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# Comment Response to Comment 3a At Site 3, there is a data gap to the south and east of the source This location is on the upgradient side of Site 3 and the VOC area. An additional grab groundwater location is recommended plume has been previously delineated on the upgradient side by six southeast of wells EW-3 and EW-4. grab-groundwater samples collected in 2009 (GMWP Figures 13, 14, and Table 3). As this location is upgradient of the source area and the upgradient extent has previously been defined, additional grab-groundwater sampling in this area is not warranted. 3b Additional grab groundwater locations are needed at Site 4 to Grab-groundwater sample GGW-09 is located to the northwest of address the lack of vertical delineation and the limited W-107 and downgradient to the southwest of W-20 and is delineation of volatile organic compounds(VOCs)at depth. In intended to be used to constrain the vertical extent of the VOC addition to the proposed locations, deep grab groundwater plume. samples are also recommended east of well W-107, south of well W-110, and northeast of well W-105. As per DTSCs The only VOC detected at W-110 during the third quarter 2018 comments(dated September 23, 2016) on the Draft monitoring event was cis-1,2-DCE at an estimated concentration Groundwater Monitoring Annual Report for 2015, deep grab of 0.92J µg/L;all other VOCs were non-detect at this well(Third groundwater samples near the source(well W-020) are needed Quarter 2018 Memorandum, Table 3). Well W-218 screened from to understand the vertical extent of the groundwater plume. 40 to 45 feet bgs is located south of W-110 and monitors the vertical extent of the plume in this area. Based on the low concentration of only a single VOC below the reporting limit at W-110 and the existing vertical delineation and monitoring south of W-110 at W-218, additional investigation of the vertical extent of VOCs south of W-110 is not warranted. The area northeast of W-105 is upgradient of the former source area and adjacent to a railroad track where it is not logistically feasible to drill. Well W-004 is screened from 49-59 feet bgs in the former source area by W-20. The only VOCs detected at W-004 during the third quarter 2018 monitoring event were cis-1,2 DCE at a concentration of 2.3 µg/L below the MCL of µg/L and vinyl chloride at an estimated concentration of 0.40J µg/L below the reporting limit and MCL for vinyl chloride of 0.5 lia. The 2 08.03.2019