FAQs

All wastewater treatment systems experience Inflow and Infiltration which is part of doing business at the low end, but a major detriment to the wastewater system at the high end: 

Infiltration is groundwater, or groundwater that is influenced by surface water, that enters sewer pipes (interceptors, collectors, manholes (MH), or side sewers) through holes, breaks, joint failures, connection failures and other openings. Quantities often exhibit seasonal variation in response to groundwater levels. Storm events can trigger a rise in groundwater levels and increase infiltration flows. The highest infiltration flows are observed following significant storm events or following prolonged periods of precipitation. Since infiltration is related to the total amount of piping in the ground and not to any specified water-use component, it is usually expressed either in terms of the total land area being served, or in terms of the lengths and diameters of sewer pipe. The unit quantity used is gallons per acre per day (GPAD). 

Inflow is surface water that enters the wastewater system from yard, roof, and footing drains, from cross-connections with storm drains and downspouts, and through holes in manhole covers. Inflow occurs as a result of storm events such as rainfall, snowfall, springs or snow melt that contribute to excessive sewer flows. Peak inflow can occur during heavy storm events when storm sewer systems are surcharged, resulting in hydraulic backups and pooling of water.

The City of Molalla is completing several projects to address I/I entering the system at high levels.  A list of the projects that have started, and their statuses is located on the main Wastewater System Project page.