Water well drillers use a variety of portable rigs to install wells. Most drill rigs are truck- or trailer-mounted so that they are easy to move between properties and well locations. Drilling methods can vary depending on the characteristics of the surface and subsurface of the land being drilled.
Auger Drill Rigs
Auger drill rigs employ either hollow-stem or solid-stem augers to create the borehole for the water well. You can find both trailer-mounted and truck-mounted auger rigs. An auger rig operates by rotating the auger into the soil. Soil cuttings expel from the subsurface by traveling up the outside of the augers to the land surface. Generally, solid-stem augers are useful when you are drilling at sites with high clay content so that the borehole will remain open when you remove the augers. For sandy soils that will collapse into the borehole, most drillers prefer to use hollow-stem augers because you can install the well through the inside of the augers. These drill rigs are common for shallow well installation because they are one of the least expensive rigs to operate. However, the presence of bedrock limits the depth to which you can drill. Auger rigs cannot generally penetrate solid rock. Most augered wells are less than 100 feet deep.
Rotary Drill Rigs
Rotary drill rigs use a rotating bit attached to a drill rod. Tricone roller bits are common with rotary drilling. The operator pumps a drilling fluid, mud, water or air down a drill pipe into the bit. The drilling fluid helps to lubricate and cool the bit, then carries the drill cuttings out of the borehole through the annular space. You can obtain good lithology data using air and water because the cuttings are generally clean when they exit the borehole. When you are drilling in sandy soils that will collapse into the borehole, water or mud will keep the borehole open during the drilling operation. Air is appropriate when you are drilling in clay soils and rock, because it will not prevent borehole collapse. Rotary drill rigs are commonly used for deeps well that intersect bedrock and are often truck-mounted. These rigs can install wells up to 1,000 feet in depth and between 3 and 24 inches in diameter.
Sonic Drill Rigs
Sonic drill rigs use a combination of drill stem rotation and vibration in conjunction with a drilling fluid to advance the borehole. You can use these rigs to obtain continuous core samples from your borehole. Sonic rigs advance a drill stem with an inner string. The inner string collects the core sample, while the outer drill stem cases the well as it drills. Drilling fluid will help keep formation soils from entering the drill stem as it advances through the subsurface. Sonic rigs are expensive to operate; however, they are generally faster than convention auger and rotary drilling. The drill rods range from 3 to 12 inches in diameter, and you can use various sizes of rods to create a telescoped borehole at one location. Sonic rigs can drill through any soil, as well as bedrock, so can install deep wells.
Direct Push Drill Rigs
Direct push drill rigs use small-diameter drill rods that advance into the subsurface using a percussion hammer. Typically, a 1- to 2-inch diameter shallow well is the maximum size achievable with this system. Most direct push rigs will not penetrate bedrock. These rigs are usually truck- or trailer-mounted and are easy and inexpensive to operate. You can collect continuous soil samples with the direct push system. These rigs are particularly useful for installing temporary wells at a property when you are trying to locate the depth to groundwater or evaluating the groundwater quality before you install the permanent monitoring well.
- Purdue University: Well Drilling Methods
- Oregon Institute of Technology: Geothermal Information and Technology Transfer
- United States Geological Survey: Groundwater: Wells
- EPA Region 4: Design and Installation of Monitoring Wells
- Miller Drilling Company: Advantages of Sonic Drilling for Environmental Investigations
- Photo Credit Jupiterimages/Photos.com/Getty Images
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