Resilient Water Supply Planning at Orange Water and Sewer Authority, North Carolina
The Carrboro-Chapel Hill region of North Carolina has experienced several severe droughts, is experiencing steady population and economic growth, and may also experience increased flooding and more severe droughts as a result of climate change. As a critical water, wastewater, and reclaimed water services provider for this area, Orange Water and Sewer Authority is preparing for an uncertain water supply future through a variety of methods. Orange Water and Sewer Authority is attempting to increase the resilience, reliability, and redundancy of its water sources, operations, and facilities, with steps such as diversifying its water supply portfolio, increasing water conservation pricing signals and water conservation education and outreach, upgrading and building new facilities to reduce water use, and working with neighboring utilities to enhance the region’s water supply planning efforts and modeling climate impacts on those supplies.
Orange Water and Sewer Authority (OWASA) supplies drinking water, wastewater, and reclaimed water services to the Carrboro-Chapel Hill region of North Carolina. North Carolina is fortunate to have ample water supply in most years, but it also occasionally experiences severe droughts. The region experienced two historic droughts in 2001-02 and 2007-08, and OWASA and many surrounding water utilities in the region found it necessary to implement mandatory water use restrictions to extend their available supplies. The two extreme droughts heightened utility and customer awareness about the importance of planning for unpredictable futures, as running out of water is not an option. In addition, the utility is concerned about the potential for extreme flood events, which are projected to accompany increasing climate variability.
To ensure stable water supply and system operation under a range of uncertainty, OWASA has been engaged in a continual movement toward climate preparedness since the late 1990s. Although many of the utility’s operational changes have helped enhance climate resiliency, more formal efforts regarding climate preparedness have emerged over time, particularly as climate science has improved and in the wake of the recent severe droughts in the region.
OWASA funds its ongoing operations and maintenance programs solely from the revenues it receives from its water, sewer, and reclaimed water customers. It has authority to debt finance capital improvements, and occasionally receives project funding support in the form of federal and state grants and partner funding. For example, design and construction of OWASA’s reclaimed water system was funded by state and federal grants totaling about $2.25 million and by The University of North Carolina at Chapel Hill, which provided about $13 million for the project.
OWASA’s first major step toward resilient water management included an effort to increase water supply capacity and diversify long-term water supply sources by acquiring an active local rock quarry for future use as a water supply reservoir. In accordance with OWASA’s agreement with the quarry operator, quarrying will cease in 2030, at which time OWASA will be able to fill the quarry pit and use it as a water storage reservoir. Purchase of this quarry provides long-term reliability in water supply by enhancing local water storage capacity and generating a water storage area that is locally managed. This no-regrets action (i.e. an action that provides benefits irrespective of climate change) also has financial benefits in the short term, as OWASA receives annual lease payments (revenue) from the company that mines the rock from the quarry. OWASA projects that at the conclusion of mining, the Quarry Reservoir will provide between 1.3 and 1.9 billion gallons of additional water storage capacity.
In 2001-2002, North Carolina experienced one of the most severe droughts on record. OWASA implemented mandatory water use restrictions and was able to meet essential water needs throughout that event, but the utility became acutely aware of the community’s vulnerability to subsequent and/or more severe droughts. Over the next several years, OWASA implemented a variety of projects to increase water conservation, reduce water demand, and increase water reuse and recycling. The agency began recycling process water at its drinking water plant, which reduced average day raw water withdrawals by about 6-7%. It also implemented various new pricing mechanisms, including seasonal water pricing (applicable to all nonresidential customers and master-metered residential developments) and increasing block water rates for individually metered residential customers to encourage conservation, especially during the peak summer season. In partnership with UNC Chapel Hill and with additional financing from federal and state grants, OWASA also designed, constructed and launched a reclaimed water system, which began operations in 2009.
The reclaimed water system now meets about 10% of the community’s total water demand, and it reduces long-term water costs for the University. The reclaimed water storage tank and pump station is designed to be resilient to climate-change impacts. During the design and construction process, OWASA and partners knew that the plant needed to be elevated, at minimum, to withstand a 100-year flood event. However, given recognition of increasing climatic variability and the potential for increased flood volumes, they elected to elevate the plant even higher in order to enhance its long-term resilience. By building climate resilience into the design and construction phases of their already funded project, OWASA implemented a low-cost adaptation strategy that will help maintain water supply resilience and reliability under a variety of future climate conditions.
In 2014, as part of its strategy to maintain a diverse portfolio of water supply options, OWASA applied to the State of North Carolina to retain the right to use a portion of the water supply storage available from Jordan Lake, a federally constructed multipurpose reservoir located south of the OWASA service area. OWASA now holds a 5% water storage allocation, and can access that Jordan Lake water by having a nearby utility withdraw, treat and deliver water to OWASA through water mains interconnections with a third utility. This arrangement is for emergency access purposes only, and does not ensure OWASA access to its water allocation when needed and in the amounts needed. OWASA has been partnering with neighboring utilities to evaluate the most cost-effective options for ensuring permanent access to the water supply available in Jordan Lake. Jordan Lake has proven to be resilient to the recent extreme regional droughts; therefore, OWASA believes that by retaining access to that reservoir, it will further reduce its vulnerability to future droughts.
Since 2007, OWASA has also been engaged in a variety of efforts to more specifically evaluate how climate change may affect its water supply. For example, the 2010 update of the utility’s Long Range Water Supply Plan includes water yield estimates that are generated from historical data that include water supply trends during historic droughts of record. OWASA also developed a “what if” water shortage scenario to evaluate how climatically driven water shortages could affect its water supply. In the scenario developed for the Long Range Water Supply Plan, OWASA assumed historic reservoir inflows would be reduced by 30%, and it examined what the impacts would be on water supply yield and evaluated how strategies and actions identified in its plan could be used to ensure an adequate water supply even given potential shortages associated with that scenario.
OWASA is now engaged in more formal climate and water supply modeling. Through a Carolinas Integrated Sciences and Assessment partnership, a PhD student at the University of South Carolina is doing research that will help OWASA apply current climate science in its water supply planning and decision-making processes. The student will use output from several downscaled climate change models as input into a hydrologic model of the OWASA system, and the results will be used to assess the resiliency of alternative water supply development scenarios. Through downscaling and comparing the results of different climate models, OWASA hopes to have a better understanding of how increasing climate variability may affect the yield and reliability of its water supply system over the long term. Although the models will not be used to predict future levels of risk, they will be used to help OWASA better understand under what climate scenarios it will not be able to support current and projected water demands. OWASA plans to identify management solutions that address these challenges and maintain reliable water supply across various scenarios, thereby building resilience into its future water management framework. These projections will also likely be incorporated into revised demand and yield projections through 2065, thereby informing the actions and investments that the utility makes in the years ahead.
OWASA operates under the general philosophy that no matter what the climate future, everyone will be better off with more efficient use of current water supply. To that end, the agency has simultaneously engaged in a variety of activities to enhance conservation and the overall reliability of its water services, including: increasing efficiency at various facilities, developing a drought response operation protocol and Water Shortage Response Plan, developing a comprehensive emergency management plan, investing in standby power generators at all critical water and wastewater facilities, and engaging in significant public outreach and education. OWASA is also engaged in climate mitigation activities, and is taking steps toward reducing its operational carbon footprint.
Outcomes and Conclusions
OWASA’s efforts to promote the conservation and sustainable management of the community’s water resources have been very successful. Efforts to recycle processed water at its drinking water facility reduced overall water withdrawals by 6-7%, and the reclaimed water system developed in 2009 now meets about 10% of the community’s total water demand. As a result of those and other efforts, annual average-day drinking water demands remain at about the same rate as in 1991-92, despite about a 60% increase in customer accounts. OWASA credits this success to a combination of operational changes and upgrades, greater conservation pricing levels, and extensive public education and outreach. OWASA continues to closely monitor water demand and supply, and is also looking for climate resilience metrics to incorporate into its monitoring framework.
Moving into the future, OWASA hopes to continue to build greater resilience, redundancy, and reliability into its operations and facilities in order to maintain a sustainable water supply in the face of an uncertain future. The redundancy of local water supply sources will expand as the quarry transitions to a water storage reservoir starting in 2030. OWASA is also exploring opportunities to gain more permanent access to a portion of the water supply available from Jordan Lake, a federally constructed reservoir that serves as a regional water supply source. Water utilities must apply to the State of North Carolina to receive water storage allocations from this lake, and OWASA currently has a 5% (5 million gallons per day) allocation. However, OWASA does not have a permanent way to access this water, aside from purchasing drinking water (that originates from Jordan Lake) from another utility. In the short term, this provides an insurance policy against running out of water during prolonged drought, but OWASA is searching for a more permanent, sustainable solution that successfully overcomes the sociopolitical and economic hurdles associated with the use of water from Jordan Lake.
Although OWASA recognizes the importance of integrating climate science with water supply planning, it has been somewhat limited by the lack of actionable science. For example, past climate-water yield analyses have been impeded by a lack of usable downscaled climate modeling data at temporal and spatial scales needed to inform for water supply planning and decision-making. However, OWASA has not let this challenge stop its efforts to enhance climate resilience. For example, to simulate water shortages in developing a long-range water supply plan, OWASA developed a simple water reduction scenario — what if reservoir inflows declined by 30 percent? This approach may lack the finer detail available with climatic modeling, but it still provided the utility with a hypothetical water shortage scenario with which to test its management policies and the potential reliability of alternative water supply investment scenarios. OWASA is now working with university partners to use downscaled climate models to inform its plans. Looking to the future, the utility is also interested in partnering on similar studies into how increasing climate variability may affect future drinking water quality and water use patterns and demands.
Much of OWASA’s success stems from strong partnerships and stakeholder support. Partnerships with regional universities, participation in the Jordan Lake Regional Water Supply Partnership, and direct representation on the EPA’s Climate-Ready Water Utilities Working Group have helped OWASA to better understand available science and adaptation options, as well as explore regional opportunities for collaboration. Strong stakeholder support and financing has also laid the foundation for many of OWASA’s largest projects, including development of the reclaimed water system in 2009. OWASA hopes to expand its partnership network with other utilities in the future in order to reduce cumulative risk and leverage opportunities to maintain a reliable and resilient water supply for the entire region.
Reynier, W. (2017). Resilient Water Supply Planning at Orange Water and Sewer Authority, North Carolina [Case study on a project by the Orange and Water Sewer Authority]. Product of EcoAdapt's State of Adaptation Program. Retrieved from CAKE: http://www.cakex.org/case-studies/resilient-water-supply-planning-orang… (Last updated December 2017)