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Ms.Lori Duncan February 28,2012 RE:2911 E.Fremont St,Stockton,CA Page 3 of 6 Soil Vapor Sampling John Lane of L&P supervised the installation and sampling of two temporary soil vapor probes(SV 1-5,SV2- 5)on February 9,2012. The temporary soil vapor probes were installed by V&W Drilling Inc.(C57-720904) using a Geoprobe 5400 Direct Push drilling rig under a permit issued by EHD. One soil vapor probe was installed and sampled within the limits of the excavation/backfilled area and one soil vapor probe was installed and sampled west of the excavation/backfilled area. Figure 2 shows the locations of the temporary soil vapor probes. V&W Drilling advanced the temporary soil vapor probes to a depth of approximately 5 feet below ground surface(bgs). The temporary soil vapor samples were collected by extracting the drilling rods at least six inches to expose the soil to the vapor probe tip,attaching a Post Run Tubing(PRT) system to the probe tip with the appropriate connection, including an o-ring for a proper seal, and attaching the tubing to a Summa canister via a specially designed,manifold provided by Air Toxics LTD,the analytical laboratory. Prior to connecting the tubing, V&W placed a 5-gallon bucket over the drilling rods with the rods protruding up through the bottom of the upended bucket through a drilled hole. The base of the bucket was sealed to the ground with a ring of bentonite and the opening of the upended bucket through which the rod protruded was also sealed with a ring of bentonite(see field notes and photograph,Attachment 2). Prior to collecting the soil vapor sample, a leak test was conducted pursuant to methodology recommended by Air Toxics by opening the purge canister and the sample canister in tum and checking that the vacuum holds for at least five minutes in each case. The manifold showed no leaks at either location. The tubing was purged for approximately 3 minutes at each location to clear ambient air from the sampling train prior to sampling. According to Air Toxics,the sampling manifold is pre-set to purge at a rate of 167 milliliters(ml)per minute,for a total purge of approximately 500 ml. Based upon the use of/4-inch tubing(approximately 5 ml per foot of tubing),and tubing lengths of approximately 10 and 12 feet at the sample locations,the volume purged was equivalent to approximately 8 to 10 volumes of air in the tubing. All down-hole equipment, including the push rods, was thoroughly cleaned with laboratory-grade, non- phosphate detergent and clean water, and then double-rinsed prior to use. A separate, pre-cleaned vapor sampling manifold was used at each location. The borings were grouted with neat cement/bentonite after sampling was completed. Each Summa canister was labeled for sample identification after sampling and delivered under chain-of- custody to Air Toxics for analysis of constituents of concern using the TO-15 analytical method. The results are summarized below. TPHg: Soil vapor samples collected on February 9,2012 contained TPHg at 3,400 pg/m3 to 4,500 pg/m3, which are below the ESL of 29,000 µg/m3 for soil vapor in commercial/industrial settings. Benzene: Concentrations of benzene in soil vapor samples were non-detect(ND<2.5)and 13 pg/m3,below the CHHSL of 120 µg/m3 for soil vapor in commercial/industrial settings. 10759-Vapor Sampling