Horizontal directional drilling (HDD) is simply another way to drill a borehole. So, if a particular technique can be used in vertical drilling, it can also be used in horizontal drilling. Since these systems are essentially the same as horizontal Soil Vapor Extraction (SVE) wells, it should come as no surprise that sub-slab vapor mitigation can be done with horizontal bores. What many people are just realizing is how well these systems work for a variety of reasons.
Perhaps most important to sub slab work, is minimizing disturbance to the existing buildings operations. HDD installed sub slab does not require equipment to be brought into the building, and therefore the facility does not need to disrupt the building or facilities daily routines.
By drilling horizontally, uninterrupted screen can span across entire areas of interest. This means the amount of communication of horizontal well is significantly more than any vertical point can have. Vertical sub slab extraction points often have 2 feet or less of “screen” with which to communicate with the subsurface. Most horizontal sub slab systems we have installed have over 100 feet of screen, per bore… i.e., by this metric, one bore has equivalent communication as perhaps 50 vertical points.
The horizontal system manifold is tiny compared to a vertical system and can exist outside the building, thereby preventing significant concrete cutting and trenching.
Depressurization System Install Inside Building
At DTD we are seeing more of these sub slab vapor mitigation or depressurization systems being installed. Some are being placed as part of a larger remediation plan, while others are simply depressurizing the sub-slab and preventing fugitive emissions. Whatever the reason for the depressurization system, horizontal drilling offers an effective installation method that minimizes site what would otherwise be significant concrete cutting and site disturbance.