Damming evidence: Communities turn to reusing wastewater as scarcity threatens
Reprinted with permission from Yale Environment 360.
When California's Orange County Water District began distributing drinking water derived from sewage in the mid-1970s, it acted out of simple need. The aquifer it relied on for most of its drinking water had been so overdrawn that saltwater from the nearby Pacific Ocean was seeping into it, and allocation limits prevented increases in exports from the Colorado River and Sierra Nevada Mountains, sources of the rest of the district's water.
Orange County was then a bastion of political conservatism, not the sort of place associated with environmental innovation, but water scarcity is a powerful motivator. To make the idea more palatable to consumers squeamish about drinking what was formerly sewage, the district treated the wastewater, then stored it in the local aquifer to dilute and further cleanse it before withdrawing it for use. The district soon became operator of the world’s largest wastewater-to-drinking-water plant, a distinction it still holds. By the time the district completes its next planned expansion in 2023, the system will generate 130 million gallons of drinking water a day, enough to serve about 1 million of its 2.5 million customers and more than four times the production of the world’s second-largest sewage-to-drinking-water facility, in Singapore.
More significantly, the district represents the vanguard of a paradigm shift in water storage and conservation in areas where scarcity is a major threat — in the U.S. West and Southwest, assorted other states, and many nations. It's a move away from reliance on distant dams and reservoirs and towards methods that can be developed locally — not just wastewater recycling but aquifer recharge and storage, stormwater capture, desalination and smart-meter-based leak detection. Compared to dams, the new sources are small, local, decentralized and custom-designed to fit the hydrological and demographic conditions of their locale.
Diversifying from dams
The latest methods are considered more reliable than reservoirs, whose water supply varies with precipitation levels and season. In the era of climate change, dams are increasingly vulnerable to drought and evaporation, while the supply of, say, urban wastewater stays roughly constant. Because most storage techniques mimic or reinforce natural processes instead of opposing them, as dams do, at worst they cause minimal environmental disruption and at best they generate substantial benefit.
Most also deliver water at prices that are lower, sometimes by multiples, than water delivered from dams — and that disparity is likely to increase. California, for example, has 1,400 large dams; the 1,401st is not likely to find an advantageous site, so water from it will be costly. In contrast, the new approaches are benefiting from innovations in fields such as membrane technology that can improve water treatment effectiveness. And unlike water from distant dams, local storage and recycling practices don't require pumping over long distances, making them more energy efficient. As it stands, water conveyed from faraway rivers and reservoirs to the Orange County Water District costs $1,000 per acre-foot; the unsubsidized cost of its recycled water is $850 per acre-foot.
"There's a shift currently away from large dams especially, particularly in nations like the U.S. where there is already a lot of infrastructure in place and we've used the most efficient dam sites," said Erin Bonney Casey, research director at Bluefield Research, a Boston-based market research firm that focuses on water management issues. In wastewater recycling alone, Bluefield expects U.S. investment to reach $21.5 billion over the next decade.
A Bluefield study last year found that in a ranking of the current cost of water delivered from six technologies, dams and reservoirs were the second-costliest. From cheapest to most expensive, the progression goes: smart-meter leak detection; desalination of brackish water (usually in aquifers); wastewater recycling; stormwater capture; reservoirs; ocean desalination. Even ocean desalination is likely to get cheaper as filtration technologies improve, while new dam water gets more expensive.
The new approaches have captured relatively little public attention, partly because they lack the monumental appearance of dams and instead function largely out of sight. That's partly why California policymakers still are considering new dams even though their cost alone ought to disqualify them. "We’ve been building a new generation of storage projects for 40 years," Nelson told me, "and the policy debate has just not caught up."
Most of the increased capacity that Nelson's paper documents entails storing water in the emptied parts of overdrawn aquifers, which amount to millions of acre-feet. In addition to augmenting water supply, filling these aquifers provides environmental benefit: their water quality usually improves as levels inside them rise, and the higher levels prevent soil compaction and surface subsidence, which eventually occurs when aquifers are left unfilled. Even taking compaction into account, the volume of unused aquifer storage in California is three times the storage volume of all of California’s surface reservoirs and lakes.
"It's sitting there waiting to be recharged," said Daniel Mountjoy, resource stewardship director at Sustainable Conservation, a San Francisco-based nonprofit that promotes an aquifer storage process called "on-farm recharge" in California's San Joaquin Valley. "It's free storage, and if we don't fill it, we're going to lose it."
Cover re-charge: A natural solution changes old habits
The simplest way to recharge aquifers is to do it the natural way, by flooding the ground over them. Before the advent of industrial society, big storms caused rivers to flood, and the floods covered adjacent ground. Mountjoy's organization is tracking more than 200 farms whose owners have agreed to allow flooding in wet years on a fraction of their land in return for water delivered at no or reduced cost. Water for farms is customarily released from dams and distributed through large aqueducts to smaller canals that link to individual farms; the capacity of those canals is the biggest constraining factor in on-farm recharge.
But even without expanding the canals' volume, a 2015 study (PDF) by RMC Water and Environment, a California consulting firm, found that recharge from November to March could reduce the region's overdraft by 12 to 20 percent, and the inclusion of additional months of recharge could hike that number to 30 percent. According to Mountjoy, water collected in this way costs only $46 to $120 per acre-foot, as little as a 30th of the estimated cost of water from the proposed Temperance Flat Dam on the San Joaquin River.
Where adverse soil composition prevents aquifer recharge by flooding, the use of "recharge wells" — wells designed to pump or drain water into aquifers — has spread. R. David G. Pyne, an engineer who pioneered the storage and withdrawal of water in aquifers for human use — a practice known as "aquifer storage and recovery (PDF)," or ASR — estimates that at least 140 recharge well fields have been installed in about 25 states, and the technique is used in about 15 other countries, including Australia, Bangladesh, Canada, England, Israel and New Zealand. Pyne believes that usable aquifers exist in most states, but so far only a few — New Jersey, Arizona, California, Colorado and Florida — have used them extensively.
The most common application of ASR is to make aquifers that contain contaminants such as salt suitable for storage. Some clean water is pumped into the aquifer to act as a buffer by pushing contaminated water to the sides of the aquifer; more clean water is then added to the aquifer's center, where it remains untainted.
Reversing its traditional approach to stormwater, the city of Los Angeles is pioneering stormwater capture. Through most of the 20th century, Southern California cities tried to prevent flooding by turning rivers into concrete watercourses that hastened flow into the Pacific Ocean. Meanwhile, they spent lavish sums to import drinking water from elsewhere in California. Marking the definitive end of that approach, Los Angeles Mayor Eric Garcetti issued a directive in 2014 to cut purchases of imported water in half within a decade.
Now the city is redesigning roads, parks and other surfaces to absorb as much water as possible so that it seeps downward into aquifers, thereby reducing flooding, cleansing itself and becoming available for reuse. A joint 2014 study (PDF) by the Natural Resources Defense Council and the Pacific Institute found that stormwater capture in the San Francisco Bay Area and urban portions of Southern California possesses the potential to increase water supplies by as much water as is used by the entire city of Los Angeles in a year.
Even leak detection can play a significant role in increasing water supply, particularly in eastern U.S. cities whose aged pipes may lose as much as 30 percent of the water passing through them. A 2004 California law requires the state's urban water utilities to install smart meters for all customers by 2025. As of 2016, about 35 percent of U.S. water utilities already had installed automated metering systems, according to a study by West Monroe Partners, a consulting firm.
Legislatively leading the way
In many places, the biggest obstacles the new approaches face are regulatory, not technological. For instance, only one state, Texas, allows distribution of treated wastewater directly into potable water systems. As a result, two Texas cities, Wichita Falls and Big Spring, operate the only "direct potable reuse" systems in the country. Eleven states allow "indirect potable reuse" — the process that the Orange County Water District uses, in which treated wastewater is stored in aquifers before being distributed as drinking water.
Some non-potable reuse systems take advantage of lower purification requirements to provide water for industry, agriculture and recreational facilities such as golf courses. But the cheaper cost of treatment is counterbalanced by the need to install separate piping systems for non-potable water. As a result, potable reuse, which doesn't need additional pipes, is likely to flourish as the so-called "yuck factor" diminishes.
The emergence of recycled sewage underlines a key tenet of all the new water storage technologies: the water of a given watershed — whether toilet water, stormwater or drinking water — must be managed as a whole in order to maximize its usefulness. After all, water traveling down a river may be diverted and transformed dozens of times, at different times serving as agricultural water or drinking water or undergoing treatment before it reaches the river's mouth.
Accordingly, the coordinated use of some or all of these approaches has become known as Integrated Water Management, or, more familiarly, One Water. A statement in author-astrophysicist Robert Kandel's book, "Water from Heaven: The Story of Water from the Big Bang to the Rise of Civilization, and Beyond," could serve as One Water's credo: "Whenever you eat an apple or drink a glass of wine, you are absorbing water that has cycled through the atmosphere thousands of times since you were born."
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