Health

Missouri could tighten ammonia limits in water for the first time since 1999

KBIA | By Najifa Farhat

Published October 14, 2025 at 4:00 AM CDT

In 2013, the Environmental Protection Agency recommended stricter limits after new research showed aquatic species are more sensitive to ammonia than previously understood.

State officials say Missouri's current standards, last revised a quarter century ago, are based on outdated science. For small rural communities, it could require major upgrades for water treatment facilities.

Missouri is preparing to update its water quality standards for ammonia for the first time in more than 20 years, a change that could mean steep costs for small towns with lagoon wastewater systems.

In 2013, the Environmental Protection Agency recommended stricter limits after new research showed mussels, snails and other aquatic life are more sensitive to ammonia than previously understood.

"EPA included additional species in its calculations, and the new recommendations are stricter than what's in our current regulations," said Mike Kruse, environmental program manager for the Missouri Department of Natural Resources' Watershed Protection Section. "We're proposing to adopt those standards to better protect aquatic life in Missouri streams and lakes."

Unlike a single fixed number, ammonia criteria typically use formulas that vary depending on factors such as pH, or water temperature. Missouri regulators plan to calculate limits by using region-specific standards.

Kruse said the impact will be felt most by small rural communities that rely on lagoon systems, which were not designed to treat ammonia at the stricter levels. "Upgrading them would mean essentially rebuilding the treatment plant," he said. "For small communities with shrinking populations, that's a pretty significant cost."

To ease the transition, the state is offering variances — temporary exceptions that let facilities show the highest level of treatment they can realistically achieve and request more time to comply with the new federal standards. Larger city plants must also meet the new requirements, but their infrastructure is better-equipped to handle the changes without major upgrades, Kruse said.

The DNRC held an open house this week to guide community representatives through the variance application process. Additional sessions are planned in the coming months.

The proposal now enters an 18-month public rulemaking process that includes writing a regulatory impact report followed by public comments and review by Missouri's Clean Water Commission, all before statewide enforcement.