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HomeMy WebLinkAboutSW6210505_O&M 2_20210524Permit Number: (to be provided by DWQ) Drainage Area Number: Wet Detention Basin Operation and Maintenance Agreement I will keep a maintenance record on this BMP. This maintenance record will be kept in a log in a known set location. Any deficient BMP elements noted in the inspection will be corrected, repaired or replaced immediately. These deficiencies can affect the integrity of structures, safety of the public, and the removal efficiency of the BMP. The wet detention basin system is defined as the wet detention basin, pretreatment including forebays and the vegetated filter if one is provided. This system (check one): ❑ does ❑ does not incorporate a vegetated filter at the outlet. This system (check one): ❑ does ❑ does not incorporate pretreatment other than a forebay. Important maintenance procedures: — Immediately after the wet detention basin is established, the plants on the vegetated shelf and perimeter of the basin should be watered twice weekly if needed, until the plants become established (commonly six weeks). — No portion of the wet detention pond should be fertilized after the first initial fertilization that is required to establish the plants on the vegetated shelf. — Stable groundcover should be maintained in the drainage area to reduce the sediment load to the wet detention basin. — If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment through the emergency drain should be minimized to the maximum extent practical. — Once a year, a dam safety expert should inspect the embankment. After the wet detention pond is established, it should be inspected once a month and within 24 hours after every storm event greater than 1.0 inches (or 1.5 inches if in a Coastal County). Records of operation and maintenance should be kept in a known set location and must be available upon request. Inspection activities shall be performed as follows. Any problems that are found shall be repaired immediately. BMP element: Potentialproblem: How I will remediate theproblem: The entire BMP Trash/debris is present. Remove the trash/debris. The perimeter of the wet Areas of bare soil and/or Regrade the soil if necessary to detention basin erosive gullies have formed. remove the gully, and then plant a ground cover and water until it is established. Provide lime and a one-time fertilizer application. Vegetation is too short or too Maintain vegetation at a height of long. approximately six inches. Form SW401-Wet Detention Basin O&M-Rev.4 Page 1 of 4 Permit Number: (to be provided by DWQ) Drainage Area Number: BMP element: Potential problem: How I will remediate the problem: The inlet device: pipe or The pipe is clogged. Unclog the pipe. Dispose of the Swale sediment off -site. The pipe is cracked or Replace the pipe. otherwise damaged. Erosion is occurring in the Regrade the Swale if necessary to Swale. smooth it over and provide erosion control devices such as reinforced turf matting or riprap to avoid future problems with erosion. The forebay Sediment has accumulated to Search for the source of the a depth greater than the sediment and remedy the problem if original design depth for possible. Remove the sediment and sediment storage. dispose of it in a location where it will not cause impacts to streams or the BMP. Erosion has occurred. Provide additional erosion protection such as reinforced turf matting or riprap if needed to prevent future erosion problems. Weeds are present. Remove the weeds, preferably by hand. If pesticide is used, wipe it on the plants rather than spraying. The vegetated shelf Best professional practices Prune according to best professional show that pruning is needed practices to maintain optimal plant health. Plants are dead, diseased or Determine the source of the dying. problem: soils, hydrology, disease, etc. Remedy the problem and replace plants. Provide a one-time fertilizer application to establish the ground cover if a soil test indicates it is necessary. Weeds are present. Remove the weeds, preferably by hand. If pesticide is used, wipe it on the plants rather than spraying. The main treatment area Sediment has accumulated to Search for the source of the a depth greater than the sediment and remedy the problem if original design sediment possible. Remove the sediment and storage depth. dispose of it in a location where it will not cause impacts to streams or the BMP. Algal growth covers over Consult a professional to remove 50% of the area. and control the algal growth. Cattails, phragmites or other Remove the plants by wiping them invasive plants cover 50% of with pesticide (do not spray). the basin surface. Form SW401-Wet Detention Basin O&M-Rev.4 Page 2 Of 4 Permit Number: (to be provided by DWQ) Drainage Area Number: BMP element: Potential problem: How I will remediate the problem: The embankment Shrubs have started to grow Remove shrubs immediately. on the embankment. Evidence of muskrat or Use traps to remove muskrats and beaver activity is present. consult a professional to remove beavers. A tree has started to grow on Consult a dam safety specialist to the embankment. remove the tree. An annual inspection by an Make all needed repairs. appropriate professional shows that the embankment needs repair. (if applicable) The outlet device Clogging has occurred. Clean out the outlet device. Dispose of the sediment off -site. The outlet device is damaged Repair or replace the outlet device. The receiving water Erosion or other signs of Contact the local NC Division of damage have occurred at the Water Quality Regional Office, or outlet. the 401 Oversight Unit at 919-733- 1786. The measuring device used to determine the sediment elevation shall be such that it will give an accurate depth reading and not readily penetrate into accumulated sediments. When the permanent pool depth reads 7979:50 feet in the main pond, the sediment shall be removed. When the permanent pool depth reads 79.50 feet in the forebay, the sediment shall be removed. Sediment Removal Bottom BASIN DIAGRAM (fill in the blanks) Permanent Pool Elevation 85.50 79.00 Pe anen Pool - - - - - - - - - - - - - - - - - - Volume Sediment Removal Elevation 79.50 Volume 78.50 -ft Min. --------------------------------------------------- Sediment Bottom Elevation 78.50 1-ft r Storage Sedimei Storage FOREBAY MAIN POND Form SW401-Wet Detention Basin O&M-Rev.4 Page 3 of 4