Drainage Report.pdf8498 Talbot Road
Edmonds, WA 98026
CSP Engineering PFN 16-002
City of Edmonds
January 26, 2017
ov�
L7
1037 NE 65h St # 153
Seattle, WA 9811 S
Phone., 206 406 9965
email@cspengineering.com
www.c-spengineering.com
Project Overview
One single family residence is proposed in conjunction with a 2 lot short plat of a 0.92 acre Site Parcel situated in the
Perrinville Creek Drainage Basin/Puget Sound Watershed. Impervious and permeable hardscape surface for the built -
out project is estimated to be less than 5,000 sf and will be comprised of NPGIS roof area, PGIS driveway asphalt
pavement, PGPS driveway permeable pavement, and NPGIS walkway. The proposed improvements will disturb —0.25
acres. Soils are classified as Alderwood-Urban Land Complex (USDA Web Soil Survey). The project is not anticipated to
create greater than 5,000 sf of impervious surface and will disturb less than 1.0 acre in land and is therefore classified
as a Category 2 Small Site Project.
Small Site Minimum Requirement #1— Preparation of Stormwater Site Plan
This final version of this report combined with the final Stormwater & Grading/Construction SWPP Plans will address
this requirement.
Small Site Minimum Requirement #2—Construction Stormwater Pollution Prevention Plan
This final version of this report combined with the final Stormwater & Grading/Construction SWPP Plans will address
this requirement.
Small Site Minimum Requirement #3 — Source Control of Pollution
Specific source controls are not required for single family residential sites.
Small Site Minimum Requirement #4 — Preservation of Natural Drainage Systems and Outfalls
The proposed development preserves the natural drainage systems and outfalls.
Small Site Minimum Requirement #5 — Onsite Stormwater Management
Onsite stormwater management BMPs will be implemented to the maximum extend feasible through the use of
permeable pavement, infiltration trenches, and the implementation of BMP T5.13 post -construction soil amendment
Infiltration tests will be performed in conjunction with the single family residential permit to determine suitability of
permeable pavements and infiltration facilities.
Small Site Minimum Requirement #6 — Runoff Treatment
The total new pollution -generating impervious surface (PGIS) is anticipated to be less than 5,000 sf and pollution -
generating pervious surfaces (PGPS) less than three-quarters (3/4) of an acre therefore stormwater treatment facilities
are not applicable.
Small Site Minimum Requirement #T — Flow Control
Stormwater flow control will be accomplished by utilizing residential onsite detention/infiltration facilities and
permeable pavement. Pavement widening along Frederick Place will be incorporated into and accounted for in the
future single family residence detention/infiltration facility. Soils infiltration tests will be performed in conjunction with
the single family residential permit to verify suitability of onsite infiltration.
Small Site Minimum Requirement #8— Wetland Protection
No wetlands are known to be located within Y mile of the subject site.
Small Site Minimum Requirement #9 — Operation and Maintenance
Operation and maintenance will be performed by the homeowner as directed by the engineer of record upon
completion of the project.
Small Site Minimum Requirement #10 — Offsite Analysis and Mitigation
The proposed single family residence is not anticipated to generate peak 100 year flows in exceedance of 0.10 ds
therefore impacts to the downstream system are not anticipated.
Small Site Minimum Requirement #11— Financial Liability
The site in not known to be located within a Critical Area triggering the requirement of a performance bond.
Appendix
168th 51 5k
1 In = 2,000 ft
Vicinity/Basin Map
0 1,000 2,000 4,000 8,000 8,000
Feel,
sols Map
Slope Map
b
97- 5034" N
szw.UFNM
Soil Map --Snohomish County Area, Washington
54wo 5%M 54M sow
MapSmle: 1:2,230 if printed on A porb-&t (8.5'x 11") dwet-
N60 :='11-1-71-1-1-1 ===1111=1 MEtM
12D 180
0 IUD 200 40D 600
Map —Pro edion: Web`P�Ley��Comer coordamtes; WGSB4 Edge txs: UTM Zone 10N WGS84
USD,% Natural Resources Web Soil Survey
Conservation Service National Cooperative Soil Survey