Characterization and Remedial Action At a Former MGP Adjacent to a Former Wood Treatment Operation Ashland, Wisconsin

摘要

Xcel Energy (formerly known as Northern States Power-Wisconsin (NSP)) is a successor to a power company that operated an MGP in Ashland, Wisconsin from 1885 until 1947. In 1989, the Wisconsin Department of Natural Resources (WDNR) responded to reports of creosote contamination on city property located between the former MGP and Lake Superior, claiming that the former MGP site was the contaminant source. However, other identified potential sources included former wood treatment operations as well as a former solid waste disposal facility located at the city property. Subsequent investigations identified dense non-aqueous phase liquid (DNAPL) contamination in sediments nearly 700 feet beyond the shoreline, at the lakefront (a city park), in a shallow "fill" aquifer, and in a deep confined aquifer at the former MGP site. DNAPL is present in all of these media. In 1998, the WDNR's consultants recommended a $50 million alternative for remediation of the lakefront and offshore sediments, largely consisting of an approximate 20 acre cap, requiring filling of the offshore area. WDNR allowed NSP to submit alternative recommendations for the lakefront and offshore sediments, along with recommendations for remediation at the former MGP property. This alternative remedial evaluation for the lakefront resulted in recommendations for a reduced capping option for the sediments, along with hot spot (DNAPL) removal and groundwater treatment at the Lakefront Park. These alternatives were estimated to cost approximately $15 million. Concurrently, NSP recommended remedial actions for the former MGP site that included capping of the upper aquifer, in conjunction with installation of a tar removal system for the deeper confined aquifer. The estimated cost for these alternatives was about $3 million. At the time these remedial technology evaluations were submitted to the WDNR, a private citizens group petitioned Region V of USEPA for listing the site on the National Priorities List (NPL). That process has recently been completed, and the site has been added to the federal NPL. Although this process has delayed remedial efforts, the WDNR approved NSP's recommendation to implement a tar removal system for the deep aquifer at the former MGP site as an Interim Action. This system was constructed during the summer of 2000. It is currently removing and separating product from the recovered groundwater, treating the residual groundwater prior to discharge to the sanitary sewer.