Western Wake Regional Wastewater Project, United States of America

Scheduled for completion by the end of 2010, the new Western Wake water reclamation facility forms the main element in a major scheme intended to provide a regional wastewater treatment solution, to meet the needs of the area's growing population through to 2030.

The project represents the culmination of extensive collaboration between a variety of state and county authorities and is being implemented as a cooperative partnership of four local towns – Apex, Cary, Holly Springs and Morrisville – led by Cary. When it comes into service the plant will increase the region's wastewater treatment capacity by 18 million (US) gallons per day, although initially it is expected to receive around half that volume.

In addition to the construction of the new treatment works, the plan also requires the expansion and rehabilitation of an existing WWTP, the provision of three new pumping stations, two force mains, an interconnecting sewer system and a new discharge point.

The total project cost is around $380m.

BACKGROUND

Regulatory, economic and demographic factors have all acted as drivers on the project.

Under the terms of an inter-basin transfer certificate issued by North Carolina, by 2011 cleaned wastewater must be returned to the Cape Fear River basin. The existing plants serving the towns of Apex, Cary, Morrisville and part of Wake County, discharge into the Neuse River basin – making the construction of new facilities inevitable to meet this new requirement. In addition, state regulators have also actively encouraged Holly Springs to change from its currently used discharge point at Utley Creek to the main body of the Cape Fear River.

The economic vitality of the region has also led to an increasing number of businesses and people relocating to Wake County – home of the state's Research Triangle Park with its universities, high-tech industries and corporate headquarters. The needs of this expanding population over the next quarter century – even if modelled at a relatively slow rate of growth – will place significant demands on the existing infrastructure.

Continued industrial and residential growth has been forecast particularly in the western portions of the local towns and along a number of the major interconnecting routes. To convey wastewater eastwards from these growth areas to the existing treatment plants – many of which have limited scope for expansion – would be both costly and difficult to achieve.

With the rational use of water resources widely accepted as one of the key factors in the long term sustainability of the region, the challenge was to provide cost-effective services while protecting the community's quality of life. Against a background of the state regulatory agencies' preference for regional wastewater management planning, the idea of a centralised solution began to take root, not least since the alternatives seemed likely to have greater environmental impact than a single new facility.

Facing the common problem of impending capacity shortfall, six of the county's local governments worked together from May 2002 to July 2004 to investigate the possible options for a regional solution to meet their needs. The study programme began with a review of 24 potential schemes, before selecting seven for further detailed evaluation and examining the financial impacts and alternative organisational models for the development.

At the end of the process, four of the six local authorities decided to go ahead with the construction of regional wastewater management facilities, joining together to form the Western Wake Partners to progress the project.

PROJECT IMPLEMENTATION

The new Western Wake water reclamation facility itself forms the main element in the project and accounts for slightly over $190m of the project budget. This plant – designed by Arcadis, responsible for devising a highly successful WWTP for Cary in the mid-90s – is to be a state-of-the-art facility offering biological nutrient removal, filtration, UV disinfection and biosolids treatment to ensure the required effluent quality. The initial plant design provides a capacity of 18 million gallons/day, with the potential for expansion to 30mgd in the future.

Sludge treatment is planned to involve a 20 day period of mixed aeration within aerobic tanks and then ultimately either tankered off-site for further processing or sent to landfill.

In addition, three new pumping stations – at West Cary, Beaver Creek and the plant – two new force mains and an outfall to Cape Fear River will be constructed, along with interlinking pipelines and improved gravity sewers.

The scheme is to be implemented in two phases. Phase I – at a cost of around $250m – is intended to meet the needs of the partner towns until 2020 and must be operational by the end of 2010. It will provide a 24mgd discharge capacity to the Cape Fear River below Buckhorn Dam to comply with the terms of the state's inter-basin transfer certificate. Scheduled for completion by the summer of 2020 and costing a further $120m, phase II will increase the discharge capacity to 38mgd and meet the projected demands of the region for the following 10 years.

KEY PLAYERS

The project partners are the towns of Apex, Cary, Holly Springs and Morrisville; Cary is the lead partner. Wake County and Fuquay-Varina were also key participants in the two-year study process that ultimately led to the decision to move forward with the regional approach. The consulting engineers are CDM and Hazen & Sawyer; CH2M HILL and Arcadis are responsible for the plant design. The North Carolina Department of the Environment and Natural Resources (NCDENR) and North Carolina Environment Management Commission (NCEMD) are the regulatory authorities.