An Asarco mining operation has agreed to pay a $60,000 fine and take preventive steps valued at $50,000 to resolve water-quality violations caused by a June 2010 pipeline spill at the Silver Bell Copper Mine near Marana, state regulators said Tuesday.
The consent judgment against Silver Bell Mining LLC follows a $170,000 fine the company paid in 2009 to settle similar charges at the same site.
Silver Bell, which is majority owned and operated by Tucson-based copper giant Asarco LLC, has agreed to preventative measures including:
• Implementing a pipeline operations and maintenance manual covering more than 20 miles of pipelines.
• Performing periodic pipeline physical inspections, tests and repairs.
• Training employees on proper procedures for fusing pipe segments together.
Silver Bell admitted no wrongdoing as part of the consent judgment, which is subject to court approval.
In the 2010 incident, a rupture in a welded pipeline seam allowed 70,000 gallons of highly acidic solution, containing about 4,000 pounds of sulfuric acid and dissolved metals, to escape into a dry wash on Silver Bell property, Arizona Department of Environmental Quality officials said.
The solution moved nearly a mile before being captured by a storm water impoundment, also on mine property.
Pollutants in the discharge exceeded Arizona aquifer water-quality standards for fluoride, arsenic, beryllium, cadmium, chromium, nickel and selenium, regulators said.
However, Silver Bell Mining workers reacted quickly and contained the discharge on the property, ADEQ noted.
"This was a serious spill, but Silver Bell reacted responsibly to contain it and clean it up and developed a plan to keep this from happening again," ADEQ Director Henry Darwin said in a news release.
Silver Bell also completed actions to prevent future similar pipeline ruptures by redesigning its pipelines, installing equipment to decrease pipeline operating pressures and changing the surface grades to direct any future flows away from washes and into lined impoundments, ADEQ said.
In 2009, Silver Bell agreed to pay a $170,000 fine to settle charges that it released 340,000 gallons of wastewater containing sulfuric acid and heavy metals into dry washes in three separate incidents between October and December 2006.
Under terms of that settlement, the company agreed to increase the frequency of its inspections to monitor for leaks from its dams, ponds and impoundments beyond what is required in its aquifer-protection permit.
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