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fS sr S EC ® R Soil and Groundwater Assessment Work Plan Addendum 7-Eleven Store#32262 October 1, 2003 Page 2 Q GROUNDWATER MONITORING WELL INSTALLATION Soil Boring, Soil Sampling and Analysis In addition to the five shallow wells proposed in the original work plan, SECOR will supervise the drilling of one deep groundwater monitoring well (MW-6D) at the location shown on Figure 2 The boring will be drilled using a truck-mounted drilling rig equipped with 8-inch diameter hollow stem augers (HSAs) to a total depth of approximately 50 feet below ground surface (bgs) The boring will then be reamed out with 15-inch diameter HSAs from ground surface to 30 feet bgs to accommodate installation of 10-inch diameter steel conductor casing, which is discussed below The 3 boring will be continuously cored from 0 to 50 feet bgs to identify any high permeability sand layers or low permeability fine-grained material at the site Soil samples will be collected continuously using a core barrell Down hole drilling equipment will be steam cleaned before drilling each borehole, and sampling equipment will be cleaned between each sampling interval Each sod sample will be screened for hydrocarbon vapors using a portable photolonization detector (PID) Sods encountered during drilling will be logged using the Unified Sod Classification System by a SECOR field geologist, working under the supervision of a California registered geologist All soil generated through drilling will be placed in Department-of-Transportation (DOT) approved 55- gallon drums on site pending characterization and disposal Water generated by steam cleaning will be contained in a steam-clean trailer and temporarily stored on site in DOT approved 55-gallon drums All sod samples collected using 2-inch diameter by 6-inch-long brass sample tubes will be sealed with Teflon sheeting and plastic caps, then labeled and placed on ice in an insulated container for delivery to Kiff Analytical located in Davis, California Sod samples collected at 10, 20, 30, 40, and 50 feet bgs will be analyzed for benzene, toluene, ethylbenzene and xylenes (BTEX), total petroleum hydrocarbons-as-gasoline (TPHg), and MtBE, diisopropyl ether (DIPS), tert-amyl-methyl ether (TAME), ethyl-tert-butyl ether (EtBE), tert-butyl alcohol (TBA), 1,2-dichloroethane (1,2-DCA) and ethylene dibromide (EDB) using Environmental Protection Agency(EPA) Method 8260B Deep Well Installation and Well Development In order to minimize the risk of cross-contamination of the deeper groundwater, a 10-inch diameter steel conductor casing will be set through the shallow groundwater zone to a depth of 30 feet bgs in well MW-&D The well will be drilled and continuously sampled to a depth of 30 feet bgs using 8-inch diameter HSAs The boring will be drilled out to 30 feet bgs using a 15-inch diameter HSA and a 10- inch diameter steel conductor casing will be tremae grouted in place through the augers using neat cement The grout in the annular space of the conductor casing will be allowed to setup for a period , of 24 hours prior to resumption of drilling The following day, well MW-6D will be continuously sampled from 30 to 50 feet bgs using 8-inch HSAs through the conductor casing The well will be constructed using 2-inch diameter polyvinyl chloride (PVC) blank casing with 0 020-inch-slot well screen set from 45 to 50 feet bgs The final completion interval of the 5-foot long screen may be adjusted depending on the type of lithology encountered during drilling A sand filter pack will be placed within the annulus of the well from the bottom of the boring to approximately two feet above the top of the well screen The annulus of the well will be sealed with two feet of bentonite on top of the sand and capped with a portland cement /bentonite slurry to the surface A traffic-rated, watertight street box will be installed to protect the well from surface traffic and a locking expansion cap will be used to seal the well within the traffic box P