Construction of an active barrier with Drain Panel® gates at a site contaminated with hydrocarbons and derived products.
The Clipper Oil site a few kilometres from Granollers in the Barcelona suburbs (Spain) was occupied for many years by a waste oil treatment shop. Ignoring environmental protection rules, this activity seriously contaminated the soil and ground water table with hydrocarbons and related products such as PCBs, PAHs and phthalates. When the business collapsed, the “Junta de Residus”, responsible for contaminated soils and sites as an agency of the Generalitat de Catalunya, invited proposals for remediating the site, which was threatening to pollute an abstraction well and nearby river.
Fifteen proposals were submitted. The successful one jointly tendered by TQMA (Tecnologia Quimica y Medio Ambiente), Rodio and Soletanche Bachy was for an active barrier using Drain Panel® technology and in situ bioremediation.
This approach was the only one offering the following advantages:
- It ensured adequate protection of the water resources downstream of the site because the polluted area is contained within a confining barrier.
- Industrial activity (mechanical engineering and glassware shop) would not be interrupted (this was one of the major specification requirements) because the remediated area did not have to be covered.
Excavation and processing of the most severely polluted soil involved no risk of aggravating pollution of the water table.
The active barrier operates on a simple principle. The enclosure is open at the top and when it rains, the water escapes through the Drain Panel® gates which have filters to trap the pollutants coming from the natural leaching process or disturbed by excavation of contaminated soil.
Description of works
Rodio, assisted by Soletanche Bachy, undertook the following works:
- Surrounding slurry trench wall, 5.2m deep, dug with a long-reach backacter. Wall permeability was less than 5 x 10-9 m/s.
- Two filter gates built with patented Drain Panel® technology in which filters trap organic contaminants such as heavy hydrocarbons, PAHs, PCBs and phthalates. The gates can operate either in series or in parallel.
Performance monitoring and maintenance
The gate filters are:
- designed to be replaced yearly on the basis of the foreseeably slow flow rate in this Mediterranean climate and the high degree of pollution,
- fitted with sampling tubes to test the filter medium for saturation.
Gate inflow and outflow analysis revealed better than 90% reduction in dissolved hydrocarbons.
All parts of the gate are readily accessible for cleaning, which simplifies maintenance.
Monitoring piezometers inside and outside the barrier indicate satisfactory overall performance of the system.
Groundwater is one of the most complex issues to be resolved in geotechnics. During the start phase of a project, the proper techniques have to be chosen for building any cut-off walls that might be required, pumping (wells, filter points, etc.) and monitoring (piezometers) resources.
Soletanche Bachy, and its subsidiary Solenvironment, provide solutions for pollution issues, involving, for example: inertisation of waste, rehabilitation and treatment of polluted sites, cleaning of discharge to required environmental control levels, construction of waste storage facilities, protection of groundwater.
Through his subsidiary Sol Environment, Soletanche Bachy provides solutions to various pollution problems: stabilisation of waste, rehabilitation and treatment of polluted sites, cleaning of discharge to required environmental control levels, construction of waste storage facilities, protection of the water table.
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