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low Geofogical Technics Inc. 2601 9?jvvr Pgad 'EnvisonmentafSpeciafists Modesto,CA 95351 (209}538-7805 January 3, 1990 Mr. Robert Barenchi R&B Trucking 1785 N. Corral Hollow Road Tracy,CA 95376 RE: ADDENDUM NO.2 PRELIMINARY SITE ASSESSMENT WORK PLAN MONITORING WELL LOCATIONS Dear Mr. Barenchi, As we have discussed previously, Geological Technics proposes to modify the location of the two new monitoring wells proposed in the first addendum. Our earlier addendum proposed to install the two wells to the north of the excavation along the proposed new street called Jenni. However, after re-evaluating the project, Geological Technics proposes to install one of the wells on the west side of the excavation (MW-3) and the other well on the south side of the excavation (MW-2). All of these wells are proposed to be contained in Lot No. 12 of the subdivision. The map given in Figure 2 shows the current layout of the lots and streets of the subdivision. Lot No. 12 is on the southwest side of the subdivision and is 55.7 feet wide and 130 to 135 feet deep. The scale on this map is .67 inches equals 60 feet(.67" = 60'). The initial well installed (MW-1) is located about 3 feet from the east side of Lot No. 12 and about 55 feet from the south end of the lot. MW-2 and MW-3 are also shown and are proposed to be installed around the tank excavation; MW-2 to the south and MW-3 to the west. The outline of the tank excavation is also shown on this map. Construction of these wells will be as proposed in the original work plan and Addendum No. 1. That information is also reiterated below and shown in the schematic diagram, Figure 4. The monitoring wells will extend to the bottom of the first saturated zone and will terminate in its lower bounding aquitard (about 25 feet). The wells will be constructed of 2-inch threaded- joint PVC pipe(schedule 40) that is perforated from the bottom of the well to about 2 feet above the water table (about 10 feet). Number 3 sand will be used to create a filter pack that extends from the bottom of the wells to 2 feet above the perforated zone (about 8 feet). A granular bentonite seal (3 feet thick) will be placed in the annular space above the filter pack while the annular space above the bentonite seal will be filled with neat cement. The monitoring well will be secured and a surface seal obtained by cementing in a water tight well box and a locking cap.