GreensandPlus removes arsenic from groundwater in the presence of iron. Chlorine is pre-injected to oxidize the iron, convert arsenite to arsenate while keeping the media regenerated. Arsenic combines with oxidized iron and filters out with GreensandPlus. Without a sufficient amount of iron present in the raw water, an iron salt such as ferric chloride is pre-injected. A general guideline is 1 mg/L of iron to remove 20 μg/L of arsenic.