DEVELOPMENT OF A SIMPLE MULTI-SENSOR SYSTEM FOR THE STUDY OF GROUNDWATER/SURFACE-WATER INTERACTION

Assessment of groundwater/surface-water (GW/SW) interaction is critical in many hydrologic and ecological studies. Temperature, and more recently electrical resistivity, measured in the water column and shallow subsurface streambed can be used as tracers to quantify GW/SW exchange. The most common method of monitoring water-column and streambed temperature is with probes containing multiple thermistors or thermocouples to measure temperature at a number of depths. A Removable, Adaptable, Multi-SEnsor System (RAMSES) was developed as an extension of conventional temperature monitoring platforms. RAMSES is inexpensive, easily deployable, and designed to enable two sampling methodologies, temperature and electrical resistivity, in the same tool. These capabilities were achieved by (1) constructing the exterior casing of thermally and electrically conductive steel couplings connected to insulating 1.5-inch inside diameter PVC sections; (2) using a simple drive rod deployment system to insert the casing into the streambed; and (3) designing a removable interior sensor array that presses the thermistors or electrodes directly against the interior walls of the steel couplings. A potential advantage of RAMSES over conventional probes is the ability to remove the sensor array from the casing for repair or calibration, to extract a water sample, or to periodically change the sensor array to perform different measurements (e.g. electrical resistivity) while leaving the external casing system in place.

In water-bath and field comparison tests, data from the RAMSES probe compare favorably with data from a conventional multi-level steel thermistor probe. Additionally, observations during the lab tests indicate reduced thermal conduction along the length of the RAMSES compared to the metal 1-D probe because of the thermal isolation provided by the PVC sections. This finding indicates probes constructed with thermal isolation components may provide more accurate temperature-depth sampling than all-metal probes. Initial field tests suggest the RAMSES may be a viable alternative to conventional 1-D probes in the study of GW/SW interaction. Additional work is needed to enable RAMSES to incorporate both electrical resistivity and thermal measurements.