1
Reclaiming Wastewater: An Overview

Growing urbanized populations and increasing constraints on the development of new water sources have spurred a variety of measures to conserve and reuse water over the last two or three decades. As part of this trend, some municipalities have begun to reuse municipal wastewater for nonpotable water needs, such as irrigation of parks and golf courses. And a small but increasing number of municipalities are augmenting or considering augmenting the general water supply (potable and nonpotable) with highly treated municipal wastewater.

These "potable reuse" projects are made possible by improved treatment technology that can turn municipal wastewater into reclaimed water that meets standards established by the Safe Water Drinking Act. However, questions remain regarding how much treatment and how much testing are necessary to protect human health when reclaimed water is used for potable purposes. Some public health and engineering professionals object in principle to the reuse of wastewater for potable purposes, because standard public health philosophy and engineering practice call for using the purest source possible for drinking water. Others worry that current techniques might not detect all the microbial and chemical contaminants that may be present in reclaimed water. Several states have issued regulations pertaining to potable reuse of municipal wastewater, but these regulations offer conflicting guidance on whether potable reuse is acceptable and, when it is acceptable, what safeguards should be in place.



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--> 1 Reclaiming Wastewater: An Overview Growing urbanized populations and increasing constraints on the development of new water sources have spurred a variety of measures to conserve and reuse water over the last two or three decades. As part of this trend, some municipalities have begun to reuse municipal wastewater for nonpotable water needs, such as irrigation of parks and golf courses. And a small but increasing number of municipalities are augmenting or considering augmenting the general water supply (potable and nonpotable) with highly treated municipal wastewater. These "potable reuse" projects are made possible by improved treatment technology that can turn municipal wastewater into reclaimed water that meets standards established by the Safe Water Drinking Act. However, questions remain regarding how much treatment and how much testing are necessary to protect human health when reclaimed water is used for potable purposes. Some public health and engineering professionals object in principle to the reuse of wastewater for potable purposes, because standard public health philosophy and engineering practice call for using the purest source possible for drinking water. Others worry that current techniques might not detect all the microbial and chemical contaminants that may be present in reclaimed water. Several states have issued regulations pertaining to potable reuse of municipal wastewater, but these regulations offer conflicting guidance on whether potable reuse is acceptable and, when it is acceptable, what safeguards should be in place.

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--> This report assesses the health effects and safety of using reclaimed water as a sole source or as a component of the potable water supply. The report was prepared by the Committee to Evaluate the Viability of Augmenting Potable Water Supplies With Reclaimed Water, which was appointed by the National Research Council (NRC) to evaluate issues associated with potable reuse of municipal wastewater. The committee members were appointed based on their widely recognized expertise in municipal water supply, wastewater reclamation and reuse, and public health. In its evaluation, the committee considered the following questions: What are the appropriate definitions of water reuse? What distinguishes indirect from direct reuse? What are the considerations for ensuring reliability and for evaluating the suitability of a water source augmented with treated wastewater? Given the recent health-effect studies that have been conducted, what further research is required? The committee based its evaluation on published literature and the expertise of committee members and others consulted during this project. The committee used as its starting point the findings and recommendations of a 1982 NRC committee that examined quality criteria that should be applied when a degraded water supply is used as a drinking water source (see Box 1-1). As part of its information gathering effort, the committee hosted a two-day workshop in Irvine, California, featuring principal investigators and project managers of several of the potable reuse projects that have conducted analytical and health-effect studies. The committee views the planned use of reclaimed water to augment potable water supplies as a solution of last resort, to be adopted only when all other alternatives for nonpotable reuse, conservation, and demand management have been evaluated and rejected as technically or economically infeasible. This report should help communities considering potable reuse make decisions that will protect the populations they serve. Some of the issues relate to similar concerns for drinking water sources that receive incidental or unplanned upstream wastewater discharges. This chapter describes the history of potable reuse of municipal wastewater, defines the different types of potable reuse, provides an overview of wastewater treatment technologies applicable to potable reuse projects, and describes existing federal guidelines and state regulations covering potable reuse. Chapter 2 describes the chemical contaminants found in wastewater, treatments aimed at reducing them, and issues re-

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--> BOX 1-1 Results of the 1982 NRC Study of Quality Criteria for Water Reuse In 1982, the National Research Council issued a report titled Quality Criteria for Water Reuse (National Research Council, 1982) The report was developed to provide input to an experimental program commissioned by Congress to study the wastewater-contaminated Potomac Estuary as a potential new water source for the District of Columbia (National Research Council, 1982). The focus of the 1982 report was on the scientific questions concerning the quality criteria that should be applied if a degraded water supply is used as a source of drinking water At the time, very few communities in the United States, aside from Denver, Los Angeles, Washington, D.C. and Orange County, California, were considering water reuse to augment drinking water supplies The report concluded that the most practical way to judge the potential health hazards of reclaimed water is to compare it with conventional supplies, which have risks, if any, that are presumed to be acceptable initially, conventional water supplies and reclaimed water should be compared on the basis of identifiable individual compounds and microbiological organisms. The results of these tests would influence the need to proceed with additional testing, because reclaimed water that failed such a comparison would be rejected as not being as suitable as a conventional supply Because of the practical impossibility of identifying and testing all of the individual compounds present in reclaimed water, the report recommended testing of mixtures of chemicals. It also recommended that the mixtures be concentrated to increase the sensitivity of the tests. The report recommended that toxicological comparisons between reclaimed and conventional water be based on the outcomes of a series of tiered tests designed to provide information on the relative toxicities of the concentrates from the two water supplies Phase 1 tests would include in vitro assessments of mutagenic and carcinogenic potential by means of microbial and mammalian cell mutation and in vivo evaluations of acute and short-term subchronic toxicity, teratogenicity (birth defects), and clastogenicity (the production of chromosomal abnormalities) Phase 2 tests would include a longer term (90-day) subchronic study and a test for reproductive toxicity Phase 3 would consist of a chronic lifetime feeding study. The report concluded that depending on the results of the various comparative test phases, a judgment could be reached that reclaimed water is as safe as, more safe than, or less safe than a conventional water supply The final decision to use treated wastewater for potable purposes or for food processing would only be made after a careful evaluation of potential health effects treatment reliability cost, necessity, and public acceptance. Still, the report "strongly endorse[d] the generally accepted concept that drinking water should be obtained from the best quality source available" and noted that "U.S. drinking water regulations were not established to judge the suitability of raw water supplies heavily contaminated with municipal and industrial wastewater" The report suggested that planners should consider ''the much greater probability that adequately safe [reclaimed] water could be provided for short-term emergencies rather than for long-term use."

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--> lated to analytical methods for measuring water quality. Chapter 3 examines similar concerns related to microbial contaminants. Chapter 4 discusses methodological issues for conducting microbiological analysis, risk analysis, toxicological safety testing, and epidemiological studies. Chapter 5 reviews the health-related studies conducted by selected potable reuse projects. And Chapter 6 evaluates reliability and quality assurance issues for potable reuse projects. Selection of Drinking Water Sources Some public health authorities have been reluctant to allow or support the planned augmentation of water supplies with reclaimed municipal wastewater under any circumstances, subscribing to the maxim that only natural water derived from the most protected source should be used as a raw drinking water supply. This maxim has guided the selection of potable water supplies for more than 150 years. It was affirmed in the 1974 draft of the National Interim Primary Drinking Water Regulations, which states, "Production of water that poses no threat to the consumer's health depends on continuous protection. Because of human frailties associated with protection, priority should be given to selection of the purest source. Polluted sources should not be used unless other sources are economically unavailable" (U.S. EPA, 1975). This principle was derived from earlier public health practices developed when understanding of drinking water contaminants was limited and when natural processes (such as dilution in rivers and natural filtration by soils), rather than technology, were relied upon to produce suitable drinking water. It is also derived from a time when the U.S. population was smaller, and our concern about protecting the environment from the impact of human-made impoundments less formalized, and when pristine water supplies were more available than they are today. While a pristine drinking water source is still the ideal sought by most municipalities, the U.S. population has expanded, so that many large cities take water from sources that are exposed to sewage contamination. When these supplies were originally developed, the only health threats perceived were attributable to microbiological vectors of infectious disease. These vectors would be attenuated during flow in rivers and then easily eliminated with conventional water treatment processes such as coagulation, filtration, and disinfection. Such water supplies were generally less costly and more easily developed than higher quality upland supplies or underground sources. Today, however, most of these supply waters receive treated wastewaters from other communities upstream. Thus, cities such as Philadelphia, Cincinnati, and New Orleans, which draw water from the Delaware, Ohio, and Mississippi rivers, re-

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--> spectively, are already practicing unplanned indirect potable reuse of municipal wastewater. In fact, more than two dozen major water utilities, serving populations from 25,000 to 2 million people, draw from rivers in which the total wastewater discharge accounts for more than 50 percent of stream flow during low flow conditions (Swayne et al., 1980). Much of the impetus for water reuse comes from municipal utilities in the arid western United States. Many communities there already use a variety of measures to offset the rising costs of importing water long distances. Moving water entails satisfying a large number of environmental and health laws and permits, as well as the corresponding interests of competing users and local, state, tribal, and federal jurisdictions. As high-quality water sources become scarcer and populations in arid regions grow, the phrase "economically unavailable" has taken on new significance. Communities looking for new water sources must examine a number of options, including water conservation, nonpotable reuse, and investing more money in the treatment of water supplies that are of poorer quality but more readily available. Most communities will readily pay a premium to obtain a pristine supply for their drinking water. But the premiums required get bigger each year, particularly in areas where water is already scarce. Potable Reuse and Current Drinking Water Standards Much of the objection to planned potable reuse of wastewater arises from a discussion of whether drinking water standards are adequate to ensure the safety of all waters regardless of source. Some argue that drinking water standards apply only to—and were designed only for—waters derived from relatively pristine sources. Although this argument has a long-standing basis in normal sanitation practice, it is becoming more difficult to determine what is the best available water source. Water sources in the United States vary from protected, pristine watersheds to waters that have received numerous discharges of various wastes, as illustrated in Figure 1-1. Highly treated wastewater does not differ substantially from some sources already being used as water supplies. Because of the continuing degradation of raw water supplies in the United States and increased public concern about water quality, federal drinking water regulations, which in 1925 addressed only a handful of contaminants and applied only to municipalities that provided water to interstate carriers (such as buses, trains, and ships), now address nearly 100 contaminants and apply to all community water systems serving 25 people or more. The role of these drinking water standards should be evaluated against the continuum of available source waters.

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--> FIGURE 1-1 Quality spectrum of various waters and wastewaters with respect to degradation from human excreta and other materials.

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--> Drinking water standards' main function is to provide a benchmark for unacceptable risk from selected contaminants for which adequate health information exists. Up to a point, increasing the number of standards increases the confidence that a particular water supply is not contaminated by harmful chemicals or pathogens. However, the standards cannot guarantee that the water poses no health hazard. Modern analytical methods detect fewer than 10 percent of the organic chemicals typically present in a water (Ding et al., 1996). Further, drinking water standards exist only for a relatively small percentage of the possible chemical contaminants. In addition, these standards do not currently require monitoring for specific microbiological contaminants, but only for coliform bacteria, which merely indicate the possible presence of microbial pathogens—and only a fraction of microbial pathogens at that. Creating more standards, therefore, does not ensure the safety of drinking water, because as more chemical contaminants and pathogenic organisms are discovered the possibilities become almost infinite in scope. In summary, caution is required when evaluating whether compliance with drinking water standards—or proposed or hypothetical additional standards—will ensure a water source is safe. As a water source comes to include (intentionally or not) increasing amounts of wastewater, a drinking water utility must become increasingly knowledgeable about contaminant inputs into the wastewater. The utility might identify potential contaminants of concern by surveying the industrial inputs into the wastewater, examining the wastewater for chemical constituents broader than those represented by drinking water standards, and/or using toxicological testing methods to ensure that the product water does not contain substantial concentrations of chemicals whose toxicological properties have not been established. Types of Water Reuse When discussing the reuse of treated municipal wastewater for potable purposes, it is useful to distinguish between "indirect" and "direct" potable reuse and between "unplanned" and "planned'' potable reuse. Indirect potable water reuse is the abstraction, treatment, and distribution of water for drinking from a natural source water that is fed in part by the discharge of wastewater effluent. Planned indirect potable water reuse is the purposeful augmentation of a water supply source with reclaimed water derived from treated municipal wastewater. The water receives additional treatment prior to distribution. For example, reclaimed water might be added to ambient water in a water supply reservoir or underground aquifer and the mixture withdrawn for subsequent treatment at a later time.

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--> Unplanned indirect potable reuse is the unintentional addition of wastewater (treated or not) to a water supply that is subsequently used (usually by downstream communities) as a water source, with additional treatment prior to delivery. As noted earlier, many communities already unintentionally practice such unplanned indirect potable reuse. Direct potable water reuse is the immediate addition of reclaimed wastewater to the water distribution system. This practice has not been adopted by, or approved for, any water system in the United States. With planned or unplanned indirect potable reuse, the storage provided between treatment and consumption allows time for mixing, dilution, and natural physical, chemical, and biological processes to purify the water. In contrast, with direct potable reuse, the water is reused with no intervening environmental buffer. With planned indirect potable reuse and direct potable reuse, the wastewater is treated to a much higher degree than it would be were it being discharged directly to a surface water without specific plans for reuse. The wastewater generally is first treated as it would be in a conventional municipal wastewater treatment plant, then subjected to various advanced treatment processes. Conventional wastewater treatment begins with preliminary screening and grit removal to separate sands, solids, and rags that would settle in channels and interfere with treatment processes (Henry and Heinke, 1989). Primary treatment follows this preliminary screening and usually involves gravity sedimentation. Primary treatment removes slightly more than one-half of the suspended solids and about one-third of the biochemical oxygen demand (BOD) from decomposable organic matter, as well as some nutrients, pathogenic organisms, trace elements, and potentially toxic organic compounds. Secondary treatment usually involves a biological process. Microorganisms in suspension (in the "activated sludge" process), attached to media (in a "trickling filter" or one of its variations), or in ponds or other processes are used to remove biodegradable organic material. Part of the organic material is oxidized by the microorganisms to produce carbon dioxide and other end products, and the remaining organic material provides the energy and materials needed to support the microorganism community. Secondary treatment processes can remove up to 95 percent of the BOD and suspended solids entering the process, as well as significant amounts of heavy metals and certain organic compounds (Water Pollution Control Federation, 1989). Conventional wastewater treatment usually ends with secondary treatment, except in special cases where tertiary treatment is needed to provide additional removal of contaminants such as microbial pathogens, particulates, or nutrients. Advanced treatment processes beyond tertiary treatment are neces-

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--> sary when wastewater is to be reclaimed for potable purposes. Table 1-1 provides a list of advanced treatment processes, arranged by the types of constituents they are designed to remove. The process used by Water Factory 21 in Orange County, California, to treat wastewater prior to injecting it into selected coastal aquifers to form a seawater intrusion barrier is illustrative (see Figure 1-2 and Box 1-2). The advanced treatment of this water includes additional removal of suspended material by chemical coagulation with lime, alum, or a ferric salt. This process is generally quite effective in removing heavy metals as well as dissolved organic materials (McCarty et al., 1980). Recarbonation by the addition of carbon dioxide then neutralizes the high pH created by the addition of lime. After that, mixed media filtration is used to remove suspended solids. The flow is then split between granular activated carbon, which removes soluble organic materials, and reverse osmosis (RO), which is used for demineralization, so that when blended with the remaining water the mixture will meet total dissolved solids requirements specified for injected water. Reverse osmosis can also remove the majority of the dissolved nonvolatile organic materials and achieve less than 1 mg/liter of dissolved organic carbon in the treated water. According to measures of identifiable contaminants, water treated in this manner is often of better quality than some polluted surface waters now used as TABLE 1-1 Constituent Removal by Advanced Wastewater Treatment Processes Principal Removal Function Description of Process Type of Wastewater Treateda Suspended solids removal Filtration Microstrainers EPT, EST EST Ammonia oxidation Biological nitrification EPT, EBT, EST Nitrogen removal Biological nitrification/ denitrification EPT, EST Nitrate removal Separate-stage biological denitrification EPT + nitrification Biological phosphorus removal Mainstream phosphorus removalb RW, EPT   Sidestream phosphorus removal RAS

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--> Principal Removal Function Description of Process Type of Wastewater Treateda Combined nitrogen and phosphorus removal by biological methods Biological nitrification/ denitrification and phosphorus removal RW, EPT Nitrogen removal by physical or chemical methods Air stripping EST   Breakpoint chlorination EST + filtration   Ion exchange EST + filtration Phosphorus removal by chemical addition Chemical precipitation with metal salts or lime RW, EPT, EBT, EST Toxic compounds and refractory organics removal Granular activated carbon adsorption EST + filtration   Powdered activated carbon adsorption EPT   Chemical oxidation EST + filtration Dissolved inorganic solids removal Chemical precipitation RW, EPT, EBT, EST   Ion exchange EST + filtration   Ultrafiltration EST + filtration   Reverse osmosis EST + filtration   Electrodialysis EST + filtration +carbon adsorption Volatile organic compounds Volatilization and gas stripping RW, EPT Microorganism removalc Reverse osmosis EST + filtration   Nanofiltration/ultrafiltration EST + filtration   Lime treatment EST   a EBT = effluent from biological treatment (before clarification); EPT = effluent from primary treatment; EST = effluent from secondary treatment; RAS = return activated sludge; and RW = raw water (untreated sewage). b Removal process occurs in the main flowstream as opposed to during sidestream treatment. c Microorganism removal is also accomplished by any of several chemical disinfection processes (e.g., free Cl2, NH2Cl, C102, 03), but these are not usually considered as advanced wastewater treatment processes. SOURCE: Adapted from Metcalf and Eddy, Inc., 1991.

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--> FIGURE 1-2 Flow schematic for Orange County Water District Water Factory 21.

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--> Type of Reuse Treatment Reclaimed Water Qualitya Augmentation of surface supplies   •   Secondaryc •   Filtrationd •   Disinfectione •   Advanced wastewater treatmentf Includes, but is not limited to, the following: •   pH = 6.5-8.5 •   Turbidity = 2 NTUi •   No detectable fecal coliforms per 100 mlj,k •   Residuall =1 mg/liter Cl2 •   Meet drinking water standards NOTE: NTU = nephelometric turbidity units. a Unless otherwise noted, recommended quality limits apply to reclaimed water at the point of discharge from the treatment facility. b Setbacks are recommended to protect potable water supply sources from contamination and to protect humans from unreasonable health risks due to exposure to reclaimed water. c Secondary treatment processes include activated sludge, trickling filters, rotating biological contactors, and many stabilization pond systems. Secondary treatment should produce effluent in which both the BOD and suspended solids do not exceed 30 mg/liter. d Disinfection means the destruction, inactivation, or removal of pathogenic microorganisms by chemical, physical, or biological means. Disinfection may be accomplished by chlorination, ozonation, other chemical disinfectants, ultraviolet radiation, membrane processes, or other processes. e Filtration means the passing of wastewater through natural undisturbed soils or filter media such as sand and/or anthracite. f Advanced wastewater treatment processes include chemical clarification, carbon adsorption, reverse osmosis and other membrane processes, air stripping, ultrafiltration, and ion exchange.

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--> Reclaimed Water Monitoring Setback Distancesb Comments       •   A higher chlorine residual and/or a longer contact time may be necessary to ensure virus inactivation •   Treatment reliability checks need to be provided Includes, but is not limited to, the following: •   pH: daily •   Turbidity: continuous •   Coliform: daily •   Cl2 residual: continuous •   Drinking water standards: quarterly •   Otherg: depends on constituent   •   Site-specific   •   Recommended level of treatment is site-specific and depends on factors such as receiving water quality, time and distance to point of withdrawal, dilution, and subsequent treatment prior to distribution for potable uses •   The reclaimed water should not contain measurable levels of pathogensh •   A higher chlorine residual and/or a longer contact time may be necessary to ensure virus inactivation •   Treatment reliability checks need to be provided g Monitoring should include measurement of the concentrations of inorganic and organic compounds, or classes of compounds, that are known or suspected to be toxic, carcinogenic, teratogenic, or mutagenic and are not included in the drinking water standards. h It is advisable to fully characterize the microbiological quality of the reclaimed water prior to implementation of a reuse program. i The recommended turbidity limit should be met prior to disinfection. The average turbidity should be based on a 24-hour time period. The turbidity should not exceed 5 NTU at any time. If suspended solids content is used in lieu of turbidity, the average suspended solids concentration should not exceed 5 mg/liter. j Unless otherwise noted, recommended coliform limits are median values determined from the bacteriological results of the last seven days for which analyses have been completed. Either the membrane filter or the fermentation tube technique may be used. k The number of fecal coliform organisms should not exceed 14/100 ml in any sample. l Total chlorine residual after a minimum contact time of 30 minutes. SOURCE: Adapted from U.S. EPA, 1992.

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--> California Wastewater Reclamation Criteria California currently includes general requirements for indirect potable water reuse via ground water recharge under the state's Wastewater Reclamation Criteria (State of California, 1978). These requirements are presently being replaced with more detailed regulations focusing specifically on ground water recharge (State of California, 1993). The proposed regulations, which have gone through several iterations, are designed to ensure that ground water extracted from an aquifer recharged by reclaimed water meets all drinking water standards and requires no treatment prior to distribution. Table 1-3 summarizes the proposed treatment process and site requirements. The criteria are intended to apply to any water reclamation project designed for the purpose of recharging ground water suitable for use as a drinking water source (Hultquist, 1995). The proposed regulations prescribe both microbiological and chemical constituent limits, some of which are summarized in Table 1-3. The proposed regulations would require that concentrations of minerals, trace inorganic chemicals, and organic chemicals in reclaimed water prior to recharge must not exceed the maximum contaminant levels established in the state's drinking water regulations. The total nitrogen concentration of the reclaimed water cannot exceed 10 mg/liter unless it is demonstrated that in the process of percolating into the ground water, enough nitrogen will be removed from the reclaimed water to meet the 10 mg/liter standard. Based principally on information and recommendations contained in a report prepared by an expert panel commissioned by California (State of California, 1987), the proposed regulations specify that extracted ground water should contain no more than 1 mg/liter of total organic carbon (TOC) of wastewater origin. TOC is considered to be a suitable measure of the gross organics content of reclaimed water for the purpose of determining organics removal efficiency in practice. The requirements shown in Table 1-3 are intended in part to ensure that the TOC concentration of wastewater origin is limited to 1 mg/liter in public water supply wells. Requirements for reduction of TOC concentrations are less restrictive for projects in which the reclaimed water is recharged into the ground via surface spreading than for projects in which the reclaimed water is injected directly into the aquifer, because additional TOC removal has been demonstrated to occur in the unsaturated zone with surface spreading projects (Nellor et al., 1984). Similarly, the proposed regulations require that the composition of the water at the point of extraction not exceed either 20 percent or 50 percent water of reclaimed water origin, depending on site-specific conditions, type of recharge, and treat-

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--> TABLE 1-3 Proposed California Ground Water Recharge Criteria Treatment and Recharge Site Requirements Project Categorya   I II III IV Required treatment   Secondary Xb X X X Filtration X X   X Disinfection X X X X Organics removal X     X Maximum allowable reclaimed water in extracted well water (%) 50 20 20 20 Depth to ground water at initial percolation rate of <0.5 cm/min (<0.2 in/min) <0.8 cm/min (<0.3 in/min) 3 m (10 ft) 6 m (20 ft) 3 m (10 ft) 6 m (20 ft) 6 m (20 ft) 15 m (50 ft) n.a.c n.a.c Minimum retention time underground (months) 6 6 12 12 Horizontal separationd 150 m (500 ft) 150 m (500 ft) 300 m (1000 ft) 600 m (2000 ft) a Categories I, II, and III are for surface spreading projects with different levels of treatment. Category IV is for injection projects. b X means that the treatment process is required. c Not applicable. d From edge of recharge operation to the nearest potable water supply well. SOURCE: Adapted from State of California, 1993. ment provided. The proposed dilution requirement must be met at all extraction wells. To ensure removal of pathogens and trace organic constituents in surface spreading operations, the criteria include standards regarding percolation rates and depth to ground water. These standards are intended to provide unsaturated vadose zones that will allow the development of aerobic biological processes that retain or degrade organic chemicals and remove microorganisms from the water. The proposed minimum vadose zone depth varies from 3 m (10 ft) to 15 m (50 ft) depending on site-specific conditions and treatment. Studies have shown that a soil's initial percolation capacity must be less than 0.8 cm/min (0.3 in/min) if it

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--> is to provide these benefits (State of California, 1979). If a soil's initial percolation capacity is less than 0.5 cm/min (0.2 in/min), the criteria provide an additional "credit" for soil column treatment that reduces the required vadose zone percolation distance. Maximum percolation capacities are to be determined from initial percolation test results conducted before the recharge operation starts and not from equilibrium infiltration rates (Hultquist, 1995). The proposed criteria for minimum underground retention time are designed to ensure further die-off or removal of enteric viruses. The retention times are typical of those in current projects judged by state regulators to be safe (Hultquist, 1995). The criteria call for the actual retention time underground to be determined annually at the first (in time) domestic water supply well to receive reclaimed water. The California Department of Health Services does not quantify the expected level of virus reduction underground. Rather, the retention time requirement simply provides an extra barrier to virus survival. California has not developed criteria for indirect potable reuse via surface water augmentation, although a framework has been proposed (California Potable Reuse Committee, 1996). Augmentation of surface drinking water sources with reclaimed water in California requires two state permits-a waste discharge or reclamation permit from a California Regional Water Quality Control Board and an amended water supply permit from the Department of Health Services. Florida Water Reuse Requirements Until the late 1970s, the primary force driving implementation of reuse projects in Florida was effluent disposal. The state's first reuse-related regulations addressed the land application of municipal wastewater (Florida Department of Environmental Regulation, 1983). In the late 1970s, however, demand for water supplies increased, treated wastewater began to be viewed as a drinking water resource, and the state embarked on a program to encourage water reuse and develop regulations that would provide appropriate public health and environmental protection. In 1989, Florida added a chapter entitled "Reuse of Reclaimed Water and Land Application" to its administrative code; these regulations have since been revised (Florida Department of Environmental Protection, 1996). Surface water augmentation is covered by Chapter 62-610 of the Florida Administrative Code (F.A.C.), entitled "Reclaimed Water and Land Application," and Chapter 62-600 F.A.C., entitled "Domestic Wastewater Facilities.'' Florida now requires the state's water management districts to identify water resource "caution areas" that have critical water supply problems or that are anticipated to have critical problems

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--> within the next 20 years (Florida Department of Environmental Protection, 1995). State legislation requires preparation of water reuse feasibility studies for wastewater treatment facilities located within such caution areas and requires a "reasonable" amount of reclaimed water use unless such reuse is not economically, environmentally, or technically feasible. In addition, if reuse is found to be feasible, disposal by surface water discharge or deep well injection is limited to backups for reuse systems. Table 1-4 summarizes Florida's requirements for reclaimed water used to augment potable water sources. Daily monitoring is required for fecal coliform organisms, carbonaceous biochemical oxygen demand (CBOD), and total suspended solids (TSS). The allowable limits for coliforms, CBOD, and TSS, as well as treatment requirements, vary depending on how the reclaimed water is discharged into the water supply source and the characteristics of the water source. The first types of water reuse shown in Table 1-4, rapid-rate infiltration basin systems and absorption field systems, have less stringent water quality limits and treatment requirements than do the other types of reuse because the water receives some treatment as it percolates through the soil. Any wastewater land application system located over a potential source of drinking water must meet these standards. For absorption fields, a more stringent TSS limitation of 10 mg/liter may be imposed to protect against formation plugging. Loading to these systems is limited to 23 cm/day (9 in/day), and wetting and drying cycles must be used. For systems having higher loading rates or unfavorable geologic conditions that rapidly move reclaimed water into aquifers, the reclaimed water must receive secondary treatment, filtration, and high-level disinfection and must meet primary and secondary drinking water standards. These criteria are similar to those in the California regulations for surface spreading of reclaimed water. The other types of water reuse shown in Table 1-4 involve rapid infiltration of reclaimed water into basins in which soil percolation will not provide appreciable additional treatment, direct injection into ground water, and discharge to class I surface waters used for potable supply. Accordingly, such waters must meet stricter standards regarding detectable fecal coliforms, total suspended solids, and chlorine residuals. The rules acknowledge that higher chlorine residuals and/or longer contact times may be needed to meet the fecal coliform requirement. For augmentation of surface water sources, outfalls for discharge of reclaimed water cannot be located within 150 m (500 ft) of a potable water intake. Water quality and treatment requirements are most stringent for injection into formations of the Floridian and Biscayne aquifers where total dissolved solids (TDS) do not exceed 500 mg/liter. For these situations

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--> TABLE 1-4 Florida Treatment and Quality Criteria for Reclaimed Water Type of Use Water Quality Limits Treatment Required Rapid infiltration basins and absorption fields 200 fecal coliform/100 ml 20 mg/liter TSSa 20 mg/liter CBODb 12 mg/liter NO3 (as N) Secondary plus disinfection Rapid infiltration basins in unfavorable geohydrologic conditions No detectable fecal coliforms/100 mlc 5.0 mg/liter TSS Primary and secondary U.S. drinking water standards Secondary, filtration, and disinfection Injection to ground water No detectable fecal coliforms/100 mla 5.0 mg/liter TSS Primary and secondary U.S. drinking water standards Secondary, filtration, and disinfection Injection to formations of Floridian or Biscayne aquifers having TDS <500 mg/liter No detectable fecal coliforms/100 mla 5.0 mg/liter TSS 5 mg/liter TOC 0.2 mg/liter TOXd Primary and secondary U.S. drinking water standards Secondary, filtration, disinfection, and activated carbon adsorption Discharge to class I surface waters used for potable supply No detectable fecal coliforms/100 mla 5 mg/liter TSS 20 mg/liter CBOD 10 mg/liter NO3 (as N) Primary and secondary U.S. drinking water standards Secondary, filtration, and disinfection a TSS = total suspended solids. b CBOD = carbonaceous BOD. c No detectable fecal coliform organisms per 100 ml in at least 75% of the samples, with no single sample to exceed 25 fecal coliform organisms/100 ml. d TOX = total organic halogen. SOURCE: Florida Department of Environmental Protection, 1993, 1996.

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--> the regulations specify that reclaimed water must meet drinking water standards, be treated with activated carbon adsorption to remove organics, and have average TOC and total organic halogen (TOX) concentrations less than 5.0 mg/liter and 0.2 mg/liter, respectively. The rules also require that such systems undergo two years of full-scale operational testing. The Florida Department of Environmental Protection (DEP) is currently refining the requirements for indirect potable reuse. The DEP is considering allowing streamlined pilot testing requirements for projects involving injection into formations of the Floridian and Biscayne aquifers where the TDS does not exceed 500 mg/liter. In addition, the average and maximum TOC limits may be reduced to 3 mg/liter and 5 mg/liter, respectively. Strict limits on TOC and TOX that are currently applicable only to high-quality (TDS < 500 mg/liter) portions of the Floridian and Biscayne aquifers may be extended to a wider range of injection applications. Arizona Water Reuse Regulations Arizona's water reclamation and reuse regulations specifically prohibit the use of reclaimed water for direct human consumption (State of Arizona, 1991). Ground water recharge projects are regulated by the Arizona Department of Environmental Quality (ADEQ) and the Arizona Department of Water Resources (ADWR). In general, ADEQ regulates ground water quality and ADWR manages ground water supply. These agencies require several different permits for any ground water recharge project. A ground water recharge project must obtain an aquifer protection permit from ADEQ. Additionally, both the owner of the wastewater treatment plant that provides the reclaimed water for ground water recharge and the owner or operator of the ground water recharge project that uses the reclaimed water must obtain permits from the ADWR before any reclaimed water can be recharged (Arizona Department of Water Resources, 1995). A single permit may be issued if the same applicant applies for both permits and the permits are sought for facilities located in a contiguous geographic area. To obtain an aquifer protection permit from ADEQ, the recharge project applicant must demonstrate that the project will not cause or contribute to a violation of an aquifer water quality standard. If aquifer water quality standards are already being violated in the receiving aquifer, the permit applicant must demonstrate that the ground water recharge project will not further degrade aquifer water quality. All aquifers in Arizona currently are classified for drinking water use, and the state has adopted National Primary Drinking Water Maximum Contami-

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--> nant Levels (MCLs) as aquifer water quality standards. These standards apply to all ground water in saturated formations yielding more than 20 liters/day (5 gal/day) of water (which is essentially all ground water in Arizona). Thus, reclaimed water must be treated to meet drinking water standards before it can be injected into an aquifer. A ground water recharge project that uses reclaimed water is also required to obtain an underground storage facility permit from ADWR. To get this permit the applicant must demonstrate that (1) the applicant possesses the technical and financial capability to construct and operate the ground water recharge project; (2) the aquifer contains sufficient capacity for the maximum amount of reclaimed water that could be in storage at any one time; (3) the storage of reclaimed water will not cause unreasonable harm to land or to other water users; (4) the applicant has applied for and received any required floodplain use permit from the county flood control district; and (5) the applicant has applied for and received an aquifer protection permit from ADEQ. If received, the underground storage facility permit will prescribe the design capacity of the ground water recharge project, the maximum annual amount of reclaimed water that may be stored, and monitoring requirements. Before recovering any of the reclaimed water that has been stored underground, the person or entity seeking to recover the water must apply to ADWR for a recovery well permit. If the recovery well permit is for a new well, ADWR must determine that the proposed recovery of the stored water will not unreasonably increase damage to surrounding land or other water users. If the recovery well permit is for an existing well, the applicant must demonstrate that it has a right to use the existing well. A recovery well permit includes provisions that specify the maximum pumping capacity of the recovery well. Conclusions The historical approach to water supply development has been to withdraw water from the best available source. In some parts of the United States, however, high-quality source waters are becoming increasingly scarce, and some municipalities are using or are beginning to consider using reclaimed municipal wastewater to augment their potable water supplies. While the maxim that drinking water should be obtained from the best available source should still be the guiding principle for water supply development, in some instances the best available source of additional water to augment natural sources of supply may be reclaimed water. No enforceable federal regulations currently govern the use of reclaimed water for potable purposes, and only a few states have developed detailed criteria for water reuse. Any water utility considering a

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--> potable water reuse project should carefully consider the public health, water treatment, and quality assurance issues discussed in this report to ensure that its consumers are protected from any potential adverse effects of water reuse. References Arizona Department of Water Resources. 1995. Environmental Quality Act. Arizona Revised Statutes Section 49-241. Phoenix: Arizona Department of Water Resources. Bouwer, H., and R. C. Rice. 1984. Renovation of wastewater at the 23rd Avenue Rapid Infiltration Project. Journal-Water Pollution Control Federation 56(1):76-83. California Potable Reuse Committee. 1996. A proposed framework for regulating the indirect potable reuse of advance treated reclaimed water by surface water augmentation in California. Sacramento: California Department of Water Resources. CH2M Hill. 1993. Tampa Water Resource Recovery Project Pilot Studies. Tampa, Fla.: CH2M Hill. Crook, J., T. Asano, and M. H. Nellor. 1990. Groundwater recharge with reclaimed water in California. Water Environment and Technology 2(8):42-49. Ding, W., Y. Fujita, E. Aeschimann, and M. Reinhard. 1996. Identification of organic residues in tertiary effluents by GC/EI-MS, GS/CI-MS, and GC/TSQ-MS. Fresenius Journal of Analytical Chemistry 354:48-55. Florida Department of Environmental Protection. 1993. Domestic wastewater facilities. Chapter 62-600, Florida Administrative Code. Tallahassee: Florida Department of Environmental Protection. Florida Department of Environmental Protection. 1995. State water policy. Chapter 62-40, Florida Administrative Code. Tallahassee: Florida Department of Environmental Protection. Florida Department of Environmental Protection. 1996. Reuse of Reclaimed Water and Land Application. Chapter 62-610, Florida Administrative Code. Tallahassee: Florida Department of Environmental Protection. Florida Department of Environmental Regulation. 1983. Land Application of Domestic Wastewater. Tallahassee: Florida Department of Environmental Regulation. Harhoff, J., and B. van de Merwe. 1996. Twenty-five years of wastewater reclamation in Windhoek, Namibia. Water Science and Technology 33(10-11):25-35. Henry, J. G., and G. W. Heinke. 1989. Environmental Science Engineering. New York: Prentice Hall. Hultquist, R. H. 1995. Augmentation of ground and surface drinking water sources with reclaimed water in California. Paper presented at AWWA Annual Conference, Workshop on Augmenting Potable Water Supplies with Reclaimed Water. June 18, 1995, Fountain Valley, Calif. Knorr, D. B. 1985. Status of El Paso, Texas recharge project. Pp. 137-152 In Proceedings of Water Reuse Symposium III. Denver, Colo.: American Water Works Association. Lauer, W.C., and S. E. Rogers. 1996. The demonstration of direct potable reuse: Denver's pioneer project. Pp. 269-289 in AWWA/WEF 1996 Water Reuse Conference Proceedings. Denver: American Water Works Association. McCarty, P. L., M. Reinhard, J. Graydon, J. Schreiner, K. Sutherland, T. Everhart, and D. G. Argo. 1980. Wastewater Contaminant Removal for Groundwater Recharge. EPA600/2-80-114. Cincinnati, Oh.: U.S. Environmental Protection Agency. Metcalf and Eddy, Inc. 1991. Wastewater Engineering: Treatment, Disposal, and Reuse. 3rd Ed. New York: McGraw-Hill.

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--> National Research Council. 1982. Quality Criteria for Reuse. Washington, D.C.: National Academy Press. National Research Council. 1984. The Potomac Estuary Experimental Water Treatment Plant. Washington, D.C.: National Academy Press. National Research Council. 1994. Ground Water Recharge Using Waters of Impaired Quality. Washington, D.C.: National Academy Press. Nellor, M. H., R. B. Baird, and J. R. Smyth. 1984. Health Effects Study—Final Report. Whittier, Calif.: County Sanitation Districts of Los Angeles County. Nellor, M. H., R. B. Baird, and J. R. Smyth. 1995. Health effects of indirect potable water reuse. Journal of the American Water Works Association 77(7):88-89. State of Arizona. 1991. Regulations for the Reuse of Wastewater. Arizona Administrative Code, Chapter 9, Article 7. Phoenix: Arizona Department of Environmental Quality. State of California. 1975. A "state-of-the-art" review of health aspects of wastewater reclamation for ground water recharge. Report prepared by the State of California Water Resources Control Board, Department of Water Resources, and Department of Health. Published by the State of California Department of Water Resources, Sacramento, Calif. State of California. 1978. Wastewater Reclamation Criteria. California Administrative Code, Title 22, Division 4, California Department of Health Services, Sanitary Engineering Section, Berkeley, Calif. State of California. 1979. Minimum Guidelines for the Control of Individual Wastewater Treatment and Disposal Systems. California Regional Water Quality Control Board, San Francisco Bay Region, Oakland, Calif. State of California. 1987. Report of the Scientific Advisory Panel on Ground Water Recharge with Reclaimed Water. G. Robeck (ed.). Prepared for the State of California Water Resources Control Board, Department of Water Resources, and Department of Health Services. Published by the State of California Department of Water Resources, Sacramento, Calif. State of California. 1993. Draft Proposed Groundwater Recharge Regulation. Prepared by the State of California Department of Health Services, Division of Drinking Water and Environmental Management, Sacramento, Calif. Swayne, M., G. Boone, D. Bauer, and J. Lee. 1980. Wastewater in Receiving Waters at Water Supply Abstraction Points. EPA-60012-80-044. Washington, D.C.: U.S. Environmental Protection Agency. U.S. Environmental Protection Agency. 1975. National Interim Primary Drinking Water Regulations. Fed. Reg. 40(248), 59566-59587 (Dec. 24, 1975). U.S. Environmental Protection Agency. 1992. Guidelines for Water Reuse. EPA/625/R92/004, U.S. Environmental Protection Agency, Center for Environmental Research Information, Cincinnati, Oh. Water Pollution Control Federation. 1989. Water Reuse: Manual of Practice, 2nd ed. Alexandria, Va.: Water Environmental Federation.