Detection and delineation of deicing materials in an unconfined aquifer via EC measurements
A ground-water prototype detection system was developed to measure in situ electrical conductivity (EC) of ground water. The system, termed “permanent conductivity points” (PCP), consisted of a number of conductivity cells individually comprised of two-array electrodes attached to a rigid pipe. This system was a “long” conductivity meter permanently installed into the aquifer. It was developed to detect and delineate deicing materials deposited into the ground water of an unconfined sandy roadside aquifer. Measurements from the PCPs provided maximum EC values, which provided a measure of the plume contaminant strength.
An extensive site characterization was performed using standard characterizing tools to provide soil, ground water, and the soil/ground-water matrix properties. This information was used to describe the research aquifer, to provide in sight for PCP installation, and to corroborate the PCP measurements.
The calibration of the PCPs was performed in the laboratory under carefully controlled conditions providing a reliable calibration factor. Numerous in situ EC measurements were compared to the PCP measurements. The most appropriate comparison was the low-flow ground-water sampling ports (WSP) that were placed directly adjacent to the conductivity cells.
Numerous profiles, cross sections, and temporal plots from PCP EC measurements were presented to better describe the delineation of the deicing material in the underlying roadside aquifer. The PCPs were monitored between 1 June 1998 and 19 December 2000 during the research project, encompassing two road-salting seasons. The PCPs proved to be useful in detecting the presence of deicing materials. The maximum contaminant plume EC PCP readings were just over 7500 μS/cm and the ambient were around 70 μS/cm. PCPs were also beneficial in delineating the shape and extent of the contaminant plume. The maximum measured width of the contaminant plume was 60 m and the maximum measured thickness was 10 to 12 m using PCP data.
A potential cost savings using PCP technology for long-term ground-water monitoring is possible for geoenvironmental engineering consulting firms when the installation cost, material cost, and personnel sampling-time needed with standard ground-water monitoring wells is considered. The PCP is a low-cost technology that is beneficial for long-term ground-water quality monitoring.
0775: Environmental engineering