Uranium (U) is a crucial contaminant in the Hanford Site. Remediation techniques to prevent contaminant migration of U located in the soils to other important water resources such as the Columbia River are of paramount importance. Given the location of the contaminant in the deep vadose zone, sequestration of U caused by ammonia (NH3) gas injections appears to be a feasible method to decrease U mobility in the contaminated subsurface via pH manipulation, ultimately converting aqueous U mobile phases to lower solubility precipitates that are stable in the natural environment. This study evaluated the stability of those U-bearing precipitates via preparation of artificial precipitates mimicking those that would be created after NH3 gas injections and sequential extractions experiment. Results showed that most of the U was recovered with the extracting solutions targeted to remove uranyl silicates and hard-to-extract U phases, suggesting that U present in the solid particles has strong bonds to the vadose zone sediments, causing the precipitates to be stable and therefore the remediation technology to be effective under the simulated conditions.