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Ground Water Recharge Using Waters of Impaired Quality 2 Source Waters and Their Treatment Water for human use comes from various sources—generally lakes, rivers, or underground aquifers. This report, which examines the potential of artificial recharge, uses the term ''source water" to mean the recharge source—the water supplied to a surface infiltration or injection well recharge system. Potential source waters of impaired quality for artificial recharge include treated municipal wastewater, stormwater runoff, and irrigation return flows. The quality of source waters may be improved by the use of various pretreatment and disinfection processes. This chapter evaluates the quality of municipal wastewater and the quality improvement gained from primary, secondary, and advanced wastewater treatment. The quality of urban stormwater runoff and its possible treatment methods are also discussed, as is the quality of irrigation return flow and the problems inherent in treating it. Industrial wastewater and industrial stormwater runoff are not considered in depth; although industrial wastewater might at times be suitable for ground water recharge, its potential use would be extremely site specific and a general evaluation is not useful. The quality of the source water considered for ground water recharge has a direct bearing on operational aspects of recharge facilities and also on the use to be made of the recovered water. The source water characteristics that affect the operational aspects of recharge facilities include suspended solids (SS), dissolved gases, nutrients, biochemical oxygen demand (BOD), microorganisms, and the sodium adsorption ratio (which affects soil permeability). The constituents that have the greatest possible adverse effects when the recharge is intended to support potable use include organic and metallic toxicants, nitrogen compounds, and pathogens.
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Ground Water Recharge Using Waters of Impaired Quality MUNICIPAL WASTEWATER Characteristics The quantity and quality of wastewater delivered from varies among communities, depending on the number of commercial and industrial establishments in the area, the per capita in-house water use (which may vary from 400 1/day or more in industrialized countries to 40 1/day or less in developing or water-short countries), and the condition of the sewer system. Raw municipal wastewater may include contributions from domestic and industrial sources, infiltration and inflow from the collection system, and, in the case of combined sewer systems, urban stormwater runoff. The typical composition of untreated municipal wastewater appears in Table 2.1. The occurrence and concentration of pathogenic microorganisms in raw wastewater depend on a number of factors, and it is not possible to predict with any degree of assurance what the general characteristics of a particular wastewater will be with respect to infectious agents. Important variables include the sources contributing to the wastewater, the original purpose of the water use, the general health of the contributing population, the existence of "disease carriers" in the population, and the ability of infectious agents to survive outside their hosts under a variety of environmental conditions. Table 2.2 lists infectious agents potentially present in untreated municipal wastewater. Table 2.3 illustrates the variety and order of magnitude of the concentration of microorganisms in untreated municipal wastewater. Viruses are not normally excreted for prolonged periods by healthy individuals, and the occurrence of viruses in municipal wastewater fluctuates widely. Viral concentrations are generally highest during the summer and early autumn months. Viruses shed from an infected individual commonly range from 1,000 to 100,000 infective or plaque forming units (pfu's) per gram (g) of feces, but may be as high as 1,000,000 pfu/g of feces (Feachem et al., 1983). Viruses as a group are generally more resistant to environmental stresses than many of the bacteria, although some viruses persist for only a short time in municipal wastewater. Vital levels in the United States have been reported to be as high as 700 pfu/100 ml, but are typically less than 100 pfu/100 ml (American Society of Civil Engineers, 1970; Melnick et al., 1978). Dissolved inorganic solids (total dissolved solids or salts, TDS) are not altered substantially in most wastewater treatment processes. In some cases, they may increase as a result of evaporation in lagoons or storage reservoirs. Therefore, unless wastewater treatment processes specifically intended to remove mineral constituents are employed, the composition of dissolved minerals in treated wastewater used for ground water recharge can be expected to be similar to the composition in the raw wastewater. The concentration of dissolved minerals in untreated wastewater is determined by the concentration in the domestic water
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.1 Typical Contaminants in Untreated Municipal Wastewater Concentration Unit Weak Medium Strong Solids, total mg/l 350 720 1,200 Dissolved, total mg/l 250 500 850 Fixed mg/l 145 300 525 Volatile mg/l 105 200 350 Suspended solids mg/l 100 220 350 Fixed mg/l 20 55 75 Volatile mg/l 80 165 275 Setteable solids mg/l 5 10 20 Biochemical oxygen demanda mg/l 110 220 275 Total organic carbon (TOC) mg/l 80 160 290 Chemical oxygen demand (COD) mg/l 250 500 1,000 Nigrogen (total as N) mg/l 20 40 85 organic mg/l 8 15 45 Free ammonia mg/l 12 25 50 Nitrites mg/l 0 0 0 Nitrates mg/l 0 0 0 Phosphorus (total as P) mg/l 4 8 15 Organic mg/l 1 3 5 Inorganic mg/l 3 5 10 Chloridesb mg/l 30 50 100 Sulfateb mg/l 20 30 50 Alkalinityc mg/l 50 100 NA Grease mg/l 50 100 150 Total coliform no./100 ml 106-107 107-108 107-109 Volatile organic compounds µg/l <100 100-400 > 400 Note: NA = not available. a 5-day, 20ºC(BOD5, 20ºC). b Values should be increased by amount present in domestic water supply. c As calcium carbonate (CaCO3). Source: Metcalf & Eddy, Inc., 1991. supply plus mineral pickup resulting from domestic water use, which in the United States varies from 200 to 400 mg/l. Wastewater treatment levels are generally classified as preliminary, primary, secondary, and advanced. The nature of each level of treatment is discussed in the following sections. (Note that the costs of treatment at least through secondary treatment is required before disposal to receiving waters and therefore would not be the responsibility of the recharge operation.)
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.2 Infectious Agents Potentially Present in Untreated Municipal Wastewater Disease Protozoa Entamoeba histolytica Amebiasis (amebic dysentery) Giardia lambliai Giardiasis Balantidium coli Balantidiasis (dysentery) Cryptosporidium Crytosporidiosis, diarrhea, fever Helminths Ascaris lumbricoides (roundworm) Ascariasis Ancylostoma duodenale (hookworm) Ancylostomiasis Necator americanus (roundworm) Necatoriasis Ancylostoma (spp.) (hookworm) Cutaneous larva migrans Strongyloides stercoralis (threadworm) Strongyloidiasis Trichuris trichuria (whipworm) Trichuriasis Taenia (spp.) (tapeworm) Teaniasis Enterobius vermicularis (pinworm) Enterobiasis Echinococcus granulosus (spp.) (tapeworm) Hydatidosis Bacteria Shigella (4 spp.) Shigellosis (dysentery) Salmonella ryphi Typhoid fever Salmonella (1,700 serotypes) Salmonellosis Vibro cholerae Cholera Escherichia coli (enterophathogenic) Gastroenteritis Yersinia enterocolitica Yersiniosis Leptospira (spp.) Leptospirosis Legionella pneumopilla Legionnaire's disease Campylobacter jejune Gastroenteritis Viruses Enteroviruses (72 types) polio, echo, coxsackie, new enteroviruses Gastroenteritis, heart anomalies meningitis, others Hepatitis A virus Infectious hepatitis Adenovirus (47 types) Respiratory disease, eye infections Rotavirus (4 types) Gastroenteritis Parvovirus (3 types) Gastroenteritis Norwalk agent Diarrhea, vomiting, fever Reovirus (3 types) Not clearly established Astrovirus (5 types) Gastroenteritis Calicivirus (2 types) Gastroenteritis Coronavirus Gastroenteritis Source: Adapted from Sagik et al., 1978; Hurst et al., 1989.
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.3 Microorganism Concentrations in Untreated Municipal Wastewater Concentration (number per 100 ml) Fecal Coliforms 104-109 Fecal streptococci 104-106 Shigella 1-103 Salmonella 102-104 Pseudomonas aeruginosa 103-104 Clostridium perfringens 103-105 Helminth ova 1-103 Giardia lamblia cysts 10-104 Cryptosporidium oocysts 10-103 Entamoeba histolytica cysts 1-101 Enteric viruses 102-104 Source: Adapted from various sources. Primary Treatment The first step in treatment, sometimes referred to as preliminary treatment, consists of the physical processes of screening, or comminution, and grit removal. Coarse screening is usually the first step and is used to remove large solids and trash that may interfere with later treatment processes. Comminution devices are sometimes used to cut up solids into a smaller size to improve downstream operations. Grit chambers are designed to remove material such as sand, gravel, cinders, eggshells, broken glass, seeds, coffee grounds, and large organic particles, such as food waste. Settling of most organic solids is prevented in the grit chamber because of the high flow velocity of wastewater through the chamber. Other preliminary treatment operations can include flocculation, odor control, chemical treatment, and pre-aeration. Past this initial screening, primary treatment consists of physical processes to remove settleable organic and inorganic solids by sedimentation and floating materials by skimming. These also removes some of the organic nitrogen, organic phosphorus, and heavy metals. Additional phosphorus and heavy metal removal can be achieved through the addition of chemical coagulants and polymers. Primary treatment, together with preliminary treatment, typically removes 50 to 60 percent of the suspended solids and 30 to 40 percent of the organic matter. Primary treatment does not remove the soluble constituents of the wastewater. Primary treatment has little effect on the removal of most biological species present in wastewater. However, some protozoa and parasite ova and cysts will settle out during primary treatment, and some particulate-associated microorgan-
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Ground Water Recharge Using Waters of Impaired Quality ism may be removed with settable matter. Primary treatment does not reduce the level of viruses in municipal wastewater. While primary treatment by itself generally is not considered adequate for ground water recharge applications, primary effluent has been successfully used in soil-aquifer treatment systems at some spreading sites where the extracted water is to be used for nonpotable purposes (Carlson et al., 1982; Lance, Rice, and Gilbert, 1980; Rice and Bouwer, 1984). The higher organic content of primary effluent may enhance nitrogen removal by denitrification in the SAT system (Lance, Rice, and Gilbert, 1980) and may enhance removal of synthetic organic compounds by stimulating greater microbiological activity in the soil (McCarty, Rittman, and Bouwer, 1984). A disadvantage of using primary effluent is that infiltration basin hydraulic loading rates may be lower because of higher suspended solids and weaker biological activity on and in the soil of the infiltration system. Also, too much organic carbon in the recharge water can have adverse effects on processes that occur in the soil and aquifer systems. In most cases, wastewater receives at least secondary treatment and disinfection, and often tertiary treatment by filtration, prior to augmentation of nonpotable aquifers by surface spreading. Secondary Treatment Secondary treatment is intended to remove soluble and colloidal biodegradable organic matter and suspended solids (SS). In some cases, nitrogen and phosphorus also are removed. Treatment consists of an aerobic biological process whereby microorganisms oxidize organic matter in the wastewater. Several types of aerobic biological processes are used for secondary treatment, including activated sludge, trickling filters, rotating biological contactors (RBCs), and stabilization ponds. Generally, primary treatment precedes the biological process; however, some secondary processes are designed to operate without sedimentation, e.g., stabilization ponds and aerated lagoons. Typical microorganism removal efficiencies for activated sludge and trickling filter secondary treatment processes are given in Table 2.4. Concentration ranges for inorganic constituents and some other parameters in secondary-treated municipal wastewater are presented in Table 2.5. Information on the concentration of trace organics in activated sludge secondary effluent from the City of Phoenix's 23rd Avenue treatment plant is given in the "Phoenix, Arizona Projects" case study in Chapter 6. The activated sludge process is considered to be a high-rate biological process because of the high concentrations of microorganisms used for the metabolization of organic matter. Trickling filters may be classified as either low-rate or high-rate based on their hydraulic and organic loading, mode of operation, and other factors. These processes accomplish biological oxidation in relatively small basins and use sedimentation tanks (secondary clarifiers) after
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.4 Typical Percent Removal of microorganisms by Conventional Treatment Processes Primary Treatment Secondary Treatment Activated Sludge Trickling Filter Fecal coliforms < 10 0-99 85-99 Salmonella 0-15 70-99 85-99 + Mycobacterium tubercolulosis 40-60 5-90 65-99 Shigella 15 80-90 85-99 Entamoeba histolytica 0-50 Limited Limited Helminth ova 50-98 Limited 60-75 Enteric viruses Limited 75-99 0-85 Source: Crook, 1992. the aerobic process to separate the microorganisms and other settleable solids from the treated wastewater. In the activated sludge process, treatment is provided in an aeration tank in which the wastewater and microorganisms are in suspension and continually mixed through aeration. Trickling filters utilize media such as stones, plastic shapes, or wooden slats in which the microorganisms become attached. RBCs are similar to trickling filters in that the organisms are attached to support media, which in this case are partially submerged rotating discs in the wastewater stream. These processes are capable of removing up to 95 percent of BOD, COD, and SS originally present in the wastewater and significant amounts of many (but not all) heavy metals and specific organic compounds (Water Pollution Control Federation, 1989). Trickling filters are not as effective as activated sludge processes in removing soluble organics because of less contact between the organic matter and microorganisms. Activated sludge treatment can reduce the soluble BOD fraction to 1 to 2 mg/l, while the trickling filter process typically reduces soluble BOD to 10 to 15 mg/l (U.S. Environmental Protection Agency, 1992). Biological treatment, including sedimentation, typically reduces the total BOD to 15 to 30 mg/l, COD to 40 to 70 mg/l, and TOC to 15 to 25 mg/ 1 (U.S. Environmental Protection Agency, 1992). Very few dissolved minerals are removed during conventional secondary treatment. Pond systems require relatively large land areas and are most widely used in rural areas and in warm climates and where land is available at reasonable cost. They are often arranged in a series of anaerobic, facultative, and maturation ponds with an overall hydraulic detention time of 10 to 50 days, depending on the design temperature and effluent quality required (Mara and Cairncross, 1989). Most organic matter removal occurs in the anaerobic and facultative ponds.
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.5 Constituent Concentrations and other Parameters for Secondary-Treated Municipal Wastewater Concentrationa (mg/l) Calcium 9-84 Potassium 9-108 Magnesium 12-176 Sodium 44-1320 Amonium 0-501 Chlorine 43-2450 Fluoride 0.2-3.8 Bicarbonate 76-563 Nitrate 0.4-30 Phosphate 1.2-46 Sulfate 14-490 Silicondioxide 10-76 Hardness (as calcium carbonate) 62-951951 pH (units) 6.3-8.4 Electrical conductivity 423-6570 µmho/cm Total dissolved solids 210-4580 Arsenic < 0.005-0.023 Boron 0.3-2.5 Cadmium < 0.005-0.22 Chromium < 0.001-0.1 Copper 0.006-0.053 Lead0.003-0.35 0.003-0.35 Molybdenum 0.001-0.018 Molybdenum 0.001-0.018 Mercury 0.001-0.018 Nichol 0.003-0.60 Zinc 0.004-0.35 Biochemical oxygen demand 1.5-30 Chemical oxygen demand 40-70 Total suspended solids 10-25 Total organic carbon 15-25 a Concentration expressed in milligrams per liter unless otherwise noted. Source: Treweek, 1985; Crook, 1992. Maturation ponds, which are largely aerobic, are designed primarily to remove pathogenic microorganisms following biological oxidation processes. Well-designed stabilization pond systems are capable of reducing the BOD to 15 to 30 mg/l, COD to 90 to 135 mg/l, and SS to 15 to 40 mg/l (Shuval et al., 1986). The organic matter remaining in the effluent consists of soluble, biodegradable organic matter present in the raw wastewater, but not removed, plus intermediate
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Ground Water Recharge Using Waters of Impaired Quality products formed during the biological degradation of organic compounds and microbial cellular constituents (Metcalf & Eddy, Inc., 1991). The suspended solids are mainly organic in nature, consisting of biological solids produced during secondary treatment and other solids that escaped treatment and separation. Stabilization ponds use algae to provide oxygen to the system. This system is considered a low-rate biological process. Mechanically aerated lagoon systems sometimes are used to provide secondary-level treatment. Stabilization ponds are capable of providing considerable nitrogen removal under certain conditions (e.g., high temperature and pH and long detention times) and are effective in removing microorganisms from wastewater. Well-designed and well-operated pond systems are capable of achieving a 6-log (99.9999 percent) reduction of bacteria, a 3-log (99.9 percent) reduction of helminths, and a 4-log (99.99 percent) reduction of viruses and cysts (Mara and Cairncross, 1989). Algae produced during pond treatment may present soil clogging problems during recharge. Tertiary Treatment The treatment of wastewater beyond the secondary or biological stage is sometimes called tertiary treatment. The term normally implies the removal of nutrients such as phosphorus and nitrogen, and a high percentage of suspended solids. However, the term tertiary treatment is now being replaced in most cases by the term advanced wastewater treatment—which refers to any physical, chemical, or biological treatment process used to accomplish a degree of treatment greater than that achieved by secondary treatment. Advanced Wastewater Treatment Advanced wastewater treatment processes are designed to remove suspended solids and dissolved substances, either organic or inorganic in nature. Advanced wastewater treatment processes generally are used when a high-quality reclaimed water is necessary, such as for direct injection into potable aquifers. Commonly used processes and their principal removal functions are given in Table 2.6. The major advanced wastewater processes associated with ground water recharge are coagulation-sedimentation, filtration, nitrification, denitrification, phoshorus removal, carbon adsorption, and reverse osmosis. Coagulation-Sedimentation Chemical coagulation with lime, alum, or ferric chloride followed by sedimentation removes suspended solids, heavy metals, trace substances, phosphorus, and turbidity. Vital inactivation under alkaline pH conditions can be accom-
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.6 Constituent Removal by Advanced Wastewater Treatment Operations and Processes Principal Removal Function Description of Operation or Process Type of Wastewater Treateda Suspended solids removal Filtration EPT, EST Microstrainers EST Ammonia oxidation Biological nitrification EPT, EBT, EST Nitrogen removal Biological nitrification/denitrification EPT, EST Nitrate removal Separate-stage biological EPT + nitrification denitrification Biological phosphorus removal Mainstream phosphorus removalb RW, EPT Sidestream phosphorus removal RAS 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 hosphorus removal by chemical addition Chemical precipitation with metal salts RW, EPT, EBT, EST Chemical precipitation with lime RW, EPT, EBT, EST Toxic compounds and refractory organics removal Carbon adsorption EST + filtration Powdered activated carbon EPT Chemical oxidation EST + filtration Dissolved inorganic 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 a EPT-effluent from primary treatment; EBT-effluent from biological treatment (before clarification); EST-effluent from secondary treatment: RW-raw (untreated sewage); and RAS-return activated sludge. b Removal process occurs in the main flowstream as opposed to sidestream treatment. Source: Metcalf & Eddy, Inc., 1991.
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Ground Water Recharge Using Waters of Impaired Quality plished using lime as a coagulant, but pH values of 11 to 12 are required before significant inactivation is obtained. Filtration Filtration is a common treatment process used to remove particulate matter prior to disinfection. Filtration involves the passing of wastewater through a bed of granular media, which retain the solids. Typical media include sand, anthracite, and garnet. Removal efficiencies can be improved through the addition of certain polymers and coagulants. Table 2.7 presents average constituent removal efficiencies for filtration. The concentrations of organic and inorganic constituents at three water reclamation plants operated by the Sanitation Districts of Los Angeles County are shown in Tables 2.8 and 2.9, respectively. All three of the treatment plants have conventional activated sludge treatment followed by filtration and disinfection. Treatment of biologically treated secondary effluent by chemical coagulation, sedimentation, and filtration has been demonstrated to remove more than 99 percent of seeded poliovirus (Sanitation Districts of Los Angeles County, 1977). This treatment chain reduces the turbidity of the wastewater to very low levels, thereby enhancing the efficiency of the subsequent disinfection process. Chemical coagulation and sedimentation alone can remove up to 99 percent of viruses, although the presence of organic matter can significantly decrease the amount of viruses removed. Direct filtration, that is, chemical coagulation and filtration without sedimentation, has also been shown to remove up to 99 percent of seeded poliovirus (Sanitation Districts of Los Angeles County, 1977). In one study, sand and dual-media filtration of secondary effluent, without coagulant addition prior to filtration, did not significantly reduce enteric viral levels (Noss et al., 1989). The primary purpose of the filtration step is not to remove viruses, but to remove protozoa and helminth eggs and floc and other suspended matter that may contain adsorbed or enmeshed microorganisms, thereby making the disinfection process more effective. Chemical coagulation and filtration followed by chlorine disinfection to very low total coliform levels can remove or inactivate 5 logs (99.999 percent) of seeded poliovirus through these processes alone and subsequent to conventional biological secondary treatment can produce effluent essentially free of measurable levels of bacterial and viral pathogens (Sanitation Districts of Los Angeles County, 1977; Sheikh et al., 1990). All parasitic cysts may not be removed by direct filtration. In one study, Giardia cysts were present in concentrations ranging from 3 to 7 cysts/100 liters after direct filtration (Casson et al., 1990). Rose and Carnahan (1992) found both Giardia and Cryptosporidium cysts and oocysts in reclaimed water after direct filtration of activated sludge effluent in about 20 percent of the samples collected. Filtered, secondary effluent from the Reedy Creek Wastewater Treat-
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Ground Water Recharge Using Waters of Impaired Quality quires such treatment. If it is unnecessary to treat the water for TDS reduction, then nitrate levels can be reduced instead by biological denitrification, a process that has been applied in the past to treat municipal wastewater effluent. Phosphorus compounds are readily removed by chemical clarification, as are most of the trace metals commonly found in irrigation return flow. Granular activated carbon (GAC) adsorption can be used if needed to remove soluble pesticide residues remaining after other treatment processes are completed. GAC is a commonly used treatment method for removing dissolved organics in drinking water supplies and has also been used to treat municipal wastewater (Treweek, 1985). SUMMARY Wastewaters considered suitable source waters for ground water recharge include municipal wastewater effluent, stormwater runoff, and irrigation return flow. Table 2.22 is a summary of advantages and disadvantages pertaining to the use of wastewaters for recharge, Table 2.23 is a summary of the qualities of the three primary types of wastewater considered in this report. Of the three, treated municipal wastewater effluent is by far the most consistent, spatially and temporally, in both quantity and quality. An exception to this generalization is where raw municipal wastewater and stormwater are commingled in a combined sewerage system. When compared to other potential impaired water sources, the quality of treated municipal wastewater has been characterized extensively for various levels of treatment because of regulations pertaining to the disposal of municipal wastewater effluent and because municipal wastewater has a history of use as a recharge water source. The body of information on quality of stormwater runoff and irrigation return flow is far less developed, especially when their greater variability is taken into account. Therefore, characterization of stormwater runoff and irrigation return flow quality must be drawn from a much less systematic and comprehensive database than is available for municipal wastewater. Constituents of concern in municipal wastewater include organic compounds, nitrogen species, pathogenic organisms, and suspended solids. Treatment processes are readily available and have been used successfully to treat municipal wastewater effluent to levels acceptable for various recharge applications. However, even when treated to a very high degree, disinfection of the effluent with chlorine results in the formation of disinfection by-products with the residual organic compounds. These DBPs are of concern if the recovered ground water is to be used for potable purposes. Urban stormwater runoff quality is affected by several factors, including rainfall quantity and intensity, the natural and anthropogenic characteristics of the drainage basin, time since the last runoff event, and, in northern areas, the time of year. Constituents of concern in urban stormwater runoff include trace
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Ground Water Recharge Using Waters of Impaired Quality metals, organic compounds, pathogenic organisms, suspended solids, and in northern climates in the winter, dissolved solids and chloride enrichment by road deicing practices. Stormwater runoff typically is not treated. However, field experience suggests that many suitable treatment methods exist that may adequately treat most stormwaters before surface infiltration. Overall, stormwater from residential areas is generally best in quality, but its quantity may be extremely erratic and unpredictable due to natural rainfall variations. Recharge with stormwater often requires surface storage and flow regulation because recharge systems do not have the capacity to allow immediate infiltration all the runoff produced by a given precipitation event. Residential area stormwater runoff is best allowed to infiltrate through source area recharge devices, such as french drains, grass filter strips, and grass drainage swales. Although not examined in depth in this report, industrial stormwater runoff is very irregular in quality, especially for toxicants. Because of this irregular quality and the great potential for severe contamination, industrial area stormwater runoff is not a good candidate for ground water recharge use. Urban snowmelt may also be a poor choice for recharge because of its high salt content. Dry weather flow in stormwater drainage systems may be associated with highly contaminated inappropriate discharges (such as raw municipal wastewater, industrial process water, and illegal dumping of hazardous materials) and should also be avoided. Therefore, to take advantage of urban stormwater runoff as a source of recharge water, care must be taken to isolate the acceptable residential area runoff from the more contaminated flows or to provide additional source area treatment for runoff from the critical areas. Irrigation return flow exhibits the widest variation in quality of the three potential source waters. It varies from having basically the same quality as high-quality surface water to having a salinity of as much as 10,000 mg/1. The quality characteristics of irrigation return flow are not well studied, except for salinity and concentrations of nitrate. In humid areas, the salt content of irrigation return flow is not a problem, but in semiarid areas it can be enriched to 8 to 10 times that of the water applied. Nitrate concentrations can be as high as 100 to 200 mg/1. Suspended solids and trace element concentrations including selenium, uranium, boron, and arsenic are also of concern. Pesticide residues may also pose problems in irrigation return flow, but in general most of the pesticide residues are associated with particulates and are readily removed with suspended solids. Treatment of irrigation return flow is not generally done, but treatment processes are available to remove the constituents of concern to acceptable levels. The cost-effectiveness of doing so for saline waters is questionable. In the past, surface and subsurface return flows from irrigated agricultural areas were simply ''disposed" of in streams, lakes, and the ocean without any environmental concerns. This attitude is changing and there is a trend toward increased management to minimize degradation of the environment, such as storage in evaporation ponds and ultimate disposal of salts as solid waste, treat-
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.22 Advantages and Disadvantages for Using Various Wastewaters in Ground Water Recharge Advantages Disadvantages Municipal Wastewater Primary-treated municipal wastewater • High TOC for possible improved denitrification • Poor water quality; higher toxicants, nutrients, BOD, and suspended solids than other municipal wastewaters • Relatively constant flow • Located near major point of use • High disinfection by-product formation potential Secondary-treated municipal wastewater • Most common • Moderate to poor water quality Relatively constant flows High volume Located near major point of use Advanced treated municipal wastewater • Best quality municipal wastewater • High cost • Low TOC for reduced disinfection by-product formation potential • Relatively constant flows • Located near major point of use Agricultural Irrigation Return Flows Irrigation return flow • High pesticides and herbicides • High nutrients and salts • Irregular flows
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Ground Water Recharge Using Waters of Impaired Quality Advantages Disadvantages Urban Stormwater Residential area stormwater • Likely best quality wastewater • Irregular flows (highly intermittent) • Most common stormwater • Located near major point of use Industrial area stormwater • Highly irregular toxicant quality (likely, contamination from industrial processes and contact with grossly polluted soils) Urban snowmelt water • High salt content in areas using common de-icing procedures Dry weather stormwater sewerage flows • High pesticides and herbicides • Likely contamination from inappropriate discharges Combined Sewage Combined sewage • contains raw sewage with pathogen contamination • higher likelihood of toxicants from stormwater from older industrial and commercial areas
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Ground Water Recharge Using Waters of Impaired Quality TABLE 2.23 Comparison of Quality Parameters for Irrigation Return Flow, Urban Stormwater Runoff, and Treated Municipal Wastewater
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Ground Water Recharge Using Waters of Impaired Quality ment, or deep-well injection into closed geologic formations. To minimize the cost of these techniques, irrigation efficiencies must be increased, and return flows must be reused as much as possible for irrigation (e.g., raising salt tolerant crops) to minimize the volume of irrigation return flow ultimately produced. The availability of wastewater for recharge can vary widely throughout the country. Total urban stormwater runoff may provide about 100 acre-feet per square mile per year in areas having about 25 cm (10 inches) of rain per year, but can increase to about 1,000 acre-feet per square mile per year in more humid areas of the United States (having about 125 cm (50 inches) of rain per year). Obviously, some of this water would be diverted from recharge facilities because of poor quality (such as that from industrial areas), reducing the amount available. Municipal wastewater flow would also vary, depending on the population served in a community. Large cities may provide as much as 1,500 acre-feet per square mile per year of wastewater for recharge, but most small towns will generate only about one-tenth as much because of lower population densities. The amount of irrigation return flow available for recharge would vary greatly, depending on irrigation practice, return flow collection efficiency, crop requirements, and rainfall amounts. The amount of irrigation return flow to surface or ground water supplies in 1985 in the United States was estimated to be about 45 million acre-feet (Solley et al., 1988). This amount is 29 percent of the 154 million acre-feet withdrawn for irrigation in 1985. California and Idaho were by far the largest users of irrigation water, together accounting for 37 percent of the national total. Finally, location of the wastewater source is also important. While urban stormwater runoff and municipal wastewater are usually located near the area of use, most irrigation return flows would be located further from populated areas. REFERENCES American Society of Civil Engineers. 1970. Engineering evaluation of virus hazard in water. J. Sanit. Eng. Div., 96(SA1):111. Amy, G. L., P. A. Chadki, and P. H. King 1984. Chlorine Utilization during formation of THM in presence of ammonia and bromide. Environ. Sci. Technol. 18:781-786. Bannerman, R., J. G. Konrad, and D. Becker. 1979. The IJC Menomonee River Watershed Study. EPA-905/4-79-029. U.S. Environmental Protection Agency. Chicago, Ill. Battigelli, D. A., M. D. Sobsey, and D. C. Lobe. 1993. The inactivation of hepatitis A virus and other model viruses by UV irradiation. Water Sci. Technol. 27(3-4):339-342. Bookman-Edmonston Engineering, Inc. 1992. Annual Report on Results of Water Quality Monitoring: Water Year 1990-91. Report prepared for the Water Replenishment District of Southern California by Bookman-Edmonston Engineering, Inc., Glendale, California. Boucher, P. R. 1984. Sediment transport by irrigation return flows in four small drains within the DID-18 drainage of the Sulphur Creek basin, Yakima County, Washington, April 1979 to October 1981: U.S. Geol. Surv. Water Resour. Invest. Rep. 83-4167, 149 pp. Bouwer, H. 1987. Effect of irrigated agriculture on groundwater. J. Irrig. Drain. Eng. 113(1):4-15. Bull, R. J., and F. C. Kopfler. 1991. Health Effects of Disinfectants and Disinfection By-products. Denver: Am. Water Works Assoc. Res. Found.
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Representative terms from entire chapter: