[en] The March 1979 accident at General Public Utilities Nuclear Corporation (GPUNC) Three Mile Island Nuclear Power Station Unit 2 (TMI-2), resulted in the transfer of more than 1100 m³ of contaminated water to the auxiliary and fuel handling building. The principal sources of the water were the makeup and letdown purification system and the containment building sump. The contaminated water was processed through an ion exchange system designated as EPICOR II. The EPICOR-II System is a three-stage process. The contaminated water passes through a first stage of ion exchange media, designated as prefilters, and then through the second and third stages, designated as demineralizers. The majority of the activity was deposited in the first-stage prefilters, which have a maximum administrative loading limit of 1300 curies. The predominant radionuclides present in the prefilters are cesium and strontium