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I <br /> a�r�r�i-Z <br /> Project svcus Update Report,Subsurface Investigation <br /> Banacr Island, Swclson, CA <br /> Sepu=bcr 17, 1992 <br /> WOW2.1 c <br /> Laboratory analysis indicated certain priority pollutant metals present above method detection <br /> limits in the sample collected from well MW-5, including antimony (20 ppb), arsenic (26 ppb), <br /> barium (570 ppb), and zinc (79 ppb). None of the levels detected exceed either the maximum <br /> Soluble Threshold Limit Concentration (STLC) values as listed in Title 22 of the California <br /> Code of Regulations or the State MCLS. The mmetalsanner ldl tteccted in the Weber Point well sample <br /> were also present in the samples collected <br /> Conc_ luslons <br /> Based on this sampling event and previous work completed at this site, RFSNA concludes the <br /> following: <br /> • Shallow groundwater flow at the Banner Island property is controlled by influx from the <br /> tidally influenced deep water channel. On August 28, 1992, the groundwater flow <br /> direction beneath the Banner Island Property was towards the northwest with a hydraulic <br /> gradient of 0.02 ft/ft; this is consistent with the previous monitoring event in March <br /> 1992. <br /> • Low levels of Title 22 metals have been detected in shallow soil and groundwater <br /> rough samples collected from borings/wells thal oftthe levels detected are-9 at the Banner <br /> e 1 below the <br /> Property. Laboratory analyses s <br /> maximum Total Threshold Limit Concentrations. <br /> • The concentrations of Title 22 metals detected during this sampling round have shown <br /> a general overall decrease since the previous sampling event in March 1992 (Table 2). <br /> 0 Historical laboratory results show that acetone has been detected <br /> was notently in wells <br /> detected above <br /> MW-1 and MW-4 at low levels (maximum of 120 ppb). Aceto <br /> method detection limits in either well MW-1 or MW-4 dung this sampling event. <br /> • Laboratory analyses of groundwater samples collected in March 1992 from two wells <br /> located directly across the Deep Water Channel from Banner Island (Table 3) indicated <br /> similar concentrations of the same metals (arsenic, barium, chromium, selenium, and <br /> zinc) detected above MCLS in the Banner Island samples. These two sites had arsenic, <br /> barium, chromium, and selenium concentrations in groundwater that exceeded State <br /> MCLS. <br /> XMIoRrsutoyo9n.Mrt. 3 <br />