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Post Construction Water Quality BMP's


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This is a presentation I put together prior to leaving the storm infrastructure industry. Please keep in mind that stormwater, especially water quality, is a rapidly evolving arena. I have not updated the presentation since leaving the business, but I hope the information is useful in a broad general way, and can point you in the direction of additional resources that you may find useful.

Gil Werntz

Post Construction Water Quality BMP's

  1. 1. Georgia Stormwater Management Manual Post Construction Water Quality BMP Overview June 16, 2009 Gil Werntz (912) 897-7813 [email_address]
  2. 2. clay Is this how you feel when you think about stormwater quality?
  3. 3. The Georgia Stormwater Manual “The Blue Book” <ul><li>2 broad Structural Stormwater Control categories. </li></ul><ul><ul><li>General Application Structural Stormwater Controls, and… </li></ul></ul><ul><ul><li>Limited Application Structural Stormwater Controls. </li></ul></ul>
  4. 4. General Application Structural Stormwater Controls <ul><li>The Georgia Stormwater Manual defines these BMP’s as being capable of removing 80% of TSS. The accepted controls in this category are: </li></ul><ul><li>Ponds </li></ul><ul><li>Wetlands </li></ul><ul><li>Bioretention </li></ul><ul><li>Sand Filters </li></ul><ul><li>Infiltration Trenches </li></ul><ul><li>Enhanced Swales </li></ul>
  5. 5. Wet Ponds
  6. 6. Stormwater Ponds Benefits <ul><li>Very good pollutant removal effectiveness. (80% TSS, 30% to 50% nutrients, 50% metals & 70% pathogens per the GSWM) </li></ul><ul><li>Widely accepted by the community. </li></ul><ul><li>Can improve property values if designed and maintained with aesthetics in mind. </li></ul><ul><li>Ponds originally designed for retention can usually be upgraded to provide water quality benefits. </li></ul><ul><li>Can be used for irrigation. Take care to analyze water balance. </li></ul>
  7. 7. Stormwater Ponds Limitations <ul><li>Not suitable for small basins. (25 acres is typically considered the minimum for wet pond, wet ED pond & 10acres for micropool ED pond) </li></ul><ul><li>Size requirement limits applicability on some sites. </li></ul><ul><li>Water temperature elevations can occur, threatening aquatic life. </li></ul><ul><li>Intersection with water table adversely impacts pollutant removal according to some studies. (GSWM requires 2’) </li></ul><ul><li>Aesthetic and safety issues if not properly designed and maintained. </li></ul><ul><li>Growing concern about potential to harm urban wildlife. </li></ul>
  8. 8. Wet Pond
  9. 9. Stormwater Ponds Additional Information <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  10. 10. Stormwater Wetlands
  11. 11. Stormwater Wetlands Benefits <ul><li>Similar benefits to ponds. </li></ul><ul><li>Provides wildlife habitat. </li></ul><ul><li>Good pollutant removal (80%TSS, 30% to 40% nutrients, 50% metals & 70% pathogens per the GSWM). </li></ul><ul><li>Relatively low maintenance requirements. Annual costs 3% to 5% of the construction value per the EPA. </li></ul>
  12. 12. Stormwater Wetlands Limitations <ul><li>Needs a continuous base flow to maintain viable wetland. </li></ul><ul><li>Not suitable for small basins. (25 acres is typically considered the minimum, 5 acres for pocket wetland). </li></ul><ul><li>Requires large area, around 3% to 5% of the basin area. </li></ul><ul><li>Can release nutrients during non- growing season. </li></ul><ul><li>Can be a mosquito breeding ground if improperly designed. </li></ul>
  13. 13. Stormwater Wetland
  14. 14. Stormwater Wetlands Additional Information <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  15. 15. Bioretention Area
  16. 16. Bioretention Areas Benefits <ul><li>Applicable on small sites. 5 acres or less is typical. </li></ul><ul><li>Good for impervious areas such as parking lots. </li></ul><ul><li>Can be used as a partial infiltration structure to promote groundwater recharge. </li></ul><ul><li>Size penalty can be offset by substituting the BMP for traditional landscaped areas. </li></ul>
  17. 17. Bioretention Areas Limitations <ul><li>The size requirements are relative to the basin is high. 5% of the basin size is typical. </li></ul><ul><li>Requires significant landscaping. </li></ul><ul><li>Can be a mosquito hatchery if not properly designed and maintained. </li></ul>
  18. 18. Bioretention Area
  19. 19. Bioretention Areas Additional Information <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  20. 20. Sand Filter
  21. 21. Sand Filters Benefits <ul><li>Small footprint. Can be used on most sites. </li></ul><ul><li>Good choice on impervious sites. </li></ul><ul><li>Easily retrofitted to existing sites. </li></ul><ul><li>Very good BMP for hot spots because the water does not interact with the groundwater. </li></ul><ul><li>Can be used in virtually any soil type for the same reason. This also makes them very good pretreatment structures. </li></ul>
  22. 22. Sand Filters Limitations <ul><li>High sediment loads and fine clays or silts can be a problem. They can be oversized to handle these conditions. </li></ul><ul><li>Relatively high initial cost. </li></ul><ul><li>High maintenance requirements. </li></ul><ul><li>They are not applicable on large sites. (10 acres max for surface systems and 2 acres max for perimeter systems.) </li></ul><ul><li>They require significant head pressure (6’ to 8’ min), so they are tricky to use on flat sites. </li></ul>
  23. 24. Sand Filters Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  24. 25. Infiltration Trench
  25. 26. Infiltration Trenches Benefits <ul><li>They have no outlet, therefore the BMP is a good choice for groundwater recharge. </li></ul><ul><li>Good choice for small sites with porous soils. </li></ul>
  26. 27. Infiltration Trenches Limitations <ul><li>Not suitable for hotspots! By design the BMP interacts with the groundwater. </li></ul><ul><li>High clogging potential. Be careful on sites with fine silts and clays. </li></ul><ul><li>Soil type is critical. At least 2 soil borings per facility are required. Infiltration can be too fast or too slow. </li></ul><ul><li>Should not be used for basins greater than 5 acres. </li></ul><ul><li>High maintenance requirement. </li></ul><ul><li>High initial cost. </li></ul>
  27. 28. Infiltration Trench
  28. 29. Infiltration Trenches Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  29. 30. Enhanced Swales
  30. 31. Enhanced Swales Benefits <ul><li>Combines conveyance with stormwater treatment. </li></ul><ul><li>Initial investment is lower than curb & gutter. </li></ul><ul><li>Slows runoff velocities. </li></ul><ul><li>Good choice for treatment of roadway runoff. </li></ul><ul><li>Highly recommended by proponents of LID. </li></ul><ul><li>Maintenance is simple. Control vegetation and remove litter. </li></ul>
  31. 32. Enhanced Swales Limitations <ul><li>The BMP is usually a poor choice for hotspots. </li></ul><ul><li>They are not suitable for basins larger than about 5 acres, and their land requirements are fairly high. </li></ul><ul><li>Large storm events can resuspend solids. Steep slopes can also contribute to this problem. </li></ul><ul><li>Can be a mosquito breeding ground. On the coast it can be difficult to achieve proper slopes. </li></ul>
  32. 33. Enhanced Swale Dry and Wet
  33. 34. Enhanced Swales Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  34. 35. Limited Application Structural Stormwater Controls <ul><li>The Georgia Stormwater Manual defines these BMP’s as not being able to remove 80% TSS alone, are intended for hotspots or specific land use constraints, and / or may have special or high maintenance requirements. Controls in this category may include: </li></ul><ul><li>Filter Strips </li></ul><ul><li>Grass Channels </li></ul><ul><li>Organic Filters </li></ul><ul><li>Underground Sand Filters </li></ul><ul><li>Gravity (Oil Grit) Separators </li></ul><ul><li>Porous Concrete </li></ul><ul><li>Modular Porous Paver Systems </li></ul><ul><li>Alum Treatment </li></ul><ul><li>Proprietary BMP Structures </li></ul>
  35. 36. Filter Strip
  36. 37. Filter Strips Reason for Limited Use <ul><li>Cannot achieve 80% TSS removal target alone. </li></ul><ul><li>50% TSS removal is typical. </li></ul>
  37. 38. Filter Strips Considerations <ul><li>Sheet flow must be maintained. Otherwise gulleys can develop. Slotted or trench drains can help. </li></ul><ul><li>Good BMP for small impervious areas, roof drains and; along with swales; roadways. </li></ul><ul><li>Should be included in riparian areas next to marshes or streams. </li></ul><ul><li>Space requirements are large, so use may be limited in urban areas. </li></ul>
  38. 39. Filter Strips Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  39. 40. Grass Channels
  40. 41. Grass Channels Reason for Limited Use <ul><li>Can not achieve the 80% TSS removal rate </li></ul><ul><li>50% TSS removal is typical. </li></ul>
  41. 42. Grass Channels Considerations <ul><li>Differs from Enhanced Swales because they do not have an engineered filter media, and are therefore less effective at pollutant removal. </li></ul><ul><li>EPA does not differentiate. </li></ul><ul><li>Main design considerations are capacity and minimization of erosion. </li></ul><ul><li>Not suitable for basins larger than 5 acres. </li></ul><ul><li>Velocities must be non erosive. The full channel velocity will typically govern. </li></ul><ul><li>Maintenance is simple. </li></ul>
  42. 43. Grass Channels Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  43. 44. Organic Filter
  44. 45. Organic Filter Reason for Limited Use <ul><li>This BMP is intended for hotspots, space limited sites and / or sites requiring enhanced pollutant removal capability. </li></ul><ul><li>This BMP is maintenance intensive </li></ul>
  45. 46. Organic Filter Considerations <ul><li>This control is a variant of surface sand filters. It uses organic media such as peat / sand mixtures or leaf compost. These media enhance removal of dissolved nutrients, metals and hydrocarbons. </li></ul><ul><li>Head requirements are 5’ to 8’ minimum, and are higher than sand filters. </li></ul><ul><li>Subject to clogging, so the BMP is not a good choice for TSS removal. </li></ul><ul><li>Sediment forebay or pretreatment is good practice. </li></ul><ul><li>Suitable for sites up to 10 acres. </li></ul><ul><li>Design criteria is the same as for sand filters. </li></ul>
  46. 47. Organic Filter Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  47. 48. Underground Sand Filter
  48. 49. Underground Sand Filter Reasons for Limited Use <ul><li>Appropriate only for limited space applications. </li></ul><ul><li>High maintenance requirements. </li></ul>
  49. 50. Underground Sand Filters Considerations’ <ul><li>Design methodology is similar to standard sand filters. The BMP is an underground variant. </li></ul><ul><li>Good removal rates for sediment, BOD and fecal coliform. </li></ul><ul><li>Sediment settling basin can be oversized for large sediment loads. </li></ul><ul><li>Excellent BMP for hotspots. Site for maintenance access. </li></ul>
  50. 51. Underground Sand Filters Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  51. 52. Oil Grit Separator
  52. 53. Oil Grit Separator Reasons for Limited Use <ul><li>High Maintenance Requirements. </li></ul><ul><li>High Initial Cost. </li></ul><ul><li>May not be able to achieve 80% TSS target. </li></ul>
  53. 54. Oil Grit Separator Considerations <ul><li>Good Pretreatment Device </li></ul><ul><li>Isolated from groundwater, so it is a good choice at hotspots. </li></ul><ul><li>Sized using Stoke’s Law. </li></ul><ul><li>Should be installed “offline”. </li></ul><ul><li>Dissolved pollutant removal is secondary and a function of TSS removal. </li></ul>
  54. 55. Oil Grit Separator Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  55. 56. Submerged Gravel Wetland
  56. 57. Submerged Gravel Wetlands Reasons for Limited Use <ul><li>Use for limited size site applications. </li></ul><ul><li>High maintenance requirements. </li></ul>
  57. 58. Submerged Gravel Wetlands Considerations <ul><li>Low land consumption. Can be used in areas designated for landscaping. </li></ul><ul><li>If not in a hotspot application, it can intersect with groundwater. </li></ul><ul><li>Cannot be installed until site construction is complete. </li></ul><ul><li>Not suitable as a regional stormwater control. </li></ul><ul><li>Slope should be less than 2%. </li></ul><ul><li>Should have a watershed of 5 acres or less. </li></ul><ul><li>Should be designed with a sediment settling forebay. </li></ul><ul><li>Use wetlands plants. </li></ul>
  58. 59. Submerged Gravel Wetlands Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  59. 60. Porous Concrete
  60. 61. Porous Concrete Reasons for Limited Use <ul><li>Data indicates high failure rates and short life span. </li></ul><ul><li>Should not be used in high permeability soils. </li></ul><ul><li>Heavy vehicles should be restricted. </li></ul><ul><li>Special attention to design, construction and maintenance required. </li></ul>
  61. 62. Porous Concrete Considerations <ul><li>Higher cost than traditional pavements. </li></ul><ul><li>Reduces runoff volume. </li></ul><ul><li>Do not use in high traffic areas. </li></ul><ul><li>Should not be used in hotspots because of potential for groundwater contamination. </li></ul><ul><li>Sediment removal is initially very good, but will clog the system. Hence, the high maintenance requirement. </li></ul><ul><li>In situ soils must have sufficient infiltration capacity. (0.5 inch / hour is preferred.) </li></ul>
  62. 63. Porous Concrete Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  63. 64. Modular Porous Pavement Systems
  64. 65. Modular Porous Pavement Systems Reasons for Limited Use <ul><li>Suitable in low traffic areas only. </li></ul><ul><li>High maintenance requirements. </li></ul>
  65. 66. Modular Porous Pavement Systems Considerations <ul><li>Very similar to porous pavements. </li></ul><ul><li>Can be designed to handle higher structural loads than porous pavement. </li></ul><ul><li>Sediment can clog the system, so maintenance is critical. </li></ul><ul><li>Readily available from many vendors. </li></ul><ul><li>Do not overcompact underlying soils. </li></ul><ul><li>Require a high degree of quality workmanship to operate properly. </li></ul>
  66. 67. Modular Porous Pavement Systems Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  67. 68. Alum Treatment System Reasons for Limited Use <ul><li>High Maintenance Requirements </li></ul><ul><li>Intended as a part of a regional control facility. </li></ul>
  68. 69. Alum Treatment System Considerations <ul><li>Requires very little land. </li></ul><ul><li>pH level must be maintained between 6.0 to 7.5. </li></ul><ul><li>High capital, maintenance and operating costs. The installation costs are consistent regardless of watershed size. </li></ul><ul><li>Very effective at removal of all targeted pollutants. </li></ul><ul><li>Can be a good solution to remediate distressed water bodies. </li></ul>
  69. 70. Alum Treatment System Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  70. 71. Proprietary Structural Controls
  71. 72. Proprietary Structural Controls Reasons for Limited Use <ul><li>Limited performance data. </li></ul><ul><li>May not be able to achieve 80% TSS reductions independently. </li></ul><ul><li>High maintenance requirements. </li></ul><ul><li>Cost. </li></ul>
  72. 73. Proprietary Structural Controls Considerations <ul><li>Many innovative technologies. </li></ul><ul><ul><li>Hydrodynamic separators, such as vortex & gravity devices. </li></ul></ul><ul><ul><li>Catch basin inserts. </li></ul></ul><ul><ul><li>Filtration systems. </li></ul></ul><ul><ul><li>Chemical treatment systems. </li></ul></ul><ul><ul><li>Prefabricated detention systems. </li></ul></ul><ul><li>Third party testing data required. </li></ul><ul><li>Can often be used as pretreatment or forebay of General Application sturctures. </li></ul><ul><li>Can provide good options on site limited projects. </li></ul><ul><li>Utilize industry resources. </li></ul><ul><li>Local permitting authorities have the final say. </li></ul>
  73. 74. Proprietary Structural Controls Additional Resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  74. 75. Additional Information on the Web <ul><li> (FHWA UltraUrban BMP website) </li></ul><ul><li> (The Georgia Stormwater Manual) </li></ul><ul><li> (The EPA Post Construction BMP site. </li></ul><ul><li> (Knox County, TN Storm ordinance. Similar to The Blue Book, but it includes maintenance checklists) </li></ul><ul><li> (The International Stormwater BMP Database) </li></ul><ul><li> (The Stormwater Manager's Resource Center is designed specifically for stormwater practitioners, local government officials and others that need technical assistance on stormwater management issues. </li></ul><ul><li> (The Center for Watershed Protection. This organization is a source for much of the Georgia Stormwater Manual. </li></ul><ul><li> (Stormwater Magazine’s website) </li></ul>
  75. 76. QUESTIONS?