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Mr. James L.L.Barton July 5, 2005 Page 4 of 5 was approximately 6.7, only marginally below the normal range pH of 7.0 to 8.2. Although Carbon Resources indicated that the adsorption capacity of its GAC would not be affected by an acid treatment, it is possible that this did occur, at least temporarily. Ms. Kim Walsh of Carbon Resources indicated that it is possible that the acid wash process, including back-flushing of the carbon units could have affected the equilibrium zone (zone of exhaustion) in the carbon units, thereby reducing the effective life of the carbon. In this case it is possible that unspent carbon remains in the carbon units. If this were the case, however, one or more polish carbon vessel(s) would be necessary to fully exploit the unused carbon in the existing vessels. Assuming the equilibrium would return in the carbon vessel in this scenario, one could estimate the initial (and assumed.maximum)concentration of MTBE in the effluent immediately after the acid wash by plotting the known concentrations of MTBE in the effluent against a timeline. Using this method, the estimated maximum concentration of MTBE discharged to the ground surface on May 11, 2005 is 85 ppb (Figure 1). Taking the average concentration of MTBE in the effluent between May 11 and May 31 and assuming breakthrough immediately upon restarting the treatment system on May 11 (43,079 gallons discharged between May 11 and May 3I), an estimated maximum of 0.02 pounds of MTBE may have been discharged to the ground surface. 2. The replacement carbon delivered by Carbon Resources in December 2004 was a different product than what was delivered in December 2003. A coconut-based carbon, such as the Sabre series CR1230C virgin carbon used in December 2003, is preferred for treating MTBE. The carbon delivered in December 2004 was Sabre series CR124013, a coal-based carbon. It is likely that the coal-based carbon used in December 2004 had a lower adsorption capacity with respect to MTBE than the coconut-based carbon used in 2003. We do not expect that this is the sole reason for the unexpected breakthrough in May 2005,although it may have been a contributing factor. 3. Decreasing efficiency of the air stripper may have contributed to somewhat increased load to the carbon units. The efficiency of the air stripper (based upon a comparison of MTBE concentrations in INF versus ASI)decreased from X99% initially(September and October 2004)to 87.8% in December 2004, 78.7% in January 2005, and 83.3% in February 2005. Even so, the maximum concentration of MTBE detected in AS] was 160 ppb in February 2005. The decreased efficiency of the air stripper could not be the sole reason for the unexpected breakthrough. CONCLUSIONS AND RECOMMENDATIONS Analytical results of treatment system sample results indicated that carbon breakthrough occurred in both carbon units on or about May 23, 2005, and perhaps as early as May 11, 2005. An estimated 12,000 to 47,000 gallons of treated water was discharged to the ground surface with MTBE concentrations between 29 and 85 ppb in violation of Waste Discharge Requirements. An estimated 0.004 to 0.02 pounds of MTBE was discharged to the ground surface. The discharged water was noted to be ponding in the discharge area, possibly due to recent changes to the ground surface by PG&E as part of the Hammer Lane freeway exit construction project. As a result a significant portion of the discharge water evaporated rather than percolated to the subsurface. Based upon past carbon use, the breakthrough was not expected to occur for many more months of operation. Several factors may have contributed to the unexpected breakthrough including treating the influent water with acidified water to loosen and remove scale that had built up inside of the treatment system piping and subsequently backflushing the carbon vessels, using coal-based GAC rather than the