On a date in late August 2026, a failed bypass pipe at the City of Pueblo's wastewater treatment facility released about 4.25 million gallons of raw sewage into the Arkansas River, an event that spilled into a public roundtable in the Lower Arkansas River Basin a week later. In a report published 11 September 2026, Colorado Public Radio detailed how long it took to detect the release, how downstream users were warned, and where the regulatory framework for agricultural contamination came up short. The Colorado Sun, in coverage published 2 September 2026, documented the plume's downstream path and the public-health response. A 10 September 2026 piece by 9News is indexed against the same public meeting.
Key takeaways
- City of Pueblo's utility estimates 4 million gallons of raw sewage reached the Arkansas River after a patch on a 40-year-old concrete bypass pipe failed; The Colorado Sun gives the release volume as 4.25 million gallons from the plant.
- It took about 24 hours for the City of Pueblo wastewater department to notice the leak, according to a presentation by utility director Andra Ahrens at a public roundtable reported by Colorado Public Radio.
- Once detected, the utility stopped the leak in roughly two hours, but farmer Kent Ricken told the roundtable that the alert to downstream irrigators was still too slow, per Colorado Public Radio.
- Samples on the river at Swink, about 50 miles southeast of the spill site, were measured at over 1,400 colony-forming units of E. coli per 100 mL against a state swim-beach standard of 235, per The Colorado Sun.
- CDPHE told the roundtable there is no Colorado E. coli standard for agricultural use and no numeric definition of "adulterated" for crops in a raw-sewage event, according to Colorado Public Radio.
What happened at the plant
The City of Pueblo was working on repairs to the main sanitary pipe that feeds its treatment plant and was running flow through a bypass on a 40-year-old concrete pipe, Colorado Public Radio reported, citing Ahrens. Pressure inside that bypass caused a patch to break. Because the utility was not running its normal SCADA-style monitoring on the bypass line, the flow readings that would have flagged the failure took longer than usual to arrive, and the leak ran for about 24 hours before staff noticed it. The utility stopped the release in about two hours once identified, and flow was returned to the regular sanitary system, according to Colorado Public Radio.
Once the leak was confirmed, Ahrens said, she and other staff spent the afternoon calling ditch companies to ask them to stop pulling water from the river. "We tried to call the ditch companies that afternoon, let everybody know, shut this down. We got four million gallons in the river, let you know, please cut it off," Ahrens told the roundtable, per Colorado Public Radio. The utility said it met the state's current notification guidelines; farmer Kent Ricken, who pulls irrigation water from the river, told the same meeting that "not only was it not caught in time," and "when you tried to notify, there was a big delay in that as well," according to Colorado Public Radio. Ricken said contaminated irrigation water was diverted for use before downstream users knew about the spill.
What happened on the river
The plume moved downriver past Pueblo and reached John Martin Reservoir east of Las Animas, The Colorado Sun reported. Samples collected through Monday in the week of the spill continued to show unsafe E. coli levels from the spill site to the reservoir, and Colorado Parks and Wildlife issued no-contact advisories for 10 state wildlife areas along the river and the Las Animas State Fish Hatchery. The state swim-beach standard is 235 CFU per 100 mL; a sample taken on Monday at Swink, about 50 miles downstream, came back over 1,400 CFU per 100 mL, The Colorado Sun reported. Early samples were testing "off the charts," per the same report.
CDPHE deputy chief medical officer Dr. Rachel Herlihy told The Colorado Sun that E. coli is being used as an indicator organism, with the assumption that high E. coli also means elevated levels of other pathogens such as Shigella, Campylobacter, norovirus, hepatitis A, giardia and cryptosporidium. The Colorado Sun also reported that public drinking-water systems downstream were notified in time to close their river intakes before the plume arrived, and that such systems have backup testing. Surface-water contamination is not expected to reach private groundwater wells, though well owners near the river can contact the Water Quality Control Division for guidance. The 9News piece indexed at 9News covers the same public-health meeting.
What the regulators and farmers said
At the roundtable, Heather Young of the Colorado Department of Health and Environment said water-quality rules cover swim beaches and treated wastewater, but "for water quality, there is no river or lake E. Coli standard to protect agricultural use," and there are no standards covering animal-feed crops or a numeric definition of "adulterated" for crops in this kind of event, Colorado Public Radio reported. She added that E. coli is being used as the primary indicator because lab turnaround is fast, even though raw sewage likely carries parasites and viruses. The department is also weighing other inputs, including potential contributions from Fountain Creek and runoff from the Aspen Acres Fire burn scar, where samplers noted black water with fine suspended particles, per Colorado Public Radio. Robert Sakata with the Colorado Department of Agriculture told the meeting that drought conditions meant farms were already relying on groundwater or unaffected ditches, and that "the risk to our food supply was really, really, really minimal," according to Colorado Public Radio. The CDPHE investigation into the cause and prevention of the event is ongoing, the department told the roundtable.
Specification read
The reported release of 4.25 million US gallons from the City of Pueblo plant converts to about 16,100 m³ on a single event, or roughly 1,160 m³/day if averaged over a 14-day impact window on the river, while the 4-million-gallon figure cited to ditch companies converts to about 15,140 m³. A release of this size is roughly equivalent to the dry-weather flow of a 15,000–20,000-population-equivalent municipal works (general industry range, not from the sources). For a plant of this class the typical treatment train is screening → grit removal → primary clarification → biological treatment (A2O, MBR, MBBR, SBR or, in older configurations, conventional activated sludge) → tertiary filtration and disinfection (chlorination or UV), and this event bears most directly on the asset-integrity layer upstream of biological treatment: the bypass piping, the structural patches on it, and the instrumentation that should have flagged the pressure failure in real time. For a buyer or operator, the engineering takeaway is that a bypass line in active service needs the same live flow, level and pressure monitoring as the main train, with alarm setpoints tied to a documented notification tree for downstream water users.
Buyers scoping a municipal Municipal works of this scale, or evaluating an Integrated Sewage Treatment package with biological and tertiary stages, should treat the Pueblo event as a reminder that bypass and repair-mode operation is part of the design basis, not an exception. Readers weighing biological-train options against this kind of emergency-loading scenario can compare side-by-side configurations in our MBR vs Conventional Activated Sludge for Food & Bev Wastewater in City Of Industry, CA: 2026 Engineering Guide. For plants in the Industries We Serve portfolio that draw process or make-up water from surface sources, the Pueblo timeline also illustrates why raw-water intake isolation and finished-water confirmatory testing are scoped as separate work packages rather than assumed as part of treatment.
FAQ
How much sewage entered the Arkansas River at Pueblo?
The City of Pueblo utility told downstream ditch companies "four million gallons" had reached the river, while The Colorado Sun reported the total release from the plant as 4.25 million gallons after a patch on a 40-year-old bypass pipe failed.
How long did the leak run before it was stopped?
About 24 hours passed before the utility noticed the leak, and roughly two hours to stop it once identified, according to Colorado Public Radio, citing utility director Andra Ahrens.
What was the E. coli level downstream, and what is the standard?
Colorado's swim-beach standard is 235 colony-forming units per 100 mL; a Monday sample at Swink, about 50 miles downstream of Pueblo, came back over 1,400 CFU per 100 mL, per The Colorado Sun. Early samples were described as testing "off the charts."
What should a buyer or operator take away for plant design and procurement?
Treat any active bypass line as in-scope for live flow, pressure and level monitoring with alarm setpoints, and document a downstream-notification tree with named contacts and call timing; these are general industry practices, not figures from the sources.
