06 Aug Sampling at the Water Treatment Plant: Strict regimen and built-in redundancies ensure water quality
12 times a day, 7 days a week, 365 days a year – that’s how often our water treatment plant operators pull samples of the water that is being treated for distribution to our service area. Why so often? The obvious reason is because we take our water quality very seriously and work very hard to ensure the provision of high quality, safe and reliable water to every single person we serve, all day and every day. But there’s another reason that may not be as obvious. The quality of the raw water we pull changes throughout the day, which often requires adjustments in the treatment process. And like so much of the work we do as a utility provider, it is imperative that water sampling is done in pristine fashion to ensure the integrity of our water supply and the safety of our customers.
With August being recognized nationally as Water Quality Month, we thought it might be fun to shed light on what a typical day of water sampling at our Water Treatment Plant looks like.
Manual sampling occurs every two hours, during which the operator on duty pulls water from all phases of the process – raw, pH adjusted raw water, and settled water. Each of these draws is tested for several factors, including pH (a measure of acidity), chlorine levels and turbidity (water clarity, which is a key measure of quality).
Let’s start with pH levels. The pH level of the sample determines the feed rate for sulfuric acid. For example, if a sample shows high pH levels, plant operators would increase the sulfuric acid feed rate to bring the pH level down. The primary reason for this is because high pH levels in the water require more coagulant to make any debris in the water clump and sink. Coagulant is more expensive than sulfuric acid, making the addition of sulfuric acid a more efficient way to balance the pH levels in the water. Water with a low pH level is also more corrosive in nature and can cause damage to the infrastructure over time. pH levels are measured on the raw water, pH balanced water and finished water, and it’s important to get it just right – just like low pH levels can cause corrosion, high pH can lead to scale buildup in pipes.
Chlorine levels are also measured every two hours in the settled water. This reading tells the operators if they need to adjust the feed rate of the bleach pumps, and if so, how much. This is an important number in that it must be enough to properly disinfect the water but not too much to be harmful.
The third element they measure is turbidity. The easiest way to explain turbidity is the clarity of the water, which really makes good sense. Anything other than pure H2O (dirt, bacteria, etc.) will cause the water to look murky – even unsettled air bubbles can cause the water to look cloudy. Settled water turbidity is tested every two hours, while finished water turbidity is measured constantly with an online monitor and then verified every four hours with a benchtop unit.
In addition to these manual samples, the Water Plant has online instrumentation that monitors water quality 24 hours a day, seven days a week. Built-in alert levels have been established to alert plant operators if any level goes outside of the acceptable range. This allows them to quickly adjust feed levels and ensure the integrity of our water at all times. Even with this real-time monitoring, the plant operators stick to their regimen of sampling every two hours. These manual samples validate the data gathered by the online instrumentation.
Now back to why we do this every two hours – it’s because water characteristics change rapidly throughout the day due to photosynthesis (growth) of algae. Not to get to scientific, but when algae grow, they use the carbon dioxide (CO2) found naturally in water. When you remove CO2 from water, you essentially lower the acidity (raise the pH). At night, when photosynthesis stops, algae release CO2 back into the water. Plant operators see this regularly – early morning samples typically have lower pH while afternoon samples show increased pH levels.
But sampling doesn’t stop there. We have another team of employees who pull samples from the field – those required monthly by the state and those generated from customer concerns. We’ll share more on that in a future post.