10-03-07-JOINT PC/CC - Laserfiche WebLink

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Page 10 of 26 Permit No: NIN R 100001 4, The temporary (or permanent) basins must be constructed and made operational concurrent with the start of soil disturbance that is upgradient of the area and contributes runoff to the pond. Where the temporary sediment basin is not attainable due to site limitations, equivalent sediment controls such as smaller sediment basins, and/or sediment traps, silt fences, vegetative buffer strips, or any appropriate combination of measures are required for all down slope boundaries of the construction area and for those side slope boundaries deemed appropriate as dictated by individual site conditions. In determining whether installing a sediment basin is attainable, the Permittee must consider public safety and may consider factors such as site soils, slope, and available area on site. This determination must be documented in the SWPPP. C. PERMANENT STORM WATER MANAGEMENT SYSTEM All storm water must be discharged in a manner that does not cause nuisance conditions, erosion in receiving channels or on downslope properties, or inundation in wetlands causing a significant adverse impact to the wetlands. Where a project's ultimate development replaces vegetation and/or other pervious surfaces with one or more acres of cumulative impervious surface, a water quality volume of '/2 inch of runoff from the new impervious surfaces created by the project must be treated by one of the methods outlined in Part III.C.1 through Part III.C.5 prior to the runoff leaving the constriction site or entering surface waters (excluding drainage systems that convey storm water to a constructed permanent storm water management_ facility designed to treat the water quality volume from the project). For those areas of a project where there is no feasible way to meet the treatment requirement for the water quality volume, other treatment such as grassed swales, smaller ponds or grit chambers is required prior to discharge to surface waters. A cumulative maximum of (3) three acres or 1% of project size whichever is larger can be treated in this manner. Where the proximity to bedrock precludes the installation of any of the permanent storm water management practices outlined in Part III.C., other treatment, such as grassed swales, smaller ponds, or grit chambers, is required prior to discharge to surface waters. For work on road projects where the lack of right of way precludes the installation of any of the permanent storm water management practices outlined in Part II1.C., other treatment such as grassed swales, smaller ponds, or grit chambers, is required prior to discharge to surface waters. 1. Wet Sedimentation Basin a. The basin must have a permanent volume of 1800 cubic feet of storage below the outlet pipe for each acre that drains to the basin. The basin's permanent volume must reach a minimum depth of at least 3 feet and must have no depth greater than 10 feet. The basin must be configured such that scour or resuspension of solids is minimized. b. The basin's water quality volume is calculated as '/2 inch of runoff from the new impervious surfaces created by the project. c. Basin outlets shall be designed such that the water quality volume is discharged at no more than 5.66 cubic feet per second (cfs) per acre of surface area of the pond. wq-strm2-51