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Mr. James Diel -2- 18 February 2011 Former Tracy Maintenance Facility • Dissolved-phase plume data. Free product removal in the vicinity of the Engine House took place from 1989 to 2007, using a variety of passive (product skimmers, bailing, bilge bags, and absorbent socks) and active (dual-phase extraction) technologies. Approximately 650 pounds (roughly 90 gallons) of product were removed. LNAPL has been consistently observed in three monitoring wells, five piezometers, and four temporary wells since 1995. Hydropunch groundwater samples collected in June 2010 indicate a previously unknown potential for TPHd near the limits of saturation beneath the former Toxic Pits Cleanup Act (TPCA) pond. As the Central Valley Water Board staff have argued since early 2008, the condition of free-phase petroleum remaining on groundwater at the Tracy site impacts the beneficial use of groundwater, and poses a threat to human health and the environment. We appreciate the effort that UP has made to delineate and characterize LNAPL occurrences. Now that this work is completed, we expect UP to proceed with a Corrective Action Plan to remove LNAPL to the extent practicable. have reviewed the Report and have the following specific comments. 1. Borings HP-11, HP-16, and HP-18 in the former TPCA pond area showed concentrations of TPHd in groundwater over 100,000 micrograms per liter. Laser-induced fluorescence in two of the three borings did not indicate the presence of LNAPL. Please reconcile the near-saturation groundwater concentrations of TPHd in this area with other lines of evidence to explain why LNAPL should not be present. Please provide a work plan for installation of a monitoring well in this area to confirm conditions and provide a permanent observation point. 2. UP has already demonstrated that LNAPL is recoverable at the site, by removing over 650 pounds of product prior to 2008. Although the previous methods for recovering LNAPL were not optimal, the results showed that LNAPL is or was somewhat more mobile than the laboratory tests and mobility calculations presented in this Report suggest. UP should reconcile the laboratory and calculated results with actual field recovery data and discuss the disparity. This information should be added to the Report, to compare the actual recovery data with calculations of estimated recoverability. 3. One way to account for natural variabilities across the site is to present multiple assumption sets (from least to most conservative site conditions), and to perform the calculations based on those scenarios. This would result in a (possibly wide) range of saturations, pore velocities, and recoverability estimates, which would assist us in determining the potential scope of impacts and alternatives to address them effectively. Please present the range of variables in scenarios identified as least to most conservative in the Report, and explain the assumptions used in your selected remedial alternative.