Recent survey analysis has shown that the basements of the Haut-Valais household waste incineration plant (UIOM) and the A9 motorway contain in some places high levels of mercury and organic pollutants such as benzidine, aniline and o/p-toluidine. , the canton wrote in a press release on Tuesday. The subsoil of the Matterhorn Gotthard Bahn railway, also analyzed, is, on the other hand, little polluted.
The highest values observed at these sites are comparable to documented pollution in other sectors of the landfill and may qualify as very high. “However, according to the data collected, the attack on the water table is not marked”, specifies the Keystone-ATS Yves Degoumois, responsible for the polluted sites, soils and groundwater section of the environment department.
The heart of priority download
No emergency measures are therefore on the agenda for these peripheral sectors of the former landfill. The risks this pollution poses to groundwater have yet to be assessed, however, so that the necessary measures – monitoring, remediation with or without excavation – can be defined. A possible reorganization of these sectors will come later.
Solving the problem of peripheral sectors is not a priority, notes Yves Degoumois. The area of the former landfill is very large, covering more than a third of the Rhône plain at this location and twenty-nine hectares were covered at a depth of almost 20 m, following the liquid waste lagoon between 1918 and 1978. clean everything at once,” he adds.
In the action plan established by the canton, it is the heart of the old landfill – almost three hectares – where the water table is reached, which will be treated first. Studies to carry out this step are still in progress. Difficult for the canton to advance an effective date for the start of the final works.
For now, groundwater downstream of the landfill has been treated by biosparging (injection of air into groundwater to accelerate the biodegradation of benzidine) since January 2020. The application for a construction permit for the last phase of The extension of biosparging has been submitted in March 2022 and its commissioning is scheduled for this year, also specifies the canton.
On Tuesday, following the canton’s announcement, Doctors for the Environment (MfE), the Haut-Valais Group for the environment and traffic, Pro Natura Haut-Valais and WWF Haut-Valais called for “safe sanitation, in one time and final of the discharge of Gamsenried”.
They point out that the ordinance on contaminated sites has been in effect since 1998 and believe that, as such, Lonza, which deposited most of the waste, is “massively behind schedule”. They demand that the company definitively solve the landfill problem within 15 years.
Site cleanup is planned in stages over several decades. And Lonza, for the time being, has provisioned 285 million francs for the first phase of the sanitation project.
The remediation of the entire landfill still needs to go through many steps. “Excavations must be carried out with all the usual precautions. We have to understand the hydrogeology, model our interventions and seek the best possible solutions with the engineers to further confine the site and then clean it up”, explains Yves Degoumois.
The project still has to be developed, through several tests and feasibility studies. Containment and sanitation measures require close coordination, as the landfill area is crossed or limited by the cantonal road, highway, tracks or even poles.
Remediation in already built-up areas also represents an additional challenge and must be proportionate. In the case of identified pollution under the motorway, several methods can be used. “One is to inject a reagent that treats the pollutants so that they decompose”, explains Yves Degoumois. Tested for the time being only in the laboratory, it has the advantage of not having to destroy what was built, unlike excavation, an effective method, “which will probably also have to be used in certain sectors of the landfill. Nothing is excluded”.
More big surprises
The municipality ordered more than 260 holes from 15 to 35 meters in length. With these latest investigations consistent with the historical information (type of waste, area and period of lagoon or deposit) in his possession, he now has “a good picture of the affected areas. And there shouldn’t necessarily be big surprises”, underlines Yves Degoumois.