When will this end?

Q. What do you mean by "one of many factors” and “a sustained, consistent downward trend in source water nitrates" and why can you not tell us a date?

A. Our lab processes over 200 samples of varying types every day to ensure that water produced by Central Iowa Water Works meets all safe drinking water standards. These samples are collected throughout our system including directly from our raw water sources. However, the results from the raw water samples, which you see in your daily update, are not the sole factor influencing the decision on when the ban can be lifted.

Other factors include the weather in the watershed. When it rains in the watershed, the nitrate concentration in the river system fluctuates. As depicted in the line graph below, rainfall can lead to a decrease in nitrate levels, followed by a rebound in the days that follow. This is what we refer to as a diluting and concentrating effect. The good news is that we are seeing the rebound happen in smaller magnitudes after each rain event as we progress further into July. While we anticipate a decrease in nitrate concentrations over the next few days due to the anticipated rainfall, the river samples will present a more complete picture in days that follow.

A period of hot and dry weather allows the landscape to dry out, which in turn decreases the amount of nitrate that flows into the river. Furthermore, it enables the plants and algae to take up the nitrate from both water and land. This helps stabilize the concentrations in the river, enabling a more precise estimation of the treatment level required for the raw water.

The treatment level required for raw water is a crucial factor in determining the system’s capacity for adding back water demand. During peak watering season, lawn watering can consume up to 40% of the system’s total capacity. The great news is that we’re seeing the rebound happen in smaller amounts after each rain event and we expect to continue to see that happen in the coming days. The Technical Committee, composed of all twelve member agencies, has been working collaboratively throughout this process to monitor the nitrate levels, and create action plans along the way. We all look forward to exiting this lawn watering ban and returning to normal operations. Until then, thank you for everything you are doing to continue providing safe drinking water to our 600,000 users.

What is the gallery depicted in the chart below? The infiltration gallery is a system of underground pipes located near the Raccoon River in Water Works Park. It used to collect water for the Fleur Drive Treatment Plant.