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3 San Joaquin County Environmental Health Department ATC January 2,2013 Shaping the future SCOPE OF WORK Planning and Permits Cardno ATC will obtain permits for the advancement and installation of three temporary soil vapor probes. Cardno ATC will schedule field personnel and equipment, notify Underground Services Alert to locate underground utilities as required, and perform other necessary field preparation and job start-up activities. Installation of Soil Vapor Probes This task includes mobilization to the site, advancing three soil borings, and completing the borings as temporary soil vapor probes. The soil vapor probes are planned to be located on site adjacent to enclosed and occupied structures. At least one soil vapor probe will be located between occupied on site structures and the source of contamination. Estimated soil vapor probe locations are shown on Figure 2. Soil vapor probe construction will be performed by a C57 licensed drilling company.The soil vapor probes will be advanced to approximately five feet bgs using either truck-mounted direct-push technology or,where truck access is not possible, a 2.5-inch diameter hand auger. Upon completion of each boring, a temporary vapor probe assembly will then be installed. Each vapor probe will be constructed using 0.25-inch outer diameter(OD)Teflon tubing fitted with a stainless steel wire screen tip implant at the base of the vapor probe. The aboveground Teflon vapor probe tip will be fitted with a swaglok valve for future purging and vapor sample collection. The bottom of the boring around the screen tip and subsurface assembly will be backfilled with four to six inches of 2/12 Monterey sand and overlain with hydrated granular bentonite to seal the annular space above the sampling interval to prevent ambient air intrusion within the boring�annulus. Each aboveground vapor probe assembly will be secured directly below the ground surface and covel*th a steel plate. Sampling Methodology In an effort to appropriately conduct soil vapor sampling on site, Cardno ATC will follow the guidelines established by the Los Angeles Regional Water Quality Control Board (LA RWQCB), the Department of Toxic Substances USS Control (DTSC), and the Interstate Technology& Regulatory Council (ITRC) in documents entitled Advisory— Active Soil Gas Investigations dated January 28, 2003 and Interim Final—Guidance For the Evaluation and/ fl Mitigation of Subsurface Vapor Intrusion to Indoor Air dated December 15, 2004, revised February 7, 2005, and Vapor Intrusion Pathway:A Practical Guideline, dated January 2007. 1] Soil Vapor Sample Collection T1yr. p S}ou[6), �+ -,a"✓.sari �E ��+__ S�' fop 1�r� � f«- 44 ,J �'? After each soil vapor probe assembly is complete, all probe assemblies will be allowed to equilibrate before sampling. Direct-push installed vapor points will be sampled after an equilibration time of no less than two hours. In the case of hand-augered soil vapor probes, Cardno ATC will return to the site to collect vapor samples no r sooner than 48 hours from installation-Once the vapor points have been allowed to stabilize,the above ground sample equipment will be assembled. A pressure gauge will be fitted to the three-way sample port assembly to measure the vacuum while purging is conducted. Three purge volumes, using a 60-millimeter(ml) syringe, will be removed from the vapor probe assembly. The purge volume will be calculated based on the internal volu?he of tubing and annular space around the probe tip and the tubing volume of the above ground assembly. s r� i� Once purging is complete, a 400,ml Summa canister, fitted with a 200 ml/minute flow restrictor, will be connected to i� the vapor probe assembly and samples collected. Prior to and during sampling, a leak check compound derived from commercial computer"dust-off'spray(such as 1,1-Difluoroethane[1,1 DFA], or similar)will be used to monitor www.cardnoatc.com