SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 

THIS SIXTH ADDENDUM TO THE PARTICIPATION AGREEMENT FOR CLEANUP OF SEA‐TAC 
INTERNATIONAL AIRPORT JET FUEL FACILITY (“Sixth Addendum”) is made effective
, 2022, by and among OLYMPIC PIPE LINE COMPANY (“Olympic”), THE PORT 
OF SEATTLE (“Port”) and UNITED AIRLINES, INC. (“United”) (hereinafter referred to as the 
“Participants” collectively and “Participant” individually). It modifies and amends that certain 
Participation Agreement for Cleanup of Sea‐Tac International Airport Jet Fuel Facility by and 
among Participants dated November 7, 1995 (hereinafter the “Participation Agreement”) and 
the Fifth Addendum to the Participation Agreement for cleanup of Sea‐Tac International Airport 
Jet Fuel Facility by and among Participants effective on or about August 5, 2014 (“Fifth 
Addendum”).
WHEREAS, the Participation Agreement continues in full force and effect, as expressly 
revised by amendment to the Fifth Addendum, and the Fifth Addendum (as amended in the 
First Amendment to the Fifth Addendum) also continues in full force and effect, except as 
expressly revised in this Sixth Addendum; 
WHEREAS, capitalized terms used in this Sixth Addendum but not defined or 
incorporated herein shall have the meanings set forth for such terms in the Participation
Agreement.
WHEREAS, this Sixth Addendum, the Fifth Addendum, the Fourth Addendum, the First 
Amendment to the Fourth Addendum, the Participation Agreement and the Escrow Agreement 
together may be referred to as “the Agreements;” 
WHEREAS, at the direction of the Participants, SLR is continuing to negotiate with the 
Washington Department of Ecology (“DOE”) in an effort to obtain a No Further Action (“NFA”) 
determination by DOE, consistent with the Agreements and the applicable provisions of the 
Washington Model Toxics Control Act (“MTCA”); and 
WHEREAS, SLR International Corporation (“SLR”) by letter dated June 22, 2022 proposed 
an additional scope of work to abandon      remaining wells, remove former remediation system 
equipment, remove sheet piling, remove fencing and concrete retaining wall, and remove a 
light post for an estimated costs of $369,771 above and beyond shared costs already paid by 
the Participants (“Additional Shared Costs”); and
WHEREAS, agreement by the Participants to Additional Shared Costs in the amount of 
$369,771 requires a Sixth Addendum. 
NOW, THEREFORE, in consideration of the mutual promises and representations set 
forth herein, the Participants, intending to be legally bound, agree as follows: 
SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
1

                  1.       Section 1 of the Participation Agreement, as amended in the Fourth and Fifth Addenda, 
is further amended by addition of the following subsection 1.6: 
1.       Participants’ Mutual Intent and Purpose. 
1.6     In addition to the matters agreed upon in subsections 1.1 through 1.5, 
the Participants further agree to perform or cause to be performed the 
Additional Work described in Exhibit A. 
2.       Section 2 of the Participation Agreement, as amended in the Fourth and Fifth Addenda, 
is further amended by the substitution of the following language in Section 2.2, and the 
addition of a new subsection 2. 8: 
2.       Shared Common Costs. 
2.2     Procedure for Payments. Each Participant shall pay or shall transfer by 
wire or automated clearing house (ACH) to the designated escrow 
account that Participant’s “pro rata” share of the Shared Costs as follows: 
(a)      Not more than thirty (30) days after execution of this Sixth 
Addendum, each Participant shall pay or transfer to the escrow 
account established by the Participants, that Participant’s “pro 
rata” share of $369,771 (including 15% Contingency) which is 
shown below on Chart I of this Sixth Addendum, and from time to 
time, its pro rata share of any escrow fees that may be charged 
periodically to maintain the escrow account.
The amounts (not including escrow fees) that each Participant 
shall be obligated to transfer to the designated escrow account 
pursuant to this Amended Agreement shall be as follows: 
Chart I 
Participant               Amount of Each Participant’s 
Payment Obligation to the 
Designated Escrow Account 
Olympic Pipeline                   $41,414 
Port of Seattle                       $78,505 
United Airlines, Inc.                 $249,852 

SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
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                                2.8     Additional Payments. The Participants hereby agree to pay Shared Costs 
of the Remedial Actions, as more specifically provided in this Sixth 
Addendum and to allocate “pro rata” among themselves all rebates, 
refunds, disbursements and escrow fees called for or resulting under the 
Participation Agreement, the Fourth Addendum, the Fifth Addendum or 
this Sixth Addendum or the Escrow Agreement.
(a)      The Additional Shared Costs of the Remedial Actions under this 
Addendum are estimated to be $369,771. Each Participant shall 
pay its designated amount of the Additional Shared Costs listed 
herein on Chart I in accordance with the Participation Agreement, 
the Fourth Addendum, the Fifth Addendum, this Sixth Addendum 
and the Escrow Agreement; provided, however, that in the event 
the costs to perform the Remedial Work exceed amounts 
remaining in the account established by the Escrow Agreement 
and the Additional Shared Costs ($369,771), and expenditures 
greater than that amount are required to achieve the objectives 
of Exhibit A to this Addendum, a written amendment to this 
Addendum signed by all Participants shall be required and 
provided further, that in the event any Participant fails to make its 
full payment of its designated amount of the Shared Costs, as 
required by the Agreements, the remaining Participants shall not 
be required to perform their obligations under the Agreements. 
(b)      Performing Participants that pay their designated amount of 
Additional Shared Costs reserve all rights of action against any 
defaulting or non‐performing Participant(s) for recovery under all 
applicable statutes or theories of law or equity.
3.       Counterparts. This Sixth Addendum may be executed in counterparts, each of 
which shall be deemed an original and all of which shall constitute one and the 
same instrument. 
4.       Future Remediation Activities. Remediation has progressed to the extent 
practicable at the Sea‐Tac International Airport Jet Fuel Facility. Residual 
impacts are understood to not pose a threat to human health and the 
environment. If in the future, DOE or another regulatory agency requires the 
Participants to address residual impacts, or if further remediation becomes 
practicable and the Port requests further remediation to be performed pursuant 
to an applicable lease obligation, the Participants will fund any necessary 
remedial activities in accordance with each Participant’s “pro rata” share of the 
Shared Costs per the existing Participation Agreement and associated addenda. 

SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
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                          5.       No Other Changes. Except as expressly modified by this Sixth Addendum, the 
Participation Agreement and Fourth and Fifth Addenda shall remain in full force 
and effect. Notices required hereunder or by the Participation Agreement or 
Fourth and Fifth Addenda shall be delivered by mail and email to the notice 
addresses listed below the signature of each Participant executing this 
Addendum. 















SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
4

                      To signify consent to and acceptance of this Sixth Addendum, an authorized officer or 
agent of each party has executed this Sixth Addendum to Participation Agreement for Cleanup 
of Sea‐Tac International Airport Jet Fuel Facility on the year and day first written above. 
United:
UNITED AIRLINES, INC. 

By:
Its:
Notice Addressees: 
United Airlines, Inc. 
518 Connecticut Avenue NW, Suite 500 
Washington, D.C 20006 
Attn: Theresa Fariello 
Senior Vice President 
Government Affairs 
Phone: (202‐521‐4333) 
Email: Theresa.fariello@united.com








SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
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                      To signify the consent to and acceptance of this Sixth Addendum, an authorized officer 
or agent of each party has executed this Sixth Addendum to Participation Agreement for 
Cleanup of Sea‐Tac International Airport Jet Fuel Facility on the year and day first written 
above. 
Olympic:                                         OLYMPIC PIPE LINE COMPANY 

By:
Its:
Notice Addressees: 
Olympic Pipe Line Company 
c/o BP Remediation Management 
201 Helios Way 
Houston, TX 77079 
Attn:  James Schaeffer 
Liability Manager 
Phone: 281‐800‐7868 
Email: Jim.Schaeffer@bp.com 








SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
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                      To signify the consent to and acceptance of this Sixth Addendum, an authorized officer 
or agent of each party has executed this Sixth Addendum to Participation Agreement for 
Cleanup of Sea‐Tac International Airport Jet Fuel Facility on the year and day first written 
above. 
The Port:                                            THE PORT OF SEATTLE 

By:
Its:
Notice Addressees: 
Port of Seattle 
Mailing Address: 
P.O. Box 68727 
Seattle, WA 98168 
Street Address: 
17801 Pacific Highway South 
Room 6012M 
Seattle, WA 98158 
Attn: Megan King, AV Environment & Sustainability 
Phone: (206) 787‐4741 
Email: King.M@portseattle.org 






SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
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                               EXHIBIT A: SLR PROPOSAL OF June 22, 2022 















SIXTH ADDENDUM TO PARTICIPATION AGREEMENT FOR CLEANUP OF 
SEA‐TAC INTERNATIONAL AIRPORT JET FUEL FACILITY 
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June 22, 2022 

Mr. Ryan Keeler 
United Airlines, Inc. 
233 South Wacker Drive 
11th Floor – WHQEN 
Chicago, IL 60606 
Mr. David Wandor 
Parsons 
3620 Park 42 Drive 
Sharonville, OH 45241 
Ms. Megan King 
Port of Seattle 
P.O. Box 68727 
Seattle, WA 98168 
Re:  Revised Proposal for Abandonment of Remaining Wells and Removal of Former
Remediation System Equipment, Former Continental-Olympic-United Fuel Farm
Area, SeaTac International Airport 
Dear Ryan, Dave, and Megan: 
SLR International Corporation (SLR) has prepared this proposed scope of work and cost
estimate for removal of the former remediation system equipment and abandonment of the
remaining wells and piezometers at the former Continental-Olympic-United fuel farm area 
(the former fuel farm area). The scope of work is detailed in the following tasks.
Task 1 – Project Management 
This task includes coordinating field activities with SLR staff, subcontractors, and the Port of
Seattle (Port); subcontracting; communications with the Continental-Olympic-United Fuel
Facility Environmental Committee (FFEC); and communications with the Washington State 
Department of Ecology (Ecology).
Task 2 – Abandon Wells 
There are currently a total of 53 remaining groundwater monitoring wells, piezometers,
inactive dual-phase extraction (DPE) wells, and inactive groundwater recovery wells at the
former fuel farm area. The wells  and piezometers are two to four inches in diameter, except
for an inactive recovery well that is 36 inches in diameter, and range in depth from
approximately 6.5 to 75 feet below ground surface (bgs).  Based on SLR’s review of
SLR International Corporation 22118 - 20th Avenue SE, Ste. G202, Bothell, WA 98021 
T: 425-402-8800   F: 425-402-8488   www.slrconsulting.com 
Offices throughout USA, Canada, UK, Ireland, Australia, South Africa 
Printed on Recycled Paper

               Mr. Ryan Keeler, David Wandor, and Megan King 
Page 2 

Ecology’s well records, a total of 43 of the wells and piezometers are registered with Ecology
and have identification numbers and driller well logs on file. 
Holt Services, Inc. (Holt) of Edgewood, Washington, will abandon or decommission the wells
and piezometers in accordance with the requirements of the Washington Administrative Code
(WAC) 173-360-381. The decommissioning work will be conducted by a licensed well driller
(in accordance with the requirements of Chapter 18.104 RCW - The Washington Well
Construction Act) under the direction of an SLR geologist. SLR will subcontract and schedule
the Port-required traffic control equipment and personnel prior to conducting any of the well
abandonment work on or adjacent to roads. 
Holt will abandon or decommission the 53 wells according to the following procedures: 
• The 43 Ecology-registered wells and piezometers will be abandoned by filling each well
casing and screen with hydrated bentonite chips and filling each surface monument or
vault with concrete to match the surrounding grade. The monument and vault lids will
be disposed off-site. 
• The nine 2- and 4-inch-diameter wells that are not registered with Ecology will be
decommissioned by removing each well monument or well vault; overdrilling the well
by using a limited-access hollow-stem auger  drill rig; removing the well casing; 
backfilling each of the overdrilled well borings with hydrated bentonite chips to a depth
of approximately 2 feet bgs; and then backfilling the top 2 feet with concrete. 
• The 36-inch-diameter inactive recovery well, which is not registered with Ecology, will
be decommissioned by disinfecting the water in the well using chlorine tablets; filling
the well with pea gravel to a depth of approximately 2 feet bgs; and then backfilling the
top 2 feet with concrete. The portion of the recovery well casing that protrudes above the
ground surface will be cut off prior to decommissioning. 
The soil cuttings from the overdrilling activities will be temporarily stored at the former fuel
farm area in properly labeled 55-gallon drums.  SLR will collect a composite sample of the
soil in the drums and submit it to Apex Laboratories (Apex) in Tualatin, Oregon, for the
analyses required by the disposal facility.  The sample analytical results will be used for
profiling of the waste. The drums will be hauled off-site by a licensed waste transporter for
disposal (as non-hazardous waste) at an Ecology-licensed facility. 
Task 3 – Remove Former Remediation System Equipment 
Wyser Construction, Inc. (Wyser) of Snohomish, Washington will remove the inactive DPE
system equipment, as well as the remaining inactive bioventing and product skimming system 
equipment. The equipment removal work will be conducted under the direction of an SLR
geologist. Prior to decommissioning the DPE system, SLR collect a composite sample of the
carbon in the vapor-phase granular activated carbon (GAC) canisters and submit it to Apex

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               Mr. Ryan Keeler, David Wandor, and Megan King 
Page 3 

for the analyses required by the disposal facility. The sample analytical results will be used for
profiling of the carbon waste. A licensed waste transporter will remove the carbon the
canisters and haul it off-site for disposal at an Ecology-licensed facility. 
Wyser’s scope of work will include the following: 
• Disconnect the power supply to the inactive DPE system inside the former Continental
Fuel Farm power supply building on the northwest portion of the former Fuel Farm. 
Wyser will subcontract a licensed electrician for this work. 
• Cut off and cap all of the underground utility lines (electrical and sewer) inside of the
fenced DPE system enclosure. 
• Remove the former DPE system equipment skid and all system components, including
the vacuum blowers, knockout tank, oil/separator, product storage tank, carbon vessels,
piping manifold, aboveground piping, hoses, conduits, control panel, and emission stack.
All of the equipment will be disposed and/or recycled off-site at Ecology-licensed
facilities. 
• Remove the former bioventing system building and the former system equipment within 
the building. The building and equipment will be hauled off-site for disposal at an
Ecology-licensed facility. 
• Remove the chain-link fencing surrounding the former system equipment enclosure and
haul it off-site for disposal at an Ecology-licensed facility. 
• Remove the fiberglass shelter and the concrete secondary containment pad for the
former product skimming system and haul them off-site for disposal at an Ecologylicensed
facility. 
• Remove the accessible underground DPE system piping from the system enclosure to
each DPE point vault, remove the vaults, backfill the vaults with imported, clean gravel 
fill, backfill the trenches to remove the system piping with the excavated material, and
finish the ground surface of each trench to match the surrounding area (either asphalt or 
topsoil and grass sod). The inaccessible underground system piping located beneath the
Air Cargo Road travel lanes will not be removed, but instead will be capped at each end
and left in place to minimize any potential impacts to airport operations.  The removed
piping will be hauled off-site for disposal at an Ecology-licensed facility. 
• The vaults for MW-3C and MW-6 will be removed prior to the well abandonment work
to allow space for Holt to overdrill those DPE points, which are not registered with
Ecology. 


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               Mr. Ryan Keeler, David Wandor, and Megan King 
Page 4 

In addition to the remediation system equipment removal and disposal work described above,
Wyser’s scope of work may include the following optional tasks: 
• Task 3a - Subcontract a licensed crane operator to remove 200 linear feet of interlocking
steel sheet piling in the former Continental Fuel Farm soil excavation area. The sheet
piling will be hauled off-site for recycling at an Ecology-licensed facility. 
• Task 3b - Remove the fencing and concrete retaining wall from the former Continental
Fuel Farm excavation area. 
• Task 3c - Remove the light post located inside the remediation system equipment
enclosure and haul it off-site for disposal at an Ecology-licensed facility. 
Task 4 – Prepare Report 
After completing the work described above, SLR will prepare a letter report that describes the
work and presents photographs that document the work. A draft version of the report will be
submitted to the FFEC for review. After receiving comments, SLR will finalize the report and
submit it to the FFEC. 
ESTIMATED COST 
The proposed scope of work will be conducted on a time and materials basis, in accordance
with the conditions of the Master Agreement for Environmental Services, dated March 1,
2002, and consistent with the attached Fee Schedule.  The total estimated cost to perform
Tasks 1 through 4 is $199,510. The estimated additional costs for the optional tasks under
Task 3 are as follows: 
• Task 3a: $105,190 
• Task 3b: $15,100 
• Task 3c: $1,740 
In addition to the assumptions described above, the cost estimate assumes that: 1) the well
abandonment work will take a total of eight working days to complete; 2) the removal of the
remediation system will take a total of 10 working days to complete; 3) all wastes (drill
cuttings and granular carbon) will be profiled as non-hazardous; 4) the work will be
conducted on weekdays during normal business hours; and 5) if any or all of Tasks 3a through
3c are included, they will be conducted concurrently with the other work under Task 3.  A
breakdown of the estimated costs is shown in the attached Table. The proposed work will be
conducted under Assignment Order No. SEA-05, which currently has the funds ($20,692 in
the project escrow account) to cover a small portion of the cost to conduct the proposed work. 

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               Mr. Ryan Keeler, David Wandor, and Megan King 
Page 5 

The estimated cost and proposed scope of work are based on information available to SLR at
this time. If conditions change, unforeseen circumstances are encountered, or work efforts are
redirected, the cost estimate may require modification. 
If the scope of work and cost estimate are acceptable, please sign below and authorize
additional funding under Assignment Order No. SEA-05.  Thank you for the continued
opportunity to provide our services on this project.  If you have any questions, please call
Chris Lee at (206) 218-5981 or Mike Staton at (425) 471-0479. 
Sincerely, 
SLR International Corporation 


Christopher Lee, L.G.                       Michael D. Staton, L.G. 
Associate Geologist                        Senior Principal Geologist 
Attachment:   Estimated Budget Table 
2022 Fee Schedule 

The proposed scope of work and cost estimate are approved. 
For United Airlines, Inc: 

_____________________ 
Ryan Keeler 
For BP: 

_____________________ 
David Wandor, Parsons 
For Port of Seattle: 

_____________________ 
Megan King 

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                                                                  Table 1
Estimated Budget
Abandonment of Remaining Wells and Removal of Former Remediation System Equipment
Former Continental-Olympic-United Fuel Farm Area
SeaTac International Airport

SLR International Corp
Direct    Subcontractor
Tasks                           Hours    Labor     Costs1      Costs2     Total Cost
1  Project Management                                      24      $4,680       $0          $0         $4,680
2  Abandon Wells                                           90     $11,430     $610       $74,600      $86,640
3  Remove Former Remediation System Equipment               117     $15,080     $760       $90,190     $106,030
4  Prepare Report                                           12      $2,160       $0          $0         $2,160
Totals   243     $33,350     $1,370      $164,790     $199,510
Estimated Project Total  $199,510
Optional Additional Tasks
3a  Remove Sheet Piling                                       16      $2,370       $80       $102,740     $105,190
3b  Remove Fencing and Concrete Retaining Wall                   8      $1,190       $80       $13,830      $15,100
3c  Remove Light Post                                          0        $0         $0         $1,740       $1,740
Totals    24      $3,560      $160       $118,310     $122,030
Estimated Project Total Including Optional Tasks  $321,540
Notes:
1 Direct costs include mileage, supplies, and field equipment.
2 Subcontractor costs include well abandonment, sample analyses, traffic control, waste disposal, and equipment/materials removal.
All subcontractor costs include a 5 percent markup.















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2022 Fee Schedule 
Former Continental-Olympic-United Fuel Farm Area 
SeaTac International Airport 
(Effective March 1, 2022) 
PROFESSIONAL SERVICES                            Hourly Rate 
Managing Principal                                         $255 
Principal Geologist, Engineer, Scientist, or Toxicologist        $225 
Senior Geologist, Engineer, Scientist, or Toxicologist            $190 
Associate Geologist, Engineer, Scientist, or Toxicologist        $165 
Project Geologist, Engineer, Scientist, or Toxicologist           $150 
Staff Geologist, Engineer, Scientist, or Toxicologist              $120 
Senior Drafter/CADD Operator                            $115 
Word Processor/Clerical                                    $105 

OTHER 
Travel (air, ferry, train, taxi, etc)                                     at cost 
Meals & Lodging                                         at cost 
Outside Services                                              at cost 
Subcontractor Mark-up                                    cost plus 5% 
Mileage                                                      IRS rate 



SLR International Corporation 22118 20th Avenue SE, Ste. G202, Bothell, WA 98021 
T: (425) 402-8800   F: (425) 402-8488  www.slrconsulting.com 
Offices throughout USA, UK, Ireland, Canada, Australia, Namibia and South Africa