Ecological risks do not need to be assessed if which condition is met?

The reasoning behind the answer focuses on the concept of ecological risks in relation to the depth of contamination and its potential impact on environmental resources. If contaminated soils are present three feet or deeper, it generally implies that there is less risk to surface ecosystems and water sources. In many regulatory frameworks and risk assessment protocols, contamination that is deeper underground is often considered to have a reduced likelihood of affecting surface water or terrestrial habitats. Since surface water and terrestrial ecosystems are crucial indicators of ecological health, the absence of impact on these resources can lead to the conclusion that ecological risks are not significant in this scenario.

In contrast, the other conditions mentioned do not eliminate the need for risk assessment. For instance, soil contamination being below acceptable levels does not automatically mean there is no risk—it may still pose potential hazards under certain circumstances. Similarly, above-ground contamination could still impact nearby organisms or ecosystems, and low contamination levels indicated by samples may not fully account for cumulative effects or long-term exposure risks. Each of these factors can require further assessment to ensure a comprehensive understanding of ecological risks involved.