Tolt Water Treatment Plant - Executive Summary

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 Seattle Public Utilities (SPU) provides retail municipal and industrial water supply to its direct service area within the coroporate boundaries of the City of Seattle, and on a wholesale basis to wholesale water purveyors throughout King County.  SPU operates three primary water treatment plants which are subject to the Risk Management Program Rule under Section 112(r) of the Clean Air Act.  These are the Lake Youngs, Landsburg, and Tolt Water Treatment Plants.  All three plants use chlorine gas for water disinfection in excess of the RMP threshold quantity of 2500 lbs. 
    The Tolt Water Treatment Plant is located on the south fork of the Tolt River, east of Duvall, WA.  It is located within the Tolt River Watershed, which is closed and inaccessible to the public.  Public access is allowed on a recreational trail parallel to the watershed access road up to a point 0.5 miles from the plant.  The Tolt Water Treatement Plant stores up to 20 tons of chlorine gas in one-ton cylinders.  
Cylinders not connected to the process line are stored in an outdoor storage bay.  The treatment process area is in an enclosed building, but there is no scrubber system present nor was the building designed for gas containment.  The treatment building is equipped with gas detetctors.  The plant is staffed 24 hours a day by one Water Treatment Operator.  During normal business hours there may be other SPU employees, contractors, and/or consultants engaged in work in the watershed or on the nearby reservoir dam facilities.  They do not enter the plant or the chlorine process area without direct supervision.  Commercial logging occurs on property adjacent to the watershed. 
      SPU management is committed to protecting employees, the public, and the environment and to preventing injury or death that could result from chlorine gas releases.  To do this, SPU has a variety of safety and emergency response policies in place that guide employees in general workplace safety, storage and han 
dling of chlorine gas, fire prevention and suppression, and emergency response actions.   
    The worst-case release scenario, as specified by EPA, would involve the release of the entire contents of a one-ton cylinder in a 10 minute period.  Based on modeling with EPA's RMP*COMP model, this could impact an area within a radius of 1.3 miles of the plant.  The worst-case scenario is highly unlikely because of the fact that, in order for the entire contents of a ton cylinder to be released within 10 minutes the cylinder would have to be split open.  Given the extreme strength of the cylinder design and the extremely safe industry-wide record of this technology, only the most direct and severe trauma to the cylinder would be capable of creating such conditions.  The LANDVIEW software estimates that approximately 2000 people reside within the 1.3 mile radius area of concern for the worst-case release scenario.   SPU believes  this to be a substantial overestimate.  However, for the purpos 
e of complying with the regulation SPU is including this figure in the RMP for this site. 
    The alternative-case release scenario involves the potential rupture of a 5/16" valve or transfer line during a cylinder maintenance or replacement operation.  This scenario estimates the impacts of the release of approximately 320 pounds of chlorine over a 60 minute period.   When modeled with RMP*COMP, this could impact an area within a 0.1 mile radius of the plant.  This area of concern would be entirely within SPU's watershed property.  
   There have been no reportable releases within the last five years from this plant.  SPU has an excellent safety record in its handling of chlorine gas.  SPU has had a corporate chlorine safety program in place for many years.  In addition to its corporate chemical safety program, SPU maintains open relations and communications with local fire departments responsible for serving its water treatment plants, including meetings and site visits.  SPU compli 
es with OSHA's Process Safety Management standard and, as a result of increased awareness brought about through compliance with the RMP rule, SPU is increasing the level of effort dedicated to its PSM compliance program.  SPU conducts ongoing training of its Water Treatment Operators in all aspects of safe plant operation, including emergency response measures, and Operators perform daily safety inspections of chlorine equipment at every shift change. 
   Interested parties should note that the existing Tolt Water Treatment Plant is scheduled to be replaced by a new Tolt Water Treatment Plant sometime in late 2000.  The new plant will be approximately 1.5 miles west of the existing plant.  The new plant is will be operated by a contractor under a long-term agreement with SPU.  The contractor is responsible for developing and implementing compliance with all applicable regulations, including Process Safety Management and Risk Management.  PSM and RMP information for the new facility is  
expected to be available in spring/summer of 2000.
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