Brown Water Treatment Plant - Executive Summary |
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City of Durham Environmental Resources Department Brown Water Treatment Plant Risk Management Program The City of Durham Brown Water Treatment Plant is located on Infinity Road in the northeastern portion of the City of Durham, North Carolina. The water plant utilizes coagulation, settling, filtration, and chemical feed processes to treat approximately 20 million gallons of water per day, the source of which is an on-site reservoir. One of the chemicals which is used by the plant is chlorine. Chlorine is used to disinfect the water at various locations in the treatment process including dosing of the finished water as it leaves the treatment plant. Chlorine is used as a gas but stored under pressure as a liquid in 2000 pound containers. The plant has up to 60,000 pounds (30 containers) of chlorine on-site. The chlorine, drawn from a common pipe header under vacuum for additional safety, is added at a prescribed dosage rate into the water by means of a rotometer on the chlorinator, which the operator can adjust to respond to changes in water quality. As the Brown Water Treatment Plant has more than 2500 pounds of chlorine on-site, it must comply with the provisions of EPA's Risk Management Program (RMP). Also, as North Carolina is an OSHA Plan State, the plant is subject to Prevention Program 3 requirements. Additionally, the plant is subject to OSHA's Process Safety Management Program (chlorine limit of 1500 pounds). The City is committed to reducing the risk to its employees and the public of injury from the accidental release of chemicals, including chlorine gas. This commitment is exhibited through an extensive employee training and safety program, continuing maintenance on process equipment, emergency response coordination such as drills with local emergency responders, public education, and throug h written policy statements such as this RMP. A management system is in place to ensure that employees from all levels are a part of the RMP Program. A number of safety measures are in place to prevent an accidental release of chlorine gas. In addition to the vacuum delivery system which stops the flow of chlorine gas in the event of a piping or equipment failure, the chlorine container storage area and the chlorinator room are continuous monitored for any possible chlorine leaks. If a leak should occur, the operator is notified immediately through an alarm system. All major chlorination components are backed-up with on-line redundant equipment. All water treatment plant operators are trained in the handling and administering of chlorine. This training includes the use of chlorination and safety equipment, identification of potential hazards, and response to accidental releases of chlorine gas. The plant has a detailed Emergency Response Plan which outlines the response measures to be taken by plant personnel in the event of a chlorine leak. Plant personnel have been trained in the use of equipment to correct small-scale leaks. This training also includes the recognition of when additional assistance from local emergency responders such as the City Fire Department/HAZMAT squad is needed to correct the problem and notify the immediate public if necessary. City personnel including management, operators, and maintenance have conducted a process hazard analysis (PHA), a brainstorming session to identify possible chlorine release situations, causes, consequences, and identify (or recommend) safeguards and corrective actions to prevent the release from occuring. This analysis involved situations ranging from the container rupture during delivery, to chlorine equipment failure, to acts of nature. Any deficiencies in the response to a release situation were identified and a plan of action was formed to resolve the deficiency. Under EPA's Risk Managemen t Program, the City applied EPA's computer program "RMP*Comp" to determine the off-site impacts of a release of chlorine. Two scenarios were modeled. The first scenario modeled a worst-case release condition, with model parameters and criteria set by EPA. Under the worst-case scenario of the release of 200 pounds of chlorine per minute for ten minutes, an impact area of 1.3 miles around the treatment plant was identified. This radius represents the distance the chlorine vapor cloud will travel before dissipating to a point that serious injury from short term exposure will no longer occur. Public receptors in this area include an estimated residential population of 1358 people as well as churches, a rehabilitation and nursing center, a community college, an elementary school, and a recreational area. No environmental receptors meeting EPA criteria (ie. national or state parks, forests, monuments, and officially designated federal wildlife santuaries, preserves, refuges, or are as that can be identified on local U.S. Geological Survey maps) were identified within the worst-case impact area. A release of chlorine under the worst-case scenario is very unlikely. The City has a number of preventive measures in place to minimize the likelihood of such a large release including standard operating procedures and continuing training of employees on the use of container unloading equipment (the time at which a worst case scenario is most likely to occur). To reflect a more likely release situation, the City also modeled an alternative release. Under the alternative release scenario an impact area of less than a 0.1 mile radius was identified. The alternative situation involved the release of chlorine within the storage room due to a failure in the common pipe header or container piping and valves (before the vacuum regulator). The impact radius of the alternative release scenario was reduced from that of the worst-case scenario due to the smaller release rate (15 pounds per minute versus 200 pounds per minute). No public or environmental receptors were identified in the alternative release impact area, which was confined generally to the limits of the water treatment plant property. The City is pleased to report that the water treatment plant has not had an accidental release of chlorine gas meeting EPA RMP criteria in the past five years. This can be directly attributed to plant personnel's high level of effort toward safe chlorine handling and use. As noted, the Emergency Response Plan for the plant includes provisions for emergency medical treatment and procedures for the summoning of outside assistance for a large chlorine leak. Outside assistance is provided by the City of Durham Fire Department and the City HAZMAT Team. Outside responders are familiar with the plant chlorination system and have recently completed an on-site training in conjunction with plant personnel. The emergency responders will be responsible for public notification in the event of a chlorine release. The City of Durham is in the process of developing as schedule for the eventual conversion of the chlorination system at the Brown Water Treatment Plant from chlorine gas to liquid sodium hypochlorite. This work will be similar to the conversion which has been designed for the City's Williams Water Treatment Plant, the construction of which is scheduled to be completed in late 1999. The conversion to sodium hypochlorite at each plant will eliminate all off-site public and environmental impacts of a gas release and increase the level of safety for palnt personnel as well. Following the conversion, the provisions of the Risk Management Plan will no longer apply for either treatment plant. |