The rias of northern Spain are protected tidal inlets, some of which support very productive ecosystems. This has led to major economic activities such as mussel farming. However, the shelters rias provide from the ocean have led to harbour development and, in turn, massive pollution problems.

Over the decades, the Ria Aviles has degraded into an open sewer separating the 90,000 citizens of Aviles on one bank from coke and steel factories and a power plant on the other. The ria has served as a sedimentation basin for the coke factory, leaving a sad heritage of contaminated sediments which include poly aromatic hydrocarbons (PAHs) and heavy metals. As the ria goes dry at low tide, these are exposed to the open air.

The Ria Aviles clean-up is a 20 month project for which the joint venture won a ? 13.75m contract through European tendering rules. Work started in May and is progressing well, with sediment removal to be completed in June 2004. After this, the river embankments will be rebuilt and urbanisation projects including revetments, green spaces and attractive strolling areas laid out. Two weirs will retain the ria water level at low tide and regulate future water supply.

The joint venture will carefully remove some 130,000m 3of contaminated sediment from a 1.9km length of ria. In the central channel, the ria narrows from 50 to 30m in width. In the lower tidal portions a cable crane on the bank is scooping up sediment while further upstream, hydraulic excavators and dumpers are executing the work in the dry.

All excavated material is brought to a nearby deposit for inert waste. A purpose built three hectare landfill cell has been constructed with an impermeable bentonite bottom, isolating HDPE liners, gravel layers and drainage pipes. Two hectares are used as a lagooning field for de-watering purposes.

After a few weeks treatment here, the dry faction is stabilised and immobilised and finally stored in the disposal site of the landfill.

DEC is currently involved in two other major European remediation operations, an immobilisation project for TBT contaminated harbour sediments in Guernsey and the mechanical de-watering of sediments on the River Lagan in Belfast.

MJ Information No: 18636