In open fields, forests, and wetlands, most rain is absorbed by the soil or is taken up by plants and trees. In developed areas, rain that falls on impermeable roofs, parking lots, streets, and lawns is not absorbed. Instead, it travels down roadways, settles in gutters and ditches, and flows through storm drains to finally end up in rivers, lakes, and wetlands. Rainwater that enters a surface water body, by flowing either overland or through a storm sewer system, is called storm water or storm water runoff.

Storm water runoff is one of the leading causes of pollution in rivers and lakes. In both urban and agricultural settings, it can dissolve and transport a variety of chemicals, fertilizers, pesticides, and litter picked up while traveling overland. Identifying sources of storm water pollution and keeping them from coming in contact with runoff is the best and most economical way to protect the quality of the nation's waters.

Tests conducted by EPA on fluid samples from service station floor drains indicate that improper disposal of waste generated during vehicle servicing poses the threat of surface water contamination. Waste oil, antifreeze, and solvents are washed into floor drains which are improperly disposed into separate storm drains. EPA prohibits the discharge of wastewaters into separate storm sewers and permits certain storm water discharges under the authority of the Clean Water Act.

In most cases, typical fluid samples exceed EPA's criteria for identifying properties or characteristics that define a waste as hazardous under the Resource Conservation and Recovery Act (RCRA). Benzene and a number of chlorinated solvents are among the 25 chemicals that have been added to EPA's Toxicity Characteristics list under RCRA.

In addition, any facility that generates more than 27 gallons of wastewater per month containing any of the listed chemicals in amounts exceeding EPA's regulatory levels needs either to recycle the material or to dispose of it as hazardous waste. Facilities that generate less than 27 gallons of wastewater per month are conditionally exempt.

To meet the requirements of Section 402 of the federal Clean Water Act, most states have developed State Storm Water Discharge Permit Programs. Check with your state environmental agency to determine if stormwater runoff or stormwater discharged from your facility requires an NPDES permit. There are three categories of storm water discharges to be regulated by NPDES permits:

 

• Storm water associated with industrial activity
  

  Facilities that engage in regulated industrial activities are typically required to develop and implement storm water pollution prevention plans. Many industrial storm water discharges may be covered under general permits.

• Storm water from construction sites disturbing over 5 acres
  

  Owners of construction activities which disturb five or more acres must develop and implement construction site erosion control and storm water management plans. Most construction activities are eligible for coverage under state-issued general permits.

• Discharges from municipal separate storm sewers serving populations over 100,000
  

  Operators of municipal separate storm sewer systems (MS4s) must develop and implement storm water management plans to reduce pollutant loadings to the maximum extent practicable, and must investigate and eliminate illicit connections to the storm sewer system.

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