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Glossary 4D Definitions are arranged alphabetically by term. For a complete reference, please see the Stormwater Management Manual for Western Washington (SWMMWW): fortress .wa gov/ecy/ershare/wjPermWFlare/2019SWMMWW]2019SWMMWW.htm Best Management Practice The schedules of activities, prohibitions of practices, maintenance procedures, (BMP) and structural and/or managerial practices, that when used singly or in combination, prevent or reduce the release of pollutants and other adverse impacts to waters of Washington State. Compaction The densification, settlement, or packing of soil in such a way that permeability of the soil is reduced. Compost Organic material that has undergone biological degradation and transformation under controlled conditions designed to promote aerobic decomposition at a solid waste facility in compliance with the requirements of Chapter 173-350 WAC, or biosolids composted in compliance with Chapter 173-308 WAC. Composting is a form of organic material recycling. Critical Area At a minimum, areaswhich includewetlands, areaswith acritical recharging effect on aquifers used for potable water, fish and wildlife habitat conservation areas, freq uentlyfl ood ed areas, geo I ogical ly hazardous areas, including unstable slopes, and associated areas and ecosystems. Dispersion Release of surface and stormwater runoff such that the flow spreads over a wide area and is located so as not to allow flow to concentrate anywhere upstream of a drainage channel with erodible underlying granular soils. Hard Surface An impervious surface, a permeable pavement, or a vegetated roof. Impervious Surface Anon -vegetated surface areawhich either prevents or retards the entryofwater into the soil mantle as under natural conditions prior to development. A non -vegetated surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces Include, but are not limited to, roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater. Open, uncovered retention/ detention facilities shall not be considered as impervious surfaces for the purposes of determining whether the thresholds for application of Minimum Requirements are exceeded. Open, uncovered retention/detention facilities shall be considered impervious surfaces for purposes of runoff modeling. City of Everett Public Works Small Proje ctStormwaterSite Plan Report April 2021 21