Item A-MWMC Facilities Plan - Laserfiche WebLink

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2. STUDY AREA CHARACTERISTICS Accident History for Chlorine and Sulfur Dioxide No accidents involving chlorine or sulfur dioxide releases have occurred on Oregon roads since 1980, according to the Oregon Department of Transportation - Accident Data Unit (ODOT-ADU; Date). No reportable leaks of sulfur dioxide have occurred since plant startup in 1984. No reportable chlorine leaks occurred at the plant between 1984 and August 14, 1993. On August 15, 1993, the plant experienced a major chlorine leak totaling 1,300 pounds. The leak was fully contained within the chemical storage building and contaminated air was neutralized by emergency scrubbers prior to release. No plant personnel were injured, and the leak posed no public health hazard. Between August 16, 1993 and July 15, 1996, four minor chlorine leaks of less than one pound each occurred at the facility. Since July 1996, nine additional minor leaks occurred. These minor leaks were fully contained, and the air was scrubbed prior to release. EPA Risk Management Program Regulation Chlorine (threshold quantity > 2,500 pounds) and sulfur dioxide (threshold quantity > 5,000 pounds) are regulated under RMP guidelines. WPCF plant operations exceed these threshold quantities; therefore, the EPA RMP rule applies to the WPCF. Under the RMP rule, the WPCF was required to prepare an RMP by June 21,1999. The WPCF is operating under an RMP and will update the Plan (following the RMP rule for 5-year updates) in 2004. Hazard Assessment Under the RMP rule, the hazard assessment focused on the offsite environment and neighbors around the facility. The assessment included an evaluation using an EPA air dispersion computer model3. The results of the assessment were based on a range of releases, including worst-case and alternative release scenarios, an analysis of potential offsite consequences, and a 5-year accident history at the facility. The worst-case scenario involves 100 percent release of a 1-ton container of chlorine or sulfur dioxide. The model calculates the concentration of the chemical in a dispersion pattern of 360 degrees until an endpoint of three parts per million (ppm) is reached (City of Eugene, 2001). The alternative scenarios were determined by facility staff in accordance with typical accidents, such as leaks during container exchanges. In all release scenarios, the regulated substance concentrations at the nearest public and/or environmental receptor were estimated based on either air dispersion models or other available data. For the worst-case scenario, the computer model indicated that an endpoint concentration of three ppm chlorine would reach a distance of 0.9 from the source. However, an important feature of the facility is the fact that both chlorine and sulfur dioxide are stored within a containment building constructed specifically for the purpose. The structure is constructed of concrete and steel so the risk from fire is negligible. The containment building is designed with tight-fitting doors and normally closed inlet louvers to contain a potential leak and to facilitate the use of a chemical scrubber system. In addition, air dispersion models are intentionally conservative in nature. This means the endpoint concentration of three ppm would not likely reach a distance of 0.9 mile as suggested by the model. 3 The scenario was modeled using RMP*Comp version 1.06, which is available via the Intemet from EPA's CEPPO Web site. Only passive mitigation is allowed in this scenario, so the containment building was factored in at 55 percent according to guidance documents. The containment building at the facility would exceed the passive mitigation factor of 55 percent. MWMC_2.0_REV23.DOC 2-13