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UPDATE 28 8-02-94 Vapor extraction has removed the BTEXs from the ground water as shown by sample results obtained from the monitoring wells. The primary MCLs have been obtained since September 11, 1992 , when MW1, tested 1 2 ppb benzene The secondary MCLS have been met since June 18 , 1993 , when MW5 tested 120 ug/L Xylenes The Secondary levels of the "Present California Water Quality Goals" have been met for more than a year, see Table 1 Fecal Coliform: i From December, 1991 through February, 1992 , monthly fecal coliform samples were collected from monitor wells MW3 , MW4 , MW5 and MW6 Samples were again collected in June, 1992 , from monitoring wells MW3 , MW4 and MW6 During the September 11, 1992 sampling, MW3 and MW6 were dry, no fecal coliform samples were obtained Table 2 shows the results of these samples the only wells that have tested positive for fecal coliform are MW4 and MW5 As of June, 1992 all these wells are below detection limits, <2 2 MPN, for fecal coliform MODELING SOIL CONTAMINATION USING SOIL SAMPLE BORING CHEMICAL RESULTS OBTAINED FEBRUARY 2 , 1994 On February 2 , 1994 , three soil borings were performed to obtain soil samples to document the effectiveness of the vapor extraction and to verify the removal of gasoline range hydrocarbons from the soil beneath this site . On July 22 , 1992 , two areas remained with hydrocarbon impacted soils, Area A (beneath the western pump island) and Area B (east- southeast of the underground storage tank area) , see Figure 3B Estimates at that time indicated approximately 3436 pounds of gasoline range hydrocarbons remained in the soil and capillary fringe, see Update Status Report #15 , page 33 The analytical results from the latest sampling (February 2 , 1994 ) show a reduction in the amounts of degraded gasoline range hydrocarbons in Area B, leaving an estimated 531 pounds remaining beneath the site This indicates a reduction of approximately 85% in two years The EPA models "VLEACH" and "BIOPLUME, TWO-DIMENSIONAL CONTAMINANT TRANSPORT UNDER THE INFLUENCE OF OXYGEN LIMITED BIODEGRADATION IN GROUND WATER" were utilized to predict the amount of hydrocarbons that may impact ground water and if/when ground water is impacted, the amount that would migrate off site, see SITE CLOSURE REQUEST, dated June 1, 1994 VLEACH simulates the following process advection, sorption, vapor-phase diffusion and three-phase equilibrium BIOPLUME simulates contaminant transport and solves the transport equation for dissolved oxygen (oxidation) These models assumed a somewhat "worst case" by considering no natural degradation or dilution occurring in the vadose zone, a dissolved oxygen of 8 mg/L in the . background ground and surface waters, and the discontinuation of the vapor extraction system (VES) VLEACH was also quite page4