Environmental Impacts of Blasting for Stone Quarries near the Bay of Fundy


Title:Environmental Impacts of Blasting for Stone Quarries near the Bay of Fundy
Authors:Mahtab, M. Ashraf; Stanton, Kemp L.; Roma, Vitantonio
Doc Type:article
Session:Paper Presentations: Session 1B: Contaminants and Ecosystem Health: Chemical and Biological Interactions
Proceedings:The Changing Bay of Fundy: Beyond 400 Years. Proceedings of the 6th Bay of Fundy Workshop, Cornwallis, NS, September 29th - October 2nd, 2004
Publisher:Environment Canada - Atlantic Region
Published:2005
Page:87-97

 

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ENVIRONMENTAL IMPACTS OF BLASTING FOR STONE QUARRIES NEAR THE BAY OF FUNDY

M. Ashraf Mahtab1, Kemp L. Stanton2, and Vitantonio Roma3

1 Sandy Cove, Digby County, NS. ashraf.mahtab@ns.sympatico.ca 2 Whale Cove, Digby County, NS. 3 Golder Associates S.r.l., Turin, Italy

Abstract

In addition to deteriorating the quality of life of the local residents, there are some major environmental impacts that can be generated by the operation of a stone quarry in the vicinity of the Bay of Fundy. Detonation of explosives near water creates compression waves that produce a rapid rise in the peak pressure and its rapid decay to the ambient pressure. This can damage the swim bladder of fish and damage their eggs/larvae. Large whales orient to objects by passively listening to underwater noise. Their exposure to the intense noise generated by blasting near the shoreline may result in damage to hearing and subsequent death by accidents. Sedimentation resulting from blasting, grinding and washing of the aggregate may cover spawning areas or reduce bottom dwelling life forms that the fish use for food. The explosive residue may pollute the groundwater and may be toxic to aquatic life. Groundwater will be drawn down from upstream of the quarry as a result of excavation with the potential for lowering the water table and drying up the wells in the neighbourhood, as well as reducing the base flow in local streams. If the aggregate produced from the quarry is to be shipped across the Bay of Fundy, the new invasive plants brought in by ballast water may displace existing plant life (such as kelp beds and rockweed) and provide inhospitable environments for critical marine species.

Introduction

The proposed projects for industrial production and shipping of aggregate from stone quarries near the Bay of Fundy shore, especially in southwest Nova Scotia, have emerged only recently. The proposals for quarrying basalt, a common rock found along the North Mountain abutting the Bay, have precipitated the concerns of the community regarding the adverse effects of a quarry on the environment and on the socio-economic well-being of the local inhabitants.

This paper addresses the environmental impact of blasting in stone quarries near the Bay of Fundy. First, an introductory explanation of blasting scheme for quarries is provided. Second, the direct impacts of blasting on fish and fish eggs, the setback distances of a blast from marine life, that are regulated by Fisheries and Oceans Canada (DFO), and the impact of noise on marine mammals are discussed. Finally, additional sources of environmental impacts of blasting for quarries near the ocean are identified and discussed, including blast residue, sedimentation, drawdown of water, and importation of ballast water.

Main Aspects of Blasting in Stone Quarries

Bench Excavation

The drill and blast technique used in quarries (or open-pit mines) involves a sequential excavation of benches (or steps) of the rock. The geometric features (shown in Figure 1) include a grid of drill holes with spacing (S) along the free face (the wall of the bench) and spacing (B) across the wall, height

(H) of the bench and corresponding length (L) of the drill hole, and diameter (D) of the drill hole. Eachhole can be thought of as having to break its own individual area (AR) which equals BxS as outlined by the dashed lines in the plan view of the bench in Figure 1. The blast design takes into account the type of rock, the ratio of B to D, the type of explosive, the delay interval between successive explosions in the same blast, and the explosive charge weight per delay (Hustrulid 1999).

Ground Vibrations Generated by Blasting

Ground vibrations from blasting are generated by the resulting seismic waves. The primary or compression wave has the highest velocity and arrives first at a point or particle. The next to arrive at the point are the secondary or shear waves. The compression and shear waves are collectively called the body waves. The slowest and last to arrive is the Rayleigh wave, which constitutes the main component of the surface waves (Siskind 2000; Roma 2001).

The velocities of compression and shear waves, VC and VS respectively, are (Kramer 1996):

)( 2VC = )21( )1(2 υρ υ − +G (1)
VS 2)( = ρ G (2)
where G = E , E = Young’s Modulus, υ = Poisson’s Ratio, and ρ= density of the medium.

2(1+υ)

Measurement of ground vibration at a point (or particle) is generally made in terms of the peak particle velocity, PPV.

Guidelines for Use of Explosives

In the guidelines for use of explosives (e.g., Hustrulid 1999; Wright and Hopky 1998), the main variables of interest are the PPV, the shock pressure in water (PW), the setback distance (SD) from the blast to the position of interest, and the explosive charge weight (W) per delay. Equations have been developed for inter-relating the main variables. For instance, the following equation (from Wright and Hopky 1998) relates PPV to SD and W, when body waves are considered:

6.1

PPV 100

⎛⎜

SD

W 5.0

⎞⎟⎠

(3)

=

where the units of the variables are as follows: PPV in cm/sec, SD in m, and W in kg.

In order to account for soil characteristics (i.e. layering, mechanical properties, surface degradation), more refined models are required to select the relevant values of the constants used in equation (3).

Direct Impacts Of Blasting

Effects on Fish

The compressional seismic waves from the detonation of the explosives produce a high peak pressure (Pmax) that rapidly decays to below the ambient hydrostatic pressure. This rapid pressure drop induces serious impacts on fish. As discussed by Wright (1982), the primary site of damage in finfish is the swimbladder, the gas-filled organ that permits most pelagic fish to maintain neutral buoyancy. The kidney, spleen, and sinus venosus may also undergo rupture and haemorrhage. Smaller fish are more susceptible to damage than larger fish.

The Canadian Guidelines (Wright and Hopky 1998) require that “no explosive is to be detonated in or near fish habitat that produces, or is likely to produce, an instantaneous pressure change (i.e., overpressure) greater than 100 kPa (14.5 psi) in the swimbladder of a fish.” The simplified formula for calculating the minimum setback distance (SD) of the onshore (in rock) blast from the fish is

5.0

SD = 03.5 W (4)

Therefore, a 100 kg charge of explosives detonated in a stone quarry requires a setback of 50.3 m from the fish in order to limit the P to 100 kPa.

max

Effects on Fish Eggs

The Canadian Guidelines (Wright and Hopky 1998) state that “vibrations from the detonation of explosives may cause damage to incubating eggs” and that “no explosive is to be detonated that produces, or is likely to produce, a peak particle velocity greater than 13 mm/sec in a spawning bed during the period of egg incubation”.

In reference to the vibrations resulting from the compressional waves, the Guidelines provide the following simplified equation for determining the setback distance, SD, from an explosion for a limiting value PPV of 1.3 cm/sec:

5.0 (5)

SD = 09.15 W

Therefore, detonation of a 100 kg charge of explosives requires a setback distance of 150.9 m from the fish eggs in order to limit the PPV to 1.3 cm/sec.

Significant Increase in Setback Distance Resulting from Rayleigh Waves

As discussed above, the setback distances from the explosives were calculated in reference to compressional (or body) waves as the source of vibrations. However, a blast in a quarry will also generate surface waves (or Rayleigh waves) as illustrated in Figure 2. The amplitude of the vibrations from body waves is inversely proportional to the distance. On the other hand, the amplitude of the vibrations from Rayleigh waves is inversely proportional to the square root of the distance. Therefore, the Rayleigh waves attenuate more slowly than body waves. Figures 3 and 4 (after Roma and Mahtab 2004) depict the significant increase in the setback distance with reference to the limits of Pmax and PPV, respectively.

For example, using a W of 100 kg and a Pmax of 100 kPa in Figure 3, the setback distances for body and Rayleigh waves, are 50 m and 300 m, respectively. For a PPV of 1.3 cm/sec, and a W of 100 kg, the setback distances associated with body and Rayleigh waves (and shown in Figure 4) are 150 m and 1,460 m, respectively.

Impact of Noise on Marine Mammals

Decibel

As an introduction, it would be useful to define the term “decibel” as a common unit used to express noise, or loudness of sound. Decibel, or dB, is a measure of a single power source with respect to a reference source.

dB = 10[log(sound power/reference power)] (6)

Some examples of the source, loudness, and qualitative nature of loudness are given in Table 1. The level of noise from a given source is a non-linear function of the distance of the observation point from the source. A rule of thumb for noise propagation is to reduce the noise level by 6 dB for each doubling of the distance. For instance, if the level of noise at 25m from a bulldozer is 80 dB, the noise level at 50 m will be 74 dB. To bring the noise level to a (moderate) 50 dB, the required distance would be 800 m.

Masking

Noise generated by blasting of rock and associated activities, such as grinding and shipping of the aggregate, can affect the marine mammals in various ways. Noise can mask communication signals that play a role in social cohesion, group activities, mating, warning, or individual identification. Noise can further interfere with environmental sounds that animals might listen to. Noise also affects the detection of sounds of predators and prey (Erbe and Farmer 2000).

Behavioural Disturbance

Noise has the potential of disrupting normal animal behaviour. Reported animal reactions include a cessation of feeding, resting, socializing, and an onset of alertness or avoidance (Richardson et al. 1995). For many marine mammals, disturbance is known to have occurred at continuous noise levels of about 120 dB. In our opinion, the normal blast per delay in a rock quarry will generate a noise that exceeds 120 dB. If noise scares the animals away from their habitat for an extended period, the effect will have a biological significance (on foraging, mating, or nursing).

Hearing Impairment

Prolonged exposure to continuous noise, such as from shipping and grinding, can also bring about hearing loss. Audiologists call this impairment “threshold shift”. On exposure to damaging noise, one’s acoustic threshold rises by a few decibels. For a marine mammal, each additional dB can mean a loss of vital information: the call of a calf, a predator, or a prospective mate (NRDC 1999).

Cumulative Effect

Repeated exposures to relatively low levels of noise may have a cumulative effect in inducing permanent hearing loss in mammals (as has been confirmed in humans and other species). Perhaps the most serious impact of noise is the debasement and depletion of habitat, as evidenced by the driving of gray whales, and possibly humpback whales, from traditional waters (NRDC 1999).

Additional Impacts of Quarrying Stone Near the Bay of Fundy

Water Pollution from Explosive Residue

As indicated above and in Figure 1, a pattern of drill holes is used to load and detonate explosives for breaking rock in a quarry. A fraction of the explosive may be left as “explosive residue” in the form of unexploded material after completion of the explosion.

As discussed by Kelleher (2002), there is evidence to support the suggestion that explosive residue is derived from a thin outer layer of the charge. The outer layer in a charged drill hole is the cylindrical surface. (The magnitude of the cylindrical surface for a given bench height is a direct function of the diameter of the drill hole.) As a general rule, the explosive residue will decrease as both the charge size and the velocity of detonation increase. However, in the case of a quarry near the ocean, the charge size per delay will need to be constrained to meet the DFO Guidelines for Peak Particle Velocity. In addition, the practical choice of the explosive for a quarry may not be associated with a high velocity of detonation. Therefore, the small charge (i.e. diameter of the drill hole) and/or the low velocity of detonation will tend to increase the percentage of the explosive residue.

The explosive residue will enter the surface water and groundwater through gravity flow and washing of the aggregate. The pollution potential of the explosive residue will depend on the chemical constituents of the explosive, such as nitrate and fuel oil. The potential hazard will be the contamination of the groundwater, its eventual flow into the Bay of Fundy, and the harmful impact on the marine life.

Sedimentation

Construction activities for a quarry near the Bay of Fundy shore may require clear cutting of the trees from the site, removing top soil, and altering the watercourses. All of these aspects will accelerate erosion, mainly by exposing large areas of soil or hills to faster flow of water during rainstorms. The rock formation along the shore is generally sloping toward the Bay. The silt-laden runoff from the site will end up in the Bay. Figure 5 shows an example of the silt being washed down the stripped hills from a proposed quarry site near the Bay of Fundy. Sedimentation or siltation from a rock quarry will also be generated by blasting, grinding, and transporting of the rock and aggregate.

As indicated in Appendix A of NS DEL (1988), one of the most serious environmental effects of siltation is the destruction of fish and fish habitat. High turbidity may induce physiological stress that makes fish susceptible to infection by disease-causing micro-organisms. High turbidity levels reduce light penetration and photosynthesis, thereby affecting the food chain and dissolved oxygen content. Sedimentation may cover spawning areas or reduce bottom dwelling life forms that the fish use for food.

Drawdown of Groundwater

The quarrying operation will progressively remove one or more benches of rock, most likely advancing from close to the Bay and proceeding away from the Bay. Depending on the cumulative height of the benches, the pit will act as a dug well which will draw down the water from the hills (or land) behind the pit toward the Bay. The extent of drawdown will depend on the rate of advance of the quarry face, level of the water table in reference to elevation of the bottom of the pit, and the hydraulic conductivity of the rock. The rock near the shore is well fractured and has high conductivity, in both horizontal and vertical directions. This conductivity would be enhanced by the effect of blasting.

The drawdown of water will adversely affect the level of water table and the use of aquifers by the neighbours. The wells in the vicinity of the quarry may run dry and the base flow in the regional streams may be reduced. The dust from blasting and grinding as well as the siltation carried by the drainage through the blasted rock will affect the quality of the groundwater.

Impact of Ballast Water

For practical reasons, a large-size stone quarry will need to ship the stone or aggregate using a marine terminal located near the quarry site and on the Bay of Fundy shore. A major concern regarding shipping the product across the Bay and Gulf of Maine would be the new invasive organisms brought by the cargo ships in the ballast water. As stated in the guidelines of Transport Canada (2001), ballast water has been associated with the unintentional introduction of a number of organisms in Canadian waters and several have been extremely harmful to both the ecosystem and the economic well-being of the nation. When a new organism is introduced to an ecosystem, negative and irreversible changes may result, including a change in biodiversity. For example, the imported plants may displace the existing plant life, such as kelp beds and rockweed, and provide inhospitable environments for critical marine species. Chapman et al. (2002) provided a comprehensive example of the introduction of alien marine vegetation and its spread in Atlantic Canada.

Conclusion

The environmental impacts of blasting for a stone quarry near the Bay of Fundy include loss of marine and terrestrial habitat, impairment of water and marine habitat due to siltation from the site, and lowering of groundwater level.

An economically feasible quarry would require shipping of the product (most likely, the aggregate) across the Bay. The traffic of bulk carriers will disrupt the movement pattern of whales. Creation of a marine terminal will jeopardize the safety of small craft that follow the shoreline. The importation of invasive species in ballast water may have a potentially severe impact on the marine life over a wide area.

Regardless of the size of a proposed quarry near the Bay, a detailed environmental assessment report needs to be furnished by the proponent of the quarry project. The federal and provincial governments and the community concerned must examine the report before the proposed project is approved.

References

Chapman, A. S., R. E. Scheibling, and R. O. Chapman. 2002. Species introductions and changes in the marine vegetation of Atlantic Canada. Pages 133–48. In: Alien Invaders in Canada’s Waters, Wetlands, and Forests. R. Claudi, P. Natel, and E. Muckle-Jeffs, Eds. Natural Resources Canada, Canadian Forest Service, Science Branch, Ottawa, ON.

Erbe, C. and D. M. Farmer. 2000. A software model to estimate zones of impact on marine mammals

around anthropogenic noise. Journal of the Acoustical Society of America 108(3, pt. 1): 1327–1331. Hustrulid, W. 1999. Blasting Principles for Open Pit Mining. Vol. 1 – General Design Concepts. A. A.

Balkema, Rotterdam, Netherlands.

Kellehr, J. D. 2002. Explosive residue: Origin and distribution. Forensic Science Communications 4(2). Online: (accessed 24 January 2005).

Kramer, S. L. 1996. Geotechnical Earthquake Engineering. Prentice Hall, NJ.

Lindeburg, M. 1982. Engineer in Training Review Manual. Professional Publications Inc., Belmont CA.

Natural Resources Defense Council (NRDC). 1999. Sounding the Depths: Supertankers, Sonar, and the Rise of Undersea Noise. NRDC, New York. Online: (Accessed 25 January 2005).

Nova Scotia Department of Environment and Labour (NSDEL). 1988. Erosion and Sedimentation Control Handbook for Construction Sites. NSDEL, Environment Assessment Division, Halifax. Richardson, W. J., C. R. Greene, C. I. Malme, and D. H. Thomson. 1995. Marine Mammals and Noise.

Academic Press, San Diego, CA.

Roma, V. 2001. Soil Properties and Site Characterization by Means of Rayleigh Waves. Ph.D. Thesis, Structural and Geotechnical Engineering Department, Technical University of Turin, Italy.

Roma, V. and Mahtab, M. A. 2004. Use of Rayleigh Waves as Reference for Determining Setback Distances for Explosions near Shorelines. Poster Session, 6th Bay of Fundy Workshop, September 29-October 2, Cornwallis Park, NS.

Siskind, D. E. 2000. Vibrations from Blasting. International Society of Explosives Engineers, Cleveland, OH.

Transport Canada. 2001. Guidelines for Control of Ballast Water Discharge from Ships in Waters Under Canadian Jurisdiction. TP 13617E. Transport Canada, Marine Safety Directorate, Ottawa, ON.

Wright, D. G. 1982. A Discussion Paper on the Effects of Explosives on Fish and Marine Mammals in Waters of the Northwest Territories. Canadian Technical Report of Fisheries and Aquatic Sciences 1052.

Wright, D. G. and G. E. Hopky. 1998. Guidelines for the Use of Explosives In or Near Canadian Fisheries Waters. Canadian Technical Report of Fisheries and Aquatic Sciences 2107.

Table 1. Sound loudness (after Lindeburg 1982)

Figure 1. Isometric view of a bench showing blast geometry and a plan view of the bench showing blast layout for one row of holes (after Hustrulid 1999)

Figure 2. Description of body waves and surface (Rayleigh) waves resulting from blasting near a shoreline (after Roma and Mahtab 2004)

Rayleigh Waves

h=depth

W=charge of explosive per delay

Figure 3. Setback distances for body and Rayleigh waves using the limit Pmax = 100 kPa for fish habitat (after Roma and Mahtab 2004)

Figure 4. Setback distances for body and Rayleigh waves using the limit PPV = 1.3 cm/sec for spawning habitat for fish habitat (after Roma and Mahtab 2004)

Figure 5. Sediment runoff from stripped hills on a proposed quarry site near the Bay of Fundy

 


 

Keywords related to the article
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Page (to)
assessment
93
biodiversity
93
disease
92
ecological change
93
environmental impact
87
93
erosion
92
fisheries
88
fisheries : spawning
87
fisheries : spawning
89
fisheries : spawning
92
food chain
92
groundwater
87
groundwater
92
groundwater
93
habitat : quality
91
habitat : quality
92
habitat : quality
93
introduced species
87
introduced species
93
marine mammal
90
91
marine mammal : whale
87
marine mammal : whale
91
marine mammal : whale
93
marine mammal : whale : humpback (Megaptera novaeangliae)
91
marine pollution : land-based
87
marine pollution : land-based
91
92
mining : aggregate
87
97
mining : compression and shear waves
88
90
mining : compression and shear waves
96
97
mining : Rayleigh waves
88
mining : Rayleigh waves
90
mining : Rayleigh waves
96
97
noise (sound)
87
noise (sound)
90
91
Nova Scotia
87
seaweed : kelp (Laminaria longicruris)
87
seaweed : kelp (Laminaria longicruris)
93
seaweed : rockweed
87
seaweed : rockweed
93
sediment : deposition
87
sediment : deposition
92
sediment : deposition
93
sediment : deposition
97
shipping
93
turbidity
92

 


 

 


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