Imports of waste into the UK for disposal are illegal under the 1996 management plan for exports and imports of waste. Provisions transferring responsibility for regulating transfrontier waste shipments from councils to the EHS - issued in 2000 as part of proposed amendments to the transfrontier shipment of waste regulations - have yet to be implemented.
The Province's 26 local authorities have long struggled with their waste management responsibilities, and some smaller councils have lacked full-time waste regulation officers.
However, in December, responsibility for waste site licensing was finally transferred from councils to the EHS, when regulations for waste management licensing took effect almost ten years after those in Britain (ENDS Report 348, p 40 ).
Recently, landfill regulation in Northern Ireland has been strongly criticised by environmental groups. Last year, Friends of the Earth called for the prosecution of a landfill operator who had allegedly accepted more than 100,000 tonnes of wastes not covered by his licence, including animal carcases and clinical waste.
Operating standards should be improved significantly once the EHS gets to grips with its new responsibilities, but waste regulation officials were not brought across from the councils and the Service has yet to recruit many of the staff it will need.
Change came sooner south of the border, where the Waste Management Act 1996 established a new national regulatory system. As operating standards were raised, so the number of landfills fell from 95 to 33 between 1995 and 2003. Estimates suggest that there could be a one million tonne shortfall in capacity this year.
Coupled with rapid growth in waste arisings, this led landfill gate fees to triple in the past four years to £70-135 per tonne - and created conditions ripe for "professional" dumping of waste across the border.
In December, the EHS set up a special team within its waste management unit to tackle the problem. According to an EHS spokesman, the unit has been uncovering one or two waste dumps per week. Landowners have been threatened or bribed, while local authority staff investigating incidents have been beaten up or had their cars burned out.
There is anecdotal evidence that increasingly sophisticated gangs are using forged papers and Northern Ireland number plates to deliver thousands of tonnes of waste from the Republic to council-owned landfills.
With a 20-tonne load worth as much as £2,500, a gang shifting four lorry loads a day could make £500,000 profit in just 12 weeks.
One dump near the border in county Tyrone was found to contain clinical waste - including used syringes and other infectious material, and sensitive bank documents.
The scandal rose up the Republic's political agenda in February when Department of Justice papers were found along with documents from financial institutions. The matter is now the subject of a Garda investigation.
The EHS is preparing to bring a number of prosecutions but declined to give details of the charges. Ireland's Environmental Protection Agency (EPA) also plans to bring prosecutions in relation to the incidents but - as in Northern Ireland - responsibility for transfrontier shipments rests with councils.
Although some waste management companies in the Republic are investing in recycling facilities and collection systems, many smaller contractors are exporting waste overseas.
In February, the EPA announced that Dutch authorities had returned 51 containers of mixed recyclable waste incorrectly classified as "green list" segregated waste suitable for recycling. Arrangements were being made for the return of a further eight containers, while another 40-80 were being held in Antwerp, Belgium.
There is also evidence of consignments of household waste being sent to Northern Ireland for sham recovery at material recycling facilities.
There are fears that as long as contractors can get away with illegal exports they will be reluctant to invest in domestic recycling and recovery facilities. Legitimate contractors are also less likely to invest when cowboy operators are undercutting them.