SAWS TPDES: Soil, Erosion and Sedimentation Methods

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Feb 21, 2014 (3 years and 3 months ago)

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TPDES: Soil, Erosion and Sedimentation Methods

Philip Handley
Supervisor-Resource Protection & Compliance
SAWS TPDES:

Soil, Erosion and
Sedimentation Methods

September 3, 2013
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 2
Soil
Common term: “Dirt”
Common Science Facts:
•It’s all over your site
•Three Primary Ingredients of soil
-Sand
-Silt
-Clay
•Soil Type on your site-Identifiable
(NRCS-SCS County Soil Survey)
•Soil (sediment) is a recognized pollutant
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 3
http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx
National Resource Conservation Service
National Web Soil Survey
If you need specific, local soil data, go to the website
provided below and navigate to your specific
desired location.

If you have some basic GIS use skills you will have
success with this program.

It is reasonably easy and has a number of information
Data sets that are valuable engineering tools

September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 4
Soil Characterization
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 5
Soil Characteristics
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 6
Soil Type Classification
NOTE:
It is rare to find a
“pure” soil type
Most Soils consists
Of various percentages
Of
•Sand
•Silt
•Clay
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 7
Is Soil a Pollutant?
Per USEPA, soil is the number one Pollutant
on the EPA pollutant list.
WHY?
•Pollutants such as hydrocarbons, liquid
pollutants, metals and other chemicals attach
themselves to soil particles
•Soil density in water (turbidity) reduces oxygen
levels and creates other biological changes to
habitat in living waters
(fish and other biological life)
•Soil transports to natural waters by storm water
runoff
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 8
Erosion and Sediment
Control
Is there a difference Between
Erosion
and
Sediment
Control?
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 9
Erosion: is were the soil particles begin
separation from the surface horizon of the
mantle and transport by storm water down
slope.

Sediment: is the accumulation of soil
particles in a settlement area where all the
Soil particles collect together at the bottom of
a slope
The Difference
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 10
So…..
Where
does
Erosion
Begin?
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 11
The Rain Drop
Raindrop typical size: 1/16” to 1/4” dia.
Fall velocity: 18 ft/sec. or about 20 mph
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 12
Raindrop Impact
on Soil
(example diagram)
Splash Pattern
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 13
Erosion
Sheet
Erosion
Rill
Erosion
Gully
Erosion
Stream Bank
Erosion
The Detachment of soil particles from the surface horizon layer of soil
due to the volume and force of storm water runoff flowing across
non-vegetated or non-covered natural soil mantle/surface horizon.
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 14
Erosion
(Soil Horizons – Eroded)
Second Horizon Soil
First Horizon Soil
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 15
Where did all the Top Soil Go???
To the MS4 = Enforcement
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 16
Erosion control
The prevention of soil particles detachment and reducing The volume
of storm water runoff through the use of practices such as minimizing
land disturbing activities, maintaining vegetative cover or substituting
for lack of growing vegetation by mulching or applying blankets,
Erosion control blankets/matting or some type of cover on disturbed or
exposed soil mantle/horizon.

Straw
Cover
Hydro
Mulching
Matting
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 17
Erosion Control
(Erosion Mats)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 18
Erosion Control
(Grassy Filter Strip)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 19
Erosion Control
(Scour and Solutions)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 20
Velocity Control
Velocity controls are used to reduce the erosion forces
Of concentrated storm water flow on a construction site.
Practices can include tracking or roughening slopes,
rock check dams and other types of check dams and diversions.
Tracking
Soil Roughening
Straw log
Check Dams
Silt Fence
Diversion
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 21
Velocity Control
(Silt Fence Placement)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 22
Sediment
Detached soil particles moving in the erosion process,
Transported hydraulically in storm water runoff.
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 23
Sediment Control
Trapping detached soil particles that are being
Transported to ensure they are deposited on site
To prevent damage to other properties and to stop
Pollution to receiving waters.

Trapping detached soil particles is achieved by such
Practices as silt fence installation, berms, filter socks
And sediment control berms.
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 24
Soil Class Settlement Times

38 seconds = 1
foot

Sand
230 days = 1 foot

Clay
33 minutes = 1 foot

Silt
1 foot
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 25
Soil Percent Seconds Minutes Hours Days
Sand 0 38 0.6333 0.010556 0.000439815
Silt 0 1980 33 0.5 0.022916667
Clay 0 19,872,000 331,200 5,220 230
Soil –Translated to “TIME”
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 26
Stoke’s Law
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 27
Sediment Control
(Silt Fence Installation)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 28
Sediment Control
(Berms)
Compost Filter Berm
Rock Check Dam
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 29
Sediment Control
(Rock Gabions)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 30
Sediment Control
(Basins)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 31
Sediment Control
(Filter Socks)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 32
Sediment Control
(Sediment Bag)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 33
Sediment Control
(Construction Exit)

(C
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 34
Sediment Control
(Inlet Protection)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 35
Pollutant Control
(Concrete Washout Pit)


September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 36
Storm Water Pollution
Prevention Plans (SWPPP)
and
Best Management
Practices (BMP’s)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 37
Why Predict Their Performance?

Historically
• Start with a plan that meets the permit requirements
and modify it as the plans failures become apparent.

Future
• Start with a plan that will meet “Performance Based”
requirements.

Results
• Better protection of the environment
• Reduced cost
• Better relations between regulated and regulators


September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 38
Current Sedimentation Control Design
• If the control fails
– get rid of it?


or

– Add more of it?

September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 39
Add More of It?
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 40
Add More of It?
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 41
Predict the Performance
• Understand what is happening at the control!

– We have sediment laden water entering the
control.
– We should have ponding of the runoff.
– Sedimentation will be occurring if we have
ponding.
– Most likely runoff will be exiting the control.

September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 42
Sedimentation

What is the one thing that we can look to
that will give us a conclusive prediction
of the effectiveness of a sedimentation
control?



(Time of concentration to pool sediment laden water allowing settlement)
“Time”
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 43
Effects of Time


When runoff is detained for a “sufficient
amount of time”, the sediment will settle out
of the storm water runoff and will not exit
the site.

• If the runoff exits the control “prior to the
required settling time”, ………
sediment will exit the control with the
runoff.

September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 44
What Do We Know So Far?

Time is the key
– Provide enough time and you can remove the
sediment.

The sedimentation time required is determined
by soil type.

Each control will have a unique soil type
therefore each control will have a unique
required sedimentation time.

Flow rate will determine the time it will take to fill
the sedimentation pool based on the pool
volume of the control.
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 45
The Problem With Soil

Sand, Silt, and Clay

Most of the time soil has all three in it.
– Clay being the biggest challenge for sedimentation
control design.
– Most of the time we cannot control what type of
soil is on the site.
– Sometimes the soil changes.
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 46
Remember the Soil settlement model?

38 seconds = 1
foot

Sand
230 days = 1 foot

Clay
33 minutes = 1 foot

Silt
1 Foot
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 47
Onsite Control Location
Location of the control on the site
– Determines the drainage area of the control

Soil type in the drainage area
– Required sedimentation time
– Amount of runoff draining to the control

Topography of the drainage area
– Amount of runoff draining to the control
– Volume of water detain by the control
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 48
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 49
•Need to install triangle
and rectangle (more storage)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 50
12”
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 51
24”
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 52
Design for Maintenance

• Predict the volume of water you need to pool.

• Predict the sediment volume.

• Provide a storage volume equal to or greater
than the total of both.
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 53
Construction Site: 43,500 S.F. (1 Acre = 43,560)

Site Dimensions: 435’ long by 100’ wide = 43,500 s.f.
1 Yr./5 min. (0.54 inch) Storm event
43,500 X 0.54 = 23,522 C.F. of stormwater runoff
Containment areas (Silt Fence)
100’ X 100’ X 1.5’= 15,000 C.F.
120’ X 100’ X1.5”/2= 9,000 C.F.
Total Containment= 24,000 C.F.

225’ Containment
120’
100’
435’ (site length)
Construction Site Containment Profile View – (n.t.s.)
Sediment
Control
18” High
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 54
Construction Site: 43,500 S.F. (1 Acre=43,560)
Site Dimensions: 435’ long by 100’ wide = 43,500 s.f.
1 Yr./5 min. (0.54 inch) Storm event
43,500 X 0.54 = 23,522 C.F. of stormwater runoff
Containment area (Sediment Basin w/skimmer)
100’ X 70’ X 3.5’ deep pond = 23,800 C.F.
Total Containment= 23,800 C.F.
435’
100’
Skimmer
70’
70’
435’
Construction Site Profile View (n.t.s.)
Construction site Plan View (n.t.s.)
3.5’
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 55
Construction Site: 43,500 S.F. (1 Acre=43,560)
“Small Site Dilemma”
Considering a current EPA Sediment Basin requirement to contain a
2 year, 24 hour storm event (Bexar Co. = 3.70” inches)……

Our 435’ X 100’ = 43,500 S.F. Construction site experiencing a 3.70”
Rain Event would produce a need to contain
160,950 C.F. of stormwater runoff

This would require this construction site (if it were flat in elevation)
to enclose the entire site with a sediment control BMP and
the entire site would be ponding stormwater runoff
(435’ X 100’ X 3.70’ = 160,950 C.F.)

“Not Practical”
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 56
10 Acre Project Site
(435,600 S.F.)
2 Year, 24 Hour storm event (Bexar Co. =3.70 inches)

435,600 S.F. Site X 3.70” rain event will produce
1,611,720 C.F. of stormwater runoff

A Sediment Pond with a skimmer device that is
500’ X 500’ X 7’ deep can contain 1,750,000

For a large site, containing a 2 Year, 24 Hour storm event
is
“Practical”
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 57
Location and Topography
(Sometimes, less in the “right place”
is more…think strategic!)

September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 58
Current Permit vs. ELG’s

Current permit

“Erosion and sediment controls” must be
designed to retain sediment on-site to the extent
practicable with consideration for local
topography, soil type, and rainfall.”

Effluent Limit Guidelines (ELG’s)
– No consideration for on-site conditions.
– No gray area of “to the extent practicable”

Meet the required standard. ??? NTU
(Nephelometric Turbidity Units)
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 59
Summary
Current NPDES
• Currently SWPPP’s are designed to meet “Extent Practical”
• SWPPP Permitted operators rely primarily on “Sediment Control”
• Designers do not consider soil types & sediment loss in SWPPP design
• SWPPP are living documents (BMP failure prompts modification)

Future NPDES
• Future EPA “ELG” will require SWPPP design to be “Performance Based”
• To control sediment, design will need more focus on “erosion control”
• Erosion control will minimize sediment in stormwater runoff
• Sediment control will be designed to contain and filter and eliminate
sediment discharge into the MS4
• Stormwater discharge water from construction sites will require testing
(turbidity or TSS?) and will have to meet specific ELG targets
September 3, 2013
Common SWPPP Issues and Soil Characterization


Page 60
Who Decides on your BMP’s?
• SWPPP’s are living documents subject to change (by you) as your
project changes
•WPAP’s are approved plans with specific BMP requirements &
permanent BMP’s can only change by an approved modification
TPDES: Soil, Erosion and Sedimentation Methods

Philip Handley
Supervisor-Resource Protection & Compliance
SAWS TPDES:

Soil, Erosion and
Sedimentation Methods

September 3, 2013