Background
The Cedar Service Incorporated Site (Site) is located in Minneapolis, near University Avenue and 31st Avenue, in Hennepin County. It is in the northwest portion of the Shoreham Facility property and is about 29 acres in size. The facility is owned by Soo Line Railroad Company, which does business as Canadian Pacific Railway (CP Railway).
The Site was initially identified by the Minnesota Pollution Control Agency (MPCA) during an inspection in 1989. Wood treatment compound contamination consisting of pentachlorophenol (PCP) and polycyclic aromatic hydrocarbons (PAHs) was documented in the soils. In 1990, the MPCA added the Site to the Permanent List of Priorities, and the Site was referred to the Minnesota Department of Agriculture (MDA) for investigation and cleanup.
As the owner of the property, CP Railway leased the property to multiple wood-treating tenants that operated from approximately 1926 to 1972. In 1994, the MDA requested that CP Railway investigate the extent and magnitude of the PCP and PAH contamination and conduct necessary cleanup activities.
Creosote was used at the Site as the primary wood treating compound from about 1944 until the early 1960s, at which time PCP in a fuel oil (petroleum hydrocarbon) solution replaced creosote as the primary wood treating compound.
Soil Investigation and Remedial Actions
The Site geology consists of unconsolidated sediments, including: fill, alluvium, glacial till, glacio-lacustrine clay, and outwash deposits, which infill a northeast/southwest trending bedrock valley. The unconsolidated sediments are approximately 200 feet thick within the bedrock valley, and approximately 20 feet thick outside of the valley. The uppermost bedrock geology is the St. Peter Sandstone and underlain by the Prairie du Chien Group which consists of sandy dolomite and dolomite.
Site investigations revealed extensive soil and groundwater contamination with PCP and related contaminants. Soil corrective actions have been completed in two separate phases. In 1997, CP Railway excavated approximately 8,700 cubic yards of contaminated soil from the Former North Disposal Area and the Former Process Area. This soil was loaded onto rail cars, transported, and disposed at a permitted hazardous waste facility in Oklahoma.
Additional soil corrective actions were completed in 2006 when CP Railway excavated approximately 10,000 cubic yards of contaminated soil from the Former Process Area, the Container Storage Area, and beneath a roadway. This soil was placed in an engineered biopile (soil mound with imbedded air ventilation pipes) to degrade PCP and related contaminants to concentrations that would allow disposal of the soil at a non-hazardous landfill. The treated soil was disposed of at a permitted industrial waste landfill in Minnesota.
Groundwater Investigation and Remedial Actions
The water table at the Site is within the alluvium and the uppermost portions of the glacial till. The shallow groundwater flows generally towards the southeast. Groundwater flow in the lower St. Peter Sandstone is towards the south with a relatively flat hydraulic gradient and has limited downward vertical flow into the Prairie du Chien Group. Groundwater flow in the upper Shakopee Formation of the Prairie du Chien Group is also to the south, corresponding with the regional groundwater flow.
In addition to the soil contamination, groundwater beneath the Site was found to be contaminated with PCP and petroleum hydrocarbons. The groundwater contamination extends off-site. The final Groundwater Response Action involves pumping from two deep wells: one near 27th Avenue NE and 6th Street NE and the other near University Avenue NE. The groundwater extraction and treatment system pumps approximately 34 gallons per minute from the two extraction wells. Granular activated carbon (a form of charcoal) is used to remove PCP and related contaminants from the groundwater. Since operation began in December 2006, more than 7,030 pounds of PCP have been removed. Treated groundwater was originally discharged to the sanitary sewer system. In December 2012, an infiltration basin was constructed within the Shoreham Facility and the treated groundwater is now discharged to the basin under permit by the MPCA.
In addition to the groundwater extraction and treatment system, water levels and samples are regularly collected from the network of monitoring wells and analyzed by CP Railway. In 2021, as part of the ground water investigation, the MDA required CP Railway to conduct a revised well search within a one-mile radius of the Site and install an additional monitoring well between the Site and the Mississippi River. CP Railway also samples private business supply wells in Northeast Minneapolis. The results of the continued groundwater monitoring and sampling, and the performance of the groundwater extraction and treatment system are reported to the MDA.
What’s Next?
The MDA and CP Railway are currently working on a notification or affidavit which will be placed on the property deed that describes the investigations, corrective actions, and remaining residual contamination for the property.
