Groundwater

The principal aquifers in the basin are composed of unconsolidated sand and gravel deposited by meltwater streams during the glacial period. The most productive of these aquifers sustain well yields of several hundred gallons per minute and lie primarily along the Shawsheen River and its major tributaries, Elm, Heath, Strong Water, and Vine Brooks. Aquifers that sustain well yields of less than 200 gal/min occur in many tributary-stream valleys and wetland areas. These aquifers are generally less than 50 ft thick and have small surface areas.

Bedrock in the basin is composed of a variety of igneous and metamorphic rocks. Wells in bedrock yield up to 100 gal/min, but generally yield much less. The median yield of 26 bedrock wells in this basin is 10 gal/min, an amount sufficient for domestic supplies.