According to Government guidance issued in 1994, "large quantities of materials such as soil" should not be landfilled if they contain more than 50ppm of PCBs. The guidance did not come out of the blue: in 1985, the Hazardous Waste Inspectorate had advised that wastes containing more than 10ppm of PCBs should not be routinely landfilled.
Remarkably, however, the Scottish Environment Protection Agency (SEPA) recently advised consultants working on a contaminated site in Hertfordshire that wastes containing up to 10,000ppm of PCBs could be tipped at Greengairs, the Shanks & McEwan (SME) landfill near Airdrie. This is because the site's licence, issued by Monklands District Council in 1990, does not include any specific controls on PCBs, and SEPA has yet to amend it in line with Government guidance.
The licence simply prohibits "special" wastes. The 1996 special waste regulations set a threshold of 50ppm above which wastes are classed as special. But SEPA argues that the licence refers to the pre-1996 threshold of 10,000ppm.
SME has a big contaminated soil business - worth around £5 million in 1997 - mostly based around its co-disposal landfills in Bedfordshire. Unlike Greengairs, these take a wide range of "special" wastes. But they cannot take PCBs above 50ppm. Many landfills prohibit PCBs above 20ppm.
Exploiting the market advantage created by the relaxed PCB controls at Greengairs, SME quoted over £1,000 per tonne for hauling and landfilling the Hertfordshire soil - well over ten times the typical fee for special wastes to landfill. The high price reflects the fact that the only alternative disposal route appeared to be high-temperature incineration - for which SME quoted £1,200 per tonne for disposal at its Rechem subsidiary.
"Because they were aware how much it costs to incinerate PCBs, the costs of landfill were not much less," said Gerald Conn of civil engineering consultants Thorburn Colquhoun, who managed the site clean-up.
The high costs meant that the bill threatened to exceed the land value when Dr Conn unearthed over 600 tonnes of contaminated soil - four times more than expected. Searching for a cheaper outlet, he contacted Royal Ordnance (RO), whose thermal treatment plant in Chorley, Lancashire, recently began burning PCB-contaminated soil. RO quoted less than a third of the price per tonne than SME.
Thorburn Colquhoun consigned the less contaminated soil to RO, whose plant cannot treat more than a few hundred parts per million of PCBs. The more contaminated fraction - 160 tonnes containing above 200-250ppm - went to Greengairs.
SEPA is now considering amendments to Greengairs' licence to restrict PCB inputs. But a spokesman insisted that it may not be necessary to impose a 50ppm limit. Instead, it is considering a formula based on the overall PCB loading rate.
Roland Williams at SME agreed that inconsistent landfill regulation meant that waste was travelling long distances. But he argued that landfill was the "best practicable environmental option" in this case, on the grounds that incineration would have required a lot of support fuel.
He also argued that the incident is "insignificant" compared with deeper inconsistencies in landfill regulation which are being exploited by competitors in the land remediation market. "The inconsistencies are astonishing and that makes the marketplace very difficult especially when you look at the amount of money we've invested in our facilities and what other companies get away with," Mr Williams said.
Competition from landfill has plagued RO's business since it started up in 1994 using a mobile plant (ENDS Report 233, p 12 ). The unit treats the soil at up to 450°C and then incinerates the off-gases at 850°C with a two-second residence time.
The plant was originally intended only to treat soils contaminated with petrol or similar hydrocarbons, not chlorinated chemicals. But RO's Jeremy Birnstingl says: "We found we simply could not compete with landfill at less than £20 per tonne."
RO has been forced into the market for soils which are too contaminated for landfill. Tough controls on PCBs at most landfills made them a prime candidate. Other chlorinated chemicals such as solvents and pesticides are also being pursued.
However, the unit has no scrubber to remove hydrogen chloride. Dr Bernstingl says that the economics do not justify investment in scrubbing. As a result, RO can only treat soils with relatively light chlorine contamination. Another concern is the combustion temperature: EC legislation stipulates that plants burning more than 1% of chlorinated chemicals must work at 1,100°C to ensure complete combustion.
A Devon capacitor manufacturing site was recently cleaned up using the RO plant. The soil was mixed to reduce hot spots and had an average PCB contamination of 120ppm. Golder Associates chose the RO plant after tests with bioremediation had failed and solvent washing appeared too time-consuming. The treated soil contained less than 0.2ppm of PCBs.