Ammonia (CAS #7664-41-7) is an Extremely Hazardous Substance (EHS), listed at 40 CFR Part 355 Appendices A and B with a reportable quantity of 100 lbs. Both ammonia and ammonium hydroxide (CAS #1336-21-6) are listed as CERCLA hazardous substances at 40 CFR 302.4. Under CERCLA, ammonia is listed with an RQ of 100 lbs and ammonium hydroxide is listed with an RQ of 1,000 lbs. A facility has a large storage tank of ammonium hydroxide solution. How does the facility report a release from this storage tank under EPCRA section 304 and CERCLA section 103? Does the CERCLA mixture rule apply to the release of ammonium hydroxide solution?

CERCLA section 103 applies to releases of CERCLA hazardous substances (40 CFR 302.4). EPCRA section 304 applies to chemicals listed as either CERCLA hazardous substances or Extremely Hazardous Substances (EHSs) (40 CFR part 355).  Both ammonia and ammonium hydroxide are listed as CERCLA hazardous substances, therefore both chemicals are subject to CERCLA section 103 and to EPCRA section 304 release reporting requirements.  However, the amounts of ammonia and ammonium hydroxide in the storage tank should be considered individually to determine whether any releases need to be reported under either CERCLA or EPCRA.  It is possible that free ammonia exists in the headspace of the ammonium hydroxide storage tank; the facility must provide notification of any release of this ammonia, if it equals or exceeds its RQ, to the National Response Center (NRC), the State Emergency Response Commission (SERC) and the Local Emergency Planning Committee (LEPC). The facility must also provide notification of any release of ammonium hydroxide solution at or exceeding its RQ to the NRC, SERC and the LEPC. For ammonium hydroxide solution releases, the facility does not need to apply the CERCLA mixture rule to determine the quantity of ammonia in the solution released.