APPROVED STM RESUB2 BLD2024-0547+Storm_Drainage_Report+11.5.2024_1.55.21_PM+4602799A
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47151421d Place SW #B, Edmonds, WA 98026
FurrEngineering@gmail.com
RESUB
Nov 05 2024
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
BLD2024-0547
Technical Information Report
REID SINGLE FAMILY RESIDENCE
Edmonds, Washington - King County
Parcel # 27032300101 100
326 Sunset Ave.
Edmonds, WA 98020
For: Kevin and Carolyn Reid
326 Sunset Ave.
Edmonds, WA 98020
ckreid93@comcast.com
April 15, 2024
Revised: 8/ 13/2024
111#1:7b11► .I
46937
GISTE
SSIONAL
Prepared by: J. Vidal, E.I.T.
Jean-luc@furrengineering.com
(206)605-8017
FES Project #23088
0/28/24
COMPLIES WITH APPLICABLE
CITY STORMWATER CODE
1 12/20/2024 1
www.furrengineering.com
Table of Contents
1.0 PROJECT OVERVIEW..........................................................................................1
2.0 CONDITIONS AND REQUIREMENTS SUMMARY................................................2
Analysis of the (9) Minimum Requirements/Additional LID Requirements .............2
Additional Requirements.......................................................................................6
3.0 OFF -SITE ANALYSIS............................................................................................7
DEFINE AND MAP THE STUDY AREA................................................................7
RESOURCE REVIEW...........................................................................................9
PugetSound......................................................................................................... 9
No mapped floodplains exist on site......................................................................9
FieldInspection...................................................................................................10
Drainage System Description and Problem Description......................................10
4.0 STORMWATER ANALYSIS AND DESIGN.........................................................12
WaterQuality......................................................................................................13
Emergency Overflow...........................................................................................13
FloodPlain..........................................................................................................13
DIRECT DISCHARGE ANALYSIS......................................................................14
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN...........................................19
6.0 SPECIAL REPORTS AND STUDIES...................................................................20
8.0 ESC ANALYSIS AND DESIGN............................................................................22
9.0 BOND QUANTITIES............................................................................................23
10.0 OPERATIONS AND MAINTENANCE MANUAL..................................................24
APPENDIX A: 332 SUNSET AVE TECHNICAL INFORMATION REPORT..................28
Page i
1.0 PROJECT OVERVIEW
The Reid SFR is in Edmonds, Washington. The site is bound by urban residential homes
to the north, south, east and west by Sunset Avenue North. More generally, the site is
located within the SE 1/4 of the NE 1/4, Section 23, Township 27 North Range 3 East WM.
The project area consists of a single parcel #27032300101100, 326 Sunset Ave. N and
approximately 0.182ac in size. The site has an existing single family residence. The site
currently takes access from an alley to the south. The site slopes to the W at
approximately 3% and is covered mostly by impervious surface (roof and paving). There
is an existing detention system that drains through a weephole in the curb along Sunset
Ave N.
The project proposes to construct a new 3-story single family residence and detached
garage. The vehicle access will be from the alley. The existing sidewalk will be replaced
with a new sidewalk. Existing detention system and weephole to be removed. Typical
urban Landscaping and screening is proposed.
Site soils analysis was performed by Cobal Geosciences, Inc. and found the site is
underlain by Whidbey Formation deposits which become denser with depth. On page 6
of the report, the soils are characterized as very fine grained and represent an aquitard
and the unweathered Whidbey Deposits act as a restrictive layer due to poor hydraulic
conductivity. Groundwater was not detected during soil investigation.
"Infiltration is not feasible due to the presence of mottled fine grained soils and a very
shallow restrictive layer. We recommend direct or perforated connection of new runoff
devices to City infrastructure." The project is subject to Category 2 Stormwater Site Plans
and is required to utilize on -site stormwater management techniques to the maximum
extent feasible. The project proposes to connect to the existing storm system in the
adjacent property owner to the north (within a recorded easement). The project
stormwater is considered "DIRECT DISCHARGE" because it is conveyed within an
engineered storm drainage system that will discharge into the Puget Sound. The facility
will be sized to Flow Control Duration Standard — Matching Forested Conditions using
WWHM 2012 in accordance with the 2019 Department of Ecology Stormwater
Management Manual of Western Washington (SWMMWW) and the 2022 City of Edmonds
Stormwater Addendum.
Page 1
2.0 CONDITIONS AND REQUIREMENTS SUMMARY
Hearing Examiners TBD
Analysis of the (9) Minimum Requirements/Additional LID Requirements
MR #1. Preparation of Stormwater Site Plans
This report will serve as the Stormwater Site Plan, prepared per City code and the
SMMWW.
MR #2. Construction Stormwater Pollution Prevention
Construction Stormwater Pollution Prevention Plans are prepared per the SMMWW to
address the 13 elements. A SWPPP will be provided as a separate document for
approval.
MR #3. Source Control of Pollution
ECDC 18.030.060.3 Source Control of Pollution. All known, available and reasonable
source control BMPs must be required for all projects approved by the city. Source control
BMPs must be selected, designed, and maintained in accordance with Volume IV of the
SWMMWW. All single-family residential projects shall, at a minimum, incorporate required
BMPs from SWMMWW Volume IV, S411 — BMPs for Landscaping and Lawn/Vegetation
Management.
BMPS for Landscaping
• All landscape clippings will be disposed of in a recycling bin picked up by the local
waste management company.
Additional BMP's for Landscaping
• Cover all "exposed" soils with 2" thick mulch per BMP C121
o for more than 1 week during the dry season
o for more that two days
• Mulch mowing when practical
BMPs for Pesticides
Use a minimum risk pesticide safe the environment.
• Remove infested vegetation by mechanical method
• if applying a pesticide use as directed only in the area of the infestation during a
day that is not windy or rain forecast
Recommended Pesticides
Wondercide Outdoor Pest Control Spray
Active Ingredients:
Cedarwood Oil 12.63%
Sesame Oil 2.73%
Sodium Lauryl Sulfate (derived from plants) 1.09%
Inert Ingredients (Water, Glyceryl Monooctanoate, Soap, Decanoic acid,
Monoester with 1,2,3-Propanetriol) 83.55%
Page 2
EcoSmart Insect Killer Granules
Active Ingredients:
Clove Oil 2.00%
Thyme Oil 0.60%
Inert Ingredients (Corn Cobbs and Wintergreen oil) 97.40%
BMPs for Vegetation Management
Prepare all soils with at least an 8" "topsoil" with at least 8% organic matter
to provide a sufficient vegetation -growing medium.
grass seed mix should be per the tables for "Landscaping Seed Mix" or
"Low -Growing Turf seed mix" in BMP C120
MR #4. Preservation of Natural Drainage Systems and Outfalls
Under existing conditions, stormwater sheet flows toward Sunset Ave N. and flows north
along the curb for approximately 250'. Stormwater enters the catch basin and flows
through an 12" pipe offsite to a discharge point within BNSF right-of-way and discharges
into the Puget Sound approximately 370ft downstream of the project site.
After development, stormwater will be conveyed by an 8" storm header to the storm
drainage system on 332 Sunset Ave N., which is itself connected to the storm drainage
system on 340 Sunset Ave N., which direct discharges to the Puget sound via a connection
to that same catch basin. Therefore, the existing drainage pattern will remain unchanged.
MR #5. On -site Stormwater Management/LID
Flow control BMPS, such as post construction soil amendment will be used for On -site
Stormwater Management.
Site soils analysis was performed by Cobal Geosciences, Inc. and found the site is
underlain by Whidbey Formation deposits which become denser with depth. On page 6
of the report, the soils are characterized as very fine -grained and represent an aguitard
and the unweathered Whidey Deposits act as a restrictive layer. "Infiltration is not feasible
due to the presence of mottled fine grained soils and a very shallow restrictive layer. We
recommend direct connection of new runoff devices to City infrastructure."
ECDC 18.030.060.D.5.b.v "Direct Discharge Requirement. Projects that discharge
directly to Puget Sound through the city's MS4 (in accordance with the restrictions
applicable to direct discharges to Puget Sound presented in Section 3.4.7 of Volume I of
the SWMMWW) do not have to achieve the LID performance standard, nor consider
bioretention, rain gardens, permeable pavement, or full dispersion, but must implement
BMP T5.13 (Post -Construction Soil Quality and Depth); BMPs T5.10A (Downspout Full
Infiltration Systems), T5.10B (Downspout Dispersion Systems), or T5.10B (Perforated
Stub -out Connections); and BMP T5.11 (Concentrated Flow Dispersion) or T5.12 (Sheet
Flow Dispersion); if feasible for all new plus replaced hard surfaces and land disturbed.
See the SWMMWW and the Edmonds Stormwater Addendum for additional details on
on -site Stormwater management BMP feasibility."
Page 3
The project proposes to implement BMP T5.13 (Post -Construction Soil Quality and
Depth)
See the following
List #2: On -site Stormwater Management BMPs for Projects Triggering Minimum
Requirements #1 through #9
For each surface, consider the BMPs in the order listed for that type of surface. Use the
first BMP that is considered feasible. No other Onsite Stormwater Management BMP is
necessary for that surface. Feasibility shall be determined by evaluation against:
• Design criteria, limitations, and infeasibility criteria identified for each BMP in the
SMMWW, and
• Competing Needs Criteria listed.
• See also Volume III, Appendix III-D for a summary of infeasibility criteria for all
BMP's
• The City of Edmonds allows bypass up to 1,OOOsf MAX, only after
demonstrating that collection of these areas is infeasible.
I. Lawn and landscaped areas:
1. Post -Construction Soil Quality and Depth BMP T5.13 on Pg. 911;
This BMP will be implemented to the maximum extent feasible. See the plan
for this BMP location and option.
II. Roofs:
1. Full Dispersion (65/10) BMP T5.30 on Pg. 939, or Downspout Full Infiltration
Systems BMP T5.10A on Pg. 905;
A minimum forested or native vegetation flowpath length of 100 feet (25 feet
for sheet flow from a nonnative pervious surface) cannot be achieved.
There is not at least 1 foot or more of permeable soil from the proposed
bottom of the infiltration system to the seasonal high groundwater table or
other impermeable layer.
2. Bioretention BMP T7.30 on Pg. 959, must have a minimum horizontally projected
surface area below the overflow which is at least 5 percent of the total surface
are draining to it;
Where the minimum vertical separation of 1 foot to the seasonal high
groundwater or other impermeable layer would not be achieved below
bioretention
3. Downspout Dispersion systems BMP T5.10B on Pg. 905;
For splash blocks, a vegetated flow path at least 50 feet in length from the
downspout to the downstream property line, structure, stream, wetland,
slope over 15 percent (unless a geotechnical assessment and soils report
is prepared addressing the potential impact of the proposed system), or
other impervious surface is not feasible.
4. Perforated Stub -out Connections BMP T5.10C on Pg. 905;
Page 4
The only location available for the perforated stub -out connection is under
impervious or heavily compacted soils.
5. Detention Vaults and Pipes;
Downstream analysis in Minimum Requirement No. 4, or available City data,
indicate that peak flow control from the site is not beneficial.
III. Other Hard Surfaces:
Full Dispersion (65/10) BMP T5.30 in accordance with Volume VI Section 2.3, or
Downspout Full Infiltration Systems BMP in accordance with Volume III, Section
3.9.3.
A minimum forested or native vegetation flowpath length of 100 feet (25 feet
for sheet flow from a nonnative pervious surface) cannot be achieved.
2. Permeable pavement BMP T5.15 in accordance with Volume III, Section 3.5.
Where the seasonal high groundwater or an underlying impermeable/low
permeable layer would create saturated conditions within 1 foot of the
bottom of the lowest gravel base course.
3. Bioretention BMP T7.30 on Pg. 959, must have a minimum horizontally projected
surface area below the overflow which is at least 5 percent of the total surface
are draining to it;
Where the minimum vertical separation of 1 foot to the seasonal high
groundwater or other impermeable layer would not be achieved below
bioretention
4. Sheet Flow Dispersion BMP T5.12 on Pg. 908 or Concentrated Flow Dispersion
BMP on Pg. 905
For flat to moderately sloped areas, at least a 10-foot-wide vegetation buffer
for dispersion of the adjacent 20 feet of contributing surface cannot be
achieved.
5. Detention Vaults and Pipes;
Downstream analysis in Minimum Requirement No. 4, or available City data,
indicate that peak flow control from the site is not beneficial.
THE PROJECT PROPOSES A "DIRECT DISCHARGE" OF ALL IMPERVIOUS
SURFACES AND THEREFORE NO OTHER "ROOF" OR "HARD SURFACES" BMP'S
WILL BE ADDRESSED.
MR #6. Runoff Treatment
The project PGHS, 1,105sf is LESS than the 5,OOOsf threshold, therefore, run off
treatment is NOT REQUIRED. The roof will be coated to eliminate pollutants entering the
drainage system.
MR #7. Flow Control
The project has a total (ON+OFF-SITE) impervious area of 6,113 sf < 10,000 sf threshold,
therefore flow control per MR #7 is NOT REQUIRED. We propose to DIRECT
DISCHARGE into the storm system that is hydraulically connected to the Puget Sound.
See section 4 of the drainage report for clarification of flow control, calculations, and
analysis.
Page 5
MR #8. Wetlands Protection
There are no wetlands on the site or nearby the site.
MR #9. Operation and Maintenance
Operation and Maintenance of the storm drainage system for this project will be provided
in Section 10.
Stormwater conveyance will be analyzed in Section 5 of this report
Financial Liability
A bond quantities worksheet for construction and landscaping will be provided.
Additional Requirements
Protection of LID Facilities during and after construction
Areas identified for LID (infiltration/bioretention) shall be shown of the TESC
plan and protected by fencing.
Construction in these areas shall be limited to light duty vehicles and/or hand
work.
After construction, surficial LID BMP's (bioretention/raingardens) shall remain
protected until site is full stabilized.
Downstream Analysis
This Category 2 Project will identify off -site impacts of stormwater
(conveyance capacity, flooding, erosion (stream bank), through site visit and
resource review.
Propose mitigation measures when stormwater issues are identified.
Page 6
3.0 OFF -SITE ANALYSIS
DEFINE AND MAP THE STUDY AREA
The site is located at 326 Sunset Ave N., Edmonds.
See Figure 1 and Figure 2 for maps of the study area.
71 7-424
O
77,23
o
WA-0
Figure 1: City of Edmonds GIS Vicinity Map
Page 7
Figure 2: City of Edmonds GIS TOPOGRAPHY
Page 8
RESOURCE REVIEW
Adopted Basin Plans:
Puget Sound
Floodplain/Floodway (FEMA) Map
No mapped floodplains exist on site.
City of Edmonds GIS
Critical Areas
o Landslide and Erosion Layers shows a "very" small Erosion Hazard Area
(15%-40%). No other landslide or erosion hazards adjacent to the site.
[.
10
6
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A small portion of the seismic hazard area is on the west edge of the site.
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Page 9
o The floodplain is west of the site.
Iff
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o review of the remaining sublayers (i.e. creeks, earth subsidence, etc.)
shows no additional critical areas on or adjacent to the site.
Field Inspection
Date: April 4, 2024
Time: 10:10 pm
Weather Observation: overcast, 46°F, 15mph wind in a NNW direction
24-hour precipitation: 0.00 inches (wunderground website)
Monthly Precipitation: 2.72 inches (wunderground website)
A field investigation was performed by Jean -Luc Vidal, E.I.T. of Furr Engineering
Services to determine the existing upstream and downstream storm drainage
patterns.
Drainage System Description and Problem Description
Upstream
There is no significant upstream run-on from the adjacent single family residences.
Downstream
Stormwater sheet flows toward Sunset Ave N. and flows north west along the curb
for approximately 250'. Stormwater enters the catch basin and flows through an
12" pipe offsite to a discharge point within BNSF right-of-way and discharges into
the Puget Sound approximately 370ft downstream of the project site.
See the exhibit on the following page.
Page 10
mm
Page 11
4.0 STORMWATER ANALYSIS AND DESIGN
The project is subject to Category 2 Stormwater Site Plans and is required to utilize
on -site stormwater management techniques to the maximum extent feasible. The
facility will be sized to Flow Control Duration Standard — Matching Forested
Conditions using WWHM 2012 in accordance with the 2019 Department of
Ecology Stormwater Management Manual of Western Washington (SWMMWW)
and the 2022 City of Edmonds Stormwater Addendum.
Existing Site Hydrology
The Reid SFR is in Edmonds, Washington. The site is bound by urban residential
homes to the north, south, east and west by Sunset Avenue North. More
generally, the site is located within the SE 1/4 of the NE 1/4, Section 23, Township
27 North Range 3 East WM. The project area consists of a single parcel
#27032300101100, 326 Sunset Ave. N and approximately 0.182ac in size. The
site has an existing single family residence. There is an existing detention system
that drains through a weephole in the curb of Sunset Ave N. The site currently
takes access from an alley to the south. The site slopes to the W at approximately
3% and is covered mostly by impervious surface (roof and paving).
This area per NRCS Soil survey classifies this area as Alderwood-Urban land
complex, 2-8 percent, hydrologic soil group "B" (moderately well drained).
See the following existing conditions area breakdown table, and the Existing
Conditions Exhibit at the end of this section.
EXISTING CONDITIONS
Sf
ac
PARCEL AREA
7,920.00
0.182
DISTURBED AREA ON -SITE
7,920.00
0.182
IMPERVIOUS
5,134
0.118
HOUSE
3,470
0.080
WALKWAY
1008
0.023
DECK
128
0.003
DRIVEWAY
528
0.012
PERVIOUS (LS)
2,786
0.064
DISTURBED AREA (OFF -SITE)
162
0.004
IMPERVIOUS
162
0.004
SIDEWALK/DRIVEWAY
162
0.004
PERVIOUS (LS)
0
0.000
Tablet: Existing Conditions area breakdown
Page 12
Developed Site Hydrology
The project proposes to construct a new 3-story single family residence and
detached garage. Vehicle access will be from the alley. The following table shows
the lot area breakdown.
PROPOSED DEVELOPED
sf
ac
DISTURBED AREA (ON -SITE)
7,920
0.182
IMPERVIOUS
6,119
0.140
PGHS
1,112
0.026
DRIVEWAY
1,112
0.026
HOUSE ROOF
3,331
0.076
GARAGE ROOF
436
0.010
CONCRETE WALL
211
0.005
WALK/PAVERS
1,030
0.024
PERVIOUS (LS)
1,801
0.041
DISTURBED AREA (OFF -SITE)
162
0.004
PGHS
136
0.003
DRIVEWAY
136
0.003
CONCRETE SIDEWALK
26
0.001
IMPERVIOUS ON/OFF-SITE
6,281
0.144
Table 2: Developed On/Off-Site area break down
The project proposes to collect all on -site runoff in trench and yard drains and
convey it along the south side of the proposed building into the storm drain system
on the 332 Sunset Ave N property. The project roof runoff will enter downspout on
the north side and discharge into the storm pipe on the north side of the house.
Stormwater will enter a Type 2, 48" CB where it will connect to the existing storm
system within the adjacent property at 340 Sunset Ave. N. A storm drainage
easement for use of the existing private storm drainage system will be required to
the project parcel. The project proposes to construct a water feature that will not
be connected to the stormwater system, HOWEVER, it is included in the above
analysis for additional conservative analysis.
Water Quality
The project PGHS, 1,248sf which is LESS than the 5,000sf threshold, therefore,
run off treatment is NOT REQUIRED. Additionally, a catch basin will be fitted with
a floatable separator. The roof will be coated to eliminate pollutants entering the
drainage system.
Emergency Overflow
Not required
Flood Plain
Review of the City website GIS map shows that this property is outside of the 100-
year flood Zone.
Page 13
DIRECT DISCHARGE ANALYSIS
The project to proposes to direct discharge into the existing drainage system,
connecting to the existing private discharge system in the adjacent property 332
Sunset Ave N. First, it must be determined that the existing drainage system has
capacity for the additional runoff associated with the new development. This will
be accomplished by using WWHM analysis of the Reid property, as well as data
concerning the existing drainage basin and properties calculated in the Technical
Information Report for 332 Sunset Ave N. (see Appendix A pages 15 and 16).
The existing drainage basin encompasses approximately 3.90ac shown in the
Basin Analysis Exhibit. Stormwater generally sheet flows to the west and enters
the catch basin within Sunset Ave N near the 340 Sunset Ave. N. address.
However, stormwater from the project site will be collected on site and
discharged into the existing discharge system within the adjacent property at 332
Sunset Ave. N. It appears that stormwater from the adjacent properties 332, 340
,and 336 Sunset Ave. N are connected to the same CB.
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Figure 3: DOWNSTREAM MAP
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J---------— — — — — — — —
Page 14
WWHM INPUT FOR REID
SF
AC
PREDEVELOPED
TOTAL
0.186
C, Forest,Flat
8,082
0.186
DEVELOPED
TOTAL
0.186
C, Pasture,Flat
1,801
0.041
DRIVEWAYS/FLAT
1,247
0.029
ROOF TOPS/FLAT
3,767
0.086
SIDEWALKS/FLAT
1,267
0.029
Table 3:WWHM input table for the Reid SFR
The previous table was used as input into WWHM to obtain the flows from the
proposed Reid SFR project. Data concerning the 100 year flows of the existing
332/340/336 Sunset Ave. N. residences, as well as the Basin area tributary are
found in Appendix A, page 15. See the following table.
REID PROPERTY
332, 336,340 ADDRESSES
SUNSET AVE N BASIN
Flow Frequency
Flow Frequency
Flow Frequency
Flow(cfs) 15m
Flow(cfs) 15m
Flow(cfs) 15m
100 Year = 0.1215
1 100 Year = 0.4845
100 Year = 2.2933
Table 4: 100 Year Flow Analysis
PIPE DATA
REACH
1
REACH
2
REACH
3
REACH
7
REACH
8
REACH
9
PIPE SIZE (IN)
12
12
12
8
8
8
PIPE MATERIAL
N12,
SD
N12,
SD
N12, SD
PVC
PVC
PVC
PIPE LENGTH (FT)
103
21
153
48
36
56
0 UP TO DOWNSTREAM (FT)
0.53
0.25
30.17
.48
.36
2.23
SLOPE (FT/FT)
0.0051
0.0119
0.1972
0.01
0.01
3.98
MANNINGS EQ. QFULL (CFS)
2.78
4.22
17.19
1.313
1.313
2.619
Table 5: Downstream Pipe Data Table
The above table shows the pipe data and Manning equation (Qfull) for the three
pipe reaches shown in the above figure.
Analysis of PIPE CAPACITY using Manning equation
Q(full) = 1.49/n*A*R2/3*S1/2 =(1.49/0.012)(7r/4*8)(0.5/2)2/3(0.006)1/2
Page 15
REACH ID
WWHM 100YR (cfs)
MANNING (Qfull cfs)
Pipe Reach 7
0.1215
<<
1.313
I Reid
Pipe Reach 8
0.1215
<<
1.313
Reid
Pipe Reach 9
0.1215
<<
2.619
Reid
Pipe Reach 1
0.6060
<<
2.78
Reid+340/336/332
Pipe Reach 2
0.6060
<<
4.22
Reid+340/336/332
Pipe Reach 3
2.293
<<
17.19
TOTAL BASIN AREA
Table 6: Flow comparison WWHM vs Manning for each Reach
Review of the above table, it can be shown that the proposed and existing pipes
have capacity to convey the proposed project stormwater runoff for the 100yr
storm.
Page 16
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PROPERTY BOUNDARY
:1 DISTURBED AREA
ROOF
a. 'd
CONCRETE
DECK
EXISTING CONDITIONS
Sf
ac
PARCELAREA
7,920
0.182
DISTURBED AREA ON -SITE
7,920
0.182
IMPERVIOUS
5,134
0.118
HOUSE
3,470
0.080
WALKWAY
1008
0.023
DECK
128
0.003
DRIVEWAY
528
0.012
PERVIOUS (LS)
2,786
0.064
DISTURBED AREA (OFF -SITE)
162
0.004
IMPERVIOUS
162
0.004
SIDEWALK/DRIVEWAY
162
0.004
PERVIOUS (LS)
0
0.000
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Date:
10/28/2024
FES Project No:
23088
Reference Sheet:
Drawing No:
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2 409185ft IE -37.1�8 PROPERTY BOUNDARY
4 pp, DOSTING 6 E IE 37.68
RESIDENCE #M2
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PN 27032300100900 56 LF DISTURBED AREA
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Date:
10/28/2024
FES Project No:
23088
\ Reference Sheet:
20 10 0 20 40
PN 270323001019008,
FIELDS MARJORIE M
GREEN
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327 2ND AVE N
xii
Drawing No:
SCALE: 1 INCH = 20 FEET
PROPOSED DEVELOPED
sf
ac
DISTURBED AREA (ON -SITE)
7,920
0.182
IMPERVIOUS
6,119
0.140
PGHS
1,112
0.026
DRIVEWAY
1,112
0.026
HOUSE ROOF
3,331
0.076
GARAGE ROOF
436
0.010
CONCRETE WALL
211
0.005
WALK/PAVERS
1,030
0.024
PERVIOUS (LS)
1,801
0.041
DISTURBED AREA (OFF -SITE)
162
0.004
PGHS
136
0.003
DRIVEWAY
136
0.003
CONCRETE SIDEWALK
26
0.001
IMPERVIOUS ON/OFF-SITE
6,281
0.144
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN
The on -site conveyance system will be designed to convey the 25-year, 24-hour
and 100-year, 24-hour storm events.
Using Mannings equation a,
6-inch pipe @ 2.0% slope has the capacity to convey 0.86cfs.
8-inch pipe @1.0% slope has the capacity to convey 1.85cfs.
Page 19
6.0 SPECIAL REPORTS AND STUDIES
Geotechnical Evaluation, Proposed Residence, 326 Sunset Avenue, Edmonds, Wa, by Cobalt
Geosciences, LLC, dated September 13, 2023
Page 20
7.0 OTHER PERMITS
The following permits and/or approvals are thought to be required as part of this
project:
• Clearing and Grading Permit
• Right -Of -Way use Permit
• Land Use Permit
Page 21
8.0 ESC ANALYSIS AND DESIGN
TESC measures are put into place to prevent sediment from leaving the site. The
site is generally flat. The proposed TESC plan will include, but not be limited to,
the following guidelines set in the jurisdictions Minimum Requirement
"Construction Stormwater Pollution Prevention".
A SWPPP will be provided to address:
Clearing Limits — Clearing limits specify the boundary of the work to be done.
Clearing are defined on the TESC plans and will be flagged in the field.
2. Cover Measures — Cover measures are involved (typically) with the means
to control erosion of exposed soil and are specified on the TESC plans.
3. Perimeter Protection — Perimeter protection keeps site sediment from leaving
the construction site. This type of protection typically involves a silt fence.
The silt fence and clearing limits are shown on the TESC plans.
4. Traffic Area Stabilization — Traffic area stabilization is addressed by a
stabilized construction entrance.
5. Sediment Retention — Retention will be established by silt fences around the
perimeter and catch basin inserts that will control of the on -site sediment -
laden water.
6. Surface Water Collection — Surface water will sheet flow to a downstream
catch basin with inlet protection per Edmonds Standard Plan ER-902.
7. Dewatering Control — Any water from dewatering shall be filtered or
contained so sediment can filter out prior to discharge downstream.
8. Dust Control — Dust control will be provided by sprinkling.
9. Wet Season Construction — Construction will be conducted according to the
jurisdiction's standards during the wet season.
10. Construction Within Sensitive Areas and Buffers - Any construction within the
wetland buffer will be subject to sensitive areas restrictions and is contained
in the TESC notes.
11. Maintenance — Maintenance requirements are detailed in the TESC notes
within the engineering plans.
12. Final Stabilization — Upon completion of the project, all disturbed areas will
be stabilized and Best Management Practices removed.
13. LID BMP's —Protect areas that will be designated as infiltration. Do not allow
turbid runoff to enter excavated infiltration facilities. If the soil porosity is
compromised, additional excavation is required to reach suitable soils.
Page 22
9.0 BOND QUANTITIES
NA
Page 23
10.0 OPERATIONS AND MAINTENANCE MANUAL
The conveyance system on this project will be privately owned and maintained by
the Owner.
See the following.
Page 24
Table V-4.5.2(5) Maintenance Standards - Catch Basins
Results
Maintenance
Conditions When Maintenance is
Expected
Component
Defect
Needed
When Main-
tenance is
performed
No Trash or
debris loc-
Trash or debris which is located imme-
ated imme-
diately in front of the catch basin opening or
diately in
is blocking inletting capacity of the basin by
front of catch
more than 10%.
basin or on
Trash or debris (in the basin) that exceeds
grate open-
60 percent of the sump depth as measured
ing.
from the bottom of basin to invert of the low-
No trash or
est pipe into or out of the basin, but in no
debris in the
Trash &
case less than a minimum of six inches
catch basin.
Debris
clearance from the debris surface to the
invert of the lowest pipe.
Inlet and out-
let pipes free
Trash or debris in any inlet or outlet pipe
of trash or
blocking more than 1/3 of its height.
debris.
General
Dead animals or vegetation that could gen-
No dead
erate odors that could cause complaints or
animals or
dangerous gases (e.g., methane).
vegetation
present
within the
catch basin.
Sediment (in the basin) that exceeds 60 per-
cent of the sump depth as measured from
the bottom of basin to invert of the lowest
pipe into or out of the basin, but in no case
No sediment
Sediment
less than a minimum of 6 inches clearance
in the catch
from the sediment surface to the invert of the
basin
lowest pipe.
Structure
Top slab has holes larger than 2 square
Top slab is
Damage to
inches or cracks wider than 1/4 inch. (Intent
free of holes
Frame and/or
is to make sure no material is running into
and cracks.
Top Slab
basin).
Frame is sit-
Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued)
Results
Maintenance
Conditions When Maintenance is
Expected
Component
Defect
Needed
When Main-
tenance is
performed
Frame not sitting flush on top slab, i.e., sep-
ting flush on
aration of more than 3/4 inch of the frame
the riser rings
from the top slab. Frame not securely
or top slab
and firmly
attached
attached.
Basin
Maintenance person judges that structure is
replaced or
unsound.
repaired to
Fractures or
design stand -
Cracks in
Grout fillet has separated or cracked wider
ards.
Basin Walls/
than 1 /2 inch and longer than 1 foot at the
g
Bottom
joint of any inlet/outlet pipe or any evidence
Pipe is
of soil particles entering catch basin through
regroutcd
cracks.
and secure at
basin wall.
Basin
Settlement/
If failure of basin has created a safety, func-
replaced or
Misalignment
tion, or design problem.
repaired to
design stand-
ards.
No veget-
Vegetation growing across and blocking
ation block -
more than 10% of the basin opening.
ing opening
to basin.
Vegetation
Vegetation growing in inlet/outlet pipe joints
No
that is more than six inches tall and less
veget-
than six inches apart.
ation or root
growth
present.
Contamination
See Detention Ponds (No. 1).
No pollution
and Pollution
present.
Cover Not in
Cover is missing or only partially in place.
Catch basin
Catch Basin
Place
Any open catch basin requires main-
cover is
Cover
tenance.
closed
Locking Mech-
Mechanism cannot be opened by one main-
Mechanism
anism Not
tenance person with proper tools. Bolts into
opens with
Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued)
Results
Maintenance
Conditions When Maintenance is
Expected
Component.
Defect
Needed
When Main-
tenance is
performed
Working
frame have less than 112 inch of thread.
proper tools.
One maintenance person cannot remove lid
Cover can be
Cover Difficult
after applying normal lifting pressure.
removed by
to Remove
(Intent is keep cover from sealing off access
one main -
tenance per -
to maintenance.)
son.
Ladder meets
design stand
Ladder Rungs
Ladder is unsafe due to missing rungs. not
ards and
Ladder
Unsafe
securely attached to basin wall, mis-
allows main -
alignment, rust, cracks, or sharp edges.
tenance per-
son safe
access.
Grate open -
Grate opening
Grate with opening wider than 7/8 inch.
ing meets
Unsafe
design stand-
ards.
Metal Grates
Trash and
Trash and debris that is blocking more than
Grate free of
(If Applic-
Debris
20% of grate surface inletting capacity.
trash and
able)
debris.
Grate is in
Damaged or
Grate missing or broken member(s) of the
place and
Missing.
grate.
meets design
standards.
APPENDIX A: 332 SUNSET AVE TECHNICAL INFORMATION REPORT
AI
p
N�GINEERING
ERMEI, PLLC
471514211 Place SW #B. Edmonds, WA 98026
FurrEngineering@gmail.com
CITY OF EDMONDS #BLD2021-1482
Technical Information Report
BURDETT SINGLE FAMILY RESIDENCE
Edmonds, Washington - King County
Parcel # 27032300100900
332 Sunset Ave.
Edmonds, WA 98020
For: Chris and Lisa Burdett
November 01, 2021
Revised: February 16, 2022
Revised: April 8, 2022
Prepared by: Dean A. Furr, P.E.
FES Project #21073
www.furrengineering.com
Table of Contents
1.0 PROJECT OVERVIEW..........................................................................................1
2.0 CONDITIONS AND REQUIREMENTS SUMMARY................................................2
Analysis of the (9) MINIMUM REQUIREMENTS/ADDITIONAL LID
REQUIREMENTS.................................................................................................2
Additional Requirements.......................................................................................6
3.0 OFF -SITE ANALYSIS............................................................................................7
DEFINE AND MAP THE STUDY AREA................................................................7
RESOURCEREVIEW...........................................................................................9
PugetSound.........................................................................................................
9
No mapped floodplains exist on site......................................................................9
FieldInspection...................................................................................................10
Drainage System Description and Problem Description......................................10
4.0 STORMWATER ANALYSIS AND DESIGN.........................................................12
ExistingSite Hydrology.......................................................................................12
Developed Site Hydrology...................................................................................12
On-Site................................................................................................................12
Off -Site (Frontage Improvements are not required).............................................13
WaterQuality......................................................................................................13
Emergency Overflow...........................................................................................14
FloodPlain..........................................................................................................14
DIRECT DISCHARGE ANALYSIS......................................................................14
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN...........................................21
6.0 SPECIAL REPORTS AND STUDIES...................................................................22
7.0 OTHER PERMITS................................................................................................23
8.0 ESC ANALYSIS AND DESIGN............................................................................24
9.0 BOND QUANTITIES............................................................................................25
10.0 OPERATIONS AND MAINTENANCE MANUAL..................................................26
Page i
1.0 PROJECT OVERVIEW
The Burdett SFR is in Edmonds, Washington. The site is bound by urban
residential homes to the north, south, east and west by Sunset Avenue North.
More generally, the site is located within the SE 1/4 of the NE 1/4, Section 23,
Township 27 North Range 3 East WM. The project area consists of a single parcel
#27032300100900, 332 Sunset Ave. N and approximately 0.27ac in size. The site
has an existing single family, detached garage and ADU. The site currently takes
access from Sunset Ave. N and the alley to the south. The site slopes to the W at
approximately 3% and is covered mostly by impervious surface (roof and paving).
The project proposes to construct a new 2-story single family residence and
attached garage. The primary vehicle access will be from the alley, while a single
on -site parking stall will be from a replaced driveway cut in Sunset Ave. N. The
existing concrete in the landscaping strip will be replaced by gravel and the existing
sidewalk will be replaced with a new sidewalk. Typical urban Landscaping and
screening is proposed.
Site soils analysis was performed by Cobal Geosciences, Inc. and found the site
is underlain by Whidbey Formation deposits which become denser with depth. On
page 6 of the report, the soils are characterized as very fine grained and represent
an aquitard and the unweathered Whidey Deposits act as a restrictive layer.
"Infiltration is not feasible due to the presence of mottled fine grained soils and a
very shallow restrictive layer. We recommend direct connection of new runoff
devices to City infrastructure."
The project is subject to Category 2 Stormwater Site Plans and is required to utilize
on -site stormwater management techniques to the maximum extent feasible. The
project proposes to connect to the existing storm system in the adjacent property
owner to the north (within a recorded easement). The project stormwater is
considered "DIRECT DISCHARGE" because it is conveyed within an engineered
storm drainage system that will discharge into the Puget Sound. The facility will be
sized to Flow Control Duration Standard — Matching Forested Conditions using
WWHM 2012 in accordance with the 2014 Department of Ecology Stormwater
Management Manual of Western Washington (SWMMWW) and the 2017 City of
Edmonds Stormwater Addendum.
Page 1
2.0 CONDITIONS AND REQUIREMENTS SUMMARY
Hearing Examiners TBD
Analysis of the (9) MINIMUM REQUIREMENTS/ADDITIONAL LID REQUIREMENTS
MR #1. Preparation of Stormwater Site Plans
This report will serve as the Stormwater Site Plan, prepared per City code and the
SMMWW.
MR #2. Construction Stormwater Pollution Prevention
Construction Stormwater Pollution Prevention Plans are prepared per the SMMWW to
address the 13 elements. A SWPPP will be provided as a separate document for
approval.
MR #3. Source Control of Pollution
ECDC 18.030.060.3 Source Control of Pollution. All known, available and reasonable
source control BMPs must be required for all projects approved by the city. Source
control BMPs must be selected, designed, and maintained in accordance with Volume IV
of the SWMMWW. All single-family residential projects shall, at a minimum, incorporate
required BMPs from SWMMWW Volume IV, S411 - BMPs for Landscaping and
Lawn/Vegetation Management.
BMPS for Landscaping
• All landscape clippings will be disposed of in a recycling bin picked up by the local
waste management company.
Additional BMP's for Landscaping
• Coverall "exposed" soils with 2" thick mulch per BMP C121
o for more than 1 week during the dry season
o for more that two days
• Mulch mowing when practical
BMPs for Pesticides
The current home owner have pets that will be in lawn/landscape areas and will only use
pesticides as a last resort. However, if they find that conventional non -chemical means of
pest control is not working, it is recommended to use a minimum risk pesticide safe for
pets and the environment.
• Remove infested vegetation by mechanical method
• if applying a pesticide use as directed only in the area of the infestation during a
day that is not windy or rain forecast
Recommended Pesticides
Wondercide Outdoor Pest Control Spray
Active Ingredients:
Cedarwood Oil 12.63%
Sesame Oil 2.73%
Page 2
Sodium Lauryl Sulfate (derived from plants) 1.09%
Inert Ingredients (Water, Glyceryl Monooctanoate, Soap, Decanoic acid,
Monoester with 1,2,3-Propanetriol) 83.55%
EcoSmart Insect Killer Granules
Active Ingredients:
Clove Oil 2.00%
Thyme Oil 0.60%
Inert Ingredients (Corn Cobbs and Wintergreen oil) 97.40%
BMPs for Vegetation Management
• Prepare all soils with at least an 8" "topsoil" with at least 8% organic matter
to provide a sufficient vegetation -growing medium.
• grass seed mix should be per the tables for "Landscaping Seed Mix" or
"Low -Growing Turf seed mix" in BMP C120
MR #4. Preservation of Natural Drainage Systems and Outfalls
The site is slopes to the west. After development the existing drainage pattern will remain
unchanged.
MR #5. On -site Stormwater Management/LID
Flow control BMPS, such as post construction soil amendment will be used for On -site
Stormwater Management.
Site soils analysis was performed by Coba/ Geosciences, Inc. and found the site is
underlain by Whidbey Formation deposits which become denser with depth. On page 6
of the report, the soils are characterized as very fine grained and represent an aguitard
and the unweathered Whidey Deposits act as a restrictive layer. 'Infiltration is not feasible
due to the presence of mottled fine grained soils and a very shallow restrictive laver. We
recommend direct connection of new runoff devices to City infrastructure. "
ECDC 18.030.060.D.b.iv "Direct Discharge Requirement. Projects that discharge
directly to Puget Sound through the city's MS4 (in accordance with the restrictions
applicable to direct discharges to Puget Sound presented in Section 2.5.7 of Volume I of
the SWMMWW) do not have to achieve the LID performance standard, nor consider
bioretention, rain gardens, permeable pavement, or full dispersion, but must meet the
following:"
(A) Projects must implement BMP T5.13 (Post -Construction Soil Quality and Depth);
BMPs T5.10A Downspout Full Infiltration Systems, T5.10B Downspout Dispersion
Systems, or T5.10B Perforated Stub -out Connections; and BMP T5.11
Concentrated Flow Dispersion or T5.12 Sheet Flow Dispersion; if feasible for all
new plus replaced hard surfaces and land disturbed. See the SWMMWW and the
Edmonds Stormwater Addendum for additional details on on -site stormwater
management BMP infeasibility.
The project proposes to implement BMP T5.13 (Post -Construction Soil
Quality and Depth)
Page 3
(B) Edmonds Way Specific Requirements. After applying the requirements in
subsection (D)(5)(b)(iv)(A) of this section, for all remaining project site runoff (e.g.,
from unmanaged surfaces, or from overflow from on -site BMPs), the post -
development 10- and 100-year recurrence interval peak flows shall not exceed
0.25 and 0.45 cubic feet per second per acre of impervious surface area,
respectively. See the Edmonds Stormwater Addendum for additional details.
The project is not along Edmonds Way.
See the following
List #2: On -site Stormwater Management BMPs for Projects Triggering Minimum
Requirements #1 through #9
For each surface, consider the BMPs in the order listed for that type of surface. Use the
first BMP that is considered feasible. No other Onsite Stormwater Management BMP is
necessary for that surface. Feasibility shall be determined by evaluation against:
Design criteria, limitations, and infeasibility criteria identified for each BMP in the
SMMWW, and
Competing Needs Criteria listed.
• See also Volume III, Appendix III-D for a summary of infeasibility criteria for all
BMP's
• The City of Edmonds allows bypass up to 1,O00sf MAX, only after
demonstrating that collection of these areas is infeasible.
I. Lawn and landscaped areas:
1. Post -Construction Soil Quality and Depth BMP T5.13 on Pg. 911;
This BMP will be implemented to the maximum extent feasible. See the plan
for this BMP location and option.
II. Roofs:
1. Full Dispersion (65/10) BMP T5.30 on Pg. 939, or Downspout Full Infiltration
Systems BMP T5.10A on Pg. 905;
These BMPs are NOT proposed, because the site does not have Native
Vegetation and "Infiltration is not feasible due to the presence of mottled fine
__grained soils and a very shallow restrictive laver" per Geotech Report.
2. Bioretention BMP T7.30 on Pg. 959, must have a minimum horizontally projected
surface area below the overflow which is at least 5 percent of the total surface
are draining to it;
This BMP is NOT proposed, because "Infiltration is not feasible due to the
presence of mottled fine __grained soils and a very shallow restrictive layer"
per Geotech Report.
3. Downspout Dispersion systems BMP T5.10B on Pg. 905;
Dispersion is NOT proposed because of the unavailable flow path required
for this BMP to perform adequately.
Page 4
4. Perforated Stub -out Connections BMP T5.10C on Pg. 905;
This BMP is NOT proposed, because "Infiltration is not feasible due to the
presence of mottled fine __grained soils and a very shallow restrictive layer"
per Geotech Report.
5. Detention Vaults and Pipes;
Any form of detention or stormwater flow control is unnecessary, because
the project proposes to "Direct Discharge" into the Puget Sound. Analysis
of the Downstream Conveyance system, Minimum Requirement #4 and the
"Direct Discharge Analysis" Section of this report shows that there is no
additional benefit to providing "Detention'; because the downstream pipes
have capacity to convey the 100 year Burdett runoff as well as the entire
100 year developed basin runoff to the Puget Sound.
III. Other Hard Surfaces:
1. Full Dispersion (65/10) BMP T5.30 in accordance with Volume VI Section 2.3, or
Downspout Full Infiltration Systems BMP in accordance with Volume III, Section
3.9.3.
These BMP's are NOT proposed, because the site does not have Native
Vegetation and "Infiltration is not feasible due to the presence of mottled fine
_grained soils and a very shallow restrictive" per Geotech Report.
2. Permeable pavement BMP T5.15 in accordance with Volume III, Section 3.5.
This BMP is NOT proposed, because "Infiltration is not feasible due to the
presence of mottled fine grained soils and a very shallow restrictive layer"
per Geotech Report.
3. Bioretention BMP T7.30 on Pg. 959, must have a minimum horizontally projected
surface area below the overflow which is at least 5 percent of the total surface
are draining to it;
This BMP is NOT proposed, because "Infiltration is not feasible due to the
presence of mottled fine _-grained soils and a very shallow restrictive layer"
per Geotech Report.
4. Sheet Flow Dispersion BMP T5.12 on Pg. 908 or Concentrated Flow Dispersion
BMP on Pg. 905
Dispersion is NOT proposed because of the unavailable flow path required
for this BMP to perform adequately.
5. Detention Vaults and Pipes;
Any form of detention or stormwater flow control is unnecessary, because
the project proposes to "Direct Discharge" into the Puget Sound. Analysis
of the Downstream Conveyance system, Minimum Requirement #4 and the
"Direct Discharge Analysis" Section of this report shows that there is no
additional benefit to providing "Detention'; because the downstream pipes
have capacity to convey the 100 year Burdett runoff as well as the entire
100 year developed basin runoff to the Puget Sound.
Page 5
THE PROJECT PROPOSES A "DIRECT DISCHARGE" OF ALL IMPERVIOUS
SURFACES AND THEREFORE NO OTHER "ROOF" OR "HARD SURFACES" BMP'S
WILL BE ADDRESSED.
MR #6. Runoff Treatment
The project PGHS, 1,549sf is LESS than the 5,OOOsf threshold, therefore, run off
treatment is NOT REQUIRED. Additionally, an on -site catch basin will be fitted with a
floatable containment structure. The roof will be coated to eliminate pollutants entering
the drainage system.
MR #7. Flow Control
The project has a total (ON+OFF-SITE) impervious area of 7,151sf < 10,000 sf threshold,
therefore flow control per MR #7 is NOT REQUIRED. We propose to DIRECT
DISCHARGE into the storm system that is hydraulically connected to the Puget Sound.
See section 4 of the drainage report for clarification of flow control, calculations, and
analysis.
MR #8. Wetlands Protection
There are no wetlands on the site or nearby the site.
MR #9. Operation and Maintenance
Operation and Maintenance of the storm drainage system for this project will be provided
in Section 10.
Stormwater conveyance will be analyzed in Section 5 of this report
Financial Liability
A bond quantities worksheet for construction and landscaping will be provided.
Additional Requirements
Protection of LID Facilities durinq and after construction
Areas identified for LID (infiltration/bioretention) shall be shown of the TESC
plan and protected by fencing.
Construction in these areas shall be limited to light duty vehicles and/or hand
work.
After construction, surficial LID BMP's (bioretention/raingardens) shall remain
protected until site is full stabilized.
Downstream Analysis
This Category 2 Project will identify off -site impacts of stormwater
(conveyance capacity, flooding, erosion (stream bank), through site visit and
resource review.
Propose mitigation measures when stormwater issues are identified.
Page 6
3.0 OFF -SITE ANALYSIS
DEFINE AND MAP THE STUDY AREA
Th offsite Analysis was prepared in accordance with Section 6.2.2 "Additional
Requirements", of the 2017 City of Edmonds Stormwater Addendum. The site is
located at 332 Sunset Ave N., Edmonds.
See Figure 1 and Figure 2 for maps of the study area.
O O
O❑
e
Figure 1: City of Edmonds GIS Vicinity Map
Page 7
Aim'. AMMOW
4.,
J46�
71 /"., rl
';77
70
��;- -
2 vq�
4— -W
PD7-1
M CR
*1 Ah. Ar 31,
Figure 2: City of Edmonds GIS TOPOGRAPHY
Page 8
RESOURCE REVIEW
Adopted Basin Plans:
Puget Sound
Floodplan/Floodway (FEMA) Map
No mapped floodplains exist on site.
City of Edmonds GIS
Critical Areas
o Landslide and Erosion Layers shows a "very" small Erosion Hazard Area
(15%-40%). No other landslide or erosion hazards adjacent to the site.
o A small portion of the seismic hazard area is on the west edge of the site.
Page 9
o The floodplain is west of the site.
o review of the remaining sublayers (i.e. creeks, earth subsidence, etc.)
shows no additional critical areas on or adjacent to the site.
Field Inspection
Date: May 10, 2021
Time: 3:30pm
Weather Observation: partly sunny, 65°F, 10mph wind in a NW direction
24-hour precipitation: 0.05 inches (wunderground website)
Monthly Precipitation: 1.23 inches (wunderground website)
A field investigation was performed by Dean A. Furr, P.E. of Furr Engineering
Services to determine the existing upstream and downstream storm drainage
patterns.
Drainage System Description and Problem Description
Upstream
There is no significant upstream run-on from the adjacent single family residences.
Downstream
Stormwater sheet flows toward Sunset Ave N. and flows north west along the curb
for approximately 165'. Stormwater enters the catch basin and flows through an
12" pipe "offsite" to a discharge point within BNSF right-of-way and discharges into
the Puget Sound approximately 250ft downstream of the project site.
See the exhibit on the following page.
Page 10
0
Page 11
4.0 STORMWATER ANALYSIS AND DESIGN
The project is subject to Category 2 Stormwater Site Plans and is required to utilize
on -site stormwater management techniques to the maximum extent feasible. The
facility will be sized to Flow Control Duration Standard — Matching Forested
Conditions using WWHM 2012 in accordance with the 2014 Department of
Ecology Stormwater Management Manual of Western Washington (SWMMWW)
and the 2017 City of Edmonds Stormwater Addendum.
Existing Site Hydrology
The Burdett SFR is in Edmonds, Washington. The site is bound by urban
residential homes to the north, south, east and west by Sunset Avenue North.
More generally, the site is located within the SE 1/4 of the NE 1/4, Section 23,
Township 27 North Range 3 East WM. The project area consists of a single parcel
#27032300100900, 332 Sunset Ave. N and approximately 0.29ac in size. The site
has an existing single family, detached garage and shed. The site currently takes
access from Sunset Ave. N and the alley to the south. The site slopes to the W at
approximately 3% and is covered mostly by impervious surface (roof and paving).
This area per NRCS Soil survey classifies this area as Alderwood-Urban land
complex, 2-8 percent, hydrologic soil group "B" (moderately well drained).
See the following existing conditions area breakdown table, and the Existing
Conditions Exhibit at the end of this section.
EXISTING CONDITIONS
sf
ac
PARCEL AREA (AFTER BLA)
12,724.30
0.29
DISTURBED AREA ON -SITE
11,833.60
0.27
IMPERVIOUS
6,754
0.16
HOUSE
1,721
0.04
GARAGE
616
0.01
ADU
561
0.01
DRIVEWAY
3857
0.09
SIDEWALK
111
0.00
PERVIOUS (LS)
5,080
0.12
DISTURBED AREA (OFF -SITE)
314
0.01
SIDEWALK/DRIVEWAY
156
0.00
CONCRETE (LANDSCAPE STRIP)
158
0.00
Table 1: Existing Conditions area breakdown
Developed Site Hydrology
On -Site
The project proposes to construct a new 2-story single family residence and
attached garage. The primary vehicle access will be from the alley, while a single
on -site parking stall will be from a replaced driveway cut in Sunset Ave. N. The
existing concrete in the landscaping strip will be replaced by gravel and the existing
Page 12
sidewalk will be replaced with a new sidewalk. Typical urban Landscaping and
screening is proposed. The following table shows the lot area breakdown.
PROPOSED DEVELOPED
Sf
ac
DISTURBED AREA (ON -SITE)
11,834
0.27
IMPERVIOUS
7,151
0.164
HOUSE
4,776
0.11
DRIVEWAY (SOUTH)
1,125
0.03
PARKING STALL
306
0.007
WATER FEATURE
84
0.002
SIDEWALK
111
0.003
PAVERS
749
0.017
PERVIOUS (LS)
4,683
0.107
DISTURBED AREA (OFF -SITE)
314
0.01
SIDEWALK/DRIVEWAY
156
0.00
GRAVEL (LANDSCAPE STRIP)
158
0.00
IMPERVIOUS ON/OFF-SITE
7,466
0.17
Table 2: Developed On/Off-Site area break down
The project proposes to collect all on -site runoff in catch basins and convey it along
the south side of the proposed building and direct discharge to the existing storm
system within Sunset Ave. N. The project roof runoff will be collected to the roof
level between the main house and garage. Stormwater will enter downspout on
the north side and discharge into the storm pipe on the north side of the house.
Stormwater will enter a Type 2, 48" CB where it will connect to the existing storm
system within the adjacent property at 340 Sunset Ave. N. A storm drainage
easement for use of the existing private storm drainage system will be required to
the project parcel. The project proposes to construct a water feature that will not
be connected to the stormwater system, HOWEVER, it is included in the above
analysis for additional conservative analysis.
Off -Site
The project proposes to replace the existing driveway with a City of Edmonds Type
III driveway. Additionally, the existing concrete within the landscape strip will be
replaced with washed gravel and existing sidewalk will be replaced and will be
ADA compliant.
DISTURBED AREA (OFF -SITE)
314
0.01
SIDEWALK/DRIVEWAY
156
0.00
GRAVEL (LANDSCAPE STRIP)
158
0.00
Table 3: Off -Site Area breakdown
Water Quality
The project PGHS, 1,549sf which is LESS than the 5,000sf threshold, therefore,
run off treatment is NOT REQUIRED. Additionally, a catch basin will be fitted with
a floatable separator. The roof will be coated to eliminate pollutants entering the
drainage system.
Page 13
Emergency Overflow
Not required
Flood Plain
Review of the City website GIS map shows that this property is outside of the 100-
year flood Zone.
DIRECT DISCHARGE ANALYSIS
The project to proposes to direct discharge into the existing drainage system.
First, it must be determined that the existing drainage system has capacity for the
additional runoff associated with the new development.
The existing drainage basin encompasses approximately 3.90ac shown in the
Basin Analysis Exhibit. Stormwater generally sheet flows to the west and enters
the catch basin within Sunset Ave N near the 340 Sunset Ave. N. address.
However, stormwater from the project site will discharge into the existing CB
within the adjacent property at 340 Sunset Ave. N. It appears that stormwater
from the Burdett SFR project and the adjacent 340/336 Sunset Ave. N
residences are connected to the same CB.
REACH 3
REACH t
REACH 2
Figure 3: DOWNSTREAM MAP
WWHM INPUT FOR
BURDETT
SF
AC
HOUSE
4,776
0.110
DWAY/STALL
1,431
0.033
SIDEWALK/PAVERS/WATER
944
0.022
PERVIOUS
4,683
0.107
TOTAL
11,833.60
0.272
WWHM INPUT FOR
340_336
AC
PARCEL
0.460
IMPERVIOUS
0.414
PERVIOUS
0.046
TOTAL
0.460
EXISTING BASIN
sf
ac
Page 14
BASIN
171,115.81
3.93
LAND USE
sf
ac
IMPERVIOUS
119,781
2.75
PERVIOUS (A/B SOIL)
51,335
1.18
ASSUME 70%
ASSUME A/B LAWN
Table 4:WWHM input table for the Burdett and adjacent 340_336 address
The previous table was used as input into WWHM to obtain the flows from the
proposed Burdett SFR project and the existing 340/336 Sunset Ave. N. residences,
as well as, the Basin area tributary to Pipe Reach 1 within Sunset Ave. N. See the
following table.
BURDETT PROJECT
340 336 ADDRESSES
Sunset Ave. N Basin
Flow Frequency
Flow Frequency
Flow Frequency
Flow(cfs) 080115m
Flow(cfs) 080215m
Flow(cfs) 050115m
2 Year = 0.0523
2 Year = 0.1327
2 Year = 0.8755
5 Year = 0.0713
5 Year = 0.1809
5 Year = 1.1937
10 Year = 0.0853
10 Year = 0.2164
10 Year = 1.4277
25 Year = 0.1046
25 Year = 0.2654
25 Year = 1.7512
50 Year = 0.1202
50 Year = 0.3051
50 Year = 2.0130
100 Year = 0.1370
100 Year = 0.3475
100 Year = 2.2933
Table 5: WWHM Developed Flow analysis
PIPE DATA
REACH
1
REACH
2
REACH
3
PIPE SIZE (IN)
12
12
12
PIPE MATERIAL
N12,
SD
N12,
SD
N12, SD
PIPE LENGTH (FT)
103
21
153
A UP TO DOWNSTREAM (FT)
0.53
0.25
30.17
SLOPE (FT/FT)
0.0051
0.0119
0.1972
MANNINGS EQ. QFULL (CFS)
2.78
4.22
17.19
Table 6: Downstream Pipe Data Table
The above table shows the pipe data and mannings equation (Qfull) for the three
pipe reaches shown in the above figure.
Analysis of PIPE CAPACITY using Mannings equation
Q(full) = 1.49/n*A*R2/3*S1/2 =(1.49/0.012)(7T/4*8)(0.5/2)2/3(0.006)1/2
REACH ID
WWHM 100YR (cfs)
MANNINGS (Qfull cfs)
Pipe Reach 1
0.4845
<<
2.78
Burdett+340/336
Pipe Reach 2
0.4845
<<
4.22
Burdett+340/336
Pipe Reach 3
2.293
<<
17.19
TOTAL BASIN AREA
Table 7: Flow comparison WWHM vs Manning for each Reach
Page 15
Review of the above table, it can be shown that the existing pipes have capacity
to convey the proposed project stormwater runoff for the 100yr storm.
Page 16
N 36.57
36.67
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-CB TYPE 1
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SCALE: 1 INCH = 30 FEET Edmonds, WA 98026
ph 206.890.8291
EXISTING CONDITIONS
Sf
ac
PARCEL AREA (AFTER BLA)
12,724.30
0.29
DISTURBED AREA ON -SITE
11,833.60
0.27
IMPERVIOUS
6,754
0.16
HOUSE
1,721
0.04
GARAGE
616
0.01
ADU
561
0.01
DRIVEWAY
3857
0.09
SIDEWALK
111
0.00
PERVIOUS (LS)
5,080
0.12
DISTURBED AREA (OFF -SITE)
314
0.01
SIDEWALK/DRIVEWAY
156
0.00
CONCRETE (LANDSCAPE STRIP)
158
0.00
EX HOUSE/CARPORT
EX DRIVEWAY
� DISTURBED AREA
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Date:
06/24/2021
Project No:
BURDE17 SFR
Reference Sheet:
21073
Drawing No:
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SCALE: 1 INCH = 30 FEET
r-,m
4715 142nd PI. SW #B,
Edmonds, WA 98026
ph 206.890.8291
PROPOSED DEVELOPED
Sf
ac
DISTURBED AREA (ON -SITE)
11,834
0.27
IMPERVIOUS
7,151
0.164
HOUSE
4,776
0.11
DRIVEWAY (SOUTH)
1,125
0.03
PARKING STALL
306
0.007
WATER FEATURE
84
0.002
SIDEWALK
111
0.003
PAVERS
749
0.017
PERVIOUS (LS)
4,683
0.107
DISTURBED AREA (OFF -SITE)
314
0.01
SIDEWALK/DRIVEWAY
156
0.00
GRAVEL (LANDSCAPE STRIP)
158
0.00
IMPERVIOUS ON/OFF-SITE
7,466
0.17
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DISTURBED AREA
PROP BUILDING
PROP PERVIOUS
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WATER FEATURE
ON -SITE PAVING/CONCRETE
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OFF -SITE PAVING/SIDEWALK
OFF ���
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Project No:
BURDE7 SFR
Reference Sheet:
Drawing No:
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DISTURBED AREA
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Sf
ac
REPLACED IMPERVIOUS
5,346
0.00
ELDGS A%D DRI''E':VAY
51:)46
0.12
NEW IMPERVIOUS
1,805
0.04
FART 0::H0USE A % D %E' lv, D':� ,'
1,505
0.04
NEW PLUS REPLACED IMPERVIOU
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0.16
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Project No:
BURDE17 SFR
Reference Sheet:
21073
Drawing No:
14LF, 12" CONC. PIPE
EX. CB
TOP 41.10
12"OUT N 36.57
12" IN E 36.67
v
DISCHARGE INTO PUGET SOUND
12" CONC. I.E. 3.7 OUT
CON. CONNECTION
12" IE 6.4 IN/OUT
EXIST. CB
TOP 39.96
12" OUT NW 35.71
CB#3 TYPE 1 12" IN S 35.81
TOP 40.82
12" W IE 36.82
12" E IE 36.92
1 /
7/
EX. CB TYPE 1 /
TOP 40.35
12" W IE 37.35 /
12" E IE 37.45
- CB TYPE 1
TOP 39.90
!� 12" W IE 37.58
8" N IE 37.68
�6"EIE37.68
BASIN LINE
EXISTING BASIN
sf
ac
BASIN
171,115.81
3.93
LAND USE
sf
ac
IMPERVIOUS
119,781
2.75
PERVIOUS (A/B SOIL)
51,335
1.18
Return Period Flow(cfs)
25 Year = 1.7512
50 Ye a r = 2.0130
100 Ye a r = 2.2933
PIPE DATA
PIPE SIZE (IN)
12
PIPE MATERIAL
N12, SD
PIPE LENGTH (FT)
153
A UP TO DOWNSTREAM (FT)
30.17
SLOPE (FT/FT)
0.1972
QFULL (CFS)
17.19
PIPE DATA
PIPE SIZE (IN)
12
PIPE MATERIAL
Conc. (avg)
PIPE LENGTH (FT)
14
A UP TO DOWNSTREAM (FT)
2.7
SLOPE (FT/FT)
0.1929
QFULL (CFS)
15.69
14
100 50 0 100 200
SCALE: 1 INCH = 100 FEET
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4715 142nd PI. SW #B,
Edmonds, WA 98026
ph 206.890.8291
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Date:
08/26/2020
Project No:
HURST SHORT PLAT
Reference Sheet:
Drawing No:
5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN
The on -site conveyance system will be designed to convey the 25-year, 24-hour
and 100-year, 24-hour storm events.
Using Mannings equation a,
6-inch pipe @ 2.0% slope has the capacity to convey 0.86cfs.
8-inch pipe @1.0% slope has the capacity to convey 1.85cfs.
Page 21
6.0 SPECIAL REPORTS AND STUDIES
Geotechnical Evaluation, Proposed Residential Development, 332
Sunset Avenue North, Edmonds, Wa, by Cobalt Geosciences, LLC,
dated May 27, 2021
Page 22
COBALT
G E 0 S C I E N C E S
May 27, 2021
Chris and Lisa Burdett
C/O Blake Fisher
blake Pblakefisherarchitecture. com
RE: Geotechnical Evaluation
Proposed Residential Development
332 Sunset Avenue North
Edmonds, Washington
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to
discuss the results of our geotechnical evaluation at the referenced site.
The purpose of our evaluation was to provide recommendations for foundation design, grading,
and earthwork.
Site Description
The site is located at 332 Sunset Avenue North in Edmonds, Washington. The site consists of one
rectangular shaped parcel (No. 27032300100900) with a total area of 0.27 acres.
The western portion of the site is developed with a single-family residence with shallow basement.
A driveway extends through much of the property. There is a detached garage in the eastern
portion of the property and another access from an alley to the south. There is an 8-12 inch tall
curb/wall along the sidewalk west of the residence.
Site vegetation includes grasses, bushes, shrubs, and small diameter trees. The site is nearly level
to very slightly sloping in multiple directions. There is a slight slope near the eastern property
line extending downward to the east and southeast.
The proposed development includes a new residence in the area of the existing residence. The
new residence may include slab -on -grade areas that would require backfilling of the current
shallow basement. Foundation loads will generally be light and grading may include cuts of 2 to 3
feet and fills of about 5 to 6 feet.
Area Geology
The Geologic Map of the Edmonds East and West Quadrangle, indicates that the site is underlain
by Whidbey Formation.
Whidbey Formation includes till like deposits, fine grained silts with sand and clay, and local
lacustrine silts. These materials are usually impermeable and are typically dense to very dense
below a weathered zone.
Soil & Groundwater Conditions
As part of our evaluation, we excavated two hand borings within the property, where accessible.
www.cobaltgeo.com (2o6) 331-1097
May 2'7, 2021
Page 2 of 10
Geotechnical Evaluation
The explorations encountered approximately 6 inches of grass and topsoil underlain by
approximately 3 to 4 feet of loose to medium dense, silty -fine to medium grained sand trace
gravel (Weathered Whidbey Formation). These materials were underlain by dense to very dense,
silty -fine to fine grained sand trace gravel (Whidbey Formation), which continued to the
termination depths of the explorations.
Groundwater was not encountered in the explorations; however, the shallow soils were mottled.
Perched groundwater could be present at shallow depths below the site during the winter months.
We anticipate that groundwater could be within 4 feet of the ground surface during the winter
months.
Water table elevations often fluctuate over time. The groundwater level will depend on a variety
of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and
soil permeability. Water levels at the time of the field investigation may be different from those
encountered during the construction phase of the project.
Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that
the site is underlain by Alderwood-Urban land complex (2 to 8 percent slopes). These soils would
have a slight erosion potential in a disturbed state depending on the slope magnitude.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping
and surface water runoff control. Typically, erosion of exposed soils will be most noticeable
during periods of rainfall and may be controlled by the use of normal temporary erosion control
measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The
typical wet weather season, with regard to site grading, is from October 31st to April ist. Erosion
control measures should be in place before the onset of wet weather.
Seismic Hazard
The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the
International Building Code (IBC). A Site Class D applies to an overall profile consisting of
stiff/medium dense soils within the upper too feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to
obtain values for Ss, Sl, FQ, and F,,. The USGS website includes the most updated published data
on seismic conditions. The following tables provide seismic parameters from the USGS web site
with referenced parameters from ASCE 7-10 and 7-16.
Seismic Design Parameters (ASCE 7-10)
Site
Spectral
Spectral
Site
Design Spectral
Design
Class
Acceleration
Acceleration
Coefficients
Response Parameters
PGA
at 0.2 sec. (g)
at 1.o sec. (g)
Fa
Fv
SDs
SD1
D
1.272
0.499
1.0
1.501
o.848
0.499
0.516
www.cobaltgeo.com (2o6) 331-1097
May 2'7, 2021
Page 3 of 10
Geotechnical Evaluation
Seismic Design Parameters (ASCE 7-16)
Site
Spectral
Spectral
Site
Design Spectral
Design
Class
Acceleration
Acceleration
Coefficients
Response Parameters
PGA
at 0.2 sec. (g)
at 1.o sec. (g)
Fa
F,
SDs
SD1
D
1.288
0.454
1.0
Null
1.031
Null
0.548
Additional seismic considerations include liquefaction potential and amplification of ground
motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a
high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null"
see Section 11.4.8 of the ASCE.
Conclusions and Recommendations
General
The site is underlain by Whidbey Formation deposits which become denser with depth. There
may be areas of fill associated with development in this part of Edmonds. Fill depths would likely
be 3 feet or less.
The proposed residence may be supported on a shallow foundation system bearing on medium
dense or firmer native soils or on structural fill placed on the native soils. Local overexcavation
or recompaction of loose weathered native soils may be necessary depending on the proposed
elevations and locations of the new footings.
Since the new residence will have slab on grade areas over a current basement. It is imperative
that the existing foundation and slabs be fully removed and that any loose soils be removed to the
level of medium dense or firmer soils prior to fill placement. New fills must be compacted per the
recommendations in this report in order to limit the likelihood of total and differential settlement
of the new building.
Site Preparation
Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich
soil and fill. Based on observations from the site investigation program, it is anticipated that the
stripping depth will be 6 to 12 inches. Deeper excavations will be necessary in areas of existing
foundation systems and in any areas underlain by undocumented fill.
The native soils consist of silty -sand with gravel to sandy silt with gravel. Most of the native soils
may be used as structural fill provided they achieve compaction requirements and are within 3
percent of the optimum moisture. Some of these soils may only be suitable for use as fill during
the summer months, as they will be above the optimum moisture levels in their current state.
These soils are variably moisture sensitive and may degrade during periods of wet weather and
under equipment traffic.
In general, we recommend importing select fill or crushed rock to support new footings and slab
areas.
www.cobaltgeo.com (2o6) 331-1097
May 2'7, 2021
Page 4 of 10
Geotechnical Evaluation
Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of
3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve).
Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted
to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the
ASTM D 1557 test method.
Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts
on the order of approximately 6 feet or less for foundation removal and utility placement.
Temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose
native soils and fill, 1H:1V in medium dense native soils and 3/41-1:1V in dense to very dense
native soils, if encountered at depth. If an excavation is subject to heavy vibration or surcharge
loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits.
Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part
N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a
qualified person during construction activities and the inspections should be documented in daily
reports. The contractor is responsible for maintaining the stability of the temporary cut slopes
and reducing slope erosion during construction.
Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather,
and the slopes should be closely monitored until the permanent retaining systems or slope
configurations are complete. Materials should not be stored or equipment operated within io feet
of the top of any temporary cut slope.
Soil conditions may not be completely known from the geotechnical investigation. In the case of
temporary cuts, the existing soil conditions may not be completely revealed until the excavation
work exposes the soil. Typically, as excavation work progresses the maximum inclination of
temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental
recommendations can be made. Soil and groundwater conditions can be highly variable.
Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that
the project can proceed and required deadlines can be met.
If any variations or undesirable conditions are encountered during construction, we should be
notified so that supplemental recommendations can be made. If room constraints or
groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed
by the WAC, temporary shoring systems may be required. The contractor should be responsible
for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences
and the project structural engineer review temporary shoring designs prior to installation, to
verify the suitability of the proposed systems.
Foundation Design
The proposed residence may be supported on a shallow spread footing foundation system bearing
on undisturbed dense or firmer native soils or on properly compacted structural fill placed on the
suitable native soils. Any undocumented fill and/or loose native soils should be removed and
replaced with structural fill below foundation elements. Structural fill below footings should
consist of clean angular rock 5/8 to 4 inches in size. We should verify soil conditions during
foundation excavation work.
www.cobaltgeo.com (2o6) 331-1097
May 2'7, 2021
Page 5 of 10
Geotechnical Evaluation
For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively,
for continuous wall and isolated column footings supporting the proposed structure. Provided
that the footings are supported as recommended above, a net allowable bearing pressure of 2,000
pounds per square foot (psf) may be used for design.
A 1/3 increase in the above value may be used for short duration loads, such as those imposed by
wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted
to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing
excavations should be inspected to verify that the foundations will bear on suitable material.
Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or
adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12
inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower.
If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column
footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most
settlement is expected to occur during construction, as the loads are applied. However, additional
post -construction settlement may occur if the foundation soils are flooded or saturated. All
footing excavations should be observed by a qualified geotechnical consultant.
Resistance to lateral footing displacement can be determined using an allowable friction factor of
0.4o acting between the base of foundations and the supporting subgrades. Lateral resistance for
footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds
per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12
inches below grade in exterior areas). The frictional and passive resistance of the soil may be
combined without reduction in determining the total lateral resistance.
Care should be taken to prevent wetting or drying of the bearing materials during construction.
Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the
footing excavations, should be removed prior to placing concrete. The potential for wetting or
drying of the bearing materials can be reduced by pouring concrete as soon as possible after
completing the footing excavation and evaluating the bearing surface by the geotechnical engineer
or his representative.
Concrete Retaining Walls
The following table, titled Wall Design Criteria, presents the recommended soil related design
parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall
system is used. This has been included for new cast in place walls, if proposed.
Wall Design Criteria
"At -rest" Conditions (Lateral Earth Pressure — EFD+)
55 pcf (Equivalent Fluid Density)
"Active" Conditions (Lateral Earth Pressure — EFD+)
35 pcf (Equivalent Fluid Density)
Seismic Increase for "At -rest" Conditions
(Lateral Earth Pressure)
21H* (Uniform Distribution) 1 in 2,500 year
event
Seismic Increase for "At -rest" Conditions
(Lateral Earth Pressure)
14H* (Uniform Distribution)1 in 500 year event
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Geotechnical Evaluation
Seismic Increase for "Active" Conditions
7H* (Uniform Distribution)
(Lateral Earth Pressure)
Passive Earth Pressure on Low Side of Wall
Neglect upper 2 feet, then 250 pcf EFD+
(Allowable, includes F.S. = 1.5)
Soil -Footing Coefficient of Sliding Friction (Allowable;
0.40
includes F.S. = 1.5)
'H is the height of the wall; Increase based on one in 500 year seismic event (10 percent probability of being exceeded in
50 years),
+EFD — Equivalent Fluid Density
The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by
water accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest
pressures on the retaining walls from vertical surcharges behind the wall may be calculated using
active and at -rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. A soil unit weight
Of 125 pcf may be used to calculate vertical earth surcharges.
To reduce the potential for the buildup of water pressure against the walls, continuous footing
drains (with cleanouts) should be provided at the bases of the walls. The footing drains should
consist of a minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed
down and enveloped by a minimum 6 inches of pea gravel in all directions.
The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should
consist of free -draining granular material. All free draining backfill should contain less than 3
percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S.
Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard
No. 4 Sieve. The primary purpose of the free -draining material is the reduction of hydrostatic
pressure. Some potential for the moisture to contact the back face of the wall may exist, even with
treatment, which may require that more extensive waterproofing be specified for walls, which
require interior moisture sensitive finishes.
We recommend that the backfill be compacted to at least 90 percent of the maximum dry density
based on ASTM Test Method D1557. In place density tests should be performed to verify
adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently,
only light hand operated equipment is recommended within 3 feet of walls so that excessive stress
is not imposed on the walls.
Stormwater Management Feasibility
The site is underlain by relatively dense Whidbey Formation. These soils are very fine grained
and represent an aquitard. The shallow soils were mostly mottled and the unweathered Whidbey
Deposits act as a restrictive layer. Infiltration is not feasible due to the presence of mottled fine
grained soils and a very shallow restrictive layer.
We recommend direct connection of new runoff devices to City infrastructure. We understand
that the proposed system includes a new tightline to a nearby catchbasin northwest of the
property.
We should be provided with final plans for review to determine if the intent of our
recommendations has been incorporated or if additional modifications are needed.
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Page 7 of 10
Geotechnical Evaluation
Slab -on -Grade
We recommend that the upper 12 inches of the existing fill and/or native soils within slab areas be
re -compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). We
anticipate that new slab on grade will be supported on deeper fills due to basement removal. All
fill must be compacted to the above standard in lifts of 12 inches or less. Compaction equipment
should include a large ho-pack or 10 ton minimum drum roller. We should verify fill suitability
and compaction during construction.
Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor
barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture
typically requires the usage of a vapor barrier. A materials or structural engineer should be
consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs
typically do not utilize vapor barriers.
The American Concrete Institutes ACI 36oR-o6 Design of Slabs on Grade and ACI 302.1R-04
Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier
selection and floor slab detailing.
Slabs on grade may be designed using a coefficient of subgrade reaction of 210 pounds per cubic
inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and
compacted as outlined in Section 8.1. A 4- to 6-inch-thick capillary break layer should be placed
over the prepared subgrade. This material should consist of pea gravel or 5/8 inch clean angular
rock.
A perimeter drainage system is recommended unless interior slab areas are elevated a minimum
Of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should
consist of a 4-inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain
rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into
the drainage system. The perimeter drainage system should discharge by gravity flow to a
suitable stormwater system.
Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate
surface water flow away from the building and preferably with a relatively impermeable surface
cover immediately adjacent to the building.
Erosion and Sediment Control
Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to
wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment
control measures should be implemented, and these measures should be in general accordance
with local regulations. At a minimum, the following basic recommendations should be
incorporated into the design of the erosion and sediment control features for the site:
• Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance
of the site soils, to take place during the dry season (generally May through September).
However, provided precautions are taken using Best Management Practices (BMP's), grading
activities can be completed during the wet season (generally October through April).
• All site work should be completed and stabilized as quickly as possible.
• Additional perimeter erosion and sediment control features may be required to reduce the
possibility of sediment entering the surface water. This may include additional silt fences, silt
www.cobaltgeo.com (2o6) 331-1097
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Page 8 of 10
Geotechnical Evaluation
fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration
systems.
• Any runoff generated by dewatering discharge should be treated through construction of a
sediment trap if there is sufficient space. If space is limited other filtration methods will need
to be incorporated.
Groundwater Influence on Construction
Groundwater was not encountered in the explorations. Groundwater could be present at shallow
depths during the wet season, perched on the dense fine grained native soils.
We do not anticipate that significant volumes of groundwater will be encountered in shallow
excavations during the dry season.
If groundwater is encountered, we anticipate that sump excavations and small diameter pumps
systems will adequately de -water short-term excavations, if required. Any system should be
designed by the contractor. We can provide additional recommendations upon request.
Utilities
Utility trenches should be excavated according to accepted engineering practices following OSHA
(Occupational Safety and Health Administration) standards, by a contractor experienced in such
work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent
to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be
avoided. Depending upon the location and depth of some utility trenches, groundwater flow into
open excavations could be experienced, especially during or shortly following periods of
precipitation.
In general, silty soils were encountered at shallow depths in the explorations at this site. These
soils have low cohesion and density and will have a tendency to cave or slough in excavations.
Shoring or sloping back trench sidewalls is required within these soils in excavations greater than
4 feet deep.
All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility
trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at
least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5
feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent
of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench
backfill in pavement areas should be compacted to at least 90 percent of the maximum dry
density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe
manufacturer's recommendations.
The contractor is responsible for removing all water -sensitive soils from the trenches regardless of
the backfill location and compaction requirements. Depending on the depth and location of the
proposed utilities, we anticipate the need to re -compact existing fill soils below the utility
structures and pipes. The contractor should use appropriate equipment and methods to avoid
damage to the utilities and/or structures during fill placement and compaction procedures.
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Page 9 of 10
Geotechnical Evaluation
CONSTRUCTION FIELD REVIEWS
Cobalt Geosciences should be retained to provide part time field review during construction in
order to verify that the soil conditions encountered are consistent with our design assumptions
and that the intent of our recommendations is being met. This will require field and engineering
review to:
■ Monitor and test structural fill placement and soil compaction
■ Observe bearing capacity at foundation locations
■ Observe slab -on -grade preparation
■ Monitor foundation drainage placement
■ Observe excavation stability
Geotechnical design services should also be anticipated during the subsequent final design phase
to support the structural design and address specific issues arising during this phase. Field and
engineering review services will also be required during the construction phase in order to
provide a Final Letter for the project.
CLOSURE
This report was prepared for the exclusive use of Chris and Lisa Burdett and their appointed
consultants. Any use of this report or the material contained herein by third parties, or for other
than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC.
The recommendations contained in this report are based on assumed continuity of soils with
those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with
final architectural and civil drawings when they become available in order that we may review our
design recommendations and advise of any revisions, if necessary.
Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is
the responsibility of Chris and Lisa Burdett who is identified as "the Client" within the Statement
of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences
should any of these not be satisfied.
Sincerely,
Cobalt Geosciences, LLC
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Page 10 of to
Geotechnical Evaluation
Statement of General Conditions
USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its
agent and may not be used by any third party without the express written consent of Cobalt
Geosciences and the Client. Any use which a third party makes of this report is the responsibility
of such third party.
BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this
report are in accordance with Cobalt Geosciences present understanding of the site specific
project as described by the Client. The applicability of these is restricted to the site conditions
encountered at the time of the investigation or study. If the proposed site specific project differs
or is modified from what is described in this report or if the site conditions are altered, this report
is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the
report to reflect the differing or modified project specifics and/or the altered site conditions.
STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in
accordance with the normally accepted standard of care in the state of execution for the specific
professional service provided to the Client. No other warranty is made.
INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and
statements regarding their condition, made in this report are based on site conditions
encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or
sampling locations. Classifications and statements of condition have been made in accordance
with normally accepted practices which are judgmental in nature; no specific description should
be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in
situ conditions can only be made to some limited extent beyond the sampling or test points. The
extent depends on variability of the soil, rock and groundwater conditions as influenced by
geological processes, construction activity, and site use.
VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be
encountered that are different from those described in this report or encountered at the test
locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected
conditions are substantial and if reassessments of the report conclusions or recommendations are
required. Cobalt Geosciences will not be responsible to any party for damages incurred as a result
of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present
upon becoming aware of such conditions.
PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and
specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next
project stage (property acquisition, tender, construction, etc), to confirm that this report
completely addresses the elaborated project specifics and that the contents of this report have
been properly interpreted. Specialty quality assurance services (field observations and testing)
during construction are a necessary part of the evaluation of sub -subsurface conditions and site
preparation works. Site work relating to the recommendations included in this report should only
be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be
responsible for site work carried out without being present.
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Proposed Residence
SITE PLAN
P.O. Box 82243
Kenmore, WA 98028
COBALT
332
Sunset Avenue North
(2o6) 331-1097
GEOSCIENCES
Edmonds, Washington
FIGURE ><
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Unified Soil Classification System (USCS)
MAJOR DIVISIONS
SYMBOL
TYPICAL DESCRIPTION
Clean Gravels
Gw
Well -graded gravels, gravels, gravel -sand mixtures, little or no fines
Gravels
(more than 50%
(less than 5%
fines)
GP
Poorly graded gravels, gravel -sand mixtures, little or no fines
COARSE
GRAINED
SOILS
of coarse fraction
retained on No. 4
sieve)
Gravels with
Fines
(more than 12%
fines)
GM
Silty gravels, gravel -sand -silt mixtures
GC
Clayey gravels, gravel -sand -clay mixtures
(more than 50%
retained on
Clean Sands
:•: sw
Well -graded sands, gravelly sands, little or no fines
No. 200 sieve)
Sands
(50% or more
of coarse fraction
(less than 5%
fines)
sP
Poorly graded sand, gravelly sands, little or no fines
passes the No. 4
sieve)
Sands with
Fines
sM
Silty sands, sand -silt mixtures
(more than 12%
fines)
sc
Clayey sands, sand -clay mixtures
ML
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
FINE GRAINED
(50% or more
Silts and Clays
(liquid limit less
than 50)
Inorganic
cL
or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays
silty clays, lean clays
Organic rganic
oL
Organic silts and organic silty clays of low plasticity
passes the
MH
Inorganic silts, micaceous or diatomaceous fine sands or silty soils,
No. 200 sieve)
Silts and Clays
(liquid limit 50 or
more)
Inorganic
elastic silt
CH
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
Organic
OHOrganic
clays of medium to high plasticity, organic silts
HIGHLY ORGANIC
SOILS
Primarily organic matter, dark in color,
and organic odor
PT
Peat, humus, swamp soils with high organic content (ASTM D4427)
Classification of Soil Constituents
MAJOR constituents compose more than 50 percent,
by weight, of the soil. Major constituents are capitalized
(i.e., SAND).
Minor constituents compose 12 to 50 percent of the soil
and precede the major constituents (i.e., silty SAND).
Minor constituents preceded by "slightly" compose
5 to 12 percent of the soil (i.e., slightly silty SAND).
Trace constituents compose o to 5 percent of the soil
(i.e., slightly silty SAND, trace gravel).
Relative Density
(Coarse Grained Soils)
Consistency
(Fine Grained Soils)
N, SPT,
Relative
N, SPT,
Relative
Blows/FT
Density
Blows/FT
Consistency
0-4
Very loose
Under 2
Very soft
4 -10
Loose
2-4
Soft
10 - 30
Medium dense
4-8
Medium stiff
30 - 50
Dense
8 -15
Stiff
Over 50
Very dense
15 - 30
Very stiff
Over 3o
Hard
Grain Size Definitions
Description
Sieve Number and/or Size
Fines
<#200 (o.o8 mm)
Sand
-Fine
#200 to #40 (o.o8 to 0.4 mm)
-Medium
#40 to #10 (0.4 to 2 mm)
-Coarse
#10 to #4 (2 to 5 mm)
Gravel
-Fine
#4 to 3/4 inch (5 to 19 mm)
-Coarse
3/4 to 3 inches (19 to 76 mm)
Cobbles
3 to 12 inches (75 to 305 mm)
Boulders
>12 inches (305 mm)
1 Moisture Content Definitions 1
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
Soil Classification Chart
Figure Ci
(2o6) 331-1097
_
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Hand Boring HB-1
Date: May 2021
Depth. 6'
Groundwater: None
Contractor:
Elevation:
Logged By: PH Checked By: SC
N
0)
o
-0
Moisture Content (%)
Plastic I Liquid
U
L
E
Limit Limit
F
�
N
Material Description
o
?
o
DCP Equivalent N-Value
C
0 10 20 30 40 50
--------
----
—
—
--
SM
Topsoil/Grass
--------------------------------------------
Loose to medium dense, silty -fine to medium grained sand with
gravel, dark yellowish brown, moist. (Weathered Whidbey Formation)
2
-Grades to sandy silt
3
4
-------
5
----.
--
SM
---------------------------------------------
Dense to very dense, silty -fine to medium grained sand with gravel,
mottled yellowish brown to grayish brown, moist. (Whidbey Formation)
6
7
End of Hand Boring 6'
9
10
Hand Boring
HB-2
Date: May 2021
Depth: 6'
Groundwater: None
Contractor:
Elevation:
Logged By: PH Checked By: SC
0
0)
J
o
-0
Moisture Content (%)
Plastic Liquid
IL
U
L
E
15
3
Limit Limit
�
�
Q
N
Material Description
c
?
o
DCP Equivalent N-Value
o
C
0 10 20 30 40 50
1
2
3
4
5
7
8
9
10
--- --- --------------------------------------------
SM Loose to medium dense, silty -fine to medium grained sand with
gravel, dark yellowish brown, moist. (Weathered Whidbey Formation)
-Grades to sandy silt
FIE_jnF
e to very dense, silty -fine to medium grained sand with gravel,
mottled yellowish brown to grayish brown, moist. (Whidbey Formation)
of Hand Boring 6'
Proposed Residence
332 Sunset Avenue North
Edmonds, Washington
Hand Boring
Logs
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(2o6) 331-1097
www.cobaltgeo.com
cobaltgeo(digmail.com
7.0 OTHER PERMITS
The following permits and/or approvals are thought to be required as part of this
project:
• Clearing and Grading Permit
Right -Of -Way use Permit
• Land Use Permit
Page 23
8.0 ESC ANALYSIS AND DESIGN
TESC measures are put into place to prevent sediment from leaving the site. The
site is generally flat. The proposed TESC plan will include, but not be limited to,
the following guidelines set in the jurisdictions Minimum Requirement
"Construction Stormwater Pollution Prevention".
A SWPPP will be provided to address:
Clearing Limits — Clearing limits specify the boundary of the work to be done.
Clearing are defined on the TESC plans and will be flagged in the field.
2. Cover Measures — Cover measures are involved (typically) with the means
to control erosion of exposed soil and are specified on the TESC plans.
3. Perimeter Protection — Perimeter protection keeps site sediment from leaving
the construction site. This type of protection typically involves a silt fence.
The silt fence and clearing limits are shown on the TESC plans.
4. Traffic Area Stabilization — Traffic area stabilization is addressed by a
stabilized construction entrance.
5. Sediment Retention — Retention will be established by silt fences around the
perimeter and catch basin inserts that will control of the on -site sediment -
laden water.
6. Surface Water Collection — An interceptor ditch with check dams is shown in
the plans and will be implemented in the field if necessary.
7. Dewatering Control — Any water from dewatering shall be filtered or
contained so sediment can filter out prior to discharge downstream.
8. Dust Control — Dust control will be provided by sprinkling.
9. Wet Season Construction — Construction will be conducted according to the
jurisdiction's standards during the wet season.
10. Construction Within Sensitive Areas and Buffers - Any construction within the
wetland buffer will be subject to sensitive areas restrictions and is contained
in the TESC notes.
11. Maintenance — Maintenance requirements are detailed in the TESC notes
within the engineering plans.
12. Final Stabilization — Upon completion of the project, all disturbed areas will
be stabilized and Best Management Practices removed.
13. LID BMP's — Protect areas that will be designated as infiltration. Do not allow
turbid runoff to enter excavated infiltration facilities. If the soil porosity is
compromised, additional excavation is required to reach suitable soils.
Page 24
9.0 BOND QUANTITIES
NA
Page 25
10.0 OPERATIONS AND MAINTENANCE MANUAL
The conveyance system on this project will be privately owned and maintained by
the Owner.
See the following.
Page 26
Table V-4.5.2(5) Maintenance Standards - Catch Basins
Results
Maintenance
Conditions When Maintenance is
Expected
Component
Defect
Needed
When Main -
tenance is
performed
No Trash or
debris loc-
Trash or debris which is located imme-
ated imme-
diately in front of the catch basin opening or
diately in
is blocking inletting capacity of the basin by
front of catch
more than 10%.
basin or on
Trash or debris (in the basin) that exceeds
grate open-
60 percent of the sump depth as measured
ing.
from the bottom of basin to invert of the low-
No trash or
est pipe into or out of the basin, but in no
debris in the
Trash &
case less than a minimum of six inches
catch basin.
Debris
clearance from the debris surface to the
invert of the lowest pipe.
Inlet and out-
let pipes free
Trash or debris in any inlet or outlet pipe
of trash or
blocking more than 1/3 of its height.
debris.
General
Dead animals or vegetation that could gen-
No dead
erate odors that could cause complaints or
animals or
dangerous gases (e.g., methane).
vegetation
present
within the
catch basin.
Sediment (in the basin) that exceeds 60 per-
cent of the sump depth as measured from
the bottom of basin to invert of the lowest
pipe into or out of the basin, but in no case
No sediment
Sediment
less than a minimum of 6 inches clearance
in the catch
from the sediment surface to the invert of the
basin
lowest pipe.
Structure
Top slab has holes larger than 2 square
Top slab is
Damage to
inches or cracks wider than 1/4 inch. (Intent
free of holes
Frame and/or
is to make sure no material is running into
and cracks.
Top Slab
basin).
Frame is sit-
Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued)
Results
Maintenance
Conditions When Maintenance is
Expected
Component
Defect
Needed
When Main-
tenance is
performed
Frame not sitting flush on top slab, i.e., sep-
ting flush on
aration of more than 314 inch of the frame
the riser rings
from the top slab. Frame not securely
or top slab
attached
and firmly
attached.
Basin
Maintenance person judges that structure is
replaced or
unsound.
repaired to
Fractures or
design stand -
Cracks in
Grout fillet has separated or cracked wider
ards.
Basin Walls/
than 112 inch and longer than 1 foot at the
g
Bottom
joint of any inlet/outlet pipe or any evidence
Pipe is
of soil particles entering catch basin through
regrouted
cracks.
and secure at
basin wall.
Basin
Settlement
If failure of basin has created a safety, func-
replaced or
%lisalignment
tion, or design problem.
repaired to
design stand-
ards.
No veget-
Vegetation growing across and blocking
ation block -
more than 10% of the basin opening.
ing opening
to basin.
Vegetation
Vegetation growing in inlet/outlet pipe joints
that is more than six inches tall and less
No veget-
than six inches apart.
ation or root
growth
present.
Contamination
"Detention
No pollution
and Pollution
See Ponds" (No. 1).
present.
Cover Not in
Cover is missing or only partially in place.
Catch basin
Catch Basin
Place
Any open catch basin requires main-
cover is
Cover
tenance.
closed
Locking Mech-
Mechanism cannot be opened by one main-
Mechanism
anism Not
tenance person with proper tools. Bolts into
opens with
Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued)
Results
Maintenance
Conditions When Maintenance is
Expected
Component
Defect
i
Needed
When Main -
tenance is
performed
Working
frame have less than 112 inch of thread.
proper tools.
One maintenance person cannot remove lid
Cover can be
Cover Difficult
after applying normal lifting pressure.
removed by
to Remove
(Intent is keep cover from sealing off access
one main -
tenance per -
to maintenance.)
son.
Ladder meets
design stand
Ladder Rungs
Ladder is unsafe due to missing rungs. not
ards and
Ladder
Unsafe
securely attached to basin wall, mis-
allows main -
alignment, rust, cracks, or sharp edges.
tenance per-
son safe
access.
Grate open -
Grate opening
Grate with opening wider than 7/8 inch.
ing meets
Unsafe
design stand-
ards.
Metal Grates
Trash and
Trash and debris that is blocking more than
Grate free of
(If Applic-
Debris
20% of grate surface inletting capacity.
trash and
able)
debris.
Grate is in
Damaged or
Grate missing or broken member(s) of the
place and
Missing.
grate.
meets design
standards.