ROAD SALT APPLICATIONS AND THEIR IMPACT ON THE MUNICIPAL WATER QUALITY IN SE MASSACHUSETTS

Municipal water supply for the Town of Norwell in SE Massachusetts is entirely from local surficial aquifers consisting of Wisconsinan glacial deposits. Water quality monitoring of finished and raw waters show a systematic increase of dissolved road salt presently reaching levels of 250 to 300 ppm of NaCl. The present trend of increasing NaCl (between 1 and 6 ppm of Cl per year) suggests that the water will reach regulatory limits for Cl of 250 mg/l (SMCL) within the next 5 to 20 years threatening the future availability of this water resource.

Collaborative research effort between the Town and the Department of Earth and Environmental Sciences at Boston College is focused on the understanding of the extent of road salt contamination resulting from road salt retention within the aquifers, understanding of road salt pathways in the shallow and deeper subsurface, hydraulic conductivities and percolation in a variable density water column. The aquifer is wedged between two major state road systems, one of which is a 4 lane interstate class highway with a major interchange. In addition major shopping mall complex and road salt storage facility are also a contributing road salt source both located upstream of the water supply exploration field. Furthermore a heterogeneous surficial geology with buried esker overlain by pitted outwash sand and silt deposits most certainly provide preferential percolation zones and pathways. Better understanding of the hydrological pathways will guide the future management practices including a consideration of high efficiency reverse osmosis water treatment plant similar to a recently built reverse osmosis plant in Dighton Massachusetts approximately 35 miles from Norwell.