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aecom.com Our Reference 60632236 6/10 Prior to sampling using the TO-15 method, the initial vacuum in the 1L Summa canister will be recorded (the 1L Summa canisters will be received from the laboratory having been evacuated to between -25 and - 30 inches of mercury). Samples will be collected in accordance with the DTSC Advisory (DTSC et al. 2015) and the sampling guide included in Appendix B i.e., samples will be collected by connecting a 1L SUMMA canister to the sampling system and opening the appropriate valves to allow for sample to pass into the 1L Summa cannister via a flow controller set to between 100 and 200 milliliters (mL) per minute until the pressure in the system increased to approximately -5 inches mercury. Prior to sampling using the TO-17 method, the TPH concentration in the well will be measured using a PID and the sample volume to be collected will be determined based on the values recommended sample volumes present in Table 2 (Buettner, personal communication, 2022). Samples will be collected in accordance with the sampling guide included in Appendix C i.e., samples will be collected using a 60 ml disposable syringe and a multibed vapor intrusion (VI) tube. Table 2 TO-17 Recommended Sample Volume TPH Concentration (ppmv)Sample Volume (ml) >1000 Not recommended for TO-17. Use canister. 100-1000 10 50-100 100 <50 200 Notes: ppmv = parts per million by volume > = greater than < = less than Samples will be transported under chain-of-custody to Eurofins Air Toxics, a State of California-certified analytical laboratory in Folsom, California. Soil vapor samples will be analyzed for (1) BTEX by EPA Modified Method TO-15, (2) naphthalene by EPA Modified Method TO-17 and (3) oxygen and helium (selected leak detection compound) by ASTM Method D-1946, as per Table 3 below. All samples will be analyzed on a standard 10-day turnaround. Table 3 Sample Container and Holding Time Requirements for Soil Vapor Samples Parameter Method Sample Container Sample Volume Preservative Holding Time BTEX TO-15 SUMMA canister 1 litre None 30 days Naphthalene TO-17 Sorbent tube To be determined 4°C 30 days Oxygen and Helium ASTM Method D-1946 SUMMA canister 1 litre None 30 days Decontamination Procedures All non-disposable reusable equipment will be decontaminated between uses. Specifically, the hand auger bucket and extension rods will be decontaminated between each lift of soil from the borings to prevent cross-contamination between soil sample locations (which are to be determined later based on recorded PID readings), and the direct-push auger rods will be decontaminated between boring locations to prevent foreign contamination of the samples. Equipment will be decontaminated using the following procedure: 1.Wash equipment with tap water and non-phosphate detergent (e.g., Liquinox or similar), using a brush as necessary; 2.Rinse using tap water; and