Wastewater System Failure
Wastewater collection systems often receive additional water during heavy storm events as a result of Inflow and Infiltration. This may cause the wastewater treatment system to reach its maximum treatment capacity. In this event, excess flow will be directed into waterways untreated, resulting in sewage contamination.
Inflow and infiltration is a problem for most communities on the Iron Range as a result of aging infrastructure. The city of Duluth has problems with its collecting systems resulting in sewer overflows. Further, the Western Lake Superior Sanitary District has seen significant sewage spills due to system failures in 2003. Cities in St. Louis County that have regular bypasses as a result of clear water inflow include Duluth, Mountain Iron and Aurora (MPCA communication).
Septic Tanks
Septic tanks are enclosures that store and process wastes where no sewer system exists, such as in rural areas or on boats. Treatment of waste in septic tanks occurs by bacterial decomposition. The resulting material is called sludge. The significant number of residences in St. Louis County is served by septic systems as opposed to public waste treatment facilities. Contamination of water from septic tanks can occur under various conditions.
- Poor placement of septic leach fields can feed partially treated wastewater into a drinking water source. Leach fields are part of the septic system for land based tanks and include an area where wastewater percolates through soil as part of the treatment process.
- Badly constructed percolation systems may allow water to escape without proper treatment. System failure can result in clogging and overflow to land or surface water.
- High density placement of tanks, as in suburban areas, can result in regions containing very high concentrations of wastewater. This water may seep to the land surface, run-off into surface water or flow directly into the water table.
History
Older communities in the County have problems in inflow and infiltration in their wastewater collection systems. During rain events this can overwhelm the capacity of the collection and treatment infrastructure and lead to the release of raw sewage. Cities in St. Louis County that have regular bypasses as a result of clear water inflow include Duluth, Mountain Iron and Aurora (MPCA communication).