Polycyclic Aromatic Hydrocarbons Released from Sealcoated Pavement--An Evaluation of the Source and Fate of PAHs in Stormwater Runoff

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Project Type: 
Research
Project Number: 
R/CE-138
Inception Date: 
2008
Completion Date: 
2010

Participants:

Tom Ballestero UNH - Department of Civil Engineering Principal Investigator
Alison Watts UNH - Stormwater Center Co-Principal Investigator

Students Involved:

Sean Mitchell UNH - Department of Civil Engineering
Abstract: 
This study determined that coal tar-based parking lot sealcoat is a significant source of polycyclic aromatic hydrocarbons (PAHs) in urban runoff.
 
In October 2007, sealcoat was applied to two separate areas of a University parking lot (Lots A and B). Stormwater runoff from these two sealcoated areas and an unsealed control lot (Lot C) was collected and monitored with automated samplers. Initial unfiltered runoff samples from the sealed lots contained 5,800ug/l total PAHs, and 640ug/l total PAHs in comparison to 1.45ug/l for the unsealed lot. Runoff PAH concentrations from the sealed lots decreased rapidly after the first month, then more slowly over the next two years, but remain higher than the PAH concentrations from the unsealed lot. The study found that over two years, approximately 30 times more PAHs were released in stormwater from the sealed parking lot surfaces than from the unsealed surface. PAH concentrations in swale sediments downstream of the coal-tar sealed lot increased from the background level of several ug/kg to over 90 ug/kg in the year after sealant was applied, which exceeds the NOAA Effects Range Median for sediments (44.7 mg/kg).
Objectives: 
The primary objective of this study was to determine if coal tar-based parking lot sealcoat is a significant source of polycyclic aromatic hydrocarbons (PAHs) in urban runoff to coastal waters. The study:
 
       Determined that using coal tar sealant increases the PAH concentration in stormwater runoff from parking lots.
 
       Determined that PAH concentrations in sediments in a stormwater swale decrease with distance from the outfall.
 
       Developed a mass balance to estimate the mass of PAHs released to the environment in stormwater from a sealcoated parking lot over a two year time span.
 
The results of this study have been disseminated to regulators and the public in the form of webinars, presentations and facts sheets intended to reduce the use of coal tar-based sealant, and to support regulations limiting its use..
Methodology: 

1. We will conduct a side-by-side comparison of PAHs released from three differently treated parking lots, one treated with coal tar-based sealant, one with asphalt-based sealant, and one unsealed.

2. PAH loads in stormwater and vapor emmissions will be measured, and sealcoat wear rates will be estimated from cores.

3. PAH removal rates will be assesed for five common stormwater treatment technologies.

4. We will develop and disseminate recommendations for the future use of coal tar-based sealants, and for the treatment of PAHs in stormwater.

Rationale: 

Sealcoat is applied to pavement to protect and enhance the appearance of the surface, but a recent study found that coal-tar based sealcoats contain up to 20% PAHs by weight. The proposed study will measure PAH concentrations in stormwater runoff from parking lots sealed with coal-tar and asphalt based sealcoat, will evaluate the effectiveness of common stormwater treatment technologies in removing PAHs from runoff, and will provide recommendations to planners and regulators about the future use of sealcoat.

Accomplishments: 

2013

UNH researchers engaging with sealcoat companies to encourage marketing environmentally friendly products
N.H. Sea Grant-funded research determined that stormwater samples collected from parking lots treated with coal tar-based sealcoat contained significantly higher polycyclic aromatic hydrocarbon (PAH) concentrations than those treated with asphalt-based sealcoat or those left unsealed. These results have contributed to nationwide research and dialogue about the impacts of coal-tar-based sealcoat, leading to proposed legislation calling for local, state and nationwide bans, and encouraging voluntary market reduction. In 2013, researchers engaged with local sealcoat applicators and buyers who were interested in improving their understanding of the study results in order to market more environmentally friendly products. This engagement is a step toward reducing PAHs in waterways while helping local sealcoat businesses remain profitable when they employ more sustainable and environmentally responsible practices.

2011

NHSG-Supported Research Leads to Proposed Legislation to Ban Coal Tar-Based Sealcoat
RELEVANCE: NHSG-funded research determined that stormwater samples collected from parking lots treated with coal tar-based sealcoat contained significantly higher polycyclic aromatic hydrocarbon (PAH) concentrations than those treated with asphalt-based sealcoat or those left unsealed.

RESPONSE: Researchers from the UNH Stormwater Center have added to national research and dialogue documenting the environmental and human health impacts of PAHs coming from coal tar sealcoat.

RESULTS: In addition to previous sealcoat bans in a few cities and states, the U.S. House of Representatives is now considering legislation that would call for a nationwide ban on coal tar sealcoat based in part on research conducted using NHSG funds. Researchers are supporting US EPA education and outreach to reduce coal tar-based sealant use, and are working with the local sealcoat companies to encourage voluntary reduction of coal tar sealcoat use.

RECAP: NHSG-funded research contributed to nationwide research and dialogue about the impacts of coal tar-based sealcoat, leading to proposed legislation calling for local, state and nationwide bans, and encouraging voluntary market reduction.

2010

PAHs in Environment Reduced by Coal Tar-based Sealcoat Bans
RELEVANCE: NHSG-funded research determined that stormwater samples collected from parking lots treated with coal-tar based sealcoat contained significantly higher polycyclic aromatic hydrocarbon (PAH) concentrations than those treated with asphalt-based sealcoat or those left unsealed. 

 

This study has generated considerable interest nationwide. Preliminary results are currently included in UNH Stormwater Center workshops, and have been presented at national conferences.

 

RESPONSE: Researchers discussed their findings in numerous workshops and conferences throughout the nation and worked with NHSG staff to produce a pamphlet explaining the potential impacts of sealcoat to homeowners.  

 

RESULTS: Sealcoat has been banned in Austin, Texas, Minneapolis/St. Paul, Minn., and the state of Washington, and several counties in Illinois and the state of Minnesota are considering banning sealcoat based in part on research conducted by the UNH Stormwater Center using NHSG funding.

 
RECAP: NHSG-funded research contributed to sealcoat bans in some areas of the country.

 

 

 
Dr. Watts has discussed these results with regulators in Minnesota, where several towns are considering banning coal tar sealant, primarily based on disposal costs associated with the disposal of PAH contaminated stormwater pond sediments.
 
In October 2008, representatives from the Pavement Coatings Technology Council (the principal organization representing sealcoat manufacturers) visited the UNH Stormwater Center to review and discuss the project, and Dr. Watts met with industry representatives and the USEPA Region 5 in Chicago in December 2008.
 
A press release issued by Sea Grant in April 2009 was taken up by numerous media, and Dr. Ballestero was interviewed on May 2, 2009 on "Greener Living with Dr. G" WTIC AM 1080.  He also presented this work at the 2010 ASCE-EWRI conference in Providence, RI.
 
Dr. Watts has discussed coal tar sealants with regulators in New England and the Mid-West who are interested in potentially restricting or banning the product.
 
A non-technical fact sheet is being developed for distribution to homeowners to encourage the use of alternative practices (e.g., not sealing surfaces, or using a more benign product).

2009

UNH Researchers Determine that Coal Tar-based Sealcoat is a Source of PAHs in Stormwater Runoff
RELEVANCE: Previous research demonstrated that coal tar-based sealcoats contain up to 20% PAHs by weight. In the environment, they attach to organic matter such as leaves and inorganic particles like silt and clay, from where they may be ingested by organisms or buried in sediments. PAHs do not easily break down and may persist in the environment for decades. If PAHs enter waterways, they can increase the contaminant burden of aquatic ecosystems and could become a human health issue for people who are regularly exposed to it.

RESPONSE: Researchers at the UNH Stormwater Center studied the impact of sealcoat PAHs on stormwater runoff. Portions of a parking lot were covered with coal tar-based sealcoat, while the remainder was left unsealed. The PAH concentration of the stormwater runoff was measured in the water draining from the sealcoated and unsealed parking lot sections, both before and after applications. In addition, waterway bed sediments were also sampled and tested for PAHs.

RESULTS: The sealcoat parking lots led to a rapid increase in PAH concentrations in the initial runoff up to 5,000 parts per billion (ppb), significantly higher than the 10 ppb levels considered as the background concentration from the unsealed lot. However, concentrations decreased after several rainstorms. The PAH concentrations in the sediments mirrored these trends; the concentrations immediately downstream of the coal tar-sealed lot increased by nearly two orders of magnitude within the first year.

RECAP: Researchers have determined that coal tar-based pavement sealcoat is a significant source of PAHs in the environment and are working with the EPA, the sealcoat industry and others to ameliorate the situation.

Publications

Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant

Journal Article

  • Watts, A., T. Ballestero, R. Roseen and J. Houle (2010). Polycyclic aromatic hydrocarbons in stormwater runoff from sealcoated pavements. Environmental Science & Technology 44(23):8849-8854, December 2010.
  • Mahler, B., P. Van Metre, J. Crane, A. Watts, M. Scoggins and E. Williams. Coal-tar-based pavement sealcoat and PAHs: implications for the environment, human health, and stormwater management. Environmental Science & Technology 46(6):3039-3045, March 2012.

Information Sheet

  • Thinking about sealcoating your driveway? Get the facts!

Webinar

  • Stormwater, coal-tar sealcoat, and polycyclic aromatic hydrocarbons (PAHs) - EPA's Stormwater Pollution Prevention Webinar Series. Presented June 14, 2012; available online.