Central Utilities Plant Underground Storage Tank Decommissioning

MFA oversaw the decommissioning of a 6,000-gallon underground storage tank adjacent to the Central Utilities Plant (CUP) at the Port of Portland’s International Airport. The tank decommissioning was necessary in order to accommodate redevelopment activities for the Parking Additions & Consolidated Rental Car (PACR) project completed in the vicinity of the tank location. The PACR project included a tunnel extension, utility relocation, and construction of a new six-story parking garage for use by the rental car agencies. 

The decommissioning process included installation of shoring to protect the CUP building prior to removal of the UST. MFA provided construction oversight for the installation of soldier piles around the immediate area of the UST. During excavation and installation of the shoring walers, the extent of pea gravel (i.e., UST backfill) was found to be more widespread than originally anticipated.

The Port and the MFA team agreed that the movement of pea gravel into the excavation during lagging installation could potentially undermine the CUP building. Based on this observed condition, MFA recommended that the shoring installation be discontinued, and that controlled-density fill be used to abandon the UST in-place. This alternative approach was implemented following coordination with and agreement by the DEQ.

Follow up soil sampling was completed via push-probe borings in accordance with DEQ guidance, and a No Further Action determination was issued for the site.