Central Utilities Plant Underground Storage Tank Decommissioning

Client: International Airport

Location: Portland, Oregon

About the Project

MFA oversaw the decommissioning of a 6,000-gallon underground storage tank adjacent to the Central Utilities Plant at this aviation facility. The decommissioning was necessary in order to accommodate construction activities.

Decommissioning Process

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 client 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.

No Further Action

Followup soil sampling was completed in accordance with DEQ guidance, and a No Further Action determination was issued for the site.