A few mining majors used geo-textiles to arrest erosion on their dumps but scientists and others see more scope for soil bioengineering as more than 50 million tones of rejection is produced every year.
The mining companies have tried coir-based geo-textiles as a cheaper and more easily available option than lateritic material to cover the clay dumps. “The thin, bio-degradable and permeable material made up of coir, cotton, jute, interwoven with nylon filaments reduces the impact of rain on dumps,” Mahesh Patil, vice-president, Sesa Goa Limited, said.
Presenting a paper at the national seminar on composting of coir pith and use of geo-textiles, organized by Coir Board, Bangalore, and ICAR research complex, Old Goa, he said that around 5 lakh sq m of geo-textiles have been used on dump slopes in all mines.
S Sridhar, executive director of Goa mineral ore exporters association (GMOEA), said the state’s major mining companies have tried bioengineering at their mining sites.
B L Manjunath, senior scientist (agronomy) from ICAR, speaking about scope for rehabilitation for mine reject soils, said Goa earns foreign exchange of nearly 1,000 crore per annum. But some 400 mining leases granted in Goa till 2002-03, covering about 30,325 hectares generate 55 million tonnes of waste every year. “This huge quantity of mining waste creates a problem for its storage, causing severe environmental pollution,” Manjunath said in his paper at the seminar.
A few mining firms, especially Sesa Goa have tried an integrated bio-technological approach for restoration of land mines. In Sanquelim, the mining company took the site as a model concept and grew horticultural crops such as coconut, banana and a variety of medicinal plants. The mine pit is also a demonstration site for pisciculture.
The geo-textiles decompose within three years but in the interim period, the dump is stabilized by growing grass and later full-fledged vegetation. “The high tensile strength of coir fibre protects steep surfaces from heavy flows and debris movement,” an official of the Bangalore-based coir board said. In Goa, run-offs from the mining dumps in the form of slimes and silts harden after drying, ruining agricultural land and filling river beds.
The geo-textiles are easy to install and hug the contour of the soil surface due to their heavy weight and ability to absorb water.
Goa miners have used geo-textiles in many areas, but representatives from the industry agree that there is scope to increase the coverage. The state’s mining belt covers about 700 sq km, especially in Bicholim, Sanguem and Quepem. The GMOEA executive director also said the coir board should consider training residents in mining areas. “The local self-help groups can prepare material from coir and give it to mining companies, creating employment opportunities,” Sridhar said. The coir board can complete the technology transfer by setting up a factory.
Sridhar said it is a good binding material to check soil erosion in dumps. “We should use more precisely to restore the soil,” he said.
But Ramesh Gawas, a Bicholim-based social activist, pointed out that the use of geo-textiles is possible if the gradient of the dump is 28 degrees and its height less than 30 m. Lease operators argue that they are forced to pile it high due to a lack of space. “With such high dumps and torrential rains, one is not sure when landslides may occur,” Gawas said.