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HomeMy WebLinkAboutRANCHERO AIRPORT NOISE EXPOSURE CONTOURS5150 Sunrise Blvd., Suite D-3 . • Fair Oaks; .CA 95628 • (916) 961-5822 • Fax: (916) 961-6418, 319 West School Ave., Visalia, CA 93291,- • (209) 627-4923 Fax: (209) 627-6284 INTRODUCTION Brown-Buntin Associates, Inc. (BBA) has completed an analysis.of aircraft/airport operations and related noise -levels for the Ranchaero. Airport to prepare Community Noise Equivalent Level (CNEL)' noise exposure maps for projected future (2005) airport traffic volumes with the existing runway configuration. The Federal Aviation Administration's (FAA) Integrated Noise Model (INM) Version 5.01 was used .to prepare CNEL noise exposure maps for the Ranchaero.Airport, based upon the FAA noise level data for single engine and twin engine aircraft, helicopters, and airport operational factors as described below. The INM was developed for the FAA, and represents the federally -sanctioned and preferred method for analyzing aircraft/airport noise exposure. Version 5:01 is the currently- available version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. _ Projected data for aircraft activity, aircraft fleet mix and airport configuration used in the noise modeling process were obtained from most recent (1988) California Aviation System Plan (CASP), and discussions with the Ranchaero Airport officials. The following report summarizes the data, methods and assumptions used in preparing the CNEL-noise exposure maps. The CNEL descriptor is a method of averaging single event noise levels over a typical 24-hour day, applying penalties to noise events. occurring .during the evening (7 p.m. to 10 p.m.) hours, and nighttime (10 p.m. to 7 a.m.) hours. CNEL is usually defined in terms of average annual conditions, so that the CNEL measured, on a given day may be either less than or greater than the annual average. ti The FAA uses the Day -Night Average Level (Ldn). descriptor to describe land use compatibility 'With' respect to aircraft noise exposures. The FAA airport noise compatibility criterion for residential land uses is 65 dB Ldn. The California Department of Transportation Division of Aeronautics uses the CNEL descriptor to describe land use compatibility with respect to aircraft noise exposures. The Caltrans Division of Aeronautics noise compatibility criterion for residential land uses is 65 dB CNEL. Generally, the predicted Ldn and CNEL values are within 1 dB of one another. Due to the low percentage of evening operations at Ranchaero Airport, noise exposure contours developed for this airport in terms of Ldp and CNEL would be virtually identical. 1. For an explanation of terms used in this report, see Appendix A. 1 AIRPORT OPERATIONS Airport operational factors.which can' significantly affect overall noise levels as' described by CNEL include the aircraft'fleet mix, the number of daily operations and the time -of day when aircraft operations occur. Runway use factors also significantly influence CNEL values. Trip length can affect aircraft single event noise levels, as an aircraft which is prepared for a long flight may carry more fuel and passengers than for a short flight. The INM applies corrections to air carrier aircraft . takeoff profiles to `account for these differences, but makes no corrections to general aviation aircraft takeoff profiles. Aircraft operational assumptions for Ranchaero Airport are based upon analyses of airport activity provided in the CASP and discussions with the Ranchaero Airport officials. These assumptions are described by Tables I and H. ,Touch and go operations North and South: 45% 1 - The flight tracks for Ranchaero Airport are identified on Figure 1. r y TABLE I AIRPORT CONFIGURATION AND USE Ranchaero Airport- Butte County Runway Configuration: - 15-33 Runway Length: 2,400 feet Field Elevation: 173 feet MSL Runway Use Factors: 55% Rwy 33 45% Rwy 15 Temporal Distribution of Operations:. 92% Day 6% Evening 2% Night Flight Tracks and Direction' Straight out and in to and from the South: 22.5% Straight out and in to and from the North: 10% r Treeline arrivals and departures to the.North: 22.5% ,Touch and go operations North and South: 45% 1 - The flight tracks for Ranchaero Airport are identified on Figure 1. a Descriptions of aircraft flight tracks were developed through discussions with the airport manager and BBA field observations. Based upon these data, generalized flight tracks were prepared for use in the noise modeling process to describe areas with a concentration of aircraft overflights. Figure 1 shows the flight tracks used for the .noise modeling process. It, is recognized that variations in flight paths -occur at the Ranchaero Airport, and that the tracks shown on Figure 1 are meant to be a general representation of those flight patterns. PREPARATION OF CNEL NOISE EXPOSURE MAPS The Integrated Noise Model (INM) Version 5.01 was used to prepare CNEL noise exposure maps for the airport based upon the aircraft noise level and airport operational factors described in the previous sections. The INM was developed for the. FAA,, and represents the federally -sanctioned and preferred method for analyzing aircraft/airport noise exposure. Version 5.01` is the most recent _version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. 3 TABLE II . . TOTAL OPERATIONS BY AIRCRAFT'TYPE Ranchaero Airport - Butte County INM Category Description Annual Daily BEC58P. Small Twin Piston Engine General Aviation Airplane 2;190 • 6.0 GASEPF General Aviation Single Engine - Fixed Propeller 7,008 19.2 GASEPV General Aviation Single Engine - Variable Pitch Propeller ' 1,.752 4.8 H300 Hughes 300 Light Utility Single Engine Helicopter., - .6,935 19.0 B206 Bell 206 Jet Ranger Light Utility Single Engine Helicopter .730 2.0 - Total Operations: • 18,615 51 Note: Touch and go operations have been counted as two operations in this table (one arrival and one departure) a Descriptions of aircraft flight tracks were developed through discussions with the airport manager and BBA field observations. Based upon these data, generalized flight tracks were prepared for use in the noise modeling process to describe areas with a concentration of aircraft overflights. Figure 1 shows the flight tracks used for the .noise modeling process. It, is recognized that variations in flight paths -occur at the Ranchaero Airport, and that the tracks shown on Figure 1 are meant to be a general representation of those flight patterns. PREPARATION OF CNEL NOISE EXPOSURE MAPS The Integrated Noise Model (INM) Version 5.01 was used to prepare CNEL noise exposure maps for the airport based upon the aircraft noise level and airport operational factors described in the previous sections. The INM was developed for the. FAA,, and represents the federally -sanctioned and preferred method for analyzing aircraft/airport noise exposure. Version 5.01` is the most recent _version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. 3 The WM calculates aircraft noise exposure by mathematically combining aircraft noise levels and airport operational factors at a series of points within a Cartesian coordinate system which defines the location of airport runways and aircraft flight tracks. User inputs to the INM include the following: a. Airport altitude and mean temperature b. Runway configuration c. Aircraft flight track definition ' d. Aircraft stage length (not pertinent for this airport) e. Aircraft departure and approach profiles f. Aircraft traffic volume and fleet mix g. Flight track utilization by aircraft types The INM data base includes aircraft performance parameters and noise level data for numerous commercial, military and general aviation aircraft classes. When the user specifies a particular aircraft class from the INM data base, the model automatically provides the necessary inputs concerning aircraft power settings, speed, - departure profile and noise levels. INM default values were used for all fixed-wing•aircraft types. BBA referred to the FAA publication Helicopter Noise Exposure Curves for use in Environmental Impact Assessment, to obtain noise emissiowdata for the two most common helicopter types -utilized at Ranchaero. After the model had been prepared for the aircraft classes described in the preceding section; BBA' created INM input files containing the number -of operations by aircraft class; time of day and flight track. for annual average day aircraft operations for each forecast scenario.. The INM was used with these. operational scenarios to prepare 65, 60 and 55 dB CNEL contours, which have been plotted on Figure 2. Total surface areas included in each of these CNEL contours are shown by Table III. TABLE.III SURFACE AREAS WITHIN YEAR 2005 CNEL CONTOURS Ranchaero Airport - Butte County ' 65 dB CNEL 60 dB CNEL 55 dB CNEL 0.04 Sq. Mi. 0.10 Sq. Mi. 0.23 Sq. Mi. `r 4 AIRCRAFT NOISE MEASUREMENTS Aircraft noise level measurements were conducted at two locations in the Ranchaero Airport vicinity to generally assess the accuracy of the INM in predicting aircraft noise levels at the nearest potentially affected residential areas. The noise measurement sites, which are.shown on Figure 1, represent the two existing residences located nearest to the airport. The meters. operated continuously from 2 p.m. on August 6, 1996 through 12 noon on August 15, 1996. The noise monitoring system consisted of two Larson -Davis Laboratories (LDL) Model 820 precision integrating sound level meters. The microphones were located at a height of approximately 5 feet above ground, and were fitted with random incidence correctors and windscreens. The meters, which were housed in weatherproof containers, were calibrated at the beginning and end of the continuous noise measurement period. Each meter had the capability of reporting instantaneous sound levels and a variety of statistical sound level descriptors. For aircraft noise events, each unit was programmed to report the duration, maximum A -weighted sound level (Lenox), and Sound Exposure Level (SEL) of noise events which exceed a selected threshold sound level. and event duration.. Each analyzer calculated the hourly average sound level (Leq), from which the CNEL was computed. The results of the aircraft noise monitoring program are summarized in Table IV. A graphical depiction of the noise level measurement results is shown on Figures 3 and 4. TABLE IV AVERAGE MEASURED AND PREDICTED CNEL VALUES Ranchaero Airport - August 6-16, 1996 No. __TSite CNEL from Measurement Data r INM 5.01 CNEL (2005) 1 52 dB 55 dB '2 55 dB 61 dB Note: the noise level measurement locations are shown on Figure 1. 5 ki W A comparison between measured and modeled CNEL values shown in Table IV reveals that the future values predicted by the INM exceed measured existing levels by 3 to 6 dB. However, because the nine day measurement period may not have been representative of typical aircraft traffic and, because the measured CNEL values reported in Table IV include noise from all sources,. not just aircraft, the significance of the noise measurement results in terms of CNEL should. not .be overstated. -Nonetheless, the Table IV. data, suggests that the predicted aircraft. CNEL values based on 2005 activity projections are not unreasonable. CONCLUSIONS The year 2005 CNEL noise contours shown on Figure 2 indicate that no existing residences would be exposed to future aircraft noise levels exceeding the Caltrans Department of Aviation and FAA recommended exterior noise level standards of 65. dB Ldp/CNEL. Existing residences in the Ranchaero Airport vicintiy will continue to be exposed to intermittent elevated noise levels during aircraft and helicopter arrivals and departures, with the, intensity of the sound dependant on the , aircraft type, location, altitude, speed and condition. Occasional straight in and out operations to the north will likely continue to be considered offensive to some residences located north of Bidwell creek. BBA observations and information provided by Ranchaero Airport Officials revealed that the vast majority of the aircraft approaching or departing to the north utilize the treeline flight path shown on Figure 1. This analysis conservatively assumed that 1'0% of the total airport operations were straight in arrivals or'straight out departures to the. north. Nonetheless, the Figure 2 noise exposure contours indicate that the contours "bend" to the , west, reflecting the higher percentages of treeline approaches and departures. A final conclusion of this analysis is that the helicopter operations generate considerably lower noise levels than the single and twin engine propel ler, airplanes which utilize this airfield., As a result, reorienting the flight paths of the helicopter operations to utilize. a midfield approach/departure . corridor to the west would not appreciably alter the locations of the noise contours depicted on Figure 2. Respectfully Submitted, PaulBollaid" untin As fates, Inc. Senior Consultant 6 7 w_»-+�Y�._'s 'm-•�' ',t�',,ax-. �,y.,,i,n� a �s- <'" , T-wy'.:sz.',�,i'iaF„aE1q^is�. ,n `v�r 'fir' is mak, 'tn �`� y.",,• .'r. i,'w�E sr'F•.. '�z -, ss..��s"'` -' t-r;{..t'- *. � �'B%°aY�Ij�Y "+ a Mr.. z,,' "'' g'�. x. 7” ��� s� g,• MITI� �6 i � r. "+ �� �h R. IN No ,s^,e.Er v, e-5.�,��+c.. „a:. gio 3�'i sk Ir -. W-15 '�x"`� �. _11- �c��'� FS�? '! IN ,gym a tb WN MHz- RPS MINIWON-19-LEM �,�.�."',� �������-��e;.=sem:_:. ,.a_: E�� -,.�- ���"��-k, _-x� ,�-• _ �,.�,�. 4,�rr� ME vAIR IR F' ..-v�,.'F¢."h .�'Sa r�.. 3:fc�...'•'o�;+.��?®av�.-__t�f�� - j� Y.N' _ a Figure 4 Measured Ambient Noise Levels - August -7-l,4,-1 996 Nearest Residence to South of Ranchaero Airport. (Values shown,are averages for the 8 day period) , 90 . � _.. ;: " , .. � _ .. fi 3 _ a ,�' 'S�=`� _ � �i'' .ii•' is '.;�+ � r � 7 a°: •. '. -.' .- - �' �: : '4; w.,r_ , y�+r-y�. , ._ y �.''''wr, �� i ��,a_dr}�h it^ � .: � .. �- . �.'.. ' " `.'-""r�1���4�nz�'"'.�$� 1'-�` ,r --�.�_'c __ Via- -Y�;s� '�; w � �sc_h »� :.cam• _ . . 80 � :X a dSyy '-�,� v '", T'4�i'u'F.''. ,Y'1 wD---, !iA'.. "�✓4,-'aY^'�iz � Y �"�4�. w �R 1••�' �'` �''.,��'� _ IN El p r i ec a ,. .. .,: � .: � - ,�..q.. �.,�`� ,'^��� ��x+` %r,,�4. a _'Dec.• , ...:� ^_,.''43< 3 a;r � �,�� '�'�� . - ,'.. ... ..'�. ',; � "�:. ��". + , �ea.''<s. P��-� �'`�.'!�':`s-"^4�1 .'�wti�"rry:, !�,�,-� - ��,7p�''- E• ��r„ `. !�i. �Y'�'' ���2'� �- _ :y - 60 _ _ = ' ism?�.,a--=�7's, ' - � .� ��5.-�Y�;;tl.�-'�•`�§! �s'�`� %;' • �rs�r '�',r.:.v . . ""' . ,r�' c .. � .. ... ._✓'r 4 .�,d�� � "'''' ,; "� ')s3"'iy�, S ,5:: s�'v-� ",�- _. +4 ��Ys ,� �`ii'rEy�J - ..,- .. . • , , .. ,,;--, � _�.:, . �� _- -- �'�5� � . �� _ - ti „may^; � - '`"` _ � � - . .. .' ..:. -.. •.. ,. �, . `��, - ��r-s-, ' -- -.<Yi4's� � �,_ - ::�:s" j'i�'�rk ..r �-+P'���F����.-� �"� mss• . -.( r .. - .. ' .'_ ' 't'y.L:-��w .�<� '''�'`...;,-,�,. *+'�' _ _ _ �`��'� ��i.. - -': s ',.:i=.rte-.r� t ., .>• - 'ti''. ...'...., �•:.., .- :, .,. :,.. - -� � .. �;.r;.._ � $-:.nye .+"•r 's`' �.r -' � . Vic.... `,r '� �.`.�:,.'w � +. - �-', ":��^�'�''�* -"3" _ •_ - .,., ., - ... � . .�,��., � � ,..� .fir 40, ,, .; _ ,. .� -� -.. _ _:.:.: •.,,. ...2 ..'a..:'4�',,,x,g :. �'_�_.s.-5�-�'va � `A$ � s s,���!�"F-;r�a a, ,LAY ..Y.. :.� �3`` _ 'y"- :.� 30 rr 12:00 PM 12:00 AM, 4:00 AM' 8:00 AM 4:00 PM 8 OO. PM 'Hour'of Day. �. — Lmax —E Lep -- L50 - + L90 I' , r _ APPENDIX A ACOUSTICAL NERMINOLOGY AMBIENT NOISE The composite of noise from all sources near and far. In this LEVEL: context, the ambient noise level constitutes the normal' or existing level of environmental noise a given location. CNEL: Community Noise Equivalent Level The average equivalent sound level during a 24-hour day, obtained after addition of approximately , five decibels to sound levels in the evening from 7:00 p.m. to 10:00 p.m. and ten decibels to- sound levels in the night before 7:00 a.m. and after 10:00 p.m. DECIBEL, dB: A unit for describing the amplitude of sound, equal to 20 times.the- logarithm to the. base 10 of the ratio of the reference pressure, which is 20 micropascals (20 micronewtons per square meter). Ld.: Day -Night Average Sound Level. The average. equivalent' sound level during a 24-hour day, obtained after addition of ten decibels to sound levels. in the night after 10:00 p.m. and. before 7:00. a.m. Lam; Equivalent Sound Level. The sound level containing the same total energy as a time varying signal over a given sample period_ . L q is typically computed over 11 8 and 24-hour sample periods. Note: CNEL and Ld„ 'represent daily levels of noise exposure averaged on an annual basis, while Lxi represents the average noise exposure for a shorter time period, typically one hour. The maximum sound level recorded during a noise event. Ln:, The sound level exceeded "n" percent of the time. during a sample . interval. 1-10 equals the level exceeded 10 percent of the time (I:O, L50, etc.) A-2 ~' - ACOU STICAL NERM INOLOGY NOISE" EXPOSURE Lines drawn about a noise source indicating constant 'levels of CONTOURS: noise exposure. CNEL and Ld„ contours are frequently utilized to describe community exposure to noise. t SEL OR SENEL: Sound Exposure Level or Single Event Noise Exposure Level The level of noise accumulated during a single noise event, such as an aircraft overflight, with reference . to a duration of one second. More specifically, it is the time -integrated A -weighted squared sound pressure level for a stated time interval or event, based on a reference pressure of 20 micropascals and a reference duration of one second: SOUND LEVEL: The sound pressure level in decibels as measured on a sound level meter. using the A=weighting - filter network. The A - weighting filter 'de-emphasizes the very low and very high frequency components of the sound in a manner similar to the response of the human ear and gives good correlation with subjective reactions to noise. "BBA 5150 Sunrise Blvd., Suite D-3 • Fair Oaks, CA 95628 • (916) 961-5822 • Fax: (916) 961-6418 319 West School Ave., Visalia, CA 93291 • (209) 627-4923 • Fax: (209) 627-6284 INTRODUCTION Brown-Buntin Associates, Inc. (BBA) has completed an analysis of aircraft/airport operations and related noise levels for the Ranchaero Airport to prepare Community Noise Equivalent Level (CNEL)' noise exposure maps for projected future (2005) airport traffic volumes with the existing runway configuration. The Federal Aviation Administration's (FAA) Integrated Noise Model (INM) Version 5.01 was used to prepare CNEL noise exposure maps for the Ranchaero Airport, based upon the FAA noise level data for single engine and twin engine aircraft, helicopters, and airport operational factors as described below. The INM was developed for the FAA, and represents the federally -sanctioned and preferred method for analyzing aircraft/airport noise exposure. Version 5.01 is the currently - available version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. Projected data for aircraft activity, aircraft fleet mix and airport configuration used in the noise modeling process were obtained from most recent (1988) California Aviation System Plan (CASP), and discussions with the Ranchaero Airport officials,. The following report summarizes the data, methods and assumptions used in preparing the CNEL noise exposure maps. The CNEL descriptor is a method of averaging single event noise levels over a typical 24-hour day, applying penalties to noise events occurring during the evening (7 p.m., to 10 p.m.) hours, and nighttime (10 p.m. to 7 a.m.) hours. CNEL is usually defined in terms of average annual conditions, so that the CNEL measured on a given day may be either less than or greater than the annual average. The FAA uses the Day -Night Average Level (LdJ descriptor to describe land use compatibility with respect to aircraft noise exposures. The FAA airport noise compatibility criterion for residential land uses is 65 dB L.. The California Department of Transportation Division of Aeronautics uses the CNEL descriptor to describe land use compatibility with respect to aircraft noise exposures. The Caltrans Division of Aeronautics noise compatibility, criterion for residential land uses is 65 dB CNEL. Generally, the predicted-Ld, and CNEL values are within 1 dB of one another. Due to the low percentage of evening operations at Ranchaero Airport, noise exposure contours developed for . this airport in terms of La„ and CNEL would be virtually identical. 1. For an explanation of terms used in this report, see Appendix A. 1 AIRPORT OPERATIONS Airport operational factors which can significantly affect overall noise levels as described by CNEL include the aircraft fleet mix, the number of daily operations and the time of day when aircraft operations occur. Runway use factors also significantly influence CNEL values. Trip length can affect aircraft single event noise levels, as an aircraft which is prepared for a long flight may carry more fuel and passengers than for a short flight. The INM applies corrections to air carrier aircraft takeoff profiles to account for these differences, but makes no correction_ s to, general' aviation aircraft takeoff profiles. Aircraft operational assumptions for Ranchaero Airport are based upon,analyses of airport activity provided in the CASP and discussions with the Ranchaero Airport officials. These assumptions are -described by Tables I and IL' TABLE I AIRPORT CONFIGURATION AND USE Ranchaero Airport - Butte County Runway Configuration: 15-33 Runway Length: 2,400.feet Field Elevation: i73 feet MSL Runway Use Factors: 55% Rwy 33 _ . 45% Rwy 15 Temporal Distribution of Operations: 92% Day 6% Evening 2% Night Flight Tracks and Direction' Straight,out and in to and from the South: 22.5% Straight out and in to and from the -North: 10%., Treeline arrivals and departures to the North: `22.5% Touch and go operations North and South: 45% 1 - The flight tracks for Ranchaero Airport are identified on Figure 1. ' ; 2 { i ival and one departure) 5 Descriptions of aircraft flight tracks were developed through discussions with the airport manager and BBA field observations. Based upon these data, generalized flight tracks were prepared for use in the noise modeling process to describe areas with a concentration of aircraft overflights. , Figure 1 shows the flight tracks used for the noise modeling process. 'It is recognized that variations in ' flight paths occur at the Ranchaero Airport, and that the tracks shown on Figure 1 are meant to be a general representation of those flight patterns., PREPARATION OF CNEL NOISE EXPOSURE MAPS The Integrated Noise Model (INM) Version 5.01'was used to prepare CNEL noise exposure maps for the airport based upon the aircraft noise level and airport operational factors described in the' previous sections. The INM was developed for the FAA', and represents the federally -sanctioned and preferred method for analyzing aircraft/airport noise exposure. Version 5.01 is the most recent version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. TABLE II TOTAL OPERATIONS BY AIRCRAFT TYPE Ranchaero Airport - Butte County INM Category Description _ Annual Daily BEC58P Small Twin Piston Engine General Aviation Airplane, 2,190 6.0 GASEPF General Aviation Single Engine - Fiked Propeller 7,008 19.2 GASEPV General Aviation Single Engine - Variable Pitch Propeller 1,752 4.8 H300 Hughes 300 Light Utility Single Engine Helicopter 6,935 19.0 B206 Bell 206 Jet Ranger Light Utility Single Engine Helicopter 730 2.0 Total Operations: 18,615 51 rNot7Touch'and'go operations have been counted as two operations in this table (one arr ival and one departure) 5 Descriptions of aircraft flight tracks were developed through discussions with the airport manager and BBA field observations. Based upon these data, generalized flight tracks were prepared for use in the noise modeling process to describe areas with a concentration of aircraft overflights. , Figure 1 shows the flight tracks used for the noise modeling process. 'It is recognized that variations in ' flight paths occur at the Ranchaero Airport, and that the tracks shown on Figure 1 are meant to be a general representation of those flight patterns., PREPARATION OF CNEL NOISE EXPOSURE MAPS The Integrated Noise Model (INM) Version 5.01'was used to prepare CNEL noise exposure maps for the airport based upon the aircraft noise level and airport operational factors described in the' previous sections. The INM was developed for the FAA', and represents the federally -sanctioned and preferred method for analyzing aircraft/airport noise exposure. Version 5.01 is the most recent version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. The INM calculates aircraft noise exposure by mathematically, combining aircraft noise levels and airport operational factors at a series of points within a Cartesian coordinate, system which defines the location of airport runways and aircraft flight tracks. User inputs to the INM include the following:. a. Airport altitude and mean temperature b. Runway configuration c. Aircraft flight track definition d. Aircraft stage length (not pertinent for this airport) , e. Aircraft departure and approach profiles f. Aircraft traffic volume and fleet mix g. Flight track utilization by aircraft types 'The INM data base includes aircraft performance parameters and noise level data for numerous commercial, military and general aviation aircraft classes. When the user specifies a particular aircraft class from the INM data base, the model automatically provides the necessary inputs concerning aircraft power settings, speed, departure profile and noise levels. INM default values were used for all fixed -wing aircraft types.. BBA referred to the FAA.publication Helicopter Noise Exposure Curves for use in Environmental Impact Assessment, to obtain noise emission data for the two` most common helicopter types utilized at Ranchaero. After the model had been prepared for the aircraft classes described in the preceding section, BBA created INM input file's containing the number of operations by aircraft class, time of day and flight { track for annual average day aircraft operations for each forecast scenario. The INM was used with these operational scenarios to.prepare 65, 60 and 55 dB CNEL contours, which have been plotted on Figure 2. Total surface areas included in each of these CNEL contours are shown by Table III. TABLE III SURFACE AREAS WITHIN YEAR 2005 CNEL CONTOURS •Ranchaero Airport - Butte County. 65 dB CNEL 0.04 Sq. Mi. - 0.10 Sq. Mi. 4 0.23 Sq. Mi. AIRCRAFT NOISE MEASUREMENTS Aircraft noise level measurements were -conducted at two locations in the Ranchaero Airport vicinity to generally assess the accuracy of the INM in predicting aircraft noise levels at the • nearest potentially affected residential areas. The noise measurement sites, which are shown on Figure 1, represent the two existing residences located nearest to the 'airport. The' meters operated continuously from 2 p.m. on August 6, 1996 through 12 noon on August 15, 1996. The noise monitoring system .consisted of two Larson -Davis Laboratories (LDL) Model 820 precision integrating sound level meters. The microphones were located at a height of approximately 5 feet above ground, and were fitted with random incidence correctors and windscreens. The meters; which were housed in weatherproof containers, were calibrated at the beginning and end of the continuous noise measurement period. Each meter had the capability of reporting instantaneous sound levels and a variety of statistical sound level descriptors. -For aircraft noise events, each unit was programmed to report the�duration; . . maximum A -weighted sound'level (Lm; and Sound Exposure Level (SEL) of noise events which. ' exceed a selected threshold sound level and event duration. Each analyzer calculated the hourly average sound level (Leq)Jrom which the CNEL was computed. The results of the aircraft noise monitoring program are summarized in Table IV. A graphical depiction of the noise level measurement results is shown on Figures 3 and 4. TABLE IV AVERAGE MEASURED AND PREDICTED CAL VALUES Ranchaero Airport - August 6-16,1996 Site No. CNEL from Measurement Data INM 5.01 CNEL'(2005) ' 1 52 dB 55 dB 2 55 dB 61 dB Note: the noise level measurement locations are shown on Figure 1. F 5 A comparison between measured and modeled CNEL. values shown in Table IV reveals that the future values predicted by the INM exceed measured existing levels by 3 to 6 dB. However, because the nine day measurement period may not have been representative of typical aircraft traffic and because the measured CNEL values reported in Table IV include noise from all sources, not just aircraft, the significance of the noise measurement results in terms of CNEL should not ,be overstated. Nonetheless, the Table IV data suggests that the predicted aircraft CNEL values based on 2005 activity projections are not unreasonable: CONCLUSIONS The year 2005 CNEL noise contours shown on Figure 2 indicate that no existing residences would be exposed to future aircraft noise levels exceeding the Caltrans Department of Aviation and FAA recommended exterior noise level standards of 65 dB Ld,,/CNEL. Existing residences in the Ranchaero Airport vicintiy will continue'to be exposed to intermittent elevated noise levels during aircraft and helicopter arrivals and departures, with the intensity of the sound dependant on the aircraft type, location, altitude, speed and condition. Occasional straight in and out operations to the north will likely continue to be considered offensive to some residences located north of Bidwell creek. BBA observations and information provided by Ranchaero Airport Officials revealed that the vast majority of the aircraft approaching or departing to the north utilize the treeline flight path shown on Figure 1. This analysis conservatively assumed that 10% of the total airport operations were straight in arrivals or straight-out departures to, the north. Nonetheless, the Figure 2 noise exposure contours indicate that the contours "bend" to the west, reflecting the higher percentages of treeline approaches and departures. A final conclusion of this analysis is that the helicopter operations generate considerably lower noise levels than the single and twin engine propeller airplanes which utilize this airfield. As a result, reorienting the flight paths of the helicopter operations to utilize a midfield approach/departure corridor to the west would, not. appreciably alter the locations of the noise contours depicted on Figure 2. Respectfully Submitted, B own- untin Ap9ciates, Inc. aul Boll , Senior Consultant D • 0 Figure 3 Measured Ambient Noise Levels - August 7-14, 1996 Nearest Residence to North of Ranchaero Airport (Values shown are averages for the 8 -day period) 8017 1 75 70 CO 65 60 ^>` W J -v 55 C 50 CO 45 777 40 35 30 12:00 AM 4:00 AM 8:00 AM 12:00 PM 4:00 PM 8:00 PM Hour of Day —e— Lmax —a Leq —9 L50 + L90 I BSA Figure 4 Measured Ambient Noise Levels - August 7-14,1996 Nearest Residence to South of Ranchaero Airport (Values shown are averages for the 8 -day period) 4:00 AM 8:00 AM 12:00 PM 4:00 PM 8:00 PM Hour of Day -� Lmax -s Leq L50 + L90 I I Pei 0 110 90 - 80 70 N J v 60 =_ o - U) 50 40 30 12:00 AM Figure 4 Measured Ambient Noise Levels - August 7-14,1996 Nearest Residence to South of Ranchaero Airport (Values shown are averages for the 8 -day period) 4:00 AM 8:00 AM 12:00 PM 4:00 PM 8:00 PM Hour of Day -� Lmax -s Leq L50 + L90 I I Pei 0 110 APPENDIX A ACOUSTICAL TERMINOLOGY � BBA AMBIENT NOISE The composite of noise from all sources .near and far. In this LEVEL: context, the ambient noise level constitutes the normal or existing level of environmental noise a given location. CNEL: Community Noise Equivalent Level. The average equivalent sound level during a 24-hour day, obtained after addition of approximately five decibels to sound levels in the evening from 7:00 p.m. to .10:00 p.m. and ten decibels to sound levels in the night before 7:00 a.m. and after 10:00 p.m. DECIBEL, dB: A unit for describing the amplitude of sound, equal to 20 times the logarithm to the base 10 of the ratio of the reference pressure, which is 20 micropascals (20 micronewtons per square meter). Ld.: Day -Night Average. Sound Level. The average equivalent sound level -during a 24-hour day, obtained after addition of ten decibels to sound levels in the night after 10:00 p.m. and. before 7:00 a.m. L : Equivalent Sound Level. The sound level containing the same total energy as a time, varying signal over a given sample period. Ley is typically computed over 1, 8 and 24-hour sample periods. Note: CNEL and Ld" represent daily levels of noise exposure averaged.on an annual basis, while Ley represents the average noise exposure for a shorter time period, typically one hour. The maximum sound level recorded during -a* noise event. The sound level exceeded "n" percent of the time during a sample interval. 1-10 equals the level exceeded 10 percent of the time (LW, L501 etc.) ' � BBA A-2 ACOUSTICAL TERMINOLOGY NOISE EXPOSURE Lines drawn about a 'noise source indicating constant levels of CONTOURS: noise exposure. CNEL and Ld,;'contours are frequently utilized -to.describe community exposure to noise. SEL OR SENEL: Sound Exposure Level or Single Event Noise Exposure Level. The level of noise accumulated during a single noise event, such as an aircraft overflight, with reference to a duration of one. second. More specifically, it is the time-integrated -A-weighted squared sound pressure level for a stated time interval or event, based on a reference *pressure of 20 micropascals and a reference duration of one second. SOUND LEVEL: The sound pressure level in decibels as measured on a sound level meter using the A-weighting filter network. The A7. . weighting filterde-emphasizes the very low • and very high frequency components of the sound in a manner similar to the response of the human . ear and gives good correlation with subjective reactions to noise. t i (BBAP -3 2 c APPENDIX B L SUGGESTED AIRPORT HAZARD ZONING ORDINANCE { L AN ORDINANCE REGULATING AND RESTRICTING THE HEIGHT OF S'iRUCTURES AND OF OBJECiS OF NATURAL GROWTH, AND OTHERWISE REGULATING THE USE OF PROPERTY AND OF AIR SPACE IN THE VICINITY OF THE OROVILLE MUNICIPAL AIRPORT BY CREATING AIRPORT APPROACH ZONES, HORIZONTAL ZONES, CONICAL ZONES, AND TRANS- ITION ZONES; ESTABLISHING THE BOUNDARIES THEREOF; 93 PROVIDING FOR CHANGES.IN THE PEST.RiCTIONS AND BOUNDARIES OF SUCH ZONES; DEFINING CERTAIN TERMS USED HEREIN; PROVIDING FOR ENFORCEMENT OF THIS ORDINANCE; AND PRESCRIBING PENALTIES FOk ViOLATiOtiS OF THIS ORDINANCE. THE OROVILL': MUNICIPAL AIRPORT L ZONING MAP IS INCORPORATED iN, AND IS i•1ADE A PART OF THIS ORDINANCE. THE CITY COUNCIL OF THE CITY OF OROVILLE DOES ORDAIii L AS FOLLOWS: SECTION l: pursuat:t to.thc 1ut1lOrity conferred by the 1 L Government Ccde of the State of California, and in conforwance t,ith the Standard. of the Federal Aviation Admin istration, this ordinance is adopted for the purpose of pro toting and safeguarding the health. safety, and gi=neral t.elfare of the inhabitants of the City of Oroiille by preve,,ting the creation, establishment )r maintenance of airport hazards, thereby I proLecting the lives and property of the usi.rs Of ,ic Oroville 6, Municipal ijir-port and of the occupants of the Mand in the v cinity of t.it0 airport, and preventi11 t.ite tae :-taction ana itnp,jired use of the Orovi:le i•lunicipai Airp0r;. and Lite P"Iic investment therein. SEC11'iON 2: The creation or establishment of an airport. ititzard is a public nuisance and an injury to the area served !9 i R-1 1. I e>• L rb. L L e, "Non -Conforming Use" means any pre-existing structure, tree, or use of land, which is inconsistent with the provisions of this ordinance or amendments thereto. f, "Person" means any individual, firm, partnership, corporation, company, association, joint stock association, city, county, or District, and includes any trustee, receiver, assignee, or similar representative of any of them. g, "?rimary Surface" means a ground surface longitudinally centered on the runway. The dimensions and limits of the primary surface shall be those prescribed in FEDERAL AVIATION REGULATiOU (FAR) 77.25 For the Oroville Municipal Airport. h. "Plannin Comrission" means the Planning Commission of the City of Oroville. i. , unw_y* means the defined area of the Oroville Municipal Airport prepared for landing and/or takeoff of aircraft along its length. j. "Structure" means any object constructed or installed by man, including, but not limited to, buildings, towers, poles, masts, antennas, smokestacks, earth formations, overhead wires or transmission lines, and guy -wires. k. "Tree" means any object of natural growth or planted. SECT -1014 5: ZO'IES: In order to carry out the purposes of this ordinance all land within the boundaries of the Oroville Municipal Airport, and oth,r lands in the vicinity of the )ro,)ch Zoncs, Transitional airport are divid^d into Run::;.; �;;p ,,ones, horizontal 'ones and C.enical Loner- The::e zones underlie the approach, transitional, ho,'izontal. and conical surfaces (Iofined in F;,R 7 bo:�"d,:ri:i> i,f r:i ic!' :,rc sl',:.;:r o❑ ti',•: OroviIle Ftunicipr.l Airport toning i•ia;:. The approved OruviIle �lunicihai Airport Zoning NZ! 11 shall be kept or. file in the office ;,f the City Clerk ,and said zoning tnc+p is ijfr, y made a par' of D-3 o this ordinance, subject to amendments as shall be made theretc from time to time. Any such amendments shall be entered on the official zoning map, which shall be maintained current at >:b all times. SECTION 6: HEIGHT LIMITATIONS: Except as otherwise provided in this ordinance, no structure or tree shall be erected, altered, maintai.ned or allowed to grow in any. zone e created by 'this ordinance to a height in excess of the applicable height limit established herein for each such zone. nq For purposes of determining these heights, the U. S. Coast and Geodetic (based) Survey has established the official { elevation reference of the Oroville Municipal Airport to be L 199 feet, and all height limits shall be based on that y elevation, as follows: a. Horizontal Zone: One hundred fifty (150) feet. b. Conical Zone: One hundred fifty (150) feet at the inner perimeter increasing uniformly at a slope of 20:1 (1 foot vertically for each 20 feet horizontally) to the outer perimeter. c. Approach Zones: For runways 1-19 and 12-30, as designated on the Oroville Municipal Airport Zoning Map, the Ireigirt shall not exceed that permitted by a 50:1 glideslope, and in no event shall the height exceed one hundred fifty (150) feet. d. Transition Zonas: The height of objects shall not be such as t:) penetrate a transitional surface commencing at the side of the primary surface and sloping upward and outward at a slope of 7:1 (1 foot v.^.rtical,y for each 7 feet horizontally) and extending to a height of 150 Beet above the airport elevation. The same restriction shall apply beginning at the sides of, and aL the same elevation as, the approach surface and extending to where the slope intersects the conical surface. 6. SECTION 7: USE RESTRICTIONS: Notwithstanding any other provisions of this ordinance, no use may be made of land (or water) within any zone established by this ordinance which will r (1) create electrical interference with navigational signals or radio communications between the airport and aircraft; L(2) make it difficult for pilots to distinguish between airport lights and other lights; (3) result in glare in the eyes of pilots using the airport; (4) impair visibility of the airport; or (5) otherwise in any way create a hazard or endanger the landing, takeoff, or maneuvering of aircraft is using or intending to use.the airport. L SECTION 8: NON -CONFORMING USES: La. Regulations not Retroactive: The regulations prescribed in this ordinance shall not be construed to require the removal, lowering, or otherwise changing or altering of any W structure or tree not conforming to the regulations as of the Leffective date of this ordinance, nor otherwise interfere with the continuation of a non -conforming use. Nothing contained L irr, this ordinance shall require any change in the construction, alteration, or intended use of any structure, Lire construction or alteration of which was begun prior to the effective date of this ordinance, and which is diligently prosecuted. r b. hlarkinq and Li hq tine: Notwithstanding the foregoing L ban on retroactivity, the owner of any existing non -conforming structure or tree is hereby required to permit the installation, 1 L operation, and maintenance thereon of such markers, markings, or lights as shall be deemed necessary by the management of the i Orovillc I•tunieipal ;airport, to indicate to pilots of aircraft in the e;cinity of the airport the presence of such hazards. Such markers and lights shall be installed, operated, and maintained at the expense of the City of Oroville. L 11 5150 Sunrise Blvd., Suite D-3 • Fair Oaks, CA 95628 t (916) 961-5822 • Fax: (916) 961-6418 319 West School Ave., Visalia, CA 93291 (209) 627-4923 • Fax: (209) 627-6284 Brown-Buntin Associates, Inca (BBA) has completed an analysis of aircraft/airport operations and related noise levels for the Ranchaero Airport to prepare Community Noise Equivalent Level (CNEL)' noise exposure maps for projected future (2005) airport traffic volumes with the existing runway configuration. The Federal Aviation Administration's (FAA) Integrated Noise Model (INM) Version 5,01 was used to prepare CNEL noise exposure maps for the Ranchaero Airport, based upon the FAA noise level data for single engine and twin engine aircraft, helicopters, and. airport operational factors as described below. The INM was developed for the FAA, and represents the federally -sanctioned and preferred method for analyzing aircraft/airport noise exposure. Version 5.01. is the currently available version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. Projected data for aircraft activity,. aircraft fleet mix and airport configuration used in the noise modeling process were obtained from most recent (1988) California Aviation System Plan,.. (CASP), and discussions with the Ranchaero Airport officials. The following report, summarizes the data, methods and assumptions used in preparing the CNEL noise exposure maps. The CNEL descriptor is a method of averaging single event noise levels over a typical 24-hour day, applying penalties to noise events occurring during the evening (7 p.m. to 10 p.m.) hours, and nighttime (10 p.m. to 7 a.m.) hours. CNEL is usually defined in terms of average annual conditions, so that the CNEL measured on a given day may be either less than or greater than the annual average. The FAA uses the Day -Night Average Level (Ld,J descriptor to describe land use compatibility with. respect to aircraft noise exposures. The FAA airport noise compatibility criterion for residential land uses is 65 dB Ldp. The California Department of Transportation Division of Aeronautics uses the CNEL descriptor to describe land use compatibility with respect to.aircraft'noise exposures: The .Caltrans Division of Aeronautics noise compatibility criterion for residential land uses is 65 dB CNEL. Generally, the predicted Ldp and CNEL values are within 1, dB of one another: Due to the low percentage of evening operations at Ranchaero Airport, noise exposure contours developed for this airport in terms of Ld„ and CNEL would be virtually identical. 1. For an explanation of terms used in this report, .see Appendix A. I ' AIRPORT OPERATIONS Airport operational factors which can significantly affect overall noise levels as described by CNEL include the aircraft fleet mix, the number of daily operations and the -time of day when aircraft .operations occur. Runway use factors also significantly influence CNEL values. Trip length can . affect aircraft single event noise levels, as an aircraft which is prepared for a long flight may carry more fuel and passengers than for a short flight. The INM applies corrections to air carrier, aircraft takeoff profiles to account for these differences, but makes no corrections to general aviation aircraft `takeoff profiles. Aircraft operational assumptions for Ranchaero`Airport are based upon analyses of airport activity providedin the CASP and discussions with the Ranchaero Airport officials. These assumptions are described -by Tables I and 11. Straight out and in to and from the North: 10% Treeline arrivals and departures to the North: 22.5% Touch and go operations North and South: 45% 1 The flight tracks for Ranchaero Airport are identified on Figure L TABLE I AIRPORT CONFIGURATION AND .USE Ranchaero Airport - Butte County Runway Configuration: ' 15-33 ' Runway Length: 2,400 feet Field Elevation: 173 feet MSL Runway Use Factors:— 55% Rwy 33 45% Rwy 15 Temporal Distribution of Operations: 92% Day 6% Evening 2% Night Flight Tracks and Direction' Straight out and in to and from the South: 22.5% Straight out and in to and from the North: 10% Treeline arrivals and departures to the North: 22.5% Touch and go operations North and South: 45% 1 The flight tracks for Ranchaero Airport are identified on Figure L Descriptions of aircraft flight tracks were developed through discussions with the airport. manager and BBA field observations. Based upon these data, generalized flight tracks were prepared for use in the noise modeling process to describe areas with a concentration of aircraft overflights. Figure 1 shows the flight tracks used for the noise modeling process. It is recognized that variations in . flight paths occur at the Ranchaero Airport, and that the tracks shown on Figure 1 are meant to be . . a general representation of those flight patterns. PREPARATION OF CNEL NOISE EXPOSURE MAPS The Integrated Noise Model (INM) Version 5.01 was used to prepare CNEL .noise exposure,maps for the airport based upon the aircraft noise level and airport operational factors described in the previous sections. The'INM was developed for the FAA,*and represents"the federally -sanctioned and preferred method for analyzing aircraft/airport, noise exposure.Version 5'01 is the most recent version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. TABLE II , TOTAL OPERATIONS BY AIRCRAFT TYPE . Ranchaero Airport -Butte County ` INM Category Description . Annual Daily BEC58P Small Twin Piston Engine General Aviation Airplane 2,190 6.0 - GASEPF General Aviation Single Engine - Fixed Propeller 7,008 19.2 GASEPV• General Aviation Single Engine - Variable Pitch Propeller 1,752 4.8. H300 Hughes 300 Light Utility Single Engine Helicopter 6,935 19.0 B206 Bell 206 Jet Ranger Light Utility Single Engine Helicopter .730 2.0 Total Operations: 18,615 51 Note: Touch and go operations have been counted as two operations in this table (one arrival and one departure) Descriptions of aircraft flight tracks were developed through discussions with the airport. manager and BBA field observations. Based upon these data, generalized flight tracks were prepared for use in the noise modeling process to describe areas with a concentration of aircraft overflights. Figure 1 shows the flight tracks used for the noise modeling process. It is recognized that variations in . flight paths occur at the Ranchaero Airport, and that the tracks shown on Figure 1 are meant to be . . a general representation of those flight patterns. PREPARATION OF CNEL NOISE EXPOSURE MAPS The Integrated Noise Model (INM) Version 5.01 was used to prepare CNEL .noise exposure,maps for the airport based upon the aircraft noise level and airport operational factors described in the previous sections. The'INM was developed for the FAA,*and represents"the federally -sanctioned and preferred method for analyzing aircraft/airport, noise exposure.Version 5'01 is the most recent version of the INM, incorporating an updated database of aircraft performance parameters and noise levels. The INM calculates aircraft noise exposure by mathematically combining aircraft noise levels and airport operational factors at a series of points within a Cartesian coordinate system which defines the location of airportrunways and aircraft flight tracks. User inputs to the INM include the following: a. Airport altitude and mean temperature b. Runway configuration ` c. Aircraft flight track definition d. Aircraft stage length (not pertinent for this airport) e. Aircraft departure and approach profiles f., Aircraft traffic volume and fleet mix g. Flight track utilization by aircraft types The INM data base includes aircraft performance parameters and noise level data for numerous commercial, military and general aviationjaircraft classes. When the user specifies a particular aircraft class from the INM data base,. the model automatically provides the necessary inputs concerning aircraft power settings, speed, departure profile and noise levels. INM default values were used for all fixed -wing aircraft types. BBA referred to the FAA publication Helicopter Noise Exposure Curves for use in Environmental Impact Assessment, to obtain noise emission data for the two most common helicopter types utilized at Ranchaero. After the model had been prepared for the aircraft classes, described in the preceding section, BBA created INM input files containing the number of operations by aircraft class, time of day and flight track for annual average day aircraft operations for each forecast scenario. The INM was used with. these operational scenarios to prepare 65, 60 and 55 dB CNEL contours, which have been plotted on Figure 2. Total surface areas included in each of these CNEL contours are shown by Table I1I. TABLE III SURFACE AREAS WITIIIN YEAR 2005 CNEL CONTOURS Ranchaero Airport - Butte County 0.04 Sq. Mi. I 60 dB CNEL 0.10 Sq. Mi.. 4 10.23 Sq. Mi. I AIRCRAFT NOISE MEASUREMENTS Aircraft noise level measurements were conducted at two locations in the Ranchaero,Airport vicinity to generally assess the accuracy of the INM- in predicting aircraft noise levels at the nearest areas. The noise measurement sites, which are shown on Figure 1, potentially affected residential represent the two existing residences located. nearest to the airport. The meters operated continuously from 2 p.m. on August 6, 1996 through 12 noon on August 15, 1996. The noise monitoring system consisted of two Larson: -Davis Laboratories (LDL)* Model, 820 precision integrating sound level meters. The microphones were located at a height of approximately 5 feet above ground, and were fitted with random incidence correctors and windscreens. The_ meters, _ which were housed in weatherproof containers, were calibrated at the beginning and -end of the continuous noise measurement period: Each meter had the capability of reporting instantaneous sound levels -and a. variety of statistical sound level descriptors. For aircraft noise events, each unit was programmed to report the duration, maximum A- -weighted sound level (Ldaj, and Sound Exposure Level (SEL) of noise events which exceed a selected threshold sound level and event duration. Each analyzer,calculated the hourly average sound level (Leq), from which the CNEL was computed. The results of the aircraft noise monitoring program are summarized in Table IV. : A graphical depiction ofthe noise level measurement results is shown on Figures 3 and 4. - TABLE IV AVERAGE MEASURED AND PREDICTED CNEL VALUES Ranchaero Airport -August 6-.16, 1996 Site No. y CNEL from Measurement Data INM 5,01 CNEL_(2005) 1 52 dB 55 dB., 2 55 dB 61 dB { Note: the noise level measurement locations are shown on Figure 1. A comparison between measured and modeled CNEL values shown in Table IV reveals that the . future values predicted by the INM exceed measured existing levels by 3 to 6 dB. However, because the nine day measurement period may not have been representative of typical aircraft traffic and because the measured CNEL values reported in Table IV include noise from all sources, not just aircraft, the significance of the noise measurement results in terms of CNEL should not be overstated. Nonetheless, the .Table.IV data suggests that the predicted aircraft CNEL values based on 2005 activity projections are not unreasonable. CONCLUSIONS The year 2005 CNEL noise contours shown on Figure 2 indicate that no existing residences would be exposed to future aircraft noise levels exceeding the Caltrans Department of Aviation and FAA recommended exterior noise level standards of 65 dB Ld,,/CNEL. Existing residences in the Ranchaero Airport vicintiy will continue to be exposed to intermittent elevated noise levels during aircraft and helicopter arrivals and departures, with the intensity of the sound dependant on the aircraft type, location, altitude, speed and condition. Occasional straight in and out operations to the north will likely continue to be considered offensive to some residences located north of Bidwell creek. BBA observations and information provided by Ranchaero Airport Officials revealed that the vast majority of the aircraft approaching or departing to the north utilize the treeline flight path shown on Figure 1. This analysis -conservatively assumed that 10% of the total airport operations were straight in arrivals or straight out departures to the north. Nonetheless, the Figure 2 noise exposure contours indicate that the contours "bend" to the west, reflecting the higher percentages of treeline approaches and departures. A final conclusion of this analysis is that the helicopter operations generate considerably lower noise levels than the single and twin engine propeller airplanes which utilize. this airfield. As a result, reorienting the flight paths of the helicopter operations to utilize a midfield approach/departure . corridor to the west would not appreciably alter the locations of the noise contours depicted on Figure 2. Respectfully Submitted, PaulBollaid" untin As fates, Inc. Senior Consultant 6 mig, ED` 'A 0l_�RWAAg-.­,.,- 0 ................... MA �MFNP-! ggl- �217-50 1, i Kli g2mg, OF RM - I 1, M-1 Not -- I 40ma ago va! 0 on= A -M MUM WON M ZONES WAS zr-,,6�, 20 AIM I I MuMMUMB M REM mt &w Mr, I - M, i org a W ME 711 e j N5 47 W -- so ft-lD- P: NUNN r All�- U. i n D en Of M ME- - NETI qg " 3i N -,;ow am Uk-m N ........ . . . . . . . . . . IN* M -�'T SlAr 504... --� WE , m 11201. M tvwM� MY H, P MONSOON i ISO &-Mffl� MEN WA -02 I NOW III MONSOON I ow -5 111-1 im �MT- k* IAM AAA Q VAN l? figure"4 Measured -Ambient Levels -August::? 14, 1996 .Noise Nearest Residence. to South of.'Ranchaero Airport _ (Values shown are averages -for the 8 day period) . .. 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'Gj��= - .. •-:' -.. ..i. � - �„�d'� _r'f�..�r'-=•�?'s'`��re� ��T� may, w' a' �, •.f _ '��- �� �'� - '50A-_ _ - ✓y - =� ���,'d``-- r � .� 5 Y =..�'+�-�•- ��' hZ�tl3vPiv� , I IN�}a ��� � -�Sr?'4.8•. ffil NeT r 'v .. .. ,..', - _ � •� .�d�yr. ��t�� �Na,l� a� .n _ ��„'� ! �f �� ���F$jsi9�T'�`��^'.�F �i,h,"`�,.. tom.. r .. ae- ` • .. ,... ,_ � � . �, . » t _ :.i. % ��°i.:. = - � � ,moi;:. .i�� ���� .ii � r��(jy 'o'- �� �3: � �"� m`!,.}� 12:00•AM 4.00 AM - - 8.00 AM ;, 12 OO.PM 4 00 PM ;. . '8 001PM _ �.ur .of Day -Lmax -s- Leq — L50 -=+-L90 BRA , APPENDIX A ACOUSTICAL TERMINOLOGY AMBIENT NOISE The composite of noise from. all sources near and far. In this LEVEL: context, the ambient noise level constitutes the normal or existing level of environmental noise a given location. CNEL: Community Noise Equivalent Level. The average equivalent sound level during a 24-hour day, obtained after addition of.approximately five decibels to sound levels in the evening from 7:00 p.m. to 10:00 p.m. and ten decibels to sound levels in the nighvbefore 7:00 a.m. and after 10:00 p.m. DECIBEL, dBs A unit for describing the amplitude of sound, equal to,.20 times the. logarithm to the base 10 of the ratio of the reference pressure, which is 20 micropascals (20 micronewtons per .square meter). Ld.; Day -Night Average Sound Level. The average equivalent. sound . level during a 24-hour day, obtained after addition of ten decibels to sound levels in the night after 10:00 p.m. and. before 7:00 a.m.. I,�; Equivalent Sound Level. The sound level containing the same total energy as a time varying signal over a given sample period. Ley is typically computed over 1, 8 and 24-hour sample periods. Note: CNEL and Ld" represent daily levels of noise exposure averaged on an annual basis, while Ley represents the average noise exposure for a shorter time. period, typically one hour. The maximum sound level recorded during `a noise event. LO: The sound level exceeded "n" percent of the time during a sample interval. 1'10 equals the level exceeded. 10 percent of the time (L�;. L50, etc.) . BBA A-2 ACOUSTICAL TERMINOLOGY NOISE. EXPOSURE Lines drawn-about a noise source indicating constant levels of CONTOURS: noise exposure. CNEL and Ldn contours are frequently utilized to describe community exposure to noise. -SEL OR SENEL: Sound Exposure Level or Single Event Noise Exposure Level. .The level of noise accumulated during a single noise event, such. as an aircraft overflight, with reference to a duration of one second. More specifically, it is the time-integrated A-weighted . . squared sound.pressure level for a stated time interval or event, based on a reference pressure of 20 micropascals and_ a reference duration of one second SOUND LEVEL: The sound pressure level in decibels as measured on a sound level meter 'using the A-weighting filter network. The A- weighting filter de-emphasizes the very low and very high frequency components of the sound -in. a manner similar. to the response of the human ear and gives good correlation with subjective reactions to noise.. FBBA..