City of Tacoma, Central Wastewater Treatment Plant - Executive Summary |
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City of Tacoma, Central Treatment Plant Risk Management Program Executive summary The accidental release prevention and emergency response policies at our facility: It is the policy of the management of the Sewer Utility, that it's treatment plants be operated in a manner consistent with the safety of the citizens of Tacoma, as well as the that of it's employees. To that end, safeguards to prevent the accidental release of chlorine are in place in the form of safety equipment and personnel experienced in its proper operation and maintenance. It is likewise policy to reduce the risk to citizens and employees should an accidental release occur. Therefore, the quantity of chlorine stored on site is limited to 5 one ton containers. Current policy directs that, in the event of a major accidental release, the trained professionals of the Tacoma Fire Departments Hazmat Team be called to respond to the emergency. Our facility and the regulated substance handled: This facility i s a wastewater treatment plant owned and operated by the City of Tacoma's Sewer Utility. The plant is located at 2201 Portland Avenue in Tacoma, Washington. The plant treats a daily average of 26 million gallons of sewage to secondary treatment standards according to a permit issued by the Washington State Department of Ecology. Before the plants effluent is discharged to Commencement Bay, it is disinfected to meet the NPDES permit requirements for fecal coliform. The method of disinfection is by chlorination. Because of the disinfection requirement, chlorine is stored on site. Since 1998, that amount has been reduced from greater then 55 tons, to a maximum of 5 tons. This reduced amount is still greater than the regulation's threshold level for chlorineof 2500 lbs. Therefore, the facility is regulated under Section 112(r) of the Clean Air Act . Chlorine disinfection is the only covered process at this facility. Three divisions of the Sewer Utility are housed at the Central Tr eatment Plant: Operations, Maintenance and Utility Services Engineering. Total staffing for the three divisions is 223. However, during the off hours, that is on weekends, holidays and between the hours of 5:00PM and 7:30AM the plant is staffed by three operators. The worst case scenario and the alternative release scenario: The regulation requires an analysis of the offsite consequences of an accidental chemical release for planning purposes. This provides information to the government and the public about the potential consequences of an accidental chlorine release at our treatment plant even though this plant has never had a reportable release. The analysis consists of a worst-case and an alternative release scenario. The worst case scenario at this facility is the release of the entire contents of the largest single vessel, a 1 ton container, in 10 minutes. Using assumptions of Class F stability, wind speed of 1.5 meters per second and an urban topography, the distance to a toxic end point of 0.0087mg/L is predicted to be 1.3 miles. This estimate is based on published EPA tables. The tables are generally acknowledged to be conservative. Other equally valid models could be found to show a shorter distance to endpoint. However, the purpose of the worst case scenario is not to illustrate an event that is likely to occur nor to provide a basis for planning a specific response. It is intended to provide a basis for comparison so that emergency response planners can have a basis for prioritization. The alternative release scenario is based on assumptions which are less extreme and more relevant to our facilitys actual process. It may also include the effects of active mitigation devices. We have chosen a scenario in which a flexible connecting tube between the chlorine container and the plant piping manifold becomes crimped and breaks open. The inside diameter of the tube is < inch. Automatic shutoff valves on the chlorine container would isolate the ton container. Based on published tables, we estimate the distance to endpoint of this scenario to be 0.1 miles. General accidental release prevention program and chemical-specific prevention steps: The treatment plant's chlorine disinfection process comes under the WISHA's Process Safety Management regulation. The 12 elements of the accident prevention program set out under that regulation meet the requirements of Risk Management Program. The accident prevention plan elements were developed in 1996 and 1997. After the initial development of the process safety information and process hazard analysis, little has changed regarding the core equipment. The greatest change resulted from the management policy limiting on site inventory of chlorine to 5 one ton containers. This move eliminated the use of the 55 ton chlorine tank car as the main on site storage container and substantially reduced any risk from a catastrophic release. The equipment central to the process consist s of a one ton container of chlorine, automatic shut off valves, evaporators, chlorinators, injectors, water pumps and interconnecting piping and valving. This equipment is fitted with industry standard safety devices including alarms which can immediately turn off the ton container and notify the operations control center. The control center is staffed 24 hours per day and recently installed camera system allows visual monitoring of the chlorine storage area. The equipment is physically checked for proper operation at least once every 12 hours as well as continuous computer monitoring. A preventative maintenance schedule which includes weekly and monthly procedures as well a other maintenance recommended by the manufacturers are ongoing. These layers of mechanical and human monitoring help ensure the mechanical integrity of the system and contribute to our excellent safety record. The five-year accident history: We have had no accidental releases resulting in injuries or off site consequences in the last five years. The emergency response plan: Although the equipment and procedures are in place to prevent an accidental release of chlorine, we still must be prepared to respond should an accidental release occur. The emergency response plan describes the actions to be taken in such an event. The response employed is determined by the severity of the leak. If the leak is minor, trained personnel from the plant will address the problem using proper protective equipment, which may include SCBA. The leak is considered minor, where the chlorine level is detectable, but less than the IDLH - Immediately Hazardous to Life and Health The IDLH is currently held to be 30ppm. However, if the release is not minor or is deemed to be uncontrollable, plant personnel will not respond directly, but will instead call 911. The Tacoma Fire Department is the designated HAZMAT team for the City and will respond to a 911 call. The dispatcher will request information to b e used by the response team and for reporting purposes, such as location and extent of leak, beeper numbers, etc. The HAZMAT team will plan enroute which gate to use and where to locate the command post, based on weather and site layout. The Fire department will assume incident command. In addition to coordination with the Tacoma Fire Department, plant operations personnel will notify other personnel on the plant site via the public address system of the situation and advise whether to evacuate or shelter in place. Designated coordinators in each building will then account for personnel and carry out shelter in place or evacuation procedures. Notifications of plant neighbors and others in the community who may be affected will be carried out in combination with the Tacoma Fire Department. Business immediately adjacent to the plant site will be called by plant personnel. Should the situation warrant, the Tacoma Fire Departments automatic dialing and messaging system, Teleminder , will be available for use. Planned changes to improve safety: The Sewer Utility has recently hired a Safety and Training coordinator to work in both Operations and Maintenance Divisions. Chlorine safety training will move into that program. Future plans may include the capability of shutting the ton container off from any location in the plant using the computer system. |