How must an owner estimate the population when defining off-site impacts?

How must an owner or operator estimate the population when defining off-site impacts as part of the facility’s risk management plan (RMP)?

The owner or operator must estimate the residential population within a circle with its center at the point of the release and a radius determined by the distance to the endpoint (§68.30). Owners or operators must estimate the residential population to two significant digits and must use the most recent census data or other information believed to be more accurate (General Guidance on Risk Management Programs for Chemical Accident Prevention (EPA550-B-04-001)).