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R604 :UPDATE 9-MARCH, 1992 <br />• RESULTS - WATER <br /> Ground Water Gradient <br /> Ground water gradient maps have been produced from the January 21, <br /> 1992 depth to water measurements, Figure 4A, from the February 4, <br /> 1992 depth to water measurements, Figure 4B and from the March 5 , <br /> 1992 depth to water measurements, Figure 4C. <br /> Figure 4A, the January, 1992 gradient shows flow to the east, with <br /> a slight trough forming at MW1. <br /> Figure 4B, the February, 1992 gradient also shows flow to the <br /> east, with a more prominent trough forming from MW6 towards MW2 . <br /> Figures 4A and 4B both indicate a cycle of discharge to the east, <br /> in the direction of the municipal wells. <br /> Figure 4C, the March, 1992 gradient shows a reversal in flow <br /> direction from the previous measurements, to the north northwest. <br /> This cycle is most likely a recharge event, and may also represent <br /> a decline in water usage of the well field to the east of the <br /> site. <br /> TOTAL PETROLEUM HYDROCARBONS <br />• Floating Product <br /> No floating product has ever been observed in any of the <br /> monitoring wells. <br /> Dissolved Petroleum Hydrocarbons in Ground Water (TFH-EPA METHOD <br /> 5030 ) . <br /> Dissolved petroleum hydrocarbons, gasoline range, were detected as <br /> very low levels in MW2 - 0 . 3 mg/L and MW5 - 0 . 083 mg/L. This <br /> analysis shows the steady decline in hydrocarbons associated with <br /> the ground water and is evident in comparing the ground water <br /> plume map generated from the December 16 , 1991 sampling, Figure <br /> 5A, to the plume map generated from the March 5 , 1992 sampling, <br /> Figure 5B. <br /> Prior to vapor extraction, November 21 , 1990 , gasoline range <br /> hydrocarbons were detected in MW1 - 2 mg/L, and MW5 - 31 mg/L. <br /> Since that time MW1 has has been below detection limits ( <0 . 5 <br /> mg/L) and MW5 was below 0 . 5 mg/L for gasoline range hydrocarbons, <br /> as noted during the June 24, 1991 sample results, see Table 1 . <br /> BTEX IN GROUND WATER (EPA Method 602 ) <br /> No BTEX' s were detected in monitoring wells from the March 5 , <br /> 1992 sampling. During the previous sampling, December 16 , 1991 <br /> only MW1 , MW2 , and MW5 , had BTEX' s in very low concentrations - <br /> vapor extraction has removed the BTEX ' s from all of the <br /> page 4 <br />