Cover Story

Filtration and Disinfection Monitoring Requirements

Public water systems that use surface water—or groundwater that is directly influenced by surface water—must remove or sufficiently inactivate microbiological contaminants to ensure that drinking water is safe. This requires at least two pathogen barriers, one to filter and one to disinfect. Water systems confirm proper filtration and disinfection by monitoring for turbidity, chlorine, pH, and temperature. We may cite systems during sanitary surveys if they are not properly monitoring for each parameter. 

For filtration, the state’s drinking water regulations establish performance criteria based on surrogate monitoring of turbidity, which is the industry standard. For chemical disinfection, performance criteria are based on pH, temperature, and chlorine residual, which correspond to an estimated treatment using log inactivation equations. Appropriate monitoring consists of several key steps.

Key steps

1. Monitoring in the correct locations
2. Selecting appropriate equipment/instruments to monitor the parameter in question
3. Using proper techniques to monitor
4. Calibrating and verifying instruments in accordance with state and federal requirements

Most of the requirements for turbidity and chlorine residual calibration originate in the federal Safe Drinking Water Act. Therefore, the state cannot set less stringent requirements. Below are summaries of the requirements for each parameter.

Turbidity 

• Online turbidity analyzers must be calibrated quarterly
• Continuous monitoring means that measurements must be recorded at least every 15 minutes
• Signals should be averaged over about 30 seconds to 1 minute but must not be averaged over 3 minutes
• Results should be verified once per week with an alternative method, but this is not required

Chlorine analyzers 

• Online chlorine analyzers must be verified with a handheld method once per week
• Continuous monitoring means that measurements must be recorded at least every 15 minutes
• Signals should be averaged over about 30 seconds to 1 minute but must not be averaged over 3 minutes

pH/Temperature 

• Must be analyzed immediately after collection and never sent to the lab
• pH must be calibrated daily 

A few systems in Colorado disinfect with ultraviolet light, chlorine dioxide, or chloramines, which require additional monitoring that will not be covered in this article. We work with systems that use these technologies on a case-by-case basis. Additional information can be found in our Policy 4 Guidance on Proper Operations of Water Treatment Processes.

Below are some resources that will give more specific information about the requirements outlined above. If you are concerned about your instrument monitoring system and calibration protocols, please contact Tyson Ingels at tyson.ingels@state.co.us.

Additional Resources

Colorado Primary Drinking Water Regulations

• 11.46 - Analytical requirements and laboratory certification rule

Safe Drinking Water Act

• Section 141.74 - Analytical and Monitoring Requirements
• Section 141.560 - Individual Filter Turbidity Requirements

➽ Tyson Ingels, lead drinking water engineer

Preparing for Harmful Algal Bloom Season

Water that is warm, slow moving and high in nutrients can cause harmful algal blooms to form in waters above ground like reservoirs. With the weather warming up, managing these waters to prevent these blooms becomes critical for water safety. Certain types of cyanobacteria, also known as blue green algae, produce unpleasant taste and odors in water. Some blue green algae are also capable of producing cyanotoxins which can create health risks for humans and animals. The toxins can be problematic for anyone that ingests them or is exposed through recreational activities. Currently, cyanobacteria is not a regulated contaminant but EPA has published non-regulatory drinking water 10-day health advisories for the cyanotoxins microcystin and cylindrospermopsin based on studies showing that these two strains cause liver, kidney and reproductive toxicity.

Responding to situations where an unregulated contaminant measures above a health advisory is very difficult because there is not a playbook with available instructions like there is with regulated contaminants. In May 2018, Oregon’s capital and second-largest city, Salem, made national headlines by declaring a state of emergency after issuing a “Do not drink” advisory due to elevated microcystin levels in their treated water. Here are a couple of the lessons learned Salem shared after the event:

Do not wait to notify your customers

After receiving initial sample results showing levels above the health advisory, the system spent a couple of days making operational changes to try and lower toxin levels before taking more samples. Because Oregon didn’t have any labs capable of cyanotoxin analysis, they had to ship samples to an out-of-state lab, causing a long turnaround time for receiving results. The system believed it was okay, since they were still responding within the 10-day health advisory window. However, those follow-up sample results came back high and the system issued a “Do-not drink” advisory. The customers and local papers were outraged because they weren’t notified sooner.

Knowing when to lift the advisory is tricky 

After receiving sample results showing microcystin levels were below the health advisory, the city lifted the initial “Do not drink” advisory. The city then issued another “Do not drink” advisory four-days later after receiving additional results showing elevated toxin levels. They waited to lift the second advisory until they had levels below the health advisory for 12 consecutive days.

Between 2018 and 2020, all drinking water systems nationwide serving over 10,000 individuals, as well as a random selection of other systems, are required to sample for cyanotoxins as part of EPA’s Unregulated Contaminant Monitoring Rule (UCMR). EPA will use the test results to see where cyanotoxins are occurring and determine whether or not to regulate them in the future. There are over 100 Colorado drinking water systems required to perform this additional testing and they have been notified. As of May 2019, there have not been detections of any UCMR cyanotoxins in treated water.

Online resources

Learn more about cyanotoxins and how to monitor and prepare for them by reviewing these resources:

• Monitoring guidance created by the Colorado Harmful Algal Bloom Workgroup.
• EPA's  toolkit and webinar Preparing for HABs season. 

➽ David Dani, Local assistance unit

Samplegeddon - 2019

Our last issue included an article regarding Samplegeddon. What is Samplegeddon? In 2019, nine-year, six-year, three-year, annual, six-month, and quarterly monitoring compliance schedules will converge - that's Samplegeddon. This only happens every nine years! As a result, the department is working diligently to remind water systems of their monitoring requirements.

Based on the figure below, as of January 15, 2018:

• Overall, approximately 60% of systems have completed their three, six, and nine year sampling schedules. However, this means that 40% of systems still have not met their monitoring requirements.  
• Great news - a majority of systems have sampled for nitrite, which is on a nine-year schedule! However, 15% of systems are still outstanding.   
• The area with the most uncompleted sampling is for synthetic organic chemicals. To date, only 43% of systems have collected their required samples.

To avoid any potential monitoring and reporting violations, please remember to:

• Review your system’s monitoring schedule to ensure samples will be collected at the appropriate sample point, during the correct collection period, and that there are not separate requirements for specific analytes within a group. Have enough sampling bottles on hand to address each requirement as it arises - you may even want a few extra.
• Collect and deliver your samples to a certified laboratory early in your compliance period. Be sure that the chosen laboratory will be able to process your sample results and report them to the department by January 10, 2020. Laboratories may be extra busy as the deadline approaches; do what you can to avoid surprises or delays! Submitting samples early helps ensure that they will be received by the department on time, and it may also ensure adequate time to re-sample or correct reporting errors if needed.
• Confirm that sample results have been received and accepted by checking your system’s online monitoring schedules. Schedules are updated every Wednesday night to reflect changes.
• Contact your drinking water compliance specialist with any questions or concerns.
• Submit your data early. Remember, the best way to submit drinking water data to the department is through the drinking water portal.
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➽ Nicole Graziano and Jamie Duvall, drinking water compliance assurance section