Providing ongoing maintenance, and routine monitoring of groundwater, surface water, wastewater and landfill gas to satisfy post-closure requirements, King County maintains custodial responsibilities for nine closed landfills (under WAC 173-304 and 173-351). At four of the closed landfills (Cedar Falls, Vashon Island, Enumclaw, and Duvall), Aspect provides hydrogeologic and engineering services to support the County in meeting reporting and compliance requirements of the Seattle-King County Department of Public Health, Ecology, and Puget Sound Clean Air Agency.
We have helped develop landfill gas and groundwater monitoring networks; provided hydrogeologic characterization and site conceptual model development, monitoring, and aquifer testing; and contributed to engineering controls development. Our hydrogeologic characterization has supported groundwater, gas, and surface water migration assessments; environmental assessments of groundwater, leachate and gas systems; and pre-design level assessments of environmental control systems. Engineering controls have included landfill gas system collection and treatment upgrades, design and monitoring of an evapotranspiration (Poplar) cover, and leachate collection improvements.