Colbert Landfill Remediation

(Spokane County, WA)  Landau Associates provided design and construction management services to Spokane County for the Colbert Landfill federal Superfund cleanup and landfill closure. The Colbert Landfill contained contaminated groundwater with chlorinated solvents over about a 2.5-square mile area. The remedial action consisted of a 1,600-gpm groundwater extraction and treatment system with an outfall to the Little Spokane River. Landau Associates was responsible for all aspects of treatment system design and construction support, including performance of pre-design treatability studies, preparations of plans and specifications, bidding assistance, construction management, construction QA/QC, and agency negotiations and permitting. 

Obtaining an NPDES permit for discharge to the Little Spokane River represented a significant project challenge, requiring extensive computer modeling of groundwater/surface water interaction and evaluation of river algal growth potential to address the impact of groundwater phosphorous loadings. Our services in support of landfill closure included preparation of closure and post-closure monitoring plans; conceptual design of the low permeability cap; gas collection, treatment, and monitoring systems; surface water collection and infiltration systems; and long-term groundwater monitoring.The groundwater pump-and-treat system has been successfully operated for 20 years by Spokane County.

Landau Associates is currently assisting Spokane County in designing and implementing a system shutdown test to evaluate whether the remaining groundwater contamination can be addressed through monitored natural attenuation. Landau Associates is assisting the county in negotiations with U.S. Environmental Protection Agency and Washington State Department of Ecology and preparation of the shutdown test, and will assist the County during plan implementation and in evaluating the post-shutdown data.

Photo 2: John Buchanan