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
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
It's also the lowest sulfate level that Arizona has required a
company to meet in protecting drinking water, said state DEQ Director
"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
Last year, the Community Water Co. of Green Valley had to close
two drinking-water wells that had sulfates at levels above 500 parts
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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