Letter to EPA on 2024 Impaired Waters List

Letter to EPA on 2024 Impaired Waters List

In November, the EPA partially approved Iowa’s 2024 Impaired Waters List, adding six additional river segments where drinking water use is impaired by high nitrate levels. I think EPA was right to do this, but I have some concerns. This is the letter I submitted during the public comment period.

Dear Water Division Staff,

I agree with the EPA’s decision to add seven river segments to Iowa’s impaired waters list.  I hope that this change will lead to greater transparency about how nitrate pollution of surface waters affects the cost and safety of drinking water, but am concerned there will be unintended consequences.

Iowa’s Credible Data Law has sometimes been a convenient excuse to assess fewer waters, and thereby discover fewer problems. However, that doesn’t seem to be the issue here. Each of the water bodies on this list had at least one “credible” nitrate sample exceeding the 10 mg/L drinking water standard during the three year assessment period. 

  • Raccoon River near Des Moines: 38 of 755 samples collected by Des Moines Water Works exceeded 10 mg/L
  • Cedar River near Cedar Rapids: 1 of 36 samples collected by the USGS, and 7 of 151 samples collected by Cedar Rapids Water Works
  • Lower Des Moines River near Ottumwa: 2 of 33 samples collected by IDNR
  • Upper Des Moines River near Des Moines: 11 of 758 samples collected by Des Moines Water Works
  • Iowa River near Iowa City: 5 of 146 samples and 18 of 2698 sensor readings collected by PWS (not sure what that refers to)
  • South Skunk River near Oskaloosa: 2 of 36 samples collected by IDNR

As I understand it, the issue is the threshold for impairment.  Since fewer than 10% of the samples (accounting for some statistical correction factor) exceeded 10 mg/L, IDNR says these sites meet the standard.  EPA says they do not. 

The Iowa DNR’s position is not defensible.  In the draft 2024 assessment, Raccoon River near Des Moines was shown as fully supporting its designated use for drinking water because

A) Nitrate in the Raccoon River exceeded 10 mg/L nitrate less than 10% of the time during the 2020-2022 assessment period

B) Nitrate in finished drinking water at the Des Moines Waterworks never exceeded 10 mg/L.

This makes no sense.  Even one sample exceeding the Maximum Contaminant Level for nitrate would constitute a violation of the Safe Drinking Water Act, requiring public notice.  To avoid this, the Des Moines Waterworks had to run its nitrate removal facility for weeks in 2022 at a cost of $10,000 a day, as well as blending water from other sources and asking residents to reduce water use.   Clearly, poor water quality is limiting that beneficial use of the river water!

However, the South Skunk River no longer supplies drinking water to the City of Oskaloosa.  The City now gets its water from an alluvial aquifer, and is able to achieve low levels of nitrate in finished water (1.17 mg/L, in the latest Consumer Confidence report) without expensive treatment.  I understand that the Clean Water Act does not allow designated uses to be removed if restoring them is still achievable.  However, I hope that in prioritizing and writing TMDLs we can be cognizant of facts on the ground.  In the unlikely event that a TMDL for the Skunk Skunk River is written and it leads to stricter effluent limits for upstream point sources, we might be imposing real costs on Ames, Story City, and Nevada without achieving real benefits for Oskaloosa.

I am also concerned that disallowing the 10% binomial rule might lead to further politicization of funding for water monitoring.  Water quality in rivers is highly variable, and daily or weekly monitoring might pick up on a short-term spike in nitrate that is missed by monthly monitoring.  If a single sample can trigger impairment but there are no rules on how often a site has to be monitored, cutting budgets for monitoring programs becomes a tempting way to evade regulation and controversy. 

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.