SCWA: Airport SZTP - Executive Summary |
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Sonoma County Water Agency (SCWA) operates the Airport Treatment Plant, and this facility is covered by the California Accidental Release Prevention (Cal-ARP) program and the EPA's Risk Management Plan (RMP) regulations because it has chlorine onsite in excess of the RMP threshold quantity. The Airport Treatment Plant is a wastewater treatment plant located on Aviation Boulevard near the town of Windsor, Sonoma County, California. It is SCWA's policy to comply with the Cal-ARP and RMP regulatory requirements. SCWA employees, supervisors and managers are all responsible for complying with these regulations. Agency employees and managers are provided with training to familiarize them with their requirements and responsibilities. SCWA has developed a process safety and risk management program that documents the policies pertaining to the prevention of accidental releases. In addition, SCWA has conducted technical studies such as the Process Hazards Analysis and the Offsite Consequence Analysis to identify and evaluate potential hazards associated with the use of chlorine at the Airport Treatment Plant. SCWA has emergency procedures and an Emergency Operations Plan (EOP), and these are coordinated with Sonoma County Department of Emergency Services. A management system is in place for implementing the RMP and Cal-ARP regulations. This system defines the scope and purpose for each program element, procedures for implementation, roles and responsibilities, and the record-keeping requirements. The SCWA Safety Officer has responsibility to coordinate the implementation of the risk management program. Delegated responsibilities are outlined in the SCWA's written programs. At the Airport Treatment Plant, chlorine is used in the wastewater treatment process for odor control and disinfection. Chlorine is supplied in one-ton containers, which are stored inside a chlorine building. The room has capacity to store five one-ton containers of chlorine (10,000 pounds). Adminis trative controls are in place to ensure that the maximum number of containers never exceeds this number. In addition to the chlorine containers, the chlorination system includes vacuum regulators, chlorinators and chlorine injectors, all connected by industry-standard pvc piping. The chlorine flow rate is set at the chlorinator to dose the correct amount of chlorine at the point of application. The design is inherently safe with the vacuum regulator placed directly on the ton container. This means that if there is any damage to the piping system downstream there will be a break in the vacuum, and the chlorine flow will stop at the regulator. All chlorine equipment is housed inside the chlorine building. Leak detectors have been installed to monitor for chlorine leaks. If chlorine is detected, it triggers a local alarm and relays an alarm signal to the SCWA's Operations Center in Santa Rosa. In developing the Offsite Consequence Analysis (OCA), the approach taken was to follow the overall guidance provided by EPA and the American Water Works Association in the Model RMP for Water Treatment Plants. This model plan was used to help select the worst-case and alternative release scenarios, and to evaluate the hazard distances for both scenarios. For the worst-case scenario, a one-ton container was used to determine the release quantity (2,000 pounds). This is the single largest vessel in the chlorine process. For the worst-case release to occur, there would have to be a container failure, allowing the entire contents to become airborne within ten minutes. Using the Model RMP tables, the distance to the chlorine toxic endpoint for this scenario would be 3.0 miles, assuming rural terrain. This type of release is extremely unlikely to occur, as it takes no account of the many safety features inherent in the design, operation and maintenance of the system, described above. For the alternative release scenario, the scenario selected from the Model Plan was a release from a sheared line about a quarter of an inch in diameter, connected to the container. Using the Model RMP tables, the distance to the toxic endpoint for this scenario would be 0.56 miles, assuming rural terrain. For the worst-case scenario, the population within the vulnerable zone circle is over 5,300, but for the alternative release scenario the number is less than 200. The SCWA has identified the public and environmental receptors within these zones, and those within the alternative release zone are addressed in the emergency response plan. During the last five years, there have been no accidents involving chlorine that resulted in any offsite impacts, and there have been no serious injuries or fatalities onsite. SCWA has implemented a comprehensive prevention program to minimize the potential for a catastrophic release of chlorine at the Airport Treatment Plant. Process safety information is available to employees, and a Process Hazards Analysis (PHA) has been conducted. E xternal events were considered in the PHA, and a seismic assessment has also been conducted. Recommendations made by the PHA team to improve safety are being addressed. Following any system modifications, a pre-startup safety review is conducted. A management of change procedure has been implemented. Standard Operating Procedures (SOPs) have been developed for normal and emergency operations. The SOPs provide written operating instructions for operating the chlorine system, and they include procedures for container deliveries and container change-outs. Equipment inspections, testing and maintenance activities are performed on a routine basis and documented in a computerized maintenance management system (MAXIMO). All operators are state-certified treatment operators, and all operators and mechanics are required to be trained in the SOPs for the chlorine system. A compliance audit procedure has been developed for the risk management program, and this will be used every three years to verify compliance with the Cal-ARP and RMP regulations. The SCWA investigates any incident or accident that results in the release of a reportable quantity of chlorine. Incident investigation procedures include root cause analysis. SCWA operators and mechanics are trained as first responders under the HAZWOPER standard for emergency response. However, only members of the HazMat team are qualified to respond to an emergency. Guidance is provided to the operators and mechanics to help them distinguish between an incidental release and an emergency. In the event of an emergency, the procedures are to notify the response agencies, evacuate to a safe area, and assess the cause of the release, if this can be done safely. The emergency response plan has been coordinated with the local response agencies, and SCWA will cooperate with these agencies to coordinate any offsite response that may be required in an emergency. Following the PHA conducted in February 1999, SCWA is implementing reco mmendations to improve safety. These improvements include equipment modifications, improvements to the detection and monitoring system, and revisions to the operating and maintenance procedures. Recommendations developed in any future MOC review will be included in the action tracking system to ensure they are addressed in a timely manner. SCWA is continually looking at new technologies to improve safety and to reduce or eliminate the use of chlorine gas. For example, a scrubber system will be installed at the Airport Treatment Plant by the end of year 2000. In summary, the design of the chlorine system at the SCWA Airport Treatment Plant, and the implementation of the safety and risk management programs provide a high level of assurance that the risks associated with the use of chlorine are effectively managed. |