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// 30 July 2004 1. AGE-NC Project No 96-0232 Page 16 of 16 • December 2003 and June 2004 (4`' year of operation) - a total 0 58 pounds of MTBE has been removed at an average PT influent concentration of 21 µg/1, based on $35,000 spent thusfar during the 4'h year of PT operation and maintenance, than the cost rate is currently x equivalent to $60,500 for every pound of MTBE removed - `_ + Furthermore,based on recent monitoring well and grab ground water analytial data, AGE strongly suspects that the third MTBE-impacted ground water plume may have been influenced by ongoing Flag City Chevron ground water extraction activities, the plume appears to have been drawn onto Flag City Chevron property and towards the ground water extraction induced cone of depression (Figures 8 and 9) The plume appears most prevalent on Banner Avenue near MW-19, as the plume was drawn towards Flag City Chevron (MW-8, P-39 and P-40), it appeared to have migrated vertically between the First Zone and Second Zone hydrogeologic units The recent migration of the third plume is further substantiated by the P-36,P-37 and P-38 grab groundwater samples collected in First Zone and Second Zone (October 2002) that were non detect for MTBE Based on the above information, AGE believes that ground water pump-and-treat activities at the Flag City Chevron may no longer be the most efficient or cost-effective remediation method The pump-and-treat system continues to capture and remove only small quantities of MTBE mass at a significantly decreased pace, and therefore, has approached a point of `diminishing returns' If ongoing ground water remediation is to be continued and/or required at the site, it may be advantageous to alter the ground water remediation method from ground water extraction to ozone sparge Additionally, due to the significant potential that the ground water pump-and-treat remediation system may be `pulling-in' a third ground water plume, and in fact causing a greater negative impact,than AGE is strongly recommending that ground water pump-and-treat operations be suspended at this time until (1) a better understanding is achieved of the third plume, or (2) an alternative ground water remediation method is selected 7.0. LIMITATIONS Our professional services were performed using that degree of care and skull ordinarily exercised by environmental consultants practicing in this or similar localities The findings were based mainly upon analytical results provided by an independent laboratory Evaluations of the hydrogeologic conditions at the site for the purpose of this investigation are made from a limited number of available data points(ground water samples), and subsurface conditions may vary away from these data points No other warranty,expressed or implied, is made as to the professional interpretations, opinions and recommendations contained in this report Advanced GeoEnvironmental,Inc