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Mr.M. Scott Mansholt—CEMC <br /> First Semi-Annual 2007 Groundwater Monitoring and Sampling Report October 29,2007 <br /> Vernalis Pump Station Page 5 of 5 <br /> PAHs have not been detected at concentrations above WQOs and/or ESLs in any of the site wells <br /> with the exception of well MW-6. PAHs were detected in well MW-6 above WQOs and/or ESLs <br /> from samples collected during the January 2006 and January 2007 sampling events. It should be <br /> noted that the PAH detections in the January 2006 sample were in the field duplicate sample and <br /> not in the primary sample aliquot; however, several of the reported PAH values were estimated <br /> concentrations detected between the method detection limit and limit of quantitation. <br /> Current and historic groundwater sampling results for this site and the apparent size and stability <br /> of the TPHd groundwater plume has led SAIC to recommend the following: <br /> • Reduce oleophilic sock inspection and replacement in well MW-1 from quarterly to semi- <br /> annual events. The semi-annual inspections should coincide with the semi-annual <br /> monitoring and sampling of the on-site wells; and <br /> • Discontinue PAH analyses for all site wells,with the exception of well MW-6. Continue <br /> collecting and analyzing PAHs from well MW-6 until non-detectable concentrations have <br /> been observed over four sequential sampling events. SAIC will recommend <br /> discontinuing PAH analysis once this occurs. <br /> CLOSING <br /> If you have any questions regarding this report,please call Tom Burns at(916) 979-3748. <br /> Sincerely, <br /> SCIENCE APPLICATIONS INTERNATIONAL CORPORATION <br /> Thomas Hope Tom urns, P.G. <br /> Project Scientist Senior Project Manager <br /> Enclosures <br /> Figure 1: Vicinity Map THOMAS <br /> N <br /> Figure 2: Site Map BURNS .� <br /> Figure 3: Potentiometric Surface Map—August 2007 6XF- 111"6 <br /> Figure 4: Potentiometric Surface Map—Second Quarter 2006 No. 8 Q 5 3 <br /> Figure 5: Petroleum Distribution in Groundwater—August 2007 q <br /> Table 1: Groundwater Elevation Data and SPO Thickness Measurements <br /> Table 2: Groundwater Analytical Results (TPH,BTEX, and MTBE) t �F CAAO1 " � <br /> Table 3: Groundwater Analytical Results (PAHs) <br /> Table 4: Monitoring Well Construction Details <br /> Attachment A: Field Data Sheets <br /> Attachment B: Data Usability Summary and Laboratory Analytical Report <br />