Don J. DeGroot
In glaciated areas till can serve as a leaky aquitard for fractured bedrock aquifers. The characterization of a leaky till mantled fractured bedrock aquifer is presented. Multiple high resolution data sets were collected in response to unprecedented changes in the hydraulic head at a research site in eastern Massachusetts. Local scale aquifer and aquitard hydraulic conductivity, transmissivity and storativity values are determined through the analysis of purge recovery tests using Ostendorf and DeGroot (2010) and Cooper et al (1967) theories. The local scale parameters are in turn used to determine large scale aquifer transmissivity and storativity through an analysis of the drawdown due to irrigation pumping using Hantush (1960). It is confirmed that the till acts as a leaky aquitard to the fractured bedrock aquifer, with geometric mean hydraulic conductivities of 7.2E-9 m/s for the till and 1.6E-7 m/s for the bedrock. The storativity of the till is 2.7E-4 while that of the fractured bedrock is 6.7E-5. The transmissivity values determined through Cooper et al. (1967) overestimate the large-scale transmissivity of the aquifer by at most a factor of 3, as previously determined by Barker and Black (1983).