Dry Creek Wastewater Facility - Executive Summary |
|
EXECUTIVE SUMMARY FOR THE DRY CREEK WASTEWATER FACILITY the Cheyenne 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 Dry Creek Wastewater Facility was constructed to provide wastewater treatment for the City of Cheyenne. The plant is located at 8911 Campstool road east of Cheyenne and is designed to treat 7 million gallons of sewage a day using the activated sludge process The final disinfection is achieved by chlorination of the plant 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, an d various safety devices. Up to five one ton containers of chlorine are handled at the facility. The plant is manned 24 hours a day, regular inspections are conducted several times during each of three eight hour shifts. The offsite concequence analysis includes a "worst case release" and an "alternative release scenario". The first scenario is defined by EPA, and assumes that the maximum quantity in the largest vessel is released as gas over a ten minute period due to an unspecified failure. The alternate scenario is defined as more likely to occur than the worst case scenario. a) Atmopheric 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 Level 2 (ERPG2). Toxic endpoint is defined by the American Industrial Hygiene Association 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 irreversable or other serious health effects or symptoms which could impair an individual's ability to take protective action. The population within a circle with a radius corrisponding to the toxic end point distance is defined as"potentially affected". The worst case release Scenario for the Dry Creek Facility involves the failure of one ton container (2000 lbs) 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 477 potentially affected. This scenario is highly unlikely to ever occur due to inspections and proper procedures in place at the plant. b) The alternative release scenario involves the rupture of the flexible connection (pigtail) attached to the one ton cylinder, possibly during tank changing operations. Using RMP*COMP the amount of chlorine released would be 133 lbs over a one minute inte rval at the rate of 133 lbs per minute. The toxic endpoint was determined to be .4 miles with an estimated population of 2 possibly affected. The possibility of this type of release is minimimal due to the use of remote vacuum chlorinators that automatically shut off the chlorine supply with any loss of vacuum such as a line rupture The general accidental release prevntion 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, wtitten with operator participation * Periodic hazard review of equipment and procedures * Utilization of an auditing and inspection program Chemical specific prevention steps include availibility of SCBA eqipment used during tank changing or minor leak investigation, operator awareness of the hazardous 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 response plan that is in accordance with the provisions of 29CFR 1910.38 (a). Cheyenne City Fire Department and Laramie County Emergency Management Agency have been notified of the presence of chlorine onsite. The plan also includes written procedues , and practice drills as outlined in the Wastewater Division's PSM program. No changes are planned in equipment or procedures at this time, however periodic training will continue along with reviews and revisions of procedures as needed. |