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ISI 4 ,I 2.2 Soil Wide spread soil contamination has not been known at this site: Soil contamination is not a concern except for petroleum impacted soil that is limited in extent to below the former USTs. The soil is typically contaminated from petroleum hydrocarbons that migrate downward through the soil from the leaking USTs until intersecting a lithologic barrier or contacting groundwater (figure 4). Once the groundwater is impacted, the petroleum hydrocarbon plume generally will migrate down-gradient. To date, the plume is contained nearly on-site and has migrated only a short distance (figure 5). 2.3 Litholo 9Y . The subsurface lithology inferred from the interval sampling conducted during monitor well installation appears to be predominantly clayey to silty sands interbedded with silty to sandy clay. Clay matrix is common throughout most samples (figure 5). However, most of the monitor wells at the site recharge quickly after purging during monitor well sampling events, indicating the lithology has sufficient porosity and permeability needed for ozone sparging to be effective. Additionally, JJW infers that the site consists of one continuous aquifer from the surface of the groundwater down to at least 130 bgs due to the observation that the watertable is the same for all the monitor wells regardless of the depth of the screened interval. 3.0 Soil remediation Soil contamination above the groundwater table is limited to the former UST locations. JJW has considered overexcavation of the former UST locations to remove additional petroleum contaminated soil that is still in place adjacent-to and under the former USTs. JJW feels that it would be premature to attempt to overexcavate at the present time. To be effective, the excavation should be dug to the depth'of the groundwater, currently at about 35 feet bgs, to remove all the contaminated soil above the water table. Due to the depth, the excavations would have to be stepped laterally to provide for sufficient slope stability and address safety concerns. The excavation could impact the residence on the neighboring property to the west, Jackson street to the north, and potentially impact and compromise buried public utilities. JJW feels that the soil contamination above the groundwater table can be readily addressed by the ozone injection system. Ozone is a strong oxidizing agent and can greatly hasten the rate at which petroleum organic compounds are oxidized in the soil as well as the groundwater. JJW proposes to install ozone sparge points at approximately 35 bgs in the former UST excavation sites where petroleum contamination of the soil is noted. This should provide significant reduction and ultimately complete elimination of the petroleum contaminates in the soil. I Soil contamination below the groundwater table in the saturated zone will effectively be dealt with and remediated in conjunction with groundwater remediation. JJW GEOSCIENCES Inc.