Tuesday, November 9, 2010

Concrete wastewater pollution in Madison

After I noticed concrete wastewater dumped at many construction sites around Madison, I decided to research the topic.  Here's what I found... so far.  Research in progress--your comments are welcome.


Concrete waste illegally dumped by Rawson Contractors close to Lake Monona at Lowell St. 11/7/10

Concrete wastewater is a white or grayish fluid.  It comes from washing equipment used to mix or deliver concrete.  It is often combined with a pile of leftover concrete.  You can spot it as a white stain--on pavement,  or on a prepared surface about to be paved.

"The wash water is alkaline and contains high levels of chromium, which can leach into the ground and contaminate groundwater.* It can also migrate to a storm drain, which can increase the pH of area waters and harm aquatic life. Solids that are improperly disposed of can clog storm drain pipes and cause flooding. Installing concrete washout facilities not only prevents pollution but also is a matter of good housekeeping at your construction site." Source

The "slurry" formed when a saw cuts concrete is just as bad as the wastewater--and must be treated with the same respect.

Concrete wastwater or slurry is supposed to be disposed of properly by placing it in a container called a concrete washout.

"Concrete washouts are used to contain concrete and liquids when the chutes of concrete mixers and hoppers of concrete pumps are rinsed out after delivery. The washout facilities consolidate solids for easier disposal and prevent runoff of liquids."  

Cement wastewater = toxic waste

"Lime is a major component of cement and is found in all concrete products. It dissolves in water to produce an alkaline solution that will burn and kill fish, insects and plants. Water that comes into contact with unset concrete or concrete dust quickly increases in alkalinity and will be highly toxic to aquatic life.

Concrete wastewater has a pH of 12 -13 and is as toxic as oven cleaner or bleach. The pH of freshwater is 6-7. Concrete wastewater causes burns in a similar way to a strong acid. A single bucket of concrete wastewater will easily kill hundreds of fish. Never allow concrete slurry or wastewater to enter the stormwater system."

"Sacking, felt cloth, weed mat, enviro-filters and hay bales do not reduce the high pH of concrete wastewater. The filtered water will still be toxic even though it looks clear."
 
Dilution is not the solution

"Never try to dilute concrete wastewater or slurry spills. It takes 25,000 gallons of fresh water to dilute a bucket of concrete wastewater to a neutral pH."
 
Can wastewater be dumped on the ground?

According to one source, it's OK to dump small amounts of concrete wastewater into small pits in the soil.  The one thing you should never do--they say--is dump it into the storm sewer.

However, I don't agree that it's OK to dump it on the ground.  For one thing, most of Madison is close to our lakes.  And in a heavily settled area, it doesn't make sense to dump toxic waste on top of your drinking water.  Eventually, it will get down to the wells.  Already Madison has lost several wells due to toxic waste, and it's VERY expensive to replace wells.

Even if the toxic waste never reaches the lakes or drinking water, it degrades and sterilizes the soil.  Soil is a rich ecosystem--and when healthy, it can break down much of the pollution passing through.  But concrete wastewater is so toxic that it can destroy this filtering effect of soil.  It makes no sense to destroy these "free public services" provided by the environment.

If concrete is toxic, does this mean we should stop using it?   No.  Concrete structures serve a purpose--and when they fail, they will be replaced.  But concrete dumped in the soil serves no purpose, and can never be economically removed.

Can concrete waste be dumped in the construction hole?


It's common for extra concrete to be dumped into the construction hole.  When the hole is backfilled, it's invisible.  At this construction site above by Parisi on Gilmore Street, 9/30, you can see excess concrete dumped on either side of the stormwater structure.  But this is just as harmful as dumping it on the surface, for the reasons given above.

Concrete pollution is common in Madison--photos

One of several large dumps by Speedway Sand & Gravel along Seoge Rd, 9/7/10.


S&L Underground & Trucking dumps concrete slurry from a saw onto N. Owen Dr, 11/10/10.

Tri-North Builders on State Street, 7/27/10.  Right next to a heavy pedestrian area. Concrete dust is harmful to eyes, and some people get an alergic reaction to it.

Several streaks of concrete wastewater dumped by Parisi Construction on Gilmore St, 10/24/10.

Pouring concrete in the rain??

You're kidding!  But it happens.  In the New Zealand manual, you're not supposed to pour concrete when rain if forecast...

Speedway Sand & Gravel smoothing fresh sidewalk on Edgewood Av. right next to L. Wingra.  During rain 7/7/10.

Concrete pollution--not on Wisconsin's radar

Google can reveal a lot about what's on the public's mind. And concrete wastewater is not on the public's radar in the US. Nothing about concrete wastewater turned up on the City's website. Very little turned up within the United States, except that EPA has a fact sheet on it. A very dull fact sheet, not designed to educate the public.

The only really good document I found on the subject was from the agency responsible for environmental protection for the capital of New Zealand. Why New Zealand?

It turns out that both New Zealand and Australia (similar countries) are ahead of the US in environmental concern. Everyone has heard about how rabbits were introduced to Australia, then swept across the continent, eating everything. Now the toxic cane toads are repeating that sad story. Australia--already a desert continent--is now experiencing a severe drought.

In new Zealand, vegetation was devastated by too many sheep, and too many introduced deer. Many species of native animals found only in New Zealand are going extinct. So these two countries have learned--the hard way--to respect the environment.

New Zealand's cities consistently rank among the most livable in the world.  So perhaps the "Kiwis" do have something we can learn from.


The bottom line

"If you or your business works with concrete, lime or other cement based products, then it is important that you ensure that no land or water pollution results from your activities."

"Remember: If you can't take the necessary steps to prevent pollution from your work..., you shouldn't be in the business."

 Comments on this article (Update Nov. 11)

Check on the reference to chromium. Try and find a material safety data sheet (MSDS) for cement. My guess is that chromium concentration depends on the source of the cement, and may not apply to what is used around here.

Washout from concrete trucks is hydrated lime (same as in the concrete) and when it drys, is no different from the concrete (without the aggregate).

Excess concrete and washout usually is buried under the soil layer during landscaping, and can properly be considered "fill."

Madison prohibits washout to streets or drains.

I think concrete wastewater would only be an issue if:

1) Washed out into a storm system or surface waters.
2) Washed our over porous soils close to the water table.


I see #1 regularly, so I suggest concentrating on that problem.

Posted by David Liebl
Faculty Associate
Dept. of Engineering Professional Development, UW
............................................................................

I haven't studied the issue of concrete wastewater much, but elevated alkalinity is probably a serious issue that is probably even more neglected than soil erosion. Thanks for highlighting it.


Posted by Doug Soldat
Assistant Professor, Turfgrass and Urban Soils
Department of Soil Science, University of Wisconsin-Madison

#     #     #
 
*  Concrete washwater contains Chromium VI, a known carcinogen and the same heavy metal which the Erin Brockovich movie focused on.

Material Safety Data Sheet for Portland Cement
EPA fact sheet about washout
Product for safely handling washout
Manual for handling washout, produced by the environmental agency for the capital of New Zealand.  All quotes above are from this manual.

A responsible contractor: Worker from D&M Concrete cleaning the gutter with a broom.
Click to enlarge.

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