Danvers Water Treatment Plant - Executive Summary

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The Town of Danvers Water Treatment Plant, located in Middleton, MA, treats on average 3.5 million gallons per day.  The facility operates two shifts most of the year and three shifts during periods of high water demand.  One step in the water treatment process is chlorination in which chlorine is used as a disinfectant to treat both water entering the treatment facility and as a final step before the water enters the distribution system.   The amount of chlorine used varies seasonally as a function of the water quality entering the treatment plant and the demand for water. 
The chlorination process consists of two 1-ton cylinders with an automatic switching mechanism, from the empty to the full cylinder.  The process also includes up to 4 additional full cylinders in storage. Chlorine is the only highly hazardous chemical used at the facility above the threshold for the RMP rules.  The facility has never had a chlorine related injury or emergency incident.   The system design incorpo 
rates several important safety features to minimize the potential for a release including: (1) only gaseous chlorine is withdrawn from the cylinders, (2) the system for injecting gaseous chlorine into the water operates under a vacuum so that if any line failed, the flow of chlorine from the cylinder would be stopped, and (3) a chlorine leak detector operates continuously in the chlorine room.   
The Town of Danvers and plant management are committed to operating the facility to provide a reliable supply of drinking water while insuring the highest standard of safety and health protection for our employees, neighbors and the environment. 
The worst case and alternative release scenarios were developed in accordance with the chlorine guidance provided in the Guidance Document for Wastewater Treatment Plants (40CFR Part 68), EPA 550-B-98-010.  As prescribed, the worst case release scenario is represented by the rupture of a 1-ton cylinder such that the entire contents are released in a  
10 minute period.  It further assumes that the release occurs outdoors.  A release of this magnitude is extremely unlikely given the design of the cylinders and precautions involved with the unloading and handling of the cylinders. 
Several alternative release scenarios were evaluated, including the failure of a valve and the rupture of a fuse plug.  The distance to the prescribed toxic endpoint for these scenarios was less than 0.10 miles or something on the order of 500 feet.    
The process hazard analysis was conducted using the checklist developed by the American Waterworks Association (AWWA).   As safely as the plant is now operated, the process hazard analysis identified additional measures that could be instituted to further reduce the potential for any accidental release.   All identified changes will be in place by September 30, 1999.  Most of the changes are administrative in nature and consist of enhanced documentation of training, maintenance and other procedures.  One imp 
ortant element will be a joint emergency training exercise with the Middleton Fire Department which serves as the Local Emergency Planning Committee (LEPC) for the facility.   
This risk management plan demonstrates commitment of the Town of Danvers and the Water Treatment Plant staff to minimize the risk to employees, the public and the environment through a program of continuous improvement and focus on safety and health.
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