6
Selected Artificial Recharge Projects

Although much can be learned from discussing the general characteristics of ground water recharge technologies, the knowledge becomes most useful when seen in light of actual examples. Examples provide an opportunity to see how theory translates into on-the-ground activity. This chapter provides brief descriptions of existing ground water recharge projects. The examples were selected to illustrate the common techniques used, show a variety of the purposes for which recharge is planned, and give concrete examples of the problems such projects sometimes face. The seven sites discussed are

  • Water Factory 21, Orange County, California

  • Montebello Forebay, California

  • Phoenix, Arizona

  • El Paso, Texas

  • Long Island, New York

  • Orlando, Florida

  • The Dan Region, Israel

These examples are illustrative and brief, and the committee did not attempt to make recommendations from these site-specific cases. Instead, the committee hopes that these descriptions will show that artificial ground water recharge is not a "technology of the future" but rather something in use today in relatively diverse settings. These examples show that properly planned and operated artificial recharge projects can increase our water management options and flexibility.



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Ground Water Recharge Using Waters of Impaired Quality 6 Selected Artificial Recharge Projects Although much can be learned from discussing the general characteristics of ground water recharge technologies, the knowledge becomes most useful when seen in light of actual examples. Examples provide an opportunity to see how theory translates into on-the-ground activity. This chapter provides brief descriptions of existing ground water recharge projects. The examples were selected to illustrate the common techniques used, show a variety of the purposes for which recharge is planned, and give concrete examples of the problems such projects sometimes face. The seven sites discussed are Water Factory 21, Orange County, California Montebello Forebay, California Phoenix, Arizona El Paso, Texas Long Island, New York Orlando, Florida The Dan Region, Israel These examples are illustrative and brief, and the committee did not attempt to make recommendations from these site-specific cases. Instead, the committee hopes that these descriptions will show that artificial ground water recharge is not a "technology of the future" but rather something in use today in relatively diverse settings. These examples show that properly planned and operated artificial recharge projects can increase our water management options and flexibility.

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Ground Water Recharge Using Waters of Impaired Quality The Water Factory 21 project in Orange County, California, is the first injection project involving highly treated municipal wastewater. The injected water provides a barrier to seawater intrusion, but also enters potable water supply aquifers. The project has been in operation since 1976 and has provided significant data on the capability and reliability of advanced wastewater treatment processes to remove microbiological and chemical constituents, ground water quality, and monitoring techniques. Another California example is the Montebello Forebay project in south-central Los Angeles County. This project demonstrates indirect potable reuse via surface spreading of reclaimed water. The Montebello Forebay project has been in operation since 1962 and has been the subject of extensive research to investigate health-related issues. The Phoenix, Arizona, example illustrates the extensive research undertaken to demonstrate the capability of soil-aquifer treatment (SAT) to treat relatively low quality treated municipal wastewater to levels acceptable for many nonpotable applications upon extraction. The El Paso, Texas, project is the first injection project in the United States where the sole intent of the project is to augment the potable water supply aquifer using reclaimed municipal wastewater. It is a relatively new project and will provide important data as it builds an operational history. The Long Island, New York, example demonstrates the effectiveness of artificial recharge in a more urbanized, eastern setting, where climate and water availability are significantly different than in the West. Stormwater runoff is recharged into infiltration basins to replenish the ground water withdrawn for use by Long Island residents, thereby also helping to retard seawater intrusion into the aquifers that provide the primary source of drinking water for the area. Another eastern project, the stormwater drainage wells in Orlando, Florida, is included to illustrate another approach to using excess stormwater runoff for artificial recharge, thus helping to solve a wastewater disposal problem as well as a water supply problem. Finally, one international example is provided. The Dan Region project in Israel provides information on a large-scale recharge operation that incorporates SAT of treated municipal wastewater and subsequent extraction of the water for extensive agricultural irrigation. The project is well documented and has been in operation for almost 20 years. WATER FACTORY 21, ORANGE COUNTY, CALIFORNIA The Orange County Water District (OCWD) was formed by a special act of the California legislature in 1933 for the purpose of protecting the Orange County ground water basin. In 1955, OCWD was given the added responsibility of water management. Early in its history, OCWD secured the right to all water in

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Ground Water Recharge Using Waters of Impaired Quality FIGURE 6.1 Orange County ground water recharge facilities and saltwater intrusion barriers. the Santa Ana River. Over 3 million acre-feet of the river's flow has been captured to recharge the Orange County ground water basin. In addition, more that 2.5 million acre-feet of water imported from northern California and the Colorado River has been recharged (Orange County Water District, 1991). The location of OCWD and its recharge facilities is shown in Figure 6.1. The Orange County ground water basin is the depositional plain of the Santa Aria River. The principal features of the region are surrounding hills and a broad, poorly drained alluvial plain with alternating gaps and minor hill systems along the coast. A major fault system parallels the coastline, which apparently

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Ground Water Recharge Using Waters of Impaired Quality seals the basin from the sea at deeper levels. However, in several gaps along the ocean front there is hydraulic continuity between seawater and ground water in the upper 45 to 60 m (150 to 200 ft) of recent alluvial fill (Argo and Cline, 1985). The aquifers in the area are composed of fine-to coarse-grained sand, separated by silt and clay layers (aquicludes and aquitards). The Talbert aquifer, the principal zone of production in the area, is of recent age and overlies Pleistocene deposits within the gap created by the Santa Aria River. The Talbert aquifer is the only aquifer in direct contact with the Pacific Ocean. The three lower zones of local production are subject to intrusion by virtue of their contact with the Talbert aquifer. The base of the freshwater-bearing sediments is more than 1,200 m (4,000 ft) deep in some inland locations but rises to a depth of 60 m (200 ft) along the coast, where seawater intrusion has occurred. Seawater intrusion was first observed in municipal wells during the 1930s as a consequence of basin overdraft. Overdrafting of the ground water continued into the 1950s. Overpumping of the ground water resulted in seawater intrusion as far as 5.6 km (3.5 miles) inland from the Pacific Ocean by the 1960s. Although OCWD prevented further intrusion through percolation of large amounts of imported water in the forebay area of the ground water basin, the need for a coastal barrier system was obvious. OCWD began pilot studies in 1965 to determine the feasibility of using effluent from an advanced wastewater treatment (AWT) facility as injection water in a hydraulic barrier system to prevent the encroachment of saltwater into potable water supply aquifers. Construction of an AWT facility known as Water Factory 21 was started in 1972 in Fountain Valley, and injection of the treated municipal wastewater into the ground began in 1976. Water Factory 21 receives activated sludge secondary effluent from the adjacent County Sanitation Districts of Orange County (CSDOC) and has a design capacity of 15 million gallons per day (mgd). Water Factory 21 has the following unit processes: lime clarification for removal of suspended solids, heavy metals, and dissolved minerals; air stripping for removal of ammonia and volatile organic compounds; recarbonation for pH control; mixed-media filtration for removal of suspended solids; activated carbon adsorption for removal of dissolved organic compounds; reverse osmosis (RO) for demineralization and removal of other constituents; and chlorination for disinfection and algae control. The current operation mode is shown in Figure 6.2. Because California rules require that total dissolved solids cannot exceed 500 milligrams per liter (mg/l) prior to injection, RO is used to demineralize up to 5 mgd of the wastewater used for injection. The feed water to the RO plant is effluent from the mixed-media filters. Effluent from granular activated carbon adsorption columns is disinfected and blended with RO water. Activated carbon is regenerated on site in a multiple-hearth furnace. Solids from the settling basins are incinerated in a multiple-hearth furnace from which lime is recovered

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Ground Water Recharge Using Waters of Impaired Quality FIGURE 6.2 Flow schematic for Orange County Water District Water Factory 21.

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Ground Water Recharge Using Waters of Impaired Quality and reused in the chemical clarifier. Brine from the RO process is pumped to the CSDOC facilities for ocean disposal. Reclaimed water produced at Water Factory 21 is injected into a series of 23 multicasing wells providing 81 individual injection points into 4 aquifers. The resulting seawater intrusion barrier is known as the Talbert injection barrier (Argo and Cline, 1985). A schematic of a typical injection well is shown in Figure 6.3. The wells are located at 183-m (600-ft) intervals in a city street approximately 5.6 km (3.5 miles) inland from the Pacific Ocean. Each well has the capacity to inject 450 gallons per minute (gpm). They vary in depth from 27 m (90 ft) to 130 m (430 ft). There are 7 extraction wells located between the injection wells and the coast. At the present time, the ground water is maintaining a positive hydraulic gradient toward the ocean, and the extraction wells are not in use. Prior to injection, the product water is blended 2:1 with deep well water from an aquifer not subject to contamination. The blended water is chlorinated in a blending reservoir before it is injected into the ground. Depending on conditions, the injected water flows toward the ocean forming a seawater barrier, inland to augment the potable ground water supply, or in both directions. On average, well over 50 percent of the injected water flows inland to augment the potable water supply. The AWT processes at Water Factory 21 reliably produce a high-quality water. No total coliform organisms were detected in any of 161 samples of blended injection water tested during 1990 (Wesner, 1991). A virus monitoring program conducted from 1975 to 1982 demonstrated to the satisfaction of the state and county health agencies that Water Factory 21 effluent is essentially free of measurable levels of viruses (McCatry et al., 1982). The average turbidity of filter effluent was 0.20 nephelometric turbidity units (NTU) and did not exceed 1.0 NTU at any time during 1990. The average chemical oxygen demand (COD) and total organic carbon (TOC) concentrations for the year were 8 mg/l and 2.8 mg/l, respectively (Wesner, 1991). The effectiveness of the RO process in the removal of inorganic constituents at Water Factory 21 is indicated in Table 2-10 in Chapter 2. The concentrations of priority organic pollutants at various steps in the treatment train are presented in Table 2.11 in Chapter 2. In 1992, the California Department of Health Services removed a restriction that required blending reclaimed water not of sewage origin prior to injection. Hence, OCWD is considering phasing out use of deep well water for blending and inject 100 percent reclaimed water. In addition, ground water studies indicate that approximately 25 mgd of injected water is needed to fully protect against seawater intrusion at the Talbert Gap, and consideration is being given to increasing the amount of water produced at Water Factory 21 by 5 to 10 mgd in future years.

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Ground Water Recharge Using Waters of Impaired Quality FIGURE 6.3 Typical reclaimed water injection well. MONTEBELLO FOREBAY GROUND WATER RECHARGE PROJECT, LOS ANGELES, CALIFORNIA Ground water is an integral component of southern California's water resources. Artificial recharge of aquifers is practiced to augment replenishment of ground water basins in several locations, including the Montebello Forebay area

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Ground Water Recharge Using Waters of Impaired Quality of south-central Los Angeles County. Waters used to recharge via surface spreading include local stormwater runoff, imported surface water (Colorado River water and State Project water), and reclaimed municipal wastewater. Imported surface water is not always available for recharge during the summer months when demands by domestic water systems are at their peak. In addition, the availability of imported surface water is likely to be severely limited in the future. When the Central Arizona Project is completed in the mid-1990s, California's allotment of imported Colorado River water could be reduced by as much as 600,000 acre-feet/year. Also, the state of California may limit deliveries from the State Project, which supplies water to southern California from the Feather River/Sacramento Delta in northern California. Reclaimed water has been used as a source of ground water replenishment in the Montebello Forebay area since 1962. At that time, approximately 12,000 acre-feet/year of disinfected activated sludge secondary effluent from the Sanitation Districts of Los Angeles County (LACSD) Whittier Narrows Water Reclamation Plant (WRP) was spread in the Montebello Forebay area of the Central Groundwater Basin, which is the main body of ground water underlying the greater Los Angeles metropolitan area. The basin has an estimated usable storage capacity of 780,000 acre-feet. In 1973, the San Jose Creek WRP was placed in service and also supplied secondary effluent for recharge. In addition, effluent from the Pomona WRP that is not reused for other purposes is discharged into San Jose Creek, a tributary of the San Gabriel River, which ultimately becomes a source of recharge water in the Montebello Forebay. The use of effluent from the Pomona WRP is expected to decrease as the reclaimed water becomes more fully used for irrigation and industrial applications in the Pomona area. The water reclamation plants were originally built as secondary treatment facilities; however, body contact recreational activities in the receiving waters dictated that additional public health protection measures be taken. In the late 1970s all three reclamation plants were upgraded to provide tertiary treatment via dual media filtration (for the Whittier Narrows and San Jose Creek WRPs) or activated carbon filtration (for the Pomona WRP), and chlorination/dechlorination (Nellor et al., 1984). The activated carbon filters at the Pomona WRP have since been converted to dual-media filters. The Montebello Forebay ground water recharge project is a cooperative effort. LACSD collects and treats municipal wastewater and monitors the effluent quality. The replenishment program is operated by the Los Angeles County Department of Public Works (LADPW), while overall management of the ground water basin is administered by the Water Replenishment District of Southern California (WRDSC). LADPW constructed special spreading areas designed to increase the indigenous percolation capacity by modifying the San Gabriel River channel and constructing off-stream spreading basins, ranging in size from 4 acres to 20 acres, adjacent to the Rio Hondo and San Gabriel rivers. The Rio

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Ground Water Recharge Using Waters of Impaired Quality FIGURE 6.4 Montebello Forebay ground water recharge facilities. Hondo spreading basins have 427 acres available for spreading. The San Gabriel River spreading basins occupy 224 acres, which include approximately 133 acres in an unlined section of San Gabriel River. The locations of the spreading basins and water reclamation plants are shown in Figure 6.4. Under normal operating conditions, the basins are rotated through a 21-day cycle consisting of (1) a 7-day flooding period during which the basins are filled to maintain a constant 1.2 m (4-ft) depth; (2) a 7-day draining period during which flow to the basins is terminated and the basins are allowed to drain; and (3) a 7-day drying period during which the basins are allowed to dry out thoroughly. This wetting/drying operation serves several purposes, including maintenance of aerobic conditions in the upper soil strata. In the aftermath of the 1976-1977 drought, there was considerable pressure

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Ground Water Recharge Using Waters of Impaired Quality to more fully use reclaimed water supplies in southern California, particularly for ground water recharge. However, concerns by the California Department of Health Services (DOHS) over potential health effects of using reclaimed water to replenish potable water supplies caused a moratorium on planned expansions. In an attempt to answer some of the health-related issues associated with ground water recharge, a Health Effects Study was initiated in 1978 (Nellor et al., 1984). The focus of the study, conducted by LACSD, was the Montebello Forebay ground water recharge project. At the time the study was conducted, the annual amount of reclaimed water spread and recharged averaged 26,500 acre-feet/year, which was 16 percent of the total inflow to the ground water basin, with no more than 32,700 acre-feet of reclaimed water spread in any given year. The percentage of reclaimed water in the ground water supply was estimated to range from 0 to 23 percent on an annual basis, and 0 to 11 percent on a long-term (1962 to 1977) basis. The primary goal of the 5-year $1.4 million study was to develop a database which could be used to enable health and regulatory authorities to determine whether the use of reclaimed water for ground water replenishment in the Montebello Forebay should be maintained at the then-current level, cut back, or expanded. A wide range of research was undertaken, including (1) water quality characterizations of ground water, reclaimed water, and other recharge sources in terms of their microbiological and inorganic chemical content; (2) toxicological and chemical studies of ground water, reclaimed water, and other recharge sources to isolate and identify health-significant organic constituents; (3) percolation studies to evaluate the efficacy of soil in attenuating inorganic and organic chemicals in reclaimed water, (4) hydrogeological studies to determine the movement of reclaimed water through ground water and the relative contribution of reclaimed water to municipal water supplies; and (5) epidemiological studies of populations ingesting recovered water to determine if their health characteristics differed significantly from a demographically similar control population. The results of the Health Effects Study indicated that the risks associated with the three sources of recharge water (i.e., imported water, stormwater, and reclaimed water), were not significantly different and the historical proportion of reclaimed water used for replenishment had no measurable impact on either ground water quality or the health of the population ingesting the water (Nellor et al., 1984). The epidemiological study findings are weakened somewhat by recognition that the minimum observed latency period for human cancers that have been linked to chemical agents is about 15 years. Because of the relatively short time period that ground water containing a substantial proportion of reclaimed water had been consumed, it is unlikely that examination of cancer mortality rates would have detected an effect, if present, of exposure to reclaimed water. Based on the results of the Health Effects Study and recommendations of a state-sponsored Scientific Advisory Panel (State of California, 1987), authoriza-

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Ground Water Recharge Using Waters of Impaired Quality tion was given by the Los Angeles Regional Water Quality Control Board (LARWQCB) and DOHS in 1987 to increase the annual quantity of reclaimed water used for replenishment by approximately 50 percent to 50,000 acre-feet/ year over a period of 3 years, contingent upon the evaluation of data generated by an expanded monitoring program. Other requirements limited the total quantity of reclaimed water spread in any year to 50 percent of the total inflow to the basin and stipulated that the reclaimed water must meet all drinking water maximum contaminant levels and action levels (i.e., concentrations of contaminants in drinking water at which adverse health effects would not be anticipated to occur, based on an annual running average). Approval also was contingent on demonstration that there was no measurable increase in organic chemical contaminants in the ground water as the result of using reclaimed water for recharge. Since the initial authorization, three increments of 7,300 acre-feet/year have been implemented, increasing the quantity of reclaimed water for ground water recharge to 50,000 acre-feet/year, or approximately 30 percent of the total inflow to the Montebello Forebay. In 1991, the LARWQCB revised permit conditions to allow recharge of up to 60,000 acre-feet of reclaimed water in any one year as long as the running 3-year average does not exceed 150,000 acre-feet. This allowed for greater flexibility in spreading operations. The Montebello Forebay ground water recharge project includes extensive sampling and analysis of reclaimed water from the Whittier Narrows, San Jose Creek, and Pomona WRPs with similar monitoring of six shallow monitoring wells within the confines of the spreading grounds, 20 production wells in and around the spreading grounds, and ground water both upgradient and downgradient of the spreading grounds. The results of this combined monitoring program indicate that there has been no degradation of the ground water quality in terms of total dissolved solids, nitrogen, trace organics, heavy metals, or microorganisms (Hartling, 1993). Sampling and analysis of reclaimed water from each of the WRPs indicate that the WRPs consistently produce reclaimed water that does not contain measurable levels of viruses, contains less than 2.2 total coliform organisms/100 ml, and has an average turbidity of less than 2 NTU. Tables 2.8 and 2.9 in Chapter 2 provide water quality data from the three water reclamation plants that provide reclaimed water for recharge in the Montebello Forebay. In addition to providing a much-needed source of water for recharge, the use of reclaimed water is attractive from an economic standpoint. In 1992, WRDSC purchased reclaimed water from the Whittier Narrows WRP for $7per/acre-foot and reclaimed water from the San Jose Creek WRP for $11.56 per/acre-foot. Reclaimed water from the Pomona WRP that is not reused for other purposes, approximately 2,000 acre-feet, is captured for ground water recharge at no cost. The cost of the reclaimed water compares favorably to the seasonal storage rate of $130 per acre-foot for imported water purchased from the Metropolitan Water District of Southern California in 1992 (Hartling, 1993). The seasonal storage

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Ground Water Recharge Using Waters of Impaired Quality pounds widely used in the plastics industries, and polycyclic aromatic hydrocarbons, such as fluoranthene, pyrene, anthracene, chrysene, and benzo-a-pyrene, commonly associated with petroleum products (Wanielista et al., 1981; German, 1989). The quality of water in the Upper Floridan aquifer in the Orlando area also has been studied. Schiner and German (1983) concluded that drainage wells and upper-producing-zone supply wells yielded water very similar in chemical characteristics, particularly major dissolved constituents. Water in the upper producing zone of the Floridan aquifer is primarily a calcium and magnesium-bicarbonate type. Bicarbonate generally accounts for more than 75 percent of the ions, and calcium and magnesium account for more than 85 percent of the cations. But in several supply wells, and several drainage wells, more than 25 percent of the anions consisted of sulfate plus chloride, and more than 15 percent of the cations consisted of sodium plus potassium. Water from the lower producing zone (also a calcium and magnesium-bicarbonate type water) was more consistent within its chemical type. This consistency may be because most samples from the lower producing zone were clustered in a small part of the study area or it may be because the zone is deeper and more isolated from surface influences. The study also noted that water from drainage wells generally has slightly higher concentrations of most constituents than water from supply wells. The primary differences in water quality between drainage wells and supply wells were for total nitrogen, total phosphorus, total recoverable iron, and total coliform. The comparisons are shown in Table 6.5. For some supply and drainage wells, color, hydrogen sulfide, iron, and manganese in these studies exceeded the National-Secondary Drinking Water Regulations, with the frequency of exceedance greater for drainage wells than for supply wells. Concentrations of metals and pesticides did not exceed the limit specified in Florida standards for potable ground water. Pesticide did not appear to be present in significant amounts. Overall, the quality of water from the group of supply wells in the Orlando area is about the same as the quality of water from wells in adjacent areas where TABLE 6.5 Differences in Water Quality for Two Types of Wells in Orlando, Florida   Drainage Wells Supply Wells Total nitrogen 1.0 mg/l 0.29 mg/l Total phosphorus 0.23 mg/l 0.07 mg/l Total recoverable iron 660 mg/l 60 µg/l Total coliform 39 per 100 mg/l 0 per 100 ml   Source: Schiner and German, 1983.

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Ground Water Recharge Using Waters of Impaired Quality no drainage wells exist. Water quality for drainage wells that receive street runoff was about the same as water quality for drainage wells that receive lake overflow, except for bacteria colony counts. Bacteria counts were considerably lower in wells that receive lake overflow than in those that receive direct street runoff. Results of the Schiner and German (1983) study indicate that drainage well recharge has not caused widespread contamination of the Floridan aquifer. Bacterial contamination found in some drainage wells appears highly localized, and water from drainage wells would generally be acceptable for public supply use as long as bacteria are not present. Another study (Bradner, 1991) of 11 supply wells in urban Orlando, where the highest density of drainage wells exists, found calcium, potassium, sodium, chloride, and ammonia in significantly higher concentrations than is samples from hydrogeologically similar areas elsewhere. Significant differences in other constituents were not indicated. Hydraulics Specific capacity data under pumping conditions are available for 21 drainage wells. At pumping rates ranging from 240 to 460 gpm, the wells reportedly had specific capacities that ranged from 27 to 1,900 gpm/feet, with the median being 310 gpm/feet. The 23 mgd of recharge from the wells in the Orlando area has created a mound in the potentiometric surface of the Upper Floridan aquifer of 1.2 m (4 ft) (Tibbals, 1990). Economic and Institutional Considerations The stormwater used in the Orlando drainage wells does not receive any pre-recharge treatment except for that provided by detention in lakes for wens receiving lake overflow, and so pre-recharge treatment costs are limited. In addition, operating costs axe low because the system operates without attention except for the infrequent need to clean out accumulated debris and sediment from the wens in order to maintain their efficiency. Most drainage wells are owned by municipalities or the Florida Department of Transportation. They are regulated as Class V injection wells under the Safe Drinking Water Act. No new drainage wells are currently being permitted. Summary Drainage wells are the most economical way of disposing of stormwater in the internally drained karst environment of the Orlando area. The drainage wells emplace, by gravity injection, 23 mgd of recharge to the Upper Floridan aquifer, which helps to balance the 51 mgd of municipal ground-water pumpage in the Orlando area. Some drainage wells accept urban stormwater runoff directly

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Ground Water Recharge Using Waters of Impaired Quality from street drains, whereas others accept overflow from lakes into which stormwater has drained. Therefore, they introduce contaminants directly to one of the aquifers used for public supply in the area. Although some water quality effects have been noted, widespread contamination has not occurred, even though usage of drainage wells began in 1904. However, at least one plume of contaminated water in the vicinity of a drainage well is known. Spills of chemicals and/ or fuels caused by accidents along transportation routes are possible and pose a risk of introducing highly concentrated contaminants into the aquifer. Alternate means of stormwater disposal in this karst area would require extensive mink sewers and pumping at considerable cost. Moreover, loss of the recharge provided by the drainage wells would result in a reduction of head in the Floridan aquifer system and the possibility of vertical encroachment of deeper-lying saltwater into supply wells. The current level of risk of severely contaminating the potable source aquifer is accepted, but no new drainage wells are being permitted. DAN REGION WASTEWATER RECLAMATION PROJECT METROPOLITAN TEL AVIV, ISRAEL Where water is scarce, municipal wastewater can serve as an unconventional source of supply that can be integrated into the regional water supply system. In Israel, the increased demands for high-quality water and the shortage of natural water sources have resulted in the development of strategies to improve the quality of secondary effluent to make it suitable for nonpotable uses, especially unrestricted agricultural reuse. The best example of this approach is the Dan Region Wastewater Reclamation Project,* which provides for the collection, treatment, recharge, and reuse of the wastewater from the largest metropolitan area of the country, including Tel Aviv-Jaffa and several other neighboring municipalities. The project serves a total population of about 1.3 million with an average municipal wastewater flow of 72 million gallons per day. The recharge-recovery method developed and practiced in the Dan Region project relies on the soil-aquifer treatment (SAT) concept. Partially treated effluent percolates through the unsaturated sod zone (fine sand) until it reaches the ground water. Itmoves radially in the aquifer until it reaches recovery wells designed to pump the recharge water for supply (Figure 6.10). Depths for ground water range from 15 to 45 m (49 to 150 ft) for the various sites. Distances between recharge basins and recovery wells range from 320 to 1,500 m (1050 to 4900 ft). If the recovery wells are adequately spaced, the recharge and recovery facilities can be operated to confine the recharged effluent between the recharge *    The committee would like to thank M. Michail and A. Kanarek of Mekorot Water Co., Israel, for their efforts in compiling the information in this section.

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Ground Water Recharge Using Waters of Impaired Quality FIGURE 6.10 SAT system in the Dan Region project, Israel. areas and the recovery wells. This underground subbasin is dedicated to the treatment and storage of effluent and represents only a small percentage of the regional aquifer. The recharge water, which can be traced and monitored by means of observation wells, is usually of high quality. It is generally appropriate for industrial uses, unrestricted agricultural uses (including irrigation of vegetables to be eaten raw and livestock watering), nonpotable municipal uses, and recreational uses. Accidental drinking of recharge water does not present a significant health hazard because of its high microbiological quality. Recharge is done with spreading basins to take advantage of the purification capacity of both the unsaturated zone and the aquifer. Operation of the recharge basins is intermittent; flooding periods are alternated with adequate drying periods to maintain high infiltration rates and to allow oxygen penetration into the soil to enhance the purification capacity of the system. Although most of the purification takes place during vertical flow through the upper soil layer and the whole unsaturated zone, additional purification (mainly breakdown of slowly biodegradable organics) is gained during horizontal flow in the aquifer, and aerobic properties that were lost in sections where anoxic conditions prevail below the recharge basins are regained. System and Site Description Stage one of the Dan Region project has been in operation since 1977. For the first 2 years, the wastewater underwent biological treatment in oxidation

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Ground Water Recharge Using Waters of Impaired Quality ponds with recirculation and chemical treatment by the high lime-magnesium process; the water then moved to polishing ponds for partial free ammonia stripping and natural recarbonation. The combination of oxidation ponds and lime treatment is roughly equivalent to secondary treatment, although the effluent quality is different in some respects. In October 1989, chemical treatment was discontinued and the oxidation pond effluent was conveyed to the polishing ponds. Stage two of the project has been in operation since 1978. About 60 percent of this wastewater is conveyed to a mechanical-biological treatment plant, where it undergoes primary treatment and secondary treatment by activated sludge with nitrification-denitrification. The remainder goes through oxidation and polishing ponds, parallel to the mechanical-biological treatment plant. The long detention times in the polishing ponds produce a high-quality effluent with relatively low algae content. The recharge sites are located in areas of rolling sand dunes near the Mediterranean coast underlain by a calcareous sandstone aquifer—one of the three main potable water supplies of the country. The climate of the zone is typically Mediterranean. Summers are warm and dry, and winters are mild with rainy spells. The average annual precipitation is 500 to 600 mm (20 to 24 in). The average temperatures usually range between 20 and 30ºC in summer and between 10 and 20ºC in winter. The recharge operation in the second stage is carried out at two sites located south of the treatment plant. One recharge site consists of four basins covering a net area of about 59 acres; each basin is divided into four subbasins. The depth of the unsaturated zone below the recharge basins varies between 27 and 36 m (89 to 120 ft). A ring of recovery wells spaced 300 to 400 m apart surrounds the recharge areas on the northern, western, and southern sides; they are located between 320 and 1,100 m (1,050 to 3,600 ft) from the nearest recharge basin. At some locations, two separate wells are drilled to different subaquifers or to different layers of the same subaquifer. A monitoring network of 20 observation wells was established between the recharge basins and the recovery wells; they are located between 20 and 570 m (65 to 1,870 ft) from the recharge basins. The second recharge site consists of three basins covering a net area of about 44 acres; each basin is divided into three subbasins. The depth of the unsaturated zone below the recharge basins varies between 40 and 43 m (131 to 141 ft), and it is similar to the first recharge site. A ring of recovery wells surrounds the recharge areas located between 350 and 1,500 m (1,150 to 4,900 ft) from the nearest recharge basins. A monitoring network of 12 observation wells was established between the recharge basins and the recovery wells; they are located between 20 and 300 m (65 and 980 ft) from the recharge basins. The spreading basins are flooded intermittently to maintain high infiltration rates and to enhance effluent purification during percolation. The water depths in the basins are generally below 0.6 m (2.0 ft). A short recharge cycle is

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Ground Water Recharge Using Waters of Impaired Quality employed, usually consisting of 1 day flooding and 2 to 3 days drying, to ensure that aerobic conditions predominate in the unsaturated zone and in the aquifer. The clogging layer on the basin bottom may reach a thickness of about 1.5 cm (0.6 in). The clogging layer is ''scratched" about once a week or every 2 weeks, especially in the winter when drying is slow, and "shaved off" completely every 1 or 2 months to restore infiltration capacity. There is no accumulation of clogging material deeper in the soil. Soil-Aquifer Treatment The major purification processes occurring in the soil-aquifer system are slow-sand filtration, chemical precipitation, adsorption, ion exchange, biological degradation, nitrification, denitrification, and disinfection. To illustrate the purification effect of soil-aquifer treatment (SAT), quality data were evaluated for the mechanical-biological plant effluent (RE) before recharge and SAT and for the reclaimed water (RW) after SAT (Tables 6.6., 6.7, 6.8). TABLE 6.6 SAT Performance: Basic Wastewater Parameters (averages for 1990)   Units Before SAT (RE) After SAT (RW) Percentage Removal Suspended solids mg/l 17 0 100 Biochemical oxygen demand (BOD) mg/l 19.9 < 0.5 > 98 BOD filtered mg/l 3.1 < 0.5 > 84 Chemical oxygen demand (COD) mg/l 69 12.5 82 COD filtered mg/l 46 12.5 73 Total organic carbon mg/l 20 3.3 84 Dissolved organic carbon mg/l 13 3.3 75 UV 254 absorbance cm-1 × 103 298 64 79 KMnO4 as O2 mg/l 14.1 2.3 84 KMnO4 filtered as O2 mg/l 12.6 2.3 82 Detergents mg/l 0.5 0.078 84 Phenols /Jgll 8 < 2 > 75 Ammonia, as N mg/l 7.56 < 0.05 99 Kjeldahl nitrogen mg/l 11.5 0.56 95 Kjeldahl nitrogen filtered mg/l 10.2 0.56 95 Nitrate mg/l 2.97 7.17   Nitrite mg/l 1.24 0.10 92 Nitrogen mg/l 15.7 7.83 50 Nitrogen filtered mg/l 14.4 7.83 46 Phosphorus calcium rag/l 3.4 0.02 99 Alkalinity, as calcium carbonate mg/l 306 300 - pH - 7.7 7.9 -

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Ground Water Recharge Using Waters of Impaired Quality TABLE 6.7 SAT Performance: Bacterial and Viral Quality (averages for 1990)   Units Before SAT (RE) After SAT (RW) Total bacteria No./ml 110,000 288 Coliforms MPN/100 ml 1,100,000 0 E. coli MPN/100 ml 130,000 0 Streptococcus faecalis MPN/100 ml 29,000 0 Enteroviruses PFU/200 1 2 0 Note: PFU = plaque-forming units; MPN = Most Probable Number. Basic Wastewater Parameters The relatively high removal efficiency obtained for a variety of parameters confirms that SAT is an integral part of the municipal wastewater treatment process in the Dan Region project. The removal of suspended solids (mostly organics) and of biochemical oxygen demand was virtually complete. The average total and filtered chemical oxygen demand were reduced from 69 and 46 mg/ l respectively, to 12.5 mg/l in each case. Average total organic carbon and dissolved organic carbon were reduced from 20 and 13 mg/l respectively, to 3.3 mg/l. Ultraviolet absorbance was reduced significantly. The concentration of detergents was reduced from 0.5 to 0.08 mg/l, and that of phenols from 8 to less than 2 µg/l. Because of the efficient and reliable removal of organics, the soil-aquifer system can be regarded as a biological treatment unit. Total and filtered nitrogen were reduced from 15.7 and 14.4 mg/l, respectively, to 7.8 mg/l. Ammonia was reduced from 7.6 mg/l as nitrogen to less than 0.95 mg/l. While most nitrogen in the recharge water is found in the unoxidized forms of ammonia and organic nitrogen, the residual nitrogen in the well water consists essentially of nitrates. Thus complete nitrification and partial denitrification occur in the soft-aquifer system. Phosphorous removal efficiencies were 25 percent in the oxidation and polishing ponds and 74 percent in the mechanical-biological treatment plant. The remaining phosphorous was removed efficiently by SAT from 3.4 mg/l in the recharge water to 0.02 mg/l in the recovered water, a concentration is similar to that in the natural ground water. Coliform bacteria, E. coli, S. faecalis, and enteroviruses were not detected in the recovered water. Irrigation-Water Quality Parameters The salinity of the recovered water is acceptable for unrestricted irrigation of all crops. The sodium adsorption ratio (SAR) in the recovered water is similar to that of the recharge water (about 4.6), which is acceptable for unrestricted

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Ground Water Recharge Using Waters of Impaired Quality TABLE 6.8 SAT Performance: Irrigation Water Quality Parameters (averages for 1990)   Units After Before SAT (RE) SAT (RW) Percentage Removal Tolerance for water used continuously on all soilsa Salinity and Sodium           Hazard           Chloride mg/l 293 276     Dissolved Solids mg/l 1,033 1,033     Electrical conductivity µmhos/cm 1,642 1,597     Sodium mg/l 194 203     Potassium mg/l 23 16 30   Sodium absorption ratio   4.6 407     Trace Elements           Boron mg/l 0.5 0.45 10 0.75b 0.33c Cadmium µg/l < 1.3 < 0.2 85 10 Chromium µg/l < 16 4 < 75 100 Cobalt µg/l < 3 3   50 Copper µg/l 15 8 47 200 Fluoride mg/l 1.3 1.25 4 1,000 Iron µg/l 134 18 87 5,000 Lead µg/l < 5 < 3 40   Manganese µg/l 48 20 58 200 Molybdenum µg/l < 3 < 3   10 Nickel µg/l 33 11 67 100 Selenium µg/l < 1.6 < 1 38 20 a According to EPA criteria. b Recommended maximum concentration for irrigating citrus. c Boron Class I for sensitive crops according to U.S. Department of Agriculture.

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Ground Water Recharge Using Waters of Impaired Quality irrigation. The sodium concentration in the recovered water is similar to that of the recharge water (about 200 mg/l), so the cation exchange process was exhausted in the area surrounding the recharge basins. Adsorption of sodium and release of calcium and magnesium are still occurring in areas further away from the recharge basins. Potassium, which is found in relatively low concentrations in the recharge water, is still removed (30 percent) by SAT. Boron in the recharge water (0.5 mg/l) is only slightly removed (10 percent) by SAT. The concentrations of trace elements in the water after SAT are below the recommended maximum limits for irrigation water used continuously on all soils. Conveyance of Recovered Water for Agricultural Reuse Since November 1989, the recovered water from the Dan Region project has been transferred by a 100-kin-long (62.5-mile-long) conveyance main called the Third Line to a distribution net for irrigated areas in the southern part of Israel. At the head of the conveyance system, the recovered water is disinfected by chlorination. Along the Third Line, there are four open operational reservoirs, each with a capacity of 13 to 26 million gallons. The reservoirs are used to compensate for changes in water pressure in the main pipe and to facilitate control of the system during peak demand periods. The retention time of water in the reservoirs is not constant and depends on operational restrictions. The monthly consumption of the recovered water conveyed by the Third Line during 1991 has ranged from 2.6 to 29 million gallons. During 2 years of operation, about 44,000 million gallons reclaimed water from the Dan Region project was reused for unrestricted irrigation in the southern part of Israel. Summary The soil-aquifer treatment (SAT) system as applied in the Dan Region Project is an efficient, low cost process ($0.03/m3 for operation and maintenance only) for water reuse. Although the concentrations of several toxic substances in the recovered water are below the maximum permissible limits for drinking water, and turbidity is reduced by SAT, the recovered water is used only for nonpotable purposes. Overall, the recharge activities in the Dan Region illustrate how an unconventional source of water can be managed to increase the supply available for a variety of nonpotable uses. The very high quality of recovered water obtained after SAT makes the water suitable for agricultural uses (including unrestricted irrigation of vegetables to be eaten raw and livestock watering), industrial uses, nonpotable municipal uses (lawn irrigation and toilet flushing), and recreational uses. The main advantages of incorporating SAT are that it provides seasonal and multiyear underground storage, it is reliable, it provides a safety barrier, and it could lead to improved public acceptance of water reuse.

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Ground Water Recharge Using Waters of Impaired Quality REFERENCES Argo, D. G., and N. M. Cline. 1985. Groundwater Recharge Operations at Water Factory 21, Orange County, California. In Artificial Recharge of Groundwater, T. Asano ed. Boston, Mass.: Butterworth. Aronson, D. A., and G. E. Seabum. 1974. Appraisal of operating efficiency of recharge basins on Long Island, New York, in 1969. U.S. Geol. Surv. Water Supply Paper 2001-D, 22 pp. Baird, R. B. 1987. GC-Negative ion CIMS and Ames mutagenicity assays of resins in advanced wastewater treatment facilities. In Advances in Sampling and Analysis of Organic Pollutants from water, I. H. Suffer and M. Malaiyandi, eds. Vol. 2, American Chemical Society, Advances in Chemistry, Washington, D.C. Bouwer, E. J., P. L. McCarty, H. Bouwer, and R. C. Rice. 1984. Organic contaminant behavior during rapid infiltration of secondary wastewater at the Phoenix 23rd Avenue Project. Water Res. 18:463-472. Bouwer, H. 1992. Agricultural and municipal use of wastewater. Water Sci. Technol. 26:1583-1591. Bouwer, H., R. C. Rice, and E. D. Escarcega. 1974a. High-rate land treatment. L Infiltration and hydraulic aspects of the Flushing Meadows Project. J. Water Pollut. Contr. Fed. 46:835-843. Bouwer, H., J. C. Lance, and M. S. Riggs. 1974b. High-rate land treatment. II. Water quality and economic aspects of the Flushing Meadows Project. J. Water Pollut. Contr. Fed. 46:844-859. Bouwer, H., R. C. Rice, J. C. Lance, and R. G. Gilbert. 1980. Rapid-infiltration research—The Flushing Meadows Project, Arizona. J. Water Pollut. Contr. Fed. 52:2457-2470. Bouwer, H., and W. L. Chase, Jr. 1984. Water reuse in Phoenix, Arizona. Pp. 337-353 in Proceedings, Water Reuse Symposium III: Future of Water Reuse, San Diego, California, August 26-31. American Water Works Association. Bouwer, H., and R. C. Rice. 1984. Renovation of wastewater at the 23rd Avenue rapid-infiltration project. J. Water Pollut. Contr. Fed. 56:76-83. Bouwer, H. and Rice, R. C. 1989. Effect of water depth in groundwater recharge basins on infiltration. J. Irrig. and Drain. Engr., 115. 556-567. Bradner, L. A. 1991. Water quality in the upper Floridan aquifer in the vicinity of drainage wells, Orlando, Florida-U.S. Geol. Surv. Water Resour. Invest. Rep. 90-4175, 57 pp. Carlson, R. R., K. D. Lindstedt, E R. Bennett, and R. B. Hartman. 1982. Rapid infiltration treatment of primary and secondary effluents. J. Water Pollut. Contr. Fed. 54:270-280. Charbeneau, R. J. 1982. Groundwater resources of the Texas Rio Grande basin. Natur. Resour. J. 22(4):957-970. German, E. R. 1989. Quantity and quality of stormwater runoff recharged w the Floridan aquifer system through two drainage wells in the Orlando, Florida, area. U.S. Geol. Surv. Water Supply Paper 2344, 51 pp. Gilbert, R. G., C. P. Serba, R. C. Rice, H. Bouwer, C. Wallis, and J. L. Melnick. 1976. Virus and bacteria removal from wastewater by land treatment. Appl. Environ. Microbiol. 32:333-338. Hartling, E. C. 1993. Impacts of the Montebello Forebay Groundwater Recharge Project. Bull. Calif. Water Pollut. Contr. Assoc. 29(3):14-26. Kimrey, J. O. 1978. Preliminary appraisal of the geohydrologic aspects of drainage wells, Orlando area, central Florida. U.S. Geol. Surv. Water Resour. Invest. Rep. 78-37, 24 pp. Kimrey, J. O., and L. D. Fayard. 1984. Geohydrologic reconnaissance of drainage wells in Florida. U.S. Geol. Surv. Water Resour. Invest. Rep. 84-4021, 67 pp. Knorr, D. B. and T. Cliett. 1985. Proposed groundwater recharge at El Paso, Texas. In Artificial Recharge of Groundwater, T. Asano ed. Boston, Mass.: Butterworth. Ku, H. F. H., and D. L. Simmons. 1986. Effect of urban stormwater runoff on ground water beneath recharge basins on Long Island, New York. U.S. Geol. Surv. Water Resour. Invest. Rep. 85-4088, 67 pp.

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Ground Water Recharge Using Waters of Impaired Quality Lance, J. C., R. C. Rice, and R. G. Gilbert. 1980. Renovation of wastewater by soil columns flooded with primary effluent. J. Water Pollut. Contr. Fed. 52:381-388. Leach, L. E., C. G. Enfield, and C. C. Harlin, Jr. 1980. Summary of Long-term Rapid Infiltration System Studies. EPA-600/2080-165. U.S. Environmental Protection Agency. Ada, Okla. McCarty, P. L., M. Reinhard, N. L. Goodman, J. W: Graydon, G. D. Hopkins, K. E. Mortel-roans, and D. G. Argo. 1982. Advanced Treatment for Wastewater Reclamation at Water Factory 21. Techn. Paper No. 267. Department of Civil Engineering, Stanford University. Stanford, Calif. McCarty, P. L., B. E. Rittman, and E. J. Bouwer. 1986. Microbiological processes affecting chemcial transformations in groundwater. Pp. 89-116, in Groundwater Pollution Microbiology, G. Bitton and C. P. Gerba, eds. New York: John Wiley. Nellor, M. H., R. B. Baird, and J. R. Smyth. 1984. Health Effects Study—Final Report. NTIS No. PB-84191-568 County Sanitation Districts of Los Angeles County. Whittier, Calif. Orange County Water District. 1991. Groundwater Management Plan. Orange County Water District. Fountain Valley, Calif. Rice, R. C., and H. Bouwer. 1984. Soil-aquifer treatment using primary effluent. J. Water Pollut. Contr. Fed. 56:84-88. Rice, R. C., and R. G. Gilbert. 1978. Land treatment of primary sewage effluent: Water and energy conservation. Pp. 33-36 in Hydrology and Water Resources in Arizona and the Southwest. Tucson, Adz: University of Arizona Press. Schiner, G. R., and E. R. German. 1983. Effects of recharge from drainage wells on quality of water in the Floridan aquifer in the Orlando area, central Florida. U.S. Geol. Surv. Water Resour. Invest. Rep. 82-4094, 124 pp. Seabum, G. E., and D. A. Aronson. 1974. Influence of recharge basins on the hydrology of Nassau and Suffolk counties, Long Island, New York. U.S. Geol. Surv. Water Supply Paper 2031, 66 PP. Semmens, M. J., and T. K. Field. 1980. Coagulation: Experiences in organics removal. J. Am. Water Works Assoc. 72:476-483. Sloss, E. M. 1993. Epidemiological assessment of groundwater recharge with reclaimed water in Los Angeles County. Proposal No. 93-019, submitted to the Water Replenishment District of Southern California by RAND, Santa Monica, Calif. State of California. 1987. Report of the Scientific Advisory Panel on Groundwater Recharge with Reclaimed Wastewater. Prepared for the California State Water Resources Control Board, Department of Water Resources, and Department of Health Services. Sacramento, Calif. Stringfield, V. T. 1933. Ground-water investigations in Florida. Flor. Geol. Surv. Geol. Bull. 11, 33 PP. Thurman, E. M. 1979. Isolation, Characterization, and Geochemical Significance of Humic Substances from Groundwater. Ph.D. dissertation. University of Colorado, Boulder, Col. Tibbals, C. H. 1990. Hydrology of the Floridan aquifer system in east central Florida. U.S. Geol. Surv. Prof. Paper 1403-E, 98 pp. U.S. Environmental Protection Agency. 1992. Guidelines for Water Reuse. Technology Transfer Manual EPA/625/R-92/004. U.S. Environmental Protection Agency. Washington, D.C. 247 pp. Wanielista, M. P., Y. A. Yousef, and S. J. Taylor. 1981. Stormwater Management to Improve Lake Water Quality. Submitted to Municipal Environmental Research Laboratory, Edison, N.J. Orlando, Fla.: University of Central Florida. 225 pp. Wesner, G. M. 1991. Annual Report, Orange County Water District Wastewater Reclamation and Recharge Project, Calendar Year 1990. Prepared for Orange County Water District, Fountain Valley, Calif.