Mapping Pollution Risks: Geo-Information and Multi-Criteria Analysis in Olive Mill Wastewater Management

This study develops a quantitative risk assessment framework to evaluate the environmental impact of Olive Mill Wastewater (OMW) pollution on surface water resources in the Keritis watershed, Western Crete. Utilizing a Multi-Criteria Analysis (MCA) approach integrated with hydrological modeling, the research assesses risk through magnitude (spatial and temporal dimensions) and probability (hazard occurrence, receptor exposure, and harm likelihood) components. Eleven criteria, including population vulnerability, precipitation, pollutant dilution potential, and lagoon conditions, were normalized and weighted via the Analytic Hierarchy Process (AHP). The methodology classified sub-catchments into five risk tiers using natural breaks, revealing significant spatial variability. Key findings identified sub-catchments 4, 5, and 9 as high-to-moderate risk zones for human health due to proximity to low-order streams, high phenol concentrations, and precipitation patterns. For NATURA sites, sub-catchments 5 and 6 faced elevated risks, driven by extensive pollutant pathways and habitat sensitivity. The analysis underscores the critical role of flow path length and dilution capacity in mitigating risks, particularly in areas with 4th- and 5th-order streams. Policy implications advocate for restricting olive mill permits in high-risk zones and adopting inorganic flocculation for cost-effective pollution control. The study highlights the framework’s adaptability to diverse pollution scenarios but calls for expanded criteria to address groundwater and soil impacts. By providing a replicable, data-driven tool, this work aids policymakers in prioritizing mitigation efforts and aligning with EU Water Framework Directive goals, balancing ecological preservation with socio-economic needs in olive oil-dependent regions.