Monday, August 24, 2009

What mining has done to Sirgao's Soil: NEERI conclusions

National Environmental Engineering Research Institute based in Nagpur presented and invstigative report titled "Assessment of the depletion of ground water sources and land degradation in Sirgaon vilalge, Goa and mitigation measures" in March 2009 to the Goa bench of Bombai High Court, Panaji in respons to Sirgaon villagers Public Interest Litigation (PIL). Below are extacts from the report's page numbers 77-78.


It is evident from the foregoing soil analysis that mining leads not only to pollution of surface and ground water but also accelerates by surface runoff which, in turn, results in deposition of mining waste in agricultural fields. Silt accumulation due to erosion by water on agricultural field result in significant changes in soil properties, which are linked with changes in crop growth properties, biomass production and seed yield. In present study, based on analysis of the different physico-chemical and microbiological properties of soil samples collected from specific sites of the study area and assessment of extent of agricultural land affected by open cast mining, following conclusions are drawn.

ü Erosion of mine overburden and mine land leads to its deposition down the slope in the command area. The silted soil belongs to the texture class “silty laom” whereas the control soil belongs to class “silty clay loam”. The low water retentivity, rapid permeability, low infiltrations (in soils with having clay pan) moisture stress conditions, etc, leads to decline in water use efficiency in irrigated areas in case of silty loam soil.

ü The water-logging problem in the silted soil was due to hard clay formed from deposition of silt which ultimately affects the growth of the plants. This has direct influence on the growth of the plants and also affects the availability of plant nutrients.

ü The information collected from farmers revealed that the acidity in the cultivated areas has been considerably increased (pH lowered) in the areas where deposition of sediments/ silt from mining took place with reduction in Paddy yield.

ü The water holding capacity, CEC, organic carbon and nutrients content of the silted soil were very low as compared to control soil. The microbial population, which is responsible for carrying out different bio-geo-chemical cycles and production of plant growth promoting hormones in the soil, which supports the plant growth, is highly affected in the silted soil as compared to good cultivated one. It is obvious that low organic matter content resulted in the reduction in CEC, nutrients and microbial activities of silted soil.

ü As silted soil developed from granite-gneiss parent rock formation of argillic horizon in the soil there is the soil there is the problem because of high free Fe2O3 and Mn contend. The overburden material rich in iron content and also contain lot of gravels and have deficiency of Ca, S and Zn.

ü Thus deposition of silt overburden from the mine waste resulted in changes in soil properties including soil texture, nutrient content and soil water status.

ü In view of the deterioration of soil quality due to silt deposition, it is essential that suitable mitigation measures are implemented for restoration of the degraded land. The mitigation measures are delineated in Chapter 4 of the report.

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