Project Location: Minneapolis
Como Student Housing Cooperative (Coop) is a popular housing complex for students with families because of the playgrounds, daycare, low costs and proximity to both St. Paul and Minneapolis campuses. The Coop houses approximately 1,000 residents. The University of Minnesota (University) retains ownership of the buildings and grounds but the cooperative is responsible for the management of the complex. Student-families agree to a specific rotating task at the cooperative, and many residents volunteer their time on various committees and on the board of directors. There is paid management staff to manage the day to day activities of the cooperative.
The University discovered contaminated soils in September 2008 during a waterproofing project on buildings located in the northern portion of the Coop. The contaminated fill material was a mixture of silt, sand and grayish-colored ash and includes debris comprised of broken glass, wood boards, bricks and concrete. The origin of the fill material appears to be from a south Minneapolis incinerator, which operated prior to 1960, as well as demolition debris from previous structures located on the Coop property. The primary contaminants detected at concentrations exceeding the Minnesota Pollution Control Agency (MPCA) residential soil reference values (RSRVs) included lead, copper, arsenic, and polynuclear aromatic hydrocarbons (PAHs).
Based on the results of investigations, the University and Minnesota Pollution Control Agency (MPCA) Voluntary Investigation and Cleanup (VIC) Program determined that the area of contamination encompassed approximately 5 acres of the 15 acre property, and included soil beneath playgrounds, ball fields, buildings, as well as green space and parking areas.
A Response Action Plan (RAP) was prepared by the University and approved by the MPCA. The University then prepared response action (RA) design documents and acquired bids from remediation contractors and implemented a portion of the RAs in 2009 and 2010. The RAs included excavation and off-site disposal of contaminated fill material over approximately 2.5 acres of the total 5 acre contamination area of the Property surrounding 3 of the apartment buildings, two playgrounds and the ball field in the center of the Coop. All of these areas were excavated to at least 3 feet; however, playground areas were excavated to 6 feet. In 2011, additional RAs were conducted in the parking (Parking Lot D) and fire lane areas. These areas were excavated to approximately 2 feet and 3 feet. The excavations were backfilled and the Property was regraded to promote proper drainage. Sidewalks in these areas were replaced as was the playground equipment and the lighting. The entire area was landscaped with new sod, plantings and trees. The parking area was replaced with permeable pavement as well as a portion of the Fire Lane to promote drainage and reduce stormwater runoff .
The RAs resulted in the excavation and disposal of approximately 16,393 tons of contaminated fill material and disposal in a local nonhazardous waste landfill, SKB Landfill in Rosemount. Even though contaminated soil remains at depth, the cleanup is protective of human health and the environment because the majority of the contamination has been removed, or it is covered by buildings and asphalt. Because the contaminants are not volatile, the contamination can remain at depth with the appropriate institutional controls.
The residential setting posed the most challenging part of this remediation project. The Coop residents are mostly young families and many are from multiple nationalities. Management of pedestrian traffic (including lots of toys, kid’s bikes and scooters) while conducting remedial activities with large construction equipment was the most important task of each day. Communication with the residents and Coop staff was critical. Residents were provided with regular project updates and provided with general safety information. Weekly construction meetings included the Coop staff and helped to address issues and provided a conduit of information regularly to the tenants. Communication, signage and continual excavation oversight were all key pieces to conducting the excavations safely. The remediation affected the families’ use of not only the playgrounds, ball fields, volleyball court and green space areas, but also egress to and from their apartments and parking lots during the remediation. Special attention was paid to ensure the safety of the residents during the project, particularly while loading the trucks and trucks entering and leaving the Property. Equipment used on site was smaller to be able to maneuver under trees and next to buildings. Construction fencing blocked off areas and the site and equipment was secured each evening. Dust control was rigorously managed and air monitoring conducted. A sand layer was placed during excavation of the center of the Property to minimize tracking of contaminated soil during trucking. Excavations were backfilled immediately.
The most controversial issue of the remediation project was the removal of existing trees within the contaminated soil areas. Several rows of large trees provide shade to the buildings and playground and green space areas and soil excavation was necessary in these areas. In order to remove as much contaminated soil as possible, many trees had to be removed so that future landscaping within areas with impacted soil did not create future liability for the University. The University, Coop staff and residents made difficult decisions as approximately 63 trees had to be removed. Working with the University’s arborist, the remediation team was able to effectively excavate within the drip line of the large oak trees next to the main playground so that the massive trees could remain in place.
Project Submitted by: Landmark Environmental, LLC