Laserfiche WebLink
<br /> <br />Exhibit A: Inflow and Infiltration Background <br /> <br />The City continues to work toward reducing <br />Inflow and Infiltration (I&I) into the City’s sanitary <br />sewer system. Infiltration is clear water that enters the <br />sanitary sewer system through broken or cracked pipes, <br />defective joints, faulty connections, or other defects in <br />the mains, services, or manholes. Inflow is clear water <br />that enters the sanitary sewer system through direct <br />connections such as rain leaders, area drains, sump pump <br />connections, foundation drain tile, or <br />commercial/industrial discharges. (see illustration to <br />right) <br />Excessive I/I can create backup problems as it <br />overwhelms our system, it is also very expensive. Orono <br />pays the Metropolitan (Met) Council to treat all of our <br />sewage. Sewage from the City flows into the Met <br />Council interceptor system and is routed to their <br />treatment plants. If clear water enters the sanitary sewer, <br />we have to pay to have it treated by the Met Council. <br />This raises the sewer rates. I&I is monitored by the <br />Metropolitan Council Environmental Services (MCES). <br />The City’s bill is adjusted year to year based on the <br />previous year’s flows going into the Met Council system. <br />In addition the city is fined for any exceedances of our <br />flow allocations. The exceedance warnings and fines are <br />closely associated with high rainfall events and saturated <br />soils pointing to an I&I issue (See charts at right). <br />To date the vast majority of I&I mitigation work <br />has been on public infrastructure (mains and manholes) <br />and while these have shown some improvement there is <br />still considerable I&I entering our system. Although <br />there is still work to be done on the city mains and <br />manholes, a key contributor to the I&I we are experience <br />is very likely the private service lines that connect to our <br />system. MCES estimates that as much as 80% of I&I <br />may come from private sources. One method of <br />addressing I&I coming into the sewer system via private <br />service lines is with a point of sale inspection policy. <br />Several Communities within the metro area have <br />developed point of sale inspection policies/ programs. The city does provide for inspections in our <br />current ordinance however it is focused on illicit discharges into the system such as cross connections <br />from sump pumps. <br />Sources of inflow and Infiltration (I&I) <br /> <br />I&I March & July 2019