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SOIL CONSERVATION SERVICE
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NONTECHNICAL SOILS DESCRIPTION REPORT
618
nap Soil name and description
Symbol
15 Colby loam, 1 to 3 percent slopes
The Colby soil is a deep, well drained soil. It is
formed on uplands from calcareous eolian material. The
surface is a loam. The underlying material is a silt
loam. The soils have moderate permeability. Their
available water holding capacity is high. Roots
penetrate to 60 inches or more. Runoff is slow and the
erosion hazard due to wind is high.
47 Olney fine sandy loam, 1 to 3 percent slopes
The Olney soil is a deep, well drained soil. It is
formed on smooth plains in mixed outwash deposits. The
surface is a fine sandy loam. The subsoil is sandy clay
loam. The underlying material is a calcareous fine
sandy loam. The soils have moderate permeability.
Their available water holding capacity is moderate.
Roots penetrate to 60 inches or more. Runoff is slow
and the erosion hazard due to wind is severe.
49 Osgood sand, 0 to 3 percent slopes
This is a deep well drained soil on smooth plains. It
formed in eolian sands. Typically the surface layer is
grayish brown sand about 22 inches thick. The subsoil
is brown sandy loam about 12 inches thick. The
substratum to a depth of 60 inches is a pale brown
loamy sand and sand. Permeability is moderately rapid,
and available water capacity is moderate. The effective
rooting depth is 60 inches. Surface runoff is very
slow. Erosion due to wind is very high.
79 Weld loam, 1 to 3 percent slopes
The Weld soil is a deep, well drained soil. It is
formed on smooth plains from eolian material. The
surface is a loam. The subsoil is a heavy clay loam and
Light clay. The underlying material is a silt loam.
The soils have slow permeability. Their available
water holding capacity is high. Roots penetrate to 60
inches or more. Runoff is slow and the erosion hazard
due to wind is low.
x"81.582
U.S. DEPARTMENT OF AGRICULTURE PAGE 1 OF 3
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
SANITARY FACILITIES
618
(The information in this report indicates the dominant soil condition but does not eliminate the need for onsite
investigation)
Map symbol Septic tank Sewage lagoon Trench Area Daily cover
and soil name absorption areas sanitary sanitary for landfill
fields landfill landfill
15:
Colby Moderate: Moderate: Slight Slight Good
percs slowly seepage,
slope
47:
Olney Moderate: Severe: Moderate: Slight Fair:
percs slowly seepage too sandy too sandy
49:
Osgood Severe: Severe: Severe: Slight Poor:
poor filter seepage too sandy seepage,
too sandy
79:
Weld Moderate: Moderate: Slight Slight Good
percs slowly seepage,
slope
981582
U.S. DEPARTMENT OF AGRICULTURE PAGE 2 OF 3
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
SANITARY FACILITIES
Endnote -- SANITARY FACILITIES
This report shows the degree and kind of soil limitations that affect septic tank absorption fields, sewage lagoons,
and sanitary landfills. The limitations are considered "Slight" if soil properties and site features generally are
favorable for the indicated use and limitations are minor and easily overcome; "Moderate" if soil properties or site
features are not favorable for the indicated use and special planning, design, or maintenance is needed to overcome or
minimize the limitations; and "Severe" if soil properties or site features are so unfavorable or so difficult to overcome
that special design, significant increases in construction costs, and possibly increased maintenance are required.
This report also shows the suitability of the soils for use as daily cover for landfills. A rating of "Good" indicates
that soil properties and site features are favorable for the use and good performance and low maintenance can be
expected; "Fair" indicates that soil properties and site features are moderately favorable for the use and one or
more soil properties or site features make the soil less desirable than the soils rated "Good"; and "Poor" indicates
that one or more soil properties or site features are unfavorable for the use and overcoming the unfavorable
properties requires special design, extra maintenance, or costly alteration.
SEPTIC TANK ABSORPTION FIELDS are areas in which effluent from a septic tank is distributed into the soil through
subsurface tiles or perforated pipe. Only that part of the soil between depths of 24 to 72 inches is evaluated. The
ratings are base on soil properties, site features, and observed performance of the soils. Permeability, a high
water table, depth to bedrock or to a cemented pan, and flooding affect absorption of the effluent. Large stones
and bedrock or a cemented pan interfere with installation. Unsatisfactory performance of septic tank absorption fields,
including excessively slow absorption of effluent, surfacing of effluent, and hillside seepage, can affect public health.
Groundwater can be polluted if highly permeable sand and gravel or fractured bedrock is less than 4 feet below the
base of the absorption field, if slope is excessive, or if the water table is near the surface. There must be
aturated soil material beneath the absorption field to filter the effluent effectively. Many local ordinances
acquire that this material be of a certain thickness.
SEWAGE LAGOONS are shallow ponds constructed to hold sewage while aerobic bacteria decompose the solid and liquid
wastes. Lagoons should have a nearly level floor surrounded by cut slopes or embankments of compacted soil. Lagoons
generally are designed to hold the sewage within a depth of 2 to 5 feet. Nearly impervious soil material for the lagoon
floor and sides is required to minimize seepage and contamination of ground water. This report gives ratings for
the natural soil that makes up the lagoon floor. The surface layer and, generally, 1 or 2 feet of soil material
below the surface layer are excavated to provide material for the embankments. The ratings are based on soil
properties, site features, and observed performance of the soils. Considered in the ratings are slope, permeability, a
high water table, depth to bedrock or to a cemented pan, flooding, large stones, and content of organic matter.
Excessive seepage due to rapid permeability of the soil or a water table that is high enough to raise the level of sewage
in the lagoon causes a lagoon to function unsatisfactorily. Pollution results if seepage is excessive or if floodwater
overtops the lagoon. A high content of organic matter is detrimental to proper functioning of the lagoon because it
inhibits aerobic activity. Slope, bedrock, and cemented pans can cause construction problems, and large stones can
hinder compaction of the lagoon floor.
SANITARY LANDFILLS are areas where solid waste is disposed of by burying it in soil. There are two types of landfill,
trench and area. In a trench landfill, the waste is placed in a trench. It is spread, compacted, and covered daily
with a thin layer of soil excavated at the site. In an area landfill, the waste is placed in successive layers on the
surface of the soil. The waste is spread, compacted, and covered daily with a thin layer of soil form a source away
from the site. Both types of landfill must be able to bear heavy vehicular traffic. Both types involve a risk of
groundwater pollution. Ease of excavation and revegetation need to be considered. The ratings in this report are based
Q81.582
U.S. DEPARTMENT OF AGRICULTURE PAGE 3 OF 3
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
SANITARY FACILITIES
Endnote -- SANITARY FACILITIES--Continued
on soil properties, site features, and observed performance of the soils. Permeability, depth to bedrock or to a
cemented pan, a high water table, slope, and flooding affect both types of landfill. Texture, stones and boulders,
highly organic layers, soil reaction, and content of salts and sodium affect trench type landfills. Unless otherwise
stated, the ratings apply only to that part of the soil within a depth of about 6 feet. For deeper trenches, a
limitation rate "Slight" or "Moderate" may not be valid. Onsite investigation is needed.
DAILY COVER FOR LANDFILL is the soil material that is used to cover compacted solid waste in an area type sanitary
landfill. The soil material is obtained offsite, transported to the landfill, and spread over the waste.
Soil texture, wetness, coarse fragments, and slope affect the ease of removing and spreading the material during wet
and dry periods. Loamy or silty soils that are free of large stones or excess gravel are the best cover for a
landfill. Clayey soils may be sticky or cloddy and are difficult to spread; sandy soils are subject to soil
blowing. After soil material has been removed, the soil material remaining in the borrow area must be thick enough
over bedrock, a cemented pan, or the water table to permit revegetation. The soil material used as final cover for a
landfill should be suitable for plants. The surface layer generally has the best workability, more organic matter than
the rest of the profile, and the best potential for plants. Material from the surface layer should be stockpiled for use
as the final cover.
53'8582
U.S. DEPARTMENT OF AGRICULTURE PAGE 1 OF 2
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
BUILDING SITE DEVELOPMENT
618
(The information in this report indicates the dominant soil condition but does not eliminate the need for onsite
investigation)
Map symbol Shallow Dwellings Dwellings Small Local roads Lawns and
and soil name excavations without with commercial and streets landscaping
basements basements buildings
15:
Colby Slight Slight Slight Slight Moderate: Slight
low strength
47:
Olney Severe: Slight Slight Slight Slight Slight
cutbanks cave
49:
Osgood Severe: Slight Slight Slight Slight Moderate:
cutbanks cave droughty,
too sandy
79:
Weld Slight Moderate: Moderate: Moderate: Moderate: Slight
shrink-swell shrink-swell shrink-swell shrink-swell,
low strength,
frost action
481.592
U.S. DEPARTMENT OF AGRICULTURE PAGE 2 OF 2
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
BUILDING SITE DEVELOPMENT
Endnote -- BUILDING SITE DEVELOPMENT
This report shows the degree and kind of soil limitations that affect shallow excavations, dwellings with and without
basements, small commercial buildings, local roads and streets, and lawns and landscaping. The limitations are
"Slight", "Moderate", or "Severe". The limitations are considered "Slight" if soil properties and site features are
generally favorable for the indicated use and limitaions are minor and easily overcome; "Moderate" if soil properties
or site features are not favorable for the indicated use and special planning, design, or maintenance is needed to
overcome or minimize the limitations; and "Severe" if soil properties or site features are so unfavorable or so
difficult to overcome that special design, significant increases in construction costs, and possibly increased
maintenance are required. Special feasibility studies may be required where the soil limitations are severe.
SHALLOW EXCAVATIONS are trenches or holes dug to a maximum depth of 5 or 6 feet for basements, graves, utility Lines,
open ditches, and other purposes. The ratings are based on soil properties, site features, and observed performance of
the soils. The ease of digging, filling, and compacting is affected by the depth to bedrock, a cemented pan, or a very
firm dense layer; stone content; soil texture; and slope. The time of the year that excavations can be made is
affected by the depth to a seasonal high water table and the susceptibility of the soil to flooding. The resistance of
the excavation walls or bands to sloughing or caving is affected by soil texture and the depth to the water table.
DWELLINGS AND SMALL COMMERCIAL BUILDINGS are structures built on shallow foundations on undisturbed soil. The load
limit is the same as that for single-family dwellings no higher than three stories. Ratings are made for small
commercial buildings without basements, for dwellings with basements, and for dwellings without basements. The ratings
are based on soil properties, site features, and observed performance of the soils. A high water table, depth to bedrock
or to a cemented pan, large stones, slope, and flooding affect the ease of excavation and construction. Landscaping
4 grading that require cuts and fills of more than 5 or 6 feet are not considered.
LOCAL ROADS AND STREETS have an all-weather surface and carry automobile and light truck traffic all year. They
have a subgrade of cut or fill soil material, a base of gravel, crushed rock, or stabilized soil material, and a
flexible or rigid surface. Cuts and fills are generally properties, site features, and observed performance of the
soils. Depth to bedrock or to a cemented pan, a high water table, flooding, large stones, and slope affect the ease of
excavating and grading. Soil strength (as inferred from the engineering classification of the soil), shrink-swell
potential, frost action potential, and depth to a high water table affect the traffic-supporting capacity.
LAWNS AND LANDSCAPING require soils on which turf and ornamental trees and shrubs can be established and
maintained. The ratings are based on soil properties, site features, and observed performance of the soils. Soil
reaction, a high water table, depth to bedrock or to a cemented pan, the available water capacity in the upper 40
inches, and the content of salts, sodium, and suLfidic materials affect plant growth. Flooding, wetness, slope,
stoniness, and the amount of sand, clay, or organic matter in the surface layer affect trafficability after vegetation
is established.
°"81.582
U.S. DEPARTMENT OF AGRICULTURE PAGE 1 OF 3
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
WATER FEATURES
618
Flooding High water table and ponding
Map symbol Hydro- Water Maximum
and soil name logic Frequency Duration Months table Kind of Months Ponding ponding
group depth water table duration depth
Ft Ft
15:
Colby B None --- --- >6.0 --- --- --- ---
47:
Olney B None --- --- >6.0 --- --- --- ---
49:
Osgood C None --- --- >6.0 --- --- --- ---
79:
Weld C None --- --- >6.0 --- --- --- ---
4'•$1582
U.S. DEPARTMENT OF AGRICULTURE PAGE 2 OF 3
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
WATER FEATURES
Endnote -- WATER FEATURES
This report gives estimates of various soil water features. The estimates are used in land use planning that involves
engineering considerations.
Hydrologic soil groups are used to estimate runoff from precipitation. Soils not protected by vegetation are
assigned to one of four groups. They are grouped according to the infiltration of water when the soils are thoroughly
wet and receive precipitation from long-duration storms. The four hydrologic soil groups are:
Group " A". Soils having a high infiltration rate (low
runoff potential) when thoroughly wet. These consist mainly
of deep, well drained to excessively drained sands or
gravelly sands. These soils have a high rate of water
transmission.
Group "B". Soils having a moderate infiltration rate when
thoroughly wet. These consist chiefly of moderately deep or
deep, moderately well drained or well drained soils that
have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group "C". Soils having a slow infiltration rate when
thoroughly wet. These consist chiefly of soils having a
layer that impedes the downward movement of water or soils
of moderately fine texture or fine texture. These soils
have a slow rate of water transmission.
Group "D". Soils having a very slow infiltration rate (high
runoff potential) when thoroughly wet. These consist
chiefly of clays that have a high shrink-swell potential,
soils that have a permanent high water table, soils that
have a claypan or clay layer at or near the surface, and
soils that are shallow over nearly impervious material.
These soils have a very slow rate of water transmission.
If a soil is assigned to two hydrologic groups in this report, the first letter is for drained areas and the second
is for undrained areas. Flooding, the temporary inundation of an area, is caused by overflowing streams, by runoff from
adjacent slopes, or by tides. Water standing for short periods after rainfall or snowmelt is not considered
flooding, nor is water in swamps and marshes. This report gives the frequency and duration of flooding and
the time of year when flooding is most likely. Frequency, duration, and probable dates of occurrence are estimated.
Frequency is expressed as "None", "Rare", "Occasional", and "Frequent". "None" means that flooding is not probable;
"Rare" that it is unlikely but possible under unusual weather conditions; "Occasional" that it occurs, on the
average, once or less in 2 years; and "Frequent" that it occurs, on the average, more than once in 2 years.
Duration is expressed as "Very brief" if less than 2 days, "Brief" if 2 to 7 days, "Long" if 7 to 30 days, and "Very
long" if more than 30 days. The information is based on evidence in the soil profile, namely thin strata of gravel,
sand, silt, or clay deposited by floodwater; irregular decrease in organic matter content with increasing depth;
and absence of distinctive horizons that form in soils that are not subject to flooding. Also considered are local
information about the extent and levels of flooding and the relation of each soil on the landscape to historic floods.
081 582
U.S. DEPARTMENT OF AGRICULTURE PAGE 3 OF 3
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
WATER FEATURES
Endnote -- WATER FEATURES--Continued
Information on the extent of flooding based on soil data is less specific than that provided by detailed engineering
surveys that delineate flood-prone areas at specific flood frequency levels.
High water table (seasonal) is the highest level of a saturated zone in the soil in most years. The depth to a
seasonal high water table applies to undrained soils. The estimates are based mainly on the evidence of a saturated
zone, namely grayish colors or mottles in the soil. Indicated in this report are the depth to the seasonal high
water table; the kind of water table, that is, "Apparent", "Artesian", or "Perched"; and the months of the year that
the water table commonly is high. A water table that is seasonally high for less than 1 month is not indicated in
this report.
An "Apparent" water table is a thick zone of free water in the soil. It is indicated by the level at which water
stands in an uncased borehole after adequate time is allowed for adjustment in the surrounding soil.
An "Artesian" water table exists under a hydrostatic beneath an impermeable layer. When the impermeable layer has been
penetrated by a cased borehole, the water rises. The final level of the water in the cased borehole is characterized as
an artesian water table.
A "Perched" water table is water standing above an unsaturated zone. In places an upper, or "Perched", water
table is separated from a lower one by a dry zone. Only saturated zones within a depth of about 6 feet are
indicated.
' ding is standing water in a closed depression. The water is removed only by deep percolation, transpiration,
. .poration, or a combination of these processes.
This report gives the depth and duration of ponding and the time of year when ponding is most likely. Depth, duration,
and probable dates of occurrence are estimated.
Depth is expressed as the depth of ponded water in feet above the soil surface. Duration is expressed as "Very
brief" if less than 2 days, "Brief" if 2 to 7 days, "Long" if 7 to 30 days, and "Very long" if more than 30 days. The
information is based on the relation of each soil on the landscape to historic ponding and on local information about
the extent and levels of ponding.
981.582
U.S. DEPARTMENT OF AGRICULTURE PAGE 1 OF 2
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
SOIL FEATURES
618
Bedrock Cemented pan Subsidence Risk of corrosion
Potential
Map symbol frost action Uncoated
and soil name Depth Hardness Depth Kind Initial Total steel Concrete
In In In In
15:
Colby >60 --- --- --- --- --- Low Low Low
47:
Olney >60 --- --- --- --- --- Low High Low
49:
Osgood >60 --- --- --- --- --- Low Moderate Low
79:
Weld >60 --- --- --- --- --- Moderate High Low
281 582
U.S. DEPARTMENT OF AGRICULTURE PAGE 2 OF 2
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
SOIL FEATURES
Endnote -- SOIL FEATURES
This report gives estimates of various soil features. The estimates are used in Land use planning that involves
engineering considerations.
Depth to bedrock is given if bedrock is within a depth of 5 feet. The depth is based on many soil borings and on
observations during soil mapping. The rock is either "Soft" or "Hard". If the rock is "Soft" or fractured, excavations
can be made with trenching machines, backhoes, or small rippers. If the rock is "Hard" or massive, blasting or
special equipment generally is needed for excavation.
Cemented pans are cemented or indurated subsurface layers within a depth of 5 feet. Such pans cause difficulty in
excavation. Pans are classified as "Thin" or "Thick". A "Thin" pan is less than 3 inches thick if continuously
indurated or less than 18 inches thick if discontinuous or fractured. Excavations can be made by trenching machines,
backhoes, or small rippers. A "Thick" pan is more than 3 inches thick if continuously indurated or more than 18
inches thick if discontinuous or fractured. Such a pan is so thick or massive that blasting or special equipment is
needed in excavation.
Subsidence is the settlement of organic soils or of saturated mineral soils of very low density. Subsidence
results from either desiccation and shrinkage or oxidation of organic material, or both, following drainage.
Subsidence takes place gradually, usually over a period of several years. This report shows the expected initial
subsidence, which usually is a result of drainage, and total subsidence, which usually is a result of oxidation. Not
shown in the report is subsidence caused by an imposed surface load or by the withdrawal of ground water throughout
an extensive area as a result of lowering the water table.
,tential frost action is the likelihood of upward or lateral expansion of the soil caused by the formation of
segregated ice lenses (frost heave) and the subsequent collapse of the soil and loss of strength on thawing. Frost
action occurs when moisture moves into the freezing zone of the soil. Temperature, texture, density, permeability,
content of organic matter, and depth to the water table are the most important factors considered in evaluating the
potential for frost action. It is assumed that the soil is not insulated by vegetation or snow and is not artificially
drained. Silty and highly structured clayey soils that have a high water table in winter are the most susceptible to
frost action. Well drained, very gravelly, or very sandy soils are the least susceptible. Frost heave and low soil
strength during thawing cause damage mainly to pavements and other rigid structures.
Risk of corrosion pertains to potential soil-induced electrochemical or chemical action that dissolves or weakens
uncoated steel or concrete. The rate of corrosion of uncoated steel is related to such factors as soil moisture,
particle-size distribution, acidity, and electrical conductivity of the soil. The rate of corrosion of concrete
is based mainly on the sulfate and sodium content, texture, moisture content, and acidity of the soil. Special
site examination and design may be needed if the combination of factors creates a severe corrosion environment. The steel
installations that intersect soil boundaries or soil layers is more susceptible to corrosion than steel in
installations that are entirely within one kind of soil or within one soil layer. For uncoated steel, the risk of
corrosion, expressed as "Low", "Moderate", or "High", is based on soil drainage class, total acidity, electrical
resistivity near field capacity, and electrical conductivity of the saturation extract.
For concrete, the risk of corrosion is also expressed as "Low", "Moderate", or "High". It is based on soil texture,
acidity, and amount of sulfates in the saturation extract.
481.582
U.S. DEPARTMENT OF AGRICULTURE PAGE 1 OF 4
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
PHYSICAL PROPERTIES OF SOILS
618
(Entries under "Erosion factors--T" apply to the entire profile. Entries under "Wind erodibility group" and
"Wind erodability index" apply only to the surface layer)
Erosion factors Wind Wind
Map symbol Depth Clay Moist Permea- Available Shrink- Organic erodi- erodi-
and soil name bulk bility water swell matter bility bility
density capacity potential K Kf T group index
In Pct g/cc In/hr In/in Pct
15:
Colby 0-7 15-27 1.25-1.40 0.60-6.00 0.14-0.18 Low 0.5-2.0 0.37 0.37 5 4L 86
7-60 18-27 1.15-1.30 0.60-2.00 0.15-0.20 Low 0.5-1.0 0.43 0.43
47:
Olney 0-10 10-20 1.35-1.50 0.60-6.00 0.13-0.15 Low 0.5-1.0 0.28 0.28 5 3 86
10-20 18-35 1.25-1.40 0.60-2.00 0.13-0.17 Low 0.5-1.0 0.24 0.24
20-25 15-30 1.25-1.40 0.60-2.00 0.11-0.15 Low 0.0-0.5 0.24 0.24
25-60 5-15 1.40-1.60 2.00-6.00 0.06-0.13 Low 0.0-0.5 0.32 0.32
good 0-22 0-5 1.45-1.60 >20.00 0.05-0.08 Low 0.5-1.0 0.17 0.17 4 1 220
22-34 15-30 1.35-1.50 2.00-6.00 0.10-0.13 Low 0.0-0.5 0.15 0.15
34-60 0-5 1.45-1.60 6.00-20.00 0.06.0.08 Low 0.0-0.5 0.10 0.10
79:
Weld 0-8 15-27 1.25-1.40 0.60-6.00 0.14-0.17 Low 2.0-4.0 0.24 0.24 3 6 48
8-15 35-50 1.30-1.40 0.06-0.20 0.18-0.20 High 0.5-2.0 0.28 0.28
15-60 20-35 1.25-1.35 0.60-2.00 0.16-0.18 Moderate 0.5-1.0 0.28 0.28
60-64 15-25 1.25-1.40 0.60-2.00 0.12-0.18 Low 0.5-1.0 0.28 0.28
QB1 582
U.S. DEPARTMENT OF AGRICULTURE PAGE 2 OF 4
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
PHYSICAL PROPERTIES OF SOILS
Endnote -- PHYSICAL PROPERTIES OF SOILS
This report shows estimates of some characteristics and features that affect soil behavior. These estimates
are given for the major layers of each soil in the survey area. The estimates are based on field observations
and on test data for these and similar soils.
CLAY as a soil separate consists of mineral soil particles that are less than 0.002 millimeter in diameter.
In this report, the estimated clay content of each major soil layer is given as a percentage, by weight, of the
soil material that is less than 2 millimeters in diameter. The amount and kind of clay greatly affect the
fertility and physical condition of the soil. They determine the ability of the soil to adsorb cations and
to retain moisture. They influence shrink-swell potential, permeability, plasticity, the ease of soil
dispersion, and other soil properties. The amount and kind of clay in a soil also affect tillage and
earthmoving operations.
MOIST BULK DENSITY is the weight of soil (ovendry) per unit volume. Volume is measured when the soil is
at field moisture capacity, the moisture content at 1/3 bar moisture tension. Weight is determined after
drying the soil at 105 degrees C. In this report, the estimated moist bulk density of each major soil
horizon is expressed in grams per cubic centimeter of soil material that is less than 2 millimeters in
diameter. Bulk density data are used to compute shrink-swell potential, available water capacity, total
pore space, and other soil properties. The moist bulk density of a soil indicates the pore space available for
water and roots. A bulk density of more than 1.6 can restrict water storage and root penetration. Moist
bulk density is influenced by texture, kind of clay, content of organic matter, and soil structure.
`MEABILITY refers to the ability of a soil to transmit water or air. The estimates indicate the
. .e of downward movement of water when the soil is saturated. They are based on soil characteristics
observed in the field, particularly structure, porosity, and texture. Permeability is considered in
the design of soil drainage systems, septic tank absorption fields, and construction where the rate of
water movement under saturated conditions affects behavior.
AVAILABLE WATER CAPACITY refers to the quantity of water that the soil is capable of storing for use by
plants. The capacity for water storage is given in inches of water per inch of soil for each major soil layer.
The capacity varies, depending on soil properties that affect the retention of water and the depth of the root
zone. The most important properties are the content of organic matter, soil texture, bulk density, and soil
structure. Available water capacity is an important factor in the choice of plants or crops to be grown and in
the design and management of irrigation systems. Available water capacity is not an estimate of the quantity of
water actually available to plants at any given time.
SHRINK-SWELL POTENTIAL is the potential for volume change in a soil with a loss or gain of moisture. Volume
change occurs mainly because of the interaction of clay minerals with water and varies with the amount and type
of clay minerals in the soil. The size of the load on the soil and the magnitude of the change in soil moisture
content influence the amount of swelling of soils in place. Laboratory measurements of swelling of undisturbed
clods were made for many soils. For others, swelling was estimated on the basis of the kind and amount of
clay minerals in the soil and on measurements of similar soils. If the shrink-swell potential is rated moderate
to very high, shrinking and swelling can cause damage to buildings, roads, and other structures. Special design
is often needed. Shrink-swell potential classes are based on the change in length of an unconfined clod as
moisture content is increased from air-dry to field capacity. The change is based on the soil fraction less
than 2 millimeters in diameter. The classes are "Low," a change of less than 3 percent; "Moderate," 3 to 6
percent; and "High," more than 6 percent. "Very high," greater than 9 percent, is sometimes used.
P81582
U.S. DEPARTMENT OF AGRICULTURE PAGE 3 OF 4
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
PHYSICAL PROPERTIES OF SOILS
Endnote -- PHYSICAL PROPERTIES OF SOILS--Continued
ORGANIC MATTER is the plant and animal residue in the soil at various stages of decomposition. In report J,
the estimated content of organic matter is expressed as a percentage, by weight, of the soil material that is
less than 2 millimeters in diameter. The content of organic matter in a soil can be maintained or increased by
returning crop residue to the soil. Organic matter affects the available water capacity, infiltration rate, and
tilth. It is a source of nitrogen and other nutrients for crops.
EROSION FACTOR K indicates the susceptibility of the whole soil (including rocks and rock fragments) to
sheet and rill erosion by water. Factor K is one of six factors used in the Universal Soil Loss Equation (USLE)
to predict the average annual rate of soil loss by sheet and rill erosion in tons per acre per year. The
estimates are based primarily on percentage of silt, sand, and organic matter (up to 4 percent) and on soil
structure and permeability. Values of K range from 0.05 to 0.69. The higher the value, the more susceptible
the soil is to sheet and rill erosion by water.
EROSION FACTOR Kf is like EROSION FACTOR K but it is for the fine-earth fraction of the soil. Rocks and
rock fragments are not considered.
EROSION FACTOR T is an estimate of the maximum average annual rate of soil erosion by wind or water that can
occur without affecting crop productivity over a sustained period. The rate is in tons per acre per year.
WIND ERODISILITY GROUPS are made up of soils that have similar properties affecting their resistance to wind
erosion in cultivated areas. The groups indicate the susceptibility of soil to wind erosion. Soils are grouped
•ording to the following distinctions:
1. Coarse sands, sands, fine sands, and very fine sands.
These soils are generally not suitable for crops. They are
extremely erodible, and vegetation is difficult to
establish.
2. Loamy coarse sands, loamy sands, loamy fine sands, loamy
very fine sands, and sapric soil material. These soils are
very highly erodible. Crops can be grown if intensive
measures to control wind erosion are used.
3. Coarse sandy foams, sandy foams, fine sandy loans, and
very fine sandy loams. These soils are highly erodible.
Crops can be grown if intensive measures to control wind
erosion are used.
4L. Calcareous loans, silt loans, clay loans, and silty clay
loams. These soils are erodible. Crops can be grown if
intensive measures to control wind erosion are used.
4. Clays, silty clays, noncalcareous clay loans, and silty
clay loams that are more than 35 percent clay. These soils
are moderately erodible. Crops can be grown if measures to
control wind erosion are used.
981582
U.S. DEPARTMENT OF AGRICULTURE PAGE 4 OF 4
NATURAL RESOURCES CONSERVATION SERVICE 01/15/98
PHYSICAL PROPERTIES OF SOILS
Endnote -- PHYSICAL PROPERTIES OF SOILS--Continued
5. Noncalcareous Loans and silt loans that are less than 20
percent clay and sandy clay Loans, sandy clays, and hemic
soil material. These soils are slightly erodible. Crops
can be grown if measures to control wind erosion are used.
6. Noncalcareous loans and silt teams that are more than 20
percent clay and noncalcareous clay loans that are less than
35 percent clay. These soils are very slightly erodible.
Crops can be grown if ordinary measures to control wind
erosion are used.
7. Silts, noncalcareous silty clay loans that are less than
35 percent clay, and fibric soil material. These soils are
very slightly erodible. Crops can be grown if ordinary
measures to control wind erosion are used.
8. Soils that are not subject to wind erosion because of
coarse fragments on the surface or because of surface
wetness.
The WIND ERODIBILITY INDEX is used in the wind erosion equation (WED). The index number indicates the
--'aunt of soil lost in tons per acre per year. The range of wind erodibility index numbers is 0 to 300.
981.582
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