Concrete Wash-Out is Getting Easier...
In the U.S., almost 340 million cubic yards of ready-mixed concrete is used each year. From a stormwater pollution and waste perspective, that results in nearly 300 million gallons of washwater and 2.5 million CY of concrete washout waste.
The estimated annual 34 million truck loads of ready-mix each generate approximately 1/16 CY of concrete material left on the chutes and use about 7 gal of washwater used to clean the chutes! Besides the caustic and contaminated washwater, concrete also has contaminants such as Chromium VI (Erin Brockovich)! This is why concrete curing compounds and the processes involving concrete finishing are so regulated by NPDES. Construction of Highway Bridges over water are especially critical.
Those of you active in planning, designing and implementing SWPPPs know that there is a big emphasis lately on concrete washout. At least that is true here in California. If your project involves concrete, you better show in your SWPPP how the concrete washout is going to be handles. Usually the BMPs involve a rather passive system of holding the washout until the water evaporates and then hauling the dried concrete to a proper facility for disposal or recycling.
The simplest BMP has been an above ground "pond" built from straw bales and lined with 10 mil plastic. These use about 12 bales of straw and hold less than 3 CY of concrete waste. There is also a "below ground" concrete waste trap, usually built for larger quantities of waste. The important thing is the plastic lining so the highly alkaline slurry cannot leak into the stormwater.
Well recently some companies have offering full service concrete waste management. For a fee the company will bring watertight, roll off containers to your construction site. When necessary they can "vacuum off" the washwater. At the project end they will remove the bins and recycle the waste. Most importantly, the service provides manifests to the Construction Site Foreman ensuring the waste was properly disposed of.
As of this year, Caltrans has 4 generally approved BMPs or SSPs (Standard Special Provisions) for concrete waste. These include above ground (straw bales and plastic), below ground, watertight bins, and the roll off management systems.
Tara and I recently visited our friends, Aubry and Wendell at California Paving Products, Anderson CA, to check out a new concrete washout device they have. This new product will surely take the place of straw bales and plastic as an approved BMP. The bags come pre-manufactured from heavy-duty polypropylene and they are lined with plastic. They look very sturdy indeed with heavy-duty bands and handles for lifting when they are full. To hold the bag open, a very simple frame was constructed from 2" PVC pipe.
It appears that these "bags" hold about 2 CY of waste. We were told they sell retail for about $75 each. This is so much more cost-effective than straw bales and plastic when you consider the disposal costs and the reduced bulk ending up in a landfill. Anybody out there experienced picking up a wet and moldy straw bale? Anybody out there tried these guys??
Need some stats? Here's some facts & figures...