USING WATER AND CHEMICAL DUST SUPPRESSANTS AT CONSTRUCTION SITES . 9

4.1 Introduction

There are numerous PM emission sources at construction sites where water and various chemical dust suppressants can be applied in order to reduce emissions. For instance, water/dust suppressants can be applied to mitigate fugitive dust from site preparation, storage piles, materials handling and transfer, unpaved roads, etc. The discussion related to the utilization of these dust control options has been confined to this chapter. This serves to reduce the length of the Best Practices document and also makes the document more reader-friendly.

The application of water is typically the most common dust control method that is employed by construction companies across Canada.

Practically all construction companies that are implementing options to reduce dust are applying water to mitigate dust generation from at least one emission source on their construction site. Water can be applied by a variety of methods, for instance trucks, water pulls, water canons, hoses, fire hydrants, sprinklers, etc.

A variety of chemical dust suppressants are available to suppress fugitive dust emissions from construction sites. While being more expensive that water, they are also more effective in suppressing dust and have to be applied much less frequently. Examples of dust suppressants include the following: (i) liquid polymer emulsions (ii) agglomerating chemicals (e.g., lignosulfonates, polyacrylamides); (iii) cementitious products (e.g., lime-based products, calcium sulphate); (iv) petroleum based products (e.g., petroleum emulsions); and (v) chloride salts (e.g., calcium chloride and magnesium chloride).

While the application of water and chemical dust suppressants are proven and effective options for mitigating dust, they have to be

applied judiciously. Their usage, while mitigating dust, can trigger other (just as serious) environmental consequences. It is important to keep these environmental consequences in mind when deciding on the extent to which water and chemical dust suppressants are to be utilized.

4.2 Factors to Consider

The following potential environmental impacts of applying chemical dust suppressants must be taken into consideration before application:

• the hazardous, biodegradable and water-soluble properties of the substance;

• the effect their application could have on the surrounding environment, including water-bodies (e.g., surface water pollution from runoff, contaminated ground water, pH) and wildlife (e.g., fisheries); and

• whether the use of chemicals has been limited due to nearby watershed considerations for protection of fish and fish habitat from surface runoff.

There are potential environmental consequences resulting from the over-application of water that must be considered. These include: runoff problems; soil instability; spreading of contaminants in the environment (e.g., oil or coolant from engines), and erosion. In addition, consideration should be given to water conservation or water allocation limitations in areas where construction occurs.

The over-application of water can also lead to equipment mobility problems and reduce the ability of earth-moving equipment to efficiently move saturated soils. If the moisture contents of soils used in construction are sufficient, water may not always need to be added prior to handling, crushing, etc.

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T a b le 5 : G u id a n ce on A pp ly ing W a te r a t C on s tr u c ti on S it es

•Material to be transported may be mixed with water prior to loading and/or the entire surface area of material may be watered after loading. Water should be available while loading and unloading in order to prevent visible dust plumes. •Material may be tested to determine moisture content and silt loading. Only materials that have optimum moisture content should be crushed or screened. •Materials may be sprayed with water 15 minutes prior to handling and/or at points of transfer. •Water may be applied at the feed and/or intermediate points in the conveyor system as needed. •Washing separated or screened materials are effective in controlling fugitive dust emissions from chutes and conveyors. •Hollow cone nozzles are believed to produce the greatest control while minimizing clogging when using wet suppression systems. Optimal droplet size for surface impaction and fine particle agglomeration is about 500 µm - finer droplets are affected by drift and surface tension and appear to be less effective. •Application of water sprays to the underside of a conveyor belt improves the performance of wet suppression systems at belt-to-belt transfer points. Road Surfaces•Water may be applied to all unpaved roads used for vehicular traffic at least once per every two hours of active operations (i.e., 3 times per normal 8 hour working day). If the area is inaccessible to water trucks due to slope conditions or other safety factors, watering may be conducted with hoses or sprinkler systems. Runoff should be controlled so it does not saturate the surface of the unpaved haul road, therefore increasing the potential of trackout. •Control efficiency of water depends on: (i) amount (per unit road surface area) of water added during each application; (ii) period of time between applications; (iii) weight, speed and number of vehicles traveling over the watered road during the period between applications; and (iv) metrological conditions that affect evaporation. Demolition and Deconstruction•Water may be applied at the following times/locations in order to minimize dust generation: (i) the exterior of building surfaces prior to initiating demolition activities as well as continuously during the knock down phase. It has been suggested that all exterior surfaces of the building, up to six stories in height (where feasible), may be wetted before and during the use of the wrecking ball; (ii) debris pile immediately following blasting and as needed afterwards; (iii) debris during handling and haulage operations; (iv) the surrounding surface area following demolition; (v) unpaved road surfaces within 30 meters of the demolition site, 1 hour prior to the actual demolition; and (vi) unpaved surface areas where equipment will operate.

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T a b le 6 : G u id a n ce on A pp ly ing D u s t S upp ressa n ts /C h e m ica l S ta b ili z e rs

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