Characterizing a fractured aquifer in Mexico using geological attributes related to open-pit groundwater

A multivariable analysis of the Rock Quality Designation (RQD) and its relation with the hydraulic conductivity of 17 dewatering wells in an open-pit mine (central Mexico) is presented as a tool for groundwater exploration in fractured aquifers. A solid model was constructed with the RQD data using three sizes for each grid cell and four interpolation methods. The inverse-distance method with a small grid gives the best results. The resulting RQD solid model was used to locate 22 pilot holes, on which an air-lift test was performed as a qualitative assessment of their usefulness. The results showed a lower water production (1.8 l/s) in shale that has low alteration, whereas in highly altered shale, breccias, and intrusive rock, the flow rate was 3.9 l/s. This implies an important relationship between the pilot-hole performance, the lithology, and the rock alteration, but it was also found that some fractures or faults, which cannot be detected clearly by the RQD, play an important role in the hydrodynamics of the aquifer. In conclusion, it is necessary to consider all available factors that can help to identify the hydrodynamic behavior of the aquifer because using only RQD data can lead to errors in prospecting for groundwater.