Subregion 3. Iron and manganese concentrations commonly exceed the recom- 

 mended limit for public supply use of 0.3 mg/1 and 0.05 mg/1 respectively 

 (kS) . Approximately ^0 percent of the wells tapping stratified drift and 

 crystalline bedrock, sampled by the U.S. Geological Survey, had excessive 

 concentrations of iron and/or manganese. Hard to very hard ground water 

 (hardness as CaCOn, greater than 120 mg/1) is common in the sedimentary 

 rocks of Subregion 3 and in parts of Subregions 5 and 6 underlain by bedrock 

 or unconsolidated materials composed of calcium and magnesium carbonate. The 

 distribution of dissolved solids, iron and manganese and hardness of ground 

 water and of streams under conditions of low flow have been summarized on 

 maps for this part of the study region (see Appendix C) . 



Other natural chemical constituents that are locally present in 

 concentrations exceeding U.S. Public Health Service (kS) or Connecticut 

 State Department of Health (7) recommended limits for drinking water include 

 sodium, fluoride, chloride and sulfate. Most of the reported excess concen- 

 trations of these constituents are from wells tapping the sedimentary bedrock 

 in Subregion 3. 



In the Connecticut part of the study region, ground water pH is 

 generally between 6 and 8 although values as low as h.k and as high as S.k 

 have been measured. The average ground-water temperature is approximately 

 50°F and at depths greater than 30 feet fluctuates slightly. Ground water at 

 depths of less than 30 feet however may seasonally vary in temperature by as 

 much as 20° F (27). 



The effect of man's activities on the hydrologic system, while 

 qualitatively similar to Long Island, are quantitatively different. Hydrolog- 

 ic imbalances resulting from overpumping or impairment of ground-water quality 

 are confined to within the area of a drainage basin. In addi t ion, only a 

 small part of the total water used on the north shore of Long Island Sound 

 is derived from the ground-water reservoirs. For example, in the lower Thames 

 River basin and in southwestern Connecticut approximately 5 to 10 percent of 

 the water used in the mid-1960's was from wells ( 37> 31) . 



The two principal activities that result in losses of water from 

 the ground-water reservoirs are (1) disposal of waste water originally derived 

 from wells to streams or the ocean and (2) increased direct runoff to streams 

 in urbanized areas. This loss is greatest in the urbanized coastal areas, 

 but no quantitative estimate of its magnitude has been made. 



Artificial recharge to the ground-water reservoirs is from septic 

 tanks, leaky water and sewer pipes and from streams and lakes adjacent to 

 centers of ground-water development. Artificial recharge from streams and 

 lakes is a very important factor in sustaining well yields. Most large pub- 

 lic and industrial supply wells tap stratified drift that is hydraul ical ly 

 connected to an adjacent stream. The effects of pumping induce the surface 

 water to move through the streambed material s and into the ground-water 

 reservoir. 



35 



