2008-01-28_REVISION - M1997054 (30)

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Il11~`I 15:32.35 FIaC)M S oad G.umor 1 U romcf, ,411wn immediate Proje~~t aria. Water chemistn~ of tlir bedrock aquifers is dlstin~K from surface and outwash aquifer waizrs. VI'ater from the Depot. Clark. ~~ ootet3 and north«•est wells has markedl}• greater TDS concentrations, plus a shin in water t}pe toward calcium-sodium sulfate. Given the presznee of sulfates and organic carbons in shaley and limey bedrock aquifers such as the Niobrara, Carlisle or Greenhorn Formations, plus the natural occurrence ofsulfate-reducing bacteria, hydrogen sulfide (gas having a rotten egg odor) can be naturally formed in these aquifers afid 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 ['rem the Niobrara, Carlisle or Greenhorn Formations, hydrogen sulfide odors may readily, and naturally, occur. Such oceurrenoes can be seasonal in response to water level and nutrient availability changes, or may be episodic due to: - longerrperiod climatio changes, - changes in net water withdrawals, andlor - local recharge of nutrient- and carbon-rich water from leach fields, pastures or feedlots. These occutYVnces have no cause-and-effect relationship to the Project. Conclosiona u 1 1 (1) The impact of the Project will be to increase the water table elevation beneath the p1aM area. This may also be reelected in the Dakota Group underlying the plant area, with its water table • or potentiometric 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 oflrset by removing irrigation from the hayfields and pastures oCthe adjacettt ranch. This change would occur at the direction of the Division of W ater itesourees, 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 do~vngradient 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 imgation is stopped, a dec]ine 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 swctural 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 fi~em bedrock aquifers structurally isolated from the Project, will be due io natural or other non-Proje~^t related factors. -~ HvdrogeologyReporr-Parkdola Pro/ect PABe 4 of J S (~F ~