Hanford Site Groundwater Monitoring for Fiscal Year 2005

This report is one of the major products and deliverables of the Groundwater Remediation and Closure Assessment Projects detailed work plan for FY 2006, and reflects the requirements of The Groundwater Performance Assessment Project Quality Assurance Plan (PNNL-15014). This report presents the results of groundwater and vadose zone monitoring and remediation for fiscal year 2005 on the U.S. Department of Energy's Hanford Site, Washington. The most extensive contaminant plumes in groundwater are tritium, iodine-129, and nitrate, which all had multiple sources and are very mobile in groundwater. The largest portions of these plumes are migrating from the central Hanford Site to the southeast, toward the Columbia River. Carbon tetrachloride and associated organic constituents form a relatively large plume beneath the west-central part of the Hanford Site. Hexavalent chromium is present in plumes beneath the reactor areas along the river and beneath the central part of the site. Strontium-90 exceeds standards beneath all but one of the reactor areas. Technetium-99 and uranium plumes exceeding standards are present in the 200 Areas. A uranium plume underlies the 300 Area. Minor contaminant plumes with concentrations greater than standards include carbon-14, cesium-137, cis-1,2-dichloroethene, cyanide, fluoride, plutonium, and trichloroethene. Monitoring for the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 is conducted in 11 groundwater operable units. The purpose of this monitoring is to define and track plumes and to monitor the effectiveness of interim remedial actions. Interim groundwater remediation in the 100 Areas continued with the goal of reducing the amount of chromium (100-K, 100-D, and 100-H) and strontium-90 (100-N) reaching the Columbia River. The objective of two interim remediation systems in the 200 West Area is to prevent the spread of carbon tetrachloride and technetium-99/uranium plumes. Resource Conservation and Recovery Act of 1976 groundwater monitoring continued at 25 waste management areas during fiscal year 2005: 15 under interim or final status detection programs and data indicate that they are not adversely affecting groundwater, 8 under interim status groundwater quality assessment programs to assess contamination, and 2 under final status corrective-action programs. During calendar year 2005, drillers completed 27 new monitoring wells, and decommissioned (filled with grout) 115 unneeded wells. Vadose zone monitoring, characterization, and remediation continued in fiscal year 2005. Remediation and associated monitoring continued at a soil-vapor extraction system in the 200 West Area, which removes gaseous carbon tetrachloride from the vadose zone. DOE uses geophysical methods to monitor potential movement of contamination beneath former waste sites