16.26.050 Regulations.
It is the intent of this section to promote practices consistent with the City’s natural topographic, vegetation, and hydrologic features, and to control substantial land alterations with associated stormwater impacts in accordance with the following adopted manuals:
A. Adopted Manuals. Design standards contained in the following manuals are adopted by reference:
1. Stormwater Design Manual. Thresholds, definitions, and minimum requirements within Volumes I through V are found in the 2019 Washington State Department of Ecology Stormwater Management Manual for Western Washington. These requirements are based on Appendix 1 of the Western Washington Phase II Municipal Stormwater Permit.
2. City of Issaquah 2022 Addendum. The City of Issaquah 2022 Addendum to the 2019 Washington State Department of Ecology Stormwater Management Manual for Western Washington contains local modifications and application of the definitions, thresholds, and minimum requirements in Issaquah.
B. The design, construction, and maintenance of all clearing, grading, and stormwater management systems and facilities shall comply with the requirements and design standards contained in the following documents:
1. This chapter; and
2. The adopted Stormwater Design Manual and Addendum, and source control BMPs; and
3. Any other applicable construction specifications, design standards and details approved under the authority of the Issaquah Municipal Code as they pertain to permitting, construction, inspection, maintenance, and enforcement of land development activities and facilities.
C. Approval Criteria and Standards. In considering whether to issue a permit, and in considering whether and what type of conditions should be imposed thereon, the Director shall apply the following standards and criteria:
1. Rough Grading. The Director may issue a permit for a rough grading project when all the following criteria are met:
a. All land use permits are issued;
b. Other agency permits are issued, if required (e.g., hydraulic project approval);
c. Site plans including conceptual utility layout are submitted;
d. SEPA review for the entire project is completed (if required);
e. Clearing, grading and temporary erosion control construction plans are submitted;
f. Preliminary stormwater plans including stormwater technical information report with low impact development feasibility assessment are submitted;
g. Resolution of all project feasibility issues (i.e., required off-site easements and improvements, significant utility design issues, etc.) as determined by the Director.
2. Clearing. All clearing of vegetation shall conform to the following criteria, unless such clearing qualifies as an exemption under IMC 16.26.040(B).
a. Existing vegetation shall be preserved, replaced or restored in accordance with the approved landscaping plans and in accordance with Chapter 18.606 or 18.812 IMC, whichever applies.
b. Except where clearing is permitted under IMC 16.26.040(B)(12), Exemptions, no clearing shall be allowed in any protected areas including an environmentally critical area, native growth protection easement, protected trees, greenbelt, open areas, or areas of native vegetation within the development site that are not part of the development proposal, without a permit and such other approvals as may be required by the Issaquah Municipal Code.
c. Prior to any clearing activity and during all construction-related activities, the limits of clearing shall be fenced as follows:
i. Protective fencing with temporary signs shall be installed around all environmentally critical areas (including streams, wetlands, steep slopes and their respective buffers), native growth protection easements (NGPEs), protected trees, greenbelt, areas of native vegetation within the development site that are not part of the development proposal, or other areas of the property or site that are separate from the development proposal and should remain undisturbed as determined by the Director. Design and location of the protective signs shall be approved by the Director.
ii. Protective fencing shall be installed around the critical root zone of all trees to be saved in accordance with the approved tree plan prior to any construction. The fencing location may be changed to the dripline or other location as recommended by a certified arborist and approved by the Director.
iii. For any construction activities permitted within 100 feet of a critical area buffer or protected tree, the applicant may be required to hire an independent qualified professional, acceptable to the Director, to be on site during construction to ensure construction does not exceed the limits indicated on this permit. Following construction activities, a licensed surveyor shall submit an affidavit to the Director attesting that the construction was contained within the approved limits.
d. In no case shall the period between the completion of work authorized under this chapter and final and complete restorative vegetation planting for a given project or project phase be more than one year unless an acceptable assurance device is posted in accordance with IMC 18.206.020. The planting shall restore the vegetation on the site to the new approved plans or, if no new approved plans, then to a condition equal to or better than the pre-cleared condition as determined by the Director. See also subsection (C)(4) of this section.
3. Grading. Changes in the site topography shall conform to the following criteria:
a. Fills, structures, and modifications of stream conveyances within areas of special flood hazard shall conform to Chapter 16.36 IMC.
b. The maximum surface grade on any artificially created slope shall not exceed three feet horizontal run to one foot vertical fall (3H:1V). Cut and fill slopes for roadways may, however, be designed at 2H:1V upon review and approval by the Director provided it meets these criteria:
i. Engineering calculations to that grade show the slope is stable with a 1.5 factor of safety; and
ii. Appropriate vegetation and irrigation are selected and installed in accordance with the recommendations of a qualified professional; and
iii. Maintenance of the slope and vegetation is shown to be safe and accessible for maintenance personnel; and
iv. Other criteria reasonably related to the issue as determined by the Director.
c. The permittee shall at all times protect improvements to adjacent private properties and public rights-of-way or easements from damage during grading operations. The permittee shall restore public improvements damaged by his/her operations to the standards in effect at the time of the issuance of the permit.
d. If construction vehicles will be refueled on a construction site or the quantity of hazardous materials that will be used or stored on the construction site exceeds 20 gallons, exclusive of the quantity of hazardous materials contained in fuel or fluid reservoirs of construction vehicles, persons obtaining construction permits shall:
i. Provide information to the Department regarding the types and quantities of hazardous materials that will be on site; and
ii. Ensure that proper BMPs are used to prevent and respond to spills.
e. An imported fill source statement is required with the permit for all projects where more than 100 cubic yards of fill will be imported to a site. Fill material and soil amendments shall not contain concentrations of contaminants that exceed cleanup standards for soil as specified in the Model Toxics Control Act (MTCA). The City may require analytical results to demonstrate that fill materials do not exceed cleanup standards when conditions are determined to require additional review. The imported fill source statement shall include:
i. Source location of imported fill; and
ii. Previous land uses of the source location.
f. Rockeries. Rockeries are considered an erosion protection method and may be used to protect cut or fill slopes.
i. Rockeries used to protect uncontrolled fill slopes may be no higher than four feet, as measured from the bottom of the base rock.
ii. Rockeries used to protect cut slopes or reinforced or engineered fill slopes may be up to a maximum height of 12 feet, as measured from the bottom of the base rock, with the approval of the Director. Any rockery that is over four feet high, as measured from the bottom of the base rock (cut slopes and reinforced or engineered fill slopes only), shall be designed by a geotechnical engineer.
iii. A wall drain must be provided for all rockeries greater than four feet in height as measured from the bottom of the base rock.
iv. The procedures and requirements in the City of Issaquah Street Standards relating to rockery design and construction must be followed, as well as any land use regulations and approvals.
v. The geotechnical engineer must provide construction monitoring and/or testing as required by the permit conditions, and submit construction inspection reports to the Department for all rockeries that require design by a geotechnical engineer. For each project, or phase of a project, the geotechnical engineer must provide a final letter or report summarizing the results of the construction monitoring for each rockery, verifying that the rockery construction meets the geotechnical recommendations and design guidelines. The final letter or report must be submitted to the Department prior to final inspection.
g. Modular Block Walls and Other Retaining Walls. Modular block walls and other retaining wall structures may be used for erosion protection of cut or fill slopes, and to provide lateral support to vertical slopes of soil. The following pertains to all such retaining wall structures:
i. Wall structures over four feet in height as measured from the bottom of the base block must be engineered and designed by a professional civil or geotechnical engineer.
ii. A wall drain must be provided for all walls greater than four feet in height as measured from the bottom of the base structural element. Weepholes and filter drains may also be required to address drainage and hydrostatic pressure.
iii. All wall structures over four feet in height shall meet the minimum requirements set forth in the latest edition of the International Building Code.
iv. The geotechnical engineer must provide construction monitoring and/or testing as required by the permit conditions, and submit construction inspection reports to the Department for all retaining walls that require design by a geotechnical engineer. For each project, or phase of a project, the geotechnical engineer must provide a final letter or report summarizing the results of the construction monitoring for each wall, verifying that the wall construction meets the geotechnical recommendations and design guidelines. The final letter or report must be submitted to the Department prior to the final inspection.
v. Land use regulations and approvals may also impact wall design.
4. Temporary Erosion and Sediment Control. All land disturbing activities shall make provisions for temporary erosion and sediment control as follows:
a. A temporary erosion and sedimentation control (TESC) plan and associated required documentation shall meet the following requirements:
i. The TESC plan shall be prepared in accordance with, and be based on the best management practices contained in, Minimum Requirement No. 2.
ii. The plan shall clearly indicate the construction sequence for establishment of all erosion control work, both temporary and permanent, for the drier season and wetter winter months.
iii. The plan shall clearly show environmentally critical areas (including streams, wetlands, steep slopes and their respective buffers), native growth protection easements (NGPEs), greenbelt, open areas, or areas of native vegetation within the development site that are not part of the development proposal to be retained, soil preservation areas, and protection of existing trees and root systems during construction.
iv. The TESC plan shall provide a monitoring discharge point to allow turbidity monitoring of water being discharged from the site.
v. For projects other than small sites, as defined in the Stormwater Design Manual, the plan shall be designed by, and carry the seal of, a civil engineer having certified erosion and sediment control lead (CESCL) certification.
vi. Erosion and sedimentation control devices shall be installed prior to initiation of construction activities and maintained by the permittee over the entire duration of the project until all possibility for erosion has passed and permanent vegetation has been established, as determined by the Director.
vii. Clearing and grading may be permitted to continue or to be initiated during the wet season (October 1st through April 30th) only if the Director grants specific approval per subsection (C)(4)(a)(ii) of this section. In determining whether to permit wet season construction, the Director shall consult with DSD engineers and inspectors to determine whether the proposal ensures slope stability and adequately protects receiving waters from increased erosion and sedimentation during construction.
(A) If clearing and grading is prohibited during the wet season, building construction can nonetheless proceed as long as no additional clearing and grading is performed and effective erosion control is in place and effectively maintained.
(B) A wet season TESC plan is required to be submitted to the Development Services Department by September 1st for approval to initiate or continue clearing and grading activity during the upcoming wet season. The Director may grant approval of the wet season TESC plan based on evaluation of site conditions, the nature of the development activity, previous performance of the contractor, and other factors such as slope, soil type, hydrology, and proximity to receiving waters, as well as erosion control measures to prevent turbid runoff from leaving the site during construction.
(C) If wet season clearing and grading is approved by the Director, and the Director subsequently issues a stop work order for insufficient erosion and sedimentation control, the wet season permit for clearing and grading activity may be suspended until the dry season.
(D) When clearing and grading is suspended during the wet season or interrupted at any time of the year due to heavy rain or other reasons, the permittee shall stabilize the site in accordance with the approved TESC plan and maintain erosion control BMPs.
b. The TESC plan shall be designed to prevent, to the maximum extent practicable, the transport of sediment from the site to drainage facilities, surface waters, and adjacent properties. Turbidity in construction runoff at any monitoring point that exceeds 100 nephelometric turbidity units (NTUs) at any time up to the 10-year/24-hour storm event, as measured at the City’s rain gauge, is considered a violation of the permit, subject to stop work and enforcement as described in IMC 16.26.150 and 16.26.190.
c. Updates to the TESC plan can be required at any time during the term of the permit if the approved TESC plan is found to be ineffective or construction sequencing or other changed site conditions make it necessary to modify the original TESC plan to make it compliant with the requirements of the Stormwater Design Manual.
d. Permanent erosion control shall be considered and set forth in the original design of the project to provide erosion control following completion of construction.
e. Vegetation shall be restored on those areas of the site disturbed by the land alteration activity which are not covered by permanent impervious surface improvement (e.g., buildings, parking lots, etc.) within seven days of the completion of grading or clearing, unless seasonal or weather conditions are unfavorable. In this case, temporary erosion control measures shall be installed and maintained until restoration can be completed. The soils shall be stabilized in the area of vegetation restoration prior to that restoration and in compliance with other applicable soil restoration and landscaping requirements for the project.
f. Areas of disturbed soil that include lawn and landscape areas shall meet post-construction soil quality and depth per the Stormwater Design Manual and detailed in IMC 18.606.050, Soil standards.
5. Stormwater Management. All land disturbing activities shall make provisions for drainage and stormwater management facilities as follows:
a. Thresholds. The thresholds for requiring drainage review are contained in the Stormwater Design Manual. The following thresholds invoke drainage review, to determine which specific criteria are triggered for flow control, runoff (water quality) treatment, low impact development, construction stormwater runoff, and other minimum requirements:
i. Land clearing: any clearing not otherwise exempt from IMC 16.26.040(B);
ii. Hard surface area: 2,000 square feet or more of new and replaced hard surface area;
iii. Drainage: addition or modification of a 12-inch or larger diameter pipe.
b. Minimum Requirements. Minimum requirements are contained in the Stormwater Design Manual, as modified by the City of Issaquah Addendum, and include the following elements:
i. Minimum Requirement No. 1: Preparation of Stormwater Site Plan;
ii. Minimum Requirement No. 2: Construction Stormwater Pollution Prevention Plan (SWPPP);
iii. Minimum Requirement No. 3: Source Control of Pollution;
iv. Minimum Requirement No. 4: Preservation of Natural Drainage Systems and Outfalls;
v. Minimum Requirement No. 5: On-Site Stormwater Management;
vi. Minimum Requirement No. 6: Runoff Treatment;
vii. Minimum Requirement No. 7: Flow Control;
viii. Minimum Requirement No. 8: Wetlands Protection;
ix. Minimum Requirement No. 9: Operations and Maintenance.
c. Stormwater Technical Information Report. Minimum Requirement No. 1 requires preparation of a stormwater site plan. The content of this plan is detailed in the Stormwater Design Manual, as modified by the City of Issaquah Addendum, the content of which is dependent on which minimum requirements are triggered. The plan must include the following chapters:
i. Project Overview;
ii. Existing Conditions Summary and Site Analysis;
iii. Off-Site Analysis Report;
iv. Permanent Stormwater Control Plan;
v. Construction Stormwater Pollution Prevention Plan (SWPPP);
vi. Special Reports and Studies;
vii. Other Permits;
viii. Operations and Maintenance Manual;
ix. Declaration of Covenant for Privately Maintained Flow Control and Treatment Facilities;
x. Declaration of Covenant for Privately Maintained On-Site Stormwater Management Facilities;
xi. Bond Quantities Worksheet.
d. Record Drawings. Upon completion of the work, a record drawing stamped by both a registered Washington professional engineer and licensed surveyor of all infrastructure (water, sewer, and stormwater utilities and roads) that will be owned and operated by the City or are connected to the City’s system shall be required. In addition, all private stormwater facilities shall also be shown regardless of ownership. The permit holder shall also provide the City with hard copy of plan sheets, scanned copy of plan sheets, and an AutoCAD drawing file of the as-built conditions in a format determined by the City upon completion of the work. The Director may require additional information in respect to any significant deviations from the approved plans, specifications or reports.
e. Signage. Signs shall be installed at all permanent flow control, runoff treatment, and on-site stormwater management facilities that are required to be maintained, identifying purpose of the facility, owner, and contact phone number for maintenance. The design of the sign shall be approved by the City.
6. Clearing and Grading on Environmentally Critical Lands.
a. Any activity governed by this chapter is prohibited on environmentally critical lands except (i) where clearing and grading is permitted under IMC 16.26.040(B)(12), and (ii) except for activities conducted in connection with the approved use allowed under the Issaquah Land Use Code.
b. Essential public services will be permitted where no feasible alternative exists in which event the development shall be accomplished in a manner which assures the protection and safety of persons and property, public and private.
c. For critical areas as defined in Chapter 18.802 IMC, special, more stringent conditions than otherwise provided for herein may be required by the Permit Director if, in the opinion of the Permit Director for reasons of health and safety, stability or environmental sensitivity, such special conditions are needed to mitigate adverse impacts.
7. Maintenance. It shall be the responsibility of the permittee to maintain all erosion control, stormwater facilities, source control BMPs, and stormwater treatment and flow control BMPs in good operating condition in accordance with the Stormwater Design Manual. The permittee shall clean and repair or replace all erosion control facilities, devices, stormwater facilities, source control BMPs, and stormwater treatment and flow control BMPs as often as necessary and as directed by the Director to maintain their effectiveness and level of performance as provided in IMC 13.28.090. In addition, the permittee shall be responsible for assuring that any such facilities damaged during floods, storms, or other adverse weather conditions are returned to normal operating condition within 24 hours.
a. Prior to issuance of any land disturbing permit, clearing, filling, and grading permit, building permit, or other approval permit that triggers application of this chapter, the Director shall require the applicant to record declaration of covenants and grant of easement as specified in the Stormwater Design Manual. The restrictions set forth in such covenant shall include, but not be limited to, provisions for notice to the persons holding title to the property that maintenance and/or repairs are necessary to the facility and a reasonable time limit in which such work is to be completed.
b. Drainage easements shall be provided in a proposed development for all stormwater conveyance systems that are not located in public rights-of-way or tracts prior to certificate of occupancy. The drainage easements shall be granted to the parties responsible for providing ongoing maintenance of the systems, and the City for inspections and monitoring.
c. Signage shall be required to identify stormwater treatment and flow control BMPs and on-site stormwater management facilities such as permeable pavement, bioretention, or rain gardens, as a designed and maintained stormwater facility. Such signs shall identify the owner of the facility responsible for maintenance, and shall be approved by the Director.
8. Property Posting. The applicant shall post a “Notification of Construction” sign for development; provided, however, that construction activities defined in IMC 18.802.030 are exempt from this requirement. The sign shall be designed in accordance with IMC 18.204.125. (Ord. 3023 § 22 (Exh. A), 2023; Ord. 2989 § 2 (Exh. A2), 2022; Ord. 2783 § 3 (Exh. A3), 2016; Ord. 2746 § 3 (Exh. C), 2015; Ord. 2560 § 3 (Exh. A2), 2009; Ord. 2546 § 6, 2008; Ord. 2500 § 3, 2007; Ord. 2487 § 1, 2007).