Nature Nut: Are stormwater ponds financial time bombs?

Almost of us drive by at least one every day. Some of us live with them in our backyards. And in the future we all might be paying higher taxes to clean them up.

With close to 500 stormwater ponds found within the city limits, Rochester joins many other cities in having a potentially serious problem on their hands.

In response to state and federal water runoff regulations, stormwater ponds became the craze of city public works departments some 20 years ago and now dot the urban landscape. They are designed to trap sediments and pollutants to keep them from eventually flowing to the Gulf of Mexico.

In Minnesota, and probably many other parts of the country, one of the main pollutants found in these ponds is a group of compounds called polycyclic aromatic hydrocarbons or PAHs. Besides affecting fish and other aquatic organisms, many PAH compounds are classified as human carcinogens.

Pollution authorities have known for a long time that the main source of PAH pollution in stormwater ponds is from coal tar sealants like many of us have undoubtedly used on driveways over the years. The problem is that when these sealants wear down due to weathering and driving on them, they often end up in stormwater ponds or go directly to local rivers or streams.


Unfortunately these ponds have a limited lifespan, often said to be around 25 years. Even more unfortunate is the fact that at the end of that time many of the ponds could require something be done with the pollutants they have trapped. This may include removing and decontaminating the pond sediment, or possibly burying it.

A Minnesota Pollution Control Agency official recently noted that cleaning up pollution in just 10 percent of the stormwater ponds in the metro area alone might run over a billion dollars. The cost to clean up just one PAH-contaminated pond in Inver Grove Heights was estimated at $450,000.

The state has banned use of the coal tar sealants in state projects but has avoided a total statewide ban. Instead, MPCA officials have encouraged individual cities to ban the coal-tar sealants.

The city of Rochester has also banned use of the coal tar sealants on city projects in favor of other less-polluting options, including asphalt sealants. However, Rochester officials have been hesitant to pursue totally banning use of the coal tar-based sealants, a step many other cities in the state have taken. Rochester stormwater officials feel "Rochester will not be experiencing the significant disposal costs that the metro communities may be facing."

When asked why there wasn't a state ban on coal-tar sealants, an MPCA official indicated it was "brought up in the 2009 legislative session," but a more voluntary approach was adopted. This seems like an odd approach, allowing a product to be sold that may carry with it health risks, along with potentially billions of dollars in future clean-up costs. As with many other ways we shoot ourselves in the foot, this decision appears to be politically motivated.

Politics aside, homeowners and businesses contemplating applying blacktop sealant should make sure you won't be using a coal tar sealant, and let contractors or suppliers know why you won't.

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