In December 2018, the US EPA approved Missouri’s standards for limiting nutrient pollution in lakes and reservoirs in the state. The Agency’s approval comes after years of past debate and litigation between US EPA and Missouri over the state’s approach to nutrient criteria and, notably, represents a reversal from US EPA’s Obama-era opposition to the state’s proposed standards. It is likely that Missouri’s framework will be used as guidance by other states in developing their approaches to lake and reservoir nutrient pollution, and it may be that US EPA’s approval will embolden states to deviate from the federally-recommended numeric nutrient criteria and develop customized plans.

Federal Approach to Nutrient Criteria

Nutrient pollution specifically refers to nitrogen and phosphorous pollution. Under the Clean Water Act, states must adopt water quality standards for their navigable waters, including nutrient criteria to control levels of nitrogen and phosphorous. These criteria must protect the waterbody’s designated use, and for waters with multiple designated uses, they must protect the most sensitive use. In 2001, US EPA issued numeric nutrient criteria recommendations that included suggested numeric limits for total nitrogen and total phosphorous amounts in lakes and reservoirs. If nutrient levels exceeded these numeric limits, the waterbody would be deemed impaired. The numeric criteria approach has long been US EPA’s favored approach for states to adopt in their water quality standards. The Agency also issued a 2013 guidance memorandum approving a “combined criterion approach,” in which a state may consider physical, chemical, and biological parameters in assessing water quality, in addition to the numeric nitrogen and phosphorous limits. This combined approach represents US EPA’s only guidance for states that wish to deviate from the strict numeric approach to develop standards better suited to their unique waterbodies.

Missouri’s Approach to Nutrient Criteria

Missouri’s nutrient criteria differs from US EPA’s 2001 numeric criteria recommendations and its 2013 guidance on the combined criterion approach. Rather than setting numeric limits for nitrogen and phosphorus as the guideposts for water quality, Missouri’s plan calls for assessing the pollutants’ effect on waters through response parameters such as morbidity events for fish and other aquatic organisms and observed shifts in aquatic diversity attributed to eutrophication (excessive nutrients). The rule establishes three regions of lakes and reservoirs, and sets forth for each region a combination of nitrogen, phosphorous, and chlorophyll a “screening values” and listed response parameters. If at least one nutrient screening value and at least one response parameter are exceeded in the same year, the waterbody would be deemed impaired. Through the combination of screening values and response parameters, Missouri’s plan focuses on the biological response to nutrients in waterbodies in order to make an impairment determination.

US EPA Approval and Effect on Other States

Before US EPA’s approval, Missouri had been entangled in debate with US EPA over its nutrient criteria dating back to 2009. In November 2009, Missouri submitted its proposed water quality standards, including nutrient criteria. In August 2011, US EPA disapproved of the majority of Missouri’s nutrient criteria because the criteria were not based on sound scientific rationale and did not demonstrate that they would protect the designated uses of the state’s waters. In February 2016, a non-profit environmental group sued US EPA for its failure to perform its duty under the Clean Water Act to propose nutrient criteria to address its 2011 disapproval. US EPA then entered into a consent decree with the environmental group setting a deadline for US EPA to take rulemaking action, unless Missouri submitted new or revised standards which were approved prior to the deadline. Missouri received US EPA’s approval for its revised standards prior to the December 2018 deadline.

In approving the plan, US EPA acknowledged that Missouri’s approach differs from its 2013 guidance, but noted that the Agency cannot mandate any specific requirements through guidance. Because US EPA determined that Missouri’s criteria are based on sound scientific principles and are intended to protect the designated uses of the state’s waters, the Agency gave a green light to the state’s deviation from established criteria.  This decision represents a reversal from EPA’s previous opposition, under the Obama administration, to the state’s response-based assessment framework as failing to establish a strong enough relationship between nutrient concentrations and biological effects.

Missouri’s response-based plan for limiting nutrient criteria could provide a template for states to follow to create plans that focus on the effects of nutrient levels on the aquatic life in their waters, rather than the amount of nutrients alone. US EPA’s approval of the plan may be another indication that the Trump Administration favors allowing states to take the lead in designing their environmental rules, and will take a flexible approach to approving state rules – even if they differ from federal guidance.