State Coalition for Remediation of Drycleaners Site Profiles
Midway Plaza, Saint Paul, Minnesota
Description
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This 37-acre site has been occupied by retail shopping mall since 1960. The site is zoned for commercial land use and is located in a commercial district. A PCE release occurred from a former drycleaning business that operated in the center. The drycleaner had two large in-ground cement tanks for storing PCE, and over a period of many years these tanks leaked. The sanitary sewer line that served the dry cleaner also served as a source of PCE contamination to the underlying soil and groundwater. |
Contaminants
Contaminants present and the highest amount
detected in both soil and groundwater.
Contaminant | Media | Concentration (ppb) | Nondetect |
---|---|---|---|
Benzene | groundwater | 22 ppb | |
cis-1,2-Dichloroethene | groundwater | 100 ppb | |
ethylbenzene | groundwater | 120 ppb | |
methylene chloride | groundwater | 34 ppb | |
methylene chloride | soil | 1,300 ppb | |
Tetrachloroethene (PCE) | groundwater | 41,000 ppb | |
Tetrachloroethene (PCE) | soil | 11,000,000 ppb | |
Trichloroethene (TCE) | groundwater | 840 ppb |
Site Hydrology
Deepest Significant Groundwater Contamination: | ||
Plume Size: | Plume Length: 250ft |
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Average Depth to Groundwater: | 29.25ft |
Lithology and Subsurface Geology
Fine to medium, red-brown sand Depth: 0-11ft bgs 11ft thick Conductivity: 6.5ft/day Gradient: 0.01ft/ft |
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Silty to clayey moderately stiff, red-brown till Depth: 11-22ft bgs 11ft thick |
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Silty, fine to medium, tan-brown sand Depth: 22-26ft bgs 4ft thick |
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Dry, stiff to very dense, clayey, fine to medium, gray sand Depth: 26-28ft bgs 2ft thick |
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well sorted fine to medium gray sand, which is laterally discontinuous and averages less than 3 ft in thickness Depth: 28-31ft bgs 3ft thick |
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Decorah shale |
shale bedrock Depth: 31ft bgs |
Pathways and DNAPL Presence
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Remediation Scenario
Cleanup
Goals: |
Groundwater: Treatment required until a soil cleanup goal of 5 mg/L PCE is achieved and a steady state level of PCE in groundwater is achieved. Soil: 19,900 µg/kg |
Technologies
In Situ Air Sparging |
Why the technology was selected: Date implemented: Final remediation design: Results to date: |
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In Situ Multi Phase Extraction |
Why the technology was selected: Date implemented: Final remediation design: Results to date: |
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In Situ Soil Vapor Extraction |
Why the technology was selected: Date implemented: Final remediation design: Results to date: |
Costs
Cost
for Assessment: |
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Cost
for Operation and Maintenance: |
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Total
Costs for Cleanup: |
Lessons Learned
1. The multi-phase extraction process was able to adequately remove a significant amount of contaminant mass from soil and groundwater. 2. The site geology complicated the system design, because the soil is primarily a fine-grained till material, and the aquifer is deep and thin (approximately 35-40 feet bgs). 3. The site cleanup decisions were made during a time period when the MPCA was taking a more cautious approach to groundwater cleanup than typically occurs at present. The lower perceived risk to potential groundwater receptors posed by this site might have resulted in a different outcome if site decisions were being made today. Perhaps the remedial option chosen would have been source area cleanup and long-term monitoring of the plume to demonstrate natural attenuation, rather than active groundwater cleanup. |
Contacts
Groundwater Atlas https://www.pca.state.mn.us/data/minnesota-groundwater-contamination-atl What's in My Neighborhood https://www.pca.state.mn.us/data/whats-my-neighborhood Consultant: Kevin Powers Leggette, Brashears & Graham Northpark Corporate Center 1210 West Cty Rd E, Suite 700 Saint Paul, MN 55112 (651) 490-1405 |