08-22-2022 City Council Packet - Laserfiche WebLink

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WSB PROJECT EXPERIENCE EXAMPLE Biological Filtration Water Treatment Plant CLIENT: CITY OF ST. MARTIN LOCATION: ST. MARTIN, MN DURATION: 2017 The City of St. Martin, Minnesota had been operating its water system with two shallow wells (Wells 1 and 2), which had benzene levels above the maximum contaminant level (MCL). The wells were located near a creek that was the outfall of a wastewater treatment system and considered vulnerable to contamination. The geology of the area is underlain with a granite shelf, making it difficult to find sites with a sufficient yield within the city limits, so the city drilled two new wells to the east of the city. The current wells are considered non -vulnerable, in contrast to the shallow wells by the creek. However, high levels of iron and manganese in the ground continued to cause aesthetic concerns, especially with the staining of fixtures in people's homes. In addition, high levels of ammonia were present in the new wells, although not as high as they had been in the previous wells. The City explored its options with WSB, Tonka Water, the Minnesota Department of Health (MDH), and the US Department of Agriculture (USDA) Rural Development. During this period St. Martin was meeting with the USDA regarding its wastewater treatment system and found out that the rates that they qualified for, based on per - capita income, could be carried over to a water system. The city decided on biological treatment, using naturally occurring microorganisms instead of chemicals to remove contaminants. The city leased a trailer to do a biological filtration pilot study. City staff did the daily testing and pilot work with oversight by WSB and Tonka Water. The pilot study was performed for four months to verify that the innovative technology would work with the city's groundwater. Upon achieving successful results from the pilot study, the city authorized WSB to design and bid the first fully biological filtration water treatment plant in Minnesota. Construction of the plant was completed in the fall of 2017. The plant has three pressure filter vessels. The first vessel is a biological iron filter, which receives water after air (partially oxygen) is added to facilitate the biological oxidation of iron. Additional air is then injected prior to the second vessel. The second vessel is an ammonia nitrification filter, in which two reactions occur. The first reaction, the oxidation of ammonia to nitrite, is accomplished by nitrosomonas genus microorganisms. The second reaction is by the nitrobacter genus to convert the nitrite to nitrate. Oxidized manganese and any remaining biological matter are filtered with anthracite and green sand in the third vessel. After filtration, three chemicals are added: fluoride for dental care, chlorine for disinfection and to maintain a residual in the distribution system, and sodium silicate for corrosion control. The filters are backwashed with non -chlorinated water from a concrete backwash holding tank in order to not disrupt the bio-growth on the filter media. The total project cost was approximately $3M, which included the plant and related infrastructure. Approximately 45% of the project was funded with a grant and the rest from a 40-year loan at an annual interest rate of 1.875%, both from USDA Rural Development. KEY WSB STAFF: GREG JOHNSON, GREG GLUNZ A Proposal for Design, Bidding, and Construction Administration for a Water Treatment Plant for City of Lino Lakes Relative Experience, Qualifications, & References 27