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i 04 September 2007 AGE-NC Project No. 95-0121 Page 4 of 9 remediation of other hydrocarbon phases. High-vacuum (vacuum pump capable ofproducing25 to 30 inches ofinercury) dual-phase extraction systems are capable of removing both hydrocarbon vapors and, depending on-site soil type, stratification, liquid and dissolved phase hydrocarbons. Extracted vapors are to be treated by incineration in catalytic oxidation and waste (impacted) ground water be stored on site in a temporary tank for later recycling and disposal. The advantages and disadvantages of DPE are discussed below. Advantages: High vacuum dual phase extraction using thermal/catalytic oxidation can quickly remediate petroleum hydrocarbons present in the vadose zone, capillary fringe and upper portion of the saturated zone. Due to the burial of the significant adsorbed contamination (Appendix D), the dual phase system can often be more effective than other options (air-sparging and soil vapor extraction). Disadvantages: The effectiveness of this technology is sometimes dependent upon sufficiently lowering the water table to allow vapor extraction to remove hydrocarbons from the capillary fringe and saturated zones. Discussion: Based on this review of site conditions (depth of impacted soil and high water table over the impacted soil, with a significant dissolved phase concentration of total petroleum hydrocarbons (TPH)/Benzene, toluene, ethylbenzene and total xylenes (BTEJ ), high vacuum dual phase extraction is considered the a viable option for this site, especially based on the drawdown observed in the extraction well during purging. The capability of remediating the three phases of hydrocarbons and treating the vadose, capillary fringe and upper saturated zones within a rapid time frame are particularly well suited to the existing conditions and requirements. 2.4. PREPARATION OF REPORT OF FINDINGS Results of the well installations and DPE pilot study results will be presented in a report of findings. The report will be in a format acceptable to the CRWQCB (Appendix A Guidelines), and will be reviewed and signed by a California Professional Geologist. Advanced GeoEnvironmental, Inc.