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PD uses living weapons in battle against dust
By Philip Franchine
PHELPS DODGE SIERRITA MINE--In the battle against dust that blows across Green Valley from the nearby copper mines, Phelps Dodge is employing cattle, algae, snowshoes, a snowcat from Canada and a marsh rover from the bayous of Louisiana.
These innovative measures are being used because dust has been a major issue in Green Valley and Sahuarita for decades. That's because 99 percent of the ore mined for its copper and molybdenum content is crushed into a gray powder finer than beach sand, called mine tailings.
Huge amounts of tailings are created. More than 18,000 gallons per minute come out of the crushers.
The tailings are mixed with water and the resulting slurry is pumped through a 10-mile long pipe system into what looks like a vast inland sea.
Just west of Green Valley, at the end of Duval Mine Road, Phelps Dodge has built an immense, 200-foot high, 3,600-acre tailings dam that holds the slurry. The dam climbs eight feet a year in height and is expected to remain in use for the life of the mines, estimated to be another 20 to 30 years. The wide blue-gray surface can be seen from Madera Canyon.
Most of the water is reclaimed and some evaporates, so most of what is inside the dam is dried powder, covered with a mineral crust about an inch thick whose surface is spiderwebbed with cracks and fissures.
A traditional method of dust control is to simply spray water or magnesium chloride on the surface, and Green Valley residents often can see plumes of liquid shooting up over the sides of the dam.
Whenever heavy monsoon rains hit the crust, dissolving it, the underlying powder is exposed and winds whip the dust across the valley, Phelps Dodge environmental manager Mike Wood said. Wood and other corporate officials led a tour of dust-control measures on Jan. 9 for members of the Green Valley Community Coordinating Council and staff of the Green Valley News & Sun.
As workers walk out on the crust with hoses of water or magnesium chloride as a dust-control measure, their weight can crack the crust and expose the powder underneath it, Wood said, and that is why snowshoes are being tried.
Residents have complained about dust problems as far back as the 1980s and 1990s, in part because the fine powdery dust can seep into homes and cause special problems for those with respiratory problems.
At times, the company has hired a crop-duster to spread magnesium chloride on the containment pond.
Both Pima County's Department of Environmental Quality and the federal Environmental Protection Agency have stepped up efforts to monitor particulate emissions around the mines in recent years.
In recent years Phelps Dodge, which bought the Sierrita mine from Cyprus in 1999, has stepped up measures to control dust as part of an overall corporate policy, Wood said.
Phelps Dodge is under enforcement action involving the Arizona Department of Environmental Quality and the federal Environmental Protection Agency, a spokeswoman with the Pima County Department of Environmental Quality said.
When that enforcement action is resolved, Phelps Dodge will fall under regulation by the county, which also regulates the nearby Asarco mines, the county spokeswoman said. (See related story, Page A1.)
"We are in negotiation on some alleged dust infractions in the late 1990s," but none are related to current dust control measures, Wood said.
"There has been an increased focus on dust control from facility and corporate management that's been driven by being a community member. We don't want to have complaints from neighbors," Wood said.
In the past year, Phelps Dodge has bought a $120,000 snow cat from Canada, which has tank-like treads and can carry 10,000 pounds of magnesium chloride liquid out onto the pond to be sprayed as a dust-control measure.
The marsh buggy from Louisiana also spreads the weight of its liquid load out so it doesn't sink.
Blue algae pond
The company also is using Sonoran blue algae on the surface of the pond.
The company has built a small algae pond, which operates much like a swimming pool left untreated. Bacteria from groundwater and the air incubate there, with help from an added algae product, and when concentrated enough, the algae are piped into the slurry.
There was concern that the slurry would crush the algae in the pipelines, but they are "hardy critters" and survived the ride to the dam, tailings dam supervisor Glenn Pitts said. At that point the slurry is shot up over the side in plastic hoses and cascades down into the pond.
After less than a year, it appears the algae are helping the tailings in the pond hold their moisture longer and thus produce less dust, based on the darker color of the tailings since the algae experiment began, plant superintendent Terry Nay said.
"If it is successful, this method could be used in construction and other dust-generating industries," Wood said.
On the sides of the pond, the company is trying different ways to vegetate the otherwise sterile tailings, which, if not treated, are gray and erode rapidly with gullies formed by even the slightest rainfall.
The company has contracted with a local rancher to keep a herd of 100 cattle grazing on 1.25 acres on the steep eastern side of the pond.
The herd provides fertilizer in the form of manure to support vegetation. Vegetation also softens the appearance of the pond, which looms over the sunsets in Green Valley.
An approach that appears to be working more rapidly is spreading a compound called Liquid Cow, which includes algae and cow urine and manure, on a half acre of the tailings.
After less than a year, knee-high mesquite bushes and other greenery have appeared and the compound is being applied to another 18 acres, along with grass seed, and after 6 months, clumps of grass have appeared there.
The annual operating costs of the dust control operation has jumped to a budgeted $462,000 for 2004 from $312,000 in 2002, and capital expenses include $500,000 last year for vehicles and other assets, with another $412,000 budgeted for this year.
The 2002 figure did not include an unbudgeted expense of about $200,000 for the crop-duster.
Are the measures working?
"We have seen a decrease in the number of dusty days--upset days--the days when Green Valley calls. We did have one day in 2003 when we exceeded our 40 percent opacity limit and in previous years there have probably been more days like that," said Wood.
"The real test for us is going to be in the monsoon season. That is habitually our problem period. This fall will be our test period," Wood said.
pfranchine@gvnews.com | 625-5511 x 28
These innovative measures are being used because dust has been a major issue in Green Valley and Sahuarita for decades. That's because 99 percent of the ore mined for its copper and molybdenum content is crushed into a gray powder finer than beach sand, called mine tailings.
Huge amounts of tailings are created. More than 18,000 gallons per minute come out of the crushers.
The tailings are mixed with water and the resulting slurry is pumped through a 10-mile long pipe system into what looks like a vast inland sea.
Just west of Green Valley, at the end of Duval Mine Road, Phelps Dodge has built an immense, 200-foot high, 3,600-acre tailings dam that holds the slurry. The dam climbs eight feet a year in height and is expected to remain in use for the life of the mines, estimated to be another 20 to 30 years. The wide blue-gray surface can be seen from Madera Canyon.
Most of the water is reclaimed and some evaporates, so most of what is inside the dam is dried powder, covered with a mineral crust about an inch thick whose surface is spiderwebbed with cracks and fissures.
A traditional method of dust control is to simply spray water or magnesium chloride on the surface, and Green Valley residents often can see plumes of liquid shooting up over the sides of the dam.
Whenever heavy monsoon rains hit the crust, dissolving it, the underlying powder is exposed and winds whip the dust across the valley, Phelps Dodge environmental manager Mike Wood said. Wood and other corporate officials led a tour of dust-control measures on Jan. 9 for members of the Green Valley Community Coordinating Council and staff of the Green Valley News & Sun.
As workers walk out on the crust with hoses of water or magnesium chloride as a dust-control measure, their weight can crack the crust and expose the powder underneath it, Wood said, and that is why snowshoes are being tried.
Residents have complained about dust problems as far back as the 1980s and 1990s, in part because the fine powdery dust can seep into homes and cause special problems for those with respiratory problems.
At times, the company has hired a crop-duster to spread magnesium chloride on the containment pond.
Both Pima County's Department of Environmental Quality and the federal Environmental Protection Agency have stepped up efforts to monitor particulate emissions around the mines in recent years.
In recent years Phelps Dodge, which bought the Sierrita mine from Cyprus in 1999, has stepped up measures to control dust as part of an overall corporate policy, Wood said.
Phelps Dodge is under enforcement action involving the Arizona Department of Environmental Quality and the federal Environmental Protection Agency, a spokeswoman with the Pima County Department of Environmental Quality said.
When that enforcement action is resolved, Phelps Dodge will fall under regulation by the county, which also regulates the nearby Asarco mines, the county spokeswoman said. (See related story, Page A1.)
"We are in negotiation on some alleged dust infractions in the late 1990s," but none are related to current dust control measures, Wood said.
"There has been an increased focus on dust control from facility and corporate management that's been driven by being a community member. We don't want to have complaints from neighbors," Wood said.
In the past year, Phelps Dodge has bought a $120,000 snow cat from Canada, which has tank-like treads and can carry 10,000 pounds of magnesium chloride liquid out onto the pond to be sprayed as a dust-control measure.
The marsh buggy from Louisiana also spreads the weight of its liquid load out so it doesn't sink.
The company also is using Sonoran blue algae on the surface of the pond.
The company has built a small algae pond, which operates much like a swimming pool left untreated. Bacteria from groundwater and the air incubate there, with help from an added algae product, and when concentrated enough, the algae are piped into the slurry.
There was concern that the slurry would crush the algae in the pipelines, but they are "hardy critters" and survived the ride to the dam, tailings dam supervisor Glenn Pitts said. At that point the slurry is shot up over the side in plastic hoses and cascades down into the pond.
After less than a year, it appears the algae are helping the tailings in the pond hold their moisture longer and thus produce less dust, based on the darker color of the tailings since the algae experiment began, plant superintendent Terry Nay said.
"If it is successful, this method could be used in construction and other dust-generating industries," Wood said.
On the sides of the pond, the company is trying different ways to vegetate the otherwise sterile tailings, which, if not treated, are gray and erode rapidly with gullies formed by even the slightest rainfall.
The company has contracted with a local rancher to keep a herd of 100 cattle grazing on 1.25 acres on the steep eastern side of the pond.
The herd provides fertilizer in the form of manure to support vegetation. Vegetation also softens the appearance of the pond, which looms over the sunsets in Green Valley.
An approach that appears to be working more rapidly is spreading a compound called Liquid Cow, which includes algae and cow urine and manure, on a half acre of the tailings.
After less than a year, knee-high mesquite bushes and other greenery have appeared and the compound is being applied to another 18 acres, along with grass seed, and after 6 months, clumps of grass have appeared there.
The annual operating costs of the dust control operation has jumped to a budgeted $462,000 for 2004 from $312,000 in 2002, and capital expenses include $500,000 last year for vehicles and other assets, with another $412,000 budgeted for this year.
The 2002 figure did not include an unbudgeted expense of about $200,000 for the crop-duster.
Are the measures working?
"We have seen a decrease in the number of dusty days--upset days--the days when Green Valley calls. We did have one day in 2003 when we exceeded our 40 percent opacity limit and in previous years there have probably been more days like that," said Wood.
"The real test for us is going to be in the monsoon season. That is habitually our problem period. This fall will be our test period," Wood said.
pfranchine@gvnews.com | 625-5511 x 28
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