1997-12-10_GENERAL DOCUMENTS - C1981041

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Please refer to Section C.11.1. (Probable Hydrologic Consequences) for further hydrologic information, including the groundwater monitoring plan. Additional information on hydrology can be found in Tabs 7, 17 and 18, of the permit and Section C.1I. of this document. Surface Water Hydrology A general description of the surface water hydrology of the permit area is found in Volume 2, Tab 7 of the permit application. Maps displaying the general surface water hydrology are found in Exhibits I and 17 of that document. Please see Section C.1I. of this document for a discussion of the Probable Hydrologic Consequences (PHC) of the Roadside Portal Mines on surface water quantity and quality and for a further discussion of the surface water monitoring plan. Alluvial valley floors(AVF's)are discussed in Section C.XI. of this document. The Colorado River is the only perennial stream in the permit area. On the west side of the river, Coal Creek and Jerry Creek flow through the Roadside North Portal portion of the permit area within deeply incised canyons draining approximately 12 and 70 square miles, respectively. Coal Creek, an ephemeral drainage, passes through surface mine disturbance near the Roadside North Portal where the channel has been diverted. Jerry Creek is an intermittent drainage located in the extreme northern portion of the permit area. In addition, a small portion of the permit area drains to Asbury Creek,which enters the Colorado River from the northwest, to the east of Jerry Creek. Flows in all of these drainages occur primarily during spring snowmelt and in response to sudden,high intensity thunderstorms,the latter of which are characterized by high peak discharges, short flow durations and high sediment loads. On the east side of the river, the Roadside Mine will undermine two additional canyons: Rapid Creek and Cottonwood Creek. Both creeks are intermittent during most years,but do flow continuously during wet years. Flows in these creeks occur primarily in response to annual snowmelt and seasonal precipitation events. Intake structures are present in both Rapid Creek and Cottonwood Creek to divert water from those drainages into reservoirs for later release which, along with water from other storage structures,can artificially increase the duration of stream flows. Several small unnamed drainages(washes)on the east side of the river will also be impacted by mining, either through surface disturbance or through undermining. The only other major surface water body within the permit area is the federally owned Highline Canal. This canal carries river water down the west side of DeBeque Canyon of the Colorado River, with siphons under the channels of Coal and Jerry Creeks. The Highline Canal is primarily used for agricultural purposes in the Grand Valley. Soils Soils in the general area are commonly high in sodium and, occasionally, saline. Soil mapping units identified within and adjacent to surface disturbed areas are Torriorthents-Warm Rock Outcrop Complex, Wrayha- Veatch-Rabbitex Complex, Barx-Clapper Complex,Cameo, Fluvaquents, and Uffens Loam. These consist primarily of gravelly to stony loams,often calcareous, with slight to moderate alkalinity. All tend to have low available water capacity,due to the stony to cobbly textures. Occasional clay loams are found with high water capacity. The stoniness limits their successful utilization. Low organic matter content and elevated SAR values also limit vegetative growth on soils in the area. Variability of the characteristics of the soils on the permit area is primarily due to slope and topography. The depth of the soils range from I inch to greater than 60 inches, with the shallower soils of 0 to 40 inches along 13