Salinity Assessment and Watershed Protection: A Study of Fish Brook Catchment Basin in NE Massachusetts

The 3.8 sq miles Fish Brook basin serves as a primary source of water for the Town of Andover, Massachusetts.  The brook is dammed at its discharge point and all water pumped back to an upstream pond where water is treated for public distribution.  The basin includes wetlands, protected lands and residential development and is criss-crossed by two interstate highways and two major interchanges.

The trend of water quality data show a near constant value of 30 ppm of Na during the 1975 to 1998 period and a steady increase toward 60 ppm in more recent years. The rise in Na is likely due to a general increase of road salt application during the last decade and the 1998 construction of a road salt storage shed inside a cloverleaf interchange. 

Stoichiometric ratios of Cl vs Na, Ca, and Mg suggest that chloride concentrations are supported by sodium in the 65 to 80% range, by calcium in the 20 to 30% range, and the rest by magnesium. Sodium chloride and calcium chloride are used for ice control on the interstate and local road surfaces which is the cause of the observed water quality changes. The Town of Andover sponsors a local committee which has conceptualized and implemented a basin wide water quality analysis, the results of which have been the switch to a low-salt application zone along the interstate highways and the proposed relocation of the in-basin salt storage facility. The committee consists of Town directors and residents with expertise in environmental and hydrological assessment. On its initiative, monitoring wells have been installed and surface water instrumented with continuous water quality sensors. Calibrated specific conductance data show elevated salt content throughout the year (400 to 700 ppm of NaCl and CaCl₂) suggesting a wide penetration of saline solution within the aquifer.