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Roseville Public Works, Environment and Transportation Commission Agenda Item. Date: March 2S, 2008 Item No: 7 Item Description: Inflow anal Infiltration Report Backgronnd: Wastewater collected in the Roseville sanitary sewer system flows into main sewer lines owned and operated by the Metropolitan Council {Met Council), who collects and treats wastewater for the seven-county metro area. Inflow and infiltration (I&I) is clear water that makes its way into the sanitary sewer system and mixes with wastewater already in the sanitary sewer pipe, increasing the amount of wastewater requiring treatment. Infiltration is a result of groundwater entering the sanitary sewer system via cracks in the sewer pipes, leaky joints, or deteriorated manholes. The main source of inflow is storrnwater that enters the sanitary system from rain leaders,. sump pump discharges or foundation drains, none of which are supposed to be connected to sanitary sewer lines. The more rain that falls, the more inflow into the system. The capacity of M.et Council's wastewater system is being consumed by I&1, which, if not corrected, would restrict future growth and potentially cause the bypass of sewer flows into the Mississippi River. Met Council approved a surcharge program in February 2006 that requires communities with excessive I&I to pay surcharges on their regional wastewater bills. Met Council has notified communities with significant I&I problems. As communities are able to reduce the excess I&I. with improvements to their sanitary sewer systems, the surcharge could be reimbursed. Met Council estimates that it would cost approximately $900 million to expand its system to treat the excessive flows. Met Council also estimates that if communities were to address the problem locally, casts would be much less, around 8150 million. M'et Council notified Roseville that the City exceeded our allowed I&I limit during two storm events in August, 2006 (August 2 and August 25}and that an annual surcharge would be imposed on the City in the amount of $82,538, beginning in 200$. As a result; the City hired Bonestroo to assist with a study that would begin to identify sources of I&I and determine appropriate steps to reduce the City's I&I. Attached is a report discussing the existing sanitary sewer system, methods used in the study to date, potential I&I sources to consider, preliminary conclusions and recommended next steps. Chuck Janksi of Bonestroo will be present at the meeting to give a brief presentation and answer questions about the report. Recommended Action: Discuss I&I report anal provide staff with feedback. on proposed 200$ work plan. Prepared by: Kristine Giga