4
Public Health Issues

A major consideration in the use of impaired quality water for artificial recharge is the possible presence of chemical and microbiological agents in the source water that may be hazardous to human health. Such concerns apply primarily to potable use, although human exposure may occur from nonpotable uses such as agricultural irrigation. In general, however, the potential for exposure to possible hazards is less for nonpotable reuse, and consequently the risks are significantly lower. Thus this chapter focuses primarily on health issues related to potable reuse.

The traditional maxim for selecting drinking water supplies has been to use the highest quality source available. This principle has guided the selection of potable water supplies for at least 150 years. Thus, although indirect potable reuse occurs throughout the nation and world wherever treated wastewater is discharged into a water course or underground and withdrawn downstream or downgradient for potable purposes, such sources are in general less desirable than using a higher quality drinking water source. The central question for artificial recharge then is: Can ground water recharged with source waters of impaired quality satisfy this maxim? If so, can users be assured that such waters do not threaten human health? How much and what kind of treatment is required prior to recharge? Was treatment planned considering (1) regulatory requirements which may prohibit ground water contamination, (2) the extent to which improvement in quality can occur in the soil and aquifer because of chemical and microbiological transformations, (3) whether the extracted water can meet drinking water standards as set by EPA, and (4) whether the extracted water will be



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Ground Water Recharge Using Waters of Impaired Quality 4 Public Health Issues A major consideration in the use of impaired quality water for artificial recharge is the possible presence of chemical and microbiological agents in the source water that may be hazardous to human health. Such concerns apply primarily to potable use, although human exposure may occur from nonpotable uses such as agricultural irrigation. In general, however, the potential for exposure to possible hazards is less for nonpotable reuse, and consequently the risks are significantly lower. Thus this chapter focuses primarily on health issues related to potable reuse. The traditional maxim for selecting drinking water supplies has been to use the highest quality source available. This principle has guided the selection of potable water supplies for at least 150 years. Thus, although indirect potable reuse occurs throughout the nation and world wherever treated wastewater is discharged into a water course or underground and withdrawn downstream or downgradient for potable purposes, such sources are in general less desirable than using a higher quality drinking water source. The central question for artificial recharge then is: Can ground water recharged with source waters of impaired quality satisfy this maxim? If so, can users be assured that such waters do not threaten human health? How much and what kind of treatment is required prior to recharge? Was treatment planned considering (1) regulatory requirements which may prohibit ground water contamination, (2) the extent to which improvement in quality can occur in the soil and aquifer because of chemical and microbiological transformations, (3) whether the extracted water can meet drinking water standards as set by EPA, and (4) whether the extracted water will be

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Ground Water Recharge Using Waters of Impaired Quality used for potable purposes or other purposes that might result in human exposure? Public health concern over the use of recovered water from ground water recharged with source waters of impaired quality centers on the difficulty in identifying and estimating human exposures to the potentially toxic chemicals and microorganisms that may be present. To some extent the assessment of possible health risks can rely on the vast body of knowledge that has been developed for water supplies using conventional source waters, such as ground water from relatively uncontaminated aquifers and surface waters. However, there is a substantial amount of uncertainty even for such waters, principally related to the presence of synthetic organic chemicals, inorganic chemicals disinfection by-products, and pathogenic organisms. Studies have been made of the chemical and microbiological characteristics of recovered water, although they are limited in number and scope. Several studies have shown that the recovered water can meet drinking water standards, even when the recharge source is treated municipal wastewater. Such findings lead some experts to the conclusion that these extracted waters are as acceptable as water supplied from traditional sources. Other experts strongly disagree, saying that water originating from an impaired source is inherently more risky. For instance, disinfection of the recharge waters may develop a different mix of disinfection by-products (DBPs), often unidentified, from those found in conventional water supplies. Also, the characterizations of the organic material and the full range of microbiological constituents are incomplete. In addition, source waters of impaired quality and recharge water withdrawn from the aquifer at the point of use may contain some contaminants at higher concentrations than are likely to be present in conventional water supplies. And throughout the whole process there is increased reliance on technology and management, leaving open the door for errors. Thus, the question arises whether drinking water standards developed for conventional water supply systems are sufficiently protective of human health when ground water is recharged with waters of impaired quality. The assessment of health risks associated with recharge using impaired sources is far from definitive because there are limited chemical and toxicological data and inherent limitations in the available toxicological and epidemiological methods. The limited data and extrapolation methodologies used in toxicological assessments provide a source of limitations and uncertainties in the overall risk characterization. Similarly, epidemiological studies suffer from the need for very long time periods required, because cancers have latency periods of 15 years or more. Also, such studies require large populations to uncover the generally low risks associated with low concentrations of toxicants. Past studies of the possible adverse health effects from reclaimed water have tended to be limited in terms of toxicological characterization and have focused on those chemicals for which drinking water standards exist. The challenge in considering the health risks from recharge systems is to

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Ground Water Recharge Using Waters of Impaired Quality assess and understand these relative risks and develop strategies for the use and operation of recharge systems to minimize them. A primary goal is the need to minimize the concentrations of possible DBPs and the potential exposures to pathogenic microorganisms. This goal takes on added dimensions, however, in recharged ground water systems because many of the organic precursors of the DBPs are different generally from those in conventional water supply systems. In addition, the behavior and fate of the microorganisms, as well as the DBPs (and, indeed, other chemical toxicants) in the ground water recharge system affect their concentrations at the point of extraction. Developing an understanding of the chemical and microbiological composition and changes in these complex recharge systems will allow the optimal use of this water augmentation strategy. RISK ASSESSMENT METHODOLOGY, APPROACHES, AND INTERPRETATION Human health risk assessment is a process used to evaluate the nature and magnitude of potential health risks associated with exposure to environmental agents, including chemicals and microorganisms. The product of the evaluation is a statement regarding the probability that populations so exposed will be harmed, and to what degree—whether expressed in quantitative or qualitative ways (NRC, 1994). Such assessments generally contain four steps (NRC, 1983): hazard identification, dose-response assessment, exposure assessment, and risk characterization. This methodology has been used extensively to characterize the risks associated with environmental and occupational hazards and can be used along with epidemiological information to provide a perspective on the possible risks related to exposures from the use of ground water recharged with waters of impaired quality. For recovered water, hazard identification entails identification of the contaminants that are suspected to pose health hazards and a description of the specific forms of toxicity (neurotoxicity, carcinogenicity, and so on) that can be caused by the contaminants of concern. Information for this step is typically derived from epidemiological and animal studies and other types of experimental work. Carcinogenic properties and noncarcinogenic effects are considered. Dose-response assessment entails a further evaluation of the conditions under which the toxic properties of a chemical might be manifested in exposed people, with particular emphasis on the quantitative relation between the dose and the toxic response. The development of this relationship may involve the use of mathematical models. A dose-response assessment identifies any toxicological endpoints associated with specified exposure levels or provides an estimate of the relationship between the increased likelihood and/or severity of adverse effects and the extent of exposure to a chemical. (A discussion of the issues pertinent to a microbial risk assessment can be found later in this chapter.)

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Ground Water Recharge Using Waters of Impaired Quality Exposure assessment involves specifying the population that might be exposed to the agent of concern, identifying the routes through which exposure can occur, and estimating the magnitude, duration, and timing of the doses that people might receive as a result of their exposure. Risk characterization involves integration of information from the first three steps to develop a qualitative or quantitative estimate of the likelihood that any of the hazards associated with the agent of concern will be realized in exposed people. This is the step in which risk assessment results are expressed. Risk characterization should also include a full discussion of the uncertainties associated with the estimates of risk. Not every risk assessment encompasses all four steps. Sometimes only a hazard identification will be conducted to evaluate the potential of a substance to cause human health effects. Regulators sometimes take the additional step of ranking the potency of chemicals—what is known as hazard ranking. Sometimes potency information is combined with exposure data to produce a risk ranking. These techniques all use some, but not all, of the four steps of the quantitative risk assessment process (NRC, 1994). For the purpose of assessing chemical constituents in recovered water, no original toxicity evaluation is done. Instead, reference toxicity values such as reference doses (for noncarcinogens) and potency factors (for carcinogens) are used. The reference dose for a noncarcinogenic end point is based on the assumption that a threshold exists for that specific toxic effect. It is an estimated dose for a daily exposure that is likely to be without an appreciable risk of deleterious effects during a lifetime. For carcinogens, cancer potency (or slope) factors are usually estimated using a linear nonthreshold mathematical extrapolation model for low-dose extrapolation. The potency factor is characterized as an upper-bound estimate or the 95th percentile confidence limit (95% UCL) of the probability of response per unit intake of chemical over a lifetime. The upper-bound estimate means that the actual risk is likely to be less than the predicted risk. The potential doses to the exposed population are calculated on the basis of known or estimated parameters. For recovered water to be used for potable purposes, the exposure is assumed to be the dose contained in 2 liters (1) of water that is consumed by an adult on a daily basis for a lifetime. However, it is recognized that there may be additional routes of exposure, such as skin absorption and inhalation of volatile chemicals from water used indoors. The potential health risks associated with the source water are characterized according to the nature and magnitude of the risk. For carcinogens, the risk is expressed as the probability of cancer occurrence. The negligible risk level generally recognized by regulatory agencies such as the Environmental Protection Agency (EPA) is 1 in 1 million (1 × 10-6). This means that there is the probability that one person in a population of 1 million will get cancer at the estimated exposure level. This also means that, for example, at the present

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Ground Water Recharge Using Waters of Impaired Quality background rate of 25 percent cancer occurrence in the U.S. population, exposure to the chemical will increase the risk of getting cancer from 250,000 in 1 million to 250,001 in 1 million. For noncarcinogens, if the exposure (or dose) is less than the reference dose, then it is not likely to be associated with health risk. As an indirect means to characterize exposure, one may compare the concentration of a chemical found in the source water to the drinking water standard established for that chemical. The comparison will be valid if the standard is derived from a reference dose and the exposure to an adult is equivalent to a dose resulting from consuming 2 liters of the water per day. Another approach is to use the hazard index for assessing the overall potential for noncarcinogenic effects posed by chemicals in the source water. The underlying assumption is that multiple subthreshold exposures could result in an adverse effect and that the magnitude of the effect will be proportional to the sum of the ratios of the subthreshold exposures to acceptable exposures. If the sum of the ratios (or hazard indices) exceeds one, the exposures may result in a potential health effect. Drinking water standards and health advisories (HAs) are published by the Office of Water of the Environmental Protection Agency (U.S. Environmental Protection Agency, 1993b). The drinking water standards include maximum contaminant level goals (MCLGs) and maximum contaminant levels (MCLs). The MCLGs (which are non-enforceable) are set at a concentration of zero for carcinogens as a matter of EPA policy. However, none of the MCLs (which are enforceable) are zero because they are based on a number of factors, including acceptable risk, detection limits, feasibility, and economic factors. The Health Advisory Program was started by EPA in 1978 to provide information and guidance to individuals and agencies concerned with potential risk from drinking water contaminants for which no national regulations currently exist. HAs are prepared for contaminants that meet two criteria: (1) the contaminant has the potential to cause adverse health effects in exposed humans, and (2) the contaminant is either known to occur or might reasonably be expected to occur in drinking water supplies. Guidance for the firt 20 contaminants was issued in 1979, and by 1994 the list contained 189 chemicals and 6 radionuclides. In assessing the potential impacts of long-term human exposure to recharged ground water, the degree to which any recovered water (after treatment) used as a public water supply meets these (enforceable) MCLs would have to be determined. However, in considering the suitability of a recharge system when the aquifer is to be used as a potable supply, the HAs should be considered as well, especially when there is no comparable MCL for a particular chemical. STUDIES OF HEALTH IMPACTS The public health implications of direct and indirect potable use of recov-

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Ground Water Recharge Using Waters of Impaired Quality ered water have been studied at a number of sites. These include studies of direct potable reuse in Windhoek, Namibia (the only city in the world with a direct potable reuse facility) and Denver, Colorado (where direct reuse was studied extensively but not adopted); studies of indirect potable reuse via surface sources at San Diego, California, and Tampa, Florida; and studies of indirect reuse via injection in Los Angeles. These studies review varying combinations of chemical characterization of source water, toxicological testing of source water, and epidemiological studies of populations using the recovered water. Most focus on chemical constituents, so limited information is available on impacts from microorganisms. The major activities that have been conducted to evaluate the health-related aspects of using recovered recharge water were conducted during the period 1975 to 1987 in California, where there is significant potential for reuse. In 1975, the State of California established a Consulting Panel on Health Aspects of Waste Water Reclamation for Groundwater Recharge to recommend a program of research that would assist in the establishment of criteria for ground water recharge to augment public water supplies and help develop programs of reclamation consistent with these criteria. In its report (State of California, 1987), the panel confined its discussions to ground water recharge by surface spreading and concluded that uncertainties exist regarding health effects from the use of reclaimed water primarily due to stable organic materials. To address the uncertainties, the panel recommended that comprehensive studies on health effects of ground water recharge be initiated at existing projects and new demonstration projects. Research was recommended for contaminant characterization, toxicology, and epidemiological studies of exposed populations. OLAC Water Reuse Study-Montebello Forebay, Los Angeles County, California In 1978, six water supply and wastewater agencies in Orange and Los Angeles counties organized the OLAC Water Reuse Study. One of the activities of the study was the initiation of a 5-year epidemiological Health Effects Study, guided by the consulting panel's recommendations, which was published (Nellor et al., 1984). The Health Effects Study was conducted at the Whittier Narrows Ground Water Replenishment Project, located in the Montebello Forebay area of Los Angeles County, where disinfected filtered secondary effluent, stormwater runoff, and imported river water have been used for replenishment since 1962. The study was designed to develop a database that would enable health and regulatory authorities to determine whether the use of reclaimed water for ground water replenishment at the project should be maintained or modified. The research included toxicological studies of ground water, reclaimed water, and other

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Ground Water Recharge Using Waters of Impaired Quality replenishment water supplies to isolate and identify health significant organic constituents, and epidemiological studies of populations ingesting recovered water to determine if their health characteristics differed significantly from those of a demographically similar control population (i.e., a geographical comparison study). The results of the studies did not demonstrate any measurable adverse impacts on the area's ground water or the health of the population ingesting this water. Specifically, a 1981 household health survey of women residing in the Montebello Forebay study area showed no elevated levels of specific illnesses or other differences in general health. The study was controlled for the potential confounding effects of factors such as smoking, alcohol consumption, bottled water usage, and length of residence. In addition, based on an evaluation of health and vital statistics data for the period from 1969 to 1980, it was reported that residents of the area that received recovered water experienced no increased rates of infectious diseases, congenital malformations, infant and neonatal mortality, low birth weight, cancer incidence, or death due to heart disease, stroke, stomach cancer, rectal cancer, bladder cancer, colon cancer, or all cancers combined, when compared with residents of two control areas that did not receive recovered water. Concentrated organic residues derived from all replenishment sources and ground waters elicited mutagenic responses in the Ames Salmonella Microsome Mutagen Assey that were related to the presence of a mixture of toxic organic compounds. Chemical and biological assays indicated that low levels of compounds belonging to the two classes of organic halides and epoxides may have contributed to the mutagenicity. The mutagenicity of whole-sample residues was not accounted for. The overall analysis identified approximately 10 percent of the total organic carbon, and the data were not adequate to judge whether or not the majority of compounds present and of greatest health concern were identified. A mammalian cell transformation assay was also used; however, the assay was complicated by problems with fungal contamination and limited number of samples. The mutagenic response of the recovered water samples fell between the surface runoff and imported river water assay values. The limited number of samples from each site and the complexity of the percolation process and aquifer systems precluded a more rigorous statistical analysis of the correlations between the mutagenic response data and the sample sites. The merits and limitations of the report on the Health Effects Study were analyzed by the Scientific Advisory Panel for Groundwater Recharge and used to prepare the Panel's guidelines (State of California, 1987). Overall, state-of-the-art procedures were used for characterization of the water samples. For inorganics, the water quality data for ground water and recovered source samples were summarized and compared with the existing drinking water standards. Traditional chemical evaluations were performed on water samples in each of four study sites. In general, all sampling well sites showed values within primary

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Ground Water Recharge Using Waters of Impaired Quality drinking water standards; 3 of the 10 Montebello Forebay wells had samples exceeding secondary standards for iron and manganese. For organic chemicals, the data suggested that a group of nontargeted organics (phthalates, solvents, petroleum by-products) may be more useful markers of future impacts of recovered water than the targeted organics because of their greater concentration in recovered water. Data also suggested that industrial solvents could be used to monitor future impacts of replenishment with reclaimed water. Certain compound groups (phthalates, chlorinated phenols, s-triazine herbicides, phenylacetic acid) may be useful indicators of impacts from replenishment by waters other than reclaimed water. Overall, the data established that ground water in the study sites is currently contaminated with a variety of organic compounds of industrial, and perhaps treatment, origin. The panel raised the issue of whether Ames mutagenicity assay data are adequate in the absence of other toxicological information to serve as a basis for risk assessment. There was some consensus that the conventional rodent studies would be needed but no clear consensus as to how such studies could or should be carried out with water samples or water sample residues. Overall, this committee, the National Research Council's Committee on Ground Water Recharge, supports the panel's view that the demographic comparison studies are useful in demonstrating the feasibility of this hypothesis and enabling a rapid assessment of potential threats to public health by using available morbidity, mortality and census information originally collected for other purposes. There is, however, a deficiency because exposure and outcome data describe characteristics of groups, and not individuals. Information is not available on potential confounding factors. The sensitivity of the studies on cancer and chronic disease rates to detect effects of recovered water is severely weakened by the short time period between first exposure to recovered water and the time of the study, especially when compared with the long latency period typically involved (15 years and more) between first exposure and cancer diagnosis and the high in-migration rates in the study area. As for the toxicological data, the present review finds that the Ames data constitute only a very small part of the full toxicological characterization that is needed and, therefore, are not adequate to support a risk assessment of the source water. Total Resource Recovery Project, City of San Diego, California The City of San Diego, which imports its water supply from other parts of the state, is projecting a need for additional water for the next decade (Western Consortium for Public Health, 1992). The city is investigating advanced treatment technologies for use of potential new sources—among which is the local municipal wastewater. A 5-year Health Effects Study was conducted for the City of San Diego to investigate whether a proposed wastewater treatment scheme can reliably reduce contaminants of concern to levels such that the health

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Ground Water Recharge Using Waters of Impaired Quality risks to the population are not-greater than those associated with the present water supply (Western Consortium for Public Health, 1992). In this study, the risks associated with using the Miramar raw water supply and with the effluent generated from the advanced wastewater treatment (AWT) plant were compared. When compared with other raw water supplies sampled throughout the United States, concentrations of metals and of the majority of organic constituents detected in AWT and Miramar waters were either in the lower portion of or below the range of averages. The same findings were reported for the local raw wastewater except that values for butylbenzyl phthalate, di-n-octyl phthalate, and bis(2-ethylhexyl) phthalate exceeded the U.S. range. Testing of organic extracts of water in the Ames assay, micronucleus test, 6-thioquanine resistance assay, and cell transformation assay indicated that the AWT water appeared to show less genotoxic or mutagenic activity than the low levels observed in the Miramar water. An epidemiological study was conducted, which included analysis of the vital statistics of San Diego County women interviewed from 1987 to 1989, and a neural tube defect survey using data from 1978 to 1985 to establish prevalence rates in California and San Diego. No significant difference for the two areas was found when the annual prevalence-at-birth rates for selected defects (anencephalus and spina bifida combined) were estimated. The study also included characterization of the reproductive health of the women but the results were not reported. A risk assessment was performed for all compounds whose reference doses (RfD) and/or unit risk values were available in the EPA's Integrated Risk Information System database. These include arsenic, barium, boron, manganese, bromodichloromethane, bromoform, benzoic acid, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, chloroform, dibromochloromethane, toluene, and trichlorofluoromethane. For carcinogens, the overall mean estimate of lifetime risk from consuming Miramar water at 21/day is about 3 in 10,000. Dermal and inhalation absorption resulted in a risk of 1.6 in 10,000. About 98 to 99 percent of this risk is derived from arsenic, and the remaining percentage from trihalomethanes (THMs), which contributed a risk of less than 1 in 100,000. The concentrations of arsenic and THMs in Miramar water are approximately 2 and 10 percent of the drinking water standards, respectively. The mean cancer risk estimate for Miramar water would be 0.9 in 10,000 when the uncertainty is removed by treating the cancer potency value as a point estimate. The cancer risk estimates for the AWT water were 4.8 × 10-7 for dermal, inhalation, and drinking exposures and 8.2 × 10-7 for drinking only. For noncarcinogens, the hazard index method was used. The chemicals included bis(2-ethylhexyl) phthalate, boron, manganese, and toluene in AWT water and barium, benzyl butyl phthalate, benzoic acid, bromoform, bromodichoromethane, chloroform, dibromochloromethane, manganese, toluene, and trichlorofluoromethane in Miramar water. The hazard indices were 0.077

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Ground Water Recharge Using Waters of Impaired Quality for AWT and 0.051 for Miramar water. Therefore these chemicals are not anticipated to present a significant health risk. Tampa Water Resource Recovery Pilot Project, Tampa, Florida In another study, Florida and the West Coast Regional Water Supply Authority (WCRWSA) investigated the potential indirect reuse of treated AWT effluent generated at the City of Tampa Hookers Point Facility. Toxicological testing was performed on product water produced from a pilot plant (treated municipal wastewater plus filtration) and reference water (treated municipal wastewater). The studies included the following: Ames test, sister chromatid exchange and micronuclei analysis for genotoxicity, 90-day subchronic garage studies in mice and rats, induction of Strain A lung adenoma, reproductive study in mice and teratological study in rats, and mouse (sencar) skin initiation-promotion study (J. Doull and J. Borzelleca, personal communication, 1992; Pickard et al., undated). The results of these studies were negative. Analytical chemistry results showed that the quality of the pilot plant effluent is as good or better than other sources of raw water such as the reference River water. The pilot plant effluent meets current and proposed EPA drinking water standards and the World Health Organization's guidelines for drinking water quality. Potable Water Reuse Demonstration Project, Denver, Colorado The Comprehensive Health Effects Testing Program for the Denver Water Department's Potable Water Reuse Demonstration Project was designed to evaluate the relative health effects of two water types: one was highly treated (including lime precipitation, activated carbon filtration, reverse osmosis, and various filtration and disinfection steps) recovered water derived from secondary treated wastewater and the other was Denver's drinking water (Lauer et al., 1990). The protocol provided for comparative testing of concentrates from Denver's drinking water (from the Foothills Water Treatment Plant), reuse demonstration plant effluent, and reuse demonstration plant effluent treated with ultrafiltration instead of reverse osmosis. In a 104-week chronic toxicity and carcinogenicity study in Fischer 344 rats and B6C3F1 mice, samples were given at 150 or 500 times the original concentration in drinking water ad libitum. No treatment-related lesions or neoplasms were observed in the animals. In a reproductive/teratology study, rats were administered the test material. No treatment-related effects on reproductive performance, growth, mating capacity, survival of offspring, or fetal development in the animals were found.

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Ground Water Recharge Using Waters of Impaired Quality Analysis of existing data base Summary information pertinent to the key health effects studies is displayed in Table 4.1. In each of these studies, efforts were made to ascertain any undesirable toxicological effects of recharging ground water with waters of impaired quality. All of the studies employed state-of-the-art methodologies to measure toxicological effects and to determine the identities of inorganic and organic chemical components. In some studies, additional experimentation was directed at measuring whole-sample mutagenicity and/or the mutagenicity of the fraction of the organic content that was not identifiable. Overall, no significant toxicological properties were found, although methodological limitations in all cases prevent interpretation of this result as indicating that no health effects are associated with human consumption of recovered water from impaired-quality sources. As is the case with any ''not detectable" result in analytical chemistry, when "no observed effect" is found in toxicological and epidemiological studies, that term must be defined. The question is, what is the most sensitive health effect that could have been detected by the methodology employed? Unfortunately, this is a more difficult question for the methods of toxicology and epidemiology than for the methods of analytical chemistry. For example, the Ames Salmonella Microsome Mutagen Assay, in the absence of other toxicological data, is not an adequate basis for the estimation of risk. Conventional animal studies, conducted for a measurable health outcome, would be preferable to complete the spectrum of toxicological testing. Single-chemical and simple in vitro toxicological evaluations are not likely to be responsive to the question of whether the aggregate organic substances in the recovered water would cause any meaningful risk to populations receiving them. For these reasons, broader evaluation strategies are necessary to estimate health risk. Confidence is gained in the analytical chemistry if one or more target organic molecules of unquestionable health risk are spiked into the sample as external standards, and compounds subject to compliance are specifically examined. Using additional in vitro tests (micronucleus test, 6-thioquanine resistance assay, cell transformation assay) may not be as helpful. Comparing the recharge water with existing or currently acceptable water in terms of genotoxicity evaluation can be helpful. In the San Diego study, for example, AWT effluent showed lower genotoxic or mutagenic activity in the above in vitro tests than the raw water supply. Geographical comparisons can be effective in demonstrating the feasibility of the hypothesis and enabling a rapid assessment of potential threats to public health by using available morbidity, mortality, and census information. The deficiency in these techniques is that exposure and outcome data describe characteristics of groups, not of individuals. A causal relationship is difficult to establish using this method. To date, the application of state-of-the-art methodology for chemical and limited toxicological analysis has failed to show that professionally managed

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Ground Water Recharge Using Waters of Impaired Quality TABLE 4.13 Risk of Contracting at Least One Infection from Exposure to Viruses in Ground Water Recharged with Chlorinated Tertiary Reclaimed Wastewater   Maximum Concentration Viruses 111 plaque-forming units 100 1-1 1 plaque-forming units 100-1 Lifetime Risk     Echovirus 12 4.13E-6 3.72E-8 Poliovirus 1 3.78E-7 3.40E-9 Poliovirus 3 1.59E-6 1.43E-8 Annual Risk     Echovirus 12 5.90E-8 5.31E-10 Poliovirus 1 5.40E-9 4.86E-11 Poliovirus 3 2.27E-8 2.04E-10 Daily Risk     Echovirus 12 1.62E-10 1.46E-12 Poliovirus 1 1.48E-11 1.33E-13 Poliovirus 3 6.21E-11 5.60E-13   Source: Asano et al., 1992. exposure to ground water recharged with reclaimed water are shown in Table 4.14. Calculated infection risks for effluent treated beyond unchlorinated secondary ranged from 8 per 100 million to 5.8 per 100 billion. RISKS FROM DISINFECTANTS AND DISINFECTION BY-PRODUCTS VERSUS RISKS FROM PATHOGENS From a public health perspective, a central issue associated with the artificial recharge of ground water is how to balance the risks associated with pathogenic microorganisms against those from disinfection by-products (DBPs). To develop an optimal strategy for the protection of public health, the relative risks associated with various concentrations of pathogenic microorganisms and DBPs must be weighed in light of the benefits brought by use of an effective disinfectant. The carcinogenic risk from the DBPs should be compared to the risk of infection from pathogens. Such a comparison grossly oversimplifies the risk-benefit ratio, however, and should serve simply as a crude comparison to obtain more information for consideration rather than an accurate quantitative assessment. The carcinogenic risks from disinfectants and DBPs have been estimated by Bull and Kopfler (1991). Bromodichloromethane presents the highest risks based on adenocarcinomas of the large intestine. The risks estimated from the chlori-

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Ground Water Recharge Using Waters of Impaired Quality TABLE 4.14 Predicted Annual Virus Infection Risk from Exposure to Ground Water Recharged with Reclaimed Water (Monte Carlo Simulation, n=500)   Treatment System Tertiary Treatment OCSD TF OCSD AS Pomona AS MRWPCA AS Full (5.2 long inactivation/removal) 8.32E-10 5.81E-11 1.69E-10 3.25E-9 Direct chlorination of secondary effluent (3.9 log inactivation/removal) 2.09E-08 1.46E-09 4.25E-09 8.17E-08 Unchlorinated secondary effluent (0 log inactivation/removal) 1.32E-4 1 .32E-6 2.68E-5 5.1 5E-4   Source: Tanaka et al., 1993. nated acetic acid are even higher when mouse liver tumors are considered. The chemicals have not been tested in a second species. As a crude comparison, Bull et al., (1990) indicated that the probability of mortality induced by improperly disinfected drinking water would exceed the carcinogenic risks introduced by chlorine by as much as 1,000-fold. If disinfection were removed from a contaminated water system that depends on such disinfection, everyone in the community would contract one or more waterborne diseases during their lifetime. Theoretically, the number of deaths from such diseases would equal the mortality rate for the same diseases. The mortality rates for various enteric bacteria and enteroviruses range from 0.12 to 0.94 percent. The carcinogenic risks from chloroform at the mean concentration found (26.4 µg/l) has been estimated to range from 0.24 to 3.0 × 10-6 based on the use of MLE or UCL 95 percent and different tumor sites (Bull and Kopfler, 1991). The risk estimates for other chemicals considered individually range from 0.00034 to 140 × 10-6. For pathogens, the estimated lifetime risk of mortality from exposure to echovirus 6 at 1 vital infections unit per 1,000 liters of water is greater than 10-5. At one infectious unit of hepatitis in 1,000 liters, the estimated annual risk of mortality is greater than 10-4. The actual risk varies depending on the presence of the number of pathogens. In domestic sewage and polluted surface water (streams) in the United States, the concentrations of enteric organisms (enteric virus, Cryptosporidium, Giardia) have ranged from 0.1 to 10 per 100 ml (Bull et al., 1990). Coliforms were estimated at 10-5 and 10-9 per 100

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Ground Water Recharge Using Waters of Impaired Quality ml. If the estimated concentration range for enteric virus is extrapolated to echovirus 6 and the lowest concentration is assumed (1 per 100 ml in polluted stream), then the concentration of echovirus 6 for 1,000 liters of water would be 1,000,000 rather than I infectious unit, and the resulting estimated lifetime risk of mortality would be significantly higher than 10-4. HEALTH IMPLICATIONS FROM NONPOTABLE USES The public health implications of nonpotable reuse, except where intended for market crops to be eaten raw, have not been addressed as extensively as the implications of potable reuse because nonpotable reuse has been practiced widely for decades without public concern and because the exposure from nonpotable reuse, and thus the risk, is more limited. An upcoming study from the National Research Council, ''Use of Treated Municipal Wastewater Effluent and Sludge in Crop Production," will address issues associated with using wastewater and sludge in food crop production in depth; the report is expected to be available in early 1995. In general, however, the health implications of using recovered ground water for nonpotable purposes are more easily addressed than those associated with potable reuse. For most nonpotable uses of water, pathogenic microorganisms represent the major health concern. However, chemical constituents may represent a health hazard for some uses, such as crop irrigation and aquaculture, where inorganic or organic constituents of health significance may accumulate in crops or fish. Recommended water quality criteria and parameters have been developed for several nonpotable water applications, such as irrigation water and industrial cooling and process water (U.S. Environmental Protection Agency, 1973, 1992; Ayers and Westcott, 1985). In addition, many states have developed comprehensive water reclamation and reuse criteria for nonpotable uses of treated municipal wastewater (State of California, 1978; Florida Department of Environmental Regulations, 1990; State of Texas, 1990; Pawlowski, 1992; State of Washington, 1993); hence, state water reuse criteria, which are principally directed at public health protection from pathogenic microorganisms, often are applicable to extracted ground water containing previously recharged wastewater. EPA's Guidelines for Water Reuse (U.S. Environmental Protection Agency, 1992) contain recommended wastewater treatment processes and water quality limits for a wide variety of nonpotable types of reuse. Pathogens are a concern where there is human exposure to the water (by contact, inhalation, or ingestion) or to food or other objects that have come in contact with the water. The types and concentrations of pathogens that may be present in source water used for recharge are presented in Chapter 2. Protection of public health is achieved by (1) reducing the concentrations of pathogenic bacteria, parasites, and enteric viruses in the source water prior to recharge; (2) disinfecting the water upon extraction, if necessary; or (3) limiting public or

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Ground Water Recharge Using Waters of Impaired Quality worker exposure to the water or fomites (objects that might be contaminated with infectious agents). While many bacteria and most, if not all, larger organisms generally are effectively removed after percolation through a short distance of the soil mantle at percolation sites, viruses have been isolated by several investigators examining a variety of recharge operations (Gerba and Goyal, 1985). Under favorable conditions, pathogens can survive for long periods on crops or in water or soil. Factors that affect survival include the number and type of organism, soil organic matter content (presence of organic matter aiding survival), temperature (longer survival at low temperatures), humidity (longer survival at high humidity), pH, amount of rainfall, amount of sunlight (solar radiation being detrimental to survival), protection provided by foliage, and competitive microbial fauna and flora. Survival times for any particular microorganism exhibit wide fluctuations under differing conditions (Feachem et al., 1983). It has been reported that viruses and other pathogens in irrigation water do not readily penetrate fruits or vegetables unless the skin is broken (Bryan, 1974). In a study in which soil was inoculated with poliovirus, viruses were detected in the leaves of plants only when the plant roots were damaged or cut (Shuval, 1978). Although adsorption of viruses by plant roots, and subsequent translocation to stems and leaves, has been reported (Murphy and Syverton, 1958), it probably does not occur with sufficient regularity to be a mechanism for the transmission of viruses. Therefore, the likelihood that pathogens would be translocated through trees or vines to the edible part of crops is extremely low. Viruses and many pathogenic bacteria are in the respirable size range; hence, a possible direct means of human infection is by inhalation of aerosols containing pathogenic microorganisms. Infection or disease also may be contracted indirectly by aerosols deposited on surfaces such as food, vegetation, and clothes. The infectious dose of some pathogens is lower for respiratory tract infections than for infections via the gastrointestinal tract; thus, for some pathogens, inhalation may be a more likely route for disease than either contact or ingestion (Hoadley and Goyal, 1976). Although bacteria and viruses in aerosols have been detected several hundred meters downwind from the point of aerosol generation (Sepp, 1971; Teltsch and Katzenelson, 1978; Johnson et al., 1980; Bausum et al., 1983; Camaan et al., 1986; Camaan et al., 1988), there have not been any documented disease outbreaks in the United States resulting from spray irrigation with treated municipal wastewater that has been disinfected (U.S. Environmental Protection Agency, 1980). For intermittent spraying using recovered water, occasional inadvertent contact should pose little microbiological health hazard from inhalation. Aerosols emitted from cooling towers used continuously may present a greater concern if the water is not properly disinfected. Although studies indicate that the health risk associated with aerosols from spray irrigation sites is low, the general prac-

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Ground Water Recharge Using Waters of Impaired Quality tice has been to limit exposure to aerosols produced from waters that are likely to contain pathogenic microorganisms until more sensitive and definitive studies can be conducted to fully evaluate the ability of pathogens contained in aerosols to cause disease. In general, the health hazards associated with the ingestion of inorganic constituents through water or food are well established (U.S. Environmental Protection Agency, 1976), and EPA has set maximum contaminant levels (MCLs) for drinking water. For crop irrigation the elements of greatest concern at elevated levels are cadmium, copper, molybdenum, nickel, and zinc. Nickel and zinc are of a lesser concern than cadmium, copper, and molybdenum because they have visible adverse effects in plants at lower concentrations than the levels harmful to animals and humans. Cadmium, copper, and molybdenum, however, can be harmful to animals at concentrations too low to affect plants. Copper is not toxic to monogastric animals, but may be toxic to ruminants; however, their tolerance to copper increases as available molybdenum increases (U.S. Environmental Protection Agency, 1981). Molybdenum can also be toxic when available in the absence of copper. Cadmium is of particular concern because it can accumulate in the food chain. It does not adversely affect ruminants in the small amounts they ingest. Most milk and beef products are also unaffected by livestock ingestion of cadmium because it is stored in the liver and kidneys of the animal instead of the fat or muscle tissue. Pretreatment of waters of impaired quality prior to surface spreading and the additional treatment provided during percolation through the vadose zone are generally sufficient to reduce the concentrations of inorganic constituents of health concern to levels that are acceptable for nonpotable uses of the recovered water. Similarly, the high levels of treatment usually required for injection water reduce inorganic constituents to low levels. Trace elements in treated municipal wastewater normally occur in concentrations of less than a few milligrams per liter, with usual concentrations less than 100 µg/l (Page and Chang, 1985). Organic constituents may be of concern where recovered water is used for crop irrigation, where the organics may bioaccumulate in the food chain, such as in fish-rearing ponds, or where the water from irrigation or other uses reaches potable supplies, which may result in exposure from direct ingestion or by inhalation or skin contact (Andelman, 1990; Wilkes et al., 1992). Crop uptake of certain pesticides has been studied (U.S. Environmental Protection Agency, 1973; Palazzo, 1976), and uptake of polychlorinated biphenyls by root crops has been demonstrated under field conditions (Iwata and Gunther, 1976). Uptake of organic compounds is affected by the solubility, size, concentration, and polarity of the organic molecules; the organic content, pH, and microbial activity of the soil; and climate. A study on health risks associated with land application of sludge found that not more than 3 percent or less of the pesticides and herbicides present in the soil passed into plant foliage (Pahren et al., 1979). It has been postulated that most trace organic compounds are too

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Ground Water Recharge Using Waters of Impaired Quality large to pass through the semipermeable membrane of plant roots (U.S. Environmental Protection Agency, 1981). SUMMARY To evaluate the health implications of the use of reclaimed water for ground water recharge, information including, but not limited to, the following is needed: types and concentrations of chemicals present in the water (source water, recovered water, water at the point of use); environmental fate, transport, degradation, transformation, and any effect of treatment or processing of the water on the parent compound .and breakdown products; toxicological properties of the chemicals; end use of the water; and characterization of human exposure. There are a number of recharge projects in the United States and other parts of the world which have provided analytical data on the contaminants found in the reclaimed water. The constituents are highly variable, depending on the source of water and specific sites involved. Some of the findings show levels exceeding the U.S. drinking water standards. A more limited number of projects have provided health effects data associated with use of recovered water. The majority of the limited health effects data do not suggest a health concern. Overall continued chemical monitoring and characterization and more toxicological evaluations are needed, however. Exposure data are lacking, and the magnitude of human exposure should be better defined. Many of the specific conclusions and recommendations made by the Scientific Advisory Panel on Ground Water Recharge (State of California, 1987) regarding toxicological evaluations and epidemiologic studies remain valid. When only mutagenicity data (obtained from the Ames assay) are available, it is clear that the database is not adequate for the assessment of health risks associated with the water. A spectrum of toxicological studies would be needed to provide the necessary data. The design of the studies would depend on what is known (e.g., point of withdrawal, chemical concentration, known constituents) about the water, the selection and preparation of which for testing would be specific for each project. Epidemiological studies can provide a baseline for future references or may assist in identifying a relationship (spatial, temporal, causal) between use of recovered water and associated health effects. However, if not properly designed and conducted with adequate resources, planning, conduct and follow-up, epidemiological studies can be limited by small sample size, existence of confounding factors, and lack of known exposure and control group. They are often of limited value in identifying a cause-and-effect relationship. Therefore, epidemiological studies are not recommended unless the criteria are met for conducting a comprehensive and valid examination. No quality standards currently exist for chemicals in recovered water intended for potable use. Criteria should be established for the evaluation of the presence of chemicals in such water. Comparison with existing water supply or

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Ground Water Recharge Using Waters of Impaired Quality drinking water standards is one common and convenient approach for evaluating the quality of the recovered water. However, drinking water standards are not based solely on health considerations but also on technical feasibility, detectability, and economic considerations. In addition, there may be other potential sources of exposure to the same chemicals. Therefore, total exposure and methods used to derive health base levels should be considered. Disinfection by-products (DBPs) are of potential concern in ground water recharge systems used for potable water, as they are in water supplies drawn from surface or non-recharged ground water. The nature and toxicity of such DBPs have been most widely studied for chlorine disinfection of potable water supplies. DBPs from the use of other disinfectants, such as ozone and chloramines, are not as well characterized. Also, the possible differences in the nature and quantifies of DBPs from the disinfection of wastewaters that may be used for ground water recharge, such as highly treated sewage and agricultural wastewaters, have for the most part not been studied. In conventional public water supply systems, humic materials are normally the major precursors in the formation of DBPs. In water from unconventional sources, however, there may be a different mix of DBPs, and the nature of the dissolved organic carbon remaining following disinfection may be different from that of humic materials. As with conventional potable water disinfection, a key issue in developing ground water recharge systems is the need to balance the risks in using chemical disinfectants to reduce the number of pathogenic microorganisms with the risks associated with the DBPs formed in the process. A variety of factors influence the pathogen content of wastewater, including season, the economic status of the population producing the wastewater, water use patterns, and the quality of the potable water supply. Almost half of the outbreaks of waterborne disease in the United States in the 1980s were associated with the use of undisinfected or inadequately disinfected ground water, with sewage most often identified as the source of contamination. The causative agents were identified in less than half of all the outbreaks. The Norwalk virus may have been responsible for many of these outbreaks. Assessing the risk of an individual from pathogens in recovered water is a difficult and uncertain task. Bacteria and parasites generally are removed to a greater extent than enteric viruses during infiltration through soils; thus viruses are of greater concern when exposure is to the affected ground water. The number and types of pathogens in recovered water depend on the level of treatment the water has received. Studies of enterovirus removal in water reclamation plants in southern California indicate that, with proper treatment, viruses can be reduced to below detectable levels. However, in general there is little information on the concentrations of several pathogens of public health concern in such studies, including hepatitis A and E viruses, rotavirus, Norwalk virus, Giardia, and Cryptosporidium. Estimates of infection risks from the accidental ingestion of 100 ml of final effluent from advanced municipal wastewater treat-

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Ground Water Recharge Using Waters of Impaired Quality ment effluent ranged from approximately 1 in 10,000 for Cryptosporidium to 2 in 100 million for viruses. Similarly, estimates of annual risks to those exposed to a specific use of ground water recharged with a chlorinated secondary sewage effluent ranged from 8 in 100 million to 1.5 in billion. Currently, the control of such risks below 1 in 10,000 is considered acceptable. On the basis of available information, there is no indication that the health risks from using reclaimed wastewater are greater than those from using existing water supplies or that the concentrations of chemicals, with several exceptions, or microorganisms are higher than those established in drinking water standards set by EPA. One limitation is that not all the chemicals identified have drinking water standards for such a comparison. There are other uncertainties, too, in such an evaluation, including the limited chemical and toxicological characterizations of source and recovered waters, and the uncertain environmental fates of the chemicals and microorganisms in the recharge systems, and the limited epidemiological data. Furthermore, it should be remembered that the EPA standards are based on water sampled from high quality sources. Such standards are often years behind our knowledge and our knowledge at any time is limited. (For example, health effects are determined for each organic compound separately, not for the inevitable mixtures of organics.) Accordingly, monitoring of potentially toxic constituents and pathogenic microorganisms should be required in using water extracted from these recharge systems. Increased reliance on technology also brings increased uncertainty and thus some risk. Given these uncertainties, where recovered recharge water is intended for potable purposes and human exposure is increased, great care is necessary (Asano et al., 1992; NRC, 1983; NRC, 1994). REFERENCES Amy, G. L., J. M. Thompson, M. K. Davis, and S. W. Krasner. 1990. Evaluation of THM preprecursor contributions from agricultural drains. J. Am. Water Works Assoc. 82(1):57-64. Ayers, R. S., and D. W. Westcott. 1985. Water Quality for Agriculture. FAO Irrigation and Drainage Paper 29, Rev. 1. United Nations Food and Agriculture. Rome. Asano, T., L. Y. C. Leong, M. G. Rigby, and R. H. Sakaji. 1992. Evaluation of the California wastewater reclamation criteria using enteric virus monitoring data. Water Sci. Technol. 26:1513-1524. Bausum, H. T., S. A. Schaub, R. E. Bates, H. L. McKim, P. W. Sehumacher, and B. E. Brockett. 1983. Microbiological Aerosols From a Field-Source Wastewater Irrigation System. J. Water Pollution Control Federal, 55(1):65-75. Bryan, F. L. 1974. Diseases Transmitted by Foods Contaminated by Wastewater. In: Wastewater Use in the Production of Food and Fiber. EPA-660/2-74-041. U.S. Environmental Protection Agency. Washington, D.C. Bull R. J., C. Gerba, and R. R. Trussell. 1990. Evaluation of the health risks associated with disinfection. Critical Reviews in Environmental Control 20:77-113. Bull R. J., and F. C. Kopfler. 1991. Health Effects of Disinfectants and Disinfection By-products. Denver, Colo.: American Water Works Association Research Foundation. Camaan, D. E., R. J. Graham, M. N. Guentzel, H. J. Harding, K. T. Kimball, B. E. Moore, R. L.

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Ground Water Recharge Using Waters of Impaired Quality Northrop, N. L. Altman, R. B. Harrist, A. H. Holguin, R. L. Mason, C. B. Popescu, and C. A. Sorber. 1986. The Lubbock Land Treatment System Research and Demonstration Project: Volume IV. Lubbock Infection Surveillance Study. EPA-600/2-86-027d. Health Effects Research Laboratory, U. S. Environmental Protection Agency. Research Triangle Park, N.C. Camaan, D. E., B. E. Moore, H. J. Harding, and C. A. Sorber. 1988. Microorganism Levels in Air Near Spray Irrigation of Municipal Wastewater: the Lubbock Infection Surveillance Study. J. Water Pollution Control Federal 60(11):1960-1970. Craun, G. F. 1990. Methods for investigation and prevention of waterborne disease outbreaks. Report No. EPA-600/1-90/005a. U.S. Environmental Protection Agency, Office of Research and Development. Cincinnati, Ohio. Craun, G. F. 1991. Causes of waterborne outbreaks in the United States. Water Sci. Technol. 24:17-20. Feachem, R. G., D. J. Bradley, H. Gatelick, and D. D. Mara. 1983. Sanitation and Disease-Health Aspects of Excreta and Wastewater Management. Chichester, England: John Wiley, The World Bank. Florida Department of Environmental Regulation. 1990. Reuse of Reclaimed Water and Land Application. Chapter 17-610, Florida Administrative Code. Tallahassee, Fla. Gerba, C. P., and S. M. Goyal. 1985. Pathogen removal from wastewater during groundwater recharge. Pp. 283-317 in Artificial Recharge of Groundwater, T. Asano, ed. Boston, Mass: Butterworth. Gerba, C. P., and J. B. Rose. 1993. Estimating viral disease risk from drinking water. Pp. 117-135 in Comparative Environmental Risk Assessment , C. R. Cothern, ed. Boca Raton, Fla: Lewis Publishers. Haas, C. N. 1983. Wastewater disinfection and infectious disease risks. Crit. Rev. Environ. Contr. 17:1-20. Herwaldt, B. L., G. F. Craun, S. L. Stokes, and D. D. Juranek. 1992. Outbreaks of waterborne disease in the United States: 1989-1990. J. Am. Water Works Assoc. 84:129-135. Herren-Freund, S. L., M. A. Pereira, and G. Olson. 1987. The carcinogenicity of trichloroethylene and its metabolites, trichloroacetic acid and dichloroacetic acid, in mouse liver. Toxicol. Appl. Pharmacol. 90:83. Hoadley, A. W., and S. M. Goyal. 1976. Public health implications of the application of wastewater to land. P. 1092 in Land Treatment and Disposal of Municipal and Industrial Wastewater, R. L. Sanks and T. Asano, eds. Ann Arbor, Mich.: Ann Arbor Science Publishers. International Agency for Research on Cancer. 1987. Overall evaluations of carcinogenicity: An updating of IAPC Monographs Volumes 1 to 42. IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man. Suppl. 7. Lyons, France: International Agency for Research on Cancer. International Agency for Research on Cancer. 1991. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans . Chlorinated Drinking-water, Chlorination By-products; Some Other Halogenated Compounds; Cobalt and Cobalt Compounds, Vol. 52. Lyons, France: International Agency for Research on Cancer, World Health Organization. Iwata, Y., and F. A. Gunther. 1976. Translocation of the polychlorinated biphenyl oroclor 1254 from soil into carrots under field conditions. Arch. Environ. Contarn. Toxicol. 4(1):44-59. Johnson, D. E., D. E. Camaan, J. W. Register, R. E. Thomas, C. A. Sorber, M. N. Guentzel, J. M. Taylor, and W. J. Harding. 1980. The Evaluation of Microbiological Aerosols Associated with the Application of Wastewater to Land: Pleasanton, CA. EPA-600/1-80-015. U.S. Environmental Protection Agency. Cincinnati, Ohio. Kaplan, J. E., G. W. Gary, R. C. Baron, W. Singh, L. B. Schonberger, R. Feldman, and H. Greenberg. 1982. Epidemiology of Norwalk gastroenteritis and the role of Norwalk virus in outbreaks of acute nonbacterial gastroenteritis. Ann. Intern. Med. 96:756-761. Keswick, B. H., T. K. Satterwhite, P. C. Johnson, H. L. DuPont, S. L. Secor, J. A. Bitsura, G. W.

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Ground Water Recharge Using Waters of Impaired Quality Gary, and J. C. Hoff. 1985. Inactivation of Norwalk virus in drinking water by chlorine. Appl. Environ. Microbiol. 50:261-264. Kronberg L., R. F. Christman, R. Singh, and L. M. Ball. 1991. Identification of oxidized and reduced forms of the strong bacterial mutagen(z)-2-chloro-3-(dichloromethyl)-4-oxobutenoic acid (MX) in extracts of chlorine treated water. Environ. Sci. Technol. 25:99-104. Lauer, W. C., F. J. Johns, G. W. Wolfe, B. A. Myers, L. W. Condie, and J. F. Borzelleca. 1990. Comprehensive Health Effects Testing Program for Denver's Potable Water Reuse Demonstration Project. J. Toxicol. Environ. Health 30:305-321. Murphy, W. H., and J. T. Syverton. 1958. Absorption and translocation of mammalian viruses by plants. II. Recovery and distribution of viruses in plants. Virology 6(3):623. National Research Council. 1983. Risk Assessment in the Federal Government: Managing the Process. Washington, D.C.: National Academy Press. National Research Council. 1994. Science and, Judgment in Risk Assessment. Committee on Risk Assessment of Hazardous Air Pollutants. Washington, D.C.: National Academy Press. Nellor, M. H., R. B. Baird, and J. R. Smyth. 1984. Summary. Health Effects Study—Final Report. County Sanitation Districts of Los Angeles County. Whittier, Calif. Office of Environmental Health Hazard Assessment. 1992. Recommended Public Health Level for Arsenic in Drinking Water. California Environmental Protection Agency, Office of Environmental Health Hazard Assessment. Berkeley, Calif. Page, A. L, and A. C. Chang. 1985. Fate of wastewater constituents in soil and groundwater: trace elements. Pp. 13-16 in Irrigation with Reclaimed Municipal Wastewater—A Guidance Manual. G. S Pettygrove and T. Asano, eds. Prepared by the California State Water Resources Control Board. Chelsea, Mich.: Lewis Publishers. Pahren, H. R., J. B. Lucas, J. A. Ryan, and G. K. Dotson. 1979. Health risks associated with land application of municipal sludge. J. Water Pollution Control Federation, 51(11):2588-2601. Palazzo, A. J. 1976. The Effects of Wastewater Applications on the Growth and Chemical Composition of Forages. Report 76-9. Cold Regions Research and Engineering Laboratory, U.S. Army Corps of Engineers. Hanover, NH. Parnell, M. J, L. D. Koller, J. H. Exon, and J. M. Arnzen. 1986. Trichloroacetic acid effects on rat liver peroxisomes and enzyme-altered loci. Environ. Health perspect. 69:73-79. Pawlowski, S. 1992. Proposed revisions to Arizona's water reuse regulations. Paper presented at the Salt River Project Water Reuse Symposium, Nov. 2, 1992, Tempe, Ariz. Payment, P., L. Richardson, M. Edwardes, E. Franco, and J. Siemiatycki. 1991. A prospective epidemiological study of drinking water related gastrointestinal illness. Water Sci. Technol. 24:27-28. Pickard, D., D. Bracciano, and D. Holmes. Undated. Determination of Anticipated Health Effects for Reuse of Municipal Wastewater. Department of Sanitary Services, Tampa, Fla. Putnam, S. W., and J. D. Graham. 1993. Chemicals versus microbials in drinking water: A decision sciences perspective. J. Am. Water. Works Assoc. 85:57-61. Rao, V. C, and J. L. Melnick. 1986. Environmental Virology. American Society for Microbiology. Washington, D.C. Regli, S., J. B. Rose, C. N. Haas, and C. P. Gerba. 1991. Modeling the risk from Giardia and viruses in drinking water. J. Am. Water Works Assoc. 83:76-84. Rose, J. B, and C. P. Gerba. 1991. Use of risk assessment for development of microbial standards . Water Sci. and Technol. 24(2):29-34. Rose, J. B, and R. P. Carnahan. 1992. Pathogen removal by full scale wastewater treatment. Prepared for Florida Department of Environmental Regulation. Tallahassee, Fla. Sepp, E. 1971. The Use of Sewage for Irrigation—A Literature Review. Bureau of Sanitary Engineering, California Department of Public Health. Berkeley, Calif. Shuval, H. I. 1978. Land treatment of wastewater in Israel. Pp. 429-436 in State of Knowledge in Land Treatment of Wastewater, Vol. 1. Proceedings of an International Symposium. Cold Regions Research and Engineering Laboratory, U.S. Army Corps of Engineers. Hanover, NH.

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Ground Water Recharge Using Waters of Impaired Quality Sobsey, M. D. 1989. Inactivation of health-related microorganisms in water by disinfection processes. Water Sci. Technol. 21:179-195. Sobsey, M. D., T. Fuji, and R. M. Hall. 1991. Inactivation of cell-associated and dispersed hepatitis A virus in water. J. Am. Water Works Assoc. 83:64-67. State of California. 1978. Wastewater Reclamation Criteria. California Administrative Code, Title 22, Division 4. California Department of Health Services, Sanitary Engineering Section, Berkeley, California. State of California. 1987. Report of the Scientific Advisory Panel on Groundwater Recharge with Reclaimed Wastewater. Department of Water Resources and Department of Health Services, State Water Resources Control Board . Sacramento, Calif. State of Texas. 1990. Use of Reclaimed Water. Texas Administrative Code, Chapter 310, Subchapter A. Texas Water Commission. Austin, Tex. State of Washington. 1993. Water Reclamation and Reuse Interim Standards. Department of Health, State of Washington. Spokane, Wash. Straub, T. M., I. L. Papper, and C. P. Gerba. 1993. Hazards from pathogenic microorganisms in land-disposed sewage sludge. Rev. of Environ. Contarn, in Toxicol. 132:55-91. Tanaka, H., T. Asano, E. D. Schroeder, and G. Tchobanoglous. 1993. Estimating the reliability of wastewater reclamation and reuse using enteric virus monitoring data. Paper presented at the 66th Water Environment Federation Annual Conference and Exposition, Oct. 3-7, Anaheim, Calif.14pp. Teltsch, B., and E. Karzenelson. 1978. Airborne Enteric Bacteria and Viruses from Spray Irrigation with Wastewater. Appl. Environ. Microbiol. 35(2):290-296. U.S. Environmental Protection Agency. 1973. Water Quality Criteria 1972. EPA-R3-73-033. A report of the Committee on Water Quality Criteria, National Academy of Sciences—National Academy of Engineering. Washington, D.C. U.S. Environmental Protection Agency. 1976. Quality Criteria for Water. U.S. Environmental Protection Agency. Washington, D.C. U.S. Environmental Protection Agency. 1980. Wastewater Aerosols and Disease. EPA-600/9-80-028. Proceedings of Symposium, Sept. 19-21, 1979. H. Pahren and W. Jakubowski, eds. Health Effects Research Laboratory, U.S. Environmental Protection Agency. Cincinnati, Ohio. U.S. Environmental Protection Agency. 1951. Process Design Manual: Land Treatment of Municipal Wastewater. EPA-625/1-81-013. Center for Environmental Research Information, U.S. Environmental Protection Agency. Cincinnati, Ohio. U.S. Environmental Protection Agency. 1986. Drinking Water Criteria Document for Chlorophenols. External review draft. ECAO-CIN-D005. U.S. Environmental Protection Agency. Washington, D.C. U.S. Environmental Protection Agency. 1992. Guidelines for Water Reuse. EPA/625/R-92/004. Center for Environmental Resources Information, Office of Technology Transfer and Regulatory Support. Cinncinnati, Ohio. U.S. Environmental Protection Agency. 1993a. Integrated Risk Information system (IRIS). U.S. Environmental Protection Agency. Washington D.C. U.S. Environmental Protection Agency. 1993b. Drinking Water Regulations and Health Advisories. Office of Water, U.S. Environmental Protection Agency. Washington, D.C. Western Consortium for Public Health. 1992. City of San Diego Total Resource Recovery Project. Health Effects Study. Western Consortium for Public Health. Berkeley, Calif. Wilkes, C. R., M. J. Small, J. B. Andelman, N. J. Giardino, and J. Marshall. 1992. Inhalation exposure model for volatile chemicals from indoor water uses. Atmos. Environ. 26A:2227-2236. Yanko, W. A. 1993. Analysis of 10 years of virus monitoring data from Los Angeles County treatment plants meeting California wastewater reclamation criteria. Water Environ. Res. 65:221-226.