Dames & Moore, 1999 - USDA Forest Service

4.2 GEOLOGY AND SOILS .............................................................................................. 4- 15
4.2.1 Regional Geology ............................................................................................... 4-15
4.2.2 Railroad Creek Geology and Mineral Resources ............................................... 4-17
4.2.3 Site Geology ....................................................................................... .............. 4-18
4.2.4 Geologic Hazards ................................................................................... ........... 4-26
4.2.5 Mine Subsidence Potential ......... ; ........................................................................ 4-33
4.2.6 Windblown Tailings ........................... : ............................................................... 4-36
4.2.7 Existing Railroad Creek Riprap .......................................................................... 4-36
4.2.8 Potential Borrow Source Areas 4-38
..........................................................................
4i3 SURFACE WATER HYDROLOGY ......................................................................... 4-40
4.3.1 Regional Climate and Hydrology ................................ : ....................................... 4-40
4.3.2 Overview of Railroad Creek Watershed Hydrology .......................................... 4-41
4.3.3 Site Climate and Hydrology ............................................................................... 4-42
4.3.4 Railroad Creek Streambank Erosion ............................................................. . 4-56
4.3.5 Basin Average climatic Water Budgets ...................... ...................................... 4-58
4.3.6 Hydraulic Analysis and Synthesis ...................................................................... 4-59
4.3.7 Baseflow and Surface WaterIGroundwater Interaction ...................................... 4-62
4.3.8 Hydrologic Conditions During the 1998 RI and Comparison With 1997
Rate .................. : .............................................................................................. 4-66
4.3.9 Interstitial Iron-Oxide Precipitate and Ferricrete ................................................. 4-' 66
4.4 HYDROGEOLOGY .................................................................................................. 4-68
4.4.1 Regional Hydrogeology ...................................................................................... 4-68
4.4.2 Overview of Railroad Creek Watershed Hydrogeology ..................................... 4-1 68
4.4.3 Site Hydrogeology . . . ...... ; ............................................................................ .......... 4-1 69
4.4.4 Site Specific Water Balance ............................................................................... 4-'78
4.5 CULTURAL RESOURCES ...................... ................................................................. 4-92
4.6 ECOLOGICAL CONDITIONS .................................................................................. 4- 93 \
4.6.1 Aquatic Biota ...................................................................................................... 4-93 ..
4.6.2 Terrestrial Biota ............................................................................................... 4- 104
4.6.3 Threatened or Endangered Species .................................................................... 4- 110
5.1 BACKGROUND AND CHEMlCAL SPECIFIC ARARs AND TBCs ......................... 5-1
5.1.1 Soil ............................................................................................................ ............ 5-2
5.1.2 Surface Water ....................................................................................................... 5-3
5.1.3 Groundwater ......................................................................................................... 5-4
5.1.4 Sediment ............................................................................................................... 5-4
5.2 SOIL ............................................................................................................................... 5-5
5.2.1 Background .......................................................................................................... 5-5
5.2.2 Holden Village ...................................................................................................... 5-7
5.2.3 Baseball Field ............ : .......................................................................................... 5-8
5.2.4 Maintenance Yard ................................................................................................ 5-8
5.2.5 Lagoon Area ......................................................................................................... 5-9
5.2.6 Tailings Piles ....................................................................................................... 5-10
5.2.7 Wind-Blown Tailings ......................................................................................... 5-12
5.2.8 Summary 5-12
G.\wpdata\OOJ\reponcUlolden.2\riWold cn2.
17693-005-0 19Vuly 29 . 1999:1:06 PM;DRAFT FINAL R1 REPORT
..............................................................................................................