If all of the stormwater from the construction activity is captured on-site and allowed to evaporate, soak into the ground on-site, or is used for irrigation (i.e., not discharged to a water of the U.S.), you do not need a permit. Under the CWA, it is illegal to have a point source discharge of pollutants to a water of the U.S. that is not authorized by the CWA. If you believe there is a potential for a discharge, EPA recommends that you apply for permit coverage before any potential discharge occurs. The controls that you use to keep the stormwater on your site so that it does not reach a water of the U.S. will be required to be effective under any size storm. You may also have an obligation to the state/tribe concerning discharges to ground water or impoundment of runoff (e.g., water rights).
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