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Indiana Department of Environmental Management

IDEM > Permitting > Water Permits > Storm Water Permitting > Storm Water Overview Storm Water Overview

Storm water runoff is a natural part of the hydrological cycle. The hydrologic cycle is the distribution and movement of water between the earth's atmosphere, land, and water bodies. Storm water runoff includes rainfall, snowmelt, and other forms of precipitation that falls to the earth's surface. When precipitation reaches the earth's surface it can either infiltrate into the natural landscape or runoff. Infiltration and runoff is heavily influenced by land use. Typically, runoff will be less from a forested landscape than that from an urbanized landscape.

Physical, chemical, and biological characteristics of a watershed are generally altered as land disturbance occurs on active construction sites and for post-construction runoff conditions. Urban storm water runoff quantity and quality are significantly affected as the watershed undergoes development. The hydrology of the land is altered and the generation of pollutants that are unique to the land use become a threat to water quality. Land that is developed undergoes a significant change when impervious surfaces replace natural landscapes. The impact of impervious surfaces typically results in increased runoff volumes and pollutant loading.

According to a United States Environmental Protection Agency (U.S. EPA) fact sheet on storm water, “When it rains or snows, the water that runs off of city streets, parking lots, and construction sites can wash sediment, oil, grease, toxics, pathogens, and other pollutants into nearby storm drains. Once this pollution has entered the sewer system, it is discharged-(usually) untreated-into local streams and waterways. Known as storm water runoff, this pollution is a leading threat to public health and the environment today.” Phase I, promulgated by U.S. EPA in November 1990, set up the initial, basic storm water program for states to adopt in the early 1990s. However, new regulations, known on the federal level as storm water Phase II, have now been established in Indiana to reduce the impacts of storm water runoff from certain construction site, industrial facility, municipal, governmental, and institutional sources. The following descriptions and links will describe these new regulations.

The emphasis of Indiana Department of Environmental Management (IDEM) storm water permits is water quality. Water quantity, while an integral part of storm water, is typically regulated through ordinances developed and implemented by local governmental entities. Following are three storm water permitting programs that are administered by IDEM and related information associated with urbanization and land development.