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The primary objective of this study was to refine the conceptual groundwater flow model for the 200-West Area and vicinity. This is the second of two reports that combine to cover the Central Plateau, an area that holds the largest inventory of radionuclide and chemical wastes on the Hanford Site. This inventory is located in underground storage tanks, the vadose zone, and the saturated zone. Within the saturated zone, groundwater contaminant plumes, originating from past-practice activities at facilities within this area, are migrating toward the Columbia River where they may be accessible to the public. This study supports the Hanford Groundwater/Vadose Integration Project objectives to better understand the impacts of groundwater contamination and potential risk to the public via the groundwater flow pathway. The primary components of the conceptual groundwater flow model are 1) the static elements of the subsurface that form the hydrogeologic framework and 2) the groundwater that moves through this framework in response to stresses within the aquifer. The previous conceptual model was used as the baseline and was updated using new data and by re-evaluating existing data and reports from previous investigations to include essentially all the suprabasalt hydrogeology and associated groundwater flow information beneath the 200-West Area and vicinity. Current groundwater monitoring and cleanup efforts are focused on the upper portion of the unconfined aquifer within the suprabasalt aquifer system. This report evaluates more completely the entire vertical sequence of the suprabasalt sediments including description of the aquifer systems separated by the Ringold Unit 8. Contaminants have been detected in groundwater at various depths within these two systems, but our current understanding of groundwater flow and contaminant transport in the lower portion of these aquifers is limited. Based on this study, hydrogeologic mapping indicates that the confining (Aquitard) Ringold Unit 8 rises to the east and is located at or near the water table of the upper unconfined aquifer in the northeast portion of the study area, downgradient from 200-West Area contaminant source areas. Groundwater and contaminants from the northern portion of the 200-West Area will likely flow northeast into more permeable Hanford formation sediments within an erosional paleochannel. Continued water-level decline will expose more of Ringold Unit 8 and the Columbia River basalt above the water table northeast of 200-West Area near Gable Gap, restricting groundwater and contaminant flow in that direction and possibly diverting contaminant plumes to the southeast across 200-East Area. The uppermost-unconfined aquifer averages about 40 m (131 ft) thick beneath most of the 200-West Area. Characterization of contaminants located in the lower three-fourths of the unconfined aquifer and the confined Ringold aquifer beneath the 200-West Area and vicinity is very limited. The assessment of these contaminants may be important in developing successful cleanup...

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