Description
Historical activity that resulted
in contamination.
| Redevelopment of a 14-acre commercial shopping center led to the discovery of two 360 gallon underground storage tanks containing PCE and there was also in the area surrounding the tanks PCE-contaminated soil and groundwater.
A coin-operated laundry and dry cleaning facility and an auto repair shop were former tenants of the property. Site was immediately enrolled in MPCA Voluntary Investigation and Cleanup program in order to address release immediately with least impact to the redevelopment schedule.
Site was initially investigated for petroleum related impacts in 1996. Soil borings indicated that no BTEX or DRO compounds were found at the site. Perched GW was found to have low level detects of benzene, toluene, xylene all below the HRL. Additionally, 1,1,2,2-PCE and 1,1,2-TCE were detected in groundwater below their HRL. The site was granted closure in October 8, 1997 for the petroleum related impacts. |
Contaminants
Contaminants present and the highest amount
detected in both soil and groundwater.
| Contaminant |
Media |
Concentration (ppb) |
Nondetect |
| Benzene |
groundwater |
290 ppb |
|
| chloroform |
groundwater |
1.2 ppb |
|
| Tetrachloroethene (PCE) |
groundwater |
2,100 ppb |
|
| Tetrachloroethene (PCE) |
soil |
15,000 ppb |
|
| Trichloroethene (TCE) |
soil |
140 ppb |
|
Site Hydrology
| Deepest Significant
Groundwater Contamination: |
|
|
| Plume Size: |
|
|
| Average Depth
to Groundwater: |
|
14ft |
Lithology and Subsurface Geology
MI River terrace deposits
|
|
medium grained, well-graded, sand
Depth: 0-17ft bgs
17ft thick
|
|
|
firm silty sandy clay
Depth: 17-27ft bgs
10ft thick
Conductivity: 10ft/day
Gradient: 0.00625ft/ft
|
|
|
Unconsolidated deposits
Depth: 27-90ft bgs
63ft thick
|
Pathways and DNAPL Presence
 Groundwater
 Sediments
Soil
DNAPL Present
|
Remediation Scenario
Cleanup
Goals: |
|
Groundwater: 7 ppb for PCE
Soil: 0.2 mg/kg PCE
|
Technologies
Ex Situ Biopile |
|
Why the technology was selected:
Since the soil contamination was shallow and construction was scheduled to occur over the release area, this technology allows significant removal of most, if not all, of the contamination and immediately addresses the concern so that planned activities can resume. Venting takes advantage of volatilization and indigenous microorganisms present in the native solids to biodegrade petroleum contaminants present in impacted solids
Groundwater plume was only defined on-site; monitoring conducted over more than a year showed that the concentrations in groundwater were generally decreasing.
Date implemented:
February 1997
Final remediation design:
Soil was excavated on February 1997 from the area where the 2 tanks were found and placed in an on-site lined berm. Approximately 5,600 cubic yards were removed. Excavation extended to 18 ft bgs.
Vertical vents were installed to allow volatilization of organic compounds. Venting pile was lined with 1 foot of crushed gravel on the bottom of the pit to create a base for drill rig access to the pile. 4-inch PVC vent pipes were installed in boreholes. The pipes were connected to all discharge to a common pipe on the top of the vent pile.
Additional soil was placed on top of the pile to complete the shape of the berm and allow for plantings to cover the pile. The soil was excavated on site for the construction of a retention pond at the southwest end of the development project.
The vent pile was initially equipped with a blower, but near the end of the project, the blower was replaced with a wind turbine to continue venting the pile.
Groundwater wells (7) were installed in April 1997. A deep well (to 39 feet bgs) was also installed. Sampling was conducted for 1 year, from 1997 – 1998. The concentrations of PCE have decreased consistently in many of the wells and stabilized in the others. Increases were observed in one well (from 110 to 2,100 ppb) and was thought to have occurred from a localized pocket of residual PCE. Trend analysis of GW elevation with concentration also indicated that higher concentrations during the spring may be due to the spring thaw (e.g. increased water table elevation and consequently contact with residual contamination).
Results to date:
Groundwater: Concentrations at the site are generally decreasing.
Soil: Site achieved closure on 6/17/02.
Next Steps:
Groundwater plume definition was limited to on-site and based on decreasing concentrations in the groundwater and a lack of identified groundwater receptors no further action was required by the MPCA.
|
Ex Situ Soil Removal |
|
Why the technology was selected:
Since the soil contamination was shallow and construction was scheduled to occur over the release area, this technology allows significant removal of most, if not all, of the contamination and immediately addresses the concern so that planned activities can resume. Venting takes advantage of volatilization and indigenous microorganisms present in the native solids to biodegrade petroleum contaminants present in impacted solids
Groundwater plume was only defined on-site; monitoring conducted over more than a year showed that the concentrations in groundwater were generally decreasing.
Date implemented:
February 1997
Final remediation design:
Soil was excavated on February 1997 from the area where the 2 tanks were found and placed in an on-site lined berm. Approximately 5,600 cubic yards were removed. Excavation extended to 18 ft bgs.
Vertical vents were installed to allow volatilization of organic compounds. Venting pile was lined with 1 foot of crushed gravel on the bottom of the pit to create a base for drill rig access to the pile. 4-inch PVC vent pipes were installed in boreholes. The pipes were connected to all discharge to a common pipe on the top of the vent pile.
Additional soil was placed on top of the pile to complete the shape of the berm and allow for plantings to cover the pile. The soil was excavated on site for the construction of a retention pond at the southwest end of the development project.
The vent pile was initially equipped with a blower, but near the end of the project, the blower was replaced with a wind turbine to continue venting the pile.
Groundwater wells (7) were installed in April 1997. A deep well (to 39 feet bgs) was also installed. Sampling was conducted for 1 year, from 1997 – 1998. The concentrations of PCE have decreased consistently in many of the wells and stabilized in the others. Increases were observed in one well (from 110 to 2,100 ppb) and was thought to have occurred from a localized pocket of residual PCE. Trend analysis of GW elevation with concentration also indicated that higher concentrations during the spring may be due to the spring thaw (e.g. increased water table elevation and consequently contact with residual contamination).
Results to date:
Groundwater: Concentrations at the site are generally decreasing.
Soil: Site achieved closure on 6/17/02.
Next Steps:
Groundwater plume definition was limited to on-site and based on decreasing concentrations in the groundwater and a lack of identified groundwater receptors no further action was required by the MPCA.
|
Ex Situ Soil Vapor Extraction |
|
Why the technology was selected:
Since the soil contamination was shallow and construction was scheduled to occur over the release area, this technology allows significant removal of most, if not all, of the contamination and immediately addresses the concern so that planned activities can resume. Venting takes advantage of volatilization and indigenous microorganisms present in the native solids to biodegrade petroleum contaminants present in impacted solids
Groundwater plume was only defined on-site; monitoring conducted over more than a year showed that the concentrations in groundwater were generally decreasing.
Date implemented:
February 1997
Final remediation design:
Soil was excavated on February 1997 from the area where the 2 tanks were found and placed in an on-site lined berm. Approximately 5,600 cubic yards were removed. Excavation extended to 18 ft bgs.
Vertical vents were installed to allow volatilization of organic compounds. Venting pile was lined with 1 foot of crushed gravel on the bottom of the pit to create a base for drill rig access to the pile. 4-inch PVC vent pipes were installed in boreholes. The pipes were connected to all discharge to a common pipe on the top of the vent pile.
Additional soil was placed on top of the pile to complete the shape of the berm and allow for plantings to cover the pile. The soil was excavated on site for the construction of a retention pond at the southwest end of the development project.
The vent pile was initially equipped with a blower, but near the end of the project, the blower was replaced with a wind turbine to continue venting the pile.
Groundwater wells (7) were installed in April 1997. A deep well (to 39 feet bgs) was also installed. Sampling was conducted for 1 year, from 1997 – 1998. The concentrations of PCE have decreased consistently in many of the wells and stabilized in the others. Increases were observed in one well (from 110 to 2,100 ppb) and was thought to have occurred from a localized pocket of residual PCE. Trend analysis of GW elevation with concentration also indicated that higher concentrations during the spring may be due to the spring thaw (e.g. increased water table elevation and consequently contact with residual contamination).
Results to date:
Groundwater: Concentrations at the site are generally decreasing.
Soil: Site achieved closure on 6/17/02.
Next Steps:
Groundwater plume definition was limited to on-site and based on decreasing concentrations in the groundwater and a lack of identified groundwater receptors no further action was required by the MPCA.
|
Costs
Cost
for Assessment:
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Cost
for Operation and Maintenance:
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Total
Costs for Cleanup:
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Contacts
Site Specific References
1. Remedial Investigation Report: Builders Square, Brooklyn Center, MN. July 25, 1996
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