Soil and Site Evaluation

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Soil and Site Evaluation

• Part 2
• The Soil
• or
• Getting the dirt on soil

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AcknowledgementThis work was supported in
part by the National Decentralized Water
Resources Capacity Development Project with
funding provided by the U.S. Environmental
Protection Agency through a Cooperative Agreement
(EPA No. CR827881-01-0) with Washington
University in St. Louis.  The results have not
been reviewed by EPA or Washington University in
St. Louis. The views expressed in this
presentation are solely those of NCSU, and
University of Arkansas and EPA and Washington
University in St. Louis do not endorse any
products or commercial services mentioned in the
presentation.
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What are 4 things we cannot live without?
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SOIL
AIR
WATER
SUNLIGHT
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SOIL
AIR
WATER
SUNLIGHT
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Does Soil Dirt?
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Dirt is the stuff under your fingernails or what
you sweep off the floor

• NO

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Soil Facts

• Soil is the largest single wastewater treatment
  unit in the US
• 25 of the US relies on soil to treat and
  disperse wastewater
• Soil is extremely effective at wastewater
  treatment
• Best of all

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Soil makes great mud pies
and is just plain fun!
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What is a soil?

• And why do we care?

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A soil is a porous natural body of mineral, air,
water and organic matter that changes, or has
changed, in response to climate, topography,
time, and organisms.
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Soil Definition

• Soil means the naturally occurring body of
  porous mineral and organic materials on the land
  surface.
• The upper limit of the soil is the land surface,
  and its lower limit is rock.

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What is a soil?

• And why do we care?

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Importance of Soil to On-site Wastewater

• Biological treatment
• Chemical treatment
• Physical treatment
• Dispersal

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How does soil treat wastewater?
Well
Aerobic soil
Groundwater
Aerobic soil is need to treat remove pathogens
and disperse the treated wastewater back into
the environment
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What are aerobic soil conditions?

• Pores filled primarily with air (oxygen)
• Aerobic organisms present
• Pores are open not smeared
• Air can move through pores not compacted
• Soil is NOT saturated or likely to become
  saturated

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What is soil made of?

• Soil is composed of
• minerals,
• organic matter,
• air,
• water

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How do you start describing the soil?

• What do you see?
• Can you make measurements?
• What is important?
• Describe/interpret from the bottom

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The Goal of Soil Description

• Determine if the soil can adequately treat the
  wastewater
• Determine if the soil can adequately disperse the
  wastewater

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Accomplishing the Goals

• Describe the soil
• Profile description
• Wetness conditions
• Restrictive horizons
• Assess suitability
• Aerobic conditions
• Internal vs. external drainage
• Use to assist in evaluating the site

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Main Components of a Soil Descriptions

• Horizon
• Depth
• Texture

• Structure
• Consistence
• Color

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Soil Profile Description and Horizons
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• Ap 10YR 4/3, SL, 2mGr, fr, ss,sp
• Bt1 7.5YR 5/8, SCL, 2mSBK, fr, ss, sp
• Bt2 7.5YR 5/6, C, 1mSBK, fr, ss, sp
• Bt3 7.5YR 5/4, C, 1mSBK, fr, ss, sp
• BC 7.5YR 5/4, 10 10YR 5/3 depletions, SCL,
  1mSBK, fr, ss, sp
• C 10YR 4/2, SL, 1mSBK, fr, ss, sp

Ap
Bt1
Bt2
Bt3
BC
C
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Soil Profile Descriptions

• Soil Horizon - A layer of soil, approximately
  parallel to the surface, having distinct
  characteristics produced by soil forming
  processes.
• Soil Profile - A vertical section of the soil
  extending through all its horizons and into the
  parent material.

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Top Soil
Subsoil
Parent Material
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A Horizon
B Horizon
C Horizon
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A Horizon
Bt1 Horizon
Bt2 Horizon
Bt3 Horizon
BC Horizon
C Horizon
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Letters of concern

• d Dense, impermeable
• g Gley grey and wet, really wet
• x Brittle, dense, impermeable
• m Cemented
• f Frozen (permafrost)
• r almost rock difficult to dig with backhoe
• R - Bedrock

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Soil Texture
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Soil Texture

• Mineral material only
• Material gt 2mm are coarse fragments
• Material lt 2mm only
• Sand - 2.0 - 0.05 mm
• Silt - 0.05 - 0.002 mm
• Clay - lt 0.002 mm

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Soil Texture

• Sand - gritty
• Silt - smooth, velvety
• Clay - slick, sticky

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Textural Triangle
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Sand vs Clay

• Sand
• Large pores
• Water moves fast
• Low surface area
• Less treatment capacity

• Clay
• Small pores
• Water moves slow
• High surface area
• More treatment capacity

• Onsite systems need to balance water movement
  with wastewater treatment

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Surface area vs particle size
Surface area 24 Volume 1 Size 1/4
Surface area 6 Volume 1 Size 1
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Soil Texture

• Texture relates to pore size
• Pore size relates to treatment
• Pore size relates to water movement
• Both treatment and water movement need to be
  maintained
• Properties related to texture can be changed due
  to installation
• Compaction
• Smearing

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Textural Groups for OSWW

• Group I
• Sand, Loamy sand
• 1.2 0.8 gpd/ft2
• Group II
• Sandy loam, Loam
• 0.8 0.6 gpd/ft2

• Group III
• Sandy clay loam, Silt loam, Clay loam, Silty clay
  loam, Silt
• 0.6 0.3 gpd/ft2
• Group IV
• Sandy clay, Silty clay, Clay
• 0.4 0.1 gpd/ft2

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Soil Structure
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Soil Structure

• Structure is the naturally occurring arrangement
  of soil particles into aggregates (peds) that
  result from pedogenic processes.

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Natural Soil Structural Units
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Structureless

• Single Grain non-coherent
• Massive - coherent
• Massive - Rock Controlled Fabric

Rock Controlled Fabric
Massive
Single-grained
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GRANULAR
SUB-ANGULAR BLOCKY
Example of structure variability in the soil
PRISMATIC and ANGULAR BLOCKY
ANGULAR BLOCKY
SUB-ANGULAR BLOCKY
MASSIVE
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Texture vs Structure

• Texture micropores
• Fine texture
• Small pores
• High porosity
• Good treatment
• Coarse texture
• Large pores
• Low porosity
• Poor treatment

• Structure macropores
• Fine Structure
• High porosity
• Good treatment
• Coarse Structure
• Low porosity
• Poor treatment
• Strong structure
• High porosity
• Good treatment
• Weak structure
• Low porosity
• Poor treatment

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Soil Abuse

• Smearing
• Reduces porosity
• Textural
• Structural
• Occurs as a thin zone (lt1/8 thick)
• Caused by bucket or blade pressure
• May occur when soil is wet or dry
• Can be repaired

• Compaction
• Reduces porosity
• Textural
• Structural
• Occurs over large area or thickness
• Caused by traffic, compression, or storage of
  heavy materials
• More likely to occur when soil is wet
• Difficult to repair

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Smearing
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Compaction
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Can texture be altered during installation?

• NO

Can properties related to texture be damaged due
to installation practices?
YES by smearing and compaction
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Can structure be altered during installation?

• YES!

Can properties related to structure be damaged
due to installation practices?
YES by smearing and compaction
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Soil Consistence

• Will the soil shrink and swell too much?

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Moist Consistence

• A measure of the strength of the soil to
  withstand an applied stress

or
Can you break a ped between your fingers?
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Moist Consistence
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Wet Consistence

• Wet consistence measures the stickiness or
  plasticity of wet soil material.
• Stickiness - The capacity of soil to adhere to
  other objects.
• Plasticity - The degree to which soil can be
  molded without crumbling.

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Stickiness

• The capacity of soil to adhere to other objects
• Estimated at moisture content that displays
  maximum adherence between thumb and fore finger

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Non-Sticky
GOOD
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Moderately Sticky
OK but not Great
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Very Sticky
UNSUITABLE
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Plasticity

• The capacity of soil to be molded
• Estimated at moisture content that displays
  maximum moldability

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Moderately Plastic
OK but not Great
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Very Plastic
2 mm diameter
4 cm long
UNSUITABLE
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Interpreting Consistence

• Shrink-swell clays will have a consistence of
• Very firm
• or
• Very sticky
• or
• Very plastic

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Can consistence be altered during installation?

• YES and NO

Can properties related to consistence be affected
by installation?
YES by smearing and compaction
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Other problems with shrink-swell clays?

• Move components out of level
• Slow down or prevent water movement
• Cause the soil to saturate and reduce treatment
• Smear easily
• Damage foundations
• Unsuitable or very low LTAR

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Soil Color
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Coloring agents in the soil

• Organic matter darkens the soil.
• Iron (Fe) is the primary coloring agent in the
  subsoil.
• Manganese (Mn) is also common in some soils.

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Why do we care about soil color?

• It is the most obvious and easily determined soil
  characteristic.
• Important characteristics can be inferred from
  soil color.
• Well drained (aerobic) soils have uniform bright
  colors.
• Soils with a seasonal saturation are mottled.
• Wet soil have more gray colors
• Color helps us determine the treatment capacity
  of the soil

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Redox Transformations
Coating of Fe2O3
Remove Fe
Gray Soil
Brown Soil
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Redox features are like MMs

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Munsell Soil Color Chart
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Whats mostimportant?

• Low chroma colors indicates the soil saturates
• Saturated soils reduce treatment of wastewater

Chromas of 2 or less
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Color Patterns

• Matrix color is the dominant color in the soil.
• Mottling is spots or blotches of color in the
  soil that differ from the matrix color.
• Wetness mottles (redoximorphic features) are
  mottles that relate to the aeration or drainage
  of the soil.

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Gray mottle wetness
Obvious
Subtle
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Gray colors over brighter colors still means
wetness
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Gray mottle wetness
Gray, weathered rock ? wetness
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Colors identify wetness
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Color helps identify the water table

• Gray color water table
• Water table saturation
• Poor treatment in saturated soil
• Keep infiltrative surface above water table
• Treatment is ensured by proper separation
  distance

Vertical Separation Distance
Water table
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Summary

• Internal drainage can be related to all soil
  properties, not just texture
• Shrink-swell clays are inferred from consistence
• Color is used to determine soil wetness even when
  the soil is dry
• A profile description is the basis for
  determining a LTAR

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Show someone the soil and theyll be dirty for a
day
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Teach someone about the soil and theyll be happy
for life
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Questions?
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Questions?

• David Lindbo, Associate Professor
• Soil Science Dept.,
• North Carolina State University
• 919-515-2635
• david_lindbo_at_ncsu.edu
• download presentation at
• www.soils.ncsu.edu/lockers/lindbo
• In folder SCDHEC subfolder Dec 2008 class