What mainly reduces the chance of termite access when using a termite barrier?

The correct answer highlights the significance of soil treatment barriers in reducing the chance of termite access. A soil treatment barrier involves the application of termiticides or other chemical agents to the soil around the foundation of a structure. This barrier creates a toxic zone that termites must cross to reach the structure, effectively preventing their entry.

In contrast, the other choices, while relevant to termite management, do not primarily address the immediate prevention of termite access through barriers. For instance, while immediate physical removal of soil might change the landscape, it does not create a long-term preventive measure against termites. A concrete foundation can deter termites to some extent due to its hardness, but it does not eliminate the risk unless it is combined with other proactive measures, such as a soil treatment barrier. Using wood additives can help protect the wood from termites, but it does not directly prevent access like a soil treatment barrier does. Thus, soil treatment barriers are essential for providing a chemical barrier against termite intrusion.