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4.2.4 Sampling Methods and Procedures <br /> This section describes the methods and procedures that will be used to collect soil gas, soil, and <br /> groundwater grab samples. All samples will be handled in accordance with approved procedures <br /> specified herein and in applicable sections of the QAPP and the LARWQCB guidance for the soil gas <br /> survey. Tables 4 to 7 show the requirements for analytical methods, detection limits, sample containers, <br /> volumes,preservatives, and holding times by parameter per matrix. <br /> 4.2.4.1 Utility Clearance <br /> Underground Services Alert (USA), and any utility companies (identified to URS) not covered by USA <br /> that may have underground utilities at the Site, will be notified of the intent to conduct subsurface <br /> investigations at least 72 hours prior to initiation of intrusive field tasks. All proposed locations of <br /> subsurface investigation will be clearly marked with white paint or surveyors flagging as required by <br /> USA. USA will contact all utility owners of record within the site vicinity and notify them of the <br /> intention to conduct subsurface investigations in proximity to buried utilities. All utility owners of <br /> record, or their designated agents, will be expected to clearly mark the position of their utilities on the <br /> ground surface throughout the area designated for investigation. <br /> 4.2.4.2 Soil Gas Sampling <br /> A qualified subcontractor will conduct the soil gas sampling survey using an onsite mobile laboratory. A <br /> description of the sample collection procedures is provided below. Any requirement of the DTSC and the <br /> LARWQCB not specifically written below is incorporated by reference to the attached LARWQCB <br /> guidance. Coring equipment will be used to cut concrete slab or pavement at the surface where <br /> necessary. <br /> As stated above, soil gas sampling will not occur during any rainfall or within seven days of a heavy rain <br /> event. <br /> Probe Installation <br /> • The soil gas probes consist of /a-inch-diameter clean, dry NylaflowTM or equivalent tubing with a <br /> soil gas inlet point located at the down-hole end of the tubing and a sample collection port at the <br /> surface end. The type of tubing used will consist of NylaflowTM, polyethylene, and/or <br /> polypropylene. To prevent entangling or collapsing of the tubing, 1-inch protective pipe may be <br /> used during the construction of the soil gas probes. <br /> • The probe will be driven into the ground using either a percussion hammer or hydraulic ram. <br /> After the probe is advanced to the desired depth, the probe shaft will be withdrawn, leaving space <br /> for the sampling tube in the ground. The tubing is then inserted into the borehole. The bottom 6 <br /> inches of the tubing is pierced in three to four locations to create slots that will allow for the free <br /> flow of soil gas from the formation through the tubing to the surface, where the samples will be <br /> subsequently obtained. Should soil caving be noted prior to installation of the tubing, then the <br /> probe will be re-driven with the tubing included within the hollow interior of the piping attached <br /> to the probe point. <br /> • Once the tubing is in place, clean sand of a suitable grain size that allows flow will be poured <br /> around the perforated section of the tubing to allow for diffusion of soil vapors. At least 1-foot of <br /> sand pack will be placed at the sampling interval. Then at least 1-foot of dry granular bentonite <br /> will be emplaced on top of each sand pack interval so as to preclude the infiltration of the <br /> hydrated bentonite pack. The remaining open probe-hole will be backfilled with hydrated <br /> Page 16 PAPEA bwkefordMork Plan\Lockeford WP.doc <br />