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M. Scott Mansholt - 4 - 14 December 2005 <br /> Chevron Environmental <br /> US Can-Welty Road <br /> 0 Elevated TPH concentrations in SB-17 soil and groundwater samples indicate that area has been <br /> affected by OVP crude oil leaks. Since this boring is more closely associated with the adjacent <br /> Vernalis investigation, it would be appropriate to include this boring with that property. <br /> However, there will be overlap as any additional investigations for defining the eastern extent of <br /> OVP impacts at the US Can-Welty Road site may be on the Vernalis property and vice-versa. <br /> ■ Concentrations of TPHd at 450 and 200 µg/L,reported in SB-13 and 14,respectively, indicates <br /> that the downgradient extent of impacts to groundwater to the north are not defined near the <br /> Western Farm services property. However, TPH compounds were not reported in soil or <br /> groundwater in SB-15/MW-5 thus impacts appear to be defined north of the site by this <br /> boring/well. <br /> • According to the historical data, downgradient boring GMX-6 was completed near a forrner <br /> gasoline station located at the northeast intersection of Welty Road and California Highway 33. <br /> Analytical results reported TPHd at 92 gg/L, 110 µg/L TPHg, and 1.5 µg/L benzene in the <br /> groundwater sample obtained from that boring in 1999. Reportedly, a Union Oil Service Station <br /> operated at this location from 1972 to the mid 1980's. Details regarding the operation and/or <br /> closure of the facility currently are not known. <br /> * The well search results indicated that two public wells were present onsite. Future groundwater <br /> monitoring and sampling should include these wells during a minimum of one event to determine <br /> if they have been impacted. Locations of the wells should be included on subsequent site <br /> groundwater maps. <br /> In order to better evaluate groundwater conditions, we concur with the plan to continue the quarterly <br /> sampling and monitoring. Samples collected from wells reporting concentrations of TPHg present, <br /> should include MTBE analysis for at least one monitoring event. <br /> After at least one hydrologic cycle of sampling for all monitoring wells has been completed (through the <br /> second quarter of 2006), additional hydrogeologic conditions will be re-evaluated. <br /> If you have any questions or comments, please contact Dean Hubbard at (559)445-5179. <br /> SHELTON R. GRAY C. DEAN HUBBARD <br /> Senior Engineering Geologist Engineering Geologist <br /> PG No. 6357 <br /> cc: Mike Infurna, San Joaquin County Public Health Services, Stockton <br /> Luis Mercado, SAIC, Sacramento <br />