MN CSW Permit Section 18 Wet Sedimentation Basin

SECTION 18 WET SEDIMENTATION BASIN

18.1

Wet Sedimentation Basin.

18.2

Permittees using a wet sedimentation basin to meet the permanent stormwater treatment requirements of this permit must incorporate the design parameters in item 18.3 through 18.10.

18.3

Permittees must design the basin to have a permanent volume of 1,800 cubic feet of storage below the outlet pipe for each acre that drains to the basin. The basin's permanent volume must reach a minimum depth of at least three (3) feet and must have no depth greater than 10 feet. Permittees must configure the basin to minimize scour or resuspension of solids.

18.4

Permittees must design the basin to provide live storage for a water quality volume (calculated as an instantaneous volume) of one (1) inch of runoff, or one (1) inch minus the volume of stormwater treated by another system on the site, from the net increase in impervious surfaces created by the project.

18.5

Permittees must design basin outlets so the water quality volume discharges at no more than 5.66 cubic feet per second (cfs) per acre of surface area of the basin.

18.6

Permittees must design basin outlets to prevent short-circuiting and the discharge of floating debris. Basin outlets must have energy dissipation.

18.7

Permittees must design the basin to include a stabilized emergency overflow to accommodate storm events in excess of the basin's hydraulic design.

18.8

Permittees must design a maintenance access, typically eight (8) feet wide, for the basin.

18.9

Permittees must locate basins outside of surface waters and any buffer zone required in item 23.11. Permittees must design basins to avoid draining water from wetlands unless the impact to the wetland complies with the requirements of Section 22.

18.10

Permittees must design basins using an impermeable liner if located within active karst terrain.