5.8. SR 12-20-2004 - Laserfiche WebLink

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the Pretreatment Building where it would discharge fi:om the channel into a 24-inch pipe directed to the flow splitter structure. PRIMARY CLARIFIER SPLITTER Flow to the two primary clarifiers is currently split at the existing grit tank, which is planned to be demolished. A new flow splitter must be constructed to facilitate flow between the two existing primary clarifiers and two future primary clarifiers. Pipes extending towards the future clarifiers would be plugged with a blind flange until they are needed. The primary clarifier splitter structure is proposed to be located at the site of the now abandoned rectangular primary clarifier. The splitter is to have a mixer installed that would aid in coagulation of phosphorus removal chemicals. Demolition of the abandoned structure would need to be completed prior to construction of the new splitter box. CHEMICAL PHOSPHORUS REMOVAL The MPCA has indicated that a phosphorus limit of 1.0 mgIL is anticipated. Elk River needs to be able to meet effluent phosphorus limitations to renew the discharge permit. Chemical phosphorus removal is reliable. Alum and ferric chloride are two chemicals that provide phosphorus removal and improve sludge settling. Feed lines would be installed into the new primary clarifier splitter and the secondary clarifier splitter for flexibility in controlling phosphorus and sludge settleability. A chemical building is proposed to the south of the splitter (Figure 1). Two 5,100-gallon tanks, housed within the chemical building, would provide storage for a two-week supply of alum or ferric chloride at future design conditions. Feed pumps, tubing, spill containment, and vent lines would be installed for chemical feeding and safety. PUMPS Grit Pumps The two existing grit pumps have been in service since 1975, and are due to be replaced. Existing pumps are flooded suction pumps located in the lower level of the northeast side of the Pretreatment Building. GTit pumps are sized to prevent settling of solids and clogging in the sludge line fi:om the grit chamber to the cyclone. Replacement with pumps sized to match the existing pumps is satisfactory. Both a duty pump and standby pump, each with a flow capacity of 200 GPM at 16 feet TDH, are recommended. Identical pumps are available for replacement !Tom Wemco. Gorman Rupp T -4 pumps, which have a flow capacity of 250 GPM, are another replacement option. Two type CT Series 6100 Morris pumps with a flow capacity of 200 GPM are an additional alternative. The isolation and check valves on each pump would also be replaced. Sump Pump The sump pump currently in the northeast comer of the Pretreatment Building would be replaced as needed. The 4-inch drainpipe, which is routed to drain into the end of the Parshall Flume, does not need to be changed. 8