SAWS TPDES: Soil, Erosion and Sedimentation Methods Philip Handley Supervisor-Resource Protection & Compliance

September 3, 2013

TPDES: Soil, Erosion and Sedimentation Methods

September 3, 2013

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

Common SWPPP Issues and Soil Characterization

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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

http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

Common SWPPP Issues and Soil Characterization

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Soil Characterization

Common SWPPP Issues and Soil Characterization

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Soil Characteristics

Common SWPPP Issues and Soil Characterization

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Soil Type Classification NOTE: It is rare to find a “pure” soil type Most Soils consists Of various percentages Of •Sand •Silt •Clay

Common SWPPP Issues and Soil Characterization

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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

Common SWPPP Issues and Soil Characterization

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Erosion and Sediment Control Is there a difference Between Erosion and Sediment Control? Common SWPPP Issues and Soil Characterization

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The Difference 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 Common SWPPP Issues and Soil Characterization

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So….. Where does Erosion Begin? Common SWPPP Issues and Soil Characterization

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The Rain Drop

Raindrop typical size: 1/16” to 1/4” dia. Fall velocity: 18 ft/sec. or about 20 mph Common SWPPP Issues and Soil Characterization

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Raindrop Impact on Soil (example diagram) Splash Pattern

Common SWPPP Issues and Soil Characterization

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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.

Sheet Erosion

Rill Erosion

Gully Erosion

Common SWPPP Issues and Soil Characterization

Stream Bank Erosion

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Erosion

(Soil Horizons – Eroded) Second Horizon Soil

First Horizon Soil

Common SWPPP Issues and Soil Characterization

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Where did all the Top Soil Go??? To the MS4 = Enforcement

Common SWPPP Issues and Soil Characterization

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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

Common SWPPP Issues and Soil Characterization

Matting

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Erosion Control (Erosion Mats)

Common SWPPP Issues and Soil Characterization

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Erosion Control (Grassy Filter Strip)

Common SWPPP Issues and Soil Characterization

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Erosion Control (Scour and Solutions)

Common SWPPP Issues and Soil Characterization

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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

Common SWPPP Issues and Soil Characterization

Silt Fence Diversion Page 20

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Velocity Control (Silt Fence Placement)

Common SWPPP Issues and Soil Characterization

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Sediment Detached soil particles moving in the erosion process, Transported hydraulically in storm water runoff.

Common SWPPP Issues and Soil Characterization

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Sediment Control

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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.

Common SWPPP Issues and Soil Characterization

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Soil Class Settlement Times Sand



Silt



Clay

1 foot



38 seconds = 1 foot

33 minutes = 1 foot

Common SWPPP Issues and Soil Characterization

230 days = 1 foot Page 24

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Soil –Translated to “TIME” 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

Common SWPPP Issues and Soil Characterization

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Stoke’s Law

Common SWPPP Issues and Soil Characterization

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Sediment Control (Silt Fence Installation)

Common SWPPP Issues and Soil Characterization

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Sediment Control

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(Berms) Rock Check Dam

Compost Filter Berm

Common SWPPP Issues and Soil Characterization

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Sediment Control (Rock Gabions)

Common SWPPP Issues and Soil Characterization

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Sediment Control (Basins)

Common SWPPP Issues and Soil Characterization

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Sediment Control (Filter Socks)

Common SWPPP Issues and Soil Characterization

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Sediment Control (Sediment Bag)

Common SWPPP Issues and Soil Characterization

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Sediment Control (Construction Exit)

(C

Common SWPPP Issues and Soil Characterization

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Sediment Control (Inlet Protection)

Common SWPPP Issues and Soil Characterization

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Pollutant Control (Concrete Washout Pit)

Common SWPPP Issues and Soil Characterization

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Storm Water Pollution Prevention Plans (SWPPP) and

Best Management Practices (BMP’s) Common SWPPP Issues and Soil Characterization

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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

Common SWPPP Issues and Soil Characterization

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

or – Add more of it?

Common SWPPP Issues and Soil Characterization

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Add More of It?

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Add More of It?

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Predict the Performance

September 3, 2013

• 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.

Common SWPPP Issues and Soil Characterization

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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” (Time of concentration to pool sediment laden water allowing settlement)

Common SWPPP Issues and Soil Characterization

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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. Common SWPPP Issues and Soil Characterization

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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. Common SWPPP Issues and Soil Characterization

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The Problem With Soil

September 3, 2013

• 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.

Common SWPPP Issues and Soil Characterization

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Remember the Soil settlement model?

Sand



Silt



Clay

1 Foot



38 seconds = 1 foot

33 minutes = 1 foot

Common SWPPP Issues and Soil Characterization

230 days = 1 foot Page 46

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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

Common SWPPP Issues and Soil Characterization

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Common SWPPP Issues and Soil Characterization

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•Need to install triangle and rectangle (more storage)

Common SWPPP Issues and Soil Characterization

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12”

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24”

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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.

Common SWPPP Issues and Soil Characterization

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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.

Construction Site Containment Profile View – (n.t.s.)

435’ (site length)

Sediment Control 18” High

120’

100’

225’ Containment

Common SWPPP Issues and Soil Characterization

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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.

Construction Site Profile View (n.t.s.)

Construction site Plan View (n.t.s.)

Skimmer

435’

100’

435’

3.5’ 70’

Common SWPPP Issues and Soil Characterization

70’

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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”

Common SWPPP Issues and Soil Characterization

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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”

Common SWPPP Issues and Soil Characterization

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

Common SWPPP Issues and Soil Characterization

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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) Common SWPPP Issues and Soil Characterization

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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

Common SWPPP Issues and Soil Characterization

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Who Decides on your BMP’s?

September 3, 2013

• 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

Common SWPPP Issues and Soil Characterization

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SAWS TPDES: Soil, Erosion and Sedimentation Methods Philip Handley Supervisor-Resource Protection & Compliance

September 3, 2013

TPDES: Soil, Erosion and Sedimentation Methods