Abstract
This paper aims to understand the general background of groundwater quality that must be considered for the 'smart city' planning of Surat city. Twenty-Six water samples collected from bore wells of the city were analyzed. The results showed that water is alkaline, as pH varies from 7.6 to 9.2. The concentration of Cl− and Na+ are correlated with EC. The highest levels of Cl− and Na+ are found near the coastal region (predominantly northwestern); Piper trilinear diagram shows 52% of samples are Na-HCO3− type and 48% NaCl type. WQI shows that most samples are potable for drinking, but a few samples from the western part are not suitable for drinking. SAR, Na%, and PI results show that most samples are suitable for irrigation. The corrosivity index indicates that 50% of samples have a CR > 1(unsafe zone), and the rest are within the safe limit. The relationship of WQI with different water quality parameters revealed that groundwater quality has deteriorated in the city's western part, which may be due to seawater intrusion in the aquifer. This work gives a basic idea of groundwater quality, which will help make Surat a smart city.
HIGHLIGHTS
Assessment of Groundwater quality for ‘smarty city’ planning.
Determination of Seawater intrusion in a coastal aquifer (Surat city).
Hydrogeochemical investigation and groundwater quality assessment for drinking and agriculture purposes.
Graphical Abstract
INTRODUCTION
Groundwater is an essential water source worldwide and is much cleaner and free from pollutants compared to surface water. It plays a significant role in agricultural production, environmental sustenance, and sustainable economic development. But the release of industrial waste material, domestic sewage, and solid waste dumping decreases its quality. Water quality and its suitability for agriculture, drinking, and household purposes are mainly determined by its chemical, physical, and bacteriological parameters. (Mohammed-Aslam & Rizvi 2020; Warsi et al. 2022). The overall goal of any water quality assessment is to give a comprehensive picture of the spatial distribution of groundwater quality. (Machiwal et al. 2018). Once groundwater is polluted, this remains the same for decades or even hundreds of years. The world's developmental activities are growing faster for economic development and prosperity, but all this is happening at the expense of water resources (Arora & Mishra 2022; Garai et al. 2022). Through development, it is necessary to manage aquifers which are the source of fresh groundwater. It should not be stressed in terms of quantity and quality for a city.
Surat city, the ninth-largest city in India, is located on the left bank of the Tapi River (Tapti) in Peninsular India along the coast of South Gujarat. This city has diamond processing, engineering, oil and port-based business, textiles, and the petrochemical industries. Because of the over-drafting of groundwater, seawater intrudes into the city's aquifers and makes the freshwater salty (Desai & Desai 2012; Chaudhari et al. 2022). This salty water highly affects areas closest to the sea. Apart from this, water availability from the Tapi River is also not vast. Currently, available water is ∼700 ML/d, decreasing daily. Paneria & Bhatt (2017) have shown that by 2050, Surat city needs 900 ML/d, and water demand will overtake more or less 200 ML/d. Considering the above situations, the present study is carried out in Surat city, which is on the way to becoming the country's first ‘smart city’ under the ‘Smart City Mission by the Govt. of India. It aims to understand the aquifer system's spatial variations in quality by analyzing the major ion chemistry of groundwater and water level measurements in and around Surat. This quantitative and qualitative assessment of water resources will provide the general background of the aquifer system to urban planners that need to be considered for ‘smart city’ planning and water management in Surat.
The motivation for the work
Water is the primary element of ‘smart city’ planning. ‘Smart city’ planning is a visionary approach by Govt of India to integrate sustainable urban planning. The supply of safe and clean water to the city's people is a significant part of the ‘smart city’ approach. Because the city is located on the bank of the Arabian Sea, it is facing saltwater intrusion into the freshwater aquifer.
Structure of the paper
Section 1 is the general introduction describing the degrading quality and depletion of water, and the introductory part of Surat city Section 2 describes the study area and its geological and hydrogeological setup. Section 3 introduces the methodologies used in carrying out physic-chemical analyses. Then finally, Section 4 is the Results and Discussion part. Section 5 concludes the entire work and provides suggestions for improvement.
STUDY AREA
Geological setup
Geographically, Gujarat state comprises three distinct zones, which are: (i) Mainland Gujarat, (ii) Saurashtra, and (iii) Kachchh. Surat district, where the present study has been conducted, lies in the south and forms a part of Mainland Gujarat.
Deccan traps surround the eastern part of the study region. In contrast, the central part is occupied by Quaternary deposits known as Gujarat alluvial plains, forming the coastal plains at the western boundary. The area consists of Quaternary alluvium, Tertiary limestone, sandstone, and Deccan Trap basalts. Deccan traps form the basement, where the formation consists of Bentonitic shale, friable sandstone, and. This is called Vagad khol Formation. Above Vagadkhol Formation is overlain by a Nummulitic limestone formation comprising Nummulitic limestone, clays with sandstone lenses. This formation is overlain by the Tadkeshwar Formation, consisting of lenses of carbonaceous clays, bentonite clay with lignite bed, sandstone, and lignite. Lignite occurs on the northern side of the area. Overlying these beds is the Babaguru Formation comprising ferruginous sandstone agate-bearing conglomerate (Chopra & Choudhury 2011).
Hydrogeological framework
MATERIAL AND METHODS
RESULTS AND DISCUSSION
The results of the hydrogeochemical analysis are shown in (Table 1).
Chemical Constituents (mg/l . | Min . | Max . | Mean . | σ . | CV . |
---|---|---|---|---|---|
pH (units) | 7.6 | 9.2 | 8.25 | 0.343 | 0.042 |
EC (μS/cm) | 614 | 5,220 | 1,832 | 1,345.4 | 0.688 |
TDS | 399 | 3,393 | 1,191 | 874.5 | 0.688 |
Ca2+ | 0.002 | 26.08 | 10.89 | 5.73 | 0.526 |
Mg2+ | 5.14 | 50.83 | 24.09 | 12.56 | 0.521 |
Na+ | 33.10 | 300.2 | 185.9 | 56.47 | 0.303 |
K+ | 0.448 | 90.62 | 20.94 | 25.87 | 1.235 |
0.000 | 90 | 37.6 | 25.6 | 0.680 | |
97.6 | 866.2 | 364.36 | 157.33 | 0.431 | |
Cl− | 22.7 | 2,240.3 | 467.82 | 574.2 | 1.227 |
0.201 | 2.73 | 0.524 | 0.506 | 0.965 | |
NO3 | 0.19 | 260.5 | 43.88 | 66.92 | 1.525 |
F | 0.134 | 2.769 | 0.647 | 0.595 | 0.919 |
Chemical Constituents (mg/l . | Min . | Max . | Mean . | σ . | CV . |
---|---|---|---|---|---|
pH (units) | 7.6 | 9.2 | 8.25 | 0.343 | 0.042 |
EC (μS/cm) | 614 | 5,220 | 1,832 | 1,345.4 | 0.688 |
TDS | 399 | 3,393 | 1,191 | 874.5 | 0.688 |
Ca2+ | 0.002 | 26.08 | 10.89 | 5.73 | 0.526 |
Mg2+ | 5.14 | 50.83 | 24.09 | 12.56 | 0.521 |
Na+ | 33.10 | 300.2 | 185.9 | 56.47 | 0.303 |
K+ | 0.448 | 90.62 | 20.94 | 25.87 | 1.235 |
0.000 | 90 | 37.6 | 25.6 | 0.680 | |
97.6 | 866.2 | 364.36 | 157.33 | 0.431 | |
Cl− | 22.7 | 2,240.3 | 467.82 | 574.2 | 1.227 |
0.201 | 2.73 | 0.524 | 0.506 | 0.965 | |
NO3 | 0.19 | 260.5 | 43.88 | 66.92 | 1.525 |
F | 0.134 | 2.769 | 0.647 | 0.595 | 0.919 |
EC is a reciprocal of resistivity and is expressed as μS/cm or mS/cm. In the study area, EC values range from 614 to 5,220 μS/cm, averaging 1,832 μS/cm. Through the area, EC > 1,500 μS/cm is found above the right bank of river Tapi but values greater than 4,000 μS/cm are found at locations 9 and 15 (Figure 6(b)). Higher EC values show that there may be an intrusion of seawater in the aquifer and also because several industries are located which contribute to the contamination of groundwater through their effluents.
TDS of the area ranges from 399 to 3,393 mg/l in this area (average 1,199 mg/l). All samples have TDS >500 mg/l except three (nos. 4, 16, and 22). The distribution map of TDS shows a similar pattern to EC, i.e., high TDS values in the western part of the area (Figure 6(c)).
Ionic distribution in the area
The concentration of major ions in the area is as follows: The order of abundance of major ions is Na > Mg > K > Ca; Cl > HCO3 > NO2 > CO3 > F > SO4.
Sodium is a constituent of clay minerals. The breakdown of clay minerals increases sodium concentration in groundwater (Fakhreddine & Fendorf 2021). The concentration of Na ranges between 33 to 300 mg/l. The higher concentration is found in the northern, central, and western areas (Figure 7(c)). The high concentration is close to the sea in the western region, resulting in seawater ingress and a high concentration of Na. Secondly, the increased Na in groundwater is likely due to the leaching of the effluents released from industries and fertilizer-irrigated water (Vushe 2019).
Potassium is found to be in a lower concentration in groundwater because of the high resistance of potash feldspar (K2O.Al2O3.6SiO2) to chemical weathering (Buvaneshwari et al. 2020). The K concentration in the area's groundwater samples ranges between 0.448 to 90.6 mg/l. The potassium concentration is increased in the western area but shows lesser values. Industrial activities and the cation-exchange process can contribute to high potassium content (Leal et al. 2013) (Figure 7(d)).
Chloride is crucial in tracing natural flow patterns because of its conservative nature. It does not readily react with minerals/chemicals and remains unaltered throughout the underground flow. The main reason for the chloride concentration in coastal areas is the ingress of seawater. Secondly, rainfall near the seacoast is enriched in chloride ions (Behera et al. 2019). Infiltrating water entering the sub-surface system increases the chloride concentration in groundwater. The concentration of Cl– varies between 22.7 to 2,240 mg/l. Although chloride concentration throughout the area is high, the spatial distribution map shows that the southern and eastern part is characterized by low values below the left bank of river Tapi. In contrast, the north and western part is characterized by higher values (Figure 7(e)). The highest concentration is found in samples 9 and 15, i.e., 1,825 and 2,240 mg/l. It can be due to the ingress of saline water.
Carbonate and bicarbonate concentrations constitute alkalinity. The concentration of Carbonates and bicarbonates is dependent upon CO2 and is also a function of pH. The source of these ions includes carbonate rocks; the other is CO2 released from decaying organic matter combined with water, which also constitutes bicarbonates in groundwater. In the study area, the concentration of carbonates is generally low (Ranges between 0 to 90 mg/l), even within those areas where the lithology is limestone. It may be because of low solubility and a minor degree of mineralization. In the central and at one location in the northern part, concentration reaches up to 90 mg/l. Otherwise, low concentration is observed in other regions (Figure 7(f) and 7). Carbonate concentration in the western part is low because of high salinity.
The sulphate concentration ranges between 0.201 to 2.73 mg/l, which is low throughout the area, and fluoride ranges between 0.13 to 2.769 mg/l, which is also within limits except at one location, within boundary limits.
Nitrates in groundwater usually come from agricultural activities utilizing fertilizers, seepage of the liquids due to sewage and septic tanks, and industrial effluents (Ducci 2018). Figure 7 shows the spatial distribution of nitrate where the concentration of nitrate is high at six places (9, 12, 13, 14, 18, and 23).
From the results of the physic-chemical analysis of groundwater samples of the study area, it has been observed that the concentration of most of the ions, mainly Ca2+, Mg2+, Na+, Cl−, are high, mainly in the western part of the area. High concentration is found in the samples collected from locations very close to the sea, suggesting that the ingress of saline water makes the ions' concentration high in groundwater. Secondly, several industries are located in this region, and the leaching of the effluents released from industries also contributes ions to the groundwater.
Classification of groundwater
Piper's trilinear diagram
Based on Piper's trilinear diagram, groundwater can be classified by plotting the concentration of cations and anions in mEq/l. This diagram helps organize the hydrochemical data into facies based on the similarity in chemical composition. The fields categorize water into different types such as CaSO4 type (Gypsum groundwater and mine drainages), CaHCO3 type (shallow fresh groundwater), NaHCO3 type (Deeper groundwater influenced by ion exchange), and NaCl type (Marine and deep ancient groundwater) (Piper 1944). Our collected samples are only confined to the two fields, 52% in sodium bicarbonate and 48% in sodium chloride. It indicates the movement of saline water to the deeper aquifers (Alaya et al. 2014). The intrusion of saline water comes from the Arabian Sea and the presence of creeks (Tena creek, Hazira Creek, Mindhola creek). It represents a constant interaction between the sea and the aquifers.
Suitability of groundwater for drinking
S. no. . | Water quality parameters . | . | . | Range in the study area . |
---|---|---|---|---|
Most desirable limit . | Maximum permissible limits . | |||
1 | pH | 6.5–8.5 | 6.5–9.5 | 7.6–9.2 |
2 | EC | 1,500 | 614–5,220 | |
3 | TDS | 500 | 600 | 399–3,393 |
4 | Ca | 75 | 200 | 0.002–26.0 |
5 | Mg | 50 | 100 | 5–50.8 |
6 | Na | 200 | 200 | 33–300 |
7 | K | 55 | 0.448–90.6 | |
8 | CO3 | – | 0–90 | |
9 | HCO3 | 1,000 | 97–866 | |
10 | Cl | 200 | 1,000 | 22.7–2,240 |
11 | SO4 | 200 | 400 | 0.201–2.7 |
12 | NO3 | 45 | 0.19–260.4 |
S. no. . | Water quality parameters . | . | . | Range in the study area . |
---|---|---|---|---|
Most desirable limit . | Maximum permissible limits . | |||
1 | pH | 6.5–8.5 | 6.5–9.5 | 7.6–9.2 |
2 | EC | 1,500 | 614–5,220 | |
3 | TDS | 500 | 600 | 399–3,393 |
4 | Ca | 75 | 200 | 0.002–26.0 |
5 | Mg | 50 | 100 | 5–50.8 |
6 | Na | 200 | 200 | 33–300 |
7 | K | 55 | 0.448–90.6 | |
8 | CO3 | – | 0–90 | |
9 | HCO3 | 1,000 | 97–866 | |
10 | Cl | 200 | 1,000 | 22.7–2,240 |
11 | SO4 | 200 | 400 | 0.201–2.7 |
12 | NO3 | 45 | 0.19–260.4 |
Parameters . | Range . | Classification . | Samples . |
---|---|---|---|
TDS | <500 | Desirable for drinking | 4, 16, 22 |
500–1,000 | Permissible for drinking | 1, 2, 3, 6, 7, 12, 17, 21, 23, 24, 25, 26 | |
1,000–3,000 | Useful for agriculture | 5, 8, 10, 11, 13, 14, 18, 19,20 | |
>3,000 | Unfit for both drinking and irrigation | 9, 15 | |
Chloride (Stuyfzand 1989) | <0.141 | Extremely fresh | |
0.141–0.846 | Very fresh | ||
0.846–4.231 | Fresh | ||
4.231–8.462 | Fresh brackish | ||
8.462–28.064 | Brackish | 1, 3, 4 | |
28.064–564.127 | Salt | 2, 5, 6, 7, 11, 12, 16, 17, 18, 21, 22, 23, 24, 25, 26 | |
>564.127 | Hyperhaline | 8, 9, 10, 13, 14, 15, 19, 20 |
Parameters . | Range . | Classification . | Samples . |
---|---|---|---|
TDS | <500 | Desirable for drinking | 4, 16, 22 |
500–1,000 | Permissible for drinking | 1, 2, 3, 6, 7, 12, 17, 21, 23, 24, 25, 26 | |
1,000–3,000 | Useful for agriculture | 5, 8, 10, 11, 13, 14, 18, 19,20 | |
>3,000 | Unfit for both drinking and irrigation | 9, 15 | |
Chloride (Stuyfzand 1989) | <0.141 | Extremely fresh | |
0.141–0.846 | Very fresh | ||
0.846–4.231 | Fresh | ||
4.231–8.462 | Fresh brackish | ||
8.462–28.064 | Brackish | 1, 3, 4 | |
28.064–564.127 | Salt | 2, 5, 6, 7, 11, 12, 16, 17, 18, 21, 22, 23, 24, 25, 26 | |
>564.127 | Hyperhaline | 8, 9, 10, 13, 14, 15, 19, 20 |
Water quality index (WQI)
Range . | Type of groundwater . | Samples . |
---|---|---|
<50 | Excellent | 1, 2, 3, 4, 16, 21, 22, 24, 26 |
50–100 | Good water | 5, 6, 7, 12, 13, 17, 18, 23, 25 |
100–200 | Poor water | 8, 10, 11, 14, 19, 20 |
200–300 | Very poor water | 9 and 15 |
>300 | Unsuitable |
Range . | Type of groundwater . | Samples . |
---|---|---|
<50 | Excellent | 1, 2, 3, 4, 16, 21, 22, 24, 26 |
50–100 | Good water | 5, 6, 7, 12, 13, 17, 18, 23, 25 |
100–200 | Poor water | 8, 10, 11, 14, 19, 20 |
200–300 | Very poor water | 9 and 15 |
>300 | Unsuitable |
Suitability of groundwater for irrigation purposes
The quality of groundwater is equally essential for irrigation, but the presence of salts in groundwater makes it undesirable. Salts in higher concentrations lead to changes in soil composition and structure, decreasing soil permeability and affecting plant growth. Salts in the soil increase the osmotic pressure and decrease water uptake to the plants. Some important parameters to judge the suitability of groundwater for irrigation purposes are sodium percentage (%Na), SAR, and permeability index (PI).
Sodium percentage (%Na)
Parameter . | Class . | Category . | Samples . |
---|---|---|---|
% Na | Class I | Excellent to good | 17, 22 |
Class II | Good to permissible | 3 | |
Class III | Permissible to doubtful | 1, 2, 4, 7, 13, 16, 21, 23, 24, 26 | |
Class IV | Doubtful to unsuitable | 5, 6, 8, 12, 14, 18, 20, 25 | |
Class V | Unsuitable | 10,19 | |
SAR | Class I | Good water | 1, 2, 3, 7, 22, 23, 26 |
Class II | Moderate water | 4, 5, 6, 8, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 24, 25 | |
Class III | Bad water | 9, 15 | |
PI | Class I | Maximum permeability | 23 |
Class II | 75% of Max. permeability | 2, 3, 5, 6, 8, 12, 13,15, 16, 20, 24 | |
Class III | 25% of Max. permeability | 1, 4, 7, 9, 10, 11, 14, 17, 18, 19, 21, 22, 25, 26 |
Parameter . | Class . | Category . | Samples . |
---|---|---|---|
% Na | Class I | Excellent to good | 17, 22 |
Class II | Good to permissible | 3 | |
Class III | Permissible to doubtful | 1, 2, 4, 7, 13, 16, 21, 23, 24, 26 | |
Class IV | Doubtful to unsuitable | 5, 6, 8, 12, 14, 18, 20, 25 | |
Class V | Unsuitable | 10,19 | |
SAR | Class I | Good water | 1, 2, 3, 7, 22, 23, 26 |
Class II | Moderate water | 4, 5, 6, 8, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 24, 25 | |
Class III | Bad water | 9, 15 | |
PI | Class I | Maximum permeability | 23 |
Class II | 75% of Max. permeability | 2, 3, 5, 6, 8, 12, 13,15, 16, 20, 24 | |
Class III | 25% of Max. permeability | 1, 4, 7, 9, 10, 11, 14, 17, 18, 19, 21, 22, 25, 26 |
Sodium adsorption ratio (SAR)
Permeability index (PI)
Corrosivity ratio (CR.)
Management of water resources in ‘smart city’ planning
WHO (2004) reported that nearly 80% of water infections are caused by polluted water consumption, and almost 35% of the deaths in developing countries are caused due to polluted consumption of water. Water pollution severely damages the ecosystem, reducing agricultural production (Karanth 1987). The study results show that aquifers in the western part of Surat city are under the influence of saltwater intrusion. Many industries are located in this area, which is the main reason for groundwater exploitation and results in seawater intrusion. It affects groundwater quality and renders them unfit for drinking or irrigation uses.
To improve groundwater quality and quantity, the following management plans are suggested that will be helpful in ‘smart city’ planning and water resource management.
Managed aquifer recharge (MAR) techniques can increase groundwater quality. It can also reduce saltwater intrusion and protects soils. MAR increases crop yields, especially in the western part of Surat city and the coastal area. Geophysical methods (ERT, VES, TEM) can be used for aquifer mapping for suitable MAR sites and safe drinking water zone. Different treatment methods for groundwater (defluoridation, demineralization of water, ion exchange, and water softening) should be used to reduce concentrations of those ions that currently exceed the permissible limit for drinking water and irrigation purposes. It is suggested to avoid the excessive use of fertilizers in the agricultural field for higher crop yields. The corrosivity index should be followed in transporting groundwater or any other pipeline beneath the earth's surface throughout the city. The selection of crop type should be based on quality, availability, and water needs. An awareness program on ‘Environmental changes and their impact on human life’ should be started to reduce human activity on pollution because we never get sustainable development without local community support.
CONCLUSION
Groundwater is mainly alkaline as pH varies from 7.6 to 9.2 (average 8.3). The groundwater quality in the northwestern part is primarily influenced by saltwater intrusion and anthropogenic activities. About 85% of samples have TDS levels above the drinking water standards. About 23% of water samples contain a more significant amount of NO3, showing the occurrence of sewage, septic tanks, and industrial effluents. The concentration of chloride (Cl) and sodium (Na) was positively correlated with electrical conductivity (EC). The highest concentration of Cl and Na were found near the coastal region, especially in the northwestern part showing the influence of the saltwater intrusion. The Piper trilinear diagram identified 52% sodium bicarbonate (Na-HCO3) type and 48% sodium chloride (NaCl) type of water in the study area, indicating the movement of saline water to the deeper aquifers. The WQI shows that for drinking, 31%, 38, 23, and 8% of the water samples are ‘excellent,’ ‘good,’ ‘poor,’ and ‘very poor.’ The results of SAR (43% ‘good, 52% moderate, and 5% unsuitable), Na% (43% good, 44% moderate, and 13% unsuitable), and PI (5% excellent, 43% good, and 52% unsuitable) show that most of the samples are suitable for irrigation. 50% of the area, especially in the northwest, has a high corrosive value of CR > 1, showing the ingress of saline water. The rest of the area, mainly the left bank of the river, offers a safe zone value of CR. The WQI with the spatial distribution of different water quality parameters revealed that groundwater quality has deteriorated on the western side of Surat city. This paper provides a general background to urban planners that need to be considered for ‘smart city’ planning and water management in Surat.
ACKNOWLEDGEMENT
The authors gratefully acknowledge Director, CSIR-NGRI, India, for permitting them to publish this paper. The authors would like to acknowledge Dr K Ram Mohan, hydro geochemistry group, NGRI, for sample analysis and his valuable suggestions. The authors also thank Dr Subhas Chandra, Veema Raju, and Dr Sahebrao Sonkamble for their help and support. This is part of the project work funded by Surat Municipality Corporation for ‘smart city’ planning.
DATA AVAILABILITY STATEMENT
Data cannot be made publicly available; readers should contact the corresponding author for details.
CONFLICT OF INTEREST
The authors declare there is no conflict.