Use of Mathematical Models to Evaluate Management Options for Reducing PCB Bioaccumulation by Fish in Two Streams at the Neal`s Landfill Site, Bloomington, IN

Neal’s Landfill received PCB-containing wastes that originated from a Westinghouse Plant in Bloomington, IN. PCBs have been transported to the groundwater beneath the site and into two nearby streams: Conard’s Branch and Richland Creek, and consequently, PCBs have impacted the water, sediments, and fish of these streams. Remedial actions conducted at the site have included removal of significant threat material from the landfill, landfill capping, sediment removal and construction of a Spring Treatment Facility (STF) to collect and treat base spring flow. These actions have achieved significant reductions in fish PCB concentrations. Since these remedial actions, CBS, Inc. has been conducting an evaluation of options to achieve additional reductions of PCB levels in fish within these two streams.

The evaluation of potential future remedial actions to further reduce PCB levels within the fish of Conard’s Branch and the upper portion of Richland Creek requires a quantitative means of linking fish tissue PCB concentrations with the remaining sources of PCBs to the fish. A mechanistic mathematical model was developed to assess the impact of management options for reducing fish PCB concentrations. The model framework consists of sub-models that simulate hydrodynamics, sediment transport, PCB fate and transport, and PCB bioaccumulation. The submodels were calibrated and validated independently to various data sets from multiple locations, including variations in stream stage height, water column PCB and suspended sediment concentrations during low flow and storm flows, and tissue PCB concentrations of two fish species.

The calibrated model provides a quantitative tool to help understand the important PCB fate and transport mechanisms within the system and properly focus the evaluation of remedial alternatives. The model has been used to simulate the long-term response of fish tissue PCB concentrations to remedial strategies consisting of varying levels of increased STF treatment and storage capacity, as well as additional measures to address base flow sources such as bank seepage and in-stream sediments.

Neal’s Landfill, which is located near Bloomington, IN, received municipal and industrial solid waste that included PCB-containing capacitors and other wastes that originated from the Westinghouse Bloomington Plant (Viacom 2004). Subsequently, PCBs associated with these wastes were transported to the groundwater beneath the site, which is underlain by a limestone formation that is characterized as karst terrain, containing numerous solution cavities, sinkholes, and emerging springs. Ths geologic setting provides a pathway for PCB-impacted groundwater to be transported to springs that emerge near the landfill and flow into Conard’s Branch, a small stream situated in the northwest corner of the site that flows into another nearby stream, Richland Creek (Figure 1). Due to the discharge of PCBs associated with spring water flowing into Conard’s Branch, PCBs have impacted the water, sediments, and fish of Conard’s Branch and the upper portions of Richland Creek.

Extensive remediation has been conducted at the landfill since the 1980s. These actions included removal of PCB contaminated materials from the landfill having PCB levels greater than 500 ppm, consolidating the remaining waste materials to higher ground and capping these materials with a RCRA subtitle C compliant cap, providing run on and run off control of surface water drainage, removing sediments from the Conard’s Branch, and construction of a spring water collection and treatment system that began operating in 1990. This system (the Spring Treatment Facility; STF) was designed to treat 450 gpm of base groundwater flow, and its effluent is discharged into Conard’s Branch. PCB levels in fish have dropped dramatically since the completion of remedial measures at the landfill and in the streams. For example, PCB levels in the Creek Chubs of Conard’s Branch have declined by more than a factor of 20. Additionally, the PCB concentrations in the spring water feeding the stream system, which is indicative of the site groundwater, appear to be steadily declining.

Despite these reductions, an evaluation of methods to achieve additional reductions of PCB levels in fish is underway. Remaining sources of PCBs to the fish in these streams include the untreated groundwater/spring flows entering Conard’s Branch, the STF effluent, additional groundwater seeps identified along Conard’s Branch, and the sediments within the streams. The PCBs associated with the untreated groundwater/spring flows include a portion of the base flow that is not captured and conveyed to the STF for treatment, as well as storm water flows. During storm conditions, the flow rates exceed the STF design flow, causing relatively large volumes of untreated spring water to bypass the STF and flow into Conard’s Branch.

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