TRANSIENT RESISTIVITY IMAGING OF A PHOSPHOROUS TRACER TEST

Phosphorus impacts to surface waters have lead to questions regarding transport through the soil and groundwater systems adjacent to these water bodies. In the Ozark ecoregion, proper management of nutrients on floodplains is critical to water quality. These gravel-rich floodplains have been shown to have high subsurface flow rates which could act as a pathway for phosphorous to be transported into adjacent streams. A tracer test is usually performed to quantify this transport capability by using piezometers to capture a visual or chemical tracer. However because of the heterogeneous anisotropic conditions that exist in the subsurface it can be very difficult to complete a traditional tracer test. At the Barren Fork Creek site, a traditional tracer test was combined with electrical resistivity imaging to capture tracer fluid distribution and velocity beyond the scope of discrete sampling points such as piezometers. A 96-hour infiltration experiment was performed using four separately injected tracers. The test was monitored using 11 piezometers and four electrical resistivity profiles. Geophysical data showed porous media piston flow, modified by three dimensional heterogeneous media flow. Data also indicated rapid movement of fluid through the subsurface during the test. Further data analysis will be used to quantify subsurface transport properties.