The Environment Agency was alerted to the incident, at a site in North Boarhunt, by an anonymous tip-off in May. Investigations revealed that the spill had occurred early in April but had not been notified to the Agency.
The Agency has declined to identify the company concerned on the grounds that legal proceedings may be taken. But the Portsmouth Evening Gazette has named it as SIS Chemicals, which buys chemicals in bulk and repackages them.
The solvent was lost shortly after it was delivered to a previously unused storage tank. SIS has told the Agency that the tank was tested prior to use, and has been asked to furnish evidence of this.
The firm initially believed that the solvent had been stolen or vented to atmosphere. It then attempted to determine whether it had leaked into the ground by drilling four boreholes with an auger within the bund around the tank. The Agency has reacted by ordering SIS to empty two other tanks containing trichloroethylene and sodium hypochlorite which share the same bund.
Consultants have now drilled three further boreholes on the site. Samples taken by the Agency have suggested that the solvent is migrating from the tank towards the river Wallington, about 150 metres away.
Up to 20mg/l of trichloroethylene has been detected in one borehole downgradient of the tank, while the surface water discharge to the river contains 10µg/l - equivalent to the environmental quality standard for freshwaters. However, levels in the river, though rising slowly, are only around 1.0µg/l, and no downstream abstractions are threatened.
The site is underlain by clay, so no serious threat to groundwater is likely. However, SIS is likely to need at least to excavate a large volume of contaminated soil, and may have to install an air stripping plant to complete the clean-up.