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Boulevard Automotive - 2 - 2 December 2020 2151 Country Club Blvd Stockton, San Joaquin County Table 1 — Sum ary of J ly 2020 Groundwater Data Hydro- logic Unit No. of Wells Screen Interval Range ftbs TPHg u/L B u/L) T (u/L) E (u/L) X (u/L) MTBE (u/L) TBA (u/L) 12 DCA (u/L HU1 15 9.5-30 19,000 7,800 1,600 2,100 9,700 5.1 <1,000 2.0 HU2 11 30-50 24,000 6,700 6.8 <250 <250 5.1 <1,000 <100 H U 3 0 -- -- -- -- -- -- -- -- -- HU4 8 69.5-80 6,100 2,900 <50 <50 <50 <1 <10 <50 HUSA 2 1 95-110 6,100 3,900 <50 I <50 <50 <1 <10 <50 HU6A 2 120-125 400 95 <2.5 <2.5 <2.5 <1 <10 <2.5 LTCP Class 4 Thresholds -- 1,000 -- -- -- 1,000 -- -- 1 PHg= total petroleum hydrocarbons as gasoline; BTEX= benzene, toluene, ethylbenzene, xylenes; MTBE= methyl tert butyl ether; TBA= tert butyl alcohol; 1,2 -DCA= 1,2-dichloroethane; ft bgs= feet below ground surface; ug/L= micrograms per liter A= most recent data from September 2017 The remaining hydrocarbon concentrations in groundwater warrant active remedial measures at the Site. As such, Central Valley Water Board staff do not believe that Monitored Natural Attenuation (MNA) is a viable remedial alternative for this Site at this time. There appears to have been significant reductions in remaining dissolved hydrocarbons in groundwater following the peroxide injections (see Table 2 below). While AGI recommends rescinding the WDRs, in the 3Q20 GMR they provide no technical justification for doing so, nor any conclusions related to the efficacy of peroxide injection at the site. Table 2 — Evaluation of Dissolved Hvdrocarbon Mass Reduction Time Peroxide Cumulative TPHg Cumulative TPHg Frame of Injection Concentrations from Concentrations from Peroxide Target g HU1/HU2 Wells HU1/HU2 Wells Difference Reduction Injections Zones during September during July 2020** 2018* (ug/L u /L Oct 2018 HU1, thru Jan HU2 528,729 140,200 388,529 73.5 2019 ug/L= micrograms per liter * For wells not sampled in September 2018, September 2017 data was used. **Data for wells not sampled in both September 2017/2018 and July 2020 was not used in these calculations. The frequency of routine groundwater sampling events has recently been inconsistent. Prior to the July 2020 groundwater sampling event, the most recent event was performed in December 2018. Per the Amended MRP, quarterly groundwater monitoring and sampling is required at the Site, with a Groundwater Monitoring Report