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<br />~ <br /> <br /> <br />~ <br />EN HILLS <br /> <br />MEMORANDUM <br /> <br />DATE: <br /> <br />March 25, 2008 <br /> <br />TO: <br /> <br />Mayor and City Council <br />Jim Willis, Interim City Administrator <br /> <br />FROM: <br /> <br />Kristine Giga, Civil Engineer <br />Greg Hoag, Public Works Director <br /> <br />SUBJECT: <br /> <br />Presentation of Inflow and Infiltration (III) Final Draft Report <br /> <br />BACKGROUNDIDISCUSSION <br /> <br />Wastewater collected in the Arden Hills sanitary sewer system flows into main sewer lines <br />owned and operated by the Metropolitan Council (Met Council), who collects and treats <br />wastewater for the seven-county metro area. Inflow and infiltration (1&1) is clear water that <br />makes its way into the sanitary sewer system and mixes with wastewater already in the sanitary <br />sewer pipe, increasing the amount of wastewater requiring treatment. Infiltration is a result of <br />groundwater entering the sanitary sewer system via cracks in the sewer pipes, leaky joints, or <br />deteriorated manholes. The main source of inflow is stormwater that enters the sanitary system <br />from rain leaders, sump pump discharges or foundation drains, none of which are supposed to be <br />connected to sanitary sewer lines. The more rain that falls, the more inflow into the system. <br /> <br />The capacity of Met Council's wastewater system is being consumed by 1&1, which, ifnot <br />corrected, would restrict future growth and potentially cause the bypass of sewer flows into the <br />Mississippi River. Met Council approved a surcharge program in February 2006 that requires <br />communities with excessive 1&1 to pay surcharges on their regional wastewater bills. Met <br />Council has notified communities with significant 1&1 problems. As communities are able to <br />reduce the excess 1&1 with improvements to their sanitary sewer systems, the surcharge could be <br />reimbursed. Met Council estimates that it would cost approximately $900 million to expand its <br />system to treat the excessive flows. Met Council also estimates that if communities were to <br />address the problem locally, costs would be much less, around $ 150 million. <br /> <br />Met Council notified Arden Hills that the City exceeded our allowed 1&1 limit during a storm <br />event on October 5, 2005 and that an annual surcharge would be imposed on the City in the <br />\\Metro-inet.us\ardenhiIls\PR&PW\Engineering\2008\Council_ Actions\3- 3 J -08Memol&l.doc <br />