What Are Gypstacks and Process Water?
Gypstack systems are a heavily regulated, federal requirement for PG storage. When making phosphate fertilizer, rock is obtained from underground, processed, and moved to manufacturing facilities where other raw materials are added. Phosphogypsum, also known as PG, is a byproduct created during this process. Thirty-year-old Federal regulations require PG to be stored in stacks because of low-levels naturally occurring radionuclides in the phosphate rock. Today, PG is approved for limited use in agriculture and research, with abundant innovations emerging for tomorrow’s use. Currently, in the US, nearly all PG is stored in engineered structures called gypstacks which are also designed to collect rainfall and store process water so it can be recycled through the manufacturing operation.
Shaped like the base of flattened pyramids, gypstacks are highly visible and instantly recognizable. When planning for a gypstack, structural integrity of the system is the primary goal. The phosphate industry undergoes a rigorous permitting process overseen by the Florida Department of Environmental Protection (DEP) and local counties. The permitting process to build or extend a stack’s life takes years to complete, with ongoing compliance and reporting requirements for the duration of the permit. Gypstack permit applications specify design requirements, construction and management parameters, with a great emphasis placed on stack integrity and environmental protective features. These features include high-density polyethylene liners throughout the stack, an extensive network of monitoring equipment and include drainage systems to recover and reuse water in the manufacturing process. Importantly, communities and residents are invited to participate in the permitting process.
Water is a key component of the manufacturing process, used by machines that extract rock by mixing it with water to create a slurry that is pumped back to processing facilities. Dubbed “process water” by the industry, it does not leave the facility, but is circulated in ponds on top of the gypstack to be recycled through the manufacturing process, reducing the need for additional water. Process water also transports PG to the stack and is used to grind and convey the rock. The amount of water contained in a gypstack changes depending on the season, rainfall and production. Ahead of Hurricane season, special planning and considerations are applied to accommodate the potential for large amounts of storm water. PG and process water are considered large volume, low hazard wastes, but are nonetheless highly regulated. They contain low levels of naturally-occurring radionuclides, sodium and sulfate. Exposure to these substances is considered safe by regulators. Only tested and treated water that meets the strictest quality standards can be discharged through permitted and monitored points.
Inspections / Maintenance
Gypstacks are monitored and assessed to ensure compliance with federal and state regulations. Inspections occur twice a day and are documented for future verification. Shift supervisors complete their own weekly inspection, and operating supervisors complete another monthly review. Annually, a third-party inspects the stacks and provides a summary of observations, maintenance recommendations, or suggests corrective actions. When a recommended change is identified, maintenance is carried out with regulatory oversight and onsite inspection.
Advanced technology and practices are applied to monitor stacks and may detect hidden, subsurface structural abnormalities and changes in soil density in and beneath the stack. Once the stack is built, additional sensor equipment can be utilized and monitored, including vibrating wire piezometers that measure changes in water levels, traditional groundwater monitoring and microseismic monitoring - using a network of instruments called geophones placed in a ring around the perimeter of the stack, providing real-time monitoring.
Naturally Occurring Radioactive Materials, NORM
Phosphate ore contains some naturally occurring, slightly radioactive elements and is similar to the ground beneath your feet or home. This type of radiation is called NORM - short for Naturally Occurring Radioactive Materials. Everyone is exposed to daily doses of radiation. Our bodies already contain it. Virtually everything we come into contact with such as granite countertops in your kitchen, ceramic dinnerware and even some types of fruits and nuts contain it.
NORM is, well, normal. Radiation is measured in doses and a dose unit is quantified in millirems per unit of time (typically per year). The Federal Environmental Protection Agency (EPA) states that an average person in the US is exposed to 600 millirems per year, split into two categories:
- Environmental exposure - like the sun or soil
- Common medical procedures, like dental x-rays and mammograms
NORM in soil is found across the country. In fact, ambient NORM found in Florida’s soil is considered to be amongst the lowest in the nation. A typical Floridan is exposed to an average of 200 millirems per year because our soil contains less radium in comparison to the 300 millirem average in other parts of the country. Because process water and PG are part of the phosphate manufacturing process, it also contains these naturally occurring elements found in our soil. NORM from process water and PG is low, even for those working near or with it daily. With this in mind, PG has been extensively reviewed by the EPA for innovative uses like road construction after many years of research, data and analysis that has demonstrated maximum lifetime exposure to NORM- even for road construction workers - is well below the agency’s risk threshold.