Improving Water Supply Reliability in Wilmington, North Carolina

Photo Credits: https://www.nature.org/en-us/about-us/where-we-work/united-states/north-carolina/stories-in-north-carolina/cape-fear-river/

Site Context

Wilmington is situated on the southeast coast of North Carolina, along the Cape Fear River. Wilmington’s location along the river is quite precarious as it is located downstream of multiple industrial towns. As a result, contaminants, specifically PFAs, infiltrate the water supply.

Wilmington is situated in the North Carolina Coastal Plain physiographic province, a region extending from the Piedmont to the North Carolina coast. Within this region lie six regional aquifers, including the Surficial Aquifer, Castle Hayne Aquifer, Peedee Aquifer, Black Creek Aquifer, and Upper and Lower Cape Fear Aquifers. These aquifers represent water-yielding formations that are relatively more permeable than the finer-grained formations (i.e. confining units) that generally overlay and/or underlie the coastal aquifers.

The City of Wilmington’s drinking water is supplied by the Cape Fear Public Utility Authority (CFPUA), which is a joint venture between the City of Wilmington and New Hanover County. The drinking water supply of CFPUA is sourced from both the Cape Fear River and the Peedee and Castle Hayne Aquifers. CFPUA was created in 2008 as a result of a merger between the City of Wilmington’s water department and the New Hanover County Water and Sewer District in order to leverage greater capital investment capacity to address combined sewer overflow issues.

Map Credit: https://www.cfpua.org/641/Your-Water-Service-Area

As a result of this history, CFPUA currently operates three unintegrated water distribution systems, each with its own independent raw water supply and service area:

Sweeney Water Treatment Plant
- Treatment Method: Granular Activated Carbon
- Raw Water Source: Cape Fear River via purchase agreement with Lower Cape Fear Water and Sewer Authority (LCFWASA)
- Treatment Capacity: 35 MGD
- Service Area: The city of Wilmington and some parts of New Hanover County
Richardson Water Treatment Plant
- Treatment Method: Nano-Filtration Reverse Osmosis
- Raw Water Source: Groundwater wells
- Treatment Capacity: 7 MGD
- Service Area: Remaining northern areas of New Hanover County
Monterey Heights
- Treatment Method: No treatment
- Raw Water Source: Groundwater wells
- Treatment Capacity: N/A (Direct, no filtration)
- Service Area: Remaining southern areas of New Hanover County

Thus, essentially, though connected to a larger regional utility authority, the City of Wilmington is effectively only served by one water treatment plant and one raw water source.

While Wilmington is situated on the shore of the Cape Fear River, it is actually located near the estuary of the river where the river is heavily influenced by ocean tides, making the water unsuitable for drinking water supply. In fact, the Cape Fear River can remain brackish even 15 miles upstream from Wilmington. Consequently, to access water from the Cape Fear River, the CFPUA relies on a purchasing agreement with the Lower Cape Fear Water and Sewer Authority (LCFWASA) which operates a water intake 20 miles upstream from Wilmington. Raw water of up to 35 million gallons per day (MGD) can then be delivered through an underground pipeline to the Sweeney plant to be treated into drinking water. Meanwhile, for similar reasons, two other neighboring counties, including Pender County to the north of Wilmington and Brunswick County to the west both purchase water from LCFWASA and utilize the same pipelines. Though the allocation of the water supply between the three users is regulated through an agreement, CFPUA’s intake is situated at the end of the pipeline, effectively making its water right junior to the other users.

Map Credits: Shawn Li

Major Issues

As CFPUA’s water treatment and distribution systems remain unintegrated, as the largest service area in the system, the City of Wilmington relies on a singular water supply. Despite CFPUA’s efforts to add redundancies to ensure that the Sweeney plant can remain operational through all types of incidents, the complexities of the raw water delivery system through a 20-mile pipeline inevitably cause unreliability issues. Failure could and has occurred at LCFWASA’s intake and pumping station; during Hurricane Florence, flood water eroded the soil around sections of the pipeline, exposing the pipes to a highly destructive storm. With more frequent and severe storms anticipated, the vulnerabilities of the current system will require more redundancies to be built into every part of the water delivery process. Combined with the fact that there are two major competitors for LCFWASA’s raw water, which can cause water shortages in Wilmington during peak demand or during low supply caused by droughts, the need for diversifying the water portfolio becomes more evident for Wilmington.

Proposed Interventions

The City of Wilmington has a water reliability issue. Using the Cape Fear River as the city’s sole source of water is irresponsible and potentially dangerous. In the event of harmful contaminants polluting the river, there is no backup water source; residents would be forced to purchase pre-packaged water bottles. Reliability and stability are at the root of Wilmington’s water issues. In order to combat this, we propose two interventions to increase the city’s resilience.

1. Expanding Local Water Storage

One way to increase the resilience of Wilmington’s water supply is by expanding the local water storage. In case of a breakdown at the Sweeney Water Treatment Plant or contamination in the water supply, having potable water on hand is essential. Currently, Wilmington’s local water supply has the capacity of less than 24 hours worth of water. The current storage at the Sweeney Water Treatment Plant is 21.5 million gallons, which is 140% of the current average daily production (15.5MGD) but 93% of peak production of 23 MGD.

We recommend expanding the current storage of 21.5 million gallons to 46 million gallons. With this amount, Wilmington would be able to supply water for 71 hours during average use and 48 hours during peak use. Expanding the local water storage ensures that even in times of crisis, Wilmington has access to safe drinking water.

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2. Establish Pipe Interconnection

Though a one-way interconnection between the Sweeney and Richardson plant has recently been added to allow Sweeney to send treated water into the Richardson service area during peak demand, the Sweeney plant does not have a backup source for raw water or treated water. Given that the granular activated carbon (GAC) filters at the Sweeney plant will be capable of also treating groundwater, we are proposing a two-way pipe interconnection to be installed so that the Sweeney plant can also draw raw water from the groundwater wells situated around the Richardson plant.

Additionally, a pipe interconnection with utilities of neighboring counties can add additional redundancies to protect against pipe failures in the raw water delivery pipeline. Though Pender County Utilities (PCU) also utilize the same raw water sources through LCFWASA, it only shares certain sections of the pipeline with CFPUA. Thus, an interconnection with PCU can allow CFPUA to leverage the redundancies and excess raw water and treatment capacity of PCU to provide relief for Wilmington water users.

Importance of Regionalization

Regionalization is the clear solution to Wilmington’s water issues. While we commend the steps taken in 2008 to merge two water authorities, further regional cooperation is necessary. However, the path to regionalization is not always a smooth one – it requires consensus among a larger group, which can be difficult to achieve. In addition, the upfront costs of merging systems can be prohibitive to smaller authorities. Taking a regional approach to water supply planning in southeast North Carolina is the path forward to ensure access to reliable drinking water in Wilmington.

In conclusion, while infrastructural solutions can be effective in addressing water supply challenges in southeastern North Carolina, a more integrated and dynamic approach to governance is necessary for long-term resiliency. Rather than relying on individual bilateral agreements, a comprehensive solution that addresses the management of water supply and related challenges is needed. By implementing such a solution, southeastern North Carolina can better ensure a sustainable and resilient water supply for years to come.