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Almost all natural waters contain chloride and sulfate ions. Their concentrations vary considerably according to the mineral content of the earth in any given area. In small amounts they are not significant. In large concentrations they present problems. Usually chloride concentrations are low. Sulfates can be more troublesome because they generally occur in greater concentrations. Low to moderate concentrations of both chloride and sulfate ions add palatability to water. In fact, they are desirable for this reason. Excessive concentrations of either, of course, can make water unpleasant to drink.
Chloride is commonly found in streams and wastewater. Chloride may get into surface water from several sources including:
• Wastewater from industries and municipalities
• Wastewater from water softening
• Road salting
• Agricultural runoff
• Produced water from gas and oil wells
The EPA Secondary Drinking Water Regulations recommend a maximum concentration of 250 mg/1 for chloride ions and 250 mg/1 for sulfate ions (expressed as Cl- and S04--, not as CaC03).
Sulfate is a constituent of TDS and may form salts with sodium, potassium, magnesium, and other cations. Sulfate is commonly found in nature and can be present at concentrations of a few to several hundred milligrams per liter. Water containing calcium sulfate ions is likely to have a characteristic taste ... somewhat bitter and astringent. In fact, it has been compared to the way dissolved gypsum might taste in water. When 30 to 40 grains per gallon of calcium sulfate are dissolved in water, most people can detect the taste.
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