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On April 27, 1995, the Tohono O'odham Nation requested assistance from the Agency for Toxic Substances and Disease Registry (ATSDR) in determining the health effects and exposure levels associated with a contaminated site in the Baboquivari District [1]. Specifically, the petitioner expressed concern that any cattle and wildlife drinking the water in the pools in the contaminated area would cause a public health hazard for anyone consuming the animal products [2]. ATSDR has incorporated responses to comments received during the public review process in this document.

For several months in 1993, a construction company operated a gravel pit and asphalt mixing plant as part of a project to resurface roads with rubberized asphalt. During the course of this project, company personnel disposed asphalt, a white material suspected to be lime, and petroleum products in a wash area known as the Choulic Gravel Pit [1].

From March to May 1993, the contractor produced large quantities of asphalt on an almost daily basis. The first batch of asphalt produced each day was unusable and would be pushed over into the Choulic Gravel Pit located at the northern bank of an unnamed arroyo (gully). The total amount of asphalt dumped into the pit is estimated to be 17,000 cubic yards [3]. In addition, there are indications that the contractor dumped oil, molten asphalt, or both into trenches which were then covered [4].

On May 3, 1995, a representative from the Indian Health Service (IHS) conducted a site visit to determine if the site posed an imminent health hazard. During the site visit, the IHS representative determined that an imminent health hazard did not appear to exist. However, as a precaution, he concurred with a recommendation that the site be fenced to prevent livestock from drinking the seasonal surface water [5].

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