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Contaminant Mass Removal 2 Former Manna Pro, Stockton GPE Project No.: 207.3 richness,we concluded that the best way to measure the extracted contaminant mass is by weighing the spent carbon from the carbon filters as it is periodically replaced. Comparison of the weight of spent carbon versus fresh carbon is assumed to represent the weight of gasoline that has been extracted. In general, the activated carbon can absorb about 25 to 30 percent of its own weight before it becomes fully saturated and gasoline breakthrough occurs. The following table summarizes the history of carbon change-outs and the resultant measurement of contaminant removed: Date Wt of Fresh Wt of Spent Net TPH Cum.TPH Carbon Carbon 5/20/02* 2,000 lbs 2,600 lbs 600 lbs 600 lbs 3/29/04 12,000lbs 16,390 lbs 41-39-0- lb-s 4,9901bs 3/29/04 2,000 lbs 500 lbs** 500 lbs 5,490 lbs 11/12/05 4,000 lbs 5,740 lbs 1,740 lbs 7,230 lbs 12/7/025____f6,000 lbs 7,795 lbs 1,795 lbs 9,025 lbs 7/20/07 6g lbs 7,800 lbs*** 1,800 lbs 10,800 lbs *=2-1000 lb filters from first phase operation **=Estimate,carbon not weighed ***=Estimate,still waiting weight on info from US Filter During the past several weeks, PID readings indicate that the carbon filters that have been in use for the past 17 months are approaching the point of breakthrough. When this occurs, an additional approximately 1,800 pounds of gasoline will have been removed, bring the total to about 12,600 pounds. Based on the sums of TPH measured in groundwater samples from the monitoring wells, the total dissolved contaminant mass as measured in the monitoring well samples has fallen about 84 percent since the remedial investigation began. Respectfully Submitted, Geo-Phase Environmental Inc. Stephen M. Lankford, PG/REA Principal Geologist 2937 Veneman Ave.,#B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 Modesto, Ca 95356 Fax: (209)569-0295