What you need to know about the Cedar River TMDL

CEDAR RAPIDS — The Iowa Department of Natural Resources has released a public notice of intent to withdraw the water quality improvement plan, or total maximum daily load (TMDL), created for the Cedar River watershed in 2006.

But what is a TMDL, how is it created and how is it implemented?

What is a TMDL?

Each state is required under the Clean Water Act to create TMDLs for impaired waterways. In Iowa, the DNR is in charge of crafting these plans.

The documents calculate the maximum amount of pollution that can safely enter a water body on a daily basis. These “pollution diets” help impaired waterways reach water quality standards, said Allen Bonini, the DNR’s watershed improvement section supervisor from 2005 until his retirement in 2021. He oversaw the creation of the Cedar River watershed nitrate TMDL.

⧉ Related article: Iowa DNR says Cedar River water quality plan isn't necessary, experts disagree

TMDLs first identify the sources of pollution in a water body and estimate their contributions. Then, the plan outlines the reductions needed to accommodate the pollution threshold and reach target water quality standards.

“It's a bridge between what we know about the water and what the water needs in order to be in compliance with the Clean Water Act,” Bonini said.

What does the Cedar River TMDL say?

The 2006 TMDL focuses on a segment of the Cedar River that extends from Bear Creek in Palo to McLoud Run in Cedar Rapids. This stretch of the river is where the City of Cedar Rapids pulls its drinking water from.

The document’s goal was to calculate the maximum amount of nitrate the river can handle on a daily basis while maintaining safe drinking water standards.

Nitrate is a form of nitrogen found in fertilizer and animal and human waste. Nitrate levels in drinking water are regulated at 10 milligrams per liter under the Safe Drinking Water Act to protect infants from blue baby syndrome. There’s also emerging evidence that elevated nitrate levels could present risks to adults, like cancer, although there’s no scientific consensus yet.

Using data collected from 2001 to 2004, the TMDL calculated that the amount of nitrate moving through the Cedar River at the time was 28,561 tons per year. The impaired segment’s highest recorded nitrate concentration was 14.66 milligrams per liter.

To meet safe drinking water standards — plus a 5-percent margin of safety — nitrate concentrations in the segment needed to reach 9.5 milligrams per liter. This required a 35-percent reduction in nitrate contributions by sources like agriculture and wildlife.

How does the TMDL regulate nitrogen pollution?

The majority of nitrogen pollution in the watershed was attributed to runoff from nonpoint sources like fertilizer, crops and manure. But those sources aren’t regulated under the Clean Water Act. TMDLs can only set limits on discharges from sources like water treatment facilities.

The TMDL took the Cedar River’s desired nitrate capacity and divvied it between the 95 Iowa facilities in the watershed at the time.

It allocated specific nitrate discharge limits — called waste load allocations — to each facility, which were supposed to be based on facilities’ existing discharges at the time. But many facilities didn’t have adequate monitoring data, so their discharge limits had to be estimated using equations and calculations.

The DNR is supposed to implement and enforce these waste load allocations through special discharge permits for each facility.

Although the TMDL couldn’t regulate nitrate contributions from agricultural and livestock sources, it emphasized the importance of pollution reductions in those sectors.

The document suggested best practices for improving the timing of nitrogen application, the incorporation of nitrogen in the soil and the application of the appropriate amounts of nitrogen. It also encouraged more land conservation practices and wetlands in the watershed.

Who approved the TMDL?

The drafted TMDL was released for public comment and then submitted to the Environmental Protection Agency for approval. It was approved in 2007.

Upon the document’s approval, the DNR was responsible for implementing it. The EPA was responsible for providing oversight over the process.

“It becomes a regulatory mechanism to ensure that — in the future, as permits are issued and as (agricultural) sources reduce their contributions — you will get to a point where the system meets the water quality standards set by the state,” Bonini said.

Brittney J. Miller is an environmental reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Comments: (319) 398-8370; brittney.miller@thegazette.com