When arsenic dissolves in water, it is transported by the water as well as diffusion. And when arsenic laden water is pumped for irrigation, it is again distributed.
In January 2001, EPA introduced new standards for arsenic. The new standard of 10 parts per billion replaced the old standard of 50 parts per billion. This rule came into effect in February 2002 and applies to drinking and irrigation water.
Some locations in the United States are known to have high concentrations of arsenic in the ground water. The concentration of arsenic in Fallon, Nevada is measured in excess of 0.08 mg/L. In Verde River in Arizona, the concentration of arsenic was measured in excess of 0.01 mg/L and this is especially true during low-flow periods when the quantity of groundwater in the river is higher.
EPA guidelines for arsenic in irrigation water were changed after the Environment Protection Agency (EPA) studied the pros and cons of lowering the maximum contaminant level of arsenic. These studies were carried out in the late 1980s and 1990s. However, no action was taken until 2001. However, the Bush administration suspended this regulation; but then some more studies were conducted and the EPA administrator approved the new 10 part per billion standard, which came into effect from January 2006.
With new regulation coming into effect, in Arizona nearly 35 percent of water supply wells were not in compliance while in California the percentage was 38 percent.
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