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Environmental Information for Sweeping Professionals

Best Practices Investigation Between Officials in Anchorage, Alaska and Drammen, Norway

Editor's Introduction:
In late 2007 published a story about how sweeping is done in Drammen, Norway. Information for the coverage had been provided by Arild Moen, that city's Chief Engineer for Municipal Enterprises. It included some of the environmental issues facing the coastal city, and the actions that Drammen officials have taken toward abatement of the problems.

After he read the article, Lawrence Taylor, Jr., QEP Program Manager for the Air Quality Monitoring and Testing Section of Anchorage, Alaska, contacted me to get the contact info he needed to follow up with Moen. The following are excerpts from the letter Taylor sent to Moen, with Moen's return comments (in blue) shown after each question. I have edited some of Moen's comments for 'clarity in translation.'

Dear Mr. Moen:
I was referred to you by Ranger Kidwell-Ross of I am assessing dust control practices for the Municipality of Anchorage, Alaska.

I read in your WorldSweeper article that Drammen has temperature inversions causing elevated PM-10. Anchorage is a winter city where PM-10 concentrations violate US National Ambient Air Quality Standards (over 150 micrograms per cubic meter) during wind storms and dry periods with temperature inversions. This occurs usually in the spring, when the ice in the gutters that has built up all winter melts, exposing a large volume of silt from traction sand and studded tire road wear particles.

We are evaluating the use of magnesium chloride as a hygroscopic (atmospheric moisture attracting) agent to hold down the silt until it can be swept up. We also have seen that after sweeping a lot of silt remains on the road, so we are evaluating using magnesium chloride to keep the silt in place so that it can dissipate gradually. The city has a number of belt (mechanical broom) sweepers and has also bought a waterless broom sweeper with low air emissions.

These are my questions:
1. Do you use controls in addition to sweeping?
Yes. When the weather is dry we also employ dust suppresson with MgCl.

2. What are the pros and cons of these controls, i.e.,:

2A. Are fines left behind by street sweepers?
To some extent, yes.

2B. Do you use de-icing chemicals and what are they?
NaCl. (Applied in a brine, wet or dry depending on conditions.)

2c. Do you use chemical dust suppression?
MgCl brine.

3. How do you ensure the quality of your dust control?
We employ a PM10 surveillance program.

4. How effective are the controls?
Their effectiveness is limited to the dust that's actually on the road surface. Dust from surrounding areas is not accessible.

5. Are there improvements that you see as the next step in Drammen to do a better job controlling ambient dust?
One thing we're looking at is the possibility of washing vehicles from construction/building sites before allowing them to enter back on to public roads.

6. What can you tell me about the cost of dust control?
Unit price 30 g MgCl brine per square meter. This makes approximately 9 g Mgcl per square meter) NOK 164 /km - ex. VAT.

Additional Remarks:
In Drammen, MgCl is used both in road tunnels and on streets. A discussion has occurred about whether the MgCl makes the road surface slippery or not, after some traffic mishaps during last spring/early summer.

One thing we're looking at is the possibility of washing vehicles from construction/building sites before allowing them to enter back on to public roads.

The program using MgCl was stopped (at one point) waiting for the results of friction investigations. The friction testing results were that the effect from using normal quantities of MgCl (Up to 54 grams of MgCl per square meter) was negligible. We expect that oil spill and/or exhaust-film from heavy vehicles have made an influence on friction conditions during the mishaps, perhaps in combination with hazardous behavior on the part of the drivers. Our decision was to continue the MgCl program.

MgCl are known to be more corrosive than NaCl. For this reason, the Norwegian Public Road Administration (NPRA) limits the use of MgCl for dust suppression purposes in some city areas, included Drammen.

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