Opportunity
The watershed formed by the Passaic River and its tributaries covers most of northern New Jersey — and even inspired the poet William Carlos Williams’ short-story collection Life Along the Passaic River.
The Passaic Water Company was incorporated in 1849, and in 1857 it began pumping water from an intake below Great Falls in the city of Paterson directly into the mains that supplied the city. As pollution worsened in the river, the intake was moved just above the falls and then to the present intake at Little Falls, five miles (eight kilometers) upstream of Paterson. In 1902, the East Jersey Water Company constructed the world’s first large rapid sand filter system at Little Falls.
The current plant, operated by the Passaic Valley Water Commission, delivers approximately 60 million gallons (227 million liters) per day of Passaic and Pompton River water to a population of more than 750,000. Built in two phases in the mid-1960s and mid-1980s, the plant used a conventional treatment process consisting of walking beam flocculators, sedimentation basins and dual media filters.
By the late 1990s, the Water Commission recognized that the plant would be unable to satisfy the Stage 1 Disinfection By-Products Rule for trihalomethanes, many of which are carcinogenic. The plant required significant rehabilitation, and compliance with coming standards for surface water treatment and disinfection was seen as problematic.
Solution
In 2000, Mott MacDonald was contracted to provide engineering services toward a new and improved treatment plan. Services included a one-year pilot study, design, permitting, construction administration, and resident engineering.
Our recommendations included the following:
- Replacing the conventional flocculation/sedimentation process with a ballasted flocculation system
- Intermediate ozonation and conversion of the dual media filters to biologically active carbon filters with air scour
- Replacing filter underdrains
- Completely renovating the analytical laboratory
The treatment process was designed to keep the existing facility in operation during the entire construction period, with only brief shutdowns to allow new systems to be tied in to existing piping.
Outcome
The Little Falls plant is now the largest ballasted flocculation plant in North America. With a capacity upgrade from 75 MGD to 120 MGD, the plant is positioned to provide clean water to northern Jersey for years to come.