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NL wastewater treatment plant to be expanded

Estimates reach $15.3 million, bids put off until May 21

NORTH LIBERTY– Even cities sometimes have to go with the flow.
Bids for North Liberty’s wastewater treatment facility expansion project were due May 7 and were expected to be considered at this week’s council meeting, but City Administrator Ryan Heiar told the council some potential contractors declined to bid because of several other large project bids due the same day.
Therefore, the bid deadline was changed to May 21.
“Our hope is that by delaying the bid two weeks, we’ll see more bidders on this project,” Heiar said. “May 21 is the new bid (due) date, pushing back the potential contract award date to May 26.”
It’s not an urgent situation. It is necessary to upgrade North Liberty’s wastewater treatment facility to meet the demands of an ever-growing population, but Heiar told the council on April 28 that the facility at its current size is keeping up. The state-of-the-art treatment plant is operated with a membrane bioreactor (MBR) system that results in the cleanest effluent possible. Completed in 2008, the existing plant was designed to treat about 1.7 million gallons of water per day based on estimated average use of 120 gallons per person, per day.
“Assuming the average resident uses 120 gallons per day, this plant would process waste for about 14,000 people,” Heiar said. “We’re obviously over that population mark, but we are able to treat waste without problems because folks are using much less than 120 gallons per day. In fact, (they are using) from 80 to 109 gallons per resident per day.”
In June 2013, a final report of a facilities study conducted by Fox Engineering indicated the City of North Liberty was fast approaching the population threshold its current sewer plant could handle. Fox recommended the existing plant be expanded in two additional phases to help distribute the cost over a broader population base, built to serve a population of about 22,000 in phase 1A. Since the population continues to grow so rapidly, engineers recommended both phase 1A and phase 2 be constructed right away.
“It made sense to go ahead and do phase 2; otherwise, as soon as we were done with this construction project, we’d be designing the next one,” Heiar said.
The plant’s addition will be designed with a capacity to treat 3.3 million gallons per day, commensurate with a population of about 27,000. If residents continue to use less than average estimates, as they have in recent years, Heiar said current data indicates it could even be possible to reach a population of 31,000 before additional capacity would be needed. According to another study completed by Fox Engineering in 2014, the City of Coralville will also hook up to North Liberty’s sewer lines as Coralville develops near North Liberty’s eastern boundary; an as-yet unofficial sharing arrangement that will be reciprocated by Coralville when North Liberty expands on its west side.
City council member Annie Pollack asked how the per-gallon treatment capacity translated to number of years between this and the next upgrade. Heiar said population trends were used in the 2013 Fox Engineering report, but it also depends on the amount of water individual residents use.
“We’ll look at the facility plan every few years to see if we are in line with those population projection levels and in terms of how much we are treating. It’s something we look at quite regularly,” said Heiar. “This project should last us a while; that’s why we went ahead and did phases 1A and 2. If the population slows down, we can push things back for a while. If it continues as it has been, we’ll be looking at something in the next decade.”
City council member Coleen Chipman said since the plant’s capacity and longevity is tied to water usage, educating the public on good water practices was still necessary.
“I still think conservation efforts will need to be directed toward people to educate them on water-saving toilets, showers, baths– all those things that take a lot of water– and how to conserve water so it ends up costing them less,” Chipman said.
The city council earmarked $15,3000 in the Fiscal Year 2016 budget toward the facility upgrade, to be repaid with revenue bonds. Staff also recommended the North Liberty City Council a 9 percent increase in sewer rates, to be applied to both the base rate and gallons used, in anticipation of the expansion. The council is expected to consider a proposed rate increase in June.