Robowell: A reliable and accurate automated data-collection process applied to reactive-wall monitoring at the Massachusetts Military Reservation, Cape Cod, Massachusetts

by Gregory E. Granato and Kirk P. Smith

ABSTRACT

Robowell was developed and tested by the U.S. Geological Survey (USGS) to automatically monitor ground-water quality. Robowell follows standard manual-sampling protocols that require monitoring and recording of properties and constituents in water pumped from a well or multilevel sampler until purge criteria have been met. The Robowell process can be used to identify changes in ground-water quality on a real-time basis without the cost of sample collection, processing, and analysis. This automated process can be tailored for different applications.

Six Robowell units have reliably sampled water in different well designs and geochemical environments during all four seasons of the year since 1994 to produce accurate real-time ground-water- quality records that are more than 96 percent complete. Performance has been verified with a program of regular quality-control samples obtained by using independent water-quality probes, manual measurements, and laboratory analyses throughout the period of record. Results of the quality-control program indicate that from 80 to more than 95 percent of the measurements of specific-conductance, pH, and dissolved-oxygen would be rated as good or better on the basis of draft USGS guidelines for water-quality measurements. These results verify the integrity of the automated-sampling records and demonstrate that the automated monitoring system can accurately measure ground-water quality over a large range of geochemical conditions.

A Robowell technology demonstration unit was installed and run on Cape Cod at the Massachusetts Military Reservation with the assistance of the USGS Toxic Substances Hydrology Research group. This unit was run to test the technology and to monitor geochemical changes caused by emplacement of a zero-valent, iron reactive wall designed to remediate volatile organic compounds in ground water. The monitoring unit recorded substantial changes in ground?water quality in a short period as the reaction byproducts of the wall and a subsequent enzyme/pH adjustment raised pH by almost a full unit, raised specific conductance by about 800 µS/cm (microsiemens per centimeter at 25 degrees Celsius), and completely depleted the dissolved oxygen in water from the well. The automated monitoring system demonstrated its success as a sentry well by notifying the project chief through phone calls from a voice modem that geochemical changes had been detected. Real-time records at the site define the variability in ground-water quality during the monitoring period.