Coal Tar Sealants

Coal Tar & Runoff

Prevention of storm water runoff pollutants from contaminating San Antonio’s river and creek channels goes beyond proper disposal of hazardous commercial waste materials and runoff pollutant best management practices. Mitigation also begins at the level of construction and selection of building materials which come into direct contact with rainfall runoff.

The City of San Antonio identifies coal tar pavement sealant products used in the construction of paved commercial lots as emitting specific environmental/health-hazardous chemical components whose long-term exposure via storm water runoff conveyance has been scientifically linked to increased incidence of certain adverse health impacts in human beings and aquatic invertebrates (insects and other small creatures that live in stream and lakes who are are particularly susceptible to contamination). Invertebrates are an important part to the food chain and are often monitored as indicators of stream quality. Pavement construction product retailers, applicators and paved property owners are strongly urged to learn more about the use and environmental/health impacts of these products in order to make conscious decisions to help reduce and prevent their application during construction of new or rehabilitated paved lots.

Downloadable Handout (PDF): Coal Tar Pavement Sealants and Storm Water Runoff.

More information on coal tar pavement sealants, impacts and product alternatives can be found by accessing the information tabs below:

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Coal tar is a byproduct produced by the coking of carbonized coal. Coal-tar-based pavement sealants are chemically treated black-colored surface-coating finishes conventionally applied by asphalt pavement construction/rehabilitation companies through spray or paint tools on the paved surfaces of parking lots, driveways and playgrounds (not on public streets or rights-of-way). Sealcoat products are primarily applied in order to create a uniform hard coating on the porous surface of paved asphalt so as to improve appearance and seal out moisture and oxygen, both of which can degrade the underlying asphalt. Sealcoats have an average half-life of two to four years from the time of application. Sealant products are often used and marketed as solutions for beautifying pavement asphalt and increasing its resistance to gasoline, motor oil and kerosene.

Polycyclic Aromatic Hydrocarbons (PAHs) are groups of chemicals formed during the incomplete burning of coal/coal tar products and other organic substances. Coal tar pavement sealants emit PAHs as part of the sealant application process which subsequently remain on the pavement surfaces. Trace amounts of these residual chemicals can then be picked up and conveyed by rainfall runoff flowing over paved surfaces into river and creek channels during a rainstorm/flood event.

According to scientific data from a study conducted in San Antonio by the U.S. Geological Survey (USGS), the presence of PAH chemicals were detected most frequently in water samples extracted from Leon Creek and local San Antonio watersheds. Data from the study suggested that the largest source of PAH infiltration in local waterways came from coal-tar sealcoat dust emitted across paved parking lots. Data from the local study corresponds with larger data published by the U.S. Environmental Protection Agency (EPA) which suggests that concentrations of PAH chemicals measured in rainfall/liquid runoff flowing from coal-tar seal-coated parking lots were 65 times higher than comparative concentrations measured in runoff flowing from unsealed parking lots.

More information on USGS Research on PAHs and Coal Tar Pavement Sealants: http://tx.usgs.gov/sealcoat.html

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Exposure to PAH chemicals through contact with contaminated water, soil or debris can inflict potentially long-term adverse health effects depending on the length, type and extent of exposure. Although PAH exposure will not necessarily result in adverse health effects, the following effects have been documented:

  • Increased incidence/risk of developing cancer (when exposed to high concentrations of PAHs over lengthy periods of time).
  • Increased incidence of skin irritation and rashes (when skin is directly exposed to high concentrations of PAHs).
  • Increased incidence/risk of developmental and reproductive effects (documented in laboratory animals exposed to high concentrations of PAHs).

PAH chemicals can adversely impact health and survivability of native wildlife species when exposed to high concentrations over time:

  • PAHs are toxic to mammals, birds, fish, amphibians, invertebrates and plants.
  • Invertebrate species that reside in bottom sediment where PAHs accumulate can potentially suffer higher rates of decreased reproduction and population shrinking.

Pavement construction contractors, sealcoat applicators and property owners have safer alternatives to coal tar pavement sealants which can help reduce and mitigate the presence of Polycyclic Aromatic Hydrocarbons (PAHs) as a carcinogenic storm water runoff pollutant:

  • Asphalt-based sealants: asphalt-based sealcoat products offer negligible PAH levels (about 1/1000th the PAH level of coal tar sealcoats) and offer faster drying of coating finishes with no risk of skin irritation. Asphalt sealcoat products also do not stain pavement surfaces as coal tar-based sealcoat products can.
  • Asphalt sealcoat emulsions are comparably priced to coal tar sealants and will still provide a black appearance for 1-2 years and can provide surface protection for 2-4 years if properly applied.
  • New construction can include creating parking lots with surfaces other than asphalt, such as concrete or permeable pavement. The upfront costs for installing concrete are higher than those for installing asphalt parking lots. Long term maintenance is likely lower, since concrete parking lots do not require sealants and have a longer lifespan. Pervious pavement, including interlocking pavers and permeable concrete, are alternative to concrete and asphalt that reduce storm water runoff and pollution.

About Remember the River

Remember the River is a community campaign focused on nonpoint source pollution prevention outreach and education. The campaign is led by the City of San Antonio.

All campaign education and outreach efforts are conducted in compliance with educational/outreach guidelines established under a TPDES Phase I Municipal Separate Storm Sewer System (MS4) discharge permit regulated by the Texas Commission on Environmental Quality.

Contact Us

Darlene Dorsey 210.207.1011

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Mailing Address:
P.O. Box 839966
San Antonio, TX 78283-3966