The use of halogenated aliphatic compounds such as TCE and their improper disposal result in serious groundwater contamination. Why?

• A. They evaporate quickly
• B. They are extremely persistent and difficult to remediate
• C. They are non-toxic at typical concentrations
• D. They degrade rapidly in groundwater

Answer: (D)

The main idea is that halogenated aliphatic solvents like TCE persist in groundwater and are hard to clean up. Their chemical structure—carbon–chlorine bonds—makes them unusually resistant to natural breakdown under typical subsurface conditions. Many of these compounds form dense, non-aqueous phase liquids (DNAPLs) that sink to the bottom of an aquifer and slowly dissolve over time, creating long-lasting plumes. Because natural attenuation is limited and remediation is technically challenging and costly, contamination from improper disposal can remain for decades. While evaporation or volatilization can occur, it doesn’t address the dissolved contaminants in groundwater, and these compounds are often toxic and mobile enough to spread, so persistence—and the difficulty of remediation—is the core issue.