Wastewater treatment and disposal systems discharging into coastal waters in the vicinity of bathing beaches must be designed to meet water quality criteria based on public health and aesthetic considerations. On parameter commonly employed as an index of public health risk is the density of fecal coliform organisms, expressed as the number of organisms per 100 ml. For example, the New South Wales State Pollution Control Commission requires that the discharge of wastewater from ocean outfalls shall not result in a geometric mean fecal coliform density in bathing waters of more than 200 organisms/100 ml (based on five samples taken during any 30-day period). In addition, the Commission requires that the fecal coliform density in 90 percent of the samples collected in bathing waters during the summer period shall be below 400 organisms/100 ml (based on not less than 30 samples collected during the 6-month period from November 1 to May 1).