Volume 2-05, Chapter 3 - City of Wichita
Volume 2-05, Chapter 3 - City of Wichita Volume 2-05, Chapter 3 - City of Wichita
Section 3.2.7 - Soakage Trench 3.2.7.1 General Description Soakage trenches represent a variation of the infiltration trench. Regular infiltration trenches receive drainage from the surface, but in highly urbanized areas there is often not a suitable area available for this type of setup. Soakage trenches utilize a perforated pipe embedded within the trench to introduce inflow, thereby minimizing the surface area required for the device. They can be located under pavement, although this is not recommended because of the expense of maintaining if the trench ultimately clogs. A sediment sump may be used to decrease this problem. Soakage trenches used for stormwater disposal are considered Class V injection devices by the EPA and fall under the Kansas UIC program. 3.2.7.2 Pollutant Removal Capabilities Pollutant removal is similar to infiltration trenches, but care should be taken to avoid clogging with sediments. The following design pollutant removal rates are average pollutant reduction percentages for design purposes derived from sampling data, modeling and professional judgment. In a situation where a removal rate is not deemed sufficient, additional controls may be put in place at the given site in a series or “treatment train” approach. • Total Suspended Solids – 90% • Total Phosphorus – 60% • Total Nitrogen – 60% • Heavy Metals – 90% • Fecal Coliform – 90% For additional information and data on pollutant removal capabilities, see the National Pollutant Removal Performance Database (2nd Edition) available at www.cwp.org and the National Stormwater Best Management Practices (BMP) Database at www.bmpdatabase.org. 3.2.7.3 Design Criteria and Specifications • The trench shall be excavated in native soil, uncompacted by heavy equipment. • The trench should be at least 3 feet deep and 2.5 feet wide as shown in Figure 3-27. The exact dimensions will depend on the drainage characteristics of the surrounding soils. • A minimum separation distance of 5 feet is required between the bottom of the trench and the elevation of the historical high water table for soakage trenches without underdrains, 2 feet for soakage trenches with underdrains. Soakage trenches shall not be used to infiltrate untreated hotspot runoff. Page 3 - 94 Volume 2, Technical Guidance
Section 3.2.7 - Soakage Trench • A sediment trap may be installed upstream of the perforated pipe if pretreatment is needed prior to discharge. • The bottom of the trench should be filled with at least 18 inches of medium sand meeting ASTM C-33 and enveloped in filter fabric. • A minimum of six inches of ¾ inch – 2 ½ inch round or crushed rock shall be placed on top of the fabric covered sand base. The crushed rock shall also be enclosed in filter fabric. • The inflow pipe should be sized based on delivery of the water quality flow to the trench, and should be a minimum of 3 inches in diameter. • The perforated distribution pipe shall be an approved leach field pipe with holes oriented downward. It shall be covered with filter fabric, with at least 12 inches of backfill above the pipe. • The trench should be sized in the same manner as a conventional infiltration trench (see Section 3.2.6.) and the pipe perforations over-sized to ensure that the sand is the limitation to flow and not the pipe perforations. • The local jurisdiction may require that the facility be placed in a reserve and/or establishment of a drainage easement the facility, which is accessible from a public road or other accessible easement. When required, the drainage easement should be at least 20 feet wide, provide a minimum traversable width of 15 feet, have a maximum slope of no more than 10%, and be appropriately stabilized to withstand maintenance equipment and vehicles. • A pipe inspection and cleanout port shall be employed to allow inspection and maintenance. 3.2.7.4 Inspection and Maintenance Requirements Regular inspection and maintenance is critical to the effective operation of stormwater management facilities. An operation and maintenance plan is required and shall include: 1. “Covenants for Permanent Maintenance of Stormwater Management Facilities” (also called the “Maintenance Covenants”). An example covenants document can be found in Volume 3. 2. “Inspection Checklist and Maintenance Guidance” for each type of stormwater facility that is located on the property. Templates for each stormwater management facility can be found in Volume 3 of this manual. These templates can be amended slightly for use in more customized O&M plans. 3. As-built drawings must accurately identify the location and layout of the facility, and also clearly identify reserves and access easements. All stormwater management facilities must be maintained in accordance with the O&M Plan. Volume 2, Technical Guidance Page 3 - 95
- Page 49 and 50: Section 3.2.1 - Stormwater Pond Fig
- Page 51 and 52: Section 3.2.1 - Stormwater Pond Fig
- Page 53 and 54: Section 3.2.2 - Extended Dry Detent
- Page 55 and 56: Section 3.2.2 - Extended Dry Detent
- Page 57 and 58: Section 3.2.2 - Extended Dry Detent
- Page 59 and 60: Section 3.2.3 - Vegetative Filter S
- Page 61 and 62: Section 3.2.3 - Vegetative Filter S
- Page 63 and 64: Section 3.2.3 - Vegetative Filter S
- Page 65 and 66: Section 3.2.3 - Vegetative Filter S
- Page 67 and 68: Section 3.2.4 - Grassed Channel 3.2
- Page 69 and 70: Section 3.2.4 - Grassed Channel 3.2
- Page 71 and 72: Section 3.2.4 - Grassed Channel 3.2
- Page 73 and 74: Section 3.2.4 - Grassed Channel max
- Page 75 and 76: Section 3.2.5 - Enhanced Swale 3.2.
- Page 77 and 78: Section 3.2.5 - Enhanced Swale Chan
- Page 79 and 80: Section 3.2.5 - Enhanced Swale B. G
- Page 81 and 82: Section 3.2.5 - Enhanced Swale High
- Page 83 and 84: Section 3.2.5 - Enhanced Swale Side
- Page 85 and 86: Section 3.2.5 - Enhanced Swale 3.2.
- Page 87 and 88: Section 3.2.6 - Infiltration Trench
- Page 89 and 90: Section 3.2.6 - Infiltration Trench
- Page 91 and 92: Section 3.2.6 - Infiltration Trench
- Page 93 and 94: Section 3.2.6 - Infiltration Trench
- Page 95 and 96: Section 3.2.6 - Infiltration Trench
- Page 97 and 98: Section 3.2.6 - Infiltration Trench
- Page 99: Section 3.2.7 - Soakage Trench 3.2.
- Page 103 and 104: Section 3.2.8 - Surface Sand Filter
- Page 105 and 106: Section 3.2.8 - Surface Sand Filter
- Page 107 and 108: Section 3.2.8 - Surface Sand Filter
- Page 109 and 110: Section 3.2.8 - Surface Sand Filter
- Page 111 and 112: Section 3.2.8 - Surface Sand Filter
- Page 113 and 114: Section 3.2.8 - Surface Sand Filter
- Page 115 and 116: Section 3.2.8 - Surface Sand Filter
- Page 117 and 118: Section 3.2.9 - Bioretention Areas
- Page 119 and 120: Section 3.2.9 - Bioretention Areas
- Page 121 and 122: Section 3.2.9 - Bioretention Areas
- Page 123 and 124: Section 3.2.9 - Bioretention Areas
- Page 125 and 126: Section 3.2.9 - Bioretention Areas
- Page 127 and 128: Section 3.2.9 - Bioretention Areas
- Page 129 and 130: Section 3.2.9 - Bioretention Areas
- Page 131 and 132: Section 3.2.9 - Bioretention Areas
- Page 133 and 134: Section 3.2.10 - Stormwater Wetland
- Page 135 and 136: Section 3.2.10 - Stormwater Wetland
- Page 137 and 138: Section 3.2.10 - Stormwater Wetland
- Page 139 and 140: Section 3.2.10 - Stormwater Wetland
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Section 3.2.7 - Soakage Trench<br />
3.2.7.1 General Description<br />
Soakage trenches represent a variation <strong>of</strong> the infiltration trench. Regular infiltration trenches<br />
receive drainage from the surface, but in highly urbanized areas there is <strong>of</strong>ten not a suitable<br />
area available for this type <strong>of</strong> setup. Soakage trenches utilize a perforated pipe embedded<br />
within the trench to introduce inflow, thereby minimizing the surface area required for the<br />
device. They can be located under pavement, although this is not recommended because <strong>of</strong><br />
the expense <strong>of</strong> maintaining if the trench ultimately clogs. A sediment sump may be used to<br />
decrease this problem.<br />
Soakage trenches used for stormwater disposal are considered Class V injection devices by<br />
the EPA and fall under the Kansas UIC program.<br />
3.2.7.2 Pollutant Removal Capabilities<br />
Pollutant removal is similar to infiltration trenches, but care should be taken to avoid clogging<br />
with sediments.<br />
The following design pollutant removal rates are average pollutant reduction percentages for<br />
design purposes derived from sampling data, modeling and pr<strong>of</strong>essional judgment. In a<br />
situation where a removal rate is not deemed sufficient, additional controls may be put in<br />
place at the given site in a series or “treatment train” approach.<br />
• Total Suspended Solids – 90%<br />
• Total Phosphorus – 60%<br />
• Total Nitrogen – 60%<br />
• Heavy Metals – 90%<br />
• Fecal Coliform – 90%<br />
For additional information and data on pollutant removal capabilities, see the National<br />
Pollutant Removal Performance Database (2nd Edition) available at www.cwp.org and the<br />
National Stormwater Best Management Practices (BMP) Database at www.bmpdatabase.org.<br />
3.2.7.3 Design Criteria and Specifications<br />
• The trench shall be excavated in native soil, uncompacted by heavy equipment.<br />
• The trench should be at least 3 feet deep and 2.5 feet wide as shown in Figure 3-27. The<br />
exact dimensions will depend on the drainage characteristics <strong>of</strong> the surrounding soils.<br />
• A minimum separation distance <strong>of</strong> 5 feet is required between the bottom <strong>of</strong> the trench and<br />
the elevation <strong>of</strong> the historical high water table for soakage trenches without underdrains, 2<br />
feet for soakage trenches with underdrains. Soakage trenches shall not be used to<br />
infiltrate untreated hotspot run<strong>of</strong>f.<br />
Page 3 - 94<br />
<strong>Volume</strong> 2, Technical Guidance
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