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EXHIBIT <br /> SAN MATEO COUNTYWIDE WATER POLLUTION PREVENTION PROGRAM <br /> 62 low -Through Planter Best uses <br /> • Treating roof runoff <br /> �� <br /> - r • Next to buildings <br /> 41 ( I I • Dense urban are <br /> I <br /> " .` -.-, ,�.� 7 i ' '' 3 „.� " • Locations where <br /> infiltration is not desired <br /> ki: I Advantages <br /> d '` • Can be adjacent to <br /> 4 structures <br /> ' , 2. -` ,-r \ i • Multi-use <br /> i; <br /> lar�:1 • Versatile <br /> r, ` • May be any shape <br /> • Low maintenance <br /> �' Limitations <br /> .. l <br /> , <br /> • Requires sufficient head <br /> • Careful selection of <br /> t plants <br /> Figure 6-7: At-grade flow-through planter. Source City of Emeryville Requires level installation <br /> • Susceptible to dogging <br /> Flow-through planters are designed to treat and detain runoff without allowing seepage into <br /> the underlying soil. They can be used next to buildings and other locations where soil <br /> moisture is a potential concern. Flow-through planters typically receive runoff via <br /> downspouts leading from the roofs of adjacent buildings. However, flow-through planters <br /> can also be set level with the ground and receive sheet flow. Pollutants are removed as the <br /> runoff passes through the soil layer and is collected in an underlying layer of gravel or drain <br /> rock. A perforated pipe underdrain must be directed to a storm drain or other discharge <br /> point. An overflow inlet conveys flows that exceed the capacity of the planter. <br /> TREATMENT DIMENSIONS AND SIZING <br /> • Flow-through planters may be designed with a 4% sizing factor (percentage of the <br /> surface area of planter compared to the surface area of the tributary impervious area). <br /> The area of impervious surface multiplied by 0.04 sizing factor will equal the footprint of <br /> the flow-through planter. Alternatively, calculations may be performed using either the <br /> hydraulic sizing criteria for flow-based treatment measures or the hydraulic sizing <br /> criteria for combination flow- and volume-based treatment measures, included in <br /> Section 5.1 . <br /> • Install an overflow weir adequate to meet municipal drainage requirements. <br /> • Flow-through planters can be used adjacent to building and within set back area. <br /> • Flow-through planters can be used above or below grade. <br /> • Size overflow trap for building code design storm, set trap below top of planter box walls. <br /> • Planter wall set against building should be higher to avoid overflow against building. <br /> • Elevation of the surface area may vary as needed to distribute stormwater flows <br /> throughout the surface area. <br /> PAGE74 CHAPTER6 <br /> ATTY/AGR.2016.231/849 Veterans RWC, LW - STMMA <br />