HomeMy WebLinkAboutSUB201700214 Study 2018-01-19Soils Report
For
Mountfair Hollow Preliminary Plat
Tax Map ID: 01400-00-00-052B0; 01400-00-00-052D0; 01400-00-00-
052E0; 01400-00-00-052FO
Item Number: SUB201700214
Prepared: January 19, 2018
Thomas Jefferson Soil & Water Conservation District
"To exercise leadership in promoting natural resource protection. "
706 Forest Street, Suite G
Charlottesville, Virginia 22903
Phone: (434) 975-0224
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38° 10' 31" N
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Soil Map —Albemarle County, Virginia
(Mountfair Hollow Preliminary Plat)
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Map Scale: 1:3,450 if printed on A portrait (8.5" x 11") sheet
Meters
N 0 50 100 200 300
Fit
0 150 300 600 900
Map projection: Web Mercator Gomer000rdinates: WGS84 Edge tics: UTM Zone 17N WGS64
USDA Natural Resources Web Soil Survey
'" Conservation Service National Cooperative Soil Survey
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Soil Map —Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Map Unit Legend
Map Unit Symbol
Map Unit Name
Acres in AOI
Percent of AOI
5B
Belvoir loam, 2 to 7 percent
12.9
32.8%
slopes
7C
Braddock loam, 7 to 15
0.5
1.2%
percent slopes
9C
Braddock very stony loam, 7 to
0.8
2.0%
15 percent slopes
67E
Parker extremely stony loam,
2.4
6.1 %
25 to 60 percent slopes
81 B
Thurmont loam, 2 to 7 percent
0.0
0.1 %
slopes
81C
Thurmont loam, 7 to 15
4.3
11.0%
percent slopes
82C
Thurmont very stony loam, 7 to
8.2
20.9%
15 percent slopes
82D
Thurmont very stony loam, 15
10.1
25.9%
to 25 percent slopes
Totals for Area of Interest
39.2
100.0%
USDA Natural Resources Web Soil Survey 1/19/2018
"iiiiiiiiiiiii Conservation Service National Cooperative Soil Survey Page 3 of 3
Map Unit Description (Brief, Generated) ---Albemarle County, Virginia
Mountfair Hallow Preliminary Plat
Map Unit Description (Brief, Generated)
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions in this
report, along with the maps, provide information on the composition of map units
and properties of their components.
A map unit delineation on a soil map represents an area dominated by one or
more major kinds of soil or miscellaneous areas. A map unit is identified and
named according to the taxonomic classification of the dominant soils. Within a
taxonomic class there are precisely defined limits for the properties of the soils.
On the landscape, however, the soils are natural phenomena, and they have the
characteristic variability of all natural phenomena. Thus, the range of some
observed properties may extend beyond the limits defined for a taxonomic class.
Areas of soils of a single taxonomic class rarely, if ever, can be mapped without
including areas of other taxonomic classes. Consequently, every map unit is
made up of the soils or miscellaneous areas for which it is named and some
minor components that belong to taxonomic classes other than those of the
major soils.
The Map Unit Description (Brief, Generated) report displays a generated
description of the major soils that occur in a map unit. Descriptions of non -soil
(miscellaneous areas) and minor map unit components are not included. This
description is generated from the underlying soil attribute data.
Additional information about the map units described in this report is available in
other Soil Data Mart reports, which give properties of the soils and the limitations,
capabilities, and potentials for many uses. Also, the narratives that accompany
the Soil Data Mart reports define some of the properties included in the map unit
descriptions.
Report —Map Unit Description (Brief, Generated)
Albemarle County, Virginia
Map Unit: 5B—Belvoir loam, 2 to 7 percent slopes
Component: Belvoir (80%)
The Belvoir component makes up 80 percent of the map unit. Slopes are 2 to 7
percent. This component is on swales, piedmonts. The parent material consists
of residuum weathered from granite and gneiss. Depth to a root restrictive layer,
fragipan, is 16 to 30 inches. The natural drainage class is somewhat poorly
drained. Water movement in the most restrictive layer is moderately high.
Available water to a depth of 60 inches is very low. Shrink -swell potential is
moderate. This soil is not flooded. It is not ponded. A seasonal zone of water
saturation is at 18 inches during January, February, March, April. Organic matter
content in the surface horizon is about 1 percent. Nonirrigated land capability
classification is 3w. This soil does not meet hydric criteria.
USDA Natural Resources Web Soil Survey 1/19/2018
ii-M Conservation Service National Cooperative Soil Survey Page 1 of 4
Map Unit Description (Brief, Generated) ---Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Component: Worsham (3%)
Generated brief soil descriptions are created for major components. The
Worsham soil is a minorcomponent.
Map Unit: 7C—Braddock loam, 7 to 15 percent slopes
Component: Braddock (80%)
The Braddock component makes up 80 percent of the map unit. Slopes are 7 to
15 percent. This component is on fans, mountains. The parent material consists
of alluvium and colluvium derived from acid crystalline rocks. Depth to a root
restrictive layer is greater than 60 inches. The natural drainage class is well
drained. Water movement in the most restrictive layer is moderately high.
Available water to a depth of 60 inches is high. Shrink -swell potential is
moderate. This soil is not flooded. It is not ponded. There is no zone of water
saturation within a depth of 72 inches. Organic matter content in the surface
horizon is about 2 percent. Nonirrigated land capability classification is 3e. This
soil does not meet hydric criteria.
Map Unit: 9C—Braddock very stony loam, 7 to 15 percent slopes
Component: Braddock (80%)
The Braddock component makes up 80 percent of the map unit. Slopes are 7 to
15 percent. This component is on fans, mountains. The parent material consists
of alluvium and colluvium derived from acid crystalline rocks. Depth to a root
restrictive layer is greater than 60 inches. The natural drainage class is well
drained. Water movement in the most restrictive layer is moderately high.
Available water to a depth of 60 inches is high. Shrink -swell potential is
moderate. This soil is not flooded. It is not ponded. There is no zone of water
saturation within a depth of 72 inches. Organic matter content in the surface
horizon is about 2 percent. Nonirrigated land capability classification is 6s. This
soil does not meet hydric criteria.
Map Unit: 67E—Parker extremely stony loam, 25 to 60 percent slopes
Component: Parker (75%)
The Parker component makes up 75 percent of the map unit. Slopes are 25 to 60
percent. This component is on interfluves, uplands. The parent material consists
of residuum weathered from granite and gneiss. Depth to a root restrictive layer,
bedrock, lithic, is 48 to 80 inches. The natural drainage class is excessively
drained. Water movement in the most restrictive layer is very low. Available water
to a depth of 60 inches is low. Shrink -swell potential is low. This soil is not
flooded. It is not ponded. There is no zone of water saturation within a depth of
72 inches. Organic matter content in the surface horizon is about 2 percent.
Nonirrigated land capability classification is 7s. This soil does not meet hydric
criteria.
USDA Natural Resources Web Soil Survey 1/19/2018
i� Conservation Service National Cooperative Soil Survey Page 2 of 4
Map Unit Description (Brief, Generated) ---Albemarle County, Virginia Mountfair Hollow Preliminary Plat
Map Unit: 81 B—Thurmont loam, 2 to 7 percent slopes
Component: Thurmont (80%)
The Thurmont component makes up 80 percent of the map unit. Slopes are 2 to
7 percent. This component is on interfluves, uplands. The parent material
consists of colluvium derived from granite, granodiorite, and granite gneiss.
Depth to a root restrictive layer is greater than 60 inches. The natural drainage
class is well drained. Water movement in the most restrictive layer is moderately
high. Available water to a depth of 60 inches is moderate. Shrink -swell potential
is low. This soil is not flooded. It is not ponded. A seasonal zone of water
saturation is at 60 inches during January, February, March, April. Organic matter
content in the surface horizon is about 1 percent. Nonirrigated land capability
classification is 2e. This soil does not meet hydric criteria.
Map Unit: 81C—Thurmont loam, 7 to 15 percent slopes
Component: Thurmont (80%)
The Thurmont component makes up 80 percent of the map unit. Slopes are 7 to
15 percent. This component is on interfluves, uplands. The parent material
consists of colluvium derived from granite, granodiorite, and granite gneiss.
Depth to a root restrictive layer is greater than 60 inches. The natural drainage
class is well drained. Water movement in the most restrictive layer is moderately
high. Available water to a depth of 60 inches is moderate. Shrink -swell potential
is low. This soil is not flooded. It is not ponded. A seasonal zone of water
saturation is at 60 inches during January, February, March, April. Organic matter
content in the surface horizon is about 1 percent. Nonirrigated land capability
classification is 3e. This soil does not meet hydric criteria.
Map Unit: 82C—Thurmont very stony loam, 7 to 15 percent slopes
Component: Thurmont (75%)
The Thurmont component makes up 75 percent of the map unit. Slopes are 7 to
15 percent. This component is on interfluves, uplands. The parent material
consists of colluvium derived from granite, granodiorite, and granite gneiss.
Depth to a root restrictive layer is greater than 60 inches. The natural drainage
class is well drained. Water movement in the most restrictive layer is moderately
high. Available water to a depth of 60 inches is moderate. Shrink -swell potential
is low. This soil is not flooded. It is not ponded. A seasonal zone of water
saturation is at 60 inches during January, February, March, April. Organic matter
content in the surface horizon is about 1 percent. Nonirrigated land capability
classification is 6s. This soil does not meet hydric criteria.
Map Unit: 82D—Thurmont very stony loam, 15 to 25 percent slopes
Corrnponent: Thurmont (75 o)
USDA Natural Resources Web Soil Survey 1/19/2018
�� Conservation Service National Cooperative Soil Survey Page 3 of 4
Map Unit Description (Brief, Generated) ---Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
The Thurmont component makes up 75 percent of the map unit. Slopes are 15 to
25 percent. This component is on interfluves, uplands. The parent material
consists of colluvium derived from granite, granodiorite, and granite gneiss.
Depth to a root restrictive layer is greater than 60 inches. The natural drainage
class is well drained. Water movement in the most restrictive layer is moderately
high. Available water to a depth of 60 inches is moderate. Shrink -swell potential
is low. This soil is not flooded. It is not ponded. A seasonal zone of water
saturation is at 60 inches during January, February, March, April. Organic matter
content in the surface horizon is about 1 percent. Nonirrigated land capability
classification is 6s. This soil does not meet hydric criteria.
Data Source Information
Soil Survey Area: Albemarle County, Virginia
Survey Area Data: Version 11, Oct 11, 2017
USDA Natural Resources Web Soil Survey 1/19/2018
Conservation Service National Cooperative Soil Survey Page 4 of 4
Dwellings and Small Commercial Buildings ---Albemarle County, Virginia Mountfair Hollow Preliminary Plat
Dwellings and Small Commercial Buildings
Soil properties influence the development of building sites, including the selection
of the site, the design of the structure, construction, performance after
construction, and maintenance. This table shows the degree and kind of soil
limitations that affect dwellings and small commercial buildings.
The ratings in the table are both verbal and numerical. Rating class terms
indicate the extent to which the soils are limited by all of the soil features that
affect building site development. Not limited indicates that the soil has features
that are very favorable for the specified use. Good performance and very low
maintenance can be expected. Somewhat limited indicates that the soil has
features that are moderately favorable for the specified use. The limitations can
be overcome or minimized by special planning, design, or installation. Fair
performance and moderate maintenance can be expected. Very limited indicates
that the soil has one or more features that are unfavorable for the specified use.
The limitations generally cannot be overcome without major soil reclamation,
special design, or expensive installation procedures. Poor performance and high
maintenance can be expected.
Numerical ratings in the table indicate the severity of individual limitations. The
ratings are shown as decimal fractions ranging from 0.01 to 1.00. They indicate
gradations between the point at which a soil feature has the greatest negative
impact on the use (1.00) and the point at which the soil feature is not a limitation
(0.00).
Dwellings are single-family houses of three stories or less. For dwellings without
basements, the foundation is assumed to consist of spread footings of reinforced
concrete built on undisturbed soil at a depth of 2 feet or at the depth of maximum
frost penetration, whichever is deeper. For dwellings with basements, the
foundation is assumed to consist of spread footings of reinforced concrete built
on undisturbed soil at a depth of about 7 feet. The ratings for dwellings are based
on the soil properties that affect the capacity of the soil to support a load without
movement and on the properties that affect excavation and construction costs.
The properties that affect the load -supporting capacity include depth to a water
table, ponding, flooding, subsidence, linear extensibility (shrink -swell potential),
and compressibility. Compressibility is inferred from the Unified classification. The
properties that affect the ease and amount of excavation include depth to a water
table, ponding, flooding, slope, depth to bedrock or a cemented pan, hardness of
bedrock or a cemented pan, and the amount and size of rock fragments.
USDA Natural Resources Web Soil Survey 1/19/2018
2111111111111 Conservation Service National Cooperative Soil Survey Page 1 of 4
Dwellings and Small Commercial Buildings ---Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Small commercial buildings are structures that are less than three stories high
and do not have basements. The foundation is assumed to consist of spread
footings of reinforced concrete built on undisturbed soil at a depth of 2 feet or at
the depth of maximum frost penetration, whichever is deeper. The ratings are
based on the soil properties that affect the capacity of the soil to support a load
without movement and on the properties that affect excavation and construction
costs. The properties that affect the load -supporting capacity include depth to a
water table, ponding, flooding, subsidence, linear extensibility (shrink -swell
potential), and compressibility (which is inferred from the Unified classification).
The properties that affect the ease and amount of excavation include flooding,
depth to a water table, ponding, slope, depth to bedrock or a cemented pan,
hardness of bedrock or a cemented pan, and the amount and size of rock
fragments.
Information in this table is intended for land use planning, for evaluating land use
alternatives, and for planning site investigations prior to design and construction.
The information, however, has limitations. For example, estimates and other data
generally apply only to that part of the soil between the surface and a depth of 5
to 7 feet. Because of the map scale, small areas of different soils may be
included within the mapped areas of a specific soil.
The information is not site specific and does not eliminate the need for onsite
investigation of the soils or for testing and analysis by personnel experienced in
the design and construction of engineering works.
Government ordinances and regulations that restrict certain land uses or impose
specific design criteria were not considered in preparing the information in this
table. Local ordinances and regulations should be considered in planning, in site
selection, and in design.
Report —Dwellings and Small Commercial Buildings
[Onsite investigation may be needed to validate the interpretations in this table
and to confirm the identity of the soil on a given site. The numbers in the value
columns range from 0.01 to 1.00. The larger the value, the greater the potential
limitation. The table shows only the top five limitations for any given soil. The soil
may have additional limitations]
Dwellings and Small Commercial Buildings —Albemarle County, Virginia
Map symbol and soil
Pct. of
Dwellings without
Dwellings with basements
Small commercial buildings
name
map
basements
unit
Rating class and
Value
Rating class and
Value
Rating class and
Value
limiting features
limiting features
limiting features
5B—Belvoir loam, 2 to
7 percent slopes
Belvoir
80
Somewhat limited
Very limited
Somewhat limited
Depth to saturated
0.98
Depth to saturated
1.00
Depth to saturated
0.98
zone
zone
zone
Depth to thin
1.00
Slope
0.14
cemented pan
USDA Natural Resources Web Soil Survey 1/19/2018
Conservation Service National Cooperative Soil Survey Page 2 of 4
Dwellings and Small Commercial Buildings ---Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Dwellings and Small Commercial Buildings —Albemarle County, Virginia
Map symbol and soil
Pct. of
Dwellings without
Dwellings with basements
Small commercial buildings
name
map
basements
unit
Rating class and
Value
Rating class and
Value
Rating class and
Value
limiting features
limiting features
limiting features
7C—Braddock loam,
7 to 15 percent
slopes
Braddock
80
Somewhat limited
Somewhat limited
Very limited
Shrink -swell
0.50
Shrink -swell
0.50
Slope
1.00
Slope
0.37
Slope
0.37
Shrink -swell
0.50
9C—Braddock very
stony loam, 7 to 15
percent slopes
Braddock
80
Somewhat limited
Somewhat limited
Very limited
Shrink -swell
0.50
Shrink -swell
0.50
Slope
1.00
Slope
0.37
Slope
0.37
Shrink -swell
0.50
67E—Parker
extremely stony
loam, 25 to 60
percent slopes
Parker
75
Very limited
Very limited
Very limited
Slope
1.00
Slope
1.00
Slope
1.00
Large stones
1.00
Large stones
1.00
Large stones
1.00
81B—Thurmont loam,
2 to 7 percent
slopes
Thurmont
80
Not limited
Somewhat limited
Somewhat limited
Depth to saturated
0.15
Slope
0.14
zone
81C—Thurmont loam,
7 to 15 percent
slopes
Thurmont
80
Somewhat limited
Somewhat limited
Very limited
Slope
0.37
Slope
0.37
Slope
1.00
Depth to saturated
0.15
zone
82C—Thurmont very
stony loam, 7 to 15
percent slopes
Thurmont
75
Somewhat limited
Somewhat limited
Very limited
Slope
0.37
Slope
0.37
Slope
1.00
Depth to saturated 0.15
zone
USDA Natural Resources Web Soil Survey 1/1912018
Conservation Service National Cooperative Soil Survey Page 3 of 4
Dwellings and Small Commercial Buildings --Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Dwellings and Small Commercial Buildings —Albemarle County, Virginia
Map symbol and soil
Pct. of
Dwellings without
Dwellings with basements
Small commercial buildings
name
map
basements
unit
Rating class and
Value
Rating class and
Value
Rating class and
Value
limiting features
limiting features
limiting features
82D—Thurmont very
stony loam, 15 to
25 percent slopes
Thurmont
75
Very limited
Very limited
Very limited
Slope
1.00
Slope
1.00
Slope
1.00
Depth to saturated 0.15
zone
Data Source Information
Soil Survey Area: Albemarle County, Virginia
Survey Area Data: Version 11, Oct 11, 2017
USA Natural Resources Web Soil Survey 1/19/2018
riiiiiiiiill Conservation Service National Cooperative Soil Survey Page 4 of 4
Physical Soil Properties ---Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Physical Soil Properties
This table shows estimates of some physical characteristics and features that
affect soil behavior. These estimates are given for the layers of each soil in the
survey area. The estimates are based on field observations and on test data for
these and similar soils.
Depth to the upper and lower boundaries of each layer is indicated.
Particle size is the effective diameter of a soil particle as measured by
sedimentation, sieving, or micrometric methods. Particle sizes are expressed as
classes with specific effective diameter class limits. The broad classes are sand,
silt, and clay, ranging from the larger to the smaller.
Sand as a soil separate consists of mineral soil particles that are 0.05 millimeter
to 2 millimeters in diameter. In this table, the estimated sand content of each soil
layer is given as a percentage, by weight, of the soil material that is less than 2
millimeters in diameter.
Silt as a soil separate consists of mineral soil particles that are 0.002 to 0.05
millimeter in diameter. In this table, the estimated silt content of each soil layer is
given as a percentage, by weight, of the soil material that is less than 2
millimeters in diameter.
Clay as a soil separate consists of mineral soil particles that are less than 0.002
millimeter in diameter. In this table, the estimated clay content of each soil layer
is given as a percentage, by weight, of the soil material that is less than 2
millimeters in diameter.
The content of sand, silt, and clay affects the physical behavior of a soil. Particle
size is important for engineering and agronomic interpretations, for determination
of soil hydrologic qualities, and for soil classification.
The amount and kind of clay affect the fertility and physical condition of the soil
and the ability of the soil to adsorb cations and to retain moisture. They influence
shrink -swell potential, saturated hydraulic conductivity (Ksat), 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, that is, the moisture content
at 1/3- or 1/10-bar (33kPa or 10kPa) moisture tension. Weight is determined after
the soil is dried at 105 degrees C. In the table, the estimated moist bulk density
of each 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
linear extensibility, 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. Depending on soil texture, a bulk
density of more than 1.4 can restrict water storage and root penetration. Moist
bulk density is influenced by texture, kind of clay, content of organic matter, and
soil structure.
uSpn Natural Resources Web Soil Survey 1/19/2018
s Conservation Service National Cooperative Soil Survey Page 1 of 8
Physical Soil Properties ---Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Saturated hydraulic conductivity (Ksat) refers to the ease with which pores in a
saturated soil transmit water. The estimates in the table are expressed in terms
of micrometers per second. They are based on soil characteristics observed in
the field, particularly structure, porosity, and texture. Saturated hydraulic
conductivity (Ksat) is considered in the design of soil drainage systems and
septic tank absorption fields.
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 soil layer. The capacity varies, depending on soil
properties that affect retention of water. 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.
Linear extensibility refers to the change in length of an unconfined clod as
moisture content is decreased from a moist to a dry state. It is an expression of
the volume change between the water content of the clod at 1/3- or 1/10-bar
tension (33kPa or 10kPa tension) and oven dryness. The volume change is
reported in the table as percent change for the whole soil. The amount and type
of clay minerals in the soil influence volume change.
Linear extensibility is used to determine the shrink -swell potential of soils. The
shrink -swell potential is low if the soil has a linear extensibility of less than 3
percent; moderate if 3 to 6 percent; high if 6 to 9 percent; and very high if more
than 9 percent. If the linear extensibility is more than 3, shrinking and swelling
can cause damage to buildings, roads, and other structures and to plant roots.
Special design commonly is needed.
Organic matter is the plant and animal residue in the soil at various stages of
decomposition. In this table, 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 by returning
crop residue to the soil.
Organic matter has a positive effect on available water capacity, water infiltration,
soil organism activity, and tilth. It is a source of nitrogen and other nutrients for
crops and soil organisms.
Erosion factors are shown in the table as the K factor (Kw and Kf) and the T
factor. Erosion factor K indicates the susceptibility of a soil to sheet and rill
erosion by water. Factor K is one of six factors used in the Universal Soil Loss
Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE) 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 and on soil structure and Ksat. Values of K range from 0.02 to
0.69. Other factors being equal, the higher the value, the more susceptible the
soil is to sheet and rill erosion by water.
Erosion factor Kw indicates the erodibility of the whole soil. The estimates are
modified by the presence of rock fragments.
Erosion factor Kf indicates the erodibility of the fine -earth fraction, or the material
less than 2 millimeters in size.
USM Natural Resources Web Soil Survey 1/19/2018
A� Conservation Service National Cooperative Soil Survey Page 2 of 8
Physical Soil Properties ---Albemarle County, Virginia
Mountfair Hollow Preliminary Plat
Erosion factor T is an estimate of the maximum average annual rate of soil
erosion by wind and/or water that can occur without affecting crop productivity
over a sustained period. The rate is in tons per acre per year.
Wind erodibi/ity groups are made up of soils that have similar properties affecting
their susceptibility to wind erosion in cultivated areas. The soils assigned to
group 1 are the most susceptible to wind erosion, and those assigned to group 8
are the least susceptible. The groups are described in the "National Soil Survey
Handbook."
Wind erodibility index is a numerical value indicating the susceptibility of soil to
wind erosion, or the tons per acre per year that can be expected to be lost to
wind erosion. There is a close correlation between wind erosion and the texture
of the surface layer, the size and durability of surface clods, rock fragments,
organic matter, and a calcareous reaction. Soil moisture and frozen soil layers
also influence wind erosion.
Reference:
United States Department of Agriculture, Natural Resources Conservation
Service. National soil survey handbook, title 430-VI. (http://soils.usda.gov)
USDA Natural Resources Web Soil Survey 1/19/2018
Conservation Service National Cooperative Soil Survey Page 3 of 8
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Soil Features --Albemarle County, Virginia Mountfair Hollow Preliminary Plat
Soil Features
This table gives estimates of various soil features. The estimates are used in
land use planning that involves engineering considerations.
A restrictive layer is a nearly continuous layer that has one or more physical,
chemical, or thermal properties that significantly impede the movement of water
and air through the soil or that restrict roots or otherwise provide an unfavorable
root environment. Examples are bedrock, cemented layers, dense layers, and
frozen, layers. The table indicates the hardness and thickness of the restrictive
layer, both of which significantly affect the ease of excavation. Depth to top is the
vertical distance from the soil surface to the upper boundary of the restrictive
layer.
Subsidence is the settlement of organic soils or of saturated mineral soils of very
low density. Subsidence generally 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. The table shows the
expected initial subsidence, which usually is a result of drainage, and total
subsidence, which results from a combination of factors.
Potential for 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, saturated hydraulic conductivity (Ksat), 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 to
pavements and other rigid structures.
Risk of corrosion pertains to potential soil -induced electrochemical or chemical
action that corrodes 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 results in a severe hazard of corrosion.
The steel or concrete in installations that intersect soil boundaries or soil layers is
more susceptible to corrosion than the steel or concrete 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 also is expressed as low, moderate, or high. It
is based on soil texture, acidity, and amount of sulfates in the saturation extract.
USDA Natural Resources Web Soil Survey 1/19/2018
Conservation Service National Cooperative Soil Survey Page 1 of 3
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