Stormwater Plan
April 5, 2019 Prepared for:
City of Edmonds
7110 210th St SW
Edmonds, WA 98026
Reviewed by:
Jenelle Taflin, P.E., LEED AP
Principal
jtaflin@navixeng.com
STORMWATER
SITE PLAN
CA Senior Living
Edmonds, Washington
STORMWATER SITE PLAN
NAVIX CA Senior Living – Edmonds, WA Page 2
Table of Contents
PROJECT SITE MAP ................................................................................................................................. 3
PROJECT OVERVIEW ............................................................................................................................... 4
SITE LOCATION ................................................................................................................................... 4
DESIGN CRITERIA ................................................................................................................................ 5
EXISTING CONDITIONS AND HYDROLOGY ............................................................................................. 6
EXISTING CONDITIONS ....................................................................................................................... 6
EXISTING SITE HYDROLOGY ................................................................................................................ 7
DEVELOPED CONDITIONS AND HYDROLOGY ......................................................................................... 9
DEVELOPED CONDITIONS ................................................................................................................... 9
DEVELOPED SITE HYDROLOGY ........................................................................................................... 9
MINIMUM REQUIREMENTS ................................................................................................................. 10
OFFSITE ANALYSIS REPORT .................................................................................................................. 14
OVERVIEW ........................................................................................................................................ 14
DOWNSTREAM ANALYSIS ................................................................................................................ 14
EXISTING IMPACTS AND CRITICAL AREAS ........................................................................................ 21
POTENTIAL OFFSITE IMPACTS .......................................................................................................... 22
100-YEAR FLOOD/OVERFLOW CONDITION ...................................................................................... 22
PERMANENT STORMWATER CONTROL PLAN...................................................................................... 23
ON-SITE STORMWATER BMPs .......................................................................................................... 23
HYDROLOGIC MODELING ................................................................................................................. 25
FLOW CONTROL SYSTEM ................................................................................................................. 26
OPERATION AND MAINTAINANCE ................................................................................................... 26
CSWPPP ANALYSIS AND DESIGN .......................................................................................................... 28
SPECIAL REPORTS AND STUDIES .......................................................................................................... 38
PERMITS ............................................................................................................................................... 38
APPENDIX: A – WWHM DATA AND OUTPUT .......................................................................... 39
B – OPERATION AND MAINTENANCE MANUAL ................................................... 76
C – GEOTECHNICAL ENGINEERING REPORT .......................................................... 82
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PROJECT SITE MAP
Figure 1: Project Site Map
Total Project Area: 33,926 SF (0.78 acres)
Total Proposed Hard Surfaces: 43,560 (0.68 acres)
Proposed Pollution Generating Hard/Impervious Surface: 2,106 SF (0.05 acres)
Proposed Pollution Generating Pervious Surface: 0 SF (0.00 acres)
Existing Unmanaged Hard Surfaces: 0 SF (0.00 acres)
Total Disturbed Area: 33,926 SF (0.78 acres)
Average Slope: 8-25%
Estimated Ultimate Infiltration Rate: ¼ inch/hour to ½ inch/hour
NRCS Soil Group: Alderwood-Urban Land Complex Soils (glacial till)
For conveyance system details, please see the stormwater plans.
For soil pit and infiltration test locations, please see the geotechnical report (Appendix C).
Stormwater
detention vault
in basement
Pump from stormwater
detention vault to
connection with existing
storm system
Intercept off-site
storm conveyance
system
Re-route off-site
conveyance to
existing storm
system
Project
Boundary
Line
Connection with
existing storm system
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PROJECT OVERVIEW
The site is currently developed as a single-story building and parking lot (see Existing Conditions
section below). Onsite stormwater outfalls to an existing storm sewer main in 72nd Avenue W, which
ultimately outfalls to Halls Creek.
The proposed development will consist of an approximately 163,100 GSF, 6-story assisted living
facility with approximately 86 assisted living units and 34 memory care units on a 0.81-acre parcel
located at 21200 72nd Avenue W in Edmonds, Washington. The project includes associated driveway
access, trash enclosure pad, landscaping areas, sidewalks, and utility connections. No existing
unmanaged hard surfaces will remain.
SITE LOCATION
Figure 2: Project Location
Location: 21200 72nd Ave W Edmonds, WA 98026 (Snohomish County)
Section, Township, Range: NW 1/4, NW 1/4, SEC. 29, TOWNSHIP 27N, RANGE 04E, W.M.
Parcel/Tax Lot: 00580700000401
Parcel Size: 0.78 acres
Total Area of Disturbance: 0.78 acres
City, County, State: Edmonds, Snohomish County, Washington
Zoning: CG, General Commercial
PROJECT
SITE
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DESIGN CRITERIA
The stormwater management facilities have been designed in accordance with the 2017 City of
Edmond’s Stormwater Management Code, which utilizes the 2014 Stormwater Management Manual
for Western Washington and the City of Edmonds Stormwater Addendum. This project will result in
greater than 5,000 SF of new plus replaced hard surface, therefore the site is classified as a Category
2 project site and shall comply with Minimum Requirements 1-9 of the City of Edmonds Stormwater
Management Code.
Table 1 below summarizes the City of Edmonds stormwater requirements.
JURISDICTIONAL REQUIREMENTS
Duration Analysis
2-year: Reduce to ½ pre-developed duration
50-year: Match pre-developed
Water Quality Volume: N/A
Water Quality Flow Rate: Full 2-year release rate from the detention
facility*
Downstream Analysis: ¼ mile
*All continuous modelling to be performed using the “Puget East 36”
precipitation time series, available in WWHM2012 by using WS-DOT data
TABLE 1: Jurisdictional Requirements
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EXISTING CONDITIONS AND HYDROLOGY
EXISTING CONDITIONS
The site is currently comprised of an existing office building with an associated parking lot area and
landscaping. It is bound to the north by 212th Street SW, to the east by 72nd Avenue W, to the south
by an apartment complex, and to the west by a townhome development. There is existing storm
drainage infrastructure on-site that runs west to east and conveys off-site stormwater from the Hyde
Park Townhomes to the municipal conveyance system in 72nd Avenue West. See Figure 3 for the
Existing Conditions Map.
Figure 3: Existing Conditions Map
The property slopes from an approximate elevation of 382 feet at the northern property line up to
about 376 feet at the southern property line (Terracon). The NRCS soils map lists the site as having
slopes in the range of approximately 8-15%. Per the City of Edmonds GIS critical areas map the site
contains areas of landslide and erosion hazards (Figure 7).
A Geotechnical Engineering Report was prepared for this project by Terracon Consultants, Inc on
December 20, 2018 (Appendix C). Per the report on-site soils are comprised of asphalt and concrete
pavement with a gravel base course at the surface; silty sand with variable gravel content with
organics at 3.5’-7.5’ below grade; sand with silt content and trace gravel (recessional glacial outwash)
at 10’-13’ below grade; and, silty sand and sandy silt with variable gravel content (glacial till) up to
Active storm pipe
conveys runoff from
Hyde Park Townhomes
Off-site storm
conveyance from
Hyde Park
Townhomes to west
Existing pipe outfall
connection to
existing storm main
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NAVIX CA Senior Living – Edmonds, WA Page 7
26’ below grade. Groundwater was encountered at 20.5 feet deep in one of four borings and was not
encountered during or after drilling in the other three borings.
There are no known surface water bodies in the immediate vicinity of the site including wetlands. A
high-pressure gas line is located to the east of the project site within the 72nd Avenue West right-of-
way, outside of the proposed development area. The site is zoned CG, General Commercial, and is
within the Highway 99 Subarea Plan.
EXISTING SITE HYDROLOGY
Surface runoff from the existing site is collected in two catch basins located in the parking lot in the
northern half of the site and is conveyed east to the existing municipal conveyance system in 72nd
Avenue West. The site is in the Halls Creek Drainage Basin (Figure 4).
The existing conditions survey prepared by Axis Survey and Mapping on January 19, 2018 indicates a
stormwater drainage easement on the property that runs from the western edge of the site at its
boundary with the Hyde Park Townhomes to the east. The easement encompasses a 12-inch storm
conveyance pipes that originates from the Hyde Park Townhomes to the west and connects to the
existing municipal conveyance system in 72nd Avenue West. This off-site storm conveyance system
will be intercepted and rerouted around the proposed development.
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Figure 4: Watershed Map
PROJECT
SITE
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DEVELOPED CONDITIONS AND HYDROLOGY
DEVELOPED CONDITIONS
The proposed project will consist of an approximately 163,100 GSF 6-story assisted living facility with
approximately 86 assisted living units and 34 memory care units on a 0.81-acre parcel located at
21200 72nd Avenue W in Edmonds, Washington. All existing on-site structures will be demolished.
DEVELOPED SITE HYDROLOGY
Stormwater runoff from newly created pervious and impervious surfaces will be collected and routed
to an on-site stormwater management system consisting of an approximately 17,518 CF underground
detention vault for flow control. Flow from the vault will be restricted to pre-development forested
conditions in accordance with City of Edmonds stormwater requirements. The controlled-released
runoff will discharge to the municipal conveyance system in 72nd Avenue West by means of a
stormwater pump system. All stormwater runoff from hard surfaces on-site will be managed and no
existing, unmanaged hard surfaces will remain.
As the project is not creating 5,000 SF or more of pollution-generating hard surface (PGHS) or 0.75
acres or more of pollution-generating pervious surface (PGPS), water quality treatment of not
required.
The total proposed non-pollution-generating impervious surface is approximately 0.63 acres, the
proposed pervious areas is approximately 0.1 acres, and the proposed pollution-generating
impervious area is 0.05 acres.
Table 2, below, summarizes the threshold discharge areas.
Threshold Discharge Area Area (AC)
Current Hard Surfaces 0.60
Proposed Hard Surfaces 0.68
New + Replaced PGPS 0.10
New + Replaced PGIS 0.05
New + Replaced PGHS 0.05
Effective Impervious Surface 0.68
Existing, Unmanaged Hard
Surface to Remian
0
Disturbed Pervious Surface 0.18
Total Additional Hard Surfaces 0.09
Table 2: Threshold Discharge Areas
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MINIMUM REQUIREMENTS
Figure 5- Minimum Requirements
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Minimum Requirement #1: Preparation of Stormwater Site Plans
The City shall require a Stormwater Site Plan from all projects meeting the thresholds in ECDC
18.30.060.C. Stormwater Site Plans shall use site-appropriate development principles to retain native
vegetation and minimize impervious surfaces to the extent feasible. Stormwater Site Plans shall be
prepared in accordance with Chapter 3 of Volume 1 of the SWMMWW and the requirements in the
Edmonds Stormwater Addendum.
Response: A stormwater site plan that includes the design drawings and this report has been
prepared for this development. The stormwater site plan has been designed using site-appropriate
development principles to meet City of Edmonds guidelines to the maximum extent feasible.
Minimum Requirement #2: Construction Stormwater Pollution Prevention Plan (SWPPP)
All development projects are responsible for preventing erosion and discharge of sediment and other
pollutants into receiving waters. Compliance with this minimum requirement can be achieved for an
individual site if the site is covered under Ecology’s General NPDES Permit for Stormwater Discharges
Associated with Construction Activities and fully implementing the requirements of that permit.
A Construction SWPPP is required for all projects which a) result in 2,000 square feet or more of new
plus replaced hard surface area, b) where a structure with an exterior hard surface area of at least
2,000 square feet is being demolished, c) which disturb 7,000 square feet or more of land, or d) when
the site falls within the Earth Subsidence Landslide Hazard Area, Landslide Hazard Area or steep slope
critical area.
Response: A preliminary Construction SWPPP has been prepared and is included in the “CSWPP
Analysis and Design” section of this report, below. A full Construction SWPPP report to be utilized by
the contractor will be submitted with this permit submittal package as a separate document.
Minimum Requirement #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.
Response: All known, available, and reasonable source control BMPs have been evaluated for
applicability to this project. This includes, but is not limited to, Dust Control at Disturbed Land Areas,
Landscaping and Lawn/Vegetation Management, and Maintenance of Stormwater Drainage and
Treatment Systems.
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Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls
Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the
natural location, to the maximum extent practicable. The manner by which runoff is discharged from
the project site must not cause a significant adverse impact to downstream receiving waters and
down gradient properties. The discharge must have an identified overflow route that is safe and
certain and leads to the ultimate outfall location (such as a receiving water or municipal drainage
system). All outfalls require energy dissipation. To demonstrate compliance with this core
requirement, all projects shall submit an off-site qualitative analysis. If an existing problem (or
potential future problem after development) is identified, mitigation will be required to prevent
worsening of that problem. A quantitative analysis may be required for any project deemed to need
additional information or where the project proponent or the City determines that a quantitative
analysis is necessary to evaluate the off-site impacts or the capacity of the conveyance system. Per
the Edmond’s Stormwater Addendum, existing upstream flows must be accommodated without
causing erosion or flooding impacts. Upstream flows shall not be routed through the project’s
conveyance, treatment, or retention/detention systems, unless those systems are sized to control
those flows. Upstream flows that are collected and routed through or around the site in a separate
conveyance shall be dispersed at the downgradient property line, if feasible, or discharged at a
project outfall (or outfalls) in a manner that does not violate the criteria below or cause the capacity
of a conveyance system to be exceeded.
Response: Natural drainage systems and outfalls will be maintained to the maximum extent feasible
for the development of this site. Onsite stormwater will be collected in a new underground detention
vault in the basement of the proposed building and routed to the existing municipal conveyance
system in 72nd Ave W. In the proposed condition the existing drainage path and connection to the
existing system in 72nd Ave W will be maintained.
Minimum Requirement #5: On-Site Stormwater Management
On-site Stormwater Management BMPs are required in accordance with the following project
thresholds, standards, and lists to infiltrate, disperse, and retain stormwater runoff on-site to the
extent feasible without causing flooding or erosion impacts. Category 2 project sites that discharge
directly or indirectly to the City’s MS4 shall use On-Site Stormwater BMPs from List No.2 for all new
plus replaced hard surfaces and land disturbed.
Response: On-site stormwater management BMP’s have been evaluated in accordance with the City
of Edmonds stormwater code requirements and the project is electing to use the List No. 2 option for
on-site stormwater BMPs selection. Please see the Permanent Stormwater Control Plan – On-Site
Stormwater Management BMP’s section of this report for more information.
Minimum Requirement #6: Runoff Treatment
The following require construction of stormwater treatment facilities:
· Projects in which the total of pollution-generating hard surface (PGHS) is 5,000 square feet or
more in a threshold discharge area of the project, or
· Projects in which the total of pollution-generating pervious surfaces (PGPS) – not including
permeable pavements – is 0.75 acres or more in a threshold discharge area, and from which
there will be a surface discharge in a natural or man-made conveyance system from the site.
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Response: The total proposed pollution-generating hard surface (PGHS) is 2,106 SF and the pollution-
generating pervious surface (PGPS) consisting of lawn and landscaping area is 4,283 SF. Therefore,
water quality treatment facilities are not required.
Minimum Requirement #7: Flow Control
Flow control is required on projects meeting the thresholds summarized below to reduce the impacts
of stormwater runoff from hard surfaces and land cover conversions. Standard Flow Control
Requirement (applies to discharges directly or indirectly to the City’s MS4, except for projects that
meet the direct discharge requirements outlined in “a” above): Stormwater discharges shall match
developed discharge durations to pre-developed durations for the range of pre-developed discharge
rates from 50 percent of the 2-year peak flow up to the full 50-year peak flow. The pre-developed
condition to be matched shall be a forested land cover.
Response: Flow control will be provided by utilizing a detention vault located in the basement level.
On-site roof drainage will be collected and routed to the detention vault prior to discharge to the
storm drainage system located in 72nd Avenue W. The detention vault is sized to meet discharge
requirements for the entire redevelopment area in accordance with the 2014 Stormwater
Management Manual for Western Washington requirements utilizing continuous modelling with
WWHM2012.
Minimum Requirement #8: Wetlands Protection
The requirements below apply only to projects whose stormwater discharges into a wetland, either
directly or indirectly through a conveyance system.
Response: This project does not discharge into a wetland.
Minimum Requirement #9: Operation and Maintenance
An operation and maintenance manual that is consistent with the provisions in Volume I and Volume
V of the SWMMWW is required for proposed Stormwater Treatment and Flow Control
BMPs/facilities. The party (or parties) responsible for maintenance and operation shall be identified
in the operation and maintenance manual. For private facilities approved by the City, a copy of the
operation and maintenance manual shall be retained on-site or within reasonable access to the site
and shall be transferred with the property to the new owner. For public facilities, a copy of the
operation and maintenance manual shall be retained in the appropriate department. A log of
maintenance activity that indicates what actions were taken shall be kept and be available for
inspection.
Response: An Operation and Maintenance Manual is included in Appendix B of this report.
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OFFSITE ANALYSIS REPORT
OVERVIEW
The project site consists of one drainage sub basin which outfalls to Halls Creek. Approximately 0.25
miles downstream is the intersection of 216th Street SW and 72nd Avenue W. See Figure X, below. No
emergency services are located along the flow path.
Figure 6: Downstream Analysis Path
DOWNSTREAM ANALYSIS
A formal downstream analysis was completed in accordance with the City of Edmond’s 2017
Stormwater Addendum. This analysis was conducted on March 7, 2019. The temperature was
approximately 40 degrees and overcast.
¼ mile
downstream
location
Project Site
Downstream
Flow Path
Outfall to Halls
Creek
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# Picture Description
1
View from the northwest side of the site
looking east.
Drainage is conveyed east across the site to
an open-grate catch basin on the northeast
side of the site.
2
View from the northeast side of the site
looking east.
Drainage is conveyed east offsite where it
turns south to a manhole in the western-
most drive lane of 72nd Ave W north of
213th Pl SW.
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3
View from the west side of 72nd Ave W
looking south.
Drainage is conveyed south through a 36”
concrete pipe to a manhole in the western-
most drive lane of 72nd Ave W.
4
View from the west side of 72nd Ave W
looking south.
Drainage is conveyed south through a 36”
concrete pipe to a manhole in the western-
most drive lane of 72nd Ave W near the
southeast corner of the Edmonds Park and
Ride.
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NAVIX CA Senior Living – Edmonds, WA Page 17
5
View from the west side of 72nd Ave W
looking south.
Drainage is conveyed south through a 36”
concrete pipe to a manhole on the west
side of 72nd Ave W.
6
View from the sidewalk on the west side of
72nd Ave W looking east.
Drainage is conveyed south through a 36”
concrete pipe to a manhole on 216th St SW.
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7
View from the southwest corner of the
intersection of 72nd Ave W and 216th St SW.
Drainage is conveyed east through a 36”
pipe to a manhole east of the intersection
of Highway 99 and 216th St SW.
Image Credit: Google Maps
8
View from the intersection of Highway 99
and 216th St SW looking northwest.
Drainage is conveyed to the southeast
corner of the intersection of Highway 99
and 212th St SW.
Image Credit: Google Maps
Storm
drain
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9
View from southeast corner of Highway 99
and 216th St SW looking east.
Drainage is conveyed east along 216th St
SW through a 36” concrete pipe to a
manhole on the south side of 212th St SW.
10
View from the south side of 216th St SW
looking east.
Drainage is conveyed east along 216th St
SW through a 36” concrete pipe to a
manhole on the south side of 212th St SW.
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11
View from the south side of 212th St SW
looking southeast.
Drainage is conveyed southeast to an
outfall along Halls Creek
12
View from the south side of the Interurban
Trail looking south.
Drainage outfalls to Halls Creek.
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EXISTING IMPACTS AND CRITICAL AREAS
Per the City’s website, there is an existing erosion hazard area along the northern and western
perimeters of the site, most likely having to do with the existing sloped/retaining wall areas in those
locations. The existing retaining wall along the western property boundary will be maintained in the
developed condition. The shorter, existing retaining wall in the southwest corner of the site will be
removed and replaced by retaining via the building. The downstream storm drainage system within
0.25 miles of the project is adjacent to existing erosion hazards, but there are no known impacts or
problems associated with the drainage system.
See Figure 7 below for the critical areas map.
Figure 7- Critical Areas Map
¼ mile
downstream
location
Project Site
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POTENTIAL OFFSITE IMPACTS
The proposed on-site stormwater management system will be designed according to the 2017 City
of Edmonds Stormwater Management Code. No impacts to groundwater, surface waters, or drainage
patterns are anticipated.
100-YEAR FLOOD/OVERFLOW CONDITION
The stormwater conveyance system for this project has been designed to address all storm events,
including the 100-year, 24-hour storm, in accordance with common industry practices. Please see
FIRM map shown in Figure 8 below. The project site is in Zone X, which is outside the 500-year
floodplain
Figure 8: FIRM Map
Project Site
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PERMANENT STORMWATER CONTROL PLAN
ON-SITE STORMWATER BMPs
This project is electing to use the List No. 2 option for selection of on-site stormwater BMPs. After
evaluating the stormwater BMPs provided in the City of Edmond’s Stormwater Addendum for
applicability to this project site, it has been determined that a stormwater detention vault is required
for on-site stormwater flow control. A vault has been sized using the Western Washington Hydrology
Model (WWHM) per City of Edmonds requirements (using WSDOT data) and a report has been
generated through the WWHM software (Appendix A).
Based on the Geotechnical Engineering Report by Terracon Consultants (Appendix C), the on-site soils
were evaluated for infiltration potential and sieve analyses were performed to estimate an infiltration
rate. The glacial till soils observed exhibited an appreciable fines content and the soils were dense to
very dense. The geotechnical engineer concluded that the site is not suitable for infiltration and,
therefore, stormwater management via infiltration is not recommended.
The following tables list the evaluated on-site BMPs and reasons for infeasibility based on the 2017
City of Edmonds Stormwater Management Code, Appendix A.
Lawn and Landscape Areas
BMP Feasible
(Yes/No)
Explanation
Post-Construction
Soil Quality and
Depth
Yes On-site disturbed areas that result in lawn or landscaping will be amended
with compost or replaced with topsoil meeting Post-Construction Soil
Quality and Depth requirements.
Roofs
BMP Feasible
(Yes/No)
Explanation
Full Dispersion
No A minimum forested or native vegetation flow path length of 100 feet (25
feet for sheet flow from a nonnative pervious surface) cannot be achieved
due to site restrictions.
Downspout Full
Infiltration Systems
No The site does not have outwash or loam soils.
Geotechnical investigation does not recommend infiltration on this site.
Bioretention or
Rain Gardens
No Professional geotechnical evaluation recommends infiltration not be used.
Downspout
Dispersion Systems
No For splashblocks, 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, or other impervious surface is not feasible.
For trenches, a vegetated flow path of at least 25 feet in between the outlet
of the trench and any property line, structure, stream, wetland, or
impervious surface is not feasible
Perforated Stub-
Out Connections
No There is not at least 1 foot of permeable soil from the proposed bottom of
the perforated stub-out connection trench to the highest estimated
groundwater table or other impermeable layer.
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Detention Vaults
and Pipes
Yes A detention vault has been sized in WWHM 2012 (Appendix A).
Other Hard Surfaces
BMP Feasible
(Yes/No)
Explanation
Full Dispersion
No A minimum forested or native vegetation flow path length of 100 feet (25
feet for sheet flow from a nonnative pervious surface) cannot be achieved
due to site restrictions.
Permeable
Pavement
No Not feasible at multi-level parking garages such as this.
Geotechnical investigation does not recommend infiltration on this site.
Bioretention or
Rain Gardens
No Professional geotechnical evaluation recommends infiltration not be used.
Sheet Flow
Dispersion
No 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.
Concentrated Flow
Dispersion
No A minimum 3-foot length of rock pad and 50-foot flowpath OR a dispersion
trench and 25-foot flowpath for every 700 sq. ft. of drainage area (within
applicable setbacks) cannot be achieved.
Detention Vaults
and Pipes
Yes A detention vault has been sized in WWHM 2012 (Appendix A).
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HYDROLOGIC MODELING
The hydrologic analysis for this project was performed using Western Washington Hydrology Model
(WWHM2012), based on matching flow durations. MGS rainfall data was used to model the site
runoff and size the stormwater facility.
The following table summarizes the surface area of the existing site conditions as input into WWHM.
Total site area is indicative of the contributing area to the proposed vault.
Basin Area (AC) Description Grade
0.78 Soil Type C, Forest Flat
Table 3: Pre-Developed Conditions
The following table summarizes the surface area of the proposed site conditions as input to WWHM.
Basin Area (AC) Description Grade
0.10 Soil Type C, Lawn Flat
0.05 Roads/Driveways Flat
0.6 Rooftops Flat
0.03 Sidewalks
Table 4: Developed Conditions
Figure 9, below, shows the predeveloped forested condition as inputted in WWHM.
Figure 9: Predeveloped Forested Condition
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Figure 10, below, shows the on-site, non-pollution generating impervious surfaces (NPGIS), pollution
generating impervious surfaces (PGIS), and pervious surfaces as inputted into WWHM
Figure 10: WWHM On-Site Areas
FLOW CONTROL SYSTEM
The proposed flow control facility was designed in accordance with the 2014 Amendment to the 2012
Stormwater Manual for Western Washington and the 2017 City of Edmonds Stormwater Code. Pre-
developed conditions are modeled as forested for all areas within the limits of disturbance. WWHM
2012 was used for flow control calculations.
The proposed detention vault will have a live storage depth of 10 feet, a width of 38.5 feet, and a
length of 45.5 feet. Basin data and results from the WWHM 2012 model are provided in Appendix A.
OPERATION AND MAINTAINANCE
The proposed development will include an approximately 17,517.5 CF detention vault located at the
basement level. The basement level will be accessible via a ramp leading down from the ground level.
It is not anticipated that the detention vault will accumulate appreciable amounts of solids because
the majority of collected runoff will be from clean roof surfaces. However, periodic maintenance is
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still required, including cleaning with a vactor truck. ProVac Clean Service has verbally confirmed that
a typical vactor truck will need a height clearance of approximately 14 feet. Therefore, the truck will
be able to access the vault through the vehicle and loading entry off of 72nd Avenue W to park in the
loading area and run the hose down the parking ramp to the detention vault at the basement level.
See Figure 11 for the proposed vactor truck parking configuration.
Figure 11: Proposed Vactor Truck Configuration
A complete on-site BMP operation and maintenance manual is included in Appendix B.
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CSWPPP ANALYSIS AND DESIGN
All erosion and sediment control measures shall be governed by the requirements of the City of
Edmonds. A temporary erosion and sedimentation control plan will be prepared to assist the
contractor in complying with these requirements. The Erosion and Sediment Control (ESC) plan will
be included with the construction plans.
Element 1: Preserve Vegetation/Mark Clearing Limits
· Before beginning land disturbing activities, including clearing and grading, clearly mark all
clearing limits, sensitive areas and their buffers, and trees that are to be preserved within
the construction area.
· Retain the duff layer, native top soil, and natural vegetation in an undisturbed state to the
maximum degree practical.
· Plastic, metal, or fabric fence may be used to mark the clearing limits. [Note: the difference
between the practical use and proper installation of silt fencing and the proper use of
clearing boundary fencing.]
· If it is not practical to retain the duff layer in place, then stockpile it on-site, cover it to
prevent erosion, and replace it immediately when you finish disturbing the site.
Element 2: Establish Construction Access
· Limit construction vehicle access and exit to one route, if possible.
· Stabilize access points with a pad of quarry spalls, crushed rock, or other equivalent BMPs, to
minimize tracking sediment onto roads.
· Locate wheel wash or tire baths on site, if the stabilized construction entrance is not effective
in preventing tracking sediment onto roads.
· If sediment is tracked off site, clean the affected roadway thoroughly at the end of each day,
or more frequently as necessary (for example, during wet weather). Remove sediment from
roads by shoveling, sweeping, or pick up and transport the sediment to a controlled sediment
disposal area.
· Conduct street washing only after sediment is removed in accordance with the above bullet.
· Control street wash wastewater by pumping back on site or otherwise preventing it from
discharging into systems tributary to waters of the State.
· Minimize construction site access points along linear projects, such as roadways. Street
washing may require local jurisdiction approval.
Element 3: Control Flow Rates
· Protect properties and waterways downstream of development sites from erosion and the
associated discharge of turbid waters due to increases in the velocity and peak volumetric
flow rate of stormwater runoff from the project site, as required by local plan approval
authority.
· Where necessary to comply with the bullet above, construct stormwater retention or
detention facilities as one of the first steps in grading. Assure that detention facilities
function properly before constructing site improvements (e.g. impervious surfaces).
· If permanent infiltration ponds are used for flow control during construction, protect these
facilities from siltation during the construction phase.
· Conduct downstream analysis if changes in off-site flows could impair or alter conveyance
systems, streambanks, bed sediment, or aquatic habitat.
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· Even gently sloped areas need flow controls such as straw wattles or other energy
dissipation / filtration structures. Place dissipation facilities closer together on steeper
slopes. These methods prevent water from building higher velocities as it flows downstream
within the construction site.
· Outlet structures designed for permanent detention ponds are not appropriate for use
during construction without modification. If used during construction, install an outlet
structure that will allow for long-term storage of runoff and enable sediment to settle.
Verify that the pond is sized appropriately for this purpose. Restore ponds to their original
design dimensions, remove sediment, and install a final outlet structure at completion of
the project.
· Erosion has the potential to occur because of increases in the volume, velocity, and peak
flow rate of stormwater runoff from the project site. The local permitting agency may
require pond designs that provide additional or different stormwater flow control. These
requirements may be necessary to address local conditions or to protect properties and
waterways downstream.
· Sites that must implement flow control for the developed site condition must also control
stormwater release rates during construction. Construction site stormwater discharges shall
not exceed the discharge durations of the pre-developed condition for the range of pre-
developed discharge rates from ½ of the 2-year flow through the 10-year flow as predicted
by an approved continuous runoff model. The pre-developed condition to be matched shall
be the land cover condition immediately prior to the development project. This restriction
on release rates can affect the size of the storage pond and treatment cells
Element 4: Install Sediment Controls
· The Permittee must design, install and maintain effective erosion controls and sediment
controls to minimize the discharge of pollutants. At a minimum, the Permittee must design,
install and maintain such controls to:
o Construct sediment control BMPs (sediment ponds, traps, filters, etc.) as one of the
first steps in grading. These BMPs shall be functional before other land disturbing
activities take place.
o Minimize sediment discharges from the site. The design, installation and
maintenance of erosion and sediment controls must address factors such as the
amount, frequency, intensity and duration of precipitation, the nature of resulting
stormwater runoff, and soil characteristics, including the range of soil particle sizes
expected to be present on the site.
o Direct stormwater runoff from disturbed areas through a sediment pond or other
appropriate sediment removal BMP before the runoff leaves a construction site or
before discharge to an infiltration facility. Runoff from fully stabilized areas may be
discharged without a sediment removal BMP but must meet the flow control
performance standard in Element #3, bullet #1.
o Locate BMPs intended to trap sediment on site in a manner to avoid interference
with the movement of juvenile salmonids attempting to enter off-channel areas or
drainages.
o Provide and maintain natural buffers around surface waters, direct stormwater to
vegetated areas to increase sediment removal, and maximize stormwater
infiltration, unless infeasible.
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o Where feasible, design outlet structures that withdraw impounded stormwater
from the surface to avoid discharging sediment that is still suspended lower in the
water column.
· Outlet structures that withdraw impounded stormwater from the surface to avoid
discharging sediment that is still suspended lower in the water column are for the
construction period only. If the pond using the construction outlet control is used for
permanent stormwater controls, the appropriate outlet structure must be installed after the
soil disturbance has ended.
· Seed and mulch earthen structures such as dams, dikes, and diversions according to the
timing indicated in Element #5.
· Full stabilization includes concrete or asphalt paving; quarry spalls used as ditch lining; or
the use of rolled erosion products, a bonded fiber matrix product, or vegetative cover in a
manner that will fully prevent soil erosion.
· The Local Permitting Authority may inspect and approve areas fully stabilized by means
other than pavement or quarry spalls.
· If installing a floating pump structure, include a stopper to prevent the pump basket from
hitting the bottom of the pond.
Element 5: Stabilize Soils
· Stabilize exposed and unworked soils by application of effective BMPs that prevent erosion.
Applicable BMPs include but are not limited to: temporary and permanent seeding, sodding,
mulching, plastic covering, erosion control fabrics and matting, soil application of
polyacrylamide (PAM), the early application of gravel base early on areas to be paved, and
dust control. Control stormwater volume and velocity within the site to minimize soil
erosion.
· Control stormwater discharges, including both peak flow rates and total stormwater
volume, to minimize erosion at outlets and to minimize downstream channel and stream
bank erosion.
· Soils must not remain exposed and unworked for more than the time periods set forth
below to prevent erosion.
o During the dry season (May 1 - Sept. 30): 7 days.
o During the wet season (October 1 - April 30): 2 days.
· Stabilize soils at the end of the shift before a holiday or weekend if needed based on the
weather forecast.
· Stabilize soil stockpiles from erosion, protect with sediment trapping measures, and where
possible, be located away from storm drain inlets, waterways, and drainage channels.
· Minimize the amount of soil exposed during construction activity.
· Minimize the disturbance of steep slopes.
· Minimize soil compaction and, unless infeasible, preserve topsoil.
· Soils must not remain exposed and unworked for more than the time periods set forth
above to prevent erosion for linear projects.
· Soil stabilization measures should be appropriate for the time of year, site conditions,
estimated duration of use, and potential water quality impacts that stabilization agents may
have on downstream waters or ground water.
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· Ensure that gravel base used for stabilization is clean and does not contain fines or
sediment.
Element 6: Protect Slopes
· Design and construct cut-and-fill slopes in a manner to minimize erosion. Applicable
practices include, but are not limited to, reducing continuous length of slope with terracing
and diversions, reducing slope steepness, and roughening slope surfaces (for example, track
walking).
· Divert off-site stormwater (run-on) or ground water away from slopes and disturbed areas
with interceptor dikes, pipes, and/or swales. Off-site stormwater should be managed
separately from stormwater generated on the site.
· At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent
erosion.
o Temporary pipe slope drains must handle the peak volumetric flow rate calculated
using a 10-minute time step from a Type 1A, 10-year, 24-hour frequency storm for
the developed condition. Alternatively, the 10-year, 1-hour flow rate predicted by an
approved continuous runoff model, increased by a factor of 1.6, may be used. The
hydrologic analysis must use the existing land cover condition for predicting flow
rates from tributary areas outside the project limits. For tributary areas on the
project site, the analysis must use the temporary or permanent project land cover
condition, whichever will produce the highest flow rates. If using the Western
Washington Hydrology Model (WWHM) to predict flows, bare soil areas should be
modeled as "landscaped" area.
· Place excavated material on the uphill side of trenches, consistent with safety and space
considerations.
· Place check dams at regular intervals within constructed channels that are cut down a slope.
· Where 15-minute time steps are available in an approved continuous runoff model, they
may be used directly without a correction factor.
· Consider soil type and its potential for erosion.
· Stabilize soils on slopes, as specified in Element #5.
· BMP combinations are the most effective method of protecting slopes with disturbed soils.
For example, use both mulching and straw erosion control blankets in combination.
Element 7: Protect Permanent Drain Inlets
· Protect all storm drain inlets made operable during construction so that stormwater runoff
does not enter the conveyance system without first being filtered or treated to remove
sediment.
· Clean or remove and replace inlet protection devices when sediment has filled one-third of
the available storage (unless a different standard is specified by the product manufacturer).
· Where possible, protect all existing storm drain inlets so that stormwater runoff does not
enter the conveyance system without first being filtered or treated to remove sediment.
· Keep all approach roads clean. Do not allow sediment and street wash water to enter storm
drains without prior and adequate treatment unless treatment is provided before the storm
drain discharges to waters of the State.
· Inlets should be inspected weekly at a minimum and daily during storm events.
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Element 8: Stabilize Channels and Outlets
· Design, construct, and stabilize all on-site conveyance channels to prevent erosion from the
following expected peak flows:
o Channels must handle the peak volumetric flow rate calculated using a 10- minute
time step from a Type 1A, 10-year, 24-hour frequency storm for the developed
condition. Alternatively, the 10-year, 1-hour flow rate indicated by an approved
continuous runoff model, increased by a factor of 1.6, may be used. The hydrologic
analysis must use the existing land cover condition for predicting flow rates from
tributary areas outside the project limits. For tributary areas on the project site, the
analysis must use the temporary or permanent project land cover condition,
whichever will produce the highest flow rates. If using the Western Washington
Hydrology Model (WWHM) to predict flows, bare soil areas should be modeled as
"landscaped area.”
· Provide stabilization, including armoring material, adequate to prevent erosion of outlets,
adjacent streambanks, slopes, and downstream reaches at the outlets of all conveyance
systems.
· The best method for stabilizing channels is to completely line the channel with a blanket
product first, then add check dams as necessary to function as an anchor and to slow the flow
of water.
Element 9: Control Pollutants
· Design, install, implement and maintain effective pollution prevention measures to
minimize the discharge of pollutants.
· Handle and dispose of all pollutants, including waste materials and demolition debris that
occur on-site in a manner that does not cause contamination of stormwater.
· Provide cover, containment, and protection from vandalism for all chemicals, liquid
products, petroleum products, and other materials that have the potential to pose a threat
to human health or the environment. On-site fueling tanks must include secondary
containment. Secondary containment means placing tanks or containers within an
impervious structure capable of containing 110% of the volume contained in the largest
tank within the containment structure. Double-walled tanks do not require additional
secondary containment.
· Conduct maintenance, fueling, and repair of heavy equipment and vehicles using spill
prevention and control measures. Clean contaminated surfaces immediately following any
spill incident.
· Discharge wheel wash or tire bath wastewater to a separate on-site treatment system that
prevents discharge to surface water, such as closed-loop recirculation or upland land
application, or to the sanitary sewer, with local sewer district approval.
· Apply fertilizers and pesticides in a manner and at application rates that will not result in
loss of chemical to stormwater runoff. Follow manufacturers’ label requirements for
application rates and procedures.
· Use BMPs to prevent contamination of stormwater runoff by pH-modifying sources. The
sources for this contamination include, but are not limited to: bulk cement, cement kiln
dust, fly ash, new concrete washing and curing waters, waste streams generated from
concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults,
concrete pumping and mixer washout waters.
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· Adjust the pH of stormwater if necessary to prevent violations of the water quality
standards.
· Assure that washout of concrete trucks is performed off-site or in designated concrete
washout areas only. Do not wash out concrete trucks onto the ground, or into storm drains,
open ditches, streets, or streams. Do not dump excess concrete on site, except in
designated concrete washout areas. Concrete spillage or concrete discharge to surface
waters of the State is prohibited.
· Obtain written approval from Ecology before using chemical treatment other than CO2 or
dry ice to adjust pH.
Element 10: Control De-Watering
· Discharge foundation, vault, and trench dewatering water, which have characteristics
similar to stormwater runoff at the site, into a controlled conveyance system before
discharge to a sediment trap or sediment pond.
· Discharge clean, non-turbid de-watering water, such as well-point ground water, to systems
tributary to, or directly into surface waters of the State, as specified in Element #8, provided
the de-watering flow does not cause erosion or flooding of receiving waters or interfere
with the operation of the system. Do not route clean dewatering water through stormwater
sediment ponds. Note that “surface waters of the State” may exist on a construction site as
well as off site; for example, a creek running through a site.
· Handle highly turbid or contaminated dewatering water separately from stormwater.
· Other treatment or disposal options may include:
o Infiltration.
o Transport off-site in a vehicle, such as a vacuum flush truck, for legal disposal in a
manner that does not pollute state waters.
o Ecology-approved on-site chemical treatment or other suitable treatment
technologies.
o Sanitary or combined sewer discharge with local sewer district approval if there is
no other option.
o Use of a sedimentation bag with outfall to a ditch or swale for small volumes of
localized dewatering.
· Channels must be stabilized, as specified in Element #8.
· Construction equipment operation, clamshell digging, concrete tremie pour, or work inside
a cofferdam can create highly turbid or contaminated dewatering water.
· Discharging sediment-laden (muddy) water into waters of the State likely constitutes
violation of water quality standards for turbidity. The easiest way to avoid discharging
muddy water is through infiltration and preserving vegetation.
Element 11: Maintain BMPs
· Maintain and repair all temporary and permanent erosion and sediment control BMPs as
needed to assure continued performance of their intended function in accordance with
BMP specifications.
· Remove all temporary erosion and sediment control BMPs within 30 days after achieving
final site stabilization or after the temporary BMPs are no longer needed.
· Note: Some temporary erosion and sediment control BMPs are bio-degradable and
designed to remain in place following construction such as compost socks.
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· Provide protection to all BMPs installed for the permanent control of stormwater from
sediment and compaction. All BMPs that are to remain in place following completion of
construction shall be examined and placed in full operating conditions. If sediment enters
the BMPs during construction, it shall be removed, and the facility shall be returned to the
conditions specified in the construction documents.
· Remove or stabilize trapped sediment on site. Permanently stabilize disturbed soil resulting
from removal of BMPs or vegetation.
Element 12: Manage the Project
· Phase development projects to the maximum degree practicable and consider seasonal
work limits.
· Inspection and monitoring – Inspect, maintain, and repair all BMPs as needed to assure
continued performance of their intended function. Conduct site inspections and monitoring
in accordance with the Construction Stormwater General Permit or local plan approval
authority.
· Maintaining an updated construction SWPPP – Maintain, update, and implement the
SWPPP in accordance with the Construction Stormwater General Permit.
· Projects that disturb one or more acres must have, site inspections conducted by a Certified
Erosion and Sediment Control Lead (CESCL). Project sites less than one acre (not part of a
larger common plan of development or sale) may have a person without CESCL certification
conduct inspections. By the initiation of construction, the SWPPP must identify the CESCL or
inspector, who shall be present on-site or on-call at all times.
· The CESCL or inspector (project sites less than one acre) must have the skills to assess the:
o Site conditions and construction activities that could impact the quality of
stormwater.
o Effectiveness of erosion and sediment control measures used to control the quality
of stormwater discharges.
· The CESCL or inspector must examine stormwater visually for the presence of suspended
sediment, turbidity, discoloration, and oil sheen. They must evaluate the effectiveness of
BMPs and determine if it is necessary to install, maintain, or repair BMPs to improve the
quality of stormwater discharges. Based on the results of the inspection, construction site
operators must correct the problems identified by:
· Reviewing the SWPPP for compliance with the 13 construction SWPPP elements and making
appropriate revisions within 7 days of the inspection.
· Immediately beginning the process of fully implementing and maintaining appropriate
source control and/or treatment BMPs as soon as possible, addressing the problems no
later than within 10 days of the inspection. If installation of necessary treatment BMPs is
not feasible within 10 days, the construction site operator may request an extension within
the initial 10-day response period.
· Documenting BMP implementation and maintenance in the site log book (applies only to
sites that have coverage under the Construction Stormwater General Permit).
· The CESCL or inspector must inspect all areas disturbed by construction activities, all BMPs,
and all stormwater discharge points at least once every calendar week and within 24 hours
of any discharge from the site. (For purposes of this condition, individual discharge events
that last more than one day do not require daily inspections. For example, if a stormwater
pond discharges continuously over the course of a week, only one inspection is required
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that week.) The CESCL or inspector may reduce the inspection frequency for temporary
stabilized, inactive sites to once every calendar month
· Phasing of Construction.
o Phase development projects where feasible in order to prevent soil erosion and, to
the maximum extent practical, and prevent transporting sediment from the site
during construction. Revegetate exposed areas and maintain that vegetation as an
integral part of the clearing activities for any phase.
o Clearing and grading activities for developments shall be permitted only if
conducted using an approved site development plan (e.g., subdivision approval) that
establishes permitted areas of clearing, grading, cutting, and filling. Minimize
removing trees and disturbing or compacting native soils when establishing
permitted clearing and grading areas. Show on the site plans and the development
site permitted clearing and grading areas and any other areas required to preserve
critical or sensitive areas, buffers, native growth protection easements, or tree
retention areas as may be required by local jurisdictions.
· Seasonal Work Limitations
o From October 1 through April 30, clearing, grading, and other soil disturbing
activities is permitted only if shown to the satisfaction of the local permitting
authority that the site operator will prevent silt-laden runoff from leaving the site
through a combination of the following:
Site conditions including existing vegetative coverage, slope, soil type, and
proximity to receiving waters.
Limit activities and the extent of disturbed areas.
Proposed erosion and sediment control measures.
o Based on the information provided and/or local weather conditions, the local
permitting authority may expand or restrict the seasonal limitation on site
disturbance. The local permitting authority has the authority to take enforcement
action –such as a notice of violation, administrative order, penalty, or stop-work
order under the following circumstances:
· If, during the course of any construction activity or soil disturbance during the seasonal
limitation period, sediment leaves the construction site causing a violation of the surface
water quality standard; or
· If clearing and grading limits or erosion and sediment control measures shown in the
approved plan are not maintained.
· The following activities are exempt from the seasonal clearing and grading limitations:
o Routine maintenance and necessary repair of erosion and sediment control BMPs;
o Routine maintenance of public facilities or existing utility structures that do not
expose the soil or result in the removal of the vegetative cover to soil.
o Activities where there is one hundred percent infiltration of surface water runoff
within the site in approved and installed erosion and sediment control facilities.
· Coordination with Utilities and Other Contractors
o The primary project proponent shall evaluate, with input from utilities and other
contractors, the stormwater management requirements for the entire project,
including the utilities, when preparing the Construction SWPPP.
· Inspection and Monitoring
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o All BMPs must be inspected, maintained, and repaired as needed to assure
continued performance of their intended function. Site inspections must be
conducted by a person knowledgeable in the principles and practices of erosion and
sediment control. The person must have the skills to 1) assess the site conditions
and construction activities that could impact the quality of stormwater, and 2)
assess the effectiveness of erosion and sediment control measures used to control
the quality of stormwater discharges.
o For construction sites one acre or larger that discharge stormwater to surface
waters of the state, a CESCL must be identified in the construction SWPPP; this
person must be on-site or on-call at all times. Certification must be obtained
through an approved training program that meets the erosion and sediment control
training standards established by Ecology.
o Appropriate BMPs or design changes shall be implemented as soon as possible
whenever inspection and/or monitoring reveals that the BMPs identified in the
Construction SWPPP are inadequate, due to the actual discharge of /or potential to
discharge a significant amount of any pollutant.
· Maintaining an Updated Construction SWPPP
o Retain the Construction SWPPP on-site or within reasonable access to the site.
o Modify the SWPPP whenever there is a change in the design, construction,
operation, or maintenance at the construction site that has, or could have, a
significant effect on the discharge of pollutants to waters of the state.
· The SWPPP must be modified if, during inspections or investigations conducted by the
owner/operator, or the applicable local or state regulatory authority, it is determined that
the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater
discharges from the site. Modify the SWPPP as necessary to include additional or modified
BMPs designed to correct problems identified. Complete revisions to the SWPPP within
seven (7) days following the inspection.
Element 13: Protect Low Impact Development BMPs
· Protect all Bioretention and Rain Garden BMPs from sedimentation through installation and
maintenance of erosion and sediment control BMPs on portions of the site that drain into
the Bioretention and/or Rain Garden BMPs. Restore the BMPs to their fully functioning
condition if they accumulate sediment during construction. Restoring the BMP must include
removal of sediment and any sediment-laden Bioretention/rain garden soils, and replacing
the removed soils with soils meeting the design specification.
· Prevent compacting Bioretention and rain garden BMPs by excluding construction
equipment and foot traffic. Protect completed lawn and landscaped areas from compaction
due to construction equipment.
· Control erosion and avoid introducing sediment from surrounding land uses onto
permeable pavements. Do not allow muddy construction equipment on the base material or
pavement. Do not allow sediment-laden runoff onto permeable pavements.
· Pavements fouled with sediments or no longer passing an initial infiltration test must be
cleaned using procedures from the local stormwater manual or the manufacturer’s
procedures.
· Keep all heavy equipment off existing soils under LID facilities that have been excavated to
final grade to retain the infiltration rate of the soils.
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· See Chapter 5: Precision Site Preparation, Construction & Inspection of LID Facilities in the
LID Technical Guidance Manual for Puget Sound (2012) for more detail on protecting LID
integrated management practices.
· Note that the LID Technical Guidance Manual for Puget Sound (2012) is for additional
informational purposes only. You must follow the guidance within this manual if there are
any discrepancies between this manual and the LID Technical Guidance Manual for Puget
Sound (2012).
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SPECIAL REPORTS AND STUDIES
Special reports and studies prepared for this project include:
· Geotechnical Engineering Report, prepared by Terracon Consultants, Inc., dated December
20, 2018
· Operation and Maintenance Manual
· CSWPP Narrative and Plans
PERMITS
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APPENDIX A
WWHM DATA AND OUTPUT
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APPENDIX B
OPERATIONS AND MAINTENANCE MANUAL
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APPENDIX C
GEOTECHNICAL REPORT
REPORT COVER PAGE
Geotechnical Engineering Report
__________________________________________________________________________
Edmonds Senior Living
Edmonds, Washington
December 20, 2018
Terracon Project No. 81185173
Prepared for:
CA Senior Living Holdings, LLC
Chicago, IL
Prepared by:
Terracon Consultants, Inc.
Mountlake Terrace, Washington
Terracon Consultants, Inc.21905 64th Ave. W, Suite 100 Mountlake Terrace, WA 98043
P (425) 771 3304 F (425) 771 3549 www.terracon.com
REPORT COVER LETTER TO SIGNDecember 20, 2018
CA Senior Living Holdings, LLC
12345 Street Name
Chicago, IL 00000
Attn: Mr. Michael Duggan – Vice President of Development
P:(312) 248-2091
E:mduggan@ca-ventures.com
Re: Geotechnical Engineering Report
Edmonds Senior Living
21200 72nd Ave. W
Edmonds, Washington
Terracon Project No. 81185173
Dear Mr. Duggan:
We have completed the Geotechnical Engineering services for the above referenced project. This
study was performed in general accordance with Terracon Proposal No. P81185173 dated
October 22, 2018. This report presents the findings of the subsurface exploration and provides
geotechnical recommendations concerning earthwork and the design and construction of building
foundations, floor slabs, and temporary shoring for the proposed project. Additionally, we provide
discussion for stormwater infiltration potential.
We appreciate the opportunity to be of service to you on this project. If you have any questions
concerning this report or if we may be of further service, please contact us.
Sincerely,
Terracon Consultants, Inc.
Zachary L. Koehn, P.E.David A. Baska, P.E.
Senior Staff Engineer Senior Engineering Consultant
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REPORT TOPICS
INTRODUCTION ............................................................................................................. 1
SITE CONDITIONS ......................................................................................................... 1
PROJECT DESCRIPTION .............................................................................................. 2
GEOTECHNICAL CHARACTERIZATION ...................................................................... 3
GEOTECHNICAL OVERVIEW ....................................................................................... 4
EARTHWORK................................................................................................................. 5
SHALLOW FOUNDATIONS ........................................................................................... 9
DEWATERING AND SUBSURFACE DRAINAGE ....................................................... 11
SEISMIC CONSIDERATIONS ...................................................................................... 12
FLOOR SLABS............................................................................................................. 13
LATERAL EARTH PRESSURES ................................................................................. 14
EXCAVATION DESIGN ................................................................................................ 16
STORMWATER MANAGEMENT ................................................................................. 18
GENERAL COMMENTS ............................................................................................... 19
Note: This report was originally delivered in a web-based format.Orange Bold text in the report indicates a
referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and
clicking on the GeoReport logo will bring you back to this page. For more interactive features, please view your
project online at client.terracon.com.
ATTACHMENTS
EXPLORATION AND TESTING PROCEDURES
PHOTOGRAPHY LOG
SITE LOCATION AND EXPLORATION PLANS
EXPLORATION RESULTS
SUPPORTING INFORMATION
Note: Refer to each individual Attachment for a listing of contents.
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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REPORT SUMMARY
Topic 1 Overview Statement 2
Project
Description
Approx. 35,000 square foot development for a senior living facility with six-stories
above ground and one below.
Assumed Max. Column loads: 500 kips
Assumed Max. Wall loads: 6 kips per linear foot
Assumed Slab-on-grade: 150 pounds per square foot
Pavements do not appear to be part of the planned development
Geotechnical
Characterization
Existing fill and recessional outwash soils over glacial till:
Loose to dense silty sandy and sandy silt with variable gravel to about 15 feet
Dense to very dense glacially consolidated soils to at least 26 ½ feet
Cobbles may be present in glacial soils
Groundwater was encountered at about 25 feet below ground surface though
perched groundwater may be present shallower
Earthwork
The planned development will include removal of topsoil, existing fill, and loose
recessional soils. As a minimum, topsoil encountered within proposed driveway or
sidewalk subgrades should be removed.
Dense, glacially consolidated soils are suitable for foundation subgrades
Foundation soils are moisture sensitive and may become unstable when exposed to
excessive moisture or are disturbed
Shallow
Foundations
Shallow foundations will be sufficient
Allowable bearing pressure (spread and wall footings) =
■Dense, Native Soil: 5,000 lbs/sq ft
Expected settlements: < 1 inch total, < ½ inch differential
Detect and remove zones of unsuitable subgrade as noted in Earthwork
Below-Grade
Structures
The planned development includes one level of below grade parking therefore
temporary shoring is required
Shoring Design Temporary shoring using either cantilevered soldier piles or soldier piles with a single
row of tiebacks with 4-inch temporary wood lagging
General
Comments
This section contains important information about the limitations of this geotechnical
engineering report.
1.If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section
of the report by simply clicking on the topic itself.
2.This summary is for convenience only. It should be used in conjunction with the entire report for design
purposes.
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INTRODUC TION Geotechnical Engineering Report
Edmonds Senior Living
21200 72nd Ave. W
Edmonds, Washington
Terracon Project No. 81185173
December 20, 2018
INTRODUCTION
This report presents the results of our subsurface exploration and geotechnical engineering
services performed for the proposed Edmonds Senior Living project to be located at 21200 72nd
Ave. W in Edmonds, Washington. The purpose of these services is to provide information and
geotechnical engineering recommendations relative to:
■Subsurface soil conditions ■Seismic considerations and liquefaction
■Groundwater conditions ■Lateral earth pressures
■Site preparation and earthwork ■Excavation design
■Foundation design and construction ■Stormwater Management
■Floor slab design and construction
The geotechnical engineering scope of services for this project included the advancement of
number soil borings to depths ranging from approximately 21 ½ to 26 ½ feet below existing site
grades, respectively.
Maps showing the site and exploration locations are shown in the Site Location and Exploration
Plan sections, respectively. The results of the laboratory testing performed on soil samples
obtained from the site during the field exploration are included on the boring logs and/or as
separate graphs in the Exploration Results section of this report.
SITE CONDITIONS
The following description of site conditions is derived from our site visit in association with the
field exploration and our review of publicly available geologic and topographic maps.
Item Description
Parcel Information
The project is located at 21200 72nd Ave. W in Edmonds, Washington.
Lot Size: 35, 284 ft2 (0.81 acres)
Latitude: 47.8067 Longitude: -122.3307 See Site Location
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Item Description
Existing
Improvements
The site is currently developed with a single-story medical office of
approximately 6,641 ft2. The lot includes paved parking areas and drive lanes
to the north and east.
Current Ground
Cover
Primarily paved parking with some planting areas around the building. Several
large diameter trees are located along the north, south, and east perimeters
of the site.
Existing Topography
(Google Earth)
The site is gently sloping with elevation of about 282 feet along the northern
property line to about 374 feet to the south.
Geology
Near-surface soils were generally fill and recessional glacial outwash
consisting primarily of loose to medium dense silty sand. Underlying the fill
and outwash is dense to very dense, glacially consolidated silty sandy and
sandy silt.
PROJECT DESCRIPTION
Our initial understanding of the project was provided in our proposal, and to the best of our
knowledge, has remained unchanged. The understanding in which our assumptions and
recommendations are based is as follows:
Item Description
Information Provided
■Email request for proposal as communicated to Terracon by CA
■Senior living facility test fit (no date or title on document)
■Edmonds development site offering memorandum prepared by Kidder
Mathews (no date on document)
Project Description
The project will include demolition of an existing single-story office structure
and development of a multi-story senior living facility with below ground
parking. The development appears to include a courtyard area between the
wings.
Proposed Structure
The proposed senior living facility development will include one building with
east and west wings constructed to 6 stories above grade (75 feet) with one
level of below grade parking (14 feet).
Building Construction
(Assumed)Wood frame over concrete basement
Finished Floor
Elevation Finished floor elevation is not known at this time
Maximum Loads
■Assumed Max. Column loads: 500 kips
■Assumed Max. Wall loads: 6 kips per linear foot
■Assumed Slab-on-grade: 150 pounds per square foot
Grading/Slopes Site grades are not known at this time.
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Item Description
Below Grade
Structures The project includes one below-grade level (approximately 14 feet)
Free-Standing
Retaining Walls
(Assumed)
Retaining walls are not anticipated as part of site development.
Pavements Paved areas do not appear to be part of the planned development
Estimated Start of
Construction Not known at this time
GEOTECHNICAL CHARACTERIZATION
We have developed a general characterization of the subsurface soil and groundwater conditions
based upon our review of the data and our understanding of the geologic setting and planned
construction. The following table provides our geotechnical characterization.
The geotechnical characterization forms the basis of our geotechnical calculations and evaluation
of foundation options. As noted in General Comments, the characterization is based upon widely
spaced exploration points across the site, and variations are likely.
Stratum Approximate Depth to
Bottom of Stratum (feet)Material Description Consistency/Density
Surface Asphalt/Concrete Approx. 1 ½ inch asphalt pavement
with 2 inch base course N/A
1 3 ½ to 7 ½
light brown to brown, silty sand with
variable gravel content, some woody
debris and cobbles (Fill)
loose to medium
dense
2 10 to 13
grayish brown to brown, sand with
silt content, trace gravel
(Recessional Glacial Outwash)
medium dense
3 1 at least 26 ½
gray to dark gray and tan, silty sand
and sandy silt with variable gravel
content (Glacial Till)
dense to very
dense/hard
1.All borings were terminated in this stratum
Conditions encountered at each boring location are indicated on the individual boring logs shown
in the Exploration Results section and are attached to this report. Stratification boundaries on
the boring logs represent the approximate location of changes in soil types; in situ, the transition
between materials may be gradual or vary spatially.
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Groundwater Conditions
The boreholes were observed while drilling and after completion for the presence and level of
groundwater. The water levels observed in the boreholes can be found on the boring logs in
Exploration Results, and are summarized below.
Boring Number
Approximate Depth to
Groundwater while Drilling
(feet)1,2
Approximate Depth to
Groundwater after Drilling
(feet)
B-1, B-2, B-3 Not encountered Not encountered
B-4 20 ½---3
1.Below ground surface
2.Groundwater is inferred from change in sample moisture
3.Water not present in borehole following extraction of augers
Groundwater was not observed borings B-1, B-2, and B-3 while drilling, and was not observed in any
boring after extraction of augers for the short duration the borings could remain open. However, this
does not necessarily mean the borings terminated above groundwater, or the water levels
summarized above are stable groundwater levels. Due to the low permeability of the soils
encountered in the borings, a relatively long period may be necessary for a groundwater level to
develop and stabilize in a borehole. Long term observations in piezometers or observation wells
sealed from the influence of surface water are often required to define groundwater levels in materials
of this type.
Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff
and other factors not evident at the time the borings were performed. Therefore, groundwater
levels during construction or at other times in the life of the structure may be higher or lower than
the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be
considered when developing the design and construction plans for the project.
GEOTECHNICAL OVERVIEW
The proposed development will result in about a 14-foot deep excavation to accommodate one
level of below grade parking and the building foundations. Although not directly observed in the
surface exploration, perched shallow groundwater is commonly present over dense, glacially
consolidated soils and therefore may be present during construction. Construction dewatering
may be required during excavation and shoring installation. Additionally, the upper 13 feet of the
subsurface consists of primarily loose to medium dense cohesionless soils with the potential for
a shallow groundwater table. Therefore, the most cost-effective shoring system is likely a
cantilever soldier pile or a soldier pile and single row of tiebacks. An easement for temporary
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tiebacks will be required from the private properties located on the south and west sides of the
project and from the City of Edmonds for anchoring in the public right of way to the north and east.
The soils anticipated at the base of the excavation are sufficiently dense for shallow foundations.
Casting of foundations may be performed directly onto the existing soils, provided care is
exercised during construction to minimize disturbance. Due to the appreciable silt content in these
soils, the subgrade could become unstable if not protected from excessive foot and construction
traffic, especially after precipitation events. Construction dewatering, if needed, should maintain
a dry excavation at least two feet below the foundation subgrade. If possible, construction should
be performed during the warmer and drier time of the year. If work is performed during the wet
months, an increased risk for possible unstable subgrade, and difficult working conditions,
persists. Additional site preparation recommendations are provided in the Earthwork section. The
Shallow Foundations and Floor Slabs sections address bearing on native soils, or lean mix
concrete if overexcavation is required due to disturbance of the subgrade.
Groundwater inflow into the excavation is anticipated to be limited to shallow, perched
groundwater zones so inflows are anticipated to be low.
Existing fill was observed up to 7 ½ feet below ground surface, which is shallower than the depth
of the planned excavation; therefore, it is not anticipated that excavation for building foundations
or the basement floor slab will encounter fill. Sidewalk and pavement subgrades outside the
building may be supported on existing fill materials. However, there is an inherent risk for the
owner that compressible fill or unsuitable materials within or buried by the fill will not be
discovered. This risk of unforeseen conditions cannot be eliminated without completely removing
the existing fill but can be reduced by removing the upper foot of fill followed by scarification and
recompaction of an additional foot (i.e. total of 2 feet of compacted material below the subgrades).
The General Comments section provides an understanding of the report limitations.
EARTHWORK
Earthwork will include clearing and grubbing, demolition and removal of existing building
foundations, and deep excavation to about 14 feet below existing grade, foundation preparation,
and utility trenching. The following sections provide recommendations for use in the preparation
of specifications for the work. Recommendations include critical quality criteria as necessary to
render the site in the state considered in our geotechnical engineering evaluation for foundations,
floor slabs, and pavements.
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Site Preparation
The subgrade should be proof-rolled with an adequately loaded vehicle or construction
equipment. The proof-rolling should be performed under the observation of the Geotechnical
Engineer. Areas excessively deflecting under the proof-roll should be delineated and
subsequently addressed by the Geotechnical Engineer. Such areas should either be removed or
recompacted in place. Excessively wet or dry material should either be removed or moisture
conditioned and recompacted.
For areas outside the proposed excavation, existing vegetation and root mats should be removed
prior to placing fill. Complete stripping of the topsoil should be performed for driveway, sidewalk,
and parking areas.
Existing Fill
As noted in Geotechnical Characterization, the surface explorations encountered existing fill.
Within the building footprint, the existing fill will be removed as part of the planned excavation.
Sidewalks and driveways that are outside the building footprint will encounter fill at the subgrade
elevation. These features can be constructed over existing fill, however, there is an inherent risk
for the owner that compressible fill or unsuitable material within or buried by the fill will not be
discovered. This risk of unforeseen conditions cannot be eliminated without completely removing
the existing fill. If the owner elects to construct sidewalks and driveways over the existing fill, at
least one-foot below the planned subgrade elevation should completely stripped followed by
proof-rolling for the entire area. Areas of soft or otherwise unsuitable material should be undercut
and replaced with either new structural fill or suitable, existing on site materials. All subgrades
should be field verified by the Geotechnical Engineer to help identify areas with unstable
subgrades. These areas should be removed and replaced with suitable fill or recompacted.
Fill Material Types
Fill required to achieve design grade should be classified as structural fill and common fill.
Structural fill is material used below, or within 10 feet of structures, pavements or constructed
slopes. Common fill is material used to achieve grade outside of these areas. Earthen materials
used for structural and common fill should meet the following material property requirements:
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Fill Type Recommended Materials Acceptable Location for
Placement
Structural
9-03.9(1)Ballast1
9-03.9(3)Crushed Surfacing Base Course1
9-03.12(1)A Gravel Backfill for Foundations Class A1
9-03.14(1)Gravel Borrow1
On-site Soils (Stratum 1 and 2)2,3
Beneath and adjacent to
structural slabs, foundations,
and pavement subgrades
Common Fill Section 9-03.14(3)Common Borrow1
On-site Soils (Stratum 1 and 2)2,3
Grade filling, utility trench
backfill outside the building
foundation
1.WSDOT Standard Specifications
2.Structural and common fill should consist of approved materials free of organic matter and debris. Frozen
material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type
should be submitted to the Geotechnical Engineer for evaluation prior to use on this site.
3.May contain local areas of higher fines content that could make this material moisture sensitive. Particles with
a nominal diameter greater than about 3 inches should be removed.
Fill Compaction Requirements
Structural and common fill should meet the following compaction requirements.
Item Structural Fill Common Fill
Maximum Lift
Thickness
8 inches or less in loose thickness when heavy,
self-propelled compaction equipment is used
4 to 6 inches in loose thickness when hand-
guided equipment (i.e. jumping jack or plate
compactor) is used
Same as Structural fill
Minimum
Compaction
Requirements 1 95% of maximum dry density Same as Structural fill
Water Content
Range 1 Typically within 2% of optimum As required to achieve min.
compaction requirements
1.Maximum density and optimum water content as determined by the modified Proctor test (ASTM D 1557).
Utility Trench Backfill
All trenches should be wide enough to allow for compaction around the haunches of the pipe, or
material such as pea gravel (provided this is allowed by the pipe manufacturer) should be used
below the spring line of the pipes to eliminate the need for mechanical compaction in this portion
of the trenches. If water is encountered in the excavations, it should be removed prior to fill
placement.
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Placement and compaction of recommended materials for utility trench backfill should be in
accordance with the recommendations presented herein for Earthwork. In our opinion, the initial
lift thickness should not exceed one foot unless recommended by the manufacturer to protect
utilities from damage by compacting equipment. Light, hand-operated compaction equipment in
conjunction with thinner fill lift thicknesses may be utilized on backfill placed above utilities if
damage resulting from heavier compaction equipment is of concern.
Flexible connections for utilities that pass through building foundations are recommended to
reduce potential stress associated with differential settlement that may occur between the building
foundation and the improvements located outside of the building footprint.
Earthwork Construction Considerations
Upon completion of filling and grading, care should be taken to maintain the subgrade water
content prior to construction of floor slabs. Construction traffic over the completed subgrades
should be avoided. The base of the excavation should also be graded to prevent ponding of
surface water on the prepared subgrades or in excavations. Water collecting over, or adjacent to,
construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is
disturbed, the affected material should be removed, or the materials should be scarified, moisture
conditioned, and recompacted, prior to construction.
Construction dewatering is discussed in Excavation Design.
Construction Observation and Testing
The earthwork efforts should be monitored under the observation of the Geotechnical Engineer.
Each lift of compacted fill should be tested, evaluated, and reworked as necessary until approved
by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested
for density and water content. In areas of foundation excavations, the bearing subgrade should
be evaluated by the Geotechnical Engineer. In the event that unanticipated conditions are
encountered, the Geotechnical Engineer should recommend mitigation options.
In addition to the documentation of the essential parameters necessary for construction, the
continuation of the Geotechnical Engineer into the construction phase of the project provides the
continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including
assessing variations and associated design changes.
Wet Weather Earthwork
The foundation soils at the base of the excavation have variable fines content based on our visual
observations and lab testing and are considered moisture sensitive. The suitability of soils used
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for structural fill depends primarily on their grain-size distribution and moisture content when they
are placed. As the fines content (the soil fraction passing the U.S. No. 200 Sieve) increases, soils
become more sensitive to small changes in moisture content. Soils containing more than about
5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when
the moisture content is more than 2 percentage points above or below optimum. Optimum
moisture content is the moisture content at which the maximum dry density for the material is
achieved in the laboratory by the ASTM D1557 test procedure.
If inclement weather or in situ soil moisture content prevents the use of on-site material as
structural fill, we recommend importing granular fill containing less than 5 percent by weight
passing the U.S. No. 200 sieve, based on the fraction passing the U.S. No. 4 sieve. Stockpiled
soils should be protected with polyethylene sheeting anchored to withstand local wind conditions
and preservation of the soil’s moisture content.
SHALLOW FOUNDATIONS
If the site has been prepared in accordance with the requirements noted in Earthwork, the
following design parameters are applicable for shallow foundations.
Design Parameters – Compressive Loads
Description Spread Footing Wall Footing
Net allowable bearing pressure 1,2
n Dense/hard, native soil 5,000 psf 5,000 psf
Minimum dimensions 24 inches 18 inches
Minimum embedment below finished grade 3 18 inches 18 inches
Approximate static total settlement from
foundation loads for condition specified4 <1 inch <1 inch
Estimated static differential settlement from
foundation loads4 About 2/3 of total settlement
Ultimate passive pressure 5,6 on native soil 350 pcf (equivalent fluid unit weight)
Ultimate coefficient of sliding friction7 0.40
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Description Spread Footing Wall Footing
1.The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding
overburden pressure at the footing base elevation. An appropriate factor of safety has been applied. These
bearing pressures can be increased by 1/3 for transient loads unless those loads have been factored to
account for transient conditions. Assumes that exterior grades are relatively level adjacent to the structure.
2.Values provided are for maximum loads noted in Project Description.
3.For frost protection and to reduce the effects of seasonal moisture variations in the subgrade soils. For
perimeter footing and footings beneath unheated areas. For sloping ground, maintain depth below the
lowest adjacent exterior grade within 5 horizontal feet of the structure.
4.Differential settlements are as measured over a span of 50 feet.
5.Use of passive earth pressures require the sides of the excavation for the spread footing foundation to be
nearly vertical and the concrete placed neat against these vertical faces or that the footing forms be
removed and compacted structural fill be placed against the vertical footing face.
6.Passive resistance in the upper 2 feet of the soil profile should be neglected.
7.Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Should
be neglected for foundations subject to net uplift conditions.
Foundation Construction Considerations
As noted in Earthwork, the footing excavation subgrades should be observed by the
Geotechnical Engineer. The base of all foundation excavations should be free of water and loose
soil, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing
soil disturbance. Care should be taken to prevent wetting or drying of the bearing materials during
construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the
footing excavations should be removed or reconditioned before foundation concrete is placed.
If unsuitable bearing soils are encountered at the base of the planned footing excavation, or if
prepared subgrades become disturbed through construction activities, the excavation should be
extended deeper to suitable soils. The excavation can be backfilled to the planned grade through
use of lean concrete as illustrated below.
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DEWATERING AND SUBSURFACE DRAINAGE
We recommend that the walls and parking garage slab are positively drained to collect and convey
ground water seepage that may be present. The drainage system should consist of a combination
of free-draining structural fill (i.e. material with less than 5 percent passing the No. 200 sieve),
wall drainage, footing drains, and a sump collection system if discharge by gravity is not possible.
To estimate the steady state flow rate of the under slab and a wall drainage system, further study
of groundwater inflows via pump testing and installation of a monitoring wells may be necessary
to better estimate the hydraulic conductivity of the foundation soils. For planning purposes, the
hydraulic conductivity can be approximated as 10-4 cm per second for the foundation soils, based
on particle size analyses.
Wall Drainage
Basement walls poured flush against the shoring should be provided with drainage by placing full
face geocomposite drain against the shoring wall. The geocomposite drain should be tied into the
footing drainage system. It is important to provide a good connection between the wall drain and
the footing drainage system. The detail of the wall/footing drain connection will depend on the
type of shoring, basement wall type, and perimeter footing. Drainage behind walls cast in open
excavations can consist of geocomposite drainage as discussed above or a minimum of a 2-foot
wide zone of clean sand and gravel fill with less than 5 percent passing the No. 200 sieve. If a
moisture-free wall is desired, a water proof barrier, such as plastic or bentonite panels, should be
placed over the geocomposite drain prior to pouring or shotcreting the concrete wall.
Footing Drains
A perimeter footing drain should also be provided and consist of a minimum 4-inch diameter heavy
walled perforated PVC pipe or equivalent. We recommend that the footing drains have a minimum
slope of 0.25 percent, and that the pipe invert is at least 12-inches below the finish floor slab. The
pipe should be bedded in at least 4-inches and surrounded by at least 6-inches, of drainage
material consisting of ¾-inch washed drain rock. We recommend use of nonwoven filter fabric
(Mirafi 140N or equivalent) to wrap the entire pipe and rock assembly. Cleanouts are
recommended for the footing drain system.
Sumps
If gravity flow is not possible, the footing and wall drainage system should drain to a sump for
pumping. The steady state or long-term groundwater flow rate should be evaluated during
construction and the permanent drainage system sized for that flow. If a sump system is used, a
backup pump with emergency power is recommended in case of mechanical breakdown. We
recommend that the sump and drain pipe clean outs be vented to the atmosphere to prevent the
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buildup of hydrostatic pressure below the floor slab in case of mechanical or electrical failure of
the sump pumps.
Dewatering Considerations
Construction dewatering is the responsibility of the contractor, who should maintain the
excavation and foundation subgrades in a dry condition. Seepage associated with groundwater
may be encountered in the excavation for the below grade parking. Based on the results of the
subsurface explorations, active dewatering may not be necessary as groundwater was only
encountered at about 20 feet below ground surface for B-4 though zones of perched groundwater
are typical in similar geologic media. Further study of groundwater inflows via pump testing and
installation of monitoring wells may be necessary to better estimate the hydraulic conductivity of
retained soils and potential for shallow groundwater.
SEISMIC CONSIDERATIONS
The seismic design requirements for buildings and other structures are based on the Seismic
Design Category. Site Classification is required to determine the Seismic Design Category for a
structure. The Site Classification is based on the upper 100 feet of the site profile defined by a
weighted average value of either shear wave velocity, standard penetration resistance, or
undrained shear strength in accordance with Section 20.4 of ASCE 7-10.
Description Value
2015 International Building Code (IBC)Site Classification1,2 D 3
Site Latitude 47.8066
Site Longitude -122.3307
SS –Short Period Spectral Acceleration, Site Class B 4 1.273 g
S1 –1-Second Period Spectral Acceleration, Site Class B 4 0.497 g
Fa –Short Period Site Coefficient 4 1.000
Fv –1-Second Period Site Coefficient4 1.503
PGA - ASCE 7-10, Peak Ground Acceleration 0.516 g
FPGA – Peak Ground Acceleration Site Coefficient 1.000
1.Seismic site classification in general accordance with the 2015 IBC, which refers to ASCE 7-10.
2.2015 IBC requires a site profile extending to a depth of 100 feet for seismic site classification. The site
properties below the exploration depth to 100 feet were estimated based on our experience and knowledge
of geologic conditions of the general area.
3.Site Class D applies to any profile having (1) soils having an average shear wave velocity of 600 to 1,200
feet per sec, (2) an average N value of 15 to 50, (3) an undrained shear strength of 1,000 to 2,000 psf.
4.These values were obtained using online seismic design maps and tools provided by the USGS
(http://earthquake.usgs.gov/hazards/designmaps/).
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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Surface-Fault Rupture
The hazard of damage from onsite fault rupture appears to be low based on review of the
Washington Department of Natural Resources Geologic Information Portal available online
(https://geologyportal.dnr.wa.gov/#natural_hazards) accessed on December 19, 2018. The
closest mapped fault is the Southern Whidbey Island fault zone, which is an inferred fault trace,
and lies approximately a 1/4 mile to the southwest.
Liquefaction
Liquefaction is the phenomenon where saturated soils develop high pore water pressures during
seismic shaking and lose their strength characteristics. This phenomenon generally occurs in
areas of high seismicity, where groundwater is shallow and loose granular soils or relatively non-
plastic fine-grained soils are present. Based on the site geology and subsurface groundwater
conditions, the risk of liquefaction of the site soils is low for this site during a design level earthquake
due to the dense nature of the glacially consolidated soils below the foundation level.
FLOOR SLABS
Design parameters for floor slabs assume the requirements for Earthwork have been followed.
Specific attention should be given to positive drainage away from the structure and. positive drainage
of the aggregate base beneath the floor slab.
Floor Slab Design Parameters
Item Description
Floor Slab Support 1 Minimum 6 inches of 9-03.12(4)Gravel Backfill for Drains 3
Compacted to at least 95% of maximum dry density (ASTM D 1557)
Estimated Modulus of
Subgrade Reaction 2
160 pounds per square inch per inch (psi/in) for point loads
40 pounds per square inch per inch (psi/in) for all other loading scenarios
1.Floor slabs should be structurally independent of building footings or walls to reduce the possibility of floor
slab cracking caused by differential movements between the slab and foundation.
2.Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade
condition, the requirements noted in Earthwork, and the floor slab support as noted in this table.
3.WSDOT Standard Specification
The use of a vapor retarder is recommended beneath concrete slabs on grade covered with wood,
tile, carpet, or other moisture sensitive or impervious coverings, or when the slab will support
equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab
designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use
and placement of a vapor retarder.
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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Saw-cut control joints should be placed in the slab to help control the location and extent of
cracking. For additional recommendations refer to the ACI Design Manual. Joints or cracks should
be sealed with a water-proof, non-extruding compressible compound specifically recommended
for heavy duty concrete pavement and wet environments.
Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other
construction objectives, our experience indicates differential movement between the walls and
slabs will likely be observed in adjacent slab expansion joints or floor slab cracks beyond the
length of the structural dowels. The Structural Engineer should account for potential differential
settlement through use of sufficient control joints, appropriate reinforcing or other means.
Floor Slab Construction Considerations
Finished subgrade within and for at least 10 feet beyond the floor slab should be protected from
traffic, rutting, or other disturbance and maintained in a relatively moist condition until floor slabs are
constructed. If the subgrade should become damaged or desiccated prior to construction of floor
slabs, the affected material should be removed and structural fill should be added to replace the
resulting excavation. Final conditioning of the finished subgrade should be performed immediately
prior to placement of the floor slab support course.
The Geotechnical Engineer should observe the condition of the floor slab subgrades immediately
prior to placement of the floor slab support course, reinforcing steel and concrete. Attention should
be paid to high traffic areas that were rutted and disturbed earlier, and to areas where backfilled
trenches are located.
LATERAL EARTH PRESSURES
Design Parameters
Structures with unbalanced backfill levels on opposite sides should be designed for earth
pressures at least equal to values indicated in the following table. Earth pressures will be
influenced by structural design of the walls, conditions of wall restraint, methods of construction
and/or compaction and the strength of the materials being restrained. Two wall restraint conditions
are shown. Active earth pressure is commonly used for design of free-standing cantilever
retaining walls and assumes wall movement. The "at-rest" condition assumes no wall movement
and is commonly used for basement walls, loading dock walls, or other walls restrained at the top.
The recommended design lateral earth pressures do not include a factor of safety and do not
provide for possible hydrostatic pressure on the walls (unless stated).
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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Lateral Earth Pressure Design Parameters
Earth Pressure
Condition 1
Coefficient for Backfill
Type2 Uniform Pressure 3, 4, 5
p1 (psf)
Effective Fluid
Pressures (psf)2, 4, 5, 6
Active (Ka)0.31 (0.31)S (40)H
At-Rest (Ko)0.47 (0.47)S (60)H
Passive (Kp)3.25 ---(350)H
Seismic 7 ---(7)H – Active
(12)H – At-Rest ---
1.For active earth pressure, wall must rotate about base, with top lateral movements 0.002 H to 0.004 H,
where H is wall height. For passive earth pressure, wall must move horizontally to mobilize resistance.
2.Uniform, horizontal backfill, compacted to at least 92 percent of the ASTM D 1557 maximum dry density,
rendering a unit weight of approximately 125 pcf.
3.Uniform surcharge, where S is surcharge pressure.
4.Loading from heavy compaction equipment is not included.
5.No safety factor is included in these values.
6.Values are in addition to static earth pressures
Backfill placed against structures should consist of granular soils or low plasticity cohesive soils.
For the granular values to be valid, the granular backfill must extend out and up from the base of
the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases,
respectively.
The basement walls connected to multiple floors are best represented by an “at-rest” earth
pressure condition due lateral movements of the walls being restrained by the floors. During
seismic loading, a moment reduction of up to 80 percent can be applied to basement walls as a
result of the stiffer, horizontal floors carrying a higher portion of the seismic load.
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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EXCAVATION DESIGN
Based on the soil conditions observed at the exploration locations and the assumed basement
floor slab depth of roughly 14 feet below existing grade, we recommend a soldier pile and lagging
shoring system to temporarily support the excavation required to construct the below grade
portions of the building. Recommendations for soldier piles that are both cantilevered and
supported laterally with a single row of tiebacks are provided. Provided adequate distance is
available, temporary slope cuts can be combined with the shoring system to reduce the height.
The shoring required to support the excavation is typically used as back forms for the permanent
basement walls.
Terracon should be included in discussions with the design team regarding design of temporary
shoring systems for this project and should review the shoring design for compliance with the
recommendations for shoring provided in this report. The following design and construction
parameters are provided for preliminary planning purposes.
Soldier Piles
Soldier piles for shoring are typically set in drilled holes and backfilled with lean concrete. If
tiebacks are used, structural concrete is placed in the bottom 5 to 10 feet. Soldier pile installation
for this site may involve casing the holes and/or drilling with a mud slurry to cut-off groundwater
seepage. Passive earth pressures acting on the embedded portion of the soldier piles resist
horizontal loads on the shoring system. We recommend using an allowable equivalent fluid unit
weight of 350 lbs per cubic ft. for passive resistance. The passive earth pressure will act over
three times the diameter of the concreted soldier pile section, or the pile spacing, whichever is
less. The active earth pressures act over the concreted pile diameter below the base of the
excavation. A minimum embedment of 10 feet is recommended.
For a shoring system with a single row of tieback anchors, we recommend the apparent earth
pressure theory for sands (i.e. Figure 24) presented in the Federal Highway Administration
Geotechnical Engineering Circular No. 4: Ground Anchors and Anchors Systems (FHWA 1999).
n For calculating the maximum ordinate of the diagram, P, assume an active earth pressure
coefficient of 0.31 and a total unit weight of 125 lbs per cubic foot (pcf)
n For traffic loads adjacent to the shoring walls, add a uniform surcharge load equivalent to 250
lbs per sq. ft;
n For other loads adjacent to the shoring (e.g., heavy construction loads and building
foundations), contact Terracon to estimate appropriate surcharge pressures.
n Seismic earth pressures are typically not included in shoring design but should be considered
if the excavation is to remain open for longer durations.
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
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Vertical capacity of the soldier piles are provided by a combination of end bearing and side friction
below the base of the excavation. The piles can be designed for an allowable end bearing capacity
and side friction of 20 ksf and 2 ksf, respectively. These values include a factor of safety of 2.
Tieback Anchors
For tieback anchors, the anchor portion of the tieback should be located sufficiently far behind the
excavation shoring to stabilize the excavation face. This “no load” zone is the area behind the
soldier pile equal to a lateral distance from the base of the excavation equal to the exposed wall
height (H in feet) divided by four, or five feet, whichever is greater, and a line sloping up and back
at 60 degrees from horizontal.
The selection of the tieback materials and installation methods should be the responsibility of the
contractor. The actual adhesion values will depend on the materials and installation method and
should be confirmed by testing. For non-pressure grouted anchors, the allowable design
concrete/soil adhesion value of 2,000 psf is recommended for the glacially consolidated soils (i.e.
bond zone at least about 13 feet below existing ground). For pressure grouted anchors, this value
can typically be increased by up to two times. For preliminary design purposes, we recommend
an ultimate pullout capacity of 10 kips/foot for 6-inch diameter, secondary pressure grouted
anchors. A factor of safety of 2 should be applied to the ultimate pullout capacity. We recommend
all tieback anchors be proof tested to at least 130% of the design capacity prior to locking off at
the specified post-tensioned design load. Prior to installation of production anchors, two
verification tests to 200% of the design pull out capacity are recommended for each soil type in
order to confirm the design anchor capacity.
The anchor spacing should be at least four feet center to center in order to avoid group effects
and the potential for anchors conflict with each other during installation. The anchor holes should
be drilled at an angle of 15 to 45 degrees down from horizontal. A minimum anchor bond of 10
feet is recommended. The location and presence of existing features such as utilities should be
checked during the design as these may affect the location and length of tieback anchors.
Lagging
We recommend timber lagging, or some other form of protection, be installed in all areas. Due to
soil arching effects, lagging may be design based on the requirements presented in presented in
the Federal Highway Administration Geotechnical Engineering Circular No. 4: Ground Anchors
and Anchors Systems (FHWA 1999). Prompt and careful installation of lagging would reduce
potential loss of ground. The requirements for lagging should be made the responsibility of the
shoring subcontractor to prevent soil failure, sloughing, and loss of ground. Proper installation of
lagging is critical to provide safe working conditions. We recommend that any voids between the
lagging and soil be backfilled promptly. However, the backfill should not allow potential hydrostatic
pressure to build-up behind the wall. Drainage behind the wall must be maintained. Voids behind
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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the lagging should be backfilled immediately with a permeable granular soil material or lean
concrete. The excavation height prior to lagging installation should not exceed 4 feet to maintain
stability of the cut face.
Soldier Pile Shoring Installation
The contractor should be required to prevent caving and loss of ground in all soldier pile drill
holes. The shoring contractor will need to use methods to minimize caving and sloughing of the
drill holes, such as the use of augercast methods or installation of casing. If more than one foot
of water is present in the bottom of the hole, placement of concrete from the bottom of the hole
using tremie methods will be required.
When drilling tieback anchor holes, casing may be required to prevent caving and loss of ground.
The anchor grout should be pumped into the anchor zone by tremie methods in order to remove
water from the hole and to provide a continuous grouted anchor.
Monitoring of Temporary Shoring
Any time an excavation is made below the level of existing buildings, utilities, or other structures,
there is risk of damage even if a well-designed shoring system has been planned. We
recommend, therefore, that a systematic program of observations be conducted on adjacent
facilities and structures. The monitoring program should include measurements of the horizontal
and vertical movements of the adjacent structures and the shoring system itself. At least two
reference lines should be established adjacent to the excavation at horizontal distances back from
the excavation space of about 1/3H and H, where H is the final excavation height. Monitoring of
the shoring system should include measurements of horizontal movements at the top of every
other soldier pile. If local wet areas are noted within the excavation, additional monitoring points
may be recommended by Terracon.
The measuring system used for shoring monitoring should have an accuracy of at least 0.01-feet.
All reference points on the existing structures should be installed and readings taken prior to
commencing the excavation. All reference points should be read prior to and during critical stages
of construction. The frequency of readings will depend on the results of previous readings and
the rate of construction. As a minimum, readings should be taken about once a week throughout
construction until the basement walls are completed. All readings should be reviewed by
Terracon.
STORMWATER MANAGEMENT
The subsurface conditions were evaluated for infiltration potential for stormwater management.
Sieve analyses were performed at 10 and 20 feet bgs for estimating an infiltration rate. In general,
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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the soils observed exhibit an appreciable fines content (i.e. percent passing the #200 sieve) which
is the soil particle size that largely influences soil permeability. The fines content observed for the
soils at these depths are about 15 and 28 percent, respectively. In addition, the soils at these
depths are dense to very dense. A soil unit that would be considered favorable for stormwater
infiltration was not encountered in any of the borings.
Based on particle size analysis alone, an infiltration rate of up to ¼ to ½ inch per hour is estimated.
However, analysis by particles size does not take soil packing density and is therefore not
necessarily representative of in situ conditions. Glacially consolidated soils, such as glacial till,
are generally very dense with small amounts of porewater space available. A pilot infiltration study
is typical required for evaluating stormwater infiltration potential of glacially consolidated soils. It
is unlikely that the results of an infiltration study would conclude that the site is suitable for
stormwater infiltration. Therefore, stormwater management via infiltration is not recommended.
Onsite storage with tie-in to the City of Edmonds stormwater system should be considered.
GENERAL COMMENTS
Our analysis and opinions are based upon our understanding of the project, the geotechnical
conditions in the area, and the data obtained from our site exploration. Natural variations will occur
between exploration point locations or due to the modifying effects of construction or weather.
The nature and extent of such variations may not become evident until during or after construction.
Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide
observation and testing services during pertinent construction phases. If variations appear, we
can provide further evaluation and supplemental recommendations. If variations are noted in the
absence of our observation and testing services on-site, we should be immediately notified so
that we can provide evaluation and supplemental recommendations.
Our Scope of Services does not include either specifically or by implication any environmental or
biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of
pollutants, hazardous materials or conditions. If the owner is concerned about the potential for
such contamination or pollution, other studies should be undertaken.
Our services and any correspondence or collaboration are intended for the sole benefit and
exclusive use of our client for specific application to the project discussed and are accomplished
in accordance with generally accepted geotechnical engineering practices with no third-party
beneficiaries intended. Any third-party access to services or correspondence is solely for
information purposes to support the services provided by Terracon to our client. Reliance upon
the services and any work product is limited to our client, and is not intended for third parties. Any
use or reliance of the provided information by third parties is done solely at their own risk. No
warranties, either express or implied, are intended or made.
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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Site characteristics as provided are for design purposes and not to estimate excavation cost. Any
use of our report in that regard is done at the sole risk of the excavating cost estimator as there
may be variations on the site that are not apparent in the data that could significantly impact
excavation cost. Any parties charged with estimating excavation costs should seek their own site
characterization for specific purposes to obtain the specific level of detail necessary for costing.
Site safety, and cost estimating including, excavation support, and dewatering
requirements/design are the responsibility of others. If changes in the nature, design, or location
of the project are planned, our conclusions and recommendations shall not be considered valid
unless we review the changes and either verify or modify our conclusions in writing.
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ATTACHMENTS
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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EXPLORATION AND TESTING PROCEDURES
Field Exploration
Number of Borings Boring Depth (feet)Planned Location
B-1 21 ½Northeast corner of lot
B-2, B-4 26 ½Northwest, Southeast corners of lot
B-3 26 ½Approx. center of lot
Boring Layout and Elevations: Terracon personnel provided the boring layout. Coordinates
were obtained with a handheld GPS unit (estimated horizontal accuracy of about ±10 feet). If
elevations and a more precise boring layout are desired, we recommend boring locations be
surveyed.
Subsurface Exploration Procedures: We advanced the borings with a track-mounted, ATV-
mounted rotary drill rig using continuous flight hollow-stem augers. Samples were obtained in 5-
foot intervals from each boring using a split-barrel sampling procedure. In this procedure, a
standard 2-inch outer diameter split-barrel sampling spoon was driven into the ground by a
140-pound automatic hammer falling a distance of 30 inches. The number of blows required to
advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the
Standard Penetration Test (SPT) resistance value. The SPT resistance values, also referred to as
N-values, are indicated on the boring logs at the test depths.
In boring B-2, the boring was inadvertently advanced through a previously abandoned borehole as
evident by the hydrated bentonite returned in the auger cutting. Due to time restriction in the day,
Terracon elected to drill out the boring until native soils were encountered, which was approximately
18 feet. Sampling, as stated above, was performed at 20 and 25 feet.
We observed and recorded groundwater levels during drilling and sampling. All borings were
backfilled with granular bentonite after their completion and pavements were patched pre-mixed
concrete.
The sampling depths, penetration distances, and other sampling information was recorded on the
field boring logs. The samples were placed in appropriate containers and taken to our soil laboratory
for testing and classification by a Geotechnical Engineer. Our exploration team prepared field
boring logs as part of the drilling operations. These field logs included visual classifications of the
materials encountered during drilling and our interpretation of the subsurface conditions between
samples. Final boring logs were prepared from the field logs. The final boring logs represent the
Geotechnical Engineering Report
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
Responsive ■Resourceful ■Reliable EXPLORATION AND TESTING PROCEDURES 2 of 2
Geotechnical Engineer's interpretation of the field logs and include modifications based on
observations and tests of the samples in our laboratory.
Laboratory Testing
The project engineer reviewed the field data and assigned laboratory tests to understand the
engineering properties of the various soil strata, as necessary, for this project. Procedural
standards noted below are for reference to methodology in general. In some cases, variations to
methods were applied because of local practice or professional judgment. Standards noted below
include reference to other, related standards. Such references are not necessarily applicable to
describe the specific test performed.
■ASTM D2216 Standard Test Methods for Laboratory Determination of Water (Moisture)
Content of Soil and Rock by Mass
■ASTM D6913 Standard Test Methods for Particle-Size Distribution (Gradation) of Soils
Using Sieve Analysis
■ASTM D1140 Standard Test Method for determining the Amount of Material Finer than
75-μm (No. 200) Sieve in Soils by Washing
The laboratory testing program often included examination of soil samples by an engineer. Based
on the material’s texture and plasticity, we described and classified the soil samples in accordance
with the Unified Soil Classification System. For further soil classification, the following index tests
were performed:
■5 – ASTM D2216 (Water Content)
■3 – ASTM D6913 (Grain Size Distribution)
■2 – ASTM D1140 (No. 200 Wash)
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SITE LOCATION AND EXPLORATION PLANS
Contents:
Site Location Plan
Exploration Plan
SITE LOCATION
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
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outside the table – please leave that alone. Limit editing to inside the table.
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it as desired, but try to keep to a single line of text to avoid reformatting the page.
SITE LOCA TION
DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS
EXPLORATION PLAN
Edmonds Senior Living ■ Edmonds, Washington
December 20, 2018 ■ Terracon Project No. 81185173
Note to Preparer: This is a large table with outside borders. Just click inside the table
above this text box, then paste your GIS Toolbox image.
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outside the table – please leave that alone. Limit editing to inside the table.
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it as desired, but try to keep to a single line of text to avoid reformatting the page.
EXPLORATION P LAN
DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS
EXPLORATION RESULTS
Contents:
Boring Logs (B-1 through B-4)
Grain Size Distribution
6-1-5N=6
8-15-16N=31
16-16-24
N=40
11-30-50/6"
N=80/12"
12
18
18
18
S-1
S-2
S-3
S-4 2814
ASPHALT, approx. 1.5 inches of asphalt over 2 inches base coarse
SANDY SILT (ML), trace gravel, fine to coarse grained, olive brown todark brown, moist to wet, soft, trace organics (FILL)
SILTY SAND (SM), reddish brown to brown, moist, medium dense,
(RECESSIONAL OUTWASH)
rust staining in top of S-2, possibly evidence of seasonal groundwater
SANDY SILT (ML), olive gray to gray, moist, very stiff, (GLACIALTILL)
SILTY SAND (SM), trace gravel, gray, moist, very dense
trace gravel, dense, interbedded silt
rock fragment in S-4, possibly over-stated blow-count
Boring Terminated at 21.5 Feet
0.6
7.5
10.5
13.0
21.5
379.5+/-
372.5+/-
369.5+/-
367+/-
358.5+/-
Hammer Type: Automatic (ETR = 88%)Stratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 81185173 EDMONDS SENIOR LI.GPJ TERRACON_DATATEMPLATE.GDT 12/20/18WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20 FIELD TESTRESULTSRECOVERY (In.)SAMPLE NUMBERPage 1 of 1
Advancement Method:Hollow Stem Auger
Abandonment Method:Boring backfilled with Auger Cuttings and/or BentoniteSurface Capped with Asphalt
21905 64th Ave W, Ste 100Mountlake Terrace, WA
Notes:
Project No.: 81185173
Drill Rig: D-50 track
BORING LOG NO. B-1
CA Senior Living Holdings, LLCCLIENT:Chicago, IL
Driller: Holocene
Boring Completed: 12-05-2018
PROJECT: Edmonds Senior Living
Elevations were estimated from Google EarthImagery
See Exploration and Testing Procedures for adescription of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation ofsymbols and abbreviations.
21200 72nd Ave. W
Edmonds, WA
SITE:
Boring Started: 12-05-2018WATER LEVEL OBSERVATIONS PERCENT FINESWATERCONTENT (%)LOCATION
Latitude: 47.8067° Longitude: -122.3303°
See Exploration Plan
GRAPHIC LOGDEPTH ELEVATION (Ft.)
Approximate Surface Elev.: 380 (Ft.) +/-SAMPLE TYPE
4-13-25
N=38
25-30-36N=66
12
18
S-4
S-5
Boring passed through an abandoned borehole of an unknownnature. Drill out upper 20 feet due to evidence of boreholebackfill.
ASPHALT, approx. 1.5 inches of asphalt over 2 inches of base coarse
DRILL OUT
POORLY GRADED SAND WITH SILT (SP-SM), light brown to brown,moist, dense, (GLACIAL TILL)
SILTY SAND (SM), reddish brown to olive gray, moist, very dense,silty sand with interbedded silt
rust staining in S-5, possibly evidence of seasonal groudwater
Boring Terminated at 26.5 Feet
0.6
20.0
22.5
26.5
381.5+/-
362+/-
359.5+/-
355.5+/-
Hammer Type: Automatic (ETR = 88%)Stratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 81185173 EDMONDS SENIOR LI.GPJ TERRACON_DATATEMPLATE.GDT 12/20/18WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20
25 FIELD TESTRESULTSRECOVERY (In.)SAMPLE NUMBERPage 1 of 1
Advancement Method:Hollow Stem Auger
Abandonment Method:Boring backfilled with Auger Cuttings and/or BentoniteSurface Capped with Asphalt
21905 64th Ave W, Ste 100Mountlake Terrace, WA
Notes:
Project No.: 81185173
Drill Rig: D-50 track
BORING LOG NO. B-2
CA Senior Living Holdings, LLCCLIENT:Chicago, IL
Driller: Holocene
Boring Completed: 12-05-2018
PROJECT: Edmonds Senior Living
Elevations were estimated from Google EarthImagery
See Exploration and Testing Procedures for adescription of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation ofsymbols and abbreviations.
21200 72nd Ave. W
Edmonds, WA
SITE:
Boring Started: 12-05-2018WATER LEVEL OBSERVATIONS PERCENT FINESWATERCONTENT (%)LOCATION
Latitude: 47.8067° Longitude: -122.331°
See Exploration Plan
GRAPHIC LOGDEPTH ELEVATION (Ft.)
Approximate Surface Elev.: 382 (Ft.) +/-SAMPLE TYPE
5-6-13N=19
15-18-13N=31
10-15-15
N=30
10-11-21
N=32
25-33-37N=70
6
16
15
18
18
S-1
S-2
S-3
S-4
S-5
Boring located in landscaped area.
1316
TOPSOIL
SAND WITH SILT (SP-SM), trace gravel, brown to grayish brown,moist, medium dense, some woody debris and cobbles (FILL)
SAND WITH SILT (SP-SM), light brown to brown, moist, mediumdense, (RECESSIONAL GLACIAL OUTWASH)
increasing silt content, transitions to silty sand
SILTY SAND (SM), light brown to brown, moist, dense, (GLACIAL
TILL)
rust staining in S-4, possibly evidence of seasonal groundwater
SANDY SILT (ML), reddish brown to olive brown, moist, hard
SAND (SP), trace silt, brown to reddish brown, moist, dense
rust staining in S-5, possibly evidence of seasonal groundwater
SILTY SAND (SM), gray to dark gray, moist, very dense
Boring Terminated at 26.5 Feet
0.5
3.5
10.0
20.521.0
25.5
26.5
377.5+/-
374.5+/-
368+/-
357.5+/-357+/-
352.5+/-
351.5+/-
Hammer Type: Automatic (ETR = 88%)Stratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 81185173 EDMONDS SENIOR LI.GPJ TERRACON_DATATEMPLATE.GDT 12/20/18WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20
25 FIELD TESTRESULTSRECOVERY (In.)SAMPLE NUMBERPage 1 of 1
Advancement Method:Hollow Stem Auger
Abandonment Method:Boring backfilled with Auger Cuttings and/or BentoniteSurface Capped with Asphalt
21905 64th Ave W, Ste 100Mountlake Terrace, WA
Notes:
Project No.: 81185173
Drill Rig: D-50 track
BORING LOG NO. B-3
CA Senior Living Holdings, LLCCLIENT:Chicago, IL
Driller: Holocene
Boring Completed: 12-05-2018
PROJECT: Edmonds Senior Living
Elevations were estimated from Google EarthImagery
See Exploration and Testing Procedures for adescription of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation ofsymbols and abbreviations.
21200 72nd Ave. W
Edmonds, WA
SITE:
Boring Started: 12-05-2018WATER LEVEL OBSERVATIONS PERCENT FINESWATERCONTENT (%)LOCATION
Latitude: 47.8066° Longitude: -122.3307°
See Exploration Plan
GRAPHIC LOGDEPTH ELEVATION (Ft.)
Approximate Surface Elev.: 378 (Ft.) +/-SAMPLE TYPE
2-2-2N=4
7-7-7N=14
16-27-28
N=55
9-20-26
N=46
18-30-36N=66
12
14
15
17
18
17
S-1
S-2
S-3
S-4
S-5
S-6
15
6
89
19
9
25
ASPHALT, approx. 1.5 inches asphalt over 2 inches base coarse
SILTY SAND WITH GRAVEL (SM), dark brown with olive brownmottling, moist, loose, woody debris (FILL)
SILTY SAND (SM), grayish brown to brown, moist, medium dense,sand with silt interbeds (RECESSIONAL GLACIAL OUTWASH)
SAND WITH SILT (SP-SM), light brown to brown, moist, dense to verydense, silt interbeds (GLACIAL TILL)
decreasing silt content
SANDY SILT (ML), light brown, moist, hard
rust staining observed in top of S-4, possible evidence of seasonalgroundwater
SAND WITH SILT (SP-SM), trace silt, brown, wet, dense
becomes dark gray, very dense
SILT (ML), trace sand, gray, moist, hard
Boring Terminated at 26.5 Feet
0.3
5.5
13.0
18.0
20.5
25.5
26.5
376.5+/-
371.5+/-
364+/-
359+/-
356.5+/-
351.5+/-
350.5+/-
Hammer Type: Automatic (ETR = 88%)Stratification lines are approximate. In-situ, the transition may be gradual.THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL 81185173 EDMONDS SENIOR LI.GPJ TERRACON_DATATEMPLATE.GDT 12/20/18WATER LEVELOBSERVATIONSDEPTH (Ft.)5
10
15
20
25 FIELD TESTRESULTSRECOVERY (In.)SAMPLE NUMBERPage 1 of 1
Advancement Method:Hollow Stem Auger
Abandonment Method:Boring backfilled with Auger Cuttings and/or BentoniteSurface Capped with Asphalt
21905 64th Ave W, Ste 100Mountlake Terrace, WA
Notes:
Project No.: 81185173
Drill Rig: D-50 track
BORING LOG NO. B-4
CA Senior Living Holdings, LLCCLIENT:Chicago, IL
Driller: Holocene
Boring Completed: 12-05-2018
PROJECT: Edmonds Senior Living
Elevations were estimated from Google EarthImagery
See Exploration and Testing Procedures for adescription of field and laboratory proceduresused and additional data (If any).
See Supporting Information for explanation ofsymbols and abbreviations.
21200 72nd Ave. W
Edmonds, WA
SITE:
Boring Started: 12-05-2018While sampling
WATER LEVEL OBSERVATIONS PERCENT FINESWATERCONTENT (%)LOCATION
Latitude: 47.8064° Longitude: -122.3304°
See Exploration Plan
GRAPHIC LOGDEPTH ELEVATION (Ft.)
Approximate Surface Elev.: 377 (Ft.) +/-SAMPLE TYPE
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
30 40 501.5 200681014413/4 1/2 60
GRAIN SIZE IN MILLIMETERSPERCENT FINER BY WEIGHTHYDROMETERU.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
4 3/8 3 10014032
GRAIN SIZE DISTRIBUTION
ASTM D422 / ASTM C136
6 16 20
PROJECT NUMBER: 81185173
SITE: 21200 72nd Ave. W Edmonds, WA
PROJECT: Edmonds Senior Living
CLIENT: CA Senior Living Holdings, LLC Chicago, IL
21905 64th Ave W, Ste 100Mountlake Terrace, WA
LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GRAIN SIZE: USCS-2 81185173 EDMONDS SENIOR LI.GPJ TERRACON_DATATEMPLATE.GDT 12/20/18silty SAND (SM)
silty SAND (SM)
SILT (ML)
0.267
0.249
19
19
2
27.5
14.5
88.8
11.8
2.1
0.0
0.084
0.133
WC (%)LL
D30 D10 %Gravel %Fines %Clay
B-1
B-4
B-4
Boring ID Depth USCS Classification PL PI Cc Cu
D100 D60
20 - 21.5
10 - 11.5
25 - 26.5
Boring ID Depth %Sand %Silt
medium
B-1
B-4
B-4
coarse coarsefine fineCOBBLESGRAVELSAND SILT OR CLAY
20 - 21.5
10 - 11.5
25 - 26.5
60.7
83.4
11.2
SUPPORTING INFORMATION
Contents:
General Notes
Unified Soil Classification System
Edmonds Senior Living Edmonds, WA
December 20, 2018 Terracon Project No. 81185173
0.25 to 0.50
> 4.00
2.00 to 4.00
1.00 to 2.00
0.50 to 1.00
less than 0.25
Unconfined Compressive Strength
Qu, (tsf)
GrabSample
StandardPenetrationTest
Trace
PLASTICITY DESCRIPTION
Water levels indicated on the soil boring logs arethe levels measured in the borehole at the times
indicated. Groundwater level variations will occurover time. In low permeability soils, accurate
determination of groundwater levels is notpossible with short term water level
observations.
DESCRIPTION OF SYMBOLS AND ABBREVIATIONS
GENERAL NOTES
> 30
11 - 30
1 - 10Low
Non-plastic
Plasticity Index
#4 to #200 sieve (4.75mm to 0.075mm
Boulders
12 in. to 3 in. (300mm to 75mm)Cobbles
3 in. to #4 sieve (75mm to 4.75 mm)Gravel
Sand
Passing #200 sieve (0.075mm)Silt or Clay
Particle Size
Water Level Aftera Specified Period of Time
Water Level After a
Specified Period of Time
Water InitiallyEncountered
Soil classification is based on the Unified Soil Classification System. Coarse Grained Soils have more than 50% of their
dry weight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand. Fine Grained Soilshave less than 50% of their dry weight retained on a #200 sieve; they are principally described as clays if they are plastic,and silts if they are slightly plastic or non-plastic. Major constituents may be added as modifiers and minor constituents
may be added according to the relative proportions based on grain size. In addition to gradation, coarse-grained soils are
defined on the basis of their in-place relative density and fine-grained soils on the basis of their consistency.
GRAIN SIZE TERMINOLOGY
RELATIVE PROPORTIONS OF FINESRELATIVE PROPORTIONS OF SAND AND GRAVEL
DESCRIPTIVE SOIL CLASSIFICATION
LOCATION AND ELEVATION NOTES
SAMPLING WATER LEVEL FIELD TESTS
N
(HP)
(T)
(DCP)
UC
(PID)
(OVA)
Standard Penetration Test
Resistance (Blows/Ft.)
Hand Penetrometer
Torvane
Dynamic Cone Penetrometer
Unconfined CompressiveStrength
Photo-Ionization Detector
Organic Vapor Analyzer
Medium
0Over 12 in. (300 mm)
>12
5-12
<5
Percent ofDry Weight
TermMajor Component of Sample
Modifier
With
Trace
Descriptive Term(s) ofother constituents
>30Modifier
<15
Percent ofDry WeightDescriptive Term(s) ofother constituents
With 15-29
High
Unless otherwise noted, Latitude and Longitude are approximately determined using a hand-held GPS device. Theaccuracy of such devices is variable. Surface elevation data annotated with +/- indicates that no actual topographical
survey was conducted to confirm the surface elevation. Instead, the surface elevation was approximately determined from
topographic maps of the area.
Standard Penetration or
N-ValueBlows/Ft.
Descriptive Term
(Density)
CONSISTENCY OF FINE-GRAINED SOILS
Hard
15 - 30Very Stiff> 50Very Dense
8 - 15Stiff30 - 50Dense
4 - 8Medium Stiff10 - 29Medium Dense
2 - 4Soft4 - 9Loose
0 - 1Very Soft0 - 3Very Loose
(50% or more passing the No. 200 sieve.)
Consistency determined by laboratory shear strength testing, field visual-manualprocedures or standard penetration resistance
STRENGTH TERMS
> 30
Descriptive Term
(Consistency)
Standard Penetration or
N-ValueBlows/Ft.
RELATIVE DENSITY OF COARSE-GRAINED SOILS
(More than 50% retained on No. 200 sieve.)Density determined by Standard Penetration Resistance
UNIFIED SOIL CLASSIFICATION SYSTEM
UNIFIED SOIL CLASSIFICATION SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A
Soil Classification
Group
Symbol Group Name B
Coarse-Grained Soils:
More than 50% retained
on No. 200 sieve
Gravels:
More than 50% ofcoarse fraction
retained on No. 4 sieve
Clean Gravels:
Less than 5% finesC
Cu ‡ 4 and 1 £ Cc £ 3 E GW Well-graded gravel F
Cu < 4 and/or [Cc<1 or Cc>3.0]E GP Poorly graded gravel F
Gravels with Fines:
More than 12% fines C
Fines classify as ML or MH GM Silty gravel F, G, H
Fines classify as CL or CH GC Clayey gravelF, G, H
Sands:
50% or more of coarse
fraction passes No. 4
sieve
Clean Sands:
Less than 5% finesD
Cu ‡ 6 and 1 £ Cc £ 3E SW Well-graded sandI
Cu < 6 and/or [Cc<1 or Cc>3.0]E SP Poorly graded sandI
Sands with Fines:
More than 12% fines D
Fines classify as ML or MH SM Silty sandG, H, I
Fines classify as CL or CH SC Clayey sand G, H, I
Fine-Grained Soils:
50% or more passes the
No. 200 sieve
Silts and Clays:
Liquid limit less than 50
Inorganic:PI > 7 and plots on or above “A”
lineJ CL Lean clayK, L, M
PI < 4 or plots below “A” line J ML Silt K, L, M
Organic:Liquid limit - oven dried < 0.75 OL Organic clayK, L, M, N
Liquid limit - not dried Organic silt K, L, M, O
Silts and Clays:
Liquid limit 50 or more
Inorganic:PI plots on or above “A” line CH Fat clayK, L, M
PI plots below “A” line MH Elastic SiltK, L, M
Organic:Liquid limit - oven dried < 0.75 OH Organic clayK, L, M, P
Liquid limit - not dried Organic silt K, L, M, Q
Highly organic soils:Primarily organic matter, dark in color, and organic odor PT Peat
A Based on the material passing the 3-inch (75-mm) sieve.
B If field sample contained cobbles or boulders, or both, add “with cobbles
or boulders, or both” to group name.
C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded
gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly
graded gravel with silt, GP-GC poorly graded gravel with clay.
D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded
sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded
sand with silt, SP-SC poorly graded sand with clay.
E Cu = D60/D10 Cc =
6010
2
30
DxD
)(D
F If soil contains ‡ 15% sand, add “with sand” to group name.
G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.
HIf fines are organic, add “with organic fines” to group name.
I If soil contains ‡ 15% gravel, add “with gravel” to group name.
J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.
KIf soil contains 15 to 29% plus No. 200, add “with sand” or “with
gravel,” whichever is predominant.
L If soil contains ‡ 30% plus No. 200 predominantly sand, add
“sandy” to group name.
MIf soil contains ‡ 30% plus No. 200, predominantly gravel, add
“gravelly” to group name.
NPI ‡ 4 and plots on or above “A” line.
OPI < 4 or plots below “A” line.
P PI plots on or above “A” line.
QPI plots below “A” line.