Foreword

Palghar, Thane, Raigad, Ratnagiri, Sindhudurg and Greater Mumbai districts of Maharashtra form the Konkan Coastal belt of Maharashtra. In the coastal areas the immediate effect of high groundwater development is often sea water intrusion. Although there were sporadic studies by earlier workers (Umrikar et al., 2007, Gupta et al. 2010) into some reported isolated cases of seawater intrusion in the coastal areas, this has been a maiden attempt to decipher the extent of seawater intrusion in the entire coastal tract of Maharashtra.The area is underlain by Dharwarian meta-sediments (Lower Precambrian age), Deccan Trap lava flows (Upper Cretaceous to Lower Eocene age), Laterites (Pleistocene age) and Coastal alluvial deposits (Recent to Sub-Recent age). Groundwater occurs under phreatic condition in the Coastal and riverine alluvium, laterites and weathered/fractured rocks. The area has been covered by systematic hydrogeological surveys, reappraisal Surveys and groundwater monitoring by CGWB. in these formations depth to water levels range from 0.6 m bgl to 8.07 m bgl. Groundwater is mildly alkaline with pH range of 6.9 to 9.0. Electrical conductivity ranges from 61 to 29370 ?S/cm at 25?C. Only two Samples from Dapoli in Raigad district show EC values higher than 3000 ?S/cm at 25?C. In general, water quality is good and suitable for domestic use and irrigation. In order to confirm the sea water intrusion, ionic ratios like Na:Cl, and Cl:CO3 + HCO3, were computed. From the analysis it is found that about 2 to 10 km wide coastal belt and the inland tidal backwaters are affected by salinity intrusion. It is revealed that about 55% of the analysed samples have indicated salinity ingress. The extent of sea water intrusion is more in the southern part progressively diminishing towards northern area. The maximum effect is observed in Sindhudurg district followed by Ratnagiri, Raigad, Palghar and Greater Mumbai.Over-exploitation of groundwater in pockets and diminishing seaward freshwater flow in the rivers are the major reasons for sea water ingression. Regulation of groundwater development in the coastal area and areas adjacent to estuaries, maintaining adequate stream flow, stopping of riverbed sand mining, construction of tidal regulators at suitable places and creation of fresh water barrier through rainwater harvesting and groundwater recharge are essential to control further sea water intrusion in the area.

Maharashtra is one of the largest states of the country and playing a vital role in the India?s economy through its agricultural and industrial growth. Agriculture is the most predominant occupation in the state and is dependent mainly on ground water irrigation. However, specific focus is being given for the demand side intervention rather than supply side interventions for management of limited ground water resources that available in the state, as the 92% of the state is underlain by hard rocks bearing limited yield potential. The rainfall is the sole source of natural recharge to aquifers and the rainy season extends for three months with barely 55 to 60 rainy days. This is the period during which aquifers get replenished and during the remaining part of this water is utilized for agriculture, domestic and industrial uses. Highest rainfall is received in the coastal areas which have very high runoff rate, whereas remaining part of the state receives rainfall varying from <400mm to 1500 mm per year. A concept plan to recharge the aquifers has been prepared, and details of the artificial recharge structures suitable for the varying geological and topographical setups have been suggested. Besides, micro irrigation techniques are also suggested for water intensive crops to regulate the ground water draft.

Chemical quality of surface and groundwater of an area is influenced by the climate, hydrological conditions, soil characteristics and geological formation. Irrespective of their source, all natural waters contain some chemical constituents and their quality changes progressively as they traverse over the land surface or infiltrate downward due to various hydro-geochemical processes. Anthropogenic factors also contribute substantially towards quality change of both surface water and ground water. In the present study an attempt has been made to understand the aquifer vulnerability to pollution, at the regional scale (Goa State), which takes into account the intrinsic hydraulic and hydrogeological parameters and environmental impacts. It is noticed that a variety of activities, such as agricultural, industrial and urban land uses, are carried out in the area, thus exposing the aquifers to a wide range of contaminants. Groundwater quality data of Goa state for the pre-monsoon seasons of 2014 and 2018 were obtained from CGWB (Bengaluru) and analysed statistically. A regional scale approach was developed which is known as ABHESHT (Aquifer type, Boundary conditions, Hydraulic Head representing static water level, Environmental impact, Solute concentration, Head variation (Water Table Fluctuation) during pre-monsoon and post-monsoon seasons and Transmissivity). The method has been applied to Goa State, west coast of India and compared with the observed groundwater quality parameters. It is found that the model has successfully delineated the wells which are prone to pollution. Using GALDIT model, seawater intrusion impact was also assessed. The study revealed that the groundwater of Goa State did not show any significant pollution indicator, however, seasonal variations in water quality parameters were observed. It is also found that the North Goa coast as well as the other tourist spots spread over the entire state show signs of pollution at various locations (Anjuna. Baga, Mapusa. Concona etc). This calls for immediate attention from the concerned authorities.

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