Item A - PH on MWMC/Metro Plan - Laserfiche WebLink

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ATTACHMENT 4 To 05-06-04 Draft MWMC Minutes plants. [Since' the NPDES permit is based on this flow and associated loads, the actual maximum month dry season flow must meet all the criteria associated with the ADWF, and thus is the proper standard for comparison of maximum month flow] It contains some I/I, but the amount is minimal. The other important design capacity is that of dry weather maximum month, which is'66 mgds. [This is not correct. This is not the current rating of the plant for dry season maximum month. This value was obtained from the 1997 Master Plan, in which the effluent requirements were different at the time of that rating. The current maximum month rating is the ADWF of 49 mgd stated in the current NPDES permit.] Some of the months classified as "dry" by DEQ, especially May, can in fact be very wet and contain substantial amounts of I/I. Therefore, the design capacity for the dry season maximum months flows is higher than that of average monthly flows to reflect the presence of the I/I. [This is incorrect. The presence of l/I into the system during critical months does not allow the plant to treat more flow just because it is slightly more dilute.' Other issues such as nitrification, mixed liquor concentrations, and secondary clarification control facility capacity under these conditions. The facility still must meet all the same criteria during this period as outlined by the ADWF permit conditions. Because of this, mass limits under these higher flow conditions pose more stringent effluent requirements than the normal concentration limits. The existing facilities would likely not achieve the 'required 30-day average effluent requirements for wastewater flows in excess of the ADWF stated in the permit.] The difference between the specific design capacity and the actual corresponding flows represents the capacity available to meet future needs. The 1997 MWMC Master Plan examined the amount of dry season average monthly flows as well as the dry season maximum monthly flows to determine the amount of capacity that was being used by current users. It also projected the available years of capacity remaining in that part of the facility. It identified the dry weather average mohth capacity as 49 mgds and the actual average monthly flow as 26 mgds (Table 3-3, page 455). It also identified the dry weather maximum month design capacity as 66 mgds (page 456).[These capacity assessments were based on NPDES permit requirements at the time of the study, no provisions for ammonia, recent SSO regulation, and thermal load limits] It reported that'"average dry weather flows were 53 percent of plant design capacity . (page 440). It estimated that there were 30 years remaining dry weather monthly average capacity and 27 remaining years of dry weather maximum month capacity - taking us to the years 2027 and 2024 respectively (Table 3-5 Remaining Life of E/SWPCF, page 457). It concluded the dry weather capacity analysis as follows: "Ample dry weather capacity remains well beyond the current LCOG planning horizon (page 456)" Attachment 4 Page 7 of 17 4-10