COMMISSION 
AGENDA MEMORANDUM                        Item No.          6b 
ACTION ITEM                            Date of Meeting    September 25, 2018 
DATE:     September 25, 2018 
TO:        Stephen P. Metruck, Executive Director 
FROM:    Greg Whiting, Manager, Aviation Utility 
Paul Shen, Sr. Civil Engineer, Aviation Facilities & Infrastructure 
SUBJECT:  Request authorization to execute new contract for sewer cleaning 
Amount of this request:               $1,500,000 
Total estimated project cost:           $1,500,000 
ACTION REQUESTED 
Request Commission authorization for the Executive Director to execute a contract for up to
five (5) years for an estimated cost of $1,500,000 for routine sanitary sewer system cleaning at
both Airport and Maritime facilities. 
EXECUTIVE SUMMARY 
This contract will perform periodic sewer system cleaning, which is required to ensure sewer
system operation, minimize sewage related costs and maximize sewer system asset life. About
90% of the anticipated expenditure will be to clean the sanitary sewer system at the Seattle-
Tacoma International Airport. The STIA sewer system processes approximately 150 million
gallons of predominantly biological and restaurant waste annually, including grease discharged
from airport restaurant facilities. The other 10% is to conduct similar routine cleaning activities
at Maritime facilities. 
JUSTIFICATION 
About 20% of the sewer cleaning covered under this contract, such as jetting and root ball
removal, are required to ensure that Airport and Maritime sewers are clear of blockages and
are functional. 
The other 80% of the request is for the specific purpose of cleaning the 16 Airport grease
interceptors, 57 times per year (total)  per  a schedule  developed by  Aviation  F&I Civil
Engineering.   Cleaning helps to minimize sewer utility biological oxygen demand (BOD) 
surcharges (currently over $400,000/year).  The surcharges are applied by the sewer utility
when chemicals that contribute to the consumption of oxygen in the water (such as fats, oils
and grease [FOG] from restaurant dishwashers) are in the sewage at a concentration greater
than 369 milligrams/liter. The Airport's average BOD is about 600 milligrams/liter and would be 
significantly higher without cleaning. 

Template revised April 12, 2018.

COMMISSION AGENDA  Action Item No. __6b__                              Page 2 of 4 
Meeting Date: September 25, 2018 

Cleaning also extends the life of the assets.  Early replacement of grease interceptors is
disproportionately expensive because  they are mostly buried beneath the airfield. I t is
desirable for them to last as long as possible. 
DETAILS 
About 20% of the sewer cleaning activities performed via this contract, such as jetting and root
ball removal, are required to ensure that the sewers are clear of blockages and are functional.
The rest of the cleaning activities are specifically required to clean the grease interceptors at
the Airport. Grease interceptors are multi-thousand-gallon tanks (see picture) that are installed
in the sewage lines. They are used to capture FOG discharged through restaurant drains. 







Wastewater flows from the main sewer line into the chamber on the left, where the grease
floats to the top, to the left of the baffle wall. Cleaning removes the grease layer shown in the
first chamber. 
If the interceptors are not periodically pumped out, the FOG layer (labeled grease in the
picture) becomes thick enough to flow underneath the baffle wall (also labeled in the picture).
Cleaning removes the FOG while it is in the interceptors, which keeps the FOG from reaching
the sewer utility and thus keeps the removed FOG from contributing to the BOD surcharge. 
Scope of Work 
The contract scope includes routine sanitary sewer cleaning activities, principally grease
interceptor pumping, but also such activities as sewer jetting and root ball removal. 


Template revised September 22, 2016; format updates October 19, 2016.

COMMISSION AGENDA  Action Item No. __6b__                              Page 3 of 4 
Meeting Date: September 25, 2018 
Schedule 
Most activities are on call as needed.  Grease interceptor cleaning is carried out per the
schedule below, which was developed by Aviation F&I  Civil Engineering. 







Cost Breakdown                                               This Request 
$250,000 in 2019, ongoing escalation             $1,500,000 (total over 5 years) 
ALTERNATIVES AND IMPLICATIONS CONSIDERED 
Alternative 1  Execute procurement process for a new contract 
Cost Implications: Direct cost of average $300,000/year (est. $250,000 in 2019); minimization
(not immediately quantifiable; a study is underway) of BOD surcharge costs associated with
grease interceptors. 
Pros: 
(1)   New competition 
(2)   Ensures continued efficient operation of sewer systems for the Aviation and Maritime
divisions, including minimizing BOD discharges to the sewer systems 
(3)   Minimizes lifecycle costs to the sewer system, including lower per unit cleaning costs,
lower BOD discharge to the sewer system, and longer service life of grease interceptor
system. 
(4)   Have an on-call resource to respond to sewer system emergencies such as blockages. 


Template revised September 22, 2016; format updates October 19, 2016.

COMMISSION AGENDA  Action Item No. __6b__                              Page 4 of 4 
Meeting Date: September 25, 2018 
Cons: 
(1)   Additional  CPO  and  management  resources  would  be  required  during  the
procurement process. 
This is the recommended alternative. 
Alternative 2  Do not have a standing contract and instead only clean the sewer systems on an
emergency basis 
Cost Implications:   In the absence of an ongoing routine cleaning contract, emergency cleaning
service costs would be incurred more often and would probably be at least twice the currently
estimated $30,000 - $45,000/year.  Grease escaping into the sanitary sewer from airport
restaurants would gradually increase as the capacity of the grease interceptors would
eventually be exceeded.   At steady state, BOD surcharges would increase from about
$400,000/year to somewhere between $800,000 - $2 million/year. 
Pros: 
(1)   Reduced sewer cleaning costs 
Cons: 
(1)   Increased sewer BOD surcharges, exceeding savings from reduced cleaning 
(2)   Higher risk that Port will exceed maximum BOD limit of sewer utility and thus have to
address BOD on an emergency basis 
(3)   Higher unit cost for routine sewer cleaning activities 
(4)   Longer response time to emergencies 
This is not the recommended alternative. 

Annual Budget Status and Source of Funds 
Budget requests are submitted annually by the Aviation Utility and by Maritime Maintenance 
and are included in the annual operating budget. 
ATTACHMENTS TO THIS REQUEST 
None 
PREVIOUS COMMISSION ACTIONS OR BRIEFINGS 
September 8, 2015  The Commission approved the previous contract (item 4e) 



Template revised September 22, 2016; format updates October 19, 2016.