ASSESSMENT OF THE DEICER DISSOLVED LOAD IN A STREAM IN SE MASSACHUSETTS

Transport of dissolved winter deicing chemicals in the subsurface is dominated by advection from hydraulic gradients and by convection driven by the density contrast between fresh water and brines. These processes are further modulated by the non-uniform brine loading along a linear pattern of roads and byways, point source loadings from deicer storage facilities, driveways, and parking areas. Furthermore a discharge of baseflow with dissolved deicers could be later re-infiltrated back into the subsurface in the areas where less concentrated deicer baseflow is encountered. Deicer transport in the Third Herring Brook catchment in Norwell, SE Massachusetts, is influenced by many of the above deicer transport attributes plus by water withdrawal for water supply along a portion of the stream. The stream is instrumented by 4 continuously operated AquaTroll 200 probes programmed to store data on temperature, specific conductance and water column pressure at regular 15 min intervals. The probes span the entire stream at regularly selected sites Sharp compositional spikes are observed in winter only where the stream is crossed by roads with hardly observable compositional responses at locations in between them. Though chemically analyzed samples show the deicers can make up to 95% of the total dissolved solid (TDS) the deicer concentration remains constant over the course of most seasons except for short intervals following precipitation events, short term dilution returning quickly to pre-event compositional levels. Total dissolved load calculation suggests that some of the deicer had been sequestered within the aquifer or is included with the distributed water supply system.