A test of the In Situ Permeable Flow Sensor at Savannah River, SC

A test of the In Situ Permeable Flow Sensor was conducted in which ground-water flow velocity measurements made by the flow sensors were directly compared to velocity estimates obtained using standard hydrologic techniques. Two flow sensors were deployed in a confined aquifer in close proximity to a well which was screened over the entire vertical extent of the aquifer. When the well was pumped at four different pumping rates, the horizontal component of the flow velocity measured by the flow sensors was directed toward the pumping well, within the uncertainty in the measurements, and the magnitude of the horizontal component of the velocity increased linearly with pumping rate, as predicted by theoretical considerations. The measured magnitudes differed from predicted values, calculated with the assumption that the hydraulic properties of the aquifer were homogeneous and isotropic, by less than a factor of two. Vertical components of ground-water flow observed with the flow sensors are qualitatively consistent with the vertical distribution of hydraulic conductivity estimated from grain-size analysis but are significantly larger in magnitude than predicted. This is likely due to the creation of a vertical conduit of increased hydraulic conductivity during emplacement of the probes. The results suggest that while the flow sensors measured the local ground-water flow velocity vector during the test quite accurately, care must be exercised to disturb the formation as little as possible during emplacement. The technology has many potential uses, particularly in the area of environmental site characterization and remediation process monitoring