about 1'f years. The wells are about 10 feet apart and are screened at different depths in stratified glacial drift, one from 50 to 70 feet, the other from 111 to 131 feet below land surface. A third well screened from 113 to 138 feet below land surface and located about 280 feet from the pond has yielded water containing little or no manganese since its construction in 1958. Concentrations of dissolved iron in water pumped from all three wells have been generally less than 0.3 milligrams per liter throughout their pumping history. Field investigations during 197'* and 1975 by the U.S. Geological Survey in cooperation with the Rhode Island Water Resources Board indicate that oxides and other forms of manganese that occur as stains and coatings on aquifer materials may be the most important source of the manganese contained in the well water. Organic-rich sediments on the bottom of the pond and river, through which infiltration is induced when the supply wells are pumped, constitute a significant but seemingly less important source material. Manganese enrichment in water in the well field seems to be related to the infiltration of surface water through the organic-rich sediments on the bottom of the pond and river. Data from an observation well screened from 3.5 to 5.8 feet below a 1.5~foot layer of organic material in the pond show that highly oxidized water in the pond becomes strongly reduced when passing through the organic sediments. The reduced infiltrate dissolves manganese and iron from aquifer materials and probably also from the lower layers of organic sediments. Concentrations of iron and manganese in the water from this observation well were as high as kQ and 1.2 milligrams per liter, respectively. Because concentrations of manganese were as high as 3.3 milligrams per liter in the deepest supply well, it is assumed that concentrations of manganese must either increase as infiltration moves to greater depths in the aquifer or that greater concentrations are developed beneath other parts of the pond. Also, because the supply wells yield water containing little or no dissolved iron, iron must be removed from solution by precipitation, or some other process, as the infiltrated water moves to greater depths in the aquifer. Hydrologic analysis indicates that most of the infiltration induced from the pond and from the Chipuxet River which flows through it is diverted to the two supply wells that yield water high in manganese. The low manganese content in water from the well farthest from the pond is attributed to the fact that this well pumps relatively little of the water induced into the aquifer from the pond and river.

Stratified g lacial drift consisting largely of sand and gravel constitutes the only aquifer capable of supporting continuous yields of 100 gpm (6.3 1/s) or more to individual we lls.The aquifer covers about a third of the 79 mi 2 (205 km 2 ) study area, occurring main ly in stream valleys that are less than a mi le wide. Its saturated thickness is commonly 40 to 60ft (12 to 18 m); its transmissivity is commonly 5,000 to 8,000 ft 2 /day (460 to 740m 2 /day).The aquifer is hydraulically connected to streams that cross it and much of the water from heavily pumped wells wi ll consist of infiltration induced from them. Potential sus tained yield from most parts of the aquifer is 1 imited chiefly by the rate at which infiltration can be induced from streams or low streamflow, whichever is smaller .Ground-water withdrawa ls deplete streamflow; and if large-scale development of ground wate r is not carefully planned and managed , periods of no streamflow may result during dry weather.Potential sustained yield varies with the scheme of well development, and is evaluated for selected areas by mathematically simulating pumping from assu med schemes of we! Is in models of the stream-aquifer system. Results indicate that sustained yields of 5.5, 3.4, 1.6, and 1.3 mgd (0.24, 0.15, 0.07, and 0.06 m 3 /s) can be obtained from the stratified-drift aquifer near Slatersville, Oakland, Harrisville, and Chepachet, respectively. Pumping at these rates wil 1 not cause streams to go dry, if the water is returned to streams near points of withdrawal.A larger ground-water yield can be obtained, if periods of no streamflow along reaches of principal streams are acceptable.Inorganic chemical quality of water in the stream-aquifer system is suitable for most purposes; the water is soft, slightly acidic, and generally contains less than 100 mi lligrams per litre of dissolved sol ids. Continued good quality ground water depends on maintenance of good quality of water in streams, because much of the water pumped from we! Is wil 1 be infiltrated from streams.

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