Coal Tar-based Sealcoat: Minnesota Local Government-FAQs
Coal tar-based pavement sealants have been found to be a significant source of contamination of storm water-pond sediments by polycyclic aromatic hydrocarbons (PAHs). This page provides answers to questions frequently asked by municipalities about management of contaminated sediments in stormwater collection systems that they own and operate.
What are PAHs?
PAHs (polycyclic aromatic hydrocarbons) are chemicals that occur naturally in coal, crude oil and gasoline, and are also present in products made from fossil fuels, such as coal-tar pitch, creosote and asphalt. PAHs also come from the burning of carbon and are present in the smoke of forest and grass fires, volcanoes, vehicle exhaust, cigarette smoke, and even in char-broiled foods.
PAHs are potentially toxic chemicals, of which some are listed in Minnesota as possible or probable carcinogens. PAHs are being discovered in concentrations of concern in the sediment of stormwater ponds across the state, primarily in urbanized areas.
What are the sources of PAHs in stormwater pond sediments?
The largest sources in Minnesota (based on current research and data) are coal tar-based sealants (60%), oil-based sources (15%), and vehicle emissions (13.5%). A wide variety of other combustion sources and natural sources make up the balance of the remaining 11.5%.
Are PAHs accumulating anyplace else besides stormwater ponds?
Yes. PAHs are accumulating in man-hole sumps, catch basins, rain gardens, ditches, underground treatment systems, street sweepings, and other parts of stormwater collection and conveyance systems where sediment accumulates. PAHs are also accumulating in the sediments of natural lakes, streams, rivers, and wetlands that receive untreated stormwater runoff.
How are PAH-contaminated sediments disposed of and what does it cost?
Disposal options depend on the concentration of PAHs in the sediment. Current standards and guidance provide two viable options for reuse or disposal. One option allows sediment to be placed as fill at an already contaminated industrial site. The Minnesota Pollution Control Agency (MPCA) does not have cost estimates for this option. The second option requires that contaminated sediment be disposed of as a solid waste at a Municipal Solid Waste (MSW) landfill that has an industrial solid waste management plan. This means contaminated sediment must go to a landfill that has a liner and a leachate collection system. Disposal costs for this option are determined by whether the sediment is being received as a daily cover material or a waste for disposal with other mixed municipal wastes. Neither option is sustainable at the expected volumes that will be generated in the coming decade.
Disposal costs include testing and laboratory analysis of the sediment to characterize the waste. Other costs include excavation, transportation, and tipping fees if those apply. Management costs vary based on the size and location of the excavation, volume of sediment being removed, and laboratory analysis. In some cases costs can be as much as $250,000 per pond when sediment removal projects include level 3 contamination. Anecdotal information provided by metro-area cities indicates typical costs range from $75,000 to $125,000 per pond when sediments need to be disposed of at an MSW facility. Projects costs to remove and manage uncontaminated sediment (level 1) are substantially less when transportation and disposal costs are not incurred.
A dredging cost equation was developed for the City of Minnetonka in 2009 as a way to estimate long term stormwater pond maintenance costs. The cost equation includes 30% for engineering and administration costs and 20% for contingencies. The equation was developed using 2009 dollars and volume is measured in acre-feet. It does not include landfill disposal costs if that applies.
Dredge Cost = 78,515*Volume^0.6727
In the seven-county Twin Cities metropolitan area there are an estimated 20,000 stormwater ponds. Conservative estimates suggest management costs in the billions of dollars for just these ponds. Most municipalities report they can’t afford the costs, so maintenance projects are currently being delayed. Possible negative impacts of delaying pond maintenance may include increased flooding, damage to public and private infrastructure, and pass-through of contamination to lakes, rivers, and wetlands as a result of stormwater retention systems not functioning properly.
Are coal tar-based sealers banned in Minnesota?
Not state-wide, but it is banned for state government use and in some cities. In May of 2009 the Minnesota Legislature restricted state agencies from purchasing coal tar sealants (2009 Session Laws, Chapter 172, and HF1231, sections 4, 26, and 28). The 2009 legislation restricts Minnesota state agencies from purchasing undiluted coal-tar sealant effective July 1, 2010. Some Minnesota cities are passing their own ordinances to ban the use of coal tar-based sealers, but these bans are confined to the jurisdiction of those municipalities.
What research has been done on this topic?
Research has been conducted by the MPCA as well as the Metropolitan Council, the U.S. Geological Survey (USGS), and the University of New Hampshire Stormwater Center. Studies have concluded that coal tar-based sealants are an important source of PAHs to urban waterways. MPCA research conducted on 15 metro-area stormwater ponds was consistent with the findings of a national USGS peer-reviewed study. The MPCA used environmental forensic techniques in the spring of 2011 to determine sources of PAHs to metro area stormwater pond sediments as shown in the following chart. The City of Austin, Texas is also conducting research on this topic and that information is available through a link on the MPCA web page.
A letter being circulated by the sealcoating industry says the MPCA has misrepresented scientific data. What is the MPCA's response?
Contractors and consultants for the sealcoating industry have used unpublished data in addition to an industry-sponsored study in Austin, Texas to try to discredit the research that shows coal tar-based sealants are an important source of PAHs to urban environments. The MPCA determined there are data-quality problems with some of the unpublished data used by the sealcoating industry and with their environmental forensic analysis. The MPCA also determined that the industry made inaccurate comparisons made between sediment data and stormwater runoff data in their analyses. The MPCA concluded that the industry’s conclusions are flawed and inaccurate, and the agency supports the findings of the research mentioned in the previous paragraph.
Where are coal tar-based sealers sold in Minnesota?
Most major retailers, local hardware stores, and commercial applicators have already started making the transition away from coal tar-based sealers to asphalt-based sealers. Coal tar-based sealants are (for the most part) already off the shelves of Minnesota retailers. Coal tar-based sealants are still in commerce with a minority of retailers and commercial applicators as well as a few Minnesota suppliers and manufacturers that services small hardware stores and commercial applicators that operate outside of metro-area municipalities that have enacted bans.
The sealcoat industry says PAHs are in food, medicines and shampoo, and that these exposures are a greater risk compared to contaminated sediment. The industry says the MPCA is presenting possible hazards as actual risks. Are PAHs really in food and shampoo?
Yes. However, the risks from food-derived sources of PAHs and medicinal uses of coal tar can not be compared fairly since these exposures are a matter of consumer choice. The choice to use a product containing coal tar as a treatment for a medical condition is weighed against the potential benefits of the exposure. Generally, medical treatments should be limited to those suffering a disease. Consumption of food containing PAHs (such as charcoal-grilled meat) is also a matter of choice. While food exposures may be the greatest exposure to PAHs for most people, typically carcinogenic PAH concentrations in contaminated sediment and soil are two or more orders of magnitude greater than carcinogenic PAH concentrations in food. Environmental exposures to PAHs can be significant for some people. Homeowners and business alike are encouraged to ask retailers and commercial applicators for products that are not coal tar-based.
Where can I go for more information about PAH contamination of stormwater sediment and coal tar-based sealant?
The most up-to-date information about the restriction of coal tar-based sealants in Minnesota is available on the MPCA Coal tar based sealants web page.