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�np A <br /> CLEARWTER <br /> G R b U P, I N C <br /> Enai ronmcntaf Seraoces <br /> GROUNDWATER MONITORING AND SAMPLING RESULTS <br /> Groundwater sampling results for gasoline range hydrocarbons are summarized as follows <br /> Depth to groundwater range 7 84 (MW-2) to 10 48 (MW-8) feet below <br /> top-of-casing (TOC) <br /> Flow direction and gradient Southeasterly at approximately 0 008 <br /> feet/foot <br /> Benzene concentration range From not detectable (MW-2, MW-3, MW- <br /> 4) to 2,800 micrograms per liter (µg/]L) in <br /> MW-5B <br /> Toluene concentration range From <0 50 µg/L (MW-2, -3, -4, -7, & MW- <br /> 8) to 820 (MW-5B) <br /> Ethylbenzene concentration range From <0 50 µg/L (MW-2, -3, -4, -7, &MW- <br /> 8) to 630 (MW-5B) <br /> Xylenes concentration range From <0 50 µg/l_ (MW-2, -3, -4, & MW-8) <br /> to 2,000 µ (MW-5B) <br /> TPH-g concentration range From <50 µg/L (MW-29 -3, & -4) to 21,000 <br /> µ (MW-5B) <br /> MTBE concentration range Not detected in concentrations exceeding <br /> indicated laboratory method reporting limits <br /> (<0 50 µ to<5 0 ) <br /> The groundwater flow direction and gradient as determined by this sampling event is <br /> substantially similar to previous monitoring events Groundwater elevation and analytical data <br /> are Included in Tables 1 and 2 Well construction data are provided in Table 3 A groundwater <br /> elevation map based on the groundwater elevation data from all monitoring wells was prepared <br /> and is presented as Figure 3 Revised dissolved-phase hydrocarbon distribution maps Including <br /> iso-concentration contours of benzene and TPHg in groundwater are presented as Figure 4 and <br /> Figure 5 respectively Analytical reports for this groundwater monitoring event are included as <br /> Appendix B <br /> Empirical Determination of Contaminant First-Order Decay Rates <br /> If all or some of the aforementioned natural attenuation processes are present within a plume, a <br /> reduction of contaminant concentrations and mass is usually observed over time This usually <br /> occurs at a site which has experienced source removal and/or some active remediation, so that <br /> ZB178C/1stQtr2004 Monitoring Rpt 6 April 15,2004 <br />