Which of the following methods is considered safest for deep-water injection?

The method identified as safest for deep-water injection is bottom placement. This technique involves strategically locating materials or treatments at the bottom of a water body, which minimizes potential exposure to non-target organisms and helps reduce the likelihood of causing harm to the aquatic ecosystem.

Bottom placement allows for controlled dispersal of the treated substance, ensuring that it interacts specifically with the targeted area or organism, while limiting surface movement and the exposure of non-target species. This method is particularly effective in deep water, where conditions can be more stable and the risk of contamination of surface waters is significantly reduced.

Other methods, such as surface spraying or aerial applications, typically involve direct exposure of the aquatic environment and its inhabitants, leading to higher risks of unintended consequences. Subsurface injections can be effective but may still pose risks to nearby organisms if not managed properly; hence, they are usually not regarded as the safest option in comparison to bottom placement.