12/19/2001 Env Bd Packet - Laserfiche WebLink

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Infiltration Basins • Before the development site is graded, the area of infiltration basin should be roped off to prevent heavy equipment from compacting the underlying soils. • Light earth- moving equipment should be used to excavate the infiltration basin. Use of heavy equipment causes compaction of the soils beneath the basin floor and side slopes, resulting in reduced infiltration capacity. Since some compaction of soils will occur during construction, the basin floor should be tilled with a rotary tiller to restore infiltration rates after final grading. Maintenance Maintenance is required for the proper operation of infiltration basins, as it is with all BMPs. Plans for infiltra- tion basins should identify owners, parties responsible for maintenance, and an inspection and maintenance schedule. The use and regular maintenance of pretreatment BMPs will significantly minimize maintenance requirements for the basin. • Pretreatment devices associated with basins should be inspected and cleaned at least twice a year, and ideally every other month. • Once the basin has gone on -line, inspections should occur after every major storm for the first few months to ensure proper stabilization and function. Attention should be paid to how long water remains standing in the basin after a storm; standing water within the basin more than 72 hours after a storm indicates that the infiltra- tion capacity may have been overestimated. Factors responsible for clogging (such as upland sediment ero- sion and excessive compaction of soils) should be repaired immediately. Also, the newly established vegetation should be inspected several times to determine if any remedial actions (reseeding, irrigation, etc.) are necessary. • Thereafter, the infiltration basin should be inspected at least twice per year. Important items to check include: differential accumulation of sediment, erosion of the basin floor, condition of riprap and the health of the vegetation. Eroded or barren spots should be replanted immediately after inspection to prevent additional erosion and accumulation of sediment. • Sediment removal within the basin should be performed when the sediment is dry enough so that it is cracked and readily separates from the basin floor. This also prevents smearing of the basin floor. • Light equipment, which will not compact the underlying soil, should be used to remove the top layer of sediment. The remaining soil should be tilled and revegetated as soon as possible. • Vegetation should be maintained to control weed growth and maintain the health of the vegetation in the basin. Weed once monthly during the first two growing seasons. After that, weeding two or three times per growing season may suffice. Metropolitan Council / Barr Engineering Co. 3-167