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4 �� Cardno� San Joaquin County Environmental Health Department ATC March 6,2013 Shaping the Future Three purge volumes, using a 60-millimeter(ml) plastic syringe dedicated to each sampling point, will be removed from the vapor probe assembly. A glass syringe will be used for this purpose if the sampling protocol requires it, but is normally only called for when a soil gas investigation employs an on-site mobile laboratory. The purge volume will be calculated based on the internal volume of tubing/and annular space around the probe tip and the ,4 tubing volume of the above ground sampling assembly. J�o;ri �( tr1 Once purging is complete, a 400 ml Summa canister, fitted with a 200 ml/minute flow restrictor, will be connected to t n J the vapor probe assembly and samples collected. Prior to and during sampling, a leak check compound derived �I4� from commercial computer"dust-off'spray(such as 1,1-Difluoroethane [1,1-DFA], or similar)will be used to s '` monitor leaks within the above ground vapor probe assembly. The"dust-off'spray will be sprayed into a plastic 1 ti bag containing several cotton cloth rags. The rags will be placed adjacent to, but not touching, each portion of the sample apparatus, including the area where the Teflon tubing exits the ground.The volatilizing leak-check compound will be present in the air surrounding the sampling assembly in sufficient concentrations to be pulled into the sample container through any vacuum leaks that may be present. If windy conditions persist during field L =5�, activities, a shroud assembly surrounding the tubing and sampling manifold may be used instead. Upon completion, the vapor probe will be removed and the boring will be backfilled/grouted with neat Portland cement from the boring terminus to ground surface. 7 Indoor Air Study Cardno ATC then proposes to collect one indoor and one outdoor vapor sample using time release certified clean summa canisters. The indoor sample will be collected in the,occupied area o the single-story commercial office structure on the site, at a height between three alj�five feet above the floor. The structure is in constant use as a business office, so a filter point similar to those used for sub-slab or soil vapor sampling will be employed to keep incidental dust and airborne particles from entering the sample container. The office will also be surveyed for consumer and household products such as cleaners, aerosol deodorants, and similar that may contain volatile compounds that could interfere with the analyses. If possible these chemicals will be removed from the office area as much as two weeks in advance of sampling, and will be inventoried if they cannot be removed or if they have been used in the office area during the two weeks prior to rs sampling G reJ�! 6 �,��.sy. r ' i_ { a. 4an'svr f- �i V r Y)at P Lc�'1/Afox �" � r�i� TJ 4-V, The summa canisters will collect samples over a period of six to eight hours. The purpose of the indoor airy r S ftp analyses will be to evaluate the potential degradation of indoor air quality compared to both the outside air ar{d the;;"� s�! projections obtained from modeling soil gas vapor data and to identify any volatile organic compounds (VOCs)",t•,' y being emitted into the building. The outdoor sample will be collected approximately 100 feet away from the site'" , structure in the prevailing up-wind direction concurrent with the indoor sample, at a location away from trees, 't automobiles,fuel tanks, and other sources of volatile organic compounds and elevated approximately six feet above the ground surface. The outdoor sample will provide a baseline for atmospheric concentratio4of the identified analytes of concern. P Sample Analysis U � `" ,� , ►y Soil vapor samples collected from the soil vapor probes and indoor air study will be immediately transferred under chain-of-custody procedures to an onsite State-certified laboratory. Each soil vapor sample will be analyzed using EPA Method TO-15. Each soil vapor sample will also be analyzed for the leak check compound, with a method detection limit of less than 10 Ng/m3. Each sample will be screened at the laboratory to evaluate for elevated IL concentrations. EPA Method 8260B may be employed for some samples to prevent an elevated dilution factor, U which would affect the detection limit of some of the compounds. For Quality Assurance/Quality Control purposes, a minimum of one duplicate sample will be collected immediately after the original sample from a selected vapor'-- probe location. Each soil vapor sample will be properly labeled and submitted under chain-of-custody procedures. V www.cardnoatc.com