Introduction
Category: Environmental Chemistry • Read Time: 10 min
Leachate is the liquid that forms when water percolates through waste. Its chemistry is a complex blend influenced by waste composition, decomposition stage, and environmental conditions.
Understanding leachate chemistry is essential for designing safe containment, treatment, and groundwater protection measures.
Key Contaminants in Leachate
- Heavy metals:
- Lead (Pb)
- Cadmium (Cd)
- Chromium (Cr)
- Mercury (Hg)
- Organic contaminants:
- VOCs
- SVOCs
- PFAS (in modern waste streams)
- Nutrients:
- Ammonia
- Nitrates
- Orthophosphate
Environmental Conditions That Influence Chemical Behaviour
1. pH
Controls metal solubility and organic breakdown.
2. Redox potential (Eh)
Influences mobility of iron, manganese, and sulfur species.
3. Microbial activity
Drives decomposition, ammonification, nitrification, and denitrification.
Contaminant Transport Mechanisms
- Advection: movement with groundwater flow
- Dispersion: spreading caused by variations in flow paths
- Diffusion: molecular movement
- Retardation: adsorption to soil or biodegradation
Understanding these controls is essential for groundwater impact modelling.