Surface water abstractions are particularly vulnerable to pollutants like pesticides, industrial chemicals and oil. The water industry is haunted by failures to spot pollution which have affected millions of customers.
One example that Severn Trent will not forget was the pollution of the river Severn by an industrial chemical in 1994. A highly odorous solvent 2DD entered the river through one of the company's own sewage works.
Severn Trent was fined £45,000 for supplying water unfit for human consumption after supplying contaminated water to 140,000 people in the Worcester area (ENDS Report 243, p 45). An inquiry found that the company did not conduct adequate tests on the quality of the incoming raw water.
Severn Trent is now using an automated laboratory testing device known as SAMOS - System for the Automated Monitoring of Organic Substances. The system is based on high performance liquid chromatography and was first used in the Netherlands in the early 1990s.
SAMOS was used for monitoring the Rhine for herbicides such as triazines and urons. Severn Trent has since developed it to monitor acid herbicides like MCPA and 2,4D.
The updated system is being tested at the company's Witches Oak intake on the River Trent, between Derby and Loughborough, senior process engineer Brian Drage told a Sensors in Water Interest Group conference in Leicestershire in January. SAMOS is being used alongside a suite of other monitoring systems, including oil detectors, a smell bell and a volatile organic compound monitor.
The Trent drains a catchment which includes both highly urbanised and intensive agricultural land. It is vulnerable to a wide range of agricultural and industrial pollutants, including ammonia, nitrates, pesticides, industrial chemicals, bromide, boron, nickel and even flame retardants.
At present Witches Oak is used as a back-up supply but Severn Trent regards it as strategically important for meeting the demands of Nottingham, Derby and Leicester in drought conditions. It expects the source to be used increasingly as the effects of climate change become more pronounced.
Pesticides are a key issue, with the works unable to meet the drinking water standard of 0.1µg/l if levels in the raw water exceed 3-4µg/l. Severn Trent aims to be informed as soon as intake levels exceed 1µg/l.
Mr Drage told ENDS that since 1996 SAMOS has found pesticide levels exceeding 1µg/l about once every two months. But only a couple of events a year exceed 3 or 4µg/l.
SAMOS greatly increases the speed of analysis. Whereas laboratory analyses of acid herbicides, triazines and substituted urea herbicides typically take two or three days,
SAMOS does the job in only a couple of hours, Mr Drage said, allowing the company to take rapid precautionary action.
Severn Trent set up SAMOS to detect half a dozen specific pesticides but it can also detect unknown pollutants. In February last year, SAMOS spotted an unknown pollutant in the river. Subsequent laboratory analysis identified the compound as an industrial biocide chloromethylphenol.
The company has 15 other river intakes and is "seriously considering" installing SAMOS at several of them in the near future, Mr Drage told ENDS. The company says the system costs around £80,000 and around £100,000 per year to run.
Other companies are also believed to be testing SAMOS including South Staffordshire, Thames and Southern Water.
Yorkshire used the new device at its Elvington treatment works on the River Derwent last year and is in talks with an equipment manufacturer to make it commercially available.
The new device is ten times more sensitive than Uvikon with a detection limit of 0.2mg/l for a wide range of aromatic organic compounds - a factor of 100 less sensitive than SAMOS. However, it is considerably cheaper. Yorkshire's Gary O'Neill told ENDS that the system cost the company only £15,000 to manufacture.