A Photographic Method for Estimating Wear of Coal Tar Sealcoat from Parking Lots

Abstract

Coal-tar-based sealcoat has been recognized as an important source of PAHs to the environment through wear and transport via stormwater runoff. Sealcoat removal rates have not been measured or even estimated in the literature due to the complex array of physical and chemical process involved. A photographic study was conducted that incorporates all sources of wear using 10 coal tar-sealed parking lots in Austin, Texas, with sealcoat age ranging from 0 to 5 years. Randomly located photographs from each parking lot were analyzed digitally to quantify black sealed areas vs lighter colored unsealed areas at the pixel level. The results indicate that coal tar sealcoat wears off of the driving areas of parking lots at a rate of approximately 4.7% per year, and from the parking areas of the lots at a rate of approximately 1.4% per year. The overall annual loss of sealcoat was calculated at 2.4%. This results in an annual delivery to the environment of 0.51 g of PAHs per m2 of coal tar-sealed parking lot. These values provide a more robust and much higher estimate of loading of PAHs from coal tar sealcoated parking lots when compared to other available measures.

Coal-Tar-Based Pavement Sealcoat and PAHs: Implications for the Environment, Human Health, and Stormwater Management

“…Asphalt is the residue remaining after the distillation of crude oil and is the binder in asphalt-based sealcoat products. Although the two sealcoat product types are similar in appearance, PAH concentrations in coal-tar-based sealcoat are about 1000 times higher than those in asphalt-based sealcoat 11 (Table 1). …”

“…An estimated 85 million gallons (320 million liters) of coal-tar-based sealcoat are used annually in the United States. 11 …”

“…Tires and snowplows, in particular, abrade the friable sealcoat surface into fine particles. 5,11 The overall annual loss of sealcoat from parking lots in a warm climate is about 2.4% of total sealcoat applied, with wear being most rapid (about 5% per year) in driving areas. 11 Higher wear rates have been noted in a cold-weather climate.…”

“…5,11 The overall annual loss of sealcoat from parking lots in a warm climate is about 2.4% of total sealcoat applied, with wear being most rapid (about 5% per year) in driving areas. 11 Higher wear rates have been noted in a cold-weather climate. 7 The mobilized sealcoat particles and associated PAHs are transported to various environmental compartments (Figure 1, Table 1).…”

Potential contributions of asphalt and coal tar to black carbon quantification in urban dust, soils, and sediments

“…It is widely used as a binding material in the aluminum and graphite industries, and as a primary ingredient of sealcoats used in pavement and building applications. Once asphalt pavement and coal-tar-based sealcoat are applied to roads, parking lots, and driveways, they weather and break into particles as a result of exposure to sunlight, freeze-thaw cycles, and abrasion by vehicle traffic (Freemantle, 1999;Mahler et al, 2005;Scoggins et al, 2009). Runoff, wind, and vehicle tracking can transport sealcoat and pavement particles to other environmental compartments, including soils, other paved surfaces, streams, and lakes (Scoggins et al, 2009;Van Metre et al, 2009).…”