Final report for targeted investigations at Murdock, Nebraska, in 2004.
On April 1, 2003, representatives of the Commodity Credit Corporation of the U.S. Department of Agriculture (CCC/USDA) and Argonne National Laboratory met with representatives of the U.S. Environmental Protection Agency, Region VII (EPA); the Nebraska Department of Environmental Quality (NDEQ); and Nebraska Health and Human Services (NHHS) to discuss the current regulatory and technical status of the environmental investigations at the former CCC/USDA grain bin site in Murdock, Nebraska. The investigations are being performed by Argonne (under the direction of the CCC/USDA) to characterize and evaluate the potential remedial needs associated with the carbon tetrachloride contamination identified in groundwater and surface waters in the vicinity of the town. This contamination has been linked to former CCC/USDA grain storage activities at Murdock. Table 1.1 presents a brief summary of the regulatory, site characterization, and remedial assessment activities to date at Murdock. Figure 1.1 illustrates the extent of the groundwater carbon tetrachloride plume, estimated on the basis of sampling performed by Argonne in June 2002. Figure 1.2 presents the 2002 interpretation of the site hydrogeology in a cross section extending northwestward from the former CCC/USDA grain storage facility, along the approximate axis of the groundwater plume. In reviewing the available information for Murdock, the EPA identified two specific areas of technical concern regarding the distribution and potential fate of the carbon tetrachloride contamination at the site that might significantly affect the selection of an appropriate remedial strategy: (1) Periodic sampling (by Argonne) of surface water at the headwaters of the unnamed tributary to Pawnee Creek northwest of Murdock and sampling of the effluent from natural seepage points and agricultural drain tile lines that contribute to the creek (Figure 1.3) demonstrated discharge of contaminated groundwater from the aquifer to the headwaters area north of Waverly Road. The EPA noted, however, that no conclusive evidence is available to demonstrate whether complete capture and removal of the carbon tetrachloride plume from the aquifer are occurring by this mechanism. Specifically, the EPA questioned whether contamination continuing to migrate in the deeper subsurface beneath the tributary to Pawnee Creek might pose a threat to groundwater resources beyond the area of presently observed contaminant discharge. (2) Concentrations of carbon tetrachloride measured in groundwater from shallow monitoring well 2S, near the north-central boundary of the property formerly occupied by the CCC/USDA grain storage facility (Figure 1.1), have remained relatively constant (at approximately 40-100 mg/L) since Argonne began periodic sampling of this well in 1991, with no clear trend of decreasing values. The observed concentrations suggest that a continuing, uncharacterized source of carbon tetrachloride contamination to groundwater remains in the vadose zone soils beneath the former grain storage facility, upgradient of this well. To address these concerns, the CCC/USDA and Argonne proposed a series of targeted field investigations at the Murdock site. Four technical objectives were originally proposed in the Work Plan for this targeted investigation (Argonne 2003), and two additional objectives were authorized as the field work progressed and information accumulated. The combined technical objectives of this investigation were to accomplish the following: (1) Determine the continuity, thickness, and hydrogeologic characteristics of the aquifer in the vicinity of the Pawnee Creek tributary. (2) Characterize the present distribution of carbon tetrachloride contamination in groundwater and surface water in the area north of Waverly Road. (3) Determine the patterns of groundwater flow in the vicinity of the Pawnee Creek tributary and their relationship to the expected migration of the identified carbon tetrachloride plume. (4) Identify and delineate the presence of carbon tetrachloride in vadose zone soils in the northern portion of the former CCC/USDA facility that might pose a continuing source of contamination to the aquifer, and determine soil properties affecting vertical contaminant migration. (5) Evaluate contaminant migration from soil to groundwater, and analyze indoor air potentially affected by vapor intrusion at residences built on the former CCC/USDA facility. (6) Evaluate the potential suitability of phytoremediation for this site.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 843180
- Report Number(s):
- ANL/ER/TR-04/007; TRN: US200517%%379
- Country of Publication:
- United States
- Language:
- ENGLISH
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