sure hydraulic gradient to deter-
mine flow velocity. Four holes are usually required for a measure-
ment using this standard technique as compared to one hole using the Colloidal Borescope. With the standard technique, information about the hydraulic conductivity of the medium is required and is generally determined using a pumping test in which large quan-
tities of water are pumped from the well. Disposal of this purge water can be difficult and expen-
sive. The standard technique mea-
sures a velocity that is averaged over a broad region, one whose dimensions are characterized by the separation of the boreholes.

The borescope is an in situ instru-
ment capable of directly observing the movement of colloidal size

particles within boreholes to quan-
tify groundwater flow rate and di-
rection. Current applications include: site characterization by determining preferential flow paths and fractures; assessing heterogeneities associated with porous media; establishing the existence of immiscible contami-
nant layers and their associated flow properties; assessing the effi-
ciency of groundwater remedia-
tion programs by determining the effective radius of influence of groundwater extraction systems; and evaluating the effects of sam-
pling on colloidal concentrations. Potential applications include pro-
viding physical observation capa-
bilities necessary to develop and confirm new, more accurate theo-
retical models of porous media flow process and assessing the