Final answer:
Unused and contaminated sites that need cleanup are hazardous waste sites that pose a significant risk to human health or the environment.
Step-by-step explanation:
Unused and contaminated sites that need cleanup are hazardous waste sites that pose a significant risk to human health or the environment. These sites require remediation to protect the well-being of individuals and the ecosystem. One example is the Love Canal tragedy, which led to the establishment of the Superfund program in the US to address uncontrolled hazardous waste sites. Currently, there are over 1,000 major hazardous waste sites in the process of being cleaned up.