Ammonia (CAS number 7664-41-7) is an EPCRA extremely hazardous substance (EHS) listed in Appendix A to Part 355. However, ammonium hydroxide, which is made by combining ammonia and water, is not listed and has a separate CAS number (CAS number 1336-21-6). For the purpose of Part 370, must the amount of ammonia in ammonium hydroxide be counted (and aggregated) towards the 500 pound EHS threshold? For example, if a facility has 9000 pounds of ammonium hydroxide (19 percent) on site at a given time, while the 10,000 pound threshold for ammonium hydroxide is not exceeded, the amount of ammonia present in the solution (1710 pounds) would exceed the EHS's threshold of 500 pounds. Does this facility have to include ammonia in its 311 and 312 reports?
The EHS list in Part 355 is defined by reference to the CAS registry number. The CAS registry considers ammonia and ammonium hydroxide as distinct chemicals, each having a registry number. Therefore, ammonia completely dissolved in aqueous solution to form ammonium hydroxide is not an extremely hazardous substance for the purposes of EPCRA 311 and 312 reporting. The facility would report only if the amount of ammonium hydroxide exceeds 10,000 lbs.