Aquifer Tests in the Snake River Basalt

The results of eleven aquifer tests and specific capacity data for 238 production wells indicate that the coefficient of transmissibility of the Snake River basaltr anges from 1 × 105 gpdper ft to 1.8 × 107 gpd per ft and averages about 4 × 106 gpd per ft. The coefficient of transmissibility of the entire thickness of the Snake River basalt probably greatly exceeds the values determined from test data because the wells for which data are available partially penetrate the aquifer. The coefficients of storage computed from test data are all in the water-table order of magnitude and range between 0.02 and 0.06. For the Snake River Plain, the average yield of the basalt to a 16-in. well during an 8-hr well-acceptance test, is about 2,100 gpm per ft. The aquifer ranks as one of the most productive in the United States. The average depth of well below l and surface is 290 ft and the average penetration below the regional water table is 100 ft.