Increasing water demands in light of limited water resources have intensified exploitation and drawdown of groundwater. On the other hand, rising water demand has accelerated wastewater production. Therefore, urban wastewater management via artificial recharge may play a significant role in aquifer management. While site selection for artificial recharge projects is a major challenge, fuzzy logic provides one of the most viable approaches for this purpose. Considering the high volume of wastewater production in Tehran, Iran, the present study investigated the efficient use of this source for recharging the Tehran-Shahriar aquifer. First, effective wastewater and recharge factors were identified. Next, fuzzy logic was used to assign appropriate weights to data layers. Then, the selected layers were merged to produce an artificial recharge location map. The results showed that the identified areas were sufficiently vast to recharge the planned volumes of treated wastewater. However, the identified areas and the gradient of groundwater flow will limit the positive impacts of recharge on the aquifer. All in all, the fuzzy site selection model implemented via geographical information system is an efficient tool to identify suitable sites for artificial recharge of aquifers with treated wastewater.

INTRODUCTION

In many parts of the world, groundwater is the most important fresh water resource. Excessive exploitation of this valuable but limited resource to meet residential, industrial, and agricultural consumption has caused the rate of aquifer depletion to be far greater than groundwater's natural recharge rate. Ground subsidence, reduced quality of groundwater resources, reduced agricultural yield, and the encroachment of salt water in coastal aquifers are several consequences of excessive exploitation of groundwater (Agarwal et al. 2013).

Artificial recharge operates as a protective mechanism that prevents groundwater level to fall due to excessive exploitation. Besides seasonal floods and surface runoff, treated wastewater can also be used as a source of water for artificial recharge. However, accurate determination of suitable locations for artificial recharge is one of the fundamental requirements for recharge projects. Classical site selection approaches cannot reflect the uncertainties involved with the effective factors. In contrast, fuzzy logic approach allows the user to employ relatively uncertain information in their analysis. Such features have made the fuzzy multi-criteria decision-making methods more popular than their classical counterparts (Amiri 2010; Cavallaro 2010).

There have been several studies on the application of geographical information system (GIS)-based methods for finding optimally located sites for artificial recharge projects (Chowdhury et al. 2010; Nirmala et al. 2011; Agarwal et al. 2013; Senanayake et al. 2016). However, in these studies, the use of treated wastewater as an alternative resource of groundwater recharge has received limited attention. Kallali et al. (2007) studied the utilization of treated wastewater for artificial recharge of an aquifer located in the Cap Bon peninsula, Tunisia. They used a multi-criteria decision-making method based on GIS and by taking into account the technical, economic, social, and environmental criteria. This study found that soil type and economic factors were the most and the aquifer depth was the least restrictive criteria.

In one recent study, Zaidi et al. (2015) used GIS and Boolean logic to identify potential artificial groundwater recharge zones in northwestern Saudi Arabia. In this study, thematic maps of various factors such as slope, soil texture, vadose zone thickness, groundwater quality (total dissolved solids), and type of water bearing formation were integrated to classify the areas suitable for recharge. Treated wastewater and excess desalinated sea water were also considered as potential sources of recharging groundwater. On the basis of the potential artificial groundwater recharge zones’ closeness to the available recharge water supply, potential zones were partitioned into high priority and low priority.

In another recent study, Yeh et al. (2016) proposed an integrated approach for assessing the characteristics of groundwater recharge using a GIS technique for the Hualian River watershed, eastern Taiwan. They produced a map of potential groundwater recharge for this mountainous basin. The results indicated that in the zone with the most effective groundwater recharge potential, the gravelly stratum and the concentration of drainage also helped the streamflow to recharge the groundwater system.

The Tehran-Shahriar plain in Iran lies over an extensive area covered with residential, agricultural, and industrial zones. Excessive groundwater withdrawal for meeting water demand is the main cause of plain subsidence. The magnitude of subsidence varies with location on the plain but the general pattern is V-shaped, with the maximum subsidence rate being estimated to about 16 cm per year (Geological Survey & Mineral Exploration 2005). Examining the time evolution of aquifer quality shows that fluctuations of qualitative parameters such as sulfate, chloride, bicarbonate, and electrical conductivity are generally concurrent and lead to no significant change (Mahab Ghodss 2008).

In the present study, the potential locations for artificial recharge of the Tehran-Shahriar groundwater aquifer were studied. Considering the role of this aquifer as a strategic water supply source, its management is pivotal in ensuring system stability, especially under drought conditions. Besides technical and economic criteria, environmental and social factors were also incorporated into the current study. All spatial operations were conducted using GIS-based fuzzy logic for integration of data layers.

With respect to quality aspects, municipal wastewater has high biological oxygen demand and chemical oxygen demand, nutrition elements, and pathogenic microorganisms. However, there is no concern over doses of heavy metals in Tehran's municipal wastewater. As a result, wastewater will be treated such that concentrations of nutrients, dissolved organic materials, and other elements meet the standard requirements listed in the Appendix, Table A1, available with the online version of this paper (Management & Planning Organization 2010).

STUDY AREA

Similar to many metropolises around the world, Tehran is confronted with increasing demand for fresh water and limited water resources. In recent years, groundwater aquifers have found a growing role as a major source of water supply, especially as the result of factors such as the occurrence of drought periods and increased water demand due to growth in residential, industrial, and agricultural sectors, landscaping, and all dependent services. Due to the imbalance between the rate of natural recharge and withdrawal from the Tehran-Shahriar aquifer, which has led to the decline in groundwater level, adequate planning and management of water resources to address the adverse effects of aquifer shrinkage have become more important. Effluent obtained from urban wastewater treatment plants (WWTPs) can be considered as a potential water resource. Wastewater treatment can also reduce the adverse environmental impacts that result from wastewaters left untreated.

This research studies the zone within and in close proximity to Tehran-Shahriar plain located in the southern foothills of the central Alborz Mountains in north-central parts of the Iranian plateau, within the geographic coordinates of 50°, 45′ to 51°, 40′ east longitude and 35°, 6′ to 35°, 50′ north latitude. The area of the studied groundwater aquifer is 2,060 km2. The minimum, maximum, and average heights of the watershed are 820, 1,777 and 1,098 m, respectively. Mean annual precipitation of this area is 215 mm and its mean annual temperature is 16.8 °C. This aquifer system consists of hydro layers, permeable and non-permeable layers, and mainly quaternary alluvial sediments of type D (Figure 1).
Figure 1

Location of study aquifer on map of Iran.

Figure 1

Location of study aquifer on map of Iran.

In recent years, there has been a significant shrinkage in the volume of this aquifer which is mainly due to long-term droughts and lack of balance between withdrawals from the aquifer and its natural recharge rate. Figure 2 shows the iso-decline contour lines of this aquifer for the years 2001–2011. It can be seen that some areas of the plain have experienced an up to 50 m drop in groundwater level.
Figure 2

Iso-decline map of the plain aquifer for 2001–2011.

Figure 2

Iso-decline map of the plain aquifer for 2001–2011.

METHODOLOGY FOR OPTIMAL LOCATION SELECTION

The strategy followed by this study is to use treated wastewater as an unconventional water source to balance the aquifer of the study area. In addition to environmental requirements, proper site location prerequisite to feasible execution of aquifer recharge plans with maximum effectiveness is another matter of great importance. Based on existing plans, 290 million cubic meters (per year) of wastewater treated by five urban WWTPs is planned to be utilized as the source of artificial recharge of the studied aquifer. Figure 3 shows the location of WWTPs, drinking water wells outside the metropolitan area, and the road network in and around the perimeters of the study area.
Figure 3

Location of WWTPs in the study area.

Figure 3

Location of WWTPs in the study area.

In this study, fuzzy logic was used to determine the locations most suited for implementation of artificial recharge projects through a surface water spreading technique; this technique is based on two principles: (a) prioritization of preliminary maps in the order of their importance; and (b) assigning a score between 0 and 1 to each map based on its importance for the purpose of the study (Juang et al. 1992).

In mathematics, fuzzy sets are defined as a set wherein each element has a degree of membership. The fuzzy set theory allows the elements to have different grades of membership; this concept is realized with the aid of a membership function-value in the real unit interval [0, 1].

To determine the best locations for recharge of an aquifer with respect to a set of factors, the layers expressing the information related to those factors must be overlaid and integrated. Among different types of fuzzy logic membership functions (operators) available for this task (SUM, PRODUCT, AND, GAMMA, and OR), this study used the gamma function for this purpose. This function is defined in terms of fuzzy sum and fuzzy product as shown in Equation (1): 
formula
1
where μCombination denotes the gamma fuzzy function and γ is a value chosen between 0 and 1. Careful selection of γ leads to the generation of outputs that represent a flexible compromise between the ‘increasing’ tendencies of the fuzzy algebraic sum and the ‘decreasing’ effects of the fuzzy algebraic product (Bonham-Carter 1991). Smaller weights of gamma lead to an overlay more similar to the product operator while larger weights cause the overlay to become more similar to the sum operator. In this study, the value of γ was selected to be 0.7. Figure 4 illustrates the flowchart of the method used in this study to determine the suitable locations for recharge of aquifers by treated wastewater. The steps are as follows:
  • Evaluation and selection of effective factors (technical, social, economic, and environmental) in artificial recharge of groundwater with treated wastewater.

  • Data collection and construction of spatial database in GIS.

  • Definition of membership functions and determining the degree of membership.

  • Storage of fuzzy maps.

  • Overlay of data layers via the gamma fuzzy operator.

  • Producing map of potential sites for artificial recharge of groundwater with effluent.

Figure 4

Flowchart of the method proposed for determination of suitable locations for artificial recharge of aquifers by treated wastewater.

Figure 4

Flowchart of the method proposed for determination of suitable locations for artificial recharge of aquifers by treated wastewater.

Table 1 lists the parameters related to technical, economic, environmental, and social criteria. Membership degree of each parameter was determined based on results of previous studies, consultation with experts, and trial and error.

Table 1

Criteria and parameters used for determination of suitable locations for recharge of aquifers by wastewater

Criteria Parameters Objective 
Technical Hydraulic gradient of groundwater Examining the technical aptness of different areas for recharge of the aquifer 
Transmissibility coefficient of the aquifer  
Thickness of the aquifer  
Land use  
Minimum area of land required for artificial recharge  
Environmental Distance of supply sites from the location of drinking water wells Ensuring compliance with environmental standard of using wastewater in recharge of aquifers 
Vertical distance from the level of groundwater table  
Social Distance from highways and freeways Preventing health risks induced by contact with treated wastewater 
Distance from residential areas   
Economic Distance of site of recharge from WWTPs Examining the economic limitations on location of recharge site 
Elevation difference between WWTPs and site of recharge  
Distance of recharge site from the rivers  
Criteria Parameters Objective 
Technical Hydraulic gradient of groundwater Examining the technical aptness of different areas for recharge of the aquifer 
Transmissibility coefficient of the aquifer  
Thickness of the aquifer  
Land use  
Minimum area of land required for artificial recharge  
Environmental Distance of supply sites from the location of drinking water wells Ensuring compliance with environmental standard of using wastewater in recharge of aquifers 
Vertical distance from the level of groundwater table  
Social Distance from highways and freeways Preventing health risks induced by contact with treated wastewater 
Distance from residential areas   
Economic Distance of site of recharge from WWTPs Examining the economic limitations on location of recharge site 
Elevation difference between WWTPs and site of recharge  
Distance of recharge site from the rivers  

Technical criteria

Four technical criteria were considered: hydraulic gradient of the aquifer, aquifer transmissibility coefficient, thickness of the aquifer, and land use. To determine the optimum values of parameters to be used in membership functions, both trial-and-error and expert views were used.

Hydraulic gradient of the aquifer

Factors changing the hydraulic gradient of an aquifer generally include relative variations of the topographic gradient in different parts of the plain, difference in granulation of sediments at different parts, shape, and gradient of the bedrock, and recharge and discharge conditions. Direction and gradient of the water table are important because they determine the direction of flow in the aquifer. Data pertaining to 22 piezometric wells were used to prepare the equipotential plot of the aquifer, which was then used to determine the flow direction at the study area. Figures 5 and 6 show the flow direction and gradient of groundwater. The greater groundwater gradients lead to faster inflow of water from recharge basins into the aquifer. In the membership function of this parameter, the gradients of more than 1% were considered to indicate the suitability of the location for recharge, and their membership degree was set to 1. Those points having a gradient of less than 1% were attributed to a 0 to 1 membership value determined by a linear function.
Figure 5

Map of the groundwater flow direction in the study area.

Figure 5

Map of the groundwater flow direction in the study area.

Figure 6

Map of the groundwater gradient in the study area (in percent).

Figure 6

Map of the groundwater gradient in the study area (in percent).

Aquifer transmissibility coefficient

Transmissibility coefficient is one of the important hydrodynamic parameters of aquifers and depends on the state, shape, and form of granulation as well as thickness of the aquifer. This parameter was calculated with the help of data acquired from exploration and operational wells. When defining the membership degrees of this parameter, areas with transmissibility of more than 1,000 m2 per day were attributed with the membership degree of 1, areas with transmissibility of less than 800 m2 per day were attributed with the membership degree of 0. For areas with transmissibility of intermediate range, a 0 to 1 membership degree determined by a linear function was considered.

Thickness of the aquifer

After examining the results of geoelectrical studies, the thickness of the aquifer within perimeters of the study area was estimated to vary from 15 to 400 m and an average thickness of the aquifer was estimated to 115 m. Thus, when defining the membership degrees of this parameter, membership degree of areas with a thickness of fewer than 50 m was set to 0 and membership degree of those with a thickness of more than 100 m was set to 1. As before, for areas with a thickness of more than 50 m but less than 100 m, a 0 to 1 membership degree determined by a linear function was considered.

Land use

Examination of land use maps yielded 10 different types of land use (hereafter referred to as LU) in the study area. After investigating the study area in regard to the aptitude of each LU to act as a potential recharge site, membership degree of each LU class was set to a value between 0 and 1 (Table 2). Considering the impossibility of using urban spaces (due to dense population) and areas in the immediate vicinity of airports and roads as recharge sites, the membership degree of these LU classes was set to 0. In other cases, membership degree was assigned by taking into account the type of land use and also the possibility of taking the ownership of the land for executing required plans.

Table 2

Membership degree of the membership function parameters for land use

Parameter City Airport Road Garden Forest Agriculture
 
Grassland
 
Barren land 
Irrigated Rainfed Average Poor 
Membership degree 0.1 0.1 0.4 0.5 0.6 
Parameter City Airport Road Garden Forest Agriculture
 
Grassland
 
Barren land 
Irrigated Rainfed Average Poor 
Membership degree 0.1 0.1 0.4 0.5 0.6 

The implementation of artificial recharge projects requires the presence of conditions and prerequisites such as sufficient land area with appropriate specifications in addition to other considered criteria. Thus, the land area required for the desired volume of treated wastewater to be fed into the aquifer through spreading technique is of great importance. Equation (2) was used to determine the minimum area required to process the targeted volume of treated wastewater (USEPA 2006): 
formula
2
where A is the required area (hectare), Q is the volume of wastewater to be used as a source of artificial recharge (cubic meters per day), and Lw is the annual hydraulic head (meters per year). Based on the volume of wastewater targeted to be produced by five urban WWTPs and be fed into the aquifer (290 million cubic meters per year) and the hydraulic head of 0.5 m per day, the area of land required for implementation of the project was set to 159 ha.

Environmental and social criteria

Environmental criteria

To ensure compliance with environmental standards, the process of using treated wastewater as a source of aquifer recharge was designed by following the guidelines proposed by USEPA. USEPA states that in the indirect use of treated wastewater for aquifer recharge through spreading technique, the conditions of the minimum horizontal distance of 150 m from drinking water wells and minimum vertical distance of 2 m from groundwater table should be complied with (USEPA 2004). In accordance with these conditions, the membership degrees of areas with the horizontal distance of less and more than 150 m were set to, respectively, 0 and 1. A map of groundwater depth was assessed to investigate the compliance with the condition of vertical distance from the groundwater table. Since the groundwater depth in all areas of the plain is more than 2 m, there are no limits in terms of vertical distance from the groundwater table (Figure 7).
Figure 7

Map of groundwater table in the study area (in meters).

Figure 7

Map of groundwater table in the study area (in meters).

Social criteria

The necessity to ensure compliance with the conditions of keeping the minimum distance from highways, freeways, and residential areas defined to prevent adverse biological hazards resulting from contact with raw wastewater was formulated as social criteria. The minimum distance highways and freeways was considered to be 400 m (Washington State Department of Health 1994). Thus, in membership function of this factor, membership degree of areas distanced less than 400 m away from highways and freeways was set to 0. However, the minimum distance between the potential recharge site and residential areas was considered to be 200 m (Kallali et al. 2007). Thus, membership degree of areas distanced less than 200 m away from residential spaces was considered to be 0. Naturally, membership degree of any area meeting none of the above-mentioned conditions was set to 1.

Economic criteria

Three economic criteria, namely distance from WWTPs, elevation difference between WWTPs and recharge site, and distance from surface resources were considered.

Distance from WWTPs

The cost of transferring treated wastewater from WWTPs to the site of artificial recharge depends directly on their distance. Thus the length of water transmission line and the resulting costs will affect the project's economic feasibility. In this study, the membership degree of areas distanced less than 3 km away from treatment plants was set to 1, as this distance was considered appropriate for the project's purpose. The membership degree of areas distanced 3 to 5 km away from treatment plants was determined with a linear function, and the membership degree of areas distanced more than 5 km away was set to 0. The best values were determined through trial and error and expert suggestions.

Elevation difference between WWTPs and recharge site

It is clear that higher elevation of recharge site with respect to elevation of WWTPs results in further costs arising from the construction of pumping stations as well as the energy required for wastewater transmission. In this study, the elevation difference of 15 m was considered as optimum, as proposed by Kallali et al. (2007). Thus, the membership degree of areas with an elevation difference of less than 15 m was set to 1, the membership degree of areas with an elevation difference of 15 to 20 m was determined by a linear function, and that of areas with an elevation difference of more than 20 m was set to 0.

Distance from surface resources

Artificial recharge can also be conducted through river banks and beds of seasonal rivers, and using this approach involves paying less or no expense for the purchase of land in and around these areas, so the distance from these areas was also considered as an economic criterion. It should be reiterated that the wastewater treated by urban WWTPs will have the necessary standards to be released into surface water sources. To determine the membership degree of this criterion, the areas distanced less than 300 m away from the axis of rivers were considered as primary flood plains, most appropriate for the project's purpose, thus, their membership degree was set to 1. The areas distanced 300 to 500 m away from the axis of rivers were considered as secondary flood plains, and considering the higher price of these lands, their membership degree was determined by a linear function with results ranging from 0 to 1. The membership degree of areas distanced more than 500 m away from rivers was set to 0.

Membership functions related to technical, environmental, social, and economic criteria considered for locating the site of artificial recharge by treated wastewater acquired from urban WWTPs are presented in Table 3.

Table 3

Membership functions considered for technical, environmental, social, and economic criteria used to locate the site of artificial recharge

Criteria Parameters Membership functions Parameters Membership functions 
Technical Gradient of groundwater (%)  Thickness of aquifer (m)  
Aquifer transmissibility coefficient (m2/day)  Land use  
Environmental Horizontal distance from drinking water wells (m)  Vertical distance from the groundwater table (m)  
Social Distance from highways (m)  Distance from residential areas (m)  
Economic Distance from WWTPs (m)  Distance from the streams (m)  
Elevation difference with respect to WWTPs (m)    
Criteria Parameters Membership functions Parameters Membership functions 
Technical Gradient of groundwater (%)  Thickness of aquifer (m)  
Aquifer transmissibility coefficient (m2/day)  Land use  
Environmental Horizontal distance from drinking water wells (m)  Vertical distance from the groundwater table (m)  
Social Distance from highways (m)  Distance from residential areas (m)  
Economic Distance from WWTPs (m)  Distance from the streams (m)  
Elevation difference with respect to WWTPs (m)    

INTEGRATION OF DATA LAYERS

The results of data layers’ integration performed to determine the potential locations for artificial recharge of the studied aquifer are shown in Figures 811. Figure 8 displays the map obtained by integration of data layers associated with different criteria (technical, environmental, social, and economic) and the locations determined as suitable for the site of artificial recharge. It can be seen that three zones with a total area of 1,000 ha exhibit the characteristics required from the site of artificial recharge. Comparing the area of these locations with the minimum required area calculated in the section ‘Technical criteria’ (159 ha) shows the adequate area of the locations suggested for artificial recharge. Nevertheless, after overlaying the position of these sites on the map of groundwater flow direction, it was found that implementation of artificial recharge at these locations will affect only 13% of the total 2,060 km2 area of the aquifer, i.e., the groundwater level will rise only in these limited ranges of areas. The rest of the areas are located in the upstream of designated sites, and because of the direction of groundwater gradient cannot be affected by artificial recharge. To explore the possibility of optimal utilization of planned volume of treated wastewater for artificial recharge of the aquifer, the economic criteria were examined in three scenarios:
  • 1. The absence of any restriction on elevation difference, i.e., on the costs pertaining to pumping operation.

  • 2. The absence of any restriction on the costs arising from building transmission lines from the treatment plants to recharge locations.

  • 3. The absence of all restrictions mentioned in clauses 1 and 2 (Figures 911).

Figure 8

Locations determined as suitable for artificial recharge of groundwater by treated wastewater, obtained with respect to all conditions listed in Table 3.

Figure 8

Locations determined as suitable for artificial recharge of groundwater by treated wastewater, obtained with respect to all conditions listed in Table 3.

Figure 9

Locations determined as suitable for artificial recharge of groundwater subject to relaxation of constraints on the cost of pumping operation.

Figure 9

Locations determined as suitable for artificial recharge of groundwater subject to relaxation of constraints on the cost of pumping operation.

Figure 10

Locations determined as suitable for artificial recharge of groundwater subject to relaxation of constraints on the cost of transmission lines.

Figure 10

Locations determined as suitable for artificial recharge of groundwater subject to relaxation of constraints on the cost of transmission lines.

Figure 11

Locations determined as suitable for artificial recharge of groundwater subject to relaxation of constraints on the cost of transmission lines and pumping operation.

Figure 11

Locations determined as suitable for artificial recharge of groundwater subject to relaxation of constraints on the cost of transmission lines and pumping operation.

Based on the obtained results, in the scenario where there is no economic restriction for pumping operation, the recharge project will be able to be implemented in 5,400 ha of the area (Figure 9). In this scenario, the direction of groundwater flow will allow the project to affect 30% of the aquifer area. In the second scenario, where there is no restriction on the costs of transmission lines and thus on the distance of recharge sites from WWTPs, the results indicate that an area of approximately 1,900 ha will have the required potential for artificial recharge (Figure 10). In the third scenario, however, this area is about 15,000 ha (Figure 11). The portion of the aquifer affected by recharge projects defined in the second and third scenarios was estimated to be 20% and 50%, respectively.

DISCUSSION AND CONCLUSION

Results and discussion

According to the flow direction and gradient maps, the general flow direction is from the higher grounds in the north towards the southern and southeastern regions. Also, the gradient of the groundwater table in the studied aquifer varies between 0.0006 and 4.76%, with northern parts showing higher gradients and southern areas exhibiting lower gradients. According to the existing studies, transmissibility coefficient of the studied aquifer was estimated to a range of 284 to 3,400 m2 per day, with the highest values obtained for the central part, and lower values obtained for the southern areas.

Based on the obtained results, the locations determined as suitable for the artificial recharge with treated wastewater (290 million cubic meters per year) can provide the land area required (159 ha) for implementation of this project. Nevertheless, the combination of the geographic position of these locations and gradient of groundwater flow beneath them will limit the positive impacts of recharge project on the aquifer.

After incorporating all technical, economic, environmental, and social parameters and integrating the resulting data layers, areas determined as suitable for artificial recharge project were mostly observed in the southern plains. The implementation of artificial recharge with wastewater was estimated to influence about 13% of the aquifer area. In this case, the downstream position of determined locations with respect to the direction of groundwater flow prevents 87% of the aquifer to be affected by the project.

The results showed that among all aspects of a project, economic factors leave the most significant impacts on the location of potential sites of artificial recharge. This result is consistent with the results of Kallali et al. (2007). The costs arising from construction and operation of pumping stations and construction of transmission lines from the treatment plants to the recharge locations are among the main economic constraints of work, but to explore the possibility of maximum utilization of artificial recharge and under the assumption of accepting financial loss, the above constraints were relaxed in three extra scenarios. The results showed that even in the absence of restrictions on the costs arising from pumping operation and transmission lines, in spite of having access to vast areas for implementation of artificial recharge project, this implementation will only affect about 50% of the aquifer area.

Despite providing access to an adequate area for implementation of artificial recharge, the scenario where there was no economic restriction on building and operating the pumping stations and the other scenario where there was no economic restriction on construction of transmission lines from treatment plants to recharge sites led to change in water level of, respectively, 30% and 20% of aquifer area. In the scenario where there is no limitation for pumping operation, the identified zones would be at higher elevations and the direction of groundwater flow would be more suitable, thus a greater area of the aquifer could be affected. However, it is observed that the selected areas are located in the central plains (Figure 9). To provide better conditions for the implementation of artificial recharge of aquifer projects with treated wastewater and to increase the efficiency, in addition to neglecting the pumping limitations, the constraints related to the construction of transmission lines from the WWTPs should also be discarded.

According to the results, due to several restrictions in artificial recharge of groundwater with wastewater via water spreading technique, even accepting severe financial losses incurred by uneconomic construction and operation of pumping stations and transmission lines cannot push the projects to affect a major area of the aquifer. Thus, with the continued absence of balance between withdrawals from the aquifer and its natural rate of recharge, most of the aquifer will be faced with serious problems.

CONCLUSIONS

In this study, the optimal location for artificial recharge of the Tehran-Shahriar aquifer from WWTPs was analyzed. The wastewater treated by WWTPs, whose volume was calculated to be 290 million cubic meters per year, was intended to be used as the source of groundwater recharge, so in addition to performing technical and economic studies on this project, its compliance with environmental and social factors was also taken into account. To investigate further the aptness of locations as the site of artificial recharge, in addition to technical, environmental, and social criteria, three extra scenarios of economic conditions were also evaluated. A fuzzy logic approach, which was based on membership degrees defined separately for each parameter, was used to integrate the data layers developed in a GIS environment. Based on the obtained results, to maximize the effects of artificial recharge project on rehabilitation of the aquifer, the recharge operations must be executed at upstream areas exhibiting good dispersion effects. However, the restrictions associated with technical, economic, social, or environmental criteria may limit the options regarding the location of recharge sites.

Based on the results of this research, the treatment plants should be located – as much as possible – at higher elevations, not only to reduce the costs associated with the transfer of treated wastewater to target recharge areas, but also to provide the possibility of covering a wider area of the aquifer to be recharged.

Construction of low-capacity local treatment plants in urban areas using wastewater treatment packages and in accordance with environmental standards can be considered as an alternative to the use of large centralized treatment plants. In this case, the use of treated wastewater for non-drinking water demands, e.g., for landscaping and industries, can be a proper substitute for withdrawal of groundwater, and can therefore contribute significantly to restoring the balance of the aquifer. All in all, the fuzzy logic model implemented in the GIS is an efficient tool to select suitable sites for artificial recharge of aquifers with treated wastewater.

REFERENCES

REFERENCES
Agarwal
R.
Garg
P. K.
Garg
R. D.
2013
Remote sensing and GIS based approach for identification of artificial recharge sites
.
Journal of Water Resources Management
27
,
2671
2689
.
Amiri
M. P.
2010
Project selection for oil-fields development by using the AHP and fuzzy TOPSIS methods
.
Journal of Expert Systems with Applications
37
,
6218
6224
.
Bonham-Carter
G. F.
1991
Geographic Information System for Geoscientists: Modeling with GIS
.
Pergamon, Ontario
,
Canada
.
Geological Survey & Mineral Exploration
2005
Investigation of Tehran-Shahriar Plain's Subsidence
.
Islamic Republic of Iran
.
Juang
C.
Lee
D.
Sheu
C.
1992
Mapping slope failure potential using fuzzy sets
.
Journal of Geotechnical Engineering
118
,
475
494
.
Kallali
H.
Anane
M.
Jellali
S.
Tarhouni
J.
2007
GIS-based multi-criteria analysis for potential wastewater aquifer recharge sites
.
Journal of Desalination
215
,
111
119
.
Mahab Ghodss Consulting Engineering Company
2008
Tehran-Karaj Groundwater Studies
.
Tehran
,
Iran
.
Management and Planning Organization
2010
Water Reuse and Effluent Environmental Standards
.
Publication No. 535
,
Tehran
,
Iran
.
Nirmala
R.
Shankara
M.
Nagaraju
D.
2011
Artificial groundwater recharge studies in Sathyamangalam and Melur villages of Kulathur Taluk, Pudukottai district, Chennai, using GIS techniques
.
International Journal of Environmental Sciences
1
,
1592
1608
.
Senanayake
I. P.
Dissanayake
D. M. D. O. K.
Mayadunna
B. B.
Weerasekera
W. L.
2016
An approach to delineate groundwater recharge potential sites in Ambalantota, Sri Lanka using GIS techniques
.
Journal of Geoscience Frontiers
7
,
115
124
.
United States Environmental Protection Agency (USEPA)
2004
Guidelines for Water Reuse
.
Washington, DC
,
USA
.
United States Environmental Protection Agency (USEPA)
2006
Process Design Manual for Land Treatment of Municipal Wastewater Effluents
.
Cincinnati, OH
,
USA
.
Washington State Department of Health
1994
Design Criteria for Municipal Wastewater Land Treatment Systems for Public Health Protection
.
WA, USA
.
Yeh
H. F.
Cheng
Y. S.
Lin
H. I.
Lee
C. H.
2016
Mapping groundwater recharge potential zone using a GIS approach in Hualian River, Taiwan
.
Journal of Sustainable Environment Research
26
,
33
43
.
Zaidi
F. K.
Nazzal
Y.
Ahmed
I.
Naeem
M.
Jafri
M. K.
2015
Identification of potential artificial groundwater recharge zones in Northwestern Saudi Arabia using GIS and Boolean logic
.
Journal of African Earth Sciences
111
,
156
169
.

Supplementary data