Proposed plan for final remedial action for the groundwater operable unit at the chemical plant area of the Weldon Spring Site, Weldon Spring, Missouri.

Abstract

This Proposed Plan (PP) presents the preferred alternative for addressing contaminated groundwater and springs at the Chemical Plant area of the Weldon Spring site, in Weldon Spring, Missouri. The site is located about 30 mi west of St. Louis, in St. Charles County (Figure 1). This proposed action constitutes the final remedial action for the Weldon Spring site. The residual contamination in groundwater and springs at the Chemical Plant area is the only remaining contamination that needs to be addressed for the site. All other contamination has been addressed by previous remedial actions. After this remedial action is implemented, long-term surveillance and maintenance activities will maintain the effectiveness of all remedial actions conducted at the Weldon Spring site, including this final remedial action for groundwater and springs that is being proposed in this plan. DOE complies with the requirements of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in conducting remedial activities at the site. National Environmental Policy Act (NEPA) values have been incorporated into the CERCLA process; that is, the analysis conducted and presented in the remedial investigation/feasibility study (RI/FS) reports included an evaluation of environmental impacts that is comparable to that performed under NEPA. This PP is required under CERCLA to (1) notify the public and present a brief analysis of the remedial action alternatives, (2) identify and present the rationale for the preferred remedial action alternative identified in the PP, (3) summarize key information from the RI/FS evaluations, including the Baseline Risk Assessment (BRA), and (4) inform the public of its role in the remedy selection process and give the public the opportunity to participate in the process. Remediation activities at the Weldon Spring site have been coordinated with the U.S. Environmental Protection Agency (EPA) and the Missouri Department of Natural Resources (MDNR). The EPA has overall oversight and approval authority, with consultation provided by the MDNR. A range of alternatives was considered in identifying the preferred alternative. The alternatives were developed after careful analysis of geological, environmental, and human health and ecological risk data and an evaluation of the effectiveness, implementability, and cost of the various technologies available for groundwater remediation at the Chemical Plant area. Monitored natural attenuation (MNA) coupled with institutional controls (ICs) and contingency activities has been selected as the preferred alternative.