Low-permeability fractured rocks constitute the bedrock of many regions worldwide. Due to the extreme heterogeneity and anisotropy, these rocks show very complex and varied drawdown-time trends when subjected to pumping. Understanding these trends is crucial for operational decisions, such as utilizing wells for water supply or managing dewatering operations in mining sites. This study examines nine pumping tests in an andesitic bedrock formation. The tests were carried out in wells of varying depths (30 - 260 m) in a region where groundwater circulation is not always continuous in the network of discontinuities. The tests lasting between 9 and 68 hours were generally carried out at constant flow rate (0.4-6 L/s) with measurements of drawdown in the pumping well and, in some cases, in an observation well. The drawdown data versus time have been analyzed through semi-log plots, the smoothed time series’ have then been represented on bi-log plots together with the first derivative of the drawdown. The trends of the drawdown and its derivative have been compared with theoretical curves, and interpretation was refined using flow dimension sequence analysis. The results show very different responses of the aquifer to pumping, which are affected by the interconnection of discontinuities, the presence of multiple hierarchical networks of discontinuities and of dykes that bisects a country-rock aquifer.
Data from pumping tests was integrated by earth tides groundwater response from 6 piezometers and by additional information deriving from RQD available for 400 boreholes to obtain a probability distribution of the hydraulic parameters to be used as prior information in numerical modelling.