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2018 ANNUAL GROUNDWATER MONITORING REPORT FORMER KEARNEY—KPF FACILITY-STOCKTON,CALIFORNIA <br /> 1,4-Dioxane <br /> Concentrations of 1,4-dioxane have declined in the intermediate zone from a historical high of 560 pg/L in 2001. In <br /> October 2018, 1,4-dioxane exceeded the CL (1.0 pg/L) in two of the intermediate zone wells sampled inside the <br /> Trigger Boundary: KEW-31J (2.8 pg/L)and KI-5 (1.2µg/L). <br /> 4.4 Discussion of Migration Potential and Plume Capture <br /> The direction of groundwater flow within and between zones is discussed in Section 3.2, Groundwater Movement, <br /> and Section 3.3, Groundwater Movement between Zones. To summarize, based on water level data, when on-site <br /> extraction wells are pumping from the upper intermediate zone, groundwater moves down from the shallow zone <br /> to the upper intermediate zone, up from the lower intermediate zone to the upper intermediate zone, and up from <br /> the deep zone to the lower intermediate zone. <br /> Horizontal movement of groundwater within the shallow, upper intermediate,and lower intermediate zones is radial <br /> toward the center of the site. These groundwater flow conditions correspond to times of groundwater extraction. <br /> The capture zone of the extraction wells encompasses the contaminant plumes; therefore, the plumes are drawn <br /> back toward the center of the site, where the contaminant mass is withdrawn by the wells and destroyed by the <br /> treatment system. As is evident from the concentrations discussed in detail in Section 4.3, there has been a <br /> sustained and substantial decrease in the areas of all of the contaminant plumes since pumping began, which <br /> remained evident in 2018.This decreasing trend has occurred since 2004 (in addition to decreases achieved from <br /> 1992 through 1999).These latter years of data demonstrate the effectiveness of the present extraction system at <br /> reducing the contaminant mass. <br /> D U D E K 10886-1 <br /> 17 March 2019 <br />