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Two Conditions Under Which You May Not Need a Permit
The U.S. Environmental Protection Agency (EPA) or your state may waive applicable requirements in a permit for a stormwater discharge from construction activities that disturb fewer than 5 acres. The intent of the waivers is to waive only sites that are highly unlikely to have a negative effect on water quality.
The two conditions for which you may be able to get a waiver from stormwater requirements for construction activities are:
- Low predicted rainfall potential, where the rainfall erosivity factor is less than 5 during the period of construction activity, or
- A determination that stormwater controls are not necessary based on either:
- A total maximum daily load (TMDL) that addresses the pollutant(s) of concern for construction activities; or
- An equivalent analysis that determines allocations are not needed to protect water quality based on consideration of instream concentrations, expected growth in pollutant concentrations from all sources, and a margin of safety.
Note: Both of these permit waivers are available for small, but not large, construction activity that meets specific requirements. As a site operator, you must provide certification to the EPA or to your state agency that the construction activity qualifies for the waiver.
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What Is the Rainfall Erosivity Factor?
The rainfall erosivity factor is used to determine whether the potential for polluted discharge is low enough to justify a waiver from the requirements. It is one of six variables used by the Revised Universal Soil Loss Equation (RUSLE)—a tool used to predict soil loss from construction sites. The rainfall erosivity factor waiver is time-sensitive and is dependent on when during the year a construction activity takes place, how long it lasts, and the expected rainfall and intensity during that time.
The EPA offers a Rainfall Erosivity Factor Calculator that can help you determine if your site and project qualify for this waiver. You will need to enter the start and end date of the project and the latitude and longitude of the site. (Note: The start date is the date of initial earth disturbance. The end date is the date of final site stabilization.) If you don’t have the latitude/longitude information, you can enter the address of the site.
Although the EPA has established the rainfall erosivity factor to qualify for the waiver to be less than 5, your permitting authority has discretion to determine when, where, and whether to offer the waiver.
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What Is the TMDL Waiver?
The stormwater control requirements may also be waived in cases where a determination that stormwater controls are not necessary based on either a TMDL that addresses the pollutant(s) of concern for construction activities or an equivalent analysis that determines allocations are not needed to protect water quality based on consideration of instream concentrations, expected growth in pollutant concentrations from all sources, and a margin of safety.
As they relate to stormwater discharge permits, the pollutant(s) of concern include sediment or a parameter that addresses sediment (i.e., total suspended solids, turbidity, or siltation) and any other pollutant that has been identified as a cause of impairment.
As the operator of the site, you must certify that the construction activity will take place, and stormwater discharges will occur within the drainage area addressed by the TMDL. Note: You should also consult with appropriate agencies for BMP requirements required by your state and local erosion and sediment control regulations and programs.