Water resources inventory of Connecticut Part 2: Shetucket River Basin

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 the
basin in the Shetucket River represents the total
amount of water potentlally available for use by man.
Annual runoff from the entire basin above the
Quinebaug River has ranged from about 13 to 42
inches since 1929, and has averaged about 23
inches (300 billion gallons). Although runoff
indicates the total amount of water potentially
available, it is usually not economically or
legally feasible for man to use all of it. On
the other hand, with increased development, It
is possible that some water will be reused several
times.
The water available may be tapped as it flows
through the area or is temporarily stored in
streams, lakes, and aquifers. The amounts that
can be developed vary from place to place and
time to time, depending on the amount of precipitation,
on the size of drainage area, on the
thickness, permeability and areal extent of aquifers,
and on the variations in chemical and
physical quality of the water.
Differences in streamflow from point to
point are due primarily to differences in the
proportion of stratified drift in the drainage
basin above each point, which affect the timing
of streamflow, and to differences in precipitation,
which affect the amount of streamflow.
Information on streamflow from gaging stations
may be extended to ungaged sites by accounting
for both of these factors ,in calculations.
Future floods on the upper Willimantic
River or the Shetucket River are unlikely to
cause major damage so long as buildings are not
constructed below the highest flood elevations to
be expected with the present system of reservoirs
for flood control.
Ground water can be obtained from wells
almost anywhere in the Shetucket River basin, but
the amount obtainable from individual wells at
any particular point depends upon the type and
water-bearing properties of the aquifers present.
For practical purposes, the earth materials in
the basin comprise three aquifers--stratified
drift, till, and bedrock,
Stratified drift is the only aquifer generally capable of yielding more than 100 gpm to
individual wells. This aquifer covers about 18
percent of the basin and occurs chiefly In lowlands
where it overlies till or bedrock. Coefficient
of permeability of the coarse-grained unit
of stratified drift averages about 1,900 gpd per
sq ft. Drilled, screened wells tapping this unit,
are known to yield from 200 to 675 gpm. Dug wells
in coarse-grained stratified drift should supply
at least 2 gpm per foot of drawdown over an 8-hour
period. Fine-grained stratified drift has an
average coefficient of permeability of about 400
gpd per sq ft and can usually yield to dug wells
supplies sufficient for household use.
Till and bedrock are widespread in extent but
can provide only small to moderate water supplies.
Till is tapped chiefly by dug wells; permanent
supplies of more than 200 gpd can be obtained from
dug wells at a majority of sites in areas of till,
but there are many sites where the till is too
impermeable or too thin to provide this much water
throughout the year. The coefficient of permeability of till ranges from about 0.2 gpd per sq ft to
55 gpd per sq it. Bedrock Is tapped chiefly by
drilled wells, about 90 percent of which will
supply at least 3 gpm. Very few, however, will
supply more than 50 gpm.
The amount of ground water potentially available
In an area depends upon the amount of groundwater
outflow, the amount of ground water in storage,
and the quantity of water available by Induced
infiltration from streams and lakes. From
data on permeability, saturated thickness, recharge,
yield from aquifer storage, well performance, and
streamflow, preliminary estimates of ground-water
availability can be made for any point in the
basin. Long-term yields estimated for 15 areas
especially favorable for development of large
ground-water supplies ranged from 1.3 to 61.8 mgd.
Detailed site studies to determine optimum yields,
drawdowns, and spacing of individual wells are
needed before major ground-water development is
undertaken In these or other areas.
The chemical quality of water in the Shetucket
basin Is generally good to excellent. Samples of
naturally occurring surface water collected from
32 sites contained less than 61 ppm of dissolved
solids and less than 32 ppm of hardness. Water
from wells is more highly mineralized than naturally
occurring water from streams. Even so only
7 percent of wells sampled yielded water with more
than 200 ppm of dissolved sol-ids and only 9 percent
yielded water with more than 120 ppm of hardness.
Even in the major rivers, which are used to
transport industrial waste, the dissolved mineral
content is less than 100 ppm and hardness rarely
exceeds 40 ppm. One notable exception occurs in
the lower reaches of Little River where an
exceptional amount of industrial waste is discharged
into the river near Versailles. This
waste is particularly noticeable during low
streamflow.
Iron and manganese In both ground water and
surface water are the only constituents whose concentrations
commonly exceed recommended limits for
domestic and industrial use. Most wells in the
basin yield clear water with little or no iron or
manganese, but distributed among them are wells
with ground water that contains enough of these dissolved
constituents to be troublesome for most uses.
iron concentrations in naturally occurring
stream water exceeded 0.3 ppm under tow-flow conditions
at 20 percent of the sites sampled. Large
concentrations of iron in stream water result
from discharge of iron-bearing ground water or
from the discharge of water from swamps. In
swamps the iron is released largely from decaying
vegetation.
Ground water more than 30 feet below the
land surface has a relatively constant temperature,
usually between 48°F and 50°F. Water
temperature in very shallow wells may fluctuate
from about 38°F in February or March to about
55°F in late summer. Water temperature in the
larger streams fluctuates much more widely,
ranging from 32°F at least for brief periods
in winter, to about 85°F occasionally during
The quantity of suspended sediment transported
by streams in the basin is negligible,
though amounts large enough to be troublesome
may occur locally at times.
The total amount of water used In the
Shetucket Rlver basin for all purposes during
1961 was about 5,810 million gallons~ which is
equivalent to 208 gpd per person, Public water
systems supplied the domestic needs of nearly
half the population of the basin; 10 systems
were sampled, all of which provided water of
better quality than the U.S. Public Health Service
suggests for drinking water standards.