Floodplain and Wetlands Involvement Notification for the Pond B Dam Repair Project at the Savannah River Site (SSR)

Pond B is one of the former production reactor cooling ponds on SRS, located near Aiken, South Carolina. Due to releases during the period of reactor operation, Pond B contains low levels of radionuclide contamination within the lakebed sediments and waters of the impoundment. The dam is an earthen embankment constructed in 1959-1960. Recent inspections of this structure by SRS engineers and the Federal Energy Regulatory Commission have found seepage conditions and erosion which threaten the stability of the dam. The DOE Savannah River Operations Office (SR) proposes to make repairs to the downstream slope and toe of the Pond B dam. These repairs would entail the following: (1) stripping of topsoil and vegetation on the face of the dam and at least a 50 to 100 foot area along the toe of the dam; (2) construction of a rock core underdrain system on the face of the dam and along the entire toe of the dam; (3) installation of weir boxes, piezometers, and lateral movement monitors; (4) and placement of an additional 30,000-50,000 cubic yards of previous material in the form of a soil blanket on the downstream face of the dam. The purpose of the proposed action is to increase the stability of the dam and reduce the risk of failure. The area of the floodplain and wetlands is dominated by an overstory of tulip tree (Lireodendron tulipifera) and red maple (Acer rubrum). A number of species are present in the understory, including tulip tree, red maple, red bay (Persea borbonia), and sweetgum (Liquidambar styraciflua). The herbaceous layer is dominated by maidencane (Panicum Hemitomon), sensitive fern (Onoclea sensibilis), and rush (Juncus spp.). Soils in this area are mapped as Fluvaquents and are listed for SRS as hydric soils. The wetland area below the dam is believed to have been natural wetlands prior to the construction of Pond B dam, although soil saturation is likely to have increased as a result of the man-made impoundment. Approximately 3 to 4 acres of wetlands would be impacted by the extension of the toe of the dam with the proposed placement of a soil blanket. During implementation of the proposed action, project activities that could take place in floodplain and wetland areas would include grading,

clearing of vegetation, and placement of fill materials. Some of these activities would require temporary construction access. A number of mitigation activities would be implemented to minimize potential impacts to the floodplain and wetland areas. Operation of construction equipment in the floodplain and wetland areas would be minimized. Depending upon the type of mechanized construction equipment to be employed, the use of platform support mats may be required to minimize the impacts to the wetland soils in the project area. Silt fences and other erosion control structures as needed would be installed to ensure there is no deposition in the downslope wetland areas. Best management practices would be employed during construction and maintenance activities associated with this proposed action. In accordance with DOE regulations for compliance with floodplain and wetland environmental review requirements (10 CFR 1022), DOE-SR will prepare a floodplain and wetlands assessment for this proposed DOE action. The assessment will be included in the environmental assessment (EA) being prepared for the proposed action in accordance with the requirements (EA) being prepared for the proposed action in accordance with the requirements of NEPA. A floodplain statement of findings will be included in any finding of no significant impact that is issued following the completion of the EA or may be issued separately.

Issued in Aiken, SC, on February 3, 1999. Lowell E. Tripp, Director, Engineering and Analysis Division, Savannah River Operations Office. [FR Doc. 99-3653 Filed 2-12-99; 8:45 am] BILLING CODE 6450-01-M