Sand and gravel deposited by streams from the melting continental glacier form the principal aquifers in the Blackstone River basin. The most productive sand and gravel aquifers occupy long stretches of valleys. These coarse-grained deposits generally yield from 100 to 1,000 gal/min. The most productive wells are near streams and lakes where pumping causes the surface water to move through sand and gravel to the wells.

Public-supply wells in sand and gravel have yields of 45 to greater than 1,100 gal/min, and average 325 gal/min. Fine-grained sand, silt, and clay were deposited in temporary lakes that formed in valleys as the glacier melted. Well yields of 5 to 50 gal/min have been obtained from sand layers within these fine-grained sediments.