New Wastewater Plant Underway …
The West Knox Utility District has experienced a continued accelerated growth of its sewer system and customer base in the last five (5) years. New developments and expansion of existing developments continue to be constructed throughout the boundaries of the Utility District. However in the last two (2) years, a noticeable increase has been seen throughout the District, but particularly on the west side of the Pellissippi Parkway.
The existing collection system has been extended to the west side of the Parkway, but the majority of the gravity sewer lines flow westward and require pumping the collected wastewater back to the east side of the parkway for transportation to the existing Karns wastewater treatment plant. Future developments in the western portions of WKUD boundaries will require new interceptor sewer lines and pump stations to collect and transport the wastewater back to the Karns treatment plant.
The WKUD management and engineering staff is concerned that the existing facilities of the sewer system (both collection system and treatment) may not be able to handle the expected flows within the next 5 to 10 years. GRW Engineers, Inc. was asked to study the future needs of the WKUD sewer system for the next 20 years and make recommendations to meet these needs.
The report evaluated past populations from Census data and looks at population projections available from planning offices for the WKUD area in the next 20 years. Wastewater flows from past years are used to determine a correlation with known populations and the number of customers to the sewer system. Future wastewater flows expected from the future projected populations are forecasted from this correlation. Evaluations of the projected flows versus the existing facilities are then used to determine future treatment plant or collection system facilities requirements. This includes possible expansion, upgrade or replacement of the treatment plant and/or parts of the collection system.
The existing Karns wastewater treatment plant is presently at about 88% of its design capacity. The current WKUD has on record requests for over 3,711 sewer services that will be needed within the next 2 to 3 years. The capacity of the Karns WWTP will be exceeded within this same period (about 2008). Projected growth of the district indicates flows of at approximately 9.0 MGD will be required by the year 2025. Providing sewer service for the projected growth will require the construction of a new wastewater treatment plant or the expansion of the existing Karns WWTP. The State has indicated in a letter that further expansion of this facility if allowed would have to overcome very significant obstacles. If an expansion was granted, nutrient removal, lower more stringent effluent (discharge) limits would be added to the NPDES permit requirements or the plant discharge would need to be moved to the Clinch River.
Expansion of the existing treatment plant to 9.0 MGD and continued discharge to Beaver Creek was determined to have a probable project cost of approximately $58,000,000 with no future ability for expansion due to the lack of land and the discharge stream. Moving the discharge of the Karns plant to the Clinch River requires discharge below all existing water treatment plant intakes; thus, a new discharge would need to be located at river mile 31.5 or below.
Moving the discharge point to the Clinch River would require the construction of an effluent pump station capable of handling the existing and future projected flows through 2025 at a cost of approximately $11,968,000 not including developmental costs (design, easements, inspection, etc). The additional treatment units necessary to treat the additional flow would also have to be built at a cost of about $5.50 per gallon if it pumped to the Clinch River. The construction cost of expanding the existing Karns WWTP another 5.0 MGD to meet the current and future needs to 2025 (9.0 MGD) would be approximately $27,500,000. Total probable project cost was estimated at approximately $47,362,000.
Based on current developments on the west side of the Pellissippi Parkway, the topography of the area, water treatment plant intakes on the Clinch River, new effluent limits and the need for sufficient land to make expansions, a new wastewater treatment plant should be located in the western portion of the district to handle the future growth.
The outfall from the new treatment plant would need to enter the Clinch River near the confluence of Hickory Creek. Large tracts of land are available in this area and should be investigated for possible purchase to construct a new WWTP. Additions to the collection system would be needed to transport the flow to the new plant. Future expansions of the I-3 collection system and treatment plant are possible at a new location. The existing Karns treatment plant has very little land available for future expansion past the current 10 year and possible 20 year needs.