Stormwater Calculator. A downloadable National Stormwater Calculator was developed EPA to help property owners, developers, landscapers, and urban planners make informed land-use decisions to protect local waterways from pollution caused by stormwater runoff... The NPDES stormwater program requires construction site operators engaged in clearing, grading, and excavating activities that disturb 1 acre or more, including smaller sites in a larger common plan of development or sale, to obtain coverage under an NPDES permit for their stormwater discharges. Most states are authorized to implement the Stormwater NPDES permitting program. EPA remains the permitting authority in a few states, territories, and on most land in Indian Country (see complete summary). In areas where EPA is the permitting authority, operators must meet the requirements of the EPA Construction General Permit... Many activities at construction sites can impact air quality, including operation of diesel engines, open..