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improperly used, stored, transported or disposed of, or otherwise managed. For purposes of chemical regulation by this manual, moderate to high toxicity and confirmed human carcinogenicity are the criteria used to identify hazardous substances. (Note: This manual does not use the Resource Conservation and Recovery Act (RCRA) definition of hazardous. For the purpose of this manual, hazardous material is intended to include hazardous, toxic, and other harmful substances.) Hazardous Material Containment Zone (HMC Zone): An area where a specific individual activity involving use of a hazardous material takes place, and where chemical quantities at that location are expected to exceed defined thresholds. HMCs may include (but are not limited to) storage and /or process areas, transportation routes, work areas, and loading /unloading facilities. Headwaters Area: The area within Eugene city limits that is above 500 feet. Headwater Streams: Streams that: (1) are identified on the Headwater Streams Map (Appendix J) as having all or a portion of their length located on slopes greater than 10 %; (2) are identified on the Sensitive Areas Map as having all or a portion of their length located in areas with highly erodible soils; (3) are at least 500 feet or longer; and, (4) drain at least 10 acres. High -Flow Bypass and /or Diversion Device: A mechanism used to route stormwater runoffs which are greater than the water quality design storm around a stormwater management facility which is only designed to treat the water quality design storm. Flows routed around the stormwater quality facility must be taken to an approved destination. High -Flow Overflow: An inlet located at an approved elevation and location within a stormwater management facility, meant to collect overflow waters and route those waters to an approved destination. High -Risk Site: A site with characteristics and /or activities that have the potential to generate pollutants that may not be addressed solely through the stormwater quality facilities presented in Chapter 2.0. High -risk site characteristics and activities are listed in Chapter 4 - Source Controls. Impervious Surface /Area: Any surface area that causes water to run off the surface in greater quantities or at an increased rate of flow from conditions pre- existing to development. Types of impervious surface include, but are not limited to, rooftops, asphalt and concrete parking lots, driveways, roads, sidewalks, and pedestrian plazas. Note: Slatted . decks are considered pervious. Gravel surfaces are considered pervious unless they cover impervious surfaces or are compacted to a degree that causes their runoff coefficient to exceed 0.8. Impervious Area Reduction Technique: Implementation of a facility used to intercept rainfall that would otherwise be impervious, such as a roof or sidewalk. Such facilities include pervious pavement, eco- roofs, contained planters, and tree credit trees. Stormwater Management Manual 1 -8 Eugene 2014