2016-05-20_GENERAL DOCUMENTS - C1981035

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4. The speed at which trucks travel has a significant effect on noise — approximately 8 dBA increase between 12 and 22 mph. During the study, trucks slowed to 10 mph on gravel road portions in the vicinity of residences 5. Haul trucks traveling at l Omph on flat portions of the road did not have an alternative effect 6. All haul trucks measured had noise levels below 86 dBA, a cited limit established by the State of Colorado Wave Engineering evaluated the potential effectiveness of noise barriers using a model that assumed a 12 - foot high wall and a break for a driveway (which greatly decreases barrier effectiveness) and made conclusions as summarized below. 1. At the Hunzeker residence, a barrier could reduce sound from the road by approximately 6 dBA 2. At the McCue residence, a barrier could reduce sound from the road by approximately 10 dBA 3. At the three residences north of the barrier along the steep hill, there is already some screening by topography and partly due to this, no increase in benefit is shown to occur with a barrier 4. Barriers may be constructed of wood, concrete, brick, masonry, or other materials. 5. Barriers may have sound -absorbing surfaces if reflection of sound across the road to another residence is a concern 6. The barrier must block line -of -sight from the road to be effective. If one can look out from a point on their home and see the road, the barrier has limited effectiveness 7. Breaks in the barrier (for access) reduce its effectiveness, especially when the residence is near the break. Effectiveness increases as the separation between the home and the break increases. 8. Factors that make barriers more effective are length, height, distance from the road 9. Barriers are most effective when they are close to the road or to the residence. Placing barriers outside of drainage ditches, while understandable, decreases their effectiveness and requires them have less effect, unless constructed higher. GCC provided a conceptual buffering plan at 2541 and 3230 CR 120 (Attachment 21). The Public Works Director requested a more detailed plan for barrier construction and interior buffering (for 2541 and 3230 CR 120), but has not received such detailed plan at this time. Buffering measures such as sound walls, landscaping, and berming are necessary to achieve compatibility when a project such as GCC's truck traffic creates noise, traffic, dust, unsightly views and other negative impacts that are perceptible by adjoining land uses along north County Road 120 between State Highway 140 and the project site (LPLUC Sec. 82-165[a]). Without such detailed buffering plan submitted by the applicant, it is not possible to determine whether an adequate mitigation will diffuse the extent of the proposed impacts proposed by the applicant. In addition to barriers and screening, which have the potential to mitigate certain impacts for those directly adjacent to the road, the following mitigations efforts would also be necessary for all residents along the road and within the rural neighborhood along the roadway: 1. Haul trucks to travel at no greater than 10 mph on gravel portions of the road within 200 feet of residential structures. - Reflected in Wave Eng sound measurement 2. Sound measurements at 50 feet from the edge of the road to not exceed 86 dBA at any time. Note that it is the opinion of Wave Engineering that Colorado Statute 25-12-107 should be assumed to apply to vehicle traffic. 3. All haul trucks to be equipped with exhaust silencers/mufflers in good working condition. - Note that Wave reports engine and transmission noise is the most significant source of noise at speeds of less than approximately 30 mph. At some point above 35 mph, tire noise begins to exceed engine noise. Project No. 2012-0089 PC 4852-5627-2942, v. 3 Page 23 of 32 (DM, VS, DP)