Borehole geophysical logging of four production wells completed in Precambrian metagranite in Fauquier County, Virginia (USA), was conducted to characterize stratigraphy, collect water-bearing fracture orientations and describe vertical hydraulic gradients in the vicinity of each borehole. Long-term (48–90 h) single-well pump test data were reevaluated for each well to better characterize this locally important aquifer system. Single-well aquifer test analyses indicate mid-to-late-time infinite acting radial flow conditions within the fractured rock aquifer, followed by increasing late-time contribution of stored groundwater from recharge boundaries. Later-time pump test results are believed to indicate that water-bearing fractures within the metagranite are ultimately recharged by groundwater stored within the regolith. Assumptions about the presence of a recharge boundary sourced by the regolith were tested with a simple groundwater flow model that was calibrated to observed drawdown data associated with one of the long-term pump tests. This study identifies fracturing associated with shear-related metamorphic fabrics in the wellbore and demonstrates the significance of these fractures as mechanisms for accessing groundwater. Results from this investigation indicate that shear-related metamorphic fabrics can be important structures for integrating transmissive fracture networks within the Marshall Metagranite and possibly within other Blue Ridge basement rocks possessing similar metamorphic history.

对在美国弗吉尼亚州福基尔县前寒武纪变花岗岩中完成的 4 口生产井进行钻孔地球物理测井，以表征地层、收集含水裂缝方向并描述每个钻孔附近的垂直水力梯度。对每口井的长期（48-90 小时）单井泵测试数据进行了重新评估，以更好地表征这一当地重要的含水层系统。单井含水层测试分析表明，裂隙岩石含水层内的中后期无限作用径向流条件，随后增加了来自补给边界的储存地下水的后期贡献。据信，后期泵测试结果表明，变花岗岩中的含水裂缝最终会被风化岩中储存的地下水补给。使用一个简单的地下水流模型测试了关于存在由风化层产生的补给边界的假设，该模型被校准为与长期泵测试相关的观察到的水位下降数据。这项研究确定了与井筒中与剪切相关的变质结构相关的裂缝，并证明了这些裂缝作为获取地下水的机制的重要性。这项调查的结果表明，与剪切相关的变质结构可能是整合 Marshall 变质花岗岩内以及可能具有类似变质历史的其他蓝岭基岩内的透射裂缝网络的重要结构。