EXPERIMENTAL EVALUATION OF A DRIVE-POINT GROUNDWATER SAMPLER FOR HYDRAULIC CONDUCTIVITY MEASUREMENT

Drive-point ground-water samplers, designed to enable delineation of t he vertical and areal extent of a contaminant plume, have been modifie d to obtain an in situ measurement of hydraulic conductivity in aquife rs. The multlevel drive-point sampler (MLDPS) consists of a 30-cm long screen pushed to a desired depth within a retractable outer sleeve an d a pressure transducer to monitor the rate of fill within a sample ch amber. The accuracy and variability of a MLDPS to measure hydraulic co nductivity was evaluated in a 50-m(3) laboratory aquifer comprised of a uniform medium sand. Twelve measurements were performed using the ML DPS followed by duplicate slug tests performed at identical locations and depths within the aquifer. MLDPS and slug test data were analyzed using the method of Widdowson et al. (1990). The MLDPS provided an est imation of hydraulic conductivity at least one order of magnitude belo w slug test-derived hydraulic conductivity and the range of hydraulic conductivity associated with a medium sand. MLDPS-derived hydraulic co nductivity values also show greater variability and range relative to the slug test-derived values. Hydraulic conductivity ranges from 0.072 to 2.3 m/d using the MLDPS (coefficient of variation = C-v = 1.3) com pared to a range of 10 to 16 m/d (C-v = 0.14) for the slug test values . Variability and magnitude of the MLDPS-derived hydraulic conductivit y is attributed to disturbance of aquifer material and experimental fa ctors inherent to the design of the instrument.