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"' ATTACHMENT 2 CHEVRON SERVICE STATION 9-0557 139 SOUTH CENTER STREET �+ STOCKTON,CALIFORNIA EXPLORATORY DRILLING AND SOIL SAMPLING The boring will be logged by a Blasland, Bouck & Lee, Inc., an ARCADIS company (BBL), geologist using standard geologic techniques. The monitoring well will be advanced using 7-inch diameter sonic `r drilling casing. Soil samples for logging purposes will be collected continuously for visual classification from 8 feet below ground surface [(bgs) utility clearance depth] to total borehole depth in the deep monitoring well(approximately 115 feet bgs). Soil samples will be collected using a 5-foot (4-inch diameter) core barrel. Down-hole sampling equipment will be washed in a tri-sodium phosphate or alconox solution between sample intervals. All down-hole drilling and sampling equipment will be steam-cleaned following the completion of the soil boring. MONITORING WELL INSTALLATION The deep soil boring will be drilled with 7-inch diameter sonic drilling casing to a depth of approximately 115 feet bgs. The actual well completion depth will be based on sediment types encountered during �+ drilling activities. As requested by the SJCEHD, a completion depth of either 105 or 115 feet bgs with a corresponding screen interval of either 100 to 105 feet bgs or 110 to 115 feet bgs will be targeted. The wells will be constructed with flush-threaded 2-inch diameter,schedule 40 poly vinyl chloride (PVC) with 0.010 inch factory slotted screen. An RMC2/16 sand pack, or equivalent, will be placed in the annular space across the entire screened interval, and will extend approximately 1 to 2 feet above the top of the screen for the well. Between the filter pack and the cement/bentonite grout, 1 to 2 feet of bentonite pellets will be placed above the filter pack. Placed above the bentonite seal will be a 5% to 10% e---S Jv bentonite-cement grout mixture to ground surface, using a tremie pipe to ensure proper placement of fn grout material. The wellheads will be completed at ground surface with locking well caps and traffic- rated bolt-down well vaults. Each vault will be installed slightly above the surrounding surface grade and finished with a cement apron to provide positive relief away from the wellhead. ORGANIC VAPOR MEASUREMENTS Soil samples will be analyzed in the field for ionizable organic compounds using a photo-ionization detector(PID)with a 10.2 eV lamp or a flame ionization detector(FID). The test procedure will involve r measuring approximately 30 grams from an undisturbed soil sample, placing this subsample in a sealed container (either a zip-lock bag or a mason jar). The container will be warmed for approximately 20 minutes (in the sun), then the head-space within will be tested for total organic vapor, measured in parts per million as benzene(ppm; volume/volume). The instrument will be calibrated prior to drilling using a 100 ppm isobutylene standard (in air) and a sensitivity factor of 55 which relates the photo ionization potential of benzene to that of isobutylene at 100 ppm. The results of the field testing will be noted on the Not boring logs. PID and FID readings are useful for indicating relative levels of contamination, but cannot be used to evaluate hydrocarbon levels with the confidence of laboratory analyses. Y�1 10/24/2006 Page 1 of 2 J:\D0006\9-055700261022Work Plan Revision Attachment 2.doc r