HomeMy WebLinkAboutRS_TIR_171221_v1DECCIO Engineering Inc.
17217 7th Avenue W.
Bothell, WA. 98012
(206) 390-8374
Fax: (425) 741-8214
Avon 2-Lot Short Plat
# 17------
Drainage Design Report,
O&M Manual & SWPP Report
Property Location:
1909 NE 14th Street
Renton, WA
December 10, 2017
Prepared for:
Avon Development
Deccio Engineering Inc Page i
TABLE OF CONTENTS
SECTION 1 PROJECT OVERVIEW
o Figure 1: TIR Worksheet
o Figure 2: Site Location Map
o Figure 3: Existing Site Conditions
SECTION 2 CONDITIONS & REQUIREMENTS SUMMARY
City of Renton Requirements
SECTION 3 OFF-SITE ANALYSIS
Sensitive Areas Map
Drainage Complaint Map
o Figure 4: Upstream and Downstream Flow Map
o Figure 5: Downstream System Table
SECTION 4 FLOW CONTROL & WATER QUALITY ANALYSIS AND DESIGN
o Figure 6: Soils Logs
o Figure 7: Developed Conditions Map
o Infiltration Requirements
o Soil Management Plan
SECTION 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN
SECTION 6 SPECIAL REPORTS AND STUDIES
SECTION 7 OTHER PERMITS
SECTION 8 CSWPPP ANALYSIS AND DESIGN
SECTION 9 BONDS, SUMMARIES AND COVENANTS
SECTION 10 OPERATIONS AND MAINTENANCE MANUAL
Operations and Maintenance Procedures
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TIR SECTION 1 PROJECT OVERVIEW
Project:
Avon Development 2-lot Short Plat
Site Information:
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 Figure 2: Vicinity
Map. The site is bordered by residential lots on the south, east, and west sides of the
site.
Pre-developed Site 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. Please refer to Figure 3: 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 14 th Street. Please refer to Figure 7:
Developed Conditions Map
The total proposed impervious area is 7,412 sf as follows:
Lot 1: 3,082 sf (Roof: 2,465 sf, Patios & Walks: 320 sf, Driveways: 297 sf)
Lot 2: 3,082 sf (Roof: 2,465 sf, Patios & Walks: 320 sf, Driveways: 297 sf)
NE 14th 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” 1 st 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 sf
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 1: TIR Worksheet
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Figure 2: Site Location Map
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Figure 3: Drainage Basins, Sub-basins and Site Characteristics
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Figure 3 Con’t: Drainage Basins, Sub-basins and Site Characteristics
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Figure 4. Soils Memo
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TIR SECTION 2 CONDITIONS & REQUIREMENTS SUMMARY
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.
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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.
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City of Renton Conditions
FINDINGS/CONCLUSIONS:
To be determined
TIR SECTION 3 OFF-SITE ANALYSIS
TASK 1 – STUDY AREA DEFINITIONS AND MAPS
Overview
This section of the TIR is a Level 1 Downstream Analysis per the City of Renton 2017 storm
water manual Section 2.3.
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., see Figure 2: Vicinity Map. The site is bordered by
residential lots on the north, south, east, and west sides of the site.
Upstream Drainage Analysis / Upstream Contributing Area
Based on the site contours, there is no off-site drainage from upstream areas draining onto the
site. To the north is NE 14th Street which serves to intercept any off-site runoff from the north.
The site itself slopes from north to south-west eliminating any off-site runoff from the east and
west sides of the site. Therefore the drainage is limited to the site itself.
TASK 2 – RESOURCE REVIEW
Adopted Basin Plan
The site is located in the East Lake Washington Basin which flows into Puget Sound.
Community Plan
The site is located in the East Lake Washington Basin Planning Area.
Basin Reconnaissance Summary Report
We are not aware of a current Basin Reconnaissance Summary Report for this area.
Critical Drainage Area
The site is not considered to be within a critical drainage area as defined by the 2009 KCSWDM.
A review of the DOE “water quality assessment” web site shows that the section of the site
discharges into is not on the DOE 303(d) list.
Sensitive Area Maps
Per City of Renton the site does contain areas of steep slope with a potential for landslide hazard
sensitive areas. (See “Sensitive Areas Map”)
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Soils Survey
The soils logs for the site show the site soils to be a till and not suitable for infiltration
Wetland / Stream Inventory
No known wetlands or streams exist with-in the area of grading.
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.
Drainage Complaints
There appeared to be no drainage complaints downstream of the site.. (See “Drainage
Complaints Map”)
TASK 3 – FIELD INSPECTION
A Level 1 site inspection was performed on November 15, 2017. The weather was overcast with
temperatures around 55 degrees. The inspection focused on identifying potential downstream
drainage and water quality problems
As previously indicated, the site slopes to the south-west with all runoff leaving along the south
side of the site
TASK 4 – DRAINAGE SYSTEM DESCRIPTION, AND PREDICTED DRAINAGE AND
WATER QUALITY PROBLEMS
OFFSITE LEVEL ONE DOWNSTREAM ANALYSIS
1. The runoff leaves the property along the south-west side then sheet flows south with:
Overland flow for a distance of 800 feet south-west, where it flows into the storm system
serving I-405.
2. The I-405 drainage system then flows west through the NE Park Drive and I-405
intersection for a distance of 1,000 feet, then west along the north side of NE Park Drive.
3. It then turns north and flows under Lake Washington Blvd discharging into a stream.
4. This stream flows for a distance of 1,500 feet though Gene Coulon Memorial park before
discharging into the south end of Lake Washington. 3,500 feet away
The total distance covered is just over 1-mile
Note: There was no access to most of the downstream area. These areas were on private property
or on I-405 right of way and not accessible to inspection.
Basin 1 Predicted Drainage and Water Quality Problems
The steep slopes located along the freeway may have erosion issues. However, since most of the
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downstream including the discharge locations were on private property and not accessible to
inspection, no drainage issues could be confirmed.
TASK 5 MITIGATION OF EXISTING OR POTENTIAL PROBLEMS
The project proposes to use small site BMP’s to address the storm water runoff from the
proposed site improvements, thus mitigating any downstream impacts.
Figure 5: Upstream Area and Downstream Flow Map
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Figure 6: Downstream System Table
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Drainage Complaints
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Erosion Hazard Map
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Landslide Hazard Map
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TIR SECTION 4 FLOW CONTROL & WATER QUALITY
ANALYSIS AND DESIGN
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.
Under Section 1.1.2.1 “Small Site Drainage Review” “Threshold” 1st Paragraph The project is
under 10,000 sf of total impervious area after January 8, 2001 and is under the 5,000 sf of NEW
impervious area and is exempt from detention.
The total proposed impervious area is 7,412 sf as follows:
Lot 1: 3,082 sf (Roof: 2,465 sf, Patios & Walks: 307 sf, Driveways: 310 sf)
Lot 2: 3,082 sf (Roof: 2,465 sf, Patios & Walks: 307 sf, Driveways: 310 sf)
NE 14th ST: 1,248 sf (Pavement: 728 sf (7’x104’) S-walk: 520 sf)
Total Imper Area – Replaced Imperv Area = 7,412 sf - 4,254 sf = 3,158 sf of new impervious area.
10-Percent Mitigation:
The City requires 10-percent mitigation of the impervious area. Each lot will have 3,082 sf of
impervious area requiring mitigation of 308 sf each. This will be accomplished by providing
driveway dispersion of each lot (at 310 sf each) per BMP T.5-12.
In addition, all downspouts will be 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 t reatment 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
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Figure 7: Developed Conditions
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TIR SECTION 5 CONVEYANCE SYSTEM ANALYSIS AND
DESIGN
PIPE CAPACITY: ROADWAY
The 12- CPEP pipe from the roadway was sized to handle the runoff from the 100-year storm from
both the roadway and site improvements. (See “Pipe Conveyance Charts” at the back of report
The pipe will convey the runoff of 6,164 sf of impervious area from the two lots and the half street
area and sideway areas of 2,400 sf from NE 14th Street.
The total area to be conveyed is 8,544 sf or 0.20 acres. With a 100-yr flow of 0.90 cfs from the
SBUH Results.
Using D.O.T. Chart 35 "Design Charts For Open Channel Flow":
12" CPEP Pipe Slope: 0.50 % Minimum Slope,
Mannings: n = .012
100-Year Dev. Flows: 0.90 cfs Design Flow
Capacity Results:
12" Pipe Capacity: = 2.50 cfs (flowing full) > 1.50 cfs required
Velocity: = 3.25 fps > 3.00 fps required
Therefore the 12" CPEP is adequate.
TIR SECTION 6 SPECIAL REPORTS AND STUDIES
None Required.
TIR SECTION 7 OTHER PERMITS
Below is the list of anticipated permits required for this project. Other permits may be required
that are not mentioned below.
Building Permit – New Single Family Residence
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TIR SECTION 8 CSWPPP ANALYSIS AND DESIGN
For the purposes of this report, several standard erosion control procedures will be utilized by the
contractor to minimize the amount of erosion and sedimentation perpetuated by the construction
of the site. Furthermore, these techniques are proposed for the Construction Stormwater Pollution
Prevention Plan (CSWPPP) and should be reviewed and instituted by the onsite contractor.
Some of the measures include filter fabric fence, and standard ground cover practices, A
construction sequence will also be used to minimize the impacts of erosion due to construction.
ESC Plan Analysis and Design (Part A)
1. At just under 12,000 sf the site is small requiring only minimal ESC measures. The 12-
Elements of a Construction CSWPPP listed below, discuss and describe the appropriate
ESC measure to be used.
2. Due to the small size of the site, no ESC facilities are proposed. Therefore, no analysis of
the site’s ESC facilities was required. The proposed BMPs consist of standard items
including: filter fences, construction entrance, CB inlet protection and plastic cover, etc.
No sediment traps are proposed.
3. The site is fairly flat and the areas of high e rosion are minimal and will be controlled by the
filter fence around the perimeter of the site.
4. There were no special reports done for the site.
5. No exceptions or modifications are proposed of the “Erosion and Sedimentation Control
Standards”
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 exp osed and
unworked for more than two days; after May 1, no exposed soil may remain exposed and
unworked for more than seven days.
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BMP's: Plastic Sheeting,
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
Since the project is for residential lots, under SCC 30.63 A.530, (2) the project does not fall under
the “High Use Sites” covering commercial or industrial sites.
BMP C-151: Concrete Handling (Design and Installation Specifications)
Concrete truck chutes, pumps, and internals shall be washed out only into formed areas awaiting
installation of concrete or asphalt. Unused concrete remaining in the truck and pump shall be
returned to the originating batch plant for recycling.
Hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels shall be
washed off only into formed areas awaiting installation of concrete or asphalt.
Equipment that cannot be easily moved, such as concrete pavers, shall only be washed in areas
that do not directly drain to natural or constructed stormwater conveyances.
Washdown from areas such as concrete aggregate driveways shall not drain directly to natural or
constructed stormwater conveyances.
When no formed areas are available, washwater and leftover product shall be contained in a lined
container. Contained concrete shall be disposed of in a manner that does not violate groundwater or
surface water quality standards
Maintenance Standards:
Containers shall be checked for holes in the liner daily during concrete pours and repaired the same
day
Soil Management Plan for “Post Construction Soil Standard”
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The top soils will be stockpile on-site and reused per “Implementation Options #4b “Amend
existing soil in place per the Post Construction Soil Standard” which requires “Stockpile existing
top soils during grading and replace it prior to planting…” In addition, the soils will be required to
be tested for organic compliance. See the following requirements.
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Amend Existing Soils, Purpose and Definition
Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions including: water
infiltration; nutrient, sediment, and pollutant adsorption; sediment and pollutant biofiltration; water interflow storage
and transmission; and pollutant decomposition. These functions are largely lost when development strips away
native soil and vegetation and replaces
it with minimal topsoil and sod. Not only are these important stormwater functions lost, but such landscapes
themselves become pollution- generating pervious surfaces due to increased use of pesticides, fertilizers and other
landscaping and household/industrial chemicals, the
concentration of pet wastes, and pollutants that accompany roadside litter.
Establishing soil quality and depth regains greater stormwater functions in the post development landscape, provides
increased treatment of pollutants and sediments that result from development and habitation, and minimizes the need
for some landscaping chemicals, thus reducing pollution through prevention.
Applications and Limitations
Establishing a minimum soil quality and depth is not the same as preservation of naturally occurring soil and
vegetation. However, establishing a minimum soil quality and depth will provide improved on-site management of
stormwater flow and water quality.
Soil organic matter can be attained through numerous materials such as compost, composted woody material,
biosolids, and forest product residuals. It is important that the materials used to meet the soil quality and depth
BMP be appropriate and beneficial to the plant cover to be established. Likewise, it is important that imported
topsoils improve soil conditions and do not have an excessive percent of clay fines.
Design Guidelines
Soil retention. The duff layer and native topsoil should be retained in an undisturbed state to the
maximum extent practicable. In any areas requiring grading remove and
stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public
resources and critical areas, to be reapplied to other portions of the site where feasible.
Soil quality. All areas subject to clearing and grading that have not been covered by impervious surface,
incorporated into a drainage facility or engineered as structural fill or slope shall, at project completion,
demonstrate the following:
I. A topsoil layer with a minimum organic matter content of ten percent dry weight in planting beds,
and 5% organic matter content (based on a loss-on-ignition test) in turf areas, and a pH from
6.0 to 8.0 or matching the pH of the original undisturbed soil. The topsoil layer shall have a
minimum depth of eight inches except where tree roots limit the depth of incorporation of
amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at
least 4 inches with some incorporation of the upper material to avoid stratified layers, where
feasible.
2. Planting beds must be mulched with 2 inches of organic material
3. Quality of compost and other materials used to meet the organic content
requirements:
a. The organic content for -pre-approved” amendment rates can be met only using compost that
meets the definition of -composted materials” in WAC I73-350-220. This code is available
online at: http://www.ecy.wa.gov/programs/swfa/facilities/350.html.
Compost used in bioretention areas should be stable, mature and derived from yard debris, wood waste, or other
organic materials that meet the intent of the organic soil amendment specification. Biosolids and manure
composts can be higher in bio-available phosphorus than compost derived from yard or plant waste and therefore
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are not allowed in bioretention areas due to the possibility of exporting bio-available phosphorus in effluent.
The compost must also have an organic matter content of 35% to 65%, and a carbon to nitrogen ratio below 25:I.
The carbon to nitrogen ratio may be as high as 35:I for plantings composed entirely of plants native to the Puget
Sound Lowlands region.
b. Calculated amendment rates may be met through use of composted materials as defined above;
or other organic materials amended to meet the carbon to nitrogen ratio requirements, and
meeting the contaminant standards of Grade A Compost.
The resulting soil should be conducive to the type of vegetation to be established.
Implementation Options: The soil quality design guidelines listed above can be met by using one of the
methods listed below.
I. Leave undisturbed native vegetation and soil, and protect from compaction during construction.
2.Amend disturbed soil according to the following procedures:
b. Scarify subsoil to a depth of one foot
c. In planting beds, place three inches of compost and till in to an eight-inch depth.
d. In turf areas, place two inches of compost and till in to an eight-inch depth.
e. Apply two to four inches of arborist wood chip, coarse bark mulch, or compost mulch to
planting beds after final planting.
Alternatively, disturbed soil can be amended on a site-customized manner so that it meets the soil
quality criteria set forth above, as determined by a licensed engineer, geologist, landscape architect, or
other person as approved by City of Renton.
3. Stockpile existing topsoil during grading, and replace it prior to planting. Stockpiled topsoil must
be amended if needed to meet the organic matter and depth requirements by following the
procedures in method (2) above).
4. Import topsoil mix of sufficient organic content and depth to meet the organic matter and depth
requirements.
5. More than one method may be used on different portions of the same site. Soil that already meets
the depth and organic matter quality standards, and is not compacted, does not need to be
amended.
Maintenance
Soil quality and depth should be established toward the end of construction and once established,
should be protected from compaction, such as from large machinery use, and from erosion.
Soil should be planted and mulched after installation.
Plant debris or its equivalent should be left on the soil surface to replenish organic matter.
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TIR SECTION 9 BONDS, SUMMARIES AND COVENANTS
All the necessary documents listed below will be included in the Full TIR report after
preliminary approval is received.
These will include:
Bond Quantities,
Flow Control and Water Quality Facility Summary Sheet and Sketch
Declaration of Covenant for Privately Maintained Flow Control and WQ Facilities
Declaration of Covenant for Privately Maintained Flow Control BMPs
TIR SECTION 10 OPERATIONS AND MAINTENANCE
MANUAL
Stormwater System Description
The stormwater system for the site is fairly basic and contains the following elements:
12-inch storm pipe
Catch basin
The stormwater runoff from the site improvements flows over to street catch basin.
Water quality treatment is not a requirement for the site since it is under the 5,000 sf threshold.