Among the many tasks in cleaning up Superfund sites is the ongoing detective work to sleuth what contaminants are there and where they came from. In the LDW cleanup, one of the key clues isn’t even in the river water itself, but in the sediment carried by stormwater.
Aspect staff have sampled stormwater sediments across the LDW Superfund site – previously for the City of Seattle and King County and currently for the Port of Seattle at Harbor Island. Our efforts studying these solids in stormwater runoff provide key information about the recent history at a site and the extent of contamination.
The Benefits of Sediment Sleuthing: Unlike Water, It Accumulates
Unlike stormwater, which runs through and beyond an outfall to receiving waters, heavier sediments and other settleable solids (relatively heavy substances that sink in water) carried by runoff drop out and accumulate. This accumulation, which occurs in key locations such as stormwater catch basins, vaults, and low-gradient pipes, provides a rich environment for valuable leads on water quality contaminants that may eventually end up in streams, rivers, lakes, wetlands, and Puget Sound. Sediment monitoring often provides a more comprehensive historical picture of pollutants compared to instantaneous or short-term sampling of water alone.
At Superfund areas, and many other sites challenged by stormwater runoff, sediment monitoring benefits clients by:
- Providing a historical picture of pollution—through accumulated sediment analysis--associated with stormwater runoff and industrial discharge.
- Identifying chronic types of pollution that may deteriorate water quality and habitat.
- Tracing the sources of pollution to their origin for purposes of management, treatment, or elimination.
- Determining sediment accumulation rates in sewers and catch basins to improve maintenance and operation needs and to anticipate and prevent flooding.
- Complying with permits, records of decision, and other legal requirements for preventing environmental degradation or requiring cleanup of polluted sites.
- Measuring the effect of land use activities and stormwater treatment best management practices (BMPs).
Tracking Hot Spots Across 600 Acres of Pavement and Buildings
Boeing Field (aka King County International Airport or KCIA) is one of the nation’s busiest primary non-hub airports and covers over 630 acres of mostly impervious surface. Managing stormwater runoff over this much area and with many industrial tenants is a challenge, especially because KCIA faces the challenge of being responsible for all discharge to the LDW from its property, even runoff or discharge in tenant-operated areas.