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Groundwater Data Gaps Site Investigation 8 March 2019 Page 3 10. The eastern portion of the Central Area was not sampled for VOCs during the 2018 monitoring event because wells W-299, W-300, and W-318 could not be located (Figure 6). Landfill Area: 11. Landfill Area connection or lack thereof of the VOC groundwater plume observed in the southern landfill area and the central landfill area(Figure 7). 12. Landfill Area vertical extent of VOCs in groundwater(Figure 7). 13. In the northern Landfill Area, the former VOC source area was not sampled during the 2018 monitoring event because monitoring wells W-323, W-324 and W-325 could not be located(Figure 7). 14. The DTSC and RWQCB requested grab-groundwater samples be collected in the Landfill Area to define the extent of the VOCs in groundwater near W-204, W-156, W-143, P-133, and between P-138 and W-040. The following data gaps were identified based on the COC evaluation: 15. Dioxins were listed as a COC in the Consent Agreement for Site 3; however, no historical groundwater dioxin data was available in the project database or historical reports with reporting limits below maximum contaminant levels (MCLs). 16. Dioxins/furans were listed as a COC in the Consent Agreement for IAS 03/04; however, no groundwater dioxin/furan data was available in the project database or historical reports. 17. Dioxins were listed as a COC in the Consent Agreement for IAS 13; however, no groundwater dioxin data was available in the project database or historical reports. PROPOSED SAMPLES Boring locations and proposed sample depths for grab-groundwater samples are shown in Table 1 and Figures 2 through 6. At Site 3, the following samples are proposed to be collected to address the data gaps identified: • GGW-01 will be collected and analyzed for VOCs to evaluate the vertical extent of VOCs in groundwater beneath the source area(Data Gap 1). 2019_0308_RRI_Revised Data Gaps Investigation Memo engineers I scientists I innovators