Soil and Site Evaluation

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Soil and Site Evaluation

• Getting the Dirt on Soils

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What is a soil?
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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 Science Society of America

• soil (i) the unconsolidated mineral or organic
  material on the immediate surface of the earth
  that serves as a natural medium for the growth of
  land plants.

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Rule .1935 (41) Soil

• Soil means the naturally occurring body of
  porous mineral and organic materials on the land
  surface. Soil is composed of sand-, silt- and
  clay-sized particles that are mixed with varying
  amounts of larger fragments and some organic
  material. Soil contains less than 50 of its
  volume as rock, saprolite, or coarse-earth
  fraction (mineral particle greater than 2 mm).
  The upper limit of the soil is the land surface,
  and its lower limit is rock, saprolite, or
  other parent materials.

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Importance of Soil to On-site Wastewater

• Biological treatment
• Chemical treatment
• Physical treatment
• Disposal

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Aerobic zone
Well
Aerobic soil
Groundwater
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What is soil made of?
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Soil is made of

• Solid material
• Minerals
• Dead organic material
• Living organic material
• Pore space
• Air
• Water

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How does a soil form?
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Factors of formation (after Hans Jenny, 1942)

• Parent Material
• Topography
• Vegetation/Biology
• Climate
• Time
• (Anthropogenic)

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Parent Material
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Parent Material

• Transported materials
• Bedrock or residual material
• Organic materials

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Marine

• Deposited in a marine environment
• Variable texture dependent on energy of
  depositional environment
• Low energy fine textured
• High energy coarse textured

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95 cm
120 cm
Sand Layer
100 cm
Absent
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Fluvial

• Sediments deposited in rivers or floodplains
• Texture coarsest near active channel

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Aerial View
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Sometimes even a blind squirrel can find a nut
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Colluvium

• Parent material deposited by earth movement
• Land slides-catastrophic, large scale
• Slump or creep-gradual, small scale
• Slope related

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Colluvial soils may show evidence of multiple
deposits
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Bedrock or Residual Material

• Properties related to mineral present in parent
  rock and weathering
• Clay mineralogy
• Inherent fertility
• Particle size variable

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• Residual Soil
• Intrusive rock
• High clay content
• Weathers to kaolinitic clay minerals

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Color may be inherited from the parent material
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Multiple Parent Materials
Aeolian
Fluvial/Alluvial
Glacial Till
Residual
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How does understanding parent material help
understand the soils?
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Clay Layer

• Thin clay layer deposit in a single flood event,
  a marsh, or in a lake bottom
• Based on the geomorphology of the area such
  layers are common and should be expected
• If ignored, the layer may act as a bowl beneath
  the septic system causing effluent to back up

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Topography
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Summit
Shoulder
Side or back slope
Foot slope
Toe slope
Drainage way
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LL
LC
CC
CL
CL
LL
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Soils on slope
Down Slope
Up Slope
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Well drained at summit
Poorly drained in low area
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Others

• Vegetation/Biology
• Climate
• Time
• Anthropogenic

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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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How do you start describing the soil?

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

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Making Soil Descriptions

• Horizon
• Depth
• Color
• Texture
• Features

• Consistence
• Structure
• Pores
• Roots
• Reaction

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Soil Color
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Coloring agents in the soil

• Organic matter darkens the soil. Organic matter
  will mask all other coloring agents.
• Iron (Fe) is the primary coloring agent in the
  subsoil. The orange brown colors associated with
  well drained soils are the result of Fe oxide
  stains coating individual particles.
• Manganese (Mn) is common in some soils resulting
  in a very dark black or purplish black color.

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Ap Horizon
Dr. Martin Rabenhorst
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Ap Horizon
-OM
Dr. Martin Rabenhorst
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Ap Horizon
-Fe
Dr. Martin Rabenhorst
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Ap Horizon
-OMFe
Dr. Martin Rabenhorst
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Ap Horizon
-OM
-Fe
-OMFe
Dr. Martin Rabenhorst
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Bt Horizon
Dr. Martin Rabenhorst
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Bt Horizon
-OM
Dr. Martin Rabenhorst
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Bt Horizon
-Fe
Dr. Martin Rabenhorst
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Bt Horizon
-OMFe
Dr. Martin Rabenhorst
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Bt Horizon
-OM
-Fe
-OMFe
Dr. Martin Rabenhorst
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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.
• Redoximorphic features are mottles that relate to
  the aeration or drainage of the soil.

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Munsell Color System

• Hue refers to the dominant wavelength of light
  (red, yellow, green, etc.).
• Value refers to the lightness and darkness of a
  color in relation to a neutral gray scale.
• Chroma is the relative purity or strength of the
  Hue.
• Notation
• Hue Value/Chroma
• 10YR 5/6

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Hue in the Munsell Soil Color Chart
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Much light reflected
Little light reflected
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Chroma in the Munsell Soil Color Chart
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Common Names and Notations givenon left-hand
side of open book
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Percent

• lt2 - few
• 2-20 - common
• gt20 - many

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Each 1/4th of any one square has the same amount
of black
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Recording Soil Colors

• Soil should be moist...This is the most common
  way soil colors are recorded.
• Always use sunlight. Do not use artificial
  light. Do not wear sunglasses or tinted glasses.
• Always use a freshly exposed face or ped. Do not
  crush or rub the soil before getting a color.
• Determine the matrix and all subordinate colors
  (mottles).

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Soil Texture
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Soil Texture

• Use texture to make inferences into pore size
• From pore size begin to estimate water movement
  and treatment
• Texture by itself is not enough information to
  determine site suitability

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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 (mineral material only)

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

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USDA Textural Classes (12)

• Sand
• Loamy Sand
• Sandy Loam
• Loam
• Silt Loam
• Silt

• Sandy Clay Loam
• Silty Clay Loam
• Clay Loam
• Sandy Clay
• Silty Clay
• Clay

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Determination of Texture

• Laboratory procedure
• Hydrometer
• Pipette
• Field procedure

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Sand Silt Clay 100
40 Sand
40 Silt
20 Clay
Texture LOAM
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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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Introduction to Soil Structure

• What is soil structure and
• Why do we care?

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Structure relates to

• Water Movement
• Aeration
• Water Retention
• Root Penetration

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Soil Structure(based on Field Book for
Describing and Sampling Soils)

• Structure is the naturally occurring arrangement
  of soil particles into aggregates (peds) that
  result from pedogenic processes.
• Three general groups
• Natural Soil Structural Units (pedogenic
  structure)
• Structureless
• Artificial Earthy Fragments or Clods

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Soil Structure

• Type
• Size
• Grade

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Natural Soil Structural Units
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Structureless

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

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Single Grain No structural units entirely
noncoherent e.g. loose sand
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Massive No structural units material is a
coherent mass (not necessarily cemented)
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Massive Rock Controlled Fabric No structural
units material is a coherent mass with the
original rock fabric is still identifiable
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Influence of structure on soil management
decisions

• Water Movement
• Gas Movement
• Adjusting LTAR

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• Texture Plays a Major Role with Micropores.
• Structure Plays a Major Role with Macropores.

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Consistence

• Rupture Resistance
• Stickiness
• Plasticity
• Manner of Failure
• Penetration Resistance

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Rupture Resistance

• A measure of the strength of the soil to
  withstand an applied stress
• Separate classes are made for
• Blocks, peds, and clods
• Surface crusts and plates
• Moisture content is also considered
• Dry
• Moist (field capacity)
• Cementation classes obtained by submergence of
  overnight air-dried samples for at lease 1 hour
  before test

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Rupture Resistance Classes Blocks, Peds, and
Clods
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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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Stickiness Classes

• Non-Sticky little or no soil adheres to fingers
  after release of pressure
• Slightly Sticky soil adheres to both fingers
  after release of pressure with little stretching
  on separation of fingers
• Moderately Sticky soil adheres to both fingers
  after release of pressure with some stretching on
  separation of fingers
• Very Sticky - soil adheres firmly to both fingers
  after release of pressure with stretches greatly
  on separation of fingers

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Non-Sticky
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Very Sticky
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Plasticity

• The degree to which puddled or reworked soil can
  be permanently deformed without rupturing
• Evaluation done by forming a 4 cm long wire of
  soil at a water content where maximum plasticity
  is expressed

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Plasticity Class

• Non-Plastic will not form a 6 mm dia, 4 cm long
  wire, or if formed , can not support itself if
  held on end
• Slightly Plastic 6 mm dia, 4 cm long wire wire
  supports itself, 4 mm dia, 4 cm long wire wire
  does not
• Moderately Plastic 4 mm dia, 4 cm long wire
  wire supports itself, 2 mm dia, 4 cm long wire
  wire does not
• Very Plastic 2 mm dia, 4 cm long wire wire
  supports itself

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Very Plastic
2 mm diameter
4 cm long
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Soil Profile Description and Horizons
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Soil Profile Descriptions

• Soil Profile - A vertical section of the soil
  extending through all its horizons and into the
  parent material.
• Soil Horizon - A layer of soil, approximately
  parallel to the surface, having distinct
  characteristics produced by soil forming
  processes.
• Soil Layer - A layer in the soil deposited by a
  geologic force (wind, water, glaciers, oceans,
  etc.) and not relating to soil forming process.

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Soil Horizon Nomenclature

• Soil horizons designated by a combination of
  CAPITAL LETTERS-lower case letters-ARABIC
  NUMERALS
• Master Horizons and Layer Major breaks in the
  soil O, A, E, B, C, and R.
• Subordinate Distinctions Lower case letters
  used as suffixes to designate specific master
  horizons. i.e. Ap, Bw, Cg
• Vertical Subdivisions A horizon designated by a
  single combination of letters which needs to be
  subdivided. i.e. Bw1, Bw2, Cg1, Cg2.

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Organic (O) Horizons

• O horizons or layers Layers dominated by
  organic material.
• Field Criteria
• 20-30 organic matter
• Dark color (never used by itself)
• Low strength, light dry weight, high fiber
  content
• Typically a surface horizon-if buried may
  indicate disturbance
• Subordinate Distinctions of O Horizon
• Oa-Highly decomposed organic material (Muck)
• Oe-Moderately decomposed organic material (Mucky
  Peat)
• Oi-Slightly decomposed organic material (Peat)

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A Horizons

• Referred to as topsoil and typically ranging from
  6-30 centimeters thick. Mineral horizon formed
  at the surface or below an O horizon.
  Characterized by an accumulation of humified
  organic matter intimately mixed with the mineral
  fraction.
• Field Criteria
• Mineral soil material
• Mix of well decomposed organic matter and mineral
  material
• Surface mineral horizon
• Typically dark in color-darker than underlying
  horizons
• Typical Subordinate Distinctions of A Horizon
• Ap-Plowing or other disturbance

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A Horizon
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Ap Horizon
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E Horizons

• Mineral horizon in the upper part of the soil
  typically underlying an O or A horizon. Light
  colored, leached horizons ranging from not being
  present to several centimeters thick
• Field Criteria
• Zone of eluviation - removal of clays, Fe, Al,
  and humus
• Lighter in color than over or underlying horizon
• Near surface, below O or A horizons and above a B
  horizon
• Formed by weak organic acids that strip coatings
  from sand grains. Light color due to the natural
  color of the mineral grains.

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E Horizon
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E Horizon
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A vs E horizon

• A horizons have a high OM content
• E horizons have low OM content
• E horizons often feel sandier (coarser) than the
  A horizon
• E horizons have a higher value and chroma

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E vs B horizon

• E horizons are sandier (coarser) than B horizons
• E horizons are higher in value and chroma
• B horizons have more clay
• B horizons have more Fe

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B Horizons

• Referred to as subsoil. the zone of accumulation
  with in the soil. In well drained soils it has
  the brightest colors. May extend over a meter
  below the surface.

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B Horizons - Field Criteria

• Subsurface horizon formed below an O, A, E
  horizon and above the C horizon
• Formed as a result of soil forming processes
• Weakest expression is color development
• Illuvial concentration-zone of accumulation

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B Horizons - Subordinate Distinctions

• Bg-Strong gleying, indicates prolonged periods of
  saturation
• Bs-Illuvial accumulation of sesquioxides (spodic)
• Bh-Illuvial accumulation of humus (spodic)
• Bt-Accumulation of clay

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Bt Horizon
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Bg Horizon
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Bs Horizon
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C Horizon

• Referred to as substratum. These horizons and
  layers are little affected by soil forming
  processes (unweathered geologic material).
• Field Criteria
• Little affected by soil-forming processes
• Geologic layering
• Lack of color development, color of unweathered
  geologic material
• Subordinate Distinctions of C Horizons
• Cg-Strong gleying, indicates prolonged periods of
  saturation

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Transitional and Mixed Horizons

• Transitional horizons
• Combine master horizon designations
• i.e. AE is an horizon that is more A than E but
  has characteristics of both, an EA is more E than
  A
• Mixed horizons
• Combine master horizons with a slash (/)
• i.e. A/E is an horizon with E material mixed into
  dominantly A material

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NRCS County Soil Survey

• An invaluable resource for landuse planning and
  land management

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Map of soil systems in state
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All soils have names and each soil has a story to
tell.
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What does the soil have to say?

• Agriculture
• Fertility
• Crop Yields
• Erosion
• Forest Productivity
• Land Use
• Roads
• Recreation
• Wildlife
• Residential Development
• Basements
• Septic Systems

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County Soil Survey
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Air photo, used to start the survey
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Need to ground truth and get the correct level of
detail
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Information from a Soil Survey

• Maps
• General
• Specific
• Map Unit Description (MUD)
• Taxonomic Unit Description (TUD)
• Growing Season Tables
• Land Use Tables

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General Soil Map for County
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Soil Map
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A Cautionary Note

• Soil Surveys are accurate to approximately 5
  acres
• Each map unit contains inclusions
• Always determine associated series to better
  understand soil/site relations
• Note Soil survey data is useful for initial
  planning, but field evaluation is necessary for
  proper site and soil evaluation

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Soil Legend
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Map Unit Description (MUD)
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Taxonomic Unit Description (TUD)
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Land Use Tables
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