Results of Groundwater Modeling for Tritium Tracking at the Hanford Site 200 Area State-Approved Land Disposal Site--2004

Abstract

The purpose of this report is to present the results of the latest assessment of the impacts of treated water from the Hanford Site 200 Area Effluent Treatment Facility (ETF) that is currently being discharged and predicted to be discharged in the future to the drain field named the State-Approved Land Disposal Site (SALDS). The SALDS facility is located immediately north of 200-West Area in the Central Plateau of the Hanford Site in southeast Washington.The objectives of this updated assessment are to:• Incorporate up-to-date historical discharge and groundwater monitoring data (hydraulic head) into the current Hanford Site-Wide groundwater flow and transport model (from SALDS and adjoining areas).• Incorporate the most recent and accurate projections of future tritium disposal and water discharge volume to the SALDS.• Predict the lateral and vertical extent of travel in the subsurface of the tritium plume emanating from the SALDS • Predict the activities of tritium at various locations within the plume.• Provide improved sequential illustrations of predicted tritium plume behavior from present through the year 2140.• Recommend strategies for future monitoring based on model results.The numerical model used for this effort is revised from that used by Barnett et al. (1997) to reflect recent refinements in the Hanford Site-Wide Groundwater Model (SGM) and to incorporate actual water volume and tritium activity release information reported through June 2004. Simulations made in this assessment consider the hydraulic effect of past historical waste water discharges in the unconfined aquifer but only evaluates the potential impacts of tritium loading from past and projected future tritium discharges at the SALDS facility. Potential impacts of other sources of groundwater contamination for other nearby source areas are not considered in this analysis.This report presents a comparison of updated treated water discharges and tritium inventory values based on discharge records to the SALDS from its startup in 1995 through 2004 with projected values used in previous modeling summarized Barnett et al. (1997). This comparison shows that while actual discharge volumes through June 2004 exceeded projections made in previous modeling efforts, actual cumulative tritium inventories contained in discharges to the facility have been about one-half of inventories projected in previous analysis through the current year (2004). ivThe model results presented in this report incorporate the reported data through June 2004, and then uses projected discharge and tritium inventory values through 2034 that have been updated with more current information. Simulation results show that the tritium concentration in the aquifer reaching a maximum of 1.6 million pCi/L in 1996. After that time, predicted concentration levels at the water table were variable ranging from just over 1 million to several hundred thousand pCi/L and on a downward trend by the year 2004. These simulated results generally reflect the changes in simulated monthly effluent...