Characterization Well R-7 Geochemistry Report

摘要

This report provides analytical results for four groundwater-sampling rounds conducted at characterization well R-7. The goal of the characterization efforts was to assess the hydrochemistry and to determine if contaminants from Technical Area (TA)-2 and TA-21 of the Los Alamos National Laboratory (LANL or the Laboratory) are present in the regional aquifer in the vicinity of the well. Figure 1.0-1 shows the well's location in the narrow upper part of Los Alamos Canyon, between the inactive Omega West reactor and the mouth of DP Canyon. Well R-7 is in an excellent location to characterize the hydrology and groundwater chemistry in both perched groundwater and the regional aquifer near sites of known Laboratory effluent release, including radionuclides and inorganic chemicals (Stone et al. 2002, 72717). The Risk Reduction and Environmental Stewardship-Remediation (RRES-R) Program (formerly the Environmental Restoration [ER] Project) installed well R-7 as part of groundwater investigations to satisfy requirements of the ''Hydrogeologic Workplan'' (LANL 1998, 59599) and to support the Laboratory's ''Groundwater Protection Management Program Plan'' (LANL 1996, 70215). Well R-7 was designed primarily to provide geochemical or water quality and hydrogeologic data for the regional aquifer within the Puye Formation. This report also presents a geochemical evaluation of the analytical results for well R-7 and provides hydrogeochemical interpretations using analytical results for groundwater samples collected at the well. Discussion of other hydrogeochemical data collected within the east-central portion of the Laboratory, however, is deferred until they can be evaluated in the context of sitewide information collected from other RRES and Hydrogeologic Workplan characterization wells (R-8A, R-9, and R-9i). Once all deep groundwater investigations in the east-central portion of the Laboratory are completed, geochemical and hydrogeologic conceptual models for the Los Alamos Canyon watershed may be included in a groundwater risk analysis. These models will include an evaluation of potential contaminant transport pathways. Well R-7 was completed on March 9, 2001, with three screens (363.2 to 379.2 ft, 730.4 to 746.4 ft, and 895.5 to 937.4 ft). Screen No.2 was dry during characterization sampling. Four rounds of groundwater characterization samples, collected from a perched zone and the regional aquifer from depths of 378.0 ft (screen No.1) and 915.0 ft (screen No.3), were chemically characterized for radionuclides, metals and trace elements, major ions, high-explosive (HE) compounds, total organic carbon, dissolved organic carbon, organic compounds, and stable isotopes (H, N, and O). Although well R-7 is primarily a characterization well, its design and construction also meet the requirements of a Resource Conservation and Recovery Act (RCRA)-compliant monitoring well as described in the US Environmental Protection Agency (EPA) document ''RCRA Groundwater Monitoring: Draft Technical Guidance,'' November 1992, EPA 530-R-93- 001. Incorporation of this well into a Laboratory-wide groundwater-monitoring program will be considered, and more specifically evaluated (e.g., sampling frequency, analytes, etc.), when the results of the well R-7 characterization activities are comprehensively evaluated in conjunction with other groundwater investigations in the ''Hydrogeologic Workplan'' (LANL 1998, 59599).