AN AVERAGE WINTER IN QUEBEC CITY
Snowfall (1991-2011): 10 feet
Service area: 2,700 lane miles
Number of dump sites: 14
Total storage capacity: 12.7 million cubic yards
Amount collected: 7.2 million cubic yards
Snow and ice control budget: $60 million
Amount related to dump operations: $1.7 million (2.8%)
After 30 years with the Quebec City Public Works Department, Engineer Eric Langlois has literally written the book on snow and ice removal. It's a subject you can't avoid in one of the world's snowiest cities, where all planning centers around a six-month winter.
Langlois wrote the city's snow removal policy, which defines level of service (including anticipated delays), prioritizes routes, and assigns material — salt, sand, or gravel — based on traffic volume. Dump sites are a crucial part of keeping operations running smoothly.
As the population has grown, residential development has decreased the number of locations suitable for the noisy, unsightly task of dumping collected snow. Finding the ideal spot is a delicate balance. The site has to be far enough from residential areas to avoid noise complaints — as most of the dumping, shoveling, and snow-blowing happens at night — but close enough to be cost-effective. “Distance is the most important cost factor in choosing a dump site,” says Langlois. “If it's too remote you'll need more trucks to keep it in constant operation, which means a bigger price tag.”
Thus, most of Quebec City's dump sites are in flat, industrial zones near highways. They're typically surrounded by a dirt bank, and sometimes trees, to mitigate noise and make the bare site more attractive year-round.
Size is another important consideration. “Design for a larger capacity than you actually need, so the snow dump can be used for 20 years or more,” says Langlois. “Try to anticipate factors such as population growth and unusually heavy snowfall.”
Optimizing design and delivery
Over the years, his team has optimized its 14 locations for more efficient use of space as well as equipment operator time, developing what Langlois considers the most effective snow dump design: a rectangular site with just the right combination of heavy equipment.
The city has always used bulldozers to pile the snow deposited by trucks. A Caterpillar 950G loader with plow channels snow into place while a Caterpillar 235C excavator equipped with an 8-cubic-yard bucket stacks it higher onto the pile. By adding heavy-duty snowblowers with 5-7,000 tons of blowing capacity per hour, crews can bank the snow up to 72 feet to maximize space — and process up to 125 truckloads every hour.
To prevent avalanches, operators maintain at least a 45-degree angle from the ground to the top of the snow bank. Abutments made from truck-loads of snow stabilize the pile, and new snow is blown over the top.
With the rectangular site design, operations are choreographed from back to front, and from outside in. The site is divided into two discharge zones, both working toward the middle (see diagram below). Trucks unload from one end and the snowblower processes discharged loads from the other.
Up to 250 trucks an hour arrive through one access point (some dumps have two access points and can process up to 500/hour), and are directed by one to four onsite signalmen, depending on dump site volume. Langlois explains their critical role, not only for traffic control, but also to keep the operation on budget. “It's very important to separate semi-trailers from 10- or 12-wheel trucks because they don't maneuver as easily and move more slowly. If the other trucks have to wait, the city pays more for lost time and the whole operation costs more.”
Before they receive a single load, dump sites are designed with a peripheral drainage ditch to collect water and graded to ensure proper runoff. Water collects in a decantation basin on one end, where it flows through an oil and grease separator before leaving the site. Sediment settles to the bottom, where it's periodically analyzed and reused or discarded according to environmental regulations.
The signalmen also separate trucks filled with snow by loaders from those filled with blown snow. The snow collected by loaders may contain larger objects that can break the dump site snowblower and paralyze operations.
As the trucks enter and leave the site, each driver's radio-frequency pager tracks delivery time and location. A validation device on the street snow-blower contacts the pagers to confirm each trip, so dump operators know where the snow has been collected and can confirm that no snow is being brought in from private areas.
At the site gate, information from pagers is automatically transferred to the city's accounting and payroll system, which calculates driver pay by volume based on truck capacity information provided by the contractor. At the end of the season, Langlois and contractors review the data, including the average amount collected in each zone, to tweak contract specifications for the coming year.
Half of the city's snow removal and all snow dump operations are handled by independent contractors, so the time and money saved by streamlining payroll and contract negotiations is significant.
Managing runoff correctly
Each Quebec City snow dump is designed with a peripheral drainage ditch to collect the runoff created by melting snow and rain. Before the Province of Quebec Ministry of Environment approves the construction of a new site, its design and location must meet many environmental specifications, especially those related to water protection and treatment. For example, the land must be properly graded to ensure water runs to a decantation basin at one end.
Here, sediment naturally settles to the bottom; public works removes and analyzes it once a year. If contamination levels are low, the muddy residue is reused in construction projects — for instance, to create banks at other snow dump sites.
Dumps return runoff to natural sources, so before leaving the site runoff goes through an oil and grease separator to remove residue from snow collected on streets or equipment leaks. “We try to use nearby streams, but they must be large enough to dilute the salt that remains in the runoff water without harming the environment.”
His advice for designing a decantation basin:
Ensure adequate capacity by calculating the number of inches in a heavy rainfall and adding the amount of snow that melts within one hour. Assuming the water in the basin is 3 feet high, you can determine the necessary surface area based on this maximum projected volume.
- Verify the need to waterproof the basin, which is determined by the nature of the site's soil and local groundwater usage. The Province of Quebec Ministry of Environment, for example, requires basins to be lined with waterproofing fabric.
- An elongated basin shape is most efficient.
A significant investment
Langlois is planning a new snow dump to replace smaller sites. The city will spend $12 million on the site — $6 million for land, and $6 million on construction.
Quebec City owns 12 of its 14 snow dump sites, a practice Langlois recommends. “If the land is owned by a private company, they can always raise the price when the contract is up and the location is even more in demand,” he says.
Although the new, 2.6-million-cubic-yard site is farther from the city and will add $300,000 to annual snow removal operations, he considers it a sound investment. “It's an old stone quarry with a 100-foot deep pit,” he says. “It will accommodate future development of the city and handle exceptional amounts of snowfall — and excavation materials if needed. This site will generate financial benefit for the next 20 years.”
For more information, contact Eric Langlois at 418-641-6411 or firstname.lastname@example.org.