2008-03-05_REVISION - M1997054 (24)

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Id1f°J8 15:32.3b FkfJkA Tuad Gnmar lU Mnch ,vbort immediate Project area. Water chemistry of the bedrock aquifers is distinct from surface and outwash aquifer waters. Water from the Depot. Clark. Wooten and northwest wells has markedly greater TDS concentrations, plus a shift in water type toward calcium-sodium sulfate. Given the presence of sulfates and organic carbons in shaley and limey bedrock aquifers such as the Niobrara, Carlisle or Greenhorn Formations, plus the natural occurrence of sulfate-reducing bacteria, hydrogen sulfide (gas having a rotten egg odor) can be naturally formed in these aquifers and produced from springs and wells. No reports of hydrogen sulfide are known in the immediate area of the project, north of the Arkansas River. South of the River, where several wells develop water supplies from the Niobrara, Carlisle or Greenhorn Formations, hydrogen sulfide odors may readily, and naturally, occur. Such occurrences can be seasonal in response to water level and nutrient availability changes, or may be episodic due to: ? longer-period climatic changes, ? changes in net water withdrawals, and/or ? local recharge of nutrient- and carbon-rich water from leach fields, pastures or feedlots. These occurrences have no cause-and-effect relationship to the Project. Conclusions (1) The impact of the Project will be to increase the water table elevation beneath the plant area. This may also be reflected in the Dakota Group underlying the plant area, with its water table or potentiometrie head increasing somewhat (2 to 5 feet), with lesser rises away from the plant. Slightly greater spring and seep flows may also result. (2) The increased water table elevation in the outwash aquifer will be more than offset by removing irrigation from the hayfields and pastures of the adjacent ranch. This change would ' occur at the direction of the Division of Water Resources, as the result of its administration of junior water rights. This may lower the water table sufficiently to reduce spring flows at the river and adversely affect downgradient springs or wells. (3) The possible increases in potentiometric head or water table in the Dakota Group could be manifested as somewhat greater bedrock spring discharge rates to the Arkansas River, if DWR does not administer the junior irrigation rights. If irrigation is stopped, a decline in bedrock spring flows may occur. (4) Hydraulic impacts to the Dakota Group and other bedrock aquifers cannot be expected to occur south of the River, as the River serves as a hydraulic boundary having nearly constant- head conditions. Furthermore, faults to the southwest, south, southeast and east of the Project create structural blocks that will be hydraulically separate bedrock units. (5) Changes in bedrock well production or water quality (including hydrogen sulfide presence) in areas south of the River, and in wells producing water from bedrock aquifers structurally isolated from the Project, will be due to natural or other non-Projev-t related factors. kydrogeologyReport-Parkdale Project Page 4 of 4 S OF a