Tftfs report summarizes the information compiled in 1986 for our assessment of the environmental impact of radionuclides discharged with aqueous releases from the Rancho Seco Nuclear Power Generating Plant. In October 1934, a liquid-effluent control program was initiated that significantly reduced the quantities of radionuclides discharged with liquid waste from the plant. However, results from our sampling program In 1986 indicate that previously discharged radionuclides persist in the

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... am environment and are found in many aquatic dietary components although at concentrations much lower than those measured in 1984 and 1985. The greatly reduced activities iri the dietary components from the aquatic environment attest to the effectiveness of the liquid-effluent control program. Concentrations in the flesh of fish from the creeps have decreased over time and with distance from the plant outfall. These changes in concentrations can be described by exponential equations, the coefficients of which are obtained from a least-squares analysis of the data. The mean concentration of 137 Cs in fish collected from Laguna Creek at locations more than 7.5 km from Rancho Seco is now comparable to the concentration determined in fresh-water fish randomly selected from Chicago, Illinois, markets. By August 1986, the mean concentration of 13^C s in the flesh of bluegill had fallen to 77. of the concentration measured in fish from comparable locations in 1981 and was 30% of the mean concentration measured in these fish during August 1985. Stable potassium in the water plays a major role in the accumulation of 137 Cs by fish. Concentrations of ^7Q S ^n ^e sur face sections of creek sediments also declined between the end of 7984 and 1986 with an effective half-life of approximately 2 y. Surface soils collected around a perimeter 11 km from Rancho Seco and from ranchlands closer to the plant showed only concentrations of 137 Cs originating from global fallout. Soils previously Irrigated with Clay Creek water retain levels of both 134 Cs and ,37 Cs.