Real-Time, In Situ Measurement of Hexavalent Chromium in Groundwater

The current method for monitoring groundwater contaminated with carcinogenic hexavalent chromium is labor intensive and costly, yields hazardous laboratory waste, and does not allow for continuous in situ monitoring. Hexavalent chromium is a known contaminant of concern at multiple industrial and Department of Energy sites across the United States. How the Problem is Being Addressed: Research has focused on developing and field testing advanced prototypes of a cost-effective, cable-deployed, submersible hexavalent chromium sensor designed for extended service in groundwater monitoring wells and other aqueous environments, and capable of continuous real-time, long-term measurements while generating no wastes. Continuing work focuses on developing a market ready, modular system for customized field installations and data telemetry. Phase I and Phase II Results and Accomplishments: Hexavalent chromium in groundwater can be measured using near-ultraviolet absorption spectrophotometry. Interference caused by suspended particulate matter (turbidity) is accurately compensated by measuring the amount of ultraviolet light scattered by the turbidity. Submersible prototypes capable of measuring hexavalent chromium concentration, with simultaneous correction for turbidity, were produced during the Phase I investigation. During the Phase II investigation, sensors were successfully tested in wells at the Washington state Hanford Site. Results led to multiple technological advancements such as the addition of solar power for each sensor, a more compact design, a programmable measurement schedule, and data telemetry via cell modem to an off-site virtual data logger. The sensors include programmed correction for turbidity and pH effects. The Phase IIB Project: Major proposed tasks include re-designing the prototype mechanical structure to reduce cost and enhance ease of manufacture, and upgrading the electronics to support remotely programmable data acquisition and fully networked well-fields featuring remote telemetry from a local hub. Also, one or more large-scale field demonstrations will showcase the effectiveness and utility of the sensor. Demonstrations, in cooperation with potential sensor customers, will be implemented at sites with known hexavalent chromium plumes and existing monitoring wells. Results will be published as case studies in peerreviewed journals. Commercial Applicationand Other benefits: This sensor system will be a valuable tool in the assessment of environmental fate and transport of hexavalent chromium and can be used to assess the effectiveness of remediation techniques. This approach provides a cost-reducing option for long-term contaminant monitoring at U.S Department of Energy Superfund sites and private sector sites such as chrome plating facilities.