Deemed the "world's worst water" by scientists, highly toxic wastewater once flowed from the Iron Mountain Mine, bringing extremely acidic waste into the Sacramento River.
The Environmental Protection Agency labeled this federal Superfund site the largest source of toxic metals in the country. More than a ton of toxins flowed into the environment each day, poisoning the drinking water source for 70,000 people in Northern California.
Today EPA officials are celebrating the opening the Slickrock Creek Retention Reservoir, designed to reduce the flow of toxins by up to 95 percent.
The mine began operating after the Gold Rush in 1860 until it was closed in 1962. Workers mined Iron Mountain in search of iron, silver, gold, copper, zinc and pyrite. In the process, they exposed the heavy metals to rain and groundwater combining to form a neon green toxic waste. Iron sulfide in the pyrite reacted with oxygen in the air and water to form sulfuric acid.
Workers attempting to clean up the waste found the pool of acid so strong that it dissolved their metal shovels overnight and copper-plated tools in minutes. Water dripping on bare skin had to be neutralized with baking soda to avoid burns.
Even scientists dressed in full-body "moon suits" with masks, goggles and gloves were overwhelmed by the toxic fumes. They concluded it was the most acidic water ever to pollute naturemore acidic than battery acid, and worse than water found in volcanic lakes.
They also discovered a microbe that thrives in the harsh conditions and dramatically speeds up the acid production.
Formed by a 150-foot-high earthen dam, the reservoir now will capture water flowing from the 4,400-acre open pit and underground mine so that it can be cleansed and released by a wastewater treatment plant that opened a decade ago. Since then, the plant has treated more than 1.3 billion gallons of acid mine drainage, EPA said Wednesday.
The treatment plant captured about 1.9 million pounds of copper and 6.6 million pounds of zinc so far, cutting the flow of copper by 80 percent and zinc by 90 percent, EPA estimated.
In one of the largest settlements in the Superfund program's history, EPA settled with the former owner, France-based Aventis CropSciences USA, for nearly $1 billion in 2000.
The settlement included $160 million to operate the treatment plant, and $700 million to $800 million for additional work at the mine.
Scientists say the biggest challenge lies ahead. It will take an estimated 2,500 years for the water runoff to return to healthy metal levels.