Every day, water companies have to meet the great demand for clean, pure drinking water. In that respect, a decrease in capacity in a well is definitely not welcome.
The formation of the aquifer in which the filter pipe is installed is very important for the optimum operation of a filter system. The casing between the pipe and the soil is referred to as “the screen”. The size of the grains of the soil determines the ideal screen and this screen determines the ideal width of the filter crevice (perforation). The proper balance between the soil composition and the perforation of the filter pipe prevents sand delivery and ensures that the filter has a high hydraulic capacity that can be regenerated.
Homogeneous vs. heterogeneous
A homogeneous soil structure makes it possible to calculate the perforation correctly. In this situation, the calculation is based on the smallest sand particle and the filter crevice is adjusted to that. In that case, when constructing a filter, we use the screen that is there naturally.
However, in both the Netherlands and abroad, the soil is far from homogeneous This makes it virtually impossible to construct a filter pipe with the proper perforation and prevent sand delivery. This is why, in the construction of vertical wells, the application of artificial screens was pretty much standard procedure.
A screen can now be applied to horizontal pipes as well
An innovative but tried method now makes it possible to use an artificial screen for a horizontal filter pipe as well. In this process, a sand pack that has been made artificially homogeneous is placed around the pipe. This makes it possible to calculate the proper size of the filter crevice again. When constructing an HDDW, the sand pack can be applied both above and below ground. An artificial screen prevents sand delivery and keeps the capacity at optimum level.
The choice between a natural and an artificial screen makes it possible to install the HDDW in almost any soil.