Issue link: https://hi.iaq.net/i/248503
www.epa.gov/iaq/moisture Site Drainage • Porous pavement is a permeable surface often built with an underlying stone reservoir that temporarily stores surface runoff before it infiltrates into the subsoil. Porous pavements may be made using asphalt or concrete. Medium-traffic areas are the ideal application for porous pavement. Porous pavement may be inappropriate in areas such as truck loading docks and areas where there is a great deal of commercial traffic. Issue Water from rain, snowmelt and irrigation systems can infiltrate a building, damaging the structure and its contents. Properly designed site drainage avoids building damage and the need for potentially costly remediation.14 Goal • Modular porous pavers are permeable surfaces that can replace asphalt and concrete; they can be used for driveways, parking lots and walkways. Alternative pavers can replace impervious surfaces, resulting in less storm water runoff. Design the site so that water from rain, snowmelt and landscape irrigation is prevented from entering the building. Guidance • The two broad categories of alternative pavers are paving blocks and other surfaces, including gravel, cobbles, wood, mulch, brick and natural stone. Guidance 1: The site drainage design creates a controlled condition to help move water away from the building. To the extent possible, the design maintains the rate of water-soil infiltration (i.e., the downward entry of water into the surface of the soil) at the site before the site was disturbed. Runoff (i.e., water that does not infiltrate into the soil) must be managed by other drainage methods. Guidance 3: Use grading to slow down runoff and achieve a more balanced infiltration rate. Topography helps determine the amount, direction and rate of runoff. To the extent possible, retain existing contours so that the existing drainage patterns can be maintained. Grading also can be used to correct drainage problems. Where steep slopes contribute to rapid runoff, re-grading to more moderate slopes can reduce runoff velocity. Guidance 2: Avoid unnecessary impervious surfaces. Avoiding unnecessary or large impermeable surfaces— or using alternative, relatively permeable paving materials—will allow more water to infiltrate, thus reducing the size and cost of systems managing runoff. Placing facilities on a site changes the site's drainage characteristics by increasing the impervious area, which, in turn, increases the volume of runoff that must be managed. Where large expanses of impervious surface are unavoidable, such as parking lots, breaking the expanse into smaller areas or using alternative permeable pavement techniques can help reduce runoff. Guidance 4: Ensure positive site drainage principles are met, including: • Making certain water is moved away from the building. • Ensuring water is not allowed to accidentally pond in low areas. • Making sure the finished floor is elevated enough so that water will not back up into the building if the drainage systems are blocked. Alternative paving materials such as pervious pavement, modular porous paver systems or other surfaces can be used to reduce runoff. 14 Figure 2-1 illustrates positive drainage principles. This document does not address flood waters from rivers or lakes, the sea or from other extreme weather events. 28