PNNL

Abstract

The Hanford Site 200 Area Effluent Treatment Facility (ETF) processes contaminated liquids derived from Hanford Site facilities. Groundwater monitoring for tritium and other constituents is required by the state-issued permit at 22 wells surrounding the facility. Water level measurements in nearby wells indicate that a small hydraulic mound exists around the SALDS facility as a result of discharges. Evaluation of this condition indicates that the network is currently adequate for tracking potential effects of the SALDS on the groundwater. During FY 2000, average tritium activities in most wells declined from average activities in 1999. The exception was deep well 699-48-77C, where tritium results were at an all-time high (710,000 pCi/L) as a result of the delayed penetration of effluent deeper into the aquifer. Of the 12 constituents with permit enforcement limits, which are monitored in SALDS proximal wells, all were within groundwater limitations during FY 2000. Analyses for conductivity, total dissolved solids, sulfate, chloride, sulfate, dissolved calcium, and dissolved sodium indicate that well 699-48-77A and, to a lesser extent, well 699-48-77D show the effects of dilute effluent entering groundwater, resulting in a depression of concentrations of these constituents below natural background levels. Recommendations for future monitoring include temporarily increasing the frequency of tritium sampling at wells 299-W7-3, 299-W7-5, and 299-W7-7 to quarterly. This measure may assist in a more accurate determination of the southern bounds of the SALDS-generated tritium plume, provide estimates of travel time for model comparisons, and help preserve the distinction between this plume and the older 200 West tritium plume further east.