Minimizing Environmental Impacts of Sealcoating

Missouri State University has decided to return to using refined coal tar-based sealant as part of the school’s parking lot maintenance program, according to an April 3, 2015, report in the Springfield News-Leader. Pavement Maintenance & Reconstruction Magazine readers might recall that use of tar-based sealant was a focus of attention in the City of Springfield, Missouri in 2009 and 2010. In reaction to misinformation spread by environmental alarmists, a few Springfield property owners began looking at pavement maintenance alternatives. MSU began testing different sealant formulations on their asphalt parking lots at its Springfield and nearby campuses. The News Leader described the results of MSU’s experiment as follows:

Application problems cited in West Plains and a large Springfield parking lot included settlement issues, equipment clogging, uneven application and spray pattern gaps. [A University official] said at the Glass Hall lot, the alternative was “very difficult to apply, the spray patterns were awkward at best and, as it rained, moisture seemed up and it was spotty.”

[The official] said the alternative is also more expensive, less effective at blocking water and lasts half as long. He said the coal tar emulsion, unlike the alternative, is resistant to ultraviolet, gas and oil.

A report summarizing the experiments was presented to MSU’s Board of Governors. At the Board March 18 meeting, the application procedure established by the Missouri Department of Conservation (MDC) to mitigate any environmental concerns was adopted by the University. According to the minutes of the MSU Board meeting, the MDC

…revised their coal tar emulsion installation method by requiring the contractor to have an absorbent boom material on hand ready for use should rain showers show up unexpectedly. Should rain occur during the installation process, the material would quickly be installed to filter any potential chemical runoff.

Contractors should always be aware of the weather forecast and not apply sealcoat if it’s likely to rain. But weather forecasts can be wrong. To minimize possible impacts if it does unexpectedly rain, following the MDC procedure of having absorbent boom material ready helps the contractor protect the environment.

Doing all you can to minimize potential environmental impacts helps protect not just the environment, but you and your customer. The common sense step of having absorbent boom material at hand helps mitigate the consequences of a wash-off event if rain unexpectedly happens during or too soon after application. Another service you can offer your customer to allay concerns about environmental impacts is to wash the newly-applied sealed surface shortly after the sealcoat cures, collecting the runoff from this first flush for proper treatment and disposal. Studies have shown that, at least for refined tar-based sealcoat, almost all of the PAHs that are going to be released are washed off in the first flush of rain (artificial or natural). Controlling the first flush effect by washing the parking lot shortly after sealcoat application and collecting the wash-off should go a long way to minimizing any potential environmental impacts.

 For more information about the Pavement Coatings Technology Council visit