Mumbai buildings under salt attack?

A BMC report has revealed that indiscriminate extraction of ground water is increasing the concentration of salinity in the soil and corroding buildings

 Mumbai's buildings are corroding due to a rise in concentration of salt in the ground water, a prelimnary BMC-commissioned study has revealed. The study, which was carried out by the Ground water Survey and Development Authority (GSDA), has also claimed that the phenomenon, known as salt attack, may have been caused by an indiscriminate extraction of ground water through bore wells. 

    According to the study, being next to the Arabian Sea, salts are naturally present in both the soils and groundwater systems in the city. But the excessive extraction of ground water has led to rapid increase in concentration of salt in the underground water as well as the soil. 

    Buildings absorb the heavily saline moisture from the soil. Over a period of time, the salt attacks (corrodes) the bricks and building structure weakens and eventually causes the bricks and structure to deteriorate. 

    According to GSDA, the problem has compounded in recent years following the BMC's policy that all new projects in the city must have a bore well for non-potable consumption. The civic body's decision had come in 2009, when the city was reeling under water scarcity after a poor monsoon. As a result, 525 bore wells and 89 ring wells came up in the city in the last three years. 

    To save the buildings now the BMC has asked GSDA to prepare a detailed report on these salt attacks and suggest a practical solution to the problem. 

    "Goregaon and Chembur are among the worst hit by the salinity problem. So in the first phase, GSDA will study M-east (Chembur) and P-south (Goregaon) wards. The GSDA will also suggest remedies on the problem," BMC hydraulic engineer Ramesh Bambale said. 

    For the next two years, the GSDA will regularly test samples of ground water from the two wards and study the change in the concentration of salt in the water and soil, and its effect on buildings in these area. They would than compare this with the water samples from other parts of the city. 

    Speaking to Mirror, BMC standing committee chairman Rahul Shewale said, "Indiscriminate and unplanned extraction of ground water could lead to wells yielding saline water for some time. But it is not only about the saline water, the extraction of ground water at this rate will also increase the surface temperature. So we have to take precaution." 

WHAT IS SALT ATTACK 

SALINITY ISSUES ARISE when the hydrological balance in the water table is disrupted, through either an increase (through irrigation or use of bore wells) or a reduction in use of ground water. 

    In a nut-shell, land use change and urban development are two key factors contributing to the expanding salinity issues. 

    Saline soil moisture is absorbed into the building structure through direct contact with saline soils. 

    Over a period of time, a direct physical attack from the mobilised salts corrodes the bricks and eventually causes the structure to deteriorate.