Impervious surfaces are any surfaces that block infiltration of water into the soil. When it comes to humans, it’s our concrete and asphalt, rooftops, and even super compacted soil that create a barrier to infiltration. As impervious surfaces increase even a little, stormwater runoff increases dramatically. As runoff increases, groundwater reserves can become depleted and surface waters receiving the runoff become impaired. While the best way to address this is to reduce our impervious surfaces, that’s not always feasible. In the meantime, a variety of best management practices (BMPs) are used to treat stormwater runoff. The removal efficiencies, which is defined as the percent reduction of pollutant from the influent of the BMP to the effluent, vary depending on the type of BMP and the types of pollutants removed. On average, however, infiltration systems, which are the key components of LID & GI, remove more pollutants than any of the other BMPs evaluated in the cited report.