In a mixed retail/residential area off University Ave. NE in Blaine, the MPCA is investigating the presence of perchloroethylene (PCE, also called “perc” or tetrachloroethylene) in the soil and groundwater. PCE is a common dry cleaning solvent and the source has been traced to the former Crest Cleaners dry cleaning business located in the adjacent Oak Park Plaza commercial property at 10855 University Ave. NE, in Blaine.
The former property owner of Oak Park Plaza, ZCOF TL Blaine LLC (ZCOF), began preparing the site for redevelopment in 2015. During soil and groundwater investigations, PCE contamination was identified. After completing several additional phases of soil and groundwater investigations, ZCOF began cleaning up contaminated soils at and near the former dry cleaner in the spring of 2016. After the soil cleanup was completed, the site was redeveloped as a as a Cub Foods grocery store.
Site investigations of soil vapor and groundwater are still in progress to the east and north of the site. The MPCA’s Voluntary Investigation and Cleanup (VIC) Program is providing technical assistance and oversight for the environmental investigations and cleanup activities.
In December 22, 2016, ZCOF sold the property to SVAP II Oak Park Plaza LLC, who intends to continue and complete the site investigations and any additional cleanup required as a voluntary party within the MPCA Brownfields Program.
The issue: Vapor intrusion
PCE-contaminated groundwater can release PCE vapor that can rise through the soil and seep through basement and foundation cracks into homes and other buildings, where it could be inhaled by people. This is known as “vapor intrusion.” If a person breathes in low levels of contaminants in indoor air for a long time, there is an increased chance that person’s health could be affected. The risk to health depends on several factors, such as how much and what kind of contamination is present and how long a person has breathed it. The Minnesota Department of Health (MDH) has a fact sheet about PCE and health: Tetrachloroethylene (PCE, Perc) in Air. The MPCA wants to identify vapor intrusion and take steps to reduce or eliminate it where possible.
Map of the Crest Cleaners site
The map below shows the vapor intrusion area of concern associated with the PCE release from the former dry cleaner at the Crest Cleaner site. The vapor area of concern includes the Stonegate Apartment at 10850 6th Street NE and residential properties north of 109th Avenue NE.
2015-2016 site investigations and soil cleanup
Extensive soil, groundwater and soil vapor investigations were conducted by ZCOF in 2015. Three monitoring wells were installed in February 2015 and found groundwater at approximately 21 to 22 feet belowground. The groundwater flow direction is northwest and PCE groundwater contamination was identified in the north and northeast portions of the Oak Park Plaza property.
Groundwater samples were collected from approximately 33 temporary locations to search for potential sources for PCE vapor contamination. PCE concentrations in groundwater on the Oak Park Plaza property were detected up to 31 parts per billion (ppb), higher than the Minn. Department of Health (MDH) drinking water standard of 4 ppb. (All homes and businesses in the area are served by municipal drinking water supplies, which are not affected by this contamination.)
Some of the PCE groundwater contamination was believed to be the result of leakage from the sanitary sewer and sewer drain field that served the business. Spills of PCE at the dry cleaning operation may have allowed the chemicals to get into the sewer which then leaked into the soils and groundwater.
In April and May 2016, ZCOF completed soil excavations of PCE-contaminated soils beneath the former dry cleaner and beneath the utilities east of the building as the utilities were removed. A total of about 1,900 cubic yards of PCE-impacted soils were excavated and transported offsite for proper disposal. With the removal of the PCE-impacted soil, the MPCA anticipates that with time, the PCE concentrations in the soil vapor and the groundwater will decrease.
Vapor intrusion investigation
Due to the PCE release to soils and groundwater, soil vapor testing was conducted at the site to assess potential vapor intrusion risks to nearby occupied buildings. Soil vapor sampling was conducted east of the site near the adjacent Stonegate apartment building at 10850 6th Street NE.
In January 2016, ZCOF conducted soil vapor testing in the west parking lot of the apartment complex with permission of the owner. A total of 10 vapor samples were collected beneath the parking lot at a depth of 8 feet. The sampling results identified PCE in soil vapor at much lower concentrations than at the Crest Cleaners site, but in 6 of the 10 samples, PCE was found at levels between 25 and 100 micrograms per cubic meter (µg/m3).
Based on these results, in April 2016, ZCOF began quarterly testing of vapors beneath the Stonegate Apartment building. Sampling beneath the building floor slab conducted in April, August and December 2016 has identified PCE in vapor, but at concentrations well below the level of 110 µg/m3 that would be a cause of concern. Additional testing beneath the Stonegate Apartment building and vapor probes installed west and adjacent to the building will be conducted in April 2017. Recent soil vapor sampling conducted east of the Stonegate Apartment building did not detect any PCE concentrations.
The new Cub Foods store located at the northern portion of the Oak Park Plaza opened in December 2016. Before the building was constructed a vapor mitigation system was installed beneath the new concrete slab upon which the Cub Foods was built. This system will prevent vapor intrusion to the Cub Foods store by actively collecting and exhausting any residual PCE vapors remaining in soil beneath the Cub Foods building.
In October and December 2016, groundwater and soil vapor sampling was conducted north of the site property along the right-of-way of the 109th Avenue NE and north and south along 4th Street NE and 5th Street NE. Soil vapor sampling has identified two residential properties within 100 feet of soil vapor samples that identified PCE above the residential screening value of 110 µg/m3.
The next step is to request access from the property owners to collect sub-slab samples at these two properties to determine if vapor mitigation is required. Additional vapor sampling will also be conducted to verify the northern extent of the vapor intrusion concerns.
If sub-slab vapor samples collected beneath residential homes are identified at levels of concern a vapor mitigation system will be installed at the homes at no cost to the homeowners. The vapor mitigation system will be installed with a qualified contractor and testing will be conducted before and after installation to verify that the system is properly designed and operating properly.
The MPCA anticipates that the removal of the contaminated soil in spring 2016 will eventually result in significantly lower PCE vapor concentrations on both the Crest Cleaners site and the adjacent properties.
|1960s – 1976||Dry cleaning businesses operate at the site|
|1976 – April 2012||Crest Cleaners operates at the location|
|July 2005||ZCOF collects soil and groundwater samples — finds no PCE|
|August 2011||Elevated PCE soil vapor concentrations found beneath former Jubilee Foods store near the dry cleaning business|
|September 2011||ZOPF purchases Oak Park Plaza|
|April 2012 – January 2015||Crest Cleaners serves as a drop-off-only business at request of ZOPF|
|January 2015||Crest Cleaners vacates the property|
|February-April 2015||Investigations conducted to determine scope of soil cleanup|
|August 2015||Soil cleanup plan prepared by ZCOF|
|September 2015||MPCA approves August 2015 soil cleanup plan|
|December 2015||ZCOF conducts additional soil sampling along sanitary sewer|
|January 2016||Soil vapor samples collected west of Stonegate Apartment building to assess vapor intrusion risks|
|March 2016||Amended soil cleanup plan submitted based on additional soil sampling along sanitary sewer|
|April 2016||Demolition of buildings to prepare site for soil cleanup and redevelopment|
|April 2016||Quarterly vapor sampling beneath the floor slab of Stonegate Apartment building initiated|
|April - May 2016||Soil cleanup conducted involving excavation of PCE contaminated soils|
|August 2016||Follow-up soil vapor samples collected west of Stonegate Apartment building to assess vapor intrusion risks|
|August and October 2016||Soil vapor sampled collected along and north of 109th Avenue NE to assess vapor intrusion risks to residential properties|
|December 2016||Soil vapor sampled along 6th St NE and north and east of Stonegate Apartment building|
Site Remediation and Redevelopment Section