U.S. Water News Online
TUCSON, Ariz. -- Phelps Dodge Corp. and state officials have agreed on a plan to reduce groundwater contamination from the Sierrita Mine near Green Valley.
Under a consent order agreement, Phelps Dodge will take steps to ensure sulfates that seep into groundwater from mine tailings ponds don't contaminate drinking-water wells at levels exceeding recommended state and federal limits.
Sulfates are sulfur-based compounds that come from copper production. They can cause diarrhea and harm the stomach and intestines, according to the Arizona Department of Environmental Quality.
There are no legally enforceable limits, but the Environmental Protection Agency recommends a maximum contamination level of 250 parts per million.
Phelps Dodge has agreed to produce a plan in 60 days to define the extent of sulfate pollution lying in groundwater downstream of the mine, which is six miles northwest of Green Valley.
The company must also outline a separate plan to prevent the pollution from contaminating any public or private well within a mile of the outer edge of the polluted water.
The agreement was announced at the same time the state approved a draft water-quality permit allowing Phelps Dodge to discharge its mine tailings into the aquifer.
It's the first time the state has used its legal authority to force a company to deal with contamination caused by a substance such as sulfates that are considered non-hazardous under federal and state laws.
It's also the lowest sulfate level that Arizona has required a company to meet in protecting drinking water, said state DEQ Director Steve Owens.
"It not only will ensure a clean drinking water supply for the community of Green Valley, it also sets the standard for dealing with other areas with sulfate contamination around the state," said Owens.
Authorities have known since the mid-1980s that sulfates seeping from the Sierrita Mine -- owned at the time by another company -- had polluted groundwater and represented a potential threat to drinking water supplies.
Last year, the Community Water Co. of Green Valley had to close two drinking-water wells that had sulfates at levels above 500 parts per million.
Phelps Dodge has since provided temporary replacement wells for the contaminated wells and paid $8 million toward helping the company build new, permanent wells to replace those that are polluted.
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