I know just a little. Arsenic can come from natural sources or pollution of groundwater. If it comes from natural sources, the more acidic the water, the greater likelihood it will go into solution and be mobile. If from nearby pollution source, the more pumping could pull in more and more due to the localized lowering of water table. Drilling and well lining methods that pass through contaminated areas that are not properly lined and sealed are more apt to have issues that wells that pass through these areas through an confine aquifer barrier into better water below. Sloppy drilling and well lining sealing off contamination may result in contaminating other areas. Understanding the local geology through the well core and possibly sampling it may help ascertain if there is a general or local problem area. If there are geology maps and cross sections of stratigraphy and reading landforms, that can help bring understanding. If the arsenic levels are not too high, there may be water treatment methods like the tanks under my home to take out some contaminants and also reverse osmosis system to take out added amounts for drinking with proper testing and system management. I would consider advice from seasoned geologist and well drillers when you want water, even well dousers (I had a great uncle in Nebraska who was one). However I do not know how well even the best can predict issues like arsenic unless specialists know if it a general problem for the area or know of industrial or other sources nearby. If you are dealing with hand dug or small equipment dug wells, you may not have so many options.
More pumping may increase the amount and concentration of arsenic as it can pull more arsenic from the surrounding natural and pollutant source and heavy metal dumping sites where poor geological survey has been made before drilling and digging the well.
If you pump groundwater in arsenic rich strata you can lower the water table, exposing strata to air and changing oxidation conditions. This can increase arsenic dissolution rates.
Thanks Alan. Here in Uruguay we have a serious problem with arsenic that is associated to volcanic ash. There are any specifications to drill or pump wells with As?
You first need to check if the mechanism I suggest is taking place.This "oxidative release" mechanism is not the only one that could be taking place. You could try some lab tests on core samples or field sampling with different pump rates etc.You could try to speciate the arsenic too and this may help identify the mechanism.
You could then determine the recharge rate of the aquifer and limit pump rates such that the water table is not drawn down too much.
However a better way would be if there is a confined aquifer below the contaminated aquifer. But you need to drill in such a way that the clean aquifer is not compromised. Use a tight fitting unscreened casing until you hit the aquitard and a bentonite seal then drill through the cased well with a narrower drill and fit the new casing screened below the aquitard. I have never used this for abstraction wells but it is commonly used for drilling sampling wells to get samples from confined aquifers beneath contaminated sites.
No real specifications since each case will be different but experienced well drillers should be capable of doing it.