Gotham

Water conservation cleans Long Island Sound, RL Swanson, DJ Tonjes

Marine vessels serving New York City, W Goyzueta, J Chen, K Byrnes, R Ferro

Line stops avoid bypass in pumping station, F Gallo

Pilot biological nutrient removal, B Bodniewicz, K Mahoney

Enhanced beach protection — 2000, FJ Oliveri, F Loncar, M Ellis

Telemetering in New York, S Rozelman, S Aziz

Job order contracting, MP Quinn, P Schrayer

Operational benefits of celebrating Water Week, RE Adamski, H Einsohn, M Keating, A Lamarche, B Olivieri

CSO signage: expanded notification, S Rozelman, P Lutz, F Loncar

Executive director's message, P Cerro-Reehil

People and places

Summer 2001 — Vol. 31, No. 2

Water conservation cleans Long Island Sound

by R.L. Swanson, David J. Tonjes

New York City has substantially improved its water supply and wastewater treatment systems over the past decade. Between 1990 and 1999, the City reduced its daily water consumption from 1.40 billion gal to 1.24 billion gal (David Warne, Bureau of Water Supply, NYCDEP. personal communication), a savings of about 11%. (See graph.) This saving was implemented despite an increase in population of roughly 410,000 (adjusted to 2000 census data). The 1999 consumption was up slightly from 1998, probably because 1999 had a particularly hot dry summer.

New York City water consumption and sewage effluent, 1990-1999 (billions of gal/day)

These reductions have come from various City programs that include increased use of low flow fixtures (low flow toilets, automatic shut-off faucets in public buildings) as well as detection and repair of water leaks. At the same time, the City has increased metering of water use to provide financial incentives to conserve while simultaneously promoting conservation through public education and outreach. In terms of per capita commercial and residential consumption, this is an impressive reduction from 185 gal/capita/day—a figure at the upper limit of cities around the world—to about 155. New York City has also worked to eliminate illegal water connections and to reduce infiltration of ground water to the sewage system.

Manifold benefits

The net result is that the City's fourteen water pollution control plants (WPCPs) are now treating about 1.33 billion gal/day (Swanson and others 2000) compared to about 1.65 BGD in 1990 (New York City Department of Environmental Protection, 1991). See Graph. A savings of 320 MGD in sewage discharge is a significant savings. This savings is considerably greater than the amount of sewage treated each day by the Newtown Creek WPCP, the City facility with the greatest flow.

The reduction in the quantity of sewage requiring treatment has provided beneficial effects:

• Apportioned additional capacity in the system
• Helped to reduce the quantity of treated sewage discharged to local waterways
• Allowed more storm water to be treated than previously, thus reducing combined sewer overflow (CSO) discharges

The extra capacity has also been beneficial for introducing biological nutrient removal at some of the WPCPs. For example, the amount of nitrogen in the effluent of the four WPCPs along the upper East River has been reduced from about 99,000 lb/day in 1993 to 70,000 lb/day in 1999. This 29% reduction in nitrogen loading to the upper East River can be measured in a 46% reduction in summertime chlorophyll a concentrations (a measure of biomass production) and improved water clarity in the very western end of Long Island Sound from the mid-1990s to the end of the decade (Swanson and others 2000).

Heretofore, much of the nitrogen/biomass from the upper East River was transported to western Long Island Sound. There, it is thought by many, it contributed to the water's frequent hypoxic conditions (O'Shea and Brosnan, 2000; Welsh, 1995).

Future benefits

While there is a need to make the water distribution and wastewater treatment system even more efficient, the citizens of New York and the New York City Department of Environmental Protection deserve credit for the significant improvements made to date. The City has demonstrated that it can use less water, an accomplishment that will be even more appreciated during the next drought. Major expansion of the WPCP infrastructure has been avoided, despite growing population.

Moreover, these savings can already be measured through water quality improvement in waterways. This achievement is helping the City meet its goals as part of the Long Island Sound Study. The reduction in consumption and the concomitant improvement in environmental quality clearly exemplify the engineer's axiom that water delivery and wastewater treatment systems are inexorably linked. The City's conservation, financial incentive, public education, and improved maintenance programs to reduce water usage are fine examples for other municipalities.
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R.L. Swanson, Ph.D. is Director of the Waste Reduction and Management Institute of the Marine Sciences Research Center, Stony Brook University. David Tonjes, Ph.D. is a research scientist there.

References

New York City Department of Environmental Protection. 1991. New York Harbor Water Quality Survey 1988-1990. New York, NY.

O'Shea, M.L. and T.M. Brosnan. 2000. Trends in indicators of eutrophication in Western Long Island Sound and the Hudson-Raritan Estuary. Estuaries 23(6): 877-901.

Swanson, R.L., D.J. Tonjes, N. Georgas, and B.W. Stephens. 2000. New York City Regional Harbor Survey. New York City Department of Environmental Protection. New York, NY.

Welsh, B.L. 1995. Hypoxia in Long Island Sound: one researcher's perspective. In: Proceedings of the Long Island Sound Research Conference: Is the Sound getting better or worse. New York Sea Grant Institute, Stony Brook University, Stony Brook, NY. pp. 3-19.