What maximum permeability can be measured with a monitoring well?

The PVC screens of recentmonitoringwells (MWs) have thin slots and a lowopen area, usually in the 2–8% range. The MW screen and filter pack may cause important head losses which are not taken into account when interpreting the data of permeability tests performed using the MW. The equivalent hydraulic conductivity K of usual PVC screens was defined by hydraulic tests in a water tank, which have shown that gas microbubbles, a common problem in MWs and filter packs, contribute to increase the parasitic head losses. Closedform equations and numerical models are used to explain by how much a field permeability test in a MW under evaluates an aquifer K value due to parasitic head losses in the screen and filter pack. TheMWcan properly measure the local soil K value only if it is markedly lower than the maximum MWvalue as obtained in a water tank. TheMWmeasuring capacity can reach 5 × 10−3 m/s for large slots and deairedwater, but ismost often between 10−5 and 10−4 m/s for small slots in field conditions, and it can be only 10−6 m/s for poorly designed and installedMWs. The limitedmeasuring capacitymay yield artificial permeability scale effects as often registered in environmental studies.

Mots clés

Monitoring well,Permeability test,Screen,Filter pack,Aquifer