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Upgrading an aging water system, cost-effectively

Benefits have included timely response to emergencies, financial savings to the City, elimination of leaks and water-main breaks, significant improvement in valve operability, improvement of water quality and volume, improved customer relations, and reduction of customer complaints.


The public water supply system in the City of Wilmington, Delaware dates from 1796. Nearly 33% of water mains in the Wilmington water distribution system are at least 75 years old and over half of the water mains are cast iron without internal cement-mortar lining.

Over the years the Wilmington water supply system has expanded to a network of surface water treatment plants, storage reservoirs, pump stations, and water mains serving 140,000 people in the city and its suburbs.

To modernize the water distribution system, the Department of Public Works was faced with the need to inspect, monitor, and upgrade water mains, hydrants, and valves, while responding to emergencies and prioritizing expenditures in order to use its resources as cost-effectively as possible.


Since 2005, Mott MacDonald has provided the City of Wilmington with a comprehensive array of engineering services, ranging from needs assessment to hydraulic modeling, design for new pipelines and rehabilitation projects, and construction oversight for the testing, cleaning, lining, and replacement of water mains, and the inspection and testing of valves and fire hydrants.

Needs assessment and asset management

In 2005, we provided a Needs Assessment Report to the Department of Public Works, outlining the benefits of initiating a capital improvement program for the City’s water system.

The report provided an overview of the water distribution system, highlighted areas where rehabilitation was needed, and provided a proposed schedule for a capital improvement program. The report also provided data for the following:

  • Age, material, and size of the existing water mains
  • Number and types of valves and hydrants in use in the system
  • Number and type of water storage facilities
  • Number of domestic and commercial services, etc.

In 2012, we prepared an update to the 2007 report, called the Water Distribution System Assessment Management Plan. Updated information on the water system infrastructure included quantities and condition of water mains, valves, hydrants, tanks and pump stations. The plan outlined completed water system rehabilitation projects and provided recommendations for additional improvements to the system, including critical areas within the system.

Hydraulic modeling

In 2012, Mott MacDonald took over and updated the City of Wilmington’s hydraulic model. We have invested considerable effort in verifying the accuracy of the model and calibrating it to more accurately reflect the City’s infrastructure. In 2013, we provided a report on the hydraulic model, detailing changes to the model and steps taken to increase its accuracy.

Pipeline construction

In 2013, we were contracted by DuPont to work with the City of Wilmington and Delmarva Power for the installation of a 12-inch (30-cm) water pipeline (as well as a 12-inch gas pipeline). The water pipeline will provide redundancy to the aging water service to the DuPont Experimental Station Laboratory and provide a connection between the Alapocas Pressure Zone and the Kennett Pressure Zone, which operate at approximately the same hydraulic gradient.

We are working with DuPont, the City of Wilmington and Delmarva Power to provide a complete design and specifications for the project. We will also provide inspection services during construction.

Rehabilitation of water mains

Since 2005, Mott MacDonald has provided water-main rehabilitation services including contract documents, contract procurement, construction oversight, and budget management.

Sliplining of water mains, Market Street, 2005

As part of a streetscaping/beautification project, we provided a minimally invasive method for cleaning, inspecting, and sliplining approximately 1,900 feet (579 meters) of existing water main and installing approximately 600 feet (183 meters) of new water main.

Cleaning and lining of water mains, Friend’s School, 2006

Following complaints of rusty water and low water pressure, we provided contract documents and plans for cleaning and lining approximately 8,500 feet (2.6 kilometers) of water main.

Cleaning and lining of water mains, Union Park Gardens and Browntown, 2008

This project was completed on time and on budget, despite challenges that included the need to replace lead or galvanized steel services, and to replace inoperable valves that prevented mains in the Union Park Garden area from being isolated.

Cleaning and lining of water mains, New Castle Avenue, Terminal Avenue, and South Market Street, 2009

For this project to clean and line approximately 10,000 feet (3 kilometers) of water main, we worked with the contractor to resolve design challenges and with an environmental engineering firm to address issues caused by the contractor’s excavation in a brownfield. We reviewed the contractor’s change orders, reducing the cost to the City by $325,000.

Cleaning and lining of water mains, Wilmington area, 2010

We helped resolve several challenges, including the realignment of a water main at Merchant Square Shopping Center and water service complaints at Gander Hill Prison.

Cleaning and lining of water mains, North Wilmington/Concord area, 2010

This project to clean and line approximately 20,000 feet (6 kilometers) of water main, and to replace hydrants and inline valves, was completed within the contracted time. Public feedback and a decrease in complaints indicated a significant improvement in water quality and volume.

Cleaning and lining of water mains, Delwood/Grayrock, Windsor Hills, Brookvalley, Fairfax, Union Park Gardens, Browntown, and Galewood, 2012

We identified several areas where new cement mortar lining had failed. These areas were repaired by the contractor, helping ensure quality workmanship and reduce costs to the City. When a hyperflushing project in the Delwynn Community failed, we provided additional plans and a cost estimate for emergency work.

Replacement of water mains

Since 2008, Mott MacDonald has provided water-main replacement services including contract documents, plans and specifications, construction oversight, and permitting documents.

Replacement and testing of water main, Railcar Avenue, 2008

We provided contract documents for the replacement and testing of a water main located under existing stockpiles, railroad tracks, and wetlands.

Replacement of water mains, Carrcroft area, 2009

We provided contract documents, construction oversight, and permitting documents for the replacement of approximately 8,000 feet (2.4 kilometers) of water mains, 30 valves, and 4 hydrants. We worked with City of Wilmington crews, the contractor, and the Delaware Department of Transportation, and addressed customer concerns.

Replacement of water main, Pennsylvania Avenue, 2012

Following several water main breaks that affected traffic in the area, we provided plans and specifications for the emergency replacement of approximately 420 feet (128 meters) of water main.

Replacement of water mains, Union Park Gardens and Hillcrest, 2012

We helped improve water quality and eliminate recurring water leaks in Philadelphia Pike by providing contract documents and construction oversight for the replacement of 1,400 feet (426 meters) of water main and the transfer of 42 water services from 2-inch (5-cm) water main to an existing 8-inch (20-cm) cleaned and lined main.

Inspection, testing, and rehabilitation of valves and hydrants

Since 2005, we have provided services for valve and hydrant services including contract documents, project oversight, budget oversight, and GIS mapping.

Valve and hydrant rehabilitation, 2005

We prioritized the necessary work and provided contract documents, contract and budget oversight, and a GIS map with work orders for each hydrant valve to be rehabilitated or replaced.

Valve inspection, exercising, and data collection, 2007

We prepared contract documents for the inspection, exercising, and data collection of valves. As a result of the project, valve operability in the distribution system increased from 39% to 82%.

Valve and hydrant rehabilitation, 2010

We provided guidelines and a GIS map with work orders to prioritize the rehabilitation of approximately 51 valves and hydrants.


In its work for the City of Wilmington, we have demonstrated that an asset improvement program for an aging water distribution system needs to have long-term sustainability, a realistic budget, and performance goals.

By supporting a program of prioritized asset renewal, we have provided the City with an excellent return on investment and the minimum possible impact on ratepayers.

Benefits of our work have included timely response to emergencies, financial savings to the City, elimination of leaks and water-main breaks, significant improvement in valve operability, improvement of water quality and volume, improved customer relations, and reduction of customer complaints.

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