WASHINGTON (AP) — The National Park Service is starting the second phase of a restoration project to allow grass to grow on the National Mall.

The agency says work is beginning between 7th and 12th streets. Grass panels and walkways across the mall will be closed to pedestrians in the area. The project is expected to last up to 18 months.

The turf restoration involves removing 4 to 5 inches of compacted and damaged soil. New irrigation drainage will be installed, along with a cistern to reuse storm water. Compaction-resistant soil will be installed similar to athletic fields, and new grass will be planted.

The park service says this will help sustain the mall as visitation is expected to increase from 25 million to 42 million annually in the next 20 years.

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