Organic Material Soil Enrichment:
Providing hydraulic functionality in situ for challenging sites
Curt Kerns, M.S., P.Biol., C.F.S.
© 2011 WetlandsPacific Corp.
Definitions
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Isotropic water movement = all directions
Anisotropic water movement = only in one direction
typically downwards
Soil amendment: The addition of organic material +
nutrients to promote plant growth
Soil enrichment: The addition of organic materials high
in carbon but low in nutrients particularly nitrogen in
order to promote isotropic water movement in soils and
to remove nitrogen
Definitions
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Soil infiltration is governed by two forces: gravity and
capillary action. While smaller pores offer greater
resistance to gravity, very small pores pull water through
capillary action in addition to and even against the force
of gravity.
Source: http://en.wikipedia.org/wiki/Infiltration_(hydrology)
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Capillary pressure comes from surface tension, curvature
and contact angle
Darcy’s Law: provides an accurate description of the flow
of ground water in almost all hydrogeologic environments
Source: http://hydrology.rice.edu/envi518/Handouts/darcy.ppt#271,9,Conditions
Definitions
Darcy’s Law holds for:
1.
2.
3.
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5.
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Saturated flow and unsaturated flow
Steady-state and transient flow
Flow in aquifers and aquitards
Flow in homogeneous and heterogeneous systems
Flow in isotropic or anisotropic media
Flow in rocks and granular media
Source: http://hydrology.rice.edu/envi518/Handouts/darcy.ppt#271,9,Conditions
The origin of top soils are from rock that weathers into
dust plus humus which comes from decayed plants
Definitions
Capillary action: In hydrology, capillary action describes the
attraction of water molecules to soil particles. Capillary
action is responsible for moving groundwater from wet
areas of the soil to dry areas. Differences in soil matric
potential (Ψm) drive capillary action in soil
Source: http://en.wikipedia.org/wiki/Capillary_action#Phenomena_and_physics_of_capillary_action
Matric Potential: A component of water potential due to
the adhesion of water molecules to nondissolved structures
of the system, i.e. the matrix, such as soil particles. It is
always negative and is significant only outside living cells in
relatively dry systems, for example soils, where much of the
water is tightly bound to soil particles
Source: A Dictionary of Biology. 2004. Encyclopedia.com. 21 Jan. 2011 , http://www.encyclopedia.com
© 2011 WetlandsPacific Corp.
Direction of Water Movement In Soil
is Determined by Interstitial Pore Sizes
Source: Managing Soil Tilth Texture, Structure and Pore Space CMG GardenNotes #213, Colorado State University
Case 1. Heavy Clay Soils
Dec 2003: During construction, local EHO required use of a sandy material over clay
– not advisable!
Case 1. Heavy Clay Soils
Jan 2004: Roof drain was found to be attached to septic tank
Case 1. Heavy Clay Soils
Jan 2004: Over 2,000 ig-day flowing into system designed for 500 ig-day
Case 1. Heavy Clay Soils
Jan 2004: Disconnected roof drain, & added more sand
Case 1. Heavy Clay Soils
July 2004: VTF functioned as designed until July when effluent began surfacing
Added sand has high clay content as soil shrinkage demonstrates
Case 1. Heavy Clay Soils
July 2004: Solution? As agriculturalists have known for 10,000 years – add organic material
Case 1. Heavy Clay Soils
Aug 2004: System functioning per design thereafter
Case 2. Heavy Marine Clay Soils
Aug 2003: Existing 5 bedroom home with failed field
Case 2. Heavy Marine Clay Soils
Sept 2003: VTF installation complete, EHO required same sandy material as in Case 1
Note clay soils beyond added sandy material
Case 2. Heavy Marine Clay Soils
July 2004: VTF functioned properly until soil dried, sandy material became very
hard causing surfacing of effluent. Solution, add organic material
Case 2. Heavy Marine Clay Soils
Sept 2004: After organic enrichment, effluent no longer surfacing, surrounding soil moist
Case 2. Value of Biological Systems
June 2005: VTF after two years, cattails are now 4.5 m x 4.5 m (15 ft x 15 ft), a 56% increase
in size with concomitant increase in rhizosphere, the most biologically active soil zone
Case 2. Heavy Marine Clay Soils
Oct 2007: VTF now 7 m x 7 m (24 ft x 24 ft) a 400% increase in size after 4 summers of
growth
Case 2. Heavy Marine Clay Soils
Sept 2009: VTF constructed wetland is now about 9 m x 9 m (30 ft x 30 ft) over 6 times
larger than original area. Cattails are turning what was clay soil into biologically rich top soil
Case 2. Heavy Marine Clay Soils
Aug 2010: Seven years after VTF installation, surface area is 12 m x 12 m (40 ft x 40 ft)
– over 10-times its original size no longer requiring secondary treatment
Case 3. Shallow, Expanding Clay Soils
May 2004: Organic material being incorporated during construction
Case 3. Shallow, Expanding Clay Soils
May 2004: Interceptor drains being installed
Case 3. Shallow, Expanding Clay Soils
Oct 2004: Five months after construction
Case 3. Shallow, Expanding Clay Soils
Oct 2006: Two years after construction
Case 4. Onsite System Built on a Logging Road
June 2006: Prior to VTF construction. Property is 1400+ ft long x 66 ft wide
House about 33.5 m (110 ft) distant. Property was a logging road for 80 years
Case 4. Onsite System Built on a Logging Road
Sept 2006: Test pit showing two layers of introduced gravel over a silty clay,
weathered, sedimentary rock of increasing density with depth
Case 4. Onsite System Built on a Logging Road
Sept 2006: Existing introduced gravel
Case 4. Onsite System Built on a Logging Road
June 2007: Gravel scraped off prior to adding organic materials
Case 4. Onsite System Built on a Logging Road
Oct 2007: After 150 yd3 added organics & VTF finished
Case 5. Topsoil Removed by Successive Owners
Dec 2009: Water table 0.5 m (18 in) depth
Case 5. Topsoil Removed by Successive Owners
Dec 2009: Prior to construction, drainage feature goes through area
Not a particularly encouraging location for onsite
Case 5. Topsoil Removed by Successive Owners
Dec 2009: After adding 150 yd3, an additional 75 yd3 were required
Organics worked in over entire dispersal area
Case 6. Failed Field, Airdrie, AB
June 2009: Failed field with surfacing effluent
Case 6. Failed Field, Airdrie, AB
June 2009: Jeff Johnson, Alberta’s first VTF installer
Case 6. Failed Field, Airdrie, AB
June 2009: After organic material incorporation, dispersal area 1600 ft2
Case 6. Failed Field, Airdrie, AB
Close up of wood waste
Case 6. Failed Field, Airdrie, AB
June 2010: Note soil shrinkage, more smaller size organics indicated
Case 6. Failed Field, Airdrie, AB
August 2010: Vegetation filling in
Case 7. Failed Field in Heavy Clay Soil
March 2010: Small yard with breakout over entire area,
due in part to perimeter drain ending in field area by tree
Case 7. Failed Field in Heavy Clay Soil
Effluent surfacing in failed field. Field was 30 cm (12 in) of imported sand
Dispersal pipes excavated into clay soil below
Case 7. Failed Field in Heavy Clay Soil
Effluent ran into frontage ditch
Case 7. Failed Field in Heavy Clay Soil
Where children played
Case 7. Failed Field in Heavy Clay Soil
April 2010: Solution - 100 yd3 of organics
Case 7. Failed Field in Heavy Clay Soil
April 2010: VTF being Installed
Note high proportion of organics
Case 7. Failed Field in Heavy Clay Soil
April 2010: Installation complete, vegetation to be planted
Lessons We’ve Learned in the Past 8 Years:
1. Always scarify, never have an abrupt change in soil textures
Source: Managing Soil Tilth Texture, Structure and Pore Space CMG GardenNotes #213, Colorado State University
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Use organics with a wide variety of particle sizes, preferably aged
Difficult to use too much organics, easy to use too little
Soil enrichment based on mass of organics not just volume
Add 30 cm (12 in) to good soil (<10% clay; 60 cm (24 in) to poor soil
(<20% clay); 90+ cm (36 in) to very poor soil (>30%); 120 cm (48 in)
to very, very poor soil (>50%)
6. Is possible to work wet soils but more organics required (≥50%)
7. Organics lower perched water tables
Lessons We’ve Learned in the Past 8 Years:
a. Add organics to sand mounds to promote isotropic (all direction) water
movement as coarse soils typically move water anisotropically (only in one direction)
downwards
b. Add organics to pressure dispersal areas, including under gravel-less chambers to
promote isotropic water movement
c. Add organics to coarse soils to slow water movement in dispersal areas or under
sand mounds
d. Add organics in proportion to clay content
e. Add organics as nitrogen sink to protect ground water
f. Add organics to promote biological soil activity and to eventually produce topsoil
Conclusion: Organic soil amendment buffer strips are now a recognized storm water
infiltration technique and can, and probably should be used throughout onsite
Proof of the Veracity of Organic
Soil Enrichment is in the Results
At the time of the last service call, all 155 VTF
installed over the past 8 years for a total of >500
VTF years (1 VTF installed for 1 year = 1 VTF year) are
functioning per design, despite being in some of the
worst soils imaginable while occupying very small
footprints
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Vegetative Tertiary Filter (VTF)
Lions Bay, BC
This small ocean side property had insufficient
room for an onsite system. The VTF system,
including tanks, was installed into an area of
50 ft (15.24 m) by 10 ft (3.05 m).
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