We have learned a lot about coal tar sealer pollution over the last decade or so. We know that uncured and recently cured coal tar sealers continue to export toxins days and weeks after application. We know this affects fish, salamanders and other aquatic species. But one line of research that hasn’t been done is the transport of coal tar sealer to groundwater. However there is sound science to support that it can. Below are two ways when this can occur.
For groundwater contamination to happen from coal tar sealers, the right kind of geological formations would need to be present. If you live in an area that is susceptible to surface contaminants, then coal tar sealers could migrate into the groundwater. Unfortunately most of the country has the kind of aquifers where surface contamination can easily show up in the aquifer. This is referred to as an unconfined surface aquifer.
Uncured Coal Tar Sealant Wash-off and Spills
The main pollutant of concern in coal tar sealers are polycyclic aromatic hydrocarbons (PAHs). PAH’s are generally hydrophobic, which means they don’t dissolve in water well and greatly adhere to soil. However an uncured sealant is a water-based emulsion with coal tar, clay, water and a little sand mixed in. It is specifically designed to mix with water. The problem occurs when a rain happens just after the sealer is applied and before it dries. This rain-sealer mix will go wherever rainfall takes it: streams, ponds, or recharge. The chemistry of the matrix allows this to happen. It is just like the way dish soap cleans an oily pan: water alone doesn’t mix with the oil to rinse away, but soap is added because it can both mix with oil and water and when it does, the oil leaves your cookware.
How often does this happen? Here’s what one honest contractor said on a public message board:
By the middle of June, the rain was down to every other day, though still very unpredictable.
I wasted many days that wound up being dry, but were forecast with a 60% rain chance.
I had to redo 18 driveways throughout the course of the summer due to washoffs.
Normally that number is below 5 in an average season.
Was there a penalty for those 18 washoff events? No, as long as there are no fish kills, it is completely unregulated and happens all the time. Most contractors feel this is just the risk of doing business. Make your best guess on the weather and if you’re wrong, the worst that can happen is a re-seal. That washed off sealed can then go wherever the rain takes it–including groundwater.
Quinoline and Coal Tar Sealers
Based on the information presented in this draft screening assessment (of coal-tar based sealers), it is proposed that quinoline is entering or may be entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity. On the basis of the carcinogenicity of quinoline, for which there may be a probability of harm at any level of exposure, it is proposed that quinoline may be entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.
How much quinoline is being used? Let’s look at one county in Illinois that is has one of those kind of unconfined aquifers: McHenry County. Here the sealant use is about 1 gallon per person per year. The concentration of quinoline in wet coal tar sealer is 1,000 mg/kg or .1%. The density of coal tar sealer is about 12 pounds per gallons and McHenry has a population just over 300,000. This translates into about 2 tons of this specific toxic chemical found in coal tar sealers spread throughout the County annually. Add this to the 100,000 pounds of PAHs from coal tar sealers used throughout the County, this is just piling onto a really bad idea.
So in short there are two pathways to groundwater contamination from coal tar sealers: improper drying time and water-soluble constituents. While I wish we knew more, isn’t this enough?
