Extended Abstract
Title: Assessment of Groundwater Resources Quality for Drinking, Agricultural, and Industrial Applications: A Case Study of the Qomsheh Plain

1. Introduction

Groundwater is a vital strategic resource, especially in arid and semi-arid regions like central Iran, where surface water is scarce and precipitation is low. The Qomsheh (Shahreza) Plain, located in Isfahan Province, is a prime example of a region heavily dependent on its groundwater aquifer for sustaining its agricultural, industrial, and domestic water needs. However, this critical resource is under immense pressure due to a combination of climatic factors, such as low average annual rainfall (around 140 mm) and high evaporation rates, and anthropogenic pressures, including intensive agricultural activities and over-extraction from hundreds of wells. Preliminary observations have indicated a decline in water levels and a simultaneous degradation of its chemical quality, posing significant risks to the region’s sustainable development.

While previous studies may have touched upon aspects of the Qomsheh aquifer, a comprehensive and integrated assessment of its suitability for drinking, agricultural, and industrial purposes simultaneously has been a significant research gap. This study aims to fill this void by providing a holistic evaluation of the aquifer’s hydrochemical characteristics. By employing a multi-faceted approach that includes various quality indices and spatial analysis, this research provides a detailed snapshot of the current state of the aquifer, identifies zones of varying water quality, and investigates the primary factors influencing its chemistry. The findings are crucial for informing local water management authorities and stakeholders in developing effective strategies for the protection and sustainable utilization of this invaluable resource.

2. Materials and Methods

The study was conducted in the Qomsheh Plain, an area of approximately 28,855 hectares, characterized by a semi-arid climate. The primary data for this research were collected from a network of 10 representative wells (8 deep wells, P1–P8; and 2 semi-deep wells, P9–P10) during the reference year of 2019 (1398). A comprehensive suite of physicochemical parameters was analyzed for each sample, including pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), and concentrations of major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and anions (HCO₃⁻, Cl⁻, SO₄²⁻). To ensure data reliability, an anion-cation balance check was performed, with all samples showing an acceptable error of less than 5%, as per the Mazor (2003) criterion.

The hydrochemical evaluation was performed using a combination of graphical methods, established indices, and spatial analysis techniques:

Hydrochemical Facies: The chemical evolution and water type were identified using Piper (1944) and Stiff diagrams, generated with the AqQA software. This helped in classifying the dominant ionic composition of the water samples.
Salinity Trend Analysis: To understand the long-term salinity behavior, a 24-year historical EC dataset (from 1994 to 2019) was analyzed. A chemograph was developed using area-weighted averages derived from Thiessen polygons created in ArcGIS to visualize temporal trends and seasonal fluctuations.
Drinking Water Quality: The suitability for human consumption was assessed using the Schuler diagram, which classifies water into “Good,” “Acceptable,” “Unsuitable,” and “Poor” categories based on a composite evaluation of six key parameters (pH, Ca²⁺, Mg²⁺, Na⁺, SO₄²⁻, Cl⁻).
Agricultural Water Quality: The Wilcox (1955) diagram was employed to evaluate the water’s suitability for irrigation. This method classifies water based on EC (as a proxy for salinity hazard) and Sodium Adsorption Ratio (SAR, as a proxy for sodicity hazard) into 16 classes from C1-S1 (excellent) to C4-S4 (unsuitable).
Industrial Water Quality: The Langelier Saturation Index (LSI) was calculated to determine the scaling or corrosive potential of the water. LSI values close to zero indicate stable water, positive values suggest a tendency for scale formation (carbonate precipitation), and negative values indicate corrosive tendencies.
Spatial Analysis: Inverse Distance Weighting (IDW) interpolation was performed in ArcGIS to generate spatial distribution maps for all quality indices, allowing for the clear delineation of zones with different water quality characteristics across the plain.
3. Results and Discussion

The physicochemical analysis revealed a wide variation in water quality across the aquifer. EC values ranged from a minimum of 1062 μS/cm (Well P9) in the southern part of the plain to a maximum of 11050 μS/cm (Well P5) in the northern part. TDS values followed a similar pattern, ranging from 690 to 7183 mg/L. The pH of all samples was near-neutral to slightly alkaline, ranging from 6.8 to 7.7.

Hydrochemical Facies: Five distinct water types were identified: Mg-Cl (P1), Na-Cl (P2, P7, P8), Ca-SO₄ (P3, P9), Ca-Cl (P4, P5, P6), and Na-HCO₃ (P10). The dominance of Cl⁻ type waters, particularly in the northern and central zones, corresponds to the highest EC and TDS values, indicating advanced mineralization and potential impacts from saline water intrusion or dissolution of salt-bearing formations.
Salinity Trend: The 24-year chemograph showed a gradual but steady increase in the average aquifer salinity, with the mean EC rising from 1919 μS/cm in 1994 to 2467 μS/cm in 2019. This long-term trend, coupled with seasonal spikes in the second half of the year due to evapoconcentration, confirms that the aquifer is under significant salinization stress. The current average EC far exceeds the permissible limits for drinking water.
Drinking Water (Schuler Index): The spatial assessment for potability showed a clear south-to-north quality decline. Only the southern wells (P1, P9, P10) were classified as “Good.” The northeastern wells (P2, P3, P4) were “Acceptable,” while the wells in the north and northwest (P5, P6, P7, P8) were predominantly “Poor” and unsuitable for drinking without treatment.
Agricultural Water (Wilcox Diagram): The analysis for irrigation suitability revealed significant limitations. Only wells P1, P2, P9, and P10 fell into the “medium” salinity class (C3-S1), making them usable with caution for salt-tolerant crops. The remaining six wells, located primarily in the northern and central areas, were classified as C4-S1, C4-S2, or C4-S3, indicating very high to extremely high salinity and rendering them unsuitable for general agriculture, as they pose a severe risk of soil salinization and reduced crop yield.
Industrial Water (Langelier Index): The LSI results showed a mixed pattern. Six wells (P2, P3, P5, P7, P8, P9) yielded water that is chemically stable and suitable for industrial use with minimal risk of scaling or corrosion. However, water from wells P4, P6, and P10 was mildly corrosive, and well P1 showed highly corrosive characteristics (LSI = -0.52), making it unsuitable for industrial applications without pre-treatment to prevent damage to pipes and equipment.
The spatial distribution maps generated for all indices consistently highlighted a geographical pattern: the southern part of the aquifer exhibits relatively better water quality, while a large area in the north and northeast is characterized by poor-quality, highly saline water. This pattern strongly correlates with the density of abstraction wells, which is highest in the northern agricultural zones.

4. Conclusion

This comprehensive study concludes that the overall quality of the Qomsheh aquifer is precarious and generally unfavorable, particularly for drinking and agricultural purposes. There is a clear spatial heterogeneity in water quality, with a significant deterioration from the southern recharge zones towards the northern discharge and high-abstraction areas. The primary drivers of this quality decline are a combination of natural and anthropogenic factors, including over-extraction leading to a drop in water tables and the mobilization of saline water, low recharge rates, and potential pollution from agricultural return flows (fertilizers and pesticides) and untreated industrial effluents.

Based on these findings, urgent management interventions are recommended. These should include:

Reducing Abstraction: Promoting water-saving irrigation technologies (e.g., drip irrigation) to increase water use efficiency and reduce the overall demand.
Pollution Control: Identifying and controlling point and non-point sources of pollution.
Continuous Monitoring: Establishing a robust, long-term water quality monitoring program to track changes and evaluate the effectiveness of management actions.
Sustainable Practices: Encouraging a shift towards the cultivation of more salt-tolerant crops in affected areas and promoting sustainable agricultural practices.
Implementing these strategies is critical to mitigating further degradation and ensuring the long-term sustainability of the Qomsheh aquifer for future generations.