Attachment 8h Attachment 3 Drafe Site Development Analysis for Regular Meeting held Feb 09, 2021 12:00pm at Remote

8h Attachment 3 Drafe Site Development Analysis

Item No. 8h_attach3
Date of Meeting February 9, 2021

PORT OF SEATTLE
DRAFT
SITE DEVELOPMENT ANALYSIS FOR
The 17 Acre Sites
REPORT PREPARED BY
INNOVA ARCHITECTS INC.
December 30, 2016
PORT OF SEATTLE CONTRACT NUMBER: P-00318122 SERVICE DIRECTIVE 20
Published by:
ARCHITECTURE Paul B. McCormick P.E.
ENGINEERING
Connie E. Linden P.E.
PLANNING
Brian S. Ludwig LEED, AP

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TABLE OF CONTENTS
Report Sections Page
Executive Summary 3 - 5
Architectural Planning Narrative 6 - 7
Civil Site Concepts Narrative 8 - 15
Report Appendices
Appendix A Vicinity Map and Site Plan of Extent of 16 - 18
Development Limits
Appendix B Conceptual Architectural Site Plans (A1 - A4) 19 - 26
and Conceptual Civil Engineering Plans (C1 C3)
Appendix C Architectural Renderings 27 - 30
Appendix D City of Des Moines Zoning, Transportation & 31 - 254
Capital Improvement Plan (Excerpts)
Appendix E City of Des Moines Storm Water & Critical Areas 255 - 537
Appendix F Utilities (Storm, Sewer, Water) GIS and As-Builts 538 - 543
Appendix G City of Des Moines CIP 544 - 689
Appendix H SR-509 Land Use 690 - 724

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1. Executive Summary
Introduction
This report is a summary of our proposed development options for the 17 Acre sites owned by
the Port of Seattle, and located in the City of Des Moines. The site is located on 18th Avenue
South, north of the intersection with South 216th Street (see the Site Vicinity Map herein). The
purpose of this report is to provide the Port with the information needed to solicit and
negotiate contracts with private developers, in order to lease the land for development
purposes. Concept plans showing three development options for each of the sites are provided
and are as follows:
Distribution Center
Manufacturing Facilities
Small Business Incubator
Office Building (Multi-story)
Each of the four options list above considers site layout based on the partial acquisition of the
adjacent WSDOT property that is located to the east of the site. No matter which site plan
option is used, we expect that this site will be developed to take advantage of the need for
nearby air cargo facilities. This site will have access to Air Cargo Road, located to the north of
the site (via 28th Avenue South transitioning into 24th Avenue South) upon the completion of
connection 28th Avenue South from South 200th Street to South208th Street. Site costs run
higher than some other sites due to the costs or earthwork, walls and storm detention facilities,
but we believe the rental structure for this product in this location with close proximity to the
airport will justify the added costs.
Each of the options presented will result in a different building coverage on the site with
different development costs and incomes structure related to the developed property and
different potential for creating jobs. The civil site design is much the same for all options, so we
only provide a single cost estimate for the site development, regardless of which design option
is used. However, cost data is provided for all the options related to the cost of the buildings
placed on the site.
This work is being done in collaboration with Property Counselors, hired by the Port of Seattle.
The scope of the Property Counselors' work is to perform market analysis for each of our
proposed development options. They will then define lease rate structures for each of the
development options in order to compile a pro-forma for each option. The work of Property
Councilors combine with our work will provide the Port of Seattle with the necessary
information to successfully market and lease the subject property, and should put the Port of
Seattle in an informed position when negotiating contracts with private developers.
Each site and building layout option includes: a site plan, marketing renderings of the proposed
buildings, and civil engineering concept plan, and the detailed report. Our work also includes
construction and development cost information provided to the Port to aid in assessing the
value of the development and thereby the value of the land to be leased to developers.

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Background
INNOVA Architects was hired by the Port of Seattle indirectly through their contract with
Commercial Real Estate Solutions LLC. That contract issued to INNOVA is Service Directive 20.
INNOVA is well qualified to perform this scope of work because INNOVA's Principals and staff
have been engaged in the feasibility analysis, as well as complete engineering and architectural
design of similar industrial properties within the Puget Sound region for the last 26 years. We
have designed over two million square feet of industrial facility in the Puget Sound region over
the last 24 months alone, and during the last 26 years have designed more than 50 million
square feet of industrial facilities.
Disclaimer to Developers
Developers may use the information in this report to better understand the information
available relating to this site. We have attempted to formulate realistic site plans and realistic
civil engineering design concepts. We state the estimated cuts and fills for earthwork, size of
buildings that can be constructed and size of storm water vaults anticipated to be required. We
also show proposed water and sewer sizes and locations, and even provide proposed road
improvement concept plans. All of this is provided as a concept for the developer to understand
what may be possible in developing this site. And although this is provided based on our best
understanding of what is possible, the developer shall not base his proposal on any of these
plans or information in the report, without first verifying with the developers own team of
consultants, that the information is correct. The developer shall engage its own design team,
consultants or experts to research and develop the plans and concepts for which his pro-forma
is based on. The Port of Seattle shall not be liable in any way for any specific size of building
proposed, or volume of earthwork, or lengths and sizes of pipes or storm vaults. In summary,
what is provided is an opinion of what might be possible, but the developer may not rely on this,
but rather must verify through his own means all information that the developer believes
necessary in support of the developer's proposal to the Port. This disclaimer applies to both the
plans and this report.
Site Description
Following this summary is a vicinity map showing the location of the site. We have defined on
the Site Plan areas currently owned by the Port of Seattle, 682,120 sf (15.65 Acres) and areas to
be acquired from WS DOT. The Port of Seattle is currently in discussion to acquire an additional
180,471 sf (4.1 Acres) to the east of their current property boundary, which is currently owned
by Washington Department of Transportation. The development area limits for the 17 Acre Site
include the area to be acquired from WS DOT. The development area, which is also the gross
site area, for this site is 19.8 acres.
The 17 Acre site is located on South 216th Street between 20th Avenue South and 14th Avenue
South, as shown on the vicinity map on page 6 of this report. The site is located within the City
of Des Moines, will have access to Air Cargo Road via 28th once the city of SeaTac completes
the connection of 26th Ave South to 24th Ave South at 208th Street.

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Scope of Work
As part of our work we have gathered and review information on: zoning, municipal code,
critical and sensitive areas mapping; Port and City inter-local agreement; adjoining roads,
including roadway classification and template requirements, planned vacations, recent
improvements, and City planned area transportation and capital improvement projects; utilities
GIS and as-built data; utilities capacity data (as available); and, other pertinent information
provided to us by the City and utility districts. We have contacted City of Des Moines planning
and engineering staff, and worked with the water, sewer, power, and gas purveyors. We have
attempted to gather the same level of information as we would need had we been a consultant
for a developer in preparation to proceed with full design of this project.
We understand the power available, the fire flow available, and the sewer elevations needed to
ensure they work with the finish floor elevations shown. We have researched what available
wetland information exists. Based on all available information, we have provided site plans we
believe can be developed, and which will prove to be a financially viable project.
We have set finished floor elevations, calculated cuts and fills, made sure sewer elevations will
be adequate for the proposed development, and calculated locations and height of all required
site retaining walls. We have spoken with city engineers to understand issues related to the
storm water, and have estimated storm water storage needed and used a combination of open
ponds where possible, and underground vaults where required. We have chosen to use
underground storm water vaults in order to achieve a higher level of building coverage on the
site. Any combination of pond and vault could be explored, but we have biased our design
concepts toward maximizing building coverage.
This report is organized as shown on the following:
Executive Summary
Architectural Narrative
Site Civil Narrative
Appendix A Vicinity Map and Site Plan of Development Limits
Appendix B Conceptual Architectural Site Plans and Civil Engineering Plans
Appendix C Architectural Renderings
Appendix D City of Des Moines Zoning, Transportation & Capital Improvement Plan
Appendix E Port of Seattle-City of SeaTac Inter-local Agreement (Excerpts)
Appendix F City of SeaTac Watershed Basin Report (Excerpts and Mapping); Port NPDES
(Excerpts); City Flow Control and Water Quality Mapping; and ESA Wetland Reconnaissance
Memo
Appendix G Utilities (Storm, Sewer, Water) GIS and As-builts
Appendix H Sanitary Sewer Pump Station As-builts
Appendix I Existing Conditions Topography & Site Drainage Basins/Existing Conditions Photos
Appendix J Site Earthwork Quantity Exhibits
Appendix K Redevelopment Cost Opinion
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2. Architectural Planning
Below is a summary of the zoning and site plan options proposed in this report.
a. Zoning
i. B-P (Business Park), this is the City's future comprehensive zoning.
Allowed uses Distribution Center, Professional and Business Offices
Of note, current zoning is R-SE (Residential Suburban Estate) but is planned to be
rezoned to B-P by the City by means of Comprehensive Plan adoption in 2017.
ii. Parking Requirements
Shown on site plans
b. Distribution Center Development Option See Attached Site Plan Sheet A1.
i. Building Access
Site access is via South 216th Street, which is a two-lane local access roadway. The
driveway can be accessed from either the east or west.
ii. Buildings
The distribution building is 291,800 SF, single-loaded truck dock.
iii. Building Width
Single loaded building. 300 feet wide.
iv. Developer/End User Profile The distribution center building type is, in our opinion,
the most marketable of the three options proposed in the current marketplace. There
has been an upswing in this (distribution) market. Developers who build speculative
spaces are prevalent and looking for more land to develop.
v. Site Development Reference civil plans Sheets C1.

c. Manufacturing Facility Option See Attached Site Plan Sheet A2.
Manufacturing Facility Option:
i. Buildings Access
Site access is via South 216th Street, which is a two-lane local access roadway. The
driveway can be accessed from either the east or west.
ii. Buildings Two manufacturing buildings
Building A 145,730 SF, single-loaded truck dock.

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Building B 149,180 SF, single-loaded truck dock.
iii. Building Width
Building A Single loaded building 385 feet wide.
Building B Single loaded building 400 feet wide.
vi. Site Development Reference civil plans Sheets C2.

d. Small Business Incubator Option See Attached Site Plan Sheet A3.
i. Buildings Access
Site access is via South 216th Street, which is a two-lane local access roadway. The
driveway can be accessed from either the east or west.
iii. Buildings
Building A 54,000 SF, with at grade truck docks
Building B 65,475 SF, with at grade truck docks
Building C 65,475 SF, with at grade truck docks
Building D 66,825 SF, with at grade truck docks
iv. Building Width
Buildings A, B, C and D: 135- feet wide
v. Developer/End User Profile This development option provides the least building
coverage on the site; however, it has the potential to offer the most jobs of the three
options and provides the highest rents.
vi. Site Development Reference civil plans Sheet C3.
e. Small Multi-Story Office Option See Attached Site Plan Sheet A4.
ii. Buildings Access
Site access is via South 216th Street, which is a two-lane local access roadway. The
driveway can be accessed from either the east or west.
vii. Building
Building A 60,500 SF footprint, 5- stories proposed.
viii. Developer/End User Profile This development option provides for a corporate office
campus and a significant building lease area. It has the potential to offer the most jobs
of all options and provides the highest rents.

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3. Civil Site Concepts
Below is the narrative for site and civil engineering issues organized by categories for easy
reference.
a. Critical Areas
i. Wetlands
Onsite Wetlands: The site was reviewed for the presents of wetland indicators by
Environmental Science Associates (ESA). ESA concluded that there are three wetlands,
labeled B2-1, B2-2 and B2-3, located within the construction boundaries. Wetland B2-
1 and B2-2 are preexisting wetlands that were previously identified on the site map.
These two wetlands have not grown in size and according the ESA report Wetland B2-
2 appears to have gotten smaller in size. The third wetland, B2-3, is similar in size to
the two predetermined wetlands. The three wetlands are described as forested and
depressional. A memorandum summarizing ESA's findings is provided in Appendix C
Mitigation Credit Program: King County offers this program as an option for projects
that result in unavoidable impacts to wetlands, rivers, streams or buffers. Included in
Appendix X is the "Using Credits from In-Lieu Fee Program" which details the
procedure to receive credits for alternate mitigation for the wetlands located on this
site.
Offsite Wetlands: From the review done by ESA, they concluded that there are two
wetlands located off site to the west.
ii. Development on a Hillside
The City of Des Moines municipal code defines a hillside with a slope of 15 percent or
greater a critical area. The city's municipal code, Chapter 16.10.220 (Hillside of 15
percent slope and greater Development standards Disturbance limitation) restricts
the maximum slope disturbance allowed on a development site. For slopes up to 15
percent there are no restrictions, for slopes from 15 25 percent, the percentage of
the slope that may be disturbed is reduced to 60 percent, for slopes 25 40 percent
the disturbed area is reduced to 45 percent and for slopes over 40 percent only 30
percent of the slope may be disturbed. For a combination for slope categories there is
a formula to be used that can be found within this section of the city code.
b. Grading
i. Existing Conditions
The site is vacant has remained undeveloped, it is current covered with prairie
grasses, brush and deciduous and conifer trees. See Appendix F for an existing
conditions map that shows topographic and utilities data. The site is fronted by
South 216th Street along the southern boundary, property currently owned by WS

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DOT along the northern and eastern boundary and residential property along the
western boundary.
The rectangular-shaped property slopes from the east to the west from a high
elevation of 276-feet to a low elevation of approximately 192-feet. Slopes range
across the site. In the western portion of the site slopes range from approximately
10- to 20-percent. Slopes in the eastern portion of the site range from gentle slopes
of approximately 3-percent to 10-percent. There are steep slopes 40-percent and
steeper located around the wetlands located along the western property line.
The development area has been kept to the east side of the property boundary. This
will allow for the least amount of grading required. Slopes greater than 25 percent
are generally only on the west side of the site around the wetlands. Conceptual
development plans included in this report show development near these steep
slopes. Keeping the development area away from the steeper slopes will limit the
disturbance on the wetlands and reduce the credits received from the Mitigation
Reserve Program.
A geotechnical study and slope assessment and analysis have not been conducted
and are outside the scope of this report. The developer is responsible for preparing
proposed development plans and providing any special studies, including
geotechnical assessments and studies, required by the City of Des Moines or other
jurisdictions having approval authority.

ii. Proposed Concept Design
There are three conceptual development options proposed for the 17 Acre site:
o Distribution Center
o Manufacturing Facility
o Small Business Incubator
Earthwork - Factors guiding conceptual site layout and grading design are:
o Maximizing building square footages
o Balancing to extent possible site cut and fill quantities
o Minimizing site retaining walls
o Minimizing site-work construction costs
Preliminary earthwork quantities were estimated for each of the development
options. Color-coded figures showing extent of cuts and fills is provided in Appendix
G. Estimated quantities are based on the conceptual design for the Distribution
Center, Manufacturing Facility, and Small Business Incubator developments. The
conceptual development options show a net export of approximately 3,700 cubic
yards for the Manufacturing Facility, 9,900 cubic yards of import for the Small
Business Incubator and 8,600 cubic yards of import for the Distribution Center. Final
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design by the developer will further refine earthwork quantities and may reduce cut
(export) and fill (import) quantities. Also, estimated earthwork quantities were
based on the conceptual layouts shown and GIS data obtained from King County.
Actual earthwork quantities may vary considerably depending on site layout and
actual site survey data; and therefore, earthwork quantities shall be determined by
each developer. Each developer shall perform their own analysis to determine
earthwork quantities for their project.
c. Site Walls
i. Existing Conditions
There is a rockery retaining wall along the edge of the shoulder on the north side of
South 216th Street. It is approximately 220 feet in length and has a maximum height
of about 6 feet at the southwest corner of the project site, which is where the rockery
wall ends.
ii. Proposed Design
Estimated wall heights are shown on the conceptual civil plans, sheets C1 C3, for
each of the three options (Distribution Center, Manufacturing Facility, and Small
Business Incubator). Site walls are anticipated to range from 2-feet to 20-feet, as
shown on the conceptual civil plans. Wall heights shown on the conceptual plans are
based on building site options shown. Each developer shall design the site to
determine the wall heights necessary for their own proposed designs.
d. Storm Design
i. Existing Site Conditions
The 17 Acre site is located within the City of Des Moines and drains into the Des
Moines Creek Basin. The Des Moines Creek Basin is approximately 3.5 miles long and
encompasses over 30 acres of wetlands. It is the largest stream flowing through the
city and flows from a high elevation of 350 to sea level where it meets the Puget
Sound at Des Moines Creek Beach Park. The drainage systems serving the 17 Acre site
will be reviewed by the City of Des Moines.

ii. Proposed Description
City of Des Moines follows the King County Surface Water Design Manual
Agency Reviews The site will drain off site through a 24-inch pipe within South 216th
Street, this drainage system flows into the Des Moines Creek Basin and ultimately in
the Puget Sound. This storm system will require the review/approval from the City of
Des Moines and the Corp of Engineers.
City of Des Moines design standards:

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o King County Surface Water Design Manual (KCSWDM) (2009 Edition)
The City of Des Moines has established in their municipal code (16.10.350
Surface Water Design Manual) to adopt the King County Surface Water Design
Manual,2009 Edition, including all subsequent revisions as the Surface Water
Design Manual for the City of Des Moines, as part of the City of Des Moines
Stormwater Management Program, updated March 2016.
o Des Moines Street Development Standards
o Washington State Department of Transportation Standard Specification for Road,
Bridge, and Municipal Construction

Proposed Storm Water Facilities
This site drains to the Des Moines Creek Basin therefore; this site would need to
meet City storm water standards, the KCSWDM 2009 edition. Flow control standards
that are to be met are Conservation Flow Control, Level 2; and, water quality
standards that are to be met are Enhanced Water Quality. In addition, Core
Requirement #9 of the KCSWDM 2016 edition would also apply. As noted above, this
core requirement calls for flow control BMPs, such as infiltration, dispersion and
application of low-impact design to the extent feasible. The developer will likely be
required by the City to provide flow control BMPs, or, show that these BMP (e.g.
onsite infiltration, dispersion, low-impact features) are not feasible. Since USGS
mapping shows those areas soils are till, which are not favorable for infiltration, the
conceptual plans show detention vaults and ponds for flow control and modular
wetlands for enhanced treatment. However, it is responsibility of the developer to
fully determine the appropriate flow control and water quality facilities necessary to
meet City standards, and whether flow control BMPs are feasible.
The approximately 8.5 acre area north of South 150th Street is shown on the
conceptual plans discharging to the existing 12-inch pipe that crosses 24th Avenue
South to the NEPL site. This 12-inch pipe is located within the City of SeaTac's rightof-way.
Although this area drains to the NEPL Pond, drainage from this area would
be conveyed through a storm pipe within the City's right-of-way and maintained by
the City. City staff indicated in preliminary discussions that the L-Shaped site is to
comply with KCSWDM 2016 edition standards and the City's Addendum. The
developer is fully responsible for determining, through coordinating with the Port
and City, applicable design standards that must be followed to meet Port and City
requirements.
e. Water
i. Existing Condition
The water district serving the 17 Acre sites is Highline Water District. There is an 18
inch cast iron main that runs along S. 216th Street. There is also an 8 inch ductile iron

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pipe that runs the western border of the site boundary which is fed from the 18 inch
main in S. 216th Street.
Available Fire Flow Highline Water District provided estimated pressure for the 18-
inch cast iron main in S 216th Street. The District indicated that the main is near a high
elevation point of their system and therefore, lower in available pressure. Also, the
District did not have flow data for the system. Therefore, flow testing is needed to
determine actual flows available to the site. District also indicated that applicant
(developer) must submit a "Water Availability" application and arrange for testing.
o Southwest corner of the 17 Acre site
Static Pressure: 119 psi
o S. 216th Street @ 18th Ave. S
Static Pressure: 93 psi
o S. 216th Street @ 20th Ave. S
Static Pressure: 82 psi
ii. Proposed Design
Site Fire Protection - The fire flow anticipated to be required for site development,
considering Type 5B construction, is 4,000 GPM (2015 International Fire Code). This
anticipated flow, 4,000 GPM, is based on taking into account a 50-percent reduction
for buildings equipped with an automatic sprinkler system. With the pressures
provided by the Highline Water District in an 18 inch cast iron main, it is assumed that
there will be sufficient flow for fire protection; however this will need to be confirmed
by the jurisdictional Fire Marshal once development design is confirmed. It is
recommended that the developer contact the District to arrange for fire flow testing
to confirm actual available flow and to determine fire system design requirements to
attain needed pressure/flow. Interior water-main loop shown on the conceptual plans
for the 17 Acre site is an 8-inch loop, connecting to S 216th Street.
Domestic Service - Domestic meter sizing will depend on demand for each of the
development options. Irrigation meters will also need to be provided with backflow
prevention.
f. Sewer
i. Existing Condition
The sewer district serving the 17 Acre site is Midway Sewer District. An 8-inch sanitary
sewer main is located for connection north of the site location. Before 18th Ave. S was
vacated a sewer manhole was installed at what was going to be the intersection of
18th Ave. S and S 212th Street. This manhole has sufficient depth to allow connection
to the site.

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ii. Proposed Design
The conceptual plans show connecting to the manhole that was to be located at the
intersection of 18th Ave. S and S 212th Street. Midway Sewer District was contacted
and confirms the availability to connect to their system at this location.
g. Gas
Gas is available to the 17 Acre sites along South 216th Street. Puget Sound Energy
(PSE), the gas purveyor, could not provide capacity data at this time, and indicated
that a "Customer Service Information Sheet" would be required to confirm capacity.
h. Power/Cable/Fiber
i. Existing Condition
The purveyor for power is Puget Sound Energy (PSE). Overhead power is available on S.
216th Street. Puget Sound Energy indicated that a power application, "Customer
Service Information Sheet" indicating power needs before power capacity can be
confirmed.
Communication lines and cable lines are located on existing power poles in 24th
Avenue South and on South 152nd Street. The purveyor is Comcast for cable and
Century Link for com lines.
ii. Proposed Design
It is anticipated that power for the 17 Acre site will be served from S 216th Street. As
mentioned in the "Existing Condition" section above, Puget Sound Energy could not
provide power capacity data, and indicated that a "Customer Service Information
Sheet", which is to include power requirements and a site map, would be required to
begin a power assessment and determine if additional feeders would be needed to
serve the sites.
Cable and fiber capacity and availability will need to be confirmed with Comcast and
Century Link. As indicated in the paragraph above, conduit will need to be routed onto
the sites to serve building facilities. In addition, the overhead lines on S 216th Street
may need to be underground since line height on the existing poles may not provide
needed vertical clearance for semi-trucks.
i. Dedications/Easements/Vacations
i. Right-of-Way (ROW) Dedications
The City of Des Moines has approved of a project to improve the South 216th Street and
24th Avenue South rights-of-way. This project is to be known as the Transportation
Gateway Project. South 216th Street from 24th Avenue South to 18th Avenue South is
to be widened to a five lane arterial with a middle turn lane. The city has waived the
requirement of a twenty (20) foot wide Type I landscaping strip including a five (5) foot
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tall earthen berm adjacent to South 24th Avenue South and South 216th Street, in lieu
the required landscaping shall be a ten (10) foot wide Type II landscaping striped as
defined by DMMC 18.195.390. It is assumed that these design standards will continue to
the west to the edge of the project boundary. The project site currently is fronted with a
rockery retaining wall with a maximum height of approximate height of 6 feet. It is the
cities intent to negotiate with the Port of Seattle to remove the retaining wall with this
portion of South 216th Street is widened and grade towards the site rather than
replacing the retaining wall. This will require a Right-of-Way dedication to the City of
Des Moines to include a slope easement.
ii. Easements
15-foot wide easements conveyed to Highline Water District will be required for the
interior 8-inch water main loops through the 17 Acre sites.
j. Assumptions/Exclusions/Unknowns & Risks
i. Further Wetland Studies
A full wetland study and assessment will be required for the 17 Acre sites to confirm
that the wetlands that exist on the sites are categorized correctly.
ii. Property Boundary
Alta Survey - An Alta Survey has not been conducted at this time, and will be required
to confirm the actual boundary of the property, as well as to confirm any dedications,
slope easements, and utilities easements.
Topography A topographic survey has not been conducted for the 17 Acre sites. GIS
data was used for the preparation of conceptual designs. Therefore, a topographic
survey and utilities locates will need to be conducted/obtained by the developer for
use in their design.

iii. Geotechnical Considerations
A geotechnical investigation/study has not been conducted for the 17 Acre Site.
Geotechnical investigation/study will need to be done by the developer to confirm site
soil conditions for site and building development. USGS mapping show area soils as till.
Infiltration testing will also be required by the City of Des Moines to confirm feasibility
of low-impact design features, including onsite infiltration.

Ravine sidewalls and bluffs The City of Des Moines defines a ravine as "a steep slope
which abuts and rises from the valley floor" the ravine will also "contain slopes
predominantly in excess of 40 percent the top of a ravine sidewall is typically a
distinct line where the slope abruptly levels out", Chapter 16.01.050 Definitions. The
Des Moines municipal code, 16.10.210 Ravine sidewalls and bluffs Development
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standards, requires a 50-foot undisturbed buffer from the top, toe and sides of all
ravines sidewalls. The municipality will allow a reduction to the buffer to a minimum
of 10-feet when a special environmental study is done by a licensed engineer
specializing in geotechnical analysis of a licensed engineering geologist.

Hillsides of 15 percent slope and greater Before site design and grade is done for the
17 Acre site a number of limitations will need to be taken into consideration. Chapter
16.10.220 Hillsides of 15 percent slope and greater is to be used to determine the area
of usable land for the site. This chapter also provided guidance for landscape and
shrub requirements.

iv. Storm-water Requirements
Per discussions with the City of SeaTac City Engineer and Storm Assets Management
Coordinator, there has not been any drainage or flooding complaints relating to the
storm conveyance system within the immediate area of the site. The City adopted the
2016 edition of the KCSWDM on January 1, 2017. Considering the 2016 edition of the
SCSWDM, City flow control mapping (see Appendix C) shows that the site is located in
a Conservation Flow Control Area. Properties located in this area designation typically
must meet Level 2 Flow Control requirements of the King County SCSWDM, which
state that developed discharge from a site must meet pre-developed durations from
50-percent of the 2-year peak flow up to the full 50-year peak flow. Pre-developed site
conditions or land cover is to be considered as "historic" conditions, or typically
forested. In addition, peak discharge rates from the developed site must meet predeveloped
peak discharge rates for the 2- and 10- year return periods. Water quality
level that will be required to protect downstream sensitive areas is enhanced water
quality facilities.
Since the southern leg of the 24th Avenue South conveyance system out-lets to the
SR-518 right-of-way, drainage systems for the L-Shaped site connected to this
conveyance line will be required to also meet WSDOT storm water standards, as
indicated in the storm water section of this report.
See the storm water section of this report for discussion on the storm water
requirements for the NEPL site.

INNOVA Architects Inc. 950 Pacific Avenue, Suite 450, Tacoma, WA 98402 (253) 572-4903 Page 15

Appendix A
Vicinity Map
And
Site Plan of Extent of Development Limits

INNOVA Architects Inc. 950 Pacific Avenue, Suite 450, Tacoma, WA 98402 (253) 572-4903 Page 16

Appendix B
Conceptual Architectural Site Plans
And
Conceptual Civil Engineering Plans