City of Bend Water Supply Contact Time Basin - Executive Summary |
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Executive Summary for the Water Supply Contact Time Basin Accidental Release Prevention Policy and Emergency Response Policy The City of Bend Water CT Basin has a redundant chlorine sensitive alarm system operating 24 hours per day connected via telemetry to a paging call system. The alarm system sensor is set to detect 3 ppm chlorine. The site also has visual and audible alarms that engage with the chlorine sensors. The containers, piping, valves and dispensers are of the highest manufacturing quality. Quality control is performed on site quarterly and encompasses all equipment used in the chlorinating process to ensure proper prevention of a release and efficient response should a release occur. Written policy thoroughly discusses all maintenance and minor leak response procedures. Training of all personnel is periodic and on going. Facility Description and Regulated Substance Identification The facility is a publicly owned and operated water treatment facility that uses ch lorine gas for disinfecting approximately 11.0 mgd potable water. Chlorine gas is stored in a concrete block building located on the north east corner of a 11 acre fenced compound. Entrance to the compound is restricted and the chlorine building is kept locked at all times. A maximum of 5 - 1 ton full cylinders are stored within the chlorine building. Only 1 ton cylinder is in use at any one time. Worst case Release Scenario The EPA RMP*Comp program was used to estimate the distance to the end point if a catastrophic release of chlorine should occur. Assuming an accident occurred while off loading a 1 ton cylinder from the delivery truck, the following scenario was developed. 1 ton of chlorine gas was released at a rate of 200 pounds per minute over a 10 minute period. The result is an off site exposure to chlorine gas above the toxic end point of 0.0087 ppm to a radius of 1.3 miles. No passive mitigating measures were considered to be in effect during this scenario. Al ternative Release Scenario The accident history for the Water CT Basin was reviewed to determine the most realistic alternative scenario to consider. There has not been a catastrophic release of any kind since the start up of the City of Bend's Water CT Basin in 1991. Therefore, a "what if " scenario was developed using worst case wind speed, temperature, and gas stability data. The passive mitigation measures include a closed building. Active mitigating measures include vacuum/pressure regulating valves, and automatic exhaust fans. The "what if" assumption that was used is as follows. A pipe attached to the chlorinator valve cracked allowing the gas in the piping to be released. This equals 3.74 pounds to be released over a period of 10 minutes. The toxic end point of 0.0087 ppm chlorine is reached at 0.1 miles. General Accidental Release Prevention Program The City of Bend Safety Policy requires that all employees expected to work with chlorine gas as part of their job duties follow OSHA/PSM rules. In addition, initial training and continuous refresher training is mandatory at a minimum of every 3 years and after any revisions to a process. Alarm systems are checked for operational integrity continuously. All release incidents regardless of severity are reviewed by a team composed of management and staff who are actively involved with the operation of the equipment. Mechanical integrity of all equipment and piping used in the chlorine distribution system is checked annually. A compliance audit is performed every 3 years. The audits shall insure that all the accidental release prevention measures are being conducted in a timely manner, that action is taken in response to all suggestions to improve release prevention, and that documentation is recorded. Five Year Accident History There have not been any accidents resulting in off site releases of chlorine gas in the past 5 years. There have not been any since the start up of the facility in 1991. Any release due to valves leaking or other minor leaks have been attended to in a safe and timely manner. Emergency Response Program Any catastrophic releases of chlorine gas will result in a response by the Bend Fire Dept. who will take command of the scene. Operation staff is expected to train and respond to minor releases that occur process equaipment. A chlorine alarm occurring while non-routine activity is being conducted shall be evaluated by trained operation employees following the safety procedure adopted by the City. The degree of the release will be determined by the trained employees witnessing the release. If it is determined that a release is beyond their ability to repair given the safety policy guidelines, the City of Bend Fire Dept shall be called to take command. The Bend Fire Dept. conducts practice drills on a semi-annual basis for the CT Basin. Public notification of a catastrophic release shall be through the County Sheriff's Dept. who uses the Emergency Broadcast System and door to door evacuation. Planned Changes to Improve Safety Any and all suggestions made by operation staff will be considered and action taken will be documented including decisions to make no change. At this review, the plan to install an intrusion alarm for the chlorine building is being considered along with fire and smoke detectors. |