Underground Storage Tank Clean Up in Residential Neighborhood

In a residential neighborhood in north Seattle, a home heating fuel release was discovered to have impacted five different adjacent properties. TRC was retained by an insurance company for one of the property owners to perform a site investigation to assess the impacts and develop a remedial approach on a path to regulatory closure.

The “Site” comprised five separate properties with soil, soil vapor, groundwater, and indoor air impacted by diesel fuel (home heating fuel) released from an underground storage tank (UST). TRC coordinated with other property owners and their counsel to gain property access for the investigative and remedial activities.

This residential setting proved to be technically challenging to conduct an investigation because the work space was limited by the existing structures. To accommodate this environment, TRC carefully planned and executed a multi-phase contaminant investigation to assess the extent of the impacts to soil, soil vapor, groundwater, and indoor air with several different technical approaches. Various drilling methods and media collection techniques were used in the limited space at the Site in order to obtain representative samples for analysis.

TRC used the results of the investigation to define a site-wide cleanup action plan. The cleanup action approved by the Washington State Department of Ecology (Ecology) included remediating soil by excavation and remediating groundwater by removing light non-aqueous phase liquid (LNAPL) and bio-chemical treatment. Impacted soil was removed using shoring and geo-technically challenging slot-cutting techniques coupled with the immediate introduction of structural fills to both remove and encapsulate contaminated soils. TRC safely performed this major soil excavation and installed bio-chemical groundwater amendments along with groundwater remediation system infrastructure down to 30 feet below ground within this compact residential setting.