SITE INFORMATION AND CORRESPONDENCE

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CHASE CHEVROLET 424 VAN BUREN,STOCKTON PAGE 3 In a meeting held at the Stockton office of Advanced Geo-Environmental,Inc. (AGE) on December 8,2000,AGE expressed that significant decreases in soil vapor concentrations extracted by the SVE system have occurred due to the rise in groundwater and resultant decrease of vadose zone since April 2000. AGE requested that the SVE system be turned off until the feasibility of ground water extraction as a remedial alternative has been evaluated. PHS/EHD agrees that the effectiveness of the SVE system has decreased significantly. The report provided a calculation that showed the equivalence of 5 gallons of gasoline was removed by the SVE/IAS system between the period of August 20 to September 7,2000,and the equivalence of 12 gallons of gasoline was removed between the period of September 7 to 28,2000,compared to the equivalence of 699 gallons of gasoline being removed between the period of November 1999 to January26,2000 as reported in Qw7wdyReport—Fint Qester 2000 dated April 20,2000 prepared by AGE. Contaminant vapors are still being removed from VW-3 and VW-5 albeit at a lower rate (i.e. 12.4 scfm in September 2000). More importantly,the PID readings in VW-5 located west of MW-3 remained fairly strong(i.e.519 ppm in September 2000). While the efficiency of the system appears reduced,gasoline is still being removed by the system according to the report. PHS/EHD recommends that the SVE system continue for another quarter since vapors are still being extracted. PHS/EHD agrees that the IAS system should be turned off to prevent possible migration of the dissolved groundwater plume as well as the vapor plume. The effectiveness of in-situ volatilization of the dissolved petroleum organic compounds in the groundwater bythe IAS system is unclear at this time. The lack of significant reduction in the quarterly monitoring well sampling maybe indicative of the ineffectiveness of the technology,but reduction of volatile contaminant concentrations in groundwater is also unlikely to be observed in the quarterly groundwater sampling if the rate of groundwater movement at the site is slow. The level of Benzene in the groundwater of MW-3 has dropped from 16,000 µg/1 in September 1999 to 3,200 µg/l in August 2000,but the level of Benzene in MW-9 remained essentially unchanged at 33 µg/l in September 1999 and 31 µg/l in August 2000. AGE reported the presence of a California Water Service municipal well down gradient and approximately 2,400 feet northeast of the site on East Poplar Street and another California Water Service municipal well 1,700 feet west of the site on Lindsay Street and Edison Street that may affect the groundwater movement at this site. In order to evaluate the effectiveness of the IAS system and the potential impact of the dissolved contamination in the future,the rate of groundwater movement must be determined. Based on the quarterly sampling reports,the SVE/AIS system has been ineffective in reducing the level of petroleum hydrocarbons in groundwater at the northern portion of the property. High concentrations of TPH-g and BTEX constituents have been historically detected in the groundwater of MW-9. No significant reduction of either TPHg or BTEX in MW-9 quarterly samples has been observed since the start up of the SVE/AIS system The concentration of the lightest BTEX compound,Benzene,remained virtually unchanged from the MW-9 groundwater sampling results in November 1999 before the start up of the SVE/AIS system By contrast,the concentration of Benzene in the groundwater samples of MW-3 located on the southern portion of the property has been steadily dropping since the start up of the SVE/AIS system.