Residents of Iowa’s largest metro area are being advised they “may need to reduce or hold off on lawn watering altogether,” as Des Moines Water Works (DMWW) and Central Iowa Water Works work to ensure the drinking water they provide to more than 20 percent of the population remains safe.
The rains in recent months that ended drought conditions in Iowa have led to heavy nitrate loads in both the Des Moines and Raccoon rivers, which are key sources of drinking water in the Des Moines metro and the rest of central Iowa, as farm field runoff dumps fertilizer into both rivers. There’s now concern that increased outdoor water use — for lawn sprinklers, etc. — may overtax the efforts to remove unsafe levels of nitrate from river water and use sources other than the two rivers.
“While there appears to be plenty of water in our rivers, we cannot rely upon them as the predominant water source with nitrate concentrations being at the level they are,” DMWW CEO and General Manager Ted Corrigan said in a statement on Monday. “High nitrate concentrations require extensive treatment, which we are currently able to do, but if lawn watering picks up, Des Moines Water Works may be unable to meet the nitrate standard.”
Federal safety standards limit the “maximum contaminant level” for nitrates in drinking water to 10 milligrams per liter. According to the DMWW, current nitrate levels in the Des Moines River is 14 mg per liter and in the Raccoon River it is 17 mg per liter.
Because excess use of fertilizer is standard practice in the intense row crop farming of corn and soybeans in Iowa — and practices to effectively limit runoff have not been widely adopted, while practices like planting fields to the edge of waterways that increase runoff are common — nitrate pollution has been is a chronic problem for water agencies in Iowa. DMMW has invested heavily over the years in methods and equipment to cope with the problem.
DMMW has a state-of-the-art reverse osmosis system that removes nitrates from river water. It costs approximately $10,000 per day to operate. The water utility is also working on other methods of securing clean water, including a series of radial collection wells along the Des Moines River.
The wells are placed next to the river, and reach a depth of up to 60 feet. The wells act like a hub for perforated pipes that run parallel to the river, or even beneath the riverbed. Those pipes collect river water that has passed through the alluvial sand and gravel, which function like a giant filter that eliminates almost all the pollutants in the river water, as well as any algae or viruses.
In the capital improvements budget it published last year, DMMW projected spending up to $50 million in coming years on its latest projects to secure clean water.
Last year, Iowa marked 10 years since the state published its official nutrient reduction strategy (NRS) that was supposed to address nitrate and phosphorus pollution in the state’s waterways. The NRS contains no mandatory actions. Everything is voluntary.
Left to its own devices, Iowa wouldn’t even have an NRS. In 2011, the EPA ordered all the states whose rivers flow into the Mississippi River to develop nutrient reduction strategies in response to the growing dead zone in the Gulf Mexico, which is caused by agricultural pollutants depleting the oxygen content of the water.
“What we have been focused on the last 10 years is not just talking about doing things, but getting work done,” Iowa Secretary of Agriculture Mike Naig said at an NRS anniversary event on a farm in Story County.
“I don’t think the amount of change that has happened thus far has made any impact on water quality,” DMWW’s Corrigan told Little Village at the time.
In its statement on Monday, DMMW said it had “been able to minimize use of river water, which has the highest nitrate concentrations, because customer demand has been low, but overall demand is starting to increase with the warmer weather and less rainfall.”
“Average customer demand for customers served by DMWW’s treatment facilities is 55 million gallons per day,” according to DMWW. “During the warmer months, that number can increase to between 80 million and 85 million, much of which is attributed to lawn watering and outdoor water use.”