Posted on February 20, 2014 by Brian

DTD recently completed soil sampling for a client in southeastern United States.  This project is similar to the small handful of sampling projects DTD completes each year.  While we’ve been doing soil sampling with Horizontal Directional Drilling (HDD) for over 10 years, there is no off-the-shelf tooling to assist us with the process. This requires DTD to develop and manufacture all of its sampling tooling. While this may be seen a disadvantage, we view it as an benefit, as each time we build a new sampler, we can easily incorporate changes necessary for the HDD environment.

HDD allows access to soil sampling locations that would otherwise be cost prohibitive or even impossible with conventional vertical sampling methods.  Sampling projects completed by DTD include sampling under nuclear facilities, landfills and water bodies.  In some cases it is physically (or financially) impossible to access the sampling site from directly overhead on the surface.  At other sites protective barriers impede access from above.  For example to test for presence of leachate under a landfill, a vertical rig would drill down through the landfill, puncturing the liners it encounters along the way.  In other words, sampling to determine if the liner is leaking, would puncture the liner.  Horizontal directional sampling enters the ground offset from the surface obstruction (i.e. liner or building) and is guided to the desired sampling location, all while leaving the surface/near-surface directly above the sample undisturbed.

DTD’s sampling process ensures accurate and reliable results.  Prior to tripping a sampler downhole a drill bit cuts a borehole, stopping just short of the desired sampling location.  Specialized samplers travel downhole in a closed position to prevent soil from collecting in the tooling before reaching the location of interest.  Once at the end of the bore the tooling is pushed into the native soils and a sample is collected within an acetate tube.  The drill string is then brought back to the surface, where the sample is removed for analysis and a drill bit readied for the next location.

Recent refinements in tooling and procedures are advancing DTD’s efforts in horizontal directional soil sampling.  Two types of samplers are currently in DTD’s inventory allowing for successful sampling in a variety of drilling conditions.  Recent tooling modifications include easier assembly/disassembly for sampler set-up and decontamination efforts.  Additional refinements include strengthening of the tooling itself.  This added durability allows DTD to sample closer to hard objects such as concrete structures and rock layers.  Where softer soil samples are encountered DTD uses custom core catchers to hold samples during the trip back process.

Feel free to contact DTD to discuss your sampling challenges and how HDD may be able to help you with your project.

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