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Friday, April 19, 2024

CU Boulder identifies possible sources of E. coli contamination in Boulder Creek

The University of Colorado Boulder has identified raccoon feces and a stormcepter as two possible reasons for elevated E. coli levels in water runoff that’s discharging into Boulder Creek.

CU Boulder was required through a permit issued by the Colorado Department of Public Health and Environment to test two outfalls over the summer where stormwater is released into Boulder Creek on campus. The testing confirmed that one of the outfalls met Environmental Protection Agency standards for E. coli levels while the other outfall, called outfall C, tested for elevated levels of E. coli.

“We believe we have an ethical responsibility to be good stewards of resources where we live and operate,” CU Boulder spokesperson Nicole Mueksch said in an email. “We will continue to collaborate with our partners at the city of Boulder and Boulder Valley School District to develop proactive solutions to water contamination, in addition to immediately addressing issues within our waterways when they arise.”

Boulder and Boulder Valley School District have their own permit coverage that requires them to monitor, or participate with another entity to monitor, E. coli discharges from their stormwater systems to Boulder Creek.

A storm sewer is a system designed to carry rainfall runoff and other drainage into a body of water, and an outfall is a point where the runoff empties into the water. Outfall C, which empties runoff into Boulder Creek on the CU Boulder campus, also has a stormcepter. A stormcepter is a separator that catches trash and other materials in the stormwater runoff before it enters the creek. Outfall C is located near Boulder Creek and Folsom Street on the CU Boulder campus.

Upon further investigation, Mueksch said, it was discovered that the stormcepter at outfall C, which collects oils, trash and sediment that E. coli bacteria feed on, contributed to elevated E. coli levels in the stormwater before the water entered Boulder Creek. CU Boulder also believes raccoon feces, which is regularly observed in the storm sewer system, is contributing to elevated levels at the outfall because raccoons excrete E. coli in their feces.

CU Boulder is engaged in several mitigation efforts for reducing E. coli, including hiring an engineering consultant to design and implement an in-depth study to better determine the source or sources of E. coli contamination, and the university aims to begin the study this summer.

“Our hope is that the engineering consultant we are in the process of hiring will help us better address the challenges at outfall C,” Mueksch said. “There are no easy solutions to the stormceptor. Bypassing the stormceptor would lead to oils, trash, sediment and other pollutants discharging into Boulder Creek. Disinfecting the stormceptor is also not an option, as those chemicals would also pollute the creek.”

The University of Colorado Boulder monitors data at an outfall on campus, called outfall C, that's tested for elevated levels of E. coli (Matthew Jonas/Staff Photographer)
The University of Colorado Boulder monitors data at an outfall on campus, called outfall C, that’s tested for elevated levels of E. coli (Matthew Jonas/Staff Photographer)

Meghan Wilson Outcalt, Boulder’s water quality senior manager, said E. coli is “complicated.” Many water bodies are impaired for E. coli, she said, and it’s hard to make improvements if there is no single source.

“In an urban area in particular, what we’re looking at is many different sources,” she said. “It can come from wildlife feces, dog feces, cross connections in the sanitary system, over-irrigation flows, grease containers that are not properly maintained.”

CU Boulder has a robust inspection and maintenance program for storm and sanitary sewers, Mueksch said, and there are no known contributions of E. coli from the sanitary sewer.

Art Hirsch, a retired environmental engineer and water quality advocate, flagged concerns in 2019 about CU Boulder’s role in E. coli impairment in Boulder Creek.

“I am encouraged that the University of Colorado and the city of Boulder are actively investigating in mitigating the E. coli sources affecting Boulder Creek,” Hirsch said. “However, Boulder Creek is still an impaired stream and much work needs to be done to repair the water quality damage.”

Monitoring data

The permit requires CU Boulder to collect and analyze 10 samples each year between May 1 and Oct. 31 to provide data on the discharges from the university’s stormwater system to Boulder Creek. It will expire on Oct. 31, 2026.

The E. coli data for outfall C collected from May to August of 2023 ranged from 152 mpn/100ml to 2,420 mpn/100ml, according to information acquired in a public records request. The EPA threshold for E. coli impairment in water is 126 mpn/100ml.

“The goal of the permit requirements is to reduce the discharges of E. coli to below 126 cfu/100 ml to help prevent contributions that could result in exceeding that level in the creek,” said John Michael, marketing and communications specialist at the Water Quality Control Division of CDPHE. “When a water body has concentrations above 126 cfu/100 ml, the creek is considered impaired.”

E. coli measurements in cfu/ml and mpn/ml are interchangeable without conversion, and both measure the number of bacteria in a water sample. MPN stands for most probable number, while CFU stands for colony forming unit.

A water body with E. coli results above the EPA standard means there’s a higher risk of potentially getting sick, Wilson Outcalt said.

“We measure E. coli as an indicator of contamination that could, but doesn’t necessarily, make people sick,” she said.

CU Boulder concluded that the stormcepter could be an issue because testing data shows that the water entering the stomceptor has significantly lower E. coli levels than the water exiting the outfall.

“The most difficult aspect of determining a source is the high variability of results we’ve seen while monitoring for E. coli,” Mueksch said. “Samples have been collected from the same sites on different days and provide entirely different results on a regular basis.”

CU Boulder submitted additional E. coli monitoring data to CDPHE from 2020 to 2022. According to those reports, E. coli levels were lower during those years on average compared to the data from 2023. Mueksch said it’s difficult to pinpoint why the numbers from 2023 are higher than what was observed in recent years.

“We do know the Boulder area received record amounts of rainfall in 2023 during the sampling period and this may have mobilized additional sources of E. coli into stormwater,” she said. “We are hopeful the study led by an engineering consultant can help to clarify the results we’ve observed.”

In addition to monitoring the data, the permit requires CU Boulder to conduct education and outreach about E. coli, clean the storm sewer, identify potential sources of E. coli and implement control measures targeting these specific sources.

“We are actively working on a remedy for this outfall through continued study and sampling,” Mueksch said in her email. “Our campus is also proactively working with the city and Boulder Valley School District to reduce potential elevated E. coli levels at another outfall with the installation of an automated head gate on the Anderson Ditch, which has been shown through studies to carry water with elevated levels of E. coli onto campus.”

An automated head gate is a smart gate that is opened and closed via remote sensors that reduce excess flows of ditch water from Anderson Ditch through the campus to an irrigation storage pond. Ditch water contains pollutants and has been found to contain E. coli when it arrives on campus.

“CU Boulder continues to be proactive and take the matter of stormwater quality and E. coli mitigation seriously to help ensure a healthy, safe environment by installing an automated head gate on the Anderson Ditch and expanding animal access projects to improve our engineered solutions for limiting wildlife impacts to storm lines,” Mueksch said. “This is a pervasive issue in public waterways that many municipalities struggle with due to multiple potential sources and the complex nature of mitigation.”

CU Boulder began installing critter guards in 2011 and updated those critter guards in 2020 with repairs and by minimizing the size of openings large enough for raccoons to enter. The university has partnered with the United States Department of Agriculture to study the effectiveness of the critter guards on keeping wildlife — specifically raccoons — out of the campus storm sewer system. Because the study is led by the USDA, Mueksch said CU Boulder does not have information on when the results will be available.

The University of Colorado Boulder is required to mitigate E. coli discharges into Boulder Creek through a permit issued by CDPHE (Matthew Jonas/Staff Photographer)
The University of Colorado Boulder is required to mitigate E. coli discharges into Boulder Creek through a permit issued by CDPHE (Matthew Jonas/Staff Photographer)


Wilson Outcalt said the city has been working on E. coli in Boulder Creek for more than two decades. The city monitors stream water quality as it relates to people recreating. Overall E. coli data trends in the creek have been relatively stable over the past five to 10 years.

“It’s not typical for a stream or a lake once it’s impaired to ever not be impaired,” she said. “But we continue to work on it and try to understand where it’s coming from and do what we can to clean it up.”

She said the cause of E. coli is likely a lot of wildlife and raccoon waste and runoff from various places. Mitigation for Boulder includes a restaurant outreach program, water quality sampling, cleaning of the storm sewer system, dog waste stations and outreach to homeowners on lawn maintenance.

People should take precautions when recreating in any water body, Wilson Outcalt said. For example, don’t swim in Boulder Creek within 48 hours of a rainstorm. Don’t go in with a baby and don’t go in if immunocompromised. After recreating in Boulder Creek, wash hands, shower and don’t swallow the water.

“We really want the public to know there is risk of going in the creek, and that’s true anywhere, and so taking those precautions is really important,” Wilson Outcalt said.

Michael said to stay out of the water with diarrhea or open wounds, shower before entering the water and take kids on bathroom breaks every hour. Change diapers away from the swimming area to keep germs out. People can help reduce the amount of E. coli in Colorado waterways by cleaning up after their pets and ensuring the waste is disposed of properly.

For more information on CU Boulder’s permit and E. coli monitoring, visit echo.epa.gov/detailed-facility-report?fid=110043760141. To view CU Boulder’s annual reports to CDPHE, visit oitco.hylandcloud.com/CDPHERMPublicAccess/index.html, do a clean water search and enter COR070028 as the permit number.

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