A number of residents in the City experience problems with the sanitary sewer system, including basement backups, during significant rain storms. The City is committed to minimizing these situations through numerous capital projects and programs designed to reduce the amount of wet weather issues. In July 2011, the City adopted a new policy concerning Private Property Infiltration and Inflow - the "extra" water that finds its way into the sanitary sewer during rain storms.The linked MMSD video explains how sewer systems are designed to carry normal sanitary flows plus a designated amount of I/I, and what happens when too much enters the system. When the actual amount of I/I exceeds the designed sewer capacity, the pipes will be overfilled, causing problems like overflows and basement backups. The flow graph shows how dramatically sewer system flows can change in a short period of time during a rain storm.
Already, City contractors are inspecting the small pipes called "laterals," that run from houses to the City sewer under the street. By finding and fixing these leaks, we all will stand a better chance of staying dry in future storm events.
There are steps that can be taken to reduce the risk of this happening, and that's where the City's Private Property Inflow/Infiltration Reduction program comes in. By targeting specific areas that are prone to these issues, the City can find and help correct these "leaks," one by one until the flows are under control. The linked fact sheet explains some of the details about the program.