PB94-964126
EPA/ROD/R05-94/252
September 1994
EPA Superfund
Record of Decision:
Olmsted County Sanitary
Landfill Site, Olmsted, MN,
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DECLARATION OF THE RECORD OF DECISION
OLMSTED COUNTY SANITARY LANDFILL
OLMSTED COUNTY. MINNESOTA
Site Name and Location:
Olmsced County Sanicary Landfill Superfund Sice, Oronoco Township,
Olmsced County, Minnesota
Statement of Basis and Purpose:
Th1s decis10n document presents che selection of the no-action
~emedial alternacive for che Olmsced County Sanicary Landfill.
Superfund Site (the Site). The selected remedial alternative was
chosen In accordance wich che Comprehensive Enviro~~ental Response.
:8mpensaclon and Liability Acc of 1980 (CERCLA); as amended by
Superfund Amendments and Reauthorization Act of 1986 (SARA). and to
the extent practicable the National Contingency Plan (NCP). Also, the
select10n is consistent with che Minnesota Environmencal Response and
Liability Act of 1983 (MERLA).
This decision is based upon the reports, information and public
comments, which constitute the Administrative Record for the Site.
The United States Environmencal Protection Agency (EPA) concurs with
the selecced no-action remedial alternacive for the Olmsted County
San1tary Landfill Superfund Site.
Description of the Selected Remedy:
No remedial action under CERCLA or MERLA is necessary at this site to
ensure procection of human health and the enV1ronment. Potential
problems associated with this site will be addressed by the Minnesoca
Solid Wasce Landfill Compliance program, the Resource Conservation and
Recovery Act and a Closure Order by Consent between the Minnesota
Pollution Concrol Agency (MPCA) and Olmsted Councy. Under these
programs. monicoring and review of the site will be continued to
verify that no unacceptable risks posed by the site occur in che
future.
The MPCA has determined, and the EPA concurs, that no further action
is necessary at this site. The reason for this determinacion is thac
the source control action taken under site closure and actions
implemented under the Closure Order by Consent between the MPCA and
Olmsted County has eliminated potential exposure to source related
contaminants. Concinued monitoring of the site and implementation of
contingency actions is specified in the Closure Order by Consent.
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Federal and State Concurrence:
The EPA and the MPCA believe that ~he selected remedy is the best
cholce balanclng of the evaluation criteria required by CERCLA.
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I.
SITE NAME.
DECISION SUMMARY
OLMSTED COUNTY SANITARY LANDFILL
OLMSTED COUNTY. MINNESOTA
LOCATION AND DESCRIPTION
The Olmsced Councy Sanicary Landfill (the Site) is located in
seccions 27 and 28 of Oronoco Townsnip, Olmsced Councy,
Minnesota. The Site encompasses 304 acres, locaced approximately
three miles north of the corporate limits of the city of
Rochester in southeastern Minnesota. The main fill area is
located on the northern one third of che site and encompasses
approximacely 52 acres. The Site is gently rolling and vegetated
with grasses and a few scattered areas of brush and trees. The
waste deposit is vegetated with shallow rooted grasses.
Incermiccenc scream valleys cross the propercy along che northern
and eascern boundaries. The land use in the vicinity is
generally small farms, rural residences and some rural
subdivislons. Off the Site ~o ehe wesc is a quarry where gravel
and limescone are mined. Beyond the quarry, ehere is a mobile
home park.
The Site is located in what is referred to as the.~tless Area
of Minnesota. This is an area which was not glac~d during the
last glacial period. The area is characterized by deeply c~t
river valleys, disappearing streams, springs, sinkholes and~
caves. The area for the most part has a relatively thin layer of
topsoil overlying soluble limestone and dolomite bedrock, with
occasional deposits of windblown loess, stream alluvium or
glacial till from earlier glacial periods. Ground water is found
in substantial quantities in the limestone and in deeper
sandstone layers in the area. Due to the lack of soil cover in
this pare of the seate, the upper aquifer, the prairie du Chien,
has been degraded by farming practices, on-site waste water
disposal from rural developmenc and ocher anthropogenic.
activities. The upper aquifer does noc meec drinking water
standards for nitrate in many cases and in some cases is
contaminaced by coliform bacteria. The deeper sandstone aquifer,
ehe Jordan, is of much better quality but contains high iron
concentrations which makes it less aesthetically. pleasing.
II.
SITE HISTORY AND ENFORCEMENT ACTIVITIES
The Site operated under Minnesoca Pollution Control Agency (MPCA)
permit SW 5 from February 1970 until March 1993, when it ceased
operation and final site closure began. The permit for the Site
was originally issued to the city of Rochester, but was assigned
to Olmsted County in 1983 after the city transferred ownership of
the site to the county. The Site accepted mixed municipal solid
waste, as well as commercial and induscrial solid waste until
March 1987, when it closed to all but demolition debris and ash
from the Rochester Public Utilities coal fired power plant.
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The first cell constructed at the site was unlined and had little
or no soil between the bottom of the waste and the top of the
bedrock. Subsequent cells were constructed with a two foot
compacted clay liner and a leachate collection system. Each cell
had a tank buried adjacent to the cell ~o store the collected
leachate. which was periodically pumped out and hauled to and
created at the municipal waste water treatment plant in
Rochester. In 1991, Olmsted County removed the individual
leachate tanks and installed a single tank w~th double walls and
installed double walled piping, in the areas outside of the cell
liners, leading to the new tank.
In May 1983, ground water samples from monitoring wells on the
Site indicated the presence of volatile organic compounds (VOCs)
in the ground water beneath the Site. Subsequent investigations
led the MPCA to evaluate whether the Site should be listed on the
Minnesota Permanent List of Priorities (PLP) or the National
Priorities List (NPL) for superfund sites potentially requiring
cleanup. The Site was added to the PLP in 1984 with a Hazard
Ranking System (HRS) score of- 34. The Site was added to the NPL
in 1986 with a HRS score of 41. The higher NPL score was due to
the discovery of documentation on the disposal of 418 cubic yards
of metal hydroxide sludge at the Site during the period from 1972
through 1975.
In May of 1989, the county initiated a dye trace investigation to
better determine the ground water flow direction and travel time
for water in the Prairie du Chien aquifer and also to determine
if there was any interconnection between the Prairie du Chien and
Jordan aquifers. This study was eventually rolled into the
Remedial Investigation.
In July 1989, the MPCA issued a Request for Response Action
(RFRA) to the city of Rochester and Olmsted County as owners and
operators of the Site. The RFRA was for a Remedial Investigation
and a Feasibility Study of the Site. After the RFRA was issued,
the city and county expressed their desire to negotiate a
Response Order by Consent (Consent Order). The MPCA and the
parties entered into negotiations and reached agreement on the
Consent Order in December 1989.
The county took the lead throughout the Consent Order
negotiations and agreed in the Consent Order to be the
agency in the investigations. After the Consent Order
executed, the County and the city began the Remedial
Investigation phase. .
lead
was
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At the conclusion of the Remedial Investlgation ln July 1992, it
was determined that additional field work was needed to examine
gas migration from the Site. A Supplemental Remedial
Investigatl0n was completed in September 1993. which completed
the lnvestigation phase. Consultatlon wlth the U.S.
Environmental Protection Agency tEPA) to the conclusion that a
Feaslbility Study would not be necessary due to the low level of
risk posed by the Site.
III. HIGHLIGHTS OF COMMUNITY PARTICIPATION
Activities at the Site have been closely followed by the
residents in the area. The Site has been of great interest to
the local community from the time it was sited. In the early
years of the Site history there was a great deal of public
opposition and the community has watched the development of the
Site very closely. 20mmunlty lnterest peaked durlng a dye trace
study of ground water flow at the Site. This involved over 200
residents, whose wells were monitored for the presence of dye.
There were public meetings held before the dye trace study began
and update meetings were held approximately every five to six
months during the first two years of the study. There was also a
public meeting held at the conclusion of the Remedial
Investigation to update the local residents on the status of the
Remedial Investigation. The Proposed Plan for the Site
recommending no further action under Superfund was published on
March 5, 1994, which began the official thirty (30) day public
comment period. The official notice was published in the
Rochester Post Bulletin in the form of a legal notice ad.
Additionally, a fact sheet discussing the proposed plan and
notification of the public meeting was mailed to interested
parties and the press.
On March 10, 1994, a public meeting was held to discuss the
proposed plan and to accept comments on that plan. The meeting
was attended by 16 local residents, four county officials and
representatives of the local media. St~te and Federal
representatives included the EPA Remedial Project Manager, four
staff from the MPCA and a representative from the Minnesota
Department of Health. For a summary of the comments received,
please refer to the Responsiveness Summary which is attached to
this Record of Decision (Attachment 1). The Public comment
period ended on April 4. 1994, and no request for extension of
the formal comment period was received by the MPCA or the EPA.
A public repository has been established in the Rochester Public
Library, 11 First Street Southeast, Rochester, Minnesota. The
public repository contains the Administrative Record for the
Site. The Administrative Record contains all documents relating
to the Remedial Investigation conducted for the Site and a
transcript of the public meeting and comments received relative
to the Proposed Plan. The Administrative Record is also located
at the MPCA's main office at 520 Lafayette Road, St. Paul,
Minnesota and at the U.S. EPA's Region V Office in Chicago,
Illinois.
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IV.
J
SITE CHARACTERIZATION
The work at the Site involved determ~n~ng the
of the contamination associated with the Site
Human Health and Ecologlcal Risk Assessment.
Investigatlon concluded in par~ ~hat:
nature and extent
and conducting a
The Remedial
o
The Prairie du Chien Dolomite increases in competence with
depth. This, combined with the regional ground water flow
patterns, provides a degree of hydrogeologic separation
between the Prairie du Chien and the Jordan aquifers.
o
The widespread occurrence of dye in the monitoring wells
indicates that an interconnected system of fractures and
solution features is found beneath the landfill. Off site,
dye was detected ~n ground water samples north-northeast of
the landfill. indicating an lnterconnection from the area
near the northeastern edge of the landfill to ground water
sampling locations to th~ north-northeast of the landfill.
Lack of dye in the Jordan supports' the model of some degree
of hydraulic separation between the prairie du Chien and
Jordan aquifers under the landfill.
o
o
The fractures intersected by the monitoring well screens are
sufficiently conductive and interconnected to sustain pumping
rates of from 2 to 18 gallons per minute (GPM) for several
hours, suggesting that the fracture and joint system in the
prairie du Chien is well developed in the vicinity of the
monitoring wells.
o
The shallower Prairie du Chien generally has higher nitrate
nitrogen and chlorlde concentrations than the deeper Jordan
aquifer. These chemical differences support the ground water
flow model that the Jordan aquifer is hydraulically separate
from the prairie du Chien aquifer.
o
Regionally, water in the Prairie du Chien flows to the
northeast toward the Middle Fork of the Zumbro River, to the
South Fork of the Zumbro River and to Zumbro Lake ~o the
northeast of the landfill under a hydraulic gradient on the
order of 0.004.
o
The large scale migration of dye (and, potentially, waste
constituents associated with the landfill) is apparently
controlled by both the hydraulic gradient and the
preferential movement of water along
northeast-southwest-trending karst features.
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o
The direction of vertical ground water flow is generally
downward. both within the Prairie du Chien and between the
Prairie du Chien and Jordan aquifers. However. apparent
decreasing hydraulic conductivity with depth through the
prairie du Chien contributes to hydraulic separation between
the aquifers beneath the landfill.
o
Water in the Jordan aquifer flows toward the northeast to the
confluence of the Middle and South Forks of the Zumbro River.
Ground water flow is strongly influenced by the South and
Middle Forks of the Zumbro River and Zumbro Lake as discharge
points. The upward flow from the Jordan aquifer to the
Zumbro River is supported by the anion studies presented by
Donohue in the Final Report for the Olmsted County Dye Trace
Investigation.
o
The cover efficiency for each of the cells (except demolition
cell 1. which was st~ll operating at the time of the RI and
has since been closed) was estimated by the HELP model to be
about 99 percent. The percolation rates estimated in this
water balance are typical for landfills with similar final
cover configurations.
o
Residential water supply wells OLRW-151 and OLRW-l08, as
identified in the RI, are the most likely existing wells in
the ground water flow path from the landfill and/or dye
introduction point. No VOCs and no inorganic constituents
greater than background levels were observed in samples from
these wells.
o
Residential well OLRW-230 is a Prairie du Chien well nearest
the apparent flow path from the landfill. No VOCs or major
. ions indicative of leachate were found in this well.
o
The landfill has had no measurable impact on the chemistry of
water discharging from springs.
o
The results of the sampling of the intermittent stream do not
indicate an ongoing release to the surface waters immediately
adjacent to the landfill.
o
The Industrial Source Complex Short Term air dispersion model
was used to estimate concentrations of airborne constituents
at hypothetical receptor points and at nearby residences.
The maximum modeled concentrations were at the landfill
property boundary. There were no exceedences of MPCA
Allowable Air Concentrations (AACs).
o
The ground water monitoring network currently in place will
adequately assess the spatial distribution of ground water
quality in the 1mmediate vicinity of the landfill. The
existing monitoring well network is in the potential
migratiOn pathway and/or is part of an interconnected
fracture network that extends across the landfill.
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Vo
SUMMARY OF SITE RISKS
Part of the Remedial Invest~gation for the Site ~nvolved
conducting a baseline risk assessment, which is ~ntended to
measure the potential current and future risks posed by chemicals
of concern at the Site. The risk assessment evaluates both human
nealth and environmental r~sks.
Human Health Risks
The human health risk assessment evaluates potential
carcinogenic, or cancer caus~ng risks, and non-carcinogenic risks
to human health. Non-carc~nogenic risks include such risks as
the potential to cause liver damage and reproductive
abnormalities. Furthermore, the risk assessment requires that
all complete contaminant exposure pathways be evaluated. Such
potential pathways include. but are not limited to: direct skin
contact w~th or ingest~on of contaminated soil. surface water,
ground water; ~nhalat~on or absorption of contaminants during
washing, showering, or bathing; and inhalation of airborne
contaminants from the Site (see figures 1 & 2) .
Air sampling and air dispersion modeling performed during the RI
indicate that exposure to soil on, or air emanating from the site
does not pose any significant health risks under current land
use. Under a potential future land use scenario where a home
would be built immediately adjacent to the original landfill
boundary, an unacceptable carcinogenic risk was identified. This
unacceptable risk was from inhalation of soil pore gas containing
vinyl chloride migrating into the basement of this hypothetical
dwelling. This potential future pathway was removed by the
county with the purchase of additional property between the
original landfill boundary and the intermittent stream valley to
the east. The ground water pathway did not pose a s~gn~ficant
health risk under present or future land use scenarios. The
conclusions of the baseline risk assessments are as follows:
o
If a constituent was detected at concentrations greater than
background levels at locations potentially affected by
landfill constituents, the constituent was included in the
risk assessment. Those constituents detected at
concentrations at or below background levels were eliminated
from the risk assessment.
o
The reasonable maximum exposure (RME) scenario under current
land use includes a nearby resident who could be exposed to
constituents of concern via ingestion of fish from Zumbro
Lake; incidental ingestion, dermal absorption, and inhalation
while swimming in Zumbro Lake, and inhalation of ambient air.
Worker exposure to constituents of concern in ambient air was
also quantified.
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::>
Under future land use. che RME scenario ~ncludes a
hypothetical future res~dent who owns a home directly
adjacent to the landfill boundar1es. and whose water supply
well is screened in the Jordan aquifer. Completed exposure
pathways are the same as for current land use w~th the
addition of soil pore gas to the res~dence. Modeled ambient
air exposure concentrations are higher because the RME
scenario places the residence adjacent to the landfill.
o
The Minnesota Water Well Construction Code allows the
installation of new potable water supply wells in the prairie
du Chien aquifer only in areas with 50 feet or more of drift
material and/or insoluble rock material over the aquifer
within a 1 mile radius of the well. The closest location
which meets these criteria is approx~mately 2 miles Southeast
of the landfill. In addition. water quality in much of the
Prairie du Chien aquifer does not meet county water quality
standards for n1trate-n~trogen. Complet1on of a new well
constructed in a formation which does not meet county water
quality standards for nitrate nitrogen would therefore be
prohibited by county code.
o
The estimated excess upperbound7lifetime cancer risk under
current land use RME is 7 x 10- , primarily the result of
inhalation of vinyl chloride in ambient air as modeled from
landfill gas vent emissions (see figure 3). This e~timated
risk is lower than the acceptable risk level of 10- (MDH,
1992) .
o
The hazard index estimate under current land use is 0.02,
which is 50 times lower than the 1.0 U.S. EPA level of
concern (see figure 4) .
o
The estimated excess upperbou~~ lifetime cancer risk under
future land use RME is 6 x 10 ,primarily the result of
inhalation of vinyl chloride at concentrations estimated from
soil pore gas results. Thi~5risk is greater than the
acceptable risk level of 10 . (This pathway has since been
eliminated through a land purchase to preclude development.)
o
The total hazard index estimate under future land use is
0.04, which is 25 times lower than the U.S. EPA level of
concern.
o
The risk and hazard estimates are likely overestimates of
actual exposure due to the conservative assumptions made in
the risk assessment.
o
The risk and hazard estimates for future land use are highly
sensitive to the assumption that institutional controls will
continue to prohibit use of the prairie du Chien for future
water supply wells in this area.
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o
The sensitivity analysis of
assumptions showed that the
sensitive to the assumption
unaffected by the landfill.
current land use exposure
risk and hazard estimates are not
that residential wells are
o
The rlsk and/or.hazard associated with methane in soil pore
gas could not be quantified due to lack of toxiCity data in
the U.S. EPA data bases. ~owever. a potential hazard to the
future hypothetical adjacent resident was eliminated by the
county's purchase of additlonal property to preclude
development in the directlon of potential migration.
Ecological Risks
A qualitative ecological risk assessment was conducted for the
Site utilizing existing published information. In addition.
surface water concentrations of landfill cnemicals of concern
were computed based on information gathered in the Remedial
Investigation and the dye trace study. The concluslons of the
qualitative assessment are as. follows:
o
No sizable aquatic environments exist within or immediately
adjacent to the Site.
o
No state or federal surface water quality criteria were
exceeded by the estimated surface water concentrations and
toxicological data for constituents without criteria suggest
there is little likelihood for adverse impacts.
o
The concentration of constituents observed in monitoring
wells at the landfill are unlikely to result in adverse
effects to aquatic organisms in the Middle Fork of the Zumbro
River.
o
Terrestrial organisms have little opportunity to come in
contact with potentially toxic waste constituents, therefore,
there is little apparent risk to these organisms.
Supolemental Remedial Investiqation
Subsequent to the Remedial Investigation it was determined that
additional field work was needed to complete the investigation. A
Supplemental Remedial Investigation was then undertaken. In part, the
conclusions of the Supplemental Remedial Investigation are as follows:
o
The intermittent stream valleys to the north and east of the
site are effective physical barriers to subsurface methane
migration.
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o
Subsurface methane mlgratlon is no longer a pathway of
concern because there are no receptors on the county's
property and there is no eVldence of methane migration
the property boundary.
beyond
o
The landfill is in compliance wlth state limits on methane
concentration at the property boundary.
o
With the abandonment of unused residential well OLRW-219/220,
this potential pathway for cross contamination between the
prairie du Chien and Jordan aqulfers in the vicinity of the
landfill has been eliminated.
o
The Post Closure Care Plan sufficiently describes the
activities necessary for proper management of the landfill
during the 20 year post closure care period. Specifically,
this plan includes detailed ground water monltoring and
landfill gas compliance monltorlng programs and describes the
response actions that should be taken for reasonably
foreseeable deviations from expected results.
Based on the findings in the Remedial Investigation and the
Supplemental Remedial Investigation, the continuation of action
under Superfund is not necessary. The low potential for site
impacts can be adequately addressed under the Minnesota Solid
Waste Rules for landfills. The continued monitoring, long-term
care and contingency actions are specified in a Closure Order and
the Post Closure Care Plan issued for the Site on March 22, 1994,
by the MPCA. Continued monitoring to insure compliance with
Minnesota Solid Waste Rules will adequately protect human health
and the environment. Annual reviews of the data collected are a
current requirement under the Rules and thus a formal five year
review will not be necessary to ensure that the selected no
actlon alternative remalns protective.
This decision document presents the selection of the no-action
remedial alternative for the Olmsted County Sanitary Landfill,
Superfund Site. The selected remedial alternative was chosen in
accordance with CERCLA; as amended by SARA, and to the extent
practicable the NCP. Also, the selection is consistent with
MER LA. This no-action alternative is the same as the preferred
remedy presented at the public meeting for the Site on
March 10, 1994.
This decision is based upon the reports, information and public
comments, which constitute the Administrative Record for the
Site.
The EPA concurs with the selected no-action remedial alternative
for the Olmsted County Sanltary Landfill Superfund Site.
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CONTAMINANT FIGURE 1 PRIMARY
SECONDARY
CONTAMINANT CONTAMINANT TRANSPORT EXPOSURE EXPOSURE EXPOSED EXPOSED
SOURCE RELEASE PATHWAY POINT ROUTE POPULATION POPULATION
Residential and Site Ingestion Offslte "ResIdents
e
Jordan Aquifer Inhalation
Future Adjacent Dermal Absorption Future Adjacent
leaching e eSI en s
Residential and Site Ingestion Residents
e
Prairie du Chien Springs Inhalation
q lor
Future Adjacent Dermal Absorption
e
Dermal Absorption
Inhalation Humans
Incidental
Surface Water ngeslon
Zumbro Rivers Terrestrial Organisms Humans Consuming
r UlNDFlll Surface Runoff and lakes Ingestion !> at Creeks and Ponds I> Terrestrial Organisms I>
CONTENTS Sediment. Ingestion
Fish in Creeks and HumansfT errestrial
Ponds Organisms Consuming Fish
Bioconcentration
Residence Offsite Residence
Subsurface Gas Inhalation
Residence Residents
Gas Vent Emissions
Ambient Air Inhalation Worker/Farmer
Future Adjacent
e e
NOTE: Highlighting and solid arrows indicate the potential
oxposure pathway is more likely to be completed.
POTENTIAL EXPOSURE PATHWAYS
(CURRENT AND FUTURE LAND USE SCENARIOS)
OLMSTED COUNTY LANDFILL
11111; ~,~olntsO~
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FIGURE 2
POTENTIAL EXPOSURE PATHWAYS
Migration Exposure Exposure Potential ::~:::":::I.~~~!J':.:q~m~I~t~7::":::: Pathway
Pathway Point Routes Receptors Current Future Quantified? Ratlonale/Comment(1)
Groundwater Private wells Ingestion Residents No No No Currently unaffected: future private
Inhalation residents must install wells in the Jordan
Dermal Absorption aquifer.
Groundwater Springs Incidental Ingestion Residents No No No Springs are unaffected by the landfill.
Discharge Inhalation
Dermal Absorption
Groundwater Zumbro Fish Ingestion Residents Yes Yes Yes Affected groundwater in Prairie du Chien
Discharge lake Bioconcentration aquifer discharges to lake.
Groundwater Zumbro Incidental Ingestion Residents Yes Yes No Infrequent exposure.
Discharge lake Inhalation (swimming, water
Dermal Absorption skiing)
Groundwater Site water Ingestion Site Workers No No No Site wells unaffected by tho landfill.
supply wells Dermal Absorption
Inhalation
Ambient Air On-Site Inhalation Site Workers/Farmers Yes Yes Yes Exposure same for current and future land
use.
Ambient Air Off. Site Inhalation nesidents Yes Ves Yes Ambient air concentrations modeled from
potential vent gases.
Soil Pore Gas Off-Site Inhalation Residents No No No Residents too distant for significant risk
under current land use.
Subsurface Soil On-Site Ingestion Site Workers No No No No exposure point for subsurface soils.
Inhalation
Dermal Absorption
Surface Streamsl Incidental Ingestion Residents No No No Surface water not affected above
Water/Sediment Rivers Dermal Absorption background levels.
(11
See text for detailed discussion of rationaleicomments.
I B36.51:RTE:o!ms0516.1
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FIGURE 3
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BASELINE RISK ESTIMATES
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EXPOSURE ROUTE
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a Baseline estimates assume no corrective action. Residential exposure unless
noted as wOri
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FIGURE 4
a
BASELINE HAZARD INDEX ESTIMATES
CURRENT fUTURE
LAND USE LAND USE
1.2
1.1
1.0
0.9
0.8
~
X
Lo.I 0.7
Q
z
Q 0.6
0:::
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-< 0.5
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0.02 D.D07 0.0006 0.002 0.0006 0.0006
o
f1SH INHALA'T1ON INIW.ATlON F1SH INIW.ATlON INHALATION
INGESTION (NoIBlEHT ~ INGESTION (AMBlEHT
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ATTACHMENT 1
RESPONSIVENESS SUMMARY
Remedial Investigation and Remedial Decision for the Olmsted County
Landfill
This respons~veness summary has been developed to document and respond
to community concerns raised during the selection of a final remedial
alternative for the Olmsted County Landfill Superfund site. Oversight
of the remedial investigation of the site has been conducted by the
Minnesota Pollution Control Agency (MPCA) under a cooperative
agreement with the U.S. Environmental Protection Agency.
OVERVIEW
The recommended alternative for the Olmsted County Landfill was
announced to the community through a legal notice and press release
sent to the Rochester Post Bulletin and the Pine Island Register, and
by a fact sheet mailed to a standing list of interested parties. The
selected alternative is that no further remedial action be taken at
this site; long-term monitoring and postclosure care will be conducted
by Olmsted County under the provisions of the MPCA's Solid Waste
Management Facility Compliance Monitoring Program. This is
essentially the same plan as was proposed for public comment in
March of 1994. A public meeting on the proposal was held in Oronoco
Township on March 10, 1994.
A number of comments were received during the public meeting on the
proposed alternative; the MPCA's response to those comments is
contained in a later section of this responsiveness summary.
SUMMARY OF COMMENTS RECEIVED AND MPCA RESPONSES
Comments received during the public comment period on the Remedial
Investigation and Proposed Plan are summarized below:
Commen t :
Several commentors during the public meeting expressed distrust of the
MPCA's conclusions about migration of methane gas from the landfill.
Some said they feared that the cover installed on the landfill will
"bottle up" landfill gas and force it to migrate downward, where it
could follow natural conduits in the subsoils and then surface a~
unpredictable locations. After hearing of the planned venting
design, some commentors still felt the venting system will be
inadequate to prevent gas build-up.
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MPCA response:
While shallow surface venting systems, such as the one insealled at
the Olmsted County site, are generally not effeceive ae preventing
subsurface rnigraeion, there are several faceors at this site which
minimize the poeential for off-site migraeion. All cells, except cell
#1, have a two-fooe clay liner beneath ehe refuse, which will block
the downward migration, if pressure builds up within the cell. There
is a quarry to the west of the landfill which would act to vent any
gas migrating to the west. To the north and to the east, there are
intermittent stream valleys which cue down co the surface of the
bedrock. These intermittene stream valleys are on the current
landfill property and will act as gas discharge points for any gas
migrating in these directions. To the south, there are clay deposits
which were used as a borrow area for landfill cover. These clay
deposits will act as a barrier co gas migration. Monitoring of gas
probes installed at various depths around the site has shown migration
beyond the cell boundaries to the northeast and east. but no migration
beyond the intermittent stream valleys.
Comment:
A number of commentors at the public meeting also distrust the
Remedial Investigation's conclusions about ground water flow direction
near the landfill. In particular, the II disappearance II of the second
dye introduction during the dye trace study causes some residents to
doubt the MPCA has sufficient information to know whether nearby
residential wells will be affected. Although staff explained the lack
of data from the second dye introduction ultimately was irrelevant,
some residents feel it actually puts most or all of the other data in
doubt. More than one person said the second dye trace was disregarded
because it didn't fit preconceptions about ground water flow.
MPCA response:
Hydrogeology in a karst seeting is certainly not an exact science.
Since the aquifer is not homogeneous, flow rates, flow direction and
flow paths can change over a relatively small area. In order to
better understand the hydrology of this site, extensive work was
completed during the RI. The level of effort was much greater on this
site than for many other larger sites simply because a higher
confidence level was needed to select an appropriate remedy. The dye
trace study was only one element of the RI and provided useful
information that could not be obtained in other ways. Other elements
of the RI included pump tests, extensive geophysical logging,
hydraulic conductivity testing, video logging, direct sampling and
computer modeling. Anyone element by itself does not yield a clear
picture, yet when combined with other elements, a better understanding
of the system is possible. The lack of dye detections from the second
dye introduceion simply proved chat there were no monitoring points
along the flow paeh from the dye introduction point.
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When che informacion from the dye trace study is coupled with other
elemencs of the RI, ic is reasonable co conclude that the ground water
mon~toring system installed at the landfill will provide adequate
warn~ng of increased contam~nation. The contingency action plan for
the site ~ncludes IItrigger concencracionsll which accivate additional
sampling of monitoring wells and residencial wells in che identified
flow pach.
Comment:
A resident claimed the capping of the landfill has drastically altered
the local watershed, causing flooding of his property and
concentrating a large volume of runoff into a smaller area, thereby
increasing loading of toxics from che landfill in the affected area.
He asked whether the Deparcmenc of Natural Resources had been
consulted about changing che watershed.
MPCA response:
Closure of the landfill has not changed the watershed, although the
amount of runoff from the cells has increased from when the site was
open and the cells were more permeable. The increased runoff from the
cells was taken into consideration when designing the closure plan and
runoff retention basins were installed on the north and east sides of
the site. These retention basins collect cell runoff and allow silt
to settle out in the basin. The basins are designed to accommodate
the once in twenty-five (25) year storm event and should adequately
slow the release of runoff to prevent flooding downstream. The
flooding reported by the commentor is most likely due to dewatering
activities at the nearby quarry. Ground water is pumped out of the
quarry and discharged into the intermittent stream valley which
crosses the landfill property on the north. The pumping at the
quarry has increased in th~ past two years as the quarry operation
goes deeper. Any further increase in pumping will require an amended
water appropriations permit from the Minnesota Department of Natural
Resources (MDNR). The MPCA will coordinate with MDNR to insure that
increased pumping rate requests do not conflict with the monitoring
system at the landfill. Sampling of the intermittent stream during
the Remedial Investigation showed no impacts from the landfill on the
quality of the water in this stream.
Comment:
A resident said he thought che numerous monitoring wells installed at
the landfill, as well as any new wells installed in the area, would
provide pathways for contaminants co move from the upper aquifers to
lower, unaffected ones, thereby jeopardizing drinking water supplies.
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MPCA response:
All mOnitoring wells installed at the site, with the except~on of #17C
are in the Prairie du Chien aquifer. They are constructed such that
they are monitoring either shallow or deep prairie du Chien water and
are sealed with neat cement from just above the well screen to the
ground surface. Well #17C is drilled through the Prairie du Chien and
into the Jordan aquifer. This well is sealed from the top of the
Jordan up to the ground surface with neat cement grout. This
construction method prevents the well from being a conduit for
contamination into the deeper aquifer. All residential wells.
installed in the past decade also had to meet this construction code.
Future wells will also have to be installed in the Jordan aquifer and
comply with both county and state well codes for construction.
Comment:
A resident expressed a concern that the landfill is "full of hazardous
material" and is a disaster waiting to happen. He and one or two
others at the meeting preferred that the unlined area of the landfill
be excavated and lined, to prevent further release of contamination
from the unlined part of the landfill.
MPCA response:
This site, like'Jmost municipal solid waste landfills, probably
contains some industrial wastes that would be considered hazardous
under current regulations.. The site also contains household waste,
of which a small portion would be considered hazardous. The unlined
cell, which was first opened in December 1972 and completed in
December 1973, contains less than twelve (12) percent of the total
waste and covered four acres of the total fifty-two (52) acres filled.
While excavating and lining this portion of the site appears
attractive at first, upon considering the above facts and the
potential for causing additional releases, this idea is much less
attractive. The refuse in this cell has been in place for over twenty
(20) years and reached its moisture holding capacity long ago. The
process of excavating this material, stockpiling and placing it back
on a liner could potentially release contaminants in higher
concentrations than would occur under the present stable conditions.
An additional concern would be how this excavation could be conducted
safely and not cause significant releases to the air.
Comment:
Several residents commented that their well water is already degraded
by nitrates and in some cases coliform bacteria, and wondered whether
the landfill was a contributing cause.
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MPCA response:
Many wells in the prairie du Chien aquifer throughout Olmsted County
and surrounding counties are degraded by nitrates and coliform
bacteria. This bedrock aquifer has very little soil overburden in
this area, and is easily contaminated by farming practices and rural
development. This vulnerability is the reason for the state well code
and the county well code which prohibit the development of new potable
water supply wells in the prairie du Chien in areas with less than 50
feet of unconsolidated material over the bedrock within two miles of
the proposed well. In addition, the landfill monitoring wells are
analyzed for nitrate and have not shown any nitrate contamination
associated with the landfill.
Comment:
Several residents expressed frustration with the landfill's impact on
their property values. One wondered whether adjacent landowners will
be prevented from developing their land while the landfill is in
long-term care.
MPCA response:
This concern, while very real for the residents, is outside the
jurisdiction of the proposed plan. The proposed plan includes
institutional controls through the state well code and county well
code. These would apply whether the landfill existed or not. The
implementation of the proposed plan will not further restrict
development of adjoining property, since the county now owns the
property where potential gas migration could impact future
development.
-1:.5. CO\.Et_,~s. PRIS71SC OFFICE: 1994-386-541/03087
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