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{Sup 99}Tc and {sup 129}I are important contributors to risk assessment due to their long half-lives and high mobility as aqueous anionic species. We analyzed {sup 99}Tc and {sup 129}I in groundwater samples in and near 11 underground nuclear tests and in melt glass and rock samples retrieved from the Chancellor test cavity, Nevada Test Site. The {sup 129}I/{sup 127}I ratio ranges from 10{sup -3} to 10{sup -6} in cavity water and 10{sup -4} to 10{sup -9} in satellite wells. The {sup 99}Tc concentration ranges from 3 to 10{sup -4} Bq/L in cavity waters and from 0.3 to 10{sup -4} Bq/L in satellite wells. Downstream migration is apparent for both radionuclides. However, it is affected by both retardation and initial distribution. In-situ {sup 99}Tc and {sup 129}I K{sub d}s calculated using rubble and water concentrations are 3 to 22 mL/g and 0 to 0.12 mL/g, respectively and are suggestive of mildly reducing conditions. {sup 129}I distribution in the melt glass, rubble and groundwater of the Chancellor test cavity is 28%, 24% and 48%, respectively; for {sup 99}Tc, it is 65%, 35% and 0.3%, respectively. Our partitioning estimates differ from those of underground tests in French Polynesia, implying that fission product distribution may vary from test to test. Factors that may influence this distribution include geologic conditions (e.g. lithology, water and CO{sub 2} content) and the cooling history of the test cavity.