HomeMy WebLinkAboutRS_Drainage_Technical_Information_Report (TIR)_v1Project R18325 Ngochan Short Plat
2/22/2019
Ngochan Short Plat
10814 SE 173rd St
Renton, WA 98055
Parcel #: 1626800010
Contact/ Owner: Doan Nguyen
TECHNICAL INFORMATION REPORT
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TABLE OF CONTENTS
1. PROJECT OVERVIEW
2. CONDITIONS AND REQUIREMENTS SUMMARY
3. OFFSITE ANALYSIS (LEVEL 1 DOWNSTREAM ANALYSIS)
Task 1: Study Area Definition and Maps
Task 2: Resource Review
Task 3: Field Inspection
Task 4: Downstream Drainage System Description and Existing and Potential Problems
4. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND
DESIGN
5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
6. SPECIAL REPORTS AND STUDIES
7. OTHER PERMITS
8. CSWPPP ANALYSIS AND DESIGN
9. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF
COVENANT
10. OPERATIONS AND MAINTENANCE MANUAL
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LIST OF APPENDICES
Appendix A – Stormwater Site Plans
Appendix B – Operations & Maintenance Manual
Appendix C – CSWPPP
Appendix D –Soil logs/ Geotech Report
LIST OF FIGURES
Figure 1 TIR Worksheet………………………… ....... ……………………………………2
Figure 2 Vicinity Map……………………………………………………………………… . 7
Figure 3 Proposed Conditions Exhibit……………………………………………………8
Figure 4 Aerial Photograph ..................................................................... ..... .10
Figure 5 Existing Site Condition .............................................................. ...... 11
Figure 6 Downstream Exhibit ......................................................... …….. .... 15
Project R18325 Ngochan Short Plat
2/22/2019
1. PROJECT OVERVIEW
This Technical Information Report (TIR) is submitted in support of the permits for
the Ngochan Short Plat . Two new single family homes are proposed within the
central-southern portion of the property along with a proposed driveways
This analysis was completed using the format set forth in the 2017 Renton Surface
Water Design Manual (RSWDM. Figure 1 – TIR Worksheet is attached on the
following page.
Project Description:
Please refer to Figure 2 – Vicinity Map and Figure 3 – Proposed Conditions Exhibit on
the following pages to aid in the project description.
The Ngochan Short Plat project proposes 2 single family homes and associated
infrastructure at Parcel #162680-0010.
The proposed work includes construction and grading of the site for building pads,
and installation of utilities, all related to a new single family home s and driveways.
The proposed storm drainage system consists of 2 infiltration trenches and
associated stormwater conveyance.
The project is subject to Directed Drainage Review (2 proposed single family
residences and driveways with 5,400 sf of impervious) which require that all 9 Core
Requirements to be addressed as well as all 5 Special Requirements.
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Figure 1 – TIR Worksheet
City of Renton
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
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Figure 2 – Vicinity Map
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Figure 3 – Proposed Conditions Exhibit
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2. CONDITIONS AND REQUIREMENTS SUMMARY
CORE REQUIREMENT #1: Discharge at the Natural Location
Onsite stormwater, in the existing condition, sheet flows into SE 174rd St and into
the City stormwater system. Stormwater, post site development, will continue to
drain into the City stormwater system via an infiltration trench and associated
stormwater conveyance system.
CORE REQUIREMENT #2: Offsite Analysis
See the Level 1 Downstream Analysis included in Section 3 of this TIR.
CORE REQUIREMENT #3: Flow Control
Infiltration trenches are proposed for each driveway and single family residence,.
See Section 4.
CORE REQUIREMENT #4: Conveyance System
Conveyance capacity will be provided to handle peak flows from the 100-year storm
event. See Section 5.
CORE REQUIREMENT #5: Erosion and Sediment Control
A construction entrance, silt fencing or compost socks, temporary drainage swales ,
and inlet protection along with appropriate cover measures will be provided for
erosion and sediment control for the site. See Section 8.
CORE REQUIREMENT #6: Maintenance and Operations
A Maintenance and Operations Manual is provided in Appendix B of this report.
CORE REQUIREMENT #7: Financial Guarantees and Liability
Bond and liability assurances will be provided by the Owner or the Contractor.
CORE REQUIREMENT #8: Water Quality
The site is located within a Basic Water Quality Area. The project proposes 1,000
sf of Pollution Generating Impervious Surface (PGIS), which does not trigger water
quality requirements, See Section 4.
CORE REQUIREMENT #9: Flow Control BMPs
The project falls under Small Lot BMP requirements. Due to site constraints, an
infiltration trench has been selected as a stormwater BMP (see Section 4)
SPECIAL REQUIREMENT #1: Other Adopted Area-Specific Requirements
Not applicable.
SPECIAL REQUIREMENT #2: Flood Hazard Area Delineation
Not Applicable.
SPECIAL REQUIREMENT #3: Flood Protection Facilities
Not applicable.
SPECIAL REQUIREMENT #4: Source Controls
Not applicable.
SPECIAL REQUIREMENT #5: Oil Control
Not applicable.
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3. OFFSITE ANALYSIS (Level 1 Downstream Analysis)
Task 1: Study Area Definition and Maps
The study area covered was the project site and upstream and downstream
drainage areas near the development property.
Task 2: Resource Review
The project site is located within the Black River Drainage Basin. Additionally, the
site is not located in a critical drainage area. Research of available data shows no
seismic hazard, landslide hazards, erosion hazards, or wetlands located on site.
The soils on the site have been classified as Vashon Aged Glacial Till, see Geotech
report.
Task 3: Field Inspection
Please refer to Figure 4 - Aerial Photograph and Figure 5 - Existing Site Conditions
below to aid in the following description.
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Figure 4 – Aerial Photograph
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Frontage of Site
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Looking west on 173rd St along project site frontage.
Catch Basin on NE corner of 108th Ave SE and SE 173rd St, collecting drainage
from ditch.
There are no signs of ponding, flooding, or erosion problems on site or downstream
of the site.
Tributary Upstream Drainage
The project site is downstream of a condominium complex which has a separate
conveyance system. As a result it is not considered to have an upstream basin.
Task 4: Downstream Drainage System Description and Existing and
Potential Problems
Based on research, and site visits there are no signs of drainage or erosion
problems. The site will be mitigated through infiltration trenches and will not
contribute significant additional drainage to the city stormwater system.
Drainage leaving the project site does so through sheet flow into a vegetated ditch
on the north side of SE 173rd St. It then enters a series of 12” to 18” pipes which
carries it south along 108th Ave SE. It then enters a vegetated swale and crosses
Benson Dr. through an 18” CMP. It then travels west through a series of 12” to 18”
pipes along SE 174th St. It reaches the 0.25 mile mark just shy of the SE 174th St
and 106th Pl SE Intersection.
Figure 6 – Downstream Exhibit
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Conclusion:
The downstream system showed no signs of erosion. No adverse impact to the
downstream drainage system is expected from the proposed project.
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4. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS
AND DESIGN
Existing Site Hydrology (Part A)
The 10,800 sf project site is currently vacant. The site is covered with dense
underbrush, deciduous trees, and evergreen trees along its frontage and property
lines. The central portion of the property has been cleared. The site topography
ranges from 0 to 15% across the property towards the southern portion of the site.
There is currently no sidewalk on the frontage of the site. There is a vegetated ditch
on the project frontage which collects and conveys stormwater to the west.
The soil is classified as a Ardents, Alderwood Material(see NRCS/Geotech Report),
0 to 15 percent slopes by the Cash M. Carr Technical Services.
The site is bordered on the north, east, and west by single family homes as is
typical of an urban residential neighborhood.
Figure 5 – Existing Site Conditions
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Developed Site Hydrology (Part B)
Total Developed Area
Total Property 10,800 0.25
Developed Area (cleared site, 100%) 10,800 0.25
Impervious 7,330 0.17
Proposed House 1 (Lot 1) 2,200 0.05
Proposed House 2 (Lot 2) 2,200 0.05
Proposed Driveways (Lot 1 & 2) 1,000 0.02
Frontage Sidewalk & Driveway 1,430 0.03
Frontage Widening 500 0.01
Total Proposed Impervious 7,330 0.17
Pervious 3,470 0.08
Performance Standards (Part C)
The project site/each lot is <22,000 sf and therefore is required to apply the
Renton Flow Control Standard OR Small Lot Flow Control BMPs. Due to the site’s
high infiltration rate (45 in/hr. from Geotech), we have chosen to meet the flow
control standard.
Area Specific flow control standards: From the “Flow Control Application Map” reference
11-A, the project is required to meet flow control duration standard (Forested Conditions).
Flow control BMPs (in this case, infiltration trenches) are required for this project and will
be explained in Part D.
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Flow Control System (Part D)
From the Small Lot BMP Requirement Feasibility Review:
1. Full Dispersion –Not Feasible. The site area is limited due to the
proximity to property lines and does not have sufficient flow path lengths.
2. Infiltration of Roof and Driveways – FEASIBLE – Based on the soil type
and the recommendations of the Geotech, we have chosen infiltration as a
stormwater BMP.
The largest lot (Lot 1) in its entirety was modeled to maintain a factor of safety. An
infiltration rate of 45 inches per hour (see Geotech report, page 13) was used:
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Each proposed residence roof downspout and footing draings will be tight-lined to
catch basin/area drain and then an infiltration trench. The model finds that 20 LF
of infiltration trench mitigates 2,200 SF of house. The develop may use a rule of
thumb of 10 LF of infiltration trench per 1,000 sf of impervious as is shown in the
plans. The proposed driveways will disperse into the existing storm system along
the north side of SE 173rd St, as it did in the existing conditions.
Peak Flow Analysis
Using WWHM 2012, and 15 minute timesteps.
0.0676 – 0.0100 = 0.0576 cfs
Difference in peak flow is 0.0576 cfs which is below the peak discharge requirement, for
the record.
Water Quality System (Part E)
The project proposes 1,500 sf (driveways and frontage widening) of Pollution Generating
Impervious Surface (PGIS), which is under the 5,000 sf threshold requirement for water
quality. Therefore, Water Quality is NOT required.
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5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
Conveyance system will be designed in accordance with the 2017 RSWDM.
For a factor of safety, the basin is modeled as the full developed impervious area,
full house, and full driveway which will be conveyed to the 6” pipe.
Using Manning’s equation to determine pipe capacity for a 6” diameter pipe
(minimum designed) at 2.0% minimum slope and a typical Manning’s coefficient of
0.012 for PVC pipe:
Pipe Capacity = 0.859 cfs > Q100 = 0.0676 cfs ➔ OK
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6. SPECIAL REPORTS AND STUDIES
-Geotechnical Report by Cash M. Carr Technical Services.
7. OTHER PERMITS
-None
8. CSWPPP ANALYSIS AND DESIGN
Less than an acre of disturbance is anticipated for this project. Proposed temporary
measures possible for this project will include the following BMP’s:
• Construction Entrance
• Filter fences or Compost Socks.
• Straw mulch, hydroseed or other mulching and planting method to
stabilized unworked areas.
• Temporary drainage swales and rock check dams.
• Inlet protection of new and existing catch basins.
Please refer to the TESC Plan included in the Engineering Submittal for details.
9. BOND QUANTITIES, FACILITY SUMMARIES AND
DECLARATION OF COVENANT
Bond and liability assurances will be provided by the Owner or the Contractor. A
Declaration of Covenant for the Flow Control BMPs will be recorded with Renton
prior to final approval.
10. OPERATIONS AND MAINTENANCE MANUAL
An Operations and Maintenance Manual is included in Appendix B of this report.
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Appendix A
Stormwater Site Plans
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Appendix B
Operations & Maintenance Manual
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Appendix C
CSPPP
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CESCL REQUIREMENT
A Certified Erosion and Sediment Control Specialist shall be identified in the Construction SWPPP
and shall be onsite or oncall at all times. Certification may be obtained by an approved training
program that meets the erosion and sediment control training criteria established by Ecology. If a
preconstruction meeting is held, this person shall attend. See attached BMPC160 Certified Erosion
and Sediment Control Lead (CESCL)
CESCL___________________________________
24hr Contact number:______________________
Fax number:______________________________
Address:_________________________________
_________________________________________
_________________________________________
ELEMENT 1: MARK CLEARING LIMITS
• Prior to beginning land disturbing activities, including clearing and grading, all clearing limits,
sensitive areas and their buffers, and trees that are to be preserved within the construction area
should be clearly marked, both in the field and on the plans, to prevent damage and offsite impacts.
• Plastic, metal, or stake wire fence may be used to mark the clearing limits.
• The duff layer, native topsoil, and natural vegetation shall be retained in an undisturbed state to the
maximum extent practicable. If it is not practicable to retain the duff layer in place, it should be
stockpiled onsite, covered to prevent erosion, and replaced immediately upon completion of the
ground disturbing activities.
Element
#1 BMP Description
X C101 Preserving Natural Vegetation
X C102 Buffer Zones
X C103 High Visibility Plastic or Metal Fence
X C104 Stake and Wire Fence
Construction and silt fencing will be used to delineate the limits of clearing for the project.
ELEMENT 2: ESTABLISH CONSTRUCTION ACCESS
• Construction vehicle access and exit shall be limited to one route if possible.
• Access points shall be stabilized with quarry spalls or crushed rock to minimize the tracking of
sediment onto public roads.
• Wheel wash or tire baths should be located onsite, if applicable.
• Public roads shall be cleaned thoroughly as needed to protect stormwater infrastructure and
downstream water resources. Sediment shall be removed from roads by shoveling or pickup
sweeping and shall be transported to a controlled sediment disposal area. Street washing will be
allowed only after sediment is removed in this manner.
• Street wash wastewater shall be controlled by pumping back onsite, or otherwise be prevented from
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discharging untreated into systems tributary to state surface waters.
Element
#2 BMP Description
X C105 Stabilized Construction Entrance
C106 Wheel Wash
C107 Construction Road/Parking Area Stabilization
The proposed construction accesses will be from SE 173rd St on the south property line.
ELEMENT 3: CONTROL FLOW RATES
• Properties and waterways downstream from development sites shall be protected from erosion due
to increases in the volume, velocity, and peak flow rate of stormwater runoff from the project site, as
required by local plan approval authority.
• Downstream analysis is necessary if changes in flows could impair or alter conveyance systems,
stream banks, bed sediment or aquatic habitat. See Chapter 3 for offsite analysis guidance.
• Where necessary to comply with Minimum Requirement #7, stormwater retention/detention facilities
shall be constructed as one of the first steps in grading. Detention facilities shall be
functional prior to construction of site improvements (e.g. impervious surfaces).
• The local permitting agency may require pond designs that provide additional or different
stormwater flow control if necessary to address local conditions or to protect properties and
• waterways downstream from erosion due to increases in the volume, velocity, and peak flow rate of
stormwater runoff from the project site.
• If permanent infiltration ponds are used for flow control during construction, these facilities shall be
protected from siltation during the construction phase and plans made for restoration after
construction.
Element
#3 BMP Description
C240 Sediment Trap
C241 Temporary Sediment Pond
ELEMENT 4: INSTALL SEDIMENT CONTROLS
• Prior to leaving a construction site, or prior to discharge to an infiltration facility, stormwater runoff
from disturbed areas shall pass through a sediment pond or other appropriate sediment removal
BMP. Runoff from fully stabilized areas may be discharged without a sediment removal BMP, but
must meet the flow control performance standard of Element #3, bullet #1. Full stabilization means
concrete or asphalt paving; quarry spalls used as ditch lining; or the use of rolled erosion products,
a bonded fiber matrix product, or vegetative cover in a manner that will
fully prevent soil erosion. The local permitting authority should inspect and approve areas stabilized
by means other than pavement or quarry spalls.
• Sediment ponds, vegetated buffer strips, sediment barriers or filters, dikes, and other BMP’s
intended to trap sediment onsite shall be constructed as one of the first steps in grading. These
BMP’s shall be functional before other land disturbing activities take place.
• Earthen structures such as dams, dikes, and diversions shall be seeded and mulched according to
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the timing indicated in Element #5.
• BMPs intended to trap sediment on site must be located in a manner to avoid interference with the
movement of juvenile salmonids attempting to enter off-channel areas or drainages, often during
nonstorm events, in response to rain event changes in stream elevation or wetted area.
Element
#4 BMP Description
C230 Straw Bale Barrier
C231 Brush Barrier
C232 Gravel Filter Berm
X C233 Silt Fence
C234 Vegetated Strip
C235 Straw Wattles
C240 Sediment Trap
C241 Temporary Sediment Pond
C250 Construction Stormwater Chemical Treatment
C251 Construction Stormwater Filtration
The proposed sediment control measures are provided on TESC found in the engineering submittal.
At minimum, the project will be required to have downstream protection (compost socks, silt fencing,
or equivalent), inlet protection, and appropriate cover measures. The proposed plan is intended as
guidance and the Contractor shall be responsible for implementing and maintaining appropriate
sediment controls based on changing site conditions.
ELEMENT 5: STABILIZE SOILS
• All exposed and unworked soils shall be stabilized by application of effective BMPs that protect the
soil from the erosive forces of raindrop impact, flowing water, and wind.
• Soils shall be stabilized as outlined below, where downstream water resources or stormwater
infrastructure may be negatively affected by sediments (i.e., runoff discharges off the development
site).
• From October 1 through April 30, no soils shall remain exposed and unworked for more than 2
days. From May 1 to September 30, no soils shall remain exposed and unworked for more than 7
days. This condition applies to all onsite soils, whether at final grade or not. The local permitting
authority may adjust these time limits if it can be shown that a development site's erosion or runoff
potential justifies a different standard.
• Applicable practices include, but are not limited to, compost addition, temporary and permanent
seeding, sodding, mulching, plastic covering, soil application of polyacrylamide (PAM), early
application of gravel base on areas to be paved, and dust control.
• Soil stabilization measures selected should be appropriate for the time of year, site conditions,
estimated duration of use, and potential water quality impacts that stabilization agents may have on
downstream waters or ground water.
• Soil stockpiles must be stabilized from erosion, protected with sediment-trapping measures, and
located away from storm drains, waterways, or drainage channels.
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• Work on linear construction sites and activities, including right-of-way and easement clearing,
roadway development, pipelines, and trenching for utilities, shall not exceed the capability of the
individual contractor for his portion of the project to install the bedding materials, roadbeds,
structures, pipelines, and/or utilities, and to re-stabilize the disturbed soils, in compliance with the
applicable 2-day or 7-day criterion listed above.
Element
#5 BMP Description
X C120 Temporary and Permanent Seeding
X C121 Mulching
C122 Nets and Blankets
X C123 Plastic Covering
X C124 Sodding
X C125 Topsoiling
C126 Polyacrylamide for Soil Erosion Protection
C130 Surface Roughening
C131 Gradient Terraces
C140 Dust Control
C180 Small Project Construction Stormwater Pollution Prevention
Temporary and permanent cover measures shall be provided based upon plans and
Contractor’s discretion per site conditions during construction.
ELEMENT 6: PROTECT SLOPES
• Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion.
• Consider soil type and its potential for erosion.
• Reduce slope runoff velocities by reducing the continuous length of slope with terracing and
diversions, reduce slope steepness, and roughen slope surface.
• Offsite stormwater (run-on) shall be diverted away from slopes and disturbed areas with interceptor
dikes and swales. Offsite stormwater should be managed separately from stormwater generated on
the site.
• To prevent erosion, at the top of slopes collect drainage in pipe slope drains or protected channels.
Temporary pipe slope drains shall handle the peak flow from a 10-year, 24-hour event; permanent
slope drains shall be sized for a 25-year, 24-hour event. Check dams shall be used within channels
that are cut down a slope.
• Provide drainage to remove ground water intersecting the slope surface of exposed soil areas.
• Stabilize soils on slopes, as specified in Element #5.
Element
#6 BMP Description
X C120 Temporary and Permanent Seeding
X C130 Surface Roughening
X C131 Gradient Terraces
C200 Interceptor Dike and Swale
C201 Grass-Lined Channels
C204 Pipe Slope Drains
C205 Subsurface Drains
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C206 Level Spreader
C207 Check Dams
C208 Triangular Silt Dike
The Contractor shall be responsible for protecting and stabilizing site slopes as required.
ELEMENT 7: PROTECT DRAIN INLETS
• As needed to protect stormwater infrastructure and downstream water resources, all storm drain
inlets made operable during construction shall be protected so that stormwater runoff shall not enter
the conveyance system without first being filtered or treated to remove sediment.
• All approach roads shall be kept clean, and all sediment and street wash water shall not be allowed
to enter storm drains without prior and adequate treatment, unless treatment is provided before the
storm drain discharges to waters of the State.
Element
#7 BMP Description
X C220 Storm Drain Inlet Protection
Both existing and proposed drain inlets shall be protected as required.
ELEMENT 8: STABILIZE CHANNELS AND OUTLETS
• All temporary onsite conveyance channels shall be designed, constructed and stabilized to prevent
erosion from the peak 10-minute flow velocity from a Type 1A 10-year 24-hour frequency storm for
the developed condition. Alternatively, the 10-year, 1-hour flow rate indicated by an approved
continuous runoff model, increased by a factor of 1.6, may be used.
• Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream
banks, slopes and downstream reaches shall be provided at the outlets of all conveyance systems.
Element
#8 BMP Description
C202 Channel Lining
X C209 Outlet Protection
Permanent conveyance channels shall be, at a minimum, lined with grass. Outlets to open
drainage areas shall be lined with rip-rap.
ELEMENT 9: CONTROL POLLUTANTS
• All pollutants, including waste materials and demolition debris that occur onsite shall be handled
and disposed of in a manner that does not cause contamination of stormwater.
• Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid
products, petroleum products, and non-inert wastes present on the site (see Chapter 173-304 WAC
for the definition of inert waste). Onsite fueling tanks shall include secondary containment.
• Maintenance and repair of heavy equipment and vehicles involving oil changes, hydraulic system
drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and
other activities which may result in discharge or spillage of pollutants to the ground or into
stormwater runoff must be conducted using spill prevention measures, such as drip pans.
Contaminated surfaces shall be cleaned immediately following any discharge or spill incident.
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Report all spills to 911. Emergency repairs may be performed onsite using temporary plastic placed
beneath and, if raining, over the vehicle.
• Wheel wash, or tire bath wastewater, shall be discharged to a separate onsite treatment system or
to the sanitary sewer if allowed by the local wastewater authority.
• Application of agricultural chemicals, including fertilizers and pesticides, shall be conducted in a
manner and at application rates that will not result in loss of chemical to stormwater runoff.
Manufacturers' label recommendations shall be followed for application rates and procedures.
• Management of pH-modifying sources shall prevent contamination of runoff and stormwater
collected on the site. These sources include, but are not limited to, bulk cement, cement kiln dust,
fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding
and sawing, exposed aggregate processes, and concrete pumping and mixer washout waters.
• Construction sites with significant concrete work shall adjust the pH of stormwater if necessary to
prevent violations of water quality standards.
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Element
#9 BMP Description
X C151 Concrete Handling
X C152 Sawcutting and Surfacing Pollution Prevention
The Contractor shall be responsible for controlling pollutants from construction activities off the
project site.
ELEMENT 10: CONTROL DE-W ATERING
• All foundation, vault, and trench de-watering water, which has similar characteristics to stormwater
runoff at the site, shall be discharged into a controlled conveyance system, prior to discharge to a
sediment trap or sediment pond. Channels must be stabilized, as specified in Element #8.
• Clean, non-turbid de-watering water, such as well-point ground water, can be discharged to
systems tributary to state surface waters, as specified in Element #8, provided the de-watering flow
does not cause erosion or flooding of the receiving waters. These clean waters should not be
routed through sediment ponds with stormwater.
• Highly turbid or otherwise contaminated dewatering water, such as from construction equipment
operation, clamshell digging, concrete tremie pour, or work inside a cofferdam, shall be handled
separately from stormwater at the site.
• Other disposal options, depending on site constraints, may include: 1) infiltration, 2) transport offsite
in vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state
waters, 3) onsite treatment using chemical treatment or other suitable treatment technologies, or 4)
sanitary sewer discharge with local sewer district approval.
The Contractor shall be responsible for discharging de-watering water in an appropriate manner.
ELEMENT 11: MAINTAIN BMP’S
• All temporary and permanent erosion and sediment control BMP’s shall be maintained and repaired
as needed to assure continued performance of their intended function. All maintenance and repair
shall be conducted in accordance with BMP’s.
• Sediment control BMP’s shall be inspected weekly or after a runoff-producing storm event during
the dry season and daily during the wet season.
• All temporary erosion and sediment control BMP’s shall be removed within 30 days after final site
stabilization is achieved or after the temporary BMP’s are no longer needed. Trapped sediment
shall be removed or stabilized on site. Disturbed soil areas resulting from removal of BMP’s or
vegetation shall be permanently stabilized.
The Contractor shall be responsible for maintaining BMP’s to assure performance of their
intended function.
ELEMENT 12: MANAGE THE PROJECT
• Phasing of Construction - Development projects shall be phased where feasible in order to prevent
soil erosion and, to the maximum extent practicable, the transport of sediment from the project site
during construction. Revegetation of exposed areas and maintenance of that vegetation shall be an
integral part of the clearing activities for any phase.
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Clearing and grading activities for developments shall be permitted only if conducted pursuant to an
approved site development plan (e.g., subdivision approval) that establishes permitted areas of clearing,
grading, cutting, and filling. When establishing these permitted clearing and grading areas, consideration
should be given to minimizing removal of existing trees and minimizing disturbance/compaction of native
soils except as needed for building purposes. These permitted clearing and grading areas and any other
areas required to preserve critical or sensitive areas, buffers, native growth protection easements, or tree
retention areas as may be required by local jurisdictions, shall be delineated on the site plans and the
development site.
All plats shall include lot-specific grading plans, including information specified by the local permitting
authority such as finished grades, finished floor elevations, buildable areas, and identified drainage outlets.
This information would normally be submitted with the construction drawings, but may be required prior to
preliminary plat approval.
• Seasonal Work Limitations
From October 1 through April 30, clearing, grading, and other soil disturbing activities shall only be permitted
if shown to the satisfaction of the local permitting authority that silt-laden runoff will be prevented from leaving
the construction site through a combination of the following:
1. Site conditions including existing vegetative coverage, slope, soil type and proximity to receiving
waters; and
2. Limitations on activities and the extent of disturbed areas; and
3. Proposed erosion and sediment control measures.
Based on the information provided, and/or local weather conditions, the local permitting authority may
expand or restrict the seasonal limitation on site disturbance. If, during the course of any construction activity
or soil disturbance during the seasonal limitation period, silt-laden runoff leaving the construction site causes
a violation of the surface water quality standard or if clearing and grading limits or erosion and sediment
control measures shown in the approved plan are not maintained, the local permitting authority may take
enforcement action, including but not limited to a notice of violation, administrative order, fine/penalty, stop-
work order, or correction notice.
The following activities are exempt from the seasonal clearing and grading limitations:
1. Routine maintenance and necessary repair of erosion and sediment control BMP’s;
2. Routine maintenance of public facilities or existing utility structures that do not (a) expose the
soil or (b) result in the removal of the soil's vegetative cover; and Self-contained project sites,
where there is complete infiltration of the water quality design event runoff within the site.
3. Local governments may restrict clearing and grading activities where site conditions may
present a significant risk of impact to property or critical areas. Contact the local permitting
authority for information on specific site restrictions. In Olympia, except where approved
chemical treatment, full dispersion or infiltration is practiced, clearing, grading, and other soil
disturbing activities are prohibited in all watersheds November through February, and in Green
Cove, Percival, Woodard, and Ellis Creek watersheds between October through April.
• Coordination with Utilities and Other Contractors
The primary project proponent shall evaluate, with input from utilities and other contractors, the stormwater
management requirements for the entire project, including the utilities, when preparing the Construction
SWPPP.
• Inspection and Monitoring
All BMP’s shall be inspected, maintained, and repaired as needed to assure continued performance of their
intended function. Site inspections shall be conducted by a person who is knowledgeable in the principles
and practices of erosion and sediment control. The person shall have the skills to (1) assess site conditions
and construction activities that could impact stormwater runoff quality, and (2) assess erosion and sediment
control measure effectiveness.
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A Certified Erosion and Sediment Control Specialist shall be identified in the construction SWPPP and shall
be onsite or on-call at all times. Certification may be obtained an approved training program that meets the
erosion and sediment control training criteria established by Ecology. If a pre-construction meeting is held,
this person shall attend.
Sampling and analysis of the stormwater discharges from a construction site may be necessary on a case-
by-case basis to ensure compliance with standards. Monitoring and reporting requirements may be
established by the local permitting authority when necessary.
The following discharge standard applies:
Runoff leaving the construction site shall be free of settle able solids, as measured with an Imhoff Cone and
in accordance with Standard Methods for the Examination of Water and Wastewater, most recent edition,
American Water Works Association. "Free of settle able solids" shall be defined as measuring less than 2.5
mL/L/hr, for storms up to the water quality design event.1
The following surface water standard applies:
1. For storms up to the water quality design event, turbidity downstream of a construction site may
not increase more than 5 NTU, if upstream turbidity is 50 NTU or less, and may not increase
more than 10 percent, if upstream turbidity is over 50 NTU. To the extent practicable, samples
should be taken far enough downstream so that the construction site discharge has been well-
mixed with the surface water.
2. Whenever inspection and/or monitoring reveals that the BMP’s identified in the Construction
SWPPP are inadequate, due to the actual discharge of or potential to discharge a significant
amount of any pollutant, appropriate BMP’s or design changes shall be implemented as soon as
possible.
• Maintaining an Updated Construction SWPPP - The SWPPP shall be retained onsite or within
reasonable access to the site.
The SWPPP shall be updated within 7 days to reflect any significant changes in the design, construction,
operation, or maintenance at the construction site that have, or could have, a significant effect on the
discharge of pollutants to waters of the state.
The SWPPP shall be updated within 7 days if during inspections or investigations by site staff or local or
state officials, it is determined that the SWPPP is ineffective in controlling pollutants such that applicable
discharge or surface water standards violations are apparent.
The objective is to control erosion and prevent sediment and other pollutants from leaving the site during
the construction phase of a project.
The Contractor shall be responsible for managing the construction phase of the project within
reasonable applications of the guidelines of this section and the SWPPP.
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SECTION 3 – CONSTRUCTION SWPPP CHECKLIST
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Appendix D
Geotech/NRCS
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Geotechnical Report
10814 SE 173rd St. Renton
Report Date: 12/9/2015
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Dear Client,
As requested, we have conducted a geotechnical soil investigation for 10814 SE 173rd St.
Renton concerning soil permeability and classification. Our findings and design criteria are
enclosed.
We trust the information provided is sufficient for your current needs. If you have any
questions please contact us.
Regards,
Cash M. Carr PE.
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Subsurface Exploration and Geotechnical Engineering Study
Regarding: Soil Permeability
Introduction
This report presents the results of our subsurface investigation and geotechnical report for
the residence located at 10814 SE 173rd St. Renton in regards to soil permeability.
Purpose and Scope
This subsurface investigation and geotechnical report is intended to determine and
present our finding for soil permeability and recommend procedures for infiltration.
Limitations
The scope of this report is limited to drainage. Structural and bearing considerations have
not been included in the scope of this report.
Field Explorations
A geotechnical borehole was constructed to a depth of 4’, a depth which is sufficient for
determining the capacity for storm water infiltration from the surface. Test was performed by
professional engineer Cash M. Carr and geologist Jackie Perkins. Disturbed samples were taken
at the lowest point on the property, as in our judgment, this point will be the worst case for
runoff saturation. Sampling was performed by professional engineer Cash M. Carr and geologist
Jackie Perkins. Our sample log is presented below.
Laboratory Testing
This grain size analysis sampled four feet of soil from the site at 10814 SE 173 St, Renton.
Samples were obtained on site, where initial observations were recorded. The samples were dried for five
days before being processed through 10, 20, 40, 60, 80, and 100 sieves.
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RESULTS:
Foot 1
Initial observations: extremely organically rich, very dark brown, moderate moisture content, grains are
rounded and range 0.2 -3.0mm with occasional fine gravel.
Starting weight: 5.4 oz*
Sieve Weight (oz) Percent wt % Passing
10 1.9 36.5 63.5
20 1.1 21.2 42.3
40 1.8 34.6 7.7
60 0.3 5.77 1.92
80 0.05 0.96 0.96
100 0.05 0.96 0.00
Total: 5.2
D10= 0.35
D30= 0.65
D60= 1.7
Cu= 4.86
Cc= 0.710
* Ounces were used in this procedure as the available scale did not produce decimals for grams.
Particle size distribution curve for foot 1:
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Foot 2
Initial observations: some organic material, moderately moist, dark brown, fine sand with silt and some
gravel, small grains are clumping together.
Starting weight: 6.1oz
Sieve Weight (oz) Percent wt % Passing
10 2.4 40.0 60.0
20 1 16.7 43.3
40 2.3 38.3 5.0
60 0.2 3.33 1.67
80 0.05 0.83 0.83
100 0.05 0.83 0.00
Total: 6.0
D10= 0.47
D30= 0.55
D60= 2
Cu= 4.255
Cc= 0.322
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Particle size distribution curve for foot 2:
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Foot 3
Initial observations: moderately moist, dark/medium orange brown, coarse sand and fine gravel with
some fine sand, a few very coarse gravel clasts (bordering on small cobbles) approximately 4cm diameter,
smaller grains clumping together from moisture.
Starting weight: 5.9
Sieve Weight (oz) Percent wt % Passing
10 2.3 39.7 60.3
20 1.2 20.7 39.7
40 1.9 32.8 6.9
60 0.3 5.2 1.7
80 0.05 0.9 0.9
100 0.05 0.9 0.0
Total: 5.8
D10= 0.46
D30= 0.59
D60= 2
Cu= 4.35
Cc= 0.378
Particle size distribution curve for foot 3:
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Foot 4
Initial observations: Organically rich, dark orange brown, fine gravels with sand and silt, some medium
gravel clasts, finer grains clump together due to moisture.
Starting weight: 7.9
Sieve Weight (oz) Percent wt % Passing
10 3.4 43.6 56.4
20 1.1 14.1 42.3
40 2.5 32.1 10.3
60 0.7 9.0 1.3
80 0.05 0.6 0.6
100 0.05 0.6 0.0
Total: 7.8
D10= 0.425
D30= 0.63
D60= 2
Cu= 4.71
Cc= 0.467
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Particle size distribution curve for foot 4:
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DATA ANALYSIS
Each of the samples yielded uniformity coefficients <6 and coefficients of gradation <1,
categorizing the soil as poorly graded gravelly sand (SP) under the grading criteria of the Unified Soil
Classification System. The top foot of soil may also be considered peat (PT) due to high organic content,
dark brown to black color, and fibrous texture. The soil is overall texturally classified as loamy sand with
gravel.
SOURCES OF ERROR
Several sources of error arose from the available equipment. The sieve with the largest diameter
mesh (no. 10) would only allow particles smaller than 2mm to pass through, which fails to allow for
distinction between coarse sand grains and gravels. This may cause the soil to be classified as more
poorly graded than it truly is. The presence of gravels and small cobbles in the soil should be taken into
account for the purpose of geoengineering, however the majority of the soil is comprised of sand.
For each sample the weight of the soil retained by the 80 and 100 sieves were between 0 and 0.1
ounces. For each of these measurements 0.05oz was recorded in order to maintain that this particle size
was present in the sample, however never greater than 1% by weight.
Soil samples were tested for permeability by spreading a ½” layer of soil from each sample across
a #80 mesh sieve. Soils were weted to saturation prior to saturation as permeability was significantly
higher in dry soil. The fully saturated condition tested represents worst case permeability.
PERMABILITY TESTING
Sample 1 Sample 2 Sample 3 Average
Soil Sample Thickness (in) 0.5 0.5 0.5
Time (s) 31 29 31
h1 (water column height start) 1 1 1
h2 (water column height end) 0.5 0.5 0.5
K (in/s) 0.012138306 0.012975 0.012138
K (in/hr) 44 47 44 45
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VICINITY MAP
TEST SITE ON
SOUTH SIDE OF
RESIDENCE
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Summary of Test Results
BOREHOLE 1
LOCATION: 44’ NORTH OF C.L. OF SE 173st, 22’ EAST OF WEST PROPERTY LINE.
0
2’
Extremely organic, rich, very dark brown, moderate moisture
content, grains are rounded and range 0.2 -3.0mm with
occasional fine gravel
TERMINATION OF TEST
SAMPLE 4
SAMPLE 2
SAMPLE 1 1’
3’
4’
SAMPLE 3
Some organic material, moderately moist, dark brown, fine
sand with silt and some gravel, small grains are clumping
together.
Moderately moist, dark/medium orange brown, coarse sand
and fine gravel with some fine sand, a few very coarse gravel
clasts (bordering on small cobbles) approximately 4cm
diameter, smaller grains clumping together from moisture.
Organic, rich, dark orange brown, fine gravels with sand and
silt, some medium gravel clasts, finer grains clump together
due to moisture.
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Conclusions
We have determined that the site is constructed upon a silt. We have furthermore
calculated that your soil has a permeability of 45 inches/hour. Hardpan was not detected to the
limits of the test dept. Soils can generally and conservatory be classified as sandy loam due to the
large amounts of organics present and generally coarse grained nature of the soil. A limited
infiltration system is recommended for this site. A trench length of 125’ is recommend for this
site.
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