The Missouri Department of Natural Resource’s Hazardous Waste Program has not completed investigations of 111 former lead smelters and 3,300 former mining sites, a state audit released Thursday said.

The report, from State Auditor Tom Schweich’s office, said DNR staff had indicated those sites had “a high probability of contamination” and also may have released hazardous substances.

Of the former mining sites, DNR has investigated 9,500 out of 12,800 known or possible former lead mining sites, the audit found. The size of mining sites range from a few square yards to several hundred acres, and date back to the early 1800s.

The audit said DNR indicated it prioritizes site investigations based on the risks to public health, but there has not been enough funding to complete all of the lead investigation work. Missouri mostly exempts lead as a hazardous substance, but a 1980 federal environmental law classified it as a dangerous substance. Missouri began adding former lead mining and production sites to a federal queue for cleanup.

DNR said in a response to the audit it will continue to conduct site investigations as required by EPA when funding allows.