Stormwater Management Program

Water Quality and Stormwater

The City Streets and Storm Division is committed to providing a safe and reliable road system throughout Snoqualmie in addition to a well-functioning storm drainage system. The division provides services such as street sweeping, mowing, sign repair, pavement markings, storm drain cleaning, and snowplowing along with pavement overlays, storm drainage construction, and street reconstruction.

NPDES II Municipal Stormwater Permit

As authorized by the Clean Water Act, the National Pollutant Discharge Elimination System (NPDES) permit program controls water pollution by regulating point sources that discharge pollutants into waters of the United States.

The City of Snoqualmie is covered under the NPDES Phase II Western Washington Municipal Stormwater Permit issued by the Washington State Department of Ecology on August 1, 2012 and modified January 16, 2015. The permit outlines actions Snoqualmie must take to minimize stormwater pollutants.

The NPDES permit requires the City of Snoqualmie to document a Stormwater Management Program (SWMP) outlining the stormwater program activities the City intends to implement during the upcoming year. The SWMP specifically addresses the permit requirements of:

  • Public involvement and participation.
  • Illicit discharge detection and elimination.
  • Controlling stormwater run-off from construction sites.
  • Operations and maintenance of stormwater facilities after construction.

The NPDES permit also requires the City to submit an annual report each spring summarizing the City's stormwater program activities completed over the previous year. The annual report and the Stormwater Management Plan are updated annually and posted on the City's website.

Washington DOE Submission Cover Letter

Water Quality Program Permit Submittal Electronic Certification (Copy of Record)

Written Description of Internal Coordination Mechanisms

Stormwater Management Program (SWMP) 2016 Activities Plan

Construction & Stormwater

Stormwater Standards, General Overview (white paper link)

2011 Snoqualmie Addendum to the 2009 KCSWDM

Ordinance No. 1081, NEW Surface and Stormwater Code

Ordinance No. 1082, NEW Clearing and Grading Code

Soil BPM Manual

Model Soil Management Plan (from Soil BPM Manual)

BioRetention Soil Mix

Stormwater System O&M Manual

Construction Stormwater General Perfmit NOI

Industrial Stormwater General Permit NOI

Stormwater Manual

All new development and redevelopment will need to follow new stormwater standards from the 2011 City of Snoqualmie Addendum to the 2009 King County Surface Water Design Manual. This update includes terminology, code, and drainage review guidance, as well as revised water quality, flow control, temporary erosion and sediment control (TESC), and other requirements. Construction and development parties are responsible for determining whether a Construction or Industrial NOI is required from Ecology – please see the NOI links at right on the City main stormwater page.

Water Quality

The Snoqualmie Addendum lists various amendments to the 2009 King County Surface Water Design Manual regarding water quality. The addendum:

  • Excludes Core Requirements and, Downstream Water Quality Problems Requiring Special Attention, and Downstream Water Quality Mitigations, respectively.
  • Modifies Basic Water Quality Treatment Areas for consistency with the 2005 Ecology Stormwater Management Manual for Western Washington (2005 SWMMWW).
  • Notes that requirements for Sensitive Lake and Sphagnum Bog Water Quality Treatment Areas are applied on a case-by-case basis.

The City will accept all water quality treatment facility-types identified in the 2005 SWMMWW, though emerging technologies are considered on a case-by-case basis provided the product has received a level of use designation from the WA Ecology TAPE program.

 Stormwater Flow Control

Flow control amendments are listed that provide consistency with the 2005 Ecology Stormwater Management Manual for Western. For instance:

 Thresholds are listed for Basic Flow Control Exemptions, Impervious Surface Exemption for Transportation Redevelopment Projects, and the cost exemption for Parcel Redevelopment Projects that are consistent with the 2005 SWMMWW.

  • For Area-Specific Flow Control Facilities, the Impervious Surface Percentage Exemption on page 1-38 is not allowed in order to maintain equivalency with the 2005 SWMMWW.
  • For Sizing Credits for use for Flow Control BMPs, various suitable alternative manuals are listed for compliance.
  • For Flow Control designs, the Addendum notes that the minimum allowable orifice diameter is increased from 0.25 to 0.5 for detention facilities, Control Structures, and in applying design criteria.
  • Refer to the 2011 Addendum for more specific information.

TESC: Temporary Erosion and Sediment Control

A Temporary Erosion and Sediment Control (TESC) plan is required for all land disturbing activities requiring a clearing and grading permit, per SMC 15.20.070 as approved in Ordinance 1082. Exempt activities that do not require a clearing and grading permit still require the use of best management practices to control erosion and sedimentation that may result from such activities.

 Amended Soil (BMP T5.13, 2005 Ecology Stormwater Management Manual for Western Washington) is required for all landscaped areas on all project sites 1 acre or larger. Amended soil is recommended for all landscaped areas on project sites smaller than 1 acre; the default BioRetention Soil Mix linked in the reference documents is recommended, though not required.

Note: A separate Department of Ecology Construction Stormwater General Permit is required for sites having 1 acre or more of disturbed area.

Modeling and Monitoring

For projects that clear 2,000ft2 or greater, the City may require the ESC Supervisor to have a turbidity meter on-site. In addition to HSPF and KCRTS the Western Washington Hydrology Model is also an acceptable tool for continuous hydrology modeling.

Drainage Review Cost Estimate

The Figure 11 flow chart in the 2011 City of Snoqualmie Addendum will help determine which of the following four drainage review types a project must meet:

1. Small Project Drainage Review          (e.g. individual lot)

2. Targeted Drainage Review                 (includes 3 different categories)

3. Full Drainage Review

4. Large Project Drainage Review          (e.g. Master Drainage Plan)

Drainage plan review costs vary depending on project size, submittal quality (i.e. package completeness, clear TIR figures and writing, etc.), the number of re‐submittals, the analyses types included in the submittal, general project complexity, sensitive area proximity, and other factors.  Accurate drainage review pricing is not possible prior to seeing an applicant’s submittal; the provided estimates are only to help provide some budgeting benchmark, and are not guarantees against additional resources needed for drainage review completion and plan approval.

The “typical cost” and “range of costs” in the below table are based on past reviews of that type within the City. The Full Drainage Review Project category has been split into the sub‐categories “Not Snoqualmie Ridge Infill Development” and “Snoqualmie Ridge Infill Development.”

 Table 1: Typical Costs and Cost Ranges for Drainage Review Types 

Drainage Review Type

Typical Cost ($)

Range of Costs ($)

1. Small Project Drainage Review


$800 – $3,000

2. Targeted  Drainage Review


$1,000 – $5,000

3.a. Full Drainage Review

 (Not Snoqualmie Ridge Infill Development1)


$1,200 – $20,000

3.a. Full Drainage Review

 (Snoqualmie Ridge Infill Development1)


$800 – $3,000

4. Large Project Drainage Review



1 Project Infill developments are those for which flow control has been provided by others via the community Master Drainage Plan.


Other Requirements


All projects must comply with applicable municipal codes, notably 15.18 Surface & Storm water and 15.20 Clearing and Grading code changes as approved in Ordinances 1081 & 1082, as well as the 2011 City of Snoqualmie Addendum. 

  • For maintenance and operations, applicable KCSWDM procedures should be used for guidance, but City specific requirements may be applied on a case by case basis.
  • In addition to the KCSWDM requirements under Core Requirement #7, there are specific City requirements for financial guarantees and liability noted in SMC 15.16.170.