An Estimate of Coal Tar Sealant Wear Rates in Austin, TX

Parking lot sealant has been shown to be a major source of PAHs to the environment, yet yields predicted by a recent USGS/City of Austin study (0.2 % per year), do not match wear rates as observed by looking at parking lots around Austin, Texas, nor with the industry recommended re-application rate of every 3-5 years. A photographic study was conducted using 10 coal tar sealed parking lots in Austin with age ranges from 0-5 years old to estimate amount of sealant on lots of different ages. Amount worn off over time was then calculated using average sealant wear and the ages of the sealant application. Although this approach is very conservative and likely underestimates total loads of sealant leaving parking lots, the results suggest that sealant wears off of parking lots at a predictive rate of at least 2.4 % per year, with a mean annual loss from our study sites of 3.2%. These values provide a starting place for estimating best-case loading scenarios for PAHs from coal tar sealed parking lots