SOURCE AND SIGNIFICANCE OF CHLORIDE IN NATURAL WATERS: 

 NEW HAMPSHIRE AS A CASE HISTORY 



by 

 Francis R. Hall 



INTRODUCTION 



Chloride is a very mobile but chemically inactive constituent in natural 

 waters. 2 For this reason, chloride is useful as a tracer and as an indicator of 

 potential problems although it is not harmful to humans except at fairly high 

 concentrations. The commonly accepted drinking water standard of 250 

 milligrams per liter (mg/£) is basically a taste threshold, people can drink up to 

 1000 mg/£ with little difficulty. However, other elements such as sodium and 

 heavy metals which may accompany chloride can be harmful at fairly low 

 concentrations. Also, chloride can contribute to corrosion and vegetational kills. 



Particular advantages for the study of chloride are: 



1. Data for many years are likely to be available in the files of various 

 agencies; 



2. Little change in analytical techniques, so data from different times should 

 be comparable; 



3. Natural sources can generally be identified. 



Chloride in the dissolved or ionized form is of major concern herein; however, 

 the following conversion factors for the two major salt compounds referred to in 

 the text may be of interest: 



sodium chloride (weight or concentration) x (0.607) = 

 chloride (weight or concentration) 



calcium chloride (weight or concentration) x (0.639) = 

 chloride (weight or concentration) 



The concentration unit used in this report is the milligram per liter (mg/£,) 

 except for solid salt where the part per million (ppm) is used. All weights are 

 given in terms of the short ton which is equal to 2,000 pounds. 



The material on which the present paper is based has come mainly from a 

 research project entitled "Preliminary Investigation of Water Quality of New 

 Hampshire with Emphasis on Chloride and Selected Minor Constituents". The 

 intent herein, however, is to consider the source and significance of chloride in 

 natural waters in a broader sense and to treat New Hampshire as a case history. 

 The general method of approach is to consider regional aspects and to avoid 

 individual or local problems. 



■'^ Professor of Hydrology, Institute of Natural and Environmental Resources, University of 

 New Hampshire 03824 



2j. D. HEM, STUDY AND INTERPRETATION OF THE CHEMICAL CHARACTER- 

 ISTICS OF NATURAL WATERS 170-175 (U. S. Geological Survey Water-Supply Paper 

 1473, 2nd ed. 1970) (hereinafter cited as HEM). 



