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5. BASIS OF PLANNING 5.1.6 Plant Reliability and Redundancy Criteria New or .expanding treatment works are required to meet minimum standards for mechanical, electrical, fluid systems, and component reliability in accordance with EPA's policy. This is to ensure that the treatment facilities will operate effectively on a day-to-day basis and that capabilities are provided for satisfactory operation during power failures, flooding, peak loads, equipment failures, and maintenance shutdowns. These reliability and redundancy standards are important to ensure that unacceptable degradation of the receiving water will not occur as a result of the interrupted operation of specific treatment operations or processes. In that regard, standards have been established for three classes of wastewater treatment works. The Reliability Class I definition is applicable for the WPCF. This reliability designation is based on the possible beneficial uses that may be negatively affected by a WPCF failure. The Reliability Class I definition consists of the following: "Works which discharge into navigable waters that could be permanently or unacceptably damaged by effluent which was degraded in quality for only a few hours. Examples of Reliability Class I works might be those discharging near drinking water reservoirs, into shellfish waters, or in close proximity to areas used for water contact sports." Table 5.1.6-1 lists the minimum backup requirements for plant components that may be provided at the WPCF facility in accordance with EPA's Works Design Criteria, Reliability Class I, for sewage treatment plants. In addition to the standards listed in the table, with the exception of primary clarification, trait operations will be designed to pass the peak hydraulic flow with one unit out of service. Also, mechanical components in the facility will be designed to enable repair or replacement without violating the effluent limitations or causing control diversion. TABLE 5.1.6-1 Reliability Class I Requirements MWMC Facility Plan, Eugene-Springfield Plant Component Requirement Raw Sewage Pumps Peak flow with largest unit out of service. Peak flow is defined as the maximum wastewater flow expected during the design period of the treatment works. Mechanical Bar One backup with either manual or mechanical cleaning (manual cleaning if only two Screens screens). Grit Removal Minimum of two units. Primary Sedimentation 50% of design flow capacity with largest unit out of service. Design flow is defined as the flow used as the design basis of the component. Activated Sludge A minimum of two equal volume basins; no backup basin required. Process Aeration Blowers Supply the design air capacity with the largest unit out of service; provide a minimum of two units. Air Diffusers Isolation of largest section of diffusers (within a basin) without measurably impairing oxygen transfer. Secondary 75% of design flow capacity with largest unit out of service. Design flow is defined as Sedimentation the flow used as the design basis of the component. Disinfectant Contact 50% of the design flow with largest unit out of service. Design flow is defined as the Basin flow used as the design basis of the component. MWMC_5.0_REV8_VKS.DOC 5-21