Soil Survey of Lubbock County, Texas Page: 30
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planning and design. A severe limitation indicates that one
or more soil properties or site features are so unfavorable
or difficult to overcome that a major increase in construc-
tion effort, special design, or intensive maintenance is
required. For some soils rated severe, such costly mea-
sures may not be feasible.
Shallow excavations are made for pipelines, sewerlines,
communications and power transmission lines, basements,
and open ditches. Such digging or trenching is influenced
by the texture and consistence of soils; the tendency of
soils to cave in or slough; and the presence of very firm,
dense soil layers, bedrock, or large stones. In addition, ex-
cavations are affected by slope of the soil and the proba-
bility of flooding. Ratings do not apply to soil horizons
below a depth of 6 feet unless otherwise noted.
In the soil series descriptions, the consistence of each
soil horizon is given, and the presence of very firm or ex-
tremely firm horizons, usually difficult to excavate, is in-
Dwellings and small commercial buildings referred to
in table 6 are built on undisturbed soil and have founda-
tion loads of a dwelling no more than three stories high.
Separate ratings are made for small commercial buildings
without basements and for dwellings with and without
basements. For such structures, soils should be suffi-
ciently stable that cracking or subsidence of the structure
from settling or shear failure of the foundation does not
occur. These ratings were determined from estimates of
the shear strength, compressibility, and shrink-swell
potential of the soil Soil texture, plasticity and in-place
density, soil wetness, and depth to a seasonal high water
table were also considered. Depth to bedrock, slope, and
large stones in or on the soil are also important considera-
tions in the choice of sites for these structures and were
considered in determining the ratings. Susceptibility to
flooding is a serious hazard.
Local roads and streets referred to in table 6 have an
all-weather surface that can carry light to medium traffic
all year. They consist of a subgrade of the underlying soil
material; a base of gravel, crushed rock fragments, or soil
material stabilized with lime or cement; and a flexible or
rigid surface, commonly asphalt or concrete. The roads
are graded with soil material at hand, and most cuts and
fills are less than 6 feet deep.
The load supporting capacity and the stability of the
soil as well as the quantity and workability of fill material
available are important in design and construction of
roads and streets. The classifications of the soil and the
soil texture, density, and shrink-swell potential are indica-
tors of the traffic supporting capacity used in making the
ratings. Soil wetness, flooding, slope, depth to hard rock
or very compact layers, and content of large stones affect
stability and ease of excavation.
Favorable soil properties and site features are needed
for proper functioning of septic tank absorption fields,
sewage lagoons, and sanitary landfills. The nature of the
soil is important in selecting sites for these facilities and
in identifying limiting soil properties and site features to
be considered in design and installation. Also, those soil
properties that affect ease of excavation or installation of
these facilities will be of interest to contractors and local
officials. Table 7 shows the degree and kind of limitations
of each soil for such uses and for use of the soil as daily
cover for landfills. It is important to observe local or-
dinances and regulations.
If the degree of soil limitation is expressed as slight,
soils are generally favorable for the specified use and
limitations are minor and easily overcome; if moderate,
soil properties or site features are unfavorable for the
specified use, but limitations can be overcome by special
planning and design; and if severe, soil properties or site
features are so unfavorable or difficult to overcome that
major soil reclamation, special designs, or intensive main-
tenance is required. Soil suitability is rated by the terms
good, fair, or poor, which, respectively, mean about the
same as the terms slight, moderate, and severe.
Septic tank absorption fields are subsurface systems of
tile or perforated pipe that distribute effluent from a sep-
tic tank into the natural soil Only the soil horizons
between depths of 18 and 72 inches are evaluated for this
use. The soil properties and site features considered are
those that affect the absorption of the effluent and those
that affect the construction of the system.
Properties and features that affect absorption of the
effluent are permeability, depth to seasonal high water
table, depth to bedrock, and susceptibility to flooding.
Stones, boulders, and shallowness to bedrock interfere
with installation. Excessive slope can cause lateral
seepage and surfacing of the effluent. Also, soil erosion
and soil slippage are hazards if absorption fields are in-
stalled on sloping soils.
In some soils, loose sand and gravel or fractured
bedrock is less than 4 feet below the tile lines. In these
soils the absorption field does not adequately filter the ef-
fluent, and ground water in the area may be con-
On many of the soils that have moderate or severe
limitations for use as septic tank absorption fields, a
system to lower the seasonal water table can be installed
or the size of the absorption field can be increased so that
performance is satisfactory.
Sewage lagoons are shallow ponds constructed to hold
sewage while aerobic bacteria decompose the solid and
liquid wastes. Lagoons have a nearly level floor and cut
slopes or embankments of compacted soil material Aero-
bic lagoons generally are designed to hold 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. Soils that are very
high in content of organic matter and those that have
cobbles, stones, or boulders are not suitable. Unless the
soil has very slow permeability, contamination of ground
water is a hazard where the seasonal high water table is
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Blackstock, Dan A.; Blakley, Earl R.; Landers, Clifford R.; Koos, William M. & Putnam, Lee A. Soil Survey of Lubbock County, Texas, book, 1979; Washington D.C.. (texashistory.unt.edu/ark:/67531/metapth130232/m1/41/: accessed May 27, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting UNT Libraries Government Documents Department.