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A ':, amec ,l 5.1.3 Additional Constituents Additional CVOC constituents including cis-1,2-dichloroethene (c12DCE), trans-1,2-- dichloroethene (t12DCE), 1,2-dichloroethane (12DCA), chloroform, and vinyl chloride and the petroleum hydrocarbon constituents benzene, toluene, ethylbenzene, and xylenes have been detected in groundwater beneath the site and the off-site area northeast of the site, typically at concentrations significantly less than PCE and TCE. In general, the additional CVOCs are found at the same locations as TCE and PCE, except for 1213CA. The petroleum hydrocarbon constituents and 12DCA in off-site groundwater are from other sources. The occurrence of these constituents at the site and potential off-site sources are described in greater detail in the CAP (AMEC, 2010a). 5.2 EXTENT OF CONSTITUENTS OF CONCERN IN GROUNDWATER FROM THE SITE The COCl in groundwater from the site are primarily PCE with lesser amounts of amounts of TCE, c12DCE, and t12DCE. Chloroform and vinyl chloride are present in groundwater at very low concentrations and are only occasionally detected. The concentrations of CDCs in groundwater from the site are highest in the area just downgradient of the eastern boundary of the site and in the vicinity of off-site wells MW-5A, MW-56, MW-5C, MW-6, and MW-8 (Figure 6). The highest concentration of PCE in groundwater is at the intermediate depth in the vicinity of monitoring well MW-513 (Figure 6). The lateral extent of COCs from the site in shallow zone groundwater is estimated to be between well MW-5A and North San Joaquin Street based on the lack of CVOC detections in discrete-depth samples collected on North San Joaquin Street. The lateral extent of COCs from the site in intermediate zone depth groundwater is estimated to be from the eastern edge of the site to a zero point east of well MW-7 based on discrete depth and well samples. The lateral extent of CDCs from the site in deep zone groundwater was estimated to be from the eastern edge of the site to a zero point west of well MW-9 based on discrete-depth and well samples (AMEC, 2010a). The axis of the plume in all three groundwater zones is along the direction of groundwater flow along a line from approximately well MW-1 through the MW-5 well cluster. No COGS have been detected in the furthest downgradient well (MW-9). The lateral extent of the plume is approximately 1,100 feet long and up to 400 feet wide (AMEC, 2010a). Discrete-depth groundwater samples were collected in 2007 from a boring located near the MW-5 well cluster at depths of 101 and 145 feet bgs. Samples from the boring contained detectable concentrations of COCs, but the concentrations of COCs at 145 feet bgs were much attenuated compared to the 101-foot sample. Additionally, in the 145-foot sample, no PCE was detected. Detected CDCs consisted entirely of daughter products, TCE, AMEC Geomatrix, Inc. 1:113000s113290V\rchive113290-49.DOG 7