Modeling Solution Aids Major Rezoning Study

by Srinivasan Rangjaragan

One of New York City's major transportation hubs, the Jamaica area of Queens, is a place people pass through — over 220,000 people use the AirTrain to John F. Kennedy airport or the Long Island Rail Road each day. But most see nothing more than the transport system they are using.

This situation is due to change with an ambitious new vision for the area as a thriving airport village with a mix of local and national stores. About $23 million has already been raised to continue development plans, led by the Greater Jamaica Development Corporation, for the run-down but improving area.

In addition to plans for retail and streetscape improvements, the area has undergone a major rezoning. In September 2007, the City Council approved the rezoning of 368 blocks, which was, at the time, the largest rezoning in the City's history.

Proponents say the former zoning along the JFK AirTrain route did not anticipate future development or new investment opportunities. They claim that the rezoning will allow for major retail and residential development in surrounding Jamaica as well as more transit-oriented development.

Critical to acceptance of the proposals was a thorough appraisal of the many potential impacts of the development. Key among these was the plan's Final Environmental Impact Statement (FEIS), prepared by the HydroQual consulting firm, which assessed Total N, fecal coliform and BOD levels at the water pollution control plant (WPCP) and in CSO discharges to Jamaica Bay as indicators of the pollutant loads. Wallingford Software's InfoWorks CS wastewater network modeling solution was used to obtain an accurate picture of the potential impacts.

The loads for these parameters were developed for three conditions — the existing situation and two future scenarios — both with and without the proposed development. This work was undertaken as laid out in the City Environmental Quality Manual, by calculating the loads for the three major sources — effluent from the WPCPs, CSOs, and non-CSO stormwater — in each of the WPCP drainage areas tributary to Jamaica Bay. The WPCPs include the 26th Ward, Coney Island, Jamaica and Rockaway WPCPs. Although the future actions are presumed only to affect the Jamaica WPCP, all four plants impact the Bay, so all were included in the analysis.

Load calculations are based on applying concentrations of the three parameters to flows for each of the three main loading sources. Concentrations and WPCP flows were based on information for 2005 obtained from the New York City Department of Environmental Protection (NYCDEP) annual progress reports.

Although not taken into account in the predictions, the development is likely to incorporate BMPs (also known as Sustainable Urban Drainage Systems, or SUDS) such as stormwater detention, enhanced water conservation practices and possibly other sustainable water supply and wastewater and stormwater management techniques.

There are also planned improvements to the sewer system, which will improve the quality of discharges from CSOs. These may be completed ahead of 2015 and would also significantly reduce the difference between the current and future scenarios. This means the calculations have an inherently conservative bias and the figures could be assumed to be a ‘worst case' scenario.

Future build and no-build WPCP flows were based on NYCDEP projections for 2015, and in the case of the Jamaica plant, on information in the 2006 draft of the draft environmental impact statement's infrastructure chapter.

To calculate the CSO and stormwater loads, base WPCP flows were used along with the concentrations, tidal and precipitation data as inputs to the models of the City's sewer system, which are in InfoWorks CS and HydroQual's Rainman solution, to calculate flows and loads.

One of New York City's major transportation hubs, the Jamaica area of Queen's, has undergone a major rezoning as part of an effort to transform the area into a thriving retail village.

Precipitation data recorded at JFK airport in 1988 (seen as a typical year) was used for the model simulations. Use of this rainfall record is consistent with other projection studies being performed in the area. Tidal patterns from the same time period were also input into the model to accurately simulate the hydraulics at the outfalls. Rainfall and tidal data was obtained from the National Oceanic and Atmospheric Administration (NOAA).

The modeling solution was used to simulate discharges into Jamaica Bay from three of the four combined sewer tributary areas: Jamaica, 26th Ward and Rockaway. Dry weather flows for wastewater and the three key pollutant concentrations for each sub-area of the study area tributary to Jamaica Bay were modeled. The model also simulated the amount of runoff and the pollutant concentrations of this runoff for each of the sub-areas, and mixed the dry weather flows and wet weather runoff during rainfall events.

The model also included the CSO regulator control decision-making rules, enabling some of the wet weather flows to be diverted to the plants, and the remainder to Jamaica Bay. Wet weather combined sewage not captured and diverted into the plant was calculated in the model as a combined sewer overflow. Stormwater running off directly into the Bay was also simulated. The models were used to calculate CSO and stormwater overflow volumes for each hour of the year for each outfall within the WPCP drainage area.

Conclusions

The modeling analysis showed that for the three external WPCPs (26th Ward, Coney Island and Rockaway), there was no difference between future build and no-build scenarios. For the Jamaica WPCP, future no-build and build flows were found to be between 2% and 6% greater than the existing conditions for all three parameters. Fecal coliform loads were estimated to be some 12% less than now due to completion of the Paerdegat CSO retention facility (which will reduce storm flows) prior to 2015.

The increases in loadings of the future build condition relative to the future no build state tends to be less than 1%. CSO discharges are likely to decrease by around 11% with completion of the Paerdegat facility. Again, there is less than 1% difference between build and no-build scenarios. The analysis confirms that the proposed actions would not have significant adverse impacts for the water quality in Jamaica Bay.

About the Author:

Dr. Srinivasan Rangarajan is an associate engineer at HydroQual Inc. (Mahwah, NJ), and a leading expert in environmental and water resources engineering. He can be contacted at [email protected].