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TAB 7 HYDROLOGICAL DESCRIPTION Regional Hydrogeology and Surface Water Characteristics The Hayden Gulch Terminal, Inc.'s (HGTI) Loadout facility is situated principally (coal handling facility area and majority of the railroad spur) in the Dry Creek drainage basin (tributary to the Yampa River). A small portion of the railroad spur exists in the Yampa River drainage basin. A regional hydrological description of this area is presented in detail in Attachment 7-1, Regional Hydrology. Site Specific Ground Water Chazacteris tics The coal handling facility area of the Hayden Gulch Loadout is situated in alluvial and colluvial materials overlying the Lewis shale of upper Cretaceous age. Two alluvial/shallow Lewis shale wells were constructed in the Loadout area prior to 1993 by the pervious operator, H-G Coal Company. One well, identified as HGDALI, is located upgradient of the Loadout area and the secontl well, identified as HGDAL2, is located downgradient of the Loadout. During October 1993, a new downgradient alluvial well, identified as HGDAL3, was constructed along Dry Creek within the Rail Loop to assure all potential groundwater impacts from the Loadout could be assessed. This downgradient well was installed to alleviate CDMG concerns regarding the possibility that wells HGDALI and HGDAL2 were partially completed in the Lewis shale. Completion information for monitor well HGDAL3 is presented in Attachment 7-2, Completion and Aquifer Test Data Well HGDAL3. in November 2005, a new upgradient alluvial monitor well, identified as HGDAL4, was constructed along Dry Creek immediately upgradient of the Facility area. Tha well was installed to address CDMG concerns that there was insufficient background alluvial water quality data against which downgradient alluvial water quality data could be compared. Completion information Por monitor mall AGDAL4 is presented in Attachment 7-4, Well HGDAL4 Completion Report. The locations of the four alluvial monitor wells are shown on Exhibit 12-2, Surface Water Control Plan, in Tab 12. Seasonal Variability and Trends. Tables 7-1, 7-2, and 7-3 present the water level and chemistry data (through 1995) for wells HGDALI, HGDAL2, and HGDAL3, respectively (recent data, including data fox well HGDAL4 are presented in the Annual Hydrology Reports, which are submitted to CDMG under separate cover) . Water level ranged from 1. 6 to 8.9 feet below ground surface (bgs), 0.7 to 13.5 feet bgs, and 0.9 to 7,5 feet bgs at wells HGDALI, HGDAL2 and HGDAL3, respectively. On 5.9.95, the water level in well HGDALI was reported as -0.42 feet, which indicates that the water level in the casing was above ground surface. Generally, no water level trends or seasonality are evident at the wells, however, water levels tend to be higher during spring snowmelt months which indicates that snowmelt may be recharging the alluvium. TR-07 1 Revised 03/06