Frequency of water quality sample collection is summarized in Table 4.3.1. The frequency of sample collection is based on data uses and the historic variability of the measurement. Comparison of hourly data collected over 48 hours (Thomas and Cooper, 1989), daily data (Westcot et al., 1992, Karkoski and Tucker, 1993), and historic data collected since 1985 of the CVRWQCB, indicate that weekly sampling adequately characterizes seasonal and temporal variations. Sampling at frequencies greater than once per week relate to compliance evaluation needs. For example, since certain water quality objectives are based on a 4-day average, samples must be taken daily at selected compliance points. In addition, daily flow and salinity measurement at key stations will allow timely assessment and coordination with downstream users to ensure the project does not adversely effect salinity conditions in the River.