SOURCES OF CHLORIDE 



In order to utilize and interpret chloride data in any meaningful way, it is 

 first necessary to establish what the normal values of chloride concentrations are 

 naturally. These values provide a baseline for evaluating changes which may be 

 attributed to human activity. The second thing that is needed then is to identify 

 the activities and assess the incremental values arising from them. 



NATURAL SOURCES 



Potential natural sources include atmospheric precipitation, dry fallout, rock 

 weathering, and saline water. Only the first two are of much importance to New 

 Hampshire or to most of the northeastern United States; however, the others can 

 be of considerable importance elsewhere. 



Atmospheric Precipitation and Dry Fallout 



The^ quantitative importance of chloride from atmospheric precipitation and 

 dry fallout varies with climate and distance from the ocean. For example, 

 considerable chloride in surface waters comes from the ocean in the southeastern 

 and northeastern parts of the United States2a, 3 whereas only a small amount 

 does in the southwestern U.S.'* With the ocean as a major source, lines of equal 

 chloride concentration (isochlors) can be expected to approximately parallel and 

 decrease inland from the ocean. This type of trend is shown in Figure 1 where 

 concentrations are about 10 mg/£ near the ocean and drop to less than one 

 inland. A comparable picture for Massachusetts is given in Motts and Saines^ and 

 for all of New England and New York in Jackson.6 



A difficult question to answer is the amount of chloride which is dissolved in 

 atmospheric precipitation and the amount which occurs as dry fallout during 

 precipitation-free periods or is washed out of the atmosphere during precipita- 

 tion. Even if chloride in rain and snow is mainly recycled sea salt this need not 

 be -the case for dry fallout which can include material extracted from dust 



2aA. W. GAMBELL & D. W. FISHER, CHEMICAL COMPOSITION OF RAINFALL, 

 EASTERN NORTH CAROLINA AND SOUTHEASTERN VIRGINIA K9 (U.S. Geo- 

 logical Survey Water-Supply Paper 15 35-K, 1966). 



^F. J. PEARSON, JR. & D. W. FISHER, CHEMICAL COMPOSITION OF ATMOS- 

 PHERIC PRECIPITATION IN THE NORTHEASTERN UNITED STATES P5-P8 (U.S. 

 Geological Survey Water-Supply Paper 1535-P, 1971). 



"•"HEM 171. 



^W. S. MOTTS & M. SAINES, THE OCCURRENCE AND CHARACTERISTICS OF 

 GROUND-WATER CONTAMINATION IN MASSACHUSETTS FIGURE 2 (University 

 of Massachusetts, Water Resources Research Center 7, 1969). 



^D. D. JACKSON, THE NORMAL DISTRIBUTION OF CHLORINE IN THE NATURAL 

 WATERS OF NEW YORK AND NEW ENGLAND PLATE 10 (U.S. Geological Survey 

 Water-Supply Paper 144, 1905). (hereinafter cited as JACKSON). 



