(C) Iowa Capital Dispatch
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Drinking water threat from nitrate persists during droughts • Iowa Capital Dispatch [1]
['Jared Strong', 'More From Author', '- March']
Date: 2024-03-14
Iowa’s drought of more than three years has significantly reduced the amount of farm fertilizers in the state’s streams, but that doesn’t guarantee a complete nitrate reprieve for the Des Moines metro area’s drinking water.
“It’s really more complex than people can believe,” said Ted Corrigan, the chief executive of Des Moines Water Works, which has one of the largest nitrate removal systems in the world. “We’re actually monitoring it on an hour-by-hour basis, all these different factors to see what’s changing: if a little bit of rainfall is going to change things, or if demand is going to pick up for some reason. We may change (water) sources multiple times in a day.”
The Des Moines and Raccoon rivers are the primary sources of drinking water for more than 600,000 metro residents. When they contain too much nitrate — which is particularly harmful to infants — DMWW can blend untainted water from two lakes and several special wells. Those aquifer storage and recovery wells are used to pump water into the ground during periods of low demand to be pumped back out when demand is high.
The utility can also activate its nitrate removal system at a cost of up to $16,000 per day. Because that system isn’t often used at full capacity, the actual cost in a recent 10-year period averaged about $4,400 per day.
Parts of Iowa have suffered from drought for more than three years — the longest stretch since the 1950s. That has potentially created a buildup of nitrate in farmland that could lead to a spike in stream contamination when typical rainfall returns. About half of the state’s cropland is drained by underground tiling, which provides a quicker path for nitrate-laden stormwater to travel into streams.
“I wouldn’t say we’re overly concerned about it, but we’re aware,” Corrigan said. “It’s been dry for a few years, and then if we have normal rains or slightly above normal rains this spring, we’re probably going to be dealing with a lot of nitrate.”
But there are a variety of factors at play. If the rains are torrential, it could dilute the nitrate concentrations in the rivers. It’s the steady, moderate rainfall that can cause the most problems.
Further, customer demand can complicate the situation. Periods of high river nitrate and high demand during warmer months are the most likely times in which DMWW operates its nitrate removal system, Corrigan said.
In the recent drought, the utility has not needed to activate the system in 2020, 2021 or 2023, according to DMWW records. But steady rainfall in 2022 required the utility to operate the system for 23 days that June at a total cost of about $150,000.
That total eclipsed the cost to run the system in each of the three years leading into the drought.
Corrigan said it is difficult to predict what will happen this year: “We’re keeping our eyes on the weather.”
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