Groundwater Monitoring for the 100-K Area Fuel-Storage Basins: July 1996 Through April 1998

This report presents the results of groundwater monitoring and summarizes current interpretations of conditions influencing groundwater quality and flow in the 100-K Area. The interpretations build on previous work, and statisticzd evaluations of contaminant concentrations were ptiormed for the period July 1996 through April 1998. No new basin leaks are indicated by data from this period. Tritium from a 1993 leak in the KE Basin has been detected in groundwater and appears to be dissi- pating. Tritium and strontium-90 from inactive injection wells/drain fields are still evident near the KW and KE Basins. These contaminants have increased as a result of infiltration of surface water or a higher- " than-average water table. Inactive condensate cribs near the KW and KE Basins resulted in very high tritium and carbon-14 activities in some wells. Recent tritium decreases are attributed to changes in groundwater-flow direction caused by the higher-than-average river stage in 1996-1998, which caused the contaminant plumes to move away from the monitoring wells. Results of the groundwater-monitoring program were used to identi~ and correct factors that may contribute to contaminant increases. For example, some sources of surface-water infiltration have been diverted. Additional work to reduce infiltration through contaminated sediments is planned for fiscal year 1999. Seismic monitoring was recently initiated in the 1OO-K Area to provide an early warning of earth- quake events that could cause basin leakage. The early warning will alert operators to check water-loss rates and consider the need for immediate action