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Home My WebLink About1.20 Noise Analysis North Hangs Mine February 2023 Appendix – Noise Study www.cerjan.com (720) 670-6720 NORTH HANGS PIT NOISE To: Ben Langenfeld – Lewicki & Associates From: Jeff Cerjan – Cerjan Acoustics CC: Shelley Morton – Cerjan Acoustics Subject: Noise Analysis Results and Compliance Assessment Date: February 14, 2023 INTRODUCTION Per your request, this memo provides the results of a noise analysis for the proposed North Hangs Pit (Project) to be located in Garfield County, Colorado. As shown in Figure 1, the 72.8 acre Project is located near Silt, Colorado on the north side of Interstate 70 with the Colorado River, railroad tracks and US 6 to the north. In general, the surrounding area is mostly vacant land with some existing mining operations. The nearest residence is about 2,500 feet to the northwest of the proposed processing area. Existing daytime noise sources include that from traffic on Interstate 70 and US 6 as well as the railroad and the other existing mining sites. Figure 1 – General Location of North Hangs Pit NORTH HANGS PIT NOISE Noise Analysis Results and Compliance Assessment APPLICABLE NOISE REGULATIONS Per Garfield County LUDC 2013, the noise limits are defined for gravel pits in Section 7-1002 Gravel Extraction – C. Noise and Vibration. This section says that the project needs to comply with Colorado Revised Statues (CRS) 25-12 unless Section 7-1002 notes any modifications. The noise limit table from Section 7-1002 is provided below in Table 1. These noise limits are to be met 25 feet inside the adjacent parcel. Note that the one difference between the State and County regulations is that for Light Industrial, the daytime and nighttime limits are reversed (i.e.: daytime should be 70 dBA and nighttime should be quieter at 65 dBA) and I would attribute this to a typo. One caveat for these limits is that during the daytime, noise levels can be increased by 10 dBA for 15 minutes in any one-hour period. A second caveat is that the noise level limit is decreased by 5 dBA for intermittent and shrill type noises. Table 1 – Garfield County Noise Threshold per Neighboring Use It is our understanding that the Project is proposed to operate only during daytime hours (7am to 7pm), thus only daytime noise level limits apply. The only existing residential land is to the north on the other side of the river with undeveloped Colorado Division of Wildlife land to the east, vacant rural lands to the west, and Interstate 70 and industrial mining lands to the south. With that said, the Project has elected to meet the residential limit of 55 dBA to the north, west, and east regardless of the existing land use. As the south is Interstate 70 and then industrial lands (mining), the 80 dBA limit is applicable. NORTH HANGS PIT NOISE Noise Analysis Results and Compliance Assessment NOISE LEVEL PREDICTION METHODOLOGY Noise levels were predicted per International Organization for Standardization (ISO) 9613-2: 1996 – Acoustics – Attenuation of Sound During Propagation Outdoors using the SoundPLAN v8.2 software package. ISO 9613-2:1996 predicts noise levels assuming slight downwind conditions (wind blowing from source to receptor) with an accepted accuracy of ±3 dB out to 1,000 meters. A sample view of the acoustical model is provided in Figure 2. The following provides descriptions of the input data used to create each SoundPLAN model. Figure 2 – Isometric View of the SoundPLAN Noise Model with Mitigation Atmospheric Conditions The air temperature, relative humidity, and atmospheric pressure were set to conditions of 10°C, 70%, and 1 atmosphere, respectively. These values represent a low amount of atmospheric absorption of sound available in the ISO 9613-2:1996 method, and result in high levels of sound reaching the receptors. Terrain and Ground Effect The ground elevation data used in the model is a combination of that from the Project for on-site elevations and the United States Geological Survey (USGS) for the surrounding areas in which a digital elevation model (1/3 arc-sec) was imported. The acoustical effect of the ground can be NORTH HANGS PIT NOISE Noise Analysis Results and Compliance Assessment modeled using ground factors from 1.0 (completely absorptive) to 0.0 (completely reflective). A ground factor of 0.2 was used for the mining and processing area with 0.5 for all other areas. The reflection order was set to 2 (two) reflections. The settings are felt to be reasonable and yet still conservative for these predictions. Noise Barriers The primary noise barriers in the noise model include the planned 4 foot deep bench to be cut below the existing ground level for the processing area, the approximate 20 foot tall stockpile that is common to these facilities, and a 160 foot long by 8 foot tall barrier (i.e.: wall, berm, haybales shipping containers, etc.) along the northwest corner of the processing area. The northwest barrier was assumed to be reflective with low sound absorption coefficient of 0.2. Receptors A total of 112 receptors (prediction points) were located along the compliance locations 25 feet inside the adjacent parcels. In addition, 14 receptors were also located at the nearest existing residences. The receptor heights were set to five feet above the ground, as is common practice. Noise Level Contours While noise receptors are predictions at a discrete point like a residence, noise level contours predict the location of a specific noise level. This provides a graphical view of the predicted levels. For this model, noise level contours were predicted at a height of five feet above the ground using a reflection order of 2 (two) to be consistent with the noise receptor point predictions. Noise Source Levels The sound power levels for each piece of equipment were determined from measurements of similar equipment from around Colorado. Note that the “sound power level” is independent of the distance from the source, ground type, etc. and represents all of the sound energy comprised into one point. All noise sources were set to six to ten feet above the ground. Table 2 provides the sound power levels of the equipment in the noise model along with their modeled height above the ground. Table 2 – Sound Power Levels of Major Noise-Producing Equipment Noise Source Height Above Ground (feet) Sound Power Level (dBA) Cone Crusher 10 112 Jaw Crusher 10 114 Power Screen 10 111 Wheel Loader Loading Hopper 10 108 Conveyor Transfer Motors x3 6 100 NORTH HANGS PIT NOISE Noise Analysis Results and Compliance Assessment NOISE LEVEL RESULTS AND COMPLIANCE ASSESSMENT The noise level predictions were made using the assumptions and methodology previously described. These predicted levels are intended to be worst-case in which all equipment is operating at its loudest constant level. All predictions per ISO 9613-2:1996 are generally considered accurate within ±3 dBA out to 3,300 feet (1,000 meters). The daytime noise level limit 25-feet inside the adjacent parcels to the west, north, and east is 55 dBA and 80 dBA to the south. Predicted Noise Levels The range of predicted noise levels along the compliance boundaries and at the fourteen nearest residences with the proposed noise mitigation in place is provided in Table 3. Figure 3 provides these results graphically as a noise level contour overlaid onto an aerial. All noise levels inside the 55 dBA contour line are louder than 55 dBA and all areas outside the 55 dBA contour line are quieter than 55 dBA. As shown, all predicted noise levels demonstrate compliance the applicable noise level limits provided the previously described noise barriers are in place and the equipment sound power levels do not exceed those noted in Table 2. Considering all this, the proposed North Hangs Pit is predicted to fully comply with Garfield County LUDC 2013 Section 7-1002 Gravel Extraction – C Noise and Vibration. Table 3 – Noise Level Results and Assessment of Compliance Location Minimum (dBA) Maximum (dBA) Noise Limit (dBA) In Compliance? East Compliance 48 52 55 Yes North Compliance 51 54 55 Yes West Compliance 45 54 55 Yes South Compliance 45 53 80 Yes Existing Residences 37 47 55 Yes NORTH HANGS PIT NOISE Noise Analysis Results and Compliance Assessment Figure 3 – Predicted Noise Level Contour with Mitigation