PORT OF SEATTLE 
MEMORANDUM 
COMMISSION AGENDA             Item No.      5h 
Date of Meeting   December 13, 2011 

DATE:    December 2, 2011 
TO:      Tay Yoshitani, Chief Executive Officer 
FROM:    Elizabeth Leavitt, Director, Aviation Planning & Environmental 
Robert Duffner, Environmental Compliance Program Manager 
SUBJECT: Department of Ecology NPDES Permit Agreed Order for the Seattle-Tacoma
International Airport 
Amount of This Request: $0     Source of Funds: 2011 and 2012 Operating Budgets; 
Future Individual Project Authorizations 
ACTION REQUESTED: 
Authorization for the Chief Executive Officer to execute an agreed order with the Washington
State Department of Ecology (Ecology), related to the Seattle-Tacoma International Airport's
National Pollutant Discharge Elimination Systems (NPDES) permit, to conduct an
environmental investigation, and to implement corrective actions as needed, to address
stormwater discharges with elevated pH (alkaline). 
SYNOPSIS: 
Since July 2010, discharges from stormwater detention ponds have periodically exceeded the
Airport's NPDES Permit upper pH effluent limit of 8.5 Standard Units. The pH exceedances
have primarily occurred in stormwater discharging from large detention ponds. There have been
18 elevated pH measurements out of 126 discharge samples collected throughout the Airport.
The acceptable pH range is from 6.5 to 8.5. The elevated pH readings have ranged from 8.7 to
9.6. Although the pH of discharges to streams has at times been elevated, no measurable effects
have been found in the water quality of the streams. 
The detention ponds associated with the elevated pH detain stormwater for extended periods of
time and then slowly release the water to local streams. The ponds have been very effective in
reducing erosive flows in our streams. However, the long-term water detention encourages the
growth of naturally occurring algae, which is likely modifying the pH of water. 
Airport staff has worked with Ecology to define the scope of this agreed order. It provides that
the Port will implement a study plan to characterize and isolate the pH source, evaluate data
collected and implement corrective actions, as needed, to eliminate future pH limit violations.

COMMISSION AGENDA 
Tay Yoshitani, Chief Executive Officer 
December 2, 2011 
Page 2 of 4 
Execution of this agreed order will require an estimated expenditure of up to $90,000 through the
end of 2012, for which funds have been included within the 2012 operating budget. Depending
upon any necessary longer-term improvements, the ultimate cost of complying with the agreed
order could be up to $3,000,000. However, if necessary, those additional costs would not be
expected to occur until 2013.
BACKGROUND: 
The Airport's NPDES Permit authorizes stormwater discharges associated with industrial
activities, which includes runoff from runways and taxiways. The Permit contains numerical
effluent limits for potential pollutants such as copper, zinc and oils, as well as limits for pH.
These limits are set at levels designed to ensure stormwater runoff discharges associated with
Airport operations do not adversely affect local streams and Puget Sound.
The Airport's NPDES Permit, as well as other environmental permits associated with Third
Runway (16R/34R) construction, requires the Port to detain stormwater runoff from impervious
surfaces that could otherwise increase erosion and flooding in local streams. Over the past 10
years, the Port has met this requirement through the construction of a series of stormwater
detention ponds and vaults.
Beginning in July 2009, discharge monitoring identified a recurring pattern of elevated pH from
three detention ponds located on the Airport's west side. These ponds receive runoff from
runways and taxiways, and discharge directly to Miller and Walker Creeks. Staff immediately
reported these permit exceedances to Ecology and initiated preliminary investigations. These
investigations indicated that the elevated pH is not directly attributable to Airport operations and 
that the pH of Miller and Walker Creeks remains in the acceptable range when the ponds are
discharging. Observations over this period noted increased algal growth in the west side ponds 
during the summer and other periods of extended sunshine, which appear to coincide with the
increased pH levels. 
The Airport's NPDES Permit requires the Port to not only investigate these pH exceedances, but
take actions necessary to prevent exceedances. Port staff worked directly with Ecology to
review potential control measures, and have implemented some operational changes to control
algal growth in the ponds. However, after a review of preliminary investigation results and the
results of these interim actions, both Port staff and Ecology agreed that additional investigations
are needed before the most appropriate solution can be identified and implemented. 
As a result of this decision, Port staff and Ecology worked collaboratively to develop a plan to
further investigate and implement actions as needed to correct the pH exceedances. This plan is
represented in the Agreed Order No. 8755, issued to the Port on November 2, 2011. The agreed
order requires that the Port prepare and implement a study plan, submit interim and final reports,
implement operational corrective actions and implement structural and/or treatment controls as
needed. A compliance schedule for completing these efforts is contained in the order. 
PROJECT JUSTIFICATION: 
This authorization request will allow the Port to continue to collaboratively work with Ecology
to further investigate elevated pH in stormwater ponds and to identify necessary control

COMMISSION AGENDA 
Tay Yoshitani, Chief Executive Officer 
December 2, 2011 
Page 3 of 4 
measures. The agreed order provides an achievable compliance schedule for completing the
investigation as well as time needed to define future actions as necessary, gain appropriate
approvals and complete a project in the event that structural and/or treatment controls are needed
to address the pH exceedances. 
PROJECT SCOPE OF WORK AND SCHEDULE: 
Primary elements of the agreed order scope of work are as follows: 
Prepare and submit a study plan to Ecology for approval no later than December 15,
2011, to isolate and characterize factors that are causing elevated pH within the
stormwater detention ponds. Port staff has completed this study plan and is prepared to
submit it to Ecology. 
Submit an interim progress report to Ecology no later than June 30, 2012. 
Implement operational corrective actions no later than July 31, 2012. 
Submit a final report to Ecology no later than October 31, 2012. 
Implement and construct necessary structural and/or treatment controls no later than
October 15, 2013. 
FINANCIAL IMPLICATIONS: 
Cost Estimate: 
The study plan investigation and reporting costs are estimated to be $80,000. A minor
expenditure will occur in December 2011 and the remaining study costs would be incurred in
2012.
Anticipated operational corrective actions in 2012 include modifications to the ongoing
management of the stormwater ponds. The cost of these modifications is not expected to exceed
$10,000.
A preliminary assessment of potential structural and/or treatment controls has been completed.
Although the need for these controls has not yet been determined, their cost has been estimated
to be less than $3,000,000. 
Budget/Authorization Summary: 
The study plan and potential operational corrective action have been anticipated and included in
the Aviation Environmental and Maintenance 2011 and 2012 operating budgets. 
Additional funding may be required for the design and construction of potential structural and/or
treatment controls. Future Commission authorization will be requested in the event such controls
are required, or if the total anticipated project costs exceed $300,000. 
ENVIRONMENT AND SUSTAINABILITY:
Implementation of the agreed order will allow the Port to determine if the elevated pH discharges
from stormwater ponds to Miller and Walker Creeks are adversely impacting these water
resources and provide a mechanism to identify and implement necessary control measures.

COMMISSION AGENDA 
Tay Yoshitani, Chief Executive Officer 
December 2, 2011 
Page 4 of 4 
STRATEGIC OBJECTIVES: 
Implementation of the agreed order would support the Port's strategic objective of exhibiting
environmental stewardship through our actions. Actions taken under the order would assure
compliance with the Airport's NPDES Permit and provide an opportunity to improve water
quality in Miller and Walker Creeks. 
BUSINESS PLAN OBJECTIVES: 
The Aviation Division's business plan seeks to lead the airport industry in environmental
innovation and minimize the Airport's environmental impacts. Implementation of the agreed
order will allow the Port to characterize any potential impacts the elevated pH discharges may
have on the environment and identify appropriate corrective actions if needed. 
TRIPLE BOTTOM LINE SUMMARY: 
Implementation of the agreed order allows the Port to ensure its operations are protective of the
environment and that its actions are transparent and open to the regulatory agency review and
approval for the benefit of local communities and interested members of the public. 
ALTERNATIVES CONSIDERED AND THEIR IMPLICATIONS: 
The following alternatives were considered for accomplishing the work described in the scope of
work: 
Alternative 1 
Do not execute the NDPES Permit agreed order for the Seattle-Tacoma International Airport
stormwater discharges. This alternative could result in the issuance of a unilateral Ecology
enforcement order to perform the work, which would eliminate Port control over the
investigation and assessment of necessary corrective actions. The imposition of penalties would
also be likely. This is not the recommended alternative. 
Alternative 2 
Execute the NPDES Permit agreed order and conduct the investigation and assessment of
necessary corrective actions. This alternative will provide a mechanism to adequately evaluate
the elevated pH and implement corrective actions as needed within an achievable compliance
schedule. This is the recommended alternative. 
OTHER DOCUMENTS ASSOCIATED WITH THIS REQUEST: 
Attachment: Department of Ecology Agreed Order Number 8755 
PREVIOUS COMMISSION ACTION: 
None.