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Borehole Log and Monitoring Well Construction Summary Austin Road Landfill, Manteca, California Page 3 Based on the soil sampling, the stratigraphy consists predominantly of fine to coarse grained sand, gravel, and silt, to a depth of approximately 135 feet bgs to 185 feet bgs. Minor amounts of silty clay are encountered sporadically. The water table was encountered at about 75 feet bgs in each borehole. A clay layer was encountered at the base of each boring drilled as part of this investigation. At AMW-21, drilling continued 35 feet into the clay to confirm its minimum thickness. Based on stratigraphic information available from NCYCC well completion logs, the clay layer is approximately 140 — 300 feet thick. AMW-13B, AMW- 22, and AMW- 23 soil sampling continued 1-6 feet into the clay to confirm its presence. The clay encountered in each of the four boreholes drilled as part of this investigation was backfilled using low-permeability grout and the monitoring wells were constructed in the sand immediately overlying the clay as described in Section 2.3 below. 2.3 Monitoring Well Construction Each of the four monitoring wells was constructed using 2-inch diameter flush threaded Schedule 80 PVC screens and 2-inch diameter Schedule 80 PVC risers. The casing joints were fitted with O-rings. The bottom cap was a flush threaded pointed Schedule 80 PVC screw-on cap fitted with a rubber O-ring. The risers each extend approximately three feet above ground surface and were fitted with lockable sanitary plugs. Figures 1-4 detail the construction materials utilized and the survey based elevations and depths associated with the installation of these monitoring wells. Filter sand (2/12 sieve size) was emplaced such that sand is located from the bottom of the screens to at least 3 feet above the top of the screens. 2/12 filter sands are designed to filter out materials which could potentially clog or pass through the casing screen from within the coarse sand and gravels that are anticipated to be adjacent to the screened interval. Similar grain sizes, such as 2/16, have been utilized in monitoring well installation projects in the past. Bentonite transition seals were placed above the primary filter sand-pack. The surface seal extends from ground surface to the top of the transition seal and is comprised of a portland cement slurry. Tremie pipes were utilized as necessary when emplacing the sand-pack, and transition and annular seals, in accordance with California well construction regulations. Additionally, the casings were supported and centered within the 8 inch borehole every 20 feet using centralizers. A steel 5-feet long locking protective cover was placed in the hole, and extended slightly above the top of the PVC casing. The protective cover was encased and secured with quickset concrete to ensure rigidity. Coarse sand was placed inside the protective cover to about 6 inches below the top of the PVC casing. Weep holes were drilled into each protective cover to ensure that moisture or condensation within the cover will drain properly. A 30-in x 30-in x 4-in concrete pad was set surrounding each well and sloped away from the base of the well to promote drainage. Three bumper posts were placed immediately outside of the pad. The posts extend approximately three feet below ground, were be cemented in place, and were filled with cement. The posts were painted bright yellow to help their visibility. Weather-resistant locks were provided by Forward, Inc. and placed on each locking well lid. The borehole geologic logging, monitoring well location, and construction details are summarized on the State of California Department of Water Resources Well Completion Report Forms included in this Summary as Appendix B.