Bioretention cells, also known as rain gardens, can be incorporated throughout your site to provide surface infiltration of stormwater runoff. Typical systems may include a grass buffer strip, sand bed, ponding area, organic or mulch layer, soil and plants. In many cases, the infiltration rate of the engineered soil in bioinfiltration systems exceeds the infiltration rate of the underlying soil. By adding storage underneath the bioretention system, you can shrink the footprint on the surface while maximizing annual infiltration and annual runoff reduction. This design practice can make bioinfiltration feasible for sites with marginal soils. Bioretention can be very space intensive – and if limited space is available, underground infiltration systems should be considered.