Anacortes, Washington Rebuilds Water Treatment Plant for Climate Change

The city of Anacortes, WA recognized that its water treatment plant, located along the Skagit River and serving 56,000 people, was vulnerable to current floods and future climate risks. In 2003, the city recognized the need to update the facility from 21.4 million gallons of water per day (mgd) to a stated capacity of 31.5 mgd. Moving the facility out of the floodplain was deemed cost prohibitive in 2008, so officials decided to rebuild on the existing site. Such a strategy can be risky unless climate projections are taken into account and adaptation strategies implemented to reduce future vulnerability.

To determine the plant’s vulnerability, Anacortes officials worked with non-profit organizations to determine the ‘best available’ climate science and the associated impacts to the plant siting. A variety of climate risks were taken into account including:

• more frequent and intense storms
• saltwater intrusion
• increased sedimentation levels

Climate change impacts were projected through the 2080s and downscaled for the Skagit River area. These vulnerabilities included an expanded 100-year floodplain, an estimated 350% increase in peak suspended sediment load in winter, and anticipated upstream migration of the salt water wedge due to the effects of sea level rise.

In design and construction of this plant, officials sought to protect against higher risk of flooding by:

• minimizing penetration below current 100 year flood elevation
• raising critical electrical equipment out of the 100 year flood level
• utilizing water proofing techniques below 40 foot elevation
• designing ring dikes for flood protection

This plant was rebuilt on site at an expected cost of $56 million dollars and improvements to this design better prepare the facility to meet increased service demand as well as projected changes in climate.

How Did They Do It?	Applicable EPA Tools
Recognized climate risk and expected vulnerability Anacortes recognized the vulnerability of the facility to flooding in 2003 and 2008, however they also identified the cost prohibitive nature of moving the facility. When upgrading the facility they received input from scientists and used downscaled climate data to inform decision making.	The EPA Coastal Inundation Toolkit can assist utilities in better understanding facility vulnerability by illustrating a range of potential sea level rise and storm surge scenarios. EPA Coastal Inundation Toolkit
Incorporated projections of climate vulnerability within plant design to adapt to future conditions Developed a design that acknowledged current vulnerability and sought to reduce future vulnerability under anticipated future conditions. Elevated critical facility structures and included ring dikes and dewatering pump systems to protect against flooding. Utilized water tight construction on the facility and used water proof membrane below 40 foot elevation. Designed to have no/minimal penetrations below 100 year flood elevation and have electrical switch gear located above 100 year flood level. Raised and strengthened levees near the plant. Increased sediment removal ability to deal with expected increase from climate change (although plant is still trying to quantify the projected increase of sediment).	EPA’s Creating Resilient Water Utilities Adaptation Strategies Guide can assist utilities in identifying low cost adaptation strategies to incorporate within plan designs. EPA’s Creating Resilient Water Utilities Adaptation Strategies Guide
Identified information gaps for future research Preliminary modeling suggests saltwater intrusion is likely to be a future concern; additional analysis is planned. Further research is needed to better understand the long term challenges associated with sediment loads.	The Climate Resilience Evaluation and Awareness Tool (CREAT) helps utilities conduct traditional risk based or scenario based vulnerability assessments to better understand information gaps and necessary future research. The Climate Resilience Evaluation and Awareness Tool (CREAT)

Similar Cases and More Information

To see how a community analyzed the impact of sea level rise on a water utility, view Manchester-by-the-Sea. For a community that recognized the prohibitive cost of protecting a highly vulnerable facility and decided to move to a safer facility, see Iowa City. Protecting the Blue Plains facility is only one of several strategies Washington, D.C. has taken to reduce the threat of flooding on the community. To see how Washington, D.C. is using green infrastructure to reduce stormwater impacts and combined sewer overflows view the DC Consent Decree.

• Manchester-by-the-Sea, Massachusetts Assesses Climate Vulnerability
• Iowa City, Iowa Closes Vulnerable Wastewater Facility
• DC Utilizes Green Infrastructure to Manage Stormwater

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References

• Skagit Climate Science Consortium (SC²) Drinking Water (PDF) (2 pp, 867 K, About PDF)
• The Co-Production of Actionable Science for Assessment and Adaptation: Six Case Studies from the Water and Clean Water Communities
• Salish Sea Ecosystem Conference: City of Anacortes Water Treatment Plant Climate Change Mitigation (PDF) (24 pp, 5.5 MB)
• 2008 Skagit County National Hazards Mitigation Plan (PDF) (19 pp, 136 K)