Groundwater monitoring:
Construction of monitoring wells
Groundwater monitoring wells are constructed through a sequence of carefully controlled steps to ensure reliable groundwater sampling and measurement.
STEP 1. Site selection
The first step is to identify a suitable location for the monitoring well. The site is selected based on the monitoring objective, local hydrogeology, groundwater flow conditions, and the target aquifer that should be observed.
STEP 2. Drilling
A borehole is drilled to the required depth using drilling methods such as rotary, auger, or cable-tool drilling. The drilling must penetrate the geological layers until the desired groundwater-bearing zone is reached.
STEP 3. Borehole cleaning
After drilling, loose sediments and drilling residues are removed from the borehole. Cleaning improves well stability and prepares the borehole for proper installation of the casing and screen.
STEP 4. Casing Installation
A PVC or steel casing is inserted into the borehole to stabilize the well and prevent collapse. The casing also protects the groundwater from contamination entering from upper soil layers.
STEP 5. Screen Installation
A slotted well screen is installed at the depth of the target aquifer. The screen allows groundwater to enter the monitoring well while keeping surrounding sediments out.
STEP 6. Filterpack Installation
Clean sand or gravel is placed around the screened interval. This filter pack improves water flow into the well and prevents fine particles from clogging the screen.
STEP 7. Sealing and completion
The upper part of the borehole is sealed with bentonite or cement to prevent contamination from the surface. Finally, a protective casing and cap are installed to secure the monitoring well for long-term use.
Typical well diameters
Well diameters vary from country to country. Following diameters are very common in Germany: