The NPDES permit limits the discharge of potential pollutants to protect the waters that receive them. The health of a water body is measured by its attainment of designated uses. If potential pollutants in a NPDES discharge are reduced to levels that allow receiving waters to meet applicable designated uses then, in effect, the pollutant discharge has been eliminated. 

For example, a freshwater stream could have designated uses of "protection of aquatic life" and (human) "drinking water." A chloride discharge to that stream is a pollutant since it could adversely affect freshwater organisms and drinking water quality. The same chloride discharge is likely not a pollutant when discharged into a saltwater body. Saltwater species are accustomed to chlorides and the water body is not used for human drinking water.

Other NPDES permit coverage options in Delaware

• Stormwater Permit Coverage for Land Disturbing Activities Relating to Construction
• NPDES Permit Coverage for Concentrated Animal Feed Operations (CAFO) 
• CAFO Information and Permitting - Frequently Asked Questions