Each spring, as snow melts across the Rocky Mountains, rivers and streams surge with fresh runoff. To the untrained eye, this appears to be newly melted snow flowing swiftly downstream. But new research shows a surprising reality: much of this water isn’t fresh snowmelt at all—it’s older groundwater that has been stored underground for years, even decades, before reemerging during seasonal high flows.
For communities across Colorado and the broader West, this finding has significant implications for water safety, contaminant transport, and long-term monitoring strategies. At CMDC Labs (Longmont, CO), we recognize that understanding the age and origin of water is just as important as analyzing what’s in it. When older groundwater dominates river systems, the pathways and risks of contamination change—and so must our approach to testing.
Understanding Groundwater Age and Runoff
Groundwater “age” refers to how long water has been stored underground before returning to the surface. While some groundwater is relatively “young” (less than 10 years old), other reserves may be decades to centuries old.
During spring runoff, rivers swell, but studies reveal that the increased volume is not just snowmelt rapidly moving downhill. Instead, snowmelt recharges aquifers, which then slowly release older groundwater into rivers.
Why this matters:
- Older groundwater is a contamination carrier: PFAS, nitrates, and heavy metals that entered aquifers years ago may now emerge at the surface.
- Long travel times mask pollution sources: If water takes decades to reach rivers, pollutants introduced long ago may only become visible now.
- Misleading assumptions: Communities often assume spring flows dilute contaminants. In reality, if flows are dominated by older groundwater, pollutants can be concentrated rather than dispersed.
PFAS in Colorado’s Watersheds
PFAS (per- and polyfluoroalkyl substances)—often called “forever chemicals”—are particularly concerning in this context. They are:
- Highly persistent: PFAS don’t break down naturally and remain in water for decades.
- Mobile in groundwater: Once in aquifers, PFAS can migrate long distances, reemerging in rivers years later.
- Linked to serious health risks: Cancer, immune disruption, thyroid disorders, and developmental impacts in children.
In Colorado, PFAS contamination has already been documented near military bases, airports, and industrial sites. When older groundwater dominates runoff, PFAS released long ago may continue cycling into rivers and drinking water supplies.
At CMDC Labs, our PFAS testing protocols use ultra-trace LC-MS/MS methods with PFAS-free sampling kits, ensuring reliable detection even at parts-per-trillion levels. This level of sensitivity is critical for protecting communities, especially when EPA and state standards continue to tighten.
Heavy Metals in Groundwater and Runoff
Older groundwater often interacts with bedrock and soils, dissolving naturally occurring metals such as:
- Arsenic (linked to cancer and skin lesions)
- Uranium (a concern in Colorado aquifers)
- Lead (from legacy infrastructure and pipes)
These metals may remain undetected until mobilized by changes in groundwater flow—such as spring snowmelt recharge.
CMDC Labs provides ICP-MS heavy metals analysis that identifies contaminants at trace levels. For municipalities, this means being able to predict and prevent exposure rather than reacting to crises.
Microbial Risks from Groundwater Flow
While chemical contaminants dominate headlines, microbial threats also persist. As older groundwater moves through soil, septic systems, or agricultural lands, it may carry bacteria, viruses, and protozoa into rivers.
Examples include:
- E. coli from failing septic systems
- Cryptosporidium and Giardia from livestock runoff
- Biofilms in aquifers that release pathogens during high flows
At CMDC Labs, our environmental microbiology team provides comprehensive microbial monitoring programs—ranging from coliform testing to next-generation sequencing (NGS) that identifies microbial communities across watersheds.
Lessons for Colorado and the West
The finding that older groundwater dominates seasonal runoff should reshape how we view water safety in the region.
1. Communities must think long-term
Contaminants introduced decades ago may still be cycling into today’s drinking water. Monitoring must extend beyond immediate pollution events.
2. Testing must cover multiple categories
Focusing on either microbes or chemicals alone isn’t enough. Integrated testing for PFAS, metals, and pathogens is essential.
3. Climate change raises the stakes
As snowpack patterns shift and drought conditions intensify, the proportion of older groundwater in rivers may rise—bringing historic contamination to the surface more often.
4. Independent labs are critical
Regulatory bodies can’t test every aquifer or river. Independent, accredited labs like CMDC Labs provide the capacity, methods, and impartial results that communities can trust.
How CMDC Labs Helps Fill the Gap
At CMDC Labs, we partner with municipalities, utilities, and community groups to deliver science-driven water safety solutions:
- PFAS-Free Sampling and Testing: Defensible ultra-trace results for PFAS.
- Heavy Metals Analysis: ICP-MS detection for arsenic, lead, mercury, uranium, and more.
- Microbial Water Testing: Coliform, E. coli, and advanced DNA-based methods.
- Long-Term Monitoring Programs: Trend analysis to track contaminant movement over time.
- Community Transparency Reports: Clear results formatted for both regulators and residents.
By combining regulatory expertise with cutting-edge analytical tools, CMDC helps communities not only detect contamination but also understand patterns and build long-term resilience.
Conclusion: The Age of Water Matters
The revelation that spring runoff in Colorado often comes from older groundwater, not fresh snowmelt, has deep implications for water safety. It means that what we see rushing through rivers today may carry contaminants from decades past.
For communities, the message is clear: water safety isn’t just about monitoring the present—it’s about understanding the history and movement of groundwater.
At CMDC Labs, we stand ready to help Colorado and Western communities meet this challenge with rigorous PFAS testing, metals analysis, and microbial monitoring. Because in the fight for safe water, knowledge is power—and only science can turn that knowledge into trust.
Sources (single line): KUNC report on groundwater age in Colorado runoff (Sept 2025); U.S. Geological Survey groundwater and contaminant transport studies; EPA PFAS Strategic Roadmap and Safe Drinking Water Act MCLs; Colorado Department of Public Health & Environment PFAS Action Plan; peer-reviewed studies on groundwater-surface water interactions, metals mobilization, and microbial contamination in Western watersheds.
