The New Orleans aquifer system includes four areally extensive aquifers (the Gramercy, Norco, Gonzales-New Orleans, and "1,200-foot" aquifers) which are separated by beds of clay. Within the aquifer system in northern Jefferson Parish, only the Gonzales-New Orleans aquifer can be considered as a major source of freshwater; overlying and underlying aquifers generally contain saltwater (water with chloride concentration greater than 250 milligrams per aquifer contains saltwater. Color generally ranges between 50 and 120 platinum cobalt unites in freshwater from the Gonzales-New Orleans aquifer. In 1986, about 1 Mgal/d (million gallons per day) of water was withdrawn from the aquifer in northern Jefferson Parish; however, areally (including adjacent parishes) a total of about 40 Mgal/d was withdrawn from the Gonzales-New Orleans aquifer.