Transcript Soils, Infiltration, and On

Applications to Stormwater
Management
Presented by:
Mr. Brian Oram, PG, PASEO
Wilkes University
GeoEnvironmental Sciences and
Environmental Engineering
Department
Wilkes - Barre, PA 18766
570-408-4619
http://www.water-research.net
Nearly 50% of Soil is Space or
Space Filled with Water
• Water – 25+ %
• Air – 25 + %
• Pore Space Makes Up
35 to 55 % of the
total Soil Volume
• This Space is called
Pore Space
Therefore, soil can be used as a storage
system, treatment system, and transport
media.
Soil Properties Critical To
Stormwater Management
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Soil Texture
Porosity and Pore Size
Water Holding Capacity
Bulk Density
Aggregate Stability
Infiltration Capacity
Hydraulic Conductivity
!!! Just to Name a Few Properties !!!!
Types of Pores
Macropores (> 1,000 microns)-Large
Mesopores (10 to 1,000 microns)- Medium
Micropores (< 10 microns)- Small
Source: http://www2.ville.montreal.qc.ca
Key Points on Soil Pores
Under gravity, water drains from macropores, where as,
water is retained in mesopores and micropores, via matrix
forces.
Coarse-textured horizons (e.g., sandy loam) tend to have a
greater proportion of macropores than micropores- but they
may not have more macropores than finer textured soils.
Soils with water stable aggregates tend to have a
higher percentage of macropores than micropores.
Proportion of micropores tends to increase with soil depth,
resulting in greater retention of water and slower flow of
water with depth.
Water Holding Capacity
Available Water Capacity
Textural Class
(Inches/Foot of Depth)
Coarse sand
0.25–0.75
Fine sand
0.75–1.00
Loamy sand
1.10–1.20
Sandy loam
1.25–1.40
Fine sandy loam
1.50–2.00
Silt loam
2.00–2.50
Silty clay loam
1.80–2.00
Silty clay
1.50–1.70
Clay
1.20–1.50
Please Do Not Use Sand in a Bio-Retention System !
Bulk Density, Porosity, and Texture
Textural Class
Bulk Density (Mg/m³)
Porosity
(%)
Sand
1.55
42
Sandy loam
1.4
48
Fine sandy loam
1.3
51
Loam
1.2
55
Silt loam
1.15
56
Clay loam
1.1
59
Clay
1.05
60
Aggregated clay
1
62
Sands – Tend to have higher bulk density and lower permeability
Please do not use sands in Bio-Retention systems!
How can a
silt loam have
more
macropores
than sand?
Source:
Brady, Nyle,
C. “ The
Nature and
Properties of
Soils” (1990).
Answer: More Water Stable Structures
Better
Structural
Development
More
Macropores
Source: Brady,
Nyle, C. “ The
Nature and
Properties of
Soils” (1990).
Water Stable Aggregates I
Aggregates on left are
more water stable, i.e.,
aggregate stays
together and do not
separate into the its
components, i.e., three
soil separates.
Water Stable Aggregates
Water Stable Aggregates – II
The Classic Photo
Source: Brady, Nyle, C. “ The Nature and Properties of Soils” (1990)
Great Desk Reference Text !!!!
Permeability
Class
Impermeable
Very Slow
Very Slow to
Moderately
Slow
Moderately
Slow to
Moderate
Moderate to
Rapid
Rapid
Inches
per hour
Material
Very Low
<0.001417
Massive, Rock,
Fragipan
Low
0.001417
to
<0.0147
Massive, Rock,
Fragipan,
clayey
Moderately
Low
0.01417
to
<0.1417
clay, silty clay,
clay loams
Moderately
High
0.1417
to
< 1.417
silt, silt loam,
loam, fine
sandy loam
High
1.417 to
< 14.17
loamy sand to
medium sand
> 14.17
coarse sand,
gravel
Ksat Class
Very High
General Guide – To Ksat and Material
Hydrologic Soil Terms
•Infiltration - The downward entry of water into the immediate
surface of soil or other materials.
•Infiltration Flux (or Rate)- The volume of water that penetrates the
surface of the soil and expressed in cm/hr, mm/hr, or inches/hr. The rate
of infiltration is limited by the capacity of the soil and rate at which
water is applied to the surface. It is a volume flux of water flowing
into the profile per unit of soil surface area (expressed as velocity).
•Infiltration Capacity (fc)- The amount of water per unit area of time
that water can enter a soil under a given set of conditions at steady state.
•Cumulative infiltration: Total volume of water infiltrated per unit area
of soil surface during a specified time period.
Horton Equation, Philip Equation, Green- Ampt Equation
Infiltration Rate
Infiltration Rate (Time Dependent)
Steady Gravity
Induced Rate
Infiltration with Time Initially
High Because of a Combination of
Capillary and Gravity Forces
f = fc +(fo-fc) e^-kt
fc does not equal K
Final Infiltration Capacity
(Equilibrium)- Infiltration
Approaches q - Flux Density
Infiltration Rate
Decreases with Time
1) Changes in Surface and
Subsurface Conditions
2) Change in Matrix
Potential and Increase in Soil
Water Content and Decrease
in Hydraulic Gradient
3) Overtime - Matrix
Potential Decreases and
4) Reaches a steady-state condition
Gravity Forces
fc – final infiltration rate
Dominate - Causing a
Reduction in the Infiltration
Rate
Infiltration Rate
Function of Slope & Texture
Source: Rainbird Corporation, derived from USDA Data (Oram,2004)
Infiltration Rate
Function of Vegetation
Source: Gray, D., “Principles of Hydrology”, 1973.
Infiltration Rate
Function of Horizon A, B, Btx, Bt, C, R
C/R Testing - Areas Fractured Rock
Source: On-site Infiltration Testing - Mr. Brian Oram, PG (2003) and
FX. Browne, Inc. (Lansdale, PA)
Infiltration
(Compaction/ Moisture Level)
Site Compaction – Can Significantly Reduce Surface Infiltration Rate
Rain Drop Impact Bare Soil
Destroys Soil Aggregates
Disperses Soil Separates
Seals Pore Space
Aids in Loss of Organic Material
Creates a Surface Crust
Source: (D. PAYNE, unpublished)
http://www.geographie.uni-muenchen.de
Percolation Rate
Percolation Rate
Percolation -Downward Movement of Water
through the soil by gravity. (minutes per inch) at a
hydraulic gradient of 1 or less.
Used and Developed for Sizing Small Flow On-lot
Wastewater Disposal Systems.
On-lot Disposal Regulations (Act 537) has preliminary
Loading equations, but for large systems regulations
typically require permeability testing.
Also none as the Perc Test, Soak-Away Test (UK)
Not Directly Correlated to
or a Component of Unsaturated or
Saturated Flow Equations
Comparison Infiltration to Percolation Testing
4.5
4
Infiltraton Test
Rate (in/hr)
3.5
3
Percolation
Testing Over
Estimated
Infiltration
Rate by 40% to
over 1000% *
Percolation Test
2.5
2
1.5
1
0.5
0
1
2
3
4
5
6
Trail
7
8
9
10
Source: On-site Soils Testing Data, (Oram, B., 2003)
Hydraulic Conductivity
Darcys Law- Saturated Flow
Vertical or Horizontal
Volume of discharge rate Q is proportional to the head
difference dH and to the cross-sectional area A of the column,
but it is inversely proportional to the distance dL of the flow path and
coefficient K is called the hydraulic conductivity of the soil.
The average flux can be obtained by dividing Q with A.
This flux is often called Darcy flux qw .
Flux Density or Hydraulic
Conductivity (Ksp)
Flux Density (q): The volume of water
passing through the soil per unit crosssectional area per unit of time.
It has units of length per unit time such as mm/sec,
mm/hour, or inches/ day (q = -K(ΔH/L ))
Actually the term is volume/area/time= q = Q/At
Hydraulic Conductivity (Ksp) quantitative measure
of a saturated soil's ability to transmit water
when subjected to a hydraulic gradient. It can be
thought of as the ease with which pores of a
saturated soil permit water movement .
Side by Side (Pagoda, J, 2004)
Testing Methods
Goals of the Field Method
• Field Measurement of the Flux Density
(qw) and calculate hydraulic conductivity –
qw = Ksp (dh/dl)
• Field Measurement of Hydraulic
Conductivity (Ksp)
Infiltrometer
Single Rings Infiltrometers
Cylinder - 30 cm in Diameter- Smaller Rings Available.
Drive 5 cm or more into Soil Surface or Horizon.
Water is Ponded Above the Surface- Typically < 6 inches.
Record Volume of Water Added with Time to Maintain a
Constant Head.
Measures a Combination of Horizontal and Vertical Flow
ASTM Double Rings Infiltrometers
Outer Rings are 6 to 24 inches in Diameter (ASTM - 12 to 24 inches)
Mariotte Bottles Can be Used to Maintain Constant Head
Rings Driven - 5 cm to 6 inches in the Soil and if necessary sealed
Very Difficult to Install and Seal – ASTM Double Rings in NEPA
Potential Leaking Areas
Significant Effort is Needed to Install and Seal Units
ASTM requires documentation of the
Depth of the Wetting Front
Other Double Rings Small Diameter
6” and 12” Double Ring
3” and 5” Double Ring
in Flooded Pit
Infiltration Data- Double Ring Test
Note: Ring Diameter – 26 cm (Oram 2005)
Infiltration Rate –cm/hr
Cumulative Infiltration
(cm)
Steady-State Rate (slope)
0.403 cm/hr
Fc = Ultimate Infiltration
Capacity (approx.0.47 cm/hr)
Estimated Methods- Based
on Grain Size
C- Factor
Hazen Method
Applicability: sandy
sediments
• K = Cd10 2
• d10 is the grain diameter
for which 10% of
distribution is finer,
"effective grain size" where D10 is between 0.1
and 0.3 cm
• C is a factor that
depends on grain size
and sorting
Very Fine
Sand, poorly
Sorted
40 - 80
Fine Sand with
fines
40 - 80
Medium Sand,
Well Sorted
80 - 120
Coarse Sand,
Poorly Sorted
80 - 120
Coarse sand,
well
Sorted, clean
120 - 150
Guelph and Amoozegar
Borehole Permeameters
$ 1500
each
Field Testing (Oram, 2000)
Photo Source:http://www.usyd.edu.au
Measuring Hydraulic Conductivity
12-inch/ 6-inch Double Ring
Constant or Falling Head Permeameter- Homemade - $ 15.00
Side by Side Testing Mr. Brian Oram and Mr. Chris Watkins, 2003.
Constant Head
Borehole Permeameters
Talsma PermeameterCould be Homemade
$ 50.00
Retail ($ 300.00)
Modified AmoozegarCould be Homemade –
$30.00- Retail ($ 200.00)
Side by Side Testing by Mr. Brian Oram and Mr. John Pagoda, 2004
Measuring Infiltration Rate
to Estimate / Calculate the Flux Density
• Infiltrometers- Yes !
– Single ring- May Not Be Advisable – Multiple tests required
– Double ring- Yes ! - May be difficult in rocky and stony areas
(i.e., Most of the Poconos !)
– Smaller Double Ring in Flood Pit – Yes !
• Flooded Infiltrometers – Yes !
• Adoption of a Strict Double Ring ASTM Method – Likely not
appropriate, but method should be used as a guide by professionals.
• Cased Borehole Permeability Test – ASTM Method– Yes !
(Minimum diameter casing 4 inches) with bentonite packing of annular
space – Maximum Pipe Height is a function of soil conditions.
My Recommendation and Opinion !
Please Do NOT Use a
Conventional Percolation Rate or
Percolation Test for Developing
Engineering Design !
Percolation Testing
• Does not directly measure permeability or a flux velocity.
• Has been used to successfully design small flow on-lot wastewater
disposal systems, but equations and designs have a number of safe
factors.
• Results may need to be adjusted to take out an estimate of the
amount of horizontal intake area.
• Without Correction Percolation Data over-estimated infiltration
rate data by 40 to over 1000 % with an adjustment for intake area
error could be reduced to 10 to 200% (Oram, 2003) , but
infiltration rate can overestimate saturated permeability by a
factor of 10 or more (Oram, 2005).
• May need to consider the use of larger safety factors and equations
similar to sizing equations used for on-lot disposal systems. Safety
factors of 50% reduction may not be enough !!
• Borehole Permeability Testing can be a Suitable
Method.
S
U
M
M
A
R
Y
• Falling Head , Constant Head, and Quasi Constant
Head Methods would be suitable.
• Permeability Data for Specific Site should be calculated
using Geometric Average.
• Equations and Methods Based on Darcy’s Law and the
result is a value for Ksp or qw.
• Do not recommend estimating permeability based on
particle size distribution – Ok for preliminary desktop
evaluations if data is available – Not for Final Design !
• Laboratory permeability testing is possible, but it may
be difficult to get a representative sample and account
for induced changes. May be Ok for Preliminary
Evaluations.
What NOW ?
The Hydrologic Cycle
Discharge Zone
Recharge Zone
Where is the Project Site ?
Save Your Client – Money
None Structural Development Practices
• Maintain Soil Quality and Maximize the Use of
Current Grading to Minimize Loss of O, A, and
upper B horizons.
• Minimize Compaction, Maximize Native
Vegetation, and Use Good Construction Practices
• Consider Hydrological Setting and Existing
Hydrological Features in Site Design and Layout
Answer: New Development/ Construction Practices and
New and Updated Ordinances and Planning Documents !
Infiltration System Approach
Individual Infiltration BMP Units
Soil: Tunkhannock Series
Soil had stratified sand
and gravel lenses
Water Table > 8 feet
Open Voids
(Gravel and Cobbles)
3 to 6 feet
Ksp Field Measured
1 to 10+ inches per hour
Reported Permeability
> 6 inches per hour
Design Used a Ksp of 0.5 inch per hour (50% reduction)
Note- A few sections of the site had permeability of 0.1 inch per hour
Infiltration Unit Configuration
Installed:
Sump and Grass Swale Prior to Unit
and Geotextile within unit to capture large organic material
Concrete – Open bottom perforated tank not filled with
gravel for storage.
Conceptual Design by:
Malcolm Pirnie (Scranton, PA) and Brian Oram
(October 2004), Anticipated Installation 2007.
Sizing Calculations- Areas 0.5 in/hr
• Impervious Area Roof and Driveway– 3500 ft2
• Design Storm – 1.3 inch
• Volume of Water to Recharge- 2840 gallons (379 ft3)
• Design Loading- Based on Field Measured Soil Permeability0.5 inch per hour or 0.5 in3/in2.hour = 7.481 gpd/ft2
• Minimum Recharge Period – 72 hours (PADEP Recommended)
• Recharge Volume per day – 945 gpd
• Minimum Recharge Area- (945 / 7.481) =126 ft2
• Internal Tank Storage – 3 ft * 8 ft perforated Concrete Tank, plus 3+ foot
perimeter and subsurface aggregate storage to generate a minimum surface
area of 150 ft2.
• Additional Gravel Layer was added to Meet System Storage Requirement.
Primary Limiting Factor is Not Recharge Capacity
but Providing Detention Storage or Storage in the System !
Sizing Calculations- Areas 0.1 in/hr
•
•
•
Impervious Area Roof and Driveway– 3500 ft2
Design Storm – 1.3 inch
Volume of Water to Recharge- 2840 gallons (379 ft3)
•
Design Loading- Based on Field Measured Soil Permeability0.1 in3/in2.hour =1.49 gpd/ft2
•
Minimum Recharge Period – 72 hours (PADEP Recommended)
•
Recharge Volume per day –945 gpd
•
Minimum Recharge Area- (945 / 1.49) =634 ft2 (over 18 % of impervious)
•
Recommended Changing the Recharge Period to 7 days to Reduce Infiltration Area to
270 ft2, but providing a system with 100 % detention storage. (7 % of impervious)
•
This could not be approved and the project implemented a bioretention/ recharge
design
0.1 inch per hour or
Primary Limiting Factor is Area Requirement Caused by Recharge Period
and not Recharge Capacity or Storage in the System !
Bio-Retention Systems
Image Source: http://www.co.monroe.in.us
Bio-Retention Concept
Sump and Grass Swale Prior to Unit and a By-pass Berm
Structure for large runoff events.
System has a controlled discharge that maintains a
discharge elevation that this consistent with natural water
table conditions.
Vegetation – Native Seed Mix
Soil Media – Native Soil from Site Modified to either a
loam texture with 2 to 5 % organic material; covered with
compost/mulch layer (on-site source).
Washed Stone at the Base of the Unit.
Sizing based on detention storage requirements and flow
routing.
Conceptual Design by: Malcolm Pirnie (Scranton, PA) and Brian Oram (2004)
Evaluating Recharge Capacity
•Step 1: Desktop Assessment - GIS
Review Published Data Related to Soils, Geology, Hydrology
•Step 2: Characterize the Hydrological Setting
•Where are the Discharge and Recharge Zones?
•What forms of Natural Infiltration or Depression
Storage Occurs?
•How does the site currently manage runoff ?
•What are the existing conditions or existing
problems?
Evaluation Recharge Capacity
•Step 3: On-Site Assessment
Deep Soil Testing Throughout Site Based on Soils and Geological
Data
Double Ring Infiltration Testing or Permeability Testing to
calculate qw and provide estimate of loading rates?
How does the water move through the site ?
•Step 4: Engineering Review and Evaluation
(meet with local reviewers and PADEP)
•Step 5: Additional On-site Testing
•Step 6: Final Design and Final BMP Selection
How Can We
Use Site
Conditons ?
Surface Boulders Created
Natural Depression Storage
Areas that appeared to range
in width from 5 to 25 feet.
Natural Depression
Storage System –
New Potential BMP !
3 feet Surface
Boulders
Use Of Manufactured Soils
Manufactured soils are loosely defined as soil amendment
products comprised of treated residuals and various industrial
by-products, such as foundry sand and coal ash.
•Use of Organic By-Products – Compost – Organic Soil and
Mulch
• Recycling of Industrial By-Products and Wood Products
•Improving Quality Structural Stability and Nutrient Content of
Unconsolidated Materials with Poor Soil Quality
• Use of Fly Ash, Incineration Ash, Recycling Remediated
Soil/Unconsolidated Material, Spent Foundry Sands
• Use of Soil Conditioners
• Use of Dredge Materials and Sediment
I did not say these were off the shelf or easy options !
Artificial Soil Quality Improvement
Aggregate Stability- Using a Polymer
No Soil Conditioner
Less Soil Conditioner
Source: Brady, N. C., 1990
Interested – Get Involved
and Stay Informed?
• Stormwater Manual Oversight Committee
Website – Keywords in Google: (stormwater
committee PA- 1st Site)
• Meets at the Rachel Carson Building – First
Floor Conference Room
• Next Meetings April 25, 2006, May 23, 2006,
and June 27, 2006.
• Download- Current Manuals, Discussions, and
Meeting Minutes
Soils, Groundwater Recharge,
and On-site Testing
Presented by:
Mr. Brian Oram, PG, PASEO
Wilkes University
GeoEnvironmental Sciences and
Environmental Engineering Department
Wilkes - Barre, PA 18766
570-408-4619
http://www.water-research.net
PADEP in the Field
Darcy Equation- What is Delta H?