City of Sevierville Intake
Sevierville Water Systems (SWS) proposes to construct a raw water treatment plant (WTP), associated intake and finished water line on McCroskey Island in Sevier County as a new primary source of potable water. The intake would be located at French Broad River Mile (FBRM) 27.5L about 5 miles below Douglas Dam. The finished water line would cross the island back channel at FBRM 27.1L. The WTP is proposed to consist of a firm capacity 12 million gallons per day (MGD) plant, utilizing state-of-the-art ultra-filtration membrane and control systems, coagulation to remove disinfection by product precursor organics and raw water pumping and transmission from the French Broad River to the WTP through approximately 1,600 feet of 36-inch diameter ductile iron pipe. The proposed intake line would be installed in phases over approximately 16 to 20 months. Intake installation would temporarily disturb approximately 1.3 acres of riverbed.
SWS currently provides water to its customers from its existing WTP, which withdraws raw water from the Middle Prong of the Little Pigeon River. The WTP does not have the hydraulic capacity to increase production at the existing WTP beyond 4 MGD, its current capacity. In addition, the raw water source is not reliable under low flow conditions. The existing WTP would be used as an alternative source and phased out in future years once this new source becomes available.
Construction techniques would vary depending upon the depth of water available for barge passage and flow rates in the Little Pigeon River and the French Broad River. Generally, in-stream construction would be accomplished using floating platforms (barges) or temporary riprap construction pads. There would be no sidecasting of excavated spoil material. Suitable excavated native material would be used as backfill to bed the piping and onshore as fill for the WTP. Excess spoil material would be placed and contained at an upland site above elevation 878.7 m sl. SWS would coordinate work phases with TVA’s River Operations, River Forecast staff so that controlled or reduced flow conditions from Douglas Dam can be achieved when some phases of construction are ongoing. See Sections 1.0, 1.1 and 1.1.2, in particular Sections 1.2, Project Changes, in the U.S. Army Corps of Engineers (USACE) EA for a more detailed description of the project proposal including the intake structure, anchoring method, dimensions and construction methods. Finished waterline construction is described in Section 1.1.2 of this document.
TVA analysis indicates that river flows would be adequate to meet the peak flow withdrawal rate of 12 MGD and still maintain the quality of the aquatic life in the river. To avoid aquatic biodiversity effects native mussels would be relocated from the direct impact area in the riverbed. Use of best management practices along with construction methods and river flow reduction will not likely adversely impacts federally listed snail darters in the river. Mitigation of adverse effects to an archaeological site on McCroskey Island has been addressed under a Memorandum of Agreement with the Tennessee State Historic Preservation Officer and other consulting parties pursuant to the regulations of the Advisory Council on Historic Preservation.
USACE, in cooperation with TVA, prepared an environmental assessment to consider the impacts of the agencies’ permit approvals. TVA’s action would be to approve the proposed water intake and WTP in the French Broad River floodplain under Section 26a of the TVA Act. The finished water line crossing is included in the “permit area” (project scope) and impacts are evaluated in the USACE EA. TVA approved the project and issued its Section 26a permit, dated February 4, 2004. SWS will abide by project conditions included in the USACE EA.
A copy of the USACE final EA, Statement of Findings and FONSI (referenced attachments) can be provided upon request. Write Stanford E. Davis, Tennessee Valley Authority, 400 W. Summit Hill Dr., WT 8C, Knoxville, TN 37902, or call him at 865-632-2915.
Comments, questions, or a request for a copy of the above information may also be sent via e-mail to Stanford E. Davis.