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Additional Soil and Groundwater Investigation Report Canepa's Car Wash(Pacific Avenue) January 21,2002 Page 3 ISoil samples collected from the monitor well borings were logged in accordance with the Unified Soil Classification System (USCS). Descriptions of the soil types encountered and other pertinent field observations were recorded on geological boring logs. The geological boring logs prepared by Condor for the soil and monitor well borings, and the CPT boring logs provided by Gregg, are included in Appendix C. 3.3 MONITOR WELL CONSTRUCTION Monitor wells MW-9 and MW-10 were constructed using 20 feet of 2-inch outside diameter, Schedule 40, flush-threaded, machine-slotted PVC screen (slot size 0.020). Monitor well MW-11 was constructed using 20 feet of 4-inch outside diameter, Schedule 40, flush-threaded, machine-slotted PVC screen (slot size 0.020). MW-12d was constructed using 10 feet of 2-inch outside diameter, Schedule 40, flush- threaded, machine-slotted PVC screen (slot size 0.020). A flush-threaded PVC bottom cap was placed at the bottom of the screen sections. Blank PVC casing was installed above the screens to the ground surface. A well construction graphic is included as part of the geological boring logs for each well (Appendix Q. Table 1, on the next page, includes construction details for the monitor wells, including the calculated quantity of annular seal materials and the approximate quantities used. For each well, a filter pack of#3 Monterey sand was emplaced through the augers into the well annulus from the bottom of the boring to approximately one foot above the screened interval. The depth of the sand in the well annulus was monitored with a weighted tape measure while the sand was being placed, and the auger gradually retracted to avoid bridging. Following emplacement of the sandpack to the desired depth, a surge block was used to settle the sandpack.After surging, the depth to the sandpack was measured and sand was added to bring the sandpack back to the desired level as necessary. To form a protective seal, approximately two feet of bentonite chips, hydrated using potable water, was installed above the sandpack as the augers were retracted. Monitor well MW-12d was completed to a depth of 110 feet bgs and, due to a substantial water column above the sandpack, coated bentonite pellets, instead of bentonite chips, were tremied to the top of the sandpack to form the seal in order to minimize the possibility of bridging. The pellets were allowed to hydrate for approximately thirty minutes following emplacement. A surface seal of neat cement was then pumped through a tremie pipe into the annulus extending from the bentonite seal to the ground surface. To verify the stability of the borehole, the augers were gradually retracted during emplacement of the grout. The grout hose retrained near the top of the bentonite seal until the pumped grout was near the surface. The remainder of the grout was pumped into the annulus from the top of the borehole. The monitor wells were then completed using traffic rated flush Imount protective covers set in concrete. 1 i CONDOR