On-Site Sewerage Facilities
Soil Texture Analysis for OSSF
Permit | Soil
Texture | Table V |
Table X | Example
Soil Texture Classes Texture
is the relative amount of the different sizes of mineral particles in a
soil. All soils are composed of sand (0.5 - 2.0 mm in size); silt, which
includes intermediate sized particles that cannot be seen with the naked
eye, but feels like flour when pressed between the fingers (0.002 - 0.05
mm); and clay, which is extremely small in size and gives cohesion to a
soil (less than 0.002 mm). The texture of the different soil horisons of
soils may be classified into five general groups which will be used for
determining the application rate in Table I.
Soil Class Ia
Sandy texture soils which contail more than 30% gravel.
Soil Class Ib
Sandy soils which contain less than or equal to 30% gravel. It includes
sand and loamy sand.
Sand: Sand has a gritty feel,
does not stain the fingers, and does not form a ribbon or ball when wet
Loamy sand: Loamy sand has a
gritty feel, stains the fingers (due to silt and clay components), forms
a weak ball, and cannot be handled without breaking.
Soil Class II
Course loamy soils which includes sandy loam and loam textures.
Sandy loam: Sandy loam has a
gritty feel and forms a ball that can be picked up with the fingers and
handled with care without breaking.
Loam: Loam may have a slightly
gritty feel but does not show a fingerprint and forms only short ribbons
from 1/4 to 1/2 inch in length. Loam will form a ball that can be handled
Soil Class III
Fine loamy textured soils which include silt, slit loam, silty clay loam,
clay loam, sandy clay loam, and sandy clay textures.
Silt: Silt has a floury feel
when moist and sticky when wet, but will not ribbon and forms a ball that
will tolerate some handling.
Silt Loam: Silt loam has a floury
feel when moist and will show a fingerprint but will not ribbon and forms
only a weak ball.
Sandy clay loam: Sandy clay
loam has a gritty feel, but contains enough clay to form a firm ball and
may ribbon from 0.75 to 1.0 inch in length.
Clay Loam: Clay loam is sticky
when moist. Clay loam forms a thin ribbon from 1.0 to 2.0 inches in length
and produces a slight sheen when rubbed with the thumbnail. Clay loam produces
a non-distinct fingerprint.
Sandy clay: Sandy clay will
ribbon more than 2.0 inches in length and will feel very gritty.
Soil Class IV
Fine textured soils which generally contail more than 40% clay-sized particles.
Class IV includes silty clay and clay textures!
Silty clay: Silty clay will
ribbon more than 2.0 inches in length and feels very smooth.
Clay: Clay will ribbon more
than 2.0 inches and will feel neither gritty or smooth.
Presence of Gravel If the
soil has greater than 30% gravel by volume, it is not considered a suitable
soil material for a standard drainfield.
National Resource Conservation Service
(NRCS) Soil Surveys for many Texas Counties can be obtained through the
local NRCS office. The Soil Survey maps provide soil evaluations for all
mapped areas and are useful for describing the general area, but the maps
are not precise enough to "replace" a site-specific field test.
Texas Natural Resource Conservation
PO Box 13087 Austin, Texas
78711-3087 (512) 239-0010
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1997-1998, D. Fehler All rights reserved.