Last August began the modifications of the waster water treatment plant "Horstermeer". The purpose of these modifications is to facilitate the biological removal of phosphorus and nitrogen from water. The modifications include, amongst others, the building of a 1-STEP® filter and an Anaerobic tank (ANT), to keep the water pumping out of the cofferdam to a minimum during the construction phase of the 1-STEP® filter and the ANT. It was decided that the best option would be a closed cofferdam with sheet piling and to build a horizontal water retaining layer at the bottom of the excavation using soil injections with water-glass hardener. B&P Bodeminjectie B.V. has already satisdactorily executed the soil injections of the 570m2 and 2,600m2 construction sites.