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ATC Diesel Performance, Inc. Proposal for Limited Phase ll ESA May 25, 2017 Page 2 3.2. VAPOR SAMPLING ATC proposes that a total of six (6) soil vapor samples be collected at locations at the site identified as RECs. Three samples will be collected in the general vicinity of the oil/water separator and wash rack, southwest of the main warehouse building. One sample will be collected along the discharge pipe from the oil/water separator. Two samples will be collected in the repair truck storage yard. All samples will be collected at five (5) feet below ground surface (bgs). Each vapor probe will be installed by advancing a 1.25-inch direct push rod to the desired depth. Each probe will then be constructed in the open hole using 0.125 or 0.25-inch outer diameter (OD) Teflon tubing fitted with a screen tip implant at the base of the vapor probe. The aboveground Teflon vapor probe tubing will be fitted with a valve for purging and vapor sample collection. The annulus will be backfilled with six inches of 2/12 Monterey sand and overlain with six inches of dry granular bentonite followed by hydrated granular bentonite to the surface to seal the annular space above the sampling interval and prevent ambient air intrusion within the boring annulus. Each aboveground vapor probe assembly will be temporarily secured to allow the two- hour stabilization interval recommended by DTSC guidelines for soil vapor sampling. Sampling will take place through a lab-supplied manifold which includes separate purging and sampling ports and pressure gauges. Each assembled manifold will be pressure tested to detect leakage and adjusted or tightened until it is determined to be tight under sampling conditions. A leak detection compound such as 1,1-DFA will be used at the surface seal to indicate the effectiveness of the installed bentonite seal. All samples will be collected in summa canisters and analyzed for VOCs by Method TO-15, and into sorbent tubes for analysis of semi-volatile compounds related to diesel fuel by Method TO-17. Results from this sampling will indicate if volatile or semi-volatile organic compounds or petroleum hydrocarbons from the oil/water separator, wash rack or long-term oil staining are a significant concern at the site. Sampling points will be grouted to the surface and finished to match existing surface conditions once sampling is complete. SJCEHD will be called to the site to inspect grouting activities. 3.3. SOIL SAMPLING ATC proposes soil samples be collected from the same locations as the soil vapor samples. Six (6) soil borings will be advanced to approximately 20 feet bgs using a truck mounted Geoprobee narrow diameter, direct push technology. Drilling will be conducted by a State-licensed (C57) drilling company. A field geologist will be present to log the soil samples. Descriptions of soil types encountered and sample collection intervals will be recorded on boring logs. Soil samples will be collected at five foot intervals, field screened with a Photo Ionization Detector (PID) or similar instrument, and an estimated one or two samples from each of the borings will be submitted for laboratory analyses. Soil sample selection will be based on PID measurements and field observations (i.e. odor and soil discoloration). Collected soil samples will be analyzed for volatile organic compounds (VOCs) including total petroleum hydrocarbons as gasoline, benzene, toluene, ethylbenzene, xylenes, and fuel