Denver’s 16th Street Improvement Project was designed to modernize one of the city’s most traveled downtown corridors—but an unexpected discovery beneath the street changed the timeline and the price tag. An “undocumented” historic brick storm sewer forced work to pause, ultimately contributing to a 301-day delay and an additional $18 million in costs that, according to a city audit, Denver City Council did not approve before the money was paid.
For property owners, retailers, and residents in Denver, Colorado, the story is more than a construction headline. It’s a reminder that hidden, aging underground infrastructure can quickly become an expensive emergency—especially when stormwater systems, drains, and sewer lines are involved.
What Denver’s 16th Street project revealed about what’s under our streets
Who was involved
The Denver Auditor’s Office released a review of the 16th Street Improvement Project and issued recommendations regarding oversight and contract controls. The City and County of Denver’s Department of Transportation and Infrastructure (DOTI) managed the project, and Denver City Council originally approved the $149 million construction contract with PCL Construction Services Inc. (PCL) in March 2021.
Other named parties in the audit reporting include the City Attorney’s Office (which provided guidance on change orders vs. contract amendments). Kiewit Corporation—identified as the largest contractor in Colorado—reportedly withdrew from bidding due in part to risks associated with the city’s brick sewer system. Business impacts were highlighted through comments from Marissa Williams, co-owner of Rocky Mountain Chocolate Factory, who said the project severely reduced customer traffic and that foot traffic has not fully recovered.
What happened underground
In May 2022—about a year into construction—crews uncovered a centuries-old brick storm sewer that was not previously documented in city mapping records. Once discovered, work stopped while the city navigated required historic-preservation processes, including a 30-day review tied to preservation agreements.
According to the audit, the discovery triggered a contractor dispute and schedule impacts. The city ultimately agreed to compensate PCL for direct costs and delay impacts through an $18 million settlement processed as a change order, extending completion by 301 calendar days.
Where it happened
The discovery occurred in downtown Denver along 16th Street (historically known as the 16th Street Mall), a signature pedestrian and transit corridor that has long served as an economic artery for Denver, Colorado businesses.
When the delay and costs became clear
The storm sewer was uncovered in May 2022. The renovated corridor was ultimately completed in September 2025, with total project costs reported at approximately $175.6 million and 11 change orders totaling $27.2 million.
Why it matters: the documentation gap in historic infrastructure
The audit emphasized that incomplete records are a known issue with older underground infrastructure across Denver. The city reportedly still has more than 69 miles of brick storm sewers built between 1880 and 1937, and the broader brick system became eligible for listing in the National Register of Historic Places in February 2013. However, a comprehensive map of brick sewer locations does not exist, leaving exact locations unknown until projects physically uncover them.
DOTI noted that during the environmental assessment phase, consultation occurred with Colorado’s State Historic Preservation Office, but the brick storm sewer system was not flagged at that time as a “historic resource” requiring consultation and mitigation. Once uncovered, the rules changed in real time—something many Denver projects can encounter when older utilities are involved.
The plumber’s perspective: why “undocumented” storm drains create real-world risk for Denver properties
From a plumbing and drainage standpoint, the biggest takeaway is simple: stormwater infrastructure doesn’t have to be inside your building to affect your building. When an aging storm sewer or brick drain system is damaged, partially collapsed, or overwhelmed, it can redirect water in unpredictable ways—leading to street flooding, seepage into basements, backups in connected lines, and accelerated deterioration of nearby utility corridors.
In Denver, Colorado—where older downtown areas often sit above generations of infrastructure—unknown drain connections and legacy materials (like brick) can complicate everything from routine repairs to major renovations. Even if a pipe “has always worked,” changes in load, vibration from construction, re-routing, or heavy rain events can expose weak points fast.
That’s why proactive inspection and fast-response drainage service matters around active construction zones and older neighborhoods: identifying vulnerabilities early can be the difference between a manageable repair and an expensive, disruptive emergency.
How this connects to everyday plumbing needs in Denver, Colorado
While the 16th Street project was a city-scale rebuild, the underlying issue—hidden drainage assets and unknown tie-ins—shows up in residential and commercial plumbing all the time. Property owners near downtown Denver, Colorado, and in older corridors throughout the metro can encounter:
1) Storm drain tie-ins that aren’t where you think they are
2) Old materials that require specialized handling
3) Blockages caused by sediment, roots, or shifted lines
4) Surprise backups after street work changes flow patterns
When these problems appear, time matters. Proper diagnosis (often involving drain inspection), targeted clearing, and repairs that respect older infrastructure can reduce repeat clogs and prevent water damage.
Why this is especially relevant right now for Denver businesses and homeowners
The audit also underscored the ripple effects of prolonged construction on small businesses along 16th Street. Marissa Williams of Rocky Mountain Chocolate Factory described the impact as severe, with ongoing recovery challenges even after completion. For many Denver, Colorado storefronts and buildings, drainage disruptions, access limitations, and water-related incidents during construction are more than inconveniences—they directly affect revenue and operations.
Whether you’re operating a business near downtown Denver or living in an older part of Denver, Colorado, it’s smart to treat drainage performance as part of your risk planning—especially during nearby infrastructure work or seasonal storms.
Actionable takeaways if you suspect a storm drain or sewer issue near your property
- If you notice repeated slow drains, gurgling, or backups after rain, document the timing and call for a professional drain evaluation before it escalates.
- Don’t assume city-side storm infrastructure can’t affect you—water follows the path of least resistance, and old connections can behave unpredictably.
- Avoid chemical drain cleaners for recurring clogs; they can damage older lines and rarely solve the underlying blockage.
- If nearby construction is underway, be extra alert for new odors, backups, or soggy areas—shifts in soil and vibration can expose weak points.
- Ask about camera inspections or diagnostic options to locate issues without unnecessary digging.
Frequently Asked Questions
Need help diagnosing a drain or sewer issue in Denver?
If you’re dealing with recurring clogs, storm-related backups, or signs of a compromised line—especially in older parts of Denver, Colorado—getting the problem accurately diagnosed is the fastest path to preventing damage and downtime.
Contact Drain Pros Plumbing Denver to schedule a drainage evaluation and get clear next steps based on what’s happening in your system.
This article is a commentary-based rewrite for informational purposes, based on this source.
