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LN r V - Soil Gas Screening Levels !ua/L of vapor) ESLs CHHSLs Residential Commercial Residential Commercial Benzene 0.084 0.28 0.0362 0.122 Toluene 63 180 135 378 E=thylbenzene 0.98 3.3 none none m,p-Xylenes 21 58 317 887 o-Xylenes 21 58 315 879 Methyl-t-butyl ether 9.4 31 4 13.4 �• 1,2 Dichloroethane 0.094 0.31 0.0496 0.167 TPH-gasoline 10 29 none none TPH-diesel 10 29 none none L. Since all soil vapor sample analyses were non-detect (table III), the potential risk of health hazards due to vapor intrusion from gasoline, gasoline related compounds, and diesel into ` indoor air in unanticipated, but theoretically possible future buildings is below current regulatory guidelines for commercial and residential sites and would pose no risk to human health. 7.0 SOIL CONTAMINATION 'r Ozone injection through shallow sparge points has been ongoing at one sparge point in each former UST excavation pit from ozone system start-up in December 2004 through March 2009, in addition to the slightly deeper ozone sparge points in and around the former �,. excavations remediating the groundwater and potentially the overlaying soil. This has aided in remediating substantial gasoline and diesel contamination that remained below the UST excavation pits, and above the groundwater table. With the additional investigational evidence provided by the soil vapor survey completed in June 2009, the remaining soil contamination is most likely very limited, if not fully remediated. Since petroleum hydrocarbon contamination may no longer be present in soil, there is no contaminant mass to calculate. 8.0 GROUNDWATER QUALITY 8.1 Attainment of Water Quality Objectives LN Concentrations of petroleum hydrocarbons in groundwater have declined significantly over time, especially since ozone injection remediation efforts commenced. The current groundwater analytical results reflect the lowest overall contaminant values seen at the subject site to date. Many of individual petroleum hydrocarbon compounds have, in all the monitor wells, become non-detect. The concentrations of residual benzene and TPH-gasoline presently exceed Water Quality Objectives (WQO) in only three groundwater monitor wells, MW-2, MW-5, and MW-7A. The large amount of monitor well analytical data, collected over a number of years, will allow a prediction of WQO attainment in these three wells. The individual compound of greatest concern is usually the aromatic hydrocarbon benzene. The analytical data trends for benzene indicate that it will degrade to below WQO even earlier than TPH-gasoline. Based on declining contaminant trends, the benzene concentration values in monitor wells w' MW-5 and MW-7A are expected to reach WQO goals within six years (figures 6 and 7). 7 JJW GEOSCIENCES Inc.