DETAILED MONITORING OF DEICER LEVELS IN STREAMS WITHIN A SMALL WATERSHED, SOUTHEASTERN MASSACHUSETTS

In May 2016 we deployed a network of four AquaTroll 200 probes (In-Situ, Inc) along 5 mile long stream from its headwaters toward downstream to monitor seasonal variations of deicer loading during different seasons. First half of the stream traverses a major highway interchange on Rt.3 in southeastern Massachusetts, flows near a major shopping mall and deicer storage shed. The second half of the stream drains a largely forested and swampy section with minimal deicer use. The probes have 3 sensors programmed to acquire data for temperature, water pressure, and specific conductance every 15 min which are stored internally; the electronics and battery can support 5 years of unattended operation with up to 200 000 readings.

Preliminary data for the first 6 month of operation (May to November 2016) indicate that during the entire time period (except immediately after rain events) deicer levels as NaCl ppm were consistently above 200 ppm. May 2016 data show the starting deicer concentration at 190 ppm at the headwaters rising to 340 ppm as the stream traversed the urbanized areas and moderating back toward 200 ppm in the lower section as the stream flowed through the wetland dominated landscape. Similar pattern is observed for November 2016 data set with the noted exception that the readings are consisteently 20% to 25% higher. One possible explanation for the increase is from a prolonged dry summer season and consequent retention of deicers in near surface ground water. Winter data sets will be included for the meeting.