Crow Creek Wastewater Facility - Executive Summary |
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EXECUTIVE SUMMARY FOR THE CROW CREEK WASTEWATER FACILITY The Ceyenne Board of Public Utilities, (BOPU) accidental release prevention policy utilizes a comprehensive approach that includes technologies, procedures, and management practices. The policy provides for the preparation of site specific response plans for each facility and emergency response services availible. The program is in accordance with OSHA Process Safety Management requirements. The Crow Creek wastewater Facility was constructed to provide wastewater treatment for the city of Cheyenne. The plant is located at 4403 Livingston east of Cheyenne and is designed to treat 4 million gallons of sewage a day using the trickling filter process. The final disinfection is achieved by chlorination of the plant's final effluent. Chlorine is the only chemical onsite in quantities over EPA threshold limits. The plant has a Chlorine building that houses liquid chlorine containers, chlorination equipment, a nd various safety devices. Up to five one ton containers of chlorine are handled at the facility. The plant is manned eight hours a day, and wastewater operators visit the plant during the remaining two unmanned shifts. Several inspections of the chlorine systems are made by these personnel each day. The offsite consequence analysis includes a "wost case release" and an "alternative scenario". The first scenario is defined by EPA, and assumes the maximum quantity in the largest vessel is released as gas over a ten minute period due to an unspecified failure. The alternnate scenario is defined as more likely to occur than the worst case scenario. a) Atmospheric dispersion modeling must be performed to determine the distance traveled by a chlorine release before reaching it's "toxic endpoint" of .0087 mg/l according to the Emergency Response Planning Guideline Level2 (ERPG2). Toxic endpoint is defined by the American Industrial Hygiene Association as the maximum airborne concentratio n below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversable or other serious health effects or symptoms which could impair an individuals ability to take protective action. The population within a circle with a radius corresponding to the toxic endpoint distance is defined as "potentially affected". The worst case release scenario for the Crow Creek Facility involves the failure of one ton container (2000lbs) losing it's entire contents in ten minutes as defined by EPA. Using RMP*COMP modeling program a toxic endpoint of 2.2 miles was established with an estimated population of 1492 potentially affected. This scenario is highly unlikely to ever occur due to inspections and procedures in place at the plant. b) The alternative release scenario involves the rupture of the flexible connection (pigtail) attached to the one ton container, possibly during tank changing operations. Using RMP*COMP the amount of chlorine released would be 1330lbs over a ten minute interval at a rate of 133lbs per minute. The toxic end point was determined to be .4 miles with an estimated population of 4 affected. The possibility of this type of release is minimized by the use of effective written procedures and a high level of operator training. The general accidental release prevention program is based on the following elements, and is in accordance with the OSHA PSM program. * Ongoing training of operators * Preventative maintenence program * Up to date safety and process equipment * Effective operating procedures written with operator participation * Periodic hazard reviews of equipment and procedures * Utilization of an auditing and inspection program Chemical specific prevention steps include availibility of SCBA equipment used during tank changing or minor leak investigation, operator awareness of the hazarduos properties of chlorine, and use of chlorine detectors in the storage and process areas. No accidental releases of chlorine have occurred in the last five years. The facility has an emergency reponse plan that is in accordance with the provisions of 29CFR 1910.38(a). Cheyenne city fire depatment and Laramie County Emergency Management Agency have been notified of the presence of chlorine on site. The plan also includes written procedures, and practice drills as outlined in the Wastewater division's PSM program. The existing pressure type chlorinators are scheduled to be replace with remote vacuum type to further minimize the quantity of a potential release. Periodic training will continue, along with reviews and revisions of procedures as needed. Investigation into the use of ultraviolet disinfection at the facility is being conducted as part of a planned plant upgrade. This method would eliminate the use of liquid or gaseous chlorine onsite, thereby eliminating the hazards of a potential release. |