Hydro-Dyne Eng. was named to the University of Florida’s (UF...
Virginia Port Authority (VPA) has the largest and deepest natural harbor on the East Coast, Hampton Roads Harbor. Because the harbor offers unobstructed transport year-round, it is the busiest port south of New York City and home to the world’s largest concentration of naval operations. It has bases representing every branch of the U.S. Armed Forces, major Coast Guard maneuvers and is home to the headquarters for the North Atlantic Treaty Organization.
Hampton Roads Harbor links the East Coast port to 250 ports and 100 countries, and services 90% of the world’s shipping lines. The busiest of the harbor terminals, Norfolk International Terminals (NIT) has about 670 acres of land, two 1,320-ft cargo piers and nearly 6,000 ft of marginal wharf served by 11 container cranes.
NIT utilizes the world’s largest Suez-class container cranes and straddle carriers for handling the containerized cargo. Easy access to the Chesapeake Bay and direct access to rail and trucking facilities make NIT the port of choice for container vessels when unloading their cargo at Hampton Roads.
NIT is located at the confluence of the Lawrence and Elizabeth rivers. The number of container units passing through NIT has nearly doubled over the past decade. VPA chose to improve handling processes and upgrade the south terminal site to ensure excellent port services for its customers and support expected future growth.
VPA knew port upgrades would have an impact on nearby wetlands and sensitive waterways, including the Elizabeth and Lawrence rivers. The wetlands attract wading and migratory birds, including osprey, and are a spawning ground for fish and frogs. Because of this, VPA wanted an environmentally friendly storm water solution that would reduce any impact.
In addition, because NIT is adjacent to an environmentally sensitive river in the Chesapeake Bay watershed, state and federal environmental regulations required that its renovations include extensive storm water treatment. Protecting the Elizabeth River, where the Hampton Road Harbor is found, became an important goal for NIT and VPA.
“Historically, NIT has managed storm water runoff proactively by carrying out several environmental initiatives along the river, including installation of an under-wharf storm water detention basin and wetland restoration,” said Pam Boatwright, River Stars’ program manager for The Elizabeth River Project.
While water quantity management was not a concern at NIT because the site generally drains to open water in the Elizabeth and Lafayette rivers, water quality was a concern. Terminal construction and future operations would create construction sediment, motor oil, grease and brake pad dust, as well as airborne pollutants. Rainfall washes these pollutants from the terminal’s impervious paved surfaces into the nearby rivers.
Storm water management
In 1988, the Virginia General Assembly enacted the Chesapeake Bay Preservation Act to impose effective pollution prevention practices for developments near the environmentally sensitive lands of the Chesapeake Bay watershed. The Virginia Stormwater Management Program protects properties and aquatic resources from damage caused by increased storm water runoff volume, frequency and peak rate because of increased urban development. The Code of Virginia (4VAC3-2 et seq.) outlines how storm water management programs must address any adverse impacts and comprehensively manage the storm water runoff quality and quantity on a watershed-wide basis.
The Virginia Department of Conservation and Recreation is the lead agency for coordinating the state’s storm water pollution control programs. Wanting to maximize the land surface on the existing terminal site and protect the Elizabeth River, the VPA contracted Moffatt & Nichol, Norfolk, Va., to develop a storm water management plan for the south terminal renovation. Because existing storm water treatment provisions were in place at the terminal, Tim Reid, senior civil engineer and vice president at Moffatt & Nichol, created a design for the storm water system that incorporated those provisions.
Reid looked at several options including a conventional treatment pond, an underground pipe detention system, an under-wharf detention basin approach, and manufactured storm water collection and treatment systems.
“Detention ponds took away valuable land for containers, so a below-grade treatment system was a better choice,” Reid said.
The VPA stipulated that the redevelopment of NIT South meet or exceed state requirements for storm water treatment. In addition, it desired to over-treat storm water runoff at the NIT South Terminal in order to compensate for under-treated or untreatable areas.
Storm water separator
Moffatt & Nichol’s solution involved a strategy combining an under-wharf storm water detention basin and several Vortechs systems, which are high-flow hydrodynamic separators from Stormwater360. Because he had used the system on similar sites, Reid favored a tried and true solution.
“We had previous experience with the Vortechs units and knew the system was already approved for use in Virginia,” he said. “This allowed us to reduce the time to obtain the necessary environmental approvals and made permitting the job much smoother.”
The under-wharf storm water detention basin at NIT South treats approximately 110 acres and removes more than 300 lb of pollutants per year. The Vortechs systems remove an additional 55 lb of pollutants per year. Combined with existing storm water treatment facilities at NIT, these new measures increased terminal-wide pollutant removal to 1,561 lb per year—401 lb more than required by regulators.
The systems also had to withstand the weight of the yard equipment and containers. Having a flexible design, Stormwater360 easily customized the precast vaults for the systems to withstand the weight of new straddle carriers at the terminal—the structural design had to support wheel loads up to 144,000 lb. Each elevated crane weighs roughly 250,000 lb and straddles, lifts and stacks containers three or four high.
Precon Construction of Chesapeake, Va., a subcontractor to the prime, installed the Vortechs systems, and a Stormwater360 representative was on site to oversee installation.
Based on comprehensive lab, field and third-party testing, the storm water separator delivers proven results and site-specific solutions for all hydrodynamic applications and rainfall conditions. A best management practice, the underground systems treat NIT onsite runoff. The units collect sediment, oil and grease before discharging storm water to any outfall from NIT into the river or harbor, removing the need for land-intensive detention ponds.
The high-performance systems at NIT use an effective combination of swirl-concentrator and flow-control technologies to maximize treatment. The features separate and capture sediment and free oil, and work to prevent re-suspension and release of previously trapped pollutants. The design of the separator system allows for easy inspection and unobstructed maintenance access.
VPA’s construction of the under-wharf storm water detention basin and separator systems eliminated the need to dedicate seven acres of valuable container handling area for the construction of a conventional storm water detention pond.
Keeping this land for containers represents almost $3 million in terminal revenues a year to the VPA. Based on the increased capacity and efficiency represented by the full renovation of NIT South, the construction costs associated with the storm water treatment system can be recouped in less than two years.