Assessing and modeling groundwater vulnerability to arsenic contamination in rural coastal aquifers using geophysical and hydrogeochemical methods

Project Abstract

This study presents a comprehensive assessment and modeling framework to evaluate groundwater vulnerability to arsenic contamination in rural coastal aquifers by integrating geophysical techniques with hydrogeochemical analyses. The research addresses spatial and temporal variability of arsenic distribution, delineates vulnerable zones, and elucidates the controlling hydrogeological processes driving arsenic mobilization in lowland coastal settings. A multi-method approach combines electrical resistivity tomography (ERT), ground-penetrating radar (GPR), and magnetic resonance sounding (MRS) to characterize aquifer geometry, hydraulic properties, and pore-water characteristics, alongside groundwater sampling for major ions, trace metals, arsenic species, redox indicators, stable isotopes, and dissolved organic carbon. Geostatistical and machine learning models, including random forests and spatially explicit inverse modeling, are employed to fuse geophysical-derived lithology and hydraulic conductivity with chemical signatures, generating high-resolution vulnerability maps that reflect both intrinsic aquifer susceptibility and anthropogenic influence. Groundwater age and recharge dynamics are inferred from isotopic tracers (?18O, ?D, 3H) and spatial-temporal pumping data to assess recharge pathways and dilution effects on arsenic concentrations. The study investigates redox-controlled arsenic mobilization mechanisms (arsenite vs arsenate speciation) under varying sedimentary facies, organic matter content, and microbial activity, considering coastal processes such as seawater intrusion, groundwater-surface water exchange, and tidal fluctuations. A coupled hydrogeochemical model is developed to simulate arsenic transport and fate under different climate and land-use scenarios, calibrated against observed field data and validated with withheld samples. The vulnerability framework integrates intrinsic susceptibility (pore-water chemistry, mineralogy, sorption capacity) with exposure and consequence layers that account for well depth, well construction integrity, irrigation practices, and exposure of affected populations. Sensitivity analyses identify key drivers and thresholds for arsenic exceedance, while scenario analyses explore the effectiveness of management strategies, including aquifer reinjection control, managed aquifer recharge timing, and targeted monitoring networks. The outputs include (i) high-resolution vulnerability maps at sub-watershed scales, (ii) a decision-support tool for prioritizing boreholes and monitoring sites, (iii) a validated conceptual-nemodel linking hydrogeology to arsenic behavior, and (iv) policy-relevant guidelines for rural coastal communities to mitigate exposure and safeguard drinking water quality. The study contributes to the understanding of arsenic mobilization in coastal aquifers and demonstrates the value of integrating geophysics with hydrogeochemistry for risk assessment, enabling proactive management under changing climatic conditions and increasing anthropogenic pressures. The findings reveal that heterogeneity in sedimentary facies and redox gradients, coupled with seawater intrusion dynamics, create distinct pockets of heightened vulnerability that persist despite moderate groundwater ages, underscoring the necessity for site-specific monitoring and adaptive resource governance.

Project Overview

What This Project Is About

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A straightforward study of how groundwater in rural coastal areas may become unsafe because of arsenic, and how to map and model that risk using simple field measurements and basic data analysis. The project combines hands-on field work with easy-to-understand modeling to show where arsenic is likely to be high and why.

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The Problem It Addresses

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Arsenic in drinking water is a major health risk in some rural coastal regions. Many places lack affordable tests or clear maps showing who is at risk. This project aims to fill that gap by linking what we measure in water and soil to how likely arsenic is to appear in groundwater.

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Objectives of the Project

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1. Identify areas within the coastal aquifers that are most vulnerable to arsenic.
2. Use simple geophysical and hydrogeochemical measurements to support vulnerability assessment.
3. Develop a basic, easy-to-use model to explain arsenic risk patterns.
4. Provide practical recommendations for safe water use in affected communities.

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What You Will Do Step by Step

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1. Review basic literature on arsenic in groundwater and risk mapping.
2. Plan and conduct field sampling of water and soil/sediment where possible.
3. Perform simple measurements (e.g., electrical resistivity proxies, basic water chemistry tests).
4. Analyze data to identify patterns linked to arsenic risk.
5. Construct a straightforward model illustrating risk zones.
6. Validate findings with local water sources and community input.
7. Prepare a user-friendly map and guidance for stakeholders.
8. Discuss limitations and areas for future work.

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Expected Outcome

A clear vulnerability map and a simple model showing where arsenic risk is highest, plus practical recommendations for safe water use and monitoring in rural coastal communities.