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 models 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 2pir, 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 2pir 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).

为评估克莱本含水层（Claiborne aquifer）作为灌溉供水水源的潜力，于佐治亚州米切尔县佐治亚大学斯特里普林灌溉研究园开展了一项为期72小时的定流量含水层抽水试验（constant-discharge aquifer test）。在斯特里普林场地，克莱本含水层厚度为260英尺。克莱本含水层与上覆的上弗罗里达含水层（Upper Floridan aquifer）之间为里斯本隔水层（Lisbon confining unit）；克莱本含水层与下伏的克莱顿含水层（Clayton aquifer）之间为威尔科克斯隔水层（Wilcox confining unit）。克莱本含水层井11J029的抽水速率为579加仑每分钟，抽水时段为2015年12月15日上午9时左右至2015年12月18日上午9时左右。在附近的一口上弗罗里达含水层观测井（11J030）与一口克莱本含水层观测井（11J025）中监测水位。克莱本含水层观测井11J025的水位降深（drawdown）斜率随对数时间呈下降趋势，未趋于稳定，表明存在向克莱本含水层的含水层越流。在上弗罗里达含水层中未监测到水位降深。为评估克莱本含水层作为灌溉供水水源的潜力，于佐治亚州厄尔利县东北部的纽伯里场地开展了另一项为期72小时的定流量含水层抽水试验。在纽伯里场地，克莱本含水层厚度为55英尺。克莱本含水层井08K026的抽水速率为291加仑每分钟，抽水时段为2016年3月14日下午1时30分左右至2016年3月17日下午1时30分左右。对抽水井本身、一口距离抽水井84英尺的上弗罗里达含水层观测井（08K001）以及一口距离抽水井201英尺的克莱本含水层观测井（08K025）的水位进行了监测。抽水3小时后，两口克莱本含水层观测井的水位降深半对数斜率（semi-log slope）由稳定转为随时间递增，表明含水层抽水试验已达到限流或无流边界（restricted-flow or no-flow boundary）。在上弗罗里达含水层观测井08K001中未监测到水位降深。解析解（analytical solution）基于相对简单的水文地质背景假设，对水力参数（hydraulic properties）进行了初步评估，并为识别影响水位降深的因素提供了思路。泰斯（Theis，1935）法与库珀-雅各布（Cooper-Jacob，1946）法基于同一解析解，该解针对承压含水层（confined aquifer）中井流问题的径向坐标系偏微分方程（radial coordinate system partial differential equation）推导而来。纽伯里场地采用了基于泰斯理论与时间叠加原理的Microsoft Excel宏（macro），以模拟多时段抽水活动的影响（SUMTheis函数；美国地质调查局U.S. Geological Survey，Keith J. Halford，2010年书面通信）。斯特里普林场地的含水层抽水试验数据通过轴对称地下水流模型（axisymmetric groundwater-flow model）模拟抽水水位降深响应进行分析。轴对称地下水流模型采用二维矩形网格，将其径向展开为以抽水井为中心的圆柱状网格。该模型的两个维度为深度与距抽水井中心的水平距离：深度由模型行表示，距抽水井的水平距离由模型列表示。深度与水平距离共同构成了传统的单一模型层。水力参数随深度变化，由模型行进行表征。水力参数包括水平渗透系数Kx（horizontal hydraulic conductivity, Kx）、垂直渗透系数Ky（vertical hydraulic conductivity, Ky）与单位储水率（specific storage），其取值需乘以2πr，其中r为代表抽水井的单元格形心（centroid）与代表矩形网格右边界的单元格中心之间的距离。将水力参数乘以2πr后，可将模型的二维矩形网格沿径向展开360°，形成圆柱状网格。关于单层或多层二维径向模型的推导细节，可参见Rutledge（1991）、Reilly与Harbaugh（1993）、Clemo（2002）、Langevin（2008）以及Halford（2009）的相关文献。