AquiferAquifer TestTest ProceduresProcedures forfor DeterminingDetermining HydrologicHydrologic PropertiesProperties Dr. Michael Strobel Deputy State Director EXHIBIT G– WATER RESOURCES Meeting Date: 03-22-06 USGS Nevada Water Science Center Document consists of 28 slides. Entire Exhibit Provided Purposes of Aquifer Tests • Measure the change, with time, in water levels as a result of withdrawals through wells • Determine the transmissivity and storage coefficient of the aquifer • Determine characteristics of confining layers • Determine well efficiency and optimum pumping rates • Determine boundary conditions (natural) and potential well interference Types of Aquifer Tests •Slug • Single-well • Multiple-wells – Time-Drawdown Analysis – Distance-Drawdown Analysis From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground- water resources: U.S. Geological Survey Circular 1186, 79 p. From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground- water resources: U.S. Geological Survey Circular 1186, 79 p. From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground- water resources: U.S. Geological Survey Circular 1186, 79 p. From Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground- water resources: U.S. Geological Survey Circular 1186, 79 p. Slug Test TIME • The rapid addition or removal of a known volume from a well stresses the aquifer. • The hydraulic conductivity (K) estimate is related to the rate of recovery with various corrections for well construction and geometry. Water level in well at time t Static water level Area of influence from slug test 1.00 K = 10 feet per day 0 y y/ 0.10 0.01 00:00 00:43 01:26 02:10 02:53 TIME, Minute:Second Wells in an aquifer with K values from slug tests 23 32 26 23 23 38 26 38 32 Contoured areas of similar K values for an aquifer 23 32 26 23 23 38 26 38 32 Q Original potentiometric surface h0-h Potentiometric surface Unconfined aquifer at time t Confining layer Confined aquifer Q Original water table h0-h Water level at time t Unconfined aquifer Q Original potentiometric surface h0-h Potentiometric surface at time t Unconfined aquifer Confining layer Confined aquifer Q Original water table h0-h Water level at time t Unconfined aquifer Hantush-Jacob Analysis 10 T = 39,000 ft2/d PERIOD MATCHED KZ/b’ = 0.0008 1/d S = 4 x 10-5 1 “MEASURED” HANTUSH-JACOB DRAWDOWN, IN FEET 10 MINUTES 0.1 0.00001 0.0001 0.001 0.01 0.1 1 10 TIME, IN DAYS Type curves for analysis of leaky confined aquifers Need for long-term aquifer tests • Stresses the system over a long period of time (weeks, months, years) to see how it reacts and when near-equilibrium is reached • Provides good analytical approach to obtaining K and storage values over large areas • Water from storage may account for most water during early parts of tests. Effects (drawdown) may be delayed. Concerns with long-term aquifer tests • Discharge of water (depending on pumping rates and length of test) •Cost • Effects on aquifer • Representation of other parts of aquifer and other basins.