Well No. 7

After low levels of a contaminant were discovered, one of the City’s seasonal wells was shut down. Staff is currently working closely with consultants and the Minnesota Department of Health (MDH) to determine the best way to treat the well.

The City of Edina provides drinking water to residents from a groundwater source. Eighteen wells, ranging in depth from 380 to 1,130 feet, draw water from the Mt. Simon and Prairie du Chien-Jordan aquifers. Seven of the wells run year-round. Eleven are seasonal, running during the peak water-consumption season from April until October.

Well No. 7, a seasonal well drawing from the Jordan aquifer, provides 0.2 to over 2.0 percent of the City’s total water supply. Well No. 7, located in Sherwood Park near the new Grandview Square development, has tested above the Maximum Contaminant Level (MCL) set by the Environmental Protection Agency (EPA) for vinyl chloride, a colorless organic gas with a sweet odor.

“The City of Edina is committed to high quality facilities and services. Our public water supply is no exception,” said City Manager Gordon Hughes. “Safe water is essential to the well being of any community. We are committed to ensuring that Edina's water supply complies with all state and federal standards and will find a way to treat Well No. 7 for this contaminant.”

Vinyl chloride is used in the manufacture of numerous products in building and construction, automotive industry, electrical wire insulation and cables, piping, industrial and household equipment and medical supplies and is depended upon heavily by the rubber, paper and glass industries. According to the EPA, vinyl chloride has the potential to cause damage to the nervous system, damage the liver and can result in cancer.

A typical source of vinyl chloride, according to the EPA, is discharge from plastics factories. Vinyl chloride is also a byproduct of degradation of other complex chlorinated compounds such as cleaning agents and solvents. The source of the contaminant in Well No. 7 has not yet been determined. The City’s wellhead protection consultant, SEH Inc., reviewed potentially hazardous sites and ruled out all known contaminated sites in Edina within a one-mile radius of the well. In addition, Well No. 7 was televised to verify the integrity of the steel well casing pipe. No evidence of any structural failure or
damage of the pipe was found. The Minnesota Department of Health is currently analyzing data collected from wells in other communities.

The EPA standard of 2.0 ppb was established based on studies of exposure and lifetime risk, public health implications and the technical and economic feasibility of removing the substance from water, among other things. There is no direct evidence that concentrations at this level are harmful.

If vinyl chloride concentration in water sources is above 0.5 ppb, the regulation of vinyl chloride, which became effective in 1989, requires water providers to take samples at the well every three months for a year to determine if the contaminant continues to be present at that level. If it is, the provider must continue to monitor until levels are consistently below 0.5 ppb. In cases where the contaminant levels are above the MCL of 2.0 ppb, the provider must take steps to reduce the level below the MCL.

In 2002, as reported in last year’s Consumer Confidence Report, the average level of vinyl chloride in Well No. 7 was 2.3 ppb. Four quarterly samples are required to determine an average compliance value for this contaminant. Two more samples were collected by MDH in 2003 and levels of vinyl chloride exceeded the MCL. As a result, there is not a violation for this contaminant. Well No. 7 was shut down in early October 2003 and will not be turned on again until the contaminant can be treated.

Progressive Consulting Engineers has completed a feasibility study for treating Well No. 7 to reduce the levels of vinyl chloride. Because vinyl chloride is a highly volatile organic compound, it is easily removed by aeration. One alternative under consideration is a packed tower aeration in combination with granular activated carbon filtration. Cost of the project is approximately $900,000 and would take at least 18 months to complete. Other options include abandoning the well and drilling a new one or piping Well No. 7 with another well and building a treatment plant. Either of those projects would cost $1.5-$2.5 million.

The City’s regular odd-even sprinkling ordinance goes into effect May 1 to conserve water. Until Sept. 1, homes with even-numbered addresses may water their lawns on even-numbered dates. Homes with odd-numbered addresses may water on odd-numbered dates. Because Well No. 7 will not be in operation this summer, though, it is possible that further watering restrictions will be put into place if drought-like conditions are present.
 

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Map	Download the map showing the possible influence area of Well No. 7