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Investigative Methods for Controlling Groundwater Flow to Underground Mine Workings
The riparian and wetland areas surrounding the Elkhorn Mine site are characterized by various combinations of soils, vegetation, and seasonally high water tables. Five riparian/wetland map units were developed to delineate these moist areas. Additionally, an upland map unit was developed for areas that were not riparian or wetland areas. These six map units are described here. Bodies of surface water large enough to be mapped comprised the seventh map unit. The map unit symbols are appropriate combinations of soil wetness and vegetation types as follows:
First digit of the map symbol:
Second digit of the map symbol:
This map unit mainly occurs adjacent to ponds and on floodplains of small perennial streams. It also occurs in sloping areas where groundwater surfaces as seeps and springs and in areas of recent slumps that have not yet developed mature drainage systems. The tree canopy is closed to fairly open and consists of conifers such as Engelmann spruce, subalpine fir, and lodgepole pine. Where the canopy is open, a luxuriant, diverse understory of hydrophytes develops, including species such as bluejoint reedgrass, Holm’s Rocky Mountain sedge, and Labrador tea. These are very wet sites and qualify as wetlands under most wetland classification and delineation systems (Cowardin and others 1979; U.S. Army Corps of Engineers 1987; U.S. Fish and Wildlife Service 1989; Brinson 1993; Committee on Characterization of Wetlands 1995; Hansen and others 1995). Soils are hydric, vegetation is hydrophytic, and water tables are at the surface or within a couple of inches of the surface for long enough and frequently enough to affect the surface soil layers and the vegetation types. Evidence of a fluctuating water table occurs within the upper 5 inches of soil in the form of redoximorphic features such as reddish iron masses and low chroma zones of iron depletion.
Less than 10 percent of the areas mapped as this map unit consist of drier soils having seasonally high water tables deeper in the soil profile. The vegetation on these areas reflects the drier soil conditions. Small areas of wet meadows similar to the ecological conditions of map unit 1H are also included in this map unit.
Dominant soils: Typic Cryaquolls, Histic Cryaquepts, and Typic Cryaquepts.
Minor soils: Typic Cryohemists, Histic Cryaquents.
Depth to saturated soil: 0 to 18 inches, season long in normal or wetter years.
Depth to redoximorphic features: 0 to 5 inches.
Dominant soil textures from 0 to 40 inches deep: organic peat and muck 2 to 20 inches thick, overlying mucky silt loam that overlies very cobbly to very gravelly sandy loam derived from glacial till.
Soil parent material: organic deposits and coarse alluvium over glacial till.
Dominant plant associations: Engelmann spruce/Holm’s Rocky Mountain sedge (undescribed type), subalpine fir/Labrador tea-bluejoint reedgrass, and Engelmann spruce/bluejoint reedgrass.
Minor plant associations: Engelmann spruce/common horsetail.
Plant species: Highest frequency of occurrence: Engelmann spruce, Holm’s Rocky Mountain sedge, Labrador tea.
Moderate frequency of occurrence: subalpine fir, brook saxifrage, arrowleaf groundsel, Jeffrey’s shootingstar.
Lowest frequency of occurrence: smallwinged sedge, common horsetail, alpine timothy, water sedge, tufted hairgrass, seep-spring arnica.
Species occurring on the drier site inclusions: green false hellebore, western twinflower, western meadowrue, sickletop lousewort, swamp currant.
This map unit occurs mainly on somewhat poorly to poorly drained terraces, on low, gently sloping glacial moraines, and on the slopes of moderately steep, colluvial stream headlands. Narrow bands of this riparian/wetland type can also be found at the edges of areas mapped as wetter types, such as map units 1F and 1H. These bands are transition zones between the lowland and upland areas and are too narrow to map at the mapping scale used for this project. The tree canopy of this map unit is mostly closed with some small openings. Tree species include Engelmann spruce, subalpine fir, and lodgepole pine. Many of these areas would qualify as wetlands under the U.S. Fish and Wildlife Service system (Cowardin 1979). Some sites might meet the U.S. Army Corps of Engineers (1987) and the Federal Interagency Committee for Wetland Delineation (U.S. Fish and Wildlife Service and others 1989) definitions of wetlands. Most of these areas would not meet the definitions because the soil is not saturated to the surface frequently enough or long enough to meet the criteria for hydric soils. In addition, the vegetation is marginally hydrophytic to nonhydrophytic, depending on local conditions. Evidence of fluctuating water tables occurs mostly at depths of 2 to 36 inches in the form of redoximorphic features such as reddish iron masses and low chroma zones of iron depletion.
Moderately dry, upland sites and wetter sites that are similar to map units 1F and 1H occupy less than 10 percent of the lands in this map unit.
Dominant soils: Aquic Dystrocryepts and Typic Cryaquolls.
Minor soils: Typic Cryaquepts.
Depth to saturated soil: seasonally high, 2 to 12 inches; seasonally low, 24 to 40 inches.
Depth to redoximorphic features: 2 to 30 inches.
Dominant soil textures from 0 to 40 inches deep: silt loam over silty clay loam or sandy clay loam.
Soil parent material: alluvium, colluvium, and glacial till.
Dominant plant associations: subalpine fir/Labrador tea-Labrador tea.
Minor plant associations: subalpine fir/bluejoint reedgrass-bluejoint reedgrass.
Plant species: Highest frequency of occurrence: Engelmann spruce, subalpine fir, Labrador tea, arrowleaf groundsel, grouse whortleberry, pinegrass, western meadowrue.
Moderate frequency of occurrence: bluejoint reedgrass, heartleaf arnica, Lupinus species.
Lowest frequency of occurrence: lodgepole pine, glacier lily, one-sided wintergreen, green false-hellebore, bracted lousewort, Jeffrey’s shooting-star, swamp currant, broadleaf arnica, red mountainheath, whitebark pine (the last two species occur only at the highest elevations in this map unit, generally above 8,400 feet).
Species occurring on the hydric soil inclusions are: common camas, tufted hairgrass, Holm’s Rocky Mountain sedge, and small-winged sedge.
This map unit is a major component of the large meadows that occur to the southwest, west, and northwest of the Elkhorn Mine site. It occurs in the wettest portions of these grassy parks. It also occurs on low floodplains of small perennial streams and in alluvial basins adjacent to or near ponds. These soils formed in relatively fine-textured alluvium and colluvium. This fine soil material is found in slowly to very slowly permeable layers that tend to perch water tables (hold at unusually high levels). A weak artesian system was observed at one location. These areas lack tree canopies. However, a few widely scattered, stunted Engelmann spruce, lodgepole pine, and subalpine fir trees can be found growing on small, raised hummocks. At some sites there is a shrub canopy of wolf willow. Other sites lack this willow component and are dominated chiefly by sedges, grasses, and forbs that have an affinity for very wet soils. Essentially all of these areas would qualify as wetlands using any of the commonly used wetland classification or delineation systems. Soils are hydric and the vegetation is hydrophytic. Wetland hydrology is prevalent throughout the map unit with soil saturated to the surface or surface water ponding, at least seasonally. Most areas within the map unit are saturated to the surface yearlong. The soils often have a 5- to 12-inch-thick layer of peat and muck at the surface. Some soils have peat and muck deeper than 40 inches and are classified as organic soils (Histosols). This accumulation of organic plant matter is caused by conditions of prolonged and frequent saturation to the soil surface. These organic materials serve as sponges, storing many times their own weight of water.
Small areas of wet forest are included in this unit. These areas have ecological conditions similar to those discussed in map unit 1F. Also included in the large parks are areas similar to map unit 2H. These occur on portions of map unit 1H that are slightly higher than the very poorly drained main part of the unit. These grassy inclusions are seasonally saturated to the surface, but the depth to saturation drops 6 to 12 inches during the latter part of the growing season.
Dominant soils: Histic Cryaquolls, Typic Cryaquolls, Cryohemists, Cryofibrists.
Minor soils: Aquic Haplocryolls, Typic Cryaquents.
Depth to saturated soil: normally saturated to the surface yearlong, some local ponding.
Depth to redoximorphic features: 0 inches.
Dominant soil textures from 0 to 40 inches deep: peat and muck over mucky silt loam to silty clay loam over sandy loam or sandy clay loam.
Soil parent material: organic deposits over alluvium or colluvium.
Dominant plant associations: water sedge, Holm’s Rocky Mountain sedge, and wolf willow/water sedge.
Minor plant associations: tufted hairgrass, beaked sedge, Drummond willow/beaked sedge.
Plant species: Highest frequency of occurrence: water sedge, tufted hairgrass, and beaked sedge.
Lowest frequency of occurrence: bluejoint reedgrass, small-winged sedge, Oregon saxifrage, seep-spring arnica, sweetmarsh butterweed, showy fleabane, Drummond willow.
Species growing on slightly raised hummocks include Engelmann spruce, subalpine fir, and lodgepole pine. The spruce and fir trees also occur as inclusions of wet, forested sites in the map unit. The slightly drier grassy meadow inclusions are dominantly tufted hairgrass communities having reduced sedge components. Inclusions comprise less than 10 percent of this map unit.
This map unit occupies major portions of the large meadows that occur to the southwest, west, and northwest of the Elkhorn Mine site. It encompasses the somewhat poorly drained to poorly drained soils of these meadows. These soils typically occur upslope from areas of the parks mapped as the wetter map unit 1H and downslope from the dry upland forested areas mapped as 3U. It is rare to find this map unit in settings other than these large, grassy parks. The soils formed in relatively fine-textured alluvium and colluvium. This fine soil material is found in slowly to very slowly permeable layers that can perch water tables. Glacial till probably underlies some areas of this alluvium. Low moraines formed basins into which the alluvium was deposited. The soils have humus mixed with the mineral soil material in the upper foot or so of the profile, reflecting abundant fine root production of graminoids and forbs along with adequate soil moisture. In most years, the depth to saturated soil is about 0 to 8 inches during the wettest periods of the year, dropping to 20 to 35 inches during the dry periods of July, August, and September. Evidence of fluctuating water tables exists in the upper 3 inches of the soil profile as redoximorphic features such as reddish iron masses and low chroma iron depletions. Except for small areas of forested land included in this unit, it has graminoid- and forb-dominated plant communities. The plant species characteristic of this map unit have a moderate affinity for saturated soils; they are fairly tolerant of soils that are seasonally saturated to the surface. Many of these species would not tolerate soils permanently saturated to the surface. Most areas within this map unit would meet the definition of wetlands in most commonly used classification and delineation systems. Soils are hydric, vegetation is hydrophytic, and the soil is saturated to the surface frequently enough and long enough to meet wetland hydrology criteria.
Forested areas with somewhat poorly drained soils are included in this mapping unit. These areas also have seasonally high water tables, but the depth to saturated soils is greater than for the grassy portions of the unit. Small areas that are wetter than the characteristic grass/forb sites occur in slight depressions and on floodplains of small streams that traverse the map unit. These sites are ecologically similar to those of map unit 1H.
Dominant soils: Aquic Argicryolls and Cumulic Cryaquolls.
Minor soils: Typic Cryaquolls and Aquic Haplocryolls.
Depth to saturated soil: seasonally high depths of 0 to 3 inches, dropping to sea-sonally low depths of 20 to 35 inches.
Depth to redoximorphic features: 0 to 3 inches.
Dominant soil textures from 0 to 40 inches deep: silt loam to bouldery silt loam overlying sandy clay loam or bouldery sandy clay loam.
Soil parent material: alluvium and colluvium over glacial till.
Dominant plant associations: tufted hairgrass.
Minor plant associations: beaked sedge and subalpine fir/bluejoint reedgrassbluejoint reedgrass occurring as inclusions.
Plant species: highest frequency of occurrence: tufted hairgrass, American bistort, small-winged sedge, alpine timothy.
Moderate frequency of occurrence: lodgepole pine in areas of inclusions.
Lowest frequency of occurrence: common camas, little larkspur, arrowleaf groundsel, showy fleabane.
This map unit occurs mainly on floodplains along moderately wide drainageways (typically 100 to 300 feet wide) and in local areas of low glacial moraines dotted with kettle depressions. The wet, forested areas within this unit resemble those in map unit 1F, but minor differences in vegetation were observed. Similarly, the wet shrub/graminoid/forb areas resemble those in map unit 1H, with minor variations in vegetation. The two types are intermixed in complex patterns at a scale too small to delineate separately at the mapping scale used. The soils are similar to those of map units 1F and 1H. The soils of the wet forested areas have organic surface horizons up to 6 inches thick overlying silty alluvium. The substratum is loamy sand. The soils of the wet shrub/graminoid/forb areas have organic surfaces up to 17 inches thick that overlie silty and clayey alluvium. The temporal patterns and duration of soil saturation are also similar to 1F and 1H. In the wet forested sites, evidence of a fluctuating water table occurs within the upper 4 inches of soil in the form of redoximorphic features such as reddish iron masses and low chroma zones of iron depletion. Soils of the wet nonforested areas are saturated to the surface yearlong in most years. Both components qualify as wetlands in commonly used wetland classification and delineation systems.
Less than 5 percent of this map unit has inclusions of areas with soils that have slightly greater depths to seasonal soil saturation; these small areas are similar to those mapped as map units 2F and 2H elsewhere.
Dominant soils: Typic Cryaquolls and Typic Cryaquepts.
Minor soils: Histic Cryaquepts.
Depth to saturated soil: 4 to 20 inches seasonlong in normal or wetter years.
Depth to redoximorphic features: 0 to 4 inches.
Dominant soil textures from 0 to 40 inches deep: organic peat and muck 3 to 6 inches thick, overlying silt loam, which overlies loamy sand.
Soil parent material: organic deposits and coarse to moderately fine-textured alluvium.
Dominant plant associations: subalpine fir/bluejoint reedgrass-bluejoint reedgrass.
Minor plant associations: Engelmann spruce/Holm’s Rocky Mountain sedge (undescribed type), subalpine fir/Holm’s Rocky Mountain sedge (undescribed type).
Plant species, highest frequency of occurrence: Engelmann spruce, Holm’s Rocky Mountain sedge, bluejoint reed-grass.
Moderate frequency of occurrence: subalpine fir.
Lowest frequency of occurrence: Labrador tea, willow.
This map unit occupies all areas of the riparian/wetland assessment area that were not mapped as units 1F, 2F, 1H, 2H, 1FH, or W. It includes areas with soil cover and nonsoil, miscellaneous areas of rock outcrop, and talus/scree. Both in the field and on color aerial photos, these areas show no evidence of riparian/wetland vegetation or soil conditions. The exceptions are areas that are too small to delineate at the mapping scale used. The soils of these upland forests and meadows are well drained to excessively drained Typic Dystrocryepts, Andic Dystrocryepts, and Lithic Dystrocryepts that formed mainly in colluvium and glacial till. The vegetation mostly consists of forests of lodgepole pine, Douglas-fir, subalpine fir, and whitebark pine. The understory consists of plant species indicative of upland soil conditions and includes grouse whortleberry, heartleaf arnica, pinegrass, and elk sedge. The dominant plant associations are subalpine fir/grouse whortleberry-pinegrass and subalpine fir-whitebark pine/grouse whortleberry.
Information about soil depths below 40 inches is not available. Water tables and saturated soils may occur below this depth, but they could not be ascertained from the soil profiles, vegetation, or aerial photos.
—References cited for the appendixes are included in the References section.
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