Aalysis of Iron and Calcium in a Geothermal System Outflow Stream

Abstract

A newly constructed building with an open-loop geothermal system outflow stream on campus provides a powerful context for student driven experimentation in an environmental chemistry course. In less than a year of operation, the rocks toward the frontend of the stream have already begun to turn orange (rusty) which has become a point of curiosity among the students. As a result, iron and calcium concentrations were monitored by atomic absorption spectroscopy along the stream in order to study the metal deposition process. The iron oxide deposition on the rocks in the stream, in-stream iron and calcium concentrations, and temperature were analyzed along the stream. As expected, the in-stream iron and calcium concentrations decreased down the stream, with a particularly larger drop in concentration following a small decorative waterfall. The concentration of iron oxide deposited on the rocks also decreased down the stream at a similar rate to the in-stream dissolved iron decline, strongly suggesting that the deposition on the rocks is the primary mode of iron removal. At less than a year in operation, the iron and calcium concentrations begin declining immediately upon entering the stream, indicating that the frontend of the stream has not yet become
saturated. The environmental chemistry course plans to repeat these studies in subsequent years to monitor if/ when the frontend becomes saturated and the deposition process begins moving farther downstream.