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Diesel Impacted Soil Removal Report May 2010 California Army National Guard Armory Lodi, CA 4.2 CONFIRMATION SAMPLING On April 2,2010, OTIE oversaw excavation and backfilling activities at the site. Following excavation activities,and prior to backfilling and compaction activities, in accordance with the strategy defined in the Workplan, OTIE collected floor and sidewall confirmation soil samples. Confirmation soil sample results for soil samples indicated in Figure 4 are summarized in Table 2 below. Laboratory analytical results for confirmation soil samples are presented on CD as Appendix D to this document. Table 2 Confirmation Soil Sample Results Sample TPH-D Sample ID Sample Location Depth (mg/kg) LODI-SO-10 Floor sample-center of spill area (northern sample) 3 feet 2.2 Y LODI-SO-11 Floor sample-center of spill area(southern sample) 3 feet 140 LODI-SO-12 Sidewall sample(center-southern sidewall) 13 inches 5.2 Y LODI-SO-13 Sidewall sample(center-western sidewall) 14 inches 3.2 Y LODI-SO-14 Sidewall sample(center-northern sidewall) 13 inches 4.8 LODI-SO-15 Sidewall sample (center-eastern sidewall) 13 inches 1.4 Y Note: Y= Sample exhibits chromatographic pattern that does not resemble the standard As noted in Table 2,results (either detections or"Y-flagged") from the six soil samples were below the 100 mg/kg threshold by a factor ranging from 20 to 50 with the exception of sample LODI-SO-11 (140 mg/kg). To confirm that the detection in this sample was replicable, OTIE requested that C&T re- analyze the sample and the re-analysis confirmed the original results. 5.0 DATA EVALUATION 5.1 Evaluation Summary To evaluate the significance of the single soil sample that exceeded the 100 mg/kg threshold used as a reference cleanup goal for the site, OTIE considered five lines of reasoning to place this result in proper context and provide a reasonable basis for judgment for a finding of NFA. The five lines of reasoning are summarized below and discussed in more detail in the narrative following our summary. ■ Interim Final Environmental Screening Levels for Groundwater Protection. Using the 2008 SFRWQCB Interim Final Environmental Screening Levels (ESLs) for TPH-D(middle distillates) under a commercial/industrial land use,the ESL for TPH-D applicable for shallow soil at sites where groundwater is not a current or potential source of drinking water is 180 mg/kg. ■ Local Groundwater Quality and Yield. Although CVRWQCB considers all groundwater to be a potential source of drinking water, local groundwater may be excluded from consideration as a potential source of drinking water if total dissolved solids(TDS) is greater than or equal to 3,000 milligrams per liter(mg/L), or if the water-bearing unit is not sufficiently permeable to produce an average sustained yield of 200 gallons of water per day. Given the long history of regional agricultural operations, it is possible that TDS concentrations are sufficiently high that the shallowest groundwater occurrence would not be considered a potential source of drinking water.