Sammamish Unified Development Code

Low Impact Development | Environment & Sustainability

b) Projects that create greater than one acre of pollution generating pervious surface, as defined in the adopted surface water design manual and SDC 21.03.050, Surface Water Management, in the Beaver Lake or Pine Lake watersheds. ii. The proposed storm water facilities shall be designed to remove 80 percent of all new total phosphorus loading on an annual basis due to new development (and associated storm water discharges) in the Beaver Lake or Pine Lake watersheds where feasible or utilize AKART if infeasible. iii. The AKART standard or best management practices for phosphorus-sensitive lakes can be fulfilled by achieving the 50 percent phosphorous removal standard from the adopted surface water design manual and SDC 21.03.050, Surface Water Management, together with additional applicant proposed measures: a) For all development proposals subject to this section, the applicant shall demonstrate that a reduction of 80 percent total phosphorous is achievable through the use of engineering design computations. b) As the adopted King County surface water design manual is updated and additional treatment options and designs for total phosphorus removal become available, new treatment systems may be approved by the City if the AKART standard for phosphorus removal can be demonstrated using the Department of Ecology’s

Technology Assessment Protocol – Ecology (TAPE protocol).

c) Where soils are suitable, on-site infiltration of storm water runoff can be pursued through the variance process as an AKART alternative using methods described in the manual, as well as providing an organic soil layer consistent with the standards of the adopted surface water design manual and SDC 21.03.050, Surface Water Management. d) Development proposals using on-site infiltration that do not comply with shall demonstrate that 80 percent, or better, phosphorus treatment can be expected with the designed on-site infiltration system, rather than by methods described in subsection 6.c.iii. of this section.

iv. Hydrologic analysis shall be determined using a continuous hydrologic model such as the

Hydrologic Simulation Program – Fortran (HSPF) or the King County runoff time series program (KCRTS) methodology. These methodologies may be revised or superseded by other methodologies for achieving the same performance goal as stipulated by future revision to the surface water design manual.

21.03.030 Low Impact Development A. Intent and goals

Low impact development (LID) is an approach to land use planning and project design that seeks to:

Effective | January 1, 2022

Title 21: Sammamish Development Code | 123

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