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f � � 3 � Cardno° San Joaquin County Environmental Health Department ATC March 6,2013 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 truck-mounted direct-push technology or,where truck access is not c possible, a rotohammer. Due to the shallow groundwater at the site, soil moisture content will be evaluated in the field to avoid placing the sampling intervals of the vapor probes in the capillary fringe where groundwater might be sucked into the sampling equipment. Upon completion of each boring, a temporary vapor probe assembly will then Y be installed. 'L 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 cove&ith a steel plate. k, Sampling Methodologyr oG�y r�in�ItF In an effort to appropriately conduct soil vapor sampling on site, Cardno AT6 will follow t e guideline established by the Los Angeles Regional Water Quality Control Board (LA RWQCB), the San Francisco Regional Water Qualityf Control Board (SF RWQCB), and the Department of Toxic Substances Control (DTSC in documents entitled 7 j� Advisory—Active Soil Gas Investigations dated April 2012 and Final—Guidance For the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air(Vapor Intrusion Guidance)dated October 2011. Soil Vapor Sample Collection One complete sample port assembly attached to a typical(but not yet installed)vapor probe assembly will be used to collect a material blank sample. x After each soil vapor probe assembly is complete, all probe assemblies will be allowed to equilibrate before sampling. Direct-push and rotohammer installed vapor points will be sampled after an equilibration time of no less than two hours. Once the vapor points have been allowed to stabilize, the above ground sample equipment will be f assembled. A pressure gauge will be fitted to the three-way sample port assembly to measure..the vacuum while purging is conducted. The sample port assembly at each vapor point will be subjected to a shut-in test to check for leaks in the assembly prior to purging and sampling. ' www.cardnoatc.com