FRANKFORT, KY - A water tank truck equipped with high velocity sprayers kept a steady stream of water shooting onto the Frankfort parking lot pavement for minutes. Hundreds of gallons of water vanished as they hit the surface, with not a rivulet in sight. Then, on this hot Tuesday afternoon of May 26, government officials and representatives of the concrete industry, all in a line, watched as Frankfort Mayor Gippy Graham and Robbie Robertson, president of the Kentucky Ready-Mix Concrete Association, wielded a giant pair of scissors to cut a big red ribbon, opening the first Kentucky government pervious concrete parking lot.
Frankfort, like Lexington and nearly everywhere across the country, has problems with storm water run-off. The "first flush" from rainfall, or initial run-off, carries with it the biggest load of pollutants that have accumulated on parking lots, sidewalks and roads - anything from oil slicks to detergents to chemical spills - and in Frankfort, it gets quickly carried into the Kentucky River. Run-off can also lead to flooding, erosion and sewage overflow. The city of Frankfort, complying with mandates of the Environmental Protection Agency, is demonstrating the effectiveness of pervious concrete pavement to help with these water issues. The EPA has recognized the use of pervious concrete as a best management practice (BMP).
Eric Brooker, senior engineer with Frankfort's Department of Public Works, had looked for over two years to find this proving ground - a space for a parking lot to demonstrate and study the effectiveness of pervious concrete. The 10,000 square feet Brooker got to use is the parking lot for the Public Safety Building on Frankfort's West Second Street. It used to be a parking lot that had 100 percent water run-off. Now it has zero run-off.
The water percolates down through eight inches of permeable concrete - a pebbly mix of concrete with no sand and only enough cement dust to join the pebbles while leaving a network of voids through which water passes. Below that, the water falls through a foot of crushed rock, reaching the earth below where it's absorbed into the water table. This process puts the water into nature's filtration system. Dr. Kamyar Mahboub, professor with the U.K. Department of Civil Engineering, will direct a team of graduate students analyzing water quality from the parking lot. Two small wells have been established on the parking lot's perimeter. The wells will provide samples of water that have passed through the pervious concrete and the ground below.
"We'll also take samples from the storm-water run-off system and see how they compare," said Mahboub. Theoretically, because of soil filtration and microbial breakdown of organic pollutants, such as motor oil, the students should find the well water much cleaner than storm water run-off.
The site has become an attraction for engineers and architects. Brooker has hosted visits from a number of building industry professionals who wanted to see the lot and learn about it. David Banks, a Frankfort architect, watched the water demonstration on the lot and spoke with Dennis O'Connell of O'Neil Contracting, the company that had employees trained by KRMCA to start the project and help city employees learn the process.
"Water is one of the biggest causes of damage to structures, especially parking structures," said Banks. "Freezing water poses dangers to people and to structures." He's looking at a job in Frankfort to solve water problems at a parking garage where water is fed from the entrance apron down the drive into the parking garage. Looking down at the new parking lot surface, he mused, "Everything is going towards green, sustainable, renewable."
For construction projects that aim to attain the U.S. Green Building Council's LEED certification, the use of pervious concrete can gain credits. The parking lot demonstration is also an effort in public education, as required by the EPA Phase II program under the Clean Water Act. Large colorful signs posted on the site explain the project. One of the signs listed the names of all the city employees who worked on the project. "Realizing that they were doing something new - that we can do this to help have a cleaner river - and nobody else is doing it yet in Kentucky, they took more pride in the work," said Finely Messick, executive director of KRMCA, which worked with the project. KRMCA gave $15,000 to the city to support the project and provided assistance.
"You don't just put down pervious concrete," said Messick. "You have to test the soil first to see what its exfiltration rate is." He pointed to a double ring infiltrometer he had set on a tabletop. It's a lightweight circular device, not much bigger around than a basketball, that when inserted into the soil and filled with water enables a reading of the soil's water absorption rate. Because the soil test results showed it was permeable enough to absorb one inch of water per hour, Messick was able to determine how deep to lay the crushed rock and layer of permeable concrete.
Brooker said that this approach to water management represents a significant shift in perspective away from just managing the flow-rate of run-off water with ponds or detention basins and drainage pipes, to actually reducing the volume of run-off. The current higher pricing of permeable concrete paving can be offset by reduced costs for drainage systems.
Permeable concrete also is said to benefit trees in urban settings, providing more oxygen and water to root systems often stifled under impervious pavements. Mouhab said that UK's Civil Engineering Department has applied to the National Science Foundation for funding to test permeable concrete in downtown Lexington settings to see how trees respond.