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San Joaquin County 12066.000.000 PCCP Mountain House Property May 7, 2015 ENVIRONMENTAL ASSESSMENT WORKPLAN Page 2 contractor to advance soil, and soil vapor sampling borings. All borings will be logged by an ENGEO geologist or engineer under the supervision of a Professional Engineer. The following activities will be performed: • A C-57 licensed direct-push drilling subcontractor will advance Geoprobe® borings at a total of four locations (Figure 1) to a depth of approximately 20 feet below the ground surface. The borings will be advanced at locations presented on Figure 1. • We will retrieve continuous soil cores from each boring. Soil samples will be collected at depths of 5, 10, 15, and 20 feet below the ground surface from each of the borings. During drilling, the soil cores will be screened for volatile organic compounds (VOCs) using a photoionization detector(PID). Samples collected at 20 feet below ground surface will be put on hold with the laboratory pending analysis of the shallow samples. • The soil samples will be submitted to a State-certified laboratory and analyzed on a discrete basis for the presence of TPH-gasoline (TPH-g) and VOCs (EPA Method 826013) and TPH diesel (TPH-d) and TPH-motor oil (TPH-mo) with silica gel cleanup (EPA Method 8015). Laboratory analysis will be performed on a standard 5-day turnaround. • The borings will be filled with grout upon completion of sampling. Soil Gas Assessment In addition to soil sampling, we propose to perform a soil gas sampling program. The purpose of our study is to assess and/or confirm that the reported release has not resulted in elevated soil gas COC concentrations that would be expected to affect proposed residential development of the Property. To perform the assessment, four soil vapor monitoring wells will be installed in locations adjacent to the soil sampling locations. The soil gas monitoring wells will be installed and sampled in accordance with the Department of Toxic Substances Control (DTSC) Final Advisory Active Soil Gas Investigations (April 2012)using the following methodology: • The soil gas monitoring well casings will consist of '/4-inch-diameter Teflon® tubing equipped with a filter at the base of the tubing. The four wells will be installed with a direct push probe rig, which will advance an approximately 4.5-inch-diameter boring. The well borings will extend to a depth of seven feet below the ground surface. The bottom of the well casing will be equipped with a filter and will be situated at a depth of six feet below the ground surface, centered in the middle of a two-foot layer of No. 3 sand. The proposed two-foot-long sand pack is designed to provide adequate flow in the low permeability geology found at the Property. Six inches of dry bentonite will be installed on top of the sand, and the remaining annular space will be filled with hydrated bentonite grout to six inches below grade. • Once the installation of the annular seal is complete, the well casings will be equipped with a permanent Swagelok® ferrule and nut. A threaded plug will then be screwed into the nut and the mandatory two-hour equilibration time will begin.