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Soil Boring Results and VEG/ISCO Work Plan Field Maintenance Shop #24 Stockton California August 2016 • VOCs and Naphthalene by EPA method 826013; • Total petroleum hydrocarbons as gasoline (TPH-g) by EPA method 826013; and • Total petroleum hydrocarbons as diesel TPH-d by EPA method 8015B. Soil confirmation samples will be compared to applicable California Tier 2 ESLs as presented in Table 1. 3.3. ISCO Remedial Measure Following the implementation of in-situ VEG, ISCO is proposed to reduce the contaminants of concern (primarily BTEX compounds and total petroleum hydrocarbons) in groundwater. The proposed treatment plan includes an application event of sodium persulfate (PersuffOx) and Oxygen Release Compound -Advanced (ORC-A) to reduce concentrations via chemical oxidation and enhanced aerobic biodegradation. The Remedial Contractor will employ Direct Push Technology (DPT) in three (3) defined treatment areas around monitoring wells FMS-MW5 (Area 2), FMS-MW6 (Area 1) and FMS-MW7 (Area 3) as shown in Figure 7. A total of 23 injection points in the vertical treatment interval of 35 to 45 feet bgs are proposed. The number of injection points per treatment area is detailed in Section 3.3.2 below, and final locations of the proposed injection points will be determined in the field. Drilling equipment will be operated by a C-57 licensed contractor. 3.3.1. ISCO Treatment Objectives The objectives of the ISCO injections is to further reduce residual petroleum hydrocarbon concentrations in Site groundwater in the vicinity of the source zone wells (FMS-MW5, FMS-MW6 and FMS-MW7). ISCO utilizing PersulfOx and ORC-A are the selected ISCO reagents to treat the residual gasoline and diesel in the source zone area at the site. These reagents have been previously approved by the CVRWQCB under the existing WDR and General Order No. R5-2008- 0149-045 for the Site and utilized at the Site during the 2014 and 2015 ISCO injections. Reagent selection, evaluation, and discussion have been previously presented to the CVRWQCB in the Work Plan for Implementing Remedial Action by In-situ Chemical Oxidation Treatment (ECM, 2014) and Remedial Action Completion Report for In-situ Chemical Injection (ECM, 2016). 3.3.2. Proposed ISCO Injection Scope PersulfOx and ORC-A will be injected in three treatment areas; Area 1 (325 square feet [ft2]), Area 2 (325 ft2), and Area 3 (300 ft2). Six (6) direct push injection points will be used for the PersulfOx application and six (6) separate injection points for ORC-A in Area 1. Six (6) and five (5) injection points will be used in Area 2 and Area 3, respectively for the ORC-A injections. All three treatment areas, will be injected from 35 to 45 ft. below ground surface (bgs). The injection interval for this target treatment area will focus on remediating the BTEX and TPH mass in submerged soil and groundwater. Treatment zone extents and amounts of reagents are provided below. Area 1 — Monitoring Well MW -6 and Former Dispenser Island • 325 ft2 • Total of 12 Injection Points • 2,204 lbs. (1,879 gallons) of PersulfOx (6 Injection Points) • 320 lbs. (104 gallons as a 30% slurry) of ORC-A (6 Injection Points) Page 8