Wastewater treatment plant - Executive Summary |
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TULLAHOMA UTILITIES BOARD WASTEWATER TREATMENT PLANT EXECUTIVE SUMMARY A. The Tullahoma Wastewater Treatment Plant (TWWTP) accidental release prevention policy involves a unified approach that integrates technologies, procedures, and management practices. All applicable procedures of the U.S. Environmental Protection Agency (EPA) Prevention Program are adhered to. The TWWTP emergency response policy involves the preparation of response plans which are tailored to the facility and to the emergency response services available in the community, and is in compliance with the EPA Emergency Response Program requirements. B. Tullahoma's wastewater treatment system has been installed to disinfect the flow out of the Tullahoma wastewater treatment plant located at 1012 South Franklin. The wastewater comes into wastewater plant, is t reated, and flows out into Rock Creek. The treatment process includes the use of chlorine and sulfur dioxide. Both chlorine and sulfur dioxide are housed together in an enclosed building. The building contains six (6) ton cylinders of chlorine, and four (4) ton cylinders of sulfur dioxide. The storage area of the building contains four (4) additional ton cylinders of chlorine and four (4) ton cylinders of sulfur dioxide. Various types of safety equipment, monitoring devices, and control devices are housed within the building, as well as access to safety equipment inside and outside the building. The facility is monitored 24 hours a day 7 days a week by on site personnel. C1. The offsite consequence analysis includes consideration of two (2) chlorine scenarios identified as "worst case release" and "alternative release" as well as consideration of two (2) sulfur dioxide scenarios also identified as "worst case release" and "alternative release" The first scenario as defined by EPA, whic h states the "the owner or operator shall assume that the...maximum quantity in the largest vessel...is released as a gas over 10 minutes", due to an unspecified failure. The alternative scenario is defined as "more likely to occur than the worst case scenario." Atmospheric dispersion modeling has to be performed to determine the distance traveled by the chlorine and sulfur dioxide released before its concentration decreases to the "toxic endpoint" selected by EPA of 3 PPM, which is the emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the American Industrial Hygiene Association (AIHA) as the "maximum airborne concentration 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 which could impair an individual's ability to take protective action." The residential population within a circle with a radius corresponding to the toxic endp oint distance has to be defined, "to estimate the population potentially affected." The worst case scenario at the Tullahoma Wastewater Plant involves total loss of ton cylinder during delivery of chlorine, dropping a one ton cylinder onto concrete from 5 feet during unloading, shearing valve. The offsite worst consequence analysis for this scenario was performed by EPA's RMP Comp Program including worst case scenarios for chlorine. The conditions pre-defined by EPA, namely release of the entire amount as a gas in 10 minutes, use the one hour average as the toxic endpoint, and consideration of the population residing within a full circle radius corresponding to the toxic endpoint distance. EPA mandated meteorological conditions, namely Stability F, wind speed of l.5m/sec, and 77 F. C1.1 When atmospheric dispersion modeling for the worst case scenario was performed on chlorine using the EPA assumptions, a distance to toxic endpoint of 0.9 miles (1.4km) and an estimate of residential pop ulation potentially affected of 3,623 was obtained. C1.2 The alternative release scenario involves a leaking valve on a one- (1) ton chorine cylinder. The chlorine released is 1800 pounds, at an average rate of one hour, of 30 pounds/minute. Toxic endpoints were obtained using EPA RMP COMP Program. The EPA mandated meteorological conditions used were Stability Class D, wind speed 3 meters/second, average air temperature of 77 F. The estimated distances traveled to toxic endpoint 0.1 miles (0.2km). Activation of the two- (2) chlorine detectors is an active mitigation measure that should be considered. Both chlorine monitors will detect chlorine and give an alarm at 1 PPM and above. Both monitors are connected to the telemetry system for a remote monitoring system. Fixed chlorine monitors are located in the chlorine cylinder room and the controller feed room. C2. The worst case scenario at the TWWTP involves the loss of one (1) ton cylinder during delivery of sulfur dioxide, dropping a one ton cylinder onto concrete from five (5) feet, shearing the valve. The offsite worst consequence analysis for this scenario was performed by EPA's RMP COMP Program including worst case scenario for sulfur dioxide. The conditions pre-defined by EPA, namely the release of the entire amount as a gas in 10 minutes, use the one (1) hour average as the toxic endpoint, and consideration of the population residing within a full circle radius corresponding to the toxic endpoint distance. EPA mandated meteorological conditions namely Stability F, wind speed of 1.5 m/sec, and 77 F. C2.1 When atmospheric dispersion modeling for the worst case scenario was performed on sulfur dioxide using the EPA assumptions, a distance to toxic endpoint of 0.9 miles (1.4km) and an estimate of residential population affected of 3,623 was obtained. C2.2 The alternative release scenario involves a leaking valve on a one-(1) ton sulfur dioxide cylinder. The sulfur dioxide release is 1088 pounds, at an average rate of one hour, of 54.4 lbs./minute. Toxic endpoints were obtained using EPA's RMP COMP Program. The EPA mandated meteorological conditions used were Stability Class D, wind speed 3 meters/second, average air of temperature 77 F. The estimated distance traveled 0.1 miles (0.2km). We are in the process of purchasing sulfur dioxide detectors as an active mitigation measure. D. The general TWWTP accidental release prevention program is based on the following key elements: -High level of training of the operators -Preventative maintenance programs -Use of state-of-the- art process and safety equipment -Use of accurate and effective operation procedures, written with the participation of the operators. -Performance of a hazard review of equipment and procedures -Implementation of an auditing and inspection program. Chemical specific prevention steps include availability of self-contained breathing apparatus (SCBA), awareness of the hazardous and toxic properties of chlorine and sulfur dio xide, as well as proper training of on site personnel in case of release. E. One accidental release of 100 pounds of chlorine in a chlorine/water mixture "Chlorine feed system overfeed" which resulted in enviromental impact only, and no sulfur dioxide release has occurred at this facility in the past 5 years. F. The facility has an emergency response program coordinated with Coffee County Emergency Management, Fire Department, and Police Department depending upon the size of the leak, weather conditions, wind speeds and direction. If advanced level of technical assistance is deemed necessary to control leak, Chemtrec may be called to give advice and assistance via 24-hour emergency number. PB & S Chemical has a first response team that can be activated with a one hour notice 24 hours a day. G. We have in place a chlorine and sulfur dioxide emergency action and process safety management plan dated M arch 30, 1999. No revisions have been found necessary at this time. |