Major Modifications must be approved by S.C. DHEC or permitting entity (MS4, Delegated Program) prior to being implemented in the field. The majoritiy of alterations that affect the volume of stormwater discharges and/or any of the site drainage patterns will be required to be submitted for review before implementation.

Minor Modifications are simple design changes that are required to address unforeseen drainage issues that may have been overlooked in the design phase. An example of this type of modification would be the addition of riprap check dams or sediment tubes in a swale to help maintain non-erosive velocities within the channel. All Minor Modifications may be implemented without approval, however all minor changes should be recorded on the on-site construction plans.

Below is a list of items that S.C. DHEC considers as Major or Minor Modifications to the Stormwater Pollution Prevention Plan (SWPPP). These are not all inclusive lists.

Major Modifications

  • Any Modification that will affect the hydrology or trapping efficiency calculations including:
    • Resizing Sediment or Detention Basin
    • Deletion of Sediment or Detention Basin or Sediment Trap
    • Relocation of Sediment or Detention Basin
    • Addition of Sediment or Detention basin
    • Modification of Sediment or Detention Basin Outlet Structure
    • Amending Construction Sequence so Basin is not Installed Before Grubbing Operations Begin
  • Point discharge location change (near property line)
  • Adding new point discharge (withing 20' of proptery line)
  • Addition of Impervious Area (which will affect curve number calculations)
  • Addition of Disturbed Area
  • Changes to Navigable Water Crossing (new CGP)
  • Addition of Sediment Trap

Please submit all Major Modifications to S.C. DHEC or Affliated Permitting Entity (MS4)
Where To Submit Modifications

Minor Modifications

  • Addition of Silt Fence, Slope Drains, Inlet Protection, Outlet Protection, or Check Dams
  • Relocation of Construction Entrance
  • Relocation of Pond Inlet Pipes (still within the pond)
  • Omission of Disturbed Area
  • Individual Lot Drainage, unless that Changes the Detention Structure or Analysis Point to which the Lot Drains. (may not be applicable with MS4s/Delegated Programs)

If you have any questions as to whether a Modification would be considered major or minor, please contact the permitting entity before proceeding with the modification.


Environment Stormwater