The Seattle District, U.S. Army Corps of Engineers environmental staff members continue to oversee efforts to clean up a fuel spill that occurred last week near Howard A. Hanson Dam in the Green River Watershed. The Corps' supervisory activities are also being monitored by the U.S. Environmental Protection Agency and the Washington Department of Ecology.
On Sept. 20, an Associated Petroleum Products (APP) fuel truck, servicing a nearby unrelated worksite, slid off the road and over a steep embankment above Howard Hanson Dam reservoir. According to responders at the scene, the incident resulted in the release of approximately 600 gallons of diesel fuel into the soil.
APP called their emergency response contractor NRC Environmental Services (NRCES) to the scene. The fuel has traveled through the soil from the spill site to the embankment above the reservoir shoreline, where it is being contained with a series of trenches filled with absorbent materials. The absorbent materials are replaced on a regular basis and remain under constant monitoring. As a preventive measure, both absorbent booms and a rigid containment boom have been placed in the water to capture and enable removal of any petroleum product that may enter the reservoir. Tacoma Water, whose major water supply source is the Green River, is closely monitoring the situation, and as a result of the efforts, is confident that the fuel spill is not likely to move beyond the reservoir and enter the drinking water supply.
The steep embankment and concerns about slope stability significantly complicate the incident response activities, but the objective of the first phase -- to contain the spill -- was successful. With the emergency phase over, work is under way to remove any residual fuel that can be captured, and to remediate the impacted soil. Responders will remain on the scene until the situation is remedied to levels that will ensure no adverse effect on Tacoma Water’s drinking water supply.
The dam, located near the headwaters of Green River in King County, provides flood control in the winter and fish enhancement in the summer. The river is the source of the primary water needs for Tacoma Water, which maintains a diversion facility three miles downstream from Howard A. Hanson Dam, which serves as a collection and purification point. The dam is surrounded by the protected Tacoma Water watershed and public access is not permitted.
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