Groundwater

The principal aquifers in the Merrimack River basin are composed of unconsolidated sand and gravel that were deposited in meltwater streams during the glacial period. Aquifers that can sustain well yields of more than 300 gal/min lie primarily along the Merrimack River and its major tributaries. The largest area of glacial deposits capable of yielding more than 300 gal/min to single wells is located in northwestern Amesbury, near the New Hampshire border.

Many small aquifers (saturated thickness less than 50 ft) in stream valleys and wetlands throughout the basin sustain wells yielding less than 100 gal/min. Igneous and metamorphic bedrock throughout the basin provides a sufficient quantity of water for most domestic wells. Yields range from less than a gallon per minute to about 100 gal/min. The median yield of 41 bedrock wells is 10 gal/min