Impervious Surface, as defined in Wellesley’s Zoning Bylaw, is “material covering the ground, including but not limited to macadam2, cement, concrete, pavement, and buildings, that does not allow surface water to penetrate into the soil.” This includes walkways, pools, and rooftops. The measurement of this surface is referred to as “impervious area” (IA). Cumulatively, more impervious area causes less groundwater infiltration and increased stormwater runoff (volume and rate of runoff) that is also more polluted and warmer. This harms our wetlands, streams, rivers, lakes, and ponds. See the short video The Impervious Problem on our website.
2Macadam: roadway or pavement constructed by compacting a layer of small broken stone along with a binder (as cement or asphalt).