Technology:
SVE, ISCO, MNA, P&T, MPE, AS
Shorty:
- Soil Vapor Extraction (SVE), In Situ Chemical Oxidation (ISCO), and Monitored Natural Attenuation (MNA)
- SVE system had 6 extraction points, with piping for the system buried 4 ft below grade; soil vents were inserted through old soil boring locations in situ; radius of influence was assumed to be 25 ft; air flow operated continuously with exhaust air flow typically around 125 scfm
- The system was turned off after 24 months
- MNA is being assessed through semi-annual groundwater monitoring
Long Prairie:
- SVE, MNA, Pump and Treat (P&T)
Colonial:
- SVE, MNA
- SVE system comprised of 5 vents; sid-mounted SVE system placed outside the rear of the store; system has a design flow of 300 cfm extracted at 24 inches of water vacuum.
Midway:
- SVE, Multi Phase Extraction (MPE), Air Sparging (AS)
- MPE implemented in one area of the site; AS/SVE implemented in another area of the site
- Total of 10 MPE extraction wells, 7 SVE wells, and 2 AS wells
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Cleanup Authority:
State
Contacts:
Varied by state |
Contaminants:
Tetrachloroethene (PCE); Trichloroethene (TCE); BTEX; Volatiles-Halogenated; Volatiles-Nonhalogenated; Semivolatiles-Nonhalogenated
Shorty:
- Groundwater - PCE - 50,000 μg/L; TCE - 5,500 μg/L; cis-1,2-dichloroethene - 5,000 μg/L; vinyl chloride - 430 μg/L; benzene - 3.3 μg/L; toluene - 34 μg/L; Naphthalene - 1,500 μg/L
- Soil - PCE - 1,200 mg/kg; TCE - 16 mg/kg; cis-1,2-dichloroethene - 6.1 mg/kg; benzene - 4 mg/kg; naphthalene - 23 mg/kg
Long Prairie:
- Groundwater - PCE - 150,000 μg/L; TCE - 760 μg/L; cis-1,2-DCE - 250 μg/L; vinyl chloride - 3 μg/L.
- Soil - PCE - 7,300,000 μg/kg; TCE - 15 μg/kg; cis-1,2-DCE - 10 μg/kg
Colonial:
- Groundwater - PCE - 3,500 μg/L; TCE - 55 μg/L; cis-1,2-DCE - 62 μg/L
- Soil - PCE - 150,000 μg/kg; cis-1,2-DCE - 110 μg/kg; methylene chloride - 3.6 μg/kg
Midway:
- Groundwater - PCE - 41,000 μg/L; TCE - 840 μg/L; cis-1,2-DCE - 100 μg/L; methylene chloride - 34 μg/L; ethylbenzene - 120 μg/L; benzene - 22 μg/L; acetone - 140 μg/L
- Soil - PCE - 11,000 mg/kg; methylene chloride - 1.3 mg/kg; acetone - 0.32 mg/kg |
Waste Source:
Waste and wastewater from drycleaning operations |
Type/Quantity of Media Treated:
Soil, Groundwater, Dense Non-aqueous Phase Liquids (DNAPLs)
Shorty:
- Depth to groundwater - 10 to 12 ft bgs
- Subsurface geology - Complex glacial lithology: 0-11 ft silty sand fill; 11-20 ft sand to silty sand (water bearing unit); 20-40 ft sand to silty sand with clay layers (clay layers are 0.25 to 11 inches thick); 40-60 ft gravelly sand; 60-120 ft bedrock
- Shallow aquifer conductivity - 0.837 to 5.47 ft/day; Deep aquifer conductivity - 0.211 to 33.40 ft/day
- Groundwater gradient: 0.318 ft/ft
Long Prairie:
- Depth to groundwater - 5-5 ft bgs
- Subsurface geology - Series of interbedded glacial till and sand and gravel outwash deposits that extend to at least 200 feet below grade; glacial drift deposits up to 700 ft thick ; western 2/3 of site underlain by sand and gravel outwash deposits that extend from the ground surface to a till layer that is about 60 to 80 feet below grade; eastern 1/3 of site is underlain by upper and lower outwash layers that are separated by an approximately 20-ft thick layer that acts as an aquitard separating the upper and lower outwash layers.
Colonial:
- Depth to groundwater - 36 to 105 ft bgs
- Subsurface geology - 0-10 ft yellow brown sand, dry, fine to coarse fill; 10-15 ft layered silt and sand; 11.5-12 ft Quaternary-aged loamy till, sandy till and lacustrine clay and silt deposits; multiple sand stringers in the predominantly silty soil; sediments overlying bedrock estimated to be 150 to 200 ft in the area; two discrete saturated zones that may be present beneath the site.
- Aquifer conductivity - 1.18 ft/day to 1.29 ft/day
- Groundwater gradient - 0.04 to 0.05 ft/ft
Midway:
- Depth to groundwater - 25.5 to 33 ft bgs
- Subsurface geology - 0-11 ft: fine to medium, red-brown sand; 11-22 ft: silty to clayey moderately stiff, red-brown till; 22-26 ft: silty, fine to medium, tan-brown sand; 26-28 ft: dry, stiff to very dense, clayey, fine to medium, gray sand overlaying a well sorted fine to medium gray sand, which is laterally discontinuous and averages less than 3 ft in thickness; groundwater in the unconsolidated glacial sediments is not hydraulically connected across the entire site; undulations in the bedrock surface appear to be the primary factor controlling the hydrogeology of the unconsolidated sediments at the site
- Aquifer conductivity - 4 to 9 ft/day
• Groundwater gradient - 0.01 ft/ft |
Purpose/Significance of Application:
Use of SVE together with other technologies to treat chlorinated solvents and BTEX in groundwater at dry cleaner facilities |
Regulatory Requirements/Cleanup Goals:
Shorty:
Groundwater - Eliminate hot spot at MW-3
; Soil - Reach asymptotic removal rates of VOCs for three consecutive quarters.
Long Prairie:
Groundwater - MCLs: 5 μg/L for PCE and TCE; 70 μg/L for DCE; Soil - PCE - 1,200 μg/kg
Colonial:
PCE - 3.8 μg/L (ecological criteria due to the presence of wetlands); no numerical standards set for soil
Midway
- Groundwater
- PCE: 5 μg/L and steady-state in groundwater; soil - PCE: 19,900 μg/kg |
Results:
Shorty:
- Concentration of degradation products has increased steadily over time, although the concentration of PCE remains high
- PCE concentration in groundwater decreased by 50% (6,200 μg/L to 3,000 μg/L) during operation of SVE, but spiked up again (10,000 μg/L) after SVE system was shut off
Long Prairie:
- Mass of chlorinated solvent contamination in the plume has been reduced, especially near the source area; concentration of chlorinated solvent contamination in the groundwater has decreased by three orders of magnitude near the source area.
- Soil cleanup goals were met after operation of the SVE system at the source area for approximately three years
- Active remediation will continue until MCLs are met or until data show MNA to be effective to meet MCLs
Colonial:
- Quarterly monitoring from 1997 to 2002 indicates that the groundwater plume is stable
- SVE system operated continuously for 36 months; system was shut down and removed after a year of groundwater monitoring following SVE operation
Midway:
- Mass removal for both MPE and SVE from February 2, 1999 to June 8, 2001 is 2,313 pounds
- Average daily contaminant recovery declined from a high of 22 lb/day to 0.2 lb/day (in January 2001)
- Exponential decay analysis indicates that the average daily recovery has reached an asymptotic level
- MPE system was authorized to be shut down on December 11, 2001
- AS/SVE system was shut down after one year of operation
- Soils meet cleanup goal of 19,900 μg/kg, therefore, closure has been requested for the soils |
Cost Factors:
- Shorty: Not provided
- Long Prairie: $300,000 annual operation and maintenance (O&M) costs
- Colonial: Total cost was approximately $300,000
- Midway: Not provided |
Description:
SVE was implemented together with other technologies at four dry cleaner sites in Minnesota contaminated with chlorinated solvents and BTEX from drycleaning operations. Initial concentrations of PCE and TCE in groundwater were as high as 150,000 μg/L and 5,500 μg/L, respectively, and 7,300 mg/kg and 16 mg/kg in soil. The remediation involved SVE with other technologies such as air sparging, in situ chemical oxidation, pump and treat, and multi phase extraction.
At the Shorty site, PCE concentrations in the groundwater continue to remain high even though the concentration of degradation products has increased steadily over time. At the Long Prairie and Midway sites, soil cleanup goals were met and the SVE system was shut down. At the Colonial site, the groundwater plume was stable and the SVE system was shut down after operating for 36 months.
At the Long Prairie site, source removal was key to reducing contaminant concentrations. |
