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iii iiiiiiiiniii iii . • Southdown , Lyons Cement Plant November 25, 1998 Ms. Gabi Hoefler Boulder County Health Department 3450 Broadway Boulder, CO 80304 Dear Ms. Hoefler: On PAonday afternoon this week, you called to report a complaint from a neighbor, Ms. Mary Lou Dobbs, regarding dusty conditions at the plant starting on Thursday, November 19 and extending through Sunday, November 22. Since I had been out town during the time period in question, I did not have an explanation but committed to respond after an internal investigation. The specific complaint was about visible dust from the main stack, roads and general plant area. I called Ms. Dobbs that afternoon to seek additional information about the nature and timing of :t'e complaint. In the course of my investigation, I spoke with several production persons who were on duty during the time in question. I also reviewed computer records and daily logs. A summary of my investigation is listed below: Thursday, November 19 Snow in plant and quarry. Normal wind conditions, 3 to 11 MPH throughout the day. No watenrvagon due to the snow conditions. No Cement Kiln Dust loading, hauling, or disposal. Stack Opacity: Normal for most of the day until about 13:41. At that time opacty went from a normal reading of 7.8% up to 25.4%. It remained above 20% for a period of 15 minutes which is a reportable condition (was reported). Although the stack opacity dropped within permit limits at 13:56 it remained abnormally high until 18:00. There is no known cause for this excursion. Inspections of the baghouse did not reveal broken bags or stuck dampers which is the normal cause of opacity spikes The only correlation in time was the startup of the Alkali Bypass fan. Although this may have been the cause, the mechanism is not understood since all gas moved by this fan is filtered through the baghouse. It is normal operation to run or shut down this fan depending on the product produced. Friday, November 20 Wet conditions in the quarry after the Thursday snow. P O Bo. 529 • Lyons. Colorado 805d0 1303) 823-2100 • FaK (7031 823.2199