What are the requirements related to the rated capacity of a water treatment plant?
• The rated capacity of a water treatment plant is based upon the ‘firm capacity’ of the facility. Firm capacity refers to the available capacity of a system or process with the largest unit out of service. Thus, the reliability and redundancy of a water treatment plant’s equipment and process units are integral to the plant’s firm capacity. As noted in Question before, reliability and redundancy requirements are based on installed redundant equipment and process units. Using analytical or statistical methods such as ‘predicted downtime’, ‘mean time between failure’ or other types of failure mode analysis to justify the reliability of systems or processes within a water treatment plant is not an acceptable means of determining the rated capacity of the plant. A water treatment plant’s rated capacity is solely based on its firm capacity. The rated capacity of a water treatment plant is critical in determining when an expansion of a plant is required. The Arizona Department of Environmen
