NPS/Katy Warner

Organ Pipe Cactus National Monument, Arizona.

OVER THE LAST DECADE THE UNITED STATES has emphasized the importance of securing its borders. The Secure Border Initiative (SBI) has provided for an increase in the number of Border Patrol agents and construction of border infrastructure such as pedestrian fences. The most recent addition to this infrastructure is surveillance towers that can detect, classify, and track human activity along the border. The Department of Homeland Security is planning for the construction of a network of these towers in and around Organ Pipe Cactus National Monument, Arizona, with the potential for additional towers at or near other national park units in the future.

The National Park Service is concerned about the impacts that construction, maintenance, and operation of the towers may have on natural and cultural resources, including the wilderness character of Organ Pipe Cactus National Monument and Sonoran pronghorn antelope, a federally designated endangered species that is sensitive to noise. The primary source of power for many of the planned surveillance towers will be gas-powered generators, which have been recorded at 70 dB(A) from a distance of 4 meters (13 ft). In anticipation of this project, the National Park Service documented the condition of the existing soundscape in April 2009—before construction—when staff from the Natural Sounds Program monitored ambient sound levels at several proposed tower sites and at an existing surveillance tower at an off-site location.

The results from the monitoring effort were shared with park staff in November 2009 and included an inventory of sounds recorded at each site along with their loudness, frequency, and duration. Not surprisingly, these data revealed that the sites were already impacted, to varying degrees, by border surveillance activities. National monument and Natural Sounds Program staff used this information in conference with the Department of Homeland Security to try to reduce the noise footprint of the generators. Additionally, once the towers are constructed, national monument staff will engage in long-term sound monitoring in order to document and mitigate impacts to the greatest extent possible, for the protection of wilderness values and sensitive Sonoran pronghorn.