![]() Numerical simulation conducted by considering a horizontal potentiometric surface as in the analytical model produced an averaged root-mean-squared-error (RMSE) of 0.055 m, which was approximately 57% higher than the RMSE value estimated with the effect of the hydraulic gradient. Calibrated aquifer properties without the boundary effect showed clear differences, where the transmissivity, anisotropy ratio and specific yield varied by 12%, 34% and 53%, respectively, as compared to the results obtained by including the boundary effect. Moreover, time varying water heads during the pumping and recovery tests were simulated numerically to determine the effect of hydraulic gradient, which does not satisfy the assumption of horizontal potentiometric surface used in the analytical solution. This site condition violates the assumption that the aquifer is of infinite areal extent. In this study, drawdown records collected in a pumping well and two monitoring wells located near a river, were analyzed to investigate the boundary effects on the estimated aquifer properties. However, numerous assumptions used to develop the analytical solution are not always compatible with the actual site conditions. In this method, measured drawdown in the pumping well and the monitoring wells are usually matched with type curves developed by various analytical methods. An additional pipe, installed for providing thermistor access, allows recording of the geothermal gradient in the well which provides a basis for estimating vertical ground-water movement in the area.The constant-rate pumping test (CRT) is commonly used to determine the aquifer properties. The pipes also permit chemical quality monitoring of water in the various aquifer zones. In the completed well each aquifer zone is isolated by cement seals, and piezometer pipes installed to zones B through H allow a basis for defining the vertical hydraulic gradient and ground-water movement in the area. The tests indicate that most of the water available to the well is from the deepest aquifer (zone H).īorehole geophysical logging supplemented the drillers log of the well and provided information on natural gamma radiation, water temperature and resistivity, and borehole diameter. Test pumping during drilling showed that the well had specific capacities of (1) 4-8 gpm (gallons per minute) per foot of drawdown when at the 255-foot depth and open to aquifers A through D, (2) 5.6 gpm per foot of drawdown when at the 640-foot depth and open to aquifers A through G, and (3) 76 5 gpm per foot of drawdown when at the full 750-foot depth and open to all eight aquifers. ![]() ![]() The well was drilled by air-rotary methods and penetrates eight aquifer zones (A through H) the upper 75 feet of the well is cased, and the remainder of the hole is open in basalt. The well provides information on aquifer characteristics in this area which are not available from existing deep irrigation wells. The 750-foot test-observation well drilled near Davenport, Wash., is one of several drilled to date (1972) to provide information on ground-water conditions in selected areas of the State.
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