ASAE Conference Proceeding
This is not a peer-reviewed article.
Toward a Science-based Agricultural Odour Program for Ontario: A Comparison of the MDS and OFFSET Odour Setback Systems
W. R. MacMillan and H. W. Fraser
Pp.336-345 in Air Pollution from Agricultural Operations III, Conference Proceedings, 12-15 October 2003 (Raleigh, North Carolina, USA), ed. Robert Burns. ,12 October 2003 . ASAE Pub #701P1403
Ontario has a long history of using prescribed separation distances to minimize nuisance disturbances related to odours from livestock facilities. The Minimum Distance Separation (MDS) system is an experiential, empirically based system that has been used to effectively minimized livestock related odour complaints for over 25 years. Odour complaints are rare where livestock facilities are properly managed and sited using MDS. In spite of its effectiveness, MDS is coming under increasing criticism from both farmers and the public as follows:
--It is subjective and not based on clear, documented scientific data
--It is cumbersome and difficult to use and understand
--The MDS expansion factor is confusing and appears to allow uncontrolled livestock operation
--MDS is outdated and unable to predict adequate separation distances for the newer, larger barns
--MDS unable to quantitatively account for odour control technologies, such as biofilters and manure treatment systems
The livestock unit (LU) based MDS system is unable to predict separation distances for independent manure storage processing facilities and other agricultural odour sources where no animals are present.
These criticisms have lead Ontario to initiate a program to reevaluate the MDS system. A first step toward modifying the MDS system is to develop analytical comparisons with some of the more science-based odour emissions models to allow calibration of the MDS curves. This paper compares separation distance predicted by MDS to those predicted by Minnesota’s Odour From Feedlot Setback Estimation Tool (OFFSET). The OFFSET model was developed using real odour emissions data and dispersion modeling techniques. To allow reasonable comparisons the OFFSET model was calibrated to Ontario’s climatic conditions and calculations were made using both systems under similar construction and management regimes for swine, poultry, dairy and beef cattle facilities. Results from the two separation distance models were compared using 93% and 96% annoyance-free criteria from the OFFSET model to emulate the MDS nearest single neighbor and high occupancy/sensitive land use criteria, respectively. Results of the comparison show that MDS separation distances compare favorably to those from the more science-based OFFSET model. Where under-barn manure storage was used, only large (> 10,000 animals) SEW weaner barns were shown to be sited too close to neighboring land uses by the MDS methodology. Where, manure was stored in uncovered, exterior storage systems only finishing and farrow-to-finish hog operations consistently meet the selected OFFSET annoyance-free criteria when sited using the MDS system. It was concluded that work is needed to verify and modify the MDS system to increase public confidence and improve the utility of the MDS system. The MDS expansion factor needs to be verified and a mechanism to account for odour control technologies should be developed. Future research should be collaborative to improve research efficiencies and improve public acceptance of the system.KEYWORDS. Agricultural odours, Barn sitting, Livestock barns, Manure odours, Separation distances, Separation formula.
The livestock and poultry industry is an important component of the overall economy of Ontario, Canada. About 20,000 livestock and poultry farms directly create about 45,000 jobs in the Province and about three times that many spin-off jobs in areas such as processing, distributing, retailing and exporting. Ontario contains only about 8% of Canada’s agricultural land area but accounts for over 25% ($3.5 billion Cdn) of Canada’s livestock and poultry farm cash receipts (Ontario Ministry of Agriculture, Food and Rural Affairs, 1995). Ontario’s diverse livestock industry includes dairy, beef, swine, poultry, sheep, and veal production. About 2 million of Ontario’s 11 million residents live in rural areas, but only about 5% of these ( ? 100,000) live on livestock or poultry farms (Fraser, 2000). The imbalance is increasing with Ontario’s population growth, especially in the south where the majority of the people and most of the livestock and poultry are concentrated. Since most rural residents have little to no family or business connection with agriculture, new rural residents often have limited knowledge of farming practices. Consequently, there is little tolerance for the nuisance factors often attributed to livestock and poultry production.
Production economics are forcing intensification of Ontario’s livestock industry. Higher land prices and uncontrolled price fluctuations have forced producers to increase animal numbers at a given production site. While livestock numbers have remained relatively steady, the normal size of livestock operations has increased substantially over the last 20 years. Fewer farms are now raising most of the animals in Ontario with the help of specialized, technical staff. Many of these operations are locating on smaller land parcels to offset increasing management costs. Large numbers of animals and an increased need for manure storage means more manure in one location and increased potential for barns and storage facilities to be located near other incompatible land uses. These factors combine to increase the potential for odour and other nuisance factors to affect rural neighbors as urban sprawl continues to consume the countryside at the urban fringe. Many modern rural residents are well educated, affluent and environmentally aware. They have the time, money and know how to effectively protest proposed and existing livestock operations that they see as threatening their quality of life. Increasing barn size and corporate involvement in livestock agriculture has resulted in decreased public trust in the industry. Concerns for environmental and public safety related to large “corporate” farms have lead to organized and impassioned community protests where such barns are proposed. Concerns range from water quality to community values and rural lifestyle to landscape aesthetics and property depreciation. More often than not one of the key issues in these community protests is odour. Historically in Ontario livestock barn developments protests appear to be focused on odour and water quality concerns. In many cases odour is the key issue especially where the concerns are related to “large” hog barn proposals?
The Minimum Distance Separation System. The minimum distance of separation (MDS) system is the currently recommended practice and official policy of the Ontario government regarding the mitigation of odour nuisance due to livestock barns and manure storage structures. The MDS system resulted from a proliferation of new, “large” livestock and poultry barns during the late 1960’s and early 1970’s. MDS has been around in various forms since its introduction in the document A Suggested Code of Practice (ODAF et al., 1970) . Farmers were encouraged to obtain a Certificate of Approval from the Department of Energy and Resources Management that addresses land base requirements to reduce environmental risks and recommended fixed minimum separation distances to reduce nuisance due to objectionable odours (Fraser, 2000). In spite of a revision to the Code in 1973, MDS did not protect farms from competing land use encroachment until the more comprehensive Agricultural Code of Practice was published in 1976 (OMAF et al., 1976). At this point, a reciprocal approach to land use separation was adopted because it was felt that non-agricultural land uses were beginning to present a threat to the long-term survival of agriculture in the more populated regions of Ontario. The 1976 Code also introduced a sliding scale concept for separation distances since fixed distances were too rigid to adequately address the variability in livestock farms and the needs of some competing land uses. MDS I and II formulae were introduced by Ministry Agricultural Engineers to establish required separation distances between new, non-agricultural land uses and existing livestock operations and between a new or expanding livestock facilities and neighboring non-agricultural land uses, respectively. MDS II is applied where a livestock development or expansion exceeds 150 livestock units (LU’s) whereas MDS I is applied where a non-agricultural land use is approved on lands zoned for agriculture and the nearest agricultural operation houses any livestock. MDS I separation distances are designed to allow the neighboring livestock operation to expand to a maximum of 150 livestock units.
In 1995 a modified version of the MSD formulae were published to reflect experience with new animal production systems and the rapidly changing rural Ontario landscape. The basic principals of the MDS system were preserved, two documents, entitled MDS I and MDS II, provided more detailed instructions for the application of the MDS formulae (OMAFRA et al, 1995). Shortly after these documents were published the authority to apply MDS was delegated to the municipal government’s planning authority under the Ontario Planning Act (OMMAH, 1990). The Provincial Policy Statement established that municipalities must “have regard for” MDS when considering land use, zoning or building permit decisions and about 95% of Ontario municipalities have enshrined MDS into bylaw. OMAF engineers and Rural Planners are available to provide technical support for the application of the MDS system. MDS I and II have been applied approximately 100,000 and 20,000 times, respectively, to determine separation distances for rezoning and livestock development. Farmers generally accept the idea of meeting MDS requirements but, where a barn development or expansion cannot meet the MDS II requirement, a municipal Committee of Adjustment may award a “Minor Variance”. A mechanism to appeal all municipal and adjustment committee decisions is available through the Ontario Municipal Board. A MDS I decision is sometimes appealed where a separation distance limits the financial viability of a planned non-farm development or where a planned lot severance is refused. MDS II variances are sometimes required to mitigate potential environmental impacts or to protect the economic viability of an existing farm. The MDS system is widely accepted in Ontario and few post development complaints arise where MDS has been properly applied (Fraser, 2001). A tribute to the utility and effectiveness of MDS is that it has been adapted for use by at least three other Canadian provinces.
The Need For Change . MDS is designed to minimize livestock farm odour nuisance through a methodical determination of separation distances. In spite of the relative lack of post development complaints, many have lost confidence in MDS due to the profusion of misconceptions about the system. Community conflict and increasing litigation between livestock producers and their neighbors are the result of competition and disagreements over the appropriate use for land, especially in the highly populated areas of Ontario. Access to information and media hype has lead to fears that barn odours create health problems, especially in the young, the elderly and those predisposed to allergies. Theories that chemical (NH 3 , H 2 S, etc.) and pathogenic emissions can cause disease, allergies and mental health effects are commonly publicized, resulting in an erosion of confidence in the MDS system to adequately protect rural residents. Further, municipal staff often does not fully understand livestock production systems, resulting in improper usage of the formulae. Misunderstanding and public pressure have resulted in inconsistent application of MDS, resulting in further confusion and erosion of the public confidence. Municipal authorities sometimes apply their own rules and in some areas MDS II is required but MDS I is ignored. Erroneous interpretation of MDS can make it difficult for producers and developers to determine their business options and opportunities.
While the MDS system has worked well historically to mitigate odour nuisance in the agricultural zone, increasing misuse, misunderstanding and public criticism is prompting the need to improve the MDS system. Critics have suggested that several points need to be addressed as follows:
MDS is subjective and not based on clear scientific data,
The MDS expansion factor needs to be better explained and scientifically justified,
The MDS method is outdated and fails to account for modern livestock operation size and production systems,
MDS needs to be modified to handle non-livestock-based operations that generate odour,
The system needs to be simplified for ease of use and understanding.
Suggested improvements to the separation distance system have varied widely and appear to depend on the perspective of the individual or group making the suggestions. Some want it to be simpler and easier to use while others want it to be more comprehensive, almost all agree on the following points:
It must be based on scientific air dispersion and odour transport factors,
It needs to quantitatively account for odour control technologies, such as biofilters and manure treatment,
Separation distances and the use of odour control technologies must be systematically inscribed into provincial law and the livestock operation permitting process.
As a result of these suggestions and criticisms, the MDS system is currently under review to make it more science-based, adaptable and reflective of the current state of farming and the changing needs of the rural community. There are many technical questions yet to be answered but the real challenge will be to achieve public trust in the new system by balancing the needs and perceptions of the livestock industry and its producers with those of rural, non-livestock producing neighbors.
Comparing Odour Models. The call for an updated and improved odour and separation distance prediction system has led the Ontario Ministry of Agriculture and Food (OMAF) to reevaluate the MDS system. An Odour Management Working Group (OMWG) consisting of OMAF engineering and planning staff and representatives from the University of Guelph was formed to review Ontario’s current odour policy and the MDS system. The working group is looking at the available odour-related separation distance systems. Odour models reviewed or considered thus far include Minnesota’s OFFSET (Jacobson, et al., 2000), Warren Springs (Williams and Thompson, 1986), Austrian (Schauberger and Piringer, 1997) and Purdue (Lim, et al., 2000) systems. The Austrian and Purdue models are limited to considerations for swine operations and the Austrian model does not consider the impact from manure storage facilities. Therefore, these systems were rejected as potential replacements for the Ontario MDS II system. Guo, et al. (2001) reviewed and compared all of the models listed above, including Ontario’s MDS II system. They found that the Warren Springs model produces very large separation distances relative to the current MDS II model, which was found to produce some of the smallest separation distances of any of the models considered. The large separation distances predicted by Warren Springs are considered to be too large for Ontario’s situation based on our historical success with complaint reduction using the MDS system to date (Fraser, 2001). Of all of the models considered by Guo et al. (2001), the Minnesota OFFSET model was found to provide the most flexibility and consistent results. The OFFSET model allows a choice of annoyance-free period criteria that can be adjusted according to population densities and occupancy frequencies. Offset can account for local weather conditions, but wind speed, direction and stability data must be available to use the model appropriately.
The OFFSET model has the advantage of being science-based, since it was developed from measured barn odour emissions and separation distances are based on scientific dispersion modeling techniques using real local weather conditions. Its reliance on a percentage “annoyance-free” periods is in line with the principal of nuisance tolerance being dependent on the frequency, intensity, duration and offensiveness of the nuisance (FIDO). The modeling process allows odour emissions to be based on facility footprint area, as opposed to livestock numbers, providing a opportunity to predict separation distances for odour sources such as mushroom operations, compost facilities and stand-alone manure storage sites. Footprint area is easier to understand than livestock facility capacity for those that are unfamiliar with livestock production systems. The use of odour emissions data allows OFFSET to account for odour control technologies that have been monitored and assessed, providing a science-based justification for quantitative reduction in separation distance requirements. The MDS expansion factor provides for direct credit of odour nuisance reduction where existing operations are expanding on the same site. OFFSET simply calculates the increase in odour emissions based on the increase in the foot print area of the facility. Consequently, the resulting separation distance is determined relative to the overall size of the operation. The overall distance separation distance predicted by OFFSET does diminish with increasing size of the operation as a result of the diminishing slope of the OFFSET nuisance-free curves.
After review of the OFFSET model the OMWG determined that it is the most appropriate odour management model available to enable the development of a science-based separation distance prediction system for Ontario’s current and future needs. However, because of our 25-year history of successfully applying the MDS model there is a reluctance to abandon MDS completely. Consequently, a comparative analysis was conducted to determine the similarities and differences between the two systems.
Calculations were made to conduct a direct comparison of separation distances predicted by Ontario’s MDS system and the OFFSET model. Comparative analysis conducted for liquid manure systems assumed the use of under-barn manure storage tanks. Under-barn manure storage is common in the confined livestock industry (i.e., tie stall dairy, finishing beef, feeder and nursery (weaner) hogs) in Ontario’s modern livestock industry. MDS and OFFSET separation distances were also predicted for dairy cattle and broiler chickens using solid manure with in-barn dry pack manure storage systems. All barns were assumed to be new developments on lands zoned for agriculture. A separate analysis was conducted to compare several types of livestock operations with uncovered, external liquid manure storage.
A set of regression equations were developed to predict odour dispersion transport for weather conditions in London, Ontario using the INPUFF II model following the procedures used by Jacobson et al. (2000). The equations were developed to reflect wind stability classes D and E and wind speeds of 3.6 to 5.4 m/s and 1.8 to 3.1 m/s, respectively. Stability Class D (more stable) conditions were then used to develop OFFSET odour annoyance-free period curves of 92.7 and 95.9%. These annoyance-free conditions were assumed to be comparable with the predicted MDS separation distances for low occupancy (i.e., nearest neighboring residence) and high occupancy (i.e., multiple residential, institutional, recreational commercial and industrial zoning) situations. The calculations were conducted for broiler chickens, dairy, beef and weaner and feeder hog operations with between 150 and 2000 livestock units in size. MDS calculations were done following the procedures described in the Minimum Separation Distance II publication (OMAF, 1995). The number of livestock in each of the example barns was calculated using Table 1 (Factor A) in the MDS II publication (OMAF, 1995). The footprint area of each barn was back calculated using the number of animals in the barn and an internal unpublished OMAF data source routinely used to assess the space requirements of livestock species for MDS purposes. The footprint area of the livestock and poultry facilities was then used along with the OFFSET odour emissions number data from Jacobson, et al. (2000) to determine the total odour emissions from each barn. Where an exterior, uncovered manure storage facility was associated with the barn, the surface area of the manure storage was added to the overall facility footprint. Separation distance requirements were then calculated using these data for each species using the OFFSET regression equations developed for London, ON conditions and graphed against the MDS II separation distance predictions. Some of the results from the analysis described above are shown graphically in Figures 1 through 4 at the end of this paper.
Figure 1. Comparison of separation distance predicted by MDSII and OFFSET for feeder hogs using liquid under-barn manure systems.
Observation of figure 1 suggests that MDS will ensure that neighbors of smaller feeder hog operations are free of odour annoyance about 96% of the time. However as operations increase in size beyond about 1500 feeder hogs the flatter inflexion of the MDS curve, relative to that of the OFFSET curves, means that the percent annoyance free period begins to approach the 93% of the time according to the OFFSET model. High occupancy land uses (e.g., residential, industrial, recreational, etc) are afforded a doubling or 2x factor under the MDS II system to account for the increased potential for complaints due to odour nuisance. Separation distances predicted by MDS for the high occupancy land uses suggests that occupants would be free from odour annoyance more than 96% of the time. Observation of the separation distances predicted for weaner hogs (Figure 2) indicates that the nearest neighbors of barns housing less that 10,000 weaner hogs would be annoyance-free at least 93% of the time where they are located using MDS. MDS predicts a much smaller separation distance than does OFFSET for larger weaner barns with visual inspection of the graph suggesting that odour nuisance from these operation might affect low occupancy neighbors more than 10% of the time. However, weaner hog operations with more than 10,000 hogs in one location would be very rare in Ontario. High occupancy land uses would also be more affected by odour from the larger weaner barns where the barns were located using MDS II rather than the 96% nuisance free curve of the OFFSET model. Weaner barns with more than 12,500 weaner hogs may affect neighboring high occupancy land uses more than 4% of the time, whereas the more common weaner operation sizes would be located far enough away from high occupancy land uses to ensure minimal odour nuisance affect.
Comparison of MDS II and OFFSET for free stall dairy barns using liquid manure systems (Fig 3) shows that facilities sited with MDS II should ensure that the nearest neighbor would be unaffected by odour annoyance more than 96% of the time for barns housing 500 cows or less. The 93% free line and the MDS II nearest neighbour lines tend to converge as animal numbers increase but since dairy operations greater than 500 milking cows are very rare in Ontario, this should not create a lot of concern. When MDS for high occupancy land uses is compared to the OFFSET 96% annoyance-free line it is evident that MDS provides a much larger separation distance than that required to ensure that occupants are affected by odour 4 % of the time or less.
Figure 2. Comparison of separation distance predicted by MDSII and OFFSET for SEW – weaner hogs using liquid under-barn manure systems.
Figure 3. Comparison of separation distance predicted by MDSII and OFFSET for dairy cattle using liquid under-barn manure systems.
Comparative separation distance graphs constructed for beef cattle using under-barn liquid manure systems (data not shown) indicated siting a barn using MDS II would result in the nearest neighbour being free from odour nuisance at least 96% of the time where under 2000 beef cattle were housed at one location. Neighbours of these beef cattle facilities barns holding more than 2000 animals would be annoyance-free less tan 96 % but more than 93% of the time. Such beef barns sited using the MDS II 2x-factor (i.e., near residential, industrial or recreational land uses) would result in those neighbours being free from odour nuisance more than 96% of the time. Anecdotally, the data suggests that MDS II would result in high occupancy land uses being free of odour nuisance about 99% of the time. Observation of the graphs developed for dairy cow (data not shown) operations using solid manure show that the nearest neighbours of these operations should be unaffected by odour nuisance more than 96% of the time. The data also suggests that, where these livestock facilities are sited using the MDS II 2x-factor, nearby high occupancy land use occupants would very rarely experience the effects of odour nuisance.
The comparative data for chicken broiler operations shown in figure 4 were very similar to those for tie stall dairy using solid manure systems. The data suggests that MDS II procedures provide more than adequate separation distances from both high and low occupancy neighbouring land uses where solid manure systems are used regardless of the livestock type. The possible exception to this rule is hogs on solid manure but no data are available to allow comparison of this type of hog production system. Recent discussions with Ontario poultry industry leaders indicated that they would oppose reducing MDS requirements for their industry due to historical precedent and other nuisance factors related to their industry that could create neighbour unrest.
Figure 4. Comparison of separation distance predicted by MDSII and OFFSET for chicken broiler barns using solid manure with an in-barn dry pack manure storage system.
Observation of figure 4 shows that, where livestock operations have uncovered exterior manure storage facilities, many of the livestock types sited using MDS II would result in low occupancy land uses being affected by odour nuisance more that 7% of the time. In fact, only finishing and farrow-to-finish hog operations sited using MDS II meet the selected annoyance-free criteria for low occupancy land uses where exterior liquid manure storages are used. Segregated sow and weaner hog operations, farrow-to-wean hog operations and free stall dairy operations using exterior, uncovered liquid manure storage systems failed to meet the 93% annoyance-free period selected for low occupancy land uses. This suggests that, in some instances livestock facilities using certain liquid manure storage options may be sited too close to their nearest neighbour.
Finally, no analysis was conducted to compare the differences in separation distance predicted by the OFFSET and MDS for expanding livestock operations. The MDS II Factor ‘C’ as defined in Table 3 of the MDS II publication is applied to both new and expanding livestock or poultry operations (OMAFRA, 1995). It is designed to allow a livestock operation to expand to approximately 2.5 times its original size without appreciably increasing the required separation distance to its nearest neighbour. As a result, the expansion factor for “new” livestock operations (1.14 multiplier) is designed to locate facilities farther away than necessary to account for this expected expansion. The MDS II factor “C” can reduce the cumulative MDS distance for expanding livestock facilities by as much as thirty percent (C = 0.7). This recognizes that livestock facilities are expected to expand as necessary for their economic survival over time. The expansion factor also assumes that improved management in the post start up period will act to decrease the initial odour emissions from a new livestock development. Furthermore, the initial fears of nearby neighbours tend to diminish over time as people come to accept the operation in their neighborhood. However, as mentioned previously in this paper, the expansion factor is one of the more frequent criticisms of the MDS system. There is no mechanism similar to the expansion factor in the OFFSET model since odour emissions are considered as an area source. As a result, although higher emissions are generated as facility size increases, the increase in the separation distance diminishes as odour emissions increase due to the shape of the curve developed by the model. Nonetheless, one would expect the OFFSET model to predict greater separation distance requirements for small livestock facility expansions than would the MDS system. This is one of the key items that will need to be addressed in any future odour monitoring and modeling programs to be conducted in Ontario.
Ontario’s MDS system has historically been a useful tool to determine required separation distances between livestock and poultry facilities and non-compatible uses in the rural community. Although MDS has general acceptance in the rural community, criticisms must be tested to ensure continued buy-in to the MDS system. Where weaknesses are found the system will need to be modified to reflect the current and anticipated state of the industry to better meet the needs of Ontario’s rural communities. Comparison of Ontario’s experiential based MDS system to the more process based OFFSET model, using Ontario climatic data, show that the MDS system provided fairly realistic odour setback distances. Weaknesses in the current MDS system seem to be related to liquid manure livestock systems that use outdoor storage facilities and very large, under-barn, covered liquid manure systems. The economic contribution of the livestock and poultry industry is important to Ontario’s economy so it is critical that programs and policies be developed to ensure its survival. An odour policy that ensures public acceptance of the industry is key to the industry’s survival. Public confidence is dependent on the policies scientific and technical defensibility. Based on the results of this study and the historic success of the MDS system it seems that any new separation distance system should not completely abandon the MDS system. Rather, future odour related research should seek to build on the MDS system, verify its expansion factor, extrapolate the curves for larger barns and develop quantitative methods to account for odour control technologies. Simplicity is also key to the acceptance of the diverse audiences of the separation distance program, as many are unfamiliar with the agricultural industry. Collaborative efforts with other jurisdictions conducting similar work will increase efficiency and help to develop a national or international odour management system. A well-tested unified system for odour separation distance prediction would also help to improve public acceptance of the system. It is recommended that future odour research programs be developed in cooperation with other jurisdictions to optimizing effectiveness and control costs.
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