THE SOUTHAMPTON SOLAR PROJECT consists of solar arrays in six locations in Southampton County, VA, covering approximately 1,400 acres. Although the arrays are on separate parcels and are not contiguous, they are in the same general area of the county; the largest parcel, designated Pod A, covers 663 acres, and the smallest just 22.6 acres.
The parcels are graded only where necessary to meet slope requirements for solar array design standards. For sediment control, super silt fencing (SSF), a chain-link fencing with regular silt fencing material attached, is used, in combination with SSF and stone outlet check dams strategically placed at low areas in lieu of temporary sediment basins. The typical contributing drainage area to the SSF outlet is between 3 and 20 acres. The total linear footage of SSF on the project is approximately 31 miles.
In April 2017, the consultant engineer from Draper Aden Associates in Richmond, VA, requested the use of CRAFS Corrugated Retention and Filtration Systems for ease of installation and removal, in addition to its increased effectiveness compared to a traditional stone outlet. The Southampton County erosion and sediment control administrator approved the use of CRAFS. The product’s corrugated design provides more length and surface area of filter fabric than does conventional silt fence, as well as greater structural stability.
The length of the CRAFS units was determined based on a process similar to that used for the traditional stone outlet. The length is based on the outlet design for a temporary sediment trap in the Virginia Erosion and Sediment Control Handbook, using six times the contributing drainage area to the temporary sediment trap. Therefore, some CRAFS can reach 150 feet in length. CRAFS structures use standard metal T posts for vertical stability and anchoring the system to the ground, per the manufacturer’s recommendations. Because of the high volume of runoff and substantial amounts of sandy loam and clay material upstream of the CRAFS units on this project, the county’s ESC administrator recommended placement of 6 inches of #57 stone, at a minimum, atop the upstream and downstream aprons of each CRAFS structure to provide additional stability, as well as to reduce velocity of sediment-laden runoff.
Extensive grading and earthwork was required in Pod B, which covers 208 acres, to achieve the required design for the solar arrays. The earthwork revealed an extreme amount of clay material. An 8- to 10-foot-high flat plain area was created for the solar array, with a 1:5 slope to the CRAFS and SmartFence combination. SmartFence is a heavy-duty, structurally enhanced silt fence that eliminates the need for reinforced wire-fence backing. Both products performed well together during a recent nor’easter event across southeastern Virginia, preventing the clay material from leaving the site. In addition to cost savings and simplicity of installation, the CRAFS product demonstrated exceptional sediment retention and rapid filtration not offered by conventional stone outlets.
The general contractor for Dominion Energy’s solar array project is Signal Energy Constructors of Chattanooga, TN. The grading and SWPPP contractor is Sukut Construction of Santa Ana, CA, and the civil engineer consultant is Draper Aden.
