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Stormwater
ADOPTED STORMWATER MANUAL
Effective February 15, 2010, permit applications will need to follow new stormwater standards from the 2009 City of Issaquah Addendum to the 2009 King County Surface Water Design Manual (2009 Addendum). This update include revised flow control, temporary erosion and sediment control (TESC), and Stormwater Low Impact Development (LID) requirements.
The 2009 Addendum can be downloaded from the link at the bottom of this page. The 2009 stormwater code that references the adopted manual can also be found there.
Stormwater Flow Control
Most projects must meet the Level 2 flow control standard assuming a historic (forested) pre-development condition. However, sites under 1.0 acre have separate requirements, and other exemptions are available. Please refer to Table 1.1.1.A in the 2009 Addendum (see link at bottom of this page).
Water Quality
Water quality treatment shall be Senstive Lake Protection (i.e., phosphorus control). The City will allow treatment BMPs that are contained any technical manual approved by the Ecology (i.e., King County, Ecology, and WSDOT), and also new BMPs that meet or are being tested under Ecology's Emerging Stormwater Treatment Technologies program.
TESC
See the TESC page for requirements on TESC. These requirements were updated in September, 2009 (see 2009 Stormwater Management Amendments link at the bottom of this page for specific code requirements).
Stormwater Low Impact Development (LID)
In the 2009 Addendumn new stormwater low impact development (LID) requirements will apply in areas of the City that are favorable for infiltration (e.g., outwash and alluvial soils). In those areas stormwater infiltration or LID techniques must be used, unless soil testing data shows the soil is unsuitable. See Special Requirement #6 for details. The City's stormwater code also allows for deviations from standards to allow Low Impact Development designs, such as narrower street widths and use of pervious pavement.
For more information on stormwater standards contact Kerry Ritland, PE, Surface Water Manager.
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