Module III
   
 
Lesson Seven: Structural BMPs
 
 

Infiltration systems

Infiltration systems consist of infiltration basins or infiltration trenches. Spill response procedures and controls should be implemented to prevent spills from reaching the infiltration systems.

An infiltration basin is a shallow impoundment that is designed to store stormwater temporarily then to remove pollutants in the stormwater through the natural filtering ability of the soil. The filtered stormwater will eventually reach the water table and recharge the groundwater. It will thus maintain low flows in stream systems. Infiltration basins perform better in well-drained permeable soils. It will have relatively higher failure rate due to clogging of the soil, if the soil of the basin has low permeability. Regular inspection and maintenance including removing debris and grass clippings, monitoring the health of vegetation, mowing the grass, and scraping the bottom and removing sediment will significantly enhance the performance of filtration basin systems.

Source: EPA image of Infiltration Basin

 

An infiltration trench is a long, narrow, rock-filled trench with no outlet that receives stormwater runoff. Runoff is stored in the void space between the stones and infiltrates through the bottom and into the soil. The removal efficiencies of infiltration trenches for both fine sediment and associated pollutants in stormwater are high. It is important to use pretreatment such as buffer strips, swales, or detention basins for an infiltration trench to reduce the amount of coarse sediment entering the trench and to prevent the clogging of the trench.

The removal efficiencies of infiltration systems for sediment, nutrients, trash, metals, bacteria, oil and grease, and organics are high. Click here to view the detailed data of removal efficiencies for infiltration systems.

      

Source: Metropolitan Washington Council of Governments, 1987.(EPA Infiltration Fact Sheet )

  A schematic of an infiltration trench (Source: MDE,2000)      
         
         
 
               
 
 

 

Copyright @ January,2005 Prepared by Transportation Environmental Resource Center (TERC)