| BACKGROUND
The Woodstock East Gerrish Motors
Site (Site) located along U.S. Route 4 in Woodstock Village has
seen a variety of commercial enterprises over the years, including
restaurants, a health club, a furniture refinishing operation,
a day-care center, a tool and die manufacturer, a carwash, a laundromat,
a retail petroleum facility, a solid waste hauling operation facility
and residential apartments. From the late 1960s through the end
of 1987, the Site held the operations, sales and service center
for the Gerrish Corporation car dealership.
A large gasoline release at a retail
petroleum facility took place at the Site in 1973. Roughly eleven
years later, the State of Vermont Agency of Natural Resources
(VTANR) began to receive complaints from fishermen who reported
seeing sheens on the Ottauquechee River. Based in part on those
concerns, VTANR initiated environmental investigations at the
Site in 1985.
ACTION TAKEN AT SITE
Since 1985, a number of studies have been
conducted. The most recent and comprehensive of these studies,
completed in October 2000, identified five major areas of concern
shown on the figure and described
briefly below:
- Area I: Former Gasoline/Diesel Underground
Storage Tank (UST) Area
Problem: Although the USTs in this area were
removed in 1994 and 1995, soil and groundwater contamination consisting
of some metals and gasoline and diesel components remains. The
area includes an underground french drain which is acting as a
conduit for contaminated groundwater.
- Area II: Former Fuel Oil UST Area
Problem: The UST in the vicinity of this area
was closed in place in 1995. Residual contamination including
chlorinated volatile organic compounds (VOCs) and diesel components
in soil and groundwater remains.
- Area III: Former Oil-Water Separator Area
Problem: There was evidence of soil contamination
in this area when the oil/water separator (which was associated
with the auto dealership service facility) was removed in 2000,
but subsequent soil sampling indicated no VOCs above detection
limits or petroleum constituents above Vermont criteria.
- Area IV: Former Waste Oil Tank Area
Problem: There has been past evidence of free
product (possibly gasoline or fuel oil) in this area, but recent
groundwater sampling showed reduced groundwater contamination.
- Area V: Former Water Supply Well
Problem: Bedrock well with low concentrations
of tetrachloroethylene (PCE) at depth.
ACTION PLANNED
A Feasibility Study and Corrective Action
Plan completed in the summer of 2001 evaluated various cleanup
alternatives for the Site that would minimize risks to both human
health and the environment from the on-site contamination. The
alternatives evaluation considered potential routes of exposure,
implementation time, technical implementability and cost. Alternatives
ranged from low cost, no action/monitoring alternatives that are
not likely to meet cleanup objectives for several years to extensive
excavation with groundwater treatment, which probably would meet
cleanup objectives very rapidly but at a high cost.
The recommended remedial alternative is a
combination of approaches which attempts to achieve site cleanup
goals in a relatively short timeframe and at a reasonable cost.
- Area I: Former Gasoline/Diesel UST Area
Proposed Action: The corrective action recommended
for Area I will include two elements: (1) removal of the french
drain and (2) an aggressive air sparge/soil vapor extraction (AS/SVE)
system to remove subsurface contamination.
- French Drain: Taking out the french drain
will eliminate a pathway for contaminated groundwater to move
off-Site and into surface water. Some soils around the french
drain will also be removed along with the pipe removal. Those
soils will be will be properly disposed off-site.
- AS/SVE System: Air sparging (AS) is the
process of injecting air into contaminated groundwater through
a series of wells. The injected air bubbles up through groundwater,
carrying volatile contaminants along with it. In addition,
the injected air also provides additional oxygen for naturally
occurring microbes in the soil that consume petroleum hydrocarbons.
The additional oxygen allows the microbe population to multiply
rapidly, greatly increasing their ability to clean up the
affected area. Soil vapor extraction (SVE) uses a vacuum system
to capture and treat contaminant vapors that are carried into
the unsaturated zone below ground surface but above the groundwater
table. Recovered vapors will be treated with carbon to prevent
contaminants from discharging to the atmosphere. The proposed
system consists of eight sparge and eight vacuum wells that
will operate in a pulsed manner to maximize the contaminant
removal during the period of operation.
- Timeframe: The AS/SVE is proposed to
operate for 5 to 6 months following which the system will
be decommissioned and the area paved as part of the Site redevelopment.
The paving will also prevent any contact with low levels of
contaminants that may remain after the system is decommissioned.
Monitoring wells will be installed upgradient and downgradient
of this area. Samples will be collected from these wells to
confirm that the cleanup has been successful and that any
remaining contamination is being degraded by natural processes.
- Area II: Former Fuel Oil UST Area
Proposed Action: The corrective action proposed
for Area II is excavation and removal of "hot spot"
soils remaining from previous tank closures that continue to contribute
to groundwater contamination. The excavation will remove the majority
of contaminant mass remaining in soil and help prevent further
contaminant transfer to groundwater in the area. This area will
be paved during the Site redevelopment. A monitoring well will
be placed downgradient of this area and samples collected to confirm
that the cleanup has been successful and that any remaining contamination
is being degraded by natural processes.
- Area III: Former Oil/Water Separator Area
Proposed Action: No further action is proposed
for Area III. During removal of the separator unit, field monitoring
indicated some soil contamination. However, subsequent soil borings
did not find contamination. This area will be paved and/or covered
by buildings during the Site redevelopment, which will prevent
contact with any contaminants that may remain.
- Area IV: Former Waste Oil Tank Area
Proposed Action: No further action is proposed
for Area IV. A well in this area contained free phase product
in 1995, but since that time the level of groundwater contamination
in the area has decreased, and free phase product no longer exists.
Also, this area is located upgradient of the Area I where the
AS/SVE system will operate. It is possible that contamination
in this area will be partially treated by the AS/SVE system and
further diminished by natural processes, including biodegradation.
- Area V: Former Water Supply Well
Solution: This bedrock will be closed in accordance
with State of Vermont guidelines. All pumps, wiring and piping
will be removed from the well. The well will be grouted to the
surface to eliminate any future use of this well.
FUTURE USE
The Woodstock East Site was entered into the
Vermont Brownfields program in 1999 to facilitate its remediation
for redevelopment. Following completion of the corrective action,
current redevelopment plans call for a 35,000-square-foot grocery
store with associated landscaping and parking.
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image of areas of concern and proposed corrective actions
OR
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the areas of concern and proposed corrective actions
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|
Waste Mangement Division 
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