Asphalt Pavement: Water Pollution Risk?

Asphalt is a near-ubiquitous substance, found in roads, on roofs, and in driveways. With the growth of farms and cities, global water resources are stretched, and concerns have been raised about rainwater filtering through piles of asphalt and leaching toxins into groundwater. However, according to tests by University of Florida engineers, old asphalt scraped off roads does not bleed toxins into groundwater and is safe to use as construction fill.

Does Asphalt Pavement Pollute Water?

Experiments show that asphalt does not pollute groundwater

Experiments have been conducted to determine whether asphalt pollutes groundwater, and the results indicate that it does not. University of Florida engineers, including Tim Townsend and Allan Brantley, performed tests on old asphalt scraped off from roads, addressing concerns about piles of old asphalt releasing toxins into the environment. The researchers used material from two roads and four piles of asphalt across Florida, each containing material from multiple roads or surfaces. The water passed through the material was subjected to the Environmental Protection Agency's standard toxicity test, as well as tests simulating outdoor conditions for pavement piles. In the EPA test, the asphalt material was immersed in water-filled containers and stirred for several hours. The results showed that pollutants, including heavy metals, polynuclear aromatic hydrocarbons, and volatile organic compounds, were either not detected or present at levels below federal standards.

These findings suggest that reclaimed asphalt pavement (RAP) does not contribute to groundwater pollution and can be safely reused as construction fill. The tests were prompted by concerns about the environmental impact of asphalt plants and new federal regulations reducing the recycling of old asphalt into new roads. The results provide reassurance that asphalt does not pose a significant risk to groundwater quality.

However, it is important to note that some studies have identified the release of trace elements and heavy metals from recycled asphalt pavement into the environment. For example, batch experiments conducted on North-RAP and Central-RAP showed that they released levels of Pb (lead) exceeding the United States Environmental Protection Agency's (USEPA) primary drinking water maximum contaminant level (MCL) of 15 μg/L. Similarly, studies by Azizian et al. (2003), Chen et al. (2013), Kayhanian et al. (2009), and others have found the release of heavy metals and organic compounds from sealed and unsealed asphalt concrete pavements, parking lots, and roofing materials.

Despite these findings, the University of Florida researchers' experiments specifically focused on the potential leaching of toxins into groundwater from old asphalt. Their results indicate that asphalt does not contaminate groundwater, which is consistent with previous studies showing that soil layers beneath asphalt pavement systems can attenuate heavy metals and improve water quality. Therefore, while recycled asphalt may release trace elements and metals into the environment, the University of Florida's experiments provide evidence that asphalt does not pollute groundwater specifically.

Asphalt is one of the most recycled products in the US

Asphalt is a mixture of aggregates, binders, and fillers, and specific recycled waste materials can be used for these purposes. Recycled glass, pig manure, used rubber tires, slags, sand, and old roof shingles can all be used as aggregates in asphalt pavement. The use of recycled asphalt pavement helps to reduce greenhouse gas emissions, with an estimated reduction of 2.9 metric tons of carbon dioxide equivalent (CO2e) in 2019, comparable to the annual emissions of more than 600,000 passenger vehicles.

The recycling and reuse of asphalt are important for creating a more sustainable future. By recycling and reusing asphalt, we can reduce the demand for virgin materials, conserve resources, and save money. Asphalt can be recycled and reused in various ways, including hot and cold in-place recycling processes, and it can be used for asphalt paving, granular fill, and road base material.

While there have been concerns about the potential environmental impact of recycling asphalt, specifically regarding the leaching of heavy metals and organic compounds into groundwater, studies have shown that the levels of these pollutants are typically below federal standards or are attenuated by the soil layers beneath asphalt pavement systems. Overall, asphalt's unique engineering properties, cost-effectiveness, and sustainability make it a popular choice for road surfacing, and its recyclability contributes to its status as one of the most recycled products in the US.

Asphalt is safe to use as construction fill

Asphalt is one of the most recycled products in the US. Much of what constitutes "new" pavement is actually reused asphalt, with only 5-6% of the total production made from crude oil or petroleum products. It is so non-toxic that it is frequently used in fish hatcheries as a barrier to keep out contaminants from hazardous landfills. Asphalt does not dissolve in water, nor does it leach chemicals into the soil. Most of the contamination blamed on asphalt is the result of human carelessness, such as trash left in parking lots, gas and oil leaks from cars, and waste that is improperly disposed of.

Tests by University of Florida engineers have shown that old asphalt scraped off roads does not bleed toxins into groundwater and is safe to use as construction fill. Researchers Brantley and Tim Townsend, an assistant professor of environmental engineering sciences, used material from two roads and four piles of asphalt around the state, each containing material from several nearby roads or surfaces. The researchers subjected water passed through the material to the Environmental Protection Agency's standard toxicity test, as well as tests aimed at mimicking outdoor conditions for pavement piles. In the EPA test, the researchers immersed the material in water-filled containers, then stirred the contents with a machine for several hours. Pollutants including heavy metals, polynuclear aromatic hydrocarbons, and volatile organic compounds were found to be at levels below federal standards or were not detected.

However, it is important to note that recent studies have revealed the potential environmental risk of recycling or storing recycled materials or debris due to the release of trace elements such as heavy metals and organic compounds into groundwater and soil. In some cases, the levels of pollutants released were greater than the United States Environmental Protection Agency's (USEPA) primary drinking water maximum contaminant level. Therefore, it is recommended to determine the releasable levels of metals for reclaimed asphalt pavement (RAP) stockpiles before using them in acidic environments.

Asphalt is non-toxic and used in fish hatcheries

Asphalt is non-toxic and does not pollute groundwater. In fact, it is frequently used in fish hatcheries as a barrier to keep out contaminants from hazardous landfills. It is also used to line and/or cap hazardous waste sites, preventing rainwater from draining through the waste and keeping groundwater safe and clean.

Asphalt is one of the most recycled products in the US, with only 5-6% of new pavement made from crude oil or petroleum products. It is a tried-and-true road pavement material that has been used for over a hundred years in the United States and Europe. It is also used to waterproof structures due to its ability to keep areas impenetrable by water and other substances.

Contrary to popular belief, asphalt does not dissolve in water, nor does it leach chemicals into the soil. Most of the contamination blamed on asphalt is actually the result of human carelessness, such as trash left in parking lots, gas and oil leaks from cars, and improperly disposed-of waste.

While asphalt and its production have been blamed for contributing to increased greenhouse gases and global warming, these claims are largely unfounded. Asphalt carries the smallest carbon footprint of all paving types, and the paving industry has invested significant resources in developing and implementing new technologies to minimise its environmental impact.

In summary, asphalt is a safe and environmentally friendly product that is frequently recycled and used to protect groundwater and maintain clean water supplies.

Asphalt releases trace elements such as heavy metals and organic compounds into groundwater

While asphalt is a near-ubiquitous substance, its chemical emissions rarely figure into urban air quality management plans. Recent studies have revealed the potential environmental risk of recycling or storing recycled materials due to the release of trace elements into groundwater and soil. These trace elements include heavy metals such as cadmium, chromium, copper, nickel, lead, and zinc, as well as organic compounds like polycyclic aromatic hydrocarbons (PAHs).

The release of these pollutants occurs in various environments, including sealed and unsealed asphalt concrete pavements, parking lots, roofing materials, and agricultural soil near highways. Some state agencies have restricted the use of reclaimed asphalt pavement (RAP) materials in specific applications due to the potential toxic pollutants that might leach from them.

Experiments have been conducted to investigate the release of trace elements from RAP and their impact on groundwater. These experiments have shown that Mn and Ni are the primary trace elements leaching from some RAP samples, and these elements are largely attenuated by the soil layers beneath the asphalt pavement systems. This attenuation effect of soil on potential pollutants suggests that RAP can be safely used in non-acidic environments (pH ≥ 5).

However, it is important to note that certain RAP stockpiles may have inconsistent pollutant levels. As a precautionary measure, it is recommended to determine the releasable levels of metals in RAP stockpiles before using them in acidic environments. If the releasable levels of metals exceed drinking water standards, further investigation into the soil mineralogy and the time duration of the soil layer between the RAP and groundwater is necessary.

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