Characterization of hydrogeologic properties for a multi-layered alluvial aquifer using hydraulic and tracer tests and electrical resistivity survey

Abstract

A multi-layered aquifer, typical of riverbank alluvial deposits in Korea, was studied to determine the hydrologic properties. The geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units: silt, sand, highly weathered and fresh bedrock layers. The electrical resistivity survey supplied information on lateral extension of hydrogeologic strata only partially identified by a limited number of the geologic loggings. The laboratory column tracer test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5.00 x 10(-2) cm/s. The slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4.32 - 7.72 x 10(-4) cm/ s. Hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2.08 x 10(-3) and 2.44 x 10(-2) cm/s with a geometric mean of 6.89 x 10(-3) cm/s, which is 7 times smaller than that from the laboratory column experiment. The trend of increasing hydraulic conductivity with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity zone as more of the aquifer is tested. The combined hydrogeologic site characterization using hydraulic tests, tracer tests, and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties of the multilayered alluvial aquifer.