Management Strategies for Odour and Air Quality
The 2015 MLA Guidebook – “Beef Cattle Feedlots: Waste Management and Utilisation” offers useful instruction on odour management. Content from this guidebook informs the following section.
There is generally some flexibility in the timing of potential odorous activities in the feedlot. CSCF management will use the basic understanding of atmospheric conditions that can disperse odours in planning pen cleaning, manure processing, composting and spreading operations.
Atmospheric conditions and their effects on odour dispersal are:
• Unstable atmosphere – typically the atmosphere is unstable on a warm sunny day when hot eddies of air rise from the land surface and cause significant mixing of the atmosphere.
Odours are rapidly dispersed and carried upwards, quickly reducing odour intensity away from the feedlot. Because these conditions promote rapid dispersion, they will be targeted for carrying out most odour-generating activities.
• Stable atmosphere – occurs on cold, still clear nights when the air at the land surface stays cool and remains trapped below an inversion layer. Little atmospheric mixing occurs below this layer and there is little dispersal of odours. Odours remain at relatively high intensity at some distance from the feedlot. These conditions are unsuitable for undertaking activities that will generate significant odour and odorous activity will be avoided in these conditions.
• Neutral atmosphere – occurs on heavy overcast days and odour dispersion is only moderate. Composted manure utilisation will occur only when the prevailing weather conditions are unlikely to result in odour and dust nuisance for nearby residents.
Management will consider the wind direction and strength, the time of day and the
atmospheric stability. The plan showing the location of all neighbours within approximately 5 kilometres and the site weather station will help to show which neighbours are at risk of odour nuisance from composted manure utilisation on particular fields. Management will develop an annual utilisation plan that takes into account seasonal wind directions, rainfall patterns and crops grown. Different paddocks will be selected for utilisation at different times of the year depending on the level of odour or dust generation risk and subject to agronomic and seasonal considerations.
To reduce potential odour nuisance to neighbours, compost turning and manure spreading will be done:
• frequently to minimise events with large odour generation
• evenly
• in the morning when the air is warming rather than late in the afternoon
• for solids, as soon as possible mechanically incorporate manure into the soil
On cold, still mornings, air will be trapped below an inversion layer, restricting odour dispersion. The specified pen foundations of imported compacted clay will help to reduce problems of odour or dust. Management will not spread manure if heavy rain is predicted.
Management will communicate with neighbours at the time of planned odorous activities to ensure that important events in neighbour’s calendars is not in conflict with the feedlot plan. A register of communications with neighbours will be kept in the FLM dairy.
Feedlot Location, Site, Situation and Woodlots
The feedlot property was selected to ensure adequate buffer distance between the feedlot (which is to be located near the centre of the property) and neighbouring potential receptor residences.
Existing tree belts and woodlots create turbulence and filter air and aid in odour dispersion and therefore reduce the likely impact on neighbours.
The proponent/operator understands the importance of the existing tree wooded areas on the property to odour dispersion and will retain and nurture the trees as an important feature of odour management.
Feedyard Pen Surface Integrity Management
Pen cleaners will be trained in pen cleaning and maintenance of surface integrity and every effort will be made by the pen cleaner to maintain and not damage the interface layer between the base of the manure pack and the compacted clay pen floor. Management will inspect and sign off on each pen as cleaning and repair are completed. Records of inspections and consequential notes will be kept in the feedlot manager’s diary.
In dry times cattle pens will be regularly cleaned of manure to ensure loose material as a dust emission source is minimised. A “clay mix” pen floor capping is specified for construction of cattle pens which should aid in forming a firm base and mitigate against pulverising to powder.
Low spots and any potholes that develop in the pen surface will be packed and repaired with suitable material at the completion of cleaning each pen prior to restocking. These problems are much less likely to occur because of the water trough design detailed in the next paragraph.
Water trough design includes elevated plug holes connected to underground drainpipe so that overflow and trough flush cleaning water flows through drainage pipes under the feedyard and exits from underground into the sedimentation structure. This design element ensures that no trough water ends up on the surface of the pen to affect pen floor integrity. This is a key design element in aiding lower odour emissions from the feedyard pad.
Prior to the monthly management meeting the feedlot manager will conduct a whole of feedyard pen floor inspection and will report findings to the meeting and develop a plan with staff to address any hazards detected.
Feedyard Pen Cleaning
Cattle pens will be cleaned on a frequency to maintain compliance with a Class 1 feedlot such that the depth on dry manure will not exceed 50mm depth. This strategy will reduce the risk of odour generation as a consequence of excessive manure loads becoming wet for an extended period and, as a consequence, odorous.
Tractor drawn box scrappers and frontend loaders will be the primary equipment used to mound manure and clean pens. A skid-steer with push bar will be used to clean along fence lines and push and pull material into the general yard cleaning zone for pick-up by the larger machines.
Manure loads will be managed to ensure that the solid dry manure pack is never greater than 50mm. On the nominated design criteria stocking density for the feedlot on a continuous stocking regime the pens will be cleaned approximately every 13 weeks. Pens will be cleaned in an autumn campaign to ready the yard for winter and a spring campaign to clean up after winter. Heat hazard manure load will be reduced in another concerted campaign prior to the end of December each year.
Pen cleaning environmental conditions will be assessed daily in line with the guidelines noted in Section 4 above including communications with neighbouring residents and if conditions are not suitable then the activity will be deferred until more suitable conditions develop. In summer months the Katestone heat load model will provide a useful forecasting tool for activity planning.
Effluent Catch Drain Cleaning
The feedpens have a specified constructed fall from bunkline to back drain. The fall is appropriate for feedlots in dry climates, such as the Wheat Belt region of WA. This slope is sufficient to create in-pen runoff to effluent catch drains in a feedlot managed to Class 1 standard but is such that the manure load generally remains in the pen and is not entrained in the pen surface effluent runoff.
In most rainfall events little manure will leave the pen and end up in the drain. However, at times, some manure will exit the pen and reach the drains. The back drains of the feedlot are specified with a constant fall from south to north.
Opens drains will be maintained by grading and solids removal to ensure all feedlot drainage-lines are weed free.
Drain cleaning environmental conditions will be assessed daily in line with the guidelines noted in sections above including communications with neighbouring residents and if climatic conditions are not suitable then the activity will be deferred until better conditions develop.
Sedimentation Structures Operation and Cleaning
Sedimentation detention structures as detailed in the Feedlot EA will be operated to detain feedyard rainfall runoff for a period of no more than 24 hours. This period is too short for the runoff water to experience anaerobic processes and become odorous at the time of decant.
Design of the structures will ensure that all liquid drains from the basis only leaving behind a layer of sediment. Each summer the structures will be assessed for sediment load and once the capacity is reduced by 20% the structures will be isolated, (see design criteria) dried out and cleaned.
Possible impact on receptor residences will be considered in planning the timing of cleaning.
Effluent Evaporation Dams Operation and Cleaning
Effluent terminates in a series of evaporation dams. Water balance detailed in the EA estimates that total design capacity of 46.25 ML is sufficient to evaporate (including effluent use in composting) all feedyard runoff in the 95th percentile wet year. See Section 6.4.4 and Appendix 3.
The drainage system has been designed to ensure that most sediment and Biochemical Oxygen Demand (BOD hereon) potential is retained in the feedyard pens and not entrained in the feedyard effluent. Constructed sedimentation structures are designed to aid solids that are entrained from the pens to settle in the sedimentation structures.
Effluent is therefore expected to contain some Total Dissolved Solids (TDS hereon) from leached nutrient and salts but significantly lower BOD in the terminal dams than other feedlots of equivalent size. Lower BOD in the effluent means lower odour potential.
In the 95th percentile year water balance calculations including use of effluent in composting, indicate that both dams are fully evaporated and empty by the end of summer.
Once holding capacity in either of the terminal dams is reduced by 20% by accumulation of sediment, inflows will be redirected to the other storages and the dams will have solids harvested for spreading on designated manure receival areas.
The feedlot manager will review weather forecasts for the planned activity period and possible impact on receptor residences will be considered in determining the timing of cleaning.
Manure Storage Area Pad Maintenance
The manure storage pad will be constructed of the same material and to the compaction and permeability standard of the feedyard pens. Runoff from the pad will be directed to the effluent settlement and evaporation system.
The pad will be managed to leave a layer of aged manure or compost over the pad. This will aid in reducing erosion. Any low spots or potholes that develop on the manure storage pad will be filled and repaired as soon as they are detected. The pad will be maintained, to remain free draining all the time. The manure storage pad will be inspected by the feedlot manager, monthly, and a report of the inspection will be logged at the monthly management meeting.
Manure Processing and Composting
As described earlier in this document, effluent water will be used in the compost production processes on the feedlot site. Turning of manure in the composting process has the potential to create odour.
Weather forecasts for possible impact on receptor residences will be considered by the Feedlot Manager in planning the timing of composting activity. Region receptor residents within 6 k’s will be advised of major manure turning and composting programs prior to commencement. Windrows during initial composting activity will be low profile so that in the event of spontaneous combustion the smouldering manure will be cut out and extinguished as soon as detected.
Composted Manure Spreading
Effectively composted manure has an earthy smell that is not classed as unpleasant by most people.
In instances when composted manure solids are spread, possible impact on receptor residences will be considered in planning the timing and location of spreading activity. The spread material will be incorporated into the soil in a timely manner.
Weather forecasts for possible impact on receptor residences will be considered by the Feedlot Manager in planning the timing of spreading activity. Neighbours within 2 kms of spreading on company land will be advised of major spreading campaign programs prior to commencement.
Manure Shipping Off Site
Any composted manure shipped off site will be transport in covered loads designed to ensure odours do not exceed acceptable levels.
Neighbours possibly impacted by loading of composted manure for shipment and passing trucks will be advised before the shipping campaign to ensure that the timing of the activity does not impinge on their amenity.
Deceased Animal Disposal and Composting
All deceased or euthanized animals will be composted at the manure storage pad in accordance with the 2015 MLA Guidelines for the composting of dead animals. The process includes opening the thoracic cavity and puncturing the rumen.
Dead animals must be delivered to the composting area and covered immediately, or, if a necropsy is conducted, then as soon as the necropsy is finished. Deceased animals found to be uncovered at the pad for more than 18 hours will be designated a notifiable incident under the feedlot QA system and will be dealt with using the Corrective Action Request program.
Feedlot Roads and Cattle Alleys - Dust
Feedlot road specifications include compacted stabilised gravel seal thereby significantly reducing the risk of dust in feed alley roads.
Cattle alleys will be regularly cleaned of slope wash manure to ensure loose material as an emission source is minimised. A sandy clay mix capping is specified for construction of cattle alleys which should aid in forming a firm floor and mitigate against pulverising to powder. If the cleaned surface becomes powdery then the use of a water tanker will be used to suppress the alley dust.