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No.2—Infiltration Facilities Maintenance Defect Conditions When Maintenance Is Needed Results Expected When Component Maintenance Is Performed Piping Discernable water flow through a compacted Piping eliminated. Erosion structural berm. Ongoing erosion with potential potential resolved. for erosion to continue. Tree growth on a compacted structural berm over 4 feet in height may lead to piping through the berm which could lead to failure of the berm. Evidence of rodent holes in berm,and/or water piping through berm via rodent holes Note:A geotechnical engineer may be needed to inspect and evaluate condition and recommend repair of condition. Emergency Tree Growth Tree growth on emergency spillways creates Trees should be removed. Overflow Spillway blockage problems and may cause failure of the If root system is small(base berm due to uncontrolled overtopping. less than 4 inches)the root system may be left in place. Otherwise the roots should be removed and the berm restored. Note:A licensed civil engineer may be needed to determine proper berm/spillway restoration. Rock Armoring Rock layer on subgrade is less than 1.0 feet Rocks and pad depth are deep and/or subgrade is exposed restored to a minimum depth of 1.0 feet. Erosion Eroded damage over 2 inches deep where cause Slopes are stabilized using of damage is still present or where there is appropriate erosion control potential for continued erosion. measure(s);e.g.,rock reinforcement,planting of grass,compaction. Pre-settling Ponds Facility or sump The settling area or sump contains Sediment/debris is removed. and Vaults filled with Sediment sediment/debris up to a depth of either 6 inches and/or debris or the sedimentation design depth. January 2016 Snohomish County Drainage Manual Volume V-Runoff Treatment BMPs 27