RECHARGE EVOLUTION TOOL: ASSIGNING RECHARGE RATES TO LOCATIONS OVER TIME USING EXISTING GIS-BASED DATA AT THE HANFORD SITE

The Recharge Evolution Tool (RET) combines derived recharge rates with the extents and histories of facilities, structures, and waste sites to estimate recharge over time and space. The RET was developed for use at the Hanford Site in southeastern Washington State, a large facility covering approximately 1520 km², where plutonium was produced. Since 1943, construction, operation, and remediation at the site has resulted in changes to ground surface cover that impact the amount of water that infiltrates to the subsurface. Given the scale of the Hanford Site, the impacts in some areas are dramatic while some areas are left undisturbed. Estimating which areas are impacted and when is the purpose of the RET. The RET is implemented as a relational geospatial database. The RET schema organizes available data at the Hanford Site as location data, recharge estimate, facility disposition, or site-specific evaluation. Once data are formatted to conform to the RET schema, they are ranked for priority based on the source of the data and geoprocessed for assignment of recharge rates. The RET then creates spatio-temporal varying recharge data, stored as geographic information system-based polygons. The tool uses available data for past and planned activities and events to estimate future recharge. By altering the planned future remedial activities listed in the database, the RET provides the means for evaluating impacts of planned remedial activities on expected recharge rates. Also, our implementation of the tool as a relational database facilitates efficient transfer of information between other hydrologic evaluations completed at the Hanford Site.