Sediment Controls

1. Sediment Controls Tom Schneider, CPESC President SCIECA EPA Region 6 MS4 Conference July 7, 2011 San Antonio, Texas How they work

2. Defining the problem • Removal of the sediment from the storm water runoff prior to it reaching surface waters.

3. Purpose of the Sediment Control on a construction site • Prevent sediment from exiting the site. • Sediment control are utilized from the time the soil is disturbed until the construction activity has ceased. At which time either temporarily or permanently erosion control can occur. • Erosion control cannot be utilized to control sediment for active areas of disturbance on construction sites.

4. Things that affect Sediment Controls • Topography • Length of slope • Percent of slope • Soil type • Sand • Silt • Clay • Storm type • Volume of runoff • Rate of runoff

5. Predicting the Performance • First we need to understand how the sediment control will remove the sediment. • Sedimentation • Filtration

6. Sediment Controls • Sedimentation • Filtration

7. Sedimentation • What is the one thing that we can look too that will give us a conclusive prediction of the effectiveness of a sedimentation control? Time

8. Effects of Time • When runoff is detained a sufficient amount of time the sediment will settle out of the storm water runoff and will not exist the site. • If the runoff exits the control prior to the required settling time, sediment will exit the control with the runoff.

9. I think they need a little more time.

10. How Much Time • What determines the amount of time that the runoff will need to be detained? Soil Type

11. Soil • Sand • Clay • Silt 38 seconds = 1 foot 230 days = 1 foot 33 minutes = 1 foot

12. Stoke’s Law

13. Sediment Controls • Sedimentation • Time required • Soil type • % sand • % silt • % clay • Filtration

14. Designing the Control for Time • Determine the flow rate to the control • Every control location will have a unique flow rate. • Geographic location • Topography • Soil type • LOCATION OF THE CONTROL ON THE SITE • Determines the drainage area of the control • TR55 • Is an accepted flow rate model used by engineers for the design of storm drainage systems.

15. Designing the Control • Relate the Time required to the Flow rate into the control. • Based on the sites conditions I have flow rate of 2 cfs (cubic feet per second). • Based on the sand silt soil type I need to retain the runoff 33 minutes (1980 seconds) • 1980 seconds x 2 cfs= 3960 cf Capacity • 3960cf / 2cfs = 1980 seconds • Capacity = Time • Based on the location of the control and the soil type of the site if the control detains 3960 cf of storm water runoff it will provide the amount of time required to remove the sediment.

16. Detain not Retain 1,980 seconds 2cfs 2cfs

17. Sediment Controls • Sedimentation • Time required • Soil type • % sand • % silt • % clay • Capacity requirement • Flow rate • Time required • Filtration

18. Designing the Control • Determining the capacity of the control • Configuration • Height • Length • Aspect to the topography • Capacity (volume) equals Time • The larger the volume the more time provided

19. Geometry

20. Designing or Evaluating the Control

21. Profile View

22. Side Area

23. Length

24. 9 9 2 9 2 20 9 20 180

25. Side Area

27. Profile View

28. 3 2 3 3 2 20 3 20 60

29. Rotate the Control

30. Predictable performance.

31. The solution is not more rows of the control the solution is to provide more time

32. Why Blame the Control • Does it matter what the control is made of? Not really

33. Hay bales, Rock berm, Concrete, Straw waddles, Marshmallows. The result will be the same .

34. Location, Location, Location The bottom of the slope is not always the best location

35. Sediment Controls • Sedimentation • Time required • Soil type • % sand • % silt • % clay • Capacity requirement • Flow rate • Time required • Capacity provided • Height of control • Topography • Filtration

36. Will the Control Work • Based on the soil I know how long I need to retain the runoff. • Based on the location of the control I know the flow rate of the runoff to the control. • Based on the soil type and flow rate I know the volume of water the control needs to detain to be successful. (volume=time) • Based on the location of the control I know the volume of water that my control will detain.(Time = Effectiveness)

37. Efficiency and Effectiveness • The term "efficient" is very much confused and misused with the term "effective". In general, efficiency is a measurable concept. In several of these cases, efficiency can be expressed as a result as percentage of what ideally could be expected, hence with 100% as ideal case. • Compare “effectiveness” , which is a vague, non-quantitative concept, mainly concerned with achieving objectives.

38. Efficiency and Effectiveness • For sedimentation controls efficiency and effectiveness are close to the same thing and are determined by amount of time the runoff is detained and the soil type contained within the drainage area of the control. • Filtration controls efficiency and effectiveness are not as closely connected. The efficiency can be high and the effectiveness be low.

39. Lopeno Flow rate of 2cfs 1,980 seconds x 2 cfs = 3,960 cf 3,960cf/2cfs=1,980 seconds Control volume 3,960 cf What percent of the sediment load did the control stop?

40. Saucel Flow rate of 2cfs 19,872,000 seconds x 2 cfs = 39,744,000 cf 39,744,000cf/2cfs=19,872,000 seconds Control volume 3,960 cf or What percent of the sediment load did the control stop? 1980 seconds

41. Kaufman Clay Flow rate of 2cfs 19,872,000 seconds x 2 cfs = 39,744,000 cf 39,744,000cf/2cfs=19,872,000 seconds Control volume 3,960 cf or What percent of the sediment load did the control stop? 1980 seconds

42. Sediment Controls • Sedimentation • Time required • Soil type • % sand • % silt • % clay • Capacity requirement • Flow rate • Time required • Capacity provided • Height of control • Topography • Effectiveness • Capacity provided • Soil type • Filtration

43. Permit Requirements

44. Effluent Limitation Guidelines • Performance driven requirement based on NTUs (Nephelometric Turbidity Units) • Controls will need to be designed to provide for the removal of the sediment not designed to meet the permit requirements • NTUs correlate more to the color of the soil than sediment load in the soil.

45. Sediment Controls • Sedimentation • Time required • Soil type • % sand • % silt • % clay • Capacity requirement • Flow rate • Time required • Capacity provided • Height of control • Topography • Effectiveness • Capacity provided • Soil type • Soil color • Filtration

46. Filtration • What is the one thing that we can look too that will give us a conclusive prediction of the effectiveness of a filtration control? • There is not one. • We need to look at • Storm water runoff flow rate • Soil type • Filter media opening size • Filter media flow rate • Size of the filter area

47. Storm Water Flow Rate • Determine the flow rate to the control • Every control location will have a unique flow rate. • Geographic location • Topography • Soil type • LOCATION OF THE CONTROL ON THE SITE • Determines the drainage area of the control • TR55 • Is an accepted flow rate model used by engineers for the design of storm drainage systems.

48. Soil Type • Soil type will determine what filter media would be appropriate. Sand Silt Clay

49. Filter Media • Criteria for selecting the correct filter media • What size soil particles will pass through the filter. • Flow rate of the filter media (how much water will pass through it in a given time per square foot). • How many square feet will be able to filter runoff.

50. Kaufman Clay 100% 32% 10% 100% What percent of the sediment load did the control stop? No one knows all we know is the efficiency of the filter media.