User:Junyue Holden Wang/Groundwater pollution

Under the subtopic "causes"

Over-Pumping
Satellite data have provided evidence that over-pumping of groundwater leads to land subsidence as well as consequential release of arsenic and possibly other heavy metals. Arsenic is found in clay strata due to their high surface area to volume ratio relative to sand-sized particles. Most pumped groundwater travels through sands and gravels with low arsenic concentration. However during over-pumping, a high vertical gradient pulls water from less-permeable clays, thus promoting arsenic release into the water.