Ultra-high-performance grout (UHPG) grout appears to be good candidate for solidification and encapsulation of waste containing 99 Tc and 129 I that benefits from low Dobs. The properties that make UHPG a good candidate for encapsulating HEPA filters would make it a good option for microencapsulating other solid secondary waste (SSW) such as granular activated carbon, silver mordenite, and ion exchange resins. Containers made of UHPG would also be good candidates for dry disposal of SSW due to its very low diffusivity which prevents contaminant migration. Contaminated high-efficiency particulate air (HEPA) filters will be generated during operation of the secondary off-gas treatment system in the Low Activity Waste (LAW) Facility of the Hanford Tank Waste Treatment and Immobilization Plant (WTP). The HEPA filters receive off-gas from the vessel vent header and primary off-gas treatment system in LAW Facility and remove particulate contaminants including 99 Tc and 129 I salts. The current disposal method for HEPA filters is encapsulation in metal containers using grout and placement in the Integrated Disposal facility (IDF), (Nichols et al., 2017). Results from calculations supporting the IDF Performance Assessment (PA) demonstrated that contaminated HEPA filters from the WTP are the largest contributors to groundwater impacts and dose to a member of the public in the future from contaminants of potential concern (CoPC), including 129 I and 99 Tc. 129 I Kd, mL/g 110 110 Rf 517 1600 Dobs, m 2 /s 3.2 x 10-13 1.7 x 10-19 Deff, m 2 /s 1.7 x 10-10 2.7 x 10-16 Note: a insufficient spike in Baseline grout to measure Kd, b not solubility controlled in Baseline grout, c solubility controlled in UHPG.