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#           Water resources inventory of Connecticut Part 2: Shetucket River Basin      

      January 1, 1967    

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The Shetucket River basin has a relatively abundant supply of water of generally good quality which is derived from precipitation that has fallen on the basin. Annual precipitation has ranged from about 30 inches to 75 inches and has averaged about 45 inches over a 35-year period. Approximately 20 inches of water are returned to the atmosphere each year by evaporation and transpiration; the remainder of the annual precipitation either flows overland to streams or percolates downward to the water table and ultimately flows out of the basin in the Shetucket River or as underflow through the deposits beneath. During the autumn and winter months precipitation normally is sufficient to cause a substantial increase in the amount of water stored underground and in surface reservoirs within the basins whereas in the summer most of the precipitation is lost through evaporation and transpiration, resulting in sharply reduced streamflow and lowered groundwater levels. The mean monthly storage of water in the basin on an average is 3.5 inches higher in November than it is in June.The amount of water that flows out of thebasin in the Shetucket River represents the totalamount of water potentlally available for use by man.Annual runoff from the entire basin above theQuinebaug River has ranged from about 13 to 42inches since 1929, and has averaged about 23inches (300 billion gallons). Although runoffindicates the total amount of water potentiallyavailable, it is usually not economically orlegally feasible for man to use all of it. Onthe other hand, with increased development, Itis possible that some water will be reused severaltimes.The water available may be tapped as it flowsthrough the area or is temporarily stored instreams, lakes, and aquifers. The amounts thatcan be developed vary from place to place andtime to time, depending on the amount of precipitation,on the size of drainage area, on thethickness, permeability and areal extent of aquifers,and on the variations in chemical andphysical quality of the water.Differences in streamflow from point topoint are due primarily to differences in theproportion of stratified drift in the drainagebasin above each point, which affect the timingof streamflow, and to differences in precipitation,which affect the amount of streamflow.Information on streamflow from gaging stationsmay be extended to ungaged sites by accountingfor both of these factors ,in calculations.Future floods on the upper WillimanticRiver or the Shetucket River are unlikely tocause major damage so long as buildings are notconstructed below the highest flood elevations tobe expected with the present system of reservoirsfor flood control.Ground water can be obtained from wellsalmost anywhere in the Shetucket River basin, butthe amount obtainable from individual wells atany particular point depends upon the type andwater-bearing properties of the aquifers present.For practical purposes, the earth materials inthe basin comprise three aquifers--stratifieddrift, till, and bedrock,Stratified drift is the only aquifer generally capable of yielding more than 100 gpm toindividual wells. This aquifer covers about 18percent of the basin and occurs chiefly In lowlandswhere it overlies till or bedrock. Coefficientof permeability of the coarse-grained unitof stratified drift averages about 1,900 gpd persq ft. Drilled, screened wells tapping this unit,are known to yield from 200 to 675 gpm. Dug wellsin coarse-grained stratified drift should supplyat least 2 gpm per foot of drawdown over an 8-hourperiod. Fine-grained stratified drift has anaverage coefficient of permeability of about 400gpd per sq ft and can usually yield to dug wellssupplies sufficient for household use.Till and bedrock are widespread in extent butcan provide only small to moderate water supplies.Till is tapped chiefly by dug wells; permanentsupplies of more than 200 gpd can be obtained fromdug wells at a majority of sites in areas of till,but there are many sites where the till is tooimpermeable or too thin to provide this much waterthroughout the year. The coefficient of permeability of till ranges from about 0.2 gpd per sq ft to55 gpd per sq it. Bedrock Is tapped chiefly bydrilled wells, about 90 percent of which willsupply at least 3 gpm. Very few, however, willsupply more than 50 gpm.The amount of ground water potentially availableIn an area depends upon the amount of groundwateroutflow, the amount of ground water in storage,and the quantity of water available by Inducedinfiltration from streams and lakes. Fromdata on permeability, saturated thickness, recharge,yield from aquifer storage, well performance, andstreamflow, preliminary estimates of ground-wateravailability can be made for any point in thebasin. Long-term yields estimated for 15 areasespecially favorable for development of largeground-water supplies ranged from 1.3 to 61.8 mgd.Detailed site studies to determine optimum yields,drawdowns, and spacing of individual wells areneeded before major ground-water development isundertaken In these or other areas.The chemical quality of water in the Shetucketbasin Is generally good to excellent. Samples ofnaturally occurring surface water collected from32 sites contained less than 61 ppm of dissolvedsolids and less than 32 ppm of hardness. Waterfrom wells is more highly mineralized than naturallyoccurring water from streams. Even so only7 percent of wells sampled yielded water with morethan 200 ppm of dissolved sol-ids and only 9 percentyielded water with more than 120 ppm of hardness.Even in the major rivers, which are used totransport industrial waste, the dissolved mineralcontent is less than 100 ppm and hardness rarelyexceeds 40 ppm. One notable exception occurs inthe lower reaches of Little River where anexceptional amount of industrial waste is dischargedinto the river near Versailles. Thiswaste is particularly noticeable during lowstreamflow.Iron and manganese In both ground water andsurface water are the only constituents whose concentrationscommonly exceed recommended limits fordomestic and industrial use. Most wells in the basin yield clear water with little or no iron ormanganese, but distributed among them are wellswith ground water that contains enough of these dissolvedconstituents to be troublesome for most uses.iron concentrations in naturally occurringstream water exceeded 0.3 ppm under tow-flow conditionsat 20 percent of the sites sampled. Largeconcentrations of iron in stream water resultfrom discharge of iron-bearing ground water orfrom the discharge of water from swamps. Inswamps the iron is released largely from decayingvegetation.Ground water more than 30 feet below theland surface has a relatively constant temperature,usually between 48°F and 50°F. Watertemperature in very shallow wells may fluctuatefrom about 38°F in February or March to about55°F in late summer. Water temperature in thelarger streams fluctuates much more widely,ranging from 32°F at least for brief periodsin winter, to about 85°F occasionally duringThe quantity of suspended sediment transportedby streams in the basin is negligible,though amounts large enough to be troublesomemay occur locally at times.The total amount of water used In theShetucket Rlver basin for all purposes during1961 was about 5,810 million gallons~ which isequivalent to 208 gpd per person, Public watersystems supplied the domestic needs of nearlyhalf the population of the basin; 10 systemswere sampled, all of which provided water ofbetter quality than the U.S. Public Health Servicesuggests for drinking water standards.

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