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Additional Subsurface Investigation and Well Installation Work Plan San Joaquin County Public Works June 19, 2017 Page 3 4. Installing one additional ozone injection well (proposed well OW-7) to provide adequate injection of ozone throughout the heart of the dissolved contaminant plume. 4.1 SITE PREPARATION Condor will prepare the well installation permit applications and will obtain the required permits from the San Joaquin County Environmental Health Department (EHD) prior to initiating the fieldwork. Condor will coordinate all field activities with the Central Valley Water Board and EHD. The proposed drilling locations will be marked with white paint and Underground Service Alert (USA) will be notified at least 48 hours in advance of the fieldwork to locate and identify underground utilities in and near the work area. In addition, a utility locator service will be utilized as necessary to identify underground utilities. Prior to commencement of fieldwork, a tailgate safety meeting will be held and a site-specific Health and Safety Plan will be discussed with, and presented to, all field personnel for their signatures. 4.2 SHALLOW SOIL BORINGS Pursuant to the Central Valley Water Board's July 27, 2016 letter, Condor will collect soil samples from the ground surface to a depth of 10 feet bgs to characterize hydrocarbon impact to shallow soil observed during ozone injection well installation. As stated in the letter, soil samples were collected from 5 and 10 feet bgs in hand auger borings HA-1 and HA-2 in March 1999. The hand auger borings were located between the southern dispenser island and UST #2, and contained total petroleum hydrocarbons as diesel (TPH-D) as high as 4,500 milligrams per kilogram (mg/kg). However, the borings are 18 years old and no samples were collected as shallow as 2 feet bgs, where hydrocarbon odor was observed during installation of ozone injection wells in May 2017. The Central Valley Water Board also noted that shallow soil assessment is required as part of the Low Threat Closure Policy (LTCP), and will aid in closure eligibility assessment of the Site in the future. A table and figure showing the soil analytical results and locations of borings HA-1 and HA-2 are presented in Appendix C. Shallow soil samples will be collected at depths of 2 feet bgs, 5 feet bgs, and 10 feet bgs at the two locations described below: Between the southern dispenser and UST #2, where petroleum odor was observed at a depth of approximately 2 feet during drilling of proposed ozone injection well OW-7 in May 2016. Well OW-7 was not installed in May 2016 because the work was halted by El-ID. The proposed shallow soil samples will be collected during drilling/installation of OW-7. These soil samples will be collected into 2-inch diameter brass sleeves using a drilling rig equipped with hollow stem augers and a split spoon soil sampler. South of former UST #3, where petroleum odors were noted in soil beginning at a depth of approximately 10 feet bgs during drilling of ozone injection well OW-6 in May 2016. The proposed shallow soil samples will be collected during drilling of deep boring CPT-2. These soil samples will be collected into 1.5-inch acetate sleeves using a direct push drilling rig. The proposed locations of the shallow soil samples collected during drilling of OW-7 and CPT-2 are presented on Figure 6 (Appendix A). The soil samples will be collected into brass or clear acetate sleeves, as appropriate, capped at each end with Teflon® tape and plastic end caps, and placed in a pre- cooled ice chest. The soil samples will be transported under chain-of-custody protocol to a state-certified analytical laboratory. 84114 * CONDOR