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sifted soil from the depth at which the porous steel will be placed. Once this soil <br /> has been compacted around the lysimeter one may want to wet the soil so that <br /> the dry soil does not extract the water from the previously wetted porous steel of <br /> the lysimeter. To work properly the porous steel should remain wet during the <br /> entire time one wants to collect liquid samples. <br /> Note that by using silica flour one introduces a different material that was not <br /> there before, and that may have different chemical characteristics than the <br /> original soil. <br /> Installation at greater depths <br /> The following are general suggestions for installation of the 2 inch OD <br /> lysimeters.Additional information can be found in ASTM D4696. <br /> Geologic conditions differ greatly from location to location. Knowledge of the <br /> local conditions should be available before installation is to begin. <br /> Correct installation of suction lysimeters requires ensuring good contact between <br /> the porous stainless steel, and the surrounding soil. It is also important that the <br /> potential for vertical migration of fluid through the borehole annulus be <br /> prevented. The following techniques assume that the borehole is constructed to <br /> the desired sampling depth using a hollow-stem auger. <br /> 1. Raise the auger flight about 2-feet from the base of the borehole (this ensures <br /> that the sampler will not become wedged within the auger). <br /> 2. Pour about 10 kilograms of silica-flour slurry (prepared by adding one <br /> pound of 200 mesh silica flour per 150 ml distilled water) through a tremie <br /> pipe extending to the base of the borehole. Silica flour is not recommended if <br /> the water sample is to be tested for virus. Slurry prepared from the soil <br /> removed from the bottom of the borehole and screened, can also be used. <br /> However, it is important that the slurry material makes good contact with <br /> the porous steel, and has good water permeability. <br /> 3. Lower the pre-wetted lysimeter assembly through the hollow-stem auger to <br /> the base of the bore hole and gently press the lysimeter into the silica flour <br /> slurry. A stainless steel or PVC centralizer may be used to ensure proper <br /> placement of the sampler within the borehole. <br />