Phosphogypsum is commonly referred to as gypsum or calcium sulfate. It is a byproduct of the fertilizer manufacturing process, and is not associated with any of Mosaic's mining projects in south-central Florida. It is created when sulfuric acid is reacted with phosphate rock to produce the phosphoric acid needed for fertilizer production.

Phosphogypsum is stored in stacks adjacent to manufacturing facilities, under exacting standards established by the Florida Department of Environmental Protection. Phosphate companies must meet stringent financial tests in order to operate gypsum stacks, and can face criminal penalties for misrepresenting the financial condition or closure of a phosphogypsum stack or stack system.

First, the process water is transferred from the top of the stack to other storage ponds, and drains are constructed to capture water from inside the stack. Careful attention is paid so that the process water does not leach into the environment. The top of the stack is graded, and a 40-mil thick high-density polyethylene (HDPE) top cover is installed. Then 18 inches of soil is applied and vegetative cover is established. The sides are also graded to ensure proper drainage, vegetative cover and grass.

Mosaic maintains several closed gypsum stacks in Central Florida. When properly maintained and operated, these closed stacks pose very little environmental risk. Trained technicians make daily inspections of the stack systems and their liners. We limit the use of our closed stacks to temporary water storage and do not place solids or fill material in the lined reservoirs. Very little physical activity occurs around the reservoirs, which minimizes risk of damage to the liner. In the event equipment must be used in the area, strict safety guidelines are followed to ensure the liner's integrity is maintained.

Phosphate rock when mined is naturally slightly radioactive - the level is typically a little higher than the naturally occurring radioactivity in other soils.

Because phosphogypsum retains some radioactivity, US regulators in the 1980s took the view that it would be safer to store the phosphogypsum in stacks, rather than continuing to use the substance in construction and agriculture. In 1992 EPA promulgated a Rule that in effect made stacking mandatory in Central Florida.

EPA banned phosphogypsum use based on the following scenario. It assumed that the by-product was used in road building or as an agricultural amendment and 100 years later a house was built on the farm field or the abandoned road. If the homeowner lived in the house 70 years, staying in the house 18 hours a day, the homeowner's risk of radon-related health concerns exceeded the EPA's acceptable limits.

The radiation emitted from phosphogypsum is at such a low level that it is difficult to measure with radiation survey meters. Phosphogypsum from Central Florida contains about 20 - 35 picoCuries (pCi/g radium). A picoCurie is 0.000,000,000,001 (one-trillionth) of a Curie, an international measurement unit of radioactivity.

Radiation is as old as the universe. The stars, as well as the earth, are radioactive. Since the beginning of their existence, humans have been exposed to ionizing radiation from natural sources. More recently, man-made ionizing radiation such as x-rays and that from numerous radioactive materials have been introduced. In addition, many of our consumer products, such as smoke detectors and luminous dials, contain radioactive substances. Thus, we are all continuously exposed to ionizing radiation from natural and man-made sources. More details are available at the Florida Industrial and Phosphate Research Institute.

Process water is used to transport the phosphogypsum from the processing plant to cooling ponds on top of stacks. The system's dikes and berms are stabilized and water levels are maintained regularly. The process water has a low pH of about 1 to 2 and contains a dilute mixture of phosphoric, sulfuric, and fluosilicic acids. It is saturated with calcium sulfate and contains numerous other ions found in the phosphate rock used as a raw material, as well as ammonia from the solid fertilizer manufacturing process.

Mosaic recycles or reuses approximately 95 percent of the water at its phosphate facilities. All manufacturing facilities are required to have process wastewater containment systems designed to contain the run-off from the 25-year, 24-hour storm event, which is approximately 8.5 inches of rain in Polk County. Mosaic's Riverview manufacturing facility is a "zero discharge facility," whereas our other two facilities must treat and meet strict standards before releasing any water into the environment. Currently, Mosaic and the Florida Industrial and Phosphate Research Institute are also aggressively seeking ways to improve the quality and reduce the quantity of process water.

Finding environmentally safe and economically feasible ways to use phosphogypsum from Central Florida has been a top research area for the Florida Industrial and Phosphate Research Institute, and has encouraged testing safe uses such as landfill cover, roadbed material, etc. Because of geological differences in phosphate rock, phosphogypsum from North Florida is slightly less radioactive than in Central Florida. Phosphogypsum from North Florida is used as a soil amendment by peanut farmers in Georgia, North Carolina, Virginia, and Alabama.