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Stantec ✓ <br /> December 8, 2010 <br /> Page 7 of 9 <br /> SOIL VAPOR SURVEY <br /> Soil Boring Advancement and Soil Sampling <br /> Stantec will supervise the advancement of five soil borings SG-12 through SG-16) utilizing a <br /> hand auger to reach the target depth of 5 feet bgs at the I cations depicted on Figure 2. Soil <br /> samples will be collected at intervals proposed on the soi sample plan (Table 5). The hand <br /> auger will be cleaned before augering each borehole and sampling equipment will be cleaned <br /> between each sampling interval. Each soil sample will be screened for hydrocarbon vapors <br /> using a portable photo ionization detector (PID). Soils encountered during the installation of the <br /> soil gas probes will be logged using the Unified Soil Classification System by a Stantec field <br /> geologist, working under the supervision of a California registered geologist. If groundwater is <br /> encountered, a new sample location will be selected nearby and samples shall be taken several <br /> inches before groundwater is encountered. <br /> All soil samples collected will be sealed with Teflon® sheets and plastic caps, then labeled and <br /> placed on ice in an insulated container for delivery to Kiff Analytical LLC, a California State <br /> certified laboratory located in Davis, California. Soil samples collected will be analyzed for <br /> TPHg, BTEX, MtBE, TBA, DIPE, EtBE and TAME using EPA Method 82608. <br /> SOIL GAS PROBE INSTALLATION <br /> Soil Gas Probe Construction <br /> Soil gas probes SG-12 through SG-16 will be constructed using 1/8-inch diameter Nylaflow® <br /> tubing and a vapor point. Approximately 2-inches of sand will be placed in the bottom of the <br /> boring prior to lowering the tubing and vapor point into the soil boring. Once the soil gas probe <br /> is placed in the boring, up to 1 foot of sand will be placed in the annulus of the soil gas point. <br /> The annulus of the soil gas probe will be sealed with approximately two feet of granular <br /> bentonite on top of the sand, and portland cement/bentonite slurry to the surface. A 6-inch <br /> diameter traffic-rated, watertight street box will be installed to protect the probe from surface <br /> traffic. <br /> SOIL GAS SAMPLING <br /> Soil Gas Sampling and Analysis <br /> Soil gas samples will be collected from SG-12 through SG-16. This work will be done in <br /> accordance with H&P Mobile Geochemistry's Active Soil Gas Collection Instructions into Mini <br /> Summas (Attachment C). A proper seal between the soil gas collection point and the sampling <br /> apparatus will be confirmed using 1,1-difluoroethane (1,1-DFA) or equivalent tracer gas. Soil <br /> gas sampling will not be performed within five days after a significant rainfall. <br /> The soil gas samples will be collected in mini Summa®canisters and analyzed by a California <br /> state-certified laboratory. The soil gas samples will be analyzed for the presence of TPHg, <br /> BTEX, MtBE, EtBE, TBA, TAME, naphthalene and 1,1-DFA (or equivalent tracer gas) by EPA <br /> Method TO-15. �'\ V�t4k-DN P'L <br /> Soil gas analytical results will be used to assess the risk to human health. The soil gas results will <br /> be compared to the CHHSLs and CRWQCB-San Francisco Bay Region (SFBR) ESLs for <br /> residential property use. If the screening level human health risk assessment indicates a <br /> 19976 Vapor Risk Assessment Report.doc <br />