The City of Ann Arbor created the Developer Offset Mitigation Program (DOM) to protect the health and safety of our community and the environment, using a whole‐city approach. The purpose of the DOM is to reduce overall flow to the sanitary sewer system. By reducing the flow in the sanitary sewer system, we do two important things:
- Reduce sanitary sewer overflows
- Reduce unnecessary treatment of storm water
The DOM program requires new developments that will place additional burdens on the sanitary sewer system to offset the flow the new development will add. The City also has a set of program guidelines (PDF) for developers engage in this program.
Why was the Developer Offset Mitigation program created?
Large rainfall events can cause massive inflow of storm water into the sanitary sewer pipes, temporarily exceeding the system’s capacity. By reducing the amount of storm water entering the sanitary sewer system, we can regain system capacity to reduce the chances of sanitary sewer overflows. Here’s a little background information that will be helpful to understand the big picture:
In structures built before 1981, footing drains (also known as foundation drains) were most often connected directly to the sanitary sewer system. In 1982, building code in Ann Arbor and many other cities changed to require footing drains to use sump pumps or similar systems to direct footing drain flows to the storm water system.
Studies performed in Ann Arbor and in other cities have shown that footing drain flows during rain events are a major cause of system capacity issues and increase collection system flows by as much as 10‐20 times the normal dry weather flow.
On average, each home with a connected footing drain adds 3,500 to 10,500 gallons per year of clean water that must be transported to the wastewater treatment plant and treated.
A number of times during the 1980s, 1990s and early 2000s, large rainstorms caused the sanitary sewer system to exceed capacity, causing sewage to back up in homes in some neighborhoods.