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4 Pre-Mining Conditions in Coal Mining Regions of the United States The conterminous United States has been divided into 28 coal regions that are grouped into six larger coal provinces (Figure 4.1~. Most coal regions are coincident with regions containing fractured carboniferous formations and associated consolidated rock aquifers (Figure 4.2~. Mining of coal affects the hydrogeology of a site and to varying degrees the surrounding area. The magnitude of change depends on the initial geologic and hydrologic conditions, including the natural recharge areas, recharge mechanisms and rates, and the methods of mining and reclamation. This chapter describes the general hydrogeology of the nation's coal regions prior to disturbance by mining. It briefly describes the coal resource and the climate; the occurrence, recharge, and discharge of ground water systems associated with coal resource areas; and the soils. A more detailed discussion of each province (but not of the soils) is presented in Coal Mining and Ground-Water Resources in the United States (NRC 1981a). EASTERN COAL PROVINCE The Rhode Island, Pennsylvania, Atlantic Coast, and Appalachian regions are included in the Eastern -41-
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-42- 100° 701°/~\ ~ - 2s i LO ~~ l Types of Coal in Fields 3001` Anthracite Low-volatile - bituminous , , Medium- and high- I ~ volatile bituminous Lignite Elf hew' r~ ~ ~ /~// ~(/ 0 500 Ml LES Sub-bituminous I ~ ' 0 500 Kl LOMETERS Provinces ( 1 Rhode Island ~r~ta~nthracise ) 2 Penn Ivania anthracit Eastern 3 Atlantic coast 4 Appalachian 5 Northern 6 Eastern Interior 7 Western 8 Southw~tem Gulf 10 Texas ( 11 Fort Union J 12 Powder River Northern Great Plains ~ 13 Black Hills ~ 14 North Central Rocky Mountain 15 Tertiary lake beds /16 Bighorn Basin 17 Wind River 18 Hams fork 19 Uinta 20 Southwestern Utah 21 San Juan River 22 Raton Mesa 23 Denver \24 Green River 25-28 Pacific Coast Province FIGURE 4.1 Coal fields of the conterminous United States. SOURCE: NRC, 1981a.
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-43- ~0° 10~° ~^o rub _ ~ Areas of extensive aquifers that Y yeild more than 50 gallons per Anna minute of freshwater Areas of less extensive aquifers - having smaller yields Fit r80° t3oo 0 200 400 MILES ,,. I ~ I I I r r r r r r r 0 200 400 600 KILOMETERS FIGURE 4.2 Ground water resources in relation to the coal fields of the conterminous United States. SOURCE: NRC, 1981a. if. |35o
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-44- Coal Province (Figure 4.1~. Eastern Kentucky, Ohio, Pennsylvania, and West Virginia contain the majority of the coal in this province. Coal is mined by underground and surface techniques from Pennsylvanian-age (280 million to 325 million years ago) deposits except where it occurs in the Triassic (190 million to 225 million years ago) deposits of the Atlantic Coast basins. The climate of the Eastern Coal Province is generally humid. ~ ~ ~ Precipitation ranges from about 75 cm to over 125 cm annually depending on the latitude and topography. Yearly potential evaporation is approximately 65 to 75 cm in the northern regions and 85 to 110 cm in the southern area (NRC, 1981a). Ground water occurs in the soils and within the underlying fractured sandstones, shales, coals, and limestones. Ground water discharge from water table aquifers and deeper confined systems creates stream baseflow. Ground water is recharged by direct precipitation on the soils that have accumulated on bedrock. Yields from wells are typically less than 200 liters/minute. Most of the soils in this province (Figure 4.3) are acid and have low inherent fertility. They vary in depth from shallow (<50 cm) on some uplands to very deep (>150 cm) on some footslopes. Soils on uplands are generally well drained to moderately well drained, but may be somewhat poorly to poorly drained in footslope positions. Although most soils have moderate permeability, some soil horizons have moderately slow to slow permeability. The eastern Kentucky coal field is an intensely dissected upland with sharp ridges, V-shaped valleys, and a local relief of up to 250 m. Surface mining by contour stripping, angering, and mountaintop removal produces about 50 percent of the region's coal. Principal coal seams are found interbedded with sandstone, shale, and siltstone and crop out in valley walls and underlie small stream valleys Eastern Kentucky receives about 114 cm of precipitation annually. Streams forming the ~ . . . . ~ ,, ~ ~ ~ _ .. ~ - ,
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-46- Figure 4.3 Aqualfs Map Legend Alfisols Ala--Aqualfs with Udalfs, Haplaquepts, Udolls; gently sloping. Boralfs A2S--Cryoboralfs with Borolls, Cryochrepts, Udalfs Cryorthods, and rock outcrops; steep. A3a--Udalfs with Aqualfs, Aquolls, Rendolls, Udolls, and Udults; gently or moderately sloping. Ustalfs A4a--Ustalfs with Ustochrepts, Ustolls, Usterts, Ustipsamments, and Ustorthents; gently or moderately sloping. Aridisols Argids Dla--Argids with Orthids, Orthents, Psamments and Ustolls; gently or moderately sloping. DlS--Argids with Orthids, gently sloping; and Torriothents, gently sloping to steep. Orthids D2a--Orthids with Argids, Orthents, gently or moderately sloping. Entisols Orthents and Xerolls , E2a--Torriorthents, steep, with borollic subgroups of Aridisols; Usterts and aridic and vertic subgroups of Borolls; gently or moderately sloping. E2Sl--Torriorthents, steep; ~ Torrifluvents, Ustolls, and Borolls, gently sloping. Aquepts Inceptisols and Argids, I2a--Haplaquepts with Aqualfs, Aquolls, and Fluvaquents; gently sloping. Udalfs,
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-47- Figure 4.3 Ochrepts Map Legend (continued) I3b--Eutochrepts with Uderts; gently sloping. I3c--Fragiochrepts with Fragiaquepts, gently or moderately sloping; and Dystrochrepts, steep. I3S--Dystrochrepts, steep, with Udalfs and Udults; gently or moderately sloping. Mollisols Aquolls Mla--Aquolls with Udalfs, Fluvents, Udipsamments, Ustipsamments, Aquepts, Eutrochrepts, and Borolls; gently sloping. Borolls M2b--Typic subgroups of Borolls with Ustipsamments, Ustorthents, and Boralfs; gently sloping. M2c--Aridic subgroups of Borolls with Borollic subgroups of Argids and Orthids, and Torriorthents; gently sloping. M2S--Borolls with Boralfs, Argids, Torriorthents, and Ustolls; moderately sloping or steep. Udolls M3a--Udolls, with Aquolls, Udalfs, Aqualfs, Fluvents, Psamments, Ustorthents, Aquepts, and Albolls; gently or moderately sloping. Ustolls - M4b--Typic subgroups of Ustolls with Ustalfs, Ustipsamments, Ustorthents, Ustochrepts, Aquolls, and Usterts; gently or moderately sloping. M4c--Aridic subgroups of Ustolls with Ustalfs, Orthids, Ustipsamments, Ustorthents, Ustochrepts, Torriorthents, Borolls, Ustolls, and Usterts; gently or moderately sloping. Xerolls M5S--Xerolls with Cryoboralfs, Xeralfs, Xerorthents, and Xererts; moderately sloping or steep.
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-48- Figure 4.3 Map Legend (continued) Spodosols Orthods S2a--Orthods with Boralfs, Aquents, Orthents. Psamments, Histosols, Aquepts, Fragiochrepts, and Dystrochrepts; gently or moderately sloping. Ultisols Udults U3a--Udults with Udalfs, Fluvents, Aquents, Quartzipsamments,.Aquepts, Dystrochrepts, and Aquults; gently or moderately sloping. U3S--Udults with Dystrochrepts; moderately sloping or steep. Vertisols Uderts Vla--Uderts with Aqualfs, Eutrochrepts, Aquolls, and Ustolls; gently sloping. Slope classes Gently sloping--Slopes mainly less than 10 percent including nearly level. Moderately sloping--Slopes mainly between 10 and 25 percent. Steep--Slopes mainly steeper than 25 percent.
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-49- headwaters of the ridge and hollow areas are perennial to intermittent with flows of 1ess3 than 1.5 m /s and more typically less than 0.3 m /s most of the year. Soils develop from weathering of the parent rock. Steep slopes and layered strata cause variation in soil depth, with flat benches containing the thickest soil cover. Kipp and Dinger (1988) instrumented a 75-hectare surface water basin prior to mining with a number of wells and developed a conceptual model of the ground water flow system operating in their study area and most likely in many similar valleys in eastern Kentucky (see Figure 3.6~. They found that ground water occurred in sandstones, which are commonly overlain and underlain by lower-permeability claystone or argillaceous siltstone. Near-surface fracturing of the rocks appears to create a hydrogeologically connected zone immediately underlying the soil zone. Water levels in wells finished in this zone with fracture permeability generally respond to recharge from precipitation. Perching of ground water occurs in . . . . . . . . — some basins at contacts between sandstones and underlying units located on valley walls and bottoms. This perching causes springs. Water level responses to precipitation were not apparent in wells finished below the near-surface pressure-relief-fractured zone. Thus the hydrologically active zone in the eastern Kentucky coal field is generally associated with the secondarily fractured units. Pre-mining ground water quality ranges from good to poor in the Eastern Coal Province. The presence of highly acidic materials in coal overburden contributes to possible acidity and to high sulfate levels. INTERIOR COAL PROVINCE The northern, eastern, western, and southwestern interior coal regions are found within the Interior Coal Province (see Figure 4.1~. The coal resources are found principally in Pennsylvanian-age
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-50- deposits, with 95 percent of the production from regions in Indiana, Illinois, and western Kentucky. Both underground and surface mining techniques are used to extract the coal. The climate is generally subhumid. Precipitation ranges from about 75 to 115 cm annually over much of the area, with lower annual rates in the westernmost portions. Yearly potential evaporation ranges from 60 to 80 cm in northern and eastern areas and up to 150 cm in the western areas (NRC, 1981a). Ground water occurs in the northern glacial drift, in alluvium and fractured sandstones, and in shales, coal, and limestone. Precipitation recharges drift, alluvium, soils, and bedrock outcrops directly. Noncropping bedrock is recharged by saturated overlying unconsolidated materials. In this province most soils are deep and very deep mollisols and alfisols (Figure 4.3~. Soils of these two orders occupy 95 percent of the land area of Illinois (Fehrenbacher et al., 1984~. Mollisols are dark-colored soils generally formed under grass with base saturation of more than 50 percent in the A and B horizons. These soils vary widely in texture, permeability, and degree of subsoil development. Alfisols have light-colored surface horizons with B horizons of clay accumulation that have a base saturation of more than 35 percent at a depth of 125 cm below the top of the B horizon. Clay contents in B horizons of some of these soils may exceed 60 percent, but most have less than 35 percent clay. Many of these soils are moderately well to well drained, but some are somewhat poorly to poorly drained. The dominant soils in upper Michigan are ~enerallv Andy textured, moderately well to well drained, and moderately to rapidly permeable. They have low base saturation. cow ~ ~ J In western Kentucky coal is extracted by slope and/or shaft mining and surface mining. Principal coal seams are found interbedded with the sandstone, shale, and limestone of the Upper, Middle, and Lower Pennsylvanian-aged formations.
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-51- The region receives 112 to 117 cm of precipitation annually. Streams are found in poorly drained, broad flat valleys. Most of the soils in the mining regions of western Kentucky formed in loess or loess over a residuum of sandstone, siltstone, and shale (Cox, 1974, 1980; Fehr et al., 1977~. Some of the soils developed in residuum with little or no loess cover. Because of the loess, soil textures are predominantly silt loam in the surface horizons and silty clay loam in the subsurface horizons. Clay loam, silty clay, or clay textures may be represented in subsurface horizons developed in residuum. Soils are moderately deep to deep and moderately well to well drained. Most soils have moderate permeability, but some have slow permeability. When unlimed, these soils are generally medium to strongly acidic. Pre-mining ground water quality is generally good in the Interior Province. There is some mineralization in shallow aquifers. Overburden is predisposed to increasing alkalinity. GULF COAL PROVINCE The Mississippi and Texas coal regions are included in the Gulf Coal Province (see Figure 4.19. The coal is a shallow lignite found interlayered with silts, clays, and coarser beds of Tertiary age (2.5 million to 6.5 million years ago). Coal is mined by surface techniques. The climate is humid. Annual precipitation ranges from 112 to 150 cm. Yearly potential evaporation ranges from 76 to 112 cm over much of the area. Surface runoff is estimated to range from 45 to 65 cm annually. Recharge occurs by direct precipitation on soils. Unconfined flow is to discharge areas, and confined flow is assumed to be down stratigraphic dip. Aquifer yields in the coal regions can exceed 4000 liters/minute.
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-52- Soils in this province developed from loamy, clayey, and sandy coastal plain sediments, loess, and fluvial materials (Pettry and Furst, 1985~. Many of the soils are siliceous, acidic, and highly leached and have low organic matter contents. Generally, they tend to be infertile until limed and fertilized. Texture is usually coarser in the surface horizons than in the subsoils, which commonly contain horizons with illuvial clay. Some of the soils have fragipans, which restrict root penetration and movement of water. Some of the soils are very deep and clayey, and other soils are clayey with high shrink-swell characteristics. Pre-mining ground water quality in the Gulf Coal Province is good to excellent. NORTHERN GREAT PLAINS COAL PROVINCE The Fort Union, Powder River, Black Hills, and North Central coal regions are included in the Northern Great Plains Coal Province (see Figure 4.1~. Coal deposits occur in sequences of sandstone and shale of the Tertiary Paleocene age (54 million to 65 million years ago) formations. Seams are also associated with clinker deposits described below. Coal is extracted by surface mines and underground mining. The climate is semiarid. Precipitation ranges from 20 to 50 cm annually. Yearly potential evaporation is 71 cm in eastern Montana. The landscape is rolling plains, with areas of greater local relief associated with major stream drainages. Recharge occurs from direct precipitation and snowmelt on alluvial, clinker, and bedrock outcrop areas. Larger streams are major receptors of ground water discharge. Numerous ephemeral drainages concentrate surface water runoff and contribute to local recharge. Sandstone, coal, and clinker deposits form principal aquifers. Well yields are typically 40 to 200 liters/minute.
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-53- Although most soils are deep to very deep, in some areas soil thickness is less than 50 cm over bedrock (WRSSWG, 1964~. Most soils ' well-developed profiles with A, B. . . ~ , have and C horizons. Some subsurface horizons are ca~careous, some have clay accumulation, and others may be saline. Base saturation of most soils is 80 percent or higher. Prope'rties affecting use of soils for reclamation are soluble salts, exchangeable sodium percentage, texture, and structure (Omodt et al., 19751. Soluble salts are normally present within 2 m of the surface in soils formed from medium- to fine-textured sedimentary beds, but are normally lacking in soils formed from glacial till, soft sandstone, loess, or local alluvium on concave slopes. Exchangeable sodium percentages greater ~ . ~ ~ , _ _ than ~ percent are common In a'' sales except ' those formed from moderately coarse-textured materials and from local alluvium. Soils formed from' glacial till commonly have less than 12 percent exchangeable sodium while those formed from medium- to fine-textured parent materials generally exceed 12 percent within 150 cm and frequently exceed this level within 90 cm. Exchangeable sodium percentages as low as 5 percent will cause dispersion and crusting or sealing if material with this level of sodium is placed on the surface of mined land. Some sodium soils have dense, dispersed B-horizon claypans. Decker Mine, Montana The Decker mine in Montana is an example of mines in the Northern Great Plains, and most of the following information was summarized from the final environmental impact statement developed for that mine (U.S. Geological Survey and Montana Department of State Lands, no date). The Decker mine lies near the northwest margin of the Powder River Basin, a large structural depression in the earth's surface that has been filled with sedimentary formations ranging in age
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-54- from Holocene (the last 10,000 years) to Cambrian (500 million to 570 million years ago). The uppermost bedrock unit is the Wasatch Formation of Eocene age (38 million to 54 million years ago), a sequence of interbedded claystone, shale, siltstone, sandstones, and thin coal beds that crop out in the southeastern part of the area. Underlying the Wasatch Formation is the Fort Union Formation of Paleocene ace (54 million to 65 million vears ado). a sequence of interbedded v ,, sandstone, siltstone, shale, and coal beds that forms the bedrock throughout most of the Decker area. ~ In general, where coal beds are unburned, they are overlain by sandy shale interbedded with varying amounts of clayey siltstone and sandstone. A prominent rock type in areas of burned overburden is clinker (also called scoria, red shale, burned shale, lava rock, porcelainite, ~ ~ - ~ ~ ~ . . . nonvolcanic glass or red dog) which occurs in shades ot red, brown, yellow, and gray. Clinker is formed by the natural burning of coal beds, the heat from which either bakes or fuses the overlying strata, depending on the thickness of the coal and the rate of burning. The baked rock has a hard bricklike appearance and generally is characterized by extreme fracturing and consequent moderate to high permeability. The fused rock often resembles porous lava and is highly permeable. The transition from baked to fused clinker is often abrupt, and in outcrop the fused rock appears to represent local vent areas where burning was accelerated by circulation of air through collapse fissures. Both baked and fused clinker are resistant rock types that cap many of the hills and ridges in the area and are easily recognized by the hummocky terrain and characteristic reddish color. Alluvial deposits of unconsolidated silt, sand, and gravel are found in the bottoms of all the larger stream valleys in the Decker area. These deposits have a maximum thickness of about 30 m in the Tongue River valley, about 12 m in the Deer Creek valley, and less than 12 m in other a. . ~ ~ t ~ t t ~ ·
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-55- stream valleys in the area. In addition, a few terrace deposits (ancient deposits of the Tongue River consisting of sand, pebbles, and cobbles) underlie the surface of several terrace remnants that lie adjacent to the Tongue River and 12 to 67 m above the present river bed. Rock strata in the Decker area are locally warped into several small flexures or folds of very low amplitude. For the most part, however, beds appear to be essentially flat-lying with a regional southeastward din of less than 1°. Several ~ , ~ northeast-trending normal faults have been mapped in this area. The principal sources of ground water that have been developed in the Decker area include the aquifers formed by beds of coal and associated lenses of sandstone and by saturated zones at the base of the clinker and alluvium. The aquifers formed by the coal beds are the most predictable sources of ground water owing to their continuity over broad areas. Although coal does not have appreciable primary porosity or permeability, beds of coal in their natural state are rendered more Permeable by fractures that provide ~ minute openings for the storage and transmission of ground water. In most locations the coal beds are sufficiently permeable to yield adequate amounts of water for domestic and stock use. - Sandstone aquifers occur as permeable discontinuous lenses in the otherwise less-permeable material that forms the overburden and interburden above and between the coal beds. They appear to be isolated bodies with very limited degrees of hydraulic connection. Withdrawal of ground water from one of these aquifers would probably have little immediate effect on one nearby. Clinker ranks as among the most permeable of the aquifer materials in the Decker area. It contains two kinds of rock openings. The baked rock is extremely fractured, while the fused rock is prone to contain tubular or pipelike openings. These two types of openings are intermixed to the extent that
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-56- in any given area the entire rock mass has a very high porosity and permeability. Water from precipitation or from surface runoff enters the clinker and accumulates to form a zone of saturation in the lower part of the porous material. Where the base of the clinker is exposed at the land surface, springs are likely to occur. Where the clinker underlies low areas, however, the top of the zone of saturation rises until it reaches a spillover level. Clinker materials adjacent to the Tongue River Reservoir tend to be recharged by inflow from the reservoir during high stage and subsequently discharge to the-'reservoir during low stage. The pattern of ground water movement in the Decker area is strongly influenced by local topography. In general, movement follows the slope of the land surface, away from the topographically high interstream areas toward the Tongue River valley, where most of the shallow ground water is discharged. The influence of topography appears to be most pronounced on the movement of ground water in the alluvium and clinker. It appears to be least pronounced on the movement of ground water in the coal aquifers. This is attributed to the fact that water in the clinker is unconfined, whereas water in the coal is confined by overlying and underlying beds of shale, mudstone, or siltstone. Other features that seem to influence ground water movement in the Decker area are the orientation of faults and fracture systems that traverse the area. The displacement of rock units along fault planes constitutes abrupt interruptions in the physical, and thus the hydraulic, continuity of aquifers. As a result, movement of ground water across a fault plane tends to be impeded. Where fault planes are oriented parallel to the prevailing hydraulic gradient, the resistance offered to ground water movement is not evident. Where the fault planes are oriented perpendicular to the gradient, however, the hydraulic effect of a fault can be appreciable.
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-57- Soils in the Decker area are formed in residuum, alluvium, or a combination of these materials. Residual soils generally occur on upland areas such as hillslopes and ridges that are source areas of sediment. As a rule, they are less than 50 cm thick, have poorly developed A and B horizons, and closely reflect the character of the underlying parent materials in color, texture, mineral composition, and~salinity. For example, light-colored sandstone generally weathers to form light-colored, nonsaline to moderately saline sandy loams that are commonly nonsodic. In contrast, siltstone and shale generally weather to form silty or clayey soils of comparable color that commonly are moderately to highly saline and contain sodium as the dominant cation. In areas where the parent rocks have been altered to clinker, soils generally are less saline than most other soils in the area. Clays in bedrock formation and in soils derived from these rocks are typically of the expanding-lattice or swelling type. Because sodium salts are generally more soluble than those of calcium and magnesium, soils in the Decker area are often leached to the extent that they contain comnarativelv little sodium. ~ ~ _ _, __ _ The existing soils, therefore, generally contain low-swell clays in which calcium and magnesium ions occupy most of the exchange sites. Sodic soils may be found in the West Decker area, where the source of sodium apparently is the predominantly fine-grained sequence of shale, siltstone, and sandstone beds exposed in escarpments. Alluvial soils are best developed in the broad valley bottoms and adjacent slopes where sediment derived from erosion of the upland has accumulated to form flood plains, terrace deposits, alluvial fans, and alluvial slopes. These soils are composed of a.heterogeneous mixture that reflects both the variety of the source areas and the depositional environment. ~~n~v loam to silty clay Textures range from _~ ~~ ~ _ , _~, Color ranges widely depending on parent materials and organic matter. Soils formed on alluvial deposits generally are
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-58- more permeable and less saline than are residual soils, and they are nonsodic. Although the soils are generally greater than 125 cm thick, the A and B horizons are only 15 to 50 cm thick. Horizon development apparently has been retarded by the semiarid climate. Pre-mining ground water quality in the Northern Great Plains is poor to good. Water in the coal ~ ~ sometimes has high salinity but is than other water in the area. and overburden more desirable ROCKY MOUNTAIN COAL PROVINCE The Tertiary lake beds, Bighorn Basin, Wind River, Hams Fork, Uinta, Southwestern Utah' San Juan River, Raton Mesa, Denver, and Green River coal regions are included in the Rocky Mountain Coal Province (see Figure 4.13. Coal occurs in the Cretaceous (65 million to 136 million years ago) and Tertiary sediments of the mountains, intermontane basins, and dissected plateaus. Both underground and surface mining techniques are used to extract the coal. The climate ranges to arid in the adjacent plateaus. Annual precipitation varies from less than 25 cm in the arid plateaus to over 125 cm in the mountains. Yearly potential evaporation ranges from 75 to 200 cm. Ground water occurs in the alluvium associated with perennial streams and in the fractured sandstone, shale, and coal. Precipitation and snowmelt directly recharge bedrock outcrops exposed at topographic highs, and soils and alluvium. Ground water discharge occurs as contact spring flow, perennial stream baseflow, and by phreatophytes. Wells completed in alluvial aquifers typically yield over 400 liters/minute, however. Soil properties in this province are quite variable because of the variability in elevation, precipitation, temperature, vegetation, and parent materials (WRSSWG, 1964~. Soils vary from those from subhumid in the mountains
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-59- with weakly developed soil profiles with coarse textures to those with strongly developed B horizons with clay accumulation (Figure 4.3~. Organic matter accumulation varies from low to high. Some soils in the arid and semiarid regions are calcareous throughout the profile, while soils in the subhumid and humid forested regions may be very strongly acidic. Pre-mining ground water quality in the Rocky Mountain Province is poor to good. In areas with poor water quality, salinity is the problem. PACIFIC COAST COAL PROVINCE The Pacific Coast Coal Province groups small valley deposits of coal in the physiographic provinces of the Cascade-Sierra Mountains, Pacific Border, and portions of the Columbia Plateau and Basin and Range (see Figure 4.1~. Coal occurs in complexly faulted and folded Tertiary age sediment. Washington State holds the largest deposits and is the focus of the following description. The climate is humid, with mountain precipitation ranging from 100 to over 500 cm annually. Soils are thin on steep slopes and thicker in the valley bottoms. Ground water occurs in the valley alluvium and fractured coal, siltstone, and sandstone. These deposits are recharged at outcrops by direct precipitation and snowmelt that originates from the surrounding higher topography, and by downward flow from overlying saturated surface deposits. Discharge is to springs and streams in the valleys. Wells finished in deposits associated with the coal usually yield adequate water for domestic use.
Representative terms from entire chapter: