Barometric fluctuation removal in water level records and solutions to flow in aquifers during sinusoidal aquifer pumping tests
Toll, Nathaniel James
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This thesis addresses two problems in ground-water evaluation related to the determination of the hydraulic properties of aquifers. The ¯rst part presents a new computer program (BETCO) that removes the e®ects of barometric pressure and other external stimuli from water level observations. Regression deconvolution is used to ¯nd the impulse response function to external stimuli, which is then used to remove the e®ects of these stimuli from the observed water levels. Barometric pressure and earth tides introduce noise into water level measurements. This noise is problematic because it can mask the response to natural and anthropogenic stimuli. Noise also complicates the analysis of pressure data using derivative techniques. The step response function found using this technique can be used to diagnose aquifer type. BETCO improves the removal of barometric e®ects from water levels over the conventional method that assumes a constant, instantaneous barometric e±ciency. The second part of this thesis presents a new method for interpreting the response in an observation well to sinusoidal pumping in a layered aquifer. The method uses a matrix eigenvalue technique to solve the vector water level problem in a multi-layer aquifer system. Sinusoidal pumping tests show promise in applications where it is undesirable to extract water from pumping wells in large quantities. This might occur when the formation water contains emerging contaminants which can not be treated or disposed of cheaply or when the water does not meet regulatory limits due to natural elements such as arsenic or salts. The multi-layer solution was derived to model the aquifer response in a forward mode. Parameter estimation is used to apply the forward model to site data. A reference hardware design is presented which may assist in the adoption of the sinusoidal aquifer testing strategy. This design is the product of laboratory and ¯eld testing. Application is made for both parts using data from the Waste Isolation Pilot Plant, a federal facility used for the storage of nuclear waste located near Carlsbad, New Mexico, USA. The results of the analysis of aquifer test data from the Waste Isolation Pilot Plant show that the method can successfully estimate the aquifer properties for a two-layer system. The hydrologic unit tested was shown to have a 1300 times greater transmissivity in the lower unit then in the upper unit. The results are consistent with the assumption that the majority of °ow is in the lower unit.