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In electronic correspondence dated February 10, 2012, the San Joaquin County Environmental Health Department (SJCEHD) provided authorization to begin ozone injection. On February 29, 2012, ozone injection was initiated utilizing a portable ozone injection system that was installed at the site. On March 91 2012, the ozone injection system was shut off pending approval from the CRWQCB in the form of a Monitoring and Reporting Plan (MRP). Approximately 8.91 pounds of ozone was injected into the groundwater from February 29 to March 9, 2012. On April 24 and May 1, 2012, pursuant to requests from the CRWQCB, ATC submitted a Notice of Intent and a draft MRP to the CRWQCB. On Monday, April 30, 20121 it was discovered that the portable ozone injection system had been stolen from the site during the previous weekend. In electronic correspondence dated May 1, 2012, the CRWQCB issued an edited version of the draft MRP and indicated ozone injection could commence at the site provided conditions in the draft MRP are followed and upon receipt of final approval from the SJCEHD. On October 16 and 17, 2012, a mobile ozone injection system was re -installed at the site and ozone injection into MW1, AS1, and AS2 commenced on November 8, 2012. From November 8 through December 281 2012, ozone was injected into the groundwater for approximately 721.85 hours resulting in approximately 90.24 pounds of ozone injected into the groundwater. Petroleum hydrocarbon concentrations decreased significantly in the groundwater samples collected from MW1, MW3, and AS2 on December 26, 2012, compared to the concentrations detected in samples collected from these wells on September 10, 2012. Petroleum hydrocarbon concentrations were not detected above maximum contaminants levels (MCLS) in the samples collected from MW1, MW3, and AS2 on December 26, 2012. The ozone sparge system was shut down on June 6, 2013. In March and April 2017, ATC conducted a subsurface investigation at the site. Soil borings SB -20 and SB - 21 were advanced to the north and east-southeast of the former UST excavation and boring SB -22 was advanced in the vicinity of the former waste oil tank. Hydropunch borings HP -1 through HP -6 were advanced along the southern, eastern, and northern perimeters of the site. Three cone penetration test (CPT) borings, CPT -1 through CPT -3 with adjacent hydropunch borings were advanced in the southwest and northeast corners of the property and one near the center of the property. Soil and groundwater samples were collected from these borings. Results of soil data collected during the March and April 2017 assessment indicate that total petroleum hydrocarbons quantified as gasoline (TPHg), benzene, Ahylbenzene, toluene, xylenes (BTEX), methyl tertiary butyl ether (MTBE), and naphthalene were not detected in the near surface soils at the property. Groundwater impacts from TPHg and benzene were limited to the deeper groundwater zone along the northern side of the property. Groundwater in the shallow groundwater zone has been delineated. ATC concluded that metals in soil are present at naturally occurring levels, shallow soil at the site does not pose a threat from direct contact or outdoor air exposure or pose a risk of vapor intrusion to indoor air, and groundwater impacts along the northern property boundary do not appear to be originating from the property's former USTs. ATC recommended additional assessment to confirm this conclusion. In November 2017, ATC conducted additional subsurface investigation at the site. Hydropunch borings HP -7, HP -8, and HP -9 were advanced along the eastern and northern sides of the on-site building. Chemical of Concern, TPHg was detected in one groundwater sample collected from HP -8 on the northwest side of the site building between 62 and 65 feet bgs at a concentration of 4,800 micrograms per liter (µg/Q. TPHg was not detected in groundwater samples collected from the remaining two borings at this depth. ATC concluded that results of groundwater data collected during the November 2017 assessment activities showed that groundwater impact from TPHg was limited to the deeper groundwater 3I Page