ISTS must be designed under this part if the system is proposed to be located in a floodplain. A system located in a floodplain must meet or exceed the following requirements:
provide flow measurement if a pump is to be employed;
meet or exceed requirements of part 7080.2150, subparts 2 and 3, except as modified in this subpart; and
meet the requirements of subparts 2 to 11.
The allowed use of systems in floodplains must be according to state and local floodplain requirements.
An ISTS must not be located in a floodway and, whenever possible, placement within any part of the floodplain should be avoided. If no alternative exists, a system is allowed to be placed within the flood fringe if the requirements in subparts 4 to 11 are met.
There must be no inspection pipe or other installed opening from the distribution media to the soil surface.
An ISTS must be located on the highest feasible area of the lot and must have location preference over all other improvements except the water supply well. If the ten-year flood data are available, the bottom of the distribution media must be at least as high as the elevation of the ten-year flood.
If a pump is used to distribute effluent to the soil treatment and dispersal system, provisions shall be made to prevent the pump from operating when inundated with floodwaters.
When it is necessary to raise the elevation of the soil treatment system to meet the vertical separation distance requirements, a mound system as specified in part 7080.2220 is allowed to be used with the following additional requirements:
the elevation of the bottom of the mound bed absorption area must be at least one-half foot above the ten-year flood elevation if ten-year flood data are available;
inspection pipes must not be installed unless the top of the mound is above the 100-year flood elevation; and
the placement of clean sand and other fill must be done according to any community-adopted floodplain management ordinance.
When the top of a sewage tank is inundated, the dwelling must cease discharging sewage into it.
Backflow prevention of liquid into the building when the system is inundated must be provided. If a holding tank is used, the system must be designed to permit rapid diversion of sewage into the holding tank when the system is inundated.
If a holding tank is used to serve a dwelling, the holding tank's liquid capacity must equal 100 gallons times the number of bedrooms times the number of days between the ten-year stage on the rising limb of the 100-year flood hydrograph and the ten-year stage on the falling limb of the hydrograph, or 1,000 gallons, whichever is greater. The holding tank must be accessible for removal of tank contents under flooded conditions.
Whenever the water level has risen above the top of a sewage tank, the tank must be pumped to remove all solids and liquids after the flood has receded and before use of the system is resumed.
October 10, 2013
Copyright © 2013 by the Revisor of Statutes, State of Minnesota. All rights reserved.