03-07-2022 Council Work Session Packet

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5.6 Miscellaneous Water Quality Parameters Other parameters that were monitored during this study included alkalinity, pH, water temperature, total organic carbon (TOC), and coliform bacteria. Water temperature and pH were tested on site while alkalinity, TOC, and coliform bacteria samples were shipped to a certified laboratory for testing. Alkalinity: Raw water alkalinity averaged 255 mg/L as CaCO3 during the pilot study. Biological filtration had minor impacts on alkalinity as the effluent concentrations were maintained around 250 mg/L as CaCO3 during the treatment performance phase. pH: Raw water pH averaged 7.0 SU during the pilot study. Effluent average pH concentrations for Filter 1 and Filter 2 were 7.2 SU and 7.3 SU, respectively. The slight increase in pH is due to the water being aerated. When water is aerated, it creates a turbulence which causes the dissolved carbon dioxide (CO2) and carbonic acid in the water to outgas. Outgasification of CO2 and carbonic acid from water results in pH increase. Effluent pH concentrations were maintained within the range set by the treatment goals. Water Temperature: Raw water temperature ranged from 50.2 OF to 53.4 OF and effluent water temperatures averaged 53.9 OF. Microorganisms thrive in warmer and stable environments and the lower water temperatures experienced during the winter months did not affect the performance of the biological filters. Water temperature increased in the pilot skid since the ambient temperature in the pilot trailer ranged between 50 IF and 60 IF on most days. TOC: The raw water TOC concentration averaged 2.6 mg/L during the study. Filter 1 and Filter 2 removed on average 14-percent and 16-percent of the influent TOC, respectively. Both removal performances are on par with results obtained in other biological filtration applications. TOC sampling was conducted both during the microbial acclimation and the treatment efficiency phases. Coliform Bacteria: Coliform bacteria were tested during both phases of the study. All laboratory results, both influent and effluent, returned absent E.Coli results. Total Trihalomethanes (TTHM): Organic carbon in groundwater is predominantly natural organic matter, which is typically derived from living or decayed vegetation. Natural organic matter can be present in particulate, dissolved, and colloidal forms, and it is usually assessed when TOC exists in the raw water. Disinfection byproducts (DBPs), which are suspected by the EPA to cause cancer, can form in the drinking water when natural organic matter is present along with chlorine. This occurs when chlorine is added to the drinking water for treatment. Higher chlorine doses and TOC concentrations will lead to more DBPs being formed. DBPs can be assessed based on the TTHM concentration in the water. The MDH waived the requirement to test for TTHMs during this study as historically, the TTHM concentrations in Lino Lakes raw water have ranged from 94-percent to 99-percent below EPA's MCL. The future TTHM concentrations in Lino Lakes are expected to be even lower if a water treatment plant is constructed as some of the TOC in the raw water will be removed at the treatment plant. In addition, the TTHMs should become even lower with biological filtration since prechlorination would not be used in the filtration process. 5.7 Filter Backwash Frequency Obstruction to water flowing through a filter increases as contaminants are removed from the water and accumulate in the media over time. This phenomenon is referred to as headloss through the filter. Headloss will eventually reach a point known as terminal headloss, at which time the filter must be backwashed. If a filter does not reach terminal headloss to initiate a backwash, weekly backwashes are still recommended to avoid channeling and breakthrough of contaminants. The terminal headloss was set to 120 inches. It is not uncommon for conventional water filtration facilities that treat groundwater to be backwashed every 2 to 3 days. On the contrary, biological filtration facilities tend to experience longer filter run times of 3 to 7 days. Usually, the main groundwater contaminant affecting headloss buildup is iron, and water treatment facilities with high raw water iron concentrations may have to backwash their filters as often as once per Water Treatment Pilot Study Report Biological Removal of Ammonia, Iron and Manganese at Well House No. 6 City of Lino Lakes, MN WSB Project No. 0 18601 -000 Page 11