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I I <br /> Mr. M. Scott Mansholt—CEMC <br /> Fourth Quarter Groundwater Monitoring and Sampling Report and <br /> 2005 Annual Summary December 22, 2005 <br /> Vernalis Pump Station, Vernalis,California Page 7 of 7 <br /> 0.2 pg/L in MW-3. A distribution map for 2005 of petroleum in groundwater is presented as <br /> Figure 4 <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> Groundwater elevations from the site wells indicate that groundwater flow was to the east- <br /> southeast at an approximate gradient of 0.001 ft/ft during 2005. No dissolved-phase TPHg, <br /> BTEX, or MTBE appears to be present at the site. Dissolved-phase, TPHd-range hydrocarbons <br /> were detected in MW-7 only during 2005, at a concentration of up to 620 pg/L. SPO has been <br /> observed in well MW-1 since 1998. Low concentrations of PAHs have been detected in the <br /> samples from wells MW-2, MW-3, MW-6, and MW-7. The PRG for direct exposure to <br /> residential tap water was slightly exceeded by naphthalene in MW-3. <br /> SAIC recommends continued quarterly groundwater monitoring and sampling of wells MW-1 <br /> through MW-7. If groundwater levels continue to decline, SAIC recommends that wells MW-I <br /> through MW-4 be destroyed and reinstalled with a more suitable screen interval. The absorbent <br /> sock in well MW-I will be monitored quarterly and replaced as necessary. Once the petroleum <br /> sheen has been removed, we recommend that well MW-1 be incorporated into the quarterly <br /> monitoring and sampling program. <br /> CLOSING <br /> If you have any questions regarding this report, please call Chris Dennis at(916) 979-3866. <br /> Sincerely, <br /> SCIENCE APPLICATIONS INTERNATIONAL CORPORATION <br /> nn A 'zelo Christopher B. Dennis,P.G. <br /> Staff Geolo ' t Senior Geologist <br /> 1IAL G10 <br /> Enclosures: �0 CHRISTOPHER N <br /> Figure 1: Site Vicinity Map B. -1 <br /> * <br /> Figure 2: Site Map with Monitoring Well Locations DENNIS <br /> Figure 3: Potentiometric Surface Map—October 18, 2005 No.7 t 84 <br /> 9 Q� <br /> Figure 4: Petroleum Distribution in Groundwater During 2005 OF <br /> CA�,FO <br /> Figure 5: Potentiometric Surface Map—July 18, 2005 <br /> Table 1: Groundwater Elevation Data and SPO Thickness Measurements EXPlres August 31 • e 7 <br /> Table 2: Groundwater Analytical Results -THPd, TPHg, and BTEX <br /> Table 3: Groundwater Analytical Results—PAHs <br /> Table 4: Summary of Groundwater Flow Direction and Gradient <br /> Table 5: Monitoring Well Construction Details <br /> Attachment A: Field Data Sheets <br /> Attachment B: Laboratory Chemical Analytical Report <br />