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M. Scott Mansholt - 2 - 23 October 2006 <br /> Chevron <br /> Mountain House #3 <br /> • Soil samples will be obtained from the upper 10-feet of each boring for consideration in <br /> a site-specific Human Health Risk Assessment (HHRH). <br /> Based on our review, we have the following comments: <br /> • SAIC stated in the workplan that samples from the domestic wells would be used to <br /> "... facilitate the use of groundwater analytical results in a HHRH — only if the <br /> groundwater is determined to be potable..."SAIC would then submit the samples for <br /> petroleum hydrocarbon constituent analysis using detection limits below "...Water <br /> Quality Objectives (WQOs) and other health-based and aesthetic standards of the <br /> RWQCB and EPA (to the extent practicable)" However, samples collected for <br /> determining the extent of affected groundwater related to a project should be submitted <br /> for analysis of the site-specific constituents of concern whether it is potable or not. <br /> • The groundwater samples obtained from the domestic wells should be analyzed for the <br /> petroleum hydrocarbons and as previously discussed with SAIC staff, a representative <br /> number of samples will be submitted for analyses of "General Minerals", electrical <br /> conductivity, ammonia as nitrogen, nitrates as nitrogen, and total nitrogen; <br /> • Rather than obtaining another groundwater sample from near MH3-2, which appears to <br /> be located within a plume of crude oil, additional work in this area should focus on the <br /> lateral and vertical delineation; and, <br /> • Positive sample results should be closely evaluated by the laboratory to determine if the <br /> TPH results are interference caused by the presence of crude oil or from another <br /> source. <br /> Regional Water Board staff concurs with the plan provided our comments outlined above are <br /> addressed. <br /> By 30 March 2007, please submit your investigative report of findings. Please notify Regional <br /> Water Board staff at least 48 hours prior to commencing the drilling activities. <br /> If you have any questions or comments, please contact Dean Hubbard at (559) 445-5179. <br /> iHELTON R. GRA C. DEAN HUBBARD <br /> Senior Engineering Geologist Engineering Geologist <br /> P.G No. 6357 <br /> cc: Mike Infurna, San Joaquin County Public Health Services, Stockton <br /> Luis Mercado, SAIC, Sacramento <br />