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NIr, `1'hamas C. Allen, Il <br />NC DEl-1:NR DAQ <br />August 25, 1998 <br />Page 2 . <br />V~Ie understand that the DAQ will now accept recalculated'~1MOC emissians using dle U.S. <br />ERA's AP~42 emissians factors and the .~andu%in emissions modeling computer program <br />developed by U.S. EPA for gas emissions estimation. Neither were used in the oxiginal <br />calculations performed by the DAQ. <br />Please note that our estimate of the in-place I~-ZS~' waste volume for the Northern disposal unit <br />has been substantially reduced from that previously, reported. 1~ urtlier reseaxch into the disposal <br />.records and history of the northern site documented that substantial. volumes of inert material <br />were placed in the northeni landfill. The inert wastes, identified by class, tonnage, and year in <br />tlxc attached spreadsheet, {Table 2), were excluded far the gas generation calculation. <br />l~ccalculation of NIVf(7C emissions were performed for the combined itilSti~ disposal units using <br />the ~crndl~in model. This simple computer program was developed specifically far estimating <br />IviSW landfill gas generation rates under the New Source Performance Standards and Emission <br />Guidelines for Municipal Solid '4~aste Landfills (NSPS. The landfill gas emission model is <br />based on a .first-ardor decomposition rate equation that estimates annual emissians aver a period <br />of time based on the input of site variables and established default values specified by the user. <br />The Lunr~YTfin software uses identical equations to the methods used by the 1_?AQ in their <br />calculations, by Orange Regional Landfill staff in preparing the 1'nitial Capacity Re~a~rt, and by <br />ALIvtES in their dernonstratrng the non-applicability of NSPS to this site. 1'he calculations ~u-e <br />sensitive to the gas generation rate factors, e.g. whether the NSPS/Clean Air Act (CAA) default <br />parameters or the US ERA's AP-42 emissions factors are used. The current A.P-42 emissions <br />factors for MS~t7J landfill gas generation as referenced in the 1.,15 EPA literature are as follows: <br />k ~ 0.04 Iiyr <br />L~ ~ 4411 f-t3 CH~;'Mg of waste in place <br />Crrti~oc = 2420 pprnv as hexane (co-disposal) <br />~-NMOC: = 595 ppmv as hexane (no ea-disposal). <br />The recalculated I~MOC emission rates for northern, southern, and combined IVIS~V units are <br />presented in 'fable l . Gas generation rate estimates were completed for I~IMOC's using both the <br />A.P-42 and NSPS/CAA. emissions factors far comparison. These emissions modeling results are <br />presented in Attachments A and >3, respectively, <br />The emissions analysis demonstrates that actual tili'v10C emissions are currently well below the <br />100 tonlyear tlzteshold established by the DAQ tp trigger the Title V operating permit program. <br />The calculations further show that predicted N?~rIOC emissians are considerably below those <br />previously calculated by the DAQ based on NSPS defaults. Recalculated 1\;I~IOC values for the <br />Orange Regional Landfill document that the landfill's potential to emit is well below all <br />applicable regulatory thresholds for the cur7ently permitted waste footprint and design capacity, <br />Substantial future expansion would be required at the site to approach the regulatory limit on <br />emissions. Nate that the Orange Regional Landfill is currently operating in a new lined Subtitle <br />ALMES & ASSOCIATES, INC. <br />CONSUETING ENGINEERS <br />P:\Document s\ChapHdi-545\R4?-S =5 ~'47-?~S.Ailen.•4.a,,~.?-25~4c,dcc <br />R97-945-545 <br />