The Morton Arboretum replaced a former degraded retention pond and asphalt parking lot with a functioning wetland system and permeable parking lot. The project was the beginning of a 20-year capital improvement master plan, aimed at expanding facilities and sites to demonstrate sustainable design to visitors. All 850,000 annual visitors to the Arboretum pass through the high performance Unilock parking area to reach the Visitor Center. The permeable parking lot, the largest of its kind in the Midwest when it was installed, infiltrates and collects rainwater through a subsurface gravel bed, channels water through bioswales, and directs overflow through to a final cleansing via the wetland area within the restored lake system. The complete project site is certified by the Sustainable SITES Initiative.

When it was installed in 2004, the permeable pavement system had a higher upfront installation cost of $42 per sq yd, compared to $17 per sq yd for asphalt. However, the real costs of both systems accumulate with maintenance: Over a 50-year period, maintenance costs for an interlocking permeable concrete paver system are projected to be $45 per sq yd, compared to $80 per sq yd for asphalt. Based on these forecasted annual costs, year 23 is projected as the break-even point for the permeable pavement system.

Full Case Study from the Landscape Architecture Foundation.