2012-03-07_PERMIT FILE - C2010088 (22)

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ALLUVIAL VALLEY FLOOR DETERMINATION CAM - COLORADO PROPOSED COAL LOADOUT NEAR FRUITA MESA COUNTY, COLORADO 7. The elevation of ground water beneath the property and the hydraulic gradient indicate the alluvial ground water is controlled by recharge from both precipitation and irrigation in the upland areas north of the property and not the Colorado River or Reed Wash. The Colorado River and Reed Wash are both gaining streams (from ground water) through this reach. 8. The water quality of the alluvial ground water indicates that either the Mancos Shale is the source of the water, or the ground water has flowed through Mancos Shale or shale- derived soils for some distance. 9. Surface water flow during the drier portion of the year (base flow) in the incised Reed Wash is probably the result of ground water discharge to the wash, mostly from irrigation return flows. 10. The swales west of Reed Wash are shallow, narrow depressions that generally drain irrigation return flows to Reed Wash. This water is perched above the water table. The following discussion integrates the facts and observations discussed above to evaluate whether the property is an AVE The proposed loadout property clearly overlies alluvium of the historic Colorado River, but the alluvium is isolated from the surface by 15 to 23 feet of nonfluvial deposits. The current water table (and probably base flow in Reed Wash) is likely maintained by infiltration of irrigation water from north of the property. Without irrigation, the "natural" water table would probably be much lower than what is currently observed. The existing water quality is poor, indicating the ground water would not be useable for agricultural purposes. The known depth to water suggests the alluvial ground water is too deep to provide effective subirrigation of the property. Because of upriver diversions and an extensive ditch network, the property has the potential to be flood irrigated; however, the NRCS stated there is no history of irrigation and no record of the property ever being farmed, nor is it likely that it would ever be farmed due to the nature of the soils (Appendix A). Although the property is relatively close to the Colorado River, the hydrologic function is not what was anticipated by the AVF regulations. The ancestral Colorado River probably deposited the alluvium beneath the property, but currently the river does not appear to have much of a role in the ground and surface water hydrology of the property. Because of flow controls on the river and major structures (i.e., I -70), high flows in the river have no impact on much of the adjacent land, such as the proposed loadout facility. The Colorado River also 7