Volume 2-05, Chapter 3 - City of Wichita

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Section 3.3.4 - Underground Sand Filter are conservative average pollutant reduction percentages for design purposes derived from sampling data. • Total Suspended Solids – 80% • Total Phosphorus – 50% • Total Nitrogen – 30% • Heavy Metals – 50% • Pathogens – 40% For additional information and data on pollutant removal capabilities for underground sand filters, see the National Pollutant Removal Performance Database (2nd Edition) available at www.cwp.org and the International Stormwater Best Management Practices (BMP) Database at www.bmpdatabase.org. 3.3.4.4 Application and Site Feasibility Criteria Underground sand filter systems are well-suited for highly impervious areas where land available for structural BMPs is limited. Underground sand filters should primarily be considered for new construction or retrofit opportunities for commercial, industrial, and institutional areas where the sediment load is relatively low, such as: parking lots, driveways, loading docks, gas stations, garages, airport runways/taxiways, and storage yards. To avoid rapid clogging and failure of the filter media, the use of underground sand filters should be avoided in areas with less than 50% impervious cover, or high sediment yield sites with clay/silt soils. The following basic criteria should be evaluated to ensure the suitability of an underground sand filter facility for meeting stormwater management objectives on a site or development. General Feasibility • Not suitable for use in a residential subdivision. • Suitable for use in high density/ultra-urban areas. • Not suitable for use as a regional stormwater control. On-site applications are typically most feasible. Physical Feasibility - Physical Constraints at Project Site • Drainage Area – 2 acres maximum for an underground sand filter. • Space Required – Function of available head at site. • Minimum Head – The surface slope across the filter location should be no greater than 6%. The elevation difference needed at a site from the inflow to the outflow is 2 to 6 feet. Page 3 - 164 Volume 2, Technical Guidance
Section 3.3.4 - Underground Sand Filter • Minimum Depth to Water Table – If used on a site with an underlying water supply aquifer, a separation distance of 2 feet is required between the bottom of the sand filter and the elevation of the seasonally high water table to prevent groundwater contamination. • Soils – Not recommended for clay/silt drainage areas that are not stabilized. Other Constraints / Considerations • Aquifer Protection – Do not allow infiltration of filtered hotspot runoff into groundwater. 3.3.4.5 Planning and Design Standards The following standards shall be considered minimum design standards for the design of underground sand filters. Underground sand filters that are not designed to these standards will not be approved. The local jurisdiction shall have the authority to require additional design conditions if deemed necessary. A. Construction Sequencing • Care shall be taken during construction to minimize the risk of premature failure of the underground sand filter due to deposition of sediments from disturbed, unstabilized areas. This can be minimized or avoided by proper construction sequencing. • Ideally, the construction of an underground filter shall take place after the construction site has been stabilized. In the event that the underground sand filter is not constructed after site stabilization, diversion of site runoff around the sand filter and installation and maintenance of appropriate erosion prevention and sediment controls prior to site stabilization is required. • Diversion berms shall be maintained around an underground sand filter during all phases of construction. No runoff shall enter the sand filter area prior to completion of construction and the complete stabilization of construction areas. Erosion prevention and sediment controls shall be maintained around the filter to prevent runoff and sediment from entering the sand filter during construction. • Underground sand filters shall not be used as a temporary sediment trap for construction activities. • During and after excavation of the underground sand filter area, all excavated materials shall be placed downstream, away from the sand filter, to prevent redeposit of the material during runoff events. B. Location and Siting • Underground sand filters shall have a contributing drainage area of 2 acres or less. • Underground sand filter systems are generally applied to land uses with a high percentage of impervious surfaces. Sand filters shall not be utilized for sites that have less than 50% impervious cover. Any disturbed or denuded areas located within the area draining to and Volume 2, Technical Guidance Page 3 - 165
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CHAPTER 3 STORMWATER CONTROLS TABLE
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Chapter 3 - Table of Contents 3.2.8
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Chapter 3 - Table of Contents LIST
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Section 3.1 - Stormwater Management
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Section 3.2.1 - Stormwater Pond 3.2
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Section 3.2.1 - Stormwater Pond Fig
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Section 3.2.1 - Stormwater Pond For
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Section 3.2.1 - Stormwater Pond •
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Section 3.2.1 - Stormwater Pond 1'
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Section 3.2.1 - Stormwater Pond 3.2
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Section 3.2.1 - Stormwater Pond Ste
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Section 3.2.2 - Extended Dry Detent
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Section 3.2.3 - Vegetative Filter S
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Section 3.2.4 - Grassed Channel 3.2
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Section 3.2.4 - Grassed Channel max
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Section 3.2.5 - Enhanced Swale 3.2.
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Section 3.2.5 - Enhanced Swale Chan
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Section 3.2.5 - Enhanced Swale B. G
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Section 3.2.5 - Enhanced Swale High
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Section 3.2.5 - Enhanced Swale Side
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Section 3.2.5 - Enhanced Swale 3.2.
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Section 3.2.6 - Infiltration Trench
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Section 3.2.7 - Soakage Trench 3.2.
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Section 3.2.7 - Soakage Trench •
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Section 3.2.8 - Surface Sand Filter
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Section 3.2.9 - Bioretention Areas
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Page 185 and 186: Section 3.4 - Other Stormwater Mana
Page 187 and 188: Section 3.4.1 - Conventional Dry De
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Page 207 and 208: Section 3.4.4 - Modular Porous Pave
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Page 215 and 216: Section 3.4.5 - Green Roof Signific
Page 217 and 218: Section 3.4.5 - Green Roof 3.4.5.3
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Volume 2-05, Chapter 3 - City of Wichita

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