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

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.ATTACHMENT 4 To 05-06-04 Draft MWMC Minutes current dry season capacity'is identified, [see Table 3.2.2-3 on page 3-11] CH2MHill suggests that the same comparison would be used. The existing average dry weather design flow for the WPCF, as stated in the current NPDES permit is 49 mgd. This is defined as the average day flow calculated from May 1 through October 31. Although stated as an average dry weather capacity, the facility must meet the effluent requirements on a 30-day average flow (monthly basis). Because any 30-day period, including the maximum 30-day flow period (or maximum month flow) during the dry season, must meet the NPDES effluent fl°w and load requirements stipulated for the average dry season flow, it is prudent to compare the actual dry season maximum month flow (DSMM) to the average dry weather'design flow in order to assess treatment capacity. This method was reviewed by DEQ staff and verified as the appropriate method. When I had talked with Mark Hamlin at DEQ on previous occasions, I was assured that DEQ only looks at output and results and that DEQ does not tell jurisdictions how to calculate capacity.[The NPDES permit defines effluent limits, which inherently define how capacity is determined] I called Mark Hamlin last Thursday after reading in the draft facilities plan that DEQ staffhad said the apples to oranges comparison was the appropriate method to calculate the dry weather capacity. Mark then told me that he had evaluated the MWMC dry weather capacity at 60% in the Fact Sheet and NPDES Wastewater Discharge Permit Evaluation. [The information in this fact sheet was developed in ~996 before there was an ammonia limit and thermal load limit placed into the NPDES permit and is therefore no longer valid ] Furthermore, it is clear in that evaluation that DEQ did not use the method being . proposed by CH2MHill. Instead, DEQ compared the average flow capacity of 49 mgds with the average flows of 28.6 mgds. IfDEQ preferred the method being proposed by CH2MHill, why wouldn't they use it themselves? [They are now saying to use maximum month.J And why would we voluntarily dismiss 29% of our current capacity as unavailable for future needs when DEQ estimates our remaining dry weather capacity at 40%, and says that "Based on the current low flows compared to the design flows, and the lack of effluent violations, no expansion of the facility is needed at this time? Liquid Effluent Wet Weather Capacity..: Wet weather capacity applies to the facility's capacity from November 1 to April 30. Just as dry weather capacity comes in two design capacities, so does wet weather capacity. One is the average monthly wet weather capacity/md the second, and probably the more important one, is peak flow capacity. The wet weather average monthly flow is similar to dry season average monthly flow. It contains a significant amount of I/I just because it is measured in the wet months, but the plant has sufficient capacity to handle the flow.[The current peak flows to the facility exceed the capacity of the facility] The Master Plan identifies the average Attachment 4 Page 10 of 17 4-13