Bismarck Water Treatment Facility - Executive Summary |
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Introduction The City of Bismarck has submitted a Risk Management Plan (RMP) for its Water Treatment Facility (WTF) to the United States Environmental Protection Agency (USEPA) to comply with the requirements of 40 CFR Part 68, the Chemical Accident Prevention Rule, herein referred to as the "Rule". As such, the City staff have completed a comprehensive review of the risk associated with the regulated process, chlorine disinfection, at the facility. Additionally, an offsite consequence analysis has been completed and a prevention program has been developed and implemented to promote safe operation of the regulated process. Emergency response procedures have been updated and communications with the Local Emergency Planning Committee (LEPC) and Fire Department have been initiated to develop a cooperative response to potential releases at the facility. The prevention program focuses on training plant employees in safe operating and maintenance procedures and to recognize the potentia l hazards of the regulated chemical and process. Background The Bismarck WTF, located on the east bank of the Missouri River, has been in operation since 1923. The facility is owned and operated by the City of Bismarck, and has a reported treatment capacity of approximately 26 million gallons per day (MGD). The facility is a conventional treatment plant that incorporates pre-treatment, lime softening, recarbonation, conventional filtration, fluoridation, stabilization, and chlorine disinfection. Gaseous chlorine, contained in one-ton chlorine containers, is introduced into the water using a vacuum feed system. The facility stores a maximum of nine one-ton containers onsite, for a combined total of 18,000 pounds of chlorine. According to the Rule, any facility with greater than 2,500 pounds of chlorine onsite is required to develop and implement a RMP. Therefore, the Bismarck WTF chlorination system is a Risk Management-regulated process. Chlorine containers are stored in the c hlorine room, which is located in a building separate from the main treatment plant, in the central portion of the WTF site. The chlorine storage room is equipped with a ventilation system. The facility has an automatic chlorine scrubber system for gas neutralization in the event of a release. The Bismarck WTF operates the facility twenty-four hours a day, seven days per week from May 1 until mid-September and from 7:00 am until 11:00 pm, seven days per week from mid-September through April 30. The chlorine room and system components are visually inspected at least once every 2 hours during operation. When the system is not in operation, the chlorination system and all related process valves are disabled. The door to the chlorine room is locked at all times. Chlorine containers are unloaded directly into the room from the transport vehicle through bay doors located on the east side of the building. Chlorine is a toxic gas stored as a liquid under pressure. Its boiling point is -29.4?F. Chlorine is irritating and corrosive to the eyes, skin, and respiratory tract and reacts violently with easily oxidized materials. Contact with evaporating chlorine or equipment releasing flashing chlorine can cause frostbite burns. Chlorine gas is heavier than air and will travel along the ground and fill low spaces and pits by displacing air. One-ton chlorine containers are welded steel tanks with removable steel protective caps over the container valves. They are built to meet Federal specifications, and are regularly inspected and pressure tested in accordance with Federal regulations. Offsite Consequence Analysis The City staff have examined the WTF chlorination system and the potential hazards it presents onsite and offsite. The results of this analysis are presented in the Offsite Consequence Analysis (Hazard Assessment section of the RMP), which is comprised of a Worst Case and Alternate (more likely) Case Analysis. Worst Case Analysis Although the USEPA ack nowledges that the Worst Case Scenario is not a likely scenario, the Bismarck WTF staff have formulated a scenario to alert the public to the worst possible release. The Worst Case Scenario for the facility involves the release of 2,000 pounds of gaseous chlorine (the entire contents of one container) over a 10-minute period. Due to the location of the facility in an urban setting (with trees or buildings nearby to dissipate the release), and the fact that chlorine containers are unloaded directly into the chlorine room (thus, the room is a passive mitigation measure), the analysis estimated that a release of this magnitude would create a radius of influence of 0.9 miles. The radius of influence represents the distance the chlorine plume would travel from the facility, under assumed meteorological conditions, before the concentration is reduced below the Emergency Response Planning Guideline 2 (ERPG-2) level, the "toxic endpoint". The USEPA's RMP Offsite Consequence Analysis Guidan ce states the ERPG-2 concentration "is that 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 that could impair an individual's ability to take protective action." A population of approximately 5,000 resides within the radius of influence under the Worst Case Scenario. Also within this radius are residential properties, schools, churches, a golf course, a bike/walking path, national guard facility, public parks, the zoo, community bowl, riverboat landing, and the Missouri River. The USEPA requires that the radius of influence be calculated considering a wind speed of 1.5 meters per second, or 3.4 miles per hour. Historically, average wind speed in the vicinity of Bismarck is 10.2 miles per hour; thus, a release would likely disperse at a faster rate than estimated under the RMP assumed conditions. Additionally, most of the receptors within this rad ius are located uphill from the facility. The USEPA's model does not account for differences in elevation, but because chlorine is 2.4 times heavier than air, it is likely that the receptors identified in this analysis would see little or no impact from a release. Alternate Case Analysis The City Public Works staff have also formulated an alternate, or more likely, release scenario for the WTF RMP. This scenario involves a release occurring inside the chlorine room. The Bismarck WTF utilizes a vacuum-operated chlorination system. The vacuum system is, for all practical purposes, virtually fail-safe. A regulating valve is installed directly onto the chlorine container, between the container and the chlorinator. For this valve to open, a vacuum must be present on the chlorinator side of the valve. The vacuum is created by water passing through an ejector. When a vacuum is present and the valve is open, gaseous chlorine may be drawn from the container, through the valve, into t he chlorinator, and injected into the water. In the absence of a vacuum on the chlorinator side of the valve, the valve closes and chlorine cannot escape through the valve on the container. In the event of equipment failure on the chlorinator side of the valve, the valve is designed to immediately close due to the absence of a vacuum. Because the regulating valve is attached directly to the chlorine container, the potential route of escape of chlorine gas from the container is between the valve stem on the container and the regulating valve. The alternate scenario modeled for this facility involves a leak from the lead gasket between the regulating valve and the chlorine container. Each time a new container is connected to the system, a new gasket is installed. Although the gasket is checked for leaks immediately after installation, the alternate scenario assumes a small leak is not detected prior to shutdown of the system at the end of the day. The leak continues throughout the night and the entire contents of the vessel is released over a period of 137 minutes (2.3 hours). Because the vessel is inside the building with the door closed, the room acts as a passive mitigation measure and contains the release. The radius of influence for this release is 0.1-mile, which includes a public bike/walking path and the Missouri River. Although there are businesses in this radius there are no residential properties affected. Ideally, the chlorine scrubber would act to mitigate the release; however, for purpose of this analysis the scrubber is not considered because the USEPA requires that a minimum radius of influence of 0.1-mile be reported. In recognition of this potential release, the Bismarck WTF will integrate Risk Management Program training with its existing training program in an effort to increase employee awareness of the consequences of even a small release. These efforts are expected to further reduce the likelihood of such a scenario occurring. Eme rgency Response Although the potential for a chlorine release exists, the City has determined that the chlorination system is safe by all industry standards and that the potential for a release at the facility is very small. The Public Works staff are working with the LEPC and the Fire Department to prepare emergency responders in the event of a major release at the facility. The WTF staff do not respond to releases other than those that can be stopped by closing a valve and will not enter the room to stop a chlorine release if the chlorine concentration is estimated to be above safe levels. The WTF staff relies on the Bismarck Fire Department and Hazardous Materials Response Team (HAZMAT), which works closely with the LEPC to plan response procedures for a major chlorine release at the WTF. The results of the Offsite Consequence Analysis have been communicated to both the LEPC and the Fire Department. Accident History The Bismarck WTF has not had an incident in the past 5 years that resulted in injury onsite or offsite. The Bismarck WTF staff is committed to ongoing employee training to increase awareness of the potential hazards associated with the chlorination process and to further reduce the likelihood of future accidents which may result in injury and equipment or property damage. Prevention Program The day-to-day result of the Rule is the mandatory implementation of a prevention program. The intent of the prevention program is to document procedures that promote safe operation of the regulated process and reduce the potential for an uncontrolled release of the regulated substance (chlorine gas). Components of the prevention program include the assembly of safety information, the performance of periodic hazard reviews, the establishment of safe operating and maintenance procedures, updating training policies, conducting routine compliance audits, the development of an incident investigation procedure, and the formalization of a management system. Safety information, such as Material Safety Data Sheets and equipment specifications, has been compiled and attached to the RMP for easy access by employees. This information specifies the safe operating limits for regulated process equipment, and lists codes and standards that apply to the equipment. Instruction manuals for regulated process equipment are also attached to this section. A hazard review has been conducted by City personnel to identify potential hazards associated with the regulated process and chemical at the WTF. A hazard review will be performed every 5 years, or prior to implementation of a new or changed process. Operating procedures relating to normal and emergency operations of the regulated process have been updated and compiled in the RMP. Maintenance procedures have been compiled in a similar fashion. These procedures will be reviewed periodically and updated as necessary. Bismarck WTF staff have historically documented employee training. An integrated training policy has been developed and training records have been reviewed and updated to reflect the current status of all employees. New employee and refresher training will be provided periodically and documented to consistently maintain safe operating and maintenance procedures. Refresher training will be conducted every 3 years, at a minimum. A compliance review policy has been developed and compliance audits, designed to scrutinize the facility's compliance with the Rule, will be conducted every 3 years. The audits will examine the components of the Risk Management Program and the implementation of each component. An incident investigation procedure has been developed to facilitate the institution of corrective actions resulting from an incident and to provide a mechanism to help prevent future incidents from occurring. This procedure establishes a timeline for the completion of incident investigations and documents any procedure changes resulting from the investigation. Lastly, a management system that assigns direct individual responsibility for each component of the Risk Management Program has been established. This system will also be reviewed periodically and updated to reflect changes in responsibilities at the facility. Conclusion In summary, the City of Bismarck is confident that although the potential for a chlorine release at the WTF that could affect the public or the environment exists, the potential is slight. The City has examined the risks associated with the chlorine system at the WTF and has committed to the development and implementation of standard operating and maintenance procedures and comprehensive employee training to prevent chlorine releases. Further, the City has prepared for such releases by modeling release scenarios, developing response procedures, and coordinating with offsite responders. The City staff have identified additional safety measures, developed a schedule for implementation, and established a chain of re sponsibility to ensure program compliance. |