CANOD and reports.pdfCity of Edmonds
Critical Area Notice of Decision
Applicant:
Property Owner:
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Permit Number:
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Site Location:
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Project Description:
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❑ Conditional Waiver. No critical area report is required for the project described above.
I There will be no alteration of a -Critical Area or its required buffer. vV440, ('0
2. The proposal is an allowed activity pursuant to ECDC 23.40,220, 23,50.220, and/or -
2 3. 80. 0-4 0. '3
3. The proposal is exempt pursuant to ECDC 23.40,230.
F -I Erosion Hazard. Project is within erosion hazard area. Applicant must prepare an erosion and
sediment control plan in compliance with ECDC 18.30.
Critical Area Report Required. The proposed project is within a critical area and/or a critical area
buffer and a critical area report is required. A critical area report has been submitted and evaluated
for compliance with the following criteria pursuant to ECDC 23.40.160:
1. The proposal minimizes the impact on critical areas in accordance with ECDC 23.40,120,
Mitigation sequencing;
2. The proposal does not pose an unreasonable threat to the public health, safety, or welfare
on or off the development proposal site;
3. The proposal is consistent with the general purposes of this title and the public interest;
4. Any alterations permitted to the critical area are mitigated in accordance with ECDC
23.40.110, Mitigation requirements.
5. The proposal protects the critical area functions and values consistent with the best
available science and results in no net loss of critical functions and values; and
6. The proposal is consistent with other applicable regulations and standards.
❑ Unfavorable Critical Area Decision. The proposed project is not exempt or does not adequately
mitigate its impacts on critical areas and/or does not comply with the criteria in ECDC 23.40,160 and
the provisions of the City of Edmonds critical area regulations. See attached findings of
noncompliance.
Favorable Critical Area Decision. The proposed project as described above and as shown on the
attached site plan meets or is exempt from the criteria iii ECDC 23.40.160, Review Criteria, and
complies with the applicable provisions of the City of Edmonds critical area regulations, Any
subsequent changes to the proposal shall void this decision pending re -review of the proposal.
Conditions. Critical Area specific condition(s) have been applied to the permit number referenced
above. See referenced permit number for specific condition(s).
Reviewer
Signature
L'/ -11 A -
Date
Appeals: Any decision to approve, condition, or deny a development proposal or other activity based on the
requirements of critical area regulations may be appealed according to, and as part of, the appeal procedure, if any,
for the permit or approval involved.
Revised 12/16/2010
PREPARED FOR:
Jeff and Maureen Lewis
P.O. box 1133
Edmonds, WA 98020
PREPARED BY:
Wetlands & Wildlife, Inc.
7721--1531d Street SE
Snohomish, Washington 98296
(425) 337-6450
Revision Date: March 24, 2015
TABLE OF CONTENTS
INTRODUCTION AND BRIEF SITE DESCRIPTION
1
STATEMENT OF QUALIFICATIONS TO CONDUCT THIS CRITICAL AREAS EVALUATION
1
BRIEF DESCRIPTION OF PROPOSED PROJECT
2
METHODOLOGIES OF CRITICAL AREAS EVALUATION
2
RESULTS AND FINDINGS OF CRITICAL AREAS EVALUATION
3
EXISTING FUNCTIONS AND VALUES ANALYSIS
4
PROPOSED IMPACTS WITHIN STANDARD CRITICAL AREA BUFFER
5
PROPOSED STREAM BUFFER REDUCTION WITH ENHANCEMENT
5
PROPOSED COMPENSATORY MITIGATION EFFORTS
6
PROPOSED GRASS SEED
8
MITIGATION PLAN PERFORMANCE STANDARDS, MONITORING, MAINTENANCE, AND CONTINGENCY
8
DISCUSSION REGARD PERFORMANCE BOND
10
PROJECTS IMPACT DETERMINATION AND POST -PROJECT FUNCTIONS AND VALUES ASSESSMENT
11
LIMITATIONS AND USE OF THIS REPORT
11
REFERENCES AND LITERATURE REVIEWED
13
ATTACHMENTS:
1. CRITICAL AREAS & MITIGATION PLAN MAP MAP SHEET CA1.00
2. CRITICAL AREAS MITIGATION PLAN (SCHEMATIC) MAP SHEET CA2.00
3. CRITICAL AREAS MITIGATION PLAN (PLANTING GUIDELINES) MAP SHEET CA3.00
4. CRITICAL AREAS MITIGATION PLAN (INSTALLATION DETAILS) MAP SHEET CA4.00
INTRODUCTION AND BRIEF SITE DESCRIPTION
The subject property is located at 18910 Sound View Place in the incorporated City of Edmonds, Washington
(located in the NW Quarter of Section 13, Township 27N, Range 03E, W.M.). The tax parcel number for the
project site follows: 00498400000400. According to the Snohomish County Assessor's Office, the subject
property encompasses approximately 0.31 acres and is currently owned by Jeff and Maureen Lewis.
Vehicular site access is gained from travelling west from Sound View Place, a public asphalt roadway. As
shown on the attached Critical Areas & Mitigation Plan Map (Map Sheet CA1.00) and other project maps,
existing site development includes a single-family residence with an attached garage and daylight basement
surrounded by maintained lawn and landscaping. As depicted on Map Sheet CA1.00, a non-anadromous
fish -bearing stream (Fruitdale On The Sound) is located off-site along the southern property line, flowing from
east to west toward the Puget Sound. The vegetation among the stream corridor contains dense vegetation,
much of which is non-native, invasive vegetation. Please see the RESULTS AND FINDINGS OF CRITICAL AREAS
EVALUATION section of this report for further information regarding the findings of our Critical Areas
evaluation.
The property owners retained Wetlands & Wildlife, Inc. to evaluate the site features and determine the extent
of Critical Area impacts and appropriate mitigation measures as required by the City of Edmonds Critical
Areas Regulations outlined in Chapter 23.90 (Fish and Wildlife Habitat Conservation Areas) of the Edmonds
City Code and Community Development Code (ECDC). Wetlands & Wildlife, Inc. conducted a site visit on
December 15, 2014 to perform detailed Critical Areas evaluations on the project site, pursuant to the ECDC
and professional industry standards. Please see the report sections below for further information regarding
our evaluations.
STATEMENT OF QUALIFICATIONS TO CONDUCT THIS CRITICAL AREAS EVALUATION
The following provides a brief overview of my experience and credentials to conduct the detailed
evaluations on the subject property. I am the Founder, Owner, and Principal Wetland and Wildlife Ecologist
of Wetlands & Wildlife, Inc. I attended the University of Montana where I graduated cum laude with a
degree in Wildlife Biology. As of 2015, 1 have 14 years of direct experience as a professional
Biologist/Ecologist in western Washington and 18 years of overall experience completing natural resource
assessments among many different ecosystems across the western United States. I have worked as a
professional Biologist/Ecologist for federal, state, and county environmental agencies, as well as several
private environmental consulting firms with specialties in wetlands, streams, rivers, lakes, and wildlife
habitat. In my 18 years of experience, I have specialized in review of proposed land use and building
development permit applications as they pertain to Critical Areas (wetlands, rivers, streams, lakes, and
habitats of protected fish and wildlife species). Much of that experience came as a Senior Reviewing
Ecologist for King County DDES and a Regulatory Biologist for Snohomish County PDS.
I am listed on several Preferred / Qualified Consultant Rosters throughout western Washington. I am highly
experienced with the required U.S. Army Corps of Engineers and Washington State wetland delineation
methods. In addition to the wetland delineation certification, I am trained by the Washington Department of
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 1
Ecology and have 10 years of experience in the use of the required Wetland Rating Form for western
Washington (since its inception). I am trained by the Washington Department of Ecology to determine
Ordinary High Water Mark (OHWM) locations for rivers, streams, and lakes. In addition to my expertise
related to wetlands and streams, I have many years of experience conducting surveys of special status
wildlife species in the western U.S. I received certifications from the Washington Department of Fish and
Wildlife for terrestrial wildlife habitat assessments and wildlife surveys of special status wildlife species in
Washington.
Over the past 18 years, I have conducted literally over 1,400 biological / ecological assessments in different
capacities on properties with many habitat types and zoning designations, from small, urban properties
(0.25 acres) to large, rural properties (up to 2,000 acres in size). I have been selected by several local city
jurisdictions to provide on-call 3rd -party environmental reviews of proposed development projects for
compliance with local Critical Areas Ordinances and the FEMA Floodplain Habitat Assessment and
Mitigation document.
BRIEF DESCRIPTION OF PROPOSED PROJECT
Please see the attached Map Sheet CA1.00 and other project maps for a depiction of the location of
proposed project activities on the subject property. Based on the survey data, the existing residence
encompasses approximately 2,314 square feet. The applicant is proposing a new garage addition
attached to the northeast corner of the existing house, a new nook attached to the northwest corner of
the existing house, a new deck located west of the northwestern portion of the house, and an interior
remodel. Please review the project site plan for further information regarding the proposed project
parameters.
The proposed additions and proposed deck will be located among areas which are currently legally
established and maintained as lawn. Due to the location of the existing house in proximity to the off-site
stream, the proposed additions to the house described above will occur within the outer limits of the
standard 75 -foot stream buffer. Although the proposed additions are located as far away from the stream
as possible given the site constraints and property line setbacks, there is no opportunity to avoid impacts
within the standard Critical Area buffer when completing this proposed project. However, the project has
been specifically designed to minimize impacts to ecological functions and the applicant will provide
compensatory mitigation as described in detail later in this report.
The vast majority of the on-site buffer is currently comprised of maintained lawn, landscaping, or existing
impervious surfaces. The applicant is proposing to continue these legally established uses unless
otherwise outlined in this report.
METHODOLOGIES OF CRITICAL AREAS EVALUATION
Per industry standards, Wetlands & Wildlife, Inc. examined the entire subject property and areas off-
site within close proximity to the proposed project's limits of disturbance, to the maximum extent
Wetlands & Wildlife, Inc. Revision Date; March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 2
possible without entering adjacent private properties due to a lack of legal access, This evaluation of
off-site properties is necessary to determine if any regulated Critical Areas exist outside of the property
boundaries which would cause associated protective buffers to extend onto the property.
In addition to on-site field reviews, Wetlands & Wildlife, Inc. examined aerial photographs and topographical
data (elevation contours) on Snohomish County SnoScape system. Soil survey maps produced by the
Natural Resources Conservation Service (NRCS), SalmonScape fish distribution maps produced by the
Washington Department of Fish and Wildlife (WDFW), StreamNet fish distribution maps produced by
Pacific States Marine Fisheries Commission, Priority Habitats and Species (PHS) maps produced by
WDFW and Forest Practices Application Review System (FPARS) maps produced by Washington
Department of Natural Resources were also evaluated as part of this project review.
The subject stream was not delineated by Wetlands and Wildlife, Inc. due to its off-site location. However,
the location of the off-site stream shown on Map Sheet CA1.00 was provided to Wetlands & Wildlife, Inc. by
Alpha Subdivision Pros, Inc.
RESULTS AND FINDINGS OF CRITICAL AREAS EVALUATION
As depicted on Map Sheet CA1.00, no regulated wetlands or streams are located on the subject property.
However, a non-anadromous fish -bearing stream is located off-site to the south of the property's southern
property boundary, flowing from east to west. Please see further discussion below.
Cowardin Classification:
According to the Cowardin System, as described in Classification of Wetlands and Deepwater Habitats of
the United States, the classification for the off-site stream follows:
Off-site Stream: Riverine, Lower Perennial, Unconsolidated Bottom, Cobble -Gravel (R2UB1)
City of Edmonds Code Classifications:
Pursuant to the City of Edmonds Critical Areas Regulations outlined in Chapter 23.90 (Fish and Wildlife
Habitat Conservation Areas), the off-site stream is classified as follows:
The off-site stream appears to originate upslope and east of the subject property. Based on review of
several map resources, the off-site stream is a perennial non-anadromous fish -bearing stream at the
location south of the subject property. Therefore, the off-site stream appears to meet the definition of a
Type F stream per the ECDC section 23.90.010.A.1.b. Per the ECDC section 23.90.040.D.1,d, the
standard buffer width required for a Type F non-anadromous fish -bearing stream equals 75 feet. Based on
this information, the standard 75 -foot buffer from the off-site stream extends onto the subject property as
shown on Map Sheet CA1.00,
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 3
Natural Resource Conservation Service Soils Description:
Based on review of the Web Soil Survey produced by the Natural Resources Conservation Service
(NRCS), the NRCS maps the subject property as being underlain by Everett gravelly sandy loam soils (8 to
15 percent slopes).
According to the MRCS, the Everett gravelly sandy loam (8 to 15 percent slopes) soils are typically formed
on terraces and plains with a parent material of glacial outwash. The depth to restrictive feature is typically
between 14 to 20 inches below the surface. This soil type is somewhat excessively drained, and the
frequency of flooding and ponding is none. Available water capacity is high. The typical soil profile is
gravelly ashy sandy loam from 0 to 6 inches below the surface, very gravelly ashy sandy loam from 6 to 18
inches below the surface, and extremely gravelly sand from 18 to 60 inches below the surface. This soil
series does not contain any listed minor inclusions.
EXISTING FUNCTIONS AND VALUES ANALYSIS
The methodologies for this functions and values analysis are based on professional opinion developed
through past field analyses and interpretations. This analysis pertains specifically to the on-site
characteristics, but is typical for assessments of similar systems throughout the Puget Sound region of
western Washington. Regulated Critical Areas and associated buffers in western Washington often provide
very valuable functions including water quality, hydrologic control / transport, and wildlife habitat functions.
These functions become extremely important in an increasingly urbanizing environment such as the project
site and surrounding vicinity.
The portions of the site adjacent to the stream (vegetated areas, associated buffers, etc.) are increasingly
important to manage appropriately as these areas aid in water quality and hydrologic control, resulting in
cleaner water entering the stream's channel. The dense vegetation among the subject riparian corridor
provides very important ecological functions. In addition to providing direct habitat for wildlife species, the
dense vegetation location among the riparian corridor provides very valuable shade, and the shade
provided by the vegetation aids in cooler water temperature for the species that use the stream as habitat.
The tree and shrub roots among this riparian corridor aid with soil / bank stabilization, thus reducing erosion
and sedimentation among the stream channel. In addition, the vegetation among this corridor provide for
future recruitment of large woody debris (LWD) to the stream channel, and LWD is known to increase the
functions among stream channels (aids in reducing water velocity, aid in blocking sediment transport,
provides local shade for aquatic species, and provides habitat for terrestrial species). In addition to the
LWD recruitment, the dense vegetation among the riparian corridor also aids in the recruitment of organic
matter to the stream.
As previously described in this report, the on-site buffer contains an existing single-family residence and
associated infrastructure, with the remainder of the property being dominated by maintained lawn. The
maintained lawn provides some water quality benefits by filtering sediment from overland flow, taking up
and binding nutrients through biological action, and reducing erosion by binding the soil. On-site wildlife
habitat is currently limited due to the lack of established native vegetation and sufficient vegetative
structure. The slope along the southern property currently contains several non-native species including
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 4
English ivy (Hedera helix linnaeus), holly (Ilex aquifolium), Himalayan blackberry (Rubus armeniacus) and
California laurel (Umbellularia californica). Based on our detailed ecological functions assessment, the on-
site buffer provides relatively low -quality functions and protection to the stream. The ecological functions
among the project site will be improved through implementation of the proposed compensatory mitigation
measures described below in this report.
In addition to the functions mentioned above, riparian corridors often provide aesthetic value, recreational
opportunities, and educational opportunities.
PROPOSED IMPACTS WITHIN STANDARD CRITICAL AREA BUFFER
As previously described, the proposed additions to the house will occur in the outer limits of the standard
75 -foot stream buffer. Due to site constraints on the subject property, it is not possible to accomplish the
entire proposed project outside of the standard stream buffer because the standard 75 -foot buffer extends
across a vast majority of the site and the proposed development also needs to be located outside of the
property line setbacks. The proposed garage and nook will be located entirely outside of the standard 75 -foot
buffer. However, a small portion of the proposed deck will be partially located within the outer limits of the
standard 75 -foot stream buffer. As previously mentioned, the City requires property line setbacks which
further constrain the subject property for the proposed project. Based on these factors, it is the professional
opinion of Wetlands & Wildlife, Inc. that the project has been specifically designed to avoid and
minimize impacts to Critical Areas and associated buffers in accordance with industry standards and the
ECDC outlined in Chapter 23.90 (Fish and Wildlife Habitat Conservation Areas). The project is proposed
to be located among legally established disturbed areas, and is also proposed to be located further from
the stream than the existing house.
PROPOSED STREAM BUFFER REDUCTION WITH ENHANCEMENT
In order to accomplish the proposed project described above, the applicant is proposing to reduce the
standard 75 -foot stream buffer width with enhancement to facilitate construction of the proposed additions
in the location depicted on Map Sheet CA1.00. The reduced stream buffer width with enhancement
proposal adheres to all of the code requirements set forth in the Edmonds City Code and Community
Development Code section 23.90.040.D.2. Per requirements set forth in ECDC 23.90.40.D.2, the proposed
stream buffer enhancement plan for this project will "conclusively demonstrate that enhancement of the
reduced buffer area will not degrade the quantitative and qualitative functions and values of the buffer area
in terms of fish and stream protection and the provision of wildlife habitat.", meeting the specific
requirements of ECDC 23.40.110, 23.40.120 and 23.40.130. The proposed stream buffer reduction with
enhancement as detailed below offers significantly better protection to the on-site ecological functions and
values than what currently exists by enhancing areas denude of native vegetation or disturbed by non-
native, invasive plant species.
The ECDC section 23.90.040.D.2.a. allows applicants to reduce the standard buffer by up to 50% when the
applicant can "Provide evidence that the reduced buffer, through enhancement, will provide functions and
Wetlands & Wildlife, Inc. Revision Date; March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 5
values in terms of stream and wildlife protections equivalent to or greater than a standard buffer without
enhancement." The applicant is proposing to reduce the standard buffer of the off-site stream from 75 feet
to the minimum of 37.5 feet (as allowed per Edmonds City Code). The proposed reduced stream buffer
width with enhancement will result in a total of 1,167 square feet of significantly enhanced stream buffer
(Buffer Enhancement Area A equals 715 square feet and Buffer Enhancement Area A equals 452 square
feet). The stream buffer area proposed for enhancement currently contains significant amounts of non-
native, invasive vegetation such as English ivy, holly, Himalayan blackberry, California laurel. The vast
majority of the remaining buffer area to be enhanced is dominated by maintained lawn. The standard
stream buffer areas outside of the proposed enhancement areas contain the single-family residence,
associated infrastructure, maintained lawn, and maintained landscaping. Therefore, the proposed stream
buffer enhancement will create a significant ecological lift among the remaining on-site buffer by removing
all non-native, invasive species and then planting the stream buffer enhancement areas with native
vegetation as outlined in the PROPOSED COMPENSATORY MITIGATION EFFORTS section below.
PROPOSED COMPENSATORY MITIGATION EFFORTS
In order to off -set the proposed reduction of the standard stream buffer from 75 feet to 37.5 feet, the
applicant is proposing to provide buffer enhancement of all areas within the remaining 37.5 feet buffer that
are dominated by non-native, invasive species and / or dominated by lawn. Please see Map Sheet CA1.00
for a depiction of the proposed buffer enhancement area locations associated with the proposed project on
the subject site.
All existing non-native, invasive vegetation among the proposed mitigation areas will be removed prior to
planting the native vegetation, and the non-native, invasive vegetation will be disposed of at an approved
off-site location. After the non-native, invasive vegetation has been removed, the applicants are
proposing to plant native vegetation among the reduced stream buffer. Any work performed within the
reduced stream buffer shall be completed using hand tools only. As described in further detail below,
the proposed stream buffer enhancement will result in planting 3 trees, 17 shrubs and 32 herbs among
the buffer enhancement areas. Please note that the southern fringe of the proposed enhancement areas
currently contain some native vegetation. Therefore, the proposed mitigation plan includes avoiding
disturbance to all native vegetation. All vegetation planted as part of this mitigation proposal among areas
currently vegetated with native species will maintain appropriate spacing from existing native vegetation.
The proposed buffer enhancement areas shown on Map Sheet CA1.00 total 1,167 square feet (715 square
feet for Buffer Enhancement Area A and 452 square feet for Buffer Enhancement Area B) and specifically
account for the existing vegetation to the south of the proposed enhancement areas. Please see Map
Sheet CA1.00 for a depiction of the 2 proposed enhancement areas, labeled as Area A and Area B
respectively. Please see below for a description of the proposed mitigation plantings among each
mitigation area.
As depicted on Map Sheet CA1.00 and described previously in this report, Buffer Enhancement Area A
equals 715 square feet. This mitigation area currently contains non-native, invasive vegetation such as
English ivy, holly, and Himalayan blackberry. Therefore, all non-native, invasive species will be removed
prior to the proposed enhancement plantings among Buffer Enhancement Area A. This mitigation proposal
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 6
includes calculating required plant quantities by planting 60% of the mitigation area with native shrubs and
planting 40% of the mitigation area with native herbs. The native shrubs are proposed to be planted on 6 -
foot centers and the native herbs are proposed to be planted on 3 -foot centers (thereby meeting industry
standards and City requirements). Using these calculations, the applicant is proposing to plant 12 shrubs
and 32 herbs among Buffer Enhancement Area A. Please see the table below for the proposed plant
schedule among Buffer Enhancement Area A on the project site, and please view Map Sheets CA1.00 and
CA2.00 attached to this report for further information regarding the location of the proposed native
enhancement plantings. Please note that the extreme southern edges of the proposed Buffer
Enhancement Area A currently contain native vegetation. Therefore, the proposed mitigation plan includes
avoiding disturbance to all native vegetation during the vegetative planting enhancement efforts. The
mitigation area planting boundaries shown on Map Sheet CA1.00 and individual plant locations shown on
Map Sheet CA2.00 may be modified slightly in order to avoid impacts to native vegetation and to ensure
that all planted vegetation among areas currently vegetated with native species will maintain appropriate
spacing from existing native vegetation.
Proposed Buffer Enhancement Plantings Among Buffer EnhancementArea A (approx. 715 SFJ
Common Name
Latin Name
Size
Spacing
Quantity
1. Beaked hazelnut
Corylus cornuta
1 -gallon
6' o.c. min.
3
2. Snowbeny
Symphoricarpos albus
1 -gallon
6' o.c. min.
3
3. Salal
Gaultheria shallon
1 -gallon
6' o.c. min.
6
4. Sword Fern
Polystichum munitum
4" pot
3' o.c. min.
10
5. False lily -of -the -valley
Maianthemum dilitatum
4" pot
3' o.c. min.
10
6. Pacific bleeding heart
Dicentra formosa
4" pot
3' o.c. min.
8
7. Goatsbeard
Aruncus dioicus
4" pot
3' o.c. min.
4
As depicted on Map Sheet CA1.00, Buffer Enhancement Area B equals approximately 452 square feet.
This mitigation area also contains non-native, invasive vegetation such as English ivy, holly, and Himalayan
blackberry. Therefore, all non-native, invasive species will be removed prior to the proposed enhancement
plantings among Buffer Enhancement Area B. The mitigation proposal among Buffer Enhancement Area B
includes calculating required plant quantities by planting 60% trees and 40% shrubs. The native trees are
proposed to be planted on 10 -foot centers and the shrubs are proposed to be planted on 6 -foot centers
(thereby meeting industry standards and City requirements). Using these calculations, the applicant is
proposing to plant 3 trees and 5 shrubs among Buffer Enhancement Area B. Please see the table
below for the proposed plant schedule among Buffer Enhancement Area B on the project site, and please
view Map Sheets CA1.00 and CA2.00 attached to this report for further information regarding the location
of the proposed plantings. Please note that the extreme southern edges of the proposed Buffer
Enhancement Area A currently contain native vegetation. Therefore, the proposed mitigation plan includes
avoiding disturbance to all native vegetation during the vegetative planting enhancement efforts. The
mitigation area planting boundaries shown on Map Sheet CA1.00 and individual plant locations shown on
Map Sheet CA2.00 may be modified slightly in order to avoid impacts to native vegetation and to ensure
that all planted vegetation among areas currently vegetated with native species will maintain appropriate
spacing from existing native vegetation.
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 7
Proposed Buffer Enhancement Plantings Among Buffer Enhancement Area B (approx. 452 SF)
Common Name
Latin Name
Size
S acin
Quantity
1. Western red cedar
Thuja plicata
2 -gallon
10' o.c. min.
2
2. Douglas fir
Pseudotsuga menziesii
2 -gallon
10' o.c. min.
1
3. Beaked hazelnut
Corylus cornuta
1 -gallon
6' o.c. min.
2
4. Salal
Gaultheria shallon
1 -gallon
6' o.c. min.
3
PROPOSED GRASS SEED
The applicant is proposing to seed any bare ground areas among the remaining stream buffer area which
are temporarily disturbed as part of this project. To aid in soils stabilization, any bare ground areas within
the remaining buffer areas shall be seeded to the native grass seed mixtures below, or a similar native
seed mixture:
Common Name
Latin Name
lbs./1 000 s.f.
Colonial bentgrass
Agrostis tenuis
0.6
Red fescue
Festuca rubra
0.3
White clover
Trifolium repens
0.2
Following the grass seeding, weed -free straw shall be placed on top of the grass seed to aid in soil
stabilization and erosion reduction while the grass seed germinates and begins root growth. Any erosion
and sediment control measures (best management practices) will remain in place until the soil is sufficiently
stabilized to prevent erosion of soil in close proximity to the off-site stream.
MITIGATION PLAN PERFORMANCE STANDARDS, MONITORING, MAINTENANCE, AND CONTINGENCY
Goals and Objectives of the Project Proposal and Mitigation Plan
The primary goals of the mitigation plan described above follow:
1. Allow for responsible residential development and associated infrastructure, while also
increasing the ecological functions provided by the on-site portion of the stream buffer.
2. Off -set the proposed buffer reduction associated with the proposed development through
compensatory mitigation and restoration activities described above;
3. Remove the non-native, invasive vegetation among the mitigation areas;
4. Increase the quantity and diversity of native vegetation within the on-site wetland and buffer
areas;
5. Provide additional BMP's as previously outlined in order to reduce the environmental footprint of
the proposed single-family residence on the project site;
6. Ensure that the proposed compensatory mitigation efforts and BMP's are successful by
maintaining and monitoring these items as described below.
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 8
Success Criteria / Performance Standards:
The applicant proposes to meet the following plant cover and survival standards among the on-site
mitigation areas in an attempt to measure success of the proposed mitigation planting plan and
compensate for project impacts among the on-site stream buffers:
Performance Standards
Monitoring Year after installation
Year One
Year Two
Year Three
Shrub and Sapling Tree Cover"
>20%
>30%
>40%
Shrub and Sapling Tree Survival"
100%
>90%
>80%
Percent Non-native, Invasive Species
<20%
<20%
<20%
"NOTE: The performance standards above include beneficial native plants in that naturally pioneer in the
planted area. Also note that the percent cover performance standards shown above are related to bare
ground areas that are planted with the full cover requirements, and these percentages do not apply to those
areas where vegetation is planted among existing vegetation (underplanted / interplanted).
Monitoring and Maintenance Duration and Schedule:
Pursuant to City of Edmonds standards and requirements, approved / installed mitigation projects shall be
monitored for a minimum of three (3) years from the date of plant installation to ensure that the
performance standards outlined in the approved mitigation plan have been met. Wetlands & Wildlife, Inc.
or another qualified professional will conduct one (1) annual monitoring visit to examine the status and
determine success among the mitigation areas. During the first annual monitoring site visit, representative
photo points shall be established among the mitigation areas. The photographs taken at these photo points
shall provide a general overview of the mitigation areas. Photographs shall be taken from the same photo
points during each subsequent monitoring visit to provide visual information from known locations. The
qualified professional will submit one (1) annual progress report to City of Edmonds for the first two (2)
years of the monitoring period. These annual monitoring reports shall assess both achievement of yearly
goals and progress towards overall achievement of the project goals. Monitoring reports will be prepared in
accordance with ecological industry standards and will include an assessment of the approximate percent
cover of native vegetation, presence of invasive vegetation, any other ecological concerns or
recommendations among the mitigation areas, and overall effectiveness of the mitigation site. A final
monitoring report will be submitted to City of Edmonds at the end of the third (3rd) year to ensure that the
performance standards outlined in the mitigation plan have been met.
During the 3 -year monitoring period, the applicant or retained professionals shall also perform maintenance
of the mitigation area(s) in accordance with industry standards and guidelines. Maintenance will include
but may not be limited to the following: regular watering, weeding around the base of installed plants,
pruning, replacement plantings as necessary to achieve performance standards, removal of all noxious and
invasive vegetation species, and any other measures needed to ensure performance standards are met
throughout the mitigation areas as outlined above.
If the project meets all of the criteria for success at the end of the three-year monitoring period, no further
action will be required by the applicant and the required financial guarantee amount described below will be
returned to the applicant(s) in full. If the definition of success is not met for any reason at the end of the
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 9
three-year monitoring period, the maintenance and monitoring period will be extended for one year at a
time until the site meets the performance standards outlined. This mitigation plan and the accompanying
maintenance / monitoring will not be considered complete until final approval is received from the City.
Contingency Plan Related to Plant Success:
If it is determined at any time during the monitoring period that the performance standards or goals of the
mitigation plan are not being met, a contingency plan will be devised to improve or alter those elements that
are deficient. If measures beyond standard maintenance of the mitigation areas are required, a plan
containing these measures shall be submitted to City of Edmonds for their review prior to implementation.
Contingency Plan Related to Property Ownership:
If the subject property changes ownership at any time during implementation of the proposed mitigation
plan described above, or during the 3 -year monitoring and maintenance period associated with the
proposed mitigation plan, the current property owner(s) shall inform the prospective real property
purchaser(s) of the mitigation requirements. The proposed mitigation plan shall run with the land (in
perpetuity), and the current property owner(s) shall ensure that the approved mitigation components are
implemented as stated, monitored for compliance with the performance standards outlined in this plan, and
maintained in accordance with this plan and ecological industry standards. If the property changes
ownership at any time during the monitoring phase, the current property owner(s) shall also inform any new
property owners of any requirements related to the monitoring and maintenance schedule. If any questions
arise regarding these contingencies related to property ownership, the current property owner should
contact City of Edmonds at the appropriate time.
DISCUSSION REGARDING PERFORMANCE BOND
Per the City of Edmonds standards and requirements, a performance bond (financial guarantee) shall be
provided to the City of Edmonds. As stated in the ECDC section 23.40.290.8. "The bond shall be in the
amount of 120 percent of the estimated cost of the uncompleted actions or the estimated cost of restoring
the functions and values of the critical area that are at risk, whichever is greater." The purpose of this
performance bond is to ensure that the proposed mitigation efforts meet the performance standards
outlined in this report. This bond shall be released at the end of three years upon a successful
determination by the City for all portions of this Critical Areas mitigation project. This project shall be
considered successful if it meets the performance standards listed in this plan. Please see below for a
discussion regarding the proposed financial guarantee related to this mitigation plan.
Install 3 2 -gallon trees @ approximately $15.00 each (installed price):
$45.00
Install 171 -gallon shrubs @ approximately $9.50 EACH (installed price):
$161.50
Install 32 herbs in 4" pots @ approximately $6.00 EACH (installed price):
$192.00
Total Estimated Cost of Plant Material and Installation Labor
$398.50
(120% of Estimated Cost of Plant Material and Installation Labor Shown Above) $478.20
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 10
PROJECT'S IMPACT DETERMINATION AND POST -PROJECT FUNCTIONS AND VALUES ASSESSMENT
The proposed additions to the existing house are located among legally established disturbed areas that
are currently maintained as lawn and landscaping. As described in detail within this report, the applicant is
proposing to reduce the standard stream buffer with enhancement in order to accommodate the proposed
additions to the existing residence. The compensatory mitigation efforts associated with the proposed
stream buffer reduction with enhancement will significantly increase the ecological functions on the site by
removing all non-native, invasive plant species within the on-site stream buffer and then planting the
remaining buffer areas with dense native vegetation.
Due to the location of the proposed additions to the house and implementation of the proposed temporary
erosion and sediment control measures, no impacts to water quality are expected. Planting additional
native trees, shrubs and herbs among the mitigation areas will further increase the ability of the riparian
corridor associated with the off-site stream to perform important water -holding capacity and hydrologic
control and filtration functions. The wildlife habitat functions on-site will also be significantly improved
through implementation of the proposed mitigation plantings. The mitigation proposal to remove all non-
native, invasive vegetation on the project site and plant dense native vegetation will significantly increase
the vegetative species quantity and diversity. The proposed mitigation plan will provide significantly higher
wildlife habitat functions for many terrestrial wildlife species as the planted vegetation matures, especially
when compared to the vegetative condition of the proposed reduction area (lawn).
Based on the detailed site evaluation and review of the proposed project on the subject property, no
significant adverse impacts are expected to occur among the stream buffer as a result of this project if the
compensatory mitigation efforts are implemented as stated in this plan. Although impacts within the
standard stream buffer are required to accommodate the proposed additions, no net loss of ecological
functions is expected to occur. The applicant's development proposal has been specifically designed for
the proposed development components to occur within the footprint of the existing disturbed areas (lawn)
and as far away from the off-site stream as practical in order to avoid impacts to native vegetation and
native soils wherever possible. All assessed ecological functions will be increased through implementation
of the proposed project when combined with the proposed stream buffer enhancement described in this
report. Based on the information contained in this report, it is the professional opinion of Wetlands &
Wildlife, Inc. that the proposed project will result in an increase (lift) in ecological functions provided by the
on-site stream buffer.
LIMITATIONS AND USE OF THIS REPORT
This Critical Areas Report and Proposed Mitigation Plan is supplied to the City of Edmonds on behalf of Jeff
and Maureen Lewis as a means of determining whether any wetlands, streams, and/or wildlife habitat
conservation areas regulated by the City of Edmonds exist on the site, to determine the extent of Critical
Area impacts, and to provide mitigation for potential impacts. This report is intended to provide information
deemed relevant in the applicant's attempt to comply with the regulations currently in effect. Wetlands &
Wildlife, Inc. did not provide analysis of other permitting requirements (i.e. structural, drainage,
geotechnical, or engineering) not discussed in this report.
Wetlands & Wildlife, Inc. Revision Date; March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 11
The work for this report has conformed to the standard of care employed by professional ecologists in the
Puget Sound region. No other representation or warranty, expressed or implied, is made concerning the
work or this report. This report is based largely on readily observable conditions and, to a lesser extent, on
readily ascertainable conditions. No attempt has been made to determine hidden or concealed conditions.
If hidden or concealed conditions arise, the information contained in this report may change based upon
those conditions.
The laws applicable to Critical Areas are subject to varying interpretations. While Wetlands & Wildlife, Inc.
upheld professional industry standards when completing this review, the information included in this report
does not guarantee approval by any federal, state, and/or local permitting agencies. Therefore, the work
associated with this proposal shall not commence until permits have been obtained from all applicable
agencies.
If any questions arise regarding this review, please contact me directly at (425) 337-6450.
Wetlands & Wildlife, Inc.
Scott Spooner
Owner/ Principal Wetland & Wildlife Ecologist
Wetlands & Wildlife, Inc. Revision Date: March 24, 2015
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds) Page 12
REFERENCES AND LITERATURE REVIEWED
Edmonds Community Development Code: Critical Areas, Title 23. City of Edmonds, Washington.
FPARS. Forest Practices Application Review System. Administered by the Washington State
Department of Natural Resources. http://fortress,wa.gov/dnr/appl/fpars/viewer.htm,
Lichvar, R.W., M. Butterwick, N.C. Melvin, and W.N. Kirchner. 2014. The National Wetland Plant List: 2014
Update of Wetland Ratings. Phytoneuron 2014-41: 1-42.
http://rsgisias.crrel.usace.army.mil/nwpl_static/data/docs/lists_2014/Regions/pdf/reg_WMVC_2014vl .pdf.
PHS on the Web. Web -based interactive map administered by the Washington Department of Fish and
Wildlife. http://wdfw.wa.gov/mapping/phs/.
SalmonScape. Interactive Mapping website administered by the Washington Department of Fish and
Wildlife. http://wdfw,wa.qov/mapping/Salmonscape/index.html.
Snohomish County Landscape Imaging Interactive Map (SnoScape). Snohomish County GIS Center in
conjunction with Snohomish County Planning and Development Services.
http://gis.snoco.org/maps/snoscape/index.htm.
U.S. Army Corps of Engineers (2010). "Regional Supplement to the Corps of Engineers Wetland
Delineation Manual: Western Mountains, Valleys, and Coast Region (Version 2.0)," ERDC/EL TR -10-3,
U.S. Army Engineer Research and Development Center, Vicksburg, MS.
U.S. Fish and Wildlife Service. National Wetlands Inventory Wetlands Mapper.
http://107.20.228.18/WetiandsMetlandsMapper.html#.
Washington State Wetlands Identification and Delineation Manual, Washington State Department of
Ecology. Publication #96-94. March 1997.
Web Soil Survey. United States Department of Agriculture. Natural Resources Conservation Service.
http://websoilsurvey.nres.usda.gov/app/HomePage.htm.
Wetlands & Wildlife, Inc.
Critical Areas Report and Proposed Mitigation Plan
Tax Parcel Number 00498400000400 (Incorporated City of Edmonds)
Revision Date: March 24, 2015
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CONSULTANTS, INC.
Jeffrey Lewis
18910 Sound View Place, Edmonds, Washington 98020
13256 Northeast 20th Street, Suite 16
.Bellevue, Washington 98005
(425) 747-5618 FAX (425) 747-8561
March 20, 2015
JN 15126
Subject: Geotechnical Engineering Study - Proposed House Addition
18910 Sound View Place, Edmonds, Washington
Dear Mr. Lewis: via email
The undersigned associate visited the subject site on March 12, 2015. The purpose of this visit was to
observe the existing site conditions, excavate a shallow hand auger test hole, and to develop opinions
regarding the steep slope and the additions to be made onto the northern and southwestern side of the
residence. The recommendations and conclusions presented in this report are professional opinions based
on the visual observations made during our site visit and on previous experience with similar projects. Only
shallow subsurface explorations were conducted for our work, no deep explorations were completed.
We were provided with architectural plans by your architect, Rod McNurlen. Based on these plans and
discussions with you, we understand that a new, single -story addition (garage) will be made onto the
northeastern side of the existing residence, that a two story addition and deck will be made onto the
northwestern side of the residence, and that a two story (infill) addition will be made onto the southwestern
corner of the residence. The northern additions will be located 40 to over 50 feet from the steep slope area
and the southwestern addition will be located about 8 to 10 feet from the edge of the steep slope area. We
generally agree with the steep slope delineation as indicated on site plan included below. The additions will be
constructed over a shallow crawlspaces or as slab on grades. No changes to the area to the south of the
addition and on the slope are proposed.
If the scope of the project changes from what we have described above, we should be provided with revised
plans in order to determine if modifications to the recommendations and conclusions of this report are
warranted.
SITE CONDITIONS
The subject site is bordered to the east by Sound View Place and by Fruitdale on the Sound Creek to the
south. Neighboring properties are developed with residences. The subject property is developed with a single
family residence.
The existing structure consists of one- to two -stories over slab on grade. The existing house is located about
8 to 10 feet from the steep southern slope that leads down to the creek. No evidence of settlement of the
house foundation on the southern side of the house was observed during our visit. We do not know how deep
the existing foundation extends, but the foundation performance appears good.
The eastern side of the site is level with the street, and the site grades drop gradually along the side of the
house to the west. The slope down to the creek runs along the southern property line and along the southern
side of the house. The slope is about 14 feet tall and is inclined at about 77 percent. The slope is very well
vegetated with bushes and undergrowth. We did not observe any indication of slope instability at the site
during our visit. There is no evidence or history of large-scale slope instability at the site.
Our understanding of the subsurface conditions at the site is based on the observations made during our
recent site visit, test pits excavated at the site by others, and on experience gained from other projects in the
site vicinity. During our visit, we excavated one shallow hand auger test hole in the area of the addition near
the slope. The approximate location of the test hole is shown in the site exploration sketch below. HA -1
revealed 1.5 feet of loose, silty sand fill and disturbed soils. Underlying the fill soils to a depth of 3 feet, we
observed native, medium -dense, brown, slightly silty sand that was fine- to medium -grained, and moist
[SP/SM]. From 3 feet to 4.5 feet we encountered gray, interbedded silty sand and sands that were medium -
dense to dense, and very moist to wet. From 4.5 feet to the bottom of our hole at 5 feet, we observed dense,
gray sandy silt that was moist. No groundwater was encountered in our exploration.
Jeffrey Lewis
March 20, 2015
JN 15126
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The approximate locations of our hand auger and the soil logs (by others) is shown in the sketch below.
= Approximate Hand Auger Location
Soil Loci Descriptions
0-30"Fill(Dark Brom Sandy Loam »'chunksofbdckandconcrataj
30.45" Brown Loamy Sand
45-72'+ Gray Fine Sand w1heavy mottling
Water encountered at 68'
0-7" Dark Brawn Sandy Loam
7-26' Brown Loamy Fine Sand
26-44' Gray Fine Sand
44-72'+ Brown Medium Sand
Water encountered at 48'
Soll Logs Recorded On 1114115
GEOTECH CONSULTANTS, INC.
Jeffrey Lewis
March 20, 2015
CONCLUSIONS AND RECOMMENDATIONS
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Our explorations near the steep slope found a minor depth of loose fill soils over medium dense to dense native
sands and dense silts. Based on our explorations and the performance of the structure, it appears that the house
foundations are bearing on the medium -dense to dense, native silty sands. The steep slope is not very tall and we
anticipate that the medium -dense to dense native sands that form the core of the slope are stable (FS static > 1.5 /
FS dynamic > 1.2) at their current inclination. Any slope instability at the site would be related to the loose surficial
soils.
Due to the steep slope, we recommend that all of the new footings on the southern end of the site be excavated to
bear directly on the medium -dense to dense native soils at least 3 feet below the existing grade. The existing
house footprint on the southern side is not being changed, but the deck area on the southwest corner is being
enclosed. The setback from the steep slope to the structure in this area is 8 to 10 feet, but given the
recommended footing embedment of 3 feet, the effective slope setback will be at least 11.5 feet (see section
above). In our opinion, this foundation embedment will be sufficient to protect the structure from potential slope
creep or any anticipated slope instability. The lowered footings would also avoid surcharging the slope with any
loads from the structure. The remaining foundations on the northern end of the addition will be located 40 or more
feet from the slope and may be supported on the medium -dense native soils or on structural fill placed above the
medium -dense native soils.
The onsite slope section to the south of the proposed additions shows no indications of large-scale instability. The
dense native soils will not be subject to any instability and transferring the proximal building loads to the dense
soils would avoid adding any building loads to the existing slope soils. Based on these conditions, we do not
anticipate any impact of the proposed development on the slope, and reciprocally, we would not anticipate slope
movements to impact the proposed additions. The proposed 10 -foot+ effective setback is appropriate for the site
conditions as long as the recommendations in this report are applied.
Any disturbance to the existing slope outside of the building limits may reduce the stability of the slope. Damage
to the existing vegetation and ground should be minimized, and any disturbed areas should be revegetated as
soon as possible. Soil from the excavation should not be placed on the slopes, and this may require the off-site
disposal of any surplus soil. Due to its detrimental effects on the slope stability, water from roof, storm water,
surface runoff, and foundation drains should not be discharged onto slopes; it should be tightlined to a suitable
outfall located away from any slopes. The proposed 50 -foot setbacks of the infiltration bays is acceptable from a
slope stability standpoint.
In accordance with EMC 23.80.060, provided our geotechnical recommendations are followed, the proposed
house additions:
1. Will not increase the threat of the geological hazard to adjacent properties beyond predevelopment
conditions;
2. Will not adversely impact other critical areas;
3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than
predevelopment conditions; and
4. Are certified as safe as designed and under anticipated conditions by a qualified engineer or geologist,
licensed in the state of Washington.
And in accordance with EMC 23.80.070
a. The development will not increase surface water discharge or sedimentation to adjacent properties beyond
predevelopment conditions;
b. The development will not decrease slope stability on adjacent properties; and
c. Such alterations will not adversely impact other critical areas;
The on-site sand soils are silty, and thus are moisture -sensitive. The silty sand soils can be reused as structural
fill, provided that they are placed in dry weather and are at, or near, the optimum moisture content. The silty sand
soils should not be placed in direct contact with foundation walls.
The erosion control measures needed during the site development will depend heavily on the weather conditions
that are encountered. While site clearing will expose a large area of bare soil, the erosion potential on the site is
relatively low due to the gentle slope of the ground. We anticipate that a silt fence will be needed around the
downslope sides of any cleared areas. Existing catch basins in, and immediately downslope of, the planned work
GEOTECH CONSULTANTS, INC.
Jeffrey Lewis JN 15126
March 20, 2015 Page 4
areas should be protected with pre -manufactured silt socks. Cut slopes and soil stockpiles should be covered with
plastic during wet weather. Any disturbance to the existing slope outside of the building limits may reduce the
stability of the slope. Damage to the existing vegetation and ground should be minimized, and any disturbed areas
should be revegetated as soon as possible. Any disturbance of the vegetation on the steep slope should only be
completed in small areas as part of an approved revegetation plan that incorporates drought -tolerant plantings with
deep root systems. No irrigation systems should be placed on or directly above the steep slope.
We recommend that Geotech Consultants, Inc. be afforded the opportunity to review the development plans, to
amend our recommendations as necessary, and to verify that the recommendations presented in this report are
adequately addressed in the design. Such a plan review would be additional work beyond the current scope of
work for this study, and it may include revisions to our recommendations to accommodate site, development, and
geotechnical constraints that become more evident during the review process.
We recommend including this report, in its entirety, in the project contract documents. This report should also be
provided to any future property owners so they will be aware of our findings and recommendations.
SEISMIC CONSIDERATIONS
In accordance with the International Building Code (SBC) (IBC), the site soil profile within 100 feet of the ground
surface is best represented by Soil Profile Type D (Stiff Soil). As required by the SBC, the design criteria
presented in this report consider the effects of a one -in -100 -years seismic event for slope stability.
The site soils in the area of the proposed structures are not susceptible to seismic liquefaction because of their
dense nature. This statement regarding liquefaction includes the knowledge of the determined peak ground
acceleration noted above.
CONVENTIONAL FOUNDATIONS
As discussed in the General section, special requirements are in order for the southern foundations of the
addition. The remaining proposed structures can be supported on conventional continuous, and/or spread
footings bearing on undisturbed, medium -dense to dense native soil, or on structural fill placed above this
competent native soil. See the section entitled General Earthwork and Structural Fill for recommendations
regarding the placement and compaction of structural fill beneath structures. Adequate compaction of structural
fill should be verified with frequent density testing during fill placement. Prior to placing structural fill beneath
foundations, the excavation should be observed by the geotechnical engineer to document that adequate bearing
soils have been exposed. We recommend that continuous and individual spread footings have minimum widths of
16 and 24 inches, respectively. Footings should also be bottomed at least 18 inches below the lowest adjacent
finish ground surface. The local building codes should be reviewed to determine if different footing widths or
embedment depths are required. Footing subgrades must be cleaned of loose or disturbed soil prior to pouring
concrete. Depending upon site and equipment constraints, this may require removing the disturbed soil by hand.
An allowable bearing pressure of 2,500 pounds per square foot (psf) is appropriate for footings supported on
competent native soil. A one-third increase in this design bearing pressure may be used when considering short-
term wind or seismic loads. For the above design criteria, it is anticipated that the total post -construction
settlement of footings founded on competent native soil will be less than one inch.
Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the bearing
soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation. For the latter
condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded
by level structural fill. We recommend using the following ultimate values for the foundation's resistance to lateral
loading:
GEOTECH CONSULTANTS, INC.
Jeffrey Lewis
March 20, 2015
Coefficient of Friction 0.45
Passive Earth Pressure 300 pcf
Where: (i) pcf is pounds per cubic foot, and (ii)
passive earth pressure is computed using the
equivalent fluid density.
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If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be
appropriate. We recommend maintaining a safety factor of at least 1.5 for the foundation's resistance to lateral
loading, when using the above ultimate values. The passive pressure given is appropriate for the depth of level
structural fill placed in front of a retaining or foundation wall only, or if the foundation is poured directly against the
native cut soils.
SLABS -ON -GRADE
The building floors can be constructed as slabs -on -grade atop existing non-organic soils, or on structural fill. The
subgrade soil must be in a firm, non -yielding condition at the time of slab construction or underslab fill placement.
Any soft areas encountered should be excavated and replaced with select, imported structural fill.
Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil to the
new constructed space above it. All interior slabs -on -grade must be underlain by a capillary break or drainage
layer consisting of a minimum 4 -inch thickness of gravel or crushed rock that has a fines content (percent passing
the No. 200 sieve) of less than 3 percent and a sand content (percent passing the No. 4 sieve) of no more than 10
percent. As noted by the American Concrete Institute (ACI) in the Guides for Concrete Floor and Slab Structures,
proper moisture protection is desirable immediately below any on -grade slab that will be covered by tile, wood,
carpet, impermeable floor coverings, or any moisture -sensitive equipment or products. ACI also notes that vapor
retarders, such as 6 -mil plastic sheeting, are typically used. A vapor retarder is defined as a material with a
permeance of less than 0.3 US perms per square foot (psf) per hour, as determined by ASTM E 96. It is possible
that concrete admixtures may meet this specification, although the manufacturers of the admixtures should be
consulted. Where plastic sheeting is used under slabs, joints should overlap by at least 6 inches and be sealed
with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. If no
potential for vapor passage through the slab is desired, a vapor barrier should be used. A vapor barrier, as
defined by ACI, is a product with a water transmission rate of 0.00 perms per square foot per hour when tested in
accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement.
In the recent past, ACI (Section 4.1.5) recommended that a minimum of 4 inches of well -graded compactable
granular material, such as a 5/8 inch minus crushed rock pavement base, should be placed over the vapor
retarder or barrier for protection of the retarder or barrier and as a "blotter" to aid in the curing of the concrete slab.
Sand was not recommended by ACI for this purpose. However, the use of material over the vapor retarder is
controversial as noted in current ACI literature because of the potential that the protection/blotter material can
become wet between the time of its placement and the installation of the slab. If the material is wet prior to slab
placement, which is always possible in the Puget Sound area, it could cause vapor transmission to occur up
through the slab in the future, essentially destroying the purpose of the vapor barrier/retarder. Therefore, if there is
a potential that the protection/blotter material will become wet before the slab is installed, ACI now recommends
that no protection/blotter material be used. However, ACI then recommends that, because there is a potential for
slab cure due to the loss of the blotter material, joint spacing in the slab be reduced, a low shrinkage concrete
mixture be used, and "other measures" (steel reinforcing, etc.) be used. ASTM E-1643-98 Standard Practice for
Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs" generally
agrees with the recent ACI literature.
We recommend that the contractor, the project materials engineer, and the owner discuss these issues and
review recent ACI literature and ASTM E-1643 for installation guidelines and guidance on the use of the
protection/blotter material. Our opinion is that with impervious surfaces that all means should be undertaken to
reduce water vapor transmission.
GEOTECH CONSULTANTS, INC.
Jeffrey Lewis
March 20, 2015
EXCAVATIONS AND SLOPES
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Excavation slopes should not exceed the limits specified in local, state, and national government safety
regulations. Temporary cuts to a depth of about 4 feet may be attempted vertically in unsaturated soil, if there are
no indications of slope instability. However, vertical cuts should not be made near property boundaries, or existing
utilities and structures. Based upon Washington Administrative Code (WAC) 296, Part N, the unsaturated, dense
native soil at the subject site would generally be classified as Type B. Therefore, temporary cut slopes greater
than 4 feet in height cannot be excavated at an inclination steeper than 1:1 (Horizontal:Vertical), extending
continuously between the top and the bottom of a cut.
The above recommended temporary slope inclination is based on the conditions exposed in our explorations, and
on what has been successful at other sites with similar soil conditions. It is possible that variations in soil and
groundwater conditions will require modifications to the inclination at which temporary slopes can stand.
Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of
foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet
weather. It is also important that surface water be directed away from temporary slope cuts. The cut slopes
should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that
sand and/or loose soil can cave suddenly and without warning. Excavation, foundation, and utility contractors
should be made especially aware of this potential danger. These recommendations may need to be modified if
the area near the potential cuts has been disturbed in the past by utility installation, or if settlement -sensitive
utilities are located nearby.
All permanent cuts into native soil should be inclined no steeper than 2:1 (H:V). Water should not be allowed to
flow uncontrolled over the top of any temporary or permanent slope. All permanently exposed slopes should be
seeded with an appropriate species of vegetation to reduce erosion and improve the stability of the surficial layer
of soil.
Any disturbance to the existing slope outside of the building limits may reduce the stability of the slope. Damage
to the existing vegetation and ground should be minimized, and any disturbed areas should be revegetated as
soon as possible. Soil from the excavation should not be placed on the slope, and this may require the off-site
disposal of any surplus soil.
GENERAL EARTHWORK AND STRUCTURAL FILL
All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other
deleterious material. It is important that existing foundations be removed before site development. The stripped
or removed materials should not be mixed with any materials to be used as structural fill, but they could be used in
non-structural areas, such as landscape beds.
Structural fill is defined as any fill, including utility backfill, placed under, or close to, a building, behind permanent
retaining or foundation walls, or in other areas where the underlying soil needs to support loads. All structural fill
should be placed in horizontal lifts with a moisture content at, or near, the optimum moisture content. The
optimum moisture content is that moisture content that results in the greatest compacted dry density. The
moisture content of fill is very important and must be closely controlled during the filling and compaction process.
The allowable thickness of the fill lift will depend on the material type selected, the compaction equipment used,
and the number of passes made to compact the lift. The loose lift thickness should not exceed 12 inches. We
recommend testing the fill as it is placed. If the fill is not sufficiently compacted, it can be recompacted before
another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. The
following table presents recommended relative compactions for structural fill:
GEOTECH CONSULTANTS, INC.
Jeffrey Lewis
March 20, 2015
Beneath footings, 95%
slabs or walkways
Filled slopes and 90%
behind retaining walls
Where: Minimum Relative Compaction is the ratio,
expressed in percentages, of the compacted dry density
to the maximum dry density, as determined in
accordance with ASTM Test Designation D 1557-91
(Modified Proctor).
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The General section should be reviewed for considerations related to the reuse of on-site soils. Structural fill that
will be placed in wet weather should consist of a coarse, granular soil with a silt or clay content of no more than 5
percent. The percentage of particles passing the No. 200 sieve should be measured from that portion of soil
passing the three -quarter -inch sieve.
ADDITIONAL SERVICES
In addition to reviewing the final plans, Geotech Consultants, Inc. should be retained to provide geotechnical
consultation, testing, and observation services during construction. This is to confirm that subsurface conditions
are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction
activities comply with the general intent of the recommendations presented in this report, and to provide
suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of
construction. However, our work would not include the supervision or direction of the actual work of the contractor
and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of
the contractor.
During the construction phase, we will provide geotechnical observation and testing services when requested by
you or your representatives. Please be aware that we can only document site work we actually observe. It is still
the responsibility of your contractor or on-site construction team to verify that our recommendations are being
followed, whether we are present at the site or not.
LIMITATIONS
The analyses, conclusions, and recommendations contained in this report are based on site conditions, as they
existed at the time of our site visit. If the subsurface conditions encountered during construction are significantly
different from those anticipated, we should be advised at once so that we can review these conditions and
reconsider our recommendations where necessary. Unanticipated soil conditions are commonly encountered on
construction sites. Such unexpected conditions frequently require making additional expenditures to attain a
properly constructed project.
The recommendations presented in this report are directed toward the protection of only the proposed additions
from damage due to slope movement. Predicting the future behavior of steep slopes and the potential effects of
development on their stability is an inexact and imperfect science that is currently based mostly on the past
behavior of slopes with similar characteristics. Landslides and soil movement can occur on steep slopes before,
during, or after the development of property. At additional cost, we can provide recommendations for reducing the
risk of future movement on the steep slopes, which could involve regrading the slopes or installing subsurface
drains or costly retaining structures. However, the owner must ultimately accept the possibility that some slope
movement could occur, resulting in possible loss of ground on the site or damage to the onsite facilities and
structures.
This report has been prepared for the exclusive use of Jeffrey Lewis, and his representatives for specific
application to this project and site. Our recommendations and conclusions are based on the site materials
observed and on previous experience with sites that have similar observed conditions. The conclusions and
recommendations are professional opinions derived in accordance with current standards of practice within the
limited scope of our services. No warranty is expressed or implied.
GEOTECH CONSULTANTS, INC.
Jeffery Lewis
March 20, 2015
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Page 8
We trust that this report meets your immediate needs for the proposed development. Please contact us if we can
be of further service.
Respectfully submitted,
James R Strange, Jr., P.E.
Associate
0
GEorECH CONSULTANTS, INC.
JHS: jhs