Final Monitoring Plan for Site Restoration at Murdock, Nebraska.

In early 2005, Argonne National Laboratory conducted an Engineering Evaluation/Cost Analysis (EE/CA; Argonne 2005b) to address carbon tetrachloride contamination identified in groundwater and surface water at Murdock, Nebraska, approximately 22 mi east-northeast of Lincoln (Figure 1.1). The EE/CA study was performed for the Commodity Credit Corporation of the U.S. Department of Agriculture (CCC/USDA), as the technical basis for a proposed removal action for the Murdock site. The EE/CA was conducted in compliance with an Administrative Order on Consent issued for Murdock by the U.S. Environmental Protection Agency (EPA 1991). Three removal action alternatives were examined through the use of site-specific data and predictive simulations of groundwater flow and contaminant transport performed with calibrated numerical models. The alternatives were evaluated individually and compared against performance criteria established under the National Oil and Hazardous Substances Pollution Contingency Plan and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). On the basis of these evaluations, an alternative employing phytoremediation in conjunction with seasonal groundwater extraction and treatment by spray irrigation was recommended by the CCC/USDA to permanently reduce the carbon tetrachloride contaminant levels in groundwater and surface water at the site. The proposed alternative is being implemented in cooperation with the EPA. Under the direction of the CCC/USDA and the EPA, implementation of the chosen removal action occurred in phases, beginning in April 2005. Installation of all the required remediation systems was completed by the end of August 2005. Specific technical objectives of the removal action are as follows: (1) To eliminate pathways for potential human exposure to carbon tetrachloride concentrations above the regulatory limit of 44.2 {micro}g/L in surface water at the site. (2) To minimize or eliminate any detrimental environmental impacts of carbon tetrachloride discharge to the surface waters of a tributary creek located immediately north of the town. (3) To permanently reduce carbon tetrachloride concentrations in the groundwater and surface water at Murdock and hence restore these resources for potential beneficial use. To evaluate the effectiveness of the selected remedy and its ability to achieve the objectives specified for this site, monitoring is required. This document outlines the proposed scope of a long-term program for monitoring of the removal action at Murdock. In this section the specific remedial objectives of the action are summarized, and a brief overview of the chosen remedy is provided. Section 2 summarizes the results of a baseline sampling event that documented the distribution of carbon tetrachloride contamination in selected media at the Murdock site immediately before cleanup activities began. Section 3 recommends a strategy for subsequent monitoring of the removal action at Murdock, as well as criteria for evaluating the performance of the remedial systems and the progress of the restoration effort