USGS Releases Studies on Hydrologic Characteristics of LID and Coal-Tar Sealants

Earlier this year, the U.S. Geological Survey (USGS) and the U.S. Environmental Protection Agency’s (EPA) Office of Research and Development released a report examining the hydrologic characteristics of low impact development (LID) stormwater control measures at two sites in northeastern Ohio. Limited long-term performance data exist for LID systems as stormwater controls. The purpose of this effort was to measure the response of LID to a broad range of precipitation and climate conditions and to understand changes in performance over time.

The report characterizes the performance of two stormwater controls along the Chagrin River watershed in Ohio by analyzing hydrologic data collected over 5 years, between 2008 and 2013. A residential site includes roadside bioswales and rain gardens used to alleviate drainage problems, and a second site, a small business development, includes a treatment train with a pervious paver system, rain garden, and bioswales. Data and local observations confirmed the continued success of the residential stormwater control at reducing flooding to prevent roadway closures. The treatment train at the business development, however, is exhibiting decreased functionality over time, with a reduced volume of runoff removed.

On April 13, USGS released two more stormwater studies, these related to coal-tar sealants. According to the studies, published in the journals Environmental Science and Technology and Science of the Total Environment, runoff from pavement with coal-tar-based sealant is toxic to aquatic life, damages DNA, and impairs DNA repair.

Rainwater runoff collected as long as 3 months after coal-tar-sealcoat application caused 100% mortality to minnows and water fleas, part of the base of the food chain, when exposed to ultra-violet radiation simulating sunlight. Exposure of fish cells to coal-tar sealant runoff damaged their DNA and impaired the ability of the cells to repair DNA damage.

Pavement sealant is a black liquid sprayed or painted on the asphalt pavement of parking lots, driveways, and playgrounds to improve appearance and protect the underlying asphalt. Pavement sealants that contain coal tar have extremely high levels of polycyclic aromatic hydrocarbons (PAHs). Coal tar is a known human carcinogen. Several PAHs are probable human carcinogens, and some are toxic to fish and other aquatic life.

A previous publication in the scientific journal Environmental Pollution detailed the chemical concentrations in runoff from coal-tar-sealed pavement at a range of times following sealant application.