De-icing salt survey at 3500 University Ave, 2/20/26

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This link displays all photos in order, with a brief caption.

This is the location of the University of Wisconsin Extension.  This facility is large, with numerous sidewalks parallel to streets and leading to parking lots.  All sidewalks had been salted this morning, but there was no evidence that the parking pavement had been salted.

I spoke to the Building Manager, Ms. Stevie Seltman, stevie.seltman@wisc.edu., whom I met while sampling.  She knows the site is oversalted and has complained.  She said she would file a complaint with building inspection. 

The contractor salting the sidewalks is Maple Leaf.  The parking areas are salted by a different contractor.  The contracts for salting are managed by U.W. Groundskeeping, which does snow removal for the central campus.  Contractors salt at 3500 because this location is separate from the university, but U.W. Groundskeeping still controls the contracts for work at 3500.  If there's ongoing snow or another problem, the Custodian at 3500 may become involved.  So, there are 4 entities who may be involved with snow and ice removal at 3500, but the Building Manager has control of only the Custodian, who is rarely involved.

Weather

Conditions for sampling were near ideal because...

• Foot traffic here is very low.
• Concrete is smooth, uniform, and new.
• Pavement had been cleaned of salt by rain. 
• Light snow triggered the salting, but snow melted before sampling.
• Meltwater dried before sampling.
• There was probably too little wind to blow salt off the pavement.

Leading up to the survey was moderate rain or several hours on the evening of 2/19, followed by temperatures dropping below freezing and about half an inch (or less) of snow. The rain ensured that all prior salt applications had washed away.  Salt stains I had noticed on previous days were now gone.

When I arrived at 1:09 pm, all show on the pavement had melted, although there were a few small patches of snow on the grass.  The areas of pavement with more than light salt were still damp (dark in tone) but quickly dried within an hour or two.  Wind was 10-15 mph, probably not enough to blow salt from the pavement, and about 1/3 of the salt was lightly adhering to the pavement anyway.  There was some salt off the pavement, but it's probable this wasn't caused by wind, but by bouncing/scattering when applied.

Overall distribution trends

Salt distribution along the sidewalks is highly non-random or clumped.  Some squares get barely any salt, while others get 3 times or more amounts of salt.  I took many photos showing half or more of all the pedestrian walks.  There was even one salt spill in the back containing multiple small piles.

Thel pattern of salt distribution suggests "sowing" by hand or from a scoop.

Besides clumping, another visible trend was for salt application to be heavier towards the entrances, on the one stair, and on other areas of concentrated traffic, such as where sidewalks meet the streets.

Significantly, I could see in numerous places where the salt had spilled over onto the lawn or shrub beds, within a few inches of the pavement.  I took a few photos of the spillover but made no attempt to quantify how much or how far the salt had strayed.

How much salt was dissolved by meltwater?

I don't believe there was enough snow--with resulting meltwater--to significantly reduce the amount of salt I could see or collect.  There were just a few places where salt was absent, with salty footprints next to the bare spots. This combination,--no salt plus salty footprints--indicates the no-salt areas had been shallow puddles that were now dry.

There were a few conspicuous white shoe prints on the pavement, evidence that while the snow was melting, one or two people had stepped in salty puddles, transporting some salt from heavily salted areas.  Except for where the footprints originated, there were no salt stains on the pavement to suggest significant dissolution or aqueous transport of salt off the pavement.

However, the salted areas remained slightly damp (wet) for an hour or so after I arrived, so a small amount of salt could be distributed in a fine solid film on the concrete surface or have been absorbed a short distance into the concrete.

In two places where I removed salt, about 1/3 of the salt particles were lightly adhering to the pavement, but I was still able to use the dust bin to easily scrape all particles towards the center for final collection with a fine brush.  This "adhesion" suggests a small amount of water surrounded some particles, then dried--indicating partial solution of these particles. But it was probably not enough to substantially reduce the salt collected.

Quantification of salt at 10 sample sites

Photos show the context of all sample sites, plus verticals and closeups of the sites.  For each site, I used P. Gascoyne's photos (calibrated by volume), trying to match the pattern I saw on the pavement to the pattern displayed in the photos.

The sidewalk concrete at this location is relatively new, light in tone, and uniform in texture, making it a good location for comparing photos to pavement (except that the light tone minimizes contrast with salt).  Foot traffic is light (about one person every two hours), reducing any pulverizing or dispersal of salt by feet.

In selecting sample locations, I selected places of heavier salting, which were found on all walkways.  Sites were selected in part because they were close to my vehicle.  I did not seek out the very heaviest clumps of salt.  So I feel the sample locations are broadly representative of the many spots where a handful of salt landed.  But not representative of salt in between these "landing spots."

For each spot, I picked a "volume" of salt from PT's diagram that I thought matched best.  Then I picked a "volume" I thought matched second best, contained in parentheses.  I found myself using how many particles touched as one helpful cue.  I did note that PT's photos did not seem entirely random, as if he had used his fingers to redistribute particles, leaving channels without salt (tracks made by fingers?).  This apparent nonrandom distribution made it a little harder to compare photos to pavement.  The third number for each spot is the weight of salt collected, and the fourth number is the volume of salt collected.

The photos below show each sample spot.  For scale, use the width of the clip board, which is XX in. (inside the rounded corners).  Sites where I swept a sample have a blue template 12 inches square.  The salt was collected by sweeping with a soft brush towards the center, then using a plastic dust bin to scrape sticking particles towards the center. Finally, I removed all gathered particles with the brush sweeping repeatedly into the bin.

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Conclusions about methods

• When refining methods, it's important to select the right location and weather (see above).
• Placing a 1 square foot template around sample is very helpful for documentation of where and provides standard dimensions.
• Standardization of method is important.  As I continued sampling, method got more reliable--and best with blue template.