Can Infrastructure Spending Help Iowa’s Polluted Rivers?

Can Infrastructure Spending Help Iowa’s Polluted Rivers?

The display department for the plans.  If you've read Douglas Adams, you'll appreciate the joke.

“But look, you found the notice didn’t you?”
“Yes,” said Arthur, “yes I did. It was on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying Beware of the Leopard.”


– Douglas Adams, The Hitchhiker’s Guide to the Galaxy 

I was reminded of this scene after spending a long day cross-referencing the Raccoon River TMDL (a pollution budget for nitrate and E. coli) with permits and monitoring data for wastewater treatment plants.  In this case, I suspected that polluters were getting away with something, but I’ve had just as much trouble finding information when I wanted to document a success story.

Effluent limits for nitrogen are not strict.  Wastewater treatment plants and meatpacking plants in the Raccoon River watershed routinely discharge treated wastewater with nitrate 4-6x the drinking water standard.  Why is this allowed?  The 2008 Raccoon River TMDL capped pollution from point sources at the existing level, rather than calling for reductions.  Due to limited data, the wasteload allocations were an over-estimate, assuming maximum flow and no removal during treatment. 

Water Treatment

That’s all above board, but someone else at the DNR went a step further.  Wasteload allocations in the TMDL were further inflated by a factor of two or three to arrive at effluent limits in the permits, using a procedure justified in an obscure interdepartmental memo.  The limits are expressed as total Kjeldahl nitrogen, even though the authors of the TMDL made it clear that other forms of nitrogen are readily converted to nitrate during treatment and in the river.   In short, the limits in the permit allow more nitrogen to be discharged than normally comes in with the raw sewage!

For example:

  • The Storm Lake sewage treatment plant has an effluent limit of 2,052 lbs/day total Kjeldahl nitrogen (30-day avg).  Total Kjeldahl nitrogen in the raw sewage is around 1000 lbs/day.
  • The Tyson meatpacking plant in Storm Lake has an effluent limit of 6,194 lbs/day total Kjeldahl nitrogen (30-day avg).  Total Kjeldahl nitrogen in the raw influent is around 4,000 lbs/day.
  • I also checked a permit affected by the (now withdrawn) Cedar River TMDL.  Same story.  The Cedar Falls sewage treatment plant has an effluent limit of 1,303 lbs/day total nitrogen (30-day avg).  Average total nitrogen in the raw sewage is between 1000-1500 lbs/day.
  • Confused about the units?  That may be deliberate.  Total Kjeldahl nitrogen includes ammonia and nitrogen in organic matter.  Nitrogen in raw sewage is mostly in these forms, which need to converted to nitrate or removed with the sludge in order to meet other limits and avoid killing fish.  Nitrogen in treated effluent is mostly in the form of nitrate.  At the Tyson plant, the effluent leaving the plant has around 78 mg/L nitrate, versus 4 mg/L TKN, but figuring that out required several calculations.  At smaller plants, the data to calculate nitrate pollution isn’t even collected.

As part of the Iowa Nutrient Reduction Strategy, large point source polluters are supposed to evaluate the feasibility of reducing nitrate to 10 mg/L, and phosphorus to 1 mg/L.  Tyson did a feasibility study for phosphorus removal, and is now adding new treatment to its Storm Lake plant.  However, it is not required to evaluate or implement further nitrogen reduction, “because it is already subject to a technology-based limit from the ELG.”  This federal Effluent Limitation Guideline was challenged in court by environmental groups this year, and is now being revised by the EPA.  It allows meatpacking plants to discharge a daily maximum of 194 mg/L total nitrogen!

Fortunately, all this creative permitting has little impact on the cost and safety of drinking water in the Des Moines metro.  According to research in the TMDL, point sources only account for about 10% of the nitrogen load, on days when nitrate in the Raccoon River exceeds the drinking water standard.  However, the figure is much higher (30%) for the North Raccoon River.  I started looking at permits and effluent monitoring because I was trying to explain some unusual data from nitrate sensors, brought to my attention by friends with the Raccoon River Watershed Association.  During a fall with very little rain (less than 0.04 inches in November at Storm Lake), nitrate in the North Raccoon River near Sac City remained very high (8 to 11 mg/L).  The two largest point sources upstream of that site can easily account for half the nitrogen load during that period.

Figure from Raccoon River TMDL

I was glad to be able to solve a mystery, and hope that this investigation can lead to some tools and teaching materials to help others identify when and where point sources could be influencing rivers.   The load-duration curves in the 200-page Raccoon River TMDL are very good, but some people might benefit from something simpler, like this table.  In general, the bigger the facility, the smaller the river, and the drier the weather, the more point sources of pollution can influence water quality, and the more wastewater treatment projects can make a difference. 

Spreadsheet for estimating impact of wastewater.

I made this table to estimate how biological nutrient removal in Nevada and Oskaloosa (about 1 MGD each) could improve water quality in the South Skunk River (about 1000 cfs on average near Oskaloosa, but there could be greater benefit in tributaries, or when rivers are lower).

Dan Haug standing by Raccoon River

In this work, I’m supported by partners around the state and a grant from the Water Foundation.  The project (Movement Infrastructure for Clean Water in Iowa) focuses on building connections and shared tools around water monitoring, and will continue through this spring and summer.  The funders’ interest is in helping the environmental movement make the most of the “once-in-generation opportunity” presented by the Inflation Reduction Act and the Bipartisan Infrastructure Law.  This fiscal year, the Bipartisan Infrastructure Law is adding $28 million to Iowa’s Clean Water State Revolving Fund, which provides low-interest loans to communities to replace aging sewer systems and treatment plants.  Can that infrastructure spending help Iowa’s polluted rivers?  We won’t know for sure without better use of water quality data, and greater transparency in state government.

Appreciating Water and Wastewater Workers

Appreciating Water and Wastewater Workers

Water and Wastewater Workers of Iowa Week!

In August the governor issued a proclamation recognizing these essential workers.  I’ve had the privilege to get to know some of the folks who make sure the water in the tap is clean enough to drink, that the wastewater we flush doesn’t contaminate rivers, and that the storm sewers drain the streets without causing downstream flooding or pollution.



governor proclamation
Ames WPCF Superintendent Tyler Ver Meer at an open house.  Note the watershed map!

Sure, these kinds of jobs can involve reading meters, reviewing construction documents, doing inspections, and testing water quality.  But it can also involve live-trapping turtles to stop them from damaging an expensive baffle curtain in a wastewater treatment lagoon by sitting on it (Tim Mattingly, City of Gilbert).  It can involve handing out rubber duckies and demonstrating a flood model for kids at a school science night (Liz Calhoun and Jake Moore, Ames Public Works).  It can involve taking time out of a busy schedule to attend meetings about watersheds and water monitoring (thanks to staff from Ames, Gilbert, Nevada, Roland, and Huxley who have come to mine).  And it can involve canceling that meeting and rushing to the sewage treatment plant to help contain a spill when a valve breaks (this happened once to Ashley Geesman and Neil Weiss, Ames Water & Pollution Control).

I’ve been getting even more appreciation for wastewater treatment plants and the people who run them as I’ve researched and filmed Facts 31-35 of our weekly video series, “The Clean Water Act: 50 Years, 50 Facts.”

At a basic level, sewage treatment involves harnessing microbes to break down organic matter that would otherwise consume the oxygen in the water as it decomposes, and improving water clarity by allowing the solid material to settle out.  Widespread secondary treatment of wastewater has taken care of some of the worst pollution that was affecting America’s rivers when the Clean Water Act was passed in 1972. But processes aimed at TSS (a metric of water clarity)and CBOD5 (a metric of oxygen consumption) doesn’t always get various forms of nitrogen (nitrate and ammonia), phosphorus, E. coli bacteria, or chloride down to an acceptable level.  We’ve seen that in some our water monitoring results.

However, communities in Iowa continue to invest in improvements to their sewage treatment systems.  NPDES permits have to be renewed every five years, and additional requirements come into play when a facility is renovated to increase capacity or replace deteriorating infrastructure.  Some examples from the South Skunk River watershed include:


  • The City of Nevada is building a new plant (to be completed in 2024) that will include systems to remove additional nitrogen and phosphorus. Ames, Oskaloosa, and Newton also are planning nutrient removal systems.
  • The City of Ames spends over $3 million each year to repair or replace aging sanitary sewers.
  • The City of Gilbert installed an extra stage to better treat ammonia during the winter months.
  • A homeowner’s association near Gilbert is switching its water source to reduce the need for water softeners and the chloride (salt) pollution that comes with it.
  • Over the last decade, UV disinfection systems to address fecal bacteria have been installed in sewage treatment plants in Ames, Newton, Story City, Huxley, Roland, Gilbert, Cambridge, and a neighborhood association. Colfax uses chlorine disinfection.  Oskaloosa, Maxwell and Nevada have upgrades in the works.
Squaw Valley Wastewater Treatment Plant

However, if non-point sources of pollution like agricultural runoff and stormwater aren’t addressed, cities and towns reach a point of diminishing returns where sewer rates are going up but water quality in the river isn’t getting noticeably better.  That’s why it’s exciting to see more water utilities breaking out of traditional silos and partnering with farmers on conservation projects in their watersheds

(Edit 2023-12-29: The numbers I was using are potentially confusing and not relevant to the point I was making, so I have deleted them.  According to models used for the Iowa Nutrient Reduction Strategy, point sources of pollution like wastewater account for 5% of the nitrogen load and 12% of the phosphorus load during the 2006-2010 benchmark period.  The South Skunk River as a whole has a similar breakdown, but the stretch between Ames and Colfax has a higher percentage of pollution from point sources.)