ENVIRONMENTAL CONSEQUENCES

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ALTERNATIVE B: RESURFACING, RESTORATION, AND REHABILITATION

This section evaluates the potential impacts of alternative B.

Soundscapes and Noise

Traffic Noise

This alternative would not add traffic volume to the roadway corridor, and changes to the horizontal or vertical alignments are slight. Therefore, the noise environment would not change and would be similar to that described for the no-action alternative.

Construction Noise

Since noise that radiates from construction equipment radiates equally in all directions, the sound intensity would diminish inversely as the square of the distance from the source. Therefore, in a free field (no reflections of sound), the Lp decreases 6 decibel (dB) with each doubling of the distance from the source. Under most conditions, reflected sound will reduce the attenuation due to distance. Therefore, doubling the distance may only result in a decrease of 4 to 5 dB (Cowan 1994).

Table 6 provides estimated sound pressure levels at a distance of 50 feet for miscellaneous heavy construction equipment.

Typical noise levels generated by these activities range from 75 to 89 dB at 50 feet from the source. At 100 feet from the source, noise levels would range from 69 dBA to 83 dBA. In the proposed wilderness area, noise levels would range from 63 to 77 dB at the wilderness boundary (200 feet), and vary by distance and forest shielding along the trail.

1 Estimated number in use at any time.

2 Source: CERL 1978.

The sensitive noise receptor (Pacific Crest Trail user) would experience a substantial increase in noise levels (15 to 29 dB at 100 feet, and 9 to 23 dB at the wilderness boundary). However, this impact would be very short in duration (only when construction is occurring on the segment in close proximity to the receptor) and affecting a small number of park visitors (less than 4% of park visitors). Therefore, the impacts are expected to be minor to moderate, short term, and adverse.

The other two noise sensitive receptors (the northern spotted owl activity center and Annie Creek Canyon Trail) are more than 800 feet away (2,952 feet and 1,320 feet, respectively). At the evaluated distance of 800 feet, ambient noise levels would be less than the 51 to 65 dBA estimated using the 6 dBA drop-off with each doubling of distance, due to shielding by the forested woodlands, and would likely approach, or be negligible above existing levels. The existing noise environment includes a negligible amount of daily traffic volume, with no additional noise sources other than the natural soundscape. Construction noise would occur during daytime hours during the summer months, and is not expected to be constant in duration. Therefore, the impacts are expected to be negligible, short term, and adverse.

Cumulative Impacts. Past, present, and reasonably foreseeable future actions that would have effects on soundscapes and noise quality within the park include the waterline replacement from Munson Springs to Garfield, lagoon project at Munson Valley, installation of vault toilet and kiosk, trail rehabilitation and relocation, reconstruction of the Rim parking lot, and rehabilitation of the superintendent’s house. The effects of these projects would be short term, adverse, and negligible parkwide. These projects would be very localized and scheduled during different years. Alternative B would possibly contribute to one or more of these project as they are scheduled during the same building season. The impact would be short term, adverse, and negligible.

Conclusion. There would be no change to the long-term soundscapes or noise environment at the park once construction is completed. There would be a minor to moderate, very short-term, adverse impact to noise quality along the wilderness boundary and near the Pacific Crest Trail. There would be a negligible, very short-term, adverse impact to sensitive receptors—the northern spotted owl activity center and users of the Annie Creek Canyon Trail. The cumulative effect of alternative B would be very short term, negligible, and adverse to the soundscapes or noise environment at the park. There would be very short-term exceedances of the Noise Abatement Criteria at the Pacific Crest Trail where it intersects the highway.

Because there would be no major adverse impacts to a resource or value whose conservation is (1) necessary to fulfill specific purposes identified in the park’s establishing legislation, (2) key to the natural or cultural integrity of the park or to opportunities for enjoyment of the park, or (3) identified as a goal in the park’s General Management Plan or other relevant National Park Service planning documents, there would be no impairment of park resources or values.