University of Connecticut OpenCommons@UConn Special Reports Connecticut Institute of Water Resources July 1968 The Quality of Connecticut's Surface Waters Chester E. Thomas Jr. USGS Follow this and additional works at: https://opencommons.uconn.edu/ctiwr_specreports Recommended Citation Thomas, Chester E. Jr., "The Quality of Connecticut's Surface Waters" (1968). Special Reports. 39. https://opencommons.uconn.edu/ctiwr_specreports/39 THE QUALITY OF CONNECTICUT'S SURFACE WATERS Report No. 6 July 1968 INSTITUTE OF WATER RESOURCES The University of Connecticut THE QUALITY OF CONNECTICUT'S SURFACE WATERS CHESTER E. THOMAS, JR. Hydrologist United States Geological Survey Hartford, Connecticut Expenses involved in publishing this Report of the Institute of Water Resources were met with funds provided by the United States Department of the Interior as authorized under the Water Resources Research Act of 1964, Public Law 88-379. FOREWORD One of the continuing activities of the Institute of Water Resources has been to sponsor lectures, open to the public, on a broad range of topics relating to water resources. In order to develop a thorough understanding of and a sound basis for planning the proper development and use of water, it first is necessary to understand the situation as it now exists. In this regard, the Institute was pleased to sponsor the lecture given on October 18, 1967 in which Mr. C. E. Thomas, Hydrologist with the U. S. Geological Survey in Hartford, discussed the quality of surface water in Connecticut. Quite properly, Mr. Thomas began his lecture by describing the hydrologic cycle and the effect which man has on water quality. He then described the comprehensive water quantity and quality survey which the U. S. Geological Survey has undertaken in coopera- tion with the Connecticut Water Resources Commission and discussed details of what is known about selected basins including those of the Thames, Norwalk, Housa- tonic and Connecticut Rivers. His conclusion that "the chemical quality of most surface waters in the state if good" is heartening to all citizens. It should be recognized, however, that there is room for substantial improvement of water quality, especially in certain areas of the State. This must be accomplished for the proper future development of Connecticut. We are pleased to publish Mr. Thomas' lecture as this report of the Institute. William C. Kennard Director Institute of Water Resources THE QUALITY OF CONNECTICUT'S SURFACE WATERS WATER QUALITY AND ENVIRONMENT 1 by Chester E. Thomas, Jr. 2 Water, one of our most important natural resources, flow when most of the water is the less mineralized is a dynamic resource. The endless movement of water overland runoff. Under natural conditions the dissolved- from the clouds to earth and back again is referred to as solids content of a stream during intermediate-flow the hydrologic cycle or water cycle. Water, with its conditions represents a blending of the quality of both unique ability to dissolve more substances than any the ground-water runoff and the direct overland runoff. other liquid can dissolve, is unable to remain chemically This content varies according to the streamflow contri- unchanged as it moves through the various phases of the bution from each source. Comparison of the average hydrologic cycle. What changes occur to the quality of chemical character of stream water during periods of water under natural conditions? Water that evaporates high flow with the chemical character of precipitation from the land and water surfaces and passes as vapor suggests that a considerable part of the dissolved-solids into the atmosphere is relatively pure. As water vapor concentration of overland runoff is already present by condenses to form rain, snow, sleet, or hail, it incorpor- the time the water reaches the land surface. ates tiny particles of dust, salt spray from the ocean, and During long dry periods, the flow of streams is other particulate matter from the air. These particles maintained by ground-water runoff. Consequently, themselves contain mineral matter dissolved from the streams generally reflect the chemical character of air, and the water picks up additional mineral content ground water during dry periods. The quality and from the gases which make up the atmosphere, including movement of ground-water are influenced by the charac- carbon dioxide, nitrogen in various forms, and sulfur ter of the water-bearing material thru which it passes. dioxide. Thus, even as it starts its journey to the land Streams may originate in one geologic setting but may surface, water is no longer "pure." Generally, precipita- be influenced by ground-water contributions from other tion is slightly acidic and low in dissolved-solids content. geologic environments before the stream reaches its The dissolved-solids concentration of the portions of mouth. Connecticut is underlain essentially by 3 rock water that reach the land surface and flow directly types: (1) noncarbonate crystallines (granite, gneiss and across the surface to discharge outlets in streams schist) in the eastern and western uplands, (2) carbonate generally does not greatly exceed the dissolved-solids crystallines (dolomitic and calcitic marble) in the west- concentration of precipitation because of the short ern part of the State, and (3) in the Connecticut Valley, period of time the water is in contact with the rocks and principally sedimentary rocks (sandstone and shale) as soil on the land surface and the general absence of shown on figure 1. In the eastern and western uplands readily soluble material. the noncarbonate crystallines are chemically similar. Water that percolates into the ground has much more Waters issuing trom these locales are low in dissolved opportunity to dissolve mineral matter from rock solids and calcium, magnesium hardness. The carbonate materials than water which flows directly across the land terranes yield ground water that is high in pH, hardness, surface. Accordingly, ground water contains more dis- bicarbonate, and dissolved solids. Most samples of solved solids than does rain water or water in streams. ground water associated with the sandstones, shales, and Most of the time, water in streams is a mixture of associated trap rock are of the calcium-sulfate type overland runoff and more highly mineralized ground- having a high dissolved-solids concentration. Most of the water runoff. For this reason, streams generally contain State is covered by the mantle of glacial drift. The glacial the greatest concentration of dissolved solids during material has been derived from one of the parent periods of low streamflow , which time most of the materials previously mentioned and the waters draining water is ground-water runof'. Streams contain the lowest this material will have influence on the water quality concentration of dissolved solids during periods of high similar to that of the parent material. 1 Publication authorized by the Director, U.S. Geologi- 2 Hydrologist, U.S. Geological Survey, Hartford, Con- cal Survey. necticut. 5 SCAL E Carbonate Noncerbonete o10 I0 20 Miles Cryrtalline Crystalline I- Rocks Rocks THE WATER RESOURCES INVENTORY OF RIVER BASINS IN CONNECTICUT PART I Quineboug River Basin PART 6 Upper Housotonic River Basin PART 2 Shetucket River Basin PART 7 Upper Connecticut River Basin PART 3 Lower Thames and Southeastern PART 8 Quinnipiac River Basin Coastal River Basins PART 9 Farmlngton River Basin PART 4 Southwestern Coastal River Basins PART 10 Lower Connecticut. and Central PART 5 Lower Housotonic River Basin Coastal River Basins Figure I-- Index map showing locations of river basins and generalized bedrock units in Connecticut. 6 Water moving across the land surface and in the precipitation and some simply settles on the land surface stream channels dislodges particles of soil, silt, sand, and as dry fallout. These materials contribute to the dis- occasionally gravel; this material is carried in suspension solved-solids content of runoff. Precipitation contacts or is rolled along channel bottoms. Generally, sediment and dissolves the contaminants as it falls through the load increases as streamflow increases and the highest atmosphere and usually becomes more acidic. This sediment loads occur during spring thaw and following acidity increases water's solvent power and its capacity severe storms such as hurricanes, when streamflows are to dissolve mineral matter. Samples of precipitation have highest. been collected that had a dissolved-solids concentration Surface-water temperatures follow a seasonal trend in of 200 ppm (generally the mean is 25 ppm) and pH response to changes in air temperature; near freezing- values as low as 3.5. Generally sulfate is the dominant point temperature is reached during the winter months chemical constituent in precipitation. Urban and indus- and maximum water temperatures commonly occur in trial areas with low infiltration capacities yield a higher July or August. Ground-water temperatures become proportion of surface runoff during most storms than relatively constant with depth. During periods of low that from a forest or cultivated lands. Runoff from roofs flow in the summer, streams are noticeably cooler where and pavements in municipal areas adds previously the relatively cold ground water enters the channels. precipitated chemical and organic pollutants to the Salty or brackish water from Long Island Sound is dissolved-solids content. Solutions from road salt used carried upstream in the estuaries by