2008-03-31_PERMIT FILE - C1980007A (34)

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West Elk Mine Springs There are three different types of springs within the permit area: Springs in Surficial Sediments - Groundwater that moves through sediments that have a limited thickness and are generally considered to be unconsolidated (i.e., alluvial, colluvium, and landslide deposits). Subsurface water moving through the alluvium emerges as a spring, and discharges into the drainage channel. Colluvial groundwater moving down-gradient emerges from the colluvium as a spring. The source of the groundwater in the colluvium can be snowmelt infiltration, rainfall infiltration; discharge from a surface channel or upgradient bedrock spring flows that infiltrate into the colluvium. Bedrock Springs - Springs can be encountered where subsurface formations outcrop. Groundwater moves along the surface of the formation and eventually daylights. Since 1978, discharge rate data have been collected from 83 springs. Available data indicate that approximately two-thirds originate from Surficial sediments and one-third have bedrock formations as their source. The locations of all springs are shown on Map 37. The currently monitored springs are shown on Map 34. The monitoring plan for the SOD and Dry Fork is presented in Exhibit 71. Spring flow data are presented in Annual Hydrology Reports and are summarized in Table 16. Although discharge data from alluvial springs are limited, it is apparent that they are highly sensitive to seasonal variations. There is also a wide variation in flow from alluvial springs during the year. This large variation suggests that: 1) The capability of the alluvial sediments to- transmit water is great, 2) The storage volume of the alluvial sediments is small relative to the recharge and discharge rates, and 3) The alluvial sediments are in good connection with surface water flows. The overall storage capacities of alluvial spring groundwater systems are large. Colluvial cover springs also display large seasonal discharge variations. These springs have very high springtime flow discharge rates, but commonly cease flowing entirely during the fall and winter months. This suggests that, like the alluvial groundwater system, the groundwater systems have an appreciable capacity to transmit water, but that the storage volumes of these systems are small relative to the recharge and discharge rates. The North Fork Valley has a long history of slope instability (Dames & Moore, 1993). One of the results of unstable slopes is landslides. A common result of some landslides is a change in surface water expression, or the relocation of springs. During the 1993 field investigation, for example, two previously identified springs in the Jumbo Mountain area, Raymond Wilcox Reservoir No. 2 and Jumbo Spring No. 7 Pond, were not located, and one new spring, Section 24 Spring No. 1 Pond, was discovered. It is probable that flow in these springs was altered due to landslides. The combined total volume of water discharged from the lam---slide springs is nearly twice that of any rock units in the mine area. Landslide deposit springs are highly influenced by seasonal variations in precipitation. Thus, the travel times from the recharge area to spring discharge locations are less than one year. Groundwater systems that sustain these springs have small storage volumes relative to the recharge and discharge rates. Many of the springs also have discharge variability that responds to climatic cycles. 2.04-82 Revised November 200=1 PR10, March 2006; Rev..4pril 2006 PRI G; Rev. A Im- 2006 PRI G; Sep. 2007 PRI2; Feb. 2008 PR12