As a precursor to issuing new permits for the land-application of sludge, the Missouri Department of Natural Resources (DNR) will hold a public informational meeting in Jefferson City at 1 p.m., May 9, regarding the proposed issuance of four new Master General Permits, including the use of one-year and five-year P-indexes for land-application.

If, like me, you don’t have an agricultural background, the phrase “P-index” (which stands for Phosphorus Index) reads a lot like Greek. Research brought a little clarity to a complex subject.

A P-index, states the University of Missouri (MU) Extension, is a management tool that integrates various factors to identify agricultural fields with a high potential for phosphorus losses in runoff (https://extension.missouri.edu/publications/g9184).

Each state is responsible for the development of its own P-index, suitable to specific conditions in that state.

The control of phosphorus and nitrogen (essential plant nutrients) in soil is critical to water resources, both for drinking and for recreation.

However, according to an AI overview, a phosphorus (P) index is often an inaccurate management tool, because “it attempts to simplify complex, site-specific environmental interactions into a single risk score, leading to inconsistent assessments across different regions and soil types.”

Inconsistent standards for phosphorus application abound because 48 states have their own P-indices. Critics of the tool say they frequently fail to account for subsurface leaching, specialized soil chemistry (e.g., high organic matter or iron), and unique landscape features like karst terrain.

Barry County is sitting on a karst wonderland, 47 square miles of which comprise the recharge basin of Roaring River Spring, the source of the water for Roaring River Hatchery, the magnet that draws over one million visitors annually to Roaring River State Park.

In karst areas, dissolved phosphorus can leach into groundwater through fissures, cracks and sinkholes, but the P-index, say critics, focuses on surface runoff without taking into consideration the possibility of dissolved phosphorus entering groundwater via cracks and holes in the bedrock below the soil.

While nitrogen and phosphorus are key plant nutrients, according to the EPA, “Too much nitrogen and phosphorus in the water can cause algae-like bacteria to grow faster than ecosystems can handle. Significant increases in algae harm water quality, food resources and habitats and decrease the oxygen that fish and other aquatic life need to survive…leading to fish illnesses or death, often in large numbers.

“Nutrient contamination in groundwater – which millions of people in the United States use as their drinking water source – can be harmful, even at low levels. Infants and young animals, in particular, are vulnerable to a nitrogen-based compound called nitrates in drinking water.”

Phosphorus is of particular concern because, according to Alabama A&M and Auburn Universities’ Extension, “Dissolved phosphorus loss in runoff water from agricultural landscapes is one of the most difficult forms of pollution to control.”

Only .08 to .1 parts per million of phosphorus can negatively affect water quality, the Alabama Extension states. Not only can relatively small amounts of phosphorus be detrimental if they access water sources, phosphorus can build up in soil over time with repeat applications and be subject to erosion and dissolution (https://www.aces.edu/blog/topics/crop-production/phosphorus-management-indices-to-measure-environmental-phosphorus-loss-risk-from-soils/).

The over-application of phosphorus can occur in areas where meat and poultry processing (MPP) wastewater residuals are land-applied, in part because of the sheer quantity of sludge represented.

According to EPA data, a poultry-processing slaughter facility that kills a live weight of 100-500 million pounds of birds a year generates an average of almost one million gallons of wastewater per day.

The wastewater residuals — the globby, solid Dissolved Air Flotation (DAF) skimmings of meat, blood, bones and other raw delicacies that form on the surface of wastewater — are loaded into tankers for land application on farms where property-owners are willing to accept them.

A contract driver for Denali Water Solutions, who spoke with The Cassville Democrat in early 2023, stated that about 10-15 loads of sludge were delivered by waste-hauling tankers during his typical workday (and through the night by other operators) until a farm reached its capacity. A tanker, he said, carried about 6,000 gallons of sludge.

Nitrogen, phosphorus and a variety of minerals and metals (including copper), bacteria and viruses are components of those wastewater residuals (https://www.epa.gov/system/files/documents/2025-09/mpp-development-document_final-action.pdf).

We’re looking at a mess waiting to happen in Barry County: an ecological disaster for our karst terrain, which hydrologist and Cave Research Foundation volunteer, Ben Miller, calls a “vast, underground plumbing system.”

The interconnected web of karst features below the Ozarks allows virtually unfiltered groundwater to move freely and rapidly.

Hydrologist Tom Aley, author of an article in “Missouri’s Caves and Karst,” an MDC publication, says groundwater travel-rates in karst areas of Missouri can average about one mile per day. Groundwater travel-rates within non-karst areas are commonly only a few feet per year, Aley says.

In Missouri, with its farmland to the north and karst-y Ozarks to the south — where dissolved phosphorus can readily leach into groundwater — a one-size-fits-all P-index may not fit the entire state.

The MU Extension does state that the P-index calculation for the Ozarks is more restrictive, but no mention is made of the reason. They’re not telling the whole story.

Read up on karst, with its proclivity for ushering contaminants into and through groundwater, and you’ll get a clearer picture.

Learn more about P-indexes and other pertinent topics by attending the DNR’s May 19 meeting. A virtual attendance option is available.

More information about proposed permits and meeting access may be found at https://dnr.mo.gov/calendar/event/303061.

Sheila Harris is a long-time Barry County resident and a sales executive and investigative reporter for the Cassville Democrat with a particular interest in environmental topics. She may be reached at [email protected].