Lake Youngs 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 Lake Youngs Water Treatment Plant is located in the suburb of Renton, southeast of Seattle. It is located within a 1200 acre reservation that is closed to the public. The plant stores up to 24 tons of chlorine gas in one-ton cylinders, in an enclosed treatment building equipped with a scrubber system, a sump, and gas detectors. 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 on the Lake Youngs Reservation, sometimes near the plant site. They do not enter the plant or the chlorine process area without direct supervision. 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 handling 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 0.9 miles of the plant. Any release from this plant would be mitigated by the fact that all of the chlorine is stored inside a sealed building that is equipped with scrubber system. The worst-case scenario is made even more unlikely by 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 package has estimated a population of approximately 7,900 within the area of concern generated by the worst-case release scenario. SPU believes this figure to be a substantial overestimate. However, for the purpose of compliance with the regulation SPU has included this figure in the RMP for Lake Youngs. 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, with the same mitigation measures of indoor containment and scrubbing being in place. 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 Lake Youngs Reservation property. There have been no reportable releases within the last five years. Prior to that, in August 1983, there was one incident related to chlorine safety in which an improperly filled one-ton cylinder was delivered to Lake Youngs and, due to the improper filling, a fusible plug discharged allowing chlorine gas to escape. Emergency response measures were put into place, a repair device installed on the cylinder, and the incident was resolved without injury, impact to the public, or environmental damage. SPU has an excellent safety record in its handling of chlorine gas. SPU has had a corporate chlorine safet y 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 complies 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 and resources 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. |