THE BLAKE AT OAKLEIGH
POROUS ASPHALT PARKING LOT
The Blake in Charlottesville, a senior living and memory care facility atop historic Oakleigh, came to S.L. Williamson Co. in 2020 for a solution to their building complex and guest parking lots. The Blake site is located high on a hill off of busy Rio Road off of 29N with no storm water management opportunity and risk of run-off flooding onto a very busy roadway system. They preferred a parking system that would take place of other forms of storm management. The owners also desired an environmentally, cost-effective solution to their lots — and did not want concrete that looks stained and grimy over time. S.L. Williamson Co. put together a Porous Asphalt Pavement plan for The Blake that is working wonders.
Our solution for The Blake, porous asphalt surfaces that do not hold water, have very low risk of moisture-related damage, and excellent runoff control. Porous asphalt pavements provide excellent parking lots and roads (obviously one of our key decision makers in choosing porous asphalt for this job) as they tend not to exhibit cracking and pothole formation problems. The surface wears well. Porous asphalt has been proven to last for decades, even in extreme climates, making it extremely cost-effective, even in areas with many late season freeze-thaw cycles, like Virginia. Using the underlying stone bed to manage stormwater for adjacent impervious areas such as roofs and gutters provides even more benefits. It also eliminates the detention basin cost and ecological damage to the site.
This was also a cost-effective solution for The Blake, as porous pavement does typically cost more than conventional pavement; on a yard-by-yard basis, the asphalt cost is approximately the same as the cost of conventional asphalt. At times, the underlying stone bed can be more expensive than a conventional compacted sub-base, but this cost difference is generally offset by the significant reduction in stormwater pipes and inlets. Additionally, porous pavement “fit into” the topography of The Blake site, so there was less earthwork and no in-depth excavations. When the cost savings provided by eliminating the detention basin were considered, the porous pavement was an economically sound choice.
of porous asphalt
detention basin cost
damage to site
CHALLENGES AND THE SPECIAL NATURE OF
THE BLAKE POROUS ASPHALT PROJECT
To say we really did our homework on this project is an understatement. We knew we needed the design to include overflow drainage to remove excess stormwater. We knew protecting the pavement from uncontrolled runoff from adjacent areas was critical. Temporary stormwater controls needed to remain in place until the site was stabilized so that soil-laden stormwater didn’t wash onto the pavement, clogging the surface and filling the voids in the stone recharge bed. We knew we needed to limit the maximum slope of porous pavement surface, and that the bottom of the infiltration bed should be flat to maximize the infiltration area.
Most challenging was the fact that we needed to try to control construction of the site, according to our scheduling as it is very important that porous pavements be protected from sediment during and after the construction process.
With The Blake project, S.L Williamson Co. completed the largest Porous project of our company’s history to date at 1,400 tons. Though permeable paving materials have been in existence since the 1970’s, their implementation has been slow in Virginia. While the porous pavement sites that have been constructed in other areas of the U.S. have seen both successes and failures, the overwhelming majority have succeeded. The many benefits conferred by the successful installations include runoff control, aquifer recharge, reduction of drainage structures needed to comply with stormwater regulations, and increased skid resistance. Snow and ice also melt at a faster rate.
In one of the only evaluations completed by the Virginia Transportation Research Council of porous asphalt used at a VDOT Park & Ride facility in 2018, the author concluded “… infiltration rates slowed substantially over the monitoring period, the lot continued to function as a stormwater best management practice (BMP) with an average infiltration rate approximately 12 times the required minimum of 10 in/hr. The different maintenance protocols tested did not have an effect on the rate of infiltration decline, indicating the reduction in permeability is likely not the result of sedimentation. It is estimated that the lot, constructed in 2013, will continue to function as an effective stormwater BMP until at least 2025 and will cost less than $1,500 per year to maintain.” We believe this Green Paving sector is bound to grow in popularity and economic and environmental success in the coming years.