Colonial Square Mall , Wayzata, Minnesota

State Coalition for Remediation of Drycleaners Site Profiles

Description
Historical activity that resulted in contamination.

The site is a 5.5 acre property containing the Colonial Square Mall complex which was built in 1958. Dry cleaning began at the site in 1972 with several different operations having been present. A release of PCE in the soil and GW beneath the property was identified on the property. The location of the source of the contamination is directly beneath the dry cleaning facility (one dry cleaner reportedly used a concrete pit for chemical waste storage) and there is a secondary source at the sewer main.

Contaminants
Contaminants present and the highest amount detected in both soil and groundwater.

Contaminant	Media	Concentration (ppb)
cis-1,2-Dichloroethene	groundwater	62 ppb
cis-1,2-Dichloroethene	soil	110 ppb
methylene chloride	soil	3.6 ppb
Tetrachloroethene (PCE)	groundwater	3,500 ppb
Tetrachloroethene (PCE)	soil	150,000 ppb
Trichloroethene (TCE)	groundwater	55 ppb
trans-1,2-Dichloroethene	groundwater	8.5 ppb

Site Hydrology

Deepest Significant Groundwater Contamination:		35ft bgs
Plume Size:		Plume Length: 900ft Plume Width: 400ft Plume Thickness: 35ft
Average Depth to Groundwater:		62.5ft

Lithology and Subsurface Geology

		yellow brown sand, dry, fine to coarse drain (fill) Depth: 0-10ft bgs 10ft thick Conductivity: 1.23ft/day Gradient: 0.045ft/ft
		layered silt and sand Depth: 10-11.5ft bgs 1.5ft thick
		Quaternary-aged loamy till, sandy till and lacustrine clay and silt deposits of the Des Moins lobe/Gransburg sublobe glaciation. Multiple sand stringers in the predominantly silty soil. Depth: 11.5-12ft bgs 0.5ft thick
		layered silt and sand Depth: 12-15ft bgs 3ft thick

Pathways and DNAPL Presence

Groundwater

Sediments

Soil

DNAPL Present

Remediation Scenario

Cleanup Goals:

Groundwater: Because of the presence of wetlands, the ecological criteria for surface water has been the preferred GW cleanup standard. No human health receptors down gradient of property exist. PCE concentrations for ecological criteria are 3.8 µg/L.

Soil: MPCA Residential Soil Reference Values

Technologies

In Situ Monitored Natural Attenuation

Why the technology was selected:
Monitored Natural Attenuation and Soil Vapor Extraction were selected because the geology at the site was not conducive to effectively supporting a proactive groundwater source control system. Biodegradation indicators (PCE daughter products and geochemical indicators) confirmed that natural attenuation was occurring.

Date implemented:
Active SVE operation from June 1999 through August 2002, follow-up groundwater monitoring conducted through June 2004.

Final remediation design:
Monitored natural attenuation required quarterly groundwater monitoring.

Results to date:
Quarterly monitoring from 1997 to 2002 indicated that the groundwater plume was stable. The SVE system operated continuously for 36 months removing approximately 1,800 pounds of VOCs. Soil confirmation results showed that residual contaminant concentrations in the source area soils were less than the MPCA Industrial and Residential Soil Reference Values. A Conditional No Further Action Determination letter was issued for the Site on September 10, 2002. The conditions in the letter included additional GW monitoring. On September 9, 2003, after a year of GW monitoring was conducted post-active SVE, approval to remove the SVE system was granted. Two additional GW sampling events were conducted over the next 12 months. These GW results indicated that the contaminant concentrations remained stable. On August 9, 2004, a No Further Action Determination was issued which stated that the conditions in the September 10, 2002 letter were met,

Next Steps:
The Site is now closed.

Cost to Design and Implement:
all technologies: $300,000 + (est. by consultant)

In Situ Soil Vapor Extraction

Date implemented:
Active SVE operation from June 1999 through August 2002, follow-up groundwater monitoring conducted through June 2004.

Final remediation design:
The SVE system was comprised of 5 vents. The vents were installed by drilling through the floor of the dry cleaning business. A skid-mounted SVE system was placed outside the rear of the store. The system had a design flow of 300 cfm extracted at 24 inches of water vacuum.

Next Steps:
The Site is now closed.

Cost to Design and Implement:
all technologies: $300,000 + (est. by consultant)

Costs

Cost for Assessment:		Investigation costs were approximately $158,000.
Cost for Operation and Maintenance:
Total Costs for Cleanup:		Investigation and remediation costs were approximately $458,000.

Lessons Learned

The removal rates of VOCs for this SVE system reached asymptotic levels after about 1.5 years of operation. The consultant proposed to shut down the system due to reaching asymptotic levels. However, the contaminant mass being removed was still quite significant. We required the system to continue operation for another 18 months.