to
Subtitle C. This regulation is neither applicable, nor relevant and
appropriate for this site.
federal
in the
RCRA, Subtitle D - Solid waste requirements. Subtitle D are federal
regulations enacted for solid waste disposal. The regulations are applicable
;to facilities which accepted waste after October 9, 1991. The Sauk County
landfill closed in 1983. The Subtitle D regulations are neither applicable,
nor relevant and appropriate for this site.
2.
Chemical Specific ARARs
Clean Air Act
to 144.426
[42 U.S.C. 7401 et seq.); Wisconsin Statutes, sections 144.30
40 CFR 50; Wi's. Adm. Code, chs. NR 404, NR 415 to NR 449 - Emission Standards.
Standards for emission of pollutants into ambient air and procedures for
measuring specific air pollutants. Cap construction could cause air emissions
of VOCs, particulate, fugitive dust or other contaminants which could
adversely affect human health and the environment. The design of the remedy
must reduce air emissions to acceptable levels or provide treatment to satisfy
these applicable standards. .
Wis. Adm. Code, NR 140 - Groundwater Quality Standards. The remedy is
designed to reduce the amount of contamination entering groundwater and
achieve compliance with standards found in NR 140.
C.
Cost Effectiveness
The selected remedy provides for overall cost effectiveness. The evaluation
showing that the existing landfill cap is having a beneficial effect on
groundwater quality provides for flexibility in choosing from the remedial
alternatives. The selected remedy will improve on the beneficial effects of
this cap by capturing VOCs with the gas system. Since Alternative B complies
with ARARs and is the least costly, Alternative B is also the most cost
effective.
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D.
Utilization of Permanent Solutions and Alternative Treatment Technologies
The selected alternative represents the best balance of alternatives with
respect to the nine evaluation criteria. The cap eliminates the direct
exposure pathway and reduces the amount of leachate generated within the site.
The active gas extraction system provides for removal and treatment of the
dominant threat to groundwater (i.e. VOCs) and will effectively control other
landfill gases. Potential future threats will be addressed, if necessary,
through the contingency aspect of the remedy.
E.
Preference for Treatment as a principal Element
By treating the waste mass with active gas extraction, the remedy satisfies
the statutory preference for remedies that employ treatment of the principal
contaminant threat to permanently and significantly reduce toxicity, mobility
or volume through treatment.
DECISION:
THE SELECTED REMEDY
:Based on an evaluation of the alternatives, the Wisconsin Department of
Natural Resources believes that Alternative a, the selected remedy, will be
protective of human health and the environment, comply with ARARs, be cost
effective, and will use permanent solutions to the maximum extent practicable.
The selected source control remedy for the site includes the following:
*
continued monitoring of the groundwater at on site groundwater
monitoring wells and off site private wells
regrading of the landfill surface to promote drainage off of the
landfill cover
fencing the landfill
installation of a gas extraction system to efficiently collect and
combust landfill gases
placing a deed restriction on the property to prohibit the disturbance
of the surface of the landfill cap in the future
future maintenance of the landfill cap
a contingency plan to address unexpected releases from the site.
*
*
*
*
*
*
Regrading of the landfill surface conforms to the applicable provisions of the
NR 500 rule series in the Wisconsin Administrative Code, including the final
cover requirements of NR 506.08(3) which require that the landfill surface
maintain at least 2\ slopes and convey surface water from the landfill cap.
The remedy also complies with the following applicable provisions of the NR
500 Rule which pertain to active landfill gas extraction and treatment:
NR 504.05(7), NR 504.07(3), NR 506.08(6) and NR 508.04. The remedy also
complies with the air emission rules in ch. NR 445.
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Annual maintenance is an important aspect of this remedy. Annual reports will
be required summarizing the previous years maintenance of the cap, and an
evaluation of the effectiveness of the gas extraction system. This report
shall also contain the results of all groundwater monitoring completed at the
site during the previous year and include an evaluation relative to compliance
with NR 140, Wis. Adm Code standards. The report is to be submitted by July
15 of each year, starting in 1995.
At the 5 year review of this source control remedy (i.e. by October 15, 1999),
WDNR will study the annual reports to determine whether the remedy continues
to effectively protect human.healthand the environment, and whether the
source control remedy is being adequately maintained. The groundwater quality
data will be evaluated to determine if the groundwater quality continues to
improve. If the data indicates that groundwater quality is no longer
improving, then WDNR may require additional source control actions.
In order to determine if the existing landfill cover continues to prevent or
abate attainment or exceedance of groundwater standards, by July 15, 2004 and
in 5 year intervals after this, a report will be prepared which summarizes the
monitoring data at all groundwater monitoring wells. The point of compliance
for groundwater quality standards is th~ edge of the waste boundary. If the
data shows that NR 140, Wis. Adm Code preventive action limits for VOCs are
not consistently met at wells in the monitoring plan, then the remedy requires
that a landfill cover as described in Alternative E of the Source Control
Focused Feasibility Study be designed and constructed on the landfill.
"Consistently met" is defined as 50\ or more of the VOC data points from each
well, within the previous three years, must be less than the NR 140 preventive
action limit for each VOC detected respectively.
The WDNR has determined that the selected remedy, Alternative B, will achieve
the source control remedial action objectives for this site.
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RESPONSIVENESS SUMMARY
This Responsiveness Summary has been prepared to meet the requirements of
Sections 113 (k) (2) (B) (iv) and 117(b) of the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980 (CERCLA), as amended by the
Superfund Amendments and Reauthorization Act of 1986 (SARA), which requires
the United States Environmental Protection Agency (EPA) or the state on state
lead sites to respond ". . . to each of the significant comments, criticisms,
and new data submitted in written or oral presentations" on a proposed plan or
draft Record of Decision for the remedial action. The Responsiveness Summary
addresses concerns by the public and potentially responsible parties (PRPs) in
written and oral comments received by the state regarding the proposed source
control remedy at the Sauk County Landfill Superfund site.
A.
OVERVIEW
I.
BACKGROUND/PROPOSED PLAN
The Sauk County landfill Superfund site is situated on a 320 acre
parcel of land located between the Cities of Reedsburg and
Baraboo. Also located on this parcel is the active Sauk county
solid waste landfill. This active landfill is located
approximately several hundred feet north of the old, closed
landfill. The active landfill is not part of this Record of
Decision (ROD).
The Sauk County landfill accepted municipal and industrial waste
from Sauk County between the years 1973 and 1983. The site was
designed as a natural attenuation landfill. This means it has no
liner or leachate collection system designed into modern
landfills. It is approximately 14 acres in size and has a volume
of about 750,000 cubic yards. The landfill accepted large
quantities of foundry sand, municipal wastes and industrial wastes
from homes and businesses located within the county.
,
The Proposed Plan for this landfill called for the construction of
a multi-layered composite landfill cap and gas extraction system.
Because of comments received during the public comment period, the
WDNR has changed the remedial action to call for additional soil
being added to the existing landfill cap which will promote
drainage off of the landfill surface, construction of an gas
extraction system, continued groundwater monitoring, and a
contingency plan to address possible future releases of VOCs from
the site.
II.
PUBLIC COMMENT PERIOD
A public comment period was held from September 8, 1993 to
November 9, 1993 to allow interested parties to comment on the
Proposed Plan in accordance with Section 117 of CERCLA. In
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addition, a public meeting was held on September 21, 1993 at the
Rock Springs Community Center. The WDNR presented the Proposed
Plan, answered questions and accepted comments from the public.
During the public comment period, WDNR received 31 written and
verbal comments concerning the Proposed Plan. These comments
focused primarily on the extent to which the existing landfill
cover is working to reduce leaching of contaminants to
groundwater, and the cost associated with implementing the
Proposed Plan.
B.
COMMUNITY INVOLVEMENT
'Public interest in the project has been high, particularly among
landowners and residents living near the landfill. The residents
organized themselves into the Evergreen Property OWners Association.
The Association applied for, and was awarded a Technical Assistance
Grant from EPA. The purpose of the grant is to provide funding which
allows parties affected by Superfund sites to retain their own technical
consultant.
The property owners primary conce~n is that the contaminated groundwater
will affect their wells, and possibly their health. In order to get
answers to their questions, residents have written letters to WDNR, and
to the Division of Health. In addition, the residents organized a
public meeting on November 30, 1992 in which staff from WDNR, the
Division of Health and Simon Hydro-Search (consultant for Sauk County)
attended and responded to questions from the public.
The Evergreen Property OWners Association submitted written comments in
support of the Proposed Plan. This group believes that the membrane cap
is a superior source control action when compared to the other
alternatives presented.
In addition to comments received from the Evergreen Property OWners
Association, Sauk County submitted comments concerning the effectiveness
of the existing cap, and the cost associated with placing the membrane
landfill cover discussed in the Proposed Plan.
The above concerns will be responded to in the following sections.
C.
SUMMARY OF SIGNIFICANT PUBLIC COMMENTS
Comment 1
Sauk County, through their consultant, commented that the existing
landfill cap is effective in reducing the contamination entering
groundwater. Evidence for this includes:
- Concentrations of total VOCs in well TW-25 have dropped from over
15,000 ppb to about 100 ppb since VOCs have been measured in this well
(1985-1993)
2
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- vinyl chloride is the only parameter for which NR 140 Enforcement
Standards are exceeded at TW-25 .
- TW-25 is located immediately downgradient of the landfill and has
historically shown the highest level of contamination
- changes for tetrachloroethylene are proposed for NR 140, Wis. Adm.
Code. Once these changes become effective, groundwater enforcement
standards will only be exceeded at wells within 150' of the landfill.
Response
These comments have been reviewed and were taken into account in re-
evaluating the alternatives for the source control remedy for the site.
Comment 2
Sauk County commented that Alternative B of the Focused Feasibility
Study calls for regrading the site to promote positive drainage from the
site. The WDNR Proposed Plan states that Alternative B doesn't address
regrading of the site.
Response
WDNR acknowledges that the Proposed Plan contained an error in the
description of Alternative B with respect to regrading the site.
comment 3
Several comments were received such that if the present cap is working,
then to require Sauk County to install a new membrane cap is a waste of
money.
Response
WDNR reviewed the technical arguments, as well as the cost
considerations in their decision on the source control remedy for the
site.
Comment 4
The Sauk County Board Chairman commented that the proper response for
this landfill is to install a gas extraction system.
Response
A gas extraction system is incorporated as part of the source control
remedial action for the site.
Comment 5
The Evergreen Property OWners Association (EPOA), through their
consultant, commented that they wish to work with WDNR to derive
3
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remedial remedies which use tax dollars wisely, and protect public
health, safety and welfare.
Response
WDNR believes the final source control remedial action is protective of
public health, safety and the environment. WDNR also believes that the
remedial action is cost effective.
Comment 6
EPOA commented that the condition of the existing cap (i.e. areas where
surface water can collect rather than drain off) is of poor quality.
Response
The selected remedial action calls for regrading of the landfill surface
to promote drainage off of the landfill surface. The remedy also
requires that the positive drainage and vegetative cover be maintained.
Comment 7
EPOA was concerned that a water balance calculation hadn't been
performed to estimate the amount of infiltration entering the waste.
Response
Simon Hydro-Search submitted (on 11/08/93) a water balance analysis
using the Hydrologic Evaluation of Landfill Performance (or HELP) model.
Simon Hydro-Search believes that the initial analysis using HELP
completed by Warzyn in 1987 was inaccurate. Warzyn estimated 4.4
inches/year of infiltration. Simon Hydro-Search, using the HELP model
predicts that 0.4 inches/year is entering the waste.
The difference between these two calculations is primarily due to the
value used for hydraulic conductivity of the clay soil capping layer.
Simon Hydro-Search believes that permeability data from lab testing of
the soils is applicable over the entire two foot thickness of the clay
layer.
WDNR believes that the Simon Hydro-Search analysis is flawed. First,
lab permeability testing is usually an order of magnitude or more less
than that measured in the field for similar soils. Second, WDNR doesn't
believe Simon Hydro-Search's assumption that the full two feet of clay
has the permeability measured in the lab is valid. This soil is only
covered by approximately 6 inches of topsoil. It is likely that cracks
from freeze/thaw and desiccation extend into the clay. It is also
likely that plant roots extend into the clay.
Regardless of the analyses from the HELP model, VOC concentrations
groundwater monitoring wells are decreasing. This is probably the
measure of the current effectiveness of the existing cap.
in
best
4
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Comment 8
EPOA commented that without water table wells installed through the
waste and directly beneath the landfill, there is no way to be certain
that leachate is not mounding up beneath the landfill.
Response
Wells installed 'through 'the waste and into' the water' table would be the
best method of determining if leachate is mounding beneath the site.
However, it is unlikely that leachate is mounding beneath the site. For
mounding to occur, water must move through the waste faster than the
underlying aquifer material can move it. The wells installed into the
waste indicate no leachate is present so the waste is not saturated and
acting as a constant source of water to the water table. In addition,
groundwater elevations measured on the edges of the landfill indicate a
flow direction at the water table from east to west. The data
corresponds to this flow direction and doesn't indicate a mound beneath
the landfill. A third factor to consider is that once the cap was
placed on the waste, infiltration was reduced and there is less water
available to support mounding of the water table.
Comment 9
EPOA has commented that the VOC data at TW-25 has stabilized in the
samples collected between 1991 and 1993. Their comment indicates this
indicates a continuing source of VOCs to groundwater.
Response
An analysis of the data from TW-25 and TW-26A was presented by Simon
Hydro-Search in their letter received on November 15, 1993. This
analysis indicates that the reduction in VOC concentrations in well
TW-25 and TW-26A can be explained by exponential decay. semi-log plots
of the data versus time indicate that the VOCs have a half-life of about
1 year. Simon Hydro-Search's analysis indicates that the contamination
has already left the landfill and the VOCs found in TW-25 are likely
reaidual contamination attached to the aquifer matrix. If significant
concentrations of VOCs were continually released from the landfill, then
the data wouldn't correspond to the analysis.
The WDNR agrees with the Simon Hydro-Search analysis of the data.
However, other factors besides exponential decay, such as minimizing
infiltration and dilution, are probably also playing a role in the
declining VOC concentrations. Future sampling and analysis of the
monitoring wells will determine if the landfill is releasing VOCs.
Comment 10
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EPOA commented that the data from TW-25A (screened in the Wonewoc
Formation) shows a continuing release to the Wonewoc Formation. EPOA is
concerned since this is the sole source drinking water aquifer to the
area.
Response
Simon Hydro-Search prepared a similar analysis using the data from TW-
26A. This well is screened in the Lone Rock Formation, just above the
Wonewoc Formation. The data from this well also indicates there doesn't
appear to be a continual" loading ofVOCs-from the rock and soil units
above. .
Because the Wonewoc Formation acts as the water supply aquifer for
residents in the area, WDNR included as part of the remedy monitoring of
private wells, and a contingency plan should VOC concentrations at
monitoring wells near the landfill start to increase. If VOCs are
released from the landfill in the future and detrimentally affect
groundwater, then a composite landfill cap is to be installed.
Comment 11
EPOA commented that the VOC data distribution isn't explained by the
groundwater. flow regimes presented in Technical Memo #3.
Response
The flow systems from the landfill towards the west are adequately
defined. The water table aquifer and the upper potentiometric surface
(i.e. the upper portion of the Lone Rock Formation) flow predominantly
to the west, southwest. Once below the confining layers of the Lone
Rock Formation, gradients indicate groundwater flow towards the east.
Additional groundwater monitoring wells were installed east of the
landfill. One well was screened at the water table; the second well was
screened in the Wonewoc Formation. Water samples collected in November,
1993 from these new wells east of the landfill had no detections of
VOCs. ¥
Comment 12
EPOA commented that the best source control solution for this landfill
is Alternative E, a composite landfill cover and gas extraction system.
Response
WDNR ini~ially selected Alternative E as the source control action for
the landfill. However, data presented during the public comment period
show that Alternative B, regrading the site and installing a gas
extraction system is the best source control remedy. The existing cap
is limiting the amount of leachate being generated by the landfill, is
cost effective and is protective of public health and the environment,
and complies with state law.
6
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Comment 13
Sauk County commented that NR 504.07, Wis. Adm. Code isn't
or Relevant and Appropriate Requirement (ARAR) because the
approved prior to the promulgation date of the NR 500 code
an Applicable
landfill was
series.
Response
NR 504 is an ARAR when a site receives a plan approval after the
promulgation date of NR 500, or when the criteria of NR 506.08(3) are
met. NR 506.08(3) states that the final cover requirements of NR 504.07
are to be used when it is necessary to..."prevent or abate attainment or
exceedances of groundwater quality standards of Ch. NR 140, Wis. Adm.
Code". Based upon the groundwater quality data from well TW-25 and
other wells at the site, the existing landfill cap is currently
preventing the exceedance of groundwater quality standards.
Comment 14
Sauk County commented that NR 140.26, Wis. Adm. Code isn't an ARAR
because it doesn't mandate a cap design or composition.
Response
NR 140.26 is an ARAR because groundwater enforcement standards in HR 140
are exceeded at monitoring wells at the site. Table 2 of NR 140.26 is a
list of actions that WDHR may take in order to achieve compliance with
the groundwater quality standards. A change in the design of a facility
is included in the list of actions. NR 140.26 is an applicable
requirement to this site.
Comment 15
Sauk County commented that the water balance presented by their
consultant shows little difference in infiltration between the existing
cap and the cap listed in Alternative E. Sauk County further comments
that if the caps behave similarly, then the more expensive composite csp
of Alternative E is not cost effective.
Response
WDNR believes the water balance presented by the County's consultant is
flawed. Please see response to Comment 7.
Comment 16
Sauk County commented that WDNR placed too great an emphasis on
permanence as compared to cost effectiveness when issuing the Proposed
Plan. Sauk County cites a court case in which the judge ruled that
7
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)
permanence has no greater emphasis than cost effectiveness or any of the
other balancing criteria.
Response
WDNR agrees that cost effectiveness and permanence
when making remedial decisions at Superfund sites.
alternative's cost effectiveness is evaluated, the
the threshold criteria.
have equal weight
But before an
alternative must meet
Comment 17
Sauk County commented that with the proposed changes to NR 140,
groundwater enforcement standards are only exceeded at wells located
within 150 feet of the site. Also, in general, the number of compounds
exceeding groundwater enforcement standards has declined over the past
several years.
Response
WDNR used this information in it'~ decision to select the source control
remedial action for the site.
Comment 18
By providing semi-log plots of time vs. concentration of total VOCs
data, Sauk County commented that the half-life of total VOCs is about
1.1 years. This estimate was provided by using data between 1985 and
1993. Assuming this relationship holds true, all of the VOCs should
fall below preventive action limits in about 2 years.
Response
WDNR has reviewed the plots of data provided by Sauk County. This data
was used by WDNR in selecting the source control remedial action for the
site. However, should the decreasing trend in VOC concentrations not
continue, the remedy includes a contingency for possible future VOC
releases from the landfill.
Comment 19
Sauk County provided plots of precipitation for Baraboo. A comparison
of the precipitation data and the total VOC data at TW-25 indicates that
wet years and dry years do not appear to have affected the amount of
VOCs being released from the landfill. Sauk County comments that this
is further data showing the landfill is not releasing significant
quantities of VOCs to groundwater.
Response
8
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WDNR has reviewed the plots of data provided by Sauk County. This data
was used by WDNR in selecting the source control remedial action for the
site.
Comment 20
Sauk County commented that except for the surface depressions from
settlement of waste, the existing landfill cap has been well maintained.
Erosion gullies have been repaired as soon as possible and the
vegetation is in good shape. In addition, all of the Alternatives,
except Alternative A (the 'no-action alternative) call for regrading the
surface of the landfill to promote positive drainage from the landfill.
Response
WDNR believes Sauk County has properly maintained the vegetation on the
existing landfill cap.
Comment 21
Sauk County commented that the decline in total VOCs as shown by the
data from TW-25 and TW-26A can be explained using the exponential decay
equation. Sauk County presented an analysis using the exponential decay
equation which concludes it is mathematically not possible for the
landfill to be releasing significant quantities of VOCs.
Response
WDNR has reviewed the analysis presented by Sauk County. WDNR used this
data in selecting the source control remedy for this site. However,
other factors, such as dilution are also contributing to the declining
VOC concentrations.
Comment 22
Sauk County commented that except for east of the landfill, the flow
regime has been defined as well as it needs to be. Preventive action
limit exceedances have been delineated. Sauk County has installed two
wells to the east of the landfill to help define the flow regimes in
that direction.
Response
WDNR agrees that with the additional wells installed to the east of the
landfill, the flow regime is adequately delineated.
9
-v.s. GOV~'~ PRINTING OFFICE: 1994-386-541/03086
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