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Safer Drinking Water and Wastewater Treatment

Safer methods water and wastewater treatment facilities could use include alternative disinfectants to chlorine gas, such as liquid bleach and ultraviolet light.

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Fifteen of the 101 highest-hazard chemical facilities are water utilities. These 15 facilities together endanger some 17 million people. Eleven of these facilities treat drinking water using chlorine gas. Chlorine disinfects water at the treatment plant and in water distribution pipes. These facilities can instead use alternate disinfectants to chlorine gas, including liquid bleach, ozone without storage, or ultraviolet light.

At least 160 large U.S. cities already use liquid bleach. A previous CAP report also identified nearly 100 water plants that have converted off chlorine gas since 1999. Several of the drinking water facilities in the top 101 use anhydrous ammonia gas in addition to chlorine gas. These facilities can switch from anhydrous to aqueous ammonia, which has far less potential to drift off site.

The other four water utilities are wastewater treatment plants that use both chlorine gas and sulfur dioxide gas. These water plants disinfect with chlorine gas and then remove residual chlorine with sulfur dioxide gas. Wastewater plants commonly replace chlorine gas with liquid bleach, and replace sulfur dioxide gas with sodium bisulfite, or avoid both by switching to ultraviolet light. Roughly two-thirds of large U.S. wastewater utilities already use a disinfectant other than chlorine gas or plan to stop using chlorine gas.

Expert reviews convened by at least three government agencies identify chlorine gas in water treatment as a preventable security concern. Some water utilities are converting off chlorine gas—pressed by requirements for chemical security, worker safety, risk management, hazard communication, emergency planning, and other obligations—but the pace of change is slow. Approximately 1,650 drinking water plants and 1,000 wastewater plants still report extremely hazardous substances, primarily chlorine gas, under the EPA’s Risk Management Planning program.

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