SAWS TPDES: Soil, Erosion and Sedimentation Methods Philip Handley Supervisor-Resource Protection & Compliance August 25, 2014 TPDES: Soil, Erosion and Sedimentation Methods
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 Page 2
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 Page 3
Soil Characterization Page 4
Soil Characteristics Page 5
Soil Type Classification NOTE: It is rare to find a pure soil type Most Soils consists Of various percentages Of Sand Silt Clay Page 6
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 Page 7
Erosion and Sediment Control Is there a difference Between Erosion and Sediment Control? Page 8
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 Page 9
So.. Where does Erosion Begin? Page 10
The Rain Drop Raindrop typical size: 1/16 to 1/4 dia. Fall velocity: 18 ft/sec. or about 20 mph Page 11
Raindrop Impact on Soil (example diagram) Splash Pattern Page 12
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 Rill Gully Stream Bank Erosion Erosion Erosion Erosion Page 13
Erosion (Soil Horizons Eroded) August 25, 2014 Second Horizon Soil First Horizon Soil Page 14
Where did all the Top Soil Go??? To the MS4 = Enforcement August 25, 2014 Page 15
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 Page 16
Erosion Control (Erosion Mats) August 25, 2014 Page 17
Erosion Control (Grassy Filter Strip) August 25, 2014 Page 18
Erosion Control (Scour and Solutions) August 25, 2014 Page 19
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 Page 20
Velocity Control (Silt Fence Placement) August 25, 2014 Page 21
Sediment Detached soil particles moving in the erosion process, Transported hydraulically in storm water runoff. Page 22
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. Page 23
1 foot August 25, 2014 Soil Class Settlement Times Sand Silt Clay 38 seconds = 1 foot 33 minutes = 1 foot 230 days = 1 foot Page 24
Soil Translated to TIME August 25, 2014 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 Page 25
Stoke s Law August 25, 2014 Page 26
Sediment Control (Silt Fence Installation) Page 27
Sediment Control (Berms) Rock Check Dam Compost Filter Berm Page 28
Sediment Control (Rock Gabions) August 25, 2014 Page 29
Sediment Control (Basins) Page 30
Sediment Control (Filter Socks) Page 31
Sediment Control (Sediment Bag) August 25, 2014 Page 32
Sediment Control (Construction Exit) (C Page 33
Sediment Control (Inlet Protection) August 25, 2014 Page 34
Pollutant Control (Concrete Washout Pit) Page 35
Storm Water Pollution Prevention Plans (SWPPP) and Best Management Practices (BMP s) Page 36
Why Predict Their Performance? August 25, 2014 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 Page 37
Current Sedimentation Control Design If the control fails get rid of it? or Add more of it? Page 38
Add More of It? August 25, 2014 Page 39
Add More of It? August 25, 2014 Page 40
Predict the Performance August 25, 2014 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. Page 41
Sedimentation August 25, 2014 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) Page 42
Effects of Time August 25, 2014 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. Page 43
What Do We Know So Far? August 25, 2014 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. Page 44
The Problem With Soil Sand, Silt, and Clay Most of the time soil has all three in it. August 25, 2014 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. Page 45
1 Foot August 25, 2014 Remember the Soil settlement model? Sand Silt Clay 38 seconds = 1 foot 33 minutes = 1 foot 230 days = 1 foot Page 46
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 August 25, 2014 Page 47
Page 48
Need to install triangle and rectangle (more storage) Page 49
12 Page 50
24 Page 51
Design for Maintenance August 25, 2014 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. Page 52
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 120 100 220 Containment Page 53
100 August 25, 2014 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.) 435 435 Skimmer 3.5 70 70 Page 54
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 Page 55
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 Page 56
Location and Topography (Sometimes, less in the right place is more think strategic!) August 25, 2014 Page 57
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) August 25, 2014 Page 58
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 Page 59
Who Decides on your BMP s? August 25, 2014 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 Page 60
SAWS TPDES: Soil, Erosion and Sedimentation Methods Philip Handley Supervisor-Resource Protection & Compliance August 25, 2014 TPDES: Soil, Erosion and Sedimentation Methods