Purpose

The ROD issued in September 1988 for the site stipulates that during the initial stages of the remedial design, contaminated soil areas will be remediated if they exceed either the risk-based soil cleanup goal of 700 ppm of cPAHs or the leaching potential-based cleanup goal ("no leaching potential"). The leaching potential-based goal is defined as the residual cPAH soil concentration that will not leach and impact groundwater beneath the site.

Although a detailed hydrogeological assessment was conducted at the site during the remedial investigation, chemical analytical data and data requirements for groundwater flow modeling are limited. A visual soil investigation was attempted to determine the extent of contaminated soils, and only select samples of the visually impacted soils were analyzed for the presence of cPAHs. The remedial investigation was concluded in 1986, and no further studies were conducted.

The development of a remedial design work plan was initiated by one of the potentially responsible parties (PRPs) in 1989 in response to the promulgation of the ROD by EPA V. In early 1991, acceptance of the Remedial Design Work Plan by EPA V was contingent upon addressing the "no leaching potential.") Meetings with the PRP and EPA V resulted in defining the no leaching potential as a total cPAH concentration in leachate emanating from contaminated soils not exceeding 10 p-g/L at the downgradient property boundary. A detection limit of 10 (Xg/L was chosen because the shallow aquifer is not categorized as a potential drinking water unit because of its low yield and general water quality. If the aquifer were categorized as a potential potable source, the proposed MCL for benzo[a]pyrene would have been selected as the minimum attainment standard for cPAHs. MCLs are enforceable standards for drinking water supplies or potential potable sources. EPA V was concerned not only with protecting the shallow water-bearing unit from further deterioration but also with the possible impact on the deep aquifer, in which an improperly abandoned well is thought to exist. An improperly abandoned deep well could act as a conduit from the shallow aquifer to the deep aquifer. The deep well was installed around 1912 but is no longer in service and has not been used since the late 1950s. However, records of proper abandonment do not exist. EPA V therefore stipulated that soil cleanup goals protective of shallow groundwater quality must also be protective of the deep aquifer, which is used as a supply of potable water in the immediate area of the site. A minimum attainment standard of 0.2 Hg/L corresponding to the proposed MCL for benzo[a]pyrene was established as the minimum attainment standard for this water-bearing zone.

EPA V also concluded that the use of models if applicable would be acceptable but subject to EPA's review and final approval.

The purpose of this section is to present the rationale for the development of a soil cleanup goal protective of groundwater quality in the shallow and deep aquifers using available site information and analytical solutions that will withstand an EPA V review. Acceptance of the soil cleanup goal by EPA V would provide the ROD-specified no leaching potential and result in the completion of the remedial design work plan for the site.

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