Geotechnical boreholes provide a direct conduit for the transport of surface and subsurface contaminants if left open or improperly sealed at the end of drilling operations. Current field practices used during the decommissioning of a drilled hole generally rely on a relatively small group of products to act as a sealant or barrier to contaminant transport. Slurries using mixtures of bentonite, portland cement and other materials and compacted barriers composed of native soil and other materials have been used as contaminant transport barriers in applications such as slurry trenches and compacted liners and may be well suited as workable borehole sealants. A literature review provides a summary of hydrologic properties of various materials which might have applications as borehole sealants. This summary is presented in a concise format along with a brief discussion of each of the classes of mixtures to act as permanent seals. In addition to this review, the results of laboratory hydraulic conductivity tests performed on a range of commercially processed bentonite products sold as seal materials are presented. Physical characteristics of various commercial bentonite products are also presented. Results of laboratory hydraulic conductivity tests performed on other typical sealant mixtures are also presented. The results of this study identify a number of alternatives for providing borehole seals to act as contaminant transport barriers in boreholes.