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i 1 ' 05 September 2002 AGE-NC Project No, 95-0100 Page 4 of 9 ' Four soil vapor samples were submitted for laboratory analysis. TPH-g was detected at concentrations ranging from 19,000 micrograms per liter(pg/1)to 24,000 µg/l. BTEX were detected in the vapor samples at concentrations ranging from 220 4g/l(ethylbenzene in VS-1) to 2,600 �Lg/l ' (toluene in VS-3). AGE prepared a Corrective Action Plan (CAP), dated 06 December 1995 that recommended ' initiation of a soil vapor extraction system, utilizing the soil vapor wells installed and possibly one additional well to aid in the rapid removal and destruction of hydrocarbon vapors. ' 3.4. COMPUTER AIDED MODELING In a letter dated 25 April 1996, the SJC-EHD requested that the property owner's consultant perform ' a risk-based decision computer modeling of the site specific conditions to better assess the need for active remediation. As an alternative to active soil remediation, a fate modeling program was utilized to better assess the need for site remediation. The American Petroleum Institute's (API) Risk/Exposure Assessment Decision Support System (DSS) is a modeling program devdloped to estimate human exposure and risk from contaminated sites. The DSS consists of four modules that include a fate and transport module. The fate and transport module induce the use of SESOIL, an unsaturated zone model and AT123D, a saturated ' zone module. The SESOIL and AT 123 D model predicted that no benzene,ethyl benzene,toluene and xylene would impact the ground water at the site. A one-hundred year estimation of hydrocarbon impact to ground water was established for the model. The results of the AT 123D risk based computer modeling program indicted that a significant increase ' of the ground water elevation at the site would cause the integrity of the ground water to be comprornised. If the ground water elevation were to increase approximately 20 feet to a depth of 35, feet bsg, a significant portion of the hydrocarbons adsorbed to soil on the site would be exposed to ' ground water and could be dissolved into the water."Concentrations of the initially benzene-impacted ground water were estimated at 25,000 µg/l. After 6.5 years the dissolved benzene concentrations would be reduced to levels below the California Department .of Health Services maximum contaminant level of 1.0 dug/l. The model also predicted that other BTEX compounds would dissolve i into the elevated ground water. Concentrations of the other BTEX compounds would also decline over a period of time. - -3.5-7 CORRECTIVE ACTION PLAN'-PREPARATIQN. Data collected from the site during the investigation of the former UST site indicates that ' hydrocarbon-impacted soil is present in the vadose zone from approximate depths of 5 to 40 feet bsg. No ground water investigation was required or performed at the Franklyn Cole site,and ground water • has not been encountered on the site during this or previous investigations. Therefore, only 1 Advanced GeoEnvironmental,Inc. i