BMP Monitoring Sites - Urban Drainage and Flood Control District

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UDFCD BMP MONITORING SITES Open Bed Sand Filter Installation Guidelines Basin Storage Volume Provide a storage volume equal to 100 percent of the WQCV based on a 40-hour drain time, above the sand bed of the basin. A. Determine the WQCV tributary catchment’s percent imperviousness. Account for the effects of DCIA or other runoff volume reducing facilities, if any, in the tributary catchments. B. Find the required storage volume (watershed inches of runoff): Determine the Required WQCV (watershed inches of runoff) based on a 40-hour drain time. C. Calculate the Design Volume in acre-feet as follows: ⎛WQCV ⎞ DesignVolu me = ⎜ ⎟ * Area ⎝ 12 ⎠ In which: Area = Area tributary to the sand filter Basin Depth/Design Filter’s Surface Area Maximum depth for the Design Volume shall be 3 feet. Calculate the minimum sand filter area (As) of the basin’s bottom using: ⎛ DesignVolume ⎞ As = ⎜ ⎟ * 43,560 (square feet) ⎝ 3 ⎠ Sand Media Provide, as a minimum, an 18-inch layer of C-33 sand. Keep the top surface flat. If side slopes need to be steeper than 3h:1v (4h:1v or flatter is preferred), use vertical walls. Granular Base and Underdrains Granular material shall have all fractured faces and meet the technical requirements of AASHTO #3, #4 or #67 aggregate.
UDFCD BMP MONITORING SITES Open Bed Sand Filter Impermeable Membrane and Geotextile Liners When expansive or NRCS Type D soils are present, or when standard percolation tests show percolation drawdown rates exceeding 60 minutes per inch, or potential for groundwater contamination exists, install a 16 mil thick impermeable liner on the bottom and sides of the basin. If vertical walls are permeable or of stacked blocks, extend the impermeable liner behind the walls. If soils are not expansive (i.e., NRCS Type A, B or C), use a woven geotextile material that meets the following ASTM requirements: o D-4751 – AOS U.S. Std. Sieve #50 to #70 o D-4633 – Trapezoidal tear strength >= 100x60 lbs o COE specified open area >= 4%. Products meeting requirements: US Fabric US 2070 and US 670, Mirafi Filterweave 500 and 700, Carthage Mills Carthage 6%. Wrap all liners to top of the sand filter basin and attach firmly with staples to the soil vertical wall using staples or concrete anchors. Provide sufficient slack so that the liners are not stretched when rock and sand/peat mix is placed. If tears are seen or discovered, repair them as recommended by manufacturer with no less than 18 inches of overlap on all sides of the tear. Outlet Works When underdrains are needed, the outlet works consists of 4” perforated HDPE pipe to convey water to the overflow outlet structure. Space perforated pipe on 20 foot centers or less. At the outlet of the HDPE pipe into the box, install an orifice sized to empty the WQCV above the sand in no less than 24 hours. Provided an overflow outlet pipe out of the overflow structure to convey flows away from the filter basin when the runoff volume exceeds the WQCV at rates required by local jurisdiction to control the flood detention, typically the 10- and the 100-year storm.
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Page 64 and 65: Orchard Pond EDB - Flow Dissipater

BMP Monitoring Sites - Urban Drainage and Flood Control District

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