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Most King County offices will be closed on Thursday and Friday, Nov. 22-23, 2018, for the Thanksgiving holiday.  
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DPER inspection staff are available to answer questions about erosion and sediment control and wet season stabilization measures for permitted activities in unincorporated King County. For more information, please contact customer service at 206-296-6600.

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To request this information in alternate formats for people with disabilities, call 206-296-6600 or TTY Relay: 711.

Worksite sketch

Packet provided by the DPER Permit Center by calling customer service at 206-296-6600.

Every year at the end of the "wet season" contractors may ask the question, "Do I need to install erosion measures (ESC) anymore?" The answer to this question is "YES."

The King County Surface Water Design Manual (KCSWDM) designates the wet season to be October 1 to April 30. For more information, please refer to:

The manual's requirements for erosion control are essentially the same all year round. The only difference is the time frame in which exposed areas are to be covered during wet to dry seasons.

Instead of covering exposed areas if not being worked within two (2) days, the time frame is extended to seven (7) days during the dry season. However, if work on these exposed areas stops, contractors are still required to cover them within 12 hours. All other ESC requirements remain the same.

Project sites greater than one (1) acre in size must obtain an NPDES construction permit from DOE. See .

It should be mentioned that an inspector may extend or shorten this time frame, based on soils, slope, proximity to critical areas, and the seven (7) day weather forecast. While some sites may need little protection during a dry week in August, it is still possible to have a site that is required to be covered at the end of each work day, based on the criteria stated above.

While we recognize it is important to accomplish as much building progress as possible during the summer months, the developer/contractor must remember that controlling erosion and keeping dirt, mud, and sediment-laden water on the construction site remains their responsibility year round.

Experience has shown us that rain events during the spring and summer months can create significant erosion problems if the proper Best Management Practices (BMPs) are not in place. These problems may lead to habitat damage, fines and/or more costly work stoppage delays until the problems are resolved.

Each fall DPER publishes information on erosion control requirements in unincorporated King County. This information has been compiled and provided to inform the building industry of current regulations, practices and restrictions during the coming wet season.

With the listing of the Chinook Salmon and the Bull Trout onto the federal Endangered Species List, erosion and sediment control (ESC) is critical. As part of the County's pro-active approach to the ESA listings, staff at DPER will perform enhanced erosion and sediment control site inspections for permitted activities. These staff will also address code violations on non-permitted sites relating to the protection of listed species.

In addition to providing revised and updated information of BMPs for residential and small construction sites, we would like to clarify code restrictions on clearing and grading work at sites. Section 16.82.095 of the King County Code states no clearing or grading can occur between October 1 and April 30 unless specific conditions have been met. These include development of a wet season erosion control plan that conforms to the requirements in the KCSWDM and approval from DPER.

In these areas after October 1st, clearing and grading work can occur only if

  • the site has 100% infiltration (no water leaves the site) OR
  • the applicant writes, submits, and obtains approval of a 'winterization' plan from DDES.

A 'winterization' plan should contain these elements:

  • Where - A plan that shows areas work is to be performed (Enhanced Erosion Control Plan)
  • How - A description of techniques to mitigate erosion to be used, construction schedule and/or sequencing
  • Who - A 24 hour contact person's phone number (person shall have demonstrated ability in Erosion Control).

BMPs must be fully implemented and maintained at the site.

In summary, for construction sites in those areas listed above, no tree can be cut, groundcover removed, dirt moved, or utility trench dug between October 1 and April 30 without first meeting these requirements. For all other areas after October 1st, construction sites are required to meet an enhanced standard of erosion control as outlined in the Surface Water Drainage Manual.

Erosion control BMPs and literature explaining the steps homebuilders must take are being attached to every building permit issued by DPER. These materials include:

DPER has abatement procedures in place for applicants that do not comply with the above requirements. Failure to control site erosion may result in a Correction Notice requiring immediate attention.

DPER field staff have been instructed to issue 'Notices' if they find mud at a building site with the potential of being deposited off-site or tracked onto roadways. These offenses will not get a 'verbal warning'.

If a builder fails to take immediate action to control the problem, DPER has contractors on-call to address the situation. The applicant also will be billed for this abatement work at the DPER standard hourly rate. Ultimately, the enforcement action may require the contractor to discontinue any further clearing or grading, except for erosion and sediment control maintenance and repair, until the end of the wet season.

We hope that builders and contractors working in King County share DPER' commitment to an effective erosion and sediment control program to protect our streams, lakes, wetlands and the aquatic species that inhabit them.

Additional technical assistance for erosion control on project sites is available. DPER inspection staff are available to offer suggestions to help you stay in compliance with County Code and permit conditions. At the same time, it is your responsibility to implement and maintain controls on the job site. We look forward to working with our customers to meet this goal.