Regulatory information, not a compliance determination.
Federal requirements are a floor — your state primacy agency's rules usually
govern and are often stricter. Confirm anything enforcement-consequential with them.
Check a result
You have a number from the lab and need to know what it means.
Watch a system
Keep an eye on one system over time, not just today's sample.
Understand a rule
Work out what a regulation actually requires of you.
After a problem
Something went wrong — find out what it triggers.