SEPA

January 2025

Communities with Combined Sewers
Adapting to a Changing Climate:

Spokane, Washington

Background

The City of Spokane, Washington, has a total population of
232,000 and sits on the traditional homelands of the Spokane
Tribe of Indians. The Spokane River flows through its downtown -
featuring two sets of falls as well as two hydroelectric facilities.

The river also provides for many recreational opportunities
including swimming, fishing and kayaking. Downstream from the
city, the Spokane River is an important resource for tribal lands.

Spokane's collection system includes about 400 miles of
combined sewers. The Spokane River is the receiving waterbody
for many discharges, including combined sewer overflows
(CSOs), the city's wastewater treatment plant (VWVTP) effluent,
and stormwater.

Challenges

Spokane has been experiencing warmer
winters and more intense storms, which
are placing greater pressure on its wet
weather infrastructure.

In 2012, the city estimated it would take
$490 million to address CSOs and wet
weather deficiencies at its VWVTP.

However, in addition to CSOs, Spokane
was also facing other water quality
challenges associated with their VWVTP
effluent and stormwater discharges
including nutrients, metals, and
polychlorinated biphenyls.

In order to balance their Clean Water Act
priorities and protect public health and the
environment, Spokane's Department of
Public Works used the U.S. EPA's Integrated
Planning Framework to develop an
Integrated Plan. This allowed for a more
holistic approach to reducing CSOs and improving the level of treatment of wastewater and stormwater, while
also increasing resiliency to changes in precipitation patterns and storm intensity.

Key Information

•	Location: Spokane, WA

•	Population served: 232,000

•	Permit Number: WA0024473

•	Key hazards: increased storm
intensity and warmer winters

~** /T\

The Spokane River is an environmental cornerstone of the City of Spokane,
running through its downtown area.


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Communities with Combined Sewers Adapting to a Changing Climate: Spokane, WA

Climate Impacts

Spokane is already experiencing impacts from changing climate
conditions, including more intense storm events during the
summer and warmer winters. Warmer winters cause precipitation
to fall as rain instead of snow, or as rain on top of melting snow,
leading to greater volumes of runoff than would be expected
under historical conditions. These more intense storms can
increase flooding and overwhelm existing drainage systems.

Solutions

Integrated Planning

The city's original plan to address CSOs was costly, left other
water quality concerns unaddressed, and did not consider the
residents' ability to pay for the upgrades.1 As of 2021, 41% of
Spokane households were defined as "asset iimited, income
constrained but employed," meaning they cannot afford basic
needs like food, housing, transportation and healthcare even
though they are working.2

Given these constraints, the city decided to instead take a more
integrated approach. In 2014, they developed their integrated
Clean Water Plan to holistically consider their Clean Water Act
requirements and water quality challenges in the Spokane River
and to identify the most cost-effective solutions. This plan
allowed the city to address their CSOs, WWTP upgrades, and
stormwater needs simultaneously with projected construction
costs of $340 million—over $100 million less than the sum of the
standalone solutions. To help fund the plan, the city sold $200
million of "green" construction bonds3 in 2014 with an interest
rate of 3.08%. This supplemental funding allowed the city to limit
future annual rate increases for rate payers to just 2.9% for more
than the following decade.

To evaluate treatment alternatives, the city used a multi-objective
decision analysis (MODA) approach within their integrated plan.
By looking at multiple factors, the city was also able to
incorporate community impacts and climate resiliency into their
selection process.

First 8: Adams Plaza

First & Adams Plaza is home to
Spokane's largest wastewater storage
tank, a 2.4-million-gailon tank in west
downtown. The city developed a plaza on
top of the tank and contracted with a
neighboring brewery that programs and
manages the plaza including
coordinating food trucks and live music.

Recreational Field

Spokane developed a recreational field
on top of a wastewater storage tank. A
charter school across the street needed
green space for physical education
classes, so the city agreed to allow the
charter school to use the field, and the
school maintains it in return.

Selected solutions within the integrated plan included: 25 CSO
storage tanks with 16 million gallons of storage capacity that are
actively managed using a Supervisory Control and Data
Acquisition (SCADA) system; an advanced membrane filtration

system at the WWTP to remove phosphorus and other contaminants; and a range of stormwater projects
including tree plantings, underground swales, and infiltration basins. For below-ground infrastructure, the city
prioritized incorporation of above-ground amenities to add more tangible value to the community, such as their
First & Adams Plaza and recreational fields. The city also involved the community throughout the design and

1	The median household income (MHI) in Spokane in 2023 was $65,016, some $12,000 less than the U.S. MHI and far less than the M HI of
Washington state,

2	Based on the ALICE (Asset Limited, Income Constrained, Employed) definition, developed by the United Way.

3	Green bonds are a bond instrument that use proceeds to finance or refinance environmental, water, or clean energy projects.

January 2025 v=,EPA


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Communities with Combined Sewers Adapting to a Changing Climate: Spokane, WA

construction process by sharing drawings of projects and distributing door hangers with additional information.
Through public outreach to the community, Spokane was able to highlight the value of protecting the river.

Enhancing Resiliency

The last CSO storage tank was installed in 2020, so Spokane is currently monitoring the system and making
operational changes as needed. By actively monitoring the tank levels through their SCADA system, Spokane can
manage tank volumes to increase effective storage capacity within the system in response to local storm events,
which also increases their resiliency to future climate regimes. It also provides the city with performance data they
can use to make ongoing adjustments to their system, such as targeted green infrastructure installations or
updated regulator settings.

CSO Overflow and CSO Tank Usage

140	250

2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024

^^¦CSO Overflow Volume CSO Tank Usage —•—CSO Overflow Frequency

From 2014 through 2024, an increasing number of CSO storage tanks have steadily captured more and
more CSO volume, so that by 2023, no overflows occurred.

Spokane also leverages additional sources of funding to continually improve the resiliency of their wet weather
infrastructure. For example, through successful grant writing, the city was able to manage runoff from its largest
stormwater basin through a series of projects totaling $25 million. Additionally, they have set up internal
partnerships with the city's Street and Parks department to create more pervious surfaces and enhance
stormwater management.

January 2025 x-/EPA


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Communities with Combined Sewers Adapting to a Changing Climate: Spokane, WA

In recent years, Spokane has conducted several studies on the impacts of changing climate conditions and
potential impacts to their system:

•	Starting in 2021, the city included climate change information from the University of Washington's Climate
Impacts Group in their Sewer Modeling Synopsis, a modeling analysis of the CSO basin and separate
sewer basins.

•	In 2023, to support the development of their 2023 Water System Plan. Spokane included a climate
assessment (Spokane Future Flows - Climate Assessment) of impacts from changes in precipitation and
temperature based on the Intergovernmental Panel on Climate Change Sixth Assessment Report.

•	In 2024, the city started working with EPA's Climate Resilience Evaluation and Awareness Tool to model
climate change impacts on their water utilities. Wth this data, the city is preparing memorandums on
climate impacts and environmental justice, as well as creating a Climate Vulnerability Index Map and
finalizing a Climate Risk and Vulnerability Assessment.

Additional Information

For more information on the City of Spokane, contact Marlene Feist, Public Works Division Director at
mfeist@spokanecitv.org. Additional information on Spokane's permit, CSOs and climate adaptation
can be found here:

•	Spokane's 2022 NPDES Permit (WA0024473)

•	The City of Spokane's Public Works and Utilities Wastewater Website

•	The City of Spokane's Integrated Clean Water Plan

EPA Publication 830-F-25-006

January 2025 *>EPA


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