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" <br /> T 5 ,��ir 11� 1 �' f ,♦ <br /> IL <br /> . r---Fr'r <br /> Figure 39: Grassy Valley groundwater compliance monitoring points(red dots,GVMW 8 and GVMW 22 labels) <br /> on 1951 USGS 1:24000 topography. The red dashed line represents the Precambrian-diatreme contact. <br /> Even though there were waste rock and tailings piles up-gradient of the two compliance monitoring points <br /> in Grassy Valley, and waste rock began to be stored in the ECOSA facility in 2013, groundwater at the <br /> compliance points has not been impacted. It is hypothesized that groundwater infiltration into the <br /> diatreme along the reach of Grassy Creek from the northwest quarter of section 16 to just upstream of <br /> GVMW 22 reduces the chemical load in groundwater resulting from historic mining and milling. <br /> Furthermore, the ECOSA facility is constructed on the diatreme, so solutes mobilized by precipitation that <br /> infiltrates the waste rock are transported into the diatreme, rather than the shallow groundwater of Grassy <br /> Valley. As a result, groundwater sampled at GVMW 8 and GVMW 22 has not been impacted by <br /> anthropogenic activity, and therefore represents background conditions. <br /> 7. Conclusions and recommendations <br /> The data and analysis presented indicate that groundwater in Arequa Gulch, Poverty Gulch and <br /> Vindicator Valley has been impacted by historic mining and milling activities. Precipitation has mobilized <br /> soluble species from mine dumps/tailings, and likely the native soils, and transported these in the <br /> groundwater. In Squaw Gulch, it appears that elevated dissolved constituents in groundwater chiefly <br /> stem from Squaw Gulch having been the discharge point from the diatreme prior to construction of the <br /> various drainage tunnels, and it is probable that historic mining activity has also contributed to the <br /> chemical load in groundwater. The solutes transported from the mineralized zones within the diatreme, <br />