Case study of an ECA Application
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In Ontario, Environmental Compliance Approvals (ECAs) are reserved for “higher-risk” facilities. We’re going to take a look at one such facility that, on the face of it, seems to produce quite simple products, but demonstrates the detail and care required to ensure that all factors are accounted for in terms of the air emissions from the facility for ECA compliance. Although this facility requires an ECA, similar technical considerations would apply to facilities required to apply for Environmental Activity and Sector Registrations (EASRs).
Air Emitting Processes at the Facility
The case-study Facility manufactures artificial stone masonry. The facility receives some of the raw materials (sand) for its manufactured stone that are stored in storage piles outdoors. Other raw materials are delivered by truck and fed directly into storage bins. Some raw materials (colourants) are delivered in sealed bags to the facility and are directly fed into the process within the Manufacturing facility. Most of the raw materials (sand, other ingredients, with added water) are mixed in a Premix plant, with the mixture then conveyed to the manufacturing plant where colourants are added before being formed into artificial stone blocks.
Screened sand is delivered by truck, which tips sand on to a “delivered sand pile”. As needed, sand is picked-up from the delivered sand pile and dropped on to a conveyor and conveyed into a Premix facility. Colourants (in powder form) are delivered in sealed bags and transported directly into the Manufacturing plant. The premix passes through the initial stage of manufacturing in the following order (dust generation in this area is controlled at various points by a baghouse that recirculates back into the manufacturing facility). Premix is conveyed into a single surge bin (active venting of process fugitives) for metered weighting into batch sizes and then dropped into one of four colour mixers where colourant is added. Coloured batches of reacted premix are then gravity fed into presses to be formed into blocks (“green blocks”). Green blocks are cured in autoclaves. A steam production system employs four gas-fired boilers, all of which are oil-dual fired for use during gas supply disruptions. The flow of steam into the autoclaves provides elevated temperatures and pressures for the curing process. The Finishing area of the plant adds textured finishes to the cured blocks.
Most processes in this area produce dust, which is somewhat controlled by ventilation systems via a large and a small baghouse; the large and small baghouses re-circulate filtered air back into the facility. In addition, process fugitives escape the Finishing area via roof-top general exhausts.
Broken or reject cured blocks and scrap material is conveyed out of the Finishing area of the Manufacturing Plant and dropped on a scrap pile. Scrap from this pile is then transferred, by front-end loader, to an intermediate scrap pile and then a final scrap storage location
Comfort Heating – consists of various gas-fired hanging unit heaters located in the Manufacturing plant for comfort heating. Various roof-top gas-fired comfort heating units are used to provide heat for front and rear offices.
Process heating – is required to produce steam for block curing in the autoclaves. High pressure steam production is provided by four steam generators, all of which are dual-fuelled and can use #2 oil in case of gas supply disruption. Only a maximum equivalent of two boilers running at full capacity will ever operate in a 24 hour period. An equivalent of three boilers running at full capacity could occur in a 1 hour period.
On-site roads consist of a mixture of paved roads and unpaved roads. Dust from some on-site unpaved roads is effectively controlled using watering to suppress dust; some are left uncontrolled based upon preliminary dispersion modelling and measured road dust tests. Dust from on-site paved roads is controlled to varying degrees by sweeping and by road maintenance activities.
Dust from delivered sand, paved and unpaved roads, baghouses that currently serve the Manufacturing Finishing areas were sampled on-site; the silt fractions from the delivered sand and road dust samples were gravimetrically separated. All samples were analyzed for mineral content. Bulk samples of baghouse captured dusts were directly analyzed for mineral content. The mineral content analysis revealed crystalline silica and other minerals as components. This is in accord with s.7.4 of the MECP’s Procedure guidance document (ESDM Procedure document), that requires assessment of any component of dust that may exceed a Ministry health limit (full speciation is required to assess for this) for an ECA permit.
Year-to-year repeat sampling has exhibited variations in species mineral occurrences and levels found. As a result, new contaminants are presumed to be emitted annually. As a result, a regular sampling program has been established to assess the potential impacts of any new contaminants or altered levels of existing dust species, especially for delivered sand to ensure on-going compliance in the face of natural ingredients with variable composition.
The facility has a number of paved roads over which vehicles travel. When vehicles travel over a surface, particulate emissions may occur. These emissions are directly related to the loose material on the surface (silt loading). Road dust sampling was conducted, and analyzed to determine species present. The results showed that the dust was largely composed of various minerals including quartz, muscovite, dolomite, and others. For example, the maximal weight percent of quartz (among all paved road silt fraction samples) was found to be 21.9%. Since crystalline silica (i.e. Silica – respirable (<10 µm diameter), quartz) is a contaminant that contributes “to a ministry POI Limit that may cause a health effect” (ESDM Procedure document), an assessment of these emissions was included for ECA permit applications. Potential emissions of crystalline silica were based on 21.9% of PM10 road dust emissions since the POI limit for crystalline silica is based on PM10. This basis was used for all crystalline silica emissions. Potential emissions of the other substances were proportioned against suspended particulate matter (SPM) emissions and were only considered significant if those other substances had a POI limit that was not the same as for SPM (i.e. 120 µg/m3).
The emissions also depend on the amount of traffic on the road; maximal 24-hr traffic frequency estimates were utilized for each road segment. Emission estimates were refined based upon updated vehicle travel and site-specific sampling of road dust, accounting for the weekly road sweeping conducted. Road dust was sampled, during worst-case conditions (dry, Summer) from a sample of road segments. Samples were taken at various intervals after a road sweeping event to determine maximum dustiness levels achieved before re-sweeping. Results indicated that some roads could achieve a 5 g/m2 silt loading criterion. However, other roads (less trafficked or well-maintained) were only able to achieve 15 or 25 g/m2 dustiness levels before re-sweeping. Modelling of these differentiated road dust levels, however, did demonstrate compliance for all road dust species concerned, and therefore demonstrated an appropriate level of mitigation for paved road dust.
Similarly, road dust sampling was done for unpaved roads. The results showed that the dust was largely composed of various minerals including quartz, muscovite, dolomite, and others. For example, the maximal weight percent of quartz (among all unpaved road silt fraction samples) was found to be 24.9%. Since crystalline silica (i.e. Silica – respirable (<10 µm diameter), quartz) is a contaminant that contributes “to a ministry POI Limit that may cause a health effect” (ESDM Procedure document) an assessment of these emissions was included for ECA permit applications. Potential emissions of crystalline silica were based on 24.9% of PM10 road dust emissions since the POI limit for crystalline silica is based on PM10. This basis was used for all crystalline silica emissions. Potential emissions of the other substances were proportioned against SPM emissions and were only considered significant if those other substances had a POI limit that was not the same as for SPM (i.e. 120 µg/m3).
The emissions also depend on the amount of traffic on the road; maximal 24-hr traffic frequency estimates were used. Emission estimates were based on AP-42 13.2.2. Based on preliminary modelling, and field sampling of road dust, certain roads are mitigated using watering. Field sampling indicated the 100% effectiveness of watering based on the 8-hr watering schedule used.
There are a number of material drops that occur in the sand storage area for which similar emissions calculations were used. The dropping of these materials will cause fugitive SPM emissions. The composition of the sand was also assessed. The emissions were estimated using the emission factor equation from AP42 13.2.4 “Aggregate Handling and Storage Piles.” The equation is presented as particulate emission per tonne of material transferred and is based on the mean wind speed and moisture content of the material:
E – emission factor
k – particle size multiplier (dimensionless)
U – mean wind speed (m/s)
M – material moisture content (%)
The equation requires the use of a (worst-case) daily average wind speed, data which is not readily available. However, based on the average of 5 years of daily instantaneous speed of maximum wind gust data it is expected that the daily average wind speed will not exceed 46 kph (=12.78 m/s) and so this value was used. The moisture content was not measured on site, rather a default value from AP42 Table 13.2.4-1 was used (non-conservative; as allowed for ECA permit applications). The value was used for municipal solid waste landfills – sand, since this was the closest description.
The press rejects are passed through a screener to eliminate over-sized material. Ultimately, the screened press rejects are added to the sand as a form of recycling. This screening operation only occurs a few times a year and it is considered here for completion. A maximum of 320 tonnes of press rejects can be screened over a 24 hour period. To calculate the emission rate of SPM, the emission factor for controlled fines screening, (AP-42 Table 11.19.2-1) 0.0018 kg/Mg, was used, as follows:
There are conveyor and material drops that are involved in the transfer of material throughout various stages in the process within the Premix/pressing area. The dropping of material will create SPM emissions. Similar processes are grouped under this section for ease of presentation.
Emissions were estimated in the same way as in previous sections (i.e., use of drop equation AP-42 Eqn. 1 from 13.2.4) except that a wind speed of 1 m/s was used since the drops occur indoors; as all the drops occur in totally enclosed environments it was conservatively assumed that a 70% control factor applies (Downs and Pfost).
Maximal flow and drop of material in these processes is 1350 tonnes/24 hours, except for the colour mixers where an extra 27 tonnes/day accounts for colourants added.
Dust is present in the general plant air in the premix/colourant area. This area possesses general area exhaust via 5 roof exhausters. Area measurements of air quality have routinely been conducted in these areas for occupational exposure purposes (total dust and crystalline silica). These measurements were examined and reasonable maximal values, close to the exhausters, were chosen to provide conservative emission concentrations. Values chosen were 5 and 0.05 mg/m3 for SPM and crystalline silica, respectively. These values, multiplied by the roof fan exhaust rate, provided the emission rate. The fans run at maximum flow for 16 hours per day and run at a lower flow for 8 hours overnight. Speciation of SPM emissions was done using the same methodology as mentioned previously. It was assumed the dust is composed of the same composition as the premix plus colourants.
Dust is present in the general plant air in the cooling/finishing areas also. This area possesses general area exhaust via 10 roof exhausters. Area measurements of air quality have routinely been conducted in these areas for occupational exposure purposes (total dust (i.e. SPM) and crystalline silica). These measurements were examined and reasonable maximal values, close to the exhausters, were chosen to provide conservative exhaust concentrations. Values chosen were 5 and 0.05 mg/m3 for SPM and crystalline silica. These values, multiplied by the roof fan exhaust rate, provided the emission rate. Values chosen were 2.5 and 0.025 mg/m3 for SPM and crystalline silica, respectively, for low dust areas representing non-production areas where very little dust is generated.
Roof vents in this area are assumed to emit ambient dust from cured blocks (blocks exiting the autoclaves). It is known that the composition of the blocks alters as part of the curing process. Therefore samples from dust captured by the (re-circulating) baghouse, controlling dust in this area, were analyzed for mineral composition. The speciation of airborne dust was assumed to equal that from the baghouse sample and therefore varied from the composition of the emitted dust in earlier processes. Dust speciation was found using the percent of each mineral from the composition analysis compared to SPM (other than crystalline silica) for ECA permit applications.
Waste block material (chips or broken blocks) are conveyed out of the building and on to a temporary storage pile. A front-end loader is used to tidy the plant scrap pile. Both the conveyor drop and use of the front-end loader causes emissions from the drop of scrap material. The particulate emissions were estimated using the controlled conveyor transfer point emission factor from AP42 Table 11.19.2-1. The emission factor is combined with the maximal amount of material dropped in 24 hours (which is 60 tonnes).
Material from this pile is then temporarily located to another pile (1 drop, maximum 40 tonnes in 24 hrs), and finally to the final scrap pile (1 drop, maximum 100 tonnes in 24 hrs).
Sample calculation for SPM for drop point:
The particulate emissions were speciated using the speciation identified for the Cooling/Finishing Area for cured block scrap
The Facility is subject to s.20 of O. Reg. 419/05 and as such, the assessment of compliance with Schedule 3 standards was carried out with the aid of the U.S. EPA AERMOD atmospheric dispersion model. Dispersion modelling was completed in accordance with the MECP’s “Air Dispersion Modelling Guideline for Ontario, Version 3.0”, dated February 2017 (ADMGO). The AERMOD modelling systems have been identified by the MECP as the approved dispersion models under O. Reg. 419/05. The following approved dispersion model and pre-processors were used in the assessment:
- AERMOD dispersion model (v. 14134);
- AERMAP surface pre-processor (v. 11103); and
- BPIP building downwash pre-processor (v. 04274).
Tests were completed with AERMOD v. 16216 and the concentrations decreased. Therefore, the use of AERMOD v. 14134 is a conservative assumption.
AERMET was not used in this assessment, as the pre-processed MECP meteorological dataset was used. methods would be similar in facilities applying for an EASR permit.
As per Section 4.5 of the ADMGO, most of the significant sources at the Facility were classified as either point or volume sources. Road dust sources were classified as line volume sources (adjacent volumes), or area line sources, following guidance from the US EPA Haul Road Workgroup Final Report (2011); line volume sources were used for all road segments except those that would encompass receptors or would have had receptors within the volume source exclusion zone (in that case, area line sources were used). Gas combustion emissions that vented into buildings, and then indirectly out into the environment, were treated as volume sources. In those cases, volume source sizes were based on the building (or group of adjacent building) sizes. Buildings were grouped according to the criteria provided in O.Reg. 346 and groupings; volume source sizes were calculated based on US EPA AERMOD specifications. For a few NOx sources some stack characteristic data were not available (flow rate and stack gas temperature); in those cases worst-case surrogate values were substituted that minimized buoyancy and momentum flux to ensure conservative modelling results. Many of the material handling operations were considered as volume sources. Defined stacks associated with operations inside buildings were modelled as point sources for ECA permit applications.
Receptors were chosen based on recommendations provided in Section 7.1 of the ADMGO, which is in accordance with s.14 of O. Reg. 419/05.
Receptors were placed every 10 metres along the property line. The area of modelling coverage is illustrated on Figure 8 -Dispersion Modelling Receptors. Since maximal POI concentrations occurred at or close to the property boundary, nested grid receptors were not always used, to save computational time, as allowed by s. 14.(4) of the regulation. As a result, in all cases, only fenceline receptors were used (e.g., traffic dust crystalline silica emissions) because it was clear that maximal POIs would occur at the fenceline.
There is no child care facility, health care facility, senior’s residence, long-term care facility or an educational facility located at the Facility. As such, same structure contamination was not considered.
The POI concentrations listed in Table 1 were compared against criteria listed in the publication, the MOECC’s Air Contaminants Benchmarks List (ACB List), Version 1.0, dated December 13, 2016.
All of the predicted POI concentrations for contaminants listed in the Emission Summary Table that are included in the ACB List, are below the corresponding limits; the highest maximum POI concentration is 71.6% of the 24-hour limit for Silica Respirable (<10µm diameter) Quartz.
There are twenty-three (23) contaminants without a POI Limit. Of the remaining 22 substances, the dolomite maximum POI was below the previously accepted limit in the original version of the ESDM (used as part of the ECA application). Of the remaining 21 substances, the aluminium hydroxide maximum POI was below the de minimus limit. Of the remaining 20 substances, a MCLA was conducted for 15 substances and submitted in 2016 for each as they were newly discovered substances at that time. Of the remaining 5 substances, a MCLA was conducted and submitted in 2018 for each as they were newly discovered substances in 2017. For all contaminants with a Guideline or MCLA POI limit that is identical to SPM (i.e. 120 µg/m3), it was assumed that the SPM analysis captures these contaminants as an aggregate assessment.
All MCLA’s indicated maximal POI’s were below recommended MCLA values.
A POI concentration for each significant contaminant emitted from the Facility was determined using the conservative emission rates and an approved atmospheric dispersion model; the results are presented in Table 4 – Emission Summary Table. The POI concentrations listed in Table 4 were compared against the ACB List. The predicted POI concentrations for contaminants listed in the Emission Summary Table are below the O.Reg. 419/05 corresponding limits. The highest maximum POI concentration is 71.6% of the 24-hour limit for Silica Respirable (<10µm diameter) Quartz.
This ESDM Report demonstrates that the Facility can operate in compliance with s.20 of O.Reg. 419/05 in application for an ECA permit or an EASR permit.
TABLE 4: EMISSIONS SUMMARY TABLE
|Contaminant Name||CAS Number||Previous Calendar Year Emission Rate (g/s)||2017 Total Emission Rate (g/s)||Air Dispersion Model Used||Previous Calendar Year Max POI Conc (ug/m3)||2017 Maximum POI Concentration (ug/m3)||Change in POI Conc (%)||Averaging Period (hours)||MOECC POI Limit (ug/m3)||Limiting Effect||Regulation Schedule||Benchmark||Percentage of MOECC POI or MCLA Limit(%)|
|Suspended Particulate Matter (SPM)||n/a||0.702750||0.703930||AERMOD||57.613||57.613||0||24||120||Visibility||3||B1||48.01|
|Silica Respirable Quartz||14808-60-07||0.052689||0.051602||AERMOD||3.760||3.580||-4.780||24||5||Health||G||B1||71.61|
|Aluminum hydroxide||21645-51-2||0.000014||0.000014||AERMOD||0.0012||0.0012||0||24||0.1||–||de minimus||B2||1.21|
|Manganese and Manganese Compounds||7439-96-5||N/A||0.000102||AERMOD||N/A||0.007||N/A||24||0.4||Health||3||B1||1.72|
Note: AERMOD v. 14134; 3 – refers to Standards in Schedule 3 of O. Reg. 419/05 (ACB List), G – refers to criteria identified as a POI Guideline in the ACB List, JSL – Jurisdictional Screening Level (ACB List), MCLA – Maximum Concentration Level Assessments