Assessment of Groundwater Quality in the Mining Areas of Goa , India

Goa is a famous International tourist destination and attracts around 2 million tourists annually. Tourism is generally limited along the coastal belt of Goa, while mining is more focused in the midland of Goa. The groundwater in the State is mainly used for drinking and industrial purposes followed by agriculture to some extent. The open cast iron ore mining in Goa had induced significant changes in groundwater quality and quantity. The objective of the present study was to assess the impact of mining activities on the qualitative scenario of ground water in the study area. The monitoring of groundwater quality was done at fourty five groundwater sampling locations on a seasonal basis (i.e. post-monsoon, winter, summer, and monsoon) from October 2011 to September 2012. Assessment of Ground water quality status was done by using the Water Quality Index method, which is an effective tool to assess spatial and temporal changes in ground water quality. Based on the descriptive categories of WQI values observed, all (100%) the sampling locations in the study area were observed with very good category. *Author for correspondence Indian Journal of Science and Technology ISSN (Print) : 0974-6846 ISSN (Online) : 0974-5645 Assessment of Groundwater Quality in the Mining Areas of Goa, India Gurdeep Singh1 and Rakesh Kant Kamal2* 1Vinoba Bhave University, Hazaribagh-825301, Jharkhand, India 2Center of Mining Environment, Department of Environmental Science and Engineering, Indian School of Mines, Dhanbad-826004, Jharkhand, India; rakesh.ism2012@gmail.com


Introduction
Groundwater is considered as one of the primary resources for development activities.The overexploitation of groundwater has detrimentally affected groundwater in terms of the quality and quantity.Groundwater quality can be adversely affected or degraded as a result of human activities that introduce contaminants into the environment, including disposal of domestic, agricultural and mining waste.The chemistry of groundwater is an important factor determining its use for domestic, irrigation and industrial purposes.Mining activities are known to affect both the surface and ground water regime during the last century.Changes in local topography and drainage sys-tem directly affect both quality and quantity of ground water 1 .There are several states in India, where more than 90% populations are dependent on groundwater for drinking and other purpose 2 .Groundwater is the major source of drinking water in both urban and rural areas 3 .The standards for drinking purposes as recommended by the World Health Organization 4 and Indian Standards 5 have been considered for the calculation of Water Quality Index (WQI).The first comprehensive hydrogeological study in Northern Goa was carried out by Subramaniam 6 .Govindarajan 7 have studied the lateritic soil of Goa.The former report by TERI India studied pollution of groundwater and reported that the wells at Digne in North Goa mining belt were contaminated with diesel, while several wells at Velguem and Pissurlem had been contaminated by excessive situation arising from mining activities.Ghosh 8 studied the rainfall contribution to groundwater recharge as 16% and evapo-transpiration and surface runoff as 32% and 52% respectively.Pathak 9 suggested the optimal design of groundwater structures together with proper selection of pumping unit in the territory to avoid hazards of seawater intrusions.Several studied also described aerial photographs and described geomorphological features of the coastal Goa.Excessive mining of Iron ore by open cast methods in the northern part of Goa has resulted in the depletion of groundwater table 10 .The depletion of ground water resources is of particular concern because its catholic importance to the mankind.Venkatraman 11 carried out environmental impact studies of iron ore mining through remote sensing in which they also studied the groundwater aspects includes depletion of groundwater due to mining.Pahala Kumar 12 carried out detailed studies in the mining areas of North Goa for evaluation of groundwater potential using remote sensing and Geographic Information System (GIS) techniques, which have indicated that iron ore beds can form aquifers.The dating of the water samples indicated that the shallow lateritic aquifers and the deeper iron ore aquifers are not hydraulically connected.(Central Ground Water Board (CGWB) 1997.Studies were carried out on the quality assessment of groundwater in and around Calangute area, in north Goa 13 .Chachadi 14 have carried out a detailed investigation of groundwater potential availability, and its vulnerability to pollution, sea water intrusion using Geographic Information System (GIS).Chachadi 15 has carried out a detailed study on impact assessment and remediation of open-cast mine dewatering on rural drinking water supplies in the mining belt of Goa.This present study deals with the extent and degree of groundwater contamination in and around mining areas of Goa from geochemical analysis of groundwater samples and by using the quality Indexing approachveloped aggregate hydroponic systems.

Study Area
Goa is the 25th State of India, attaining statehood in May 1987.It is a relatively small state which lies between the latitudes 14°53'54" N & 15°40'00" N and longitudes 73°40'33" E & 74°20'13" E with geographical area of 3,702 km 2 and a coastline of 105 km (63 miles).Goa is well connected to rest of India and some international destinations via air, road, rail and waterways.The state is divided into two districts: North Goa and South Goa.Panaji is the headquarters of the North Goa district and Margao of the South Goa district.The districts are further divided into talukas.North Goa district has six talukas viz., Pernem, Bardez, Tiswadi, Bicholim, Sattari and Ponda.South Goa district had 5 talukas viz., Salcete, Marmugao, Sanguem, Quepem and Canacona.In April 2011, a portion of Ponda taluka from North Goa district and Sanguem taluka from South Goa district were separated to form Dharbandora taluka which was added to South Goa district.Since April 2011, both North Goa district and South Goa district has six talukas each.The languages spoken are Konkani, Marathi, English and Portuguese.The State of Goa receives rainfall from southwest monsoon between the months of june-september.The average annual rainfall in the mining area varies between 3500 to over 4000 mm.The temperature ranges between 20 and 34 o C. The relative humidity is higher during the months of July to September ranges between 60 percent to 90 percent.

Water Quality Index Method
A Water Quality Index (WQI) describes the general situa-tion of water bodies by changing water quality parameters levels into a numerical score using mathematical tools16-18.It is calculated from the view of human consumption.WQI can be evaluated on the basis of physical, chemical and biological parameters.The concept of water quality to categorize water according to its degree of purity or pollution dates back to 1848 in Germany [19][20][21] .

The Calculation Involves the Following Steps
The standards for drinking purposes as recommended by Indian Standards : 10500, have been considered for the calculation of WQI.In this method, the weightage for various water quality parameters is assumed to be inversely proportional to the recommended standards for the corresponding parameters22,23.
Accordingly, the weightage of ithparameter is calculated by following formula: Where, is the unit weight for the i th parameter; the recommended standard for ith parameter and i = 1, 2, 3, ..., 16; and the constant of proportionality The calculation involves the following steps: (a) First, the calculation of the quality rating for each of the water quality parameters (b) Second, a summation of these sub-indices in the overall index The individual quality rating is given by the expression: Where, is the measured value of the ith parameter in groundwater samples under consideration and the standard or permissible limit for the i th parameter.The WQI is then calculated as follows: Where, Q is the sub index of ith parameter.W is the ith unit weightage for ith parameter, n is the number of parameters considered.The descriptor categories of water based on the WQI values are determined as per

Result and Discussion
The WQI was calculated for all the groundwater monitoring stations in four seasons, i.e. post monsoon, winter, summer and monsoon seasons and were presented in Table 3.The overall water quality index of ground water in the study area is presented in Figure 1.The data for 3 sampling locations for the summer season was not available since they are dried up completely, namely GW7 (Shrigao), ity of all sampling stations was observed with very good category in all four seasons showing little variation in the quality which may be accounted for seasonal changes.In general the water quality index was found comparatively higher in winter and summer seasons than post monsoon and monsoon seasons, showing maximum water quality index in the winter season.The lower value of the index during monsoon and post-monsoon seasons might be attributed to the copious recharge of groundwater due to heavy rainfall during monsoon season.Overall, it can be estimated from the above discussion that the groundwater quality of the iron ore mining region of Goa is not under very much threat due to mining activities except at some locations where drying of wells were observed during summer season.The physic-chemical properties of groundwater were observed slightly deteriorated despite of heavy stress of mining activities, which represents the proper maintenance of sufficient volume of groundwater throughout the year and plentiful recharge.

Conclusion
The present study was intended to assess the impact of mining activities on the qualitative scenario of groundwater in the iron ore mining region of Goa, using WQI at forty five groundwater monitoring locations on a seasonal basis (i.e.post-monsoon, winter, summer, and monsoon) from October 2011 to September 2012.The observed values of WQI at all (100%) the sampling locations in the study area were observed with very good category category in all four seasons, showing little variation in the quality which may be accounted for seasonal changes.
The values of WQI of the samples were found in the range of 5-11 in post-monsoon, 6-21 in winter, 7-12 in summer season and 5-12 in monsoon.The careful observation of the water table indicates that, mining activities at specific locations have a profound impact on the quantitative scenario of both shallow groundwater as well as moderately deep groundwater systems.The study clearly evidenced that the groundwater of the study area is suitable for drinking and agriculture purposes, except few locations which needs adequate treatment before usage.Based on the observations, the study also portrays the need of effective management of water resources to protect it from the threats of the prevailing contamination.

Figure 1 .
Figure 1.Seasonal variation of WQI at various locations of groundwater.GW1 Dhandkal (Honda) and GW22 (Pissurlem).Based on the descriptive categories of WQI values, all (100%) the samples in the study area were observed with very good category.The values of WQI of the samples were found in the range of 5-11 in post-monsoon, 6-21 in winter, 7-12 in summer season and 5-12 in monsoon.The water qual-

Table 1 .
Unit weightage of different parameters is calculated and represented

Table 2 .
Descriptor categories of WQI Values