Systems in floodplain areas are usually associated with existing structures as new construction would be prohibited in the floodplain. An existing structure in a floodplain with a failing system may need a replacement system.
A septic system located in a floodplain.
The concerns about floodplain areas during flood events include surface water contamination and system damage by fine soil particles contained in the flood waters. A system cannot be located in the floodway but may be sited in the Flood Fringe as shown in Figure 2.13.
Figure 2.13 Floodplain Profile
For more information about building systems in Floodplain areas see Sections 2 and 4 of the Manual for Septic System Professionals in Minnesota (.pdf).