SALT FLUX IN A SUBURBAN STREAM, WESTON, MASSACHUSETTS – A COLLABORATION WITH 6TH GRADE STUDENTS

Bogle Brook supplies water to ponds with links to public water supply in Wellesley and Natick, Massachusetts, including the wells supplying Wellesley College. Rapidly increasing salt content of supply wells is of concern to both towns. The Massachusetts Turnpike (I-90) and a highway maintenance facility are the apparent source for much of the salt, as streams crossing the turnpike from north to south show large increases in salinity next to the salt storage and highway ramps. The goal of this study is to quantify the rate of salt removal by this stream over a period of one to several years, and to estimate how much may be stored yearly in groundwater and how much is flushed out.

A new gaging station has been established on the campus of Rivers School, the closest convenient access point to Bogle Brook downstream from the Turnpike. A stream gage was set, and periodic flow measurements have developed a rating curve. Stream levels are now being monitored both by AquaTroll 200 depth/conductivity/temperature probe, and by daily gage height readings taken by the two 6^thgrade classes at Rivers School. Samples will be analyzed for common metals by ICP spectroscopy with the assistance in the laboratory of the two classes, an opportunity for them to use modern analytical equipment in environmental analysis, and compare their specific conductivity measurements with the measured chemistry of the samples. As earth science is generally in the middle school curriculum in Massachusetts, this is an effort to catch the imagination and enthusiasm of younger students with their participation in a study directly related to their water supply. Student participation is key to obtaining frequent samples and measuring gage height.

Autumn 2015 measurements of discharge are from 10 to 121 liters per second, and chloride concentrations estimated from specific conductivity ranges from 230 to 273 mg/L. Total salt flux (g/s) and discharge have a linear correlation coefficient of R² = 0.996, partly because discharge factors into salt flux. There is no correlation between salt concentration and discharge, suggesting that a simple dilution model is not applicable. We hope to capture any effects from rainfall totals, rainfall intensity, air temperature, ice formation, and seasonal road salt application.