HomeMy WebLinkAboutAppendix B18.30.070 Stormwater management standards.
All new development and redevelopment must conform to the standards and minimum requirements
set by the most current version of the Washington Department of Ecology Stormwater Management
Manual for Western Washington (SMM) and obtain a stormwater management permit if required by
subsection (5) of this section. The administrator may require additional measures as indicated by the
environmental review or other site plan review.
(1) Definitions. For the purposes of this section, the definitions at Section I-2.3 of the SMM shall
apply:
(a) “New development” includes land-disturbing activities, including Class IV general forest
practices that are conversions from timber land to other uses; structural development, including
construction or installation of a building or other structure; creation of impervious 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.
(b) “Redevelopment” includes, on a site that is already substantially developed (i.e., has 35
percent or more of existing impervious surface coverage), the creation or addition of impervious
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 impervious surface that is not part of a routine maintenance activity;
and land-disturbing activities.
(c) “Impervious surface” means a hard surface area that either prevents or retards the entry of
water into the soil mantle as under natural conditions prior to development, a hard 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
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.
(d) “Land-disturbing activity” is any activity that results in movement of earth, or a change in the
existing soil cover (both vegetative and nonvegetative) and/or the existing soil topography. Land-
disturbing activities include, but are not limited to, clearing, grading, filling, and excavation.
The Jefferson County Code is current through Ordinance 5-17, passed December 18, 2017.
Jefferson County Code 18.30.070 Stormwater management standards.Page 1 of 4
01/09/2018 | Page 1 of 4
Compaction that is associated with stabilization of structures and road construction shall also be
considered a land-disturbing activity. Vegetation maintenance practices are not considered land-
disturbing activity.
(2) Exemptions. Commercial agriculture, road maintenance activities, and forest practices regulated
under WAC Title 222, except for Class IV general forest practices and COHPs (see JCC 18.20.160),
pursuant to SMM Section I-2.2, are exempt from the provisions of the minimum requirements.
(3) Development and Redevelopment Minimum Requirements. Development and redevelopment
meeting the criteria of subsection (1)(a) of this section shall be required to control erosion and
sediment during construction and to permanently stabilize soil exposed during construction. Such
development shall:
(a) Comply with the minimum requirements for development of small parcels in Section I-2.5 of
the SMM;
(b) Applicants for all development and redevelopment meeting the criteria for subsection (1)(a) of
this section, except for detached single-family residences and duplexes creating or adding less
than 2,000 square feet and land-disturbing activities of less than 7,000 square feet, shall prepare
a stormwater site plan (or show on other diagrams being prepared for the project, if appropriate)
showing:
(i) Vicinity map;
(ii) Location of the structure and its access;
(iii) All applicable setback requirements;
(iv) Location of all applicable erosion and sediment control BMPs; and
(v) Existing site features and sensitive areas.
(4) New Development Minimum Requirements.
(a) All new development and redevelopment shall be required to comply with Minimum
Requirement No. 2 (Construction Stormwater Pollution Prevention) as contained in the SMM.
(b) New development that includes: (i) the creation or addition of 2,000 square feet, or greater, of
new, replaced, or new plus replaced impervious surface area; or (ii) has land-disturbing activities
of 7,000 square feet or greater shall comply with Minimum Requirements Nos. 1 through 5 as
contained in the SMM.
(c) New development that includes: (i) the creation or addition of 5,000 or more square feet of
The Jefferson County Code is current through Ordinance 5-17, passed December 18, 2017.
Jefferson County Code 18.30.070 Stormwater management standards.Page 2 of 4
01/09/2018 | Page 2 of 4
impervious surface; or (ii) converts three-quarters acre, or more, of native vegetation to lawn or
landscaped areas; or (iii) converts 2.5 acres, or more, of native vegetation to pasture shall
comply with Minimum Requirements Nos. 1 through 10 as contained in the SMM.
(d) Redevelopment that includes: (i) new, replaced, or total of new plus replaced impervious
surface of 2,000 square feet or more; or (ii) 7,000 square feet or more of land-disturbing activity
shall comply with Minimum Requirements Nos. 1 through 5 as contained in the SMM.
(e) Stormwater Site Plan. Stormwater site plans shall be developed to the standards of Volume I,
Chapter 3 of the SMM, and include:
(i) Project overview;
(ii) Plot plan, including the elements of subsection (3)(b) of this section;
(iii) Locations of structures and other impervious surfaces;
(iv) Locations of stormwater runoff treatment and flow control facilities;
(v) Road rights-of-way and easements;
(vi) Preliminary conditions summary;
(vii) Analysis of off-site water quality impacts (including groundwater) resulting from the
project, and mitigation measures;
(viii) Analysis and design of proposed stormwater runoff control facilities, including flow
control, treatment, and source control BMPs (cf. Volume I, Section I-4 of the SMM, which
provides a list of and selection process for BMPs);
(ix) Construction stormwater pollution prevention plan;
(x) Special reports and studies;
(xi) Stormwater and drainage system maintenance specifications.
(f) Commercial and industrial developments, subdivisions or other projects requiring stormwater
management facilities including collection, conveyance, treatment, detention, and infiltration
facilities shall enter into a stormwater management facility maintenance agreement with
Jefferson County to operate and maintain the facilities as per the approved plans. The public
works department will prepare the agreement after approval of the project stormwater site plan
and submit it to the applicant. The applicant shall file the agreement with the Jefferson County
auditor prior to final project approval by Jefferson County.
The Jefferson County Code is current through Ordinance 5-17, passed December 18, 2017.
Jefferson County Code 18.30.070 Stormwater management standards.Page 3 of 4
01/09/2018 | Page 3 of 4
(5) Stormwater Management Permit and Plan Review. All grading of 500 cubic yards or more (not
exempted under subsection (5)(b) of this section), land-disturbing activities of 7,000 square feet or
more, or creation of 2,000 square feet or more of impervious surface shall be subject to a stormwater
management permit. Prior to issuance of a stormwater management permit, the applicant shall submit
the required stormwater management plans to the administrator for review and approval. The
administrator shall issue the stormwater management permit consistent with a Type I permit process
(as specified in Chapter 18.40 JCC) only upon a finding that the proposed use or activity meets all
applicable requirements of JCC 18.30.060 and this section, and any other applicable requirements of
this code.
(a) Applications for grading projects or land-disturbing activities which require a stormwater
management permit shall include the following information. The administrator may waive specific
submittal requirements determined to be unnecessary for review of the application.
(i) Source of fill material and deposition of excess material;
(ii) Physical characteristics of fill material;
(iii) Proposed methods of placement and compaction consistent with the applicable
standards in of the International Building Code;
(iv) Proposed surfacing material;
(v) Proposed method(s) of drainage and erosion control;
(vi) Methods for restoration of the site;
(vii) Demonstration that in-stream flow of water will remain unobstructed;
(viii) Demonstration that erosion and sedimentation from outflow channels will be minimized
by vegetation or other means; and
(ix) Demonstration that pond runoff will be controlled to protect adjacent property from
damage. [Ord. 8-06 § 1]
The Jefferson County Code is current through Ordinance 5-17, passed December 18, 2017.
Jefferson County Code 18.30.070 Stormwater management standards.Page 4 of 4
01/09/2018 | Page 4 of 4