Environmental consultants talked guardedly at the IBC conference on groundwater pollution. They were particularly careful to ensure that slides and papers gave no clues to the identity of clients who are involved in clean-up operations. Nevertheless, a growing number of cases of groundwater pollution are coming to light. Those mentioned at the conference included:
A large petrol station has contaminated the underlying aquifer with unleaded petrol containing MTBE. Two drinking water supplies 0.5 kilometres away have been affected by the chemical, and the site is being investigated by the National Rivers Authority (NRA).
A school in Dundee which was shut by the local authority for six months in the early 1970s after persistent odour problems. Ground contamination from a nearby petrol station was suspected, and new oil interceptors were fitted and eight boreholes constructed. The fumes were finally eliminated by an interception trench around the school. However, documents recently examined by Dr Iain Spence at the Dundee Institute of Technology indicate that the fumes were not petrol and their source remains undiscovered.
A total of 14 public groundwater sources and about 10 private supplies are currently receiving treatment to remove solvents, according to Bob Harris of the NRA. However, over 100 boreholes are in some degree affected by solvent pollution.
A former lubricating oil storage depot has contaminated a shallow riverside aquifer. The groundwater contained up to 1,000mg/l of petroleum hydrocarbons. Consultants Dames & Moore claim to have carried out a successful in situ remediation programme.
Routine losses from solvent handling on an industrial site in southern England have contaminated a chalk aquifer with trichloroethene (TCE). Soil vapour extraction, groundwater pumping, air stripping and catalytic incineration are being used in a clean-up operation designed by ERM Enviroclean.
Another industrial site has contaminated an Upper Chalk aquifer with trichloroethane, TCE and tetrachloroethene at levels of up to 104µg/l, 937µg/l and 197µg/l respectively. Dames & Moore has designed a clean-up programme involving vapour extraction, groundwater pumping and air stripping.
A leak of aviation fuel has contaminated the gravel aquifer at Heathrow, last year's IBC groundwater pollution conference heard. The site has been under remediation by scavenge pumping for the last four years and over 30,000 litres of fuel have been recovered. However, much of the fuel is trapped in the aquifer and may remain a pollution source for many years.
Companies may be wary of talking openly about their environmental liabilities because they believe it may adversely affect the value of their business. However, the secrecy is stifling debate about the long-term direction of groundwater clean-up programmes.
Although some consultants make unrealistic claims for clean-up technologies, others now acknowledge that in situ treatment methods rarely, if ever, reach an end-point. In practice, aquifer solvent levels may never reach drinking water standards, but there has been insufficient debate about what constitutes a practical and satisfactory standard of remediation.