Spring melting has caused significant water quality concerns for Des Moines Water Works, in particular ammonia present in our rivers from livestock runoff and other upstream land uses. Many customers may have noticed a chlorine taste and smell in their drinking water. Weeks of disinfection treatment has been necessary to reduce runoff impacts; however, disinfection has its own risks, including potential health risks if continued over the long term.
Des Moines Water Works aggressively and continuously monitors for the presence of drinking water contaminants. Tests indicating a “snap shot” of drinking water quality are taken often in the Des Moines Water Works system. Testing results received on March 21, 2014, show Des Moines Water Works exceeded the regulatory standard for Total Trihalomethanes (TTHM). The standard for TTHM is 0.080 milligrams per liter (mg/L), or 80 parts per billion. Des Moines Water Works’ result for TTHM during the monitoring period, which ended in the first quarter, was 0.090 mg/L in the Des Moines Public Water Supply (PWS) and 0.0926 mg/L in the Southeast Polk Rural Water District PWS.
“First and foremost, we take very seriously our responsibility to customers to provide a safe, reliable, and abundant water supply, and recognize that responsibility was not met here,” said Bill Stowe, CEO and General Manager. “Safe drinking water standards exist to protect public health – some for immediate health considerations, and others that protect against unwanted long-term effects. This exceedance falls within the second category. What is important here is that we respond with a sense of urgency to remedy the issue so it does not have the opportunity to become long-term. Our customers need to understand that there is not an immediate concern with respect to the drinking water – it remains safe to consume and customers do not need to use alternative sources of drinking water, nor use additional treatment techniques.”
Trihalomethanes are one of the most common disinfection by-products. Disinfection by-products form when chlorine used for disinfection reacts with organic matter present in the water. Some people who drink water containing Trihalomethanes in excess of the standard over many years may experience problems with their liver, kidneys or central nervous system.
The violation occurred due to the interaction between chlorine and organic matter in the water system.
“At the time of the violation, Des Moines Water Works saw elevated levels of ammonia and other organic matter in both the Des Moines and Raccoon Rivers,” said Stowe.
Disinfection with chlorine is more difficult when ammonia is present in source waters. Ammonia consumes chlorine, leaving it unavailable for disinfection. This requires adding additional chlorine to eliminate the ammonia and obtain proper disinfection during the final stage of treatment. For that reason, chlorine levels have been purposefully higher since early January. Elevated levels of organic matter, at a time when chlorine is being dosed aggressively, causes the formation of the undesirable disinfection by-products.
High levels of organic matter and ammonia in the rivers are often the result of agriculture runoff, especially livestock operations and manure fertilized fields.
“Runoff into the Des Moines and Raccoon Rivers has once again created significant water quality and water treatment concerns,” said Stowe. “We are completely at the mercy of what is in our rivers each day.”
“Investing in multi-million dollar capital improvements to adjust treatment processes is one viable solution to eradicate similar violations in the future, but the source of the problem remains in our rivers,” said Stowe. “This should be a call to action for all central Iowans to advocate for cleaner source water and to question if voluntary water protection measures work.”
Des Moines Water Works customers will receive the public notice required by Iowa Department of Natural Resources in their April bill statement. Copies of the notices can be found here:
- Public Notice for all DMWW full and total service customers, except Southeast Polk, south of I-80
- Public Notice for Southeast Polk customers (Runnells and Southeast Polk, south of I-80)
The regulation requires averaging the samples obtained in the last four calendar quarters. Because of the high results in the first quarter of 2014, similar notices will be sent to customers in future quarters unless and until the average falls below the standard. Customers can expect three additional notices in 2014.