2008-02-22_APPLICATION CORRESPONDENCE - C2008086 (42)

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The proposed rail alignment crosses the Government Highline Canal, which is another main irrigation canal in the Grand Valley. Government Highline Canal originates just north of the Grand Valley Canal from the Colorado River in Palisade, CO. The canal parallels the Grand Valley Canal to the north until the Grand Valley Canal turns south near 13 Road. Government Highline Canal continues west distributing irrigation water to lateral ditches north and west of Mack (Figures 1 & 6). The canal terminates at West Salt Creek. West Salt Creek flows into Salt Creek, which flows into the Colorado River. Irrigation ditches within the project area have been constructed in uplands. These ditches do not capture or convey jurisdictional waters of the US from tributaries along their flow path. The dry washes that are crossed flow only in times of heavy precipitation events (BOR 1977) and do not exhibit any wetland indicators such as hydric soils or wetland vegetation. Aerial photos in Figures 7 and 8 show distinct land surface changes in previously non-irrigated land that has been converted into agricultural production in the Mack area. Prior to the construction of these ditches the area was considered salt shrub desert and wetlands were confined to perennial washes. Transit loss and leakage from ditches have created wetland hydrology in some areas where it was previously non-existent. Unlined ditches and laterals, depending on substrate and sediment load, have losses of up to 2 cubic feet per square foot of ditch area per day (BOR 1986). During the last century of agricultural irrigation in the Grand Valley, a shallow perched water table has developed from water infiltrating weathered fractures in the Mancos shale (BOR 1986 & 1977). Water is leached through the fractures down to an impermeable layer of shale, which creates a perched water table. The impermeable shale can be 30 feet below the ground surface or just a few feet from the ground surface (BOR 1985 & 1977). Ground water is derived almost entirely from deep percolation of irrigation water and seepage from irrigation systems. Natural ground water recharge is less than 1% of the recharge occurring in the Grand Valley (BOR 1977 & 1985). The perched water table in the Grand Valley would be non existent without irrigation (BOR 1977). Aerial photos show the distinct vegetative boundaries between irrigation canals, lateral ditches, and the non-irrigated naturally arid salt-shrub desert (see Figures 7 and 8). Several local soil scientists were interviewed regarding their professional opinions as to the causes and extent of wetland redoximorphic soil features and groundwater soil inclusions in the project area. All of these individuals are considered local soil experts and have been involved in numerous projects and studies involving soils and groundwater. The following paragraph is based on the professional opinions they provided during discussions about the project area in Mack, Colorado. Ken Weston, Bureau of Reclamation Project Manager retired, Grand Junction Office. Extensive involvement in the Colorado River Basin Salinity Control Project and connected research. Bob Rayer, NRCS Soil Survey Project Manager, Grand Junction Office WestWater Engineering Page 8 of 75 January 2008 DBMS 429