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High chloride levels found in two city wells

Wastewater used to flood state wetlands might be culprit
Tuesday, July 15, 2008 | 9:05 p.m. CDT; updated 2:51 p.m. CDT, Tuesday, July 22, 2008

Two wells that supply drinking water to Columbia have unusually high chloride levels, according to documents supplied to the Missourian by the city Department of Water and Light.

High chloride levels in samples taken throughout the city’s well field indicate that effluent being used to flood Eagle Bluffs Conservation Area may be seeping into the well field, according to a 2002 study by Brenda Smith of the U. S. Geological Survey in Columbia. The sewage is treated at Columbia’s wastewater plant and piped to the Missouri River bottoms near McBaine for additional treatment in municipal wetland cells.

Barry Kirchhoff, superintendent of the city water treatment plant, said he’s aware of the Geological Survey findings and the possibility that treated effluent used to flood the state-owned conservation wetlands is affecting groundwater in the Missouri River bottoms that the city relies on for drinking water.

Chloride is a major component of salt. Wastewater is high in chloride because urine, which is salty, breaks down and leaves chloride behind. Chloride is not known to be harmful to people, but its presence in the wells is an indicator of change in the water in the alluvial plane that the city’s 15 wells tap into.

Former Columbia Water Plant Superintendent John Betz, who gave a June 22 presentation at Columbia’s First Unitarian Church on possible reasons for high trihalomethane levels in Columbia’s drinking water, is concerned that city residents aren’t receiving enough information about their water supply and its problems.

Betz voiced the possibility that organic matter could be carried along with chloride in the slow groundwater flow from the Eagle Bluffs wetlands to the well field. If organic matter is carried into the wells, it could contribute to elevated levels of trihalomethane, a carcinogen, in the city’s drinking water.

Betz suggested that shutting off wells 5 and 6 and continuing to monitor trihalomethane levels is a feasible step the city could take to find out if water from these wells is affecting trihalomethane levels in drinking water.

Trihalomethanes are a byproduct of disinfection used to rid drinking water of harmful bacteria that can be associated with organic matter.

Kirchhoff said the city could meet its water demands without those two wells, but additional testing information is needed before considering taking them out of service.

Kirchhoff acknowledged the possibility that chloride from wastewater used to flood the Eagle Bluffs Conservation Area could be contributing to the levels found in wells 5 and 6. “Could it get there?” he said. “I suspect it’s possible.”

Smith’s 2002 study for the United States Geological Survey on the groundwater that supplies Columbia’s well field concluded that groundwater under Eagle Bluffs is higher than in adjacent areas. This causes a slow flow of groundwater to surrounding areas with lower water, such as the well field, where the city wells average about 100 feet deep.

The hill of water under the Eagle Bluffs Conservation Area “indicates potential for ground-water flow toward the city of Columbia well field,” Smith wrote in 2002. The study also noted that elevated levels of chloride, potassium, sulfate and calcium found in samples taken in or near the well field indicate that water is flowing from Eagle Bluffs Conservation Area toward the well field.

Columbia’s wells 5 and 6 began to show above-average chloride levels in 2000, according to documents provided by the Department of Water and Light. With few exceptions, since 2000, wells 5 and 6 have had at least two times the chloride levels found in the city’s other wells, with well 5 hitting a high of 159.6 parts per million in May 2007. When chloride testing of the wells began in 1999, well 5 averaged 18 parts per million for the year.

Chloride levels in wastewater are normally about 240 parts per million, and chloride levels in the Missouri River are about 20 parts per million, Smith said. Chloride levels in the city’s unaffected wells are also around 20 parts per million, according to the Water and Light documents.

The use of treated effluent to seasonally flood the Missouri Department of Conservation’s Eagle Bluffs wetlands dates to 1994, Kirchhoff said. When the wastewater is not used to flood the wetlands, it is routed into the Missouri River. Tim James of the Department of Conservation said that use of the wastewater saves a tremendous amount of money compared with pumping water from the Missouri River.

Everett Baker, an environmental engineer for the Missouri Department of Natural Resources, said there are three possible reasons for the high chloride levels in wells 5 and 6: treated wastewater entering the wells, a crack in the bedrock beneath the wells that is leaking in highly mineralized water, or a salt or brine disposal site near the wells. The city has no knowledge of a brine disposal site near the well field, Everett said.

The Water Resources Research Center at the University of Missouri is conducting research for the city that includes testing the levels of organic matter in wells 5 and 6. The center is also sampling drinking water in the distribution system for trihalomethanes.

Enos Inniss, assistant professor in the MU College of Engineering, said the Water Resources Research Center has no results available on the organic matter levels in wells 5 and 6. Smith said a study she authored that contains information on organics levels in the wells will be published later this year. She would not comment on the findings before the study is released.


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