Which of the following is NOT a common method for remediating contaminated groundwater?

Desalination is the process of removing salts and minerals from water to produce freshwater, primarily for drinking or irrigation purposes. While it is a significant method for addressing water scarcity, it is not specifically a remediation technique used to treat contaminated groundwater. In contrast, the other methods listed—pump and treat systems, bioremediation, and natural attenuation—are directly focused on the removal or degradation of contaminants in groundwater.

Pump and treat systems involve extracting contaminated groundwater, treating it to remove pollutants, and then reinjecting or disposing of the clean water. Bioremediation utilizes microorganisms to break down hazardous substances into less harmful forms, effectively reducing contamination levels. Natural attenuation relies on the natural processes occurring in the environment to diminish contaminant concentrations over time. Therefore, desalination does not fit within the context of groundwater remediation, making it the correct answer to the question.