The Municipal Storm Water Permitting Program regulates storm water discharges from municipal separate storm sewer systems (MS4s). Municipal or urban areas commonly include large impervious surfaces which contribute to an increase in stormwater runoff. On April 30, 2003 as part of Phase II, the California State Water Resources Control Board issued a General Permit for the Discharge of Storm Water from Small MS4s (WQ Order No. 2003-0005-DWQ) to provide permit coverage for smaller municipalities (population less than 100,000), and non-traditional Small MS4s which includes Caltrans. For more information please reference the State Water Resources Control Board Phase II Small MS4 permit web page at https://www.waterboards.ca.gov/water_issues/programs/stormwater/phase_ii_municipal.html.