If you have NPDES coverage you will need to have a SWPPP.The SWPPP should be completed prior to applying for coverage.
Your site specific SWPPP explains how you will control pollutants in stormwater runoff from your facility. It is a written document that identifies the sources of pollution and industrial activities conducted at the site, including stormwater control practices which the operator will use to prevent pollutants from making their way into stormwater runoff.