Drycleaner Site Profiles

Long Prairie, Long Prairie, Minnesota

Description
Historical activity that resulted in contamination.

This site originated from a drycleaner operation located in the downtown area. Contamination spread over a 10-block area and impacted two municipal wells before it was detected. Remedies included pumpouts along the heart of the mile-long plume and GAC treatment of contaminated water, SVE at the source, and alternative water supply. Also, most affected private wells were abandoned, and residences were put on city water. This site was remediated under the state and federal Superfund programs.

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


Contaminant Media Concentration (ppb) Nondetect
cis-1,2-Dichloroethene groundwater 85 ppb
cis-1,2-Dichloroethene soil 10 ppb
1,1-Dichloroethene groundwater 1 ppb ND
Tetrachloroethene (PCE) groundwater 140 ppb
Tetrachloroethene (PCE) soil 1,200 ppb
Trichloroethene (TCE) groundwater 80 ppb
Vinyl Chloride groundwater 1 ppb ND

Site Hydrology

Deepest Significant Groundwater Contamination:   75ft bgs
Plume Size:   Plume Length: 5,280ft
Average Depth to Groundwater:   30ft

Lithology and Subsurface Geology

 
  interbedded glacial till and sand and gravel outwash deposits
Depth: 0-200ft bgs
200ft thick

Pathways and DNAPL Presence

checkGroundwater
Sediments
checkSoil
checkDNAPL Present

Remediation Scenario

Cleanup Goals:
  Groundwater: The targets for groundwater are MCLs (5 ppb for PCE and TCE and 70 ppb for DCE).

Surface Water: Discharge of treated water at MCLs also meets the chronic surface water quality standards.

Soil: PCE 1,200 ppb

Technologies

In Situ Soil Vapor Extraction
 

Why the technology was selected:
These technologies were selected because the FS showed them to be an effective remedy that could meet the 9 ROD criteria.

Date implemented:
1984 -- Alt water supply 1987 -- Granular Activated Carbon 1997 -- SVE 1997 -- Alt water supply 2000 -- Additional extraction wells

Results to date:
Groundwater: New municipal wells were installed to replace old contaminated wells. Over 150 properties that formerly relied on private water supply systems in and near the plume were connected to the municipal water supply The mass of chlorinated solvent contamination in the plume has been reduced significantly, especially near the source area. The concentration of chlorinated solvent contamination in the ground water has decreased by up to 1000 times near the source area. Recovery wells at the site have continued to control the ground water flow gradient and plume migration to protect nearby municipal wells and the Long Prairie River. The recovery system removes and treats over 100 million gallons of water each year. The downgradient extent of the plume still has not changed significantly since remedial actions were initiated. The size and length of the plume is decreasing as ground water near the source area becomes clean. Soil: Met soil cleanup goals after operating an SVE system at the source area for approximately three years.

Next Steps:
In accordance with the ROD for this site, active remediation will be continued until MCLs are met or until data shows that MCLs are not achievable due to technical infeasibility. At that point, alternate target levels may need to be established. At this point, we are planning to continue removing and treating contaminated groundwater at least until gradient control is no longer needed to protect nearby municipal water wells and it appears that the plume would no longer discharge to the Long Prairie River or wetlands. At that point, we will evaluate whether continued active remediation and gradient control is warranted.

Cost to Design and Implement:
RD $369,147 + RA and O&M $6,673,000

Ex Situ Carbon Adsorption
 

Why the technology was selected:
These technologies were selected because the FS showed them to be an effective remedy that could meet the 9 ROD criteria.

Date implemented:
1984 -- Alt water supply 1987 -- Granular Activated Carbon 1997 -- SVE 1997 -- Alt water supply 2000 -- Additional extraction wells

Results to date:
Groundwater: New municipal wells were installed to replace old contaminated wells. Over 150 properties that formerly relied on private water supply systems in and near the plume were connected to the municipal water supply The mass of chlorinated solvent contamination in the plume has been reduced significantly, especially near the source area. The concentration of chlorinated solvent contamination in the ground water has decreased by up to 1000 times near the source area. Recovery wells at the site have continued to control the ground water flow gradient and plume migration to protect nearby municipal wells and the Long Prairie River. The recovery system removes and treats over 100 million gallons of water each year. The downgradient extent of the plume still has not changed significantly since remedial actions were initiated. The size and length of the plume is decreasing as ground water near the source area becomes clean. Soil: Met soil cleanup goals after operating an SVE system at the source area for approximately three years.

Next Steps:
In accordance with the ROD for this site, active remediation will be continued until MCLs are met or until data shows that MCLs are not achievable due to technical infeasibility. At that point, alternate target levels may need to be established. At this point, we are planning to continue removing and treating contaminated groundwater at least until gradient control is no longer needed to protect nearby municipal water wells and it appears that the plume would no longer discharge to the Long Prairie River or wetlands. At that point, we will evaluate whether continued active remediation and gradient control is warranted.

Cost to Design and Implement:
RD $369,147 + RA and O&M $6,673,000

Ex Situ Pump and Treat
 

Why the technology was selected:
These technologies were selected because the FS showed them to be an effective remedy that could meet the 9 ROD criteria.

Date implemented:
1984 -- Alt water supply 1987 -- Granular Activated Carbon 1997 -- SVE 1997 -- Alt water supply 2000 -- Additional extraction wells

Results to date:
Groundwater: New municipal wells were installed to replace old contaminated wells. Over 150 properties that formerly relied on private water supply systems in and near the plume were connected to the municipal water supply The mass of chlorinated solvent contamination in the plume has been reduced significantly, especially near the source area. The concentration of chlorinated solvent contamination in the ground water has decreased by up to 1000 times near the source area. Recovery wells at the site have continued to control the ground water flow gradient and plume migration to protect nearby municipal wells and the Long Prairie River. The recovery system removes and treats over 100 million gallons of water each year. The downgradient extent of the plume still has not changed significantly since remedial actions were initiated. The size and length of the plume is decreasing as ground water near the source area becomes clean. Soil: Met soil cleanup goals after operating an SVE system at the source area for approximately three years.

Next Steps:
In accordance with the ROD for this site, active remediation will be continued until MCLs are met or until data shows that MCLs are not achievable due to technical infeasibility. At that point, alternate target levels may need to be established. At this point, we are planning to continue removing and treating contaminated groundwater at least until gradient control is no longer needed to protect nearby municipal water wells and it appears that the plume would no longer discharge to the Long Prairie River or wetlands. At that point, we will evaluate whether continued active remediation and gradient control is warranted.

Cost to Design and Implement:
RD $369,147 + RA and O&M $6,673,000

Costs

Cost for Assessment:
  $363,998
Cost for Operation and Maintenance:
  $300,000 annually
Total Costs for Cleanup:
 

Lessons Learned

1. Source removal/extraction is key to plume concentrations reduction and should be the first response action. Lateral spread is hard to control. I agree. Findings from this site clearly show the importance of finding the source (highly contaminated soil and groundwater including DNAPL directly beneath the area of release) and removing it as soon as possible. The magnitude of dissolved contamination in the groundwater began to decrease dramatically as soon as source removal was implemented. It appears that the plume is now beginning to shrink and natural attenuation is now taking affect. At present, natural attenuation data is being collected so that the rate of natural attenuation and an estimate of when remediation will be completed are currently being calculated.
2. This is a good example of how far and fast a chlorinated solvent plume can spread under the right hydrogeologic conditions. Before the site was discovered in the mid 1980s, the length of the plume was captured and contained by municipal wells located about one-third of a mile downgradient. After these wells were shut down, the plume rapidly (in less than ten years) migrated another two-thirds of a mile downgradient to the Long Prairie River.
3. Conducting periodic and updated water supply well surveys and keeping area land owners and residents informed over the life of a long-term remediation project is very important. Due to the shallow groundwater at this site, it is not unusual for the area residents to install their own shallow sand point wells for secondary use. There has been a number of instances at this site where new residence or land owner have installed wells in the plume, and where new residents used old secondary wells without knowing about potential groundwater contamination.

Contacts

Maureen Johnson
Minnesota Pollution Control Agency
520 Lafayette Road North
St. Paul, MN 55155-4194
651-296-7353

Current Consultant (O&M):
Dave Wolfgram
Terracon
33535 Hoffman Road East
White Bear Lake, MN 55110
651-770-1500 ext 126
djwolfgram@terracon.com

Former Consultant (Design, Construction, early O&M):
Dale Finnesgaard,
Barr Engineering
8300 Norman Center Drive
Minneapolis, MN 55437-1026
(952) 832-2667Dfinnesgaard@Barr.com

Site Specific References

1. Long Prairie ROD & 2 ESDs, June 1988, June 1991, May 1994
2. Long Prairie Ground Water Contamination Five-Year Review, MPCA and EPA, 9/30/02