Relevance of research. The organization of the environmental monitoring system, particularly, in groundwater, is becoming important because of developing the nuclear power production and the increase in the amounts of radioactive materials in nuclear complex facilities. Nuclear power plant facilities are sources of anthropogenic radionuclides in groundwater and produce aureole contamination. The study focuses on an area with several nuclear facilities that affect the environment and each other. The aim of the research is to determine the content of anthropogenic radionuclides in the groundwater of the North-West Nuclear Complex in the Leningrad Region; to identify the major sources of radioactive contamination based on the data collected. Objects and methods. Groundwater from the Quaternary and Lower-Cambrian horizons contaminated by anthropogenic radionuclides is being studied. The study was based on large volumes of data from engineering surveys conducted at the construction sites of the operating and planned Leningrad NPP, radioactive waste storage facilities, and other sites. Borehole drilling data, hydrogeological sampling data, and monitoring observations, including radiological data, were used. Results. The article discusses the zoning of the North-West Nuclear Complex based on the impact of contamination sources on groundwater radiological conditions, controlled by unstable isotopes of ¹³⁷Cs, ⁹⁰Sr, and ³H. In several areas of the North-West Nuclear Complex, the natural background radiological level in groundwater was exceeded. Maximum radionuclide activities (up to values above the action level) have been observed near the radioactive waste storage facility.