Does the distance to endpoint start at the process or stationary source boundary?

When selecting the worst-case release scenario for Program 2 and 3 processes as required by 40 CFR §68.25, a stationary source owner or operator must analyze the release scenario that results in the greatest distance to an endpoint. Does the "greatest distance to an endpoint" refer to the greatest total distance from the process (e.g., vessel or pipeline), or to the distance beyond the stationary source boundary?

The greatest distance to an endpoint will ultimately refer to the distance beyond the stationary source boundary. When selecting a worst-case release scenario, the stationary source owner or operator must first evaluate potential releases from all Program 2 and 3 covered processes. Each release is modeled as a circle, with its center at the process and with a radius equaling the distance to the endpoint concentration (Response to Comments document, Ch. 5, pg. 5-109). The owner or operator must then choose the scenario that results in the greatest distance to an endpoint (40 CFR 68.25(a)(2)). If a scenario with a smaller overall distance to an endpoint, however, could result in a greater distance to an endpoint beyond the stationary source boundary (e.g., the process is very close to the facility boundary), it must be chosen as the worst-case release scenario (40 CFR §68.25(h)).