A Creek With a Genuinely Historic Flood Record
From September 11 to 15, 2013, Longmont experienced the most devastating flash flood event in its recorded history. The St. Vrain Creek's flow exceeded 37,000 cubic feet per second, well past the 10,000 cfs that defines a 100-year event here, and the flood swept past even the 500-year flow estimates for every stream and ditch in the city. The river breached its banks west of town and pushed six to eight feet of water into neighborhoods that sat entirely outside the FEMA-mapped floodplain, destroyed a mobile home park, knocked out six of the city's seven raw water sources, and caused roughly $150 million in infrastructure damage. Longmont was cut in two for days, with only a single route left connecting the north and south sides of the city.
The city has spent more than a decade on the Resilient St. Vrain channel redesign in direct response, and in September 2025 Longmont earned recognition as the first Resilience Hub in the United States for that recovery work. Most of what we actually respond to has nothing to do with the creek directly, a slab leak, a failed water heater, a supply line giving out. But that flood history is part of why we treat water intrusion here as worth taking seriously.
Why Longmont Homes Leak the Way They Do
Longmont's bentonite clay swells during spring snowmelt and contracts through the dry months, putting cyclical pressure on the copper supply lines embedded in slab foundations across the city. Homes in Loomiller and Mill Village, built through the 1950s and 60s, carry the oldest copper in town and have been through fifty-plus annual wet-dry cycles. Homes in Spring Valley and Quail Crossing, from the 1980s and early 90s, are now entering the age range where pinhole failures become statistically likely, especially with medium-hard St. Vrain surface water scaling the pipe interior for decades.
Extraction and Drying, Run as One Job
Once we've confirmed the source, a slab leak, a failed appliance, storm-driven intrusion, extraction and structural drying happen in the same visit rather than as separate appointments days apart. Air movers and a commercial dehumidifier go in immediately, and we log moisture readings daily in framing, subfloor, and drywall until the numbers confirm a stable baseline. Stopping short of that because the floor feels dry is the most common reason a water event here turns into a mold problem a month later.
What Water Category Actually Decides
A burst supply line is Category 1, clean water that just needs extraction and drying. Water that's picked up contamination from an appliance or come in from outside during a storm moves to Category 2 or 3 and needs real disinfection first. We classify the source on the first visit, since it decides what gets dried in place versus pulled out entirely, and it's exactly the detail your insurance adjuster will ask about.
| Water Category | What's Involved | Typical Cost |
|---|---|---|
| Category 1, clean, contained quickly | Extraction and drying only | $1,300 – $4,300 |
| Category 2, some contamination | Extraction, drying, disinfection | $3,200 – $10,800 |
| Extensive, flood or slab access | Removal, drying, rebuild | $8,800 – $27,500+ |