5.0. SR 04-24-1993 - Laserfiche WebLink

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774-6021 MAIER STEWART ASSOC. 123 P03 APR 21' 93 .. 15 : ~3 Mr. Klaers Apri119, 1993 Page 1Wo . As we discussed before, the U.S. Census predicted the population growth rate in the City of Elk River to be 3 to 5 percent annually until the Year 2000. The 2.2 MGD treatment capacity was estimated based on a 4 percent annual growth rate for the Year 2012 and the 3.0 MGD capacity was based on a 5 percent annual growth rate. We recommend the treatment plant be expanded to a 2.2 MGD capacity with the trickling filter/solids contact process. Construction cost for the proposed plant is about $5,335,000. Although the conventional activated sludge system has several advantages in its operational flexibility and reliability, the system is expensive and complicated to operate. The existing plant has experienced many operational problems and major equipment breakdowns with the RBC system. Similar problems have also been ~enced in many other RBC facilities in the country. New design parameters have been developed to try to avoid those problems. The construction cost for the RBC plant using those parameters turns out to not be cost effective. The trickling futer/solids contact (TF/SC) process has been very successful in many installations. Mr. Mack and MSA staff visited the Litchfield V4Stewater treatment plant this past February. The operators were all satisfied with the TF/SC process. Among the three processes studied, the TF/SC process is the most cost-effective alternative and the most preferred treatment process . as indicated by Mr. Mack. As shown in Exhibit 1, the construction cost difference between the 2.2 MGD and the 3.0 MGD plants is substantial. From the treatment process point of view, low sewage flows often create a detrimental effect in a large plant, particularly for the trickling f1lters where bacteria on the media may suffer from insufficient wetting and "food" due to a low flow. Current wastewater flow received at the treatment plant is about 0.57 MGD. Expanding the treatment capacity to 2.2 MGD would provide reasonable operation during the start-up of the new plant. Additional capacity can be added 15 or 20 years later if needed. If Otsego.s sewage were to be treated at the Elk River WWTP, the capacity of this expansion would need to be increased by 0.35 MGD (according to their consultant) to 2.55 MGD. In addition to the additional construction cost due to a larger capacity plant, Orsego would also be responsible for its sewage metering and sampling costs, as well as a share of the value of the existing facilities. It is estimated that, excluding the lift station and forcemain from Otsego to Elk River, the cost for the City of Otsego would be approximately $1,155,000 (as shown in Exhibit 2) which is significantly higher than what was estimated in Otsego's 1990 study report. Part of the reason is due to the more extensive treatment facilities being designed in Elk River to comply with a more stringent effluent limitation. Annual operation and maintenance (0 & M) cost to the City of Otsego is estimated at $1.40 per 1000 gallons of sewage treated based on 1988 cost accounting records. Future charges to Otsego should be calculated and adjusted each year from the actual expenses and volume of wastewater received. . l(l.lcnl_