Keeping Dirt Onsite

Trackout and wheel wash systems

Credit: MOBYDICK
Roosevelt Island

The scope of work for BMP Contractors in ­Riverside, CA, has greatly expanded with new construction permit requirements, notes ­company president Doug Sadler.

“Everybody is affected by the activity of the stormwater pollution prevention plan [SWPPP] now,” he says. “Anything over an acre, somebody has to do something.”

With construction activity picking up these days, keeping the sediment it generates from leaving the site often requires techniques such as trackout systems, wheel washers, and other techniques.

BMP Contractors’ jobs are across the board in the industrial, commercial, government, and residential sectors. In working on various sites, Sadler prefers using Rumble Track, manufactured by Contractor’s-Services. The system is placed on job site exit roads that adjoin public streets. It removes dirt, mud, and other debris from vehicle tires and addresses PM10 dust abatement, soil stabilization, and debris trackout. The Rumble Track is designed to reduce the need for water trucks and sweeping time and to keep job site traffic moving freely.

Sadler has used trackout systems for 15 years and Rumble Track for 11 years. He says using the Rumble Track enables him to comply with Rule 403 of the South Coast Air Quality Management District, dealing with fugitive dust.

“In general, they work,” he says. “Some construction areas use rock only, and it defeats the purpose. The rock helps loosen everything up without rattling the dirt out of the treads of the tire, which is missing one of the most important steps.

“As people are driving over the rock, the dirt is spreading out and maybe a little bit is getting dropped, but it drops right in the rock,” he adds. “After a week or two weeks with no rain, the rock voids are already completely full. It almost makes a smooth surface, which defeats the purpose.”

In contrast, dirt is shaken loose before it hits the street once vehicles drive over the plates of the Rumble Track.

“We like the system without even using the rock in some areas,” notes Sadler. “It works just as fine and we’ve had great results with that as well.”

Sadler says some job site managers are requesting his company install the plates across the entire rock embedment. “The whole construction entrance is completely covered in trackout plates, so they are not even utilizing the rock,” he adds.

Sadler considers a few options in dealing with the material generated in construction activity: It can be hauled to a quarry and washed and reused, or reused onsite before crews start paving. The latter is preferred. “The cost to deliver the rock is $800. To remove that rock and haul it back costs about $1,600 because you have to rent a piece of equipment, move it in, and you’ve got labor involved. A lot of contractors try to save money on that aspect and use it on the job site.”

For dust suppression at the construction entrance, Sadler says, “It’s usually two guys with a broom every day or so for a few hours toward the end of the day, sweeping the Rumble Track to keep the dust from tracking out.”

If a construction-site entrance is designed correctly, it works well for a contractor in taking care of both dirt and dust, Sadler points out.

“Usually it’s rock, plates, and then rocks. These will usually rattle the dirt off right into the voids of the three-inch minus rock and eliminate the trackout, which also eliminates the dust,” he says.

California’s recent drought conditions have underscored the need for a trackout system that doesn’t rely on water. “Especially where we are at in California, we have extremely strict regulations on everything,” notes Sadler. “We don’t really use a wheel washing system here because it creates a bigger mess and also requires the owner of the project to file for a hazardous waste permit when they dispose of this water at a hazardous waste facility, because it will have grease, brake dust, and all kinds of contaminants from washing the wheels. You’ve turned your $1,800 construction entrance into a $5,000 or $6,000 entrance when it’s all said and done.”

Sadler says that being in the erosion control business, “We try to use the most sophisticated, up-to-date BMPs that are out there. We want maximum protection at minimal costs in most instances, but a lot of these engineers seem like they’re 20 years back using old details from their engineering programs. It makes it tough and very expensive and I don’t think it’s as efficient as it could be.”

Sadler uses other BMPs to supplement trackout measures. “As we’re building these SWPPPs and [specifying] erosion control, it’s a complete field project,” he says. “We’ll have fiber rolls, silt fence, or gravel bags on the perimeter and will close it off right to the construction entrance.”

Of late, he’s used ProWattle from Ertec Environmental Systems as part of perimeter control. It is designed to allow water flow-through, reduce water velocity, and filter particulates. It is constructed of recycled post-consumer or post-industrial content and is recyclable as HDPE at the end of its life.

“We stick it in front of the construction entrance, so it would be up against the rock and the asphalt and creates a lip as vehicles are driving out; that means the whole perimeter of the property is sealed,” says Sadler. “It’s resilient where the trucks are driving in and out—you just run it over.”

When it comes to designing SWPPPs, Sadler says his clients are finally starting to understand that the rainy season is essentially considered to be January to December. “It used to be from October to April. Our contractors and some of our clients are old school, and their thought process is that in certain months it doesn’t rain, and that’s not the case anymore.”

Under the new general permit, disturbed sites of an acre or more need to have protection year round, Sadler points out, adding that California mandates that each client have a Qualified SWPPP Practitioner, or QSP, onsite for weekly inspections.

“It’s been helping, because there is more maintenance going on,” he says. “We’re onsite a little bit more. I think they understand with some of the fines that the state government is not messing around once they’re out of compliance. Everything has to be uploaded quarterly to SMARTS now, so these guys are having to monitor themselves.”

SMARTS, the Storm Water Multiple Application and Report Tracking System, is an online database for dischargers to electronically file their stormwater permit documents, which can be accessed by everyone from the public to regional and state board staff.

“It’s good for everybody,” notes Sadler. “It’s good for the environment, the storm systems, and also our clients, because some of the fines that have been given out have been in the millions. California is coming down hard on these guys who aren’t putting out their basic approved BMP plan. It has to be approved by the City before they start working.”

Roosevelt Island
Meanwhile, on the East Coast, to comply with the erosion control requirements of the New York City Department of Environmental Protection, Ferreira Construction has utilized two MobyDick Wheel Washing Systems in a project on Roosevelt Island, a narrow island on the city’s East River.

The project is on the Cornell Tech campus, where the university is building what its officials describe as an “innovative, sustainable, academic campus made up of a combination of state-of-the-art academic space, an executive education center and hotel, housing for faculty, students, and staff, and publicly accessible open space.”

The first of multiple phases opens this year. For a construction project encompassing more than 2 million square feet, Tishman Construction is providing the pre-construction services. Ferreira Construction has been involved in the landscaping and utilities package portion of the project.

MobyDick Wheel Washing Systems are offered in various models as both drive-through units and roller units that correspond to the amount and type of soiling experienced on a job site, from “dusty” to “sticky, cohesive soil.”

The systems Ferreira Construction is using are ConLine (Construction Line) Mobile C units. The portable wheel wash system, made for the rental industry, has a modular building block design; it can be converted into six different models depending on site considerations, says Robert Lodi of MobyDick.

The system features a 13-foot-long wash platform with two side-spray bar assemblies and a 2,900-gallon scraper conveyor and solids separation removal system. It also has water recycling capabilities. It can be assembled as a one- or two-tire revolution system.

Ricardo Barahona, project manager for Ferreira Construction, says his company has placed the units in two locations where a great deal of traffic leaves the site. The units prevent material from being carried off the site into the local streets.

Typical vehicles at the site include dump trucks, tractor-trailers, and smaller vehicles, says Barahona. In addition to the MobyDick Wheel Washing Systems, a water truck is onsite for dust suppression, as well as a sweeper to prevent material from going off the site.

Because the site is small, “there’s not much open space, so you work within the limits and constraints of the site,” says Barahona. To comply with SWPPP requirements, other perimeter control measures include hay bales. Catch basins are protected with silt fence. Ferreira Construction’s goal is twofold: keeping sediment from the city streets, and keeping it from entering the East River.

The collected solids from the wheel wash systems are tested for contamination, says Barahona. If the solids are free of contaminants, they are spoiled onsite. If they do contain contaminants, they are sent to Bayshore Recycling in Keasbey, NJ, for handling.

The MobyDick systems are configured at Roosevelt Island to accommodate the site’s high water table and to minimize loss of water during the wheel washing process, Lodi says.

Ferreira Construction started its work in May 2016 and is expected to have it completed later this year.

Choosing a System
The choice of a wheel wash system, where it is placed, and how it is used are significant factors in deriving the optimal benefit from it, says Mark Kestner, president of the National Environmental Service Company. The company manufactures dust abatement equipment as well as a portable wheel wash system. He notes that not only construction sites but also quarries, ready-mix plants, and other industrial facilities have become the targets of increasingly stringent regulations designed to prevent trackout of mud, dust, and dirt on to public roads.

The primary driver of the regulations is a response to EPA designating many cities as “non-attainment areas” for their failure to comply with air-quality standards for fine particulates, he points out. The particulates—PM10 and fine respirable PM2.5—are now regarded as the primary health hazard in urban environments, says Kestner.

“These particles are so small that they become lodged in the alveoli of the lungs, where they can cause or aggravate a variety of respiratory diseases including asthma, emphysema, and lung cancer,” he says.

Local governments in non-attainment areas must comply with fine particulate standards or face the loss of federal highway funds, says Kestner.

Whether driven by regulations or simply the desire to be a good neighbor, many companies are using rumble grates and tire wash systems on construction sites, he says.

Kestner points out there are four types of wheel washes: flooded basins, countercurrent channels, low-pressure inundation, and high-pressure cleaning, all of which will do an effective job if properly designed, operated, and maintained.

Flooded basin washes consist of a shallow basin long enough to permit at least one tire rotation as the vehicle passes through it, says Kestner, adding that typical basin washes are 20 to 60 feet long. The bottom may be equipped with rumble strips to improve tire agitation.

“For best performance, fresh makeup water should be supplied to flush dirty water from the basin for collection and treatment,” he says.

Kestner says the main advantages of a basin-style wash are low cost, no nozzles, continuous operation with no automation, and the fact that the vehicles do not get wet. He cites as disadvantages the fact that the basin requires daily cleaning for optimum performance; mud flaps or wheel wells cannot be washed where dirt can accumulate; and the basin requires a large footprint.

Countercurrent channel washes are long, shallow, inclined channels for left- and right-side tires, says ­Kestner. “Water continuously flushes the ­channel countercurrent to the ­direction of traffic. Dirty water drains to a sump where it is collected for disposal or treatment. Channel washes require a great deal of space. A typical channel wash may be 100 to 300 feet long, requiring 1,500 to 4,500 square feet of space. Channels can include rumble strips or other texture to agitate or
open tire treads.”

Kestner says the advantages and disadvantages of a channel wash are similar to those of the flooded basin.

Low-pressure inundation washes are designed to clean the tires, mud flaps, and undercarriages using large amounts of low-pressure water, with water consumption ranging from 1,000 to 3,000 gallons per truck depending on the size of the trucks and duration of the spray cycle.

“These washes generally use multiple pumps capable of handling dirty water, and because of the high water consumption rate, require a large reservoir,” says Kestner. “A typical inundation wash uses sprays directed at the truck from the sides and bottom and may be combined with a rumble grate. Inundation washes operate intermittently and use one or more sensors to detect when trucks enter and exit the wash zone. The wash zone is located over a catch basin that directs dirty water into a reservoir where it can be collected and treated.”

The main advantages of an inundation wash are its ability to wash tires, mud flaps, and undercarriage and its small footprint, says Kestner. Its disadvantages include high water consumption, the risk of spray nozzles plugging or wearing out from contact with dirty water, the need for sensors and controls for automatic operation, and the fact that the system may remove lube oils and greases from the undercarriage.

Credit: MOBYDICK
A portable system on Roosevelt Island

High-pressure cleaning washes use water at pressures in excess of 150 psi to promote cleaning efficiency and reduce water ­consumption, with water consumption ranging from 40 to 100 gallons per truck depending on the speed of the truck through the wash zone, says Kestner.

“They are designed to wash tires and mud flaps and are usually not used to wash the undercarriage, because sprays designed to shoot up under the truck may obscure the driver’s vision,” he adds.

A typical high-pressure system consists of a 150- to 200-gpm pump, surge tank, and two or more vertical spray nozzle manifolds that are sufficiently separated to permit at least one full tire revolution. High-pressure systems require cleaner water, because the abrasive effects of sediment wear pumps and nozzles out more quickly, says Kestner.

He says the main advantages of a high-pressure cleaning wash are that it washes tires and mud flaps, requires a small footprint, and has low water consumption. As with the inundation wash, disadvantages include the risk of spray nozzles plugging or wearing out and the need for sensors and controls.

Basin and channel-type washes are designed to operate continuously and require no automation, says Kestner. Low-pressure inundation and high-pressure cleaning washes are designed to operate intermittently in order to conserve water and reduce wear and tear on equipment.

Water tracked from the wash can dry and leave fine silt behind that becomes airborne, says Kestner.

“For stationary wheel washes, an in-ground magnetic induction loop is preferred,” he says. “This is the same type of sensor used to activate traffic signals. It consists of an approximately 4-foot by 8-foot loop of braided wire that establishes a magnetic field at the entrance of the wash zone. When this field is perturbed by a large metal object like a truck, the sensor activates the spray nozzles.

“A second sensor at the exit can be used to turn nozzles off, but it is more common to use a single loop in conjunction with an adjustable time delay to control the duration of the wash cycle. The main advantage of the magnetic loop is that it requires no maintenance and is extremely reliable. Because it is placed in the pavement, it cannot be damaged or vandalized.”

Portable washes have two basic types of electronic sensors: electric “eyes” and proximity switches, says Kestner. Electric eyes use a transmitter and receiver to establish a beam of light. Spray nozzles are activated when the beam is broken by a passing truck. When the beam is re-established after the truck exits the wash zone, nozzles are switched off.

“While these detectors are highly reliable, they require periodic cleaning and maintenance,” he says. “The receiver and transmitter also need adjustment to keep the beam targeted. Like any aboveground sensor, they are susceptible to accidental damage or vandalism.”

Proximity switches, akin to the type that open a supermarket door, also use focused beams of light but combine the transmitter and receiver into a single unit, which substantially reduces the requirement for cleaning and maintenance, says Kestner, adding while they are very reliable, they are also subject to damage or vandalism.

“Either type can work well, but care should be taken when locating the detector,” he says. “If it is installed too close to the wash zone, mist from the spray nozzles may interfere with the beam and cause the system to run on. Sensors should be located in protected positions and armored or set in concrete to protect them.”

Just as important as the type of wheel wash system chosen is its location on the site. Consider distance from the exit of the site and proximity to water and drainage, says Kestner.

“Locating the wheel wash as far as possible from the exit will help tires to dry before trucks leave the site,” he says. “If possible, the wheel wash should be set back at least 1,500 feet.”

Kestner points out that while tires may appear clean, trucks track water out of the wash and onto the pavement. When this water evaporates, a residue of very fine dust is left on the road surface that can be re-entrained by passing traffic.

“Because the finest particles are the best light-scatterers, the haze over the road appears out of all proportion to the tiny amount of the dust that is actually in the air—especially at sunrise and sunset,” says Kestner.

Many plants have scales located at the exit with less than 100 feet of paved surface before trucks go on the road, says Kestner.

“At construction sites, there is often no paved surface and trucks often exit over a bed of riprap at the curb,” he adds. “In either case, the residue left by clean trucks has to be swept or flushed from the road. A wet vacuum sweeper is the preferred method. Water drains into a settlement pit where it is collected for treatment and recirculation to the wheel wash.”

Proximity to water and drainage is another important factor. At large quarries with more than 500 trucks per day, for example, an inundation wash that uses 1,000 gallons per truck is going to require 500,000 gallons daily, Kestner points out. “Even a pressure wash at 100 gallons per truck is going to need 50,000 gallons a day,” he says. “Whether a large plant or small, the wheel wash has to drain somewhere. Since it is easier to pump fresh water to the wheel wash than it is to drain dirty water from it, try to locate the wash close to a retention pond. If no pond exists, the wheel wash will require the construction of a 3,000 to 5,000 cubic feet settlement pit.”

Portable plants and construction sites rarely have access to a pond or pit and have to use a temporary collection basin, says Kestner. “This could be as simple as a precast concrete sump or as sophisticated as a dewatering bin that uses a liner and filter,” he adds.

Traffic pattern is another key factor in wheel wash location. “One of the biggest problems is truckers who try to bypass the wash,” says Kestner. “Consequently, truck traffic must be funneled into the wheel wash using concrete blocks or other barricades. Likewise, traffic from unpaved areas on the site must be prevented from entering the paved road leading from the wash to the exit. Moreover, truckers should not be allowed to trim their loads on clean paved surface when it can aggravate trackout.”

Take advantage of the topography, Kestner advises. “If there is a long incline up to a scale, for example, this might be an ideal location for a channel wash where wash water flows countercurrent to the direction of traffic,” he says. “Locating the wash where there is natural drainage to a sump or pond can save a great deal of money.”

Stormwater regulations in most parts of the country require that no water be discharged without collection and treatment, he points out. “Recycling dirty water can easily triple the cost of a wheel wash. Large, stationary quarries are fortunate in that they generally have large retention ponds they can use to recirculate water to the wheel wash. However, construction sites, recycling plants, and other smaller facilities do not. In the absence of a retention pond, stationary plants have to construct and install a sump or settlement pit to collect dirty water.”

The size of the retention pond depends primarily on the number of trucks washed in a day, and ponds are often equipped with one or more weirs that allow clean water to overflow into a sump where it can be recirculated.

“Many washes employ pumps that can handle this muddy water, but using it to wash tires can aggravate silt carryout,” points out Kestner.

Water can be filtered through bag and sand filters. “Bag filters are relatively inexpensive and are available in configurations that use two or more bags so that they can be changed while the filter is online,” says Kestner. “Bag filters, however, require periodic replacement and can significantly increase maintenance costs. Sand filters are also high-capacity filters, but they can be back-flushed to keep them clean. While more expensive than bag filters, maintenance requirements are much lower.”

Portable plants and ­construction sites can use dewatering bins to ­collect and filter water, he says, typically 30- or 40-cubic-yard roll-off containers fitted with a mesh liner and filter. The liner is used to keep the filter away from the walls and promote flow through it. The filter should be porous enough to allow a sufficiently high water flow but fine enough to capture the bulk of the dirt, says Kestner, adding that a typical filter of this type will generally remove any particles over 130 to 150 microns in diameter.

Dewatering bins are suitable for sites handling fewer than 50 trucks a day unless they are used in parallel so that one can be cleaned while another is in service, he notes.

Of all the factors affecting wheel wash performance, the speed of the truck through the wash zone is the most important, says Kestner. “The slower the truck speed, the better the cleaning. A speed of 5 miles per hour through the wash is generally considered the slowest practical rate. Unfortunately, most truckers are in a rush to get out on the road, and tire washes often incorporate speed bumps or rumble strips to slow them down.”

The volume and pressure of water are important determinants of cleaning efficiency, says Kestner. “The performance of basin and channel washes that do not use spray to wash tires are directly proportional to the volume of water used per truck—the more the better,” he says. “The performance of low-pressure inundation washes also is highly dependent on the volume of water used per truck, since spray pressures are usually low enough that sprayed water is used to rinse rather than blast dirt from tires.

“In contrast, the efficiency of high-pressure wheel washes is less dependent on water flow rates and rely more on targeted sprays to dislodge material from the tire.”

The amount and type of mud and dirt on the truck affects performance, Kestner points out. “Most stationary plants, like stone quarries, generally have a stable unpaved route through the plant, while trucks at construction sites are more likely to have wheel wells and mud flaps fouled with dirt,” he says. “Mud and dirt that contains a lot of clay or reactive material like lime or cement can solidify into very hard deposits that are extremely difficult to remove.”

Rumble grates can significantly improve cleaning efficiencies by agitating the tires and flexing their treads to help dislodge material. Concrete or asphalt rumble strips can improve agitation but do not possess a sharp edge that causes treads to deform and flex, he says.

“While rumble grates can be effective, they become quickly fouled with compacted debris and require frequent cleaning or flushing to keep them in good operating condition,” he adds.

Many wheel wash installations are temporary and require portable equipment, says Kestner. All styles feature one or more skid-mounted pumps and portable spray manifolds; only low-pressure inundation and high-pressure cleaning washes are suitable for portable applications.

“Some sites may permit use of a basin that can be demolished or abandoned in lieu of a temporary wash,” he says. “High-pressure washes using vertical spray manifolds are quite compact and can be housed in a trailer along with a surge tank that can be towed from site to site. Low-pressure inundation washes utilize a portable spray frame that is placed onto the ground. The spray frame may or may not use a catch basin, depending upon its design and application.”

Because a retention pond or settlement pit is often not available or feasible, some portable washes include a dewatering box or concrete basin to collect and recirculate dirty water, says Kestner. At sites where silt carryout is a problem or when pumps need to be protected from abrasive solids, a portable filter and other solids handling equipment may be required.

Kestner advises that costs can be kept down by determining how clean trucks have to be. “If mud flaps and undercarriages do not contribute to the problem, there is no reason to clean them,” he contends. “Setting the wheel wash as far from the exit of the plant as possible can go a long way toward simplifying its design and maintenance.

“To avoid the high costs of collecting and recirculating clean water, it may be more cost-effective to use dirty water to wash tires and operate a vacuum sweeper to clean silt from the road.”

In climates where water is scarce or in cities where it is expensive, the lower water consumption of a high-pressure wash can help control costs over the long term, says Kestner. Some states provide tax exemptions or rebates for the installation of control measures, he adds.

The cost of a basin or channel wash depends primarily on the volume of truck traffic and cleaning efficiency required, says Kestner. Small facilities with fewer than 50 trucks a day may be able to get by with a simple basin that is cleaned and flushed daily, he says, and larger plants handling 500 trucks a day located adjacent to residential or commercial property will require a substantially higher investment.

The price of commercial tire washes varies, with the high end being an automated pump system with spray manifolds and frame, says Kestner. There are extra costs involved in site preparation and water treatment. Inundation washes may require the construction of a large settlement pit as a reservoir in addition to a concrete pad to support the spray frame and basin, which adds more costs.

“High-pressure washes have a smaller footprint but still require a level concrete pad and some means of water collection and treatment that can add significantly to its cost,” points out Kestner.

It is important to institute control measures that will ensure that truckers use the wash properly, notes Kestner. “Erecting concrete barricades to funnel traffic into the wash zone and using speed bumps or rumble grates to slow them down will help you to get your money’s worth from your investment.”

Credit: TRACKING PADS LLC
Tracking Pads in place at the Walmart site

Contractors faced a sticky situation (literally) at the site of a Walmart store whose parking lots were being resurfaced. Asphalt and debris were adhering to the tires of construction vehicles. There was no room to install a rock trackout control on the site, and even if there had been space for it, the contractor was concerned that the rocks themselves would also stick to the tires and be carried offsite. As an alternative, Tracking Pads LLC recommended installing a series of tabbed mats, or Tracking Pads, with the blocks running parallel to the construction traffic. The voids in the mats trap material, reducing sediment leaving the site, and the parallel blocks are also designed to grip and flex the sidewalls of the tires, wiping the asphalt from the tires as they pass over it.

Tracking Pads are flexible, heavy-duty rubber mats, each measuring 12 feet square and weighing 2,400 pounds. The mats are heavy enough to stay put without pins or other anchoring devices, but they can be folded or rolled for transport. The mats have been tested with a 78,000-pound steeltracked excavator spinning on top with scarcely noticeable damage. (See the video at www.trackingpads.com).

EC_bug_web

Comments

Leave a Reply

Enter Your Log In Credentials
×