Detecting Distant Drawdowns with Water-Level Modeling

Presented on Wednesday, May 7, 2014
Keith J. Halford, Ph.D.1 and Joseph M. Fenelon2, (1)U.S. Geological Survey, Carson City, NV, (2)U.S. Geological Survey, Henderson, NV

Pumping-induced changes of less than 0.1 ft have been differentiated reliably from environmental fluctuations with models of continuous water-level records. Environmental fluctuations are simulated by summing time series of barometric pressures, earth and gravity tides, and water levels in background wells. Pumping effects are simulated by superimposing multiple Theis solutions that translate pumping schedules into water-level responses. Environmental and pumping signals in water levels are differentiated with the water-level modeling software SeriesSEE, which is an Excel add-in. Once differentiated, drawdowns estimated from water-level models can be input into analytical or numerical models to estimate the transmissivity and storage coefficient of the aquifer being tested.

Drawdowns on the Nevada National Security Site (NNSS) have been detected definitively in observation wells more than a mile from pumping wells with water-level modeling in SeriesSEE. Pumping-induced changes from aquifer testing in volcanic rock beneath Pahute Mesa in the northwestern corner of the NNSS were detected in dozens of wells at distances of up to two miles. Elsewhere, drawdown was detected more than 30 miles from a pumping well in the southeastern part of the NNSS. A strong and unique signal was induced in the regional carbonate aquifer beneath Yucca Flat by a 500-gallon per minute, 90-day aquifer test at well ER-6-1-2 during 2004. Continuous water levels in Tracer Well 3, located in Amargosa Desert, responded to pumping and environmental fluctuations. A maximum drawdown of 0.05 ft was estimated in Tracer Well 3 from pumping ER-6-1-2.



Keith J. Halford, Ph.D.
U.S. Geological Survey, Carson City, NV
Keith Halford is a research hydrologist at the U.S. Geological Survey and has served as Hydrologist and Groundwater Specialist in California, Florida, and Nevada offices of the USGS since 1987. He wrested a Ph.D. in petroleum engineering from Louisiana State University. His areas of expertise are aquifer tests, borehole geophysics, geostatistics, groundwater simulation, and parameter estimation. Developing methods and software for modeling water levels to estimate drawdowns has been the focus of recent publications.

Joseph M. Fenelon
U.S. Geological Survey, Henderson, NV
Joseph Fenelon has been a U.S. Geological Survey hydrologist since 1986 and worked from USGS offices in Indiana and Nevada. His areas of expertise are water-level trends and the hydrology of southern Nevada. A recent publication, “Groundwater Flow Systems at the Nevada Test Site, Nevada: A Synthesis of Potentiometric Contours, Hydrostratigraphy, and Geologic Structures,” was recognized as an outstanding paper by Ike Winograd.
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