D St Petroleum

The D Street Petroleum cleanup site is on D Street, between 3rd and 7th streets and next to the Thea Foss Waterway. The site was used to store petroleum since the 1920s. Seepage of petroleum from the site into the Thea Foss Waterway (Thea Foss) was noted starting in 1971.

Between 1971 through 1998, Mobil Oil did a number of actions to clean up pollution at the site. This included:

• Using retaining booms in the Thea Foss in front of the site.
• Removing petroleum from the groundwater by pumping from extraction wells.
• Removing petroleum from two removal trenches next to the Thea Foss.
• Groundwater monitoring.

A remedial investigation was done in 1990. In 1991, Mobil Oil, Shell Oil and Union Oil Company of California (Unocal) entered into agreement to clean up the site’s soil and groundwater. Final cleanup actions used:

• A groundwater treatment system (with groundwater and soil vapor extraction, and petroleum product removal).
• Groundwater and surface water monitoring.
• An asphalt cap to reduce movement of surface water runoff into polluted soils.

About 101,800 total gallons of petroleum hydrocarbons were removed from the site.

By 2006, contaminants were below site cleanup levels in most of the monitoring wells. With Ecology approval, the companies paused use of the treatment system to see if natural attenuation was occurring. This could treat any leftover pollution. It showed that a natural breakdown of petroleum was likely taking place. By 2008, they shut the system down.

The companies monitor groundwater and surface water four times a year.  During the last round, benzene and ethylbenzene were slightly above cleanup levels in four upland wells.  This does not impact the Thea Foss.

The original agreement to clean up the site includes total petroleum hydrocarbons (TPH) cleanup levels for oil and grease in groundwater, but does not include current cleanup levels for other petroleum-related compounds. However, the companies are monitoring for other parameters per current state cleanup requirements. To date, results show none of the added parameters above state cleanup levels (MTCA Method A) in the wells.

Ecology reviews cleanup sites at least every five years to make sure they still protect human health and the environment. Ecology determined cleanup actions at the site appear and will likely continue to be protective of human health and the environment.

Ecology held a public comment period for the periodic review report in 2014.