COMMISSION 
AGENDA MEMORANDUM                Item No.       7a 
BRIEFING ITEM                   Date of Meeting      July 25, 2017 
DATE:    June 21, 2017 
TO:     Dave Soike, Interim Chief Executive Officer 
FROM:   Michael Ehl, Director, Airport Operations 
Wayne Grotheer, Director, Aviation Project Management Group 
Clare Gallagher, Director, Capital Project Delivery/Public Affairs 
SUBJECT:  Flight Corridor Safety Program  Sites P-4 and P-5 Briefing 
EXECUTIVE SUMMARY 
This project is part of a multi-year program approved in November, 2016 by Commission to
manage obstructions consisting of trees and other vegetation at and around Seattle-Tacoma
International Airport, and replanting lower-height vegetation on or near the removal sites.
Phase 1 work, the removal and replanting of obstructions on Port property, is partially 
complete. Work in two sites (P-4 and P-5) along South 200th Street has been deferred at the
request of the Commission to allow for additional public input and for Port staff to further
evaluate the removal and replanting approach for these sites based upon the input received.
Port staff held a public workshop on June 5, 2017, created an online open house
http://seasafecorridor.infocommunity.org/, responded to correspondence, and held meetings
with individual members of the community when requested. Based on the public's input, Port
staff has revised the approach so that the obstruction removal of sites P-4 and P-5 occurs in a
phased manner by limiting the removal to only removing the existing obstructions and
protecting the potential obstructions and understory vegetation to the degree possible. The
revised replanting approach includes planting lower-growing conifers and other trees within P-4
and P-5, increasing the size of trees and density for buffer areas, and adding a replant area to
the south of Sites P-4 and P-5 where tall-growing conifers can grow without risk of becoming
future obstructions.
This briefing details the progress made over the last quarter on developing a revised approach 
for Areas P-4 and P-5. 
Alternatives Development 
To identify alternatives, Port staff executed a service directive with CH2M Hill (Consultant) to
provide up to twelve removal and replanting alternatives for sites P-4 and P-5.  These
alternatives were developed with both qualitative (site observation and public comments) and
quantitative (number of obstructions and disturbed areas) considerations.  The summary
evaluations included an analysis of the removal alternatives, phasing, obstruction quantities,
planting options for trees and shrubs, and invasive species treatment.

Template revised September 22, 2016.

COMMISSION AGENDA  Briefing Item No. __7a__                    Page 2 of 4 
Meeting Date: July 25, 2017 

Port staff comprised of Aviation Operations, Aviation Project Management Group, Public
Affairs, Environmental  and Construction Management conducted an internal alternative
selection workshop to review the twelve proposed alternatives. The alternatives were assessed
and weighed against a combination of public interest and Port objectives. Four removal
alternatives and three replanting alternatives were selected from the initial twelve.
Alternatives eliminated from further consideration included those relying upon tree topping
and lighting to mitigate the obstructions. Tree topping alternatives were not considered
further as this action would create raptor nesting habitat and thereby increase wildlife hazard
to aircraft. Alternatives relying upon lighting obstructions were eliminated due to the number
of obstructions that would need to be addressed, the impact to airport operations and Federal
Aviation Administration guidance regarding vegetation and obstructions. 
The remaining following four removal alternatives were considered feasible for both sites P-4
and P-5: 
(1) Removal of existing obstructions (trees currently penetrating the Flight Safety
Corridor), potential obstructions (trees within 6' of penetrating the Flight Safety
Corridor) and all understory vegetation (non-obstruction vegetation consisting of
smaller trees and shrubs growing beneath large trees). 
(2) Removal of existing obstructions and potential obstructions with future obstructions
removed in 7 to 10 years as determined necessary (protect understory) 
(3) Removal of existing obstructions only (protect potential obstructions and understory) 
with potential obstructions removed in approximately 5 years and future obstruction
in 7 to 10 years as determined necessary. 
(4) Phased removal of existing obstructions, potential obstructions and understory 
The following three replanting alternatives were considered feasible for both sites P-4 and P-5: 
(1) Re-establish a low-growing forest on-site 
(2) Re-establish a low-growing forest on-site with a vegetation barrier 
(3) Replace trees on-site and create a tall-growing forest in close proximity to sites P-4
and P-5 
After selecting the four removal and three replanting alternatives, Port staff developed a plan
to engage the local community and gain their input on the preferred alternative. 
Community Engagement 
The Port hosted a Public Workshop on June 5, 2017 to seek public input on the removal and
replanting approaches for sites P-4 and P-5. Attendees received presentations on the removal
alternatives and replanting alternatives. Port staff and consultants answered questions and
discussed concerns and issues regarding the various alternatives. 
Attendees were asked to vote and provide their input on their preferred removal and
replanting alternatives. For the removal alternatives, the majority of the attendees selected

Template revised September 22, 2016.

COMMISSION AGENDA  Briefing Item No. __7a__                    Page 3 of 4 
Meeting Date: July 25, 2017 
Alternative No. 3 "Removal of existing obstructions only (protect potential obstructions and
understory)." For the replanting the public proposed a new fourth alternative; "re-establish a
low-growing forest on-site with a vegetation barrier and create a tall-growing forest in close
proximity to sites P-4 and P-5". This fourth alternative, a combination of alternative two and
three, was overwhelmingly voted for by the public.
In conjunction with the workshop at McMicken Heights Elementary School, the Port also
initiated an online open house workshop with the information that was presented on 6/5/17.
The online open house provided a forum to engage members of the community who were
unable to attend the live meeting and allowed for comments and feedback to be submitted to
the Port. 
Port staff also visited, in person, the approximately 65 homes immediately adjacent to site P-5,
to talk with homeowners, gather feedback and leave information. The primary information
gathered that day was around Port attention to removing the invasive species and improving
the maintenance of the property. 
Recommended Removal and Replanting Alternative 
After engaging the community, receiving their feedback, questions and concerns, Port staff will
undertake the following removal and replanting alternatives for Sites P-4 and P-5: 
(1) Recommended Removal Approach 
Alternative 3  Public Favored 
Remove existing obstructions only (protect potential obstructions and protect
understory to the maximum extent feasible) (see attachment X) 
(2) Recommended Replanting Approach 
Alternative 4  Public Favored 
Replant on-site at a 1:1 minimum replacement ratio with higher densities as
needed to re-establish a low-growing forest, replant in off-site location with
taller growing conifers, provide vegetation barrier adjacent to residential
properties and road frontage 
ATTACHMENTS TO THIS BRIEFING 
(1)   Presentation slides 
PREVIOUS COMMISSION ACTIONS OR BRIEFINGS 
February 21, 2017   Commission authorized  for the Chief Executive Officer to  prepare
environmental, design and contract bid documents for the Flight Corridor Safety Program
now-combined Phase 2 and Phase 3 at Seattle-Tacoma International Airport for $2,373,000.
The total estimated project cost is $7,227,000. 


Template revised September 22, 2016.

COMMISSION AGENDA  Briefing Item No. __7a__                    Page 4 of 4 
Meeting Date: July 25, 2017 
November 22, 2016  Commission authorized (1) to award and execute a major works
construction contract to the lowest responsible bidder, notwithstanding the low bid
exceeding the engineer's estimate by more than 10 percent; (2) change the contract
duration as necessary and include additional scope that may be identified, including
deferral of work on selected sites; (3) increase the project budget by an amount not to
exceed $475,000 for a total new project cost of $3,206,000. 
November 1, 2016  Commission public meeting and briefing on the Flight Corridor Safety
Obstruction Management program. The briefing provided an overview of state and federal
laws/requirements, and staff's recommendation of options to modify the current program.
The public meeting also included an extensive public comment period. 
October 25, 2016  Commission considered authorization to award the irregular bid exceeding
10 percent of the engineer's estimate to the lowest responsible bidder but took no action. 
October 11, 2016  Commission considered authorization to award the irregular bid exceeding
10 percent of the engineer's estimate to the lowest responsible bidder but took no action. 
August 23, 2016  A special announcement to Commission by Aviation Operations Director,
Michael Ehl, in regards to the Port issuing the final environmental Mitigated Determination
of Non-Significance (MDNS) for tree removal and replanting as part of the Flight Corridor
Safety Program in Phase One. 
August 9, 2016  Commission authorized to advertise and execute a major works construction
contract in the amount of $1,831,000 for a total project cost of $2,731,000. 
February 9, 2016  Commission authorized to design, advertise and execute a major works
construction contract in the amount of $750,000 for a total estimate project cost of
$900,000. 
November 24, 2015   Commission briefed on the Flight Corridor Safety Obstruction
Management program. The briefing provided an overview of state and federal
laws/requirements, and staff's recommendation of a phased delivery approach to complete
the program. 






Template revised September 22, 2016.