COMPLIANCE INFO_FILE 8 - Laserfiche WebLink

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Mr. James Diel -3- 18 February 2011 Former Tracy Maintenance Facility 4. One of the findings of the Report should have been a range of estimated volumes of both total and recoverable LNAPL. We recognize that such calculations are based on assumptions that may differ from site-specific conditions. However, this information should be provided to support future decision making regarding the LNAPL plume. Please provide this information. 5. Please explain the rationale for selecting the soil core from boring LIF-02 for relative permeability testing of soils (Section 4.1.4, fourth paragraph). How was it determined that this soil core was representative of permeabilities within the overall footprint of the LNAPL occurrence? 6. Observed increases in LNAPL thickness in well MW-06A and four others over the past 12-18 months are not explained in the Report. Review of Figures 4 through 6 indicates that seasonal water level fluctuation is not the cause of these changes. Please describe and explain the recent increases in LNAPL thickness in these wells. 7. Section 5.2.2 discusses residual saturation and LNAPL field saturation. The text should provide a correlation of residual saturations with relative mobility. What ranges of field LNAPL saturation values represent negligible, moderate, and high potential for mobility? What range of saturation values indicates potential mobility at the plume scale, as opposed to the pore scale? What do these two scales of mobility indicate about potential approaches to recovery? 8. We would appreciate a recapitulation of the data, calculations, and interpretations that were performed to support the design of the DPE system in the late 1990s. It is clear that this Report draws radically different conclusions about the recoverability of LNAPL from those derived by the prior consultant. How did the evaluations of LNAPL mobility conducted at the time of DPE system design, and in the rebound study in 2003, differ from the one presented in this report? Did all of the DPE wells perform as expected? Please summarize differing interpretations, assumptions, or data gaps that existed in the late 1990s that have since been addressed. 9. Results in the Report seem to indicate somewhat more favorable conditions for recovery of LNAPL in the vicinity of borings LIF-02 and LIF-10. Certain depth intervals appear to have more favorable conditions for mobility than others in these borings. Dual-phase extraction well DPEX-4 is located within 20 feet of LIF- 02, and presumably this well performed satisfactorily (see Item 8 above). However, no extraction has been attempted to date in the vicinity of LIF-10. Please evaluate the potential for focused LNAPL recovery in the context of the results shown in Figures 12 and 13. Include an evaluation of optimizing and re- starting the DPE system to focus on the DPEX-4 area. 10. In Section 5.2.5, the Report states that the dissolved TPHd plume is stable, i.e., not expanding. We accept ARCADIS' interpretation that the LNAPL plume has insufficient head pressure to continue to move into unaffected pore space and is, in that sense, stable. However, as the LNAPL continues to maintain equilibrium