May 2008, Vol. 20, No.5
New Water Supply Makes Its Way to Tap in Southern California
Reclaimed wastewater is giving 2.5 million Orange County, Calif., residents a new, reliable, locally controlled, droughtproof source of drinking water. After 4 years of construction, the Groundwater Replenishment System — the world’s largest advanced water purification plant of its kind —
began taking secondary treated effluent in January from the Orange County Sanitation District and putting it through a state-of-the-art three-step purification process that includes microfiltration, reverse osmosis, and ultraviolet light with hydrogen peroxide.
Roughly half of the 264,950 m3/d (70 mgd) of produced water is being injected into a seawater barrier to prevent ocean water from contaminating the groundwater supply. The other half is being pumped to spreading basins, from where it will mix with other water sources and percolate into the groundwater basin.
“The GWR System produces the highest-quality water we can put into our groundwater basin and ensures water reliability for northern and central Orange County at a time when alternative water resources in the state and Colorado River basin are in jeopardy,” said Steve Sheldon, board president of the Orange County Water District (OCWD; Fountain Valley), which developed the project jointly with OCSD.
The need for such “new” water has grown dramatically in recent years.
Orange County receives an average of only 330 to 380 mm (13 to 15 in.) of rainfall annually, according to OCWD statistics. A massive groundwater basin underlying the northwestern half of the county is the source of about 75% of OCWD’s drinking water supply. The remaining 25% is imported from the Colorado River and Northern California. However, an 8-year drought has diminished the water imports from the Colorado River, and supplies from the north have been cut back 30% for environmental protection efforts in the San Francisco Bay and Sacramento–San Joaquin Delta, said Ron Wildermuth, OCWD’s communications director. Added to these pressures are large population increases projected for the future. OCWD expects water demand in the region to increase nearly 20% by 2020.
“It’s clear that this project is needed to maintain the water reliability that everyone’s accustomed to,” said Jeff Mosher, executive director of the National Water Research Institute (NWRI; Fountain Valley). “Treated wastewater effluent, a water resource that’s typically dumped into the ocean and lost, can accomplish this.”
Krista Clark, director of regulatory affairs for the Association of California Water Agencies (Sacramento), agreed. “We’re really excited about the project,” she said, adding that “it’s an example of very aggressive treatment, high-quality produced water, and great management of the groundwater basin.”
In the GWR System, secondary treated effluent undergoes further treatment that includes two membrane filtration systems — microfiltration and RO, followed by disinfection and treatment by UV light and hydrogen peroxide.
The low-pressure microfiltration process takes small suspended particles, bacteria, and other materials out of the water, preparing it for the RO step. Then, the high-pressure RO membrane filters out viruses and inorganic contaminants, as well as many organic contaminants. The final safety measure involving UV light and hydrogen peroxide treatment eliminates any remaining organic compounds in the water by breaking them down to their most basic elements of carbon dioxide and water.
Various studies have concluded that the water produced through this multiple-barrier treatment process is safe for human consumption and is actually of higher quality than any other current source of drinking water for Orange County.
“The entire treatment process is very effective in producing water that meets all drinking water standards and removes or reduces all of the unregulated organics to extremely low nanogram-per-liter levels, which haven’t been shown to present health problems,” said James Crook, an environmental engineering consultant based in Boston. Crook chaired an independent NWRI review panel that assessed the GWR System project, concurring with other studies and giving the project its stamp of approval.
The water that comes out of the system “is so pure that we have to add minerals back to it before we put it in the pipeline, because otherwise it would leach minerals from the piping and destroy it,” Wildermuth said. Over time, as the produced water mixes with the existing groundwater in the basin, overall water quality is expected to improve.
The project’s capital cost stands at $486 million, which includes $74 million for a pipeline, $300 million for the water purification plant, and $16 million for expanding the seawater barrier, according to OCWD. Operations and maintenance costs will add another $26 million per year, with the largest portion, $11 million, going toward power costs.
An estimated 88.8 million m3 (72,000 ac-ft) is expected to be produced annually during the project’s first phase, Wildermuth noted. One acre-foot of water is 1.2 million L (326,000 gal), or enough water to supply the needs of two Orange County families for a year. Capacity can be expanded to 492,050 m3/d (130 mgd) as water demand increases.
Where the Water Goes
Once purified, half of the reclaimed water is injected into wells drilled along the coast to form a barrier against saltwater intrusion from the Pacific Ocean, Wildermuth explained. The injected water creates a pressurized mound, or hydraulic dam, of fresh water that keeps ocean water from contaminating the groundwater basin.
This part of the project builds on OCWD’s 30-year experience with Water Factory 21, the first project in California to purify wastewater to drinking water standards to act as a seawater intrusion barrier. Water Factory 21 had a design capacity of 56,775 (15 mgd), but as Orange County’s use of groundwater has increased, OCWD found it necessary to expand the barrier’s size and increase the amount of water being injected. Roughly 90% of that water eventually ends up in the county’s drinking water supply by seeping into the groundwater basin.
The other half of the reclaimed water is piped 21 km (13 mi) from Fountain Valley to OCWD’s recharge lakes in Anaheim, Calif., according to Wildermuth. From there, it filters through the bottom of the lakes, taking the same path as rainwater as it seeps through clay, sand, and rock to the underlying aquifer, where it blends with other water sources from the Santa Ana River, Northern California, and the Colorado River.
Water injected into the seawater barrier remains in the groundwater basin for at least a year before being withdrawn, Wildermuth noted. The portion sent to the recharge lakes can be withdrawn through drinking water wells as early as 6 months after it went in.
Surmounting the ‘Yuck’ Factor
The GWR System project has succeeded where other similar reclaimed water projects have failed in California. Wildermuth attributes its success to the public outreach his utility has engaged in during the last 10 years. “We give about 120 talks and 70 tours a year to civic groups, environmental groups, schools, public officials — anyone who is interested,” Wildermuth explained.
Mosher pointed to OCWD’s decades of experience with Water Factory 21. “They have the public’s trust to pull this project off,” he said.
Crook agreed, adding that the utility has done extensive pilot-plant testing and water quality monitoring. “They have a good handle on the treatment technologies and data that they’ve obtained at their own facility on proposed treatments,” he said, noting that “they’re also well respected by state regulatory agencies and the public.”
Cost is also a factor. OCWD studies have shown the GWR System to be the least expensive source of new water for ratepayers. At approximately $0.42/m3 ($525/ac-ft) — comparable to the cost of Orange County’s imported water — this high-quality produced water is substantially cheaper than seawater desalination, which costs $0.65 to $1.62/m3 ($800 to $2000/ac-ft) to produce, Wildermuth said.
Added to this is the fact that “we can produce this water for about half the energy it takes to pump water over the mountains from Northern California,” Wildermuth said, noting that the amount of energy saved is enough to power 21,000 homes per year.
Additionally, the project reduces the amount of treated wastewater being released into the ocean, delaying indefinitely the need for another ocean outfall, despite a growing population, Wildermuth pointed out. Cost savings here amount to roughly $170 million.
“The GWR System serves as a model for public agency collaboration on one of the most significant water projects in California’s history,” said Jim Ferryman, OCSD board chair.
Mosher agreed. “We have growing populations and people moving to places where there’s not a lot of water,” he noted. With rivers and groundwater basins already tapped out, utilities have limited options to address this issue. Conservation efforts and increased water efficiency are crucial, Mosher said, but more and more communities will have to reuse wastewater and even purify ocean water.
“This project serves as an example, not just for Southern California but [for] the world, as an example of what can be done to augment water supplies with this resource in a time of increasing water scarcity,” Mosher said.
Other utilities are considering similar projects to satisfy their water needs.
“We’ve had visits of interest from the cities of Monterey, Calif.; and Denver, Colo.; as well as Israel, Spain, Turkmenistan, Japan, Korea, Thailand, and Singapore,” Wildermuth said. Singapore already has replicated the GWR System.
For more information about the GWR System, see www.gwrsystem.com.
— Kris Christen, WE&T
‘When Will Lake Mead Go Dry?’
New research paints bleak future for Southwest water supply
There is a 50% chance that Lake Mead, a key source of water for millions of people in the southwestern United States, will be dry by 2021 if the climate changes as expected and future water usage is not curtailed, according to a pair of researchers at Scripps Institution of Oceanography at the University of California–San Diego.
Moreover, even if water agencies follow their current drought contingency plans, this might not be enough to counter natural forces, especially if the region enters a period of sustained drought or if human-induced climate changes occur, as currently predicted.
Research marine physicist Tim Barnett and climate scientist David Pierce detail these possibilities in their paper, “When Will Lake Mead Go Dry?” which at press time had been accepted for publication in the peer-reviewed journal Water Resources Research, published by the American Geophysical Union (Washington, D.C.).
“We were stunned at the magnitude of the problem and how fast it was coming at us,” Barnett said. “Make no mistake, this water problem is not a scientific abstraction but rather one that will impact each and every one of us that live in the [U.S.] Southwest.”
Currently, the upper and lower basins of the Colorado River receive allocations of 15 million ac-ft/yr. (An acre-foot is the volume of one acre of surface area to a depth of one foot; it is equivalent to 1233.5 m3.) The upper basin includes Colorado, New Mexico, Utah, and Wyoming, and the lower basin includes Arizona, California, and Nevada.
“Right now, there are 15 million ac-ft [18.5 billion m3] used per year out of the system, and that is just about what Mother Nature puts in,” Barnett said. (He noted that the system actually is already overdrawn by about 1.2 billion m3/yr [1 million ac-ft/yr] but is assuming equal inflow and outflow for this scenario.) “If you suddenly start supplying less water [for recharge] through climate change, somebody’s not going to get their allocation,” Barnett said.
The two major reasons for less inflow to the system are a natural variability of rainfall and climate change. Currently, the system is only at half capacity because of a recent string of dry years, and the team estimates that the system has already entered an era of deficit. Barnett explained that models developed using tree-ring data that stretch back 1200 years have shown that the recent past has been an unusually rainy period for the region.
“There’s little doubt that this last century, under which the Southwest really grew, has been one of the wettest in a thousand years,” Barnett said.
Additionally, climate change effects likely will reduce inflow to the system even more. Barnett and Pierce note that several other studies in recent years have estimated that climate change will lead to reductions in runoff to the Colorado River system. Those analyses consistently forecast reductions of between 10% and 30% during the next 30 to 50 years, which could affect the water supply of between 12 million and 36 million people.
Using these predictions, the researchers estimate that there is a 10% chance that Lake Mead could be dry by 2014. Dry, as used in the report, is a relative term that refers to exhausting the lake’s live storage. Live storage is the reservoir space that can be drained by gravity. The water remaining when live storage has been exhausted is called dead pool. Lake Mead contains about 2.5 billion m3 (2 million ac-ft) of dead pool, Barnett said.
The researchers further predict that there is a 50% chance that reservoir levels will drop too low — 320 m (1050 ft) above sea level — to allow hydroelectric power generation by 2017. The report shows that the water’s current surface elevation is only about 18 m (60 ft) above that level.
Barnett said that the researchers chose to go with conservative estimates of the situation in their analysis, though the water shortage is likely to be more dire in reality. The team based its findings on the premise that climate change effects only started in 2007, though most researchers believe that human-caused changes in climate likely started decades earlier.
Conservation, Reclamation, Retention
Although the picture for Lake Mead and the Colorado River system is grim, measures exist that can at least postpone this resource from being decimated. The most straightforward adjustment is to drain less water. The question becomes how much?
The paper examines the effects of several reductions in allocation levels. These reductions would take effect when lake storage drops to 18.5 billion m3 (15 million ac-ft).
Assuming 20% less inflow to the system due to dry conditions and climate change, as well as no reductions in the outgoing water allocations, there is a 50% chance that Lake Mead would run dry by 2028, the report states. Reducing water allocations by 10% postpones reaching dead pool by about 6 years. Reductions of 25% are needed to make a real difference in when the lake runs dry, the report states.
The smallest allocation reduction assessed in the paper is 10% and “hardly makes a dent,” according to Barnett. However, the current reduction plan by the U.S. Bureau of Reclamation, the agency that controls water allocation, calls for only a 5% reduction, he said.
“Basically, their long-term plan for the river is not viable,” Barnett said.
However, Barnett called water conservation, reclamation, and recycling sources of hope for this issue.
“Let’s suppose one of the estimates is [that] roughly by 2050 we have 3 million ac-ft [3.7 billion m3] less water coming into the river because of climate change,” Barnett said. “Well, could we make that up somewhere in the system through conservation? Through reclamation?”
Barnett pointed to Las Vegas as a good example of how to manage water resources. The city reclaims about 6.6% of its wastewater for landscape irrigation and returns the rest to the Colorado River system, according to the city’s Web site. In 2006, Las Vegas produced 6.4 billion L (1.68 billion gal) of recycled water to irrigate golf courses and parks, and to provide cooling water for power plants.
The region also is seeking to reduce demand. The Southern Nevada Water Authority (Las Vegas) pays residents about $16/m2 ($1.50/ft2) to convert grass to water-efficient landscaping through its Water Smart Landscapes Rebate Program.
Since the program’s inception in 1999, community residents and businesses have converted more than 9.3 million m2 (100 million ft2) of grass to water-smart landscaping, saving more than 68 billion L (18 billion gal) of water. Moreover, southern Nevadans consumed 57 billion L (15 billion gal) less water in 2007 than in 2002, despite the addition of 400,000 residents during that span and more than 40 million visitors in 2007, according to the Southern Nevada Water Authority.
Investments in infrastructure also could help to safeguard what water is available, Barnett said. For example, lining 37 km (23 mi) of the All-American Canal, the aqueduct that brings Colorado River water to the Imperial Valley in California, to prevent seepage is expected to conserve 83.5 million m3/yr (67,700 ac-ft/yr), according to the Imperial (Calif.) Irrigation District, which operates the canal.
“And that’s just a 23-mi-long [37-km-long] section of canal,” Barnett said. “What about the rest? There may be tremendous savings out there available.”
However, the lining project is controversial because the water seeping out along that stretch of canal irrigates a large portion of the agriculture across the border in the Mexican state of Baja California and creates wetlands where wildlife thrive.
“It seems like a very logical thing to do, but there are losers on it,” Barnett said.
Time To Act
The positive message to take away from this study is that there is some time to act, Barnett said. Water supply issues such as these are not unique to this region. What is different is that this is one of the first cases where the problem has been carefully measured and analyzed, and the information is available to inform decisions.
“It’s an optimal situation, in one sense, for decision-makers,” Barnett said. “Now, whether they want to step up and make the hard decision is a whole other story.”
However, Barnett said, the longer action is postponed, the more likely litigation over water rights will become.
“I think the moral of the story here is that we’re just about up to the sustainable level of society in the Southwestern desert — at least those served by the Colorado,” Barnett said.
— Steve Spicer, WE&T