Air Quality Impact Assessment Report for the Proposed Limpopo Coal Mining Operation

Stuart Thompson
2009-05-07
SSI, Environmental

1 INTRODUCTION

Limpopo Coal Company (Pty) Ltd (Limpopo Coal) has acquired the prospecting rights to prospect for coal on the farms Overvlakte 125 MS (Ptn 3,4,5,6,13, RE), Bergen op Zoom 124 MS, Semple 155 MS and Voorspoed 836 MS in Limpopo Province and is currently evaluating the feasibility of establishing an opencast and underground coal mine (Figure 1- 1).

Jacana Environmentals cc was appointed to develop the Environmental Management Programme for the proposed Vele Colliery Project, who in turn appointed The Air Quality Unit of Bohlweki-SSI Environmental to conduct the air quality impact assessment.

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Figure 0-1: Locality map showing locations of identified farms

 

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The mine consists of an open pit, underground operations, associated workshops and a coal processing plant. Rock waste dumps, coal storage piles as well as overburden storage piles will be generated from the mining and processing operations. Other facilities at the mine site will include the following:

  • Discard bins;
  • Coal crusher and storage;
  • Conveyors from the crusher to storage silos and from silos to the crusher;
  • Earthmoving vehicle workshop; and
  • Main entrance gate security and freight area.

The current investigation aims to identify potential air quality impacts which may result due to the proposed operations. This assessment forms part of the environmental impact assessment phase of this investigation and will focus on the impacts from the proposed mine in order to provide a better understanding of the magnitude of these impacts.

The terms of reference of the current investigation can briefly be summarized as follows:

  • Environmental assessment study
  • The determination of the key aspects of air pollution that may result from the construction, operation and decommissioning phases of the project; and
  • The overview of the potential impacts which could result due to the release of the identified priority pollutants.

 

2 METHODOLOGY

Emissions of particulate matter (PM) of less than 10 micrometres in diameter (PM10) and nuisance dust will result from mineral plant operations such as crushing, screening and processing for final transportation. Fugitive emissions are also possible from roads and open stockpiles.

South African ambient air quality standards will be used as a base for comparison, however reference will be made to international guidelines to ensure complete compliance. This is primarily due to the close proximity of the proposed mine to the Botswana and Zimbabwe borders.

Dispersion modelling will be undertaken using the US-EPA approved Industrial Source Complex (ISC) Model version 3. This model is based on the Gaussian plume equation and is capable of providing ground level concentration estimates of various averaging times, for any number of meteorological and emission source configurations (point, area and volume sources for gaseous or particulate emissions).

The ISC/AERMOD View model is used extensively to assess pollution concentrations and deposition from a wide variety of sources. ISC/AERMOD View is a true, native Microsoft Windows application and runs in Windows 2000/XP and NT4 (Service Pack 6).

The ISCST3 (Industrial Source Complex Short Term Version 3) dispersion model used during the current investigation, is a steady state Gaussian plume model which can be used to assess pollutant concentrations and /or deposition fluxes from a wide variety of sources associated with an industrial source complex. Some of the ISC-ST3 modelling capabilities are summarised as follows:

  • ISC-ST3 may be used to model primary pollutants and continuous releases of toxic hazardous waste pollutants;
  • ISC-ST3 model can handle multiple sources, including point, volume, area and open pit source types. Line sources may also be modelled as a string of volume sources or as elongated area sources;
  • Source emission rates can be treated as constant or may be varied by month, season, hour of day, or other periods of variation, for a single source or for a group of sources;
  • The model can account for the effects aerodynamic downwash due to nearby buildings on point source emissions;
  • The model contains algorithms for modelling the effects of settling and removal (through dry deposition) of large particulates and for modelling the effects of precipitation scavenging from gases or particulates;
  • Receptor locations can be specified as gridded and/or discrete receptors in a Cartesian or polar coordinate system;
  • ISC-ST3 incorporates the COMPLEX1 screen model dispersion algorithms for receptors in complex terrain;
  • ISC-ST3 model uses real-time meteorological data to account for the atmospheric conditions that affect the distribution of air pollution impact on the modelling area; and
  • Output results are provided for concentration, total deposition, dry deposition, and/or wet deposition flux.

Input data to the ISC-ST3 model includes: source and receptor data, meteorological parameters, and terrain data. The meteorological data includes: wind velocity and direction, ambient temperature, mixing height and stability class.

The uncertainty of the ISC-ST3 model predictions is considered to be equal to 2, thus it is possible for the results to be over predicting by double or under predicting by half, it is therefore recommended that monitoring be carried out at the proposed more during operation to confirm the modelled results, to ensure legal standards are maintained

 

2.1 Inhalable Particulates (PM10)

Particulate matter (PM) is the collective name for fine solid or liquid particles added to the atmosphere by processes at the earth's surface. PM includes dust, smoke, pollen and soil particles (Kemp, 1998). PM has been linked to a range of serious respiratory and cardiovascular health problems. The key effects associated with exposure to ambient particulate matter include: premature mortality, aggravation of respiratory and cardiovascular disease, aggravated asthma, acute respiratory symptoms, chronic bronchitis, decreased lung function, and an increased risk of myocardial infarction (USEPA, 1996).

PM represents a broad class of chemically and physically diverse substances. Particles can be described by size, formation mechanism, origin, chemical composition, atmospheric behaviour and method of measurement. The concentration of particles in the air varies across space and time, and is related to the source of the particles and the transformations that occur in the atmosphere (USEPA, 1996).

PM can be principally characterized as discrete particles spanning several orders of magnitude in size, with inhalable particles falling into the following general size fractions (USEPA, 1996):

  • PM10 (generally defined as all particles equal to and less than 10 microns in aerodynamic diameter; particles larger than this are not generally deposited in the lung);
  • PM2.5, also known as fine fraction particles (generally defined as those particles with an aerodynamic diameter of 2.5 microns or less);
  • PM10-2.5, also known as coarse fraction particles (generally defined as those particles with an aerodynamic diameter greater than 2.5 microns, but equal to or less than a nominal 10 microns); and
  • Ultra fine particles generally defined as those less than 0.1 microns.

Fine and coarse particles are distinct in terms of the emission sources, formation processes, chemical composition, atmospheric residence times, transport distances and other parameters. Fine particles are directly emitted from combustion sources and are also formed secondarily from gaseous precursors such as sulphur dioxide, nitrogen oxides, or organic compounds. Fine particles are generally composed of sulphate, nitrate, chloride and ammonium compounds, organic and elemental carbon, and metals. Combustion of coal, oil, diesel, gasoline, and wood, as well as high temperature process sources such as smelters and steel mills, produce emissions that contribute to fine particle formation. Fine particles can remain in the atmosphere for days to weeks and travel through the atmosphere hundreds to thousands of kilometres, while most coarse particles typically deposit to the earth within minutes to hours and within tens of kilometres from the emission source. Some scientists have postulated that ultra fine particles, by virtue of their small size and large surface area to mass ratio may be especially toxic. There are studies which suggest that these particles may leave the lung and travel through the blood to other organs, including the heart. Coarse particles are typically mechanically generated by crushing or grinding and are often dominated by resuspended dusts and crustal material from paved or unpaved roads or from construction, farming, and mining activities (USEPA, 1996).

 

Table 2-1 outlines the various international health risk criteria used for the assessment of inhalable particulate matter (PM10). Guidelines and standards are provided for a 24-hour exposure and annual average exposure period respectively.

 

Table 2-1:   Available Local and International Health Risk Criteria Used for the evaluation of Inhalable Particulate Matter (PM10).

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Notes:  

(1) Standard laid out in the National Environment Management: Air Quality Act. No. 39 of 2004:

(2)  As outlined by the South African National Standards (SANS). 1929:2005 - Ambient  air

quality – limits for common pollutants.

(3) Target Level

(4) As prescribed under the old guidance documentation, prior to these limits being adopted by the Act.

(5) Compliance by 1 January 2010

(6)                    World        Bank        Air       Quality        Standards         summary                        obtainable                 at         URL http://www.worldbank.org/html/fpd/em/power/standards/airqstd.stm#paq.

(7)       European     Union     Air     Quality    Standards     summary    obtainable     at   URL

http://europa.eu.int/smartapi/cgi/sga_doc?smartapi!celexplus!prod!DocNumber&lg=en&typ e_doc=Directive&an_doc=1999&nu_doc=30.

(8)   United  States  Environmental  Protection  Agencies  National  Air  quality    Standards

obtainable at URL http://www.epa.gov/air/criteria.html

(9) To attain this standard, the 3-year average of the weighted annual mean PM10 concentration at each monitor within an area must not exceed 50 ug/m3.

(10)                 United     Kingdom      Air     Quality   Standards      and          objectives    obtainable                                 at        URL http://www.airquality.co.uk/archive/standards.php

(11) WHO = World Health Organisation

(12) Guidance on the concentrations at which increasing, and specified mortality responses due to PM are expected based on current scientific insights (WHO, 2005).

(13) Air quality guideline

 

2.2    Nuisance Dust

Nuisance dust may be defined as coarse fraction of airborne particulates. Nuisance dust is known to result in the soiling of materials and has the potential to reduce visibility. Nuisance dust has a long history of having little adverse effect on the lungs. Any reaction that may occur from nuisance dust is potentially reversible. However, excessive concentrations of nuisance dust in the workplace may reduce visibility, may cause unpleasant deposits in eyes, nasal passages and may cause injury to the skin or mucous membranes by the chemical or mechanical action. The light is scattered and visibility is diminished by the atmospheric particulate.

Various costs are associated with the loss of visibility, including: the need for artificial illumination and heating; delays, disruption and accidents involving traffic; vegetation growth reduction associated with reduced photosynthesis; and commercial losses associated with aesthetics. The soiling of building and materials due to dust frequently gives rise to damages and costs related to the increased need for washing, cleaning and repainting. Dustfall may also impact negatively on sensitive industries, e.g. bakeries or textile industries. Certain elements in dust may damage materials. For instance it was found that sulphur and chlorine if present in dust may cause damage to copper (Maeda et al., 2001).

Nuisance dust can also cause serious aesthetic deterioration in the surrounding environment and communities. Fortunately due to relatively large particulate matter sizes associated with the mining emissions and the relatively short release height of the pollutants, such negative impacts are usually confined in relatively small areas. Within these areas of impact, fugitive dust may result in damage to the vegetation and agriculture. The deposited particulate matter may block the plant leaf stomata hence inhibit gas exchange, or smother the plant leaf surfaces reducing photosynthesis levels. Besides the impacts on vegetation, health effects of particulates on mine personnel and public may also be significant.

Air pollution is a recognized health hazard for man and domestic animals (Newman et al., 1979). Air pollutants have had a worldwide effect on both wild birds and wild mammals, often causing decreases in local animal populations (Newman et al., 1979). The major effects of industrial air pollution on wildlife include direct mortality, debilitating industrial-related injury and disease, physiological stress, anaemia, and bioaccumulation. Some air pollutants have caused a change in the distribution of certain wildlife species.

South Africa is one of the only countries who have issued guideline limits for the evaluation of nuisance dust levels and so will be used as an example. A four banding system has traditionally been used which describes the dust deposition as resulting in a slight, moderate, heavy or very heavy nuisance impact. These criteria are summarised as follows:

Slight: < 250 mg/m²/day

Moderate: > 250 mg/m²/day < 500 mg/m²/day Heavy: > 500 mg/m²/day < 1200 mg/m²/day Very

Heavy: > 1200 mg/m²/day

The South African Department of Minerals and Energy (DME) use the 1 200 mg/m²/day threshold level as an action level. In the event that on-site dustfall exceeds this threshold, the specific causes of high dustfall should be investigated and remedial steps taken.

"Slight" dustfall is barely visible to the naked eye. "Heavy" dustfall indicates a fine layer of dust on a surface; with "very heavy" dustfall being easily visible should a surface not be cleaned for a few days. Dustfall levels of > 2000 mg/m²/day constitute a layer of dust thick enough to allow a person to "write" words in the dust with their fingers. Local experience, gained from the assessment of impacts due to dust from mine tailings dams in Gauteng, has shown that complaints from the public will be activated by repeated dustfall in excess of ~2000 mg/m²/day. Dustfall in excess of 5000 mg/m²/day impacting on residential or industrial areas generally provoke prompt and angry complaints.

The primary effects of particulate matter on vegetation are reduced growth and productivity due to interference with photosynthesis and phytotoxic impacts as a result of particle composition. The mechanisms of action are through:

  • smothering of the leaf;
  • physical blocking of the stomata;
  • bio-chemical interactions; and
  • Indirect effects through the soil.

Deposition of PM to vegetated surfaces depends on the size distribution of the particles and, to a lesser extent, on the chemistry. Coating with dust may cause abrasion and radiative heating, and may reduce the photosynthesis. Acidic and alkaline materials may cause leaf surface injury while other materials may be taken up across the cuticle. A more likely route is through metabolic uptake and impact on vegetation and ecosystems is through deposited directly onto the soil which can influence nutrient cycling, especially that of nitrogen

Agricultural crops can be injured when exposed to high concentrations of various air pollutants. Injury ranges from visible markings on the foliage, to reduced growth and yield, to premature death of the plant. The development and severity of the injury depends not only on the concentration of the particular pollutant, but also on a number of other factors. These include the length of exposure to the pollutant, the plant species and its stage of development as well as the environmental factors conducive to a build-up of the pollutant and to the preconditioning of the plant, which make it either susceptible or resistant to injury. Air pollution injury to plants can be evident in several ways. Injury to foliage may be visible in a short time and appear as necrotic lesions (dead tissue), or it can develop slowly as a yellowing or chlorosis of the leaf. There may be a reduction in growth of various portions of a plant. Plants may be killed outright, but they usually do not succumb until they have suffered recurrent injury.

 

2.3 Methane

Methane is not toxic to humans but is of concern in terms of its explosion potential and its impact on the global climate. The most commonly accepted flammability ranges for methane in air mixtures are given as 5.3% to 14%. The flammability range becomes slightly extended to 5.0% to 15% when mixtures of methane in air are retained within a small void such as might occur should the gas collect within an enclosed voids (Campbell, 1996). Methane is one of the most significant greenhouse gases known (21 times stronger than carbon dioxide). Over the last two centuries, methane concentrations in the atmosphere have more than doubled, largely due to human-related activities.

The potential exists for pockets of methane to be present in the coal seams which are mined.  This methane  will enter  the atmosphere when  it’s  disturbed  or  exposed  to the atmosphere. Due to recent studies undertaken using IPCC developed models it is difficult to accurately determine the amount and concentration of the methane which will be released, especially with reference to surface and open cast mining operations. This uncertainty is caused by the rate of methane release being influenced by the atmospheric pressure, the rate of excavation and the depth of the coal seam, with shallow coal seams having lower concentrations. As the potential for explosion does exist it is recommended that regular monitoring of the methane be carried out to ensure the levels are well below explosive limits, especially in the underground mining sectors where ventilation should be well maintained.

 

3 PROJECT DESCRIPTION

The proposed mine will consist of an opencast and underground operation, as well as associated infrastructure. The planned plant will also include crushers, and a processing plant, to clean the coal before being transported from the site. The mine is planned to start operating in 2010 and will continue for a period of about 29 years. Opencast mining will start in the north eastern section of the mining area and move south-westward over time. Initially stockpiles will be developed for the storage of material, however once the mining has commenced, all waste rock and material will be loaded back into the pit in order to reduce potential impacts.

 

4 DESCRIPTION OF AFFECTED ENVIRONMENT

4.1 Meso-scale meteorology and site-specific dispersion potential

The information presented in the subsections which follow detail the dispersion potential of the area under investigation. Meteorological data for the period January 2006 to June 2008 were obtained from the Unified Model data run by the South African Weather Service.

A period wind rose for the Vele site is presented in Figure 4-1. Wind roses comprise of 16 spokes which represent the directions from which winds blew during the period. The colours reflect the different categories of wind speeds. The dotted circles provide information regarding the frequency of occurrence of wind speed and direction categories.

 

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Figure 4-1: Period wind rose for the Vele site for the period 2006 to 2008.

 

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Figure 4-2: Wind class frequency distribution for the Vele for the period 2006 to 2008

Looking at Figure 4-1 and Figure 4-2 respectively, it can be seen that Vele is not an area of high wind speeds on average. At the Vele site, 6.4% of the time, calm conditions existed over the area. The highest frequency of wind speeds lie between 0.5 to 2.1 m/s which occurred for 41.3% of the time. The second highest wind class (3.6 – 5.7 m/s) occurs 22.5% of the time. Figure 4-1 shows that the prevailing winds are from an easterly direction with a second weaker wind field from the south-east. This wind pattern is consistent with the wind fields following the major landforms in the area, in this case the Limpopo River Valley.

 

4.2 Atmospheric Stability

Atmospheric stability is commonly categorised into six stability classes. These are briefly described in Table 4-1. The atmospheric boundary layer is usually unstable during the day due to turbulence caused by the sun's heating effect on the earth's surface. The depth of this mixing layer depends mainly on the amount of solar radiation, increasing in size gradually from sunrise to reach a maximum at about 5-6 hours after sunrise. The degree of thermal turbulence is increased on clear warm days with light winds. During the night- time a stable layer, with limited vertical mixing, exists. During windy and/or cloudy conditions, the atmosphere is normally neutral. From Figure 4-3 it can be seen that the site experiences very stable atmospheric conditions for the majority of the time with a 33% frequency of occurrence. This thus indicates an area with a low dispersion potential.

Table 4-1:      Atmospheric stability classes

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Figure 4-3:     Stability Classes for the Vele Site

 

 

4.3 Identified Sensitive Receptors

The proposed mine is located on the southern banks of the Limpopo River. Due to the mines location, the distances to any large settlements is in the order of 50 km resulting in little chance of impacts as a direct result of the mine. It must be noted that smaller settlements as well as surrounding farms are more likely to be affected as a result of the mining activity. Public roads are also noted to pass close to the proposed site, as a result of this particular care needs to be taken to avoid dust blown across these roads.

 

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Figure 4-4: Showing the location of major sensitive receptors (assessed samereceptors as Noise Study).

 

During the operation of the mine, all miners will be housed offsite, however, it is noted that a contractor’s camp is to be temporarily setup on site for the initial construction of the plant. Dust monitoring should be setup in these areas to ensure the workers health and safety, whilst on the site.

 

Table 4-2:       Sensitive Receptors

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*Please refer to the noise assessment for a full list of receptors

4.4    Assessment of current Air Quality Impacts

Currently a detailed emissions inventory for the area under investigation has not been undertaken. Based on site visits, aerial photo’s and site descriptions of the area, the following sources of air pollution have been identified:

  • Vehicle entrainment and exhaust gas emissions;
  • Veldt fires;
  • Agricultural Activities; and
  • Other mining activities across the Limpopo River on the Zimbabwe side.

A qualitative discussion on each of these source types is provided in the subsections which follow. These subsections aim to highlight the possible extent of cumulative impacts which may result due to the proposed operations.

 

4.4.1         Vehicle entrained dust and exhaust emissions

Dust emissions occur when soil is being crushed by a vehicle, as a result of the soil moisture level being low. Vehicles used on the roads will generate PM-10 emissions throughout the area and they carry soils onto the paved roads which would increase entrainment PM-10 emissions. The quantity of dust emissions from unpaved roads varies linearly with the volume of traffic.

Vehicle exhausts contain a number of pollutants including carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons, oxides of nitrogen (NOx), sulphur and PM10. Tiny amounts of poisonous trace elements such as lead, cadmium and nickel are also present. The quantity of each pollutant emitted depends upon the type and quantity of fuel used, engine size, speed of the vehicle and abatement equipment fitted. Once emitted, the pollutants are diluted and dispersed in the ambient air. Pollutant concentrations in the air can be measured or modelled and then compared with ambient air quality criteria.

 

4.4.2         Veld Fires

Veld fires are widespread across the world, occurring in autumn, winter and early spring. In addition to controlled burning for fire-breaks and veld management, many fires are set deliberately for mischievous reasons. Some are accidental, notably those started by motorists throwing cigarettes out of car windows. Emissions from veld fires are similar to those generated by coal and wood combustion. Whilst veld fire smoke primarily impacts visibility and landscape aesthetic quality, it also contributes to the degradation of regional scale air quality.

Dry combustible material is consumed first when a fire starts. Surrounding live, green material is dried by the large amount of heat that is released when there are veld fires, sometimes this material can also burn.

Factors that affect the rate of fire spread:

  • Weather( wind velocity, ambient temperature and relative humidity);
  • Fuels ( fuel type, fuel bed array, moisture content and fuel size;
  • Topography ( slope and profile); and
  • Logistical problems (size of the burning area).

 

The major pollutants from veld burning are particulate matter, carbon monoxide, and volatile organics. Nitrogen oxides are emitted at rates from 1 to 4 g/kg burned, depending on combustion temperatures. Emissions of sulphur oxides are negligible (USEPA, 1996).

 

4.4.3                                   Agricultural Activities

Agricultural activities currently taking part within the study area include predominantly citrus and cotton farming with game farming also being undertaken. Agricultural activities can be considered a significant contributor to particulate emissions.

The main focus internationally with respect to emissions generated due to agricultural activity is related to animal husbandry, with special reference to malodours generated as a result of the feeding and cleaning of animals. Animal feeding operation and other agricultural activities are more likely to contribute air pollutants such as particulate matter to the atmosphere during hot, dry weather. Ammonia emissions from animal agriculture account for about 50% of the total ammonia emissions into terrestrial systems. Ammonia, through chemical reactions in the atmosphere, causes acid rain increasing acidity of surface waters and soils. Nitrogen emissions, as ammonia, are a major nutrition issue.

Little information is available with respect to the emissions generated due to the growing of crops. The activities responsible for the release of particulates and gasses to atmosphere would however include:

  • Particulate emissions generated due to wind erosion from exposed areas;
  • Particulate emissions generated due to the mechanical action of equipment used for tilling and harvesting operations;
  • Vehicle entrained dust on paved and unpaved road surfaces;
  • Gaseous and particulate emissions due to fertilizer treatment; and
  • Gaseous emissions due to the application of herbicides and pesticides.

 

4.4.4                                   Mining Activities

Due to an existing mine located on the Zimbabwean Border it is possible for the mitigation measures and rehabilitation plans to differ from those in South Africa. As a result of this there is the possibility that air quality impacts from that mine could influence the cumulative air quality impacts at and near the site.

 

5 ENVIRONMENTAL IMPACT ASSESSMENT

5.1CONSTRUCTION PHASE

During the construction assessment phase it is expected that, the main sources of impact will result due to the construction of haul roads, the plant area and the initial box cut associated with open pit mining. These predicted impacts cannot be quantified, primarily due to the lack of detailed information related to scheduling and positioning of construction related activities. Instead a qualitative description of the impacts will be provided. This will involve the identification of possible sources of emissions and the provision of details related to their impacts.

Construction is commonly of a temporary nature with a definite beginning and end. Construction usually consists of a series of different operations, each with its own duration and potential for dust generation. Dust emission will vary from day to day depending on the phase of construction, the level of activity, and the prevailing meteorological conditions (USEPA, 1996).

The following possible sources of fugitive dust have been identified as activities which could potentially generate dust during construction operations at the mine:

 

  1. Creation and Grading of Haul Roads
  • Scraping;
  • Debris handling;
  • Debris stockpiles; and
  • Truck transport and dumping of debris.

       2. Preparation of plant area

  • Clearing of area for infrastructure;
  • Debris handling;
  • Debris stockpiles; and
  • Truck transport and dumping of debris.

       3. Set up of mining operations

  • Removal of overburden; and
  • Setting up of site offices and workshop

 

5.1.1         Creation and Grading of Haul Roads

Haul roads are constructed by the removal of overlying topsoil, whereby the exposed surface is graded to provide a smooth compacted surface for vehicles to drive on. Material removed is often stored in temporary piles close to the road edge, which allows for easy access once the road is no longer in use, whereby the material stored in these piles can be re-covered for rehabilitation purposes. Often however, these unused haul roads are left as is in the event that sections of them could be reused at a later stage.

Haul trucks generate the majority of dust emissions from surface mining sites. Observations of dust emissions from haul trucks show that if the dust emissions are uncontrolled, they can be a safety hazard by impairing the operator’s visibility. Substantial secondary emissions may be emitted from material moved out from the site during grading and deposited adjacent to roads (USEPA, 1996). Passing traffic can thus re-suspend the deposited material. To avoid these impacts material storage piles deposited adjacent to the road edge should be vegetated, with watering of the pile prior to the establishment of sufficient vegetation cover. Piles deposited on the verges during continued grading along these routes should also be treated using wet or chemical suppressants depending on the nature and extent of their impacts.

Regular watering and application of chemical dust suppressants are the only alternatives in controlling mine haul road dust emissions.

 

5.1.2         Preparation of areas identified for the construction of the plant and supporting infrastructure.

Removal of material usually takes place with a bulldozer, extracted material is then stored in piles for later use during rehabilitation procedures. Construction sites are good candidates for dust control measures because land disturbance from clearing and excavation generates a large amount of soil disturbance and open space for wind to pick up dust particles. Dust problems can also be generated during the transportation of the extracted material, usually by truck, to the stock piles. This dust can take the form of entrainment from the vehicle itself or due to dust blown from the back of the trucks during transportation.

The use of long-term stockpiles on site should be avoided wherever possible to reduce wind erosion. It should be noted that emissions generated by wind are also dependent on the frequency of disturbance of the erodable surface. Each time material is added to or removed from a storage pile or surface, the potential for erosion by wind is restored. Any crusting of the surface binds the erodable material (USEPA, 1996). All stockpiles should be damped down, especially during dry weather or re-vegetated.

 

5.1.3         Preparation of the open pit mining areas

Open pit mining will start with the set up of the initial box cut. This will involve the removal of topsoil, and overburden by front end loader with the drilling and blasting of the overlying rock required in order to gain access to the mineral bearing ore. Bulldozing, drilling and blasting operations can result in the liberation of dust to atmosphere. Dust liberated during bulldozing activity can be reduced by increasing watering the material being removed thus increasing the moisture content. An attempt can also be made to coincide blasting operations with winds blowing away from local communities, as well as periods when poor atmospheric dispersion are expected i.e. early morning and late evening.

The removed topsoil will have to be transported to a designated collection point from where it can be recovered later during site rehabilitation. The removal of this material for storage should be routed to adjacent haul roads which will be watered, to reduce the amount  of vehicle  entrained dust  which  can be  kicked up during these activities. The waste rock that has been removed form the pit will be discarded at a waste rock stock pile. To reduce the amount of dust being blown from the load in the haul roads, the material being transported can be watered or the back of the vehicles can be covered with plastic tarpaulin covers.

 

5.1.4                                   Overview of potential Impacts

The following components of the environment may possibly be impacted upon during the construction phase:

  • ambient air quality;
  • local residents and neighbouring communities;
  • employees;
  • the aesthetic environment;
  • agricultural activities; and
  • fauna and flora

The impact on air quality and air pollution of fugitive dust is dependent on the quantity and drift potential of the dust particles (USEPA, 1996).Most dust particles are to large too be displaced over greater distances, they settle out near the source and cause a nuisance problem. However, fine dust particles can be dispersed over greater distances. Fugitive dust emissions can have a serious effect on day-to-day operations such as reduced visibility, congested breathing, and increased vehicle maintenance, soiling of buildings, impaired growth and production in vegetation and storm water run-off problems. The impacts would be on a temporary basis, during the construction period.

Sensitive receptors were identified in section 4.3. Given the short duration and low level of activity expected during construction, but bearing in mind that no quantitative emission figures exist, no significant adverse impacts are anticipated on these receptors. Impact of fugitive dust emissions on employees on site could however be significant during the construction phase, but will vary between phases, with level of activity and meteorological conditions.

Due to the lack of quantitative dust emissions data for the site, it is recommended that the precautionary principle be followed and dust control measures be implemented. Recommendations for the control of fugitive dust emissions are given in Table 5-1. Wet suppression with water is the least expensive of the possible control measures but is temporary in nature, however due to the scarcity of water, chemical suppressants may be a preferred option.

 

Table 5-1:      Recommendations for the control of fugitive dust emissions during theconstruction phase (USEPA, 1996).

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Note:   (1)  Dust control plans should contain precautions against watering programs    that generate excessive mud.

(2) Loads could be covered to avoid loss of material in transport, especially if material is transported offsite.

(3)  Chemical stabilization is usually cost-effective for relatively long-term or   semi-permanent unpaved roads.

 

Wet suppression is one of the common methods used to control open dust sources at construction sites. It is possible for water to be combined with a surfactant as wetting agent. Surfactants increase the surface tension of water, reducing the quantity of water required. The Dust-A-Side (DAS) product binds with the aggregate used to build on-site roads. However the treatment with chemical stabilizer can have an effect on plant and animal life and the contamination of the treated material (USEPA, 1996).

Dust and mud should be controlled at vehicle exit and entry points to prevent the dispersion of dust and mud beyond the site boundary. Daily removal of mud and dirt carried out from the site to adjacent paved roads. Facilities for the washing of vehicles could be provided at the entry and exit points. Vehicles should travel at a speed of 40km/ hr at over exposed areas and where stockpiles are situated (USEPA, 1996).

All stockpiles should be maintained for as short a time as possible and a water spray system should be operated at any gravel stockpile and should be shielded from wind.

During the transfer of material to stockpiles, drop heights should be minimised to control the dispersion of materials being transferred (USEPA, 1996).

 

5.2   OPERATIONAL PHASE

This section aims to deal with the estimated air quality impacts which result due to the proposed operations. Details regarding the source characteristics were provided from a site layout plan provided and a questionnaire filled in by the client. The sources to be included in this assessment can be categorised as follows:

  • Material transfer operations;
  • Wind erosion from exposed storage piles; and
  • Vehicle entrained dust from both paved and unpaved road surfaces.

First however it is necessary to outline the processes which are proposed to take place at the site.

 

5.2.1  Process Description

5.2.1.1  Coal Abstraction

When coal seams are near the surface, it may be economical to extract the coal using open pit mining methods. Typically, for coal, strip mining is used. Strip mining exposes the coal by the advancement of an open pit. The earth above the coal seam is known as overburden. A strip of overburden next to the previously mined strip is usually drilled. The drill holes are filled with explosives and blasted. The overburden is then removed using large earthmoving equipment. This overburden is put into the previously mined and now empty strip. When all the overburden is removed, the underlying coal seam will be exposed as a strip known as a block. The coal may be drilled and blasted and using large shovels loaded onto haul trucks for transport to the coal processing plant. In areas where the coal depth can accommodate underground works, shafts will be sunk, and the coal abstracted with the aid of a conveyor system to the surface. Due to the grade of coals from the opencast to underground these streams will be processed separately, to ensure optimal processing is maintained.

 

5.2.1.2   Coal Processing

A Coal Washing Plant is a facility that washes coal of soil and rock, as well as removing the soluble fraction of sulphur which is present in the coal. The more of this waste material that can be removed from coal, the greater its market value and the lower its transportation costs. The coal delivered from the mine that reports to the Coal Washing Plant is called Run-of-mine, or ROM, coal. This is the raw material for the plant, and consists of coal, rocks, minerals and contamination. In the preparation phase coal, the ROM is unloaded, stored and conveyed, crushed and classified by the screening into coarse and fine fractions. The coal is then conveyed into their respective cleaning processes. Fine coal is removed from the top of the fluidized bed and the heavy coal is removed at the bottom of the bed. and then prepared for transportation.

5.3   Emissions Inventory

For the modelling process a worse case scenario was chosen for all dispersion modelling, assuming a plant at full production rate.

Materials Handling Operations

Materials handling operations refers to the transfer of various raw materials and waste products by means of tipping, loading and off-loading of trucks, conveyors, etc. Emission factors used to calculate the impacts (the USEPA), are dependent on the material moisture content and the wind speed at the time. Trucks will be used to transport various raw materials from the pit, with waste products and processed coal being handled via conveyor. Tipping, loading and off-loading of trucks will be the day- to- day activities.

Wind erosion from exposed areas

Windblown dust (wind erosion) from exposed storage piles and the mine tailings impound can be a significant contributor to particulate emissions on-site, especially when large quantities of material are stored at any given point. Table 5-2 details the source characteristics of the storage piles and waste dump on-site, which were included in the current assessment of particulate impacts.

 

Table 5-2:      Parameters pertaining to the storage piles

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Notes: Information supplied by Jacana Environmental CC; CE = control efficiency

 

Vehicle entrainment

Unpaved roads are used during the day-to-day operations on site. Action of vehicle wheels on road surfaces results in the lifting and entrainment of particulates deposited on these surfaces.

The total suspended particulate loads and inhalable particulate fraction were estimated on the unpaved roads in the area based on the vehicle types and movements during operations (Table 5-3).

 

Table 5-3:              Parameters used to calculate emissions from vehicle-entrained dust on unpaved roads on the Vele site.

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An unpaved road will be used by these haul trucks. Mitigation should be put in place to reduce impact on the residence residing close and around the proposed mine. This will apply to both the dust and noise impact resulting due to mining operations. Mitigation to reduce vehicle exhaust gas emissions should also be undertaken.

 

5.3.1  Dispersion Simulation Results: Proposed Operating Conditions

Dispersion simulations were undertaken to reflect the combined impacts from the sources of inhalable particulate and nuisance dust deposition rates from the proposed Vele site operations (Figure 5-1, 5-2 and 5-3). This included the simulation of all point, area, line and volume sources identified.

Isopleth plots reflect gridded contours which represent zones of impact at various distances from the contributing sources. The patterns generated by the contours are representative of the maximum predicted ground level concentrations for the averaging period being represented. These averaging periods are defined as being the maximum exposure level in a given time period, usually, as in this case daily and annual. An example of this is the 180µg/m³ daily limit for particulate matter. This is the maximum concentration exposure that a person can tolerate in a single day (short duration). This compared to the 60µg/m³ concentration over an annual period, i.e. long term exposure.

When simulations were undertaken for all sources at the Vele site (assuming no mitigation measures are put in place), comparison of predicted daily and annual average ground level concentrations to the current RSA Standards of 180µg/m³ and 60µg/m³ respectively, indicated that there was no exceedance at or within the Vele site boundary. When comparison is made to the stricter SANS 1929 daily limit (75µg/m³), there were exceedances noted for the daily averaging period, however these still remain within the site boundary.

Dispersion simulations were undertaken for predicted dust fallout impacts. Dust fallout impacts are noted to fall above the SANS 1929 threshold deemed accepted for residential (600 mg/m²/day) and industrial areas (1200    mg/m²/day).          With the exceedance of the residential limit noted to occur outside of the mine lease area.

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Figure 5-1: Highest Predicted Daily Average PM10 Ground Level Concentrations at the Vele Site without Mitigation (SANS Limit - 75 µg/m³).

 

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Figure 5-2: Highest Predicted Annual Average PM10 Ground Level Concentrations at the Vele Site without Mitigation (SANS Limit - 40 µg/m³).

 

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Figure 5-3: Monthly Dust Deposition Levels Predicted at the Vele Site without Mitigation.

 

Figure 5-1 and 5-2 represent the daily and annual average predicted ground level concentrations for inhalable particulate matter that could results during the operation of the mine (assuming no mitigation is put in place). Figure 5-3 similarly represents the monthly dust deposition concentration predicted for these proposed mining activities.

Figures 5-4 to 5-6 shows the maximum predicted ground level concentrations with planned mitigation measures in place. As a result of these mitigation measures all predicted emissions fall below the South Africa Standards of 180µg/m³ and 60µg/m³ as well as the stricter SANS limits of 75µg/m³ and 40 µg/m³ for daily and annual limits respectively. This is with the exception of the residential dust fallout limit of 600 mg/m²/day which is still noted to be exceeded for a short distance outside of the southern most border of the mine lease area.

Mitigation measures that have been identified and assessed are, the increased moisture content of the ROM material when entering the crusher, wetting of all haul and temporary roads, the covering of temporary or reused storage piles, and the revegetation of permanent storage piles.

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Figure 5-4: Highest Predicted Daily Average PM10 Ground Level Concentrations Predicted at the Vele Site with mitigation (SANS Limit - 75 µg/m³).

 

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Figure 5-5: Highest Predicted Annual Average PM10 Ground Level Concentrations Predicted at the Vele Site with mitigation (SANS Limit - 40 µg/m³).

 

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Figure 5-6: Monthly Dust Deposition Levels Predicted at the Vele Site, with mitigation.

 

5.4   DECOMMISSIONING PHASE

The decommissioning phase is associated with activities related to the demolition of infrastructure and the rehabilitation of disturbed areas. The following activities are associated with the decommissioning phase (US-EPA, 1996):

  • Existing buildings and structures demolished, rubble removed and the area levelled;
  • Remaining exposed excavated areas filled and levelled using overburden recovered from stockpiles;
  • Stockpiles to be smoothed and contoured;
  • Topsoil replaced using topsoil recovered from stockpiles; and
  • Disturbed land prepared for revegetation.

 

Possible sources of fugitive dust emission during the closure and post-closure phase include:

  • Smoothing of stockpiles by bulldozer;
  • Grading of sites;
  • Transport and dumping of overburden for filling;
  • Infrastructure demolition;
  • Infrastructure rubble piles;
  • Transport and dumping of building rubble;
  • Transport and dumping of topsoil; and
  • Preparation of soil for revegetation – ploughing and addition of fertiliser, compost etc.

 

Exposed soil is often prone to erosion by water. The erodability of soil depends on the amount of rainfall and its intensity, soil type and structure, slope of the terrain and the amount of vegetation cover (Brady, 1974). Revegetation of exposed areas for long- term dust and water erosion control is commonly used and is the most cost-effective option. Plant roots bind the soil, and vegetation cover breaks the impact of falling raindrops, thus preventing wind and water erosion. Plants used for revegetation should be indigenous to the area, hardy, fast-growing, nitrogen-fixing, provide high plant cover, be adapted to growing on exposed and disturbed soil (pioneer plants) and should easily be propagated by seed or cuttings.

 

6 MITIGATION MEASURES PROPOSED

The following chapter aims to summarise the general conclusions and recommendations presented in the report.

 

6.1 Conclusions

Isopleth Plots presented in Figures 5-1, 5-2 and 5-3 represent a maximum predicted ground level inhalable particulate (PM10) and fallout levels. No exceedances were noted for inhalable particulates over the adjacent areas when comparisons are made to the stricter SANS 1929 daily and annual limits. Exceedances are noted for the fallout limits set for residential areas which is 600 mg/m²/day but not for the industrial limit of 1200 mg/m²/day, however with the planned mitigation measures in place, these exceedances are significantly reduced.

A consideration which is recommended is the possible uses of alternatives for the transportation of coal from the mine site. This could be by train or conveyor as a replacement to trucks. Due to the large number of trucks that are required for the daily transport of coal, the impacts on the carbon dioxide budget would be greatly increased and so increasing climate change impacts.

 

6.2 Recommendations

Based on the results presented the following recommendations are outlined:

  • It is recommended that ambient air quality monitoring be undertaken to establish the baseline condition prior to the onset of operations on-site and in order to establish the level at which the proposed operations are noted to impact on the ambient air quality.
  • Fallout monitoring should be included to assess the level of nuisance dust associated with both mining and process related operations. Sampling of fallout should be undertaken within the neighbouring areas as well as on-site.

 

Dust fallout monitoring should ideally be located on-site, around the pit and shafts, at the crusher and in the vicinity of major storage piles, with the more sensitive areas to the south (due to predicted levels of exceedance) and to the west (due to the proximity of sensitive receptors) of the site being focused on. Buckets along major transport routes as well as at major transport junctions, such as the tipping areas for trucks and rail, should also be considered for monitoring. Figure 6-1 below shows possible locations for dust monitoring buckets, these site locations are based on the ambient modelling    results   as   well   as   the   major   vehicle    routes   which    are    used. It is recommended that additional monitoring also be carried on site to determine occupational exposure limits.

 

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Figure 6-1:  Map showing possible locations for dust monitoring. These sites take into account major transport routes and predominant wind direction.

Due to emissions being generated from roads and storage piles it is recommended that all piles should be maintained for as short a time as possible and all permanent stockpiles should be vegetated. The use of a water spray system at transitional stockpiles is also recommended. Wind breaks can similarly be used in close proximity to stockpile areas in order to reduce the potential erosive forces of the wind. During the transfer of material to piles, drop heights should be minimised to control the dispersion of materials being transferred (USEPA, 1996).

Wet suppression is one of the common methods used to control open dust sources at sites and on roads, because a source of water is readily available on a construction and mine site. Water may also be combined with a surfactant as wetting agent. Surfactants increase the surface tension of water, reducing the quantity of water required. The Dust-A-Side (DAS) or Dust Stop type product binds with the aggregate used to build on-site roads. Similar products include:

 

However the treatment with chemical stabilizer can have an effect on plant and animal life and the contamination of the treated material, and care should be taken before such a product is used (USEPA 1996).

 

7 GLOSSARY

Air quality – A measure of exposure to air which is not harmful to your health. Air quality is measured against health risk thresholds (levels) which are designed to protect ambient air quality. Various countries including South Africa have Air Quality Standards (legally binding health risk thresholds) which aim to protect human health due to exposure to pollutants within the living space.

Ambient air - the air of the surrounding environment.

Baseline - the current and existing condition before any development or action.

Boundary layer - the layer directly influenced by a surface.

Climatology - the study of the long term effect of weather over a certain area during a certain period.

Concentration - when a pollutant is measured in ambient air it is referred to as the concentration of that pollutant in air. Pollutant concentrations are measured in ambient air for various reasons, i.e. to determine whether concentrations are exceeding available health risk thresholds (air quality standards); to determine how different sources of pollution contribute to ambient air concentrations in an area; to validate dispersion modelling conducted for an area; to determine how pollutant concentrations fluctuate over time in an area; and to determine the areas with the highest pollution concentrations.

Condensation - the growth of water or ice by diffusion from contiguous water vapour.

Dispersion model - a mathematical model which can be used to assess pollutant concentrations and deposition rates from a wide variety of sources. Various dispersion modelling computer programs have been developed.

Dispersion potential - the potential a pollutant has of being transported from the source of emission by wind or upward diffusion. Dispersion potential is determined by wind velocity, wind direction, height of the mixing layer, atmospheric stability, presence of inversion layers and various other meteorological conditions.

Emission - the rate at which a pollutant is emitted from a source of pollution.

Emission factor - a representative value, relating the quantity of a pollutant to a specific activity resulting in the release of the pollutant to atmosphere.

Evaporation - the opposite of condensation.

Front - a synoptic-scale swath of cloud and precipitation associated with a significant horizontal zonal temperature gradient. A front is warm when warm air replaces cold on the passage of the front; with a cold front cold air replaces warm air.

Fugitive dust - dust generated from an open source and is not discharged to the atmosphere in a confined flow stream.

High pressure cells - regions of raised atmospheric pressure.

Inversion - an increase of atmospheric temperature with an increase in height.

Mesoscale - a spatial scale intermediate between small and synoptic scales of weather systems.

Mixing layer - the layer of air within which pollutants are mixed by turbulence. Mixing depth is the height of this layer from the earth’s surface.

Particulate matter (PM) - the collective name for fine solid or liquid particles added to the atmosphere by processes at the earth's surface and includes dust, smoke, soot, pollen and soil particles. Particulate matter is classified as a criteria pollutant, thus national air quality standards have been developed in order to protect the public from exposure to the inhalable fractions. PM can be principally characterised as discrete particles spanning several orders of magnitude in size, with inhalable particles falling into the following general size fractions:

*   PM10 (generally defined as all particles equal to and less than 10 microns in aerodynamic diameter; particles larger than this are not generally deposited in the lung);

*   PM2.5, also known as fine fraction particles (generally defined as those particles with an aerodynamic diameter of 2.5 microns or less) ;

*   PM10-2.5, also known as coarse fraction particles (generally defined as those particles with an aerodynamic diameter greater than 2.5 microns, but equal to or less than a nominal 10 microns); and

*   Ultra fine particles generally defined as those less than 0.1 microns.

PM10 - refers to particulate matter that is 10µm or less in diameter. PM10 is generally subdivided into a fine fraction of particles 2.5µm or less (PM2.5), and a coarse fraction of particles larger than 2.5µm. Particles less than 10µm in diameter are also termed inhalable particulates.

Precipitation - ice particles or water droplets large enough to fall at least 100 m below the cloud base before evaporating.

Relative Humidity - the vapour content of the air as a percentage of the vapour content needed to saturate air at the same temperature.

Total suspended particulates (TSP) -. all particulates which can become suspended and generally noted to be less than 75µm in diameter (TSP).

Vehicle entrainment - the lifting of dust particles in the turbulent wake of a vehicle passing over an unpaved road or exposed area. The force of the wheels on the road causes pulverisation of the surface material and the particles are lifted and dropped by the rolling wheels.

 

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