Post #2090: Documenting the post-snowmelt salt spike in my drinking water. Part 2, not obviously a fool’s errand.

 

In this post, I do a back-of-the-envelope calculation on salt in my drinking water.

Is the road-salt-driven spike, in salt in my drinking water, likely to be big enough that I can detect it with a cheap total-dissolved-solids (TDS) meter?

If not, this is a fool’s errand.

Spoiler:  Yes, the increase in ions (here, part of total dissolved solids), from this hypothetical “salt spike” in the drinking water, as a result of the road salt washing off the roads, should be more than big enough to be detected using just a cheap TDS meter.

All I really need to do is stick that meter into a freshly drawn glass of water, once a day.  And record the results.  No muss, no fuss, almost no effort.

If there’s no “spike” in ions — interpreted by the meter as a sharp rise in TDS — then that’s that.  No matter what I thought I tasted in the water.

As a bonus, I get to use grains of water hardness in a calculation involving metric units.


Chapter 1:  Wherein Sodium and Chlorine, who had been bound together as Rock Salt for hundreds of millions of years, are now Released, and Go Their Separate Ways.

One of the stranger twists in this whole road-salt-life-cycle saga is that the sodium and chlorine ions from the road salt now permanently part ways.  Or, at least, in the typical case, do so.

This is usually expressed as “the sodium does not travel as far”.  In hindsight, I think this means that if you filter the salt water through dirt, the sodium ions will preferentially stick to the dirt. I vaguely sense that “ion exchange” is at work here.

This tendency for the sodium to “stay put” is also why the sodium is fingered as the cause of the localized damage to vegetation.  Apparently, that’s why rock salt (NaCl) “burns” lawn at the edge of salted sidewalk, but not so (or as much) calcium chloride (CaCl2).

For all intents and purposes, magic happens. What begins as simple salt water ends up passing along just the chloride ion, out of the salt (NaCl).

Presumably, that chloride ion is now dragging along god-knows-what ion-of-the-street with it.  Something it picked up in the dirt, no doubt.  Calcium, maybe, from the soil it passed through.  Apparently, it doesn’t matter, or something, because I can’t find a ready discussion of what takes sodium’s place.

In any case, so the story goes, what starts off as salt does not end up as simple dilute salt water.  Stuff happens along the way.  I suspect that contact with the dirt plays a major role in that.

So Chloride ion travels, but Sodium ion stays at home.  Or so they say. 

Except sometimes?  Flashy urban environment.

I noted that much of the research on road salt in the water was done in New Hampshire where a) they apparently use a lot of road salt, and b) the issue is contaminating water wells.  So that research is clearly talking about well water, which is most assuredly water that has percolated extensively through soil.  (Although, in fairness, they also manage to salt up quite a few lakes and streams.)

Here in NoVa, by contrast, I think we’re at the opposite end of the percolation spectrum.  Around here, it’s road runoff to culvert to storm sewer, to clay-banked “flashy” urban stream.  To the Potomac.  In my mind, I’m not seeing a lot of filtration of any sort take place.  As a result, I’d bet that what starts out as salt water mostly ends up salt water, sodium intact, in the Potomac.

But I don’t really know.

All I know is that, as with many divorces, the tale you’ll be told about the breakup of Sodium ion and Chloride ion can’t possibly be the full story.  Ions have charge, and charge must balance.  So that the only way chloride can drop its ex — the sodium ion — is to pick up a suitable replacement.  I can only guess that, somehow, whatever that replacement ion is just doesn’t much matter. So nobody talks about it.

They dump on the ex (sodium) for killing the vegetation at the site of application.  But nobody bothers to name Chloride’s current partner.

Either that, or I fundamentally misunderstand something about this.

 


Grains of hardness should set my TDS baseline.

Horsepower.  Tons of cooling. British thermal units.  Teaspoons.

Grains of water hardness.

There’s just something about crazy old units of measurement that simply refuse to die.

At any rate, here’s where this stands.

I’ve ordered a cheap TDS (total-dissolved-solids) meter.  Assuming it works, it’ll give me good information on the density of ions on my drinking water.  Expressed in parts-per-million (ppm).

I’m going to draw daily samples of water for the next N days (like, 14 or boredom, whichever comes first).  By samples, I mean fill a mason jar with water and give it a labeled plastic top.  Kitchen faucet (so I know it’s well-used every day).

Plus, no at-home science project is really complete if it doesn’t use a mason jar.

Then I’m going to do the obvious things.  Test the water, using the meter.  And, with the aid of my wife, taste the water, blinded as to which mason jar is which.  Hoping that “ion count is up” and “tastes like salt” days a) exist, and b) coincide.

This, assuming that TDS is normally slow-varying, and doesn’t just like spike at random times all year long.  (Or, for that matter, does not spike following rainfall, regardless of salt on the pavement, something I would in theory need to test for.  These are things that I hope are true — basically, that my water’s TDS does not normally have short-term intense spikes of ions.  But this is something that I hope is true, not something that I know or have shown to be true.

But how big a blip can I reasonably expect?  Will I even be able to register it, with this cheap meter? 

That’s what this post is about.

The commonly-stated standard for drinking water taste is that water should not exceed 250 ppm (parts per million) chloride ions.   At least, this seems to be what Google’s AI tells me, expressed as 250 milligrams chloride per liter of water.   Above this level, a salty taste is evident.  (To some, I guess.  Salt sensitivity varies across individuals and over time, but 250 ppm is what gets cited as a common standard for avoiding salt taste in the drinking water.)

So if I can taste the salt in my water, that ought to correspond to that level of chloride, or higher, in the water.

That’s going to add to the total dissolved solids that are routinely in my water, that is, my “baseline” TDS.  Which my town’s legally-mandated annual water quality report helpfully lists as being in the range of 5 to 10 grains of hardness.  By weight, I believe that’s almost entirely calcium carbonate.

And 10 grains of hardness works out to be 640 mg of dissolved minerals (mostly harmless calcium carbonate) per gallon of water.

(So “a grain” is weight, now equal to about 64 milligrams.  The answer above is what you’ll get from Google’s AI.  And a grain of water hardness is a grain of dissolved minerals, per gallon of water.)

The term grain comes from exactly where you’d think.  Its supposed to be the weight of an idealized grain of wheat.  Or so they say.  But it is widely listed as equaling 1/7000th of a common (avoirdupois) pound, and so it doesn’t play nicely with standard U.S. units.  Aside from the fact that a grain is tiny, I think this explains why grains are not used in the U.S. (outside of ammunition and water hardness, and I guess alchemical receipts.  But never in the day-to-day.

To put those two numbers on common footing, note that a gallon is four liters.  So ten grains of water hardness is (640 mg/4 liters =~) 160 ppm dissolved solids.

Or close enough.  (When I ask Google, it helpfully tells me that a grain of hardness works out to be 17.1 ppm, or ten grains of hardness is just over 170 ppm.  Plenty close enough to the prior estimate, for this work.

And, because, by weight, calcium carbonate makes up the vast majority of what’s dissolved in my drinking water, that should be my baseline TDS reading.

Which means that the expected minimum taste-able chloride spike (250 ppm) should easily show up on top of my background TDS of around 170 ppm (10 grains of hardness).

Things could still go wrong.  Perhaps the day-to-day TDS level of my drinking water is erratic, spiking up and down all the time.  Perhaps it kicks up after every significant rainstorm (so that the expected coming spike might have nothing to do with salt.)  Perhaps this $6 meter is so unreliable that random meter errors will swamp the expected salt-driven increase in TDS.

But if none of that is true, then if I can taste the salt in the water, the concomitant jump in ion concentration in the drinking water should easily register on a cheap TDS meter.


Conclusion

So far, this is not a fool’s errand.

A cheap TDS meter should be good enough to document the expected salt spike in my drinking water.


Addendum:  Initial impression of cheap TDS meter.

My $6 TDS meter arrived.  Worked right out of the box.  At any point in time, it seems to give a consistent reading.

But glasses of water drawn three hours apart differed almost 10% in their measured TDS.  I don’t know whether that’s the native uncertainty of the meter, poor water-draw technique on my part, or actual hour-to-hour variation in my tap water’s TDS.

After a little poking about, I find a few things.

First, weirdly enough, there are different procedures for drawing water to test the water, as opposed to drawing water to test the plumbing.  If you’re testing the (incoming) water, common advice is to let the tap run full-on for five minutes, then take a sample.  By contrast, if you’re (e.g.) testing for lead in the pipes, apparently, you want to catch and test what’s sitting in the pipe, and you don’t want to flush the pipe at all.

I’m only letting the kitchen tap run 30 seconds.  (But, honestly, if the difference across readings is due to stuff coming out of my pipes, I’d kind of like to know that.)  I may try some five-minute flushes to see if that gives me more consistent readings.

In any event, change of plan.  I’m just going to measure the TDS of my kitchen tap water several times a day, over the next couple of weeks, and record the results.

With luck, my $6 meter will last the full two weeks.

Post #2089: Documenting the post-snowmelt salt spike in my drinking water. Part 1.

 

Major snowstorms in my area (Northern Virginia) are often followed by salty-tasting tap water, some days later.  Salt that was spread on the roads gets dissolved by the melting snow (or rain), runs off into the creeks, down to the Potomac, and from there, into our drinking water.

This is a well-known phenomenon across the northern U.S.

Here in Northern Virginia, sodium and chloride levels in the drinking water have been rising for decades, as documented by the Washington Suburban Sanitary Commission:

Source:  WSSC.

As the WSSC states:

The levels peak in the winter months and are higher in years where we experience more winter weather events. Because there is no economically feasible way to remove salt during filtration, higher levels end up in the drinking water.

Those annual averages are interesting, but here I want to document the short-term increase in salt in the drinking water following a big snowstorm.  Right now, all I have to back up my claim that road salt makes the water taste salty is a) my taste buds, and b) my recollection of salty-tap-water events of the past.

So this time, I’m going to try to capture that post-snow-melt salt spike in my tap water, in hard data. 

Measure it.  Day-by-day.  As it flushes through the system.


Cheap water quality testers are all water conductivity testers.

If you look on (say) Amazon, you can buy cheap little meters to measure total dissolved solids (TDS) in water.  As above.  These are often included with high-end countertop water filters, so you can see that something has been removed from the water, in passing it through the filter.  (My understanding is that consumers use the TDS reduction as a marker for when to change the water filter cartridge.)

You can also buy remarkably similar-looking meters to measure water salinity.  These are often targeted toward (e.g.) aquarium owners, and pool owners, either of whom may need to keep water salinity within a defined range.

You can even buy meters labeled for measuring the electrical conductivity of water.  Need I say that those cheap water-conductivity meters look almost identical to the first two?

Turns out, those are all the same meter.  They all measure the electrical conductivity of water.  They just label the resulting output on different scales.

Maybe — I haven’t quite figured this out one way or the other — there may be non-linear adjustments linked to the named use (salinity, TDS).  Maybe not.  I don’t think my $5 is going to buy me a lot of sophistication.  But these days, you never know.


Starting off with a DIY flop

 

So, assuming I have deciphered the technical stuff right (below), to capture the salt spike, all I need to do is measure the electrical resistance of my water.  Day after day, in a repeatable fashion.  For, I’m guessing, a couple of weeks max.

The salt, passing through the system, should show up as a temporary spike in the conductivity of the water.

To be clear, I don’t think I’m looking for some little hiccup in the data.  Back-of-the-envelope, I’m hoping for roughly a doubling of the conductivity for the days in which the salt spike passes through.  Which I have already predicted will be this coming Wednesday, based on my hazy recollection of the past.

I’ve got an ohm meter.  Somewhere.  It can measure resistance (ohms).  How hard could it be, to rig up some way to use my VOM (volt-ohm meter) to track the resistance (the mathematical inverse of conductivity) of my tap water.

Long story short, this DIY water-conductivity meter failed.  I was unable to make a reliable measurement.  After assembling the hardware (two bolts, stuck to a plastic lid, in a mason jar of water, connected to a VOM), the estimated electrical resistance of the water wandered all over the place.  Substituting stainless bolts for the galvanized bolts shown above did nothing to correct the problem.  I think that, perhaps, my VOM was just not up to the task.

After giving it a couple of tries with this DIY approach, I gave up and ordered the $6 meter pictured above.

I still don’t really know why my DIY water-resistance meter didn’t work.   Might have been as simple as a bad battery in the meter.  Not worth pursuing, when I can buy a meter for $6.


It really is this simple?  The theory.

Pure (distilled) water is a poor conductor of electricity.

But if you add ions to the water — from dissolved salt (Na+Cl-) or calcium carbonate (Ca++ C03–) or baking soda (Na+ HC03-) or hydrochloric acid (H+ Cl-) or whatnot — the ions act as charge carriers, and so allow electricity to flow more easily in the water.

The more ions you add, the better the water conducts electricity. (Within reason or at modest dilution.)   All the ions in the water contribute to the increased conductivity of the water.  Those could be “dissolved solids” ions, as from calcium carbonate in hard water.  Those could be “salt” ions, as in, the salt in a salt water aquarium.

In fact, all of these super-cheap TDS/salinity/conductivity meters measure the conductivity of the water.  Period.  They just put a different label, and perhaps a different scale, on that measured conductivity.

The first thing to note is that these meters can’t distinguish salt from other ions.  All they do is tell how conductive the water is.  That depends on the concentration of current-carrying ions in the water.  All ions of all types contribute to that.

The bottom line is that, strictly speaking, my $6 salt meter does not measure salt in the water.  It measures the total ion concentration in the water, of which salt contributes a part.  It does that by measuring the conductivity of the water.  And then it displays the result in units that match salt-concentration units (like ppm NaCl and such).  (I am also pretty sure it makes a temperature correction as well, as water conductivity varies with temperature, and the standard for reporting is conductivity of water at 25C.)

But, while these meters react to all ions in the water, they are blind to dissolved non-ionic compounds.  Like, sugar, say.  Sugar molecules remain intact (and carry no charge) when dissolved in water.  Dissolved sugar does not materially affect the conductivity of water, and so a cheap “TDS” meter will not respond to dissolved sugar or other dissolved non-ionic organic matter in the water.

The upshot is that the thing that’s sold as a “TDS” meter … isn’t.  Not if “total” includes things like sugar dissolved organic material that is not ionic in nature.  It’s blind to that stuff, because that stuff doesn’t affect the conductivity of the water.

But that’s only fair, because the “salinity meter” version of it doesn’t measure salinity, either.  For example, I’m pretty sure that adding vinegar to the water will cause the conductivity to increase. On a meter labeled as a “salinity tester”, that increased conductivity would be labeled as increased saltiness.

As far as I can tell — and certainly at this price-point — the only way to measure the different ions separately is through chemistry.  Old school, you add reagents to react with certain ions, precipitate them out of the water.  You then filter out, dry, and weigh the precipitate to infer the quantity of the selected ion in the batch of water.  (Or you buy a meter with exotic-material electrodes that react chemically with certain ions and not other.)  Either way, that level of effort and expense is way beyond what I contemplate here.

Separately, and well known, the fact that these meters react the same to all dissolved ions means that “TDS” isn’t a good measure of drinking water cleanliness.  For most drinking water, TDS is simply measuring the total dissolved mineral content.  For me, here in the Town of Vienna VA, almost all the dissolved solids are from a water hardness of around 5 to 10 grains (per our mandated water quality report.)  This is almost entirely from harmless calcium carbonate, dissolved in the water.  The relatively high TDS in this case doesn’t mean that my tap water is bad, just that it has dissolved minerals in it.


Conclusion

I hope this has been clarificatory.

There is only one underlying type of cheap water quality meter.

Cheap (sub $10 on Amazon) TDS meters, salinity meters, and water conductivity meters all measure the electrical conductivity of water.  Water conductivity is driven by the concentration of ions present in the water.  All ions are lumped together by this measurement.  And these meters are blind to dissolved non-ionic material, because (e.g.) stuff like sugar doesn’t materially affect water conductivity.

So, really, at least at this price point, there are no salinity meters or TDS meters.  There are only water conductivity meters, and the labels placed on them.

The situation isn’t as dumb as I’ve painted it.  If you know what’s going into your water — say you are trying to adjust the salt level in a swimming pool — then yeah, that meter will function for you as a salt meter.  Because you know that it’s your salt that’s increasing the ion count and pushing up the conductivity of the water.

Similarly, if dissolved organic non-ionic compounds are not an issue for you  — no sugar in your water, that you know of — then the same meter may well serve as a useful TDS meter.  For drinking water — where dissolved organic matter is assumed to be minimal — these simple conductivity meters work well as total-dissolved-solids meters.  In other contexts — such as sampling raw water from a lake or stream — that would not be true.

For the moment, all I need to do is take a water sample a day, from my kitchen faucet.  Just a mason jar, rinsed and filled.  Store that away.

And then, if the story is as I think it is, in a couple of weeks, I should be able to go back through the samples and identify the “salty” days through blind taste-test.  And, if all goes well, my $6 TDS meter will highlight the same days as high TDS days.

If it all goes to plan, I’ll have documented the post-snowstorm salt spike in our drinking water by both blind taste test, and by measured dissolved solids.

Post #2088: Why are there always little piles of salt left in the road?

 

It’s going to rain all day today.  The forecast is for half an inch or more.

Today, therefore, I must appreciate the little piles of salt that are left in the roadway.

Because tomorrow, they shall all be gone.

They will have begun their journey to return to Mother Ocean.  Whence they originated, back when dinosaurs roamed the earth.

Think of it as a salty circle-of-life kind of thing.


Observation:  There is (always!) excess salt left on the roadway.

We have reached the ugly end stage of this last snowstorm.  Patches of white snow remain, but only here and there, on lawns and roofs.  Parking lots remain clogged with great dirty piles of snow.

And roadways are littered with ugly little piles of salt.  As they always are, after a snowstorm in this area.

Call those ubiquitous little piles of left-over road salt the “excess salt”.  (Which is kind of judgemental, but for now, I just need something to call them).

I’m not talking about private parking lots, or walkways, or whatnot.  Places where the property owner spreads salt in some catch-as-catch-can manner.  I’m just talking about little piles of leftover salt, on the public roadways.

If you think about them, at all, it’s not as if VDOT set out to leave a bunch of salt lying around, when they salted the roads last week.

For one thing, those piles of excess salt are a deadweight loss.  It takes money to buy and spread that salt.  But the left-overs didn’t do anything useful.  They just add to the subsequent salt burden on local rivers and, in my case, the water supply.

In fact, it’s fair to say that every state DOT is aiming to use less salt.  Not just for the environmental impact, but because it rusts out cars, bridges, rebar embedded in concrete, and so on.

Paradoxically, part of this push to reduce the use of road salt is the now-common practice of “brining” the roads ahead of a snowfall.  That is, spraying everything with salt water, which then evaporates to leave a microscopically thin, uniform layer of salt.  This is used for anti-icing (to prevent snow from sticking to the road), as opposed to traditional de-icing (un-sticking already-frozen snow).  That preventive approach to disbondment (see prior post) results in less salt being used, in total.  In Virginia, brining the roads only came into general use in the 21st century, and was relatively uncommon as late as the mid-1990s (reference, .pdf). 

Finally, as far as I have been able to tell, VDOT (and similar) aim for a uniform application of salt, just sufficient to achieve “debondment” between ice/snow and pavement.

And yet, little piles of salt in the “corners” of the roadway remain a fixture of the urban winter landscape.  Post-snowstorm, we always end up with deposits of rock salt in the dead space next to the curb, sometimes between the lanes, and in general, on the road surface wherever tires do not routinely roll.

So that’s a little bit of a puzzle, isn’t it.  Everybody involved is trying their damnedest to use as little road salt as possible.  The salt is applied by professionals using the best known techniques.  They aim for a uniform application of salt sufficient for debondment.  But we still end up with little piles of excess salt everywhere.

 


Why?  Mere carelessness is not an adequate explanation.

Why is there always excess salt, in little drifted piles, on the road, after a snowstorm?

This is a surprisingly hard question to answer.  Around here, the excess salt piles show up at intersections.  There’s no obvious explanation for that.

My best guess is that this occurs because a) the pavement of an intersection gets double-salted (one salt-truck pass for the main street, one for the side street), and b), as a matter of geometry, larger intersections effectively result in higher piles of excess salt at the curb.

Other explanations do not seem to hold water.

Mere sloppiness?  No. 

Naively, you might think that we see these excess salt piles because VDOT went at it with too heavy a hand.  Or spilled some extra in those spots.  You can try to dismiss it as the result of mere sloppiness.

But attributing those ubiquitous piles of excess salt to “good enough for government” work does not stand up to scrutiny.  For one thing, even a bit of research shows you how seriously VDOT (et al.) take the the timing and calibration of their salt spreading and spread rates.  It’s as close to a science as they can make it.  For another, those little excess salt piles show up everywhere, pretty much, regardless of which government entity or contractor put the salt down on the public road.   No matter which year.  And they have done so, ever since I can remember.

Nor does the excess salt pile up everywhere, as it would if VDOT simply applied it with too heavy a hand.  Around here, I see those excess salt piles at intersections, on highway overpasses, and where lanes merge.  I specifically see none — no visible salt crystals whatsoever — along sections of road between intersections.

But what would be the systematic reason for them?

So, to the contrary, I’m going to start from the notion that there’s probably a reason that we always end up with little piles of left-over road salt.  A reason those show up in the intersections.  And I’m betting it’s something inherent about salting the roads that leads to this.

In other words, I’m betting that we always end up with little piles of excess salt because that’s an inherent and unavoidable part of salting the roads.

I can’t prove that, but here are my best guesses as to why we only see those excess salt piles in certain locations.

Guess 1:  All VDOTs, everywhere, put extra salt down at intersections?  And always have.  Presumably on purpose, as a safety measure?  To roughly the same level of excess.  So, in effect, the excess salt was put there, on purpose by VDOT.

If so, they have all, collectively, been pretty quiet about doing that.  I have found exactly zero evidence to suggest this is true.  No directions to do so, no mention of doing that in a “best practices” manual, and so on.

(There may be some governments that only salt intersections, but VDOT is not one of them.  Nor is the Town of Vienna.  Near as I can tell, every street in Vienna got salted.)

In addition, most truck-mounted salt spreaders aren’t set up for a lot of fine-tuning on the fly.  Like, turning them up, as you cross an intersection.  For the simplest salt-spreader rigs, the only in-cab control is an on-off toggle switch (top, below).  More modern ones let you control the flow of salt, on the fly (bottom, below).  Neither style looks like it’s set up to encourage the truck driver to fiddle with it, while driving a piece of heavy equipment.  Say, at night, in a driving snow, with traffic.

Source:  A couple of installation manuals for truck-mounted salt spreaders.

So, while it’s not out of the question that VDOTs around the country somehow turn up the salt flow at intersections, this seems unlikely.  I can find no mention of this as a standard practice, and it runs contrary to the fundamental notion that salt, for road use, is for disbondment of ice/snow on pavement.

Plus there’s no obvious way to do it, other than asking the salt truck drivers to slow down at every intersection.

Guess 2:  The pavement of the intersection gets double-salted (once for salting the street, once for salting the cross-street).

That’s a fact.  If you’ve set the salt spreader to provide X salt per 1000 square feet of road, then road intersections get 2X.  Once for the main street, and again for the cross street.  And, really, you might end up laying down extra salt anywhere salt trucks have to make multiple passes to completely salt a stretch of pavement (e.g., where there are an odd number of lanes, or where lanes begin or end, or merge areas.)

Guess 2A:  Large intersections should generate more noticeable piles of salt  at the curb line (compared to small intersections). 

That’s also more-or-less a fact, owing to geometry.  The area of an intersection increases with the square of the number of lanes.  Salt is spread over the entire area.  But the length of curb line is … roughly constant, at least until you get to the point where there’s a divider between the lanes.  The upshot is that an intersection between six-lane roads ought to give curb-side excess salt piles that are nine times higher than you’d find at the intersection of a pair of two-lane roads.

Guess 3:  Salt is applied uniformly on the roadway, but somehow migrates to the intersections?  I don’t think this is true, but I can’t prove it.

For sure, salt migrates short distances on the roadways.  It moves out of the path of actual tire contact, which is why the excess salt piles are always in the “dead” spots in or around the roadway.  But that would account for salt moving a few feet, not hundreds or thousands of feet down a typical suburban street or arterial roadway.  Which is the only way this hypothesis would explain salt at the intersections.

In addition, VDOT puts a lot of thought into keeping the salt where they put it.  It is common practice to pre-wet the salt, both so that it stick better, and so that it starts melting snow faster.  In addition, best practices call for applying road salt only after some snow has fallen, specifically so that the salt will stay put.

Finally, I think the contrast of intersections and surrounding roadways is too pronounced to have been produced by such a sloppy process as salt being pushed around by tires.  With this last snowfall, I see no salt crystals at all on the road, until I’m literally at the intersection.

Upshot:  Of the three mechanisms that would generate salt piles at intersections (only), and particularly at large intersections, I think it’s due to the inherent double-salting of the intersection pavement, coupled with simple geometry that results in higher excess salt piles at larger intersections.


Drinking water contamination, or, why do I even care about road salt?

I care because I’ll be tasting salt in my tap water sometime next week.  Based on past experience, I’d bet that’ll start around Wednesday or so.  That, as a result of the road salt being washed into the Potomac River by today’s rains.

There are enough reports of road salt contaminating drinking water that I’m pretty sure I’m not fooling myself about the salty taste of the water.  This, even though my wife can’t taste the salt.  Sensitivity to the taste of salt varies substantially across individuals.  And, for an individual, it varies considerably with the amount of salt in the diet.  (Unsurprisingly, the more salt-deprived you are, the more sensitive you are to the taste of salt).

Of more scientific interest, the fact that I can taste the snow-melt salt in my drinking water suggests that post-snowfall salt (chloride ion) content of my drinking water routinely exceeds 250 parts-per-million, the lowest threshold at which some people can taste the salt.  At least a quarter-teaspoon of salt, per gallon.  Not a health hazard for most, but enough that I can taste it.

But is that plausible?  Do we really put down enough road salt to make the drinking water salty?

Yep.  A simple and conservative back-of-the-envelope calculation says that if the Town of Vienna, VA applies road salt a standard rate, it would plausibly generate a brine salty enough to taste, as that salt mixes with half-an-inch of rain.

Further research shows that in a big snowfall, Vienna applies orders of magnitude more salt.  The Town newsletter reported 600 tons of salt used for a January 2016 snowstorm that dropped about 30 inches of snow (Vienna Voice, March 2016, page 6).  Or roughly 60 times as much salt as was assumed for the calculation above.

The upshot is that yes, a single application of road salt, at a middle-of-the-road rate, followed by half-an-inch of rain, should result in runoff from the Town of Vienna that has a noticeably salty taste.  And that exceeds current EPA water-quality standards for salt in the water.

I may or may not be able to taste the salt, with this modest snowfall.  After all, that will depend on the rate of salt use across the entire Potomac watershed.

I may yet invest $20 in a cheap salt meter, and track the chloride ion content of the water.  Just to see if that’s accurate enough to document the wave of road salt that will be passing through my local water supply next week.


Conclusion?

This is a bit of an odd post, even for me.

You’ve probably seen little piles of excess salt on the roadway all of your life.  And yet, each time, if you thought about them at all, you probably just tut-tutted them away.  Dismissed them with some sort of ad-hoc explanation.  Maybe your local DOT (or alternative) is just sloppy, or something, and over-applies the salt.  Or maybe cars effectively sweep the salt along, until it gets to the intersections, where it stops.  Or maybe VDOT specifically and purposefully over-salts intersections.

I don’t think any of those simple explanations is correct. They do not explain the consistency and ubiquity of these little piles of excess salt.  No matter the year, or the jurisdiction, if they salt the roads, little piles of excess salt are a normal and expected part of the urban winter landscape.

My best guess is that the ubiquitous piles of excess salt are an inherent and inadvertent part of salting the roads in winter.  The most plausible explanation of why the excess road salt is consistently where it is, around here, is a straightforward double-salting of the intersections.  If you are salting the pavement adequately in all directions, then you are salting the pavement of each road intersection twice adequately.

And for larger intersections, that over-salting-rate gets amplified, as the salt strewn over the collection area of the intersection (which rises with the square of number of road lanes) gets squeezed against more-or-less the same length of curb.  So that an intersection with twice the lanes should yield four times the concentration of excess salt pushed to the curb.

But in the end, it comes down to whether or not there’s anything actionable.  Is there any way to avoid those piles of excess salt?  And would it make any material difference, if you did?

And there, I think the answer is no.  No, you can’t avoid over-salting intersections, with manually-controlled salt spreaders.  For most, the driver simply turns the salt spreader on when the truck is moving, and off when the truck is stopped.  (Having salt spreaders that are synced to vehicle speed is considered a big step up from the standard setup.)

When you get down to it, the problem is the use of road salt.  Full stop.  Modest over-use on intersections adds trivially to that problem, for the simple reason that intersection area is a small fraction of total road area.  So the problem of excess salt in the intersections is not worth addressing, particularly if that would require use of more sophisticated (e.g., GPS-run) salt spreader controls, to avoid dumping salt twice on the same intersection.

My guess is that as long as we salt the roads, we’re going to see little piles of excess salt in the road intersections.  I think that’s an inherent and unavoidable part of the process.  But that, empirically, that additional salt in the intersections is a drop in the bucket, compared to the total amount of salt spread on the roads.

End of story.

The only followup will be to try to document the spike in salt in my drinking water, as a consequence of the runoff from this most recent storm.  And that will depend on whether or not I feel like shipping $20 off to China, via an American oligarch, by the purchase of a cheap salt tester on Amazon.

Post #2086: Disbondment, my next road salt lesson.

 

The big boys — VDOT and its road-plowing bretheren — they salt the pavement when it snows.

So, why can’t I do the same, with my driveway?

Turns out, the reason VDOT salts the roadway is completely different from the reason I salted my driveway.

Huh.  Maybe you knew that, but I sure didn’t.

And as a corollary, recommended salt spreading rates for salting roadways have nothing to do with the amount of salt I needed melt the snow off my driveway.


Let’s not belabor this.

VDOT clears snow off the roads by plowing the snow off.  Their goal is to plow down to bare pavement when possible.  But they can’t do that if the snow and ice is stuck fast to the pavement.  VDOT uses salt to keep snow/slush/ice from adhering to the roadway.

Hence, disbondment.  The act of taking ice and snow that are frozen hard to the underlying pavement, and getting them loose.  Dis-bonding them from the underlying pavement.

Typically, VDOT’s goal is to use salt to melt just the very bottom layer of the snow/ice pack, where that touches the pavement.  They want to weaken that interface, so that the snow/ice can be scraped off with a normal snowplow.

I, by contrast, was using salt to clear the pavement.  That is, I wanted to melt the entire predicted thickness of the coming snowfall.  That, because I specifically didn’t want to scrape the snow and ice off the pavement.  I wanted them to run off, as salty water.  (I admit that I was right tired of shoveling, at this point in our most recent winter storms.)

Guess what?  If you’re only trying to melt that very thin interface between snowpack and pavement, a) you’re happy to use snow-melt pellets that just melt a little hole in the snow, until they get down to pavement, and b) overall, disbonding-then-plowing uses a lot less salt than melting the full thickness of the snow pack with salt.

A typical manufacturer recommendation for home use of de-icers (e.g., rock salt, calcium chloride pellets) works out to around one 50-pound bag of salt for every 1000 square feet.  Whereas the (reportedly) most common recommended rate for VDOT salting the road is about five pound per 1000 square feet.

 


Conclusion

There are a few fairly big conclusions, from the simple observation that VDOT’s use of salt and my use of salt are not at all the same.

First, just because VDOT salts the roads doesn’t mean I have an excuse to do it.  If for no other reason, what VDOT is trying to do with salt (disbondment of snow/pavement interface) has nothing what I’m trying to do (melt the entire thickness of the falling snow).

Second, you can’t take recommended salt spreading rates for road use, and apply those to melt the snow off your driveway.  It’s not nearly enough salt.  You will end up committing homeopathic ice melting, as described two posts back.

Third, using salt to melt snow in bulk — say, the full thickness of a light snowfall, off my driveway — that may be a remarkably stupid thing to do.  Again, per square foot, it takes vastly more salt to do that, than it does to treat the roadways.

While my road salt is but a minor contributor to the problems caused by society’s reliance on road salt, there’s no point in my adding fuel to the fire, needlessly.  Maybe in some climates, some locations, you absolutely have no choice but to use road salt on your driveway and walkways.  But Virginia, USDA Zone 7B, ain’t one of them.

I may take one more stab at this topic, trying to assess environmental safety of various road salts/ice melters.

And I may not.  Environmentally, the best choice is to use nothing.  So I’m not really feeling compelled to suss out various road salts’ claims of environmental friendliness or minimal impact on machinery and the built environment.

I may be done with salt.

Post #2085: The mess that is the ice-melt market, in one phrase: Pet-safer.

 

I am still trying to get up to speed on ice-melting compounds.  So far, two things appear crystal clear.

First, rock salt — sodium chloride, NaCl, halite — is the worst ice-melting compound, in terms of metal and concrete damage, environmental harm, and pet safety.

Second, most of the claims, made by most ice melters, are, at best, exaggerations.


Pet-safer:  Crossing the line on exaggerated product claims.

But some ice-melter claims — particularly regarding “pet-safe” and “eco-friendly” — are purposefully deceptive.

And, oddly enough, those purposefully-deceptive claims of “pet-safe” and “eco-friendly” ice melts work exactly the same way.  In order to be legal, they only claim to be pet-safer or eco-friendlier.  Than what, you might ask?  Than pure rock salt.  So the first takeaway is that anything that’s even trivially better than pure rock salt — such as rock salt with some tiny amount of additives — can advertise itself as both “pet-safer” and “eco-friendlier” (…. than rock salt).


Surely we agree that rock salt is not pet safe?

By way of making this as clear as possible, let me narrow it to dogs.  And focus on the bottom of the barrel — rock salt.

A dog will get sick if it ingests too much (table, NaCl) salt.  One reference listed a dog-lethal dose of sodium chloride (salt) as 4 grams per kilogram body weight (Source:  Veterinary Toxicology, 4th Edition.)  Thus a 30-pound dog that manages to eat two ounces of rock salt, and keep it down, might reasonably die from doing that.  (That’s about three level tablespoons of table salt.)

And a dog could pretty clearly get sick from a lower dose than that.  Salt poisoning leads to vomiting, diarrhea, and, if it proceeds far enough, to neurological symptoms (e.g., inability to walk).

Salt poisoning of dogs does not appear to be very common.  Another reference said that in 1998, there were just 50 such cases reported to ASPCA poison control hot line.  Currently, salt poisoning doesn’t make the top 10 list of common pet poisons.

And, from reading a few case reports, ice-melt poisoning can occur if a dog takes a big gulp of the stuff, straight out of the bag.  But, in general, that’s not the problem being addressed by use of “pet-safe” de-icers.  A mouthful of de-icer is going to be bad for your pet, no matter what.

Instead, people who buy pet-safe ice melt are worried about dogs walking on areas treated with (e.g.) rock salt as an ice-melter.  First, salt irritates dogs’ paws.  And second, dogs ingest salt from licking off salt crystals stuck on or in their paws,

The upshot of all that is that rock salt (NaCl) is something you don’t want to see in a “pet-safe” ice melt.

So what do I find, off the crack of the bat, on the Home Depot website?

And that’s not a one-off accident.  Here’s the same nonsense from Uline, a supplier of industrial products of all types:


So …

Once you move beyond colored rock salt — clearly not pet-safe — there’s some real ambiguity as to what’s safe or not.

Urea is typically considered fully safe for dogs and cats (but is not safe for ruminants).  But urea is basically high-potency nitrogen fertilizer.

I can’t see myself dumping a 50-pound bag of 43-0-0 fertilizer on the driveway in winter.  Or in any season, really.

Plus, it’s a poor ice melter, and you’d be hard-pressed to find it bagged in bulk for consumer ice-melt use.  Apparently, it is only commonly used in specialty situations such as elevated metal walkways, where lack of metal corrosion is the key concern for the ice-melt.

Acetate ice melters (calcium magnesium acetate (CMA) and potassium acetate (KAC)) are considered pet-safe by some.  But these, too, perform relatively poorly as ice-melters, and are expensive per effective melting dose, as well.  They have the additional advantage of not being chloride salts, and so being less toxic to the aquatic environment than (say) rock salt.

Beware “with CMA”, just as you should beware pet friendlier.  A lot of ice-melt blends want to bask in the glow of CMA without the bother and expense of actually including much of it in their blend.   (Plus, the ice melter probably works better as an ice melter if you go light on the CMA, because CMA apparently is not a very good ice melter.  It just has the big advantage of killing less stuff than chloride salts do.)

Magnesium chloride is considered safer for pets than other chloride salts.  It is sold, for example, by both PetSmart and PetCo as a pet-safer de-icer.  It also performs quite well as a de-icer.  From a pet-safety standpoint, the only drawback appears to be price.  In retail packaging, MgCl2 appears to cost anywhere from five to ten times as much as rock salt.  But, as a chloride salt, this is not materially better than rock salt, from the standpoint of toxicity to the aquatic environment.  And some references suggest that it causes more damage to concrete than rock salt does, particular to newer (under-one-year-old) concrete.


Conclusion

I have no dog in this fight, if you will excuse the phrase.  I don’t own a pet, so this isn’t my problem.  I only stumbled across it in looking for ice melts that aren’t chloride salts, hoping for lower environmental impact.  And was vaguely outraged once I figured the whole pet-friendlier thing as discussed above.

But I note that it is a common and accepted practice in the ice-melt market to take a bag of common rock salt, color it (green or blue, inevitably), sprinkle in some actually pet-safe materials, slap “pet-safer” on the bag, and then double the amount charged for it. 

Unlike pet food, nobody appears to regulate anything about “pet-safer” de-icers.  Even though the danger arises from pets eating the stuff.  Contrast that the the multi-agency Federal regulation of pet food.  (Not that the Feds need to regulate de-icers per se, but the use of “pet-safer” and similar legal-but-misleading claims.)

Unsurprisingly, then, a lot of stuff offered in the big-box hardware stores as “pet-safer” ice melt is just rock salt (plus a tiny amount of additives) sold at a steep markup.

Caveat emptor.

Post #2084: Homeopathic pavement treatment.

 

I’m no longer going to use pavement de-icer (rock salt, road salt, ice melt).

For now, at least.

That’s because, upon inspection, much about the modern road salt/pavement de-icer market confuses me.

But in my defense, I had a lot of help, getting confused.  The whole retail “de-icer” market pings my bullshit detector in some strong and unpleasant ways.  Not just the simple stuff (“melts as low as … ).  More importantly, “pet-safe” and “eco-friendly” have quietly morphed into their mealy-mouthed “safer” and “friendlier” versions.  And not in a good way.

Road salt is a deep topic, but I have to start somewhere.

As described in Section 1 below, I did not intend to fuse the principles of homeopathy with those of winter pavement maintenance.  That happened entirely as a result of my own stupidity.

But, per Section 2 (next post), I had a lot of help being stupid about it.  Pavement de-icers are arguably the worst consumer product I’ve ever seen, in terms of manufacturers’ claims and deliberately misleading marketing.

Plus, Section 3, the practical use of chemical pavement de-icer is complicated. Even absent all the baloney presented by sellers of de-icers, there’s a lot to unpack.  I’m not sure I understand the chemistry part of it, yet, let alone the weather’s contribution.

And, Section 4, most (perhaps all) commonly-used de-icers are crap for the environment, especially the aquatic environment.  I can’t complain about the taste of road salt in the drinking water if I’m spreading this stuff on my own driveway.

This is just the first of several posts on pavement de-icer.


Part 1:  Driveway homeopathy

1A:  The hasty but satisfying post-hoc conclusion

Source:  Good ol’ clipart-library.com, which has upped its game with an on-the-fly AI picture generator.

A few days ago, I salted my driveway, using calcium chloride pellets.  The idea was that the (calcium chloride) salt would melt a coming light snow, causing it to run off my driveway as (slightly salty) water, and, ideally, leaving me with bare pavement. Instead of a driveway with an inch of snow on it.  This, as being preferable to re-shoveling my driveway to remove a light coating of snow.  And this to be achieved despite temperatures consistently (but not hugely) below 32F.

By the end of the next day, my driveway was dry and snow/ice free.

So the salt obviously worked, right?  End-of-story.

Part 2:  But … science

As I was patting myself on the back, I could not help but notice that all my neighbors’ driveways were also dry and snow-free.

Which, after a moment’s solemn reflection, pretty strongly suggested that my salting my driveway was a complete waste of time.

I’m pretty sure none of my neighbors salted theirs.

Part 3:  thus was born the short-lived science of driveway homeopathy.

First, I found a pretty chart.  (This is, in fact, an excellent chart from an excellent practical reference.)

Source:  National Tank Outlet.  These folks sell the tanks you need to store this stuff at industrial scale.

Those substances are all salts, chemically speaking:

  • CaCl2 — calcium chloride
  • NaCl — salt– rock salt — halite — sodium chloride
  • MgCL2 — magnesium chloride
  • CMA — calcium magnesium acetate ( calcium acetate and magnesium acetate).
  • KAC — potassium acetate.

Then doing this crude calculation:

And then, only as a last resort, actually reading the directions on the bag.  Which, they just flat out say, per for 1000 square feet, for some “typical” conditions (I guess), I should use just touch more than what I calculated above.

The upshot is that I should use at least an entire 50-pound bag of calcium chloride.  On a 1000-square-foot section of driveway.  That, to get rid of an (one) inch of typical snowfall.  That should make a brine strong enough to have all that snow turn to water and run off, even though the weather is (maybe) 10 degrees below freezing.  This, instead of shoveling the driveway, again, for the new inch of snow that fell.

I’ve never used it at anything close to that rate.  I use it a few pounds at a time.  (And, correspondingly, my first (and current) bag of calcium chloride is at least a decade old.)  Nor will I ever.

Ergo, I have been engaging in homeopathic ice melting.  Sure, I start off with strong brine, when those first few snowflakes hit those salt (calcium chloride) crystals (pellets).  Implicitly, I must have believed that after adding a whole lot more water (in the form of an inch of snow), the resulting very dilute brine would somehow recall the strength it once had, and so continue to melt the snow.

Contrary to the laws of physics and chemistry.  Or common sense.

Or the directions on the bag.

Or all of the above.


Conclusion

For now, the simple message is that homeopathic pavement de-icer helps no-one.  Avoid it.

It achieves nothing while causing slight environmental harm. It’s a net negative, except perhaps in (easily deceived) the mind of the user.

So, with regard to salting the pavement:  Do.  Or do not.

Crazily enough, I have a lot more to say about ice melters.  That’ll come out in the next posts.

Post #2080: Vienna, VA sidewalks in the snow.

 

In Vienna, VA, we are religious about shoveling the snow off our sidewalks.

God put the snow there.

God will remove it when he’s good and ready.


I tried to take a walk yesterday morning …

… without walking on snow and ice.

But, because I live in the Town of Vienna, that meant spending a lot of time walking in the road.

There’s no requirement to shovel your sidewalk in the Town of Vienna.  Unsurprisingly, some sidewalks are shoveled, some aren’t.  Which means that you typically can’t walk the length of a block without either walking on an un-shoveled sidewalk, or walking in the road.

This got me to thinking about what the snow-clearance laws are in Northern Virginia.  I know there’s no ordinance requiring it in Vienna.  But what about the rest of Northern Virginia?

Turns out, Vienna is in the minority.  Most of the jurisdictions around here require residents and business owners to shovel their sidewalks promptly after a snowfall.

I find that to be an oddly mixed bag.  Loudoun County is in general far more rural than Fairfax County, yet they require snow shoveling while Fairfax does not.

In all cases, the penalties for failure to clear a sidewalk are nugatory, so it’s not clear whether any of the laws are or are not effective.  I considered taking a field trip to the People’s Republic of Falls Church to see if their sidewalks really do get cleared or not.  But it hardly seems worth it.  Give it another few days, and the snow will be gone.

In the end, it’s just another oddity of living in No. Va.  These jurisdictions all have the same weather and have pretty much the same population demographics.  I’m guessing that the presence or absence of a shoveling ordinance is mostly a matter of historical accident.

In any case, in Vienna, we clear our sidewalks the old fashioned way, via religious observance.

Addendum:  Businesses in Vienna VA?

I know there’s no ordinance requiring homeowners to shovel their sidewalks in Vienna, but I was immediately questioned about businesses.  You can, and many places do, have different shoveling laws apply for business versus residential.

Old news reporting says that Vienna Town Council turned down any sort of shoveling ordinance in 2011 (Reference The Patch).

And that’s the last Google seems to have heard of it.

A search of MuniCode for Vienna VA for snow yields 13 mentions, none of which have to do with requiring businesses to shovel snow.

A search of the Town Website yields nothing useful, but that’s never definitive.

For sure, the Maple Avenue sidewalks were cleared around here.  Here’s Pleasant and Maple, looking west and east.

So, I don’t know.  There doesn’t seem to be an ordinance requiring it, but something resulted in the clearance of the Maple Avenue sidewalks in my area.  This is distinctly different from (say) Nutley, also a multi-lane road, but with large sections of un-shoveled sidewalk.

If it’s due to an ordinance, that ordinance appears well-hidden.

Post #2077: I opened the hood of my car.

 

Finally.  I finally opened the hood of my 2020 Chevy Bolt, a year after I bought it (Post #1924).

I never saw a reason to look under the hood, figuring I’d have no idea what I was looking at.  It being an EV, and all.

Now that I’ve opened the hood, I was not disappointed.

Not ringing a lot of bells with me.  I think I recognize a brake master cylinder and tan plastic reservoir mounted to the firewall, driver’s side.  But all those big metal thingies?  No clue.

Luckily, one can be ignorant and still drive a car.  That, proven daily, I’d say.

Even now, I wouldn’t have bothered to open the hood, ever, except that with the recent winter storm, and the resulting sloppy roads, I figured I should top off windshield wiper fluid.  Seeing as how that hadn’t been done in a year.

I was able to do that without reading the manual.  The hood release was in an obvious place, the hood emergency latch was easy to find, and (shown below) the right place for windshield wiper fluid is pretty clearly marked.  Even had a hood prop where I expected to find it.

So thumbs up to Chevy for making that much obvious.

Weirdly, I swear there’s a fan and radiator in there somewhere.  For sure, there are several little reservoirs that look like they hold coolant.  Plausibly that’s all part of whatever manages the temperature of the battery and the electronics.

It’s magic, as far as I’m concerned.

Plus it runs at a lethal 350V DC.  As long is to works, leave it be.

And pour carefully.

Post #2027: Toilet paper and self-fulfilling prophecies

 

It says something deeply, deeply weird about the soul of America, that people are panic-buying toilet paper in response to the East and Gulf Coast port strike.

I had a few responses to this, in no particular order.

First, guess I’m glad I haven’t worked my way through my pandemic stockpile yet.

Second, maybe I had better pick up some toilet paper at the store today.  Just in case.

I fully realize that toilet paper doesn’t move through these ports.  Almost all toilet paper used in the U.S. is produced domestically, call it 93% (reference Yahoo).   The rest that is consumed in the U.S. is produced in Canada and Mexico, and isn’t shipped by ocean-going freighter.

And yet, it’s a fallacy to say that toilet paper should be unaffected by the port strike.  If enough people are stupid and irrational about it, and the target of their stupidity is toilet paper, then toilet paper is very much affected by it.

Oddly, if you substitute “Springfield, OH” for “toilet paper” in the last sentence, it still makes perfect sense.

Anyway, the consequence being that if you need to buy TP, you’ll be every bit as much out of luck, even though a shortage is purely a result of irrationality, as if there some actual disruption of the toilet paper supply chain.

Some consumer items will likely go out of stock from this strike.  Bananas being the poster child for that.  But who would have guessed that TP remains the canary-in-the-coal mine for American anxiety.

Source: Clipart-library.com

Post #2008: Pedestrian traffic counts via cheap camera.

 

It took about an hour to construct the vehicle and foot traffic counts you see here.  The hardware was an $18 Kasa camera, plus my laptop to view the resulting footage.

I let the camera film the street in front of my house.  That was not intrinsically different from (e.g.) a Ring doorbell.  (It is legal in Virginia to film anything in the public right-of-way, or anything you can view while in the public right-of-way, other than restricted areas such as military installations, as long as you don’t record conversations that you are not part of.)

I then did the simplest thing possible.  I transferred the SD card from camera to laptop, and watched the video on fast-forward.  It was like the worlds most boring, yet tense, home video.  I stopped the film when something happened, and put down tally marks.

The fastest I could comfortably watch was 16X.  Doing that, recording the events in eight hours of video took about an hour.  (The camera itself is capable of noting the passage of cars, via built-in motion detection, but would not identify passing pedestrians at the distance this was from the street.)

If nothing else, this confirms what my wife and I had both noticed, that this street is used by a lot of dog-walkers.

This is just a proof-of-concept.  Today it’s drizzly, and there’s a school holiday, so this would not be representative of typical Friday morning foot traffic.

The context is the value of sidewalk improvements in the Town of Vienna.  With rare exception, there are no counts of pedestrian traffic in any of the Town’s various studies.  (I did find one, once, but they referred to rush-hour pedestrian street crossing counts along selected corners of Maple Avenue, our main thoroughfare).

The idea being that there’s more value in putting a sidewalk where people will use it, than putting it where they won’t.  Assuming that current foot traffic along a route is a good indicator for eventual foot traffic there, once a sidewalk is built.  (There could be exceptions to that.  But in the main, I think that’s right.)

And that, for planning purposes, you’d like to have some idea of what they’re using a particular route for.

There are currently at least two ways to get pedestrian count data on (e.g.) suburban side-streets that do not have traffic lights.  Other than the old-fashioned approach of having somebody sit by the street and count passers-by.

One is to use cell-phone data, because many cell phones track and report their user’s location on a flow basis, and that information is sold commercially.  Courtesy of the improved accuracy of GPS, data vendors can now tell you (e.g.) how long the average customer walks around a store, based on how long their cell phones linger there.

(I am not sure that this tracking is entirely “voluntary” or not.  That is, did you download an app that, had you bothered to scrutinize the dozens of pages of fine print before clicking “ACCEPT”, would have revealed that you gave that app the right to collection and transmit your location to some central source?  Or, just as plausibly, if you don’t manage to turn off every blessed way that your phone can track you, then somebody’s picking up your location on a flow basis, you just have no clue whom?  For sure, the phone companies themselves always have a crude idea of where your phone is (based on which cell tower your area nearest), and I’m pretty sure they also get your GPS data, nominally so that they may more accurately predict when your signal needs to switch from one cell tower to the next.)

The problem with counts based on cell-phone tracking that it is of an unknown completeness.  Plausibly, some people manage to keep themselves from being continuously tracked.  Or, more likely, any one data vendor only buys that data from a limited number of app providers.   Generally, it’s fine for making relative statements about one area versus another, but needs to be “calibrated” to real-world observations in order to get a rule-of-thumb for inflating the number of tracked phones in an area, to the actual on-the-ground pedestrian count.

Plus, it costs money, and it’s geared toward deep-pocketed commercial users.

Finally, it’s likely that certain classes of pedestrians will be systematically under-represented in cell phone data, most importantly school children, but also possibly joggers.

The other way to do it in the modern world is to use a cheap camera.  Then count by eye.

So, as an alternative, I decided to see how hard it would be to gather that information this way.  Turns out, it’s not hard at all, even with doing the counts manually.  All it takes is a cheap camera, my eyes, and, for eight hours of data, an hour of fast-forwarding.

Not sure where I’m going with this, in the context of writing up the multi-million-dollar make-over of my little street.  I just wanted to prove that it’s not at all hard to get data-based counts of pedestrian traffic on any street.  All you need is a camera, and a place to put it.  And the time to view the results, if you can’t figure out an automated system for that.

My approach may be a bit low-tech for the 21st century in the surveillance state.  But it works.  Fill in the hourly wage of (say) the employee who would have to watch that video, and you come up with a pretty cheap way to provide hard data on need for sidewalks, as evidenced by counts of pedestrian foot traffic.

If you’re going to spend millions of dollars on sidewalks … how could you not do this first, to see that the expenditure is efficient, in the sense of pedestrians served per dollar of expense?

More on this still to come.


Coda

As if to underscore the power of the surveillance state, about six hours after I posted this, I got my first-ever email from Kasa, with an offer for a video doorbell.

That, presumably, because this blog post had the words “Kasa” and “doorbell” in it.

This happens enough that I know the root cause of it.

Sure enough, yesterday I signed into Google, using this browser, to access something via my Google account, and I foolishly forgot to sign out.  Google was therefore somewhat aware of just about everything I did on this browser in the meantime.

Presumably Google ratted me out to Kasa.

Somewhere, the ghost of Orwell is surely laughing.