Please note that there is no definitive answer about how far apart a disaster recovery site should be.
Main ISO standards covering this topic (ISO 27001, for information security, and ISO 22301 for business continuity), as well as most regulations and industry practices, do not define any specific distance to recovery sites, because many factors can affect what would be considered a “safe” distance (e.g., type of disaster, access to public services, risk level, etc.). From our experience, we suggest you start a discussion suggesting a distance between 30 miles (50 kilometers) and 100 miles (160 kilometers) away from your primary location, and from that analyze your organization's context (a geographic situation, available resources, required investment, etc.).
This article will provide you with a further explanation of the distance of the recovery site: