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PSI Project Number:0575-1504 On Guggenheim—Stockton,CA July 22, 2019 Page 3 3 SCOPE OF WORK—SUBSURFACE SAMPLING This section describes the proposed methodology to conduct a subsurface investigation at the site. The objective of our proposed work is to establish protocols for conducting an investigation that will provide data for completion of the Subsurface Investigation Report for the subject property and to assess whether former practices at the former gas station have impacted the subject property. 3.1 PRE-FIELD ACTIVITES A minimum of three working days prior to performing the field services, PSI will mark the site and call Underground Service Alert to notify utilities and public service agencies of the proposed excavation. Additionally, a private utility locator will clear sampling locations, as well attempt to identify whether USTs are still present associated with the former gas station. 3.2 SOIL-VAPOR SAMPLING / v Soil-vapor locations have been selected to provide sampling in the areas where former USTs and associated piping and fuel dispensers are expected to have been located. PSI is proposing to complete soil-vapor sampling in five locations. The locations of the proposed soil-vapor samples are presented in Figure 2. Soil vapor samples will be collected by driving a temporary soil vapor sampling point in an open hole created by a direct push probe rod inserted to a depth of S feet bgs. An inert, plastic sparge implant tip will be installed in the middle of a one-foot sand pack with 1/8 or%-inch diameter Nylaflow tubing running from the tip to the surface. Dry bentonite will be placed in the hole above the sand pack, followed by hydrated bentonite to the surface, to complete the vapor point installation and seal the sand pack zone from other zones and ambient air. The vapor implant will be allowed to equilibrate for a minimum of two hours before sampling, After equilibration, a shut-in test will be performed to check for leaks in the above ground fittings. The shut-in test consists of assembling the above ground section of the sampling train (e.g. valve lines, fittings, flow controllers, and Summa canister downstream from the top of the probe), and evacuating the flow lines to a measured vacuum of about 100 inches of water, then shutting the valves at either end of the above ground section of the sampling train including the valve attached to the Summa canister and observing the vacuum for a minimum of one minute. If there is any observable loss of vacuum,the fittings are adjusted as needed until the vacuum in the above ground section of the sample train does not noticeably dissipate. After the shut-in test is successful, sampling, with a leak-check, will be performed. The leak check consists of applying the leak check compound (1,1-difluoroethane (1-1 DFA))to clean towels and placing the towels near the bentonite seal surrounding the drill rod and near connections along the sample train. The leak-check compound will be included in the laboratory analyte list and the laboratory will quantify and annotate all detections of the leak-check compound at the reporting limit of the target analytes. www.intertek.com/building