CAPPING OF A GOLD MINEIN ROSIA MONTANA, ROMANIA

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 (waterproofi ng), gravel (drainage) and sand (fi lter and separation). These materials are scarce in the environment and are diffi cult, expensive and slow to place, especially on slopes. In the capping of Rosia Montana’s gold mine, discussed in this case study, the fi nal capping design was based on the placement of a drainage geosynthetic for rainwater drainage and a high density polyethylene geomembrane for waterproofi ng.

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 signifi cantly reduce surcharge.

Waterproofi ng and fl ow 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.

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

CAPPING OF A GOLD MINEIN ROSIA MONTANA, ROMANIA

Topsoil 20 cm -

Soil cover 20 cm - Sealing layer

Drainage Geocomposite 1 cm INTERDRAIN GM 412

Smooth HDPE Geomembrane 1 cm Junifol PEHD

Soil 30 cm - Regularization and slope formation

Waste material - - -

SCOPEThe projected capping for Rosia Montana’s gold mine had to cover 170,000 m2 guaranteeing several factors:

Full capping waterproofi ng.

Rainwater drainage.

Topsoil cover to reduce superfi cial erosion and improve aesthetics.

Long-term stability for the capping with a slope inclination of 2,5H–1V.

TABLE 2. MATERIALS, THICKNESSES AND FUNCTIONS OF THE DIFFERENT CAPPING LAYER IN THE GOLD MINE

SOLUTIONThe fi nal capping design was based in the placement of a regularization soil cover over the waste material, a HDPE geomembrane for waterproofi ng and a drainage geocomposite for rainwater drainage.

MATERIAL THICKNESS PRODUCT FUNCTION

Filter + Drainage (rainwater) + Waterproofi ng Protection.

Eliminates hydrostatic pressure.

Regularization and slope formation

Reduce superfi cial erosion and improve aesthetics

CAPPING OF A GOLD MINEIN ROSIA MONTANA, ROMANIA

USED PRODUCTS

Rainwater drainageINTERDRAIN 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.

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.

Mass per unit area g/cm2 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

PROPERTY UNIT INTERDRAIN GM 412 STANDARD

TABLE 3. INTERDRAIN GM 412 MAIN CHARACTERISTICS

Top Soil

2,5

1 cm

1

Soil CoverLayer

Geomembrane

RegularizationLayer

Waste Material

InterDrain©

CAPPING OF A GOLD MINEIN ROSIA MONTANA, ROMANIA

INSTALLATION PROCESSThe 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.

WaterproofingThe 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.

Density g/cm3 0.94 EN ISO 1183

Thickness mm 1.5 EN 1849-2

Surface - Smooth -

Permeability to liquids m3/(m2·d) EN 14150

Tensile strenght MD/CD N/mm2 30/30

Elongation % 800/800

Puncture resistance kN 4.5 EN ISO 12236

Tear strength N/mm 140 ISO 34-1

PROPERTY UNIT JUNIFOL PEHD STANDARD

TABLE 4. JUNIFOL HDPE 1.5 MAIN CHARACTERISTICS

U= 1.75·10-6

D= 1.66·10-6

EN ISO 527-1,3Specimen Type 5

CAPPING OF A GOLD MINEIN ROSIA MONTANA, ROMANIA

CONCLUSIONSDrainage geocomposites manufactured by Intermas Nets and bentonite layers manufactured by Juta guarantee all the important characteristics in a capping:

Complete waterproofi ng

Rainwater drainage

Long-term stability of the capping

The use of geosynthetic products in this project certifi es:

The use of INTERDRAIN drainage geocomposite and Junifol PEHD waterproofi ng is suitable for gold mine cappings.

Geosynthetic installation is fast, easy and economic.

INTERDRAIN’s fl ow capacities and Junifol PEHD’s waterproofi ng capacities 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.