Data collected for Claiborne aquifer study in southwestern Georgia during 2015 to 2016

A 72-hour constant-discharge aquifer test was performed at the University of Georgia Stripling Irrigation Research Park, Mitchell County, Georgia, in order to assess the potential of the Claiborne aquifer as a source of water for irrigation supply. At the Stripling site the Claiborne aquifer is 260 feet thick.  Between the Claiborne aquifer and the overlying Upper Floridan aquifer is the Lisbon confining unit; between the Claiborne aquifer and the underlying Clayton aquifer is the Wilcox confining unit. Claiborne aquifer well 11J029 was pumped at a rate of 579 gallons per minutes from about 2015 December 15 at about 9:00 a.m. to 18 at about 9:00 a.m. Water levels were monitored in a nearby Upper Floridan aquifer well (11J030) and Claiborne aquifer well (11J025). The slope of drawdown in Claiborne aquifer monitor well 11J025 decreased and did not become constant with log(time), which indicated some aquifer leakage to the Claiborne aquifer. No drawdown was detected in the Upper Floridan aquifer.
A 72-hour constant-discharge aquifer test was performed at the Newberry site, northeast Early County, Georgia, in order to assess the potential of the Claiborne aquifer as a source of water for irrigation supply. At the Newberry site the Claiborne aquifer is 55 feet thick.  Claiborne aquifer well 08K026 was pumped at a rate of 291 gallons per minutes from 2016 March 14 at about 1:30 p.m. to 17 at about 1:30 p.m. Water levels were monitored in the pumped well, an Upper Floridan aquifer well (08K001, 84 feet from the pumped well), and a Claiborne aquifer well (08K025, 201 feet from the pumped well). After three hours of pumping the semi-log slope of drawdown in both Claiborne aquifer wells went from stable to increasing with time, which indicated that the aquifer-test withdrawal reached a restricted-flow or no-flow boundary. No drawdown was detected in Upper Floridan monitor well 08K001.
Analytical solutions provided preliminary assessments of hydraulic properties using assumptions of a relatively simple hydrogeologic setting and provided insight into what factors might be affecting drawdown. Theis (1935) and Cooper-Jacob (1946) methods are based on the same analytical solution for the radial coordinate system partial differential equation for flow to a well in a confined aquifer. A Microsoft Excel macro that uses Theis concepts and temporal superposition was used at the Newberry site to simulate the effects of multiple pumping events through time (SUMTheis function; Keith J. Halford, U.S. Geological Survey, written commun., 2010). 
Aquifer-test data at the Stripling site were analyzed by simulating drawdown response to pumping using an axisymmetric, groundwater-flow model. An axisymmetric-flow model uses a two-dimensional rectangular grid that is radially fanned out into a cylinder with the pumped well at its center. The model’s two dimensions are depth and distance from the center of pumping. Depth is represented by rows and horizontal distance from pumping is represented by columns. The depth and distance make up the one traditional model layer. Hydraulic properties vary as a function of depth, represented by the model rows. Values of hydraulic properties (horizontal hydraulic conductivity, Kx, vertical hydraulic conductivity, Ky, and specific storage) are multiplied by 2πr, where r is the distance between the centroid of the cell representing the pumping well and the center of the cell representing the right edge of the rectangular grid. Multiplying the hydraulic properties by 2πr radially fans the two-dimensional rectangle of the model out 360 degrees to form the cylinder. Full descriptions of the derivation of two-dimensional radial models using a single layer or multiple layers are provided in Rutledge (1991), Reilly and Harbaugh (1993), Clemo (2002), Langevin (2008), and Halford (2009).

Tags: aquifer-pumping-test, claiborne-aquifer, environment, usgs-5851a1dee4b0f99207c4f1ba
Organization: Department of the Interior