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2.2.3 Groundwater Sample Collection Methods Groundwater samples will be collected from each boring. Based upon previous borings at the Site and logs from the Diamond Walnut site, the first-encountered aquifer is expected to be a fine sand layer at approximately 46 to 48 feet bgs. LNAPL may be present in the samples. Prior to purging and sampling, the depth and thickness of the LNAPL and the static water level will be measured using a multiphase interface monitoring probe. To collect the groundwater sample, after the boring has been drilled a 5-foot section of new slotted %-inch diameter PVC well screen and new PVC blank casing will be installed into the cased borehole, and the casing will be retracted 5 feet to expose the aquifer. Groundwater will be purged with a stainless-steel bailer or by attaching a stainless-steel check valve to new tubing, and oscillating the tubing to displace the water to the surface. If the aquifer is adequately transmissive, water will be purged until the sediment is visually decreased or at least 1 liter has been purged. The sample will be collected into containers provided by the laboratory. Sample names will refer to the boring number and groundwater sample depth interval, and labels will also show the date and time collected and proposed analyses. Samples will be placed in a cooler chilled to 4 degrees Celsius pending delivery to the laboratory using chain-of-custody procedures. 2.2.4 Laboratory Analysis Soil samples will be analyzed for TPHd by EPA Method 8015M with silica gel preparation by EPA Method 3630C (Table 1). Two containers will be filled for each groundwater sample. The samples will be filtered in the laboratory with a 0.45-micron filter, prepared by silica gel cleanup, and analyzed for TPHd by EPA Method 8015M. The sample holding time is the length of time that a sample or sample extract can be expected to remain representative of environmental conditions. The holding time for TPHd is 14 days. It is anticipated that samples will be delivered to the laboratory or transferred to a laboratory courier. If samples are shipped, they will be handled in accordance with Kennedy/Jenks SOG on Sample Packaging and Shipping included in Appendix D. 2.2.5 Laboratory Quality Assurance/Quality Control (QA/QC) Laboratory QC consists of a laboratory and a matrix component. The laboratory component measures the performance of the laboratory analytical process during sample analyses, while the matrix component measures the effects of a specific medium on the method performance. Corrective actions for instrument calibrations or QC sample data that are out of compliance are typically described in the laboratory-specific QA/QC program. Additional Soil and Groundwater Sampling Work Plan, BNSF Mormon Yard, Stockton CA Page 7 Iftybnsf211onsfwp \ wp1201811899020 00_mormon_yard1work_plan_id12018 mormon yard sampling wp_mwm doc