Detecting Distant Drawdowns with Water-Level Modeling

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.