On-site waste water treatment (ANC) is a device ensuring the collection, the treatment and the evacuation of domestic waste waters in an autonomous way, near the dwelling where collective infrastructure would be too expensive. The research carried out within the framework of the project Gessol Ancres considers the efficiency of such a system and in particular of its non drained sand filter in the elimination of carbon, nitrogen and of the emerging micropolluants parabens and triclosan. A new ANC device was equipped with a sampling system and was monitored during 18 months. The first results indicate a reduction of more than 80% of the carbonaceous pollution entering, with a considerable contribution from the ground. With regard to parabens and triclosan, in the first case we observed an elimination of 87% between the septic tank and the outlet of the sand filter. The ground does not contribute significantly to the elimination of parabens. The overall abatement of triclosan was 72% with a major contribution (47%) in the soil. The differences between the two substances are probably due to their molecular structure. © 2015, Institut National de la Research Scientifique. All rights reserved.