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WINZLER�KELLY C 0 N 5 U L T 1 N G E N G I N E E R 5 Mr James Ueda ' May 26, 2004 Page 4 ' percentage recovery of known analyte spikes The recovery percentages for all of the sample analytes were within acceptable ranges The complete laboratory report, QA/QC data, and the chain-of- custody form for the groundwater samples are included in Appendix C ' SITE GEOLOGY AND HYDROGEOLOGY The subsurface sods encountered in well boring MW-4 consisted primarily of interbedded layers of silts and clays of moderate to good plasticity Groundwater equilibrated at approximately 3 73 feet below top of casing This is similar to the three shallow wells ' No sands or gravels were encountered in the well borehole during drilling The well was screened across a saturated silt unit from 30 to 35 feet bgs A copy of the boring log is provided in Appendix ' D CONCLUSIONS ' Monitoring well MW-4 was installed in order to define the vertical extent of contamination downgradient of the former UST The laboratory analysis of the soil and groundwater samples collected from this well did not identify the presence of any petroleum related constituents at concentrations above the laboratory's RDLs The absence of these constituents indicates that the lower aquifer is not Impacted by contamination from the former UST ' The concentrations of the constituents detected in the groundwater samples collected from monitoring wells MW-1 through MW-3 indicate that contaminant concentrations in the shallow groundwater zone are very low and are declining with time In addition, the concentrations of ' petroleum-related constituents detected in these wells are below the State of California primary drinking water maximum contaminant levels (MCLS) For example, the MC�Ls for total xylenes and { MTBE2 the two contaminants detected in the groundwater on April 7,2004, are 1,750 and 13' ug/L,respectively In comparison, total xylenes were detected In monitoring well MW-2 at 1 1 ug/L whle MTBE was detected in MW-2 and MW-3 at 1 S and 14 ug/L,respectively ' RECOMMENDATIONS The April 7, 2004 sampling event verified that the concentrations of petroleum hydrocarbons in the groundwater at the site are very low and continuing to decline In addition, the deep well (MW-4) did not contain any petroleum related constituents, indicating that the lower aquifer is not impacted Based on this, the site no longer represents a threat to groundwater, and Winzler& Kelly ' recommends that the site be closed 1 i I 1