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Mining, Smelting, and Refining Site Assessments and Remediation
This project was initiated late in 2006 through dialogue with the Yunnan Environmental Protection Bureau (YEPB). In 2007, TerraGraphics (TG) was invited to visit three contaminated sites in the Yunnan Province of China: the Nan Hua Arsenic Mine/Smelter Site, the Huaning Mine/Smelter and Waste Recovery/Recycling Plant, and the Wenshan Arsenic Refinery Plants. TG served as technical advisor on the sites to provide local officials with recommended remediation actions. Contamination of local water supplies was identified as a key issue surrounding several small abandoned mine sites in Yunnan Province, Southern China. This region has abundant rainfall (1750 mm annually), 80% of which occurs in the rainy season of May-October in the form of heavy storms which lead to flooding and erosion. These conditions exacerbate the spread of contaminants from small sites into local water supplies and then into the larger river systems.
The YEPB proposed the three villages be included in the project with the objective of developing practical remediation approaches, serving as models for other mountain villages with similar problems. All three sites were small abandoned mining sites high in the mountains with owners that could not be easily traced and too small to gain much political attention or support. Toxic heavy metals (arsenic, cadmium, lead) were being released into the local environment from the abandoned processing facilities. The project was structured to provide direction and momentum for a wider effort by the province to address mining pollution and water contamination challenges.
The focus of the work was human public health as these sites typically drain heavy metal contaminated water into local waterways and terraced farm plots. Local populations were at serious exposure risk. One flooding incident in Wenshan resulted in the release of contaminated materials and the subsequent deaths of 36 water buffalo, severely impacting local farming families. TG proposed remediation plans and stabilization and excavation actions aimed at reducing runoff into the rivers and agricultural fields of the mountainous region. The resulting site assessments included site contamination levels, prognosis for sustainability, and feasibility of implementing various remedies for each of the three locations. This model was used by Yunnan officials when they began remediation work in 2008 at Wenshan.
Wenshan Arsenic Refinery Complex
An extensive former mining complex, consisting of four arsenic processing plants, this area was operational from 1958-2004. In 2002 the surrounding area was designated a national biodiversity reserve and the county government ordered the factory to be relocated. However, the accumulated waste from over 40 years of smelting operations remained on site and continued to threaten the local environment. Following the failure of a tailings pond in 2000, some work had been done to stabilize the residues by constructing a retaining dam. However, testing of local streams providing irrigation water for several hundred farms showed more than 1.0 mg/L arsenic. The YEPB chose to carry out remediation plans designed by TerraGraphics at the Wenshan site in 2008. Subsequent testing of arsenic levels in the drainage systems following remediation was 0.048 mg/L according to the local Environmental Protection Bureau, within the 0.05 mg/L limit and representing a twenty-fold reduction in arsenic levels.
Principal human health risks at Wenshan:
- Failure of the residue pond resulting in transport down drainage and into water supply
- Ingestion of sediments eroding from site
- Direct contact with site wastes
- Consumption of contaminated water
- Inhalation of airborne particulates
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Remedial Action Objectives (RAOs) for Wenshan:
- Stabilize on-site wastes to prevent contaminant migration
- Develop source controls to minimize leaching into groundwater
- Establish on-site controls to minimize exposures during operation
- Establish adequate disposal facilities to permanently retain the ash
- Off-site: determine degree of off-site contamination; including sampling, exposure assessments
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Nan Hua Arsenic Mining and Smelting Site
Nan Hua is a former arsenic trioxide mine and processing plant that closed in 2000. The site is located about 5 km upstream from the nearest village. An estimated 50,000 tons of arsenic residue and 500 tons of rock remained on the site, covering an area of 53,000 square meters. Serious concerns had been expressed by village officials and local environmental and health department officials. The waste piles are unstable and their collapse could easily release toxic materials into the water supply. In October 2004 residents from Long Tan Village (population roughly 1400) transported residue by trucks and dumped it outside the local government office in protest against the pollution caused by the waste remaining at the site.
Remediation options suggested by TerraGraphics included stabilizing existing waste piles using local clay and gravel sources and the excavation and armoring of diversion channels to prevent further erosion during the rainy season.
Principal human health risks at Nan Hua:
- Catastrophic failure of the lower dam resulting in massive transport of contaminants down drainage
- Ingestion of sediments eroding from site
- Direct contact with site wastes
- Consumption of contaminated water
- Inhalation of airborne particulates
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Remedial Action Objectives (RAOs) for Nan Hua:
- Stabilization of on-site wastes to prevent contaminant migration (includes measures to prevent catastrophic dam failure)
- Develop appropriate source controls to minimize leaching of arsenic into surface and ground water
- Establish appropriate institutional controls to prevent unauthorized access, salvage and scavenging
- Off-site: determine degree of off-site contamination; include sampling, exposure assessments
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Huaning Mining and Smelting Waste Recovery/Recycling Plant
This factory recovered zinc oxide from mine and smelter waste through a rotary kiln fuming process. As a result, large residues of ash and slag accumulated around the plant during its operational history. Yunnan officials had earlier been informed that the plant was closed, however there was evidence that the site was in use for reprocessing at the time of TG's visit. The size of the residue piles had increased noticeably, new equipment had been installed and the kiln was still hot. This change of status meant that the site could no longer be considered abandoned and initial plans for intervention had to be reconsidered.
Principal human health risks at Huaning:
- On-site residue storage poses continued threat of contaminant migration (runoff, leaching, wind/sloughing)
- Failure of the dumps and makeshift sludge pond resulting in transport down the drainage
- Ingestion of sediments eroding from site
- Direct contact with site wastes
- Consumption of contaminated water
- Inhalation of airborne particulates
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Remedial Action Objectives (RAOs) for Huaning:
- Stabilize on-site wastes to prevent contaminant migration
- Develop source controls to minimize leaching into groundwater
- Establish on-site controls to minimize exposures during operation
- Investigate secondary uses for ash product as an aggregate amendment
- Establish adequate disposal facilities to permanently retain the ash
- Off-site: determine degree of off-site contamination; include sampling, exposure assessments
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