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July 13, 1992 <br /> 10433 382 <br /> Mr. Chuck Kolesar Harding Lawson Associates <br /> Page 2 <br /> collection, the hydropunch holes will be grouted using a cement- <br /> bentonite grout. <br /> The proposed hydropunch sampling locations are shown on Plate 1. The <br /> hydropunch samples will be collected in two phases of work. Phase I <br /> will comprise collection of four samples in an east-west trending line <br /> located approximately 200 feet downgradient of the site property <br /> boundary, one sample from the southwestern corner of the Shell property, <br /> and three samples along the eastern edge of the Shell property (Plate <br /> 1) . The Phase I samples will be analyzed by a mobile laboratory or <br /> local laboratory with 24-hour turnaround. The Phase II samples will be <br /> collected at locations to be determined based on the analytical results <br /> of the Phase I samples. For example, if the four samples collected in <br /> the east-west trending line south of the site do not contain dissolved <br /> petroleum hydrocarbons, Phase II samples will be collected between the <br /> Phase I samples and the downgradient Bite property boundary (Plate 1) . <br /> However, if the four samples collected in the east-west trending line do <br /> contain dissolved petroleum hydrocarbons, Phase II samples will be <br /> collected downgradient of the Phase I samples (Plate 1) . In this <br /> manner, the number of samples required to characterize the offsite <br /> petroleum hydrocarbon plume can be minimized. <br /> Following collection and analysis of the hydropunch samples, a <br /> monitoring well network will be designed and installed, as described <br /> below. <br /> Monitoring Well Installation <br /> Based on the results of the hydropunch sample analyses, HLA will <br /> supervise the drilling of exploratory borings and installation of up to <br /> four shallow monitoring wells at the Shell plant. The tentative well <br /> locations are shown on Plate 1; note that the locations may change based <br /> on the results of the hydropunch sample program. <br /> All drilling work will be conducted by West Hazmat Drilling Company <br /> using a truck-mounted hollow stem auger rig, and will be performed under <br /> the supervision of an HLA geologist. Relatively undisturbed soil <br /> samples will be collected at 3- to 5-foot intervals for lithologic <br /> logging and/or chemical analysis. Lithologic logs of the borings will <br /> be prepared using the Unified Soil Classification System. Prior to <br /> drilling, all downhole drilling equipment will be cleaned using a high- <br /> pressure hot water washer (steam cleaner) . Soil sampling equipment will <br /> also be cleaned with a steam cleaner and phosphate-free soap, and rinsed <br /> with clean tap water and deionized water. All drill cuttings will be <br /> retained in labeled 55-gallon drums and analyzed for petroleum <br /> hydrocarbons prior to disposal. <br /> The monitoring wells will be completed to a depth of approximately 30 <br /> feet bgs. The borehole diameter will be 10 inches. The well casing and <br />