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Final Release LLNL Site 300 (USDOE) intermittent stream flowing west to east along the southern and southeastern boundaries of Site 300 (LLNL 1999). The impact of stormwater runoff from Site 300 is monitored in Corral Hollow Creek. Fourteen wetlands have been identified on Site 300 based upon the type of vegetation found there. Ten of these wetlands are located at springs or low-lying areas where the soil is moist enough to support diagnostic vegetation. The other four wetlands are artificial in that they result from cooling tower discharges or other processes at Site 300. Contaminants of Concern No anthropogenic substances have been detected in any off-site springs (LLNL 1994). Two sampling locations have been established along Corral Hollow Creek, one upstream (CARW), that is unaffected by Site 300, and one downstream (GEOCRK). LLNL procedures specify, if possible, sampling two storms per rainy season. Samples from 2001 resulted in gross alpha and gross beta levels (0.31 and 0.96 Bq/L, respectively) at around half of the maximum contaminant levels (MCLs) (0.56 and 1.85 Bq/L, respectively) (LLNL 2002). As part of the eastern GSA treatment facility NPDES permit, Corral Hollow Creek water has also been sampled for a wide variety of chemicals,but no contaminants of concern have been detected. There are no contaminants of concern in the off-site surface water. Air Background LLNL evaluates the ambient air to ensure their compliance with local, state and federal laws and regulations. Concentrations of various radionuclides and beryllium are monitored at LLNL Site 300 and various other locations in the city of Tracy and throughout the Livermore Valley. Site 300 air monitoring results indicate levels of radionuclides such as plutonium 239+240,uranium 238, and tritium at levels that are not statistically different than background levels. The median gross alpha and gross beta activities are 6.3 x 10-5 Bq/m3 (1.7 x 10-15 Ci/m3) and 5.1 x 10-4 Bq/m3 (1.4 x 10-14 Ci/m),respectively. The primary sources of gross alpha and beta activity are naturally occurring radioisotopes of uranium and thorium(LLNL 2002). Also, since surface soil analyses from Site 300 were negative for elevated(above background) levels of contaminants, it is evident that there has been no appreciable atmospheric transport or deposition of contaminants from on-site explosives testing. Contaminants of Concern There are no contaminants of concern in the ambient air at or in the vicinity of Site 300. Quality Assurance and Quality Control In preparing this PHA, ATSDR reviewed and evaluated environmental data provided to ATSDR scientists directly from LLNL or in various reports prepared by LLNL and the University of California. Documents prepared for LLNL Site 300 have oversight of the DOE San Francisco Field Office,LLNL, and LLNL contractors. Additional review of the data is provided by EPA 18