"Fortunately, permeable paving materials allow stormwater to soak into the earth, where naturally occurring bacteria help digest contaminants before they reach the water table. Called pervious or porous pavement, these systems keep groundwater clean, help tree roots breathe, reduce the severity of flash-flooding and reduce the urban heat-island effect because they absorb water into the ecosystem and don’t reflect heat back into the environment."
Options for allowing seepage:
Porous Concrete Pavement is another great option. Here's a helpful site: http://www.perviouspavement.org/ And from that site: "Pervious concrete pavement systems provide a valuable stormwater management tool under the requirements of the EPA Storm Water Phase II Final Rule. Phase II regulations provide programs and practices to help control the amount of contaminants in our waterways. Impervious pavements-- particularly parking lots-- collect oil, anti-freeze, and other automobile fluids that can be washed into streams, lakes, and oceans when it rains."