Lancaster officials want to update the city’s parking lot ordinance to require help control stormwater runoff.

The update, which must be approved by city council, is part of the city's ongoing efforts to reduce the amount of stormwater that ends up in the city’s sanitary sewer system. During heavy rains, the system overflows into the Conestoga River and ultimately the Chesapeake Bay.

City administration officials presented a draft of the proposed ordinance at Monday’s council committee meeting, noting that surface parking lots are a significant contributor to stormwater runoff.

Surface parking lots make up 32 percent of the city’s impervious surface.

The ordinance update would require using green infrastructure when reconstructing, resurfacing or repairing existing parking lots. The requirements would essentially kick in when more than 10 percent of the lot is being reconstructed or resurfaced; minor repairs such as patching potholes wouldn't trigger the requirements so long as they account for less than 240 square feet.

Green infrastructure methods would include using porous pavement or concrete that would allow water to drain through it to a stone reservoir underneath.

From the reservoir, the stormwater would gradually filter into the ground or into sewer system.

The proposed update also addresses landscaping and lighting, among other requirements.

Council is expected to give the proposed ordinance a first reading at its July 14 meeting.

Lancaster is under federal pressure to reduce stormwater runoff and is trying to avoid a potentially costly consent decree with the federal government that would dictate how the city handles stormwater.