Spatiotemporal Assessment of Groundwater Quality in the Hamedan-Bahar Plain Using GIS and Hierarchical Clustering

Document Type : Research Paper

Authors

• Alireza Bodaghi ¹
• Ali Moridi ²
• Reza Khalili ³

¹ Department of Environmental Engineering, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran.

² Civil, Water and Environmental Engineering Faculty, Shahid Beheshti University

³ Department of Water, Wastewater and Environmental Engineering, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran.

Abstract

Keywords

• Groundwater
• Hamedan-Bahar Plain
• Water Quality
• Nitrate

Main Subjects

• منابع آب

Introduction

Groundwater resources play a vital role as the main source of drinking water, agriculture, and industry in many arid and semi-arid regions of Iran. Limited surface water availability, population growth, agricultural and industrial expansion, and frequent droughts have significantly increased reliance on groundwater in recent decades. However, groundwater quality is under serious threat due to the overuse of chemical fertilizers and pesticides, discharge of municipal and industrial effluents, and excessive abstraction. The Hamedan–Bahar plain, located in the northwest of Hamedan Province with a cold semi-arid climate, covers about 880 km² and supplies over 80% of agricultural and nearly half of urban drinking water needs. Assessing its spatiotemporal variations in groundwater quality is therefore of critical importance. This study focuses on monitoring four key parameters—pH, nitrate, electrical conductivity (EC), and bicarbonate—during the period 2020–2024. The use of Geographic Information System (GIS) for spatial mapping of critical zones and Hierarchical Cluster Analysis (HCA) for classifying wells constitutes the main innovation of this research, providing a practical framework for groundwater management and strategic planning.

Methodology

Data from 20 production wells in the Hamedan–Bahar plain were collected over a five-year period (2020–2024). The dataset included annual measurements of pH, nitrate (NO₃⁻), bicarbonate (HCO₃⁻), and electrical conductivity (EC), recorded by the Regional Water Authority of Hamedan Province. Sampling wells were selected from different land-use zones—agricultural, industrial, urban, and peripheral areas—to ensure adequate representation. All procedures followed national and international standards, and samples were analyzed in the laboratory. For spatial analysis, the Inverse Distance Weighting (IDW) interpolation method was applied in ArcGIS Pro to generate continuous maps of groundwater quality. For statistical analysis, five-year averages of each parameter were calculated and normalized, followed by Hierarchical Cluster Analysis (HCA) using Ward’s linkage and Euclidean distance to classify wells into groups with similar quality characteristics.

Results

The five-year analysis revealed significant spatiotemporal variations in groundwater quality. The pH values ranged from 6.7 to 7.9 and remained within the national drinking water standard (6.5–8.5). Slightly lower values occurred in the eastern and southern regions, while higher values were found in the west and north. Nitrate concentrations showed a clear increasing trend, rising from 28 mg/L in 2020 to 51 mg/L in 2024. By the end of the monitoring period, about 30% of wells exceeded the permissible limit of 50 mg/L, with the highest concentrations in the southern and eastern zones where fertilizer use is more intensive. Electrical conductivity values in some wells surpassed 2400 µS/cm, indicating the onset of salinity. Although the maximum occurred in 2020 and the minimum in 2022, the overall trend showed gradual increases, especially in the eastern and northeastern sectors. In contrast, bicarbonate remained relatively stable, always below 10 mg/L across the plain. HCA grouped the wells into four categories: wells with good quality, wells with moderate pollution, wells with elevated nitrate and EC, and critically polluted wells concentrated in the south and east.

Discussion and Conclusion

The findings demonstrate that groundwater quality in the Hamedan–Bahar plain is facing increasing pressure. Rising nitrate levels and gradual salinization, particularly in the southern and eastern parts of the plain, are mainly linked to excessive fertilizer application, infiltration of agricultural and industrial effluents, and over-abstraction. These trends pose significant risks to public health, agricultural productivity, and ecosystem sustainability. HCA proved effective in identifying critical zones and prioritizing management interventions. The results highlight the urgent need for continuous monitoring, reduced use of nitrogen fertilizers, improved wastewater management, and adoption of modern irrigation technologies in vulnerable areas. Integrating GIS-based spatial mapping with temporal monitoring provides a comprehensive and transferable framework for groundwater management that can also be applied to other aquifers. To ensure long-term sustainability, regular monitoring programs, stricter regulation of illegal withdrawals, better agricultural input management, development of wastewater treatment facilities, and the application of predictive models are recommended. When combined with community participation and stronger policy enforcement, these measures can safeguard the Hamedan–Bahar aquifer and serve as a model for sustainable groundwater management in similar regions.

Author Contributions

All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

Data Availability Statement

Data available on request from the authors.

Acknowledgements

The authors would like to thank the reviewers and editor for their critical comments that helped to improve the paper.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

The author declares no conflict of interest.