Maintenance Plan for Bioretention Facility and Drainage Channel

The purpose of this project is to provide a Maintenance Plan for an existing bioretention facility at the Central Virginia Community College (CVCC) campus (location shown as “Area C” on Sheet C3.00 of the accompanying plan). The Maintenance Plan is intended to restore the intended function of the bioretention facility. Specifically, the maintenance plan addresses the following: The forebay to the bioretention facility was designed and installed with an eight foot drop over a stone weir to the bioretention facility. The eight-foot drop has resulted in severe erosion over the steep slope and, as a result, deposited three to five inches of silt onto the bioretention filter surface, sealing the surface of the bioretention facility and preventing stormwater infiltration through the bioretention filter media. This plan addresses this issue with a "riser" structure provided in the forebay that instead pipes flows through a mild slope and discharges them to the bioretention surface. This maintenance modification prevents erosion on the steep slope and introduces flows to the bioretention at a low velocity, dissipated by stone. The maintenance plan also requires the removal of the silt on the filter surface that will regain the function of the facility as indicated from infiltration tests performed in a sample location where silt was removed. No equipment will be used on the bioretention filter surface. Accumulated silt shall be removed, by shovel or other hand tools, to the depth where the dark soil (existing bioretention soils media) is reached. Once reaching the bioretention soil mix, a concerted effort will be made not to remove the bioretention soil media. Once silt is removed, the surface of the filter will be raked to provide a level surface. The outfall from the bioretention facility (\earthen weir) was originally designed and constructed without any stabilization to the outfall channel which currently has about a 5' vertical drop into an existing channel (no stabilization in receiving channel appears to have been provided, as shown on the original design plan). The Maintenance Plan provides for stabilization and even distribution of flows using a bumper block for a weir and riprap stone to stop existing erosion. The bioretention facility’s receiving channel has severely eroded, head-cutting from the existing channel back toward the top of a steep slope. The existing channel drops about hirty vertical feet over about ninety feet and was supposed to be already armored by riprap per the original design plan, which appears to have never happened during original construction. The Maintenance Plan provides for armoring of the channel as shown on sheet C3.00. Consistent with original design plans, armoring is also provided in another location of active erosion as shown on Sheet C3.00 (Area ‘A’). Stairs are also provided as part of the Maintenance Plan to provide for access for long-term regular maintenance. The area of disturbance resulting from implementation of the Maintenance Plan is approximately 4,200 square feet (SF), exceeding the land disturbance threshold in Lynchburg for requiring an Erosion and Sediment Control (ESC) Plan (1,000 SF). However, the Maintenance Plan is exempt from Stormwater Management regulatory criteria since the inherent purpose of the plan is for immediate and long-term routine maintenance to preserve the original construction of the project. This narrative also provides basic computations demonstrating the post-activity condition will not result in changes to runoff characteristics. The Maintenance Plan ensures compliance with the Virginia Community College System (VCCS) Standards and Specifications for ESC and SWM during the maintenance activities with implementation of ESC measures, ESC maintenance and ESC inspections.

Division 31 -	Earthwork, Erosion and Sedimentation Controls.
Division 33 -	Utilities, Storm Drainage Utilities, Ponds and Reservoirs.