Air Dispersi?n Modeling for the Determination of Geothermal Airsheds for Bacon-Manito, Leyte. North Cotabato and Southern Negros Geothermal Areas, Philippines

Abstract

In accordance with the Philippine Clean Air Act (PCAA) of 1999 and the Department of Environment and Natural Resources (DENR) Memorandum Circular No. 13, Sen'es of 2002 (MC 2002-13) requiringt he esfab/ishmenot f geothermala irshedsf or existingg eothermala reas by air drspersionm odeling, PNOC EDC in conjunction with the geothermal power ptant operatorsc onducteda n air quality study in 2003 to detineate the geothermal airsheds for Bacon- Manito, Leyte, North Cotabato, and Southern Negros geothermal production fields. This paper highlights the activities done in coniunction with the aforementioned air quality study, and descnbes in detait the air drsperston madel; modeling assu/npfions limitations,inputs,and results;a nd the delineated geothermal airsheds.

ln the absence of the prescribed air dispersion models from the DENR, the steady-state air dispersio n model of the United Sfafes Environmental Protection Agency fU.S.EPA) named AERMOD was emptoyed in the study. AERMOD was se/ecfed because it can simulated r'spersrbno f air pollutants from various typeso f sources( e.9., multiple-poinat nd area sources,) over flat and complex topographtes. The study took into account the locations, configurationsa, nd sourcee mission characteristicso f anthropogenic and natural sources of Hydrogen Sutfide (HzS) at the geothermal areas, topographies of the geothermal and adiacent areas, background ambient levels of HzS, and "worst'case" meteorotogical conditions in all possib/e wind directions.

Resu/fs of modeling showed varied profiles of predicted ground-level concentrations of 0.07-ppm HzS among the four geothermal areas depending mainly on the topography, and locations and strengthso f emissions ources. The delineationo f the finat airshed boundanes considered the predicted 0.07-ppmg round-levecl oncentrationso f HzS,a nd the extent of the geothermal proiect area. Based on the resulfs of the modeling study, the DENR on May 18, 2004, issued Administrative Order Nos. 11, 12, 13, and 14 (DAOsN o. 11, 12, 13,a nd 14)d esignatintgh e geothermal airsheds for Bacon-Manito, Leyte, North Cotabato, and Southern Negros geothermal areas