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OCR for page 41
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-
OCR for page 42
-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.
OCR for page 43
-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
OCR for page 44
-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
~ . . . . ~
,,
~ ~ ~ _ .. ~
-
,
OCR for page 45
—45—
a-'.
CO
o
He—~5~ J
i .~,, N
11~ )~ ~~
a)
U]
·rl
o
U:
·.
Cal
o
CQ
OCR for page 46
-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,
OCR for page 47
-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.
OCR for page 48
-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.
OCR for page 49
-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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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.
OCR for page 51
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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.
OCR for page 52
-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.
OCR for page 53
-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
OCR for page 54
-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 ~ ·
OCR for page 55
-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
OCR for page 56
-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.
OCR for page 57
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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
OCR for page 58
-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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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:
moderately sloping
