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-, Abdelwahed Facility, Ultra)Mfr Site No. 13792 V May 5, 2012 Stockton California Work Plan Well for DPE Well Installation and Soil Gas Investigation To increase the likelihood of adequate soil permeability, the soil gas investigation will not be conducted during or within one day after a significant rain event (e.g., 0.5 inch or greater). Soil gas collection probes shall be advanced to 5 to 6 feet below surface grade (bsg) utilizing a direct -push rig. If advancement of the soil probes to the target depth is unsuccessful, the sample probe shall be re -advanced 3 to 5 feet from the initial location. Advancement of soil probes to target depth shall be attempted up to three times prior to abandoning the location or, depending on the refusal depth, the sample may be collected at a shallower depth. Soil gas samples shall be analyzed on site immediately after collection utilizing an on-site mobile laboratory. Installation of soil gas collection probes, sample collection and sample analyses shall be conducted by a soil gas investigation contractor in general accordance with the DTSC and Cal EPA guidelines, and with the drilling contractor protocol. Fieldwork by Horizon shall be conducted in accordance, where applicable, with the attached Horizon Methods and Procedures. The proposed soil gas investigation shall consist of the following tasks: Task 1 Retain a C57 -licensed contractor experienced in conducting SGIs and which operates a mobile analytical laboratory; obtain permits, as required, from the EHD; notify Underground Services Alert (USA) to identify locations of underground utilities that may be in the area of the sample locations; and update the Site-specific Health and Safety Plan to include SGI fieldwork. Task 2 Core pavement or open the surrounding surface at each proposed soil gas sampling location; hand auger to a minimum depth of 3 feet bsg to clear for utilities; advance temporary soil gas sampling probes SG -1 through SG -4 to a depth of approximately 5 feet bsg rig; pull back driving rod to expose the inlets of the soil gas probe; verify the soil gas flow conditions; re -advance sampling probe if flow testing indicates a vacuum greater than 10 inches of mercury column or if the maximum attainable flow rate is less than 10 ml/min; and abandon all borings by backfilling with bentonite/cement grout; finish the surface to match surrounding area. Conduct the purge -volume test at the SG -1 location (the location that is likely to yield the highest constituent concentrations) for evaluation of the appropriate purge volume for the remaining locations; calculate the apparatus volume for the sampling setup that includes the annular space around the open sample probe and the sample tubing; conduct purge tests of 1, 3 and 7 apparatus volumes; select the purge volume that results in the highest constituent concentrations; and if vapor concentrations are not detected in any of the purge tests, purge a default of 3 apparatus volumes prior to collecting each subsequent sample. Conduct leak testing with shroud at each sample location utilizing 1,1- difluoroethane (DFA) as tracer compound; and if tracer compound is 1792 DPE Well WP Project No. 1792.26 6 HORIZON ENVIRONMENTAL INC.