Low impact development standards that reduce water quality impacts, reduce stormwater runoff, reduce impervious surfaces, and preserve open space shall be integrated in the project design to the full extent practical. The following minimum low impact development (LID) standards shall be incorporated where appropriate into the MDP handbook that shall accompany all master development plan applications.

(Ord. 01-08 (part), 2008).

The MDP shall, to the extent practical, incorporate reduced roadway widths to the minimum amount of impervious surface necessary, while still accommodating emergency vehicle access, and utilizing pervious pavements where most applicable. (Note: Existing applicable county road standards, Chapter 16.48, shall apply except as modified below.)

(1)

Lane widths for access streets, secondary collectors within an MDP of a maximum of ten feet for each traveled way, with a minimum two-foot wide gravel shoulders on both sides.

(2)

Curbs and gutters are discouraged for use as stormwater collection systems in conjunction with catch basins and pipes on major collection and arterial roads. Vegetated swales can replace curb and gutter systems that convey runoff.

(3)

Example road sections appropriate for use in an MDP are shown in "Low Impact Development, Technical Guidance Manual for Puget Sound" January 2005. The director of public works may allow the use of an equivalent manual for LID techniques.

(Ord. 01-08 (part), 2008).

(a)

Paving surfaces for LID road designs may utilize alternative paving surfaces, such as porous pavement, porous concrete, grid or lattice rigid plastic or paving blocks where the holes are filled with soil, sand, or gravel, and cast-in-place paver systems. However, use of porous surfaces within the traveled lane areas is not allowed. Porous paving surfaces adjacent to the traveled lane (e.g., in pull out parking, shoulders, sidewalks, trails or for pathways) is allowed provided the subgrade of the traveled lane will not become saturated by infiltrating runoff through the porous surfaces.

(b)

Cement/concrete pavement strips (two-foot wide strips of concrete that act as a transition between the traveled lane and non-rigid porous pavement surfaces or shoulders adjacent to the traveled way) may be utilized to delineate the traveled lane areas. These delineator strips may be included as a portion of the traveled way and shall be at least six inches thick with expansion joints every ten feet.

(Ord. 01-08 (part), 2008).

(a)

Any parking lot space above the required minimum amount shall be constructed of pervious materials or accommodated in a multi-storied or underground parking structure.

(b)

On-Street Parking.

(1)

The use of roadside parking can reduce the need for wide or long private driveways to accommodate additional vehicles or guest parking. The minimum width of the guest on-street parking stall shall be seven feet for parallel parking stalls, and eight and one-half feet for angled parking stalls.

(2)

On-street parking may either be parallel or angled to the roadway.

(Ord. 01-08 (part), 2008).

(a)

Alleys may be constructed with alternative paving surfaces, such as porous pavement, porous concrete, grid or lattice rigid plastic or paving blocks where the holes are filled with soil, sand or gravel and cast-in-place paver systems. These porous surfaces shall be designed to accommodate pedestrian, bicycle, truck, and auto traffic while allowing infiltration and storage of stormwater.

(Ord. 01-08 (part), 2008).

The following are methods to reduce the amount of impervious surface associated with driveways and enhance the neighborhood character:

(1)

Residential driveways may be constructed using alternative paving surfaces and graded in such a manner to prevent stormwater runoff from saturating the subgrade of the traveled lane portion of the roadway. Infiltrated stormwater runoff should drain either to a rain garden, vegetated open channel, or vertically in adequately porous soils. Alternative paving surfaces include porous pavement, porous concrete, grid or lattice rigid plastic or paving blocks where the holes are filled with soil, sand or gravel and cast-in-place paver systems. Design, installation and maintenance of alternative paving surfaces shall be according to manufacturer recommendations.

(2)

When driveways serving single-family residential uses that exceed eighteen feet of width shall be constructed with a pervious material.

(3)

Runoff from driveways constructed of impervious surfaces should be directed to vegetated infiltration areas such as soil-amended lawns, rain gardens, or bioretention areas, if practical.

(Ord. 01-08 (part), 2008).

Promote the use of curbs when the sidewalk is adjacent and connected to the traveled way provided they are used only on one side of the road and the road cross slope is away from the curb or if curb cuts are utilized, as shown in the standard drawings, and drain to a vegetated open channel or bioretention area behind the curb.

(Ord. 01-08 (part), 2008).

Sidewalks and trails may be constructed of porous materials provided the runoff through the material will not be directed towards the subgrade of the traveled lane portion of a roadway. Porous materials for sidewalks and trails, which abut lots, in lieu of a roadside sidewalk, shall be ADA compliant. Porous asphalt and porous concrete will be considered ADA compliant in regards to surface texture.

(Ord. 01-08 (part), 2008).

(a)

To the extent practical, implement LID site design and management strategies to meet flow control objectives identified in the Department of Ecology Stormwater Management Manual for Western Washington. Table I identifies approved LID techniques recommended for implementation in the site design for MDP and FCC's. Please refer to Low Impact Development Technical Guidance Manual for Puget Sound, January 2005, for further details on implementation. The director of public works may allow the use of an equivalent manual for LID techniques.

(b)

Distributed and Integrated Management Practices.

(1)

Increase reliability of the stormwater management system by providing multiple or redundant LID flow control practices.

(2)

Integrate LID stormwater controls into the development design and utilize the controls as amenities — create a multifunctional landscape.

Table I. LID Techniques

(Ord. 01-08 (part), 2008).

The use of LID techniques such as bioretention areas should be implemented and to the extent practical integrated with other LID practices to achieve best performance.

(Ord. 01-08 (part), 2008).