A key pollutant of the Florida Everglades is total phosphorous (TP). Chance (Summer 2003) reported on a study to establish standards for TP water quality in the Everglades. The Florida Department of Environmental Protection (DEP) collected data on TP concentrations at 28 Everglades sites. The 75th percentile of the TP distribution was found to be 10 micrograms per liter. The DEP recommended this value be used as a TP standard for the Everglades; i.e., any site with a TP reading exceeding 10 micrograms per liter would be considered unsafe. Interpret this 75th percentile value. Give a reason why it was selected as a TP standard by the DEP.