City of Groton, Water Treatment Facility - Executive Summary |
|
The City of Groton accidental release prevention policy and process safety management (PSM) program involves an approach that combines technologies, procedures and management practices made up of both union and management representatives. All applicable prevention procedures of the U.S. Environmental Protection Agency's (EPA) Risk Management Program will be adhered to. The City of Groton's PSM program and emergency preparedness plan, including an emergency contingency plan and an oil spill prevention control and countermeasure plan, involve preparation, evacuation and notification procedures and coordination of emergency response with the Southeastern Connecticut Emergency Response Task Force and the local fire department. Groton Utility's water treatment plant (WTP) was originally built in 1939, with plant improvements from 1950 through 1990, upgrading their plant from 2 to 14 million gallons per day. The Groton WTP is located at 1268 Poquonnock Road. The WTP contains a chlorine building consisting of a chlorine storage room, which contains liquid chlorine ton cylinders, and a chlorinator room, which mixes the chlorine with finished water at a rate of 2 ppm and regulates the flow of chlorine to various stages of the treatment process. Groton is equipped with safety equipment and controls, including continuous chlorine monitoring for leak detection and a scrubber system for the chlorine building. Within the storage room, two one-ton cylinders are on-line and up to eight one-ton cylinders may be in reserve. The system is also equipped to detect a loss of vacuum in the feed system. The water treatment plant's offsite consequence analysis includes consideration of two release scenarios involving chlorine. These scenarios are identified as "worst-case" and "alternative". EPA states that for the worst-case scenario "the owner or operator shall assume that the maximum quantity in the largest vessel is released as a gas over 10 minutes". The worst-case scenari o is to result from an unspecified failure. EPA defines the alternative scenario as one that is "more likely to occur that the worst-case scenario". The purpose of the release scenarios is to determine the distance to "toxic endpoint", which is defined by the American Industrial Hygiene Association as the "maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action". Additionally, the residential population within a circle, which is made using the distance to toxic endpoint as its radius, has to be defined as an estimate of the population potentially affected. For the purpose of determining worst-case and alternative release scenarios distance to toxic endpoint, the water treatment plant utilized EPA's RMP*Comp software and EPA's "Risk Management Program Guidance for Wastewater Treatment Plants". The worst-case release scenario at the WTP involves a failure of a one-ton cylinder. The distance to toxic endpoint was determined to be 1.3 miles and an estimate of the residential population potentially affected of 6,000 was obtained. The water treatment plant used, as an alternative release scenario, the rupture of a 1-inch pipe which carries the gaseous chlorine from the ton cylinder to the chlorinator room. Groton's safety systems for the chlorine building include constant chlorine monitoring for leak detection, a scrubber to handle major leaks, safety air packs, respirators and repair kits for minor incidents, and an alarm system identifying a loss of vacuum in the chlorine injection system. For purposes of the alternative release scenario, the use of the scrubber for mitigating purposes is estimated to decrease the release by 90%. The scrubber is designed to handle a complete cylinder with no release to the outside. The distance to toxic endpoint for the alternative scenario was determined to be 0.1 mile and an estimate of the residential population potentially affected to be zero. The general City of Groton's emergency contingency plan and PSN program for an accidental release are based on training of operators, implementation of preventive maintenance, auditing and inspection programs, continual review and upgrade of process and safety equipment, use of accurate and effective operating procedures (developed with the participation of the operators), and execution of periodic hazard reviews of equipment and procedures. No accidental releases of chlorine have occurred at the Groton WTP in the past five years. The water treatment plant has coordinated its emergency response procedures with City of Groton Fire Department and the Southeastern Connecticut Emergency Response Task Force. Procedures have been developed for the effective and timely notification of response personnel and the community and for the safe evacu ation of employees. |