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===Subgrade===
===Subgrade===
For infiltrating pavements, subgrade slopes should be minimized so that runoff will be able to infiltrate evenly through the entire surface. For steeply sloped sites (>5%), check dams, berms or weir structures on the native soils of the pavement should be considered. If the system is not designed for infiltration, the bottom should be sloped at 1 to 5% toward the underdrain. Subgrades should be compacted to 95% Standard Proctor Density. If a lesser value is desired to promote infiltration, a thicker sub-base should be considered. Subgrade soils should not be scarified.
For infiltrating pavements, subgrade slopes should be minimized so that runoff will be able to infiltrate evenly through the entire surface. For steeply sloped sites (>5%), check dams, berms or weir structures on the native soils of the pavement should be considered. If the system is not designed for infiltration, the bottom should be sloped at 1 to 5% toward the underdrain. Subgrades should be compacted to 95% Standard Proctor Density. If a lesser value is desired to promote infiltration, a thicker sub-base should be considered. Subgrade soils should not be scarified.
===Geotextile===
The use of geotextile fabric between layers within the permeable pavement cross-section can limit infiltration rates due to the collection of solids on the filter fabric that slows infiltration as the pavement ages. While the use of geotextile fabric can improve retention of total suspended solids, the potential for clogging and the cost of rehabilitation typically negate the advantages of geotextile fabric.<ref> Weiss, P., Kayhanian, M., Gulliver, J.S., Khazanovich, L. 2019. Permeable pavement in northern North American urban areas: research review and knowledge gaps. International Journal of Pavement Engineering.Vol. 20, No. 2, 143-162. https://www.tandfonline.com/doi/full/10.1080/10298436.2017.127948</ref>
===Pretreatment===
===Pretreatment===