Technical and Regulatory Guidance for In Situ Chemical ... - ITRC

8. Service Station Site in Madison, WI
Background
The service station site located in Madison, Wisconsin, is an operating gasoline service station. The
existing underground storage tank (UST) system consists of one 4,000-gallon gasoline tank, one
4,000-gallon diesel tank, and two dispenser islands. In addition, one 550-gallon waste oil tank and
one 550-gallon fuel oil tank exists on the property. On August 14, 1995, one 8,000-gallon gasoline
tank was removed from the site. The remaining four USTs are proposed to be removed prior to
remedial activities. All of the USTs are registered with the Wisconsin Department of Commerce
(DCOM).
A petroleum release was detected on May 11, 1994, from a soil sample collected from beneath the
east unleaded dispenser island and analyzed for Gasoline Range Organics (GRO). The test results
indicated a GRO concentration of 4,200 mg/kg, which is above the soil cleanup standards for GRO
of 100 mg/kg. The WDNR was immediately notified of the release.
Site Hydrogeology
Soil types encountered during the investigation consisted of silty clay native to fill material with
sand and gravel and organic matter extending to depths ranging from 6 to 11 feet below ground
surface (bgs). These fill soils are underlain by brown to grey brown to red-brown silty sand to
sand and gravel. This sandy gravelly soil extends to depths ranging from 15 to 17 feet bgs.
Beneath the dense sandy/gravelly soil is friable light brown to white to pink sandstone bedrock to
the maximum explored depth of 26 feet bgs. Groundwater is present at 16 to 20 feet below
ground surface.
Depth to groundwater in the site monitoring wells ranges from 16 to 20 feet below ground
-5
surface with a hydraulic conductivity of 10 . As evidenced during water sample collection,
recharge is moderate, which is typical of saturated silty sand. The groundwater flow direction is
predominantly toward the north/northwest. The flow direction is consistent with local
topography.
Design/Implementation
Following the completion of the subsurface investigation, a remedial alternatives comparison
was prepared and submitted to the DCOM for review and approval. The selected and approved
remedial alternative was a limited hot-spot contaminated soil excavation with the injection of
Hydrogen Peroxide/Ferrous Sulfate (HP/FS) injection to remediate contaminated groundwater
within shallow bedrock. A wordplay was prepared and submitted to the WDNR for approval.
Approval for the remedial approach was granted by the WDNR in March, 1998.
Approximately 2,100 tons of contaminated soil were excavated and transported to the Madison
Prairie Bio-Site on July 6 and 7, 1998. The chemical oxidation vendor performed a HP/FS
injection pilot-test during the week of July 13, 1998. Based on the results of the pilot test,
including contaminant destruction, the absence of vapor migration based on screening of vent
wells and subsurface utilities and neighboring basements; as well as other factors, full-scale
treatment was determined to be feasible utilizing this technology. In late July/early August, 1998,
45 injector wells (15 foot to 17 foot radius), and 14 vent wells were installed at the site covering
an area of 220 foot by 200 foot. Full-scale chemical oxidation treatment of the petroleumcontaminated
groundwater, saturated soils (including capillary fringe), and bedrock was
performed from late August to September 11, 1998. Approximately 15,000-gallons of Fenton’s
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