Roseville street maintenance worker Josh Dix was slated to present in-person at the Road Salt Symposium last February, but Mother Nature had other ideas.
On the morning of the conference, a heavy, wet snow started falling, and it didn’t stop. Dix was kind enough to stop at home in the middle of his plow route so that he could still give his presentation remotely before heading back out into the flurry.
Roseville is trying to use more brine to reduce the impact of road salt on water quality. At the time of the symposium, the city had already used 35,000 gallons of brine during the 2018–2019 winter. Dix credits the increased usage to two easy, inexpensive changes they made to their plow trucks.
No nozzle
Dix says he took a "smart salting" course when he first started working for the City of Roseville and learned that 10 gallons per ton was a good brine rate. He measured Roseville’s rates and found they were low. The fan nozzles on the gravity output were allowing only 0.35 gallon per minute.
“It’s barely a trickle, so we took the nozzles out,” Dix said. “It’s really as simple as that.”
Removing the nozzle increased brine output up to four times, up to 1.3 gallons per minute. Driving 20 miles per hour with a granular rate set to 400 pounds per mile, the rate was 5.25 gallons per ton with the nozzle. Without it, the rate increased to 19.5 ga/ton. At 30 miles per hour, the rate was 3.5 ga/ton with the nozzle. Without it, 13 ga/ton.
There was some variation with different tank levels, but the increase overall remained significantly higher than with a nozzle. “If you’re thinking you’re going to lose that coverage, it really wasn’t there to begin with. You’re not losing much,” Dix explained.
Hydraulic pre-wet pumps
December 2013 was very cold, with no sun and a lot of icy hard pack. “We really wanted to get more liquid, especially treated liquid, on our salt to keep breaking down that hard pack,” Dix said. “So that’s when we made the decision to start buying trucks with hydraulic control pumps rather than gravity.”
Dix likes the hydraulic pre-wet pumps because you can easily calibrate them, just like road salt. They also have speed control to keep your rate even as you drive faster, they allow higher rates so you're able to get more brine out, and you're able to keep accurate records of your brine usage with the pumps. “With gravity, it was a rough estimate at best,” Dix said.
He was hesitant at first after hearing bad things—such as seizing pumps—from some people. Roseville has had a few issues, but Dix said they've mainly been due to their own negligence. Pumps need to be cleaned out and prepped for summer properly and kept filled with liquid instead of air at all times. “The one that we took care of has not had any issues,” he said.
With the controller, the pump can be set to a max of 72 gallons per ton, and the VariTech Industries pre-wet pump is capable of a maximum of 10 gallons per minute. The flow seemed restricted at higher rates, Dix said, with not much liquid coming out. “Once again, I ended up pulling the nozzles out,” he said, in order to get the full flow that the pump is capable of.
Pre-wet vs. DLA
Brine pre-wet is measured using gallons per ton while liquid deicing uses gallons per mile. Because the liquid pre-wet rate is tied to the granular rate, at low granular rates the liquid rates are exceptionally low.
Dix guessed the common direct liquid application (DLA) rates are 50 to 100 gallons per mile. DLA rates are generally higher than anti-icing rates.
If salt is set to 100 pounds and pre-wet to 15 gallons per ton, that converts to 0.75 gallons per mile. If you increase your salt to 200 pounds at the same pre-wet rate, that equals 1.5 gallons per mile. “That’s pretty much nothing,” Dix explained. “Think about taking a gallon jug of brine and spreading it out over a mile. I can’t imagine why that would do very well.”
Dix wanted to get to 25 gallons per mile—at the low end for anti-icing, but a good starting point— and to get the pump to max capacity. However, the controller limited the pump to 72 gallons per ton. This didn't require an equipment change, just a programing change.
For around $100, Force America (of which VariTech is a subsidiary) will email you a file. You put it on a thumb drive and load it into the controller. “It’s as simple as that,” he said. “You load it and it resets, and now it thinks your pre-wet pump is a direct application pump.”
You have to adjust a few calibration settings: disable “pre-wet,” enable “direct,” and remember your previous calibration rate. Dix ran out of brine quickly at 25 gallons per mile so he backed it down to 10 gallons, which has been the best balance on a single axle for Roseville. At a granular rate of 200 pounds per mile, this compares to a pre-wet rate of 100 gallons per ton of salt. With cold pavement temperatures, the city has been experimenting with 15 to 20 gallons per mile.
Salt use down
During the 2017–2018 winter, Dix's modified truck averaged 34 percent less salt than an average of other comparable routes over eight events. For three of those events, the modified truck averaged 42 to 68 percent less. During one event, it was over the average by 20 percent.
“That’s pretty huge, I think, to be using two-thirds less salt than the average of my coworkers,” Dix said. “I’m really excited about the possibility that that gives us in still maintaining a really high service level but using quite a bit less salt to do it.”
This past winter they modified a second truck. This driver had previously been one of the higher salt users, but with the modified truck during this past winter’s New Year's Eve storm, his salt use was 33 percent less than the average of the other seven trucks, and similar to Dix's modified truck.
There are some challenges. For starters, you run out of brine quickly. Dix wants more liquid capacity, and to be able to drive faster than 20 miles per hour without maxing out the pump.
But with two simple, low-cost changes, Dix and the City of Roseville achieved significant salt reductions. Removing the nozzle increased brine output on their gravity systems nearly 400 percent. In hydraulic systems, he concluded, if you’ve gone to pumps, reprogram the controller to maximize pump output. “Without any big purchases or an increase in cost, it’s possible to use a lot more brine.”
—Paul McDivitt, LTAP freelancer
