Construction Management Services at a Former Landfill

Client: Machinery Repair Facility

Location: Portland, Oregon

Project Overview

As part of MFA’s investigation of a former unpermitted landfill adjacent to the Columbia Slough, MFA evaluated source control at the site and sampled stormwater from a pipe discharging directly from the property to the Columbia Slough, as well as sampling soil from the bank of the slough. Groundwater and soil were characterized throughout the landfill footprint area. In 2013, MFA designed, permitted, and implemented a remedy for this portion of the property.

Decommissioning and Demolition

The completed remedial action consisted primarily of decommissioning the stormwater infrastructure and monitoring wells; demolition of a 17,000-square-foot building; soil capping; construction of an erosion-control wall; and plantings along the bank of the Columbia Slough.

The building was removed under a demolition permit with the city. A concrete slab was crushed in place, as recommended by the geotechnical engineer. After the building demolition and storm system decommissioning were completed, the area was prepared for backfilling. The fill material was placed as a structural fill, until the grade reached the elevation of surrounding grades. Well-graded sand was imported, after sampling results demonstrated that the material source was clean. Approximately 3,300 cubic yards of backfill material was installed, ranging from 4 feet to 7 feet in thickness. One foot of clean soil cap material (approximately 2,700 yards) was installed over the remainder of the site and the adjacent right-of-way.

Project Results

Through this remedial work, MFA was also able to negotiate with the City of Portland the vacation of an adjacent right-of-way to enhance the property and assist in the implementation of the cleanup. As a result of the work, the DEQ issued a No Further Action determination for the property and the former landfill area.