Mining runoffs hit water supply to south Goa

PANAJI: High content of manganese in raw water at Selaulim water treatment plant has forced authorities to restrict water supply by about 40 million litres daily (mld) to the densely populated talukas of Salcete and Mormugao.
The plant in Selaulim pumps out a total of about 180 mld, but heavy concentration of manganese due to runoffs from mining dumps in catchment areas brought down the output to around 140 mld.The problem has been plaguing the treatment of raw water for the past fortnight.
"The rate of filtration reduces due to presence of manganese," PWD superintending engineer SR Paranjape said. A content of 1 mg per litre of manganese is permissible, but after heavy rains in the hilly areas, the quantum has gone up gradually.
"The content has risen to 3.5 mg per litre, which is very high as compared to the permissible level," Paranjape said. The rise had been gradual during the fortnight, but reached excessive levels during the past three days. "Now it has started coming down," he added.
The state has around 300 mining leases and at least 180 of them are located near water bodies. The problem is also acute in Selaulim's catchment areas with 17 leases being worked within 200 metres of the reservoir. A few are close to the submergence area when the water level rises during the monsoon.
The impact of pollution from manganese increases thrice annually-first during the monsoon, then when the canal is opened to release water for irrigation in November and when the water level in the dam recedes to the lowest level in May.
The construction of a 100 mld plant at a lower level on the hill is expected to help in aeration of the raw water before treatment. The work is in progress and after completion of this unit, another one of identical capacity will be set up nearby.
The present plant is located at 110 feet above sea level and there is no space on the hill top for a bigger settling tank for raw water. Diffused air is forced in the settling tank before treating it. "When manganese comes in contact with air in a large surface, it oxidizes," Paranjape said. The raw water will be treated at a lower level and pumped to a reservoir.
The cost of the Selaulim project was estimated at Rs 9.61 crore when it was sanctioned in 1971, but by 2007 this had exceeded Rs 170 crore.