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M. Scott Mansholt - 2 - 15 December 20 <br /> Chevron/UPRR — TAOC Tra( 'ravel Pits <br /> The metals results are within the range(s) expected for naturally occurring background values. <br /> VOC concentrations were ND to low values and correspond to soil samples having elevated <br /> TPH concentrations. <br /> TPHd at 770 ug/I and 1,100 ug/I was reported in two of five groundwater samples and ND in <br /> the others. PAHs were ND except for low concentrations of two PAHs in one sample; the <br /> B(a)P factors and VOCs were ND. <br /> A search of DWR records did not identify supply wells immediately downgradient, north of the <br /> site. An industrial well located on adjacent property to the west is completed to 75-feet and <br /> screened at 40 to 60-feet. Data provided in previous and current investigations indicated that <br /> the depth to groundwater is approximately 55-feet and the gradient is northerly. <br /> Regional Water Board staff concurs that the site investigations have partially delineated areas <br /> where petroleum hydrocarbons were identified in soil. However, Chevron and UPRR are <br /> evaluating post-closure options for the site and additional soil and groundwater investigations <br /> are needed. <br /> TPHd concentrations to 1,100 ug/I were reported in groundwater samples from borings located <br /> near the northern property boundary. The offsite extent of impacts has not been determined. <br /> Consequently, additional groundwater characterization is needed to determine the extent of <br /> soil and downgradient groundwater impacts. <br /> For Regional Water Board staff to make a more thorough assessment of potential water <br /> quality impacts, water quality parameters for a representative number of site groundwater <br /> samples (in addition to TDS) should include General Minerals, electrical conductivity, ammonia <br /> as nitrogen, nitrate as nitrogen and total nitrogen are needed. In addition, the industrial well <br /> identified by the well search, should be sampled and analyzed for water quality parameters as <br /> well as the TPH constituents of concern. <br /> By 1 February 2007, please submit a workplan outlining the next phase of site <br /> characterization activities for review. <br /> If you have any questions or comments, please contact Dean Hubbard at (559) 445-5179. <br /> l ^ ,� �'s:z <br /> SHELT N R. GRAY C. DEAN HUBBARD <br /> Senior Engineering Geologist Engineering Geologist <br /> P.G. No. 6357 <br /> Attachment <br /> cc: Michael J. Infurna, San Joaquin County EHD, Stockton <br /> James Levy, UPRR, Roseville <br /> Luis Mercado, SAIC, Sacramento <br />