Aggregate Use in Road Construction
The Ontario Ministry of Transportation has improved highway construction standards over time in order to increase pavement longevity and respond to increased traffic loads. This has included more stringent standards for the key raw materials in highway construction, primarily crushed stone, gravel and sand. Collectively, these materials are called mineral aggregate, and they are an important nonrenewable resource, regulated by the Ministry of Natural Resources. However, the environmental consequences of higher rigor in road construction standards have not been assessed or communicated to the public.
To provide context, there are approximately 2,800 licensed aggregate pits and quarries in Ontario. Pits produce loose material, usually sand and gravel. Quarries excavate bedrock (consolidated) material via blasting. Although aggregate pits and quarries make up less than 1 per cent of land in central Ontario, they are often at the centre of land use conflicts. The ECO frequently receives letters of complaint and EBR applications about aggregate operations, raising concerns about interference with groundwater flow and well function. (See pages 175-176 of the Supplement to this report regarding concerns about a site plan amendment to an aggregate operation.) Noise and dust from aggregate operations can also result in adverse impacts, and homeowners living close to aggregate operations frequently believe that their property values are depreciated.
One source of conflict is that the Provincial Policy Statement (PPS), which guides all land use planning under Ontario’s Planning Act, outlines policies that appear to be contradictory. On the one hand, the PPS uses clear language to emphasize the importance of aggregate resources and aggregate operations: “As much of the mineral aggregate resources as is realistically possible will be made available to supply mineral resource needs, as close to markets as possible. Mineral aggregate operations will be protected from activities that would preclude or hinder their expansion or continued use or which would be incompatible for reasons of public health, public safety or environmental impact.” But the Provincial Policy Statement also clearly states that “natural heritage features and areas will be protected from incompatible development.”
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Impacts of Aggregate Extraction
Operators of pits and quarries remove virtually all vegetation, topsoil, and subsoil to reach the aggregate underneath. By necessity, this also removes any natural habitat that may have been on a site, and disrupts any pre-existing streamflow. Aggregate operations invariably create new final grades on the land, and alter drainage patterns. Since aggregate deposits act as underground water reservoirs, once the aggregate is gone, the water storage capacity is lost as well.
In some cases a large portion of a stream’s volume is derived from groundwater, which maintains a “base flow” for streams. Base flow is important, as it often ensures that stream flow is maintained, even in the very dry summer season. Hence, land disturbance from pit and quarry activity can negatively affect flow, even if the excavation doesn’t extend below the water table.
Since many areas of southern Ontario have only small remnant patches of natural terrestrial habitat, the siting of pits and quarries can become very controversial. This is especially true on the Niagara Escarpment, one of Canada’s most significant landforms, designated a UNESCO World Biosphere Reserve. The Niagara Escarpment provides a variety of unique habitats, but also offers extremely high quality aggregate for industry. Land use conflicts of this type are not unique to the Niagara Escarpment. In southwestern Ontario there are significant aggregate deposits under Carolinian forestlands. If aggregate is removed from these locations, the existing remnant Carolinian forest is destroyed.
Once aggregate extraction sites are no longer in operation, often after decades of extraction, they can be rehabilitated and returned (with some investment of capital) to productive land uses. Examples of rehabilitated end uses include agriculture, natural habitat or recreational uses such as golf courses. For this reason, aggregate extraction is often described as an interim use of land. In Ontario, the Aggregate Resources Act, administered by the Ministry of Natural Resources, requires aggregate operations to rehabilitate sites once the extraction phase is over. However, evidence indicates that land is being degraded at a faster rate than pit and quarry sites are being rehabilitated. For example, provincial data indicate that from 1992 to 2000, an average of 1,064 hectares of new area was disturbed on an annual basis, while over the same time period an average of only 449 hectares of land was rehabilitated each year. Over this time span, approximately 5,500 hectares of degraded land has accumulated due to aggregate extraction.
In 1992, MNR published a “state of the resource report” on aggregate resources in southern Ontario, stating that “ …the Aggregate Resources Act represents a major step towards addressing environmental concerns and ensuring effective rehabilitation of pit and quarry sites.” The 1992 report also suggests that the monitoring of licensed aggregate sites “over the next five year period should begin to demonstrate the effects of the new Aggregate Resources Act on rehabilitation.” Evidently, MNR was anticipating that a greater amount of rehabilitation would occur. Regrettably, this has not been the case, and unless the rehabilitation rate improves significantly, the validity of the “interim land use” concept in the aggregate sector will be a serious concern.
Demand for Aggregates
Aggregates are consumed in large quantities to meet road construction and other infrastructure development activities. It is important to recognize that aggregate is not just dirt or soil that is readily available from an unlimited number of locations. Aggregate, in fact, includes many distinct grades of sand and gravel, varying both in their geologic origin and in their subsequent processing. Commonly used processing techniques include crushing, screening and washing. Each product type is manufactured to meet set engineering specifications.
Ontario’s demand for aggregate is large, with production in the province exceeding 160 million tonnes in 2001, equaling more than one-third of the annual aggregate production for Canada. Estimates indicate that over 55 per cent of all Ontario aggregates are consumed in road construction, utilizing a wide range of aggregate products obtained from different pits or quarries. Some of the top aggregate- producing locations are identified in the figure below.
The construction of a local two-lane highway can consume over 15,000 tonnes of aggregate per kilometer. New construction of a six-lane asphalt freeway consumes over 48,000 tonnes of aggregates for each kilometer of roadway. The provincially managed highway network is comprised of 19,396 kilometers, as expressed in terms of two-lane equivalents, and the vast majority of provincially managed roadways are paved. The Ministry of Transportation has the mandate of building, rehabilitating and maintaining the provincial highway network.
Municipalities are responsible for highways in their local jurisdictions, and, in fact, the municipal highway network is the largest in the province — approximately 141,000 kilometers, as expressed in two-lane kilometer equivalents. (As a result of a recommendation of the “Who Does What” consultations in 1996, responsibility for approximately 5,000 kilometers of road was transferred to municipalities from the province in the late 1990s.)
Factors Influencing Aggregate Consumption
Part of MTO’s mandate is to develop engineering standards, policies and guidelines for the design, construction, operation and rehabilitation of Ontario’s highways. To promote consistency, MTO and the Municipal Engineers Association rely on the Ontario Provincial Standards for Roads and Public Works (OPS). OPS objectives include the development of the design for roads, specifications for materials, and promotion of the use of OPS specifications on a provincial basis. Municipalities commonly adopt OPS specifications.
Aggregate specifications for highways have changed over time with the intention of improving pavement longevity and reducing the frequency of disruptive and expensive repairs. In addition, highway designers are responding to a heavier vehicle fleet and increased traffic loads. Key changes in aggregate specifications have included increased percentages of stone, with increased amounts of crushed particles. For example, in the late 1990s, MTO increased the crushed material content requirement in Granular A aggregate, used as a base in highways, from 50 per cent to 60 per cent.
A more sophisticated evaluation of the geologic origin of aggregate is also taking place, since the composition of source rock can have a bearing on the long-term performance of highways. As a result of new specifications in Ontario, fewer aggregate pits are deemed suitable sources, resulting in increased demand for quarry products, particularly for stronger asphalt pavement and concrete. More specifically, demand has increased for aggregate from quarries on the Niagara Escarpment and the Carden Plain. Also, some of MTO’s highest specification aggregates are used in asphalt paving materials for high-volume freeways. In this case, suitable aggregate is not available in the Greater Toronto Area or immediate vicinity, since the appropriate geology does not exist in this part of the province, and the aggregate must be brought south from the Canadian Shield.
Changes in aggregate specifications have brought about increased transportation distances for aggregates in Ontario in recent years. Longer hauling distances require more trucks. This means an increase in fuel consumption, resulting in higher aggregate costs, and a corresponding increase in the release of hydrocarbon emissions to the atmosphere, resulting in higher environmental costs. In the public eye, truck traffic in some locations is considered excessive, and there is evidence that the transportation of aggregate contributes to the deterioration of roads.
Pressure for aggregate use continues to come from many directions. Aggregate is used not only in the construction of new major highways, but also in reconstruction, widening and rehabilitation of existing highways. Road standard changes over time have resulted in more aggregate being laid down per unit area of highway. The base layers that support the pavement on highways have become more substantial and major highways have become prominent features on the landscape.
Conserving Aggregates
One strategy for conserving aggregate resources and reducing the demand for virgin aggregate is to recycle and reuse materials in road construction. MTO specifications allow for the reuse of reclaimed aggregates/concrete and asphalt pavement, with qualifying criteria. The specifications also allow the use of selected industrial byproducts, including particular types of slag and materials such as crushed glass or ceramics, which exhibit good engineering and environmental characteristics.
Up to 100 per cent of stripped or older asphalt pavement is now used in new pavements and in the granular-base layers that support the pavements on both provincial and municipal highways. MTO and OPS permit 100 per cent use of Recycled Asphalt Pavement (RAP) in certain hot mix asphalt products. In practice, these products usually contain approximately 40 per cent RAP or less, because air emissions during paving work can become problematic at higher concentrations.
Highly urbanized areas also generate significant volumes of non-virgin materials, such as crushed concrete, that could be used in road construction. Although the widespread use of approved non-virgin materials would have a small impact on Ontario’s total aggregate production, it is still significant in terms of resource conservation.
However, Ontario is not taking full advantage of the opportunity to conserve aggregate. Estimates suggest that only 3 per cent of Ontario’s aggregate consumption is supplied by non-virgin materials, in great part because of the lack of incentive. In other jurisdictions, road construction contracts and bid-preference systems encourage the use of non-virgin materials. MTO does not use these systems, nor does the ministry monitor how much non-virgin material is used in highways. And municipalities use only a minimal level of recycled materials. (Peel Region, however, did use mixed broken glass as an aggregate in road construction and, although the volumes used were small, Peel was able to divert this waste from landfilling.)
It is anticipated that over the next 20 years, MTO highway initiatives will require very large volumes of aggregate, equal to or greater than what has been consumed in the past two decades. Significant increases in the consumption of aggregates by municipalities are also predicted. Road width at the municipal level is an important factor. Under older neighbourhood design, many residential streets were constructed with a 6.5-meter pavement width. The most common pavement width used today for local streets is 8.5 meters. The ECO speculates that a review of the design standards for urban streets and new subdivisions could serve a dual purpose, both conserving aggregate and reducing urban sprawl.
An Integrated Approach Needed
Aggregate specification changes over the last decade have had significant impacts on how our aggregate resources are being managed. Under the Environmental Bill of Rights, ministries have an obligation to explain such impacts to the public. MNR and MTO should be articulating the environmental, social and economic implications of changing road standards, and sharing these implications with the public. Right now, the public is unaware of changes in highway standards, the consequences for aggregate consumption, or the implications of future aggregate demands on the southern Ontario landscape.
MNR has also not informed the public about the current status of our aggregate resources. The ministry’s 1992 State of the Resource study noted concern about existing aggregate reserves and described a need to secure additional reserves to avoid longer transportation hauls. In the fall of 2002, MNR made a presentation to the Central Ontario Smart Growth Panel, indicating that the majority of high quality crushed stone for the Central Ontario Zone was produced from five quarries located in the Niagara Escarpment Plan Area, and that the reserves on these sites are becoming critically low. MNR should be undertaking a new State of the Resource report, based on a range of plausible future scenarios for aggregate consumption.
More generally, the ECO has observed a lack of meaningful inter-ministerial consultation regarding road standards, aggregate use and the implications for other natural resources. Several ministries should have a role in such discussions, including the Ministries of Natural Resources, Transportation, Environment, and Municipal Affairs and Housing. Since these ministries represent a wide range of mandates, effective conflict resolution mechanisms will be needed. For example, MTO has a relatively straightforward mandate as the ministry responsible for transportation infrastructure. MNR’s mandate is more complex: it must grapple with competing interests, including both the protection of natural heritage features and the development of mineral aggregate resources. Ministries will need to think beyond the “near and now,” and find integrative solutions that address the big picture and long-range concerns.
| Recommendation 2:
The ECO recommends that the Ministries of Natural Resources and Transportation collaborate on a strategy for conserving Ontario’s aggregate resources. This strategy, which should be developed with public consultation, should consider both road construction needs and the need to conserve aggregate resources. |
| This is an article from the 2002/03 Annual Report to the Legislature from the Environmental Commissioner of Ontario. |
Citing This Article
Environmental Commissioner of Ontario. 2003. "Aggregate Use in Road Construction." Thinking Beyond the Near and Now, ECO Annual Report, 2002-03. Toronto, ON : Environmental Commissioner of Ontario. 29-35.
