Drilling Fluid Regulations
Usually a "drilling mud" such as fluid bentonite clay is injected into the bore during cutting and reaming to stabilize the bore hole and remove soil cuttings. Drilling mud can be made from clay or polymers. If clay represents a large component of the native soil in the construction site, a polymer additive may be more appropriate. The primary clay for drilling mud is sodium montmorillonite (bentonite). Properly ground and refined bentonite is added to fresh water to produce a "mud." The mud reduces drilling torque, and gives stability and support to the bored hole. The fluid must have sufficient gel strength to keep cuttings suspended for transport, to form a filter cake on the borehole wall that contains the water within the drilling fluid, and to provide lubrication between the pipe and the borehole on pullback. Drilling fluids are designed to match the soil and cutter. They are monitored throughout the process to make sure the bore stays open, pumps are not overworked, and fluid circulation throughout the borehole is maintained. Loss of circulation could cause a locking up and possibly overstressing of the pipe during pullback. Drilling muds are thixotropic and thus thicken when left undisturbed after pullback.
Typical drilling fluid components are not hazardous materials, with the waste material usually considered as excavation spoils, not requiring special disposal procedures. The volume of spoils to be removed from the site may be significantly reduced by means of drilling fluid recirculating systems. The additive materials should be chemically inert, biodegradable, and non-toxic, and petroleum-based or detergent additives should not be used.
Although the bentonite-water, or commonly used polymer-water, slurry is not inherently a hazardous material, special disposal may be required when drilling in an area known to contain toxic pollutants. In such cases, disposal must be in accordance with local laws and regulations, and it may be necessary to de-water the spoils, transport the solids to an appropriate disposal site, and treat the water to meet disposal requirements. It may be also necessary to add grouting to the drilling fluid to ensure proper sealing of the bore hole to eliminate a possible passage for contaminants. Special drilling fluid pumps may then be required.
In order to maintain a neat, orderly work site, occasional small pits must be available for collecting the excess drilling fluid or slurry exiting from the bore hole. A clean work site will help ensure the installation of a clean product pipe, reducing the need to later flush out mud or debris from within the pipe and provide a safe work area. Excessive drilling fluid and mud in the area may impair the connections and associated grounding characteristics of the equipotential grid mat system. Pits may already be present or required such as for utility access or connections at the ends or along the bore, thereby serving as convenient receptacles. If not otherwise present, small pits should be provided at the ends, and possible intermediate points to serve this function. The pits should be emptied as necessary.