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❑ Design systems with permanent water sources such as wetlands, ponds, sumps, and basins to minimize mosquito habitat and plan for routine larval mosquito inspection and control activities with the assistance of a local mosquito control program. Stormwater Conveyance ❑ Provide proper grades along conveyance structures to ensure that water flows freely. ❑ Inspect on a routine basis to ensure the grade remains as designed and to remove accumulations of sediment, trash, and debris. ❑ Keep inlets free of accumulations of sediment, trash, and debris to prevent standing water from backing up on roadways and gutters. ❑ Design outfalls to prevent scour depressions that can hold standing water. Stormwater Storage and Infiltration Systems (Aboveground) ❑ Design structures so that they do not hold standing water for more than 96 hours to prevent mosquito development. Features to prevent or reduce the possibility of clogged discharge orifices (e.g., debris screens) should be incorporated into the design. The use of weep holes is not recommended due to rapid clogging. ❑ Provide a uniform grade between the inlets and outlets to ensure that all water is discharged in 96 hours or less. Routine inspection and maintenance are crucial to ensuring the grade remains as designed. ❑ Avoid the use of electric pumps. They are subject to failure and often require permanent-water sumps. Structures that do not require pumping should be favored over those that have this requirement. ❑ Avoid the use of loose rock rip-rap that may hold standing water. ❑ Design distribution pumping and containment basins with adequate slopes to drain fully. The design slope should take into consideration buildup of sediment between maintenance periods. Stormwater Structures with Permanent-Water Sumps or Basins (Belowground) ❑ Where possible, seal access holes (e.g., pick holes in manhole covers) to belowground structures designed to retain water in sumps or basins to minimize entry of adult mosquitoes. If using covers or screens, maximum allowable gaps of 1/16 inch (2 mm) will exclude entry of adult mosquitoes. Inspect barriers frequently and replace when needed. ❑ If the sump or basin is completely sealed against mosquitoes, with the exception of the inlet and outlet, the inlet and outlet should be completely submerged to reduce the available surface area of water for mosquitoes to lay eggs (female mosquitoes can fly through pipes). ❑ Where possible, design belowground sumps with the equipment necessary to allow for easy dewatering of the unit. 2