Drainage and Land Disturbing Activity
For projects vested on or after September 30, 2010:
What stormwater management forms do I need?
What are the resources for developing a site plan?
Washington Stormwater Center: Assistance, Research and Training
NPDES Public Outreach - Technical Assistance Workshop Series
New drainage review / land disturbing activity exemptions and thresholds
Due to NPDES Permit requirements adopted in the new stormwater regulations, applicants for projects that meet or exceed new development and redevelopment thresholds will likely need to obtain professional assistance in preparing land disturbing activity, stormwater site and stormwater pollution prevention plans. Please plan accordingly to ensure a quality application submittal and a timely permitting process.
General Exemptions and General Threshold Overview
For exempt activities see SCC 30.63A.200 and 30.63B.070
For drainage review thresholds see SCC 30.63A300 and SCC 30.63A310
General Threshold Overview
Projects that result in or add 2,000 square feet or greater of new, replaced or new plus replaced impervious surface area; or cause land disturbing activity including clearing of 7,000 square feet or greater or those that do not meet the grading exemptions in SCC 30.63B.070 will require a land disturbing activity permit.
Lower thresholds may apply and trigger an LDA permit if a proposal is located within a critical area, critical area buffer and/or setback (except floodplains and aquifer recharge areas of low to moderate sensitivity to groundwater contamination).
Drainage review is required for all new development and redevelopment unless exempt. Certain exempt projects must also comply with Minimum Requirement 2 Stormwater Pollution Prevention Plan (SCC 30.63A.445 through 30.63A.510) to control soil erosion and sedimentation and to manage the project.
Stormwater Pollution Prevention Plans (MR 2)
All new development and redevelopment shall submit a Stormwater Pollution Prevention Plan (SWPPP) to comply with Minimum Requirement (MR) 2 and to control soil erosion and sedimentation unless MR 2 is not required for an exempt activity pursuant (see SCC 30.63A.200). When a stormwater site plan is required, the SWPPP is one component of the stormwater site plan. Applicants with small projects (SCC 30.63A.810) may submit an abbreviated non-engineered SWPPP.
Stormwater Site Plans
A stormwater site plan is the comprehensive report containing all of the technical information and analysis necessary for the evaluation of a proposed new development or redevelopment project’s compliance with the county’s stormwater regulations and which includes drainage reports, plans, designs and when applicable, calculations, prepared by the applicant to comply with minimum requirements. A stormwater pollution prevention plan (SWPPP) is a component of a stormwater site plan when a stormwater site plan is required, or may be required to control erosion and sediment when no stormwater site plan is triggered.
Targeted Stormwater Site Plan (MRs 1-5 - SCC 30.63A.400 through 30.63A.605)
A targeted stormwater site plan is required when new and replaced impervious surfaces and/or the land disturbed will result in or add 2,000 square feet or greater of new, replaced or new plus replaced impervious surface area; or cause land disturbing activity of 7,000 square feet or greater.
Full Stormwater Site Plan (MRs 1-9 in SCC 30.63A.400 - 30.63A.605)
A full stormwater site plan is required if the new impervious surfaces and converted pervious surfaces if the new development will:
- Result in or add 5,000 square feet or more of new impervious surface area;
- Convert three-quarters of an acre or more of native vegetation to lawn or landscaped areas; or
- Convert 2.5 acres or more of native vegetation to pasture.
Redevelopment Projects (SCC 30.63A.310) that also require Full Stormwater Site Plan
If runoff from the replaced and new impervious surfaces (including pavement, shoulders, curbs and sidewalks) shall meet minimum requirements 1 through 9 (SCC 30.63A.400 through 30.63A.605) if the new impervious surfaces total 5,000 square feet or more and total 50 percent or more of the existing impervious surfaces within the project limits. The project limits shall be defined by the length of the project and the width of the right-of-way.
All redevelopment projects, except road-related projects covered by SCC 30.63A.310(5), shall comply with minimum requirements 1 through 9 (SCC 30.63A.400 through 30.63A.605) for the new plus replaced impervious surfaces when:
- The total of the new plus replaced impervious surfaces totals 5,000 square feet or more; and
- The value of proposed improvements including interior improvements exceeds 50 percent of the assessed value of the existing site improvements.
Waivers, Modifications, Deviations (SCC 30.63A.170)
Requests for modifications or waivers from the requirements of chapters 30.63A and 30.63B SCC, the Drainage Manual, and chapter 5 of the EDDS and any submittal checklist item pertaining to the requirements of chapters 30.63A and 30.63B SCC shall be processed under SCC 30.63A.830 through SCC 30.63A.842. Requests for modifications of certain chapters of Title 30 SCC to facilitate low impact development are regulated by chapter 30.63C SCC.
Forms, Checklists, Applications and Resources
Permit application submittals are by appointment only. Schedule online or by calling (425) 388-3311, ext. 2790.
Regulations and Standards
SCC Chapter 30.63A Drainage
SCC Chapter 30.63B Land Disturbing Activity
SCC Chapter 30.63C Low Impact Development
Snohomish County Drainage Manual
Engineering and Design Standards (EDDS)
Appendix B, Stormwater Facility Landscaping
New Stormwater Regulations FAQ, Bulletin #95
Exemption Consultation Form
Critical Area Regulations: 30.63A, 30.63B, and 30.62C
Channel Migration Zone Maps
Land Disturbing Activity
Land Disturbing Activity Terms, Bulletin #85
Land Disturbing Activity Permit Exemptions, Bulletin #86
Land Disturbing Activity Emergency Actions, Bulletin #87
LDA Application cover sheet
LDA Application and Submittal Requirements
Exemption Consultation Form
Cross section example
Vegetative Maintenance Rule 3046
Drainage Review, Bulletin #89
Drainage Review Submittal Checklist and Form
Snohomish County Drainage Manual Appendix I-A
(Low Impact Development Best Management Practices)
Snohomish County Drainage Manual Appendix I-D
(Wetlands and Stormwater Management)
Other Drainage Review Links
Drainage Needs Report and Maps
Stormwater Facility Easement (Commercial)
Stormwater Facility Easement Submittal Checklist
Wash. State Dept. of Transportation Highway Runoff Manual
Wash. State Dept of Transportation Hydraulics Manual
Impaired Waters: 303-d List
Notice of Intent Application Form for Construction Stormwater General Permit
Forest Practices – Clearing and Drainage Review, Bulletin #97
Low Impact Development
Low Impact Development, Bulletin #22
Record Drawing (As-Builts) Checklist
Soil Amendments (Chapter 30.63A SCC Minimum Requirement 5)
Achieving the Post Construction Standard, Bulletin #94 (Minimum Requirement #5)
Compost and Topsoil Calculation Worksheet
Soil Management Plan Summary Form
Notice of Soil Amendment Inspection Procedures
Soil Testing Laboratories
Stormwater Site Plans For Projects Vested on or after September 30, 2010
Targeted Stormwater Site Plan Submittal Checklist
Construction / Full Stormwater Site Plan Submittal Checklist
Stormwater Pollution Prevention Plan (SWPPP)
(Stand alone or part of a stormwater site plan when one is required)
Construction/Full (SWPPP) Submittal Checklist and Instructions (SCC 30.63A.445 - SCC 30.63A.510)
Stormwater Pollution Prevention for Small Projects, Bulletin #90
Small Project SWPPP
Preparing a Small Project Stormwater Pollution Prevention Plan (SWPPP) Bulletin # 91
Best Management Practices for Small Project SWPPPS, Bulletin #92
Best Management Practices for Small Project SWPPPs, Illustrated Guide
Small Project SWPPP Narrative and Plan Submittal
SWPPP BMPS – Do’s and Don’ts
Snohomish County Drainage Manual Appendix I-F
Strahler Streams Crossing Map (30.63A.530 - MR 6 Runoff treatment requirements)
Strahler Stream ADT 4th and 5th Order Stream Crossing Map
Strahler Stream Order Spreadsheet
Threshold Discharge Area Graphic (30.63A.530 - MR 6 Runoff treatment requirements)
Threshold Discharge Area (SCC Figure 30.91T.054B)
Stormwater Regulation/Rule Waivers and Modifications
Modification or Waiver Request Form
EDDS Deviations (SCC 30.63A.170)
Reconsideration Request Form
Outside Agency Requirements (applicant’s responsibility)
Snohomish Health District
Washington Dept. of Fish and Wildlife - HPA permits
Federal Army Corp of Engineers
Washington State Department of Transportation
General Questions - AskPermitTech
For all other inquiries, please call or visit the Customer Permitting Center.
Comments or suggestions about this web page?
Complete and submit the appropriate checklist; incomplete submittals may be rejected.