BROMIDE TRACER TESTING OF A STANDING-COLUMN WELL IN CAMBRIDGE, MASSACHUSETTS

A bromide solution was added to a standing-column well to evaluate the exchange of fresh groundwater under circulating conditions without a bleed discharge. The solution was added directly to the annulus of a standing-column well, and samples were taken every four hours using an automated sampler and submitted for bromide analysis. The well was circulated at a rate of roughly 70 gallons per minute under normal operating conditions, while the well was isolated from the other three wells in the four-well geothermal system, except it was disconnected from the heat pump. Bromide concentrations declined over time due to groundwater exchange over the roughly four-day test. The estimated groundwater exchange rate was less than 1% of the circulation rate. The results indicate that flow rates encountered during drilling (approximately 200 gpm in this particular well) provide little indication of the potential for exchange of fresh groundwater by advective flow or localized hydraulics around an operating standing-column well.