City of Everett Public Works
Small Project Stormwater Site Plan Report-Dec 2019 22
Land Disturbing Activity Any activity that results in a change in the existing soil cover (both vegetative and
non-vegetative) and/or the existing soil topography. Land disturbing activities
include, but are not limited to clearing, grading, filling, and excavation. Compaction
that is associated with stabilization of structures and road construction shall also
be considered a land disturbing activity. Vegetation maintenance practices,
including landscape maintenance and gardening, are not considered land-disturbing
activity. Stormwater facility maintenance is not considered land disturbing activity
if conducted according to established standards and procedures.
New development Land disturbing activities, including Class IV-general forest practices that are
conversions from timberland to other uses; structural development, including
construction or installation of a building or other structure; creation of hard
surfaces; and subdivision, short subdivision and binding site plans, as defined and
applied in Chapter 58.17 RCW. Projects meeting the definition of redevelopment
shall not be considered new development.
New Impervious Surface A surface that is:
changed from a pervious surface to an impervious surface (e.g.
resurfacing by upgrading from dirt to gravel, asphalt, or concrete), or
upgraded from gravel to asphalt or concrete, or
upgraded from a bituminous surface treatment (“chip seal”) to asphalt or
Pervious Surface A surface material that allows stormwater to infiltrate into the ground. Examples
include lawn, landscape, pasture, native vegetation areas, and permeable
Rain Garden A non-engineered shallow landscaped depression, with compost-amended native
soils and adapted plants. The depression is designed to pond and temporarily store
stormwater runoff from adjacent areas, and to allow stormwater to pass through the
amended soil profile. See BMP T5.14: Rain Gardens.
Redevelopment On a site that is already substantially developed (i.e., has 35% or more of existing
hard surface coverage), the creation or addition of hard surfaces; the expansion of
a building footprint or addition or replacement of a structure; structural development
including construction, installation or expansion of a building or other structure;
replacement of hard surface that is not part of a routine maintenance activity; and
land disturbing activities.
Replaced Hard Surface For structures, the removal and replacement of hard surfaces down to the
foundation. For other hard surfaces, the removal down to bare soil or base course
Sheet flow Runoff that flows over the ground surface as a thin, even layer, not concentrated in
Manual for Western
Prepared by Ecology, contains BMPs to prevent, control or treat pollution in
stormwater and reduce other stormwater-related impacts to waters of the State.
The SWMMWW is intended to provide guidance on measures necessary in western
Washington to control the quantity and quality of stormwater runoff from new
development and redevelopment.