SITE INFORMATION AND CORRESPONDENCE

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Mr. Jeff Baker -4 - 16.June 2010 Stockton Terminals Tech nic9ommittee • concentration reductions on the order of those that are currently being observed. These low concentrations later rebounded to elevated concentrations. As such, we do not concur with STTC's conclusions that (1) overall hydrocarbon concentration trends in groundwater beneath and downgradient of the Site appear relatively stable to decreasing, and (2) results from the ozone injection monitoring program indicate the East and West remedial systems are effectively mitigating off-site migration of petroleum hydrocarbons. Instead, our observations of the overall rising TBA concentrations in AR/MW-18B and TPHd in OW-4B and OW-4C both suggest that the perimeter ozonation system is not effective at controlling offsite migration, particularly in the lower water bearing zones. 2. Table 8 displays the four quarters of baseline data collected pursuant to Title 27 Section 20415(e)(6) to establish baseline conditions for the hydrogen peroxide study. However, Tesoro did not use the data to calculate the baseline concentrations for the five parameters prior to initiating the study in March. In order to expedite this task, we suggest that the overall mean for each compound should be calculated by dividing the sum of the concentrations for each parameter in the four wells by the sum of the total number of samples. Tesoro needs to submit the result of this baseline calculation by 7 July 2010. Title 27 Section 20415(e)(8)(A) through (E)7 provides a list of allowable data analytical methods for determining measurably significant changes to baseline concentrations. Section (e)(7) requires the method chosen to be identified before it is implemented. However, Tesoro has implemented the pilot study before identifying the statistical method. By 7 July 2010, Tesoro needs to submit its selection of a hypothesis testing method, pursuant to Section (e)(7), for our approval. 3. Our 11 March 2010 letter required BP to submit the evaluation of alternate remedial technologies referenced in its 29 October 2009 Helium Tracer Study for Biosparging Feasibility Report by 1 May 2010. Our letter stated that the evaluation must also include a method for mitigating MBAS based on groundwater monitoring data which show that WAS is widely distributed throughout the ARCO facility. That evaluation has not been submitted. However, since STTC intends to expand MBAS sampling to the wells downgradient of the BP facility, the 1 May 2010 deadline will be extended to allow the collection of four quarters of MBAS data in downgradient wells. Therefore, the evaluation of alternate remedial technologies is now due 1 May 2011. In summary, by 7 July 2010, please submit the results of the baseline metals calculations and the proposed statistical method to evaluate changes in the baseline values. If you have any questions regarding this letter, you may contact me at (916) 464-4811 orb mail at betaylor@waterboards.ca.gov. BRIAN TA .- OR, P.G. Engineering Geologist cc list on next page