República Dominicana


Metamorfosis del río Margajita (artículo en Ingles por Barrick Beyond Borders)
12 / Noviembre / 2013

After running dark and dormant for decades, the Margajita River has been returned to its natural hue and is showing signs of life
Before draining into the Hatillo Reservoir, the Margajita River flows under a small bridge that takes cars and pedestrians into the village of Hatillo. On a sweltering summer day in this sleepy village in the Dominican Republic, a boy and his father stand fishing near the bridge patiently waiting for some tilapia to be enticed by their bait. Another angler, many years their senior, is packing up for the day, his bucket filled with tilapia. Cristian De Jesus has fished in the area his entire life, but only recently returned to this spot after spurning it for more than 12 years.

“If the water here was still acidic,” he says, “the fish wouldn’t have returned.”

The Margajita River is about six kilometers long, skirting the Pueblo Viejo mine before winding its way into the Hatillo Reservoir, the largest fresh-water body in the Dominican Republic. As far back as most people here can remember, the waters of the Margajita River were colored a dark, ominous red – a product of acid rock drainage (ARD).

“It used to be called the ‘blood river,’” says Carlos Tamayo, Environmental Manager at the Pueblo Viejo Dominicana Corporation (PVDC), a joint venture between Barrick (60 percent) and Goldcorp (40 percent) that owns the Pueblo Viejo mine.

ARD refers to the acidification of water that occurs when sulfurbased rock is exposed to air and water. It occurs naturally in the area around the Margajita River and, if not properly treated, can be exacerbated by the large open pits and waste rock produced during the mining process.

Mining activity at Pueblo Viejo dates back hundreds of years. In recent times, before Barrick acquired its majority stake in Pueblo Viejo, the mine’s previous operator often discharged acidic water that had not been properly treated into the Margajita River. When the mine closed in 1999, it closed without proper environmental remediation, leaving a legacy of contaminated water and soil.

“When there were heavy rainfalls there would be lots of dead fish floating in the Hatillo Reservoir,” says Maria Magdalena Cedẽno, a long-time resident in the nearby community of El Zinc.

Cleaning up the past

In 2001, Placer Dome won the concession rights to restart mining at Pueblo Viejo, which still contained millions of ounces of gold. The Special Lease Agreement that Placer signed with the Dominican government required the company to remediate environmental damage within the mine development boundary left by the previous operation. Barrick inherited this obligation when it acquired control of Pueblo Viejo in 2006. The government is responsible for the clean-up of areas outside the mine development boundary. PVDC agreed to provide $75 million to the Dominican government to remediate environmental impacts of the old Pueblo Viejo mine in areas that fall under the government’s responsibility.

Since acquiring control of Pueblo Viejo, PVDC has re-vegetated 3,500 hectares of land, built a large water treatment plant to treat water on site before discharging it into the Margajita River and, acting as an agent of the government, removed 180,000 cubic meters of contaminated soil left from prior operations.

High precipitation region

Pueblo Viejo is located in a sub-tropical region of the Dominican where average annual rainfall is nearly two meters. Weather conditions can change rapidly, going from cloudless and scorching to downpours of seemingly Biblical proportions and back again in the space of an hour. The mountainous terrain around the mine is a sea of lush green, filled with an endless variety of trees, shrubs and flowers.

Inside the 11-square-kilometer mine site, haul trucks transfer thousands of tons of ore each day from two open pits to large stockpiles to await processing. Many of the rocks are tinged with an orange hue, a telltale sign of sulfur. When the rains come, the water that cascades over the stockpiles and open pits is diverted via a series of canals, channels and sedimentation ponds into two large collection ponds. One of the ponds can store up to 620,000 cubic meters of water and is lined with high-density polyethylene to prevent seepage. The other can hold 500,000 cubic meters and has a clay base that serves as a natural insulant. The water is pumped from the ponds to the site’s water treatment plant 24 hours a day, seven days a week.

More than 40,000 cubic meters of water treated daily

At the treatment plant, which began operating in the summer of 2012, water undergoes a three-stage treatment process. In the first stage, the water enters a large silo where limestone slurry is added along with pure oxygen. This triggers a chemical reaction that removes trace metals from the water.

In the second stage, the water is transferred into a large, vertical tub where milk of lime is added to raise the water’s pH level. Water typically arrives at the plant with pH levels in the 2.5 range, which is highly acidic. Milk of lime adds alkalinity, raising the water’s pH level to the 7-to-9 range, in line with Dominican government requirements. In the final stage, the water is transferred into a large, flat tank where all remaining sediments are removed and pumped to the site’s tailings pond. Approximately 40,000 cubic meters of water are treated daily at the plant.

“The treatment method is not unique, but the scale of the plant is,” says Rodolfo Espinel, Process Plant Technical Services Superintendent at Pueblo Viejo. “It’s huge.”

The water treatment process is closely monitored and controlled using state-of-the-art technology. Water samples are collected every 10 minutes and composites of those samples are analyzed twice daily at an on-site laboratory. The composites are checked for pH, the presence of cyanide and five different metals: iron, lead, zinc, copper and mercury.

State audits of the water treatment plant are conducted regularly to ensure the company is in compliance with government standards, and independent consultants representing the project’s lenders visit Pueblo Viejo three times a year to ensure the site’s environmental management system and other site procedures are aligned with International Finance Corporation (IFC) guidelines.

Changes to Margajita River evident within days

When the water treatment plant began operating last summer, changes in the Margajita River were evident within days. Instead of dark red, the water turned clear, reflecting its natural state. The water’s pH level climbed dramatically and, more recently, there are early signs of aquatic life returning to the river.

“Not long after we began treating the water, we came by to collect samples from one of the water monitoring stations,” Tamayo says. “While we were there, a woman, a local school teacher, came by and noticed the change in the color of the river. Well, she got so excited. She started jumping up and down and yelling over and over again, ‘I can’t believe it, I can’t believe it!’ ”

Water samples are collected on a weekly basis from the discharge point into the Margajita River and analyzed to ensure the quality is in line with government standards and IFC guidelines.

Barrick also monitors the condition of the river at various points downstream, collecting and analyzing samples on a quarterly basis. However, the company is not responsible for these areas, which fall well outside the mine development boundary. Downstream water quality is not as high as the water quality at the discharge point because several tributaries – some of which have been impacted by naturally occurring ARD, as well as ARD generated by previous mining operations – feed into this section of the river.

Still, the overall condition of the Margajita has improved dramatically in the past year because the volume of water treated at Pueblo Viejo and discharged into the river far exceeds the volume of water entering the river from the tributaries.

Community water monitoring

In the summer of 2012, Barrick invited local communities to participate in downstream monitoring of the Margajita River. Initially, six communities agreed to participate, but the program has since expanded to 18 communities with nearly 40 participants. Community members are taught how to take samples, use the sampling equipment and fill out the required paperwork. Samples are sent for analysis to independently certified laboratories in Puerto Rico or Canada. To date, seven sampling events have taken place and results have shown a significant improvement in water quality.

“We’re the first company in the Dominican Republic to implement participatory monitoring,” Tamayo says. “It helps build credibility because credibility is based on facts, and people believe what they can see.”

Because the water is very shallow in the upstream section of the Margajita River, aquatic life was never abundant, but there are signs it is returning. Several months ago, for instance, the mine’s environmental staff began observing river crabs in the water, and at the river delta where the Margajita widens and deepens before emptying into the Hatillo Reservoir, the fish are becoming more plentiful.

“This used to be a dead river,” says Maria Magdalena Cedẽno. “Now people are fishing on the bridge.”

11 / Abril / 2016
Unigold amplía extensión Candelones depósito intersección 7,0 metros con un promedio de 8,9 g/t Au; 37.1 g/t Ag; 0.2% Cu; 2.4% Zn en blanco C TORONTO,...

Leer mas »

16 / Junio / 2014
PAÍNO ABREU COLLADO   “Se puede engañar a algunos todo el tiempo y a todos algún tiempo, pero no se puede engañar a todos todo el tiempo”.Abrahan...

Leer mas »

13 / Abril / 2019
En la semana del 8 al 13 de abril 2019, se estuvo celebrando el 8vo. congreso internacional de Artrópodos, Insectos Fósiles y Ámbar en la República Dominicana. Este...

Leer mas »

13 / Junio / 2019
En el 53 aniversario de esta prestigiosa institución, queremos exhortar y seguir promoviendo el desarrollo de la industria minero-metalúrgica de nuestro país....

Leer mas »