Groundwater

The principal aquifers in the Concord River basin are composed of stratified sand and gravel, up to 140 ft thick, deposited in stream channels at the end of the glacial period. Some areas with high potential well yields lie along Stony Brook in Westford; adjacent to Lake Cochituate in Framingham, Natick, and Wayland; and along River Meadow Brook in Chelmsford.

Many broad lowlands in the Concord River basin mark the sites of glacial lakes, such as Lake Sudbury, which extended from South Framingham to Weston and from Concord to Wellesley, and Lake Assabet, which was located mainly in Westborough, Southborough, and Northborough.

The Concord River basin is underlain by a variety of crystalline rocks. Wells drilled in bedrock for domestic-water supplies are commonly 100 to 300 ft deep and yield 2 to 10 gal/min, although yields up to 225 gal/min have been reported. Fine-grained lake deposits generally yield less than 100 gal/min to wells, but, if interspersed with coarser deposits, can yield 100 to 300 gal/min.