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Drainage Memorandum
To: City of Renton
From: Chris Tebaldi, P.E., Tebaldi Engineering, LLC
Date: February 4, 2023
Re: Gaspaire Single Family Residence
2/4/2023
This project is located in the City of Renton on tax parcel number 0923059101. The project proposes to
construct a new single-family residence on the subject property. The existing topography ranges from
elevation 420 to elevation 415. The site gently slopes from north to south and the slope ranges from 0 to 10
percent. The property is currently vacant.
The proposed development consists of the new impervious surface as indicated below.
The proposed project is subject to the City of Renton stormwater requirements which follow the 2022 City of
Renton Surface Water Design Manual. Per the drainage review requirements flow chart, the project qualifies
for Simplified Drainage Review since it is within the Urban Growth Area on outwash soils with less than 6,872
square feet of target impervious. As the project is on a lot smaller than 22,000 square feet the Small Lot BMP
Requirements apply. The Small Lot BMP Requirements have been summarized below for feasibility:
Full Dispersion: This BMP is infeasible due to lack of available flow path and native vegetation.
Full Infiltration: This BMP is infeasible as the existing soils are not outwash soils.
Area Summary
Predeveloped Developed
Proposed roof 0 SF 1,380 SF
Proposed driveway 0 SF 412 SF
Proposed road 0 SF 1,006 SF
Proposed sidewalk 0 SF 514 SF
Total 0 SF 3,312 SF
DEVELOPMENT ENGINEERING
yqi 07/10/2024
Surface Water Enginering
JFarah 07/11/2024
Limited Infiltration: This BMP is infeasible due to available setbacks not being able to be met between the
proposed rear of house to the rear property line. In addition, the depth to restrictive layers (hardpan) is
located approximately 20-inches below the surface.
Bioretention: This BMP is infeasible due to available setbacks not being able to be met between the
proposed rear of house to the rear property line. In addition, the depth to restrictive layers (hardpan) is
located approximately 20-inches below the surface.
Permeable Pavement: This BMP is infeasible as the area of the proposed driveway has previously been
compacted. In addition, the depth to restrictive layers (hardpan) is located approximately 20-inches below
the surface.
Basic Dispersion: This BMP is feasible and will be utilized for the project.
Reduced Impervious Surface Credit: Not applicable as basic dispersion is proposed.
Soil Amendment: All disturbed soils will be amended in accordance with the City of Renton manual.
Perforated Pipe Connection: Not applicable as all surfaces will utilize basic dispersion.
Based on the above analysis, the BMPs and storm drainage design for the proposed development have been
designed in accordance with the City of Renton requirements. The driveway will be sheetflow dispersed to
the west to the natural discharge location. The rooftop will be discharged onto downspout splashblocks with
50-foot vegetated flowpaths.
The proposed development will not have an adverse impact on downstream properties.
Soil Map—King County Area, Washington
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/6/2023
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562762 562767 562772 562777 562782 562787 562792
47° 29' 32'' N 122° 10' 0'' W47° 29' 32'' N122° 9' 58'' W47° 29' 30'' N
122° 10' 0'' W47° 29' 30'' N
122° 9' 58'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 10 20 40 60
Feet
0 3 6 12 18
Meters
Map Scale: 1:220 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: King County Area, Washington
Survey Area Data: Version 18, Sep 8, 2022
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 31, 2022—Aug 8,
2022
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—King County Area, Washington
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/6/2023
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Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
AgC Alderwood gravelly sandy
loam, 8 to 15 percent slopes
0.1 51.4%
AmC Arents, Alderwood material, 6
to 15 percent slopes
0.1 48.6%
Totals for Area of Interest 0.2 100.0%
Soil Map—King County Area, Washington
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/6/2023
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