Monitoring Under the Clean Water Act for Compliance with Biologically Determined Limitations

Under the Clean Water Act, effluent limitations for point source dischargers are determined by the available pollution control technology or water quality criteria protective of aquatic life. These limitations are based on processes with variabilities determined by time constants on the order of hours, for water quality criteria, and, at most, days for the technology based criteria. Typical monitoring schedules call for sampling a few times per month. There is no information in the monitoring data at frequencies that are biologically relevant. Hence the monitoring data provide no assurance that the biological criteria are being met. This paper discusses a strategy the Environmental Protection Agency could use to deal with this problem, so some assurance is obtained that the desired degree of biological protection is achieved, while not increasing the generally accepted monitoring frequencies.