Porous Concrete Surface for the Parking Lot

We will drill several test holes in the parking lot in early August to determine if we can specify in the construction documents that the building contractor repave the parking lot with a porous concrete surface.

The District of Columbia's building code requires us to contain water that would otherwise run off a roof or a parking lot into the storm sewers. This goal is also important as we try to meet an environmental standard.

Where will rainwater from the parking lot drain? One idea that our Design Building Team is exploring is a porous concrete surface for the parking lot, but we have to determine if this solution is feasible by testing to see if the soil under the existing parking lot is sufficiently permeable.

Several holes will be drilled in the parking lot at various levels into the subsoil to determine the infiltration rate. If it is not fast enough the District will require the construction of an underground chamber filled with with sand and gravel along with an overflow drain to the storm sewer. We will realize cost savings if surface water will infiltrate the soil.

Steve Goley, P.E., LSA Associates, contributed to this post.