BOISE, Idaho (AP) — Monsanto Co. mining officials are investigating the engineering and safety of the water treatment system at its new phosphate mine after a holding pond sprung a leak and dumped water and sediment into a nearby wetland.

Monsanto reported the March 29 failure to government officials, triggering a review of the water management system at the Blackfoot Bridge Mine near Soda Springs. The breach occurred at a pond built to hold storm water and snow melt that collects at the site. The failure allowed an estimated 3 million gallons of water to leak from the pond. The project was permitted in 2011.

Monsanto has touted its mining plan for incorporating state-of-the-art engineering. Environmentalists oppose activity in southeast Idaho's phosphate patch due to concerns about selenium — a toxic mining byproduct.