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it CLEARWATER C R O U P • Envrronmenial Servrees GROUNDWATER MONITORING AND SAMPLING RESULTS Groundwater sampling results for gasoline range hydrocarbons are summarized as follows Depth to groundwater range 9 65 (MW-2) to 1178 (MW-8) feet below top-of-casing (TOC) Flow direction and gradient Southeast at approximately 0 006 feet/foot Benzene concentration range From not detectable (MW-2, MW-3, MW- 4) to 120 micrograms per liter (µg/]L) in MW-5B Toluene concentration range From <0 50 µg/L (MW-2, -3, -4, -7, & MW- 8) to 40 (MW-5B) Ethylbenzene concentration range From <0 50 µg/1- (MW-2, -3, -4, -7, &MW- 8) to 40 µ (MW-5B) Xylenes concentration range From <0 50 µg/L (MW-2, -3, -4, -7 & MW- 8) to 81 µ (MW-5B) TPH-g concentration range From <50 µg/L (MW-2and MW-4) to 3,100 µ (MW-5B) • MTBE concentration range Not detected in concentrations exceeding indicated laboratory method reporting limits (<0 50 to<5 0 µ ) The groundwater flow direction and gradient as determined by this sampling event is substantially similar to previous monitoring events Groundwater elevation and analytical data are included in Table 1 A groundwater elevation map based on the groundwater elevation data from all monitoring wells was prepared and 1s presented as Figure 3 A revised dissolved-phase hydrocarbon distribution map including iso-concentration contours of TPHg and benzene in groundwater is presented as Figure 4 and Figure 4A respectively Analytical reports for this groundwater monitoring event are included as Appendix C MONITORED NATURAL ATTENUATION TESTING As suggested in Clearwater's Corrective Action Plan and subsequently approved by the SJC/SJC/EHD, MNA testing was continued at the site this quarter The testing included field measurement of dissolved oxygen (DO), and the collection and submittal of additional groundwater samples to CytoCulture for bacterial enumeration, and inorganic chemical and nutrient assay ZB178C/4Q03 Monitoring Rpt 6 January 29,2004