ARCHIVED REPORTS_SEMI ANNUAL GROUNDWATER MONITORING OCTOBER 2010

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AXOM Mr. James L. L. Barton Regional Water Quality Control Board —Central Valley October 27, 2010 Page 6 Hydrostratigraphic unit A/B — MW-2, MW-3, MW-11 Hydrostratigraphic unit D— MW-81D. The April 2008 baseline concentrations and the results from the second and third rebound evaluation sampling events are presented in the table below. April 2008 Groundwater Second Rebound Third Rebound Sampling Concentrations Sampling Event(February Event(August 27, 2010) Well ID (µyL) 19, 2010) (µg/l_) (µg/L) TPHg Benzene TPHg Benzene TPHg Benzene MW-2 15,000 350 490 4J 160 <0.5 MW-3 32,000 4,500 2,100 4 500 <0.5 MW-8D 7,300 1,800 <50 <0.5 <50 <0.5 MWA1 5,200 1,300 <50 <0.5 460 56 µg/L=micrograms per liter TPHg=total petroleum hydrocarbons as gasoline J =estimated value Bold indicates concentration exceeds"Significant'Rebound Concentration Criteria(>10%of the baseline concentrations) The TPHg and benzene concentrations exhibit a downward trend from the 2008 baseline concentrations to the second and the third rebound evaluation concentrations, with the exception of a slight increase in well MW-11 from the second to third rebound events. Well MW-81D remains at non- detect since the baseline concentrations. The TPHg and benzene concentrations show reductions up to three orders of magnitude from the April 2008 baseline concentrations. Discussion On January 21, 2010, representatives for Stone Bros. and CEMC met with the CVWB. The following criteria was discussed and accepted by the parties with respect to decisions for future remediation system operations: • TPHg concentrations <2,000 ag/L— remediation system remains OFF until the next semi- annual monitoring event(—August 2010), • TPHg concentrations>2,000 <10,000 µg/L—operate AS system in bio-sparge mode (air flow rate 5-10 cubic feet per minute), without SVE, until next the semi-annual monitoring event (August 2010); • TPHg concentrations>10,000 <30,000 µg/L—continue pulsing the AS/SVE system as proposed in the Rebound Testing Schedule; and • TPHg concentrations>30,000 pg/L—operate the AS/SVE system continuously.