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Former Thrifty Co.Station No.172 Workplan for Additional Soil and Groundwater Assessment May 8,2017 hydrocarbon concentrations in the recently-installed monitoring wells were observed in deep- screened wells MW-21 and MW-22. The results of shallow soil vapor sampling indicated that a potential vapor intrusion risk is present in the vicinity of SV-3. Soil and groundwater have been assessed and defined down-gradient of deep-screened monitoring well MW-22 in off-site well MW-23. Additional assessment is needed in the vicinity of off-site well MW-23 in the shallow zone and deep zone below 75 feet bgs. 3.0 SCOPE OF WORK The purpose of the additional soil and groundwater assessment is to evaluate the groundwater in the deep and shallow aquifers downgradient from the site and to assess soil conditions in the vicinity of the former waste oil tank. The scope of work in brief includes permitting and installing a monitoring well in the shallow and deep aquifers, sample soil in the vicinity of the former waste oil UST, collection of soil and groundwater samples, analysis of samples, and preparation of a report detailing site activities and results. The scope of work is described in detail in the following paragraphs 3.1 Monitoring Well Installation • Site Safety Plan. As required by the Occupational Safety and Health Administration (OSHA) Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910.120), and by the California OSHA (Cal-OSHA) "Hazardous Waste Operations and Emergency Response" guidelines (CCR Title 8, Section 5192), a Health and Safety Plan (HASP) will be prepared. The HASP will be reviewed by the field staff and contractors before beginning field operations at the site for all tasks described in this workplan. • Permitting. Drilling permits for the proposed monitoring wells and soil boring will be obtained from the SJCEHD. An encroachment permit will be obtained from the City of Stockton. • Utility Locating. Prior to drilling, ATC will mark the locations of the proposed boring and wells for all tasks described in this workplan and use a private utility locator to clear the locations. Underground Service Alert (USA) will be called to allow the local underground utility companies to identify the location of any utilities in the area of the proposed work. The boring will be cleared using air knife methodologies to a minimum depth of 5 feet bgs. The drilling locations may require adjustment due to the presence of underground utilities and/or overhead lines. • Monitoring Well Installation. ATC will contract with a C-57 Licensed drilling company to install two monitoring wells. One monitoring well proposed to be screened in the deep zone, below 75 feet bgs, will be installed at the location shown on Figure 2. The borehole will be advanced using 8-inch diameter hollow stem auger drilling equipment and completed with 2-inch diameter schedule 40 PVC casing, with a well screen consisting of 0.010-inch slot screen. Based on previous site assessment activities, ATC's recommended monitoring well construction details are presented in Table 1; however, the precise depth and screened interval of the monitoring well will 7