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Comprehensive Sanitary Sewer Plan City of Arden Hills, MN WSB Project No. 3455-20 Page 16 INFLOW AND INFILTRATION General Inflow is water, typically stormwater, which enters the sewer system through broken manhole covers, sewer cleanouts, sump pumps, foundation drains, and rain leaders. Infiltration is water, typically groundwater, which leaks into the sewer system through cracks in the sewer mains, laterals, joints, and manholes. Water from inflow and infiltration (I/I) can consume available capacity in the wastewater collection system and increase the flow into treatment facilities. In extreme cases, the added flow can cause bypasses or overflows of raw wastewater. This extra flow also requires a larger capacity in the city’s collection and treatment components, which results in increased capital, operation and maintenance, and replacement costs. As a sewer system ages and deteriorates, I/I can become an increasing burden on a City’s system. Therefore, it is imperative that I/I be reduced whenever it is cost effective to do so. In 2006, the MCES began an Ongoing I/I Program which requires communities within their service area to eliminate excessive I/I. The MCES establishes annual I/I goals for each community discharging wastewater into the Metropolitan Disposal System (MDS) based on average daily flows, adjustments for community growth, and I/I mitigation peaking factors. The City of Arden Hills was assessed a surcharge in 2007 and initiated an I/I identification program that year to diagnose the extent and location of the I/I and to prepare a reduction plan. The City also had exceedances in MCES Metershed M051 from a June 21, 2013 storm and in MCES Metersheds M051 and M054 from a June 19, 2014 storm. Over the past ten years, the City has performed flow monitoring, smoke testing, televising, manhole rehabilitation, sump pump inspections, sewer lining, and sewer replacement. More details on these activities is provided in the I/I Reduction section. Flow metering data is available for the MCES Meters that measure the City’s wastewater flow, and an analysis of this data as it relates to I/I is presented on the following page. The City’s strategies, programs, investments, and goals for reducing I/I are listed in this section as well.