We will convert combined sewers into HLSSand integrate HLSSinto major new developments, as appropriate
High Level Storm Sewers (HLSS) are one strategy for alleviating pressure on the combined sewer system and limiting CSO events. HLSS are designed to capture 50% of the rainfall, before it enters our pipes, and divert it directly into the waterways through permitted outlets, reducing the volume of flows that pass through the treatment plants and the combined sewer system. In addition, they alleviate street flooding in problematic areas.

But we cannot simply install these separated sewers at every site. Since they require a separate pipe and outlet to a waterbody, this strategy is only cost-effective for developments near the water's edge.

Therefore, the City will analyze each site carefully on a case-by-case basis to determine the appropriateness of this strategy. One area that is clearly a good candidate is the Hudson Yards area. Other developments that may also be appropriate for HLSS or for the complete separation of their sewer infrastructure include the Bronx Terminal Market, Queens West development, Gateway Estates in Brooklyn, and the Columbia University expansion in Manhattanville. (See case study above: Hudson Yards)

Progress (as of 4/22/08):
In April 2007, the Department of Environmental Protection (DEP) completed the drainage plan for the installation of High Level Storm Sewers (HLSS) in the Laurelton section of Queens. DEP has also identified additional drainage areas for HLSS in Throgsneck, Gowanus, Hudson Yards, Manhattanville, and the Yellowstone Boulevard area of Queens.