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Work Plan for Monitoring Well InRtaations Austin Road Landfill Unit,California Page 2 Two groundwater zones have been identified at the Austin Road Landfill. The first water bearing zone at the facility(Shallow Zone)occurs in a continuous sand layer encountered at an average depth of approximately 80 feet and extending to a depth ranging between approximately 90 and 120 feet below ground surface. The Shallow Zone is separated from a lower sand unit by varying thicknesses of silt and clay. The lower sand interval extends from about 120 feet to about 185 feet and hosts Deep Zone groundwater. Lateral groundwater t flow in the Shallow Zone is toward the northeast. Groundwater flow in the Deep Zone is toward the north, based on information obtained from existing Deep Zone monitoring wells located on the landfill and north of the facility. Recent investigative activities are summarized in corrective action evaluation reports that have been submitted to the RWQCB on an annual basis for several years, a Down-gradient Well Sampling Plan submitted to RWQCB in January 2009,a Source Control Plan submitted to RWQCB in February of 2009,a Confirmation of Source Control Upgrades submitted to RWQCB in May 2009, a Technical Report — Modified Corrective Action System submitted to RWQCB in September 2009, and a Well Installation Report and Vertical-Lateral Extent Summary submitted to RWQCB in November 2009. The Well Installation Report and Vertical-Lateral Extent Summary included results from installed and sampled monitoring wells north of the Austin Road Landfill. This work plan proposes to collect supplemental data to more completely monitor groundwater flow along Newcastle Road,both in the Deep Zone and the Shallow Zone. PROPOSED DRILLING AND MONITORING WELL INSTALLATION PROTOCOLS The proposed boreholes will be drilled using mud rotary drilling techniques that were successfully employed during drilling of Deep Zone monitoring wells in 2008-2010. Soil sampling will occur every 5 feet beginning at ground surface during the drilling of each of the Deep Zone monitoring well boreholes. Shallow Zone monitoring wells will be set according to lithologies and/or hydrologic conditions encountered during the adjacent Deep Zone well installations. A Herst&Associates, Inc. environmental professional,under the direction of a California registered geologist, will log and characterize all soil samples. Actual total depths of the boreholes will be determined by the lithologies and/or hydrologic conditions encountered. Cuttings, logged samples, and drilling mud will be containerized and properly disposed of off-site if proven hazardous by analytical testing. As tabulated below,the wells will be installed at the approximate depths noted. Well/borehole No. Estimated Total Depth* AMW-31 150 feet AMW-32 150 feet AMW-31 S 125 feet AMW-32S 125 feet * Estimated total depths for proposed wells are based on total depths of the closest existing monitoring well cluster(AMW-21 and AMW-21 S). Wells will be constructed using 2-inch diameter flush threaded Schedule 80 PVC screens and 2-inch diameter Schedule 80 PVC risers. The casing joints will be fitted with O-rings. The bottom cap will be a flush threaded pointed Schedule 80 PVC screw-on cap fitted with a rubber O-ring. The risers will extend approximately 2.5 feet above ground surface and be fitted with lockable sanitary plugs. Screen slot size will be 0.010-inch factory slotted to prevent sands and other fine grained materials from entering the screened portion of the casing. Screen length will be nominal 20 feet. Filter sand(2/12 sieve size)will be 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 l