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Additional Subsurface Investigation and Well Installation Work Plan San Joaquin County Public Works June 19, 2017 Page 4 Shallow soil samples will be analyzed for the following constituents: Total petroleum hydrocarbons as kerosene (TPH-K) and TPH-D by EPA Method 8015M; Total petroleum hydrocarbons as gasoline (TPH-G) and volatile organic compounds (VOCs) using EPA Method 8260B. VOCs, at a minimum, will include benzene, toluene, ethylbenzene, and xylenes (BTEX), naphthalene, and the gasoline oxygenates/additives methyl t-butyl ether (MTBE), di-isopropyl ether (DIPE), ethyl t-butyl ether (ETBE), t-amyl methyl ether (TAME), t- butyl alcohol (TBA), 1,2-dichloroethane (1,2-DCA), and ethylene dibromide (EDB). 4.3 DEEP SOIL BORINGS BY CONE PENETROMETER TESTING The deep soil boring investigation will be conducted to an anticipated depth of approximately 80 feet bgs. Deep borings will be drilled and characterized at the two locations described below: Slightly downgradient of former UST #3, near well MW-2, where dissolved petroleum hydrocarbon constituents have been consistently detected in the shallow water bearing zone. Immediately south of former UST #3, near well MW-1, where dissolved petroleum hydrocarbon constituents have also been consistently detected in the shallow water bearing zone, and where petroleum hydrocarbon constituents were detected in soil samples collected in March 1999 at depths ranging from approximately 28 feet bgs to 60 feet bgs. The proposed locations of the deep borings (CPT-1 and CPT-2) are presented on Figure 6 (Appendix A). The deep borings will be advance by a state-licensed (C-57 drilling license) drilling contractor equipped with a Cone Penetrometer Testing (CPT) drilling rig. Site characterization will be conducted using a Membrane Interface Probe (MIP) and Hydraulic Profiling Tool (HPT), collective known as MI-HPT. The MI-HPT system will include the following detectors: electron capture device (ECD), halogen specific detector (XSD), photoionization detector (PD), and flame ionization detector (FID). The MI- HPT detects volatile contaminants, measures soil electrical conductivity, and measures HPT injection pressure using a down-hole transducer. The probe array will allow evaluation of relative contamination by petroleum hydrocarbons throughout the depth of the boring. VOCs in the subsurface diffuse across the membrane and partition into a stream of carrier gas, where they can be swept to the detector(s). The membrane is heated so that travel by VOCs across the membrane is almost instantaneous. If relatively high levels of VOCs are detected, the heated probe can be held at that depth in order to "burn off' contaminants prior to advancing in depth, thus minimizing the potential to smear contaminants downward as the probe progresses in depth. The detector information, the electrical conductivity of the soil, and the hydraulic conductivity are logged and graphed, allowing the rig operator and geologist to determine the location of the contaminant, relative concentration of the contaminant, the depth of soil in which the contaminant is located, and an indication of the hydraulic properties of the soil. After the CPT rig reaches the desired depth and MI-HPT sampling is complete, the rods and tooling will be removed and the CPT borings will filled with neat cement grout to the ground surface using a tremie pipe. 4.4 SHALLOW MONITORING WELL INSTALLATION PROCEDURES Three shallow monitoring wells will be installed at the locations shown on Figure 2 (Appendix A). The bore holes will be drilled to a total depth of approximately 50 to 55 feet bgs using a drilling rig equipped Itosor;:, CONDOR