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Soil Vapor Monitoring Wells � Installation and Sampling Work Plan San Joaquin County Public Works 1810 E. Hazelton Avenue,Stockton,CA Page 4 QA/QC procedures to be implemented include shut-in testing, and quantitative leak detection using a shroud. The shut-in test is described in Section 4.2.1 of the Advisory and consists of applying a constant vacuum to the sampling train and equipment with a valve to the sampling probe closed. Any observed change in vacuum would reveal a leak somewhere in the sampling train setup. Quantitative leak detection using a shroud is described in Appendix C of the Advisory. The leak detection method consists of placing a shroud over the sampling train and equipment, applying a leak detection compound such as helium under the shroud, and then quantifying the concentration under the should via real-time measurement equipment or by collection of under-shroud air samples. The concentration of helium under the shroud can then be compared to the concentration of helium in the sample to confirm sample validity. The field technician will maintain a field log containing sample identification, date and time of sampling, sampling depth, weather conditions, sampling method, purge volume, apparent moisture content, and other pertinent observations. Collected samples will be delivered to laboratory under chain-of-custody procedures. 5.4 LABORATORY ANALYSES The samples will be analyzed for constituents of concerned based upon historical Site data as follows: Sample Type Location Depth Sampling Sample Analytical QC Point Rate/Time Analysis Method Measures TPH-G, BTEX, Shut-in test, SVP-I Soil See Figure 7, 5 to 6 100-200 MTBE, TO-151 quantitative through Vapor Appendix A feet bgs mUmin Naphthalene, ASTM D leak SVP-3 Oxygen, 1946-90 detection Helium Notes: BTEX=benzene,toluene,ethylbenzene,xylene;bgs=below ground surface;QC=quality control;mVmin=milliliter per minute; NA—not applicable;TPH-G=total petroleum hydrocarbons as gasoline The soil vapor samples collected into the Stemma canisters will be analyzed for TPH as gasoline, benzene, toluene, ethylbenzene, and xylenes (BTEX), MTBE, and naphthalene by EPA Method TO-15 using GUMS. Quantitative leak testing tracers will include oxygen and helium. 6.0 REPORTING Condor will prepare a report detailing results of the soil vapor well installations and sampling activities for submittal to the Central Valley Water Board. The report will include a discussion of the field and laboratory procedures, geologic logs of the borings, a discussion and presentation of the analytical results, a comparison of laboratory analytical results to applicable regulatory screening levels, and recommendations. Condor will also submit the report in electronic format to GeoTracker. 1s CONDOR