City of Redmond requirements have been updated to complement the 2005 Department of Ecology Stormwater Management Manual for Western Washington (2005 Ecology Manual). References have been updated to reflect that the City’s stormwater code was moved from Redmond Community Development Guide (RCDG) 20E.90 to Redmond Municipal Code (RMC) 15.24.

The Stormwater Notebook has been reorganized and a detailed table of contents has been added to make things easier to find. There are numerous changes throughout the document, to improve consistency and readability.

Key changes in organization include:

• Eliminated “Part” organization.
• New Chapter 1, Introduction added.
• Old Chapter 1 is new Chapter 2.
• Old Chapter 2 is consolidated into new Chapter 8.
• Old Chapter 3 remains as new Chapter 3.
• Old Chapter 4 remains as new Chapter 4.
• Old Chapter 5 and 6 combined as new Chapter 5.
• Old Chapters 7, 8, 9, and 10 combined as new Chapter 6.
• Old Chapter 11 is new Chapter 7.
• Old Chapter 12 is consolidated into new Chapter 8.
• Old Chapters 13 and 14 is new Chapter 9.
• Old Chapter 15 is new Chapter 10.
• Appendices reorganized.

Permitting

• Threshold Discharge Areas, as used in the Ecology Manual are now accepted in Redmond (Chapter 2).
• Project classification information is updated along with descriptions of the permit process for small, medium, and large projects (Chapters 3, 4, 5, and 6).
• Guidance regarding other associated permits is expanded (Chapter 1).
• Drainage report outline is included (Chapter 2).
• Plan review checklist is updated (Appendix F).
• Project submittal data for stormwater facilities is updated (Chapter 6).

Low Impact Development (LID)

• Low Impact Development is encouraged and accommodated. LID BMPs approved in the Ecology Manual are permitted in Redmond under suitable site conditions. New section on LID in Redmond is added (Chapter 8).
• Ecology Manual guidance for modeling low impact development is used.
• Use Redmond-specific guidance for modeling compost-amended soil (Chapter 2).
• Apply maintenance standards for low impact development (Appendix P).
• Follow guidance for use of compost-amended soil (Appendix Q).
• For additional information on LID or to download of copy of the LID Technical Guidance Manual for Puget Sound, visit the Puget Sound Action Team website.

Wellhead Protection

• Infiltration of clean water is encouraged in Redmond (Chapter 2). 
• Infiltration of stormwater is encouraged (with treatment) in Wellhead Protection Zone 4, but is restricted in Wellhead Protection Zones 1, 2, and 3 (Chapter 2).
• Infiltration from pollution generating impervious surfaces (PGIS) following enhanced treatment is permitted in Wellhead Protection Zone 3 (Chapter 2).
• Infiltration from non-pollution generating impervious surfaces that are demonstrated to be clean, is permitted in Wellhead Protection Zones 1, 2, and 3 (Chapter 2).
• To make site design without infiltration from PGIS feasible, in Wellhead Protection Zones 1, 2, or 3, outwash soils may be considered to be till for the purpose of detention pond sizing (Chapter 2).

Stormwater Flow Control

• Modified flow control standard allows some sites that discharge to stormwater pipes that drain directly to the river or lake to release the 50-year developed peak at the 10-year developed peak (Chapter 2).
• In Wellhead Protection Zones 1, 2, or 3, outwash soils may be considered to be till for the purpose of detention pond sizing (Chapter 2).
• Direct discharge conveyance capacity requirement reduced from 100-year to 50-year storm (Chapter 2).
• Projects with less than 0.1 cfs increase of the 100-year flood frequency may be exempt from flow control (Chapter 2).
• Contribution in lieu of detention is updated to reflect new City program for Regional Facilities (Chapter 8).
• Map of historical land cover is added (Appendix N).

Stormwater Quality Treatment

• Emerging technologies may be considered for use in Redmond (Chapter 2).
• Biofiltration swale design was changed in the Ecology Manual to be more like the 1992 manual’s design standard (Chapter 2).
• Contribution in lieu of stormwater quality treatment is updated to reflect new City program for Regional Facilities (Chapter 8).
• Water quality facility types permitted in Ecology manual are allowed in Redmond, although some are preferred over others (Chapter 2).

Regional Facilities Plan

• The City has identified proposed locations for many new regional stormwater facilities that will be designed to meet the flow control or stormwater quality requirements of new development throughout the City (Chapter 8).
• Contribution toward construction of regional flow control or stormwater quality treatment facilities is mandatory in regional surcharge areas and optional in watersheds where proposed regional facilities have been identified. The project proponent is responsible for preparing a Contribution in Lieu proposal that evaluates potential impacts from the project (Chapter 8).
• Fee in lieu of compensatory flood storage has been removed from the Notebook.

Stormwater Conveyance and Facility Specifications

• PVC, ductile iron, or fusion-welded HDPE pipe are preferred for stormwater conveyance systems (Chapter 8).
• Freeboard standards for conveyance design updated (Chapter 8).
• Manhole spacing updated (Chapter 8).
• Catch basin and area drain maximum depths specified (Chapter 8).
• Vertical clearance from utilities updated (Chapter 8).
• Shear gates are now permitted (Chapter 2).
• Stormwater ponds shall be signed (Chapter 2).
• Installation of groundwater monitoring wells shall be coordinated with the City’s wellhead protection program (Chapter 2).
• Guidance for pumping stormwater added (Chapter 8).
• Stormwater pipe inspection protocol requires enhanced inspection of all new pipe (Appendix R).

Temporary Erosion and Sedimentation Control

• Reference Ecology manual for guidance (Chapter 9).
• Added reference to NPDES permit for construction stormwater discharge (Chapter 9).
• No changes to Rainy Season Guidelines (Chapter 10).