City of Florence Wastewater Treatment Plant - Executive Summary |
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EXECUTIVE SUMMARY The City of Florence Wastewater Treatment Plant places high priority on safety and protection of the environment. The accidental release policy involves safety mechanisms within the process, precautionary management practices, and conservative operating procedures. Safety practices are based on guidelines set forth by the U. S. Environmental Protection Agency. Management of the facility is committed to onsite employee safety as well as the safety of the neighboring resident population. The Wastewater Treatment Plant has coordinated emergency response procedures with the Florence Fire Department and endeavors to maintain compliance with EPA emergency response requirements. The Florence Wastewater Treatment Plant treats the town's wastewater before discharging to the Pee Dee River. The Chlorination Process at the Wastewater Treatment Plant has been installed to implement the UV disinfection process at the plant. Chlorination of the wastewater stream will help in sure disinfection limits are met, such that the integrity of the downstream environment is preserved. The chlorination system starts with the eight [1] ton cylinders (four on line and four on reserve) in the Chlorination Building. The chlorine gas mixes with supply water in the chlorinator unit to form a chlorine solution. This chlorine solution passes through underground piping from the Chlorination Building to the UV disinfection chamber where it is injected into the outgoing treated wastewater stream. A visual and audible alarm is incorporated into the system to detect improper process conditions. Operators make daily inspections of the chlorination process. Safety equipment and repair kits are located on site. Consideration must be made for offsite effects of a release. Both a worst-case release scenario and an alternative release scenario are considered. In the worst-case release scenario, the maximum capacity of the largest vessel is released over a ten minute time period due to an unspecified failure. The alternative release scenario takes into account a more likely to occur situation than the worst-case release scenario. Since the Florence Wastewater Treatment Plant uses one ton cylinders of chlorine, the worst-case release scenario is that 2000 pounds of chlorine is released in a matter of only ten minutes. This would most likely require the rupture of a cylinder. The distance to the toxic endpoint was estimated to be 2.2 miles using EPA's RMP*Comp Ver. 1.06. Weather assumptions made about this scenario include a wind speed of 3.4 mph, air temperature at 77 degree F, and meteorological conditions at a stability class F. The topography of Florence is relatively flat and unobstructed. The chlorine cylinders, though in a building, are in direct contact with the outside air. The toxic endpoint used by the RMP*Comp program is 0.0087 mg/L (EPRG-2). This is the maximum airborne concentration of chlorine which is believed nearly all individuals can withstand for one hour without the exposure causing irreversible or other serious side effects or symptoms that might prevent an individual from taking actions to protect themselves from further exposure. The 2.2 mile distance was used as a radius around the plant to determine the affected area. Since wind direction was not predicted, a circle around the plant should supply significant information for offsite consequences. The residential population within the circle is estimated to be 17,000, with multiple different public receptors. A worst-case release scenario would require a mass evacuation. A more probable situation was considered as an alternative release scenario. A piping leak was examined since the Treatment Plant had experienced the same type leak while using the old system. A 5/16" hole was used in the analysis. This would represent a substantial leak in the piping and connections. Using Exhibit 4-15 of the EPA Risk Management Program Guidance for Wastewater Tre atment Plants, a release rate of 15 pounds per minute was estimated. This release rate is representative of the actual release rate experienced in the previous incident. According to Exhibit 4-15, the chlorine vapor would travel 0.2 miles. Because of the Treatment Plant location, this release is estimated to affect up to 90 of the surrounding residents. This scenario is only a guess as to what could happen. All releases, great or small, should be handled with public safety as priority. The chlorination process is designed to help prevent releases. Vacuum is used to transfer the chlorine gas through the majority of the piping from the cylinder to the chlorinators. By using a vacuum process, piping leak releases are greatly reduced. As a result of the previous incident, an audible and visual alarm was installed to warn against detected leaks. Shutoffs are in place and emergency repair kits and breathing apparatus are located on site. Training and awareness for chlorine have in creased. Operating procedures stress the dangers of chlorine gas and promote better process management. A Process Safety Management Plan has been instituted in compliance with EPA and OSHA regulations. The Florence Wastewater Treatment Plant has had one accidental chlorine release in the past five years. The release was estimated to be between 50 and 100 pounds of chlorine gas. The chlorine at the hot water heater broke. The exhaust fan sent the hazardous fumes out of the room to where contractors were working. Several men were sent to the hospital but there were no offsite consequences. The accident triggered changes within the process. The alarms were added to warn people in the immediate area of a detected leak. Contractor awareness of chlorine hazards along with increased training was also instituted. Within the Process Safety Manual, emergency planning and response procedures are outlined. These procedures include instructions for different scenarios. Emergency respo nse efforts will be coordinated with the Florence Fire Department. Steve Osborne or Robbie Mott should investigate the severity of a leak. Training programs at the Florence Treatment Plant involve safe working practices, safety and health hazards and emergency operations. Only specially trained and equipped personnel (plant personnel, fire department, and compressed gas supplier) should respond. Strategic gas monitoring (downwind) will dictate response actions to be implemented. Plant personnel will assist emergency personnel in the evacuation of any community residence anticipated of being affected by a release. Since chlorination process at the Florence Wastewater Treatment Plant is a newly modified process, as of now, no changes to the process are expected. Training is the major focus of the facility to improve safety. |