Rosia Montana has always been rich in mineral resources, especially in gold. Unfortunately the accident at Baia Mare in 2000 brought home to Romanians the dangers of cyanide leaching due to the use of this chemical for gold mining. As a consequence waste material derived from mining operations had to be capped to avoid water to move easily through this material. Traditionally a capping construction involves large quantities of natural materials such as clay (waterproofing), gravel (drainage) and sand (filter and separation). These materials are scarce in the environment and are difficult, expensive and slow to place, especially on slopes. In the capping of Rosia Montana s gold mine, discussed in this case study, the final capping design was based on the placement of a drainage geosynthetic for rainwater drainage and a high density polyethylene geomembrane for waterproofing. TABLE 1. ROSIA MONTANA'S GOLD MINE CAPPING DATASHEET JOB: CAPPING OF A GOLD MINE IN ROSIA MONTANA PROVINCE: TRANSYLVANIA COUNTRY: ROMANIA CLIENT: ROMANIAN MINISTRY OF TRANSPORT AND INFRASTRUCTUREFOUNDED BY THE EUROPEAN COMMUNITY PRODUCTS: INTERDRAIN GM 412 AND JUNIFOL PEHD GEOMEMBRANE MANUFACTURER: INTERMAS NETS, SA AND JUTA A.S. CONSTRUCTOR: SELINA DISTRIBUTOR / INSTALLER: CON-CYN CONSTRUCT SRL For over two decades geosynthetics manufactured by Intermas Nets have been used in cappings with great success around the world due to their many advantages over natural elements: Geosynthetic s reduced thicknesses allow a greater volume of operation. They can be installed in steep slopes. Due to their low weight they significantly reduce surcharge. Waterproofing and flow capacities are homogeneous as they are industrial products. Comfortable, quick and easy to install and they require no heavy equipment. They are a better solution for the environment, constituted by safe, non-polluting and recyclable materials.
SCOPE The projected capping for Rosia Montana s gold mine had to cover 170,000 m 2 guaranteeing several factors: Full capping waterproofing. Rainwater drainage. Topsoil cover to reduce superficial erosion and improve aesthetics. Long-term stability for the capping with a slope inclination of 2,5H 1V. SOLUTION The final capping design was based in the placement of a regularization soil cover over the waste material, a HDPE geomembrane for waterproofing and a drainage geocomposite for rainwater drainage. TABLE 2. MATERIALS, THICKNESSES AND FUNCTIONS OF THE DIFFERENT CAPPING LAYER IN THE GOLD MINE MATERIAL THICKNESS PRODUCT FUNCTION Topsoil 20 cm - Reduce superficial erosion and improve aesthetics Soil cover 20 cm - Sealing layer Drainage Geocomposite 1 cm INTERDRAIN GM 412 Smooth HDPE Geomembrane 1 cm Junifol PEHD Filter + Drainage (rainwater) + Waterproofing Protection. Eliminates hydrostatic pressure. Regularization and slope formation Soil 30 cm - Regularization and slope formation Waste material - - -
USED PRODUCTS Rainwater drainage INTERDRAIN GM 412, a product manufactured by Intermas Nets, SA was placed as rainwater drainage layer. It is constituted by a high density polyethylene (HDPE) geonet and 1 polypropylene (PP) geotextiles heat-bonded to the net. The geonet is formed by two over-crossed strands at 60º, whose geometry creates channels with high flow capacities even under high pressures and at very low gradients (placed almost horizontally). The geonet s main function is drainage while the geotextiles act as waterproofing protection, filter elements and fine particle anti-pollutants. 1 cm 2,5 1 Top Soil Soil Cover Layer InterDrain Geomembrane Regularization Layer Waste Material The main reasons why INTERDRAIN GM 412 was selected are: High flow capacity. High tensile and crush resistance which allow usual construction loads (vehicle traffic, compacting process, tensions due to land disposal, etc.) without any damage in the product. Excellent creep and fatigue behavior that guarantees a longterm drainage solution. Durability. PP and HDPE are chemically inert, imperishable and not sensitive to saline water or microorganisms. TABLE 3. INTERDRAIN GM 412 MAIN CHARACTERISTICS PROPERTY UNIT INTERDRAIN GM 412 STANDARD Mass per unit area g/cm 2 620 ISO 9864 Thickness at 2 kpa/200 kpa mm 4,5/4,0 ISO 9863-1 Peak tensile strenght MD/CD kn/m 12/9 ISO 10319 Elongation at break MD/CD % 50/50 ISO 10319 Flow capacity (MD, i=1, H/H) - - - s = 20 kpa l/sec m 1,26 ISO 12958 s = 50 kpa l/sec m 1,11 ISO 12958 s = 200 kpa l/sec m 0,76 ISO 12958 s = 400 kpa l/sec m 0,43 ISO 12958 Geotextile opening size mm 170 ISO 12956
Waterproofing The gold mine s waterproofing was carried by placing a high density polyethylene geomembrane manufactured by Juta as. Junifol PEHD is a 1.5 mm geosynthetic geomembrane commonly used in waste storage and disposal sites. Junifol s main characteristics are: It guarantees full waterproofing of the capping. Rolls available in widths up to 8 m. Stabilized against UV radiation. Withstands the effects of chemicals, acid, alkaline and salt solutions and are not affected by mildew and microorganisms. Cannot be penetrated by the roots from surrounding vegetation. TABLE 4. JUNIFOL HDPE 1.5 MAIN CHARACTERISTICS PROPERTY UNIT JUNIFOL PEHD STANDARD Density g/cm 3 0.94 EN ISO 1183 Thickness mm 1.5 EN 1849-2 Surface - Smooth - Permeability to liquids m 3 /(m 2 d) U= 1.75 10-6 D= 1.66 10-6 EN 14150 Tensile strenght MD/CD N/mm 2 30/30 Elongation % 800/800 EN ISO 527-1,3 Specimen Type 5 Puncture resistance kn 4.5 EN ISO 12236 Tear strength N/mm 140 ISO 34-1 INSTALLATION PROCESS The steps followed in the installation process are: Extension and compaction of a soil layer for waste regularization. Opening of geosynthetic anchor trenches on the crest of the slopes. Installation of Junifol PEHD geomembrane. In general, seams must be oriented parallel to the line of the maximum slope. The membrane must be overlapped prior to seaming to affect a good weld and allow for proper testing with a minimum overlap of 7.5 cm. Placement of INTERDRAIN GM 412 for rainwater drainage. In case of adverse climate conditions (wind) it is convenient to join the geotextiles with a hot-air gun to prevent lifting. Minimum geotextile overlap is 10 cm. Extension and compaction of a 20 cm tick soil cover. Extension and slight compaction of a 20 cm thick organic topsoil cover.
CONCLUSIONS Drainage geocomposites manufactured by Intermas Nets and bentonite layers manufactured by Juta guarantee all the important characteristics in a capping: Complete waterproofing Rainwater drainage Long-term stability of the capping The use of geosynthetic products in this project certifies: The use of INTERDRAIN drainage geocomposite and Junifol PEHD waterproofing is suitable for gold mine cappings. Geosynthetic installation is fast, easy and economic. INTERDRAIN s flow capacities and Junifol PEHD s waterproofi n g c a p acities are reliable, homogeneous (industrial products) and can substitute gravel and clay layers respectively (products with heterogeneous characteristics). Geosynthetics usage in cappings is a better environmental option because PP and HDPE are non-polluting products and 100% recyclable. On the other hand, large quantities of natural materials are needed, which are scarce elements in nature and whose extraction creates a great environmental impact.