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Final Release LLNL Site 300 (USDOE) This list includes release sites for which a monitoring-only remedy was selected. Figure 3 shows the eight OUs. In this PHA the subdivision of Site 300 into Operable Units will be referenced because of its relevance to environmental contamination and the potential for human exposure. Additionally,because Site 300 was listed on the NPL and is undergoing CERCLA cleanup to address groundwater contamination, this PHA will concentrate on contaminated groundwater. Because access to Site 300 is restricted, it is unlikely that anyone from the community will come in contact with contaminated soil at Site 300. Site 300 lies in the southeast Altamont Hills of the Diablo Range. Six map-able geologic formations have been identified: 1. late.Cretaceous Great Valley sequence (Kgv), 2. the late Paleocene to mid-Eocene Tesla Formation (Tts), 3. the mid-Miocene Cierbo Formation (Tmss), 4. the late Miocene Neroly Formation (Tn), 5. the Pliocene non-marine unit(Tps), and 6. Quaternary alluvial deposits (Qal). Lithologic characteristics of these formations vary from fine-grained claystones to coarse conglomerates, and the stratigraphic units are discontinuous. Consequently, Site 300 is very hydro geologically diverse (LLNL 1999). Two main water-bearing zones facilitate most contaminant movement on and off site: the Neroly Formation (Tn)bedrock aquifer and the shallow, Quaternary alluvial aquifer (Qal). The Neroly Formation is broken into four distinct strata: 1. Tnsc2, a claystone/siltstone layer that occurs in the HE Process Area, the Building 832 Canyon OU, and around Buildings 833 and 834; 2. Tnscl, a fine-grained layer that serves as a confining layer in the HE Process Area, Buildings 833, 834, central GSA, and in the northern part of the site;however, in the Building 832 Canyon OU, it is a contaminated water-bearing zone; 3. Tnbs1, a major water-bearing zone that is present throughout the site; and 4. Tnbs?, that is saturated in the southeast portion of Site 300. The Qal beds occur primarily off-site along the Corral Hollow River floodplain and as valley fill throughout the site (LLNL 1999). Groundwater occurs in confined,unconfined and flowing artesian conditions at the site. However, there are extensive fractures and fissures in the bedrock,particularly claystone beds. Where present, these fractures can influence groundwater flow (LLNL 2002). Groundwater flow throughout Site 300 is generally influenced by the attitude of the underlying bedrock. Three low- amplitude folds exist on-site: 4