The Highway 96 Dump Site, located north of Highway 96 and west of Allendale Drive in White Bear Township, was operated as a small burning dump from the 1920s to 1973. During operation, the former dump accepted primarily solid waste. Some hazardous wastes were also disposed of at the dump.
What's the problem
In 1986, a study conducted by the U.S. Environmental Protection Agency showed that groundwater beneath the dump site was contaminated with volatile organic compounds (VOCs) including industrial, solvent-like chemicals. As a result of the study, the Minnesota Pollution Control Agency (MPCA) requested potentially responsible parties including Reynolds Metal Company, Whirlpool Corporation, and Red Arrow Waste Disposal Company to investigate and clean up the contamination. Additional investigations found waste in drums, soil contamination, and landfill gas below the surface.
The investigations identified waste in two areas: the North Disposal Area (NDA) and the South Disposal Area (SDA), as shown on the overview map below.
What's been done
Contractors for the responsible parties began source area clean-up work at the site in August 1987. The NDA and SDA waste material was screened for buried drums and associated contaminated soil. Contaminated soil and hazardous waste identified during the screening process was removed and hauled off-site for disposal. The contractors also drained the pond located within NDA.
All of the pond water was discharged to the sanitary sewer. Sediment and material from the pond bottom were screened and drums of waste were removed. After screening the NDA and the pond, the contractors transferred all waste material from the SDA to the NDA, which is now called the consolidated waste area (CWA). Tests of the SDA showed no residual contamination. Next, the SDA was backfilled with clean soil. NDA material was compacted and capped with two feet of clean soil and remains on the property.
Groundwater contamination is present at the site and has migrated to the west, in the direction of groundwater flow. The main groundwater contaminant found below the waste is vinyl chloride. Other contaminants of potential concern include 1-1 dichloroethane, benzene, toluene, trichloroethene, methyl ethyl ketone, and trans -1, 2 – dichloroethane.
Since June 1989, a groundwater extraction system has been in operation at the site. The extraction system collects groundwater from aquifers below the surface to stop the spread of contamination. The groundwater extraction system has been effective in limiting the spread of contamination and removing contaminants from the groundwater. The contaminated groundwater from the extraction system is discharged to the sanitary sewer for treatment. Regular groundwater monitoring by the responsible parties will continue for many years.
In late 1994, a leachate collection well was installed directly under the CWA. Its purpose is to collect contaminated leachate before it reaches deeper, drinking-water aquifers. Leachate is produced when rain and melting snow filter through the waste and dissolve chemicals from the waste. The leachate collection well operated until 2018, when it was determined that there was no longer enough contamination present in the waste to leach into the shallow groundwater for the well to operate efficiently.
Prior to installation of the extraction system, the contaminated groundwater migrated to the west toward Gilfillan Lake. The responsible parties have taken actions to address this off-site contamination. In 1994, 60 North Oaks homes with private wells were connected to the White Bear Township municipal water system. In 2004, vinyl chloride was detected in private wells to the west of Gilfillan Lake. The responsible parties began sampling additional wells on the west side of Gilfillan Lake, and private wells that had detections of vinyl chloride above action criteria were replaced with newer, deeper wells.
Residential well monitoring outside the municipal water service area is ongoing. No well contamination outside the municipal water service area has been found above limits that would require some sort of corrective action since 2012.
Decomposing garbage creates what is commonly referred to as landfill gas. It is primarily methane and it can migrate off-site. The responsible parties installed passive landfill vents at the CWA. Builders of the Weston Woods townhouse complex installed a gas monitoring network and two landfill gas interceptor trenches in 2001 and 2002 to prevent this gas from migrating into homes.
What's being proposed
Because vinyl chloride has not been detected at any well location since 2014, and no other VOCs have been detected above action levels, the MPCA approves of the proposed changes to how frequently private wells in this area are sampled. The original sampling plan developed in 2008 includes:
- 28 private wells sampled twice a year
- 34 wells sampled annually
- 15 wells sampled every 2 years
The proposed sampling plan includes:
- 28 private wells to be sampled annually
- 42 private wells to be sampled every five years
- 7 private wells to no longer be sampled (these private wells never had detections of VOCs, and are not in the contaminant flow path)
The map below shows the new proposed schedule. The draft Second amendment to the Minnesota Decision Document shows the sampling frequency for each residence.
Comments on the private well sampling changes being proposed can be emailed to either of the MPCA staff members below. The deadline for submitting comments is May 31.