Northeastern Section–41st Annual Meeting (20–22 March 2006)

Paper No. 6
Presentation Time: 9:45 AM


HON, Rudolph1, DILLON, Peter1 and GRADY, Sara P.2, (1)Department of Geology & Geophysics, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467, (2)North and South Rivers Watershed Association, 214 South St, P.O. Box 43, Norwell, MA 02061,

Wildcat and Third Herring Brooks are two tributaries flowing into the North River and the Atlantic Ocean within the South Coastal Basin of SE Massachusetts. Each stream is approximately 5 mile long and each drains one of two side-by-side small watershed basins of approximately the same size (3.5 mi2) along a border between the Towns of Hanover and Norwell. Near their confluence the watersheds form an aquifer, a drinking water source for both towns. Other important activity is a Third Herring Brook Restoration Project to restore the historically active fish habitats. The present drainage landscape is approximately 50% forested land, 30 to 40% urban land, approximately 5% wetlands, and approximately 10% other land use. Due to the Third Herring Brook proximity to the secondary roads of Hanover and Norwell as well as Rt. 3, snowmelt mixed with road salt runs off these roads into the brook and its surrounding soils. Wildcat Brook area is similar except with the lesser urban and road densities. For the past seven years we have sampled waters from each stream run at fixed sites and from a select group of monitoring wells within the aquifer to study quality of water contributing to the drinking water supply and more recently for the restoration project. In this paper we report data on sodium and chloride levels, a single most dominant anthropogenic contaminant that threatens both the drinking water supply and the aquatic life habitats. Secondary drinking water standard for chloride is 250 mg/L and for aquatic life the limits are 230 mg/L for chronic exposure and 860 mg/L for acute exposure. Our data show that the chloride levels in drinking waters have been steadily rising from the late 1980's, now in the 130 to 150 mg/L range. Exceptions are periods of extended uncompensated evapotranspiration which can raise the chloride levels up to 613 mg/L and periods of winter/spring runoffs carrying elevated chloride levels that are 3 to 5 times the normal stream base flow. An analysis of winter puddle water (snow melt plus deicing salt) showed 30,000 mg/L chloride and 17,340 mg/L sodium. The spring snowmelt unfortunately coincides with herring migration season. Although adult herrings are quite capable of switching their body chemistry to cope with the changes in salinity during their migration, herring embryos and eggs require low salinities to survive.