Sustain-ablility

Sustainable development of wastewater infrastructure, GT Daigger, D Burack, V Rubino

Wastewater management and sustainability, GT Daigger, D Burack, V Rubino

Pollution prevention applies to wastewater treatment, KN Irvine, TR Hersey Jr, MC Rossi, J Caruso, JE Jordan

Educating for sustainability, A Ahmadi

Energize with state-of-the-art technologies, BR Klett, RJ Wilson

Sustainability for New York's drinking water, TA Endreny

The “greening” of the building industry, MA Stallone

Water conservation in a water-intensive industry, G. Wainwright

Sustainable design at NYCDEP, P Zimmerman, J Tyler, VJ DeSantis,N Ramanan

People and places

Fall 2001 — Vol. 31, No. 3

Source expansion, user conservation, and climate prediction
by Theodore A. Endreny, PhD

Sustainability with regard to a drinking water supply applies to:

— Modification of water supply quantity and quality
— Expansion and adjustment of water use
— Climate factors influencing use and supply.

Ensuring that wholesome water reaches the faucets of future New York City generations has required, and will continue to require, that the City monitor and respond to changes in supply sources, consumptive uses, and the controlling climate. City officials and environmental professionals must meet challenges in engineering, science, policy, and management to retain a sustainable drinking water supply.

Source area searches

The perils of water scarcity have loomed over New York City since 1664 when a shortage of drinking water caused the Dutch, surrounded by salty waters, to lose control of New Amsterdam to the British, sailing on boats carrying sweet fresh water. Although the next few generations of Manhattan leaders installed a greater number of public wells, contamination by human and animal waste, along with pumping-induced saltwater intrusion, rapidly fouled these shallow aquifers.

Through the 1700s, New York City's residents, primarily residing below Canal Street, were forced to boil much of their water into beer, rely on one unspoiled downtown Tea Water pump, or pay for waters hauled from Manhattan's 48-acre, 58-ft deep Collect Pond and sources farther north. As the population tripled to 60,000 from 1776 to 1800, water supply policy and engineering limited New York City's Manhattan Company to pump the long polluted Collect Pond, a repository for dead animals and tanning waste, as the source for all piped water.

By 1830 advances in hydraulic and civil engineering, coupled with a drinking water supply policy oriented toward sustaining New York City's growing population, the City turned to a supply from the Croton River of Westchester County. Ingenious dam and aqueduct engineering delivered 90 million gallons per day (MGD) of Croton water by 1842, but population growth outstripped the source area supply by the late 1800s, and the Croton was no longer adequate.

The system was expanded to twelve reservoirs and three controlled lakes by 1898, but even this addition failed to support the rapidly growing population's water use needs. In 1911 New York City engineers were in the Catskills. By 1915, New York caused a major dislocation to slake its thirst: 1800 bodies were disinterred, 2000 residents relocated, and 35 stores, 10 churches, 10 schools, a gristmill, and 7 sawmills were flooded when the Ashokan Reservoir was created (Calhoun 1997).

Even bold feats of hydraulic engineering, such as an 1100-ft siphon tunnel beneath the Hudson, and a water policy of appropriation could not deliver enough water for the City's succeeding generations. To supply a growing population, source areas were expanded in the Catskills. Next, the City looked to the Delaware River. New Jersey attempted to enjoin the City from using the water of any Delaware tributary. The U.S. Supreme Court, resolved the case in New York's favor.
 

New York's population grew while water engineers and policy-makers struggled to overcome water shortages, one after another.

Indicators of a possible water shortage

In retrospect, the actions of previous generations of water engineers and policy-makers have provided the current residents adequate water. Water for future generations is not so certain, and source area expansion is no longer considered a viable measure.
 

Compared with national trends, NYC's expansion of its source area was not necessarily caused by excessive per capita use but instead by large population growth (USGS 1991).

New York's consumption of 200 gal/day per capita is just above average national rates. It is half the average rate of use in Arkansas, Utah, and Nevada but outstrips its source area's safe yield. Yet, if New York City could implement conservation measures and get three-quarters toward the low-volume water use of states such as Kentucky, North Dakota, West Virginia, and Rhode Island, to 125 gal/day per capita. The current source area safe yield could then reliably serve nearly 10.5 million consumers of New York City water. It should be noted that a significant fraction of the city's water supplies industrial and commercial users, and they could be the focus for conservation measures.

Population growth and water consumption

Population growth between 1990 and 2000 in New York City and surrounding counties could portend an uncertain supply. In a report on the future of the City's water supply, the National Research Council predicted New York would stay near the 7.3 million of 1990 and not return to 1970 levels of 7.9 million. The 2000 Census actually shows that growth was larger, exceeding 8 million residents.

Further concern arises due to the growth of communities using the City's water:

• 85% of Westchester County
• 5 to 10% of Orange, Putnam and Ulster Counties.

The City also releases water to augment flow and for conservation in the lower Delaware as required by the 1954 U.S. Supreme Court decree. In 1988 and 1989, these secondary uses accounted for 22% of New York City's water supply.
 

Growth in four counties using NYC's water was 4% above the state's average (5.5%) indicating that that future demands on this system will grow. Provisions allow emergency withdrawals by west-of-Hudson communities.

Effect of climate change on drought and safe yield

The influence of droughts on New York City water supply has been pronounced. As a drought progresses from watch to warning to emergency, based on predicted June 1 reservoir levels, New York City imposes various bans on water use, searches for and repairs leaks, reduces system pressure pumps between 40 and 70 MGD from the Queens aquifer, and at times searches for alternative supplies. Nearly 40 miles of old and leaky pipe are replaced each year, and a 700-foot deep valve repair in fall of 2000 on Shaft 6 of the Delaware Aqueduct now allows for DEP to work on aqueduct leaks of between 9 and 100 MGD.*

In 1952 the City responded to a drought by attempting to seed clouds above the Catskill reservoirs; in 1981 the City consumed 20 MGD of New Jersey water delivered by a large pipeline cabled to the lower deck of the George Washington Bridge. In droughts of 1985 and 1989, New York City used the Chelsea Pumping Station to tap and filter upwards of 100 MGD of the Hudson River. As recent as 1999, the City entered drought emergency stage III (of IV) and banned outdoor water use and water-dependent air conditioners operating below 79°F.

Predicted climate change trends provide another indicator that formidable challenges may face New York City in its quest for a dependable water supply. The sustainability of water supply and use under climate scenarios generated by internationally respected modeling groups is based on assumptions of:

• New York City reservoirs' safe yield
• Prediction of future droughts.

Safe yield is defined as the amount of water that could be supplied should the worst drought on record recur. The safe yield of the New York City supply was set at 1290 MGD during its worst drought on record (1960-1968). Before that, the safe yield had been 1800 MGD, nearly 40% greater than the current figure. Safe yields for the City's systems are summarized below:
 

System	Safe yield (MGD)	Maximum withdrawal (MGD)
Croton	240	200
Catskill	470	600
Delaware	580	750

With the City's acquisition of 33 MGD of safe yields from ground water reserves in Queens, the safe yield of the entire system has been adjusted to 1323 MGD. During droughts, the Croton supply, often considered least desirable because of taste and color, moves from 10% to 30% of the mixed New York City supply.

Values of the Palmer Drought Severity Index (PDSI) range between ±4 indicating severe shortages or excess. The PDSI was computed for New York City using temperature and precipitation output from both the Hadley and Canadian Centre General Circulation Models (GCMs). Once calibrated by predicting historic climate, these physically based models examine change in climate that occurs with a doubling of atmospheric carbon dioxide levels. Simulations with both models regularly predict increased temperature, but simulations of precipitation vary from a slackening to an increase.

Simulations that assume decreased rainfall yield PDSI values of -4 by 2050, indicating that New York City's safe yield of 1323 MGD would need readjustment. Model sensitivity to precipitation was significant, however, and a change of ±20% caused the PDSI to move between -3 and +2.5. Thus, precipitation-based, but not temperature-based, drought conditions are uncertain (Major and Goldberg 2000).

Responses to climate change

The effects of climate change are uncertain, yet to ensure a sustainable water supply for future generations the City should examine the likelihood of system failure and plan appropriately.

Examples of how the City is prepared for climate uncertainty match two general suggestions of the Intergovernmental Panel on Climate Change:

Salt water intrusion

Climate change is widely predicted to raise sea level, which would potentially threaten threaten sustainability of the Long Island aquifer supplies (Brooklyn, Queens, Nassau, and Suffolk counties). Just as the Manhattan residents of the 1600s suffered salt contamination of their aquifer, higher sea levels may increase salt water intrusion and reduce the safe yield of the Long Island aquifers.
 

Three scenarios for future NYC water demand: use at current rate, use at conservation rate, and use at conservation rate for the combined NYC and Long Island populations

Should this occur, New York City will have to negotiate service to the Nassau and Suffolk population of 2.75 million—34% of the current New York City user demand as well as nearly 500,000 Queens residents using their local aquifer. Of course, by the time such a climate change-induced scenario could occur, the City's own demand will have changed, as forecast by water demand experts.

In all of the scenarios illustrated above, the current safe yield will not match anticipated water demand. Any consideration of source area expansion, such as increased Hudson River pumping and tapping of various Adirondack waters, will face challenges from other vested environmental and human uses. Unless demand is reduced, the sustainability of the water supply is unlikely.

Benefits of conserving water

Reducing water demand in New York City, though not a trivial task, is both a reasonable conservation goal and no-regrets endeavor. New York City already must comply with the State's Environmental Conservation Law (§15-0314), which mandates conservation of natural waters, and recent revision of this law required new construction to use water-saving plumbing fixtures and limit faucets to 3 gal/min and toilets to 1.6 gal/flush. These conservation provisions are important to guide development in the west-of-Hudson water supply counties, which according to Census 2000 figures are losing many farm-based jobs.

Table 1 shows relatively large daily usage for many commonplace services operating in New York City. In each case, there may be readily accessible opportunities to achieve user conservation goals with water recycling, aeration, and low-flow fixtures employed during peak usage. Some points to consider:

• The steadily increasing volume of water used as
an individual ages—progressing from elementary school through college and then from nursing home to hospital
• The ability of new office buildings to consume a
lower average but higher peak water volume
• The benign consumption attendant with leisure
activities such as dinner out, the theater, and retail shopping.

In New York City's boroughs and Westchester residences, the activities listed in Table 2 indicate that low-flow fixtures and time-consciousness when using water can lead to significant savings. It is worth noting that the combined activities of a bath and load of laundry place a person above the 104 gal/day of water budgeting states, as does the combination of a fast-leaking faucet, watering a 1/5-acre lawn, and keeping an uncovered pool. Conservation not only requires New York City policy, but also user education and the deliberate choice to participate.
 
Table 2. Average water use by activity compared with water rates for some conservation fixtures (Mays 2001)

Activity	Water use unit	Average
Washing machine	gal/load	56
Standard toilet	gal/flush	6
Low-volume toilet	gal/flush	2
Silent leak	gal/day	42
Nonstop running Toilet	gal/day	6
Dishwasher	gal/load	24
Low-volume dishwasher	gal/load	20
Dishes w/ faucet running	gal/minute	6
Dishes w/ filled sink		8
Shower	gal/minute	7
Low-flow shower	gal/minute	2
Bathtub		56
Water lawn of 1/5 acre	gal/month	24
Slow-drip faucet	gal/day	17
Fast-leak faucet	gal/day	71
Uncovered pool	gal/day	9

Adoption of a conservation policy closes the chapter on New York City's expansion to new water sources and addresses uses that jeopardize the provision of water to future generations. In the mid-1980s when the City's water use was between 1400 and 1470 MGD, exceeding the safe yield of 1323 MGD, the City looked to conservation:
 

Year	Action
1986	Spent $350 million to install 600,000 meters and introduce use-based pricing to discourage wasteful consumption
1991	Invested in low-flow showerheads and faucets, aerators, toilet tank displacement bags, and low-flow toilets for 10,000 1- to 3-family residences
1993	Implemented a leak-detection program in 8,000 residences and 80,000 apartments and installed additional low-flow fixtures

The benefits were noticeable, and by 1995 demand dropped to nearly 1300 MGD (NRC 2000).

Conclusion

Sustainable water supply requires good planning, engineering, policy, and luck. The planning is needed for regulating and predicting population growth and user demand; the engineering is needed to maintain the infrastructure that provides the potable supply; the policy is needed to ensure implementation of conservation strategies; and the luck is needed to counterbalance the unpredictable nature of drought.
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* Updated March 2002. The source for this change is Hudson RiverKeeper, and Robert Kennedy Jr. had said, in the Times Herald-Record (April 4, 2001 article "How Long will NYC's Leaking Aqueduct Last?" by Michael Randall), that between 33 million and 100 million gallons of water leak every day from the aqueduct. In a later article by the Times Herald-Record (July 26, 2001, by Wayne Hall), the Riverkeeper claims that the leak is 37 MGD, and the DEP claims it is between 9 and 23 MGD. Further, a 12/7/2001 press release by the NYC DEP, "Valve Repair Completed at Shaft 6 on NYC's Delaware Aqueduct in Chelsea," states that the 700-ft work was completed on valve 6 and that now the leaks can be fixed. In summary, the major aqueduct leaks have not yet been fixed, and the magnitude of the leaks ranges from 9 to 100 MGD, with a best estimate of them maybe at 37 MGD. Further, as an update, according to a 1/24/02 press release by the DEP, NYC had just completed initial testing of a autonomous underwater vehicle that will inspect the aqueduct for leaks and help in subsequent repair.
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Theodore A. Endreny, PhD is with the SUNY College of Environmental Science and Forestry where he teaches and advises student research in the area of water resources science and engineering. Phone 315-470-6565.

References