DEICER DISSOLVED LOAD DURING A PRECIPITATION EVENT IN EASTERN MASSACHUSETTS

In aquifers where de-icers are regularly applied on road surfaces during the winter seasons surface waters show stream elevated chloride levels during the entire year indicative of aquifer storage capacity of contaminated saline solutions. The object of this study is to document variation of total dissolved load during precipitation events namely are the stream waters simple mixtures of 2 component system consisting of baseflow and surface runoff?

The studied site is Saugus River at Saugus Ironworks (USGS station 01102345) with drainage area of 20.8 sq.mi. in suburban setting in Eastern Massachusetts. The sampled precipitation event occurred on October 25 & October 26, 2008 following 4 weeks of no precipitation. The stream immediately prior to precipitation had a flow of 6.0 cfs and specific conductance of 690 microS/cm. Following the precipitation event of 0.73 inches during a 14 hour period the flow increased to 26 cfs and spec. cond. dropped to 300-400 microS/cm range. Water samples were collected at 30 min intervals starting just before the onset of the event and ending after the event. All samples were analyzed by IC for constituent anions and cations.

The most surprising observation is the non-uniform distribution of total dissolved load calculated for 15 min intervals during the precipitation event. Prior to the event the total dissolved load for each 15 min was 58 - 62 kg/15 min. During the first 6 hours of the event the total dissolved load increased up to 230 kg/15 min. After the first 6 hours the total dissolved load fluctuated between 100 and 150 kg/15 min, eventually stabilizing at pre-event levels after 2 additional days. We interpret the presence of this extra dissolved load from the remobilized solid left near the surface by evapotranspiration processes during the preceding precipitation free period of 4 to 5 weeks.