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Report Second Phase Subsurface lnveaiption <br /> City of Stockton, Banner bland, Stockton,CA <br /> May 20, 1942 <br /> w06M.1 D <br /> i <br /> On March 19, 1992, the groundwater movement beneath the site was in a northwesterly <br /> direction with a hydraulic gradient of 0.018 foot per foot or 95 feet per mile. On March 31, <br /> 1992, depth to water was measured in the nine wells, again to evaluate the groundwater <br /> movement beneath the site. The hydraulic gradient beneath the site was again 0.018 ft/ft or 95 <br /> feet per mile in a northwesterly direction. The groundwater contours are plotted on Figures 7 <br /> and 8. Table 3 summarizes the groundwater monitoring data. The groundwater monitoring data <br /> and well purge logs are included in Appendix E. <br /> 5.0 LABORATORY METHODS <br /> Soil samples collected from borings MW-3 through MW-9 and groundwater samples collected <br /> from wells MW-1 through MW-9 were analyzed for California Title 22 Metals and Volatile <br /> Organics (EPA method 8240). The soil samples submitted were selected for laboratory analysis <br /> based on: 1) areas where the presence of heavy metals and volatile organics in the soil and <br /> groundwater beneath the Banner Island property were suspected; and, 2) due to the poor <br /> mobility of the contaminants, the S foot sample was selected. <br /> 6.0 RESULTS OF LABORATORY ANALYSIS <br /> 6.1 cLQ it <br /> Laboratory analysis recorded certain priority pollutant metals above method detection levels in <br /> the soil samples collected from borings/wells MW-3 through MW-9 at 5.5 feet below grade. <br /> Although none of the levels detected exceeded the Total Threshold Limit Concentration CMC) <br /> values as listed in Title 22 of the California Code of Regulations, some of the samples contained <br /> lead concentrations that were ten times greater than the Soluble Threshold Limit Concentration <br /> (STLC) maximum limit. Because of the sample dilution factor of 10 used in the waste extraction <br /> test protocol, it was considered possible that these samples exceeded the STLC for lead <br /> (Marshack, 1989) therefore, these samples (BI-MW-3, 4, 6, and 7) were reanalyzed for soluble <br /> Ro•osszs�r 9 <br />