SITE INFORMATION AND CORRESPONDENCE_FILE 1

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J.R. Simplot - 4 - 21 March 2008 Lathrop, San Joaquin Count, 17. The highly mobile and persistent nature of nitrate and nitrogen in ammonia-impacted soils requires that soil and groundwater sampling in the tank area include a step-out protocol to delineate the extent of downgradient impacts of this release. Please revise Section 5.4 to include a protocol to try to complete horizontal and vertical delineation in one field effort. 18. A select number of soil samples collected in the UN-32 Release Area should be analyzed using the Waste Extraction Test with deionized water to evaluate leachability of pollutants and used in an evaluation of potential to impact underlying water quality. 19. Characterization of groundwater in the UN-32 Release Area is proposed with three grab groundwater samples and sampling from monitoring well LP-8 "during the site's normal quarterly monitoring event." We expect that all groundwater samples will be collected at the same time, with the exception of step-out borings (see comment #12). LP-8 should be sampled as close as possible in time to the sampling of the proposed grab samples. AMMONIUM SULFATE RELEASE AREA 20. The depths and locations of samples previously collected in the ammonium sulfate release area are not provided. Figure 9, showing the location of the release, does not show the limits of the excavation, or the existing and proposed sampling locations. We request a single, scale drawing that shows the location of the release, the limits of the excavation, and the locations of the confirmation samples (past and proposed). Please add text that provides a rationale for the proposed sampling locations. 21. Section 4.5, Section 5.5, and Appendix C - Ammonium Sulfate Release. A select number of soil samples should be analyzed using the Waste Extraction Test (with deionized water) to evaluate leachability of pollutants and used in an evaluation of potential to impact underlying water quality. 22. Please provide information on the source of backfill used in the Ammonium Sulfate Release excavation. 23 Background levels of ammonium (as N) vary between 14-310 mg/kg in the Ammonium Sulfate Release Area and 2-7 mg/kg in the Process Water Release Area. The difference in these values further support the need to develop defensible background concentrations (in areas outside of the facility activities) for ammonium and general minerals in soil and groundwater (see comment #5). Please propose 3 to 8 soil boring locations that meet these criteria for evaluation of background. 24. The Regional Water Board staff requested that the Work Plan include three wells at a minimum, or at least one grab groundwater sample, to characterize the release at the Ammonium Sulfate Release Area. Please clarify in an addendum to the Work Plan the rationale for the choice of one grab groundwater sample at location EB-AS and how it will satisfy the requirement to delineate lateral and vertical extent of pollutants at this release site.