Conclusions and Recommendations
Water Quality Supports Aquatic Life
Water quality conditions throughout the watershed are generally supportive of healthy aquatic life. Most analytes are within acceptable ranges to support healthy aquatic life and meet Colorado’s aquatic life use standards throughout the watershed. Metals concentrations occasionally approach standards during periods of low hardness (hardness-based standards for metals drop to lower levels when hardness is reduced by snowmelt in the streams). Metals in the watershed are predominately influenced by local geology and groundwater rather than human-sourced pollution. Other challenges exist around E. coli spikes during the summer, and higher nutrient concentrations below treated wastewater discharge points.
As time and resources allow, the partnership should continue to monitor and investigate these influences and possible mitigation strategies. Additional, more specific observations and related recommendations have been provided below for key areas of concern.
Treated Effluent and Nutrients
Each stream monitored by KICP receives effluent from and is influenced by municipal wastewater treatment facilities. The influence of these facilities varies by parameter. In this watershed, parameters such as pH, dissolved oxygen, and metals in effluent have a limited impact on their receiving streams. Many metals concentrations actually decrease downstream of effluent discharge points because the effluent contains lower metal concentrations than the receiving streams.
These facilities have invested in a variety of upgrades over the last few decades that have measurably decreased nutrient concentrations. Proposed instream nutrient standards may still present a compliance challenge in the future. As time and resources allow, the partnership should continue to pursue opportunities for nutrient reductions from both effluent and non-point sources within the watershed.
The KICP’s monitoring program includes consistent monitoring of multiple nutrients. Maintaining this comprehensive nutrient monitoring program and continuing to evaluate trends and the impacts of management and mitigation will be beneficial when stream standards are adopted in the future.
E. coli and Urban Streams
E. coli remains a priority pollutant within the watershed and Boulder Creek, Saint Vrain Creek, and Coal Creek all have segments that experience E. coli spikes throughout the year. The partnership and their monitoring data support these general conclusions regarding E. coli within the watershed:
Common Problem: E. coli exceedances occur within the KICP watershed and are a common problem across the Front Range, Colorado, and the United States. E. coli concentrations do not provide information about the sources, but common sources of E. coli that have been observed within the watershed include wildlife, pets, trash, and human influence.
Recreate Safely: When wading or swimming in any natural water body you may be exposed to E. coli and other microorganisms. Most types of E. coli do not cause illness, but there are certain strains that can cause gastrointestinal illness. All streams monitored in this study periodically exceed the level of E. coli deemed safe for recreational use by the U.S. Environmental Protection Agency.
Seasonal Variations: E. coli concentrations in the watershed are typically highest in the summer and early fall. The warmer water temperatures and lower streamflows during this time are more favorable for bacteria growth. Results indicate that there is no single or easily controllable source of E. coli causing impairments, but rather a variety of dispersed sources that include urban wildlife, pets, humans, and trash.
General Stability: Most monitoring locations continue to have stable (no significant increasing or decreasing trends) E. coli concentrations over the last five years, suggesting general stability throughout the watershed.
Other Non-point and Natural Sources
Non-point source pollution is the result of rainfall or snowmelt moving over and through the ground, picking up natural and artificial pollutants along the way, ultimately depositing them into streams. Natural influences on a stream, such as underlying geology, groundwater, or stream bed conditions can also lead to elevated concentrations of some pollutants. In addition to E. coli discussed above, three other constituents appear to have elevated concentrations that may be driven by dispersed, non-point source or natural contributions to the streams. These include:
Dissolved Selenium - Elevated levels in the lower reaches of Boulder and St. Vrain Creeks and throughout Coal Creek appear predominantly related to natural geology and groundwater influences. However, the proximity of stations with elevated concentrations to urbanization as well as agriculture suggest that human influences should not be discounted.
Dissolved Silver - Low hardness during spring runoff creates conditions where the calculated standard for dissolved silver is also very low. Dissolved silver concentrations during these periods, although driven by natural influences, may occasionally result in stream standard exceedances. Monitoring for dissolved silver is limited on Coal Creek and it is difficult to draw conclusions about sources or patterns in that stream. Dissolved silver has not been detected in St. Vrain Creek since monitoring began in 2020.
Conductivity - Conductivity increases consistently upstream-to-downstream in all three streams. The most likely cause is increased metals, which also increase upstream-to-downstream due to hydrogeologic conditions. Wastewater treatment facility discharge tends to lower conductivity in all the streams, diluting existing elevated stream concentrations. High conductivity could also be influenced by surface runoff from surrounding urban areas bringing in components that affect conductivity such as calcium, chloride, magnesium, potassium, sodium and sulfate. Monitoring for these related components is currently limited, therefore the impacts of urbanization on conductivity cannot be readily assessed.
Expanding KICP’s monitoring program to include more storm sampling and consistent, comprehensive sampling for the constituents mentioned here will help develop a better understanding of how non-point sources may be affecting Boulder, St. Vrain, and Coal Creeks. With this understanding, future KICP efforts can focus on mitigation and control measures that target known causes of non-point source pollution in the watershed.
Future Considerations
Municipal Treatment Upgrades
Future upgrades and modifications to wastewater treatment processes that limit nutrient concentrations in effluent will be most advantageous in addressing elevated nutrient levels in the watershed.
Agricultural Best Practices
Implementing best management practices (BMPs) in agricultural land and livestock management throughout the watershed can further support efforts to reduce nutrient pollution. While much of the study area is within urban corridors, there may be some instances where agricultural BMPs can have a beneficial impact.
Stormwater Control
As urbanization of the watershed continues, it will be important to leverage sustainable urban planning practices related to stormwater control measures to reduce runoff, manage flooding and improve water quality. Such measures could include (but are not limited to) green infrastructure, detention basins, rain gardens, and vegetated swales. Implementation of buffer strips along waterways to filter runoff can help to restore wetlands which act as natural filtration systems. Completing stream restoration projects to improve riparian zones will enhance erosion control, also helping to control pollutant loading from stormwater runoff.
Macroinvertebrate Monitoring
Although macroinvertebrate data was not analyzed in this report, prior reports have included this analysis. The inclusion of macroinvertebrate monitoring data (density, distribution, and population composition) in future reports would help provide a more holistic understanding of watershed health.
Overall Monitoring Program Consistency
There is some variability in monitoring frequency and location for some key parameters. A program with consistently scheduled monitoring of key parameters at all locations supports accurate comparisons across streams and allows for better tracking of changes over time. Uniform monitoring ensures that data can be meaningfully compared, trends can be reliably identified, and the effectiveness of management practices can be assessed.