Abstract
There are different sources of groundwater pollution among them industrial water disposal, seawater ingress, usage of pesticides and fertilizers in agricultural fields, and municipal and residential wastewater disposal. The aim of the study is to assess groundwater vulnerability in terms of quality using the GOD method using the Geographical Investigation System approach for Surat and its surroundings. Groundwater confinement, overlying strata and depth to water table are the three parameters that are used in the assessment of groundwater vulnerability. In this study, all three parameters are given by the conventional weights which are suggested by Foster 1987. Based on the study Mahuva, Mandvi, Umarpada and some parts of the Bardoli talukas lie in very high-vulnerability zones whereas another part of the study area lies in a high-vulnerability zone. Almost 35.98% of the area of the district lies in the higher-vulnerability zone. Depth to the water table and the overlying strata are very important parameters that effectively cause groundwater vulnerability. This study may help in groundwater quality management, and watershed management as well as it is very much useful for the policymakers and local authorities as well as the government.
HIGHLIGHTS
To assess the groundwater vulnerability in Surat district, the GIS approach-based GOD method is effectively used.
This study helps to improve the quality of the groundwater in the study area.
This study helps to improve groundwater management policies.
Effective and authentic data provided by the government bodies are used for the assessment.
From this study, we can achieve sustainable water use management.
Graphical Abstract
INTRODUCTION
Precipitation is a very important and major source of water and water is very important for all living organisms. Groundwater is an important source of water and it provides about half of all drinking water on the planet, as well as 43% of all irrigation water used in agriculture (Patel et al. 2022). Also, groundwater is comparatively safe in terms of quality and reliability compared to all-surface water sources (Kaddour et al. 2018). Groundwater is the water that exists below the ground surface. Groundwater systems are extremely dynamic and they are more compatible with pollution because water is constantly moving downward (Vijayakumar et al. 2021; Patel et al. 2022). Groundwater sources are our current and future water demand reserves and they differ from other water sources in that they perform a critical function in terms of cleanliness and accessibility that cannot be replaced (Shirazi et al. 2013). Industrial activities, agricultural activities such as the use of fertilizers and pesticides and soil pollution play a major role in groundwater pollution. Groundwater is easily contaminated but it is difficult to remediate so in today's time it is very important to manage the quality of the groundwater (Khodabakhshi et al. 2015). Pollution control and removal of contaminants from the groundwater is a very costly and challenging task (Khodabakhshi et al. 2015; Rukmana et al. 2020). So, a proper and effective quality management technique is very much required for groundwater (Chowdary et al. 2005).
The vulnerability of groundwater is defined as ‘the tendency or possibility of contaminants reaching a specified position in the groundwater system after introduction at some location above the uppermost aquifer’ (National Research Council 1993; Foster et al. 2002). The concept of groundwater vulnerability assessment is that the aquifer does not have the same characteristics in all locations and that some geographical areas are more vulnerable to deterioration in terms of quantity and quality (Gogu et al. 2003). Groundwater vulnerability assessment is a crucial process in determining how vulnerable a certain region is to a specific threat, whether natural or man-made (Mendoza & Barmen 2006). Vulnerability of assessment is very much helpful to know about the quality of the groundwater in the area and ultimately it is helpful in the management of groundwater as well as the environment (Piscopo 2001; Mendoza & Barmen 2006; Rukmana et al. 2020). Also, the groundwater levels are decreasing, demanding long-term planning to safeguard these vital resources (Narendra & Rao 2006).
There are different types of groundwater vulnerability assessment methods, among them overlay and index methods are very effective and easy methods to find pollution-prone areas of the groundwater (Sener 2021; Patel et al. 2022). In overlay and index methods, parameter maps are prepared and then overlay methods with respect to some effective weights are given by the different authors as well as researchers (Sener 2021; Patel et al. 2022). There are many overlay and index methods among them DRASTIC (Aller 1985), SINTACS (Civita & De Maio 1997), GOD (Foster 1987), AVI (Stempvoort et al. 1993) and PI (Golds cheider et al. 2000) are the commonly used and known methods. The GOD method gives good results in the areas where groundwater quality is to some extent too good as well as where the groundwater pollution is more affected by the aquifer as well as the depth to the water table (Foster 1987). For checking the primary risk or for the smaller-scale vulnerability assessment, the GOD method gives an effective result (Kaddour et al. 2018). GOD is a well-known system for determining the aquifer's pollution vulnerability promptly (Maria 2018). The GOD method is effectively applied in India as well as in the other countries for groundwater vulnerability assessment. At small–moderate scales, the GOD approach may be sufficient for vulnerability mapping in aquifers (Maria 2018). The GOD method is very easy and effective for designing a large area for land management (Maria 2018). The GOD method gives the best result compared with all other methods in the small urban-type aquifers, so it is more helpful in small urban areas to assess the groundwater quality vulnerability as a primary risk factor (Maria 2018). The study area is affected by industrial activities, agricultural activities and solid waste management so the groundwater of the study area may be polluted by these sources. In this study, the GOD method is used for the assessment of groundwater vulnerability. Basically, in the GOD method three parameters are considered, groundwater confinement, overlaying strata and depth to water table as an important parameter are responsible for groundwater pollution. This GOD method shows the vulnerable areas, so this method helps in improving the groundwater management policies as well as water resources management.
STUDY AREA
Surat district is in the western area of India, in the state of Gujarat. Due to immigration from within the state and other Indian states, it is one of India's most active districts, with one of the fastest growth rates. Surat is a very important state of Gujarat with a population of 7.7 million. Surat is the ninth most populated city in India. ‘The City Chairman Establishment, a global research organization’ focusing on urban issues, ranks Surat fourth in a global survey of the fastest-growing cities. Surat is situated on the banks of the Tapi River, with the Arabian Sea to the west, between latitudes 21°06° N and 21°15° N, and longitudes 72°45° E and 72°54° E. It is 13 meters above sea level. It is a densely populated district of Gujarat state. It is 306 km far away from the Gujarat state capital, Gandhinagar. It is connected on the west by the Arabian Sea, on the north by Bharuch, on the south by the Valsad district, on the southeast by the Dang district and on the east by the Tapi district. Surat district is divided into nine groups of villages, basically we call it a taluka, i.e., Bardoli, Choryasi, Kamrej, Mahuva, Mandvi, Mangrol, Olpad, Palsana and Umarpada, it covers an area of about 4,418 sq. km.
In the district's middle sections, the Tapi river passes over alluvial fields (CGWB 2013). Tapi features a reasonably wide meandering canal with terraces built into it. The area's topography is mostly level, with the exception of a minor slope in the west. The area's lowest point is 45 meters above sea level. The elevations are frequently under 60 meters above sea level.
The groundwater is largely unconfined and most likely caused by the presence of clay objects.
DATA COLLECTION
All the parameters of the GOD method are collected and collated to create a layer for each parameter in the ArcGIS (Aeronautical Reconnaissance Coverage Geographic Information system) software. All the data related to the parameter are collected from the different governmental organizations and government bodies’ research data, which are mentioned in Table 1.
Data sources of different parameters
Parameter . | Data source . |
---|---|
Groundwater confinement (G) | Collected from the Central Ground Water Board Report for the Surat district. |
Overlaying strata (O) | Collected from the website of the Commission of Geology and Mining by the industries and Mines Department of the Government of Gujarat. |
Depth to water table (D) | Collected from the Water Resources Information System portal for the last year. |
Parameter . | Data source . |
---|---|
Groundwater confinement (G) | Collected from the Central Ground Water Board Report for the Surat district. |
Overlaying strata (O) | Collected from the website of the Commission of Geology and Mining by the industries and Mines Department of the Government of Gujarat. |
Depth to water table (D) | Collected from the Water Resources Information System portal for the last year. |
METHODOLOGY
Overview of the GOD method



Groundwater confinement (G)
This parameter includes the confinement or the occurrence of the groundwater. Generally, there are unconfined as well as confined types of aquifers which may store the groundwater. So, this parameter shows the occurrence of groundwater.
Overlaying strata (O)
This parameter shows the aquifer geology type which considerably lies in the respective study areas. There are different types of aquifers and their geology is different. Geology is the main concern for groundwater occurrence and storage.
Depth to water table (D)
This parameter is one of the most important parameters for groundwater quality. It includes the depth of the water table. If the depth of the water table is very less, then the contaminants can easily reach the groundwater and if the depth is more, it is not easily reached. So, it is directly dependent on the quality of the groundwater.
After applying the rates according to Table 2, and after preparation of the vulnerability map prepared and based on the vulnerability map, the study area is divided into the different vulnerability classes which are included in Table 3. Supplementary Annexure 1 includes the data collection and steps for creating the parameter map.
Standard GOD parameters
Layer . | Range/Type . | Rating . |
---|---|---|
Groundwater occurrence (G) | Confined aquifer | 0.2 |
Semi-confined aquifer | 0.4 | |
Unconfined aquifer | 0.6 | |
Overlaying strata (O) | Basalt | 1.0 |
Karst limestone | 0.9 | |
Massive sandstone | 0.7 | |
Sand and gravel | 0.8 | |
Depth to water table (D) | 0–2.0 m | 1.0 |
2.0–5.0 m | 0.9 | |
5.0–20.0 m | 0.8 | |
20.0–50.0 m | 0.7 | |
>50 m | 0.6 |
Layer . | Range/Type . | Rating . |
---|---|---|
Groundwater occurrence (G) | Confined aquifer | 0.2 |
Semi-confined aquifer | 0.4 | |
Unconfined aquifer | 0.6 | |
Overlaying strata (O) | Basalt | 1.0 |
Karst limestone | 0.9 | |
Massive sandstone | 0.7 | |
Sand and gravel | 0.8 | |
Depth to water table (D) | 0–2.0 m | 1.0 |
2.0–5.0 m | 0.9 | |
5.0–20.0 m | 0.8 | |
20.0–50.0 m | 0.7 | |
>50 m | 0.6 |
Vulnerability class for the GOD method
Vulnerability class . | Index value . |
---|---|
Negligible | 0–0.1 |
Low | 0.1–0.3 |
Moderate | 0.3–0.5 |
High | 0.5–0.7 |
Very high | 0.7–1.0 |
Vulnerability class . | Index value . |
---|---|
Negligible | 0–0.1 |
Low | 0.1–0.3 |
Moderate | 0.3–0.5 |
High | 0.5–0.7 |
Very high | 0.7–1.0 |
RESULTS AND DISCUSSION
CONCLUSION
In this paper, the GOD method is effectively used with the geoinformatics approach for groundwater vulnerability assessment. Based on the above study, it is observed that almost 36% of the total study area is under the higher vulnerability zone and other parts of the area are under the moderate vulnerability zone. It is also observed that Umarpada and some parts of the Bardoli, Mandvi and Mahuva talukas are under the higher vulnerability zone. This may be due to the shallow depth of the water table as well as the type of overlaying strata being basalt type. So, based on the above study, depth to the water table and the overlaying strata are the important parameters that mostly affect groundwater vulnerability. This GOD method is an effective and valuable method for the assessment of groundwater vulnerability using the geoinformatics approach. Primary-level treatment of industrial waste can prevent groundwater pollution before it is released into the environment. Reducing pumping rates, relocating pumping wells, using physical surface or subsurface barriers, using natural or artificial recharge (pressure or positive barriers), pumping saline water along the seashore (abstraction or negative barriers) and combining techniques can all help reduce seawater ingress (mixed barriers). Thus, it ultimately improves the quality of groundwater. This study can identify the groundwater vulnerable areas so that effective management policies can be applied in vulnerable areas. So, this result may be useful in the management of groundwater policies as well as in monitoring and maintaining the groundwater quality of a particular area.
FUNDING
This research received no external funding.
DATA AVAILABILITY STATEMENT
All relevant data are available from an online repository at https://indiawris.gov.in/wris/.
CONFLICT OF INTEREST
The authors declare there is no conflict.