Groundwater withdrawal


During the low flow period of July to September, groundwater or "base flow" seeps into the river and its tributaries from adjacent aquifers providing the relatively cool, clean water important to maintaining good habitat for fish and other aquatic creatures. In the tributaries baseflow is essential to keep the streams from drying up in the summer. In the mainstem rivers it provides dilution for the nutrients and other pollutants in the wastewater effluent being discharged by wastewater treatment plants or coming from stormwater. In drier summers the proportion of effluent to baseflow in the mainstem Assabet gets very high. For example, during the July 1999 TMDL field survey, ENSR found that 80% of the flow in the Assabet at the USGS gage in Maynard could be accounted for by wastewater effluent.

Unfortunately, the three rivers have already lost much of their baseflow because of existing groundwater withdrawals, sewering, and extensive paved and otherwise impervious surfaces where water can't infiltrate back into the aquifers. For this reason, the impacts of new or increased groundwater withdrawals from the watershed must be carefully evaluated to ensure that they will not reduce groundwater or baseflow contributions to the river. Additional losses of these flows will exacerbate the river's existing eutrophication problem and undermine existing and future investments in nutrient control.

Read more about Water Use and Balance in the watershed.