In a natural watershed (with 0% impervious surface), ground water infiltration is 50%, but as development increases, impervious surface penetration decreases ranging from 42% infiltration—in low density development to areas—down to 15% infiltration in urban watersheds.

A great refresher video, provided here by The Watershed Institute, as how human activity and development impacts stormwater run-off: https://youtu.be/qmbw5qO9v74

Also, did you know that similar helpful environmental resources and planning tools are nicely organized and provided by ANJEC, the Association of New Jersey Environmental Commissions available at: http://www.anjec.org/ToolsResources.htm