Liberty Island water tunnel

Opportunity

The Statue of Liberty is a World Heritage Site and a universal symbol of freedom and democracy. Since 1992, visitors have depended on drinking water delivered through a single high-density polyethylene (HDPE) pipe 3 inches (7.6 cm) in diameter, and wastewater service using an HDPE force main 2.5 inches (6.4 cm) in diameter.

Designing new systems was challenging due to the extremely limited construction area on Liberty Island, the need to protect existing buildings, utilities, and historic seawalls, and the need to limit disruption to staff and the public.

Solution

Mott MacDonald was retained to design a new system to replace the existing pipelines. The National Park Service, which maintains and operates facilities on the island, chose pipebursting and horizontal directional drilling (HDD) as the preferred techniques.

In response to the difficult ground conditions, we conducted eight geotechnical borings to determine the quality of the bedrock. We recommended the use of conductor casings on each end of the HDD crossings, designed temporary systems to maintain water and sewer service during construction, obtained necessary permits, and coordinated with park officials to maintain visitor access during construction.

Outcome

To cope with the unstable fill beneath both Liberty Island and Liberty State Park, the exceptionally strict limits on construction, and unanticipated obstacles due to incomplete documentation, we delivered an effective solution that could be modified to respond to actual field conditions.

The end result is a robust and resilient water and wastewater solution that serves staff and visitors at one of America’s most iconic tourist destinations.