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<br /> ATC Associates Inc
<br /> 1117 Lone Palm Avenue, Suite B
<br /> Modesto, California 95351
<br /> 209-579-2221
<br /> ASSOCIATES I NC FaX 209-579-2225
<br />' GROUNDWATER FLOW DIRECTION
<br /> DTW was measured in MW 1 through MW6, MW8, and MW9 on May 24, 2006, and ranged
<br /> from 68 48 feet (MW4) to 74 16 feet (MW8) below the top-of-casing elevations, representing a
<br /> net average decrease in the groundwater table elevation of 1 10 feet since the February 17, 2006
<br /> monitoring event (Table 1) The DTW was used to develop the groundwater elevation contour
<br /> map (Figure 3) Based on the May 24, 2006, momtonng data, the average hydraulic gradient is
<br /> calculated to be 0 03 ft/fl, approximately 158 4 ft/mile, towards the southeast
<br />' GROUNDWATER ANALYTICAL RESULTS--May 24, 2006
<br /> TPHg was detected in groundwater samples collected from MW1 through MW6 at
<br /> concentrations of 400 micrograms per liter (ug/L), 29,000 ug/L, 120 ug/L, 440 ug/L, 510 ug/L
<br /> and 1,600 ug/L, respectively Figure 4 depicts the isoconcentration relationship of dissolved
<br /> TPHg across the monitoring well network The greatest TPHg concentration was observed in
<br />' MW2, which is located in proximity to the former USTs and product-dispensing island
<br /> Benzene was detected in groundwater samples collected from MW1 through MW6 at
<br /> concentrations of 13 ug/L, 4,100 ug/L, 8 6 ug/L, 8 1 ug/L, 6 2 ug/L, and 54 ug/L, respectively
<br /> Figure 5 depicts the isoconcentration relationship of dissolved benzene across the monitoring
<br /> well network The greatest benzene concentration was observed in MW2, which is located in
<br /> proximity to the former USTs and product-dispensing island
<br /> Toluene was detected in groundwater samples collected from MW1, MW2, MW5, and MW6 at
<br /> concentrations of 14 ug/L, 1,400 ug/L, 0 6 ug/L, and 13 ug/L, respectively
<br /> Ethylbenzene was detected in groundwater samples collected from MW I, MW2, and MW6 and at
<br /> concentrations of 19 ug/L, 680 ug/L, and 2 0 ug/L, respectively
<br /> Total Xylenes were detected in groundwater samples collected from MWI, MW2, and MW6 at
<br /> concentrations of 6 7 ug/L, 1,900 ug/L, and 5 8 ug/L, respectively
<br />' MTBE was detected in groundwater samples collected from MW 1 through MW6 at
<br /> concentrations of 2 2 ug/L, 23 ug/L, 2 0 ug/L, 10 uglL, 2 7 ug(L, and 200 ug/L, respectively
<br /> Figure 6 depicts the isoconcentration relationship of dissolved MTBE across the monitoring well
<br />' network The greatest MTBE concentration was observed in MW6, which is located in proximity
<br /> to the former USTs and product-dispensing island
<br /> 1,2-DCA was detected in groundwater samples collected from MW 1 through MW6 at 15 ug/L,
<br /> 43 ug/L, 9 9 ug/L, 6 7 ug/L, 10 ug/L, and 450 ug/L, respectively
<br />' S 16258&031quadu1yl2.nd qtr-2006 dm 4
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