Water Well Drilling Methods

Abstract

Abstract Water well installation, for domestic or public water supply purposes, groundwater monitoring projects or for irrigation involves a variety of drilling techniques, depending on subsurface conditions, groundwater depth, access, and other factors. The three most common drilling methods for potable water supply wells are rotary drilling, auger drilling, and cable tool drilling. More recently sonic drilling has been used in certain for potable water well construction. The main challenge in drilling is to drive the drill string to the target depth while removing the drill cuttings and maintaining borehole wall integrity. Each drilling location has site‐specific surface and subsurface conditions, selecting the optimal drilling method is critical to installing a successful well. Drilling method selection relates to a variety of factors, including rig and crew availability, site accessibility, time and cost of project, sediment type (consolidated rock or unconsolidated soils), special drilling problems (unconsolidated sediments and soils, pressurized saturated sands, lost circulation zones, cobbles, and boulders), soil/rock sample type desired (undisturbed vs. disturbed), and sample integrity. For contaminant studies and environmental projects, monitoring and remediation water wells (and vapor wells) are installed, which frequently relate to chemical spillage on or near the surface. The most common drilling method for installing shallow monitoring and remediation wells is hollow stem auger drilling which works well in soil and unconsolidated sediments, and soft rocks. Hard rock drilling required for environmental projects have used air rotary or cable tool drilling rigs, and to a lesser degree, mud rotary drilling rigs. Soil/rock, soil vapor, and groundwater collection and integrity are critical for environmental projects where depth discrete sampling is common as well as vadose zone sampling. The vadose zone, also called the unsaturated zone, includes the zone immediately above the water table to the surface. The lower vadose zone includes the capillary fringe, the zone where water is drawn upward by capillary force. The water table is the top of the saturated or phreatic zone within the aquifer. Other drilling methods are used for contaminant studies, including direct push and sonic drilling.