Storm Water Management
Storm water discharges are generated by runoff from land and impervious areas such as paved streets, parking lots, and building rooftops during rainfall and snow events that often contain pollutants in quantities that could adversely affect water quality. Most storm water discharges are considered point sources and require coverage by an NPDES permit. The primary method to control storm water discharges is through the use of best management practices.
MS4s are defined as a conveyance or system of conveyances owned by a state, city, town, or other public entity that discharges to waters of the United States and is designed or used for collecting or conveying storm water. Regulated conveyance systems include roads with drains, municipal streets, catch basins, curbs, gutters, storm drains, piping, channels, ditches, tunnels and conduits. It does not include combined sewer overflows and publicly owned treatment works.
MS4 conveyances within urbanized areas have one of the greatest potentials for polluted storm water runoff. The Federal Register Final Rule explains the reason as: “urbanization alters the natural infiltration capacity of the land and generates…pollutants…causing an increase in storm water runoff volumes and pollutant loadings.” Based on increased population and proportionally higher pollutant sources, urbanization results “in a greater concentration of pollutants that can be mobilized by, or disposed into, storm water discharges.”
The federal Clean Water Act requires storm water discharges from certain types of urbanized areas to be permitted under the National Pollutant Discharge Elimination System (NPDES) program. In 1990, Phase I of these requirements became effective, and municipalities with a population served by a municipal separate storm sewer system (MS4) of 100,000, or more, were regulated. In 1999, Phase II became effective, and any entity responsible for an MS4 conveyance, regardless of population size, could potentially be regulated.
Under Phase I, Indianapolis was the only city to meet the population threshold criteria of 100,000. Since Indianapolis was the only city to meet the Phase I criteria, Indiana Department of Environmental Management (IDEM) chose to issue the city an individual storm water permit. Under Phase II, 327 IAC 15-13 was written to regulate most MS4 entities (cities, towns, universities, colleges, correctional facilities, hospitals, conservancy districts, homeowner’s associations and military bases) located within mapped urbanized areas, as delineated by the United States Census Bureau, or, for those MS4 areas outside of urbanized areas, serving an urban population greater than 7,000 people.
Warrick County as well as Newburgh and Boonville have received notification letters from IDEM that they were subject to Rule 13. Each of these entities can apply for an individual permit or agree to be covered by a general permit, thereby, sharing the responsibilities. The Phase II regulations mandate six minimum control measures for inclusion in the NPDES permit. These measures are:
Public Education and Outreach,
Illicit Discharge Detection and Elimination
Construction Site Runoff Control,
Post-Construction Storm Water Management in New and Redevelopment, and
Pollution Prevention/Good Housekeeping for Municipal Operations.