The “nasty nuisance” that has led to many a “rusty water phone call” in Mound is getting a more serious look now that the Minnesota Department of Health has set advisory limits for manganese and found elevated levels of the contaminant at each of Mound’s two municipal water wells.
Spot testing by MDH at each of the city’s wells in December revealed manganese levels between .45 mg per liter and .72 mg per liter. MDH has set advisory limits of .30 mg per liter for adults and .10 mg per liter for infants. Subsequent testing at the wells in January and February affirmed that the initial results were not an anomaly. The city has said it is notifying its residents directly of the health department’s findings.
Manganese found in drinking water at levels above the department’s health advisory limit do not pose an immediate threat, said Karla Peterson, supervisor of the Community Public Water Supply Unit at MDH, in an interview. But they could through prolonged exposure have detrimental health effects, particularly in infants, she said.
The testing done in Mound was part of a new course of testing MDH is pursuing. The department had updated its health guidance values for manganese in 2018 following changes made to the Environmental Protection Agency’s (EPA’s) rules on unregulated contaminants.
The EPA had tested some larger communities in the U.S. at the time it made those changes, and MDH’s Peterson said her department was now filling in the gaps by testing for manganese in cities throughout the state of Minnesota.
“It’s not a regulated contaminate but there are concerns about the health risk and so we’re going sort of beyond the Safe Drinking Water Act in working with these communities,” said Peterson.
The science behind manganese is not as well established as that behind other, regulated metals like lead and copper, for which Mound tests its wells annually and for which MDH has delineated clear guidelines for advisory and toxic limits, said Brian Simmons, city engineer for Mound.
Mound is also not alone in seeing its manganese levels register above the new MDH limits. Both Chaska and Waverly registered levels as Mound for at least one of their well sites, according to numbers provided by MDH. Chaska’s highest reading was .60 mg per liter while at least one well in Waverly registered levels of .76 mg per liter.
The levels found in Mound are also below that of other communities, like Montrose, where the highest reading at one of that city’s wells was 1.4 mg per liter or more than four times the advisory limit.
Peterson said that deeper wells are more likely to have high readings of manganese but that well depth is also a bit of a tradeoff since shallower wells are more susceptible to contaminates found in surface water.
Mound will be initiating a feasibility study for determining water treatment options now that council members sanctioned that action by unanimous vote. That report will balance, as city manager Eric Hoversten put it, “funding versus benefit, risk versus responsibility” of different treatment options. The report is expected to be completed in the next two months.
Barring any outside funding, treatment options could run the city anywhere from $150,000 for sequestering to $50 million for a water treatment plant, according to the city engineer’s estimates.
Neither of these options seemed especially likely, though. Simmons referred to a full treatment plant as the “Cadillac option,” too costly for the city and too burdensome for rate-payers who bear the brunt of it. Simmons also explained that the cheaper sequestering does not actually remove the manganese from the water, only the discoloration it causes, by altering how the metal oxidizes.
Manganese and iron—another unregulated contaminant—have behind the numerous “rusty water phone calls” the city receives for the way they can turn water a yellow-brown color, said Simmons. Sequestering would fix this but not the actual levels of the contaminants.
A more likely solution is the construction of a filtration system at each of the city’s wells. That option has an initial cost estimate of $12 million to $18 million. That would translate into a rate increase of $250-$275 per year or about $62-$69 per quarter for the typical Mound resident.
That might not be a happy prospect for the Mound residents who came out to Westonka PAC for council’s session March 9. The city already has one of the highest base rates in the area for its water as well as some of the highest usage rates, which city officials attribute to 15 years of investment in Mound’s water utility infrastructure.
But the city also isn’t dead-set on adding a filtration system or other kind of remedy at the source.
“The first step is the feasibility study and determining what the problem is, how bad the problem is, if it is very bad or whatever the case is and what our options are going forward,” said Mound Mayor Ray Salazar.
Apart from what the city can do at its wells, residents also have the option of remedying the problem themselves through use of a water softener or in-home filtration system.
“Is it more cost-effective for customers to make customer choices at the household level or for us to force a rate change into their household finances?” asked city manager Hoversten, who said the stakes are raised now that MDH has set health advisory limits. “All of that [decision making] requires a significant more amount of diligence and discipline because we’re talking about a health matter versus a nasty nuisance.”