Continual Groundwater Monitoring with Inexpensive Chloride Sensors
Abstract
A simple chloride sensor technology, using an oxidized silver rod and reference electrode attached to a data logger, can be used as an inexpensive yet effective tool for the continuous measurement of chloride concentration in groundwater. The sensor is seen to be responsive at concentrations from less than 35 mg/l to 35,000 mg/l, with an error of less than 7% after the sensor is corrected for drift. When monitoring changes in groundwater salinity, the sensor has shown to be particularly useful when chloride concentrations are under 100 mg/l; at these lower salinities, conductivity probes become less responsive, whereas the chloride sensor is still able to register the smaller concentration changes. The sensor is particularly useful for continuous monitoring. Calibration and drift adjustment can be accomplished by simply taking a water sample in the beginning and at the end of the monitoring period. This allows the sensor to be adjusted for drift within the signal over the monitoring period. Occasional samples taken during the monitoring period provide control on the drift during the monitoring period. Chloride concentration from the control samples can be accurately and inexpensively calculated through titration methods, and do not need to be sent to an external laboratory for analysis. Tests have shown the sensor to be robust during long-term monitoring. When the sensor has been applied in unconfined aquifers, there has been virtually no observable difference in the responsiveness of the sensors. However, when the sensors are applied in reduced groundwater conditions, gradual fouling of the sensor surface has been seen to reduce the responsiveness of the sensor over time. Thus fouling can be an issue when applying the sensor in reduced conditions. The chloride sensors have shown to be very effective at measuring changes in chloride concentration in groundwater over short time spans. Therefore, the sensors would be particularly useful in monitoring changes in the saltwater - freshwater interface and seawater intrusion, as well as in groundwater tracer tests. In addition, the sensors could be easily applied in monitoring spills from waste disposal sites or well sites conducting hydraulic fracturing, where chloride would be one of the potential leachates to groundwater.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.H11I1287T
- Keywords:
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- 1831 HYDROLOGY / Groundwater quality;
- 1895 HYDROLOGY / Instruments and techniques: monitoring