Abstract: A method and apparatus for emplacement of dry particulate filter pack and seal material into a borehole to form a monitoring zone for groundwater monitoring which allows the material to be emplaced in dry form. The method involves inserting a tube into the borehole to a depth above a desired monitoring zone and consecutively injecting a first layer of seal material, a layer of filter material and a second layer of seal material, while supplying gas to the tube to prevent groundwater from contacting particulate material while in the tube. The apparatus comprises an injector, including a container and valve assembly adapted for connection to a pressurized gas supply, that allows sequential placement of seal material and filter material while continuously supplying gas to the injection tube.