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Mr. Brendan Kenny Central Valley Regional Water Quality Control Board November 23, 2020 Page 3 analyzed for these constituents depending on the analytical results of the first round of sampling as described in the response to Comment 1. 3) Due to the observed shallow groundwater conditions at the site (approximately 10 feet below ground surface and 5 feet below the base of the ponds) the proposed soil sample depths for borings B 1 through B8 and SW-1 through SW-3 of 0-6 inches below the asphalt liner, 5 feet, 10 ft, and 15 ft, should be modified such that four samples are collected from each boring above the water table. The Regional Board also suggests that groundwater levels are checked prior to the investigation to provide data for selecting sampling intervals above the water table. Simplot proposes to advance the first boring of the initial sampling round down to groundwater (maximum of 15 feet below ground surface [bgs]) to evaluate the depth to groundwater before collecting soil samples. Samples will be collected at 0 to 6 inches below the pond liner and at 5 feet.The depth of the third deepest sample will be adjusted to be approximately 1 foot above first groundwater, if practicable. 4) The proposed single surface soil sample from the agricultural field owned byJ.R. Simplot to be used establish background soils characterization is not adequate because the land continues to be used for comingled stormwater and wastewater application. Therefore, the Discharger needs to select a new background location(s) that has not been subject to waste discharge during the life of this facility as J.R. Simplot or Occidental Chemical Company. Further, the Discharger needs to propose soil sampling intervals that correlate with the elevations of the southwest pond sidewalls as well as below the pond bottom. Finally, the Discharger may consider multiple background locations be sampled and the data pooled, to help account for spatial variability. The agricultural field owned by Simplot located south of the Southwest Pond was formerly used for wastewater application and may contain soils affected by that historic use. Simplot owns farmland southeast of McKinley Avenue that is used for farming and was never used for wastewater application. Simplot proposes to collect samples from the surface, 5 feet bgs, and 10 feet bgs at two locations shown on Figure 1 to represent background concentration for the site. Based on experience, the field is known to contain very soft-tilled soil. Depending on the conditions, the actual locations of the boring may need to be adjusted to locations closer to the edge of the field to facilitate drilling rig access. 5) Because J.R. Simplot is not permitted to dispose of solids on-site, the accumulated sediments in the Southwest Pond should be characterized for disposal at a local landfill. Depending on the results of the analyses, off-site disposal may or may not be the preferred option for excavated pond material. Simplot will consult with the RWQCB should the data indicate alternative handling methods. 6) The Discharger should also check with the location that will be receiving any of the pond liner or potentially contaminated soil for their waste acceptance criteria. That way J.R. Simplot can collect that information at the same time the other soil sampling is occurring.