CHLORIDE IN NEW HAMPSHIRE 



A useful way to illustrate what can be done with chloride information is to 

 make approximate chloride balances for New Hampshire at two different times, 

 1920 and 1970, and to consider what happened during the intervening period. 

 Additional insights may be obtained from examples of chloride change in surface 

 water and ground water. 



STATEWIDE BALANCE, 1920 



It is assumed for purposes of this paper that Figure 1 gives a reasonable 

 picture of "natural" chloride distribution in New Hampshire and that 1920 is a 

 reasonable year for a "natural" chloride balance. True natural distribution of 

 chloride in the state probably can never be determined because New Hampshire 

 has been settled for a long time, and data are available for only a short, recent 

 period. Nevertheless, human activities are not likely to have had much influence 

 except locally before the Civil War or even later. Where the data exist, a town by 

 town comparison shows little or no change between data given by Jackson^^at 

 the turn of the century and the 1918-1924 data collected for the present study. 



By 1918, however, there is definite evidence for unusually high chloride in 

 some drinking water, mainly from wells. The likely source of chloride is 

 probably a cesspool or perhaps in a few cases calcium chloride for dust control. 

 Such high values were not used in preparation of Figure 1, but the possibility 

 still exists that some of the higher values on the map particularly in the southern 

 part of the state reflect human influences. Where possible, data used on Figure 1 

 are from municipal or industrial supplies and from public institutions. To fill in 

 gaps, however, data from private, usually home supplies, are used. Also, only 

 ground-water data are used where possible. In a few cases lakes are used, but not 

 streams. 



The approximate chloride balance for 1920 is given in Table 1. The balance is 

 based on the simple assumption that annual inflow equals annual outflow plus or 

 minus a change in storage. The implicit assumption is made that the residence 

 time of chloride and water is one year, and that the system is in a more or less 

 steady state condition so that the change in storage is negligible. These 

 assumptions pose few problems for 1920 except for a possible slight increase in 

 storage occurring due to human influence. 



The precipitation and runoff figures are statewide averages given by 

 McGuinness.^"* The difference between precipitation and runoff of 20 inches 

 represents the loss of water by evaporation and use of water by vegetation. As 

 this is about 50 percent, chloride concentration in rainfall- can be expected to 

 double after reaching the earth's surface. Therefore, if average chloride in 1920 

 in the waters of the state was one mg/£, then chloride in precipitation should 



^^JACKSON 15-18. 



^"^MCGUINNESS, THE ROLE OF GROUND WATER IN THE NATIONAL WATER 

 SITUATION 524 (U.S. Geological Survey Water-Supply Paper 1800, 1963). 



