Drainage Plan.pdf`,� • MWISMIN
for
Christopher & Merin Mione
19011 Olympic View Dr.
Edmonds, WA 98020
SITE LOCATION:
19011 Olympic View Dr.
Edmonds, WA 98020
Tax Parcel: 00434600007800
Prepared by:
Philip D. Mann, E.I.T.
Checked by:
Joseph M, Smeby, RE,
Job No: 14-0608
July, 2014
M4 6 00191
TABLEOF CONTENTS.....................................................................................................1
LISTOF FIGURES.............................................................................................................2
1. INTRODUCTION & SITE CLASSIFICATION..............................................................3
2. STORMWATER SITE PLAN .................................................... ,.............................4
3, SWPPP NARRATIVE..................................................................................................4
A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT....................................5
B. SWPPP MINIMUM ELEMENTS.................................................................................5
4. WATER POLLUTION SOURCE CONTROL...............................................................7
5. PRESERVATION OF NATURAL DRAINAGE SYSTEM..............................................7
6. ON-SITE STORMWATER MANAGEMENT................................................................7
7. RUN-OFF TREATMENT.............................................................................................8
8. FLOW CONTROL.......................................................................................................8
9. WETLANDS PROTECTION........................................................................................8
10. OPERATIONS AND MAINTENANCE MANUAL...........................................................9
11. OFFSITE ANALYSIS AND MITIGATION......................................................................9
12. FINANCIAL LIABILITY. ................................................................................................ 9
APPENDIX A - STORMWATER CALLS, SOILS, PHOTOS, M&O
APPENDIX B - GEOTECH REPORT
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 11
ITEM PAGE
FIGUREVICINITY MAP ....................................... ..................... ...... .................. 1O
FIGURE EXISTING DRAINAGE BASIN MAP ...................................................... 11
FIGURE DEVELOPED DRAINAGE BASIN MAP ................................................. 12
13
FIGURE SNDH(}M|SHCOUNTY 80LGK�AP—'.—..---.—.------~.FIGURE 5 UP STREAM/DOWN STREAM TRIBUTARY AREA MAP ........................ 14
Mione 2Lot Short Plat 14-000
ju|y.2O14 Page
This document is intended to provide engineering information necessary to support the
building permit application submittal to the City of Edmonds for the new SFR and driveway
for this short plat. The current parcel is approximately 1.23 acres. The existing site
consists of an asphalt driveway, house, pool, pool house and covered parking area.. No
existing impervious structures will be removed or replaced for this project. The western
parcel will total approximately 15,000 sf and approximately 57% of the new parcel will be
cleared/graded to construct the proposed improvements. Access to the site will be from
the existing roadway, Olympic View Dr., to the west along the western property line.
The total area of disturbance including clearing and grading does not exceed 3/4 acres and
the new total impervious surfaces does not exceed 5,000 sf. Therefore, this project is
classified as a Category 1 Small Site Project. This classification was completed using
figure 2-1 of the 2010 Storm water Code Supplement to Edmonds Community
Development Code Chaper 18.30. Due to the existing soil conditions, on-site infiltration
shall be used for this project. As a result only minimum requirements 1-5, 7-9, and 11 will
be required to be reviewed and addressed if applicable.
This proposed project will create approximately 4,534 sf of new impervious surfaces
including the proposed SFR and driveway. No impervious surfaces will be considered
removed or replaced for this project. All of the new impervious surfaces, will be mitigated
using on-site stormwater management BMPs including dry wells and amended soils; both
LID techniques.
The site is located at 19011 Olympic View Dr, Edmonds, WA 98020, and in Section 13,
Township 27N, Range 3E, Willamette Meridian, See Figure 1 - Vicinity Map..
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 3
APR1L2010
Figure 2-1: Project Classification
Start'
Does the project involve 1-
acre or more of land-
disturbing
anddisturbing activity?
Is the project part of a larger
common plan of development
or sale where the total
disturbed area for the entire
plan will total 1 -acre or more
of land -disturbing activity?
Does the Project involve one or more of the
following:
2,000 square feet or more of new impervious
surface, replaced impervious surface or new
plus replaced impervious surface?
OR
7,000 square feet of land -disturbing activity?
OR
50 cubic yards or more of either grading, fill,
or excavation as defined in Chapter 18.40.000
ECDC?
� P<
Minor Site Project:
Read Chapter 3 and see
Chapter 6 for requirements
Large Site Project:
Read Chapter 3 and see
Chapter 4 for
requirements
Does the project create or add 5,000 square feet of
new impervious surface, replaced impervious surface
or new plus replaced impervious surface?
OR
es Convert'/ acre or more of native vegetation to lawn
or landscaped area
OR
Through a combination of creating effective
impervious surface and converted pervious
surfaces, causes an increase of 0.1 cubic feet per
second in the 100 -year flow frequency from a
threshold discharge area as estimated using an
approved model?
No
Category 1 Small Site Project:
Read Chapter 3 and see Chapter 5
for requirements
r Assumes the project in question meets applicability requirements of ECDC18,30,030.
d/ ;08-U41d0-ODU enmards tmmrnvYersupp/anent flnaG doo
Category 2 Small Site Project:
Read Chapter 3 and see Chapter
5 for requirements
2,0 CLASSIFYING PROJECTS 6
As noted in Section 1 of this report this project is classified as a Category 1 Small Site
Project. Therefore, this drainage design has been prepared to address the requirements
contained in the City of Edmonds Stormwater Supplement and applicable handouts. This
document is intended to provide the supporting information to justify the BMPs used and to
detail how the design of the selected BMPs meet the required standards.
For this project some LID techniques were used to aid in minimizing the projects impacts
to the neighboring properties and downstream system. The new NPGIS runoff will be
infiltrated on-site and the soils within the proposed areas of disturbance will be amended
to landscaping conditions as per BMP T5.13 out of the 2005 DOE Manual. This is done to
reduce the stormwater runoff generated by the proposed impervious surfaces.
Clearing, grading, and temporary erosion and sediment control plans have been prepared
as part of the drainage plan drawings. However, since a construction site is dynamic it will
be necessary to reassess the erosion control BMP's during construction and install
additional measures when necessary.
Proposed temporary measures possible for this project will include the following BMP's:
® Installation of stabilized construction entrance.
® Retention of Existing Vegetation
® Straw mulch, hydroseed or other mulching and planting method to stabilized
unworked areas,
® Silt fencing if necessary
Permanent measures to reduce or eliminate erosion or water quality degradation will
include the following BMPs:
® Paving all traffic areas (concrete)
® Permanent landscaping in pervious areas.
® Limiting cut and fill slopes to 2:1 maximum and 3:1 maximum where exposed to
standing water.
® Routine maintenance and inspection of the grounds and response to developing
problems.
The listed erosion control BMP's will be engineered for anticipated conditions in
compliance with Snohomish County and DOE guidelines, With proper installation,
maintenance and inspection the proposed BMP's should result in minimal impact to the
surrounding environment. The County retains the authority by code to require additional
measures should the existing measures prove insufficient.
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 4
Area proposed to be cleared/worked: 8495 sf = 0.20 acres
Average slope for the site (w/in the area of disturbance): 18%
Erosion Hazard of Soil Moderate
Critical Areas downslope No
Site is upstream of an ESA Stream No
Based on the above information and the fact that the site will retain so much existing
vegetation and construction site runoff will filter through the soil, and that if site conditions
warrant, additional BMP's can be implemented as corrective measures the Risk Category
for this site is Low Risk.
k
1: Mark Clearing Limits
The first step in the "Construction Sequence" included on the clearing and grading plan
sheets is for the limits of clearing to be flagged and to have construction fencing placed
along the limits prior to any other construction activity.
2: Establish Construction Access
The SWPPP calls for the proposed construction entrance to be installed as the second
step after the staking of clearing limits. A detail is provided on the plans.
3: Control Flow Rates
This project is below the thresholds requiring flow control for the project.
4: Install Sediment Controls
This site and SWPPP proposes to construct/maintain a construction entrance, retained
vegetation and silt fencing. These features are intended to minimize the opportunity for
sediment to leave the site via stormwater or on vehicles. The construction of these
features is one of the first items required in the "Construction Sequence". Mulch will also
be used on the exposed soil as necessary to limit erosion.
5: Stabilize Soils
The "Construction Sequence" calls for the stabilization of soils that remain unworked for
certain lengths of time based on the time of year. Stabilization techniques may include but
not limited to mulching, plastic sheeting or hydroseeding, notes have been added to the
plan regarding protection for the stock pile area if necessary. A stockpile area has been
identified on the SWPPP and is setback a minimum of 100 -feet from any down slope
property line.
6: Protect Slopes
All disturbed slopes on site during construction are required to be protected with mulch or
other means as specified in the construction sequence. No concentrated runoff or
significant amounts of sheet flow will be directed to new cut or fill slopes during
construction
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 5
7: Protect Drain Inlets
No new or existing culverts are proposed or affected by this project.
8: Stabilize Channels and Outlets
No new channels or outlets are proposed for this site.
9: Control Pollutants
No outside chemicals are expected to be necessary for the construction of this project. All
vehicles working on and around the site would need to meet the State requirements for
emissions.
10: Control DeWatering
DeWatering will not be necessary for this project. However, the existing vegetation
retained on site would be available to spread any water from construction for disposal.
11: Maintain BMPs
The construction supervisor will be responsible for maintaining all BMPs during
construction and working with the City to relocate or add BMPs as necessary as site
conditions change.
12: Manage the Project
It will: be the responsibility of the Contractor and Developer to manage this project and
coordinate with the City Inspector and Engineer.
Inspection and Monitoring:
Site inspections shall be done by a person who is knowledgeable in the principles and
practices of erosion and sediment control. The person must have skills to first assess the
site conditions and construction activities that could impact the quality of stormwater, and
second assess the effectiveness of erosion and sediment control measures used to
control the quality of stormwater discharges.
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, appropriate BMPs or design changes shall
be implemented as soon as possible.
Maintaining an Updated Construction SWPPP:
The construction SWPPP shall be retained on-site or within reasonable access to the site.
The SWPPP shall be modified 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 shall 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. The SWPPP shall be modified as necessary to include
additional or modified BMPs designed to correct problems identified, Revisions to the
SWPPP shall be completed within seven days following inspection.
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 6
The City of Edmonds Stormwater Supplement and DOE Drainage manual was reviewed to
determine if the proposed land -use for this project required any site specific source control
BMPs to be constructed. SFR projects are not listed as a proposed use that requires
source control. Therefore, no site/development specific source control BMPs are required
for this project.
The runoff from the on-site basin drains to the west towards the western property line and
the right-of-way of Olympic View Dr. It was determined that the runoff from the site
improvements will be both infiltrated and dispersed on-site. The proposed driveway will
disperse flows over amended soils first, followed by undisturbed soils. This will allow the
maximum amount of runoff to be treated and naturally infiltrate into the on-site soils. By
not grading or compacting the majority of the pervious surfaces to remain after
construction in the area of disturbance a maximum amount of site runoff from the
developed project will be absorbed and infiltrated into the existing on-site soils.
The on-site soils for this project were verified by Andrew Glandon and Jamey Battermann
of South Fork Geosciences, The on-site soils were found to be fill material on top of
Vashon Advance Outwash. The depth to the top of the Vashon till layer is between 0-9
feet below the existing grade. Refer to the Geotechnical report, soil logs and locations of
the soil logs within Appendix `A'. The soils were also identified with the USDA Web Soil
Survey, The Soil survey shows the on-site soils within the proposed area of disturbance to
be Alderwood Gravely Sandy Loam. The soil unit is gravelly ashy sandy loam. Refer to
Figure 4 to view Soils map. This project proposes to construct approximately 1,872 sf of
new plus replaced roof surfaces, The geotech recommends that infiltration of the
stormwater roof runoff should be infiltrated on-site. This will be done by the installation of
drywells. The drywells have been designed as per section 3.1,1 of the 2005 DOE Manual,
The proposed NPGIS will be infiltrated by the use of 2 dry wells and each dry well will be
limited to a maximum of 1,000 sf of impervious surfaces. The dry wells will be located to
the west of the proposed SFR.
A total of approximately 2,662 sf of PGIS is proposed for this project. The runoff
generated by the impervious driveway surfaces will be dispersed on-site via amended
soils along the length of the downhill edge of the proposed driveway. Dispersed flows will
have a minimum 25 foot vegetated flow path before flows leave the project parcel.
All future pervious surfaces will be amended as required by the City standards. Therefore,
all dispersed flows will pass over the amended soils prior to being collected and
discharged offsite.
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 7
This project proposes to construct less than 5,000 sf of new PGIS and is therefore exempt
from any run-off treatment.
For this project LID methods will be used to address the runoff impacts from the proposed
improvements. In order to protect the downstream systems to the west it is necessary to
use an LID methods designed for this site. The NPGIS will be infiltrated on-site via 2 dry
wells and the disturbed soils will be amended as per BMP T5.13 out of the 2005 DOE
Manual
By maximizing the use of the LID methods and preparing a site plan that provides the
space necessary on this lot, the over all drainage impacts to the downstream system and
surrounding area can be reduced. Therefore, this design has been laid out to provide an
opportunity for site runoff to be absorbed back into the soil layer to aid in attenuating flows
and providing some groundwater recharge while protecting the existing neighboring
properties from flooding or erosive impacts.
. .: .. • -.. __ G
This project will not impact any wetland on-site or downstream of the project site.
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 8
i •' .- �; Y
The Property Owner will be responsible for maintaining the stormwater and landscaping
facilities within this development. Included in this manual are checklists for each feature
specific to this project. Copies should be made of the checklists as necessary during
routine inspections and required maintenance, Specific problems can be recorded along
with the appropriate action taken.
These checklists are a guide for inspections and maintenance, The frequency of the
inspections/maintenance is identified in the left hand column with the following
abbreviations:
A = Annual (March or April preferred)
M = Monthly
S = After Major Storms (Use 1 -inch in 24 hours as a guideline)
Routine inspections and maintenance will improve the long-term performance of the
stormwater facilities. If at any time you are unsure if a problem exists or how to address a
specific problem contact a Professional Engineer.
Refer to Appendix A for a list of each facility to be maintained and the appropriate
maintenance checklist.
Runoff from the proposed disturbance area of the project parcel sheet flows to the west
over moderately sloped to steep landscaping and leaves the site over the western property
line. The runoff enters the right -of way of Olympic View Drive and is captured by a catch
basin opposite of the adjacent parcel to the north, and is part of the City of Edmonds
stormwater conveyance system, This catch basin directs runoff north to a series of catch
basins and pipes. The outfall of the conveyance system could not be verified in the field,
but it is expected that the receiving water body is the Puget Sound. See Figure 5 for a
depiction of the project basin and downstream path.
Since this is a single-family residential project and it does not fall within a Critical Area, per
the City of Edmonds Stormwater Supplement no bonds or other financial guarantees are
required.
Mione 2 Lot Short Plat 14-0608
July, 2014 Page 9
Mr � .. � �-
ADDITIONAL STUDIES; CALCS & SITE PHOTOS
S1 TE
VICINITY MAP- N
SCALE: V = 2,000'
OME4GA
ENGINEERING, INC.
2829 Rockefeller Ave.
Everest WA 98201
(o)42087.3820 (f) 425.259.1958
VICINITY MAP
MIONE 2 LOT SHORT PLAT
DATE � JOB NO. � SCALE SHEET
FEET
7/7/2014 114-0608 1" = 2000' 1 1 OF 1
7711 �7
EX. HOUSE
60' �� I i I I \� \ 1 1 ' ' / ' ' • I • EX: FOOL
27'
Err
EX POOL HOUSE
EX
m V COVERED
PARKING
180
ti
53,412 SO. FT.
1.226 ACRES
TOTAL
ti
X
CL
n
v
J4\
----- 190th PL SW
H
nOMEIGA EXISTING BASIN MAP
ENGINEERING, INC. MIONE 2 LOT SHORT -PLAT
2829 Rockefeller Ave. DATE JOB NO. SCALE SHEET
e Evee WA 98201 7/7/2014 � 14-0608 1" = 50P 1 OF 1
(0)425 387.3820 (f) 425.259.1gs8
PROP. l
6ARACEO,� ^ �Y �� 1 / J , _ p
`\ DRY Wj V
I I \ ✓SE� ELL
ETAIL / 5' G EX. HOUSE
1 E%. POOL I
~ \\ 1 (tI LAND, AP N WA t<
DSI
\ ^ y \ , • ,5;.t t.'y ti.: t}, .': t 51 wiY'?{I t.; , I r ."� I ) §11�i r' EX. POOL HOUSE
FLOW �ll'r P . �, EX. \
C.WREO `
PARKING
CONTRACTOfl
TO CgAO� 1 PROP.!
DRWEW Y TO EE fL W LANOSCAPI O L
RUNOFF ONiO STHHE AOJppCEtFT y E GN BY 0 ERS
_\ \.. tANosdaPlrJc FbR TryE 1 t 1 p t80 `
LENGTtfY1K'dliEyoRl fAY._.--. — -i-�- 1t„�1.....__.�,•, 1\ • ; - _ •� `�ti
SOL 3 PG t4
170
�(L
Iii. •.,>J� ��_ _..
of
L7_--
... ( r ..._� ,,.. J•/ l l 11 :� 1f � + � \ I \ �`��, ` yrs
� i 1
-- — �-'—� ..-�_�___. �_ '~ � •�� � � / `� l y --f `_ ��,>,`( •rel p
190th PL, 5W j
s I ft
FIG.
DEVELOPED BASIN MAP
ENGINEERING, INC. MIONE 2 LOT SHORT PLAT
2029 Rockefeller Ave. DATE JOB NO,SCALE SHEET
Evere#t WA 90201
(0)425. 87.3820 (f) 425.259.1950 ' 7/7/2014 14-0608 1" — 503 1 OF 1
,zz ZZT
3
»»z*ZZT
[ (
* #
a . a
+<s ORL+ OOZL6ZS OEZZ6ZS o + OTZL6ZS OOZZ G 06TL6ZS me m+s ec
:�n
,s=ue ){
( . (
f &
a . C
§
�\
\\
0
$
2/§
$
y
)
.
@
7
e G @
®
[
}
�
/
r
2
!_
\
«
$}
co
A;
u$
( \
% (
9 o
=
\
�@
_
)/
,»z —
&
yr
SOUTH FORK GEOSCIENCES
PO Box 1275
NORTH BEND, WA 98045
(425) 831-2023
AGLAN DONCOCOM CAST. NET
April 1, 2014
Project #: 14012
Subsurface Exploration, Geologic Hazards,
and Preliminary Geotechnical Engineering Report
Parcel # 00434600007800
19011 Olympic View Driyl3i
Edmonds, Washington
Introduction
The purpose of this study was to gain subsurface information to be utilized in the feasibility and
permitting of a short plat subdivision of the subject property. It is our understanding that Chris
and Merin Mione intend to subdivide the property to create a new lot suitable for construction of
a single family residence on the western portion of the property. Authorization to proceed with
this study was provided by Chris Mione via e-mail on March 15, 2014. This report was prepared
for Mr. and Mrs. Mione and their agents for specific use in support of this project. The location
of the subject property is shown in the attached Vicinity Map. An excerpt of the site survey
prepared by Greene Land Surveying and the approximate locations of the subsurface
explorations logged for this study are shown on the attached Site and Exploration Plan.
The subject property was located at 19011 Olympic View Drive in Edmonds, Washington. The
property was irregularly shaped and was approximately 300 feet in the east -west direction and
ranged from approximately 150 to 200 feet in the north -south direction. Based on information
from the Snohomish County Assessor website, the property was 1.23 acres in size. The property
sloped gently to moderately from the east down to the west. Based on a review of the site
survey, the slope on the west portion of the property was on the order of 2.5H:1 V
(Horizontal:Vertical)to6H:IV. The slope immediately adjacent to Olympic View Drive was on
the order of IH:lV to 1.5H:1 V, but this slope was obviously created by the road construction.
Based on the surveyed elevations, there is approximately 65 feet of total relief on the property.
The property was bordered on the west by Olympic View Drive, and to the north, south, and east
by residential properties.
SOUTH FORK GEOSCIENCES, PO Box 1275, NORTH BEND, WA 98045, (4-25) 831-2023
The eastern portion of the property has an existing residence which is to remain on the site. The
western portion of the property where the new lot will be created will be the area of focus of this
report. A significant part of the western portion of the property had been cleared and was
covered with grass. There were some large Douglas fir trees and native forest vegetation near
the in the southwest corner of the property. We did not observe any signs of accelerated soil
erosion or soil movement during our site reconnaissance.
Subsurface Conditions
Subsurface conditions on the property were inferred from a visual reconnaissance of the property, a
review of the referenced geologic map (Minard, 1983) and three hand auger boring explorations
performed on the property. The explorations were logged by the undersigned licensed engineering
geologist and were immediately backfilled. The approximate locations of the subsurface
explorations are shown in the Site and Exploration Plan and the exploration logs are attached to this
report. Our interpretation of the native soils as Vashon advance outwash is in agreement with the
referenced geologic map. We also used subsurface information from a prior study on the adjacent
property to the south in our interpretation of the site geology (Johnson Residence, SFG, Jan, 2014).
Stratigraphy
Fill Soils
Fill soils were not encountered in the subsurface explorations performed for this study, but we
know that there are some existing fill soils associated with the sewer pipe and the water service
that extend up to the existing residence from Olympic View Drive. Based on the topography,
there also appears to be some fill soils in the area marked as "old road" on the site survey. We
have marked the approximate areas on the Site and Exploration Plan. Since the placement and
compaction of the fill soils is unknown, proposed structures should not be founded on existing
fill soils. The following section titled "Site Preparation and Site Grading" explains how to deal
with existing fill soils when encountered during construction.
Vashon Advance Outwash
Vashon advance outwash sediments were encountered in all of the hand auger borings logged for
this study from the ground surface to the total depth explored. The advance outwash sediments
generally consisted of medium dense to dense, fine to medium sand with gravel with varying
amounts of silt. Vashon advance outwash sediments are alluvial and fluvial sediments that were
deposited by meltwater streams and channels from the advancing Vashon glacial ice sheet. As
the glacial ice advanced, the advance outwash sediments were overridden and consolidated by
the glacial ice. As such, the advance outwash sediments are typically dense, relatively
permeable, and moisture insensitive due to the past glacial consolidation and the small amount of
silt and clay present. Due to their relatively coarse grain size distribution, the advance outwash
sediments are moderately resistant to erosion, except when subjected to concentrated water
flows.
2
SOUTH FORK GEOSCIENCES, PO Box 1275, NORTH BEND, WA 98045, (425) 831-2023
Hydrology
There was no groundwater seepage observed in any of the explorations performed for this study.
Soil conditions observed were generally dry for the time of year, which is indicative of permeable
soils. Also, there were no signs of ponding water or flowing water observed. Groundwater
conditions are subject to change depending on seasonal weather conditions, but based on the
permeable advance outwash soils observed, we do not anticipate encountering adverse groundwater
conditions during construction.
The following discussion of potential geologic hazards is based on the visual reconnaissance of the
site, the subsurface explorations, reviews of aerial photographs and regional topographic and
geologic maps of the area, and review of the applicable City of Edmonds Municipal Code and maps
that are available online.
Based on our comparison of the City of Edmonds Municipal Code to the topographic and geologic
features of the subject property, the property does not fulfill the criteria for an erosion hazard area,
landslide hazard area, or a seismic hazard area. The following two sections of this report will set
forth some basic erosion control best management practices for use in construction and will address
general seismic risks and design parameters associated with a seismic event.
Erosion Concerns
Though special mitigations are not necessary, a temporary erosion and sediment control (TESC) plan
should be created and implemented during site construction. It is our opinion that implementation of
a relatively basic erosion control plan will prevent off site sediment transport. The proper use of
"best management practices" (BMPs) should be utilized during earthwork activities to reduce the
potential for erosion and sediment transport off of the property. The following is a partial list of
BMPs that should be implemented:
® Phasing and scheduling earthwork activities during dry conditions
® Rock construction entrances
® Straw mulch
® Plastic sheeting
® Silt fence
® Keeping exposed soils and stockpiles covered when not actively worked
® Establish temporary/permanent vegetation as soon as possible after foundation and utility
installation
Implementation of a TESC plan will likely be a requirement of the clearing and grading or building
permit. South Fork Geosciences is available to design the TESC plan and to provide any required
inspections during construction.
3
SOUTH FORK GEOSCIENCES, PO BOX 1275, NORTH BEND, WA 98045, (425) 831-2023
Seismic Concerns
Generally, there are four types of potential geologic hazards associated with large seismic events:
1) ground rupture; 2) seismically induced landslides; 3) liquefaction; and 4) ground motion. The
potential for each of these to impact the site is discussed below.
Ground Rupture
Most large earthquakes in the Puget Sound area are sub -crustal events with epicenters ranging
from 50 to 70 kilometers in depth. The subject property is approximately 5 to 6 miles south of
the Southern Whidbey Island Fault Zone (SWIFZ). Though the subject property is near the
SWIFZ, to our knowledge, there are no signs of past ground rupture in the immediate vicinity of
the subject property. Based on the location of the subject property to the south of the known
fault zone and the lack of sufficient information to infer a recurrence interval for earthquakes on
the SWIFZ (Johnson, et al., 2004), it is our opinion that the probability of ground surface rupture
impacting the subject property is low, and no mitigations are necessary.
Seismically Induced Landslides
Due the topography and absence of steep slopes on the subject property, it is our opinion that the
potential for seismically induced slope failures on the site is low and no mitigations are
necessary.
Liquefaction
Liquefaction is a condition where loose, saturated, fine sandy soils lose their shear strength due
to rapid pore pressure build-up when subjected to high intensity cyclic loads, such as occur
during earthquakes. Due to the medium dense, well -graded, native soils encountered in the
subsurface explorations and the absence of adverse ground water conditions, the liquefaction
potential of this site is very low, and no mitigations are necessary.
Ground Motion
Seismic hazards that will affect the structure would likely be due to the intensity and duration of
the ground shaking. The structural design of the project should be consistent with 2009
International Building Code (2009 IBC) guidelines (Section 1613). Based on the results of our
subsurface explorations and our estimation of soil properties at depth utilizing available geologic
data, Site Class "C" as defined by Table 1613.5.2 of the IBC may be used for the design of the
proj ect.
' •� i �• �,
Our exploration indicates that, from a geotechnical standpoint, the subject property is suitable for
the proposed subdivision of the property and the presumed future development, provided the
risks discussed are accepted and the recommendations contained herein are properly followed.
The near surface, native Vashon advance outwash sediments will be capable of providing
support for future structures. Since there are no current development plans for the new lot being
created, the following recommendations should be considered preliminary and any future
development plans should be reviewed by South Fork Geosciences prior to construction. South
4
SOUTH FORK GEOSCIENCES, PO Box 1275, NORTH BEND, WA 98045, (425) 831-2023
Fork Geosciences is available for further consultation with respect to specific design items, if
needed.
Site Preparation and Site Grading
It is likely that structural fill soils will be required to establish grades for the project. Any fill soil
placed beneath a foundation, retaining wall, or driveway/parking area must be constructed as a
structural fill. In areas that will provide structural support, any existing fill soils or loose soils
should be removed and replaced with structural fill as described below, or the fill soils should be
mitigated as described in later sections for specific applications.
Structural fill is defined as non-organic soil, placed in maximum 8 -inch loose lifts, with each lift
being compacted to at least 95 percent of the maximum dry density, using the modified Proctor
test (ASTM: D1557) as the standard. Prior to placing any structural fill the exposed soils must
either be undisturbed or be compacted to a dense, non -yielding condition and be approved for
structural fill placement. In the case of utility trench filling, the backfill should be placed and
compacted in accordance with the applicable City of Edmonds or utility franchise standards.
If fill soil will be imported to the site, it should be free of organics and other deleterious material.
Mineral soils with more than 5 percent fines are considered to be moisture sensitive. The use of
moisture sensitive soils should be confined to dry weather conditions. The moisture condition of the
imported soil should be within a few percent of the optimum moisture content of the soil. Soils that
are too dry or too wet of the optimum moisture content to achieve suitable compaction will need to
be moisture conditioned prior to final compaction. The Vashon advance outwash sediments are not
moisture sensitive, but due to the relatively dry soil conditions observed, these soils may require the
addition of water to be placed as structural fill. In the case that moisture sensitive soils are used in
structural fills, this type of work should be limited to the summer months and good weather
conditions.
Placement and compaction of the structural fill should be monitored by a competent field
technician. In situ density testing should be performed during fill placement to verify proper
compaction of the fill soil. A sample of the planned structural fill soil will need to be available at
least 48 hours prior to fill placement for laboratory analysis.
Temporary cut slopes may be necessary to allow the installation of the foundations and for utility
installation. Temporary cut slopes should be limited to 1H:1V (Horizontal:Vertical) in the
existing fill soils and %2H:1 V in the Vashon advance outwash sediments. Stability of the cut
slopes is the responsibility of the on-site contractor and a safe work environment should be
maintained at all times. A trench shield or trench box should be used to install all utilities over 4
feet in depth or the sides of trenches and excavations should be sloped back per OSHA/WISHA
standards.
SOUTH FORK GEOSCIENCES, PO Box 1275, NORTH BEND, WA 98045, (425) 831-2023
Foundations
Spread footings may be used for building support when founded on medium dense native soils
or approved structural fill soils. To limit differential settlements between footings that bear on
both structural fill and medium dense to dense native soils, we recommend that an allowable
bearing pressure of 2,000 pounds per square foot (psf) be utilized for design purposes, including
both dead and live loads. An increase of one-third may be used for short-term wind or seismic
loading. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost
protection; interior footings require only 12 inches burial. However, all footings must penetrate
to the prescribed bearing stratum, and no footing should be founded in or above loose, organic,
or existing fill soils.
It should be noted that the area bounded by lines extending downward at 1 H: IV from any
footing must not intersect another footing or intersect a filled area that has not been compacted to
at least 95 percent of ASTM:D 1557. In addition, a 1.5H:1 V line extending down from any
footing must not daylight because sloughing or raveling may eventually undermine the footing.
Thus, footings should not be placed near the edge of steps or near vertical cuts in the bearing
soils.
Anticipated settlements of footings founded on the medium dense native soils or approved rock
trenches should be less than 1 inch. Loose or disturbed surface soils, excessive moisture present or
poor foundation subgrade preparation could result in larger settlements. South Fork Geosciences
should perform a foundation bearing evaluation prior to concrete placement to verify that the design
bearing capacity of the soil has been attained. A foundation bearing evaluation will likely be
required by the City of Edmonds Building Department as a condition of the building permit.
Perimeter footing drains should be provided as discussed under the section titled Drainage
Considerations.
Lateral loads can be resisted by friction between the foundation and the supporting soils, and/or by
passive earth pressure acting on the buried portions of the foundations. The spread footings must be
backfilled with structural fill compacted to a dense, non -yielding condition to achieve the passive
resistance provided below. The structural fill must extend horizontally outward from the embedded
portion of the foundation a distance equal to at least three times the embedment depth over which the
passive resistance is applied. We recommend the following design parameters.
® Passive equivalent fluid = 300 pcf
Coefficient of friction = 0.30
The above values are allowable and include a factor of safety of at least 1.5.
Lateral Earth Pressure
Cast -in-place, concrete foundation walls or retaining walls should be designed to resist "at -rest"
lateral soil pressure conditions if the concrete walls will not be free to yield laterally at the top.
Restrained walls should be designed to resist an "at -rest" equivalent fluid pressure of 55 pounds per
cubic foot (pcf). Concrete walls that are free to yield laterally at the top of the wall may be designed
6
SOUTH FORK GEOSCIENCES, PO Box 1275, NORTH BEND, WA 98045, (425) 831-2023
using an active soil pressure of 35 pcf. Surcharges from sloping backfill conditions or adjacent
structural loads should be added to the above lateral soil pressures. Full height drainage of
foundation walls will need to be installed to prevent hydrostatic pressures from acting on the walls.
Detaining Walls
We presume that future development may require retaining walls to provide grade separation. South
Fork Geosciences should review all proposed retaining walls prior to construction.
Floor Support
We anticipate that a single-family home built on the new lot would utilize slab -on -grade floors or
a combination of slab -on -grade floors and structural/crawlspace floors. Slab -on -grade concrete
floors should be cast atop a prepared subgrade of structural fill soil compacted to a minimum of
90 percent of the modified Proctor maximum dry density. A capillary break with a minimum
thickness of 4 inches should be placed atop the prepared subgrade. The capillary break material
should be a gap graded material consisting of pea gravel, 3/4 -inch washed drain rock, or clean
crushed rock with less than 5 percent fines (material passing the No.200 sieve). The capillary
break will reduce the potential for moisture wicking through the floor slab. A 10 -mil thick
plastic vapor barrier should also be placed atop the capillary break material. All concrete
placement should follow the guidelines set forth by the American Concrete Institute (ACI).
In areas that structural/crawl space -type floors are used, provisions should be made to slope
internal crawlspace areas to lows that may be drained to the footing drain system around the
perimeter of the foundation to prevent the accumulation of standing water within the crawlspace
areas. The soil surface should be covered with a minimum I0 -mil thick moisture barrier.
Drainage Considerations
A perimeter foundation drain should be established to protect the floor slab and internal crawlspace
areas from ground water intrusion. The level of the foundation drain should be set at, or slightly
below, the base of the footing elevation. The drain should consist of 4 -inch diameter, rigid,
perforated, PVC drain pipe and should be set to allow for gravity discharge. The drainpipe should be
surrounded by a minimum of 6 inches of pea gravel or washed drain rock. Roof drains should not tie
into the footing drain but should be collected in a separate, tightline drain. The drain lines should be
set to discharge via gravity to a dispersion or infiltration area or to an approved stormwater drainage.
In addition, all footing stem walls that enclose conditioned space should be lined with a 12 -inch -
thick (minimum) washed gravel blanket provided over the height of the wall that ties into the footing
drain. The washed gravel blanket should be ended one foot below the desired ground surface and the
top of the gravel should be covered with filter fabric. The remaining one foot should be filled with
compacted soil to reduce the amount of surface water entering the wall and footing drain system.
7
SOUTH FORK GEOSCIENCES, PO Box 1275, NORTH BEND, WA 98045, (425) 831-2023
Site Drainage
We have not reviewed any plans for stormwater disposal at this time. The native, Vashon advance
outwash sediments are well suited for infiltration methods due to their relatively coarse grain size
distribution and lack of fine sediments. With the relatively large lot size and the gently sloping area
on the western portion of the property, we presume that infiltration methods such as a series of
drywells or infiltration trenches in the native sediments will be used to dispose of stormwater
generated from the site. Based on our visual assessment of the native Vashon advance outwash
soils, we believe that the soil would be classified as "sand" in the USDA Soil Textural Triangle.
South Fork Geosciences is available for additional consultation with respect to site drainage, if
necessary.
MIM
Our findings and recommendations provided in this report were prepared in accordance with
generally accepted principles of engineering geology and geotechnical engineering as practiced in
the Puget Sound area at the time this report was submitted. We make no other warranty, either
expressed or implied. Our observations, findings, and opinions are a means to identify and reduce
the inherent risks to the owner.
We are available to provide additional design recommendations and consultation throughout the
development of this project. Since there are no current development plans, the recommendations in
this report should be considered preliminary. South Fork Geosciences should be contacted to review
any architectural or grading plans and to provide additional geotechnical information and input prior
to construction. We are also available to provide construction monitoring services during
construction for earthwork quality control and to help ensure that the recommendations in this report
are properly implemented. We have enjoyed working with you and we are confident that this report
will aid in the design of your project. If there are any questions, please contact us at (425) 8312023.
Sincerely,
O� VV C1 &
0
N
'".mol
Andrew L. Clan on
Andrew L. Glandon, LEG, CPESC
Geologist / Owner
South Fork Geosciences
60P,
b,
Jamey S. Battermann, PE
Geotechnical Engineer
8
SOUTH FORK GEOSCIENCES, PO Box 1275, NORTH BEND, WA 98045,(425) 831-2023
Attachments: Vicinity Map
Site and Exploration Plan
Exploration Pit Logs
References:
Minard, James P., "Geologic map of the Edmonds East and Part of the Edmonds West
Quadrangles, Washington" U.S. Geological Survey, Miscellaneous Field Studies Map MF- 1541,
scale 1:24,000, 1983
Edmonds Municipal Code
�ll(C�:// v ✓ �.���kunua; In�.fi rr�r, ..aulucu LLdi ,I k
.
City of Edmonds Maps
United States Department ofAgricultureNatural Resources Conservation Service,
Illi,�I'F,��vW/lw�1l^.R1lG`,k4k',�;�/ (1nC CA'16�4.4k4V�i
Snohomish County Assessor Property Account Summary
03J7 ,w, ll"3,.�s�t�/s���r: �b � ,E`.' � Gi�tE.[.,,�:�.� 7:67. r 00d")d
USGS Quaternary Faults Web Mapping Application
Johnson, S.Y., Blakely, R.J., Brocher, T.M., Sherrod, B.L., Kelsey, H.M., and Lidke, D.J.,
compilers, 2004, Fault number 572, Southern Whidbey Island fault zone, in Quaternary fault and
fold database of the United States: U.S. Geological Survey website,
¢flr//6.,�6'fV�rClcb[ rr� sup,.g,aar�/CIBp�,fal`�iE,/�����I�IIE�k, accessed 01/10/2014 03:28 PM
"Subsurface Exploration, Geologic Hazards, and Geotechnical Engineering Report, Johnson
Residence, Parcel # 00434600007901, 9527 190th Place SW, Edmonds, Washington" South
Fork Geosciences, Project #12058, January, 14, 2014
9
SOUT1-I FOLK GE_OSCIENCES, (DC7 BOX 1275, NOR -H -I BEND, WA 913045, (425) 831-2023
SOUTH FORK GEOSCIENCES
PO Box 1275
NORTH BEND, WA 98045
(425) 831 -2023
AGLANDON@)C-OMCAST.NET
Vicinity Map
Mione Short Plat, '11019 Olympic View Drive, Edmonds, WA Project #140,12
41JON
t�
awfol)
2
Qj
u
0
V)
Wool
10-
Date: -0-2014
Depth
Number: HB -1
0 Sod (0-2")
Vashon Advance Outwash
loose to medium dense, moist, black brown to
light brown, fine to medium SAND with gravel
1 and silt (SP -SM)
becomes medium dense @ 1.5ft
2 d dense, moist, tan -light brown, fine to medium
SAND with gravel, trace silt (SP)
3 Total Depth = 3.Oft, Refusal due to gravels
No seepage observed
No caving observed
4
5
6
7
BoringHand Auger
Log
The subsurface conditions shown on this field log represent our observations at the time and location of excavation, modified by geologic interpretation
and judgment, and where noted, by engineering analysis and laboratory testing. The conditions shown may not be representative of conditions at other
times. South Fork Geosciences will not be responsible for use or interpretation by others of information presented on these logs.
Project # 14012
rR
.1 Box 1275
NORTH BEND, WA 904
PHONE:•,
Date: ®2-®9
Depth
ft Number: HB -2
0 Forest Duff/Topsoil (0-4")
Vashon Advance Outwash
loose to medium dense, moist, light brown to
brown, fine to medium SAND with gravel and
1 silt (SP -SM)
2 1 1roots present to 2ft, medium dense @ 2ft
3 1 medium dense to dense, moist, gray -light
brown, fine to medium SAND with gravel, trace
silt (SP)
Total Depth = 3.5ft, Refusal due to gravels
No seepage observed
4 A No caving observed
5
6
7
The subsurface conditions shown on this field log represent our observations at the time and location of excavation, modified by geologic interpretation
and judgment, and where noted, by engineering analysis and Laboratory testing. The conditions shown may not be representative of conditions at other
times. South Fork Geosciences will not be responsible for use or interpretation by others of information presented on these logs.
Project # 14012
P• Box
.o`:BEND, WA 9804.
Depth
0
I
2
3
rd
5
D
7
1 ..
917MV93TIKIM
Number: -
Vashon Advance Outwash
medium dense to dense, moist, gray -light
brown, fine to medium SAND with gravel, trace
silt (SP)
Total Depth = 1.0ft
No seepage observed
No caving observed
Located in road cut exposure
-confirmed cut into native sediments
Approximately 4 to 5 feet below base of wood
fence
The subsurface conditions shown on this field log represent our observations at the time and location of excavation, modified by geologic interpretation
and judgment, and where noted, by engineering analysis and laboratory testing. The conditions shown may not be representative of conditions at other
times. South Fork Geosciences will not be responsible for use or interpretation by others of information presented on these logs.
Project # 14012
Box 1275
PHONE:NORTH BEND, WA 98045