- The present study is an outcome of the directives of the Honourable Mumbai High Court at Goa (PIL No. 1/2008) to focus on the alleged depletion of water resources, degredation of agricultural fields’s vis-ả-vis the mining activity in Sirirgaon village (Bicholim Taluka) in the North Goa District.
- The study area (60 sq. km) has been delieanated on the basis of watershed and covers the working mining pits of the three mining companies namely M/s Dempo Mining Corporation Pvt Ltd., M/s. Rajaram Bandekar (Sirigaon) Mines Pvt. Ltd. And M/s Chowgule and Company Pvt. Ltd. It covers most of the dug wells in the Sirigaon village.
- The study area is covered by the Survey of India (SOI) toposheet No. 48E/14/SE (scale 1:25,000). The elevation in the village outside the mining pit varies from 0.095 m to 8.639 m.
- The topography in the nearby Sirigaon village has been altered significantly due to the open cast mining activity. The topographic highs which were present earlier have now been removed during the mining activity and large depressions have been created in the form of Mine pits. In view of the sustained mining activity, depressions have been created with the bottom level varying between -20 m (amsl) to 43 m (amsl).
- Goa receives rainfall from the Southwest monsoon and spans four months i.e. from June to September. The rainfall data for the last five years indicate that the average annual rainfall is approximately 2846 mm out of which 2785 mm is contributed by the south west monsoon.
- The Geology of the study area comprises of laterites followed by manganeferous clay. The manganeferous clay is underlain by iron ore formation. The thickness of laterites varies from 3 m to 15 m as evident in the lithologs provided M/s Chowgule & Company Private limited and M/s Rajaram Bandekar (Sirigaon) Mines Pvt. Ltd. The laterites are followed by manganeferous clay which is followed by limonitic clays.
- The iron ore formations underlie the clay formations. The iron ore formations vary from friable ore to powedery ore. At places, friable ore is followed by powdery ore though friable ore is absent at many places and only powdery ore is encountered. The available lithologs provided by M/s Chowgule and Company Pvt. Ltd. Indicates that the thickness of powdery ore zone varies from 10 m to 32 m in one of their drilling sites.
- The top lateritic formation constitutes the unconfined aquifer in the study area. The zone comprising the ore body serves as the confined aquifer. The unconfined aquifer is tapped for extraction of water. All the dug wells located in the Sirigaon village are tapping the unconfined aquifer only.
- Field visits were undertaken for assessing the water resources in the village in months of August, October and December 2008. Inspection was made for design and implementation of the recharge structures for augmentation of water resources in the month of January 2009. Observation well network was established for measurement of water levels and collection of samples for physicochemical and heavy metal analysis. It is observed that the water table in August’2008 varied from 0.50 m to 6.55 m. In October 2008 and December 2008, it varied from 0.90 m to 10.30 m and 2.70 m to 9.70 m respectively. The groundwater scenario was worse in December 08, when almost all the dug wells in Sirigaon village had dried up. However, the wells from nieghbouring villages had water column even in the month of December, 08.
- The mine pit water levels for all the three mines is below -20 m (amsl). The flow direction is indicative of water flow from the aquifer to the mine pit. Water seepage to the pit from the mine wall on the village side is also noticed during the field visits. Schematic diagram of ground water profile in the Sirigaon and mine area is presented in the Figure.
- The deepening of the mines has led to loss of recharge area for the dug wells seated at the foot hills of the plateau. Hence, the water scarcity in the viallge dug wells is attributed to the loss of recharge area as well as the deepening of the mine.
- Water samples were collected from the mining pit of the three companies and dug wells of the Sirigaon viallge. The water samples were analysed for physicochemical parameters and heavy metals levels. The analysis results indicate that the water quality is within permissible limits (BIS 10500:1991) for drinking water as well as for irrigation purpose as per the guidelines (BIS 11624:1986)
- Groundwater balance study was carried out for the Sirigaon village. It is established that the requirement of the village can be met by undertaking artificial recharge scheme in a holistic way. Roof top rain water harvesting, water absorption trench, sub-surface dykes and bentonite grout have been proposed for artificial recharge and control of water seepage to the mine pits.
- The State Government has provided organized piped water supply scheme to the Sirigaon village
- Artificial recharge schemes have been commissioned recently on a small scale by M/s Rajaram Bandekar Mines Pvt. Ltd. And M/s Chowgule and Company Pvt. Ltd. During the field visits it was observed that the recharge to the nearby dug wells was very insignificant.
- Roof top rainwater harvesting is proposed as Priority I to address the water scarcity problem in the village. Creation of recharge trench and control of mine water seepage are advocated as Priority II. Aquifer storage recovery (ASR) by construction of sub-surface dyke is proposed aas priority III. It is suggested that the artificial recharge of ground water is initiated stepwise. Roof top rainwater harvesting, if not adequate, is to be followed by the construction of recharge trench. Priority III is the last alternative.
- An estimated cost of Rs.660.25 lakhs will be incurred towards installation of the comprehensive recharge schemes to address the water scarcity in the village. The estimate includes the cost towards DPR preparation, maintenance charges and the post-project monitoring charges.
- Soil samples were collected from the silt affected area as well as the control sites. The collected soil samples were characterized for various physicochemical and microbiological parameters (such as bulk density, texture, pH, exchangeable calcium, magnesium, sodium, potassium, available N, P, K, heavy metals and enumeration of different soil microbes).
- The soil analysis results indicate that the silt deposition from the mining overburdens has degraded the soil fertility in the agricultural fields of Sirigaon village.
- Proper slope stabilization needs to be carried out in the mining areas to minimize runoff of the overburden dump material to the nearby agricultural fields.
- Integrated Biotechnological Approach (IBA) is suggested as mitigation measures for restoring the soil quality of the silt affected area. The cost estimated for remediation of silt affected soil by implementation of IBA technology has been worked out to be approximately 1.8 lakhs per hectares area which includes the material costs, land preparation cost and labour cost etc.
Monday, August 24, 2009
Sirigao: NEERI Report to High Court - Executive Summery
Nagpur based National Environmental Engineering Research Institute (NEERI) under Council of Scietific & Industrial Research of the Government of India submitted to the Goa Bench of Bombay High Court, Panaji, the Investigation report in March 2009 after being directed to do so by the Honourable High Court on the Public Interest Litigation of Sirgaon villagers (PIL No. 1/2008, dated 16th June 2008). The title of this 110 page report is "Assessment of the depletion of ground water sources and land degradation in sirigaon vilalge, Goa and mitigation measures". The executive summery is reporduced below in public interest