The plains of Méry-sur-Oise/Pierrelaye, Achères, and Carrières-sous-Poissy/Triel-sur-Seine in the Val-d'Oise and Yvelines departments have been the site of the application of raw or partially treated wastewater, leading to diffuse soil contamination. Some plots have gradually evolved into residential areas, notably with the construction of buildings housing children or single-family homes. Beginning in 2007, the Île-de-France Regional Health Agency (ARS) and the SIAAP, with the support of the Île-de-France Regional Environmental Agency (CIRE), conducted studies to identify this pollution and assess the health risks in the affected area. These studies notably revealed the presence of lead in the soil at levels exceeding the regional background level. The ARS referred the matter to the Cire to assess the relevance of screening for childhood lead poisoning in the affected areas. In accordance with the recommendations of the HCSP, given the levels of soil contamination, a health risk assessment was conducted for children living on the site. Risk calculations were performed based on four exposure scenarios. Regardless of the exposure scenario, the health assessment concluded that it is not possible to rule out the occurrence of a health effect linked to the presence of lead in the soil for children aged 0 to 6 years at the site. The conclusions of this study support measures to reduce exposure and encourage screening for childhood lead poisoning. However, this study alone cannot propose or define the implementation details of these measures, which must take into account other technical and economic factors in accordance with the recommendations issued by the HCSP.