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Geosyntec'' 3. FIELD INVESTIGATION Geotechnical pre-design data will need to be collected to support the aeration system design. The aeration system is expected to be constructed above ground, southwest of the existing GWETS (Figure 2). As discussed in Section 2, the conceptual design for the aeration system includes three (3) 120,000-gallon aboveground steel bolted tanks, each with diameter of about 34 feet and a height of 25 feet. The scope of work for the geotechnical investigation, based on the available information summarized above, is presented below. 3.1 Pre-Field Activities Geosyntec will prepare a health and safety plan (HASP) for the work. Geosyntec will obtain permits (if required) for the advancement of four soil borings for geotechnical purposes from San Joaquin County to confirm stratigraphy and to conduct geotechnical testing at the Site. The approximate locations of the proposed borings are shown on Figure 3. Geosyntec will mark the boring locations and notify USA prior to beginning subsurface activities. Geosyntec will also contract with a private utility locator to conduct underground utility survey around the proposed investigation locations and the aeration system location. 3.2 Field Investigation and Sampling Methods Four borings are proposed for geotechnical investigation related to settlement and liquefaction of the tanks. Three of the four borings are planned to a depth of 70 feet below ground surface (bgs) using a mud rotary drill rig. One deep boring will be advanced to 110 feet bgs for seismic design characterization. An experienced Geosyntec field engineer or geologist will record soil observations using the Unified Soil Classification System (USCS) for soil logging according to ASTM standard D2487-11 under review of Professional Geologist. Samples for laboratory testing, as well as field characterization, will be collected at approximately 5-foot intervals or where the stratigraphy changes based on the drill cuttings. In the top 15 feet, samples may be collected at a shorter interval. Below a depth of 15 feet, the sampling frequency may be decreased to sample every 5 feet or as needed so that a sufficient sample is obtained for triaxial testing. Bulk soil samples will also be collected from cuttings generated within the upper 5 feet at all borehole locations. Bulk samples will be contained in plastic buckets with lids for transportation. All samples will be labeled with their location and sampling interval. Sampling of the clays and silts will be performed by pushing Shelby tubes into the formation. The Shelby tube will be 3-inch diameter,thin-walled,and 3-feet long. An Osterberg Sampler, Gregory Undisturbed (GUS) sampler, or Pitcher Barrel will be used if Shelby tubes are not suitable. The minimum recovery inside the Shelby tube collected should be 24 inches to allow for triaxial testing and characterization. If a sample has recovery less than 24 inches, the driller will drill the distance sampled by the Shelby tube and go back into the borehole with another sampler. At each sample depth, if no recovery is obtained, another sample below the previous attempt will be obtained. Each 3-foot-long-Shelby tube will not be overpushed. The type of sampler used will be recorded on the boring log. Pre-Design Data Collection Work Plan 4 July 22,2019