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1 thMensouC;wininra,� sk.rf S�bvh Banat re;,F„'he xwz014 WT whether the concentmtioe of these constituents represent an unacceptable risk endlor could impact ground water above MCLs. A Work Plan for these activities was approvM by the regulatory agencies and the field work was conducted in September 2014. 2.2. Geulogic/Ilydrogeologic Setting this section describes the general hydrageologic setting for the Eastern GSA Pont= of the GSA 00 including the unsaturated rune and the hydrearatigraphic units (HStls) underlying the 2.11. Vadme (Umea uratcd) Zone In the eastern portion or the Central GSA (near the sewage treatment pond) and the Eastern GSA, the vadom zone is comprised of the newfound portion of the Quatemary alluvial (Qal) silty clay, sand, and gravel deposits and the underlying Tertiary Newly Lower Ehm Sandstone (Tnbsi). In the Eastern GSA, these deposits arc unscrewed to a depth of approximately 10 f 15 a logs. 'them is no significant centamimtion present f the unsaturated Qal and Tabs, units in the Eastern GSA. 2.2.2. Saturated ZOYC An HSU consists of one or more snatigraphic intervals that comprise a water-bearing vane exhibiting similar hydraulic and geochemical properties. Them are two primary I ISUs beneath the raiders GSA: one shallow HSU and one deeper HSU. The shallow IISU consists of the Qal-Tnbr HSU, a water-bearing wane that is present throughout the Eastern GSA. This HSU is compri d of Qwl deposits and the portion of the underlying Newly Tabs, bedrock cash that is in direct hydraulic communication with the Got. The depth to gwuml water in Got-1'nhar HSU is 10 to 20 it has depending on seasonal minfwll. Ground water in this HSU generally flows toward the east and north along the Consist Hollow Creek drainage at a velocity of R5 to 3 Wday. The deeper HSU consists or the regional Newly Tnbs bedrock aquifer. Depth to ground water n the I'nbsr HSU in the Lavern GSA varies fi an 10 f 25 ❑ logs depending primarily on seacoast rainfall. Crossed water generally flows to the vwth-southeast at a velocity of approximately 0.3 May in the Tubs regional aquifer. Historically, contaminants have been detecfd in the Tabor I ISU only sporadically and at low mncentmtiOle 2.3. Previous Investigations As discussed in Section 2.1, DOE begaw environmental investigations in the GSA in 1982. Review of historical records and photogemphs and interviews with present, former, and retired I.LNL employees were conducted t0 identify and evaluate activities condumeit in the Eastern GSA that may have resulted in contamimnt misuses. These named revievn and employee interviews; indicated that debris generated in Central GSA craft shops bad bcur burial in trenches in the Eastern GSA during the 1960s and 1400s. The appwnhnme locations of the Eastern GSA debris burial trenches are shown on Figure 3. To better determine the exact location of the debris burial trenches, DOYILLNL used historical air photo interpretation, sail vapor surveys, a" magnetic and ground penetrating radar (UPS) surveys. An air photo taken in 1968 showed one trench and two other possible trenches