Auditors found violations were issued to private industry and sewage treatment plants in just 33 of 558 instances serious enough for such citations under DNR policies over the last 10 years.

Municipal and industrial dischargers submit monthly electronic monitoring reports that DNR uses to identify violations, but auditors said when it came to CAFOs, problems with DNR record-keeping made it impossible to determine how often violations led to enforcement action.

CAFOs are expected to notify the DNR if they spill manure or apply it to fields in a way that endangers groundwater or threatens to run off into streams and lakes where it can cause beach closings and unnatural growths of weeds and algae. Violations also can be discovered through citizen complaints and DNR inspections.

The DNR has increased the number of CAFO inspections it conducts, but often their value was questionable because they were performed so far in advance of — or in some cases after — a permit was renewed, auditors said.

And even after average annual inspection numbers peaked from 2010 to 2014, fewer than half of the large livestock feeding operations were being inspected twice during each five-year permit term, the goal the state set for itself.