Industry Controls Dust, Water

(from the August/September Editor's Note of AsphaltPro Magazine)

Welcome to the issue dedicated to aggregate concerns. Of course we have plenty of hot mix discussions in this edition of AsphaltPro, but, if you readers don't mind, I feel the need to ramble a bit about rocks and crushing and how nicely our industry is watching out for dust. (I'll call your attention to our Here's How it Works department featuring the DustPro system on page 37 as just one example, and I'll dive into the topic here in a minute.) First, I have to tell you why the aggregate issue is so intriguing to me.

Maybe I was just a strange girl, but I thought it was pretty neat when my dad gave me a geode 30 someodd years ago. The outside of the rock was just your average ol' rocky brown and gray stuff you see in any ol' pile, but when I turned it over—oh, wow! It was purple inside. And crystal-like. And there were layers of color and sharpness angled down through a hollowed crevice in the center. That, my friends, was cool.

During my childhood, I wanted to hear stories of Grandpa working in the coal mines and how they got the material up out of the ground. When I had science electives in college, this English major took geology. When I sat down to write a fantasy trilogy, I gave my main character the all-important-to-the-plot birthmark of an amethyst on her cheekbone, high up near the corner of her right eye. (And, yes, it's under contract; the second book is due out this fall.)

All of that interest in rocks translates to overzealous research now that I'm including so much information about crushing, screening, stockpiling, monitoring, hauling, weighing, testing, mix designing, etc., in a professional asphalt magazine. In my research for this issue, I focused quite a bit on dust control and the recent Notice of Proposed Rulemaking on New Source Performance Standards (NSPS) Subpart OOO from the Environmental Protection Agency (EPA). All that is also called "the opacity rule" and it deals with the visible emissions/dust that a non-metallic mineral processing plant gives off around crushers, screens, conveyor transfer points, etc.

The folks at the National Stone, Sand and Gravel Association (NSSGA) seem confident that the EPA final changes to the opacity rule won't require big changes to producers' current equipment or visible emissions testing. That's excellent news, especially considering the controls both aggregate and HMA producers already have in place to keep stray dust down.

Most equipment manufacturers are a little gunshy when it comes to talking about environmental issues, but the folks at Astec Industries, Chattanooga, and National Environmental Service Co. (NESCO), Mendham, N.J., were eager to point out how cautious industry members are and how effective current equipment is at controlling dust from normal operations. As Larry Thomas, an engineer at Astec pointed out, a 40 mile-an-hour gust of wind will kick up dust on any site, be it a ball field, nursery lot, or crushing operation, but plant owners have means of keeping dust under control with hoods and covers, dust return systems, baghouses and, of course, water. As Thomas reminded me, though, producers use caution with water, as well.

"Controlling dust at the site is not just a matter of throwing water on it," he said. He recommended producers use high pressure (100 to 200 psi), low volume systems to spray small droplets of water over areas to "capture" and weigh down dust. The small droplets allow producers to keep dust down without allowing enormous amounts of water into the material, which would increase drying times. And we all know what that leads to.

The dust suppression systems the Astec family incorporates in its conveying, crushing and screening equipment use this high pressure, low volume spray of water to help keep dust down at the areas producers target. Other companies using similar systems and producers incorporating such retrofits and aftermarket systems prove the conscientious effort this industry makes to keep visible dust to a minimum.

One of the reasons to watch your water spray is, of course, the time and fuel consumption rate it adds when overly wet material hits the HMA drum, but another is compliance with the Clean Water Act. While current issues focus on storm water runoff, any water runoff is up for scrutiny. This issue is a point for the aggregate industry to keep an eye on. While EPA currently focuses on storm water runoff at ready mixed concrete plants, the entity's officers also look at potential storm water runoff issues from aggregate facilities co-located with ready mixed concrete plants.

I checked with NSSGA to make sure HMA plants weren't a target yet, and Vice President of Environmental Services John Hayden reported that EPA's "priorities" for 2008 don't include asphalt plants. It looks as though this segment of the industry is still trusted to regulate itself when it comes to water issues. NSSGA is working with EPA to develop educational materials to help aggregate producers understand what's required of them under the storm water requirements of the Clean Water Act, and additional water runoff from water trucks and spray systems needs to be kept to a minimum. Hayden reminded me that NSSGA has a storm water management guide for aggregate producers that evaluates their permitting and control operations for storm water available at www.nssga.org.

As luck would have it, OEMs already have their customers in the aggregate and asphalt industry covered when it comes to keeping dust and water runoff under control. With high pressure, low volume systems delivering atomized mists and small droplets of water to coat and suppress dust, minimal water is left to pool or run off the site.

Who would have thought that as a 6- or 7-year-old child I would some day look at that pretty purple rock from Dad and wonder how much dust was suppressed to get it out of the ground? Or how much water was used in the suppression of the dust? Luckily, we have an industry that takes the neighbors' children into consideration when getting rock out of the ground, processing it, transporting it and putting it in HMA mixes. What we end up with is an industry that considers the environmental aspects of beginning, operating and closing down aggregate facilities before the first blasting charge goes off. It's an intriguing part of asphalt production to me.

Stay Safe,
Sandy Lender

Tags: AsphaltPro, Asphalt Pro, aggregate, dust suppression