Gerald J. Gonthier | Geology Reports

USGS2011

Summary of hydrologic testing of the Floridan aquifer system at Fort Stewart, coastal Georgia, 2009-2010

Two test wells were completed at Fort Stewart, coastal Georgia, to investigate the potential for using the Lower Floridan aquifer as a source of water to satisfy anticipated, increased water needs. The U.S. Geological Survey, in cooperation with the U.S. Department of the Army, completed hydrologic testing of the Floridan aquifer system at the study site, including flowmeter surveys, slug tests, and 24- and 72-hour aquifer tests by mid-March 2010. Analytical approaches and model simulation were applied to aquifer-test results to provide estimates of transmissivity and hydraulic conductivity of the multilayered Floridan aquifer system. Data from a 24-hour aquifer test of the Upper Floridan aquifer were evaluated by using the straight-line Cooper-Jacob analytical method. Data from a 72-hour aquifer test of the Lower Floridan aquifer were simulated by using axisymmetric model simulations. Results of aquifer testing indicated that the Upper Floridan aquifer has a transmissivity of 100,000 feet-squared per day, and the Lower Floridan aquifer has a transmissivity of 7,000 feet-squared per day. A specific storage for the Floridan aquifer system as a result of model calibration was 3E-06 ft–1. Additionally, during a 72-hour aquifer test of the Lower Floridan aquifer, a drawdown response was observed in two Upper Floridan aquifer wells, one of which was more than 1 mile away from the pumped well.

Georgia↗

USGS2009

Analysis of complex pumping interactions during an aquifer test conducted at a well field in the coastal plain near Augusta, Georgia, October 2009

A 24-hour aquifer test was conducted in Well Field 2 near Augusta, Georgia, October 21–22, 2009, to characterize the hydraulic properties of the Midville aquifer system. The selected well was pumped at a rate of 684 gallons per minute. At the initiation of aquifer-test pumping, water levels in each of eight wells monitored for the test were still recovering from the well-field production. Because water levels had not stabilized, data analyses were needed to account for the ongoing recovery. Hydraulic properties of the Midville aquifer system were estimated by an approach based on the Theis model and superposition. The Midville aquifer system was modeled as a Theis aquifer. The principle of superposition was used to sum the effects of multiple pumping and recovery events from a single pumped well and to sum the effects of all pumped wells as the estimated total drawdown at a monitored well. Simulated drawdown at each monitored well was determined by using a spreadsheet (SUMTheis) function of aquifer transmissivity and storativity. Simulated drawdown values were transformed into simulated water levels, accounting for longterm water-level trends. The transmissivity and storativity values that were used to calibrate the simulated water levels to measured water levels (roughly 4,000 square feet per day and 2E-04, respectively) provide estimates of the transmissivity and storativity of the Midville aquifer system in the vicinity of Well Field 2. The approach used in this study can be applied to similar well-field tests in which incomplete drawdown recovery or other known pumping is evident.

Georgia↗