Item 2C: Adoption of Resolution Amending MWMC Regional Wastewater SDC Methodology

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Current average flow (presented as DSMM) = ((129 x 217,737 x 1.5)/1,000,000) + 1. 7 = 43.8 i Where: 129 is the average gallons per capita per day (gpcd) of the dry season values from - 1990 to 2002 217,737 is the population served in 2002 - 1.5 is the selected peaking factor to convert average dry season flow to maximum - month dry season flow (based on 1990 to 2002 data) 1.7 is the current industrial flow in mgd - i The available capacity in terms of average flow is 5.2 mgd (49 – 43.8). The projected 2025 average flow is determined as follows: Projected 2025 average flow (presented DSMM) = ((129 x 297,585 x 1.5)/1,000,000) + 1. 7 = 59.3 mgd Where: 129 is the average gpcd of the dry season values from 1990 to 2002 - 297,585 is the projected population to be served in 2025 - 1.5 is the selected peaking factor to convert average dry season flow to maximum - month dry season flow (based on 1990 to 2002 data) 1.7 is the projected industrial flow in mgd (it has been assumed that the - industrial flow will remain constant over the study period) The total required capacity to meet the needs of growth in terms of average flow is 15.5 mgd (59.3 – 43.8). Peak Flow A summary of the peak flow breakdown is presented in Table C-2. The existing capacity in terms of peak flow is not defined in the NPDES permit, but the plant was originally designed for a peak flow of 175 mgd, and therefore that is defined as the existing capacity. MWMC does not currently have the collection and treatment capabilities to accommodate the existing peak flow (which is greater than 175 mgd), and therefore the current peak flow loading (required capacity) cannot be explicitly measured at the WPCF. Using a computer model of the collection system MWMC is able to estimate the current peak flow. DEQ defines the peak flow as the peak hour or peak instantaneous flow that occurs during the 5-year, 24-hour storm (3.9 inches of rainfall). Under these rainfall conditions, the model predicts a current flow of 264 mgd. Therefore, there is no available capacity in terms of peak flow. Since the current average flow is 43.8 mgd, the current wet season I/I is 220.2 mgd (264 less 43.8). Using the projected future 2025 population and land use, the model predicts peak flows of 294 mgd without I/I reduction efforts outlined in the 2000 WWFMP and 277 mgd with I/I Page 30 OF 39