Appendix B - Emission Estimation Method
B.1 Emission Factor Equations Applied
Unpaved Roads
The emissions factor for unpaved roads is taken from USEPA AP42 Chapter 13.2.2 Unpaved Roads (November 2006) as follows:
E = k (s/12)a(W/3)b Where:
E = Emissions Factor (lb/VMT, i.e. pounds per vehicle miles travelled) s = surface material silt content (%)
W = mean vehicle weight (Short Tonnes US).
BMC BMP Determination 22 Feb 2012.docx Page B-2 The following constants are applicable:
Constant TSP (based on PM30) PM10 PM2.5
K (lb/VMT) 4.9 1.5 0.15
A 0.7 0.9 0.9
B 0.45 0.45 0.45
The metric conversion from lb/VMT to g/VKT (grams per vehicle kilometre travelled) is as follows:
1 lb/VMT = 0.2819 kg/VKT
The surface material silt content and mean vehicle weight information is site specific as documented in the following section.
Rainfall Adjustment Factor
All roads are subject to some natural mitigation due to precipitation. The above unpaved road emission factor can be extrapolated to annual average uncontrolled conditions (but including natural mitigation dur to precipitation) under the simplifying assumption that annual average emissions are inversely proportional to the number of days with measureable (more than 0.254 mm) precipitation as follows:
Eext = E [(365-P)/365]
where:
Eext = annual size-specific emission factor extrapolated for natural mitigation (lb/VMT) E = unpaved road emission factor (given above)
P = number of days in a year with at least 0.254 mm of precipitation
Paved Roads
The emissions factor for paved roads is taken from USEPA AP42 Chapter 13.2.1 Paved Roads (January 2011) as follows:
E = k (sL)0.91(W)1.02 Where:
E = Emissions Factor (g/VKT, i.e. grams per vehicle kilometre travelled)
K = particle size multiplier for particle size range and units of interest (See table below) sL = Road surface silt loading (grams per square meter) (g/m2), and
W = mean vehicle weight (tonnes) The following constants are applicable:
Constant TSP (based on PM30) PM10 PM2.5
K 3.23 0.62 0.15
Questions have been raised in regard to the accuracy of the January 2011 revision of the Paved Road equation. OEH has however indicated that emission factors from AP42 Section 13.2.1 January 2011 should be used in the quantification of paved road emissions since this is official USEPA guidance (personal communication, Mitchell Bennett, Office of Environment and Heritage, 10 October 2011).
The road surface silt loading and mean vehicle weight information is site specific as documented in the following section.
Topsoil Scraper
The emissions factors for topsoil scraping activities are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. No PM10 and PM2.5 factors defined for this activity, with reference made to the PM10/TSP and PM2.5/TSP ratios specified for this activity within the OEH 2008 GMR Emissions Inventory. The emission factors are expressed in kilograms of emissions per tonne of material (topsoil) stripped.
Activity TSP PM10 PM2.5 Units
Topsoil stripping 0.029 TSP*0.32 TSP x 0.0468 kg/tonne
Scraper unloading (batch drop)
0.02 TSP*0.32 TSP x 0.0468 kg/tonne
Dragline
The emissions factors for dragline activities are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. The emission factors are expressed in kg of emissions per bulk cubic metre of material (overburden) moved.
TSP PM10 PM2.5 Units
0.0046(π)1.1 (π)0.3
0.0029(π)0.7
(π)0.3 Γ 0.75 0.0046(π)1.1
(π)0.3 Γ 0.017 kg/mΒ³
Where: d = drop height (m)
M = material moisture content (%)
BMC BMP Determination 22 Feb 2012.docx Page B-4 The average drop height and material moisture content is site specific and is provided in the next section.
Blasting
Emissions factors for blasting are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. The emission factors are expressed in kilogram of emissions per blast, with a single emissions factor specified for blasting of coal and overburden.
Material TSP PM10 PM2.5 Units
Overburden or Coal 0.00022(A)1.5 TSP x 0.52 TSP x 0.03 kg/blast
Where: A= horizontal area (m2) with blasting depth β€ 21.
The average blast area is site specific and is addressed in the subsequent section.
Drilling
The TSP emissions factors for drilling activities are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. The emission factors are expressed in kilogram of emissions per hole drilled, with separate factors specified for drilling of coal and overburden. Given that there are no PM10 and PM2.5 emissions factors for drilling, the PM10 and PM2.5 to TSP ratios for blasting overburden and coal were applied.
Material TSP PM10 PM2.5 Units
Overburden 0.59 TSP x 0.52 TSP x 0.03 kg/hole
Coal 0.1 TSP x 0.52 TSP x 0.03 kg/hole
The number of holes is site specific and is addressed in the subsequent section.
Bulldozing
The emissions factors for bulldozing activities are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. The emission factors are expressed in kilogram of emissions per hour of dozer activity, with separate factors specified for dozers operating on coal and overburden.
Material TSP PM10 PM2.5 Units
Overburden 2.6(π )1.2
(π)1.3 0.45(π )1.5 (π)1.4 Γ 0.75
2.6(π )1.2
(π)1.3 Γ 0.105 kg/hr
Coal 35.6(π )1.2
(π)1.3 8.44(π )1.5 (π)1.4 Γ 0.75
35.6(π )1.2
(π)1.3 Γ 0.022 kg/hr
Where: s = material silt content (%) M = material moisture content (%)
The material silt content and material moisture content are site specific and are addressed in the subsequent section.
Trucks Loading Coal and Overburden
The emissions factors for truck loading are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. These emission factors, expressed in kilogram of emissions per metric tonne of material loaded, are applicable for operations involving loading by shovels, excavator or front end loaders. In the case of truck loading of overburden, this chapter only specifies a TSP emission factor. To derive PM10 and PM2.5 emissions factors for truck loading of overburden, reference was made to the PM10/TSP and PM2.5/TSP ratios for bulldozing of overburden.
Material TSP PM10 PM2.5 Units
Coal 0.58
(π)1.2
0.0596
(π)0.9 Γ 0.75 TSP x 0.019 kg/Mg
Overburden (a) 0.018 πππ Γ 0.29 TSP x 0.105 kg/Mg
(a) See justification for use of this emission factor provided below.
Where: M = material moisture content (%)
The material moisture content is site specific and are provided in the subsequent section.
OEH recommended that the material handling emission factor equation from USEPA AP42 Chapter 13.2.4 Aggregate Handling and Storage Piles (November 2006) be applied in the estimation of truck loading of overburden (as documented below) (personal communication, Mitchell Bennett, Office of Environment and Heritage, 10 October 2011). Although this emission factor equation, which takes into account the site-specific wind speed, was initially applied it was found to substantially under predict the emissions from this activity for the site when site-specific wind data was applied. This confirmed the conclusion reached by Pitts (2005) that there is an apparent large underestimation in emissions when using the materials handling equation compared to measurements at Australian mines.
The AP42 materials handling equation gives lower dust emissions when compared to measurements undertaken during Australian research (NERDCC, 1988 and SPCC, 1983), and earlier US research (1981). Holmes (1998) indicated that this is likely to be due to earlier equations treating the entire loading operation as a single operation. The entire operation comprises the use of a shovel/excavator or front end loader scooping up a load, moving into a loading position, dumping material into a truck, reloading and repeating the process. The materials handling equation by comparison considers the batch or continuous load-out operation in isolation, and is therefore more applicable for estimating emissions for conveyor transfers or loading from a conveyor to a stockpile.
To provide a more realistic (potentially upper bound) estimate of emissions from trucks loading overburden reference was therefore made to the default emission factor from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table above.
BMC BMP Determination 22 Feb 2012.docx Page B-6 Trucks Dumping Coal and Overburden
The emissions factors for trucks dumping of coal are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. The emission factors are expressed in kilogram of emissions per metric tonne of material dumped.
In the case of trucks dumping overburden, reference is made to the materials handling equation from USEPA AP42 Chapter 13.2.4 Aggregate Handling and Storage Piles (November 2006) as recommended by OEH. Whereas the default βtruck loading overburdenβ emission factor was applied to more comprehensively account for the entire loading process, the truck dumping of overburden represents a more simple batch drop process render in the use of the material handling equation for its quantification appropriate.
Material TSP PM10 PM2.5 Units
Coal (a) 0.58
(π)1.2
0.0596
(π)0.9 Γ 0.75 TSP x 0.019 kg/Mg
Overburden Refer to the Materials Handling Equation (b)
(a) AP42 Chapter 11.9 gives a default TSP emission factor for truck dumping of coal (0.033 kg/Mg). OEH however recommended that the emission factors for trucks loading coal be applied, as drawn from this chapter of the AP42 and documented above (personal communication, Mitchell Bennett, Office of Environment and Heritage, 10 October 2011).
(b) AP42 Chapter 11 gives a default TSP emission factor for truck dumping of overburden (0.001 kg/Mg). OEH however recommended that the materials handling equation from USEPA AP42 Chapter 13.2.4 Aggregate Handling and Storage Piles (November 2006) be applied in the estimation of trucks dumping overburden (personal communication, Mitchell Bennett, Office of Environment and Heritage, 10 October 2011).
The material moisture content (%) specified in the above equation is site specific and is provided in the subsequent section.
Grading
Emissions factors for grading are taken from USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as documented in the table below. The emission factors are expressed in kilogram of emissions per vehicle kilometre travelled (VKT).
TSP PM10 PM2.5 Units
0.0034 (S)2.5 0.0056 (S)2.0 x 0.6 TSP x 0.031 kg/VKT
Where:
VKT= Vehicles Kilometres Travelled S = mean vehicle speed (km/h)
The mean vehicle speed of the grader when operating is site specific and is documented in the subsequent section.
Materials Handling
Reference was made to the materials handling equation from USEPA AP42 Chapter 13.2.4 Aggregate Handling and Storage Piles (November 2006) for the quantification of emissions from the following batch and continuous drop operations:
β’ Trucks dumping overburden
β’ Conveyor transfer points
β’ Stacking to stockpiles
This equation is expressed as follows:
πΈ = π 0.0016 οΏ½π 2.2οΏ½1.3οΏ½π
2οΏ½β1.4 Where:
E = Emissions factor (kg/Mg)
k = 0.74 for particles less than 30 micrometres k = 0.35 for particles less than 10 micrometres k = 0.053 for particles less than 2.5 micrometres U = mean wind speed (m/s)
M = material moisture content (%).
The mean wind speed and material moisture content are site specific and are documented in the subsequent section.
Crushing and Screening of Coal
No specific emission factors are given for coal crushing and screening operations within AP42 or within other widely referenced emission estimation methodologies. A conservative approach (i.e. expected to provide an upper bound emission estimate) is adopted in which reference is made to emissions factors for crushing and screening contained within USEPA AP42 Chapter 11.24 Metallic Minerals Processing (January 1995). The emissions factors from this chapter are documented for high moisture content and low moisture content ores, with high moisture content defined as being greater than or equal to 4 percent by weight.
According to USEPA AP42 Chapter 11.24, a single crushing operation is likely to include a hopper or ore dump, screen(s), crusher, surge bin, apron feeder, and conveyor belt transfer points, with emissions from these various pieces of equipment frequently being ducted to a single control device. The emission factors provided for in USEPA AP42 Chapter 11.24 for primary, secondary, and tertiary crushing operations are for process units that are typical arrangements of the aforementioned equipment. For this reason the emission factors for crushing were taken to be applicable for the quantification of coal crushing and screening operations.
BMC BMP Determination 22 Feb 2012.docx Page B-8 No PM2.5 factors are given within USEPA AP42 Chapter 11.24, reference was therefore made to the PM2.5 fraction specified for Category 3 emissions within USEPA AP42 Appendix B.2 Generalized Particle Size Distribution (January 1995). Category 3 covers materials handling and processing of aggregate and unprocessed ore, including emissions from milling, grinding, crushing, screening, conveying, cooling, and drying of material.
A summary of the emission factors applied for coal crushing and screening operations is given in the table below, expressed as kilograms of emissions per metric tonne of coal.
Material Process TSP PM10 PM2.5 Units
High moisture coal (β₯4% wt)
Primary Crushing 0.01 0.004 TSP x 0.15 kg/Mg
Secondary Crushing 0.03 0.012 TSP x 0.15 kg/Mg
Tertiary Crushing 0.03 0.01 TSP x 0.15 kg/Mg
Low moisture coal (<4% wt)
Primary Crushing 0.2 0.02 TSP x 0.15 kg/Mg
Secondary Crushing 0.6 0.24(b) TSP x 0.15 kg/Mg
Tertiary Crushing 1.4 0.08 TSP x 0.15 kg/Mg
Wind Erosion of Overburden Emplacement Areas and Other Exposed Areas
The TSP emissions factor taken from the USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) was applied in the quantification of wind blown dust from overburden emplacement areas and other exposed areas (but excluding coal stockpiles). In designating PM10 and PM2.5 emission factors, reference was made to the PM10/TSP and PM2.5/TSP ratios specified within USEPA AP42 Chapter 13.2.5 Industrial Wind Erosion (November 2006). Emission factors, expressed in metric tonnes per hectare of exposed area per year (Mg/ha/yr), are given in the table below.
TSP PM10 PM2.5 Units
0.85 TSP x 0.5 TSP x 0.075 Mg/ha/yr
The TSP emission factor is specified for seeded land, stripped overburden and graded overburden. This factor was derived based on upwind downwind sampling of exposed areas at coal mines in the US. Pitts (2005) noted that these coal mines, documented within the background document to USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998), are located within reasonably dry areas (rainfall in the range of 280 to 430 mm/year) characterised by relatively high wind speeds (four sites with average wind speeds of 4.8 to 6 m/s, and one with 2.3 m/s). Pitts (2005) therefore concluded that the equation appears to be based on reasonably dry and windy sites.
The above emission factors are applied in the assessment of wind erosion from shaped and unshaped overburden emplacement areas, including freshly placed areas, graded areas and seeded areas. The factors are also applied to vegetated overburden emplacement areas, with control factors being taken into account contingent upon the level of vegetation coverage achieved.
These emission factors are also applied in the quantification of wind blown dust from other general exposed areas, such as unsealed roads, active mining areas and topsoil stockpiles. Wind erosion of coal stockpiles is however not quantified using these factors.
Wind Erosion of Active Coal Stockpile
A TSP emission factor for active coal storage piles is given in USEPA AP42 Chapter 11.9 Western Surface Coal Mining (October 1998) as follows:
ETSP = 1.8 x u
Where:
ETSP = TSP emissions in kg/ha/hr (kilograms per hectare per hour) U = mean wind speed (m/s)
The above emission factor is however given for wind erosion and stockpile maintenance. The Mining Activities defined by OEH for BMP determination purposes lists specifically wind erosion of coal stockpiles, with dozers on coal being defined as a separate activity. This distinction is understandable given that separate measures may be applied to address particular emissions arising from wind erosion of stockpiles and maintenance of such stockpiles by mobile equipment. Given that the above emission factor does not distinguish between wind erosion and maintenance emissions, an alternative approach was adopted. Bulldozer operations were addressed using the bulldozer on coal emission factors documented previously.
Wind blown dust from coal stockpiles was estimated by applying the complex, predictive emission estimation procedure documented within USEPA AP42 Chapter 13.2.5 Industrial Wind Erosion (November 2006) as described below.
The predictive emission factor equation for industrial wind erosion is given as follows:
πΈπππ π πππ ππππ‘ππ = π οΏ½ ππ
π
π=1
Where,
k = particle size multiplier (k = 1 for TSP, 0.5 for PM10 and 0.075 for PM2.5) N = number of disturbances per year
Pi = erosion potential corresponding to the observed (or probable) fastest mile of wind for the ith period between disturbances (g/mΒ²), calculated by:
P = 58(u* - ut*)2 + 25(u* - ut*) P = 0 for u* β€ ut*
BMC BMP Determination 22 Feb 2012.docx Page B-10 Where,
u* = friction velocity (m/s)
ut* = threshold friction velocity (m/s)
The following steps were followed in applying this equation:
Step 1 β The fastest mile of wind was determined between disturbances.
The coal stockpiles were conservatively assumed to be subject to disturbance on a continuous (hourly) basis to provide an upper bound estimate of emissions (i.e. N=8760). Emissions were calculated on an hourly basis for the base case emission inventory year based on measured site-specific wind speed data for this year.
The fastest mile of wind was calculated from the hourly average wind speed based on the gust factor range documented by Pitts (2005) drawing on the work of Krayer and Marshall (1992). Fastest mile wind speeds are given by Pitts (2005) as being in the range of approximately 1.18 to 1.27 times the hourly wind speed. A factor of 1.27 was used to provide an upper bound estimate of emissions.
Step 2 β The friction velocity was derived for several stockpile sub-areas to account for different wind exposures.
Given that coal stockpiles typically penetrate the surface wind layer (i.e. piles with height-to-base ratios exceeding 0.2), it is necessary to consider that different areas of a stockpile have different exposures to the wind. The friction velocity (u*) must therefore be calculated taking into account the surface wind speed distribution (us
+) which is estimated as follows:
+ +
= u
10u u u
r s
s
where,
us+ = surface wind speed distribution
us = surface wind speed (m/s), measured at 25 cm from the pileβs surface
ur = approach wind speed (m/s), or reference wind speed measured at a height of 10 m.
π’10+= gust wind speed at reference height of 10 m for periods between disturbances (m/s)
The shape of the pile and its orientation to the prevailing wind determine wind exposure patterns (us/ur
ratios) at the pile surface. USEPA AP42 Chapter 13.2.5 Industrial Wind Erosion (November 2006) documents wind exposure patterns for two coal stockpile configurations based on wind tunnel studies undertaken. The two pile shapes are a conical pile and an oval pile with a flat top, both with 37 degree side slopes. Contours of normalised surface wind speeds (us/ur) for both pile shapes are illustrated Figure B.1, with provision made for differences in the contours for the oval, flat topped stockpile given different approach wind bearings. The percentage of the pile surface areas represented by us/ur ratio is given in the table below.
Figure B.1 Contours of normalised surface wind speed (us/ur) for conical and oval, flat topped stockpiles (after USEPA AP42 Chapter 13.2.5 Industrial Wind Erosion, November 2006)
Pile Sub-area (us/ur)
Percent of Pile Surface Area
Pile A Pile B1 Pile B2 Pile B3 Generic
0.2 40% 36% 31% 28% 27%
0.6 48% 50% 51% 54% 54%
0.9 12% 14% 15% 14% 15%
1.1 0% 0% 3% 4% 4%
BMC BMP Determination 22 Feb 2012.docx Page B-12 Allowing for variations in actual stockpile shapes, a generic set of pile surface areas was established for application in the emission estimates (as shown in above table). In deriving this generic set reference was made to the maximum areas across stockpile types covered by sub-areas with higher us/ur ratios.
Based on the surface wind speed distribution (us
+), the friction velocity (u*) was calculated for each pile sub-area, taking into account the non-uniform wind exposure of stockpiles, by applying the following equation:
+ +
=
= u
su
su 0 . 10
5 ) . 0 ln ( 25
4 .
* 0
Step 3 β A threshold friction velocity was determined.
Reference was made to the literature to identify threshold friction velocities for use in the erosion potential calculations. Threshold friction velocities for coal piles are given as being in the range of 0.7 m/s to 1.12 m/s (USEPA, 1988; USEPA AP42 Chapter 13.2.5 Industrial Wind Erosion, November 2006; Sullivan and Ajwa, 2011). For the purpose of this assessment the lower threshold friction velocity of 0.7 m/s was applied.
Step 4 β Calculation of annual erosion potential for the entire pile
The erosion potential (P) was calculated for each stockpile sub-area, for each hour, based on the calculated friction velocity (u*) and the selected threshold friction velocity (ut*) as follows:
P = 58(u* - ut*)2 + 25(u* - ut*) P = 0 for u* β€ ut*
The erosion potentials were then summed across stockpile sub-areas and across hours to give the total annual erosion potential for the entire pile.