RCRA Closure of Coal Tar Decanter Sludge (K087) Mixing Area
Coal tar decanter sludge from coking operations is a listed (K087) RCRA hazardous waste. At a large Midwestern integrated steel mill, coal tar decanter sludge was mixed with coal for blending and recycling through the coke ovens. The blending and staging of the K087 between the time it was mixed with coal and placed on the conveyor for recycling was characterized by the state regulatory agency as storage in a waste pile prior to recycling and considered subject to RCRA closure. The closure was complicated by impacts from more than a century of historical land use of similar coal, petroleum coke, and coal tar-based material beneath the area used for mixing of K087. A closure plan had been submitted by a previous consultant. Cox-Colvin was retained following failed negotiation of the closure plan with the state agency.
Cox-Colvin revised the closure approach and plan to incorporate a conceptual site model, well developed decision statements, and closure standards. The area subject to closure, which existed within a large coal field, was identified through detailed aerial photograph review and release verification using statistically derived background limits. Comparison of concentrations of constituents of potential concern to background statistical limits indicated the exceedance of background and preliminary remedial goals at two locations. Despite the detailed evaluation required due to the Sole Source Aquifer designation beneath the site, Cox-Colvin demonstrated an incomplete migration to groundwater pathway beneath the closure area. Based on a firm understanding of extent and subsurface conditions, Cox-Colvin evaluated and presented cost-benefit analysis of closure alternatives, including landfill type closure, risk-based clean closure, and closure by removal. Closure performance standards were achieved through the removal of soil containing benzene and toluene above statistically-derived background limits.