LITTLE ROCK — Arkansas and Oklahoma officials have agreed to conduct a comprehensive study of phosphorus concentrations in the Illinois River watershed.

Arkansas Attorney General Dustin McDaniel, his Oklahoma counterpart Scott Pruitt and agency directors in both states signed a "Second Statement of Joint Principles and Actions," which outlines how the study will proceed.

The agreement signed Wednesday averts the potential for costly litigation over Oklahoma’s regulatory standard for phosphorus concentrations within the watershed, McDaniel said. Arkansas has maintained that the standard is unattainable.

Both states agreed to be bound by the outcome of the study, which is expected to take three years to complete.

"Arkansas has worked diligently to reduce phosphorus concentrations in the Illinois River watershed over the last decade, and we will continue to do so," McDaniel said in a statement. "The results of this study will guide farmers, businesses and municipalities in Northwest Arkansas in their future planning, as both Arkansas and Oklahoma remain committed to improving water quality. I applaud Attorney General Pruitt and officials in Oklahoma for working together with us on this important issue."

The study, known as a stressor response study, will determine the amount of phosphorus that can be contained within the watershed without negatively affecting water quality. The study will be conducted using EPA-approved testing methods that ensure scientifically reliable data collection and analysis.

A six-member committee will oversee the study and select the vendor to conduct it. The panel will be composed of three members selected by Arkansas Gov. Mike Beebe and three members selected by Oklahoma Gov. Mary Fallin.

Arkansas will work to secure funding for the study, which is expected to cost about $600,000. The funds will be administered by the Arkansas-Oklahoma Arkansas River Compact Commission, which includes representatives from both states.

McDaniel, state Department of Environmental Quality Director Teresa Marks and state Natural Resources Commission Director Randy Young, along with their counterparts in Oklahoma, negotiated the agreement and are signatories to the document.

The agreement is a continuation of an initial pact both states signed in 2003, committing to improve water quality in the Illinois River and other scenic rivers in the watershed.