Results of Tritium Tracking and Groundwater Monitoring at the Hanford Site 200 Area State-Approved Land Disposal Site--Fiscal Year 2001

Abstract

The Hanford Site 200 Area Effluent Treatment Facility (ETF) processes contaminated aqueous wastes derived from Hanford Site facilities. The treated wastewater occasionally contains tritium, which is not removed by the ETF, and is discharged to the 200 Area State-Approved Land Disposal Site (SALDS). Groundwater monitoring for tritium and other constituents is required by the state-issued permit at 3 monitoring and 19 tritium-tracking wells.Water level measurements in nearby wells indicates the persistence of a small hydraulic mound beneath the SALDS facility as a result of discharges. This feature is directing groundwater flow radially outward a short distance before the regional northeasterly flow predominates. This condition also places several wells south of the SALDS hydraulically downgradient of the facility. With the continued monitoring of these wells, the network is currently adequate for tracking potential effects of the SALDS on the groundwater.During FY 2001, tritium activities in the SALDS proximal well 699-48-77A increased (maximum 670,000 pCi/L) as a result of the resumption of tritium disposal in September 2000, following a 16-month hiatus in significant tritium discharges. Well 699-48-77C, where tritium results reached a maximum value of 980,000 pCi/L, is reflecting the result of the delayed penetration of effluent deeper into the aquifer from 1999 SALDS tritium discharges. Speculation in FY 2000 that tritium may have reached two wells due south of the facility is probably premature. FY 2001 results indicate no departures from historical levels of tritium in these wells.Of the 11 constituents with permit enforcement limits, which are monitored in SALDS proximal wells, all were within permit groundwater limitations during FY 2001. Analyses for conductivity, total dissolved solids, chloride, sulfate, dissolved calcium, and dissolved sodium indicate that SALDS proximal wells show the effects of dilute effluent entering groundwater, resulting in a depression of concentrations of these constituents below natural background levels. Earlier elevated levels of these constituents were the result of the dissolution of natural soil salts by SALDS effluent.Recommendations for future monitoring include retaining in the well network all current tritium tracking wells to the south of the SALDS. This measure will provide 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 farther east. v