ToI: An expensive flush at Opa

An expensive flush at Opa Paul Fernandes, TNN | Aug 8, 2012, 05.21AM IST OPA: High levels of turbidity at Opa due to mining operations in the upstream of Khandepar river is costing the state exchequer dearly, as several million litres per day (MLD) of treated water is wasted in cleaning the clogged filters every year. The turbidity level shot up to 300 naphelo turbidity units (NPU) on Tuesday, heavily clogging the filters and necessitating a wasteful and time-consuming clean-up to ensure safe drinking water for consumers. "The water was released only at 5pm as backwashing of filters took time," an official said. The Opa plant supplies about 140 MLD to Ponda and Tiswadi, but the supply on Tuesday is likely to be slashed by five to 15 MLD due to muddy raw water. "If it continues raining on Wednesday, the problem may persist," the official said. After raw water is drawn into a receiving chamber from the river, it flows into sedimentation tanks to allow settling of the silt. Next, the water passes through three stages from sand filter beds to the chlorination plant and into the main balancing reservoir (MBR) for storage and supply. But sources said the filters quickly become non-functional due to the density of the mining sediment. A total of 21 filters at the plant had to be washed 2,215 times during the six-month period from June to December, 2011. This information was provided by PWD's works division III under right to information (RTI) to social activist, Ramesh Gawas. "This means that washing 21 filters at the rate of 10 cubic metres per filter required 210 cubic metres on each occasion," Gauns said. The total wastage of 2,100 cubic metres for six months at the rate of 2.50 per cubic metre charged for domestic consumers' works out to 5.25 lakh. Gauns had sought the information of the backwashing cost for seven years. "The real picture of the water wastage and the exact revenue loss cannot be quantified as PWD did not provide the information," Gauns said. No flow meters are installed at Opa plant to ensure quantification of water used for backwashing. "It depends on the turbidity level, but in a worst case scenario more than 5 MLD may be required on a single day," a source said. A site inspection conducted by Goa Foundation on December 4, 1999, at the behest of Indian bureau of mines had revealed that huge costs of cleaning the muck at Opa plant are borne by lakhs of people. The report was submitted to the government with recommendations to compensate the losses from the mining companies. Backwashing of filters involves several types of costs, wear and tear of machinery, extra work for the personnel consumption of power, and additional cost of treating more water, the report stated. "Around 30% of the state population and industries are impacted by the silt in the water," Gauns said. http://timesofindia.indiatimes.com/city/goa/An-expensive-flush-at-Opa/articleshow/15398110.cms