Volume 30, Issue 1 (January 2007)
Detecting and Quantifying Leakage Through Defective Borehole Seals: A New Methodology and Laboratory Verification
A new method for quantifying leakage through poorly sealed boreholes is presented and verified using a laboratory scale sandbox experiment. The method applies to a leaky borehole between two aquifers separated by an aquitard. A nonreactive tracer is injected into an upper aquifer piezometer, and the lower aquifer is pumped at a fixed rate. First, the presence of the tracer in the recovered water indicates the existence of the hydraulic short-circuit and cross-contamination. The leakage rate associated with the pumping rate can then be determined by measurement of the recovered tracer concentration. By correlating the leakage rate with the pumping rate, the hydraulic properties of the defective seal can be determined and the degree of cross-contamination can be predicted for any pumping rate. The method will be useful for practitioners who need to evaluate the quality of a borehole seal. The method is successfully tested using a laboratory sandbox experiment.