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Noise ReportP.O. IN 17 0 Newim Mmnna S0624 Id (406) 457-0401 a fit (406� 449-3ssl wwbokyumfiaxom Big Sky AcmtiCS, LLC MEMORANDUM DATE: June 8, 2009 TO: Hubert Turner / Willow Creek Subdivision FROM: Sean Connolly, P.E. RE: WiHow Creek Subdivision — May 2009 (BSA Project #07108B) Revised Preliminary Traffic Noise Contours 1.0 INTRODUCTION Big Sky Acoustics (BSA) has updated the traffic noise level contours at the proposed Willow Creek Subdivision property due to the proposed Kalispell Bypass in Kalispell, Montana. It is the understanding of BSA that the City of Kalispell Planning Department has expressed concerns about the Bypass traffic noise on the subdivision property, and would like traffic noise mitigation measures to be implemented so that the 60 dBA traffic noise contour does not cross the subdivision lots. BSA previously provided traffic noise contours and recommendations for traffic noise barriers and berms to shield the Willow Creek Subdivision in a memo to CTA Architects Engineers (CTA) dated march 4, 2008. The information in that memo was based on a subdivision layout and grading plan from 2007 prepared by CTA. In May 2009, BSA was notified that the subdivision grading and lot layout had changed significantly, an 8-foot tall berm had been included between the subdivision and the Bypass, and that the noise contours needed to be updated based on the new information. 'Ibis report updates the traffic noise analysis for the subdivision property, including the preliminary location of the 60 dBA traffic noise contour based on current sources of information. This analysis was based on information from the February 2009 subdivision grading plan (WMW 2009), the Final Traffic Noise Technical Study for the Kalispell Bypass (Carter & Burgess 2006), and drawings from the Plan -In -Hand Submittal for the Bypass dated March, 2007 (Stelling 2007). If the traffic counts or traffic mix projected for the Bypass, elevations of the Bypass roadway, subdivision grading elevations, location of the Bypass centerline, or other information contained in the documents used for this analysis changes as the projects progress, then the predicted location of the traffic noise contours will need to be updated. Tlie Willow Creek property is located north of the existing Foys Lake Road along the west side of the Bypass. It is the understanding of BSA that the subdivision buildings may be two stories. For this analysis, BSA developed contours for both first -floor and second -floor elevations. The Page I of ; Memorandum Willow Creek Traffic Noise Analysis — May 2009 June B, 2009 Big Sky Acoustics, LLC grading contours for the Willow Creek Subdivision indicate that an 8-foot high berm is being considered along the eastern edge of the property (WMW 2009)_ 2.0 NOISE TERMINOLOGY Noise levels are quantified using units of decibels (dB). Noise levels can also be expressed as A - weighted decibels (dBA). Humans typically have reduced hearing sensitivity at low frequencies c0l'Tarcd with tlicir response at high frequencies, and the A -weighting of noisc levels closely correlates to the frequency response of non-nal human hearing. By utilizing A -weighted noise levels in a study, a person's response to noise can be assessed. Decibels are logarithmic values, and cannot be combined using non-nal algebraic addition. For example, the combined noise level of two 50-dBA noise sources would be 53 dBA, not 100 dBA. Noise can be quantified using many different metrics and time periods. For environmental noise studies, ambient noise levels and noise impact criteria are typically based on A -weighted equivalent noise levels, L,,,, during a certain time period. The equivalent noise level during a one -hour period is represented as L,q(h) and is the metric used by the Federal Highway Administration (FHWA) and MDT for traffic noise studies. 'Me equivalent noise level is defined as the steady state noise level that has the same acoustical energy as the actual, time -varying noise signal during the same time period. The L,q(h) metric is useful for traffic noise studies because it uses a single number to describe the constantly fluctuating ambient noise levels at a receptor location during one hour of time. All noise levels used in this memo refer to the L,q(h) metric unless noted otherwise. Barriers are used for noise control by shielding a receptor location from a noise source, such as a roadway. A barrier is most effective when it is continuous and solid, and blocks the direct line - of -sight between the entire roadway and a receptor. Barriers can be constructed using built up dirt to create a berm, using concrete, concrete block, other similar masonry materials, metal panels, or thick wood to create a wall, or a combination of a berm with a shorter wall on top. Although it may be used for visual screening, vegetation, such as trees and shrubs, are not considered effective barrier material since sound passes readily through vegetation. An earthen berm typically has a very large base for support and may also require additional land to accommodate construction. To be effective, the barrier wall must be continuous and solid with no gaps, holes or openings in it, including between the bottom edge of the barrier wall and the ground surface. 3.0 ANALYSIS BSA iised FfTWA's approved computer program Trnffic Noise Model (TNM) Version 25 to predict the location of traffic noise contours on the Willow Creek property and the effect of noise mitigation measures on the noise contour locations. TNM 2.5 uses a three-dimensional coordinate system (x, y, and z) to define the location and elevation of the roadway, receptor locations and terrain elevations. The projected design hourly volume (DHV) of vehicles traveling on a roadway, traffic mix of automobiles and trucks, and vehicle speed are also entered into the inodel. Page 2 of S Memorandum Willow Creek Traffic Noise Analysis — May 2009 June B, 2009 Big Sky Acoustics, LLC The projected DT-TV, frnffic mix and trnffe speed for the Bypass, between I JS 2 and Foyq I..9ke Road were obtained from the Final Traffic Noise Study (Carter & Burgess 2006). Traffic data used for the analysis is shown in Table 3-1. Table 3-1: Bypass TratTic Data Used for Noise Level Predictions Road Direction Year DIIV Cars NIT HT Speed Bypass between US 2 and Foys NB 2030 1,265 92% 3% 5% 60 mph Lake Road Bypass between US 2 and Foys SB 2030 1,300 92% 3% 5% 60 mph Lake Road I Foys Lake Road SB off -ramp NB 2030 50 95% i 3% 2% Notes: NB Northbound SB Southbound DHV Design Hourly Volume Cars Vehicles with two axles and four tires MT Medium truck, vehicles with six tires on two axles RT T4P.HVY tn]Ok� VAIiOle.- VAtfl MOM tliNn two:ixles 3.1 1st Floor Contours The preliminary traffic noise contours at a I" floor elevation on the Willow Creek property with the pfoposed 8-foot berni are shown on Figure 1. The contoufs afe based on a receptof height of 5 feet above the ground level, as required by MDT's Noise Policy (MDT 2001). As shown, the 60 dBA traffic noise contour 5-feet above the ground is not predicted to fall across any of the lots. Therefore, the City's requirement would be met at a Is' floor elevation if the proposed 8- foot berm were constructed. 3.2 2 "d Floor Contours The preliminary traffic noise contours at a 2 d floor elevation on the Willow Creek property with the proposed 8-foot berm are shown on Figure 2. The contours are based on a receptor height of 14 feet above the ground level to approximate a second -story location. As shown, the 60 dBA traffic noise contour 14-feet above the ground is predicted to cross 10 lots. Therefore, the City's requirement would not be met on these lots if two-story buildings are constructed. However, single story buildings at these lots would meet the City's requirements if the proposed 8-foot hen,n was, constructed (Sectioin 3.1)_ To meet the City's requirement for 2`1 floor elevations, BSA analyzed potential changes to the proposed benn. Figure 2A shows the predicted noise contours associated with a 10-foot benn. With the 10-foot berm, the 2d floor 60 dBA contour would not cross any lots (Figure 2A), which would meet the City's requirements at 2 d floor elevations. Page 3 of S Memorandum Willow Creek Traffic Noise Analysis — May 2009 June B, 2009 4.0 CONCLUSION Big Sky Acoustics, LLC BSA updated the traffic noise level contours on the proposed Willow Creek Subdivision property due to the proposed Kalispell Bypass based on current information about the location, elevation and projected traffic for the Bypass, and new topographic elevations for the subdivision. The grading contours for the Willow Creek Subdivision indicate that an 8-foot high berm is being considered along the eastern edge of the property (WMW 2009). The analysis was necessary to deterininc what noise initigation incasurc(s) would be necessary so the 60 dBA traffic noise contour does not cross the subdivision lots. For this analysis, BSA developed contours for both first -floor and second -floor elevations. The predicted noise contours with the proposed 8-foot berm along the east side of the subdivision property are shown on Figures I and 2. As shown on Figure 1, the 60 dBA traffic noise contour at 5-fect above ground level is not predicted to fall across any of the lots, and therefore, the City's requirement would be met at a 1st floor elevation if the proposed 8-foot berm was constructed. As shown on Figure 2, the 60 dBA traffic noise contour at 14-feet above ground level with the proposed 8-foot berm in place is predicted to cross 10 lots, and therefore, the City's requirement would not be met on these lots if two-story buildings were constructed. However, if the berm height was increased to 10 feet, then the 2 nd floor 60 dBA traffic noise contour would not cross any lots (Figure 2A), which would meet the City's requirements at 2 nd floor elevations. If you have any questions or comments, do not hesitate to contact me at (406) 457-0407 or seanAbi2sk-vacoustics.com. 5.0 REFERENCES Carter & Burgess, Inc. 2006. Final Traffic Noise Technical Study for the Kalispell Bypass. August 2006. Montana Department of Transportation (MDT). 2001. Traffic Noise Analysis andAbatement: Policy and Procedure Allanual. June 2001. Stelling Engineers, Inc. 2007. Plan -In -Hand Submittal Drawings for the Kalispell Bypass. Sheets 59, 70, 71, 100-107, and 114-126. March, 2007. WMW Engineering (WMW). 2009. AutoCAD drawing ACAD2000-Grading.dwg provided by Jeff Rogers via email on June 1, 2009. Drawing dated February 23, 2009. Page 4 of S Memorandum Willow Creek Traffic Noise Analysis — May 2009 June B, 2009 6.0 STANDARD OF CARE Big Sky Acoustics, LLC To complete this report, Big Sky Acoustics, LLC has endeavored to perform its work in a manner consistent with that degree of care and skill ordinarily exercised by members of the acoustical profession currently practicing under similar circumstances. Big Sky Acoustics, LLC makes no warranty, either express or implied, as to the professional services it has rendered to complete this report. For the completion of this report, Big Sky Acoustics, LLC has used data provided by WMW Engineering, Stelling Engineers, Inc., and Carter & Burgess, Inc. in performing its services and is entitled to rely upon the accuracy and completeness thereof. Therefore, -if the infori-nation and assumptions used to create this report change, then the noise analysis and the recommended noise control measures will need to be reevaluated. Page S of S FIGURE 1 PRELIMINARY 2030 TRAFFIC NOISE CONTOURS: Big Sky Acoustics, LLC PROPOSED 8 ft. BERM: Ist FLOOR CONTOURS Willow Creek Subdivision Scale; I " = 200' FIGURE 2 Big Sky AcouStiCS, LLC PRELIMINARY 2030 TRAFFIC NOISE CONTOURS: PROPOSED 8 ft. BERM: 2nd FLOOR CONTOURS Willow Creek Subdivision Scale: V= 200' �qtsmgm FIGURE 2A Big Sky AcouStiCS, LLC PRELIMINARY 2030 TRAFFIC NOISE CONTOURS: 10 ft BERM: 2nd FLOOR CONTOURS Willow Creek Subdivision Scale: 1"=200'