In September, the Arizona Game and Fish Department released a noise study for a proposed shooting range on a site that lies 1-3 miles from the boundary of Walnut Canyon National Monument, east of Flagstaff. The results have spurred the Superintendent of Walnut Canyon to express concerns to the Game and Fish Department about the effects of the noise on visitors and wildlife, in the hopes that planned berming and other noise mitigation measures at the facility can reduce noise to the point that it is inaudible in key areas.

The Foster Ranch Shooting Range site was purchased last year after a 16-year effort to find a suitable location for a state-run range in Northern Arizona; previous sites fell victim to local resistance or grazing leases that were still active.  The noise study found that shooting was audible, but well within state noise limits, at all locations monitored, which included a nearby residence, random sites a mile away, and one site at Walnut Canyon, 3 miles from the range (download pdf of study). At Walnut Canyon, gunshot noise ranged up to 52dB, though in most tests it was in the 43-47dB range, and was sometimes barely audible.  Ambient sound levels were measured as low as 31dB, but were more commonly above 40dB.  In general, any sound 5dB over ambient is perceptible and can affect some wildlife behavior, and a sound 10dB over ambient is often annoying to wildlife and people.

In the NPS letter, Superintendent Diane Chung stressed that the Park Service’s mission includes the protection of soundscapes in its Park units, and detailed several specific ways that noise from the range could create negative impacts on visitors and wildlife.  She noted that the test sounds were clearly audible from the primary overlook trail used by many visitors to view the Cliff Dwellings, and that noise at Cherry Canyon Pools, the only natural perennial water on the monument (1 mile from the range) could disrupt wildlife use there.  Other known and possible wildlife corridors on nearby National Forest land were also of concern.  Chung concluded by noting the fact that there are plans to construct berms and use other design features to reduce the levels of noise leaving the site and stressed the Monument’s desire to work with the range planners “to assure that we can preserve the visitor experience and minimize wildlife impacts.”

In a letter to the editor of the local paper, the Friends of Walnut Canyon claim that a third of the Monument is close enough that the noise would not be allowed if homes were there; it’s not clear what figures they are drawing on in this claim, as all locations monitored at a mile away were well under state limits, though clearly audible (at one closer property line, distance not noted, noise was over the limit when all guns were firing simultaneously).  Meanwhile, another letter chides the Park Service for wanting to manage land outside its boundaries and favors the National Forest management that does not preclude new noise intrusions or other non-preservation uses.

Clearly, the range could impact the Monument soundscape if proper mitigation is not in place.  Effective design will be critical to assuring that the National Park mission is fulfilled in this location.  In October 2009, a Federal Judge affirmed NPS’s commitment to protection of sound resources when he blocked oil and gas drilling that would have impacted the soundscape at Great Sand Dunes National Park (the drilling plans were withdrawn, but in October 2010 the US Fish and Wildlife Service began the process of environmental assessment to allow drilling to proceed)..