IMPLICATIONS OF RCRA GROUNDWATER QUALITY ASSESSMENT RESULTS FOR HANFORD’S SINGLE SHELL TANK WASTE MANAGEMENT AREAS

Leaks or spills from nearly half of Hanford’s 149 single-shell tanks (SST) are known (or suspected) to have occurred. Retrieval, processing and final disposal of the SST waste will take place over the next 30 - 40 years. During the interim, the tanks are considered active treatment, storage and disposal units regulated under the Resource Conservation and Recovery Act (RCRA) and require groundwater monitoring. Mobile tank waste constituents (e.g., 99Tc, CrO4 =, NO3 -) have appeared in some of the downgradient wells near four of seven SST waste management areas. Field observations suggest episodic water sources and preferential pathways account for the transient nature of contaminant occurrences in groundwater. Possible implications are: 1) additional interim corrective measures may be needed; and 2) decisions concerning retrieval of contaminated soil and tank farm closure options could be affected. Groundwater and vadose zone characterization currently underway will provide input to assess the extent of the potential impacts.