Determination of Specific Storage by Measurement of Aquifer Compression Near a Pumping Well

Abstract

Abstract Aquifer tests of confined aquifers in deep formations can yield inaccurate specific–storage and storage‐coefficient estimates if the distance between the pumped and observation wells is imprecisely known. The distance between the wells can be uncertain because small deviations in the vertical alignment of deep wells can markedly change the distance between the perforated intervals of the wells. Uncertain distance between wells may seriously degrade the accuracy of specific‐storage or storage–coefficient values calculated from aquifer–test data obtained from closely spaced wells. A method is proposed whereby compression of the aquifer matrix can be measured during an aquifer test and used to calculate specific‐storage and storage–coefficient values without knowledge of the distance between the pumped and observation wells. In a field trial of the method, specific–storage and storage‐coefficient values calculated from aquifercompression data were 8.16 × 10 ‐7 and 3.04 × 10 ‐4 , which is nearly identical to values (8.04 × 10 ‐7 and 2.99 × 10 ‐4 ) obtained from longer–term monitoring of aquifer barometric efficiency. Additional comparison with results of a Theis analysis of drawdown data indicates that the aquifer compression data may provide a more accurate determination of specific–storage and storage–coefficient values than would be possible even if the vertical alignment of the pumped and observation wells had been surveyed.