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![Elevation above extraordinary groundwater
18C.3.5.3.: "Perched groundwater layers shall be
considered as those distinct layers of groundwater of
limited area caused by the blockage of normal seepage
of rainwater/snowmelt/runoff by an impervious soil
layer [...] If the perched groundwater table after
permanent lowering is less than two feet below the
bottom of the lagoon, the lagoon shall be provided with
a synthetic liner."](https://image.slidesharecdn.com/2016-0913presentation-lagoonlinersandbaffles-v0006-160914064436/75/Lagoon-liners-and-baffle-curtains-75-2048.jpg)
Uploaded byBrian Gongol
Lagoon liners and baffle curtains
The document discusses the design and implementation of lagoon liners and baffles in Iowa, detailing methods to enhance water flow, prevent short-circuiting, and improve aeration efficiency. It outlines the regulatory framework for lagoon construction, including materials choices such as geomembranes and additional sealing options to protect groundwater. The text emphasizes the importance of proper installation techniques and environmental considerations in lagoon management.
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Lagoon liners and baffle curtains
- 1. LAGOON LINERS ANDBAFFLES Brian Gongol DJ Gongol & Associates, Inc. September 14, 2016 Iowa AWWA Fall Short Course Ankeny, Iowa
- 2. Iowa rules permittwo types of lagoons
- 3.
- 4. #2: Flow-through aeratedsystems
- 5. Baffle curtains canserve purposes in both
- 6. Lagoon liners areindependent of treatment
- 7. Let's first un-bafflethe mystery of baffles
- 8. Purpose of bafflecurtains There's not just one
- 9.
- 10. Going with theflow Water seeks its own level Water follows the path of least resistance If you don't create a path, water will short-circuit
- 11. Break down deadzones This is important to both disinfection and aeration
- 12. Water is lazy:It takes path of least resistance
- 13. Iowa rules say:Prevent short-circuiting 18C.7.4.5.: "Discharge into each cell should be at the opposite end from the drawoff out of the cell to enhance plug flow and minimize short circuiting."
- 14. The byproduct ofshort circuits: Dead zones
- 15. A flow pathmakes the entire cell "active"
- 16. Maximize efficiency ofmechanical aeration
- 17. Aerators aren't sentient Ifyou don't move the water past them like an assembly line, they won't pick up and chase the untreated water
- 18. Repurpose existing cellsinto multiple zones Get a whole new zone without moving a shovel of dirt
- 19. Much easier thana complete reconstruction
- 20. Baffles can helprepurpose lagoons for NH3 A likely course of application in the years ahead
- 21. Design features ofbaffle curtains
- 22.
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- 25. Berm anchors andtop tension
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- 27.
- 28. Lateral anchors forvery long baffles
- 29. The right anchorscan let you turn corners
- 30. Baffle curtain materials Infairness, it doesn't necessarily have to be a geomembrane
- 31. Wood Requires pilings Breaks down over time Not adaptable
- 32. Concrete Heavy Immovable Requires drawdown Requires foundation
- 33. Geomembranes Can beretrofitted without drawdown Can be adjusted in the future Field-repairable Cost-effective Factory-assembled
- 34. Plus, geomembrane bafflescan adapt
- 35. Reinforced vs. non-reinforced Non-reinforced is cheaper Reinforced is more wear-resistant Reinforced can handle loads without deformation
- 36. Seaming Fewer seamsare better than more Field-repairable seams are better than not Factory-seamed products are better than field-seamed Heat or dielectric seams only -- never sewn
- 37. So, what doesit take to put them in?
- 38. Installation of bafflecurtains
- 39. Berm posts arethe toughest part
- 40. Should be accordion-foldedby factory
- 41. Purpose of lagoonliners
- 42.
- 43. #2: Prevent embankmenterosion
- 44. #3: Improve recoveryof biosolids
- 45. Design features oflagoon liners
- 46.
- 47.
- 48.
- 49. Sand bases Sand isgood as a base for the same reason it's good in sandbags for flood control
- 50. Lagoon liner materialsand options How do you keep lagoon water in and groundwater out?
- 51.
- 52. Bentonite 18C.7.3.2.: "Wherebentonite is used, the minimum seal thickness shall be four inches."
- 53. Alternative additives 18C.7.3.2.:"Alternate sealing materials such as membranes, soil cement or asphalt may be used." Soda ash Soil cement Asphalt
- 54.
- 55.
- 56.
- 57. Synthetic material regulations 18C.7.3.2.: "Synthetic liners shall have a minimum thickness of 30 mills"
- 58. Material choices Thickness isnot a good standard for making material selections
- 59. The walls ofan airplane aren't thick
- 60. HDPE Cheap upfront Often sold at 60 mil thickness Very rigid, thus hard to install Requires lots of field seaming (creating a hidden installation cost and risk) Highly prone to environmental stress cracking (like flexing a rigid credit card over and over) Hard to repair
- 61. PVC Susceptible toUV breakdown Must be backfilled for protection Similar puncture resistance at 20 mils as 60-mil HDPE Can be supplied in large panels Large panels reduce field seaming Plasticizers may migrate or leach, turning PVC brittle
- 62. Polypropylene Popular formunicipal sewage Also very popular in potable water Easier to factory-seam than HDPE Very flexible Excellent dimensional stability
- 63. Hypalon An oldfavorite Manufacturing discontinued by DuPont Repairs become more difficult with age
- 64. XR-3/XR-5 Heavily usedfor baffle curtains UV-stabilized XR-5 handles chemicals well
- 65. EnviroLiner/LLDPE Good whenbackfilled or UV-stabilized Flexible, making large panels possible Low surface friction, so texturing is required High flexibility means lower dimensional stability Factory-fabricated in much larger panels than HDPE
- 66.
- 67. Groundwater protection: Seepage 18C.7.3.2.: "Ponds shall be sealed such that seepage loss through the seal is as low as practically possible. The percolation rate shall not exceed 1/16 inch per day at a water depth of six feet."
- 68. Perhaps a visualinstead
- 69. Elevation above bedrock 18C.3.6.2.: "A separation of ten feet between the pond bottom and any bedrock formations is recommended with a minimum separation of four feet required. A synthetic liner shall be required if the lagoon bottom is to be located less than ten feet above a carbonate or sandstone formation."
- 70.
- 71. Elevation above groundwater 18C.3.5.2.: "A minimum separation of four feet between the pond seal and the maximum groundwater table is recommended; however, in no case shall the top of the pond seal be below the maximum groundwater table."
- 72.
- 73. Elevation above groundwater 18C.3.5.2.: "If the maximum anticipated groundwater table is less than two feet below the bottom of the lagoon, the lagoon shall be provided with a synthetic liner."
- 74.
- 75. Elevation above extraordinarygroundwater 18C.3.5.3.: "Perched groundwater layers shall be considered as those distinct layers of groundwater of limited area caused by the blockage of normal seepage of rainwater/snowmelt/runoff by an impervious soil layer [...] If the perched groundwater table after permanent lowering is less than two feet below the bottom of the lagoon, the lagoon shall be provided with a synthetic liner."
- 76.
- 77. Fractured limestone 18C.3.6.1.:"If the facility is located in an area of known or suspected fractured limestone, all cells must be lined with a synthetic liner."
- 78.
- 79.
- 80.
- 81. Hydrostatic uplift fromflooding
- 82.
- 83.
- 84.
- 85.
- 86. Sand layers 18C.7.3.2.:"If the subgrade is very gravelly and contains angular rocks that could possibly damage the liner, a minimum bedding of 3 inches of sand should be provided directly beneath the liner."
- 87.
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- 100.
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- 102.
- 103.
- 104.
- 105. Uniform bottom excavation 18C.7.3.4.: "The pond bottom shall be as level as possible at all points. Finished elevations shall not be more than +/-3 inches from the average elevation of the bottom."
- 106. Trenching 18C.3.4.: "Erosionprotection shall be provided for all external stormwater ditches as needed to prevent erosion of the outer pond embankments."
- 108.
- 109. Regulation on prevailingwinds 18C.3.3.: "If practical, the pond should be located so that prevailing winds will be in the direction of uninhabited areas"
- 110.
- 111.
- 112.
- 113.