07-06-2020 Council Work Session Packet

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Feasibility Study Water Treatment Plant City of Lino Lakes, MN WSB Project No. 015822-000 Page 17 6. WATER TREATMENT OPTIONS 6.1 Current Water Treatment Capacity Needs The Year 2020 projected maximum day demand for the City of Lino Lakes is 4.95 MGD (see Section 4.3). Therefore, an initial treatment plant capacity of 4,125 gpm is needed to supply 4.95 MGD over a 20-hour period to account for the cycling of pumps and filter backwashing throughout the day. The plant should be designed, however, with adequate capacity to treat at least the Year 2040 projected maximum day demand of 7.24 MGD or 6,034 gallons per minute over a 20-hour period. A plant constructed near the City’s central well field with this capacity could initially treat Well Nos. 1, 3, 5, 6 and provide additional capacity to treat future Well Nos. 7 and 8 if needed. Well Nos. 2 and 4 could then be used as non-treated peaking wells during maximum day demands or as back-up wells if any of the treated wells need to be removed from service for maintenance. 6.2 Future Water Treatment Capacity Needs The plant should be designed to allow for a future plant expansion or additional treatment processes. Prior to Year 2040, the regional hydrogeology should be studied in detail to determine if an adequate number of future wells can be constructed within one mile of the plant to justify a plant expansion in the future, or if a new well field will need to be developed in another area of the City in addition to a second water treatment plant. The City’s ultimate development will require a total treatment capacity of 12.45 MGD, or 10,375 gpm, over a 20-hour period. Therefore, the original design of the plant should allow space on site to add approximately 5 MGD of additional treatment capacity for a future plant expansion. 6.3 Water Treatment Needs The City’s raw water system has high concentrations of manganese and iron that should be treated. Customers with water softeners should continue to soften their water to remove hardness as municipal water softening would likely double to cost of a treatment plant if softening was added as an additional treatment process. A conventional or biological filtration water treatment plant with greensand or silica sand filter media will effectively treat the high concentrations of manganese and iron in the City’s raw water. The water quality testing data for the emerging contaminants do not require any additional treatment processes at this time. Most organic chemicals, if detected in the future, can be treated with granular activated carbon filter media. Volatile organic compounds (VOCs) from petroleum products can be removed with aeration. Greensand filter media can remove radionuclides (radium, gross alpha, etc.) if this natural contaminant is detected in future wells. Arsenic should easily be removed with conventional or biological filtration if detected. Filter membranes such as reverse osmosis can also be installed downstream of conventional or biological filters to remove most contaminants that cannot be removed by a conventional gravity or biological water treatment plant. 6.4 Water Treatment Options The City’s water treatment needs described in the previous section can be achieved with either Conventional Gravity Filtration, Biological Gravity Filtration, or Pressure Filtration as described as follows.