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5.5. SR 06-07-1993 ITEM 5.5. CONSULTING ENGINEERS Maier Stewart & Associates Inc. June 3, 1993 File: 230-151-80 Mr. Patrick Klaers City Administrator City of Elk River P.O. Box 490 13065 Orono Park.-way Elk River, Mn 55330-1800 RE: ELK RIVER WWTP EXPANSION: FEASIBILITY STUDY JOINT SEWAGE TREATMENT WITH OTSEGO DIGESTER REHABILITATION Dear Mr. Klaers: FEASffiILITY STUDY The feasibility study of the Elk River wastewater treatment plant expansion has been completed and a report will follow shortly. This report contains a "prudent and feasible alternatives" evaluation as requested by the Minnesota Pollution Control Agency (MPCA) who will determine whether less stringent effluent limitations can be granted. If the less stringent limitations can be granted, it could save the City approximately 1.5 million dollars of construction cost. In the meantime, we are proceeding with the design of the facilities that will not be affected by the MPCA's decision. JOINT SEWAGE TREATMENT WITH OTSEGO We also updated Otsego's costs assuming the response from the MPCA is negative. We feel this assumption is appropriate since the NPDES permit is renewed every five years. Even though the less stringent effluent limitations can be granted at this time, it does not guarantee that the same limitations will be granted in the future. Redesign and administration fees are added to Otsego's cost, recognizing that several months of discussion and negotiation would be involved once both cities become interested. If the sewer annexation were to be implemented, a significant amount of redesign work would be involved and the project schedule would be lengthened. The project delay will potentially impact the treatment plant operation since the plant has experienced some effluent quality problems earlier this year. A draft letter to Otsego (attached) has been prepared for your convenience to address these issues. 1959 SLOAN PLACE, SUITE 200, ST. PAUL, MINNESOTA 55117 612-774-6021 9800 SHELARD PARKWAY, SUITE 102, MINNEAPOLIS, MINNESOTA 55441 612-546..0432 · Equal Opportunity Employer Mr. Patrick Klaers June 3, 1993 Page Two In summary, Otsego should pay 1.5 million dollars for the construction and $2.00 per 1,000 gallons of sewage treated at Elk River. DIGESTER REHABILITATION A structural and mechanical inspection of the existing primary anaerobic digester was performed on May 17, 1993, following the digester cleaning. We were surprised to find that, after 15 years of service, the digester is still in good condition. To prolong the service life of the existing digester and to be operational with future WWTP expansions, we recommend the following remedial repairs. The interior inspection of the steel dome revealed several areas of total coating failure with approximately 15 % to 25 % steel plate section loss from corrosion Due to the highly corrosive environment inside the digester, these exposed areas of steel will continue to corrode at an accelerated rate causing potentially dangerous structural conditions throughout the dome if it is left unattended. It is recommended that the interior of the dome be completely sand blasted and recoated with a high build coal tar epoxy. The steel dome interior surface restoration work would cost approximately $9,000, but will extend the service life another 15-20 years. If such preventive repair is not implemented, it will eventually cost the City more than $120,000 for a new steel dome replacement. The reinforced concrete walls and floor slab are structurally sound. However, there are some areas with spalled and pitted concrete. The deterioration of the concrete will continue at a much slower and less damaging rate than that of the steel dome. We feel at this time that the recoating of the walls and floor slab are not critical to the future operation of the digester tank. It is recommended that future wall and floor inspections be scheduled with any future digester cleanings to monitor and evaluate it's performance uncoated. Although minor corrosion is also found on the interior piping, repair is not recommended at this time since it will be cheaper to replace it in the future than to sand blast and recoat it now. The existing interior piping appears sound and does not require replacement at the present time. The piping is either ductile iron pipe or cast iron pipe. An additional 15-year service life for these pipes can be expected. Other immediate rehabilitation needs include steel dome anchorage repair, a 6" pipe support, a new sewage gas pipe connection, and an additional 24-inch access manway, which will provide conformance with OSHA confined space entry requirements and additional ventilation during the interior surface preparation and coating, as shown in Table 1. The total cost for this work is estimated at $12,600. Since the digester interior was just thoroughly cleaned for inspection and is now clean enough for repair work, it is recommended to perform this repair work now to avoid another $18,000 digester cleaning cost to the City when the WWTP is expanded. It is our understanding that the digester can be temporarily out of service and repaired sometime during the next several months. Mr. Patrick Klaers June 3, 1993 Page Three Sketches and specifications for the rehabilitation will be prepared upon authorization. Please note that other rehabilitation work which does not require digester cleaning will be incorporated into the WWTP expansion project, such as a new sewage gas boiler, new sewage gas piping, new exterior wall cover, insulation and roof gutter system, and digester cover insulation. If you have any questions, please feel free to call me. Sincerely, MAIER STEWART & ASSOCIATES, INC. 18~ Bill Chang, P .E. BC:tp 151-0101.jun TABLE 1 - PROBABLE COST FOR THE DIGESTER REHABILITATION ELK RIVER W ASTEW A TER TREATMENT PLANT Maier Stewart & Associates, Inc. June 1993 Description A~ Sand Blast and Recoat the Interior of the Digester Steel Domel $ 9, 100 B. Digester Dome Anchorage Repair2 1 , 000 c. 6-inch Sludge Transfer Pipe Support 500 D. Sewage Gas Pipe Connection 500 E. 24-inch Access Manway 1 ~500 TOTAL $12,600 Notes: SSPC-SP6 commercial blast cleaning and 1 coat of coal tar epoxy. 2 Includes full penetration pressure grouting of approximately 5 LF of thermal related concrete cracking under two observed anchorage points. This also includes approximately 3 LF of seal welding the anchorage clips to the steel dome. The seal welds will eliminate water infiltration and prevent corrosive gases from escaping. June , 1993 Honorable Mayor and City Council Otsego City Hall 13474 NE 95th Street Otsego, MN 55330 RE: JOINT SEWAGE TREATMENT PLAN Dear Council Members: The City of Elk River has recently conducted a feasibility study for the expansion of the City 1 S wastewater treatment plant (WWTP). I would like to take this opportunity to share the results of this study with you. Since the City of Otsego has been interested in the concept of joint sewage treatment with Elk River, it is important for us to inform you of the high construction cost we are facing for the proposed expansion as a result of more stringent effluent limitations. OUf feasibility study has suggested that the existing WWTP be expanded to a 2.2 million gallon per day (MGD) capacity to handle the City's sewage flow in the next 20 years. A Trickling Filter/Solids Contact process is proposed for the new treatment system. Currently, Elk River WWTP effluent is discharging into the reach of the Mississippi River classified as an "Outstanding Resource Value Water1l (ORVW). The upgraded facilities have to provide sewage treatment to nearly tertiary effluent quality. Construction cost for an expansion project of this capacity would probably be about six million dollars. If the joint sewage treatment plan is implemented, the plant's capacity \\'ould be increased to 2.55 MGD and the construction would cost an additional one million dollars. Other costs include the sharing of existing facilities, metering and sampling of Otsego' s sewage, and redesign and administration fees as shown in the attached Exhibit. Total construction cost for Otsego would probably be $1,500,000 without taking into account the collection system and lift stations for sewage conveyance. The subsequent sewage treatment charge would probably be $2.00/1,000 gallons for the first year (1995) and would be subject to adjustment each year. Design of the WWTP expansion has begun due to the fact that the existing facilities appeared to reach the critical operational capacity earlier this year. All of our treatment units had to be operated in order to control the effluent quality. The joint plan will inevitably delay the project schedule and may potentially cause the existing plant to violate effluent standards. Therefore, we strongly recommend the City of Otsego to consider other sewage treatment options and reinvestigate the cost effectiveness of all options. The impact of project delay is hard to predict at the present time. We could evaluate it if Otsego is still interested in sharing our WWTP after investigating other options. In the meantime, we will continue to design our proposed expansion. If you have any questions, please feel free to contact me. Very truly yours, Patrick D. Klaers Clerk Administrator City of Elk River EXHIBIT EXPENSES FOR THE CITY OF OTSEGO WASTEWATER TREATMENT PLANT EXPANSION City of Elk River, Minnesota Maier Stewart & Associates, Inc. June 1993 Design Capacity, Million Gallons per Day (MGD) City of Elk River City of Otsego Total 2.20 0.35 2.55 Influent biochemical oxygen demand (BOD), mg/l total suspended solids (TSS), mg/l BOD, mg/l TSS, mg/l 2001 2251 10 12 Effluent Construction Cost for 2.2 MOD Expansion $6,000,000 $7,000,000 Construction Cost for 2.55 MGD Expansion Otsego I S Cost: A. Additional Construction Cost $1,000,000 B. Share of Existing Facilities ($1,500,000 x 0.35/2.55) $200,000 c. Metering and Sampling of Otsego 1 s Sewage $100,000 D. Redesign Fee $100,000 E. Administration Fee $100~OOO TOTAL2 $1,500,000 Estimated Annual O&M Cost in 19953 $2.00/1,000 gallon Probable Annual O&M Cost for Otsego $2.00 x 350 x 365 = $256,000 NOTES: Industrial wastewater with higher BOD and TSS concentrations should be pretreated to this level before entering the treatment plant. 2 Does not include the lift station and forcemain from Otsego to Elk River. 3 Actual annual O&M cost should be calculated and adjusted each .year based on the actual expenses and volume of wastewater received.