US EPA

8626592 

Journal Article 

Phosphate mine reclamation in Tennessee 

Griffith, EJ; Lyles, HN 

1997 

PNW_GTR 

389 

59-68 

English 

Throughout the life of the Columbia Tennessee Elemental Phosphorus Plant, it was necessary to beneficiate our phosphate ore by washing illite clay from the ore. The clay was delivered as a 4% slurry to large tailings ponds where the solids were settled and de-watered. The largest talings pond (number 15) was almost 200 feet deep in settled clay and over 400 acres at the surface. When settled and drained, the clay in the ponds have a consistency similar to mayonnaise, but dry to a solid cracked crust on the surface, causing them to appear deceitfully safe. This is particularly true after scrub vegetation covered the surface of an abandoned mud flat. After a few years, men can usually be supported by the dried crust of an abandoned tailings pond, but machinery can break through the crust and sink into the soggy slimes below. Settled waterlogged clays are thixotropic and can easily be liquified when suddenly stressed. In the event of a dam failure, this could result in a dangerous undesirable event. To render our effete tailings pond system safe and environmentally pleasing, an asset to the state of Tennessee, the decision was made to plant the pond surfaces with 3,500,000 cypress trees. This report is a history of the planting, care for, and maturing of Monsanto's Columbia Tennessee Cypress Garden. Some of our cypress trees are more than 55 feet tall in less than twenty years. A 1,350 year old tennessee cypress tree grew to the amazing height of 175 feet, and is reported to be the largest tree east of the Mississippi River. Our best growth has been 2.75 feet per year. If the growth continued at this rate, the trees will be 175 tall in only 65 years.