Which term describes rates that account for physical, chemical, and biological changes in a contaminant over time?

• A. Transformation and degradation
• B. Advection
• C. Dispersion
• D. Attenuation

Answer: (A)

Transformation and degradation describes how a contaminant changes over time due to physical, chemical, and biological processes. It captures the rates at which the contaminant’s chemical form is altered or the mass is reduced through reactions such as biodegradation by microbes, hydrolysis, oxidation-reduction, and other abiotic transformations. This focuses on the actual change in the contaminant itself, not just its movement or dilution. Advection is about transport with groundwater flow, not changes in the contaminant’s state. Dispersion describes spreading due to velocity variations and diffusion, not chemical or biological alteration. Attenuation refers to the overall reduction in concentration from multiple processes, including dilution and sorption, but it’s a broader term that doesn’t isolate the rate of chemical/biological transformation. Transformation and degradation is the precise concept for these time-dependent changes.