Environmental drilling method for groundwater monitoring well
Before the construction of the groundwater monitoring wells, it is necessary to conduct a preliminary investigation of the site, to determine the subsurface site stratigraphy (e.g., soil type and bedrock determination, and to confirm the approximate distribution of the contaminants. This will aid in the selection of the appropriate monitoring well construction and the depth of the well that needs to be installed. To carry out this work, it is required to use drill rigs to collect soil samples in order to conduct the initial screening of the soil for contaminants. These data provide the basis for the development of long-term groundwater monitoring programs for the site including the depth and location of the monitoring wells.
Environmental monitoring wells are used to obtain representative groundwater samples, so their construction cannot use materials and tools that alter the physical and chemical properties of groundwater.
The types of drilling methods are mainly determined by the use or non-use of circulating drilling fluids. These fluid contains a complex polymer which may not be suitable for environmental drilling. Once into the groundwater, it may increase the difficulty and cost of purging the well. However, the use of these drilling methods maybe necessary depending on the depth of the monitoring well and the geologic formation. Some drilling methods use compressed air, which may also bring oil and contaminate the subsurface soil.
The following are some common environmental drilling methods:
1. Hollow Stem Auger
Hollow Stem Auger (HAS)is the most common drilling method. HAS can be used to obtain continuous soil core samples. The drilling method does not require use of any drilling slurry, suitable for semi-consolidated and non-consolidated soil to complete less than 30 meters deep of drilling work. HSA can also install pre-packed monitoring wells to expedite the process of well installation. But the HAS will produce drill cuttings wastes.
2. Direct Push Drilling
Direct push drill rigs are compact and designed not use any drilling fluid during operation. There are no drill cuttings produced by direct push rigs. The sampling process has little perturbation to soil core samples. It can be used in the semi-consolidated and non-consolidated soil with drilling depth of up to 60 meters. Direct push drilling rigs are widely used in environmental site characterization to conduct soil, vapor and groundwater sampling with various sampling and analytical equipment. Direct push rigs are able to push analytical equipment into the soil formation during drilling to analyze the hydrogeological condition and the distribution of pollutants in order to achieve a rapid site survey. Direct push rigs can also be fitted with pre-packed wells for installation.
3. Air Swirl Drill
This type of rig is suitable for drilling work in the bed rock zone. During the drilling process, high-pressure air is injected into the borehole through the drill bit. When the drill is rotated, the formation is cut into small pieces, and the compressed air takes the cuttings to the top of the hole where it is easily collected.
4. Sonic Drilling
Sonic drilling is a very powerful drilling method utilizing high frequency amplitude resonant energy to promote soil liquefaction. It is effective for all types of soil, including gravel and bedrock. Drilling depth can reach up to 100 meters or more. Sonic drilling is able to collect high quality core samples, and the perturbation of the sample is minimal. The drilling process does not require any drilling fluid and can carry a variety of detection equipment during the drilling process to investigate the distribution of hydrogeological features and contaminants.
Coordinator: EnvGuide Team