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, <br /> Health Services Department letter sent to Mobil Oil Corporation on September 9, 1994. The <br /> borings have been located according to the following constraints: <br /> • To further characterize soil hydrocarbon concentrations to the west of the site two borings <br /> will be drilled. The borings will be located in the PGE right-of-way west of boring SB- <br /> 10. <br /> Further characterization of soil hydrocarbon concentrations to the north of the site is <br /> limited by site specific conditions. Several factors limit locating additional borings further <br /> north of the site in Grantline Road. Overhead power lines run above the sidewalk on the <br /> south side of Grantline Road. Numerous utility lines prevent drilling in the east bound <br /> lanes of Grantline Road and under the sidewalk on the south side of the road. Previously <br /> proposed borings in the center of Grantline Road were not drilled as a Chevron pipeline <br /> is located under the center median of Grantline Road. In addition, the soil on the north <br /> side of Grantline Road has been characterized in borings completed in previous years and <br /> apparently has not been affected by hydrocarbons from the Mobil site. For these reasons <br />` no borings are proposed north of the site in Grantline Road. <br /> Soil samples will be collected at 5-foot intervals, changes in lithology and were hydrocarbon <br /> affected soil is encountered in the borings. Samples will be collected for soil description, field <br /> hydrocarbon vapor screening, and select samples will be submitted to a state-certified laboratory <br /> for analysis. Refer to Appendix A for general field procedures. <br /> • Select soil samples will be analyzed for the following: <br /> • total petroleum hydrocarbons (TPH) using EPA Method 8015 modified for gasoline <br /> (TPH-G) and diesel (TPH-D); and <br /> • benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Method 8020. <br /> 4.3 MONITORING WELL CONSTRUCTION <br /> Select borings may be converted to monitoring wells based on conditions encountered in the field. <br /> Borings located proximal to existing monitoring wells will not be converted to monitor wells. <br /> Monitoring wells will be constructed using 4-inch-diameter PVC casing with an expected <br /> screened interval from 5 to 20 feet below grade. Well construction details and development <br /> procedures are outlined in Appendix A. <br /> 4.4 ELEVATION SURVEY AND FLUID-LEVEL MONITORING <br /> Well top elevations will be surveyed relative to a city benchmark and recorded to the nearest <br /> 0.01 foot by a licensed surveyor. Fluid level monitoring will be combined with regularly <br /> scheduled quarterly ground water monitoring. Fluid levels in the monitoring wells will be <br /> measured to obtain data <br /> 4 <br />