Commercial activities in the past (chemical laundry, waste dumping) in the Van Leeuwenpark and its surroundings in Leiderdorp have led to Volatile Organic Chlorohydrocarbon (VOCl) contamination in the soil. The contamination is located in the soil (source) and the groundwater and extends from the source location, behind the chemical laundry plant, to an area adjacent to the A4 motorway, up to a depth of approx. 50 m-mv. The soil contamination has been established to be severe, which calls for immediate remediation with an eye on an unacceptable risk of the contamination spreading. The Remediation Plan (RP) distinguishes between separate approaches for the source area, the location where the contamination originated, and for the transition area, the part of the plume where the largest load is currently located. Tackling the rest of the plume (monitoring) is not part of this contract.
The activities that will be carried out to remediate the source area consist mainly of:
- Performing direct substrate and bacteria injections in the source area
- Installing 5 filters with filter settings between 7-10 m-mv to inject substrate and bacteria in the aquifer;
- Installing two screens with infiltration and extraction filters respectively, namely:
Screen 1: 10 filters with filter settings between 5-12 m-mv and 10 filters with settings between 15-22 m-mv
Screen 2: 6 filters set to between 10-17 m-mv and 6 filters with settings between 33-40 m-mv.
- Installing a remediation unit with a bio-reactor to extract and infiltrate groundwater, to dose substrate and to inject the appropriate bacteria population;
- Installing a pipe system leading to and from the filter screens and remediation unit;
- Installing a number of monitoring filters;
- Carrying out active remediation by flushing liquid from screen 1 to screen 2 for a period of 6 months;
- Second round of injections in the infiltration filters installed in the source area.
The soil remediation system has now been installed. After months of preparation and implementation, Alderman Jeff Gardeniers officially started the process system (BEAT concept) on 12 October 2018, in the presence of the Province of Zuid Holland, the Midden-Holland Environmental Service and the West-Holland Environmental Service. This event also saw the unveiling of a rotating cube providing information about the remediation process.
Over the coming months, bacteria will be working hard to convert the contamination into harmless residual products. The active phase is expected to last about 30 weeks.