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C L E AWATER C a 0 u P Environmental Servrcrs Before sampling, each well was purged until water quality parameters had stabilized Stabilization occurred after approximately three wetted casing volumes had been removed Prior to purging, all wells were checked for the presence of light non-aqueous-phase liquids (LNAPL), none was observed to be present in any well Stabilization measurements of purged groundwater temperature, conductivity, and pH were made and recorded on Monitoring Well Data Sheets for each well Well stabilization data are enclosed in Appendix B Following purging, each well was allowed to recharge to at least 80% of its static water level prior to sampling Groundwater samples were obtained from each well using disposable polyethylene bailers and decanted into clean laboratory supplied bottles Samples were labeled, documented on a chain-of-custody form, and placed on ice in a cooler for transport to the project laboratory Groundwater samples were analyzed by Kiff Analytical Labs, a California State- certified laboratory, for concentrations of TPHg, BTEX and MTBE by EPA Method 8260B Groundwater samples collected for MNA data were delivered to CytoCulture Environmental Biotechnology Laboratories (CytoCulture) in Richmond, California All field work was conducted in accordance with Clearwater's Groundwater Monitoring and Sampling Field Procedures and Natural Attenuation Processes and Recommended Monitoring Guidelines included in this report as Appendix A GROUNDWATER MONITORING AND SAMPLING RESULTS Groundwater sampling results for gasoline range hydrocarbons are summarized as follows Depth to groundwater range 8 88 (MW-2) to 1104 (MW-8) feet below top-of-casing (TOC) Flow direction and gradient Southeast at approximately 0 0058 feet/foot Benzene concentration range From not detectable (MW-2, MW-3, MW- 4) to 2,300 micrograms per liter (p.g/L) in MW-5B Toluene concentration range From <0 50 Rg/L (MW-2, -3, -4, -7, & MW- 8) to 910 gg/L(MW-5B) Ethylbenzene concentration range From <0 50 µg/L (MW-2, -3, -4, -7, &MW- 8) to 660 g/L (MW-5B) Xylenes concentration range From <0 50 µg/L (MW-2, -3, -4, & MW-8) to 1,700 MW-5B) TPH-g concentration range From <50 pg/L, (MW-2, -3, and MW-4) to 23,000 MW-5B) MTBE concentration range Not detected in concentrations exceeding indicated laboratory method reporting limits (<0 50 pg/L to<20 µg/L) • ZB178C/1Q03 Monitoring Rpt 4 April 23,2003