Environment & Sustainability | Environmentally Critical Areas
area to risk of landslide or erosion and that the purpose of the no-disturbance area is not compromised in any way; 2) The development activities shall be mitigated, monitored and bonded consistent with the mitigation requirements applicable to environmentally critical areas; 3) The development activities are limited to the minimal area and duration necessary for construction; and 4) The development activities are consistent with this chapter. ii. New single-family home construction or modifications or additions to existing single-family homes on existing legal lots that will result in a total site impervious surface of more than 2,000 square feet shall provide a drainage design, using the following sequential measures, which appear in order of preference: a) Infiltration of all site runoff shall be required to the maximum extent technically feasible in existing soil conditions, consistent with the infiltration system design requirements of the KCSWDM; b) Development proposals that meet the goals of low impact development, as follows: 1) Sixty-five percent of the site shall remain as open space.
2) No more than 10 percent of the gross site area may be covered with impervious surface. 3) The development proposal’s storm water system shall limit storm water discharge volumes to match the average annual volume discharged from the predeveloped forested site conditions as determined using a calibrated continuous simulation hydrologic model based on the EPA’s HSPF program or an approved equivalent model. The City may modify these requirements based upon site- specific analysis of the feasibility of required improvements, standards and specifications. Such analysis shall include evaluation of site and vicinity soils, hydrology, and other factors, as determined by the City, affecting the successful design of the storm water or low impact development improvements. The City shall consider purpose, effectiveness, engineering feasibility, commercial availability of technology, best management practices, safety and cost of the proposal when evaluating a waiver or modification request. The applicant shall bear the burden of proof that a waiver or modification is warranted; c) For development proposals that cannot infiltrate all site runoff, the applicant shall design a drainage system that provides a drainage outlet designed using the best available science techniques in addition to the applicable flow control and water quality treatment standards
82 | Title 21: Sammamish Development Code
Effective | January 1, 2022
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