Arsenic Water Quality Standards

 

Right now - arsenic is regulated in wastewaters statewide due to water quality standards that were conceived of over 20 years ago. Because arsenic can be quite detrimental to human health and for surface waters that are a source of drinking water, it is important to protect the drinking water supply by adopting protective standards.

Colorado has surface water standards to protect both drinking water (water supply) and fish ingestion. The surface water standard for water supply is 20 nanograms per liter (ng/L). This is quite low, and comparable to the PFAS maximum contaminant levels proposed by EPA (4 nanograms per liter).

The Safe Drinking Water Act regulates arsenic at 10 micrograms per liter (ug/L), or 10,000 nanograms per liter as a maximum contaminant level (or MCL). Also, the practical quantitation limit, or PQL for arsenic currently stands at about 1 micrograms per liter. Having such large discrepancies between the water quality standard, the drinking water MCL, and the PQL creates challenges in implementation of standards within the permitting framework.

The division worked with stakeholders and the commission throughout the 2010s and the early part of this decade to implement statewide temporary modifications because of uncertainty in what the standard should be, and the challenges presented by these discrepancies. While being an interim solution that is unique to Colorado, this solution is only temporary. Each time we extend it, we have to get it approved by our partners at EPA Region 8. Colorado has utilized the temporary modification tool since 2011 (Reg. No. 38.79) to recognize the underlying, use-based standard as a goal while using the level generally deemed to be technologically feasible to set permit limits (i.e., 0.02-3 ug/L). Currently, the arsenic temporary modification is scheduled to expire in 2029. 

As part of the Water Quality Roadmap, the division is currently scoping out what implementation of the protective arsenic standards will look like in the permitting framework. Keep informed of our progress through our quarterly roadmap meetings, which will also offer regular stakeholder input opportunities. The next Roadmap meeting will be held on March 5, 2026.

➽ Tyson Ingels, Watershed & Engineering Program Manager

Strategic Planning

Developing a 10-year Road Map for the Safe Drinking Water Program

The Water Quality Control Division has two programs for two different federal rules. The Safe Drinking Water Program implements the Safe Drinking Water Act, and the Clean Water Program oversees the Clean Water Act. In 2017, the Clean Water Program developed a 10-year roadmap outlining its strategy to address water quality issues related to ammonia, nutrients (nitrogen phosphorus and chlorophyll), selenium, temperature, arsenic and cadmium through 2027. The roadmap strategies include goal development, evidence development, goal implementation,work group efforts and outreach. The roadmap also includes specific timeline milestones for those strategies and rulemakings involving key regulations 31 and 85. The Safe Drinking Water Program intends to develop a similar planning roadmap for the 2020s. 

The Alamosa waterborne disease outbreak investigation report completed in November 2009 contained nine major recommendations for the department to reduce the risk of waterborne disease outbreak associated with drinking water at public water systems in Colorado. Implementing those recommendations essentially became the Safe Drinking Water Program's roadmap for the 2010s though we never formally made that designation. All of the recommendations from the report have been implemented and continue to be followed, although addressing aging infrastructure is an ongoing national struggle.

Looking ahead at developing a roadmap for the 2020s means evaluating federal actions that the state is required to adopt and implement, like the long term revisions to the lead and copper rule, and other federal activities like unregulated contaminant monitoring. Additionally, we will look at what kinds of revisions we can make to regulations, policies and guidance to help improve our program implementation and best protect public health considering resource limitations. Stakeholder input will be critical to develop a comprehensive roadmap. Please watch for more information, and join the conversation.

➽ Ron Falco, safe drinking water program manager