Bone Valley - Risks of Mining

Risks of Mining

Phosphate is a declining export to China. Previously, significant amounts of rock were shipped to China, where it was processed into phosphate fertilizer. The majority of phosphate mining in Florida is done in the Peace River watershed. Phosphate mining companies use draglines to remove surface soils up to 60 feet (18.29 m) deep over thousands of contiguous acres. Once land is mined, state law requires that it be reclaimed. Wetlands are reclaimed on an acre for acre, type for type basis. Most modern mining permits actually require companies to recreate more wetlands than were initially present on the land. More than 180,000 acres (728 km2) have already been mined and reclaimed in the Peace River watershed. As reserves in the northern portion of the bone valley are depleting, mining companies are now seeking permits for another 100,000 acres (405 km2), which will replace reclaimed mines to the north.

One byproduct of the extraction process is clay, which is stored in settling ponds and eventually comprise thirty to forty percent of a mine site. Some of these ponds can measure thousands of acres. Rain drains slower through these clay-laden ponds than typical soil. Critics argue that this, in turn, reduces baseflow to the Peace River. Some studies have indicated that reclaimed lands actually provide a more consistent baseflow because the sandier soils of the reclaimed land provide faster baseflow, while the clay provides a slower steady flow, creating more flow during dry periods than native land. Since the 1960s, the average annual flow of the middle Peace River has declined from 1,350 cubic feet (38.23 m3) to 800 cubic feet (22.65 m3) per second (38.23 to 22.65 m³/s). Critics argue that this flow reduction is due to phosphate mining, but studies by the Southwest Florida Water Management District have shown that the reduction in flow is due to multidecadal oscillation in Atlantic Ocean temperatures.

Critics argue that each holding pond has been perceived as a risk that threatens water quality, public health, wildlife, and the regional economy. Dams restraining the ponds have overflowed or burst, sending a slurry of clay into the river, and coating the riverbed for many miles with a toxic clay slime that suffocates flora and fauna. One such incident in 1971 killed over three million fish when 2 million US gallons (7,600 m3) of phosphate waste swept into the river, causing an estimated 5-foot-tall (1.5 m) tide of slime that spread into adjacent pastures and wetlands. Since the 1971 spill, clay settling areas are now constructed as engineered dams. No such spills have occurred from any settling areas built to these standards. The current dams even withstood three hurricanes which crossed directly over the Bone Valley in 2004.

Most recently, in 2004, during Hurricane Frances, a phosphogypsum stack was overwhelmed by hurricane rains and the levees were breached, sending over 18,000 US gal (68,137 L) of acidic process water into Tampa Bay. Cargill Crop Nutrition, who owned the stack, added lime into the affected areas in an attempt to neutralize the highly-acidic runoff. Due to the extraordinary amount of runoff created by the hurricane, the spill was quickly diluted and environmental damage was minimal. In a consent agreement with the Department of Environmental Protection, Cargill greatly increased its water treatment capacity at the facility. The facility is a no discharge facility and was overwhelmed by the above normal rainfall in 2004, in addition to being affected by three hurricanes.

On occasion, clay slime spills have prevented the Peace River Manasota Water Supply Authority from using river flows for drinking water, forcing municipalities to seek water supplies elsewhere, or rely on stored supplies. On several occasions, the effects of heavy rainfall have created sinkholes beneath the settling ponds.