Abel, Malakye2025-06-192025-06-192025https://hdl.handle.net/1828/22403Interpreting pumping test responses for fractured bedrock aquifers is challenging, particularly when estimating the transmissivity of an aquifer and the long-term sustainable yield of a well. This study applies the derivative method (e.g., Renard et al., 2009) on the pumping and recovery phase of six pumping tests from bedrock wells on Vancouver Island and the Gulf Islands, sourced from local consultants, to characterize flow regimes to determine how transmissivity calculations can be improved. The van der Kamp method (van der Kamp, 1989) was also tested for its effectiveness in the extrapolation of pumping responses and its potential for improving the ability to estimate a sustainable pumping rate for a 100-day dry season (Q100) that is often prescribed when licencing a well. Two pumping tests studied were for fractured sedimentary bedrock aquifers while four were for fractured crystalline bedrock aquifers. The tests lasted 12-72 hours and were followed by recovery monitoring of a similar duration. The results showed that for the fractured sedimentary bedrock aquifers, linear flow may precede infinite-acting radial flow for several hundred minutes. For the tests that exhibited infinite-acting radial flow as the final derivative response, the duration was approximately 0.3 log cycles of time, cut off when pumping ended. Infinite-acting radial flow identified using the recovery phase derivative often matched the pumping phase derivative in symmetry, though was sometimes different in magnitude. Identifying periods of radial flow from the pumping and recovery phases facilitated the calculation of transmissivity using various analytical solutions. Transmissivity values calculated using the Theis curve-matching (Theis, 1935) and Cooper-Jacob (Cooper & Jacob, 1946) methods, from the same radial drawdown data, were similar (within 0.5 log transmissivity values). For three pumping tests, transmissivity values calculated from the symmetrical recovery phase using the Theis recovery method (Theis, 1935) were noticeably different (over 0.19 orders of magnitude smaller or larger) than those calculated from the pumping phase. The van der Kamp method did not work for all pumping tests analyzed. The extended drawdown calculated using the van der Kamp method for the same three tests exhibited various non-ideal responses. Two tests exhibited a rising static water level, where the water level in the well at the start of the pumping test was erroneously assumed to be not changing. An unaccounted-for rising static water level induces a drift in the drawdown and subsequent recovery data, causing a discrepancy in the transmissivity calculated from the pumping and recovery phase, evident by a difference in the magnitude of the pumping and recovery derivative plots. The third test may have been subject to dewatering or a falling static water level late in the recovery phase which caused a steepening of the extended drawdown. When the “static” water level is not static, the extended drawdown does not improve the extrapolation of the drawdown to 100 days, which is required when estimating Q100. When the static water level was stable, as for the three other pumping tests, it lent confidence to the extrapolation of drawdown to 100 days to calculate Q100, reducing the reliance on an empirical straight-line extrapolation of drawdown to 100 days. A rising static water level, if not identified before pumping, negatively affects Q100 estimates; especially for high-yield wells where the drawdown rate is slower and may be more sensitive to static water level shifts. The drawdown rate drifts do not as negatively alter transmissivity calculations because transmissivity values are log-normally distributed. Minor drifts in drawdown rate have less impact on the relative accuracy. To enhance test reliability and facilitate the application of the van der Kamp method, future tests should confirm a “static” water level before proceeding with testing. Additionally, to extract maximal utilization of the van der Kamp method and recovery derivative, the recovery phase should last at least as long as the pumping phase, rather than ending at 90% recovery as is currently recommended by the B.C. Ministry of Environment (MoE, n.d.). Supervisors: Mike Wei and Lucinda Leonardengroundwaterpumping testsaquiferfractured bedrockVancouver IslandHonours thesis