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<br />K:\021336-000\Admin\Docs\Design Memos\MEMO Lino Lakes WTP Capacity Sensitivity Analysis.docx 178 E 9TH STREET | SUITE 200 | SAINT PAUL, MN | 55101 | 651.286.8450 | WSBENG.COM Technical Memorandum
<br />
<br />To: Michael Grochala, City of Lino Lakes
<br /> Diane Hankee, City of Lino Lakes
<br /> Justin Wiliams, City of Lino Lakes
<br />
<br />From: Jon Christensen, WSB
<br />
<br />Date: January 19, 2024
<br />
<br />Re: Water Treatment Plant (WTP)
<br /> City of Lino Lakes, MN
<br /> WSB Project No. 021336-000
<br />
<br />
<br />WSB is designing a gravity filtration water treatment plant (WTP) for the City of Lino Lakes that
<br />will be capable of operating either conventionally or biologically. Biological filters, where a
<br />microbial population is promoted in the filters to perform iron, manganese, and ammonia removal,
<br />can often be operated at a higher loading rate – thereby increasing the WTP capacity. Note that
<br />this capacity increase is only feasible under biological filtration, not conventional filtration.
<br />
<br />In this case, the biological WTP capacity could potentially increase from 6,000 gallons per minute
<br />(gpm) to 10,000 gpm with no changes to the filters. However, oversizing of other components of
<br />the WTP and the water distribution system would be needed to accommodate the higher flow
<br />rate. This technical memorandum summarizes those impacts, to inform a decision on whether or
<br />not to proceed with the changes.
<br />
<br />For context, the water demands and capacities considered in this memo are far in the future. The
<br />City’s existing maximum day demand is about 3,150 gpm (based on a 20-hour supply window
<br />instead of 24-hour to be conservative). The City’s projected 2040 max day demand is about 6,000
<br />gpm, and the ultimate max day demand is about 10,000 gpm. Therefore, the capacities
<br />contemplated in this memo are looking ahead to roughly a doubling and tripling of existing water
<br />demands, and the City’s Comprehensive Water Supply Plan will be revisited multiple times before
<br />these demands are realized.
<br />
<br />The baseline WTP sizing and potential WTP upsizing are summarized in Table 1 for comparison.
<br />The oversized components were limited to those considered absolutely necessary, and to allow
<br />for the modular addition of equipment wherever possible.
<br />
<br />Table 1 – WTP Sizing Comparison
<br />Component 6,000 gpm Sizing 10,000 gpm Sizing
<br />Wells 1, 3, 5, 6 = 5,275 gpm
<br />Future 7 = 1,000 gpm
<br />1, 3, 5, 6 = 5,275 gpm
<br />Fut. 7, 8, 9, 10, 11 = 5,000 gpm
<br />Aerators 2 x 11’ x 11’ 4 x 11’ x 11’
<br />Detention Tank 180,000 gal 180,000 gal
<br />Filters 6 x 15’ x 22’ 6 x 15’ x 22’
<br />Filter Loading Rate 3 gpm/ft2 5 gpm/ft2
<br />Clearwell 364,000 gal 364,000 gal
<br />Backwash Tank 230,000 gal 230,000 gal
<br />High Service Pumps* 3 x 3,333 gpm 4 x 3,333 gpm
<br />*High Service Pump (HSP) quantity is based on firm capacity with one pump out of service.
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