SITE INFORMATION AND CORRESPONDENCE

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CONESTOGA-ROVERS & ASSOCIATES January 6, 2011 7 Reference No. 632277 • Helium was not detected in any of the vapor samples and the detected oxygen and carbon dioxide concentrations were consistent with subsurface levels. Therefore, the samples appear to be representative of subsurface conditions and the results are assumed to be valid. CONCLUSIONS Third and Fourth Quarter 2010 Groundwater Monitoring • Hydrocarbons remain in shallow groundwater in the area of the former USTs and dispensers. Concentrations have decreased and the remaining concentrations are low, and are stable to declining. Based on the results in the downgradient wells, the extent is adequately defined. Decreasing hydrocarbon concentration trends suggest that natural attenuation is occurring in the former source areas. • Based on the results in wells MW-5 and MW-6B, deeper groundwater is not significantly impacted. • Following the significant (two to three orders of magnitude) increase in concentrations in crossgradient well MW-4 during first quarter 2008, concentrations have again decreased and only a low concentration of TPHd (just above the reporting limit) remains. Based on the location of this well and the consistent groundwater flow direction to the northwest, the 2008 increase appears to have been due to an offsite source. • Elevated TPHd and TPHg concentrations have periodically been detected in crossgradient well MW-7 for the pastseveral 1 tears. A_ gaiinbased on the location of this well and the flow direction, the detections appear to be due to an offsite source. As discussed in previous reports, elevated concentrations of petroleum hydrocarbons were detected in groundwater samples collected in 2003 in this area on the Tracy Express property as well as upgradient of this area in West Grant Line Road as part of an investigation at 541 West Grant Line Road. • Following a significant (up to three orders of magnitude) increase in concentrations in the sump during second quarter 2009, concentrations have been decreasing. Based on the sudden increase and subsequent decrease in concentrations at the sump, the increase likely is attributable to activities at Tracy Express (car washing, vehicle maintenance, etc.) . Additional Soil Vapor Sampling • Elevated TPHg and benzene concentrations were again detected in VP-1. Toluene and MTBE were not detected in VP-1 during the current event after having been detected during the previous event. Ethylbenzene and xylenes were detected in VP-1 after not being detected during the previous event; however, the previous reporting limits were elevated. Higher TPHg concentrations were detected in VP-2 and VP-3 during the current event; benzene was only detected in VP-2, and only at a low concentration. The fluctuation in hydrocarbon concentrations may be attributable to seasonal fluctuations in groundwater. Worldwide Engineering, Environmental, Construction, and IT Services