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Documentation of single-well aquifer tests and integrated borehole analyses, Pahute Mesa and Vicinity, Nevada

September 4, 2018
Single-well aquifer testing has been carried out at Pahute Mesa in southern Nevada since 1962. These tests include single-well pumping and slug tests to estimate geologic formation hydraulic properties. Initially, aquifer tests focused on identifying low-permeability rocks suitable for testing large-yield nuclear devices, whereas later hydrologic investigations focused on potential subsurface transport of radionuclides away from Pahute Mesa. 
The number of single-well aquifer tests analyzed for Pahute Mesa and vicinity was much greater than the number of actual tests because each response to a water-level displacement was interpreted multiple times using different analytical models by different investigators, which were reported as distinct, individual aquifer tests. Some aquifer tests also were reinterpreted multiple times because the wells had not been defined uniquely. Previous databases and reports identified wells by different borehole names, reported various depths to top and bottom of open intervals, and used inconsistent wetted-aquifer thicknesses, which were coupled with inappropriate analytical methods to interpret aquifer-test data.
This work standardized the reporting of single-well aquifer-test results at Pahute Mesa and vicinity. A hydraulic-parameter database was created that uniquely identifies tested wells, reports all replicated aquifer tests in each well, and identifies the best transmissivity estimate for each well. Datasets, interpreted models, and results from 1,459 analyses are presented and evaluated for 360 unique wells. 
Integrated borehole analyses were used to estimate hydraulic conductivity by depth in Pahute Mesa because vertical variations in hydraulic conductivity greatly affect groundwater velocities, which directly affect subsurface transport rates and directions. The integrated analyses reconciled differences between transmissivity estimated from pumping tests and the summed transmissivity from straddle-packer slug tests done at different depth intervals in a borehole. An integration borehole database was created that presents integrated aquifer-test results from 17 boreholes.