Wastewater Can groundwater recharge safely address the drinking-water needs of rapidly growing urban areas?
GINGER PINHOLSTER
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s the 21st century approaches, communities around the world, faced with population growth and increased urbanization, scramble to find new sources of drinking water. “Most cities have already fully exploited the readily available water resources,” EPA warns ( 1 ) . The California Department ofwater Resources braces for annual water shortages ranging from 3.7 million to 5.7 million acre-feet (1.2 million to 1.8 million gallons, or 4.6 billion to 7 billion cubic meters) by 2020 (2). To meet growing population needs, US.planners traditionally have built new dams, levees, and canals. But public willingness to pay for new water facilities “has declined dramatically from the dambuilding heyday of the 1950s and 1960s.” according to a recent report by the National Research Council (3). Consequently, communities throughout the United States a e studying the safety, economics, and feasibility of directing treated sewer water into the ground to replenish dwindling aquifers-even those tapped for drinking water. The practice, known as artificial groundwater recharge, typically involves injecting treated city wastewater directly into aqui-
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fers or spreading it onto the ground to infiltrate the surface. It is unclear exactly how many regions practice groundwater recharge, but James Crook, director ofwater reuse at Black &Veatch (Cambridge.MA), estimates that “hundreds” of U S . cities are recycling wastewater for nonpotable purposes from crop imigation in arid western states to landscaping at Florida’s Walt Disney World. A half-dozen cities, including El Paso, TX,and Los Angeles are recharging potable aquifers; a dozen more communities are considering similar projects, says Crook. Though reclaimed wastewater has been used to augment drinking-water supplies in Los Angeles County since 1962, mounting public concern about the safety of recycled water is sparking renewed debate among the scientificcommunity. Debate has focused on whether treated wastewater can be clean enough to drink and is free from viruses and hazardous substances. But economics also is a concern: Is it cheaper to treat wastewater to replenish aquifers or “import” water from other sources? A National Research Council (NRC) report titled “Ground Water Recharge: Using Waters of Impaired Quality,” released in September 1994, offers a promising, though qualified, endorsement of groundwa0013-936x10510929-174A$09.00/00 1995 American Chemical Society
Two ways to replenish aquifers
Two methods for returning treated waste water to the aquiferare through (A) spreading grounds and percolation and (B) direct injection.The former provides an extra treatment: The soil strips contaminants and viruses out 31 water as it
percolates through. Recycled water that is injected directly must first be treated thoroughly.
I ter recharge practices. Treated city wastewater can be used to boost potable aquifers under certain conditions, when no “better quality” water exists, according to the report. The committee was careful to add, however, that recharge technologies are “especially well-suited to nonpotable uses such as landscape irrigation.” For water managers facing public opposition to recharge projects using treated wastewater, the report provides new ammunition. Coincidentally, it was released the same week that the Miller Brewing Company filed a lawsuit to block a $25 million recharge effort in Upper San Gabrielvalley, CA.If successful, the1awsuit“wouldreallygivewaterreuseablackeye,” says Crook, who served on the NRC groundwater recharge committee. Miller’s lawsuit charges that use of treated wastewater “will irreversibly pollute the basin,” possibly damaging its product. Cass Luke, a spokeswoman for the Upper San GabrielValley Water District, says Miller’s objections are based solely on public relations concerns, rather than scientific evidence of a health hazard. The brewery supports the principle of groundwater recharge, but the company has a problem with this specific case, says Miller spokesman Victor Franco. The spreading ground for the treated wastewater, adjacent to the brewery, is a very porous soil, according to Franco. and the filtering effect as water percolates through the soil would not occur because the water would “cascade through.” The lawsuit underscores recurring questions about the safety of treated wastewater. Given proper treatment, reclaimed wastewater can be as safe or safer than traditional drinking-water sources, according to
Herman Bouwer, chief engineer for the US. Department of Agriculture’s Water Conservation Laboratory in Phoenix, AZ. After all, be says, wastewater slated for use in aquifers typically is subjected to primary, secondary, and sometimes advanced cleanup procedures-from settling of solids to biological oxidation of organics to salt extraction via reverse osmosis and adsorption of synthetic organics by granular activated carbon. ‘about half the people in our country use groundwater [fordrinking],”says Bouwer, an NRC committee member, “but not all groundwaters are pure and pristine.” Surface water supplies fiom rivers, streams, and lakes frequently are polluted by sewage effluent upstream. Runofffrom cattle farms can contaminate surface waters with potentially deadly parasites such as Cryptosporidium,which can resist disinfection. But other researchers insist that uncertainties related to the chemical composition of reclaimed wastewater could jeopardize public health. “Human sewage is a mish-mash of complex organic materials, only some of which have been identified,” says Henry Ongerth, former sanitary engineer for California’s Department of Public Health. “Of the substances that have been identified, only a fraction have been studied for their toxicity. ...Why add to the risks we already face?“
Is it safe to drink? Nonpotable aquifers frequently are recharged without fuss or fanfare. “For car washes, street sweeping, and golf-courseirrigation, no one is opposed to this type of recycling,” says Forest Tennant, a physician in West Covina, CA,who is head of the grassVOL. 29. NO. 4.19951 ENVIRONMENTAL SCIENCE &TECHNOLOGY. 1 7 5 A
Wastewater since 1962. The two projects supply different aquifer systems. however. as the geology in the Merced Hills, Puente Hills, and Whittier Narrows region keeps the two groundwater systems from intermingling,
San Jose Creek Water Reclamation plant
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rhe Montebello Fore Groundwater Recharg ?‘
Project usesthe R
astewater, storm runoff and imponed surface water Reclaimed wastewater accounts for nearly 30% of recharge inflow at Montebello Forebay
roots group Citizens for Clean Water.YetTennant and others staunchly oppose refilling potable aquiferswith treated wastewater. Tennant hopes to thwart the recharge project in Upper San Gabriel Valley. When it comes to groundwater recharge, the controversy most often hinges on whether treated city wastewater is safe to drink. Questions focus mainly on two constituents of treated wastewater: viruses and disinfection byproducts. According to a 1993 analysis of virus-monitoring data collected over a 10-yearperiod from six California wastewater treatment plants, secondarylevel treatment effectively removes 99.8% of detectable viruses ( 4 ) . Large quantities of treated wastewater, averaging 275 gallons per sample, were collected monthly. Only one of 590 samples tested positive for enteric viruses, reports study author William A. Yanko, a laboratory supervisor for the Los An1 1 6 A rn VOL. 29.
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geles County Sanitation District (LACSD).Yank0 says his data show that California’sexisting treatment requirements ensure “essentially virus risk-free effluents” for recharge projects. But another 1993sNdy of viral risks was less conclusive (5).In that report, author David K. Powelson of the University of Arizona at Tucson notes that although soil can strip remaining viruses from treated wastewater as the water infiltrates an aquifer, studies have shown that “virus removal is dependent on virus type and environmental conditions.” Removal or inactivation of two types of viruses (MS2 and PRD1) from treated effluent directed into test basins composed primarily of sand and gravel varied depending on sample depths. At a depth of 4.3 meters, for example, virus removal ranged from 37% to 99.7%. Eade Hartling, water recycling coordinator for the
LACSD, says viruses require a host and therefore are inactivated quickly in underground aquifers. “All a virus does is invade a cell, take over the DNAreplicating machinery of the cell, and cause disease. It does not survive long periods [in an aquifer] because it has no opportunity to replicate itself,” says Hartling, who has been known to delight news photographers by chugging vials of treated wastewater. As proof that viruses pose no threat in recharged aquifers, Hartling and others frequently cite a landmark 1984 health effects study prepared by Margaret H. Nellor and colleagues (6).Over a 5-year period, the authors say, “No viruses were detected in groundwater or chlorinated reclaimed water samples” collected from three sites in California. Bob Hultquist, senior sanitary engineer for the California Department of Health Services, counters that ‘‘virusesdon’t live very long, but it’s all relative because they can live in excess of a year.” Therefore proper pretreatment of recycled wastewater is critical, he adds.
Disinfection hazards To eliminate viruses, wastewater usually is disinfected with chlorine and less frequently with alternative disinfectants such as ozone, monochloramine, or ultraviolet radiation. Unfortunately, a host of chlorine disinfection byproducts (DBPs) are thought to be hazardous to human health, Philip C. Singer, professor of environmental science and engineering at the University of North CarolinaChapel Hill, notes in a 1994 study (7). In 1976, for example, the National Cancer Institute deemed chloroform, a trihalomethane (THM), to be carcinogenic. Hundreds of other DBPs have been found since in drinking water, including dichloroacetic acid, which “is believed to be a more potent carcinogen than any of the THMs, based on animal studies,”says Singer. “There’s very clear evidence that these compounds are carcinogenic,but the doses must be very high,” says Richard J. Bull of Washington State University in Pullman, author of a major study on DBP health effects (8).“Now, whether they’re dangerous at the concentrations you would find in drinking water is a question.” Nellor’s data indicate “no increased rates of infectious diseases, congenital malformations. . . or all cancers combined,”and thus don’tlinkDBPs to cancer, the National Research Council report notes. However, cancers may remain latent for more than 15 yearslonger than the period of Nellor’s study, it adds. Chlorine DBPs in reclaimed water could be minimized by expanding the use of alternative disinfection processes, the report notes. But it cautions that little is known about the byproducts of ozone, monochloramine, and ultraviolet disinfection. Potential problems associated with alternative disinfectants were discussed in a recent one-year study of DBPs at Jefferson Parish, LA (9).A treatment strategy of preozonation and postchloramination produced the lowest levels of 18 halogenated DBPs, based on total organic carbon and total organic halide. Author Benjamin W. Lykins, Jr., points out that ozonation results in increased assimilable carbon, which must be controlled to prevent microbial regrowth.
Ozonation byproducts such as aldehydes, ketones, and acids also are a concern, says Lykins, chief of the EPA’s Systems and Field Evaluation Branch in Cincinnati, OH. In general, the National Research Council report says the body of existing health effects studies “do not suggest a health concern” associated with treated wastewater. For example, in a 20-year study in Denver, 344 rats showed no toxicologic, carcinogenic, or reproductive effects after drinking samples of treated water, even when concentration levels were amplified 500 times (10). But study author William C. Lauer notes that “as little as 10% of the measurable total organic carbon [in treated wastewater] has been estimated to be amenable to identification.”
Entering the aquifer Two recharge methods, surface infiltration and directwell injection, are available to water managers when importing water is not an option. These methods can also be used to prevent seawater from contaminating a coastal fresh water aquifer. The Montebello Forebay Groundwater Recharge Project in south-central Los Angeles County, CA, established in 1962, is an off-channel surface infiltration-type system. Wastewater at Montebello Forebay is subjected to advanced treatment, including chemical coagulation,dual-media filtration,and chlorine disinfection, Hartling explains. Then it is combined with other sources, such as storm water runoff and surface waters from northern California and Colorado. Spreading basins are flooded and dried alternately to prevent clogging and mosquito breeding and to promote aerobic soil conditions. Reclaimed water currently represents 20-30% of the inflow to the Montebello Forebay aquifer. The other groundwater recharge method, directwell injection, has been practiced at Water Factory 21 in Orange County, CA, since 1976. Construction of the facility began in 1972 to prevent seawater intrusion into four overtapped groundwater aquifers, says Mike Wehner, health and regulatory director for the Orange County Water District. Today, highly treated wastewater is mixed with deep well water and injected into threatened aquifers through a series of 23 multiple-casing wells located about 3.5 miles from the shore. The direct-well approach enables Orange County to penetrate aquifers through a thick layer of clay. The same method lets the city of El Paso recharge a 350-foot-deep aquifer. At both locations, wastewater is extensively treated prior to injection. Pretreatment of activated sludge secondary effluent at Water Factory 21 begins with lime clarification, which removes suspended solids, heavy metals, dissolved minerals, and many viruses by elevating the water’s pH level. Recarbonation then normalizes the pH, and mixed-media filtration removes more suspended solids. In a final step, some water is fed through an activated carbon adsorption system where organic molecules latch onto complex carbon pores before the remaining flow is rechlorinated.Another stream is forced under high pressure through a reverse-osmosis membrane, which removes salt and organics. Soil infiltration recharge systems may offer the adVOL. 29, NO. 4, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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verse osmosis) to more than 523 million for a system that includes a full suite of treatment technologies. Because direct-well injection recharge provides no soil-aquifer treatment, reclaimed water tends to require more advanced, and more costly, pretreatment, Vaux notes.
Reg~~latory issues
vantage of scrubbing additional contaminants from treated wastewater. According to Hartling, the soil infiltration system at Montebello Forebay reduces total organic carbon by as much as 90% (though this could be either by removal or dilution) and removes SOW of all nitrogen. Soil infiltration also can remove parasites that tend to be resistant to disinfection. Given the right soil conditions, "parasites like Cryptospondium and Giardia can be filtered out mechanically by nature," says Herman Bouwer of the USDA's Water Conservation Lab.
Recharge price tags Recharge may be an increasingly attractive option as competition for water grows and public funding for new water facilities shrinks, says HenryVaux. Jr., professor of resource economics at the University of California-Riverside. Costs associated with artificial recharge "are going to he quite variable." he says, hut reclaimed water can be less expensive than imported water. When the Orange County Water District completed an internal economic feasibility study in 1993, Vaux says, the price tag for nearby surface water was $600 per acre-foot (31.Transporting this surface water to spreading grounds would have cost the district an additional $82.40 per acre-foot, for a total of $682.40 per acre-foot. Conversely, reclaimed water is readily available for recharge purposes and the cost of advanced treatment ranges from $251 to $387 per acre-foot. Upper San Gabriel Valley has proposed building a new nine-mile pipeline tn fnnnel treated wastewater from the San Jose Creek Water Reclamation Plant to nearby spreading grounds. Water District Manager Bob Berlien says the project would be costeffective over the long term because the region currently imports water for 5235 per acre-foot, whereas reclaimed water would cost just 5200 per acre-foot. Groundwater recharge costs also are affected dramatically by the level of pre- and posttreatment required to ensure compliance with drinkingwater standards. At I.ake BuenaVista, FL, where the Reedy Creek Improvement District is studying the feasibility of discharging treated wastewater into a recreational lake, researchers predicted the costs of four treatment options (11). Estimated capital costs ranged from $1 1.3 million for a treatment system based on biological "deep b e d denitrification (rather than re178
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Water drawn from recharged US.groundwater aquifers must comply with maximum part-per-million type standards set by the Safe Drinking Water Act. Aside from that, however, no federal regulations directly govern recharge practices such as the level of monitoring or pre- and posttreatment needed to ensure water quality ( I ) . Many states have regulations governing recharge. According to a 1993survey, 36 states have regulations or guidelines related to water recycling, hut only 10 directly address the use of reclaimed water for purposes other than irrigation (12).In states without regulations, EPA's Guidelinesfor Water Reuse m a n ual serves as a blueprint for water reuse projects, says James Crook, a principal author of the publication. "There's no formal agency position saying that we're strongly encouraging or discouraging [recharge],'' said Robert Bastian, an environmental scientist with EPA's Office of Wastewater Management, but EPAtypically has been "very positive toward water reuse practices," he adds. Michael Cook, director of EPA's Officeofwastewater Management,recently offered a qualified endorsement of the proposed recharge project in Upper San GabrielValley. In a letter accompanying an Environmental Impact Report commissioned hy the water district, Cook says that "comprehensive research and demonstration projects as well as monitoring of existing operating systems have documented the environmental safety and lack of public health hazards associated with well-run water reclamation and reuse practices in the United States, including projects involving the recharge of potable surface water reservoirs and groundwater aquifers." He softens his support, however, by adding, "concernsare often raised when new reuse projects such as [the San Gabriel project1 are proposed." Public concerns may be based on a "lack of knowledge," a fear of plummeting property values, or "the negative consinner image of drinking reclaimed water," Cook says. California and Florida are revising their recharge regulations. Title 22 of the California Administrative Code defines a minimum treatment level for reclaimed water slated for nonpotahle reuse (a cycle of coagulation, flocculation, sedimentation, filtration, and disinfection). A brief 1978 amendment to Title 22 (Article 5.1) notes that requirements for potable reuse will be established "on an individual case basis." A committee directed hy the California Depanment of Health Services is refining a more specific set of regulations that include minimum performance standards, based on water quality analysis, for potable recharge systems. The proposed regulations also would require that reclaimed water be held underground for at least six months prior to reuse-"long enough to get a high percentage of [virus] die-off," says Bob Hultquist. He expects the draft regulations to be approved in early 1995.
Florida is revising Chapter 62-610of its Administrative Code, which deals mainlywith nonpotable water reuse systems. The state Environmental Regulation Commission will review revised regulations in May, reports DaveYork, reuse coordinator with the Florida Department of Environmental Protection.The draft regulations would set maximum contaminant levels for groundwater recharge. While dealing with more stringent maximum contaminant levels in the future, recharge managers also will have to comply with new EPA limits on DBPs, according to Philip Singer (7). EPXs revised rules probably will include requirements for collecting data on raw water quality, tougher treatment safeguards against Giardia and Cryptosporidium, and maximum contaminant levels for total THMs and other DBPs, Singer says. Russell Christman, professor of environmental sciences at the University of North Carolina-Chapel Hill, fears that existing federal regulations may not ensure public safety when potable aquifers are recharged. "When you have a [water]source that can't be entirely characterized-if only 10 or 20% of its organic content can he identified-of what comfort is the fact that the water meets existing drinking water standards?" asks Christman.
Microfiltration devices show promise Before use in recharging aquifers, city wastewater is subjected to costly, complex cleanup procedures. To reduce costs, engineers arc trying an advanced treatment called microfiltration, says Richard Sudak, president of Separation Process, Inc., of San Marcos. CA. Early microfiltration devices fouled too rapidly and weren't amenable to cleaning, Sudak says. But new devices are more promising. A microfilter marketed by Memtec America Corporation's Memcor Division (Sari Oiego. CA, and Timonium. MOL uses a gas-pulse backwash system to remove clogs. It is being evaluated in Scoitsdale, AZ. Orange County, CA. and several other regions, he says. It is a polypropylene membrane made of tiny, hollow fibers with very small pore sizes-about 0.2 micrometers. When secondary effluent is forced through at low pressures 11-20 Iblin.?, pores trap 99% of suspended and colloidal solids, bacteria, and viruses, whereas existing technology removes only 95%. according to Sudak. A blast of gas created by a sudden pressure drop dislodges clogs. Microfiltration may replace lime clarification, recarbonation, and granular media filtration at Water Factory 21 in Orange County, where treated wastewater is injected into groundwater aquifers to prevent seawater intrusion, says Mike Wehner, the water districfs health and regulatory director. But reverse osmosis will still be user for salts and organics removal. -GINGER PINHOLSTER
A critical test case Concerns about public safety are driving the San Gabrielvalley lawsuit, according to Miller Brewing Company. To prove its case, attorneys for the company have collected expert declarations from researchers including Daniel A. Okun, Kenan professor of environmental engineering, emeritus, at the University of North Carolina-Chapel Hill. No long-term health hazards have been linked to the 32-year-old Montebello Forebay recharge project, Okun notes. But he also claims that "San Gabriel doesn't have quite the same aquifer situation [because1the soil there is more permeable and less likely to remove trace organics." Planners have proposed tertiary treatment based on conventional granular filtration. More advanced technologies, such as reverse osmosis, would be needed to remove organics, Okun says. Recharge into San Gabriel aquifers might disturb a Superfund site containing a plume of industrial contamination, groundwater activist Tennant charges. But the contamination is located well upstream from the proposed recharge sites, countered the water district's Cass Luke. In an August 9, 1994, letter to water district manager Bob Berlien, a representativeof the California Regional Water Quality Control Board wrote that questions about water quality were "satishctorily addressed" by a draft 1993 Environmental Impact Report (13). "We believe the District's project will have positive regional and statewide benefits," wrote Robert P Ghirelli, an executive officer for the Control Board. US.water managers are following the Miller lawsuit closely. "We are worried that it might have negative impacts because public perception ofwater reuse is very, very important." says Bahman Sheikh, water resources and reuse policy specialist for the West Basin Municipal District. Already there have been two delays in getting to court, and the first hearings were delayed until February, Victor Franco said.
In Los Angeles County, Earle Hartling began receiving calls from concerned citizens shortky after the Miller lawsuit was filed. "The reverberations and repercussions are starting already," he says. "This is scary, given the fact that reclaimed water will be critical to wmpensate for impending water shortages."
References ( I ) "Guidelines for Water Reuse";US. Environmental Protection Agency: Washington, DC, 1992 EPA/625/R-92/ 004. (2) "CaliforniaWater Balance: CaliforniaWater Plan Update";California Depanmentofwater Resources, 1994: Bulletin 160-93. (3) '"GroundWater Recharge:UsingWaterS of Impaired Qudity"; National Research Council: Washington, DC, 1994. (4) Yanko. W. A. Water Enuiron. Res. 1993, 65,221-26. (5) Powelson. D. K.; Gerba. C. F!;Yahya, M.T. WaterRes.1993, 27(4), 583-90. (6) "Summary: Health Effects Study Final Report";Nellor, M. H.; Baird, R. B.; Smyth, J. R. County Sanitation Districts of 1.0s Angeles County: Los Angeles. CA. 1984. (7) Singer, P. C. I. Enuiron.Eng. 1994, 120(41, 727-44. (8) "Health Effects of Disinfectants and Disinfection Byproducts";Bull, R. I.; Kopfler. E C. American Waterworks Association Research Foundation: Denver, CO, 1991. (9) Lykins, B. W.; Koffskey, W. E.; Patterson, K. S. 1.Enuiron. Eng. 1994, 120(4), 745-58. (IO) Lauer, W. C.; Wolfe, G. W.; Condie, L. W. Toxicol. Ckem. Mixzures 1994,6341. ( I l l "AdvancedWastewater Reclamation Program Final Report";CH2M Hill: Gainesville, FL, 1993; prepared for the
Ginger Pinholster is afreelance science writer based in Wilmington, DE. She has written for Science, Popular Science, and Environmental Health Perspectives. VOL. 29, NO. 4,1995 I ENVIRONMENTAL SCIENCE &TECHNOLOGY
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