I assume that the Question refers to waste water treatment plants in housing estates that are not in the charge of local authorities, and are dependent on developer provided water services infrastructure for the provision of their waste water services.
I can confirm that all local authorities have, under legislation, the appropriate powers of inspection and investigation, and where issues are found, power to enforce improvements. In particular, the Local Government (Water Pollution) Acts 1977, as amended, provides the legislative basis to protect water quality, public health and the environment from risks posed by failures in such systems.
My Department does not maintain data on the information requested and for the reasons stated, local authorities are best placed to provide the Deputy with this information.