PNNL

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). During fiscal year (FY) 2003 to date (through August 31, 2003), approximately 96-million liters (25.3-million gallons) of water have been discharged to the SALDS. Groundwater monitoring for tritium and other constituents, and water-level measurements are required by the state-issued permit at the SALDS. The current network consists of 3 proximal monitoring wells and 16 tritium-tracking wells. Proximal wells were sampled in October 2002, and January, February, April, and September of 2003. Tritium-tracking wells were sampled in January and September of 2003, but September results were delayed because of fire hazards near the wellheads. Water-level measurements in three wells nearest the SALDS indicate the continuation 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. Some of the wells south of the SALDS in the tritium-tracking network have dried or are projected to soon be dry. Wells 299-W7-6 went dry during FY 2003, preventing collection of the September sample from this well. Tritium activities decreased in all three SALDS proximal wells during FY 2003, compared with FY 2002. Timing between detections of tritium and other constituents in well 699-48-77C suggest a delay of approximately 3 years from detection in wells 699-48-77A and 699-48-77D. Sporadic detections in well 299-W7-5 suggest that tritium from SALDS may be reaching the northern edge of the 200 West Area, south of the facility and may be at the extreme southern edge of the plume. Comparison of head distribution in March 2003 and reported FY 2003 tritium activities, with numerical predictions of these quantities for 2000 and 2005, suggests that modeling performed in 1997 only slightly overestimated the areal spread of tritium around the SALDS to date.