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Request#5: 3.4.2 Water Table(continued) <br /> Please also provide a cross-section oriented roughly perpendicular to the cross-sections <br /> requested above, showing the same features (as applicable). This cross-section should <br /> particularly display the nature of the Grassy Valley perched aquifer, and does not necessarily <br /> need to be located beneath the ECOSA footprint. <br /> Please ensure all cross-sections show shallow bedrock groundwater, groundwater flow direction, <br /> and indicate the saturated zone (either visually or in notes provided on the cross-section). These <br /> cross-sections should provide a unifying picture of the hydrogeology of the area specified, <br /> showing the relationships between the ECOSA, the ECOSA underdrains, Grassy Valley Creek, <br /> the contact between the diatreme and Precambrian rocks, and the additional features shown on <br /> Plate 9 (Rev. 1) and Plate 17 (Rev. 1), with the local groundwater regime. <br /> Response: <br /> The location of the cross section is presented in Plate 28. The section selected runs along the <br /> approximate thalweg of Grassy Valley, from the location of deep carbonate borehole CPC14-3 to <br /> the west, to the proposed compliance wells GVMW-23A/23B to the east. The section is underlain <br /> by deep volcanic rock to the west, Precambrian Rock to the west, with the northernmost extent of <br /> the Eastern Volcanic Overflow Apron penetrating the section before Grassy Creek flows out onto <br /> the Precambrian rock that surrounds the entire diatreme. This section shows the interaction <br /> between Grassy Creek and the underlying colluvium and bedrock. <br /> The resulting cross section is Section C-C', presented in Plate 31. <br /> The section has been prepared by the following process: <br /> 1. Assembling all groundwater data for the colluvial ("soil") surface aquifer in the vicinity of the <br /> section and plotting the resulting "water table" which represents the top of the zone of <br /> saturation (where present) in the colluvium on the section. <br /> 2. Assembling all groundwater head/pressure data for the underlying bedrock in the vicinity of <br /> the section, selecting the elevation at each monitored location that best represents the top <br /> of the zone of saturation in the bedrock, and plotting these values on the section. <br /> 3. Drawing direction arrows on the section to indicate groundwater flow direction, as <br /> requested. It should be noted that the section cuts through a three-dimensional flow regime <br /> and the flow arrows indicate the component of flow in the plane of the section. In this <br /> section flow is predominantly vertically downward in the colluvial aquifer, vertically <br /> downward in the unsaturated bedrock, and both downward and out of plane towards the <br /> viewer in the saturated bedrock (ultimately flowing toward groundwater collection by the <br /> Carlton Tunnel, to the southwest of this section). Note the local variation to this flow at the <br /> location where the stream exits the diatremal section to the east, where infiltrating flow is <br /> 2observed to upwell back into the stream, providing permanent flow at and below the <br /> diatreme outcrop to the east. <br /> Page 7 of 16 <br />