Regulatory

The Noise Control Act of 1972 and the Quiet Communities Act of 1978 delegate authority to the states to regulate environmental noise. 

2021 Colorado Code Title 25 - Public Health and Environment Article 12 - Noise Abatement § 25-12-103. Maximum Permissible Noise Levels sets standards for sound levels, with specific directives for time of day, types, frequencies, and periodic timing of sound.  The Code also provides exemptions for certain activities (race tracks, industrial, construction).  With regards to electrical development, Colorado Code § 25-12-103 includes:

• 12. a. “the public utilities commission may determine, while reviewing utility applications for certificates of public convenience and necessity for electric transmission facilities, whether Projected noise levels for electric transmission facilities are reasonable.”
• 12. b. Because of the statewide need for reliable electric service and the public benefit provided by electric transmission facilities, notwithstanding any other provision of law, no municipality or county may adopt an ordinance or resolution setting noise standards for electric transmission facilities that are more restrictive than this subsection (12). The owner or operator of an electric transmission facility shall not be liable in a civil action based upon noise emitted by electric transmission facilities that comply with this subsection (12).

EPA guidelines, state that outdoor sound in excess of 55 decibels (dB) Day-Night Average Sound Level are normally unacceptable for noise-sensitive land uses including residences (USEPA, 1974).

Baseline Conditions

The proposed Project area is set amongst a rural ranching community, with section roads bounding the site on three sides.  According to the Wright’s Mesa Master Plan, the proposed Project area is within an area zoned as rural residential / agricultural.  Based on the Google Earth aerial imagery dated 2019, there are 19 residences within ¼ mile (1,320 ft), and 46 residences within ½ mile (2,640 ft) of the proposed Project area. There are no industrial properties in the Project area.  Observations made at various points near the proposed Project site along Y43, 45Y and Lone Cone Road indicate that sounds in the area are consistent with a rural agricultural setting.  Intermittent vehicles along Y43, 45Y and Lone Cone Road, sounds of cattle and sheep, wind, birds and occasional overhead jets create the soundscape in the Project area.  Ambient background sound is subtle.  During hay season, tractors may be heard in surrounding fields.  During cattle drives the cattle can be heard throughout the area.

According to standard charts, the natural ambient sound of quiet rural landscapes is 30-40 dBA (FAA 2024). National Park Service studies indicate that median natural ambient sound levels ranged between 19.3 to 39 dBA during the daytime hours and between 15 to 38 dBA during nighttime hours (NPS 2024). For the purposes of this analysis, standard dBA of 30-40 will be used.

Consequences

Workforce and Traffic

The proposed Project would employ 300 workers and take 3-4 years to develop, design, and construct.  In a town of approximately 600 people, the workforce required to construct the Project would significantly affect traffic patterns along Y43, 45Y and Lone Cone Road, throughout the town of Norwood, and along Hwy 145 during morning and evening hours as workforce traffic commutes to/from the job site.  Noise from traffic would likely be most intense nearer the Project site, but would also increase ambient noise levels in all areas where increased traffic levels occur.

Construction

Construction would require 2-3 years of daily activity involving multiple pieces of heavy machinery and equipment to clear and grade the area, deliver materials, transport personnel, install and construct PV arrays, construct the substation and switchyard and plow/bury the gen-tie cabling throughout the site.  Table 2-2 provides a list of the typical equipment used during construction of a solar facility.

A complete acoustic analysis of the Project area is outside of the scope of this EA.  Therefore, this analysis will tier to the analysis of impacts to the soundscape taken from the GEMINI SOLAR PROJECT Final Resource Management Plan Amendment and Environmental Impact Statement (DOI-BLM-NV-S010-2018-0051-EIS) December 27, 2019. (Gemini EIS) (DOI BLM, 2019) The Gemini Solar Project is a PV array project currently being constructed outside of Las Vegas, Nevada.  Though the Gemini Project is substantially larger (5,000 acres) than the proposed Project (1009.4 acres), the Project is similar in design features (i.e., PV array, substation, BESS, switchyard, buried gen-tie cables). 

Information regarding construction methods and equipment were not provided during the May 16, 2023, meeting or on the Project website.  For the purposes of this EA, it is assumed that equipment and machinery necessary for the proposed Project would be similar to that used for construction and operations of the Gemini project. The analysis of sound impacts in the Gemini EIS are based on attenuation of sound from the two loudest equipment types used for each Project activity, and not a composite of all equipment sound operating on any given day, which would be a factor of Project size.  Therefore, the Gemini EIS sound analysis provides a general idea of potential sound impacts that would occur if the proposed Project were implemented.   

Sound analysis from Gemini Solar EIS

The construction and operations noise analyses are based on typical equipment and vehicle noise levels and attenuation of noise, representing a conservative noise level.  Maximum noise levels from construction equipment and vehicles were estimated using in the Federal Highway Administration’s Roadway Construction Noise Model, in accordance with the methodology detailed in the Federal Transit Administration’s Transit Noise and Vibration Impact Assessment (2006).  Information regarding noise levels associated with equipment used during the construction, operations, and decommissioning of Solar facility are provided in Appendix F.

Construction and Decommissioning

Equipment used during construction and decommissioning are similar.  Therefore, sound impacts associated with these phases of the Project would be similar.

Construction/decommissioning would require several to over a hundred pieces of industrial equipment. Noise levels at 50 ft (15 m) from the two loudest equipment types for each construction activity, would generally range from 70 to 80 dBA Leq at 50 ft. Backup alarms would intermittently sound, resulting in a level of approximately 70 dBA Lmax at 50 ft.  Noise levels from the loudest construction activity would dissipate to 55 dBA Leq at approximately 1,350 ft from the noise source.

EPA guidelines, state that outdoor sound levels in excess of 55 decibels (dB) are normally unacceptable for noise-sensitive land uses such as residences.  Nineteen residences are within 1,320 ft of the proposed project site and would be adversely impacted by noise generated from construction (2-3 years) and decommissioning (estimated one year).

Operation and Maintenance

Solar array trackers, inverters, transformers, and transmission lines emit low levels of ongoing noise during operation. Maintenance activities also generate intermittent and occasional noise.  Noise emitted from equipment associated with the solar facility would be less than 55 dBA at 50 ft.  Equipment and vehicles used during maintenance activities would result in occasional higher noise levels, with a Leq of 55 dBA at 315 ft from the source. 

Operations and maintenance would result in minor adverse impacts to the soundscape for residences within 1,320 ft of the Project site.

Consequences

Implementing the proposed Project would transform the soundscape of the area from rural agricultural to industrial. Construction activities would increase ambient sound in the Project area from 30-40 dBA to 70 to 80 dBA. And average increase 40 dBA. Operations (average 55dBA) would increase the ambient sounds in the Project area by 25-15 dBA. There are 19 residences within ¼ mile (1,320 ft), and 46 residences within ½ mile (2,640 ft) of the proposed Project.  The proposed Project would have a significant adverse impact to the soundscape experience of residences within the analysis area. 

The proposed Project would also impact soundscape features throughout Wright’s Mesa as workforce traffic would significantly affect traffic patterns and noise during the period of construction.  Analyzing traffic patterns and associated noise is outside the scope of this EA.  The proposed Project would have long-term (several years of construction) direct adverse effects on the ambient acoustic environment in the immediate vicinity of the Project area, as well as surrounding areas.

Countless species rely on acoustic communication for survival.  Rocky Mountain elk are exceedingly vocal during rut and mating season and rely on acoustic communication to attract mates and as part of territorial establishment amongst bulls.  Coyotes and foxes rely on acoustic communication to attract mates, establish and defend territories, and detect potential predators.  Nearly all birds species rely on song and calls to successfully breed and establish nesting territories.  Soundscapes free of noise pollution are critical to survival of wildlife in the Project area.

No Action Alternative

The Project would not be built under the No Action Alternative, and no changes to the acoustic environment would occur.