Polycyclic aromatic hydrocarbons (PAHs) 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. They also come from burning carbon, forest and grass fires, vehicle exhaust, and even char-broiled foods. Some PAHs are listed in Minnesota as possible carcinogens. PAHs have been found in the sediment of stormwater ponds across the state, primarily in urbanized areas. Sixty-seven percent of the PAH contamination in stormwater-pond sediments comes from coal tar-based pavement sealants.
PAHs are also 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. They 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: The sediment may be used as fill at an already contaminated industrial site, or disposed of as solid waste at a municipal solid waste landfill that has a liner and a leachate collection system. The MPCA doesn't have cost estimates for the first option. The cost of the second option depends on whether the sediment is used as daily cover material by the landfill or is disposed of with other municipal wastes. Neither option is sustainable at the volumes that will likely 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 sediment contaminated above the industrial and commercial soil reference values. 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 municipal solid waste facility. Projects costs to remove and manage uncontaminated sediment (not regulated as a solid waste) are substantially less when transportation and disposal costs are limited and/or 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 15,000 stormwater ponds. Conservative estimates suggest management costs may be measured in the billions of dollars for just these ponds. Most municipalities report that 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.
- Do all driveway and parking lot sealers contain PAHs?
No. Acrylic sealers do not contain PAHs, but asphalt-based sealers do. However, coal tar-based sealcoat products have much higher concentrations (up to 1,000 times more) PAHs than the asphalt products.
- When a city “chip-seals” a road does the coating or sealer used in that process have PAHs?
Yes. Chip-sealing uses an asphalt-based emulsion product that contains trace amounts of PAHs, but not in sufficient concentrations to accumulate to problem levels.
- 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.
- How do I know if coal tar-based sealcoat was applied to a driveway or parking lot?
Laboratory analysis with an accredited lab experienced in testing for PAHs is the most accurate way of determining this. However, coal tar-based sealcoats typically have a strong mothball-like odor. Asphalt and acrylic sealcoats do not. In addition, officials in Austin, Texas, came up with an inexpensive alternative. Use a screwdriver or razor blade to scrape off a small amount of pavement sealant and place it in a glass vial filled with mineral spirits. Seal the vial, shake it, and allow it to sit for 30 minutes. If the liquid is dark and coffee-colored, the sealant likely is asphalt-based. If it looks like amber-colored tea and remains more clear, assume it's coal tar-based.
- Can cities or others responsible for operating and maintaining stormwater collection systems, require a responsible party to remove coal tar-based sealers if they have been applied after January 1, 2014?
Yes. Cities who have already enacted their own ordinance to restrict the use of coal tar-based sealcoats, or cities who enact an ordinance in order to exercise the enforcement authority of the 2013 state law (Minn. Stat. § 116.202) may require property owners to remove and properly dispose of coal tar-based sealcoat within the cities discretion and enforcement authority.
- Where can I dispose of unused or unusable coal tar-based sealcoat?
If you are a homeowner you may dispose of unused or unusable product, at your local household hazardous waste collection site. Contact your county for more information.
If you are a business and a Very Small Quantity Generator of hazardous waste:
- Does the state-wide ban apply to out of state commercial applicators under contract to apply coal tar-based sealcoat as part of a commercial or industrial operation and maintenance plan on properties in Minnesota?
Yes. The ban applies to companies outside Minnesota who may be under contract to maintain properties in Minnesota. Coal tar-based sealcoat may not be applied in Minnesota on or after January 1, 2014, unless specifically exempted by Minn. Stat. § 116.202