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Closure Appeal, Flag City Chevron,6421 Capitol Avenue,Lodi,California Page 4 of 5 3) The mass of MTBE remaining in groundwater was incorrectly calculated and the result was a gross underestimation of MTBE remaining in groundwater at the site. This underestimated mass calculation was used in the risk model to close the Subject Property. The Closure Summary Report prepared by AGE dated August 31, 2005 calculates the mass of MTBE remaining in groundwater at the Subject Property at 1.75 pounds (Appendix M). There are multiple problems with this mass calculation. AGE uses a contaminated aquifer thickness of 20 feet (b=10 feet where b is half the thickness of the aquifer) and uses the equation for a conical shape to estimate the volume of the dissolved phase MTBE plume remaining at the Subject Property. However, Figure 14 in the Closure Summary Report illustrates the dissolved phase MTBE plume thickness at 80 feet consistently under the Subject Property. The thickness and shape errors in the calculation would increase the amount of dissolved phase MTBE in groundwater from 1.75 pounds to 14 pounds. It should be noted that only 13.33 pounds of MTBE was remediated from the site. Apex recommends correcting the mass of MTBE still remaining in groundwater under the Subject Property and rerunning the risk model. 4) The Closure Summary Report prepared by AGE dated August 31, 2005 states that natural groundwater flow direction is consistently to the north northeast. This direction is towards Gilbert and Eileen Moore's Flag City Shell well MW-6B which recently had a detection of MTBE and suggests the Flag City Chevron plume may be migrating. Apex prepared a Workplan for Monitoring Well Installations dated April 24, 2006 for the Gilbert and Eileen Moore's Flag City Shell site which was approved by the San Joaquin County Environmental Health Department on May 9, 2006. The workplan proposes that two wells are installed just to the northeast of the Subject Property. These wells should provide additional data on the migration of the dissolved phase plume. It would be premature to consider the Subject Property for closure until the new wells are installed and more information is acquired about the source of MTBE in well MW-6B.