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GCI TECH NOTES©
AMBIENT SO2 5-MINUTE PEAK RULE
The EPA is proposing the possible adoption of a tough new rule. As proposed, Option 1 of this addition to the National Ambient Air Quality Standard (NAAQS) would limit ambient SO2 concentration to a single annual exceedence of the 5-minute peak value of 0.60 ppmv. This new standard is intended to provide greater protection to a small subgroup of the population, "asthmatics who exercise". The two other less extreme options are: Option 2; exceedences (as many as 5) of the 0.60 ppmv 5-minute value would trigger state regulator involvement in correcting the violation, and Option 3; put additional focus by the regulators on the sources likely to produce high 5-minute values to ensure that the existing standards are being met.
Currently facilities must meet a <0.14 ppmv value averaged over 24 hours and a <0.03 ppmv arithmetic mean value over a year. The EPA currently reports the annual average ambient SO2 levels at <0.004 ppmv in rural areas and >0.03 ppmv in the most polluted urban industrial areas. In the proposed rule (FR Vol. 59, No. 219) on page 58968, column 1, the EPA Admini-strator states: "In her judgement, the current 3-hour, 24-hour, and annual standards appear to provide substantial protection against the health effects associated with short-term SO2 exposures. As indicated by the air quality analysis described above, the current standards, together with implementation of Title IV of the Act, markedly limit the frequency and extent of short-term concentrations of concern." (Emphasis added.) Such a conclusion, however, does not stop the EPA from proposing a new short-term exposure standard to provide greater protection to a small subgroup of the population.
The need for this rule is based on the contentious assertion that asthmatics suffer significant episodes of distress from breathing ambient air contaminated with 0.5 to 1 ppmv of SO2. Indeed the document reports: (page 58965, col.2) "Opinions on the significance of the effect expressed by the Clean Air Scientific Advisory Committee (CASAC) and others have been widely divergent. Some CASAC members and outside commentors feel that the responses reported in the range of 0.6 to 1.0 ppm SO2 are not significant, especially when viewed in the context of the frequency with which asthmatics ordinarily experience similar effects in the course of their daily lives." Other CASAC members and commentors disagreed and felt the exposed asthmatic was placed at an "unacceptable risk of harm." The document presents data on "controlled human exposure studies." This data, however, is not supported by epidemio-logical evidence. The document states: (page 58967, col. 1) "Available epidemio-logical studies show no evidence of significant associations between either 24-hour or 1-hour average ambient air SO2 concentrations above 0.1 ppm and increased visits to hospital emergency rooms for asthma." In order to demonstrate that 5-minute peaks of ambient SO2 concentrations above 0.6 ppmv can potentially create distress for asthmatics, the EPA had to present data on the effect of such exposure on asthmatics who were conducting "moderately heavy exercise" (such as jogging or tennis) and assumed that these individuals had not premedi-cated themselves with a beta-agonist bronchodilator. Recently, an article published in the December 8, 1994 New England Journal of Medicine described two studies on asthma mortality. Although asthma mortality is not the issue here, mortality studies would indicate the effect of current conditions. In a study conducted by the Mayo Clinic that followed 2,499 people with asthma for an average of 14 years, only 6 died from asthma. The lead author of the study stated: "The vast number of patients with asthma in the United States don't have an increased risk of death, and death is rare." The Philadelphia study, however, determined that the death rate of asthmatics among the poor was higher than among their more affluent neighbors, regardless of race. Ambient air quality does not appear to be the reason for this increased death rate. The Philadelphia researchers noted that the asthma death rate had declined between 1969 and 1977, then began to increase to its current level, despite the improvement in ambient air quality. The editorial suggested two possible causes for this increased asthma death rate: Exposure to such substances such as cat dander, mold and cockroach bodies. This is because houses are sealed more tightly than in the past, trapping these materials inside. Second, the use of medicinal inhalers may mask the severity of the problem, thereby causing the individual to seek assistance too late during an episode. As for the disparity between the poor and the more affluent, the experts suggest that it may be due to poor access to health care as well as unclean living conditions. Clearly then, EPA's claim that a reduction in high 5-minute peak instances will materially impact the quality of life of exercising asthmatics is not supported by epidemiological studies as noted above, nor do the mortality studies indicate that asthmatics who exhibit proper care of themselves have shorter lives.
Having concluded that some people somewhere might possibly be affected by ambient SO2 levels above 0.6 ppmv, the EPA proceeded to demonstrate that such levels exist. The staff conducted a statistical analysis using available hourly averages. The method used for calculating the incidence of short-term peaks is contained in a Staff Paper Supplement (EPA, 1994b) and has not been examined for inclusion in this review. However, in addition to EPA's intent of demonstrating that incidences of 5-minute peaks exceeding 0.6 ppmv of SO2 in the ambient air do occur, the data also indicates that such peaks may be beyond the control of the source emitters. The EPA, in their exposure frequency estimate as reported on page 58967, col. 2, states: "This analysis also suggests that the number of sites likely to record multiple high 5-minute peaks in a single year or over several years, can vary considerably." (Emphasis added.) Many people might assume that this variability is the result of a variability in the emission rate of the SO2 from the source. This is highly unlikely. The source facilities are keenly aware that to consistently achieve the existing standard, the SO2 emission rate from the stack must be kept below a certain value. Indeed, the EPA is aware that the site of the monitoring device "...may be the largest potential source of underestimation of SO2 peaks." The EPA draws the reasonable conclusion that if there were different monitoring sites or more monitoring sites, there may be even higher numbers of high 5-minute peaks. Obviously this points out that some major factor has a very large effect on the ground level ambient SO2 concentration. What major factor could account for such a wide variability of SO2 ground level concentration in both time and space? That factor is weather, a factor that is totally outside of the control of the SO2 emitter. Indeed, the facility could have an exemplary record for many months, perhaps even a year or so. Then, through no fault of their own, perhaps even while operating at SO2 stack emission rates in the lower third of their normal operating range, the ambient SO2 monitoring device records multiple high 5-minute peaks in excess of the 0.60 ppmv standard. Such a "violation" would initiate action by the regulatory agencies in the form of fines and mandatory corrective measures. Such a scenario is valid for a major utility with a tall stack. For non-utility sources with shorter stacks in complex terrain, such a scenario is a virtual certainty.
As an example, a cement kiln near a small town burns coal that emits SO2 from it's stack at a concentration of 200-300 ppmv. Using an EPA approved stack air modeling program, it is possible to calculate the maximum annual ground level impact point concentration, a value of 0.0008 ppmv, a value that is considered to be conservatively high. This value is well below the annual and 24-hour values set in the regulation. However, during certain weather conditions, the plume does not dissipate as modeled. This is not unreasonable because the model is based on five years of daily, not minute by minute meteorological data from a nearby weather station. On some days there are reports of the odor of sulfur dioxide. This happens a few times each year normally in the spring and fall. Even if the facility could accurately define the weather conditions that create this event, and (using that definition) monitor the weather to predict an upcoming incident, to what emission value would the facility have to limit the SO2 concentration in the plume to comply with the 0.6 ppmv 5-minute peak value? However, since prediction of the weather conditions that would create such an event is not sufficiently reliable, the only possible way that these facilities can comply with the regulation is to reduce their SO2 emission rate to some guessed-at value on a permanent basis. The establishment of this emission rate would be arrived at by trial and error over a long period of time (at least all four seasons) with each error after the first a violation. Even then, if the weather pattern were to change the following year, the facility could be out of compliance. Basically, the EPA has proposed a regulation that puts the emitter's attempts at compliance totally at the whim of the weather. The only certain way that these facilities can comply with the regulation is to reduce their SO2 emission rate to a value below the concentration of 0.6 ppmv in the stack plume. Based on such a compliance scheme, EPA's cost estimate is undoubtedly low.
As currently proposed, EPA estimates the cost of compliance for non-utility facilities at $250 million annually for Option 1, the less stringent Option 2 is estimated by the EPA to cost $160 million annually. For the utility sector, the extra costs are expected to be $1.5 billion for Option 1 and a mere $400 million for Option 2. Option 3 is stated to be only a minimal cost over current programs. As with all of EPA's compliance cost estimates, the true cost will not be known until after the regulation is already in place.
The implementation scheme to enforce this proposed regulation has been delayed in printing. It is expected that these documents will be published in the Federal Register by the end of the year. Consequently, the comment period will be extended until March 15th. The implemen-tation would likely consist of the installation of four ambient air monitors. Placement of these monitors, by the agency, is discretionary, generally however, one of these would be placed at the property line in the primary wind direction, another at the calculated maximum impact point, a third and fourth in the secondary wind direction. As for the selection of the sources that will be subjected to this regulation, the document only states: "...focusing on those sources or source types likely to produce high 5-minute peak SO2 concentrations."
From a regulators standpoint, this is the perfect regulation. First, the ambient air is already deemed safe. The vast majority of the people will be pleased with what has been accomplished. Second, no matter how hard the source emitters try to comply with the regulation, there will always be violations to investigate, corrections to be made, and fines to be levied.