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Harding Lawson Associates <br /> July 13, 1998 <br /> 41017 002 <br /> Margaret Lagorio, Supervising REHS <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> Page 2 <br /> silty clay with sand soils were observed only in a narrow (approximately one to two feet wide) <br /> discontinuous annulus adjacent to the UST sidewalls. Apparently clean soils were observed over the <br /> southern half of the UST excavation bottom in which the concrete had been removed by the excavator. <br /> The bottom of the excavation is at a depth of approximately 8 feet bgs. <br /> The Regional Water Quality Control Board(RWQCB) has required quarterly sampling of four monitoring <br /> wells around the UST and analytical results have not detected any analytes above method reporting limits <br /> to date. Depth to groundwater was measured on July 9, 1998 at approximately 13 feet bgs. <br /> OVEREXCAVATION AND SAMPLING <br /> Prior to proceeding with overexcavation of impacted soil the remaining half of the concrete UST sidewalls <br /> and bottom will be removed on Monday July 13, 1998. On Tuesday July 14, 1998, with the approval of <br /> this workplan, overexcavation of impacted soil will proceed and soils will be stockpiled on visqueen <br /> onsite for subsequent profiling and disposal at Forward landfill in Stockton. A registered hauler identified <br /> in the application permit will be used to transport the soils in accordance federal, state, and local <br /> regulations. Overexcavation will be guided by subjective observations of soil discoloration and <br /> hydrocarbon odors as well as soil screening by a photionization detector(PID). Mr. Kith of the PHS/EHD <br /> had verbally agreed to performing oversight of the remaining tank-removal sampling at the same time as <br /> the confirmation sampling that would be required after overexcavation of impacted soils. It is estimated <br /> that the volume of impacted soil to be excavated would range from 100 to 200 cubic yards. Confirmation <br /> samples collected after overexcavation will be collected in locations designated by the PHS/EHD staff or a <br /> maximum frequency of one sample for 20 linear feet of excavation sidewall. Samples will be collected in <br /> clean 6-inch long by 2-inch wide brass sample tubes from the excavator bucket. The sample tubes will be <br /> pounded into the soil in the bucket with a rubber mallet. <br /> ANALYTICAL PROGRAM <br /> Confirmation samples will be analyzed for Total Petroleum Hydrocarbons as diesel (TPHd) and TPH as <br /> motor oil (TPHmo) with EPA Method 8015 modified and for benzene, toluene, ethylbenzene, and total <br /> xylenes with EPA Method 8020. If the results of the sample analyses indicate that detectable TPHd, <br /> TPHmo, and/or BTEX is still present, then the sample with the highest concentrations will be analyzed for <br /> soluble TPHd and TPHmo. <br /> REPORTING <br /> The results of the confirmation sampling will be summarized along with other relevant information in the <br /> Closure Report that is to be submitted to the PHS/EHD UST group at the completion of the project. An <br /> additional copy of the Closure Report will be submitted to Site Mitigation Group. <br />