CORRECTED COPY October 24, 2016 
COMMISSION AGENDA  Action Item No. 6c 
Meeting Date: October 25, 2016 
Flight Corridor Safety Program  Phase I 
ATTACHMENT A 
Environmental Overview  Phase I 
The Port of Seattle issued a Mitigated Determination of Non-Significance (MDNS) as the State
Environmental Policy Act (SEPA) determination on July 15, 2016 and was followed by a two
week public comment period. During the public comment period, four comments were
received through the SEPA process, one from the Department of Ecology, one from the City of
SeaTac, and two from private residents. The Port of Seattle (Port) issued a final MDNS on
August 26, 2016. The City for SeaTac appealed the Port's issuance of MDNS on September 15,
2016. The Port and the City are currently discussing the City's concerns. 
Environmental review under SEPA for the Flight Corridor Safety Program was supported by a
comprehensive series of assessments and planning efforts consisting of: 
Conceptual Plan; 
Phase 1 Critical Areas Special Study; and 
Phase 1 Implementation Plan. 
Each of these supporting planning efforts is described below. 
Conceptual Plan 
Conceptual planning was initiated in the fall of 2015 with the goal of identifying and comparing
alternatives for removing existing obstructions at STIA, both on and off Port-owned properties,
and to recommend an approach to obstruction removal. A Conceptual Plan was developed that
provides the background and guiding objectives for the flight corridor safety program. It also
summarizes the existing site conditions and how these conditions affect obstruction removal
strategies. This Conceptual Plan provides the basis for communication with local jurisdictions 
and WSDOT concerning the planning, environmental review, and permitting that may be
necessary during implementation. 
In 2014 the Port conducted a LiDAR (Light Detection and Ranging) aerial survey to identify the
locations of obstructions around the airport.  LiDAR studies identify the locations of
obstructions, but do not identify the specific number of objects that make up the obstruction
on the LiDAR image. The 2014 LiDAR study identified 1600 obstructions, and the subsequent
Conceptual Plan provided a further assessment to identify obstruction location based on land
ownership (i.e., Port, other public properties, private, and commercial). While most of the

COMMISSION AGENDA  Action Item No. 6c                      Page 2 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A 
obstructions have been identified as trees, the height, health, species, number of trees per
obstruction, and associated land use vary by site.  Site characteristics were defined for
obstructions located on Port-owned, WSDOT, and other public properties.
Utilizing general site condition information, the Conceptual Plan identified and assessed the
suitability of methods for obstruction removal, material processing and disposal, site treatment
(to minimize future obstructions and stabilize the site), and monitoring. The methods are also
evaluated against the guiding principles of the flight corridor safety program as they relate to
FAA policies, Port policies, and overall cost. Methods considered included: 
Clearing, tree removal in congested area (hand work); 
Clearing, tree removal without stump removal; 
Selective clearing, grubbing, and grading; 
Clearing, grubbing, and grading; 
Topping trees; 
Leave material on site with little or no processing; 
Process material for use on site (wood chips, restoration features); 
Process material for Port use off site (wood chips, lumber, restoration features); 
Salvage understory plant materials and replant following obstruction removal; 
Dispose off-site (no reuse conditions); 
Engage materials exchange network for beneficial reuse by other parties; 
Revegetate site with shrubs and groundcovers; 
Revegetate site using low growing trees, shrubs, and groundcovers; and 
Erosion control best management practices (geotextiles, armoring slopes). 
Based on the information available at that time and range of alternatives, the following steps to
implementing the obstruction removal plan were recommended. 
Confirm existing conditions (including actual tree surveys) at each obstruction removal
site through ongoing field work; 
Confirm degree of intrusion for each obstruction removal site; 
Identify preferred removal method for each site; 
Develop grouping of sites for bid packages that prioritizes removal; 
Coordinate with local jurisdictions and regulatory agencies; and 
Complete obstruction removals. 
The Conceptual Plan will be updated for Phases 2 and 3 based on the results of Phase 1 work.

COMMISSION AGENDA  Action Item No. 6c                      Page 3 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A 
Critical Areas Special Study  Phase 1 
A Critical Areas Special Study was completed in April 2016 based on the prioritized actions
recommended in the Conceptual Plan. The Critical Areas Special Study identifies and assesses
regulated critical areas (i.e. wetlands, wetland buffers, stream buffers, and steep slopes) on
sites owned by the Port of Seattle within the City of SeaTac (critical areas were not identified
within the cities of Burien and Des Moines for Phase 1) that are proposed for tree and
vegetation removal performed pursuant to the Seattle-Tacoma International Airport's Flight
Corridor Safety Program. Identified critical areas include wetlands, streams, and steep slopes.
The Study provides identification and characterization, including functional assessments and/or
ratings and supporting documentation, for wetlands, streams, and associated buffers found
within the obstruction management sites. The Study also provides a geotechnical evaluation
assessing stability of identified steep slopes. 
The Critical Areas Special Study reviewed current wetland and stream delineation reports
consistent with current regulations and other information including SeaTac Municipal Code
(SMC), SeaTac Critical Areas Maps, National Wetland Inventory Map, King County Soil Survey
Map, and King County Critical Areas Maps. The Study identified three SMC-regulated
environmentally critical areas including wetlands, streams, and steep slopes. 
Critical areas identified on obstruction management sites on Port property within the city of
SeaTac are summarized in Table 1. 
Table 1: Critical Areas on Obstruction Management Sites Located on Port-Owned
Properties 
Wetlands 
Site          Wetland    Wetland Size (acres)  City of SeaTac Buffer Width 
P-1            3            0.48                  35 
P-2            39           1.73                  35 
P-2           44a           3.01                  50 
P-3a           28          29.64                100 
P-3a         IWS a-b         1.09                 50 
P-3b          52b          0.80                 35 
P-3b          G4          0.03                 35 
P-3b          G12          0.46                 50 
Streams 
P-3b          NA           NA                 50 
Steep Slopes 
P-1, P-2, P-3a, P-3b, P-5     NA            NA                   50

COMMISSION AGENDA  Action Item No. 6c                      Page 4 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A 
In order to protect these critical areas, impact minimization and mitigation measures were
identified. Key minimization measures identified included but were not limited to the
following: 
Perform manual tree removal within critical areas; 
Protect existing native shrubs and groundcovers during tree removal to extent practical; 
Leave stumps and roots in place on steep slopes; 
Remove invasive species in obstruction removal areas; 
Replant vegetation during dormant season (October through March); 
Replant sites with a mixture of native vegetation made up of low-growing trees and
shrubs; 
Implement a Spill, Prevention, Control, and Countermeasure Plan; 
Implement and maintain temporary erosion and sediment control BMPs; and 
Properly maintain construction equipment and vehicles to prevent them from leaking
fuel or lubricants. 
Tree replacement and revegetation measures to offset obstruction removal were identified
included the following: 
Sites will be replanted with a mixture of native vegetation made up of low-growing trees
and shrubs. 
The vegetation mix will be designed to provide the same function as the removed trees,
but will not grow to a size that could constitute a future obstruction.
Minimum tree replacement ratios to offset impacts to critical area habitat were
identified in accordance with SMC as follows: 
o  1:1 for steep slopes 
o  1:1 for Class III wetland and wetland buffer and Class 2 stream buffer ("no net
loss") 
o  2:1 for Class I and Class II wetland and wetland buffer 
A critical areas special study will be conducted for Phases 2 and 3.
Implementation Plan  Phase 1 
Following the identification of obstructions using LiDAR technology, the number of individual
trees comprising the detected obstructions was completed in 2015 through ground-truthing.
The field reconnaissance also characterized the obstructions by species type and size (stem
diameter and estimated height). On Port sites, the reconnaissance also identified future
obstructions (i.e. objects that were like to become obstructions within 5 years), and where

COMMISSION AGENDA  Action Item No. 6c                      Page 5 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A 
applicable, quantified the understory trees that would be removed or impacted during removal
activities. Overall the process has identified 1,167 trees on Port-owned properties for removal.
Using this quantified obstruction data as well as other site characterization information and
methodology contained in the Conceptual Plan and Critical Areas Special Study, an
Implementation Plan was completed in April 2016. This plan includes a characterization of
obstructions and potential obstructions; a discussion of obstruction management methods; site
plans that describe how these methods should be applied to these various Port, public, and
private sites; cost estimates that can be used for budget planning; and a detailed schedule for
implementing the Flight Corridor Safety Program (Program). 
Table 2 provides a summary of existing and potential obstructions for different types of
property ownership within three local jurisdictions as identified in the Implementation Plan.
The presence of critical areas (wetlands, wetland buffers, stream buffers, and steep slopes) in
proximity to obstructions is also identified. Although the Implementation Plan was developed
for Phase I, the plan did report number of obstructions on other publicly owned properties and
private properties.
Detailed obstruction removal and revegetation plans were developed for sites located on Portowned
property and other publically-owned property as a guide for the preparation of contract
documents. Obstruction characterization and removal methods were also discussed for
obstructions located on private properties, however the Implementation Plan recognized the
need to for land owner input particularly with respect to revegetation preference and final site
treatment. 
Site plans for each site included a site description including identification of critical areas on or
adjacent the site, obstruction summary, access and staging information, site-specific
obstruction removal and material disposal descriptions, revegetation plans, and monitoring
requirements. Much of the plan details are summarized in a series of maps provided for each
site. As an example, illustrated plan details for Site P-1 is provided in Figure 1 through 5 below.
Final Vegetation Replanting Plan 
In accordance with the Implementation Plan, site revegetation plans were initially developed on a
minimum of 1:1 in non-critical areas and 2:1 tree replacement ratios for tree replanting in critical areas.
In addition to the minimum tree replacement requirement, the Port included a site revegetation
objective to restore native forest or shrub communities.. Designed tree density (~280/acre) and shrub
densities (~1700/acres) are based on past mitigation design and outcomes. The designed tree density
well exceeds minimum tree replacement ratio requirements in order to: 
ensure dense native forest and shrub communities establish, including partially offsetting
anticipated planting mortality,

COMMISSION AGENDA  Action Item No. 6c                      Page 6 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A 
increase site habitat structure and ecological function, 
and prevent future obstructions from re-establishing. 
As a result the current design documents have a tree replacement ratio of approximately 4 to 1.

COMMISSION AGENDA  Action Item No. 6c                                            Page 7 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A 
Table 2:   Obstruction Removal Summary by Location 
Obstruction Removal                         Understory
Jurisdiction                Existing       Potential       Total       Obstructions Within Sensitive Areas         Tree      Total Trees 
Property Ownership 
Obstructions1   Obstructions2   Obstructions    Existing     Potential      Total3     Removal    Removed 
City of SeaTac 
Port (Phase 1)              362           478          840         149         238         387         327        1,167 
WSDOT             484        119       603       0        0        0       6214      1,224 
Public                    87            41           128          4          11          15          0          128 
Residential                46            22           68           0          0          0           0          68 
Commercial/Religious        22           22          44          2          5          7          0         44 
Subtotal                1,001         682         1,683                            409        948        2,631 
City of Burien 
Public                    6             0            6           0           0           0           0           6 
Residential                58            14           72           0          0          0           0          72 
Commercial              0           0          0         0         0         0         0         0 
Subtotal                 64           14          78                              0          0         78 
City of Des Moines 
Public                    0             0            0           0           0           0           0           0 
Residential                16            22           38           1          1          2           0          38 
Commercial              0           0          0         0         0         0         0         0 
Subtotal                 16           22          38                              2          0         38 
Total      1,081          718         1,799                              411         948        2,747 
Notes: 
1. Existing obstructions are trees that are currently within the navigable airspace for STIA. 
2. Potential obstructions are trees that are predicted to enter the navigable airspace within 5 years. 
3. Totals are adjusted to reflect the actual number of tree obstructions within sensitive areas, and remove double counting (e.g., individual trees that
are within both steep slope and wetland buffer areas). 
4. Estimated understory quantity is preliminary and subject to change (derived from aerial photograph analysis)

COMMISSION AGENDA  Action Item No. 6c                       Page 8 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A 







Figure 1 
Site P-1 Overview Diagram 








Figure 2 
Site P-1 Representative Site Photographs

COMMISSION AGENDA  Action Item No. 6c                                             Page 9 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A

COMMISSION AGENDA  Action Item No. 6c                                             Page 10 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A

COMMISSION AGENDA  Action Item No. 6c                                             Page 11 of 11 
Meeting Date: October 25, 2016 
ATTACHMENT A