Water Treatment Plant #2 - Executive Summary

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I. Weber Basin Water Conservancy District (WBWCD), Water Treatment Plant #2 is located at 4805 Old Post Rd., Ogden, UT.  The plant handles 8000-lb of chlorine, which exceeds the OSHA threshold quantity.  The plant maintains a process safety management (PSM) program that entails the emergency response and emergency prevention procedures.  The accidental release prevention policy involves an integration of procedures, management practices, and technologies.  The emergency response policy involves procedures specifically designed for this plant.   
II. Weber Basin Water Conservancy District Plant #2 is a water treatment facility that uses chlorine as part of its treatment process. The chlorine is only used in the water treatment process to disinfect the effluent culinary water.  The water from this plant mainly serves Ogden and the South Weber County area.  The chlorine storage room contains the chlorine tanks and the chlorination room, next to the chlorine storage room 
, contains the chlorinators and instrument panel.  The various safety equipment is stored in the room adjacent to the chlorination room.  Four 2,000-lb cylinders are typically stored at this facility.  Two of the cylinders are connected to the system while two remain on standby.  This facility is manned 24 hr/day 7 days/wk.  Technicians at the plant routinely check the chlorine system and respond promptly to any alarms that might occur. 
III. An offsite analysis was done based on two scenarios, the first being a worst-case release scenario and the second being an alternative release scenario.  The worst-case scenario was set and defined by the EPA as the quantity contained in the largest vessel released as a gas over a ten-minute period caused by an unspecific failure.  The alternative release scenario is based on a more realistic accidental release at the facility. 
For each of the scenarios above, the distance traveled by the released chlorine until it reaches its toxic endpoint must 
be known.  The EPA has set the toxic endpoint as 3 ppm (0.0087 mg/l) which is the Emergency Response Planning Guideline Level 2 (ERPG 2).  The residential population that reside within a circular area with a radius corresponding to the toxic endpoint distance has to be estimated to determine the population potentially affected by the accidental release. 
The worst-case scenario selected for Plant #2 entails a complete failure of one of the 2,000-lb chlorine tank.  The hazard assessment analysis for this scenario was done according to the pre-set EPA conditions.  These conditions include the following: 
A. Release of the entire quantity of gas over ten minutes. 
B. Use of the ERPG 2 toxic endpoint level. 
C. Population potentially affected based on a circular area with a radius corresponding to the toxic endpoint distance. 
D. Atmospheric stability class F. 
E. Wind speed of 1.5 m/sec. 
F. Temperature of 77oF. 
G. Humidity of 50%. 
An atmospheric dispersion model was performed using these inp 
ut parameters. A supplementary manual to the Risk Management Programs 40 CFR Part 68 made especially for chlorine gas was prepared and distributed by Jim Peterson from Region 8 of the EPA.  Using the reference table given in this manual, a toxic endpoint distance of 0.9 miles was found for this scenario. The residential population potentially affected using the EPA assumptions is 8475.    
IV.    The accidental release program established by WBWCD is in compliance with OSHA PSM and EPA RMP rules.  The program includes detection alarms set at a sensitivity of 1 ppm, ventilation system, extensive training of employees and routine equipment checks.  Safety equipment is readily accessible and employees are trained to respond to potential failures and accidental releases.  Weber County Emergency Response Committee is aware of the hazardous chemical storage and the associated hazards.  Incase of larger releases of chlorine, plans with the county emergency response have been implemented for evac 
uation of the potentially affected areas. 
V.    Over the past five years, this plant has had no accidental releases that have resulted in serious onsite or offsite injuries, death, or damages.  There is one case of a minute release of chlorine gas that resulted in minor respiratory problems for one employee.  The release was due to a valve being open prior to the tank being sealed.  There was no hospitalization due to the release. 
VI. The source has an emergency response plan that is coordinated with the Weber County Emergency Response Committee.  They have a Hazmat Response Team and will respond to a chlorine release incident.  They may not try to repair or make repairs to the chlorine container or source of release, but will assist in management of public safety in the area.
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