BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

• Typically a dropinlet insert providesminimal capacity toretain suspendedsediment or debrisbefore maintenanceis needed.• Initial cost savingsfrom use of thisrelativelyinexpensive BMPmay be offset by thenumber of unitsrequired forprotection of a largedrainage system andthe costs associatedwith frequentmaintenance orreplacement ofmultiple units.Installation of a drop inlet insert for a commercialparking lot.DESIGN CONSIDERATIONSThe following describes three types of drop inlet inserts that may be applicablefor use.• Tray insert – consists of a series of trays, with the top tray serving as aninitial sediment trap. Underlying trays often contain filters composed of avariety of different types of media including polypropylene, porouspolymers, treated cellulose, and activated carbon.• Box insert – typically constructed of plastic or wire mesh with filteringmedia that fits directly into the box. Hydrocarbons are removed as thestormwater passes through the media. Trash, debris, and sediment remainsin the box as the stormwater flows through. Both tray and box type dropinlet inserts typically provide overflow features.• Sock insert –filter fabric (usually polypropylene) is either attached to a frameor directly to the drop inlet grate. Each of these options provides very littlestorage capacity and frequent maintenance may be required depending onthe quality of stormwater. Some models allow for sediment removal with avacuum truck, while others require physically removing the insert forcleaning.Chapter 4: BMP ToolkitTRPA BMP Handbook4.4.2.1-Drop Inlet Insert 2012Page 2