SITE INFORMATION AND CORRESPONDENCE_1988-1993

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Harding Lawson Associates July 12, 1993 10433 003 Mr. Chuck Kolesar Shell Oil Company Page 2 It is anticipated that Monitoring Well DW-1 will be completed to a depth of approximately 60 to 70 feet below ground surface (bgs). The borehole through the uppermost aquifer will be 12 inches in diameter to facilitate the installation of a temporary conductor casing (Plate 2). The conductor casing will be installed to a depth of approximately 40 feet bgs and pushed a minimum of two feet into the aquitard material. A bentonite seal will also be installed at the bottom of the conductor casing to further reduce potential connection of aquifers. The boring will then be drilled to total depth using 10-inch diameter hollow stem augers. The well casing and screen will be constructed of a 4-inch diameter, Schedule 40, flush-joint threaded PVC. The screen slots will be factory milled, and the slot size will conform with both the sand pack and aquifer formation. The top of the screened interval will be located approximately 3 feet below the bottom of the aquitard to allow for the installation of the sand pack above the screen and a bentonite seal. A sand pack of clean water- washed sand (sized to be compatible with both the aquifer formation and well screen) will be placed adjacent to the entire screened interval and will extend a minimum distance of 2 feet above the top of the screen. No screen or sand pack will be emplaced that interconnects two or more hydrostratigraphic units. A 3-foot bentonite pellet seal will be placed above the sand pack. Levels of sand and bentonite will be confirmed by sounding. After the bentonite seal has hydrated, the annular space above the bentonite seal will be grouted with a cement-bentonite grout as the temporary conductor casing is removed. After the cement-bentonite grout has set for a minimum of 24 hours, the well will be developed by swabbing, surging, bailing, and/or pumping. The well will be developed until it is visibly clear and free of sediment. Fluids removed from the well during development will be transferred to an existing onsite treatment system. Ground surface and well casing elevations will be surveyed to the nearest 0.01 foot by a licensed Land Surveyor. It is anticipated that Monitoring Well DW-1 will be sampled during the upcoming semiannual sampling event. If the semiannual sampling has already occurred, the well will be sampled after it is constructed and developed. The groundwater samples collected will be analyzed for total petroleum hydrocarbons calibrated as gasoline and diesel using EPA Test Method 8015 (modified); benzene, toluene, ethylbenzene, and xylenes using EPA Test Method 8020; and total lead using EPA method 7421. The analytical results from this new well will be discussed in ongoing semiannual monitoring reports. Deep monitoring well DW-1 will be installed with the additional shallow groundwater monitoring wells during the next phase of plume characterization. As stated in Shell Oil Company's letter to RWQCB dated June 7, 1993, the next phase of plume characterization will proceed upon approval of access to Navy property.