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DEL MONTE/DISCO <br /> Page 3 <br /> The data collected to date regarding intrinsic bioremediation (ITB) fails to support the statement found <br /> on page 17, bullet number 6, under the title"Summary/Conclusions". This"finding ... (which suggests <br /> that the ITB demonstration project clearly reveals the) presence of gasoline reducing constituents" is not <br /> with any degree of consistency supported by the LLNL report (Recommendations To Improve <br /> theCleanup Process for California's Leaking Underground Fuel Tanks) or data presented in this report. <br /> Any relationship references made to this site and the LLNL report is inappropriate since the plume at this <br /> site (currently>500 ft along the upgradient north - south axis, BTEX in MW-DIS-1 and MW-DIS-4) far <br /> exceeds the 250 foot length generalization in the LLNL report and has yet to be defined vertically and <br /> laterally. <br /> PHS/EHD does not concur with the statement in bullet number 1 under the title "Future <br /> Activities/Recommendations". ITB data collected to date does not "adequately describe(s) the <br /> biochemical potential for degradation of gasoline constituents at the Disco Property". The data reported <br /> is at this time considered to be inconclusive and ambiguous at best considering the following. Table 4 <br /> "Summary of ITB Geochemical Indicators" reports a greater average background concentration for total <br /> BTEX in MW-DIS-4 (which is listed by CH2M HILL as their only "background" sampling point) than <br /> plume fringe wells MW-DIS-3, 8S, 8D, and 9 combined. Carrying CH2M HILL's previously employed <br /> logic into this scenario(MW-DIS-4)where total BTEX is higher than other wells one would assume that <br /> Dissolved Oxygen (DO) would decrease or be lower than those points sampled within the plume core, <br /> yet, DO has remained relatively constant. A more appropriate expectation would include an inverse <br /> relationship between DO concentration and constituent concentration. Over all, MW-DIS-4 which is <br /> listed as a"background well"has been documented as a sampling point with tremendous variability with <br /> respect to dissolved methane concentration over time which is commonly employed to correlate <br /> degradation by-product formation with loss of parent compounds over time. In this instance the <br /> formation or presence of averaged dissolved methane concentration in ground water is not significantly <br /> different (less than 0.0007 mg/L averaged variance) from those levels observed in samples from MW- <br /> DIS-2, 3, 8S, or 8D further discounting the reliability of conclusions provided in this report. <br /> It is important that project proponents collect the proper data to support the potential for full scale ITB <br /> implementation in the future or ITB related conclusions. While collecting this data the continuous <br /> evaluation of the approach to the data collection and reporting process must occur to insure the success <br /> of the project objective. Accordingly, rational changes should be made when appropriate to further <br /> enhance the proponents ability to support their professional opinions. In many cases, such as this case, <br /> these data may be inconclusive or ambiguous. Uncertainty with respect to ITB data and conclusions is <br /> anticipated by most regulatory agencies. Some uncertainty may be associated with the technical <br /> difficulties in collecting data in the field and in the laboratory methodology employed. The allowable <br /> uncertainty in technical data should be proportional to the risk posed by the contaminated site and in <br /> relation to any potential receptor. For sites where no such receptor currently exists or is anticipated, a <br /> higher level of uncertainty may be acceptable. However, it is extremely important that an ITB based <br /> remedial action alternative proposed in a sensitive watershed or environment be supported by a <br /> preponderance of the technical data available. It would be unreasonable or unlikely to expect this or any <br /> regulatory agency to approve implementation of ITB as the final remedial action plan in a high risk site <br /> where supporting technical data is judged to be ambiguous or inconclusive. In summary, if the level of <br /> confidence in the technical rationale and the supporting data are insufficient to clearly support the <br /> implementation of ITB at this site,this option would likely be screened out by the feasibility study as any <br />