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For a county famous for being socially and politically conservative, Orange County, CA, has placed itself on the cutting edge of a radical new water management technology-wastewater reclamation.
By Daniel P. Duffy
Orange County has invested $490 million in its new wastewater reclamation facility, which is designed to treat 70 million gallons of wastewater effluent and turn it into drinking water. Considered to be “the world’s largest, most modern reclamation plant,” its genesis, development, and future operation provides a case study in successful, large-scale, long-term water resource planning.
Demographics, Supply and Demand
With an estimated population of over three million residents, Orange County is the fifth most populous county in the US, and one of the wealthiest, with a median family income higher than $75,000. Orange County is home to a wealth of Americana, from its “Surf City” image, epitomizing the California lifestyle, to the original pop- icon theme park, Disneyland. As a cultural symbol, it is the only county in America with multiple television shows and movies devoted to the county and the lifestyles of the people who live there.
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Photo: Steve Crise Courtesy of AWWA |
Orange County also happens to be part of the California South Coast Hydrologic Region. This region has experienced a demographic boom, with its population increasing by over 18% from 1990 (16.3 million people) to 2000 (19.3 million). Demographic projections estimate that the region’s population growth will continue unabated with the population increasing to over 22 million in 2010 and over 25 million by 2020. That represents a 55% increase in only 30 years (equivalent to an average annual growth rate of about 1.5%).
Average monthly summertime water demand in California’s South Coast region (based on 1991 data) varies from 11,250 gallons for small towns like Hemet, to 15,000 gallons for the megalopolis of Los Angeles, to 18,000 gallons for wealthy Beverly Hills. Average winter monthly use varies from 80% to 50% of summertime use. Cost per acre-foot (including service charges) to the consumers varies from about $450 to $875 per acre-foot. Water demand for the region matches that of the state average, approximately 200 gallons per capita per day. The general planning metric for per family annual water demand is about 0.5 acre-feet (21,780 cubic feet or almost 163,000 gallons). The proposed water reclamation and Groundwater Replenishment System will provide enough water for 200,000 families.
Local water supply in Orange County is provided by both local and regional sources. The water district primarily draws water directly from groundwater storage basins that provide 75% of the district’s water needs. These basins are recharged by water from the Santa Ana River (the district holds rights to all the Santa Ana River flows above the Prado Dam) and from Los Angeles’ Metropolitan Water District of Southern California (MWD). The basins have a storage capacity of 1.25 to 1.5 million acre-feet of usable storage volume. Given the dependency of the very existence of Orange County on wisely managing their water resources, the county has come to treat these groundwater basins as a priceless treasure trove.
So, it is not surprising that Orange County has one of the most extensive and thorough water conservation programs in the country. Conservation impacts have had a big impact on water consumption in the region. According to a recent study performed by the Southern California Association of Governments, total water consumption fell 3% (3.3 million acre-feet). Per-capita, daily water use has also fallen from 210 gallons to 183 gallons.
Despite these successes, population and economic growth continues unabated. Even a 3% decrease in water usage will get swamped by a 55% increase in population. The bottom line is that, despite strenuous and successful water conservation measures, Orange County has come to realize that conservation is not enough to cover anticipated shortfalls. The responsibility for bridging this gap falls on the shoulders of the county’s water district.
Government and Water Management Agencies
Since 1933, the government agency responsible for supplying water to 2.3 million residents in the coastal, central, and northern portions of the county is the Orange County Water District (OCWD). Its mission statement is, “to provide local water retailers with a reliable, adequate, high-quality water supply at the lowest reasonable cost in an environmentally responsible manner.”
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Photo: Steve Crise Courtesy of AWWA |
| Reverse Osmosis is a high-pressure process that removes minerals and other contaminants at the
molecular level, primarily salts, viruses, and chemicals such as pesticides. |
In fact, if it weren’t for the county’s completely engineered and “unnatural” water supply, the region would revert back to it natural desert condition (the county only receives 13 to 15 inches of rainfall annually). However, by applying engineering skills and farsighted planning, the OCWD has performed the technological miracle of creating an industrial and agricultural powerhouse, while providing the basis for one of the highest standards of living anywhere on the globe.
Other civilizations, beginning with Egypt, the Indus Valley, and Mesopotamia, have relied on existing water supplies; Orange County created its own from scratch and made a desert bloom. In doing so, they haven’t forgotten the other half of their mission statement, to provide all this water without damaging the environment. To meet this requirement, the OCWD has emphasized the storage of water in underground basins, water transfers from areas with water surpluses, a strong water conservation effort—even during non-drought times—water reuse, and its new water reclamation and groundwater replenishment project.
The other side of the coin, managing wastewater, is the responsibility of the Orange County Sanitation District (OCSD). As the third largest wastewater treatment agency west of the Mississippi River, the OCSD provides sanitation services to 2.5 million people, and collects, treats, and disposes of 230 million gallons of wastewater every day.
The OCSD is an equal partner with the OCWD, splitting the capital and construction costs for the water reclamation and groundwater replenishment system evenly, as well as half of the first year’s operating costs.
Genesis and Future of the Reclamation System
Like all water utility planners everywhere, the OCWD has its work cut out for them. Of all the types of utility service planning, water resource planning is the most hazardous and most likely to fail. Failure may not be an option when literally hundreds of millions of dollars have been committed, and the economic vitality of a community is at stake, but failure has a high probability of occurring.
Like all planning, water resource planning is more art than science. Projections can be made, graphs plotted, and plans laid out, but mother nature and human nature both often conspire to invalidate the assumptions that underlie the planning. Droughts and floods are not controllable by any planning board. Groundwater supplies are derived from hydrogeological systems that are not always fully understood, and are often extracted from complicated geological formations that are never completely mapped. Estimates of groundwater yields and well field-pumping capacities are just that, estimates.
Human nature can be just as variable. Water-demand patterns are based on averages of aggregate data with variations that often vary widely from the mean. Just because one factory or farm requires ‘x’ or ‘y’ million gallons of water annually to operate, doesn’t mean that a similar, or even identical, facility located somewhere else will have matching water demands. Water demand for households and individuals vary considerably with levels of wealth and hour of the day. Population patterns are forever changing, driven by economic forces (employment demand, business formations, wealth creation, and others) that are out of the control or understanding of water resource planners. Whether a community’s population is expanding or shriveling often depends on unforeseeable events, such as overseas competition or changes in lending rates. A community that was planned when interest rates were low could be left to die on the vine, should those same interest rates increase to the point that the planned housing is no longer affordable. The water and sewer systems planned or installed as part of this community’s development will also be left unused. Conversely, an unexpected job boom can place unanticipated demands on already overtaxed water and sewer systems, forcing a water planning board to scramble in order to keep up with skyrocketing demand.
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Photo: Steve Crise Courtesy of AWWA |
| Microfiltration is a low-pressure process where small particles and bacteria are removed—the effluent discharged into basins lined with microfilters. |
In any case, water resource planning can never be 100% accurate or based on complete knowledge of all the variables that will affect demand. Though not completely random or based purely on conjecture, water resource planning’s inherent unpredictability is compounded by the long timelines requires to plan, finance, and construct required water and sewer systems. Short-term planning is measured in years or decades. Advanced, long-term planning horizons can extend out to 50 years or more. With a longer time scale comes increasing and unavoidable unknowns, and unforeseeable variables. With all this in mind, the OCWD projected the needs of its community, evaluated its potential supplies, and arrived at a radical solution to its looming shortfall.
The shortfall, which normally would have been caused by increasing population and economic growth, was brought into sharp focus recently by legal actions completely out of control of the county planners. Two of the county’s primary water sources are the Sacramento-San Joaquin Delta and the Colorado River. In late 2007, a Federal judge at the circuit court in Fresno declared that Orange County’s water demand on the Sacramento-San Joaquin Delta put a local fish species—the delta smelt—in danger. Since the smelt is a threatened species, the judged ordered a 30% reduction in Orange County’s extraction of fresh water from the delta. Drought has also affected the availability of water from the Colorado River in past years.
This is why the water district has searched for a steady-and-reliable water supply option. Unpredictable reductions in water supply, either by drought or court action, makes long-term planning difficult to impossible. This is especially true for a community experiencing a population boom. But where to find a reliable source of drinking water? The answer was under their noses (or rather, under their feet in sanitary sewers) the whole time. The problem was how to utilize this water source in a cost-effective, environmentally safe manner protective of human health. And so, the “Groundwater Replenishment System” was born.
The Water Reclamation System
So how does this system work? The technology is derived from experience gained in 25 years of operating Water Factory 21. Water factory 21 produces water that is a blend of three sources: reverse osmosis (RO)-treated water, carbon absorption-treated water, and deep well water. One of the largest water purification plants in the world, it reclaims 15 million gallons per day, and, with the mix of deep well water, produces 23 million gallons per day. The quality of its water meets California-safe drinking water standards. The new water reclamation project based on this technology, and the subsequent groundwater replenishment system, involve a six-step process.
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Photo: Steve Crise Courtesy of AWWA |
| Ultraviolet-light purification, combined with the addition of hydrogen peroxide, eliminates remaining biological agents and traces organic chemicals. |
The process begins with the flush of a toilet or the gurgle of a drainpipe. Wastewater produced by homes and businesses gets carried by the county’s sanitary sewer system to the sanitation treatment plant at Fountain Valley. The existing sanitary sewer system is utilized without need for modifications directly related to the reclamation system.
Next, once effluent arrives at the sanitation plant, it goes initially through a standard wastewater treatment process involving removal of solids and grit, aeration, and settlement to remove remaining solids. Approximately 80% of the wastewater that achieves this level of treatment is discharged to the oceans, while the remaining 20% goes onto the next stage for more advanced treatment. The water that goes on for further advanced treatment is still brackish and unsafe to drink.
Then, this advanced stage involves more intense treatment including microfiltration, RO, and sterilization with ultra violet light. These three operations convert the treated effluent into safe, potable drinking water:
- Microfiltration is a low-pressure process where small particles and bacteria are removed. During this stage, the effluent is discharged into a series of 26 holding basins lined with about 270 million micro filters. These micro filters are membranes that resemble small, flexible, porous straws that are arranged in arrays that are filled with hundreds of thousands of these tiny filters. They are designed to remove bacteria-sized particles (0.2 micron, or about one-one hundredths the diameter of a human hair). Use of micro filters eliminates the need for clarification or tertiary filtration.
- RO is a high-pressure process that removes minerals and other contaminants at the molecular level, primarily salts, viruses, and chemicals such as pesticides. The water is forced through thin plastic membranes shaped into tubes and installed in impermeable cylinders. The water enters from the end of the cylinder along its axis and into the interior of the membrane tubes. It forces its way out through the membranes that filter out the impurities as the water passes through them. Once the water passes through the membranes it fills the interstitial zone between the membrane tubes and the interior walls of the cylinders and flows out to the next stage.
- The ultraviolet-light purification, combined with the addition of hydrogen peroxide, eliminates any remaining biological agents and traces organic chemicals. Use of ultraviolet light is more effective than standard methods, involving the addition of chemical disinfectants such as chlorine and iodine. By causing genetic damage to bacteria and virus pathogens, ultraviolet-light treatment inactivates these organisms and prevents them from breeding. It achieves these results in approximately 30 seconds, as opposed to 30 minutes for a chlorine disinfection system. Since the first two steps have removed larger particles, remaining organisms are exposed to the full effect of the ultraviolet radiation. The final result of this advanced purification process is a potable water that has achieved levels of purity nearly equal to that of distilled water.
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Photo: Steve Crise Courtesy of AWWA |
| By causing genetic damage to bacteria and virus pathogens, ultraviolet-light treatment inactivates these organisms and prevents them from breeding. |
In the next step, impurities have to actually be reintroduced into what is now ultra-pure water, so it can be safely piped through the county’s water mains. Small quantities of calcium carbonate (lime) are added to the water to prevent it from leaching out minerals from the concrete carrier pipes. Over the long term, such leaching could result in weakening or cracking of the concrete pipe as its walls are eroded away.
The now potable water is piped 13 miles from the Fountain Valley treatment plant to the filtering basins and holding ponds in Anaheim. Water discharged into the basins percolates through the basins’ floor and into aquifers located underneath. Some of the cleaned water is also discharged directly into the aquifers by means of deep-injection wells. This replenishment of the local groundwater does double duty, both as an additional natural filtration process that cleans the water further, and as a means to displace salty seawater and prevent it from infiltrating the aquifers. In effect, re-injected potable water serves as a barrier against saltwater intrusion from the ocean.
The effects of the natural soil filtration is more psychological than real. The water is safe to drink even before this stage. However, public acceptance of the system depends on perceptions of the cleanliness of the resultant drinking water. By extracting groundwater, instead of directing tapping into discharge from the advanced purification system, the link between effluent and potable water is broken. As such, the concerns over “toilet to tap” (or “hospital to tap,” or “pesticides to tap,” or “industrial cleaners to tap”) process flows are largely alleviated.
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Photo: Steve Crise Courtesy of AWWA |
| The final result of the advanced purification process is a potable water nearly equal to distilled water. |
Lastly, the water used to recharge the aquifers is extracted by groundwater supply wells for use by households and businesses. As with the sanitary sewer system utilized in the first stage of the process, water distribution is accomplished with existing water mains and distribution pipes. So again there is no need for an overhaul or expansion of existing water supply infrastructure. Once the full potential of the system is realized, it could serve as a source of an additional 130 million gallons of water per day to the county’s water supply.
What are the costs of water produced by this system and how do these costs compare to other sources? OCWD planners estimate that the cost of this water to consumers will run about $520 to $550 per acre-foot (equivalent to 43560 cubic feet or almost 326,000 gallons). This is equivalent to 0.0016 to 0.0017 cents per gallon. Since a typical family serviced by the OCWD utilizes about 163,000 gallons per year, the costs per family should run almost $270 per year. These projected costs compare favorably with water obtained from southern California’s primary water supply, Los Angeles’ MWD, which costs $540 per acre-foot. Water supplied by sources in northern California is somewhat more expensive. The cost of water from the Colorado River is only $250 per acre-foot, which is less than half the projected cost of the reclaimed water. However, the Colorado River is an unreliable source due to legal actions, droughts, and demands on its water by other communities.
Does the increased cost of treated effluent, compared to water from the Colorado River (when it is actually available), translate into higher water bills for Orange County taxpayers? In the long run, a dependable man-made source of drinking water removed from the variables associated with natural water sources will have a leveling affect on water rates.
Part of the costs of running a water utility, which show up on the taxpayer’s water bill, incorporates the unknowns of future planning. By providing a level, steady-and-predictable source of a large portion of its water needs, the water district can reduce the long-term planning unknowns. Furthermore, water supply is only half of the picture.
The diversion of effluent to the water reclamation facility reduces the strain on the county’s sewage system. By not needing to overhaul or expand their sanitary sewer system, the county can avoid significant capital outlays. For example, once the water reclamation system achieves full capacity, the county may not have to build a new sanitary sewer ocean outfall discharge at a cost of $300 million.
The Value of Water Reclamation
Cost savings are only one part of the benefits anticipated from this system. The positive environmental impacts are also significant and should not be overlooked.
First, there will be an immediate reduction of 15,000 acre-feet (4.88 billion gallons) in the discharge of treated effluent to the oceans. The strain of demand on the already overtaxed Colorado River will be greatly eased. A steady-and-reliable source of clean water can be available to serve as a barrier against saltwater intrusions in the local aquifers. A much-needed buffer against the effects of drought is also established.
The ideal water reclamation system would achieve 100% levels of reclamation, with every gallon of effluent being recaptured and treated for discharge into the county’s storage basins. In such a scenario, no effluent would ever be discharged into the ocean.
But, even if this ideal situation were achievable, don’t expect Orange County to forego its existing water conservation and water efficiency programs. In no way is water reclamation a substitute or replacement for either conservation or efficiency. The three may be related, but they mean completely different things. They also complement each other, making it easier by working together to meet each effort’s goals.
Water reclamation is the act of restoring wastewater to a state that will allow for beneficial reuse. It’s a post-use activity, and is a type of comprehensive recycling. Conservation and efficiency occur prior to use, and during use, respectively. Conservation reduces demand.
For example, the use of low-flush toilets requires less water than a standard toilet, and, therefore, represents a conservation effort. Drip-leg irrigation requires less water than spray irrigation, and is also an act of conservation. Conservation reduces use by reducing need at the point of application. As such, conservation ensures the efficient management and application of available water sources.
It is a mistake to use the terms efficiency and conservation interchangeably. While conservation reduces use, efficiency reduces waste. As such, an efficient water distribution system is one that utilizes proper construction techniques and engineering design, to deliver water with the least amount of energy required, while minimizing water losses through leaks in the system.
To use an automobile analogy, conservation is the minimizing of the use of the car for transport by taking mass transit instead, while efficiency would be getting more miles per gallon of fuel when you do drive your car. Water reclamation would then be equivalent to magically converting exhaust pipe emissions back into fuel.
Daniel P. Duffy, P.E. is an environmental engineer for URS Corp. in Akron, OH.
WE May/June 2008
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