Paper No. 5
Presentation Time: 2:50 PM
USE OF RESIDENTIAL WATER WELL DATA TO MAP THE BEDROCK FRACTURE ZONES UNDER GLACIAL DRIFT
The purpose of this study was to test the feasibility of identifying bedrock fractured zones, fracture distribution and frequency, and regional trend(s) under the blanket of glacial till by using the well production data provided with the drillers’ Well Log and Drilling Reports. Typical Well Log and Drilling Reports include a rudimentary lithological column along with the following data from the well production test: (1) static water level, (2) time duration of pumping or bailing, (3) the rate of pumping or bailing and (4) water level at the end of the production test. The data was used to estimate hydraulic conductivity from the tests in water wells within the Sharon Sandstone aquifer of Geauga County, Ohio by applying Cooper and Jacob (1946) and Jacob’s (1950) approximation to Theis’ (1935) non-equilibrium radial flow equation. As all the wells in our study were not cased or screened within the aquifer and the production test rates were low (5-20gpm) the well loss can be assumed negligible and the drawdown computed as the difference between the initial and the final water level valid. The resulting hydraulic conductivity values followed quasi-normal distribution with the geometric mean of 9.88x10-6m/s. The values were mapped and grouped into two distinct populations: the low values presumably corresponding to the primary porosity zones within the aquifer and high values assumed corresponding to the fractured zones. The mapped patterns of the highest hydraulic conductivity zones clearly followed two distinct orientations: N340E and N440W. Trends on our map of hydraulic conductivity correlated fairly well with the trends of N210E and N570W obtained for Southwestern Pennsylvania and Northwestern West Virginia with equal amount of separation between the joint systems (Bench et al., 1997). However, the results slightly differed with respect to ENE trend of fractures in Devonian Shale (Engelder T. et al, 2006) which can easily be attributed to the differences in the locations of the two study sites in relation to the Appalachian paleo-stress field.