7C, Final Draft of I&I Report - Laserfiche WebLink

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City of Arden Hills March 2008 The purpose of this study and report is to begin the process of quantifying the III in the Arden Hills sanitary sewer system, isolating areas with the most significant problems, and preparing a plan of action for additional work to identify and remove sources of the III in order to eliminate the need for the MCES III Surcharge in the future. II. Background According to the Metropolitan Council Water Resource Management Policy Plan, the City of Arden Hills is expected to grow in population from 9,652 in 2000 to 22,500 in 2030 and grow in households from 2,959 in 2000 to 8,000 in 2030 (Note that the current Arden Hills Comprehensive Plan, which has not been adopted yet, anticipates a 2030 population of 13,500 people and 4,600 households. The reduction is due to a less aggressive development schedule for the TCAAP Area). This growth will increase the demands on the local and regional infrastructure including the wastewater collection and treatment systems that are the subject of this report. Wastewater flow from the City of Arden Hills is measured and recorded by the MCES at four separate meter sites (MOS1, MOS2, M054, and MOS9) located as shown on Figure 1. The existing Arden Hills sanitary sewer system includes approximately 232,300 feet of 8 inch to 21 inch diameter sewer pipe divided into four districts or "meter sheds" as shown in Table 1. Table 1 - Sanitary Sewer Inventory Meter Number Range of pipe diameters Length Comments On) (It) M051 8"-18" 66,100 M052 8" 8,900 M054 8"-21" 71,300 M059 8"-21" 82,600 Unmetered (lS 7) 8" 3,400 Total 232,300 The total wastewater from the City of Arden Hills is estimated by summing the total flow {rom each of the four meter5 and adding an estimate for the un-metered area served by lift station 7. The annual average daily flow5 for the metered areas for each of the past three years are listed in Table 2. Table 2 - Annual Averaoe Dail Flow bv Meter Shed in mod Meter Number 2004 2005 2006 MCES 3Yr Avg Allowable Peak M051 0.448 0.432 0.435 0.44 1.54 M052 0.038 0.039 0.038 0.04 0.16 M054 0.198 0.197 0.183 0.19 0.27 M059 0.317 0.312 0.286 0.32 1.15 Total 1.001 0.980 0.942 0.99 The annual average daily flow has declined slightly each year during this monitoring period. During runoff conditions following a rain event or snowmelt period, the flows increase markedly due to infiltration and inflow (III) entering the sanitary sewer system. In September 2007, the City wastewater flow peaked in response to a 1.83 inch rainfall event. The peak hourly flows recorded at each MCES meter site are listed in Table 3. Page 4 of 12