HomeMy WebLinkAboutPN_Narrative_180315_v1SAZEI Design Group, LLC
6608 110th Ave. N. E. Te l: (425) 214-2280
Kirkland, WA. 98033
Avon Development, Inc.
1011 North 37th Street
Renton, Washington 98056
PROJECT NARRATIVE
Prepared For:
Avon Development
2-Lot Short Plat
1909 NE 14th Street
Renton, Washington
Prepared BY:
SAZEI Design Group, LLC
6608 110th Ave NE, Kirkland, WA 98033
January 16, 2018
The proposed project is the construction of a 2-lot short plat. The site is located 1909 NE 14th
Street, Renton WA. More generally the site is located within SE ¼ of of the SE ¼ of Section 05,
Township 23 North, Range 05 East, W.M., see below: Vicinity Map. The site is bordered by
residential lots on the south, east, and west sides of the site.
Site Existing Conditions:
The site is 11,960 sf and contains an existing home, driveway, patio and walkway and landscaping
with a total existing impervious area of 4,254 sf. The lot slopes from north-east to south-west
with all runoff leaving the site along the south-west property line. There are no known sensitive
areas on site. The soils report prepared for the site show the site soils to be till and not suitable
for infiltration. Please refer to Figure below: Existing Conditions Map..
Developed Site Conditions:
The project will consist of construction of a 2-lot short plat with two single family dwellings and
driveways. Half Street frontage improvements in the form of curbs, gutters, sidewalks and
landscape strip will be required on NE 14th Street. Please refer to Figure Below: Developed
Conditions Map
The total proposed impervious area is 7,412 sf as follows:
th ST: 1,248 sf (Pavement: 728 sf (7’x104’) S-walk: 520 sf)
Total Area – Replaced Area = 7,412 sf - 4,254 sf = 3,158 sf of new impervious area.
Under Section 1.1.2.1 “Small Site Drainage Review” “Threshold” 1st Paragraph, since project is
under 10,000 sf of total impervious area after January 8, 2001 and under the 5,000 sf of NEW
impervious area, it is exempt from detention and therefore qualifies for Small Site Drainage
Review.
However, since the site is proposing a new storm pipe a “Targeted Drainage Report” is required
per Table 1.1.2.A.
The project will use the Design Requirement’s under “Appendix C” of the 2017 City of Renton
Surface Water Design Manaul.
Project proposes two dwelling units
as allowed and demonstrated below:
Project General Information, and Zoning data
Project Cost:
Project total estimated construction cost will be $485,000 for
each house including the site development expenditures.
Existing trees:
There are “NO” trees on site.
Land Dedication to the
City:
6.5 feet of the lot along NE 14th street
will be dedicated to the City for
construction of the frontage
improvements and pedestrian.
On-site temporary structures:
There will be NO job shacks, sales trailers, and/or model
homes on site during or after completion of the construction.
Site Drainage Assessment & Design requirements:
The City of Renton has adopted the City of Renton 2017 storm
water manual which governs the design of stormwater systems
to serve this project. The Core and Special Requirements are
being met in the following manner:
City of Renton 2017 storm water manual Core
Requirements:
1. Discharge at the Natural Location
Under 1.2.1-2, The surveyed contours show all runoff leaves
the site towards the south-west. The drainage design proposes
to use BMP’s to address the runoff with the flow leaving the site
along the south-west side maintaining the natural discharge
location.
2. Off-site Analysis
The Level 1 downstream analysis showed that there will be
minimal impacts on the downstream conditions, since the site
proposes to use small site BMP’s to address all stormwater
runoff.
3. Flow Control
The site is exempt from flow control and will provide BMP’s as
outlined in Appendix C Small Site Drainage requirements.
4. Conveyance System
A new 12-inch storm pipe is required on the frontage
improvements on NE 14th Street. The flow is minimal since it
only picks up 106 feet of the roadway and the on -site
improvements .
5. Temporary Erosion & Sediment Control
All TESC measures proposed will conform to the 2009
KCSWDM during construction, Refer to Section 9 of this TIR for
additional information. The measures shown on the TESC plans
include: Clearing limits, sediment control, soil stabilization,
BMP’s maintenance and construction sequence
6. Maintenance & Operations
Maintenance and Operations manual has been provided. Note
that a “Declaration of Covenant” may be required. See Section
10.
7. Financial Guarantees & Liability
A completed bond quantity worksheet is not required
8. Water Quality
Since new pollution generating impervious surface is less than
5,000 sf, water quality is not required. Refer to Section 4 of this
report.
Total Area – Replaced Area = 7,412 sf - 4,254 sf = 3,158 sf of
new impervious area.
Under Section 1.1.2.1 “Small Site Drainage Review”
“Threshold” 1st Paragraph, since project is under 10,000 sf of
total impervious area after January 8, 2001 and under the 5,000
sf of NEW impervious area, it is exempt from detention and
therefore qualifies for Small Site Drainage Review.
However, since the site is proposing a new storm pipe a
“Targeted Drainage Report” is required per Table 1.1.2.A.
The project will use the Design Requirement’s under “Appendix
C” of the 2017 City of Renton Surface Water Design Manual.
Specifically, Section C.1.3.2 for small lots under 22,000 s f
City of Renton 2017 storm water manual Special
Requirements:
1. Other Adopted Area-Specific Requirements
There are no area-specific requirements for this project site.
2. Floodplain/Floodway Delineation
A review of the FEMA FIRM panels for the site, shows that the
site and area of work is outside any floodplain areas and site
does not contain any floodplain/floodway delineations.
3. Flood Protection Facilities
There are no flood protection facilities located on or directly
adjacent to the site.
4. Source Control
This final site does not meet the threshold for source control
requirements.
5. Oil Control
This final site does not meet the threshold for oil control
requirements.
Per Appendix C Section C.1.3.1, the following BMP’s were
reviewed and analyzed for use:
Full Infiltration: The soils were found to not be suitable for
infiltration.
Limited Infiltration: The soils were found to not be suitable
for infiltration.
Rain Gardens: Not feasible due to site constraints and with
NO safe overflow path (overflow would be onto adjacent
properties.)
Bioretention: Not feasible due to site constraints and with
NO safe overflow (overflow would be onto adjacent properties)
Permeable Pavement: The soils are not suitable for
infiltration.
Basic Dispersion: (Splash Locks, Rock Pads, Gravel Filled
Trenches, Sheet Flow) Not feasible, the 25-foot flow paths
cannot be met.
Reduced Impervious Surface Credit: The amount of
impervious area is just enough to allow driveway access and
parking.
Native Growth Retention Credit: Not feasible due to the
small area of each lot.
Tree reduction Credit: not feasible, the site has no
significate trees.
Soil Amendment BMP’s: Will be used on site
Perforated Pipe Connection: Will be used.
Due to the site constraints and soils type the only BMP that is
feasible is having all downspouts tied into perforated stub outs
prior to discharging into the street’s storm drain system
The project will use the BMP’s as outlined in the Small Site
Drainage Design under “Appendix C” of the City of Renton 2017
storm water manual. Specifically, Section C.1.3.2 for small lots
under 22,000 sf
Since the total driveway PGIS area is under 5,000 sf, water
quality treatment is not required.
Water Quality Exemption
Since the total PGIS surface is 1,322 sf and under the 5,000 sf
threshold, the site is exempt from water quality
Project Construction Stormwater Pollution
Prevention Plan & Design requirements:
ESC Plan Analysis and Design (Part B)
A full SWPP Plan and report will be prepared for the site after preliminary
approval is received.
THE 12 ELEMENTS OF A CONSTRUCTION CSWPPP
1. Preserve Vegetation/Mark Clearing Limits: The clearing limits are
indicated on the plan sheet. Furthermore, clearing and grading will be
limited to only areas that need to be disturbed for grading/construction of
the road surface to preserve as much natural vegetation as possible.
Field marking the clearing limits shall be completed prior to clearing and
grubbing activities.
BMP's: Preserve Natural Vegetation (VEG)
Field Marking Clearing Limits (CL)
2. Establish Construction Access: Access to the construction site shall
be limited to the rock construction entrance. The construction entrance
shall be extended to provide access to the construction
vehicle/equipment staging and employee parking areas.
BMP's: Stabilized Construction Entrance (CE)
3. Control of Flow Rates: Storm water detention: No detention is
proposed for the site since the increase in volume is minimal
4. Installation of Perimeter Sediment Controls: Sediment control will
be provided through a combination of filtration through the surround on-
site vegetation, filter fence, straw bails,
BMP's: Silt Fence (FF)
5. Soils Stabilization: Temporary and permanent soil stabilization will
be provided. Temporary stabilization will be provided through the
application of straw and/or plastic sheeting to exposed, worked earth.
From October 1 until April 30, no exposed soil may remain exposed and
unworked for more than two days; after May 1, no exposed soil may
remain exposed and unworked for more than seven days.
6. Slope Protection: Slopes shall be protected from erosion through
cover and prevention of concentrated surface runoff flows.
BMP's: Plastic Sheeting,
7. Protection of Permanent Drain Inlets and Dust/Mud Control: Inlet
protection will be provided for all catch basins.
BMP’s: Inlet Protection
BMP’s: Street Sweeping and watering of dust areas
8. Stabilization of Channels and Outlets: All channel slopes shall be
constructed and protected against erosion in accordance with City of
Renton
BMP's: None required
9. Pollutant Control: Pollutants shall be controlled as described in the
Potential Pollutants section of this SWPPP.
10. Dewatering Control: De-watering: Interception of the water table is
not expected to occur, even if there is an increase in precipitation.
However, should ground water flows be encountered, the flows can be
directed to on site native vegetation for cleanup.
BMP's: Native vegetation (As Required)
11. BMP Maintenance: All BMP's and SWPPP elements shall be
inspected daily and maintained as required.
12. Project Management: The project shall be managed in a
cooperative effort by the project manager, contractor, engineer, and the
county inspector. During the construction process, if unforeseen issues
arise that cannot be resolved on site, construction activity (other than
SWPPP maintenance) shall be halted and the county inspector and the
project engineer are to be contacted and informed of the situation. The
Erosion Control Lead TBD