The 2006 prohibition on the use of coal-tar-based pavement sealants in Austin, Texas, has resulted in a substantial reduction in polycyclic aromatic hydrocarbon (PAH) levels, according to a new study published in the scientific journal Environmental Science and Technology by the U.S. Geological Survey (USGS).
PAHs are an environmental health concern because several are probable human carcinogens, and they are toxic to fish and other aquatic life. Pavement sealants containing coal tar have extremely high PAH levels compared to asphalt-based pavement sealants and other urban PAH sources, including vehicle emissions, used motor oil, and tire particles.
In 2006, Austin became the first jurisdiction in the U.S. to ban the use of coal-tar sealants. USGS scientists evaluated the effect of the ban on PAH concentrations in lake sediments by analyzing PAH trends in sediment cores and surficial bottom sediments collected in 1998, 2000, 2001, 2012, and 2014 from Lady Bird Lake, a reservoir on the Colorado River in central Austin. Average PAH concentrations in the lower part of the lake have declined 58% since the ban, reversing a 40-year upward trend.
A sediment core collected by the USGS from Lady Bird Lake in 1998 was part of a study of 40 lakes across the U.S. using chemical fingerprinting to determine that coal-tar sealants were, on average, the largest contributor of PAH to the lakes studied. Chemical fingerprinting of sediment collected for the new study indicates that coal-tar-based sealant continues to be the largest source of PAHs to Lady Bird Lake sediment, implying that PAH concentrations should continue to decrease as existing coal-tar-sealant stocks are depleted.
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New USGS Publication Overlooks Impact of Closed Power Plant
ALEXANDRIA, Virginia, June 17, 2014 – A newly released publication by U.S. Geological Survey (USGS) neglected to consider the impact of the now closed Holly Street Power Plant on Austin’s Lady Bird Lake. In trying to account for a decrease in PAH concentrations in Lady Bird Lake sediment, the USGS focused almost entirely on Austin’s 2006 ban on coal tar sealants and excluded from its analysis the closing of the Holly Street Power Plant in 2007.
A review of the history of the Holly Street Power Plant, as prepared by the City of Austin and readily available online, confirms that construction began in 1958 and operations started shortly thereafter in 1960. Lady Bird Lake was created “solely to provide cooling water for the Holly Street Power Plant.” According to the USGS, PAH concentrations in the Lake increased about 20-fold from 1959 to 1998. During these years, there were repeated fuel oil spills and fires with heavy smoke that contaminated the area and the nearby community. Oil spills and fires are well known sources of PAHs. Pressure from community activists and politicians forced closure of the Plant in 2007. The USGS acknowledges in its new publication that PAH levels in the lake sediment began to drop soon thereafter, but suggested that this was due to the Austin ban on coal tar sealants that coincidentally occurred at approximately the same time.
The USGS paper glosses over the common observation that PAHs in urban sediment nationwide have been decreasing for more than a decade, well before Austin banned coal tar sealants. A 2012 report by the City of Austin shows that the nationwide trend holds true in Austin sediments. Generally, the decrease has been attributed to improved vehicular and power plant emission controls, which have long been known to be a principal source of PAHs in urban environments. Regardless of the source, earlier publications by the USGS establish that the level of PAH contamination found in Lady Bird Lake sediment is well below any “probable effects concentration,” posing no threats to human health or the environment.
In support of its opinions about the source of PAHs, the USGS authors once again relied on modeling for PAH source identification – using the same model that has been repeatedly called into question and challenged in peer reviewed articles published by scientists outside the USGS. PavementCouncil.org has challenged the USGS on these and other related issues via three Information Act filings since May, 2013, available on the USGS web site. That process is still ongoing. For those interested in assessing the merits, limitations and flaws of the forensic modeling offered by the USGS, peer reviewed publications on this topic are listed at pavementcouncil.org.