MARYVILLE, Mo. — Representatives from HDR Engineering laid out their initial recommendations to overhaul the city’s drinking water systems Monday evening, leaving City Council members to begin the process of deciding whether, to pursue a new water treatment facility.
Commissioned this summer to analyze the water system from source to tap in the wake of increasing taste and odor issues in the drinking water, HDR’s recommendations — summarized during a presentation at Monday’s City Council meeting — contained no major surprises. The plans offered both short-term and long-term recommendations for the two areas that city officials have long said would require the most attention: the water treatment plant, and Mozingo Lake and its surrounding watershed area.
Causes of algae
Over the past three years, taste and odor issues have plagued the city’s drinking water more and more frequently, though it has always remained safe to drink.
The cause was pinpointed as cyanobacteria, or blue-green algae, which have continued to cause additional problems. Blue-green algae are typically caused by an overabundance of nutrients — particularly nitrogen and phosphorous — in runoff into a body of water, like the city’s source for drinking water, Mozingo Lake.
“This is a growing trend we’re seeing across the country right now, and it’s fairly complex because there’s several different things that are going on at the same time,” said Trent Stober, regulatory and financing specialist at HDR. “We’re starting to see some increased temperatures, which probably exacerbates some of the issues. Meanwhile, in some of these cases, we have shallower water, potentially sedimentation of the lake and so forth.”
That’s true of Mozingo Lake as well, Stober said.
“The interesting thing with reservoirs is that it’s very dynamic,” he said. “So here at Mozingo Lake, you’ve got a fairly young lake in general when we look across the state. It’s pretty large, but it’s relatively shallow, which I think is one of the issues that’s driving the issues that you have right now. And while it’s what we call ‘highly productive,’ meaning it has a lot of biological activity in it — which drives a great fishery — that becomes a challenge when you treat the water and deliver it to your customers.”
The biological activity has likely helped fuel algae growths that have increased in volume over the past few years, coinciding with increased incidences of taste and odor issues in drinking water.
“Back from when it was really beginning, there’s been a number of these algae — called blue-green algae — that are usually associated more with impacts to a lake,” Stober said. “We saw them in the early 2000s actually, but now there’s been a shift in the types of algae since like, maybe 2017, probably, into ones that are more problematic.”
According to data gathered by the city and presented by HDR on Monday, algae blooms in 2018 and 2019 had appeared on the lake during the late summer and early fall. But in late 2019, the August-October bump in algae was followed in the winter by an unprecedented spike in Pseudanabaena, a type of cyanobacteria, which triggered the closing of the lake in January 2020.
“This is not a typical algae cycle that you would see, given that that’s cold water — so that’s when your lake’s frozen over and you’ve got a major algal bloom happening,” said Aaron Robison, HDR project manager, at Monday’s meeting. “Now when I say it’s not typical, it does happen, but it’s not typically something you see in Missouri reservoirs.”
That algae died off by the spring, and was followed by the usual August bloom. Last month, city officials said a spike in levels of the compound geosmin was the cause of renewed taste and odor issues with drinking water. Robison said that the algae that formed in August contained geosmin, and as it died off, the geosmin was released into the lake.
“(The water treatment plant is) doing a good job of cutting it down, I mean, they’re really knocking down sometimes 90 percent of what that geosmin is, and that’s pretty impressive with the system that they have,” Robison said. “But, … as you all have experienced in person — I mean, it was bad in November and December. I was up here, I smelled it, but I didn’t have to live it like you all did.”
Although up to 90 percent of the geosmin is being removed by the existing powder activated carbon processes at the water treatment plant, humans are particularly sensitive to the taste of geosmin, which can be detected at levels as small as 10 nanograms per liter. This winter, the geosmin levels at Mozingo Lake peaked at more than 1,800 ng/L.
The best way to address those taste and odor issues, HDR said in its recommendations, is to try and eliminate the cause of the issues at the source — Mozingo Lake — and to introduce more effective methods to the water treatment process to catch anything that does come through.
Lake and watershed management
Although in general harmful algae blooms can be caused by nutrient runoff, especially nitrogen and phosphorous, the specific factors in play at Mozingo Lake haven’t been researched enough to provide a clear picture of exactly what’s happening inside the lake, which compounds are proving to be the most problematic and where they’re coming from.
“One of the things that, I think, right out of the gate we need to do is take a proactive approach to monitoring the lake and the watershed, and understanding what exactly is going on with different mechanisms,” Stober said.
Gathering more data, he said, will inform all the long-term goals for the lake and watershed as well. The city has already begun some initiatives in this area, like partnering with the U.S. Geological Survey last year to map the bottom of the lake, which will give some insight into sedimentation and composition.
Once more information becomes available, Stober said, they’ll have a better idea of how they can create a more targeted long-term plan on how to address watershed and lake management plans.
In the meantime, at HDR’s recommendation, the city planned to begin regular applications of algicide to parts of the lake to help inhibit the growth of troublesome algae in the first place. But a shipping issue caused the algicide to arrive to Maryville too late to be applied before the lake froze over. Once it warms up, the algicide can begin to be applied as part of the short-term algae mitigation strategy.
In the long term, Stober said HDR recommends focusing on working with landowners to change agricultural practices that could be leading to the high amounts of nutrient runoff, working to stabilize streams and channels that could be carrying excess nutrients and sediment into the lake, and possibly incorporating wetlands into the watershed to act as a natural sponge that would help to slow and collect some of the runoff before it reaches the lake.
“But for watershed management to be effective, we’ve got to get buy-in from the landowners and implement practices that make sense,” Stober said.
The city has already made some progress on that front, and has worked with federal and state agencies to dole out hundreds of thousands of dollars already in incentives to adjust some farming practices. City officials are coordinating with more than a dozen state and federal agencies and other organizations — including the USGS, the U.S. Department of Agriculture, the Missouri Department of Natural Resources and many more — to lay out options for watershed management plans and how to fund them.
After initially delaying them because of COVID-19, city officials, in collaboration with the Missouri Rural Water Association, plan to begin meetings soon with landowners in the watershed.
When Maryville’s water treatment plant was first constructed in 1956, the city was getting its water from the One Hundred and Two River — a practice that continued until after Mozingo Lake was formed in 1994. That means the current water treatment facility wasn’t designed to treat water from a lake. The two types of treatment plants are similar, Robison said, but can have some different characteristics.
It’s just one of the many ways in which the facility has shown its age, nearly 65 years after it first went into service.
“The treatment plant that you all have now only has one, really, tool in its toolbelt to deal with geosmin, and that’s powder activated carbon,” Robison said. “… That’s the only thing in that treatment process that can really help the taste and odor issues.”
But only so much can be added before it starts to harm water quality, and it can be hard on the water filtration membranes used at the plant as well. When geosmin levels spiked in December, the plant was using the maximum amount of PAC it could without crossing safety thresholds.
In the short-term, Robison said the top priority, in combination with the methods used at the lake itself, is finding a new way to help remove taste and odor issues through the treatment process. That will buy time to evaluate and implement long-term options.
HDR recommended installing granular activated carbon absorbers to the existing process, which Robison likened to carbon filters available for the home.
“This is … just a different type of carbon — it’s a little larger — and we’re recommending kind of a pellet-sized type carbon,” he said. “And what that does is it binds to and absorbs any of those taste and odor constituents as it flows past it.”
Robison said such a system would probably cost in the neighborhood of $1 million, including upgrades to existing infrastructure to accommodate the new equipment. He said the recommendation is to have the absorbers installed within six months in order to ensure they’re operational around the time when the algae blooms have typically started to spike in late summer. Coupled with algicide treatments to Mozingo Lake in the intervening months, the short-term strategy is designed to reduce the taste and odor issues as much as possible.
That combination would be the primary methods of improving the drinking water aesthetics while city officials work toward a long-term solution. Robison said that would give the city a window of about five to nine years — the estimated operational life of new filtration membranes installed last year — to plan and implement such a solution.
The long-term options, though, boil down to one issue: will the City Council, and city residents, be willing to spend tens of millions on a new water treatment facility?
City Manager Greg McDanel has said a new facility, which would likely be constructed on an available plot of land near Mozingo Lake, would cost between $26 million and $32 million.
HDR’s recommendations lay out two options: one for a new water treatment plant, and one for overhauling the existing facility.
“When we’re talking about modifying the existing plant for the long term, we had to compare that against building a new plant,” Robison said. “In order to do that, we had to get your existing plant up to a point where it can compare to a new plant — from the life expectancy of the infrastructure to the mechanical kit, everything — so that it’s more of a fair comparison. So we did a thorough, detailed analysis … of the entire facility — all the electrical gear, the structures — to come up with an idea of what it would take to bring that structure basically up to modern standards.”
The recommendations include overhauling the flocculation and sedimentation processes — where particles in the raw water are caused to clump together and then separated from the water through sedimentation — and installing the GAC absorbers, which are part of the short-term recommendation package as well. Additionally, HDR recommended adding redundancies to the existing systems to ensure that water treatment can continue if part of the process breaks down.
An additional challenge of overhauling the existing plant would be doing it while continuing to use the plant to treat the city’s water.
But if it’s affordable, the preferred recommendation from HDR is to construct a new, state-of-the-art water treatment plant that would last the city the next 50 years.
Such a plant would have added features that the current plant does not, including ozone filtration and biologically active filters.
“It’s really the best available technology for treating taste and odor, and it’s a tried and true, proven process,” Robison said.
In its summary, HDR estimated that a new plant would take about three years from preliminary design to completion, if everything goes smoothly. After a preliminary design phase, the methods to be used in the plant would need to be calibrated during pilot testing to determine what combination would work best for the city’s specific circumstance. Then the project would enter a final design phase, followed by a regulatory review. Only after that would the project be ready for bidding and construction.
Next, HDR will consider feedback from the council and assemble a final public report.
PWSD No. 1
After the presentation from HDR, the council passed a resolution stating its intent to collaborate with Nodaway County Public Water Supply District No. 1 on discussing options for water treatment, including the possibility of PWSD No. 1 providing some financing for any improvements made to the treatment facility.
The water supply district has purchased water from the city since 1972, and is the city’s largest water customer, buying more than 120 million gallons per year — nearly 30 percent of the water that leaves the plant, according to McDanel.
The resolution has no binding effect, but does indicate that the two bodies could discuss cost-sharing arrangements, including renegotiating the existing contract.
Other City Council notes
- Four candidates — Ashlee Hendrix, Dannen Merrill, John McBride and Tim Jackson — have filed for two open seats on the City Council and will appear on the April 6 ballot. The four will compete for the seats currently held by Jason McDowell and Matt Johnson, neither of whom are seeking re-election.
- The council approved the city’s participation in the annual Show Me Green Sales Tax holiday period from April 19-25. Consumers can purchase qualifying “Energy Star” appliances without applying state or city sales taxes.
- City Council members approved the purchase of the old MPS headquarters at 222 E. Third St. and an adjoining parking lot by the Maryville Elks Lodge for $185,000. In October, the Elks had initially bid $163,000 to purchase the properties, a bid the council rejected for being too far off from the third-party appraisal value of $205,000.