In a continued effort to limit the amount of stormwater flowing into New York Harbor, the city Department of Environmental Protection (DEP) established a rule last week requiring all new construction projects to include excess water controls.

The rule is part of the NYC Green Infrastructure Plan, which proposed a $2.4 billion investment over the next 20 years to improve harbor water quality.

New York City is largely serviced by a combined sewer system, in which stormwater and wastewater are carried in the same pipe to treatment plants. During heavy storms, the system can fill up and is designed to overflow into the harbor to protect the city's water treatment plants.

The city's stormwater runoff sites include the Gowanus Canal, Newtown Creek, Flushing Creek, Flushing Bay and the Jamaica Bay tributaries.

“New developments will now be part of the solution in our efforts to have a cleaner and more beautiful harbor,” DEP Commissioner Carter Strickland said. “In the past, runoff from buildings and pavement added significant volume in our combined sewer system that ultimately discharges a mix of stormwater and sewage directly into the city's surrounding waterways when it rains.”

The stormwater rule requires new construction projects and major building alterations to capture stormwater runoff using “cost-effective” detention, infiltration and recycling techniques such as blue roofs, green roofs, sub -surface gravel beds and stormwater chambers.

According to DEP, the rule will limit stormwater runoff from development lots by an estimated 10 percent. The rule is expected to reduce overflows by as much as 800 million gallons over the next 20 years.

The expected cost added to a development project is expected to be between .3 and 1.5 percent of total construction costs. Existing homes and developments will not be affected by the rule.

“The cost of operating the city's water and sewer infrastructure is a cost that all New Yorkers in some way share,” said New York Real Estate Board President Steven Spinola. “The stormwater rule, as a critical part of of the city's Green Infrastructure Plan that will reap billions in savings over the next 20 years, will provide great relief to residents and businesses during economically difficult times.”

The rule takes effect six months after its January 4th publication. It, along with a Guidelines for the Design and Construction of Stormwater Management Systems, can be found at nyc.gov/dep.