Template revised April 12, 2018.
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.
COMMISSION AGENDA – Action Item No. __6b__ Page 2 of 4
Meeting Date: September 25, 2018
Template revised September 22, 2016; format updates October 19, 2016.
Cleaning also extends the life of the assets. Early replacement of grease interceptors is
disproportionately expensive because they are mostly buried beneath the airfield. It 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.
COMMISSION AGENDA – Action Item No. __6b__ Page 3 of 4
Meeting Date: September 25, 2018
Template revised September 22, 2016; format updates October 19, 2016.
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
$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.
COMMISSION AGENDA – Action Item No. __6b__ Page 4 of 4
Meeting Date: September 25, 2018
Template revised September 22, 2016; format updates October 19, 2016.
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)