Single Packer Method for Characterizing Water Contributing Fractures in Crystalline Bedrock Wells

The water levels and water quality obtained from open borehole wells in fractured bedrock are flow weighted averages that are a function of the hydraulic heads and transmissivities of water contributing fractures, which are rarely known. Without such knowledge using water levels and water quality data form fractured bedrock wells to assess contaminant conditions can be highly misleading. This study demonstrates a cost effective single packer fracture characterization method that can be used in fractured bedrock to determine the hydraulic heads and transmissivities of individual fracture zones. The method entails inflating a pipe plug to isolate sections of an open borehole at different depths and monitoring changes in water level with time. At each depth, the change in water level with time was used to determine the sum of fracture transmissivities above the packer and then to solve for individual fracture transmissivity. Steady state heads along with the transmissivities were used to determine fracture heads by solving for individual heads using the weighted average head equation. The method was tested in five wells in crystalline bedrock located at the University of Connecticut in Storrs. The wells had been previously logged with both conventional logging methods and the dissolved oxygen alteration method. The single packer head and transmissivity results were found to agree with borehole flow conditions determine by these other methods.