DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. Executive SummaryA three-dimensional ground-water flow model has been developed for the uppermost unconfined aquifer at the Hanford Site in south-central Washington. This model is being developed to support the Hanford Site Ground-Water Surveillance Project objectives of 1) identifying and quantifying existing, emerging, or potential ground-water quality problems, and 2) assessing the potential for contaminants to migrate from the Hanford Site through the groundwater pathway.The approach to develop the three-dimensional model was to 1) refine the conceptual hydrogeologic model, 2) calibrate a two-dimensional version of the model with an inverse calibration method, and 3) develop the three-dimensional model based on all available information.The model is based on the Coupled Fluid, Energy, and Solute Transport (CFEST) code; however, the database of geologic and hydrologic information is constructed so that the conceptual model can be implemented in codes other than CFEST.The model consists of 10 hydrogeologic layers. Layers 1 through 9 correspond to the hydrogeologic units comprising the unconfined aquifer system. Layer 10 corresponds to basalt. The conceptual model was developed using the ground surface as the top of the model. The numerical model uses only the saturated portion of the sediments below the ground surface (i.e., the unconfined aquifer). Hydraulic conductivities were assigned to layers based on data from aquifer pumping tests, slug tests, and some laboratory tests. Some layers were assigned a constant value of hydraulic conductivity, while others were zoned with different hydraulic conductivities being assigned to each zone. The goal of the three-dimensional model calibration was to preserve the total transmissivity calculated by the two-dimensional inverse calibration, while honoring data available for hydrogeologic layers.The model grid consists of 821 surface nodes and 721 surface elements. The placement of nodes in the grid was selected so that 1) sources would be represented as closely as possible by nodes, 2) potential contours and gradients could be resolved, and 3) geologic layer extents and other important three-dimensional hydrogeologic aspects of the problem could be represented as accurately as possible. Boundary and source conditions used in the model are similar to previous ... lu efforts at the Site. A natural areal recharge distribution was included to reflect infiltration and recharge to the unconfined aquifer.Steady-state predictions from the three-dimensional model for the 1979 calibration period compared well with the observed water table. There is close agreement in most areas of the Site. The three-dimensional model is ready for routine application in steady-state, and we are proceeding with the construction of transport models for tritium, iodine-129, and nitrate based on the flow model.In addition to the three-dimensional model dev...

et al. (1996) in support of the Environmental Restoration Program. However, the current three-dimensional model has resulted in higher estimates of peak concentrations at shallow depths and less vertical migration than was predicted in previous site-wide yodel applications. These discrepancies are attributable to differences in basic assumptions made about the hydrogeologic framework and the horizontal and vertical V discretization used in each model. The differences in assumptions resulting from each modeling approach affect lateral and vertical distributions of predicted hydraulic heads and contaminants in the unconfined aquifer.The near-term impacts of existing plumes to on-site drinking water supplies were examined by evaluating predicted concentration levels in the vicinity of identified on-site water supplies over the next Farm, will be impacted by future transport of these contaminants.vi

Hydrologie test analysis based on the derivative of pressure (i.e., rate of pressure change) with respect to the natural logarithm of time has been shown to significantly improve the diagnostic and quantitative analysis of slug and constant‐rate pumping tests. The improvement in test analysis is attributed to the sensitivity of the derivative to small variations in the pressure change that occurs during testing, which would otherwise be less obvious with standard pressure change versus time analysis. The sensitivity of the pressure derivative to pressure change facilitates its use in identifying the effects of wellbore storage, boundaries, and establishment of radial flow conditions on the test. DERIV is a program for converting slug and pumping test data and associated type curves to derivative format. The program has features that permit the smoothing of noisy test data, accounts for pressure derivative end‐effects, and can be used to convert slug test data to equivalent pumping test responses. Test examples that demonstrate the use of pressure derivatives also are provided.

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