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Mr.Jeffrey M.Baker,P.E Baseline Assessment for Soil Boring and Monitoring Well stallation April 30, 2004 �-' Page 4 Discussion Field screening with a PID detected volotile organic val ors above the threshold established in the Baseline Conditions Requirements provided by Tesoro and USA As a result, groundwater monitoring wells were installed at the site. However, concentrations of petroleum hydrocarbons in the gasoline range, BTEX, and oxygenates were not detected in soil samples submitted to the laboratory for chemical analyses, with the exception of tert-amyl methyl ether (TAME) in the sample collected from boring MW-1 at 35 feet bsg. The concentration was only 0.042 milligrams per kilogram (mg/Kg). Concentrations of diesel range hydrocarbons were detected in soil sample collected from the boring for MW-1 ranging from 6 to 12 mg/Kg. The laboratory reported that the chromatograms for these samples did nol exhibit a typical diesel pattern. Also, they consider the values as estimates because the analyses were performed outside of the hold time. The results are summarized in Table 1 and the laboratory reports are presented in Enclosure D. Groundwater samples were collected from monitoring well MW-1,MW-2, and MW-3 during the fourth quarter of 2003 (December 17) and the first quarter of 2004(Marc 19). The results are summarized in Table 2 and the laboratory reports are presented in Enclosure D. With one exception,BTEX or TPH in the gasoline range were not detected in the laboratory analyses. Toluene was detected in the sample from MW-1 at a concentration of 0.83 micrograms per liter (µg/Q, which is only slightly above the laboratory reporting limit of 0.5 µg/L. Concentrations of TPH in the diesel range were detected uring both quarters in MW-1 and MW-2, and during the second sampling event in MW-3. The laboratory reported concentrations ranging from X50 4g/L to 130 µg/L. The laboratory also noted that the concentrations observed in the soil samples collected from the boring for MW-1 did not exhibit a typical diesel chromatographic pattern. The laboratory chromatograms are presented in Enclosure D. The laboratory reported concentrations of MTBE in groundwater samples ranged from <0.50 µg/L to 630 pg/L. The MTBE concentrations did not exceed 1.0 µg/L in monitoring wells MW-2 and MW-3. However, concentrations in MW-1 on December 17,2003, was 410 p g/L and on March 19,2004,was 630 µg/L. Recommendations Delta recommends that monitoring well MW-1 be r laced by a new monitoring well to be located approximately 20 to 50 feet further down-gradient. Mon toring well MW-1 is very close to the underground gasoline storage tanks and may be influenced by fuel vap associated with tank filing operations rather than a gasoline leak. A liquid leak should result in the migration of gasoline-range hydrocarbons or BTEX to the well; however, they were not detected. MTBE concentrations n fuel vapors are much more likely to dissolve into groundwater than are other gasoline constituents. Concen rations of MTBE in the new well could establish the validity of this theory. Remarks The recommendations contained in this report representDelta's professional opinions based upon the currently available information and are arrived at in accordance with currently acceptable professional standards. This report is based upon a specific scope of work requested by the client. The Contract between Delta and its client outlines the scope of work, and only those tasks specifically authorized by that contract or outlined in this report were performed. This report is intended only for the use of Delta's Client and anyone else specifically listed on this report. Delta will not and cannot be liable for unauthc rized reliance by any other third party. Other than as contained in this paragraph,Delta makes no express or implied warranty as to the contents of this report.