SCE’s monitoring of impingement since 1983 is used as a benchmark to judge the effectiveness of the Fish Return System and Fish Chase procedures. Fish impingement losses were variable, averaging about 23 metric tons per year during the period 1983-1999. The savings in fish biomass resulting from the FRS are unknown, as these data are not routinely collected. However, savings from the Fish Chase procedure added in 1991 to the Heat Treatment procedure at SONGS have been quantified and have exceeded the requirement that 2 or more metric tons of fish, equivalent to a 10% decrease in impingement, be returned to the ocean each year. As a result of the Fish Chase procedure, through 1999 an average of more than 4.3 metric tons of fish that would have been killed and impinged during heat treatment have been returned to the ocean alive via the FRS every year. Put another way, impingement was reduced by an average of about 17% per year since implementing the Fish Chase procedure (based on data collected during 1992-1999).