Drainage & Land Disturbing Activity

(Projects vested September 30, 2010 through January 21, 2016)


Snohomish County maintains regulations that govern land disturbing activities (SCC 30.63B), drainage (SCC 30.63A), and low impact development (SCC 30.63C), in accordance with State policy. The current set of regulations became effective on September 30, 2010. All projects vested on or after this date are subject to these codes.

The term "land disturbing activity” is broadly defined by Snohomish County as any activity that will result in movement of earth or a change in the existing soil cover or the existing soil topography. This includes to soils that are vegetative and non-vegetative by nature. Land disturbing activities often result in the creation and replacement of impervious surfaces (broadly interpreted to be any hard surface that prevents or retards water penetration of the soil) as well as the grading and clearing of land.

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 permits, stormwater site plans, and stormwater pollution prevention plans. Please plan accordingly to ensure a quality application submittal and a timely permitting process. 

Key Codes and Manuals
Chapter 30.63A SCC: DrainageChapter 30.63B SCC: Land Disturbing ActivityChapter 30.63C SCC: Low Impact DevelopmentSnohomish County Drainage ManualEngineering and Design Standards (EDDS), and Appendix B: Stormwater Facility Landscaping.

Submittal. Any drainage and land disturbing activity permits may be submitted in conjunction with residential building permit applications on a first-come first-serve basis in our office. Standalone submittals or in conjunction with complex commercial building permits and/or land use applications are submitted by appointment only.

Applicants may request an appointment to submit a pre-application and hold a consultation meeting for Pre-Application.

Fees. Applicants can estimate fees for SWPPPs and LDAs using the County's online fee code or bulletin. Separate fees are issued for stormwater modifications, waivers, and reconsideration.

Minimum Requirements and Plans
The Drainage and Land Disturbing Activity codes enumerate specific triggers, thresholds, and exemptions for project compliance with regulations. For the convenience of prospective applicants, these are generally described in the sections below. However, it is important understand the relationship between Minimum Requirements, stormwater pollution prevention plans (SWPPPs), and stormwater site plans. Projects that are required to comply with drainage regulations must meet standards set by the Snohomish County Drainage Manual.

Minimum Requirements. The Drainage code consists of nine Minimum Requirements (MRs). Not all project types must show compliance with each of the nine MRs, except for Minimum Requirement 2 (MR 2). MR 2 consists of the Stormwater Pollution Prevention Plan (SWPPP).

Stormwater Pollution Prevention Plans (SWPPPs). All new development and redevelopment subject to Drainage code regulations and permitting must provide a Stormwater Pollution Prevention Plan (SWPPP) in order to comply with Minimum Requirement 2 (MR 2). The purpose of a SWPPP is to show that a project will control soil erosion, sedimentation, and runoff during all phases of construction. A SWPPP addresses 12 different elements (e.g. planned techniques for flow control, soil stabilization, and controlling pollutants) by describing if the elements apply and how they will be carried out. Best Management Practices that are planned to be implemented through the project are graphically depicted on a site plan. A SWPPP is not required if an activity is specifically exempted by the Drainage code (see SCC 30.63A.200). 

All projects must comply with Minimum Requirement 2 of the Drainage code, but may additionally be subject to the other Minimum Requirements in code. Snohomish County has created three separate processes for permitting these activities: one for small projects and two for projects of larger scale. Small projects generally only need to comply with Minimum Requirement 2 of the Drainage code by providing a Small Project Stormwater Pollution Prevention Plan (Small Project SWPPP). Larger projects must comply with both the Drainage and Land Disturbing Activity codes by demonstrating how they meet Minimum Requirements 1 through 5 or Minimum Requirements 1 through 9 depending upon the scale of the proposal.

Stormwater Site Plans. A stormwater site plan is a comprehensive report containing all technical information and analysis necessary to evaluate a proposed development or redevelopment. The stormwater site plan shows compliance with the County's stormwater regulations and includes drainage reports, plans, designs, and calculation (if necessary).

Triggers and Thresholds for Review
Small Projects. Small projects may be required to submit a Small Project Stormwater Pollution Prevention Plan (SWPPP) as part of a building permit application to control onsite drainage. SWPPPs cover project types that propose to:

  • Create and/or replace less than 2,000 square feet of impervious surfaces;
  • Clear less than 7,000 square feet; and/or
  • Move less that 100 cubic yards of material graded onsite or 500 cubic yards of material under the foundation of building; and
  • The land is less than one acre in size. 

Generally, a SWPPP is required if the project is proposed on a property where no previous approval was granted for an onsite drainage plan or other small development projects. Small Project SWPPPs may be non-engineered and prepared by the applicant (SCC 30.63A.810).

Small Project SWPPPs are very common review items for residential and small scale commercial projects. The County requires submittal of a Small Project SWPPP narrative and site plan that addresses all 12 elements of MR 2. A variety of best management practices (BMPs) can be implemented to meet each of the SWPPP elements. A helpful guide shows what these BMPs look like in the field, but there also some important BMP Do's and Don'ts to take note of.

Land Disturbing Activity Permit. Projects that exceed the scale and quality of the SWPPP process likely fall into the category of a Land Disturbing Activity (LDA) Permit. LDA permits can be issued standalone, as part of a land use entitlement, or in conjunction with a building permit. LDA permits are triggered if a project will:

  • Result in or add 2,000 square feet or greater of new, replaced, or new plus replaced impervious surface area (per SCC 30.63A.300 and SCC 30.63A.310);
  • Cause land disturbing activity including clearing of 7,000 square feet or greater (per SCC 30.63A.300 and SCC 30.63A.310); or
  • Does not meet the grading exemptions in SCC 30.63B.070 will require a land disturbing activity permit.

Although, 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 otherwise exempt by code. Certain exempt projects must also comply with the 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.

All new development and redevelopment applications subject to an LDA permit must provide a stormwater site plan unless a particular activity is exempt from Minimum Requirement 2 (SCC 30.63A.200). When a stormwater site plan is required, elements of the SWPPP must be incorporated into the stormwater site plan. 

Targeted Stormwater Site Plan. Minimum Requirements 1 through 5 must be met by a project proposal subject to the Targeted Stormwater Site Plan (refer to SCC 30.63A.400 through 30.63A.605 for requirements). Applicants must ensure that their site plan conforms to the standards of the Targeted Stormwater Site Plan Submittal Checklistwhich shall be submitted with the Land Disturbing Activity Permit Application / Checklist. A Targeted Stormwater Site Plan is required when a project will:

  • Create new and replaced impervious surfaces;
  • Result in or add 2,000 square feet or more of new, replaced, or new plus replaced impervious surface area; or
  • Cause a land disturbing activity of 7,000 square feet or more.

Full Stormwater Site Plan. Minimum Requirements 1 through 9 must be met by a project proposal subject to the Full Stormwater Site Plan (refer to SCC 30.63A.400 through 30.63A.605 for requirements). Applicants must ensure that their site plan conforms to the standards of the Construction / Full Stormwater Site Plan Submittal Checklist and Construction / Full Stormwater Site Plan SWPPP Checklist, which shall be submitted with the Land Disturbing Activity Permit Application / Checklist. A Full Stormwater Site Plan is required when a project will:

  • Result in or add 5,000 square feet or more of new impervious surface area;
  • Convert 0.75 acres or more of native vegetation to lawn or landscaped areas; or
  • Convert 2.5 acres or more of native vegetation to pasture.
Waivers, Modifications, and Deviations
Applicants may request relief from strict standards of the County's drainage and land disturbing activity codes. Modifications and waivers may be permitted for SCC 30.63A (Drainage), SCC 30.63B (Land Disturbing Activities), EDDS Chapter 5, the Snohomish County Drainage Manual, and checklist item noted for submittal pertaining to SCC 30.63A and SCC 30.63B. Applicants may also seek modifications and deviations when proposing low impact development governed by SCC 30.63C.

Applications and FormsModification or Waiver Request FormEDDS Deviations, and Reconsideration Request Form.

Stormwater Facility Easements
Should a project necessitate recordation of a stormwater facility easement against the subject property, it is incumbent upon the applicant to prepare an agreement that grants Snohomish County an easement to stormwater facilities. The County has an approved version of the agreement for use by applicants. Applicants should insert appropriate information and details as noted in the Stormwater Facility Easement form. 

An appointment must be made with a member of staff to process the stormwater facility easement. The project manager should be able to direct applicants to the appropriate staff member to intake the easement agreement. Any questions regarding the process and review of Stormwater Facility Easements may be submitted to said staff member.

Forms and Checklists
Stormwater Facility Easement Form (Word Document) and Stormwater Facility Easement Submittal Checklist.

Additional Resources
Special Forms and ChecklistsDrainage Review Submittal Checklist and FormNotice of Intent Application Form for Construction Stormwater General Permit and Record Drawing (As-Builts) Checklist.

Manuals. Snohomish County Drainage Manual Appendix I-A (Low Impact Development Best Management Practices), Snohomish County Drainage Manual Appendix I-DWashington State Department of Transportation Highway Runoff Manual, and Washington State Department of Transportation Hydraulics Manual.

Assistance BulletinsDrainage Review (Bulletin 89), Forest Practices: Clearing and Drainage Review (Bulletin 97), Land Disturbing Activity Terms (Bulletin 85), Land Disturbing Activity Permit Exemptions (Bulletin 86), Land Disturbing Activity Emergency Actions (Bulletin 88), Low Impact Development (Bulletin 22), and Preparing a Small Project Stormwater Pollution Prevention Plan (SWPPP) (Bulletin 91).

Soil Amendments (Minimum Requirement 5). Post Construction Standard (Bulletin 94), Compost and Topsoil Calculation Worksheet, Soil Management Plan Summary Form, Notice of Soil Amendment Inspection Procedures, and Soil Testing Laboratories.

Runoff Treatment Requirements (Minimum Requirement 6)Strahler Stream ADT fourth and fifth Order Stream Crossing MapStrahler Stream Order Spreadsheet, and Threshold Discharge Area (SCC Figure 30.91T.054B).