Issue link: https://hi.iaq.net/i/248503
www.epa.gov/iaq/moisture Figure 2-1 Positive Drainage Principles • Retention or detention control methods such as wet or dry ponds. Guidance 5: When runoff must be controlled and redirected away from the building, identify and design water runoff management approaches appropriate for the site's characteristics. Potential approaches to use include: yy Wet ponds—storm water ponds, wet retention ponds and wet extended-detention ponds—are constructed basins that contain a permanent pool of water throughout the year or at least throughout the wet season. Ponds treat incoming runoff by allowing particles to settle and algae to take up nutrients. The primary removal mechanism is settling, which occurs as runoff resides in the pond. Pollutant uptake, particularly of nutrients, occurs through biological activity. Wet ponds traditionally have been widely used as a storm water best management practice. • Infiltration control methods such as swales or infiltration trenches. yy A swale (i.e., a grassed channel, dry swale, wet swale, biofilter or bioswale) is a vegetated, open-channel management practice designed specifically to treat and attenuate runoff for specified water quality and volume. As water flows along these channels, vegetation slows it to allow sedimentation; the water filters through a subsoil matrix or infiltrates the underlying soils or both. yy Dry detention ponds—dry ponds, extended detention basins, detention ponds and extended detention ponds—hold runoff for some minimum time to allow particles and associated pollutants to settle. Unlike wet ponds, these facilities do not have a large permanent pool of water; however, they are often designed with small pools at the basin's inlet and outlet. Dry detention ponds also can contribute to flood control by providing additional flood water storage. yy An infiltration trench (i.e., infiltration galley) is a rock-filled trench with no outlet that receives runoff. The runoff passes through some combination of pretreatment measures, such as a swale and detention basin, and into the trench. Runoff is stored in the spaces between the stones in the trench and from there infiltrates through the trench bottom and into the soil. The primary pollutant removal mechanism of this practice is filtering through the soil. 29