Permittees are required to monitor the WWTP influent, effluent, and biosolids for all "pollutants of concern" or POCs (i.e. all parameters for which you have local limits) each year under the IPP requirements in their NPDES permits (subpart o.11.) The results are reported in their IPP annual reports.
For many IPP Control Authorities, there are two sets of overlapping monitoring requirements in their NPDES permits. Some permittees have "Additional Monitoring Requirements," usually in Part I.A.2. of their permits, where they are required to monitor the WWTP effluent for various potential pollutants (whole effluent toxicity, hardness, metals, VOCs, acid-extractable compounds, and base-neutral compounds, etc.) in four months specified in the permit. The results are reported in their NPDES application.
The requirements are different but overlap; therefore, if a permittee conducts sampling for its Additional Monitoring Requirements, the permittee has likely addressed its IPP-required effluent sampling, although influent and biosolids monitoring for POCs would still be needed. Also, there is one year with no Additional Monitoring Requirements permit cycle, usually the year that the application is due. For that year, to meet the IPP monitoring requirements, permittees need to conduct influent, effluent, and biosolids monitoring for all POCs.