Groundwater

The most productive sources of groundwater in the Buzzards Bay basin are sand and gravel deposits in southward-sloping Rochester-Wareham-Marion outwash plain, and along the north-to-south trending valleys of the Mattapoisett, Acushnet, Paskamanset, and East Branch Westport Rivers.

The western part of the outwash plains is generally more gravelly than the eastern part, which includes the southern part of the adjacent South Coastal Shore basin. Also, outwash deposits grade to finer material to the south, especially in the Rochester-Marion area. The aquifer comprising the Rochester-Wareham-Marion outwash plain has been extensively investigated and results indicate that the aquifer can yield 100 to 300 gal/min to single wells in some areas.

The Mattapoisett River valley can probably yield about 4 Mgal/d without causing the river to be dry during low-flow periods in years of average precipitation. In 1965, the town of Acushnet tested the aquifer bordering the Acushnet River near the New Bedford Reservoir and located three sites capable of yielding between 0.2 and 0.5 Mgal/d. Several industrial wells in the upper Paskamanset River basin probably could yield 0.5 to 1.0 Mgal/d; in the middle part of the basin, the town of Dartmouth has three wells that can yield a total of about 1 Mgal/d.

Where sand and gravel deposits are thinner and generally less permeable, the bedrock aquifer is commonly used. The Buzzards Bay basin is underlain mainly by granitic and metamorphic rocks, which are exposed on knolls, hills, and cliffs. Water from these rocks is obtained mostly from fractures. In general, yields range from 1 to 150 gal/min and average about 8 gal/min.