In situ solidification / stabilization (ISS) projects require a significant amount of characterization, sampling, and bench scale testing in the design or feasibility phase to ensure a successful project. During this phase, the proposed construction methods need to be considered, taking into account such things as slurry proportions, untreated soil type / density, treated soil consistency, and soil / contaminant variability. As the project moves from the preconstruction phase into the construction phase, the results of the design phase are used to refine key project objectives which may include target improvements for permeability, strength, and / or leachability. A quality control / quality assurance monitoring program, which may include a combination of process controls, in-situ testing, and laboratory testing on grab samples, is then developed to confirm that the key project objectives are achieved. Process controls provide immediate feedback, but generally do not directly measure the target properties. Many of the available in situ testing methods were not developed for ISS mixtures and are therefore limited for use in this application. Finally, many of the laboratory tests conducted on field collected grab samples, specifically leachability tests, require long lead times and therefore provide limited real time feedback. In order to account for the advantages and disadvantages of each monitoring method, the quality control / quality assurance monitoring program should include a combination of short and long turnaround testing to be used collectively to predict the long term performance of the improved material.