You can look at it a number of ways: efficient effluent disposal, closing the water cycle, creating a new source of potable water. The fact is that in Orange County, CA, the benefits include all three, the result of a coordinated project undertaken by county’s water and sanitation districts that will dispose of 100 million gallons a day of wastewater effluent and, in the process, create 70 million gallons each day of locally generated drinking water.
“Nothing is more certain than the water you already have,” says Rep. Ken Calvert (R-Corona). “When water can be reclaimed and reused, you absolutely know it’s going to be there for you.” Establishing a reliable, locally controlled source of drinking water is no small achievement in southern California, which is facing cuts in critical imports from northern California and the Colorado River, concurrent with projections that a population jump of 15 million will spark a statewide water crisis over the next 20 years.
The Orange County Groundwater Replenishment System achieved critical mass when county water and sanitation managers realized each had sticky challenges ahead. The county sanitation district, which is the third-largest west of the Mississippi River and serves 2.2 million customers, was looking at $170 million (and stiff public opposition) to construct a second ocean outfall to dispose of effluent from sewage treatment. At the same time, the water district (established in 1938 to manage the groundwater basin under central and northern Orange County), was looking for a way to safeguard its freshwater aquifers from encroaching seawater. Although the basin has been protected by a 3-mile seawater intrusion barrier of 28 injection wells, the rate at which groundwater was being drawn down was causing salt water to intrude around the barrier. Adding to the challenges were predictions of a 20% jump in the county’s water use over the next 15 years.
The solution to this intertwined set of challenges turned out to be straightforward: remove the source of irritation on one front—the proposed outfall—by using wastewater effluent that would ordinarily be disposed of in the ocean to feed the 3-mile-long underground pressure dam that protects the county’s groundwater supply. Additional benefits included the production of enough drinking water for 144,000 families every year (at four persons per family, that effectively covered a big chunk of the county’s projected population increase) and the establishment of a locally controlled supply of fresh water to reduce reliance on dwindling imported supplies.
According to Ron Wildermuth, who managed the water district’s campaign to sell the project to the public, the district has been using wastewater effluent in its seawater intrusion barrier since the 1970s. “What we needed,” says Wildermuth, “was to double the barrier from 15 million gallons to 30-40 million gallons a day. With future challenges to imported supplies of fresh water, we knew water reuse was the way to go. But being in an urban area where there was insufficient land available for surface groundwater recharge, we also knew we needed more space-efficient technology to produce the amount of water required for the barrier. We determined given our space constraints, that microfiltration, reverse osmosis, and UV—the same technologies used to purify baby food and bottled water—would work.”
According to Wildermuth, the county also considered desalinization. Typically a more expensive option, it penciled out at $800-$2,000 per acre-foot compared to $476 per acre-foot for groundwater recharge. The $486 million cost of the groundwater recharge project (over $90 million came from state and federal grants) included construction of a new water purification facility, eight new injection wells at the seawater barrier and a pipeline to deliver treated water from the new treatment facility 14 miles inland to existing spreading ponds.
The completion date is scheduled for 2007, but the project is already producing 5 mgd of purified water for the seawater barrier.
Longstanding Technology
The concept of artificial groundwater recharge has been around since the 19th century and is currently in use in the Netherlands and Germany as well as the United States. One of the oldest ongoing groundwater recharge projects in this country is the Montebellow Forebay Natural Groundwater Recharge Project, which began operation in 1962. Run by the Water Replenishment District of Southern California, it filters an average of 45 mgd of treated sewer water into the Los Angeles Central Groundwater Basin. The water meets state and federal primary drinking water standards and makes up about 35% of the total recharge to the groundwater basin, which in combination with imported water serves 3.7 million residents. Also in southern California the Los Angeles County West Basin Municipal Water District’s sewer water purification facility, which has been online since 1995, produces 7.5 mgd of purified sewer water for a one-half-mile-long seawater barrier of 100 injection wells. Plans call for the plant to expand to 12.5 mgd by 2006 using microfiltration and reverse osmosis.
Elsewhere, the Hueco Bolson Aquifer provides approximately 40% of the municipal water of El Paso, TX, and its surrounding area, plus 100% of the municipal supply for Ciudad Juarez, Mexico, and Fort Bliss, TX. Because the aquifer receives limited recharge in the arid climate, the El Paso Water District opted to decrease the rate at which reserves were being depleted by using artificial recharge with highly treated wastewater effluent. The project went into full operation in 1985 at 10 mgd. On the other side of the world, in Singapore, the NEWater Project uses an advanced purification process of microfiltration, reverse osmosis and ultraviolet disinfection similar to Orange County’s. Long-term plans call for adding NEWater to Singapore’s reservoirs before piping it to residential homes and commercial and industrial customers.
According to Wildermuth what differentiates the Orange County project is its scale and multiplicity of purpose. The aquifer the system will recharge supplies 75% of the water needs of 14 communities (the remainder comes from the Colorado River and northern California.). The basin is 2,000 feet deep and 365 square miles around the top and naturally holds between 10-40 million acre-feet of water, of which about 1 million acre-feet are usable. The basin is bordered by mountains on the east and north. This, combined with the localized seawater intrusion barrier, makes it feasible to manage the reclaimed water. Additionally there are only the two points of basin recharge: direct surface recharge through existing inland spreading ponds, wherein the water moves from the land surface via percolation through the soil to the aquifers, and direct subsurface recharge using the intrusion wells at the seawater barrier. As the delta of the Santa Ana River, the area is topographically well-suited to artificial groundwater recharge, and the basin has in fact undergone regular artificial recharge through the water district’s inland spreading ponds using water from the Santa Ana River, in combination with imported supplies, at an average annual rate of 250,000 acre-feet a year.
Three Steps Toward Purification
Orange County’s new Groundwater Replenishment System Advanced Purification Facility receives secondarily treated effluent from an adjacent wastewater treatment facility operated by its sister agency, the same quality water the sanitation district discharges into its existing ocean outfall. The three-step purification process begins with microfiltration of the same type that produces particle-free water for computer chip manufacturers. This first step in the purification process works like a screen to remove small suspended particles, protozoa, bacteria, and some viruses. The water district’s assistant director of engineering, Shivaji Deshmukh, describes microfiltration as a pretreatment for the critical step of reverse osmosis.
“The pretreatment allows reverse osmosis to concentrate on smaller, microscopic salts and organic constituents in the water,” says Deshmukh. “In RO, water is forced under high pressure through thin membranes that eliminate salts, pesticides, and most organic compounds, creating near-distilled quality water. Eighty-five percent of the water comes out as very pure water, the remaining 15% as brine [about 5000 milligrams per liter of salt compared to about 39,000 mgl for ocean water], which is discharged, along with other sanitation district effluent, into the existing ocean outfall.
From RO, the product water goes on to ultraviolet light and hydrogen peroxide treatment, considered the most effective way to eliminate any remaining organic compounds. “First hydrogen peroxide is dosed into the stream,” says Deshmukh. “The UV helps breaks that down into hydroxyl radicals. Ultraviolet light disinfects the water and photolizes any organic constituents. Hydroxyl radicals are also able to oxidize constituents that may be present at low levels following RO. The TDS [total dissolved salt] in water coming out of the plant is 50 parts per million, which is enough to leach minerals of conventional concrete pipes. We add lime to take it to around 100 parts per million. This is very similar to what the bottled water companies do in order to get a better taste and stabilize their water.”
UV also addresses the issue of trihalomethanes, a recurrent issue of public concern. “There are two issues,” says Deshmukh. “The trihalomethanes are entirely removed in reverse osmosis. However, the advantage of using UV instead of chlorine as a disinfectant is that you are not making any additional trihalomethanes after the water’s been cleaned. And although the majority of endocrine disrupters would be removed by reverse osmosis, if some may get through, ultraviolet light is able to address those. Also it’s very safe and it has no harmful byproducts.”
The final step is filtration of the processed water through soil. “Soil filtration is the intermediary step that makes this an indirect potable reuse project,” says Wildermuth. “The highly purified effluent is discharged into the aquifers, where it will blend with other water sources to become part of the drinking water supply.”
Mike Wehner, water quality and technology director for the Orange County Water District, explains it further. “As far as the state Department of Health Services is concerned, this last step is more of a retention process. Although it’s anticipated that given the extensive barriers we are using there wouldn’t be anything breaking through, the department sees time underground as a final, additional barrier to any existing microbes. In the area of our spreading ponds we are required to have six months retention time underground before the water can be extracted. At the injection barrier, where there isn’t the opportunity to filter the water through soil, we have to have the water underground for a year before it can be extracted. Retention time also provides an opportunity to monitor and detect any problems before the water actually gets to the production wells.”
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Bob Hultquist, chief of the Northern California Drinking Water Field Branch for the Department of Health Service, confirms that the department considers retention time underground a barrier to viruses. “In drinking water treatment we usually talk in terms of log [logarithmic] reduction of organisms. Any standard wastewater disinfection will usually kill a percent of organisms, although not all of them. Depending on the amount of chlorine you add, you’ll get a certain percent, 90 to 99 to 99.9%. In order to achieve our goal for viruses in groundwater recharge, each of these nine is a log. So if you’re reducing it by 90%, that’s one log; 99.9% is a two-LOG reduction. The goal of our groundwater recharge recycling criteria is a 12-log reduction, which means we’re talking about much better virus reduction than other standard forms of wastewater or wastewater treatment. And because you can’t measure that kind of log reduction, that is, you can’t demonstrate that you’re getting it through any kind of engineered treatment, we’ve required that it be achieved through a number of different barriers. The last barrier, good for at least six logs of virus reduction, is retention time underground.”
Orange County’s Groundwater Replenishment System is operated under a permit from the Santa Ana Regional Quality Control Board, which is part of a statewide network of localized water quality boards administered by the California Water Resources Control Board. The permit is the vehicle through which the Department of Health Services incorporates its water quality and water monitoring criteria.
“As with any wastewater disposal or reuse project, there are a number of contaminants we’re concerned about, Hultquist explains. “Primarily where there’s public exposure, pathogenic microorganisms are the biggest concern. Second would be nitrogen compounds because they’re present in such high quantities and there is a health effect from nitrates and nitrites. Third would be all the other regulated contaminants. By regulated I mean that the state has standards for them and we know they are of concern in drinking water. Fourth is the potential for unregulated contaminants in the final effluent that might work their way into a drinking water supply in concentrations that could eventually threaten the drinking water. To address those classes of unregulated contaminants likely to be present in wastewater, we have established both treatment and monitoring requirements.”
Hultquist says source control is a major consideration. “We definitely look at what’s tributary to the sewer system for a facility as far as industries and special wastes that might occur in a service area. We want to see monitoring in the form of extensive evaluation of the raw wastewater and effluent from secondary treatment. We want facilities to make an extra effort to look for those chemicals that may survive the treatment processes that could be toxic in drinking water supplies. One-four Dioxane is a chemical that was not adequately controlled under existing federal source control programs. It cropped up in the wastewater system of the Orange County Water District and is a good example of what we expect of any water utility that’s going to recharge groundwater used as a drinking water supply. We want them to look at the industries that are discharging into their wastewater system for chemicals like 1-4 Dioxane and make sure it’s either eliminated or in harmless concentrations.
“We expect that more drinking water standards are going to be established over time as we get smarter about how to analyze for chemicals. Right now we address uncertainties through treatment requirements. In the case of a project like Orange County’s, for example, we require project water go through reverse osmosis, but not any reverse osmosis. It has to be a very efficient reverse osmosis membrane at removing the kinds of contaminants we’re worried about. And then subsequently it has to pass through advanced oxidation using UV and hydrogen peroxide.
“There are two types of groundwater recharge systems presently in use in California, those like the Orange County project in which wastewater undergoes three-step processing and final percolation through soil, and a second type, which is used by the Los Angeles County Sanitation Districts, where wastewater is subject to secondary treatment, then subsequent filtration and disinfection and then put into spreading basins. This type of system is designed to have very effective soil and aquifer treatment so that dilution accomplishes the same thing as reverse osmosis.
“I think for a long time to come we’re going to have these two fundamentally different kinds of projects,” says Hultquist, based in part on location. “On the coast it’s fairly easy to get rid of the brine produced by reverse osmosis. Inland it’s almost impossible. Our fresh water criteria are written so they accommodate either one.”
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| The Santa Ana River flowing past the Orange County Groundwater Recharge System recharge ponds after a storm. |
Standards for blending are also spelled out in the project’s regional board permit, based again on the Department of Health Services’ recommendations.
“The blending requirement is to control unregulated chemicals in the wastewater,” says Hultquist. It’s part of a set of methods you can use to achieve a total organic carbon (TOC) limit in wastewater. Our TOC goal used to be 1 mg/L. It’s now .5 mg/L. You can achieve this through any combination of treatment or through dilution or any combination. It gets tougher and rougher if you decide on all treatment, because we expect more reliability. Dilution, on the other hand, is very effective. In the past we wanted at least 50% dilution. It’s only in the last few years that we’ve developed confidence in achieving the entire reduction through treatment. However, there will always be certain locations and certain kinds of projects where dilution is the most economical way to meet the standard.”
“For a number of years at the Orange County Water District,” says Wehner, “we were held to the standard that no more than two-thirds of the water injected at the seawater intrusion barrier could be of recycled water origin. In the permit for our new operation, the limit has been changed to three-quarters. And after we’ve demonstrated to the Department of Health Services and the regional board that between 60% and 75% water of recycled water origin has reached monitoring wells and that it hasn’t affected water quality, then according to the terms of our permit we will be able to use 100% recycled water. Which means that we will no longer have to blend water we apply to the ground. Currently water used for blending is imported water purchased from the Metropolitan Water District and water from deeper aquifers that has color and generally isn’t used for drinking. In the area of the recharge lakes the water used for blending is captured stormwater from the Santa Ana River.
“When Water Factory 21 [the county’s our original groundwater recharge treatment facility] was first developed,” says Wehner, “the state-of-the art for organics removal was granular activated carbon. With our experience and the experience of other treatment facilities, the Department of Health Services has become more comfortable with RO to lower levels of organic carbon.
“Regarding total organic carbon,” says Gary Yamamoto, chief of the Drinking Water Technical Programs Branch at the Department of Health Services, “we called for reverse osmosis because we wanted to address other contaminants that were inorganic in nature. Instead of adding another process, we wanted one that could do both.”
A Million for Monitoring
“For a long time now in our draft criteria we’ve had requirements for extensive monitoring of recycled water as it’s applied to the groundwater,” says Hultquist. “We also have quite rigorous monitoring requirements, that is, the number of contaminants that have to be monitored for and the frequency of monitoring both for the monitoring wells in the recharge area and for the drinking water wells to have an early warning of any problems.” (The criteria Hultquist refers to remain in draft stage, and the Department of Health Services has not identified a target date for adoption.)
“We anticipate over a million dollars a year for monitoring,” says Wehner. “That covers monitoring at the plant and water as it’s being produced at the advanced treatment facility, as well monitoring water as it’s being put into the ground and at the monitoring wells where water is extracted. That’s actually a requirement of our permit—that we’re not adversely affecting groundwater. The Department of Health Services wants us to use the same electronic data reporting system used for drinking water supply wells. We already have this ability, because we do chemical testing for the local water agencies that extract water from the groundwater basin.
“Historically we have injected into four aquifers. In the future the plant will be injecting into five aquifers, and we will have to test all five; that is, we will have to have a monitoring system that will enable us to look for effects in any zones where we put water. Another thing that has been recommended, and our staff agrees with, is that dedicated pumps be installed at the monitoring wells to reduce the risk of any cross-contamination from sampling in one zone to another.
“The fact is we’re monitoring for a wide range of contaminants that is much greater than is required for drinking water suppliers. But even in areas where we don’t currently have regulations, the Department of Health Services is asking cutting-edge projects such as ours to look for some of their emerging targets, the kind of contaminants for which no regulatory agency at the state or federal level has developed criteria yet, such as the pharmaceuticals and hormones.”
“Orange County is a really remarkable agency,” says Yamamoto. “For a long time they’ve supported a very large research program to develop the science and technology needed to make this kind of project work. There are a number of agencies that have very aggressively advanced the science of these kinds of projects. And some of our particular criteria have come directly from the recommendations of their science advisory panels.”
As to the future of using purified sewer water to supplement potable water supplies, Hultquist reports that a number of communities throughout California are evaluating the option. What’s yet to be sorted out is the level of resources required. “I don’t see how a smaller utility could afford this right now,” says Hultquist. “I think we’re talking a large, sophisticated agency.”
PENELOPE GRENOBLE O'MALLEY specializes in environmental topics.
OW - March/April 2006 |
