Environmentally Critical Areas

Peat Settlement-Prone Areas

Peat deposits are highly compressible and are prone to settlement when compacted by new structures and fill or when the groundwater table is lowered. Settlement activity can result in serious damage to buildings, roads, sidewalks and utilities.  Peat Settlement-prone areas are specifically defined in 25.09.020. 

The intent of the Peat Settlement-prone Area regulations is to to protect public safety and property by requiring new development in these areas to be safely constructed and to avoid negative impacts on adjacent properties.

Related Codes

• Seattle Municipal Code 25.09 Regulations for Environmentally Critical Areas
  • 25.09.020 ECA Definitions
  • 25.09.110 Peat Settlement-prone Areas.

Related CAMs  

• CAM 325, Environmentally Critical Areas: Peat Deposits
• CAM 327A, Environmentally Critical Areas Exemptions, Relief from Prohibition on Steep Slope Development, and Modifications to Submittal Requirements — Application Instructions and Submittal Requirements
• CAM 327B, Environmentally Critical Areas — Small Project Waivers Application Instructions and Submittal Requirements
• CAM 328, ECA Exceptions

Related Director's Rules

• DR 3-93, General Duties and Responsibilities of Geotechnical Engineers
• DR 13-2008, Requirements for Measuring the Annual High Static Groundwater Level
• DR 14-2008, Infiltration Facilities in Peat Settlement-prone Areas

Mapping

• Peat Settlement-prone Areas Detail Maps (September 2007): These 26 maps delineate the extent of regulated areas at a detailed scale.
  
  (NOTE: Parcels greater than 50,000 square feet may request a parcel-specific delineation of the peat settlement-prone area boundary on the parcel. Consequently, the regulated area on these parcels may be smaller than noted on the detail maps.)
  • Map A1: Greenwood
  • Map A2: Licton Springs/Northgate
  • Map A3: Lake City
  • Map A4: Dahl Playfield and Surroundings
  • Map A5: Matthew's Beach
  • Map A6: Warren G. Magnuson Park
  • Map A7: I-5 and 50th Street NE
  • Map A8: North Union Bay/University
  • Map A9: Portage Bay
  • Map A10: South Union Bay/Arboretum
  • Map A11: South Lake Union
  • Map A12: Madison Valley
  • Map A13: Pioneer Square
  • Map A14: I-90 Bend
  • Map A15: Alki
  • Map A16: SW Manning Street and 35th Avenue SW
  • Map A17: South Beacon Hill
  • Map A18: Colman Park
  • Map A19: Genesee Park
  • Map A20: West Seattle Junction
  • Map A21: Lakewood/Seward Park
  • Map A22: MLK Jr Way S and S Graham Street
  • Map A23: S Myrtle Street and Beacon Ave South
  • Map A24: Westwood/Roxhill
  • Map A25: South Park
  • Map A26: Rainier Beach

Background Documents

• Peat Settlement-prone Areas City-wide Map (Dec. 2009): This map delineates the extent of regulated areas at a city-wide scale.
• Best Available Science Report (August 2007): This report details the Best Available Science on settlement of peat deposits used to inform this proposal.
• Director’s Report (August 2007): This report provides description and analysis of the ECA proposal.
• Adopted Peat Settlement-prone Area Ordinance (July 2008) Ordinance implementing Peat Settlement-prone area legislation.
• Greenwood Subsurface Characterization Study (April 2004): This study was commissioned by Seattle Public Utilities to determine the geologic and hydrologic conditions that existed in Greenwood in order to address settlement issues occurring in the neighborhood.