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ATC Associates Inc. <br /> YVATC <br /> 1117 Lone Palm Avenue,Suite 201 <br /> Modesto,California 95351 <br /> 209-579-2221 <br /> A E S O C I A T E 5 I N C. fax:209-579-2225 <br /> Zone B and Zone C Vertical Delineation <br /> As previously reported, petroleum hydrocarbons were detected at elevated concentrations in a <br /> grab groundwater sample collected from CPT-2 at approximately 41 feet bgs on October 14, <br /> 2004. Petroleum hydrocarbons were also detected in a grab groundwater sample collected from <br /> CPT-2 at an approximate depth of 67 feet bgs on October 14, 2004. <br /> Two groundwater monitoring wells are proposed to be installed at the site to evaluate the vertical <br /> extent of petroleum hydrocarbon impacted groundwater; one screened into the identified B water <br /> bearing zone and one in the identified C water bearing zone. These wells will be installed on-site <br /> between soil boring CPT-2 and groundwater monitoring well MW-5. Additionally, these wells <br /> will be installed inside conductor casing to reduce the potential for cross contamination of <br /> petroleum hydrocarbons between identified water bearing zones. <br /> The borings will initially be drilled using 1.5-inch diameter hollow-stem augers to the desired <br /> depth of the conductor casing. The conductor casing to be used will be 8 5/8-inch inside <br /> diameter 20 foot length sections. The conductor casing sections will be welded together as <br /> appropriate to ensure the overall effectiveness of the conductor casing. Once in place, the <br /> annulus outside of the conductor casing will be grouted in place using a neat cement grout slurry <br /> mix and will be allowed to cure for at least 48 hours prior to the continuation of the well <br /> installation activities. Additionally, the base of the conductor casing will be backfilled <br /> approximately two to five feet with bentonite and groundwater within the conductor will'? <br /> removed and stored on-site. Depth to water measurements will be collected prior to the —7 <br /> continued well installation activities to evaluate the integrity of the conductor casing. Once the <br /> conductor casing has been set, allowed to cure, and the integrity has been evaluated, drilling will <br /> be continued using 8-inch diameter hollow stem augers to the desired depths of the proposed <br /> groundwater monitoring wells. The proposed ground&ater monitoring well associated with the B <br /> water bearing zone will be advanced to approximately'45 feet bgs using approximately 30 feet of <br /> conductor casing. The proposed groundwater monitoring well associated with the C water <br /> bearing zone will be advanced to approximatel '1% feet bgs using approximately 60 feet of <br /> conductor casing. <br /> Soil sampling will be conducted continuously from the surface to approximately 30 feet bgs. <br /> Soil sampling at five-foot intervals will be conducted from approximately 30 to 45 feet bgs in the <br /> B zone borehole and to approximately 75 feet bgs in the C zone borehole. A field geologist will <br /> be present to log drill cuttings. Descriptions of soil types encountered will be recorded on well <br /> logs. An estimated four soil samples will be collected for laboratory analyses from each boring, <br /> one from vadose zone soil above the capillary fringe, one from the capillary fringe, and two from <br /> the saturated zone. Soil collected within the saturated zone or capillary fringe may not accurately <br /> represent adsorbed-phase petroleum concentrations, if present, due to the water component of the <br /> sample. <br /> S:\Environmenta1\25847\37 Tracy\Reports\wkp-addendum 2009.doc 6 <br />