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let f <br /> 14800.Highway.99 <br /> Page 2 of 2 <br /> • Assuming that the petroleum hydrocarbon release occurred prior.to 1988, AGE believes <br /> contaminant migration advanced vertically to approximately 15.feet below surface grade <br /> (bsg) where a clayey sand/silt/clayey silt layer retarded the advancement of contaminants. <br /> This is evidenced by the detection of TPH-g at 250. milligrams per. kilogram (mg/kg), <br /> TPH-diesel (TPH-d) at 190. mg/kg, and total xylenes at 0.51. mg/kg in soil samples <br /> collected at 15 feet bsg in B 1. Contaminants were not detected in B 1. at 25.and 35. feet <br /> bsg,nor were contaminants detected in soil samples collected from borings B2 and B3... <br /> • A one-hundred-year. fate and transport study submitted by AGE predicted "that there <br /> should not be any. impact to groundwater at the dispenser D1 location from the aged <br /> petroleum hydrocarbon-impacted soil.". (AGE calculated a TPH mass estimate of 52 <br /> pounds and noted that first-encountered groundwater occurred between approximately 25. <br /> to. 35 feet bsg and groundwater flow direction was toward the northeast, with some <br /> exceptions, during the groundwater.monitoring events between 1992 and 1997). <br /> Based upon the information presented above, EHD.concurs with AGE's closure recommendation- <br /> EHD will submit Case Closure Summary. to. California Regional Water Quality Control Board, <br /> Central Valley.Region for their review and recommendation. <br /> If you have any questions regarding this letter.please contact Vicki McCartney.at(209)468-3456 <br /> or by electronic mail at vmccartney@sjcehd.com.. <br /> Donna Heran,REHS,Director. <br /> Environmental Health Department , <br /> Victoria L.Mc artney, Senior REHS Nuel C.Henderson,Jr.,PG. <br /> Unit IV-Site Mitigation Unit IV-Site Mitigation <br /> c: Robert E. Marty.-AGE <br /> James L.L. Barton,PG--CVRWQCB <br /> F <br />