COPIES OF TECHNICAL CORRESPONDENCE The attached letters contain details of the technical findings summarized in the preceding pages. In response to your recent request, we have reviewed the letter of 23 September 1976 from Roger Strelow to Representative Paul G. Rogers, Chairman of the House Subcommittee on Health and the Environment. The Strelow letter was prepared in response to a request by Representative Rogers for information on terrain and stack height considerations in the various EPA and FEA analyses of the potential effects of the House and Senate NSD provisions on coal-fired power plants. The following paragraphs summarize our comments on the Strelow letter. The Strelow letter summary numbers are all based on individual facility use of the "full increment", instead of "partial increments". All of the analyses cited in the Strelow letter relate to use of the full available increment by each individual facility. Several earlier reports and letters have discussed the probability that only a fraction of the allowable increments would be permitted to an individual facility, in view of possible future growth of the facility, collocation of other facilities, and general growth of emission sources in each region. EPA has described the effects of 1/4 and 1/2 increment limits in earlier reports to the Congress. If the (larger) 1/2 increment limit is adopted, the "House Summary" power plant capacity limitations presented in the Strelow letter would become: Mr. George C. Freeman, Jr. -2 September 27, 1976 (The capacity limits do not scale exactly linearly, because of differences in the effect of plume rise. However, the linear scaling is suitable within the accuracy of the other approximations in the analyses.) Note that in hilly terrain (i.e., terrain where elevations in the surrounding regions rise above the stack top plus plume rise) the projected capacity limits are very low: 100 MW for plant operation at NSPS, 275 MW for eastern plants operating with FGD, and 100 MW for western plants using low sulfur coal and FGD. Even in the flat or moderate terrain cases the capacity limits are less than the projected site capacities of most new power plants. Even with the "full increment" allowance, the House Class II limits effect a substantial fraction of the 74 planned new plants considered in the EPA/FEA study. As the Strelow letter notes, 25 out of the 74 plants (i.e., one-third of all the sample) operated at NSPS would not comply with the House Class II increments if they used 500 foot stacks with BACT, 18 plants would still not comply in the 500 foot case. If a 1000 foot stack is assumed for all these plants, the number of non-complying plants drops to 15 for NSPS and 10 for BACT. Although the numbers do not match exactly, the results attributed to the EPA/FEA report in the Strelow letter are similar to the following finding quoted directly from the report document (page 39): "...the capacity affected by the House Class II increment is It should also be noted that the average planned stack height for the 74 new plants (based on the data presented in the report) is approximately 600 feet; many facilities are planned to incorporate stacks of 800 feet or greater. Credit for these planned tall stacks would apparently not be allowed under the House language. Note also that most of the 74 plants included in the EPA/FEA sample were planned before the energy shortage of the 1973-74 winter. It is reasonable to expect that future plants will, whenever possible, be located in coal producing regions, which are characteristically hilly and mountainous. The discussion of typical building and stack heights in the Strelow letter may be misleading. In its second to last paragraph the Strelow letter indicates that the largest physical structures (e.g., boiler buildings) in the EPA tall stack analysis group were on the order of 250 feet. Typical structure height for Mr. George C. Freeman, Jr. -3 September 27, 1976 existing plants was cited as 200 feet, resulting in a frequent good engineering practice stack height of 500 feet. These statements, taken together, may imply that new power plant buildings are becoming taller, and would therefore permit taller GEP stacks under the House language. While it is true that small boiler buildings and related structures (i.e., less than 100 foot heights) are not normally designed for modern, large capacity plants, it does not follow that boiler buildings are becoming larger for newly designed facilities. We have examined the structure heights and related stack heights in the EPA tall stack analysis sample, and find that the maximum structure height is approximately 250 feet, as indicated in the Strelow letter. However, the average structure height for facilities in the sample is 177 feet, not 200 feet. This difference is important because the maximum nearplant ambient concentration is (approximately) inversely proportional to the square of the stack height. The difference in emission limits required by a GEP stack of 625 feet (related to a 250 foot facility) compared to a stack of 442 feet (related to a 177 foot facility) will be approximately a factor of 2. Note also that 25 out of the 74 plants in the EPA/FEA study are planned to have stacks taller than 625 feet, which is the Strelow letter estimate of maximum "frequent good engineering practice" stack height. Summary The following summary comments are based on our experience with air pollution impact analyses, and our review of the language of the House and Senate bills. 1. 2. 3. The design of stack height is almost always determined by the The NSD language requires consistent achievement of low con- A simultaneous requirement to limit stack height to 2-1/2 times topic. Please let me know if we can provide any further information on this ERT ENVIRONMENTAL RESEARCH & TECHNOLOGY, INC. August 26, 1976 Mr. William Megonnell National Association of Electric Companies Suite 1010 1140 Connecticut Avenue Washington, DC 20036 Prevention of Significant Deterioration of Air Quality: Dear Mr. Megonnell: I am writing in response to our recent discussions concerning the possibility of a "permitted frequency of exceedance" of the short-term (3 and 24 hour) increment limits in the provisions for prevention of significant deterioration of air quality contained in H. R. 10498. Based on experience with a large number of air pollution impact model studies for emitting facilities in various regions of the United States, I offer the following suggestions and recommendations: Summary Recommendation I recommend that the language on the prevention of significant deterioration in the proposed Clean Air Act Amendments of 1976 be modified to permit the short-term (3 and 24 hour) increment limits for all three area classifications to be exceeded a small percentage of the time within the area of each proposed new or modified emitting facility. This modification would greatly reduce the possibilities of regional and national scale anomalies in the application of a policy of prevention of deterioration of air quality, but it would not significantly modify the general national requirement for stringent emission limits and careful site planning and selection for all new facilities. The basis for this recommendation is presented in the remaining sections of this letter. Difference Between Annual and Short-Term Increment Limits (a) Annual Increment Limits No change is recommended in the application of the annual increment limits; these should continue to be met at all locations. The annual increment is the best measure of the overall change in air 696 VIRGINIA ROAD CONCORD, MASSACHUSETTS 01742 (617) 369-8910 TELEX: 923 335 ENVIRORES CNCM CABLE ERTCON |