Should two adjacent sources be combined for air permitting purposes? On the surface this may seem like a simple question. However, guidance from the EPA on this topic has switched over the years. Originally, in 1980, the EPA focused on combining sources that were adjacent in terms of physical proximity as well as industrial grouping and common control. Over the years the policy has been interpreted differently by using case-specific facts related to shared equipment, shared workforce, ownership and contracts.
On November 26, 2019 the EPA issued a new memorandum providing guidance on this issue. This memo focuses on using a common dictionary definition of contiguous which means that two pieces of land should be in physical contact with one another. The new memo can be found here: https://www.epa.gov/sites/production/files/2019-11/documents/adjacent_guidance.pdf
It is important to note that each scenario is different and often an attorney should review the facts specific to each case. This most recent memo from the EPA provides guidance for permitting authorities. They are encouraged to, but do not have to follow this guidance.