1’1 s the 21st century approaches, commu- nities around the world, faced with pop- ulation growth and increased urbaniza- tion, scramble to find new sources of drinking water. “Most cities have al- ready fully exploited the readily avail-

able water resources,” EPA warns ( 1 ) . The Califor- nia Department ofwater Resources braces for annual water shortages ranging from 3.7 million to 5.7 mil- lion 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 tra- ditionally have built new dams, levees, and canals. But public willingness to pay for new water facili- ties “has declined dramatically from the dam- building heyday of the 1950s and 1960s.” accord- ing 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 ar- tificial groundwater recharge, typically involves in- jecting treated city wastewater directly into aqui-

A

Wastewater Can groundwater recharge safely address the drinking-water needs of rapidly growing urban areas?

GINGER PINHOLSTER

fers or spreading it onto the ground to infiltrate the surface. It is unclear exactly how many regions prac- tice groundwater recharge, but James Crook, direc- tor ofwater reuse at Black &Veatch (Cambridge. MA), estimates that “hundreds” of US. cities are recy- cling wastewater for nonpotable purposes from crop imigation in arid western states to landscaping at Flor- ida’s Walt Disney World. A half-dozen cities, includ- ing El Paso, TX, and Los Angeles are recharging po- table 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 de- bate among the scientific community. Debate has fo- cused on whether treated wastewater can be clean enough to drink and is free from viruses and haz- ardous substances. But economics also is a con- cern: 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 prom- ising, though qualified, endorsement of groundwa-

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Two ways to replenish aquifers Two methods for returning treated waste water to the aquifer are 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.

ter recharge practices. Treated city wastewater can be used to boost potable aquifers under certain con- ditions, when no “better quality” water exists, ac- cording to the report. The committee was careful to add, however, that recharge technologies are “espe- cially well-suited to nonpotable uses such as land- scape irrigation.”

For water managers facing public opposition to recharge projects using treated wastewater, the re- port provides new ammunition. Coincidentally, it was released the same week that the Miller Brewing Com- pany filed a lawsuit to block a $25 million recharge effort in Upper San Gabrielvalley, CA. If successful, the1awsuit“wouldreallygivewaterreuse ablackeye,” says Crook, who served on the NRC groundwater re- charge committee.

Miller’s lawsuit charges that use of treated waste- water “will irreversibly pollute the basin,” possibly damaging its product. Cass Luke, a spokeswoman for the Upper San GabrielValley Water District, says Mill- er’s objections are based solely on public relations concerns, rather than scientific evidence of a health hazard.

The brewery supports the principle of ground- water recharge, but the company has a problem with this specific case, says Miller spokesman Victor Franco. The spreading ground for the treated waste- water, adjacent to the brewery, is a very porous soil, according to Franco. and the filtering effect as wa- ter percolates through the soil would not occur be- cause the water would “cascade through.”

The lawsuit underscores recurring questions about the safety of treated wastewater. Given proper treat- ment, reclaimed wastewater can be as safe or safer than traditional drinking-water sources, according to

I

Herman Bouwer, chief engineer for the US. Depart- ment of Agriculture’s Water Conservation Labora- tory in Phoenix, AZ. After all, be says, wastewater slated for use in aquifers typically is subjected to pri- mary, secondary, and sometimes advanced cleanup procedures-from settling of solids to biological ox- idation of organics to salt extraction via reverse os- mosis and adsorption of synthetic organics by gran- ular activated carbon.

‘about half the people in our country use ground- water [for drinking],” says Bouwer, an NRC commit- tee member, “but not all groundwaters are pure and pristine.” Surface water supplies fiom rivers, streams, and lakes frequently are polluted by sewage efflu- ent upstream. Runoff from cattle farms can contam- inate surface waters with potentially deadly para- sites such as Cryptosporidium, which can resist disinfection.

But other researchers insist that uncertainties re- lated to the chemical composition of reclaimed wastewater could jeopardize public health. “Hu- man sewage is a mish-mash of complex organic ma- terials, only some of which have been identified,” says Henry Ongerth, former sanitary engineer for Cali- fornia’s Department of Public Health. “Of the sub- stances 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 with- out fuss or fanfare. “For car washes, street sweep- ing, and golf-course irrigation, no one is opposed to this type of recycling,” says Forest Tennant, a phy- sician in West Covina, CA, who is head of the grass-

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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

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 aquifers with treated wastewater. Tennant hopes to thwart the re- charge project in Upper San Gabriel Valley.

When it comes to groundwater recharge, the con- troversy 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-monitor- ing data collected over a 10-year period from six Cal- ifornia wastewater treatment plants, secondary- level 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 Wil- liam A. Yanko, a laboratory supervisor for the Los An-

- I

geles County Sanitation District (LACSD). Yank0 says his data show that California’s existing treatment re- quirements ensure “essentially virus risk-free efflu- ents” for recharge projects.

But another 1993 sNdy of viral risks was less con- clusive (5). In that report, author David K. Powel- son of the University of Arizona at Tucson notes that although soil can strip remaining viruses from treated wastewater as the water infiltrates an aquifer, stud- ies have shown that “virus removal is dependent on virus type and environmental conditions.” Re- moval or inactivation of two types of viruses (MS2 and PRD1) from treated effluent directed into test ba- sins 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

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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 DNA- replicating machinery of the cell, and cause dis- ease. It does not survive long periods [in an aqui- fer] because it has no opportunity to replicate itself,” says Hartling, who has been known to delight news photographers by chugging vials of treated waste- water. As proof that viruses pose no threat in re- charged 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 sam- ples” collected from three sites in California.

Bob Hultquist, senior sanitary engineer for the Cal- ifornia Department of Health Services, counters that ‘‘viruses don’t live very long, but it’s all relative be- cause they can live in excess of a year.” Therefore proper pretreatment of recycled wastewater is crit- ical, he adds.

Disinfection hazards To eliminate viruses, wastewater usually is disin- fected with chlorine and less frequently with alter- native disinfectants such as ozone, monochlora- mine, 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 en- gineering at the University of North Carolina- Chapel Hill, notes in a 1994 study (7). In 1976, for ex- ample, the National Cancer Institute deemed chloroform, a trihalomethane (THM), to be carci- nogenic. 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 com- pounds are carcinogenic, but the doses must be very high,” says Richard J. Bull of Washington State Uni- versity 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 wa- ter is a question.”

Nellor’s data indicate “no increased rates of infec- tious diseases, congenital malformations. . . or all can- cers combined,” and thus don’t link DBPs to cancer, the National Research Council report notes. However, can- cers may remain latent for more than 15 years- longer than the period of Nellor’s study, it adds. Chlo- rine DBPs in reclaimed water could be minimized by expanding the use of alternative disinfection pro- cesses, the report notes. But it cautions that little is known about the byproducts of ozone, monochlora- mine, and ultraviolet disinfection.

Potential problems associated with alternative dis- infectants were discussed in a recent one-year study of DBPs at Jefferson Parish, LA (9). A treatment strat- egy of preozonation and postchloramination pro- duced the lowest levels of 18 halogenated DBPs, based on total organic carbon and total organic halide. Au- thor Benjamin W. Lykins, Jr., points out that ozona- tion 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 Cin- cinnati, 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 Den- ver, 344 rats showed no toxicologic, carcinogenic, or reproductive effects after drinking samples of treated water, even when concentration levels were ampli- fied 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 es- timated to be amenable to identification.”

Entering the aquifer Two recharge methods, surface infiltration and direct- well injection, are available to water managers when importing water is not an option. These methods can also be used to prevent seawater from contaminat- ing a coastal fresh water aquifer.

The Montebello Forebay Groundwater Recharge Project in south-central Los Angeles County, CA, es- tablished in 1962, is an off-channel surface infiltra- tion-type system. Wastewater at Montebello Fore- bay is subjected to advanced treatment, including chemical coagulation, dual-media filtration, and chlo- rine disinfection, Hartling explains. Then it is com- bined with other sources, such as storm water run- off and surface waters from northern California and Colorado. Spreading basins are flooded and dried al- ternately to prevent clogging and mosquito breed- ing and to promote aerobic soil conditions. Re- claimed water currently represents 20-30% of the inflow to the Montebello Forebay aquifer.

The other groundwater recharge method, direct- well injection, has been practiced at Water Factory 21 in Orange County, CA, since 1976. Construction of the facility began in 1972 to prevent seawater in- trusion 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, waste- water is extensively treated prior to injection. Pre- treatment of activated sludge secondary effluent at Water Factory 21 begins with lime clarification, which removes suspended solids, heavy metals, dis- solved minerals, and many viruses by elevating the water’s pH level. Recarbonation then normalizes the pH, and mixed-media filtration removes more sus- pended 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. An- other stream is forced under high pressure through a reverse-osmosis membrane, which removes salt and organics.

Soil infiltration recharge systems may offer the ad-

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vantage of scrubbing additional contaminants from treated wastewater. According to Hartling, the soil in- filtration system at Montebello Forebay reduces to- tal organic carbon by as much as 90% (though this could be either by removal or dilution) and re- moves SOW of all nitrogen. Soil infiltration also can remove parasites that tend to be resistant to disin- fection. Given the right soil conditions, "parasites like Cryptospondium and Giardia can be filtered out me- chanically 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., pro- fessor of resource economics at the University of Cal- ifornia-Riverside. Costs associated with artificial re- charge "are going to he quite variable." he says, hut reclaimed water can be less expensive than im- ported water.

When the Orange County Water District com- pleted 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 wa- ter to spreading grounds would have cost the dis- trict 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 waste- water from the San Jose Creek Water Reclamation Plant to nearby spreading grounds. Water District Manager Bob Berlien says the project would be cost- effective over the long term because the region cur- rently imports water for 5235 per acre-foot, whereas reclaimed water would cost just 5200 per acre-foot.

Groundwater recharge costs also are affected dra- matically by the level of pre- and posttreatment re- quired to ensure compliance with drinkingwater standards. At I.ake BuenaVista, FL, where the Reedy Creek Improvement District is studying the feasibil- ity of discharging treated wastewater into a recre- ational 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 re-

verse osmosis) to more than 523 million for a sys- tem that includes a full suite of treatment technol- ogies. Because direct-well injection recharge provides no soil-aquifer treatment, reclaimed water tends to require more advanced, and more costly, pretreat- ment, Vaux notes.

Reg~~latory issues Water drawn from recharged US. groundwater aqui- fers must comply with maximum part-per-million type standards set by the Safe Drinking Water Act. Aside from that, however, no federal regulations di- rectly govern recharge practices such as the level of monitoring or pre- and posttreatment needed to en- sure water quality ( I ) .

Many states have regulations governing re- charge. According to a 1993 survey, 36 states have reg- ulations or guidelines related to water recycling, hut only 10 directly address the use of reclaimed water for purposes other than irrigation (12). In states with- out regulations, EPA's Guidelines for 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 [re- charge],'' said Robert Bastian, an environmental sci- entist with EPA's Office of Wastewater Manage- ment, but EPAtypically has been "very positive toward water reuse practices," he adds. Michael Cook, di- rector of EPA's Office ofwastewater Management, re- cently offered a qualified endorsement of the pro- posed 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 re- charge of potable surface water reservoirs and groundwater aquifers." He softens his support, how- ever, by adding, "concerns are 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 val- ues, or "the negative consinner image of drinking re- claimed water," Cook says.

California and Florida are revising their re- charge regulations. Title 22 of the California Admin- istrative Code defines a minimum treatment level for reclaimed water slated for nonpotahle reuse (a cy- cle of coagulation, flocculation, sedimentation, fil- tration, 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 spe- cific set of regulations that include minimum per- formance standards, based on water quality analy- sis, for potable recharge systems. The proposed regulations also would require that reclaimed wa- ter 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.

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Florida is revising Chapter 62-610 of its Admin- istrative Code, which deals mainlywith nonpotable water reuse systems. The state Environmental Reg- ulation 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 con- taminant 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 prob- ably will include requirements for collecting data on raw water quality, tougher treatment safeguards against Giardia and Cryptosporidium, and maxi- mum contaminant levels for total THMs and other DBPs, Singer says.

Russell Christman, professor of environmental sci- ences at the University of North Carolina-Chapel Hill, fears that existing federal regulations may not en- sure public safety when potable aquifers are re- charged. "When you have a [water] source that can't be entirely characterized-if only 10 or 20% of its or- ganic content can he identified-of what comfort is the fact that the water meets existing drinking wa- ter standards?" asks Christman.

A critical test case Concerns about public safety are driving the San Gab- rielvalley lawsuit, according to Miller Brewing Com- pany. To prove its case, attorneys for the company have collected expert declarations from researchers including Daniel A. Okun, Kenan professor of envi- ronmental engineering, emeritus, at the University of North Carolina-Chapel Hill. No long-term health hazards have been linked to the 32-year-old Mon- tebello Forebay recharge project, Okun notes. But he also claims that "San Gabriel doesn't have quite the same aquifer situation [because1 the soil there is more permeable and less likely to remove trace organ- ics." 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 dis- turb a Superfund site containing a plume of indus- trial contamination, groundwater activist Tennant charges. But the contamination is located well up- stream from the proposed recharge sites, coun- tered the water district's Cass Luke.

In an August 9, 1994, letter to water district man- ager Bob Berlien, a representative of the California Re- gional Water Quality Control Board wrote that ques- tions about water quality were "satishctorily addressed" by a draft 1993 Environmental Impact Report (13). "We believe the District's project will have positive re- gional and statewide benefits," wrote Robert P Ghi- relli, an executive officer for the Control Board. US. water managers are following the Miller law-

suit closely. "We are worried that it might have neg- ative impacts because public perception ofwater re- use 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 hear- ings were delayed until February, Victor Franco said.

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 ame- nable to cleaning, Sudak says. But new devices are more promis- ing. A microfilter marketed by Memtec America Corporation's Mem- cor Division (Sari Oiego. CA, and Timonium. MOL uses a gas-pulse backwash system to remove clogs. It is being evaluated in Scoits- dale, 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 ex- isting 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 a n d organics removal. -GINGER PINHOLSTER

In Los Angeles County, Earle Hartling began receiv- ing calls from concerned citizens shortky after the Miller lawsuit was filed. "The reverberations and repercus- sions are starting already," he says. "This is scary, given the fact that reclaimed water will be critical to wm- pensate for impending water shortages."

References ( I ) "Guidelines for Water Reuse"; US. Environmental Pro-

tection Agency: Washington, DC, 1992 EPA/625/R-92/ 004.

(2) "California Water Balance: California Water Plan Up- date"; California Depanment ofwater Resources, 1994: Bul- letin 160-93.

(3) '"Ground Water Recharge: UsingWaterS of Impaired Qud- ity"; 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 By-

products"; 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 "Advanced Wastewater Reclamation Program Final Re- port"; 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.

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