Launch Slideshow

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Bringing drinking water to an island community

Bringing drinking water to an island community

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    The first settlers came to Roanoke Island in 1585. Like the Dare County Water Department's other 12 service areas, the 18-square-mile island between North Carolina's coast and the Atlantic Ocean experienced chronic saltwater intrusion. Map: Mark Darwin, CDM Smith; Photos: CDM Smith

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    Horizontal directional drilling has been used to install 1,010 linear feet of 16-inch HDPE pipe over three locations; jack-and-bore for 36 road crossings in carrier sizes from 6 to 16 inches. This is a pipe-jacking heading east from the northwest corner of an intersection on Roanoke Island.

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    In addition to 56 miles of 6- to 16-inch pipeline, the Dare County Water Department's construction manager at risk (CMAR) contract with CDM Smith includes improvements that will increase pumping capacity from 800 - 900 gpm to a maximum 1,950 gpm under typical operating conditions. New, 100-hp pumps have replaced two 30-hp high-service pumps; transmission pumps have been rehabilitated.

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    When the project's completed this year, North Carolina's Dare County Water Department will have more than doubled Roanoke Island's storage capacity. This new, 300,000-gallon tank is located at an abandoned county facility.

Structuring bid packages

In 2009, the Dare County Board of Commissioners saw an opportunity to address the island's water issues and reinvigorate the economy. Aided by a $500,000 North Carolina Rural Economic Development Center grant, they decided to move forward with the proposed expansion. In addition to providing high-quality water, the project would support local businesses and create much-needed jobs on the island.

In March 2009, through a qualifications-based selection process, the Water Department selected CDM Smith as the design engineer; and in August 2009, through a separate qualifications-based selection, selected CDM Constructors as the construction manager at risk (CMAR).

“From experience with three previous projects, we believe CMAR provides a high level of coordination early in the project, resulting in improved schedule management and controlling project costs,” says Dare County Finance Director David Clawson. “In addition, references are essential for firms to be able to obtain future work — an incentive to provide a quality project.”

In November 2010, at approximately the 30% design level, CDM Smith's team developed a guaranteed maximum price (GMP) of $20,387,815; and in January 2011 began construction.

The CMAR approach offered a number of advantages over traditional design-bid-build methods. Establishing a GMP early, while the bidding environment was favorable, ensured the county wouldn't be affected by economic factors that could increase costs. These savings will ultimately be passed on to ratepayers.

In addition, the procurement method provides flexibility that streamlines the design process, which at 50% completion is estimated to have saved $900,000. In one instance, the CDM Smith team coordinated with electrical and mechanical pump room subcontractors and Water Department employees to develop a sequence of work that required only short-term shutdowns. Existing water systems remained operational while the new pumping system was installed, avoiding costly bypass pumping and saving nearly $100,000. And in several areas of the distribution system, the firm's team worked with pipeline subcontractors and the local DOT to make minor revisions to the alignment and reduce pipe lengths or repaving.

These savings have helped offset other unforeseen conditions and keep the project on budget. Unexpected issues included pavement that was found to be 12 inches thick from several overlaying treatments over the years. In other instances, work restrictions or additional paving were needed to work around areas where easement couldn't be obtained without condemnation.

The method also generated subcontracts in a size range that was both attractive to and manageable by local contractors. The project was divided into five design packages that were then divided into more than 15 separate procurement and construction packages. The first design package included the pump room improvements and new ground and elevated storage tanks. The remaining four design packages included the 56 miles of water main, which were divided up geographically.

It's worked: At the halfway point, nearly 85% of the work has gone to regional subcontractors and allowed approximately 60% of the construction work to be performed by subcontractors located in Dare County.

With a great deal of construction taking place on private property, the level of communication CMAR requires has greatly facilitated resolution of right-of-way issues. The CDM Smith construction team and county quickly identified areas where easements were unavailable. Working closely with pipeline subcontractors and the local DOT has averted costly condemnation proceedings. To date, the county hasn't had to condemn a single easement. All easements have been obtained through negotiations or avoided by modifying construction means and methods.

Throughout the project, construction continues to be guided by the county's desire to protect the island's wildlife and wetlands. An environmental assessment was performed to identify habitats and areas considered environmentally sensitive. Where possible, trenchless technology is being used to install pipelines — under a stream or designated wetland, for example — in ways that don't disturb sensitive areas.

In November 2011, residential customers were brought online; and in December the Dare County Justice Center and municipal complex was connected to the system — both key milestones. When finished, the project may provide the additional benefit of lowering fire insurance premiums for county residents and businesses.

—Irby (irbykc@cdmsmith.com) is an associate with CDM Smith, the engineering consulting company formerly known as CDM; Flatt (kenf@darenc.com) is the Dare County Water Department's utilities director; and Hernandez (hernandezy@cdmsmith.com) is a principal with CDM Smith.