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Project Status Update Report, Subsurface Investigation ' <br /> i` <br /> ` <br /> Banner Island, Stoclaon, CA <br /> Scptcmbcr 17, 1992 <br /> W0602.1C <br /> an arsenic level higher than any recorded on the subject property and two of the sites <br /> exceed the MCL for selenium with levels that are almost identical to the subject property <br /> samples. <br /> The importance of this comparison is to show that <br /> metallic MCLs are routinely <br /> approached or exceeded at many widely separated sites in the Stockton area. But even <br /> more importantly these sites show very similar chemical signatures even though they <br /> ce of <br /> have significantly different operation <br /> al <br /> is non-point int or reg. This ional n indicatesngly ope uch�asrthose <br /> IV <br /> the poor quality sh-'low groundwaterPo <br /> identified above. <br /> A very likely non-point source of metallic constituents would be infiltration of channel <br /> water which has received discharges of metal bearing wastes from multiple sources. This <br /> is consistent with investigations of Mormon Slough which enters the deep water channel <br /> ping of metal bearing wastes into Mormon Slough <br /> near the subject property. The dum <br /> has been documented at various locations along Charter Way to the southeast. Such a <br /> source mechanism (infiltration from the deep water channel) is also consistent with the <br /> gradient data shown on Figure 3. This figure indicates recharge from the channel is <br /> controlling local gradients and could serve as a source of poor quality water to each of <br /> ~ the sites discussed above. <br /> 0 The presence ovarying <br /> f levels of Title 22 Metals in shallow soils and groundwater <br /> beneath the Banner Island property does not appear to present any risks with respect to <br /> fuiure development plans at the site. The levels are substantially the same as those <br /> present beneath a large area of Stockton and are consistent with regional non-point <br /> sources of contamination. No further investigation is warranted based on the results of <br /> the two Subsurface assessments and subsequent groundwater sampling events. <br /> ROxrSU R09o9s2.FZ L 5 <br />