Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

Runoff Treatment Control Measure Fact SheetInfiltration TrenchStep 3 – Calculate minimum surface area of infiltration trench bottom (A min )whereA min = WQV/D maxA min = minimum area required (ft 2 )D max= maximum allowable depth (ft)Step 4 – Design Observation WellProvide a vertical section of perforated PVC pipe, four (4) to six (6) inches in diameter, installed flushwith the top of the infiltration trench on a PVC footplate and with a locking, removable cap. Theobservation well is needed to monitor the infiltration rate in the infiltration trench and is useful formarking the location of the trench.Step 5 – Design BypassProvide for bypass or overflow of runoff volumes in excess of the WQV by means of a screened overflowpipe connected to the downstream storm drain system or a grated overflow outlet.Construction Considerations• If possible, stabilize the entire tributary area to the infiltration trench before construction begins.If this is not possible, divert flow around the trench site to protect it from sediment loads duringconstruction.• Once construction is complete, stabilize the entire tributary area to the trench before allowingrunoff to enter the trench facility.• Install filter fabric on sides, bottom, and one foot below the surface of the trench (see Figure IT-1). Provide generous overlap at all seams.• Store excavated material at least 10 feet from the trench to avoid backsliding and cave-ins.• Place clean, washed 1-3 inch gravel in the excavated trench in lifts and lightly compact it with aplate compactor. Using unwashed gravel can result in clogging.Long-Term MaintenanceThe local permitting agencies in the Sacramento and South Placer areas will require execution of amaintenance agreement or permit with the property owner for projects including an infiltration trench.Check with the local permitting agency about the timing for execution of the agreement. Such agreementswill typically include requirements such as those outlined in Table IT-2. The property owner or his/herdesignee will be responsible for compliance. See Appendix B for additional information aboutmaintenance requirements and sample agreement language.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsIT-4 May 2007