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�. Mr. James L.L. Barton January 5, 2004 Page 3 of 3 pump likely resulted in some free product being pumped through the lead carbon unit, which would have accelerated the adsorption rate. 2. The carbon in the units at the time of startup was not virgin carbon. The carbon units have been in storage for several years, having come off a Iow-level gasoline contamination site in October 1996. Based upon analytical results of influent samples and the operational flow rate of the previous treatment system, it was estimated that approximately 88-90% adsorption capacity remained in the carbon units. Analytical results of a sample from the carbon collected in October 1996 was ND for VOCs (EPA Method 8240 TCLP). However, it is suspected that biofouling and scaling within the carbon units, as evidenced by the general mineral analyses (Table 2), contributed to the reduced carbon adsorption capacity. PROPOSED REMEDY Based upon the analysis of breakthrough summarized above, we feel that the primary factors that contributed to the accelerated breakthrough of the carbon, namely excessive drawdown in the extraction well and biofouling/scaling in the carbon units, have been remedied. Between December 11, 2003 and January 2, 2004 approximately 47,929 gallons of water has been treated with no breakthrough of carbon in the lead carbon unit, a substantial increase from the first week of operation. These results appear to support our analysis of the reasons for the rapid breakthrough. As a precaution, however, Ground Zero added a 200-pound carbon unit to supplement the adsorption capacity of the lag carbon unit in order to protect against a rapid breakthrough in the effluent in the event that contaminant breakthrough is detected in sample C 1- The criteria for replacing the carbon in all carbon units will remain breakthrough detected in sample C 1. In addition to adding the supplemental carbon unit, Ground Zero recommends installing a compact, low-profile air stripper prior to and in series with the liquid phase carbon units, which would allow a substantial increase in flow capacity of the treatment system. Ground Zero has contacted Pacific Gas & Electric to evaluate the current service to the facility in order to determine if sufficient electrical capacity is present. The vendors predict that MTBE would be reduced to less than 50 ppb by the air stripper, which would greatly increase the life of the carbon units. Please contact John Lane at(209) 83 8-98 88 if you hav uestions regarding this submittal. V--D G �/ Respectfully, Groi4nd Zero Analysis, Inc. 0C�' .ION N P. —� u L Nr'_ o No. 6795 John P. Lane —N 7 �I r CA Registered Geologist No. 6795 4rC �. OF cc: Mr. Jeffrey Wong, San Joaquin County Environmental Health Department Mr. Ray Baglietto/Mr. Frank Rauzi