Ground water

The principal aquifers of the Taunton River basin are sand and gravel deposits within stratified drift. Stratified-drift deposits are exposed at land surface over about 62 percent of the basin. They are primarily ice-contact (kame), outwash, and lake-bottom sediments, which were deposited in preglacial bedrock valleys and in water-filled depressions in the till surface during retreat of the last glacier. Stratified drift is more abundant in the central and southern parts of the basin than in the northern part. In the northern one-third of the basin, stratified drift fills narrow, north-south trending valleys, which are bounded by till-bedrock uplands.

Aquifer yields for normal climatic conditions were estimated for 26 aquifers in the northern half of the basin (Lapham, 1988). The highest yields, 7.7 and 7.3 Mgal/d, were obtained for aquifers in hydraulic connection with the lower Matfield and Taunton Rivers in Bridgewater and East Bridgewater, and with the lower Canoe River in Norton and Taunton. The other 24 aquifers have potential yields of 3 Mgal/d or less.

Individual wells in the Taunton River basin can yield more than 100 gal/min if located in areas underlain by permeable sand and gravel. About 80 percent of stratified drift in the basin consists of these permeable materials; the remainder consists of poorly permeable clay, silt, and fine sand. About 25 mi2 of the area underlain by permeable deposits can yield at least 300 gal/min of water to single wells. Many of these high-yielding deposits are in depressions in the valleys of a pre-glacial drainage system that has little similarity to the present-day drainage system.

Volcanic and granitic rocks underlie both the northern and southern margins of the Taunton River basin, and sedimentary rocks consisting of sandstone, shale, siltstone, conglomerate, and coal beds underlie the interior of the basin (Williams and Willey, 1973). Yields to single wells in bedrock in the basin range from about 0.5 to 250 gal/min. Most bedrock wells, however, yield less than 10 gal/min. The yield of bedrock wells depends partly on their intended use. Many homes, which require only 5 gal/min, have wells that are not drilled to great depth or developed to their maximum potential.