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} 5.2 Depth to Groundwater _ The normal seasonal rise in the water table continued during the quarter (Table 1) A rise of ' approximately 4 feet took place, bringing the water to its highest level in more than 6 years 5.3 Groundwater Gradient,and Flow Direction As in most previous quarters, groundwater flow is east-southeastward, with a prominent trough beneath the Apache building (Figure 5) 5.4 Groundwater Contamination Despite the rise in the static water level, benzene and TPH-g concentrations in MW-5 have declined to their lowest levels in more than 2 years (Table 2) In fact, benzene was not detected for the first ' time However, low concentrations of benzene, toluene, and xylene were detected in MW-4 Previously, no contaminants had been detected in any samples from this well Hence, the laboratory result is probably in error, and may be due to improper cleaning of lab equipment after a previous ' sample As expected, gasoline and BTEX were detected at moderate concentrations in VE-1 "deep" ' Concentrations have risen since this well was sampled in May 1996, and are about the same as when this well was sampled in February 1996 5.0 CONCLUSIONS ' Based on long-term trends m the concentration of hydrocarbon vapors being withdrawn from the extraction wells, it is clear that the vapor extraction system has been successful in lowering the concentration of gasoline liquids in the soil Quantitative laboratory data indicate that concentrations in the shallow well vapor stream have declined from a high of 4,800 ppmv in November 1994 to a few hundred ppmv at the present time, and field measurements show a similar ' decline Fewer laboratory data are available for the deep zone, but concentrations decreased from 22,600 ppmv in November 1994 to 5,290 ppmv in September 1995, a reduction of more than 75% PID data show a steep decline in concentrations from December '1994 to July 1995, but at least ' some of this decline is due to a rise in the water table, reducing the air flow through the deep zone It is also apparent from Figures 3 and 4 that PID readings on field samples usually exceed the ' laboratory results of tedlar bag samples The disparity is probably attributable to the differences in equipment ' The total volume of vapor that has been extracted since July of 1994 is approximately 62,000,000, cubic feet The calculated weight of extracted hydrocarbons exceeded 15,000 pounds as of December 1996, which is roughly equivalent to 2,300 gallons of gasoline 6