RecDoc 2016-104272 STMMA (849 Veterans)

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C . 3 S T O R M W A T E R TECHNICAL GUIDANCE Table 6-2: Types of Pervious Paving and Possible Applications Paver Type Description Possible Applications Porous Asphalt Open-graded asphalt concrete over an open- Low traffic use, such as parking graded aggregate base, over a draining soil. lots, travel lanes, parking stalls. Contains very little fine aggregate (dust or sand) Surface may be too rough for and is comprised almost entirely of stone bicycle path. aggregate and asphalt binder; surface void content of 12-20%. Pervious Concrete A discontinuous mixture of coarse aggregate, Sidewalks and patios, low traffic hydraulic cement and other cementitious volume and low speed (less than materials, admixtures, and water which have a 30 mph limit) bikeways, streets, surface void content of 15-25% allowing water to travel lanes, parking stalls, and pass through. residential driveways. Permeable Discrete units set in a pattern on a prepared Parking stalls and lots, private Interlocking base. Typically made of precast concrete in driveways, walkways, patios, Concrete Pavers shapes that form interlocking patterns. Solid unit alleys, travel lanes, low volume (PICP) pavers are made of impermeable materials, but streets. are spaced to expose a permeable joint filled with permeable aggregates and set on a permeable base. Pervious Concrete Discrete units set in a pattern on a prepared Lighter traffic pedestrian and Pavers base. Constructed of pervious concrete. vehicle areas. Source: Design Guidelines for Permeable Pavements, Redwood City Design and Sizing Guidelines The design of each layer of the pavement must be determined by the likely traffic loadings and the layer's required operational life. The thickness of the base layer is also affected by hydrologic sizing considerations. To provide satisfactory performance, the following criteria shall be considered. SUBGRADE AND SITE REQUIREMENTS • The soil sub-grade shall be able to sustain anticipated traffic loading without excessive deformation while temporarily saturated. • The sub-grade shall be either ungraded in-situ material with an infiltration rate that allows detained flows to infiltrate within 72 hours, or the paving system can be installed with an underdrain that will remove detained flows within the pervious paving and base. • Depth to seasonal high groundwater level should be at least 5 feet from the bottom of the base of the pervious paving system, unless a different separation is recommended by the geotechnical engineer. • Pervious paving systems should not be used where site conditions do not allow infiltration.Grading of the soil subgrade below the pervious pavement should be relatively flat (not to exceed 2% slope) to promote infiltration across the entire area. • A slope of 1 % is recommended for pavement surface. Slopes of pervious pavement should not exceed 5%, or up to 16% with underdrains. Slopes exceeding 3% typically require berms or check dams placed laterally over the soil subbase to slow the flow of water and provide some infiltration. Alternatively, pervious pavement CHAPTER 6 6-29 ATTY/AGR.2016.231/849 Veterans RWC, LLC - STMMA